Authorship：Lead author,　Corresponding author   Language：English  

Language：English  

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

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

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

DOI： 10.1016/j.scriptamat.2023.115368

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Scopus

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

DOI： 10.1016/j.jpcs.2023.111273

Web of Science

Scopus

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

DOI： 10.1016/j.actamat.2023.118738

Web of Science

Scopus

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

DOI： 10.1111/jace.18853

Web of Science

Scopus

Publisher：Journal of Physics and Chemistry of Solids  

To accurately predict low-energy structures for symmetric tilt grain boundaries (GBs) in Si and Ge, artificial-neural-network (ANN) interatomic potentials are constructed and are combined with a simulated annealing (SA) method based on molecular dynamics simulations. The ANN-driven SA method is demonstrated to predict GB structures that are in good agreement with previous electron microscopy observations, without prior knowledge about their atomic configurations. Their GB energies also reasonably agree with density-functional-theory (DFT) calculations. By contrast, a conventional empirical potential fails to predict those GB structures. For misorientation angles 2θ≥93.37°, the lowest-energy structures are found to contain atomic configurations that cannot be reproduced by one repeat unit of the perfect crystal along the tilt axis. Such GB structures cannot be obtained using the γ-surface method, although it is most commonly used for exploring low-energy GB structures. These results highlight the importance of using simulation cells with multiple repeat units along the tilt axis and of performing the SA method with high-accuracy interatomic potentials transferable to GBs.

DOI： 10.1016/j.jpcs.2022.111114

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Scopus

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

DOI： 10.1103/PhysRevMaterials.7.013603

Web of Science

Scopus

Language：English  

Language：English  

Language：English  

Authorship：Lead author,　Corresponding author   Language：English  

Language：English  

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

DOI： 10.2320/materia.61.629

CiNii Research

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

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

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

Open Access

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Scopus

Language：English   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

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

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

DOI： 10.2320/materia.60.30

CiNii Research