研究者詳細 - 石丸　学

論文 - 石丸　学

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Fabrication of YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf> Superconducting Nanocomposite Film on Silicon Substrate 査読有り

Bertrand A., Voulhoux M., Kuroki M., Ishimaru M., Horide T.

ACS Applied Electronic Materials 6 ( 6 ) 4601 - 4607 2024年06月

記述言語：英語掲載種別：研究論文（学術雑誌）

Fabrication of YBa2Cu3O7 nanocomposite films on silicon substrates is required for superconducting electromagnetic devices. Low-temperature deposition is effective in suppressing the chemical reaction between YBa2Cu3O7 and Si, while sufficient diffusion is required to form the well-defined nanocomposite structure. The fabrication of the YBa2Cu3O7 nanocomposite films on Si substrates should simultaneously satisfy these conflicting requirements. A YSZ (yttrium stabilized zirconia) buffer layer was epitaxially grown on Si substrates to suppress the chemical reaction. Then, the YBa2Cu3O7 + Ba2YbNbO6 films were fabricated on the YSZ/Si. The nanorods with diameters of 9-17 nm were elongated along the c-axis even at the low deposition temperature. The YBa2Cu3O7 + Ba2YbNbO6 nanocomposite film exhibited a critical temperature of 86.0 K, which is comparable to the critical temperature of 85.6 K in the pure film. The irreversibility temperature was slightly improved by the nanorods. Thus, we demonstrate the formation of nanorods in the YBa2Cu3O7 films on Si substrates without lowering the critical temperature. This opens the superconducting electromagnetic devices integrated with high-temperature superconductors and semiconductors.

DOI： 10.1021/acsaelm.4c00612

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Stability of ion-beam-induced bixbyite phase in δ-Sc<inf>4</inf>Hf<inf>3</inf>O<inf>12</inf> under heat treatments and electron beam irradiations 査読有り

Iwasaki M., Patel M.K., Baldinozzi G., Sickafus K.E., Ishimaru M.

Journal of the European Ceramic Society 44 ( 5 ) 3131 - 3138 2024年05月

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）

Oxygen-deficient compounds A4B3O12 have a δ-type structure with a regular long-range arrangement of oxygen vacancies induced by compensation of the charge difference between A3+ and B4+ cations, while A and B cations do not order long-range and only display weak short-range correlations. The δ-type compounds in the Sc2O3-HfO2 and Sc2O3-ZrO2 systems exhibit excellent resistance to radiation-induced amorphization, but the long-range ordered δ-phase was transformed into a short-range ordered bixbyite phase. Since this structural change was not predicted from the phase diagram, the validity of the formation of the bixbyite phase and its stability are still unclear. In the present study, the changes of radiation-induced microstructures in δ-Sc4Hf3O12 under heat treatments and electron beam irradiations were examined by ex-situ and in-situ transmission electron microscopy. It was found that the ion-beam-induced metastable bixbyite phase is transformed into the δ and fluorite phases by the rearrangement of the oxygen vacancies.

DOI： 10.1016/j.jeurceramsoc.2023.12.063

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Metastable Substitution of an Isovalent Anion Element in SnSe Films to Control the Thermoelectric Property 査読有り

Yamaguchi K., Ishimaru M., Horide T.

ACS Applied Electronic Materials 6 ( 2 ) 1071 - 1077 2024年02月

記述言語：英語掲載種別：研究論文（学術雑誌）

To improve the thermoelectric properties of SnSe films, carrier control is required, but elemental doping is difficult due to the thermodynamic solubility limit. Isovalent elements may generate holes or electrons not in a direct manner but in the manner to form point defects. In this study, the Sn(Se,Te) films were fabricated by a pulsed laser deposition (PLD) method to control the carrier concentration by substituting isovalent Te for Se. The coexistence of the orthorhombic and cubic phases at the tens of nanometer scale in the SnSe0.5Te0.5 film was clarified by the structural observation, which is consistent with the equilibrium phase diagram. In spite of the phase coexistence, the lattice parameters linearly increased with an increase in the Te content in the Sn(Se,Te) films. This demonstrates the metastable composition situation for each phase, namely, the carrier control beyond the thermodynamic limit due to the nonequilibrium growth in PLD. As a result, the Seebeck coefficient decreased, and the electrical conductivity increased to increase the power factor, especially in a low temperature near room temperature. The Te substitution in the nonequilibrium PLD increases the hole concentration beyond the thermodynamic solubility limit and thus is effective in controlling the carrier in the SnSe films where carrier doping is difficult.

DOI： 10.1021/acsaelm.3c01490

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Carrier Control of Bi-Doped SnSe Films for Fabrication of π-Type Thermoelectric Film Modules 査読有り国際誌

Horide T., Nakamura K., Ishimaru M.

ACS Applied Energy Materials 7 ( 1 ) 346 - 352 2024年01月

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）

Thermoelectric energy conversion is promising for high-efficiency power generation. The p- and n-type thermoelectric materials are required to fabricate high-performance thermoelectric modules. SnSe is one of the highest-performance thermoelectric materials, and SnSe films should be fabricated for small-scale applications. While the p-type SnSe films can be easily prepared without precise control of the doping, it is difficult to control the electron concentration in the n-type SnSe films. In this study, the Bi-doped SnSe films were fabricated at low deposition temperatures by using the self-buffer layer, namely, the SnSe-based buffer layers. The low-temperature deposition on the buffer layer increased the concentration of doped Bi, although the contribution of the buffer layer to the electronic conduction was observed. The π-type thermoelectric module consisting of p-type SnSe and n-type SnSe/buffer layers was fabricated. The output power of 0.09 μW and the open-circuit voltage of 0.11 V were obtained at 155 °C at the cold end and 255 °C at the hot end. The feasibility of fabricating the π-type SnSe film module was demonstrated. By optimizing the buffer layer thickness and increasing the number of legs, we expect the module performance to be further improved.

DOI： 10.1021/acsaem.3c02683

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アモルファス炭化ホウ素の電子線動径分布解析招待有り査読有り

石丸学

表面と真空 ( 公益社団法人日本表面真空学会 ) 66 ( 12 ) 719 - 724 2023年12月

担当区分：筆頭著者,　最終著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）

<p>Short-range and medium-range ordered structures of amorphous materials can be evaluated by radial distribution functions and atomic pair-distribution functions extracted by quantitative analyses of diffraction intensities. Because of the strong interaction of electrons with materials and the short wavelength of high-energy electrons, electron diffraction can produce intensity profiles up to high scattering angles comparable to those of neutron diffraction and synchrotron x-ray diffraction in a short time. Here, we present an example of electron diffraction radial distribution function analysis of amorphous boron carbide by electron diffraction techniques.</p>

DOI： 10.1380/vss.66.719

その他リンク： https://www.jstage.jst.go.jp/article/vss/66/12/66_20181187/_pdf

Modulation of vortex pinning by matrix defects in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>nanocomposite film 査読有り

Horide T., Higashi K., Ishimaru M., Okada T., Awaji S., Matsumoto K.

Superconductor Science and Technology 36 ( 10 ) 2023年10月

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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Nano- to microscale structural and compositional heterogeneity of artificial pinning centers in pulsed-laser-deposited YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7−y</inf> thin films 査読有り

Kuroki M., Horide T., Matsumoto K., Ishimaru M.

Journal of Applied Physics 134 ( 4 ) 2023年07月

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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Explosive crystallization of amorphous germanium-tin films by irradiation with a 3-keV electron beam 査読有り

Nakamura R., Miyamoto M., Ishimaru M.

Journal of Applied Physics 133 ( 18 ) 2023年05月

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

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Planar defects-induced low thermal conductivity in a superhard material SiB<inf>6</inf> 査読有り国際誌

Tanusilp S.a., Kumagai M., Ohishi Y., Ishimaru M., Sadayori N., Kurosaki K.

Journal of Alloys and Compounds 939 2023年04月

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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Microstructure and Phase Transformation in Fe<inf>20</inf>Co<inf>20</inf>Ni<inf>20</inf>Cr<inf>20</inf>B<inf>20</inf><sup>1</sup><inf>x</inf>Si<inf>x</inf> Alloys Prepared by Mechanical Alloying 査読有り

Zhang Y., Ishimaru M., Tokunaga T., Era H.

Materials Transactions ( 公益社団法人日本金属学会 ) 64 ( 11 ) 2568 - 2574 2023年01月

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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Impact of supercooled liquid structures on the crystallization processes of amorphous Ge 査読有り

Nagaoka S., Tahara C., Ishimaru M.

Applied Physics Express 16 ( 1 ) 2023年01月

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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Thermoelectric Property of SnSe Films on Glass Substrate: Influence of Columnar Grain Boundary on Carrier Scattering 査読有り国際誌

Horide T., Murakami Y., Ishimaru M., Matsumoto K.

ACS Applied Electronic Materials 4 ( 12 ) 6364 - 6372 2022年12月

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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Investigation of Nanoscale Phase Formation in Rapidly Solidified Fe20Co20Ni20Cr20B201xSix Alloys 査読有り国際誌

Zhang Yicheng, Inoue Koji, Ishimaru Manabu, Tokunaga Tatsuya, Era Hidenori

MATERIALS TRANSACTIONS ( 公益社団法人日本金属学会 ) advpub ( 0 ) 1211 - 1216 2022年09月

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 Fe<sub>20</sub>Co<sub>20</sub>Ni<sub>20</sub>Cr<sub>20</sub>B<sub>20−</sub><i><sub>x</sub></i>Si<i><sub>x</sub></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 Cr<sub>2</sub>B phases. Furthermore, in addition to the nanoscale FCC and Cr<sub>2</sub>B phases, a nanoscale Cr<sub>3</sub>Ni<sub>5</sub>Si<sub>2</sub> phase was observed when the Si content exceeded 7.5 at.%.</p>

DOI： 10.2320/matertrans.mt-m2022058

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Anomalous structural phase transformation in swift heavy ion-irradiated δ-Sc<inf>4</inf>Hf<inf>3</inf>O<inf>12</inf> 招待有り査読有り国際誌

Iwasaki M., Kanazawa Y., Manago D., Patel M.K., Baldinozzi G., Sickafus K.E., Ishimaru M.

Journal of Applied Physics 132 ( 7 ) 2022年08月

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

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Self-Organized Nanocomposite Structure Controlled by Elemental Site Occupancy to Improve Vortex Pinning in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>Superconducting Films 査読有り国際誌

Horide T., Yoshida Y., Kita R., Gondo M., Ishimaru M., Matsumoto K.

ACS Applied Electronic Materials 4 ( 6 ) 3018 - 3026 2022年06月

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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Impact of annealing on electric and elastic properties of 10-nm Hf<inf>0.5</inf>Zr<inf>0.5</inf>O<inf>2</inf> films prepared on Si by sputtering 査読有り国際誌

Bolotov L., Migita S., Fujio R., Ishimaru M., Hatayama S., Uchida N.

Microelectronic Engineering 258 2022年04月

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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Electron diffraction radial distribution function analysis of amorphous boron carbide synthesized by ion beam irradiation and chemical vapor deposition 査読有り国際誌

Ishimaru M., Nakamura R., Zhang Y., Weber W.J., Peterson G.G., Ianno N.J., Nastasi M.

Journal of the European Ceramic Society 42 ( 2 ) 376 - 382 2022年02月

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

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Aligned Self-Organization Induced by Epitaxial Stress and Shear Deformation in Jahn–Teller Spinel ZnMnGaO<inf>4</inf> 査読有り

Horide T., Morishita K., Horibe Y., Usuki M., Ishimaru M., Matsumoto K.

Journal of Physical Chemistry C 126 ( 1 ) 806 - 814 2022年01月

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

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85122695672&origin=inward

Thermoelectric Property of n-Type Bismuth-Doped SnSe Film: Influence of Characteristic Film Defect 査読有り

Horide T., Nakamura K., Hirayama Y., Morishita K., Ishimaru M., Matsumoto K.

ACS Applied Energy Materials 4 ( 9 ) 9563 - 9571 2021年09月

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

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85114701295&origin=inward

Review of “12th Japanese-Polish joint seminar on micro and nano analysis (August 29-September 1, 2018)” 査読有り

Ishimaru M.

Materials Transactions ( 公益社団法人日本金属学会 ) 62 ( 9 ) 1420 - 1423 2021年09月

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

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85113424475&origin=inward

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