研究者詳細 - 仲村　龍介

論文 - 仲村　龍介

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Diffusion of oxygen in amorphous HfO2 査読

Yuna Motozu, Ryusuke Nakamura, Sota Hoshishima, Takeyuki Suzuki

Journal of Physics and Chemistry of Solids 199 112499.1 - 112499.66 2025年4月

Chemical Diffusion in Ni-V Solid Solution and in Ni3V 査読

D. Inoue, R. Nakamura, H. Numakura

Journal of Phase Equilibria and Diffusion 44 240 - 254 2023年5月

Explosive crystallization of amorphous germanium-tin films by irradiation with a 3-keV electron beam 査読国際誌

R. Nakamura, M. Miyamoto, M. Ishimaru

Journal of Applied Physics 133 185304.1 - 185304.8 2023年5月

Diffusion of boron in an amorphous iron-boron alloy 査読国際誌

Takumi Hamaguchi, Ryusuke Nakamura, Kohta Asano, Takeshi Wada, Takeyuki Suzuki

Journal of Non-Crystalline Solids 601 122070.1 - 122070.6 2023年2月

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

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2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the European Ceramic Society 参加形態：共同（副担当）

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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Explosive crystallization of sputter-deposited amorphous germanium films by irradiation with an electron beam of SEM-level energies 査読国際誌

Nakamura R., Matsumoto A., Ishimaru M.

Journal of Applied Physics 129 ( 21 ) 215301.1 - 215301.6 2021年6月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（主担当）

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

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Permeation and diffusion of hydrogen in vanadium using deoxidation and glow-discharge surface cleaning techniques 査読

Fujimura N., Asano K., Nakamura R., Iijima Y.

Journal of Membrane Science 614 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（副担当）

Vanadium (V) is an attractive hydrogen separation membrane material. However, its diffusion behavior under hydrogen permeation is not well understood mainly because of surface oxidation. Here, we have attempted to observe the permeation of hydrogen through V by subjecting V samples to different surface treatments e.g., electropolishing and plasma-induced cleaning using a glow-discharge technique. We have achieved a high flux of hydrogen controlled by long-range diffusion under a low hydrogen potential at 723–973 K. The diffusion coefficients of hydrogen in defect-free and high-purity samples analyzed from the permeation curves at 823–973 K are almost consistent with the literature data obtained by Gorsky effect and absorption measurements. However, the activation energy of diffusion (19 kJ mol−1) is 8–14 kJ mol−1 higher than the literature values. This difference in activation energy suggests that permeation through the active surface of V is highly sensitive to trapping by oxygen—a slight amount of oxygen dissolved from a very thin native oxide layer would segregate near the surface to trap hydrogen. Furthermore, we have found that residual strain, grain boundaries, and lattice defects, induced by mechanical deformation, reduce the flux and retard the diffusion considerably.

DOI： 10.1016/j.memsci.2020.118522

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Dual crystallization modes of sputter-deposited amorphous SiGe films 査読国際誌

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

Journal of Applied Physics 128 ( 1 ) 015303.1 - 015303.9 2020年7月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（主担当）

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 査読国際誌

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

Japanese Journal of Applied Physics 59 ( 7 ) 075506.1 - 075506.7 2020年7月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（主担当）

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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二次イオン質量分析法によるα鉄中のホウ素の拡散浸透プロファイルの測定と拡散係数の決定査読

濱名桂佑 , 仲村龍介 , 沼倉宏 , 鈴木健之

鉄と鋼 106 ( 6 ) 302 - 309 2020年6月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本鉄鋼協会参加形態：共同（主担当）

We report an attempt to determine the diffusion coefficient of B in α Iron by measuring the penetration profile by means of secondary-ion mass spectrometry (SIMS). Pure iron plates of grain-size of 1 to 3 mm were prepared, and thin films of Fe-B alloy (200 nm) and alumina (50 nm) were deposited on the surface as a B source and a capping layer, respectively. The samples were subjected to diffusion annealing at 700ºC, 800ºC, and 900ºC for certain periods of time, and the intensity of secondary ions of B was measured as a function of depth by SIMS. The mesa method was employed, in which a groove is prepared first around the target area by sputtering, and then the depth profile of B through the inner pillar was obtained. The concentration profiles thus obtained were analysed with the thin-film solution, the error-function solution, and also using Hall’s method, depending on the form of the profile. The diffusion coefficient was of the order of 10–18 m2 s–1 in all the cases, which is seven to eight orders of magnitude smaller than those evaluated from deboronising experiments in the 1950 s, but is close to recent theoretical prediction for substitutional diffusion.

DOI： 10.2355/tetsutohagane.TETSU-2019-104

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

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

Journal of Applied Physics 127 ( 20 ) 205304.1 - 205304.9 2020年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Applied Physics 参加形態：共同（副担当）

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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Direct observations of crystallization processes of amorphous GeSn during thermal annealing: A temperature window for suppressing Sn segregation 査読国際誌

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

Journal of Applied Physics 125 ( 17 ) 175703.1 - 175703.8 2019年5月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（副担当）

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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The relation between amorphous structure and explosive crystallization of sputter-deposited amorphous germanium thin films 査読国際誌

Okugawa M., Nakamura R., Numakura H., Heya A., Matsuo N., Yasuda H.

Japanese Journal of Applied Physics 58 ( 4 ) 045501.1 - 045501.6 2019年1月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（主担当）

In amorphous germanium (a-Ge) and amorphous silicon films, extremely rapid crystallization, called explosive crystallization, is known to occur by instantaneous processes such as mechanical stimulation, laser irradiation, and electron irradiation. In the present study, using transmission electron microscopy, we have investigated crystallization of a-Ge induced by electron irradiation and flash-lamp annealing (FLA). We have found that the mode of crystallization depends on the amorphous state: explosive crystallization occurred by both electron irradiation and FLA in pristine films, while it did not occur in those aged at room temperature for over 6 months. In a previous paper [Okugawa et al., J. Appl. Phys. 119, 214309 (2016)], it was reported that liquid-like high-density amorphous (HDA) regions were formed in a-Ge films by the long-term aging. The explosive crystallization observed in pristine a-Ge films is suggested to occur via liquid-like HDA interfaces at the growth front.

DOI： 10.7567/1347-4065/ab0909

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Synthesis of high Sn concentration GeSn by recrystallization of amorphous phase 査読

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

Materials Science and Technology 2018, MS and T 2018 284 - 287 2019年1月

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）参加形態：共同（副担当）

Amorphous structures of germanium-tin (GeSn) thin films as well as their recrystallization processes during thermal annealing were examined by means of transmission electron microscopy. The specimens were prepared by radio-frequency magnetron sputtering. The as-sputtered GeSn thin films possessed an amorphous structure with 16.4 at.%Sn. The specimen crystallized at 325 °C, and Sn atoms were substitutionally incorporated in a diamond structure. The Sn atoms were ejected from Ge at 350 °C, and molten Sn were formed. In the cooling process, it was confirmed that the molten Sn remained at 150 o C which is much lower than the eutectic temperature of the Ge-Sn binary system. Finally, a remarkable Sn precipitates were formed at room temperature.

DOI： 10.7449/2018/MST_2018_284_287

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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

仲村龍介 , 半谷祐樹 , 石丸学 , 和田武

鉄と鋼 105 ( 10 ) 1017 - 1021 2019年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本鉄鋼協会参加形態：共同（主担当）

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.

DOI： 10.2355/tetsutohagane.TETSU-2019-032

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Structure of crystallized particles in sputterdeposited amorphous germanium films 査読

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）参加形態：共同（主担当）

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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Low-temperature synthesis of crystalline GeSn with high Sn concentration by electron excitation effect 査読国際誌

Kimura T., Ishimaru M., Okugawa M., Nakamura R., Yasuda H.

Japanese Journal of Applied Physics 56 ( 10 ) 100307.1 - 100307.3 2017年10月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（副担当）

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

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Inhomogeneous crystallization of sputter-deposited amorphous Ge films 招待査読

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

AM-FPD 2017 - 24th International Workshop on Active-Matrix Flatpanel Displays and Devices: TFT Technologies and FPD Materials, Proceedings 276 - 278 2017年8月

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）参加形態：共同（主担当）

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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Crystallization Processes of Amorphous GeSn Thin Films by Heat Treatment and Electron Beam Irradiation 査読国際誌

Kimura T , Ishimaru M , Okugawa M , Nakamura R , Yasuda H

Microscopy and Microanalysis 23 ( S1 ) 2046 - 2047 2017年

Thermal crystallization of sputter-deposited amorphous Ge films: Competition of diamond cubic and hexagonal phases 査読国際誌

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

AIP Advances 6 ( 12 ) 125035.1 - 125035.9 2016年12月

記述言語：英語掲載種別：研究論文（学術雑誌）参加形態：共同（主担当）

Following our previous studies on crystallization induced by electron irradiation, we have investigated the crystallization of sputter-deposited amorphous germanium films by heat treatments. On continuous heating, samples aged for 3 days and 4 months at room temperature crystallized at 500°C to form coarse spherical particles of a hexagonal structure, of about 100 nm in diameter, whereas samples aged for 7 months turned to homogeneous nanograins of the diamond cubic structure at 600°C. When the films aged for 4 months at room temperature were annealed at 350°C for 2 h and then heated, they crystallized at 550°C to form a mixture of the two microstructures, and those annealed at 350°C and further at 500°C for 1 h crystallized at 600°C mostly to nanograins. Crystallization by electron irradiation at 350°C to 4-month-aged samples has also been studied. With increasing annealing time at 350°C, coarse particles of a hexagonal structure ceased to appear, and were replaced by fine nanograins of the diamond cubic structure. These observations can be understood in terms of structural instability of sputter-deposited amorphous films. Medium-range ordered clusters must initially be present in the films and serve as nuclei of the metastable hexagonal phase. They are unstable, however, and are eliminated by annealing, resulting in the reduction in size and number of coarse particles with a metastable structure.

DOI： 10.1063/1.4972282

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