記述言語：英語   掲載種別：研究論文（学術雑誌）

Nanorods are a very effective pinning center in YBa2Cu3O7 films, and the vortex pinning mechanism should be understood to further improve the critical current density (J c) in the nanocomposite films. Matrix defects are naturally formed during nanocomposite growth, and in this study the effect of matrix defects on the J c in the YBa2Cu3O7 films containing nanorods is discussed. YBa2Cu3O7 + BaHfO3 and YBa2Cu3O7 + BaSnO3 films were prepared by varying the laser repetition frequency to control the matrix defects. All the films contained the nanorods. The YBa2Cu3O7 + BaHfO3 film of 2 Hz exhibits high J c for magnetic field parallel to the c-axis (B//c) due to the nanorods and the isolated random point defects. In the YBa2Cu3O7 + BaHfO3 film of 10 Hz, while the short stacking faults and networked random point defects decreased the J c for B//c, the short stacking faults improved the J c for tilted magnetic field. In the YBa2Cu3O7 + BaSnO3 film of 10 Hz, the isolated random point defects improved J c regardless of the magnetic field direction. While the ab-plane correlated defects are analyzed by the structural observation, the network or isolated nature of the random point defects can be discussed by the normal state resistivity. The matrix defects of YBa2Cu3O7 nanocomposite films should be designed considering the correlated/network/isolated nature which is determined by the morphology and defect concentration.

DOI： 10.1088/1361-6668/acecad

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The structure, composition, and spatial distribution heterogeneity of artificial pinning centers affect the critical current density of REBa2Cu3O7−y (RE: rare earth) coated conductors. Nanoscale structures and compositions have been analyzed with transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). However, microscale heterogeneity has been difficult to characterize. Here, YBa2Cu3O7−y thin films doped with double-perovskite Ba2YbNbO6 were prepared via pulsed-laser deposition and characterized with TEM, STEM, and scanning electron microscopy (SEM). Cross-sectional and plan-view TEM/STEM imaging revealed hybrid pinning structures consisting of nanorods, nanoparticles, and planar defects that were formed spontaneously. Nanorods were imaged with high spatial resolution via field-emission SEM of thin-foil specimens. Focused-ion-beam (FIB) micro-sectioning enables SEM imaging of microscale heterogeneity in nanorod spatial distributions. By using TEM/STEM in conjunction with FIB-SEM, the coated conductor inhomogeneity was directly evaluated from the nano- to micrometer scales.

DOI： 10.1063/5.0155145

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Much effort has been expended to obtain thin films of metastable solid solutions of germanium (Ge) that contain as high tin (Sn) content as possible because of their excellent electronic and optoelectronic properties. On the basis of our previous study on amorphous Ge, we demonstrated in this study that irradiation of substrate-free films of amorphous Ge100−xSnx (x = 8, 11, and 19 at. %) with a low-energy electron beam of 3 keV at ambient temperature can induce instantaneous wide-area crystallization (explosive crystallization). Characteristic spiral crystal growth associated with explosive crystallization occurred with areas exceeding 50 μm in diameter around a scanned area of the electron beam of 8 × 8 μm2. As a result, solid solutions of GeSn with Sn concentration up to 19 at. % were obtained with the suppression of precipitation of β-Sn. The region of explosive crystallization reduced in size with increasing Sn content. In addition, thermal analyses revealed that the heat released during crystallization of amorphous GeSn films decreased with increasing Sn content. This relationship indicates that the heat release at the growth front plays a key role in the propagation of explosive crystallization of a-GeSn.

DOI： 10.1063/5.0147022

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Generally materials with low thermal conductivity require weaker interatomic bonding, considered as soft materials. Here we demonstrate that SiB6 with planar structural defects shows low thermal conductivity, but uncommonly high strength. Planar defects-induced polycrystalline SiB6 (PD-SiB6) has a relatively large Vickers hardness, which is comparable to those of well-known superhard materials, despite of relatively low thermal conductivity (<10 W m-1 K-1 at 300 K). Transmission electron microscopy observations confirmed the presence of numerous planar defects, which were thought to contribute to the improvement of hardness. Thanks to the special characteristics of a trade-off relationship between low thermal conductivity and high strength, we believe that PD-SiB6 can be used in new strategies of controlling thermal and mechanical properties in various functional materials.

DOI： 10.1016/j.jallcom.2023.168744

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In this study, microstructure and phase transformation behavior in Fe20Co20Ni20Cr20B201xSix alloys prepared by the mechanical alloying (MA) method were investigated by X-ray diffraction (XRD) measurements, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry (DSC). The Fe20Co20Ni20Cr20B201xSix alloys prepared by the melt-spinning method were composed of FCC and compounds, and the FCC and BCC phases predicted by the valance electron concentration parameter were not formed. However, alloy powders prepared by the MA method were revealed to be composed of the FCC and BCC phases. Small amounts of unreacted pure B and Si particles were observed in alloy powders with high and low B content, respectively. XRD and DSC measurements revealed that the BCC phase in MA powder disappeared, and compounds were formed by heating up to 700°C. Especially the compound formation temperature was higher than that of the same alloy prepared by the melt-spinning method, suggesting that the thermal stability of the alloy powders prepared by the MA method was higher than that of the alloy ribbons prepared by the melt-spinning method. [doi:10.2320/matertrans.MT-M2023040]

DOI： 10.2320/matertrans.MT-M2023040

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

The crystallization processes of amorphous Ge as well as the atomistic structures of the growth front were examined by molecular-dynamics simulations. An amorphous Ge network was annealed in a thermal bath with a temperature gradient. Crystallization proceeded via the supercooled liquid, and changed from random nanocrystallization to large-oriented grain growth. The resultant structures qualitatively reproduced the explosive crystallization observed with pulsed-laser irradiation and flash lamp annealing. The supercooled liquid was found to transform from a tetrahedral liquid to a more highly-coordinated liquid with increasing temperature, which was attributed to the change in growth mode.

DOI： 10.35848/1882-0786/aca87a

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Thermoelectric SnSe exhibits a very high figure of merit, and the a-axis orientation is needed because a high thermoelectric property is obtained along the bc-plane. Here, in spite of the amorphous nature of glass, a-axis-oriented SnSe films were fabricated using pulsed laser deposition on a glass substrate, which is more practical than single-crystal oxide substrates. Transmission electron microscopy indicated that a-axis-oriented SnSe films with a columnar grain structure grew on amorphous SiO2. The electrical conductivity and the Seebeck coefficient at room temperature showed almost the same trend with respect to the hole concentration in both the SnSe/glass and SnSe/single-crystal-substrate films. The electrical conductivity increased with increasing temperature more slowly in SnSe/glass films than in SnSe/single-crystal-substrate films. This indicates that the grain boundary contribution to carrier scattering is significant at high temperatures, while the grain boundary contribution is as strong as the orthorhombic domain boundary contribution at room temperature. In spite of the grain boundary effect, the power factor in SnSe/glass was as high as that for single-crystal SnSe at high temperatures. Considering the grain boundary effect on electrical conductivity, the structure and process of SnSe films on amorphous substrates should be designed.

DOI： 10.1021/acsaelm.2c01486

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記述言語：英語   掲載種別：研究論文（学術雑誌）

<p>In this study, nanoscale phase formation in rapidly solidified Fe₂₀Co₂₀Ni₂₀Cr₂₀B₂₀₋<i>_x</i>Si<i>_x</i> alloys was investigated using atom probe tomography (APT) and transmission electron microscopy (TEM). According to previous X-ray diffraction measurements and scanning electron microscopy with energy-dispersive X-ray spectroscopy results, it was thought that this alloy system was composed of almost a single face-centered cubic (FCC) solid solution phase when the Si content was 5 at.%. However, APT and TEM results at the nanoscale showed that both an FCC solid solution and compound phases formed for all alloy compositions. The rapidly solidified alloy ribbon with a Si content of 5 at.% showed the presence of nanoscale FCC and Cr₂B phases. Furthermore, in addition to the nanoscale FCC and Cr₂B phases, a nanoscale Cr₃Ni₅Si₂ phase was observed when the Si content exceeded 7.5 at.%.</p>

DOI： 10.2320/matertrans.mt-m2022058

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Swift heavy ion irradiation was carried out to examine the ionization effects on structural changes of δ-Sc4Hf3O12 in which oxygen vacancies are regularly arranged. The specimens were irradiated at room temperature with 92 MeV xenon ions to fluences ranging from 3 × 1012 to 1 × 1014/cm2 and characterized by grazing (glancing) incidence x-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy. It was found that the pristine long-range ordered rhombohedral δ-phase undergoes a reconstructive transformation toward a long-range disordered cubic oxygen-deficient fluorite phase promoted by ionization effects. In addition, an ordered phase with a short-range structure different from the δ-type was formed in a layer going from the surface to a depth of ∼4.5 μm in the specimen irradiated to a fluence of 1 × 1014/cm2. It was found that the ordered phase is formed from the disordered cubic fluorite phase. This structural change is anomalous, because it is the opposite process of the usual irradiation-induced structural change, the order-to-disorder phase transformation. Electron diffraction experiments revealed that short-range ordered regions in this layer possess an oxygen-excess bixbyite organization (C-type heavy rare-earth oxides) with randomly filled anion vacant sites to account for the different stoichiometry and a long-range average oxygen-deficient fluorite phase.

DOI： 10.1063/5.0098518

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

To fabricate high performance YBa2Cu3O7 superconducting films and tapes, the critical current density (Jc) should be enhanced and the nanocomposite structure should be very effective in controlling the vortex pinning and Jc. Although the nanoscale morphology has been a basic parameter from the early stages of nanorod control, compositional factors should be discussed to effectively control not only the superconducting order parameter distribution but also the thermodynamic parameter relating to crystal growth. In this study, a double perovskite oxide, Ba2RENbO6 (RE = Yb, Lu), was incorporated in YBa2Cu3O7 films, where the site occupancy of the RE element is focused to control the nanocomposite structure. The elongated nanorods were formed in both the YBa2Cu3O7+Ba2YbNbO6 and YBa2Cu3O7+Ba2LuNbO6 films. While Lu mainly existed in the nanorods, Yb was observed not only in the nanorods but also in the matrix. As a result, at the fixed nanorod content, while the matching field was larger for the YBa2Cu3O7+Ba2YbNbO6 film, the Jc in the high magnetic field was larger for the YBa2Cu3O7+Ba2LuNbO6 film. The angular dependence of Jc depended on the RE due to the pinning contribution from the Y-rich nanoparticles. These are unconventional phenomena that are not observed in the YBa2Cu3O7+BaMO3 (M = Zr, Sn, Hf) films. Thus, the site occupancy of the RE element affects the Jc characteristics. The self-organization and the nanocomposite structure can be designed by considering the site occupancy as a variable parameter.

DOI： 10.1021/acsaelm.2c00438

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記述言語：英語   掲載種別：研究論文（学術雑誌）

HfO2-based films are important materials used in broad range of electronic applications from high-performance transistors and memory cells, to thermoelectric and energy harvesting elements. By employing scanning probe methods, we made nanoscale comparison of chemical composition, surface morphology, the elastic modulus and the surface potential of bare 10-nm thick Hf0.5Zr0.5O2 films prepared on Si by a carbon-free sputtering process. The composition mapping confirmed uniform distribution of Hf and Zr in the film along wafer size. Suppression of the monoclinic phase in films annealed at 600 - 800 °C had strong impact on spatial variations of film properties. Small surface roughness, large electric domain sizes (50–200 nm at 700 °C) and small fluctuations of the surface potential (40–50 meV) in Si coated with the films are appealing for gate-stack applications. Films annealed at 600-700 °C showed the elastic modulus of about 169 GPa and the ferroelectric polarization reversal at a field of ~1 MV/cm as observed by nanoscale poling with a Pt-coated scanning probe. In contrast, properties of films annealing at 800 °C were affected by growth of thick interfacial oxide layer. The presented nanoscale approach is beneficial in optimizing of physical and mechanical properties of thin dielectric films.

DOI： 10.1016/j.mee.2022.111770

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Amorphous boron carbide (a-BxC) networks consist of light elements, and their low atomic scattering factors makes structural analysis by x-ray diffraction difficult. Electron diffraction has an advantage of detecting the light elements, because of the strong interaction between the matter and electrons. We prepared a-BxC by ion beam technologies and plasma-enhanced chemical vapor deposition, and characterized their structures via atomic pair-distribution functions derived from electron diffraction intensity profiles. It was found that a pentagonal pyramid is the most favorable cluster in a-B4C generated by ion irradiation, while C[sbnd]C homonuclear bonds were formed in the deposited a-BxC thin film. X-ray photoemission spectroscopy revealed that the a-BxC thin film possesses more carbon than B4C, which is responsible for the formation of the homonuclear bonds.

DOI： 10.1016/j.jeurceramsoc.2021.10.020

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Spinel ZnMnGaO4 exhibits the characteristic self-organization dominated by phase separation and strain to realize an ordered nanostructure. To control the self-organization, ZnMnGaO4 films fabricated using pulsed laser deposition were postannealed. While the ordered nano-checkerboard and the slightly coarse nanolamellar structures were observed for the moderate annealing temperature and the long annealing time, the twin structure was formed in the films annealed at the low temperature for the short annealing time. The cross-sectional observation showed the vertically aligned nanostructure near the surface (twin, nano-checkerboard, or nanolamellar) and the nondefective epitaxial layer near the substrate. The ZnMnGaO4 films exhibited the same in-plane lattice parameter as that of MgO along the MgO[110]//ZMGO[101] regardless of annealing conditions, and the stress analysis indicates that the epitaxial stress at the epitaxial ZnMnGaO4/MgO and the shear stress at the epitaxial ZnMnGaO4/twinned ZnMnGaO4 determined the vertical structure and the twin width. The thermodynamic stability and the Mn and Ga diffusion basically bring about the self-organized nanostructure formation as in bulk, and the epitaxial stress and the interface shear stress align the self-organization in the films. Thus, the highly aligned self-organized nanostructures can be fabricated in the annealed ZnMnGaO4 films by tuning these factors.

DOI： 10.1021/acs.jpcc.1c09324

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Highly aligned SnSe exhibits very high thermoelectric properties, and orientation control in films is very promising for developing high-performance thermoelectric modules. While SnSe films with intrinsic p-type nature have been reported, fabrication of the highly aligned n-type SnSe films is difficult due to thermodynamic restriction on the solubility of the doping elements. Here, highly oriented SnSe films doped with Bi were successfully fabricated using pulsed laser deposition. Characteristic film structures were observed: doped Bi in the SnSe matrix; domain boundaries with a spacing of ∼200 nm; self-organized Bi precipitates with a bimodal size distribution; and stacking faults. The most important result is observation of the n-type Hall resistivity and the n-type Seebeck coefficient. The stacking faults and the doped Bi in the films degraded the room-temperature Seebeck coefficient. While the electron carrier mobility in room temperature was smaller than that in the single crystal due to the domain boundary scattering, the domain boundary scattering was suppressed in the high temperature of 300 °C. Thus, the characteristic film structures significantly affect the thermoelectric properties of SnSe. The doped Bi in the SnSe matrix, the stacking faults, and the domain boundaries should be controlled for further improvement of the thermoelectric properties in the Bi-SnSe films, and the self-organized Bi nanoprecipitates are very promising for achieving high-performance Bi-SnSe with decreased thermal conductivity.

DOI： 10.1021/acsaem.1c01722

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：記事・総説・解説・論説等（学術雑誌）

“The 12th Japanese-Polish Joint Seminar on Micro and Nano Analysis” was held in Fukuoka, Japan from August 29 to September 1, 2018, and the proceedings were published in May, 2019, as a special issue of Materials Transactions (Vol. 60, No. 5). The main purpose of this seminar is to discuss the structural analysis of materials by electron microscopy techniques. Among the papers presented at the seminar, this article briefly reviews the following topics: observations of dislocations in a thick specimen by ultra-high voltage electron microscopy, suppression of geometric phase shift due to antiphase boundaries in dark-field electron holography, and structural characterization of amorphous materials by electron diffraction techniques.

DOI： 10.2320/matertrans.MT-M2021094

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The crystallization of sputter-deposited substrate-free films of amorphous germanium was induced by electron irradiation at SEM-level energies of less than 20 keV at ambient temperature using an electron probe microanalyzer. Instantaneous crystallization, referred to as explosive crystallization, occurred consistently at 2-20 keV; the threshold of electron fluxes is 1015-1016 m−2 s−1, which is five to six orders of magnitude lower than those at 100 keV reported previously. This process is expected to be advantageous in the production of polycrystalline Ge films since it is rapid, requires little energy, and results in negligible damage to the substrate.

DOI： 10.1063/5.0052142

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Double perovskite Ba2LuNbO6 (BLNO)-doped YBa2Cu3O7-y (YBCO) thin films are fabricated on a SrTiO3 (001) substrate by pulsed laser deposition, and their nanostructures are characterized by transmission electron microscopy and scanning transmission electron microscopy. Cross-sectional observations and elemental mapping reveal that BLNO self-assembles during thin film deposition, and consequently, nanorods extending straight from the substrate to the surface are formed in the YBCO thin films. It is confirmed that stacking faults perpendicular to the growth direction disturb the formation of BLNO nanorods. Strain maps extracted by geometric phase analysis reveal that the tensile strain occurs in the YBCO matrix around the BLNO nanorods. Misfit dislocations are periodically introduced at the interface between the nanorod and the matrix, which results in the inhomogeneous strain of YBCO around the BLNO nanorods. The superconducting properties of the YBCO + BLNO thin films are compared with those of other previously reported YBCO thin films with normal perovskite and double perovskite nanorods.

DOI： 10.1063/5.0048693

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

A pair of n-type Bi2Te3-xSex and p-type (Bi,Sb)2Te3 is known as a promising candidate for assembling a high thermoelectric efficiency module operating at near room temperature. While the dimensionless figure of merit (zT) of p-type (Bi,Sb)2Te3 is commonly larger than 1.0, n-type Bi2Te3-xSex has a lower zT value of μ0.8 at room temperature. Here, we aim to enhance the zT of n-type Bi2Te3-xSex through the energy filtering effect that can improve the Seebeck coefficient by adding Au. In the Bi2Te2.8Se0.2 + 5 at % Au composite, the Seebeck coefficient is significantly improved, and the electrical resistivity does not change significantly, leading to an approximately twice as high power factor as that of the non-Au-added one at near room temperature. Also, the addition of Au suppresses the thermal conductivity. These advantages result in a maximum zT of over 1.0 at room temperature and average zT value of 1.05 at T = 300-400 K, an μ75% improvement, which is comparable to those of the reported n-type Bi2Te3-based materials. Also, Au addition shows no negative effect on the mechanical properties as well as high-temperature stability of Bi2Te3-xSex. These results indicate that Au addition is a promising method to improve the thermoelectric properties of n-type Bi2Te3-xSex used for assembling a practical thermoelectric module operating at near room temperature.

DOI： 10.1021/acsaem.1c02560

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Hf0.5Zr0.5O2, (HZO) films are anticipated as a noval insulating material for ferroelectric field-effect transistors. These materials are fabricated by crystallization of amorphous HZO, and therefore knowledge of crystallization processes is required. We examined thermally-induced crystallization processes of amorphous HZO prepared by sputtering using x-ray diffraction and transmission electron microscopy. It was found that a metastable orthorhombic phase is formed in 10 nm thick HZO films after thermal annealing at 500°C.

DOI： 10.1109/SNW51795.2021.00018

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担当区分：筆頭著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）

DOI： 10.2320/materia.59.662

記述言語：英語   掲載種別：研究論文（学術雑誌）

Self-organized nanorods in YBa2Cu3O7-δ films are important pinning centers from the technical and fundamental views. While influence of nanoscale factors (>4-5 nm) on the vortex pinning has already been discussed in detail, the interface control of nanorods (at the smaller scale) has not yet been performed. Here, it is demonstrated that the stacking faults can control the nanorod interface to improve the vortex pinning. The stacking faults were formed across the nanorods by post-annealing the YBa2Cu3O7-δ films containing BaMO3 (M = Zr, Sn, Hf) nanorods. The strong bonding between YBa2Cu3O7-δ and BaMO3 varies the atomic position of YBa2Cu3O7-δ, degrading an interface sharpness and an elementary pinning force of the nanorod. Scanning transmission electron microscopy and density functional theory calculation clarified that the stacking faults broke the strong bonding between YBa2Cu3O7-δ and BaMO3 at the nanorod interface, and reduced the local strain around the nanorods, improving the elementary pinning force. As a result, the critical current density was improved in low temperature and low magnetic field when magnetic field was aligned with the c-axis. Thus, the combined effect of nanoinclusions and crystalline defects, in the present case, nanorods and stacking faults, can control the interface of nanoinclusion pinning centers, opening the interface design to realize the ideal pinning situation.

DOI： 10.1088/1361-6668/abaebf

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The irradiation stability of a material in the temperature range from 300°C to 500°C represents an important step for a variety of nuclear applications. Here we used dual-beam irradiation to investigate the response of an amorphous silicon oxycarbide (SiOC) to extreme environments (temperature and irradiation). The amorphous SiOC was prepared in thin film form by sputtering and then fabricated into cross-sectional transmission electron microscopy (TEM) specimens, and finally irradiated with helium (He) and krypton (Kr) ions inside a TEM. In-situ TEM observations revealed that He bubble and void formation are highly suppressed after irradiation up to 95 dpa with simultaneous He implantation up to 231 at.%. Atomic pair-distribution functions suggested that the amorphous structures are almost the same before and after irradiation, and no crystallization, nor phase separation was detected. This study demonstrates the stability of amorphous SiOC under dual-beam irradiation at nuclear reactor operation temperatures, suggesting that this material is applicable as a structural material for advanced nuclear reactors.

DOI： 10.1007/s11837-020-04332-z

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Nanoscale pinning centers are introduced into YBa2Cu3O7 (YBCO) films and tapes to improve vortex pinning and critical current density (J c) for coated conductor application. While pinning with a single type of pinning center has been mainly investigated, hybrid pinning with multiple types of pinning center is expected to be more promising for simultaneously achieving high J c values and suppressing J c anisotropy. In the present study, a three-phase-nanocomposite film consisting of an YBCO matrix, BaHfO3 nanorods and Y-O nanoparticles was fabricated. A global pinning force maximum (F p,max, where F p = J c B) of 1.57 TN m-3 at 4.2 K, which is as high as the record level of F p,max, was achieved by the hybrid pinning of BaHfO3 nanorods and Y-O nanoparticles. Furthermore, the hybrid pinning improved the angular dependence of J c. The pinning contribution from nanoparticles increased with lowering temperature, which can explain the high J c at low temperature. Thus, the present study successfully demonstrates a highly effective structure that can simultaneously achieve suppressed J c anisotropy and a record level of J c.

DOI： 10.1088/1361-6668/aba544

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記述言語：英語   掲載種別：研究論文（学術雑誌）

The crystallization behavior of sputter-deposited films of amorphous Si (a-Si) and SiGe alloys (a-SiGe) induced by electron irradiation at room temperature and by thermal annealing was investigated by in situ transmission electron microscopy. On electron irradiation at room temperature, extremely rapid crystallization, so-called explosive crystallization, occurred at a higher electron flux but not at a lower electron flux. On in situ thermal annealing, explosive crystallization occurred preferentially and partially at low temperatures in Ge-rich a-SixGe100-x for x < 50 but not for x > 50. These results indicate that the increase of Si content in a-SiGe prevents the occurrence of explosive crystallization. We previously proposed that explosive crystallization can occur in pristine a-Ge films via the interface of a liquid-like, high-density amorphous state at the growth front. An increase in the instability of this high-density amorphous state caused by the increase of Si in a-SiGe apparently gives rise to the suppression of explosive crystallization.

DOI： 10.1063/5.0010202

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記述言語：英語   掲載種別：研究論文（学術雑誌）

We examined by transmission electron microscopy the structure and crystallization behavior of hydrogenerated and non-hydrogenerated amorphous germanium films (a-Ge:H and a-Ge) prepared by sputtering to figure out the effects of hydrogen on them. In pair-distribution function, first and second peaks at the interatomic distance of 0.26 and 0.40 nm, respectively, were found to be higher and sharper in a-Ge:H than in a-Ge; therefore amorphous structure was organized in a more ordered state within a short range by hydrogeneration. On thermal annealing, fine nanograins (FGs) of about 10 nm in size appeared preferentially at 350 °C and above in a-Ge:H, which is in contrast with the formation of coarse particles of about 100 nm in size at 500 °C in a-Ge. Hydrogeneration would make a certain number of short-range ordered clusters distributed in the amorphous matrix, inducing the preferential formation of FGs at lower temperatures.

DOI： 10.35848/1347-4065/ab9cd9

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Crystallization processes of amorphous germanium–tin (GeSn) under low-energy electron-beam irradiation were examined using transmission electron microscopy (TEM). Freestanding amorphous GeSn thin films were irradiated with a 100 keV electron beam at room temperature. The amorphous GeSn was athermally crystallized by electron-beam irradiation, when the electron flux exceeded the critical value. Heterogeneous structures consisting of nano- and micro-crystallites were formed after crystallization of amorphous GeSn with ∼24 at. % Sn in the as-sputtered amorphous state. In situ TEM observations of structural changes under electron-beam irradiation revealed that random nucleation and growth of nanocrystallites occur at the early stage of crystallization, followed by rapid formation of micro-grains surrounding the nanocrystals. It has been suggested that the growth of micro-grains progresses via supercooled liquid Sn at the amorphous/crystalline interface. The resultant GeSn grains with a size of a few micrometers contained ∼15 at. % Sn, much larger than the solubility limit of Sn in Ge (∼1 at. % Sn).

DOI： 10.1063/5.0006416

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Improvement of critical current density (Jc) in magnetic fields is required in YBa2Cu3O7 films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa2Cu3O7+BaHfO3 films to control the nanorod structure, and its influence on Jc was analyzed. The YBa2Cu3O7+BaHfO3 film deposited at 850°C exhibited pinning force maximum (Fp,max.) as high as 413GN/m3 at 40 K, while the Fp,max. for the deposition temperature of 850°C at 77K was smaller than that in the YBa2Cu3O7+BaHfO3 film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the Fp,max. in high temperatures, since the critical temperature and matching field dependences of Jc value dominate the Fp,max. On the other hand, low deposition temperature improves the Fp,max. in low temperatures since the Fp shift in accordance with matching field is dominant to the Fp,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa2Cu3O7 films containing nanorods considering the Jc variation with critical temperature and matching field.

DOI： 10.2320/matertrans.MT-M2019303

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 Author(s). Thin-film transistors (TFTs) on insulator substrates are widely used in applications from liquid crystal displays to sensor devices. However, insulator substrates with low heat conductivity lead to unfavorable self-heating effects in the channel regions. Herein, the carrier and heat transport properties of polycrystalline GeSn films on SiO2/Si substrates were improved by suppressing Sn segregation in the films to fabricate GeSn channel TFTs. Alloying with 5.5% Sn enabled the formation of larger grains than those in poly-Ge films after low-temperature annealing (below 520 °C) without Sn segregation. In addition, the films had a hole mobility of 40 cm2 V-1 s-1 at a hole density of 1.1 × 1018 cm-3 and a thermal conductivity of 12.1 Wm-1 K-1 at room temperature. The temperature dependences of the carrier and heat transport properties of the poly-GeSn films were investigated to accurately simulate a device with a poly-GeSn channel TFT. This was achieved by using the carrier transport measurements and numerical simulations of the heat transport in the Debye model. The simulated device allowed an accurate assessment of the self-heating effects of the TFT and thus provides a design guide for TFTs.

DOI： 10.1063/1.5085470

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 American Chemical Society. Single-crystal SnSe exhibits extremely high thermoelectric properties, and fabrication of SnSe films is promising for practical application and basic research on properties. However, the high thermoelectric properties have not yet been reported in SnSe films and their thermoelectric properties and nanostructure have not yet been analyzed in detail. In the present study, a-axis-oriented epitaxial SnSe films were prepared to discuss the thermoelectric properties of the SnSe films. While the electrical conductivity of the films was orders of magnitude smaller than that in the single crystals at room temperature, surprisingly, the thermoelectric property (power factor) of the films was slightly higher than that in the single crystals at high temperatures (∼300 °C). The SnSe films contained orthorhombic domain boundaries with a spacing of several hundred nanometers. The orthorhombic domain boundaries caused carrier scattering and degraded the mobility of the films at room temperature, but their effect decreased with increasing temperature. Thus, the carrier scattering at domain boundaries results in characteristic temperature dependence of thermoelectric properties in the SnSe films. High thermoelectric properties at high temperatures were successfully achieved in the SnSe films in spite of the existence of domain boundaries, demonstrating the possibility of high-performance of SnSe thermoelectric films.

DOI： 10.1021/acsami.9b04868

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 IOP Publishing Ltd. Composite multilayer films (CMLs) comprising YBa2Cu3O7 + BaHfO3 (4.7 vol%)/YBa2Cu3O7 + BaHfO3 (3.1 vol%) were fabricated, and vortex behavior in the CMLs was evaluated to discuss inhomogeneous depinning of vortices. Magnetic field and angular dependences of critical current density (J c) in the CMLs were similar to those in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) single layer film (SL). Variation of the CML structure shifted the matching field effect in global pinning force and irreversibility temperature. The J c in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) SL was smaller than that in the YBa2Cu3O7 + BaHfO3 (3.1 vol%) SL, suggesting that vortices preferentially moved along the low-J c layers in the CMLs. The high-J c layers pinned the vortices in the low-J c layers, resulting in a shift of the matching field effect. These observations are characteristic of inhomogeneous depinning of vortices in the CMLs. The inhomogeneous depinning as well as pinned configuration should be considered for understanding J c and for structural design of pinning centers in YBa2Cu3O7 films.

DOI： 10.1088/1361-6668/ab1d2c

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 Author(s). The solubility limit of tin (Sn) in germanium (Ge) is very small, and, therefore, it is difficult to synthesize high Sn concentration GeSn crystals by conventional methods. An amorphous phase can contain elements beyond the solubility limit of the crystal state, and, therefore, recrystallization of the amorphous alloy is one of the possible ways to realize materials far from the equilibrium state. To suppress Sn precipitation during thermal annealing, knowledge of crystallization processes is required. In the present study, amorphous GeSn thin films with different Sn concentrations were prepared by sputtering, and their crystallization processes were examined by in situ transmission electron microscopy. It was found that the crystallization temperature decreases with increasing Sn concentration, and it became lower than the eutectic temperature when the Sn concentration exceeded ∼25 at. %. Radial distribution function analyses revealed that phase decomposition occurs in the amorphous state of the specimens which crystallize below the eutectic temperature, and Sn crystallites were simultaneously precipitated with crystallization. On the other hand, no remarkable phase decomposition was detected in amorphous GeSn with <25 at. % Sn. Sn precipitation occurred at a higher temperature than the crystallization in these specimens, and the difference between the crystallization and Sn precipitation temperatures became large with decreasing Sn concentration. Because of the existence of this temperature difference, a temperature window for suppressing Sn segregation existed. We demonstrated that large GeSn grains with high Sn concentration could be realized by annealing the specimens within the temperature window.

DOI： 10.1063/1.5086480

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 Elsevier B.V. Relationships between amorphous structures and radiation tolerance of silicon oxycarbide (SiOC) glasses with different composition, SiO 2 :SiC = 2:1 (SiO 2 -rich), 1:1 (equiatomic), and 1:2 (SiC-rich), were examined by transmission electron microscopy and atomic pair-distribution function (PDF). These specimens were irradiated with 120 keV helium (He) ions at room temperature. The PDF results indicated that the structure of SiOC alloys are almost the same in irradiation and implantation regions. It was found that SiO 2 -rich specimens show a greater radiation resistance than SiC-rich ones: the formation of He bubbles was highly suppressed in the SiO 2 -rich and equiatomic compositions after even 90 at.% He implantation, whereas pronounced swelling occurred in the SiC-rich composition. The first sharp diffraction peak revealed that the size of network voids formed by connecting the SiO x C 4-x tetrahedra in SiO 2 -rich and equiatomic specimens is much larger than the diameter of He atom, suggesting that He atoms can easily migrate in the amorphous SiOC networks.

DOI： 10.1016/j.jnucmat.2019.03.012

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 American Physical Society. Elastic strain and defects are important key words for controlling structure and properties in films. While epitaxial strain and misfit dislocations have been discussed in conventional films, the evolution of strain and defect can be significantly varied by nanocomposite strain and complicated defects in oxides. In the present study, long stacking faults with a spacing of 5-30 nm and a length of >500nm were self-organized by ex situ annealing highly strained nanocomposite films of YBa2Cu3O7-δ(YBCO)+BaMO3(M=Hf,Sn). It is surprising that the nonlocal nature of stacking faults, namely, the structural correlation over >500nm, was observed in spite of the local configuration of the nanocomposite interface. This kind of structural variation was not observed in the pure YBCO film without nanorods, even when the same annealing was performed. A strain energy analysis showed that the stacking fault formation led to the strain energy minimum by reducing the nanocomposite strain. The layered structure of YBCO stacking faults and the large nanocomposite strain realized the present nonlocal self-organization, which is not observed in the conventional systems with epitaxial strain and misfit dislocations.

DOI： 10.1103/PhysRevMaterials.3.013403

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 The Japan Society of Applied Physics. Molecular-dynamics simulations of the pressure-induced structural changes of amorphous Si have been performed using the Tersoff interatomic potential to examine the validity of this potential. Amorphous Si with a tetrahedral network was prepared by melt-quenching methods, and it was then compressed under isothermal-isobaric conditions. The changes of the atomic pair-distribution functions and static structure factors with increasing pressure were in agreement with those observed experimentally. The pressure-induced amorphous structures contained a short-range order similar to the β-tin and Imma structures. These results suggest that the Tersoff potential is suitable for describing the structural changes of amorphous Si under high pressure.

DOI： 10.7567/1347-4065/ab42f3

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 The Japan Institute of Metals and Materials. Improvement of critical current density (Jc) in magnetic fields is required in YBa2Cu3O7 films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa2Cu3O7+BaHfO3 films to control the nanorod structure, and its influence on Jc was analyzed. The YBa2Cu3O7+BaHfO3 film deposited at 850°C exhibited pinning force maximum(Fp,max) as high as 413 GN/m3 at 40 K, while the Fp,max for the deposition temperature of 850°C at 77 K was smaller than that in the YBa2Cu3O7+BaHfO3 film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the Fp,max in high temperatures, since the critical temperature and matching field dependences of Jc value dominate the Fp,max. On the other hand, low deposition temperature improves the Fp,max in low temperatures since the Fp shift in accordance with matching field is dominant to the Fp,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa2Cu3O7 films containing nanorods considering the Jc variation with critical temperature and matching field.

DOI： 10.2320/jinstmet.JA201902

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

<p>Amorphous Fe-B thin films of the concentration range between 12 and 25 at.% B were prepared by radio frequency sputtering techniques, and their local structures were examined by transmission electron microscopy. Pair-distribution-function analyses of Fe-12, -18 and -25 at.%B for a region of 300 nm in diameter revealed a systematic trend according to the concentration; with the increase in B concentration, the intensity of the weak shoulder peak at 0.205 nm for the Fe-B pair increases whereas those of main peaks for Fe-Fe pair decrease. In electron diffraction patterns of the samples taken by a probe size of 2 nm, the specific spots of iron-borides, such as Fe₃B and Fe₂₃B₆, were detected, suggesting the atomic arrangement of the compounds in the amorphous matrices.</p>

DOI： 10.2355/tetsutohagane.TETSU-2019-032

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担当区分：筆頭著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）

<p>材料が照射場に曝されると欠陥が導入され，欠陥蓄積に伴い構造変化が引き起こされる．照射環境下における材料の損傷過程は，「はじき出し効果」と「電子励起効果」によるものに大別される．電子線照射においては，加速電圧が高いときには前者が，低いときには後者が顕著になる．これらの効果は構造解析に対して負の影響を与えるため，電子顕微鏡観察に際しては極力避けるべきものである．一方，照射効果を利用することにより，通常の手法では実現することが難しい平衡状態から離れた材料の創製が可能である．本稿では，低エネルギー電子線照射によるアモルファスの結晶化を利用して，次世代フレキシブルディスプレイとしての応用が期待されている多結晶GeSn薄膜を，非熱的過程により作製した例を紹介する．</p>

DOI： 10.11410/kenbikyo.54.3_126

CiNii Article

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担当区分：筆頭著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）

DOI： 10.11410/kenbikyo.54.3_109

CiNii Article

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2018 American Chemical Society. Ternary compounds with a tetragonal chalcopyrite structure, such as CuGaTe2, are promising thermoelectric (TE) materials. It has been demonstrated in various chalcopyrite systems, including compounds with quaternary chalcopyrite-like structures, that the lattice parameter ratio, c/a, being exactly 2.00 to have a pseudo-cubic structure is key to increase the degeneracy at the valence band edge and ultimately achieve high TE performance. Considering the fact that ZnSnSb2 with a chalcopyrite structure is reported to have c/a close to 2.00, it is expected to have multiple valence bands leading to a high p-type zT. However, there are no complete investigations on the high temperature TE properties of ZnSnSb2 mainly because of the difficulty of obtaining a single-phase ZnSnSb2. In the present study, pure ZnSnSb2 samples with no impurities are synthesized successfully using a Sn flux-based method and TE properties are characterized up to 585 K. Transport properties and thermal analysis indicate that the structure of ZnSnSb2 remains chalcopyrite with no order-disorder transition and clearly show that ZnSnSb2 can be made to exhibit a high zT in the low-to-mid temperature range through further optimization.

DOI： 10.1021/acsami.8b16717

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2018 International Union of Crystallography. Pristine thin films of amorphous Ge prepared by sputtering are unstable and form coarse crystalline particles of 100 nm in size upon crystallization by electron irradiation. These crystalline particles exhibit unusual diffraction patterns that cannot be understood from the diamond cubic structure. The structure has previously been assumed to be a metastable hexagonal form. In the present work, the structure of the coarse crystalline particles has been analysed in detail by transmission electron microscopy, considering the possibility that those diffraction patterns might occur with the diamond cubic structure if the particle consists of thin twin layers. By high-resolution lattice imaging the particles have been shown to be of the diamond cubic structure containing a high density of twins and stacking faults parallel to {111}. With such defects, diffraction patterns can be complex because of the following effects: superposition of two or more diffraction patterns of the same structure but of different orientations, double diffraction through twin crystals, and streaks parallel to the thin crystal which give rise to extra diffraction spots. It is found that diffraction patterns taken from various orientations can be explained in terms of these effects.

DOI： 10.1107/S1600576718012153

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2018 The Japan Society of Applied Physics. Solid phase epitaxial (SPE) recrystallization of amorphous Si on a Si(001) substrate was examined by large-scale (6144-129024 Si atoms), longtime (up to 2000 ns) molecular-dynamics (MD) simulations using the empirical Tersoff interatomic potential. We particularly focused on the effects of the MD cell size, simulation time, and ensemble on the SPE growth rate. We found that the simulations under the isothermal-isochoric conditions (NVT ensemble) show a higher crystallization rate than those under the isothermal-isobaric conditions (NPT ensemble). The system size dealt with in the present MD simulation, i.e., >6144 Si atoms, was enough to estimate the SPE growth rate. The Arrhenius plot of the growth rate between 1300 and 1600 K exhibited a single activation energy, >2.4 eV, which is in agreement with the experimental value (>2.7 eV). However, the growth rate at temperatures below 1300 K deviated from the extrapolated ones from 1300 to 1600 K, which is because recrystallization does not reach a steady state: long-time MD simulations are required to estimate the growth rate at low temperature. The structure analysis of amorphous/ crystalline interfaces suggested that the braking of atomic bonds parallel to the interface becomes a rate-limiting step of the SPE growth.

DOI： 10.7567/JJAP.57.095503

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2018 IOP Publishing Ltd. Critical current density (Jc) was investigated in YBa2Cu3O7-δfilms containing nanorods prepared with various nanorod materials, with variation of nanorod content, substrate temperature, and oxidization condition. Three types of compositional situation were realized: films containing strain induced oxygen vacancies; fully oxidized films containing cation compositional deviation; and oxygen deficient films. Normalized Jc-B behavior was determined via the matching field, which is a geometric factor, regardless of the compositional details. A Jc-critical temperature (Tc) relation depending on distribution and fraction of compositional deviation (cation compositional deviation and strain induced oxygen vacancies) was found: the Jcvalues decreased with decreasing Tcdue to the effect of Tcon nanorod pinning strength in the fully oxidized films; Jcdecreased with decreasing oxygen pressure in the film cooling process after film deposition in spite of Tcremaining almost the same, due to reduction of the effective area for current flow in the oxygen deficient films. Thus, a Jclandscape based on geometric and compositional factors was obtained. The study highlights the importance of the Jc-Tcanalysis in the understanding of Jcin YBa2Cu3O7-δfilms containing nanorods.

DOI： 10.1088/1361-6668/aabe68

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担当区分：筆頭著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）

DOI： 10.2320/materia.57.631

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 American Chemical Society. The development of an unconventional synthesis method has a large potential to drastically advance materials science. In this research, a new synthesis method based on a solid-state electrochemical reaction was demonstrated, which can be made available for intercalation and ion substitution. It was referred to as proton-driven ion introduction (PDII). The protons generated by the electrolytic dissociation of hydrogen drive other monovalent cations along a high electric field in the solid state. Utilizing this mechanism, Li + , Na + , K + , Cu + , and Ag + were intercalated into a layered TaS 2 single crystal while maintaining high crystallinity. This liquid-free process of ion introduction allows the application of high voltage around several kilovolts to the sample. Such a high electric field strongly accelerates ion substitution. Actually, compared to conventional solid-state reaction, PDII introduced 15 times the amount of K into Na super ionic conductor (NASICON)-structured Na 3-x K x V 2 (PO 4 ) 3 . The obtained materials exhibited a thermodynamically metastable phase, which has not been reported so far. This concept and idea for ion introduction is expected to form new functional compounds and/or phases.

DOI： 10.1021/jacs.7b09328

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© The Author 2017. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. Formation of metastable phases in Zr-ion-irradiated corundum alumina (Al 2 O 3 ) upon thermal annealing was examined using transmission electron microscopy. A metastable cubic spinel phase was formed in the topmost layer of the as-irradiated microstructure. During thermal annealing at temperatures ranging from 1073 to 1273 K, this spinel layer grew in extent via an unusual corundum-to-spinel phase transformation. A normal spinel-to-corundum phase transformation was observed at post-irradiation annealing temperatures greater than 1473 K. In addition, ZrO 2 nanocrystals embedded in α-Al 2 O 3 were observed to form at these higher temperatures. High-resolution transmission electron microscopy observations and electron diffraction experiments revealed that the structure of the ZrO 2 precipitates observed in this study are consistent with a highpressure metastable orthorhombic phase of ZrO 2 known as the Ortho-I phase.

DOI： 10.1093/jmicro/dfx028

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 The Author(s). Despite recent interest in amorphous ceramics for a variety of nuclear applications, many details of their structure before and after irradiation/implantation remain unknown. Here we investigated the short-range order of amorphous silicon oxycarbide (SiOC) alloys by using the atomic pair-distribution function (PDF) obtained from electron diffraction. The PDF results show that the structure of SiOC alloys are nearly unchanged after both irradiation up to 30 dpa and He implantation up to 113 at%. TEM characterization shows no sign of crystallization, He bubble or void formation, or segregation in all irradiated samples. Irradiation results in a decreased number of Si-O bonds and an increased number of Si-C and C-O bonds. This study sheds light on the design of radiation-tolerant materials that do not experience helium swelling for advanced nuclear reactor applications.

DOI： 10.1038/s41598-017-04247-x

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 The Japan Society of Applied Physics. The low-temperature synthesis of high-Sn-concentration GeSn is challenging in realizing flexible thin-film transistors and solar cells. Because of athermal processes, irradiation with energetic particles is anticipated to significantly reduce the processing temperature for device fabrication. Here, we demonstrated that polycrystalline Ge with 30 at.% Sn can be realized at room temperature by the electron-beam-induced recrystallization of amorphous GeSn. We found that inelastic electronic stopping, the so-called electron excitation effect, plays an important role in the recrystallization of amorphous GeSn.

DOI： 10.7567/JJAP.56.100307

Kyutacar

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CiNii Article

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Crystallization of amorphous germanium films induced by electron irradiation was investigated by in-situ transmission electron microscopy under a low electron-eneigy of 125 keV with various pre-Aging treatments at room temperature. Different microstructures were observed depending on the aging time: coarse and spherical nanoparticles grew rapidly in samples aged for less than 3 months, while a homogeneous nanociystalline structure with a grain size of about 10 nm appealed in samples aged for over 7 months. Analyses by the pair distribution lunction revealed that the initial structure is inhomogeneous, consisting of a mixture of amorphous regions and some ordered arrangements, but turned spontaneously to homogeneous random amorphous structures during aging. Such inhomogeneity could be an origin of the rapid growth of nanoparticles in the samples not subjected to the long-Time aging.

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 IOP Publishing Ltd. High critical current density (J c ) was achieved in low temperatures of 40 and 20 K in YBa 2 Cu 3 O 7-δ films containing elongated BaHfO 3 nanorods and stacking faults, which were prepared using pulsed laser deposition and post-oxygen-annealing. The YBa 2 Cu 3 O 7-δ + BaHfO 3 film exhibited global pinning force maximum (F p,max ) of 312 GNm -3 at 40 K and 619 GNm -3 at 20 K due to strong pinning by nanorods. These Fp,max values are comparable to those in the previously-reported high-J c films with almost the same matching field. Thus, the present study demonstrated that YBa 2 Cu 3 O 7-δ superconducting matrix realized high J c in low temperatures like other REBa 2 Cu 3 O 7-δ (RE = Gd, Sm, (Gd, Y)). Furthermore, high J c was obtained also for magnetic field parallel to the ab-plane, indicating hybrid pinning of nanorods and stacking faults. Thus, the stacking faults significantly affected the J c properties in the YBa 2 Cu 3 O 7-δ films containing nanorods.The present film structure with strong c-axis correlated pinning and hybrid pinning is effective in simultaneous control of J c values and J c anisotropy in YBa 2 Cu 3 O 7-δ films.

DOI： 10.1088/1361-6668/aa70d3

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 Author(s).The pin size effect and mixed pinning of nanorods and matrix defects are discussed for YBa2Cu3O7-δ films containing nanorods. BaSnO3 nanorods with a diameter of 11 nm and BaHfO3 nanorods with a diameter of 7 nm were prepared, and critical current density (Jc) and resistivity were measured in the films. When the coherence length was larger than the nanorod size at high temperatures near the critical temperature, the trapping angle and activation energy of the vortex flow depended on the nanorod diameter. At a moderate temperature of 65−77 K, the pin size effect on Jc disappeared since the coherence length became smaller than the nanorod size. At a low temperature of 20 K, the contribution from matrix pinning became comparable to that of nanorods in a high magnetic field due to the small coherence length. Thus, the temperature-dependent coherence length caused the pin potential situation to vary significantly, namely, the pin size effect and mixed pinning, which strongly affected vortex pinning in YBa2Cu3O7-δ containing nanorods.

DOI： 10.1063/1.4975300

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 The Japan Institute of Metals and Materials.The structural relaxation of amorphous germanium was examined by molecular dynamics simulations based on the empirical Tersoff interatomic potential. Although the Tersoff potential overestimated both the melting and glass transition temperatures, it was able to reproduce the structural relaxation behavior. The potential energy decreases with thermal annealing below the glass transition temperature, but occasionally increases during structural relaxation. The mean square displacement of atoms also increases in these periods. These changes were attributed to cooperative atomic motion during the structural relaxation. Atomic trajectories revealed that structural changes are induced by spatially- and temporally-inhomogeneous atomic motions: atomically mobile and immobile regions coexist during structural relaxation.

DOI： 10.2320/matertrans.M2017036

Scopus

CiNii Article

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85019624457&origin=inward

記述言語：日本語   掲載種別：研究論文（学術雑誌）

© 2016 The Japan Institute of Metals and Materials.Structural relaxation of amorphous germanium has been examined by molecular dynamics simulations based on the empirical Tersoff interatomic potential. Although the Tersoff potential overestimated both the melting and glass transition temperatures, it was found that this potential can reproduce the behavior of structural relaxation. The potential energy decreased with thermal annealing below the glass transition temperature, but it sometimes increased during structural relaxation. The mean square displacement of atoms also increased at the corresponding period. These changes were attributed to the cooperative atomic motion during structure relaxation. Atomic trajectories revealed that structural changes are induced by spatially- and temporally-inhomogeneous atomic motions: atomic mobile and immobile regions coexisted during structural relaxation.

DOI： 10.2320/jinstmet.J2016051

Scopus

CiNii Article

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85013986475&origin=inward

担当区分：筆頭著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）

<p>照射場を利用した材料創製では，通常の手法では得ることが難しい平衡状態から離れた準安定構造を実現することが出来る．また，機能性材料および構造用材料の照射誘起構造変化に関する研究は，宇宙空間や原子炉等の極限環境下で使用される材料の信頼性を知る上で重要である．本稿では，照射場と材料の相互作用による構造変化およびそれを利用した材料創製に関する最近の研究成果について報告する．準安定構造の形成に関しては，イオン照射アルミナの熱処理過程において見出された，通常の熱処理では起こらないコランダム→スピネル型構造相変態について報告する．一方，耐照射性材料の開発に関する一連の研究では，ナノ構造制御により炭化ケイ素の耐照射性を向上させた例について紹介する．</p>

DOI： 10.11410/kenbikyo.52.1_24

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007689241

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4973121

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4972282

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DOI： 10.1063/1.4964332

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1021/jacs.6b04976

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.jnucmat.2016.06.031

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.2320/matertrans.E-M2016805

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CiNii Article

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4953234

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DOI： 10.1063/1.4942463

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DOI： 10.1063/1.4937386

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DOI： 10.1016/j.nimb.2015.06.005

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DOI： 10.1016/j.jnucmat.2015.06.036

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DOI： 10.1039/c4nr04470c

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DOI： 10.1063/1.4898672

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DOI： 10.1063/1.4889800

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DOI： 10.1016/j.nimb.2013.10.095

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DOI： 10.1557/jmr.2014.44

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DOI： 10.1016/j.nimb.2013.12.012

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DOI： 10.1002/pssb.201349226

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DOI： 10.1016/j.actamat.2013.09.029

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DOI： 10.7567/JJAP.52.110120

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DOI： 10.1063/1.4822300

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/10031194761

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.jcrysgro.2012.12.106

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DOI： 10.1063/1.4813593

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DOI： 10.1063/1.4790705

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DOI： 10.1063/1.4767992

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.intermet.2012.03.025

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DOI： 10.1016/j.intermet.2012.03.041

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DOI： 10.1063/1.4765362

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DOI： 10.1063/1.4751245

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DOI： 10.1063/1.4748340

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1039/c2cp42342a

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.2320/matertrans.E-M2012810

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1143/JJAP.51.065202

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.jmmm.2011.12.009

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DOI： 10.1002/pssr.201206058

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DOI： 10.1016/j.nimb.2011.12.054

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DOI： 10.1016/j.nimb.2011.01.120

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DOI： 10.1016/j.scriptamat.2011.10.033

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DOI： 10.1080/09500839.2011.630686

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DOI： 10.1063/1.3639290

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DOI： 10.1002/pssc.201001024

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DOI： 10.1016/j.actamat.2011.04.008

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DOI： 10.1063/1.3602314

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DOI： 10.1007/s11664-010-1479-7

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DOI： 10.1063/1.3583662

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DOI： 10.1002/pssc.201000440

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DOI： 10.1063/1.3552987

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DOI： 10.1002/pssc.201000484

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DOI： 10.1016/j.scriptamat.2010.09.043

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DOI： 10.1063/1.3525979

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DOI： 10.1063/1.3430046

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DOI： 10.1063/1.3373419

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1088/0022-3727/43/8/085303

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記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

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記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

開催期間： 2012年09月11日 - 2012年09月13日   発表言語：英語   講演種別：特別講演   開催地：Sieniawa, Poland  

開催期間： 2012年06月24日 - 2012年06月29日   発表言語：英語   講演種別：特別講演   開催地：Santa Fe, New Mexico, USA  

開催期間： 2011年08月19日 - 2011年08月22日   発表言語：英語   講演種別：特別講演   開催地：Jinan, Shandong, China  

開催期間： 2011年05月09日 - 2011年05月13日   発表言語：英語   講演種別：特別講演   開催地：Nice, France  

開催期間： 2010年11月29日 - 2010年12月03日   発表言語：英語   講演種別：特別講演   開催地：Boston, Massachusetts, USA  

開催期間： 2010年09月05日 - 2010年09月08日   発表言語：英語   講演種別：特別講演   開催地：Uji, Kyoto  

開催期間： 2010年08月08日 - 2010年08月13日   発表言語：英語   講演種別：特別講演   開催地：, Fort Worth, Texas, USA  

開催期間： 2008年08月31日 - 2008年09月05日   発表言語：英語   講演種別：特別講演   開催地：Dresden, Germany  

開催期間： 2008年02月27日 - 2008年02月28日   発表言語：英語   講演種別：特別講演   開催地：Daejeon, Korea  

開催期間： 2007年09月30日 - 2007年10月05日   発表言語：英語   講演種別：特別講演   開催地：Mumbai, India  

開催期間： 2006年12月15日 - 2006年12月16日   発表言語：英語   講演種別：基調講演   開催地：Mumbai, India  

開催期間： 2006年08月20日 - 2006年08月25日   発表言語：英語   講演種別：特別講演   開催地：Fort Worth, Texas, USA  

受賞国：日本国

受賞国：日本国

受賞国：日本国

受賞国：日本国

受賞国：日本国