Updated on 2023/09/11

写真a

 
OGURA Yu
 
Organization
Graduate School of Engineering Materials Physics 2 Assistant Professor
Graduate School
Graduate School of Engineering
Undergraduate School
School of Engineering Physical Science and Engineering
Title
Assistant Professor
External link

Degree 1

  1. 博士(工学) ( 2021.3   名古屋大学 ) 

Research Interests 3

  1. 転位

  2. 光学特性

  3. 結晶塑性

 

Papers 20

  1. Shedding new light on the dislocation-mediated plasticity in wurtzite ZnO single crystals by photoindentation

    Li Yan, Fang Xufei, Tochigi Eita, Oshima Yu, Hoshino Sena, Tanaka Takazumi, Oguri Hiroto, Ogata Shigenobu, Ikuhara Yuichi, Matsunaga Katsuyuki, Nakamura Atsutomo

    JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY   Vol. 156   page: 206 - 216   2023.9

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    Publisher:Journal of Materials Science and Technology  

    Dislocation-mediated plasticity in inorganic semiconductors and oxides has attracted increasing research interest because of the promising mechanical and functional properties tuned by dislocations. In this study, we investigated the effects of light illumination on the dislocation-mediated plasticity in hexagonal wurtzite ZnO, a representative third-generation semiconductor material. A (0001) 45o off sample was specially designed to preferentially activate the basal slip on (0001) plane. Three types of nanoindentation tests were performed under four different light conditions (550 nm, 334 nm, 405 nm, and darkness), including low-load (60 μN) pop-in tests, high-load (500 μN) nanoindentation tests, and nanoindentation creep tests. The maximum shear stresses at pop-in were found to approximate the theoretical shear strength regardless of the light conditions. The activation volume at pop-ins was calculated to be larger in light than in darkness. Cross-sectional transmission electron microscope images taken from beneath the indentation imprints showed that all indentation-induced dislocations were located beneath the indentation imprint in a thin-plate shape along one basal slip plane. These indentation-induced dislocations could spread much deeper in darkness than in light, revealing the suppressive effect of light on dislocation behavior. An analytical model was adopted to estimate the elastoplastic stress field beneath the indenter. It was found that dislocation glide ceased at a higher stress level in light, indicating the increase in the Peierls barrier under light illumination. Furthermore, nanoindentation creep tests showed the suppression of both indentation depth and creep rate by light. Nanoindentation creep also yielded a larger activation volume in light than in darkness.

    DOI: 10.1016/j.jmst.2023.02.017

    Web of Science

    Scopus

  2. Grain-boundary thermodynamics with artificial-neural-network potential: Its ability to predict the atomic structures, energetics, and lattice vibrational properties for Al

    Yokoi Tatsuya, Matsuura Maya, Oshima Yu, Matsunaga Katsuyuki

    PHYSICAL REVIEW MATERIALS   Vol. 7 ( 5 )   2023.5

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    Publisher:Physical Review Materials  

    An artificial neural network (ANN) potential for Al, trained with density-functional-theory (DFT) data, is constructed to accurately predict lattice vibrational properties and thermodynamics of grain boundaries (GBs) in Al. The ANN potential is demonstrated to accurately predict not only atomic structures and energetics of the GBs at 0 K but also partial phonon densities of states and vibrational entropies, even for GBs absent in the training data sets. In addition, their total potential energies and atomic forces by DFT at elevated temperatures up to 800 K can also be well reproduced by molecular dynamics with the ANN potential. In contrast, a modified embedded atom method (MEAM) potential shows larger errors in phonon frequencies and atomic forces for atoms at GBs, as well as in the bulk, than the ANN potential. The MEAM potential is thus likely to be inadequate to quantitatively predict thermodynamic properties of GBs, particularly at high temperature. The present ANN potential is also applied to systematically examine thermodynamic stability of asymmetric tilt GBs. It is predicted that for the ς9 system, the GB free-energy profile as a function of inclination angle exhibits a cusp at elevated temperatures, due to its larger vibrational entropies of asymmetric tilt GBs than those of ς9 symmetric tilt GBs.

    DOI: 10.1103/PhysRevMaterials.7.053803

    Web of Science

    Scopus

  3. Atomic and electronic structure of grain boundaries in a-Al<inf>2</inf>O<inf>3</inf>: A combination of machine learning, first-principles calculation and electron microscopy Reviewed International coauthorship

    Yokoi T., Hamajima A., Wei J., Feng B., Oshima Y., Matsunaga K., Shibata N., Ikuhara Y.

    Scripta Materialia   Vol. 229   2023.5

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.scriptamat.2023.115368

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  4. Atomic structures of grain boundaries for Si and Ge: A simulated annealing method with artificial-neural-network interatomic potentials Reviewed

    Yokoi T., Oshima Y., Matsunaga K.

    Journal of Physics and Chemistry of Solids   Vol. 176   2023.5

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jpcs.2023.111273

    Web of Science

    Scopus

  5. Ca-vacancy effect on the stability of substitutional divalent cations in calcium-deficient hydroxyapatite Reviewed

    Saito Tatsushi, Ishikawa Yuto, Noda Yusuke, Yokoi Tatsuya, Oshima Yu, Nakamura Atsutomo, Matsunaga Katsuyuki

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY   Vol. 106 ( 2 ) page: 1587 - 1596   2023.2

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1111/jace.18853

    Web of Science

    Scopus

  6. Atomic structures of grain boundaries for Si and Ge: A simulated annealing method with artificial-neural-network interatomic potentials Reviewed

    Yokoi Tatsuya, Kato Hirotaka, Oshima Yu, Matsunaga Katsuyuki

    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS   Vol. 173   2023.2

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jpcs.2022.111114

    Web of Science

    Scopus

  7. Room-temperature plastic deformation modes of cubic ZnS crystals Reviewed

    Kitou Shunsuke, Oshima Yu, Nakamura Atsutomo, Matsunaga Katsuyuki, Sawa Hiroshi

    ACTA MATERIALIA   Vol. 247   2023.2

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    Authorship:Lead author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.actamat.2023.118738

    Web of Science

    Scopus

  8. DFT calculations of carrier-trapping effects on atomic structures of 30° partial dislocation cores in zincblende II-VI group zinc compounds Reviewed

    Hoshino S., Oshima Y., Yokoi T., Nakamura A., Matsunaga K.

    Physical Review Materials   Vol. 7 ( 1 )   2023.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevMaterials.7.013603

    Web of Science

    Scopus

  9. Frontiers of Novel Functionality at Dislocation Cores

    Yoshiya Masato, Nakamura Atsutomo, Fujii Susumu, Oshima Yu, Yokoi Tatsuya, Matsunaga Katsuyuki

    Materia Japan   Vol. 61 ( 10 ) page: 629 - 633   2022.10

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    DOI: 10.2320/materia.61.629

    CiNii Research

  10. Room-temperature Deformation Behavior of Inorganic Semiconductor Materials Depending on External Fields Reviewed

    Nakamura Atsutomo, Oshima Yu, Matsunaga Katsuyuki

    KENBIKYO   Vol. 56 ( 3 ) page: 110 - 115   2021.12

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    Language:Japanese   Publisher:The Japanese Society of Microscopy  

    <p>In recent years, it was reported that semiconductor materials, which were regarded to be brittle, can exhibit high plasticity even at room temperature. For example, in strontium titanate crystals, room-temperature plasticity can be improved by controlling the ratio of the constituent elements. In addition, zinc sulfide crystals are brittle under light irradiation, but show high plasticity in the dark. These unusual plasticity of semiconductor crystals, which had not even been imagined before, has attracted a great deal of attention. These “brittle” materials were not suitable as structural materials before, and consequently have been used exclusively as functional materials. However, the understanding of the mechanisms that can overcome the brittleness of these materials is very useful for various material systems, and the wider application of materials are expected. Here we discuss the recent studies on the improvement of the plasticity of strontium titanate and zinc sulfide based on the in-situ observation of the samples and TEM observations of the dislocation substructures.</p>

    DOI: 10.11410/kenbikyo.56.3_110

    CiNii Research

  11. Photoindentation: A Method to Understand Dislocation Behavior of Inorganic Semiconductors in Light at the Nanoscale

    NAKAMURA Atsutomo, FANG Xufei, MATSUBARA Ayaka, OSHIMA Yu, MATSUNAGA Katsuyuki

    Journal of the Japan Society of Powder and Powder Metallurgy   Vol. 68 ( 11 ) page: 469 - 475   2021.11

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    Language:Japanese   Publisher:Japan Society of Powder and Powder Metallurgy  

    <p>The science and technology related with light has revolutionized modern society, and understanding the effects of light on semiconducting materials has become crucial to current science and technology. Although much research has been done on the effects of light on the electronic and optical properties of materials, the effects of light on the mechanical properties of materials are not well understood. It was recently found that extraordinarily large plasticity appears in bulk compression of single-crystal ZnS in complete darkness even at room-temperature. This is believed to be due to the less interactions between dislocations and photo-excited electrons and/or holes. However, methods for evaluating dislocation behavior in such semiconductors with small dimensions under a particular light condition had not been well established. Here we show a new nanoindentation method that incorporates well designed lighting system for exploring dislocation behavior depending on the light conditions in advanced semiconductors. We used single-crystal ZnS as a model material because its bulk deformation behavior has been well investigated. It is confirmed that the decrease of dislocation mobility with light observed in conventional bulk deformation tests can be understood even by the nanoindentation tests at room-temperature. It is remarkable that we experimentally demonstrate that dislocation mobility appears to be more sensitive to light exposure than dislocation nucleation.</p>

    DOI: 10.2497/jjspm.68.469

    Scopus

    CiNii Research

  12. Switching the fracture toughness of single-crystal ZnS using light irradiation

    Zhu Tingting, Ding Kuan, Oshima Yu, Amiri Anahid, Bruder Enrico, Stark Robert W., Durst Karsten, Matsunaga Katsuyuki, Nakamura Atsutomo, Fang Xufei

    APPLIED PHYSICS LETTERS   Vol. 118 ( 15 )   2021.4

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    Language:Japanese   Publisher:Applied Physics Letters  

    An enormous change in the dislocation-mediated plasticity has been found in a bulk semiconductor that exhibits the photoplastic effect. Herein, we report that UV (365 nm) light irradiation during mechanical testing dramatically decreases the fracture toughness of ZnS. The crack tip toughness on a (001) single-crystal ZnS, as measured by the near-tip crack opening displacement method, is increased by ∼45% in complete darkness compared to that in UV light. The increase in fracture toughness is attributed to a significant increase in the dislocation mobility in darkness, as explained by the crack tip dislocation shielding model. Our finding suggests a route toward controlling the fracture toughness of photoplastic semiconductors by tuning the light irradiation.

    DOI: 10.1063/5.0047306

    Web of Science

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  13. Photoindentation: A New Route to Understanding Dislocation Behavior in Light

    Nakamura Atsutomo, Fang Xufei, Matsubara Ayaka, Tochigi Eita, Oshima Yu, Saito Tatsushi, Yokoi Tatsuya, Ikuhara Yuichi, Matsunaga Katsuyuki

    NANO LETTERS   Vol. 21 ( 5 ) page: 1962 - 1967   2021.3

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    Language:Japanese   Publisher:Nano Letters  

    It was recently found that extremely large plasticity is exhibited in bulk compression of single-crystal ZnS in complete darkness. Such effects are believed to be caused by the interactions between dislocations and photoexcited electrons and/or holes. However, methods for evaluating dislocation behavior in such semiconductors with small dimensions under a particular light condition had not been well established. Here, we propose the "photoindentation"technique to solve this issue by combining nanoscale indentation tests with a fully controlled lighting system. The quantitative data analyses based on this photoindentation approach successfully demonstrate that the first pop-in stress indicating dislocation nucleation near the surface of ZnS clearly increases by light irradiation. Additionally, the room-temperature indentation creep tests show a drastic reduction of the dislocation mobility under light. Our approach demonstrates great potential in understanding the light effects on dislocation nucleation and mobility at the nanoscale, as most advanced technology-related semiconductors are limited in dimensions.

    DOI: 10.1021/acs.nanolett.0c04337

    Web of Science

    Scopus

    PubMed

  14. Extraordinarily large plasticity of zinc sulfide single crystals in the dark

    NAKAMURA Atsutomo, OSHIMA Yu, MATSUNAGA Katsuyuki

    Oyo Buturi   Vol. 90 ( 3 ) page: 176 - 179   2021.3

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    Language:Japanese   Publisher:The Japan Society of Applied Physics  

    <p>Inorganic semiconductors tend to fail in a brittle manner when subjected to an external force. Such poor mechanical properties limit their application range. Recently, we report extraordinary plasticity in an inorganic semiconductor, ZnS in darkness. Room-temperature deformation tests of ZnS were performed under varying light conditions. ZnS crystals immediately fractured when they deformed under light. On the other hand, it was found that ZnS crystals can be plastically deformed up to a plastic strain of 45 % in darkness. In addition, the optical band-gap of the deformed ZnS was decreased by 0.6 eV. These results suggest that dislocations in ZnS become extremely mobile in darkness and that multiplied dislocations can affect the optical band-gap over the whole crystal.</p>

    DOI: 10.11470/oubutsu.90.3_176

    CiNii Research

  15. Multiscale Analysis for Understanding the Effect of Light Environment on Mechanical Properties of Inorganic Semiconductors

    Nakamura Atsutomo, Oshima Yu, Matsunaga Katsuyuki

    Materia Japan   Vol. 60 ( 1 ) page: 30 - 34   2021.1

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    Language:Japanese   Publisher:The Japan Institute of Metals and Materials  

    DOI: 10.2320/materia.60.30

    CiNii Research

  16. Carrier-trapping induced reconstruction of partial-dislocation cores responsible for light-illumination controlled plasticity in an inorganic semiconductor Reviewed

    K. Matsunaga, S. Hoshino, M. Ukita, Y. Oshima, T. Yokoi, A. Nakamura

    Acta Materialia     2020.8

  17. Room-temperature creep deformation of cubic ZnS crystals under controlled light conditions Reviewed

    Y. Oshima, A. Nakamura, K.P.D. Lagerlöf, T. Yokoi, K. Matsunaga

    Acta Materialia     2020.8

  18. Theoretical Calculations of Characters and Stability of Glide Dislocations in Zinc Sulfide Reviewed

    M. Ukita, R. Nagahara, Y. Oshima, A. Nakamura, T. Yokoi, K. Matsunaga

    Materials Transactions     2019.1

  19. Extraordinary plasticity of an inorganic semiconductor in darkness Reviewed

    Y. Oshima, A. Nakamura, K. Matsunaga

    Science     2018.3

  20. Structure of the basal edge dislocation in ZnO Reviewed

    A. Nakamura, E. Tochigi, R. Nagahara, Y. Furushima, Y. Oshima, Y. Ikuhara, T. Yokoi, K. Matsunaga

    Crystals     2018.3

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KAKENHI (Grants-in-Aid for Scientific Research) 2

  1. 無機半導体転位における光応答の実験的観測

    Grant number:22K14500  2022.4 - 2024.3

    科学研究費助成事業  若手研究

    大島 優

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    Authorship:Principal investigator 

    Grant amount:\4680000 ( Direct Cost: \3600000 、 Indirect Cost:\1080000 )

    近年の理論解析により,代表的なII-VI族化合物半導体の1つである硫化亜鉛(ZnS)において,転位がキャリアをトラップすることにより原子・電子構造を変化させうることが明らかとなってきた.一方で,キャリアトラップ時の転位コアにおける原子・電子構造変化について実験的な観測は未だ行われていない.そこで本研究では,転位を導入した無機半導体結晶について光吸収特性評価を実施し,光励起による転位の電子構造変化について観測を試みる.

  2. 無機半導体結晶の変形挙動における光環境効果と転位物性の解明

    Grant number:21K20484  2021.8 - 2023.3

    科学研究費助成事業  研究活動スタート支援

    大島 優

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    Authorship:Principal investigator 

    Grant amount:\3120000 ( Direct Cost: \2400000 、 Indirect Cost:\720000 )

    無機半導体中の転位は,局所的な組成の偏りに起因して,しばしば正もしくは負に帯電することが知られている.その結果,転位は自由電子やホールと相互作用を生じうる.しかしながら,そうした相互作用が結晶の変形特性(転位の運動性)や転位機能に及ぼす影響については不明な点が多い.そこで本研究では,無機半導体結晶について光環境制御下における機械的変形試験を実施し,変形特性における光環境効果を調査する.また,転位を導入した結晶について物性測定を行い,転位機能の評価を実施する.
    無機半導体中の転位は,その中心部において結合欠損が生じており,局所的な組成の偏りを有するため,しばしば正もしくは負に帯電することが知られている.その結果として,転位は電荷を有するキャリアと相互作用を生じうる.しかしながら,そうした転位-キャリア間で生じる相互作用が無機半導体の変形特性(転位の運動性)に及ぼす影響については不明な点が多い.そこで当該年度には,酸化チタン(TiO2)結晶について光環境制御下における硬さ試験を実施し,光励起によるキャリア発生が結晶の硬さに及ぼす影響について評価を実施した.
    まず,光照射による硬さの変化を正確に評価するための環境整備を行った.光照射下において硬さが上昇することが既に報告されている硫化亜鉛(ZnS)結晶を用いて,光照射による硬さ変化を抽出できることを確認した.
    続いて,光が存在しない暗所下および波長の異なる様々な光照射下について,酸化チタン(TiO2)結晶表面の硬さ測定を実施した.硬さ試験後に表面形状の観察を行ったところ,いずれの光環境条件下においても,圧痕周辺にすべり線および微小クラックの形成がみとめられた.圧子の押込みにより,転位の運動によるすべり運動,および,クラックの発生・伝播が生じていると考えられる.また,暗所下および光照射下それぞれについて圧痕の形状から硬さを算出したところ,光照射により硬さが変化する傾向にあることがわかった.このようにして,酸化チタン結晶において光環境がその変形特性に影響を及ぼす可能性があることが示唆された.
    光環境制御下における硬さ測定により,光環境が酸化チタン(TiO2)の変形特性に影響を及ぼしうることが確認された.この結果に基づいて,バルクを用いた機械的変形試験について検討が可能であり,おおむね順調に進展していると考えられる.
    これまでは光環境制御下における硬さ測定を実施してきた.そこで今後は,光環境制御下における機械的変形試験へと実験系を拡張し評価を行う.さらに,対象材料を酸化チタン(TiO2)以外の無機半導体結晶にも広げる予定である.