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2. Tunable polymorphism of epitaxial iron oxides in the four-in-one ferroic-on-GaN system with magnetically ordered {\alpha}-, {\gamma}-, {\epsilon}-Fe2O3 and Fe3O4 layers

Author

Suturin, Sergey, Korovin, Alexander, Gastev, Sergey, Volkov, Mikhail, Tabuchi, Masao, and Sokolov, Nikolai

Subjects
Condensed Matter - Materials Science
Abstract

Hybridization of semiconducting and magnetic materials into a single heterostructure is believed to be potentially applicable to the design of novel functional spintronic devices. In the present work we report epitaxial stabilization of four magnetically ordered iron oxide phases (Fe3O4, {\gamma}-Fe2O3, {\alpha}-Fe2O3 and most exotic metastable {\epsilon}-Fe2O3) in the form of nanometer sized single crystalline films on GaN(0001) surface. The epitaxial growth of as many as four distinctly different iron oxide phases is demonstrated within the same single-target Laser MBE technological process on a GaN semiconductor substrate widely used for electronic device fabrication. The discussed iron oxides belong to a family of simple formula magnetic materials exhibiting a rich variety of outstanding physical properties including peculiar Verwey and Morin phase transitions in Fe3O4 and {\alpha}-Fe2O3 and multiferroic behavior in metastable magnetically hard {\epsilon}-Fe2O3 ferrite. The physical reasons standing behind the nucleation of a particular phase in an epitaxial growth process deserve interest from the fundamental point of view. The practical side of the presented study is to exploit the tunable polymorphism of iron oxides for creation of ferroic-on-semiconductor heterostructures usable in novel spintronic devices. By application of a wide range of experimental techniques the surface morphology, crystalline structure, electronic and magnetic properties of the single phase iron oxide epitaxial films on GaN have been studied. A comprehensive comparison has been made to the properties of the same ferrite materials in the bulk and nanostructured form reported by other research groups., Comment: 25 pages, 12 figures

Published
2017
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21. Correlation between crystal structure and magnetism in PLD grown epitaxial films of e-Fe2O3 on GaN.

Author

Suturin, Sergey M., Korovin, Alexander M., Sitnikova, Alla A., Kirilenko, Demid A., Volkov, Mikhail P., Dvortsova, Polina A., Ukleev, Victor A., Tabuchi, Masao, and Sokolov, Nikolai S.

Subjects
CRYSTAL structure, MAGNETISM, MAGNETIC anisotropy, MAGNETIC storage, MAGNETIC circular dichroism, MAGNETIZATION reversal, GALLIUM nitride films
Abstract

In the present paper we discuss correlations between crystal structure and magnetic properties of epitaxial e-Fe2O3 films grown on GaN. The large magnetocrystalline anisotropy and room temperature multiferroic properties of this exotic iron oxide polymorph, make it a perspective material for the development of low power consumption magnetic media storage devices. Extending our recent progress in PLD growth of e-Fe2O3 on the surface of technologically important nitride semiconductors, we apply reciprocal space tomography by electron and x-ray diffraction to investigate the break of crystallographic symmetry occurring at the oxide-nitride interface resulting in the appearance of anisotropic crystallographic disorder in the sub-100 nm e-Fe2O3 films. The orthorhombic-on-hexagonal nucleation scenario is shown responsible for the development of a peculiar columnar structure observed in e-Fe2O3 by means of HRTEM and AFM. The complementary information on the direct and reciprocal space structure of the columnar e-Fe2O3 films is obtained by various techniques and correlated to their magnetic properties. The peculiar temperature dependence of magnetization studied by the small-field magnetization derivative method and by neutron diffraction reveals the existence of a magnetic softening below 150 K, similar to the one observed earlier solely in nanoparticles. The magnetization reversal in e-Fe2O3 films probed by X-ray magnetic circular dichroism is found different from the behavior of the bulk averaged magnetization measured by conventional magnetometry. The presented results fill the gap between the numerous studies performed on randomly oriented e-Fe2O3 nanoparticles and much less frequent investigations of epitaxial epsilon ferrite films with lattice orientation fixed by the substrate. [ABSTRACT FROM AUTHOR]

Published
2021
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22. Layer structure analysis of Er delta-doped InP by x-ray crystal truncation rod scattering

Author

Takeda, Yoshikazu, Fujita, Keiji, Matsubara, Naoteru, Yamada, Naoki, Ichiki, Satofumi, Tabuchi, Masao, and Fujiwara, Yasufumi

Subjects
Crystals -- Structure, Layer structure (Solids) -- Research, Physics
Abstract

A one monolayer level study was conducted on the crystal and layer structures of an Er delta-doped layer in InP using an x-ray crystal truncation rod scattering measurement and synchroton radiation-based x-ray interference. Measurements and computer simulation reveal that the rocksalt structure ErP are developed by Er atoms delta-dpoed in InP. Results also show that the Er atoms are confined in 5 ML.

Published
1997

23. Enhanced oxygen reduction activity of size-selected platinum subnanocluster catalysts: Ptn(n= 3–9)Electronic supplementary information (ESI) available: Mass spectra of Pt NC, hydrodynamic voltammograms, evolutions of XANES spectra for Pt L3edge, XPS spectra of Pt 4f against O2exposures, evolution of XAFS oscillations, computational model, optimized structures by DFT, FEFF simulation results for XAFS, radial distributions for Pt–Pt bonds, calculated partial density of states of Pt NC/Gr, Bader charge and d-band center, coordinates of isomers. See DOI: 10.1039/d1cy00573a

Author

Ohnuma, Akira, Takahashi, Koki, Tsunoyama, Hironori, Inoue, Tomoya, Zhao, Pei, Velloth, Archana, Ehara, Masahiro, Ichikuni, Nobuyuki, Tabuchi, Masao, and Nakajima, Atsushi

Abstract

Nanoclusters (NCs) are promising candidates to improve catalytic activity despite the controversial size specificity, because atomicity is a crucial parameter that determines the activity of platinum (Pt) NCs. This paper demonstrates the enhanced catalytic activity based on the charge redistribution in Pt sub-NCs containing three to nine Pt atoms (Ptn; n= 3–9) on a glassy carbon substrate. The sub-NCs show 1.6–2.2 times higher activity than the standard Pt/C catalysts with a Pt crystallite diameter of 2 nm. The geometric structures are identified using rigorous structure analyses by X-ray absorption fine structure spectroscopy and density functional theory, and the activity origin within the supported Pt sub-NCs is theoretically discussed from viewpoints of energetics for reaction intermediates in the electrochemical processes. It should be possible to use sub-NCs in future fuel cell technologies as an active catalyst with a high atomic efficiency.

Published
2022
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27. In situ X-ray investigation of changing barrier growth temperatures on InGaN single quantum wells in metal-organic vapor phase epitaxy.

Author

Ju, Guangxu, Honda, Yoshio, Tabuchi, Masao, Takeda, Yoshikazu, and Amano, Hiroshi

Subjects
INDIUM gallium nitride, QUANTUM wells, CRYSTAL growth, VAPOR phase epitaxial growth, X-ray diffractometers, PHOTOLUMINESCENCE
Abstract

The effects of GaN quantum barriers with changing growth temperatures on the interfacial characteristics of GaN/InGaN single quantum well (SQW) grown on GaN templates by metalorganic vapour phase epitaxy were in situ investigated by X-ray crystal truncation rod (CTR) scattering and X-ray reflectivity measurements at growth temperature using a laboratory level X-ray diffractometer. Comparing the curve-fitting results of X-ray CTR scattering spectra obtained at growth temperature with that at room temperature, the InxGa1-xN with indium composition less than 0.11 was stabile of the indium distribution at the interface during the whole growth processes. By using several monolayers thickness GaN capping layer to protect the InGaN well layer within temperature-ramping process, the interfacial structure of the GaN/InGaN SQW was drastically improved on the basis of the curve-fitting results of X-ray CTR scattering spectra, and the narrow full width at half-maximum and strong luminous intensity were observed in room temperature photoluminescence spectra. [ABSTRACT FROM AUTHOR]

Published
2014
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28. Tunable polymorphism of epitaxial iron oxides in the four-in-one ferroic-on-GaN system with magnetically ordered ��-, ��-, ��-Fe2O3 and Fe3O4 layers

Author

Suturin, Sergey, Korovin, Alexander, Gastev, Sergey, Volkov, Mikhail, Tabuchi, Masao, and Sokolov, Nikolai

Subjects
Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences
Abstract

Hybridization of semiconducting and magnetic materials into a single heterostructure is believed to be potentially applicable to the design of novel functional spintronic devices. In the present work we report epitaxial stabilization of four magnetically ordered iron oxide phases (Fe3O4, ��-Fe2O3, ��-Fe2O3 and most exotic metastable ��-Fe2O3) in the form of nanometer sized single crystalline films on GaN(0001) surface. The epitaxial growth of as many as four distinctly different iron oxide phases is demonstrated within the same single-target Laser MBE technological process on a GaN semiconductor substrate widely used for electronic device fabrication. The discussed iron oxides belong to a family of simple formula magnetic materials exhibiting a rich variety of outstanding physical properties including peculiar Verwey and Morin phase transitions in Fe3O4 and ��-Fe2O3 and multiferroic behavior in metastable magnetically hard ��-Fe2O3 ferrite. The physical reasons standing behind the nucleation of a particular phase in an epitaxial growth process deserve interest from the fundamental point of view. The practical side of the presented study is to exploit the tunable polymorphism of iron oxides for creation of ferroic-on-semiconductor heterostructures usable in novel spintronic devices. By application of a wide range of experimental techniques the surface morphology, crystalline structure, electronic and magnetic properties of the single phase iron oxide epitaxial films on GaN have been studied. A comprehensive comparison has been made to the properties of the same ferrite materials in the bulk and nanostructured form reported by other research groups., 25 pages, 12 figures

Published
2017
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29. In situ X-ray reflectivity of indium supplied on GaN templates by metal organic vapor phase epitaxy.

Author

Ju, Guangxu, Fuchi, Shingo, Tabuchi, Masao, and Takeda, Yoshikazu

Subjects
INDIUM, VAPOR phase epitaxial growth, X-ray research, CRYSTAL growth, PARTICLES (Nuclear physics), SCANNING electron microscopes
Abstract

The indium supplied on c-plane GaN templates using Metal organic vapor phase epitaxy was studied by in situ X-ray reflectivity (XRR) at 800 °C. The presence of liquid indium layers on the GaN (0001) surface was demonstrated using data-fitting of XRR measurements, ex situ atomic force microscope, auger electron spectroscopy, and cross-sectional scanning electron microscope. These measurements demonstrated that a liquid indium layer coexisted with indium droplets on top of the GaN (0001) surface at 800 °C. The liquid indium film thicknesses increased with increasing TMIn supply time and did not change during cooling from 800 °C to room temperature. [ABSTRACT FROM AUTHOR]

Published
2013
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43. Protein crystallography beamline BL2S1 at the Aichi synchrotron.

Author

Nagae, Takayuki, Tabuchi, Masao, Watanabe, Nobuhisa, Yamada, Yusuke, Tomita, Ayana, and Matsugaki, Naohiro

Subjects
*PROTEIN crystallography, *SYNCHROTRONS, *X-ray diffraction measurement, *NUCLEIC acids, *PROTEINS
Abstract

The protein crystallography beamline BL2S1, constructed at one of the 5 T superconducting bending-magnet ports of the Aichi synchrotron, is available to users associated with academic and industrial organizations. The beamline is mainly intended for use in X-ray diffraction measurements of single-crystals of macromolecules such as proteins and nucleic acids. Diffraction measurements for crystals of other materials are also possible, such as inorganic and organic compounds. BL2S1 covers the energy range 7-17 keV (1.8-0.7 Å) with an asymmetric-cut curved single-crystal monochromator [Ge(111) or Ge(220)], and a platinum-coated Si mirror is used for vertical focusing and as a higher-order cutoff filter. The beamline is equipped with a single-axis goniometer, a CCD detector, and an open-flow cryogenic sample cooler. High-pressure protein crystallography with a diamond anvil cell can also be performed using this beamline. [ABSTRACT FROM AUTHOR]

Published
2017
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