| Zhu, R., Liang, H., Bai, H., Zhu, T. and Mei, Z. Double is better: achieving an oxide solar-blind UV detector with ultrahigh detectivity and fast-refreshing capability APPLIED MATERIALS TODAY 29 (2022) |
| Abstract: Oxygen vacancy (VO) defects are common in oxide semiconductors, which
are generally believed to be double-edged in detectors. They contribute to a photo gain effect and consequently high responsivity. However, VO defects typically result in high dark current and long persistent photoconductivity (PPC), severely affecting the weak-light detecting and quick refreshing abilities. Here, a simple two-terminal architecture is constructed on amorphous Ga2O3 double layers. By adopting a periodic bias-switching working method, we found that the PPC is stably suppressed and a robustly high refresh rate is achieved, accompanied with the ultra-high photo-to-dark current ratio (> 109), detectivity (8.7x10(17 )Jones) and UV-vis rejection ratio (> 10(8)). The combination of VO- gradient double-layer structure and new working method enables an unimpeded transportation of photo generated electrons under light illumination and a swift block of the trap-released electrons in dark. The methodology may be hopefully extended to other oxide semiconductors for high-performance photodetection. |
BibTeX:
@article{WOS:000824144000002,
author = {Zhu, Rui and Liang, Huili and Bai, He and Zhu, Tao and Mei, Zengxia},
title = {Double is better: achieving an oxide solar-blind UV detector with ultrahigh detectivity and fast-refreshing capability},
journal = {APPLIED MATERIALS TODAY},
year = {2022},
volume = {29},
doi = {https://doi.org/10.1016/j.apmt.2022.101556}
}
|
| Forooqi Motlaq, V., Adlmann, F.A., Hernandez, V.A., Vorobiev, A., Wolff, M. and Bergstrom, L.M. Dissolution mechanism of supported phospholipid bilayer in the presence of amphiphilic drug investigated by neutron reflectometry and quartz crystal microbalance with dissipation monitoring BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 1864, 10 (2022) |
| Abstract: The influence and interaction of the ionizable amphiphilic drug
amitriptyline hydrochloride (AMT) on a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipid bilayer supported on a silica surface have been investigated using a combination of neutron reflectometry and quartz crystal microbalance with dissipation monitoring. Adding AMT solutions with concentrations 3, 12, and 50 mM leaves the lipid bilayer mainly intact and we observe most of the AMT molecules attached to the head-group region of the outer bilayer leaflet. Virtually no AMT penetrates into the hydrophilic head-group region of the inner leaflet close to the silica surface. By adding 200 mM AMT solution, the lipid bilayer dissolved entirely, indicating a threshold concentration for the solubilization of the bilayer by AMT. The observed threshold concentration is consistent with the observation that various bilayer structures abruptly transform into mixed AMT-DOPC micelles beyond a certain AMT-DOPC composition. Based on our experimental observations, we suggest that the penetration of drug into the phospholipid bilayer, and subsequent solubilization of the membrane, follows a two-step mechanism with the outer leaflet being removed prior to the inner leaflet. |
BibTeX:
@article{WOS:000814689700001,
author = {Forooqi Motlaq, V. and Adlmann, F. A. and Hernandez, V. Agmo and Vorobiev, A. and Wolff, M. and Bergstrom, L. M.},
title = {Dissolution mechanism of supported phospholipid bilayer in the presence of amphiphilic drug investigated by neutron reflectometry and quartz crystal microbalance with dissipation monitoring},
journal = {BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES},
year = {2022},
volume = {1864},
number = {10},
doi = {https://doi.org/10.1016/j.bbamem.2022.183976}
}
|
| Bollmann, T.R.J. and Jankowski, M. Kinetics and the crystallographic structure of bismuth during liquefaction and solidification on an insulating substrate SURFACE SCIENCE 723 (2022) |
| Abstract: Here we study the kinetics of liquefaction and solidification of thin
bismuth films grown on an insulating substrate by pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) and investigated by in situ electron and X-ray diffraction. By PLD, we can grow films similar to those obtained using MBE, studied by ex-situ AFM, KPFM, XRR, and XRD. The liquefaction-solidification transition is monitored in real-time by RHEED and synchrotron XRD, observing thereby the dewetting phenomenon and the formation of spherical droplets which size depends on the initial film thickness. Studying this phase transition in more detail, we find abrupt liquefaction and solidification, resulting in formation of the nanodots oriented with the (110) crystallographic plane parallel to the substrate. Furthermore, by analysis of the recorded specular diffraction rods, we propose growth by initial deposition, followed by a transformation into nandots, followed by further deposition. Overall, we demonstrate that controlling the growth scenario for Bi nanostructures, here shown by PLD and MBE, one is able to steer its resulting shape, size and corresponding (materials) properties. |
BibTeX:
@article{WOS:000805185100001,
author = {Bollmann, Tjeerd R. J. and Jankowski, Maciej},
title = {Kinetics and the crystallographic structure of bismuth during liquefaction and solidification on an insulating substrate},
journal = {SURFACE SCIENCE},
year = {2022},
volume = {723},
doi = {https://doi.org/10.1016/j.susc.2022.122106}
}
|
| Adamo, F.C., Ciuchi, F., De Santo, M.P., Astolfi, P., Warner, I., Scharrer, E., Pisani, M., Vita, F. and Francescangeli, O. Nanoscale Structure of Langmuir-Blodgett Film of Bent-Core Molecules NANOMATERIALS 12, 13 (2022) |
| Abstract: Bent-core mesogens (BCMs) are a class of thermotropic liquid crystals
featuring several unconventional properties. However, the interpretation and technological exploitation of their unique behavior have been hampered by the difficulty of controlling their anchoring at surfaces. To tackle this issue, we report the nanoscale structural characterization of BCM films prepared using the Langmuir-Blodgett technique. Even though BCMs are quite different from typical amphiphilic molecules, we demonstrate that stable molecular films form over water, which can then be transferred onto silicon substrates. The combination of Brewster angle microscopy, atomic force microscopy, and X-ray reflectivity measurements shows that the molecules, once transferred onto a solid substrate, form a bilayer structure with a bottom layer of flat molecules and an upper layer of upright molecules. These results suggest that Langmuir-Blodgett films of BCMs can provide a useful means to control the alignment of this class of liquid crystals. |
BibTeX:
@article{WOS:000825643000001,
author = {Adamo, Fabrizio Corrado and Ciuchi, Federica and De Santo, Maria Penelope and Astolfi, Paola and Warner, Isabelle and Scharrer, Eric and Pisani, Michela and Vita, Francesco and Francescangeli, Oriano},
title = {Nanoscale Structure of Langmuir-Blodgett Film of Bent-Core Molecules},
journal = {NANOMATERIALS},
year = {2022},
volume = {12},
number = {13},
doi = {https://doi.org/10.3390/nano12132285}
}
|
| Kim, S., Pathak, S., Rhim, S.H., Cha, J., Jekal, S., Hong, S.C., Lee, H.H., Park, S.-H., Lee, H.-K., Park, J.-H., Lee, S., Steinruck, H.-G., Mehta, A., Wang, S.X. and Hong, J. Giant Orbital Anisotropy with Strong Spin-Orbit Coupling Established at the Pseudomorphic Interface of the Co/Pd Superlattice ADVANCED SCIENCE early access (JUN 2022) |
| Abstract: Orbital anisotropy at interfaces in magnetic heterostructures has been
key to pioneering spin-orbit-related phenomena. However, modulating the interface's electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low-energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co3O4/Pd superlattices during irradiation. Structural investigations corroborate that progressive reduction of Co3O4 into Co establishes pseudomorphic growth with sharp interfaces and atypically large tensile stress. The normal component of orbital to spin magnetic moment at the interface is the largest among those observed in layered Co systems, which is associated with giant orbital anisotropy theoretically confirmed, and resulting very large interfacial magnetic anisotropy is observed. All results attribute not only to giant orbital anisotropy but to enhanced interfacial spin-orbit coupling owing to the pseudomorphic nature at the interface. They are strongly supported by the observation of reversal of polarity of temperature-dependent Anomalous Hall signal, a signature of Berry phase. This work suggests that establishing both giant orbital anisotropy and strong spin-orbit coupling at the interface is key to exploring spintronic devices with new functionalities. |
BibTeX:
@article{WOS:000815013600001,
author = {Kim, Sanghoon and Pathak, Sachin and Rhim, Sonny H. and Cha, Jongin and Jekal, Soyoung and Hong, Soon Cheol and Lee, Hyun Hwi and Park, Sung-Hun and Lee, Han-Koo and Park, Jae-Hoon and Lee, Soogil and Steinruck, Hans-Georg and Mehta, Apurva and Wang, Shan X. and Hong, Jongill},
title = {Giant Orbital Anisotropy with Strong Spin-Orbit Coupling Established at the Pseudomorphic Interface of the Co/Pd Superlattice},
journal = {ADVANCED SCIENCE},
doi = {https://doi.org/10.1002/advs.202201749}
}
|
| Nussupov, K.K., Beisenkhanov, N.B., Keiinbay, S. and Sultanov, A.T. Silicon carbide synthesized by RF magnetron sputtering in the composition of a double layer antireflection coating SiC/MgF2 OPTICAL MATERIALS 128 (2022) |
| Abstract: In this paper, the optimal thickness of SiC film for an antireflection
coating was determined by computer simulations using Lumerical FTDT and SCOUT software. The simulation was carried out for the SiC/MgF2 system, where silicon carbide films were deposited at a magnetron power of 100, 150, 200, 250 W, while the thickness of the magnesium fluoride films remained unchanged and amounted to 130 nm. The simulation results showed that the optimal parameters for the synthesis of SiC antireflection layer are 100 W/50 nm. With these parameters, the reflection is less than 3% in the widest wavelength range of 475-1020 nm. The dependence of the physical properties of the synthesized films on the power of the magnetron is investigated. Using reflection and transmission spectroscopy it was experimentally revealed that a decrease in the magnetron power from 250 to 100 W leads to a decrease in the refractive index. According to our results the best antireflection effect can be achieved with SiC/MgF2 coatings when SiC films are deposited at 100 W magnetron power. The reflectance spectra are consistent with the simulation spectra, especially in the 475-1020 nm range, where the surface reflects only 0.2-3.0% of the incident light. The obtained results are explained by the correlation between the structural properties, composition of amorphous silicon carbide films and antireflection properties. |
BibTeX:
@article{WOS:000797198600005,
author = {Nussupov, Kair Kh. and Beisenkhanov, Nurzhan B. and Keiinbay, Symaiyl and Sultanov, Assanali T.},
title = {Silicon carbide synthesized by RF magnetron sputtering in the composition of a double layer antireflection coating SiC/MgF2},
journal = {OPTICAL MATERIALS},
year = {2022},
volume = {128},
doi = {https://doi.org/10.1016/j.optmat.2022.112370}
}
|
| Droulias, S.A., Granas, O., Hartmann, O., Komander, K., Hjorvarsson, B., Wolff, M. and Palsson, G.K. Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices PHYSICAL REVIEW B 105, 19 (2022) |
| Abstract: The deuterium-induced changes of the optical transmission in Fe/V (001)
and Cr/V (001) superlattices are found experimentally to be dominated by the volume changes of the vanadium layers and thus indirectly linked to concentration. The deuterium-induced expansion is 67% larger in Cr/V 2/14 monolayers (ML) as compared to Fe/V 2/14 ML. This large difference can be explained by a difference in the site of deuterium from tetrahedral in Fe/V to octahedral in Cr/V. First-principles calculations based on this assumption give quantitative agreement with both the measured optical transmission and the deuterium-induced expansion coefficient. Placing hydrogen in the middle of the vanadium layers results in total energies at 0 K that favor tetrahedral occupancy at low concentrations, although the energy difference is of the order of the thermal energy available in the experiments. Hence small changes in strain, defect concentration, and/or vibrational spectrum of the superlattices may tip the balance to octahedral occupancy at low concentrations. Given this link to concentration and the linear scaling, optical transmission can, therefore, be used in a straightforward way to obtain pressure-composition isotherms also in thin metal films that do not undergo metal-insulator transitions upon hydrogenation. |
BibTeX:
@article{WOS:000809498100007,
author = {Droulias, S. A. and Granas, O. and Hartmann, O. and Komander, K. and Hjorvarsson, B. and Wolff, M. and Palsson, G. K.},
title = {Influence of deuterium-induced volume changes on optical transmission in Fe/V (001) and Cr/V (001) superlattices},
journal = {PHYSICAL REVIEW B},
year = {2022},
volume = {105},
number = {19},
doi = {https://doi.org/10.1103/PhysRevB.105.195438}
}
|
| Wan, H.-W., Cheng, Y.-T., Cheng, C.-K., Hong, Y.-J., Chu, T.-Y., Chang, M.-T., Hsu, C.-H., Kwo, J. and Hong, M. High-Ge-Content Si1-xGex Gate Stacks with Low-Temperature Deposited Ultrathin Epitaxial Si: Growth, Structures, Low Interfacial Traps, and Reliability ACS APPLIED ELECTRONIC MATERIALS 4, 6, pp. 2641-2647 (2022)early access (MAY 2022) |
| Abstract: Si1-xGex with Ge contents higher than x = 0.5 is expected to boost
on-current and improve reliability of p-channel metal-oxide-semiconductor (pMOS) devices. However, unavoidable GeOx formation at the high-kappa/Si1-xGex interface with high Ge-contents (HGC) has caused high interfacial trap density, posing a challenge for employing the HGC Si(1-x)Ge(x )as the channel in sub-3 nm complementary MOS technology. In this work, we have deposited epitaxial Si (epi-Si) of six monolayer thickness on Si1-xGex at temperatures of 260-280 degrees C to minimize Ge diffusion and segregation. Si1-xGex layers with a wide range of HGC (0.5 < x <= 0.8) were grown to investigate the effectiveness of the epi-Si on the Si1-xGex To minimize the GeOx formation caused by the oxidation of the segregated Ge on the epi-Si surface, HfO2 was subsequently deposited via e-beam evaporation on the epi-Si. The measurements using reflection high-energy electron diffraction, high-resolution synchrotron radiation X-ray diffraction, and scanning transmission electron microscopy with high-angle annulardark-field imaging have revealed the high crystallinity of the epi-Si, the Si1-xGex layers, and abrupt interfaces of the high-kappa/epi-Si/Si1-xGex layers. The well-controlled interfaces have enabled the achievement of low interfacial trap densities (D-it) of (3-6) x 10(11) eV(-1) cm(-2) in these high-kappa/epi-Si/(HGC)Si1-xGex samples. The minimum D-it values remained at 3 x 10(11) eV(-1) cm(-2) regardless of the Ge content, confirming the effective passivation of the low-temperature deposited epi-Si. By extracting the effective charge sheet densities for the Si1-xGex gate stacks via examination of capacitance-voltage (C-V) hysteresis with decreasing stress voltage in the accumulation region of the MOS capacitors, we have attained very high acceleration factors of 8-12, indicating high reliability of the HfO2/epi-Si/SiGe pMOS gate stacks. |
BibTeX:
@article{WOS:000818954400001,
author = {Wan, Hsien-Wen and Cheng, Yi-Ting and Cheng, Chao-Kai and Hong, Yu-Jie and Chu, Tien-Yu and Chang, Mu-Tung and Hsu, Chia-Hung and Kwo, Jueinai and Hong, Minghwei},
title = {High-Ge-Content Si1-xGex Gate Stacks with Low-Temperature Deposited Ultrathin Epitaxial Si: Growth, Structures, Low Interfacial Traps, and Reliability},
journal = {ACS APPLIED ELECTRONIC MATERIALS},
year = {2022},
volume = {4},
number = {6},
pages = {2641-2647},
doi = {https://doi.org/10.1021/acsaelm.2c00062}
}
|
| Bromley, D., Wright, A.J., Jones, L.A.H., Swallow, J.E.N., Beesley, T., Batty, R., Weatherup, R.S., Dhanak, V.R. and O'Brien, L. Electron beam evaporation of superconductor-ferromagnet heterostructures SCIENTIFIC REPORTS 12, 1 (2022) |
| Abstract: We report on the electronic and magnetic properties of
superconductor-ferromagnet heterostructures fabricated by electron beam evaporation on to unheated thermally oxidised Si substrates. Polycrystalline Nb thin films (5 to 50 nm thick) were shown to possess reliably high superconducting critical temperatures (T-c), which correlate well with the residual resistivity ratio (RRR) of the film. These properties improved during ex-situ annealing, resulting in Delta T-c and Delta RRR increases of up 2.2 K (similar to 40% of the pre-annealed T-c) and 0.8 (similar to 60% of the pre-annealed RRR) respectively. Nb/Pt/Co/Pt heterostructures showed substantial perpendicular anisotropy in the ultrathin limit (<= 2.5 nm), even in the extreme limit of Pt(0.8 nm)/Co(1 nm)/Pt(0.6 nm). These results point to the use of electron beam evaporation as route to line-of-sight deposited, low-thickness, high quality Nb-based superspintronic multilayers. |
BibTeX:
@article{WOS:000794011500082,
author = {Bromley, D. and Wright, A. J. and Jones, L. A. H. and Swallow, J. E. N. and Beesley, T. and Batty, R. and Weatherup, R. S. and Dhanak, V. R. and O'Brien, L.},
title = {Electron beam evaporation of superconductor-ferromagnet heterostructures},
journal = {SCIENTIFIC REPORTS},
year = {2022},
volume = {12},
number = {1},
doi = {https://doi.org/10.1038/s41598-022-11828-y}
}
|
| Cheema, S.S., Shanker, N., Hsu, S.-L., Rho, Y., Hsu, C.-H., Stoica, V.A., Zhang, Z., Freeland, J.W., Shafer, P., Grigoropoulos, C.P., Ciston, J. and Salahuddin, S. Emergent ferroelectricity in subnanometer binary oxide films on silicon SCIENCE 376, 6593, pp. 648+ (2022) |
| Abstract: The critical size limit of voltage-switchable electric dipoles has
extensive implications for energy-efficient electronics, underlying the importance of ferroelectric order stabilized at reduced dimensionality. We report on the thickness-dependent antiferroelectric-to-ferroelectric phase transition in zirconium dioxide (ZrO2) thin films on silicon. The emergent ferroelectricity and hysteretic polarization switching in ultrathin ZrO2, conventionally a paraelectric material, notably persists down to a film thickness of 5 angstroms, the fluorite-structure unit-cell size. This approach to exploit three-dimensional centrosymmetric materials deposited down to the two-dimensional thickness limit, particularly within this model fluorite-structure system that possesses unconventional ferroelectric size effects, offers substantial promise for electronics, demonstrated by proof-of-principle atomic-scale nonvolatile ferroelectric memory on silicon. Additionally, it is also indicative of hidden electronic phenomena that are achievable across a wide class of simple binary materials. |
BibTeX:
@article{WOS:000796932700047,
author = {Cheema, Suraj S. and Shanker, Nirmaan and Hsu, Shang-Lin and Rho, Yoonsoo and Hsu, Cheng-Hsiang and Stoica, Vladimir A. and Zhang, Zhan and Freeland, John W. and Shafer, Padraic and Grigoropoulos, Costas P. and Ciston, Jim and Salahuddin, Sayeef},
title = {Emergent ferroelectricity in subnanometer binary oxide films on silicon},
journal = {SCIENCE},
year = {2022},
volume = {376},
number = {6593},
pages = {648+},
doi = {https://doi.org/10.1126/science.abm8642}
}
|
| Anyfantis I, D., Ballani, C., Kanistras, N., Barnasas, A., Kapaklis, V., Schmidt, G., Papaioannou, E.T. and Poulopoulos, P. Growth, Magnetic Anisotropies and Exchange Bias of Thin Ni0.95Fe0.05/NiFeO Multilayers COATINGS 12, 5 (2022) |
| Abstract: Ni0.95Fe0.05/NiFeO multilayers were fabricated by radio frequency
magnetron sputtering and natural oxidation. Doping of Ni by only 5 at. % Fe results in enhanced layering quality as X-ray reflectivity reveals. Due to magnetostatic anisotropy, the multilayers were found to be in-plane magnetized. The influence of mild thermal annealing (T = 525 K) on the magnetic properties of NiFe/NiFeO multilayers is also investigated. Annealing results in the enhancement of perpendicular magnetic anisotropy, mainly due to an increase in the uniaxial volume anisotropy term. Temperature-dependent hysteresis measurements between 4-400 K revealed considerable enhancement of coercivity and appearance of exchange bias effect. |
BibTeX:
@article{WOS:000803368400001,
author = {Anyfantis, I, Dimitrios and Ballani, Camillo and Kanistras, Nikos and Barnasas, Alexandros and Kapaklis, Vassilios and Schmidt, Georg and Papaioannou, Evangelos Th and Poulopoulos, Panagiotis},
title = {Growth, Magnetic Anisotropies and Exchange Bias of Thin Ni0.95Fe0.05/NiFeO Multilayers},
journal = {COATINGS},
year = {2022},
volume = {12},
number = {5},
doi = {https://doi.org/10.3390/coatings12050627}
}
|
| Zhang, X., Penn, A.N., Wysocki, L., Zhang, Z., van Loosdrecht, P.H.M., Kornblum, L., LeBeau, J.M., Lindfors-Vrejoiu, I. and Kumah, D.P. Thickness and temperature dependence of the atomic-scale structure of SrRuO3 thin films APL MATERIALS 10, 5 (2022) |
| Abstract: The temperature-dependent layer-resolved structure of 3 to 44 unit cell
thick SrRuO3 (SRO) films grown on Nb-doped SrTiO3 substrates is investigated using a combination of high-resolution synchrotron x-ray diffraction and high-resolution electron microscopy to understand the role that structural distortions play in suppressing ferromagnetism in ultra-thin SRO films. The oxygen octahedral tilts and rotations and Sr displacements characteristic of the bulk orthorhombic phase are found to be strongly dependent on temperature, the film thickness, and the distance away from the film-substrate interface. For thicknesses, t, above the critical thickness for ferromagnetism (t > 3 uc), the orthorhombic distortions decrease with increasing temperature above T-C. Below T-C, the structure of the films remains constant due to the magneto-structural coupling observed in bulk SRO. The orthorhombic distortions are found to be suppressed in the 2-3 interfacial layers due to structural coupling with the SrTiO3 substrate and correlate with the critical thickness for ferromagnetism in uncapped SRO films. (C) 2022 Author(s). |
BibTeX:
@article{WOS:000800200500002,
author = {Zhang, Xuanyi and Penn, Aubrey N. and Wysocki, Lena and Zhang, Zhan and van Loosdrecht, Paul H. M. and Kornblum, Lior and LeBeau, James M. and Lindfors-Vrejoiu, Ionela and Kumah, Divine P.},
title = {Thickness and temperature dependence of the atomic-scale structure of SrRuO3 thin films},
journal = {APL MATERIALS},
year = {2022},
volume = {10},
number = {5},
doi = {https://doi.org/10.1063/5.0087791}
}
|
| Ibarra, R., Lesne, E., Ouladdiaf, B., Beauvois, K., Sukhanov, A.S., Schnelle, W., Devishvili, A., Inosov, D.S., Felser, C. and Markou, A. Noncollinear magnetic order in epitaxial thin films of the centrosymmetric MnPtGa hard magnet APPLIED PHYSICS LETTERS 120, 17 (2022) |
| Abstract: Magnetic systems exhibiting spin-canted states have garnered much
attention recently for their promising rich exotic properties driven by the real-space spin textures and competing magnetic orders. In this study, we present the structural and magnetic properties of hexagonal 60 nm MnPtGa epitaxial thin films grown by magnetron sputtering on Al2O3(0001) single-crystalline substrates. The MnPtGa film crystallizes in the centrosymmetric P6(3)/mmc (No. 194) space group, showing perpendicular magnetic anisotropy along the c-axis, with a Curie temperature T-C = 263 K. In addition, the MnPtGa film undergoes a spin reorientation transition at T-sr = 160 K. We investigated the MnPtGa magnetic ground states using single-crystal neutron diffraction. A structurally forbidden (001) magnetic Bragg reflection emerges below T-sr, indicating the existence of a spin-canted state, where the magnetic moments align ferromagnetically perpendicular to the basal plane, and a non-zero in-plane component exhibits an antiferromagnetic ordering along the c-axis. At 2 K, the refined magnetic moments of Mn are mu(z) = 4.2(4) mu(B) and mu(x) = 1.5(3) mu(B), projected onto the c-axis and basal plane, respectively. Hence, we determined a 20 degrees Mn spin canting angle off from the c-axis. (C) 2022 Author(s). |
BibTeX:
@article{WOS:000793222000002,
author = {Ibarra, R. and Lesne, E. and Ouladdiaf, B. and Beauvois, K. and Sukhanov, A. S. and Schnelle, W. and Devishvili, A. and Inosov, D. S. and Felser, C. and Markou, A.},
title = {Noncollinear magnetic order in epitaxial thin films of the centrosymmetric MnPtGa hard magnet},
journal = {APPLIED PHYSICS LETTERS},
year = {2022},
volume = {120},
number = {17},
doi = {https://doi.org/10.1063/5.0090009}
}
|
| Morisset, A., Famprikis, T., Haug, F.-J., Ingenito, A., Ballif, C. and Bannenberg, L.J. In Situ Reflectometry and Diffraction Investigation of the Multiscale Structure of p-Type Polysilicon Passivating Contacts for c-Si Solar Cells ACS APPLIED MATERIALS & INTERFACES 14, 14, pp. 16413-16423 (2022) |
| Abstract: The integration of passivating contacts based on a highly doped
polycrystalline silicon (poly-Si) layer on top of a thin silicon oxide (SiOx) layer has been identified as the next step to further increase the conversion efficiency of current mainstream crystalline silicon (c-Si) solar cells. However, the interrelation between the final properties of poly-Si/SiOx contacts and their fabrication process has not yet been fully unraveled, which is mostly due to the challenge of characterizing thin-film stacks with features in the nanometric range. Here, we apply in situ X-ray reflectometry and diffraction to investigate the multiscale (1 angstrom-100 nm) structural evolution of poly-Si contacts during annealing up to 900 degrees C. This allows us to quantify the densification and thinning of the poly-Si layer during annealing as well as to monitor the disruption of the thin SiOx layer at high temperature >800 degrees C. Moreover, results obtained on a broader range of thermal profiles, including firing with dwell times of a few seconds, emphasize the impact of high thermal budgets on poly-Si contacts' final properties and thus the importance of ensuring a good control of such high-temperature processes when fabricating c-Si solar cells integrating such passivating contacts. Overall, this study demonstrates the robustness of combining different X-ray elastic scattering techniques (here XRR and GIXRD), which present the unique advantage of being rapid, nondestructive, and applicable on a large sample area, to unravel the multiscale structural evolution of poly-Si contacts in situ during high-temperature processes. |
BibTeX:
@article{WOS:000800533100051,
author = {Morisset, Audrey and Famprikis, Theodosios and Haug, Franz-Josef and Ingenito, Andrea and Ballif, Christophe and Bannenberg, Lars J.},
title = {In Situ Reflectometry and Diffraction Investigation of the Multiscale Structure of p-Type Polysilicon Passivating Contacts for c-Si Solar Cells},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2022},
volume = {14},
number = {14},
pages = {16413-16423},
doi = {https://doi.org/10.1021/acsami.2c01225}
}
|
| Beiranvand, A., Liedke, M.O., Haalisto, C., Laehteenlahti, V., Schulman, A., Granroth, S., Palonen, H., Butterling, M., Wagner, A., Huhtinen, H. and Paturi, P. Manipulating magnetic and magnetoresistive properties by oxygen vacancy complexes in GCMO thin films JOURNAL OF PHYSICS-CONDENSED MATTER 34, 15 (2022) |
| Abstract: The effect of in situ annealing is investigated in Gd0.1Ca0.9MnO3 (GCMO)
thin films in oxygen and vacuum atmospheres. We show that the reduction of oxygen content in GCMO lattice by vacuum annealing induced more oxygen complex vacancies in both subsurface and interface regions and larger grain domains when compared with the pristine one. Consequently, the double exchange interaction is suppressed and the metallic-ferromagnetic state below Curie temperature turned into spin-glass insulating state. In contrast, the magnetic and resistivity measurements show that the oxygen treatment increases ferromagnetic phase volume, resulting in greater magnetization (M (S)) and improved magnetoresistivity properties below Curie temperature by improving the double exchange interaction. The threshold field to observe the training effect is decreased in oxygen treated film. In addition, the positron annihilation spectroscopy analysis exhibits fewer open volume defects in the subsurface region for oxygen treated film when compared with the pristine sample. These results unambiguously demonstrate that the oxygen treated film with significant spin memory and greater magnetoresistance can be a potential candidate for the future memristor applications. |
BibTeX:
@article{WOS:000757599800001,
author = {Beiranvand, A. and Liedke, M. O. and Haalisto, C. and Laehteenlahti, V and Schulman, A. and Granroth, S. and Palonen, H. and Butterling, M. and Wagner, A. and Huhtinen, H. and Paturi, P.},
title = {Manipulating magnetic and magnetoresistive properties by oxygen vacancy complexes in GCMO thin films},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2022},
volume = {34},
number = {15},
doi = {https://doi.org/10.1088/1361-648X/ac4eac}
}
|
| Cheema, S.S., Shanker, N., Wang, L.-C., Hsu, C.-H., Hsu, S.-L., Liao, Y.-H., San Jose, M., Gomez, J., Chakraborty, W., Li, W., Bae, J.-H., Volkman, S.K., Kwon, D., Rho, Y., Pinelli, G., Rastogi, R., Pipitone, D., Stull, C., Cook, M., Tyrrell, B., Stoica, V.A., Zhang, Z., Freeland, J.W., Tassone, C.J., Mehta, A., Saheli, G., Thompson, D., Suh, D.I., Koo, W.-T., Nam, K.-J., Jung, D.J., Song, W.-B., Lin, C.-H., Nam, S., Heo, J., Parihar, N., Grigoropoulos, C.P., Shafer, P., Fay, P., Ramesh, R., Mahapatra, S., Ciston, J., Datta, S., Mohamed, M., Hu, C. and Salahuddin, S. Ultrathin ferroic HfO2-ZrO2 superlattice gate stack for advanced transistors NATURE 604, 7904, pp. 65+ (2022) |
| Abstract: With the scaling of lateral dimensions in advanced transistors, an
increased gate capacitance is desirable both to retain the control of the gate electrode over the channel and to reduce the operating voltage'. This led to a fundamental change in the gate stack in 2008, the incorporation of high-dielectric-constant HfO2 (ref. 2 ), which remains the material of choice to date. Here we report HfO2-ZrO2 superlattice heterostructures as a gate stack, stabilized with mixed ferroelectric-antiferroelectric order, directly integrated onto Si transistors, and scaled down to approximately 20 angstroms, the same gate oxide thickness required for high-performance transistors. The overall equivalent oxide thickness in metal-oxide-semiconductor capacitors is equivalent to an effective SiO2 thickness of approximately 6.5 angstroms. Such a low effective oxide thickness and the resulting large capacitance cannot be achieved in conventional HfO2-based high-dielectric-constant gate stacks without scavenging the interfacial SiO2, which has adverse effects on the electron transport and gate leakage current'. Accordingly, our gate stacks, which do not require such scavenging, provide substantially lower leakage current and no mobility degradation. This work demonstrates that ultrathin ferroic HfO2-ZrO2 multilayers, stabilized with competing ferroelectric-antiferroelectric order in the two-nanometre-thickness regime, provide a path towards advanced gate oxide stacks in electronic devices beyond conventional HfO2-based high-dielectric-constant materials. |
BibTeX:
@article{WOS:000779100400017,
author = {Cheema, Suraj S. and Shanker, Nirmaan and Wang, Li-Chen and Hsu, Cheng-Hsiang and Hsu, Shang-Lin and Liao, Yu-Hung and San Jose, Matthew and Gomez, Jorge and Chakraborty, Wriddhi and Li, Wenshen and Bae, Jong-Ho and Volkman, Steve K. and Kwon, Daewoong and Rho, Yoonsoo and Pinelli, Gianni and Rastogi, Ravi and Pipitone, Dominick and Stull, Corey and Cook, Matthew and Tyrrell, Brian and Stoica, Vladimir A. and Zhang, Zhan and Freeland, John W. and Tassone, Christopher J. and Mehta, Apurva and Saheli, Ghazal and Thompson, David and Suh, Dong Ik and Koo, Won-Tae and Nam, Kab-Jin and Jung, Dong Jin and Song, Woo-Bin and Lin, Chung-Hsun and Nam, Seunggeol and Heo, Jinseong and Parihar, Narendra and Grigoropoulos, Costas P. and Shafer, Padraic and Fay, Patrick and Ramesh, Ramamoorthy and Mahapatra, Souvik and Ciston, Jim and Datta, Suman and Mohamed, Mohamed and Hu, Chenming and Salahuddin, Sayeef},
title = {Ultrathin ferroic HfO2-ZrO2 superlattice gate stack for advanced transistors},
journal = {NATURE},
year = {2022},
volume = {604},
number = {7904},
pages = {65+},
doi = {https://doi.org/10.1038/s41586-022-04425-6}
}
|
| Greco, A., Starostin, V., Edel, E., Munteanu, V., Russegger, N., Dax, I., Shen, C., Bertram, F., Hinderhofer, A., Gerlach, A. and Schreiber, F. Neural network analysis of neutron and X-ray reflectivity data: automated analysis using mlreflect, experimental errors and feature engineering JOURNAL OF APPLIED CRYSTALLOGRAPHY 55, 2, pp. 362-369 (2022) |
| Abstract: The Python package mlreflect is demonstrated, which implements an
optimized pipeline for the automated analysis of reflectometry data using machine learning. The package combines several training and data treatment techniques discussed in previous publications. The predictions made by the neural network are accurate and robust enough to serve as good starting parameters for an optional subsequent least-mean-squares (LMS) fit of the data. For a large data set of 242 reflectivity curves of various thin films on silicon substrates, the pipeline reliably finds an LMS minimum very close to a fit produced by a human researcher with the application of physical knowledge and carefully chosen boundary conditions. The differences between simulated and experimental data and their implications for the training and performance of neural networks are discussed. The experimental test set is used to determine the optimal noise level during training. The extremely fast prediction times of the neural network are leveraged to compensate for systematic errors by sampling slight variations in the data. |
BibTeX:
@article{WOS:000778776600017,
author = {Greco, Alessandro and Starostin, Vladimir and Edel, Evelyn and Munteanu, Valentin and Russegger, Nadine and Dax, Ingrid and Shen, Chen and Bertram, Florian and Hinderhofer, Alexander and Gerlach, Alexander and Schreiber, Frank},
title = {Neural network analysis of neutron and X-ray reflectivity data: automated analysis using mlreflect, experimental errors and feature engineering},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2022},
volume = {55},
number = {2},
pages = {362-369},
doi = {https://doi.org/10.1107/S1600576722002230}
}
|
| Griggs, W. and Thomson, T. Repeatable and deterministic all electrical switching in a mixed phase artificial multiferroic SCIENTIFIC REPORTS 12, 1 (2022) |
| Abstract: We demonstrate a repeatable all-electric magnetic switching behaviour in
a PM N-PT/FeRh thin film artificial multiferroic. The magnitude of the effect is significantly smaller than expected from conventional thermomagnetic switching of FeRh thin films and we explore properties of the PMN-PT/FeRh system in order to understand the origin of this reduction. The data demonstrate the importance of the crystallographic phase of PMN-PT and show how a phase transition at similar to 100 degrees C modifies the magneto-electric coupling. We demonstrate a large strain remanence effect in the PM N-PT substrate, which limits the magnetoelectric coupling on successive cycling of the applied electric field. |
BibTeX:
@article{WOS:000775227200046,
author = {Griggs, W. and Thomson, T.},
title = {Repeatable and deterministic all electrical switching in a mixed phase artificial multiferroic},
journal = {SCIENTIFIC REPORTS},
year = {2022},
volume = {12},
number = {1},
doi = {https://doi.org/10.1038/s41598-022-09417-0}
}
|
| Swindells, C., Glowinski, H., Choi, Y., Haskel, D., Michalowski, P.P., Hase, T., Stobiecki, F., Kuswik, P. and Atkinson, D. Magnetic damping in ferromagnetic/heavy-metal systems: The role of interfaces and the relation to proximity-induced magnetism PHYSICAL REVIEW B 105, 9 (2022) |
| Abstract: Damping and spin transport in spintronic multilayered systems continues
to be a topic of active research. The enhancement of damping in ferromagnet (FM)/spacer layer (SL)/heavy-metal (HM) thin-film systems was studied for Co25Fe75/SL/Pt with a nonmagnetic (NM) SL of either Au or Cu with variable thickness, in order to understand the correlation with proximity-induced magnetism (PIM) in the HM. Structural, PIM and magnetic damping measurements were undertaken on the same samples. Specifically, secondary ion mass spectroscopy, element specific x-ray magnetic reflectivity and x-ray magnetic circular dichroism at the Pt and Au L-3 edges, and ferromagnetic resonance methods were used. With increasing thickness of a Cu or Au SL directly between the FM and the Pt layer, the Pt PIM and the damping both fall rapidly, with a relationship between damping and PIM that depends on the SL material. The PIM observed in the Au layer showed a complex dependence on the layer thickness, suggesting some hybridization with the Pt. The role of the number and location of interfaces on the damping was demonstrated with the addition of a SL within the Pt layer, which showed that the specific details of the NM/HM interface also affects the damping. The insertion of a Cu SL within the Pt showed a measurable increase in the overall enhancement of the damping while the insertion of a Au SL into Pt had almost no effect on the damping. Together these results demonstrate the role of both PIM and of additional interfaces in the enhancement of damping in FM/HM systems, which is not fully accounted for by existing theory. |
BibTeX:
@article{WOS:000800669700001,
author = {Swindells, C. and Glowinski, H. and Choi, Y. and Haskel, D. and Michalowski, P. P. and Hase, T. and Stobiecki, F. and Kuswik, P. and Atkinson, D.},
title = {Magnetic damping in ferromagnetic/heavy-metal systems: The role of interfaces and the relation to proximity-induced magnetism},
journal = {PHYSICAL REVIEW B},
year = {2022},
volume = {105},
number = {9},
doi = {https://doi.org/10.1103/PhysRevB.105.094433}
}
|
| Guasco, L., Khaydukov, Y.N., Puetter, S., Silvi, L., Paulin, M.A., Keller, T. and Keimer, B. Resonant neutron reflectometry for hydrogen detection NATURE COMMUNICATIONS 13, 1 (2022) |
| Abstract: The detection and quantification of hydrogen is becoming increasingly
important in research on electronic materials and devices, following the identification of the hydrogen content as a potent control parameter for the electronic properties. However, establishing quantitative correlations between the hydrogen content and the physical properties of solids remains a formidable challenge. Here we report neutron reflectometry experiments on 50 nm thick niobium films during hydrogen loading, and show that the momentum-space position of a prominent waveguide resonance allows tracking of the absolute hydrogen content with an accuracy of about one atomic percent on a timescale of less than a minute. Resonance-enhanced neutron reflectometry thus allows fast, direct, and non-destructive measurements of the hydrogen concentration in thin-film structures, with sensitivity high enough for real-time in-situ studies. The detection and quantification of hydrogen is becoming increasingly important in research on electronic materials and devices. Here the authors show that waveguide resonances enhance the sensitivity of neutron reflectometry, enabling fast, direct, and nondestructive measurements of hydrogen incorporation in thin-film structures. |
BibTeX:
@article{WOS:000770716000011,
author = {Guasco, L. and Khaydukov, Yu N. and Puetter, S. and Silvi, L. and Paulin, M. A. and Keller, T. and Keimer, B.},
title = {Resonant neutron reflectometry for hydrogen detection},
journal = {NATURE COMMUNICATIONS},
year = {2022},
volume = {13},
number = {1},
doi = {https://doi.org/10.1038/s41467-022-29092-z}
}
|
| Niti, Kumar, Y., Seema, Reddy, V.R., Vas, J.V., Gupta, S., Stahn, J., Gupta, A. and Gupta, M. Stabilizing effects of Ag doping on structure and thermal stability of FeN thin films JOURNAL OF PHYSICS-CONDENSED MATTER 34, 11 (2022) |
| Abstract: In this work, we investigated the effect of Ag doping (2-20 at.%) on
the phase formation of iron mononitride (FeN) thin films. Together with deposition of FeN using reactive dc magnetron sputtering, Ag was also co-sputtered at various doping levels between 2-20 at.%. We found that doping of Ag around 5 at.% is optimum to not only improve the thermal stability of FeN but also to reduce intrinsic defects that are invariably present in (even in epitaxial) FeN. Conversion electron Mossbauer spectroscopy and N K-edge x-ray near edge absorption measurements clearly reveal a reduction of defects in Ag doped FeN samples. Moreover, Fe self-diffusion measurements carried out using secondary ion mass spectroscopy depth-profiling and polarized neutron reflectivity in Fe-57 enriched samples exhibit an appreciable reduction in Fe self-diffusion in Ag doped FeN samples. Ag being immiscible with Fe and non-reactive with N, occupies grain-boundary positions as nanoparticles and prohibits the fast Fe self-diffusion in FeN. |
BibTeX:
@article{WOS:000740043600001,
author = {Niti and Kumar, Yogesh and Seema and Reddy, V. R. and Vas, Joseph Vimal and Gupta, Surbhi and Stahn, Jochen and Gupta, Ajay and Gupta, Mukul},
title = {Stabilizing effects of Ag doping on structure and thermal stability of FeN thin films},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2022},
volume = {34},
number = {11},
doi = {https://doi.org/10.1088/1361-648X/ac4074}
}
|
| Lai, C.-C., Boyd, R., Svensson, P.-O., Hoglund, C., Robinson, L., Birch, J. and Hall-Wilton, R. Effect of substrate roughness and material selection on the microstructure of sputtering deposited boron carbide thin films SURFACE & COATINGS TECHNOLOGY 433 (2022) |
| Abstract: Amorphous boron carbide (B4C) thin films are by far the most popular
form for the neutron converting layers in the 10B-based neutron detectors, which are a rising trend in detector technologies in response to the increasing scarcity and price of( 3)He, the standard material for neutron detection. The microstructure of the B4C films is closely related to the important properties, e.g. density and adhesion, for the converting layers, which eventually affect the detection efficiency and the long-term stability of the detectors. To study the influence from substrates of different roughness and materials, the B4C films were deposited on polished Si substrates with Al, Ti, and Cu buffer layers and unpolished Si, Al, Ti, and Cu substrates by direct current magnetron sputtering at a substrate temperature of 623 K. The tapered columnar grains and nodular defects, generally observed in SEM images, indicated a strong shadowing effect where voids were introduced around the grains. The change in the grain size did not show a direct dependence to the substrate roughness, acquired from the surface profile, nor to the mass density of the films, obtained from reflectivity patterns. However, films with non-uniform size of columnar grains were deposited on substrates with high skewness, leading to a drop of mass density from-95% down to-70% of tabulated bulk density. On the other hand, similar microstructures and mass density were obtained from the films deposited on Al, Ti, and Cu of different roughness and good adhesion were observed from cross-cut adhesion tests, showing the reliability of sputtering deposited B4C films on common structural materials in neutron detectors. |
BibTeX:
@article{WOS:000782695200001,
author = {Lai, Chung-Chuan and Boyd, Robert and Svensson, Per-Olof and Hoglund, Carina and Robinson, Linda and Birch, Jens and Hall-Wilton, Richard},
title = {Effect of substrate roughness and material selection on the microstructure of sputtering deposited boron carbide thin films},
journal = {SURFACE & COATINGS TECHNOLOGY},
year = {2022},
volume = {433},
doi = {https://doi.org/10.1016/j.surfcoat.2022.128160}
}
|
| Derrien, T.L., Lauritzen, A.E., Kaienburg, P., Hancox, E., Nicklin, C. and Riede, M. Interfacial rearrangements and strain evolution in the thin film growth of ZnPc on glass PHYSICAL REVIEW MATERIALS 6, 3 (2022) |
| Abstract: We report on the characterization of the growth of vacuum-deposited zinc
phthalocyanine (ZnPc) thin films on glass through a combination of in situ grazing incidence x-ray scattering, x-ray reflectivity, and atomic force microscopy. We found that the growth at room temperature proceeds via the formation of two structurally unique substrate-induced interfacial layers, followed by the growth of the gamma-ZnPc polymorph thereafter (thickness approximate to 1.0 nm). As the growth of the bulk gamma-ZnPc progresses, a substantial out-of-plane lattice strain (approximate to 15% relative to gamma-ZnPc powder) is continually relaxed during the thin film growth. The rate of strain relaxation was slowed after a thickness of approximate to 13 nm, corresponding to the transition from layer growth to island growth. The findings reveal the real-time microstructural evolution of ZnPc and highlight the importance of substrate-induced strain on thin film growth. |
BibTeX:
@article{WOS:000769317700001,
author = {Derrien, Thomas L. and Lauritzen, Andreas E. and Kaienburg, Pascal and Hancox, Ellis and Nicklin, Chris and Riede, Moritz},
title = {Interfacial rearrangements and strain evolution in the thin film growth of ZnPc on glass},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2022},
volume = {6},
number = {3},
doi = {https://doi.org/10.1103/PhysRevMaterials.6.033401}
}
|
| Moon, E.J. and Goyal, A. Combinatorial synthesis of heteroepitaxial, multi-cation, thin-films via pulsed laser deposition coupled with in-situ, chemical and structural characterization SCIENTIFIC REPORTS 12, 1 (2022) |
| Abstract: Combinatorial synthesis via a continuous composition spread is an
excellent route to develop thin-film libraries as it is both time- and cost-efficient. Creating libraries of functional, multicomponent, complex oxide films requires excellent control over the synthesis parameters combined with high-throughput analytical feedback. A reliable, high-throughput, in-situ characterization analysis method is required to meet the crucial need to rapidly screen materials libraries. Here, we report on the combination of two in-situ techniques-(a) Reflection high-energy electron diffraction (RHEED) for heteroepitaxial characterization and a newly developed compositional analysis technique, low-angle x-ray spectroscopy (LAXS), to map the chemical composition profile of combinatorial heteroepitaxial complex oxide films deposited using a continuous composition spread method via pulsed laser deposition. This is accomplished using a unique state-of-the-art combinatorial growth system with a fully synchronized four-axis mechanical substrate stage without shadow masks, alternating acquisition of chemical compositional data using LAXS at various different positions on the similar to 41 mm x 41mm range and sequential deposition of multilayers of SrTiO3 and SrTi0.8RU0.2O3 on a 2-inch (50.8 mm) LaAlO3 wafer in a single growth run. Rutherford backscattering spectrometry (RBS) is used to calibrate and validate the compositions determined by LAXS. This study shows the feasibility of combinatorial synthesis of heteroepitaxial, functional complex oxide films at wafer-scale via two essential in-situ characterization tools-RHEED for structural analysis or heteroepitaxy and LAXS for compositional characterization. This is a powerful technique for development of new films with optimized heteroepitaxy and composition. |
BibTeX:
@article{WOS:000765922600042,
author = {Moon, E. J. and Goyal, A.},
title = {Combinatorial synthesis of heteroepitaxial, multi-cation, thin-films via pulsed laser deposition coupled with in-situ, chemical and structural characterization},
journal = {SCIENTIFIC REPORTS},
year = {2022},
volume = {12},
number = {1},
doi = {https://doi.org/10.1038/s41598-022-06955-5}
}
|
| Russegger, N., Valencia, A.M., Merten, L., Zwadlo, M., Duva, G., Pithan, L., Gerlach, A., Hinderhofer, A., Cocchi, C. and Schreiber, F. Molecular Charge Transfer Effects on Perylene Diimide Acceptor and Dinaphthothienothiophene Donor Systems JOURNAL OF PHYSICAL CHEMISTRY C 126, 8, pp. 4188-4198 (2022) |
| Abstract: The interactions between organic donor and acceptor molecules and the
related charge transfer (CT) effects are of great interest in organic optoelectronics. Here, we present a comprehensive investigation of cocrystal formation and charge transfer effects in weakly interacting organic semiconductor mixtures. As a model system, we choose dinaphthothienothiophene (DNTT) as a donor molecule and two different perylene diimide derivatives (PTCDI-C-8-CN2 and PDIF-CN2) as acceptors, which differ in the fluorination of the side chains in the imide position. Experimentally, both systems show a small ground-state CT governed by hybridized HOMO-1 and LUMO+1 levels. In contrast, the respective HOMO and LUMO levels of the complex are localized on the acceptor and donor molecule. This leads to the observation of a nearly pure charge transfer excitation from the acceptor to the donor in the absorption spectra. We discuss the general impact of localized HOMO and LUMO levels on the optoelectronic properties in CT complexes dependent on comparison with first-principles calculations based on density functional theory and many-body perturbation theory. |
BibTeX:
@article{WOS:000773651500041,
author = {Russegger, Nadine and Valencia, Ana M. and Merten, Lena and Zwadlo, Matthias and Duva, Giuliano and Pithan, Linus and Gerlach, Alexander and Hinderhofer, Alexander and Cocchi, Caterina and Schreiber, Frank},
title = {Molecular Charge Transfer Effects on Perylene Diimide Acceptor and Dinaphthothienothiophene Donor Systems},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2022},
volume = {126},
number = {8},
pages = {4188-4198},
doi = {https://doi.org/10.1021/acs.jpcc.1c10281}
}
|
| Andrejevic, N., Chen, Z., Nguyen, T., Fan, L., Heiberger, H., Zhou, L.-J., Zhao, Y.-F., Chang, C.-Z., Grutter, A. and Li, M. Elucidating proximity magnetism through polarized neutron reflectometry and machine learning APPLIED PHYSICS REVIEWS 9, 1 (2022) |
| Abstract: Polarized neutron reflectometry is a powerful technique to interrogate
the structures of multilayered magnetic materials with depth sensitivity and nanometer resolution. However, reflectometry profiles often inhabit a complicated objective function landscape using traditional fitting methods, posing a significant challenge for parameter retrieval. In this work, we develop a data-driven framework to recover the sample parameters from polarized neutron reflectometry data with minimal user intervention. We train a variational autoencoder to map reflectometry profiles with moderate experimental noise to an interpretable, low-dimensional space from which sample parameters can be extracted with high resolution. We apply our method to recover the scattering length density profiles of the topological insulator-ferromagnetic insulator heterostructure Bi2Se3/EuS exhibiting proximity magnetism in good agreement with the results of conventional fitting. We further analyze a more challenging reflectometry profile of the topological insulator-antiferromagnet heterostructure (Bi,Sb)(2)Te-3/Cr2O3 and identify possible interfacial proximity magnetism in this material. We anticipate that the framework developed here can be applied to resolve hidden interfacial phenomena in a broad range of layered systems. (C) 2022 Author(s). |
BibTeX:
@article{WOS:000779058400002,
author = {Andrejevic, Nina and Chen, Zhantao and Thanh Nguyen and Fan, Leon and Heiberger, Henry and Zhou, Ling-Jie and Zhao, Yi-Fan and Chang, Cui-Zu and Grutter, Alexander and Li, Mingda},
title = {Elucidating proximity magnetism through polarized neutron reflectometry and machine learning},
journal = {APPLIED PHYSICS REVIEWS},
year = {2022},
volume = {9},
number = {1},
doi = {https://doi.org/10.1063/5.0078814}
}
|
| Pantousa, S., Mergia, K., Ionescu, A., Manios, E., Dellis, S., Kinane, C., Langridge, S., Caruana, A., Kentsch, U. and Messoloras, S. Fe+ ion irradiation effects in Fe-10at%Cr films irradiated at 300 degrees C NUCLEAR MATERIALS AND ENERGY 30 (2022) |
| Abstract: Fe-Cr alloys constitute the model systems for the investigation of
radiation damage effects in ferritic-martensitic steels which are candidate structural materials for fusion reactors. In the current study Fe-10at%Cr alloy films of 70 nm thickness were irradiated by 490 keV Fe + ions at 300 degrees C at doses ranging from 0.5 up to 20 displacements per atom (dpa). The Fe + ion energy chosen corresponds to the energy of primary Fe(Cr) knock-on atoms from 14 MeV neutrons. The irradiation effects were investigated employing X-ray diffraction and X-ray and polarized neutron reflectivity. The irradiation produced dose dependent: a) lattice constant increase, b) grain size growth and c) Cr depletion in the matrix. These changes occur largely up to 4 dpa and afterwards the system attains a dynamic equilibrium. |
BibTeX:
@article{WOS:000777623100002,
author = {Pantousa, S. and Mergia, K. and Ionescu, A. and Manios, E. and Dellis, S. and Kinane, C. and Langridge, S. and Caruana, A. and Kentsch, U. and Messoloras, S.},
title = {Fe+ ion irradiation effects in Fe-10at%Cr films irradiated at 300 degrees C},
journal = {NUCLEAR MATERIALS AND ENERGY},
year = {2022},
volume = {30},
doi = {https://doi.org/10.1016/j.nme.2022.101147}
}
|
| Steinhoff, M.K., Holzapfel, D.M., Karimi Aghda, S., Neuss, D., Poellmann, P.J., Hans, M., Primetzhofer, D., Schneider, J.M. and Azina, C. Ag Surface and Bulk Segregations in Sputtered ZrCuAlNi Metallic Glass Thin Films MATERIALS 15, 5 (2022) |
| Abstract: We report on the formation of Ag-containing ZrCuAlNi thin film metallic
glass (nano)composites by a hybrid direct-current magnetron sputtering and high-power pulsed magnetron sputtering process. The effects of Ag content, substrate temperature and substrate bias potential on the phase formation and morphology of the nanocomposites were investigated. While applying a substrate bias potential did not strongly affect the morphological evolution of the films, the Ag content dictated the size and distribution of Ag surface segregations. The films deposited at low temperatures were characterized by strong surface segregations, formed by coalescence and Ostwald ripening, while the volume of the films remained featureless. At higher deposition temperature, elongated Ag segregations were observed in the bulk and a continuous Ag layer was formed at the surface as a result of thermally enhanced surface diffusion. While microstructural observations have allowed identifying both surface and bulk segregations, an indirect method for detecting the presence of Ag segregations is proposed, by measuring the electrical resistivity of the films. |
BibTeX:
@article{WOS:000768014600001,
author = {Steinhoff, Michael K. and Holzapfel, Damian M. and Karimi Aghda, Soheil and Neuss, Deborah and Poellmann, Peter J. and Hans, Marcus and Primetzhofer, Daniel and Schneider, Jochen M. and Azina, Clio},
title = {Ag Surface and Bulk Segregations in Sputtered ZrCuAlNi Metallic Glass Thin Films},
journal = {MATERIALS},
year = {2022},
volume = {15},
number = {5},
doi = {https://doi.org/10.3390/ma15051635}
}
|
| Cummins, C., Flamant, Q., Dwivedi, R., Alvarez-Fernandez, A., Demazy, N., Bentaleb, A., Pound-Lana, G., Zelsmann, M., Barois, P., Hadziioannou, G., Baron, A., Fleury, G. and Ponsinet, V. An Ultra-Thin Near-Perfect Absorber via Block Copolymer Engineered Metasurfaces JOURNAL OF COLLOID AND INTERFACE SCIENCE 609, pp. 375-383 (2022) |
| Abstract: Producing ultrathin light absorber layers is attractive towards the
integration of lightweight planar components in electronic, photonic, and sensor devices. In this work, we report the experimental demonstration of a thin gold (Au) metallic metasurface with near-perfect visible absorption (similar to 95 %). Au nanoresonators possessing heights from 5 - 15 nm with sub-50 nm diameters were engineered by block copolymer (BCP) templating. The Au nanoresonators were fabricated on an alumina (Al2O3) spacer layer and a reflecting Au mirror, in a film-coupled nanoparticle design. The BCP nanopatterning strategy to produce desired heights of Au nanoresonators was tailored to achieve near-perfect absorption at approximate to 600 nm. The experimental insight described in this work is a step forward towards realizing large area flat optics applications derived from subwavelength-thin metasurfaces. (C) 2021 Elsevier Inc. All rights reserved. |
BibTeX:
@article{WOS:000767972700001,
author = {Cummins, Cian and Flamant, Quentin and Dwivedi, Ranjeet and Alvarez-Fernandez, Alberto and Demazy, Nils and Bentaleb, Ahmed and Pound-Lana, Gwenaelle and Zelsmann, Marc and Barois, Philippe and Hadziioannou, Georges and Baron, Alexandre and Fleury, Guillaume and Ponsinet, Virginie},
title = {An Ultra-Thin Near-Perfect Absorber via Block Copolymer Engineered Metasurfaces},
journal = {JOURNAL OF COLLOID AND INTERFACE SCIENCE},
year = {2022},
volume = {609},
pages = {375-383},
doi = {https://doi.org/10.1016/j.jcis.2021.11.163}
}
|
| Griggs, W., Bull, C., Barton, C.W., Griffiths, R.A., Caruana, A.J., Kinane, C.J., Nutter, P.W. and Thomson, T. Polarized neutron reflectometry characterization of interfacial magnetism in an FePt/FeRh exchange spring PHYSICAL REVIEW MATERIALS 6, 2 (2022) |
| Abstract: We report on the depth-sensitive, temperature-dependent exchange
coupling in an FePt/FeRh thin-film exchange-spring structure. The depth-dependent in-plane magnetization is measured as a function of applied magnetic field and sample temperature using polarized neutron reflectometry (PNR). The magnetization profiles are interpreted in terms of the competition between anisotropy, exchange coupling, and dipolar coupling as the FeRh undergoes the magnetic phase transition from antiferromagnetic to ferromagnetic ordering. The PNR data are combined with bulk magnetometry and x-ray characterization, allowing us to determine characteristic length scales over which the exchange-spring mechanism is effective at ambient and elevated temperatures. |
BibTeX:
@article{WOS:000754627300002,
author = {Griggs, W. and Bull, C. and Barton, C. W. and Griffiths, R. A. and Caruana, A. J. and Kinane, C. J. and Nutter, P. W. and Thomson, T.},
title = {Polarized neutron reflectometry characterization of interfacial magnetism in an FePt/FeRh exchange spring},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2022},
volume = {6},
number = {2},
doi = {https://doi.org/10.1103/PhysRevMaterials.6.024403}
}
|
| Nagy, B., Campana, M., Khaydukov, Y.N. and Ederth, T. Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes LANGMUIR 38, 5, pp. 1725-1737 (2022) |
| Abstract: We have prepared a series of ampholytic polymer films, using a
self-initiated photografting and photopolymerization (SI-PGP) method to sequentially polymerize first anionic (deuterated methacrylic acid (dMAA)) and thereafter cationic (2-aminoethyl methacrylate (AEMA)) monomers to investigate the SI-PGP grafting process. Dry films were investigated by ellipsometry, X-ray, and neutron reflectometry, and their swelling was followed over a pH range from 4.5 to 10.5 with spectroscopic ellipsometry. The deuterated monomer allows us to separate the distributions of the two components by neutron reflectometry. Growth of both polymers proceeds via grafting of solution-polymerized fragments to the surface, and also the second layer is primarily grafted to the substrate and not as a continuation of the existing chains. The polymer films are stratified, with one layer of near 1:1 composition and the other layer enriched in one component and located either above or below the former layer. The ellipsometry results show swelling transitions at low and high pH but with no systematic variation in the pH values where these transitions occur. The results suggest that grafting density in SI-PGP-prepared homopolymers could be increased via repeated polymerization steps, but that this process does not necessarily increase the average chain length. |
BibTeX:
@article{WOS:000763586100009,
author = {Nagy, Bela and Campana, Mario and Khaydukov, Yury N. and Ederth, Thomas},
title = {Structure and pH-Induced Swelling of Polymer Films Prepared from Sequentially Grafted Polyelectrolytes},
journal = {LANGMUIR},
year = {2022},
volume = {38},
number = {5},
pages = {1725-1737},
doi = {https://doi.org/10.1021/acs.langmuir.1c02784}
}
|
| Kumar, S., Ojha, S.K., Patel, R.K., Mandal, P., Bhattacharya, N. and Middey, S. Electronic and magnetic properties of epitaxial thin film of Nd0.5Ba0.5MnO3 APPLIED PHYSICS LETTERS 120, 6 (2022) |
| Abstract: Contradictory reports about the electronic and magnetic behavior of bulk
Nd0.5Ba0.5MnO3 with uniform disorder exist in the literature. In this work, we investigated single crystalline, A-site disordered thin films of Nd0.5Ba0.5MnO3, grown on the SrTiO3 substrate by pulsed laser deposition. The epitaxial growth of these films in the layer-by-layer fashion has been confirmed by in situ reflection high energy electron diffraction, atomic force microscopy, x-ray reflectivity, and x-ray diffraction measurements. Interestingly, these films are found to be electrically insulating and exhibit spin-glass behavior at low temperatures. This offers a distinct approach to study Ba based half-doped manganites and an opportunity to further manipulate competing charge/orbital ordering and ferromagnetism in such systems, through heterostructure engineering. |
BibTeX:
@article{WOS:000753132400003,
author = {Kumar, Siddharth and Ojha, Shashank Kumar and Patel, Ranjan Kumar and Mandal, Prithwijit and Bhattacharya, Nandana and Middey, S.},
title = {Electronic and magnetic properties of epitaxial thin film of Nd0.5Ba0.5MnO3},
journal = {APPLIED PHYSICS LETTERS},
year = {2022},
volume = {120},
number = {6},
doi = {https://doi.org/10.1063/5.0083625}
}
|
| Tauchert, S.R., Volkov, M., Ehberger, D., Kazenwadel, D., Evers, M., Lange, H., Donges, A., Book, A., Kreuzpaintner, W., Nowak, U. and Baum, P. Polarized phonons carry angular momentum in ultrafast demagnetization NATURE 602, 7895, pp. 73-77 (2022) |
| Abstract: Magnetic phenomena are ubiquitous in nature and indispensable for modern
science and technology, but it is notoriously difficult to change the magnetic order of a material in a rapid way. However, if a thin nickel film is subjected to ultrashort laser pulses, it loses its magnetic order almost completely within femtosecond timescales(1). This phenomenon is widespread(2-7) and offers opportunities for rapid information processing(8-11) or ultrafast spintronics at frequencies approaching those of light(8,9,12). Consequently, the physics of ultrafast demagnetization is central to modern materials research(1-7,13-28), but a crucial question has remained elusive: if a material loses its magnetization within mere femtoseconds, where is the missing angular momentum in such a short time? Here we use ultrafast electron diffraction to reveal in nickel an almost instantaneous, long-lasting, non-equilibrium population of anisotropic high-frequency phonons that appear within 150-750 fs. The anisotropy plane is perpendicular to the direction of the initial magnetization and the atomic oscillation amplitude is 2 pm. We explain these observations by means of circularly polarized phonons that quickly absorb the angular momentum of the spin system before macroscopic sample rotation. The time that is needed for demagnetization is related to the time it takes to accelerate the atoms. These results provide an atomistic picture of the Einstein-de Haas effect and signify the general importance of polarized phonons for non-equilibrium dynamics and phase transitions. |
BibTeX:
@article{WOS:000750429600021,
author = {Tauchert, S. R. and Volkov, M. and Ehberger, D. and Kazenwadel, D. and Evers, M. and Lange, H. and Donges, A. and Book, A. and Kreuzpaintner, W. and Nowak, U. and Baum, P.},
title = {Polarized phonons carry angular momentum in ultrafast demagnetization},
journal = {NATURE},
year = {2022},
volume = {602},
number = {7895},
pages = {73-77},
doi = {https://doi.org/10.1038/s41586-021-04306-4}
}
|
| Mueller, S., Spriestersbach, F., Min, C.h., Fornari, C.I. and Reinert, F. Molecular beam epitaxy of TmTe thin films on SrF2 (111) AIP ADVANCES 12, 2 (2022) |
| Abstract: The odd parity nature of 4f states characterized by strong spin-orbit
coupling and electronic correlations has led to a search for novel topological phases among rare earth compounds, such as Kondo systems, heavy Fermions, and homogeneous mixed-valent materials. Our target system is thulium telluride thin films whose bandgap is expected to be tuned as a function of lattice parameter. We systematically investigate the growth conditions of TmxTey thin films on SrF2 (111) substrates by molecular beam epitaxy. The ratio between Te and Tm supply was precisely tuned, resulting in two different crystalline phases, which were confirmed by x-ray diffraction and x-ray photoemission spectroscopy. By investigating the crystalline quality as a function of the substrate temperature, the optimal growth conditions were identified for the desired Tm1Te1 phase. Additional low energy electron diffraction and reflective high energy electron diffraction measurements confirm the epitaxial growth of TmTe layers. X-ray reflectivity measurements demonstrate that homogeneous samples with sharp interfaces can be obtained for varied thicknesses. Our results provide a reliable guidance to prepare homogeneous high-quality TmTe thin films and thus serve as a basis for further electronic investigations. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). |
BibTeX:
@article{WOS:000761004500006,
author = {Mueller, S. and Spriestersbach, F. and Min, C. -h. and Fornari, C. I. and Reinert, F.},
title = {Molecular beam epitaxy of TmTe thin films on SrF2 (111)},
journal = {AIP ADVANCES},
year = {2022},
volume = {12},
number = {2},
doi = {https://doi.org/10.1063/5.0083276}
}
|
| Lofstrand, A., Vorobiev, A., Mumtaz, M., Borsali, R. and Maximov, I. Sequential Infiltration Synthesis into Maltoheptaose and Poly(styrene): Implications for Sub-10 nm Pattern Transfer POLYMERS 14, 4 (2022) |
| Abstract: Vapor phase infiltration into a self-assembled block copolymer (BCP) to
create a hybrid material in one of the constituent blocks can enhance the etch selectivity for pattern transfer. Multiple pulse infiltration into carbohydrate-based high-chi BCP has previously been shown to enable sub-10 nm feature pattern transfer. By optimizing the amount of infiltrated material, the etch selectivity should be further improved. Here, an investigation of semi-static sequential infiltration synthesis of trimethyl aluminum (TMA) and water into maltoheptaose (MH) films, and into hydroxyl-terminated poly(styrene) (PS-OH) films, was performed, by varying the process parameters temperature, precursor pulse duration, and precursor exposure length. It was found that, by decreasing the exposure time from 100 to 20 s, the volumetric percentage on included pure Al2O3 in MH could be increased from 2 to 40 vol% at the expense of a decreased infiltration depth. Furthermore, the degree of infiltration was minimally affected by temperature between 64 and 100 degrees C. Shorter precursor pulse durations of 10 ms TMA and 5 ms water, as well as longer precursor pulses of 75 ms TMA and 45 ms water, were both shown to promote a higher degree, 40 vol%, of infiltrated alumina in MH. As proof of concept, 12 nm pitch pattern transfer into silicon was demonstrated using the method and can be concluded to be one of few studies showing pattern transfer at such small pitch. These results are expected to be of use for further understanding of the mechanisms involved in sequential infiltration synthesis of TMA/water into MH, and for further optimization of carbohydrate-based etch masks for sub-10 nm pattern transfer. Enabling techniques for high aspect ratio pattern transfer at the single nanometer scale could be of high interest, e.g., in the high-end transistor industry. |
BibTeX:
@article{WOS:000762290000001,
author = {Lofstrand, Anette and Vorobiev, Alexei and Mumtaz, Muhammad and Borsali, Redouane and Maximov, Ivan},
title = {Sequential Infiltration Synthesis into Maltoheptaose and Poly(styrene): Implications for Sub-10 nm Pattern Transfer},
journal = {POLYMERS},
year = {2022},
volume = {14},
number = {4},
doi = {https://doi.org/10.3390/polym14040654}
}
|
| Jeong, S.G., Kim, J., Seo, A., Park, S., Jeong, H.Y., Kim, Y.-M., Lauter, V., Egami, T., Han, J.H. and Choi, W.S. Unconventional interlayer exchange coupling via chiral phonons in synthetic magnetic oxide heterostructures SCIENCE ADVANCES 8, 4 (2022) |
| Abstract: Chiral symmetry breaking of phonons plays an essential role in emergent
quantum phenomena owing to its strong coupling to spin degree of freedom. However, direct experimental evidence of the chiral phonon-spin coupling is lacking. In this study, we report a chiral phonon-mediated interlayer exchange interaction in atomically controlled ferromagnetic metal (SrRuO3)-nonmagnetic insulator (SrTiO3) heterostructures. Owing to the unconventional interlayer exchange interaction, we have observed rotation of spins as a function of nonmagnetic insulating spacer thickness, resulting in a spin spiral state. The chiral phonon-spin coupling is further confirmed by phonon Zeeman effect. The existence of the chiral phonons and their interplay with spins along with our atomic-scale heterostructure approach unveil the crucial roles of chiral phonons in magnetic materials. |
BibTeX:
@article{WOS:000799989900016,
author = {Jeong, Seung Gyo and Kim, Jiwoong and Seo, Ambrose and Park, Sungkyun and Jeong, Hu Young and Kim, Young-Min and Lauter, Valeria and Egami, Takeshi and Han, Jung Hoon and Choi, Woo Seok},
title = {Unconventional interlayer exchange coupling via chiral phonons in synthetic magnetic oxide heterostructures},
journal = {SCIENCE ADVANCES},
year = {2022},
volume = {8},
number = {4},
doi = {https://doi.org/10.1126/sciadv.abm4005}
}
|
| Hanifpour, F., Canales, C.P., Fridriksson, E.G., Sveinbjornsson, A., Tryggvason, T.K., Lewin, E., Magnus, F., Ingason, A.S., Skulason, E. and Flosadottir, H.D. Investigation into the mechanism of electrochemical nitrogen reduction reaction to ammonia using niobium oxynitride thin-film catalysts ELECTROCHIMICA ACTA 403 (2022) |
| Abstract: Niobium oxynitride (NbOxNy) thin films with varying combined non-metal
vs. metal stoichiometries ( x + y ) and N/O stoichiometric ratios (y/x) are investigated for their ability to catalyze the nitrogen re-duction reaction and ammonia synthesis at ambient conditions. Electrochemical impedance spectroscopy and ammonia measurements show stark differences both in nitrogen vs. argon media on each surface and on the surfaces in the series when the combined stoichiometry of N + O vs. Nb increases. Surface stability checks at fixed intervals during the experiments and surface characterization after the experiments us -ing X-ray diffraction reveal the least changes occurred to the surface with the highest N + O stoichiometry. Based on these observations, an ammonia synthesis mechanism is proposed. Isotope labeling experiments on the most promising surface of the series, however, show no sign of catalytically produced ammonia, possibly due to the lack of stability of the surface to endure through the ammonia production cycle. (c) 2021 Elsevier Ltd. All rights reserved. |
BibTeX:
@article{WOS:000784296000004,
author = {Hanifpour, Fatemeh and Canales, Camila P. and Fridriksson, Emil G. and Sveinbjornsson, Arnar and Tryggvason, Tryggvi K. and Lewin, Erik and Magnus, Fridrik and Ingason, Arni S. and Skulason, Egill and Flosadottir, Helga D.},
title = {Investigation into the mechanism of electrochemical nitrogen reduction reaction to ammonia using niobium oxynitride thin-film catalysts},
journal = {ELECTROCHIMICA ACTA},
year = {2022},
volume = {403},
doi = {https://doi.org/10.1016/j.electacta.2021.139551}
}
|
| Ceballos, A., Charilaou, M., Molina-Ruiz, M. and Hellman, F. Coexistence of soft and hard magnetic phases in single layer amorphous Tb-Co thin films JOURNAL OF APPLIED PHYSICS 131, 1 (2022) |
| Abstract: Amorphous, ferrimagnetic Tb-Co thin films prepared with a thin Ta
underlayer and either a Ta or a Pt overlayer show evidence of both soft and hard magnetic phases. At room temperature, the films exhibit conventional ferromagnetism, but low temperature magnetometry measurements reveal the decoupling of the two magnetic phases with decreasing temperature due to increased anisotropy energy of the hard layer at lower temperatures. Decreasing the film thickness to 2nm, slightly above the superparamagnetic limit found at 1nm, a soft, low-density phase was isolated and found to be present in all the films as confirmed with x-ray reflectivity and Rutherford backscattering spectrometry measurements. For greater thicknesses, the bottom layer retains its soft magnetic nature, while the remainder of the film is denser and has strong perpendicular magnetic anisotropy, leading to the exchange-spring behavior when the anisotropy becomes large, either at low temperatures or via a Pt overlayer that adds a strong interfacial anisotropy to the layer. Micromagnetic simulations of a soft/hard bilayer model with the experimentally determined anisotropy and magnetization parameters into a soft/hard bilayer model reproduced the experimental hysteretic behavior very well. These findings demonstrate how the magnetic state and the response of a-Tb-Co films to external fields can be controlled, providing a high degree of tunability that is promising for high-performance nanoscale devices. Published under an exclusive license by AIP Publishing. |
BibTeX:
@article{WOS:000802219200004,
author = {Ceballos, A. and Charilaou, M. and Molina-Ruiz, M. and Hellman, F.},
title = {Coexistence of soft and hard magnetic phases in single layer amorphous Tb-Co thin films},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2022},
volume = {131},
number = {1},
doi = {https://doi.org/10.1063/5.0074314}
}
|
| Jin, Q., Wang, Z., Zhang, Q., Yu, Y., Lin, S., Chen, S., Qi, M., Bai, H., Huon, A., Li, Q., Wang, L., Yin, X., Tang, C.S., Wee, A.T.S., Meng, F., Zhao, J., Wang, J.-O., Guo, H., Ge, C., Wang, C., Yan, W., Zhu, T., Gu, L., Chambers, S.A., Das, S., Charlton, T., Fitzsimmons, M.R., Liu, G.-Q., Wang, S., Jin, K.-J., Yang, H. and Guo, E.-J. Room-Temperature Ferromagnetism at an Oxide-Nitride Interface PHYSICAL REVIEW LETTERS 128, 1 (2022) |
| Abstract: Heterointerfaces have led to the discovery of novel electronic and
magnetic states because of their strongly entangled electronic degrees of freedom. Single-phase chromium compounds always exhibit antiferromagnetism following the prediction of the Goodenough-Kanamori rules. So far, exchange coupling between chromium ions via heteroanions has not been explored and the associated quantum states are unknown. Here, we report the successful epitaxial synthesis and characterization of chromium oxide (Cr2O3)-chromium nitride (CrN) superlattices. Room-temperature ferromagnetic spin ordering is achieved at the interfaces between these two antiferromagnets, and the magnitude of the effect decays with increasing layer thickness. First-principles calculations indicate that robust ferromagnetic spin interaction between Cr3+ ions via anion-hybridization across the interface yields the lowest total energy. This work opens the door to fundamental understanding of the unexpected and exceptional properties of oxide-nitride interfaces and provides access to hidden phases at low-dimensional quantum heterostructures. |
BibTeX:
@article{WOS:000750028700001,
author = {Jin, Qiao and Wang, Zhiwen and Zhang, Qinghua and Yu, Yonghong and Lin, Shan and Chen, Shengru and Qi, Mingqun and Bai, He and Huon, Amanda and Li, Qian and Wang, Le and Yin, Xinmao and Tang, Chi Sin and Wee, Andrew T. S. and Meng, Fanqi and Zhao, Jiali and Wang, Jia-Ou and Guo, Haizhong and Ge, Chen and Wang, Can and Yan, Wensheng and Zhu, Tao and Gu, Lin and Chambers, Scott A. and Das, Sujit and Charlton, Timothy and Fitzsimmons, Michael R. and Liu, Gang-Qin and Wang, Shanmin and Jin, Kui-Juan and Yang, Hongxin and Guo, Er-Jia},
title = {Room-Temperature Ferromagnetism at an Oxide-Nitride Interface},
journal = {PHYSICAL REVIEW LETTERS},
year = {2022},
volume = {128},
number = {1},
doi = {https://doi.org/10.1103/PhysRevLett.128.017202}
}
|
| Horky, M., Arregi, J.A., Patel, S.K.K., Stano, M., Medapalli, R., Caha, O., Vojacek, L., Horak, M., Uhlir, V. and Fullerton, E.E. Controlling the Metamagnetic Phase Transition in FeRh/MnRh Superlattices and Thin-Film Fe50-xMnxRh50 Alloys ACS APPLIED MATERIALS & INTERFACES early access (JAN 2022) |
| Abstract: Equiatomic and chemically ordered FeRh and MnRh compounds feature a
first-order metamagnetic phase transition between antiferromagnetic and ferromagnetic order in the vicinity of room temperature, exhibiting interconnected structural, magnetic, and electronic order parameters. We show that these two alloys can be combined to form hybrid metamagnets in the form of sputter-deposited superlattices and alloys on single-crystalline MgO substrates. Despite being structurally different, the magnetic behavior of the alloys with substantial Mn content resembles that of the FeRh/MnRh superlattices in the ultrathin individual layer limit. For FeRh/MnRh superlattices, dissimilar lattice distortions of the constituent FeRh and MnRh layers at the antiferromagnetic-ferromagnetic transition cause double-step transitions during cooling, while the magnetization during the heating branch shows a smooth, continuous trend. For Fe(50-x)Mn(x)Rh(50 )alloy films, the substitution of Mn at the Fe sites introduces an effective tensile in-plane strain and magnetic frustration in the highly ordered epitaxial films, largely influencing the phase transition temperature T-M (by more than 150 K). In addition, Mn acts as a surfactant, enabling the growth of continuous thin films at higher temperatures. Thus, the introduction of hybrid FeRh-MnRh systems with adjustable parameters provides a pathway for the realization of tunable spintronic devices based on magnetic phase transitions. |
BibTeX:
@article{WOS:000742725000001,
author = {Horky, Michal and Arregi, Jon Ander and Patel, Sheena K. K. and Stano, Michal and Medapalli, Rajasekhar and Caha, Ondrej and Vojacek, Libor and Horak, Michal and Uhlir, Vojtech and Fullerton, Eric E.},
title = {Controlling the Metamagnetic Phase Transition in FeRh/MnRh Superlattices and Thin-Film Fe50-xMnxRh50 Alloys},
journal = {ACS APPLIED MATERIALS & INTERFACES},
doi = {https://doi.org/10.1021/acsami.1c22460}
}
|
| Chen, T., Ahmadi-Majlan, K., Lim, Z.H., Zhang, Z., Ngai, J.H. and Kumah, D.P. Effect of buffer termination on intermixing and conductivity in LaTiO3/SrTiO3 heterostructures integrated on Si(100) JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 40, 1 (2022) |
| Abstract: The control of chemical exchange across heterointerfaces formed between
ultrathin functional transition-metal oxide layers provides an effective route to manipulate the electronic properties of these systems. By determining the layer-resolved structural profile across the interface between the Mott insulator, LaTiO3 (LTO) grown epitaxially on SrTiO3 (STO)-buffered silicon by molecular beam epitaxy, we find that interfacial cationic exchange depends on the surface termination of the strained STO buffer. Using a combination of temperature-dependent transport and synchrotron x-ray crystal truncation rods and reciprocal space mapping, an enhanced conductivity in STO/LTO/SrO-terminated STO buffers compared to heterostructures with TiO 2-terminated STO buffers is correlated with La/Sr exchange and the formation of metallic La 1 - xSr xTiO 3. La/Sr exchange effectively reduces the strain energy of the system due to the large lattice mismatch between the nominal oxide layers and the Si substrate. |
BibTeX:
@article{WOS:000726614800002,
author = {Chen, Tongjie and Ahmadi-Majlan, Kamyar and Lim, Zheng Hui and Zhang, Zhan and Ngai, Joseph H. and Kumah, Divine P.},
title = {Effect of buffer termination on intermixing and conductivity in LaTiO3/SrTiO3 heterostructures integrated on Si(100)},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2022},
volume = {40},
number = {1},
doi = {https://doi.org/10.1116/6.0001464}
}
|
| Guo, Q., Ren, Z., Bai, H., Wang, X., Yu, G., He, W., Teng, J. and Zhu, T. Current-induced magnetization switching in perpendicularly magnetized V/CoFeB/MgO multilayers PHYSICAL REVIEW B 104, 22 (2021) |
| Abstract: The perpendicular magnetic anisotropy properties of CoFeB/MgO films on
3d light-metal vanadium have been experimentally investigated. The interfacial magnetic anisotropy is 1.4 erg/cm2 for the V/CoFeB/MgO multilayers annealed at 240 degrees C. A sign change of the effective torque fields with the increase of V thickness has been observed, which is confirmed by current-induced magnetization switching measurements, suggesting a competition of multiple effects on current-induced torques in the weakly spin-orbit coupled V/CoFeB/MgO multilayers. These findings have implications for the fundamental understanding of current-induced torque and further device applications using 3d light transition-metal based heterostructures. |
BibTeX:
@article{WOS:000753768800004,
author = {Guo, Qixun and Ren, Zhongxu and Bai, He and Wang, Xuemin and Yu, Guanghua and He, Wei and Teng, Jiao and Zhu, Tao},
title = {Current-induced magnetization switching in perpendicularly magnetized V/CoFeB/MgO multilayers},
journal = {PHYSICAL REVIEW B},
year = {2021},
volume = {104},
number = {22},
doi = {https://doi.org/10.1103/PhysRevB.104.224429}
}
|
| Koutsioubas, A. anaklasis: a compact software package for model-based analysis of specular neutron and X-ray reflectometry data sets JOURNAL OF APPLIED CRYSTALLOGRAPHY 54, 6, pp. 1857-1866 (2021) |
| Abstract: anaklasis constitutes a set of open-source Python scripts that
facilitate a range of specular neutron and X-ray reflectivity calculations, involving the generation of theoretical curves and the comparison/fitting of interfacial model reflectivity against experimental data sets. The primary focus of the software is twofold: on one hand to offer a more natural framework for model definition, requiring minimum coding literacy, and on the other hand to include advanced analysis methods that have been proposed in recent work. Particular attention is given to the ability to co-refine reflectivity data and to the estimation of model-parameter uncertainty and covariance using bootstrap analysis and Markov chain Monte Carlo sampling. The compactness and simplicity of model definition together with the streamlined analysis do not present a steep learning curve for the user, an aspect that may accelerate the generation of reproducible, easily readable and statistically accurate reports in future neutron and X-ray reflectivity related literature. |
BibTeX:
@article{WOS:000727770700032,
author = {Koutsioubas, Alexandros},
title = {anaklasis: a compact software package for model-based analysis of specular neutron and X-ray reflectometry data sets},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2021},
volume = {54},
number = {6},
pages = {1857-1866},
doi = {https://doi.org/10.1107/S1600576721009262}
}
|
| Khaydukov, Y.N., Lenk, D., Zdravkov, V., Morari, R., Keller, T., Sidorenko, A.S., Tagirov, L.R., Tidecks, R., Horn, S. and Keimer, B. Chirality of Bloch domain walls in exchange-biased CoO/Co bilayer studied by waveguide-enhanced neutron spin-flip scattering PHYSICAL REVIEW B 104, 17 (2021) |
| Abstract: The magnetic state of exchanged biased CoO(20 nm)/Co(dF) bilayers (dF =
5-20 nm) was studied by means of polarized neutron reflectometry. By introducing a Nb(20 nm) spacer layer between the CoO/Co bilayer and the Al2O3 substrate, we designed a resonator structure with significantly enhanced intensity of the spin-flip (SF) scattering at the position of the optical resonances. For the trained sample with thinnest Co layer (dF = 5 nm), we detected strong SF scattering at the resonance position to the amount of 30% of the incoming intensity, pointing to a high degree of non-collinearity of the magnetization. With increasing dF, the intensity of the SF scattering decreases linearly. Furthermore, an unconventional asymmetry of up-down and down-up scattering channels at the resonance positions was observed, which we ascribe to the out-of-plane magnetic stray field generated by chiral Bloch domain walls. This field leads to Zeeman splitting of the neutron energies depending on the initial neutron spin polarization. The chirality of the domain walls is assigned to the Dzyaloshinskii-Moriya interaction emerging at the CoO/Co interface. Our observations might prove useful for the design of spintronic devices based on the exchange bias effect. |
BibTeX:
@article{WOS:000725514100001,
author = {Khaydukov, Yu N. and Lenk, D. and Zdravkov, V and Morari, R. and Keller, T. and Sidorenko, A. S. and Tagirov, L. R. and Tidecks, R. and Horn, S. and Keimer, B.},
title = {Chirality of Bloch domain walls in exchange-biased CoO/Co bilayer studied by waveguide-enhanced neutron spin-flip scattering},
journal = {PHYSICAL REVIEW B},
year = {2021},
volume = {104},
number = {17},
doi = {https://doi.org/10.1103/PhysRevB.104.174445}
}
|
| McNulty, J.F., Temst, K., Van Bael, M.J., Vantomme, A. and Anton, E.-M. Epitaxial growth of (100)-oriented SmN directly on (100)Si substrates PHYSICAL REVIEW MATERIALS 5, 11 (2021) |
| Abstract: We demonstrate growth of epitaxial (100)SmN thin films directly on
(100)Si surfaces. By using physical vapor deposition of Sm metal in an N-2 atmosphere we show that careful control of substrate temperature, N-2 pressure, and postannealing steps leads to epitaxial SmN without the formation of samarium silicide impurity phases. While rare-earth silicide formation competes with and is favored over nitride formation at high growth temperatures, we find that low-temperature grown SmN seed layers are stable against high-temperature annealing, and thus allow for subsequent high-temperature growth of SmN with a clear epitaxial relationship to the Si substrate. The relatively low lattice mismatch of SmN with (100)Si, compared to other commonly available substrates, coupled with the low cost and maturity of Si processing technology provide a promising route for further studies of the fundamental properties of SmN and other isostructural members of the rare-earth nitride series. Because SmN is a ferromagnetic semiconductor, which also becomes superconducting close to 4 K under sufficient doping, integration with Si technology presents new opportunities for spin-transport devices. |
BibTeX:
@article{WOS:000724500400005,
author = {McNulty, J. F. and Temst, K. and Van Bael, M. J. and Vantomme, A. and Anton, E-M},
title = {Epitaxial growth of (100)-oriented SmN directly on (100)Si substrates},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2021},
volume = {5},
number = {11},
doi = {https://doi.org/10.1103/PhysRevMaterials.5.113404}
}
|
| Lin, S., Wang, Z., Zhang, Q., Chen, S., Jin, Q., Yao, H., Xu, S., Meng, F., Yin, X., Wang, C., Ge, C., Guo, H., Tang, C.S., Wee, A.T.S., Gu, L., Jin, K.-j., Yang, H. and Guo, E.-J. Exchange Coupling in Synthetic Anion-Engineered Chromia Heterostructures ADVANCED FUNCTIONAL MATERIALS 32, 10 (2022)early access (NOV 2021) |
| Abstract: Control of magnetic states by external factors has garnered a mainstream
status in spintronic research for designing low power consumption and fast-response information storage and processing devices. Previously, magnetic-cation substitution was the conventional approach to induce ferromagnetism in an intrinsic antiferromagnet. Theoretically, anion doping is proposed to be another means to change magnetic ground states. Here, the authors demonstrate the synthesis of high-quality single-phase chromium oxynitride thin films using in-situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and insulating state, as demonstrated by the combination of multiple magnetization probes and theoretical calculations. With increasing the nitrogen content, the crystal structure of chromium oxynitride transits from trigonal (R3 over bar c) to tetragonal (4 mm) phase and its saturation magnetization reduces significantly. Furthermore, they achieve a large and controllable exchange bias field in the chromia heterostructures by synthetic anion engineering. This work reflects the anion engineering in functional oxides towards potential applications in giant magnetoresistance and tunnelling junctions of modern magnetic sensors and read heads. |
BibTeX:
@article{WOS:000722527900001,
author = {Lin, Shan and Wang, Zhiwen and Zhang, Qinghua and Chen, Shengru and Jin, Qiao and Yao, Hongbao and Xu, Shuai and Meng, Fanqi and Yin, Xinmao and Wang, Can and Ge, Chen and Guo, Haizhong and Tang, Chi Sin and Wee, Andrew T. S. and Gu, Lin and Jin, Kui-juan and Yang, Hongxin and Guo, Er-Jia},
title = {Exchange Coupling in Synthetic Anion-Engineered Chromia Heterostructures},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2022},
volume = {32},
number = {10},
doi = {https://doi.org/10.1002/adfm.202109828}
}
|
| Hong, H., Fang, X., Wrobel, F., Lin, M.-K., Zhang, Z., Peterson, K.M., Bhattacharya, A., Fong, D.D. and Chiang, T.-C. On the Development of Order and Interfaces during the Growth of Ultrathin La2CuO4 Films by Molecular Beam Epitaxy ACS APPLIED ELECTRONIC MATERIALS 3, 11, pp. 5124-5130 (2021) |
| Abstract: While the atomic structure of interfaces in complex oxide
heterostructures created by epitaxial growth has been investigated extensively, few studies have been conducted on how interfaces form and restructure at the initial stage of film growth. The dynamic aspects of the growth behavior can strongly influence the final interfacial atomic structure, which may lead to the emergence of interface-specific properties, such as the rise of interfacial superconductivity between certain Ruddlesden-Popper oxide materials. Here, the structural development of La2CuO4 thin films grown by molecular beam epitaxy on a LaSrAlO4 substrate is investigated by X-ray diffraction measurements with rapid scans over a volume of reciprocal space. This method provides far more detailed information on interface formation than traditional fixed-point measurements. The results show that the atomic structure of the interface becomes fully established after just a single unit cell of growth. Interestingly, restructuring continues to occur within the topmost half to one unit cell of the film during the deposition process. However, diffraction intensity oscillations from both reflection high-energy electron and X-ray measurements stabilize only after the growth of two unit cells, indicating that the growth front morphology continues to evolve until the start of the third unit cell. This multimodal investigation provides insights into the atomic processes taking place during layered oxide interface formation, including the dynamical rearrangement of LaO and CuO2 layers. Such information is not only relevant to the engineering and optimization of functional layer structures but can also be critical for ultrathin films. |
BibTeX:
@article{WOS:000756989100049,
author = {Hong, Hawoong and Fang, Xinyue and Wrobel, Friederike and Lin, Meng-Kai and Zhang, Zhan and Peterson, Kevin M. and Bhattacharya, Anand and Fong, Dillon D. and Chiang, Tai-Chang},
title = {On the Development of Order and Interfaces during the Growth of Ultrathin La2CuO4 Films by Molecular Beam Epitaxy},
journal = {ACS APPLIED ELECTRONIC MATERIALS},
year = {2021},
volume = {3},
number = {11},
pages = {5124-5130},
doi = {https://doi.org/10.1021/acsaelm.1c00860}
}
|
| Bai, Q., Zhai, Y., Yun, J., Zhang, J., Chang, M., Zuo, Y. and Xi, L. Highly efficient spin-current generation from Pt/Ru multilayers APPLIED PHYSICS LETTERS 119, 21 (2021) |
| Abstract: Increasing spin Hall angle of heavy metals has attracted considerable
attention due to their potential applications in spintronic technology. Here, we demonstrate that the spin Hall angle could be enhanced dramatically in the Ta/[Pt/Ru](n)/Pt/Co/Ta multilayers. The spin Hall angle reaches a maximum value of 0.28 when n=5 from the loop-shift method with a relative low resistivity of approximately 48 mu Omega cm. Meanwhile a minimum critical switching current density approximately 3.2 x 10(6) A/cm(2) under an in-plane bias magnetic field around 5% of the perpendicular anisotropy field was obtained for the sample with n=5 in current-induced magnetization switching experiment. We find that the extrinsic spin Hall mechanism changes from the spin skew scattering when n<2 to spin side-jump mechanism when n>2. This work provides an effective way in increasing spin Hall angle for low-power consumption spintronics devices. Published under an exclusive license by AIP Publishing. |
BibTeX:
@article{WOS:000749549600012,
author = {Bai, Qiaoning and Zhai, Yongbo and Yun, Jijun and Zhang, Jianrong and Chang, Meixia and Zuo, Yalu and Xi, Li},
title = {Highly efficient spin-current generation from Pt/Ru multilayers},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {119},
number = {21},
doi = {https://doi.org/10.1063/5.0069820}
}
|
| Konh, M., Wang, Y., Chen, H., Bhatt, S., Xiao, J.Q. and Teplyakov V, A. Selectivity in atomically precise etching: Thermal atomic layer etching of a CoFeB alloy and its protection by MgO APPLIED SURFACE SCIENCE 575 (2022)early access (NOV 2021) |
| Abstract: The central unit in an integrated memory device is a magnetic tunnel
junction (MTJ) consisting of two ferromagnetic layers, often using complex alloys such as CoFeB, separated by an insulating barrier such as MgO. Atomic level precision is required to fabricate miniaturized devices, and atomic layer etching (ALE) is one of the most promising methods to do this. However, at the nanoscale, it is imperative to maintain the concentration of each element in an alloy during etching, and it is important to not affect the insulating barrier, i.e. the etching process should stop at MgO. Here we use thermal dry etching of CoFeB alloy thin films with sequential doses of chlorine and 2,4-pentanedione (acetylacetone, acacH). Patterned samples are modified with atomic level precision, and the process is completely selective to the removal of CoFeB alloy in ALE regime without changing the alloy composition and without etching MgO that is used as a protecting layer. The etching process was investigated by comparing the film thickness on a patterned surface before and after ALE process using atomic force microscopy (AFM). The viable key features of the reaction mechanism were proposed by detection of key desorbing fragments during a heating ramp via temperature-programmed desorption (TPD) experiments. Ex-situ X-ray photoelectron spectroscopy (XPS) was performed to characterize the surface during ALE process. |
BibTeX:
@article{WOS:000730849100001,
author = {Konh, Mahsa and Wang, Yang and Chen, Hang and Bhatt, Subhash and Xiao, John Q. and Teplyakov, V, Andrew},
title = {Selectivity in atomically precise etching: Thermal atomic layer etching of a CoFeB alloy and its protection by MgO},
journal = {APPLIED SURFACE SCIENCE},
year = {2022},
volume = {575},
doi = {https://doi.org/10.1016/j.apsusc.2021.151751}
}
|
| Cao, L., Petracic, O., Wei, X.-K., Zhang, H., Duchon, T., Gunkel, F., Koutsioubas, A., Zhernenkov, K., Rushchanskii, K.Z., Hartmann, H., Wilhelm, M., Li, Z., Xie, Y., He, S., Weber, M.L., Stellhorn, A., Mayer, J., Zhou, S., Brueckel, T. and Veltruska, K. Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions SMALL 17, 51 (2021)early access (NOV 2021) |
| Abstract: Oxygen diffusivity and surface exchange kinetics underpin the ionic,
electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La0.7Sr0.3MnO3-delta epitaxial thin films, both at the surface and throughout the bulk. Using polarized neutron reflectometry, a quantitative depth profile of the oxygen content gradient is achieved, which, alongside atomic-resolution scanning transmission electron microscopy, uniquely reveals the formation of a novel structural phase near the surface. Surface-sensitive X-ray spectroscopies further confirm a significant change of the electronic structure accompanying the transition. The anisotropic features of this novel phase enable a distinct oxygen diffusion pathway in contrast to conventional observation of oxygen motion at moderate temperatures. The results provide insights furthering the design of solid oxygen ion conductors within the framework of topotactic phase transitions. |
BibTeX:
@article{WOS:000719613100001,
author = {Cao, Lei and Petracic, Oleg and Wei, Xian-Kui and Zhang, Hengbo and Duchon, Tomas and Gunkel, Felix and Koutsioubas, Alexandros and Zhernenkov, Kirill and Rushchanskii, Konstantin Z. and Hartmann, Heinrich and Wilhelm, Marek and Li, Zichao and Xie, Yufang and He, Suqin and Weber, Moritz L. and Stellhorn, Annika and Mayer, Joachim and Zhou, Shengqiang and Brueckel, Thomas and Veltruska, Katefina},
title = {Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions},
journal = {SMALL},
year = {2021},
volume = {17},
number = {51},
doi = {https://doi.org/10.1002/smll.202104356}
}
|
| Prakash, D.J., Chen, Y., Debasu, M.L., Savage, D.E., Tangpatjaroen, C., Deneke, C., Malachias, A., Alfieri, A.D., Elleuch, O., Lekhal, K., Szlufarska, I., Evans, P.G. and Cavallo, F. Reconfiguration of Amorphous Complex Oxides: A Route to a Broad Range of Assembly Phenomena, Hybrid Materials, and Novel Functionalities SMALL 18, 1 (2022)early access (NOV 2021) |
| Abstract: Reconfiguration of amorphous complex oxides provides a readily
controllable source of stress that can be leveraged in nanoscale assembly to access a broad range of 3D geometries and hybrid materials. An amorphous SrTiO3 layer on a Si:B/Si1-xGex:B heterostructure is reconfigured at the atomic scale upon heating, exhibiting a change in volume of approximate to 2% and accompanying biaxial stress. The Si:B/Si1-xGex:B bilayer is fabricated by molecular beam epitaxy, followed by sputter deposition of SrTiO3 at room temperature. The processes yield a hybrid oxide/semiconductor nanomembrane. Upon release from the substrate, the nanomembrane rolls up and has a curvature determined by the stress in the epitaxially grown Si:B/Si1-xGex:B heterostructure. Heating to 600 degrees C leads to a decrease of the radius of curvature consistent with the development of a large compressive biaxial stress during the reconfiguration of SrTiO3. The control of stresses via post-deposition processing provides a new route to the assembly of complex-oxide-based heterostructures in 3D geometry. The reconfiguration of metastable mechanical stressors enables i) synthesis of various types of strained superlattice structures that cannot be fabricated by direct growth and ii) technologies based on strain engineering of complex oxides via highly scalable lithographic processes and on large-area semiconductor substrates. |
BibTeX:
@article{WOS:000719155400001,
author = {Prakash, Divya J. and Chen, Yajin and Debasu, Mengistie L. and Savage, Donald E. and Tangpatjaroen, Chaiyapat and Deneke, Christoph and Malachias, Angelo and Alfieri, Adam D. and Elleuch, Omar and Lekhal, Kaddour and Szlufarska, Izabela and Evans, Paul G. and Cavallo, Francesca},
title = {Reconfiguration of Amorphous Complex Oxides: A Route to a Broad Range of Assembly Phenomena, Hybrid Materials, and Novel Functionalities},
journal = {SMALL},
year = {2022},
volume = {18},
number = {1},
doi = {https://doi.org/10.1002/smll.202105424}
}
|
| Larsson, A., D'Acunto, G., Vorobyova, M., Abbondanza, G., Lienert, U., Hegedus, Z., Preobrajenski, A., Merte, L.R., Eidhagen, J., Delblanc, A., Pan, J. and Lundgren, E. Thickness and composition of native oxides and near-surface regions of Ni superalloys JOURNAL OF ALLOYS AND COMPOUNDS 895, 1 (2022)early access (NOV 2021) |
| Abstract: The surface chemistry and thickness of the native oxide, hydroxide, and
modified sub-surface layer of three Ni superalloys (alloy 59, 625, and 718) were determined by synchrotron X-ray Photoelectron Spectroscopy (XPS) and X-ray Reflectivity (XRR). Taking advantage of the synchrotron radiation techniques, a procedure for normalizing the photoelectron intensity was employed, which allowed for accurate quantitative analysis revealing a total oxide thickness for all samples of 12-13 A, a hydroxide layer of 2-3 A, and a thickness of the sub-surface alloy layer of 20-35 A. The thickness results were compared to structural atomic models suggesting that the oxide thickness corresponds to four planes of metal cations in the oxide matrix. The XPS data revealed that the native oxides were enriched in Cr3+, Mo-(4,Mo-5,Mo-6)+, and Nb5+, while no Ni oxide was detected. The hydroxide layer mainly contained Ni2+ and Cr3+ hydroxide. The sub-surface layer was enriched in Ni and depleted in Cr, Fe, Mo, and Nb. The obtained oxide composition can be explained using thermodynamics, and it was found that the oxide composition correlates with the enthalpy of oxide formation for the metal elements in the alloys. Finally, the advantages of synchrotron radiation for composition and thickness determination are discussed. (C) 2021 The Authors. Published by Elsevier B.V. |
BibTeX:
@article{WOS:000720143000005,
author = {Larsson, Alfred and D'Acunto, Giulio and Vorobyova, Mariya and Abbondanza, Giuseppe and Lienert, Ulrich and Hegedus, Zoltan and Preobrajenski, Alexei and Merte, Lindsay R. and Eidhagen, Josefin and Delblanc, Anna and Pan, Jinshan and Lundgren, Edvin},
title = {Thickness and composition of native oxides and near-surface regions of Ni superalloys},
journal = {JOURNAL OF ALLOYS AND COMPOUNDS},
year = {2022},
volume = {895},
number = {1},
doi = {https://doi.org/10.1016/j.jallcom.2021.162657}
}
|
| Magnus, F., Arnalds, U.B., Palonen, H., Palsson, G.K., Ali, H., Leifer, K. and Hjorvarsson, B. Tuneable exchange-spring stiffness in amorphous magnetic trilayer structures JOURNAL OF PHYSICS-CONDENSED MATTER 33, 44 (2021) |
| Abstract: We investigate the magnetic properties of amorphous
Sm10Co90/Co-60(Al70Zr30)(40)/Co-85(Al70Zr30)(15) exchange-spring magnet trilayers. The magnetically soft Co-85(Al70Zr30)(15) layer is coupled to the magnetically hard Sm10Co90 layer through the weakly magnetic low-T (c) Co-60(Al70Zr30)(40) spacer layer. The strength of the coupling can be controlled with temperature and the coupling persists above the intrinsic T (c) of the spacer layer due to a long-range magnetic proximity effect. Polarized neutron reflectivity is used to examine the magnetic profile of the trilayers during magnetization reversal. A two-step switching occurs, with the switching angle of the soft layer strongly dependent on the strength of the coupling. In the strong coupling regime a magnetic state can be achieved where the soft layer magnetization is perpendicular to the hard layer whereas in the weak coupling regime the soft layer reverses fully. |
BibTeX:
@article{WOS:000687837700001,
author = {Magnus, F. and Arnalds, U. B. and Palonen, H. and Palsson, G. K. and Ali, H. and Leifer, K. and Hjorvarsson, B.},
title = {Tuneable exchange-spring stiffness in amorphous magnetic trilayer structures},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2021},
volume = {33},
number = {44},
doi = {https://doi.org/10.1088/1361-648X/ac1c2c}
}
|
| Ohtsuka, Y., Kanazawa, N., Hirayama, M., Matsui, A., Nomoto, T., Arita, R., Nakajima, T., Hanashima, T., Ukleev, V., Aoki, H., Mogi, M., Fujiwara, K., Tsukazaki, A., Ichikawa, M., Kawasaki, M. and Tokura, Y. Emergence of spin-orbit coupled ferromagnetic surface state derived from Zak phase in a nonmagnetic insulator FeSi SCIENCE ADVANCES 7, 47 (2021) |
| Abstract: FeSi is a nonmagnetic narrow-gap insulator, exhibiting peculiar charge
and spin dynamics beyond a simple band structure picture. Those unusual features have been attracting renewed attention from topological aspects. Although the surface conduction was demonstrated according to size-dependent resistivity in bulk crystals, its topological characteristics and consequent electromagnetic responses remain elusive. Here, we demonstrate an inherent surface ferromagnetic-metal state of FeSi thin films and its strong spin-orbit coupling (SOC) properties through multiple characterizations of two-dimensional conductance, magnetization, and spintronic functionality. Terminated covalent bonding orbitals constitute the polar surface state with momentum-dependent spin textures due to Rashba-type spin splitting, as corroborated by unidirectional magnetoresistance measurements and first-principles calculations. As a consequence of the spin-momentum locking, nonequilibrium spin accumulation causes magnetization switching. These surface properties are closely related to the Zak phase of the bulk band topology. Our findings propose another route to explore noble metal-free materials for SOC-based spin manipulation. |
BibTeX:
@article{WOS:000720347400012,
author = {Ohtsuka, Yusuke and Kanazawa, Naoya and Hirayama, Motoaki and Matsui, Akira and Nomoto, Takuya and Arita, Ryotaro and Nakajima, Taro and Hanashima, Takayasu and Ukleev, Victor and Aoki, Hiroyuki and Mogi, Masataka and Fujiwara, Kohei and Tsukazaki, Atsushi and Ichikawa, Masakazu and Kawasaki, Masashi and Tokura, Yoshinori},
title = {Emergence of spin-orbit coupled ferromagnetic surface state derived from Zak phase in a nonmagnetic insulator FeSi},
journal = {SCIENCE ADVANCES},
year = {2021},
volume = {7},
number = {47},
doi = {https://doi.org/10.1126/sciadv.abj0498}
}
|
| Bannenberg, L.J., Boshuizen, B., Nugroho, F.A.A. and Schreuders, H. Hydrogenation Kinetics of Metal Hydride Catalytic Layers ACS APPLIED MATERIALS & INTERFACES 13, 44, pp. 52530-52541 (2021)early access (OCT 2021) |
| Abstract: Catalyzing capping layers on metal hydrides are employed to enhance the
hydrogenation kinetics of metal hydride-based systems such as hydrogen sensors. Here, we use a novel experimental method to study the hydrogenation kinetics of catalyzing capping layers composed of several alloys of Pd and Au as well as Pt, Ni, and Ru, all with and without an additional PTFE polymer protection layer and under the same set of experimental conditions. In particular, we employ a thin Ta film as an optical indicator to study the kinetics of the catalytic layers deposited on top of it and which allows one to determine the absolute hydrogenation rates. Our results demonstrate that doping Pd with Au results in significantly faster hydrogenation kinetics, with response times up to five times shorter than Pd through enhanced diffusion and a reduction in the activation energy. On the other hand, the kinetics of non-Pd-based materials turn out to be significantly slower and mainly limited by the diffusion through the capping layer itself. Surprisingly, the additional PTFE layer was only found to improve the kinetics of Pd-based capping materials and has no significant effect on the kinetics of Pt, Ni, and Ru. Taken together, the experimental results aid in rationally choosing a suitable capping material for the application of metal hydrides and other materials in a hydrogen economy. In addition, the used method can be applied to simultaneously study the hydrogenation kinetics in thin-film materials for a wide set of experimental conditions. |
BibTeX:
@article{WOS:000718271300068,
author = {Bannenberg, Lars J. and Boshuizen, Bart and Nugroho, Ferry Anggoro Ardy and Schreuders, Herman},
title = {Hydrogenation Kinetics of Metal Hydride Catalytic Layers},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2021},
volume = {13},
number = {44},
pages = {52530-52541},
doi = {https://doi.org/10.1021/acsami.1c13240}
}
|
| Will, J., Wierzbicka, E., Wu, M., Goetz, K., Yokosawa, T., Liu, N., Tesler, A.B., Stiller, M., Unruh, T., Altomare, M., Schmuki, P. and Spiecker, E. Hydrogenated anatase TiO2 single crystals: defects formation and structural changes as microscopic origin of co-catalyst free photocatalytic H-2 evolution activity JOURNAL OF MATERIALS CHEMISTRY A 9, 44, pp. 24932-24942 (2021)early access (OCT 2021) |
| Abstract: Herein we systematically investigate the influence of hydrogenation time
and temperature on defects formation, structural changes, and co-catalyst free photocatalytic activity for epitaxially grown anatase thin films on strontium titanate single crystals. The photocatalytic activity trend of the anatase epi layers is similar to that of anatase powders and brookite single crystals in reported recent literature, that is, the H-2 evolution rate exhibits a typical maximum upon hydrogenation under moderate annealing temperatures (500 degrees C). By combining surface sensitive X-ray diffraction methods and analytical high-resolution electron microscopy techniques we reveal quantitatively the oxygen loss from the epi-layer ascribed to the hydrogenation (H-2 reduction) treatment. We observe specific physicochemical changes associated with the introduction of oxygen vacancies: (i) the formation of a nanoscale strained crystal surface, (ii) the agglomeration of point defects in the bulk of the anatase epi layer, and (iii) a transition towards a Ti2O3 like symmetry at the film surface, i.e. an evident oxygen deficiency at the epi layer surface in particular prominent for the most active sample as a function of the hydrogenation parameters. These extensive experimental findings allow us to propose an empirical model, which links detrimental and beneficial effects of Ti3+ centers and oxygen vacancies in the bulk and at the surface and their abundance to an optimum point defect configuration for water splitting via ``grey'' anatase. |
BibTeX:
@article{WOS:000713781600001,
author = {Will, Johannes and Wierzbicka, Ewa and Wu, Mingjian and Goetz, Klaus and Yokosawa, Tadahiro and Liu, Ning and Tesler, Alexander B. and Stiller, Markus and Unruh, Tobias and Altomare, Marco and Schmuki, Patrik and Spiecker, Erdmann},
title = {Hydrogenated anatase TiO2 single crystals: defects formation and structural changes as microscopic origin of co-catalyst free photocatalytic H-2 evolution activity},
journal = {JOURNAL OF MATERIALS CHEMISTRY A},
year = {2021},
volume = {9},
number = {44},
pages = {24932-24942},
doi = {https://doi.org/10.1039/d1ta04809k}
}
|
| Love, C.J., Kuerbanjiang, B., Kerrigan, A., Yamada, S., Hamaya, K., van der Laan, G., Lazarov, V.K. and Cavill, S.A. Substrate dependent reduction of Gilbert damping in annealed Heusler alloy thin films grown on group IV semiconductors APPLIED PHYSICS LETTERS 119, 17 (2021) |
| Abstract: A structural and FMR study is presented for epitaxial thin films of the
Heusler alloy Co2FeAl0.5Si0.5 (CFAS) grown on Ge(111) and Si(111) substrates. All films, as-grown and post-annealed, show B2 ordering; full chemical order (L2(1)) is not obtained over the range of anneal temperatures used in this study. As-grown films show a lower Gilbert damping constant, alpha, when grown on a Si(111) substrate compared to Ge(111). Annealing the films to 450 degrees C significantly reduces alpha for CFAS on Ge while increasing alpha for CFAS on Si. This is related to a substrate dependent competition between improvements in lattice structure and increased interfacial intermixing as a function of anneal temperature. The optimal annealing temperature to minimize alpha is found to differ by similar to 100 K between the two substrates. Above an anneal temperature of 500 degrees C, films grown on both substrates have increased coercivity, decreased saturation magnetization, and show characteristic two-magnon scattering features. |
BibTeX:
@article{WOS:000730999400020,
author = {Love, C. J. and Kuerbanjiang, B. and Kerrigan, A. and Yamada, S. and Hamaya, K. and van der Laan, G. and Lazarov, V. K. and Cavill, S. A.},
title = {Substrate dependent reduction of Gilbert damping in annealed Heusler alloy thin films grown on group IV semiconductors},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {119},
number = {17},
doi = {https://doi.org/10.1063/5.0060213}
}
|
| Liu, J. and Hesjedal, T. Magnetic Topological Insulator Heterostructures: A Review ADVANCED MATERIALS early access (OCT 2021) |
| Abstract: Topological insulators (TIs) provide intriguing prospects for the future
of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. The combination of topological properties and magnetic order can lead to new quantum states including the quantum anomalous Hall effect that was first experimentally realized in Cr-doped (Bi,Sb)(2)Te-3 films. Since magnetic doping can introduce detrimental effects, requiring very low operational temperatures, alternative approaches are explored. Proximity coupling to magnetically ordered systems is an obvious option, with the prospect to raise the temperature for observing the various quantum effects. Here, an overview of proximity coupling and interfacial effects in TI heterostructures is presented, which provides a versatile materials platform for tuning the magnetic and topological properties of these exciting materials. An introduction is first given to the heterostructure growth by molecular beam epitaxy and suitable structural, electronic, and magnetic characterization techniques. Going beyond transition-metal-doped and undoped TI heterostructures, examples of heterostructures are discussed, including rare-earth-doped TIs, magnetic insulators, and antiferromagnets, which lead to exotic phenomena such as skyrmions and exchange bias. Finally, an outlook on novel heterostructures such as intrinsic magnetic TIs and systems including 2D materials is given. |
BibTeX:
@article{WOS:000708559500001,
author = {Liu, Jieyi and Hesjedal, Thorsten},
title = {Magnetic Topological Insulator Heterostructures: A Review},
journal = {ADVANCED MATERIALS},
doi = {https://doi.org/10.1002/adma.202102427}
}
|
| Yun, J., Sheng, Y., Guo, X., Zheng, B., Chen, P., Cao, Y., Yan, Z., He, X., Jin, P., Li, J., Cui, M., Shen, T., Wang, Z., Yang, D., Zuo, Y. and Xi, L. Tuning the spin-flop transition in perpendicularly magnetized synthetic antiferromagnets by swift heavy Fe ions irradiation PHYSICAL REVIEW B 104, 13 (2021) |
| Abstract: Synthetic antiferromagnets (SAFs) with perpendicular magnetic anisotropy
(PMA) have recently attracted intensive attention for their potential applications in domain-wall-based racetrack memory. In this paper, swift heavy Fe ion irradiation is introduced to tune the magnetic properties of Pt/Co/Pt/Ru/Pt/Co/Ta SAFs from spin-flip to spin-flop transition. The evolutions of magnetic domain and domain wall motion are investigated to obtain the microscopic insight into the change of magnetic states. Both the experimental and the simulated results demonstrate that different responses of the effective PMA constant and the interlayer-exchange-coupling strength to ion irradiation determine the magnetic-phase transitions. The structure evolution from experiments and theoretical simulations suggests that the ion-irradiation-induced damage mainly happens at the Pt/Co interface. The damage leads to the different decrease rates of the effective PMA constant and the interlayerexchange-coupling strength due to their intrinsic direct and Ruderman-Kittel-Kasuya-Yosida interaction nature, respectively. A quite good thermal stability of samples is obtained with ion fluence <1.5 x10(14) ions/cm(2). In this paper, we demonstrate that ion irradiation is a promising method to tailor magnetic properties of SAFs. Additionally, the ion-irradiation-induced well-controlled antiferromagnetically coupled domains could show potential applications in spintronic devices. |
BibTeX:
@article{WOS:000708655300001,
author = {Yun, Jijun and Sheng, Yanbin and Guo, Xi and Zheng, Bowen and Chen, Peng and Cao, Yang and Yan, Ze and He, Xiaodong and Jin, Peng and Li, Jing and Cui, Minghuan and Shen, Tielong and Wang, Zhiguang and Yang, Dezheng and Zuo, Yalu and Xi, Li},
title = {Tuning the spin-flop transition in perpendicularly magnetized synthetic antiferromagnets by swift heavy Fe ions irradiation},
journal = {PHYSICAL REVIEW B},
year = {2021},
volume = {104},
number = {13},
doi = {https://doi.org/10.1103/PhysRevB.104.134416}
}
|
| Swindells, C., Glowinski, H., Choi, Y., Haskel, D., Michalowski, P.P., Hase, T., Kuswik, P. and Atkinson, D. Proximity-induced magnetism and the enhancement of damping in ferromagnetic/heavy metal systems APPLIED PHYSICS LETTERS 119, 15 (2021) |
| Abstract: The relationship between proximity-induced magnetism (PIM) at the heavy
metal/ferromagnet interface and spin-transport across such interfaces has generated significant debate. To investigate the link between the two, element specific x-ray magnetic circular dichroism and ferromagnetic resonance measurements were made on the same CoFe/Au/Pt and NiFe/Au/Pt thin film samples with varying Au thickness, with complementary SIMS analysis, which shows evidence of Ni diffusion from NiFe into the Pt. An approximately linear relationship is observed between the magnitude of Pt PIM and magnitude of damping enhancement in both systems. The results demonstrate that electronic hybridization of the heavy metal and ferromagnet is required for a full understanding of damping enhancement and interfacial spin-transport for spintronic devices. |
BibTeX:
@article{WOS:000743113500002,
author = {Swindells, C. and Glowinski, H. and Choi, Y. and Haskel, D. and Michalowski, P. P. and Hase, T. and Kuswik, P. and Atkinson, D.},
title = {Proximity-induced magnetism and the enhancement of damping in ferromagnetic/heavy metal systems},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {119},
number = {15},
doi = {https://doi.org/10.1063/5.0064336}
}
|
| Weber, T., Vonk, V., Escalera-Lopez, D., Abbondanza, G., Larsson, A., Koller, V., Abb, M.J.S., Hegedues, Z., Baecker, T., Lienert, U., Harlow, G.S., Stierle, A., Cherevko, S., Lundgren, E. and Over, H. Operando Stability Studies of Ultrathin Single-Crystalline IrO2(110) Films under Acidic Oxygen Evolution Reaction Conditions ACS CATALYSIS 11, 20, pp. 12651-12660 (2021)early access (SEP 2021) |
| Abstract: The anodic corrosion behavior of 50 angstrom thick single-crystalline
IrO2 (110) films supported on slightly bulk-reduced TiO2 (110) single crystals is studied during acidic water splitting by a unique combination of operando techniques, namely, synchrotron-based high-energy X-ray reflectivity (XRR) and surface X-ray diffraction (SXRD) together with highly sensitive inductively coupled plasma mass spectrometry (ICP-MS). Corrosion-induced structural and morphological changes of the IrO2 (110) model electrode can be followed on the atomic scale by operando XRR and SXRD that are supplemented with ex situ scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), whereas with ICP-MS, the corrosion rate can be quantified down to 1 pg.cm(-2).s(-1) with a time resolution on the second scale. The operando synchrotron-based X-ray scattering techniques are surprisingly sensitive to Ir corrosion of about 0.10 monolayer of IrO2 (110) in similar to 26 h, i.e., 0.4 pg.cm(-2).s(-1). The present study demonstrates that single-crystalline IrO2 (110) films are much more stable than hitherto expected. Although the dissolution rate is very small, ICP-MS experiments reveal a significantly higher dissolution rate than the operando high-energy XRR/SXRD experiments. These differences in dissolution rate are suggested to be due to the different modi operandi encountered in ICP-MS (dynamic) and operando XRR/ SXRD experiments (steady state), a fact that may need to be considered when hydrogen production is coupled to intermittent energy sources such as renewables. |
BibTeX:
@article{WOS:000709692900021,
author = {Weber, Tim and Vonk, Vedran and Escalera-Lopez, Daniel and Abbondanza, Giuseppe and Larsson, Alfred and Koller, Volkmar and Abb, Marcel J. S. and Hegedues, Zoltan and Baecker, Thomas and Lienert, Ulrich and Harlow, Gary S. and Stierle, Andreas and Cherevko, Serhiy and Lundgren, Edvin and Over, Herbert},
title = {Operando Stability Studies of Ultrathin Single-Crystalline IrO2(110) Films under Acidic Oxygen Evolution Reaction Conditions},
journal = {ACS CATALYSIS},
year = {2021},
volume = {11},
number = {20},
pages = {12651-12660},
doi = {https://doi.org/10.1021/acscatal.1c03599}
}
|
| Cheema, S.S., Shanker, N., Hsu, C.-H., Datar, A., Bae, J., Kwon, D. and Salahuddin, S. One Nanometer HfO2-Based Ferroelectric Tunnel Junctions on Silicon ADVANCED ELECTRONIC MATERIALS 8, 6, SI (2022)early access (SEP 2021) |
| Abstract: In ferroelectric materials, spontaneous symmetry breaking leads to a
switchable electric polarization, which offers significant promise for nonvolatile memories. In particular, ferroelectric tunnel junctions (FTJs) have emerged as a new resistive switching memory which exploits polarization-dependent tunnel current across a thin ferroelectric barrier. This work integrates FTJs with complementary metal-oxide-semiconductor-compatible Zr-doped HfO2 (Zr:HfO2) ferroelectric barriers of just 1 nm thickness, grown by atomic layer deposition on silicon. These 1 nm Zr:HfO2 tunnel junctions exhibit large polarization-driven electroresistance (>20 000%), the largest value reported for HfO2-based FTJs. In addition, due to just a 1 nm ferroelectric barrier, these junctions provide large tunneling current (>1 A cm(-2)) at low read voltage, orders of magnitude larger than reported thicker HfO2-based FTJs. Therefore, this proof-of-principle demonstration provides an approach to simultaneously overcome three major drawbacks of prototypical FTJs: a Si-compatible ultrathin ferroelectric, large electroresistance, and large read current for high-speed operation. |
BibTeX:
@article{WOS:000700950500001,
author = {Cheema, Suraj S. and Shanker, Nirmaan and Hsu, Cheng-Hsiang and Datar, Adhiraj and Bae, Jongho and Kwon, Daewoong and Salahuddin, Sayeef},
title = {One Nanometer HfO2-Based Ferroelectric Tunnel Junctions on Silicon},
journal = {ADVANCED ELECTRONIC MATERIALS},
year = {2022},
volume = {8},
number = {6, SI},
doi = {https://doi.org/10.1002/aelm.202100499}
}
|
| Cao, L., Herklotz, A., Rata, D., Yin, C., Petracic, O., Kentsch, U., Helm, M. and Zhou, S. Metal-Insulator Transition via Ion Irradiation in Epitaxial La0.7Sr0.3MnO3-delta Thin Films PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 15, 11 (2021)early access (SEP 2021) |
| Abstract: Complex oxides provide rich physics related to ionic defects. For the
proper tuning of functionalities in oxide heterostructures, it is highly desired to develop fast, effective, and low-temperature routes for the dynamic modification of defect concentration and distribution. Herein, the use of helium implantation to efficiently control the vacancy profiles in epitaxial La0.7Sr0.3MnO3-delta thin films is reported. The viability of this approach is supported by lattice expansion in the out-of-plane lattice direction and dramatic change in physical properties, i.e., a transition from ferromagnetic metallic to antiferromagnetic insulating. In particular, a significant increase of resistivity up to four orders of magnitude is evidenced at room temperature, upon implantation of highly energetic He ions. The result offers an attractive means for tuning the emergent physical properties of oxide thin films via strong coupling between strain, defects, and valence. |
BibTeX:
@article{WOS:000696764700001,
author = {Cao, Lei and Herklotz, Andreas and Rata, Diana and Yin, Chenyang and Petracic, Oleg and Kentsch, Ulrich and Helm, Manfred and Zhou, Shengqiang},
title = {Metal-Insulator Transition via Ion Irradiation in Epitaxial La0.7Sr0.3MnO3-delta Thin Films},
journal = {PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS},
year = {2021},
volume = {15},
number = {11},
doi = {https://doi.org/10.1002/pssr.202100278}
}
|
| Huon, A., Yoon, S., Fitzsimmons, M.R., Charlton, T.R., Ok, J.M., dela Cruz, C. and Lee, H.N. Effects of Sn substitution in SrRuO3 epitaxial films APPLIED PHYSICS LETTERS 119, 11 (2021) |
| Abstract: Epitaxial SrRu1-xSnxO3 (0 <= x <= 1) thin films were deposited on SrTiO3
(001) substrates by sequential two-target synthesis using pulsed laser deposition to achieve stable phases in this family of quaternary perovskites. The SrRu1-xSnxO3 films exhibit a good crystalline quality, a sharp interface between film and substrate, and an atomically smooth surface. A gradual expansion of the c-axis lattice parameter was observed with Sn doping serving as a means to tune chemical pressure and magnetism. With an increase in Sn doping, the resistivity of the film increased, and the ferromagnetism decreased. These results illustrate use of lattice engineering, e.g., tuning of c-axis lattice parameter with chemical doping, to control electronic and magnetic properties of epitaxial thin films for applications in oxide electronics.(c) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http:// creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0061902 |
BibTeX:
@article{WOS:000697124600002,
author = {Huon, Amanda and Yoon, Sangmoon and Fitzsimmons, Michael R. and Charlton, Timothy R. and Ok, Jong Mok and dela Cruz, Clarina and Lee, Ho Nyung},
title = {Effects of Sn substitution in SrRuO3 epitaxial films},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {119},
number = {11},
doi = {https://doi.org/10.1063/5.0061902}
}
|
| Li, Y., Sun, W., Yang, J., Cai, X., Guo, W., Gu, Z., Zhu, Y. and Nie, Y. Impact of Cation Stoichiometry on the Crystalline Structure and Superconductivity in Nickelates FRONTIERS IN PHYSICS 9 (2021) |
| Abstract: The recent discovery of superconductivity in infinite-layer nickelate
films has aroused great interest since it provides a new platform to explore the mechanism of high-temperature superconductivity. However, superconductivity only appears in the thin film form and synthesizing superconducting nickelate films is extremely challenging, limiting the in-depth studies on this compound. Here, we explore the critical parameters in the growth of high-quality nickelate films using molecular beam epitaxy. We found that stoichiometry is crucial in optimizing the crystalline structure and realizing superconductivity in nickelate films. In precursor NdNiO3 films, optimal stoichiometry of cations yields the most compact lattice while off-stoichiometry of cations causes obvious lattice expansion, influencing the subsequent topotactic reduction and the emergence of superconductivity in infinite-layer nickelates. Surprisingly, in-situ reflection high energy electron diffraction indicates that some impurity phases always appear once Sr ions are doped into NdNiO3 although the X-ray diffraction data are of high quality. While these impurity phases do not seem to suppress the superconductivity, their impacts on the electronic and magnetic structure deserve further studies. Our work demonstrates and highlights the significance of cation stoichiometry in the superconducting nickelate family. |
BibTeX:
@article{WOS:000696894000001,
author = {Li, Yueying and Sun, Wenjie and Yang, Jiangfeng and Cai, Xiangbin and Guo, Wei and Gu, Zhengbin and Zhu, Ye and Nie, Yuefeng},
title = {Impact of Cation Stoichiometry on the Crystalline Structure and Superconductivity in Nickelates},
journal = {FRONTIERS IN PHYSICS},
year = {2021},
volume = {9},
doi = {https://doi.org/10.3389/fphy.2021.719534}
}
|
| Kupferer, A., Mensing, M., Lehnert, J., Mandl, S. and Mayr, S.G. Carbon and Neon Ion Bombardment Induced Smoothing and Surface Relaxation of Titania Nanotubes NANOMATERIALS 11, 9 (2021) |
| Abstract: Titania nanotube arrays with their enormous surface area are the subject
of much attention in diverse fields of research. In the present work, we show that not only 60 keV and 150 keV ion bombardment of amorphous titania nanotube arrays yields defect creation within the tube walls, but it also changes the surface morphology: the surface relaxes and smoothens in accordance with a curvature-driven surface material's transport mechanism, which is mediated by radiation-induced viscous flow or radiation-enhanced surface diffusion, while the nanotubes act as additional sinks for the particle surface currents. These effects occur independently of the ion species: both carbon and neon ion bombardments result in comparable surface relaxation responses initiated by an ion energy of 60 keV at a fluence of 1 x 10(16) ions/cm(2). Using atomic force microscopy and contact angle measurements, we thoroughly study the relaxation effects on the surface topography and surface free energy, respectively. Moreover, surface relaxation is accompanied by further amorphization in surface-near regions and a reduction in the mass density, as demonstrated by Raman spectroscopy and X-ray reflectivity. Since ion bombardment can be performed on global and local scales, it constitutes a versatile tool to achieve well-defined and tunable topographies and distinct surface characteristics. Hence, different types of nanotube arrays can be modified for various applications. |
BibTeX:
@article{WOS:000699867500001,
author = {Kupferer, Astrid and Mensing, Michael and Lehnert, Jan and Mandl, Stephan and Mayr, Stefan G.},
title = {Carbon and Neon Ion Bombardment Induced Smoothing and Surface Relaxation of Titania Nanotubes},
journal = {NANOMATERIALS},
year = {2021},
volume = {11},
number = {9},
doi = {https://doi.org/10.3390/nano11092458}
}
|
| Doucet, M., Archibald, R.K. and Heller, W.T. Machine learning for neutron reflectometry data analysis of two-layer thin films * MACHINE LEARNING-SCIENCE AND TECHNOLOGY 2, 3 (2021) |
| Abstract: Neutron reflectometry (NR) is a powerful tool for probing thin films at
length scales down to nanometers. We investigated the use of a neural network to predict a two-layer thin film structure to model a given measured reflectivity curve. Application of this neural network to predict a thin film structure revealed that it was accurate and could provide an excellent starting point for traditional fitting methods. Employing prediction-guided fitting has considerable potential for more rapidly producing a result compared to the labor-intensive but commonly-used approach of trial and error searches prior to refinement. A deeper look at the stability of the predictive power of the neural network against statistical fluctuations of measured reflectivity profiles showed that the predictions are stable. We conclude that the approach presented here can provide valuable assistance to users of NR and should be further extended for use in studies of more complex n-layer thin film systems. This result also opens up the possibility of developing adaptive measurement systems in the future. |
BibTeX:
@article{WOS:000660872600001,
author = {Doucet, Mathieu and Archibald, Richard K. and Heller, William T.},
title = {Machine learning for neutron reflectometry data analysis of two-layer thin films *},
journal = {MACHINE LEARNING-SCIENCE AND TECHNOLOGY},
year = {2021},
volume = {2},
number = {3},
doi = {https://doi.org/10.1088/2632-2153/abf257}
}
|
| Mironov, D., Durant, J.H., Mackenzie, R. and Cooper, J.F.K. Towards automated analysis for neutron reflectivity MACHINE LEARNING-SCIENCE AND TECHNOLOGY 2, 3 (2021) |
| Abstract: We describe a neural network-based tool for the automatic estimation of
thin film thicknesses and scattering length densities from neutron reflectivity curves. The neural network sits within a data pipeline, that takes raw data from a neutron reflectometer, and outputs data and parameter estimates into a fitting program for end user analysis. Our tool deals with simple cases, predicting the number of layers and layer parameters up to three layers on a bulk substrate. This provides good accuracy in parameter estimation, while covering a large portion of the use case. By automating steps in data analysis that only require semi-expert knowledge, we lower the barrier to on-experiment data analysis, allowing better utility to be made from large scale facility experiments. Transfer learning showed that our tool works for x-ray reflectivity, and all code is freely available on GitHub (neutron-net 2020, available at: https://github.com/xmironov/neutron-net) (Accessed: 25 June 2020). |
BibTeX:
@article{WOS:000660868600001,
author = {Mironov, Daniil and Durant, James H. and Mackenzie, Rebecca and Cooper, Joshaniel F. K.},
title = {Towards automated analysis for neutron reflectivity},
journal = {MACHINE LEARNING-SCIENCE AND TECHNOLOGY},
year = {2021},
volume = {2},
number = {3},
doi = {https://doi.org/10.1088/2632-2153/abe7b5}
}
|
| Maruyama, R., Yamazaki, D., Aoki, H., Akutsu-Suyama, K., Hanashima, T., Miyata, N., Soyama, K., Bigault, T., Saerbeck, T. and Courtois, P. Improved performance of wide bandwidth neutron-spin polarizer due to ferromagnetic interlayer exchange coupling JOURNAL OF APPLIED PHYSICS 130, 8 (2021) |
| Abstract: Ferromagnetic (FM) interlayer exchange coupling of ion-beam sputtered
Fe/Ge multilayers was investigated by off-specular polarized neutron scattering measurements. We observed a monotonously growing correlation of magnetic moments in the out-of-plane direction with decreasing Ge thickness. The magnetic properties of the multilayers with and without the FM interlayer exchange coupling agree well with the three- and two-dimensional random anisotropy model, respectively, assuming an FM interlayer exchange coupling comparable to the direct exchange interaction within the sample plane. The results of the Fe/Ge multilayers were used to invoke FM interlayer exchange coupling in a neutron polarizing supermirror in order to extend its bandwidth. Typically, the bandwidth is limited due to a Curie temperature close to room temperature of the thinnest Fe layers with less than 3 nm. We propose a modified layer sequence of the neutron polarizing supermirror, where the minimum Fe thickness was set to 3.5 nm, whereas the Ge thickness was reduced. A performance test of the neutron polarizing supermirror showed that the FM interlayer exchange coupling contributed to the presence of the magnetization comparable to the bulk and resulted in a marked extension in the bandwidth. |
BibTeX:
@article{WOS:000689641400002,
author = {Maruyama, R. and Yamazaki, D. and Aoki, H. and Akutsu-Suyama, K. and Hanashima, T. and Miyata, N. and Soyama, K. and Bigault, T. and Saerbeck, T. and Courtois, P.},
title = {Improved performance of wide bandwidth neutron-spin polarizer due to ferromagnetic interlayer exchange coupling},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2021},
volume = {130},
number = {8},
doi = {https://doi.org/10.1063/5.0062072}
}
|
| Steffen, A., Glavic, A., Gutberlet, T., Ambaye, H., Schubert, J., Gepraegs, S., Barthel, J., Mattauch, S., Zander, W., Kruth, M., Schoeffmann, P., Puetter, S. and Brueckel, T. Unexpected precipitates in conjunction with layer-by-layer growth in Mn-enriched La2/3Sr1/3MnO3 thin films THIN SOLID FILMS 735 (2021)early access (AUG 2021) |
| Abstract: In recent years, layer-by-layer heteroepitaxy has become a versatile
tool for depositing novel materials not accessible in bulk form. While it is possible to control the mono layer sequence on an atomic scale with the help of sophisticated analysis techniques, not all important features of the thin film growth are detectable. We report on a detailed analysis of layer-by-layer deposited Mn-enriched La2/3Sr1/3MnO3 thin films using various, complementary experimental techniques. Our results show that, contrary to the expectations from the growth parameters and initial characterization, the films did not grow as atomic planes but segregated into layers of La2/3Sr1/3MnO3 with additional embedded precipitant crystals. We attribute this separation to a Volmer-Weber island-like growth of Mn3O4 crystals within layers of La2/3Sr1/3MnO3 due to increased surface tension inhibiting La and Sr oxides from sticking to nucleated Mn3O4 surfaces during the growth at high temperatures. |
BibTeX:
@article{WOS:000704918900006,
author = {Steffen, Alexandra and Glavic, Artur and Gutberlet, Thomas and Ambaye, Haile and Schubert, Juergen and Gepraegs, Stephan and Barthel, Juri and Mattauch, Stefan and Zander, Willi and Kruth, Maximilian and Schoeffmann, Patrick and Puetter, Sabine and Brueckel, Thomas},
title = {Unexpected precipitates in conjunction with layer-by-layer growth in Mn-enriched La2/3Sr1/3MnO3 thin films},
journal = {THIN SOLID FILMS},
year = {2021},
volume = {735},
doi = {https://doi.org/10.1016/j.tsf.2021.138862}
}
|
| Bopp, S.E., Qian, H. and Liu, Z. Influence of Hafnium Defects on the Optical and Structural Properties of Zirconium Nitride PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 15, 10 (2021)early access (AUG 2021) |
| Abstract: Recently, the application of transition metal mononitrides (TMNs) to
plasmonics and nonlinear optics has grown at an astounding rate. TiN and ZrN have emerged as the dominating materials in this direction. However, even though ZrN is reported to have lower dielectric losses and enhanced tunability in plasmonic applications when compared with TiN, the body of work regarding TiN is much more mature than that of ZrN. This imbalance of work regarding ZrN may be in part an effect of pollution in precursor materials for the fabrication of ZrN, leading to an increased imaginary part of permittivity and frustration in reproduction of ZrN with literature-like properties. Herein, the effects of Hf defects (a common pollutant in Zr) on the optical properties of nitride films grown with radio frequency (RF) magnetron sputtering are reported. Hf defects are introduced into nitride films with a sputtering target made of the Hf-polluted ``grade 702'' Zr alloy. Hf defects are found in all analyzed films with concentrations at around approximate to 0.5-1 at %. Chemical, structural, and optical properties of RF magnetron-sputtered Hf- x :Zr y N z films (x MUCH LESS-THAN y,z) are characterized and discussed. |
BibTeX:
@article{WOS:000685416800001,
author = {Bopp, Steven Edward and Qian, Haoliang and Liu, Zhaowei},
title = {Influence of Hafnium Defects on the Optical and Structural Properties of Zirconium Nitride},
journal = {PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS},
year = {2021},
volume = {15},
number = {10},
doi = {https://doi.org/10.1002/pssr.202100372}
}
|
| Chen, H., Zhan, X., Liu, X., Wang, L., Hai, Y., Xu, J., Zhu, T. and Yin, W. The helium behavior and thermal stability of W/Ta bilayer nanocomposite investigated by neutron reflectometry NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 504, pp. 43-49 (2021)early access (AUG 2021) |
| Abstract: The helium behavior and thermal stability of W/Ta bilayer nanocomposite
were investigated by neutron reflectometry. The results show the W/Ta interface is stable after He+ ion irradiation and annealing. Under He+ ion irradiation, the helium enriched and denuded sublayers are formed at W/Ta interfacial region, due to the migration of helium from the W layer towards the Ta layer. That results from the lowest He solution energy and electron density of Ta layer, and negative energy barrier from W to Ta layer. This mechanism enlightens us that dispersing Ta-nanoparticles into tungsten can relieve helium deleterious effect in tungsten. |
BibTeX:
@article{WOS:000691201700006,
author = {Chen, Huaican and Zhan, Xiaozhi and Liu, Xiao and Wang, Liming and Hai, Yang and Xu, Juping and Zhu, Tao and Yin, Wen},
title = {The helium behavior and thermal stability of W/Ta bilayer nanocomposite investigated by neutron reflectometry},
journal = {NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS},
year = {2021},
volume = {504},
pages = {43-49},
doi = {https://doi.org/10.1016/j.nimb.2021.06.023}
}
|
| Jafri, Y., Singh, S., Gupta, S., Fukuma, Y., Sharma, K., Gupta, M., Reddy, V.R., Sharma, G. and Gupta, A. Investigation of structural, magnetic and electronic properties of FeTa films for varying Ta concentration at different annealing temperatures JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 538 (2021)early access (AUG 2021) |
| Abstract: In the present work, temperature dependent magnetic, structural and
electronic properties of FeTa films with increasing Ta concentration are investigated. X-ray reflectivity (XRR) studies reveal densification of the film with increasing Ta concentration. Thermal annealing also results in an increased electron density relative to asdeposited film, concurrent with increase in grain size as observed from X-ray diffraction (XRD) and results of Soft-X-ray absorption spectroscopy (SXAS). However, grain growth is inhibited with increasing Ta concentration by presence of Ta in grain boundary (GB) region. This also results in increase in magnetic coercivity (greater than150 %) as observed from magneto-optical Kerr effect (MOKE). The structural properties were further correlated with magnetic properties as observed from Polarized neutron reflectivity (PNR) and Ferromagnetic resonance (FMR). Effective magnetic moment of the samples, as observed from PNR decreases with increasing Ta concentration and increases with increasing annealing temperature, which is in agreement with FMR results. Scattering length density profiles, observed from simultaneous fitting of XRR and PNR show presence of an oxide layer at surface, as also confirmed from SXAS measurements. |
BibTeX:
@article{WOS:000686134100008,
author = {Jafri, Yasmeen and Singh, Surendra and Gupta, Surbhi and Fukuma, Yasuhiro and Sharma, Kavita and Gupta, Mukul and Reddy, V. R. and Sharma, Gagan and Gupta, Ajay},
title = {Investigation of structural, magnetic and electronic properties of FeTa films for varying Ta concentration at different annealing temperatures},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2021},
volume = {538},
doi = {https://doi.org/10.1016/j.jmmm.2021.168306}
}
|
| Tokac, M. Influence of tantalum concentrations on the magnetic properties of amorphous CoFeTaB thin-films JOURNAL OF NON-CRYSTALLINE SOLIDS 572 (2021)early access (AUG 2021) |
| Abstract: The structural and magnetic properties of amorphous CoFeTaB thin-films
were studied as a function of tantalum concentration. The investigations of the structural properties of amorphous CoFeTaB thin-films were undertaken to confirm layer thickness, interface roughness, and their amorphous structure. Temperature dependent magnetic characterizations were performed in order to extract Curie temperatures and their saturation magnetizations of each structure. Curie temperatures and saturation magnetizations of amorphous CoFeTaB thin-films show similar behaviour, where both quantities decrease with increasing tantalum concentration in thin-film structures. These reductions can be attributed to a result of a transfer of electrons from the metalloid atoms to the unfilled d holes of the 3d transition metals, and diffusion of tantalum atoms towards the ferromagnetic layer during thin-film deposition. Investigation of tuning both Curie temperature and magnetization by the addition of a non-magnetic transition metal is crucial for the development of spintronic applications. |
BibTeX:
@article{WOS:000696310300011,
author = {Tokac, M.},
title = {Influence of tantalum concentrations on the magnetic properties of amorphous CoFeTaB thin-films},
journal = {JOURNAL OF NON-CRYSTALLINE SOLIDS},
year = {2021},
volume = {572},
doi = {https://doi.org/10.1016/j.jnoncrysol.2021.121080}
}
|
| Durant, J.H., Wilkins, L., Butler, K. and Cooper, J.F.K. Determining the maximum information gain and optimizing experimental design in neutron reflectometry using the Fisher information JOURNAL OF APPLIED CRYSTALLOGRAPHY 54, 4, pp. 1100-1110 (2021) |
| Abstract: An approach based on the Fisher information (FI) is developed to
quantify the maximum information gain and optimal experimental design in neutron reflectometry experiments. In these experiments, the FI can be calculated analytically and used to provide sub-second predictions of parameter uncertainties. This approach can be used to influence real-time decisions about measurement angle, measurement time, contrast choice and other experimental conditions based on parameters of interest. The FI provides a lower bound on parameter estimation uncertainties, and these are shown to decrease with the square root of the measurement time, providing useful information for the planning and scheduling of experimental work. As the FI is computationally inexpensive to calculate, it can be computed repeatedly during the course of an experiment, saving costly beam time by signalling that sufficient data have been obtained or saving experimental data sets by signalling that an experiment needs to continue. The approach's predictions are validated through the introduction of an experiment simulation framework that incorporates instrument-specific incident flux profiles, and through the investigation of measuring the structural properties of a phospholipid bilayer. |
BibTeX:
@article{WOS:000683118400008,
author = {Durant, James H. and Wilkins, Lucas and Butler, Keith and Cooper, Joshaniel F. K.},
title = {Determining the maximum information gain and optimizing experimental design in neutron reflectometry using the Fisher information},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2021},
volume = {54},
number = {4},
pages = {1100-1110},
doi = {https://doi.org/10.1107/S160057672100563X}
}
|
| Lee, J., Ryu, S., Kim, I., Byeon, M., Jeong, M.-H., Lee, J.S., Hong, T.E., Cho, J., Lee, J., Park, J.K. and Jeen, H. Large enhancement of magnetic moment in nitridated CeFe12 JOURNAL OF ALLOYS AND COMPOUNDS 886 (2021)early access (JUL 2021) |
| Abstract: Due to success of desired doping, ion implantation has been widely used
for semiconductor processing. In this work, we used nitrogen ion implantation to enhance magnetism in CeFe12 epitaxial thin films. To optimize nitrogen contents in CeFe12 and minimize the damage caused by the high-energy ion beam, we varied the thickness of the capping Mo layer. The saturation magnetization increased nearly 25% by nitrogen ion implantation into CeFe12 thin film. This phenomenon is explained by density functional theory calculations and confirmed by the magnetic resonance technique. The ion implantation and design strategy can be used for light-ion implantation into lattices to modulate magnetic, optical, and electrical properties. (c) 2021 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000697282500003,
author = {Lee, Joonhyuk and Ryu, Sangkyun and Kim, Inhwan and Byeon, Mirang and Jeong, Myung-Hwan and Lee, Jae S. and Hong, Tae Eun and Cho, Jinhyung and Lee, Jaekwang and Park, Jun Kue and Jeen, Hyoungjeen},
title = {Large enhancement of magnetic moment in nitridated CeFe12},
journal = {JOURNAL OF ALLOYS AND COMPOUNDS},
year = {2021},
volume = {886},
doi = {https://doi.org/10.1016/j.jallcom.2021.161245}
}
|
| Sarkar, P., Biswas, A., Rai, S., Modi, M.H., Ghorai, G., Sahoo, P.K. and Bhattacharyya, D. Evolution of the interface microstructure of short-period Cr/Ti multilayers with increase in number of bi-layers THIN SOLID FILMS 734 (2021)early access (JUL 2021) |
| Abstract: Evolution of interface microstructure with addition of more number of
layers has been investigated on Cr/Ti multilayer which is important for application as a mirror or monochromator in the ``water window'' soft X-ray spectral regime. Two sets of Cr/Ti multilayers at moderate and low bi-layer thickness regime have been prepared for this purpose using Ion Beam Sputtering technique. In one set, Cr/Ti multilayer with 25, 50, 60 and 100 numbers of bilayers with moderate bi-layer thickness of 3.8 nm have been deposited. In another set, four samples each having low bilayer thickness of 2.4 nm with 25, 50, 75 and 100 number of bi-layers have been prepared and the multilayers have subsequently been characterized with Specular X-ray reflectivity and diffuse X-ray scattering measurements at grazing incidence with hard X-rays. It is observed that cumulative effect of interface imperfections became more pronounced with increasing number of bilayers resulting in continuous increase in the interface width in both the thickness regimes; however, its evolution is not exactly same for the two sets of samples. Diffuse X-ray scattering result reveals that for the first set of samples, interface imperfections are dominated by interface roughness with no change in the interface diffusion with increase in number of layers, while for the second set, both interface roughness as well as interface diffusion contribute towards the cumulative accumulation of interface imperfections which is also confirmed by cross-sectional Transmission Electron Microscopy. Finally, performance of the multilayers in water window regime has been checked by soft X-ray reflectivity measurements using synchrotron radiation. The above results have direct implication in utilisation of these multilayers over a wide bi-layer thickness regime required to cover the full `water-window' spectrum. |
BibTeX:
@article{WOS:000686067600006,
author = {Sarkar, P. and Biswas, A. and Rai, S. and Modi, M. H. and Ghorai, Gurupada and Sahoo, Pratap K. and Bhattacharyya, D.},
title = {Evolution of the interface microstructure of short-period Cr/Ti multilayers with increase in number of bi-layers},
journal = {THIN SOLID FILMS},
year = {2021},
volume = {734},
doi = {https://doi.org/10.1016/j.tsf.2021.138840}
}
|
| Rego, T., Spagnoli, S., Faure, M.-C., Allain, C., Coasne, B., Malinge, J., Shen, C., Fontaine, P. and Goldmann, M. Unexpected Order-Disorder Transition in Diacetylene Alcohol Langmuir Films LANGMUIR 37, 30, pp. 9034-9042 (2021)early access (JUL 2021) |
| Abstract: The phase diagram of the Langmuir film of diacetylene
alcohol-henicosa-5,7-diyn-1-ol-is investigated by means of surface pressure versus surface area isotherms, Brewster angle microscopy, X-ray reflectivity, and grazing incident Xray diffraction. Among the usual phases described in the generic phase diagram of small head group molecules, one observes an unexpected reversible transition from an ordered condensed phase to a disordered one upon increasing the surface pressure. We postulate that the origin of this unusual, unprecedented transition results from the competition between the interactions between the diacetylene blocks in the hydrophobic chain and the hydrogen bonds between head groups and water. |
BibTeX:
@article{WOS:000683367100017,
author = {Rego, Tomas and Spagnoli, Sylvie and Faure, Marie-Claude and Allain, Clemence and Coasne, Benoit and Malinge, Jeremy and Shen, Chen and Fontaine, Philippe and Goldmann, Michel},
title = {Unexpected Order-Disorder Transition in Diacetylene Alcohol Langmuir Films},
journal = {LANGMUIR},
year = {2021},
volume = {37},
number = {30},
pages = {9034-9042},
doi = {https://doi.org/10.1021/acs.langmuir.1c01038}
}
|
| Waring, H.J., Li, Y., Moutafis, C., Vera-Marun, I.J. and Thomson, T. Magnetization dynamics in synthetic ferromagnetic thin films PHYSICAL REVIEW B 104, 1 (2021) |
| Abstract: Synthetic ferromagnets (SFMs) possess the same layer structure found in
the widely studied synthetic antiferromagnets. This consists of two ferromagnetic (FM) layers separated by a nonmagnetic (NM) spacer forming the structure FM1/NM/FM2, but SFMs describe the case where the interlayer exchange coupling promotes the parallel alignment of the magnetizations of the FM layers. The frequency and phase of the dynamic response of these structures depends sensitively on the interlayer exchange coupling as well as on the individual layer magnetizations. Through experiments and numerical simulations, we show that the dynamic response of the two ferromagnetic layers has an orthogonal dependence on the difference in layer magnetization and interlayer coupling allowing both parameters to be determined accurately. In addition, we are able to obtain the phases of the resonant modes, a hitherto challenging measurement, and thus show that the conventional acoustic and optical description does not fully capture the intricacies of SFM dynamics. These findings are directly applicable to the creation of tailored SFMs for spintronic devices such as STT/SOT-MRAM where magnetization and interlayer coupling are key parameters. |
BibTeX:
@article{WOS:000674314300003,
author = {Waring, H. J. and Li, Y. and Moutafis, C. and Vera-Marun, I. J. and Thomson, T.},
title = {Magnetization dynamics in synthetic ferromagnetic thin films},
journal = {PHYSICAL REVIEW B},
year = {2021},
volume = {104},
number = {1},
doi = {https://doi.org/10.1103/PhysRevB.104.014419}
}
|
| Ivanov, M.S., Buryakov, A.M., Vilarinho, P.M. and Mishina, E.D. Impact of compressive and tensile epitaxial strain on transport and nonlinear optical properties of magnetoelectric BaTiO3-(LaCa)MnO3 tunnel junction JOURNAL OF PHYSICS D-APPLIED PHYSICS 54, 27 (2021) |
| Abstract: This work is devoted to disclosing the effect of epitaxial strain on
crystallographic, transport, and nonlinear optical properties of a bilayer structure consisting of one ferroelectric (FE) (BaTiO3 with a thickness of 4 nm) and one ferromagnetic (La0.7Ca0.3MnO3 with the thickness of 12 nm) layers. Both tensile (of about similar to 6% caused by the MgO substrate) and compressive (of about similar to 1% caused by the SrTiO3 substrate) strains reduce the bulk metal-to-insulator phase transition temperature of the La0.7Ca0.3MnO3 layer from 240 K towards 195 K and 160 K, respectively. The appearance of the effect of colossal electroresistance, linear and nonlinear current-voltage behaviours and contribution of FE polarization switching in the BaTiO3 layer to the conductivity are associated with the influence of epitaxial strain. The predominance of the compressive over the tensile strain leads to the hysteresis behaviour of electroresistance, maximum conductivity caused by the resonant-tunnelling mechanism, and strong nonlinear optical dependence on the applied electric field. |
BibTeX:
@article{WOS:000645531700001,
author = {Ivanov, M. S. and Buryakov, A. M. and Vilarinho, P. M. and Mishina, E. D.},
title = {Impact of compressive and tensile epitaxial strain on transport and nonlinear optical properties of magnetoelectric BaTiO3-(LaCa)MnO3 tunnel junction},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2021},
volume = {54},
number = {27},
doi = {https://doi.org/10.1088/1361-6463/abf80a}
}
|
| Chiu, I.-T., Lee, M.-H., Cheng, S., Zhang, S., Heki, L., Zhang, Z., Mohtashami, Y., Lapa, P.N., Feng, M., Shafer, P., N'Diaye, A.T., Mehta, A., Schuller, J.A., Galli, G., Ramanathan, S., Zhu, Y., Schuller, I.K. and Takamura, Y. Cation and anion topotactic transformations in cobaltite thin films leading to Ruddlesden-Popper phases PHYSICAL REVIEW MATERIALS 5, 6 (2021) |
| Abstract: Topotactic transformations involve structural changes between related
crystal structures due to a loss or gain of material while retaining a crystallographic relationship. The perovskite oxide La0.7Sr0.3CoO3 (LSCO) is an ideal system for investigating phase transformations due to its high oxygen vacancy conductivity, relatively low oxygen vacancy formation energy, and strong coupling of the magnetic and electronic properties to the oxygen stoichiometry. While the transition between cobaltite perovskite and brownmillerite (BM) phases has been widely reported, further reduction beyond the BM phase lacks systematic studies. In this paper, we study the evolution of the physical properties of LSCO thin films upon exposure to highly reducing environments. We observe the rarely reported crystalline Ruddlesden-Popper phase, which involves the loss of both oxygen anions and cobalt cations upon annealing where the cobalt is found as isolated Co ions or Co nanoparticles. First-principles calculations confirm that the concurrent loss of oxygen and cobalt ions is thermodynamically possible through an intermediary BM phase. The strong correlation of the magnetic and electronic properties to the crystal structure highlights the potential of utilizing ion migration as a basis for emerging applications such as neuromorphic computing. |
BibTeX:
@article{WOS:000665792200006,
author = {Chiu, I-Ting and Lee, Min-Han and Cheng, Shaobo and Zhang, Shenli and Heki, Larry and Zhang, Zhen and Mohtashami, Yahya and Lapa, Pavel N. and Feng, Mingzhen and Shafer, Padraic and N'Diaye, Alpha T. and Mehta, Apurva and Schuller, Jon A. and Galli, Giulia and Ramanathan, Shriram and Zhu, Yimei and Schuller, Ivan K. and Takamura, Yayoi},
title = {Cation and anion topotactic transformations in cobaltite thin films leading to Ruddlesden-Popper phases},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2021},
volume = {5},
number = {6},
doi = {https://doi.org/10.1103/PhysRevMaterials.5.064416}
}
|
| Beiranvand, A., Liedke, M.O., Haalisto, C., Lahteenlahti, V., Schulman, A., Granroth, S., Palonen, H., Butterling, M., Wagner, A., Huhtinen, H. and Paturi, P. Tuned AFM-FM coupling by the formation of vacancy complex in Gd0.6Ca0.4MnO3 thin film lattice JOURNAL OF PHYSICS-CONDENSED MATTER 33, 25 (2021) |
| Abstract: The effect of in situ oxygen and vacuum annealings on the low bandwidth
manganite Gd1-x Ca (x) MnO3 (GCMO) thin film with x = 0.4 was investigated. Based on the magnetic measurements, the AFM-FM coupling is suppressed by the vacuum annealing treatment via destroying the double exchange interaction and increasing the unit cell volume by converting the Mn4+ to the Mn3+. Consequently, resistance increases significantly compared to pristine film. The results are explained by a model obtained from the positron annihilation studies, where the vacuum annealing increased the annihilation lifetime in A and B sites due to the formation of vacancy complexes V (A,B)-V-O, which was not the case in the pristine sample. The positron annihilation analysis indicated that most of the open volume defects have been detected in the interface region rather than on the subsurface layer and this result is confirmed by detailed x-ray reflection analysis. On the other hand, the effect of oxygen annealing on the unit cell volume and magnetization was insignificant. This is in agreement with positron annihilation results which demonstrated that the introduction of oxygen does not change the number of cation vacancies significantly. This work demonstrates that the modification of oxygen vacancies and vacancy complexes can tune magnetic and electronic structure of the epitaxial thin films to provide new functionalities in future applications. |
BibTeX:
@article{WOS:000655288100001,
author = {Beiranvand, A. and Liedke, M. O. and Haalisto, C. and Lahteenlahti, V and Schulman, A. and Granroth, S. and Palonen, H. and Butterling, M. and Wagner, A. and Huhtinen, H. and Paturi, P.},
title = {Tuned AFM-FM coupling by the formation of vacancy complex in Gd0.6Ca0.4MnO3 thin film lattice},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2021},
volume = {33},
number = {25},
doi = {https://doi.org/10.1088/1361-648X/abf9ba}
}
|
| Jiao, P., Xi, Z., Zhang, X., Han, Y., Wu, Y. and Wu, D. Electroresistance in metal/ferroelectric/semiconductor tunnel junctions based on a Hf0.5Zr0.5O2 barrier APPLIED PHYSICS LETTERS 118, 25 (2021) |
| Abstract: Ferroelectric Hf0.5Zr0.5O2 films, 5.8 nm in thickness, were deposited on
Nb:SrTiO3 semiconductor substrates to form a Pt/Hf0.5Zr0.5O2/Nb:SrTiO3 metal/ferroelectric/semiconductor ferroelectric tunnel junction (FTJ). A high tunneling electroresistance ratio of 800 was achieved at room-temperature. It is observed that in the low resistance state, the transport characteristic obeys direct tunneling, while in the high resistance state, it is dominated by thermal emission. It implies that the Schottky barrier on the surface of the semiconductive electrode is modulated by the polarization in the ferroelectric Hf0.5Zr0.5O2 barrier, generating the high electroresistance ratio. The FTJ also exhibits excellent retention for more than 10 000 s and good switching endurance for more than 1500 cycles. The results suggest the potential of this HfO2-based FTJ for next generation nonvolatile memories. |
BibTeX:
@article{WOS:000664033400003,
author = {Jiao, Peijie and Xi, Zhongnan and Zhang, Xiaoyu and Han, Yajie and Wu, Yang and Wu, Di},
title = {Electroresistance in metal/ferroelectric/semiconductor tunnel junctions based on a Hf0.5Zr0.5O2 barrier},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {118},
number = {25},
doi = {https://doi.org/10.1063/5.0053959}
}
|
| Liu, C., Liu, Y., Zhang, B., Sun, C.-J., Lan, D., Chen, P., Wu, X., Yang, P., Yu, X., Charlton, T., Fitzsimmons, M.R., Ding, J., Chen, J. and Chow, G.M. Ferroelectric Self-Polarization Controlled Magnetic Stratification and Magnetic Coupling in Ultrathin La0.67Sr0.33MnO3 Films ACS APPLIED MATERIALS & INTERFACES 13, 25, pp. 30137-30145 (2021)early access (JUN 2021) |
| Abstract: Multiferroic oxide heterostructures consisting of ferromagnetic and
ferroelectric components hold the promise for nonvolatile magnetic control via ferroelectric polarization, advantageous for the low-dissipation spintronics. Modern understanding of the magnetoelectric coupling in these systems involves structural, orbital, and magnetic reconstructions at interfaces. Previous works have long proposed polarization-dependent interfacial magnetic structures; however, direct evidence is still missing, which requires advanced characterization tools with near-atomic-scale spatial resolutions. Here, extensive polarized neutron reflectometry (PNR) studies have determined the magnetic depth profiles of PbZr0.2Ti0.8O3/La(0.6)7Sr(0.33)MnO(3) (PZT/LSMO) bilayers with opposite self-polarizations. When the LSMO is 2-3 nm thick, the bilayers show two magnetic transitions on cooling. However, temperature-dependent magnetization is different below the lower-temperature transition for opposite polarizations. PNR finds that the LSMO splits into two magnetic sublayers, but the inter-sublayer magnetic couplings are of opposite signs for the two polarizations. Near-edge X-ray absorption spectroscopy further shows contrasts in both the Mn valences and the Mn-O bond anisotropy between the two polarizations. This work completes the puzzle for the magnetoelectric coupling model at the PZT/LSMO interface, showing a synergic interplay among multiple degrees of freedom toward emergent functionalities at complex oxide interfaces. |
BibTeX:
@article{WOS:000670430100086,
author = {Liu, Chao and Liu, Yaohua and Zhang, Bangmin and Sun, Cheng-Jun and Lan, Da and Chen, Pingfan and Wu, Xiaohan and Yang, Ping and Yu, Xiaojiang and Charlton, Timothy and Fitzsimmons, Michael R. and Ding, Jun and Chen, Jingsheng and Chow, Gan Moog},
title = {Ferroelectric Self-Polarization Controlled Magnetic Stratification and Magnetic Coupling in Ultrathin La0.67Sr0.33MnO3 Films},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2021},
volume = {13},
number = {25},
pages = {30137-30145},
doi = {https://doi.org/10.1021/acsami.1c02300}
}
|
| Bimashofer, G., Smetaczek, S., Gilardi, E., Schneider, C.W., Limbeck, A., Lippert, T. and Stahn, J. Growth of LixLaySrzMnO3 thin films by pulsed laser deposition: complex relation between thin film composition and deposition parameters APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 127, 6 (2021) |
| Abstract: LixLaySrzMnO3 thin films of various compositions (x,y,z) have been grown
using pulsed laser deposition. The compositions of the films have been studied as a function of deposition temperature, target-to-substrate distance and deposition pressure with respect to different cation ratios of the targets by inductively coupled plasma mass spectrometry. When growing multi-elemental oxide thin films containing lithium (with its large mass difference to other elements), lithium loss is most probably inevitable. But the desired thin film composition can be achieved by selecting specific growth conditions and different target compositions. The experiments also elucidate some of the mechanisms behind the incongruent lithium transfer from the targets to thin films. |
BibTeX:
@article{WOS:000724166800004,
author = {Bimashofer, G. and Smetaczek, S. and Gilardi, E. and Schneider, C. W. and Limbeck, A. and Lippert, T. and Stahn, J.},
title = {Growth of LixLaySrzMnO3 thin films by pulsed laser deposition: complex relation between thin film composition and deposition parameters},
journal = {APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING},
year = {2021},
volume = {127},
number = {6},
doi = {https://doi.org/10.1007/s00339-021-04506-9}
}
|
| Guo, Q.-X., Ren, Z.-X., Huang, Y.-Y., Zheng, Z.-C., Wang, X.-M., He, W., Zhu, Z.-D. and Teng, J. Effects of post-annealing on crystalline and transport properties of Bi2Te3 thin films* CHINESE PHYSICS B 30, 6 (2021) |
| Abstract: A well-established method is highly desirable for growing topological
insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi2Te3 films with the carrier density down to 4.0 x 10(13) cm(-2). In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi2Te3 thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi2Te3 thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length (similar to 228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi2Te3 thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications. |
BibTeX:
@article{WOS:000667466200001,
author = {Guo, Qi-Xun and Ren, Zhong-Xu and Huang, Yi-Ya and Zheng, Zhi-Chao and Wang, Xue-Min and He, Wei and Zhu, Zhen-Dong and Teng, Jiao},
title = {Effects of post-annealing on crystalline and transport properties of Bi2Te3 thin films*},
journal = {CHINESE PHYSICS B},
year = {2021},
volume = {30},
number = {6},
doi = {https://doi.org/10.1088/1674-1056/abee6c}
}
|
| Esashi, Y., Tanksalvala, M., Zhang, Z., Jenkins, N.W., Kapteyn, H.C. and Murnane, M.M. Influence of surface and interface roughness on X-ray and extreme ultraviolet reflectance: A comparative numerical study OSA CONTINUUM 4, 5, pp. 1497-1518 (2021) |
| Abstract: The influence of surface and interface roughness on X-ray and extreme
ultraviolet (EUV) reflectometry is becoming increasingly important as layer thicknesses decrease to a few nanometers in next-generation nanodevices and multilayer optics. Here we simulate two different approaches for numerically modeling roughness, the Nevot-Croce factor and the graded-interface method, in the Parratt formalism of calculating the complex reflectance of multilayer systems. The simulations were carried out at wavelengths relevant to widely used metrology techniques, including 0.154 nm for X-ray reflectometry and 13.5 nm for EUV lithography. A large discrepancy is observed between the two approaches in several situations: when the roughness is large with respect to the wavelength, for interfaces with large changes in refractive index across the boundary, as well as around reflectance peaks due to interference effects. Caution is thus required when using either approach to model roughness in these situations. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement |
BibTeX:
@article{WOS:000651530600001,
author = {Esashi, Yuka and Tanksalvala, Michael and Zhang, Zhe and Jenkins, Nicholas W. and Kapteyn, Henry C. and Murnane, Margaret M.},
title = {Influence of surface and interface roughness on X-ray and extreme ultraviolet reflectance: A comparative numerical study},
journal = {OSA CONTINUUM},
year = {2021},
volume = {4},
number = {5},
pages = {1497-1518},
doi = {https://doi.org/10.1364/OSAC.422924}
}
|
| Lofstrand, A., Jam, R.J., Mothander, K., Nylander, T., Mumtaz, M., Vorobiev, A., Chen, W.-C., Borsali, R. and Maximov, I. Poly(styrene)-block-Maltoheptaose Films for Sub-10 nm Pattern Transfer: Implications for Transistor Fabrication ACS APPLIED NANO MATERIALS 4, 5, pp. 5141-5151 (2021)early access (MAY 2021) |
| Abstract: Sequential infiltration synthesis (SIS) into
poly(styrene)-block-maltoheptaose (PS-b-MH) block copolymer using vapors of trimethyl aluminum and water was used to prepare nanostructured surface layers. Prior to the infiltration, the PS-b-MH had been self-assembled into 12 nm pattern periodicity. Scanning electron microscopy indicated that horizontal aluminalike cylinders of 4.9 nm diameter were formed after eight infiltration cycles, while vertical cylinders were 1.3 nm larger. Using homopolymer hydroxyl-terminated poly(styrene) (PS-OH) and MH films, specular neutron reflectometry revealed a preferential reaction of precursors in the MH compared to PS-OH. The infiltration depth into the maltoheptaose homopolymer film was found to be 2.0 nm after the first couple of cycles. It reached 2.5 nm after eight infiltration cycles, and the alumina incorporation within this infiltrated layer corresponded to 23 vol % Al2O3. The alumina-like material, resulting from PS-b-MH infiltration, was used as an etch mask to transfer the sub-10 nm pattern into the underlying silicon substrate, to an aspect ratio of approximately 2:1. These results demonstrate the potential of exploiting SIS into carbohydrate-based polymers for nanofabrication and high pattern density applications, such as transistor devices. |
BibTeX:
@article{WOS:000657373800088,
author = {Lofstrand, Anette and Jam, Reza Jafari and Mothander, Karolina and Nylander, Tommy and Mumtaz, Muhammad and Vorobiev, Alexei and Chen, Wen-Chang and Borsali, Redouane and Maximov, Ivan},
title = {Poly(styrene)-block-Maltoheptaose Films for Sub-10 nm Pattern Transfer: Implications for Transistor Fabrication},
journal = {ACS APPLIED NANO MATERIALS},
year = {2021},
volume = {4},
number = {5},
pages = {5141-5151},
doi = {https://doi.org/10.1021/acsanm.1c00582}
}
|
| Ksoll, P., Mandal, R., Meyer, C., Schuler, L., Roddatis, V. and Moshnyaga, V. Emergent double perovskite phase at LaMnO3/LaNiO3 interfaces: Coupled charge transfer and structural reconstruction PHYSICAL REVIEW B 103, 19 (2021) |
| Abstract: We report [( LaNiO3)(n)/(LaMnO3)(n)] M/SrTiO3(111) superlattices [n
= 20, 10, 5, 2, and 1 unit cells (u.c.)] as ``precursor'' heterostructures for a double perovskite La2NiMnO6. A charge transfer at the LaNiO3/LaMnO3 interfaces and formation of the emergent La2NiMnO6 phase with Ni2+ and Mn4+ oxidation states was evidenced by in situ optical ellipsometry and supported by magnetic and Raman measurements. The 10/10 and 5/5 superlattices revealed a complex magnetic behavior with two ferromagnetic phase transitions with TC-low = 170K and TC-high similar to 250-280K, originating from the ferromagnetic LaMnO3 and the emergent interfacial La2NiMnO6 phase, respectively. With decreasing thickness of individual layers, the magnetism of 2/2 and 1/1 superlattices transforms into that of the ordered double perovskite La2NiMnO6. Furthermore, a structural reconstruction into a monoclinic (P-12) structure of the ordered La2NiMnO6 at the interface, evidenced by Raman spectroscopy, goes ahead with the charge transfer and magnetic La2NiMnO6 behavior. |
BibTeX:
@article{WOS:000655877500003,
author = {Ksoll, P. and Mandal, R. and Meyer, C. and Schuler, L. and Roddatis, V and Moshnyaga, V},
title = {Emergent double perovskite phase at LaMnO3/LaNiO3 interfaces: Coupled charge transfer and structural reconstruction},
journal = {PHYSICAL REVIEW B},
year = {2021},
volume = {103},
number = {19},
doi = {https://doi.org/10.1103/PhysRevB.103.195120}
}
|
| Armstrong, A.J., McCoy, T.M., Welbourn, R.J.L., Barker, R., Rawle, J.L., Cattoz, B., Dowding, P.J. and Routh, A.F. Towards a neutron and X-ray reflectometry environment for the study of solid-liquid interfaces under shear SCIENTIFIC REPORTS 11, 1 (2021) |
| Abstract: A novel neutron and X-ray reflectometry sample environment is presented
for the study of surface-active molecules at solid-liquid interfaces under shear. Neutron reflectometry was successfully used to characterise the iron oxide-dodecane interface at a shear rate of 7.0x102s-1 using a combination of conventional reflectometry theory coupled with the summation of reflected intensities to describe reflectivity from thicker films. Additionally, the structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide-dodecane interface at a shear rate of 7.0x102s-1 was studied. It was found that GMO forms a surface layer that appears unaltered by the effect of shear, where the thickness of the GMO layer was found to be 24.3-10.2+9.9 angstrom under direct shear at 7.0x102s-1 and 25.8-5.2+4.4 angstrom when not directly under shear. Finally, a model to analyse X-ray reflectometry data collected with the sample environment is also described and applied to data collected at 3.0x103s-1. |
BibTeX:
@article{WOS:000656988100021,
author = {Armstrong, Alexander J. and McCoy, Thomas M. and Welbourn, Rebecca J. L. and Barker, Robert and Rawle, Jonathan L. and Cattoz, Beatrice and Dowding, Peter J. and Routh, Alexander F.},
title = {Towards a neutron and X-ray reflectometry environment for the study of solid-liquid interfaces under shear},
journal = {SCIENTIFIC REPORTS},
year = {2021},
volume = {11},
number = {1},
doi = {https://doi.org/10.1038/s41598-021-89189-1}
}
|
| Ojha, S.K., Hazra, S., Mandal, P., Patel, R.K., Nigam, S., Kumar, S. and Middey, S. Electron Trapping and Detrapping in an Oxide Two-Dimensional Electron Gas: The Role of Ferroelastic Twin Walls PHYSICAL REVIEW APPLIED 15, 5 (2021) |
| Abstract: The choice of electrostatic gating over the conventional chemical doping
for phase engineering of quantum materials is attributed to the fact that the former can reversibly tune the carrier density without affecting the system?s level of disorder. However, this proposition seems to break down in field-effect transistors involving SrTiO3 (STO)-based two-dimensional electron gases. Such peculiar behavior is associated with electron trapping under an external electric field. However, the microscopic nature of the trapping centers remains an open question. In this paper, we investigate electric-field-induced chargetrapping and charge-detrapping phenomena at the conducting interface between the band insulators ? -Al2O3 and STO. Our transport measurements reveal that the charge trapping under a positive back-gate voltage (Vg) above the tetragonal-to-cubic structural transition temperature (Tc) of STO has a contribution from electric-field-assisted thermal escape of electrons from the quantum well, and from clustering of oxygen vacancies as well. We observe an additional source of trapping below Tc, which arises from the trapping of free carriers at ferroelastic twin walls in the STO. Application of a negative Vg results in charge detrapping, which vanishes above Tc. This feature demonstrates the crucial role of structural domain walls in the electrical transport properties of STO-based heterostructures. The number of charges trapped (detrapped) at (from) a twin wall is controlled by the net polarity of the wall and is completely reversible with a sweep of Vg. |
BibTeX:
@article{WOS:000656836400003,
author = {Ojha, Shashank Kumar and Hazra, Sankalpa and Mandal, Prithwijit and Patel, Ranjan Kumar and Nigam, Shivam and Kumar, Siddharth and Middey, S.},
title = {Electron Trapping and Detrapping in an Oxide Two-Dimensional Electron Gas: The Role of Ferroelastic Twin Walls},
journal = {PHYSICAL REVIEW APPLIED},
year = {2021},
volume = {15},
number = {5},
doi = {https://doi.org/10.1103/PhysRevApplied.15.054008}
}
|
| Dong, J., Gerlach, D., Koutsogiannis, P., Rudolf, P. and Portale, G. Boosting the Thermoelectric Properties of PEDOT:PSS via Low-Impact Deposition of Tin Oxide Nanoparticles ADVANCED ELECTRONIC MATERIALS 7, 5 (2021)early access (MAY 2021) |
| Abstract: Poly(3,4-ethylenedioxy thiophene):poly(styrenesulfonate) (PEDOT:PSS)
exhibits valuable characteristics concerning stability, green-processing, flexibility, high electrical conductivity, and ease of property modulation, qualifying it as one of the most promising p-type organic conductors for thermoelectric (TE) applications. While blending with inorganic counterparts is considered a good strategy to further improve polymeric TE properties, only a few attempts succeed so far due to inhomogeneous embedding and the non-ideal organic-inorganic contact. Here a new strategy to include nanoparticles (NPs) without any ligand termination inside PEDOT:PSS thin films is proposed. Spark discharge-generated tin oxide NPs (SnOx-NPs) are ``gently'' and homogenously deposited through low-energy diffusion mode. Strong interaction between naked SnOx-NPs and PSS chains occurs in the topmost layer, causing a structural reorganization towards an improved PEDOT chains crystalline packing at the bottom, providing a positive contribution to the electrical conductivity. Meanwhile, dedoping and energy filtering effect introduced by the SnOx-NPs cause dramatic Seebeck coefficient enhancement. The optimized power factor of 116 mu Wm(-1) K-2 achieved is more than six times higher than the value found for the film without NPs. This easy and efficient strategy promises well for future mass production of flexible TE devices and the mechanism revealed may inspire future research on TEs and flexible electronics. |
BibTeX:
@article{WOS:000646543000001,
author = {Dong, Jingjin and Gerlach, Dominic and Koutsogiannis, Panagiotis and Rudolf, Petra and Portale, Giuseppe},
title = {Boosting the Thermoelectric Properties of PEDOT:PSS via Low-Impact Deposition of Tin Oxide Nanoparticles},
journal = {ADVANCED ELECTRONIC MATERIALS},
year = {2021},
volume = {7},
number = {5},
doi = {https://doi.org/10.1002/aelm.202001284}
}
|
| Volk, A.A., Kim, J.-S., Jamir, J., Dickey, E.C. and Parsons, G.N. Oxidative molecular layer deposition of PEDOT using volatile antimony(V) chloride oxidant JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 39, 3 (2021) |
| Abstract: Molecular layer deposition and chemical vapor deposition are emerging
and promising techniques for the incorporation of high-performance conductive polymers into high surface area devices, such as sintered tantalum anodes for electrolytic capacitors. Until recently, vapor-phase synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) has relied on solid reactants which require relatively high temperatures and complex dosing schemes for sequential layer-by-layer processes. This work introduces a facile and high-performing layer-by-layer oxidative molecular layer deposition (oMLD) scheme using the volatile liquid oxidant antimony(V) chloride (SbCl5) to deposit PEDOT thin films. Effects of reactor parameters on PEDOT film characteristics are described, and the necessary foundation for future studies aiming to understand the nucleation and growth of layer-by-layer oMLD PEDOT is detailed. |
BibTeX:
@article{WOS:000643734900001,
author = {Volk, Amanda A. and Kim, Jung-Sik and Jamir, Jovenal and Dickey, Elizabeth C. and Parsons, Gregory N.},
title = {Oxidative molecular layer deposition of PEDOT using volatile antimony(V) chloride oxidant},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2021},
volume = {39},
number = {3},
doi = {https://doi.org/10.1116/6.0000791}
}
|
| Ishizaki, Y., Yamamoto, S., Miyashita, T. and Mitsuishi, M. dpH-Responsive Ultrathin Nanoporous SiO2 Films for Selective Ion Permeation LANGMUIR 37, 18, pp. 5627-5634 (2021)early access (APR 2021) |
| Abstract: Ultrathin nanoporous (NP) films are an emerging field for selective and
effective ion/molecular separation and electrochemical sensing applications. We describe selective ion permeation in surface-functionalized ultrathin NP SiO2 films (NP SiO2-NH2). The ultrathin NP SiO2 films with ca. 8 nm thickness were prepared from silsesquioxane-containing blend polymer Langmuir-Blodgett films (nanosheets) using the photo-oxidation method. The porous SiO2 surface was modified with a pH-responsive amine-containing silane coupling agent. Selective ion permeation was demonstrated under acidic pH conditions (pH <= 6) using two equally sized redox probes: negative (Fe(CN)(6)(3)(-/)(4-)) and positive (Ru(NH3)(6)(2+)(/)(3+)) ions. The current density for Fe(CN)(6)(3-/4- )decreased as the pH value increased to pH = 6, whereas it increased for Ru(NH3)(6)(2+/3+). Control measurements revealed that the probes can penetrate the pores of nonfunctionalized SiO2 films irrespective of pH values, indicating that both the size and the surface charge response contributed to selective ion permeation. Results obtained from this study pave the way for new applications in molecular separation and sensing applications based on ultrathin nanoporous films (<10 nm) and tailored surfaces. |
BibTeX:
@article{WOS:000651528200020,
author = {Ishizaki, Yuya and Yamamoto, Shunsuke and Miyashita, Tokuji and Mitsuishi, Masaya},
title = {dpH-Responsive Ultrathin Nanoporous SiO2 Films for Selective Ion Permeation},
journal = {LANGMUIR},
year = {2021},
volume = {37},
number = {18},
pages = {5627-5634},
doi = {https://doi.org/10.1021/acs.langmuir.1c00486}
}
|
| Mao, J., Yao, Z.H., Zhang, X., Yun, J., Chang, M., Zuo, Y. and Xi, L. Crystallographic direction related spin current transmission in MgO(001)/Fe0.79Si0.21(001)/Pt(111) epitaxial bilayers PHYSICAL REVIEW B 103, 13 (2021) |
| Abstract: Spin-pumping and spin-orbit torque efficiencies in ferromagnetic/heavy
metal bilayers, which usually consist of the polycrystalline grains, are related to the spin current transmission from ferromagnets to heavy metals and vice versa, respectively. In this work, epitaxial Fe0.79Si0.21(001)/Pt(111) films were fabricated to investigate the spin-pumping efficiency and spin-orbit torque efficiency by ferromagnetic resonance and harmonic Hall resistance measurement techniques, respectively. Ferromagnetic resonance results show that the incremental magnetic damping constants in epitaxial Fe0.79Si0.21(001)/Pt(111), compared with those of the epitaxial Fe0.79Si0.21(001)/AlOx reference sample, depend on whether the external magnetic field is applied along the in-plane easy or hard axes of Fe0.79Si0.21. The Pt thickness-dependent anisotropic damping constant was ascribed to the anisotropic spin current absorption in epitaxial Pt(111) layer. When electric currents were applied along the easy and hard axes of Fe0.79Si0.21 in epitaxial Fe0.79Si0.21(001)/Pt(111) bilayers, a large difference between spin-orbit torques generated from Pt(111) was observed by a harmonic Hall resistance measurement method. Both of the results suggest that spin current transmission efficiency is related to the anisotropic spin Hall effect of epitaxial Pt(111) layer due to the different spin-orbit interaction energies along the different crystallographic directions of Pt. |
BibTeX:
@article{WOS:000646309900002,
author = {Mao, Jian and Yao, Zhi Heng and Zhang, Xu and Yun, Jijun and Chang, Meixia and Zuo, Yalu and Xi, Li},
title = {Crystallographic direction related spin current transmission in MgO(001)/Fe0.79Si0.21(001)/Pt(111) epitaxial bilayers},
journal = {PHYSICAL REVIEW B},
year = {2021},
volume = {103},
number = {13},
doi = {https://doi.org/10.1103/PhysRevB.103.134432}
}
|
| Schenk, T., Bencan, A., Drazic, G., Condurache, O., Valle, N., El Adib, B., Aruchamy, N., Granzow, T., Defay, E. and Glinsek, S. Enhancement of ferroelectricity and orientation in solution-derived hafnia thin films through heterogeneous grain nucleation APPLIED PHYSICS LETTERS 118, 16 (2021) |
| Abstract: In this work, we demonstrate an approach for improving ferroelectric
properties of La:HfO2 thin films by shifting the grain growth regime toward heterogeneous nucleation. A dilute 0.083 M instead of a 0.25 M solution together with an annealing step after every spin-coating cycle film gives rise to a significant improvement of ferroelectric properties. While a remanent polarization of 7 mu C/cm(2) was found for randomly oriented conventional films, the value of 15 mu C/cm(2) for the dilute solution is a result of a mixed 111 and 002 preferential orientation. A more than 50% improved breakdown voltage stems from a global density improvement from 8.0 to 8.4g/cm(3) as obtained from x-ray reflectivity (XRR). We also find superstructure peaks in XRR hinting on periodic alternations of the local density throughout the film thickness. Scanning transmission electron microscopy and secondary ion mass spectrometry confirm this periodicity. The sensitivity of XRR for this periodicity was leveraged to gain further insights in the origin of this superstructure with additional experiments. We conclude that both orientation and the superstructure are caused by a ``layered structure'' according to Schuler's microstructural zone model. However, our data also provide evidence for parallel chemical effects of cap formation in each stacked sub-layer. While this work shows a significant enhancement of ferroelectric properties, it also provides insights into further optimization potential of solution deposition of HfO2/ZrO2 thin films. Our XRR-based approach supplemented with suitable additional analysis can be of great value for the optimization of other solution-derived thin films beyond the material class studied here. |
BibTeX:
@article{WOS:000642214900001,
author = {Schenk, Tony and Bencan, Andreja and Drazic, Goran and Condurache, Oana and Valle, Nathalie and El Adib, Brahime and Aruchamy, Naveen and Granzow, Torsten and Defay, Emmanuel and Glinsek, Sebastjan},
title = {Enhancement of ferroelectricity and orientation in solution-derived hafnia thin films through heterogeneous grain nucleation},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {118},
number = {16},
doi = {https://doi.org/10.1063/5.0045966}
}
|
| Rao, R.R., Huang, B., Katayama, Y., Hwang, J., Kawaguchi, T., Lunger, J.R., Peng, J., Zhang, Y., Morinaga, A., Zhou, H., You, H. and Shao-Horn, Y. pH- and Cation-Dependent Water Oxidation on Rutile RuO2(110) JOURNAL OF PHYSICAL CHEMISTRY C 125, 15, pp. 8195-8207 (2021)early access (APR 2021) |
| Abstract: Noncovalent interactions at electrified interfaces are key to improving
activity for the oxygen evolution reaction (OER). Here, we showed that on RuO2(110) in alkaline solutions, OER activity is cation-dependent, being largest in 0.1 M KOH compared to LiOH and NaOH. Using crystal truncation rod analysis, -O is detected on the coordinatively unsaturated site at 1.5 V-RHE in 0.1 M KOH, suggesting that the rate-determining step is -O + OH- -> -OOH + e(-), which is different from that in acid involving the final deprotonation of -OOH. The ordering of interfacial water in base was found to decrease with increasing potential and independent of cations. Using surface-enhanced infrared spectroscopy, the density of isolated water molecules (zero H-bonds) was found to increase, and the density of icelike water molecules (four H-bonds) decreases from Li+ to K+ at OER potentials. The higher activity of more isolated interfacial OH - ions in the case of K+ and the lesser stabilization of -O intermediates by hydration water of K+ compared to Na+ and Li+ can result in higher OER activity for KOH. This work provides molecular details of the interface as a function of potential and electrolyte and enables the design of more active electrochemical interfaces. |
BibTeX:
@article{WOS:000644438400018,
author = {Rao, Reshma R. and Huang, Botao and Katayama, Yu and Hwang, Jonathan and Kawaguchi, Tomoya and Lunger, Jaclyn R. and Peng, Jiayu and Zhang, Yirui and Morinaga, Asuka and Zhou, Hua and You, Hoydoo and Shao-Horn, Yang},
title = {pH- and Cation-Dependent Water Oxidation on Rutile RuO2(110)},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2021},
volume = {125},
number = {15},
pages = {8195-8207},
doi = {https://doi.org/10.1021/acs.jpcc.1c00413}
}
|
| Rogers, M., Walton, A., Flokstra, M.G., Al Ma'Mari, F., Stewart, R., Lee, S.L., Prokscha, T., Caruana, A.J., Kinane, C.J., Langridge, S., Bradshaw, H., Moorsom, T., Ali, M., Burnell, G., Hickey, B.J. and Cespedes, O. Spin-singlet to triplet Cooper pair converter interface COMMUNICATIONS PHYSICS 4, 1 (2021) |
| Abstract: Magnetic molecules deposited on a metallic substrate constitute a method
to engineer the spin properties of the molecule and has potential application in low-power information storage devices. Here, the authors investigate a superconductor/molecule/normal metal heterostructure and demonstrate spin-ordering and proximity induced superconducting properties at the metallo-molecular interface. Combining magnetic and superconducting functionalities enables lower energy spin transfer and magnetic switching in quantum computing and information storage, owing to the dissipationless nature of quasi-particle mediated supercurrents. Here, we put forward a system where emergent spin-ordering and diffusion of Cooper pairs are achieved at a non-intrinsically magnetic nor superconducting metallo-molecular interface. Electron transport, magnetometry and low-energy muon spin rotation are used to probe time-reversal symmetry breaking in these structures. By comparing the Meissner expulsion in a system including a Cu/C-60 spin-converter interface to one without, we observe a paramagnetic contribution that can be explained due to the conversion of spin-singlet Cooper pair states into odd-frequency triplet states. These results demonstrate the potential of metallo-molecular interfaces to achieve singlet to triplet Cooper pair conversion, a capability not present in either metal or molecule separately that could be used in the generation and controlled diffusion of spin polarised dissipationless currents. |
BibTeX:
@article{WOS:000638138900001,
author = {Rogers, Matthew and Walton, Alistair and Flokstra, Machiel G. and Al Ma'Mari, Fatma and Stewart, Rhea and Lee, Stephen L. and Prokscha, Thomas and Caruana, Andrew J. and Kinane, Christian J. and Langridge, Sean and Bradshaw, Harry and Moorsom, Timothy and Ali, Mannan and Burnell, Gavin and Hickey, Bryan J. and Cespedes, Oscar},
title = {Spin-singlet to triplet Cooper pair converter interface},
journal = {COMMUNICATIONS PHYSICS},
year = {2021},
volume = {4},
number = {1},
doi = {https://doi.org/10.1038/s42005-021-00567-7}
}
|
| Reisz, B., Empting, E., Zwadlo, M., Hodas, M., Duva, G., Belova, V., Zeiser, C., Hagenlocher, J., Maiti, S., Hinderhofer, A., Gerlach, A., Oettel, M. and Schreiber, F. Thin film growth of phase-separating phthalocyanine-fullerene blends: A combined experimental and computational study PHYSICAL REVIEW MATERIALS 5, 4 (2021) |
| Abstract: Blended organic thin films have been studied during the last decades due
to their applicability in organic solar cells. Although their optical and electronic features have been examined intensively, there is still a lack of detailed knowledge about their growth processes and resulting morphologies, which play a key role in the efficiency of optoelectronic devices such as organic solar cells. In this study, pure and blended thin films of copper phthalocyanine (CuPc) and the Buckminster fullerene (C-60) were grown by vacuum deposition onto a native silicon oxide substrate at two different substrate temperatures, 310 and 400 K. The evolution of roughness was followed by in situ real-time x-ray reflectivity. Crystal orientation, island densities, and morphology were examined after the growth by x-ray diffraction experiments and microscopy techniques. The formation of a smooth wetting layer followed by rapid roughening was found in pure CuPc thin films, whereas C-60 shows a fast formation of distinct islands at a very early stage of growth. The growth of needlelike CuPc crystals losing their alignment with the substrate was identified in co-deposited thin films. Furthermore, the data demonstrate that structural features become larger and more pronounced and that the island density decreases by a factor of four when going from 310 to 400 K. Finally, the key parameters roughness and island density were well reproduced on a smaller scale by kinetic Monte Carlo simulations of a generic, binary lattice model with simple nearest-neighbor interaction energies. A weak molecule-substrate interaction caused a fast island formation and weak interaction between molecules of different species was able to reproduce the observed phase separation. The introduction of different same-species and cross-species Ehrlich-Schwoebel barriers for interlayer hopping was necessary to reproduce the roughness evolution in the blend and showed the growth of CuPc crystals on top of the thin film in agreement with the experiment. |
BibTeX:
@article{WOS:000655931600006,
author = {Reisz, Berthold and Empting, Eelco and Zwadlo, Matthias and Hodas, Martin and Duva, Giuliano and Belova, Valentina and Zeiser, Clemens and Hagenlocher, Jan and Maiti, Santanu and Hinderhofer, Alexander and Gerlach, Alexander and Oettel, Martin and Schreiber, Frank},
title = {Thin film growth of phase-separating phthalocyanine-fullerene blends: A combined experimental and computational study},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2021},
volume = {5},
number = {4},
doi = {https://doi.org/10.1103/PhysRevMaterials.5.045601}
}
|
| Kolesnikov, A.G., Stebliy, M.E., Davydenko V, A., Kozlov, A.G., Osmushko, I.S., Korochentsev, V.V., Ognev V, A., Gerasimenko V, A., Sadovnikov V, A., Gubanov, V.A., Nikitov, S.A., Wang, X., Wan, C.H., Fang, C., Zhao, M., Han, X.F. and Samardak, A. Magnetic properties and the interfacial Dzyaloshinskii-Moriya interaction in exchange biased Pt/Co/NixOy films APPLIED SURFACE SCIENCE 543 (2021) |
| Abstract: We show that a trilayer magnetic structure, consisting of a heavy metal
(Platinum) as a buffer, an ultrathin ferromagnet (Cobalt) as a functional layer, and an antiferromagnetic insulator (Nickel oxide, NixOy) as a capping, is a host of intriguing physical phenomena desirable for spintronics. X-ray photoelectron spectroscopy revealed changes in the ratio of NixOy phases with different stoichiometry. Due to strong spin-orbit coupling, the Pt layer induces perpendicular magnetic anisotropy in Co, breaks its structural inversion symmetry, and causes an additive effect of Pt/Co and Co/NixOy interfaces to the effective interfacial Dzyaloshinskii-Moriya interaction (D-eff). Manipulation the magnetic anisotropy can be realized by the ferromagnetic layer thickness variation and modification of the Co/NixOy interface. The NixOy capping layer induces the exchange bias in Co, which effective field vertical bar Beb vertical bar can be controlled in the range from 0 to 24 mT. The magnitude and direction of B-eb does not affect D-eff. The increase of Ar pressure leads to structural transformation of the Co/NixOy interface and, consequently, to decrease of the surface Dzyaloshinskii-Moriya interaction (D-s), the source of which is the NiO phase. We demonstrate that the studied Pt/Co/NixOy system has a number of functional properties useful for future logic and memory applications. |
BibTeX:
@article{WOS:000613941800008,
author = {Kolesnikov, A. G. and Stebliy, M. E. and Davydenko, V, A. and Kozlov, A. G. and Osmushko, I. S. and Korochentsev, V. V. and Ognev, V, A. and Gerasimenko, V, A. and Sadovnikov, V, A. and Gubanov, V. A. and Nikitov, S. A. and Wang, X. and Wan, C. H. and Fang, C. and Zhao, M. and Han, X. F. and Samardak, Alexander},
title = {Magnetic properties and the interfacial Dzyaloshinskii-Moriya interaction in exchange biased Pt/Co/NixOy films},
journal = {APPLIED SURFACE SCIENCE},
year = {2021},
volume = {543},
doi = {https://doi.org/10.1016/j.apsusc.2020.148720}
}
|
| Bai, Q., Mao, J., Yun, J., Zhai, Y., Chang, M., Zhang, X., Zhang, J., Zuo, Y. and Xi, L. In-plane crystallographic orientations related spin-orbit torque in epitaxial Pt(111)/Co/Ta heterostructures APPLIED PHYSICS LETTERS 118, 13 (2021) |
| Abstract: Current induced spin-orbit torque (SOT) in heavy metals with strong
spin-orbit coupling strength has attracted considerable attention due to its potential applications in spintronic technology. Pt, as one of the mostly used heavy metals in SOT-based spintronic devices, shows large spin Hall angle (hSH) with its single phase and alloy counterparts. In this work, the in-plane crystallographic orientations related hSH of epitaxial Pt(111) layer is reported in MgO(111)/Pt(111)/Co/Ta heterostructures with strong perpendicular magnetic anisotropy. The hSH shows a quite large difference with values, respectively, around 0.083 and 0.057 when the current applied along the 1/2 110 similar to and 1/2 112 similar to crystallographic directions of Pt(111) by the damping-like SOT efficiency using the harmonic Hall voltage measurement technique. The critical switching current densities also show large difference between these two orthogonal crystallographic orientations with the trend of that the larger SOT efficiency leads to the smaller critical switching current density. It independently confirms the generation of different dampinglike SOT efficiency when current along 1/2 110 similar to and 1/2 112 similar to directions of Pt(111). Moreover, a perpendicularly magnetized Pt/Co/Ta reference heterostructures with Pt having polycrystalline phase shows tiny variation of damping-like SOT efficiency in in-plane two orthogonal directions, which also indirectly indicates the crystallographic orientations related hSH in epitaxial Pt(111) layers. This study indicates that the hSH of epitaxial Pt is a crystallographic orientations related parameter. |
BibTeX:
@article{WOS:000636342600003,
author = {Bai, Qiaoning and Mao, Jian and Yun, Jijun and Zhai, Yongbo and Chang, Meixia and Zhang, Xu and Zhang, Jianrong and Zuo, Yalu and Xi, Li},
title = {In-plane crystallographic orientations related spin-orbit torque in epitaxial Pt(111)/Co/Ta heterostructures},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {118},
number = {13},
doi = {https://doi.org/10.1063/5.0024153}
}
|
| Bondaz, L., Cousin, F., Muller, F., Pantoustier, N., Perrin, P., Luchini, A., Goldmann, M. and Fontaine, P. pH-sensitive behavior of the PS-b-PDMAEMA copolymer at the air - water interface POLYMER 221 (2021)early access (MAR 2021) |
| Abstract: We investigated the behavior of a pH-responsive
polystyrene-b-poly(2-dimethylamino)ethyl methacrylate (PS-b-PDMAEMA) diblock copolymer at the air/water interface. We synthetized different copolymers with a small hydrophobic PS block of constant length attached to polyelectrolyte PDMAEMA blocks of various lengths. We demonstrate that a Langmuir monolayer is formed with the hydrophobic collapsed PS block anchoring the hydrophilic polyelectrolyte at the interface. By combining macroscopic surface pressure measurements and specular neutron reflectivity, we studied the monolayers as a function of surface density sigma and pH of the subphase. At pH = 2, the PDMAEMA is fully charged and the system at high s behaves as a polyelectrolyte brush with chains protruding in water with a gaussian profile. At pH = 10 where the PDMAEMA is neutral, the system exhibits a phase transition between the pancake configuration to the brush configuration, with a threshold that depends on the PDMAEMA chain length, in agreement with theoretical predicted scaling laws. |
BibTeX:
@article{WOS:000640575200003,
author = {Bondaz, Louis and Cousin, Fabrice and Muller, Francois and Pantoustier, Nadege and Perrin, Patrick and Luchini, Alessandra and Goldmann, Michel and Fontaine, Philippe},
title = {pH-sensitive behavior of the PS-b-PDMAEMA copolymer at the air - water interface},
journal = {POLYMER},
year = {2021},
volume = {221},
doi = {https://doi.org/10.1016/j.polymer.2021.123619}
}
|
| Gilroy, E.R., Wu, M.-H., Gradhand, M., Springell, R. and Bell, C. Magnetic anisotropy in Fe/U and Ni/U bilayers PHYSICAL REVIEW B 103, 10 (2021) |
| Abstract: Magnetometry measurements of Fe/U and Ni/U bilayer systems reveal a
nonmonotonic dependence of the magnetic anisotropy for U thicknesses in the range of 0-8 nm with the Fe/U bilayers showing a more prominent effect as compared to Ni/U. The stronger response for Fe/U is ascribed to the stronger 3d-5f hybridization of Fe and U. This nonmonotonic behavior is thought to arise from quantum well states in the uranium overlayers. Estimating an oscillation period from the nonmonotonic data, and comparing it to Density Functional Theory calculations, we find that wave vector matches to the experimental data can be made to regions of high spectral density in (010) and (100) cuts of the electronic structure of a-U, consistent with the measured texture in the films. Unexpectedly, there are also indications of perpendicular magnetic anisotropy in a subset of Fe/U samples at relatively large U thickness. |
BibTeX:
@article{WOS:000646540600002,
author = {Gilroy, E. R. and Wu, M-H and Gradhand, M. and Springell, R. and Bell, C.},
title = {Magnetic anisotropy in Fe/U and Ni/U bilayers},
journal = {PHYSICAL REVIEW B},
year = {2021},
volume = {103},
number = {10},
doi = {https://doi.org/10.1103/PhysRevB.103.104426}
}
|
| Bannenberg, L., Schreuders, H. and Dam, B. Tantalum-Palladium: Hysteresis-Free Optical Hydrogen Sensor Over 7 Orders of Magnitude in Pressure with Sub-Second Response ADVANCED FUNCTIONAL MATERIALS 31, 16 (2021)early access (MAR 2021) |
| Abstract: Hydrogen detection in a reliable, fast, and cost-effective manner is a
prerequisite for the large-scale implementation of hydrogen in a green economy. Thin film Ta1-yPdy is presented as an effective optical sensing material with extremely wide sensing ranges covering at least 7 orders of magnitude in hydrogen pressure. Nanoconfinement of the Ta1-yPdy layer suppresses the first-order phase transitions present in bulk and ensures a sensing response free of any hysteresis. Unlike other sensing materials, Ta1-yPdy features the special property that the sensing range can be easily tuned by varying the Pd concentration without a reduction of the sensitivity of the sensing material. Combined with a suitable capping layer, sub-second response times can be achieved even at room temperature, faster than any other known thin-film hydrogen sensor. |
BibTeX:
@article{WOS:000623497200001,
author = {Bannenberg, Lars and Schreuders, Herman and Dam, Bernard},
title = {Tantalum-Palladium: Hysteresis-Free Optical Hydrogen Sensor Over 7 Orders of Magnitude in Pressure with Sub-Second Response},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2021},
volume = {31},
number = {16},
doi = {https://doi.org/10.1002/adfm.202010483}
}
|
| Tayal, A., Amir, S.M., Puetter, S., Mattauch, S., Gupta, M. and Seema Structural, electronic, and magnetic properties of Co4N thin films deposited using HiPIMS JOURNAL OF ALLOYS AND COMPOUNDS 863 (2021)early access (FEB 2021) |
| Abstract: We studied the growth behavior, structural, electronic, and magnetic
properties of cobalt nitride (Co-N) thin films deposited using direct current (dc) and high power impulse magnetron sputtering (HiPIMS) processes. The N-2 partial gas flow (RN2) was varied in close intervals to achieve the optimum conditions for the growth of the tetra cobalt nitride (Co4N) phase. We found that Co-N films grown using the HiPIMS process adopt (111) orientation as compared to the growth taking place along the (100) direction in the dcMS process. It was observed that HiPIMS grown Co-N films were superior in terms of crystallite size and uniform surface morphology. The local structure of films was investigated using x-ray absorption fine structure (XAFS) measurements. We found that the high energy of adatoms in the HiPIMS technique assisted in the more excellent stabilization of fcc-Co and the novel Co4N phase relative to the dcMS process. Magnetic properties of Co-N thin films were studied using magneto-optical Kerr effect, vibrating sample magnetometry and polarized neutron reflectivity. It was found that though the saturation magnetization remains almost similar in films grown by dcMS or HiPIMS processes, they differ in terms of their magnetic anisotropy. Such variation can be understood in terms of differences in the growth mechanisms in dcMS and HiPIMS processes affecting the resulting Co4N phase's local structure. (C) 2020 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000621714200004,
author = {Tayal, Akhil and Amir, S. M. and Puetter, Sabine and Mattauch, S. and Gupta, Mukul and Seema},
title = {Structural, electronic, and magnetic properties of Co4N thin films deposited using HiPIMS},
journal = {JOURNAL OF ALLOYS AND COMPOUNDS},
year = {2021},
volume = {863},
doi = {https://doi.org/10.1016/j.jallcom.2020.158052}
}
|
| Sahoo, A.K., Chelvane, J.A. and Mohanty, J. Effect of Ti underlayer thickness on the magnetic anisotropy of TbFe thin films JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS 32, 6, pp. 7567-7573 (2021)early access (FEB 2021) |
| Abstract: In this study, we address the impact of Ti underlayer thickness (UL:
0-40 nm) on the structural, magnetic, and microscopic properties of TbFe thin films. The structural analysis confirmed the intermixing at interfaces of the Ti and TbFe layer with the increment of UL thicknesses. Out-of-plane (OOP) coercivity (H-c), and saturation field (H-s) gradually increased with an increase in UL thickness. For UL = 10 nm, the domain contrast and OOP stray field strength were enhanced, which may be due to the extent of d-d hybridization dominated over the influence of interfacial roughness. While for UL = 20, and 40 nm, the extent of interfacial roughness dominated the hybridization effects. In the case of UL: 20 nm, H-c increased by nearly 6 times more than the bare TbFe system. We observed a state with high OOP Hc combined with nearly zero OOP stray fields that are found to coexist in the sample. The magnetization reversal studies on a large area reveal domain nucleation followed by domain wall motion in all the films. The idea of tuning magnetic properties by varying thicknesses of Ti UL may be useful in spintronics applications. |
BibTeX:
@article{WOS:000620440500010,
author = {Sahoo, Ajit Kumar and Chelvane, J. Arout and Mohanty, J.},
title = {Effect of Ti underlayer thickness on the magnetic anisotropy of TbFe thin films},
journal = {JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS},
year = {2021},
volume = {32},
number = {6},
pages = {7567-7573},
doi = {https://doi.org/10.1007/s10854-021-05471-y}
}
|
| Wang, J., Shin, Y., Paudel, J.R., Grassi, J.D., Sah, R.K., Yang, W., Karapetrova, E., Zaidan, A., Strocov, V.N., Klewe, C., Shafer, P., Gray, A.X., Rondinelli, J.M. and May, S.J. Strain-Induced Anion-Site Occupancy in Perovskite Oxyfluoride Films CHEMISTRY OF MATERIALS 33, 5, pp. 1811-1820 (2021)early access (FEB 2021) |
| Abstract: Anion ordering is a promising route to engineer physical properties in
functional heteroanionic materials. A central challenge in the study of anion-ordered compounds lies in developing robust synthetic strategies to control anion occupation and in understanding the resultant implications for electronic structure. Here, we show that epitaxial strain induces preferential occupation of F and O on the anion-sites in perovskite oxyfluoride SrMnO2.5-delta F gamma films grown on different substrates. Under compressive strain, F tends to occupy the apical-like sites, which was revealed by F and O K-edge linearly polarized X-ray absorption spectroscopy and density functional theory calculations, resulting in an enhanced c-axis expansion. Under tensile strain, F tends to occupy the equatorial-like sites, enabling the longer Mn-F bonds to lie within the plane. The oxyfluoride films exhibit a significant orbital polarization of the 3d electrons, distinct F-site dependence to their valence band density of states, and an enhanced resistivity when F occupies the apical-like anion-site compared to the equatorial-like site. By demonstrating a general strategy for inducing preferential anion-site occupancy in oxyfluoride perovskites, this work lays the foundation for future materials design and synthesis efforts that leverage this greater degree of atomic control to realize new polar or quasi-two-dimensional materials. |
BibTeX:
@article{WOS:000629032600027,
author = {Wang, Jiayi and Shin, Yongjin and Paudel, Jay R. and Grassi, Joseph D. and Sah, Raj K. and Yang, Weibing and Karapetrova, Evguenia and Zaidan, Abdulhadi and Strocov, Vladimir N. and Klewe, Christoph and Shafer, Padraic and Gray, Alexander X. and Rondinelli, James M. and May, Steven J.},
title = {Strain-Induced Anion-Site Occupancy in Perovskite Oxyfluoride Films},
journal = {CHEMISTRY OF MATERIALS},
year = {2021},
volume = {33},
number = {5},
pages = {1811-1820},
doi = {https://doi.org/10.1021/acs.chemmater.0c04793}
}
|
| Konefal, M., Cernoch, P., Patsula, V., Pavlova, E., Dybal, J., Zaleski, K. and Zhigunov, A. Enhanced Ordering of Block Copolymer Thin Films upon Addition of Magnetic Nanoparticles ACS APPLIED MATERIALS & INTERFACES 13, 7, pp. 9195-9205 (2021)early access (FEB 2021) |
| Abstract: The influence of magnetite nanoparticles coated with poly(acrylic acid)
(Fe3O4@PAA NPs) on the organization of block copolymer thin films via a self-assembly process was investigated. Polystyrene-b-poly(4-vinylpyridine) films were obtained by the dipcoating method and thoroughly examined by X-ray reflectivity, transmission electron microscopy, atomic force microscopy, and grazing incidence small-angle scattering. Magnetic properties of the films were probed via superconducting quantum interference device (SQUID) magnetometry. It was demonstrated that due to the hydrogen bonding between P4VP and PAA, the Fe3O4@PAA NPs segregate selectively inside P4VP domains, enhancing the microphase separation process. This in turn, together with employing carefully optimized dip-coating parameters, results in the formation of hybrid thin films with highly ordered nanostructures. The addition of Fe3O4@PAA nanoparticles does not change the average interdomain spacing in the film lateral nanostructure. Moreover, it was shown that the nanoparticles can easily be removed to obtain well-ordered nanoporous templates. |
BibTeX:
@article{WOS:000623228500131,
author = {Konefal, Magdalena and Cernoch, Peter and Patsula, Vitalii and Pavlova, Ewa and Dybal, Jiri and Zaleski, Karol and Zhigunov, Alexander},
title = {Enhanced Ordering of Block Copolymer Thin Films upon Addition of Magnetic Nanoparticles},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2021},
volume = {13},
number = {7},
pages = {9195-9205},
doi = {https://doi.org/10.1021/acsami.0c21549}
}
|
| Dawidek, R.W., Hayward, T.J., Vidamour, I.T., Broomhall, T.J., Venkat, G., Al Mamoori, M., Mullen, A., Kyle, S.J., Fry, P.W., Steinke, N.-J., Cooper, J.F.K., Maccherozzi, F., Dhesi, S.S., Aballe, L., Foerster, M., Prat, J., Vasilaki, E., Ellis, M.O.A. and Allwood, D.A. Dynamically-Driven Emergence in a Nanomagnetic System ADVANCED FUNCTIONAL MATERIALS 31, 15 (2021)early access (FEB 2021) |
| Abstract: Emergent behaviors occur when simple interactions between a system's
constituent elements produce properties that the individual elements do not exhibit in isolation. This article reports tunable emergent behaviors observed in domain wall (DW) populations of arrays of interconnected magnetic ring-shaped nanowires under an applied rotating magnetic field. DWs interact stochastically at ring junctions to create mechanisms of DW population loss and gain. These combine to give a dynamic, field-dependent equilibrium DW population that is a robust and emergent property of the array, despite highly varied local magnetic configurations. The magnetic ring arrays' properties (e.g., non-linear behavior, ``fading memory'' to changes in field, fabrication repeatability, and scalability) suggest they are an interesting candidate system for realizing reservoir computing (RC), a form of neuromorphic computing, in hardware. By way of example, simulations of ring arrays performing RC approaches 100% success in classifying spoken digits for single speakers. |
BibTeX:
@article{WOS:000616748600001,
author = {Dawidek, Richard W. and Hayward, Thomas J. and Vidamour, Ian T. and Broomhall, Thomas J. and Venkat, Guru and Al Mamoori, Mohanad and Mullen, Aidan and Kyle, Stephan J. and Fry, Paul W. and Steinke, Nina-Juliane and Cooper, Joshaniel F. K. and Maccherozzi, Francesco and Dhesi, Sarnjeet S. and Aballe, Lucia and Foerster, Michael and Prat, Jordi and Vasilaki, Eleni and Ellis, Matthew O. A. and Allwood, Dan A.},
title = {Dynamically-Driven Emergence in a Nanomagnetic System},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2021},
volume = {31},
number = {15},
doi = {https://doi.org/10.1002/adfm.202008389}
}
|
| Koohfar, S., Ozbek, Y., Bland, H., Zhang, Z. and Kumah, D.P. Interface-driven magnetic anisotropy in relaxed La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures on MgO JOURNAL OF APPLIED PHYSICS 129, 5 (2021) |
| Abstract: We investigate the structural and magnetic properties of
La 0.7 Sr 0.3 CrO 3 ( LSCO ) / La 0.7 Sr 0.3 MnO 3 (LSMO) heterostructures grown on (001)-oriented MgO by molecular beam epitaxy. Due to the large film-substrate lattice mismatch, strain relaxation is found to occur within the first 2-3 unit cells (uc) of the film as evidenced by reflection high energy electron diffraction and high-resolution synchrotron x-ray reciprocal space mapping. We find that the presence of the LSCO spacer and capping layers leads to ferromagnetism in ultra-thin LSMO layers with thicknesses of the order of 2 uc with the magnetic easy axis oriented in the film plane. Net magnetic moments of 1.4 and 2.4 mu B / Mn are measured for (2 uc LSCO/2 uc LSMO) and (2 uc LSCO/4 uc LSMO) superlattices, respectively, by superconducting quantum interference device magnetometry. The effective magnetic anisotropy of the relaxed (2 uc LSCO/4 uc LSMO) heterostructure is found to be an order of magnitude higher than bulk LSMO highlighting the critical role of interfacial interactions in tuning magnetic anisotropy at complex oxide interfaces. |
BibTeX:
@article{WOS:000617505800001,
author = {Koohfar, Sanaz and Ozbek, Yasemin and Bland, Hayden and Zhang, Zhan and Kumah, Divine P.},
title = {Interface-driven magnetic anisotropy in relaxed La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures on MgO},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2021},
volume = {129},
number = {5},
doi = {https://doi.org/10.1063/5.0033236}
}
|
| Roth, J., Kuznetsova, T., Miao, L., Pogrebnyakov, A., Alem, N. and Engel-Herbert, R. Self-regulated growth of [111]-oriented perovskite oxide films using hybrid molecular beam epitaxy APL MATERIALS 9, 2 (2021) |
| Abstract: Exotic material properties and topological nontrivial surface states
have been theoretically predicted to emerge in [111]-oriented perovskite layers. The realization of such [111]-oriented perovskite superlattices has been found challenging, and even the growth of perovskite oxide films along this crystallographic direction has been proven as a formidable task, attributed to the highly polar character of the perovskite (111) surface. Successful epitaxial growth along this direction has so far been limited to thin film deposition techniques involving a relatively high kinetic energy, specifically pulsed laser deposition and sputtering. Here, we report on the self-regulated growth of [111]-oriented high-quality SrVO3 by hybrid molecular beam epitaxy. The favorable growth kinetics available for the growth of perovskite oxides by hybrid molecular beam epitaxy on non-polar surfaces was also present for the growth of [111]-oriented films, resulting in high-quality SrVO3(111) thin films with residual resistivity ratios exceeding 20. The ability to grow high-quality perovskite oxides along energetically unfavorable crystallographic directions using hybrid molecular beam epitaxy opens up opportunities to study the transport properties of topological nontrivial and correlated electron systems. |
BibTeX:
@article{WOS:000630911000001,
author = {Roth, Joseph and Kuznetsova, Tatiana and Miao, Leixin and Pogrebnyakov, Alexej and Alem, Nasim and Engel-Herbert, Roman},
title = {Self-regulated growth of [111]-oriented perovskite oxide films using hybrid molecular beam epitaxy},
journal = {APL MATERIALS},
year = {2021},
volume = {9},
number = {2},
doi = {https://doi.org/10.1063/5.0040047}
}
|
| Cui, D., Xu, Y., Zhou, L., Zhang, L., Luan, Z., Li, C., Wu, D. and Wu, D. Electrically tunable inverse spin Hall effect in SrIrO3/Pb(Mg1/3Nb2/3)(0.7) Ti0.3O3 heterostructures through interface strain coupling APPLIED PHYSICS LETTERS 118, 5 (2021) |
| Abstract: Oxide spin detector materials are highly desired for emergent all-oxide
spintronics. In this work, Permalloy/SrIrO3/Pb(Mg1/3Nb2/3)(0.7) Ti0.3O3 (Py/SIO/PMNPT) heterostructures were prepared by pulsed laser deposition of SIO thin films epitaxially on (001)-oriented single crystalline PMNPT substrates, followed by sputter deposition of Py films upon SIO through a shadow mask. The paramagnetic SIO layer, with a large spin-orbit coupling, serves as a detector to check the spin current pumped from the adjacent ferromagnetic Py layer through the inverse spin Hall effect (ISHE). It is observed that the spin pumping amplitude can be reversibly tuned by about 50% through applying a 10kV/cm electric field on the piezoelectric PMNPT substrate. The ISHE voltage shows a butterfly hysteresis resembling the strain-field curve of PMNPT, indicating the relevance of strain coupling at the SIO/PMNPT interface. In situ x-ray diffraction reveals that both in-plane and out-of-plane lattice parameters of SIO vary with the field applied on PMNPT. These results highlight that SIO is a promising candidate material for spin detection, and the efficiency of spin to charge conversion in SIO can be tuned electrically in SIO/PMNPT heterostructures. |
BibTeX:
@article{WOS:000630485900004,
author = {Cui, Dapeng and Xu, Yeming and Zhou, Lifan and Zhang, Lunyong and Luan, Zhongzhi and Li, Chen and Wu, D. and Wu, Di},
title = {Electrically tunable inverse spin Hall effect in SrIrO3/Pb(Mg1/3Nb2/3)(0.7) Ti0.3O3 heterostructures through interface strain coupling},
journal = {APPLIED PHYSICS LETTERS},
year = {2021},
volume = {118},
number = {5},
doi = {https://doi.org/10.1063/5.0027125}
}
|
| Reisz, B., Belova, V., Duva, G., Zeiser, C., Hodas, M., Hagara, J., Siffalovic, P., Pithan, L., Hosokai, T., Hinderhofer, A., Gerlach, A. and Schreiber, F. Polymorphism and structure formation in copper phthalocyanine thin films JOURNAL OF APPLIED CRYSTALLOGRAPHY 54, 1, pp. 203-210 (2021) |
| Abstract: Many polymorphic crystal structures of copper phthalocyanine (CuPc) have
been reported over the past few decades, but despite its manifold applicability, the structure of the frequently mentioned alpha polymorph remained unclear. The base-centered unit cell (space group C2/c) suggested in 1966 was ruled out in 2003 and was replaced by a primitive triclinic unit cell (space group P (1) over bar). This study proves unequivocally that both alpha structures coexist in vacuum-deposited CuPc thin films on native silicon oxide by reciprocal space mapping using synchrotron radiation in grazing incidence. The unit-cell parameters and the space group were determined by kinematic scattering theory and provide possible molecular arrangements within the unit cell of the C2Ic structure by excluded-volume considerations. In situ X-ray diffraction experiments and ex situ atomic force microscopy complement the experimental data further and provide insight into the formation of a smooth thin film by a temperature-driven downward diffusion of CuPc molecules during growth. |
BibTeX:
@article{WOS:000613988600022,
author = {Reisz, Berthold and Belova, Valentina and Duva, Giuliano and Zeiser, Clemens and Hodas, Martin and Hagara, Jakub and Siffalovic, Peter and Pithan, Linus and Hosokai, Takuya and Hinderhofer, Alexander and Gerlach, Alexander and Schreiber, Frank},
title = {Polymorphism and structure formation in copper phthalocyanine thin films},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2021},
volume = {54},
number = {1},
pages = {203-210},
doi = {https://doi.org/10.1107/S1600576720015472}
}
|
| Liu, Y., Huang, Q., Qi, R., Xiao, L., Zhang, Z., Li, W., Yi, S. and Wang, Z. Microstructure evolution and hard x-ray reflectance of ultrathin Ru/C multilayer mirrors with different layer thicknesses MATERIALS RESEARCH EXPRESS 8, 2 (2021) |
| Abstract: Nanoscale Ru/C multilayers are essential reflective optics in the hard
x-ray region of 7-20 keV. To understand the layer growth behavior and develop ultrathin Ru/C multilayer mirrors with periods smaller than 3.0 nm, multilayers with different periods of 6.2-1.5 nm were fabricated and studied. It is found that the average interface width started to increase obviously when the period became smaller than 2.5 nm while the surface roughness of different multilayers remained almost the same. The intrinsic stress of the multilayer gradually decreased with decreasing period and reached a very low value of -82 MPa at d = 2.3 nm. High reflectance of 54% and 65% (at E = 8.04 keV) were demonstrated for the multilayers with periods of 2.5 nm and 3.0 nm, respectively, whereas that for 1.9 nm period was significantly lower. To further analyze the layer microstructure, x-ray diffraction and transmission electron microscopy were used. The polycrystallized structure of Ru remained similar for the multilayers with period less than 2.5 nm, while a non-continuous layer growth and severe intermixing between Ru and C were observed for the multilayer with period of 1.9 nm. The increased intermixing between Ru and C was found to be the main reason for the larger interface width and lower reflectance of the multilayers with period smaller than 2.5 nm. It also indicated that the layer thickness threshold for a Ru/C multilayer growing with good layer quality is 1.0-1.2 nm. |
BibTeX:
@article{WOS:000615212300001,
author = {Liu, Yang and Huang, Qiushi and Qi, Runze and Xiao, Liangxing and Zhang, Zhong and Li, Wenbin and Yi, Shengzhen and Wang, Zhanshan},
title = {Microstructure evolution and hard x-ray reflectance of ultrathin Ru/C multilayer mirrors with different layer thicknesses},
journal = {MATERIALS RESEARCH EXPRESS},
year = {2021},
volume = {8},
number = {2},
doi = {https://doi.org/10.1088/2053-1591/abdf13}
}
|
| Mondal, B., Vadawale, S.V., Mithun, N.P.S., Vaishnava, C.S., Tiwari, N.K., Goyal, S.K., Panini, S.S., Navalkar, V., Karmakar, C., Patel, M.R. and Upadhyay, R.B. DarpanX: A python package for modeling X-ray reflectivity of multilayer mirrors ASTRONOMY AND COMPUTING 34 (2021)early access (JAN 2021) |
| Abstract: Multilayer X-ray mirrors consist of a coating of a large number of
alternate layers of high Z and low Z materials with a typical thickness of 10-100 angstrom, on a suitable substrate. Such coatings play an important role in enhancing the reflectivity of X-ray mirrors by allowing reflections at angles much larger than the critical angle of X-ray reflection for the given materials. Coating with an equal thickness of each bilayer (constant period multilayers) enhances the reflectivity at discrete energies, satisfying Bragg condition for the given thickness. However, by systematically varying the bilayer thickness in the multilayer stack (depth graded multilayers), it is possible to design X-ray mirrors having enhanced reflectivity over a broad energy range. One of the most important applications of such a depth graded multilayer mirror is to realize hard X-ray telescopes for astronomical purposes. Design of such multilayer X-ray mirrors and their characterization with X-ray reflectivity measurements require appropriate software tools that can compute X-ray reflectivity for the given set of parameters and geometry. We have initiated the development of hard X-ray optics for future Indian X-ray astronomical missions, and in this context, we have developed a program, DarpanX, to calculate X-ray reflectivity for single and multilayer mirrors. It can be used as a stand-alone tool for designing multilayer mirrors with required characteristics. But more importantly, it has been implemented as a local model for the popular X-ray spectral fitting program, XSPEC, and thus can be used for accurate fitting of the experimentally measured X-ray reflectivity data. DarpanX is implemented as a Python 3 module, and an API is provided to access the underlying algorithms. Here we present details of DarpanX implementation and its validation for different types of multilayer structures. We also demonstrate the model fitting capability of DarpanX for experimental X-ray reflectivity measurements of single and multilayer samples. (C) 2021 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000624436800013,
author = {Mondal, B. and Vadawale, S. V. and Mithun, N. P. S. and Vaishnava, C. S. and Tiwari, N. K. and Goyal, S. K. and Panini, S. S. and Navalkar, V. and Karmakar, C. and Patel, M. R. and Upadhyay, R. B.},
title = {DarpanX: A python package for modeling X-ray reflectivity of multilayer mirrors},
journal = {ASTRONOMY AND COMPUTING},
year = {2021},
volume = {34},
doi = {https://doi.org/10.1016/j.ascom.2020.100446}
}
|
| Brandt, L.R., Salvati, E., Wermeille, D., Papadaki, C., Le Bourhis, E. and Korsunsky, A.M. Stress-Assisted Thermal Diffusion Barrier Breakdown in Ion Beam Deposited Cu/W Nano-Multilayers on Si Substrate Observed by in Situ GISAXS and Transmission EDX ACS APPLIED MATERIALS & INTERFACES 13, 5, pp. 6795-6804 (2021)early access (JAN 2021) |
| Abstract: The thermal stability of Cu/W nano-multilayers deposited on a Si
substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX-a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems. |
BibTeX:
@article{WOS:000619638400089,
author = {Brandt, Leon Romano and Salvati, Enrico and Wermeille, Didier and Papadaki, Chrysanthi and Le Bourhis, Eric and Korsunsky, Alexander M.},
title = {Stress-Assisted Thermal Diffusion Barrier Breakdown in Ion Beam Deposited Cu/W Nano-Multilayers on Si Substrate Observed by in Situ GISAXS and Transmission EDX},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2021},
volume = {13},
number = {5},
pages = {6795-6804},
doi = {https://doi.org/10.1021/acsami.0c19173}
}
|
| Deng, K., Cole, J.M., Cooper, J.F.K., Webster, J.R.P., Haynes, R., Al Bahri, O.K., Steinke, N.-J., Guan, S., Stan, L., Zhan, X., Zhu, T., Nye, D.W. and Stenning, G.B.G. Electrolyte/Dye/TiO2 Interfacial Structures of Dye-Sensitized Solar Cells Revealed by In Situ Neutron Reflectometry with Contrast Matching LANGMUIR 37, 5, pp. 1970-1982 (2021)early access (JAN 2021) |
| Abstract: The nature of an interfacial structure buried within a device assembly
is often critical to its function. For example, the dye/TiO2 interfacial structure that comprises the working electrode of a dye-sensitized solar cell (DSC) governs its photovoltaic output. These structures have been determined outside of the DSC device, using ex situ characterization methods; yet, they really should be probed while held within a DSC since they are modulated by the device environment. Dye/TiO2 structures will be particularly influenced by a layer of electrolyte ions that lies above the dye self-assembly. We show that electrolyte/dye/TiO2 interfacial structures can be resolved using in situ neutron reflectometry with contrast matching. We find that electrolyte constituents ingress into the self-assembled monolayer of dye molecules that anchor onto TiO2. Some dye/TiO2 anchoring configurations are modulated by the formation of electrolyte/dye intermolecular interactions. These electrolyte-influencing structural changes will affect dye-regeneration and electron-injection DSC operational processes. This underpins the importance of this in situ structural determination of electrolyte/dye/TiO2 interfaces within representative DSC device environments. |
BibTeX:
@article{WOS:000618892400034,
author = {Deng, Ke and Cole, Jacqueline M. and Cooper, Joshaniel F. K. and Webster, John R. P. and Haynes, Richard and Al Bahri, Othman K. and Steinke, Nina-Juliane and Guan, Shaoliang and Stan, Liliana and Zhan, Xiaozhi and Zhu, Tao and Nye, Daniel W. and Stenning, Gavin B. G.},
title = {Electrolyte/Dye/TiO2 Interfacial Structures of Dye-Sensitized Solar Cells Revealed by In Situ Neutron Reflectometry with Contrast Matching},
journal = {LANGMUIR},
year = {2021},
volume = {37},
number = {5},
pages = {1970-1982},
doi = {https://doi.org/10.1021/acs.langmuir.0c03508}
}
|
| Warnatz, T., Magnus, F., Strandqvist, N., Sanz, S., Ali, H., Leifer, K., Vorobiev, A. and Hjorvarsson, B. The impact of number of repeats N on the interlayer exchange in [Fe/MgO]N(001) superlattices SCIENTIFIC REPORTS 11, 1 (2021) |
| Abstract: The strength of the interlayer exchange coupling in [Fe/MgO]N(001)
superlattices with 2 <= N <= 10 depends on the number of bilayer repeats (N). The exchange coupling is antiferromagnetic for all the investigated thicknesses while being nine times larger in a sample with N = 4 as compared to N = 2. The sequence of the magnetic switching in two of the samples (N = 4, N = 8) is determined using polarized neutron reflectometry. The outermost layers are shown to respond at the lowest fields, consistent with having the weakest interlayer exchange coupling. The results are consistent with the existence of quantum well states defined by the thickness of the Fe and the MgO layers as well as the number of repeats (N) in [Fe/MgO]N(001)superlattices. |
BibTeX:
@article{WOS:000612982200085,
author = {Warnatz, Tobias and Magnus, Fridrik and Strandqvist, Nanny and Sanz, Sarah and Ali, Hasan and Leifer, Klaus and Vorobiev, Alexei and Hjorvarsson, Bjoergvin},
title = {The impact of number of repeats N on the interlayer exchange in [Fe/MgO]N(001) superlattices},
journal = {SCIENTIFIC REPORTS},
year = {2021},
volume = {11},
number = {1},
doi = {https://doi.org/10.1038/s41598-021-81441-y}
}
|
| Song, L., Schenk, T., Defay, E. and Glinsek, S. Highly conductive low-temperature combustion-derived transparent indium tin oxide thin film MATERIALS ADVANCES 2, 2, pp. 700-705 (2021) |
| Abstract: Combustion synthesis is a well-known method for synthesis of transparent
metal oxide thin films at low temperature (<400 degrees C). However, their functional properties are often inferior due to high residual porosity originating from a release of large amounts of gaseous products during combustion reaction. In this paper, indium tin oxide (ITO) transparent conductive oxide thin films are prepared through combustion synthesis at 350 degrees C and the porosity issue is explored via multilayer deposition. When the thickness of individual layers is downscaled from 12 to 3 nm, the density increases from 5.8 to 7.0 g cm(-3) and porosity decreases from 20 to 3%. This causes a strong boost of conductivity sigma (f) from 220 to 620 S cm(-1), the latter being one of the highest values ever reported for low-temperature processed ITO films. The effectiveness of this approach is attributed to a large specific surface area of thinner individual layers, which strongly enhances gas transport during the combustion process. We also show that improved crystallinity and a strong increase in tensile in-plane stress strongly contribute to the boost in conductivity. |
BibTeX:
@article{WOS:000616240100011,
author = {Song, Longfei and Schenk, Tony and Defay, Emmanuel and Glinsek, Sebastjan},
title = {Highly conductive low-temperature combustion-derived transparent indium tin oxide thin film},
journal = {MATERIALS ADVANCES},
year = {2021},
volume = {2},
number = {2},
pages = {700-705},
doi = {https://doi.org/10.1039/d0ma00872a}
}
|
| Allen, F.J., Truscott, C.L., Welbourn, R.J.L. and Clarke, S.M. Influence of surfactants on a pre-adsorbed cationic layer: Removal and modification JOURNAL OF COLLOID AND INTERFACE SCIENCE 588, pp. 427-435 (2021)early access (JAN 2021) |
| Abstract: Removal of organic species from solid surfaces is a crucial process. The
use of oppositely charged surfactants provides a potential method for enhanced removal. Neutron reflectometry has been used to investigate the complex behaviour of a pre-adsorbed and tenacious layer of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on a mica surface, during exposure to different organic species in solution. The anionic surfactant sodium dodecylsulfate (SDS) was shown to be able to remove the cationic layer, but only if anionic micelles were present in solution. To facilitate comparison with the behaviour of a non-ionic surfactant, the direct adsorption of pentaethylene glycol monododecyl ether (C12E5) to mica was also studied; low surface coverage adsorption was seen at the critical micelle concentration and above. C12E5 was then found not to remove the cationic layer, but did include into the layer to some degree. The presence of cationic surfactant on the mica was however shown to significantly modify the adsorption behaviour of the non-ionic surfactant. (C) 2020 Elsevier Inc. All rights reserved. |
BibTeX:
@article{WOS:000618704500042,
author = {Allen, Finian J. and Truscott, Chris L. and Welbourn, Rebecca J. L. and Clarke, Stuart M.},
title = {Influence of surfactants on a pre-adsorbed cationic layer: Removal and modification},
journal = {JOURNAL OF COLLOID AND INTERFACE SCIENCE},
year = {2021},
volume = {588},
pages = {427-435},
doi = {https://doi.org/10.1016/j.jcis.2020.12.047}
}
|
| Quach, N., Kim, I., Chang, J.-H., Lee, C., Kang, U.-B., Lee, J. and Won, Y. Fluorescence Microscopy Methodology for Visualizing Microscale Interfacial Defects In Packaging Materials PROCEEDINGS OF THE TWENTIETH INTERSOCIETY CONFERENCE ON THERMAL AND THERMOMECHANICAL PHENOMENA IN ELECTRONIC SYSTEMS (ITHERM 2021), pp. 1154-1161 (2021) |
| Abstract: Polydimethylsiloxane (PDMS) is widely used in the packaging industry in
conjunction with passivated silicon dioxide, SiO2, to protect semiconducting devices. However, defects on the SiO2 film have been shown to affect adhesion between the PDMS and the SiO2 film. In this study, x-ray reflectivity and x-ray diffraction are used to confirm metrology fidelity. In addition, confocal fluorescence microscopy is used to visualize defects quickly and non-invasively. We show that imaging surface defects as small as 1 mu m is possible on SiO2 films. Single molecule fluorescent tracking is conducted to examine the diffusion coefficient of PDMS. The diffusion of the polymer chain into the substrate microcavities can be used determine possibilities of improving adhesion between the two interfaces. Adhesion is estimated by area measurements of residue after peeling PDMS from the SiO2 surface as well as changes to surface roughness. To validate our methodology, various sized defects on substrates such as filter paper and microporous aluminum foil are visualized. |
BibTeX:
@inproceedings{WOS:000703033800145,
author = {Quach, Nhi and Kim, Ilhwan and Chang, Jong-Hyeon and Lee, ChungSun and Kang, Un-Byoung and Lee, JongHo and Won, Yoonjin},
title = {Fluorescence Microscopy Methodology for Visualizing Microscale Interfacial Defects In Packaging Materials},
booktitle = {PROCEEDINGS OF THE TWENTIETH INTERSOCIETY CONFERENCE ON THERMAL AND THERMOMECHANICAL PHENOMENA IN ELECTRONIC SYSTEMS (ITHERM 2021)},
year = {2021},
pages = {1154-1161},
note = {20th InterSociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), ELECTR NETWORK, JUN 01-04, 2021},
doi = {https://doi.org/10.1109/ITherm51669.2021.9503140}
}
|
| Swekis, P., Sukhanov, A.S., Chen, Y.-C., Gloskovskii, A., Fecher, G.H., Panagiotopoulos, I., Sichelschmidt, J., Ukleev, V., Devishvili, A., Vorobiev, A., Inosov, D.S., Goennenwein, S.T.B., Felser, C. and Markou, A. Magnetic and Electronic Properties of Weyl Semimetal Co2MnGa Thin Films NANOMATERIALS 11, 1 (2021) |
| Abstract: Magnetic Weyl semimetals are newly discovered quantum materials with the
potential for use in spintronic applications. Of particular interest is the cubic Heusler compound Co2MnGa due to its inherent magnetic and topological properties. This work presents the structural, magnetic and electronic properties of magnetron co-sputtered Co2MnGa thin films, with thicknesses ranging from 10 to 80 nm. Polarized neutron reflectometry confirmed a uniform magnetization through the films. Hard x-ray photoelectron spectroscopy revealed a high degree of spin polarization and localized (itinerant) character of the Mn d (Co d) valence electrons and accompanying magnetic moments. Further, broadband and field orientation-dependent ferromagnetic resonance measurements indicated a relation between the thickness-dependent structural and magnetic properties. The increase of the tensile strain-induced tetragonal distortion in the thinner films was reflected in an increase of the cubic anisotropy term and a decrease of the perpendicular uniaxial term. The lattice distortion led to a reduction of the Gilbert damping parameter and the thickness-dependent film quality affected the inhomogeneous linewidth broadening. These experimental findings will enrich the understanding of the electronic and magnetic properties of magnetic Weyl semimetal thin films. |
BibTeX:
@article{WOS:000610665100001,
author = {Swekis, Peter and Sukhanov, Aleksandr S. and Chen, Yi-Cheng and Gloskovskii, Andrei and Fecher, Gerhard H. and Panagiotopoulos, Ioannis and Sichelschmidt, Jorg and Ukleev, Victor and Devishvili, Anton and Vorobiev, Alexei and Inosov, Dmytro S. and Goennenwein, Sebastian T. B. and Felser, Claudia and Markou, Anastasios},
title = {Magnetic and Electronic Properties of Weyl Semimetal Co2MnGa Thin Films},
journal = {NANOMATERIALS},
year = {2021},
volume = {11},
number = {1},
doi = {https://doi.org/10.3390/nano11010251}
}
|
| Liu, Y., Huang, Q., Qi, R., Xiao, L., Zhang, Z. and Wang, Z. Improvement of the Microstructure and X-ray Performance of Ultrathin Ru/C Multilayer Mirror after High Temperature Treatment COATINGS 11, 1 (2021) |
| Abstract: Ru/C multilayer mirrors with a period of 2.5 nm and 150 bilayers were
studied under high-temperature annealing and long-term storage. A general increase in the reflectivity was observed after annealing at different temperatures from 300 to 700 degrees C, during which a maximum enhancement of around 14% was obtained at 600 degrees C. The highest reflectance measured at 8 keV reached 69% after 600 degrees C annealing. This was accompanied by a 6% expansion of the layer period, which could be mainly attributed to carbon layers. The surface roughness was not affected by the annealing, whereas the polycrystallization of Ru with crystallographic planes parallel to the layer interfaces was enhanced. Combining the transmission-electron microscopy measurements, it was found that the interdiffusion at the C-on-Ru interface was significantly suppressed. The decreased interdiffusion, enhanced optical contrast, and larger multilayer period were the main reasons for the increased reflectance. The 600 degrees C annealed Ru/C multilayer remained intact after 13 months of storage in air, which also demonstrated significant temporal stability. |
BibTeX:
@article{WOS:000610005000001,
author = {Liu, Yang and Huang, Qiushi and Qi, Runze and Xiao, Liangxing and Zhang, Zhong and Wang, Zhanshan},
title = {Improvement of the Microstructure and X-ray Performance of Ultrathin Ru/C Multilayer Mirror after High Temperature Treatment},
journal = {COATINGS},
year = {2021},
volume = {11},
number = {1},
doi = {https://doi.org/10.3390/coatings11010045}
}
|
| Li, F., Zou, Y., Han, M.-G., Foyevtsova, K., Shin, H., Lee, S., Liu, C., Shin, K., Albright, S.D., Sutarto, R., He, F., Davidson, B.A., Walker, F.J., Ahn, C.H., Zhu, Y., Cheng, Z.G., Elfimov, I., Sawatzky, G.A. and Zou, K. Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal SCIENCE ADVANCES 7, 2 (2021) |
| Abstract: Titanium monoxide (TiO), an important member of the rock salt 3d
transition-metal monoxides, has not been studied in the stoichiometric single-crystal form. It has been challenging to prepare stoichiometric TiO due to the highly reactive Ti2+. We adapt a closely lattice-matched MgO(001) substrate and report the successful growth of single-crystalline TiO(001) film using molecular beam epitaxy. This enables a first-time study of stoichiometric TiO thin films, showing that TiO is metal but in proximity to Mott insulating state. We observe a transition to the superconducting phase below 0.5 K close to that of Ti metal. Density functional theory (DFT) and a DFT-based tight-binding model demonstrate the extreme importance of direct Ti-Ti bonding in TiO, suggesting that similar superconductivity exists in TiO and Ti metal. Our work introduces the new concept that TiO behaves more similar to its metal counterpart, distinguishing it from other 3d transition-metal monoxides. |
BibTeX:
@article{WOS:000606331400021,
author = {Li, Fengmiao and Zou, Yuting and Han, Myung-Geun and Foyevtsova, Kateryna and Shin, Hyungki and Lee, Sangjae and Liu, Chong and Shin, Kidae and Albright, Stephen D. and Sutarto, Ronny and He, Feizhou and Davidson, Bruce A. and Walker, Frederick J. and Ahn, Charles H. and Zhu, Yimei and Cheng, Zhi Gang and Elfimov, Ilya and Sawatzky, George A. and Zou, Ke},
title = {Single-crystalline epitaxial TiO film: A metal and superconductor, similar to Ti metal},
journal = {SCIENCE ADVANCES},
year = {2021},
volume = {7},
number = {2},
doi = {https://doi.org/10.1126/sciadv.abd4248}
}
|
| Sarkar, P., Biswas, A., Abharana, N., Rai, S., Modi, M.H. and Bhattacharyya, D. Interface modification of Cr/Ti multilayers with C barrier layer for enhanced reflectivity in the water window regime JOURNAL OF SYNCHROTRON RADIATION 28, 1, pp. 224-230 (2021) |
| Abstract: The influence of a carbon barrier layer to improve the reflectivity of
Cr/Ti multilayers, intended to be used in the water window wavelength regime, is investigated. Specular grazing-incidence X-ray reflectivity results of Cr/Ti multilayers with 10 bilayers show that interface widths are reduced to similar to 0.24 nm upon introduction of a similar to 0.3 nm C barrier layer at each Cr-on-Ti interface. As the number of bilayers increases to 75, a multilayer with C barrier layers maintains almost the same interface widths with no cumulative increase in interface imperfections. Using such interface-engineered Cr/C/Ti multilayers, a remarkably high soft X-ray reflectivity of similar to 31.6% is achieved at a wavelength of 2.77 nm and at a grazing angle of incidence of 16.2 degrees, which is the highest reflectivity reported so far in the literature in this wavelength regime. Further investigation of the multilayers by diffused grazing-incidence X-ray reflectivity and grazing-incidence extended X-ray absorption fine-structure measurements using synchrotron radiation suggests that the improvement in interface microstructure can be attributed to significant suppression of inter-diffusion at Cr/Ti interfaces by the introduction of C barrier layers and also due to the smoothing effect of the C layer promoting two-dimensional growth of the multilayer. |
BibTeX:
@article{WOS:000605205600027,
author = {Sarkar, P. and Biswas, A. and Abharana, N. and Rai, S. and Modi, M. H. and Bhattacharyya, D.},
title = {Interface modification of Cr/Ti multilayers with C barrier layer for enhanced reflectivity in the water window regime},
journal = {JOURNAL OF SYNCHROTRON RADIATION},
year = {2021},
volume = {28},
number = {1},
pages = {224-230},
doi = {https://doi.org/10.1107/S1600577520013429}
}
|
| Coffey, B.M., Nallan, H.C. and Ekerdt, J.G. Vacuum ultraviolet enhanced atomic layer etching of ruthenium films JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 39, 1 (2021) |
| Abstract: Vacuum ultraviolet (VUV) enhanced atomic layer etching (ALE) of thin
(similar to 8nm) Ru films is demonstrated. Oxidation half-cycles of 2-5min VUV/O-2 co-exposure are used to oxidize near-surface Ru to RuO2 at 1Torr O-2 and 100-150 degrees C. In situ x-ray photoelectron spectroscopy measurements indicate that RuO2 formation saturates after similar to 5min of VUV/O-2 exposure at 100 and 150 degrees C. The depth of Ru oxidation is limited by the rate of oxidation and can be controlled with substrate temperature and exposure time. Etching half-cycles are performed by exposing the oxidized Ru film to HCOOH vapor at 0.50Torr for 30s isothermally, which results in the removal of the oxidized Ru layer. The amount of Ru removed per ALE cycle is determined by comparing ex situ x-ray reflectivity (XRR) measurements of the film before and after etching. When using 2min VUV/O-2 co-exposure, approximately 0.8 and 0.9 angstrom of Ru is etched per cycle at 100 and 150 degrees C, respectively. XRR and atomic force microscopy measurements indicate that the as-deposited and sputtered Ru film surface becomes smoother as ALE is performed. The etch rate decreases with ALE cycles and corresponds to a slowing oxidation rate, which is likely associated with the decrease in surface roughness. Density functional theory is used to study the adsorption of oxidants in a model Ru system, and nudged elastic band (NEB) calculations describe O diffusion into the Ru substrate by following an O ``probe'' atom as it moves between Ru(002) atomic planes with 0.50 monolayer (ML) O on the surface. NEB results reveal an approximate energetic barrier to diffusion, E-a, of 5.10eV for O to move through the second and third atomic Ru layers when O, which can form an RuOx species, is subsurface. This E-a is in excess of the energetic gain of 4.23eV in adsorbing an O atom to Ru(002) with 0.50ML O. The difference in E-a and the adsorption energy likely contributes to the self-limiting nature of the oxidation and explains the observation that VUV/O-2 co-exposure time must be increased to allow additional time for O diffusing into the subsurface as it overcomes the barrier to subsurface O diffusion. The self-limiting oxidation of Ru arising from VUV/O-2 at low temperatures, in turn, enables an ALE process for Ru. |
BibTeX:
@article{WOS:000603067400001,
author = {Coffey, Brennan M. and Nallan, Himamshu C. and Ekerdt, John G.},
title = {Vacuum ultraviolet enhanced atomic layer etching of ruthenium films},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2021},
volume = {39},
number = {1},
doi = {https://doi.org/10.1116/6.0000742}
}
|
| Squillace, O., Perrault, T., Gorczynska, M., Caruana, A., Bajorek, A. and Brotons, G. Design of tethered bilayer lipid membranes, using wet chemistry via aryldiazonium sulfonic acid spontaneous grafting on silicon and chrome COLLOIDS AND SURFACES B-BIOINTERFACES 197 (2021) |
| Abstract: We describe a bottom-up surface functionalization to design hybrid
molecular coatings that tether biomembranes using wet chemistry. First, a monolayer was formed by immersion in a NH2-Ar-SO3H solution, allowing aryldiazonium salt radicals to spontaneously bind to it via strong C bonding. After formation of the air-stable and dense molecular monolayer (-Ar-SO3H), a subsequent activation was used to form highly reactive -Ar-SO2Cl groups nearly perpendicular to the monolayer. These can bind commercial surfactants, PEGylated oligomers and other inexpensive molecules via their -OH, -COOH, or -NH2 chain end-moieties, to build hybrid coatings. Metal and oxidized chromium, semi-conductor n-doped silicon (111), are the substrates tested for this protocol and the aromatic organic monolayers formed at their surface are characterized by X-ray photoelectron spectroscopy (XPS). XPS reveals unambiguously the presence of C-Cr and C-Si bonds, ensuring robustness of the coatings. Functional sulfur groups (-SO3H) cover up to 6.5 x 10(-10) mol cm(-2) of the silicon interface and 4.7 x 10(-10) mol cm(-2) of the oxidized chromium interface. These surface concentrations are comparable to the classic values obtained when the prefunctionalisation is driven by electrochemistry on conductors. Tethered lipid membranes formed on these coatings were analyzed by neutron reflectivity at the interface of functionalized n-doped silicon substrates after immersion in a solution of lipid vesicles and subsequent fusion. Results indicate a rather compact hybrid coating of Brij anchor-harpoon molecules that maintain a single lipid bilayer above the substrate, on top of a hydrated PEO cushion. |
BibTeX:
@article{WOS:000602406400007,
author = {Squillace, Ophelie and Perrault, Thomas and Gorczynska, Magdalena and Caruana, Andrew and Bajorek, Anna and Brotons, Guillaume},
title = {Design of tethered bilayer lipid membranes, using wet chemistry via aryldiazonium sulfonic acid spontaneous grafting on silicon and chrome},
journal = {COLLOIDS AND SURFACES B-BIOINTERFACES},
year = {2021},
volume = {197},
doi = {https://doi.org/10.1016/j.colsurfb.2020.111427}
}
|
| Pilkington, G.A., Welbourn, R., Oleshkevych, A., Watanabe, S., Pedraz, P., Radiom, M., Glavatskih, S. and Rutland, M.W. Effect of water on the electroresponsive structuring and friction in dilute and concentrated ionic liquid lubricant mixtures PHYSICAL CHEMISTRY CHEMICAL PHYSICS 22, 48, pp. 28191-28201 (2020) |
| Abstract: The effect of water on the electroactive structuring of a tribologically
relevant ionic liquid (IL) when dispersed in a polar solvent has been investigated at a gold electrode interface using neutron reflectivity (NR). For all solutions studied, the addition of small amounts of water led to clear changes in electroactive structuring of the IL at the electrode interface, which was largely determined by the bulk IL concentration. At a dilute IL concentration, the presence of water gave rise to a swollen interfacial structuring, which exhibited a greater degree of electroresponsivity with applied potential compared to an equivalent dry solution. Conversely, for a concentrated IL solution, the presence of water led to an overall thinning of the interfacial region and a crowding-like structuring, within which the composition of the inner layer IL layers varied systematically with applied potential. Complementary nanotribotronic atomic force microscopy (AFM) measurements performed for the same IL concentration, in dry and ambient conditions, show that the presence of water reduces the lubricity of the IL boundary layers. However, consistent with the observed changes in the IL layers observed by NR, reversible and systematic control of the friction coefficient with applied potential was still achievable. Combined, these measurements provide valuable insight into the implications of water on the interfacial properties of ILs at electrified interfaces, which inevitably will determine their applicability in tribotronic and electrochemical contexts. |
BibTeX:
@article{WOS:000603167900024,
author = {Pilkington, Georgia A. and Welbourn, Rebecca and Oleshkevych, Anna and Watanabe, Seiya and Pedraz, Patricia and Radiom, Milad and Glavatskih, Sergei and Rutland, Mark W.},
title = {Effect of water on the electroresponsive structuring and friction in dilute and concentrated ionic liquid lubricant mixtures},
journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
year = {2020},
volume = {22},
number = {48},
pages = {28191-28201},
doi = {https://doi.org/10.1039/d0cp05110a}
}
|
| Lee, J., Park, J.K., Lee, J.W., Heo, Y., Oh, Y.S., Lee, J.S., Cho, J. and Jeen, H. Formation of buried superconducting Mo2N by nitrogen-ion-implantation RSC ADVANCES 10, 72, pp. 44339-44343 (2020) |
| Abstract: Nitrogen ion implantation is a useful technique to put nitrogen ions
into lattices. In this work, nitrogen ion implantation into epitaxial Mo films is performed to create a buried superconducting gamma-Mo2N. Atomically flat epitaxial (110) Mo films are grown on (0001) Al2O3. By impinging nitrogen ions, where the beam energy is fixed to 20 keV, we observe (111) gamma-Mo2N diffraction and the formation of a gamma-Mo2N layer from X-ray reflectivity. Magnetization and transport measurements clearly support a superconducting layer in the implanted film. Our strategy shows that formation of a buried superconducting layer can be achieved through ion implantation and self-annealing. |
BibTeX:
@article{WOS:000599804300038,
author = {Lee, Joonhyuk and Park, Jun Kue and Lee, Joon Woo and Heo, Yunseok and Oh, Yoon Seok and Lee, Jae S. and Cho, Jinhyung and Jeen, Hyoungjeen},
title = {Formation of buried superconducting Mo2N by nitrogen-ion-implantation},
journal = {RSC ADVANCES},
year = {2020},
volume = {10},
number = {72},
pages = {44339-44343},
doi = {https://doi.org/10.1039/d0ra08533b}
}
|
| Chen, J., Zheng, L., Yin, W., Zhang, M., Lu, Y., Zhang, Z., Klar, P.J., Li, M. and He, Y. Two-dimensional SnO ultrathin epitaxial films: Pulsed laser deposition growth and quantum confinement effects PHYSICA B-CONDENSED MATTER 599 (2020) |
| Abstract: Two-dimensional (2D) ultrathin oxides are crucial for modern quantum
electronic devices. However, the well -controlled growth of 2D oxide materials is highly challenging. In this work, ultrathin single-crystal SnO epitaxial films were achieved on r-sapphire by pulsed laser deposition. The quasi-2D SnO films have thicknesses ranging from 3.4 to 25.4 nm, allowing observation of quantum confinement effects in the optical bandgap. The critical thickness where the films relax in plane is around 19 nm. Below 19 nm, the films are strained compressively in plane and tensilely along the c-axis. Quantum confinement effects are observed by UV-IR spectroscopy for the optical transition at the direct bandgap. By fitting Brus equation, the reduced effective mass is deduced to be 0.137 +/- 0.016 me. The exciton radius and binding energy are 4.62 +/- 0.61 nm and 10.8 +/- 1.2 meV, respectively. These parameters are crucial for the design and application of SnO-based quantum devices. |
BibTeX:
@article{WOS:000583242900008,
author = {Chen, Jian and Zheng, Lilan and Yin, Weiling and Zhang, Mi and Lu, Yinmei and Zhang, Zaoli and Klar, Peter J. and Li, Mingkai and He, Yunbin},
title = {Two-dimensional SnO ultrathin epitaxial films: Pulsed laser deposition growth and quantum confinement effects},
journal = {PHYSICA B-CONDENSED MATTER},
year = {2020},
volume = {599},
doi = {https://doi.org/10.1016/j.physb.2020.412467}
}
|
| Wang, B.-Y., Chen, C.-J., Lin, K., Hsu, C.-Y., Ning, J.-Y., Tsai, M.-S., Chuang, T.-H., Wei, D.-H. and Weng, S.-C. Promoting exchange bias coupling in Fe/MgO(001) films by controlling interface oxide distribution APPLIED SURFACE SCIENCE 533 (2020) |
| Abstract: MgO-based magnetic heterostructures are crucial building blocks in
state-of-the-art spintronic devices. In this study, we performed thermal annealing to control the formation and distribution of FeO across the interface of a Fe-MgO system. The exchange bias phenomenon (i.e., a horizontal shift of magnetic hysteresis loops) was extended from involving only interface spins to involving the full-volume magnetization of the Fe film. The extended and reinforced exchange bias coupling in the annealed Fe/MgO(0 0 1) films can be attributed to the formation of a Fe-FeO matrix-like structure at the Fe/MgO interface under an increasing degree of interface roughness and the reduction or diffusion of oxygen from the interfacial oxides, as indicated by X-ray absorption near edge structures and X-ray reflectivity measurements. Moreover, the thermal stability of exchange bias coupling in the annealed Fe/MgO(0 0 1) films (maximum value at approximately 600 K) was considerably higher than that in conventional thin-film-based Fe/FeO structures (approximately 50 K). |
BibTeX:
@article{WOS:000580616900062,
author = {Wang, Bo-Yao and Chen, Chia-Ju and Lin, Kai and Hsu, Chun-Yao and Ning, Jing-Yu and Tsai, Ming-Shian and Chuang, Tzu-Hung and Wei, Der-Hsin and Weng, Shih-Chang},
title = {Promoting exchange bias coupling in Fe/MgO(001) films by controlling interface oxide distribution},
journal = {APPLIED SURFACE SCIENCE},
year = {2020},
volume = {533},
doi = {https://doi.org/10.1016/j.apsusc.2020.147501}
}
|
| Anyfantis, D.I., Kanistras, N., Barnasas, A., Poulopoulos, P., Papaioannou, E.T., Conca, A., Trachylis, D. and Politis, C. Effects of Thermal Annealing and Ni Addition on the Magnetic Properties of Co-CoO Multilayers SPIN 10, 4 (2020)early access (DEC 2020) |
| Abstract: The influence of mild thermal annealing and nickel addition on the
magnetic properties of Co-CoO multilayers is investigated. Co-CoO and CoNi-CoNiO multilayers were fabricated by radio-frequency magnetron sputtering and natural oxidation. Their magnetic properties have been studied via the magneto-optical Kerr effect and a vector network analyzer ferromagnetic resonance setup. The Co-CoO multilayers were annealed up to 90min at 250 degrees C and they were found to be always in-plane magnetized. The value of Gilbert damping was evaluated. The multilayers after annealing or Ni addition show a small increase in coercivity without considerable changes in their anisotropy. The phenomenon of inverted hysteresis with negative remanence, with the field being applied perpendicular to the film plane, has been recorded. It was modeled with two coexisting magnetic moments with in-plane and perpendicular anisotropies, respectively. |
BibTeX:
@article{WOS:000599356300001,
author = {Anyfantis, D. I. and Kanistras, N. and Barnasas, A. and Poulopoulos, P. and Papaioannou, E. TH. and Conca, A. and Trachylis, D. and Politis, C.},
title = {Effects of Thermal Annealing and Ni Addition on the Magnetic Properties of Co-CoO Multilayers},
journal = {SPIN},
year = {2020},
volume = {10},
number = {4},
doi = {https://doi.org/10.1142/S2010324720500307}
}
|
| Cho, D., Ryu, S. and Jeen, H. Effect of Growth Temperature on Magnetism of GdFe12 Epitaxial Thin Films JOURNAL OF THE KOREAN MAGNETICS SOCIETY 30, 6, pp. 189-194 (2020) |
| Abstract: Alloys of rare earth metal and transition metal with ThMn12 structure
are expected to have high saturation magnetization and high magnetic anisotropy. Despite its advantages, it has not been commercialized because of its metastability. GdFe12 is a material having ThMn12 structure. Therefore, it is expected to be difficult to stabilize GdFe12 in bulk form. In this study, GdFe12 was fabricated in the form of epitaxial thin films to stabilize the phase. The films were grown epitaxially from 500 degrees C to 200 degrees C. From the results of x-ray diffraction and x-ray absorption, it was confirmed that a (330) GdFe12 thin films were grown. The epitaxial GdFe12 thin film had a saturation magnetization (M-s) = 1130 emu/cm(3) and coercivity = 712 Oe at a deposition temperature of 400 degrees C. |
BibTeX:
@article{WOS:000604544700002,
author = {Cho, Daegill and Ryu, Sangkyun and Jeen, Hyoungjeen},
title = {Effect of Growth Temperature on Magnetism of GdFe12 Epitaxial Thin Films},
journal = {JOURNAL OF THE KOREAN MAGNETICS SOCIETY},
year = {2020},
volume = {30},
number = {6},
pages = {189-194},
doi = {https://doi.org/10.4283/JKMS.2020.30.6.189}
}
|
| Griggs, W., Eggert, B., Liedke, M.O., Butterling, M., Wagner, A., Kentsch, U., Hirschmann, E., Grimes, M., Caruana, A.J., Kinane, C., Wende, H., Bali, R. and Thomson, T. Depth selective magnetic phase coexistence in FeRh thin films APL MATERIALS 8, 12 (2020) |
| Abstract: We demonstrate the manipulation of magnetic phases in FeRh thin films
through atomic displacements and the distribution of structural defects. Atomic scale disorder can be controlled via irradiation with light noble gas ions, producing depth-varying nanoscale phase configurations of distinct antiferromagnetic, ferromagnetic, and paramagnetic regions. Here, we perform a spatial characterization of the magnetic phases and the local magnetic environment around the Fe atoms, as well as the variation of the open-volumes around atomic sites. Thus, a direct correspondence between the existence of the three magnetic phases and lattice defects is revealed. By careful selection of the irradiating fluence, we show that it is possible to produce simple and thermally stable magnetic configurations, such as uniform magnetization or a bilayer phase structure. Furthermore, the thin film surface and interfaces are observed as the nucleation sites for the transitions between the phases. These results demonstrate a sensitive nanoscale manipulation of magnetic properties, shedding light on magnetic ordering in alloy lattices and broadening the scope for applications. |
BibTeX:
@article{WOS:000598766100001,
author = {Griggs, W. and Eggert, B. and Liedke, M. O. and Butterling, M. and Wagner, A. and Kentsch, U. and Hirschmann, E. and Grimes, M. and Caruana, A. J. and Kinane, C. and Wende, H. and Bali, R. and Thomson, T.},
title = {Depth selective magnetic phase coexistence in FeRh thin films},
journal = {APL MATERIALS},
year = {2020},
volume = {8},
number = {12},
doi = {https://doi.org/10.1063/5.0032130}
}
|
| Li, J., Guan, M.-X., Nan, P.-F., Wang, J., Ge, B.-H., Qiao, K.-M., Zhang, H.-R., Liang, W.-H., Hao, J.-Z., Zhou, H.-B., Shen, F.-R., Liang, F.-X., Zhang, C., Liu, M., Meng, S., Zhu, T., Hu, F.-X., Wu, T., Guo, J.-D., Sun, J.-R. and Shen, B.-G. Topotactic phase transformations by concerted dual-ion migration of B-site cation and oxygen in multivalent cobaltite La-Sr-Co-O-x films NANO ENERGY 78 (2020) |
| Abstract: Manipulating topotactic phase transformations via orderly ion transfer
in complex oxides ABO(x) is ubiquitous in advanced applications such as ionotronics, ion-batteries and catalysts. Most of such ion-mediated transformations are accomplished by the transfer of oxygen or A-site ions. However, implementing the transformation via the transfer of B-site ions, despite the great challenge to overcome a large cohesive energy, has unique advantage since they host most functional properties of materials. Here, we present a tri-state phase transformation from perovskite (P) to brownmillerite (BM) and to single-layered perovskite (SL) structure via the concerted migration of oxygen and B-site Co-ions in La0.7Sr0.3CoO3 thin films. Ac-STEM, XPS, XAS, PNR, magnetic and electric measurements demonstrated that presented B-site Co-cation transfer is along the CoO4 tetrahedral sub-layer of the BM film, which leads to the reconfiguration of 3d-electrons and spin state in remanent Co ions and causes tremendous changes in magnetic and electric properties: from canted-antiferromagnetic insulator in BM phase to ferromagnetic insulator in SL phase. First-principles calculations revealed that the La3+-doping at A-site largely reduces the cohesive energy of Co-ions in CoO4 and destabilize the CoO4 tetrahedron of BM phase, which explains the formation of Co-ions transfer channel in the CoO4 tetrahedral sub-layer. The present study highlights the effectiveness of regulating topotactic transformation via B-site ions transfer and provides a new pathway for manipulating the topotactic transformation with diverse functionalities. |
BibTeX:
@article{WOS:000595296400003,
author = {Li, Jia and Guan, Meng-Xue and Nan, Peng-Fei and Wang, Jing and Ge, Bing-Hui and Qiao, Kai-Ming and Zhang, Hong-Rui and Liang, Wen-Hui and Hao, Jia-Zheng and Zhou, Hou-Bo and Shen, Fei-Ran and Liang, Fei-Xiang and Zhang, Cheng and Liu, Miao and Meng, Sheng and Zhu, Tao and Hu, Feng-Xia and Wu, Tom and Guo, Jian-Dong and Sun, Ji-Rong and Shen, Bao-Gen},
title = {Topotactic phase transformations by concerted dual-ion migration of B-site cation and oxygen in multivalent cobaltite La-Sr-Co-O-x films},
journal = {NANO ENERGY},
year = {2020},
volume = {78},
doi = {https://doi.org/10.1016/j.nanoen.2020.105215}
}
|
| Prakash, A., Wang, T., Choudhary, R., Haugstad, G., Gladfelter, W.L. and Jalan, B. Precursor selection in hybrid molecular beam epitaxy of alkaline-earth stannates JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 38, 6 (2020) |
| Abstract: One of the challenges of oxide molecular beam epitaxy (MBE) is the
synthesis of oxides containing metals with high electronegativity (metals that are hard to oxidize). The use of reactive organometallic precursors can potentially address this issue. To investigate the formation of radicals in MBE, we explored three carefully chosen metal-organic precursors of tin for SnO2 and BaSnO3 growth: tetramethyltin (TMT), tetraethyltin (TET), and hexamethylditin (HMDT). All three precursors produced single-crystalline, atomically smooth, and epitaxial SnO2 (101) films on r-Al2O3 ( 10 1 presence of oxygen plasma. The study of growth kinetics revealed reaction-limited and flux-limited regimes except for TET, which also exhibited a decrease in the deposition rate with increasing temperature above similar to 800 degrees C. Contrary to these similarities, the performance of these precursors was dramatically different for BaSnO3 growth. TMT and TET were ineffective in supplying adequate tin, whereas HMDT yielded phase-pure, stoichiometric BaSnO3 films. Significantly, HMDT resulted in phase-pure and stoichiometric BaSnO3 films even without the use of an oxygen plasma (i.e., with molecular oxygen alone). These results are discussed using the ability of HMDT to form tin radicals and therefore assisting with Sn -> Sn4+ oxidation reaction. Structural and electronic transport properties of films grown using HMDT with and without oxygen plasma are compared. This study provides guideline for the choice of precursors that will enable the synthesis of metal oxides containing hard-to-oxidize metals using reactive radicals in MBE. |
BibTeX:
@article{WOS:000588466400001,
author = {Prakash, Abhinav and Wang, Tianqi and Choudhary, Rashmi and Haugstad, Greg and Gladfelter, Wayne L. and Jalan, Bharat},
title = {Precursor selection in hybrid molecular beam epitaxy of alkaline-earth stannates},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2020},
volume = {38},
number = {6},
doi = {https://doi.org/10.1116/6.0000590}
}
|
| Kim, K.-Y., Park, G., Cho, J., Kim, J., Kim, J.-S., Jung, J., Park, K., You, C.-Y. and Oh, I.-H. Intrinsic Magnetic Order of Chemically Exfoliated 2D Ruddlesden-Popper Organic-Inorganic Halide Perovskite Ultrathin Films SMALL 16, 52 (2020)early access (NOV 2020) |
| Abstract: Thin film fabrication of 2D layered organic-inorganic hybrid perovskites
(2D-OIHPs) for spintronic applications has been attempted using solution-based process like Langmuir-Blodgett technique. However, monolayer or few-layered 2D magnets are not yet realized, even though a wide spectrum of 2D Ruddlesden-Popper (RP) OIHPs are known as quasi-2D Heisenberg magnets in bulk compounds. Here, chemical exfoliation by solvent engineering is applied to successfully synthesize large-sized, few unit-cell-thick 2D RP-OIHPs. Comprehensive structural characterization reveals that binary co-solvents with high relative polarity in spin coating technique are the most effective among nine kinds of solvents. Above all, this enables few-layered 2D RP-OIHP ultrathin films sustaining their intrinsic magnetic order. It is found that XY-like magnetic anisotropy driven by Jahn-Teller effect responsible for ferromagnetism in seven-layered (C6H5CH2CH2NH3)(2)CuCl4 ultrathin films remains very robust, whereas Ising-like dipolar anisotropy responsible for canted antiferromagnetism in ten-layered (C6H5CH2CH2NH3)(2)MnCl4 ultrathin films is greatly reduced. It is expected that ferromagnetism even at monolayer limit should be possible by means of further sophisticated solvent engineering as long as Jahn-Teller effect is active. The chemical exfoliation using solvent engineering unambiguously can bring about a new breakthrough in the development of 2D RP-OIHP van der Waals magnets for ultrahigh energy-efficient spintronic, opto-spintronic devices. |
BibTeX:
@article{WOS:000592210500001,
author = {Kim, Ki-Yeon and Park, Garam and Cho, Jaehun and Kim, Joonwoo and Kim, June-Seo and Jung, Jinyong and Park, Kwonjin and You, Chun-Yeol and Oh, In-Hwan},
title = {Intrinsic Magnetic Order of Chemically Exfoliated 2D Ruddlesden-Popper Organic-Inorganic Halide Perovskite Ultrathin Films},
journal = {SMALL},
year = {2020},
volume = {16},
number = {52},
doi = {https://doi.org/10.1002/smll.202005445}
}
|
| Lakner, P.H., Brinker, M., Seitz, C., Jacobse, L., Vonk, V., Lippmann, M., Volkov, S., Huber, P. and Keller, T.F. Probing the Electrolyte Transfer in Ultrathin Polypyrrole Films by In Situ X-ray Reflectivity and Electrochemistry LANGMUIR 36, 45, pp. 13448-13456 (2020) |
| Abstract: This study reports on the potential-induced charge and mass transfer
between an ultrathin polypyrrole (PPy) film and an electrolyte by simultaneous in situ X-ray reflectivity (XRR) and electrochemistry (EC) utilizing their sensitivity to electrons. An about 30 nm thin PPy film was deposited on a silicon single crystal by fast potential cycling, providing a dense film of an extraordinary small surface roughness. XRR was recorded from the PPy film in an aqueous 0.1 M perchloric acid at electric potentials between -0.2 V and +0.5 V vs Ag/AgCl. The PPy film shows typical reversible and linear changes in film thickness and electron density arising from the potential-dependent electrolyte incorporation. By introducing EC-XRR, a comprehensive analysis combining in situ XRR and EC, the net number of electrons passing through the PPy-electrolyte interface was deduced along with the potential-induced thickness variations, indicating a complex exchange mechanism. Evidently, along with the anion transfer, parallel charge compensation by protons and a volume and electron compensating counterflow of solvent molecules take place. Complementary time-dependent EC-XRR scans indicate that these exchange mechanisms are individual in two potential ranges. The low actuation along with a high pseudocapacitance suggest the fast potentiodynamically deposited PPy film as a promising supercapacitor material. |
BibTeX:
@article{WOS:000592840500008,
author = {Lakner, Pirmin H. and Brinker, Manuel and Seitz, Christoph and Jacobse, Leon and Vonk, Vedran and Lippmann, Milena and Volkov, Sergey and Huber, Patrick and Keller, Thomas F.},
title = {Probing the Electrolyte Transfer in Ultrathin Polypyrrole Films by In Situ X-ray Reflectivity and Electrochemistry},
journal = {LANGMUIR},
year = {2020},
volume = {36},
number = {45},
pages = {13448-13456},
doi = {https://doi.org/10.1021/acs.langmuir.0c02068}
}
|
| Yurakov, Y.A., Peshkov, Y.A., Ivkov, S.A., Kannykin, S.V., Sitnikov, A.V. and Domashevskaya, E.P. The state of individual layers and interfaces in multilayer nanostructures [(Co40Fe40B20)(34)(SiO2)(66)/ZnO/C](46) SURFACE AND INTERFACE ANALYSIS 53, 2, pp. 244-249 (2021)early access (NOV 2020) |
| Abstract: The multilayer nanostructures have drawn attention in fields from
spintronics to microwave electronics. The purpose of this work was to determine the composition of individual layers and to control interfaces in three-layer superstructures [(Co40Fe40B20)(34)(SiO2)(66)/ZnO/C](46) by means of X-ray diffraction and X-ray reflectivity. The samples with different thicknesses of metal-containing composite layers together with zinc oxide and carbon interlayers were deposited on the glass substrate by ion-beam sputtering of three targets, one of which was a composite (Co40Fe40B20)(34)(SiO2)(66). X-ray diffraction results showed the X-ray amorphous state of the ferromagnetic metal clusters CoFeB, the dielectric matrix of silicon oxide SiO2, and carbon interlayers. However, the intermediate layers of the zinc oxide ZnO were found to have a nanocrystalline structure. The X-ray reflectivity measurements indicate a good agreement between the experimental and nominal values of both the periods of three-layer superstructures and the thicknesses of metal-containing composite layers and interlayers. |
BibTeX:
@article{WOS:000588356100001,
author = {Yurakov, Yury A. and Peshkov, Yaroslav A. and Ivkov, Sergey A. and Kannykin, Sergey V. and Sitnikov, Alexander V. and Domashevskaya, Evelina P.},
title = {The state of individual layers and interfaces in multilayer nanostructures [(Co40Fe40B20)(34)(SiO2)(66)/ZnO/C](46)},
journal = {SURFACE AND INTERFACE ANALYSIS},
year = {2021},
volume = {53},
number = {2},
pages = {244-249},
doi = {https://doi.org/10.1002/sia.6908}
}
|
| Coffey, B.M., Nallan, H.C., Engstrom, J.R. and Ekerdt, J.G. A Vacuum Ultraviolet-Enhanced Oxidation Mechanism for Pd: Near-Surface Oxidation for Atomic Layer Etching ACS APPLIED MATERIALS & INTERFACES 12, 45, pp. 50985-50995 (2020) |
| Abstract: Density functional theory (DFT) is used to better understand the
oxidation of Pd metal using vacuum ultraviolet (VUV) light co-exposed with O-2, which is known to produce O and O-3. The oxidation of Pd metal arising from O, O-2, and O-3 is assessed on bare Pd, Pd with a 0.25 monolayer of adsorbed atomic O, and Pd with increasing O incorporation into the substrate. DFT calculations are complemented experimentally by co-exposing 20 nm Pd films to 1 Torr of O-2 and VUV photons (6.5 < h nu < 11.3 eV) from a D-2 lamp at temperatures ranging from 50 to 200 degrees C and times from 30 s to 40 min. Oxidation of Pd is characterized using in situ X-ray photoelectron spectroscopy. Co-exposures at 50 degrees C and 1 Torr O-2 are performed with the Pd illuminated by the VUV light and shadowed from the VUV light in attempting to select for the oxidant that impinges on the Pd surface and causes oxidation. Results suggest that atomic O incident from the gas phase is responsible for oxidation of Pd, as no PdOx formation is observed for the same time period with the sample shadowed. Growth of PdOx via O diffusion is studied with the nudged elastic band method. Atomic O diffusion through Pd has an activation energy barrier of similar to 2.87 eV with respect to a surface O. This decreases to similar to 1.80 eV once the 0.25 monolayer of O occupies the surface. The extent of Pd oxidation is limited to the near-surface Pd region for all times and temperatures investigated. PdOx formation does not appear to exceed one to two atomic layers of Pd for conditions explored herein. |
BibTeX:
@article{WOS:000592481300078,
author = {Coffey, Brennan M. and Nallan, Himamshu C. and Engstrom, James R. and Ekerdt, John G.},
title = {A Vacuum Ultraviolet-Enhanced Oxidation Mechanism for Pd: Near-Surface Oxidation for Atomic Layer Etching},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2020},
volume = {12},
number = {45},
pages = {50985-50995},
doi = {https://doi.org/10.1021/acsami.0c13898}
}
|
| Alvarez-Fernandez, A., Nallet, F., Fontaine, P., Cummins, C., Hadziioannou, G., Barois, P., Fleury, G. and Ponsinet, V. Large area Al2O3-Au raspberry-like nanoclusters from iterative block-copolymer self-assembly RSC ADVANCES 10, 67, pp. 41088-41097 (2020) |
| Abstract: In the field of functional nanomaterials, core-satellite nanoclusters
have recently elicited great interest due to their unique optoelectronic properties. However, core-satellite synthetic routes to date are hampered by delicate and multistep reaction conditions and no practical method has been reported for the ordering of these structures onto a surface monolayer. Herein we show a reproducible and simplified thin film process to fabricate bimetallic raspberry nanoclusters using block copolymer (BCP) lithography. The fabricated inorganic raspberry nanoclusters consisted of a similar to 36 nm alumina core decorated with similar to 15 nm Au satellites after infusing multilayer BCP nanopatterns. A series of cylindrical BCPs with different molecular weights allowed us to dial in specific nanodot periodicities (from 30 to 80 nm). Highly ordered BCP nanopatterns were then selectively infiltrated with alumina and Au species to develop multi-level bimetallic raspberry features. Microscopy and X-ray reflectivity analysis were used at each fabrication step to gain further mechanistic insights and understand the infiltration process. Furthermore, grazing-incidence small-angle X-ray scattering studies of infiltrated films confirmed the excellent order and vertical orientation over wafer scale areas of Al2O3/Au raspberry nanoclusters. We believe our work demonstrates a robust strategy towards designing hybrid nanoclusters since BCP blocks can be infiltrated with various low cost salt-based precursors. The highly controlled nanocluster strategy disclosed here could have wide ranging uses, in particular for metasurface and optical based sensor applications. |
BibTeX:
@article{WOS:000588975500045,
author = {Alvarez-Fernandez, Alberto and Nallet, Frederic and Fontaine, Philippe and Cummins, Cian and Hadziioannou, Georges and Barois, Philippe and Fleury, Guillaume and Ponsinet, Virginie},
title = {Large area Al2O3-Au raspberry-like nanoclusters from iterative block-copolymer self-assembly},
journal = {RSC ADVANCES},
year = {2020},
volume = {10},
number = {67},
pages = {41088-41097},
doi = {https://doi.org/10.1039/d0ra08730k}
}
|
| Prescimone, F., Benvenuti, E., Natali, M., Lorenzoni, A., Dinelli, F., Liscio, F., Milita, S., Chen, Z., Mercuri, F., Muccini, M., Facchetti, A. and Toffanin, S. 3D versus 2D Electrolyte-Semiconductor Interfaces in Rylenediimide-Based Electron-Transporting Water-Gated Organic Field-Effect Transistors ADVANCED ELECTRONIC MATERIALS 6, 12 (2020)early access (NOV 2020) |
| Abstract: Water-gated organic field-effect transistors (WGOFETs) are relevant
devices for use in the fields of biosensors and biosystems. However, real applications require very stringent performance in terms of electrochemical stability and charge mobility to the organic semiconductor in contact with an aqueous environment. Here, a comparative study of two small-molecule electron-transporting perylenediimide semiconductors, which differ only in the N-substituents named PDIF-CN2 and PDI8-CN2 is reported. The two materials present similar solid-state arrangements but, while the PDI8-CN2 shows a more 3D growth modality and electron mobility independent of the semiconductor layer thickness (approximate to 10(-4) cm(2) V-1 s(-1)), the PDIF-CN2 has an almost-2D growth modality and the mobility increases with the semiconductor film thickness, reaching a maximum value of approximate to 5 x 10(-3) cm(2) V-1 s(-1) at 30 nm. Above this thickness, the PDIF-CN2 switches to a more 3D growth modality, and the mobility drops by one order of magnitude. XRR analysis indicates that a PDIF-CN2 film can be modeled as a dense layered structure in which each layer is decoupled from the others due to the presence of fluorocarbon-chains. The availability of additional pathways for charge transport from buried layers and the 2D versus 3D growth can explain the mobility dependence on the film thickness. |
BibTeX:
@article{WOS:000587478600001,
author = {Prescimone, Federico and Benvenuti, Emilia and Natali, Marco and Lorenzoni, Andrea and Dinelli, Franco and Liscio, Fabiola and Milita, Silvia and Chen, Zhihua and Mercuri, Francesco and Muccini, Michele and Facchetti, Antonio and Toffanin, Stefano},
title = {3D versus 2D Electrolyte-Semiconductor Interfaces in Rylenediimide-Based Electron-Transporting Water-Gated Organic Field-Effect Transistors},
journal = {ADVANCED ELECTRONIC MATERIALS},
year = {2020},
volume = {6},
number = {12},
doi = {https://doi.org/10.1002/aelm.202000638}
}
|
| Weber, T., Vonk, V., Abb, M.J.S., Evertsson, J., Sandroni, M., Drnec, J., Stierle, A., Lundgren, E. and Over, H. Extraordinary Stability of IrO2(110) Ultrathin Films Supported on TiO2(110) under Cathodic Polarization JOURNAL OF PHYSICAL CHEMISTRY LETTERS 11, 21, pp. 9057-9062 (2020) |
| Abstract: Down to a cathodic potentials of -1.20 V versus the reversible hydrogen
electrode, the structure of IrO2(110) electrodes supported by TiO2(110) is found to be stable by in situ synchrotron-based X-ray diffraction. Such high cathodic potentials should lead to reduction to metallic Ir (Pourbaix diagram). From the IrO2 lattice parameters, determined during cathodic polarization in a H2SO4 electrolyte solution (pH 0.4), it is estimated that the unit cell volume increases by 1% due likely to proton incorporation, which is supported by the lack of significant swelling of the IrO2(110) film derived from X-ray reflectivity experiments. Ex situ X-ray photoelectron spectroscopy suggests that protons are incorporated into the IrO2(110) lattice below -1.0 V, although Ir remains exclusively in the IV+ oxidation state down to -1.20 V. Obviously, further hydrogenation of the lattice oxygen of IrO2(110) toward water is suppressed for kinetic reasons and hints at a rate-determining chemical step that cannot be controlled by the electrode potential. |
BibTeX:
@article{WOS:000589920000020,
author = {Weber, Tim and Vonk, Vedran and Abb, Marcel J. S. and Evertsson, Jonas and Sandroni, Martina and Drnec, Jakub and Stierle, Andreas and Lundgren, Edvin and Over, Herbert},
title = {Extraordinary Stability of IrO2(110) Ultrathin Films Supported on TiO2(110) under Cathodic Polarization},
journal = {JOURNAL OF PHYSICAL CHEMISTRY LETTERS},
year = {2020},
volume = {11},
number = {21},
pages = {9057-9062},
doi = {https://doi.org/10.1021/acs.jpclett.0c02730}
}
|
| Sarkar, P., Biswas, A., Rai, S., Srivastava, H., Mandal, S., Modi, M.H. and Bhattacharyya, D. Interface evolution of Cr/Ti multilayer films during continuous to discontinuous transition of Cr layer VACUUM 181 (2020) |
| Abstract: Cr/Ti multilayers with moderate to low bi-layer thickness have been
deposited by Ion beam sputtering system and have been investigated thoroughly by specular grazing incidence X-ray reflectivity (GIXR) and diffused X-ray scattering (both in coplanar and non-coplanar configurations) measurements. The investigation is important for development of Cr/Ti soft X-ray multilayer mirrors for ``water window'' applications in the wavelength regime of 2.2-4.4 nm. Initially few multilayers have been deposited and the highest reflectivity at first Bragg peak positions of the GIXR plots have been obtained for the Cr layer to bi-layer thickness ratio of 0.4. Subsequently, keeping the ratio fixed a set of five samples with bi-layer thickness varying from 3.8 nm to 2.1 nm have been prepared. For the all five ML samples reported in this communication, Ti layer thickness is greater than 1.3 nm, however, the Cr layer thickness varies from 1.5 to 0.8 nm in the above range of bi-layer thickness and it undergoes continuous-to discontinuous transition. Cr films undergo significant change in morphology as the thickness changes and thus the interfaces are also evolved differently. Analysis of the diffused X-ray scattering data shows that interface imperfection of Ti-on-Cr interfaces is dominated by interface diffusion at low Cr thickness (discontinuous) regime and by interface roughness at high Cr thickness (continuous) regime, while in case of Cr-on-Ti interfaces, interface roughness dominates throughout the whole thickness regime. For the sample with highest bi-layer thickness of 3.8 nm high Bragg peak reflectivity value close to the ideal case is obtained manifesting high thickness uniformity, very low interface imperfection and high vertical correlation length across the interfaces for this sample which is also confirmed by cross-sectional Transmission Electron Microscopy. A 50 bi-layer sample prepared with the above bi-layer thickness shows high reflectivity of 5.6% at 2.84 nm water window soft X-ray wavelength. |
BibTeX:
@article{WOS:000580600700016,
author = {Sarkar, P. and Biswas, A. and Rai, S. and Srivastava, H. and Mandal, S. and Modi, M. H. and Bhattacharyya, D.},
title = {Interface evolution of Cr/Ti multilayer films during continuous to discontinuous transition of Cr layer},
journal = {VACUUM},
year = {2020},
volume = {181},
doi = {https://doi.org/10.1016/j.vacuum.2020.109610}
}
|
| Ciuciulkaite, A., Mishra, K., Moro V, M., Chioar, I.-A., Rowan-Robinson, R.M., Parchenko, S., Kleibert, A., Lindgren, B., Andersson, G., Davies, C.S., Kimel, A., Berritta, M., Oppeneer, P.M., Kirilyuk, A. and Kapaklis, V. Magnetic and all-optical switching properties of amorphous TbxCo100-x alloys PHYSICAL REVIEW MATERIALS 4, 10 (2020) |
| Abstract: Amorphous TbxCo100-x magnetic alloys exhibit a list of intriguing
properties, such as perpendicular magnetic anisotropy, high magneto-optical activity, and magnetization switching using ultrashort optical pulses. Varying the Tb:Co ratio in these alloys allows for tuning properties such as the saturation magnetic moment, coercive field, and the performance of light-induced magnetization switching. In this paper, we investigate the magnetic, optical, and magneto-optical properties of various TbxCo100-x thin-film alloy compositions. We report on the effect the choice of different seeding layers has on the structural and magnetic properties of TbxCo100-x layers. We also demonstrate that for a range of alloys, deposited on fused silica substrates, with Tb content of 24-30 at. %, helicity-dependent all-optical switching of magnetization can be achieved, albeit in a multishot framework. We explain this property to arise from the helicity-dependent laser-induced magnetization on the Co sublattice due to the inverse Faraday effect. Our paper provides an insight into material aspects for future potential hybrid magnetoplasmonic TbCo-based architectures. |
BibTeX:
@article{WOS:000582803600002,
author = {Ciuciulkaite, Agne and Mishra, Kshiti and Moro, V, Marcos and Chioar, Ioan-Augustin and Rowan-Robinson, Richard M. and Parchenko, Sergii and Kleibert, Armin and Lindgren, Bengt and Andersson, Gabriella and Davies, Carl S. and Kimel, Alexey and Berritta, Marco and Oppeneer, Peter M. and Kirilyuk, Andrei and Kapaklis, Vassilios},
title = {Magnetic and all-optical switching properties of amorphous TbxCo100-x alloys},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {10},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.104418}
}
|
| Weber, T., Abb, M.J.S., Evertsson, J., Sandroni, M., Drnec, J., Vonk, V., Stierle, A., Lundgren, E. and Over, H. In situ studies of the cathodic stability of single-crystalline IrO2(110) ultrathin films supported on RuO2(110)/Ru(0001) in an acidic environment PHYSICAL CHEMISTRY CHEMICAL PHYSICS 22, 40, pp. 22956-22962 (2020) |
| Abstract: We investigate with in situ surface X-ray diffraction (SXRD) and X-ray
reflectivity (XRR) experiments the cathodic stability of an ultrathin single-crystalline IrO2(110) film with a regular array of mesoscopic rooflike structures that is supported on a RuO2(110)/Ru(0001) template. It turns out that the planarity of the single-crystalline IrO2(110) film is lost in that IrO2(110) oxide domains delaminate at a cathodic potential of -0.18 V. Obviously, the electrolyte solution is able to reach the RuO2(110) layer presumably through the surface grain boundaries of the IrO2(110) layer. Subsequently, the single-crystalline RuO2(110) structure-directing template is reduced to amorphous hydrous RuO2, with the consequence that the IrO2(110) film loses partly its adhesion to the template. From in situ XRR experiments we find that the IrO2(110) film does not swell upon cathodic polarization down to -0.18 V, while from in situ SXRD experiments, the lattice constants of IrO2(110) are shown to be not affected. The rooflike mesostructure of the IrO2(110) flakes remains intact after cathodic polarization to -0.18 V, evidencing that the crystallinity of IrO2(110) is retained. |
BibTeX:
@article{WOS:000581596800011,
author = {Weber, Tim and Abb, Marcel J. S. and Evertsson, Jonas and Sandroni, Martina and Drnec, Jakub and Vonk, Vedran and Stierle, Andreas and Lundgren, Edvin and Over, Herbert},
title = {In situ studies of the cathodic stability of single-crystalline IrO2(110) ultrathin films supported on RuO2(110)/Ru(0001) in an acidic environment},
journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
year = {2020},
volume = {22},
number = {40},
pages = {22956-22962},
doi = {https://doi.org/10.1039/d0cp03811c}
}
|
| Kotsonis, G.N., Meisenheimer, P.B., Miao, L., Roth, J., Wang, B., Shafer, P., Engel-Herbert, R., Alem, N., Heron, J.T., Rost, C.M. and Maria, J.-P. Property and cation valence engineering in entropy-stabilized oxide thin films PHYSICAL REVIEW MATERIALS 4, 10 (2020) |
| Abstract: We present data for epitaxial thin films of the prototypical
entropy-stabilized oxide (ESO), Mg0.2Ni0.2Co0.2Cu0.2Zn0.2O, that reveals a systematic trend in lattice parameter and properties as a function of substrate temperature during film growth with negligible changes in microstructure. A larger net Co valence in films grown at substrate temperatures below 350 degrees C results in a smaller lattice parameter, a smaller optical band gap, and stronger magnetic exchange bias. Observation of this phenomena suggests a complex interplay between thermodynamics and kinetics during ESO synthesis; specifically thermal history, oxygen chemical potential, and entropy. In addition to the compositional degrees of freedom available to ESO systems, subtle nuances in atomic structure at constant metallic element proportions can strongly influence properties, simultaneously complicating physical characterization and providing opportunities for property tuning and development. |
BibTeX:
@article{WOS:000579794700001,
author = {Kotsonis, George N. and Meisenheimer, Peter B. and Miao, Leixin and Roth, Joseph and Wang, Baomin and Shafer, Padraic and Engel-Herbert, Roman and Alem, Nasim and Heron, John T. and Rost, Christina M. and Maria, Jon-Paul},
title = {Property and cation valence engineering in entropy-stabilized oxide thin films},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {10},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.100401}
}
|
| Cao, Y., Waehler, T., Park, H., Will, J., Prihoda, A., Moses Badlyan, N., Fromm, L., Yokosawa, T., Wang, B., Guldi, D.M., Goerling, A., Maultzsch, J., Unruh, T., Spiecker, E., Halik, M., Libuda, J. and Bachmann, J. Area-Selective Growth of HfS(2)Thin Films via Atomic Layer Deposition at Low Temperature ADVANCED MATERIALS INTERFACES 7, 23 (2020)early access (OCT 2020) |
| Abstract: The transition-metal dichalcogenide HfS(2)is a promising alternative
semiconductor with adequate band gap and high carrier mobility. However, a controllable growth of continuous HfS(2)films with selectivity for specific surfaces at a low temperature on a large scale has not been demonstrated yet. Herein, HfS(2)films are grown at 100 degrees C by atomic layer deposition (ALD) based on the precursors tetrakis(dimethylamido)hafnium and H2S. In situ vibrational spectroscopy allows for the definition of the temperature range over which (Me2N)(4)Hf chemisorbs as one monolayer. In that range, sequential exposures of the solid surface with (Me2N)(4)Hf and H2S result in self-limiting reactions that yield alternating surface termination with dimethylamide and thiol. Repeating the cycle grows smooth, continuous, stoichiometric films of thicknesses adjustable from angstroms to >100 nm, as demonstrated by spectroscopic ellipsometry, XRR, AFM, UV-vis and Raman spectroscopy, XPS, and TEM. The well-defined surface chemistry enables one to deposit HfS(2)selectively using, for example, patterns generated in molecular self-assembled monolayers. This novel ALD reaction combines several attractive features necessary for integrating HfS(2)into devices. |
BibTeX:
@article{WOS:000579224000001,
author = {Cao, Yuanyuan and Waehler, Tobias and Park, Hyoungwon and Will, Johannes and Prihoda, Annemarie and Moses Badlyan, Narine and Fromm, Lukas and Yokosawa, Tadahiro and Wang, Bingzhe and Guldi, Dirk M. and Goerling, Andreas and Maultzsch, Janina and Unruh, Tobias and Spiecker, Erdmann and Halik, Marcus and Libuda, Joerg and Bachmann, Julien},
title = {Area-Selective Growth of HfS(2)Thin Films via Atomic Layer Deposition at Low Temperature},
journal = {ADVANCED MATERIALS INTERFACES},
year = {2020},
volume = {7},
number = {23},
doi = {https://doi.org/10.1002/admi.202001493}
}
|
| Liu, W., Huang, H., Jiang, Z., Wang, J., Yang, Y., Chen, Z., Liu, H., Huang, Q., Peng, R., Fu, Z. and Lu, Y. Interfacial Titanium Diffusion Self-Adapting Layer in Ultrathin Epitaxial MnO2/TiO2 Heterostructures ACS APPLIED MATERIALS & INTERFACES 12, 41, pp. 47010-47017 (2020) |
| Abstract: The electrochemical performance of supercapacitors is suppressed by a
large number of defects in the interface of heterostructure due to lattice mismatch. In this paper, the (001) oriented rutile MnO2 thin films with different thicknesses were grown on rutile TiO2 substrates. The lattice mismatch between film and substrate was minimized through a Ti diffusion self-adapting layer. The energy-dispersive spectroscopy mappings were used to measure the diffusion range of Ti. The results of high-resolution X-ray diffraction confirmed that the dependence of the out-of-plane lattice parameter on the thickness was consistent with the self-adapting interface model, indicating that Ti diffusion can indeed alleviate the lattice mismatch. In addition, the results of the synchrotron soft X-ray absorption spectrum indicated that the capacitance of the thin films with a large proportion of Ti diffusion increased with electrons involved in the reaction. Although the decrease of carrier density and conductivity of the thinner films depressed the electrochemical activity, it is worth mentioning that the film we designed still has considerable specific capacitance even when it is very thin, which can provide a new idea for the development of thinner and larger capacity potential micro-supercapacitors. |
BibTeX:
@article{WOS:000582345700133,
author = {Liu, Wenyi and Huang, Haoliang and Jiang, Zhongyuan and Wang, Jianlin and Yang, Yuanjun and Chen, Zezhi and Liu, Huan and Huang, Qiuping and Peng, Ranran and Fu, Zhengping and Lu, Yalin},
title = {Interfacial Titanium Diffusion Self-Adapting Layer in Ultrathin Epitaxial MnO2/TiO2 Heterostructures},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2020},
volume = {12},
number = {41},
pages = {47010-47017},
doi = {https://doi.org/10.1021/acsami.0c13532}
}
|
| Rani, P., Muscas, G., Stopfel, H., Andersson, G. and Jonsson, P.E. Rigid Exchange Coupling in Rare-Earth-Lean Amorphous Hard/Soft Nanocomposites ADVANCED ELECTRONIC MATERIALS 6, 11 (2020)early access (OCT 2020) |
| Abstract: Electrification of vehicles and renewable energy is increasing the
demand for permanent magnets, but the cost and scarcity of rare-earth metals is an obstacle. Creating nanocomposites of rigidly exchange-coupled hard and soft magnets, for which the magnetization reversal occurs as in a single magnetic-phase material, is a promising route toward rare-earth-lean permanent magnets with high energy products. The hard/soft exchange coupling is, however, often reduced due to rough interfaces and structural defects, resulting in exchange-spring behavior rather than rigid exchange coupling. Here, it is shown that artificially sandwiched hard and soft amorphous magnets produced by magnetron sputtering exhibit smooth interfaces, and the first order reversal curve (FORC) technique is used to show that the hard and the soft phases are rigidly exchange coupled. Micromagnetic simulations, using a random-anisotropy model, are used to predict the thickness limit of the rigid exchange coupling. A great advantage of amorphous hard/soft composites is the possibility to obtain a wide range of magnetic properties by finely tuning the composition of the individual phases. |
BibTeX:
@article{WOS:000578017600001,
author = {Rani, Parul and Muscas, Giuseppe and Stopfel, Henry and Andersson, Gabriella and Jonsson, Petra Erika},
title = {Rigid Exchange Coupling in Rare-Earth-Lean Amorphous Hard/Soft Nanocomposites},
journal = {ADVANCED ELECTRONIC MATERIALS},
year = {2020},
volume = {6},
number = {11},
doi = {https://doi.org/10.1002/aelm.202000573}
}
|
| Kane, A.M., Chiu, I.-T., Ahlm, N.J., Chopdekar V, R., N'Diaye, A.T., Arenholz, E., Mehta, A., Lauter, V. and Takamura, Y. Controlling Magnetization Vector Depth Profiles of La0.7Sr0.3CoO3/La0.7Sr0.3MnO3 Exchange Spring Bilayers via Interface Reconstruction ACS APPLIED MATERIALS & INTERFACES 12, 40, pp. 45437-45443 (2020) |
| Abstract: The La0.7Sr0.3CoO3-d/La0.7Sr0.3MnO3-delta (LSCO/LSMO) bilayer system is
an ideal perovskite oxide platform for investigating interface reconstruction and its effect on their magnetic properties. Previous studies have shown that LSCO can separate into magnetic sublayers, which possess distinct trends as the total LSCO thickness increases. In this study, we used polarized neutron reflectometry to quantify changes in the magnetic and chemical depth profiles, and it confirms the formation of similar to 12 angstrom-thick interfacial LSCO and LSMO layers, characterized by a decreased nuclear scattering length density compared to the bulk of the layers. This decrease is attributed to the combined effects of oxygen vacancy formation and interfacial charge transfer, which lead to magnetically active Co2+ ions with ionic radii larger than the Co3+/Co4+ ions typically found in bulk LSCO or single-layer films. The interfacial magnetization values, as well as Co2+ ion and oxygen vacancy concentrations, depend strongly on the LSCO layer thickness. These results highlight the sensitive interplay of the cation valence states, oxygen vacancy concentration, and magnetization at interfaces in perovskite oxide multilayers, demonstrating the potential to tune their functional properties via careful design of their structure. |
BibTeX:
@article{WOS:000579956100105,
author = {Kane, Alexander M. and Chiu, I-Ting and Ahlm, Nolan J. and Chopdekar, V, Rajesh and N'Diaye, Alpha T. and Arenholz, Elke and Mehta, Apurva and Lauter, Valeria and Takamura, Yayoi},
title = {Controlling Magnetization Vector Depth Profiles of La0.7Sr0.3CoO3/La0.7Sr0.3MnO3 Exchange Spring Bilayers via Interface Reconstruction},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2020},
volume = {12},
number = {40},
pages = {45437-45443},
doi = {https://doi.org/10.1021/acsami.0c09417}
}
|
| Qviller, A.J., Frommen, C., Hauback, B.C., Magnus, F., Kirby, B.J. and Hjorvarsson, B. Direct observation of magnetic proximity effects in amorphous exchange-spring magnets by neutron reflectometry PHYSICAL REVIEW MATERIALS 4, 10 (2020) |
| Abstract: In this paper, we report a direct observation of a magnetic proximity
effect in an amorphous thin-film exchange-spring magnet by the use of neutron reflectometry. The exchange-spring magnet is a trilayer consisting of two ferromagnetic layers with high T-c separated by a ferromagnetic layer, which is engineered to have a significantly lower T-c than the embedding layers. This enables us to measure magnetization depth profiles at which the low-T-c material is in a ferromagnetic or paramagnetic state, while the embedding layers are ferromagnetic. A clear proximity effect is observed 7 K above the intrinsic T-c of the embedded layer, with a range extending 50 angstrom. |
BibTeX:
@article{WOS:000579411900003,
author = {Qviller, A. J. and Frommen, C. and Hauback, B. C. and Magnus, F. and Kirby, B. J. and Hjorvarsson, B.},
title = {Direct observation of magnetic proximity effects in amorphous exchange-spring magnets by neutron reflectometry},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {10},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.104404}
}
|
| Kagerer, P., Fornari, C.I., Buchberger, S., Morelhao, S.L., Vidal, R.C., Tcakaev, A., Zabolotnyy, V., Weschke, E., Hinkov, V., Kamp, M., Buechner, B., Isaeva, A., Bentmann, H. and Reinert, F. Molecular beam epitaxy of antiferromagnetic (MnBi2Te4)(Bi2Te3) thin films on BaF2 (111) JOURNAL OF APPLIED PHYSICS 128, 13 (2020) |
| Abstract: The layered van der Waals compounds (
MnBi 2 Te 4)( Bi 2 Te 3) were recently established as the first intrinsic magnetic topological insulators. We report a study on the epitaxial growth of ( MnBi 2 Te 4 ) m ( Bi 2 Te 3 ) n films based on the co-deposition of MnTe and Bi 2 Te 3 on BaF 2 (111) substrates. X-ray diffraction and scanning transmission electron microscopy evidence the formation of multilayers of stacked MnBi 2 Te 4 septuple layers and Bi 2 Te 3 quintuple layers with a predominance of MnBi 2 Te 4. The elemental composition and morphology of the films is further characterized by x-ray photoemission spectroscopy and atomic force microscopy. X-ray magnetic circular and linear dichroism spectra are comparable to those obtained for MnBi 2 Te 4 single crystals and confirm antiferromagnetic order in the films. |
BibTeX:
@article{WOS:000578522500001,
author = {Kagerer, P. and Fornari, C. I. and Buchberger, S. and Morelhao, S. L. and Vidal, R. C. and Tcakaev, A. and Zabolotnyy, V. and Weschke, E. and Hinkov, V. and Kamp, M. and Buechner, B. and Isaeva, A. and Bentmann, H. and Reinert, F.},
title = {Molecular beam epitaxy of antiferromagnetic (MnBi2Te4)(Bi2Te3) thin films on BaF2 (111)},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2020},
volume = {128},
number = {13},
doi = {https://doi.org/10.1063/5.0025933}
}
|
| Ni, H., Huang, Q., Liu, G., Qi, R., Zhang, Z., Li, X., Li, Z., Wang, J. and Wang, Z. Comparative Study of Pd/B4C X-ray Multilayer Mirrors Fabricated by Magnetron Sputtering with Kr and Ar Gas MATERIALS 13, 20 (2020) |
| Abstract: Ultrathin Pd/B4C multilayers are suitable X-ray mirrors working at the
photon energy region of 7-20 keV. To further improve the layer structure, Pd/B4C multilayers with a d-spacing of 2.5 nm were fabricated by magnetron sputtering using the heavy noble gas Kr and compared with the conventional ones fabricated by Ar. Although the Kr-sputtering process can work at a lower pressure, the interface width-especially the interface roughness-is a little larger than that made by Ar. A stronger polycrystallization and a lower content of sputter gas atoms were found in the Kr-made sample, which can be explained by the joint effect from less recoiled particles and lower sputtering pressure. A good reflectance of 68% of the Kr made multilayer was measured at 10 keV, which is only slightly lower than that of the Ar made sample (71%). |
BibTeX:
@article{WOS:000585557300001,
author = {Ni, Hangjian and Huang, Qiushi and Liu, Genchang and Qi, Runze and Zhang, Zhong and Li, Xiuhong and Li, Zhongliang and Wang, Jie and Wang, Zhanshan},
title = {Comparative Study of Pd/B4C X-ray Multilayer Mirrors Fabricated by Magnetron Sputtering with Kr and Ar Gas},
journal = {MATERIALS},
year = {2020},
volume = {13},
number = {20},
doi = {https://doi.org/10.3390/ma13204504}
}
|
| Awana, G., Cox, C., Stuffins, L., Venkat, G., Morrison, K., Zhou, Z. and Backes, D. Magnetic and structural properties of CoFeB thin films grown by pulsed laser deposition MATERIALS RESEARCH EXPRESS 7, 10 (2020) |
| Abstract: The emergence of thin film CoFeB has driven research and industrial
applications in the past decades, with the magnetic random access memory (MRAM) the most prominent example. Because of its beneficial properties, it fulfills multiple functionalities as information-storing, spin-filtering, and reference layer in magnetic tunnel junctions. In future, this versatility can be exploited beyond the traditional applications of spintronics by combining with advanced materials, such as oxide-based materials. Pulsed laser deposition (PLD) is their predominant growth-method, and thus the compatibility of CoFeB with this growth technique will be tested here. This encompasses a comprehensive investigation of the structural and magnetic propoperties. In particular, we find a substantial `dead' magnetic layer and confirm that it is caused by oxidation employing the x-ray magnetic circular dichroism (XMCD) effect. The low damping encountered in vector network analyzer-based ferromagnetic resonance (VNA-FMR) renders them suitable for magnonics applications. These findings demonstrate that CoFeB thin films are compatible with emergent, PLD-grown materials, ensuring their relevance for future applications. |
BibTeX:
@article{WOS:000583407900001,
author = {Awana, Geet and Cox, Chris and Stuffins, Laura and Venkat, Guru and Morrison, Kelly and Zhou, Zhaoxia and Backes, Dirk},
title = {Magnetic and structural properties of CoFeB thin films grown by pulsed laser deposition},
journal = {MATERIALS RESEARCH EXPRESS},
year = {2020},
volume = {7},
number = {10},
doi = {https://doi.org/10.1088/2053-1591/abc124}
}
|
| Fallarino, L., Stienen, S., Gallardo, R.A., Arregi, J.A., Uhlir, V., Lenz, K., Huebner, R., Oelschlaegel, A., Hellwig, O. and Lindner, J. Higher-order ferromagnetic resonances in out-of-plane saturated Co/Au magnetic multilayers PHYSICAL REVIEW B 102, 9 (2020) |
| Abstract: Artificial ferromagnetic (FM)/nonmagnetic multilayers, with large enough
FM thickness to prevent the dominance of interface anisotropies, offer a straightforward insight into the understanding and control of perpendicular standing spin wave (PSSW) modes. Here we present a study of the static and dynamic magnetic properties of [Co(3.0 nm)/Au(0.6nm)](1 <= N <= 30) multilayers. Magnetometry reveals that the samples exhibit magnetization reversal properties typical of an effective single layer with weak perpendicular anisotropy, with the distinctive thickness-dependent magnetization reorientation transition from uniform in-plane to out-of-plane stripe domains at remanence. However, when such multilayer systems are out-of-plane saturated, the dynamic response reveals the existence of several different ferromagnetic resonances in the form of PSSW modes that strongly depend on the material modulation characteristics along the total thickness. These modes are induced by the layer stacking itself as the effective single layer model fails to describe the observed complex dynamics. In contrast to most systems considered in the past, described by a dynamic model of a single effectively homogeneous thick layer, the specific structures investigated here provide a unique platform for a large degree of tunability of the mode frequencies and amplitude profiles. We argue that the combination of periodic magnetic properties with vertical deformation gradients, arising from heteroepitaxial strain relaxation, converts the Au interlayer regions into a vertical regular array of magnetic pinning planes for the PSSW modes, which promotes the complex dynamics observed in this system. |
BibTeX:
@article{WOS:000572817200003,
author = {Fallarino, L. and Stienen, S. and Gallardo, R. A. and Arregi, J. A. and Uhlir, V and Lenz, K. and Huebner, R. and Oelschlaegel, A. and Hellwig, O. and Lindner, J.},
title = {Higher-order ferromagnetic resonances in out-of-plane saturated Co/Au magnetic multilayers},
journal = {PHYSICAL REVIEW B},
year = {2020},
volume = {102},
number = {9},
doi = {https://doi.org/10.1103/PhysRevB.102.094434}
}
|
| Burn, D.M., Zhang, S.L., Yu, G.Q., Guang, Y., Chen, H.J., Qiu, X.P., van der Laan, G. and Hesjedal, T. Depth-Resolved Magnetization Dynamics Revealed by X-Ray Reflectometry Ferromagnetic Resonance PHYSICAL REVIEW LETTERS 125, 13 (2020) |
| Abstract: Magnetic multilayers offer diverse opportunities for the development of
ultrafast functional devices through advanced interface and layer engineering. Nevertheless, a method for determining their dynamic properties as a function of depth throughout such stacks has remained elusive. By probing the ferromagnetic resonance modes with element-selective soft x-ray resonant reflectivity, we gain access to the magnetization dynamics as a function of depth. Most notably, using reflectometry ferromagnetic resonance, we find a phase lag between the coupled ferromagnetic layers in [CoFeB/MgO/Ta](4) multilayers that is invisible to other techniques. The use of reflectometry ferromagnetic resonance enables the time-resolved and depth-resolved probing of the complex magnetization dynamics of a wide range of functional magnetic heterostructures with absorption edges in the soft x-ray wavelength regime. |
BibTeX:
@article{WOS:000572282800006,
author = {Burn, D. M. and Zhang, S. L. and Yu, G. Q. and Guang, Y. and Chen, H. J. and Qiu, X. P. and van der Laan, G. and Hesjedal, T.},
title = {Depth-Resolved Magnetization Dynamics Revealed by X-Ray Reflectometry Ferromagnetic Resonance},
journal = {PHYSICAL REVIEW LETTERS},
year = {2020},
volume = {125},
number = {13},
doi = {https://doi.org/10.1103/PhysRevLett.125.137201}
}
|
| Pilkington, G.A., Oleshkevych, A., Pedraz, P., Watanabe, S., Radiom, M., Reddy, A.B., Vorobiev, A., Glavatskih, S. and Rutland, M.W. Electroresponsive structuring and friction of a non-halogenated ionic liquid in a polar solvent: effect of concentration PHYSICAL CHEMISTRY CHEMICAL PHYSICS 22, 34, pp. 19162-19171 (2020) |
| Abstract: Neutron reflectivity (NR) measurements have been employed to study the
interfacial structuring and composition of electroresponsive boundary layers formed by an ionic liquid (IL) lubricant at an electrified gold interface when dispersed in a polar solvent. The results reveal that both the composition and extent of the IL boundary layers intricately depend on the bulk IL concentration and the applied surface potential. At the lowest concentration (5% w/w), a preferential adsorption of the IL cation at the gold electrode is observed, which hinders the ability to electro-induce changes in the boundary layers. In contrast, at higher IL bulk concentrations (10 and 20% w/w), the NR results reveal a significantly larger concentration of the IL ions at the gold interface that exhibit significantly greater electroresponsivity, with clear changes in the layer composition and layer thickness observed for different potentials. In complementary atomic force microscopy (AFM) measurements on an electrified gold surface, such IL boundary layers are demonstrated to provide excellent friction reduction and electroactive friction (known as tribotronics). In agreement with the NR results obtained, clear concentration effects are also observed. Together such results provide valuable molecular insight into the electroactive structuring of ILs in solvent mixtures, as well as provide mechanistic understanding of their tribotronic behaviours. |
BibTeX:
@article{WOS:000567772700036,
author = {Pilkington, Georgia A. and Oleshkevych, Anna and Pedraz, Patricia and Watanabe, Seiya and Radiom, Milad and Reddy, Akepati Bhaskar and Vorobiev, Alexei and Glavatskih, Sergei and Rutland, Mark W.},
title = {Electroresponsive structuring and friction of a non-halogenated ionic liquid in a polar solvent: effect of concentration},
journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
year = {2020},
volume = {22},
number = {34},
pages = {19162-19171},
doi = {https://doi.org/10.1039/d0cp02736g}
}
|
| Hong, D., Anand, N., Liu, C., Liu, H., Arslan, I., Pearson, J.E., Bhattacharya, A. and Jiang, J.S. Large anomalous Nernst and inverse spin-Hall effects in epitaxial thin films of kagome semimetal Mn3Ge PHYSICAL REVIEW MATERIALS 4, 9 (2020) |
| Abstract: Synthesis of crystallographically well-defined thin films of topological
materials is important for unraveling their mesoscale quantum properties and for device applications. Mn3Ge, an antiferromagnetic Weyl semimetal with a chiral magnetic structure on a kagome lattice, is expected to have enhanced Berry curvature around Weyl nodes near the Fermi energy, leading to large anomalous Hall/Nernst effects and a large spin-Hall effect. Using magnetron sputtering, we have grown epitaxial thin films of hexagonal D0(19) Mn3Ge that are flat and continuous. Large anomalous Nernst and inverse spin-Hall effects are observed in thermoelectric and spin-pumping devices. The anomalous Nernst signal in our Mn3Ge films is estimated to be 0.1 mu,V/K and is comparable to that in ferromagnetic Fe, despite Mn3Ge having a weak magnetization of similar to 3.5 m mu(B)/Mn at room temperature. The spin-mixing conductance is 90.5 nm(-2) at the Py/Mn3Ge interface, and the spin-Hall angle in Mn3Ge is estimated to be about eight times of that in Pt. |
BibTeX:
@article{WOS:000572480200001,
author = {Hong, Deshun and Anand, Naween and Liu, Changjiang and Liu, Haihua and Arslan, Ilke and Pearson, John E. and Bhattacharya, Anand and Jiang, J. S.},
title = {Large anomalous Nernst and inverse spin-Hall effects in epitaxial thin films of kagome semimetal Mn3Ge},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {9},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.094201}
}
|
| Wildes, A.R., Ward, R.C.C., Wells, M.R., Hill, J.P. and Cowley, R.A. High-resolution x-ray scattering from epitaxial thin films of Y/Nb on Al2O3 JOURNAL OF PHYSICS-CONDENSED MATTER 32, 37 (2020) |
| Abstract: During the 1990s, Roger Cowley had a strong interest in the crystal and
magnetic structures of rare-earth superlattices as a means to understand the rich and exotic magnetic properties of the rare-earth metals. High-quality samples can be grown by molecular beam epitaxy on sapphire substrates by first depositing a thin epitaxial layer of niobium, then a layer of yttrium or lutetium as a seed. High-resolution x-ray scattering is an excellent probe to characterise the crystal quality and was used to study the structure of the niobium layer. However, relatively little attention was paid to the seed layer. This article summarises some of the x-ray experiments performed by the Cowley group to study the structure of epitaxial (110) niobium on (11 (2) over bar0) sapphire, and extends the work to report some results on the structure of thin (0 00 1) yttrium seed layers. The structure of the yttrium films is shown to have a strong dependence on the thickness of the niobium buffer, with the buffer needing to be thicker than a critical value of similar to 80 degrees A for the formation of misfit dislocations at the Nb/Al2O3 interface before highly coherent Y films can be grown. Yttrium films grown on Nb buffers thinner than similar to 500 degrees A show a similar two-peak line shape in q(perpendicular to) scans through their specular Bragg peaks to that seen in the specular Nb Bragg peaks, with a resolution-limited feature on a broader diffuse peak. The resolution-limited feature depends on the thickness of the yttrium film, becoming weaker and having a stronger decay with increasing q(parallel to) as the film thickness increases, while the width of the yttrium broad peak evolves as the square root of the width of the niobium Bragg peak. The data are discussed within the context of theories describing the scattering from films with misfit dislocations. |
BibTeX:
@article{WOS:000543027900001,
author = {Wildes, A. R. and Ward, R. C. C. and Wells, M. R. and Hill, J. P. and Cowley, R. A.},
title = {High-resolution x-ray scattering from epitaxial thin films of Y/Nb on Al2O3},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2020},
volume = {32},
number = {37},
doi = {https://doi.org/10.1088/1361-648X/ab6cc1}
}
|
| Chen, A., Huang, H., Wen, Y., Liu, W., Zhang, S., Kosel, J., Sun, W., Zhao, Y., Lu, Y. and Zhang, X.-X. Giant magnetoelectric effect in perpendicularly magnetized Pt/Co/Ta ultrathin films on a ferroelectric substrate MATERIALS HORIZONS 7, 9, pp. 2328-2335 (2020) |
| Abstract: Perpendicularly magnetized layers are essential for information storage
to increase the storage density. Modulating perpendicular magnetization by an electric field offers a promising solution to lower energy consumption. Here, we demonstrate a remarkable electric field modulation of perpendicular magnetization in perpendicularly magnetized Pt/Co/Ta ultrathin films on a ferroelectric substrate. By measuring the anomalous Hall effect under in situ electric fields, we observe a giant magnetoelectric effect with the large converse magnetoelectric coefficient of -2.1 x 10(-6) s m(-1) at H-perpendicular to = -20 Oe and -0.9 x 10(-6) s m(-1) at H-perpendicular to = 0 Oe, which is comparable to that in multiferroic heterostructures with in-plane magnetization. Additionally, Kerr imaging shows that electric fields observably affect magnetic domain structures of the Pt/Co/Ta ultrathin films indicating a giant magnetoelectric effect. We further measure in situ X-ray diffraction and X-ray reflectivity with electric fields, which suggests that this giant magnetoelectric effect is attributed to strain-mediated magnetoelectric coupling and is closely related to electric-field-varied interface roughness. Our findings highlight the role of interface roughness in exploring electrical control of perpendicular magnetization. |
BibTeX:
@article{WOS:000565115500022,
author = {Chen, Aitian and Huang, Haoliang and Wen, Yan and Liu, Wenyi and Zhang, Senfu and Kosel, Jurgen and Sun, Weideng and Zhao, Yonggang and Lu, Yalin and Zhang, Xi-Xiang},
title = {Giant magnetoelectric effect in perpendicularly magnetized Pt/Co/Ta ultrathin films on a ferroelectric substrate},
journal = {MATERIALS HORIZONS},
year = {2020},
volume = {7},
number = {9},
pages = {2328-2335},
doi = {https://doi.org/10.1039/d0mh00796j}
}
|
| Swindells, C., Nicholson, B., Inyang, O., Choi, Y., Hase, T. and Atkinson, D. Proximity-induced magnetism in Pt layered with rare-earth-transition-metal ferrimagnetic alloys PHYSICAL REVIEW RESEARCH 2, 3 (2020) |
| Abstract: The proximity-induced moment (PIM) in heavy metal layers may play a
significant role in heterostructured spintronic systems. In particular, the PIM of a heavy metal adjacent to a magnetic layer has been linked to interfacial spin transport behavior. Element-resolved x-ray magnetic measurements were used to investigate PIM in Pt layered with two different rare-earth (RE):3d transition-metal (TM) ferrimagnetic alloys in which the net moment was dominated by either the RE or the TM at room temperature. We observed significant PIM in Pt confined to a 2-nm interfacial region for Pt/Co77Gd23 and Pt/(Fe50Co50)(77)Gd-23 and, in both cases, the PIM was parallel to the TM sublattice rather than the RE or the net moment. Our results highlight the prominence of the d - d mediated interactions between the Pt and the constituents of the ferrimagnetic RE:TM alloys over the net macroscopic moment. |
BibTeX:
@article{WOS:000604157200008,
author = {Swindells, C. and Nicholson, B. and Inyang, O. and Choi, Y. and Hase, T. and Atkinson, D.},
title = {Proximity-induced magnetism in Pt layered with rare-earth-transition-metal ferrimagnetic alloys},
journal = {PHYSICAL REVIEW RESEARCH},
year = {2020},
volume = {2},
number = {3},
doi = {https://doi.org/10.1103/PhysRevResearch.2.033280}
}
|
| Li, W., Zhu, B., Zhu, R., Wang, Q., Lu, P., Sun, Y., Cafolla, C., Qi, Z., Chen, A., Gao, P., Wang, H., He, Q., Zhang, K.H.L. and MacManus-Driscoll, J.L. Atomic-Scale Control of Electronic Structure and Ferromagnetic Insulating State in Perovskite Oxide Superlattices by Long-Range Tuning of BO(6)Octahedra ADVANCED FUNCTIONAL MATERIALS 30, 40 (2020)early access (AUG 2020) |
| Abstract: Control of BO(6)octahedral rotations at the heterointerfaces of
dissimilar ABO(3)perovskites has emerged as a powerful route for engineering novel physical properties. However, its impact length scale is constrained at 2-6 unit cells close to the interface and the octahedral rotations relax quickly into bulk tilt angles away from interface. Here, a long-range (up to 12 unit cells) suppression of MnO(6)octahedral rotations in La(0.9)Ba(0.1)MnO(3)through the formation of superlattices with SrTiO(3)can be achieved. The suppressed MnO(6)octahedral rotations strongly modify the magnetic and electronic properties of La(0.9)Ba(0.1)MnO(3)and hence create a new ferromagnetic insulating state with enhanced Curie temperature of 235 K. The emergent properties in La(0.9)Ba(0.1)MnO(3)arise from a preferential occupation of the out-of-plane Mnd(3)(z)(-)(r)(2)(2)orbital and a reduced Mn e(g)bandwidth, induced by the suppressed octahedral rotations. The realization of long-range tuning of BO(6)octahedra via superlattices can be applicable to other strongly correlated perovskites for exploring new emergent quantum phenomena. |
BibTeX:
@article{WOS:000554485200001,
author = {Li, Weiwei and Zhu, Bonan and Zhu, Ruixue and Wang, Qiang and Lu, Ping and Sun, Yuanwei and Cafolla, Clodomiro and Qi, Zhimin and Chen, Aiping and Gao, Peng and Wang, Haiyan and He, Qing and Zhang, Kelvin H. L. and MacManus-Driscoll, Judith L.},
title = {Atomic-Scale Control of Electronic Structure and Ferromagnetic Insulating State in Perovskite Oxide Superlattices by Long-Range Tuning of BO(6)Octahedra},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2020},
volume = {30},
number = {40},
doi = {https://doi.org/10.1002/adfm.202001984}
}
|
| Zhang, J., Zhang, Y., Gao, Y., Zhao, G., Qiu, L., Wang, K., Dou, P., Peng, W., Zhuang, Y., Wu, Y., Yu, G., Zhu, Z., Zhao, Y., Guo, Y., Zhu, T., Cai, J., Shen, B. and Wang, S. Magnetic Skyrmions in a Hall Balance with Interfacial Canted Magnetizations ADVANCED MATERIALS 32, 38 (2020)early access (AUG 2020) |
| Abstract: Magnetic skyrmions are attracting interest as efficient
information-storage devices with low energy consumption, and have been experimentally and theoretically investigated in multilayers including ferromagnets, ferrimagnets, and antiferromagnets. The 3D spin texture of skyrmions demonstrated in ferromagnetic multilayers provides a powerful pathway for understanding the stabilization of ferromagnetic skyrmions. However, the manipulation mechanism of skyrmions in antiferromagnets is still lacking. A Hall balance with a ferromagnet/insulating spacer/ferromagnet structure is considered to be a promising candidate to study skyrmions in synthetic antiferromagnets. Here, high-density Neel-type skyrmions are experimentally observed at zero field and room temperature by Lorentz transmission electron microscopy in a Hall balance (core structure [Co/Pt](n)/NiO/[Co/Pt](n)) with interfacial canted magnetizations because of interlayer ferromagnetic/antiferromagnetic coupling between top and bottom [Co/Pt](n)multilayers, where the Co layers in [Co/Pt](n)are always ferromagnetically coupled. Micromagnetic simulations show that the generation and density of skyrmions are strongly dependent on interlayer exchange coupling (IEC) and easy-axis orientation. Direct experimental evidence of skyrmions in synthetic antiferromagnets is provided, suggesting that the proposed approach offers a promising alternative mechanism for room-temperature spintronics. |
BibTeX:
@article{WOS:000554475100001,
author = {Zhang, Jingyan and Zhang, Ying and Gao, Yang and Zhao, Guoping and Qiu, Lei and Wang, Kaiyou and Dou, Pengwei and Peng, Wenlin and Zhuang, Yuan and Wu, Yanfei and Yu, Guoqiang and Zhu, Zhaozhao and Zhao, Yunchi and Guo, Yaqin and Zhu, Tao and Cai, Jianwang and Shen, Baogen and Wang, Shouguo},
title = {Magnetic Skyrmions in a Hall Balance with Interfacial Canted Magnetizations},
journal = {ADVANCED MATERIALS},
year = {2020},
volume = {32},
number = {38},
doi = {https://doi.org/10.1002/adma.201907452}
}
|
| Andersson, J., Bilotto, P., Mears, L.L.E., Fossati, S., Ramach, U., Koeper, I., Valtiner, M. and Knoll, W. Solid-supported lipid bilayers - A versatile tool for the structural and functional characterization of membrane proteins METHODS 180, pp. 56-68 (2020) |
| Abstract: The cellular membrane is central to the development of single-and
multicellular life, as it separates the delicate cellular interior from the hostile environment. It exerts tight control over entry and exit of substances, is responsible for signaling with other cells in multicellular organisms and prevents pathogens from entering the cell. In the case of bacteria and viruses, the cellular membrane also hosts the proteins enabling invasion of the host organism. In a very real sense therefore, the cellular membrane is central to all life. The study of the cell membrane and membrane proteins in particular has therefore attracted significant attention. Due to the enormous variety of tasks performed by the membrane, it is a highly complex and challenging structure to study. Ideally, membrane components would be studied in isolation from this environment, but unlike water soluble proteins, the amphiphilic environment provided by the cellular membrane is key to the structure and function of the cell membrane. Therefore, model membranes have been developed to provide an environment in which a membrane protein can be studied. This review presents a set of tools that enable the comprehensive characterization of membrane proteins: electrochemical tools, surface plasmon resonance, neutron scattering, the surface forces apparatus and atomic force microscopy are discussed, with a particular focus on experimental technique and data evaluation. |
BibTeX:
@article{WOS:000579657500007,
author = {Andersson, Jakob and Bilotto, Pierluigi and Mears, Laura L. E. and Fossati, Stefan and Ramach, Ulrich and Koeper, Ingo and Valtiner, Markus and Knoll, Wolfgang},
title = {Solid-supported lipid bilayers - A versatile tool for the structural and functional characterization of membrane proteins},
journal = {METHODS},
year = {2020},
volume = {180},
pages = {56-68},
doi = {https://doi.org/10.1016/j.ymeth.2020.09.005}
}
|
| Seema, Gupta, M. and Stahn, J. Magnetization of Fe4N thin films: Suppression of interfacial intermixing using buffer layers JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 507 (2020) |
| Abstract: We studied the magnetization (M-s) of 60 nm thick polycrystalline Fe4N
thin films deposited using reactive dc magnetron sputtering. The optimum substrate temperature (T-s) to grow an stoichiometric Fe4N phase is about 673 K, in agreement with earlier works. However, at this T-s, we found that significant intermixing is taking place at the substrate-film interface, affecting the M-s of Fe4N film, adversely. We performed secondary ion mass spectroscopy (SIMS) measurements to extract the extent of such intermixing. It was found that Si from the SiO2 substrate get interdiffused into Fe4N film forming an undesired interface extending up to almost half of the film. As a result, the average M-s of Fe4N film get reduced by about 25% as compared to its theoretical value. To prohibit such intermixing, we placed thin layers of Ag, Cu, or CrN as a buffer layer between the substrate and Fe4N film. Such buffer layer suppress the extent of interdiffusion remarkably. From SIMS measurements, we found that among all buffer layers, CrN is most suitable as it reduces the extent of intermixing to a minimum level. Magnetization measurements performed using bulk magnetization and polarized neutron reflectivity (PNR) methods also clearly revealed that the M-s was the highest when CrN buffer layer was used. From these results, it becomes apparent that the intermixing taking place at the substrate-film interface plays a vital role in affecting the M-s of Fe4N thin films. To further suppress such intermixing an attempt was also made to bring down the T-s from 673 to 523 K. Obtained results are presented and discussed in this work. |
BibTeX:
@article{WOS:000531564100004,
author = {Seema and Gupta, Mukul and Stahn, Jochen},
title = {Magnetization of Fe4N thin films: Suppression of interfacial intermixing using buffer layers},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2020},
volume = {507},
doi = {https://doi.org/10.1016/j.jmmm.2020.166806}
}
|
| Cordova, D.L.M., Kam, T.M., Gannon, R.N., Lu, P. and Johnson, D.C. Controlling the Self-Assembly of New Metastable Tin Vanadium Selenides Using Composition and Nanoarchitecture of Precursors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 142, 30, pp. 13145-13154 (2020) |
| Abstract: In solid-state chemistry, the direct reaction of elements at low
temperatures is limited by low solid-state interdiffusion rates. This and the limited number of processing parameters often prevent the synthesis of metastable compounds. Precisely controlling the number of atoms and nanoarchitecture of layered elemental precursors enabled the selective synthesis of two closely related metastable tin vanadium selenides via near-diffusionless reactions at low temperatures. Although the nanoarchitectures of the precursors required to form [(SnSe2)(0.80)](1)(VSe2)(1) and [(SnSe)(1.15)](1) (VSe2)(1) are very similar, controlling the local composition of the SnISe layers in the precursors enables the selective synthesis of either compound. The metastable alloy SnxV1-xSe2 was preferentially formed over [(SnSe2)(0.80)](1)(VSe2)(1), which has the identical composition, by modifying the nanoarchitecture of the precursor. Ex situ in-plane X-ray diffraction and X-ray reflectivity collected as a function of annealing temperature provided information on lateral and perpendicular growth of [(SnSe2)(0.80)](1)(VSe2)(1). The presence of Laue oscillations throughout the self-assembly provided atomic-scale information on the thickness of the [(SnSe2)(0.80)](1)(VSe2)(1) domains, giving insights into the self-assembly process. A reaction mechanism is proposed and used to rationalize how composition and nanoarchitecture control the reaction pathway through the free energy landscape. |
BibTeX:
@article{WOS:000557854400029,
author = {Cordova, Dmitri Leo Mesoza and Kam, Taryn Mieko and Gannon, Renae N. and Lu, Ping and Johnson, David C.},
title = {Controlling the Self-Assembly of New Metastable Tin Vanadium Selenides Using Composition and Nanoarchitecture of Precursors},
journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY},
year = {2020},
volume = {142},
number = {30},
pages = {13145-13154},
doi = {https://doi.org/10.1021/jacs.0c05505}
}
|
| Cresi, J.S.P., Carla, F., Znaiguia, R., Isern, H., Benedetti, F., Gasperi, G., Amidani, L., Valeri, S., Boscherini, F. and Luches, P. Structure of Reduced Cerium Oxide Ultrathin Films on Pt(111): Local Atomic Environment and Long-Range Order ADVANCED MATERIALS INTERFACES 7, 18 (2020)early access (JUL 2020) |
| Abstract: To optimize the catalytic functionality of cerium oxide it is important
to understand the structural modifications associated with reduction and the role of the proximity of metals, which are often coupled with the oxide in the applications. For this purpose, the evolution of the short- and long-range structure of cerium oxide ultrathin epitaxial films and nanostructures supported on Pt(111) is investigated using X-ray absorption spectroscopy at the Ce L(3)edge and surface X-ray diffraction, during reduction by thermal treatments in vacuum. In epitaxial nanoislands reduction is associated with a contraction of the Ce-O distance and with the appearance of Ce-Pt bonds. The formation of a phase with a (2 x 2) periodicity after a thermal treatment at 1023 K is ascribed to the formation of a Pt5Ce alloy. Films of 3 nm thickness do not show, on average, significant structural modifications with the same thermal treatment, consistent with the hypothesis that the reduction involves only the topmost surface layers and it does not influence significantly the bulk structure of the material. This study demonstrates a strong interaction between cerium oxide and platinum, which has implications for the reactivity and stability of catalysts based on metals combined with reducible oxides. |
BibTeX:
@article{WOS:000553334000001,
author = {Cresi, Jacopo Stefano Pelli and Carla, Francesco and Znaiguia, Raja and Isern, Helena and Benedetti, Francesco and Gasperi, Gabriele and Amidani, Lucia and Valeri, Sergio and Boscherini, Federico and Luches, Paola},
title = {Structure of Reduced Cerium Oxide Ultrathin Films on Pt(111): Local Atomic Environment and Long-Range Order},
journal = {ADVANCED MATERIALS INTERFACES},
year = {2020},
volume = {7},
number = {18},
doi = {https://doi.org/10.1002/admi.202000737}
}
|
| Coffey, B.M., Nallan, H.C., Engstrom, J.R., Lam, C.H. and Ekerdt, J.G. Vacuum Ultraviolet-Enhanced Oxidation-A Route to the Atomic Layer Etching of Palladium Metal CHEMISTRY OF MATERIALS 32, 14, pp. 6035-6042 (2020) |
| Abstract: Low-temperature, plasma-free atomic layer etching (ALE) of Pd-0 is
explored. A vacuum ultraviolet (VUV) light source (115 < lambda < 400 nm) is used in conjunction with a controlled O-2 gas exposure to produce PdOx at 100 degrees C. The amount of PdOx that forms is dependent on the duration of coexposure of O-2 at 1 Torr and VUV irradiation. A minimum coexposure time of 1 min is required to partially oxidize 2 nm Pd while 3 min is required for 20 nm Pd films, which is verified in situ using X-ray photoelectron spectroscopy (XPS). Formic acid vapor is used to complete the etch cycle, which does not etch Pd-0 and only removes the PdOx that forms. Repeated etch cycles on a similar to 20 nm Pd thin film yield an etch rate of 2.81 angstrom/cycle, which is characterized in situ using XPS and ex situ using X-ray reflectivity. The morphology of the Pd-0 surface does not change appreciably with etching. The only observed effect of repeated ALE cycles is a reduction in the roughness of the Pd film, which is measured using atomic force microscopy. |
BibTeX:
@article{WOS:000557753300011,
author = {Coffey, Brennan M. and Nallan, Himamshu C. and Engstrom, James R. and Lam, Chon Hei and Ekerdt, John G.},
title = {Vacuum Ultraviolet-Enhanced Oxidation-A Route to the Atomic Layer Etching of Palladium Metal},
journal = {CHEMISTRY OF MATERIALS},
year = {2020},
volume = {32},
number = {14},
pages = {6035-6042},
doi = {https://doi.org/10.1021/acs.chemmater.0c01379}
}
|
| Wang, J., Lefler, B.M. and May, S.J. Synthesis and Characterization of SrFexMn1-x(O,F)(3-delta) Oxide (delta=0 and 0.5) and Oxyfluoride Perovskite Films INORGANIC CHEMISTRY 59, 14, pp. 9990-9997 (2020) |
| Abstract: We report the synthesis and characterization of asgrown SrFexMn1-xO2.5
epitaxial films, which were also subjected to postgrowth oxidation and topotactic fluorination to obtain SrFexMn1-xO3 and SrFexMn1-xO2.5-delta F gamma films. We show how both the B-site cation and anion composition influence the structural, electronic, and optical properties of this family of perovskite materials. The Fe substitution of Mn in SrMnO2.5 is gradually expands the c-axis parameter, as indicated by X-ray diffraction. With increasing x, the F content incorporated under identical fluorination conditions increases, reaching its maximum in SrFeO2.5-delta F gamma. In the compounds with mixed B-site occupation, the Fe 2p photoemission peaks are shifted upon fluorination, while the Mn 2p peaks are not, suggesting inductive effects lead to asymmetric responses in how F alters the Mn and Fe bonds. Electronic transport measurements reveal all compounds are insulators, with the exception of SrFeO3, and demonstrate that fluorination increases resistivity for all values of x. Optical absorption spectra in the SrFexMn1-xO2.5 and SrFexMn1-xO3 films evolve systematically as a function of x, consistent with a physical scenario in which optical changes with Fe substitution arise from a linear combination of Mn and Fe 3d bands within the electronic structure. In contrast, the F incorporation induces nonlinear changes to the optical response, suggesting a more complex impact on the electronic structure in materials with concurrent B-site and anion site substitution. |
BibTeX:
@article{WOS:000552287100053,
author = {Wang, Jiayi and Lefler, Benjamin M. and May, Steven J.},
title = {Synthesis and Characterization of SrFexMn1-x(O,F)(3-delta) Oxide (delta=0 and 0.5) and Oxyfluoride Perovskite Films},
journal = {INORGANIC CHEMISTRY},
year = {2020},
volume = {59},
number = {14},
pages = {9990-9997},
doi = {https://doi.org/10.1021/acs.inorgchem.0c01148}
}
|
| Venkat, G., Cox, C.D.W., Voneshen, D., Caruana, A.J., Piovano, A., Cropper, M.D. and Morrison, K. Magnon diffusion lengths in bulk and thin film Fe3O4 for spin Seebeck applications PHYSICAL REVIEW MATERIALS 4, 7 (2020) |
| Abstract: The magnon diffusion length (MDL) is understood to play a major role in
the thickness dependence of spin Seebeck effect (SSE) voltages in Fe3O4/Pt thin films. Here we extract the MDL in an Fe3O4 single crystal using inelastic neutron scattering (INS) and in Fe3O4/Pt thin films using accurate heat flux SSE and static magnetization measurements. The INS MDLs were 34 +/- 8 nm at 300 K and 27 +/- 6 nm at 50 K. The SSE MDLs decreased with temperature (19 +/- 2 nm at 300 K and 13 +/- 4 nm at 50 K), but were markedly smaller. Whilst the bulk MDL is expected to be an upper limit of the MDL in thin films, we show that the film magnetization must be considered to obtain MDLs from SSE measurements. This study highlights the importance of disentangling the role of various effects in SSE measurements which is crucial in increasing the efficiencies of thermomagnetic energy harvesting devices. |
BibTeX:
@article{WOS:000548459500002,
author = {Venkat, G. and Cox, C. D. W. and Voneshen, D. and Caruana, A. J. and Piovano, A. and Cropper, M. D. and Morrison, K.},
title = {Magnon diffusion lengths in bulk and thin film Fe3O4 for spin Seebeck applications},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {7},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.075402}
}
|
| Krieger, J.A., Pertsova, A., Giblin, S.R., Doebeli, M., Prokscha, T., Schneider, C.W., Suter, A., Hesjedal, T., Balatsky V, A. and Salman, Z. Proximity-Induced Odd-Frequency Superconductivity in a Topological Insulator PHYSICAL REVIEW LETTERS 125, 2 (2020) |
| Abstract: At an interface between a topological insulator (TI) and a conventional
superconductor (SC), superconductivity has been predicted to change dramatically and exhibit novel correlations. In particular, the induced superconductivity by an s-wave SC in a TI can develop an order parameter with a p-wave component. Here we present experimental evidence for an unexpected proximity-induced novel superconducting state in a thin layer of the prototypical TI, Bi2Se3 proximity coupled to Nb. From depth-resolved magnetic field measurements below the superconducting transition temperature of Nb, we observe a local enhancement of the magnetic field in Bi2Se3 that exceeds the externally applied field, thus supporting the existence of an intrinsic paramagnetic Meissner effect arising from an odd-frequency superconducting state. Our experimental results are complemented by theoretical calculations supporting the appearance of such a component at the interface which extends into the TI. This state is topologically distinct from the conventional Bardeen-Cooper-Schrieffer state it originates from. To the best of our knowledge, these findings present a first observation of bulk odd-frequency superconductivity in a TI. We thus reaffirm the potential of the TI-SC interface as a versatile platform to produce novel superconducting states. |
BibTeX:
@article{WOS:000547338400010,
author = {Krieger, Jonas A. and Pertsova, Anna and Giblin, Sean R. and Doebeli, Max and Prokscha, Thomas and Schneider, Christof W. and Suter, Andreas and Hesjedal, Thorsten and Balatsky, V, Alexander and Salman, Zaher},
title = {Proximity-Induced Odd-Frequency Superconductivity in a Topological Insulator},
journal = {PHYSICAL REVIEW LETTERS},
year = {2020},
volume = {125},
number = {2},
doi = {https://doi.org/10.1103/PhysRevLett.125.026802}
}
|
| Roth, J., Paul, A., Goldner, N., Pogrebnyakov, A., Agueda, K., Birol, T., Alem, N. and Engel-Herbert, R. Sputtered SrxNbO3 as a UV-Transparent Conducting Film ACS APPLIED MATERIALS & INTERFACES 12, 27, pp. 30520-30529 (2020) |
| Abstract: Expanding the application space of transparent electrodes toward the
ultraviolet range has been found challenging when utilizing the conventional approach to degenerately dope semiconductors with band gaps larger than ZnO or In2O3. Here, it is shown that the correlated metal SrxNbO3 with x < 1 is ideally suited as a UV-transparent electrode material, enabling UV light-emitting diodes for a wide range of applications from water disinfection to polymer curing. It is demonstrated that SrxNbO3 thin films can be grown by radio frequency (RF) sputtering and that they remain in the perovskite phase despite a sizeable Sr deficiency. The electrical and optical properties are characterized and compared to those of commonly used indium tin oxide (ITO) and Sn-doped Ga2O3 transparent conductor standards. SrxNbO3 films were found to have sheet resistances as low as 30 Omega sq(-1) with optical transmission at a wavelength of 280 nm up to 86%, marking a two-order-of-magnitude increase over the performance of traditional UV-transparent conductors. The compatibility of SrxNbO3 with a physical vapor deposition technique that is widely employed in the transparent conductor coating industry along with the robustness of the highly electrically conducting and optically transparent perovskite phase makes it an ideal transparent electrode for applications in the UV spectrum. |
BibTeX:
@article{WOS:000550633400050,
author = {Roth, Joseph and Paul, Arpita and Goldner, Nathan and Pogrebnyakov, Alexej and Agueda, Kleyser and Birol, Turan and Alem, Nasim and Engel-Herbert, Roman},
title = {Sputtered SrxNbO3 as a UV-Transparent Conducting Film},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2020},
volume = {12},
number = {27},
pages = {30520-30529},
doi = {https://doi.org/10.1021/acsami.0c04854}
}
|
| Kirk, E., Bull, C., Finizio, S., Sepehri-Amin, H., Wintz, S., Suszka, A.K., Bingham, N.S., Warnicke, P., Hono, K., Nutter, P.W., Raabe, J., Hrkac, G., Thomson, T. and Heyderman, L.J. Anisotropy-induced spin reorientation in chemically modulated amorphous ferrimagnetic films PHYSICAL REVIEW MATERIALS 4, 7 (2020) |
| Abstract: The ability to tune the competition between the in-plane and
out-of-plane orientation of magnetization provides a means to construct thermal sensors with a sharp spin reorientation transition at specific temperatures. We have observed such a tuneable, temperature-driven spin reorientation in structurally amorphous, ferrimagnetic rare-earth transition-metal alloy thin films using scanning transmission x-ray microscopy and magnetic measurements. The nature of the spin reorientation transition in FeGd can be fully explained by a nonequilibrium, nanoscale modulation of the chemical composition of the films. This modulation leads to a magnetic domain pattern of nanoscale speckles superimposed on a background of in-plane domains that form Landau configurations in mu m-scale patterned elements. It is this speckle magnetic structure that gives rise to a sharp two-step reversal mechanism that is temperature dependent. The possibility to balance competing anisotropies through the temperature opens opportunities to create and manipulate topological spin textures. |
BibTeX:
@article{WOS:000581100800003,
author = {Kirk, E. and Bull, C. and Finizio, S. and Sepehri-Amin, H. and Wintz, S. and Suszka, A. K. and Bingham, N. S. and Warnicke, P. and Hono, K. and Nutter, P. W. and Raabe, J. and Hrkac, G. and Thomson, T. and Heyderman, L. J.},
title = {Anisotropy-induced spin reorientation in chemically modulated amorphous ferrimagnetic films},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {7},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.074403}
}
|
| Choudhury, D., Mandia, D.J., Langeslay, R.R., Yanguas-Gil, A., Letourneau, S., Sattelberger, A.P., Balasubramanium, M., Mane, A.U., Delferro, M. and Elam, J.W. Atomic layer deposition of HfO2 films using carbon-free tetrakis(tetrahydroborato)hafnium and water JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 38, 4 (2020) |
| Abstract: Thin hafnium oxide films were prepared by atomic layer deposition using
a carbon-free precursor, tetrakis(tetrahydroborato)hafnium [Hf(BH4)(4)], and H2O. Film growth was studied using an in situ quartz crystal microbalance and Fourier transform infrared spectroscopy measurements. Self-limiting growth was observed between 100 and 175 degrees C, but the thermal decomposition of the Hf precursor occurred at higher temperatures. The film properties were investigated using x-ray photoelectron spectroscopy, x-ray reflectivity, x-ray diffraction, ellipsometry, time-of-flight secondary ion mass spectrometry, and x-ray absorption spectroscopy. The as-deposited films were found to consist of an amorphous mixture of HfO2 and B2O3, and had a lower density and lower refractive index compared to pure HfO2 thin films. Annealing the films to >750 degrees C yielded crystalline monoclinic HfO2 with a density of 9g/cm(3) and a refractive index of 2.10. |
BibTeX:
@article{WOS:000544059600001,
author = {Choudhury, Devika and Mandia, David J. and Langeslay, Ryan R. and Yanguas-Gil, Angel and Letourneau, Steven and Sattelberger, Alfred P. and Balasubramanium, Mahalingam and Mane, Anil U. and Delferro, Massimiliano and Elam, Jeffrey W.},
title = {Atomic layer deposition of HfO2 films using carbon-free tetrakis(tetrahydroborato)hafnium and water},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2020},
volume = {38},
number = {4},
doi = {https://doi.org/10.1116/6.0000053}
}
|
| Book, A. and Kienzle, P.A. Retrieval of the complex reflection coefficient below the critical edge for neutron reflectometry PHYSICA B-CONDENSED MATTER 588 (2020) |
| Abstract: The reference layer method allows the reconstruction of the complex
neutron reflection for thin films only above the critical edge. Without the information below the critical edge, inverting the reflection to recover the samples scattering potential is futile. To retrieve the reflection below the critical edge, a fixed-point algorithm is presented which uses only the knowledge of the total film thickness. The convergence and uniqueness of the algorithm is proven in the Born approximation and numerical studies for both realistic and random thin films are successfully carried out in the dynamical theory. |
BibTeX:
@article{WOS:000537133500014,
author = {Book, Alexander and Kienzle, Paul A.},
title = {Retrieval of the complex reflection coefficient below the critical edge for neutron reflectometry},
journal = {PHYSICA B-CONDENSED MATTER},
year = {2020},
volume = {588},
doi = {https://doi.org/10.1016/j.physb.2020.412181}
}
|
| Dippel, A.-C., Gutowski, O., Klemeyer, L., Boettger, U., Berg, F., Schneller, T., Hardtdegen, A., Aussen, S., Hoffmann-Eifert, S. and Zimmermann, M.V. Evolution of short-range order in chemically and physically grown thin film bilayer structures for electronic applications NANOSCALE 12, 24, pp. 13103-13112 (2020) |
| Abstract: Functional thin films are commonly integrated in electronic devices as
part of a multi-layer architecture. Metal/oxide/metal structurese.g.in resistive switching memory and piezoelectric microelectrochemical devices are relevant applications. The films are mostly fabricated from the vapour phase or by solution deposition. Processing conditions with a limited thermal budget typically yield nanocrystalline or amorphous layers. For these aperiodic materials, the structure is described in terms of the local atomic order on the length scale of a few chemical bonds up to several nanometres. Previous structural studies of the short-range order in thin films have addressed the simple case of single coatings on amorphous substrates. By contrast, this work demonstrates how to probe the local structure of two stacked functional layers by means of grazing incidence total X-ray scattering and pair distribution function (PDF) analysis. The key to separating the contributions of the individual thin films is the variation of the incidence angle below the critical angle of total external reflection, In this way, structural information was obtained for functional oxides on textured electrodes,i.e.PbZr(0.53)O(0.47)O(3)on Pt[111] and HfO(2)on TiN, as well as HfO2-TiO(x)bilayers. For these systems, the transformations from disordered phases into periodic structuresviathermal teatment are described. These examples highlight the opportunity to develop a detailed understanding of structural evolution during the fabrication of real thin film devices using the PDF technique. |
BibTeX:
@article{WOS:000545599900040,
author = {Dippel, Ann-Christin and Gutowski, Olof and Klemeyer, Lars and Boettger, Ulrich and Berg, Fenja and Schneller, Theodor and Hardtdegen, Alexander and Aussen, Stephan and Hoffmann-Eifert, Susanne and Zimmermann, Martin V.},
title = {Evolution of short-range order in chemically and physically grown thin film bilayer structures for electronic applications},
journal = {NANOSCALE},
year = {2020},
volume = {12},
number = {24},
pages = {13103-13112},
doi = {https://doi.org/10.1039/d0nr01847c}
}
|
| Tober, S., Creutzburg, M., Arndt, B., Krausert, K., Mattauch, S., Koutsioubas, A., Puetter, S., Mohd, A.S., Volgger, L., Hutter, H., Noei, H., Vonk, V., Lott, D. and Stierle, A. Observation of iron diffusion in the near-surface region of magnetite at 470 K PHYSICAL REVIEW RESEARCH 2, 2 (2020) |
| Abstract: Experiments are reported, which allow us to quantify the near-surface
cation diffusion in (001) oriented Fe3O4 single crystals at temperatures between 470 and 770 K. Thin homoepitaxial films of magnetite, grown using isotopically labeled Fe-57, were investigated by neutron reflectivity and time-of-flight secondary ion mass spectrometry. By heating the thin films in high vacuum to different temperatures for a well-defined time and determining the Fe-57 distribution along the surface normal, the diffusion lengths are obtained. For the investigated temperature range, diffusion constants of the order of 10(-20) m(2)/s are deduced. These results are important in view of near-surface mass transport induced by oxygen chemical potential differences occurring when magnetite is exposed to different gas atmospheres or by adsorbates. |
BibTeX:
@article{WOS:000603643500003,
author = {Tober, Steffen and Creutzburg, Marcus and Arndt, Bjoern and Krausert, Konstantin and Mattauch, Stefan and Koutsioubas, Alexandros and Puetter, Sabine and Mohd, Amir Syed and Volgger, Lukas and Hutter, Herbert and Noei, Heshmat and Vonk, Vedran and Lott, Dieter and Stierle, Andreas},
title = {Observation of iron diffusion in the near-surface region of magnetite at 470 K},
journal = {PHYSICAL REVIEW RESEARCH},
year = {2020},
volume = {2},
number = {2},
doi = {https://doi.org/10.1103/PhysRevResearch.2.023406}
}
|
| Inyang, O., Rafiq, A., Swindells, C., Ali, S. and Atkinson, D. The role of low Gd concentrations on magnetisation behaviour in rare earth:transition metal alloy films SCIENTIFIC REPORTS 10, 1 (2020) |
| Abstract: The magnetisation reversal behaviour as a function of composition was
studied in low rare earth concentration alloys. 30nm thick rare earth:transition-metal films of composition GdxCo100-x, GdxFe100-x and Gd-x(Co50Fe50)(100-x) were prepared by magnetron sputtering, where x ranged from 4 to 13 atomic%. Magnetisation behaviour was studied using MOKE and Hall hysteresis measurements. The magnetic reversal behaviour as a function of Gd content is strongly dependent on the transition metal. With increasing Gd content the film structure transitions from crystalline to amorphous and the saturation magnetisation decreases linearly. For GdCo, the reversal field, H-c, increases by less than a factor of two with Gd doping of 11%, while for Fe, the coercivity falls by a factor of ten with 8% Gd. This may be attributed to changes in the crystalline morphology. GdCoFe shows a similar trend with Gd doping for the in-plane reversal field to that of GdFe. With 13% Gd in Fe there is evidence indicating the presence of a weak perpendicular magnetic anisotropy, PMA. With Gd doping the anomalous Hall resistivity of Co, Fe and CoFe increases significantly with the largest increase observed for GdCoFe. |
BibTeX:
@article{WOS:000543956500007,
author = {Inyang, O. and Rafiq, A. and Swindells, C. and Ali, S. and Atkinson, D.},
title = {The role of low Gd concentrations on magnetisation behaviour in rare earth:transition metal alloy films},
journal = {SCIENTIFIC REPORTS},
year = {2020},
volume = {10},
number = {1},
doi = {https://doi.org/10.1038/s41598-020-66595-5}
}
|
| Qiu, C., Chen, W., Schmidt, M., Majs, F., Douglas, T.A. and Trainor, T.P. Selective Adsorption of Pb(II) on an Annealed Hematite (1102) Surface: Evidence from Crystal Truncation Rod X-ray Diffraction and Density Functional Theory ENVIRONMENTAL SCIENCE & TECHNOLOGY 54, 11, pp. 6651-6660 (2020) |
| Abstract: The Pb(II)-binding mechanism on an annealed hematite (1 (1) over bar 02)
surface was studied using crystal truncation rod (CTR) X-ray diffraction coupled with density functional theory (DFT) calculations. The best fit CTR model suggested that Pb(II) sorbed selectively to one type of edge-sharing surface site (ES2) over two other potential surface sites. From the best fit model structure, it was found that the Pb surface complex species forms a trigonal pyramid geometry. The base consists of three oxygen groups, two of which are associated with the substrate surface (O-I and O-III) and one that is a distal O extending toward solution. The trigonal pyramid geometry is slightly distorted with Pb-O bond lengths ranging from 2.21 to 2.31 angstrom and O-Pb-O bond angles ranging from 72 degrees to 75 degrees. Under this structural distortion, the nearest distance between Pb and Fe is found to be 3.39(1) angstrom. Consistent with the CTR results, DFT calculations indicate the Pb binding energy at the ES2 site is at least 0.16 eV more favorable than that at the other two potential binding sites considered. Using bond-valence rules we propose a stoichiometry of Pb(II) binding on the hematite (1 (1) over bar 02) surface which indicates proton release through the deprotonation of all oxygen groups bonding to Pb. |
BibTeX:
@article{WOS:000538420500022,
author = {Qiu, Canrong and Chen, Wei and Schmidt, Moritz and Majs, Frantisek and Douglas, Thomas A. and Trainor, Thomas P.},
title = {Selective Adsorption of Pb(II) on an Annealed Hematite (1102) Surface: Evidence from Crystal Truncation Rod X-ray Diffraction and Density Functional Theory},
journal = {ENVIRONMENTAL SCIENCE & TECHNOLOGY},
year = {2020},
volume = {54},
number = {11},
pages = {6651-6660},
doi = {https://doi.org/10.1021/acs.est.0c00060}
}
|
| Wang, L.-M., Li, Q., Liu, S., Cao, Z., Cai, Y.-P., Jiao, X., Lai, H., Xie, W., Zhan, X. and Zhu, T. Quantitative Determination of the Vertical Segregation and Molecular Ordering of PBDB-T/ITIC Blend Films with Solvent Additives ACS APPLIED MATERIALS & INTERFACES 12, 21, pp. 24165-24173 (2020) |
| Abstract: The vertical component distribution of bulk heterojunction (BHJ) active
film shows a significant impact on determining the device performance in polymer solar cells (PSCs). Processing solvent additives are well known for regulating the BHJ active layer morphology; however, there are few reports regarding the quantitative evaluation of the effect. Herein, a study of the quantitative determination of the vertical segregation in combination of molecular ordering of PBDB-T/ITIC blend films with various 1,8-diiodooctane (DIO) contents is provided. A 0.5% (volume ratio) DIO-added blend film achieves the highest power conversion efficiency of 10.75%. The reduced performance of the PSCs resulted from the excessive vertical component segregation and overcrystallization investigated by various techniques. X-ray photoelectron spectroscopy indicates that DIO aggravates the PBDB-T enrichment region at the air side. Neutron reflectivity further quantitatively figures out the phase separation effect. Although increased crystallinity of ITIC and a higher face-on ratio of PBDB-T in active layer were obtained with increased DIO content approved by grazing-incidence wide-angle X-ray scattering (GIWAXS), the enhanced vertical distribution along with the enhanced crystal size of ITIC leads to the reduced performance of the PSCs due to the reduced carrier transportation paths between donor and acceptor. |
BibTeX:
@article{WOS:000537731900054,
author = {Wang, Li-Ming and Li, Qingduan and Liu, Shengjian and Cao, Zhixiong and Cai, Yue-Peng and Jiao, Xuechen and Lai, Haojie and Xie, Weiguang and Zhan, Xiaozhi and Zhu, Tao},
title = {Quantitative Determination of the Vertical Segregation and Molecular Ordering of PBDB-T/ITIC Blend Films with Solvent Additives},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2020},
volume = {12},
number = {21},
pages = {24165-24173},
doi = {https://doi.org/10.1021/acsami.0c02843}
}
|
| Albertin, S., Gustafson, J., Zhou, J., Pfaff, S., Shipilin, M., Blomberg, S., Merte, L.R., Gutowski, O., Dippel, A.-C., Zetterberg, J., Lundgren, E. and Hejral, U. Surface optical reflectance combined with x-ray techniques during gas-surface interactions JOURNAL OF PHYSICS D-APPLIED PHYSICS 53, 22 (2020) |
| Abstract: High energy surface x-ray diffraction (HESXRD), x-ray reflectivity
(XRR), mass spectrometry (MS) and surface optical reflectance (SOR) have been combined to simultaneously obtain sub-second information on the surface structure and morphology from a Pd(100) model catalyst during in situ oxidation at elevated temperatures and pressures resulting in Pd bulk oxide formation. The results show a strong correlation between the HESXRD and SOR signal intensities during the experiment, enabling phase determination and a time-resolved thickness estimation of the oxide by HESXRD, complemented by XRR measurements. The experiments show a remarkable sensitivity of the SOR to changes in the surface phase and morphology, in particular to the initial stages of oxidation/reduction. The data imply that SOR can detect the formation of an ultrathin PdO surface oxide layer of only 2-3 angstrom thickness. |
BibTeX:
@article{WOS:000523432900001,
author = {Albertin, S. and Gustafson, J. and Zhou, J. and Pfaff, S. and Shipilin, M. and Blomberg, S. and Merte, L. R. and Gutowski, O. and Dippel, A-C and Zetterberg, J. and Lundgren, E. and Hejral, U.},
title = {Surface optical reflectance combined with x-ray techniques during gas-surface interactions},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2020},
volume = {53},
number = {22},
doi = {https://doi.org/10.1088/1361-6463/ab77df}
}
|
| Kimbell, G., Sass, P.M., Woltjes, B., Ko, E.K., Noh, T.W., Wu, W. and Robinson, J.W.A. Two-channel anomalous Hall effect in SrRuO3 PHYSICAL REVIEW MATERIALS 4, 5 (2020) |
| Abstract: The Hall effect in SrRuO3 thin films near the thickness limit for
ferromagnetism shows an extra peak in addition to the ordinary and anomalous Hall effects. This extra peak has been attributed to a topological Hall effect due to two-dimensional skyrmions in the film around the coercive field; however, the sign of the anomalous Hall effect in SrRuO3 can change as a function of saturation magnetization. Here we report Hall peaks in SrRuO3 in which volumetric magnetometry measurements and magnetic force microscopy indicate that the peaks result from the superposition of two anomalous Hall channels with opposite sign. These channels likely form due to thickness variations in SrRuO3, creating two spatially separated magnetic regions with different saturation magnetizations and coercive fields. The results are central to the development of strongly correlated materials for spintronics. |
BibTeX:
@article{WOS:000533505600002,
author = {Kimbell, Graham and Sass, Paul M. and Woltjes, Bart and Ko, Eun Kyo and Noh, Tae Won and Wu, Weida and Robinson, Jason W. A.},
title = {Two-channel anomalous Hall effect in SrRuO3},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {5},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.054414}
}
|
| Rao, R.R., Kolb, M.J., Giordano, L., Pedersen, A.F., Katayama, Y., Hwang, J., Mehta, A., You, H., Lunger, J.R., Zhou, H., Halck, N.B., Vegge, T., Chorkendorff, I., Stephens, I.E.L. and Shao-Horn, Y. Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces NATURE CATALYSIS 3, 6, pp. 516-525 (2020)early access (MAY 2020) |
| Abstract: Understanding the nature of active sites is central to controlling the
activity of a given catalyst. This work combines operando characterization and computational techniques to examine the oxygen evolution reaction mechanism on RuO2 surfaces. Understanding the nature of active sites is central to controlling (electro)catalytic activity. Here we employed surface X-ray scattering coupled with density functional theory and surface-enhanced infrared absorption spectroscopy to examine the oxygen evolution reaction on RuO2 surfaces as a function of voltage. At 1.5 V-RHE, our results suggest that there is an -OO group on the coordinatively unsaturated ruthenium (Ru-CUS) site of the (100) surface (and similarly for (110)), but adsorbed oxygen on the Ru-CUS site of (101). Density functional theory results indicate that the removal of -OO from the Ru-CUS site, which is stabilized by a hydrogen bond to a neighbouring -OH (-OO-H), could be the rate-determining step for (100) (similarly for (110)), where its reduced binding on (100) increased activity. A further reduction in binding energy on the Ru-CUS site of (101) resulted in a different rate-determining step (-O + H2O - (H+ + e(-)) -> -OO-H) and decreased activity. Our study provides molecular details on the active sites, and the influence of their local coordination environment on activity. |
BibTeX:
@article{WOS:000531778200001,
author = {Rao, Reshma R. and Kolb, Manuel J. and Giordano, Livia and Pedersen, Anders Filsoe and Katayama, Yu and Hwang, Jonathan and Mehta, Apurva and You, Hoydoo and Lunger, Jaclyn R. and Zhou, Hua and Halck, Niels Bendtsen and Vegge, Tejs and Chorkendorff, Ib and Stephens, Ifan E. L. and Shao-Horn, Yang},
title = {Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces},
journal = {NATURE CATALYSIS},
year = {2020},
volume = {3},
number = {6},
pages = {516-525},
doi = {https://doi.org/10.1038/s41929-020-0457-6}
}
|
| John, P., Rotella, H., Deparis, C., Monge, G., Georgi, F., Vennegues, P., Leroux, M. and Zuniga-Perez, J. Crystalline magnesium nitride (Mg3N2): From epitaxial growth to fundamental physical properties PHYSICAL REVIEW MATERIALS 4, 5 (2020) |
| Abstract: Single-crystalline Mg3N2 thin films are grown on MgO (100) substrates
with plasma-assisted molecular beam epitaxy. To prevent the oxidation of the Mg3N2 films and allow further physical characterization, a polycrystalline MgO cap is deposited in situ. The growth orientation of the Mg3N2 films can be tuned from (100) to (111) by changing the growth conditions, and the associated epitaxial relationships have been determined by means of x-ray diffraction. The lattice constant of Mg3N2 films has been monitored as a function of temperature from 300 to 900 K, determining thereby the linear thermal expansion coefficient. Transmission measurements indicate an optical bandgap of crystalline Mg3N2 around 2.9 eV at room temperature, consistent with diffuse reflectance measurements on micrometric Mg3N2 particles. These results demonstrate the possibility of exploiting Mg3N2 as a new crystalline semiconductor in the blue-violet range. |
BibTeX:
@article{WOS:000531460800003,
author = {John, P. and Rotella, H. and Deparis, C. and Monge, G. and Georgi, F. and Vennegues, P. and Leroux, M. and Zuniga-Perez, J.},
title = {Crystalline magnesium nitride (Mg3N2): From epitaxial growth to fundamental physical properties},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {5},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.054601}
}
|
| Zhou, Y., Kouser, S., Borisevich, A.Y., Pantelides, S.T. and May, S.J. Evidence for Interfacial Octahedral Coupling as a Route to Enhance Magnetoresistance in Perovskite Oxide Superlattices ADVANCED MATERIALS INTERFACES 7, 9 (2020) |
| Abstract: Engineering octahedral rotations in oxide heterostructures is a
promising route for controlling magnetic properties in perovskites, with recent work focusing on magnetic-ordering temperatures and magnetic anisotropies. Here the effects of interfacial octahedral coupling on magnetoresistance are demonstrated in a series of (La0.7Sr0.3MnO3)(n)/(LaFeO3)(10) superlattices grown on (001)- and (111)-oriented SrTiO3 substrates. The different crystallographic orientations allow for the interfacial octahedral connectivity to be tuned, with weaker interfacial coupling present at the (001)-oriented than the (111)-oriented structures as revealed by density functional theory calculations. In n = 14 superlattices, the effect of orientation on the physical properties is minimal with both (001)- and (111)-oriented samples exhibiting similar magnetoresistance. As the fraction of interfacial volume within the LSMO layers is increased by decreasing n, the magnetoresistive behavior of the samples diverges with significantly larger magnetoresistance magnitudes present in the (111)-oriented superlattices. The results are consistent with octahedral coupling playing a greater role in the functional properties at (111)-heterointerfaces and demonstrate a structure-driven approach to tuning interfacial magnetoresistance in complex-oxide heterostructures. |
BibTeX:
@article{WOS:000532290500015,
author = {Zhou, Yu and Kouser, Summayya and Borisevich, Albina Y. and Pantelides, Sokrates T. and May, Steven J.},
title = {Evidence for Interfacial Octahedral Coupling as a Route to Enhance Magnetoresistance in Perovskite Oxide Superlattices},
journal = {ADVANCED MATERIALS INTERFACES},
year = {2020},
volume = {7},
number = {9},
doi = {https://doi.org/10.1002/admi.201901576}
}
|
| Cappelli, E., Tromp, W.O., Walker, S.M., Tamai, A., Gibert, M., Baumberger, F. and Bruno, F.Y. A laser-ARPES study of LaNiO3 thin films grown by sputter deposition APL MATERIALS 8, 5 (2020) |
| Abstract: Thin films of the correlated transition-metal oxide LaNiO3 undergo a
metal-insulator transition when their thickness is reduced to a few unit cells. Here, we use angle-resolved photoemission spectroscopy to study the evolution of the electronic structure across this transition in a series of epitaxial LaNiO3 films of thicknesses ranging from 19 u.c. to 2 u.c. grown in situ by RF magnetron sputtering. Our data show a strong reduction in the electronic mean free path as the thickness is reduced below 5 u.c. This prevents the system from becoming electronically two-dimensional, as confirmed by the largely unchanged Fermi surface seen in our experiments. In the insulating state, we observe a strong suppression of the coherent quasiparticle peak, but no clear gap. These features resemble previous observations of the insulating state of NdNiO3. |
BibTeX:
@article{WOS:000532388200001,
author = {Cappelli, Edoardo and Tromp, Willem O. and Walker, Siobhan McKeown and Tamai, Anna and Gibert, Marta and Baumberger, Felix and Bruno, Flavio Y.},
title = {A laser-ARPES study of LaNiO3 thin films grown by sputter deposition},
journal = {APL MATERIALS},
year = {2020},
volume = {8},
number = {5},
doi = {https://doi.org/10.1063/1.5143316}
}
|
| Mergia, K., Tsompopoulou, E.O., Dellis, S., Marrows, C.H., Michelakaki, I., Kinane, C., Caruana, A., Langridge, S., Douvalis, A.P., Cabet, C. and Messoloras, S. Phase stability of Fe-5at%Cr and Fe-10at%Cr films under Fe+ ion irradiation JOURNAL OF PHYSICS-CONDENSED MATTER 32, 18 (2020) |
| Abstract: This work is within the objective of understanding the effects caused to
Fe-Cr alloys by fast Fe ion irradiation. As the penetration length of Fe ion is of the order of hundreds of nanometers, 70 nm Fe-5at%C and Fe-10at%Cr films were irradiated at room temperature with 490 keV Fe+ ions at increasing fluence corresponding to a maximum damage of 50 displacements per atom (dpa). In Fe-5at%Cr alloy the Cr solute concentration remains unaltered even after a damage of 50 dpa. In the 10at%Cr the Cr solute concentration is reduced, with the increase of damage, asymptotically to a value of 7.2 at%. |
BibTeX:
@article{WOS:000524295200002,
author = {Mergia, K. and Tsompopoulou, E. O. and Dellis, S. and Marrows, C. H. and Michelakaki, I and Kinane, C. and Caruana, A. and Langridge, S. and Douvalis, A. P. and Cabet, C. and Messoloras, S.},
title = {Phase stability of Fe-5at%Cr and Fe-10at%Cr films under Fe+ ion irradiation},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2020},
volume = {32},
number = {18},
doi = {https://doi.org/10.1088/1361-648X/ab69a1}
}
|
| Biswas, A., Abharana, N., Rai, S. and Bhattacharyya, D. Early recrystallization of Ni/Ti multilayer due to disorder in the Ni layer JOURNAL OF APPLIED PHYSICS 127, 16 (2020) |
| Abstract: Disorders present at the interfaces drive solid state amorphization
(SSA) and recrystallization in Ni/Ti multilayers. In this communication, the effect of disorders present in the bulk Ni layers is studied on SSA and recrystallization. The disorder in the Ni layers is created by sputtering Ni layers of the Ni/Ti multilayers under the mixed ambience of argon and nitrogen. It has been observed recently that the neutron optical performances of Ni/Ti graded multilayers or supermirrors can be improved by sputtering of Ni layers under the mixed ambience of argon and nitrogen. In this work, Ni/Ti periodic multilayers deposited under pure argon ambience and under mixed ambience of argon and nitrogen have been annealed under vacuum at 200 degrees C, 400 degrees C, and 600 degrees C for 2 h. All the annealed multilayer samples along with as-deposited multilayers are characterized by x-ray diffraction and grazing incidence x-ray reflectivity measurements in specular and non-specular modes. Atomic diffusion within the layers and across interfaces has been studied as a function of annealing temperature for both sets of multilayers. It is found that the interstitial nitrogen atoms present in the Ni layers play a crucial role in the diffusivity at room temperature as well as high temperature and thus influence the SSA and recrystallization phenomena. |
BibTeX:
@article{WOS:000530349300001,
author = {Biswas, A. and Abharana, N. and Rai, S. and Bhattacharyya, D.},
title = {Early recrystallization of Ni/Ti multilayer due to disorder in the Ni layer},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2020},
volume = {127},
number = {16},
doi = {https://doi.org/10.1063/5.0008177}
}
|
| Watanabe, S., Pilkington, G.A., Oleshkevych, A., Pedraz, P., Radiom, M., Welbourn, R., Glavatskih, S. and Rutland, M.W. Interfacial structuring of non-halogenated imidazolium ionic liquids at charged surfaces: effect of alkyl chain length PHYSICAL CHEMISTRY CHEMICAL PHYSICS 22, 16, pp. 8450-8460 (2020) |
| Abstract: Control of the interfacial structures of ionic liquids (ILs) at charged
interfaces is important to many of their applications, including in energy storage solutions, sensors and advanced lubrication technologies utilising electric fields. In the case of the latter, there is an increasing demand for the study of non-halogenated ILs, as many fluorinated anions have been found to produce corrosive and toxic halides under tribological conditions. Here, the interfacial structuring of a series of four imidazolium ILs ([C(n)C(1)Im]) of varying alkyl chain lengths (n = 5, 6, 7, 10), with a non-halogenated borate-based anion ([BOB]), have been studied at charged interfaces using sum frequency generation (SFG) spectroscopy and neutron reflectivity (NR). For all alkyl chain lengths, the SFG spectra show that the cation imidazolium ring responds to the surface charge by modifying its orientation with respect to the surface normal. In addition, the combination of SFG spectra with electrochemical NR measurements reveals that the longest alkyl chain length (n = 10) forms a bilayer structure at all charged interfaces, independent of the ring orientation. These results demonstrate the tunability of IL interfacial layers through the use of surface charge, as well as effect of the cation alkyl chain length, and provide valuable insight into the charge compensation mechanisms of ILs. |
BibTeX:
@article{WOS:000537175100016,
author = {Watanabe, Seiya and Pilkington, Georgia A. and Oleshkevych, Anna and Pedraz, Patricia and Radiom, Milad and Welbourn, Rebecca and Glavatskih, Sergei and Rutland, Mark W.},
title = {Interfacial structuring of non-halogenated imidazolium ionic liquids at charged surfaces: effect of alkyl chain length},
journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
year = {2020},
volume = {22},
number = {16},
pages = {8450-8460},
doi = {https://doi.org/10.1039/d0cp00360c}
}
|
| Wang, Q., Juarez-Perez, E.J., Jiang, S., Xiao, M., Qian, J., Shin, E.-Y., Noh, Y.-Y., Qi, Y., Shi, Y. and Li, Y. Approaching isotropic transfer integrals in crystalline organic semiconductors PHYSICAL REVIEW MATERIALS 4, 4 (2020) |
| Abstract: Dynamic disorders, which possess a finite charge delocalization, play a
critical role in the charge transport properties of high-mobility molecular organic semiconductors. The use of two-dimensional (2D) charge transport in crystalline organic semiconductors can effectively facilitate reducing the sensitivity of charge carriers to thermal energetic disorders existing in even single crystals to enhance the carrier mobility. An isotropic transfer integral among adjacent molecules enables a dimensional transition from quasi-one-dimensional to 2D for charge transport among molecules. Herein, a tuned molecular packing, especially molecular rotation, was achieved in highly crystalline organic thin films via a brush-coating method. This tuned molecular packing was favorable for approaching isotropic transfer integrals. Consequently, high-performance organic transistors with a carrier mobility up to 21.5 cm(2) V-1 s(-1) and low angle dependence were obtained. This work presents a unique modulation of molecular packing at the molecular scale to enable less sensitivity of the charge transport to dynamic disorders, providing an alternative route for enhancing the electrical performance of organic electronic devices. |
BibTeX:
@article{WOS:000528783700003,
author = {Wang, Qijing and Juarez-Perez, Emilio J. and Jiang, Sai and Xiao, Mingfei and Qian, Jun and Shin, Eul-Yong and Noh, Yong-Young and Qi, Yabing and Shi, Yi and Li, Yun},
title = {Approaching isotropic transfer integrals in crystalline organic semiconductors},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2020},
volume = {4},
number = {4},
doi = {https://doi.org/10.1103/PhysRevMaterials.4.044604}
}
|
| Waschk, M., Sarkar, A., Barthel, J., Voigt, J., Schroeder, S., Zakalek, P., Schmitz, M., Kirby, B.J., Puetter, S., Schubert, J. and Brueckel, T. Impact of growth kinetics on the interface morphology and magnetization in La1/3Sr2/3FeO3/La2/3Sr1/3MnO3 heterostructures JOURNAL OF PHYSICS-CONDENSED MATTER 32, 16 (2020) |
| Abstract: The ability to create atomically perfect, epitaxial heterostructures of
correlated complex perovskite oxides using state-of-art thin film deposition techniques has generated new physical phenomena at engineered interfaces. Here we report on the impact of growth kinetics on the magnetic structure and exchange coupling at the interface in heterostructures combining layers of antiferromagnetic La1/3Sr2/3FeO3 (LSFO) and ferromagnetic La2/3Sr1/3MnO3 (LSMO) on (0 0 1)-oriented SrTiO3 (STO) substrates. Two growth orders are investigated, (a) LSMO/LSFO/STO(0 0 1) and (b) LSFO/LSMO/STO(0 0 1), where the LSFO layer is grown by molecular beam epitaxy and the LSMO layer by high oxygen pressure sputtering. The interface has been investigated using electron microscopy and polarized neutron reflectometry. Interdiffusion over seven monolayers is observed in LSMO/LSFO (a) with an almost 50% reduction in magnetization at the interface and showing no exchange coupling. However, the exchange bias effect ( mT at 10 K) could be realized when the interface is atomically sharp, as in LSFO/LSMO (b). Our study therefore reveals that, even for well ordered and lattice-matched structures, the kinetics involved in the growth processes drastically influences the interface quality with a strong correlation to the magnetic properties. |
BibTeX:
@article{WOS:000520153200001,
author = {Waschk, M. and Sarkar, A. and Barthel, J. and Voigt, J. and Schroeder, S. and Zakalek, P. and Schmitz, M. and Kirby, B. J. and Puetter, S. and Schubert, J. and Brueckel, T.},
title = {Impact of growth kinetics on the interface morphology and magnetization in La1/3Sr2/3FeO3/La2/3Sr1/3MnO3 heterostructures},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2020},
volume = {32},
number = {16},
doi = {https://doi.org/10.1088/1361-648X/ab678c}
}
|
| Saerbeck, T., Huckfeldt, H., Toperverg, B.P. and Ehresmann, A. Magnetic Structure of Ion-Beam Imprinted Stripe Domains Determined by Neutron Scattering NANOMATERIALS 10, 4 (2020) |
| Abstract: We present a detailed analysis of the in-plane magnetic vector
configuration in head-to-head/tail-to-tail stripe domain patterns of nominal 5 mu m width. The patterns have been created by He-ion bombardment induced magnetic patterning of a CoFe/IrMn3 exchange bias thin-film system. Quantitative information about the chemical and magnetic structure is obtained from polarized neutron reflectometry (PNR) and off-specular scattering (OSS). The technique provides information on the magnetic vector orientation and magnitude along the lateral coordinate of the sample, as well as the chemical and magnetic layer structure as a function of depth. Additional sensitivity to magnetic features is obtained through a neutron wave field resonance, which is fully accounted for in the presented analysis. The scattering reveals a domain width imbalance of 5.3 to 3.7 mu m of virgin and bombarded stripes, respectively. Further, we report that the magnetization in the bombarded stripe significantly deviates from the head-to-head arrangement. A domain wall of 0.6 mu m with homogeneous magnetization direction is found to separate the two neighboring domains. The results contain detailed information on length scales and magnetization vectors provided by PNR and OSS in absolute units. We illustrate the complementarity of the technique to microscopy techniques for obtaining a quantitative description of imprinted magnetic domain patterns and illustrate its applicability to different sample systems. |
BibTeX:
@article{WOS:000539577200155,
author = {Saerbeck, Thomas and Huckfeldt, Henning and Toperverg, Boris P. and Ehresmann, Arno},
title = {Magnetic Structure of Ion-Beam Imprinted Stripe Domains Determined by Neutron Scattering},
journal = {NANOMATERIALS},
year = {2020},
volume = {10},
number = {4},
doi = {https://doi.org/10.3390/nano10040752}
}
|
| Al-Tawhid, A.H. and Kumah, D.P. Correlating polar distortions and interfacial charge at the polar/non-polar LaCrO3/SrTiO3 (001) interface AIP ADVANCES 10, 4 (2020) |
| Abstract: The relationship between the sheet carrier concentration, n(s), of
LaCrO3(LCO)/SrTiO3(STO) heterostructures and their structural properties has been investigated. Under low oxygen partial pressure, the STO substrate is reduced during growth as evidenced by a high n(s) of 10(16) cm(-2). By controlling the post-growth annealing conditions, heterostructures with n(s) of 10(13)-10(16) cm(-2) are achieved. The atomic-scale structure of the samples is obtained using high-resolution synchrotron x-ray diffraction measurements. For heterostructures with n(s) at or below 3 x 10(13) cm(-2), polar distortions are present within the LCO layers and increase in magnitude with a decrease in sheet carrier concentration. These distortions are absent for samples with n(s) on the order of 10(15)-10(16) cm(-2) where interfacial carriers play a role in alleviating the polar discontinuity at the LCO/STO interface. These results suggest that interfacial charge carriers and polar distortions can act as complementary mechanisms to alleviate the polar discontinuity at polar/non-polar complex oxide interfaces. |
BibTeX:
@article{WOS:000530388200001,
author = {Al-Tawhid, A. H. and Kumah, D. P.},
title = {Correlating polar distortions and interfacial charge at the polar/non-polar LaCrO3/SrTiO3 (001) interface},
journal = {AIP ADVANCES},
year = {2020},
volume = {10},
number = {4},
doi = {https://doi.org/10.1063/5.0002298}
}
|
| Penn, A.N., Koohfar, S., Kumah, D.P. and LeBeau, J.M. On the redistribution of charge in La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 multilayer thin films AIP ADVANCES 10, 4 (2020) |
| Abstract: The atomic and electronic structures of La0.7Sr0.3MnO3
(LSMO)/La0.7Sr0.3CrO3 (LSCO) multilayer thin films are investigated using aberration corrected scanning transmission electron microscopy (STEM) imaging and spectroscopy. Atomic resolution high angle annular dark-field reveals that LSMO layers have an expanded out-of-plane lattice parameter compared to compressed LSCO layers, contrasting with x-ray diffraction measurements. The expansion is found to result from preferential oxygen vacancy formation in LSMO during STEM sample preparation as determined by electron energy-loss spectroscopy. The La/Sr atom column intensity is also found to oscillate by about 4% between the LSMO and LSCO layers, indicative of La/Sr concentration variation. Using energy-dispersive x-ray spectroscopy in combination with image simulations, we confirm the La/Sr inhomogeneity and elucidate the origin of charge redistribution within the multilayer. These results illuminate the sensitivity of the technique to subtle structural, chemical, and electronic features that can arise to compensate charge imbalances in complex oxide heterostructures. |
BibTeX:
@article{WOS:000526756000001,
author = {Penn, Aubrey N. and Koohfar, Sanaz and Kumah, Divine P. and LeBeau, James M.},
title = {On the redistribution of charge in La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 multilayer thin films},
journal = {AIP ADVANCES},
year = {2020},
volume = {10},
number = {4},
doi = {https://doi.org/10.1063/1.5140352}
}
|
| Nagai, K., Anada, M., Nakanishi-Ohno, Y., Okada, M. and Wakabayashi, Y. Robust surface structure analysis with reliable uncertainty estimation using the exchange Monte Carlo method JOURNAL OF APPLIED CRYSTALLOGRAPHY 53, 2, pp. 387-392 (2020) |
| Abstract: The exchange Monte Carlo (MC) method is implemented in a surface
structure refinement software using Bayesian inference. The MC calculation successfully reproduces crystal truncation rod intensity profiles from perovskite oxide ultrathin films, which involves about 60 structure parameters, starting from a simple model structure in which the ultrathin film and substrate surface have an atomic arrangement identical to the substrate bulk crystal. This shows great tolerance of the initial model in the surface structure search. The MC software is provided on the web. One of the advantages of using the MC method is the precise estimation of uncertainty of the obtained parameters. However, the parameter uncertainty is largely underestimated when one assumes that the diffraction measurements at each scattering vector are independent. The underestimation is caused by the correlation of experimental error. A means of estimation of uncertainty based on the effective number of observations is demonstrated. |
BibTeX:
@article{WOS:000524119500009,
author = {Nagai, Kazuki and Anada, Masato and Nakanishi-Ohno, Yoshinori and Okada, Masato and Wakabayashi, Yusuke},
title = {Robust surface structure analysis with reliable uncertainty estimation using the exchange Monte Carlo method},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2020},
volume = {53},
number = {2},
pages = {387-392},
doi = {https://doi.org/10.1107/S1600576720001314}
}
|
| Mandal, S., Roy, S., Mandal, A., Ghoshal, T., Das, G., Singh, A. and Goswami, D.K. Protein-Based Flexible Moisture-Induced Energy-Harvesting Devices As Self-Biased Electronic Sensors ACS APPLIED ELECTRONIC MATERIALS 2, 3, pp. 780-789 (2020) |
| Abstract: Thin protein films of gelatin molecules grown on flexible substrates
have been utilized to fabricate moisture-induced energy-harvesting devices, which work as self-biased sensors. Adsorbed water molecules from ambient moisture generate protons inside the film. A proton transfer path is formed through the hydrogen-bonded water molecules with protein around 55% relative humidity condition, and the protons are transferred due to the gradient of absorbed water molecules within the protein films. The devices are capable of harvesting electric power up to 5.5 mu W/cm(2) with an induced voltage of 0.71 V. Our findings not only provide a futuristic clean power generation concept from protein film as flexible power generator but also demonstrate the use of the energy-harvesting devices as self-biased electronic sensors for various flexible and wearable applications. The devices showed exceptional performance as humidity sensors and have been used for flexible healthcare applications, such as continuous monitoring of breathing pattern and lateral mapping of moisture levels at the finger tip for monitoring the wound healing process. Nevertheless, the diode-like response of the devices with humidity has been found to be suitable as a self-biased humidity-controlled electronic switch. |
BibTeX:
@article{WOS:000526415200020,
author = {Mandal, Suman and Roy, Satyajit and Mandal, Ajoy and Ghoshal, Tanmay and Das, Gangadhar and Singh, Arnab and Goswami, Dipak K.},
title = {Protein-Based Flexible Moisture-Induced Energy-Harvesting Devices As Self-Biased Electronic Sensors},
journal = {ACS APPLIED ELECTRONIC MATERIALS},
year = {2020},
volume = {2},
number = {3},
pages = {780-789},
doi = {https://doi.org/10.1021/acsaelm.9b00842}
}
|
| Yi, S.-H., Huang, K.-W., Lin, H.-C. and Chen, M.-J. Low-temperature crystallization and paraelectric-ferroelectric phase transformation in nanoscale ZrO2 thin films induced by atomic layer plasma treatment JOURNAL OF MATERIALS CHEMISTRY C 8, 11, pp. 3669-3677 (2020) |
| Abstract: In recent years, Hf/ZrO2-based thin films have emerged as promising
candidates for ferroelectric materials in various applications. However, achieving ferroelectricity with a low-temperature process has remained a challenging task. In this study, the atomic layer plasma treatment (ALPT) technique, where an in situ Ar plasma treatment is introduced into each cycle of atomic layer deposition (ALD), was used to achieve crystallization and ferroelectricity in as-deposited ZrO2 thin films at a low temperature of 250 degrees C. The ALPT treatment effectively contributes to a high-temperature annealing effect, leading to enhanced crystallization and densification of the films. In addition, the ALPT process also induces a transformation from paraelectric to ferroelectric orthorhombic phase in the as-deposited ZrO2 thin films, exhibiting a high ferroelectric switching polarization of 30 mu C cm(-2) along with great endurance characteristics up to 10(8) switching cycles. This study demonstrates that ALPT is an effective approach to enhance and tailor the crystallization and dielectric characteristics of nanoscale thin films at a low temperature, which is highly advantageous and demanded in a variety of applications and research fields encompassing nanoelectronic, energy storage, and biomedical devices. |
BibTeX:
@article{WOS:000528591300004,
author = {Yi, Sheng-Han and Huang, Kuei-Wen and Lin, Hsin-Chih and Chen, Miin-Jang},
title = {Low-temperature crystallization and paraelectric-ferroelectric phase transformation in nanoscale ZrO2 thin films induced by atomic layer plasma treatment},
journal = {JOURNAL OF MATERIALS CHEMISTRY C},
year = {2020},
volume = {8},
number = {11},
pages = {3669-3677},
doi = {https://doi.org/10.1039/c9tc04801d}
}
|
| Blaschke, D., Munnik, F., Grenzer, J., Rebohle, L., Schmidt, H., Zahn, P. and Gemming, S. A correlation study of layer growth rate, thickness uniformity, stoichiometry, and hydrogen impurity level in HfO2 thin films grown by ALD between 100 degrees C and 350 degrees C APPLIED SURFACE SCIENCE 506 (2020) |
| Abstract: Hafnium oxide was deposited from tetrakis(dimethylamino)hafnium (TDMAHf)
and water by atomic layer deposition (ALD) on heated 4 `' Si wafers covered with native oxide in the temperature range from 100 degrees C to 350 degrees C. Optimized self-limiting ALD reaction and smallest hydrogen impurity level have been realized for a substrate temperature of 300 degrees C. The stoichiometry of deposited films and hydrogen impurity level were measured by elastic recoil detection analysis. The hafnium to oxygen ratio showed the expected 1:2 value. Besides hydrogen, no other impurities could be detected. Furthermore, a strong correlation between the growth rate per cycle (GPC), film uniformity and level of hydrogen impurities was observed. In addition, the characterization of the crystal structure showed the appearance of some crystallites in an amorphous matrix already for a growth temperature of 250 degrees C and a pure crystalline layer at a growth temperature of 350 degrees C. The increased crystallinity with increasing growth temperature was attributed to a higher seed concentration and a nearly constant crystal size. |
BibTeX:
@article{WOS:000512983600079,
author = {Blaschke, D. and Munnik, F. and Grenzer, J. and Rebohle, L. and Schmidt, H. and Zahn, P. and Gemming, S.},
title = {A correlation study of layer growth rate, thickness uniformity, stoichiometry, and hydrogen impurity level in HfO2 thin films grown by ALD between 100 degrees C and 350 degrees C},
journal = {APPLIED SURFACE SCIENCE},
year = {2020},
volume = {506},
doi = {https://doi.org/10.1016/j.apsusc.2019.144188}
}
|
| Chiu, I.-T., Kane, A.M., Chopdekar, R.V., Lyu, P., Mehta, A., Rouleau, C.M., N'Diaye, A.T., Arenholz, E. and Takamura, Y. Phase transitions and magnetic domain coexistence in Nd0.5Sr0.5MnO3 thin films JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 498 (2020) |
| Abstract: We present a study of the physical properties of perovskite oxide
Nd0.5Sr0.5MnO3 (NSMO) thin films grown on (110)-oriented SrTiO3 substrates. In bulk form, NSMO displays coupled magnetic and electronic transitions from paramagnetic/insulator to ferromagnetic (FM)/metal and then to antiferromagnetic (AFM)/charge-ordered insulator with decreasing temperature. In thin films, the AFM ordering only occurs when the films exist in an anisotropic strain state such as those obtained on (110)-oriented cubic substrates. In this work, resonant X-ray reflectivity, soft X-ray photoemission electron microscopy (X-PEEM), and magnetometry measurements showed that the NSMO film displays both vertical and lateral magnetic phase separation. Specifically, the film consists of three layers with different density and magnetic properties. The FM and AFM properties of the main NSMO layer were probed as a function of temperature using soft X-ray magnetic spectroscopy, and the coexistence of lateral FM and AFM domains was demonstrated at 110 K using X-PEEM. |
BibTeX:
@article{WOS:000504845300094,
author = {Chiu, I-Ting and Kane, Alexander M. and Chopdekar, Rajesh V. and Lyu, Peifen and Mehta, Apurva and Rouleau, Chris M. and N'Diaye, Alpha T. and Arenholz, Elke and Takamura, Yayoi},
title = {Phase transitions and magnetic domain coexistence in Nd0.5Sr0.5MnO3 thin films},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2020},
volume = {498},
doi = {https://doi.org/10.1016/j.jmmm.2019.166116}
}
|
| Waring, H.J., Johansson, N.A.B., Vera-Marun, I.J. and Thomson, T. Zero-field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet PHYSICAL REVIEW APPLIED 13, 3 (2020) |
| Abstract: Antiferromagnets have considerable potential as spintronic materials.
Their dynamic properties include resonant modes at frequencies higher than can be observed in conventional ferromagnetic materials. An alternative to single-phase antiferromagnets are synthetic antiferromagnets (SAFs), engineered structures of exchange-coupled ferromagnet/nonmagnet/ferromagnet trilayers. SAFs have significant advantages due to the wide-ranging tunability of their magnetic properties and inherent compatibility with current device technologies, such as those used for Spin-transfer-torque magnetic random-access memory production. Here we report the dynamic properties of fully compensated SAFs using broadband ferromagnetic resonance and demonstrate resonant optic modes in addition to the conventional acoustic (Kittel) mode. These optic modes possess the highest zero-field frequencies observed in SAFs to date with resonances of 18 and 21 GHz at the first and second peaks in antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, respectively. In contrast to previous SAF reports that focus only on the first RKKY antiferromagnetic coupling peak, we show that a higher optic mode frequency is obtained for the second antiferromagnetic coupling peak. We ascribe this to the smoother interfaces associated with a thicker nonmagnetic layer. This demonstrates the importance of interface quality to achieving high-frequency optic mode dynamics entering the subterahertz range. |
BibTeX:
@article{WOS:000519719700003,
author = {Waring, H. J. and Johansson, N. A. B. and Vera-Marun, I. J. and Thomson, T.},
title = {Zero-field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet},
journal = {PHYSICAL REVIEW APPLIED},
year = {2020},
volume = {13},
number = {3},
doi = {https://doi.org/10.1103/PhysRevApplied.13.034035}
}
|
| Vaughan, M., Satchell, N., Ali, M., Kinane, C.J., Stenning, G.B.G., Langridge, S. and Burnell, G. Origin of superconductivity at nickel-bismuth interfaces PHYSICAL REVIEW RESEARCH 2, 1 (2020) |
| Abstract: Unconventional superconductivity has been suggested to be present at the
interface between bismuth and nickel in thin-film bilayers. In this work, we study the structural, magnetic, and superconducting properties of sputter deposited Bi/Ni bilayers. As-grown, our films do not display a superconducting transition; however, when stored at room temperature, after about 14 days our bilayers develop a superconducting transition up to 3.8 K. To systematically study the effect of low temperature annealing on our bilayers, we perform structural characterization with x-ray diffraction and polarized neutron reflectometry, along with magnetometry and low-temperature electrical transport measurements on samples annealed at 70 degrees C. We show that the onset of superconductivity in our samples is coincident with the formation of ordered NiBi3 intermetallic alloy, a known s-wave superconductor. We calculate that the annealing process has an activation energy of (0.86 +/- 0.06) eV. As a consequence, gentle heating of the bilayers will cause formation of the superconducting NiBi3 at the Ni/Bi interface, which poses a challenge to studying any distinct properties of Bi/Ni bilayers without degrading that interface. |
BibTeX:
@article{WOS:000602695400003,
author = {Vaughan, Matthew and Satchell, Nathan and Ali, Mannan and Kinane, Christian J. and Stenning, Gavin B. G. and Langridge, Sean and Burnell, Gavin},
title = {Origin of superconductivity at nickel-bismuth interfaces},
journal = {PHYSICAL REVIEW RESEARCH},
year = {2020},
volume = {2},
number = {1},
doi = {https://doi.org/10.1103/PhysRevResearch.2.013270}
}
|
| Warren, J.L., Barton, C.W., Bull, C. and Thomson, T. Topography dependence of the metamagnetic phase transition in FeRh thin films SCIENTIFIC REPORTS 10, 1 (2020) |
| Abstract: The equiatomic alloy FeRh is of great scientific and technological
interest due its highly unusual first-order antiferromagnetic (AF) to ferromagnetic (FM) phase transition. Here we report an exploration of the interplay between topography and phase evolution with a comprehensive magnetic force microscopy study of nominal 50 nm thick FeRh thin films and subtractively patterned wires of width 0.2 mu m-2 mu m. In continuous films where the surface morphology had not been optimised for smoothness, the topographical variation was observed to dominate the distribution of the magnetic transition temperatures and dictates the nucleation and growth of the magnetic phases. This observation was repeated for patterned elements, where the effects of surface morphology were more significant than those of spatial confinement. These results have clear implications for future studies of low-dimensional FeRh films, as surface topography must be considered when analysing and comparing the transition behaviour of FeRh thin films. |
BibTeX:
@article{WOS:000563276200014,
author = {Warren, J. L. and Barton, C. W. and Bull, C. and Thomson, T.},
title = {Topography dependence of the metamagnetic phase transition in FeRh thin films},
journal = {SCIENTIFIC REPORTS},
year = {2020},
volume = {10},
number = {1},
doi = {https://doi.org/10.1038/s41598-020-60767-z}
}
|
| Rossi, T.C., Grolimund, D., Cannelli, O., Mancini, G.F., Bacellar, C., Kinschel, D., Rouxel, J.R., Ohannessian, N., Pergolesi, D. and Chergui, M. X-ray absorption linear dichroism at the Ti K-edge of rutile (001) TiO2 single crystal JOURNAL OF SYNCHROTRON RADIATION 27, 2, pp. 425-435 (2020) |
| Abstract: X-ray absorption linear dichroism of rutile TiO2 at the Ti K-edge
provides information about the electronic states involved in the pre-edge transitions. Here, linear dichroism with high energy resolution is analyzed in combination with ab initio finite difference method calculations and spherical tensor analysis. It provides an assignment of the three pre-edge peaks beyond the octahedral crystal field splitting approximation and estimates the spatial extension of the corresponding final states. It is then discussed for the first time the X-ray absorption (XAS) of pentacoordinated titanium atoms due to oxygen vacancies and it is found that, similarly to anatase TiO2, rutile is expected to exhibit a transition on the low-energy side of peak A3. Its apparent absence in the experiment is related to the degree of p-d orbital mixing which is small in rutile due to its centrosymmetric point group. A recent XAS linear dichroism study on anatase TiO2 single crystals has shown that peak A2 has an intrinsic origin and is due to a quadrupolar transition to the 3d energy levels. In rutile, due to its centrosymmetric point group, the corresponding peak A2 has a small dipole moment explaining the weak transition. The results are confronted with recent picosecond X-ray absorption spectroscopy on rutile TiO(2 )nanoparticles. |
BibTeX:
@article{WOS:000519725000019,
author = {Rossi, T. C. and Grolimund, D. and Cannelli, O. and Mancini, G. F. and Bacellar, C. and Kinschel, D. and Rouxel, J. R. and Ohannessian, N. and Pergolesi, D. and Chergui, M.},
title = {X-ray absorption linear dichroism at the Ti K-edge of rutile (001) TiO2 single crystal},
journal = {JOURNAL OF SYNCHROTRON RADIATION},
year = {2020},
volume = {27},
number = {2},
pages = {425-435},
doi = {https://doi.org/10.1107/S160057752000051X}
}
|
| Lin, E.L., Posadas, A.B., Zheng, L., Wu, H.W., Chen, P.-Y., Coffey, B.M., Lai, K., Demkov, A.A., Smith, D.J. and Ekerdt, J.G. Epitaxial integration of ferroelectric and conductive perovskites on silicon JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 38, 2 (2020) |
| Abstract: BaTiO3 (BTO) and LaxSr1 - xTiO3 (x <= 0.15) perovskite heterostructures
are deposited epitaxially on SrTiO3 (STO)-buffered Si(001) via atomic layer deposition (ALD) to explore the formation of a quantum metal layer between a ferroelectric film and silicon. X-ray diffraction and scanning transmission electron microscopy show the crystallinity of the heterostructure deposited by ALD. After postdeposition annealing of the La-doped STO film in ultrahigh vacuum at 600 degrees C for 5 min, x-ray photoelectron spectra show the lack of La-dopant activation when the film is deposited on 10 nm-thick BTO. The same postdeposition annealing condition activates the La-dopant when LaxSr1 - xTiO3 films are deposited on STO-buffered Si(001) surfaces consisting of 2.8 nm of STO(001) on Si(001). Annealing of LaxSr1 - xTiO3 films sandwiched between BTO and STO-buffered Si(001) layers in air at temperatures <= 350 degrees C preserves the La-dopant activation. Piezoresponse force microscopy demonstrates the ferroelectric behavior of BTO films grown on LaxSr1 - xTiO3 surfaces. Sheet resistance and capacitance-voltage measurements further demonstrate the conductivity of the LaxSr1 - xTiO3 films sandwiched between the BTO film and the Si(001) substrate. |
BibTeX:
@article{WOS:000517425200001,
author = {Lin, Edward L. and Posadas, Agham B. and Zheng, Lu and Wu, Hsin Wei and Chen, Pei-Yu and Coffey, Brennan M. and Lai, Keji and Demkov, Alexander A. and Smith, Davis J. and Ekerdt, John G.},
title = {Epitaxial integration of ferroelectric and conductive perovskites on silicon},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2020},
volume = {38},
number = {2},
doi = {https://doi.org/10.1116/1.5134077}
}
|
| Sharma, A., Hoffmann, M.A., Matthes, P., Hellwig, O., Kowol, C., Schulz, S.E., Zahn, D.R.T. and Salvan, G. Crystallization of optically thick films of CoxFe80-xB20: Evolution of optical, magneto-optical, and structural properties PHYSICAL REVIEW B 101, 5 (2020) |
| Abstract: CoFeB alloys are highly relevant materials for spintronic applications.
In this work, the crystallization of CoFeB alloys triggered by thermal annealing was investigated by x-ray diffraction techniques and scanning electron microscopy, as well as spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy for annealing temperatures ranging from 300 to 600 degrees C. The transformation of similar to 100-nm-thick CoxFe(80-x)B20 films from amorphous to polycrystalline was revealed by the sharpening of spectral features observed in optical and magneto-optical dielectric functions spectra. The influence of B on the dielectric function was assessed both experimentally and by optical modeling. By analyzing the Drude component of the optical dielectric function, a consistent trend between the charge-carrier scattering time/resistivity and the annealing temperature was observed, in agreement with the electrical investigations by means of the four-point-probe method. |
BibTeX:
@article{WOS:000517204900003,
author = {Sharma, Apoorva and Hoffmann, Maria A. and Matthes, Patrick and Hellwig, Olav and Kowol, Cornelia and Schulz, Stefan E. and Zahn, Dietrich R. T. and Salvan, Georgeta},
title = {Crystallization of optically thick films of CoxFe80-xB20: Evolution of optical, magneto-optical, and structural properties},
journal = {PHYSICAL REVIEW B},
year = {2020},
volume = {101},
number = {5},
doi = {https://doi.org/10.1103/PhysRevB.101.054438}
}
|
| Disa, A.S., Walker, F.J. and Ahn, C.H. High-Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces ADVANCED MATERIALS INTERFACES 7, 6 (2020)early access (FEB 2020) |
| Abstract: In crystalline materials, the presence of surfaces or interfaces gives
rise to crystal truncation rods (CTRs) in their X-ray diffraction patterns. While structural properties related to the bulk of a crystal are contained in the intensity and position of Bragg peaks in X-ray diffraction, CTRs carry detailed information about the atomic structure at the interface. Developments in synchrotron X-ray sources, instrumentation, and analysis procedures have made CTR measurements into extremely powerful tools to study atomic reconstructions and relaxations occurring in a wide variety of interfacial systems, with relevance to chemical and electronic functionalities. In this review, an overview of the use of CTRs in the study of atomic structure at interfaces is provided. The basic theory, measurement, and analysis of CTRs are covered and applications from the literature are highlighted. Illustrative examples include studies of complex oxide thin films and multilayers. |
BibTeX:
@article{WOS:000514373500001,
author = {Disa, Ankit S. and Walker, Frederick J. and Ahn, Charles H.},
title = {High-Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces},
journal = {ADVANCED MATERIALS INTERFACES},
year = {2020},
volume = {7},
number = {6},
doi = {https://doi.org/10.1002/admi.201901772}
}
|
| Koohfar, S., Georgescu, A.B., Hallsteinsen, I., Sachan, R., Roldan, M.A., Arenholz, E. and Kumah, D.P. Effect of strain on magnetic and orbital ordering of LaSrCrO3/LaSrMnO3 heterostructures PHYSICAL REVIEW B 101, 6 (2020) |
| Abstract: We investigate the effect of strain and film thickness on the orbital
and magnetic properties of LaSrCrO3 (LSCO)/LaSrMnO3 (LSMO) heterostructures using bulk magnetometry, soft x-ray magnetic spectroscopy, first-principles density-functional theory, high-resolution electron microscopy, and x-ray diffraction. We observe an antiparallel ordering of the magnetic moments between the ferromagnetic LSMO layers and the LSCO spacers, leading to a strain-independent ferromagnetic ground state of the LSCO/LSMO heterostructures for LSMO layers as thin as two unit cells. As the LSMO thickness is increased, a net ferromagnetic state is maintained, however, the average magnetic moment per Mn is found to be dependent on the magnitude of the substrate-induced strain. The differences in the magnetic responses are related to preferential occupation of the Mn x(2) - y(2) (in-plane) d orbitals for tensile strain and 3z(2) - r(2) (out-of-plane) orbitals under compressive strain, leading to competing ferromagnetic and antiferromagnetic exchange interactions within the LSMO layers. These results underscore the relative contributions of orbital, structural, and spin degrees of freedom and their tunability in atomically thin crystalline complex oxide layers. |
BibTeX:
@article{WOS:000514315100005,
author = {Koohfar, Sanaz and Georgescu, Alexandru B. and Hallsteinsen, Ingrid and Sachan, Ritesh and Roldan, Manuel A. and Arenholz, Elke and Kumah, Divine P.},
title = {Effect of strain on magnetic and orbital ordering of LaSrCrO3/LaSrMnO3 heterostructures},
journal = {PHYSICAL REVIEW B},
year = {2020},
volume = {101},
number = {6},
doi = {https://doi.org/10.1103/PhysRevB.101.064420}
}
|
| Yun, J., Bai, Q., Yan, Z., Chang, M., Mao, J., Zuo, Y., Yang, D., Xi, L. and Xue, D. Tailoring Multilevel-Stable Remanence States in Exchange-Biased System through Spin-Orbit Torque ADVANCED FUNCTIONAL MATERIALS 30, 15 (2020)early access (FEB 2020) |
| Abstract: Multilevel remanence states have potential applications in
ultra-high-density storage and neuromorphic computing. Continuous tailoring of the multilevel remanence states by spin-orbit torque (SOT) is reported in perpendicularly magnetized Pt/Co/IrMn heterostructures. Double-biased hysteresis loops with only one remanence state can be tuned from the positively or negatively single-biased loops by SOT controlled sign of the exchange-bias field. The remanence states associated with the heights of the sub-loops are continually changed by tuning the ratio of the positively and negatively oriented ferromagnetic domains. The multilevel storage cells are demonstrated by reading the remanent Hall resistance through changing the sign and/or the magnitude of current pulse. The synaptic plasticity behaviors for neuromorphic computing are also simulated by varying the remanent Hall resistance under the consecutive current pulses. This work demonstrates that SOT is an effective method to tailor the remanence states in the double-biased heavy metal/ferromagnetic/antiferromagnetic system. The multilevel-stable remanence states driven by SOT show potential applications in future multilevel memories and neuromorphic computing devices. |
BibTeX:
@article{WOS:000513997900001,
author = {Yun, Jijun and Bai, Qiaoning and Yan, Ze and Chang, Meixia and Mao, Jian and Zuo, Yalu and Yang, Dezheng and Xi, Li and Xue, Desheng},
title = {Tailoring Multilevel-Stable Remanence States in Exchange-Biased System through Spin-Orbit Torque},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2020},
volume = {30},
number = {15},
doi = {https://doi.org/10.1002/adfm.201909092}
}
|
| Budhathoki, S., Sapkota, A., Law, K.M., Nepal, B., Ranjit, S., Shambhu, K.C., Mewes, T. and Hauser, A.J. Low Gilbert damping and linewidth in magnetostrictive FeGa thin films JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 496 (2020) |
| Abstract: Fabrication of voltage tunable high-frequency devices using
magnetostrictive ferromagnet-piezoelectric hybrid structures requires materials with low damping and narrow linewidth to achieve low microwave loss. Galfenol exhibits superior magnetostriction, stability over a wide range of temperatures, and is free of rare earth elements, making it an economical and promising candidate, if the microwave losses can be minimized. We report the fabrication, structural and magnetic characterization, and study of dynamic properties of epitaxial FeGa thin films exhibiting an ultra-low residual linewidth, Delta H-0 = 13 +/- 1 Oe - a requirement for low microwave loss and effective damping parameter, alpha(eff), as low as 0.0065(-0.0001)(+0.0005) for the 16 nm thick film. Similarly, we found alpha(eff )= 0.0039(-0.0007)(+0.0028) and Delta H-0 = 71 +/- 1 Oe for the 24 nm thick film, demonstrating its potential for applications in magnetic memory and high frequency devices. |
BibTeX:
@article{WOS:000491941800028,
author = {Budhathoki, Sujan and Sapkota, Arjun and Law, Ka Ming and Nepal, Bhuwan and Ranjit, Smriti and Shambhu, K. C. and Mewes, Tim and Hauser, Adam J.},
title = {Low Gilbert damping and linewidth in magnetostrictive FeGa thin films},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2020},
volume = {496},
doi = {https://doi.org/10.1016/j.jmmm.2019.165906}
}
|
| Warnatz, T., Skovdal, B.E., Magnus, F., Stopfel, H., Primetzhofer, D., Stein, A., Brucas, R. and Hjorvarsson, B. The influence of diameter on the magnetic saturation in Fe84Cu16/MgO [001] multilayered islands JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 496 (2020) |
| Abstract: The saturation field of circular islands, consisting of
[Fe84Cu16/MgO](9)Fe84Cu16 multilayers, increases with decreasing diameter of the islands. When the diameter of the islands is below 450 nm the field induced changes are dominated by a coherent rotation of the moment of the Fe84Cu16 layers. For diameters of 2 mu m and larger, a signature of domain nucleation and evolution is observed. The changes in the saturation field with diameter of the islands are ascribed to the interplay between interlayer exchange coupling, stray field coupling at the edges and the crystalline anisotropy of the Fe84Cu16 layers. |
BibTeX:
@article{WOS:000491941800003,
author = {Warnatz, Tobias and Skovdal, Bjorn Erik and Magnus, Fridrik and Stopfel, Henry and Primetzhofer, Daniel and Stein, Aaron and Brucas, Rimantas and Hjorvarsson, Bjorgvin},
title = {The influence of diameter on the magnetic saturation in Fe84Cu16/MgO [001] multilayered islands},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2020},
volume = {496},
doi = {https://doi.org/10.1016/j.jmmm.2019.165864}
}
|
| Svechnikov, M. Multifitting: software for the reflectometric reconstruction of multilayer nanofilms JOURNAL OF APPLIED CRYSTALLOGRAPHY 53, 1, pp. 244-252 (2020) |
| Abstract: Multifitting is a computer program designed specifically for modeling
the optical properties (reflection, transmission, absorption) of multilayer films consisting of an arbitrary number of layers in a wide range of wavelengths. Multifitting allows a user to calculate the reflectometric curves for a given structure (direct problem) and to find the parameters of the films from the experimentally obtained curves (inverse problem), either manually or automatically. Key features of Multifitting are the ability to work simultaneously with an arbitrary number of experimental curves and an ergonomic graphical user interface that is designed for intensive daily use in the diagnosis of thin films. Multifitting is positioned by the author as the successor to the IMD program, which has become the standard tool in research and technology groups synthesizing and studying thin-film coatings. |
BibTeX:
@article{WOS:000512316900028,
author = {Svechnikov, Mikhail},
title = {Multifitting: software for the reflectometric reconstruction of multilayer nanofilms},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2020},
volume = {53},
number = {1},
pages = {244-252},
doi = {https://doi.org/10.1107/S160057671901584X}
}
|
| Pospelov, G., Van Herck, W., Burle, J., Loaiza, J.M.C., Durniak, C., Fisher, J.M., Ganeva, M., Yurov, D. and Wuttke, J. BornAgain: software for simulating and fitting grazing-incidence small-angle scattering JOURNAL OF APPLIED CRYSTALLOGRAPHY 53, 1, pp. 262-276 (2020) |
| Abstract: BornAgain is a free and open-source multi-platform software framework
for simulating and fitting X-ray and neutron reflectometry, off-specular scattering, and grazing-incidence small-angle scattering (GISAS). This paper concentrates on GISAS. Support for reflectometry and off-specular scattering has been added more recently, is still under intense development and will be described in a later publication. BornAgain supports neutron polarization and magnetic scattering. Users can define sample and instrument models through Python scripting. A large subset of the functionality is also available through a graphical user interface. This paper describes the software in terms of the realized nonfunctional and functional requirements. The web site https://www.bornagainproject.org/ provides further documentation. |
BibTeX:
@article{WOS:000512316900030,
author = {Pospelov, Gennady and Van Herck, Walter and Burle, Jan and Loaiza, Juan M. Carmona and Durniak, Celine and Fisher, Jonathan M. and Ganeva, Marina and Yurov, Dmitry and Wuttke, Joachim},
title = {BornAgain: software for simulating and fitting grazing-incidence small-angle scattering},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2020},
volume = {53},
number = {1},
pages = {262-276},
doi = {https://doi.org/10.1107/S1600576719016789}
}
|
| Hoffmann, M.A., Sharma, A., Matthes, P., Okano, S., Hellwig, O., Ecke, R., Zahn, D.R.T., Salvan, G. and Schulz, S.E. Spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy study of thermally treated Co60Fe20B20 thin films JOURNAL OF PHYSICS-CONDENSED MATTER 32, 5 (2020) |
| Abstract: We report the optical and magneto-optical properties of amorphous and
crystalline Co60Fe20B20 films with thicknesses in the range of 10 nm to 20 nm characterized using spectroscopy ellipsometry (SE) and magneto-optical Kerr effect (MOKE) spectroscopy. We derived the spectral dependence of the dielectric tensor from experimental data for samples prior and after annealing in vacuum. The features of the dielectric function can be directly related to the transitions between electronic states and the observed changes upon annealing can be ascribed to an increase of the crystalline ordering of CoFeB. |
BibTeX:
@article{WOS:000507377000001,
author = {Hoffmann, Maria A. and Sharma, Apoorva and Matthes, Patrick and Okano, Shun and Hellwig, Olav and Ecke, Ramona and Zahn, Dietrich R. T. and Salvan, Georgeta and Schulz, Stefan E.},
title = {Spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy study of thermally treated Co60Fe20B20 thin films},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2020},
volume = {32},
number = {5},
doi = {https://doi.org/10.1088/1361-648X/ab4d2f}
}
|
| Swindells, C., Hindmarch, A.T., Gallant, A.J. and Atkinson, D. Spin current propagation through ultra-thin insulating layers in multilayered ferromagnetic systems APPLIED PHYSICS LETTERS 116, 4 (2020) |
| Abstract: Spin current pumping from a ferromagnet through an insulating layer into
a heavy metal was studied in a CoFeB/ SiO 2/Pt system in relation to the thickness and interfacial structure of the insulating layer. The propagation of spin current from the ferromagnet into the heavy metal falls rapidly with sub-nanometer thicknesses of SiO 2 and is suppressed beyond a nominal thickness of 2 nm. Structural analysis shows that SiO 2 only forms a complete barrier layer beyond around 2 nm, indicating that the presence of a discontinuous insulating barrier, and not tunneling or diffusion, explains the main observations of spin-pumping with thin insulating layers. |
BibTeX:
@article{WOS:000518032900020,
author = {Swindells, C. and Hindmarch, A. T. and Gallant, A. J. and Atkinson, D.},
title = {Spin current propagation through ultra-thin insulating layers in multilayered ferromagnetic systems},
journal = {APPLIED PHYSICS LETTERS},
year = {2020},
volume = {116},
number = {4},
doi = {https://doi.org/10.1063/1.5119787}
}
|
| Yamamura, A., Fujii, H., Ogasawara, H., Nordlund, D., Takahashi, O., Kishi, Y., Ishii, H., Kobayashi, N., Niitsu, N., Blulle, B., Okamoto, T., Wakabayashi, Y., Watanabe, S. and Takeya, J. Sub-molecular structural relaxation at a physisorbed interface with monolayer organic single-crystal semiconductors COMMUNICATIONS PHYSICS 3, 1 (2020) |
| Abstract: Arranging molecules into highly symmetric, topological crystal
structures has been recognized as the best approach to functionalize electronic properties in molecular crystals, where the constituent molecules have been assumed to be rigid in shape. Here, in striking contrast, we demonstrate that the molecules in a monolayer organic crystal can undergo a significant deformation in proximity to the substrate, which is reflected by an asymmetry in the electron density profile. X-ray reflectivity and X-ray absorption spectroscopies in conjunction with density-functional theory calculations reveal that the highly planarized pi-core are deformed into a bent shape, while the bulk lattice parameters are maintained. The molecular shape change is found to be perfectly suppressed in a bilayer single crystal, which leads to a 40% increase in mobility in the bilayer crystal. Our finding of a unique, sub-molecular scale shape change in monolayer single crystals can offer possibilities for functionalizing electrical properties via nano-scale physisorption. Organic molecules exhibit intrinsic semiconducting properties as well as increased flexibility in comparison to their silicon counterparts and consequently are playing an increasing role in semiconductor technologies. Here, the authors demonstrate that monolayers of organic crystals can undergo deformation at the molecular level when in proximity to a substrate and that this has an effect on their electronic structure. |
BibTeX:
@article{WOS:000511426200001,
author = {Yamamura, Akifumi and Fujii, Hiromasa and Ogasawara, Hirohito and Nordlund, Dennis and Takahashi, Osamu and Kishi, Yuutaro and Ishii, Hiroyuki and Kobayashi, Nobuhiko and Niitsu, Naoyuki and Blulle, Balthasar and Okamoto, Toshihiro and Wakabayashi, Yusuke and Watanabe, Shun and Takeya, Jun},
title = {Sub-molecular structural relaxation at a physisorbed interface with monolayer organic single-crystal semiconductors},
journal = {COMMUNICATIONS PHYSICS},
year = {2020},
volume = {3},
number = {1},
doi = {https://doi.org/10.1038/s42005-020-0285-7}
}
|
| Cox, C.D.W., Caruana, A.J., Cropper, M.D. and Morrison, K. Anomalous Nernst effect in Co2MnSi thin films JOURNAL OF PHYSICS D-APPLIED PHYSICS 53, 3 (2020) |
| Abstract: Separation of the anomalous Nernst and spin Seebeck voltages in bilayer
devices is often problematic when both layers are metallic, and the anomalous Nernst effect (ANE) becomes non-negligible. Co2MnSi, a strong candidate for the spin generator in spin Seebeck devices, is a predicted half-metal with 100% spin polarisation at the Fermi energy, however, typically B2 or L2(1) order is needed to achieve this. We demonstrate the optimisation of thin film growth of Co2MnSi on glass, where choice of deposition and annealing temperature can promote various ordered states. The contribution from the ANE is then investigated to inform future measurements of the spin Seebeck. A maximum ANE coefficient of 0.662 ;V K-?1 is found for an A2 disordered polycrystalline Co2MnSi film. This value is comparable to ordered Heusler thin films deposited onto single crystal substrates but obtained at a far lower fabrication temperature and material cost. |
BibTeX:
@article{WOS:000499958000001,
author = {Cox, C. D. W. and Caruana, A. J. and Cropper, M. D. and Morrison, K.},
title = {Anomalous Nernst effect in Co2MnSi thin films},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2020},
volume = {53},
number = {3},
doi = {https://doi.org/10.1088/1361-6463/ab4eeb}
}
|
| Mayr, S., Ye, J., Stahn, J., Knoblich, B., Klein, O., Gilbert, D.A., Albrecht, M., Paul, A., Boeni, P. and Kreuzpaintner, W. Indications for Dzyaloshinskii-Moriya interaction at the Pd/Fe interface studied by in situ polarized neutron reflectometry PHYSICAL REVIEW B 101, 2 (2020) |
| Abstract: Using in situ polarized neutron reflectometry, the depth-resolved
evolution of the magnetism and structure in a Pd/Fe/Pd trilayer thin film is measured during growth. The initial film structure of Pd/Fe shows a small proximity-induced magnetism in the underlayer and a magnetization in the Fe layer of approximate to 1.6 mu(B) per Fe atom, less than the expected bulk value of 2.2 mu(B). Deposition of the Pd capping layer initially follows an islandlike growth mode with subsequent coalescence. With increasing Pd deposition the Fe moment and the proximity-induced magnetism in the Pd capping layer decrease. After final deposition of the Pd capping layer, the magnetic profile is structurally and magnetically symmetric across the Fe layer, with magnetism induced in Pd up to 0.92 nm from the interface. Throughout the Pd deposition the Pd/Fe/Pd trilayer structure is becoming increasingly symmetric, a fact which points to a Dzyaloshinskii-Moriya interaction as a likely cause of the observed magnetic behavior. |
BibTeX:
@article{WOS:000506582800003,
author = {Mayr, Sina and Ye, Jingfan and Stahn, Jochen and Knoblich, Birgit and Klein, Oliver and Gilbert, Dustin A. and Albrecht, Manfred and Paul, Amitesh and Boeni, Peter and Kreuzpaintner, Wolfgang},
title = {Indications for Dzyaloshinskii-Moriya interaction at the Pd/Fe interface studied by in situ polarized neutron reflectometry},
journal = {PHYSICAL REVIEW B},
year = {2020},
volume = {101},
number = {2},
doi = {https://doi.org/10.1103/PhysRevB.101.024404}
}
|
| Callori, S.J., Saerbeck, T., Cortie, D.L. and Lin, K.-W. Using polarized neutron reflectometry to resolve effects of light elements and ion exposure on magnetization 71SOLID STATE PHYSICS, VOL 71, pp. 72-115 (2020) |
BibTeX:
@incollection{WOS:000608763100004,
author = {Callori, Sara J. and Saerbeck, Thomas and Cortie, David L. and Lin, Ko-Wei},
title = {Using polarized neutron reflectometry to resolve effects of light elements and ion exposure on magnetization},
booktitle = {SOLID STATE PHYSICS, VOL 71},
year = {2020},
volume = {71},
pages = {72-115},
doi = {https://doi.org/10.1016/bs.ssp.2020.09.002}
}
|
| Zhong, Y., Kurokawa, Y., Nagashima, G., Horiike, S., Hanashima, T., Schoenke, D., Krautscheid, P., Reeve, R.M., Klaeui, M. and Yuasa, H. Determination of fine magnetic structure of magnetic multilayer with quasi antiferromagnetic layer by using polarized neutron reflectivity analysis AIP ADVANCES 10, 1 (2020) |
| Abstract: We carried out polarized neutron reflectivity (PNR) analysis to
determine the fine magnetic structure of magnetic multilayers with quasi-antiferromagnetic (quasi-AFM) layers realized by 90-deg coupling using two Co90Fe10 layers, and quantitatively evaluated the magnetization of quasi-AFM layers. Two types of samples with different buffer layers, Ru buffer and a NiFeCr buffer, were investigated and the average angles between the respective magnetization of the two Co90Fe10 layers were estimated to be +/- 39 degrees and +/- 53 degrees. In addition, less roughness was found in the NiFeCr buffer sample resulting stronger 90-deg coupling. A perfect quasi-AFM is expected to be realized by a flat interface of the magnetic multilayer. (C) 2020 Author(s). |
BibTeX:
@article{WOS:000525829300130,
author = {Zhong, Yongshi and Kurokawa, Yuichiro and Nagashima, Gen and Horiike, Shu and Hanashima, Takayasu and Schoenke, Daniel and Krautscheid, Pascal and Reeve, Robert M. and Klaeui, Mathias and Yuasa, Hiromi},
title = {Determination of fine magnetic structure of magnetic multilayer with quasi antiferromagnetic layer by using polarized neutron reflectivity analysis},
journal = {AIP ADVANCES},
year = {2020},
volume = {10},
number = {1},
note = {64th Annual Conference on Magnetism and Magnetic Materials (MMM), Las Vegas, NV, NOV 04-08, 2019},
doi = {https://doi.org/10.1063/1.5130445}
}
|
| Morley, S.A., Marquez, H. and Lederman, D. Epitaxial strain and the magnetic properties of canted antiferromagnetic perovskite NaNiF3 thin films APL MATERIALS 8, 1 (2020) |
| Abstract: The perovskite crystal structure is known to exhibit a multitude of
interesting physical phenomena owing to the intricate coupling of the electronic and magnetic properties to the structure. Fluoroperovskites offer an alternative chemistry to the much more widely studied oxide materials, which may prove advantageous for applications. It is demonstrated here for the first time that the antiferromagnetic perovskite fluoride, NaNiF3, can be synthesized in thin film form. The films were grown via molecular beam epitaxy on SrTiO3 (100) substrates to produce high quality epitaxial films in the thickness range of 5-50 nm. The Pnma structure of the films was confirmed by x-ray diffraction. There was a decrease in the out-of-plane lattice spacing from the bulk value corresponding to a maximum strain of 1.7% in the thinnest film. Canted antiferromagnetism was measured in all films using magnetometry and a negative change in the antiferromagnetic ordering temperature of Delta T-N = - 9.1 +/- 0.7 K was observed with increasing strain. |
BibTeX:
@article{WOS:000519597800001,
author = {Morley, Sophie A. and Marquez, Humberto and Lederman, David},
title = {Epitaxial strain and the magnetic properties of canted antiferromagnetic perovskite NaNiF3 thin films},
journal = {APL MATERIALS},
year = {2020},
volume = {8},
number = {1},
doi = {https://doi.org/10.1063/1.5126601}
}
|
| Granovskii, A.B., Soboleva, E.A., Fadeev, E.A., Dubenko, I.S., Aryal, A., Samassekou, H., Pandey, S., Stadler, S., Mazumdar, D., Ali, N. and Lahderanta, E. Martensitic Phase Transition in Magnetic Thin Films Based on Inverse Mn2FeSi Heusler Alloys JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 130, 1, pp. 117-122 (2020) |
| Abstract: Magnetic Heusler alloys X(2)BZ (where X and B are 3d elements and Z
belongs to the sp group) exhibit diverse magnetic and structural properties, which are important for designing multifunctional smart materials. Electronic band structure calculations demonstrate that, if the valence of element B is higher than that of element X, such alloys (so-called inverse Heusler alloys) can behave differently as compared to traditional Heusler alloys. The growth, the crystal structure, and the magnetic properties of thin films of a new Mn2FeSi Heusler alloy deposited under various conditions (including various substrates and annealing temperatures) are studied in this work. A temperature-induced structural transition into a low-magnetization martensitic phase and a thermally stable austenitic phase are detected. A magnetic field of 500 Oe applied to some samples at a temperature of 380 K is found to cause a large exchange bias (about 1 kOe) at T = 10 K. The influence of the type of substrate and the annealing temperature on the magnetic and structural properties of the films is discussed. |
BibTeX:
@article{WOS:000519349400016,
author = {Granovskii, A. B. and Soboleva, E. A. and Fadeev, E. A. and Dubenko, I. S. and Aryal, A. and Samassekou, H. and Pandey, S. and Stadler, S. and Mazumdar, D. and Ali, N. and Lahderanta, E.},
title = {Martensitic Phase Transition in Magnetic Thin Films Based on Inverse Mn2FeSi Heusler Alloys},
journal = {JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS},
year = {2020},
volume = {130},
number = {1},
pages = {117-122},
doi = {https://doi.org/10.1134/S1063776119120033}
}
|
| LaTorre, A., Kwong, M.T., Garcia-Grajales, J.A., Shi, R., Jerusalem, A. and Pena, J.-M. Model calibration using a parallel differential evolution algorithm in computational neuroscience: Simulation of stretch induced nerve deficit JOURNAL OF COMPUTATIONAL SCIENCE 39 (2020) |
| Abstract: Neuronal damage, in the form of both brain and spinal cord injuries, is
one of the major causes of disability and death in young adults worldwide. One way to assess the direct damage occurring after a mechanical insult is the simulation of the neuronal cells functional deficits following the mechanical event. In this study, we use a coupled electrophysiological-mechanical model with several free parameters that are required to be calibrated against experimental results. The calibration is carried out by means of an evolutionary algorithm (differential evolution, DE) that needs to evaluate each configuration of parameters on six different damage cases, each of them taking several minutes to compute. To minimise the simulation time of the parameter tuning for the DE, the stretch of one unique fixed-diameter axon with a simplified triggering process is used to speed up the calculations. The model is then leveraged for the parameter optimization of the more realistic bundle of independent axons, an impractical configuration to run on a single processor computer. To this end, we have developed a parallel implementation based on OpenMP that runs on a multi-processor taking advantage of all the available computational power. The parallel DE algorithm obtains good results, outperforming the best effort achieved by published manual calibration, in a fraction of the time. While not being able to fully capture the experimental results, the resulting nerve model provides a complex averaging framework for nerve damage simulation able to simulate gradual axonal functional alteration in a bundle. (C) 2019 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000514022900005,
author = {LaTorre, Antonio and Kwong, Man Ting and Garcia-Grajales, Julian A. and Shi, Riyi and Jerusalem, Antoine and Pena, Jose-Maria},
title = {Model calibration using a parallel differential evolution algorithm in computational neuroscience: Simulation of stretch induced nerve deficit},
journal = {JOURNAL OF COMPUTATIONAL SCIENCE},
year = {2020},
volume = {39},
doi = {https://doi.org/10.1016/j.jocs.2019.101053}
}
|
| Deng, K., Cole, J.M., Rawle, J.L., Nicklin, C., Chen, H., Yanguas-Gil, A., Elam, J.W. and Stenning, G.B.G. Dye Nanoaggregate Structures in MK-2, N3, and N749 Dye center dot center dot center dot TiO2 Interfaces That Represent Dye-Sensitized Solar Cell Working Electrodes ACS APPLIED ENERGY MATERIALS 3, 1, pp. 900-914 (2020) |
| Abstract: The working electrode of a dye-sensitized solar cell (DSSC) consists of
dye molecules adsorbed onto nanoparticles of a semiconductor such as TiO2. A reliable prediction of the DSSC photovoltaic performance of a given dye requires in-depth knowledge about the precise structure of the dye center dot center dot center dot TiO2 interface. X-ray reflectometry (XRR) and grazing-incidence small-angle X-ray scattering (GISAXS) are herein employed to determine the dye center dot center dot center dot TiO2 interfacial structure and associated dye aggregation behavior of three high-performance DSSC dyes, i.e., a metal-free organic dye, MK-2, and the two archetypal ruthenium-based organometallic dyes, N3 and N749 (Black Dye). Results show that all three dyes form nanoaggregates in dye center dot center dot center dot TiO2 interfaces. We determine the dye nanoaggregate separations, sizes, distribution densities, and the extent of short-range order within each dye self-assembly in the longitudinal and lateral directions. Dye center dot center dot center dot TiO2 composites fabricated using dye solutions of varying concentrations are analyzed. We find that nanoaggregates of the three dyes are separated by several hundred nanometers (158-203 nm) in dye center dot center dot center dot TiO2 interfaces that have been fabricated using concentrated dye solutions (0.5 mM or 1.0 mM). MK-2 and N749 dyes also display smaller interparticle separations. Dye nanoparticle diameters are of the order of 156-198 nm, sizes that are comparable to the largest interparticle separations. Thus, no extraneous dye particles can be fitted into gaps between particles, so the dye self-assembly is saturated. Self-assemblies of all three dyes exhibit both lateral and longitudinal short-range order; N3 displays a particularly short coherence length along the TiO2 surface, with extensive structured disorder along the longitudinal direction. The operation of DSSC working electrodes would therefore seem to be dependent on a dye self-assembly that may exhibit several levels of structural granularity and dye aggregation effects. |
BibTeX:
@article{WOS:000510104700098,
author = {Deng, Ke and Cole, Jacqueline M. and Rawle, Jonathan L. and Nicklin, Christopher and Chen, Hao and Yanguas-Gil, Angel and Elam, Jeffrey W. and Stenning, Gavin B. G.},
title = {Dye Nanoaggregate Structures in MK-2, N3, and N749 Dye center dot center dot center dot TiO2 Interfaces That Represent Dye-Sensitized Solar Cell Working Electrodes},
journal = {ACS APPLIED ENERGY MATERIALS},
year = {2020},
volume = {3},
number = {1},
pages = {900-914},
doi = {https://doi.org/10.1021/acsaem.9b02002}
}
|
| Sarkar, P., Biswas, A., Ghosh, S.K., Rai, S., Modi, M.H. and Bhattacharyya, D. Interface evolution of Co/Ti multilayers with ultra-short period THIN SOLID FILMS 693 (2020) |
| Abstract: Behaviour of interface properties and propagation of interfacial atomic
diffusion have been investigated systematically in Co/Ti multilayers with ultra-short (similar to 18 angstrom) bi-layer thickness. Co/Ti multilayers with 10,20,40,60 and 80 bi-layers have been grown using an indigenously built in-line dc magnetron sputtering system having application as reflecting optics in the water window soft X-ray regime of 23-44 angstrom. Specular and diffused Grazing Incidence X-ray reflectivity measurements with hard X-rays have been used to evaluate detailed interfacial structure of the multilayers. It is observed that interfacial atomic diffusion of Co into Ti layers is significant in such ultra-short period multilayer structures and it increases as more number of layers are added in the multilayer stack. As a result of Co diffusion into Ti the physical density of Ti layer increases and also effective thickness of Co layer decreases. Since the thickness of the Ti layers are in sub-nm range, it is found that this diffusion is not limited only to the interface region of Co-on-Ti, rather it spreads throughout the bulk of Ti layer. Finally, soft X-ray reflectivity measurement on the multilayers with synchrotron radiation at 28 angstrom wavelength shows that the peak reflectivity is limited by the significant diffusion at the Co/Ti interfaces. |
BibTeX:
@article{WOS:000501775900026,
author = {Sarkar, P. and Biswas, A. and Ghosh, S. K. and Rai, S. and Modi, M. H. and Bhattacharyya, D.},
title = {Interface evolution of Co/Ti multilayers with ultra-short period},
journal = {THIN SOLID FILMS},
year = {2020},
volume = {693},
note = {10th International Conference on Hot Wire (Cat) and Initiated Chemical Vapor Deposition (HWCVD), Kitakyushu, JAPAN, SEP 03-06, 2018},
doi = {https://doi.org/10.1016/j.tsf.2019.137688}
}
|
| Schenk, T., Godard, N., Mahjoub, A., Girod, S., Matavz, A., Bobnar, V., Defay, E. and Glinsek, S. Toward Thick Piezoelectric HfO2-Based Films PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 14, 3 (2020)early access (DEC 2019) |
| Abstract: For HfO2-based films, which are mainly prepared by atomic layer
deposition, the desired ferroelectric (FE) properties typically vanish while extending the thickness beyond a limit of about 50 nm. Herein, the successful fabrication of a 1 mu m-thick piezoelectric La:HfO2 film is demonstrated using chemical solution deposition, paving the way toward sensor and actuator applications. After identifying the optimal La content, the film thickness is increased from 45 nm to 1 mu m. Polarization and strain measurements evidence the persistence of the FE properties at all thicknesses and even a slight improvement due to a better orientation of the polar axis at higher thicknesses. Scanning electron microscopy and X-ray reflectivity reveal a fine-grained microstructure and a density of only 80% of the theoretical value, which seems to be a common issue of solution-deposited HfO2-based films, based on the performed literature survey. Using tilt-angle-dependent X-ray diffraction scans, homogeneous nucleation is found to be the likely root cause of the observed microstructure. It is suggested that this microstructure issue is key for the optimization of cycling stability of solution-based films to exploit the full potential of the HfO2 for cost-efficient, thick piezoelectric films. |
BibTeX:
@article{WOS:000503251100001,
author = {Schenk, Tony and Godard, Nicolas and Mahjoub, Aymen and Girod, Stephanie and Matavz, Aleksander and Bobnar, Vid and Defay, Emmanuel and Glinsek, Sebastjan},
title = {Toward Thick Piezoelectric HfO2-Based Films},
journal = {PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS},
year = {2020},
volume = {14},
number = {3},
doi = {https://doi.org/10.1002/pssr.201900626}
}
|
| Li, Q., Wang, L.-M., Liu, S., Zhan, X., Zhu, T., Cao, Z., Lai, H., Zhao, J., Cai, Y., Xie, W. and Huang, F. Impact of Donor-Acceptor Interaction and Solvent Additive on the Vertical Composition Distribution of Bulk Heterojunction Polymer Solar Cells ACS APPLIED MATERIALS & INTERFACES 11, 49, pp. 45979-45990 (2019) |
| Abstract: The vertical composition distribution of a bulk heterojunction (BHJ)
photoactive layer is known to have dramatic effects on photovoltaic performance in polymer solar cells. However, the vertical composition distribution evolution rules of BHJ films are still elusive. In this contribution, three BHJ film systems, composed of polymer donor PBDB-T, and three different classes of acceptor (fullerene acceptor PCBM, small-molecule acceptor ITIC, and polymer acceptor N2200) are systematically investigated using neutron reflectometry to examine how donor acceptor interaction and solvent additive impact the vertical composition distribution. Our results show that those three BHJ films possess homogeneous vertical composition distributions across the bulk of the film, while very different composition accumulations near the top and bottom surface were observed, which could be attributed to different repulsion, miscibility, and phase separation between the donor and acceptor components as approved by the measurement of the donor acceptor Flory Huggins interaction parameter chi. Moreover, the solvent additive 1,8-diiodooctane (DIO) can induce more distinct vertical composition distribution especially in nonfullerene acceptor-based BHJ films. Thus, higher power conversion efficiencies were achieved in inverted solar cells because of facilitated charge transport in the active layer, improved carrier collection at electrodes, and suppressed charge recombination in BHJ solar cells. |
BibTeX:
@article{WOS:000502689000064,
author = {Li, Qjngduan and Wang, Li-Ming and Liu, Shengjian and Zhan, Xiaozhi and Zhu, Tao and Cao, Zhixiong and Lai, Haojie and Zhao, Jiaji and Cai, Yuepeng and Xie, Weiguang and Huang, Fei},
title = {Impact of Donor-Acceptor Interaction and Solvent Additive on the Vertical Composition Distribution of Bulk Heterojunction Polymer Solar Cells},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2019},
volume = {11},
number = {49},
pages = {45979-45990},
doi = {https://doi.org/10.1021/acsami.9b15753}
}
|
| Matalla-Wagner, T., Rath, M.-F., Graulich, D., Schmalhorst, J.-M., Reiss, G. and Meinert, M. Electrical Neel-Order Switching in Magnetron-Sputtered CuMnAs Thin Films PHYSICAL REVIEW APPLIED 12, 6 (2019) |
| Abstract: Antiferromagnetic materials as active components in spintronic devices
promise insensitivity against external magnetic fields, the absence of own magnetic stray fields, and ultrafast dynamics at the picosecond time scale. Materials with certain crystal symmetry show an intrinsic Neel-order spin-orbit torque that can efficiently switch the magnetic order of an antiferromagnet. The tetragonal variant of CuMnAs has been shown to be electrically switchable by this intrinsic spin-orbit effect and its use in memory cells with memristive properties has recently been demonstrated for high-quality films grown using molecular-beam epitaxy. Here, we demonstrate that the magnetic order of magnetron-sputtered CuMnAs films can also be manipulated by electrical current pulses. The switching efficiency and relaxation as a function of the temperature, the current density, and the pulse width can be described by a thermal-activation model. Our findings demonstrate that CuMnAs can be fabricated with an industry-compatible deposition technique, which will accelerate the development cycle of devices based on this remarkable material. |
BibTeX:
@article{WOS:000500014400003,
author = {Matalla-Wagner, T. and Rath, M-F and Graulich, D. and Schmalhorst, J-M and Reiss, G. and Meinert, M.},
title = {Electrical Neel-Order Switching in Magnetron-Sputtered CuMnAs Thin Films},
journal = {PHYSICAL REVIEW APPLIED},
year = {2019},
volume = {12},
number = {6},
doi = {https://doi.org/10.1103/PhysRevApplied.12.064003}
}
|
| Greco, A., Starostin, V., Karapanagiotis, C., Hindcrhofer, A., Gerlach, A., Pithan, L., Liehr, S., Schreiber, F. and Kowarik, S. Fast fitting of reflectivity data of growing thin films using neural networks JOURNAL OF APPLIED CRYSTALLOGRAPHY 52, 6, pp. 1342-1347 (2019) |
| Abstract: X-ray reflectivity (XRR) is a powerful and popular scattering technique
that can give valuable insight into the growth behavior of thin films. This study shows how a simple artificial neural network model can be used to determine the thickness, roughness and density of thin films of different organic semiconductors [diindenoperylene, copper(II) phthalocyanine and alpha-sexithiophene] on silica from their XRR data with millisecond computation time and with minimal user input or a priori knowledge. For a large experimental data set of 372 XRR curves, it is shown that a simple fully connected model can provide good results with a mean absolute percentage error of 8-18% when compared with the results obtained by a genetic least mean squares fit using the classical Parratt formalism. Furthermore, current drawbacks and prospects for improvement are discussed. |
BibTeX:
@article{WOS:000501810200011,
author = {Greco, Alessandro and Starostin, Vladimir and Karapanagiotis, Christos and Hindcrhofer, Alexander and Gerlach, Alexander and Pithan, Linus and Liehr, Sascha and Schreiber, Frank and Kowarik, Stefan},
title = {Fast fitting of reflectivity data of growing thin films using neural networks},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2019},
volume = {52},
number = {6},
pages = {1342-1347},
doi = {https://doi.org/10.1107/S1600576719013311}
}
|
| Ortmann, J.E., McCartney, M.R., Posadas, A., Smith, D.J. and Demkov, A.A. Epitaxial Oxides on Glass: A Platform for Integrated Oxide Devices ACS APPLIED NANO MATERIALS 2, 12, pp. 7713-7718 (2019) |
| Abstract: The fabrication of epitaxial, ultrathin SrTiO3 (STO) on thick SiO2
without the need for complicated wafer-bonding processes has been demonstrated. The resulting transition metal oxide (TMO)-on-glass layer stack is analogous to traditional silicon-on-insulator (SOI) wafers, where the crystalline device silicon layer of SOI has been replaced by a crystalline functional TMO layer. Fabrication starts with ultrathin body SOI on which crystalline STO is grown epitaxially by molecular beam epitaxy. The device silicon layer is subsequently fully oxidized by ex situ high-temperature dry O-2 annealing, as confirmed by X-ray photoelectron spectroscopy, X-ray reflectivity, and high-resolution electron microscopy. STO maintains its epitaxial registry to the carrier silicon substrate after annealing, and no evidence for degradation of the STO crystalline quality as a result of the TMO-on-glass fabrication process is observed. The ease of fabricating the TMO-on-glass platform without the need for wafer bonding will enable rapid progress in the development of state-of-the-art TMO-based electronic and photonic devices. |
BibTeX:
@article{WOS:000505626600029,
author = {Ortmann, J. Elliott and McCartney, Martha R. and Posadas, Agham and Smith, David J. and Demkov, Alexander A.},
title = {Epitaxial Oxides on Glass: A Platform for Integrated Oxide Devices},
journal = {ACS APPLIED NANO MATERIALS},
year = {2019},
volume = {2},
number = {12},
pages = {7713-7718},
doi = {https://doi.org/10.1021/acsanm.9b01778}
}
|
| Anjum, F., Fryauf, D.M., Gold, J., Ahmad, R., Cormia, R.D. and Kobayashi, N.P. Study of optical and structural properties of sputtered aluminum nitride films with controlled oxygen content to fabricate Distributed Bragg Reflectors for ultraviolet A OPTICAL MATERIALS 98 (2019) |
| Abstract: Aluminum nitride (AlN) films with controlled oxygen content were
deposited on silicon substrates, and optical properties studied with dependency on film morphology. Combinations of argon (Ar) and nitrogen (N-2) gases were used in RF magnetron sputtering of an AlN target. The resulting refractive index ranging from 1.6 to 2.0 at 400 nm was tuned by controlling the sputter gas flow rate ratio of Ar and N-2. The resulting refractive index is associated with density and aluminum nitride content of the thin films. Distributed Bragg Reflectors (DBRs) optimized for ultraviolet-A reflectivity were fabricated with pairs of alternating AlN thin films using an explicit combination of low-n and high-n to further investigate the thin film optical properties. The effect of structural transformation in the DBR stack on the progress of optical properties was studied. The DBRs exhibit a negligible extinction coefficient, utilizing precise control of oxygen incorporation with one sputtering target. |
BibTeX:
@article{WOS:000505108100001,
author = {Anjum, Faiza and Fryauf, David M. and Gold, Jeff and Ahmad, Riaz and Cormia, Robert D. and Kobayashi, Nobuhiko P.},
title = {Study of optical and structural properties of sputtered aluminum nitride films with controlled oxygen content to fabricate Distributed Bragg Reflectors for ultraviolet A},
journal = {OPTICAL MATERIALS},
year = {2019},
volume = {98},
doi = {https://doi.org/10.1016/j.optmat.2019.109405}
}
|
| Schanzer, C., Valloppilly, S.R. and Boeni, P. Specular and off-specular scattering from supermirror: Reflection of x-rays from the back side NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 946 (2019) |
| Abstract: The interface roughness of supermirrors with m = 4 times the critical
angle of nickel has been investigated by the reflection of x-rays from the back side of the mirrors. Reflectivity measurements from the front side do not contain useful information about the morphology of the layers because most photons are totally reflected from the top layer, which has typically a thickness of approximately 80 nm. Therefore, it is not straightforward to obtain information about the interface roughness of the layers underneath, which are decisive for the reflectivity of the supermirrors. In contrast, specular and off-specular measurements from the back side provide quantitative information on the buildup of roughness at the interfaces as well as the lateral and vertical correlation lengths of the roughness. As the intensity of laboratory x-ray sources is much higher than the intensity of neutron beams, it is possible to probe up to 8 harmonics of the supermirror sequence corresponding to m = 32. We demonstrate that the sheets caused by resonant diffuse scattering off supermirrors with a high reflectivity have a lower intensity and larger lateral correlation lengths than mirrors with a low reflectivity. We show that the reflection of x-rays from the back side of supermirrors is an alternative method for their characterization. |
BibTeX:
@article{WOS:000503433900022,
author = {Schanzer, Christian and Valloppilly, Shah R. and Boeni, Peter},
title = {Specular and off-specular scattering from supermirror: Reflection of x-rays from the back side},
journal = {NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT},
year = {2019},
volume = {946},
doi = {https://doi.org/10.1016/j.nima.2019.162628}
}
|
| Rullik, L., Evertsson, J., Johansson, N., Bertram, F., Nilsson, J.-O., Zakharov, A.A., Mikkelsen, A. and Lundgren, E. Surface oxide development on aluminum alloy 6063 during heat treatment SURFACE AND INTERFACE ANALYSIS 51, 12, SI, pp. 1214-1224 (2019) |
| Abstract: We report on the influence of oxygen partial pressure for the
development of surface oxides covering the industrial aluminum alloy standard 6063 at temperatures ranging from room temperature to 500 degrees C. Using an array of synchrotron-based techniques, we followed the change in oxide thickness, chemical composition, and the lateral distribution of alloying elements. The impact of the oxygen chemical potential is most visible at high temperatures where the oxide composition changes from mostly Al based to mostly Mg based. This is in stark contrast to the ultra-high vacuum (UHV) conditions where only a partial compositional transition is observed. The microscopy data demonstrate that in the UHV case, Mg segregation onto the surface occurs firstly at grain boundaries at 300 degrees C and secondly at sites over the entire surface at 400 degrees C. Further, the initial oxide thickness is 45 angstrom, as determined by XPS and XRR, decreases in all observed cases after heating to 300 degrees C. At higher temperatures, however, the oxygen partial pressure highly influences the resulting oxide thickness as evident from our X-ray reflectivity data. |
BibTeX:
@article{WOS:000494824500012,
author = {Rullik, Lisa and Evertsson, Jonas and Johansson, Niclas and Bertram, Florian and Nilsson, Jan-Olov and Zakharov, Alexei A. and Mikkelsen, Anders and Lundgren, Edvin},
title = {Surface oxide development on aluminum alloy 6063 during heat treatment},
journal = {SURFACE AND INTERFACE ANALYSIS},
year = {2019},
volume = {51},
number = {12, SI},
pages = {1214-1224},
note = {8th Symposium of Aluminium Surface Science and Technology (ASST), Helsingor, DENMARK, MAY 27-31, 2018},
doi = {https://doi.org/10.1002/sia.6616}
}
|
| Pandey, N., Puetter, S., Amir, S.M., Reddy, V.R., Phase, D.M., Stahn, J., Gupta, A. and Gupta, M. Effect of interfacial interdiffusion on magnetism in epitaxial Fe4N films on LaAlO3 substrates PHYSICAL REVIEW MATERIALS 3, 11 (2019) |
| Abstract: Epitaxial Fe4N thin films grown on LaAlO3 (LAO) substrate using
sputtering and molecular beam epitaxy techniques have been studied in this work. Within the sputtering process, films were grown with conventional direct current magnetron sputtering (dcMS) and using a high power impulse magnetron sputtering (HiPIMS) process. Surface morphology and depth profile studies on these samples reveal that HiPIMS deposited film has the lowest roughness, the highest packing density, and the sharpest interface. We found that the substrate-film interface and the microstructure play a vital role in affecting the electronic hybridization and magnetic properties of Fe4N films. La from the LAO substrate and Fe from the film interdiffuse and form an undesired interface. The magnetic moment (M-s) was compared using bulk, element-specific and magnetic depth profiling techniques. We found that M-s was the highest when the thickness of the interdiffused layer was lowest and such conditions can only be achieved in the HiPIMS grown samples. The presence of a small moment at the N site was also evidenced by element-specific x-ray circular dichroism measurement in the HiPIMS grown sample. A large variation in the M-s values of Fe4N films found in the experimental works carried out so far could be due to such an interdiffused layer which is generally not expected to form in otherwise stable oxide substrate at a low substrate temperature approximate to 675K. In addition, a consequence of substrate-film interdiffusion and microstructure resulted in the different kinds of magnetic anisotropies in Fe4N films grown using different techniques. A detailed investigation of the substrate-film interface and microstructure on the magnetization of Fe4N film is presented and discussed in this work. |
BibTeX:
@article{WOS:000498902800003,
author = {Pandey, Nidhi and Puetter, S. and Amir, S. M. and Reddy, V. R. and Phase, D. M. and Stahn, J. and Gupta, Ajay and Gupta, Mukul},
title = {Effect of interfacial interdiffusion on magnetism in epitaxial Fe4N films on LaAlO3 substrates},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {11},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.114414}
}
|
| Li, S., Wang, J., Zhang, Q., Roldan, M.A., Shan, L., Jin, Q., Chen, S., Wu, Z., Wang, C., Ge, C., He, M., Guo, H., Gu, L., Jin, K.-j. and Guo, E.-J. Maximization of ferromagnetism in LaCoO3 films by competing symmetry PHYSICAL REVIEW MATERIALS 3, 11 (2019) |
| Abstract: Spin state transition in perovskite cobaltite is delicately controlled
by the competition between exchange interaction energy and crystal-field energy. The latter is mainly governed by the change of bond length and bonding angle. Previous work has revealed that the electronic configuration associated with spin state transition in LaCoO3 (LCO) thin films can be effectively modulated by epitaxial strain. However, a systematic study on the spin state transition of Co3+ ions in LCO films with different crystallographic symmetry is still missing. Here, keeping the in-plane strain unchanged, we report that the magnetization of LCO films can be manipulated with crystallographic symmetry. The ultrathin LCO layers, constrained by the cubic substrate, have pseudotetragonal structure and small magnetization. Upon increasing the layer thickness, the monoclinic structure dominates the LCO film and maximizes its ferromagnetism. For the LCO films with a thickness beyond 35 unit cells, the symmetry relaxes gradually towards its rhombohedral bulk form, and meanwhile the magnetization reduces. These results highlight the importance of spin-lattice entanglement in a ferroelastic material and provide a concise way to maximize its functionality using symmetry engineering. |
BibTeX:
@article{WOS:000496933100001,
author = {Li, Sisi and Wang, Jiesu and Zhang, Qinghua and Roldan, Manuel A. and Shan, Lin and Jin, Qiao and Chen, Shuang and Wu, Zhenping and Wang, Can and Ge, Chen and He, Meng and Guo, Haizhong and Gu, Lin and Jin, Kui-juan and Guo, Er-Jia},
title = {Maximization of ferromagnetism in LaCoO3 films by competing symmetry},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {11},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.114409}
}
|
| Stubbs, J.E., Legg, B.A., Lee, S.S., Dera, P., De Yoreo, J.J., Fenter, P. and Eng, P.J. Epitaxial Growth of Gibbsite Sheets on the Basal Surface of Muscovite Mica JOURNAL OF PHYSICAL CHEMISTRY C 123, 45, pp. 27615-27627 (2019) |
| Abstract: The growth of aluminum (oxyhydr)oxide films on the basal surface of
muscovite mica is an excellent model system for studying mineral nucleation, growth, and reactivity. Using off-specular crystal truncation rod X-ray scattering, we have determined the atomic-scale epitaxial relationships between muscovite and monolayer overgrowths of a gibbsite-like material. We observe that dioctahedral sheets of aluminum (oxyhydr)oxide grow in three structurally distinct domains, separated by antiphase boundaries. Vacancies in the dioctahedral sheets overlie either the silicate tetrahedra or the ditrigonal cavities of the underlying muscovite surface. High-resolution atomic force microscopy indicates lateral island sizes of similar to 10nm separated by 1-2 nm spaces. Together, the X-ray and microscopy data provide insights into the coordination chemistry and morphology of films formed by heterogeneous nucleation and growth. |
BibTeX:
@article{WOS:000497260100035,
author = {Stubbs, Joanne E. and Legg, Benjamin A. and Lee, Sang Soo and Dera, Przemyslaw and De Yoreo, James J. and Fenter, Paul and Eng, Peter J.},
title = {Epitaxial Growth of Gibbsite Sheets on the Basal Surface of Muscovite Mica},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2019},
volume = {123},
number = {45},
pages = {27615-27627},
doi = {https://doi.org/10.1021/acs.jpcc.9b08219}
}
|
| Inyang, O., Bouchenoire, L., Nicholson, B., Tokac, M., Rowan-Robinson, R.M., Kinane, C.J. and Hindmarch, A.T. Threshold interface magnetization required to induce magnetic proximity effect PHYSICAL REVIEW B 100, 17 (2019) |
| Abstract: Proximity-induced magnetization (PIM) has broad implications across
interface-driven spintronics applications employing spin currents. We directly determine the scaling between PIM in Pt and the temperature-dependent interface magnetization in an adjacent ferromagnet (FM) using depth-resolved magnetometry. The magnetization due to PIM does not follow the generally expected linear scaling with the FM interface magnetization, as a function of temperature. Instead, it vanishes while the FM interface magnetization remains. The effective magnetic susceptibilities of heavy-metal (HM) layers are shown to give rise to the previously unexplained asymmetric PIM found in HM/FM/HM trilayers. |
BibTeX:
@article{WOS:000496567800002,
author = {Inyang, O. and Bouchenoire, L. and Nicholson, B. and Tokac, M. and Rowan-Robinson, R. M. and Kinane, C. J. and Hindmarch, A. T.},
title = {Threshold interface magnetization required to induce magnetic proximity effect},
journal = {PHYSICAL REVIEW B},
year = {2019},
volume = {100},
number = {17},
doi = {https://doi.org/10.1103/PhysRevB.100.174418}
}
|
| Waduge, W.L.I., Chen, Y., Zuo, P., Jayakodiarachchi, N., Kuech, T.F., Babcock, S.E., Evans, P.G. and Winter, C.H. Solid-Phase Epitaxy of Perovskite High Dielectric PrAlO3 Films Grown by Atomic Layer Deposition for Use in Two-Dimensional Electronics and Memory Devices ACS APPLIED NANO MATERIALS 2, 11, pp. 7449-7458 (2019) |
| Abstract: An atomic layer deposition (ALD) process is reported for the growth of
nanoscale PrAlO3 thin films for two-dimensional electronics and memory device applications using tris(isopropylcyclopentadienyl)- praseodymium (Pr(C(5)H(4)iPr)(3)), trimethylaluminum (AlMe3), and water. Pr(C(5)H(4)iPr)(3) was first evaluated as a precursor for the formation of thin films of the binary oxide Pr2O3 by using water as the coreactant. Self-limited growth of Pr2O3 was demonstrated for pulse lengths of >= 3 s, with a growth rate of similar to 0.85 angstrom/cycle. The ALD growth of PrAlO3 films was examined on Si, thermal SiO2, and (001)-oriented SrTiO3 substrates. Self-limited growth was demonstrated for Pr(C(5)H(4)iPr)(3), AlMe3, and water at 300 degrees C by using a 1:1 ratio of the number of Pr(C(5)H(4)iPr)(3) and AlMe3 pulses. An ALD window was observed from 275 to 325 degrees C with a growth rate of similar to 1.7 angstrom/cycle. The as-deposited PrAlO3 films on all substrates were amorphous, had smooth surfaces, and contained <0.5% carbon, as analyzed by grazing incidence wide-angle X-ray scattering, X-ray reflectivity, and X-ray photoelectron spectroscopy, respectively. Films grown with a 1:1 ratio of Pr(C(5)H(4)iPr)(3) and AlMe3 pulses were aluminum-rich (Pr:Al similar to 1:1.2-1.4). Heating PrAlO3 layers deposited on SrTiO3 to 800 degrees C for 3 h resulted in fully crystallized PrAlO3 films. The crystallized PrAlO3 films were highly (001)-oriented. The PrAlO3 00L and SrTiO3 00L reflections appeared on the same rod of reciprocal space, further indicating that the amorphous PrAlO3 film transforms into an epitaxial layer. The rocking curve width of the PrAlO3 (001) reflection was 7 degrees. By contrast, PrAlO3 films deposited on Si substrates with native oxide remained amorphous after annealing at 1000 degrees C for 8 h. The difference in the crystallization between PrAlO3 layers deposited on crystalline SrTiO3 and amorphous native SiO2 substrates indicates that PrAlO3 on SrTiO3 crystallized by solid-phase epitaxy, in which the nucleation and orientation of the crystallized layer are set by the atomic configuration at the substrate-film interface. |
BibTeX:
@article{WOS:000499740800071,
author = {Waduge, Wathsala L. I. and Chen, Yajin and Zuo, Peng and Jayakodiarachchi, Navoda and Kuech, Thomas F. and Babcock, Susan E. and Evans, Paul G. and Winter, Charles H.},
title = {Solid-Phase Epitaxy of Perovskite High Dielectric PrAlO3 Films Grown by Atomic Layer Deposition for Use in Two-Dimensional Electronics and Memory Devices},
journal = {ACS APPLIED NANO MATERIALS},
year = {2019},
volume = {2},
number = {11},
pages = {7449-7458},
doi = {https://doi.org/10.1021/acsanm.9b02153}
}
|
| Abharana, N., Biswas, A., Sarkar, P., Rai, S., Singh, S., Kumar, S., Jha, S.N. and Bhattacharyya, D. Effect of argon-nitrogen mixed ambient Ni sputtering on the interface diffusion of Ni/Ti periodic multilayers and supermirrors VACUUM 169 (2019) |
| Abstract: Interface roughness and interface diffusion are two very crucial
parameters in determining the performances of thin film multilayer devices for applications in X-ray optics, neutron optics, giant magneto resistance devices etc. Preparation of these thin film multilayers with sharp interfaces is a technological challenge and researchers are using different methods to reduce the interface imperfections. It has been observed that by mixing nitrogen with argon in sputtering ambience during deposition of Ni layers, neutron reflectivity of Ni/Ti neutron supermirrors can be improved significantly.To elucidate the physical mechanism behind this observation, two sets of Ni/Ti periodic multilayers have been prepared using an indigenously built in-line magnetron sputtering system, in one set pure Ar has been used in sputtering ambience and in the other set a mixed ambience of Ar + N-2 has been used for deposition of Ni layers. Both the sets of multilayers have been thoroughly characterized by specular and diffused Grazing Incidence X-ray Reflectivity, Nuclear Resonance Reaction, X-ray diffraction and Grazing Incidence Extended X-ray Absorption Fine Structure measurements using synchrotron radiation. All the above complementary measurements unambiguously establish that the reason for improved performance of the supermirror deposited with Ar + N-2 ambience is the reduction of interface diffusion at Ti-on-Ni interfaces. |
BibTeX:
@article{WOS:000494887000017,
author = {Abharana, N. and Biswas, A. and Sarkar, P. and Rai, S. and Singh, S. and Kumar, S. and Jha, S. N. and Bhattacharyya, D.},
title = {Effect of argon-nitrogen mixed ambient Ni sputtering on the interface diffusion of Ni/Ti periodic multilayers and supermirrors},
journal = {VACUUM},
year = {2019},
volume = {169},
doi = {https://doi.org/10.1016/j.vacuum.2019.108864}
}
|
| Tran, V.N., Ha, S.S., Oh, H., Kim, S.M., Cho, I.H., Chung, J., Mun, B.S., Seo, O. and Noh, D.Y. Atomic interdiffusion in Pt-Ni thin films at low temperatures: An in-situ Xray reflectivity study THIN SOLID FILMS 689 (2019) |
| Abstract: We have investigated the kinetic process of the atomic interdiffusion
across the interface in thin platinum-nickel (Pt-Ni) bilayer films at temperatures ranging from 230 degrees C to 300 degrees C by in-situ X-ray reflectivity (XRR). The Pt-Ni interface width obtained by analyzing the XRR curve provides the time evolution of the diffusion length in nanometer scale and the diffusivity of atoms across the interface. We find that the interdiffusion is dominated by Ni atoms with an associated activation energy Q of 0.87 +/- 0.05 eV. The analysis of the anomalous XRR measured with various X-ray energies across the K absorption edge of Ni provides more accurate electron density profile near the interface. |
BibTeX:
@article{WOS:000485256900001,
author = {Van Nhi Tran and Ha, Sung Soo and Oh, Hojun and Kim, Sun Min and Cho, In Hwa and Chung, Jinwook and Mun, Bongjin Simon and Seo, Okkyun and Noh, Do Young},
title = {Atomic interdiffusion in Pt-Ni thin films at low temperatures: An in-situ Xray reflectivity study},
journal = {THIN SOLID FILMS},
year = {2019},
volume = {689},
doi = {https://doi.org/10.1016/j.tsf.2019.137518}
}
|
| Gupta, M., Seema, Pandey, N., Amir, S.M., Puetter, S. and Mattauch, S. Synthesis, structure and magnetization of Co4N thin films JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 489 (2019) |
| Abstract: We reviewed magnetic tetra metal nitrides - Fe4N and Co4N for their
structure, magnetization and the thermodynamics of phase formation. Opposed to Fe4N, the formation of a stoichiometric Co4N turns out to be extremely difficult. A review of the literature of Co4N compound suggest that the experimental lattice parameter (LP) was always found to be smaller than the theoretical predicted value. It can also be seen that as the substrate temperature (T-s) increases, the LP of Co4N film decreases. In this work, we deposited Co4N films using molecular beam epitaxy (MBE), direct current magnetron sputtering (dcMS) and high power impulse MS (HiPIMS). Films were characterized using X-ray diffraction, X-ray reflectivity and atomic force microscopy. It was found that at high T-s, N out-diffusion significantly affects the growth of Co4N phase. We found that the MBE deposited films did not show any signature of Co4N phase when T-s < 703 K but at T-s = 703 K, the phase formed can be assigned to fcc Co rather than Co4N. On the other hand, the dcMS and HiPIMS grown films clearly show the presence of Co4N phase even at T-s = 300 K. Detailed analysis of Co4N films grown using dcMS and HiPIMS reveals that HiPIMS grown films are single phase and have a denser microstructure. The density of HiPIMS deposited film was also found to be close to the theoretical value. Magneto optical Kerr effect and polarized neutron reflectivity measurements were carried out to study magnetic properties. Differences in the magnetic moment and magnetic anisotropy were correlated with structural parameters. Obtained results are presented and discussed in terms of involved thin film growth mechanism. |
BibTeX:
@article{WOS:000473578000073,
author = {Gupta, Mukul and Seema and Pandey, Nidhi and Amir, S. M. and Puetter, S. and Mattauch, S.},
title = {Synthesis, structure and magnetization of Co4N thin films},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2019},
volume = {489},
doi = {https://doi.org/10.1016/j.jmmm.2019.165376}
}
|
| Blank, M., Schneider, G., Ordonez-Miranda, J. and Weber, L. Role of the electron-phonon coupling on the thermal boundary conductance of metal/diamond interfaces with nanometric interlayers JOURNAL OF APPLIED PHYSICS 126, 16 (2019) |
| Abstract: Thermal boundary conductance (TBC) of the Ag/diamond and Au/diamond
interfaces with a nanometer-thick interface layer of either nickel or molybdenum is measured by time domain thermoreflectance and modeled based on a 3-layer two-temperature model (3l-TTM). The rationale for this study is to critically assess the role of the electron-phonon coupling factor of the interlayer along with its thickness on the TBC. It is shown that the TBC of both systems rapidly increases with the interlayer thickness until reaching a stable plateau for thicknesses greater than 1.5 nm. The plateau average value is 15%-25% lower than the intrinsic TBC between the interlayer material and the diamond substrate. This behavior and values of the TBC of both systems are in good agreement with the predictions of the 3l-TTM. The predictability of this model is also analyzed for a Cu interlayer inserted at Au/silicon interfaces with thicknesses ranging from 1.5 to 20 nm. While the room temperature TBC of this system is well described by the 3l-TTM, the values measured at 80 K can only be predicted by the 3l-TTM, provided that the interlayer electron-phonon coupling factor is reduced by a factor of 2, as was experimentally observed for Ag and Au. The obtained experimental results along with the proposed model can thus be useful for tailoring the TBC of metallic interfaces in a wide range of temperatures. Published under license by AIP Publishing. |
BibTeX:
@article{WOS:000504001300039,
author = {Blank, Maite and Schneider, Gionata and Ordonez-Miranda, Jose and Weber, Ludger},
title = {Role of the electron-phonon coupling on the thermal boundary conductance of metal/diamond interfaces with nanometric interlayers},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2019},
volume = {126},
number = {16},
doi = {https://doi.org/10.1063/1.5115823}
}
|
| Bai, H., Zhan, X.Z., Li, G., Su, J., Zhu, Z.Z., Zhang, Y., Zhu, T. and Cai, J.W. Characterization of YIG thin films and vacuum annealing effect by polarized neutron reflectometry and magnetotransport measurements APPLIED PHYSICS LETTERS 115, 18 (2019) |
| Abstract: Nanometer-thick Y3Fe5O12 (YIG) films epitaxially grown on (111)
Gd3Ga5O12 with a magnetic dead layer as thin as about 1.2 nm are quantified by polarized neutron reflectivity and magnetization measurements. Vacuum annealing on YIG at 300-400 degrees C leads to substantial reduction in the anomalous Hall effect, spin Hall magnetoresistance, and spin pumping in YIG/Pt bilayers but causes large enhancement in the spin Seebeck effect. The structural, static, and dynamic magnetic measurements show that the annealing has no discernible influence on the global oxidization states and saturation magnetization of YIG films but introduces subtle defects possibly in the form of oxygen vacancies. This study suggests that subtle defects in thin YIG films have multiple effects on the spin transport properties, and caution should be taken in annealing YIG in vacuum. |
BibTeX:
@article{WOS:000494458100032,
author = {Bai, He and Zhan, X. Z. and Li, Gang and Su, Jian and Zhu, Z. Z. and Zhang, Ying and Zhu, T. and Cai, J. W.},
title = {Characterization of YIG thin films and vacuum annealing effect by polarized neutron reflectometry and magnetotransport measurements},
journal = {APPLIED PHYSICS LETTERS},
year = {2019},
volume = {115},
number = {18},
doi = {https://doi.org/10.1063/1.5124832}
}
|
| Blank, M. and Weber, L. Influence of interfacial structural disorder and/or chemical interdiffusion on thermal boundary conductance for Ti/Si and Au/Si couples JOURNAL OF APPLIED PHYSICS 126, 15 (2019) |
| Abstract: This work aims at experimentally assessing the effect of structural
disorder and/or chemical interdiffusion on thermal boundary conductance (TBC) at metal/dielectric interfaces. To this end, the TBC of Au/Si and Ti/Si interfaces was measured by time domain thermoreflectance in the as-deposited state and after various heat treatments. Transmission electron microscopy (TEM) was used to determine the structure of the interface for each heat treatment condition. The TBC at the Au/Si interface was found to be highest in the as-deposited state and to be somewhat reduced after heat treatments. TEM images showed that the highest TBC was obtained when the interface contained a disordered transition layer with some degree of interdiffusion as present in the as-deposited state. Heat treatments led to the separation of species and to more abrupt interfaces with lower TBC. Whether this change in TBC was linked to disorder or to interdiffusion could not be distinguished. The TBC at the Ti/Si interfaces was observed to decrease with the heat treatment duration. TEM investigations revealed the presence of a thin disordered layer that did not evolve much with heat treatments. The evolution of the TBC was hence rationalized by interdiffusion facilitated by heat treatments that most likely modified the diffusion zone thickness and chemical composition, as well as the disordered layer's chemical composition. These changes result in modified interfacial properties, which ultimately affect the TBC. A quantitative exploration of the TBC dependence on the composition was not possible in this work, due to the extreme thinness of the regions under consideration preventing any reliable STEM-energy dispersive x-ray measurement. Published under license by AIP Publishing. |
BibTeX:
@article{WOS:000503996400033,
author = {Blank, Maite and Weber, Ludger},
title = {Influence of interfacial structural disorder and/or chemical interdiffusion on thermal boundary conductance for Ti/Si and Au/Si couples},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2019},
volume = {126},
number = {15},
doi = {https://doi.org/10.1063/1.5114671}
}
|
| Boas, C.R.S.V., Sturm, J.M. and Bijkerk, F. Oxidation of metal thin films by atomic oxygen: A low energy ion scattering study JOURNAL OF APPLIED PHYSICS 126, 15 (2019) |
| Abstract: In this study, we combine low-energy ion scattering (LEIS) static and
sputter depth profiles for characterization of the oxidation kinetics on Zr, Mo, Ru, and Ta films of various thicknesses, followed by exposure to atomic oxygen at room temperature (similar to 20 degrees C). A method for nondestructive determination of the oxide growth rate via LEIS static depth profiling (static DP) is presented in detail. This method shows high sensitivity to the oxide thickness formed, and the results are in agreement with those obtained by X-ray reflectometry and sputter depth profiling (sputter DP). Sequential exposures of oxygen isotopes in combination with LEIS sputter DP are applied to elucidate the growth mechanism of the oxide films. The results indicate that the oxidation kinetics at the applied experimental conditions is directly influenced by the metal work function, characterizing a Cabrera-Mott growth type. The maximum thickness of the formed oxide and oxide growth rate are in the order Zr approximate to Ta > Mo > Ru. The combining of analysis by LEIS static DP and isotope tracing sputter DP is decisive in the characterization of oxidation kinetics in the room temperature regime. Published under license by AIP Publishing. |
BibTeX:
@article{WOS:000503996400032,
author = {Boas, C. R. Stilhano Vilas and Sturm, J. M. and Bijkerk, F.},
title = {Oxidation of metal thin films by atomic oxygen: A low energy ion scattering study},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2019},
volume = {126},
number = {15},
doi = {https://doi.org/10.1063/1.5115112}
}
|
| Ukleev, V., Tarnavich, V., Tartakovskaya, E., Lott, D., Kapaklis, V., Oleshkevych, A., Gargiani, P., Valvidares, M., White, J.S. and Grigoriev V, S. Coherent charge and magnetic ordering in Ho/Y superlattice revealed by element-selective x-ray scattering PHYSICAL REVIEW B 100, 13 (2019) |
| Abstract: Magnetic rare-earth/nonmagnetic metal superlattices are well-known to
display chiral spin helices in the rare-earth layers that propagate coherently across the nonmagnetic layers. However, the underlying mechanism that preserves the magnetic phase and chirality coherence across the nonmagnetic layers has remained elusive. In this paper, we use resonant and element-specific x-ray scattering to evidence directly the formation of two fundamentally different long-range modulations in a holmium/yttrium (Ho/Y) multilayer: the known Ho chiral spin helix with periodicity 25 angstrom and a newly observed charge density wave with periodicity 16 angstrom that propagates through both the Ho and nonmagnetic Y layer. With x-ray circular magnetic dichroism measurements ruling out the existence of a magnetic proximity effect induced moment in the nonmagnetic Y layers, we propose that the charge density wave is also chiral, thus providing the means for the transmittance of magnetic chirality coherence between Ho layers. |
BibTeX:
@article{WOS:000489820500003,
author = {Ukleev, V and Tarnavich, V and Tartakovskaya, E. and Lott, D. and Kapaklis, V and Oleshkevych, A. and Gargiani, P. and Valvidares, M. and White, J. S. and Grigoriev, V, S.},
title = {Coherent charge and magnetic ordering in Ho/Y superlattice revealed by element-selective x-ray scattering},
journal = {PHYSICAL REVIEW B},
year = {2019},
volume = {100},
number = {13},
doi = {https://doi.org/10.1103/PhysRevB.100.134417}
}
|
| Ren, K., Wang, Y., Lv, S., Zhu, S., Xin, T. and Song, Z. Reducing structural change in the phase transition of Ge-doped Bi0.5Sb1.5Te3 to enable high-speed and low-energy memory switching JOURNAL OF MATERIALS CHEMISTRY C 7, 38, pp. 11813-11823 (2019) |
| Abstract: The improving efficiency in obtaining renewable energy has promoted the
deployment of electronic systems in the area of limited wired power-supply, whereas the use of devices with reduced threshold-voltage and power-consumption is essential for guaranteeing continuous working capability. Herein, Bi0.5Sb1.5Te3 was optimized by introducing Ge for high-speed and low-energy phase change memory (PCM) application. The high speed of 10 ns and the low threshold voltage of 1.6 V have been achieved, originating from the crystal-like octahedral motifs in the amorphous phase, in which crystallization can be accomplished by the shifting or rotation of these motifs. The good endurance of 10(5) cycles is due to the small volume change of 4.6% and the formation of a homogenous phase during crystallization, which reduces the risk of stress- and segregation-induced device failure. The nucleation-dominated crystallization behavior of Ge1.3Bi0.5Sb1.5Te3 is observed, where the Ge atoms with lowest electronegativity are preferred to occupy the center cation layers in the nonuple-layer block, whereas the less metallic Bi and Sb atoms sit on the edged cation layers. The high-speed, low threshold voltage, and low power consumption have made the Ge1.3Bi0.5Sb1.5Te3 PCM film a promising candidate for application in self-powered electronic systems, i.e. Internet of Things systems with solar energy supply. |
BibTeX:
@article{WOS:000489049000010,
author = {Ren, Kun and Wang, Yong and Lv, Shilong and Zhu, Shuaishuai and Xin, Tianjiao and Song, Zhitang},
title = {Reducing structural change in the phase transition of Ge-doped Bi0.5Sb1.5Te3 to enable high-speed and low-energy memory switching},
journal = {JOURNAL OF MATERIALS CHEMISTRY C},
year = {2019},
volume = {7},
number = {38},
pages = {11813-11823},
doi = {https://doi.org/10.1039/c9tc03494c}
}
|
| Gebhard, M., Letourneau, S., Mandia, D.J., Choudhury, D., Yanguas-Gil, A., Mane, A., Sattelberger, A.P. and Elam, J.W. Formation of Unsaturated Hydrocarbons and Hydrogen: Surface Chemistry of Methyltrioxorhenium(VII) in ALD of Mixed-Metal Oxide Structures Comprising Re(III) Units CHEMISTRY OF MATERIALS 31, 19, pp. 7821-7832 (2019) |
| Abstract: We present the full investigation of the atomic layer deposition (ALD)
of a mixed rhenium-aluminum oxide, namely ReAl2O3CH3, a material with tunable resistance, comprising the building unit of conductive rhenium oxides, ReOx. The deposition, involving methyltrioxorhenium(VII) (MeReO3, MTO) and trimethylaluminum (TMA), was analyzed by employing complementary in situ diagnostic quartz-crystal microbalance (QCM), Fourier-transform infrared (FT-IR) spectroscopy, and quadrupole mass spectrometry (QMS) to explore and reveal the underlying growth mechanism of this material. A proposed mechanism includes reductive elimination steps, thereby creating a stable Re(III)-containing thin film, making this ALD process unique regarding its growth. In addition, as proven by QMS, the surface reactions include the formation of hydrogen and unsaturated hydrocarbons. From this straightforward process, an extraordinarily high growth rate of 4.5 angstrom cycle(-1) at temperatures as low as 150 degrees C was obtained. This material was found to exhibit highly promising electrical properties in terms of low thermal coefficient of resistance (TCR) in combination with high resistivity. By blending thin films of ReAl2O3CH3 with additional layers (1, 2, or 3) of Al2O3, we were able to fine-tune the electrical resistivity in the range of 3.9 x 10(6) -1.5 x 10(11) Omega.cm. Simultaneously, the TCR was lowered to about -0.014 degrees C--1,C- making this material highly resistive over a broad temperature range and a promising candidate for advanced detector applications, e.g., multichannel plates (MCPs). |
BibTeX:
@article{WOS:000489678800003,
author = {Gebhard, Maximilian and Letourneau, Steven and Mandia, David J. and Choudhury, Devika and Yanguas-Gil, Angel and Mane, Anil and Sattelberger, Alfred P. and Elam, Jeffrey W.},
title = {Formation of Unsaturated Hydrocarbons and Hydrogen: Surface Chemistry of Methyltrioxorhenium(VII) in ALD of Mixed-Metal Oxide Structures Comprising Re(III) Units},
journal = {CHEMISTRY OF MATERIALS},
year = {2019},
volume = {31},
number = {19},
pages = {7821-7832},
doi = {https://doi.org/10.1021/acs.chemmater.9b01408}
}
|
| Bull, C., Barton, C.W., Griggs, W., Caruana, A., Kinane, C.J., Nutter, P.W. and Thomson, T. PNR study of the phase transition in FeRh thin films APL MATERIALS 7, 10 (2019) |
| Abstract: y The first order antiferromagnetic to ferromagnetic metamagnetic phase
transition of equiatomic FeRh offers new opportunities for novel antiferromagnetic memories and spintronic devices with the caveat that it can be utilized in thin film structures (<50 nm). Here, we report a polarized neutron reflectivity (PNR) study for three representative film thicknesses (5, 20, and 50 nm) aimed at determining the physical and magnetic structure of FeRh at room temperature and partway through the transition. The PNR results are analyzed with reference to X-ray diffraction, X-ray reflectivity, and atomic force microscopy data which together provide a consistent description of the magnetic and physical state of the FeRh thin films. The data demonstrate that the nucleation of the ferromagnetic phase initiates at the MgO substrate, and results from structural and magnetic measurements demonstrate that the magnetic behavior and strain properties of FeRh correlate with the evolving topography of the three films investigated. (C) 2019 Author(s). |
BibTeX:
@article{WOS:000509790200022,
author = {Bull, C. and Barton, C. W. and Griggs, W. and Caruana, A. and Kinane, C. J. and Nutter, P. W. and Thomson, T.},
title = {PNR study of the phase transition in FeRh thin films},
journal = {APL MATERIALS},
year = {2019},
volume = {7},
number = {10},
doi = {https://doi.org/10.1063/1.5120622}
}
|
| Chang, M., Yun, J., Mao, J., Zuo, Y. and Xi, L. Effect of Inserting a Transition Metal Cu Layer on the Spin-Orbit Torque-Induced Magnetization Switching in Pt/Co/Ta Structures PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 13, 12 (2019)early access (OCT 2019) |
| Abstract: Current induced spin-orbit torque (SOT) in perpendicularly magnetized
heavy metal/ferromagnetic metal/heavy metal trilayers has been widely studied to achieve the current-induced magnetization switching. Decreasing the critical switching current-density (J(C)) is a primary factor in the performance of memory or logic devices because J(C) directly affects the power consumption of the devices. This work demonstrates the influences of inserting a transition metal copper (Cu) layer between the Co/Ta interface in the Pt/Co/Ta structures with perpendicular magnetic anisotropy (PMA) on the J(C), SOT, coercive field, and perpendicular magnetic anisotropy field (H-an). The results show that J(C) decreases significantly when the thickness of Cu layer is above 3 nm, compared with the Pt/Co/Ta control sample, under consideration of the shunting effect of Cu layer. The decrease of J(C) is the result of the competition between the modified SOT and H-an due to the insertion of Cu. The study suggests that the critical switching current-density of SOT-switching can be decreased by inserting a transition metal Cu layer. |
BibTeX:
@article{WOS:000488373100001,
author = {Chang, Meixia and Yun, Jijun and Mao, Jian and Zuo, Yalu and Xi, Li},
title = {Effect of Inserting a Transition Metal Cu Layer on the Spin-Orbit Torque-Induced Magnetization Switching in Pt/Co/Ta Structures},
journal = {PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS},
year = {2019},
volume = {13},
number = {12},
doi = {https://doi.org/10.1002/pssr.201900437}
}
|
| Trappen, R., Grutter, A.J., Huang, C.-Y., Penn, A., Mottaghi, N., Yousefi, S., Haertter, A., Kumari, S., LeBeau, J., Kirby, B.J. and Holcomb, M.B. Effect of oxygen stoichiometry on the magnetization profiles and negative magnetization in LSMO thin films JOURNAL OF APPLIED PHYSICS 126, 10 (2019) |
| Abstract: The depth-dependent magnetization in thin film oxygen stoichiometric and
oxygen-deficient La0.7Sr0.3MnO3 is investigated by using polarized neutron reflectivity and DC bulk magnetometry. The polarized neutron reflectivity results reveal that the stoichiometric sample shows enhanced interfacial magnetization relative to the rest of the film. The oxygen-deficient sample exhibits a reduced average magnetization from the optimized recipe. Both films show regions of suppressed magnetization at the surface regardless of the growth pressure. The oxygen stoichiometric film does not show an interfacial dead layer, whereas the oxygen-deficient film exhibits a dead layer whose thickness changes with temperature. At a low applied field, we observe striking differences in the depth dependence of the magnetic ordering, with the oxygen-deficient film exhibiting exchange spring behavior, while the stoichiometric film shows a constant magnetization direction across the film. These results suggest that the incorporation of oxygen vacancies during growth leads to an accumulation of vacancies at the interface, which is enhanced at higher temperature due to increased oxygen mobility, creating a region of reduced magnetism that couples to the rest of the film. These results offer insight into the complex behavior and role of oxygen vacancies in the magnetism of these systems. Additionally, the study reveals further details of the negative magnetization in La0.7Sr0.3MnO3 reported in previous studies, which are discussed here. |
BibTeX:
@article{WOS:000486028500003,
author = {Trappen, Robbyn and Grutter, Alexander J. and Huang, Chih-Yeh and Penn, Aubrey and Mottaghi, Navid and Yousefi, Saeed and Haertter, Allison and Kumari, Shalini and LeBeau, James and Kirby, Brian J. and Holcomb, Mikel B.},
title = {Effect of oxygen stoichiometry on the magnetization profiles and negative magnetization in LSMO thin films},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2019},
volume = {126},
number = {10},
doi = {https://doi.org/10.1063/1.5111858}
}
|
| Wang, J., Shin, Y., Gauquelin, N., Yang, Y., Lee, C., Jannis, D., Verbeeck, J., Rondinelli, J.M. and May, S.J. Physical properties of epitaxial SrMnO2.5-delta F gamma oxyfluoride films JOURNAL OF PHYSICS-CONDENSED MATTER 31, 36 (2019) |
| Abstract: Recently, topotactic fluorination has become an alternative way of
doping epitaxial perovskite oxides through anion substitution to engineer their electronic properties instead of the more commonly used cation substitution. In this work, epitaxial oxyfluoride SrMnO2.5-delta F gamma films were synthesized via topotactic fluorination of SrMnO2.5 films using polytetrafluoroethylene as the fluorine source. Oxidized SrMnO3 films were also prepared for comparison with the fluorinated samples. The F content, probed by x-ray photoemission spectroscopy, was systematically controlled by adjusting fluorination conditions. Electronic transport measurements reveal that increased F content (up to gamma = 0.14) systematically increases the electrical resistivity, despite the nominal electron-doping induced by F substitution for O in these films. In contrast, oxidized SrMnO3 exhibits a decreased resistivity and conduction activation energy. A blue-shift of optical absorption features occurs with increasing F content. Density functional theory calculations indicate that F acts as a scattering center for electronic transport, controls the observed weak ferromagnetic behavior of the films, and reduces the inter-band optical transitions in the manganite films. These results stand in contrast to bulk electron-doped La(1-x)Ce(x)Mno(3), illustrating how aliovalent anionic substitutions can yield physical behavior distinct from A-site substituted perovskites with the same nominal B-site oxidation states. |
BibTeX:
@article{WOS:000472232000002,
author = {Wang, Jiayi and Shin, Yongjin and Gauquelin, Nicolas and Yang, Yizhou and Lee, Christopher and Jannis, Daen and Verbeeck, Johan and Rondinelli, James M. and May, Steven J.},
title = {Physical properties of epitaxial SrMnO2.5-delta F gamma oxyfluoride films},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2019},
volume = {31},
number = {36},
doi = {https://doi.org/10.1088/1361-648X/ab2414}
}
|
| Samajdar, R.N., Kumar, C., Viswanath, P. and Bhattacharyya, A.J. Studying Hemoglobin and a Bare Metal-Porphyrin Complex Immobilized on Functionalized Silicon Surfaces Using Synchrotron X-ray Reflectivity JOURNAL OF PHYSICAL CHEMISTRY B 123, 35, SI, pp. 7492-7503 (2019) |
| Abstract: We evaluate here, using synchrotron X-ray reflectivity, hemoglobin
adsorption characteristics on silicon substrates with varying chemical functionalities. Hemoglobin at isoelectronic point and at negative charge is immobilized on functionalized hydrophilic (hydroxyl, carboxylic, amine) and hydrophobic (alkylated) silicon surfaces for the study. As a control, the bare cofactor hemin (containing only the metal and porphyrin with no amino acid residues) is also studied under similar conditions. Ordered layers (grown using the Langmuir-Blodgett technique) are observed to be less affected by the surface chemistry compared to the multilayers formed by physical absorption. Surface chemistry and charge of the proteins are critical in controlling the protein adsorption characteristics on silicon, such as thickness (correlated to molecule size) and roughness. In this study, this is very well realized by varying both the hydrophobicity and hydrophilicity of the substrate. The fundamental studies discussed here provide us with a set of important guidelines as to how electrode surface functionalization can control molecular conformation/orientation, especially protein adsorption on the substrate. This in turn is expected to have a significant impact on the protein electrochemical function and response of biomolecular devices. |
BibTeX:
@article{WOS:000484882800002,
author = {Samajdar, Rudra N. and Kumar, Chandan and Viswanath, P. and Bhattacharyya, Aninda J.},
title = {Studying Hemoglobin and a Bare Metal-Porphyrin Complex Immobilized on Functionalized Silicon Surfaces Using Synchrotron X-ray Reflectivity},
journal = {JOURNAL OF PHYSICAL CHEMISTRY B},
year = {2019},
volume = {123},
number = {35, SI},
pages = {7492-7503},
doi = {https://doi.org/10.1021/acs.jpcb.9b03085}
}
|
| Ukleev, V., Volkov, M., Korovin, A., Saerbeck, T., Sokolov, N. and Suturin, S. Stabilization of epsilon-Fe2O3 epitaxial layer on MgO(111)/GaN via an intermediate gamma-phase PHYSICAL REVIEW MATERIALS 3, 9 (2019) |
| Abstract: In the present study we have demonstrated epitaxial stabilization of the
metastable magnetically hard epsilon-Fe2O3 phase on top of a thin MgO(111) buffer layer grown onto the GaN (0001) surface. The primary purpose to introduce a 4-nm-thick buffer layer of MgO in between Fe2O3 and GaN was to stop thermal migration of Ga into the iron oxide layer. Though such migration and successive formation of the orthorhombic GaFeO3 was supposed earlier to be a potential trigger of the nucleation of the isostructural epsilon-Fe2O3, the present work demonstrates that the growth of single crystalline uniform films of epsilon ferrite by pulsed laser deposition is possible even on the MgO capped GaN. The structural properties of the 60-nm-thick Fe2O3 layer on MgO/GaN were probed by electron and x-ray diffraction, both suggesting that the growth of epsilon-Fe2O3 is preceded by formation of a thin layer of gamma-Fe2O3. The presence of the magnetically hard epsilon ferrite was independently confirmed by temperature dependent magnetometry measurements. The depth-resolved x-ray and polarized neutron reflectometry reveal that the 10 nm iron oxide layer at the interface has a lower density and a higher magnetization than the main volume of the epsilon-Fe2O3 film. The density and magnetic moment depth profiles derived from fitting the reflectometry data are in a good agreement with the presence of the magnetically degraded gamma-Fe2O3 transition layer between MgO and epsilon-Fe2O3. The natural occurrence of the interface between magnetoelectric epsilon- and spin caloritronic gamma-iron oxide phases can enable further opportunities to design novel all-oxide-on-semiconductor devices. |
BibTeX:
@article{WOS:000483945800002,
author = {Ukleev, Victor and Volkov, Mikhail and Korovin, Alexander and Saerbeck, Thomas and Sokolov, Nikolai and Suturin, Sergey},
title = {Stabilization of epsilon-Fe2O3 epitaxial layer on MgO(111)/GaN via an intermediate gamma-phase},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {9},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.094401}
}
|
| Chen, P.-Y., Lam, C.H., Edmondson, B., Posadas, A.B., Demkov, A.A. and Ekerdt, J.G. Epitaxial BaSnO3 and SrSnO3 perovskite growth on SrTiO3(001) via atomic layer deposition JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 37, 5 (2019) |
| Abstract: The authors report epitaxial BaSnO3(001) and SrSnO3(001) growth on
SrTiO3(001) (STO) substrates via atomic layer deposition (ALD) at 180 degrees C, where the BaSnO3 growth rate is 0.46 +/- 0.03 angstrom and the SrSnO3 growth rate is 0.69 +/- 0.04 angstrom per ALD unit cycle. Reflection high-energy electron diffraction, x-ray diffraction (XRD), and rocking curve analyses verify the single crystalline nature of BaSnO3(001) and SrSnO3(001) thin films on STO(001), while the atomic force microscopy analyses reveal the smooth surface of the stannate films with rms roughness values of similar to 0.4 nm, which is only slightly higher than the STO substrate roughness of 0.32 nm. Out-of-plane XRD and reciprocal space mapping show that both BaSnO3(001) and SrSnO3(001) (similar to 10 nm) are fully relaxed on STO(001), owing to the large lattice mismatches (5.1% for BaSnO3/STO and 3.2% for SrSnO3/STO). The visible light transmittance spectra indicate that ALD-grown BaSnO3 and SrSnO3 thin films have high transparency at 400-800 nm that matches the transparency of STO(001) substrates. |
BibTeX:
@article{WOS:000486214700001,
author = {Chen, Pei-Yu and Lam, Chon Hei and Edmondson, Bryce and Posadas, Agham B. and Demkov, Alexander A. and Ekerdt, John G.},
title = {Epitaxial BaSnO3 and SrSnO3 perovskite growth on SrTiO3(001) via atomic layer deposition},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2019},
volume = {37},
number = {5},
doi = {https://doi.org/10.1116/1.5111969}
}
|
| Liu, Z., Zarotti, F., Shi, Y. and Yang, N. Dislocations Promoted A-Site Nonstoichiometry and Their Impacts On the Proton Transport Properties of Epitaxial Barium Zirconate Thin Films JOURNAL OF PHYSICAL CHEMISTRY C 123, 34, SI, pp. 20698-20704 (2019) |
| Abstract: In the epitaxial barium zirconate (BaZrO3) thin films deposited on
NdGaO3 substrates through pulsed laser deposition, the large lattice mismatch between film and substrate can be accommodated by generating a large amount of misfit dislocations at the interface. With careful structural and chemical analyses, an enhancement in barium vacancy concentration together with charge compensating oxygen vacancies is believed to be formed near the dislocation defects, which should be mainly responsible for the great improvement of the proton conductivity. However, the crystallinity deteriorates with increasing film thickness due to the dislocations propagation. Such behavior could lead to a detrimental impact on the proton transport properties. These results could be useful for rational design of coating electrolytes with high proton conductivity by strain engineering for in-plane solid oxide fuel cell applications. |
BibTeX:
@article{WOS:000484075800003,
author = {Liu, Zhao and Zarotti, Francesca and Shi, Yanuo and Yang, Nan},
title = {Dislocations Promoted A-Site Nonstoichiometry and Their Impacts On the Proton Transport Properties of Epitaxial Barium Zirconate Thin Films},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2019},
volume = {123},
number = {34, SI},
pages = {20698-20704},
doi = {https://doi.org/10.1021/acs.jpcc.9b03749}
}
|
| Konefal, M., Zhigunov, A., Pavlova, E., Cernoch, P., Pop-Georgievski, O. and Spirkova, M. Adjustable self-assembly in polystyrene-block-poly(4-vinylpyridine) dip-coated thin films POLYMER 177, pp. 35-42 (2019) |
| Abstract: This work studies the influence of dip-coating parameters on
self-assembly in ultra-thin films of asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymers from a 1-chloropentane solution using a combination of several experimental techniques. Small-Angle X-ray Scattering, Atomic Force Microscopy, Grazing Incidence Small Angle X-ray Scattering and Transmission Electron Microscopy were used to characterize the fabricated films. We have shown a facile fabrication route to smooth films with a wide range of thicknesses. Arranged domains of P4VP oriented perpendicularly to the substrate were observed. The domain sizes and spacing varied in the range from 13 up to 35 nm and from 39 to 115 nm, respectively. |
BibTeX:
@article{WOS:000483429700005,
author = {Konefal, Magdalena and Zhigunov, Alexander and Pavlova, Ewa and Cernoch, Peter and Pop-Georgievski, Ognen and Spirkova, Milena},
title = {Adjustable self-assembly in polystyrene-block-poly(4-vinylpyridine) dip-coated thin films},
journal = {POLYMER},
year = {2019},
volume = {177},
pages = {35-42},
doi = {https://doi.org/10.1016/j.polymer.2019.05.057}
}
|
| Fourmental, C., Bellec, A., Repain, V., Lagoute, J., Chacon, C., Girard, Y., Rousset, S., Dappe, Y.J., Vlad, A., Resta, A., Garreau, Y. and Coati, A. Deep metallic interdiffusion in a model ferromagnetic/molecular system PHYSICAL REVIEW MATERIALS 3, 8 (2019) |
| Abstract: Understanding the structure of ferromagnetic/molecular interfaces
obtained by the deposition of metal on a molecular layer is a key parameter to master for the development of molecular spintronic devices. Here we studied by means of grazing incidence x-ray diffraction and x-ray reflectivity a model Co/C-60/Co(0001) system. Prior to Co deposition, the grown C-60 layer is crystallized in a face centered cubic lattice with the presence of two twins. The Co overlayer, presenting a polycrystalline hexagonal close packed structure with stacking faults, induces an amorphization of the topmost C-60 layers. Most importantly, we observe a deep diffusion of Co atoms in the octahedral sites of the crystallized C-60 film which could strongly affect the spin transport properties of the molecular layer and thus the magnetoresistance of the final device. |
BibTeX:
@article{WOS:000482589300001,
author = {Fourmental, Cynthia and Bellec, Amandine and Repain, Vincent and Lagoute, Jerome and Chacon, Cyril and Girard, Yann and Rousset, Sylvie and Dappe, Yannick J. and Vlad, Alina and Resta, Andrea and Garreau, Yves and Coati, Alessandro},
title = {Deep metallic interdiffusion in a model ferromagnetic/molecular system},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {8},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.083603}
}
|
| Barry, K., Zhang, B., Anand, N., Xing, Y., Vailionis, A., Neu, J., Heikes, C., Cochran, C., Zhou, H., Qiu, Y., Ratcliff, W., Siegrist, T. and Beekman, C. Modification of spin-ice physics in Ho2Ti2O7 thin films PHYSICAL REVIEW MATERIALS 3, 8 (2019) |
| Abstract: We present an extensive study on the effect of substrate orientation,
strain, stoichiometry, and defects on spin-ice physics in Ho2Ti2O7 thin films grown onto yttria-stabilized-zirconia substrates. We find that growth in different orientations produces different strain states in the films. All films exhibit similar c-axis lattice parameters for their relaxed portions, which are consistently larger than the bulk value of 10.1 angstrom. Transmission electron microscopy reveals antisite disorder and growth defects to be present in the films, but evidence of stuffing is not observed. The amount of disorder depends on the growth orientation, with the (110) film showing the least. Magnetization measurements at 1.8 K show the expected magnetic anisotropy and saturation magnetization values associated with a spin ice for all orientations; shape anisotropy is apparent when comparing in- and out-of-plane directions. Significantly, only the (110)-oriented films display the hallmark spin-ice plateau state in magnetization, albeit less well defined compared to the plateau observed in a single crystal. Neutron-scattering maps on the more disordered (111)-oriented films show the Q = 0 phase previously observed in bulk materials, but the Q = X phase giving the plateau state remains elusive. We conclude that the spin-ice physics in thin films is modified by defects and strain, leading to a reduction in the temperature at which correlations drive the system into the spin-ice state. |
BibTeX:
@article{WOS:000481473800002,
author = {Barry, Kevin and Zhang, Biwen and Anand, Naween and Xing, Yan and Vailionis, Arturas and Neu, Jennifer and Heikes, Colin and Cochran, Charis and Zhou, Haidong and Qiu, Y. and Ratcliff, William and Siegrist, Theo and Beekman, Christianne},
title = {Modification of spin-ice physics in Ho2Ti2O7 thin films},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {8},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.084412}
}
|
| Lin, E.L., Posadas, A.B., Zheng, L., Ortmann, J.E., Abel, S., Fompeyrine, J., Lai, K., Demkov, A.A. and Ekerdt, J.G. Atomic layer deposition of epitaxial ferroelectric barium titanate on Si(001) for electronic and photonic applications JOURNAL OF APPLIED PHYSICS 126, 6 (2019) |
| Abstract: Epitaxial barium titanate (BTO) thin films are grown on strontium
titanate-buffered Si(001) using atomic layer deposition (ALD) at 225 degrees C. X-ray diffraction confirms compressive strain in BTO films after the low temperature growth for films as thick as 66nm, with the BTO c-axis oriented in the out-of-plane direction. Postdeposition annealing above 650 degrees C leads to an in-plane c-axis orientation. Piezoresponse force microscopy was used to verify the ferroelectric switching behavior of ALD-grown films. Electrical and electro-optic measurements confirm BTO film ferroelectric behavior in out-of-plane and in-plane directions, respectively, at the micrometer scale. |
BibTeX:
@article{WOS:000481451900004,
author = {Lin, Edward L. and Posadas, Agham B. and Zheng, Lu and Ortmann, J. Elliott and Abel, Stefan and Fompeyrine, Jean and Lai, Keji and Demkov, Alexander A. and Ekerdt, John G.},
title = {Atomic layer deposition of epitaxial ferroelectric barium titanate on Si(001) for electronic and photonic applications},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2019},
volume = {126},
number = {6},
doi = {https://doi.org/10.1063/1.5087571}
}
|
| Coffey, B.M., Lin, E.L., Chen, P.-Y. and Ekerdt, J.G. Area-Selective Atomic Layer Deposition of Crystalline BaTiO3 CHEMISTRY OF MATERIALS 31, 15, pp. 5558-5565 (2019) |
| Abstract: Patterned, crystalline BaTiO3 (BTO) films were formed directly on
STO(001) surfaces using atomic layer deposition and restricting Ba and Ti precursor adsorption to STO(001) by passivating regions of the substrate with a polystyrene blocking layer. Patterns were prepared by spin-coating polystyrene onto STO(001), UV-crosslinking the polystyrene, and rinsing away uncrosslinked polystyrene with toluene. Amorphous 9-12 nm thick BTO films were deposited at 225 degrees C on polystyrene-patterned STO(001) surfaces. These films were crystallized upon annealing at elevated temperatures. Atomic force microscopy, scanning electron microscopy, and time of flight secondary ion mass spectroscopy were used after growth of BTO and removal of polystyrene resist and reveal BTO features with dimensions similar to the shadow mask. Reflection high-energy electron diffraction and X-ray diffraction show that BTO epitaxially crystallizes to the substrate, forming BTO(001), after annealing under vacuum at >= 770 degrees C with an oxygen partial pressure of 1 X 10(-6) Torr. |
BibTeX:
@article{WOS:000480826900024,
author = {Coffey, Brennan M. and Lin, Edward L. and Chen, Pei-Yu and Ekerdt, John G.},
title = {Area-Selective Atomic Layer Deposition of Crystalline BaTiO3},
journal = {CHEMISTRY OF MATERIALS},
year = {2019},
volume = {31},
number = {15},
pages = {5558-5565},
doi = {https://doi.org/10.1021/acs.chemmater.9b01271}
}
|
| Silber, R., Stejskal, O., Beran, L., Cejpek, P., Antos, R., Matalla-Wagner, T., Thien, J., Kuschel, O., Wollschlaeger, J., Veis, M., Kuschel, T. and Hamrle, J. Quadratic magneto-optic Kerr effect spectroscopy of Fe epitaxial films on MgO(001) substrates PHYSICAL REVIEW B 100, 6 (2019) |
| Abstract: The magneto-optic Kerr effect (MOKE) is a well known and handy tool to
characterize ferro-, ferri-, and antiferromagnetic materials. Many of the MOKE techniques employ effects solely linear in magnetization M. Nevertheless, a higher-order term being proportional to M-2 and called quadratic MOKE (QMOKE) can additionally contribute to the experimental data. Here, we present detailed QMOKE spectroscopy measurements in the range of 0.8-5.5 eV based on a modified eight-directional method applied on ferromagnetic bcc Fe thin films grown on MgO substrates. From the measured QMOKE spectra, two further complex spectra of the QMOKE parameters G(s) and 2G(44) are yielded. The difference between those two parameters, known as Delta G, denotes the strength of the QMOKE anisotropy. Those QMOKE parameters give rise to the QMOKE tensor G, fully describing the perturbation of the permittivity tensor in the second order in M for cubic crystal structures. We further present experimental measurements of ellipsometry and linear MOKE spectra, wherefrom permittivity in the zeroth and the first order in M are obtained, respectively. Finally, all those spectra are described by ab initio calculations. |
BibTeX:
@article{WOS:000478992200002,
author = {Silber, Robin and Stejskal, Ondrej and Beran, Lukas and Cejpek, Petr and Antos, Roman and Matalla-Wagner, Tristan and Thien, Jannis and Kuschel, Olga and Wollschlaeger, Joachim and Veis, Martin and Kuschel, Timo and Hamrle, Jaroslav},
title = {Quadratic magneto-optic Kerr effect spectroscopy of Fe epitaxial films on MgO(001) substrates},
journal = {PHYSICAL REVIEW B},
year = {2019},
volume = {100},
number = {6},
doi = {https://doi.org/10.1103/PhysRevB.100.064403}
}
|
| Welbourn, R.J.L. and Clarke, S.M. New insights into the solid-liquid interface exploiting neutron reflectivity CURRENT OPINION IN COLLOID & INTERFACE SCIENCE 42, pp. 87-98 (2019) |
| Abstract: We outline recent progress exploiting neutron reflectivity for
structural and compositional investigations of the solid-liquid interface. There has been extensive activity in this area, with key areas of development: (i) an increased range of accessible substrates (e.g. metals and minerals), (ii) novel liquid phases and (iii) strong themes in electrochemistry (e.g. batteries), corrosion, polymers and increasing application of extreme conditions. |
BibTeX:
@article{WOS:000497250500008,
author = {Welbourn, R. J. L. and Clarke, S. M.},
title = {New insights into the solid-liquid interface exploiting neutron reflectivity},
journal = {CURRENT OPINION IN COLLOID & INTERFACE SCIENCE},
year = {2019},
volume = {42},
pages = {87-98},
doi = {https://doi.org/10.1016/j.cocis.2019.03.007}
}
|
| Maruyama, R., Bigault, T., Saerbeck, T., Honecker, D., Soyama, K. and Courtois, P. Coherent Magnetization Rotation of a Layered System Observed by Polarized Neutron Scattering under Grazing Incidence Geometry CRYSTALS 9, 8 (2019) |
| Abstract: The in-plane magnetic structure of a layered system composed of
polycrystalline grains smaller than the ferromagnetic exchange length was studied to elucidate the mechanism controlling the magnetic properties considerably different from the bulk using polarized neutron scattering under grazing incidence geometry. The measured result, together with quantitative analysis based on the distorted wave Born approximation, showed that the in-plane length of the area with a uniform orientation of moments ranging from 0.5-1.1 mu m was not significantly varied during the process of demagnetization followed by remagnetization. The obtained behavior of moments is in good agreement with the two-dimensional random anisotropy model where coherent magnetization rotation is dominant. |
BibTeX:
@article{WOS:000482996000035,
author = {Maruyama, Ryuji and Bigault, Thierry and Saerbeck, Thomas and Honecker, Dirk and Soyama, Kazuhiko and Courtois, Pierre},
title = {Coherent Magnetization Rotation of a Layered System Observed by Polarized Neutron Scattering under Grazing Incidence Geometry},
journal = {CRYSTALS},
year = {2019},
volume = {9},
number = {8},
doi = {https://doi.org/10.3390/cryst9080383}
}
|
| Duffy, L.B., Steinke, N.-J., Burn, D.M., Frisk, A., Lari, L., Kuerbanjiang, B., Lazarov, V.K., van der Laan, G., Langridge, S. and Hesjedal, T. Magnetic profile of proximity-coupled (Dy,Bi)(2)Te-3/(Cr,Sb)(2)Te(3 )topological insulator heterostructures PHYSICAL REVIEW B 100, 5 (2019) |
| Abstract: Magnetic topological insulators (TIs) are an ideal playground for the
study of novel quantum phenomena building on time-reversal symmetry-broken topological surface states. By combining different magnetic TIs in a heterostructure, their magnetic and electronic properties can be precisely tuned. Recently, we have combined high-moment Dy:Bi2Te3 with high transition temperature Cr: Sb2Te3 in a superlattice, and we found, using x-ray magnetic circular dichroism (XMCD), that long-range magnetic order can be introduced in the Dy:Bi2Te3 layers. Accompanying first-principles calculations indicated that the origin of the long-range magnetic order is a strong antiferromagnetic coupling between Dy and Cr magnetic moments at the interface extending over several layers. However, based on XMCD alone, which is either averaging over the entire thin-film stack or is surface-sensitive, this coupling scenario could not be fully confirmed. Here we use polarized neutron reflectometry, which is ideally suited for the detailed study of superlattices, to retrieve the magnetization in a layer- and interface-resolved way. We find that the magnetization is, in contrast to similar recent studies, homogeneous throughout the individual layers, with no apparent interfacial effects. This finding demonstrates that heterostructure engineering is a powerful way of controlling the magnetic properties of entire layers, with the effects of coupling reaching beyond the interface region. |
BibTeX:
@article{WOS:000478043500002,
author = {Duffy, L. B. and Steinke, N-J and Burn, D. M. and Frisk, A. and Lari, L. and Kuerbanjiang, B. and Lazarov, V. K. and van der Laan, G. and Langridge, S. and Hesjedal, T.},
title = {Magnetic profile of proximity-coupled (Dy,Bi)(2)Te-3/(Cr,Sb)(2)Te(3 )topological insulator heterostructures},
journal = {PHYSICAL REVIEW B},
year = {2019},
volume = {100},
number = {5},
doi = {https://doi.org/10.1103/PhysRevB.100.054402}
}
|
| Jochum, J.K., Saerbeck, T., Lazenka, V., Joly, V., Shan, L., Boyen, H.-G., Temst, K., Vantomme, A. and Van Bael, M.J. Magnetic characterization of oblique angle deposited Co/CoO on gold nanoparticles JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 483, pp. 76-82 (2019) |
| Abstract: The influence of a patterned substrate on obliquely deposited, exchange
biased Co/CoO films was studied. It was found that substrates decorated with nanoparticle patterns provide the option to manipulate the orientation of the magnetic easy axis in obliquely deposited thin films. The complementary methods of SQUID magnetometry and polarized neutron reflectometry were used to disentangle the different contributions to the magnetic hysteresis of such complex magnetic systems. |
BibTeX:
@article{WOS:000471858100013,
author = {Jochum, Johanna K. and Saerbeck, Thomas and Lazenka, Vera and Joly, Vincent and Shan, Lianchen and Boyen, Hans-Gerd and Temst, Kristiaan and Vantomme, Andre and Van Bael, Margriet J.},
title = {Magnetic characterization of oblique angle deposited Co/CoO on gold nanoparticles},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2019},
volume = {483},
pages = {76-82},
doi = {https://doi.org/10.1016/j.jmmm.2019.03.098}
}
|
| Jaiswal, S., Lee, K., Langer, J., Ocker, B., Klaeui, M. and Jakob, G. Tuning of interfacial perpendicular magnetic anisotropy and domain structures in magnetic thin film multilayers JOURNAL OF PHYSICS D-APPLIED PHYSICS 52, 29 (2019) |
| Abstract: We investigate the magnetic domain structures and the perpendicular
magnetic anisotropy (PMA) arising in CoFeB films interfaced with selected heavy metal (HM) layers with large spin Hall angles in HM/CoFeB/MgO (HM = W, Pt, Pd, WxTa1-x) stacks as a function of CoFeB thickness and composition for both as-deposited and annealed materials stacks. The coercivity and the anisotropy fields of annealed material stacks are higher than for the as-deposited stacks due to crystallisation of the ferromagnetic layer. Generally a critical thickness of MgO > 1 nm provides adequate oxide formation at the top interface as a requirement for the generation of PMA. We demonstrate that in stacks with Pt as the HM, the PMA depends crucially on the alloy composition of the ferromagnet requiring a Co rich alloy to achieve PMA, i.e. it is important to have a large number of Pt-Co hybrid bonds at the interface compared to Pt-Fe hybrid bonds. In Pd/CoFeB/MgO layers, we observe for appropriate PMA a special stripe domain configuration that also includes circular skyrmion-like spin structures. Three different means of selective tuning of the PMA are discussed apart from the conventional FM thickness variation: Changing the number of repetitions of a multilayer stack is shown to change the PMA and strong PMA is found for certain compositions of WxTa1-x that also result in very low coercive fields (<1 mT) of the CoFeB. The PMA has also been shown to be tuned via annealing, very strong anisotropy fields of up to 1 T and low pinning of domain structures were measured in W/CoFeB/MgO, making these multilayers stacks a promising candidate for MRAM development. |
BibTeX:
@article{WOS:000468491900001,
author = {Jaiswal, S. and Lee, K. and Langer, J. and Ocker, B. and Klaeui, M. and Jakob, G.},
title = {Tuning of interfacial perpendicular magnetic anisotropy and domain structures in magnetic thin film multilayers},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2019},
volume = {52},
number = {29},
doi = {https://doi.org/10.1088/1361-6463/ab1c42}
}
|
| Yun, J., Zuo, Y., Mao, J., Chang, M., Zhang, S., Liu, J. and Xi, L. Lowering critical current density for spin-orbit torque induced magnetization switching by ion irradiation APPLIED PHYSICS LETTERS 115, 3 (2019) |
| Abstract: In ferromagnet/heavy metal heterostructures, critical current density
(J(C)) refers to the minimum current density required to generate spin-orbit torque (SOT) for effective magnetization manipulation, including switching of magnetization and moving of domain walls and magnetic skyrmions. This critical current density is a key factor for next-generation SOT-based magnetic random access memory, racetrack memory, and logic devices. In this work, the critical current density for magnetization switching and the thermal stability of Pt/Co/Ta heterostructures in response to ion irradiation are studied. It is found that ion irradiation represents a promising approach for the wide tuning of the magnetic properties, such as the coercive force and the perpendicular magnetic anisotropy constant. It is also found that J(C) is significantly reduced after 500eV Ar+ irradiation. Meanwhile, the ratio between the thermal stability factor E/k(B)T and J(C) increases with an increase in the irradiation dose, although E/k(B)T decreases slightly with the irradiation dose. This work demonstrates that J(C) can be significantly reduced by an appropriate ion irradiation process and thereby demonstrates a promising approach for effective reduction of the power consumption in SOT-based spintronic devices. |
BibTeX:
@article{WOS:000476586900031,
author = {Yun, Jijun and Zuo, Yalu and Mao, Jian and Chang, Meixia and Zhang, Shengxia and Liu, Jie and Xi, Li},
title = {Lowering critical current density for spin-orbit torque induced magnetization switching by ion irradiation},
journal = {APPLIED PHYSICS LETTERS},
year = {2019},
volume = {115},
number = {3},
doi = {https://doi.org/10.1063/1.5111937}
}
|
| Frisk, A., Ahlberg, M., Muscas, G., George, S., Johansson, R., Klysubun, W., Jonsson, P.E. and Andersson, G. Magnetic and structural characterization of CoFeZr thin films grown by combinatorial sputtering PHYSICAL REVIEW MATERIALS 3, 7 (2019) |
| Abstract: We report on a detailed investigation of structural and magnetic
properties of thin CoFeZr films, produced by combinatorial cosputtering, with compositions in the ranges 30-85 at.% Co, 12-63 at.% Fe, and 4-8 at.% Zr. Extended x-ray absorption fine structure and x-ray diffraction measurements reveal that alloys with a Zr content below 5 at.% are polycrystalline with a bcc structure, while an amorphous morphology is stabilized at Zr contents above 6 at.%. All samples display a growth-induced in-plane uniaxial anisotropy, which is closely related to the Zr concentration gradients across the wafers. A model for the angular dependence of the reduced remanence, including a Gaussian distribution of easy/hard anisotropy axes, is presented and successfully used to fit the data for all samples. The magnetic moments of the polycrystalline films approximately follow the Slater-Pauling curve, and the magnetic moments of the amorphous films follow a similar trend, but with about 20 % lower values. X-ray magnetic circular dichroism measurements show, for the amorphous films, that the Co moments are virtually constant at 1.7(2)mu(B)/atom. |
BibTeX:
@article{WOS:000474390900005,
author = {Frisk, Andreas and Ahlberg, Martina and Muscas, Giuseppe and George, Sebastian and Johansson, Robert and Klysubun, Wantana and Jonsson, Petra E. and Andersson, Gabriella},
title = {Magnetic and structural characterization of CoFeZr thin films grown by combinatorial sputtering},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {7},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.074403}
}
|
| Lefler, B.M., Duchon, T., Karapetrov, G., Wang, J., Schneider, C.M. and May, S.J. Reconfigurable lateral anionic heterostructures in oxide thin films via lithographically defined topochemistry PHYSICAL REVIEW MATERIALS 3, 7 (2019) |
| Abstract: Laterally structured materials can exhibit properties uniquely suited
for applications in electronics, magnetoelectric memory, photonics, and nanoionics. Here, a patterning approach is presented that combines the precise geometric control enabled by lithography with topochemical anionic manipulation of complex oxide films. Utilizing oxidation and fluorination reactions, striped patterns of SrFeO2.5/SrFeO3, SrFeO2.5/SrFeO2F, and SrFeO3/SrFeO2F have been prepared with lateral periodicities of 200, 20, and 4 mu m. Coexistence of the distinct chemical phases is confirmed through x-ray diffraction, optical and photoemission microscopies, and optical spectroscopy. The lateral heterostructures exhibit highly anisotropic electronic transport and also enable transience and regeneration of patterns through reversible redox reactions. This approach can be broadly applied to a variety of metal-oxide systems, enabling chemically reconfigurable lateral heterostructures tailored for specific electronic, optical, ionic, thermal, or magnetic functionalities. |
BibTeX:
@article{WOS:000474390900002,
author = {Lefler, Benjamin M. and Duchon, Tomas and Karapetrov, Goran and Wang, Jiayi and Schneider, Claus M. and May, Steven J.},
title = {Reconfigurable lateral anionic heterostructures in oxide thin films via lithographically defined topochemistry},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {7},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.073802}
}
|
| Mogi, M., Nakajima, T., Ukleev, V., Tsukazaki, A., Yoshimi, R., Kawamura, M., Takahashi, K.S., Hanashima, T., Kakurai, K., Arima, T.-h., Kawasaki, M. and Tokura, Y. Large Anomalous Hall Effect in Topological Insulators with Proximitized Ferromagnetic Insulators PHYSICAL REVIEW LETTERS 123, 1 (2019) |
| Abstract: We report a proximity-driven large anomalous Hall effect in
all-telluride heterostructures consisting of the ferromagnetic insulator Cr2Ge2Te6 and topological insulator (Bi, Sb)(2)Te-3. Despite small magnetization in the (Bi, Sb)(2)Te-3 layer, the anomalous Hall conductivity reaches a large value of 0.2e(2)/h in accord with a ferromagnetic response of the Cr2Ge2Te6. The results show that the exchange coupling between the surface state of the topological insulator and the proximitized Cr(2)Ge(2)Te(6 )layer is effective and strong enough to open the sizable exchange gap in the surface state. |
BibTeX:
@article{WOS:000473540500006,
author = {Mogi, Masataka and Nakajima, Taro and Ukleev, Victor and Tsukazaki, Atsushi and Yoshimi, Ryutaro and Kawamura, Minoru and Takahashi, Kei S. and Hanashima, Takayasu and Kakurai, Kazuhisa and Arima, Taka-hisa and Kawasaki, Masashi and Tokura, Yoshinori},
title = {Large Anomalous Hall Effect in Topological Insulators with Proximitized Ferromagnetic Insulators},
journal = {PHYSICAL REVIEW LETTERS},
year = {2019},
volume = {123},
number = {1},
doi = {https://doi.org/10.1103/PhysRevLett.123.016804}
}
|
| Hoenicke, P., Detlefs, B., Nolot, E., Kayser, Y., Muehle, U., Pollakowski, B. and Beckhoff, B. Reference-free grazing incidence x-ray fluorescence and reflectometry as a methodology for independent validation of x-ray reflectometry on ultrathin layer stacks and a depth-dependent characterization JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 37, 4 (2019) |
| Abstract: Nanolayer stacks are technologically very relevant for current and
future applications in many fields of research. A nondestructive characterization of such systems is often performed using x-ray reflectometry (XRR). For complex stacks of multiple layers, low electron density contrast materials, or very thin layers without any pronounced angular minima, this requires a full modeling of the XRR data. As such a modeling is using the thicknesses, the densities, and the roughnesses of each layer as parameters, this approach quickly results in a large number of free parameters. In consequence, cross correlation effects or interparameter dependencies can falsify the modeling results. Here, the authors present a route for validation of such modeling results which is based on the reference-free grazing incidence x-ray fluorescence (GIXRF) methodology. In conjunction with the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt, the method allows for reference-free quantification of the elemental mass depositions. In addition, a modeling approach of reference-free GIXRF-XRR data is presented, which takes advantage of the quantifiable elemental mass depositions by distributing them depth dependently. This approach allows for a reduction of the free model parameters. Both the validation capabilities and the combined reference-free GIXRF-XRR modeling are demonstrated using several nanoscale layer stacks consisting of HfO 2 and Al 2 O 3 layers. |
BibTeX:
@article{WOS:000480781300010,
author = {Hoenicke, Philipp and Detlefs, Blanka and Nolot, Emmanuel and Kayser, Yves and Muehle, Uwe and Pollakowski, Beatrix and Beckhoff, Burkhard},
title = {Reference-free grazing incidence x-ray fluorescence and reflectometry as a methodology for independent validation of x-ray reflectometry on ultrathin layer stacks and a depth-dependent characterization},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2019},
volume = {37},
number = {4},
doi = {https://doi.org/10.1116/1.5094891}
}
|
| Weber, T., Pfrommer, J., Abb, M.J.S., Herd, B., Khalid, O., Rohnke, M., Lakner, P.H., Evertsson, J., Volkov, S., Bertram, F., Znaiguia, R., Carla, F., Vonk, V., Lundgren, E., Stierle, A. and Over, H. Potential-Induced Pitting Corrosion of an IrO2(110)-RuO2(110)/Ru(0001) Model Electrode under Oxygen Evolution Reaction Conditions ACS CATALYSIS 9, 7, pp. 6530-6539 (2019) |
| Abstract: Sophisticated IrO2(110)-based model electrodes are prepared by
deposition of a 10 nm thick single-crystalline IrO2(110) layer supported on a structure-directing RuO2(110)/Ru(0001) template, exposing a regular array of mesoscopic rooflike structures. With this model electrode together with the dedicated in situ synchrotron based techniques (SXRD, XRR) and ex situ characterization techniques (SEM, ToF-SIMS, XPS), the corrosion process of IrO2(110) in an acidic environment (pH 0.4) is studied on different length scales. Potential-induced pitting corrosion starts at 1.48 V vs SHE and is initiated at so-called surface grain boundaries, where three rotational domains of IrO2(110) meet. The most surprising result is, however, that even when the electrode potential is increased to 1.94 V vs SHE 60-70% of the IrO2 film still stays intact down to the mesoscale and atomic scale and no uniform thinning of the IrO2(110) layer is encountered. Neither flat IrO2(110) terraces nor single steps are attacked. Ultrathin single crystalline IrO2(110) layers seem to be much more stable to anodic corrosion than hitherto expected. |
BibTeX:
@article{WOS:000474812400072,
author = {Weber, Tim and Pfrommer, Johannes and Abb, Marcel J. S. and Herd, Benjamin and Khalid, Omeir and Rohnke, Marcus and Lakner, Pirmin H. and Evertsson, Jonas and Volkov, Sergey and Bertram, Florian and Znaiguia, Raja and Carla, Francesco and Vonk, Vedran and Lundgren, Edvin and Stierle, Andreas and Over, Herbert},
title = {Potential-Induced Pitting Corrosion of an IrO2(110)-RuO2(110)/Ru(0001) Model Electrode under Oxygen Evolution Reaction Conditions},
journal = {ACS CATALYSIS},
year = {2019},
volume = {9},
number = {7},
pages = {6530-6539},
doi = {https://doi.org/10.1021/acscatal.9b01402}
}
|
| Palonen, H., Mukhamedov, B.O., Ponomareva, A.V., Palsson, G.K., Abrikosov, I.A. and Hjorvarsson, B. The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice APPLIED PHYSICS LETTERS 115, 1 (2019) |
| Abstract: The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70
superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. Published under license by AIP Publishing. |
BibTeX:
@article{WOS:000474211400020,
author = {Palonen, H. and Mukhamedov, B. O. and Ponomareva, A. V. and Palsson, G. K. and Abrikosov, I. A. and Hjorvarsson, B.},
title = {The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice},
journal = {APPLIED PHYSICS LETTERS},
year = {2019},
volume = {115},
number = {1},
doi = {https://doi.org/10.1063/1.5102121}
}
|
| Tryus, M., Nikolaev V, K., Makhotkin, I.A., Schubert, J., Kibkalo, L., Danylyuk, S., Giglia, A., Nicolosi, P. and Juschkin, L. Optical and structural characterization of orthorhombic LaLuO3 using extreme ultraviolet reflectometry THIN SOLID FILMS 680, pp. 94-101 (2019) |
| Abstract: A thin orthorhombic LaLuO3 film, grown on SrTiO3 substrate by pulsed
laser deposition, is characterized using multi-angle spectral extreme ultraviolet reflectometry (EUVR). Layer structure parameters and optical constants of LaLuO3 are determined simultaneously by fitting angular reflectivity curves in a wide spectral range (70-200 eV). From near-edge optical constant analysis, La: Lu stoichiometry ratio and the film density are derived. Sample structure is additionally analyzed using XRR, AFM and TEM methods. EUVR as a method of structural characterization is discussed in comparison with XRR. Correlation error analysis of the layer structure parameters, obtained from independent EUVR and XRR fits, is presented. |
BibTeX:
@article{WOS:000467389900015,
author = {Tryus, Maksym and Nikolaev, V, Konstantin and Makhotkin, Igor A. and Schubert, Juergen and Kibkalo, Lidia and Danylyuk, Serhiy and Giglia, Angelo and Nicolosi, Piergiorgio and Juschkin, Larissa},
title = {Optical and structural characterization of orthorhombic LaLuO3 using extreme ultraviolet reflectometry},
journal = {THIN SOLID FILMS},
year = {2019},
volume = {680},
pages = {94-101},
doi = {https://doi.org/10.1016/j.tsf.2019.04.037}
}
|
| Pandey, N., Gupta, M., Gupta, R., Hussain, Z., Reddy, V.R., Phase, D.M. and Stahn, J. Structural and magnetic properties of stoichiometric Co4N epitaxial thin films PHYSICAL REVIEW B 99, 21 (2019) |
| Abstract: In this work, we measured N self-diffusion in the Co-N system and found
an unexpected result that N diffuses out almost completely around 500 K, leaving behind fcc Co irrespective of the amount of N used to deposit Co-N. On the other hand, in previous attempts the Co4N phase has always been grown at 550 K or above. In view of our finding, it appears that fcc Co could have been mistaken for Co4N, probably due to the closeness of their lattice parameters (LP; fcc Co = 3.54 angstrom, Co4N = 3.74 angstrom). Therefore, Co4N - an interesting material for its high spin-polarization ratio and high magnetic moment remained unexplored. By bringing down the growth temperature, we report the growth of stoichiometric Co4N epitaxial thin films. Films were grown using a direct current reactive magnetron sputtering process on LaAlO3 (LAO mismatch 1.4%) and MgO (mismatch 11.3%) substrates and their structural and magnetic properties were studied. Precise magnetic moment (Ms) of Co4N samples were measured using polarized neutron reflectivity and compared with bulk magnetization results. We found that the Ms of Co4N is higher due to a magnetovolume effect. Unlike previous findings, we observed that substrates induce misfit strain and strain inhomogeneity is the cause of modifications in magnetic ensemble such as coercivity, saturation magnetization, and magnetic anisotropy. A consequence of incoherent strain present in our samples is also reflected in the magnetic anisotropy leading to a superposition of strong fourfold and a small fraction of uniaxial magnetic anisotropy. Obtained results are presented and discussed in this work. |
BibTeX:
@article{WOS:000473010000002,
author = {Pandey, Nidhi and Gupta, Mukul and Gupta, Rachana and Hussain, Zaineb and Reddy, V. R. and Phase, D. M. and Stahn, Jochen},
title = {Structural and magnetic properties of stoichiometric Co4N epitaxial thin films},
journal = {PHYSICAL REVIEW B},
year = {2019},
volume = {99},
number = {21},
doi = {https://doi.org/10.1103/PhysRevB.99.214109}
}
|
| Lapano, J., Brahlek, M., Zhang, L., Roth, J., Pogrebnyakov, A. and Engel-Herbert, R. Scaling growth rates for perovskite oxide virtual substrates on silicon NATURE COMMUNICATIONS 10 (2019) |
| Abstract: The availability of native substrates is a cornerstone in the
development of microelectronic technologies relying on epitaxial films. If native substrates are not available, virtual substrates - crystalline buffer layers epitaxially grown on a structurally dissimilar substrate - offer a solution. Realizing commercially viable virtual substrates requires the growth of high-quality films at high growth rates for large-scale production. We report the stoichiometric growth of SrTiO3 exceeding 600 nm hr(-1). This tenfold increase in growth rate compared to SrTiO3 grown on silicon by conventional methods is enabled by a self-regulated growth window accessible in hybrid molecular beam epitaxy. Overcoming the materials integration challenge for complex oxides on silicon using virtual substrates opens a path to develop new electronic devices in the More than Moore era and silicon integrated quantum computation hardware. |
BibTeX:
@article{WOS:000470084000002,
author = {Lapano, Jason and Brahlek, Matthew and Zhang, Lei and Roth, Joseph and Pogrebnyakov, Alexej and Engel-Herbert, Roman},
title = {Scaling growth rates for perovskite oxide virtual substrates on silicon},
journal = {NATURE COMMUNICATIONS},
year = {2019},
volume = {10},
doi = {https://doi.org/10.1038/s41467-019-10273-2}
}
|
| Koohfar, S., Georgescu, A.B., Penn, A.N., LeBeau, J.M., Arenholz, E. and Kumah, D.P. Confinement of magnetism in atomically thin La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures NPJ QUANTUM MATERIALS 4 (2019) |
| Abstract: At crystalline interfaces where a valence-mismatch exists, electronic,
and structural interactions may occur to relieve the polar mismatch, leading to the stabilization of non-bulk-like phases. We show that spontaneous reconstructions at polar La0.7Sr0.3MnO3 interfaces are correlated with suppressed ferromagnetism for film thicknesses on the order of a unit cell. We investigate the structural and magnetic properties of valence-matched La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 interfaces using a combination of high-resolution electron microscopy, first principles theory, synchrotron X-ray scattering and magnetic spectroscopy and temperature-dependent magnetometry. A combination of an antiferromagnetic coupling between the La0.7Sr0.3CrO3 and La0.7Sr0.3MnO3 layers and a suppression of interfacial polar distortions are found to result in robust long-range ferromagnetic ordering for ultrathin La0.7Sr0.3MnO3. These results underscore the critical importance of interfacial structural and magnetic interactions in the design of devices based on two-dimensional oxide magnetic systems. |
BibTeX:
@article{WOS:000470242300001,
author = {Koohfar, Sanaz and Georgescu, Alexandru B. and Penn, Aubrey N. and LeBeau, James M. and Arenholz, Elke and Kumah, Divine P.},
title = {Confinement of magnetism in atomically thin La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures},
journal = {NPJ QUANTUM MATERIALS},
year = {2019},
volume = {4},
doi = {https://doi.org/10.1038/s41535-019-0164-1}
}
|
| Petukhov, D.I., Chumakov, A.P., Kan, A.S., Lebedev, V.A., Eliseev, A.A., Konovalov, O.V. and Eliseev, A.A. Spontaneous MXene monolayer assembly at the liquid-air interface NANOSCALE 11, 20, pp. 9980-9986 (2019) |
| Abstract: Here we report on the spontaneous assembly of Ti3C2Tx MXene flakes into
monolayer films at the liquid-air interface. According to X-ray reflectivity and grazing incidence X-ray fluorescence both the structure of the layers and assembly kinetics depends on the pH value of the solution. At pH > 4 MXene flakes form a single approximate to 1.5 nm thick layer carrying a negative charge, while in the acidic medium the layer contains coordinated anions with the formation of the Br-aq(-)/Ti3C2Tx/subphase interface. The surface layer compression allows the assembling of MXene flakes into a dense monolayer films with the surface coverage of up to 96% and surface pressure exceeding 40 mN m(-1) in the case of the acidic subphase. The films can readily be transferred onto solid substrates by the conventional Langmuir-Blodgett approach or modified by surfactants to form MXene/surfactant composite films. |
BibTeX:
@article{WOS:000469246100016,
author = {Petukhov, D. I. and Chumakov, A. P. and Kan, A. S. and Lebedev, V. A. and Eliseev, Artem A. and Konovalov, O. V. and Eliseev, Andrei A.},
title = {Spontaneous MXene monolayer assembly at the liquid-air interface},
journal = {NANOSCALE},
year = {2019},
volume = {11},
number = {20},
pages = {9980-9986},
doi = {https://doi.org/10.1039/c9nr00525k}
}
|
| Thorarinsdottir, K.A., Palonen, H., Palsson, G.K., Hjorvarsson, B. and Magnus, F. Giant magnetic proximity effect in amorphous layered magnets PHYSICAL REVIEW MATERIALS 3, 5 (2019) |
| Abstract: Here we study the magnetic proximity effect in amorphous layered magnets
of alternating high- and low-T-c materials using magnetometry and polarized neutron reflectivity. By altering the thickness of either the high-or low-T-c layer we are able to extract the induced magnetic moment in the low-T-c layer directly and study how it scales with thickness. We observe that the ordering temperature of the low-T-c layer is enhanced and above which a second magnetically ordered state with a very large extension is observed. This induced magnetic state survives to a temperature at least three times that of the ordering temperature of the low-T-c layer and the induced magnetization is approximately constant throughout at least a 10-nm-thick layer. The induced magnetic region within the low-T-c layer does not depend on the thickness of the adjacent high-T-c layer. |
BibTeX:
@article{WOS:000469048500002,
author = {Thorarinsdottir, K. A. and Palonen, H. and Palsson, G. K. and Hjorvarsson, B. and Magnus, F.},
title = {Giant magnetic proximity effect in amorphous layered magnets},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {5},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.054409}
}
|
| Cwalina, K.L., Ha, H.M., Ott, N., Reinke, P., Birbilis, N. and Scully, J.R. In Operando Analysis of Passive Film Growth on Ni-Cr and Ni-Cr-Mo Alloys in Chloride Solutions JOURNAL OF THE ELECTROCHEMICAL SOCIETY 166, 11, pp. C3241-C3253 (2019) |
| Abstract: The instantaneous kinetics of oxide formation and growth, in competition
with passive film dissolution and breakdown, were investigated for Ni-22 Cr and Ni-22 Cr-6 Mo (wt%) during single step passivation at +0.2 V-SCE. Experiments were conducted in selected acidic and alkaline chloride-containing environments using simultaneous AC and DC electrochemistry; including on-line Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). In parallel experiments, in-situ neutron reflectometry (NR) and ex-situ X-ray photoelectron spectroscopy (XPS) were utilized to characterize the formation of surface oxide films as a function of time. The specific roles of pH and Mo during passivation and breakdown kinetics are highlighted, providing an insight into the fate of the elements which comprise the alloys, and their effects on passivation behavior. It was observed that early oxidation of both Ni and Cr-species occurred in acidic electrolyte. Preferential dissolution of Ni2+ at later times enabled gradual Cr3+ enrichment within the surface film. However, greater relative stability of NiO and Ni(OH)(2) was observed in the alkaline condition. Upon alloying Ni-Cr with Mo, Cr3+ became increasingly enriched in the surface film during anodic polarization. Oxides were interpreted to consist of non-stoichiometric solid solutions formed via solute capture. (C) The Author(s) 2019. Published by ECS. |
BibTeX:
@article{WOS:000468399300003,
author = {Cwalina, Katie Lutton and Ha, Hung M. and Ott, Noemie and Reinke, Petra and Birbilis, Nick and Scully, John R.},
title = {In Operando Analysis of Passive Film Growth on Ni-Cr and Ni-Cr-Mo Alloys in Chloride Solutions},
journal = {JOURNAL OF THE ELECTROCHEMICAL SOCIETY},
year = {2019},
volume = {166},
number = {11},
pages = {C3241-C3253},
doi = {https://doi.org/10.1149/2.0261911jes}
}
|
| Guo, E.-J., Desautels, R., Lee, D., Roldan, M.A., Liao, Z., Charlton, T., Ambaye, H., Molaison, J., Boehler, R., Keavney, D., Herklotz, A., Ward, T.Z., Lee, H.N. and Fitzsimmons, M.R. Exploiting Symmetry Mismatch to Control Magnetism in a Ferroelastic Heterostructure PHYSICAL REVIEW LETTERS 122, 18 (2019) |
| Abstract: In the bulk, LaCoO3 (LCO) is a paramagnet, yet the low-temperature
ferromagnetism (FM) is observed in tensile strained thin films, and its origin remains unresolved. Here, we quantitatively measured the distribution of atomic density and magnetization in LCO films by polarized neutron reflectometry (PNR) and found that the LCO layers near the heterointerfaces exhibit a reduced magnetization but an enhanced atomic density, whereas the film's interior (i.e., its film bulk) shows the opposite trend. We attribute the nonuniformity to the symmetry mismatch at the interface, which induces a structural distortion related to the ferroelasticity of LCO. This assertion is tested by systematic application of hydrostatic pressure during the PNR experiments. The magnetization can be controlled at a rate of -20.4% per GPa. These results provide unique insights into mechanisms driving FM in strained LCO films while offering a tantalizing observation that tunable deformation of the CoO6 octahedra in combination with the ferroelastic order parameter. |
BibTeX:
@article{WOS:000467404300011,
author = {Guo, Er-Jia and Desautels, Ryan and Lee, Dongkyu and Roldan, Manuel A. and Liao, Zhaoliang and Charlton, Timothy and Ambaye, Haile and Molaison, Jamie and Boehler, Reinhard and Keavney, David and Herklotz, Andreas and Ward, T. Zac and Lee, Ho Nyung and Fitzsimmons, Michael R.},
title = {Exploiting Symmetry Mismatch to Control Magnetism in a Ferroelastic Heterostructure},
journal = {PHYSICAL REVIEW LETTERS},
year = {2019},
volume = {122},
number = {18},
doi = {https://doi.org/10.1103/PhysRevLett.122.187202}
}
|
| Wood, M.H., Humphreys, E.K. and Welbourn, R.J.L. Structural Changes in Adsorbed Cytochrome c upon Applied Potential Characterized by Neutron Reflectometry LANGMUIR 35, 18, pp. 6055-6063 (2019) |
| Abstract: The structural behavior of an electron-transfer protein, cytochrome c,
at the 316L stainless steel electrode/aqueous interface was investigated over a range of applied potentials using neutron reflectometry supported by solution depletion isotherms, X-ray reflectometry, and quartz crystal microbalance measurements. A custom-made electrochemical cell allowed in situ observation of the adsorbed protein across a range of applied potentials; models fitted to the NR data showed a compact inner protein layer at the metal/electrolyte interface and a further thicker but highly diffuse layer that could be removed by rinsing. The overall amount adsorbed was found to be strongly dependent on the applied potential and buffer pH. Subtle but significant changes in the structure of the adsorbed protein layer were seen as the potential was swept between +/- 0.40 V, reflecting changing attractive/repulsive interactions between the protein's charged side groups and the surface. At greater applied potentials, irreversible changes in the stainless steel film structure were also observed and attributed to deuterium absorption into the metal. |
BibTeX:
@article{WOS:000467641300008,
author = {Wood, Mary H. and Humphreys, Elizabeth K. and Welbourn, Rebecca J. L.},
title = {Structural Changes in Adsorbed Cytochrome c upon Applied Potential Characterized by Neutron Reflectometry},
journal = {LANGMUIR},
year = {2019},
volume = {35},
number = {18},
pages = {6055-6063},
doi = {https://doi.org/10.1021/acs.langmuir.9b00691}
}
|
| Mican, S., Benea, D., Takacs, A., Mossang, E., Isnard, O. and Pop, V. Influence of ferromagnetic layer thickness on the magnetic properties of Cr/Fe1-xCox bilayers JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 21, 5-6, pp. 407-417 (2019) |
| Abstract: The influence of Fe1-xCox thickness on the magnetic properties of
Cr/Fe1-xCox bilayers is investigated. Electronic structure calculations showed that the Cr moments are suppressed by Co addition and by the deposition of multiple Fe1-xCox layers. Cr/Fe65Co35 bilayers were studied experimentally. Structural investigations showed the presence of strain and a rough Cr/Fe65Co35 interface in the measured samples. The magnetic data was analyzed using the Mauri-Siegmann model, which showed that the interfacial Cr moments decrease with increasing Fe65Co35 thickness. A large bias field of 0.09T was found at 4K for the sample with a 10 nm thick Fe65Co35 layer, around 10 times larger than previous reports. |
BibTeX:
@article{WOS:000495887400018,
author = {Mican, S. and Benea, D. and Takacs, A. and Mossang, E. and Isnard, O. and Pop, V.},
title = {Influence of ferromagnetic layer thickness on the magnetic properties of Cr/Fe1-xCox bilayers},
journal = {JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS},
year = {2019},
volume = {21},
number = {5-6},
pages = {407-417}
}
|
| Galletti, L., Schumann, T., Kealhofer, D.A., Goyal, M. and Stemmer, S. Absence of signatures of Weyl orbits in the thickness dependence of quantum transport in cadmium arsenide PHYSICAL REVIEW B 99, 20 (2019) |
| Abstract: In a Weyl orbit, the Fermi arc surface states on opposite surfaces of
the topological semimetal are connected through the bulk Weyl or Dirac nodes. Having a real-space component, these orbits accumulate a sample-size-dependent phase. Following recent work on the three-dimensional Dirac semimetal cadmium arsenide (Cd3As2), we have sought evidence for this thickness-dependent effect in quantum oscillations and quantum Hall plateaus in (112)-oriented Cd3As2 thin films grown by molecular beam epitaxy. We compare quantum transport in films of varying thicknesses at apparently identical gate-tuned carrier concentrations and find no clear dependence of the relative phase of the quantum oscillations on the sample thickness. We show that small variations in carrier densities, difficult to detect in low-field Hall measurements, lead to shifts in quantum oscillations that are commensurate with previously reported phase shifts. Future claims of Weyl orbits based on the thickness dependence of quantum transport data require additional studies that demonstrate that these competing effects have been disentangled. |
BibTeX:
@article{WOS:000466411400001,
author = {Galletti, Luca and Schumann, Timo and Kealhofer, David A. and Goyal, Manik and Stemmer, Susanne},
title = {Absence of signatures of Weyl orbits in the thickness dependence of quantum transport in cadmium arsenide},
journal = {PHYSICAL REVIEW B},
year = {2019},
volume = {99},
number = {20},
doi = {https://doi.org/10.1103/PhysRevB.99.201401}
}
|
| Bright, E.L., Rennie, S., Siberry, A., Samani, K., Clarke, K., Goddard, D.T. and Springell, R. Comparing the corrosion of uranium nitride and uranium dioxide surfaces with H2O2 JOURNAL OF NUCLEAR MATERIALS 518, pp. 202-207 (2019) |
| Abstract: Uranium mononitride, UN, is considered a potential accident tolerant
fuel due to its high uranium density, high thermal conductivity, and high melting point. Compared with the relatively inert UO2, UN has a high reactivity in water, however, studies have not considered the significant effect of radiation, which is known to cause corrosion of UO2. This study uses 0.1 M H2O2 to simulate the effects of water radiolysis in order to compare the radiolytic corrosion rates of UO2, UN, and U2N3 thin films at room temperature. X-ray reflectivity was used to investigate the changes in film morphology as a function of H2O2 exposure time, allowing changes in film thickness and roughness to be observed on the Angstrom length-scale. Results showed significant differences between UO2, UN, and U2N3, with corrosion rates of 0.083(3), 0.020(4), and 0.47(8) angstrom/s, respectively, showing that UN corrodes more slowly than UO2 in 0.1 M H2O2. (C) 2019 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000464940700020,
author = {Bright, E. Lawrence and Rennie, S. and Siberry, A. and Samani, K. and Clarke, K. and Goddard, D. T. and Springell, R.},
title = {Comparing the corrosion of uranium nitride and uranium dioxide surfaces with H2O2},
journal = {JOURNAL OF NUCLEAR MATERIALS},
year = {2019},
volume = {518},
pages = {202-207},
doi = {https://doi.org/10.1016/j.jnucmat.2019.03.006}
}
|
| Burrows, C.W., Hase, T.P.A. and Bell, G.R. Hybrid Heteroepitaxial Growth Mode PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 216, 8, SI (2019) |
| Abstract: A ``hybrid'' surface growth mode is studied by in situ scanning
tunneling microscopy and ex situ synchrotron X-ray diffraction. Heteroepitaxial growth of MnSb(0001) on GaAs(111) leads to the direct formation of islands, but the islands themselves grow in a local layer-by-layer fashion, having low aspect ratio and flat tops. Strained and relaxed islands co-exist prior to island coalescence, confirming that dislocation formation occurs locally over a range of average film thicknesses. |
BibTeX:
@article{WOS:000466554600006,
author = {Burrows, Christopher W. and Hase, Thomas P. A. and Bell, Gavin R.},
title = {Hybrid Heteroepitaxial Growth Mode},
journal = {PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE},
year = {2019},
volume = {216},
number = {8, SI},
note = {Spring Meeting of the European-Materials-Research-Society / Symposium BB / Symposium V, Strasbourg, FRANCE, JUN 18-22, 2018},
doi = {https://doi.org/10.1002/pssa.201800600}
}
|
| Fujii, H., Wakabayashi, Y. and Doi, T. Kinetics of Iron Passivation Studied by Sub-Second Resolution Realtime X-ray Reflectivity Technique JOURNAL OF THE ELECTROCHEMICAL SOCIETY 166, 8, pp. E212-E216 (2019) |
| Abstract: The early stage of electrochemically-induced Fe(001) passivation is
investigated via a sub-second resolution real-time X-ray reflectivity technique. Static measurements clearly demonstrate that the passive layer is composed of two distinct layers comprising a dense inner oxide layer and a loosely packed outer layer. The growth of the inner passive layer is mostly completed within 1 s, while the growth rate in the later process is much slower and is qualitatively consistent with typical growth models such as the high-field model and point defect model. The rate-determining mechanism in the early stage is clearly different from that in the later stage. (C) 2019 The Electrochemical Society. |
BibTeX:
@article{WOS:000465203200001,
author = {Fujii, Hiromasa and Wakabayashi, Yusuke and Doi, Takashi},
title = {Kinetics of Iron Passivation Studied by Sub-Second Resolution Realtime X-ray Reflectivity Technique},
journal = {JOURNAL OF THE ELECTROCHEMICAL SOCIETY},
year = {2019},
volume = {166},
number = {8},
pages = {E212-E216},
doi = {https://doi.org/10.1149/2.0161908jes}
}
|
| McBriarty, M.E., Stubbs, J.E., Eng, P.J. and Rosso, K.M. Reductive Dissolution Mechanisms at the Hematite-Electrolyte Interface Probed by in Situ X-ray Scattering JOURNAL OF PHYSICAL CHEMISTRY C 123, 13, SI, pp. 8077-8085 (2019) |
| Abstract: The electron-catalyzed dissolution and reprecipitation of iron
(oxyhydr)oxides constitute critical steps in natural geochemical iron cycling. However, the atomic-scale mechanisms of reductive dissolution and oxidative precipitation of Fe2+ remain poorly understood because they are difficult to directly experimentally probe. Using in situ synchrotron X-ray scattering and a novel electrochemical cell, we interrogate the interfacial structure between the hematite (alpha-Fe2O3) (1 (1) over bar 02) surface and acidic aqueous solution (5 mM Na2SO4, pH 4.0) under controlled electrochemical potential from the open circuit condition to cathodic bias as the reductive dissolution potential is approached and then exceeded. The crystalline order of the surface improves under mild reducing conditions, and the surface Fe stoichiometry changes with cathodic bias. After significant reductive dissolution occurs and cathodic bias is removed, dissolved Fe is redeposited, forming a disordered interface. Unlike at circumneutral pH, water layers at the hematite interface with acidic solution are poorly ordered, likely due to the adsorption of sulfate from the electrolyte. These results provide a novel atomic-scale view into the behavior of reducible transition metal oxide surfaces under fluctuating (electro)chemical conditions. |
BibTeX:
@article{WOS:000463844500056,
author = {McBriarty, Martin E. and Stubbs, Joanne E. and Eng, Peter J. and Rosso, Kevin M.},
title = {Reductive Dissolution Mechanisms at the Hematite-Electrolyte Interface Probed by in Situ X-ray Scattering},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2019},
volume = {123},
number = {13, SI},
pages = {8077-8085},
doi = {https://doi.org/10.1021/acs.jpcc.8b07413}
}
|
| Plech, A., Krause, B., Baumbach, T., Zakharova, M., Eon, S., Girmen, C., Buth, G. and Bracht, H. Structural and Thermal Characterisation of Nanofilms by Time-Resolved X-ray Scattering NANOMATERIALS 9, 4 (2019) |
| Abstract: High time resolution in scattering analysis of thin films allows for
determination of thermal conductivity by transient pump-probe detection of dissipation of laser-induced heating, TDXTS. We describe an approach that analyses the picosecond-resolved lattice parameter reaction of a gold transducer layer on pulsed laser heating to determine the thermal conductivity of layered structures below the transducer. A detailed modeling of the cooling kinetics by a Laplace-domain approach allows for discerning effects of conductivity and thermal interface resistance as well as basic depth information. The thermal expansion of the clamped gold film can be calibrated to absolute temperature change and effects of plastic deformation are discriminated. The method is demonstrated on two extreme examples of phononic barriers, isotopically modulated silicon multilayers with very small acoustic impedance mismatch and silicon-molybdenum multilayers, which show a high resistivity. |
BibTeX:
@article{WOS:000467768800017,
author = {Plech, Anton and Krause, Barbel and Baumbach, Tilo and Zakharova, Margarita and Eon, Soizic and Girmen, Caroline and Buth, Gernot and Bracht, Hartmut},
title = {Structural and Thermal Characterisation of Nanofilms by Time-Resolved X-ray Scattering},
journal = {NANOMATERIALS},
year = {2019},
volume = {9},
number = {4},
doi = {https://doi.org/10.3390/nano9040501}
}
|
| Chen, Y., Tilka, J.A., Ahn, Y., Park, J., Pateras, A., Zhou, T., Savage, D.E., McNulty, I., Holt, M.V., Paskiewicz, D.M., Fong, D.D., Kuech, T.F. and Evans, P.G. Seeded Lateral Solid-Phase Crystallization of the Perovskite Oxide SrTiO3 JOURNAL OF PHYSICAL CHEMISTRY C 123, 12, pp. 7447-7456 (2019) |
| Abstract: Crystallization from an amorphous precursor presents a new route to
control the properties of complex oxides by selecting their nanoscale morphology. A key challenge in crystal growth from the amorphous form is to select the locations of nucleation and the crystallographic orientation of the resulting crystals. Nucleation sites for crystallization of the prototypical perovskite complex oxide SrTiO3 (STO) from its amorphous form can be reproducibly introduced using nanoscale seed crystals. The results of two seeding strategies are reported here: (i) SrRuO3 (SRO) (001)-oriented nanomembranes and (ii) STO nanocrystalline seeds. Amorphous STO crystallizes laterally over distances of several microns from the seeds before encountering separately nucleated crystals. The lateral crystallization rates for both types of seeding methods are close to the values measured in solidphase epitaxy (SPE) of STO on single-crystal substrates. The lateral crystallization distances along different crystallographic orientations are equal, indicating that the lateral crystallization rate is isotropic. The isotropic crystallization suggests that the rate-limiting steps for crystallization occur within the amorphous STO away from the amorphous/crystalline interface. In addition to the lateral crystallization, STO crystallizes on top of the planar SRO nanomembrane seeds via SPE, forming partially relaxed [001]-oriented heteroepitaxial STO layers. The in-plane orientation of laterally crystallized STO near the SRO nanomembrane seeds exhibits overall polycrystallinity with regions in which micron-scale grains of laterally crystallized STO share the same in-plane orientation as the SRO nanomembrane seeds. Crystallization from seed crystals provides opportunities to create a wide range of other perovskite oxides in nanoscale geometries. |
BibTeX:
@article{WOS:000463115500055,
author = {Chen, Yajin and Tilka, Jack A. and Ahn, Youngjun and Park, Joonkyu and Pateras, Anastasios and Zhou, Tao and Savage, Donald E. and McNulty, Ian and Holt, Martin V. and Paskiewicz, Deborah M. and Fong, Dillon D. and Kuech, Thomas F. and Evans, Paul G.},
title = {Seeded Lateral Solid-Phase Crystallization of the Perovskite Oxide SrTiO3},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2019},
volume = {123},
number = {12},
pages = {7447-7456},
doi = {https://doi.org/10.1021/acs.jpcc.9b00078}
}
|
| Ha, H.M. and Fritzsche, H. In-Situ Polarized Neutron Reflectometry Study of the Passive Film Growth on Fe-20Cr Alloy JOURNAL OF THE ELECTROCHEMICAL SOCIETY 166, 11, pp. C3064-C3067 (2019) |
| Abstract: Metal dissolution and passivation of Fe-20Cr alloy in an alkaline
solution were investigated using in-situ polarized neutron reflectometry. The dissolution of the alloy, the thickness of sub-layers in the passive film, the interfacial roughness between layers, and the scattering length density profile of the passive film were measured with sub-nanometer resolution. An anodization ratio for oxide growth of 3.4 +/- 0.4 nm/V was determined. The oxide formation efficiency and the layer density at different applied potentials were also quantified. (C) The Author(s) 2019. Published by ECS. |
BibTeX:
@article{WOS:000486946100001,
author = {Ha, Hung M. and Fritzsche, Helmut},
title = {In-Situ Polarized Neutron Reflectometry Study of the Passive Film Growth on Fe-20Cr Alloy},
journal = {JOURNAL OF THE ELECTROCHEMICAL SOCIETY},
year = {2019},
volume = {166},
number = {11},
pages = {C3064-C3067},
doi = {https://doi.org/10.1149/2.0081911jes}
}
|
| McCluskey, A.R., Sanchez-Fernandez, A., Edler, K.J., Parker, S.C., Jackson, A.J., Campbell, R.A. and Arnold, T. Bayesian determination of the effect of a deep eutectic solvent on the structure of lipid monolayers PHYSICAL CHEMISTRY CHEMICAL PHYSICS 21, 11, pp. 6133-6141 (2019) |
| Abstract: In this work, we present the first example of the self-assembly of
phospholipid monolayers at the interface between air and an ionic solvent. Deep eutectic solvents are a novel class of environmentally friendly, non-aqueous, room temperature liquids with tunable properties, that have wide-ranging potential applications and are capable of promoting the self-assembly of surfactant molecules. We use a chemically-consistent Bayesian modelling of X-ray and neutron reflectometry measurements to show that these monolayers broadly behave as they do on water. This method allows for the monolayer structure to be determined, alongside the molecular volumes of the individual monolayer components, without the need for water-specific constraints to be introduced. Furthermore, using this method we are able to better understand the correlations present between parameters in the analytical model. This example of a non-aqueous phospholipid monolayer has important implications for the potential uses of these solvents and for our understanding of how biomolecules behave in the absence of water. |
BibTeX:
@article{WOS:000462659300025,
author = {McCluskey, Andrew R. and Sanchez-Fernandez, Adrian and Edler, Karen J. and Parker, Stephen C. and Jackson, Andrew J. and Campbell, Richard A. and Arnold, Thomas},
title = {Bayesian determination of the effect of a deep eutectic solvent on the structure of lipid monolayers},
journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
year = {2019},
volume = {21},
number = {11},
pages = {6133-6141},
doi = {https://doi.org/10.1039/c9cp00203k}
}
|
| Blank, M. and Weber, L. Towards a coherent database of thermal boundary conductance at metal/dielectric interfaces JOURNAL OF APPLIED PHYSICS 125, 9 (2019) |
| Abstract: The thermal boundary conductance (TBC) of metal/dielectric couples was
measured for a large variety of metals on silicon, sapphire, and diamond using time domain thermoreflectance and compared to data previously obtained on diamond. In the case of silicon, HF-cleaned and RF-etched surfaces were tested. The detailed structure of these interfaces was studied, allowing distinction of two different cases of M/Si couples: (i) some amount of interfacial reaction exists for both surface terminations, resulting in similar TBCs; and (ii) chemically abrupt interfaces are achieved, resulting in TBC values that are always lower for RF-etched samples. The TBC values obtained on different substrates allowed identifying a tendency of the TBC to scale with the maximum transmission limit. A possible influence of the substrate was evaluated using both the diffuse mismatch model (DMM), which predicts a strong dependence on the substrate properties, and a newly developed approach based on the metal irradiance (IM), which predicts no dependence on the substrate properties. The DMM was implemented using a Debye model with either a linear (DMMLinear) or a Sine-Type (DMMSineType) dispersion, while the IM was implemented using a Sine-Type (IMSineType) dispersion. The DMMLinear and the IMSineType were found to be more suitable than the DMMSineType and to be equally precise in predicting TBC at metal/silicon and metal/sapphire interfaces. The IMSineType is found to be better suited than both the DMMLinear and the DMMSineType to predict TBC at metal/diamond interfaces. IMSineType being the only model tested that is suitable for all three substrates, it appears to be the most appropriate choice. As a corollary, we find that the TBC dependence on substrate properties is much weaker than predicted by the DMM. |
BibTeX:
@article{WOS:000460784900032,
author = {Blank, Maite and Weber, Ludger},
title = {Towards a coherent database of thermal boundary conductance at metal/dielectric interfaces},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2019},
volume = {125},
number = {9},
doi = {https://doi.org/10.1063/1.5085176}
}
|
| Jiang, W., Zhang, S., Wang, X., Phatak, C., Wang, Q., Zhang, W., Jungfleisch, M.B., Pearson, J.E., Liu, Y., Zang, J., Cheng, X., Petford-Long, A., Hoffmann, A. and te Velthuis, S.G.E. Quantifying chiral exchange interaction for Neel-type skyrmions via Lorentz transmission electron microscopy PHYSICAL REVIEW B 99, 10 (2019) |
| Abstract: Magnetic skyrmions are topological spin textures that have been observed
in bulk magnets and magnetic multilayers. For bulk magnetic materials, their noncollinear spin profiles have often been studied by using Lorentz transmission electron microscopy (TEM). We experimentally utilized Lorentz TEM imaging to study an inversion asymmetric [Pt(1.5nm)/Co(1 nm)/W(1 nm)](8) heterostructure that exhibits Neel-type skyrmions at zero field. By tracking the evolution of skyrmion diameters as a function of magnetic fields, we determined the strength of the interfacial Dzyaloshinskii-Moriya interaction (DMI). Our results suggest that in situ Lorentz TEM imaging combined with simulations can provide valuable quantitative information about the interfacial DMI strengths, which can be helpful for optimizing skyrmion materials. Furthermore, we show that in theory, Lorentz TEM can identify the spin chirality of Neel-type skyrmions, although an experimental verification is challenging due to the relatively low signal-to-noise ratio. |
BibTeX:
@article{WOS:000460720200003,
author = {Jiang, Wanjun and Zhang, Sheng and Wang, Xiao and Phatak, Charudatta and Wang, Qiang and Zhang, Wei and Jungfleisch, Matthias Benjamin and Pearson, John E. and Liu, Yizhou and Zang, Jiadong and Cheng, Xuemei and Petford-Long, Amanda and Hoffmann, Axel and te Velthuis, Suzanne G. E.},
title = {Quantifying chiral exchange interaction for Neel-type skyrmions via Lorentz transmission electron microscopy},
journal = {PHYSICAL REVIEW B},
year = {2019},
volume = {99},
number = {10},
doi = {https://doi.org/10.1103/PhysRevB.99.104402}
}
|
| Lau, C., Kim, Y., Albright, S., Char, K., Ahn, C.H. and Walker, F.J. Structural characterization of the LaInO3/BaSnO3 interface via synchrotron scattering APL MATERIALS 7, 3 (2019) |
| Abstract: The alkaline earth stannate BaSnO3 is a semiconductor with high carrier
mobility at room-temperature when doped with La3+. When a thin epitaxial layer of LaInO3 is grown on lightly doped BaSnO3, a polar discontinuity between the orthorhombic, polar LaInO3 and the cubic, nonpolar Ba0.998La0.002SnO3 leads to an electronic reconstruction, where LaInO3 remotely dopes Ba0.998La0.002SnO3, creating carriers for high mobility devices. We determine aspects of the crystalline structure of the LaInO3/BaSnO3 film that affect the polar discontinuity using synchrotron x-ray diffraction. Specifically, we examine the role of oxygen octahedral rotations and anti-parallel cation displacements in influencing the polarization of the LaInO3/BaSnO3 interface. These structural distortions are characterized by measuring half-order Bragg peaks of thin film LaInO3/BaSnO3/SrTiO3 heterostructures grown by pulsed laser deposition. We find that for films as thin as 3 unit cells, epitaxial LaInO3 has 2 distinct domains, one with the same Glazer tilt pattern as that of bulk LaInO3, a(+)b(-)b(-), and a second rotated 90 in-plane from the first and having tilt pattern b a(+)b Additionally, we observe a sudden and large increase in cation displacements along the [011] and [101] directions across the LaInO3/BaSnO3 interface due to the strength of the octahedral rotations. (C) 2019 Author(s). |
BibTeX:
@article{WOS:000462880800011,
author = {Lau, Claudia and Kim, Youjung and Albright, Stephen and Char, Kookrin and Ahn, C. H. and Walker, F. J.},
title = {Structural characterization of the LaInO3/BaSnO3 interface via synchrotron scattering},
journal = {APL MATERIALS},
year = {2019},
volume = {7},
number = {3},
doi = {https://doi.org/10.1063/1.5084058}
}
|
| Fritzsche, H., Ellis, B., Patel, J. and Lang, J. The long-term stability of deuterated thin titanium films INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 44, 12, pp. 6031-6035 (2019) |
| Abstract: Using neutron reflectometry, we investigated the deuterium desorption of
Pd-covered Ti films that have been deuterated at 1 bar deuterium at room temperature and then exposed to air. The deuterium content was monitored continuously for the first two days. Thereafter, measurements were conducted periodically, spanning a period of up to 2 years. The films were in the thickness range of 10-300 nm and the desorption behaviour showed a strong dependence on the film thickness. The smaller the Ti film thickness the faster the Ti films desorbed the stored deuterium. Crown Copyright (C) 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. All rights reserved. |
BibTeX:
@article{WOS:000461410200037,
author = {Fritzsche, H. and Ellis, B. and Patel, J. and Lang, J.},
title = {The long-term stability of deuterated thin titanium films},
journal = {INTERNATIONAL JOURNAL OF HYDROGEN ENERGY},
year = {2019},
volume = {44},
number = {12},
pages = {6031-6035},
doi = {https://doi.org/10.1016/j.ijhydene.2019.01.053}
}
|
| Al-Tawhid, A., Frick, J.R., Dougherty, D.B. and Kumah, D.P. Growth-temperature dependence of conductivity at the LaCrO3/SrTiO3 (001) interface JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 37, 2 (2019) |
| Abstract: The effect of growth conditions and postgrowth treatment on the
structural and electronic properties of the polar/nonpolar LaCrO3/SrTiO3 (LCO/STO) interface has been investigated. Under low oxygen partial pressure, oxygen vacancies are formed in the STO substrate resulting in metallicity with a measured sheet carrier concentration of 10(16) cm(-2). Annealing postgrowth in flowing oxygen causes the sheet carrier concentration to saturate to 10(13) cm(-2), which is consistent with the reported values of a two-dimensional gas at other polar/STO interfaces. However, growth under nonreducing growth conditions leads to insulating behavior. High-resolution synchrotron x-ray-based structural determination of the atomic-scale structures of both metallic and insulating LCO/STO interfaces shows chemical intermixing and an interfacial lattice expansion. Published by the AVS. |
BibTeX:
@article{WOS:000460437200039,
author = {Al-Tawhid, Athby and Frick, Jordan R. and Dougherty, Daniel B. and Kumah, Divine P.},
title = {Growth-temperature dependence of conductivity at the LaCrO3/SrTiO3 (001) interface},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2019},
volume = {37},
number = {2},
doi = {https://doi.org/10.1116/1.5085334}
}
|
| Abharana, N., Biswas, A., Sarkar, P., Rajput, P., Rajnarayan, D., Rao, K.D., Modi, M.H., Bhattacharyya, D., Jha, S.N. and Sahoo, N.K. Interface studies of Mo/Si multilayers with carbon diffusion barrier by grazing incidence extended X-ray absorption fine structure THIN SOLID FILMS 673, pp. 126-135 (2019) |
| Abstract: Single layer Mo and Si thin films deposited for different deposition
times on c-Si substrates by Ion beam sputtering technique have been characterized by Grazing Incidence X-ray Reflectivity (GIXRR) measurements. Subsequently, few Mo/Si multilayers having 5 bi-layers with different Mo to bi-layer thickness ratio (Gamma) at a fixed bi-layer thickness have been deposited and characterized by GIXRR measurements. Investigation has been carried out on the different behaviors of the interfaces and also variation of the interface width with Gamma has been studied. Finally, 25 bi-layer Mo/Si multilayer samples having the lowest Gamma value and with and without carbon diffusion barrier layer at both the Mo/Si interfaces are deposited and the interfaces have been characterized by hard X-ray and soft X-ray reflectivity measurements. The study shows improvement in reflectivities of the multilayer with carbon diffusion barrier layer from 38% to 54% at 130 angstrom wavelength. To have further insight into the modification of the interface due to introduction of the carbon barrier layer, depth selective study of both the multilayers have been carried out by Grazing Incidence Extended X-ray Absorption Fine Structure measurements using synchrotron radiation and thereby investigating the local structures around Mo atoms in Si bulk region and Si-on-Mo interface. This study confirms the reduction of diffusion of Mo and Si layer into each other when the carbon buffer layers are present at the interfaces, thus reducing the chance of formation of MoSi2. |
BibTeX:
@article{WOS:000458272100019,
author = {Abharana, N. and Biswas, A. and Sarkar, P. and Rajput, P. and Rajnarayan, De and Rao, K. D. and Modi, M. H. and Bhattacharyya, D. and Jha, S. N. and Sahoo, N. K.},
title = {Interface studies of Mo/Si multilayers with carbon diffusion barrier by grazing incidence extended X-ray absorption fine structure},
journal = {THIN SOLID FILMS},
year = {2019},
volume = {673},
pages = {126-135},
doi = {https://doi.org/10.1016/j.tsf.2019.01.033}
}
|
| Machhadani, H., Zichi, J., Bougerol, C., Lequien, S., Thomassin, J.-L., Mollard, N., Mukhtarova, A., Zwiller, V., Gerard, J.-M. and Monroy, E. Improvement of the critical temperature of NbTiN films on III-nitride substrates SUPERCONDUCTOR SCIENCE & TECHNOLOGY 32, 3 (2019) |
| Abstract: In this paper, we study the impact of using III-nitride semiconductors
(GaN, AlN) as substrates for ultrathin (11 nm) superconducting films of NbTiN deposited by reactive magnetron sputtering. The resulting NbTiN layers are (111)-oriented, fully relaxed, and they keep an epitaxial relation with the substrate. The higher critical superconducting temperature (T-c = 11.8 K) was obtained on AIN-on-sapphire, which was the substrate with smaller lattice mismatch with NbTiN. We attribute this improvement to a reduction of the NbTiN roughness, which appears associated with the relaxation of the lattice misfit with the substrate. On AlN-on-sapphire, superconducting nanowire single photon detectors were fabricated and tested, obtaining external quantum efficiencies that are in excellent agreement with theoretical calculations. |
BibTeX:
@article{WOS:000458129800001,
author = {Machhadani, Houssaine and Zichi, Julien and Bougerol, Catherine and Lequien, Stephane and Thomassin, Jean-Luc and Mollard, Nicolas and Mukhtarova, Anna and Zwiller, Val and Gerard, Jean-Michel and Monroy, Eva},
title = {Improvement of the critical temperature of NbTiN films on III-nitride substrates},
journal = {SUPERCONDUCTOR SCIENCE & TECHNOLOGY},
year = {2019},
volume = {32},
number = {3},
doi = {https://doi.org/10.1088/1361-6668/aaf99d}
}
|
| Joress, H., Arlington, S.Q., Weihs, T.P., Brock, J.D. and Woll, A.R. X-ray reflectivity with a twist: Quantitative time-resolved X-ray reflectivity using monochromatic synchrotron radiation APPLIED PHYSICS LETTERS 114, 8 (2019) |
| Abstract: We have developed an improved method of time-resolved x-ray reflectivity
(XRR) using monochromatic synchrotron radiation. Our method utilizes a polycapillary x-ray optic to create a range of incident angles and an area detector to collect specular reflections. By rotating the sample normal out of the plane of the incident fan, we can separate the surface diffuse scatter from the reflectivity signal, greatly improving the quality of the XRR spectra compared to previous implementations. We demonstrate the time-resolved capabilities of this system, with the temporal resolution as low as 10 ms, by measuring XRR during the annealing of Al/Ni nano-scale multilayers, and use this information to extract the activation energy for interdiffusion in this system. Published under license by AIP Publishing. |
BibTeX:
@article{WOS:000460134000009,
author = {Joress, Howie and Arlington, Shane Q. and Weihs, Timothy P. and Brock, Joel D. and Woll, Arthur R.},
title = {X-ray reflectivity with a twist: Quantitative time-resolved X-ray reflectivity using monochromatic synchrotron radiation},
journal = {APPLIED PHYSICS LETTERS},
year = {2019},
volume = {114},
number = {8},
doi = {https://doi.org/10.1063/1.5085063}
}
|
| Weber, T., Abb, M.J.S., Khalid, O., Pfrommer, J., Carla, F., Znaiguia, R., Vonk, V., Stierle, A. and Over, H. In Situ Studies of the Electrochemical Reduction of a Supported Ultrathin Single-Crystalline RuO2(110) Layer in an Acidic Environment JOURNAL OF PHYSICAL CHEMISTRY C 123, 7, pp. 3979-3987 (2019) |
| Abstract: With in situ surface X-ray diffraction (SXRD) and X-ray reflectivity
(XRR) in combination with ex situ characterization by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry, the electrochemical reduction of an ultrathin (1.66 nm thick) single-crystalline RuO2(110) layer supported on Ru(0001) is studied in an acidic environment, providing clear-cut evidence and mechanistic details for the transformation of RuO2 to hydrous RuO2 and metallic Ru. The reduction process proceeds via proton insertion into the RuO2(110) lattice. For electrode potentials (0 to -50 mV vs standard hydrogen electrode), the layer spacing of RuO2(110) increased, maintaining the octahedral coordination of Ru (SXRD). Continuous proton insertion at -100 to -150 mV leads to the transformation of the lattice oxygen of RuO2 to OH and water, which destroys the connectivity among the Ru-O-6 octahedrons and eventually leads to the loss of crystallinity (SXRD) in the RuO2(110) film at -200 mV accompanied by a swelling of the layer with a well-defined thickness (XRR). During the protonation process, soluble Ru complexes may form. With XPS the transformation of RuO2(110) to a hydrous RuO2 layer is followed, a process that proceeds first homogeneously and at higher cathodic potentials heterogeneously by re-deposition of previously electrochemically dissolved Ru complexes. |
BibTeX:
@article{WOS:000459836900007,
author = {Weber, Tim and Abb, Marcel J. S. and Khalid, Omeir and Pfrommer, Johannes and Carla, Francesco and Znaiguia, Raja and Vonk, Vedran and Stierle, Andreas and Over, Herbert},
title = {In Situ Studies of the Electrochemical Reduction of a Supported Ultrathin Single-Crystalline RuO2(110) Layer in an Acidic Environment},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2019},
volume = {123},
number = {7},
pages = {3979-3987},
doi = {https://doi.org/10.1021/acs.jpcc.8b10741}
}
|
| Mitterhuber, L., Kraker, E. and Defregger, S. Structure Function Analysis of Temperature-Dependent Thermal Properties of Nm-Thin Nb2O5 ENERGIES 12, 4 (2019) |
| Abstract: A 166-nm-thick amorphous Niobium pentoxide layer (Nb2O5) on a silicon
substrate was investigated by using time domain thermoreflectance at ambient temperatures from 25 degrees C to 500 degrees C. In the time domain thermoreflectance measurements, thermal transients with a time resolution in (sub-)nanoseconds can be obtained by a pump-probe laser technique. The analysis of the thermal transient was carried out via the established analytical approach, but also by a numerical approach. The analytical approach showed a thermal diffusivity and thermal conductivity from 0.43 mm(2)/s to 0.74 mm(2)/s and from 1.0 W/mK to 2.3 W/mK, respectively to temperature. The used numerical approach was the structure function approach to map the measured heat path in terms of a RthCth-network. The structure function showed a decrease of R-th with increasing temperature according to the increasing thermal conductivity of Nb2O5. The combination of both approaches contributes to an in-depth thermal analysis of Nb2O5 film. |
BibTeX:
@article{WOS:000460667700036,
author = {Mitterhuber, Lisa and Kraker, Elke and Defregger, Stefan},
title = {Structure Function Analysis of Temperature-Dependent Thermal Properties of Nm-Thin Nb2O5},
journal = {ENERGIES},
year = {2019},
volume = {12},
number = {4},
doi = {https://doi.org/10.3390/en12040610}
}
|
| Foster, N.D., Edmondson, B.I., Ekerdt, J.G., Smith, D.J. and Downer, M.C. Strain-dependence of chi((2)) in thin film barium strontium titanate AIP ADVANCES 9, 2 (2019) |
| Abstract: Optical second-harmonic generation (SHG) in reflection characterized
variations in the second- order nonlinear optical susceptibility chi((2)) of Ba1-xSrxTiO3 (BSTO) alloy films grown epitaxially on SrTiO3(001) (STO) as Sr molar ratio x changed from 0 to 1 and thickness from 10 to 50 nm. X-ray diffraction showed that BSTO films with x & 0.1 were highly crystalline and compressively strained with out-of-plane (in-plane) lattice constant 4.09 > c > 3.97 (3.903 < a < 3.907 angstrom, pinned to substrate) for 0 < x < 1. Spectroscopic ellipsometry showed that the BSTO dielectric function was nearly x-invariant in the range of fundamental (780 nm) and SH (390 nm) wavelengths. SHG intensity peaked at x similar to 0.3 for a given film thickness, suggesting that composition control can optimize ferroelectric and electro-optic properties of BSTO films grown on STO buffer layers. (c) 2019 Author(s). |
BibTeX:
@article{WOS:000460029500100,
author = {Foster, Natalie D. and Edmondson, Bryce I. and Ekerdt, John G. and Smith, David J. and Downer, Michael C.},
title = {Strain-dependence of chi((2)) in thin film barium strontium titanate},
journal = {AIP ADVANCES},
year = {2019},
volume = {9},
number = {2},
doi = {https://doi.org/10.1063/1.5055731}
}
|
| Cooper, C.B., Beard, E.J., Vazquez-Mayagoitia, A., Stan, L., Stenning, G.B.G., Nye, D.W., Vigil, J.A., Tomar, T., Jia, J., Bodedla, G.B., Chen, S., Gallego, L., Franco, S., Carella, A., Thomas, K.R.J., Xue, S., Zhu, X. and Cole, J.M. Design-to-Device Approach Affords Panchromatic Co-Sensitized Solar Cells ADVANCED ENERGY MATERIALS 9, 5 (2019) |
| Abstract: Data-driven materials discovery has become increasingly important in
identifying materials that exhibit specific, desirable properties from a vast chemical search space. Synergic prediction and experimental validation are needed to accelerate scientific advances related to critical societal applications. A design-to-device study that uses high-throughput screens with algorithmic encodings of structure-property relationships is reported to identify new materials with panchromatic optical absorption, whose photovoltaic device applications are then experimentally verified. The data-mining methods source 9431 dye candidates, which are auto-generated from the literature using a custom text-mining tool. These candidates are sifted via a data-mining workflow that is tailored to identify optimal combinations of organic dyes that have complementary optical absorption properties such that they can harvest all available sunlight when acting as co-sensitizers for dye-sensitized solar cells (DSSCs). Six promising dye combinations are shortlisted for device testing, whereupon one dye combination yields co-sensitized DSSCs with power conversion efficiencies comparable to those of the high-performance, organometallic dye, N719. These results demonstrate how data-driven molecular engineering can accelerate materials discovery for panchromatic photovoltaic or other applications. |
BibTeX:
@article{WOS:000459624100001,
author = {Cooper, Christopher B. and Beard, Edward J. and Vazquez-Mayagoitia, Alvaro and Stan, Liliana and Stenning, Gavin B. G. and Nye, Daniel W. and Vigil, Julian A. and Tomar, Tina and Jia, Jingwen and Bodedla, Govardhana B. and Chen, Song and Gallego, Lucia and Franco, Santiago and Carella, Antonio and Thomas, K. R. Justin and Xue, Song and Zhu, Xunjin and Cole, Jacqueline M.},
title = {Design-to-Device Approach Affords Panchromatic Co-Sensitized Solar Cells},
journal = {ADVANCED ENERGY MATERIALS},
year = {2019},
volume = {9},
number = {5},
doi = {https://doi.org/10.1002/aenm.201802820}
}
|
| Nelson, A.R.J. and Prescott, S.W. refnx: neutron and X-ray reflectometry analysis in Python JOURNAL OF APPLIED CRYSTALLOGRAPHY 52, 1, pp. 193-200 (2019) |
| Abstract: refnx is a model-based neutron and X-ray reflectometry data analysis
package written in Python. It is cross platform and has been tested on Linux, macOS and Windows. Its graphical user interface is browser based, through a Jupyter notebook. Model construction is modular, being composed from a series of components that each describe a subset of the interface, parameterized in terms of physically relevant parameters (volume fraction of a polymer, lipid area per molecule etc.). The model and data are used to create an objective, which is used to calculate the residuals, log-likelihood and log-prior probabilities of the system. Objectives are combined to perform co-refinement of multiple data sets and mixed-area models. Prior knowledge of parameter values is encoded as probability distribution functions or bounds on all parameters in the system. Additional prior probability terms can be defined for sets of components, over and above those available from the parameters alone. Algebraic parameter constraints are available. The software offers a choice of fitting approaches, including least-squares (global and gradient-based optimizers) and a Bayesian approach using a Markov-chain Monte Carlo algorithm to investigate the posterior distribution of the model parameters. The Bayesian approach is useful for examining parameter covariances, model selection and variability in the resulting scattering length density profiles. The package is designed to facilitate reproducible research; its use in Jupyter notebooks, and subsequent distribution of those notebooks as supporting information, permits straightforward reproduction of analyses. |
BibTeX:
@article{WOS:000457697200021,
author = {Nelson, Andrew R. J. and Prescott, Stuart W.},
title = {refnx: neutron and X-ray reflectometry analysis in Python},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2019},
volume = {52},
number = {1},
pages = {193-200},
doi = {https://doi.org/10.1107/S1600576718017296}
}
|
| Hoang, H., Hori, T., Yasuda, T.-o., Kizu, T., Tsukagoshi, K., Nabatame, T., Trinh, B.N.Q. and Fujiwara, A. Si-doping effect on solution-processed In-O thin-film transistors MATERIALS RESEARCH EXPRESS 6, 2 (2019) |
| Abstract: In this work, silicon-doped indium oxide thin-film transistors (TFTs)
have been fabricated for the first time by a solution processing method. By varying the Si concentration in the In2O3-SiO2 binary oxide structure up to 15 at%, the thicknesses, densities, and crystallinity of the resulting In Si-O (ISO) thin films were investigated by x-ray reflectivity (XRR) and x-ray diffraction techniques, while the produced TFTs were characterized by a conventional three-probe method. The results of XRR analysis revealed that the increase in the content of Si dopant increased the thickness of the produced film and reduced its density, and that all the Si-doped ISO thin films contained only a single amorphous phase even after annealing at temperatures as high as 800 degrees C. The manufactured ISO TFTs exhibited a reduction in the absolute value of threshold voltage V-T close to 0 V and low current in the off-state, as compared to those of the non-doped indium oxide films, due to the reduced number of oxygen defects, which was consistent with the behavior of ISO TFTs fabricated by a sputtering method. The ISO TFT with a Si content of 3 at% annealed at 400 degrees C demonstrated the smallest subthreshold swing of 0.5 V/dec, V-T of -5 V, mobility of 0.21 cm(2) Vs(-1,) and on/off current ratio of about 2 x 10(7). |
BibTeX:
@article{WOS:000450228200005,
author = {Hoang, Ha and Hori, Tatsuki and Yasuda, To-oru and Kizu, Takio and Tsukagoshi, Kazuhito and Nabatame, Toshihide and Bui Nguyen Quoc Trinh and Fujiwara, Akihiko},
title = {Si-doping effect on solution-processed In-O thin-film transistors},
journal = {MATERIALS RESEARCH EXPRESS},
year = {2019},
volume = {6},
number = {2},
doi = {https://doi.org/10.1088/2053-1591/aaecf9}
}
|
| Kane, A.M., Chopdekar, R.V., N'Diaye, A.T., Scholl, A., Arenholz, E., Mehta, A. and Takamura, Y. Decoupling exchange bias and coercivity enhancement in a perovskite oxide exchange spring bilayer PHYSICAL REVIEW MATERIALS 3, 1 (2019) |
| Abstract: A wedge bilayer of epitaxial 4-8 nm La0.7Sr0.3CoO3(LSCO)/6-nm
La0.7Sr0.3MnO3 (LSMO), hard and soft ferromagnets (FM) respectively, was studied using soft x-ray magnetic spectroscopy to elucidate the interplay between the magnetic and electronic properties of the constituent layers. This system exhibits magnetic and electronic segregation within the LSCO layer characterized by soft FM Co2+ ions at the interface (s-LSCO), which is biased by the underlying hard LSCO layer (h-LSCO), characterized by predominantly Co3+/Co4+ FM ions. For a 5.1-nm layer, the interfacial Co2+ ion concentration is maximized and the h-LSCO coercivity is minimized, while the opposite is true for a 7.8-nm LSCO layer. These dual trends in Co2+ ion concentration and h-LSCO coercivity within the LSCO serve to independently affect the exchange bias and coercivity of the soft FM layer, resulting in inverse trends between these properties that typically vary simultaneously. |
BibTeX:
@article{WOS:000456796500002,
author = {Kane, Alexander M. and Chopdekar, Rajesh V. and N'Diaye, Alpha T. and Scholl, Andreas and Arenholz, Elke and Mehta, Apurva and Takamura, Yayoi},
title = {Decoupling exchange bias and coercivity enhancement in a perovskite oxide exchange spring bilayer},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2019},
volume = {3},
number = {1},
doi = {https://doi.org/10.1103/PhysRevMaterials.3.014413}
}
|
| Morrison, K. Diffraction techniques CHARACTERISATION METHODS IN SOLID STATE AND MATERIALS SCIENCE (2019) |
| Abstract: In this chapter a broad overview of diffraction techniques for the study
of crystal structure and thin films will be given. This will start with a discussion of the theory of elastic scattering, including the cross section, and structural and magnetic form factors for specific elements. Key details on the general methods, such as sources and detectors will then be presented, followed by more detailed treatment of each experimental technique. The aim will be to provide the reader with a broad understanding of the limiting factors in such measurements, with enough detail to meaningfully compare the advantages of using x-rays or neutrons (for example) for a particular material system. Finally, some examples of these approaches will be highlighted, followed by questions specific to data analysis. |
BibTeX:
@incollection{WOS:000550569600003,
author = {Morrison, Kelly},
title = {Diffraction techniques},
booktitle = {CHARACTERISATION METHODS IN SOLID STATE AND MATERIALS SCIENCE},
year = {2019},
doi = {https://doi.org/10.1088/2053-2563/ab2df5ch3}
}
|
| Anyfantis I, D., Sarigiannidou, E., Rapenne, L., Stamatelatos, A., Ntemogiannis, D., Kapaklis, V. and Poulopoulos, P. Unexpected Development of Perpendicular Magnetic Anisotropy in Ni/NiO Multilayers After Mild Thermal Annealing IEEE MAGNETICS LETTERS 10 (2019) |
| Abstract: We report on the significant enhancement of perpendicular magnetic
anisotropy of Ni/NiO multilayers after mild annealing up to 90 min at 250 degrees C. Transmission electron microscopy shows that after annealing, a partial crystallization of the initially amorphous NiO layers occurs. This turns out to be the source of the anisotropy enhancement. Magnetic measurements reveal that even multilayers with Ni layers as thick as 7 nm, which in the as-deposited state showed in-plane anisotropy with square hysteresis loops, show reduced in-plane remanence after thermal treatment. Hysteresis loops recorded with the field in the normal-to-film-plane direction provide evidence for perpendicular magnetic anisotropy with up and down magnetic domains at remanence. A plot of effective uniaxial magnetic anisotropy constant times individual Ni layer thickness as a function of individual Ni layer thickness shows a large change in the slope of the data attributed to a drastic change of volume anisotropy. Surface anisotropy showed a small decrease because of some layer roughening introduced by annealing. |
BibTeX:
@article{WOS:000480349000001,
author = {Anyfantis, I, Dimitrios and Sarigiannidou, Eirini and Rapenne, Laetitia and Stamatelatos, Alkeos and Ntemogiannis, Dimitrios and Kapaklis, Vassilios and Poulopoulos, Panagiotis},
title = {Unexpected Development of Perpendicular Magnetic Anisotropy in Ni/NiO Multilayers After Mild Thermal Annealing},
journal = {IEEE MAGNETICS LETTERS},
year = {2019},
volume = {10},
doi = {https://doi.org/10.1109/LMAG.2019.2925315}
}
|
| Szklarska, M., Losiewicz, B., Dercz, G., Zubko, M., Albrecht, R. and Stroz, D. CHARACTERIZATION OF LONG-TERM CORROSION PERFORMANCE OF Ti15Mo ALLOY IN SALINE SOLUTION ARCHIVES OF METALLURGY AND MATERIALS 64, 2, pp. 773-778 (2019) |
| Abstract: The Ti15Mo alloy has been studied towards long-term corrosion
performance in saline solution at 37 degrees C using electrochemical impedance spectroscopy. The physical and chemical characterization of the material were also investigated. The as-received Ti15Mo alloy exhibits a single beta-phase structure. The thickness of single-layer structured oxide presented on its surface is similar to 4 nm. Impedance measurements revealed that the Ti15Mo alloy is characterized by spontaneous passivation in the solution containing chloride ions and formation of a double-layer structured oxide composed of a dense interlayer being the barrier layer against corrosion and porous outer layer. The thickness of this oxide layer, estimated based on the impedance data increases up to similar to 6 nm during 78 days of exposure. The observed fall in value of the log vertical bar Z vertical bar(f) (=) (0.01) (Hz) indicates a decrease in pitting corrosion resistance of Ti15Mo alloy in saline solution along with the immersion time. The detailed EIS study on the kinetics and mechanism of corrosion process and the capacitive behavior of the Ti15Mo electrode vertical bar passive layer vertical bar saline solution system was based on the concept of equivalent electrical circuit with respect to the physical meaning of the applied circuit elements. Potentiodynamic studies up to 9 V vs. SCE and SEM analysis show no presence of pitting corrosion what indicates that the Ti15Mo alloy is promising biomaterial to long-term medical applications. |
BibTeX:
@article{WOS:000473163500055,
author = {Szklarska, M. and Losiewicz, B. and Dercz, G. and Zubko, M. and Albrecht, R. and Stroz, D.},
title = {CHARACTERIZATION OF LONG-TERM CORROSION PERFORMANCE OF Ti15Mo ALLOY IN SALINE SOLUTION},
journal = {ARCHIVES OF METALLURGY AND MATERIALS},
year = {2019},
volume = {64},
number = {2},
pages = {773-778},
doi = {https://doi.org/10.24425/amm.2019.127612}
}
|
| Sedrpooshan, M., Ahmadvand, H., Gonzalez, D.L. and van Dijken, S. Magneto-optical study of anomalous magnetization reversal in the presence of anisotropy dispersion in CoPd thin films PHYSICAL REVIEW B 98, 21 (2018) |
| Abstract: Magnetization reversal is investigated in the presence of anisotropy
dispersion in weakly disordered CoxPd100-x(x = 23, 36, 43) thin films. A fourfold in-plane magnetic anisotropy is observed for x = 23, whereas an increase of the Co:Pd ratio induces a uniaxial anisotropy in x = 36 and 43 films. Anomalous magnetization reversal appears along the hard axes (referred to as collapse of hard axes) in x = 23 and 36 films, but disappears for x = 43. The results are consistent with the two-grain Stoner-Wohlfarth model. It is argued that the collapse of the hard axes can be controlled by intergranular exchange interaction. Quadratic magneto-optical Kerr effect (QMOKE) is also observed in the films and is found to weaken if the in-plane anisotropy is lowered through the Co:Pd ratio. QMOKE is observed for magnetic field orientations near the hard axes but not exactly along it, in agreement with the two-grain Stoner-Wohlfarth model. |
BibTeX:
@article{WOS:000454629800003,
author = {Sedrpooshan, Mehran and Ahmadvand, Hossein and Gonzalez, Diego Lopez and van Dijken, Sebastiaan},
title = {Magneto-optical study of anomalous magnetization reversal in the presence of anisotropy dispersion in CoPd thin films},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {98},
number = {21},
doi = {https://doi.org/10.1103/PhysRevB.98.214444}
}
|
| Huang, H., Chen, Z., Feng, C., Yang, Y., Wang, J., Zhang, J., Hong, B., Hu, S., Zhai, X., Peng, R., Fu, Z., Zhao, Y. and Lu, Y. Distinguishing charge and strain coupling in ultrathin (001)-La0.7Sr0.3MnO3/PMN-PT heterostructures APPLIED PHYSICS LETTERS 113, 26 (2018) |
| Abstract: Interfacial charge and strain distributions inside artificial perovskite
ABO(3) heterostructures often affect intriguing physical properties that are important to device performance. Normally, both charge and strain coexist across the interfaces, and their exact roles in determining the properties remain elusive. In the present work, La0.7Sr0.3MnO3 (LSMO) ultrathin films were grown on (001)-0.7Pb(Mg1/3Nb2/3) O-3-0.3PbTiO(3) (PMNPT) single-crystal substrates to discriminate between the effect of charge and strain on the transport and magnetoelectric properties. In heterostructures with thicker LSMO films, the strain effect dominates the resistance and the magnetic moment depends on the external electric field. With the decreasing LSMO thickness, the butterfly-like resistance-electric-field (R-E) and magnetization-electric-field (M-E) curves become loop-like, indicating that charge effects dominate strain effects in determining the electric field that controls the transport and magnetic properties. Furthermore, soft-x-ray absorption spectra of 32 and 4 nm LSMO/PMNPT samples at the Mn L edge under an applied electric field of +/- 6 kV/cm indicate that orbital reconstruction also plays an important role in interfacial magnetoelectric coupling. Published by AIP Publishing. |
BibTeX:
@article{WOS:000454616700021,
author = {Huang, Haoliang and Chen, Zezhi and Feng, Ce and Yang, Yuanjun and Wang, Jianlin and Zhang, Jie and Hong, Bin and Hu, Sixia and Zhai, Xiaofang and Peng, Ranran and Fu, Zhengping and Zhao, Yonggang and Lu, Yalin},
title = {Distinguishing charge and strain coupling in ultrathin (001)-La0.7Sr0.3MnO3/PMN-PT heterostructures},
journal = {APPLIED PHYSICS LETTERS},
year = {2018},
volume = {113},
number = {26},
doi = {https://doi.org/10.1063/1.5051324}
}
|
| Guo, T., Song, S., Zheng, Y., Xue, Y., Yan, S., Liu, Y., Li, T., Liu, G., Wang, Y., Song, Z., Qi, M. and Feng, S. Excellent thermal stability owing to Ge and C doping in Sb2Te-based high-speed phase-change memory NANOTECHNOLOGY 29, 50 (2018) |
| Abstract: The contradictory nature between transition speed and thermal stability
of phase-change materials has always been the key limitation to the achievement of wide applications under harsh conditions. Ge2.3Sb2.0Te phase-change alloy is proposed here to feature high thermal stability (10 year data retention above 220 degrees C) and fast switching speed (SET programming speed up to 5 ns) for electronic storage. In mushroom-shaped device cells, the nanocomposite materials implement an endurance life of nearly 1 x 10(5) cycles. Such operation speed among high-temperature alloys is the best ever reported. And the moderate incorporation of C offers intriguing benefits that include enhanced thermal stability and reduced RESET voltage in the above-mentioned Ge-rich Sb2Te-based memory cells. Through microscopic analysis, the local segregation of C dopants can further refine the crystalline grains and thus induce a lower volume change and roughness upon heating. These properties are crucial with regard to the application potential in high-performance and high-density embedded memories. |
BibTeX:
@article{WOS:000448130100001,
author = {Guo, Tianqi and Song, Sannian and Zheng, Yonghui and Xue, Yuan and Yan, Shuai and Liu, Yuxiang and Li, Tao and Liu, Guangyu and Wang, Yong and Song, Zhitang and Qi, Ming and Feng, Songlin},
title = {Excellent thermal stability owing to Ge and C doping in Sb2Te-based high-speed phase-change memory},
journal = {NANOTECHNOLOGY},
year = {2018},
volume = {29},
number = {50},
doi = {https://doi.org/10.1088/1361-6528/aae4f4}
}
|
| Shrivastava, U.N., Fritzsche, H. and Karan, K. Interfacial and Bulk Water in Ultrathin Films of Nafion, 3M PFSA, and 3M PFIA lonomers on a Polycrystalline Platinum Surface MACROMOLECULES 51, 23, pp. 9839-9849 (2018) |
| Abstract: Water at the interface and in the bulk of ultrathin ionomer films
confined to platinum surfaces affects the electrochemical activity and proton transport in electrochemical devices, yet it is little explored. This is the first study wherein the water distribution and the hygroexpansion of three different sulfonated fluoropolymers, varying in the composition and length of sulfonic group terminating side chains, as confined thin films (similar to 15 nm) on a Pt surface are examined by neutron reflectometry, ellipsometry, and quartz crystal microbalance. For the shorter side-chain perfluorosulfonated acid (PFSA) ionomers, Nafion EW 1100 and 3M EW 725, one to two monolayers equivalent of interfacial water, similar to adsorbed water on bare Pt, under wet conditions (97% humidity) was observed. In contrast, for the longer chain perfluoroimide acid (PFIA) ionomer, five monolayers equivalent of interfacial water was observed. In the bulk phase of the films, the PFIA ionomer exhibited a multilamellar structure comprising a water-rich layer near the interface region whereas the PFSA ionomer had a more uniform distribution of water. Our study for the first time demonstrates the strong effect of the side chain of sulfonated fluoropolymers on the Pt/ionomer interfacial water. |
BibTeX:
@article{WOS:000453489600040,
author = {Shrivastava, Udit N. and Fritzsche, Helmut and Karan, Kunal},
title = {Interfacial and Bulk Water in Ultrathin Films of Nafion, 3M PFSA, and 3M PFIA lonomers on a Polycrystalline Platinum Surface},
journal = {MACROMOLECULES},
year = {2018},
volume = {51},
number = {23},
pages = {9839-9849},
doi = {https://doi.org/10.1021/acs.macromol.8b01240}
}
|
| Shahbazi, K., Hrabec, A., Moretti, S., Ward, M.B., Moore, T.A., Jeudy, V., Martinez, E. and Marrows, C.H. Magnetic properties and field-driven dynamics of chiral domain walls in epitaxial Pt/Co/AuxPt1-x trilayers PHYSICAL REVIEW B 98, 21 (2018) |
| Abstract: Chiral domain walls in ultrathin perpendicularly magnetized layers have
a Ned structure stabilized by a Dzyaloshinskii-Moriya interaction (DMI) that is generated at the interface between the ferromagnet and a heavy metal. Different interface materials or properties are required above and below a ferromagnetic film in order to generate the structural inversion asymmetry needed to ensure that the DMI arising at the two interfaces does not cancel. Here we report on the magnetic properties of epitaxial Pt/Co/AuxPt1-x, trilayers grown by sputtering onto sapphire substrates with 0.6 nm thick Co. As x rises from 0 to 1, a structural inversion asymmetry is progressively generated. We characterize the epilayer structure with x-ray diffraction and cross-sectional transmission electron microscopy, revealing (111) stacking. The saturation magnetization falls as the proximity magnetization in Pt is reduced, whilst the perpendicular magnetic anisotropy K-u rises. The micromagnetic DMI strength D was determined using the bubble expansion technique and also rises from a negligible value when x = 0 to similar to 1 mJ/m(2) for x = 1. The depinning field at which field-driven domain wall motion crosses from the creep to the depinning regime rises from similar to 40 to similar to 70 mT, attributed to greater spatial fluctuations of the domain wall energy with increasing Au concentration. Meanwhile, the increase in DMI causes the Walker field to rise from similar to 10 to similar to 280 mT, meaning that only in the x = 1 sample is the steady flow regime accessible. The full dependence of domain wall velocity on driving field bears little resemblance to the prediction of a simple one-dimensional model, but can be described very well using micromagnetic simulations with a realistic model of disorder. These reveal a rise in Gilbert damping as x increases. |
BibTeX:
@article{WOS:000452687500005,
author = {Shahbazi, Kowsar and Hrabec, Ales and Moretti, Simone and Ward, Michael B. and Moore, Thomas A. and Jeudy, Vincent and Martinez, Eduardo and Marrows, Christopher H.},
title = {Magnetic properties and field-driven dynamics of chiral domain walls in epitaxial Pt/Co/AuxPt1-x trilayers},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {98},
number = {21},
doi = {https://doi.org/10.1103/PhysRevB.98.214413}
}
|
| Yuan, Y., Lu, Y., Stone, G., Wang, K., Brooks, C.M., Schlom, D.G., Sinnott, S.B., Zhou, H. and Gopalan, V. Three-dimensional atomic scale electron density reconstruction of octahedral tilt epitaxy in functional perovskites NATURE COMMUNICATIONS 9 (2018) |
| Abstract: Octahedral tilts are the most ubiquitous distortions in
perovskite-related structures that can dramatically influence ferroelectric, magnetic, and electronic properties; yet the paradigm of tilt epitaxy in thin films is barely explored. Non-destructively characterizing such epitaxy in three-dimensions for low symmetry complex tilt systems composed of light anions is a formidable challenge. Here we demonstrate that the interfacial tilt epitaxy can transform ultrathin calcium titanate, a non-polar earth-abundant mineral, into high-temperature polar oxides that last above 900 K. The comprehensive picture of octahedral tilts and polar distortions is revealed by reconstructing the three-dimensional electron density maps across film-substrate interfaces with atomic resolution using coherent Bragg rod analysis. The results are complemented with aberration-corrected transmission electron microscopy,film superstructure reflections, and are in excellent agreement with density functional theory. The study could serve as a broader template for non-destructive, three-dimensional atomic resolution probing of complex low symmetry functional interfaces. |
BibTeX:
@article{WOS:000452282900001,
author = {Yuan, Yakun and Lu, Yanfu and Stone, Greg and Wang, Ke and Brooks, Charles M. and Schlom, Darrell G. and Sinnott, Susan B. and Zhou, Hua and Gopalan, Venkatraman},
title = {Three-dimensional atomic scale electron density reconstruction of octahedral tilt epitaxy in functional perovskites},
journal = {NATURE COMMUNICATIONS},
year = {2018},
volume = {9},
doi = {https://doi.org/10.1038/s41467-018-07665-1}
}
|
| Luckyanova, M.N., Mendoza, J., Lu, H., Song, B., Huang, S., Zhou, J., Li, M., Dong, Y., Zhou, H., Garlow, J., Wu, L., Kirby, B.J., Grutter, A.J., Puretzky, A.A., Zhu, Y., Dresselhaus, M.S., Gossard, A. and Chen, G. Phonon localization in heat conduction SCIENCE ADVANCES 4, 12 (2018) |
| Abstract: Nondiffusive phonon thermal transport, extensively observed in
nanostructures, has largely been attributed to classical size effects, ignoring the wave nature of phonons. We report localization behavior in phonon heat conduction due to multiple scattering and interference events of broadband phonons, by measuring the thermal conductivities of GaAs/AlAs superlattices with ErAs nanodots randomly distributed at the interfaces. With an increasing number of superlattice periods, the measured thermal conductivities near room temperature increased and eventually saturated, indicating a transition from ballistic to diffusive transport. In contrast, at cryogenic temperatures the thermal conductivities first increased but then decreased, signaling phonon wave localization, as supported by atomistic Green's function simulations. The discovery of phonon localization suggests a new path forward for engineering phonon thermal transport. |
BibTeX:
@article{WOS:000454369600013,
author = {Luckyanova, M. N. and Mendoza, J. and Lu, H. and Song, B. and Huang, S. and Zhou, J. and Li, M. and Dong, Y. and Zhou, H. and Garlow, J. and Wu, L. and Kirby, B. J. and Grutter, A. J. and Puretzky, A. A. and Zhu, Y. and Dresselhaus, M. S. and Gossard, A. and Chen, G.},
title = {Phonon localization in heat conduction},
journal = {SCIENCE ADVANCES},
year = {2018},
volume = {4},
number = {12},
doi = {https://doi.org/10.1126/sciadv.aat9460}
}
|
| Rennie, S., Bright, E.L., Sutcliffe, J.E., Darnbrough, J.E., Burrows, R., Rawle, J., Nicklin, C., Lander, G.H. and Springell, R. The role of crystal orientation in the dissolution of UO2 thin filmsd CORROSION SCIENCE 145, pp. 162-169 (2018) |
| Abstract: Single crystal [0 0 1], [1 1 0], and [1 1 1]-oriented UO2 thin
films were utilised to investigate the orientational dependence of radiolytic dissolution. The films were exposed to water in the presence of a synchrotron X-ray source to induce dissolution, with X-ray reflectivity (XRR) used to observe changes in morphology as a function of exposure time. The [0 0 1] and [1 1 0]-oriented films were found to corrode at comparable rates, however, the [1 1 1] film was significantly more corrosion resistant, passivating after the initial 90 s dissolution period. This result shows the orientational dependence of UO2 dissolution, which may have important consequences for theoretical dissolution models. |
BibTeX:
@article{WOS:000452577100016,
author = {Rennie, S. and Bright, E. Lawrence and Sutcliffe, J. E. and Darnbrough, J. E. and Burrows, R. and Rawle, J. and Nicklin, C. and Lander, G. H. and Springell, R.},
title = {The role of crystal orientation in the dissolution of UO2 thin filmsd},
journal = {CORROSION SCIENCE},
year = {2018},
volume = {145},
pages = {162-169},
doi = {https://doi.org/10.1016/j.corsci.2018.09.012}
}
|
| Droulias, S.A., Palsson, G.K., Hjorvarsson, B. and Wolff, M. Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers JOURNAL OF APPLIED CRYSTALLOGRAPHY 51, 6, pp. 1556-1563 (2018) |
| Abstract: The limitations of a phenomenological fitting approach compared to
simulations of the optical model including reflection and refraction at all interfaces are demonstrated using the example of hydrogen loading in ultra-thin vanadium layers. Fe/V superlattices are loaded with deuterium and the lattice expansion and deuterium concentration are extracted from neutron reflectivity data. A noticeable difference is found between the extraction of concentrations and bilayer thicknesses directly from the superlattice peaks and fits of the density profile using the Parratt formalism. The results underline the importance of carefully considering the limitations of phenomenological approaches, in order to obtain robust results. The limitations of the kinematic approximation for the analysis are discussed in detail. |
BibTeX:
@article{WOS:000451833600006,
author = {Droulias, Sotirios A. and Palsson, Gunnar K. and Hjorvarsson, Bjorgvin and Wolff, Max},
title = {Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2018},
volume = {51},
number = {6},
pages = {1556-1563},
doi = {https://doi.org/10.1107/S1600576718013092}
}
|
| Lichtensteiger, C. InteractiveXRDFit: a new tool to simulate and fit X-ray diffractograms of oxide thin films and heterostructures JOURNAL OF APPLIED CRYSTALLOGRAPHY 51, 6, pp. 1745-1751 (2018) |
| Abstract: InteractiveXRDFit is a custom-made MATLAB program that calculates the
X-ray diffracted intensity for oxide thin films and heterostructures based on a library of inorganic materials. |
BibTeX:
@article{WOS:000451833600026,
author = {Lichtensteiger, Celine},
title = {InteractiveXRDFit: a new tool to simulate and fit X-ray diffractograms of oxide thin films and heterostructures},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2018},
volume = {51},
number = {6},
pages = {1745-1751},
doi = {https://doi.org/10.1107/S1600576718012840}
}
|
| Fernandez-Outon, L.E., Schmidt, W.G., Fortini, A.M., Martins, M.D. and Macedo, W.A.A. Tailoring magnetocrystalline perpendicular anisotropy in Co60Fe40/Pt multilayers JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 467, pp. 139-144 (2018) |
| Abstract: We report on the investigation of perpendicular magnetic anisotropy in
magnetron sputtered Pt/[Co60Fe40/Pt](5) multilayers, and the behaviour of the anisotropy field as function of the growth rate of the Pt buffer layer (4 nm thick). Highly crystallized, atomically flat (1 1 1) fcc-textured [CoFe/Pt] multilayers were obtained, as confirmed by high resolution transmission electron microscopy along with fast Fourier transform patterns and X-ray diffraction. Equivalent lattice relaxation between the Pt buffer and the CoFe/Pt multilayer was observed in all samples, indicating that the magnetic anisotropy is not dominated by magnetoelastic effects. Our results indicate that the formation of an ordered phase of CoFePt with fcc (1 1 1) texture, which is affected by the Pt buffer layer growth rate, regulates the anisotropy field in these multilayer systems, suggesting a magnetocrystalline origin of the observed perpendicular anisotropy. An optimum growth rate of the Pt buffer layer was obtained (similar to 0.7 angstrom/s), which allows enhancing the fcc (1 1 1) texture of the alloy-like CoFe/Pt multilayer, for which an uniaxial anisotropy energy constant of 3.5 x 10(6) erg/cc and an anisotropy field of 13 kG were obtained. |
BibTeX:
@article{WOS:000441872500020,
author = {Fernandez-Outon, L. E. and Schmidt, W. G. and Fortini, A. M. and Martins, M. D. and Macedo, W. A. A.},
title = {Tailoring magnetocrystalline perpendicular anisotropy in Co60Fe40/Pt multilayers},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2018},
volume = {467},
pages = {139-144},
doi = {https://doi.org/10.1016/j.jmmm.2018.07.068}
}
|
| Lee, J., Ahn, E., Seo, Y.-S., Kim, Y., Jeon, T.-Y., Cho, J., Lee, I. and Jeen, H. Redox-Driven Nanoscale Topotactic Transformations in Epitaxial SrFe0.8Co0.2O3-x under Atmospheric Pressure PHYSICAL REVIEW APPLIED 10, 5 (2018) |
| Abstract: Oxygen ion exchanges at the surface of transition metal oxides have been
extensively studied for understanding their nanoscale ionic behavior as well as for realizing multifunctionalities such as exotic magnetism, insulator-to-metal transition, band gap tuning, etc. To activate this exchange behavior, in many cases extreme conditions such as high temperature, high electric fields, and high vacuum are often required. These conditions have blocked the promising materials from being applied on real devices such as solid-oxide fuel cells and other electrochemical devices. In this article, we show that redox-driven reversible topotactic transformation in epitaxial SrFe0.8Co0.2O3-x thin films can be achieved at low temperature and at atmospheric pressure. This transformation triggers changes in electronic structures as well. These reversible redox reactions and/or associated changes at low temperature and under atomospheric pressure are particularly needed to develop a cathode for low solid-oxide fuel cells. |
BibTeX:
@article{WOS:000450270700001,
author = {Lee, Joonhyuk and Ahn, Eunyoung and Seo, Yu-Seong and Kim, Younghak and Jeon, Tae-Yeol and Cho, Jinhyung and Lee, Inwon and Jeen, Hyoungjeen},
title = {Redox-Driven Nanoscale Topotactic Transformations in Epitaxial SrFe0.8Co0.2O3-x under Atmospheric Pressure},
journal = {PHYSICAL REVIEW APPLIED},
year = {2018},
volume = {10},
number = {5},
doi = {https://doi.org/10.1103/PhysRevApplied.10.054035}
}
|
| Guo, E.-J., Roldan, M.A., Sang, X., Okamoto, S., Charlton, T., Ambaye, H., Lee, H.N. and Fitzsimmons, M.R. Influence of chemical composition and crystallographic orientation on the interfacial magnetism in BiFeO3/La1-xSrxMnO3 superlattices PHYSICAL REVIEW MATERIALS 2, 11 (2018) |
| Abstract: The emergence of magnetism unique to the interface between the
multiferroic BiFeO3 (BFO) and ferromagnetic La1-xSrxMnO3 (LSMO) offers an opportunity to control magnetism in nanoscale heterostructures with electric fields. In this paper, we investigate the influence of chemical composition and crystallographic orientation on the interfacial magnetism of BFO/LSMO superlattices. Our results reveal that the induced net magnetic moment in the BFO layers increases monotonically with increasing saturation magnetization of the LSMO layers. For the (100)-BFO/LSMO (x = 0.2) superlattice, the induced moment reaches a record high value of similar to 2.8 mu(B)/Fe. No interfacial magnetization is observed at the (100)-BFO/LSMO interface when LSMO is an antiferromagnet. In contrast to (100)-oriented superlattices, no induced moment is observed in (111)-BFO layers. Our results suggest the interfacial structural reconstruction may not be a sufficient condition for the enhanced net moment in BFO layer. Instead, spin canting induced by interfacial exchange coupling is proposed in the (100)-but not in the (111)-BFO, leading to the large net magnetization at the (100)-oriented interface. This work further demonstrates the importance of exchange coupling across heterointerfaces for spin canting in nominally antiferromagnets, providing a pathway to control the magnetic properties of artificial oxide heterostructures. |
BibTeX:
@article{WOS:000450573200004,
author = {Guo, Er-Jia and Roldan, Manuel A. and Sang, Xiahan and Okamoto, Satoshi and Charlton, Timothy and Ambaye, Haile and Lee, Ho Nyung and Fitzsimmons, Michael R.},
title = {Influence of chemical composition and crystallographic orientation on the interfacial magnetism in BiFeO3/La1-xSrxMnO3 superlattices},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2018},
volume = {2},
number = {11},
doi = {https://doi.org/10.1103/PhysRevMaterials.2.114404}
}
|
| Chen, T., Ahmadi-Majlan, K., Lim, Z.H., Zhang, Z., Ngai, J.H., Kemper, A.F. and Kumah, D.P. Interfacial structure of SrZrxTi1-xO3 films on Ge APPLIED PHYSICS LETTERS 113, 20 (2018) |
| Abstract: The interfacial structure of SrZrxTi1-xO3 films grown on semiconducting
Ge substrates is investigated by synchrotron X-ray diffraction and first-principles density functional theory. By systematically tuning the Zr content x, the effects of bonding at the interface and epitaxial strain on the physical structure of the film can be distinguished. The interfacial perovskite layers are found to be polarized as a result of cation-anion ionic displacements perpendicular to the perovskite/semiconductor interface. We find a correlation between the observed buckling and valence band offsets at the SrZr(x)Ti(1-)xO(3)/Ge interface. The trends in the theoretical valence band offsets as a function of Zr content for the polar structures are in agreement with reported X-ray photoelectron spectroscopy measurements. These results have important implications for the integration of functional oxide materials with established semiconductor based technologies. Published by AIP Publishing. |
BibTeX:
@article{WOS:000450279900006,
author = {Chen, Tongjie and Ahmadi-Majlan, Kamyar and Lim, Zheng Hui and Zhang, Zhan and Ngai, Joseph H. and Kemper, Alexander F. and Kumah, Divine P.},
title = {Interfacial structure of SrZrxTi1-xO3 films on Ge},
journal = {APPLIED PHYSICS LETTERS},
year = {2018},
volume = {113},
number = {20},
doi = {https://doi.org/10.1063/1.5046394}
}
|
| Uddin, M.F., Jiang, Z., Raymond, A., Goodson, A.D., Lwoya, B.S. and Albert, J.N.L. Thin film confinement reduces compatibility in symmetric ternary block copolymer/homopolymer blends JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS 56, 21, pp. 1443-1451 (2018) |
| Abstract: The thin film phase behavior of ternary blends consisting of symmetric
poly(styrene) (PS)-b-poly(dimethylsiloxane)(PDMS), PS, and PDMS was investigated using X-ray reflectivity (XRR) and atomic force microscopy (AFM). This system is strongly segregated, and the homopolymers are approximately the same length as the corresponding blocks of the copolymer. The XRR and AFM data are used to quantify changes in domain spacing (L) and morphology evolution with increasing homopolymer content (phi(H)). In 100 nm thick films, from phi(H) = 0 to 0.20, the system maintains a perfect parallel lamellar structure and domains swell as predicted based on theory; however, from phi(H) = 0.30 to 0.50, a morphology transition to a ``dot pattern'' morphology (tentatively identified as perforated lamellae) and mixed morphologies were observed before macrophase separation. In thicker films, dot patterns were observed for a broad range of phi(H) before macrophase separation. The absence of the bicontinuous microemulsion phase reported for bulk blends and thin films of perpendicular lamellae and the presence of dot patterns/perforated lamellae are attributed to preferential migration of the PDMS homopolymer to the wetting layers located at the substrate and free air interfaces, which leads to an asymmetric composition within the film and morphology transition. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1443-1451 |
BibTeX:
@article{WOS:000449863600002,
author = {Uddin, Md Fakar and Jiang, Zhang and Raymond, Andrew and Goodson, Amy D. and Lwoya, Baraka S. and Albert, Julie N. L.},
title = {Thin film confinement reduces compatibility in symmetric ternary block copolymer/homopolymer blends},
journal = {JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS},
year = {2018},
volume = {56},
number = {21},
pages = {1443-1451},
doi = {https://doi.org/10.1002/polb.24732}
}
|
| Trappen, R., Zhou, J., Tra, V.T., Huang, C.-Y., Dong, S., Chu, Y.-H. and Holcomb, M.B. Depth-dependent atomic valence determination by synchrotron techniques JOURNAL OF SYNCHROTRON RADIATION 25, 6, pp. 1711-1718 (2018) |
| Abstract: The properties of many materials can be strongly affected by the atomic
valence of the contained individual elements, which may vary at surfaces and other interfaces. These variations can have a critical impact on material performance in applications. A non-destructive method for the determination of layer-by-layer atomic valence as a function of material thickness is presented for La0.7Sr0.3MnO3 (LSMO) thin films. The method utilizes a combination of bulk- and surface-sensitive X-ray absorption spectroscopy (XAS) detection modes; here, the modes are fluorescence yield and surface-sensitive total electron yield. The weighted-average Mn atomic valence as measured from the two modes are simultaneously fitted using a model for the layer-by-layer variation of valence based on theoretical model Hamiltonian calculations. Using this model, the Mn valence profile in LSMO thin film is extracted and the valence within each layer is determined to within an uncertainty of a few percent. The approach presented here could be used to study the layer-dependent valence in other systems or extended to different properties of materials such as magnetism. |
BibTeX:
@article{WOS:000449627100014,
author = {Trappen, Robbyn and Zhou, Jinling and Vu Thanh Tra and Huang, Chih-Yeh and Dong, Shuai and Chu, Ying-Hao and Holcomb, Mikel B.},
title = {Depth-dependent atomic valence determination by synchrotron techniques},
journal = {JOURNAL OF SYNCHROTRON RADIATION},
year = {2018},
volume = {25},
number = {6},
pages = {1711-1718},
doi = {https://doi.org/10.1107/S1600577518011724}
}
|
| Cropper, M.D. Thin films of AlCrFeCoNiCu high-entropy alloy by pulsed laser deposition APPLIED SURFACE SCIENCE 455, pp. 153-159 (2018) |
| Abstract: Pulsed laser deposition has been used to prepare thin films of the high
entropy alloy AlCrFeCoNiCu. The 35 nm films were deposited in ultra-high vacuum onto glass at room temperature and above and analysed using X-ray diffraction and X-ray photoelectron spectroscopy. Films deposited at room temperature exhibit a mix of FCC and BCC reflections, the FCC crystallites having size similar to the film thickness, but the BCC crystallites are larger. The intensity of the reflections from both crystal structures reduce with increasing deposition temperature, the fall in BCC commencing at lower temperature than the FCC associated with a reduction of the content of Al and Cu. X-ray photoelectron spectroscopy shows that the films deposited at room temperature are closer to stoichiometry than those at higher temperatures. An important feature of the X-ray photoelectron spectroscopy depth profiles is surface segregation, the outer 3 nm of the high entropy alloy films has higher concentration of Al and, to a lesser extent, Cr. |
BibTeX:
@article{WOS:000438578700018,
author = {Cropper, M. D.},
title = {Thin films of AlCrFeCoNiCu high-entropy alloy by pulsed laser deposition},
journal = {APPLIED SURFACE SCIENCE},
year = {2018},
volume = {455},
pages = {153-159},
doi = {https://doi.org/10.1016/j.apsusc.2018.05.172}
}
|
| Suturin, S.M., Korovin, A.M., Bursian, V.E., Lutsev V, L., Bourobina, V., Yakovlev, N.L., Montecchi, M., Pasquali, L., Ukleev, V., Vorobiev, A., Devishvili, A. and Sokolov, N.S. Role of gallium diffusion in the formation of a magnetically dead layer at the Y3Fe5O12/Gd3Ga5O12 epitaxial interface PHYSICAL REVIEW MATERIALS 2, 10 (2018) |
| Abstract: We have clarified the origin of a magnetically dead interface layer
formed in yttrium iron garnet (YIG) films grown at above 700 degrees C onto a gadolinium gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The diffusion-assisted formation of a Ga-rich region at the YIG/GGG interface is demonstrated by means of composition depth profiling performed by x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and x-ray and neutron reflectometry. Our finding is in sharp contrast to the earlier expressed assumption that Gd acts as a migrant element in the YIG/GGG system. We further correlate the presence of a Ga-rich transition layer with considerable quenching of ferromagnetic resonance and spin wave propagation in thin YIG films. Finally, we clarify the origin of the enigmatic low-density overlayer that is often observed in neutron and x-ray reflectometry studies of the YIG/GGG epitaxial system. |
BibTeX:
@article{WOS:000446916400001,
author = {Suturin, S. M. and Korovin, A. M. and Bursian, V. E. and Lutsev, V, L. and Bourobina, V and Yakovlev, N. L. and Montecchi, M. and Pasquali, L. and Ukleev, V and Vorobiev, A. and Devishvili, A. and Sokolov, N. S.},
title = {Role of gallium diffusion in the formation of a magnetically dead layer at the Y3Fe5O12/Gd3Ga5O12 epitaxial interface},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2018},
volume = {2},
number = {10},
doi = {https://doi.org/10.1103/PhysRevMaterials.2.104404}
}
|
| Qiu, C., Majs, F., Douglas, T.A., Schmidt, M. and Trainor, T.P. In Situ Structural Study of Sb(V) Adsorption on Hematite (1(1)over-bar02) Using X-ray Surface Scattering ENVIRONMENTAL SCIENCE & TECHNOLOGY 52, 19, pp. 11161-11168 (2018) |
| Abstract: The binding mechanism of Sb(V) on a single-crystal hematite (1 (1) over
bar 02) surface was studied using crystal truncation rod X-ray diffraction (CTR) under in situ conditions. The best-fit CTR model indicates Sb(V) adsorbs at the surface as an inner-sphere complex forming a tridentate binding geometry with the nearest Sb-Fe distance of 3.09(4) angstrom and an average Sb-O bond length of 2.08(5) angstrom. In this binding geometry, Sb is bound at both edge-sharing and corner-sharing sites of the surface Fe-O octahedral units. The chemical plausibility of the proposed structure was further verified by bond valence analysis, which also deduced a protonation scheme for surface O groups. The stoichiometry of the surface reaction predicts the release of one OH- group at pH 5.5. |
BibTeX:
@article{WOS:000446542100029,
author = {Qiu, Canrong and Majs, Frantisek and Douglas, Thomas A. and Schmidt, Moritz and Trainor, Thomas P.},
title = {In Situ Structural Study of Sb(V) Adsorption on Hematite (1(1)over-bar02) Using X-ray Surface Scattering},
journal = {ENVIRONMENTAL SCIENCE & TECHNOLOGY},
year = {2018},
volume = {52},
number = {19},
pages = {11161-11168},
doi = {https://doi.org/10.1021/acs.est.8b03903}
}
|
| Rizal, C. Microstructure, Surface Plasmon, Magneto-Optic Surface Plasmon, and Sensitivity Properties of Magneto-Plasmonic Co/Au Multilayers IEEE TRANSACTIONS ON MAGNETICS 54, 10 (2018) |
| Abstract: Micro-structure properties of (Co 1.2 nm/Au 2 nm) x N = 20 multilayers
(MLs) prepared using dc-magnetron sputtering are reported using X-ray reflectivity (XRR) and X-ray diffraction (XRD) analysis. XRR profiles of these MLs showed excellent bilayer periodicity. The XRD spectra displayed Co layer thickness-dependent properties. Annealing increased lateral tensile strain, however, decreased compressive strain along the substrate normal direction. While surface roughness, crystallite grain size, and strain are affected by Co layer thickness, microstructure and periodicity are dominated by fcc-Au (111). Surface plasmon resonance (SPR) and magneto-optic SPR (MOSPR) study of an optimized Co/Au multilayer in Kretschmann configuration for air-He and water-methanol media showed an enhancement in sensitivity by over 4X when excited at lambda = 785 nm compared to the conventional SPR configuration when excited at lambda = 632.8 nm. This enhancement in MOSPR sensitivity means that the detection limit of this class of transducers can he substantially improved by tuning Co/Au layer thickness, wavelength, and incident angle of optical radiation. |
BibTeX:
@article{WOS:000445244300001,
author = {Rizal, Conrad},
title = {Microstructure, Surface Plasmon, Magneto-Optic Surface Plasmon, and Sensitivity Properties of Magneto-Plasmonic Co/Au Multilayers},
journal = {IEEE TRANSACTIONS ON MAGNETICS},
year = {2018},
volume = {54},
number = {10},
doi = {https://doi.org/10.1109/TMAG.2018.2854663}
}
|
| Joshi, T., Borisov, P. and Lederman, D. Structural and electrical characterization of polycrystalline NbO2 thin film vertical devices grown on TiN-coated SiO2/Si substrates JOURNAL OF APPLIED PHYSICS 124, 11 (2018) |
| Abstract: We report on the electrical properties of polycrystalline NbO2 thin film
vertical devices grown on TiN coated SiO2/Si substrates using pulsed laser deposition. First, we analyzed the thickness and contact size dependences of threshold switching of NbO2 films grown in 10 mTorr Ar/O-2 mixed growth pressure, where 25.1%/74.9% of NbO2/Nb(2)O(5 )surface composition content was estimated by ex-situ x-ray photoelectron spectroscopy. Then the threshold switching and self-sustained current oscillatory behavior of films with different NbO2/Nb2O5 composition ratios was measured and analyzed. The current-voltage measurement revealed that the leakage current property in the insulating state was dominated by the trap-charge assisted Poole-Frankel conduction mechanism. All films showed threshold switching behavior in agreement with the previously proposed Joule heating mechanism. The second film was grown in lower (1 mTorr) growth pressure, which resulted in a higher (34.2%/65.8%) NbO2/Nb2O5 film surface composition. The film grown in higher growth pressure demonstrated lower off-state leakage current, faster switching, and self-sustained oscillations with higher frequency than the film grown in lower growth pressure. Published by AIP Publishing. |
BibTeX:
@article{WOS:000445367200015,
author = {Joshi, Toyanath and Borisov, Pavel and Lederman, David},
title = {Structural and electrical characterization of polycrystalline NbO2 thin film vertical devices grown on TiN-coated SiO2/Si substrates},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2018},
volume = {124},
number = {11},
doi = {https://doi.org/10.1063/1.5038837}
}
|
| Blank, M. and Weber, L. Influence of the thickness of a nanometric copper interlayer on Au/dielectric thermal boundary conductance JOURNAL OF APPLIED PHYSICS 124, 10 (2018) |
| Abstract: The influence of the thickness of a thin (1.5-30 nm) copper layer on the
thermal boundary conductance (TBC) at the interface between gold and silicon, sapphire and diamond, respectively, was studied using Time Domain Thermoreflectance. Overall, a monotonic increase in the TBC was observed over the first 10 nm, before reaching a plateau. In some cases, it was also observed that an interlayer reduces the TBC as compared to the reference system. This is rationalized by assuming that the TBC evolution as a function of the interlayer thickness is controlled by (i) a contribution of the gold layer that has to be taken into account for all phonons having a wavelength larger than the interlayer thickness and (ii) a thickness-dependent resistance within the interlayer that appears when the electron-phonon coupling is incomplete, i.e., typically over the first 10 nm. A model is proposed in which the contribution to thermal boundary conductance by phonons coming directly from the gold layer is estimated using a simple Debye approximation, while the resistance that appears within the interlayer is estimated by g(T) times h with g(T) the electron-phonon coupling factor and h the interlayer thickness. This results in a system with three resistances in series, i.e., the metal-metal and metal-dielectric interfacial resistances and the interlayer resistance, and a contribution due to phonons of the gold layer. A reasonably good agreement between this model and experimental data is observed. Published by AIP Publishing. |
BibTeX:
@article{WOS:000444757200038,
author = {Blank, Maite and Weber, Ludger},
title = {Influence of the thickness of a nanometric copper interlayer on Au/dielectric thermal boundary conductance},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2018},
volume = {124},
number = {10},
doi = {https://doi.org/10.1063/1.5030049}
}
|
| Yamamoto, S., Nishina, N., Matsui, J., Miyashita, T. and Mitsuishi, M. High-Density and Monolayer-Level Integration of pi-Conjugated Units: Amphiphilic Carbazole Homopolymer Langmuir-Blodgett Films LANGMUIR 34, 36, pp. 10491-10497 (2018) |
| Abstract: Precise integration of pi-conjugated units is a key issue to achieve
molecular (nano) electronic devices based on organic semiconductor materials. We specifically examine the Langmuir-Blodgett technique, which allows high-density integration of pi-conjugated units. In this study, we designed a carbazole containing acrylamide-based homopolymer [poly(9-ethyl-3-carbazolyl acrylamide) (pCzAA)], in which the pi-conjugated unit is connected with a hydrophilic amide unit directly as a side chain. Its Langmuir-Blodgett film formation properties were investigated. The pCzAA polymer took a stable monolayer formation in the presence of a small amount (ca. 10 mol %) of poly(N-dodecylacrylamide) (pDDA). Compared with amphiphilic carbazole-containing copolymers described in earlier reports, the direct connection of pi-conjugated units through amide bonding enables the Cz content in monolayers to exceed that of the copolymer monolayers (ca. 30 mol %) dramatically. pCzAA:pDDA takes highly ordered layer structures toward the out-of-plane direction, although no structural order is formed in the in-plane direction. This method is a practical means to develop low-dimensional and high-density integration of ir-conjugated units for molecular electronics. |
BibTeX:
@article{WOS:000444792500004,
author = {Yamamoto, Shunsuke and Nishina, Nanae and Matsui, Jun and Miyashita, Tokuji and Mitsuishi, Masaya},
title = {High-Density and Monolayer-Level Integration of pi-Conjugated Units: Amphiphilic Carbazole Homopolymer Langmuir-Blodgett Films},
journal = {LANGMUIR},
year = {2018},
volume = {34},
number = {36},
pages = {10491-10497},
doi = {https://doi.org/10.1021/acs.langmuir.8b01694}
}
|
| Stack, A.G., Stubbs, J.E., Srinivasan, S.G., Roy, S., Bryantsev, V.S., Eng, P.J., Custelcean, R., Gordon, A.D. and Hexel, C.R. Mineral-Water Interface Structure of Xenotime (YPO4) 100\ JOURNAL OF PHYSICAL CHEMISTRY C 122, 35, pp. 20232-20243 (2018) |
| Abstract: Crystal truncation rod (CTR) measurements and density functional theory
(DFT) calculations were performed to determine the atomic structure of the mineral-water interface of the 100\ surface of xenotime (nominally YPO4). This mineral is important, because it incorporates a variety of rare earth elements (REEs) in its crystal structure. REEs are critical materials necessary for a variety of renewable and energy efficient technologies. Current beneficiation techniques are not highly selective for REE ore minerals, and large amounts go to waste; this is a first step toward designing more efficient beneficiation. Evidence is found for minor relaxation of the surface within the topmost monolayer with little or no relaxation in subsurface layers. Justification for ordered water at the interface is found, where water binds to surface cations and donates hydrogen bonds to surface phosphates. The average bond lengths between cations and oxygens on water are 228 pm in the best fit to the CTR data, versus 243 and 251 pm for the DFT. No agreement on water positions bound to surface phosphates is obtained. Overall, the findings suggest that ligands used in beneficiation with a single anionic headgroup, such as fatty acids, will have limited selectivity for xenotime relative to undesirable minerals. |
BibTeX:
@article{WOS:000444355400019,
author = {Stack, Andrew G. and Stubbs, Joanne E. and Srinivasan, Sriram G. and Roy, Santanu and Bryantsev, Vyacheslav S. and Eng, Peter J. and Custelcean, Radu and Gordon, Alexander D. and Hexel, Cole R.},
title = {Mineral-Water Interface Structure of Xenotime (YPO4) 100\},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2018},
volume = {122},
number = {35},
pages = {20232-20243},
doi = {https://doi.org/10.1021/acs.jpcc.8b04015}
}
|
| Rizal, C. Magneto-Optic Surface Plasmon Resonance Ti/Au/Co/Au/P-c Configuration and Sensitivity MAGNETOCHEMISTRY 4, 3 (2018) |
| Abstract: Magneto-optic surface plasmon resonance (MOSPR)-based sensors are highly
attractive as next-generation biosensors. However, these sensors suffer from oxidation leading to degradation of performance, reproducibility of the sensor surface, because of the difficulty of removing adsorbed materials, and degradation of the sensor surface during surface cleaning and these limit their applications. In this paper, I propose MOSPR-based biosensors with 0 to 15 nm thick inert polycarbonate laminate plastic as a protective layer and theoretically demonstrate the practicability of my approach in water-medium for three different probing samples: ethanol, propanol, and pentanol. I also investigate microstructure and magnetic properties. The chemical composition and layered information of the sensor are investigated using X-ray reflectivity and X-ray diffraction analyses and these show distinct face-centered-cubic (fcc)-Au (111) phases, as dominated by the higher density of conduction electrons in Au as compared to Co. The magnetic characterization measured with the in-plane magnetic field to the sensor surface for both the as-deposited and annealed multilayers showed isotropic easy axis magnetization parallel to the multilayer interface at a saturating magnetic field of <100 Oersted (Oe). The sensor showed a maximum sensitivity of 5.5 x 10(4)%/RIU (refractive index unit) for water-ethanol media and the highest detection level of 2.5 x 10(-6) for water-pentanol media as the protective layer is increased from 0 to 15 nm. |
BibTeX:
@article{WOS:000446026300004,
author = {Rizal, Conrad},
title = {Magneto-Optic Surface Plasmon Resonance Ti/Au/Co/Au/P-c Configuration and Sensitivity},
journal = {MAGNETOCHEMISTRY},
year = {2018},
volume = {4},
number = {3},
doi = {https://doi.org/10.3390/magnetochemistry4030035}
}
|
| Bright, E.L., Rennie, S., Cattelan, M., Fox, N.A., Goddard, D.T. and Springell, R. Epitaxial UN and alpha-U2N3 thin films THIN SOLID FILMS 661, pp. 71-77 (2018) |
| Abstract: Single crystal epitaxial thin films of UN and alpha-U2N3 have been grown
for the first time by reactive DC magnetron sputtering. These films provide ideal samples for fundamental research into the potential accident tolerant fuel, UN, and U2N3 , its intermediate oxidation product. Films were characterised using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), with XRD analysis showing both thin films to be [001] oriented and composed of a single domain. The specular lattice parameters of the UN and U2N3 films were found to be 4.895 angstrom and 10.72 angstrom, respectively, with the UN film having a miscut of 2.6 degrees. XPS showed significant differences in the N-1 s peak between the two films, with area analysis showing both films to be stoichiometric. |
BibTeX:
@article{WOS:000440074500011,
author = {Bright, E. Lawrence and Rennie, S. and Cattelan, M. and Fox, N. A. and Goddard, D. T. and Springell, R.},
title = {Epitaxial UN and alpha-U2N3 thin films},
journal = {THIN SOLID FILMS},
year = {2018},
volume = {661},
pages = {71-77},
doi = {https://doi.org/10.1016/j.tsf.2018.07.018}
}
|
| Goncalves, R.S., Barrozo, P., Brito, G.L., Viana, B.C. and Cunha, F. The effect of thickness on optical, structural and growth mechanism of ZnO thin film prepared by magnetron sputtering THIN SOLID FILMS 661, pp. 40-45 (2018) |
| Abstract: In this contribution we discuss the structural, morphological and
optical properties of ZnO thin films deposited on glass substrates by radio frequency magnetron sputtering technique. Our results indicate that an increase in deposition time leads to a change in the film growth mechanism. Three different growth regimes can be observed when the deposition time changes. Islands initially start to nucleate and grow into rough and highly stressed films. Increasing the surface population leads to island coalescence compatible with a planar architecture, where the stress is relieved, and the roughness is minimized. Longer still deposition times induce the growth of columnar structures. The increase in deposition time brings about a stress relaxation and grain growth together with a reduction of the texture coefficient, c-lattice contraction and an increase of band gap values. |
BibTeX:
@article{WOS:000440074500006,
author = {Goncalves, R. S. and Barrozo, Petrucio and Brito, G. L. and Viana, B. C. and Cunha, F.},
title = {The effect of thickness on optical, structural and growth mechanism of ZnO thin film prepared by magnetron sputtering},
journal = {THIN SOLID FILMS},
year = {2018},
volume = {661},
pages = {40-45},
doi = {https://doi.org/10.1016/j.tsf.2018.07.008}
}
|
| Qiu, C., Majs, F., Eng, P.J., Stubbs, J.E., Douglas, T.A., Schmidt, M. and Trainor, T.P. In situ structural study of the surface complexation of lead(II) on the chemically mechanically polished hematite (1(1)over-bar02) surface JOURNAL OF COLLOID AND INTERFACE SCIENCE 524, pp. 65-75 (2018) |
| Abstract: A structural study of the surface complexation of Pb(II) on the (1 (1)
over bar 02) surface of hematite was undertaken using crystal truncation rod (CTR) X-ray diffraction measurements under in situ conditions. The sorbed Pb was found to form inner sphere (IS) complexes at two types of edge-sharing sites on the half layer termination of the hematite (1 (1) over bar 02) surface. The best fit model contains Pb in distorted trigonal pyramids with an average Pb-O bond length of 2.27(4) angstrom and two characteristic Pb-Fe distances of 3.19(1) angstrom and 3.59(1) angstrom. In addition, a site coverage model was developed to simulate coverage as a function of sorbate-sorbate distance. The simulation results suggest a plausible Pb-Pb distance of 5.42 angstrom, which is slightly larger than the diameter of Pb's first hydration shell. This relates the best fit surface coverage of 0.59(4) Pb per unit cell at monolayer saturation to steric constraints as well as electrostatic repulsion imposed by the hydrated Pb complex. Based on the structural results we propose a stoichiometry of the surface complexation reaction of Pb(II) on the hematite (1 (1) over bar 02) surface and use bond valence analysis to assign the protonation schemes of surface oxygens. Surface reaction stoichiometry suggests that the proton release in the course of surface complexation occurs from the Pb-bound surface O atoms at pH 5.5. (C) 2018 Elsevier Inc. All rights reserved. |
BibTeX:
@article{WOS:000434494400008,
author = {Qiu, Canrong and Majs, Frantisek and Eng, Peter J. and Stubbs, Joanne E. and Douglas, Thomas A. and Schmidt, Moritz and Trainor, Thomas P.},
title = {In situ structural study of the surface complexation of lead(II) on the chemically mechanically polished hematite (1(1)over-bar02) surface},
journal = {JOURNAL OF COLLOID AND INTERFACE SCIENCE},
year = {2018},
volume = {524},
pages = {65-75},
doi = {https://doi.org/10.1016/j.jcis.2018.04.005}
}
|
| Luan, Z.Z., Chang, F.F., Wang, P., Zhou, L.F., Cooper, J.F.K., Kinane, C.J., Langridge, S., Cai, J.W., Du, J., Zhu, T. and Wu, D. Interfacial coupling and negative spin Hall magnetoresistance in Pt/NiO/YIG APPLIED PHYSICS LETTERS 113, 7 (2018) |
| Abstract: Inserting an antiferromagnetic layer of NiO between Pt and Y3Fe5O12
(YIG) changes the positive sign of the spin Hall magnetoresistance (SMR) in Pt/YIG to a negative sign at low temperature. Here, we use polarized neutron reflectometry to explore the coupling between NiO and YIG to understand the mechanism of the negative SMR. A weak uncompensated magnetic moment is observed in the NiO and the direction of this moment is perpendicular to YIG. Therefore, we infer that the spin axis of NiO is perpendicular to YIG. This result directly supports the explanation that the negative SMR results from the pure spin current reflected back by the NiO layer and the spin-flop coupling between NiO and YIG. Published by AIP Publishing. |
BibTeX:
@article{WOS:000441994200030,
author = {Luan, Z. Z. and Chang, F. F. and Wang, P. and Zhou, L. F. and Cooper, J. F. K. and Kinane, C. J. and Langridge, S. and Cai, J. W. and Du, J. and Zhu, T. and Wu, D.},
title = {Interfacial coupling and negative spin Hall magnetoresistance in Pt/NiO/YIG},
journal = {APPLIED PHYSICS LETTERS},
year = {2018},
volume = {113},
number = {7},
doi = {https://doi.org/10.1063/1.5041865}
}
|
| Rao, R.R., Kolb, M.J., Hwang, J., Pedersen, A.F., Mehta, A., You, H., Stoerzinger, K.A., Feng, Z., Zhou, H., Bluhm, H., Giordano, L., Stephens, I.E.L. and Shao-Horn, Y. Surface Orientation Dependent Water Dissociation on Rutile Ruthenium Dioxide JOURNAL OF PHYSICAL CHEMISTRY C 122, 31, pp. 17802-17811 (2018) |
| Abstract: Rutile RuO2 is a highly active catalyst for a number of
(electro)chemical reactions in aqueous solutions or in humid environments. However, the study of the interaction of RuO2 surfaces with water has been confined largely to the ultrahigh vacuum environment and to the thermodynamically stable (110) surface. In this work, we combine ambient-pressure X-ray photoelectron spectroscopy, in situ surface diffraction, and density functional theory calculations to investigate how four different facets of RuO2 interact with water under humid and electrochemical environments. The vacant coordinatively unsaturated Ru site (CUS) allows for the adsorption and dissociation of water molecules. Different surfaces exhibit unique binding energetics for -H2O and -OH and can allow for different degrees of hydrogen bonding between the adsorbates. Consequently, the degree of water dissociation is found to be sensitive to the surface crystallographic orientation-being maximum for the (101) surface, followed by the (110), (001) and (100) surfaces. This study identifies crystallographic orientation as an important parameter to tune not only the density of active sites but also the energetics for water dissociation; this finding is of great significance for many catalytic reactions, where water is a key reactant, or product. |
BibTeX:
@article{WOS:000441484600024,
author = {Rao, Reshma R. and Kolb, Manuel J. and Hwang, Jonathan and Pedersen, Anders Filsoe and Mehta, Apurva and You, Hoydoo and Stoerzinger, Kelsey A. and Feng, Zhenxing and Zhou, Hua and Bluhm, Hendrik and Giordano, Livia and Stephens, Ifan E. L. and Shao-Horn, Yang},
title = {Surface Orientation Dependent Water Dissociation on Rutile Ruthenium Dioxide},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2018},
volume = {122},
number = {31},
pages = {17802-17811},
doi = {https://doi.org/10.1021/acs.jpcc.8b04284}
}
|
| Guo, T., Song, S., Song, Z., Ji, X., Xue, Y., Chen, L., Cheng, Y., Liu, B., Wu, L., Qi, M. and Feng, S. SiC-Doped Ge2Sb2Te5 Phase-Change Material: A Candidate for High-Density Embedded Memory Application ADVANCED ELECTRONIC MATERIALS 4, 8 (2018) |
| Abstract: Phase-change memory is one of the most attractive solutions for embedded
applications, thanks to the low cost of integration with current manufacturing processes and the good scaling behavior. Despite intensive research efforts that are devoted to the modification of Ge2Sb2Te5 (GST) phase-change material, the obtained improvements are still unsatisfactory for high-performance applications. In this paper, SiC-modification is first introduced to enhance the amorphous stability of GST without sacrificing its transition speed. Several enhancements can be demonstrated, including better thermal stability (10-year data retention above 120 degrees C), lower RESET voltage (about 3.0 V at 20 ns pulse width), reduced volume change (smaller than 3.0%), and expected operation cycles (more than 1.0 x 10(5)). According to the findings, the local bonding nature of Ge/Te atoms can be tuned by C/Si dopants through forming CGe and SiTe bonds. Apart from strengthening the atomic binding network for desirable data retention, the element interdiffusion is also effectively controlled and suppressed. Together with finer grains, smaller density change, and more uniform morphology, the modified structure transition finally contributes to the reduced switching voltage and long-term endurance. Hence, it is envisaged that SiC-doped GST with such advantages will give a competitive option for high-density and high-performance embedded memory. |
BibTeX:
@article{WOS:000441125200009,
author = {Guo, Tianqi and Song, Sannian and Song, Zhitang and Ji, Xinglong and Xue, Yuan and Chen, Liangliang and Cheng, Yan and Liu, Bo and Wu, Liangcai and Qi, Ming and Feng, Songlin},
title = {SiC-Doped Ge2Sb2Te5 Phase-Change Material: A Candidate for High-Density Embedded Memory Application},
journal = {ADVANCED ELECTRONIC MATERIALS},
year = {2018},
volume = {4},
number = {8},
doi = {https://doi.org/10.1002/aelm.201800083}
}
|
| Akansel, S., Venugopal, V.A., Kumar, A., Gupta, R., Brucas, R., George, S., Neagu, A., Tai, C.-W., Gubbins, M., Andersson, G. and Svedlindh, P. Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films JOURNAL OF PHYSICS D-APPLIED PHYSICS 51, 30 (2018) |
| Abstract: Fe65Co35 thin films have been deposited on SiO2 substrates using
sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0 x 10(-3) and 4.5 x 10(-3) were obtained from in-plane and out-of-plane measurements, respectively, for the as prepared samples, values that were reduced to about 6.5 x 10(-3) and 4.0 x 10(-3) for annealed samples. |
BibTeX:
@article{WOS:000437408700001,
author = {Akansel, Serkan and Venugopal, Vijayaharan A. and Kumar, Ankit and Gupta, Rahul and Brucas, Rimantas and George, Sebastian and Neagu, Alexandra and Tai, Cheuk-Wai and Gubbins, Mark and Andersson, Gabriella and Svedlindh, Peter},
title = {Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2018},
volume = {51},
number = {30},
doi = {https://doi.org/10.1088/1361-6463/aaccc0}
}
|
| Wang, J., Shin, Y., Arenholz, E., Lefler, B.M., Rondinelli, J.M. and May, S.J. Effect of fluoropolymer composition on topochemical synthesis of SrMnO3-delta F gamma oxyfluoride films PHYSICAL REVIEW MATERIALS 2, 7 (2018) |
| Abstract: We report the synthesis of SrMnO3-delta F gamma perovskite oxyfluoride
thin films using a vapor transport method to fluorinate as-grown SrMnO2.5 epitaxial thin films. The influence of the fluoropolymer, which acts as a fluorine vapor source, was investigated by utilizing polyvinyl fluoride (PVF), polyvinylidene difluoride (PVDF), and polytetrafluoroethylene (PTFE) in the reaction. The same process was carried out with polyethylene to isolate the role of carbon in the vapor transport process. The F distribution was probed by x-ray photoemission spectroscopy, which confirmed the incorporation of F into the films and revealed higher F concentrations in films exposed to PVF and PVDF compared to PTFE. The c-axis parameter expands after fluorination, a result consistent with density functional theory calculations that attribute the volume expansion to elongated Mn-F bonds compared to shorter Mn-O bonds. Using x-ray absorption spectroscopy, we show that the fluorination process reduces the nominal Mn oxidation state suggesting that F substitutes on O sites in the lattice as opposed to filling anion vacancy sites, a finding further supported by calculated formation energies of different F site occupancies. These results provide insights into topochemical fluorination of perovskite oxides, which should enable future synthesis and design efforts focused on oxyfluoride heterostructures. |
BibTeX:
@article{WOS:000440417500002,
author = {Wang, Jiayi and Shin, Yongjin and Arenholz, Elke and Lefler, Benjamin M. and Rondinelli, James M. and May, Steven J.},
title = {Effect of fluoropolymer composition on topochemical synthesis of SrMnO3-delta F gamma oxyfluoride films},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2018},
volume = {2},
number = {7},
doi = {https://doi.org/10.1103/PhysRevMaterials.2.073407}
}
|
| Guo, E.-J., Roldan, M.A., Charlton, T., Liao, Z., Zheng, Q., Ambaye, H., Herklotz, A., Gai, Z., Ward, T.Z., Lee, H.N. and Fitzsimmons, M.R. Removal of the Magnetic Dead Layer by Geometric Design ADVANCED FUNCTIONAL MATERIALS 28, 30 (2018) |
| Abstract: The proximity effect is used to engineer interface effects such as
magnetoelectric coupling, exchange bias, and emergent interfacial magnetism. However, the presence of a magnetic dead layer adversely affects the functionality of a heterostructure. Here, it is shown that by utilizing (111) polar planes, the magnetization of a manganite ultrathin layer can be maintained throughout its thickness. Combining structural characterization, magnetometry measurements, and magnetization depth profiling with polarized neutron reflectometry, it is found that the magnetic dead layer is absent in the (111)-oriented manganite layers, however, it occurs in the films with other orientations. Quantitative analysis of local structural and elemental spatial evolutions using scanning transmission electron microscopy and electron energy loss spectroscopy reveals that atomically sharp interfaces with minimal chemical intermixing in the (111)-oriented superlattices. The polar discontinuity across the (111) interfaces inducing charge redistribution within the SrTiO3 layers is suggested, which promotes ferromagnetism throughout the (111)-oriented ultrathin manganite layers. The approach of eliminating problematic magnetic dead layers by changing the crystallographic orientation suggests a conceptually useful recipe to engineer the intriguing physical properties of oxide interfaces, especially in low dimensionality. |
BibTeX:
@article{WOS:000439738200008,
author = {Guo, Er-Jia and Roldan, Manuel A. and Charlton, Timothy and Liao, Zhaoliang and Zheng, Qiang and Ambaye, Haile and Herklotz, Andreas and Gai, Zheng and Ward, T. Zac and Lee, Ho Nyung and Fitzsimmons, Michael R.},
title = {Removal of the Magnetic Dead Layer by Geometric Design},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2018},
volume = {28},
number = {30},
doi = {https://doi.org/10.1002/adfm.201800922}
}
|
| Ren, K., Li, R., Shen, J., Xin, T., Lv, S., Ji, Z. and Song, Z. Study on the phase change behavior of nitrogen doped Bi2Te3 films JOURNAL OF ALLOYS AND COMPOUNDS 754, pp. 227-231 (2018) |
| Abstract: Bi2Te3 has been widely used as thermoelectric material due to its
overall good properties, such as low thermal conductivity, high electrical conductivity, and flexible atoms arrangement for structural optimization et al. However, its potential in phase change memory (PCM) application is not well evaluated due to its unstable amorphous state. In this work, stability of amorphous Bi2Te3 has been improved by N doping. Crystallization temperature of 175 degrees C and data retention of 43.6 degrees C have been achieved. Smaller and defective grains have been directly observed. Abnormal volume expansion of 7.2% has been observed after crystallization. Low-power consumption and good reversible phase change ability of N doped Bi2Te3 has been verified in PCM cell. (C) 2018 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000432675600029,
author = {Ren, Kun and Li, Ruiheng and Shen, Jiabin and Xin, Tianjiao and Lv, Shilong and Ji, Zhenguo and Song, Zhitang},
title = {Study on the phase change behavior of nitrogen doped Bi2Te3 films},
journal = {JOURNAL OF ALLOYS AND COMPOUNDS},
year = {2018},
volume = {754},
pages = {227-231},
doi = {https://doi.org/10.1016/j.jallcom.2018.04.294}
}
|
| Ortmann, J.E., Posadas, A.B. and Demkov, A.A. The MBE growth of arbitrarily thick SrTiO3/LaAlO3 quantum well heterostructures for use in next-generation optoelectronic devices JOURNAL OF APPLIED PHYSICS 124, 1 (2018) |
| Abstract: While the SrTiO3/LaAlO3 (STO/LAO) materials system has been widely
studied in the hopes of integrating it into transition metal oxide (TMO) electronic devices, recent reports have focused on its optical properties. Electronic confinement in STO quantum wells (QWs) and the optical modulation of confined charge carriers have recently been demonstrated, suggesting the feasibility of producing TMO-based QW optoelectronic devices. However, before these devices can be realized, it is necessary to develop the capability to grow such structures arbitrarily thick while maintaining high crystalline quality. We report on the fabrication of STO/LAO QW heterostructures and demonstrate via reflection high-energy electron diffraction, X-ray diffraction, reciprocal space mapping, and X-ray reflectivity measurements that these heterostructures can be grown arbitrarily thick while maintaining a high crystalline quality and uniform periodicity, in contrast to previous reports. While we focus primarily on the STO/LAO system in this report, we believe the growth and design principles contained herein can inform the growth of a multitude of different TMO QW heterostructures, paving the way for the next generation of TMO-based QW optoelectronic devices. Published by AIP Publishing. |
BibTeX:
@article{WOS:000437702400011,
author = {Ortmann, J. Elliott and Posadas, Agham B. and Demkov, Alexander A.},
title = {The MBE growth of arbitrarily thick SrTiO3/LaAlO3 quantum well heterostructures for use in next-generation optoelectronic devices},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2018},
volume = {124},
number = {1},
doi = {https://doi.org/10.1063/1.5026234}
}
|
| Qviller, A.J., Marstein, E.S., You, C.C., Haug, H., Webster, J.R.P., Hjorvarsson, B., Frommen, C. and Hauback, B.C. Hydrogen Concentration in Photovoltaic a-Si:H Annealed at Different Temperatures Measured by Neutron Reflectometry IEEE JOURNAL OF PHOTOVOLTAICS 8, 4, pp. 1098-1101 (2018) |
| Abstract: Amorphous hydrogenated silicon (a-Si:H) is an important material for
surface defect passivation of photovoltaic silicon (Si) wafers in order to reduce their recombination losses. The material is, however, unstable with regard to hydrogen (H) desorption at elevated temperatures, which can be an issue during processing and device manufacturing. In this work, we determine the temperature stability of a-Si:H by structural characterization of a-Si:H/Si bilayers with neutron reflectometry and X-ray reflectometry combined with photoconductance measurements, yielding the minority carrier lifetime. The neutrons are sensitive to light elements such as H, while the X-rays, which are insensitive to the H concentration, provide an independent constraint on the layer structure. It is shown that H desorption takes place at a temperature of approximately T = 425 degrees C, and that the H content and minority carrier lifetimes have a strongly correlated linear relationship, which can be interpreted as one H atom passivating one defect. |
BibTeX:
@article{WOS:000436007400027,
author = {Qviller, Atle Jorstad and Marstein, Erik Stensrud and You, Chang Chuan and Haug, Halvard and Webster, John R. P. and Hjorvarsson, Bjorgvin and Frommen, Christoph and Hauback, Bjorn Christian},
title = {Hydrogen Concentration in Photovoltaic a-Si:H Annealed at Different Temperatures Measured by Neutron Reflectometry},
journal = {IEEE JOURNAL OF PHOTOVOLTAICS},
year = {2018},
volume = {8},
number = {4},
pages = {1098-1101},
doi = {https://doi.org/10.1109/JPHOTOV.2018.2838447}
}
|
| Mukhtarova, A., Redaelli, L., Hazra, D., Machhadani, H., Lequien, S., Hofheinz, M., Thomassin, J.-L., Gustavo, F., Zichi, J., Zwiller, V., Monroy, E. and Gerard, J.-M. Polarization-insensitive fiber-coupled superconducting-nanowire single photon detector using a high-index dielectric capping layer OPTICS EXPRESS 26, 13, pp. 17697-17704 (2018) |
| Abstract: Superconducting-nanowire single photon detectors (SNSPDs) are able to
reach near-unity detection efficiency in the infrared spectral range. However, due to the intrinsic asymmetry of nanowires, SNSPDs are usually very sensitive to the polarization of the incident radiation, their responsivity being maximum for light polarized parallel to the nanowire length (transverse-electric (TE) polarization). Here, we report on the reduction of the polarization sensitivity obtained by capping NbN-based SNSPDs with a high-index SiNx dielectric layer, which reduces the permittivity mismatch between the NbN wire and the surrounding area. Experimentally, a polarization sensitivity below 0.1 is obtained both at 1.31 and 1.55 mu m, in excellent agreement with simulations. (C) 2018 Optical Society of America under the terms of the OS.A Open Access Publishing Agreement |
BibTeX:
@article{WOS:000436226800140,
author = {Mukhtarova, Anna and Redaelli, Luca and Hazra, Dibyendu and Machhadani, Houssaine and Lequien, Stephane and Hofheinz, Max and Thomassin, Jean-Luc and Gustavo, Frederic and Zichi, Julien and Zwiller, Val and Monroy, Eva and Gerard, Jean-Michel},
title = {Polarization-insensitive fiber-coupled superconducting-nanowire single photon detector using a high-index dielectric capping layer},
journal = {OPTICS EXPRESS},
year = {2018},
volume = {26},
number = {13},
pages = {17697-17704},
doi = {https://doi.org/10.1364/OE.26.017697}
}
|
| Zarotti, F., Di Castro, D., Felici, R. and Balestrino, G. Structural differences between superconducting and non-superconducting CaCuO2/SrTiO3 interfaces PHYSICA B-CONDENSED MATTER 539, pp. 123-127 (2018) |
| Abstract: A study of the interface structure of superconducting and
non-superconducting CaCuO2/SrTiO3 heterostructures grown on NdGaO3(110) substrates is reported. Using the combination of high resolution x-ray reflectivity and surface diffraction, the crystallographic structure of superconducting and non-superconducting samples has been investigated. The analysis has demonstrated the excellent sharpness of the CaCuO2/SrTiO3 interface (roughness smaller than one perovskite unit cell). Furthermore, we were able to discriminate between the superconducting and the non-superconducting phase. In the former case, we found an increase of the spacing between the topmost Ca plane of CaCuO2 block and the first TiO2 plane of the overlaying STO block, relative to the non-superconducting case. These results are in agreement with the model that foresees a strong oxygen incorporation in the interface Ca plane in the superconducting heterostructures. |
BibTeX:
@article{WOS:000432750900019,
author = {Zarotti, Francesca and Di Castro, Daniele and Felici, Roberto and Balestrino, Giuseppe},
title = {Structural differences between superconducting and non-superconducting CaCuO2/SrTiO3 interfaces},
journal = {PHYSICA B-CONDENSED MATTER},
year = {2018},
volume = {539},
pages = {123-127},
doi = {https://doi.org/10.1016/j.physb.2018.04.008}
}
|
| Ukleev, V., Suturin, S., Nakajima, T., Arima, T.-h., Saerbeck, T., Hanashima, T., Sitnikova, A., Kirilenko, D., Yakovlev, N. and Sokolov, N. Unveiling structural, chemical and magnetic interfacial peculiarities in epsilon-Fe2O3/GaN (0001) epitaxial films SCIENTIFIC REPORTS 8 (2018) |
| Abstract: The metastable epsilon-Fe2O3 is known to be the most intriguing
ferrimagnetic and multiferroic iron oxide phase exhibiting a bunch of exciting physical properties both below and above room temperature. The present paper unveils the structural and magnetic peculiarities of a few nm thick interface layer discovered in these films by a number of techniques. The polarized neutron reflectometry data suggests that the interface layer resembles GaFeO3 in composition and density and is magnetically softer than the rest of the epsilon-Fe2O3 film. While the in-depth density variation is in agreement with the transmission electron microscopy measurements, the layer-resolved magnetization profiles are qualitatively consistent with the unusual wasp-waist magnetization curves observed by superconducting quantum interference device magnetometry. Interestingly a noticeable Ga diffusion into the epsilon-Fe2O3 films has been detected by secondary ion mass spectroscopy providing a clue to the mechanisms guiding the nucleation of exotic metastable epsilon ferrite phase on GaN at high growth temperature and influencing the interfacial properties of the studied films. |
BibTeX:
@article{WOS:000434376700043,
author = {Ukleev, Victor and Suturin, Sergey and Nakajima, Taro and Arima, Taka-hisa and Saerbeck, Thomas and Hanashima, Takayasu and Sitnikova, Alla and Kirilenko, Demid and Yakovlev, Nikolai and Sokolov, Nikolai},
title = {Unveiling structural, chemical and magnetic interfacial peculiarities in epsilon-Fe2O3/GaN (0001) epitaxial films},
journal = {SCIENTIFIC REPORTS},
year = {2018},
volume = {8},
doi = {https://doi.org/10.1038/s41598-018-25849-z}
}
|
| Spencer, C.S., Gayles, J., Porter, N.A., Sugimoto, S., Aslam, Z., Kinane, C.J., Charlton, T.R., Freimuth, F., Chadov, S., Langridge, S., Sinova, J., Felser, C., Bluegel, S., Mokrousov, Y. and Marrows, C.H. Helical magnetic structure and the anomalous and topological Hall effects in epitaxial B20 Fe1-yCoyGe films PHYSICAL REVIEW B 97, 21 (2018) |
| Abstract: Epitaxial films of the B20-structure compound Fe1-yCoyGe were grown by
molecular beam epitaxy on Si (111) substrates. The magnetization varied smoothly from the bulklike values of one Bohr magneton per Fe atom for FeGe to zero for nonmagnetic CoGe. The chiral lattice structure leads to a Dzyaloshinskii-Moriya interaction (DMI), and the films' helical magnetic ground state was confirmed using polarized neutron reflectometry measurements. The pitch of the spin helix, measured by this method, varies with Co content y and diverges at y similar to 0.45. This indicates a zero crossing of the DMI, which we reproduced in calculations using first-principles methods. We also measured the longitudinal and Hall resistivity of our films as a function of magnetic field, temperature, and Co content y. The Hall resistivity is expected to contain contributions from the ordinary, anomalous, and topological Hall effects. Both the anomalous and topological Hall resistivities show peaks around y similar to 0.5. Our first-principles calculations show a peak in the topological Hall constant at this value of y, related to the strong spin polarization predicted for intermediate values of y. Our calculations predict half-metallicity for y = 0.6, consistent with the experimentally observed linear magnetoresistance at this composition, and potentially related to the other unusual transport properties for intermediate value of y. While it is possible to reconcile theory with experiment for the various Hall effects for FeGe, the large topological Hall resistivities for y similar to 0.5 are much larger than expected when the very small emergent fields associated with the divergence in the DMI are taken into account. |
BibTeX:
@article{WOS:000434256300002,
author = {Spencer, Charles S. and Gayles, Jacob and Porter, Nicholas A. and Sugimoto, Satoshi and Aslam, Zabeada and Kinane, Christian J. and Charlton, Timothy R. and Freimuth, Frank and Chadov, Stanislav and Langridge, Sean and Sinova, Jairo and Felser, Claudia and Bluegel, Stefan and Mokrousov, Yuriy and Marrows, Christopher H.},
title = {Helical magnetic structure and the anomalous and topological Hall effects in epitaxial B20 Fe1-yCoyGe films},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {97},
number = {21},
doi = {https://doi.org/10.1103/PhysRevB.97.214406}
}
|
| Wood, M.H., Wood, T.J., Welbourn, R.J.L., Poon, J., Madden, D.C. and Clarke, S.M. An X-ray and Neutron Reflectometry Study of Iron Corrosion in Seawater LANGMUIR 34, 21, pp. 5990-6002 (2018) |
| Abstract: The corrosive breakdown of thin iron films supported on silicon
substrates under a number of conditions is presented-in particular to understand better how iron, and hence ferritic steel, behaves in a salty water environment. A combination of X-ray and neutron reflectometry was used to monitor the structures of both metal and oxide surface layers and also organic corrosion inhibitors adsorbed at the iron/aqueous interface. A range of behavior in seawater was observed, including complete dissolution and void formation under the metal surface. Importantly, two simple treatments-UV/ozone or soaking in ultrapure water-were found to significantly protect the iron surface for considerable lengths of time, although evidence of pitting corrosion began after around 10 days. The underlying causes of the efficacies of these treatments were further investigated using X-ray photoelectron spectroscopy. In addition, three potential corrosion inhibitors were investigated: (i) dodecyltrimethylammonium bromide (DTAB) demonstrated no ability to protect the surface; (ii) sodium dodecyl sulfate (SDS) appeared to accelerate corrosion; and (iii) bis(2-ethylhexyl)phosphate showed an impressive level of protection (the neutron reflectometry results indicated a thick diffuse layer of surfactant of 23% surface coverage). These findings have been interpreted in terms of preferential inhibitor adsorption at cathodic and anodic surface sites (depending on the nature of the inhibitor). |
BibTeX:
@article{WOS:000434000500005,
author = {Wood, Mary H. and Wood, Thomas J. and Welbourn, Rebecca J. L. and Poon, Jeffrey and Madden, David C. and Clarke, Stuart M.},
title = {An X-ray and Neutron Reflectometry Study of Iron Corrosion in Seawater},
journal = {LANGMUIR},
year = {2018},
volume = {34},
number = {21},
pages = {5990-6002},
doi = {https://doi.org/10.1021/acs.langmuir.8b00378}
}
|
| Duffy, L.B., Steinke, N.-J., Krieger, J.A., Figueroa I, A., Kummer, K., Lancaster, T., Giblin, S.R., Pratt, F.L., Blundell, S.J., Prokscha, T., Suter, A., Langridge, S., Strocov, V.N., Salman, Z., van der Laan, G. and Hesjedal, T. Microscopic effects of Dy doping in the topological insulator Bi2Te3 PHYSICAL REVIEW B 97, 17 (2018) |
| Abstract: Magnetic doping with transition metal ions is the most widely used
approach to break time-reversal symmetry in a topological insulator (TI)-a prerequisite for unlocking the TI's exotic potential. Recently, we reported the doping of Bi2Te3 thin films with rare-earth ions, which, owing to their large magnetic moments, promise commensurately large magnetic gap openings in the topological surface states. However, only when doping with Dy has a sizable gap been observed in angle-resolved photoemission spectroscopy, which persists up to room temperature. Although disorder alone could be ruled out as a cause of the topological phase transition, a fundamental understanding of the magnetic and electronic properties of Dy-doped Bi2Te3 remained elusive. Here, we present an x-ray magnetic circular dichroism, polarized neutron reflectometry, muon-spin rotation, and resonant photoemission study of the microscopic magnetic and electronic properties. We find that the films are not simply paramagnetic but that instead the observed behavior can be well explained by the assumption of slowly fluctuating, inhomogeneous, magnetic patches with increasing volume fraction as the temperature decreases. At liquid helium temperatures, a large effective magnetization can be easily introduced by the application of moderate magnetic fields, implying that this material is very suitable for proximity coupling to an underlying ferromagnetic insulator or in a heterostructure with transition-metal-doped layers. However, the introduction of some charge carriers by the Dy dopants cannot be excluded at least in these highly doped samples. Nevertheless, we find that the magnetic order is not mediated via the conduction channel in these samples and therefore magnetic order and carrier concentration are expected to be independently controllable. This is not generally the case for transition-metal-doped topological insulators, and Dy doping should thus allow for improved TI quantum devices. |
BibTeX:
@article{WOS:000433061200003,
author = {Duffy, L. B. and Steinke, N-J and Krieger, J. A. and Figueroa, I, A. and Kummer, K. and Lancaster, T. and Giblin, S. R. and Pratt, F. L. and Blundell, S. J. and Prokscha, T. and Suter, A. and Langridge, S. and Strocov, V. N. and Salman, Z. and van der Laan, G. and Hesjedal, T.},
title = {Microscopic effects of Dy doping in the topological insulator Bi2Te3},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {97},
number = {17},
doi = {https://doi.org/10.1103/PhysRevB.97.174427}
}
|
| Quarterman, P., Sun, C., Garcia-Barriocanal, J., Mahendra, D.C., Lv, Y., Manipatruni, S., Nikonov, D.E., Young, I.A., Voyles, P.M. and Wang, J.-P. Demonstration of Ru as the 4th ferromagnetic element at room temperature NATURE COMMUNICATIONS 9 (2018) |
| Abstract: Development of novel magnetic materials is of interest for fundamental
studies and applications such as spintronics, permanent magnetics, and sensors. We report on the first experimental realization of single element ferromagnetism, since Fe, Co, and Ni, in metastable tetragonal Ru, which has been predicted. Body-centered tetragonal Ru phase is realized by use of strain via seed layer engineering. X-ray diffraction and electron microscopy confirm the epitaxial mechanism to obtain tetragonal phase Ru. We observed a saturation magnetization of 148 and 160 emu cm(-3) at room temperature and 10 K, respectively. Control samples ensure the ferromagnetism we report on is from tetragonal Ru and not from magnetic contamination. The effect of thickness on the magnetic properties is also studied, and it is observed that increasing thickness results in strain relaxation, and thus diluting the magnetization. Anomalous Hall measurements are used to confirm its ferromagnetic behavior. |
BibTeX:
@article{WOS:000433066900002,
author = {Quarterman, P. and Sun, Congli and Garcia-Barriocanal, Javier and Mahendra, D. C. and Lv, Yang and Manipatruni, Sasikanth and Nikonov, Dmitri E. and Young, Ian A. and Voyles, Paul M. and Wang, Jian-Ping},
title = {Demonstration of Ru as the 4th ferromagnetic element at room temperature},
journal = {NATURE COMMUNICATIONS},
year = {2018},
volume = {9},
doi = {https://doi.org/10.1038/s41467-018-04512-1}
}
|
| Magnus, F., Warnatz, T., Palsson, G.K., Devishvili, A., Ukleev, V., Palisaitis, J., Persson, P.O.A. and Hjorvarsson, B. Sequential magnetic switching in Fe/MgO(001) superlattices PHYSICAL REVIEW B 97, 17 (2018) |
| Abstract: Polarized neutron reflectometry is used to determine the sequence of
magnetic switching in interlayer exchange coupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 angstrom thick MgO layers we obtain a 90 degrees periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the top layer switches first followed by its second-nearest neighbor. For 16.4 angstrom MgO layers, a 180 degrees periodic alignment is obtained at remanence and with increasing applied field the layer switching starts from the two outermost layers and proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensional magnetic structures with a predefined discrete switching sequence. |
BibTeX:
@article{WOS:000433028500004,
author = {Magnus, F. and Warnatz, T. and Palsson, G. K. and Devishvili, A. and Ukleev, V and Palisaitis, J. and Persson, P. O. A. and Hjorvarsson, B.},
title = {Sequential magnetic switching in Fe/MgO(001) superlattices},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {97},
number = {17},
doi = {https://doi.org/10.1103/PhysRevB.97.174424}
}
|
| Pilkington, G.A., Harris, K., Bergendal, E., Reddy, A.B., Palsson, G.K., Vorobiev, A., Antzutkin, O.N., Glavatskih, S. and Rutland, M.W. Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance JOURNAL OF CHEMICAL PHYSICS 148, 19 (2018) |
| Abstract: Using neutron reflectivity, the electro-responsive structuring of the
non-halogenated ionic liquid (IL) trihexyl(tetradecyl)phosphonium-bis(mandelato)borate, [ P-6,P-6,P-6,P-14][BMB], has been studied at a gold electrode surface in a polar solvent. For a 20% w/w IL mixture, contrast matched to the gold surface, distinct Kiessig fringes were observed for all potentials studied, indicative of a boundary layer of different composition to that of the bulk IL-solvent mixture. With applied potential, the amplitudes of the fringes from the gold-boundary layer interface varied systematically. These changes are attributable to the differing ratios of cations and anions in the boundary layer, leading to a greater or diminished contrast with the gold electrode, depending on the individual ion scattering length densities. Such electro-responsive changes were also evident in the reflectivities measured for the pure IL and a less concentrated (5% w/w) IL-solvent mixture at the same applied potentials, but gave rise to less pronounced changes. These measurements, therefore, demonstrate the enhanced sensitivity achieved by contrast matching the bulk solution and that the structure of the IL boundary layers formed in mixtures is strongly influenced by the bulk concentration. Together these results represent an important step in characterising IL boundary layers in IL-solvent mixtures and provide clear evidence of electro-responsive structuring of IL ions in their solutions with applied potential. Published by AIP Publishing. |
BibTeX:
@article{WOS:000432853800010,
author = {Pilkington, Georgia A. and Harris, Kathryn and Bergendal, Erik and Reddy, Akepati Bhaskar and Palsson, Gunnar K. and Vorobiev, Alexei and Antzutkin, Oleg. N. and Glavatskih, Sergei and Rutland, Mark W.},
title = {Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance},
journal = {JOURNAL OF CHEMICAL PHYSICS},
year = {2018},
volume = {148},
number = {19},
doi = {https://doi.org/10.1063/1.5001551}
}
|
| Wood, M.H., Payagalage, C.G. and Geue, T. Bovine Serum Albumin and Fibrinogen Adsorption at the 316L Stainless Steel/Aqueous Interface JOURNAL OF PHYSICAL CHEMISTRY B 122, 19, pp. 5057-5065 (2018) |
| Abstract: The binding of bovine serum albumin (BSA) to a 316L stainless steel
surface from a buffer solution has been characterized using neutron reflectometry and quartz crystal microbalance measurements; coverage at all concentrations up to a near-physiological concentration was found to be relatively low (<20%); the protein followed a two-step isotherm adsorption model type and the overall thickness at higher concentrations (around 80 (A) over-circle) suggested possible multilayering and/or protein unfolding. As it has been postulated that BSA may inhibit the further adsorption of another blood plasma protein-fibrinogen-the effects of preadsorbing BSA on fibrinogen adsorption were examined, first by prior physisorption of BSA to the stainless steel surface and second by pretreating the stainless steel with a layer of sodium dodecyl sulfate (SDS) to render it more hydrophobic. Although the preadsorption of BSA to an untreated stainless steel surface did slightly decrease the amount of fibrinogen adsorbed initially, it had no inhibiting effect if a solution containing solely fibrinogen subsequently flowed through. In contrast, the SDS-treated surface yielded both an increased BSA adsorption and consistently decreased fibrinogen adsorption. |
BibTeX:
@article{WOS:000432754100011,
author = {Wood, Mary H. and Payagalage, Charanee Galabada and Geue, Thomas},
title = {Bovine Serum Albumin and Fibrinogen Adsorption at the 316L Stainless Steel/Aqueous Interface},
journal = {JOURNAL OF PHYSICAL CHEMISTRY B},
year = {2018},
volume = {122},
number = {19},
pages = {5057-5065},
doi = {https://doi.org/10.1021/acs.jpcb.8b01347}
}
|
| Kolesnikov, A.G., Ognev, A.V., Stebliy, M.E., Chebotkevich, L.A., Gerasimenko, A.V. and Samardak, A.S. Nanoscale control of perpendicular magnetic anisotropy, coercive force and domain structure in ultrathin Ru/Co/W/Ru films JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 454, pp. 78-84 (2018) |
| Abstract: Development of fast and energy-efficient spintronic devices requires
novel nanoscaled materials with controllable magnetic properties. Here we show that the introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular magnetic anisotropy (PMA) and dramatically reduce the coercive force and size of magnetic domains. We find that the Ru/Co/W/Ru films with up to 0.35 nm of the nominal thickness of W have robust PMA. The observed formation of a dendritic domain structure with small domains having homochiral Neel domain walls is an indicator of the interfacial Dzyaloshinskii-Moriya interaction appearing in trilayers with asymmetrical interfaces. The inversion-symmetry-broken Ru/Co/W/Ru films are a potential host for nucleation and manipulation of non-trivial spin textures like chiral domain walls and skyrmions. (C) 2018 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000426421800012,
author = {Kolesnikov, A. G. and Ognev, A. V. and Stebliy, M. E. and Chebotkevich, L. A. and Gerasimenko, A. V. and Samardak, A. S.},
title = {Nanoscale control of perpendicular magnetic anisotropy, coercive force and domain structure in ultrathin Ru/Co/W/Ru films},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2018},
volume = {454},
pages = {78-84},
doi = {https://doi.org/10.1016/j.jmmm.2018.01.056}
}
|
| Zabolotnyy, V.B., Fuersich, K., Green, R.J., Lutz, P., Treiber, K., Min, C.-H., Dukhnenko, A.V., Shitsevalova, N.Y., Filipov, V.B., Kang, B.Y., Cho, B.K., Sutarto, R., He, F., Reinert, F., Inosov, D.S. and Hinkov, V. Chemical and valence reconstruction at the surface of SmB6 revealed by means of resonant soft x-ray reflectometry PHYSICAL REVIEW B 97, 20 (2018) |
| Abstract: Samarium hexaboride (SmB6), a Kondo insulator with mixed valence, has
recently attracted much attention as a possible host for correlated topological surface states. Here, we use a combination of x-ray absorption and reflectometry techniques, backed up with a theoretical model for the resonant M-4,M-5 absorption edge of Sm and photoemission data, to establish laterally averaged chemical and valence depth profiles at the surface of SmB6. We show that upon cleaving, the highly polar (001) surface of SmB6 undergoes substantial chemical and valence reconstruction, resulting in boron termination and a Sm3+ dominated subsurface region. Whereas at room temperature, the reconstruction occurs on a timescale of less than 2 h, it takes about 24 h below 50 K. The boron termination is eventually established, irrespective of the initial termination. Our findings reconcile earlier depth resolved photoemission and scanning tunneling spectroscopy studies performed at different temperatures and are important for better control of surface states in this system. |
BibTeX:
@article{WOS:000432966100009,
author = {Zabolotnyy, V. B. and Fuersich, K. and Green, R. J. and Lutz, P. and Treiber, K. and Min, Chul-Hee and Dukhnenko, A. V. and Shitsevalova, N. Y. and Filipov, V. B. and Kang, B. Y. and Cho, B. K. and Sutarto, R. and He, Feizhou and Reinert, F. and Inosov, D. S. and Hinkov, V.},
title = {Chemical and valence reconstruction at the surface of SmB6 revealed by means of resonant soft x-ray reflectometry},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {97},
number = {20},
doi = {https://doi.org/10.1103/PhysRevB.97.205416}
}
|
| Muscas, G., Brucas, R. and Jonsson, P.E. Bringing nanomagnetism to the mesoscale with artificial amorphous structures PHYSICAL REVIEW B 97, 17 (2018) |
| Abstract: In the quest for materials with emergent or improved properties, an
effective route is to create artificial superstructures. Novel properties emerge from the coupling between the phases, but the strength of this coupling depends on the quality of the interfaces. Atomic control of crystalline interfaces is notoriously complicated and to elude that obstacle, we suggest here an all-amorphous design. Starting from a model amorphous iron alloy, we locally tune the magnetic behavior by creating boron-doped regions by means of ion implantation through a lithographic mask. This process preserves the amorphous environment, creating a non-topographic magnetic superstructure with smooth interfaces and no structural discontinuities. The absence of inhomogeneities acting as pinning centers for the magnetization reversal is demonstrated by the formation of magnetic vortexes for ferromagnetic disks as large as 20 mu m in diameter embedded within a paramagnetic matrix. Rigid exchange coupling between two amorphous ferromagnetic phases in a microstructured sample is evidenced by an investigation involving first-order reversal curves. The sample consists of a soft matrix with embedded elements constituting a hard phase where the anisotropy originates from an elongated shape of the elements. We provide an intuitive explanation for the micrometer-range exchange coupling mechanism and discuss how to tailor the properties of all-amorphous superstructures. |
BibTeX:
@article{WOS:000432028500002,
author = {Muscas, G. and Brucas, R. and Jonsson, P. E.},
title = {Bringing nanomagnetism to the mesoscale with artificial amorphous structures},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {97},
number = {17},
doi = {https://doi.org/10.1103/PhysRevB.97.174409}
}
|
| Hang, X., Zhang, X., Ma, B., Lauter, V. and Wang, J.-P. Epitaxial Fe16N2 thin film on nonmagnetic seed layer APPLIED PHYSICS LETTERS 112, 19 (2018) |
| Abstract: Metastable alpha `'-Fe16N2 has attracted much interest as a candidate
for rare-earth-free hard magnetic materials. We demonstrate that Fe16N2 thin films were grown epitaxially on Cr seed layers with MgO (001) substrates by facing-target sputtering. Good crystallinity with the epitaxial relation MgO (001)[110] parallel to Cr (001)[100] parallel to Fe16N2 (001)[100] was obtained. The chemical order parameter, which quantifies the degree of N ordering in the Fe16N2 (the N-disordered phase is alpha'-Fe8N martensite), reaches 0.75 for Cr-seeded samples. Cr has a perfect lattice constant match with Fe16N2, and no noticeable strain can be assigned to Fe16N2. The intrinsic saturation magnetization of this non-strained Fe16N2 thin film at room temperature is determined to be 2.31 T by polarized neutron reflectometry and confirmed with vibrating sample magnetometry. Our work provides a platform to directly study the magnetic properties of high purity Fe16N2 films with a high order parameter. Published by AIP Publishing. |
BibTeX:
@article{WOS:000431980100023,
author = {Hang, Xudong and Zhang, Xiaowei and Ma, Bin and Lauter, Valeria and Wang, Jian-Ping},
title = {Epitaxial Fe16N2 thin film on nonmagnetic seed layer},
journal = {APPLIED PHYSICS LETTERS},
year = {2018},
volume = {112},
number = {19},
doi = {https://doi.org/10.1063/1.5028396}
}
|
| Rizal, C., Pisana, S., Hrvoic, I. and Fullerton, E.E. Microstructure and magneto-optical surface plasmon resonance of Co/Au multilayers JOURNAL OF PHYSICS COMMUNICATIONS 2, 5 (2018) |
| Abstract: Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a
magneto-optic enhancement with respect to surface plasmon resonance (SPR) sensors, making these devices attractive for biosensing applications. Typical design compromises seek to balance magneto-optic effects and optical losses associated with surface plasmon waves extending to the ferromagnetic layer. Here, we demonstrate that Co/Au multilayers can yield sizeable MOSPR improvements in spite of the relative high total Co layer thickness. Co(t(Co))/Au(2 nm) multilayers, with 1.2 <= t(Co) <= 1.8 nm are prepared and characterized. X-ray analysis shows that the microstructure maintains high layer periodicity and improves upon annealing. The multilayer structures were then modeled to study their SPR/MOSPR sensitivities, suggesting that the MOSPR sensitivity is enhanced by a factor of up to 3 and 4 with respect to the SPR sensitivity when the devices are operated in Air and Water media, respectively. We find that multilayers provide a particular advantage when operating the sensors in Water-based media. |
BibTeX:
@article{WOS:000435001300012,
author = {Rizal, Conrad and Pisana, Simone and Hrvoic, Ivan and Fullerton, Eric E.},
title = {Microstructure and magneto-optical surface plasmon resonance of Co/Au multilayers},
journal = {JOURNAL OF PHYSICS COMMUNICATIONS},
year = {2018},
volume = {2},
number = {5},
doi = {https://doi.org/10.1088/2399-6528/aac0e0}
}
|
| Chang, S., Vijayan, S., Aindow, M., Jursich, G. and Takoudis, C.G. Hydrogen annealing effects on local structures and oxidation states of atomic layer deposited SnOx JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 36, 3 (2018) |
| Abstract: Divalent tin is of great interest, but comes with a drawback-its
metastable nature. In pursuing divalent tin, the authors systematically examine the change in oxidation states of Sn using a set of ALD SnOx films annealed in different atmospheres at temperatures ranging from 350 to 650 degrees C. Although the majority of Sn in the film was tetravalent after deposition, x-ray photoelectron spectroscopy and x-ray absorption near-edge structure verified the presence of divalent Sn after annealing in H-2, and the divalent Sn content increased as the annealing temperature was raised. The local structures of Sn processed under these conditions were probed using extended x-ray absorption fine structure. Data from samples annealed in H-2 at 350, 450, and 550 degrees C were fitted well using a rutile SnO2 model; the sample annealed in H-2 at 650 degrees C could only be fitted using a hybrid of SnO2 and SnO models. Annealing in N-2 and O-2 resulted in tetravalent Sn. X-ray reflectivity showed that the density of the as-deposited film was as low as 50% of that for bulk SnO2; annealing in H-2 first increased the critical angle, but the lowest density was found in films annealed in H-2 at 650 degrees C. Scanning and transmission electron microscopy analysis revealed that the as-deposited films were amorphous whereas the annealed films underwent a dewetting process after annealing for 30 min in H-2 at 550 degrees C; the resulting structure was separated into tin-rich spheres with oxygen-rich outer shells and SnO clusters, possibly due to the lattice mismatch between Sn and SnO after disproportionation. Published by the AVS. |
BibTeX:
@article{WOS:000432372400046,
author = {Chang, Siliang and Vijayan, Sriram and Aindow, Mark and Jursich, Gregory and Takoudis, Christos G.},
title = {Hydrogen annealing effects on local structures and oxidation states of atomic layer deposited SnOx},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2018},
volume = {36},
number = {3},
doi = {https://doi.org/10.1116/1.5026696}
}
|
| Maruyama, R., Yamazaki, D., Akutsu, K., Hanashima, T., Miyata, N., Aoki, H., Takeda, M. and Soyama, K. Development of high-polarization Fe/Ge neutron polarizing supermirror: Possibility of fine-tuning of scattering length density in ion beam sputtering NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 888, pp. 70-78 (2018) |
| Abstract: The multilayer structure of Fe/Si and Fe/Ge systems fabricated by ion
beam sputtering (IBS) was investigated using X-ray and polarized neutron reflectivity measurements and scanning transmission electron microscopy with energy-dispersive X-ray analysis. The obtained result revealed that the incorporation of sputtering gas particles (Ar) in the Ge layer gives rise to a marked reduction in the neutron scattering length density (SLD) and contributes to the SLD contrast between the Fe and Ge layers almost vanishing for spin-down neutrons. Bundesmann et al. (2015) have shown that the implantation of primary Ar ions backscattered at the target is responsible for the incorporation of Ar particles and that the fraction increases with increasing ion incidence angle and increasing polar emission angle. This leads to a possibility of fine-tuning of the SLD for the IBS, which is required to realize a high polarization efficiency of a neutron polarizing supermirror. Fe/Ge polarizing supermirror with m = 5 fabricated under the same condition showed a spin-up reflectivity of 0.70 at the critical momentum transfer. The polarization was higher than 0.985 for the q(2). range where the correction for the polarization inefficiencies of the beamline works properly. The result of the polarized neutron reflectivity measurement suggests that the ``magnetically-dead'' layers formed at both sides of the Fe layer, together with the SLD contrast, play a critical role in determining the polarization performance of a polarizing supermirror. (c) 2018 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000425974100010,
author = {Maruyama, R. and Yamazaki, D. and Akutsu, K. and Hanashima, T. and Miyata, N. and Aoki, H. and Takeda, M. and Soyama, K.},
title = {Development of high-polarization Fe/Ge neutron polarizing supermirror: Possibility of fine-tuning of scattering length density in ion beam sputtering},
journal = {NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT},
year = {2018},
volume = {888},
pages = {70-78},
doi = {https://doi.org/10.1016/j.nima.2018.01.068}
}
|
| Belova, V., Wagner, B., Reisz, B., Zeiser, C., Duva, G., Rozboril, J., Novak, J., Gerlach, A., Hinderhofer, A. and Schreibert, F. Real-Time Structural and Optical Study of Growth and Packing Behavior of Perylene Diimide Derivative Thin Films: Influence of Side-Chain Modification JOURNAL OF PHYSICAL CHEMISTRY C 122, 15, pp. 8589-8601 (2018) |
| Abstract: We study the growth of two n-type small-molecule organic semiconductors
from the perylene diimide family: N,N'-bis-(2-ethylhexyl)dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDIR-CN2) and N,N'-1H,1H-perfluorobutyl-dicjyanoperylene-3,4: 9,10-bis (dicarboximide) (PDIF-CN2) whose chemical structures differ only in the imide substituents, branched alkyl chains -C8H16 and linear fluoroalkyl chains -C4F7H2, respectively. Both types of substituents introduce some degree of steric hindrance for intermolecular interactions, affecting solid-state packing during thin film formation, and thus induce specific structure-dependent optoelectronic properties in thin films. The transition from an amorphous structure to crystalline domains with strong intermolecular coupling was followed in situ and in real time during growth. We investigated the structural and morphological properties by X-ray diffraction and atomic force microscopy as a function of the substrate temperature and chemical structure. We examined the relationship between the structural properties and thin film optical signatures probed via differential reflectance spectroscopy, ellipsometry, and temperature-dependent photoluminescence. A new crystalline PDIR-CN2 polymorph at high temperatures emerges. In addition, we observed in PDIF-CN2 that the fluorinated chains contribute to crystallization inhibition because of the higher overall steric hindrance compared to the alkyl chains. |
BibTeX:
@article{WOS:000430896500062,
author = {Belova, Valentina and Wagner, Benjamin and Reisz, Berthold and Zeiser, Clemens and Duva, Giuliano and Rozboril, Jakub and Novak, Jiri and Gerlach, Alexander and Hinderhofer, Alexander and Schreibert, Frank},
title = {Real-Time Structural and Optical Study of Growth and Packing Behavior of Perylene Diimide Derivative Thin Films: Influence of Side-Chain Modification},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2018},
volume = {122},
number = {15},
pages = {8589-8601},
doi = {https://doi.org/10.1021/acs.jpcc.8b00787}
}
|
| Fuersich, K., Zabolotnyy, V.B., Schierle, E., Dudy, L., Kirilmaz, O., Sing, M., Claessen, R., Green, R.J., Haverkort, M.W. and Hinkov, V. Theory-restricted resonant x-ray reflectometry of quantum materials PHYSICAL REVIEW B 97, 16 (2018) |
| Abstract: The delicate interplay of competing phases in quantum materials is
dominated by parameters such as the crystal field potential, the spin-orbit coupling, and, in particular, the electronic correlation strength. Whereas small quantitative variations of the parameter values can thus qualitatively change the material, these values can hitherto hardly be obtained with reasonable precision, be it theoretically or experimentally. Here we propose a solution combining resonant x-ray reflectivity (RXR) with multiplet ligand field theory (MLFT). We first perform ab initio DFT calculations within the MLFT framework to get initial parameter values, which we then use in a fit of the theoretical model to RXR. To validate our method, we apply it to NiO and SrTiO3 and obtain parameter values, which are amended by as much as 20% compared to the ab initio results. Our approach is particularly useful to investigate topologically trivial and nontrivial correlated insulators, staggered moments in magnetically or orbitally ordered materials, and reconstructed interfaces. |
BibTeX:
@article{WOS:000430058200004,
author = {Fuersich, Katrin and Zabolotnyy, Volodymyr B. and Schierle, Enrico and Dudy, Lenart and Kirilmaz, Ozan and Sing, Michael and Claessen, Ralph and Green, Robert J. and Haverkort, Maurits W. and Hinkov, Vladimir},
title = {Theory-restricted resonant x-ray reflectometry of quantum materials},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {97},
number = {16},
doi = {https://doi.org/10.1103/PhysRevB.97.165126}
}
|
| Guo, E.-J., Liu, Y., Sohn, C., Desautels, R.D., Herklotz, A., Liao, Z., Nichols, J., Freeland, J.W., Fitzsimmons, M.R. and Lee, H.N. Oxygen Diode Formed in Nickelate Heterostructures by Chemical Potential Mismatch ADVANCED MATERIALS 30, 15 (2018) |
| Abstract: Deliberate control of oxygen vacancy formation and migration in
perovskite oxide thin films is important for developing novel electronic and iontronic devices. Here, it is found that the concentration of oxygen vacancies (V-O) formed in LaNiO3 (LNO) during pulsed laser deposition is strongly affected by the chemical potential mismatch between the LNO film and its proximal layers. Increasing the V-O concentration in LNO significantly modifies the degree of orbital polarization and drives the metal-insulator transition. Changes in the nickel oxidization state and carrier concentration in the films are confirmed by soft X-ray absorption spectroscopy and optical spectroscopy. The ability to unidirectional-control the oxygen flow across the heterointerface, e.g., a so-called oxygen diode, by exploiting chemical potential mismatch at interfaces provides a new avenue to tune the physical and electrochemical properties of complex oxides. |
BibTeX:
@article{WOS:000430101200009,
author = {Guo, Er-Jia and Liu, Yaohua and Sohn, Changhee and Desautels, Ryan D. and Herklotz, Andreas and Liao, Zhaoliang and Nichols, John and Freeland, John W. and Fitzsimmons, Michael R. and Lee, Ho Nyung},
title = {Oxygen Diode Formed in Nickelate Heterostructures by Chemical Potential Mismatch},
journal = {ADVANCED MATERIALS},
year = {2018},
volume = {30},
number = {15},
doi = {https://doi.org/10.1002/adma.201705904}
}
|
| Glavic, A., Summers, B., Dahal, A., Kline, J., Van Herck, W., Sukhov, A., Ernst, A. and Singh, D.K. Spin Solid versus Magnetic Charge Ordered State in Artificial Honeycomb Lattice of Connected Elements ADVANCED SCIENCE 5, 4 (2018) |
| Abstract: The nature of magnetic correlation at low temperature in two-dimensional
artificial magnetic honeycomb lattice is a strongly debated issue. While theoretical researches suggest that the system will develop a novel zero entropy spin solid state as T -> 0 K, a confirmation to this effect in artificial honeycomb lattice of connected elements is lacking. This study reports on the investigation of magnetic correlation in newly designed artificial permalloy honeycomb lattice of ultrasmall elements, with a typical length of approximate to 12 nm, using neutron scattering measurements and temperature-dependent micromagnetic simulations. Numerical modeling of the polarized neutron reflectometry data elucidates the temperature-dependent evolution of spin correlation in this system. As temperature reduces to approximate to 7 K, the system tends to develop novel spin solid state, manifested by the alternating distribution of magnetic vortex loops of opposite chiralities. Experimental results are complemented by temperature-dependent micromagnetic simulations that confirm the dominance of spin solid state over local magnetic charge ordered state in the artificial honeycomb lattice with connected elements. These results enable a direct investigation of novel spin solid correlation in the connected honeycomb geometry of 2D artificial structure. |
BibTeX:
@article{WOS:000430460200014,
author = {Glavic, Artur and Summers, Brock and Dahal, Ashutosh and Kline, Joseph and Van Herck, Walter and Sukhov, Alexander and Ernst, Arthur and Singh, Deepak K.},
title = {Spin Solid versus Magnetic Charge Ordered State in Artificial Honeycomb Lattice of Connected Elements},
journal = {ADVANCED SCIENCE},
year = {2018},
volume = {5},
number = {4},
doi = {https://doi.org/10.1002/advs.201700856}
}
|
| Bollmann, T.R.J. Studying Pulsed Laser Deposition conditions for Ni/C-based multi-layers APPLIED SURFACE SCIENCE 436, pp. 941-949 (2018) |
| Abstract: Nickel carbon based multi-layers are a viable route towards future hard
X-ray and soft gamma-ray focusing telescopes. Here, we study the Pulsed Laser Deposition growth conditions of such bilayers by Reflective High Energy Electron Diffraction, X-ray Reflectivity and Diffraction, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and cross-sectional Transmission Electron Microscopy analysis, with emphasis on optimization of process pressure and substrate temperature during growth. The thin multi-layers are grown on a treated SiO substrate resulting in Ni and C layers with surface roughnesses (RMS) of <= 0.2 nm. Small droplets resulting during melting of the targets surface increase the roughness, however, and cannot be avoided. The sequential process at temperatures beyond 300 degrees C results into intermixing between the two layers, being destructive for the reflectivity of the multi-layer. (C) 2017 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000425723100111,
author = {Bollmann, Tjeerd R. J.},
title = {Studying Pulsed Laser Deposition conditions for Ni/C-based multi-layers},
journal = {APPLIED SURFACE SCIENCE},
year = {2018},
volume = {436},
pages = {941-949},
doi = {https://doi.org/10.1016/j.apsusc.2017.12.178}
}
|
| Roth, J., Arriaga, E., Brahlek, M., Lapano, J. and Engel-Herbert, R. Temperature-dependent growth window of CaTiO3 films grown by hybrid molecular beam epitaxy JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 36, 2 (2018) |
| Abstract: The authors report the effects of growth temperature on the
self-regulated growth window of CaTiO3 thin films grown by hybrid molecular beam epitaxy (hMBE). Films were grown on (001) (La0.3Sr0.7)(Al0.65Ta0.35)O-3 at temperatures between 700 and 950 degrees C. Calcium was supplied by a standard thermal effusion cell, while the metalorganic precursor titanium tetra-isopropoxide (TTIP) was used as the titanium source. The stoichiometric growth conditions were mapped using a combination of x-ray diffraction, reflection high energy electron diffraction, and atomic force microscopy. It is found that the growth window widened and shifted to higher TTIP fluxes with increasing temperature. Further, the shift of the growth window edge to Ti-rich conditions is three times larger than the growth window edge to Ca-rich conditions, which is discussed in general terms of the kinetic processes involved in hMBE. |
BibTeX:
@article{WOS:000426978500014,
author = {Roth, Joseph and Arriaga, Eddy and Brahlek, Matthew and Lapano, Jason and Engel-Herbert, Roman},
title = {Temperature-dependent growth window of CaTiO3 films grown by hybrid molecular beam epitaxy},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2018},
volume = {36},
number = {2},
doi = {https://doi.org/10.1116/1.5011384}
}
|
| Carlomagno, I., Drnec, J., Vlaic, S., Vinogadrov, N., Carla, F., Isern, H., Meneghini, C. and Felici, R. Co film stretching induced by lattice mismatch and annealing: The role of Graphene APPLIED SURFACE SCIENCE 432, A, pp. 22-26 (2018) |
| Abstract: Thin Co films intercalated between a Graphene capping layer and the
Ir(111) surface are of interest for spintronics applications due to their peculiar magnetic properties and to their chemical stability. The structure, and then the magnetic properties, of the Co films depend on the intercalation process which is strongly influenced by the temperature, total amount of Cobalt and quality of the capping Graphene layer. In order to identify and disentangle the effects of these contributions, we report on the structural characterisation of four Co films as a function of thickness, annealing temperature, and Graphene capping. From the structural point of view, the deposition of Co on a hot Ir substrate mimics quite well the intercalation process proving the validity of the colander model describing the Graphene role during the process. (C) 2017 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000416965500005,
author = {Carlomagno, I. and Drnec, J. and Vlaic, S. and Vinogadrov, N. and Carla, F. and Isern, H. and Meneghini, C. and Felici, R.},
title = {Co film stretching induced by lattice mismatch and annealing: The role of Graphene},
journal = {APPLIED SURFACE SCIENCE},
year = {2018},
volume = {432},
number = {A},
pages = {22-26},
note = {32nd European Conference on Surface Science (ECOSS), Paris, FRANCE, AUG 28-SEP 02, 2016},
doi = {https://doi.org/10.1016/j.apsusc.2017.07.287}
}
|
| Brahlek, M., Sen Gupta, A., Lapano, J., Roth, J., Zhang, H.-T., Zhang, L., Haislmaier, R. and Engel-Herbert, R. Frontiers in the Growth of Complex Oxide Thin Films: Past, Present, and Future of Hybrid MBE ADVANCED FUNCTIONAL MATERIALS 28, 9 (2018) |
| Abstract: Driven by an ever-expanding interest in new material systems with new
functionality, the growth of atomic-scale electronic materials by molecular beam epitaxy (MBE) has evolved continuously since the 1950s. Here, a new MBE technique called hybrid-MBE (hMBE) is reviewed that has been proven a power-ful approach for tackling the challenge of growing high-quality, multi-component complex oxides, specifically the ABO(3) perovskites. The goal of this work is to (1) discuss the development of hMBE in a historical context, (2) review the advantageous surface kinetics and chemistry that enable the self-regulated growth of ABO(3) perovskites, (3) layout the key components and technical challenges associated with hMBE, (4) review the status of the field and the materials that have been successfully grown by hMBE which demonstrate its general applicability, and (5) discuss the future of hMBE in regards to technical innovations and expansion into new material classes, which are aimed at expanding into industrial realm and at tackling new scientific endeavors. |
BibTeX:
@article{WOS:000426154500024,
author = {Brahlek, Matthew and Sen Gupta, Arnab and Lapano, Jason and Roth, Joseph and Zhang, Hai-Tian and Zhang, Lei and Haislmaier, Ryan and Engel-Herbert, Roman},
title = {Frontiers in the Growth of Complex Oxide Thin Films: Past, Present, and Future of Hybrid MBE},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2018},
volume = {28},
number = {9},
doi = {https://doi.org/10.1002/adfm.201702772}
}
|
| McBriarty, M.E., Stubbs, J.E., Eng, P.J. and Rosso, K.M. Potential-Specific Structure at the Hematite-Electrolyte Interface ADVANCED FUNCTIONAL MATERIALS 28, 8 (2018) |
| Abstract: The atomic-scale structure of the interface between a transition metal
oxide and aqueous electrolyte regulates the interfacial chemical reactions fundamental to (photo)electrochemical energy conversion and electrode degradation. Measurements that probe oxide-electrolyte interfaces in situ provide important details of ion and solvent arrangements, but atomically precise structural models do not exist for common oxide-electrolyte interfaces far from equilibrium. Using a novel cell, the structure of the hematite (alpha-Fe2O3) (1 (1) over bar 02)-electrolyte interface is measured under controlled electrochemical bias using synchrotron crystal truncation rod X-ray scattering. At increasingly cathodic potentials, charge-compensating protonation of surface oxygen groups increases the coverage of specifically bound water while adjacent water layers displace outwardly and became disordered. Returning to open circuit potential leaves the surface in a persistent metastable state. Therefore, the flux of current and ions across the interface is regulated by multiple electrolyte layers whose specific structure and polarization change in response to the applied potential. The study reveals the complex environment underlying the simplified electrical double layer models used to interpret electrochemical measurements and emphasizes the importance of condition-specific structural characterization for properly understanding catalytic processes at functional transition metal oxide-electrolyte interfaces. |
BibTeX:
@article{WOS:000425448200021,
author = {McBriarty, Martin E. and Stubbs, Joanne E. and Eng, Peter J. and Rosso, Kevin M.},
title = {Potential-Specific Structure at the Hematite-Electrolyte Interface},
journal = {ADVANCED FUNCTIONAL MATERIALS},
year = {2018},
volume = {28},
number = {8},
doi = {https://doi.org/10.1002/adfm.201705618}
}
|
| Salvati, E., Brandt, L.R., Papadaki, C., Zhang, H., Mousavi, S.M., Wermeille, D. and Korsunsky, A.M. Nanoscale structural damage due to focused ion beam milling of silicon with Ga-ions MATERIALS LETTERS 213, pp. 346-349 (2018) |
| Abstract: The exposure of sample to Focused Ion Beam leads to Ga-ion implantation,
damage, material amorphisation, and the introduction of sources of residual stress; namely eigenstrain. In this study we employ synchrotron X-ray Reflectivity technique to characterise the amorphous layer generated in a single crystal Silicon sample by exposure to Ga-ion beam. The thickness, density and interface roughness of the amorphous layer were extracted from the analysis of the reflectivity curve. The outcome is compared with the eigenstrain profile evaluated from residual stress analysis by Molecular Dynamics and TEM imaging reported in the literature. (c) 2017 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000419049300087,
author = {Salvati, E. and Brandt, L. R. and Papadaki, C. and Zhang, H. and Mousavi, S. M. and Wermeille, D. and Korsunsky, A. M.},
title = {Nanoscale structural damage due to focused ion beam milling of silicon with Ga-ions},
journal = {MATERIALS LETTERS},
year = {2018},
volume = {213},
pages = {346-349},
doi = {https://doi.org/10.1016/j.matlet.2017.11.043}
}
|
| Will, J., Hou, Y., Scheiner, S., Pinkert, U., Hermes, I.M., Weber, S.A.L., Hirsch, A., Halik, M., Brabec, C. and Unruh, T. Evidence of Tailoring the Interfacial Chemical Composition in Normal Structure Hybrid Organohalide Perovskites by a Self-Assembled Monolayer ACS APPLIED MATERIALS & INTERFACES 10, 6, pp. 5511-5518 (2018) |
| Abstract: Current-voltage hysteresis is a major issue for normal architecture
organo-halide perovskite solar cells. In this manuscript we reveal a several-angstrom thick methylammonium iodide-rich interface between the perovskite and the metal oxide. Surface functionalization via :self-assembled monolayers allowed us to control the composition.of the interface monolayer from Pb poor to Pb rich, which, in parallel, suppresses hysteresis in perovskite solar cells. The bulk of the perovskite films is not affected by the interface engineering and remains _highly- crystalline in the surface normal direction over the whole film thickness. The subnanometer structural modifications of the buried interface were revealed by X-ray reflectivity, which is most sensitive to monitor changes in the mass density of only several-angstrom thin interfacial layers as a function of substrate functionalization. From Kelvin probe force microscopy study on a solar cell cross section, we further demonstrate local variations of the potential on different electroriAransporting layers within a solar cell. Ori-the basis of these findings, we present a unifying model explaining hysteresis in perovskite solar cells, giving an insight into,one crucial aspect of hysteresis for the first time and paving way for new strategies in the field of perovskite-based opto-electronic devices. |
BibTeX:
@article{WOS:000425572700039,
author = {Will, Johannes and Hou, Yi and Scheiner, Simon and Pinkert, Ute and Hermes, Ilka M. and Weber, Stefan A. L. and Hirsch, Andreas and Halik, Marcus and Brabec, Christoph and Unruh, Tobias},
title = {Evidence of Tailoring the Interfacial Chemical Composition in Normal Structure Hybrid Organohalide Perovskites by a Self-Assembled Monolayer},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2018},
volume = {10},
number = {6},
pages = {5511-5518},
doi = {https://doi.org/10.1021/acsami.7b15904}
}
|
| Glover, S.E., Saerbeck, T., Kuerbanjiang, B., Ghasemi, A., Kepaptsoglou, D., Ramasse, Q.M., Yamada, S., Hamaya, K., Hase, T.P.A., Lazarov, V.K. and Bell, G.R. Magnetic and structural depth profiles of Heusler alloy Co2FeAl0.5Si0.5 epitaxial films on Si(111) JOURNAL OF PHYSICS-CONDENSED MATTER 30, 6 (2018) |
| Abstract: The depth-resolved chemical structure and magnetic moment of
Co2FeAl0.5Si0.5, thin films grown on Si(111) have been determined using x-ray and polarized neutron reflectometry. Bulk-like magnetization is retained across the majority of the film, but reduced moments are observed within 45 angstrom of the surface and in a 25 angstrom substrate-interface region. The reduced moment is related to compositional changes due to oxidation and diffusion, which are further quantified by elemental profiling using electron microscopy with electron energy loss spectroscopy. The accuracy of structural and magnetic depth-profiles obtained from simultaneous modeling is discussed using different approaches with different degree of constraints on the parameters. Our approach illustrates the challenges in fitting reflectometry data from these multi-component quaternary Heusler alloy thin films. |
BibTeX:
@article{WOS:000422879400001,
author = {Glover, Stephanie E. and Saerbeck, Thomas and Kuerbanjiang, Balati and Ghasemi, Arsham and Kepaptsoglou, Demie and Ramasse, Quentin M. and Yamada, Shinya and Hamaya, Kohei and Hase, Thomas P. A. and Lazarov, Vlado K. and Bell, Gavin R.},
title = {Magnetic and structural depth profiles of Heusler alloy Co2FeAl0.5Si0.5 epitaxial films on Si(111)},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2018},
volume = {30},
number = {6},
doi = {https://doi.org/10.1088/1361-648X/aaa4c8}
}
|
| Zhang, J., Meng, D., Huang, H., Cai, H., Huang, Q., Wang, J., Yang, Y., Zhai, X., Fu, Z. and Lu, Y. Phase competition in the growth of SrCoOx/LaAlO3 thin films AIP ADVANCES 8, 2 (2018) |
| Abstract: The reversible topotactic phase transformation between brownmillerite
SrCoO2.5 to perovskite SrCoO3 has attracted more and more attention for potential applications as solid oxide fuels and electrolysis cells. However, the relatively easy transformation result from small thermal stable energy barriers between the two phases leads to unstable the structures. In the paper, amounts of SrCoO3-delta films have been prepared by pulsed laser deposition at optimized growth conditions with the temperature range of 590-720 degrees C. The X-ray diffraction (XRD) results demonstrated that a phase competition emerged around 650 degrees C. The Gibbs free energies of two phases at high temperature revealed the difference of stability of these two phases under different growth temperature. The optical spectroscopies and X-ray photoelectron spectroscopies were used to verify the electronic structure and chemical state differences between the two phases with distinct crystal structures. (c) 2018 Author(s). |
BibTeX:
@article{WOS:000426580900094,
author = {Zhang, Jie and Meng, Dechao and Huang, Haoliang and Cai, Honglei and Huang, Qiuping and Wang, Jianlin and Yang, Yuanjun and Zhai, Xiaofang and Fu, Zhengping and Lu, Yalin},
title = {Phase competition in the growth of SrCoOx/LaAlO3 thin films},
journal = {AIP ADVANCES},
year = {2018},
volume = {8},
number = {2},
doi = {https://doi.org/10.1063/1.5022411}
}
|
| Wang, Q., Chen, A.P., Guo, E.J., Roldan, M.A., Jia, Q.X. and Fitzsimmons, M.R. Upper limit for the effect of elastic bending stress on the saturation magnetization of La0.8Sr0.2MnO3 PHYSICAL REVIEW B 97, 1 (2018) |
| Abstract: Using polarized neutron reflectometry, we measured the influence of
elastic bending stress on the magnetization depth profile of a La0.8Sr0.2MnO3 (LSMO) epitaxial film grown on a SrTiO3 substrate. The elastic bending strain of +/- 0.03% has no obvious effect on the magnetization depth profile at saturation. This result is in stark contrast to that of (La1-xPrx)(1-y),Ca-y,MnO3 (LPCMO) films for which strain of +/- 0.01% produced dramatic changes in the magnetization profile and Curie temperature. We attribute the difference between the influence of strain on the saturation magnetization in LSMO (weak or none) and LPCMO (strong) to a difference in the ability of LSMO (weak or none) and LPCMO (strong) to phase separate. Our observation provides an upper limit of tuning LSMO saturation magnetization via elastic strain effect. |
BibTeX:
@article{WOS:000423656300002,
author = {Wang, Q. and Chen, A. P. and Guo, E. J. and Roldan, M. A. and Jia, Q. X. and Fitzsimmons, M. R.},
title = {Upper limit for the effect of elastic bending stress on the saturation magnetization of La0.8Sr0.2MnO3},
journal = {PHYSICAL REVIEW B},
year = {2018},
volume = {97},
number = {1},
doi = {https://doi.org/10.1103/PhysRevB.97.014437}
}
|
| Frisk, A., Ali, H., Svedlindh, P., Leifer, K., Andersson, G. and Nyberg, T. Composition, structure and magnetic properties of ultra-thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001) THIN SOLID FILMS 646, pp. 117-125 (2018) |
| Abstract: Sputter deposited symmetric multilayers of (n Fe)/(n Ni), with
individual thicknesses from n = 4 to n = 48 monolayers (ML), were deposited on epitaxial Cu/Si(001), and their microstructural evolution and magnetic properties versus n have been studied. Elemental layering can be seen with transmission electron microscopy down to n = 4 ML layer thickness, although an intermixed region characterized by a finite interface width is found to be present. This width is composed of the interface roughness as well as the interdiffusion between layers, but the relative contributions from these two sources could not be concluded by the techniques used. The measured elemental layering and X-ray reflectivity (XRR) give an upper limit to the interface width which must be smaller than the thinnest layers, 4 ML. Electron energy loss spectroscopy (EELS), depth profiling X-ray photoelectron spectroscopy (XPS) and also XRR reveal that Fe has a higher tendency to mix with Ni than vice versa. XPS does not have the resolution to measure this thin elemental layering: composition variations for n = 8 ML which are clearly seen by EELS are barely resolved by XPS. The structure was determined by X-ray diffraction, and an epitaxial fcc (001) structure is found to be maintained throughout the multilayers up to n less than or similar to 8 ML. For larger n values, relaxation starts by Fe-fcc(001) layers changing into Fe-bcc(110), which is then followed by Ni-fcc(001) changing from (001) to (111) orientation along the growth direction. A decreased total measured magnetic moment for the fully epitaxial multilayers can be explained by the fcc Fe layers being partly anti-ferromagnetic, whereas the relaxed multilayers exhibit the expected magnetic properties of (bcc Fe) +(fcc Ni). |
BibTeX:
@article{WOS:000418575900017,
author = {Frisk, Andreas and Ali, Hasan and Svedlindh, Peter and Leifer, Klaus and Andersson, Gabriella and Nyberg, Tomas},
title = {Composition, structure and magnetic properties of ultra-thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001)},
journal = {THIN SOLID FILMS},
year = {2018},
volume = {646},
pages = {117-125},
doi = {https://doi.org/10.1016/j.tsf.2017.11.023}
}
|
| Loving, M.G., Barua, R., Le Graet, C., Kinane, C.J., Heiman, D., Langridge, S., Marrows, C.H. and Lewis, L.H. Strain-tuning of the magnetocaloric transition temperature in model FeRh films JOURNAL OF PHYSICS D-APPLIED PHYSICS 51, 2 (2018) |
| Abstract: The chemically ordered B2 phase of equiatomic FeRh is known to absorb or
evolve a significant latent heat as it traverses its first-order phase transition in response to thermal, magnetic, and mechanical drivers. This attribute makes FeRh an ideal magnetocaloric material testbed for investigation of relationships between the crystalline lattice and the magnetic spins, which are especially experimentally accessible in thin films. In this work, epitaxial FeRh films of nominal 30 nm and 50 nm thicknesses with out-of-plane c-axis orientation were sputter-deposited at high temperature onto (001)-MgO or (0001)-Al2O3 substrates and capped with Al, Au, Cr, or W after in situ annealing at 973 K to promote CsCl-type chemical order. In this manner a controlled strain state was invoked. Experimental results derived from laboratory and synchrotron x-ray diffraction combined with magnetometry indicate that the antiferromagnetic (AF)-ferromagnetic (FM) magnetostructural phase transformation in these films may be tuned over an similar to 50 degrees range (373 K-425 K) through variation in the c/a ratio derived from lattice strain delivered by the substrate and the capping layers. These results supply fundamental information that might be used to engineer the magnetocaloric working material in new system designs by introducing targeted values of passive strain to the system. |
BibTeX:
@article{WOS:000418111800001,
author = {Loving, M. G. and Barua, R. and Le Graet, C. and Kinane, C. J. and Heiman, D. and Langridge, S. and Marrows, C. H. and Lewis, L. H.},
title = {Strain-tuning of the magnetocaloric transition temperature in model FeRh films},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2018},
volume = {51},
number = {2},
doi = {https://doi.org/10.1088/1361-6463/aa9d1f}
}
|
| Mitterhuber, L., Kraker, E. and Defregger, S. Thermal Characterization of Nm-thin Nb2O5 by Applying Thermal Impedance Methods to Time Domain Thermoreflectance Measurements 2018 24TH INTERNATIONAL WORKSHOP ON THERMAL INVESTIGATIONS OF ICS AND SYSTEMS (THERMINIC) (2018) |
| Abstract: The time domain thermal reflectance (TDTR) method enables thermal
investigations of films in the nanometre range, which can be found in microelectronic devices. In this study, a 166 nm thick Diniobium pentoxide layer (Nb2O5), which is used in capacitors, optical devices as well as precursors, was investigated by using TDTR method. This layer was studied by its thermal transients in the (sub-)nanosecond time range at temperatures from 25 degrees C to 500 degrees C. In this paper, these thermal transients of the Nb2O5 layer were analysed by three evaluation approaches: One analytical and two numerical approaches, the relative thermal resistance method and the structure function method. The analytical approach revealed that its thermal diffusivity and thermal conductivity increases with rising temperature from (0.43 to 0.74) mm(2)/s and from (1.0 to 2.3) W/mK. The numerical approaches enables to get rid of certain up-front assumptions, which are necessary when applying analytical solution and enables deeper understanding of the Nb2O5 thermal behaviour. |
BibTeX:
@inproceedings{WOS:000467096000001,
author = {Mitterhuber, Lisa and Kraker, Elke and Defregger, Stefan},
title = {Thermal Characterization of Nm-thin Nb2O5 by Applying Thermal Impedance Methods to Time Domain Thermoreflectance Measurements},
booktitle = {2018 24TH INTERNATIONAL WORKSHOP ON THERMAL INVESTIGATIONS OF ICS AND SYSTEMS (THERMINIC)},
year = {2018},
note = {24th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC), Stockholm, SWEDEN, SEP 26-28, 2018}
}
|
| Doucet, M., Leal, R.M.F. and Hobson, T.C. Web interface for reflectivity fitting SOFTWAREX 7, pp. 287-293 (2018) |
| Abstract: The Liquids Reflectometer at Oak Ridge National Laboratory's Spallation
Neutron Source provides neutron reflectometry capability for an average of about 30 experiments each year. In recent years, there has been a large effort to streamline the data processing and analysis for the instrument. While much of the data reduction can be automated, data analysis remains something that needs to be done by scientists. For this purpose, we present a reflectivity fitting web interface that captures the process of setting up and executing fits while reducing the need for installing software or writing Python scripts. (c) 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). |
BibTeX:
@article{WOS:000457139300048,
author = {Doucet, M. and Leal, R. M. Ferraz and Hobson, T. C.},
title = {Web interface for reflectivity fitting},
journal = {SOFTWAREX},
year = {2018},
volume = {7},
pages = {287-293},
doi = {https://doi.org/10.1016/j.softx.2018.09.001}
}
|
| Bennett, S.P., Herklotz, A., Cress, C.D., Ievlev, A., Rouleau, C.M., Mazin, I.I. and Lauter, V. Magnetic order multilayering in FeRh thin films by He-Ion irradiation MATERIALS RESEARCH LETTERS 6, 1, pp. 106-112 (2018) |
| Abstract: The heterointerfacing of different materials with competing magnetic
orders forms the basis for today's spintronic devices, however materials compatibility has remained a major limitation to the conception of new multilayered systems. Here, we uncover a multilayer of competing magnetic orders within a single layer of FeRh after low-energy He-ion irradiation: metamagnetic, ferromagnetic, and spin glass. Polarized neutron reflectometry, irradiation modeling, and density functional theory calculations reveal a direct correlation between the disorder concentration, the depth-dependent magnetic ordering, and the onset of the metamagnetic transition. Such a heterostructure opens the door to new paradigms in antiferromagnetic electronics and ultra-low-power magnetization controllability. [GRAPHICS] . |
BibTeX:
@article{WOS:000428141500016,
author = {Bennett, S. P. and Herklotz, A. and Cress, C. D. and Ievlev, A. and Rouleau, C. M. and Mazin, I. I. and Lauter, V.},
title = {Magnetic order multilayering in FeRh thin films by He-Ion irradiation},
journal = {MATERIALS RESEARCH LETTERS},
year = {2018},
volume = {6},
number = {1},
pages = {106-112},
doi = {https://doi.org/10.1080/21663831.2017.1402098}
}
|
| Perret, E., Sen, K., Khmaladze, J., Mallett, B.P.P., Yazdi-Rizi, M., Marsik, P., Das, S., Marozau, I., Uribe-Laverde, M.A., Prada, R.d.A., Strempfer, J., Dobeli, M., Biskup, N., Varela, M., Mathis, Y.-L. and Bernhard, C. Structural, magnetic and electronic properties of pulsed-laser-deposition grown SrFeO3-delta thin films and SrFeO3-delta/La2/3Ca1/3MnO3 multilayers JOURNAL OF PHYSICS-CONDENSED MATTER 29, 49 (2017) |
| Abstract: We studied the structural, magnetic and electronic properties of
SrFeO3-delta (SFO) thin films and SrFeO3-delta/La2/3Ca1/3MnO3 (LCMO) superlattices that have been grown with pulsed laser deposition (PLD) on La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrates. X-ray reflectometry and scanning transmission electron microscopy (STEM) confirm the high structural quality of the films and flat and atomically sharp interfaces of the superlattices. The STEM data also reveal a difference in the interfacial layer stacking with a SrO layer at the LCMO/SFO and a LaO layer at the SFO/LCMO interfaces along the PLD growth direction. The x-ray diffraction (XRD) data suggest that the as grown SFO films and SFO/LCMO superlattices have an oxygen-deficient SrFeO3-delta structure with I4/mmm space group symmetry (delta <= 0.2). Subsequent ozone annealed SFO films are consistent with an almost oxygen stoichiometric structure (delta approximate to 0). The electronic and magnetic properties of these SFO films are similar to the ones of corresponding single crystals. In particular, the as grown SrFeO3-delta films are insulating whereas the ozone annealed films are metallic. The magneto-resistance effects of the as grown SFO films have a similar magnitude as in the single crystals, but extend over a much wider temperature range. Last but not least, for the SFO/LCMO superlattices we observe a rather large exchange bias effect that varies as a function of the cooling field. |
BibTeX:
@article{WOS:000415305900001,
author = {Perret, E. and Sen, K. and Khmaladze, J. and Mallett, B. P. P. and Yazdi-Rizi, M. and Marsik, P. and Das, S. and Marozau, I. and Uribe-Laverde, M. A. and Prada, R. de Andres and Strempfer, J. and Dobeli, M. and Biskup, N. and Varela, M. and Mathis, Y-L and Bernhard, C.},
title = {Structural, magnetic and electronic properties of pulsed-laser-deposition grown SrFeO3-delta thin films and SrFeO3-delta/La2/3Ca1/3MnO3 multilayers},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2017},
volume = {29},
number = {49},
doi = {https://doi.org/10.1088/1361-648X/aa93a6}
}
|
| Le Biavan, N., Hugues, M., Montes Bajo, M., Tamayo-Arriola, J., Jollivet, A., Lefebvre, D., Cordier, Y., Vinter, B., Julien, F.H., Hierro, A. and Chauveau, J.M. Homoepitaxy of non-polar ZnO/(Zn,Mg)O multi-quantum wells: From a precise growth control to the observation of intersubband transitions APPLIED PHYSICS LETTERS 111, 23 (2017) |
| Abstract: We have developed a method to grow and characterize the state of the art
non-polar ZnO/(Zn,Mg)O multi-quantum wells on m-plane ZnO substrates as a prerequisite for applications based on intersub-band transitions. The epilayer interfaces exhibit a low roughness, and the layer thickness remains constant within one monolayer in these heterostructures. The optical properties have been studied in the UV and IR domains by means of photoluminescence and absorption experiments, respectively. In the UV, the photoluminescence is very well described by an excitonic transition, with the clear effect of quantum confinement as a function of the well thickness in the absence of the internal field. In the IR, the intersubband transitions can be precisely modeled if a large depolarization shift is taken into account. Overall, we demonstrate a very good control in the design and fabrication of ZnO quantum wells (QWs) for intersubband transitions. Our result gives a clear understanding of the ISBTs in ZnO QWs. (C) 2017 Author(s). |
BibTeX:
@article{WOS:000418349100017,
author = {Le Biavan, N. and Hugues, M. and Montes Bajo, M. and Tamayo-Arriola, J. and Jollivet, A. and Lefebvre, D. and Cordier, Y. and Vinter, B. and Julien, F. -H. and Hierro, A. and Chauveau, J. -M.},
title = {Homoepitaxy of non-polar ZnO/(Zn,Mg)O multi-quantum wells: From a precise growth control to the observation of intersubband transitions},
journal = {APPLIED PHYSICS LETTERS},
year = {2017},
volume = {111},
number = {23},
doi = {https://doi.org/10.1063/1.5003146}
}
|
| Ukleev, V., Snigireva, I. and Vorobiev, A. Polarized neutron reflectometry study from iron oxide nanoparticles monolayer SURFACES AND INTERFACES 9, pp. 143-146 (2017) |
| Abstract: We report on the polarized neutron reflectometry investigation of
monolayer of magnetic iron oxide nanoparticles assembled by the Langmuir-Schaefer method. After deposition onto a solid substrate the polarized neutron reflectometry measurements in the external magnetic field were carried out. Thickness, density, roughness and in-depth resolved magnetization profile of the resulted layer were obtained from accurate fitting routine. |
BibTeX:
@article{WOS:000418617000018,
author = {Ukleev, V. and Snigireva, I. and Vorobiev, A.},
title = {Polarized neutron reflectometry study from iron oxide nanoparticles monolayer},
journal = {SURFACES AND INTERFACES},
year = {2017},
volume = {9},
pages = {143-146},
doi = {https://doi.org/10.1016/j.surfin.2017.09.001}
}
|
| Rao, R.R., Kolb, M.J., Halck, N.B., Pedersen, A.F., Mehta, A., You, H., Stoerzinger, K.A., Feng, Z., Hansen, H.A., Zhou, H., Giordano, L., Rossmeisl, J., Vegge, T., Chorkendorff, I., Stephens, I.E.L. and Shao-Horn, Y. Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolution ENERGY & ENVIRONMENTAL SCIENCE 10, 12, pp. 2626-2637 (2017) |
| Abstract: While the surface atomic structure of RuO2 has been well studied in
ultra high vacuum, much less is known about the interaction between water and RuO2 in aqueous solution. In this work, in situ surface X-ray scattering measurements combined with density functional theory (DFT) were used to determine the surface structural changes on single-crystal RuO2(110) as a function of potential in acidic electrolyte. The redox peaks at 0.7, 1.1 and 1.4 V vs. reversible hydrogen electrode (RHE) could be attributed to surface transitions associated with the successive deprotonation of -H2O on the coordinatively unsaturated Ru sites (CUS) and hydrogen adsorbed to the bridging oxygen sites. At potentials relevant to the oxygen evolution reaction (OER), an -OO species on the Ru CUS sites was detected, which was stabilized by a neighboring -OH group on the Ru CUS or bridge site. Combining potential-dependent surface structures with their energetics from DFT led to a new OER pathway, where the deprotonation of the -OH group used to stabilize -OO was found to be rate-limiting. |
BibTeX:
@article{WOS:000417255900015,
author = {Rao, Reshma R. and Kolb, Manuel J. and Halck, Niels Bendtsen and Pedersen, Anders Filsoe and Mehta, Apurva and You, Hoydoo and Stoerzinger, Kelsey A. and Feng, Zhenxing and Hansen, Heine A. and Zhou, Hua and Giordano, Livia and Rossmeisl, Jan and Vegge, Tejs and Chorkendorff, Ib and Stephens, Ifan E. L. and Shao-Horn, Yang},
title = {Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolution},
journal = {ENERGY & ENVIRONMENTAL SCIENCE},
year = {2017},
volume = {10},
number = {12},
pages = {2626-2637},
doi = {https://doi.org/10.1039/c7ee02307c}
}
|
| Chen, Y., Yusuf, M.H., Guan, Y., Jacobson, R.B., Lagally, M.G., Babcock, S.E., Kuech, T.F. and Evans, P.G. Distinct Nucleation and Growth Kinetics of Amorphous SrTiO3 on (001) SrTiO3 and SiO2/Si: A Step toward New Architectures ACS APPLIED MATERIALS & INTERFACES 9, 46, pp. 41034-41042 (2017) |
| Abstract: Integration of emerging complex-oxide compounds into sophisticated
nanoscale single-crystal geometries faces significant challenges arising from the kinetics of vapor phase thin-film epitaxial growth. A comparison of the crystallization of the model perovskite SrTiO3 (STO) on (001) STO and oxidized (001) Si substrates indicates that there is a viable alternative route that can yield three-dimensional epitaxial synthesis, an approach in which STO is crystallized from an amorphous thin film by postdeposition annealing. The crystallization of amorphous STO on single crystal (001) STO substrates occurs via solid-phase epitaxy (SPE), without nucleation and with a temperature-dependent amorphous/crystalline interface velocity. In comparison, the crystallization of STO on SiO2/(001) Si substrates nucleation, resulting in a polycrystalline film with crystal sizes on the order of 10 nm. A comparison of the temperature dependence of the nucleation and growth processes for these two substrates indicates that it will be possible to create crystalline STO materials using low-temperature crystallization from a crystalline seed, even in the presence of interfaces with other materials. These processes provide a potential route for the formation of single crystals with intricate three-dimensional nanoscale geometries. |
BibTeX:
@article{WOS:000416614600127,
author = {Chen, Yajin and Yusuf, M. Humed and Guan, Yingxin and Jacobson, R. B. and Lagally, Max G. and Babcock, Susan E. and Kuech, Thomas F. and Evans, Paul G.},
title = {Distinct Nucleation and Growth Kinetics of Amorphous SrTiO3 on (001) SrTiO3 and SiO2/Si: A Step toward New Architectures},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2017},
volume = {9},
number = {46},
pages = {41034-41042},
doi = {https://doi.org/10.1021/acsami.7b12978}
}
|
| Pradipkanti, L., Chowdhury, M. and Satapathy, D.K. Stratification and two glass-like thermal transitions in aged polymer films PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19, 43, pp. 29263-29270 (2017) |
| Abstract: Using X-ray reflectivity, spectroscopic ellipsometry and Raman
spectroscopy, we have studied the stratified structure and the two glass-like thermal transitions in sufficiently aged glassy polystyrene films. We find that favorable interaction between the solid substrate and the polymer film induces stratification within the film resulting in different densities across the film thickness. Existence of two glass-like thermal transitions (one at 70 degrees C and the other at 95 degrees C) is independently confirmed by temperature dependent spectroscopic ellipsometry and Raman spectroscopy measurements. Interestingly, the thermal coefficient of expansion of the polymer film displays anomalous behavior with temperature and is found to have the lowest value over the temperature range 70-95 degrees C, i.e. between the two observed glass-like thermal transition temperatures. |
BibTeX:
@article{WOS:000414773100027,
author = {Pradipkanti, L. and Chowdhury, Mithun and Satapathy, Dillip K.},
title = {Stratification and two glass-like thermal transitions in aged polymer films},
journal = {PHYSICAL CHEMISTRY CHEMICAL PHYSICS},
year = {2017},
volume = {19},
number = {43},
pages = {29263-29270},
doi = {https://doi.org/10.1039/c7cp05726a}
}
|
| Stubbs, J.E., Biwer, C.K., Chaka, A.M., Ilton, E.S., Du, Y., Bargar, J.R. and Eng, P.J. Oxidative Corrosion of the UO2 (001) Surface by Nonclassical Diffusion LANGMUIR 33, 46, pp. 13189-13196 (2017) |
| Abstract: Uranium oxide is central to every stage of the nuclear fuel cycle, from
mining through fuel fabrication and use, to waste disposal and environmental cleanup. Its chemical and mechanical stability are intricately linked to the concentration of interstitial O atoms within the structure and the oxidation state of U. We have previously shown that, during corrosion of the UO2 (111) surface under either 1 atm of O-2 gas or oxygenated water at room temperature, oxygen interstitials diffuse into the substrate to form a superlattice with three-layer periodicity. In the current study, we present results from surface X-ray scattering that reveal the structure of the oxygen diffusion profile beneath the (001) surface. The first few layers below the surface oscillate strongly in their surface -normal lattice parameters, suggesting preferential interstitial occupation of every other layer below the surface, which is geometrically consistent with the interstitial network that forms below the oxidized (111) surface. Deeper layers are heavily contracted and indicate that the oxidation front penetrates similar to 52 angstrom below the (001) surface after 21 days of dry O-2 gas exposure at ambient pressure and temperature. X-ray photoelectron spectroscopy indicates U is present as U(IV), U(V), and U(VI). |
BibTeX:
@article{WOS:000416498800004,
author = {Stubbs, Joanne E. and Biwer, Craig K. and Chaka, Anne M. and Ilton, Eugene S. and Du, Yingge and Bargar, John R. and Eng, Peter J.},
title = {Oxidative Corrosion of the UO2 (001) Surface by Nonclassical Diffusion},
journal = {LANGMUIR},
year = {2017},
volume = {33},
number = {46},
pages = {13189-13196},
doi = {https://doi.org/10.1021/acs.langmuir.7b02800}
}
|
| Moon, E.J., He, Q., Ghosh, S., Kirby, B.J., Pantelides, S.T., Borisevich, A.Y. and May, S.J. Structural ``delta Doping'' to Control Local Magnetization in Isovalent Oxide Heterostructures PHYSICAL REVIEW LETTERS 119, 19 (2017) |
| Abstract: Modulation and delta-doping strategies, in which atomically thin layers
of charged dopants are precisely deposited within a heterostructure, have played enabling roles in the discovery of new physical behavior in electronic materials. Here, we demonstrate a purely structural ``delta-doping'' strategy in complex oxide heterostructures, in which atomically thin manganite layers are inserted into an isovalent manganite host, thereby modifying the local rotations of corner-connected MnO6 octahedra. Combining scanning transmission electron microscopy, polarized neutron reflectometry, and density functional theory, we reveal how local magnetic exchange interactions are enhanced within the spatially confined regions of suppressed octahedral rotations. The combined experimental and theoretical results illustrate the potential to utilize noncharge-based approaches to ``doping'' in order to enhance or suppress functional properties within spatially confined regions of oxide heterostructures. |
BibTeX:
@article{WOS:000414664200007,
author = {Moon, E. J. and He, Q. and Ghosh, S. and Kirby, B. J. and Pantelides, S. T. and Borisevich, A. Y. and May, S. J.},
title = {Structural ``delta Doping'' to Control Local Magnetization in Isovalent Oxide Heterostructures},
journal = {PHYSICAL REVIEW LETTERS},
year = {2017},
volume = {119},
number = {19},
doi = {https://doi.org/10.1103/PhysRevLett.119.197204}
}
|
| Tokac, M., Kinane, C.J., Atkinson, D. and Hindmarch, A.T. Temperature dependence of magnetically dead layers in ferromagnetic thin-films AIP ADVANCES 7, 11 (2017) |
| Abstract: Polarized neutron reflectometry has been used to study interface
magnetism and magnetic dead layers in model amorphous CoFeB: Ta alloy thin-film multilayers with Curie temperatures tuned to be below room-temperature. This allows temperature dependent variations in the effective magnetic thickness of the film to be determined at temperatures that are a significant fraction of the Curie temperature, which cannot be achieved in the material systems used for spintronic devices. In addition to variation in the effective magnetic thickness due to compositional grading at the interface with the tantalum capping layer, the key finding is that at the interface between ferromagnetic film and GaAs(001) substrate local interfacial alloying creates an additional magnetic dead-layer. The thickness of this magnetic dead-layer is temperature dependent, which may have significant implications for elevated-temperature operation of hybrid ferromagnetic metal-semiconductor spintronic devices. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). |
BibTeX:
@article{WOS:000416825700022,
author = {Tokac, M. and Kinane, C. J. and Atkinson, D. and Hindmarch, A. T.},
title = {Temperature dependence of magnetically dead layers in ferromagnetic thin-films},
journal = {AIP ADVANCES},
year = {2017},
volume = {7},
number = {11},
doi = {https://doi.org/10.1063/1.4997366}
}
|
| Gaowei, M., Ding, Z., Schubert, S., Bhandari, H.B., Sinsheimer, J., Kuehn, J., Nagarkar, V.V., Marshall, M.S.J., Walsh, J., Muller, E.M., Attenkofer, K., Frisch, H.J., Padmore, H. and Smedley, J. Synthesis and x-ray characterization of sputtered bi-alkali antimonide photocathodes APL MATERIALS 5, 11 (2017) |
| Abstract: Advanced photoinjectors, which are critical to many next generation
accelerators, open the door to new ways of material probing, both as injectors for free electron lasers and for ultra-fast electron diffraction. For these applications, the nonuniformity of the electric field near the cathode caused by surface roughness can be the dominant source of beam emittance. Therefore, improving the photocathode roughness while maintaining quantum efficiency is essential to the improvement of beam brightness. In this paper, we report the demonstration of a bi-alkali antimonide photocathode with an order of magnitude improved roughness by sputter deposition from a K2CsSb sputter target, using in situ and operando X-ray characterizations. We found that a surface roughness of 0.5 nm for a sputtered photocathode with a final thickness of 42 nm can be achieved while still yielding a quantum efficiency of 3.3% at 530 nm wavelength. (C) 2017 Author(s). |
BibTeX:
@article{WOS:000416826100004,
author = {Gaowei, M. and Ding, Z. and Schubert, S. and Bhandari, H. B. and Sinsheimer, J. and Kuehn, J. and Nagarkar, V. V. and Marshall, M. S. J. and Walsh, J. and Muller, E. M. and Attenkofer, K. and Frisch, H. J. and Padmore, H. and Smedley, J.},
title = {Synthesis and x-ray characterization of sputtered bi-alkali antimonide photocathodes},
journal = {APL MATERIALS},
year = {2017},
volume = {5},
number = {11},
doi = {https://doi.org/10.1063/1.5010950}
}
|
| Li, M., Song, Q., Zhao, W., Garlow, J.A., Liu, T.-H., Wu, L., Zhu, Y., Moodera, J.S., Chan, M.H.W., Chen, G. and Chang, C.-Z. Dirac-electron-mediated magnetic proximity effect in topological insulator/magnetic insulator heterostructures PHYSICAL REVIEW B 96, 20 (2017) |
| Abstract: The possible realization of dissipationless chiral edge current in a
topological insulator/magnetic insulator heterostructure is based on the condition that the magnetic proximity exchange coupling at the interface is dominated by the Dirac surface states of the topological insulator. Here we report a polarized neutron reflectometry observation of Dirac-electron-mediated magnetic proximity effect in a bulk-insulating topological insulator (Bi0.2Sb0.8)(2)Te-3/magnetic insulator EuS heterostructure. We are able tomaximize the proximity-induced magnetism by applying an electrical back gate to tune the Fermi level of topological insulator to be close to the Dirac point. A phenomenological model based on diamagnetic screening is developed to explain the suppressed proximity-induced magnetism at high carrier density. Our work paves the way to utilize the magnetic proximity effect at the topological insulator/magnetic insulator heterointerface for low-power spintronic applications. |
BibTeX:
@article{WOS:000414133800002,
author = {Li, Mingda and Song, Qichen and Zhao, Weiwei and Garlow, Joseph A. and Liu, Te-Huan and Wu, Lijun and Zhu, Yimei and Moodera, Jagadeesh S. and Chan, Moses H. W. and Chen, Gang and Chang, Cui-Zu},
title = {Dirac-electron-mediated magnetic proximity effect in topological insulator/magnetic insulator heterostructures},
journal = {PHYSICAL REVIEW B},
year = {2017},
volume = {96},
number = {20},
doi = {https://doi.org/10.1103/PhysRevB.96.201301}
}
|
| Svechnikov, M., Pariev, D., Nechay, A., Salashchenko, N., Chkhalo, N., Vainer, Y. and Gaman, D. Extended model for the reconstruction of periodic multilayers from extreme ultraviolet and X-ray reflectivity data JOURNAL OF APPLIED CRYSTALLOGRAPHY 50, 5, pp. 1428-1440 (2017) |
| Abstract: An extended model for the reconstruction of multilayer nanostructures
from reflectometry data in the X-ray and extreme ultraviolet ranges is proposed. In contrast to the standard model approach, where the transitional region is defined in advance as a specific function, the transition layer is sought as a linear combination of several functions at once in the extended model. This allows one to describe a much wider class of multilayer structures with different dominant physical mechanisms for the formation of transition regions. The extended model occupies an intermediate position between the classical model approach and the so-called model-free methods. The efficiency of the described method is illustrated in detail in numerical simulations and in a real experiment on the annealing of a multilayer Mo/Be mirror. |
BibTeX:
@article{WOS:000412088300019,
author = {Svechnikov, Michael and Pariev, Dmitry and Nechay, Andrey and Salashchenko, Nikolay and Chkhalo, Nikolay and Vainer, Yuly and Gaman, Dmitry},
title = {Extended model for the reconstruction of periodic multilayers from extreme ultraviolet and X-ray reflectivity data},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2017},
volume = {50},
number = {5},
pages = {1428-1440},
doi = {https://doi.org/10.1107/S1600576717012286}
}
|
| Sarkar, P., Biswas, A., De, R., Rao, K.D., Ghosh, S., Modi, M.H., John, S., Barshilia, H.C., Bhattacharyya, D. and Sahoo, N.K. Performance of Co/Ti multilayers in a water window soft x-ray regime APPLIED OPTICS 56, 27, pp. 7525-7532 (2017) |
| Abstract: The DC magnetron sputter grown Co/Ti multilayers, with ultra-low
bi-layer thicknesses and with Co layers deposited under mixed ambience of argon and dry air, have been investigated for use in the water window soft x-ray regime of 23 - 44 angstrom. Initially, deposition parameters have been optimized for obtaining smooth and continuous low thickness Co and Ti single-layer films, and, then, multilayers with five bi-layers of various bi-layer thicknesses were deposited. The samples have been primarily characterized by the grazing incidence x-ray reflectivity (GIXR) measurements with a hard x-ray laboratory source. Subsequently, a set of multilayers with an increasing number of bi-layers has been deposited with a constant bi-layer thickness of 42 angstrom. GIXR results show that hard x-ray reflectivity at the first Bragg peak is maximum for the 20 bi-layer sample, beyond which the reflectivity decreases. Finally, the samples with the most promising hard x-ray GIXR have been used for soft x-ray reflectivity measurement with synchrotron radiation, and similar to 2.5% peak reflectivity has been obtained in the multilayer sample at a 30.7 angstrom wavelength for a 21.5 degrees grazing angle of incidence. The fitting results for both hard and soft x-ray reflectivities have been thoroughly investigated to find out the cause of the saturation of reflectivity with the increase in the number of bi-layers. (C) 2017 Optical Society of America |
BibTeX:
@article{WOS:000411378800004,
author = {Sarkar, Piyali and Biswas, Arup and De, Rajnarayan and Rao, K. Divakar and Ghosh, Subir and Modi, M. H. and John, Siju and Barshilia, H. C. and Bhattacharyya, Dibyendu and Sahoo, Naba Kishor},
title = {Performance of Co/Ti multilayers in a water window soft x-ray regime},
journal = {APPLIED OPTICS},
year = {2017},
volume = {56},
number = {27},
pages = {7525-7532},
doi = {https://doi.org/10.1364/AO.56.007525}
}
|
| Mitra, A., Cespedes, O., Ramasse, Q., Ali, M., Marmion, S., Ward, M., Brydson, R.M.D., Kinane, C.J., Cooper, J.F.K., Langridge, S. and Hickey, B.J. Interfacial Origin of the Magnetisation Suppression of Thin Film Yttrium Iron Garnet SCIENTIFIC REPORTS 7 (2017) |
| Abstract: Yttrium iron garnet has a very high Verdet constant, is transparent in
the infrared and is an insulating ferrimagnet leading to its use in optical and magneto-optical applications. Its high Q-factor has been exploited to make resonators and filters in microwave devices, but it also has the lowest magnetic damping of any known material. In this article we describe the structural and magnetic properties of single crystal thin-film YIG where the temperature dependence of the magnetisation reveals a decrease in the low temperature region. In order to understand this complex material we bring a large number of structural and magnetic techniques to bear on the same samples. Through a comprehensive analysis we show that at the substrate -YIG interface, an interdiffusion zone of only 4-6 nm exists. Due to the interdiffusion of Y from the YIG and Gd from the substrate, an addition magnetic layer is formed at the interface whose properties are crucially important in samples with a thickness of YIG less than 200 nm. |
BibTeX:
@article{WOS:000410916100032,
author = {Mitra, A. and Cespedes, O. and Ramasse, Q. and Ali, M. and Marmion, S. and Ward, M. and Brydson, R. M. D. and Kinane, C. J. and Cooper, J. F. K. and Langridge, S. and Hickey, B. J.},
title = {Interfacial Origin of the Magnetisation Suppression of Thin Film Yttrium Iron Garnet},
journal = {SCIENTIFIC REPORTS},
year = {2017},
volume = {7},
doi = {https://doi.org/10.1038/s41598-017-10281-6}
}
|
| Biswas, A., Porwal, A., Bhattacharya, D., Prajapat, C.L., Ghosh, A., Nand, M., Nayak, C., Rai, S., Jha, S.N., Singh, M.R., Bhattacharyya, D., Basu, S. and Sahoo, N.K. Effect of dry air on interface smoothening in reactive sputter deposited Co/Ti multilayer APPLIED SURFACE SCIENCE 416, pp. 168-177 (2017) |
| Abstract: Top surface roughness and interface roughness are one of the key
elements which determine the performance of X-ray and neutron thin film multilayer devices. It has been observed that by mixing air with argon in sputtering ambience during deposition of Co layers, polarized neutron reflectivity (PNR) of Co/Ti supermirror polarizers can be improved substantially. Cross-sectional HRTEM measurement reveals that sharper interfaces in the supermirror can be achieved in case of deposition of the multilayer under mixed ambience of argon and air. In order to investigate this interface modification mechanism further, in this communication two sets of tri-layer Co/Ti/Co samples and 20-layer Co/Ti periodic multilayer samples have been prepared; in one set all the layers are deposited only under argon ambience and in the other set, Co layers are deposited under a mixed ambience of argon and air. These samples have been characterized by measuring specular and non-specular X-ray reflectivities (GIXR) with X-rays of 1.54 angstrom wavelength and polarized neutron reflectivity (PNR) with neutron of 2.5 angstrom wavelength at grazing angle of incidence. It has been observed that the X-ray and neutron specular reflectivities at Bragg peaks of 20 layer periodic multilayer increase when Co layers are deposited under mixed ambience of argon and air. The detail information regarding the effect of air on the interfaces and magnetic properties has been obtained by fitting the measured spectra. The above information has subsequently been supplemented by XRD and magnetic measurements on the samples. XPS and XANES measurements have also been carried out to investigate whether cobalt oxide or cobalt nitride layers are being formed due to use of air in sputtering ambience. (C) 2017 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000402461900020,
author = {Biswas, A. and Porwal, A. and Bhattacharya, Debarati and Prajapat, C. L. and Ghosh, Arnab and Nand, Mangla and Nayak, C. and Rai, S. and Jha, S. N. and Singh, M. R. and Bhattacharyya, D. and Basu, S. and Sahoo, N. K.},
title = {Effect of dry air on interface smoothening in reactive sputter deposited Co/Ti multilayer},
journal = {APPLIED SURFACE SCIENCE},
year = {2017},
volume = {416},
pages = {168-177},
doi = {https://doi.org/10.1016/j.apsusc.2017.04.131}
}
|
| Bonatout, N., Muller, F., Fontaine, P., Gascon, I., Konovalov, O. and Goldmann, M. How exfoliated graphene oxide nanosheets organize at the water interface: evidence for a spontaneous bilayer self-assembly NANOSCALE 9, 34, pp. 12543-12548 (2017) |
| Abstract: In this study, we have characterized graphene oxide films formed at the
air-water interface by X-ray reflectivity and grazing incidence X-ray diffraction using synchrotron sources. Surprisingly, the results of both measurements show that at non zero surface pressures, the film is organized as a bilayer of sheets interfaced between air and water with water molecule bridges. Such a spontaneous bilayer structure and its evolution with respect to the surface pressure has been observed for the first time. These results should allow precise control of the density of sheets deposited on the substrate when these films are transferred through the Langmuir Blodgett or Schaefer procedures. Indeed, graphene oxide keeps on attracting more and more attention, increasing the need for the production of well-controlled graphene oxide thin films due to its application in energy devices or in sensor domains. |
BibTeX:
@article{WOS:000409215300038,
author = {Bonatout, Nathalie and Muller, Francois and Fontaine, Philippe and Gascon, Ignacio and Konovalov, Oleg and Goldmann, Michel},
title = {How exfoliated graphene oxide nanosheets organize at the water interface: evidence for a spontaneous bilayer self-assembly},
journal = {NANOSCALE},
year = {2017},
volume = {9},
number = {34},
pages = {12543-12548},
doi = {https://doi.org/10.1039/c7nr03403b}
}
|
| Rizal, C. and Fullerton, E.E. Perpendicular magnetic anisotropy and microstructure properties of nanoscale Co/Au multilayers JOURNAL OF PHYSICS D-APPLIED PHYSICS 50, 35 (2017) |
| Abstract: We investigated the role of microstructure and Co layer thickness on the
perpendicular magnetic anisotropy of as-deposited and annealed Ta (5 nm)/[Co (t(Co))/Au (2 nm)] x N = 20 multilayers with 1 <= t(Co) <= 2 nm prepared using dc-magnetron sputtering. These multilayers were characterized using a vibrating sample magnetometer, a p-MOKE magnetometer and a microscopy magnetometer, small angle x-ray reflection (XRR), and wide angle x-ray diffraction (XRD) analysis. These multilayers demonstrated strong perpendicular magnetic anisotropy with their saturation magnetization close to the bulk magnetization of Co. Magnetization and magnetic anisotropy increased with annealing and this increase is directly linked to the strain relaxation and sharpening of the interfaces after annealing. Using XRR analysis before and after annealing, and fitting these XRR data, the multilayer periodicities are extracted and the refined layer thickness and surface roughness are determined. Using XRD analysis and fitting these XRD spectra, information regarding both the average lattice spacing of atoms and the strain developed on an individual layer were determined. |
BibTeX:
@article{WOS:000407697300001,
author = {Rizal, C. and Fullerton, E. E.},
title = {Perpendicular magnetic anisotropy and microstructure properties of nanoscale Co/Au multilayers},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2017},
volume = {50},
number = {35},
doi = {https://doi.org/10.1088/1361-6463/aa7c5b}
}
|
| Cooper, J.F.K., Kinane, C.J., Langridge, S., Ali, M., Hickey, B.J., Niizeki, T., Uchida, K., Saitoh, E., Ambaye, H. and Glavic, A. Unexpected structural and magnetic depth dependence of YIG thin films PHYSICAL REVIEW B 96, 10 (2017) |
| Abstract: We report measurements on yttrium iron garnet (YIG) thin films grown on
both gadolinium gallium garnet (GGG) and yttrium aluminum garnet (YAG) substrates, with and without thin Pt top layers. We provide three principal results: the observation of an interfacial region at the Pt/YIG interface, we place a limit on the induced magnetism of the Pt layer, and confirm the existence of an interfacial layer at the GGG/YIG interface. Polarized neutron reflectometry (PNR) was used to give depth dependence of both the structure and magnetism of these structures. We find that a thin film of YIG on GGG is best described by three distinct layers: an interfacial layer near the GGG, around 5 nm thick and nonmagnetic, a magnetic ``bulk'' phase, and a nonmagnetic and compositionally distinct thin layer near the surface. We theorize that the bottom layer, which is independent of the film thickness, is caused by Gd diffusion. The top layer is likely to be extremely important in inverse spin Hall effect measurements, and is most likely Y2O3 or very similar. Magnetic sensitivity in the PNR to any induced moment in the Pt is increased by the existence of the Y2O3 layer; any moment is found to be less than 0.02 mu(B)/atom. |
BibTeX:
@article{WOS:000409253700004,
author = {Cooper, J. F. K. and Kinane, C. J. and Langridge, S. and Ali, M. and Hickey, B. J. and Niizeki, T. and Uchida, K. and Saitoh, E. and Ambaye, H. and Glavic, A.},
title = {Unexpected structural and magnetic depth dependence of YIG thin films},
journal = {PHYSICAL REVIEW B},
year = {2017},
volume = {96},
number = {10},
doi = {https://doi.org/10.1103/PhysRevB.96.104404}
}
|
| Top, M., Fahlteich, J. and De Hosson, J.T.M. Influence of the applied power on the barrier performance of silicon-containing plasma polymer coatings using a hollow cathode-activated PECVD process PLASMA PROCESSES AND POLYMERS 14, 9 (2017) |
| Abstract: A hollow cathode arc discharge is used for the roll-to-roll deposition
of silicon-containing plasma polymer thin films on a polymer substrate. It is found that the fragmentation of the used monomer hexamethyldisiloxane (HMDSO) increases with increasing plasma power. The higher fragmentation was related to a reduced hydrogen content as a result of breaking CH bonds. This allowed for a higher degree of cross-linking. The latter has a positive effect on the barrier performance of the coatings. A hollow cathode arc discharge with separate anode allowed the deposition of a plasma polymer with a water vapor transmission rate (WVTR) of 0.16gm(-2)day(-1) (measured at 38 degrees C and 90% r.h.) on a PET substrate while maintaining a deposition rate of approximately 450nmmmin(-1). |
BibTeX:
@article{WOS:000410773200011,
author = {Top, Michiel and Fahlteich, John and De Hosson, Jeff T. M.},
title = {Influence of the applied power on the barrier performance of silicon-containing plasma polymer coatings using a hollow cathode-activated PECVD process},
journal = {PLASMA PROCESSES AND POLYMERS},
year = {2017},
volume = {14},
number = {9},
doi = {https://doi.org/10.1002/ppap.201700016}
}
|
| Droulias, S.A., Palsson, G.K., Palonen, H., Hasan, A., Leifer, K., Kapaklis, V., Hjorvarsson, B. and Wolff, M. Crystal perfection by strain engineering: The case of Fe/V (001) THIN SOLID FILMS 636, pp. 608-614 (2017) |
| Abstract: We study the effect of bilayer thickness at fixed volume fraction on the
structural quality of Fe/V (001) superlattices. We find that such artificial metallic superlattices can be manufactured with excellent crystal quality and layering up to at least 50 angstrom in repeat distance (K = L-Fe + L-V). For an intended fixed ratio of the constituents: L-Fe/L-V=1/7, out-of-plane coherence lengths comparable to the thicknesses of the samples were obtained. We evaluate the strain in- and out-of-plane of both layers as a function of the bilayer thickness and comment on the growth using the framework of linear elasticity theory. We interpret the stability of the superlattice against crystal degradation due to the alternating compressive and tensile strain, yielding close to ideal lattice matching to the substrate. (C) 2017 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000408037800086,
author = {Droulias, S. A. and Palsson, G. K. and Palonen, H. and Hasan, A. and Leifer, K. and Kapaklis, V. and Hjorvarsson, B. and Wolff, M.},
title = {Crystal perfection by strain engineering: The case of Fe/V (001)},
journal = {THIN SOLID FILMS},
year = {2017},
volume = {636},
pages = {608-614},
doi = {https://doi.org/10.1016/j.tsf.2017.07.005}
}
|
| Guo, E.-J., Petrie, J.R., Roldan, M.A., Li, Q., Desautels, R.D., Charlton, T., Herklotz, A., Nichols, J., van Lierop, J., Freeland, J.W., Kalinin, S.V., Lee, H.N. and Fitzsimmons, M.R. Spatially Resolved Large Magnetization in Ultrathin BiFeO3 ADVANCED MATERIALS 29, 32 (2017) |
| Abstract: Here, a quantitative magnetic depth profile across the planar interfaces
in BiFeO3/La0.7Sr0.3MnO3 (BFO/LSMO) superlattices using polarized neutron reflectometry is obtained. An enhanced magnetization of 1.83 +/- 0.16 mu(B)/Fe in BFO layers is observed when they are interleaved between two manganite layers. The enhanced magnetic order in BFO persists up to 200 K. The depth dependence of magnetic moments in BFO/LSMO superlattices as a function of the BFO layer thickness is also explored. The results show the enhanced net magnetic moment in BFO from the LSMO/BFO interface extends 3-4 unit cells into BFO. The interior part of a thicker BFO layer has a much smaller magnetization, suggesting it still keeps the small canted AFM state. The results exclude charge transfer, intermixing, epitaxial strain, and octahedral rotations/tilts as dominating mechanisms for the large net magnetization in BFO. An explanation-one suggested by others previously and consistent with the observations-attributes the temperature dependence of the net magnetization of BFO to strong orbital hybridization between Fe and Mn across the interfaces. Such orbital reconstruction would establish an upper temperature limit for magnetic ordering of BFO. |
BibTeX:
@article{WOS:000407995100016,
author = {Guo, Er-Jia and Petrie, Jonathan R. and Roldan, Manuel A. and Li, Qian and Desautels, Ryan D. and Charlton, Timothy and Herklotz, Andreas and Nichols, John and van Lierop, Johan and Freeland, John W. and Kalinin, Sergei V. and Lee, Ho Nyung and Fitzsimmons, Michael R.},
title = {Spatially Resolved Large Magnetization in Ultrathin BiFeO3},
journal = {ADVANCED MATERIALS},
year = {2017},
volume = {29},
number = {32},
doi = {https://doi.org/10.1002/adma.201700790}
}
|
| Evertsson, J., Bertram, F., Rullik, L., Harlow, G. and Lundgren, E. Anodization of Al(100), Al(111) and Al Alloy 6063 studied in situ with X-ray reflectivity and electrochemical impedance spectroscopy JOURNAL OF ELECTROANALYTICAL CHEMISTRY 799, pp. 556-562 (2017) |
| Abstract: We present results from the anodization of single crystal Al(100) and
Al(111) surfaces and the aluminum alloy AA 6063 studied in situ by X-ray reflectivity and electrochemical impedance spectroscopy. We observe that the anodic oxide layer grows linearly with the anodization potential and that the thicknesses are similar for all samples. However, the thicknesses obtained from X-ray reflectivity are higher than that obtained from electrochemical impedance spectroscopy. We attribute the higher thicknesses to an outer porous oxide layer, which is not detected by electrochemical impedance spectroscopy. Both, electrochemical impedance spectroscopy and X-ray reflectivity suggests that a more heterogeneous and rough oxide is formed on AA 6063 due to the influence of the alloying elements and intermetallic particles during the growth. |
BibTeX:
@article{WOS:000411847300074,
author = {Evertsson, Jonas and Bertram, Florian and Rullik, Lisa and Harlow, Gary and Lundgren, Edvin},
title = {Anodization of Al(100), Al(111) and Al Alloy 6063 studied in situ with X-ray reflectivity and electrochemical impedance spectroscopy},
journal = {JOURNAL OF ELECTROANALYTICAL CHEMISTRY},
year = {2017},
volume = {799},
pages = {556-562},
doi = {https://doi.org/10.1016/j.jelechem.2017.07.010}
}
|
| Wood, M.H. and Clarke, S.M. Neutron Reflectometry for Studying Corrosion and Corrosion Inhibition METALS 7, 8 (2017) |
| Abstract: Neutron reflectometry is an extremely powerful technique to monitor
chemical and morphological changes at interfaces at the angstrom-level. Its ability to characterise metal, oxide and organic layers simultaneously or separately and in situ makes it an excellent tool for fundamental studies of corrosion and particularly adsorbed corrosion inhibitors. However, apart from a small body of key studies, it has yet to be fully exploited in this area. We present here an outline of the experimental method with particular focus on its application to the study of corrosive systems. This is illustrated with recent examples from the literature addressing corrosion, inhibition and related phenomena. |
BibTeX:
@article{WOS:000408843200023,
author = {Wood, Mary H. and Clarke, Stuart M.},
title = {Neutron Reflectometry for Studying Corrosion and Corrosion Inhibition},
journal = {METALS},
year = {2017},
volume = {7},
number = {8},
doi = {https://doi.org/10.3390/met7080304}
}
|
| Koohfar, S., Disa, A.S., Marshall, M.S.J., Walker, F.J., Ahn, C.H. and Kumah, D.P. Structural distortions at polar manganite interfaces PHYSICAL REVIEW B 96, 2 (2017) |
| Abstract: Electronic, lattice, and spin interactions at the interfaces between
crystalline complex transition-metal oxides can give rise to a wide range of functional electronic and magnetic phenomena not found in bulk. At heterointerfaces, these interactions may be enhanced by combining oxides where the polarity changes at the interface. The physical structure between nonpolar SrTiO3 and polar La1-x Sr-x MnO3 (x = 0.2) is investigated using high-resolution synchrotron x-ray diffraction to directly determine the role of structural distortions in compensating the polar discontinuity. At both the oxide-oxide interface and vacuum-oxide interfaces, the lattice is found to expand and rumple along the growth direction. The SrTiO3/La1-x Sr-x MnO3 interface also exhibits intermixing of La and Sr over a few unit cells. The results thus demonstrate that polar distortions and ionic intermixing coexist and both pathways play a significant role at interfaces with polar discontinuities. |
BibTeX:
@article{WOS:000406630400001,
author = {Koohfar, S. and Disa, A. S. and Marshall, M. S. J. and Walker, F. J. and Ahn, C. H. and Kumah, D. P.},
title = {Structural distortions at polar manganite interfaces},
journal = {PHYSICAL REVIEW B},
year = {2017},
volume = {96},
number = {2},
doi = {https://doi.org/10.1103/PhysRevB.96.024108}
}
|
| Disa, A.S., Georgescu, A.B., Hart, J.L., Kumah, D.P., Shafer, P., Arenholz, E., Arena, D.A., Ismail-Beigi, S., Taheri, M.L., Walker, F.J. and Ahn, C.H. Control of hidden ground-state order in NdNiO3 superlattices PHYSICAL REVIEW MATERIALS 1, 2 (2017) |
| Abstract: The combination of charge and spin degrees of freedom with electronic
correlations in condensed matter systems leads to a rich array of phenomena, such as magnetism, superconductivity, and novel conduction mechanisms. While such phenomena are observed in bulk materials, a richer array of behaviors becomes possible when these degrees of freedom are controlled in atomically layered heterostructures, where one can constrain dimensionality and impose interfacial boundary conditions. Here, we unlock a host of unique, hidden electronic and magnetic phase transitions in NdNiO3 while approaching the two-dimensional (2D) limit, resulting from the differing influences of dimensional confinement and interfacial coupling. Most notably, we discover a phase in fully 2D, single-layer NdNiO3, in which all signatures of the bulk magnetic and charge ordering are found to vanish. In addition, for quasi-two-dimensional layers down to a thickness of two unit cells, bulk-type ordering persists but separates from the onset of insulating behavior in a manner distinct from that found in the bulk or thin-film nickelates. Using resonant x-ray spectroscopies, first-principles theory, and model calculations, we propose that the single-layer phase suppression results from an alternative mechanism of interfacial electronic reconstruction based on ionicity differences across the interface, while the phase separation in multilayer NdNiO3 emerges due to enhanced 2D fluctuations. These findings provide insights into the intertwined mechanisms of charge and spin ordering in strongly correlated systems in reduced dimensions and illustrate the ability to use atomic layering to access hidden phases. |
BibTeX:
@article{WOS:000416561000001,
author = {Disa, Ankit S. and Georgescu, Alexandru B. and Hart, James L. and Kumah, Divine P. and Shafer, Padraic and Arenholz, Elke and Arena, Dario A. and Ismail-Beigi, Sohrab and Taheri, Mitra L. and Walker, Frederick J. and Ahn, Charles H.},
title = {Control of hidden ground-state order in NdNiO3 superlattices},
journal = {PHYSICAL REVIEW MATERIALS},
year = {2017},
volume = {1},
number = {2},
doi = {https://doi.org/10.1103/PhysRevMaterials.1.024410}
}
|
| Smolin, S.Y., Choquette, A.K., Wilks, R.G., Gauquelin, N., Felix, R., Gerlach, D., Ueda, S., Krick, A.L., Verbeeck, J., Bear, M., Baxter, J.B. and May, S.J. Energy Level Alignment and Cation Charge States at the LaFeO3/LaMnO3 (001) Heterointerface ADVANCED MATERIALS INTERFACES 4, 14 (2017) |
| Abstract: The electronic properties of LaFeO3/LaMnO3 epitaxial heterojunctions are
investigated to determine the valence and conduction band offsets and the nominal Mn and Fe valence states at the interface. Studying a systematic series of (LaFeO3)(n)/(LaMnO3)(m) bilayers (m approximate to 50) epitaxially grown in the (001) orientation using molecular beam epitaxy, layer-resolved electron energy loss spectroscopy reveals a lack of significant interfacial charge transfer, with a nominal 3+ valence state observed for both Mn and Fe across the interface. Through a combination of variable angle spectroscopic ellipsometry and hard X-ray photoelectron spectroscopy, type I energy level alignments are obtained at the LaFeO3/LaMnO3 interface with positive valence and conduction band offsets of (1.20 +/- 0.07) eV and (0.5-0.7 +/- 0.3) eV, respectively, with minimal band bending. Variable temperature resistivity measurements reveal that the bilayers remain insulating and that the presence of the heterojunction does not result in a conducting interface. |
BibTeX:
@article{WOS:000406068400011,
author = {Smolin, Sergey Y. and Choquette, Amber K. and Wilks, Regan G. and Gauquelin, Nicolas and Felix, Roberto and Gerlach, Dominic and Ueda, Shigenori and Krick, Alex L. and Verbeeck, Johan and Bear, Marcus and Baxter, Jason B. and May, Steven J.},
title = {Energy Level Alignment and Cation Charge States at the LaFeO3/LaMnO3 (001) Heterointerface},
journal = {ADVANCED MATERIALS INTERFACES},
year = {2017},
volume = {4},
number = {14},
doi = {https://doi.org/10.1002/admi.201700183}
}
|
| Belova, V., Beyer, P., Meister, E., Linder, T., Halbich, M.-U., Gerhard, M., Schmid, S., Zeche, T., Meisel, T., Generalov, A.V., Anselmo, A.S., Scholz, R., Konovalov, O., Gerlach, A., Koch, M., Hinderhofer, A., Opitz, A., Bruetting, W. and Schreibert, F. Evidence for Anisotropic Electronic Coupling of Charge Transfer States in Weakly Interacting Organic Semiconductor Mixtures JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 139, 25, pp. 8474-8486 (2017) |
| Abstract: We present a comprehensive investigation of the charge-transfer (CT)
effect in weakly interacting organic semiconductor mixtures. The donor-acceptor pair diindenoperylene (DIP) and N,N'-bis(2-ethylhexyl)-1,7-dicyanoperylene-3,4/9,10-bis(dicarboxyimide) (PDIR-CN2) has been chosen as a model system. A wide range of experimental methods was used in order to characterize the structural, optical, electronic, and device properties of the intermolecular interactions. By detailed analysis, we demonstrate that the partial CT in this weakly interacting mixture does not have a strong effect on the ground state and does not generate a hybrid orbital. We also find a strong CT transition in light absorption as well as in photo- and electroluminescence. By using different layer sequences and compositions, we are able to distinguish electronic coupling in-plane vs out-of-plane and, thus, characterize the anisotropy of the CT state. Finally, we discuss the impact of CT exciton generation on charge-carrier transport and on the efficiency of photovoltaic devices. |
BibTeX:
@article{WOS:000404809600022,
author = {Belova, Valentina and Beyer, Paul and Meister, Eduard and Linder, Theresa and Halbich, Marc-Uwe and Gerhard, Marina and Schmid, Stefan and Zeche, Thomas and Meisel, Tino and Generalov, Alexander V. and Anselmo, Ana Sofia and Scholz, Reinhard and Konovalov, Oleg and Gerlach, Alexander and Koch, Martin and Hinderhofer, Alexander and Opitz, Andreas and Bruetting, Wolfgang and Schreibert, Frank},
title = {Evidence for Anisotropic Electronic Coupling of Charge Transfer States in Weakly Interacting Organic Semiconductor Mixtures},
journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY},
year = {2017},
volume = {139},
number = {25},
pages = {8474-8486},
doi = {https://doi.org/10.1021/jacs.7b01622}
}
|
| Sahu, S.S., Siva, V., Pradhan, P.C., Nayak, M., Senapati, K. and Sahoo, P.K. Progressive magnetic softening of ferromagnetic layers in multilayer ferromagnet-nonmagnet systems and the role of granularity JOURNAL OF APPLIED PHYSICS 121, 21 (2017) |
| Abstract: We report a study of the structural and magnetic behavior of the topmost
magnetic layer in a ferromagnet-nonmagnet (Co-Au) multilayer system. Glancing angle X-ray diffraction measurements performed on a series of multilayers showed a gradual decrease in the grain size of the topmost magnetic layer with the increasing number of bilayers. Concurrently, the magnetic hardness and magneto-crystalline anisotropy of the top Co layer were found to decrease, as observed by magneto-optical Kerr effect measurements. This magnetic softening has been discussed in the light of Herzer's random anisotropy model. Micromagnetic simulations of the multilayer system also corroborated these observations. Published by AIP Publishing. |
BibTeX:
@article{WOS:000407490100006,
author = {Sahu, Siddharth S. and Siva, Vantari and Pradhan, Paresh C. and Nayak, Maheswar and Senapati, Kartik and Sahoo, Pratap K.},
title = {Progressive magnetic softening of ferromagnetic layers in multilayer ferromagnet-nonmagnet systems and the role of granularity},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2017},
volume = {121},
number = {21},
doi = {https://doi.org/10.1063/1.4985120}
}
|
| Guo, E.-J., Charlton, T., Ambaye, H., Desautels, R.D., Leemd, H.N. and Fitzsirnrnons, M.R. Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces ACS APPLIED MATERIALS & INTERFACES 9, 22, pp. 19307-19312 (2017) |
| Abstract: Understanding the magnetism at the interface between a ferromagnet and
an insulator is essential because the commonly posited magnetic dead layer close to an interface can be problematic in magnetic tunnel junctions. Previously, degradation of the magnetic interface was attributed to charge discontinuity across the interface. Here, the interfacial magnetism was investigated using three identically prepared La0.67Sr0.33MnO3 (LSMO) thin films grown on different oriented SrTiO3 (STO) substrates by polarized neutron reflectometry. In all cases the magnetization at the LSMO/STO interface is larger than the film bulk. We show that the interfacial magnetization is largest across the LSMO/STO interfaces with (001) and (111) orientations, which have the largest net charge discontinuities across the interfaces. In contrast, the magnetization of LSMO/STO across the (110) interface, the orientation with no net charge discontinuity, is the smallest of the three orientations. We show that a magnetically degraded interface is not intrinsic to LSMO/STO heterostructures. The approach to use different crystallographic orientations provides a means to investigate the influence of charge discontinuity on the interfacial magnetization. |
BibTeX:
@article{WOS:000403136400099,
author = {Guo, Er-Jia and Charlton, Timothy and Ambaye, Haile and Desautels, Ryan D. and Leemd, Ho Nyung and Fitzsirnrnons, Michael R.},
title = {Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2017},
volume = {9},
number = {22},
pages = {19307-19312},
doi = {https://doi.org/10.1021/acsami.7b03252}
}
|
| Jan, H.E., Hoang, H., Nakamura, T., Koga, T., Ina, T., Uruga, T., Kizu, T., Tsukagoshi, K., Nabatame, T. and Fujiwara, A. Amorphous In-Si-O Films Fabricated via Solution Processing JOURNAL OF ELECTRONIC MATERIALS 46, 6, pp. 3610-3614 (2017) |
| Abstract: We report the characteristics of an amorphous oxide semiconductor
In-Si-O fabricated via solution processing. In-Si-O thin films with nominal silicon concentration of 0 at.%, 1 at.%, 3 at.%, 5 at.%, 9 at.%, 50 at.%, and 100 at.% were fabricated via spin coating. The films were characterized via thermal desorption spectroscopy (TDS), x-ray reflectivity, x-ray diffraction (XRD), extended x-ray absorption fine structure (EXAFS), and electrical resistance measurements. TDS analysis suggested that organic residues, such as organic functional groups from raw materials and solvents, were almost completely desorbed from the films at approximately 400A degrees C. The XRD and EXAFS analyses confirmed that pure In2O3 crystallizes at approximately 350A degrees C and that the crystallization temperature increases with the silicon concentration. In-Si-O films with silicon concentration above 3 at.% exhibited high electrical resistance, indicating that films fabricated via spin coating contain few oxygen vacancies. These results suggest that In-Si-O thin films have significant potential for use as channels in field-effect transistors designed for next-generation flat-panel displays. |
BibTeX:
@article{WOS:000400560400047,
author = {Jan, Hani Esmael and Hoang, Ha and Nakamura, Tsubasa and Koga, Tomoaki and Ina, Toshiaki and Uruga, Tomoya and Kizu, Takio and Tsukagoshi, Kazuhito and Nabatame, Toshihide and Fujiwara, Akihiko},
title = {Amorphous In-Si-O Films Fabricated via Solution Processing},
journal = {JOURNAL OF ELECTRONIC MATERIALS},
year = {2017},
volume = {46},
number = {6},
pages = {3610-3614},
doi = {https://doi.org/10.1007/s11664-017-5506-9}
}
|
| Samassekou, H., Alkabsh, A., Wasala, M., Eaton, M., Walber, A., Walker, A., Pitkanen, O., Kordas, K., Talapatra, S., Jayasekera, T. and Mazumdar, D. Viable route towards large-area 2D MoS2 using magnetron sputtering 2D MATERIALS 4, 2 (2017) |
| Abstract: Structural, interfacial, optical, and transport properties of large-area
MoS2 ultra-thin films on BN-buffered silicon substrates fabricated using magnetron sputtering are investigated. A relatively simple growth strategy is demonstrated here that simultaneously promotes superior interfacial and bulk MoS2 properties. Few layers of MoS2 are established using x-ray reflectivity, diffraction, ellipsometry, and Raman spectroscopy measurements. Layer-specific modeling of optical constants show very good agreement with first-principles calculations. Conductivity measurements reveal that few-layer MoS2 films are more conducting than many-layer films. Photo-conductivity measurements reveal that the sputter deposited MoS2 films compare favorably with other large-area methods. Our work illustrates that sputtering is a viable route for large-area device applications using transition metal dichalcogenides. |
BibTeX:
@article{WOS:000393975200002,
author = {Samassekou, Hassana and Alkabsh, Asma and Wasala, Milinda and Eaton, Miller and Walber, Aaron and Walker, Andrew and Pitkanen, Olli and Kordas, Krisztian and Talapatra, Saikat and Jayasekera, Thushari and Mazumdar, Dipanjan},
title = {Viable route towards large-area 2D MoS2 using magnetron sputtering},
journal = {2D MATERIALS},
year = {2017},
volume = {4},
number = {2},
doi = {https://doi.org/10.1088/2053-1583/aa5290}
}
|
| Kreuzpaintner, W., Wiedemann, B., Stahn, J., Moulin, J.-F., Mayr, S., Mairoser, T., Schmehl, A., Herrnberger, A., Korelis, P., Haese, M., Ye, J., Pomm, M., Boeni, P. and Mannhart, J. In situ Polarized Neutron Reflectometry: Epitaxial Thin-Film Growth of Fe on Cu(001) by dc Magnetron Sputtering PHYSICAL REVIEW APPLIED 7, 5 (2017) |
| Abstract: The stepwise growth of epitaxial Fe on Cu(001)/Si(001), investigated by
in situ polarized neutron reflectometry is presented. A sputter deposition system was integrated into the neutron reflectometer AMOR at the Swiss neutron spallation source SINQ, which enables the analysis of the microstructure and magnetic moments during all deposition steps of the Fe layer. We report on the progressive evolution of the accessible parameters describing the microstructure and the magnetic properties of the Fe film, which reproduce known features and extend our knowledge on the behavior of ultrathin iron films. |
BibTeX:
@article{WOS:000401242200001,
author = {Kreuzpaintner, Wolfgang and Wiedemann, Birgit and Stahn, Jochen and Moulin, Jean-Francois and Mayr, Sina and Mairoser, Thomas and Schmehl, Andreas and Herrnberger, Alexander and Korelis, Panagiotis and Haese, Martin and Ye, Jingfan and Pomm, Matthias and Boeni, Peter and Mannhart, Jochen},
title = {In situ Polarized Neutron Reflectometry: Epitaxial Thin-Film Growth of Fe on Cu(001) by dc Magnetron Sputtering},
journal = {PHYSICAL REVIEW APPLIED},
year = {2017},
volume = {7},
number = {5},
doi = {https://doi.org/10.1103/PhysRevApplied.7.054004}
}
|
| Giaccherini, A., Cinotti, S., Guerri, A., Carla, F., Montegrossi, G., Vizza, F., Lavacchi, A., Felici, R., Di Benedetto, F. and Innocenti, M. Operando SXRD study of the structure and growth process of Cu2S ultra-thin films SCIENTIFIC REPORTS 7 (2017) |
| Abstract: Electrochemical Atomic Layer Deposition (E-ALD) technique has
demonstrated to be a suitable process for growing compound semiconductors, by alternating the under-potential deposition (UPD) of the metallic element with the UPD of the non-metallic element. The cycle can be repeated several times to build up films with sub-micrometric thickness. We show that it is possible to grow, by E-ALD, Cu2S ultra-thin films on Ag(111) with high structural quality. They show a well ordered layered crystal structure made on alternating pseudohexagonal layers in lower coordination. As reported in literature for minerals in the Cu-S compositional field, these are based on CuS3 triangular groups, with layers occupied by highly mobile Cu ions. This structural model is closely related to the one of the low chalcocite. The domain size of such films is more than 1000 angstrom in lateral size and extends with a high crystallinity in the vertical growth direction up to more than 10 nm. E-ALD process results in the growth of highly ordered and almost unstrained ultra-thin films. This growth can lead to the design of semiconductors with optimal transport proprieties by an appropriate doping of the intra metallic layer. The present study enables E-ALD as an efficient synthetic route for the growth of semiconducting heterostructures with tailored properties. |
BibTeX:
@article{WOS:000400870500005,
author = {Giaccherini, Andrea and Cinotti, Serena and Guerri, Annalisa and Carla, Francesco and Montegrossi, Giordano and Vizza, Francesco and Lavacchi, Alessandro and Felici, Roberto and Di Benedetto, Francesco and Innocenti, Massimo},
title = {Operando SXRD study of the structure and growth process of Cu2S ultra-thin films},
journal = {SCIENTIFIC REPORTS},
year = {2017},
volume = {7},
doi = {https://doi.org/10.1038/s41598-017-01717-0}
}
|
| Magnfalt, D., Melander, E., Boyd, R.D., Kapaklis, V. and Sarakinos, K. Synthesis of tunable plasmonic metal-ceramic nanocomposite thin films by temporally modulated sputtered fluxes JOURNAL OF APPLIED PHYSICS 121, 17 (2017) |
| Abstract: The scientific and technological interest for metal-dielectric
nanocomposite thin films emanates from the excitation of localized surface plasmon resonances (LSPRs) on the metal component. The overall optical response of the nanocomposite is governed by the refractive index of the dielectric matrix and the properties of the metallic nanoparticles in terms of their bulk optical properties, size, and shape, and the inter-particle distance of separation. In order to tune the film morphology and optical properties, complex synthesis processes which include multiple steps-i. e., film deposition followed by post-deposition treatment by thermal or laser annealing-are commonly employed. In the present study, we demonstrate that the absorption resonances of Ag/AlOxNy nanocomposite films can be effectively tuned from green (similar to 2.4 eV) to violet (similar to 2.8 eV) using a single-step synthesis process that is based on modulating the arrival pattern of film forming species with sub-monolayer resolution, while keeping the amount of Ag in the films constant. Our data indicate that the optical response of the films is the result of LSPRs on isolated Ag nanoparticles that are seemingly shifted by dipolar interactions between neighboring particles. The synthesis strategy presented may be of relevance for enabling integration of plasmonic nanocomposite films on thermally sensitive substrates. Published by AIP Publishing. |
BibTeX:
@article{WOS:000400623700020,
author = {Magnfalt, D. and Melander, E. and Boyd, R. D. and Kapaklis, V. and Sarakinos, K.},
title = {Synthesis of tunable plasmonic metal-ceramic nanocomposite thin films by temporally modulated sputtered fluxes},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2017},
volume = {121},
number = {17},
doi = {https://doi.org/10.1063/1.4979139}
}
|
| Ellis, B.L., Fritzsche, H., Patel, J., Lang, J. and Suppiah, S. Titanium Tritide Films as Betavoltaic Power Sources FUSION SCIENCE AND TECHNOLOGY 71, 4, pp. 660-665 (2017) |
| Abstract: Tritium betavoltaics are one of the family of nuclear batteries which
convert natural radioactive decay from a radioisotope into electricity that can provide continuous power without the requirement for replacement or recharging. Tritium is ideally suited to this application due to its high specific activity, low shielding requirements and relatively high availability. Owing to safety and environmental concerns over tritium leakage, metal tritides films are preferred as tritium betavoltaic sources. Titanium hydride and deuteride films were studied as analogues to titanium tritide films. The quality of the films depended on the temperature of hydrogen loading as films loaded at elevated temperatures (>100 degrees C) were brittle and delaminated from the semiconductor substrate while those exposed to hydrogen at room temperature continued to adhere to the substrate. For the latter films, evidence of hydrogen isotope loss was observed when left under ambient conditions over the course of a few weeks. |
BibTeX:
@article{WOS:000402489900036,
author = {Ellis, Brian L. and Fritzsche, H. and Patel, J. and Lang, J. and Suppiah, S.},
title = {Titanium Tritide Films as Betavoltaic Power Sources},
journal = {FUSION SCIENCE AND TECHNOLOGY},
year = {2017},
volume = {71},
number = {4},
pages = {660-665},
note = {11th International Conference on Tritium Science and Technology (Tritium), Charleston, SC, APR 17-22, 2016},
doi = {https://doi.org/10.1080/15361055.2017.1290952}
}
|
| Sapkota, Y.R., Alkabsh, A., Walber, A., Samassekou, H. and Mazumdar, D. Optical evidence for blue shift in topological insulator bismuth selenide in the few-layer limit APPLIED PHYSICS LETTERS 110, 18 (2017) |
| Abstract: Optical bandgap properties of high-quality few-layer topological
insulator Bi2Se3 thin films are investigated using broadband absorption spectroscopy. We provide direct optical evidence for blue shift in the bulk bandgap of Bi2Se3 as it approaches the two-dimensional limit. The blue shift is robust and observed in both protected (capped) and exposed (uncapped) thin films. The behavior is strongest below six quintuple layers (QLs), particularly at the 2 and 3 QL level, where finite-size effects are known to be most significant in Bi2Se3. A further bandgap increase is observed in all films that we attribute to the Burstein-Moss effect. Our result provides additional insights into the scaling behavior of topological materials. The bandgap increase has a significant impact on the electronic and optoelectronic applications of topological insulators. |
BibTeX:
@article{WOS:000400931900018,
author = {Sapkota, Yub Raj and Alkabsh, Asma and Walber, Aaron and Samassekou, Hassana and Mazumdar, Dipanjan},
title = {Optical evidence for blue shift in topological insulator bismuth selenide in the few-layer limit},
journal = {APPLIED PHYSICS LETTERS},
year = {2017},
volume = {110},
number = {18},
doi = {https://doi.org/10.1063/1.4982631}
}
|
| Jaris, M., Lau, D., Sokalski, V. and Schmidt, H. Magnetization dynamics and damping behavior of Co/Ni multilayers with a graded Ta capping layer JOURNAL OF APPLIED PHYSICS 121, 16 (2017) |
| Abstract: Magnetization dynamics of a Co/Ni multilayer film capped by a wedged Ta
(0.3-1.3 nm) layer were investigated using time-resolved magneto-optic Kerr microscopy. The ferromagnetic resonance was observed for a wide range of magnetic fields in a variety of geometries. Using a macro-spin approximation and the Kittel formula to evaluate the relaxation frequency, a significant increase of the effective anisotropy field was observed as the Ta layer thickness is increased. Furthermore, the damping behavior of the magnetization precession also shows a strong dependence on the Ta layer thickness. Using a model to account for variations of the local anisotropy fields, we reproduce the field evolution of the observed damping using a single Gilbert damping parameter for the Co/Ni system. These findings have direct implications for the rational design of novel spintronic devices. Published by AIP Publishing. |
BibTeX:
@article{WOS:000400382200010,
author = {Jaris, M. and Lau, D. and Sokalski, V. and Schmidt, H.},
title = {Magnetization dynamics and damping behavior of Co/Ni multilayers with a graded Ta capping layer},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2017},
volume = {121},
number = {16},
doi = {https://doi.org/10.1063/1.4982163}
}
|
| Moon, E.J., May, A.F., Shafer, P., Arenholz, E. and May, S.J. Growth and electrical transport properties of La0.7Sr0.3MnO3 thin films on Sr2IrO4 single crystals PHYSICAL REVIEW B 95, 15 (2017) |
| Abstract: We report the physical properties of La0.7Sr0.3MnO3 thin films on
Sr2IrO4 single crystals. The manganite films are deposited using oxide molecular beam epitaxy on flux-grown (001)-oriented iridate crystals. Temperature-dependent magnetotransport and x-ray magnetic circular dichroism measurements reveal the presence of a ferromagnetic metallic ground state in the films, consistent with films grown on SrTiO3 and La0.3Sr0.7Al0.65Ta0.35O3. A parallel resistance model is used to separate conduction effects within the Sr2IrO4 substrate and the La0.7Sr0.3MnO3 thin films, revealing that the measured resistance maximum does not correspond to the manganite Curie temperature but results from a con(v)olution of properties of the near-insulating substrate and metallic film. The ability to grow and characterize epitaxial perovskites on Sr2IrO4 crystals enables a new route for studying magnetism at oxide interfaces in the presence of strong spin-orbit interactions. |
BibTeX:
@article{WOS:000399796800001,
author = {Moon, E. J. and May, A. F. and Shafer, P. and Arenholz, E. and May, S. J.},
title = {Growth and electrical transport properties of La0.7Sr0.3MnO3 thin films on Sr2IrO4 single crystals},
journal = {PHYSICAL REVIEW B},
year = {2017},
volume = {95},
number = {15},
doi = {https://doi.org/10.1103/PhysRevB.95.155135}
}
|
| Jankowski, M., Kaminski, D., Vergeer, K., Mirolo, M., Carla, F., Rijnders, G. and Bollmann, T.R.J. Controlling the growth of Bi(110) and Bi(111) films on an insulating substrate NANOTECHNOLOGY 28, 15 (2017) |
| Abstract: We demonstrate the controlled growth of Bi(110) and Bi(111) films on an
alpha-Al2O3(0001) substrate by surface x-ray diffraction and x-ray reflectivity using synchrotron radiation. At temperatures as low as 40. K, unanticipated pseudo-cubic Bi(110) films are grown with thicknesses ranging from a few to tens of nanometers. The roughness at the film-vacuum as well as the film-substrate interface, can be reduced by mild heating, where a crystallographic orientation transition of Bi(110) towards Bi(111) is observed at 400. K. From 450. K onwards high quality ultrasmooth Bi(111) films form. Growth around the transition temperature results in the growth of competing Bi(110) and Bi(111) domains. |
BibTeX:
@article{WOS:000398507700002,
author = {Jankowski, Maciej and Kaminski, Daniel and Vergeer, Kurt and Mirolo, Marta and Carla, Francesco and Rijnders, Guus and Bollmann, Tjeerd R. J.},
title = {Controlling the growth of Bi(110) and Bi(111) films on an insulating substrate},
journal = {NANOTECHNOLOGY},
year = {2017},
volume = {28},
number = {15},
doi = {https://doi.org/10.1088/1361-6528/aa61dd}
}
|
| Voegeli, W., Kamezawa, C., Arakawa, E., Yano, Y.F., Shirasawa, T., Takahashi, T. and Matsushita, T. A quick convergent-beam laboratory X-ray reflectometer using a simultaneous multiple-angle dispersive geometry JOURNAL OF APPLIED CRYSTALLOGRAPHY 50, 2, pp. 570-575 (2017) |
| Abstract: An X-ray reflectometer using a laboratory X-ray source for quick
measurements of the specular X-ray reflectivity curve is presented. It uses a bent-twisted crystal to monochromatize and focus the diverging X-rays (Cu K alpha(1)) from a laboratory point source onto the sample. The reflected X-rays are recorded with a two-dimensional detector. Reflectivity curves can be measured without rotating the sample, detector or X-ray source during measurements. The instrument can separate the specularly reflected X-rays from the diffuse scattering background, so low reflectivities can be measured accurately. For a gold thin film on silicon, the reflectivity down to the order of 10(-6) was obtained with a measurement time of 100 s and that down to 10(-5) with a measurement time of 10 s. Reflectivity curves of a silicon wafer and a liquid ethylene glycol surface are shown as well. Time-resolved measurements of a TiO2 surface during UV irradiation are also reported. |
BibTeX:
@article{WOS:000399010000027,
author = {Voegeli, Wolfgang and Kamezawa, Chika and Arakawa, Etsuo and Yano, Yohko F. and Shirasawa, Tetsuroh and Takahashi, Toshio and Matsushita, Tadashi},
title = {A quick convergent-beam laboratory X-ray reflectometer using a simultaneous multiple-angle dispersive geometry},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2017},
volume = {50},
number = {2},
pages = {570-575},
doi = {https://doi.org/10.1107/S1600576717002461}
}
|
| Top, M., Schoenfeld, S., Fahlteich, J., Bunk, S., Kuehnel, T., Straach, S. and De Hosson, J.T. Hollow-cathode activated PECVD for the high-rate deposition of permeation barrier films SURFACE & COATINGS TECHNOLOGY 314, pp. 155-159 (2017) |
| Abstract: This paper shows a study on the variation of the flow ratio between
oxygen and Hexamethyldisiloxane (HMDSO) in a hollow cathode arc PECVD process. Dynamic deposition rates were measured between 300 and 500 nm * m/ min. The deposited plasma polymer films were analyzed using visible light spectroscopy, X-ray photo -electron spectroscopy (XPS), X-ray reflectivity (XRR), Fourier -transformed infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and water vapor transmission rate (WVTR) measurements. The deposited samples were compared to a reactively sputtered SiO2 thin film. By increasing the oxygen to HMDSO flow ratio, the chemical, density and optical properties of the coating approached the sputtered Si02 film. However the permeation barrier of the SiO2 film only shows a slight improvement over that of the bare PET substrate. The organic coating with high power and low oxygen flow, which was deposited with a deposition rate of 450 nm * m/min, approached the barrier of the sputtered SiO2 thin film with a WVTR of 0.16 g/(m' day). 2016 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000397696400024,
author = {Top, Michiel and Schoenfeld, Steffen and Fahlteich, John and Bunk, Sebastian and Kuehnel, Thomas and Straach, Steffen and De Hosson, Jeff T.},
title = {Hollow-cathode activated PECVD for the high-rate deposition of permeation barrier films},
journal = {SURFACE & COATINGS TECHNOLOGY},
year = {2017},
volume = {314},
pages = {155-159},
note = {59th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), Indianapolis, IN, MAY 10-13, 2016},
doi = {https://doi.org/10.1016/j.surfcoat.2016.09.003}
}
|
| Ribera, R.C., van de Kruijs, R.W.E., Sturm, J.M., Yakshin, A.E. and Bijkerk, F. Intermixing and thermal oxidation of ZrO2 thin films grown on a-Si, SiN, and SiO2 by metallic and oxidic mode magnetron sputtering JOURNAL OF APPLIED PHYSICS 121, 11 (2017) |
| Abstract: The initial growth of DC sputtered ZrO2 on top of a-Si, SiN, and SiO2
layers has been studied by in vacuo high-sensitivity low energy ion scattering for two gas deposition conditions with different oxygen contents (high-O and low-O conditions). This unique surface sensitive technique allowed the determination of surface composition and thicknesses required to close the ZrO2 layer on all three substrates for both conditions. The ZrO2 layer closes similarly on all substrates due to more favorable enthalpies of formation for ZrO2 and ZrSiO4, resulting in passivation of the Si from the substrate. However, this layer closes at about half of the thickness (similar to 1.7 nm) for low-O conditions due to less oxidative conditions and less energetic particles arriving at the sample, which leads to less intermixing via silicate formation. In contrast, for high-O conditions, there is more ZrSiO4 and/or SiOx formation, giving more intermixing (similar to 3.4 nm). In vacuo X-ray photoelectron spectroscopy (XPS) measurements revealed similar stoichiometric ZrO2 layers deposited by both conditions and a higher interaction of the ZrO2 layer with the underlying a-Si for high-O conditions. In addition, oxygen diffusion through low-O ZrO2 films on a-Si has been investigated by ex situ angular-resolved XPS of samples annealed in atmospheric oxygen. For temperatures below 400 degrees C, no additional oxidation of the underlying a-Si was observed. This, together with the amorphous nature and smoothness of these samples, makes ZrO2 a good candidate as an oxidation protective layer on top of a-Si. Published by AIP Publishing. |
BibTeX:
@article{WOS:000397421400043,
author = {Ribera, R. Coloma and van de Kruijs, R. W. E. and Sturm, J. M. and Yakshin, A. E. and Bijkerk, F.},
title = {Intermixing and thermal oxidation of ZrO2 thin films grown on a-Si, SiN, and SiO2 by metallic and oxidic mode magnetron sputtering},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2017},
volume = {121},
number = {11},
doi = {https://doi.org/10.1063/1.4978367}
}
|
| McElhinny, K.M., Huang, P., Joo, Y., Kanimozhi, C., Lakkham, A., Sakurai, K., Evans, P.G. and Gopalan, P. Optically Reconfigurable Monolayer of Azobenzene Donor Molecules on Oxide Surfaces LANGMUIR 33, 9, pp. 2157-2168 (2017) |
| Abstract: The structural configuration of molecules assembled at organic-inorganic
interfaces within electronic materials strongly influences the functional electronic and vibrational properties relevant to applications ranging from energy storage to photovoltaics. Controlling and characterizing the structural state of an interface and its evolution under external stimuli is crucial both for the fundamental understanding of the factors influenced by molecular structure and for the development of methods for material synthesis. It has been challenging to create complete molecular monolayers that exhibit external reversible control of the structure and electronic configuration. We report a monolayer/inorganic interface consisting of an organic monolayer assembled on an oxide surface, exhibiting structural and electronic reconfiguration under ultraviolet illumination. The molecular monolayer is linked to the surface through a carboxylate link, with the backbone bearing an azobenzene functional group and the head group consisting bipyridine group. Optical spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray reflectivity show that closely packed monolayers are formed from these molecules via the Langmuir-Blodgett technique. Reversible photoisomerization is observed in solution and in monolayers assembled on Si and quartz substrates. The reconfiguration of these monolayers provides additional means to control excitation and charge transfer processes that are important in applications in catalysis, molecular electronics, and solar energy conversion. |
BibTeX:
@article{WOS:000395964100011,
author = {McElhinny, Kyle M. and Huang, Peishen and Joo, Yongho and Kanimozhi, Catherine and Lakkham, Arunee and Sakurai, Kenji and Evans, Paul G. and Gopalan, Padma},
title = {Optically Reconfigurable Monolayer of Azobenzene Donor Molecules on Oxide Surfaces},
journal = {LANGMUIR},
year = {2017},
volume = {33},
number = {9},
pages = {2157-2168},
doi = {https://doi.org/10.1021/acs.langmuir.6b04585}
}
|
| Hsieh, W.-C., Wadekar, P.V., Liu, H.-H., Lee, C.-H., Chang, C.-F., Tu, L.-W., You, S.-T., Chen, Q.Y., Huang, H.-C., Ho, N.-J., Seo, H.-W. and Chu, W.-K. Water-modulated oxidation in the growth of m-ZnO epitaxial thin film by atomic layer deposition JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 35, 2 (2017) |
| Abstract: The effects of extra H2O-modulated oxidation are reported on the
structural, optical, and electrical properties of nonpolar m-plane ZnO thin films grown on m-plane Al2O3 substrates by atomic layer deposition. Films without modulation, one modulated layer, and two modulated layers are compared. Structural properties studied using x-ray reflectivity, x-ray diffraction, and transmission electron microscopy show that all the films have a largely similar thickness and epitaxial relations with their substrates, but the rocking curves grow broader as the number of modulations increases. However, the extra layer of water modulation reduces the surface roughness drastically and also improves the electrical properties as compared to the unmodulated ZnO films. Water modulation is believed to serve as a source of atomic oxygen that promotes compensation of the pre-existing oxygen vacancies. The films tend to exhibit larger mosaicity around the a-axis as compared to that around the c-axis. (C) 2017 American Vacuum Society. |
BibTeX:
@article{WOS:000397762400037,
author = {Hsieh, Wan-Chen and Wadekar, Paritosh Vilas and Liu, Hua-Huei and Lee, Chiao-Han and Chang, Chun-Fu and Tu, Li-Wei and You, Shou-Ting and Chen, Quark Yungsung and Huang, Hui-Chun and Ho, New-Jin and Seo, Hye-Won and Chu, Wei-Kan},
title = {Water-modulated oxidation in the growth of m-ZnO epitaxial thin film by atomic layer deposition},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2017},
volume = {35},
number = {2},
doi = {https://doi.org/10.1116/1.4975073}
}
|
| Pachlhofer, J.M., Martin-Luengo, A.T., Franz, R., Franzke, E., Koestenbauer, H., Winkler, J., Bonanni, A. and Mitterer, C. Industrial-scale sputter deposition of molybdenum oxide thin films: Microstructure evolution and properties JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 35, 2 (2017) |
| Abstract: The current work investigates the microstructure and property relations
of molybdenum oxide thin films synthesized by reactive dc magnetron sputtering in an industrial-scale sputter deposition plant using a rotatable molybdenum target with varying oxygen/argon gas flow ratio. The evolution of microstructure and chemical bonds as a function of oxygen partial pressure was studied by x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy. With oxygen partial pressure raising from 0% to 100%, the film growth rate decreased from 350 to 50 nm/min, while the oxygen content within the films increased up to 75 at. %. The films were dominated by MoO2, polymorphs of Mo4O11 and Mo9O26, and MoO3 phases. The electrical properties changed from electrically conductive to insulating with increasing oxygen partial pressure. The optical properties are versatile, e.g., transmittance values up to 80%, absorbance values between 50% and 80% and reflectance values up to 55%, depending on the oxygen content. In general, it can be concluded that microstructure and properties of molybdenum oxide thin films can be adjusted by varying the oxygen/argon gas flow ratio and might thus enable their use in a wide range of optical and electronic applications. (C) 2017 American Vacuum Society. |
BibTeX:
@article{WOS:000397762400030,
author = {Pachlhofer, Julia M. and Martin-Luengo, Aitana Tarazaga and Franz, Robert and Franzke, Enrico and Koestenbauer, Harald and Winkler, Joerg and Bonanni, Alberta and Mitterer, Christian},
title = {Industrial-scale sputter deposition of molybdenum oxide thin films: Microstructure evolution and properties},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2017},
volume = {35},
number = {2},
doi = {https://doi.org/10.1116/1.4973214}
}
|
| Herklotz, A., Guo, E.-J., Wong, A.T., Meyer, T.L., Dai, S., Ward, T.Z., Lee, H.N. and Fitzsimmons, M.R. Reversible Control of Interfacial Magnetism through Ionic-Liquid Assisted Polarization Switching NANO LETTERS 17, 3, pp. 1665-1669 (2017) |
| Abstract: The ability to control magnetism of materials via electric field enables
a myriad of technological innovations in information storage, sensing, and computing. We use ionic liquid-assisted ferroelectric switching to demonstrate reversible modulation of interfacial magnetism in a multiferroic hetero-structure composed of ferromagnetic (FM) La0.8Sr0.2MnO3 and ferroelectric (FE) PbZr0.2Ti0.8O3. It is shown that ionic liquids can be used to persistently and reversibly switch a large area of a FE film. This is a prerequisite for polarized neutron reflectometry (PNR) studies that are conducted to directly probe magneto electric coupling of the FE polarization to the interfacial magnetization. |
BibTeX:
@article{WOS:000396185800051,
author = {Herklotz, Andreas and Guo, Er-Jia and Wong, Anthony T. and Meyer, Tricia L. and Dai, Sheng and Ward, T. Zac and Lee, Ho Nyung and Fitzsimmons, Michael R.},
title = {Reversible Control of Interfacial Magnetism through Ionic-Liquid Assisted Polarization Switching},
journal = {NANO LETTERS},
year = {2017},
volume = {17},
number = {3},
pages = {1665-1669},
doi = {https://doi.org/10.1021/acs.nanolett.6b04949}
}
|
| Gu, Z., Imbrenda, D., Bennett-Jackson, A.L., Falmbigl, M., Podpirka, A., Parker, T.C., Shreiber, D., Ivill, M.P., Fridkin, V.M. and Spanier, J.E. Mesoscopic Free Path of Nonthermalized Photogenerated Carriers in a Ferroelectric Insulator PHYSICAL REVIEW LETTERS 118, 9 (2017) |
| Abstract: We show how finite-size scaling of a bulk photovoltaic effect-generated
electric field in epitaxial ferroelectric insulating BaTiO3(001)films and a photo-Hall response involving the bulk photovoltaic current reveal a large room-temperature mean free path of photogenerated nonthermalized electrons. Experimental determination of mesoscopic ballistic optically generated carrier transport opens a new paradigm for hot electron-based solar energy conversion, and for facile control of ballistic transport distinct from existing low-dimensional semiconductor interfaces, surfaces, layers, or other structures. |
BibTeX:
@article{WOS:000396043900009,
author = {Gu, Zongquan and Imbrenda, Dominic and Bennett-Jackson, Andrew L. and Falmbigl, Matthias and Podpirka, Adrian and Parker, Thomas C. and Shreiber, Daniel and Ivill, Mathew P. and Fridkin, Vladimir M. and Spanier, Jonathan E.},
title = {Mesoscopic Free Path of Nonthermalized Photogenerated Carriers in a Ferroelectric Insulator},
journal = {PHYSICAL REVIEW LETTERS},
year = {2017},
volume = {118},
number = {9},
doi = {https://doi.org/10.1103/PhysRevLett.118.096601}
}
|
| Kc, A., Borisov, P., Shvartsman, V.V. and Lederman, D. Weak ferromagnetism and short range polar order in NaMnF3 thin films APPLIED PHYSICS LETTERS 110, 9 (2017) |
| Abstract: The orthorhombically distorted perovskite NaMnF3 has been predicted to
become ferroelectric if an a = c distortion of the bulk Pnma structure is imposed. In order to test this prediction, NaMnF3 thin films were grown on SrTiO3 (001) single crystal substrates via molecular beam epitaxy. The best films were smooth and single phase with four different twin domains. In-plane magnetization measurements revealed the presence of antiferromagnetic ordering with weak ferromagnetism below the Neel temperature T-N = 66 K. For the dielectric studies, NaMnF3 films were grown on a 30 nm SrRuO3 (001) layer used as a bottom electrode grown via pulsed laser deposition. The complex permittivity as a function of frequency indicated a strong Debye-like relaxation contribution characterized by a distribution of relaxation times. A power-law divergence of the characteristic relaxation time revealed an order-disorder phase transition at 8 K. The slow relaxation dynamics indicated the formation of superdipoles (superparaelectric moments) that extend over several unit cells, similar to polar nanoregions of relaxor ferroelectrics. Published by AIP Publishing. |
BibTeX:
@article{WOS:000397871600041,
author = {Kc, Amit and Borisov, Pavel and Shvartsman, Vladimir V. and Lederman, David},
title = {Weak ferromagnetism and short range polar order in NaMnF3 thin films},
journal = {APPLIED PHYSICS LETTERS},
year = {2017},
volume = {110},
number = {9},
doi = {https://doi.org/10.1063/1.4977421}
}
|
| McBriarty, M.E., von Rudorff, G.F., Stubbs, J.E., Eng, P.J., Blumberger, J. and Rosso, K.M. Dynamic Stabilization of Metal Oxide-Water Interfaces JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 139, 7, pp. 2581-2584 (2017) |
| Abstract: The interaction of water with metal oxide surfaces plays a crucial role
in the catalytic and geochemical behavior of metal oxides. In a vast majority of studies, the interfacial structure is assumed to arise from a relatively static lowest energy configuration of atoms, even at room temperature. Using hematite (alpha-Fe2O3) as a model oxide, we show through a direct comparison of in situ synchrotron X-ray scattering with density functional theory-based molecular dynamics simulations that the structure of the (1 (1) over bar 02) termination is dynamically stabilized by picosecond water exchange. Simulations show frequent exchanges between terminal aquo groups and adsorbed water in locations and with partial residence times consistent with experimentally determined atomic sites and fractional occupancies. Frequent water exchange occurs even for an ultrathin adsorbed water film persisting on the surface under a dry atmosphere. The resulting time averaged interfacial structure consists of a ridged lateral arrangement of adsorbed water molecules hydrogen bonded to terminal aquo groups. Surface pK(a) prediction based on bond valence analysis suggests that water exchange will influence the proton-transfer reactions underlying the acid/base reactivity at the interface. Our findings provide important new insights for understanding complex interfacial chemical processes at metal oxide water interfaces. |
BibTeX:
@article{WOS:000394829200012,
author = {McBriarty, Martin E. and von Rudorff, Guido Falk and Stubbs, Joanne E. and Eng, Peter J. and Blumberger, Jochen and Rosso, Kevin M.},
title = {Dynamic Stabilization of Metal Oxide-Water Interfaces},
journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY},
year = {2017},
volume = {139},
number = {7},
pages = {2581-2584},
doi = {https://doi.org/10.1021/jacs.6b13096}
}
|
| Satchell, N., Witt, J.D.S., Burnell, G., Curran, P.J., Kinane, C.J., Charlton, T.R., Langridge, S. and Cooper, J.F.K. Probing the spiral magnetic phase in 6 nm textured erbium using polarised neutron reflectometry JOURNAL OF PHYSICS-CONDENSED MATTER 29, 5 (2017) |
| Abstract: We characterise the magnetic state of highly-textured, sputter deposited
erbium for a film of thickness 6 nm. Using polarised neutron reflectometry it is found that the film has a high degree of magnetic disorder, and we present some evidence that the film's local magnetic state is consistent with bulk-like spiral magnetism. This, combined with complementary characterisation techniques, show that thin film erbium is a strong candidate material for incorporation into device structures. |
BibTeX:
@article{WOS:000390350700001,
author = {Satchell, N. and Witt, J. D. S. and Burnell, G. and Curran, P. J. and Kinane, C. J. and Charlton, T. R. and Langridge, S. and Cooper, J. F. K.},
title = {Probing the spiral magnetic phase in 6 nm textured erbium using polarised neutron reflectometry},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2017},
volume = {29},
number = {5},
doi = {https://doi.org/10.1088/1361-648X/29/5/055801}
}
|
| Lorch, C., Novak, J., Banerjee, R., Weimer, S., Dieterle, J., Frank, C., Hinderhofer, A., Gerlach, A., Carla, F. and Schreiber, F. Influence of C-60 co-deposition on the growth kinetics of diindenoperylene-From rapid roughening to layer-by-layer growth in blended organic films JOURNAL OF CHEMICAL PHYSICS 146, 5 (2017) |
| Abstract: We investigated the growth of the two phase-separating materials
diindenoperylene (DIP) and buckminsterfullerene C-60 with different mixing ratio in real-time and in situ by X-ray scattering experiments. We found that at room temperature, mixtures with an excess of DIP show a growth mode which is very close to the perfect layer-by-layer limit with DIP crystallites forming over the entire film thickness. An unexpected increase in the island size is observed for these mixtures as a function of film thickness. On the other hand, equimolar and C-60 dominated mixtures grow with poor crystallinity but form very smooth films. Additionally, it is observed that higher substrate temperatures lead to an increase in the length scale of phase separation with film thickness. Published by AIP Publishing. |
BibTeX:
@article{WOS:000394576600009,
author = {Lorch, C. and Novak, J. and Banerjee, R. and Weimer, S. and Dieterle, J. and Frank, C. and Hinderhofer, A. and Gerlach, A. and Carla, F. and Schreiber, F.},
title = {Influence of C-60 co-deposition on the growth kinetics of diindenoperylene-From rapid roughening to layer-by-layer growth in blended organic films},
journal = {JOURNAL OF CHEMICAL PHYSICS},
year = {2017},
volume = {146},
number = {5},
doi = {https://doi.org/10.1063/1.4966583}
}
|
| Ding, Z., Gaowei, M., Sinsheimer, J., Xie, J., Schubert, S., Padmore, H., Muller, E. and Smedley, J. In-situ synchrotron x-ray characterization of K2CsSb photocathode grown by ternary co-evaporation JOURNAL OF APPLIED PHYSICS 121, 5 (2017) |
| Abstract: K2CsSb is a promising photocathode candidate to serve as an electron
source in next-generation light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). As the traditional recipe for creation of K2CsSb photocathodes typically results in a rough surface that deteriorates electron beam quality, significant effort has been made to explore novel growth methods for K2CsSb photocathodes. In this paper, a method of ternary co-evaporation of K, Cs, and Sb is described. By using in-situ synchrotron X-ray techniques, the quality of the photocathode is characterized during and after the growth. K2CsSb photocathodes grown by this method on Si (100) and MgO (001) substrates show strong (222) texture, and the two photocathodes exhibit 1.7% and 3.4% quantum efficiencies at a wavelength of 530 nm, with a rms surface roughness of about 2-4 nm. This represents an order of magnitude reduction in roughness compared to typical sequential deposition and should result in a significant improvement in the brightness of the generated electron beam. Published by AIP Publishing. |
BibTeX:
@article{WOS:000394345700045,
author = {Ding, Z. and Gaowei, M. and Sinsheimer, J. and Xie, J. and Schubert, S. and Padmore, H. and Muller, E. and Smedley, J.},
title = {In-situ synchrotron x-ray characterization of K2CsSb photocathode grown by ternary co-evaporation},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2017},
volume = {121},
number = {5},
doi = {https://doi.org/10.1063/1.4975113}
}
|
| Welbourn, R.J.L., Truscott, C.L., Skoda, M.W.A., Zarbakhsh, A. and Clarke, S.M. Corrosion and inhibition of copper in hydrocarbon solution on a molecular level investigated using neutron reflectometry and XPS CORROSION SCIENCE 115, pp. 68-77 (2017) |
| Abstract: The behaviour and molecular structure of three organic additives
adsorbed from oil onto a copper surface rich in copper (II) oxide is presented. The variation in the ability of these three agents to prevent corrosion of the copper oxide surface by exposure to sulphur is also included. A combination of visible observations, X-ray photoelectron spectroscopy (XPS) and neutron reflection (NR) are used to characterise both the adsorbed layer and underlying copper oxide. The model additives are chosen to represent `effective', `intermediate' and `ineffective' inhibitors for copper. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.orgflicenses/by/4.0/). |
BibTeX:
@article{WOS:000392164500007,
author = {Welbourn, Rebecca J. L. and Truscott, C. L. and Skoda, M. W. A. and Zarbakhsh, A. and Clarke, S. M.},
title = {Corrosion and inhibition of copper in hydrocarbon solution on a molecular level investigated using neutron reflectometry and XPS},
journal = {CORROSION SCIENCE},
year = {2017},
volume = {115},
pages = {68-77},
doi = {https://doi.org/10.1016/j.corsci.2016.11.010}
}
|
| Kim, J.-Y., Ionescu, A., Mansell, R., Farrer, I., Oehler, F., Kinane, C.J., Cooper, J.F.K., Steinke, N.-J., Langridge, S., Stankiewicz, R., Humphreys, C.J., Cowburn, R.P., Holmes, S.N. and Barnes, C.H.W. Structural and magnetic properties of ultra-thin Fe films on metal-organic chemical vapour deposited GaN(0001) JOURNAL OF APPLIED PHYSICS 121, 4 (2017) |
| Abstract: Structural and magnetic properties of 1-10 nm thick Fe films deposited
on GaN(0001) were investigated. In-situ reflecting high energy electron diffraction images indicated a alpha-Fe(110)/GaN(0001) growth of the 3D Volmer-Weber type. The alpha-Fe(110) X-ray diffraction peak showed a 1 degrees full-width at half-maximum, indicating approximate to 20 nm grain sizes. A significant reduction in Fe atomic moment from its bulk value was observed for films thinner than 4 nm. Both GaN/Fe interface roughness and Fe film coercivity increased with Fe thickness, indicating a possible deterioration of Fe crystalline quality. Magnetic anisotropy was mainly uniaxial for all films while hexagonal anisotropies appeared for thicknesses higher than 3.7 nm. Published by AIP Publishing. |
BibTeX:
@article{WOS:000393480100010,
author = {Kim, Jun-Young and Ionescu, Adrian and Mansell, Rhodri and Farrer, Ian and Oehler, Fabrice and Kinane, Christy J. and Cooper, Joshaniel F. K. and Steinke, Nina-Juliane and Langridge, Sean and Stankiewicz, Romuald and Humphreys, Colin J. and Cowburn, Russell P. and Holmes, Stuart N. and Barnes, Crispin H. W.},
title = {Structural and magnetic properties of ultra-thin Fe films on metal-organic chemical vapour deposited GaN(0001)},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2017},
volume = {121},
number = {4},
doi = {https://doi.org/10.1063/1.4973956}
}
|
| Troughton, J.G., Downs, P., Price, R. and Atkinson, D. Densification of a-IGZO with low-temperature annealing for flexible electronics applications APPLIED PHYSICS LETTERS 110, 1 (2017) |
| Abstract: Amorphous InGaZnO (a-IGZO) thin-film transistors are a leading contender
for active channel materials in next generation flat panel displays and flexible electronics. Improved electronic functionality has been linked to the increased density of a-IGZO, and while much work has looked at hightemperature processes, studies at temperatures compatible with flexible substrates are needed. Here, compositional and structural analyses show that short term, low-temperature annealing (< 6 h) can increase the density of sputtered a-IGZO by up to 5.6% for temperatures below 300 degrees C, which is expected to improve the transistor performance, while annealing for longer times leads to a subsequent decrease in density due to oxygen absorption. |
BibTeX:
@article{WOS:000392834600016,
author = {Troughton, J. G. and Downs, P. and Price, R. and Atkinson, D.},
title = {Densification of a-IGZO with low-temperature annealing for flexible electronics applications},
journal = {APPLIED PHYSICS LETTERS},
year = {2017},
volume = {110},
number = {1},
doi = {https://doi.org/10.1063/1.4973629}
}
|
| Martin-Luengo, A.T., Koestenbauer, H., Winkler, J. and Bonanni, A. Processing and charge state engineering of MoOx AIP ADVANCES 7, 1 (2017) |
| Abstract: The effects of wet chemical processing employed in device fabrication
standards are studied on molybdenum oxide (MoOx) ultra-thin films. We have combined x-ray photoelectron spectroscopy (XPS), angle resolved XPS and x-ray reflectivity to gain insight into the changes in composition, structure and electronic states upon treatment of films with different initial stoichiometry prepared by reactive sputtering. Our results show significant reduction effects associated with the development of gap states in MoOx, as well as changes in the composition and structure of the films, systematically correlated with the initial oxidation state of Mo. (C) 2017 Author(s). |
BibTeX:
@article{WOS:000395789900034,
author = {Martin-Luengo, Aitana Tarazaga and Koestenbauer, Harald and Winkler, Joerg and Bonanni, Alberta},
title = {Processing and charge state engineering of MoOx},
journal = {AIP ADVANCES},
year = {2017},
volume = {7},
number = {1},
doi = {https://doi.org/10.1063/1.4974880}
}
|
| Fisher, Z., Jackson, A., Kovalevsky, A., Oksanen, E. and Wacklin, H. Biological Structures 49NEUTRON SCATTERING - APPLICATIONS IN BIOLOGY, CHEMISTRY, AND MATERIALS SCIENCE, pp. 1-75 (2017) |
BibTeX:
@incollection{WOS:000439545300002,
author = {Fisher, Zoe and Jackson, Andrew and Kovalevsky, Andrey and Oksanen, Esko and Wacklin, Hanna},
title = {Biological Structures},
booktitle = {NEUTRON SCATTERING - APPLICATIONS IN BIOLOGY, CHEMISTRY, AND MATERIALS SCIENCE},
year = {2017},
volume = {49},
pages = {1-75},
doi = {https://doi.org/10.1016/B978-0-12-805324-9.00001-7}
}
|
| Zhu, M. Component Optimization of Ti for Ti-Sb-Te Alloy TI-SB-TE PHASE CHANGE MATERIALS: COMPONENT OPTIMISATION, MECHANISM AND APPLICATIONS, pp. 41-58 (2017) |
BibTeX:
@incollection{WOS:000428995600004,
author = {Zhu, Min},
title = {Component Optimization of Ti for Ti-Sb-Te Alloy},
booktitle = {TI-SB-TE PHASE CHANGE MATERIALS: COMPONENT OPTIMISATION, MECHANISM AND APPLICATIONS},
year = {2017},
pages = {41-58},
doi = {https://doi.org/10.1007/978-981-10-4382-6%5C_3}
}
|
| Tsuyuki, Y., Fujimura, T., Kunimoto, M., Fukunaka, Y., Pianetta, P. and Homma, T. Analysis of Cathodic Reaction Process of SiCl4 during Si Electrodeposition in Ionic Liquids JOURNAL OF THE ELECTROCHEMICAL SOCIETY 164, 14, pp. D994-D998 (2017) |
| Abstract: Elementary steps in the electrochemical reduction process of SiCl4 in
trimethyl-n-hexylammonium bis(trifluoromethylsulfonyl) imide (TMHATFSI) was investigated, focusing on molecular level behavior of the reactants at solid-liquid interface. Electrochemical measurements using an electrochemical quartz crystal microbalance (EQCM) identified a reduction peak corresponding to Si electrodeposition and several elementary steps with stable intermediates forming prior to the deposition. For detailed analysis, X-ray reflectivity (XRR) measurements with synchrotron radiation were applied in situ. The change in reflectivity of the electrode surface during the deposition was found to be due to the formation of a polymer-like Si such as Si2Cl6, which is an intermediate layer during the deposition process. These results were theoretically supported by density functional theory (DFT) calculations: after an electron transfers from the electrode, the Si in SiCl4 forms the bond with another SiCl4, rather than the Si of the substrate, resulting in the formation of the intermediate structure. These data suggest an elementary step in the SiCl4 reduction process which can be described as follows; when SiCl4 is reduced, a polymer-like Si form such as Si2Cl6 is generated. This intermediate species further reacts with other Si reactants after receiving additional electrons, which then finally deposits as Si on the substrate. (c) The Author(s) 2017. Published by ECS. All rights reserved. |
BibTeX:
@article{WOS:000419187700089,
author = {Tsuyuki, Yasuhiro and Fujimura, Tatsuki and Kunimoto, Masahiro and Fukunaka, Yasuhiro and Pianetta, Piero and Homma, Takayuki},
title = {Analysis of Cathodic Reaction Process of SiCl4 during Si Electrodeposition in Ionic Liquids},
journal = {JOURNAL OF THE ELECTROCHEMICAL SOCIETY},
year = {2017},
volume = {164},
number = {14},
pages = {D994-D998},
doi = {https://doi.org/10.1149/2.0761714jes}
}
|
| Ha, H., Fritzsche, H., Burton, G. and Ulaganathan, J. Polarized Neutron Reflectometry of Metal Consumption and Passive Film Growth on Nickel Exposed to an Alkaline Deuterium Oxide (D2O) Solution JOURNAL OF THE ELECTROCHEMICAL SOCIETY 164, 12, pp. C699-C707 (2017) |
| Abstract: Electrochemical behavior of Ni in an alkaline heavy water electrolyte
was studied using cyclic voltammetry and polarized neutron reflectometry. Delays in the hydrogen and oxygen evolution reactions on Ni electrodes and slower kinetics of the reactions in heavy water compared to light water were observed. However, in both 0.01 mol/L NaOH light and heavy water solutions, Ni oxidation and passive film formation occurred at the same potential with similar passive current densities indicating a minor isotope effect of deuterium on passive film formation and growth. Polarized neutron reflectometry detected a passive film growth coefficient of 11.5 +/- 1.1 angstrom/V. The Ni consumption coefficient was determined to be 7.3 +/- 1.5 angstrom/V. Ni oxidation and passive film growth occurred mostly during the transient period after the applied potential increase but was negligible at the steady state. The electric field strength across the passive film was 8 x 106 V/cm. The Pilling-Bedworth ratio of the passive film during potentiostatic growth was close to the value of NiO grown on bulk Ni. This work demonstrated the capability of neutron reflectometry in the study of passive films on metals and alloys. (C) The Author(s) 2017. Published by ECS. All rights reserved. |
BibTeX:
@article{WOS:000415283600105,
author = {Ha, Hung and Fritzsche, Helmut and Burton, Gordon and Ulaganathan, Jaganathan},
title = {Polarized Neutron Reflectometry of Metal Consumption and Passive Film Growth on Nickel Exposed to an Alkaline Deuterium Oxide (D2O) Solution},
journal = {JOURNAL OF THE ELECTROCHEMICAL SOCIETY},
year = {2017},
volume = {164},
number = {12},
pages = {C699-C707},
doi = {https://doi.org/10.1149/2.0171713jes}
}
|
| Mazzei, L., Wolff, M., Pergolesi, D., Dura, J.A., Borjesson, L., Gutfreund, P., Bettinelli, M., Lippert, T. and Karlsson, M. Structure and Conductivity of Epitaxial Thin Films of In-Doped BaZrO3-Based Proton Conductors JOURNAL OF PHYSICAL CHEMISTRY C 120, 50, pp. 28415-28422 (2016) |
| Abstract: Epitaxial thin films of the proton-conducting perovskite
BaZr0.53In0.47O3-delta H0.47-2 delta, grown by pulsed laser deposition, were investigated in their hydrated and dehydrated conditions through a multitechniqu approach with the aim to study the structure and proton concentration depth profile and their relationship to proton conductivity. The techniques used were X-ray diffraction, X-ray and neutron reflectivity, nuclear reaction analysis, and Rutherford backscattering, together with impedance spectroscopy. The obtained proton conductivity and activation energy are comparable to literature values for the bulk conductivity of similar materials, thus showing that grain-boundary conductivity is negligible due to the high crystallinity of the film. The results reveal an uneven proton concentration depth profile, with the presence of a 3-4 nm thick, proton-rich layer with altered composition, likely characterized by cationic deficiency. While this surface layer either retains or reobtains protons after desorption and cooling to room temperature, the bulk of the film absorbs and desorbs protons in the expected mariner. It is suggested that the protons in the near-surface, proton rich region are located in proton sites characterized by relatively strong O-H bonds due to weak hydrogen-bond interactions to neighboring oxygen atoms and that the mobility of protons in these sites is generally lower than in proton sites associated with stronger hydrogen bonds. It follows that strongly hydrogen-bonding configurations are important for high proton mobility. |
BibTeX:
@article{WOS:000390735600005,
author = {Mazzei, Laura and Wolff, Max and Pergolesi, Daniele and Dura, Joseph A. and Borjesson, Lars and Gutfreund, Philipp and Bettinelli, Marco and Lippert, Thomas and Karlsson, Maths},
title = {Structure and Conductivity of Epitaxial Thin Films of In-Doped BaZrO3-Based Proton Conductors},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2016},
volume = {120},
number = {50},
pages = {28415-28422},
doi = {https://doi.org/10.1021/acs.jpcc.6b08570}
}
|
| Manna, P.K., Skoropata, E., Ting, Y.-W., Lin, K.-W., Freeland, J.W. and van Lierop, J. Interface mixing and its impact on exchange coupling in exchange biased systems JOURNAL OF PHYSICS-CONDENSED MATTER 28, 48 (2016) |
| Abstract: Exchange bias and interlayer exchange coupling are interface driven
phenomena. Since an ideal interface is very challenging to achieve, a clear understanding of the chemical and magnetic natures of interfaces is pivotal to identify their influence on the magnetism. We have chosen Ni80Fe20/CoO(t(CoO))/Co trilayers as a model system, and identified non-stoichiometric Ni-ferrite and Co-ferrite at the surface and interface, respectively. These ferrites, being ferrimagnets typically, should influence the exchange coupling. However, in our trilayers the interface ferrites were found not to be ferro-or ferri-magnetic; thus having no observable influence on the exchange coupling. Our analysis also revealed that (i) interlayer exchange coupling was present between Ni80Fe20 and Co even though the interlayer thickness was significantly larger than expected for this phenomenon to happen, and (ii) the majority of the CoO layer (except some portion near the interface) did not contribute to the observed exchange bias. We also identified that the interlayer exchange coupling and the exchange bias properties were not interdependent. |
BibTeX:
@article{WOS:000385928600001,
author = {Manna, P. K. and Skoropata, E. and Ting, Y-W and Lin, K-W and Freeland, J. W. and van Lierop, J.},
title = {Interface mixing and its impact on exchange coupling in exchange biased systems},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2016},
volume = {28},
number = {48},
doi = {https://doi.org/10.1088/0953-8984/28/48/486004}
}
|
| Joshi, T., Borisov, P. and Lederman, D. The role of defects in the electrical properties of NbO2 thin film vertical devices AIP ADVANCES 6, 12 (2016) |
| Abstract: Epitaxial NbO2 thin films were grown on Si: GaN layers deposited on
Al2O3 substrates using pulsed laser deposition. Pulsed current-voltage (IV) curves and self-sustained current oscillations were measured across a 31 nm NbO2 film and compared with a similar device made from polycrystalline NbO2 film grown on TiN-coated SiO2/Si substrate. Crystal quality of the as grown films was determined from x-ray diffractometry, x-ray photoelectron spectroscopy and atomic force microscopy data. The epitaxial film device was found to be more stable than the defect-rich polycrystalline sample in terms of current switching and oscillation behaviors. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). |
BibTeX:
@article{WOS:000392091500029,
author = {Joshi, Toyanath and Borisov, Pavel and Lederman, David},
title = {The role of defects in the electrical properties of NbO2 thin film vertical devices},
journal = {AIP ADVANCES},
year = {2016},
volume = {6},
number = {12},
doi = {https://doi.org/10.1063/1.4971818}
}
|
| Mohd, A.S., Puetter, S., Mattauch, S., Koutsioubas, A., Schneider, H., Weber, A. and Brueckel, T. A versatile UHV transport and measurement chamber for neutron reflectometry under UHV conditions REVIEW OF SCIENTIFIC INSTRUMENTS 87, 12 (2016) |
| Abstract: We report on a versatile mini ultra-high vacuum (UHV) chamber which is
designed to be used on the MAgnetic Reflectometer with high Incident Angle of the Julich Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum in Garching, Germany. Samples are prepared in the adjacent thin film laboratory by molecular beam epitaxy and moved into the compact chamber for transfer without exposure to ambient air. The chamber is based on DN 40 CF flanges and equipped with sapphire view ports, a small getter pump, and a wobble stick, which serves also as sample holder. Here, we present polarized neutron reflectivity measurements which have been performed on Co thin films at room temperature in UHV and in ambient air in a magnetic field of 200 mT and in the Q-range of 0.18 angstrom(-1). The results confirm that the Co film is not contaminated during the polarized neutron reflectivity measurement. Herewith it is demonstrated that the mini UHV transport chamber also works as a measurement chamber which opens new possibilities for polarized neutron measurements under UHV conditions. Published by AIP Publishing. |
BibTeX:
@article{WOS:000392096800038,
author = {Mohd, A. Syed and Puetter, S. and Mattauch, S. and Koutsioubas, A. and Schneider, H. and Weber, A. and Brueckel, T.},
title = {A versatile UHV transport and measurement chamber for neutron reflectometry under UHV conditions},
journal = {REVIEW OF SCIENTIFIC INSTRUMENTS},
year = {2016},
volume = {87},
number = {12},
doi = {https://doi.org/10.1063/1.4972993}
}
|
| Cao, C., Steinruck, H.-G., Shyam, B., Stone, K.H. and Toney, M.F. In Situ Study of Silicon Electrode Lithiation with X-ray Reflectivity NANO LETTERS 16, 12, pp. 7394-7401 (2016) |
| Abstract: Surface sensitive X-ray reflectivity (XRR) measurements were performed
to investigate the electro-chemical lithiation of a native oxide terminated single crystalline silicon (100) electrode in real time during the first galvanostatic discharge cycle. This allows us to gain nanoscale, mechanistic insight into the lithiation of Si and the formation of the solid electrolyte interphase (SEI). We describe an electrochemistry cell specifically designed for in situ XRR studies and have determined the evolution of the electron density profile of the lithiated Si layer (LixSi) and the SEI layer with subnanometer resolution. We propose a three stage lithiation mechanism with a reaction limited, layer-by layer lithiation of the Si at the LixSi/Si interface. |
BibTeX:
@article{WOS:000389963200013,
author = {Cao, Chuntian and Steinruck, Hans-Georg and Shyam, Badri and Stone, Kevin H. and Toney, Michael F.},
title = {In Situ Study of Silicon Electrode Lithiation with X-ray Reflectivity},
journal = {NANO LETTERS},
year = {2016},
volume = {16},
number = {12},
pages = {7394-7401},
doi = {https://doi.org/10.1021/acs.nanolett.6b02926}
}
|
| Nedelkoski, Z., Kuerbanjiang, B., Glover, S.E., Sanchez, A.M., Kepaptsoglou, D., Ghasemi, A., Burrows, C.W., Yamada, S., Hamaya, K., Ramasse, Q.M., Hasnip, P.J., Hase, T., Bell, G.R., Hirohata, A. and Lazarov, V.K. Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111) SCIENTIFIC REPORTS 6 (2016) |
| Abstract: Halfmetal-semiconductor interfaces are crucial for hybrid spintronic
devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow similar to 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors. |
BibTeX:
@article{WOS:000388163700001,
author = {Nedelkoski, Zlatko and Kuerbanjiang, Balati and Glover, Stephanie E. and Sanchez, Ana M. and Kepaptsoglou, Demie and Ghasemi, Arsham and Burrows, Christopher W. and Yamada, Shinya and Hamaya, Kohei and Ramasse, Quentin M. and Hasnip, Philip J. and Hase, Thomas and Bell, Gavin R. and Hirohata, Atsufumi and Lazarov, Vlado K.},
title = {Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111)},
journal = {SCIENTIFIC REPORTS},
year = {2016},
volume = {6},
doi = {https://doi.org/10.1038/srep37282}
}
|
| Shi, Y., Stone, K.H., Guan, Z., Monti, M., Cao, C., El Gabaly, F., Chueh, W.C. and Toney, M.F. Surface structure of coherently strained ceria ultrathin films PHYSICAL REVIEW B 94, 20 (2016) |
| Abstract: Cerium oxide, or ceria, is an important material for solid oxide fuel
cells and water splitting devices. Although the ceria surface is active in catalytic and electrochemical reactions, how its catalytic properties are affected by the surface structure under operating conditions is far from understood. We investigate the structure of the coherently strained CeO2 ultrathin films on yttria-stabilized zirconia (001) single crystals by specular synchrotron x-ray diffraction (XRD) under oxidizing conditions as a first step to study the surface structure in situ. An excellent agreement between the experiment data and the model is achieved by using a ``stacks and islands'' model that has a two-component roughness. One component is due to the tiny clusters of nanometer scale in lateral dimensions on each terrace, while the other component is due to slightly different CeO2 thickness that span over hundreds of nanometers on neighboring terraces. We attribute the nonuniform thickness to step depairing during the thin film deposition that is supported by the surface morphology results on the microscopic level. Importantly, our model also shows that the polarity of the ceria surface is removed by a half monolayer surface coverage of oxygen. The successful resolution of the ceria surface structure using in situ specular synchrotron XRD paves the way to study the structural evolution of ceria as a fuel cell electrode under catalytically relevant temperatures and gas pressures. |
BibTeX:
@article{WOS:000387892800010,
author = {Shi, Yezhou and Stone, Kevin H. and Guan, Zixuan and Monti, Matteo and Cao, Chuntian and El Gabaly, Farid and Chueh, William C. and Toney, Michael F.},
title = {Surface structure of coherently strained ceria ultrathin films},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {94},
number = {20},
doi = {https://doi.org/10.1103/PhysRevB.94.205420}
}
|
| Cassidy, A., Jorgensen, M.R.V., Rosu-Finsen, A., Lasne, J., Jorgensen, J.H., Glavic, A., Lauter, V., Iversen, B.B., McCoustra, M.R.S. and Field, D. Dipole-Oriented Molecular Solids Can Undergo a Phase Change and Still Maintain Electrical Polarization JOURNAL OF PHYSICAL CHEMISTRY C 120, 42, pp. 24130-24136 (2016) |
| Abstract: It has recently been demonstrated that nanoscale molecular films can
spontaneously assemble to self-generate intrinsic electric fields that can exceed 10(8) V/m. These electric fields originate from polarization charges in the material that arise because the films self-assemble to orient molecular dipole moments. This has been called the spontelectric effect. Such growth of spontaneously polarized layers of molecular solids has implications for our understanding of how intermolecular interactions dictate the structure of molecular materials used in a range of applications, for example, molecular semiconductors, sensors, and catalysts. Here we present the first in situ structural characterization of a representative spontelectric solid, nitrous oxide. Infrared spectroscopy, temperature-programmed desorption, and neutron reflectivity measurements demonstrate that polarized films of nitrous oxide undergo a structural phase transformation upon heating above 48 K A mean-field model can be used to describe quantitatively the magnitude of the spontaneously generated field as a function of film-growth temperature, and this model also recreates the phase change. This reinforces the spontelectric model as a means of describing long-range dipole-dipole interactions and points to a new type of ordering in molecular thin films. |
BibTeX:
@article{WOS:000386640800025,
author = {Cassidy, Andrew and Jorgensen, Mads R. V. and Rosu-Finsen, Alexander and Lasne, Jerome and Jorgensen, Jakob H. and Glavic, Artur and Lauter, Valeria and Iversen, Bo B. and McCoustra, Martin R. S. and Field, David},
title = {Dipole-Oriented Molecular Solids Can Undergo a Phase Change and Still Maintain Electrical Polarization},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2016},
volume = {120},
number = {42},
pages = {24130-24136},
doi = {https://doi.org/10.1021/acs.jpcc.6b07296}
}
|
| Li, B., Chopdekar, R.V., N'Diaye, A.T., Mehta, A., Byers, J.P., Browning, N.D., Arenholz, E. and Takamura, Y. Tuning interfacial exchange interactions via electronic reconstruction in transition-metal oxide heterostructures APPLIED PHYSICS LETTERS 109, 15 (2016) |
| Abstract: The impact of interfacial electronic reconstruction on the magnetic
characteristics of La0.7Sr0.3CoO3 (LSCO)/La0.7Sr0.3MnO3 (LSMO) heterostructures was investigated as a function of layer thickness using a combination of soft x-ray magnetic spectroscopy and bulk magnetometry. We found that the magnetic properties of the LSCO layers are impacted by two competing electronic interactions occurring at the LSCO/substrate and LSMO/LSCO interfaces. For thin LSCO layers (<5 nm), the heterostructures exist in a highly coupled state where the chemically distinct layers behave as a single magnetic compound with magnetically active Co2+ ions. As the LSCO thickness increases, a high coercivity LSCO layer develops which biases a low coercivity layer, which is composed not only of the LSMO layer but also an interfacial LSCO layer. These results suggest an intriguing route to tune the magnetic properties of transition metal oxide heterostructures through careful control of the interface structure. Published by AIP Publishing. |
BibTeX:
@article{WOS:000386534800028,
author = {Li, Binzhi and Chopdekar, Rajesh V. and N'Diaye, Alpha T. and Mehta, Apurva and Byers, J. Paige and Browning, Nigel D. and Arenholz, Elke and Takamura, Yayoi},
title = {Tuning interfacial exchange interactions via electronic reconstruction in transition-metal oxide heterostructures},
journal = {APPLIED PHYSICS LETTERS},
year = {2016},
volume = {109},
number = {15},
doi = {https://doi.org/10.1063/1.4964407}
}
|
| Ukleev, V., Khassanov, A., Snigireva, I., Konovalov, O. and Vorobiev, A. X-ray scattering characterization of iron oxide nanoparticles Langmuir film on water surface and on a solid substrate THIN SOLID FILMS 616, pp. 43-47 (2016) |
| Abstract: In the present study we compare a structure of a Langmuir film assembled
from magnetic iron oxide nanoparticles on water surface and a structure of the same film after its transfer to a solid substrate by the Langmuir-Schaefer method. In contrast to most of related studies, where different techniques are used to characterize the films before and after the deposition, we use the same combination of X-ray reflectometry and Grazing Incidence Small-Angle X-ray scattering. In both cases - on a liquid and on a solid substrate - the film was identified as a well-ordered monolayer of the nanoparticles laterally organized in a two-dimensional hexagonal lattice. However parameters of the lattice were found to be slightly different depending on the type of the substrate. It is also demonstrated that Langmuir-Schaefer technique is the right way for deposition of such kind of the particles on a solid substrate. (C) 2016 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000389388600007,
author = {Ukleev, V. and Khassanov, A. and Snigireva, I. and Konovalov, O. and Vorobiev, A.},
title = {X-ray scattering characterization of iron oxide nanoparticles Langmuir film on water surface and on a solid substrate},
journal = {THIN SOLID FILMS},
year = {2016},
volume = {616},
pages = {43-47},
doi = {https://doi.org/10.1016/j.tsf.2016.07.060}
}
|
| Fabbris, G., Meyers, D., Okamoto, J., Pelliciari, J., Disa, A.S., Huang, Y., Chen, Z.Y., Wu, W.B., Chen, C.T., Ismail-Beigi, S., Ahn, C.H., Walker, F.J., Huang, D.J., Schmitt, T. and Dean, M.P.M. Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels PHYSICAL REVIEW LETTERS 117, 14 (2016) |
| Abstract: Resonant inelastic x-ray scattering is used to investigate the
electronic origin of orbital polarization in nickelate heterostructures taking LaTiO3 - LaNiO3 - 3 x (LaAlO3), a system with exceptionally large polarization, as a model system. We find that heterostructuring generates only minor changes in the Ni 3d orbital energy levels, contradicting the often-invoked picture in which changes in orbital energy levels generate orbital polarization. Instead, O K-edge x-ray absorption spectroscopy demonstrates that orbital polarization is caused by an anisotropic reconstruction of the oxygen ligand hole states. This provides an explanation for the limited success of theoretical predictions based on tuning orbital energy levels and implies that future theories should focus on anisotropic hybridization as the most effective means to drive large changes in electronic structure and realize novel emergent phenomena. |
BibTeX:
@article{WOS:000385971800012,
author = {Fabbris, G. and Meyers, D. and Okamoto, J. and Pelliciari, J. and Disa, A. S. and Huang, Y. and Chen, Z. -Y. and Wu, W. B. and Chen, C. T. and Ismail-Beigi, S. and Ahn, C. H. and Walker, F. J. and Huang, D. J. and Schmitt, T. and Dean, M. P. M.},
title = {Orbital Engineering in Nickelate Heterostructures Driven by Anisotropic Oxygen Hybridization rather than Orbital Energy Levels},
journal = {PHYSICAL REVIEW LETTERS},
year = {2016},
volume = {117},
number = {14},
doi = {https://doi.org/10.1103/PhysRevLett.117.147401}
}
|
| Jiang, J., Hirano, K. and Sakurai, K. Micro-imaging of buried layers and interfaces in ultrathin films by X-ray reflectivity JOURNAL OF APPLIED PHYSICS 120, 11 (2016) |
| Abstract: X-ray reflectivity is a promising technique for characterizing buried
layers and interfaces in ultrathin films because of its ability to probe the electron density profile along the depth in a non-destructive manner. While routine X-ray reflectivity assumes the in-plane uniformity of the sample to be measured, it is also quite important to see buried inhomogeneous/patterned layers and interfaces. The present paper describes the addition of spatial resolution and imaging capability to an X-ray reflectivity technique to visualize surfaces and buried interfaces. To visualize quite wide viewing area size quickly, the image reconstruction scheme has been employed instead of the scanning of microbeam. Though the mathematics is quite close to X-ray computer tomography, the technique gives the image contrast caused by the difference in reflectivity at each in-plane point in the thin film sample. By choosing a grazing angle, the image gives inhomogeneity of X-ray reflectivity at the specific wavevector transfer. With a collimated monochromatic synchrotron X-ray beam of 0.05mm (H) x 8mm (V), the intensity profiles of X-ray reflection projections have been taken at many different in-plane rotation angles, from 0 degrees to 180 degrees. We have succeeded in visualizing buried layers and interfaces of the 8mm dia area with the spatial resolution of better than 20 mu m. Because of the brilliance of synchrotron radiation, the typical measuring time is shorter than 1min. Three analytical cases have been discussed: (i) imaging of a buried layer and an interface covered by a protection layer, (ii) distinguishing different local parts of different thicknesses in an ultrathin film, and (iii) selective imaging of a specific metal in the thin film form. Published by AIP Publishing. |
BibTeX:
@article{WOS:000384573200022,
author = {Jiang, Jinxing and Hirano, Keiichi and Sakurai, Kenji},
title = {Micro-imaging of buried layers and interfaces in ultrathin films by X-ray reflectivity},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2016},
volume = {120},
number = {11},
doi = {https://doi.org/10.1063/1.4962311}
}
|
| Lee, J. and Park, S. Systematic determination of the thickness of a thin oxide layer on a multilayered structure by using an X-ray reflectivity analysis JOURNAL OF THE KOREAN PHYSICAL SOCIETY 69, 5, pp. 789-792 (2016) |
| Abstract: X-ray reflectometry was used to determine the chemical structure of
oxidized Permalloy films grown at different oxidation times. The oxidation time-dependent thickness, roughness and chemical density of each layer were examined simultaneously using the Parratt formalism. With increasing oxidation time, the Permalloy thickness decreased while forming a new oxide layer. After oxidation for 40 sec, the Permalloy film's thickness remained the same for further oxidation, indicating the formation of an oxidation barrier with a scattering length density much lower than that of the Permalloy. The interfacial roughness between the interface layer and the top protective layer remained the same regardless of the oxidation time. |
BibTeX:
@article{WOS:000384550200016,
author = {Lee, Jisung and Park, Sungkyun},
title = {Systematic determination of the thickness of a thin oxide layer on a multilayered structure by using an X-ray reflectivity analysis},
journal = {JOURNAL OF THE KOREAN PHYSICAL SOCIETY},
year = {2016},
volume = {69},
number = {5},
pages = {789-792},
doi = {https://doi.org/10.3938/jkps.69.789}
}
|
| Ambwani, P., Xu, P., Haugstad, G., Jeong, J.S., Deng, R., Mkhoyan, K.A., Jalan, B. and Leighton, C. Defects, stoichiometry, and electronic transport in SrTiO3-delta epilayers: A high pressure oxygen sputter deposition study JOURNAL OF APPLIED PHYSICS 120, 5 (2016) |
| Abstract: SrTiO3 is not only of enduring interest due to its unique dielectric,
structural, and lattice dynamical properties, but is also the archetypal perovskite oxide semiconductor and a foundational material in oxide heterostructures and electronics. This has naturally focused attention on growth, stoichiometry, and defects in SrTiO3, one exciting recent development being such precisely stoichiometric defect-managed thin films that electron mobilities have finally exceeded bulk crystals. This has been achieved only by molecular beam epitaxy, however (and to a somewhat lesser extent pulsed laser deposition (PLD)), and numerous open questions remain. Here, we present a study of the stoichiometry, defects, and structure in SrTiO3 synthesized by a different method, high pressure oxygen sputtering, relating the results to electronic transport. We find that this form of sputter deposition is also capable of homoepitaxy of precisely stoichiometric SrTiO3, but only provided that substrate and target preparation, temperature, pressure, and deposition rate are carefully controlled. Even under these conditions, oxygen-vacancy-doped heteroepitaxial SrTiO3 films are found to have carrier density, mobility, and conductivity significantly lower than bulk. While surface depletion plays a role, it is argued from particle-induced X-ray emission (PIXE) measurements of trace impurities in commercial sputtering targets that this is also due to deep acceptors such as Fe at 100's of parts-per-million levels. Comparisons of PIXE from SrTiO3 crystals and polycrystalline targets are shown to be of general interest, with clear implications for sputter and PLD deposition of this important material. Published by AIP Publishing. |
BibTeX:
@article{WOS:000383091600045,
author = {Ambwani, P. and Xu, P. and Haugstad, G. and Jeong, J. S. and Deng, R. and Mkhoyan, K. A. and Jalan, B. and Leighton, C.},
title = {Defects, stoichiometry, and electronic transport in SrTiO3-delta epilayers: A high pressure oxygen sputter deposition study},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2016},
volume = {120},
number = {5},
doi = {https://doi.org/10.1063/1.4960343}
}
|
| Wardenga, H.F. and Klein, A. Surface potentials of (111), (110) and (100) oriented CeO2-x thin films APPLIED SURFACE SCIENCE 377, pp. 1-8 (2016) |
| Abstract: Differently oriented CeO2 thin films were prepared by radio frequency
magnetron sputter deposition from a nominally undoped CeO2 target. (111), (110) and (100) oriented films were achieved by deposition onto A1203(0001)/Pt( 111), MgO( 110)/Pt( 110) and SrTiO3:Nb(100) substrates, respectively. Epitaxial growth is verified using X-ray diffraction analysis. The films were analyzed by in situ photoelectron spectroscopy to determine the ionization potential, work function, Fermi level position and Ce3+ concentration at the surface in dependence of crystal orientation, deposition conditions and post-deposition treatment in reducing and oxidizing atmosphere. We observed a very high variation of the work function and ionization potential of more than 2 eV for all surface orientations, while the Fermi level varies by only 0.3 eV within the energy gap. The work function generally decreases with increasing Ce3+ surface concentration but comparatively high Ce3+ concentrations remain even after strongly oxidizing treatments. This is related to the presence of subsurface oxygen vacancies. (C) 2016 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000376819100001,
author = {Wardenga, Hans F. and Klein, Andreas},
title = {Surface potentials of (111), (110) and (100) oriented CeO2-x thin films},
journal = {APPLIED SURFACE SCIENCE},
year = {2016},
volume = {377},
pages = {1-8},
doi = {https://doi.org/10.1016/j.apsusc.2016.03.091}
}
|
| Ingason, A.S., Palsson, G.K., Dahlqvist, M. and Rosen, J. Long-range antiferromagnetic order in epitaxial Mn2GaC thin films from neutron reflectometry PHYSICAL REVIEW B 94, 2 (2016) |
| Abstract: The nature of the magnetic structure in magnetic so-called MAX phases is
a topic of some controversy. Here we present unpolarized neutron-diffraction data between 3.4 and 290.0 K and momentum transfer between Q = 0.0 and 1.1 angstrom(-1), as well as complementary x-ray-diffraction data on epitaxial thin films of the MAX phase material Mn2GaC. This inherently layered material exhibits neutron-diffraction peaks consistent with long-ranged antiferromagnetic order with a periodicity of two structural unit cells. The magnetic structure is present throughout the measured temperature range. The results are in agreement with first-principles calculations of antiferromagnetic structures for this material where the Mn-C-Mn atomic trilayers are found to be ferromagnetically coupled internally but spin flipped or rotated across the Ga layers. The present findings have significant bearing on the discussion regarding the nature of the magnetic structure in magnetic MAX phases. |
BibTeX:
@article{WOS:000379501200005,
author = {Ingason, A. S. and Palsson, G. K. and Dahlqvist, M. and Rosen, J.},
title = {Long-range antiferromagnetic order in epitaxial Mn2GaC thin films from neutron reflectometry},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {94},
number = {2},
doi = {https://doi.org/10.1103/PhysRevB.94.024416}
}
|
| Choquette, A.K., Smith, C.R., Sichel-Tissot, R.J., Moon, E.J., Scafetta, M.D., Di Gennaro, E., Granozio, F.M., Karapetrova, E. and May, S.J. Octahedral rotation patterns in strained EuFeO3 and other Pbnm perovskite films: Implications for hybrid improper ferroelectricity PHYSICAL REVIEW B 94, 2 (2016) |
| Abstract: We report the relationship between epitaxial strain and the
crystallographic orientation of the in-phase rotation axis and A-site displacements in Pbnm-type perovskite films. Synchrotron diffraction measurements of EuFeO3 films under strain states ranging from 2% compressive to 0.9% tensile on cubic or rhombohedral substrates exhibit a combination of a(-)a(+)c(-) and a(+)a(-)c(-) rotational patterns. We compare the EuFeO3 behavior with previously reported experimental and theoretical work on strained Pbnm-type films on nonorthorhombic substrates, as well as additional measurements from LaGaO3, LaFeO3, and Eu0.7Sr0.3MnO3 films on SrTiO3. Compiling the results from various material systems reveals a general strain dependence in which compressive strain strongly favors a(-)a(+)c(-) and a(+)a(-)c(-) rotation patterns and tensile strain weakly favors a(-)a(-)c(+) structures. In contrast, EuFeO3 films grown on Pbnm-type GdScO3 under 2.3% tensile strain take on a uniform a(-)a(+)c(-) rotation pattern imprinted from the substrate, despite strain considerations that favor the a(-)a(-)c(+) pattern. These results point to the use of substrate imprinting as a more robust route than strain for tuning the crystallographic orientations of the octahedral rotations and A-site displacements needed to realize rotation-induced hybrid improper ferroelectricity in oxide heterostructures. |
BibTeX:
@article{WOS:000379702300003,
author = {Choquette, A. K. and Smith, C. R. and Sichel-Tissot, R. J. and Moon, E. J. and Scafetta, M. D. and Di Gennaro, E. and Granozio, F. Miletto and Karapetrova, E. and May, S. J.},
title = {Octahedral rotation patterns in strained EuFeO3 and other Pbnm perovskite films: Implications for hybrid improper ferroelectricity},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {94},
number = {2},
doi = {https://doi.org/10.1103/PhysRevB.94.024105}
}
|
| Tiwari, M.K. and Das, G. An interactive graphical user interface (GUI) for the CATGIXRF program - for microstructural evaluation of thin film and impurity doped surfaces X-RAY SPECTROMETRY 45, 4, pp. 212-219 (2016) |
| Abstract: This paper is a continuation and extension of our earlier work (X-ray
Spectrom. 2010, 39, 127-134, DOI:10.1002/xrs.1215) on the development of a software platform CATGIXRF, as a solution to provide non-destructive evaluation of nanostructured materials. Here, we describe an interactive graphical user interface (GUI) for the CATGIXRF program. The newly developed GUI interface facilitates determination of microstructural parameters on angstrom length scale for the nanostructured thin layered materials using synchrotron as well as laboratory X-ray sources. It allows combined analysis capabilities for both the X-ray reflectivity and grazing incidence X-ray fluorescence (GIXRF) data simultaneously, thus enabling us a greater sensitivity for the determination of microstructural parameters such as thickness, interface mixing, and roughness of a thin film medium with improved accuracies. The utility and various newly added salient features of the GUI-CATGIXRF program are described by providing example calculations as well as by analyzing experimentally a few thin film structures with different surface-interface properties. Copyright (c) 2016 John Wiley & Sons, Ltd. |
BibTeX:
@article{WOS:000378561800005,
author = {Tiwari, M. K. and Das, Gangadhar},
title = {An interactive graphical user interface (GUI) for the CATGIXRF program - for microstructural evaluation of thin film and impurity doped surfaces},
journal = {X-RAY SPECTROMETRY},
year = {2016},
volume = {45},
number = {4},
pages = {212-219},
doi = {https://doi.org/10.1002/xrs.2692}
}
|
| Collins-McIntyre, L.J., Duffy, L.B., Singh, A., Steinke, N.J., Kinane, C.J., Charlton, T.R., Pushp, A., Kellock, A.J., Parkin, S.S.P., Holmes, S.N., Barnes, C.H.W., Van der Laan, G., Langridge, S. and Hesjedal, T. Structural, electronic, and magnetic investigation of magnetic ordering in MBE-grown CrxSb2-xTe3 thin films EPL 115, 2 (2016) |
| Abstract: We report the structural, electronic, and magnetic study of Cr-doped
Sb2Te3 thin films grown by a two-step deposition process using molecular-beam epitaxy (MBE). The samples were investigated using a variety of complementary techniques, namely, x-ray diffraction (XRD), atomic force microscopy, SQUID magnetometry, magneto-transport, and polarized neutron reflectometry (PNR). It is found that the samples retain good crystalline order up to a doping level of x = 0.42 (in CrxSb2-xTe3), above which degradation of the crystal structure is observed by XRD. Fits to the recorded XRD spectra indicate a general reduction in the c-axis lattice parameter as a function of doping, consistent with substitutional doping with an ion of smaller ionic radius. The samples show soft ferromagnetic behavior with the easy axis of magnetization being out-of-plane. The saturation magnetization is dependent on the doping level, and reaches from similar to 2 mu B to almost 3 mu B per Cr ion. The transition temperature (T-c) depends strongly on the Cr concentration and is found to increase with doping concentration. For the highest achievable doping level for phase-pure films of x = 0.42, a T-c of 125K was determined. Electric transport measurements find surface-dominated transport below similar to 10K. The magnetic properties extracted from anomalous Hall effect data are in excellent agreement with the magnetometry data. PNR studies indicate a uniform magnetization profile throughout the film, with no indication of enhanced magnetic order towards the sample surface. open access editor's choice Copyright (C) EPLA, 2016 |
BibTeX:
@article{WOS:000384457900026,
author = {Collins-McIntyre, L. J. and Duffy, L. B. and Singh, A. and Steinke, N. -J. and Kinane, C. J. and Charlton, T. R. and Pushp, A. and Kellock, A. J. and Parkin, S. S. P. and Holmes, S. N. and Barnes, C. H. W. and Van der Laan, G. and Langridge, S. and Hesjedal, T.},
title = {Structural, electronic, and magnetic investigation of magnetic ordering in MBE-grown CrxSb2-xTe3 thin films},
journal = {EPL},
year = {2016},
volume = {115},
number = {2},
doi = {https://doi.org/10.1209/0295-5075/115/27006}
}
|
| Wood, M.H., Browning, K.L., Barker, R.D. and Clarke, S.M. Using Neutron Reflectometry to Discern the Structure of Fibrinogen Adsorption at the Stainless Steel/Aqueous Interface JOURNAL OF PHYSICAL CHEMISTRY B 120, 24, pp. 5405-5416 (2016) |
| Abstract: Neutron reflectometry has been successfully used to study adsorption on
a stainless steel surface by means of depositing a thin steel film on silicon. The, film was characterized using XPS (X-ray photoelectron spectroscopy), TOF-SIMS (time-of-flight secondary ion mass spectrometry), and GIXRD (grazing incidence X-ray diffraction), demonstrating the retention both of the austenitic phase and of the required composition for 316L stainless steel. The adsorption of fibrinogen from a physiologically-relevant solution onto the steel surface was studied using neutron reflectometry and QCM (quartz crystal microbalance) and compared to that on a deposited chromium oxide surface. It was found that the protein forms an irreversibly bound layer at low concentrations, with maximum protein concentration a distance of around 20 A from the surface. Evidence for a further diffuse reversibly-bound layer forming at higher concentrations was also observed. Both the structure of the layer revealed by the neutron reflectometry data and the high water retention predicted by the QCM data suggest that there is a significant extent of protein unfolding upon adsorption. A lower extent of adsorption was seen on the chromium surfaces, although the adsorbed layer structures were similar, suggesting comparable adsorption mechanisms. |
BibTeX:
@article{WOS:000378663600010,
author = {Wood, Mary H. and Browning, Kathryn L. and Barker, Robert D. and Clarke, Stuart M.},
title = {Using Neutron Reflectometry to Discern the Structure of Fibrinogen Adsorption at the Stainless Steel/Aqueous Interface},
journal = {JOURNAL OF PHYSICAL CHEMISTRY B},
year = {2016},
volume = {120},
number = {24},
pages = {5405-5416},
doi = {https://doi.org/10.1021/acs.jpcb.6b02341}
}
|
| Kim, D.H. and Bark, C.W. Structural properties of LaAlO3/SrTiO3 interfaces deposited by using off-axis RF sputtering JOURNAL OF THE KOREAN PHYSICAL SOCIETY 68, 12, pp. 1395-1398 (2016) |
| Abstract: To demonstrate the capability of growing conductive interfaces through
large-scale deposition, we deposited amorphous LaAlO3(LAO)/SrTiO3(STO) by using off-axis RF-sputtering. The LAO/STO thin film deposited within the 2.0-inch range exhibited conducting properties. To confirm the structural properties and ensure accurate characterization of the LAO/STO films prepared by using off-axis sputtering, we performed X-ray reflectivity (XRR) and scanning electron microscopy (SEM) measurements. This paper reports on the structural properties of LAO/STO interfaces and discusses the interfacial quality and layer-to-layer uniformity based on a fitting of the XRR data. In terms of structural properties, the LAO/STO film deposited within the 1.35-inch range had the best surface among all investigated samples. |
BibTeX:
@article{WOS:000378943400004,
author = {Kim, Do Hyun and Bark, Chung Wung},
title = {Structural properties of LaAlO3/SrTiO3 interfaces deposited by using off-axis RF sputtering},
journal = {JOURNAL OF THE KOREAN PHYSICAL SOCIETY},
year = {2016},
volume = {68},
number = {12},
pages = {1395-1398},
doi = {https://doi.org/10.3938/jkps.68.1395}
}
|
| Li, P., Huang, Q., Jiang, L., Li, W., Fei, J., Zhu, J., Zhang, Z. and Wang, Z. Structure and depth profile composition analysis of Cr/(B4C)/V/(B4C) multilayer for water window application VACUUM 128, pp. 85-90 (2016) |
| Abstract: Ultrathin B4C barrier layers have been recently used to reduce the
interface widths of soft X-ray Cr/V multilayers and improve the reflectance at the water window region. To further study the chemical changes in the multilayer induced by the barrier layers, Cr/V multilayers (period equals to 4 nm) with and without B4C barrier layers were characterized by grazing incidence X-ray reflectometry (GIXR) and X-ray photoelectron spectroscopy (XPS). The GIXR results show that the B4C barrier layers significantly reduce the interface widths of the 4 nm-period Cr/V multilayer as already observed for the short-period multilayer. The XPS depth profile confirms an enhanced elemental contrast between Cr and V in the multilayer with B4C, as compared to the one with no barriers. According to the fitting results of the photoelectron peaks, the compound formation of VB2, extra VC and B4C were found in the structure with barrier layers. These compounds help suppress the interdiffusion between Cr and V and contribute to the small interface widths of the multilayer. (C) 2016 Elsevier Ltd. All rights reserved. |
BibTeX:
@article{WOS:000376052500012,
author = {Li, Pin and Huang, Qiushi and Jiang, Li and Li, Wenbin and Fei, Jiani and Zhu, Jie and Zhang, Zhong and Wang, Zhanshan},
title = {Structure and depth profile composition analysis of Cr/(B4C)/V/(B4C) multilayer for water window application},
journal = {VACUUM},
year = {2016},
volume = {128},
pages = {85-90},
doi = {https://doi.org/10.1016/j.vacuum.2016.02.014}
}
|
| Krick, A.L., Lee, C.-W., Sichel-Tissot, R.J., Rappe, A.M. and May, S.J. Interplay between Cation and Charge Ordering in La1/3Sr2/3FeO3 Superlattices ADVANCED ELECTRONIC MATERIALS 2, 6 (2016) |
| Abstract: The electronic properties of digital superlattices are reported, which
are cation-ordered analogs of the perovskite La1/3Sr2/3FeO3, a material that undergoes a charge-ordering transition. Superlattices of LaFeO3 (LFO), an antiferromagnetic insulator, and SrFeO3 (SFO), a conductor with a helical magnetic ground state, are fabricated via oxide molecular beam epitaxy. Three isocompositional superlattices with repeat structures of SSLSSL (S2), SSSLSL (S3), and SSSSLL (S4) (S = SFO, L = LFO) are studied with cation orderings along the [001] and [111] directions for experimental and computational work, respectively. The experimental superlattice structures are confirmed via synchrotron X-ray diffraction and corresponding simulations of (00 L) crystal truncation rods. The S2 and S3 superlattices are found to undergo an electronic phase transition as measured by a discontinuity in the temperature-dependent resistivity similar to the random alloy, indicating that the superlattices do not behave as a simple combination of LFO and SFO. The charge-ordering transition is not observed in the S4 sample. The electronic structure calculations using density functional theory, confirming the energetic favorability of charge ordering in the S2 and S3 structures compared to the S4 structure, are consistent with experimental trends. |
BibTeX:
@article{WOS:000379912100009,
author = {Krick, Alex L. and Lee, Chan-Woo and Sichel-Tissot, Rebecca J. and Rappe, Andrew M. and May, Steven J.},
title = {Interplay between Cation and Charge Ordering in La1/3Sr2/3FeO3 Superlattices},
journal = {ADVANCED ELECTRONIC MATERIALS},
year = {2016},
volume = {2},
number = {6},
doi = {https://doi.org/10.1002/aelm.201500372}
}
|
| Maruyama, R., Bigault, T., Wildes, A.R., Dewhurst, C.D., Soyama, K. and Courtois, P. Study of the in-plane magnetic structure of a layered system using polarized neutron scattering under grazing incidence geometry NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 819, pp. 37-53 (2016) |
| Abstract: The in-plane magnetic structure of a layered system with a
polycrystalline grain size less than the ferromagnetic exchange length was investigated using polarized neutron off-specular scattering and grazing incidence small angle scattering measurements to gain insight into the mechanism that controls the magnetic properties which are different from the bulk. These complementary measurements with different length scales and the data analysis based on the distorted wave Born approximation revealed the lateral correlation on a length scale of sub-mu m due to the fluctuating orientation of the magnetization in the layer. The obtained in-plane magnetic structure is consistent with the random anisotropy model, i.e. competition between the exchange interactions between neighboring spins and the local magnetocrystalline anisotropy. (C) 2016 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000372318800007,
author = {Maruyama, R. and Bigault, T. and Wildes, A. R. and Dewhurst, C. D. and Soyama, K. and Courtois, P.},
title = {Study of the in-plane magnetic structure of a layered system using polarized neutron scattering under grazing incidence geometry},
journal = {NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT},
year = {2016},
volume = {819},
pages = {37-53},
doi = {https://doi.org/10.1016/j.nima.2016.02.059}
}
|
| Sen, K., Perret, E., Alberca, A., Uribe-Laverde, M.A., Marozau, I., Yazdi-Rizi, M., Mallett, B.P.P., Marsik, P., Piamonteze, C., Khaydukov, Y., Doebeli, M., Keller, T., Biskup, N., Varela, M., Vasatko, J., Munzar, D. and Bernhard, C. X-ray absorption study of the ferromagnetic Cu moment at the YBa2Cu3O7/La2/3Ca1/3MnO3 interface and variation of its exchange interaction with the Mn moment PHYSICAL REVIEW B 93, 20 (2016) |
| Abstract: With x-ray absorption spectroscopy and polarized neutron reflectometry
we studied how the magnetic proximity effect at the interface between the cuprate high-T-C superconductor YBa2Cu3O7 (YBCO) and the ferromagnet La2/3Ca1/3MnO3 (LCMO) is related to the electronic and magnetic properties of the LCMO layers. In particular, we explored how the magnitude of the ferromagnetic Cu moment on the YBCO side depends on the strength of the antiferromagnetic (AF) exchange coupling with the Mn moment on the LCMO side. We found that the Cu moment remains sizable if the AF coupling with the Mn moments is strongly reduced or even entirely suppressed. The ferromagnetic order of the Cu moments thus seems to be intrinsic to the interfacial CuO2 planes and related to a weakly ferromagnetic intraplanar exchange interaction. The latter is discussed in terms of the partial occupation of the Cu 3d(3z2)-r(2) orbitals, which occurs in the context of the so-called orbital reconstruction of the interfacial Cu ions. |
BibTeX:
@article{WOS:000376250800004,
author = {Sen, K. and Perret, E. and Alberca, A. and Uribe-Laverde, M. A. and Marozau, I. and Yazdi-Rizi, M. and Mallett, B. P. P. and Marsik, P. and Piamonteze, C. and Khaydukov, Y. and Doebeli, M. and Keller, T. and Biskup, N. and Varela, M. and Vasatko, J. and Munzar, D. and Bernhard, C.},
title = {X-ray absorption study of the ferromagnetic Cu moment at the YBa2Cu3O7/La2/3Ca1/3MnO3 interface and variation of its exchange interaction with the Mn moment},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {93},
number = {20},
doi = {https://doi.org/10.1103/PhysRevB.93.205131}
}
|
| Fornari, C.I., Rappl, P.H.O., Morelhao, S.L. and Abramof, E. Structural properties of Bi2Te3 topological insulator thin films grown by molecular beam epitaxy on (111) BaF2 substrates JOURNAL OF APPLIED PHYSICS 119, 16 (2016) |
| Abstract: Structural properties of topological insulator bismuth telluride films
grown epitaxially on (111) BaF2 with a fixed Bi2Te3 beam flux were systematically investigated as a function of substrate temperature and additional Te flux. A layer-by-layer growth mode is observed since the early stages of epitaxy and remains throughout the whole deposition. Composition of the epitaxial films produced here stays between Bi2Te3 and Bi4Te5, as determined from the comparison of the measured x-ray diffraction curves with calculations. The substrate temperature region, where the growth rate remains constant, is found to be the most appropriate to obtain ordered Bi2Te3 films. Line width of the L = 18 Bi2Te3 diffraction peaks as low as 140 arcsec was obtained, indicating high crystalline quality. Twinning domains density rises with increasing growth temperature and reducing Te extra flux. X-ray reflectivity curves of pure Bi2Te3 films with thickness from 165 to 8 nm exhibited well defined interference fringes, evidencing homogeneous layers with smooth surface. Our results demonstrate that Bi2Te3 films with very well controlled structural parameters can be obtained. High structural quality Bi2Te3 films as thin as only eight quintuple layers grown here are promising candidates for intrinsic topological insulator. Published by AIP Publishing. |
BibTeX:
@article{WOS:000375929900037,
author = {Fornari, Celso I. and Rappl, Paulo H. O. and Morelhao, Sergio L. and Abramof, Eduardo},
title = {Structural properties of Bi2Te3 topological insulator thin films grown by molecular beam epitaxy on (111) BaF2 substrates},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2016},
volume = {119},
number = {16},
doi = {https://doi.org/10.1063/1.4947266}
}
|
| Glavic, A., Dixit, H., Cooper, V.R. and Aczel, A.A. Constructing a magnetic handle for antiferromagnetic manganites PHYSICAL REVIEW B 93, 14 (2016) |
| Abstract: An intrinsic property of antiferromagnetic materials is the compensation
of the magnetic moments from the individual atoms that prohibits the direct interaction of the spin lattice with an external magnetic field. To overcome this limitation we have created artificial spin structures by heteroepitaxy between two bulk antiferromagnets SrMnO3 and NdMnO3. Here, we demonstrate that charge transfer at the interface results in the creation of thin ferromagnetic layers adjacent to A-type antiferromagnetism in thick NdMnO3 layers. A novel interference based neutron diffraction technique and polarized neutron reflectometry are used to confirm the presence of ferromagnetism in the SrMnO3 layers and to probe the relative alignment of antiferromagnetic spins induced by the coupling at the ferro-to antiferromagnet interface. A density functional theory analysis of the driving forces for the exchange reveals strong ferromagnetic interfacial coupling through quantifiable short range charge transfer. These results confirm a layer-by-layer control of magnetic arrangements that constitutes a promising step on a path towards isothermal magnetic control of antiferromagnetic arrangements as would be necessary in spin-based heterostructures like multiferroic devices. |
BibTeX:
@article{WOS:000374945100001,
author = {Glavic, Artur and Dixit, Hemant and Cooper, Valentino R. and Aczel, Adam A.},
title = {Constructing a magnetic handle for antiferromagnetic manganites},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {93},
number = {14},
doi = {https://doi.org/10.1103/PhysRevB.93.140413}
}
|
| Moubah, R., Magnus, F., Warnatz, T., Palsson, G.K., Kapaklis, V., Ukleev, V., Devishvili, A., Palisaitis, J., Persson, P.O.A. and Hjorvarsson, B. Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices PHYSICAL REVIEW APPLIED 5, 4 (2016) |
| Abstract: We report on a discrete layer-by-layer magnetic switching in Fe/MgO
superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90 degrees and 180 degrees periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe/MgO/Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices. |
BibTeX:
@article{WOS:000374562100001,
author = {Moubah, R. and Magnus, F. and Warnatz, T. and Palsson, G. K. and Kapaklis, V. and Ukleev, V. and Devishvili, A. and Palisaitis, J. and Persson, P. O. A. and Hjorvarsson, B.},
title = {Discrete Layer-by-Layer Magnetic Switching in Fe/MgO(001) Superlattices},
journal = {PHYSICAL REVIEW APPLIED},
year = {2016},
volume = {5},
number = {4},
doi = {https://doi.org/10.1103/PhysRevApplied.5.044011}
}
|
| Wasala, M., Zhang, J., Ghosh, S., Muchharla, B., Malecek, R., Mazumdar, D., Samassekou, H., Gaither-Ganim, M., Morrison, A., Lopez, N.-P., Carozo, V., Lin, Z., Terrones, M. and Talapatra, S. Effect of underlying boron nitride thickness on photocurrent response in molybdenum disulfide - boron nitride heterostructures JOURNAL OF MATERIALS RESEARCH 31, 7, pp. 893-899 (2016) |
| Abstract: Here we report on the photocurrent response of two-dimensional (2D)
heterostructures of sputtered MoS2 on boron nitride (BN) deposited on (001)-oriented Si substrates. The steady state photocurrent (I-ph) measurements used a continuous laser of lambda = 658 nm (E = 1.88 eV) over a broad range of laser intensities, P (similar to 1 mu W < P < 10 mu W), and indicate that I-ph obtained from MoS2 layers with the 80 nm BN under layer was similar to 4 times higher than that obtained from MoS2 layers with the 30 nm BN under layer. We also found super linear dependence of I-ph on P (Iph proportional to P-gamma, with gamma > 1) in both the samples. The responsivities obtained over the range of laser intensity studied were in the order of mA/W (similar to 12 and similar to 2.7 mA/W with 80 nm BN and 30 nm BN under layers, respectively). These investigations provide crucial insight into the optical activity of MoS2 on BN, which could be useful for developing a variety of optoelectronic applications with MoS2 or other 2D transition metal dichalcogenide heterostructures. |
BibTeX:
@article{WOS:000376178400007,
author = {Wasala, Milinda and Zhang, Jie and Ghosh, Sujoy and Muchharla, Baleeswaraiah and Malecek, Rachel and Mazumdar, Dipanjan and Samassekou, Hassana and Gaither-Ganim, Moses and Morrison, Andrew and Lopez, Nestor-Perera and Carozo, Victor and Lin, Zhong and Terrones, Mauricio and Talapatra, Saikat},
title = {Effect of underlying boron nitride thickness on photocurrent response in molybdenum disulfide - boron nitride heterostructures},
journal = {JOURNAL OF MATERIALS RESEARCH},
year = {2016},
volume = {31},
number = {7},
pages = {893-899},
doi = {https://doi.org/10.1557/jmr.2015.364}
}
|
| Wakabayashi, Y., Fujii, H., Kimura, T., Sakata, O., Tajiri, H., Koyama, T. and Chiba, D. Confirmation of no Structural and Chemical Changes in Curie Temperature Variable Co Ultrathin Films by Electric Field ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS 230, 4, SI, pp. 569-575 (2016) |
| Abstract: A cobalt ultrathin film, which shows a large change in Curie temperature
by an electric field application, has been studied by x-ray reflectometry with applying electric fields. The cobalt film was made by the sputtering method on top of a Pt buffer layer, and capped with a MgO layer. X-ray reflectometry shows that the change in Co thickness caused by the applied voltage up to +/- 10 V was less than 0.06 angstrom. The reflectivity signal intensity shows a characteristic kink at the Co K-absorption edge. The spectrum does not show any change with applying voltage. As a result, electric field effects on the structure and chemical states of Co in the Co ultrathin film were found to be minor. |
BibTeX:
@article{WOS:000372615700011,
author = {Wakabayashi, Yusuke and Fujii, Hiromasa and Kimura, Tsuyoshi and Sakata, Osami and Tajiri, Hiroo and Koyama, Tomohiro and Chiba, Daichi},
title = {Confirmation of no Structural and Chemical Changes in Curie Temperature Variable Co Ultrathin Films by Electric Field},
journal = {ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS},
year = {2016},
volume = {230},
number = {4, SI},
pages = {569-575},
doi = {https://doi.org/10.1515/zpch-2015-0648}
}
|
| Kumah, D.P., Dogan, M., Ngai, J.H., Qiu, D., Zhang, Z., Su, D., Specht, E.D., Ismail-Beigi, S., Ahn, C.H. and Walker, F.J. Engineered Unique Elastic Modes at a BaTiO3/(2 x 1)-G(001) Interface PHYSICAL REVIEW LETTERS 116, 10 (2016) |
| Abstract: The strong interaction at an interface between a substrate and thin film
leads to epitaxy and provides a means of inducing structural changes in the epitaxial film. These induced material phases often exhibit technologically relevant electronic, magnetic, and functional properties. The 2 x 1 surface of a Ge(001) substrate applies a unique type of epitaxial constraint on thin films of the perovskite oxide BaTiO3 where a change in bonding and symmetry at the interface leads to a non-bulk-like crystal structure of the BaTiO3. While the complex crystal structure is predicted using first-principles theory, it is further shown that the details of the structure are a consequence of hidden phases found in the bulk elastic response of the BaTiO3 induced by the symmetry of forces exerted by the germanium substrate. |
BibTeX:
@article{WOS:000371721200003,
author = {Kumah, D. P. and Dogan, M. and Ngai, J. H. and Qiu, D. and Zhang, Z. and Su, D. and Specht, E. D. and Ismail-Beigi, S. and Ahn, C. H. and Walker, F. J.},
title = {Engineered Unique Elastic Modes at a BaTiO3/(2 x 1)-G(001) Interface},
journal = {PHYSICAL REVIEW LETTERS},
year = {2016},
volume = {116},
number = {10},
doi = {https://doi.org/10.1103/PhysRevLett.116.106101}
}
|
| Jia, Y., Chopdekar, R.V., Arenholz, E., Liu, Z., Biegalski, M.D., Porter, Z.D., Mehta, A. and Takamura, Y. Thickness dependence of exchange coupling in (111)-oriented perovskite oxide superlattices PHYSICAL REVIEW B 93, 10 (2016) |
| Abstract: Epitaxial La0.7Sr0.3MnO3 (LSMO)/La0.7Sr0.3FeO3 (LSFO) superlattices on
(111)-oriented SrTiO3 substrates with sublayer thicknesses ranging from 3 to 60 unit cells (u.c.) were synthesized and characterized. Detailed analysis of their structural, electronic, and magnetic properties were performed to explore the effect of sublayer thickness on the magnetic structure and exchange coupling at (111)-oriented perovskite oxide interfaces. In the ultrathin limit (3-6 u.c.), we find that the antiferromagnetic (AF) properties of the LSFO sublayers are preserved with an out-of-plane canting of the AF spin axis, while the ferromagnetic (FM) properties of the LSMO sublayers are significantly depressed. For thicker LSFO layers (>9 u.c.), the out-of-plane canting of the AF spin axis is only present in superlattices with thick LSMO sublayers. As a result, exchange coupling in the form of spin-flop coupling exists only in superlattices which display both robust ferromagnetism and out-of-plane canting of the AF spin axis. |
BibTeX:
@article{WOS:000371400100003,
author = {Jia, Yue and Chopdekar, Rajesh V. and Arenholz, Elke and Liu, Zhiqi and Biegalski, Michael D. and Porter, Zachary D. and Mehta, Apurva and Takamura, Yayoi},
title = {Thickness dependence of exchange coupling in (111)-oriented perovskite oxide superlattices},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {93},
number = {10},
doi = {https://doi.org/10.1103/PhysRevB.93.104403}
}
|
| Siva, V., Pradhan, P.C., Babu, G.S., Nayak, M., Sahoo, P.K. and Senapati, K. Superconducting proximity effect in NiBi3-Ni-NiBi3 trilayer system with sharp superconductor-ferromagnet boundaries JOURNAL OF APPLIED PHYSICS 119, 6 (2016) |
| Abstract: We have studied the superconducting proximity effect in a series of
e-beam evaporated Bi-Ni-Bi trilayers, where diffusion of Bi into Ni spontaneously formed superconducting NiBi3 layers at both Ni-Bi interfaces, effectively resulting in superconductor-ferromagnet-superconductor (S-F-S) trilayers. The thickness of top and bottom superconducting layers was found to be different with slightly different transition temperatures. Both resistive transition temperatures in the series of S-F-S trilayers showed 0-pi crossover as a function of ferromagnetic Ni thickness. The zero bias conductance calculated from the in-plane current-voltage measurements also confirmed the 0-pi crossovers. The possibility of proximity effect in the superconducting fluctuation regime, above transition temperature, was investigated via in-plane magneto-transport measurements at 4 K. We observed clear modulations in magneto-resistance (MR) and in low-field MR-hysteresis at 4 K, in contrast to their monotonic behavior at 10 K. Although the period of these modulations was commensurate with the observed periodicity of 0-pi crossovers, the nature of these modulations was found to be the same in both 0 and pi regimes. This observation suggested that in the superconducting fluctuation regime the apparent modulations of MR and MR-hysteresis were due to the variations in densities of superconducting fluctuations in individual NiBi3 layers, and not due to the proximity coupling between the superconducting layers. (C) 2016 AIP Publishing LLC. |
BibTeX:
@article{WOS:000370974200005,
author = {Siva, Vantari and Pradhan, Paresh C. and Babu, G. Santosh and Nayak, Maheswar and Sahoo, Pratap K. and Senapati, Kartik},
title = {Superconducting proximity effect in NiBi3-Ni-NiBi3 trilayer system with sharp superconductor-ferromagnet boundaries},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2016},
volume = {119},
number = {6},
doi = {https://doi.org/10.1063/1.4941726}
}
|
| Zheng, Y., Cheng, Y., Zhu, M., Ji, X., Wang, Q., Song, S., Song, Z., Liu, W. and Feng, S. A candidate Zr-doped Sb2Te alloy for phase change memory application APPLIED PHYSICS LETTERS 108, 5 (2016) |
| Abstract: Here, Zr-doped Sb2Te alloy is proposed for phase change memory (PCM).
Zr-doping enhances the crystallization temperature and thermal stability of Sb2Te alloy effectively. Crystalline Zr-2(Sb2Te)(98) film is manifested as a single phase without phase separation and the growth of crystal grain is dramatically suppressed. The density change of Zr-2(Sb2Te)(98) material between amorphous and crystalline is similar to 2.65 +/- 0.03%, which is much smaller than that of Ge2Sb2Te5 (6.5%). Phase change memory cells based on Zr-2(Sb2Te)(98) material can be reversibly switched by applying 40-400 ns width voltage pulses, and the reset current is relatively small when comparing with the prototypical Ge2Sb2Sb5 material. The resistance ON-OFF ratio of about 1.3 orders of magnitude is enough for figuring ``0'' and ``1'' out. Besides, endurance up to 4.1 x 10(4) cycles makes Zr-doped Sb2Te alloy a potential candidate for PCM. (C) 2016 AIP Publishing LLC. |
BibTeX:
@article{WOS:000373055700038,
author = {Zheng, Yonghui and Cheng, Yan and Zhu, Min and Ji, Xinglong and Wang, Qing and Song, Sannian and Song, Zhitang and Liu, Weili and Feng, Songlin},
title = {A candidate Zr-doped Sb2Te alloy for phase change memory application},
journal = {APPLIED PHYSICS LETTERS},
year = {2016},
volume = {108},
number = {5},
doi = {https://doi.org/10.1063/1.4941418}
}
|
| Gerelli, Y. Aurore: new software for neutron reflectivity data analysis JOURNAL OF APPLIED CRYSTALLOGRAPHY 49, 1, pp. 330-339 (2016) |
| Abstract: Aurore is a free software application based on MATLAB scripts designed
for the graphical analysis, inspection and simulation of neutron reflectivity data. Its architecture, combined with graphics and other advantages of the MATLAB environment, should allow continued development of this software and inclusion of new features and analysis methods. The development of the software was driven by the necessity for a non-commercial open-source application for the analysis of neutron reflectivity data. Aurore provides a robust and reliable method for evaluation of parameter uncertainty, a feature almost absent in similar software applications. In the present paper the main functionalities of the software are presented, together with a comprehensive description of the modeling approaches available at the moment. The code is released under a Creative Commons Attribution Non-Commercial License V2.0. The software application can be downloaded at http://aurorenr.sourceforge.net/. |
BibTeX:
@article{WOS:000369389300038,
author = {Gerelli, Yuri},
title = {Aurore: new software for neutron reflectivity data analysis},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2016},
volume = {49},
number = {1},
pages = {330-339},
doi = {https://doi.org/10.1107/S1600576716000108}
}
|
| Kinane, C.J., Kirichek, O., Charlton, T.R. and McClintock, P.V.E. Influence of the liquid helium meniscus on neutron reflectometry data LOW TEMPERATURE PHYSICS 42, 2, pp. 152-155 (2016) |
| Abstract: Neutron reflectometry offers a unique opportunity for the direct
observation of nanostratification in He-3-He-4 mixtures in the ultra-low temperature limit. Unfortunately the results of recent experiments could not be well-modelled on account of a seemingly anomalous variation of reflectivity with momentum transfer. We now hypothesize that this effect is attributable to an optical distortion caused by the liquid's meniscus near the container wall. The validity of this idea is tested and confirmed through a subsidiary experiment on a D2O sample, showing that the meniscus can significantly distort results if the beam size in the horizontal plane is comparable with, or bigger than, the diameter of the container. The meniscus problem can be eliminated if the beam size is substantially smaller than the diameter of the container, such that reflection takes place only from the flat region of the liquid surface thus excluding the meniscus tails. Practical measures for minimizing the meniscus distortion effect are discussed. (C) 2016 Author(s). |
BibTeX:
@article{WOS:000390593300014,
author = {Kinane, C. J. and Kirichek, O. and Charlton, T. R. and McClintock, P. V. E.},
title = {Influence of the liquid helium meniscus on neutron reflectometry data},
journal = {LOW TEMPERATURE PHYSICS},
year = {2016},
volume = {42},
number = {2},
pages = {152-155},
doi = {https://doi.org/10.1063/1.4941005}
}
|
| Azzawi, S., Ganguly, A., Tokac, M., Rowan-Robinson, R.M., Sinha, J., Hindmarch, A.T., Barman, A. and Atkinson, D. Evolution of damping in ferromagnetic/nonmagnetic thin film bilayers as a function of nonmagnetic layer thickness PHYSICAL REVIEW B 93, 5 (2016) |
| Abstract: The evolution of damping in Co/Pt, Co/Au, and Ni81Fe19/Pt bilayers was
studied with increasing nonmagnetic (NM) heavy-metal layer thicknesses in the range 0.2 nm <= t(NM) <= 10 nm, where t(NM) is the NM layer thickness. Magnetization precession was measured in the time domain using time-resolved magneto-optical Kerr effect magnetometry. Fitting of the data with a damped sinusoidal function was undertaken in order to extract the phenomenological Gilbert damping coefficient a. For Pt-capped Co and Ni81Fe19 layers a large and complex dependence of a on the Pt layer thickness was observed, while for Au capping no significant dependence was observed. It is suggested that this difference is related to the different localized spin-orbit interaction related to intermixing and to alpha hybridization of Pt and Au at the interface with Co or Ni81Fe19. Also it was shown that damping is affected by the crystal structure differences in FM thin films and at the interface, which can modify the spin-diffusion length and the effective spin-mixing conductance. In addition to the intrinsic damping an extrinsic contribution plays an important role in the enhancement of damping when the Pt capping layer is discontinuous. The dependence of damping on the nonmagnetic layer thickness is complex but shows qualitative agreement with recent theoretical predictions. |
BibTeX:
@article{WOS:000369390100006,
author = {Azzawi, S. and Ganguly, A. and Tokac, M. and Rowan-Robinson, R. M. and Sinha, J. and Hindmarch, A. T. and Barman, A. and Atkinson, D.},
title = {Evolution of damping in ferromagnetic/nonmagnetic thin film bilayers as a function of nonmagnetic layer thickness},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {93},
number = {5},
doi = {https://doi.org/10.1103/PhysRevB.93.054402}
}
|
| Davy, N.C., Man, G., Kerner, R.A., Fusella, M.A., Purdum, G.E., Sezen, M., Rand, B.P., Kahn, A. and Loo, Y.-L. Contorted Hexabenzocoronenes with Extended Heterocyclic Moieties Improve Visible-Light Absorption and Performance in Organic Solar Cells CHEMISTRY OF MATERIALS 28, 2, pp. 673-681 (2016) |
| Abstract: The large band gaps of existing contorted hexabenzocoronene derivatives
severely limit visible-light absorption, restricting the photocurrents generated by solar cells utilizing contorted hexabenzocoronene (cHBC). To decrease the band gap and improve the light-harvesting properties, we synthesized cHBC derivatives having extended heterocyclic moieties as peripheral substituents. Tetrabenzofuranyldibenzocoronene (cTBFDBC) and tetrabenzothienodibenzocoronene (cTBTDBC) both exhibit broader absorption of the solar spectrum compared to cHBC, with peak absorbances on the order of 10(5) cm(-1) in the near-ultraviolet and in the visible. Planar-heterojunction organic solar cells comprising cTBFDBC or cTBTDBC as the donor and C-70 as the acceptor surpass those having cHBC in photocurrent generation and power-conversion efficiency. Interestingly, devices containing cTBFDBC/C-70 exhibit the highest photocurrents despite cTBTDBC having the smallest band gap of the three cHBC derivatives. X-ray reflectivity of the active layers indicates a rougher donor-acceptor interface when cTBFDBC is employed instead of the other two donors. Consistent with this observation, internal quantum efficiency spectra suggest improved charge transfer at the donor acceptor interface when cTBFDBC-as opposed to cTBTDBC or cHBC-is used as the donor. |
BibTeX:
@article{WOS:000368949900035,
author = {Davy, Nicholas C. and Man, Gabriel and Kerner, Ross A. and Fusella, Michael A. and Purdum, Geoffrey E. and Sezen, Melda and Rand, Barry P. and Kahn, Antoine and Loo, Yueh-Lin},
title = {Contorted Hexabenzocoronenes with Extended Heterocyclic Moieties Improve Visible-Light Absorption and Performance in Organic Solar Cells},
journal = {CHEMISTRY OF MATERIALS},
year = {2016},
volume = {28},
number = {2},
pages = {673-681},
doi = {https://doi.org/10.1021/acs.chemmater.5b04503}
}
|
| Yazdi, M.B., Major, M., Wildes, A., Wilhelm, F., Rogalev, A., Donner, W. and Alff, L. Possible evidence for a spin-state crossover in the Verwey state in Fe3O4 thin films PHYSICAL REVIEW B 93, 1 (2016) |
| Abstract: In epitaxial thin films of magnetite a large change in magnetization
across the Verwey transition has been observed. In the Verwey state, the sample magnetization appeared to be strongly reduced, in some samples even close to zero. Using superconducting quantum interference magnetometry, x-ray absorption near edge spectroscopy, and polarized neutron reflectometry, a simple rotation of the magnetization vector due to a change in magnetocrystalline anisotropy was excluded. The experimental data rather suggest an intrinsic loss of magnetic moment due to a possible transition into a low or intermediate spin state of Fe2+. This observation discloses a different aspect of the Verwey transition. |
BibTeX:
@article{WOS:000369216200001,
author = {Yazdi, Mehrdad Baghaie and Major, Marton and Wildes, Andrew and Wilhelm, Fabrice and Rogalev, Andrei and Donner, Wolfgang and Alff, Lambert},
title = {Possible evidence for a spin-state crossover in the Verwey state in Fe3O4 thin films},
journal = {PHYSICAL REVIEW B},
year = {2016},
volume = {93},
number = {1},
doi = {https://doi.org/10.1103/PhysRevB.93.014439}
}
|
| Smolin, S.Y., Scafetta, M.D., Choquette, A.K., Sfeir, M.Y., Baxter, J.B. and May, S.J. Static and Dynamic Optical Properties of La1-xSrxFeO3-delta: The Effects of A-Site and Oxygen Stoichiometry CHEMISTRY OF MATERIALS 28, 1, pp. 97-105 (2016) |
| Abstract: Perovskite oxides are a promising material class for photovoltaic and
photocatalytic applications due to their visible band gaps, nanosecond recombination lifetimes, and great chemical diversity. However, there is limited understanding of the link between composition and static and dynamic optical properties, despite the critical role these properties play in the design of light-harvesting devices. To clarify these relationships, we systemically studied the optoelectronic properties in La1-xSrxFeO3-delta epitaxial films, uncovering the effects of A-site cation substitution and oxygen stoichiometry. Variable-angle spectroscopic ellipsometry was used to measure static optical properties, revealing a linear increase in absorption coefficient at 1.25 eV and a red-shifting of the optical absorption edge with increasing Sr fraction. The absorption spectra can be similarly tuned through the introduction of oxygen vacancies, indicating the critical role that nominal Fe valence plays in optical absorption. Dynamic optoelectronic properties were studied with ultrafast transient reflectance spectroscopy, revealing similar nanosecond photoexcited carrier lifetimes for oxygen deficient and stoichiometric films with the same nominal Fe valence. These results demonstrate that while the static optical absorption is strongly dependent on nominal Fe valence tuned through cation or anion stoichiometry, oxygen vacancies do not appear to play a significantly detrimental role in the recombination kinetics. |
BibTeX:
@article{WOS:000368322600015,
author = {Smolin, Sergey Y. and Scafetta, Mark D. and Choquette, Amber K. and Sfeir, Matthew Y. and Baxter, Jason B. and May, Steven J.},
title = {Static and Dynamic Optical Properties of La1-xSrxFeO3-delta: The Effects of A-Site and Oxygen Stoichiometry},
journal = {CHEMISTRY OF MATERIALS},
year = {2016},
volume = {28},
number = {1},
pages = {97-105},
doi = {https://doi.org/10.1021/acs.chemmater.5b03273}
}
|
| Top, M., Schoenfeld, S., Fahlteichl, J., Bunk, S., Kuehnell, T., Straach, S. and De Hosson, J.T. Hollow-Cathode-Activated PECVD for the High-Rate Deposition of Permeation Barrier Films SOCIETY OF VACUUM COATERS 59TH ANNUAL TECHNICAL CONFERENCE PROCEEDINGS, 2016, pp. 398-404 (2016) |
| Abstract: This paper shows a study on the variation of the flow ratio between
oxygen and hexamethyldisiloxane (HMDSO) in a hollow cathode arc discharge plasma-enhanced chemical vapor deposition (PECVD) process. The thin films were analyzed using visible light spectroscopy, X-ray photo-electron spectroscopy (XPS), X-ray reflectivity (XRR), and water vapor transmission rate (WVTR) measurements. The deposited samples were compared to a reactively sputtered SiO2 thin film. By increasing the oxygen to HMDSO flow ratio, the chemical, density, and optical properties of the coating approached those of the sputtered SiO2 film. However the permeation barrier of the SiO2 film only showed a slight improvement over that of the bare polyethylene terephthalate (PET) substrate. The organic coating with high power and low oxygen flow, however, approached the barrier of the sputtered SiO2 thin film. |
BibTeX:
@inproceedings{WOS:000405161400058,
author = {Top, Michiel and Schoenfeld, Steffen and Fahlteichl, John and Bunk, Sebastian and Kuehnell, Thomas and Straach, Steffen and De Hosson, Jeff T.},
title = {Hollow-Cathode-Activated PECVD for the High-Rate Deposition of Permeation Barrier Films},
booktitle = {SOCIETY OF VACUUM COATERS 59TH ANNUAL TECHNICAL CONFERENCE PROCEEDINGS, 2016},
year = {2016},
pages = {398-404},
note = {59th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), Indianapolis, IN, MAY 09-13, 2016},
doi = {https://doi.org/10.14332/svc16.proc.0050}
}
|
| Steffen, A., Glavic, A., Holderer, O., Frielinghaus, H., Ambaye, H., Puetter, S. and Brueckel, T. Frozen O-2 layer revealed by neutron reflectometry Results in Physics 6, pp. 263-264 (2016) |
| Abstract: A 63 angstrom thick film originating from frozen air on a solid
substrate has been investigated via neutron reflectometry. The experiment shows that neutron reflectometry allows performing chemical surface analysis by quantifying the composition of this frozen layer and identifies the film to be frozen oxygen. (C) 2016 The Authors. Published by Elsevier B.V. |
BibTeX:
@article{WOS:000389770300063,
author = {Steffen, A. and Glavic, A. and Holderer, O. and Frielinghaus, H. and Ambaye, H. and Puetter, S. and Brueckel, T.},
title = {Frozen O-2 layer revealed by neutron reflectometry},
journal = {Results in Physics},
year = {2016},
volume = {6},
pages = {263-264},
doi = {https://doi.org/10.1016/j.rinp.2016.05.010}
}
|
| Singh, S. and Basu, S. Simultaneous Parameter Optimization of X-ray and Neutron Reflectivity Data Using Genetic Algorithms 1731DAE SOLID STATE PHYSICS SYMPOSIUM 2015 (2016) |
| Abstract: X-ray and neutron reflectivity are two non destructive techniques which
provide a wealth of information on thickness, structure and interracial properties in nanometer length scale. Combination of X-ray and neutron reflectivity is well suited for obtaining physical parameters of nanostructured thin films and superlattices. Neutrons provide a different contrast between the elements than X-rays and are also sensitive to the magnetization depth profile in thin films and superlattices. The real space information is extracted by fitting a model for the structure of the thin film sample in reflectometry experiments. We have applied a Genetic Algorithms technique to extract depth dependent structure and magnetic in thin film and multilayer systems by simultaneously fitting X-ray and neutron reflectivity data. |
BibTeX:
@inproceedings{WOS:000380371600281,
author = {Singh, Surendra and Basu, Saibal},
title = {Simultaneous Parameter Optimization of X-ray and Neutron Reflectivity Data Using Genetic Algorithms},
booktitle = {DAE SOLID STATE PHYSICS SYMPOSIUM 2015},
year = {2016},
volume = {1731},
note = {DAE Solid State Physics Symposium, Amity Univ, Noida, INDIA, DEC 21-25, 2015},
doi = {https://doi.org/10.1063/1.4947885}
}
|
| Khodakarimi, S., Hekmatshoar, M.H. and Abbasi, F. X-ray reflectivity and topography of the solvent-treated P3HT:PCBM thin films JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS 27, 1, pp. 182-190 (2016) |
| Abstract: P3HT:PCBM (poly(3-hexylthiophene):[6,6]-phenyl C-61 butyric acid
methyl ester) thin films are widely used as an active layer in organic solar cells. The influence of solvent (1,8-diiodooctane) was studied on electron density and topography of thin spin-coated P3HT:PCBM films. The structural properties were studied by grazing incidence X-ray diffraction technique. It was found that the crystallinity of the investigated films was significantly increased after solvent treatment. Using X-ray reflectivity (XRR) analysis, data from P3HT:PCBM/air and P3HT:PCBM/glass interfaces were collected and compared with a theoretical model. The electron density, film thickness, and interface roughness were determined with a few angstroms accuracy by simulating the XRR curves. The XRR data were then analyzed using a scheme based on the distorted-wave Born approximation. It was found that the addition of diiodooctane did not change the absorption coefficient but changed electron density and roughness. The XRR simulation results were in good agreement with the experimental results obtained from AFM measurements. |
BibTeX:
@article{WOS:000368054600025,
author = {Khodakarimi, S. and Hekmatshoar, M. H. and Abbasi, F.},
title = {X-ray reflectivity and topography of the solvent-treated P3HT:PCBM thin films},
journal = {JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS},
year = {2016},
volume = {27},
number = {1},
pages = {182-190},
doi = {https://doi.org/10.1007/s10854-015-3735-3}
}
|
| Liu, Y., McElhinny, K., Alley, O., Evans, P.G. and Katz, H.E. Reduced-temperature solution-processed transparent oxide low-voltage-operable field-effect transistors MRS COMMUNICATIONS 5, 4, pp. 605-611 (2015) |
| Abstract: Metal oxide-based transistors can be fabricated by low-cost, large-area
solution processing methods, but involve a trade-off between low processing temperature, facile charge transport and high-capacitance/low-voltage transistor gates. We achieve these simultaneously by fabricating zinc oxide and sodium-incorporated alumina (SA) thin films with temperature not exceeding 200 to 250 degrees C using aqueous and combustion precursors, respectively. X-ray reflectivity shows a compositionally distinct SA boundary layer forming near the substrate and that a portion of the SA is chemically removed during the subsequent semiconductor deposition. Improved etch resistance and reduced dielectric leakage was obtained when (3-glycidoxypropyl) trimethoxysilane was included in the SA precursor. |
BibTeX:
@article{WOS:000367378500009,
author = {Liu, Yu and McElhinny, Kyle and Alley, Olivia and Evans, Paul G. and Katz, Howard E.},
title = {Reduced-temperature solution-processed transparent oxide low-voltage-operable field-effect transistors},
journal = {MRS COMMUNICATIONS},
year = {2015},
volume = {5},
number = {4},
pages = {605-611},
doi = {https://doi.org/10.1557/mrc.2015.79}
}
|
| Dieterle, J., Broch, K., Hinderhofer, A., Frank, H., Novak, J., Gerlach, A., Breuer, T., Banerjee, R., Witte, G. and Schreibert, F. Structural Properties of Picene-Perfluoropentacene and Picene-Pentacene Blends: Super lattice Formation versus Limited Intermixing JOURNAL OF PHYSICAL CHEMISTRY C 119, 47, pp. 26339-26347 (2015) |
| Abstract: The structure and morphology of mixed thin films of picene (C22H14, PIC)
and perfluoropentacene (C22F14, PFP) as well as mixed thin films of PIC and pentacene (C22H14, PEN) grown by simultaneous coevaporation is investigated using X-ray diffraction, atomic force microscopy, and near-edge X-ray absorption spectroscopy. For both systems we find mixing on the molecular level and the formation of mixed structures. However, due to the strongly different interactions in both mixtures the ordering is fundamentally different. For the equimolar PFP:PIC mixtures, we observe the formation of two different mixed polymorphs with unit cells containing 2 PIC and 2 PFP molecules depending on the growth temperature. One of these polymorphs is a superlattice with in-plane compound segregation. The other polymorph is less symmetric and results only in a very short ranged in-plane ordering. In contrast, the PEN:PIC mixtures form crystals with unit cell parameters continuously changing with the molar concentrations between those of the pure compounds. The position of molecular species within the crystal lattice is statistical. Surprisingly, for higher concentrations of PIC we observe phase separation of surplus PIC molecules which corresponds to a limited intermixing of the two compounds. Finally, the results are discussed in the context of other organic semiconductor binary mixtures showing that besides chemical composition and steric compatibility the intramolecular arrangement of the atoms important for intermolecular interactions significantly influences the structure formation in organic semiconductor blends. |
BibTeX:
@article{WOS:000366006400012,
author = {Dieterle, Johannes and Broch, Katharina and Hinderhofer, Alexander and Frank, Heiko and Novak, Jiri and Gerlach, Alexander and Breuer, Tobias and Banerjee, Rupak and Witte, Gregor and Schreibert, Frank},
title = {Structural Properties of Picene-Perfluoropentacene and Picene-Pentacene Blends: Super lattice Formation versus Limited Intermixing},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2015},
volume = {119},
number = {47},
pages = {26339-26347},
doi = {https://doi.org/10.1021/acs.jpcc.5b08866}
}
|
| Lorch, C., Frank, H., Banerjee, R., Hinderhofer, A., Gerlach, A., Li Destri, G. and Schreiber, F. Controlling length-scales of the phase separation to optimize organic semiconductor blends APPLIED PHYSICS LETTERS 107, 20 (2015) |
| Abstract: The length-scale of phase separation in organic semiconductor
donor-acceptor mixtures, while being crucially important for applications, is a non-trivial parameter to control in non-equilibrium thin film growth. We present a comprehensive study of all the important parameters that can be used to tailor the length-scale of phase separation in organic semiconductor mixtures. We employed different substrate temperatures, different growth rates, time-dependent deposition rates, and surface functionalization layers. We found not only that the substrate temperature is most prominent in influencing the length-scale of phase separation in the studied parameter range, but also that other routes can be used to tailor this length-scale. (C) 2015 AIP Publishing LLC. |
BibTeX:
@article{WOS:000365688700024,
author = {Lorch, C. and Frank, H. and Banerjee, R. and Hinderhofer, A. and Gerlach, A. and Li Destri, G. and Schreiber, F.},
title = {Controlling length-scales of the phase separation to optimize organic semiconductor blends},
journal = {APPLIED PHYSICS LETTERS},
year = {2015},
volume = {107},
number = {20},
doi = {https://doi.org/10.1063/1.4935545}
}
|
| Prakash, A., Dewey, J., Yun, H., Jeong, J.S., Mkhoyan, K.A. and Jalan, B. Hybrid molecular beam epitaxy for the growth of stoichiometric BaSnO3 JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 33, 6 (2015) |
| Abstract: Owing to its high room-temperature electron mobility and wide bandgap,
BaSnO3 has recently become of significant interest for potential room-temperature oxide electronics. A hybrid molecular beam epitaxy (MBE) approach for the growth of high-quality BaSnO3 films is developed in this work. This approach employs hexamethylditin as a chemical precursor for tin, an effusion cell for barium, and a radio frequency plasma source for oxygen. BaSnO3 films were thus grown on SrTiO3 (001) and LaAlO3 (001) substrates. Growth conditions for stoichiometric BaSnO3 were identified. Reflection high-energy electron diffraction (RHEED) intensity oscillations, characteristic of a layer-by-layer growth mode were observed. A critical thickness of similar to 1 nm for strain relaxation was determined for films grown on SrTiO3 using in situ RHEED. Scanning transmission electron microscopy combined with electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy confirmed the cube-on-cube epitaxy and composition. The importance of precursor chemistry is discussed in the context of the MBE growth of BaSnO3. (C) 2015 American Vacuum Society. |
BibTeX:
@article{WOS:000365503800008,
author = {Prakash, Abhinav and Dewey, John and Yun, Hwanhui and Jeong, Jong Seok and Mkhoyan, K. Andre and Jalan, Bharat},
title = {Hybrid molecular beam epitaxy for the growth of stoichiometric BaSnO3},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2015},
volume = {33},
number = {6},
doi = {https://doi.org/10.1116/1.4933401}
}
|
| Drnec, J., Bizzotto, D., Carla, F., Fiala, R., Sode, A., Balmes, O., Detlefs, B., Dufrane, T. and Felici, R. An in-situ X-ray diffraction study on the electrochemical formation of PtZn alloys on Pt(111) single crystal electrode APPLIED SURFACE SCIENCE 354, B, pp. 443-449 (2015) |
| Abstract: The electrochemical formation and dissolution of the oxygen reduction
reaction (ORR) PtZn catalyst on Pt(1 1 1) surface is followed by in-situ X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements. When the crystalline Pt surface is polarized to sufficiently negative potential values, with respect to an Ag/AgCl vertical bar KCl reference electrode, the electrodeposited zinc atoms diffuse into the bulk and characteristic features are observed in the X-ray patterns. The surface structure and composition during deposition and dissolution is determined from analysis of XRR curves and measurements of crystal truncation rods. Thin Zn-rich surface layer is present during the alloy formation while a Zn-depleted layer forms during dissolution. (C) 2015 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000363673500029,
author = {Drnec, J. and Bizzotto, D. and Carla, F. and Fiala, R. and Sode, A. and Balmes, O. and Detlefs, B. and Dufrane, T. and Felici, R.},
title = {An in-situ X-ray diffraction study on the electrochemical formation of PtZn alloys on Pt(111) single crystal electrode},
journal = {APPLIED SURFACE SCIENCE},
year = {2015},
volume = {354},
number = {B},
pages = {443-449},
note = {European Conference on Surface Science (ECOSS), Antalya, TURKEY, AUG 31-SEP 05, 2014},
doi = {https://doi.org/10.1016/j.apsusc.2015.04.072}
}
|
| Lorch, C., Banerjee, R., Dieterle, J., Hinderhofer, A., Gerlach, A., Drnec, J. and Schreiber, F. Templating Effects of alpha-Sexithiophene in Donor-Acceptor Organic Thin Films JOURNAL OF PHYSICAL CHEMISTRY C 119, 40, pp. 23211-23220 (2015) |
| Abstract: Small-molecule organic photovoltaic cells often employ a planar
heterojunction (PHJ) geometry where the electron donor and acceptor materials are stacked one on top of the other. The thin-film growth scenario of such PHJs can be very different from the one of a single compound on a bare substrate. We have investigated the growth of PHJs, consisting of two different donor acceptor pairs, namely, alpha-serithiophene (6T)/C-60 and 6T/diindenoperylene (DIP) using real-time in situ X-ray scattering. For both donor acceptor material combinations, we observe that the coherent in-plane crystalline size of the second material strongly correlates with the one of the bottom one, and hence a strong templating effect of the 6T on the material deposited subsequently, indicating a strong interaction between the two materials in the PHJ. Furthermore, a change in the structure of the 6T film during the deposition of the second material was observed, which shows that the deposition of an additional material on top of a templating layer can partially change the crystal structure of the templating film itself. |
BibTeX:
@article{WOS:000362702100052,
author = {Lorch, C. and Banerjee, R. and Dieterle, J. and Hinderhofer, A. and Gerlach, A. and Drnec, J. and Schreiber, F.},
title = {Templating Effects of alpha-Sexithiophene in Donor-Acceptor Organic Thin Films},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2015},
volume = {119},
number = {40},
pages = {23211-23220},
doi = {https://doi.org/10.1021/acs.jpcc.5b06064}
}
|
| Glinka, Y.D., Babakiray, S. and Lederman, D. Plasmon-enhanced electron-phonon coupling in Dirac surface states of the thin-film topological insulator Bi2Se3 JOURNAL OF APPLIED PHYSICS 118, 13 (2015) |
| Abstract: Raman measurements of a Fano-type surface phonon mode associated with
Dirac surface states (SS) in Bi2Se3 topological insulator thin films allowed an unambiguous determination of the electron-phonon coupling strength in Dirac SS as a function of film thickness ranging from 2 to 40 nm. A non-monotonic enhancement of the electron-phonon coupling strength with maximum for the 8-10 nm thick films was observed. The non-monotonicity is suggested to originate from plasmon-phonon coupling which enhances electron-phonon coupling when free carrier density in Dirac SS increases with decreasing film thickness and becomes suppressed for thinnest films when anharmonic coupling between in-plane and out-of-plane phonon modes occurs. The observed about four-fold enhancement of electron-phonon coupling in Dirac SS of the 8-10 nm thick Bi2Se3 films with respect to the bulk samples may provide new insights into the origin of superconductivity in this-type materials and their applications. (C) 2015 AIP Publishing LLC. |
BibTeX:
@article{WOS:000362668400049,
author = {Glinka, Yuri D. and Babakiray, Sercan and Lederman, David},
title = {Plasmon-enhanced electron-phonon coupling in Dirac surface states of the thin-film topological insulator Bi2Se3},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2015},
volume = {118},
number = {13},
doi = {https://doi.org/10.1063/1.4932667}
}
|
| Celedon, C.E., Sanchez, E.A., Alarcon, L.S., Guimpel, J., Cortes, A., Vargas, P. and Arista, N.R. Band structure effects in the energy loss of low-energy protons and deuterons in thin films of Pt NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 360, pp. 103-110 (2015) |
| Abstract: We have investigated experimentally and by computer simulations the
energy-loss and angular distribution of low energy (E < 10 key) protons and deuterons transmitted through thin polycrystalline platinum films. The experimental results show significant deviations from the expected velocity dependence of the stopping power in the range of very low energies with respect to the predictions of the Density Functional Theory for a jellium model. This behavior is similar to those observed in other transition metals such as Cu, Ag and Au, but different from the linear dependence recently observed in another transition metal, Pd, which belongs to the same Group of Pt in the Periodic Table. These differences are analyzed in term of the properties of the electronic bands corresponding to Pt and Pd, represented in terms of the corresponding density of states. The present experiments include also a detailed study of the angular dependence of the energy loss and the angular distributions of transmitted protons and deuterons. The results are compared with computer simulations based on the Monte Carlo method and with a theoretical model that evaluates the contributions of elastic collisions, path length effects in the inelastic energy losses, and the effects of the foil roughness. The results of the analysis obtained from these various approaches provide a consistent and comprehensive description of the experimental findings. (C) 2015 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000361859500016,
author = {Celedon, C. E. and Sanchez, E. A. and Alarcon, L. Salazar and Guimpel, J. and Cortes, A. and Vargas, P. and Arista, N. R.},
title = {Band structure effects in the energy loss of low-energy protons and deuterons in thin films of Pt},
journal = {NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS},
year = {2015},
volume = {360},
pages = {103-110},
doi = {https://doi.org/10.1016/j.nimb.2015.08.018}
}
|
| Porter, N.A., Spencer, C.S., Temple, R.C., Kinane, C.J., Charlton, T.R., Langridge, S. and Marrows, C.H. Manipulation of the spin helix in FeGe thin films and FeGe/Fe multilayers PHYSICAL REVIEW B 92, 14 (2015) |
| Abstract: Magnetic materials without structural inversion symmetry can display the
Dzyaloshinskii-Moriya interaction, which manifests itself as chiral magnetic ground states. These chiral states can interact in complex ways with applied fields and boundary conditions provided by finite sample sizes that are of the order of the length scale of the chiral states. Here we study epitaxial thin films of FeGe with a thickness close to the helix pitch of the helimagnetic ground state, which is about 70 nm, by conventional magnetometry and polarized neutron reflectometry. We show that the helix in an FeGe film reverses under the application of a field by deforming into a helicoidal form, with twists in the helicoid being forced out of the film surfaces on the way to saturation. An additional boundary condition was imposed by exchange-coupling a ferromagnetic Fe layer to one of the interfaces of an FeGe layer. This forces the FeGe spins at the interface to point in the same direction as the Fe, preventing node expulsion and giving a handle by which the reversal of the helical magnet may be controlled. |
BibTeX:
@article{WOS:000362084000005,
author = {Porter, Nicholas A. and Spencer, Charles S. and Temple, Rowan C. and Kinane, Christian J. and Charlton, Timothy R. and Langridge, Sean and Marrows, Christopher H.},
title = {Manipulation of the spin helix in FeGe thin films and FeGe/Fe multilayers},
journal = {PHYSICAL REVIEW B},
year = {2015},
volume = {92},
number = {14},
doi = {https://doi.org/10.1103/PhysRevB.92.144402}
}
|
| Busby, Y., Nau, S., Sax, S., List-Kratochvil, E.J.W., Novak, J., Banerjee, R., Schreiber, F. and Pireaux, J.J. Direct observation of conductive filament formation in Alq3 based organic resistive memories JOURNAL OF APPLIED PHYSICS 118, 7 (2015) |
| Abstract: This work explores resistive switching mechanisms in non-volatile
organic memory devices based on tris(8-hydroxyquinolie) aluminum (Alq(3)). Advanced characterization tools are applied to investigate metal diffusion in ITO/Alq(3)/Ag memory device stacks leading to conductive filament formation. The morphology of Alq(3)/Ag layers as a function of the metal evaporation conditions is studied by X-ray reflectivity, while depth profile analysis with X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry is applied to characterize operational memory elements displaying reliable bistable current-voltage characteristics. 3D images of the distribution of silver inside the organic layer clearly point towards the existence of conductive filaments and allow for the identification of the initial filament formation and inactivation mechanisms during switching of the device. Initial filament formation is suggested to be driven by field assisted diffusion of silver from abundant structures formed during the top electrode evaporation, whereas thermochemical effects lead to local filament inactivation. (C) 2015 AIP Publishing LLC. |
BibTeX:
@article{WOS:000360441900051,
author = {Busby, Y. and Nau, S. and Sax, S. and List-Kratochvil, E. J. W. and Novak, J. and Banerjee, R. and Schreiber, F. and Pireaux, J. -J.},
title = {Direct observation of conductive filament formation in Alq3 based organic resistive memories},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2015},
volume = {118},
number = {7},
doi = {https://doi.org/10.1063/1.4928622}
}
|
| Li, M., Chang, C.-Z., Kirby, B.J., Jamer, M.E., Cui, W., Wu, L., Wei, P., Zhu, Y., Heiman, D., Li, J. and Moodera, J.S. Proximity-Driven Enhanced Magnetic Order at Ferromagnetic-Insulator-Magnetic-Topological-Insulator Interface PHYSICAL REVIEW LETTERS 115, 8 (2015) |
| Abstract: Magnetic exchange driven proximity effect at a
magnetic-insulator-topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. Here we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic- TI EuS/Sb2-xVxTe3 hybrid heterostructure, where V doping is used to drive the TI (Sb2Te3) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering. |
BibTeX:
@article{WOS:000359872000006,
author = {Li, Mingda and Chang, Cui-Zu and Kirby, Brian. J. and Jamer, Michelle E. and Cui, Wenping and Wu, Lijun and Wei, Peng and Zhu, Yimei and Heiman, Don and Li, Ju and Moodera, Jagadeesh S.},
title = {Proximity-Driven Enhanced Magnetic Order at Ferromagnetic-Insulator-Magnetic-Topological-Insulator Interface},
journal = {PHYSICAL REVIEW LETTERS},
year = {2015},
volume = {115},
number = {8},
doi = {https://doi.org/10.1103/PhysRevLett.115.087201}
}
|
| Behera, B.C., Padhan, P. and Prellier, W. Influence of substrate in all-ferromagnetic superlattices JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 388, pp. 22-27 (2015) |
| Abstract: The Rarnan scattering and magnetization of the superlarrices consisting
of uhrarhin layer of two metal like ferromagneLs La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) grown on (001) oriented LaAlO3(LAO) and SrTiO3(STO) substrates, were studied. The Raman spectrum of LAO/[1-u.c. LSMO/2-u.c. SRO](x60) super lattice shows modes which are shifted towards higher frequencies relative to that of LAO/[2-u.c. SRO/1-u. c. LSMO](x60) superlattice. However, the Raman spectra of these superlattices indicate the presence or orthorhombic structures of LSMO and SRO for both stacking orders. The STO/[1-u.c. LSMO/2-u.c. SRO](x60) superlattices exhibit Curie temperature (T-C) at similar to 270 K and Neel temperature (TN) at similar to 140 K. Surprisingly, T-C of superlattice on LAO grown simultaneously with STO reduces to similar to 209 K for in-plane magnetic held and to similar to 99 K for out-plane held. But for the reverse stacking grown on LAO the T-C increases to similar to 121 and similar to 218 K for in-plane and out-of-plane orientation of held, respectively. The superlattices grown On LAO do not show any signature of T-N. Our result clearly indicates the influence of substrate induced stress and stacking order on exchange coupling between the LSMO and SRO in the superlattices, providing a useful tool towards tailoring the magnetic properties of heterostructures. (C) 2015 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000353525400005,
author = {Behera, B. C. and Padhan, P. and Prellier, W.},
title = {Influence of substrate in all-ferromagnetic superlattices},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2015},
volume = {388},
pages = {22-27},
doi = {https://doi.org/10.1016/j.jmmm.2015.04.018}
}
|
| Ribera, R.C., van de Kruijs, R.W.E., Yakshin, A.E. and Bijkerk, F. Determination of oxygen diffusion kinetics during thin film ruthenium oxidation JOURNAL OF APPLIED PHYSICS 118, 5 (2015) |
| Abstract: In situ X-ray reflectivity was used to reveal oxygen diffusion kinetics
for thermal oxidation of poly-crystalline ruthenium thin films and accurate determination of activation energies for this process. Diffusion rates in nanometer thin RuO2 films were found to show Arrhenius behaviour. However, a gradual decrease in diffusion rates was observed with oxide growth, with the activation energy increasing from about 2.1 to 2.4 eV. Further exploration of the Arrhenius pre-exponential factor for diffusion process revealed that oxidation of polycrystalline ruthenium joins the class of materials that obey the Meyer-Neldel rule. (C) 2015 AIP Publishing LLC. |
BibTeX:
@article{WOS:000359376700038,
author = {Ribera, R. Coloma and van de Kruijs, R. W. E. and Yakshin, A. E. and Bijkerk, F.},
title = {Determination of oxygen diffusion kinetics during thin film ruthenium oxidation},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2015},
volume = {118},
number = {5},
doi = {https://doi.org/10.1063/1.4928295}
}
|
| Tokac, M., Bunyaev, S.A., Kakazei, G.N., Schmool, D.S., Atkinson, D. and Hindmarch, A.T. Interfacial Structure Dependent Spin Mixing Conductance in Cobalt Thin Films PHYSICAL REVIEW LETTERS 115, 5 (2015) |
| Abstract: Enhancement of Gilbert damping in polycrystalline cobalt thin-film
multilayers of various thicknesses, overlayered with copper or iridium, was studied in order to understand the role of local interface structure in spin pumping. X-ray diffraction indicates that cobalt films less than 6 nm thick have strong fcc(111) texture while thicker films are dominated by hcp(0001) structure. The intrinsic damping for cobalt thicknesses above 6 nm is weakly dependent on cobalt thickness for both overlayer materials, and below 6 nm the iridium overlayers show higher damping enhancement compared to copper overlayers, as expected due to spin pumping. The interfacial spin mixing conductance is significantly enhanced in structures where both cobalt and iridium have fcc(111) structure in comparison to those where the cobalt layer has subtly different hcp(0001) texture at the interface. |
BibTeX:
@article{WOS:000358863000005,
author = {Tokac, M. and Bunyaev, S. A. and Kakazei, G. N. and Schmool, D. S. and Atkinson, D. and Hindmarch, A. T.},
title = {Interfacial Structure Dependent Spin Mixing Conductance in Cobalt Thin Films},
journal = {PHYSICAL REVIEW LETTERS},
year = {2015},
volume = {115},
number = {5},
doi = {https://doi.org/10.1103/PhysRevLett.115.056601}
}
|
| Babakiray, S., Johnson, T.A., Borisov, P., Holcomb, M.B., Lederman, D., Marcus, M.A. and Tarafder, K. Structural properties of Bi2-xMnxSe3 thin films grown via molecular beam epitaxy JOURNAL OF APPLIED PHYSICS 118, 4 (2015) |
| Abstract: The effects of Mn doping on the structural properties of the topological
insulator Bi2Se3 in thin film form were studied in samples grown via molecular beam epitaxy. Extended x-ray absorption fine structure measurements, supported by density functional theory calculations, indicate that preferential incorporation occurs substitutionally in Bi sites across the entire film volume. This finding is consistent with x-ray diffraction measurements which show that the out of plane lattice constant expands while the in plane lattice constant contracts as the Mn concentration is increased. X-ray photoelectron spectroscopy indicates that the Mn valency is 2+ and that the Mn bonding is similar to that in MnSe. The expansion along the out of plane direction is most likely due to weakening of the Van der Waals interactions between adjacent Se planes. Transport measurements are consistent with this Mn 2+ substitution of Bi sites if additional structural defects induced by this substitution are taken into account. (C) 2015 AIP Publishing LLC. |
BibTeX:
@article{WOS:000358928000060,
author = {Babakiray, Sercan and Johnson, Trent A. and Borisov, Pavel and Holcomb, Mikel B. and Lederman, David and Marcus, Matthew A. and Tarafder, Kartick},
title = {Structural properties of Bi2-xMnxSe3 thin films grown via molecular beam epitaxy},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2015},
volume = {118},
number = {4},
doi = {https://doi.org/10.1063/1.4927171}
}
|
| Monteiro, P.M.S., Baker, P.J., Hine, N.D.M., Steinke, N.-J., Ionescu, A., Cooper, J.F.K., Barnes, C.H.W., Kinane, C.J., Salman, Z., Wildes, A.R., Prokscha, T. and Langridge, S. Elevated Curie temperature and half-metallicity in the ferromagnetic semiconductor LaxEu1-xO PHYSICAL REVIEW B 92, 4 (2015) |
| Abstract: Here we study the effect of La-doping in EuO thin films using
superconducting quantum interference device magnetometry, muon spin rotation (mu SR), polarized neutron reflectivity (PNR), and density functional theory (DFT). The mu SR data shows that the La0.15Eu0.85O is homogeneously magnetically ordered up to its elevated T-C. It is concluded that bound magnetic polaron behavior does not explain the increase in T-C and an Ruderman-KittelKasuya-Yosida-like (RKKY-like) interaction is consistent with the mu SR data. The estimation of the magnetic moment by DFT simulations concurs with the results obtained by PNR, showing a reduction of the magnetic moment per LaxEu1-xO for increasing lanthanum doping. This reduction of the magnetic moment is explained by the reduction of the number of Eu-4f electrons present in all the magnetic interactions in EuO films. Finally, we show that an upwards shift of the Fermi energy with La or Gd doping gives rise to half-metallicity for doping levels as high as 3.2%. |
BibTeX:
@article{WOS:000357636300006,
author = {Monteiro, Pedro M. S. and Baker, Peter J. and Hine, Nicholas D. M. and Steinke, Nina-J. and Ionescu, Adrian and Cooper, Joshaniel F. K. and Barnes, Crispin H. W. and Kinane, Christian J. and Salman, Zaher and Wildes, Andrew R. and Prokscha, Thomas and Langridge, Sean},
title = {Elevated Curie temperature and half-metallicity in the ferromagnetic semiconductor LaxEu1-xO},
journal = {PHYSICAL REVIEW B},
year = {2015},
volume = {92},
number = {4},
doi = {https://doi.org/10.1103/PhysRevB.92.045202}
}
|
| Smith, C.R., Lang, A.C., Shutthanandan, V., Taheri, M.L. and May, S.J. Effects of cation stoichiometry on electronic and structural properties of LaNiO3 JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 33, 4 (2015) |
| Abstract: LaNiO3 films with varying La: Ni ratios were deposited onto SrTiO3 (001)
substrates via molecular beam epitaxy to elucidate the effects of cation off-stoichiometry. The physical properties of La-deficient films are found to differ substantially from those of Ni-deficient films, with La-deficient films exhibiting lower electrical resistivities and smaller c-axis parameters than Ni-deficient films. No evidence of secondary phases is observed; however, transmission electron microscopy reveals an abundance of defects, the nature of which differs in lanthanum-and nickel-deficient films. This work illustrates the nontrivial role that cation stoichiometry can play on the functional properties of complex oxides. (C) 2015 American Vacuum Society. |
BibTeX:
@article{WOS:000357826400022,
author = {Smith, Cole R. and Lang, Andrew C. and Shutthanandan, Vaithiyalingam and Taheri, Mitra L. and May, Steven J.},
title = {Effects of cation stoichiometry on electronic and structural properties of LaNiO3},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2015},
volume = {33},
number = {4},
doi = {https://doi.org/10.1116/1.4922346}
}
|
| Wood, M.H., Welbourn, R.J.L., Zarbakhsh, A., Gutfreund, P. and Clarke, S.M. Polarized Neutron Reflectometry of Nickel Corrosion Inhibitors LANGMUIR 31, 25, pp. 7062-7072 (2015) |
| Abstract: Polarized neutron reflectometry has been used to investigate the
detailed adsorption behavior and corrosion inhibition mechanism of two surfactants on a nickel surface under acidic conditions. Both the corrosion of the nickel surface and the structure of the adsorbed surfactant layer could be monitored in situ by the use of different solvent contrasts. Layer thicknesses and roughnesses were evaluated over a range of pH values, showing distinctly the superior corrosion inhibition of one negatively charged surfactant (sodium dodecyl sulfate) compared to, a positively charged example (dodecyl trimethylammonium bromide) due to its stronger binding interaction with the surface. It was found that adequate corrosion inhibition occurs at significantly less than full surface coverage. |
BibTeX:
@article{WOS:000357435600016,
author = {Wood, Mary H. and Welbourn, Rebecca J. L. and Zarbakhsh, Ali and Gutfreund, Philipp and Clarke, Stuart M.},
title = {Polarized Neutron Reflectometry of Nickel Corrosion Inhibitors},
journal = {LANGMUIR},
year = {2015},
volume = {31},
number = {25},
pages = {7062-7072},
doi = {https://doi.org/10.1021/acs.langmuir.5b01718}
}
|
| Stubbs, J.E., Chaka, A.M., Ilton, E.S., Biwer, C.A., Engelhard, M.H., Bargar, J.R. and Eng, P.J. UO2 Oxidative Corrosion by Nonclassical Diffusion PHYSICAL REVIEW LETTERS 114, 24 (2015) |
| Abstract: Using x-ray scattering, spectroscopy, and density-functional theory, we
determine the structure of the oxidation front when a UO2 (111) surface is exposed to oxygen at ambient conditions. In contrast to classical diffusion and previously reported bulk UO2+x structures, we find oxygen interstitials order into a nanoscale superlattice with three-layer periodicity and uranium in three oxidation states: IV, V, and VI. This oscillatory diffusion profile is driven by the nature of the electron transfer process, and has implications for understanding the initial stages of oxidative corrosion in materials at the atomistic level. |
BibTeX:
@article{WOS:000356484700003,
author = {Stubbs, Joanne E. and Chaka, Anne M. and Ilton, Eugene S. and Biwer, Craig A. and Engelhard, Mark H. and Bargar, John R. and Eng, Peter J.},
title = {UO2 Oxidative Corrosion by Nonclassical Diffusion},
journal = {PHYSICAL REVIEW LETTERS},
year = {2015},
volume = {114},
number = {24},
doi = {https://doi.org/10.1103/PhysRevLett.114.246103}
}
|
| Ganguly, K., Ambwani, P., Xu, P., Jeong, J.S., Mkhoyan, K.A., Leighton, C. and Jalan, B. Structure and transport in high pressure oxygen sputter-deposited BaSnO3-delta APL MATERIALS 3, 6 (2015) |
| Abstract: BaSnO3 has recently been identified as a high mobility wide gap
semiconductor with significant potential for room temperature oxide electronics. Here, a detailed study of the high pressure oxygen sputter-deposition, microstructure, morphology, and stoichiometry of epitaxial BaSnO3 on SrTiO3(001) and MgO(001) is reported, optimized conditions resulting in single-phase, relaxed, close to stoichiometric films. Most significantly, vacuum annealing is established as a facile route to n-doped BaSnO3-delta, leading to electron densities above 10(19) cm(-3), 5 m Omega cm resistivities, and room temperature mobility of 20 cm(2) V-1 s(-1) in 300-angstrom-thick films on MgO(001). Mobility limiting factors, and the substantial scope for their improvement, are discussed. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. |
BibTeX:
@article{WOS:000357608900020,
author = {Ganguly, Koustav and Ambwani, Palak and Xu, Peng and Jeong, Jong Seok and Mkhoyan, K. Andre and Leighton, C. and Jalan, Bharat},
title = {Structure and transport in high pressure oxygen sputter-deposited BaSnO3-delta},
journal = {APL MATERIALS},
year = {2015},
volume = {3},
number = {6},
doi = {https://doi.org/10.1063/1.4919969}
}
|
| Collins-McIntyre, L.J., Wang, W., Zhou, B., Speller, S.C., Chen, Y.L. and Hesjedal, T. Growth of Bi2Se3 and Bi2Te3 on amorphous fused silica by MBE PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 252, 6, pp. 1334-1338 (2015) |
| Abstract: Topological insulator (TI) thin films of Bi2Se3 and Bi2Te3 have been
successfully grown on amorphous fused silica (vitreous SiO2) substrates by molecular beam epitaxy. We find that such growth is possible and investigations by X-ray diffraction reveal good crystalline quality with a high degree of order along the c-axis. Atomic force microscopy, electron backscatter diffraction and X-ray reflectivity are used to study the surface morphology and structural film parameters. Angle-resolved photoemission spectroscopy studies confirm the existence of a topological surface state. This work shows that TI films can be grown on amorphous substrates, while maintaining the topological surface state despite the lack of in-plane rotational order of the domains. The growth on fused silica presents a promising route to detailed thermoelectric measurements of TI films, free from unwanted thermal, electrical, and piezoelectric influences from the substrate. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim |
BibTeX:
@article{WOS:000355756200020,
author = {Collins-McIntyre, L. J. and Wang, W. and Zhou, B. and Speller, S. C. and Chen, Y. L. and Hesjedal, T.},
title = {Growth of Bi2Se3 and Bi2Te3 on amorphous fused silica by MBE},
journal = {PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS},
year = {2015},
volume = {252},
number = {6},
pages = {1334-1338},
doi = {https://doi.org/10.1002/pssb.201552003}
}
|
| Kalisvaart, W.P., Fritzsche, H. and Merida, W. Water Uptake and Swelling Hysteresis in a Nafion Thin Film Measured with Neutron Reflectometry LANGMUIR 31, 19, pp. 5416-5422 (2015) |
| Abstract: Water uptake and swelling in a thin (similar to 15 nm) Nafion film on
SiO2 native oxide on a Si wafer is studied as a function of relative humidity (8-97%) at room temperature and as a function of temperature (25-60 degrees C) at 97% relative humidity by neutron reflectometry. This is the first report on the behavior of thin Nafion films at elevated temperatures and high humidity. Large hysteresis is observed during the temperature cycle. The observed swelling strain in the film at 60 degrees C is 48% as compared to the as-deposited state, which is far above any previously observed trend at room temperature. A small decrease in the average SLD suggests that part of the additional swelling is due to thermal expansion, but the estimated D2O/SO3 ratio also increases by 70%. Half of the ``excess'' absorption and 73% of the additional swelling are retained during cooling back to room temperature. The results provide new insights into the dynamics of Nafion on nanometer scales under fuel cell operating conditions. |
BibTeX:
@article{WOS:000355057500019,
author = {Kalisvaart, W. Peter and Fritzsche, Helmut and Merida, Walter},
title = {Water Uptake and Swelling Hysteresis in a Nafion Thin Film Measured with Neutron Reflectometry},
journal = {LANGMUIR},
year = {2015},
volume = {31},
number = {19},
pages = {5416-5422},
doi = {https://doi.org/10.1021/acs.langmuir.5b00764}
}
|
| Kornblum, L., Jin, E.N., Kumah, D.P., Ernst, A.T., Broadbridge, C.C., Ahn, C.H. and Walker, F.J. Oxide 2D electron gases as a route for high carrier densities on (001) Si APPLIED PHYSICS LETTERS 106, 20 (2015) |
| Abstract: Two dimensional electron gases (2DEGs) formed at the interfaces of oxide
heterostructures draw considerable interest owing to their unique physics and potential applications. Growing such heterostructures on conventional semiconductors has the potential to integrate their functionality with semiconductor device technology. We demonstrate 2DEGs on a conventional semiconductor by growing GdTiO3-SrTiO3 on silicon. Structural analysis confirms the epitaxial growth of heterostructures with abrupt interfaces and a high degree of crystallinity. Transport measurements show the conduction to be an interface effect, similar to 9 x 10(13) cm(-2) electrons per interface. Good agreement is demonstrated between the electronic behavior of structures grown on Si and on an oxide substrate, validating the robustness of this approach to bridge between lab-scale samples to a scalable, technologically relevant materials system. (C) 2015 AIP Publishing LLC. |
BibTeX:
@article{WOS:000355009400005,
author = {Kornblum, Lior and Jin, Eric N. and Kumah, Divine P. and Ernst, Alexis T. and Broadbridge, Christine C. and Ahn, Charles H. and Walker, Fred J.},
title = {Oxide 2D electron gases as a route for high carrier densities on (001) Si},
journal = {APPLIED PHYSICS LETTERS},
year = {2015},
volume = {106},
number = {20},
doi = {https://doi.org/10.1063/1.4921437}
}
|
| Muneshwar, T. and Cadien, K. Low temperature plasma enhanced atomic layer deposition of conducting zirconium nitride films using tetrakis (dimethylamido) zirconium and forming gas (5% H-2+95% N-2) plasma JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 33, 3 (2015) |
| Abstract: Zirconium nitride (ZrN) has the lowest bulk electrical resistivity and
high thermal stability among group IV and V transition metal nitrides, which makes it a promising material for ULSI applications such as a diffusion barrier for Cu interconnects, contact metal in III-V semiconductor devices, and in high density memory structures. Plasma enhanced atomic layer deposition (PEALD) of conducting ZrN thin films using Zr[N(CH3)(2)](4) and forming gas (5% H-2 + 95% N-2) plasma is reported in this article. The growth per cycle (GPC) for every deposition was determined from analysis of dynamic in-situ spectroscopic ellipsometry (d-iSE) measurements. An experimental design is proposed for faster determination of ALD growth saturation curves. At substrate temperature of 150 degrees C, a GPC of 0.10 nm/cycle was observed for self-limiting ZrN PEALD growth. The electrical resistivity of ZrN films deposited on SiO2 substrate was found to be 559.5 +/- 18.5 mu Omega cm with negligible change in resistivity even after similar to 1000 h exposure to air. The metallic behavior of our ZrN films was evident from the free electron dispersion component in dielectric response, the broad band of photoelectron emission across Fermi level and the positive temperature coefficient for resistivity of 0.0088/degrees C. (C) 2015 American Vacuum Society. |
BibTeX:
@article{WOS:000355741800014,
author = {Muneshwar, Triratna and Cadien, Ken},
title = {Low temperature plasma enhanced atomic layer deposition of conducting zirconium nitride films using tetrakis (dimethylamido) zirconium and forming gas (5% H-2+95% N-2) plasma},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2015},
volume = {33},
number = {3},
doi = {https://doi.org/10.1116/1.4915122}
}
|
| Vieira, C.E.P., Gasperini, A.A.M., Freitas, P.P.S., Oliveira, R.G. and Cavalcanti, L.P. Characterization of a Pt mirror to be used to deflect synchrotron radiation beam onto Langmuir monolayers JOURNAL OF SYNCHROTRON RADIATION 22, 3, SI, pp. 859-861 (2015) |
| Abstract: A homemade mirror for X-rays has been built to prepare a diffraction
beamline for liquid surface diffraction and scattering measurements. This simple approach is in operation at the XRD2 bending-magnet beamline at the Brazilian Synchrotron Light Laboratory. |
BibTeX:
@article{WOS:000353920300054,
author = {Vieira, Carlos E. P. and Gasperini, Antonio A. M. and Freitas, Pedro P. S. and Oliveira, Rafael G. and Cavalcanti, Leide P.},
title = {Characterization of a Pt mirror to be used to deflect synchrotron radiation beam onto Langmuir monolayers},
journal = {JOURNAL OF SYNCHROTRON RADIATION},
year = {2015},
volume = {22},
number = {3, SI},
pages = {859-861},
doi = {https://doi.org/10.1107/S1600577515001496}
}
|
| Xia, M., Zhu, M., Wang, Y., Song, Z., Rao, F., Wu, L., Cheng, Y. and Song, S. Ti-Sb-Te Alloy: A Candidate for Fast and Long-Life Phase-Change Memory ACS APPLIED MATERIALS & INTERFACES 7, 14, pp. 7627-7634 (2015) |
| Abstract: Phase-change memory (PCM) has great potential for numerous attractive
applications on the premise of its high-device performances, which still need to be improved by employing a material with good overall phase-change properties. In respect to fast speed and high endurance, the Ti-Sb-Te alloy seems to be a promising candidate. Here, Ti-doped Sb2Te3 (TST) materials with different Ti concentrations have been systematically studied with the goal of finding the most suitable composition for PCM applications. The thermal stability of TST is improved dramatically with increasing Ti content. The small density change of T0.32Sb2Te3 (2.24%), further reduced to 1.37% for T0.56Sb2Te3, would greatly avoid the voids generated at phase-change layer/electrode interface in a PCM device. Meanwhile, the exponentially diminished grain size (from similar to 200 nm to similar to 12 nm), resulting from doping more and more Ti, enhances the adhesion between phase-change film and substrate. Tests of TST-based PCM cells have demonstrated a fast switching rate of similar to 10 ns. Furthermore, because of the lower thermal conductivities of TST materials, compared with Sb2Te3-based PCM cells, T0.32Sb2Te3-based ones exhibit lower required pulse voltages for Reset operation, which largely decreases by similar to 50% for T0.43Sb2Te3-based ones. Nevertheless, the operation voltages for T0.56Sb2Te3-based cells dramatically increase, which may be due to the phase separation after doping excessive Ti. Finally, considering the decreased resistance ratio, TixSb2Te3 alloy with x around 0.43 is proved to be a highly promising candidate for fast and long-life PCM applications. |
BibTeX:
@article{WOS:000353177000025,
author = {Xia, Mengjiao and Zhu, Min and Wang, Yuchan and Song, Zhitang and Rao, Feng and Wu, Liangcai and Cheng, Yan and Song, Sannian},
title = {Ti-Sb-Te Alloy: A Candidate for Fast and Long-Life Phase-Change Memory},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2015},
volume = {7},
number = {14},
pages = {7627-7634},
doi = {https://doi.org/10.1021/acsami.5b00083}
}
|
| Le Graet, C., Charlton, T.R., McLaren, M., Loving, M., Morley, S.A., Kinane, C.J., Brydson, R.M.D., Lewis, L.H., Langridge, S. and Marrows, C.H. Temperature controlled motion of an antiferromagnet-ferromagnet interface within a dopant-graded FeRh epilayer APL MATERIALS 3, 4 (2015) |
| Abstract: Chemically ordered B2 FeRh exhibits a remarkable
antiferromagnetic-ferromagnetic phase transition that is first order. It thus shows phase coexistence, usually by proceeding though nucleation at random defect sites followed by propagation of phase boundary domain walls. The transition occurs at a temperature that can be varied by doping other metals onto the Rh site. We have taken advantage of this to yield control over the transition process by preparing an epilayer with oppositely directed doping gradients of Pd and Ir throughout its height, yielding a gradual transition that occurs between 350 K and 500 K. As the sample is heated, a horizontal antiferromagnetic-ferromagnetic phase boundary domain wall moves gradually up through the layer, its position controlled by the temperature. This mobile magnetic domain wall affects the magnetisation and resistivity of the layer in a way that can be controlled, and hence exploited, for novel device applications. (C) 2015 Author(s). |
BibTeX:
@article{WOS:000353828400029,
author = {Le Graet, C. and Charlton, T. R. and McLaren, M. and Loving, M. and Morley, S. A. and Kinane, C. J. and Brydson, R. M. D. and Lewis, L. H. and Langridge, S. and Marrows, C. H.},
title = {Temperature controlled motion of an antiferromagnet-ferromagnet interface within a dopant-graded FeRh epilayer},
journal = {APL MATERIALS},
year = {2015},
volume = {3},
number = {4},
doi = {https://doi.org/10.1063/1.4907282}
}
|
| Perez, F.A., Borisov, P., Johnson, T.A., Stanescu, T.D., Trappen, R., Holcomb, M.B., Lederman, D., Fitzsimmons, M.R., Aczel, A.A. and Hong, T. Phase Diagram of a Three-Dimensional Antiferromagnet with Random Magnetic Anisotropy PHYSICAL REVIEW LETTERS 114, 9 (2015) |
| Abstract: Three-dimensional antiferromagnets with random magnetic anisotropy (RMA)
that have been experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of FexNi1-xF2 epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean-field theory. Regions with uniaxial, oblique, and easy-plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs. |
BibTeX:
@article{WOS:000350976700025,
author = {Perez, Felio A. and Borisov, Pavel and Johnson, Trent A. and Stanescu, Tudor D. and Trappen, Robbyn and Holcomb, Mikel B. and Lederman, David and Fitzsimmons, M. R. and Aczel, Adam A. and Hong, Tao},
title = {Phase Diagram of a Three-Dimensional Antiferromagnet with Random Magnetic Anisotropy},
journal = {PHYSICAL REVIEW LETTERS},
year = {2015},
volume = {114},
number = {9},
doi = {https://doi.org/10.1103/PhysRevLett.114.097201}
}
|
| Hoenicke, P., Detlefs, B., Mueller, M., Darlatt, E., Nolot, E., Grampeix, H. and Beckhoff, B. Reference-free, depth-dependent characterization of nanolayers and gradient systems with advanced grazing incidence X-ray fluorescence analysis PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 212, 3, pp. 523-528 (2015) |
| Abstract: Thin high-k layers and stacks as well as ultra shallow dopant profiles
are technologically relevant nanoscaled systems for current and future electronic devices. The characterization of such systems presents several metrological challenges and requires further development of the available analytical techniques. Grazing incidence X-ray fluorescence (GIXRF) in combination with X-ray reflectometry (XRR) can significantly contribute to the characterization of nanoscaled samples by improved modeling of the X-ray standing wave (XSW) field induced by the incident X-rays. In conjunction with the in-house built radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt, the method allows for reference-free quantitative in-depth analysis. The capabilities of the combined XRR-GIXRF method are shown on the example of several nanoscaled systems, including ultra-shallow Al dopant profiles in Si, HfO2, and Al2O3 nanolaminates and self-assembled multilayers of organic tetralactam macrocycles. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim |
BibTeX:
@article{WOS:000351530800006,
author = {Hoenicke, Philipp and Detlefs, Blanka and Mueller, Matthias and Darlatt, Erik and Nolot, Emmanuel and Grampeix, Helen and Beckhoff, Burkhard},
title = {Reference-free, depth-dependent characterization of nanolayers and gradient systems with advanced grazing incidence X-ray fluorescence analysis},
journal = {PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE},
year = {2015},
volume = {212},
number = {3},
pages = {523-528},
doi = {https://doi.org/10.1002/pssa.201400204}
}
|
| Choquette, A.K., Colby, R., Moon, E.J., Schlepuetz, C.M., Scafetta, M.D., Keavney, D.J. and May, S.J. Synthesis, Structure, and Spectroscopy of Epitaxial EuFeO3 Thin Films CRYSTAL GROWTH & DESIGN 15, 3, pp. 1105-1111 (2015) |
| Abstract: Rare earth iron perovskites RFeO3, where R is a rare earth cation,
exhibit an array of magnetic, catalytic, optical, and electrochemical properties. Here we study EuFeO3 films synthesized by molecular beam epitaxy to improve our understanding of the optical properties of ferrites. A combination of X-ray diffraction, X-ray reflectivity, Rutherford backscattering spectroscopy, and scanning transmission electron microscopy was used to characterize the film structure and cation composition. X-ray absorption spectroscopy confirms the nominal 3+ valence states of Eu and Fe. The optical properties of EuFeO3 were investigated using variable-angle spectroscopic ellipsometry between the photon energies of 1.25 and 5 eV. We find that EuFeO3 is a semiconductor with an onset of optical absorption near 2.5 eV. The absorption spectrum of EuFeO3 is blue-shifted with respect to LaFeO3 films, a result that is attributed to the structural differences between the two materials. |
BibTeX:
@article{WOS:000350614400014,
author = {Choquette, Amber K. and Colby, Robert and Moon, Eun Ju and Schlepuetz, Christian M. and Scafetta, Mark D. and Keavney, David J. and May, Steven J.},
title = {Synthesis, Structure, and Spectroscopy of Epitaxial EuFeO3 Thin Films},
journal = {CRYSTAL GROWTH & DESIGN},
year = {2015},
volume = {15},
number = {3},
pages = {1105-1111},
doi = {https://doi.org/10.1021/cg501403m}
}
|
| Jaksch, S., Lipfert, F., Koutsioubas, A., Mattauch, S., Holderer, O., Ivanova, O., Frielinghaus, H., Hertrich, S., Fischer, S.F. and Nickel, B. Influence of ibuprofen on phospholipid membranes PHYSICAL REVIEW E 91, 2 (2015) |
| Abstract: A basic understanding of biological membranes is of paramount importance
as these membranes comprise the very building blocks of life itself. Cells depend in their function on a range of properties of the membrane, which are important for the stability and function of the cell, information and nutrient transport, waste disposal, and finally the admission of drugs into the cell and also the deflection of bacteria and viruses. We have investigated the influence of ibuprofen on the structure and dynamics of L-alpha-phosphatidylcholine (SoyPC) membranes by means of grazing incidence small-angle neutron scattering, neutron reflectometry, and grazing incidence neutron spin echo spectroscopy. From the results of these experiments, we were able to determine that ibuprofen induces a two-step structuring behavior in the SoyPC films, where the structure evolves from the purely lamellar phase for pure SoyPC over a superposition of two hexagonal phases to a purely hexagonal phase at high concentrations. A relaxation, which is visible when no ibuprofen is present in the membrane, vanishes upon addition of ibuprofen. This we attribute to a stiffening of the membrane. This behavior may be instrumental in explaining the toxic behavior of ibuprofen in long-term application. |
BibTeX:
@article{WOS:000350107200006,
author = {Jaksch, Sebastian and Lipfert, Frederik and Koutsioubas, Alexandros and Mattauch, Stefan and Holderer, Olaf and Ivanova, Oxana and Frielinghaus, Henrich and Hertrich, Samira and Fischer, Stefan F. and Nickel, Bert},
title = {Influence of ibuprofen on phospholipid membranes},
journal = {PHYSICAL REVIEW E},
year = {2015},
volume = {91},
number = {2},
doi = {https://doi.org/10.1103/PhysRevE.91.022716}
}
|
| Doig, K.I., Peters, J.J.P., Nawaz, S., Walker, D., Walker, M., Lees, M.R., Beanland, R., Sanchez, A.M., McConville, C.F., Palkar, V.R. and Lloyd-Hughes, J. Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1-xFex)(n)O3n+1-delta Ruddlesden-Popper superstructures SCIENTIFIC REPORTS 5 (2015) |
| Abstract: Bulk crystals and thin films of PbTi1-xFexO3-delta ( PTFO) are
multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pbn+1(Ti1-xFex)(n)O3n+1-delta forms spontaneously during pulsed laser deposition of PTFO on LaAlO3 substrates. High-resolution transmission electron microscopy, x-ray diffraction and x-ray photoemission spectroscopy were utilised to perform a structural and compositional analysis, demonstrating that n similar or equal to 8 and x similar or equal to 0.5. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes and the observation of second harmonic generation establishes a non-centrosymmetric point group for Pbn+1(Ti1-xFex)(n)O3n+1-delta, a prerequisite for (but not proof of) ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic. |
BibTeX:
@article{WOS:000347902300002,
author = {Doig, K. I. and Peters, J. J. P. and Nawaz, S. and Walker, D. and Walker, M. and Lees, M. R. and Beanland, R. and Sanchez, A. M. and McConville, C. F. and Palkar, V. R. and Lloyd-Hughes, J.},
title = {Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1-xFex)(n)O3n+1-delta Ruddlesden-Popper superstructures},
journal = {SCIENTIFIC REPORTS},
year = {2015},
volume = {5},
doi = {https://doi.org/10.1038/srep07719}
}
|
| Disa, A.S., Kumah, D.P., Malashevich, A., Chen, H., Arena, D.A., Specht, E.D., Ismail-Beigi, S., Walker, F.J. and Ahn, C.H. Orbital Engineering in Symmetry-Breaking Polar Heterostructures PHYSICAL REVIEW LETTERS 114, 2 (2015) |
| Abstract: We experimentally demonstrate a novel approach to substantially modify
orbital occupations and symmetries in electronically correlated oxides. In contrast to methods using strain or confinement, this orbital tuning is achieved by exploiting charge transfer and inversion symmetry breaking using atomically layered heterostructures. We illustrate the technique in the LaTiO3-LaNiO3-LaAlO3 system; a combination of x-ray absorption spectroscopy and ab initio theory reveals electron transfer and concomitant polar fields, resulting in a similar to 50% change in the occupation of Ni d orbitals. This change is sufficiently large to remove the orbital degeneracy of bulk LaNiO3 and creates an electronic configuration approaching a single-band Fermi surface. Furthermore, we theoretically show that such three-component heterostructuring is robust and tunable by choice of insulator in the heterostructure, providing a general method for engineering orbital configurations and designing novel electronic systems. |
BibTeX:
@article{WOS:000348735500004,
author = {Disa, Ankit S. and Kumah, Divine P. and Malashevich, Andrei and Chen, Hanghui and Arena, Dario A. and Specht, Eliot D. and Ismail-Beigi, Sohrab and Walker, F. J. and Ahn, Charles H.},
title = {Orbital Engineering in Symmetry-Breaking Polar Heterostructures},
journal = {PHYSICAL REVIEW LETTERS},
year = {2015},
volume = {114},
number = {2},
doi = {https://doi.org/10.1103/PhysRevLett.114.026801}
}
|
| Lorch, C., Banerjee, R., Frank, C., Dieterle, J., Hinderhofer, A., Gerlach, A. and Schreiber, F. Growth of Competing Crystal Phases of alpha-Sexithiophene Studied by Real-Time in Situ X-ray Scattering JOURNAL OF PHYSICAL CHEMISTRY C 119, 1, pp. 819-825 (2015) |
BibTeX:
@article{WOS:000347744700089,
author = {Lorch, C. and Banerjee, R. and Frank, C. and Dieterle, J. and Hinderhofer, A. and Gerlach, A. and Schreiber, F.},
title = {Growth of Competing Crystal Phases of alpha-Sexithiophene Studied by Real-Time in Situ X-ray Scattering},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2015},
volume = {119},
number = {1},
pages = {819-825},
doi = {https://doi.org/10.1021/jp510321k}
}
|
| Xu, Z., Liu, B., Chen, Y., Gao, D., Wang, H., Xia, Y., Song, Z., Wang, C., Zhu, N., Ren, J. and Zhan, Y. The Suppressing of Density Change in Nitrogen Doped Ge2Sb2Te5 for High Performance Phase Change Memory ECS SOLID STATE LETTERS 4, 12, pp. P105-P108 (2015) |
| Abstract: During back-end-of-line fabrication of phase change memory (PCM), the
crystallization of Ge2Sb2Te5 (GST) with big density change results in voids and peeling of GST film. Doping with 6.9 at.% nitrogen content shows the smallest density change of about 5.4% by X-ray reflection experiment, which is attributed to the refining of grain size and suppressing the transformation of face-centered-cubic phase to hexagonal phase during phase change. Good cross section profile and convergent initial resistance distribution are obtained in PCM structure and device cells with 6.9 at.% nitrogen content doping, which is better for improving the yield and reliability of PCM. (C) 2015 The Electrochemical Society. All rights reserved. |
BibTeX:
@article{WOS:000365282400009,
author = {Xu, Zhen and Liu, Bo and Chen, Yifeng and Gao, Dan and Wang, Heng and Xia, Yangyang and Song, Zhitang and Wang, Changzhou and Zhu, Nanfei and Ren, Jiadong and Zhan, Yipeng},
title = {The Suppressing of Density Change in Nitrogen Doped Ge2Sb2Te5 for High Performance Phase Change Memory},
journal = {ECS SOLID STATE LETTERS},
year = {2015},
volume = {4},
number = {12},
pages = {P105-P108},
doi = {https://doi.org/10.1149/2.0121512ssl}
}
|
| Bruener, P., Grehl, T., Brongersma, H., Detlefs, B., Nolot, E., Grampeix, H., Steinbauer, E. and Bauer, P. Thin film analysis by low-energy ion scattering by use of TRBS simulations JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 33, 1 (2015) |
| Abstract: Low energy ion scattering (LEIS) spectra of thin film structures are
analyzed by Monte-Carlo simulations using the TRBS code. Although originally developed for the analysis of Rutherford backscattering (RBS) spectra, the TRBS code can be used to obtain valid simulations of LEIS data, which take place at energies several orders of magnitude lower than in RBS, when the appropriate adjustments are made. Experimental results from a set of Al2O3/HfO2 thin film stacks are shown, and their analysis by means of TRBS simulations is demonstrated. The authors show that the simulations yield valuable insights, especially in the case of ultrathin films <1 nm, where traditional evaluation methods using empirical models can be misleading. (C) 2014 American Vacuum Society. |
BibTeX:
@article{WOS:000355735400022,
author = {Bruener, Philipp and Grehl, Thomas and Brongersma, Hidde and Detlefs, Blanka and Nolot, Emmanuel and Grampeix, Helen and Steinbauer, Erich and Bauer, Peter},
title = {Thin film analysis by low-energy ion scattering by use of TRBS simulations},
journal = {JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A},
year = {2015},
volume = {33},
number = {1},
doi = {https://doi.org/10.1116/1.4901451}
}
|
| Springell, R., Rennie, S., Costelle, L., Darnbrough, J., Stitt, C., Cocklin, E., Lucas, C., Burrows, R., Sims, H., Wermeille, D., Rawle, J., Nicklin, C., Nuttall, W., Scott, T. and Lander, G. Water corrosion of spent nuclear fuel: radiolysis driven dissolution at the UO2/water interface FARADAY DISCUSSIONS 180, pp. 301-311 (2015) |
| Abstract: X-ray diffraction has been used to probe the radiolytic corrosion of
uranium dioxide. Single crystal thin films of UO2 were exposed to an intense X-ray beam at a synchrotron source in the presence of water, in order to simultaneously provide radiation fields required to split the water into highly oxidising radiolytic products, and to probe the crystal structure and composition of the UO2 layer, and the morphology of the UO2/water interface. By modeling the electron density, surface roughness and layer thickness, we have been able to reproduce the observed reflectivity and diffraction profiles and detect changes in oxide composition and rate of dissolution at the Angstrom level, over a timescale of several minutes. A finite element calculation of the highly oxidising hydrogen peroxide product suggests that a more complex surface interaction than simple reaction with H2O2 is responsible for an enhancement in the corrosion rate directly at the interface of water and UO2, and this may impact on models of long-term storage of spent nuclear fuel. |
BibTeX:
@article{WOS:000358249600016,
author = {Springell, Ross and Rennie, Sophie and Costelle, Leila and Darnbrough, James and Stitt, Camilla and Cocklin, Elizabeth and Lucas, Chris and Burrows, Robert and Sims, Howard and Wermeille, Didier and Rawle, Jonathan and Nicklin, Chris and Nuttall, William and Scott, Thomas and Lander, Gerard},
title = {Water corrosion of spent nuclear fuel: radiolysis driven dissolution at the UO2/water interface},
journal = {FARADAY DISCUSSIONS},
year = {2015},
volume = {180},
pages = {301-311},
doi = {https://doi.org/10.1039/c4fd00254g}
}
|
| Qviller, A.J., Dennison, A.J.C., Haug, H., You, C.C., Hasle, I.M., Ostreng, E., Fjellvag, H., Vorobiev, A., Hjorvarsson, B., Marstein, E.S., Frommen, C. and Hauback, B.C. Thermal stability of photovoltaic a-Si:H determined by neutron reflectometry APPLIED PHYSICS LETTERS 105, 23 (2014) |
| Abstract: Neutron and X-ray reflectometry were used to determine the layer
structure and hydrogen content of thin films of amorphous silicon (a-Si:H) deposited onto crystalline silicon (Si) wafers for surface passivation in solar cells. The combination of these two reflectometry techniques is well suited for non-destructive probing of the structure of a-Si:H due to being able to probe buried interfaces and having sub-nanometer resolution. Neutron reflectometry is also unique in its ability to allow determination of density gradients of light elements such as hydrogen (H). The neutron scattering contrast between Si and H is strong, making it possible to determine the H concentration in the deposited a-Si:H. In order to correlate the surface passivation properties supplied by the a-Si:H thin films, as quantified by obtainable effective minority carrier lifetime, photoconductance measurements were also performed. It is shown that the minority carrier lifetime falls sharply when H has been desorbed from a-Si:H by annealing. (C) 2014 AIP Publishing LLC. |
BibTeX:
@article{WOS:000346266000041,
author = {Qviller, A. J. and Dennison, A. J. C. and Haug, H. and You, C. C. and Hasle, I. M. and Ostreng, E. and Fjellvag, H. and Vorobiev, A. and Hjorvarsson, B. and Marstein, E. S. and Frommen, C. and Hauback, B. C.},
title = {Thermal stability of photovoltaic a-Si:H determined by neutron reflectometry},
journal = {APPLIED PHYSICS LETTERS},
year = {2014},
volume = {105},
number = {23},
doi = {https://doi.org/10.1063/1.4904340}
}
|
| Ciudad, D., Gobbi, M., Kinane, C.J., Eich, M., Moodera, J.S. and Hueso, L.E. Sign Control of Magnetoresistance Through Chemically Engineered Interfaces ADVANCED MATERIALS 26, 45, pp. 7561-7567 (2014) |
BibTeX:
@article{WOS:000345969400004,
author = {Ciudad, David and Gobbi, Marco and Kinane, Christy J. and Eich, Marius and Moodera, Jagadeesh S. and Hueso, Luis E.},
title = {Sign Control of Magnetoresistance Through Chemically Engineered Interfaces},
journal = {ADVANCED MATERIALS},
year = {2014},
volume = {26},
number = {45},
pages = {7561-7567},
doi = {https://doi.org/10.1002/adma.201401283}
}
|
| Moon, E.J., Colby, R., Wang, Q., Karapetrova, E., Schlepuetz, C.M., Fitzsimmons, M.R. and May, S.J. Spatial control of functional properties via octahedral modulations in complex oxide superlattices NATURE COMMUNICATIONS 5 (2014) |
| Abstract: Control of atomic structure, namely the topology of the corner-connected
metal-oxygen octahedra, has emerged as an important route to tune the functional properties at oxide interfaces. Here we investigate isovalent manganite superlattices (SLs), [(La0.7Sr0.3MnO3) n/(Eu0.7Sr0.3MnO3) n] x m, as a route to spatial control over electronic bandwidth and ferromagnetism through the creation of octahedral superstructures. Electron energy loss spectroscopy confirms a uniform Mn valence state throughout the SLs. In contrast, the presence of modulations of the MnO6 octahedral rotations along the growth direction commensurate with the SL period is revealed by scanning transmission electron microscopy and X-ray diffraction. We show that the Curie temperatures of the constituent materials can be systematically engineered via the octahedral superstructures leading to a modulated magnetization in samples where the SL period is larger than the interfacial octahedral coupling length scale, whereas a single magnetic transition is observed in the short-period SLs. |
BibTeX:
@article{WOS:000347229300006,
author = {Moon, E. J. and Colby, R. and Wang, Q. and Karapetrova, E. and Schlepuetz, C. M. and Fitzsimmons, M. R. and May, S. J.},
title = {Spatial control of functional properties via octahedral modulations in complex oxide superlattices},
journal = {NATURE COMMUNICATIONS},
year = {2014},
volume = {5},
doi = {https://doi.org/10.1038/ncomms6710}
}
|
| Collins-McIntyre, L.J., Watson, M.D., Baker, A.A., Zhang, S.L., Coldea, A.I., Harrison, S.E., Pushp, A., Kellock, A.J., Parkin, S.S.P., van der Laan, G. and Hesjedal, T. X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi2Se3 thin films AIP ADVANCES 4, 12 (2014) |
| Abstract: We report the growth of Mn-doped Bi2Se3 thin films by molecular beam
epitaxy (MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to similar to 7.5 atomic-% Mn, determined by Rutherford back-scattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mn is observed with increasing doping concentration. A magnetic moment of 5.1 mu(B)/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 mu(B)/Mn from surface-sensitive XMCD. At similar to 2.5 K, XMCD at the Mn L-2,L-3 edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K. (C) 2014 Author(s). |
BibTeX:
@article{WOS:000347170100067,
author = {Collins-McIntyre, L. J. and Watson, M. D. and Baker, A. A. and Zhang, S. L. and Coldea, A. I. and Harrison, S. E. and Pushp, A. and Kellock, A. J. and Parkin, S. S. P. and van der Laan, G. and Hesjedal, T.},
title = {X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi2Se3 thin films},
journal = {AIP ADVANCES},
year = {2014},
volume = {4},
number = {12},
doi = {https://doi.org/10.1063/1.4904900}
}
|
| Kinane, C.J., Loving, M., de Vries, M.A., Fan, R., Charlton, T.R., Claydon, J.S., Arena, D.A., Maccherozzi, F., Dhesi, S.S., Heiman, D., Marrows, C.H., Lewis, L.H. and Langridge, S. Observation of a temperature dependent asymmetry in the domain structure of a Pd-doped FeRh epilayer NEW JOURNAL OF PHYSICS 16 (2014) |
| Abstract: Using x-ray photoelectron emission microscopy we have observed the
coexistence of ferromagnetic and antiferromagnetic phases in a (3 at%) Pd-doped FeRh epilayer. By quantitatively analyzing the resultant images we observe that as the epilayer transforms there is a change in magnetic domain symmetry from predominantly twofold at lower temperatures through to an equally weighted combination of both four and twofold symmetries at higher temperature. It is postulated that the lowered symmetry Ising-like nematic phase resides at the near-surface of the epilayer. This behavior is different to that of undoped FeRh suggesting that the variation in symmetry is driven by the competing structural and electronic interactions in the nanoscale FeRh film coupled with the effect of the chemical doping disorder. |
BibTeX:
@article{WOS:000346764100011,
author = {Kinane, C. J. and Loving, M. and de Vries, M. A. and Fan, R. and Charlton, T. R. and Claydon, J. S. and Arena, D. A. and Maccherozzi, F. and Dhesi, S. S. and Heiman, D. and Marrows, C. H. and Lewis, L. H. and Langridge, Sean},
title = {Observation of a temperature dependent asymmetry in the domain structure of a Pd-doped FeRh epilayer},
journal = {NEW JOURNAL OF PHYSICS},
year = {2014},
volume = {16},
doi = {https://doi.org/10.1088/1367-2630/16/11/113073}
}
|
| Kumah, D.P., Malashevich, A., Disa, A.S., Arena, D.A., Walker, F.J., Ismail-Beigi, S. and Ahn, C.H. Effect of Surface Termination on the Electronic Properties of LaNiO3 Films PHYSICAL REVIEW APPLIED 2, 5 (2014) |
| Abstract: The electronic and structural properties of thin LaNiO3 films grown by
using molecular beam epitaxy are studied as a function of the net ionic charge of the surface terminating layer. We demonstrate that electronic transport in nickelate heterostructures can be manipulated through changes in the surface termination due to a strong coupling of the surface electrostatic properties to the structural properties of the Ni-O bonds that govern electronic conduction. We observe experimentally and from first-principles theory an asymmetric response of the structural properties of the films to the sign of the surface charge, which results from a strong interplay between electrostatic and mechanical boundary conditions governing the system. The structural response results in ionic buckling in the near-surface NiO2 planes for films terminated with negatively charged NiO2 and bulklike NiO2 planes for films terminated with positively charged LaO planes. The ability to modify transport properties by the deposition of a single atomic layer can be used as a guiding principle for nanoscale device fabrication. |
BibTeX:
@article{WOS:000344344300001,
author = {Kumah, Divine P. and Malashevich, Andrei and Disa, Ankit S. and Arena, Dario A. and Walker, Frederick J. and Ismail-Beigi, Sohrab and Ahn, Charles H.},
title = {Effect of Surface Termination on the Electronic Properties of LaNiO3 Films},
journal = {PHYSICAL REVIEW APPLIED},
year = {2014},
volume = {2},
number = {5},
doi = {https://doi.org/10.1103/PhysRevApplied.2.054004}
}
|
| Ahlberg, M., Zamani, A., Ostman, E., Fashandi, H., Hjorvarsson, B. and Jonsson, P.E. Reversed interface effects in amorphous FeZr/AlZr multilayers PHYSICAL REVIEW B 90, 18 (2014) |
| Abstract: We report an anomalous enhancement of the critical temperature (T-c)
when the thickness (d) of the magnetic layer is decreased from 60 to 20 angstrom in amorphous FeZr/AlZr multilayers. Further reduction of the thickness causes a decrease of T-c, as expected by finite-size scaling, while the magnetic moment decreases monotonically for all values of d. The increase of the critical temperature is attributed to a reversed interface effect where local changes in the nearest-neighbor distance and coordination number gives a higher effective magnetic coupling at the interfaces compared to the interior of the layer. We have successfully described the results within a model where such interface effects are combined with finite-size scaling. |
BibTeX:
@article{WOS:000344487600002,
author = {Ahlberg, Martina and Zamani, Atieh and Ostman, Erik and Fashandi, Hossein and Hjorvarsson, Bjorgvin and Jonsson, Petra E.},
title = {Reversed interface effects in amorphous FeZr/AlZr multilayers},
journal = {PHYSICAL REVIEW B},
year = {2014},
volume = {90},
number = {18},
doi = {https://doi.org/10.1103/PhysRevB.90.184403}
}
|
| Mooij, L., Perkisas, T., Palsson, G., Schreuders, H., Wolff, M., Hjorvarsson, B., Bals, S. and Dam, B. The effect of microstructure on the hydrogenation of Mg/Fe thin film multilayers INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 39, 30, pp. 17092-17103 (2014) |
| Abstract: Nanoconfined magnesium hydride can be simultaneously protected and
thermodynamically destabilized when interfaced with materials such as Ti and Fe. We study the hydrogenation of thin layers of Mg (<14 nm) nanoconfined in one dimension within thin film Fe/Mg/Fe/Pd multilayers by the optical technique Hydrogenography. The hydrogenation of nanosized magnesium layers in Fe/Mg/Fe multilayers surprisingly shows the presence of multiple plateau pressures, whose nature is thickness dependent. In contrast, hydrogen desorption occurs via a single plateau which does not depend on the Mg layer thickness. From structural and morphological analyses with X-ray diffraction/reflectometry and cross-section TEM, we find that the Mg layer roughness is large when deposited on Fe and furthermore contains high-angle grain boundaries (GB's). When grown on Ti, the Mg layer roughness is low and no high-angle GB's are detected. From a Ti/Mg/Fe multilayer, in which the Mg layer is flat and has little or no GB's, we conclude that MgH2 is indeed destabilized by the interface with Fe. In this case, both the ab- and desorption plateau pressures are increased by a factor two compared to the hydrogenation of Mg within Ti/Mg/Ti multilayers. We hypothesize that the GB's in the Fe/Mg/Fe multilayer act as diffusion pathways for Pd, which is known to greatly alter the hydrogenation behavior of Mg when the two materials share an interface. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. |
BibTeX:
@article{WOS:000343839000031,
author = {Mooij, Lennard and Perkisas, Tyche and Palsson, Gunnar and Schreuders, Herman and Wolff, Max and Hjorvarsson, Bjorgvin and Bals, Sara and Dam, Bernard},
title = {The effect of microstructure on the hydrogenation of Mg/Fe thin film multilayers},
journal = {INTERNATIONAL JOURNAL OF HYDROGEN ENERGY},
year = {2014},
volume = {39},
number = {30},
pages = {17092-17103},
doi = {https://doi.org/10.1016/j.ijhydene.2014.08.035}
}
|
| Ribera, R.C., van de Kruijs, R.W.E., Kokke, S., Zoethout, E., Yakshin, A.E. and Bijkerk, F. Surface and sub-surface thermal oxidation of thin ruthenium films APPLIED PHYSICS LETTERS 105, 13 (2014) |
| Abstract: A mixed 2D (film) and 3D (nano-column) growth of ruthenium oxide has
been experimentally observed for thermally oxidized polycrystalline ruthenium thin films. Furthermore, in situ x-ray reflectivity upon annealing allowed the detection of 2D film growth as two separate layers consisting of low density and high density oxides. Nano-columns grow at the surface of the low density oxide layer, with the growth rate being limited by diffusion of ruthenium through the formed oxide film. Simultaneously, with the growth of the columns, sub-surface high density oxide continues to grow limited by diffusion of oxygen or ruthenium through the oxide film. (C) 2014 AIP Publishing LLC. |
BibTeX:
@article{WOS:000343031700013,
author = {Ribera, R. Coloma and van de Kruijs, R. W. E. and Kokke, S. and Zoethout, E. and Yakshin, A. E. and Bijkerk, F.},
title = {Surface and sub-surface thermal oxidation of thin ruthenium films},
journal = {APPLIED PHYSICS LETTERS},
year = {2014},
volume = {105},
number = {13},
doi = {https://doi.org/10.1063/1.4896993}
}
|
| Moorsom, T., Wheeler, M., Khan, T.M., Al Ma'Mari, F., Kinane, C., Langridge, S., Ciudad, D., Bedoya-Pinto, A., Hueso, L., Teobaldi, G., Lazarov, V.K., Gilks, D., Burnell, G., Hickey, B.J. and Cespedes, O. Spin-polarized electron transfer in ferromagnet/C-60 interfaces PHYSICAL REVIEW B 90, 12 (2014) |
| Abstract: The contact between a molecule and a metallic electrode contributes to
or even determines the characteristics of organic devices, such as their electronic properties. This is partly due to the charge transfer that takes place when two materials with different chemical potentials are put together. In the case of magnetic electrodes, the transfer can be accompanied by the transmission of a net spin polarization or spin doping. In nanocarbon systems, hybridization and spin doping can suppress the moment of a transition metal ferromagnet through the loss of majority spin electrons to the organic. Here, C-60 is shown to become ferromagnetic as a result of spin doping from cobalt with an induced moment of 1.2 mu(B) per cage while suppressing the moment of the ferromagnet by up to 21%. Polarized neutron reflectivity and x-ray magnetic circular dichroism reveal the presence of an antiferromagnetic coupling of the interfacial layers of cobalt and C-60, and weakly coupled induced magnetism propagating into the bulk organic. Thus, it is shown that the deposition of molecules with high electron affinity can be used to induce zero-voltage spin injection. |
BibTeX:
@article{WOS:000344016400009,
author = {Moorsom, Timothy and Wheeler, May and Khan, Taukeer Mohd and Al Ma'Mari, Fatma and Kinane, Christian and Langridge, Sean and Ciudad, David and Bedoya-Pinto, Amilcar and Hueso, Luis and Teobaldi, Gilberto and Lazarov, Vlado K. and Gilks, Daniel and Burnell, Gavin and Hickey, Bryan J. and Cespedes, Oscar},
title = {Spin-polarized electron transfer in ferromagnet/C-60 interfaces},
journal = {PHYSICAL REVIEW B},
year = {2014},
volume = {90},
number = {12},
doi = {https://doi.org/10.1103/PhysRevB.90.125311}
}
|
| Macke, S. and Goering, E. Magnetic reflectometry of heterostructures JOURNAL OF PHYSICS-CONDENSED MATTER 26, 36 (2014) |
| Abstract: Measuring the magnetic configuration at complex buried layers and
interfaces is an important task, which requires especially a non-destructive probing technique. X-ray resonant magnetic reflectometry (XRMR) combines the non-destructive depth profiling potential of x-ray reflectometry with the excellent sensitivity for magnetic phenomena, utilizing the x-ray magnetic circular dichroism effect. It provides the magnetic spatial distribution with a precision down to the angstrom scale, combined with element and symmetry specificity, sub-monolayer sensitivity, and the possible separation of spin and orbital magnetic moments. This review provides an overview to the XRMR technique in a tutorial way. We focus on the introduction to the theory, measurement types, and data simulation. We provide related experimental examples and show selected applications. |
BibTeX:
@article{WOS:000341112800001,
author = {Macke, S. and Goering, E.},
title = {Magnetic reflectometry of heterostructures},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2014},
volume = {26},
number = {36},
doi = {https://doi.org/10.1088/0953-8984/26/36/363201}
}
|
| Hase, T.P.A., Brewer, M.S., Arnalds, U.B., Ahlberg, M., Kapaklis, V., Bjoerck, M., Bouchenoire, L., Thompson, P., Haskel, D., Choi, Y., Lang, J., Sanchez-Hanke, C. and Hjoervarsson, B. Proximity effects on dimensionality and magnetic ordering in Pd/Fe/Pd trialyers PHYSICAL REVIEW B 90, 10 (2014) |
| Abstract: The element-specific magnetization and ordering in trilayers consisting
of 0.3-1.4 monolayer (ML) thick Fe layers embedded in Pd(001) has been determined using x-ray resonant magnetic scattering. The proximity to Fe induces a large moment in the Pd which extends similar to 2 nm from the interfaces. The magnetization as a function of temperature is found to differ significantly for the Fe and Pd sublattices: The Pd signal resembles the results obtained by magneto-optical techniques with an apparent three-dimensional (3D) to two-dimensional (2D) transition in spatial dimensionality for Fe thickness below similar to 1 ML. In stark contrast, the Fe data exhibits a 2D behavior. No ferromagnetic signal is obtained from Fe below the 2D percolation limit in Fe coverage (similar to 0.7 ML), while Pd shows a ferromagnetic response for all samples. The results are attributed to the temperature dependence of the susceptibility of Pd and a profound local anisotropy of submonolayered Fe. |
BibTeX:
@article{WOS:000341239100007,
author = {Hase, Thomas P. A. and Brewer, Matthew S. and Arnalds, Unnar B. and Ahlberg, Martina and Kapaklis, Vassilios and Bjoerck, Matts and Bouchenoire, Laurence and Thompson, Paul and Haskel, Daniel and Choi, Yongseong and Lang, Jonathan and Sanchez-Hanke, Cecilia and Hjoervarsson, Bjoergvin},
title = {Proximity effects on dimensionality and magnetic ordering in Pd/Fe/Pd trialyers},
journal = {PHYSICAL REVIEW B},
year = {2014},
volume = {90},
number = {10},
doi = {https://doi.org/10.1103/PhysRevB.90.104403}
}
|
| Collins-McIntyre, L.J., Harrison, S.E., Schoenherr, P., Steinke, N.J., Kinane, C.J., Charlton, T.R., Alba-Veneroa, D., Pushp, A., Kellock, A.J., Parkin, S.S.P., Harris, J.S., Langridge, S., van der Laan, G. and Hesjedal, T. Magnetic ordering in Cr-doped Bi2Se3 thin films EPL 107, 5 (2014) |
| Abstract: We report the structural and magnetic study of Cr-doped Bi2Se3 thin
films using x-ray diffraction (XRD), magnetometry and polarized neutron reflectometry (PNR). Epitaxial layers were grown on c-plane sapphire by molecular beam epitaxy in a two-step process. High-resolution XRD shows the exceptionally high crystalline quality of the doped films with no parasitic phases up to a Cr concentration of 12% (in % of the Bi sites occupied by substitutional Cr). The magnetic moment, measured by SQUID magnetometry, was found to be similar to 2.1 mu B per Cr ion. The magnetic hysteresis curve shows an open loop with a coercive field of similar to 10 mT. The ferromagnetic transition temperature was determined to be 8.5K analyzing the magnetization-temperature gradient. PNR shows the film to be homogeneously ferromagnetic with no enhanced magnetism near the surface or interface. Copyright (C) EPLA, 2014 |
BibTeX:
@article{WOS:000341559900029,
author = {Collins-McIntyre, L. J. and Harrison, S. E. and Schoenherr, P. and Steinke, N. -J. and Kinane, C. J. and Charlton, T. R. and Alba-Veneroa, D. and Pushp, A. and Kellock, A. J. and Parkin, S. S. P. and Harris, J. S. and Langridge, S. and van der Laan, G. and Hesjedal, T.},
title = {Magnetic ordering in Cr-doped Bi2Se3 thin films},
journal = {EPL},
year = {2014},
volume = {107},
number = {5},
doi = {https://doi.org/10.1209/0295-5075/107/57009}
}
|
| Xie, Y.J., Scafetta, M.D., Moon, E.J., Krick, A.L., Sichel-Tissot, R.J. and May, S.J. Electronic phase diagram of epitaxial La1-xSrxFeO3 films APPLIED PHYSICS LETTERS 105, 6 (2014) |
| Abstract: The electronic phase diagram of epitaxial La1-xSrxFeO3 films is
presented. The films were grown on SrTiO3 using molecular beam epitaxy with post-growth annealing to minimize oxygen vacancies. Insulating behavior is observed from x = 0-0.9, with metallic conduction only present for x = 1.0. While the La-rich compounds exhibit polaron conduction over all temperatures measured, the Sr-rich films exhibit an electronic phase transition within the compositional window of x = 0.49-0.9 as revealed by temperature-dependent resistivity measurements. The transition temperatures are found to decrease with increasing Sr content. The constructed phase diagram is discussed in the context of other 3d e(g) perovskite systems including manganites and cobaltites. (C) 2014 AIP Publishing LLC. |
BibTeX:
@article{WOS:000341188700039,
author = {Xie, Y. J. and Scafetta, M. D. and Moon, E. J. and Krick, A. L. and Sichel-Tissot, R. J. and May, S. J.},
title = {Electronic phase diagram of epitaxial La1-xSrxFeO3 films},
journal = {APPLIED PHYSICS LETTERS},
year = {2014},
volume = {105},
number = {6},
doi = {https://doi.org/10.1063/1.4893139}
}
|
| Devlin, R.C., Krick, A.L., Sichel-Tissot, R.J., Xie, Y.J. and May, S.J. Electronic transport and conduction mechanism transition in La1/3Sr2/3FeO3 thin films JOURNAL OF APPLIED PHYSICS 115, 23 (2014) |
| Abstract: We report on the electronic transport properties of epitaxial
La1/3Sr2/3FeO3 films using temperature dependent resistivity, Hall effect, and magnetoresistance measurements. We show that the electronic phase transition, which occurs near 190 K, results in a change in conduction mechanism from nonadiabatic polaron transport at high temperatures to resistivity behavior following a power law temperature dependence at low temperatures. The phase transition is also accompanied by an abrupt increase in apparent mobility and Hall coefficient below the critical temperature (T*). We argue that the exotic low temperature transport properties are a consequence of the unusually long-range periodicity of the antiferromagnetic ordering, which also couples to the electronic transport in the form of a negative magnetoresistance below T* and a sign reversal of the Hall coefficient at T*. By comparing films of differing thicknesses, stoichiometry, and strain states, we demonstrate that the observed conduction behavior is a robust feature of La1/3Sr2/3FeO3. (C) 2014 AIP Publishing LLC. |
BibTeX:
@article{WOS:000338106000029,
author = {Devlin, R. C. and Krick, A. L. and Sichel-Tissot, R. J. and Xie, Y. J. and May, S. J.},
title = {Electronic transport and conduction mechanism transition in La1/3Sr2/3FeO3 thin films},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2014},
volume = {115},
number = {23},
doi = {https://doi.org/10.1063/1.4883541}
}
|
| Rath, T., Novak, J., Amenitsch, H., Pein, A., Maier, E., Haas, W., Hofer, E. and Trimmel, G. Real time X-ray scattering study of the formation of ZnS nanoparticles using synchrotron radiation MATERIALS CHEMISTRY AND PHYSICS 144, 3, pp. 310-317 (2014) |
| Abstract: We investigate the growth of ZnS nanoparticles by a real-time
simultaneous small and wide angle X-ray scattering (SAXS, WAXS) study using synchrotron radiation. Zinc chloride and elemental sulfur were dissolved in oleylamine. The formation of nanoparticles was induced by heating to 170 degrees C and 215 degrees C. The influence of temperature, reaction time, and sulfur concentration was investigated. After a short phase of rapid growth, saturation in size and a slower growth is observed depending on the temperature. The final size of the nanoparticles ranges between 2 and 6 nm for the investigated growth conditions and increases with the reaction temperature and sulfur concentration. SAXS analysis allows for determination of the size of the nanoparticles and proves also the existence of an organized layer of oleylamine molecules covering the nanoparticles' surfaces, which, however, appears only for diameters of the nanoparticles larger than approximately 2.8 nm. The investigation of the measured structure factor of the nanoparticle assemblies showed that the distance of an attractive interaction is 2.5 nm, which was interpreted as a consequence of the ordered oleylamine surface layer. (C) 2014 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000333493400014,
author = {Rath, T. and Novak, J. and Amenitsch, H. and Pein, A. and Maier, E. and Haas, W. and Hofer, E. and Trimmel, G.},
title = {Real time X-ray scattering study of the formation of ZnS nanoparticles using synchrotron radiation},
journal = {MATERIALS CHEMISTRY AND PHYSICS},
year = {2014},
volume = {144},
number = {3},
pages = {310-317},
doi = {https://doi.org/10.1016/j.matchemphys.2013.12.045}
}
|
| Das, S., Sen, K., Marozau, I., Uribe-Laverde, M.A., Biskup, N., Varela, M., Khaydukov, Y., Soltwedel, O., Keller, T., Doebeli, M., Schneider, C.W. and Bernhard, C. Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La1.85Sr0.15CuO4/La2/3Ca1/3MnO3 superlattices on (001)-oriented LaSrAlO4 substrates PHYSICAL REVIEW B 89, 9 (2014) |
| Abstract: Epitaxial La1.85Sr0.15CuO4/ La2/ 3Ca1/ 3MnO3 ( LSCO/ LCMO) superlattices
on ( 001)-oriented LaSrAlO4 substrates have been grown with pulsed laser deposition technique. Their structural, magnetic, and superconducting properties have been determined with in situ reflection high-energy electron diffraction, x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy, electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO (a = 0.3779 nm) and LCMO (a = 0.387 nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the LaSrAlO4 substrate, a sizable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMOlayers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of T onset c approximate to 36 K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for H parallel to ab and a sizable paramagnetic shift for H parallel to c that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of T Curie approximate to 190 K and a large low-temperature saturation moment of about 3.5(1) mu(B) per Mn ion. These results suggest that the LSCO/ LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on YBa2Cu3O7-x/ La2/ 3Ca1/ 3MnO3 superlattices, may allow one to identify the relevant mechanisms. |
BibTeX:
@article{WOS:000332629300003,
author = {Das, S. and Sen, K. and Marozau, I. and Uribe-Laverde, M. A. and Biskup, N. and Varela, M. and Khaydukov, Y. and Soltwedel, O. and Keller, T. and Doebeli, M. and Schneider, C. W. and Bernhard, C.},
title = {Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La1.85Sr0.15CuO4/La2/3Ca1/3MnO3 superlattices on (001)-oriented LaSrAlO4 substrates},
journal = {PHYSICAL REVIEW B},
year = {2014},
volume = {89},
number = {9},
doi = {https://doi.org/10.1103/PhysRevB.89.094511}
}
|
| Xie, Y., Scafetta, M.D., Sichel-Tissot, R.J., Moon, E.J., Devlin, R.C., Wu, H., Krick, A.L. and May, S.J. Control of Functional Responses Via Reversible Oxygen Loss in La1-xSrxFeO3-delta Films ADVANCED MATERIALS 26, 9, pp. 1434-1438 (2014) |
| Abstract: La0.3Sr0.7FeO3-delta films undergo dramatic changes in electronic and
optical properties due to reversible oxygen loss induced by low-temperature heating. This mechanism to control the functional properties may serve as a platform for new devices or sensors in which external stimuli are used to dynamically control the composition of complex oxide heterostructures. |
BibTeX:
@article{WOS:000335669400012,
author = {Xie, Yujun and Scafetta, Mark D. and Sichel-Tissot, Rebecca J. and Moon, Eun Ju and Devlin, Robert C. and Wu, Hanqi and Krick, Alex L. and May, Steven J.},
title = {Control of Functional Responses Via Reversible Oxygen Loss in La1-xSrxFeO3-delta Films},
journal = {ADVANCED MATERIALS},
year = {2014},
volume = {26},
number = {9},
pages = {1434-1438},
doi = {https://doi.org/10.1002/adma.201304374}
}
|
| Kumah, D.P., Disa, A.S., Ngai, J.H., Chen, H., Malashevich, A., Reiner, J.W., Ismail-Beigi, S., Walker, F.J. and Ahn, C.H. Tuning the Structure of Nickelates to Achieve Two-Dimensional Electron Conduction ADVANCED MATERIALS 26, 12, pp. 1935-1940 (2014) |
BibTeX:
@article{WOS:000333523600012,
author = {Kumah, Divine P. and Disa, Ankit S. and Ngai, Joseph H. and Chen, Hanghui and Malashevich, Andrei and Reiner, James W. and Ismail-Beigi, Sohrab and Walker, Frederick J. and Ahn, Charles H.},
title = {Tuning the Structure of Nickelates to Achieve Two-Dimensional Electron Conduction},
journal = {ADVANCED MATERIALS},
year = {2014},
volume = {26},
number = {12},
pages = {1935-1940},
doi = {https://doi.org/10.1002/adma.201304256}
}
|
| Shcherbina, M.A., Chvalun, S.N., Ponomarenko, S.A. and Kovalchuk, M.V. Modern approaches to investigation of thin films and monolayers: X-ray reflectivity, grazing-incidence X-ray scattering and X-ray standing waves RUSSIAN CHEMICAL REVIEWS 83, 12, pp. 1091-1119 (2014) |
| Abstract: The review concerns modern experimental methods of structure
determination of thin films of different nature. The methods are based on total reflection of X-rays from the surface and include X-ray reflectivity, grazing-incidence X-ray scattering and X-ray standing waves. Their potential is exemplified by the investigations of various organic macromolecular systems that exhibit the properties of semiconductors and are thought to be promising as thin-film transistors, light-emitting diodes and photovoltaic cells. It is shown that combination of the title methods enable high-precision investigations of the structure of thin-film materials and structure formation in them, i.e., it is possible to obtain information necessary for improvement of the operating efficiency of elements of organic electronic devices. |
BibTeX:
@article{WOS:000347028200002,
author = {Shcherbina, M. A. and Chvalun, S. N. and Ponomarenko, S. A. and Kovalchuk, M. V.},
title = {Modern approaches to investigation of thin films and monolayers: X-ray reflectivity, grazing-incidence X-ray scattering and X-ray standing waves},
journal = {RUSSIAN CHEMICAL REVIEWS},
year = {2014},
volume = {83},
number = {12},
pages = {1091-1119},
doi = {https://doi.org/10.1070/RCR4485}
}
|
| Mihai, A.P., Whiteside, A.L., Canwell, E.J., Marrows, C.H., Benitez, M.J., McGrouther, D., McVitie, S., McFadzean, S. and Moore, T.A. Effect of substrate temperature on the magnetic properties of epitaxial sputter-grown Co/Pt APPLIED PHYSICS LETTERS 103, 26 (2013) |
| Abstract: Epitaxial Co/Pt films have been deposited by dc-magnetron sputtering
onto heated C-plane sapphire substrates. X-ray diffraction, the residual resistivity, and transmission electron microscopy indicate that the Co/Pt films are highly ordered on the atomic scale. The coercive field and the perpendicular magnetic anisotropy increase as the substrate temperature is increased from 100-250 degrees C during deposition of the Co/Pt. Measurement of the domain wall creep velocity as a function of applied magnetic field yields the domain wall pinning energy, which scales with the coercive field. Evidence for an enhanced creep velocity in highly ordered epitaxial Co/Pt is found. (C) 2013 AIP Publishing LLC. |
BibTeX:
@article{WOS:000329977400037,
author = {Mihai, A. P. and Whiteside, A. L. and Canwell, E. J. and Marrows, C. H. and Benitez, M. J. and McGrouther, D. and McVitie, S. and McFadzean, S. and Moore, T. A.},
title = {Effect of substrate temperature on the magnetic properties of epitaxial sputter-grown Co/Pt},
journal = {APPLIED PHYSICS LETTERS},
year = {2013},
volume = {103},
number = {26},
doi = {https://doi.org/10.1063/1.4856395}
}
|
| Sichel-Tissot, R.J., Devlin, R.C., Ryan, P.J., Kim, J.-W. and May, S.J. The effect of oxygen vacancies on the electronic phase transition in La1/3Sr2/3FeO3 films APPLIED PHYSICS LETTERS 103, 21 (2013) |
| Abstract: Synchrotron x-ray diffraction and electrical resistivity were used to
probe the electronic phase transition in two strained La1/3Sr2/3FeO3 films on (001) SrTiO3 substrates, one nominally stoichiometric and one with a higher concentration of oxygen vacancies. We present evidence that oxygen vacancies inhibit the size of charge ordered domains and reduce the abruptness of the phase transition. Additionally, the correlation lengths measured from (4/3 4/3 4/3) peaks, arising from charge disproportionation, increase rapidly across the transition, suggesting that the resistivity increase at the transition temperature is caused by the nucleation and growth of charge ordered domains. (C) 2013 AIP Publishing LLC. |
BibTeX:
@article{WOS:000327590400059,
author = {Sichel-Tissot, Rebecca J. and Devlin, Robert C. and Ryan, Philip J. and Kim, Jong-Woo and May, Steven J.},
title = {The effect of oxygen vacancies on the electronic phase transition in La1/3Sr2/3FeO3 films},
journal = {APPLIED PHYSICS LETTERS},
year = {2013},
volume = {103},
number = {21},
doi = {https://doi.org/10.1063/1.4833276}
}
|
| Broch, K., Gerlach, A., Lorch, C., Dieterle, J., Novak, J., Hinderhofer, A. and Schreiber, F. Structure formation in perfluoropentacene:diindenoperylene blends and its impact on transient effects in the optical properties studied in real-time during growth JOURNAL OF CHEMICAL PHYSICS 139, 17 (2013) |
| Abstract: We discuss the result of the competing effects of favourable
intermolecular interactions and steric incompatibilities due to the size mismatch of perfluoropentacene (PFP) and diindenoperylene (DIP) on the structure formation and associated optical properties in mixed films. Using real-time grazing incidence X-ray diffraction we investigate the size of coherently scattering islands l(s) as a function of film thickness and mixing ratio. We find that for PFP: DIP 1: 2 blends l(s) is by a factor of similar to 4 smaller than in pure DIP films, while l(s) of the PFP: DIP 2: 1 blends is not significantly reduced compared with pure PFP. Yet, we observe an increase in l(s) with film thickness for all of the samples, independent on the mixing ratio. In parallel with the structural characterization we investigate the evolution of the absorption spectra in the visible spectral range and its dependence on l(s) in situ during film growth using differential reflectance spectroscopy. We observe a surprisingly strong effect of changes in the structural order on the shape of epsilon(2, xy)(E), evident by a pronounced evolution of characteristic peaks in the thickness range from 1.6 nm to 9.6 nm. The combined results of the real-time experiments allow to identify the thickness dependent crystal grain size as the origin of the observed transient effects in the absorption spectra. (C) 2013 AIP Publishing LLC. |
BibTeX:
@article{WOS:000326922300047,
author = {Broch, K. and Gerlach, A. and Lorch, C. and Dieterle, J. and Novak, J. and Hinderhofer, A. and Schreiber, F.},
title = {Structure formation in perfluoropentacene:diindenoperylene blends and its impact on transient effects in the optical properties studied in real-time during growth},
journal = {JOURNAL OF CHEMICAL PHYSICS},
year = {2013},
volume = {139},
number = {17},
doi = {https://doi.org/10.1063/1.4827868}
}
|
| Zamani, A., Hallen, A., Nordblad, P., Andersson, G., Hjorvarsson, B. and Jonsson, P.E. Tuning magnetic properties by hydrogen implantation in amorphous Fe100-xZrx thin films JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 346, pp. 138-141 (2013) |
| Abstract: Thin films of amorphous Fe100-xZrx (x=7.6-12.9 at%) were synthesized by
dc-magnetron sputtering. Samples with compositions of x=11.6 and 12.0 at% were hydrogenated by implantation. The Curie temperature increases with hydrogen content from 232 K for as-grown Fe88Zr12 to 370 K for a sample hydrogenated to 31 at%. The coercivity decreases dramatically upon hydrogenation, yielding films with tunable transition temperatures and soft magnetic properties. (C) 2013 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000324311200024,
author = {Zamani, Atieh and Hallen, Anders and Nordblad, Per and Andersson, Gabriella and Hjorvarsson, Bjorgvin and Jonsson, Petra E.},
title = {Tuning magnetic properties by hydrogen implantation in amorphous Fe100-xZrx thin films},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2013},
volume = {346},
pages = {138-141},
doi = {https://doi.org/10.1016/j.jmmm.2013.07.031}
}
|
| Knut, R., Svedlindh, P., Mryasov, O., Gunnarsson, K., Warnicke, P., Arena, D.A., Bjoerck, M., Dennison, A.J.C., Sahoo, A., Mukherjee, S., Sarma, D.D., Granroth, S., Gorgoi, M. and Karis, O. Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers PHYSICAL REVIEW B 88, 13 (2013) |
| Abstract: To address the amount of disorder and interface diffusion induced by
annealing, all-Heusler multilayer structures, consisting of ferromagnetic Co2MnGe and nonmagnetic Rh2CuSn layers of varying thicknesses, have been investigated by means of hard x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism. We find evidence for a 4 angstrom thick magnetically dead layer that, together with the identified interlayer diffusion, are likely reasons for the unexpectedly small magnetoresistance found for current-perpendicular-to-plane giant magnetoresistance devices based on this all-Heusler system. We find that diffusion begins already at comparably low temperatures between 200 and 250 degrees C, where Mn appears to be most prone to diffusion. |
BibTeX:
@article{WOS:000325497600001,
author = {Knut, Ronny and Svedlindh, Peter and Mryasov, Oleg and Gunnarsson, Klas and Warnicke, Peter and Arena, D. A. and Bjoerck, Matts and Dennison, Andrew J. C. and Sahoo, Anindita and Mukherjee, Sumanta and Sarma, D. D. and Granroth, Sari and Gorgoi, Mihaela and Karis, Olof},
title = {Interface characterization of Co2MnGe/Rh2CuSn Heusler multilayers},
journal = {PHYSICAL REVIEW B},
year = {2013},
volume = {88},
number = {13},
doi = {https://doi.org/10.1103/PhysRevB.88.134407}
}
|
| Le Graet, C., de Vries, M.A., McLaren, M., Brydson, R.M.D., Loving, M., Heiman, D., Lewis, L.H. and Marrows, C.H. Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers JOVE-JOURNAL OF VISUALIZED EXPERIMENTS, 80 (2013) |
| Abstract: Chemically ordered alloys are useful in a variety of magnetic
nanotechnologies. They are most conveniently prepared at an industrial scale using sputtering techniques. Here we describe a method for preparing epitaxial thin films of B2-ordered FeRh by sputter deposition onto single crystal MgO substrates. Deposition at a slow rate onto a heated substrate allows time for the adatoms to both settle into a lattice with a well-defined epitaxial relationship with the substrate and also to find their proper places in the Fe and Rh sublattices of the B2 structure. The structure is conveniently characterized with X-ray reflectometry and diffraction and can be visualised directly using transmission electron micrograph cross-sections. B2-ordered FeRh exhibits an unusual metamagnetic phase transition: the ground state is antiferromagnetic but the alloy transforms into a ferromagnet on heating with a typical transition temperature of about 380 K. This is accompanied by a 1% volume expansion of the unit cell: isotropic in bulk, but laterally clamped in an epilayer. The presence of the antiferromagnetic ground state and the associated first order phase transition is very sensitive to the correct equiatomic stoichiometry and proper B2 ordering, and so is a convenient means to demonstrate the quality of the layers that can be deposited with this approach. We also give some examples of the various techniques by which the change in phase can be detected. |
BibTeX:
@article{WOS:000209228800010,
author = {Le Graet, Chantal and de Vries, Mark A. and McLaren, Mathew and Brydson, Richard M. D. and Loving, Melissa and Heiman, Don and Lewis, Laura H. and Marrows, Christopher H.},
title = {Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers},
journal = {JOVE-JOURNAL OF VISUALIZED EXPERIMENTS},
year = {2013},
number = {80},
doi = {https://doi.org/10.3791/50603}
}
|
| Nascimento, V.P., Merino, I.L.C., Passamani, E.C., Alayo, W., Tafur, M., Pelegrini, F., Magalhaes-Paniago, R., Alvarenga, A.D. and Saitovitch, E.B. Clarifying roughness and atomic diffusion contributions to the interface broadening in exchange-biased NiFe/FeMn/NiFe heterostructures THIN SOLID FILMS 542, pp. 360-367 (2013) |
| Abstract: NiFe(30 nm)/FeMn(13 nm)/NiFe(10 nm) heterostructures prepared by
magnetron sputtering at different argon working pressures (0.27, 0.67 and 1.33 Pa) were systematically investigated by using specular and off-specular diffuse X-ray scattering experiments, combined with ferromagnetic resonance technique, in order to distinguish the contribution from roughness and atomic diffusion to the total structural disorder at NiFe/FeMn interfaces. It was shown that an increase in the working gas pressure from 0.27 to 1.33 Pa causes an enhancement of the atomic diffusion at the NiFe/FeMn interfaces, an effect more pronounced at the top FeMn/NiFe interface. In particular, this atomic diffusion provokes a formation of non-uniform magnetic dead-layers at the NiFe/FeMn interfaces (NiFeMn regions with paramagnetic or weak antiferromagnetic properties); that are responsible for the substantial reduction of the exchange bias field in the NiFe/FeMn system. Thus, this work generically helps to understand the discrepancies found in the literature regarding the influence of the interface broadening on the exchange bias properties (e.g., exchange bias field) of the NiFe/FeMn system. (C) 2013 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000323859400061,
author = {Nascimento, V. P. and Merino, I. L. C. and Passamani, E. C. and Alayo, W. and Tafur, M. and Pelegrini, F. and Magalhaes-Paniago, R. and Alvarenga, A. D. and Saitovitch, E. B.},
title = {Clarifying roughness and atomic diffusion contributions to the interface broadening in exchange-biased NiFe/FeMn/NiFe heterostructures},
journal = {THIN SOLID FILMS},
year = {2013},
volume = {542},
pages = {360-367},
doi = {https://doi.org/10.1016/j.tsf.2013.06.097}
}
|
| Ahlberg, M., Papaioannou, E.T., Nowak, G. and Hjorvarsson, B. Temperature dependence of magnetic properties in weakly exchange coupled Fe/V superlattices JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 341, pp. 142-147 (2013) |
| Abstract: We use Fe(3)/V(x)Fe(3)/V(x) superlattices, x = 16-27 monolayers (ML) to
explore the interlayer exchange coupling (IEC) as a function of both spacer layer thickness and temperature. Fe/V is a common model system for studies addressing the IEC, but the behavior in the weakly exchange coupled regime, complemented with the temperature dependence of the magnetic properties, have remained unexplored. We observe clear regions with ferro- and antiferromagnetic coupling, which is manifested in oscillations in the saturation field, the remanence and the critical temperature. The oscillation in the interlayer coupling (J') has a period of 5.8(1) ML. This is approximate to 0.8 ML smaller than observed for Fe(7)/V(x) superlattices which illustrates the influence of the magnetic layer thickness on the interlayer coupling. The temperature dependence of the remanent magnetization was proven to be significantly affected by the strength of the ferromagnetic coupling, leading to high values of the effective critical exponent beta(eff). (c) 2013 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000320583800026,
author = {Ahlberg, Martina and Papaioannou, Evangelos Th and Nowak, Gregor and Hjorvarsson, Bjorgvin},
title = {Temperature dependence of magnetic properties in weakly exchange coupled Fe/V superlattices},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2013},
volume = {341},
pages = {142-147},
doi = {https://doi.org/10.1016/j.jmmm.2013.04.058}
}
|
| Podkaminer, J.P., Hernandez, T., Huang, M., Ryu, S., Bark, C.W., Baek, S.H., Frederick, J.C., Kim, T.H., Cho, K.H., Levy, J., Rzchowski, M.S. and Eom, C.B. Creation of a two-dimensional electron gas and conductivity switching of nanowires at the LaAlO3/SrTiO3 interface grown by 90 degrees off-axis sputtering APPLIED PHYSICS LETTERS 103, 7 (2013) |
| Abstract: Two-dimensional electron gas (2DEG) formed at the interface between two
oxide band-insulators LaAlO3 and SrTiO3 raises the possibility to develop oxide nanoelectronics. Here, we report the creation of a 2DEG at the LaAlO3/SrTiO3 heterointerfaces grown by 90 degrees off-axis sputtering which allows uniform films over a large area. The electrical transport properties of the LaAlO3/SrTiO3 heterointerface are similar to those grown by pulsed laser deposition. We also demonstrate room-temperature conductive probe-based switching of quasi-one-dimensional structures. This work demonstrates that a scalable growth process can be used to create the two-dimensional electron gas system at oxide heterointerfaces. (C) 2013 AIP Publishing LLC. |
BibTeX:
@article{WOS:000323769000014,
author = {Podkaminer, J. P. and Hernandez, T. and Huang, M. and Ryu, S. and Bark, C. W. and Baek, S. H. and Frederick, J. C. and Kim, T. H. and Cho, K. H. and Levy, J. and Rzchowski, M. S. and Eom, C. B.},
title = {Creation of a two-dimensional electron gas and conductivity switching of nanowires at the LaAlO3/SrTiO3 interface grown by 90 degrees off-axis sputtering},
journal = {APPLIED PHYSICS LETTERS},
year = {2013},
volume = {103},
number = {7},
doi = {https://doi.org/10.1063/1.4817921}
}
|
| Moser, A., Salzmann, I., Oehzelt, M., Neuhold, A., Flesch, H.-G., Ivanco, J., Pop, S., Toader, T., Zahn, D.R.T., Smilgies, D.-M. and Resel, R. A disordered layered phase in thin films of sexithiophene CHEMICAL PHYSICS LETTERS 574, pp. 51-55 (2013) |
| Abstract: This Letter reports the impact of the evaporation rate on the
crystallographic phase formation of vacuum deposited alpha-sexithiophene thin films studied by X-ray diffraction methods. The experiments reveal the formation of two crystal phases, one of which is a thermodynamically stable phase occurring at low rates, while the second is favored by high rates. This second phase exhibits an increased layer spacing and diffraction features typical for two-dimensional crystals which are laterally ordered but without interlayer correlations of the molecular positions. This disordered layered phase comprises molecules of nonuniform conformations, and is kinetically induced. (C) 2013 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000320430800009,
author = {Moser, Armin and Salzmann, Ingo and Oehzelt, Martin and Neuhold, Alfred and Flesch, Heinz-Georg and Ivanco, Jan and Pop, Sergiu and Toader, Teodor and Zahn, Dietrich R. T. and Smilgies, Detlef-Matthias and Resel, Roland},
title = {A disordered layered phase in thin films of sexithiophene},
journal = {CHEMICAL PHYSICS LETTERS},
year = {2013},
volume = {574},
pages = {51-55},
doi = {https://doi.org/10.1016/j.cplett.2013.04.053}
}
|
| Yang, Y., Schlepuetz, C.M., Bellucci, F., Allen, M.W., Durbin, S.M. and Clarke, R. Structural investigation of ZnO O-polar (000(1)over-bar) surfaces and Schottky interfaces SURFACE SCIENCE 610, pp. 22-26 (2013) |
| Abstract: We report on the atomic structures of bare and metal-coated ZnO O-polar
(000 (1) over bar) surfaces as determined by model fitting of surface X-ray diffraction data. O-polar surfaces measured under typical device fabrication conditions are significantly rougher than Zn-polar (0001) surfaces, exhibiting Gaussian-shaped roughness profiles with a width of about 1.5 unit cells, regardless of the existence of a metal over-layer. All samples show a decreased layer distance between the topmost oxygen and zinc layers, consistent with theoretical predictions. Clear differences are observed in the occupations of the topmost oxygen layer in oxidized-metal-coated samples. (C) 2013 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000316092800005,
author = {Yang, Yongsoo and Schlepuetz, Christian M. and Bellucci, Francesco and Allen, Martin W. and Durbin, Steven M. and Clarke, Roy},
title = {Structural investigation of ZnO O-polar (000(1)over-bar) surfaces and Schottky interfaces},
journal = {SURFACE SCIENCE},
year = {2013},
volume = {610},
pages = {22-26},
doi = {https://doi.org/10.1016/j.susc.2012.12.018}
}
|
| Uribe-Laverde, M.A., Satapathy, D.K., Marozau, I., Malik, V.K., Das, S., Sen, K., Stahn, J., Ruehm, A., Kim, J.H., Keller, T., Devishvili, A., Toperverg, B.P. and Bernhard, C. Depth profile of the ferromagnetic order in a YBa2Cu3O7/La2/3Ca1/3MnO3 superlattice on a LSAT substrate: A polarized neutron reflectometry study PHYSICAL REVIEW B 87, 11 (2013) |
| Abstract: Using polarized neutron reflectometry (PNR) we have investigated a
[YBa2Cu3O7(10 nm)/La2/3Ca1/3MnO3 (9 nm)] 10 (YBCO/LCMO) superlattice grown by pulsed laser deposition on a La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrate. Due to the high structural quality of the superlattice and the substrate, the specular reflectivity signal extends with a high signal-to-background ratio beyond the fourth-order superlattice Bragg peak. This allows us to obtain more detailed and reliable information about the magnetic depth profile than in previous PNR studies on similar superlattices that were partially impeded by problems related to the low-temperature structural transitions of the SrTiO3 substrates. In agreement with the previous reports, our PNR data reveal a strong magnetic proximity effect showing that the depth profile of the magnetic potential differs significantly from the one of the nuclear potential that is given by the YBCO and LCMO layer thickness. We present fits of the PNR data using different simple blocklike models for which either a large ferromagnetic moment is induced on the YBCO side of the interfaces or the ferromagnetic order is suppressed on the LCMO side. We show that a good agreement with the PNR data and with the average magnetization as obtained from dc magnetization data can only be obtained with the latter model where a so-called depleted layer with a strongly suppressed ferromagnetic moment develops on the LCMO side of the interfaces. We also show that the PNR data are still compatible with the presence of a small, ferromagnetic Cu moment of 0.25 mu(B) on the YBCO side that was previously identified with x-ray magnetic circular dichroism and x-ray resonant magnetic reflectometry measurements on the same superlattice [D. K. Satapathy et al., Phys. Rev. Lett. 108, 197201 (2012)]. We discuss that the depleted layer thus should not be mistaken with a ``dead'' layer that is entirely nonmagnetic but rather may contain a canted antiferromagnetic or an oscillatory type of ordering of the Mn moments that is not detected with the PNR technique. DOI: 10.1103/PhysRevB.87.115105 |
BibTeX:
@article{WOS:000315731400001,
author = {Uribe-Laverde, M. A. and Satapathy, D. K. and Marozau, I. and Malik, V. K. and Das, S. and Sen, K. and Stahn, J. and Ruehm, A. and Kim, J. -H. and Keller, T. and Devishvili, A. and Toperverg, B. P. and Bernhard, C.},
title = {Depth profile of the ferromagnetic order in a YBa2Cu3O7/La2/3Ca1/3MnO3 superlattice on a LSAT substrate: A polarized neutron reflectometry study},
journal = {PHYSICAL REVIEW B},
year = {2013},
volume = {87},
number = {11},
doi = {https://doi.org/10.1103/PhysRevB.87.115105}
}
|
| Scafetta, M.D., Xie, Y.J., Torres, M., Spanier, J.E. and May, S.J. Optical absorption in epitaxial La1-xSrxFeO3 thin films APPLIED PHYSICS LETTERS 102, 8 (2013) |
| Abstract: We report the dependence of optical absorption on Sr concentration in
La1-xSrxFeO3 (LSFO) (x <= 0.4) perovskite thin films. Strained epitaxial films were deposited on SrTiO3 substrates using oxide molecular beam epitaxy. We find systematic changes in the optical absorption spectra with increasing x including a red-shift of transition energies and the increasing presence of a lower energy transition within the fundamental gap of pure LaFeO3. These results serve as a demonstration of the complex manner in which absorption spectra can be altered in complex oxides via heterovalent A-site substitution. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794145] |
BibTeX:
@article{WOS:000315597000036,
author = {Scafetta, M. D. and Xie, Y. J. and Torres, M. and Spanier, J. E. and May, S. J.},
title = {Optical absorption in epitaxial La1-xSrxFeO3 thin films},
journal = {APPLIED PHYSICS LETTERS},
year = {2013},
volume = {102},
number = {8},
doi = {https://doi.org/10.1063/1.4794145}
}
|
| Devishvili, A., Zhernenkov, K., Dennison, A.J.C., Toperverg, B.P., Wolff, M., Hjorvarsson, B. and Zabel, H. SuperADAM: Upgraded polarized neutron reflectometer at the Institut Laue-Langevin REVIEW OF SCIENTIFIC INSTRUMENTS 84, 2 (2013) |
| Abstract: A new neutron reflectometer SuperADAM has recently been built and
commissioned at the Institut Laue-Langevin, Grenoble, France. It replaces the previous neutron reflectometer ADAM. The new instrument uses a solid state polarizer/wavelength filter providing a highly polarized (up to 98.6%) monochromatic neutron flux of 8 x 10(4) n cm(-2) s(-1) with monochromatization Delta lambda/lambda = 0.7% and angular divergence Delta alpha = 0.2 mrad. The instrument includes both single and position sensitive detectors. The position sensitive detector allows simultaneous measurement of specular reflection and off-specular scattering. Polarization analysis for both specular reflection and off-specular scattering is achieved using either mirror analyzers or a He-3 spin filter cell. High efficiency detectors, low background, and high flux provides a dynamic range of up to seven decades in reflectivity. Detailed specifications and the instrument capabilities are illustrated with examples of recently collected data in the fields of thin film magnetism and thin polymer films. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790717] |
BibTeX:
@article{WOS:000316954600076,
author = {Devishvili, A. and Zhernenkov, K. and Dennison, A. J. C. and Toperverg, B. P. and Wolff, M. and Hjorvarsson, B. and Zabel, H.},
title = {SuperADAM: Upgraded polarized neutron reflectometer at the Institut Laue-Langevin},
journal = {REVIEW OF SCIENTIFIC INSTRUMENTS},
year = {2013},
volume = {84},
number = {2},
doi = {https://doi.org/10.1063/1.4790717}
}
|
| Moubah, R., Magnus, F., Zamani, A., Kapaklis, V., Nordblad, P. and Hjorvarsson, B. Strain induced changes in magnetization of amorphous Co95Zr5 based multiferroic heterostructures AIP ADVANCES 3, 2 (2013) |
| Abstract: A clear change in the magnetic anisotropy in a layer of amorphous
Co95Zr5 is obtained at the orthorhombic phase transition of the BaTiO3 substrate. The use of an amorphous buffer layer between the ferroelectric substrate and amorphous magnetic film shows that bulk strain governs the change in themagnetic anisotropy of our ferromagnetic-ferroelectric heterostructure. Moreover, we show that the thermal magnetization curves exhibit anisotropic behavior. Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4792050] |
BibTeX:
@article{WOS:000315596600013,
author = {Moubah, Reda and Magnus, Fridrik and Zamani, Atieh and Kapaklis, Vassilios and Nordblad, Per and Hjorvarsson, Bjorgvin},
title = {Strain induced changes in magnetization of amorphous Co95Zr5 based multiferroic heterostructures},
journal = {AIP ADVANCES},
year = {2013},
volume = {3},
number = {2},
doi = {https://doi.org/10.1063/1.4792050}
}
|
| Garcia-Barriocanal, J., Kobrinskii, A., Leng, X., Kinney, J., Yang, B., Snyder, S. and Goldman, A.M. Electronically driven superconductor-insulator transition in electrostatically doped La2CuO4+delta thin films PHYSICAL REVIEW B 87, 2 (2013) |
| Abstract: Using an electronic double layer transistor we have systematically
studied the superconductor-to-insulator transition in La2CuO4+delta thin films grown by ozone-assisted molecular-beam epitaxy. We have confirmed the high crystalline quality of the cuprate films and have demonstrated the suitability of the electronic double layer technique to continuously vary the charge density in a system that is otherwise characterized by the presence of miscibility gaps. The transport and magnetotransport results highlight the role of electron-electron interactions in the mechanism of the transition due to the proximity of the Mott-insulating state. |
BibTeX:
@article{WOS:000313423900004,
author = {Garcia-Barriocanal, J. and Kobrinskii, A. and Leng, X. and Kinney, J. and Yang, B. and Snyder, S. and Goldman, A. M.},
title = {Electronically driven superconductor-insulator transition in electrostatically doped La2CuO4+delta thin films},
journal = {PHYSICAL REVIEW B},
year = {2013},
volume = {87},
number = {2},
doi = {https://doi.org/10.1103/PhysRevB.87.024509}
}
|
| Ostreng, E., Sonsteby, H.H., Sajavaara, T., Nilsen, O. and Fjellvag, H. Atomic layer deposition of ferroelectric LiNbO3 JOURNAL OF MATERIALS CHEMISTRY C 1, 27, pp. 4283-4290 (2013) |
| Abstract: The ferroelectric and electro-optical properties of LiNbO3 make it an
important material for current and future applications. It has also been suggested as a possible lead-free replacement for present PZT-devices. The atomic layer deposition (ALD) technique offers controlled deposition of films at an industrial scale and thus becomes an interesting tool for growth of LiNbO3. We here report on ALD deposition of LiNbO3 using lithium silylamide and niobium ethoxide as precursors, thereby providing good control of cation stoichiometry and films with low impurity levels of silicon. The deposited films are shown to be ferroelectric and their crystalline orientations can be guided by the choice of substrate. The films are polycrystalline on Si (100) as well as epitaxially oriented on substrates of Al2O3 (012), Al2O3 (001), and LaAlO3 (012). The coercive field of samples deposited on Si (100) was found to be similar to 220 kV cm(-1), with a remanent polarization of similar to 0.4 mu C cm(-2). Deposition of lithium containing materials is traditionally challenging by ALD, and critical issues with such deposition are discussed. |
BibTeX:
@article{WOS:000320709200012,
author = {Ostreng, Erik and Sonsteby, Henrik H. and Sajavaara, Timo and Nilsen, Ola and Fjellvag, Helmer},
title = {Atomic layer deposition of ferroelectric LiNbO3},
journal = {JOURNAL OF MATERIALS CHEMISTRY C},
year = {2013},
volume = {1},
number = {27},
pages = {4283-4290},
doi = {https://doi.org/10.1039/c3tc30271g}
}
|
| Gandrud, K.B., Pettersen, A., Nilsen, O. and Fjellvag, H. High-performing iron phosphate for enhanced lithium ion solid state batteries as grown by atomic layer deposition JOURNAL OF MATERIALS CHEMISTRY A 1, 32, pp. 9054-9059 (2013) |
| Abstract: Atomic layer deposition (ALD) is an excellent tool for realisation of
uniform coating of cathode materials on highly 3D-nanostructured microbatteries. We have developed an ALD-process for deposition of iron phosphate, FePO4, as a cathode material and characterised its electrochemical properties towards a lithium metal anode. Thin films were deposited between 196 and 376 degrees C using the precursor pairs: trimethyl phosphate (TMP, Me3PO4) with both H2O and ozone (O-3) as an oxygen source, and Fe(thd)(3) (Hthd = 2,2,6,6-tetramethyl-3,5-heptanedionate) with O-3. The as-deposited films are amorphous and crystallize to trigonal FePO4 after heat treatment in air at 600 degrees C. The amorphous FePO4 films were characterised electrochemically proving exceptional cyclability and capacities almost reaching the 100% theoretical value (178 mA h g(-1)) for 1 hour charge-discharge rates. |
BibTeX:
@article{WOS:000322121300008,
author = {Gandrud, Knut Bjarne and Pettersen, Anders and Nilsen, Ola and Fjellvag, Helmer},
title = {High-performing iron phosphate for enhanced lithium ion solid state batteries as grown by atomic layer deposition},
journal = {JOURNAL OF MATERIALS CHEMISTRY A},
year = {2013},
volume = {1},
number = {32},
pages = {9054-9059},
doi = {https://doi.org/10.1039/c3ta11550j}
}
|
| Walker, D.E., Major, M., Baghaie Yazdi, M., Klyszcz, A., Haeming, M., Bonrad, K., Melzer, C., Donner, W. and von Seggern, H. High Mobility Indium Zinc Oxide Thin Film Field-Effect Transistors by Semiconductor Layer Engineering ACS APPLIED MATERIALS & INTERFACES 4, 12, pp. 6834-6840 (2012) |
| Abstract: Indium zinc oxide thin-film transistors are fabricated via a precursor
in solution route on silicon substrates with silicon dioxide gate dielectric. It is found that the extracted mobility rises, peaks, and then decreases with increasing precursor concentration instead of rising and saturating. Investigation with scanning probe techniques reveals full thickness variations within the film which are assumed to adversely affect charge transport. Additional layers are coated, and the extracted mobility is observed to increase up to 19.7 cm(2) V-1 s(-1). The reasons for this are examined in detail by direct imaging with scanning tunneling microscopy and extracting electron density profiles from X-ray reflection measurements. It is found that the optimal concentration for single layer films is suboptimal when coating multiple layers and in fact using many layers of very low concentrations of precursor in the solution, leading to a dense, defect and void free film, affording the highest mobilities. A consistent qualitative model of layer formation is developed explaining how the morphology of the film develops as the concentration of precursor in the initial solution is varied. |
BibTeX:
@article{WOS:000313149800058,
author = {Walker, Daniel E. and Major, Marton and Baghaie Yazdi, Mehrdad and Klyszcz, Andreas and Haeming, Marc and Bonrad, Klaus and Melzer, Christian and Donner, Wolfgang and von Seggern, Heinz},
title = {High Mobility Indium Zinc Oxide Thin Film Field-Effect Transistors by Semiconductor Layer Engineering},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2012},
volume = {4},
number = {12},
pages = {6834-6840},
doi = {https://doi.org/10.1021/am302004j}
}
|
| Kim, J.H., Vrejoiu, I., Khaydukov, Y., Keller, T., Stahn, J., Ruehm, A., Satapathy, D.K., Hinkov, V. and Keimer, B. Competing interactions at the interface between ferromagnetic oxides revealed by spin-polarized neutron reflectometry PHYSICAL REVIEW B 86, 18 (2012) |
| Abstract: We have investigated the magnetization profiles in superlattices
composed of the two ferromagnets La0.7Sr0.3MnO3 and SrRuO3 using spin-polarized neutron reflectometry. In combination with magnetometry, the neutron data indicate a noncollinear spin configuration where orientation of the Ru moments changes from in plane at the interface to out of plane deep inside the SrRuO3 layers. The spin structure originates in a competition between antiferromagnetic exchange interactions of Mn and Ru moments across the interface, and the magnetocrystalline anisotropy of the Ru moments, and it is closely related to the ``exchange spring'' structures previously observed in multilayers composed of ferromagnetic elements and alloys. |
BibTeX:
@article{WOS:000310848800002,
author = {Kim, J. -H. and Vrejoiu, I. and Khaydukov, Y. and Keller, T. and Stahn, J. and Ruehm, A. and Satapathy, D. K. and Hinkov, V. and Keimer, B.},
title = {Competing interactions at the interface between ferromagnetic oxides revealed by spin-polarized neutron reflectometry},
journal = {PHYSICAL REVIEW B},
year = {2012},
volume = {86},
number = {18},
doi = {https://doi.org/10.1103/PhysRevB.86.180402}
}
|
| Demeter, J., Menendez, E., Schrauwen, A., Teichert, A., Steitz, R., Vandezande, S., Wildes, A.R., Vandervorst, W., Temst, K. and Vantomme, A. Exchange bias induced by O ion implantation in ferromagnetic thin films JOURNAL OF PHYSICS D-APPLIED PHYSICS 45, 40 (2012) |
| Abstract: Exchange bias (EB) is induced by oxygen implantation in three different
ferromagnetic materials: polycrystalline Co, highly textured Co and polycrystalline Ni. These systems are compared in order to study the influence of the grain boundary density and the intrinsic ferromagnet/antiferromagnet coupling strength on the implantation-induced EB. Special emphasis is given to the role of the implantation profile in the EB properties. The implantation profile is thoroughly characterized and its correlation with the magnetic depth profile, i.e. the magnetization as a function of depth, for different magnetic states is studied. This is achieved by modelling the implanted system as a layered system. In the three systems, the magnetization reversal mechanism is studied. In this way the effect of the implantation process on the reversal mechanism is unraveled. Irrespective of the particular system, the magnetization reverses solely by domain wall nucleation and motion, as opposed to Co/CoO bilayer systems, where a change in the reversal mechanism is observed upon the first reversal. |
BibTeX:
@article{WOS:000309265100008,
author = {Demeter, J. and Menendez, E. and Schrauwen, A. and Teichert, A. and Steitz, R. and Vandezande, S. and Wildes, A. R. and Vandervorst, W. and Temst, K. and Vantomme, A.},
title = {Exchange bias induced by O ion implantation in ferromagnetic thin films},
journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS},
year = {2012},
volume = {45},
number = {40},
doi = {https://doi.org/10.1088/0022-3727/45/40/405004}
}
|
| Pappas, S.D., Kapaklis, V., Delimitis, A., Jonsson, P.E., Papaioannou, E.T., Poulopoulos, P., Fumagalli, P., Trachylis, D., Velgakis, M.J. and Politis, C. Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers JOURNAL OF APPLIED PHYSICS 112, 5 (2012) |
| Abstract: Ni/NiO multilayers were grown by magnetron sputtering at room
temperature, with the aid of the natural oxidation procedure. That is, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer (similar to 1.2 nm) is formed. Simulated x-ray reflectivity patterns reveal that layering is excellent for individual Ni-layer thickness larger than 2.5 nm, which is attributed to the intercalation of amorphous NiO between the polycrystalline Ni layers. The magnetization of the films, measured at temperatures 5-300 K, has almost bulk-like value, whereas the films exhibit a trend to perpendicular magnetic anisotropy (PMA) with an unusual significant positive interface anisotropy contribution, which presents a weak temperature dependence. The power-law behavior of the multilayers indicates a non-negligible contribution of higher order anisotropies in the uniaxial anisotropy. Bloch-law fittings for the temperature dependence of the magnetization in the spin-wave regime show that the magnetization in the multilayers decreases faster as a function of temperature than the one of bulk Ni. Finally, when the individual Ni-layer thickness decreases below 2 nm, the multilayer stacking vanishes, resulting in a dramatic decrease of the interface magnetic anisotropy and consequently in a decrease of the perpendicular magnetic anisotropy. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4750026] |
BibTeX:
@article{WOS:000309072200095,
author = {Pappas, S. D. and Kapaklis, V. and Delimitis, A. and Jonsson, P. E. and Papaioannou, E. Th and Poulopoulos, P. and Fumagalli, P. and Trachylis, D. and Velgakis, M. J. and Politis, C.},
title = {Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2012},
volume = {112},
number = {5},
doi = {https://doi.org/10.1063/1.4750026}
}
|
| Arnalds, U.B., Hase, T.P.A., Papaioannou, E.T., Raanaei, H., Abrudan, R., Charlton, T.R., Langridge, S. and Hjorvarsson, B. X-ray resonant magnetic scattering from patterned multilayers PHYSICAL REVIEW B 86, 6 (2012) |
| Abstract: We report on x-ray resonant magnetic scattering from laterally patterned
arrays of amorphous Co68Fe24Zr8/Al2O3 multilayers. The arrays are composed of circular and ellipsoidal elements which display distinct individual magnetic responses enabling the investigation of the dependence of the observed magnetization on the scattering condition. We focus our attention to special points in reciprocal space, relating to the lateral and perpendicular structure of the samples, thereby revealing the magnetic structure of the multilayered arrays. This allows a comparison of the observed magnetization under different scattering conditions to magneto-optical measurements. The scattering data are supported by micromagnetic simulations which further enhance our understanding of the intricate charge and magnetic scattering from three dimensional patterns. |
BibTeX:
@article{WOS:000307719400003,
author = {Arnalds, Unnar B. and Hase, Thomas P. A. and Papaioannou, Evangelos Th and Raanaei, Hossein and Abrudan, Radu and Charlton, Timothy R. and Langridge, Sean and Hjorvarsson, Bjorgvin},
title = {X-ray resonant magnetic scattering from patterned multilayers},
journal = {PHYSICAL REVIEW B},
year = {2012},
volume = {86},
number = {6},
doi = {https://doi.org/10.1103/PhysRevB.86.064426}
}
|
| Yao, J.H., Hostert, C., Music, D., Frisk, A., Bjorck, M. and Schneider, J.M. Synthesis and mechanical properties of Fe-Nb-B thin-film metallic glasses SCRIPTA MATERIALIA 67, 2, pp. 181-184 (2012) |
| Abstract: Fe-Nb-B. thin-film metallic glasses (TFMGs) were synthesized via a
combinatorial sputtering approach to probe the property-composition correlation. The boron content was found to dominate the mechanical properties of the TFMGs. The similar to 10% smaller strength of Fe-Nb-B TFMGs compared to existing bulk metallic glass with similar composition may be attributed to the absence of a network-like structure based on (Fe,M)(23)B-6 phase due to the extreme quenching conditions employed. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. |
BibTeX:
@article{WOS:000305771700016,
author = {Yao, J. H. and Hostert, C. and Music, D. and Frisk, A. and Bjorck, M. and Schneider, J. M.},
title = {Synthesis and mechanical properties of Fe-Nb-B thin-film metallic glasses},
journal = {SCRIPTA MATERIALIA},
year = {2012},
volume = {67},
number = {2},
pages = {181-184},
doi = {https://doi.org/10.1016/j.scriptamat.2012.04.011}
}
|
| Demydenko, M., Protsenko, S. and Siffalovic, P. Null-ellipsometry investigations of the optical properties and diffusion processes in spin-valve structures based on Co and Cu THIN SOLID FILMS 520, 17, pp. 5722-5726 (2012) |
| Abstract: The influence of annealing temperature (T-a = 300-900 K) on optical
properties of the Au (4 nm)/Co (3 nm)/Cu (6-12 nm)/Co (20 nm)/SiO2/Si spin-valve structures was studied. The model of Co, Au, and Cu atom inter-diffusion was proposed based on the experimental data analysis. The formation of solid solutions at the thin layer interfaces Au/Co and Cu/Co was studied, and as a result the most intensive formation of solid solutions was identified at annealing temperature of T-a = 750 K. The optical parameters of the samples were calculated using the genetic algorithm. The spin-valve systems remain relatively unperturbed until 750 K, but the optical properties change significantly from 750 to 900 K. It can be explained by the formation of the interphase in multilayer thin film systems. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000305770200038,
author = {Demydenko, M. and Protsenko, S. and Siffalovic, P.},
title = {Null-ellipsometry investigations of the optical properties and diffusion processes in spin-valve structures based on Co and Cu},
journal = {THIN SOLID FILMS},
year = {2012},
volume = {520},
number = {17},
pages = {5722-5726},
doi = {https://doi.org/10.1016/j.tsf.2012.04.018}
}
|
| Wolff, M., Palsson, G.K., Korelis, P.T., Dura, J.A., Majkrzak, C. and Hjorvarsson, B. Hydrogen distribution in Nb/Ta superlattices JOURNAL OF PHYSICS-CONDENSED MATTER 24, 25 (2012) |
| Abstract: The distribution of hydrogen in Nb/Ta superlattices has been
investigated by combined neutron reflectivity and x-ray scattering. We provide evidence to support that strain modulations determined with x-ray diffraction can be interpreted as modulations in hydrogen content. We show that the hydrogen concentration is modulated and favors Nb, in agreement with previous studies. We measure the concentration directly using neutron reflectivity and demonstrate no detectable change in the distribution of hydrogen with temperature, in stark contrast to previous studies. |
BibTeX:
@article{WOS:000304875600009,
author = {Wolff, Max and Palsson, Gunnar K. and Korelis, Panagiotis T. and Dura, Joseph A. and Majkrzak, Charles and Hjorvarsson, Bjorgvin},
title = {Hydrogen distribution in Nb/Ta superlattices},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2012},
volume = {24},
number = {25},
doi = {https://doi.org/10.1088/0953-8984/24/25/255306}
}
|
| Munbodh, K., Perez, F.A. and Lederman, D. Changes in magnetic properties of Co/Pd multilayers induced by hydrogen absorption JOURNAL OF APPLIED PHYSICS 111, 12 (2012) |
| Abstract: The saturation magnetization (M-S) and perpendicular anisotropy energy
(K-P) of Co/Pd multilayers were studied when the samples were exposed to 1 atm of H-2 at room temperature. The samples had fixed Co nominal thicknesses of 2.5 angstrom and 4.5 angstrom and Pd thickness values ranging from 0 angstrom to 25 angstrom. The interface structure was determined from the x-ray scattering length density (SLD) profile. When the Pd thickness was less than 10 angstrom, there was a large amount of interface disorder which resulted in no change in M-S and K-P. As the Pd thickness increased, the SLD contrast between the Co and Pd layers also increased, leading to a decrease in M-S and K-P after H-2 absorption. This can be explained by a decrease in H-2 solubility as interface alloying became more dominant for thinner layers, which resulted from a smaller hydrogen electron transfer to the Pd 4d band. The changes in M-S and K-P in the less interdiffused samples also resulted from this electron transfer. Magnetic changes were reversible with characteristic absorption and desorption times of approximately 40 s for 1 atm of H-2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729797] |
BibTeX:
@article{WOS:000305832100093,
author = {Munbodh, Kineshma and Perez, Felio A. and Lederman, David},
title = {Changes in magnetic properties of Co/Pd multilayers induced by hydrogen absorption},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2012},
volume = {111},
number = {12},
doi = {https://doi.org/10.1063/1.4729797}
}
|
| Poulopoulos, P., Lewitz, B., Straub, A., Pappas, S.D., Droulias, S.A., Baskoutas, S. and Fumagalli, P. Band-gap tuning at the strong quantum confinement regime in magnetic semiconductor EuS thin films APPLIED PHYSICS LETTERS 100, 21 (2012) |
| Abstract: Ultraviolet-visible absorption spectra of nanoscaled EuS thin films
reveal a blue shift of the energy between the top-valence and bottom-conduction bands. This band-gap tuning changes smoothly with decreasing film thickness and becomes significant below the exciton Bohr diameter similar to 3.5 nm indicating strong quantum confinement effects. The results are reproduced in the framework of the potential morphing method in Hartree Fock approximation. The large values of the effective mass of the holes, due to localization of the EuS f-states, limit the blue shift to about 0.35 eV. This controllable band-gap tuning of magnetic semiconductor EuS renders it useful for merging spintronics and optoelectronics. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4720167] |
BibTeX:
@article{WOS:000304489900018,
author = {Poulopoulos, Panagiotis and Lewitz, Bjoern and Straub, Andreas and Pappas, Spiridon D. and Droulias, Sotirios A. and Baskoutas, Sotirios and Fumagalli, Paul},
title = {Band-gap tuning at the strong quantum confinement regime in magnetic semiconductor EuS thin films},
journal = {APPLIED PHYSICS LETTERS},
year = {2012},
volume = {100},
number = {21},
doi = {https://doi.org/10.1063/1.4720167}
}
|
| Hostert, C., Music, D., Kapaklis, V., Hjorvarsson, B. and Schneider, J.M. Density, elastic and magnetic properties of Co-Fe-Ta-Si metallic glasses by theory and experiment SCRIPTA MATERIALIA 66, 10, pp. 765-768 (2012) |
| Abstract: Ab initio molecular dynamics simulations were employed to study the
density, elastic and magnetic properties of Co-Fe-Ta-Si metallic glass thin films. A density of 8.03 g cm(-3), a Young's modulus of 187 GPa and a volume magnetization of 0.089 mu(B) angstrom(-3) were calculated and validated by thin film experiments. The extensive stiffness of this glass may be related to the existence of strong (Fe,Co)-Si clusters as revealed by ab initio chemical short-range order data. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. |
BibTeX:
@article{WOS:000302756400012,
author = {Hostert, C. and Music, D. and Kapaklis, V. and Hjorvarsson, B. and Schneider, J. M.},
title = {Density, elastic and magnetic properties of Co-Fe-Ta-Si metallic glasses by theory and experiment},
journal = {SCRIPTA MATERIALIA},
year = {2012},
volume = {66},
number = {10},
pages = {765-768},
doi = {https://doi.org/10.1016/j.scriptamat.2012.01.060}
}
|
| Aldous, J.D., Burrows, C.W., Maskery, I., Brewer, M.S., Hase, T.P.A., Duffy, J.A., Lees, M.R., Sanchez-Hanke, C., Decoster, T., Theis, W., Quesada, A., Schmid, A.K. and Bell, G.R. Depth-dependent magnetism in epitaxial MnSb thin films: effects of surface passivation and cleaning JOURNAL OF PHYSICS-CONDENSED MATTER 24, 14 (2012) |
| Abstract: Depth-dependent magnetism in MnSb(0001) epitaxial films has been studied
by combining experimental methods with different surface specificities: polarized neutron reflectivity, x-ray magnetic circular dichroism (XMCD), x-ray resonant magnetic scattering and spin-polarized low energy electron microscopy (SPLEEM). A native oxide similar to 4.5 nm thick covers air-exposed samples which increases the film's coercivity. HCl etching efficiently removes this oxide and in situ surface treatment of etched samples enables surface magnetic contrast to be observed in SPLEEM. A thin Sb capping layer prevents oxidation and preserves ferromagnetism throughout the MnSb film. The interpretation of Mn L-3,L-2 edge XMCD data is discussed. |
BibTeX:
@article{WOS:000302120500016,
author = {Aldous, J. D. and Burrows, C. W. and Maskery, I. and Brewer, M. S. and Hase, T. P. A. and Duffy, J. A. and Lees, M. R. and Sanchez-Hanke, C. and Decoster, T. and Theis, W. and Quesada, A. and Schmid, A. K. and Bell, G. R.},
title = {Depth-dependent magnetism in epitaxial MnSb thin films: effects of surface passivation and cleaning},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2012},
volume = {24},
number = {14},
doi = {https://doi.org/10.1088/0953-8984/24/14/146002}
}
|
| Schlepuetz, C.M., Yang, Y., Husseini, N.S., Heinhold, R., Kim, H.-S., Allen, M.W., Durbin, S.M. and Clarke, R. The presence of a (1 x 1) oxygen overlayer on ZnO(0001) surfaces and at Schottky interfaces JOURNAL OF PHYSICS-CONDENSED MATTER 24, 9 (2012) |
| Abstract: The atomic surface and interface structures of uncoated and metal-coated
epi-polished ZnO(0001) Zn-polar wafers were investigated via surface x-ray diffraction. All uncoated samples showed the presence of a fully occupied (1 x 1) overlayer of oxygen atoms located at the on-top position above the terminating Zn atom, a structure predicted to be unstable by several density functional theory calculations. The same oxygen overlayer was clearly seen at the interface of ZnO with both elemental and oxidized metal Schottky contact layers. No significant atomic relaxations were observed at surfaces and interfaces processed under typical device fabrication conditions. |
BibTeX:
@article{WOS:000300641000009,
author = {Schlepuetz, Christian M. and Yang, Yongsoo and Husseini, Naji S. and Heinhold, Robert and Kim, Hyung-Suk and Allen, Martin W. and Durbin, Steven M. and Clarke, Roy},
title = {The presence of a (1 x 1) oxygen overlayer on ZnO(0001) surfaces and at Schottky interfaces},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2012},
volume = {24},
number = {9},
doi = {https://doi.org/10.1088/0953-8984/24/9/095007}
}
|
| Defaux, M., Gholamrezaie, F., Wang, J., Kreyes, A., Ziener, U., Anokhin, D.V., Ivanov, D.A., Moser, A., Neuhold, A., Salzmann, I., Resel, R., de Leeuw, D.M., Meskers, S.C.J., Moeller, M. and Mourran, A. Solution-Processable Septithiophene Monolayer Transistor ADVANCED MATERIALS 24, 7, pp. 973+ (2012) |
| Abstract: Septithiophene with endgroups designed to form liquid crystalline phases
and allows controlled deposition of an electrically connected monolayer. Field effect mobilies mobilities of charge carriers and spectroscopic properties of the monolayer provide evidence of sustainable transport and delocalization of the excitation through intermolecular interactions within the layer. |
BibTeX:
@article{WOS:000299944200019,
author = {Defaux, Matthieu and Gholamrezaie, Fatemeh and Wang, Jingbo and Kreyes, Andreas and Ziener, Ulrich and Anokhin, Denis V. and Ivanov, Dimitri A. and Moser, Armin and Neuhold, Alfred and Salzmann, Ingo and Resel, Roland and de Leeuw, Dago M. and Meskers, Stefan C. J. and Moeller, Martin and Mourran, Ahmed},
title = {Solution-Processable Septithiophene Monolayer Transistor},
journal = {ADVANCED MATERIALS},
year = {2012},
volume = {24},
number = {7},
pages = {973+},
doi = {https://doi.org/10.1002/adma.201103522}
}
|
| Smith, C.R., Sloppy, J.D., Wu, H., Santos, T.S., Karapetrova, E., Kim, J.W., Ryan, P.J., Taheri, M.L. and May, S.J. Structural Investigation of Perovskite Manganite and Ferrite Films on Yttria-Stabilized Zirconia Substrates JOURNAL OF THE ELECTROCHEMICAL SOCIETY 159, 8, pp. F436-F441 (2012) |
| Abstract: Thin films of La0.7Sr0.3MnO3 and La0.7Sr0.3FeO3 have been deposited on
single crystal yttria-stabilized zirconia (YSZ) substrates using molecular beam epitaxy. Due to the large lattice mismatch, three-dimensional growth is observed with strain relaxation occurring within 1-2 unit cells. The as-grown perovskite/YSZ interfaces are abrupt, despite the imperfections associated with strain relaxation. The films exhibit a single crystallographic orientation along the growth direction, with the perovskite [011] parallel to the YSZ [001]. Synchrotron diffraction and plan view transmission electron microscopy reveal the presence of a columnar grain structure with the in-plane [100] and [01 (1) over bar] film directions preferentially orientated along the YSZ < 100 >. The stabilization of perovskites on YSZ substrates with abrupt interfaces and a well-defined crystallographic orientation allows for the use of thin film model systems to study cathode/electrolyte interfacial reactions and morphological changes relevant to solid oxide fuel cells. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.032208jes] |
BibTeX:
@article{WOS:000308559400064,
author = {Smith, C. R. and Sloppy, J. D. and Wu, H. and Santos, T. S. and Karapetrova, E. and Kim, J. -W. and Ryan, P. J. and Taheri, M. L. and May, S. J.},
title = {Structural Investigation of Perovskite Manganite and Ferrite Films on Yttria-Stabilized Zirconia Substrates},
journal = {JOURNAL OF THE ELECTROCHEMICAL SOCIETY},
year = {2012},
volume = {159},
number = {8},
pages = {F436-F441},
doi = {https://doi.org/10.1149/2.032208jes}
}
|
| Delimitis, A., Pappas, S.D., Grammatikopoulos, S., Poulopoulos, P., Kapaklis, V., Trachylis, D. and Politis, C. Microstructural Investigation of SiOx Thin Films Grown by Reactive Sputtering on (001) Si Substrates JOURNAL OF NANO RESEARCH 17, pp. 147-156 (2012) |
| Abstract: In the current study, the structural characteristics of SiOx thin films
grown by magnetron sputtering on Si substrates are reported. High resolution transmission electron microscopy revealed the formation of amorphous SiOx films for the as-deposited samples, as well as the ones annealed in ambient air for 30 min at 950 degrees C and of Si nanocrystals, embedded in amorphous SiOx, after Ar annealing for 1-4 hours at 1000 degrees C. The nanocrystals, with sizes up to 6 nm, predominately exhibit 111\ lattice planes. Energy-dispersive X-ray analysis showed that the Si/O ratio is between 0.5-1, i.e. the amorphous films comprise of a mixture of SiO2 and SiO. Phase images and corresponding strain maps created using Fourier filtering revealed a uniform contrast in the nanocrystals, which shows that the Si lattice constant does not vary significantly. The residual strain variations, around 4%, may account for the possible existence of a small percentage of highly disordered Si or SiOx residual clusters inside the regular Si matrix, in full agreement with photoluminescence measurements performed on the same materials. |
BibTeX:
@article{WOS:000301027500011,
author = {Delimitis, A. and Pappas, S. D. and Grammatikopoulos, S. and Poulopoulos, P. and Kapaklis, V. and Trachylis, D. and Politis, C.},
title = {Microstructural Investigation of SiOx Thin Films Grown by Reactive Sputtering on (001) Si Substrates},
journal = {JOURNAL OF NANO RESEARCH},
year = {2012},
volume = {17},
pages = {147-156},
doi = {https://doi.org/10.4028/www.scientific.net/JNanoR.17.147}
}
|
| Fong, D.D. Synchrotron X-ray scattering studies of oxide heterostructures MULTIFUNCTIONAL OXIDE HETEROSTRUCTURES, pp. 99-122 (2012) [ BibTeX] |
BibTeX:
@incollection{WOS:000399094100005,
author = {Fong, Dillon D.},
title = {Synchrotron X-ray scattering studies of oxide heterostructures},
booktitle = {MULTIFUNCTIONAL OXIDE HETEROSTRUCTURES},
year = {2012},
pages = {99-122}
}
|
| Munbodh, K., Cheon, M., Lederman, D., Fitzsimmons, M.R. and Dilley, N.R. Interfacial coupling between ferromagnets and random and dilute antiferromagnets PHYSICAL REVIEW B 84, 21 (2011) |
| Abstract: Depth profiles for pinned and unpinned magnetizations were determined
across the interface between a ferromagnet (F) and random and dilute antiferromagnets (RAF and DAF) exemplified by Fe0.45Ni0.55F2/Co and Fe0.34Zn0.66F2/Co bilayers, respectively, using polarized neutron reflectivity (PNR). PNR measurements were complemented by magnetometry using applied fields as large as 160 kOe to assure saturation of the entire sample, including magnetic moments that are normally pinned at lower fields. The locations of pinned and unpinned magnetization in the ferro-and antiferromagnets were identified. The origin of exchange bias in the RAF system is noticeably different than that of the DAF system. In the RAF system, a domain wall is formed at the RAF/F interface when the ferromagnet's magnetization is reversed. In the DAF system, some domains within the bulk of the DAF are reversed upon reversal of the ferromagnet while others remain pinned. In this case, the interface magnetization is entirely reversed. |
BibTeX:
@article{WOS:000298550900005,
author = {Munbodh, Kineshma and Cheon, Miyeon and Lederman, David and Fitzsimmons, M. R. and Dilley, Neil R.},
title = {Interfacial coupling between ferromagnets and random and dilute antiferromagnets},
journal = {PHYSICAL REVIEW B},
year = {2011},
volume = {84},
number = {21},
doi = {https://doi.org/10.1103/PhysRevB.84.214434}
}
|
| Bjoerck, M. Fitting with differential evolution: an introduction and evaluation JOURNAL OF APPLIED CRYSTALLOGRAPHY 44, 6, pp. 1198-1204 (2011) |
| Abstract: Differential evolution is a global optimization algorithm that has
started to find widespread use in the scattering community because of its proven effectiveness. In this article the performance of the algorithm is evaluated by fitting an X-ray reflectivity data set and investigating its convergence behavior as a function of its tuning parameters. The results offer important insights for applying differential evolution algorithms to scattering problems and provide some rules of thumb on how to tune the parameters. It is shown that, by choosing optimal tuning parameter values, the speed of the fitting process can be increased by an order of magnitude. |
BibTeX:
@article{WOS:000297279800009,
author = {Bjoerck, Matts},
title = {Fitting with differential evolution: an introduction and evaluation},
journal = {JOURNAL OF APPLIED CRYSTALLOGRAPHY},
year = {2011},
volume = {44},
number = {6},
pages = {1198-1204},
doi = {https://doi.org/10.1107/S0021889811041446}
}
|
| Hostert, C., Music, D., Bednarcik, J., Keckes, J., Kapaklis, V., Hjorvarsson, B. and Schneider, J.M. Ab initio molecular dynamics model for density, elastic properties and short range order of Co-Fe-Ta-B metallic glass thin films JOURNAL OF PHYSICS-CONDENSED MATTER 23, 47 (2011) |
| Abstract: Density, elastic modulus and the pair distribution function of
Co-Fe-Ta-B metallic glasses were obtained by ab initio molecular dynamics simulations and measured for sputtered thin films using x-ray reflectivity, nanoindentation and x-ray diffraction using high energy photons. The computationally obtained density of 8.19 g cm(-3) for Co43Fe20Ta5.5B31.5 and 8.42 g cm(-3) for Co45.5Fe24Ta6B24.5, as well as the Young's moduli of 273 and 251 GPa, respectively, are consistent with our experiments and literature data. These data, together with the good agreement between the theoretical and the experimental pair distribution functions, indicate that the model established here is useful to describe the density, elasticity and short range order of Co-Fe-Ta-B metallic glass thin films. Irrespective of the investigated variation in chemical composition, (Co, Fe)-B cluster formation and Co-Fe interactions are identified by density-of-states analysis. Strong bonds within the structural units and between the metallic species may give rise to the comparatively large stiffness. |
BibTeX:
@article{WOS:000297212100004,
author = {Hostert, C. and Music, D. and Bednarcik, J. and Keckes, J. and Kapaklis, V. and Hjorvarsson, B. and Schneider, J. M.},
title = {Ab initio molecular dynamics model for density, elastic properties and short range order of Co-Fe-Ta-B metallic glass thin films},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2011},
volume = {23},
number = {47},
doi = {https://doi.org/10.1088/0953-8984/23/47/475401}
}
|
| Moser, A., Novak, J., Flesch, H.-G., Djuric, T., Werzer, O., Haase, A. and Resel, R. Temperature stability of the pentacene thin-film phase APPLIED PHYSICS LETTERS 99, 22 (2011) |
| Abstract: This work presents the influence of temperatures above 300 K on the
crystal structure and morphology of pentacene thin films. The thermal expansion of the unit cell and the relative amount of different phases are investigated via grazing incidence x-ray diffraction. Geometrical considerations about the specific molecular packing of the thin-film phase explain the anisotropic non-linear expansion. Furthermore, around 480 K, a phase transformation of the thin-film phase to the bulk phase is observed. In contrast, only a weak influence of the temperature on the height distribution of the thin-film phase crystallites is found. (C) 2011 American Institute of Physics. [doi:10.1063/1.3665188] |
BibTeX:
@article{WOS:000298244500026,
author = {Moser, Armin and Novak, Jiri and Flesch, Heinz-Georg and Djuric, Tatjana and Werzer, Oliver and Haase, Anja and Resel, Roland},
title = {Temperature stability of the pentacene thin-film phase},
journal = {APPLIED PHYSICS LETTERS},
year = {2011},
volume = {99},
number = {22},
doi = {https://doi.org/10.1063/1.3665188}
}
|
| Rodrigo, K., Heiroth, S., Pryds, N., Kuhn, L.T., Esposito, V., Linderoth, S., Schou, J. and Lippert, T. The effects of thermal annealing on the structure and the electrical transport properties of ultrathin gadolinia-doped ceria films grown by pulsed laser deposition APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 104, 3, pp. 845-850 (2011) |
| Abstract: Ultrathin crystalline films of 10 mol% gadolinia-doped ceria (CGO10)
are grown on MgO (100) substrates by pulsed laser deposition at a moderate temperature of 400A degrees C. As-deposited CGO10 layers of approximately 4 nm, 14 nm, and 22 nm thickness consist of fine grains with dimensions a parts per thousand currency signa1/411 nm. The films show high density within the thickness probed in the X-ray reflectivity experiments. Thermally activated grain growth, density decrease, and film surface roughening, which may result in the formation of incoherent CGO10 islands by dewetting below a critical film thickness, are observed upon heat treatment at 400A degrees C and 800A degrees C. The effect of the grain coarsening on the electrical characteristics of the layers is investigated and discussed in the context of a variation of the number density of grain boundaries. The results are evaluated with regard to the use of ultrathin CGO10 films as seeding templates for the moderate temperature growth of thick solid electrolyte films with improved oxygen transport properties. |
BibTeX:
@article{WOS:000293963200014,
author = {Rodrigo, K. and Heiroth, S. and Pryds, N. and Kuhn, L. Theil and Esposito, V. and Linderoth, S. and Schou, J. and Lippert, T.},
title = {The effects of thermal annealing on the structure and the electrical transport properties of ultrathin gadolinia-doped ceria films grown by pulsed laser deposition},
journal = {APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING},
year = {2011},
volume = {104},
number = {3},
pages = {845-850},
doi = {https://doi.org/10.1007/s00339-011-6424-y}
}
|
| Poulopoulos, P., Baskoutas, S., Pappas, S.D., Garoufalis, C.S., Droulias, S.A., Zamani, A. and Kapaklis, V. Intense Quantum Confinement Effects in Cu2O Thin Films JOURNAL OF PHYSICAL CHEMISTRY C 115, 30, pp. 14839-14843 (2011) |
| Abstract: Thin Cu2O films in the thickness range 0.75-230 nm have been prepared on
high-quality corning glass, quartz, and Si(100) substrates by radio frequency magnetron sputtering of Cu targets and subsequent oxidation in a furnace under air. Ultraviolet-visible light absorption spectroscopy experiments reveal a blue shift of the energy between the top valence and the first excited conduction sub-bands. The shift increases smoothly as the film thickness decreases. The maximum value observed for the thinnest film is very large, reaching a value of 1.2 eV. Such a shift was not easy to be observed in the past due to the very small Bohr radius of Cu2O. The experimental results, which indicate the presence of intense quantum confinement effects, are well-described by theoretical calculations based on the potential morphing method in the Hartree-Fock approximation. |
BibTeX:
@article{WOS:000293192100050,
author = {Poulopoulos, Panagiotis and Baskoutas, Sotirios and Pappas, Spiridon D. and Garoufalis, Christos S. and Droulias, Sotirios A. and Zamani, Atieh and Kapaklis, Vassilios},
title = {Intense Quantum Confinement Effects in Cu2O Thin Films},
journal = {JOURNAL OF PHYSICAL CHEMISTRY C},
year = {2011},
volume = {115},
number = {30},
pages = {14839-14843},
doi = {https://doi.org/10.1021/jp203145n}
}
|
| Tabor, P., Keenan, C., Urazdhin, S. and Lederman, D. Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110) APPLIED PHYSICS LETTERS 99, 1 (2011) |
| Abstract: The structural and electronic properties of thin Bi2Se3 films grown on
Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 degrees C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3609326] |
BibTeX:
@article{WOS:000292639200062,
author = {Tabor, Phillip and Keenan, Cameron and Urazdhin, Sergei and Lederman, David},
title = {Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)},
journal = {APPLIED PHYSICS LETTERS},
year = {2011},
volume = {99},
number = {1},
doi = {https://doi.org/10.1063/1.3609326}
}
|
| Ahlberg, M., Andersson, G. and Hjorvarsson, B. Two-dimensional XY-like amorphous Co68Fe24Zr8/Al70Zr30 multilayers PHYSICAL REVIEW B 83, 22 (2011) |
| Abstract: We present an experimental realization of a magnetic two-dimensional XY
system using amorphous materials. The classification of the dimensionality is based on the critical behavior of amorphous Co68Fe24Zr8(d)/Al70O30 (20 angstrom) multilayers, where d = 11 - 16 angstrom. Analysis of the remanent magnetization, the magnetic isotherms, the initial susceptibility, and the magnetic correlation length shows that the magnetic phase transition can be described by the 2D XY model. The samples are not paramagnetic above the critical temperature but are characterized by local magnetic order manifested in the field and temperature dependence of the magnetization. Furthermore, an average spin-spin interaction length of 8.1 angstrom was estimated using the thickness dependence of the Curie temperature. |
BibTeX:
@article{WOS:000291727600006,
author = {Ahlberg, Martina and Andersson, Gabriella and Hjorvarsson, Bjorgvin},
title = {Two-dimensional XY-like amorphous Co68Fe24Zr8/Al70Zr30 multilayers},
journal = {PHYSICAL REVIEW B},
year = {2011},
volume = {83},
number = {22},
doi = {https://doi.org/10.1103/PhysRevB.83.224404}
}
|
| Keenan, C., Chandril, S., Myers, T.H. and Lederman, D. In-situ stoichiometry determination using x-ray fluorescence generated by reflection-high-energy-electron-diffraction JOURNAL OF APPLIED PHYSICS 109, 11 (2011) |
| Abstract: A major challenge in the stoichiometric growth of complex oxide
compounds is the control of the relative compositions of the constituent materials. A potential avenue for compositional analysis during growth is the use of x-ray fluorescence generated during reflection high energy electron diffraction measurements. Using this technique, relative compositions of Y and Mn in molecular beam epitaxy grown YMnO(3) samples were studied. Comparing the results with Rutherford back scattering spectroscopy suggests that the technique has the potential for real-time analysis of elemental fluxes and stoichiometry control during sample growth. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3592219] |
BibTeX:
@article{WOS:000292214700128,
author = {Keenan, Cameron and Chandril, Sandeep and Myers, T. H. and Lederman, David},
title = {In-situ stoichiometry determination using x-ray fluorescence generated by reflection-high-energy-electron-diffraction},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2011},
volume = {109},
number = {11},
doi = {https://doi.org/10.1063/1.3592219}
}
|
| Morenzoni, E., Wojek, B.M., Suter, A., Prokscha, T., Logvenov, G. and Bozovic, I. The Meissner effect in a strongly underdoped cuprate above its critical temperature NATURE COMMUNICATIONS 2 (2011) |
| Abstract: The Meissner effect and associated perfect `bulk' diamagnetism together
with zero resistance and gap opening are characteristic features of the superconducting state. In the pseudogap state of cuprates, unusual diamagnetic signals and anomalous proximity effects have been detected, but a Meissner effect has never been observed. Here we probe the local diamagnetic response in the normal state of an underdoped La(1.94)Sr(0.06)CuO(4) layer (T'(c)less than or similar to 5 K), which is brought into close contact with two nearly optimally doped La(1.84)Sr(0.16)CuO(4) layers (T(c)approximate to 32 K). We show that the entire `barrier' layer of thickness, much larger than the typical c axis coherence lengths of cuprates, exhibits a Meissner effect at temperatures above T'(c) but below T(c). The temperature dependence of the effective penetration depth and superfluid density in different layers indicates that superfluidity with long-range phase coherence is induced in the underdoped layer by the proximity to optimally doped layers, but this induced order is sensitive to thermal excitation. |
BibTeX:
@article{WOS:000289983800010,
author = {Morenzoni, Elvezio and Wojek, Bastian M. and Suter, Andreas and Prokscha, Thomas and Logvenov, Gennady and Bozovic, Ivan},
title = {The Meissner effect in a strongly underdoped cuprate above its critical temperature},
journal = {NATURE COMMUNICATIONS},
year = {2011},
volume = {2},
doi = {https://doi.org/10.1038/ncomms1273}
}
|
| Mullen, K.M., Ardia, D., Gil, D.L., Windover, D. and Cline, J. DEoptim: An R Package for Global Optimization by Differential Evolution JOURNAL OF STATISTICAL SOFTWARE 40, 6, pp. 1-26 (2011) |
| Abstract: This article describes the R package DEoptim, which implements the
differential evolution algorithm for global optimization of a real-valued function of a real-valued parameter vector. The implementation of differential evolution in DEoptim interfaces with C code for efficiency. The utility of the package is illustrated by case studies in fitting a Parratt model for X-ray reflectometry data and a Markov-switching generalized autoregressive conditional heteroskedasticity model for the returns of the Swiss Market Index. |
BibTeX:
@article{WOS:000289228700001,
author = {Mullen, Katharine M. and Ardia, David and Gil, David L. and Windover, Donald and Cline, James},
title = {DEoptim: An R Package for Global Optimization by Differential Evolution},
journal = {JOURNAL OF STATISTICAL SOFTWARE},
year = {2011},
volume = {40},
number = {6},
pages = {1-26}
}
|
| Munbodh, K., Perez, F.A., Keenan, C., Lederman, D., Zhernenkov, M. and Fitzsimmons, M.R. Effects of hydrogen/deuterium absorption on the magnetic properties of Co/Pd multilayers PHYSICAL REVIEW B 83, 9 (2011) |
| Abstract: The effects of hydrogen (H-2) and deuterium (D-2) absorption were
studied in two Co/Pd multilayers with perpendicular magnetic anisotropy (PMA) using polarized neutron reflectivity (PNR). PNR was measured in an external magnetic field H applied in the plane of the sample with the magnetization M confined in the plane for mu H-o = 6.0 T and partially out of plane at 0.65 T. Nominal thicknesses of the Co and Pd layers were 2.5 and 21 angstrom, respectively. Because of these small values, the actual layer chemical composition, thickness, and interface roughness parameters were determined from the nuclear scattering length density profile (rho(n)) and its derivative obtained from both x-ray reflectivity and PNR, and uncertainties were determined using Monte Carlo analysis. The PNR rho(n) showed that although D2 absorption occurred throughout the samples, absorption in the multilayer stack was modest (0.02 D per Pd atom) and thus did not expand. Direct magnetometry showed that H-2 absorption decreased the total M at saturation and increased the component of M in the plane of the sample when not at saturation. The PNR magnetic scattering length density (rho(m)) revealed that the Pd layers in the multilayer stack were magnetized and that their magnetization was preferentially modified upon D-2 absorption. In one sample, a modulation of M with twice the multilayer period was observed at mu H-o = 0.65 T, which increased upon D-2 absorption. These results indicate that H-2 or D-2 absorption decreases both the PMA and total magnetization of the samples. The lack of measurable expansion during absorption indicates that these changes are primarily governed by modification of the electronic structure of the material. |
BibTeX:
@article{WOS:000288944800004,
author = {Munbodh, K. and Perez, F. A. and Keenan, C. and Lederman, D. and Zhernenkov, M. and Fitzsimmons, M. R.},
title = {Effects of hydrogen/deuterium absorption on the magnetic properties of Co/Pd multilayers},
journal = {PHYSICAL REVIEW B},
year = {2011},
volume = {83},
number = {9},
doi = {https://doi.org/10.1103/PhysRevB.83.094432}
}
|
| Poulopoulos, P., Pappas, S.D., Kapaklis, V., Jonsson, P.E., Papaioannou, E.T., Delimitis, A., Trachylis, D., Velgakis, M.J., Meletis, E.I. and Politis, C. Growth and Magnetism of Natural Multilayers JOURNAL OF NANO RESEARCH 15, pp. 95-103 (2011) |
| Abstract: In this work, we present a simple method to fabricate high quality
Ni/NiO multilayers with the use of a single magnetron sputtering head. Namely, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer (similar to 1nm) is formed by natural oxidation. The process is reproducible and the result is the formation of a multilayer with excellent layering. Magnetization hysteresis loops recorded at 5 K and room temperature reveal a tendency for perpendicular magnetic anisotropy as the thickness of the individual Ni layers decreases. It is shown that the Ni/NiO interface has sizeable positive surface/interface anisotropy, i.e. it favors the development of perpendicular magnetic anisotropy. This is rather unusual for a Ni-based multilayered system and may render Ni/NiO multilayers useful for magneto-optical recording applications. |
BibTeX:
@article{WOS:000295909100010,
author = {Poulopoulos, P. and Pappas, S. D. and Kapaklis, V. and Jonsson, P. E. and Papaioannou, E. Th and Delimitis, A. and Trachylis, D. and Velgakis, M. J. and Meletis, E. I. and Politis, C.},
title = {Growth and Magnetism of Natural Multilayers},
journal = {JOURNAL OF NANO RESEARCH},
year = {2011},
volume = {15},
pages = {95-103},
doi = {https://doi.org/10.4028/www.scientific.net/JNanoR.15.95}
}
|
| Kumah, D.P., Reiner, J.W., Segal, Y., Kolpak, A.M., Zhang, Z., Su, D., Zhu, Y., Sawicki, M.S., Broadbridge, C.C., Ahn, C.H. and Walker, F.J. The atomic structure and polarization of strained SrTiO3/Si APPLIED PHYSICS LETTERS 97, 25 (2010) |
| Abstract: For thin film devices based on coupling ferroelectric polarization to
charge carriers in semiconductors, the role of the interface is critical. To elucidate this role, we use synchrotron x-ray diffraction to determine the interface structure of epitaxial SrTiO3 grown on the (001) surface of Si. The average displacement of the O octahedral sublattice relative to the Sr sublattice determines the film polarization and is measured to be about 0.05 nm toward the Si, with Ti off-center displacements 0.009 nm away from the substrate. Measurements of films with different boundary conditions on the top of the SrTiO3 show that the polarization at the SrTiO3/Si interface is dominated by oxide-Si chemical interactions. (C) 2010 American Institute of Physics. [doi:10.1063/1.3529460] |
BibTeX:
@article{WOS:000285764300020,
author = {Kumah, D. P. and Reiner, J. W. and Segal, Y. and Kolpak, A. M. and Zhang, Z. and Su, D. and Zhu, Y. and Sawicki, M. S. and Broadbridge, C. C. and Ahn, C. H. and Walker, F. J.},
title = {The atomic structure and polarization of strained SrTiO3/Si},
journal = {APPLIED PHYSICS LETTERS},
year = {2010},
volume = {97},
number = {25},
doi = {https://doi.org/10.1063/1.3529460}
}
|
| Palsson, G.K., Kapaklis, V., Dura, J.A., Jacob, J., Jayanetti, S., Rennie, A.R. and Hjorvarsson, B. Deuterium-induced volume expansion in Fe0.5V0.5/V superlattices PHYSICAL REVIEW B 82, 24 (2010) |
| Abstract: Neutron reflectometry was used to investigate the deuterium uptake in a
thin metal superlattice that displays an anisotropic elastic response [Fe0.5V0.5/V (6/21 monolayers)]. We see evidence of the presence of a coexistence region which has never before been seen in vanadium-based superlattices. The loading process is completely reversible from which we conclude that the phases must be coherent, in stark contrast to bulk VDx, where the two-phase region displays hysteresis. The deuterium-induced volume expansion exhibits changes in slope that correlate with the plateau region and the expansion is comparable and even larger than in the bulk. The spectacular cooperation between the elastic fields seems to be found only in one-dimensionally confined structures with biaxial compressive strain states. |
BibTeX:
@article{WOS:000286897000006,
author = {Palsson, Gunnar K. and Kapaklis, Vassilios and Dura, Joseph A. and Jacob, Julie and Jayanetti, Sumedha and Rennie, Adrian R. and Hjorvarsson, Bjorgvin},
title = {Deuterium-induced volume expansion in Fe0.5V0.5/V superlattices},
journal = {PHYSICAL REVIEW B},
year = {2010},
volume = {82},
number = {24},
doi = {https://doi.org/10.1103/PhysRevB.82.245424}
}
|
| Korelis, P.T., Liebig, A., Bjorck, M., Hjorvarsson, B., Lidbaum, H., Leifer, K. and Wildes, A.R. Highly amorphous Fe90Zr10 thin films, and the influence of crystallites on the magnetism THIN SOLID FILMS 519, 1, pp. 404-409 (2010) |
| Abstract: A method for depositing highly amorphous, iron-rich Fe100-xZrx thin
films on to room temperature substrates is presented. The method involves co-depositing Fe and Zr on to an amorphous AlZr layer. Experimental proof that the structures are completely amorphous is given by transmission electron microscopy and polarized neutron reflectometry. The reflectometry measurements also give an indication of the impact that Fe crystallite impurities have on the magnetic structure and properties of amorphous FeZr. The results are consistent with previous investigations on bulk samples, which showed that crystalline impurities make the magnetic structure more non-collinear. (C) 2010 Published by Elsevier B.V. |
BibTeX:
@article{WOS:000283955200071,
author = {Korelis, P. T. and Liebig, A. and Bjorck, M. and Hjorvarsson, B. and Lidbaum, H. and Leifer, K. and Wildes, A. R.},
title = {Highly amorphous Fe90Zr10 thin films, and the influence of crystallites on the magnetism},
journal = {THIN SOLID FILMS},
year = {2010},
volume = {519},
number = {1},
pages = {404-409},
doi = {https://doi.org/10.1016/j.tsf.2010.07.084}
}
|
| Arnalds, U.B., Papaioannou, E.T., Hase, T.P.A., Raanaei, H., Andersson, G., Charlton, T.R., Langridge, S. and Hjorvarsson, B. Magnetic structure and diffracted magneto-optics of patterned amorphous multilayers PHYSICAL REVIEW B 82, 14 (2010) |
| Abstract: We present magneto-optical Kerr effect measurements of patterned arrays
of Co68Fe24Zr8 / Al2O3 amorphous multilayers. The multilayers were patterned in two dimensions into two different arrangements of circular and ellipsoidal islands. Magnetization loops were recorded in a longitudinal geometry using both the specularly reflected beam as well as diffracted beams scattered off the patterned films. The magnetization of the patterned structures is significantly different from the magnetization of a continuous multilayer owing to the lateral confinement of the pattern and the introduction of additional dipolar coupling between the layers at the edges of the islands. By investigating the magnetic response at the different diffraction orders from the two different configurations of islands we are able to observe the magnetization at different length scales and determine the magnetic response of the circular and ellipsoidal islands individually. |
BibTeX:
@article{WOS:000283423000004,
author = {Arnalds, Unnar B. and Papaioannou, Evangelos Th. and Hase, Thomas P. A. and Raanaei, Hossein and Andersson, Gabriella and Charlton, Timothy R. and Langridge, Sean and Hjorvarsson, Bjorgvin},
title = {Magnetic structure and diffracted magneto-optics of patterned amorphous multilayers},
journal = {PHYSICAL REVIEW B},
year = {2010},
volume = {82},
number = {14},
doi = {https://doi.org/10.1103/PhysRevB.82.144434}
}
|
| Spirk, S., Ehmann, H.M., Kargl, R., Hurkes, N., Reischl, M., Novak, J., Resel, R., Wu, M., Pietschnig, R. and Ribitsch, V. Surface Modifications Using a Water-Stable Silanetriol in Neutral Aqueous Media ACS APPLIED MATERIALS & INTERFACES 2, 10, pp. 2956-2962 (2010) |
| Abstract: Surface modifications of glass slides employing the sterically hindered
tert-butyl substituted silanetriol are described. To the best of our knowledge, this is the first time that a stable silanetriol has been directly used for this purpose. So far unprecedented, this process runs under neutral aqueous conditions and in the absence of organic solvents, which makes coating protocols accessible to acid-sensitive substrates. The layer thickness and surface topography are investigated by the Sarfus technique, by X-ray reflectivity, and by atomic force microscopy (AFM). These techniques yield values of 0.8 +/- 0.1 (XRR) and 0.6 +/- 0.2 nm (Sarfus) for layer thickness and 0.33 nm for root mean square roughness (AFM). The modified surfaces have hydrophobic and oleophilic character and contact angles (CA) between 60 degrees (formamide, CH2I2) and 90 degrees (water) are obtained. The thin coatings allow a structuring by UV/ozone treatment in order to get hydrophilic and hydrophobic compartments on the surfaces. For all coatings, surface free energies are calculated using different models. To determine the isoelectric points (IEP) of the modified surfaces, we performed zeta-potential measurements. Correlations between zeta potentials and hydrophilicity of the surfaces are shown. |
BibTeX:
@article{WOS:000283463700043,
author = {Spirk, Stefan and Ehmann, Heike M. and Kargl, Rupert and Hurkes, Natascha and Reischl, Martin and Novak, Jiri and Resel, Roland and Wu, Ming and Pietschnig, Rudolf and Ribitsch, Volker},
title = {Surface Modifications Using a Water-Stable Silanetriol in Neutral Aqueous Media},
journal = {ACS APPLIED MATERIALS & INTERFACES},
year = {2010},
volume = {2},
number = {10},
pages = {2956-2962},
doi = {https://doi.org/10.1021/am100644r}
}
|
| Fong, D.D., Lucas, C.A., Richard, M.I. and Toney, M.F. X-Ray Probes for In Situ Studies of Interfaces MRS BULLETIN 35, 7, pp. 504-513 (2010) |
| Abstract: Surfaces and buried interfaces play critical roles in many
environmental, catalytic, and tribological processes and in a wide variety of applications, including microelectronics and optoelectronics. Interfacial structure and composition are closely coupled to their surroundings, and probes that yield information about materials in situ are essential to obtain a thorough understanding of interface functions and properties. The highly brilliant, hard x-rays available from synchrotron light sources can easily penetrate through gas or liquid environments, or even solid thin-film overlayers, and enable real-time monitoring of the evolving chemistry and structure of the interface with atomic-scale resolution. Here we review the in situ study of interfaces by a variety of synchrotron x-ray scattering techniques and provide several examples of their application in electrochemical processes and thin-film island growth. We also discuss recent advances in analytical techniques and x-ray optics that are facilitating the in situ study of surfaces and buried interfaces with direct imaging. |
BibTeX:
@article{WOS:000279980400016,
author = {Fong, D. D. and Lucas, C. A. and Richard, M. -I. and Toney, M. F.},
title = {X-Ray Probes for In Situ Studies of Interfaces},
journal = {MRS BULLETIN},
year = {2010},
volume = {35},
number = {7},
pages = {504-513},
doi = {https://doi.org/10.1557/mrs2010.599}
}
|
| Beale, T.A.W., Hase, T.P.A., Iida, T., Endo, K., Steadman, P., Marshall, A.R., Dhesi, S.S., van der Laan, G. and Hatton, P.D. RASOR: An advanced instrument for soft x-ray reflectivity and diffraction REVIEW OF SCIENTIFIC INSTRUMENTS 81, 7 (2010) |
| Abstract: We report the design and construction of a novel soft x-ray
diffractometer installed at Diamond Light Source. The beamline endstation RASOR is constructed for general users and designed primarily for the study of single crystal diffraction and thin film reflectivity. The instrument is comprised of a limited three circle (theta, 2 theta, and chi) diffractometer with an additional removable rotation (phi) stage. It is equipped with a liquid helium cryostat, and post-scatter polarization analysis. Motorized motions are provided for the precise positioning of the sample onto the diffractometer center of rotation, and for positioning the center of rotation onto the x-ray beam. The functions of the instrument have been tested at Diamond Light Source, and initial test measurements are provided, demonstrating the potential of the instrument. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3458004] |
BibTeX:
@article{WOS:000281033400041,
author = {Beale, T. A. W. and Hase, T. P. A. and Iida, T. and Endo, K. and Steadman, P. and Marshall, A. R. and Dhesi, S. S. and van der Laan, G. and Hatton, P. D.},
title = {RASOR: An advanced instrument for soft x-ray reflectivity and diffraction},
journal = {REVIEW OF SCIENTIFIC INSTRUMENTS},
year = {2010},
volume = {81},
number = {7},
doi = {https://doi.org/10.1063/1.3458004}
}
|
| Baldi, A., Palsson, G.K., Gonzalez-Silveira, M., Schreuders, H., Slaman, M., Rector, J.H., Krishnan, G., Kooi, B.J., Walker, G.S., Fay, M.W., Hjorvarsson, B., Wijngaarden, R.J., Dam, B. and Griessen, R. Mg/Ti multilayers: Structural and hydrogen absorption properties PHYSICAL REVIEW B 81, 22 (2010) |
| Abstract: Mg-Ti alloys have uncommon optical and hydrogen absorbing properties,
originating from a ``spinodal-like'' microstructure with a small degree of chemical short-range order in the atomic distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities. Notwithstanding the large lattice mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. On exposure to H-2 gas a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. From in situ measurements of the bilayer thickness Lambda at different hydrogen pressures, we observe large out-of-plane expansions of Mg and Ti layers on hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. On unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces. |
BibTeX:
@article{WOS:000278492600002,
author = {Baldi, A. and Palsson, G. K. and Gonzalez-Silveira, M. and Schreuders, H. and Slaman, M. and Rector, J. H. and Krishnan, G. and Kooi, B. J. and Walker, G. S. and Fay, M. W. and Hjorvarsson, B. and Wijngaarden, R. J. and Dam, B. and Griessen, R.},
title = {Mg/Ti multilayers: Structural and hydrogen absorption properties},
journal = {PHYSICAL REVIEW B},
year = {2010},
volume = {81},
number = {22},
doi = {https://doi.org/10.1103/PhysRevB.81.224203}
}
|
| Poulopoulos, P., Kapaklis, V., Jonsson, P.E., Papaioannou, E.T., Delimitis, A., Pappas, S.D., Trachylis, D. and Politis, C. Positive surface and perpendicular magnetic anisotropy in natural nanomorphous Ni/NiO multilayers APPLIED PHYSICS LETTERS 96, 20 (2010) |
| Abstract: Ni/NiO multilayers with excellent sequencing are grown via
radiofrequency magnetron sputtering with the use of one Ni target and natural oxidation. Ni layers consist of very small Ni nanocrystals interrupted by amorphous NiO layers. When Ni is deposited at 0.3 Pa Ar-pressure, the hard-magnetization axis is the film normal and saturation field decreases by decreasing Ni layer thickness. Considerable positive surface anisotropy is found, which is remarkable for Ni-based multilayers. If Ni is deposited at 3 Pa Ar-pressure, perpendicular magnetic anisotropy is observed at low temperatures even for 5.4 nm thick Ni layers. This anisotropy results in the formation of stripe magnetic domains. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3428791] |
BibTeX:
@article{WOS:000277969700033,
author = {Poulopoulos, P. and Kapaklis, V. and Jonsson, P. E. and Papaioannou, E. Th. and Delimitis, A. and Pappas, S. D. and Trachylis, D. and Politis, C.},
title = {Positive surface and perpendicular magnetic anisotropy in natural nanomorphous Ni/NiO multilayers},
journal = {APPLIED PHYSICS LETTERS},
year = {2010},
volume = {96},
number = {20},
doi = {https://doi.org/10.1063/1.3428791}
}
|
| Martoccia, D., Bjoerck, M., Schlepuetz, C.M., Brugger, T., Pauli, S.A., Patterson, B.D., Greber, T. and Willmott, P.R. Graphene on Ru(0001): a corrugated and chiral structure NEW JOURNAL OF PHYSICS 12 (2010) |
| Abstract: We present a structural analysis of the graphene/Ru(0001) system
obtained by surface x-ray diffraction. The data were fitted using Fourier-series-expanded displacement fields from an ideal bulk structure plus the application of symmetry constraints. The shape of the observed superstructure rods proves a reconstruction of the substrate, induced by strong bonding of graphene to ruthenium. Both the graphene layer and the underlying substrate are corrugated, with peak-to-peak heights of (0.82 +/- 0.15)angstrom and (0.19 +/- 0.02)angstrom for graphene and the topmost Ru-atomic layer, respectively. The Ru corrugation decays slowly over several monolayers into the bulk. The system also exhibits chirality, whereby in-plane rotations of up to 2.0 degrees in those regions of the superstructure where the graphene is weakly bound are driven by elastic energy minimization. |
BibTeX:
@article{WOS:000276742000001,
author = {Martoccia, D. and Bjoerck, M. and Schlepuetz, C. M. and Brugger, T. and Pauli, S. A. and Patterson, B. D. and Greber, T. and Willmott, P. R.},
title = {Graphene on Ru(0001): a corrugated and chiral structure},
journal = {NEW JOURNAL OF PHYSICS},
year = {2010},
volume = {12},
doi = {https://doi.org/10.1088/1367-2630/12/4/043028}
}
|
| Palsson, G.K., Wang, Y.T., Azofeifa, D., Raanaei, H., Sahlberg, M. and Hjorvarsson, B. Influence of titanium and vanadium on the hydrogen transport through amorphous alumina films JOURNAL OF ALLOYS AND COMPOUNDS 494, 1-2, pp. 239-244 (2010) |
| Abstract: The influence of titanium and vanadium on the hydrogen transport rate
through thin amorphous alumina films is addressed. Only small changes in the transport rate are observed when the Al2O3 are covered with titanium or vanadium. This is in stark contrast to results with a Pd overlayer, which enhances the transport by an order of magnitude. Similarly, when titanium is embedded into the alumina the transport rate is faster than for the covered case but still slower than the undoped reference. Embedding vanadium in the alumina does not yield an increase in uptake rate compared to the vanadium covered oxide layers. These results add to the understanding of the hydrogen uptake of oxidized metals, especially the alanates, where the addition of titanium has been found to significantly enhance the rate of hydrogen uptake. The current findings eliminate two possible routes for the catalysis of alanates by Ti, namely dissociation and effective diffusion short-cuts formed by Ti. Finally, no photocatalytic enhancement was noticed on the titanium covered samples. (c) 2010 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000276532300048,
author = {Palsson, G. K. and Wang, Y. T. and Azofeifa, D. and Raanaei, H. and Sahlberg, M. and Hjorvarsson, B.},
title = {Influence of titanium and vanadium on the hydrogen transport through amorphous alumina films},
journal = {JOURNAL OF ALLOYS AND COMPOUNDS},
year = {2010},
volume = {494},
number = {1-2},
pages = {239-244},
doi = {https://doi.org/10.1016/j.jallcom.2009.12.178}
}
|
| Orna, J., Algarabel, P.A., Morellon, L., Pardo, J.A., de Teresa, J.M., Lopez Anton, R., Bartolome, F., Garcia, L.M., Bartolome, J., Cezar, J.C. and Wildes, A. Origin of the giant magnetic moment in epitaxial Fe3O4 thin films PHYSICAL REVIEW B 81, 14 (2010) |
| Abstract: We study the enhanced magnetic moment observed in epitaxial magnetite
(Fe3O4) ultrathin films (t < 15 nm) grown on MgO (001) substrates by means of pulsed laser deposition. The Fe3O4 (001) thin films exhibit high crystallinity, low roughness, and sharp interfaces with the substrate, and the existence of the Verwey transition at thicknesses down to 4 nm. The evolution of the Verwey transition temperature with film thickness shows a dependence with the antiphase boundaries density. Superconducting quantum interference device (SQUID) and vibrating sample magnetometry measurements in ultrathin films show a magnetic moment much higher than the bulk magnetite value. In order to study the origin of this anomalous magnetic moment, polarized neutron reflectivity (PNR), and x-ray magnetic circular dichroism (XMCD) experiments have been performed, indicating a decrease in the magnetization with decreasing sample thickness. X-ray photoemission spectroscopy measurements show no metallic Fe clusters present in the magnetite thin films. Through inductively coupled plasma mass spectroscopy and SQUID magnetometry measurements performed in commercial MgO (001) substrates, the presence of Fe impurities embedded within the substrates has been observed. Once the substrate contribution has been corrected, a decrease in the magnetic moment of magnetite thin films with decreasing thickness is found, in good agreement with the PNR and XMCD measurements. Our experiments suggest that the origin of the enhanced magnetic moment is not intrinsic to magnetite but due to the presence of Fe impurities in the MgO substrates. |
BibTeX:
@article{WOS:000277210200084,
author = {Orna, J. and Algarabel, P. A. and Morellon, L. and Pardo, J. A. and de Teresa, J. M. and Lopez Anton, R. and Bartolome, F. and Garcia, L. M. and Bartolome, J. and Cezar, J. C. and Wildes, A.},
title = {Origin of the giant magnetic moment in epitaxial Fe3O4 thin films},
journal = {PHYSICAL REVIEW B},
year = {2010},
volume = {81},
number = {14},
doi = {https://doi.org/10.1103/PhysRevB.81.144420}
}
|
| Springell, R., Langridge, S., Wildes, A., Wilkins, S.B., Sanchez-Hanke, C., Moore, K.T., Butterfield, M.T., Chivall, J., Ward, R.C.C., Wells, M.R. and Lander, G.H. Chemical and magnetic structure of uranium/gadolinium multilayers studied by transmission electron microscopy, neutron scattering, and x-ray reflectivity PHYSICAL REVIEW B 81, 13 (2010) |
| Abstract: We present a multitechnique approach to study the detailed chemical and
magnetic structure of uranium/gadolinium multilayers. At low temperature the saturation magnetization is found to be similar to 60% of that of bulk gadolinium. We address this problem, which is found in many other multilayers and suggest a model that may have wider applications. transmission electron microscopy images indicate a microstructure, consistent with a columnar growth of Gd with crystallites of the order 20 -> 100 angstrom. Off-specular neutron scattering is most strongly visible at saturation field, indicating that Gd moments are not aligned with the applied field. X-ray resonant magnetic scattering provides proof of coupled in-plane length scales for both the structural and the magnetic roughness. A detailed x-ray scattering study of both the specular and off-specular reflectivities has been used to investigate the in-plane structure of the multilayers. We calculate the roughness and transverse correlation cut-off length, xi(x) = 120 +/- 30 angstrom, and present a simple model to determine an average column size of 27 +/- 6 angstrom and a reduction in the magnetic saturation of similar to 40%. |
BibTeX:
@article{WOS:000277207900069,
author = {Springell, R. and Langridge, S. and Wildes, A. and Wilkins, S. B. and Sanchez-Hanke, C. and Moore, K. T. and Butterfield, M. T. and Chivall, J. and Ward, R. C. C. and Wells, M. R. and Lander, G. H.},
title = {Chemical and magnetic structure of uranium/gadolinium multilayers studied by transmission electron microscopy, neutron scattering, and x-ray reflectivity},
journal = {PHYSICAL REVIEW B},
year = {2010},
volume = {81},
number = {13},
doi = {https://doi.org/10.1103/PhysRevB.81.134434}
}
|
| Lidbaum, H., Raanaei, H., Papaioannou, E.T., Leifer, K. and Hjorvarsson, B. Structural and magnetic properties of Co68Fe24Zr8/Al2O3 multilayers JOURNAL OF CRYSTAL GROWTH 312, 4, pp. 580-586 (2010) |
| Abstract: The structural and magnetic properties of Co68Fe24Zr8/Al2O3 multilayers
grown by using magnetron Sputtering were investigated with X-ray reflectivity, transmission electron microscopy and magnetooptical Kerr effect. The Co68Fe24Zr8 form amorphous islands when the nominal thickness of the Co68Fe24Zr8 layers is 10 angstrom, exhibiting an isotropic superparamagnetic behavior. Continuous layers with mostly a nano-crystalline structure are instead formed when the nominal thickness of the Co68Fe24Zr8 layers is increased to 20 angstrom. The continuous layers exhibit random, in-plane, magnetic anisotropy resulting from the growth Process. However, induced uniaxial anisotropy is obtained when growing the sample in the presence of an applied magnetic field, regardless of the combination of amorphous and nano-crystalline material. (C) 2009 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000274761900017,
author = {Lidbaum, Hans and Raanaei, Hossein and Papaioannou, Evangelos Th and Leifer, Klaus and Hjorvarsson, Bjorgvin},
title = {Structural and magnetic properties of Co68Fe24Zr8/Al2O3 multilayers},
journal = {JOURNAL OF CRYSTAL GROWTH},
year = {2010},
volume = {312},
number = {4},
pages = {580-586},
doi = {https://doi.org/10.1016/j.jcrysgro.2009.11.025}
}
|
| Hase, T., Raanaei, H., Lidbaum, H., Sanchez-Hanke, C., Wilkins, S., Leifer, K. and Hjorvarsson, B. Spin and orbital moment in amorphous Co68Fe24Zr8 layers PHYSICAL REVIEW B 80, 13 (2009) |
| Abstract: The ratio of the orbital to the spin magnetic moment was determined for
both Fe and Co in amorphous Co68Fe24Zr8 layers using x-ray circular dichroism. The investigations were performed on both thick Co68Fe24Zr8 layers as well as on amorphous Co68Fe24Zr8/Al70Zr30 multilayers grown by dc sputtering. Structural characterization was performed using x-ray reflectometry, x-ray diffraction, and transmission electron microscopy. X-ray circular dichroism, x-ray magnetic scattering as well as the magneto-optic Kerr effect were used to characterize the magnetic properties of the amorphous materials. The ratio of the orbital to spin moments in the single CoFeZr-layer sample was 0.012 +/- 0.005 for Fe and 0.078 +/- 0.005 for Co. Substantial reduction in the the ratio of the orbital to spin moments was observed with decreasing CoFeZr-layer thickness. |
BibTeX:
@article{WOS:000271351300052,
author = {Hase, Thomas and Raanaei, Hossein and Lidbaum, Hans and Sanchez-Hanke, Cecilia and Wilkins, Stuart and Leifer, Klaus and Hjorvarsson, Bjorgvin},
title = {Spin and orbital moment in amorphous Co68Fe24Zr8 layers},
journal = {PHYSICAL REVIEW B},
year = {2009},
volume = {80},
number = {13},
doi = {https://doi.org/10.1103/PhysRevB.80.134402}
}
|
| Raanaei, H., Nguyen, H., Andersson, G., Lidbaum, H., Korelis, P., Leifer, K. and Hjorvarsson, B. Imprinting layer specific magnetic anisotropies in amorphous multilayers JOURNAL OF APPLIED PHYSICS 106, 2 (2009) |
| Abstract: We demonstrate how layer specific in-plane magnetic anisotropy can be
imprinted in amorphous multilayers. The anisotropy is obtained by growing the magnetic layers in the presence of an external field and the anisotropy direction can thereby be arbitrarily chosen for each of the magnetic layers. We used Co68Fe24Zr8 and Al70Zr30 layers as building blocks for demonstrating this effect. The imprinting is expected to be obtainable for a wide range of amorphous materials when grown at temperatures below the magnetic ordering temperature. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3169523] |
BibTeX:
@article{WOS:000268613000101,
author = {Raanaei, Hossein and Nguyen, Hugo and Andersson, Gabriella and Lidbaum, Hans and Korelis, Panagiotis and Leifer, Klaus and Hjorvarsson, Bjorgvin},
title = {Imprinting layer specific magnetic anisotropies in amorphous multilayers},
journal = {JOURNAL OF APPLIED PHYSICS},
year = {2009},
volume = {106},
number = {2},
doi = {https://doi.org/10.1063/1.3169523}
}
|
| Marcellini, M., Parnaste, M., Hjorvarsson, B. and Wolff, M. Influence of the distribution of the inherent ordering temperature on the ordering in layered magnets PHYSICAL REVIEW B 79, 14 (2009) |
| Abstract: We study the influence of gradients in the inherent ordering temperature
of coupled layered magnets on the overall magnetic ordering. The gradients were accomplished by growing Fe(001) layers with thicknesses ranging from two to three monolayers, all separated by seven monolayers of V(001). Two types of gradient superstructures were grown: one with the highest and one with the lowest inherent ordering temperature in the center of the samples. The superstructure with the thinnest outermost Fe layers exhibits lower ordering temperature, demonstrating the importance of the sequence of the layers. Both these structures order at temperatures significantly lower than a superlattice with a constant thickness of the Fe layers (three monolayers). The results highlight the intricate collective aspects of the magnetic ordering in layered magnets, which are not captured by current models in magnetism research. |
BibTeX:
@article{WOS:000265943200088,
author = {Marcellini, Moreno and Parnaste, Martin and Hjorvarsson, Bjorgvin and Wolff, Maximilian},
title = {Influence of the distribution of the inherent ordering temperature on the ordering in layered magnets},
journal = {PHYSICAL REVIEW B},
year = {2009},
volume = {79},
number = {14},
doi = {https://doi.org/10.1103/PhysRevB.79.144426}
}
|
| Tremayne, M., Chong, S.Y. and Bell, D. Optimisation of algorithm control parameters in cultural differential evolution applied to molecular crystallography FRONTIERS OF COMPUTER SCIENCE IN CHINA 3, 1, pp. 101-108 (2009) |
| Abstract: Evolutionary search and optimisation algorithms have been used
successfully in many areas of materials science and chemistry. In recent years, these techniques have been applied to, and revolutionised the study of crystal structures from powder diffraction data. In this paper we present the application of a hybrid global optimisation technique, cultural differential evolution (CDE), to crystal structure determination from powder diffraction data. The combination of the principles of social evolution and biological evolution, through the pruning of the parameter search space shows significant improvement in the efficiency of the calculations over traditional dictates of biological evolution alone. Results are presented in which a range of algorithm control parameters, i.e., population size, mutation and recombination rates, extent of culture-based pruning are used to assess the performance of this hybrid technique. The effects of these control parameters on the speed and efficiency of the optimisation calculations are discussed, and the potential advantages of the CDE approach demonstrated through an average 40% improvement in terms of speed of convergence of the calculations presented, and a maximum gain of 68% with larger population size. |
BibTeX:
@article{WOS:000207970900010,
author = {Tremayne, Maryjane and Chong, Samantha Y. and Bell, Duncan},
title = {Optimisation of algorithm control parameters in cultural differential evolution applied to molecular crystallography},
journal = {FRONTIERS OF COMPUTER SCIENCE IN CHINA},
year = {2009},
volume = {3},
number = {1},
pages = {101-108},
doi = {https://doi.org/10.1007/s11704-009-0009-3}
}
|
| Bjorck, M., Andersson, G., Sanyal, B., Hedlund, M. and Wildes, A. Segregation and interdiffusion in (Fe,Co)/Pt superlattices PHYSICAL REVIEW B 79, 8 (2009) |
| Abstract: We report on the chemical structure of (Fe,Co)/Pt superlattices, which
recently have shown high uniaxial magnetocrystalline anisotropy combined with high saturation magnetic moments. In particular, the homogeneity of the (Fe,Co) alloy is studied with a combination of x-ray and neutron reflectometry-the latter in a configuration where magnetic scattering is negligible. It is deduced, with support from off-specular x-ray reflectivity patterns and corresponding simulations, that the lower (Fe,Co)-on-Pt interface contains more Co than the upper Pt-on-(Fe,Co) interface. This can occur as Co interdiffuses into Pt more easily than Fe, as shown by density-functional calculations. The effect of this interdiffusion and segregation on the uniaxial anisotropy is discussed, and it is found that the previously observed discrepancy between experimental and theoretical anisotropy values can be quantitatively accounted for. |
BibTeX:
@article{WOS:000263816000090,
author = {Bjorck, M. and Andersson, G. and Sanyal, B. and Hedlund, M. and Wildes, A.},
title = {Segregation and interdiffusion in (Fe,Co)/Pt superlattices},
journal = {PHYSICAL REVIEW B},
year = {2009},
volume = {79},
number = {8},
doi = {https://doi.org/10.1103/PhysRevB.79.085428}
}
|
| Bjoerck, M., Schlepuetz, C.M., Pauli, S.A., Martoccia, D., Herger, R. and Willmott, P.R. Atomic imaging of thin films with surface x-ray diffraction: introducing DCAF JOURNAL OF PHYSICS-CONDENSED MATTER 20, 44 (2008) |
| Abstract: A direct method for the retrieval of electron density maps from surface
x-ray diffraction data is presented and its performance is evaluated. The method, DCAF (difference map using the constraints of atomicity and film shift), is based on the difference map iteration scheme and uses, apart from the traditional constraints of atomicity, positivity and film thickness, a novel constraint, which we have named the `film shift', whereby the real space solution is shifted up by an out-of-plane unit cell size of the underlying bulk substrate material if the topmost region of the same thickness contains insignificant electron density. This relaxes the film thickness constraint, which is necessarily loose in order to accommodate structural uncertainties at the film-substrate interface due to intermixing, roughness, and heteroepitaxial strain. DCAF's performance was evaluated by retrieval of the electron density distribution from a real data set, recorded from a five-monolayer film of LaAlO3 on SrTiO3, which resulted in an electron density in good agreement with the previously solved structure. Importantly, the stability and reproducibility of the final solution compares favorably with constraint combinations in which the film shift projection is omitted, highlighting the power of this new method. In addition, an example of a full structural solution for a three-monolayer-thick film of La1-xSrxMnO3 on SrTiO3 is presented, where DCAF electron density retrieval followed by model building and refinement was conducted. It will be shown that DCAF can be successfully applied to thin films for retrieving physically meaningful electron densities, and that it can also serve as a starting point for subsequent structure refinement. |
BibTeX:
@article{WOS:000260028500007,
author = {Bjoerck, M. and Schlepuetz, C. M. and Pauli, S. A. and Martoccia, D. and Herger, R. and Willmott, P. R.},
title = {Atomic imaging of thin films with surface x-ray diffraction: introducing DCAF},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2008},
volume = {20},
number = {44},
doi = {https://doi.org/10.1088/0953-8984/20/44/445006}
}
|
| Bjorck, M., Hedlund, M. and Andersson, G. Magnetic moments in Fe-Co/Pt superlattices JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 320, 21, pp. 2660-2664 (2008) |
| Abstract: The element specific spin and orbital moments for Fe and Co in
Fe40Co60/Pt (001) superlattices, with layer thicknesses d(FeCo) = 4-10 ML and d(Pt) = 8 ML, have been studied by X-ray magnetic circular dichroism with focus on the interfacial magnetic moments of the Fe40Co60 layers. The spin moments of Fe and Co showed the same relative decrease at the interfaces with respect to the bulk alloy. The change at the interface was found to be -0.9(1) of the bulk alloy spin moment. The orbital moment for Fe also decreased at the interfaces, whereas the Co orbital moment did not show any appreciable change at the interfaces. In addition, SQUID measurements of the total magnetization allowed the extraction of the induced Pt magnetic moment, which was found to be 0.6(3)mu B/atom and is discussed with respect to previous studies. (C) 2008 Elsevier B.V. All rights reserved. |
BibTeX:
@article{WOS:000258395400021,
author = {Bjorck, M. and Hedlund, M. and Andersson, G.},
title = {Magnetic moments in Fe-Co/Pt superlattices},
journal = {JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS},
year = {2008},
volume = {320},
number = {21},
pages = {2660-2664},
doi = {https://doi.org/10.1016/j.jmmm.2008.05.029}
}
|
| Palsson, G.K., Rennie, A.R. and Hjorvarsson, B. Examination of the reliability of X-ray techniques for determining hydrogen-induced volume changes PHYSICAL REVIEW B 78, 10 (2008) |
| Abstract: The Bragg peaks in x-ray diffraction experiments are generally taken to
be a reliable measure of the average lattice distance in crystals. We show that this assumption can be misleading when determining hydrogen-induced volume changes. Experiments based on simultaneous determination of the position of the Bragg peak and the sample volume of an Fe/V(001) superlattice while expanding the lattice by in situ hydrogen loading serve as an illustration of this counter-intuitive effect. |
BibTeX:
@article{WOS:000259690400035,
author = {Palsson, G. K. and Rennie, A. R. and Hjorvarsson, B.},
title = {Examination of the reliability of X-ray techniques for determining hydrogen-induced volume changes},
journal = {PHYSICAL REVIEW B},
year = {2008},
volume = {78},
number = {10},
doi = {https://doi.org/10.1103/PhysRevB.78.104118}
}
|
| Nylander, T., Campbell, R.A., Vandoolaeghe, P., Cardenas, M., Linse, P. and Rennie, A.R. Neutron reflectometry to investigate the delivery of lipids and DNA to interfaces BIOINTERPHASES 3, 2, pp. FB64-FB82 (2008) |
| Abstract: The application of scattering methods in the study of biological and
biomedical problems is a field of research that is currently experiencing fast growth. In particular, neutron reflectometry (NR) is a technique that is becoming progressively more widespread, as indicated by the current commissioning of several new reflectometers worldwide. NR is valuable for the characterization of biomolecules at interfaces due to its capability to provide quantitative structural and compositional information on relevant molecular length scales. Recent years have seen an increasing number of applications of NR to problems related to drug and gene delivery. We start our review by summarizing the experimental methodology of the technique with reference to the description of biological liquid interfaces. Various methods for the interpretation of data are then discussed, including a new approach based on the lattice mean-field theory to help characterize stimulus-responsive surfaces relevant to drug delivery function. Recent progress in the subject area is reviewed in terms of NR studies relevant to the delivery of lipids and DNA to surfaces. Lastly, we discuss two case studies to exemplify practical features of NR that are exploited in combination with complementary techniques. The first case concerns the interactions of lipid-based cubic phase nanoparticles with model membranes (a drug delivery application), and the second case concerns DNA compaction at surfaces and in the bulk solution (a gene delivery application). (C) 2008 American Vacuum Society. [DOI: 10.1116/1.2976448] |
BibTeX:
@article{WOS:000264979100028,
author = {Nylander, Tommy and Campbell, Richard A. and Vandoolaeghe, Pauline and Cardenas, Marite and Linse, Per and Rennie, Adrian R.},
title = {Neutron reflectometry to investigate the delivery of lipids and DNA to interfaces},
journal = {BIOINTERPHASES},
year = {2008},
volume = {3},
number = {2},
pages = {FB64-FB82},
doi = {https://doi.org/10.1116/1.2976448}
}
|
| Raanaei, H., Lidbaum, H., Liebig, A., Leifer, K. and Hjorvarsson, B. Structural coherence and layer perfection in Fe/MgO multilayers JOURNAL OF PHYSICS-CONDENSED MATTER 20, 5 (2008) |
| Abstract: A series of Fe/MgO multilayers was grown on single-crystal MgO(001)
substrates at different temperatures using magnetron sputtering. The structural quality of the samples was investigated by x-ray reflectometry, x-ray diffraction and transmission electron microscopy. The results show a strong dependence of the structural quality on the growth temperature. Although good epitaxial layers are obtained at 165 degrees C, the sample does not exhibit any superlattice diffraction peaks. This effect is shown to be related to a continuous variation of the distance between the Fe layers as well as between the MgO layers. |
BibTeX:
@article{WOS:000252923400015,
author = {Raanaei, Hossein and Lidbaum, Hans and Liebig, Andreas and Leifer, Klaus and Hjorvarsson, Bjorgvin},
title = {Structural coherence and layer perfection in Fe/MgO multilayers},
journal = {JOURNAL OF PHYSICS-CONDENSED MATTER},
year = {2008},
volume = {20},
number = {5},
doi = {https://doi.org/10.1088/0953-8984/20/5/055212}
}
|
| Herger, R., Willmott, P.R., Schlepuetz, C.M., Bjoerck, M., Pauli, S.A., Martoccia, D., Patterson, B.D., Kumah, D., Clarke, R., Yacoby, Y. and Doebeli, M. Structure determination of monolayer-by-monolayer grown La(1-x)Sr(x)MnO(3) thin films and the onset of magnetoresistance PHYSICAL REVIEW B 77, 8 (2008) |
| Abstract: Surface x-ray diffraction was used to determine the atomic structures of
La(1-x)Sr(x)MnO(3) thin films, grown monolayer by monolayer on SrTiO(3) by pulsed laser deposition. Structures for one-, two-, three-, four-, six-, and nine-monolayer-thick films were solved using the Coherent Bragg rod analysis phase-retrieval method and subsequent structural refinement. Four important results were found. First, the out-of-plane lattice constant is elongated across the substrate-film interface. Second, the transition from substrate to film is not abrupt, but proceeds gradually over approximately three unit cells. Third, Sr segregates towards the topmost monolayer of the film: we determined a Sr-segregation enthalpy of -15 kJ/mol from the occupation parameters. Finally, the electronic bandwidth W was used to explain the onset of magnetoresistance for films of nine or more monolayers thickness. Resistivity measurements of the nine monolayer-thick film confirm magnetoresistance and the presence of a dead layer with mostly insulating properties. |
BibTeX:
@article{WOS:000253764300084,
author = {Herger, R. and Willmott, P. R. and Schlepuetz, C. M. and Bjoerck, M. and Pauli, S. A. and Martoccia, D. and Patterson, B. D. and Kumah, D. and Clarke, R. and Yacoby, Y. and Doebeli, M.},
title = {Structure determination of monolayer-by-monolayer grown La(1-x)Sr(x)MnO(3) thin films and the onset of magnetoresistance},
journal = {PHYSICAL REVIEW B},
year = {2008},
volume = {77},
number = {8},
doi = {https://doi.org/10.1103/PhysRevB.77.085401}
}
|
| Andersson, G. and Hjorvarsson, B. Effects of strain on magnetic anisotropy in Fe- and Co-based heterostructures PHASE TRANSITIONS 81, 7-8, pp. 679-701 (2008) |
| Abstract: The magnetic ordering in transition metals is strongly affected by any
strain in the lattice, due to the close connection between strain and anisotropy. This article reviews recent developments, both experimental and theoretical, in the field of strain-induced magnetic anisotropies, with focus on films and multilayers based on Fe and Co. It is demonstrated that the reorientation of preferred magnetization directions can be controlled through both the growth direction and the strain state, which is caused by interleaving with suitable spacers, as well as by tuning the chemical composition if the magnetic material is an alloy. Both in-plane and out-of-plane easy directions can be forced upon the films and superlattices in this manner. Some methods for local structural manipulation are also reviewed. |
BibTeX:
@article{WOS:000258026200006,
author = {Andersson, Gabriella and Hjorvarsson, Bjorvin},
title = {Effects of strain on magnetic anisotropy in Fe- and Co-based heterostructures},
journal = {PHASE TRANSITIONS},
year = {2008},
volume = {81},
number = {7-8},
pages = {679-701},
doi = {https://doi.org/10.1080/01411590801975385}
}
|