研究者詳細 - 石丸　学

論文 - 石丸　学

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Simultaneous achievement of high J <inf>c</inf>and suppressed J <inf>c</inf>anisotropy by hybrid pinning in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>three-phase-nanocomposite film 査読有り国際誌

Horide T., Torigoe K., Ishimaru M., Kita R., Awaji S., Matsumoto K.

Superconductor Science and Technology 33 ( 10 ) 2020年10月

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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Dual crystallization modes of sputter-deposited amorphous SiGe films 査読有り

Okugawa M., Nakamura R., Numakura H., Ishimaru M., Yasuda H.

Journal of Applied Physics 128 ( 1 ) 2020年07月

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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Effects of hydrogen on structure and crystallization behavior of sputter-deposited amorphous germanium films 査読有り

Hanya Y., Nakamura R., Okugawa M., Ishimaru M., Oohata G., Yasuda H.

Japanese Journal of Applied Physics 59 ( 7 ) 2020年07月

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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Deposition-temperature dependence of vortex pinning property in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>+BaHfO<inf>3</inf> films 査読有り

Horide T., Torigoe K., Kita R., Nakamura R., Ishimaru M., Awaji S., Matsumoto K.

Materials Transactions ( 日本金属学会 ) 61 ( 3 ) 449 - 454 2020年01月

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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Liquid-mediated crystallization of amorphous GeSn under electron beam irradiation 査読有り

Inenaga K., Motomura R., Ishimaru M., Nakamura R., Yasuda H.

Journal of Applied Physics 127 ( 20 ) 2020年01月

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

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Carrier and heat transport properties of poly-crystalline GeSn films for thin-film transistor applications 査読有り

Uchida N., Hattori J., Lieten R., Ohishi Y., Takase R., Ishimaru M., Fukuda K., Maeda T., Locquet J.

Journal of Applied Physics 126 ( 14 ) 2019年10月

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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Thermoelectric Property in Orthorhombic-Domained SnSe Film 査読有り

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

ACS Applied Materials and Interfaces 11 ( 30 ) 27057 - 27063 2019年07月

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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Observation of inhomogeneous depinning in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf> composite multilayers 査読有り

Horide T., Ishimaru M., Matsumoto K.

Superconductor Science and Technology 32 ( 8 ) 2019年06月

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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Direct observations of crystallization processes of amorphous GeSn during thermal annealing: A temperature window for suppressing Sn segregation 査読有り

Higashiyama M., Ishimaru M., Okugawa M., Nakamura R.

Journal of Applied Physics 125 ( 17 ) 2019年05月

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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Compositional effects on radiation tolerance of amorphous silicon oxycarbide 査読有り

Mizuguchi S., Inoue S., Ishimaru M., Su Q., Nastasi M.

Journal of Nuclear Materials 518 241 - 246 2019年05月

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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Nonlocal self-organization of long stacking faults from highly strained nanocomposite film of complex oxide 査読有り

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

Physical Review Materials 3 ( 1 ) 2019年01月

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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Application of the Tersoff interatomic potential to pressure-induced polyamorphism of silicon 査読有り国際誌

Mukuno R., Ishimaru M.

Japanese Journal of Applied Physics 58 ( 10 ) 2019年01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）

© 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

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特集にあたって査読有り

石丸学

顕微鏡 ( 公益社団法人日本顕微鏡学会 ) 54 ( 3 ) 109 - 109 2019年01月

低エネルギー電子線照射によるアモルファスGeSnの結晶化査読有り

石丸学, 仲村龍介

顕微鏡 ( 公益社団法人日本顕微鏡学会 ) 54 ( 3 ) 126 - 130 2019年01月

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

その他リンク： https://ci.nii.ac.jp/naid/130007783749

スパッタリング法によるアモルファスFe-B合金薄膜の作製と透過型電子顕微鏡による構造解析査読有り

仲村龍介, 半谷祐樹, 石丸学, 和田武

鉄と鋼 ( 日本鉄鋼協会 ) 105 ( 10 ) 1017 - 1021 2019年01月

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 Fe<sub>3</sub>B and Fe<sub>23</sub>B<sub>6</sub>, were detected, suggesting the atomic arrangement of the compounds in the amorphous matrices.</p>

DOI： 10.2355/tetsutohagane.TETSU-2019-032

その他リンク： https://ci.nii.ac.jp/naid/130007719957

Deposition-temperature dependence of vortex pinning property in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>+BaHfO<inf>3</inf> Film 査読有り

Horide T., Torigoe K., Kita R., Nakamura R., Ishimaru M., Awaji S., Matsumoto K.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals ( 公益社団法人日本金属学会 ) 83 ( 9 ) 320 - 326 2019年01月

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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Chalcopyrite ZnSnSb<inf>2</inf>: A Promising Thermoelectric Material 査読有り

Nomura A., Choi S., Ishimaru M., Kosuga A., Chasapis T., Ohno S., Snyder G., Ohishi Y., Muta H., Yamanaka S., Kurosaki K.

ACS Applied Materials and Interfaces 10 ( 50 ) 43682 - 43690 2018年12月

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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Structure of crystallized particles in sputterdeposited amorphous germanium films 査読有り

Okugawa M., Nakamura R., Hirata A., Ishimaru M., Yasuda H., Numakura H.

Journal of Applied Crystallography 51 ( 5 ) 1467 - 1473 2018年10月

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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Molecular-dynamics simulations of solid phase epitaxy in silicon: Effects of system size, simulation time, and ensemble 査読有り

Kohno K., Ishimaru M.

Japanese Journal of Applied Physics 57 ( 9 ) 2018年09月

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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Geometric and compositional factors on critical current density in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-δ</inf>films containing nanorods 査読有り

Horide T., Nagao S., Izutsu R., Ishimaru M., Kita R., Matsumoto K.

Superconductor Science and Technology 31 ( 6 ) 2018年05月

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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