研究者データベース

渡辺 精一(ワタナベ セイイチ)
工学研究院 附属エネルギー・マテリアル融合領域研究センター 光・熱エネルギー変換材料分野
教授

基本情報

所属

  • 工学研究院 附属エネルギー・マテリアル融合領域研究センター 光・熱エネルギー変換材料分野

職名

  • 教授

学位

  • 理学博士(Ph.D.)(State University of New York at Buffalo)
  • 修士(北海道大学)

ホームページURL

科研費研究者番号

  • 60241353

ORCID ID

Researcher ID

  • E-2622-2012

J-Global ID

研究キーワード

  • ナノテクノロジー   光化学   光物性   材料物性   量子ビーム科学   照射効果   ナノ材料   非平衡材料   Nonequilibrium Physics and Chemistry   Materials Science   

研究分野

  • ナノテク・材料 / エネルギー化学 / グリーンエネルギー
  • ナノテク・材料 / 光工学、光量子科学 / 光物性
  • ナノテク・材料 / 基礎物理化学 / 光化学
  • ナノテク・材料 / グリーンサステイナブルケミストリー、環境化学 / 結晶光合成
  • ナノテク・材料 / 金属材料物性
  • ナノテク・材料 / ナノ構造物理
  • ナノテク・材料 / ナノ構造化学

職歴

  • 2019年04月 - 現在 北海道大学 大学院 工学研究院 エネルギー・マテリアル融合領域研究センター センター長
  • 2012年 - 現在 北海道大学 電子科学研究所 グリーンナノテクノロジー研究センター 教授(兼務)
  • 2010年 - 現在 北海道大学 大学院 工学研究院 エネルギー・マテリアル融合領域研究センター 教授
  • 2013年 九州大学 工学部 非常勤講師
  • 2005年 - 2010年 北海道大学 エネルギー変換マテリアル研究センター 教授
  • 2005年 - 2006年 東北大学 学際科学国際高等研究センター 客員教授
  • 1997年 - 2005年 北海道大学大学院工学研究科 助教授 助教授
  • 1997年 - 2005年 Hokkaido University Faculty of Engineering Associate Professor
  • 1994年 - 1997年 北海道大学エネルギー先端工学研究センター 助手
  • 1994年 - 1997年 Research Associate,CARET, Hokkaido University
  • 1992年 - 1994年 北海道大学工学部 助手
  • 1992年 - 1994年 Research Associate,1992 - 1994 Research Associate, Metals Research Institute, Hokkaido University

学歴

  •         - 1993年   ニューヨーク州立大学バッファロー校   大学院博士課程(Ph.D)修了   物理
  •         - 1993年   State Unversity of New York at Buffalo
  •         - 1987年   北海道大学   工学研究科   修士課程金属工学専攻
  •         - 1985年   北海道大学   工学部   金属工学科

所属学協会

  • 光化学協会   応用物理学会   日本鉄鋼協会   日本金属学会   日本顕微鏡学会   米国物理学会(APS)   米国材料学会(MRS)   Atomic Energy Society of Japan   Physical Society of Japan   Materials Research Society   Japanese Society of Microscopy   Japan Institute of Metals   American Physical Society   

研究活動情報

論文

  • Zhehan Yu, Lihua Zhang, Seiichi Watanabe
    Materials Today Communications 33 104213 - 104213 2022年12月 [査読有り]
  • Satoshi Takai, Shuntaro Murakami, Lihua Zhang, Kenichi Ohsasa, Seiichi Watanabe
    ACS Applied Engineering Materials 2022年09月13日 [査読有り]
  • Yi Xu, Pak Man Yiu, Yu-Kun Wang, Xiao-Meng Qin, Tamaki Shibayama, Seiichi Watanabe, Masato Ohnuma, Da-Zhu Chen, Hua Cheng, Chan-Hung Shek, Zhou-Guang Lu, Chen Liu
    Rare Metals 2022年08月16日 [査読有り]
  • Zhehan Yu, Shilei Zhu, Lihua Zhang, Seiichi Watanabe
    Optical Materials 127 112297 - 112297 2022年05月 [査読有り]
  • Yuki Takahashi, Melbert Jeem, Lihua Zhang, Seiichi Watanabe
    Applied Materials Today 26 101359 - 101359 2022年03月 [査読有り]
  • Jumpei Tsukamura, Yuki Takahashi, Lihua Zhang, Melbert Jeem, Kazumasa Okamoto, Seiichi Watanabe
    Microelectronic Engineering 256 111727 - 111727 2022年02月 [査読有り]
  • Shuntaro Murakami, Lihua Zhang, Melbert Jeem, Kazumasa Okamoto, Yuki Nakagawa, Tamaki Shibayama, Masato Ohnuma, Seiichi Watanabe
    Optical Materials 124 111966 - 111966 2022年02月 [査読有り]
  • Souta Fujii, Shuntaro Murakami, Lihua Zhang, Seiichi Watanabe
    Materials Letters 302 130344 - 130344 2021年11月 
    Tungsten nano-oxides of WO3 and H2WO4 have been studied as promising candidates for photocatalytic and chromic materials. To date, WO3 and H2WO4 nanoparticles are generally prepared by hydrothermal synthesis, which requires high temperature environment and pH adjustment. In this paper, we report on fabricating WO3 nanoparticles via photosynthesis by UV irradiation of the solution made from dissolving tungsten in hydrogen peroxide. Similarly, we have succeeded in fabricating H2WO4 nanoparticles by changing the concentration of hydrogen peroxide solution. Furthermore, an electrochromic device was fabricated by coating the WO3 nanoparticles on an ITO substrate, and the chromic properties are then confirmed.
  • Longfei Guo, Noriyuki Okinaka, Lihua Zhang, Seiichi Watanabe
    Optical Materials 119 111295 - 111295 2021年09月
  • Shilei Zhu, Zhehan Yu, Lihua Zhang, Seiichi Watanabe
    ACS Applied Nano Materials 4 4 3940 - 3948 2021年04月23日 [査読有り]
  • Longfei Guo, Noriyuki Okinaka, Lihua Zhang, Seiichi Watanabe
    Materials Chemistry and Physics 262 124273 - 124273 2021年04月 [査読有り]
  • Shuntaro Murakami, Lihua Zhang, Seiichi Watanabe
    Scientific Reports 10 1 2020年12月 [査読有り]
     
    AbstractWe report a water decomposition mode called ‘Aquaionic Splitting (AiS)’ by means of iron corrosion in aqueous solution. In this paper, we investigated the phenomenon by controlling the reaction between iron and water. A pseudo-sacrificial protection method with oil paint was employed to select the anode and cathode formation locations that govern iron corrosion. Then, the AiS reaction was visualized by using BTB solution, whose colour corresponds to pH, to produce colour patterning that corresponds to the aquaion distribution. It has become clear that water can be selectively separated into protons and hydroxide ions by corrosion control treatment. In this vein, the diffusion coefficient of protons was estimated by using the colour patterning of BTB solution that accompanies iron corrosion, and aquaion distribution was then computer simulated by solving the diffusion equation.
  • Tomoya Gotoh, Melbert Jeem, Lihua Zhang, Noriyuki Okinaka, Seiichi Watanabe
    Journal of Physics and Chemistry of Solids 142 109436 - 109436 2020年07月 [査読有り]
  • Yang Zhan-Bing, Yang Su-Bing, Qu Xiao-Jian, Tamaki Shibayama, Seiichi Watanabe
    CHINESE JOURNAL OF STRUCTURAL CHEMISTRY 39 4 623 - 629 2020年04月 
    A nanosecond pulse laser source head (Nd:YAG laser, Inlite II-20, Continuum) was equipped to a high-voltage electron microscope (HVEM, Hitachi, H-1300) to develop a laser-HVEM system at Hokkaido University. Using the laser-HVEM, new methods for in-situ observation on the formation process of laser-induced lattice point defects at the internal of crystalline solid are achieved; some striking phenomena and potential mechanisms are explored. In the present paper, we review our progresses on in-situ experiments of lattice defects behavior in metal using the laser-HVEM. These progresses are expected to provide insight for a broader application of laser-HVEM in scientific research.
  • Junichi Mizuno, Melbert Jeem, Yuki Takahashi, Masaya Kawamoto, Kiyotaka Asakura, Seiichi Watanabe
    ACS Applied Nano Materials 3 2 1783 - 1791 2020年02月28日 [査読有り]
  • Kosuke Kuwabara, Yuzo Daigo, Kazuya Shinagawa, Seiichi Watanabe, Tadashi Fujieda
    NACE - International Corrosion Conference Series 2020-June 2020年 
    Microstructure modification of CoCrFeNiTi-based multi-principal element alloy (MPEA) manufactured by selective laser melting (SLM) is conducted to obtain high-strength and corrosion resistant alloys for harsh environments. Mechanical properties are improved by the microstructure control of ' nano-precipitates and -plate precipitates by a set of heat treatment process including solution heat treatment and aging heat treatment. The alloy after aging heat treatment exhibited the tensile strength of 1,548 MPa with the elongation of 23 % and Charpy impact value of 29 J/cm2. The developed SLM products showed the corrosion resistance in H2SO4 and HCl comparable to those of the precipitation-hardened nickel alloys. The relationship between morphologies of precipitates and the alloys' mechanical properties and corrosion behaviors will be discussed.
  • 先進ナノ構造・状態解析共用拠点(北海道大学)
    柴山 環樹, 松尾 保孝, Agus Subagyo, 坂口 紀史, 渡辺 精一
    まてりあ 58 12 758 - 762 2019年12月 [査読有り][招待有り]
  • Yuki Takahashi, Kento Hiraiwa, Melbert Jeem, Lihua Zhang, Seiichi Watanabe
    Applied surface science 489 313 - 320 2019年06月 [査読有り][通常論文]
  • Kento Hiraiwa, Yuki Takahashi, Junichi Mizuno, Melbert Jeem, Seiichi Watanabe
    Applied Surface Science 489 269 - 277 2019年06月 [査読有り][通常論文]
  • Lihua Zhang, Melbert Jeem, Kazumasa Okamoto, Seiichi Watanabe
    ISIJ INTERNATIONAL 59 12 2352 - 2358 2019年 [査読有り][通常論文]
     
    Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO and CuO nanostructures have been successfully fabricated via this method. In this work, the SPSC process was applied for the fabrication of iron oxide and hydroxide nanoparticles. The experiments were conducted under visible light, ultraviolet light, and gamma-ray irradiation conditions and the morphologies of the obtained nanoparticles were observed and compared with that obtained without illumination. Then, the mechanism of the SPSC process for the fabrication of iron oxide nanoparticles was discussed. The results show that various kinds of morphologies of nanocrystallites were obtained on the Fe plate surface and the main morphologies are different under different conditions. For example, most FeOOH with the morphologies of nanorod and nanofiber exist by visible light irradiation; most faceted crystals of FeOOH and Fe2O3 with the morphologies of nanograular and nanorod exist by ultraviolet irradiation. In the SPSC process, light irradiation generates center dot OH at the crystal tips and promote the crystallization in apical growth of FeOOH.
  • Tadashi Fujieda, Meichuan Chen, Hiroshi Shiratori, Kosuke Kuwabara, Kenta Yamanaka, Yuichiro Koizumi, Akihiko Chiba, Seiichi Watanabe
    Additive Manufacturing 25 25 412 - 420 2019年01月 [査読有り][通常論文]
     
    © 2018 Elsevier B.V. The effectiveness of applying selective laser melting (SLM) to a CoCrFeNiTi-based high-entropy alloy was compared with that of using electron beam melting (EBM). The higher solidification rate during SLM promoted a fine uniform microstructure with no visible segregation, which led to superior tensile properties (yield strength: 773.0 ± 4.2 MPa, ultimate tensile strength: 1178.0 MPa, elongation: 25.8 ± 0.6%) and a higher pitting potential (0.88 ± 0.03 V versus Ag/AgCl in a 3.5% NaCl solution at 353 K) in comparison to the EBM specimens (743.4 ± 11.6, 932.2 ± 4.8 MPa, 4.0 ± 0.2%, and 0.50 ± 0.04 V versus Ag/AgCl, respectively). The effect of a solution treatment on the tensile properties and pitting-corrosion resistance of the SLM specimens was then examined. The effect of the solution treatment on these properties depended on the cooling method used during the treatment. In particular, the tensile properties and pitting-corrosion resistance improved as a result of water quenching. On the other hand, the properties of the solution-treated specimens depended on the size and volume fraction of very fine-ordered particles, with diameters of tens of nanometers that contained Ni and Ti. The as-built and solution-treated SLM specimens exhibited excellent tensile strength and exceptional pitting-corrosion resistance; they had higher tensile strength and pitting-corrosion resistance than the conventional high-corrosion-resistant alloys.
  • Xiaoya Wei, Si Lan, Zhenduo Wu, Masato Ohnuma, Tamaki Shibayama, Seiichi Watanabe, Jie Zhou, Zhaoping Lu, Yang Ren, X. -L.Wang
    Intermetallics 105 105 173 - 178 2019年01月 [査読有り][通常論文]
     
    A well-designed experimental method has been presented to in-situ visualize the amorphous-to-crystalline phase transformation of two glass formers at the atomic length scale in the supercooled liquid region using a high voltage electron microscopy (HVEM). Analysis of the HVEM high-resolution images, supported by the in situ synchrotron diffraction, further confirms previous observations of distinctively different crystallization pathways in the two Zr-Cu-Al alloys. Moreover, the HVEM results illustrate that isolated distributed nanocrystals with mutual orientation easily grew up from the Zr56Cu36Al8, an average glass former, which follows a classical crystallization pathway; while density population poorly ordered atomic clusters with large misorientation suspended the growth in the Zr46Cu46Al8, a good glass former, which might follow an unusual crystallization pathway. In addition, in-situ synchrotron diffraction measurements confirm that the Zr56Cu36Al8 alloy finally crystallized into an extended structure, in contrast, the final crystalline product of Zr46Cu46Al8 alloy possesses a damped structure. Our study provides a detailed microscopic understanding of the crystallization behaviors in the supercooled liquids, showing that the density population nucleation site with large misorientation and the confined final crystalline structure contribute to the stability of Zr-Cu-Al supercooled liquids.
  • Lihua Zhang, Melbert Jeem, Kazumasa Okamoto, Seiichi Watanabe
    Scientific Reports 8 1 177  2018年12月01日 [査読有り][通常論文]
     
    Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO nanostructures have been successfully fabricated via this method. However, the photochemical reactions involved in the SPSC process and especially the role of light are still unclear. In the present work, we discuss the reaction mechanism for SPSC-fabricated ZnO nanostructures in detail and clarify the role of light in SPSC. The results show that both photoinduced reactions and hydrothermal reactions are involved in the SPSC process. The former produces OH radicals, which is the main source of OH - at the ZnO crystal tips, whereas the latter generates ZnO. Although ZnO nanocrystals can be obtained under both UV irradiation and dark conditions with the addition of thermal energy, light promotes ZnO growth and lowers the water pH to neutral, whereas thermal energy promotes ZnO corrosion and increases the water pH under dark conditions. The study concludes that the role of light in the submerged photosynthesis of crystallites process is to enhance ZnO apical growth at relatively lower temperature by preventing the pH of water from increasing, revealing the environmentally benign characteristics of the present process.
  • Xu Y, Cheng J, Yiu PM, Shan G, Shibayama T, Watanabe S, Ohnuma M, Shek CH
    Nanoscale 10 39 18846 - 18856 2018年10月 [査読有り][通常論文]
     
    Current fabrication methods of nanoporous gold (NPG) mainly rely on dealloying Ag-Au binary crystalline precursors, typically Ag65Au35, with the "dealloying threshold" or "parting limit" above 55 at%. Here we report a simple chemical dealloying process, through selective dissolution of one element from a Au55Cu25Si20 metallic glass ribbon with low 'parting limit', and a novel peculiar three-dimensional 'cone shaped protrusion' nanoporous structure which has never been reported before. In this structure, a metastable gold silicide formed in the initial dealloying stage was decomposed into gold nanoparticles and amorphous SiOx in the later coarsening stage. Our finding provides insights into the underlying relationship between 'parting limit' and atomic level structure of metallic glass. Comprehensive discussions on the porosity evolution stages as well as the correlation between the porous 'cone shaped protrusion' development and potential energy landscape are made in this report. The fabricated 3D NPG also exhibited excellent electro-oxidation catalytic ability attributed to the high density of low-coordinated atomic sites provided by the gold particle inside of 'cone shaped protrusion'.
  • Shuichiro Adachi, Takeshi Nojiri, Takahiko Kato, Seiichi Watanabe, Masato Yoshida
    Journal of Alloys and Compounds 757 757 333 - 339 2018年08月15日 [査読有り][通常論文]
     
    In this paper, we show the first production of Cu-based electrode materials including self-assembled barrier layers which can prevent Cu-Si inter-diffusion during sintering and are expected to be applicable to crystalline Si photovoltaics. The characteristics of electrodes produced by mixed Cu-P/Sn pastes at various compositions were evaluated. Electrodes sintered in an atmospheric environment showed electrical resistivity of below 1 × 10−4 Ω・cm. In addition, the formation of compounds such as Cu3Si at the Si surface was prevented with a Sn particle ratio ranging between 20 and 60 wt%. The structural analysis revealed that the electrode included not only a Cu-Sn IMCs network but also a self-assembled Sn-P-O glass phase between the Cu-Sn IMCs network and the Si substrate, capable of forming a barrier layer to prevent Cu-Si inter-diffusion. These results may enable the widespread use of atmospherically sintered Cu-based electrode for the mass production of next-generation crystalline Si solar cells. Subsequently, the manner in which the Sn-P-O glasses were formed was discussed using a thermos-dynamical approach.
  • Yutaka Yoshida, Ko Ohnishi, Yasutaka Matsuo, Seiichi Watanabe
    AIP Advances 8 4 045122  2018年04月01日 [査読有り][通常論文]
     
    For design the patterned nanostructure array (PNSA) on material surface using a nanosecond pulsed laser, we investigated the influence of phase shift between scattered lights on silicon (Si) substrate using 30-nm-wide gold lines (GLs) spacings. At a spacing of 5,871 nm, ten nanodot (ND) arrays were formed at intervals of 533 nm by nanosecond pulsed laser. The results show that the formation of the PNSA was affected by the resonance of scattered light. We conclude that ND arrays were formed with a spacing of Λ = nλ. And we have designed PNSA comprising two ND arrays on the substrate. The PNSA with dimensions of 1,600 nm × 1,600 nm was prepared using GLs.
  • Rafiq Mirza BIN JULAIHI Muhammad, Peter Nai Yuh Yek, Shigeo Yatsu, Seiichi Watanabe
    ISIJ International 58 6 1162 - 1167 2018年 [査読有り][通常論文]
     
    Stainless steel has shown potential as a catalytic material in bulk form. However, it only becomes active in an aqueous acidic environment and elevated temperatures. This study aims to produce stainless steel nanoparticles that have high photocatalytic activity in a neutral medium and at room temperature and to elucidate the photocatalytic activity mechanism of the nanoparticles. Spherical, photocatalytic nanoparticles called “nanoballs” were synthesized by the submerged glow-discharge method. Stainless steel SUS316L grade wire was used as the cathode, platinum mesh was used as the anode while the electrolyte was potassium carbonate. The nanoballs were obtained after centrifuging and washing with water. The physical characteristics of the photocatalytic nanoballs were analysed by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. The nanoballs were mixed with methylene blue and irradiated with ultraviolet light for the evaluation of photocatalytic reaction. The photodecomposition samples were determined using UV-vis spectrometry. The by-products of the photodecomposition were evaluated using mass spectrometry. The results show that stainless steel nanoballs have photocatalytic activity when irridiated with ultraviolet light at room temperature. Submerged glow-discharge plasma method can synthesize nanoparticles rapidly using only metal wires as the electrode.
  • Yi Xu, Pak Man Yiu, Guangcun Shan, Tamaki Shibayama, Seiichi Watanabe, Masato Ohnuma, Wei Huang, Chan-Hung Shek
    ChemNanoMat 4 1 88 - 97 2018年 [査読有り][通常論文]
     
    Nanoporous gold (NPG) with bi-continuous ligaments and pores structure has promising potential in functional applications, among which one prominent example is fuel cell electrocatalysts. However, current application of NPG is mostly limited to methanol electro-oxidation (MOR) due to its weak catalytic performance. Here we report a simple chemical dealloying process for generating peculiar three-dimensional (3D) free-standing NPG with ‘parting limit’ as low as 25 % (lower than theoretical ‘paring limit’ 55 %) and high specific surface area (maximum ≈31 m2 g−1) associated with a novel porous ‘cone shaped protrusion’ morphology. This NPG structure possesses the highest specific activity of MOR catalytic performance reported NPG catalysts so far. In addition, taking advantage of this excellent structural feature of the NPG, a nanoporous Pd catalyst (NPG@Pd) thin film was fabricated on the NPG substrate. The NPG@Pd catalyst exhibited greatly enhanced MOR performance (maximum MOR specific activity 2.14 mA cm−2). We attribute the enhancement of MOR activity to the increase of active sites as well as the modification of surface composition and electronic structure due to migration of Au to the Pd thin film layer.
  • Yutaka Yoshida, Shigeo Yatsu, Seiichi Watanabe, Akira Yamauchi, Jun-ichi Shibano
    Journal of Physics and Chemistry of Solids 109 46 - 49 2017年10月 [査読有り][通常論文]
     
    The composite consists of disordered and ordered iron platinum (FePt) alloys was induced by nanosecond pulsed laser (NPL) irradiation. The process was investigated by laser high-voltage electron microscopy (laser-HVEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses. The structural transformation upon NPL irradiation was monitored by laser-HVEM imaging, with the structure being modified in a short second after the one pulse. XRD analyses revealed expanded and contracted lattice distances before and after NPL irradiation, respectively. According to the XRD and TEM results, the surface of FePt alloys was transformed from fct to fcc structure with structural strain by NPL irradiation.
  • Xuan Meng, Tamaki Shibayama, Ruixuan Yu, Junya Ishioka, Seiichi Watanabe
    CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE 21 4 177 - 188 2017年08月 [査読有り][招待有り]
     
    Noble metal nanoparticles strongly adhered to dielectric matrices have been extensively studied because of their potential applications in plasmonic devices based on tunable localized surface plasmon (LSP) excitation. Compared with conventional synthesis methods, the noble metal nanoparticles formed by ion-beam irradiation draw significant interest in recent years because a single layer dispersion of nanoparticles strongly bonded on the dielectric substrate can be obtained. In this paper, important phenomena related to ion-beam surface nanostructuring including ion-induced reshaping of metal nanoparticles, ion-induced core-satellite structure formation, and ion-induced burrowing of these nanoparticles are discussed, with their individual effects on LSP excitation. Consequently, ion-induced surface nanostructuring of Ag-Au bimetallic films on amorphous silica glass and sapphire with tunable LSP excitation are presented. In addition, theoretical studies of far-field and near-field optical properties of these nanoparticles under ion irradiation are introduced, and the enhanced localized electric field (hot spot) is interpreted. Finally, the futures and challenges of the emerging plasmonic applications based on tunable LSP excitations in bio-sensing and surface enhanced Raman spectroscopy (SERS) are presented. (C) 2017 Elsevier Ltd. All rights reserved.
  • Ruixuan Yu, Tamaki Shibayama, Junya Ishioka, Xuan Meng, Yanhua Lei, Seiichi Watanabe
    NANOTECHNOLOGY 28 27 2017年07月 [査読有り][通常論文]
     
    The in situ observation of Au dot formation and the self-assembly dynamics of Au nanoparticles (NPs) was successfully demonstrated via dewetting of Au thin films on SiO2 glass substrates under nano-second pulsed laser irradiation using a multi-quantum beam high-voltage electron microscope. Moreover, using electron energy-loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM), the plasmonic properties of the formed Au/SiO2 nanostructure were analyzed to demonstrate its validity in advanced optical devices. The uniformly distributed Au NPs evolved into a dot alignment through movement and coalescence processes was demonstrated in this in situ observation. We carried out the plasmon-loss images of the plan view and the cross-section of the Au/SiO2 nanostructures were obtained at the plasmon-loss peak energy for investigate the three-dimensional distribution of surface plasmon. Furthermore, discrete-dipole approximation (DDA) calculations were used to simulate the plasmonic properties, such as the surface plasmon resonance and the surface plasmon field distribution, of isolated single Au/SiO2 nanostructures. This STEM-EELS-acquired surface plasmon map of the cross-sectional sample is in excellent agreement with the DDA calculations. This results demonstrated the influence of the contact condition between Au NP and SiO2 glass on the plasmonic properties, and may improve the technology for developing advanced optical devices.
  • Subing Yang, Zhanbing Yang, Hui Wang, Seiichi Watanabe, Tamaki Shibayama
    JOURNAL OF NUCLEAR MATERIALS 488 215 - 221 2017年05月 [査読有り][通常論文]
     
    Large amounts of void swelling still limit the application of austenitic stainless steels in nuclear reactors due to radiation-induced lattice point defects. In this study, laser and/or beam irradiation was conducted in a temperature range of 573-773 K to explore the suppression of void swelling. The results show that during sequential laser-electron beam irradiation, the void nucleation is enhanced because of the vacancy clusters and void nuclei formed under pre-laser irradiation, causing greater void swelling than single electron beam irradiation. However, simultaneous laser-electron dual-beam irradiation exhibits an obvious suppression effect on void swelling due to the enhanced recombination between interstitials and vacancies in the temperature range of 573-773 K; especially at 723 K, the swelling under simultaneous dual-beam irradiation is 0.031% which is only 22% of the swelling under electron beam irradiation (0.137%). These results provide new insight into the suppression of void swelling during irradiation. (C) 2017 Elsevier B.V. All rights reserved.
  • Fumika Nishino, Melbert Jeem, Lihua Zhang, Kazumasa Okamoto, Satoshi Okabe, Seiichi Watanabe
    SCIENTIFIC REPORTS 7 1 1063  2017年04月 [査読有り][通常論文]
     
    We report the fabrication of flower-like CuO nanostructured surfaces via submerged photo-synthesis of crystallites (SPSC), which requires only UV illumination in neutral water. In this paper, we discuss the reaction mechanism of the photochemical formation of the SPSC-fabricated CuO nanostructures in detail based on surface microstructural analyses and a radiation-chemical consideration with additional gamma-ray irradiation. Since the SPSC method for surface nanostructural fabrication can work at low temperatures at atmospheric pressure without using harmful substances, it is a potential fabrication method for green nanotechnology applications. In this vein, the antibacterial activity of the nano-flowered CuO surfaces was tested against Gram-positive (Staphylococcus aureus) bacteria and Gram-negative (Escherichia coli K12) bacteria, and the results demonstrate that the nano-flowered CuO nanostructures act as an effective antimicrobial agent.
  • J. Ishioka, K. Kogure, K. Ofuji, K. Kawaguchi, M. Jeem, T. Kato, T. Shibayama, S. Watanabe
    AIP ADVANCES 7 3 035220  2017年03月 [査読有り][通常論文]
     
    ZnO photocatalysts in water react with environmental water molecules and corrode under illumination. ZnO nanorods in water can also grow because of water splitting induced by UV irradiation. To investigate their morphological behavior caused by crystal growth and corrosion, here we developed a new laser-equipped high-voltage electron microscope and observed crystal ZnO nanorods immersed in ionic liquid. Exposing the specimen holder to a laser with a wavelength of 325 nm, we observed the photo-corrosion in situ at the atomic scale for the first time. This experiment revealed that Zn and O atoms near the interface between the ZnO nanorods and the ionic liquid tended to dissolve into the liquid. The polarity and facet of the nanorods were strongly related to photocorrosion and crystal growth. (C) 2017 Author(s).
  • S. Lan, Y. Ren, X. Y. Wei, B. Wang, E. P. Gilbert, T. Shibayama, S. Watanabe, M. Ohnuma, X. -L. Wang
    NATURE COMMUNICATIONS 8 14679  2017年03月 [査読有り][通常論文]
     
    An anomaly in differential scanning calorimetry has been reported in a number of metallic glass materials in which a broad exothermal peak was observed between the glass and crystallization temperatures. The mystery surrounding this calorimetric anomaly is epitomized by four decades long studies of Pd-Ni-P metallic glasses, arguably the best glass-forming alloys. Here we show, using a suite of in situ experimental techniques, that Pd-Ni-P alloys have a hidden amorphous phase in the supercooled liquid region. The anomalous exothermal peak is the consequence of a polyamorphous phase transition between two supercooled liquids, involving a change in the packing of atomic clusters over medium-range length scales as large as 18 angstrom. With further temperature increase, the alloy reenters the supercooled liquid phase, which forms the room-temperature glass phase on quenching. The outcome of this study raises a possibility to manipulate the structure and hence the stability of metallic glasses through heat treatment.
  • Melbert Jeem, Lihua Zhang, Junya Ishioka, Tamaki Shibayama, Tomio Iwasaki, Takahiko Kato, Seiichi Watanabe
    NANO LETTERS 17 3 2088 - 2093 2017年03月 [査読有り][通常論文]
     
    When applied in optoelectronic devices, a ZnO semiconductor dominantly absorbs or emits ultraviolet light because of its direct electron transition through a wide energy bandgap. On the contrary, crystal defects and nanostructure morphology are the chief key factors for indirect, interband transitions of ZnO optoelectronic devices in the visible light range. By ultraviolet illumination in ultrapure water, we demonstrate here a conceptually unique approach to tune the shape of ZnO nanorods from tapered to capped end via apical surface morphology control. We show that oxygen vacancy point defects activated by excitonic effects near the tip-edge of a nanorod serve as an optoelectrical hotspot for the light-driven formation and tunability of the optoelectrical properties. A double increase of electron energy absorption on near band edge energy of ZnO was observed near the tip-edge of the tapered nanorod. The optoelectrical hotspot explanation rivals that of conventional electrostatics, impurity control, and alkaline pH control-associated mechanisms. Thus, it highlights a new perspective to understanding light-driven nanorod formation in pure neutral water.
  • Tadashi Fujieda, Hiroshi Shiratori, Kosuke Kuwabara, Mamoru Hirota, Takahiko Kato, Kenta Yamanaka, Yuichiro Koizumi, Akihiko Chiba, Seiichi Watanabe
    MATERIALS LETTERS 189 148 - 151 2017年02月 [査読有り][通常論文]
     
    We succeeded in fabricating a Co1.5CrFeNi1.5Ti0.5Mo0.1 high entropy alloy with superior tensile strength and corrosion resistance by a combination of additive manufacturing using selective electron beam melting (SEBM) and solution treatment (ST). The SEEM specimens exhibited superior tensile properties to those of the corresponding casting specimen. Furthermore, the tensile properties and corrosion properties of the SEEM specimens markedly improved by ST. These notable improvements are ascribed to homogeneous precipitation of very fine particulate ordering-phase particles whose diameters are several tens of nanometers with Ni and Ti concentrations. The solution-treated SEBM specimens also exhibited both high strength and high pitting potential, which in combination are superior to the conventional alloys used in severe corrosion environments.
  • Shuichiro Adachi, Yutaka Yoshida, Takeshi Nojiri, Takahiko Kato, Seiichi Watanabe, Masato Yoshida
    Journal of Alloys and Compounds 695 3353 - 3359 2017年02月 [査読有り][通常論文]
     
    In this study, we propose a reaction mechanism for atmospherically sintered copper-phosphorus (CueP) alloy electrodes which are expected to replace silver (Ag) electrodes. Structural analysis using transmission electron microscopy (TEM) has revealed that not only copper phosphide (Cu3P) but also copper phosphates of Cu2P2O7, Cu-3(PO4)(2) and Cu2PO4 distributed mainly at the P-concentrated region of the metallic part, where Cu3P distributed before sintering. In addition, the ordered superstructures which have a period based on the specific lattice spacing of Cu3P {002} were newly discovered. From structural analysis, we estimated the mechanisms comprised of the decomposition of Cu3P accompanied by a lack of Cu and P, then formation of metastable phases involving structural vacancies, and eventual transition to the copper phosphates. We also discussed another manner of forming the copper phosphates by the thermo-dynamical approach. Our results may provide a way to reduce the electrical resistivity of Cu-P alloy electrodes by controlling the structures including the deoxidized Cu. (C) 2016 Elsevier B.V. All rights reserved.
  • Y. H. Lei, R. X. Yu, T. Shibayama, J. Ishioka, S. Watanabe
    MATERIALS LETTERS 164 164 202 - 205 2016年02月 [査読有り][通常論文]
     
    Herein is reported the dots alignment of Au nano-submicron particles (Au-NPs) on a chemical vapor-deposited beta-SiC substrate through nanosecond-pulsed laser irradiation-induced dewetting of an Au thin film, which was successfully observed by in-situ high-voltage electron microscopy. The initial stages of the Au-NPs array arrangement were also successfully observed, and long-range quasi-two-dimensional Au-NPs arrangements were found after laser irradiation. Moreover, the effect of Rayleigh instability to form multiple Au-NPs in each line of the network structure after the hole growth in the Au thin film was confirmed. (C) 2015 Elsevier B.V. All rights reserved.
  • Mari Miyano, Yuichi Kitagawa, Satoshi Wada, Akira Kawashima, Ayako Nakajima, Takayuki Nakanishi, Junya Ishioka, Tamaki Shibayama, Seiichi Watanabe, Yasuchika Hasegawa
    PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES 15 1 99 - 104 2016年 [査読有り][通常論文]
     
    Luminescent silicon nanoparticles have attracted considerable attention for their potential uses in various applications. Many approaches have been reported to protect the surface of silicon nanoparticles and prevent their easy oxidation. Various air-stable luminescent silicon nanoparticles have been successfully prepared. However, the effect of interactions of the pi-electron system with the silicon surface on the excited state properties of silicon nanoparticles is unclear. In this study, we have successfully prepared silicon nanoparticles protected with three organic compounds (styrene, 1-decene, and 1-vinyl naphthalene) and have examined their photophysical properties. The ligand pi-electron systems on the silicon surface promoted the light harvesting ability for the luminescence through a charge transfer transition between the protective molecules and silicon nanoparticles and also enhanced the radiative rate of the silicon nanoparticles.
  • In-Situ TEM Observation of Dynamic Nehavior of Metal-Based Nanoparticles in Ionic Liquid
    K. Kogure, J. Ishioka, K. Ofuji, R. Mirza, S. Yatsu, T. Shibayama, S. Watanabe
    Extended abstract of 2015 international Conference on Solid State Devices and Materials 2015年09月 [査読有り][通常論文]
  • Shuichiro Adachi, Yutaka Yoshida, Takeshi Nojiri, Yasushi Kurata, Takahiko Kato, Seiichi Watanabe, Masato Yoshida
    IEEE Journal of Photovoltaics 5 5 1325 - 1334 2015年09月 [査読無し][通常論文]
     
    In this study, we evaluate the atmospheric sintering behavior and characteristics of electrodes produced by copper-phosphorus (Cu-P) alloy paste containing various amounts of B2O3-Bi2O3-SiO2 glass frits. We demonstrate the need for a certain extent of glass frits to expand the applicable temperature for use of Cu-P alloy paste shifted to the higher temperature side, where commercial pastes for crystalline silicon (Si) photovoltaics are sintered, although the minimum electrical resistivity of the Cu-P alloy electrode increased by increasing the amount of glass frits. Based on the characteristics of the Cu-P alloy electrode, the need to expand the Cu crystal network and prevent the oxidization of generated Cu has emerged to reduce electrical resistivity. A crystalline BiPO4 was formed in the sintered Cu-P alloy electrode, which suggests a reaction between partially crystallized glass frits and P2O5 generated from Cu-P-O glass derived from the Cu-P alloy that has occurred. Subsequently, the sintering behavior of Cu-P alloy paste, including the glass frits, was discussed based on the results of X-ray diffraction, transmission electron microscopy, scanning transmission electron microscopy energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy.
  • Muhammad Rafiq Mirza bin Julaihi, Shigeo Yatsu, Melbert Jeem, Seiichi Watanabe
    JOURNAL OF EXPERIMENTAL NANOSCIENCE 10 12 965 - 982 2015年08月 [査読有り][通常論文]
     
    Stainless steel nanoparticles or 'nanoballs' have been synthesised using submerged glow-discharge plasma. Transmission electron microscopy showed that the nanoballs are uniformly spherical and size distribution estimation showed that their diameters are below 200nm. The decomposition of methylene blue solution under ultraviolet light with the wavelength of 354nm was observed in the presence of stainless steel nanoballs. A mixture of stainless steel nanoballs and 0.1% methylene blue dye was irradiated with ultraviolet light. The concentration of methylene blue was reduced to baseline level in 72hours. This shows that the stainless steel nanoballs have photocatalytic ability. In stainless steel nanoballs, methylene blue showed two different decomposition pathways; showing fast and slow reactions. Also, methylene blue was oxidised into sulphoxide before reducing into lighter by-products. X-ray diffraction analysis has shown that the nanoballs consist of Fe2O3 and Cr2O3, which are photocatalytically active species.
  • Muhammad Rafiq Mirza bin Julaihi, Shigeo Yatsu, Melbert Jeem, Seiichi Watanabe
    JOURNAL OF EXPERIMENTAL NANOSCIENCE 10 12 965 - 982 2015年08月 [査読有り][通常論文]
     
    Stainless steel nanoparticles or 'nanoballs' have been synthesised using submerged glow-discharge plasma. Transmission electron microscopy showed that the nanoballs are uniformly spherical and size distribution estimation showed that their diameters are below 200nm. The decomposition of methylene blue solution under ultraviolet light with the wavelength of 354nm was observed in the presence of stainless steel nanoballs. A mixture of stainless steel nanoballs and 0.1% methylene blue dye was irradiated with ultraviolet light. The concentration of methylene blue was reduced to baseline level in 72hours. This shows that the stainless steel nanoballs have photocatalytic ability. In stainless steel nanoballs, methylene blue showed two different decomposition pathways; showing fast and slow reactions. Also, methylene blue was oxidised into sulphoxide before reducing into lighter by-products. X-ray diffraction analysis has shown that the nanoballs consist of Fe2O3 and Cr2O3, which are photocatalytically active species.
  • Melbert Jeem, Muhammad Rafiq Mirza bin Julaihi, Junya Ishioka, Shigeo Yatsu, Kazumasa Okamoto, Tamaki Shibayama, Tomio Iwasaki, Takahiko Kato, Seiichi Watanabe
    SCIENTIFIC REPORTS 5 11429  2015年06月 [査読有り][通常論文]
     
    We report a new production pathway for a variety of metal oxide nanocrystallites via submerged illumination in water: submerged photosynthesis of crystallites (SPSC). Similar to the growth of green plants by photosynthesis, nanocrystallites shaped as nanoflowers and nanorods are hereby shown to grow at the protruded surfaces via illumination in pure, neutral water. The process is photocatalytic, accompanied with hydroxyl radical generation via water splitting; hydrogen gas is generated in some cases, which indicates potential for application in green technologies. Together with the aid of ab initio calculation, it turns out that the nanobumped surface, as well as aqueous ambience and illumination are essential for the SPSC method. Therefore, SPSC is a surfactant-free, low-temperature technique for metal oxide nanocrystallites fabrication.
  • Xuan Meng, Tamaki Shibayama, Ruixuan Yu, Junya Ishioka, Seiichi Watanabe
    AIP ADVANCES 5 2 027112  2015年02月 [査読有り][通常論文]
     
    The influence of a directly adjacent or an anisotropic surrounding medium alters the plasmonic properties of a nanoparticle because it provides a mechanism for symmetry breaking of the scattering. Given the success of ion irradiation induced embedment of rigid metallic nanospheroids into amorphous substrate, it is possible to examine the effect of the silica glass substrate on the plasmonic properties of these embedded nanospheroids. In this work presented here, discrete dipole approximation (DDA) calculations for the Au nanospheroids' optical properties were performed based on 3-dimensional (3D) configuration extracted from planar SEM micrographs and cross-sectional TEM micrographs of the Au nanospheroids partially embedded in the silica glass, and the well-matched simulations with respect to the experimental measurements could demonstrate the dielectric constant at the near surface of silica glass decreased after Ar-ion irradiation. (C) 2015 Author(s).
  • Yutaka Yoshida, Seiichi Watanabe, Hideo Kaiju, Junji Nishii, Kyosuke Yoshimi
    JOURNAL OF APPLIED PHYSICS 117 4 045305-045305-5  2015年01月 [査読無し][通常論文]
     
    We investigate the laser wavelength dependence of structural and magnetic transitions on the surface of an iron-aluminum (FeAl) alloy induced by nanosecond pulsed laser irradiation. The formation of self-organized FeAl stripes with a wavelength-dependent period is observed in a local area on the (111)-oriented plane. Focused magneto-optical Kerr effect measurements reveal that the coercivity reaches up to 1.2 kOe with increasing the magnetic field rotation angle, which is estimated from the stripe direction, in FeAl stripes irradiated at 355 nm, and its magnetization reversal can be explained by the domain-wall motion model. On the other hand, the magnetization reversal agrees with the Stoner-Wohlfarth model in FeAl stripes irradiated at 1064 nm. This magnetic transition originates from the B2-to-A2 phase transition in stripe structures and bulk regions. These results indicate that the magnetic transition from the incoherent to coherent mode as well as the structural transformation of stripe patterns can be controlled by the incident laser wavelength. (C) 2015 AIP Publishing LLC.
  • 柴山環樹, 渡辺精一
    軽金属 64 12 654 - 662 軽金属学会 2014年12月30日 [査読無し][通常論文]
  • H. Kaiju, Y. Yoshida, S. Watanabe, K. Kondo, A. Ishibashi, K. Yoshimi
    Journal of The Magnetics Society of Japan 38 4 157 - 161 The Magnetics Society of Japan 2014年08月 [査読有り][通常論文]
     
    We investigate magnetic properties of FeAl stripes and dots formed on the surface of Fe52Al48 induced by nanosecond pulsed laser irradiation. According to the in-plane magneto-optical Kerr effect (MOKE) measurements, the magnetization reversal in FeAl stripes can be explained by the domain-wall (DW) motion model, indicating that the magnetization rotates incoherently. In contrast, the in-plane and polar MOKE measurements reveal that the magnetic easy axis of the FeAl dots exists along the out-of-plane direction and the coercive force Hc shows as large as 1 kOe. These results indicate that the nanosecond pulsed laser irradiation can be expected to serve as a useful tool for obtaining magnetic nanostructures and creating high-Hc materials.
  • Yutaka Yoshida, Kazuya Oosawa, Jyunya Wajima, Seiichi Watanabe, Yasutaka Matsuo, Takahiko Kato
    APPLIED SURFACE SCIENCE 307 24 - 27 2014年07月 [査読無し][通常論文]
     
    We report a technique for formation of two-dimensional (2D) nanodot (ND) patterns on gaillium antimoide (GaSb) using a nanosecond pulsed laser irradiation with 532 nm wavelength. The patterns have formed because of the interference and the self-organization under energy deposition of the laser irradiation, which induced the growth of NDs on the local area. The NDs are grown and shrunken in the pattern by energy depositions. In the laser irradiation with average laser energy density of 35 mJ cm(-2), large and small NDs are formed on GaSb surface. The large NDs have grown average diameter from 160 to 200 nm with increase of laser pulses, and the small NDs have shrunken average diameter from 75 to 30 nm. The critical dot size is required about 107 nm for growth of the NDs in the patterns. Nanosecond pulsed laser irradiation can control the self-organized ND size on GaSb in air as a function of the laser pulses. (c) 2014 Elsevier B.V. All rights reserved.
  • H. Kaiju, Y. Yoshida, S. Watanabe, K. Kondo, A. Ishibashi, K. Yoshimi
    JOURNAL OF APPLIED PHYSICS 115 17 17B901  2014年05月 [査読有り][通常論文]
     
    We demonstrate the formation of magnetic nanostripes on the surface of Fe52Al48 induced by nanosecond pulsed laser irradiation and investigate their magnetic properties. The magnetic stripe consists of a disordered A2 phase of Fe-Al alloys with Al-oxide along the [110] direction on the (111)-oriented plane. According to the focused magneto-optical Kerr effect measurement, the coercive force of the magnetic stripe obeys the 1/cos theta law, where theta is the field rotation angle estimated from the stripe direction. Also, the jump field can be observed in the magnetic hysteresis loop. These results indicate that the magnetization reversal in the magnetic stripe originates from the domain pinning, showing that the magnetization rotates incoherently. (C) 2014 AIP Publishing LLC.
  • Ruixuan Yu, Tamaki Shibayama, Xuan Meng, Shinya Takayanagi, Shigeo Yatsu, Junya Ishioka, Seiichi Watanabe
    JOURNAL OF APPLIED PHYSICS 115 14 143104-143104-8  2014年04月 [査読無し][通常論文]
     
    Ion irradiation and short-pulsed laser irradiation can be used to form nanostructures on the surfaces of substrates. This work investigates the synergistic effects of ion and nanosecond-pulsed laser co-irradiation on surface nanostructuring of Au thin films deposited under vacuum on SiO2 glass substrates. Gold nanoparticles are randomly formed on the surface of the substrate after nanosecond-pulsed laser irradiation under vacuum at a wavelength of 532 nm with a repetition rate of 10 Hz and laser energy density of 0.124 kJ/m(2). Gold nanoparticles are also randomly formed on the substrate after 100-keV Ar+ ion irradiation at doses of up to 3.8 x 10(15) ions/cm(2), and nearly all of these nanoparticles are fully embedded in the substrate. With increasing ion irradiation dose (number of incident laser pulses), the mean diameter of the Au nanoparticles decreases (increases). However, Au nanoparticles are only formed in a periodic surface arrangement after co-irradiation with 6000 laser pulses and 3.8 x 10(15) ions/cm(2). The periodic distance is similar to 540 nm, which is close to the wavelength of the nanosecond-pulsed laser, and the mean diameter of the Au nanoparticles remains at similar to 20 nm with a relatively narrow distribution. The photoabsorption peaks of the ion-or nanosecond-pulsed laser-irradiated samples clearly correspond to the mean diameter of Au nanoparticles. Conversely, the photoabsorption peaks for the co-irradiated samples do not depend on the mean nanoparticle diameter. This lack of dependence is likely caused by the periodic nanostructure formed on the surface by the synergistic effects of co-irradiation. (C) 2014 AIP Publishing LLC.
  • Ruixuan Yu, Tamaki Shibayama, Xuan Meng, Shinya Takayanagi, Yutaka Yoshida, Shigeo Yatsu, Seiichi Watanabe
    APPLIED SURFACE SCIENCE 289 274 - 280 2014年01月 [査読無し][通常論文]
     
    In this study, we investigated nanostructure formations on the surface of Au thin films deposited on SiO2 glass substrates after nanosecond-pulsed laser irradiation, also the correlation between the nanostructures parameters and the photoabsorption peak. Spherical Au nanoparticle/SiO2 glass nanocomposites were formed on the surface of the Au thin films deposited on the SiO2 glass substrates after nanosecondpulsed laser irradiation in air with a wavelength of 532 nm at a repetition rate of 2 Hz and a laser energy density of 0.7 kJ/m(2). Au nanoparticles were periodically arranged on the substrates under laser irradiation perpendicular to the direction of the electrical field vector of the laser light, the average diameter of Au nanoparticles was increased from 59.3 to 67.4 nm and the average distance of the laser induced periodical structure was decreased from 1.3 to 1.0 mu m as the number of laser pulses increased from 1000 to 1500. After 2000 pulses irradiation, an additional laser irradiation induced periodical structure was formed in the direction parallel to the electrical field vector of the laser. The average periodicity of this nanostructure perpendicular to the initial nanostructure was 560 nm, which is close to the wavelength of the nanosecond-pulsed laser used in this study. The average diameter of these Au nanoparticles is 41.9 nm which is smaller than that of the Au nanoparticles formed after 1000 pulses irradiation. Au nanoparticles were generally dispersed on the surface while some were embedded in the substrate. After 1500 pulses irradiation, the diameter of the Au nanoparticles on the Au(30 nm)/SiO2(0.8 mm) is relatively larger than that of the Au nanoparticles on the Au(20 nm)/SiO2(0.1 mm). Each of laser irradiated sample showed an own photoabsorption peak clearly in this study. Furthermore, effects of the average diameter of the Au nanoparticles on the photoabsorption peak are discussed. (C) 2013 Elsevier B.V. All rights reserved.
  • 鴇田 駿, 粉川 博之, 佐藤 裕, 藤井 啓道, 坂口 紀史, 柴山 環, 渡辺 精一
    溶接学会全国大会講演概要 2014 226 - 227 一般社団法人 溶接学会 2014年 
    ニッケル合金PE16への粒界工学の適用可能性を調査するために、ニッケル合金PE16にひずみ焼き鈍し法による粒界工学制御を行い、熱時効処理後の耐粒界腐食性の評価を行った。その結果、粒界工学の適用によりニッケル合金PE16の熱時効処理による耐粒界腐食性の低下を大幅に抑制することが示唆された。
  • Xuan Meng, Tamaki Shibayama, Ruixuan Yu, Shinya Takayanagi, Seiichi Watanabe
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 314 112 - 116 2013年11月 [査読無し][通常論文]
     
    Effects of Ar-ion induced surface nanostructuring were studied using 100 key Ar-ion irradiation of 30 nm Ag-Au bimetallic films deposited on Al2O3 single crystals, under irradiation fluences ranging from 5.0 x 10(15) cm(-2) to 6.3 x 10(16) cm(-2). Scanning electron microscope was used to study the ion-beam-induced surface nanostructuring. As the irradiation fluence increased, dewetting of the bimetallic films on the Al2O3 substrate was observed, and formation of isolated Ag-Au nanostructures sustained on the substrate were obtained. Next, thermal annealing was performed under high vacuum at 1073 K for 2 h; a layer of photosensitive Ag-Au alloy nanoballs partially embedded in the Al2O3 substrate was obtained when higher fluence irradiation (>3.8 x 10(16) cm(-2)) was used. The microstructures of the nanoballs were investigated using a transmission electron microscope, and the nanoballs were found to be single crystals with a FCC structure. In addition, photoabsorption spectra were measured, and localized surface plasmon resonance peaks were observed. With increase in the irradiation fluence, the size of the Ag-Au nanoballs on the substrate decreased, and a blue-shift of the LSPR peaks was observed. Further control of the LSPR frequency over a wide range was achieved by modifying the chemical components, and a red-shift of the LSPR peaks was observed as the Au concentration increased. In summary, ion irradiation is an effective approach toward surface nanostructuring, and the nanocomposites obtained have potential applications in optical devices. (C) 2013 Elsevier B.V. All rights reserved.
  • Akira Kawashima, Takayuki Nakanishi, Tamaki Shibayama, Seiichi Watanabe, Koji Fujita, Katsuhisa Tanaka, Hitoshi Koizumi, Koji Fushimi, Yasuchika Hasegawa
    CHEMISTRY-A EUROPEAN JOURNAL 19 43 14438 - 14445 2013年10月 [査読有り][通常論文]
     
    Remarkable magneto-optical properties of a new isolator material, that is, europium sulfide nanocrystals with gold (EuS-Au nanosystem), has been demonstrated for a future photo-information technology. Attachment of gold particles that exhibit surface plasmon resonance leads to amplification of the magneto-optical properties of the EuS nanocrystals. To construct the EuS-Au nanosystems, cubic EuS and spherical Au nanocrystals have been joined by a variety of organic linkers, that is, 1,2-ethanedithiol (EDT), 1,6-hexanedithiol (HDT), 1,10-decanedithiol (DDT), 1,4-bisethanethionaphthalene (NpEDT), or 1,4-bisdecanethionaphthalene (NpDDT). Formation of these systems was observed by XRD, TEM, and absorption spectra measurements. The magneto-optical properties of the EuS-Au nanosystem have been characterized by using Faraday rotation spectroscopy. The Faraday rotation angle of the EuS-Au nanosystem is dependent on the Au particle size and interparticle distance between EuS and Au nanocrystals. Enhancement of the Faraday rotation of EuS-Au nanosystems was observed. The spin configuration in the excited state of the EuS-Au nanosystem was also investigated using photo-assisted electron paramagnetic resonance.
  • Xuan Meng, Tamaki Shibayama, Ruixuan Yu, Shinya Takayanagi, Seiichi Watanabe
    JOURNAL OF APPLIED PHYSICS 114 5 054308-054308-9  2013年08月 [査読無し][通常論文]
     
    Ag-Au bimetallic nanospheroids with tunable localized surface plasmon resonance (LSPR) were synthesized by 100 keV Ar-ion irradiation of 30 nm Ag-Au bimetallic films deposited on SiO2 glass substrates. A shift of the LSPR peaks toward shorter wavelengths was observed up to an irradiation fluence of 1.0 x 10(17) cm(-2), and then shifted toward the longer wavelength because of the increase of fragment volume under ion irradiation. Further control of LSPR frequency over a wider range was realized by modifying the chemical components. The resulting LSPR frequencies lie between that of the pure components, and an approximate linear shift of the LSPR toward the longer wavelength with the Au concentration was achieved, which is in good agreement with the theoretical calculations based on Gans theory. In addition, the surface morphology and compositions were examined with a scanning electron microscope equipped with an energy dispersive spectrometer, and microstructural characterizations were performed using a transmission electron microscope. The formation of isolated photosensitive Ag-Au nanospheroids with a FCC structure partially embedded in the SiO2 substrate was confirmed, which has a potential application in solid-state devices. (C) 2013 AIP Publishing LLC.
  • Yutaka Yoshida, Kazuya Oosawa, Seiichi Watanabe, Hideo Kaiju, Kenji Kondo, Akira Ishibashi, Kyosuke Yoshimi
    APPLIED PHYSICS LETTERS 102 18 183109-1 - 183109 -4 2013年05月 [査読有り][通常論文]
     
    We have studied nanopatterns induced by nanosecond pulsed laser irradiation on (111) plane surfaces of a polycrystalline iron-aluminum alloy and evaluated their magnetic properties. Multiple nanosecond pulsed laser irradiation induces a wavelength-dependent surface transformation of the lattice structure from a B2-type to a supersaturated body centered cubic lattice. The selective formation of surface nanopatterns consisting of holes, stripes, polygonal networks, and dot-like nanoprotrusions can be observed. Furthermore, focused magneto-optical Kerr effect measurements reveal that the magnetic properties of the resultant nanostructured region changes from a paramagnetic to a ferromagnetic phase in accordance with the number of laser pulses. (C) 2013 AIP Publishing LLC.
  • Zhanbing Yang, Seiichi Watanabe
    ACTA MATERIALIA 61 8 2966 - 2972 2013年05月 [査読有り][通常論文]
     
    A high-voltage electron microscope (HVEM) equipped with a laser head (laser-HVEM) was developed at Hokkaido University and is used to investigate the surface modification of semiconductors and the behaviour of lattice point defects in metals under various irradiations of laser (photon) and/or electron beams. In the present study, the annealing effect of pulsed laser irradiation on a face-centred-cubic metal was experimentally investigated and theoretically calculated. The systematic assessment of dislocation loop evolution under laser-electron sequential irradiation and laser-electron dual-beam irradiation was performed. Our results show that the rapid heating and quenching that occurred during pulsed laser irradiation caused vacancies to be introduced at the surface of the specimen and to diffuse to the interior, which led to the formation and growth of vacancy-type (V-type) dislocation loops. These loops gradually shrank and finally disappeared during the subsequent electron irradiation of the sample. During laser-electron simultaneous dual-beam irradiation, the type of loop formed, interstitial-type (I-type) or V-type loops, is determined by the relative intensities of the laser beam and electron beam, which indicates that the loop type can be controlled by changing the relative intensities of the beams. Accordingly, models of dislocation loop formation during various irradiations were proposed. The newly developed laser-HVEM instrument is expected to be employed in the exploration of mechanisms in material science, as well as in other scientific fields. (c) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • N. Sakaguchi, M. Endo, S. Watanabe, H. Kinoshita, S.Yamashita, H.Kokawa
    J. Nuclear Materials 434 1-3 65 - 71 2013年03月 [査読有り][通常論文]
     
    The behavior of radiation-induced segregation (RIS) and intergranular corrosion at random grain boundaries and Sigma 3 coincidence site lattice (CSL) boundaries in proton-irradiated 316L stainless steel was examined. The frequency of the CSL boundaries was enhanced up to 86.6% by grain boundary engineering treatment prior to irradiation. Significant nickel enrichment and chromium depletion were induced at the random grain boundary owing to the RIS. At faceted Sigma 3 CSL boundaries, chromium depletion occurred at the asymmetrical boundary facet plane whereas no RIS was observed at the coherent twin boundary. After the electrochemical etching test, an intergranular corrosion groove was found along the random grain boundaries because of the low chromium concentration (similar to 12%) at the boundaries. At the faceted Sigma 3 CSL boundaries, the discontinuous groove along the asymmetric facet plane was completely disrupted by the non-corrosive coherent twin boundary. (C) 2012 Elsevier B.V. All rights reserved.
  • Zhanbing Yang, Seiichi Watanabe, Takahiko Kato
    SCIENTIFIC REPORTS 3 01201  2013年02月 [査読有り][通常論文]
     
    Randomly distributed lattice point defects such as supersaturated vacancies (SVs) and Frenkel-pairs (FPs, an interstitial and a vacancy) can be simultaneously introduced into the crystal by energetic beam irradiation in outer space and/or nuclear reactors, but their behavior has not been fully understood. Using a high-voltage electron microscope equipped with a laser (laser-HVEM), we show the striking effects of simultaneous laser-electron (photon-electron) dual-beam irradiation on void formation. Our results reveal that during laser-electron sequential irradiation, pre-laser irradiation enhanced void nucleation and subsequent electron irradiation enhanced void growth. However, the laser-electron dual-beam irradiation was analyzed to depress void swelling remarkably because the recombination of SVs and interstitials was enhanced. The results provide insight into the mechanism underlying the dual-beam radiation-induced depression of void swelling in solids.
  • Xuan Meng, Tamaki Shibayama, Ruixuan Yu, Shinya Takayanagi, Seiichi Watanabe
    JOURNAL OF MATERIALS SCIENCE 48 2 920 - 928 2013年01月 [査読有り][通常論文]
     
    Effects of the irradiation dose on surface nanostructuring accompanied with the dewetting process of Au films deposited on SiO2 glass were examined using an atomic force microscope and a scanning electron microscope. In addition, the microstructural evolution and the chemical concentration of Au films were investigated using a transmission electron microscope equipped with an energy-dispersive spectrometer. As increasing the Ar ion irradiation dose, the lattice expansion of Au nanoscale islands sustained on the SiO2 glass was observed and irradiation-induced lattice defects together with irradiation-induced interface ion mixing were accounted for this lattice expansion. Finally a layer of photosensitive Au nanoballs with highly spherical shape embedded in a SiO2 substrate was obtained after Ar ion irradiation to 10.0 x 10(16)/cm(2) and some of Au nanoballs were found to be single crystals. As the irradiation energy of the Ar ions increased from 100 to 150 keV, the average diameter of the Au nanoballs in the substrate increased and the red shift of the SPR peak was observed. This tendency of the experimental SPR peaks corresponded with that of the theoretically calculated SPR peaks using Mie solution.
  • N. Sakaguchi, Y. Ohguchi, T. Shibayama, S. Watanabe, H. Kinoshita
    J. Nuclear Materials 432 1-3 23 - 27 2013年01月 [査読有り][通常論文]
     
    The relationship between surface cracking at grain boundaries and the grain boundary nature in helium implanted 316L austenitic stainless steel was investigated by in situ annealing in a high-voltage electron microscope, and by SEM and TEM observations. The nucleation and growth of helium bubbles at a random grain boundary was observed during annealing up to 973 K. After annealing, surface cracking was observed at the random grain boundaries and some coincidence site lattice (CSL) boundaries because of the formation and rupture of the helium bubbles at these grain boundaries. At the faceted CSL boundaries, surface cracking occurred only on one boundary facet plane. This indicates that the twin boundary and pure tilt Sigma 9 CSL boundary show the highest resistance to cracking because of their low boundary energies. (c) 2012 Elsevier B.V. All rights reserved.
  • S. Yatsu, H. Takahashi, H. Sasaki, N. Sakaguchi, K. Ohkubo, T. Muramoto, S. Watanabe
    ARCHIVES OF METALLURGY AND MATERIALS 58 2 425 - 429 2013年 [査読有り][通常論文]
     
    The electric plasma discharge method involves the application of a voltage between a cathode and anode in a conductive electrolytic solution to create a discharge plasma at the cathode. When certain material is used as the cathode, small droplets are emitted with the plasma discharge, and the melted droplets are rapidly cooled in the solution to form nanoscale particles of the material. In this work, nanoparticles of Al, Au, Si, and various alloys of between 100 nm and less than 10 nm in size were produced and characterized. Characterization of Si nanoparticles is especially important because their use in lithium batteries greatly influences battery performance. It was found by high resolution electron microscopy and microstructural surface analysis that oxidation layers of a few nm in thickness were formed on the surface of the Si nanoparticles.
  • Shigeru Saito, Kenji Kikuchi, Dai Hamaguchi, Masao Tezuka, Masanori Miyagi, Hiroyuki Kokawa, Seiichi Watanabe
    J. Nuclear Materials 431 1-3 91 - 96 2012年12月 [査読有り][通常論文]
     
    To evaluate the lifetime of structural materials utilized in a spallation neutron source, corrosion tests in lead-bismuth eutectic (LBE) have been done at JAEA. Austenitic steels are preferable as the structural material for ADS. However, previous studies have revealed that austenitic steel SS316 shows severe corrosion-erosion in LBE because of LBE penetration through grain boundaries and separation of grains. So it was considered that GBE (grain-boundary engineered) materials may be effective to improve the corrosion resistance of austenitic steels in LBE. In this study, the results of corrosion tests on austenitic steel SS316L-BM (base metal) and SS316L-GBEM (grain-boundary-engineered material) under flowing LBE conditions will be reported. The corrosion test was performed using the JAEA lead-bismuth material corrosion loop (JLBL-1). The experimental conditions were as follows: The high and low temperature parts of the loop were 450 degrees C and 350 degrees C, respectively. The flow velocity at the test specimens was about 0.7 m/s. The oxygen concentration in LBE was not controlled and was estimated to have been very low. After the 3600 h of operation, macroscopic, SEM, and SIM observations and EDX analysis were carried out. The results showed that the corrosion depth and LBE penetration through the grain boundaries of the 316SS-GBEM were smaller than those of the 316S5-BM. (C) 2011 Elsevier B.V. All rights reserved.
  • Masayoshi Kawai, Hiroaki Kurishita, Hiroyuki Kokawa, Seiichi Watanabe, Norihito Sakaguchi, Kenji Kikuchi, Shigeru Saito, Toshimasa Yoshiie, Hiroshi Iwase, Takahiro Ito, Satoshi Hashimoto, Yoshihisa Kaneko, Masatoshi Futakawa, Shiori Ishino
    JOURNAL OF NUCLEAR MATERIALS 431 1-3 16 - 25 2012年12月 [査読無し][通常論文]
     
    This report describes the status review of the JSPS Grant Team to develop advanced materials for the spallation neutron sources and modeling of radiation damage. One of the advanced materials is a toughness enhanced, fine-grained tungsten material (W-TiC) having four-times larger fracture toughness than ordinary tungsten and appreciable RT ductility in the recrystallized state. The other is an intergranular crack (IGC)-resistant austenitic stainless steel which was processed by the grain-boundary engineering (GBE). The experimental results are devoted to corrosion in a lead-bismuth eutectic, arrest of corrosion of weld-decay, radiation damage and creep rupture as well as new technique of GEE using a laser and annealing procedure. New technique seems to be applicable to large or complicated-shaped components. A series of the multi-scale models is built up from nuclear reaction between incident particles and medium nuclei to material property change due to radiation damage. Sample calculation is made on 3 mm-thick nickel bombarded by 3 GeV protons. (C) 2011 Elsevier B.V. All rights reserved.
  • Zhanbing Yang, Norihito Sakaguchi, Seiichi Watanabe, Masayoshi Kawai
    SCIENTIFIC REPORTS 1 190 DOI:10.1038/srep00190  2011年12月 [査読無し][通常論文]
     
    Vacancies and interstitial atoms are primary lattice (point) defects that cause observable microstructural changes, such as the formation of dislocation loops and voids in crystalline solids. These defects' diffusion properties determine the phase stability and environmental resistibility of macroscopic materials under ambient conditions. Although in situ methods have been proposed for measuring the diffusion energy of point defects, direct measurement has been limited. In this study, we propose an alternative in situ method to measure the activation energy for vacancy migration under laser irradiation using a pulsed laser beam from a laser-equipped high-voltage electron microscope (laser-HVEM). We made in situ observations that revealed the formation and growth of vacancy dislocation loops in an austenitic stainless steel during laser irradiation. These loops continued to grow when thermal annealing was performed after laser irradiation at the same temperature. We anticipate that laser-HVEM will provide a new method for investigating lattice defects.
  • Genichiro Matsuoa, Tamaki Shibayamab, Hirotatsu Kishimotoc, Kouichi Hamadab, Seiichi Watanabe
    J. Nuclear Materials 417 1-3 391 - 394 2011年10月 [査読無し][通常論文]
     
    W and SiC joining has an attractive feature for high-temperature energy conversion systems. However, it is unclear and that is necessary to study the microstructure of the reaction phase between W and SIC by using the thermal diffusion bonding method. This work demonstrates the strengthening mechanism of W and SiC joining through a microstructure analysis of the reaction phase by FE-TEM/EDS and the observation of the interface in W and SiC after the crack propagation in HVEM. The reaction phase was amorphous, with a gap from 500 to 600 nm between W and SiC. Fine precipitates with a diameter of several tens nanometer were formed in the reaction phase. The reaction phase and precipitates did not match the chemical composition of the equilibrium compound. It is conceivable that the reaction phase and precipitates exist as a non-equilibrium condition before they reach equilibrium condition. (C) 2011 Elsevier B.V. All rights reserved.
  • Yutaka Yoshida, Seiichi Watanabe, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa, Takahiko Kato
    NANOTECHNOLOGY 22 37 375607-1-375607-7  2011年09月 [査読無し][通常論文]
     
    A gold/silicon nanocomposite structure (NCS) was formed on a Si(100) surface by nanosecond pulsed laser irradiation. The Au/Si NCS contained both Au nanoparticles (NPs) and Au-Si alloy layers. We report that the use of laser irradiation to form Au NPs comprises two competing processes: a top-down effect involving decomposition into smaller NPs and a bottom-up effect involving self-assembly or self-organization into larger NPs. The formation of the periodic structure involved self-organization, i.e., the bottom-up effect, and was observed in situ using a pulsed-laser-equipped high-voltage electron microscope. The NCS formed by laser irradiation can be controlled by adjusting the laser energy density and the number of laser pulses.
  • M. Sekine, N. Sakaguchi, M. Endo, H. Kinoshita, S. Watanabe, H. Kokawa, S. Yamashita, Y. Yano, M. Kawai
    JOURNAL OF NUCLEAR MATERIALS 414 2 232 - 236 2011年07月 [査読無し][通常論文]
     
    Austenitic stainless steel PNC316 was subjected to grain boundary engineering (GBE). It was found that the grain boundary engineered PNC316 (PNC316-GBEM) had a coincidence site lattice (CSL) fraction of 86% and that the network of random grain boundaries was perfectly divided by the CSL boundaries. The thermal stability and the void swelling behavior of PNC316-GBEM were investigated by means of SEM and TEM analyses. After thermal aging at 973 K for 100 h, structural changes were observed neither in the grain boundary networks of PNC316-GBEM nor in another sample of PNC316-GBEM subjected to 20% additional cold rolling, PNC316-GBEM20%CW. PNC316-GBEM showed a higher void swelling rate than as-received PNC316 (PNC316-AS). However, with additional 20% cold rolling after GBE, the void swelling rate decreased to as low as that of PNC316-AS. (C) 2011 Elsevier B.V. All rights reserved.
  • WATANABE Kei, SAKAGUCHI Norihito, WATANABE Seiichi
    Journal of Materials Science 46 13 4568 - 4573 2011年07月 [査読無し][通常論文]
     
    The crystalline structures of zinc oxide (ZnO) formed by the internal oxidation of a Pd-Zn alloy were examined at elevated temperatures. Metastable sphalerite ZnO with a tetrahedral shape preferentially nucleated in the Pd matrix, while plate-like precipitates consisting of a wurtzite ZnO phase preferentially grew at a high temperature. Unique ZnO precipitates with trapezoidal cross-section and consisting of inter-layered sequences with sphalerite ZnO and wurtzite ZnO were also examined at an intermediate temperature. It is inferred that the formation of stacking faults in the sphalerite ZnO is strongly related to the nucleation of the wurtzite-type ZnO sequence.
  • Yutaka Yoshida, Norihito Sakaguchi, Seiichi Watanabe, Takahiko Kato
    APPLIED PHYSICS EXPRESS 4 5 055202-1-055202-3  2011年05月 [査読無し][通常論文]
     
    We report a periodic two-dimensional (2D) array of uniquely shaped dotlike nanoprotrusions (NPs), which simultaneously self-organize on a Si surface under pulsed laser irradiation. The shape of the dotlike NPs can be controlled by adjusting the number of laser pulses. The flask-shaped dotlike NP array is named a vidro-nanodot (VND) array. We present a detailed analysis of the internal structure of VND using high-resolution electron microscopy. (C) 2011 The Japan Society of Applied Physics
  • Norihito Sakaguchi, Makito Miyake, Seiichi Watanabe, Heishichiro Takahashi
    MATERIALS TRANSACTIONS 52 3 276 - 279 2011年03月 [査読無し][通常論文]
     
    Faceted Sigma 3 CSL grain boundaries in silicon were investigated by high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS) and ab-initio calculation. A {112} Sigma 3 CSL boundary consisted of two segments which differed in atomic structure. The segment near the connected corner to {111} Sigma 3 CSL boundary showed symmetric structure and the other long segment, being distant region from the corner, showed asymmetric structure. In the symmetric segment a 5-fold coordinated atom presented, which produced a deep state in the band gap. A pronounced shoulder, which could be attributed to the defect state above Fermi level, was detected only in Si-L-23 energy-loss near-edge spectra (ELNES) acquired from the symmetric segment of the {112} Sigma 3 CSL boundary near the CSL junction. [doi:10.2320/matertrans.MB201018]
  • Chunyu Zhu, Norihito Sakaguchi, Sou Hosokai, Seiichi Watanabe, Tomohiro Akiyama
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 5 3600 - 3605 2011年03月 [査読無し][通常論文]
     
    In this paper, we presented an investigation of the phase transformation of MgH2 to Mg, in which a sample of a single-crystal MgH2 nanofiber was prepared by hydriding chemical vapor deposition (HCVD) and observed by in situ (high-resolution) transmission electron microscopy (TEM). The results indicated that the orientation relationship between MgH2 and Mg during the phase change was: one of the zone axis of MgH2 < 110 > parallel to Mg [0001] zone axis, or one of the plane {110} of MgH2 parallel to the basal plane of Mg (0001). On the basis of the obtained results, we proposed a structural model for the phase change of MgH2 to Mg. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
  • 渡辺精一, 谷津茂男, 大久保賢二
    顕微鏡 46 151 - 155 2011年 [査読無し][通常論文]
  • Tamaki Shibayama, Genichiro Matsuo, Kouichi Hamada, Seiichi Watanabe, Hirotatsu Kishimoto
    3RD INTERNATIONAL CONGRESS ON CERAMICS (ICC3): CERAMICS AND COMPOSITES FOR ADVANCED NUCLEAR ENERGY AND HAZARDOUS WASTE TREATMENT APPLICATIONS 18 2011年 [査読有り][通常論文]
     
    We have been successfully done in situ observation on the sequence of fracture event at the interface of NITE SiC/SiC composite examined by using miniaturized double notched shear specimen for TEM prepared by Focused Ion Beam method. In this study, we used nano-mechanics TEM experimental apparatus to investigate not only microstructure evolution and but also load and displacement curve at once in High Voltage Electron Microscope. Our results summarize as follows. Cracks were initiated at the interface between carbon coating layer on the SiC fiber and SiC matrices, and propagated along the interface. Load drop in the load and displacement curve during in-situ TEM was clearly observed at the crack initiation. The shear strength by using the miniaturized specimen is about ten times higher than that obtained by the standard testing.
  • S. Watanabe, Y. Yoshida, S. Kayashima, S. Yatsu, M. Kawai, T. Kato
    JOURNAL OF APPLIED PHYSICS 108 10 103510-1-103510-5  2010年11月 [査読有り][通常論文]
     
    An in situ observation of the formation of a laser-irradiation-induced nanodot array on a Si surface was performed using a pulsed-laser-equipped high-voltage electron microscope (laser-HVEM). Under multiple nanosecond (ns) pulsed laser irradiation shots, atomic clusters were first formed and distributed on the surface in order to grow them epitaxially into protruded dots with diameters of ten nanometers or less. This is followed by their diffusion induced by successive laser shots to cannibalize and merge them into a ripple line with aligned, larger dots. We conclude that the present subwavelength two-dimensionally-ordered nanodot array is formed by self-organization under pulsed laser irradiation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3512888]
  • Genki Saito, Sou Hosokai, Tomohiro Akiyama, Souki Yoshida, Shigeo Yatsu, Seiichi Watanabe
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 8 083501-1-083501-3  2010年08月 [査読有り][通常論文]
     
    We report the size control of Ni nanoparticles generated via solution glow discharge and focus on the effect of electrolyte concentration on Ni nanoparticles. In our experiments, voltage was applied to generate a plasma in NaOH electrolytes with concentrations ranging from 1.0 to 0.001 kmol m(-3). The applied voltage strongly depended on the electrolyte concentration, and interestingly, product size decreased with electrolyte concentration; for example, (mean diameter, applied voltage, electrolyte concentration) = (148 nm, 90 V, 0.5 kmol m(-3)), and (70 nm, 590 V, 0.001 kmol m(-3)). These results suggested the possibility of using plasma electrolysis for synthesizing size-controlled nanoparticles by changing only electrolyte concentration.
  • Yasuhide Yano, Shinichiro Yamashita, Satoshi Ohtsuka, Takeji Kaito, Naoaki Akasaka, Tamaki Shibayama, Seiichi Watanabe, Heishichiro Takahashi
    JOURNAL OF NUCLEAR MATERIALS 398 1-3 59 - 63 2010年03月 [査読無し][通常論文]
     
    The in-reactor creep rupture tests of 11Cr-0.5Mo-2W, V. Nb F/M steel were carried out in the temperature range from 823 to 943 K using materials open test assembly in the fast flux test facility and tensile and temperature-transient-to-burst specimens were irradiated in the experimental fast reactor JOYO at temperatures between 693 and 1013 K to fast neutron doses ranging from 11 to 102 dpa. The results of post-irradiation mechanical tests showed that there was no significant degradation in tensile and transient burst strengths even after neutron irradiation below 873 K, but that there was significant degradation in both strengths at neutron irradiation above 903 K. On the other hand, the in-reactor creep rupture times were equal or greater than those of out-reactor creep even after neutron irradiation at all temperatures. This creep rupture behavior was different from that of tensile and transient burst specimens. (C) 2009 Elsevier B.V. All rights reserved.
  • Self-Organized Dots Formation on Si Substrate by Nd: YAG Laser Irradiation
    Y. Yoshida, S. Yatsu, S. Watanabe, M. Kawai, T. Kato
    Proceedings of ICEP (International Conference on Electronics Packaging), Sapporo, May 12, 2010 (JIEP, Tokyo, Japan) 800 - 803 2010年 [査読有り][通常論文]
  • N. Sakaguchi, Y. Suzuki, K. Watanabe, S. Iwama, S. Watanabe, H. Ichinose
    PHILOSOPHICAL MAGAZINE 88 10 1493 - 1509 2008年04月 [査読有り][通常論文]
     
    Atomic and electronic structures of interfaces in an internally oxidized Pd/ZnO system were Studied by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). {0001}(ZnO) polar planes tend to be parallel to the interface. A ZnO precipitate was terminated by an oxygen (0001) surface at one end of the precipitate and by a zinc (0001) surface at the other end of the precipitate. A pre-edge peak was detected only in O-K energy-loss near-edge spectra (ELNES) acquired from the oxygen-terminated interface. Ab initio, calculations indicated that the origin of the pre-edge peak could be attributed to the strong chemical bonding and hybridization of Pd-d and O-p orbitals at the oxygen-terminated polar interface.
  • Study of Nano-Microstructures on SCC in 316L Stainless Steel
    H. Takahashi, R. Ishibashi, T. Kato, N. Sakaguchi, S. Watanabe
    Proceedings of 7th Polish-Japanese Joint Seminar on Micro and Nano Analysis, Warsaw, Poland, September 7-10, 2008 (The Institute of Electron Technology, Warsaw, Poland) Paper No. B2. 2  2008年 [査読有り][通常論文]
  • Hiroshi Kinoshita, Heishichiro Takahashi, Dwi Gustiono, Norihito Sakaguchi, Tamaki Shibayarna, Seiichi Watanabe
    MATERIALS TRANSACTIONS 48 5 924 - 930 2007年05月 [査読有り][通常論文]
     
    Phase transformation behaviors of the austenitic 301 stainless steel was studied under Fe+, Ti+ and Ar+ ions implantation at room temperature with 100, 200 and 300 keV up to fluence of 1 x 10(21) ions/m(2) and the microstructures were observed by means of transmission electron microscopy (TEM). The plane and cross-sectional observations of the implanted specimen showed that the induced-phases due to implantation from the gamma matrix phase were identified as alpha' martensite phases with the orientation relationship of (1 (1) over bar0)(alpha) //(11 (1) over bar)gamma and [111](alpha) // [011](gamma) close to the Kurdjumov-Sachs (K-S). The ion implantation induced phases nucleated near the surface region and the depth position of the nucleation changed depending on the ion accelerating energy and ion species. It was also found that the induced marten sites phases nucleate under the influence of the stress distribution, which is introduced due to the concentration of implanted ions, especially due to the stress gradient caused by the corresponding concentration gradient.
  • S Watanabe
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY 46 3 646 - 650 2005年03月 [査読有り][通常論文]
     
    The autocorrelation function of the multi-Lorentzian spectra is shown to be in accord with a 1/f- type noise having a multi-relaxation time distribution, r(-alpha), and yields scaling relation forms when 0 < alpha < 2 (alpha not equal 1). The dependences of alpha on temporal autocorrelation functions in the entire range of 0 <= alpha <= 2, the corresponding power spectra of f(-2+alpha) noise and, the time reversal symmetry on the power number alpha are discussed based on the multi-Lorentzian model. The present results should be applicable to fluctuating phenomena, such as flicker noise effects and self-organized critical phenomena.
  • N Sakaguchi, S Watanabe, H Takahashi
    JOURNAL OF MATERIALS SCIENCE 40 4 889 - 893 2005年02月 [査読有り][通常論文]
     
    We have developed a new model for radiation-induced grain boundary migration (RIGM) and radiation-induced segregation (RIS) for austenitic iron-chromium-nickel alloy system. It was assumed that the RIS was induced by diffusional and annihilation processes of excess point defects at the grain boundary, and the RIGM occurred due to rearrangement process of atoms on one of the interfacial planes by annihilation of point defects. The calculated results indicated that the region of RIS was enlarged by the RIGM and asymmetrical concentration profiles were observed around the migrated grain boundary. The present model could explain the RIS behavior with or without grain boundary migration as comparing with our previous experimental results. (C) 2005 Springer Science + Business Media, Inc.
  • Microstructure of SCC in a Surface-worked 316L Stainless Steel in High Temperature Water
    H. Takahashi, R. Ishibashi, T. Kato, T. Horiuchi, T. Shibayama, N. Sakaguchi, S. Watanabe
    Proceedings of International Workshop on Influence of Atomic Displacement Rate, Neutron Spectrum and Irradiation Temperature on Radiation Induced Ageing of Power Reactor Components: Experiment and Modeling, Dimitrovgrad, Russia, October 5, 2005 (The Resea 1 - 12 2005年 [査読有り][通常論文]
  • T Tanaka, K Oka, S Ohnuki, S Yamashita, T Suda, S Watanabe, E Wakai
    JOURNAL OF NUCLEAR MATERIALS 329 294 - 298 2004年08月 [査読有り][通常論文]
     
    The purpose of this study is to evaluate the synergistic effect of helium and hydrogen on Fe-Cr ferritic model alloys, to provide basic understanding concerning development of fusion reactor components. Single, dual and triple ion-beams consisting of Fe3+, He+ and H+ were used for irradiation, at temperatures 470-600 degreesC and dose to 50 dpa at 1 mum. The dual beam irradiation with He enhanced cavity nucleation extensively to swelling of about 0.4%, whereas the dual beam irradiation with H did not significantly affect the microstructure. In the case of triple ion irradiation, the synergistic effect of He and H was confirmed clearly; relative large void formation and enhanced swelling to almost 5%. The synergistic effect suggests that the role of H is important for void growth and dislocation bias. (C) 2004 Elsevier B.V. All rights reserved.
  • Y Wang, M Kanedome, T Yasuda, T Suda, S Watanabe, S Ohnuki, T Nagasaka, T Muroga
    JOURNAL OF NUCLEAR MATERIALS 329 477 - 480 2004年08月 [査読有り][通常論文]
     
    To clarify hydrogen effects on mechanical properties of pure vanadium, two kinds of tensile tests were performed using hydrogen charged miniature specimens at room temperature. One is with hydrogen charging prior to testing, and the other is with hydrogen charging during testing with continuous or intermittent methods. The cathodic hydrogen charging was carried out electrolytically in various concentrations of H2SO4 with different current densities. The hydrogen charged specimens were tested to obtain stress-strain curves. The fractography was performed by SEM, and hydride formation and microstructural change were examined by TEM. Hydrogen-induced softening and hardening in vanadium resulted from hydrogen charging. The variations in mechanical property of specimens depended on the amount of dissolved hydrogen, that was determined by hydrogen diffusion and hydrogen desorption. Dislocation motion also plays a role in the variation of flow stress. (C) 2004 Elsevier B.V. All rights reserved.
  • S Ohnuki, T Yasuda, T Suda, S Watanabe, BM Oliver
    JOURNAL OF NUCLEAR MATERIALS 329 481 - 485 2004年08月 [査読有り][通常論文]
     
    To understand hydrogen behavior in V and V based alloys, static and dynamic hydrogen chargings were carried out for unirradiated and irradiated V and V-4Cr-4Ti. Hydrogen can be trapped by lattice defects, dislocations, vacancies and voids, which are effective up to 500degreesC. Unexpected softening occurred at low levels of hydrogen, and hardening occurred at high levels. Alloying elements intensified the hardening, which are seen as general phenomena in V and V based alloys. A significant effect was seen for dynamic charging, which was attributed to fast diffusion and interactions with mobile dislocations. (C) 2004 Elsevier B.V. All rights reserved.
  • N Sakaguchi, S Watanabe, H Takahashi, RG Faulkner
    JOURNAL OF NUCLEAR MATERIALS 329 1166 - 1169 2004年08月 [査読有り][通常論文]
     
    We investigated the dependence of radiation-induced segregation (RIS) in austenitic stainless steels on grain boundary orientation by numerical calculations. A new rate equation model for RIS that incorporates the grain boundary sink strength for point defects was developed. The sink strength was determined as functions of misorientation angle and Sigma values using interaction energies of vacancy near grain boundaries as determined by molecular dynamics (MD) and statics (MS). It was shown that the calculated results can reproduce the experimental data obtained by electron and proton irradiation experiments. The good agreement supports the validity of the present model. (C) 2004 Elsevier B.V. All rights reserved.
  • S Watanabe, H Takahashi, NQ Lam
    RADIATION EFFECTS AND ION-BEAM PROCESSING OF MATERIALS 792 159 - 170 2004年 [査読有り][通常論文]
     
    Spatio-temporal nanostructural fluctuations brought about by transient, metastable atom-cluster formation and the manifold nature of inherent atomic ordering in electron-irradiation-amorphized NiTi were investigated by using a combination of in situ observations inside a high-resolution high-voltage electron microscope (HR-HVEM) and image analyses of molecular-dynamics-simulated atom configurations. Nanometer-sized clusters were found to appear and disappear in the irradiated region. The random formation and annihilation of such nanoclusters are believed to be responsible for nanostructural fluctuations which appear to be related to transitions among manifold inherent structural states, involving multirelaxation processes. Temporal fluctuations in the amorphized structure were manifested through the dose-dependent local amorphization parameter, potential energy, volume, and inherent cluster bonding. The observed fluctuations obey a universal power law. Within the framework of the multi-Lorentzian picture, the resultant power law describes the distribution of multirelaxation times or cluster lifetimes. In addition, a unified relation for the temporal autocorrelation function for such fluctuation phenomena has been determined.
  • T Maruyama, M Iwanami, S Ohnuki, T Suda, S Watanabe, K Ikezawa
    Effects of Radiation on Materials: 21st International Symposium 1447 670 - 679 2004年 [査読有り][通常論文]
     
    Two kinds of hot-pressed B4C specimens were irradiated with 15MeV He+ from 4.3 x 10(14) to 1.13x 10(16) ion/cm(2) at 400-760 T, and with 100keV He+ from 1.0x10(13) to 2.0x10(17)ion/cm(2) at room temperature. After ion irradiation, the microstructure of specimens was analyzed by transmission electron microscopy (TEM). The ion-irradiation by 15MeV helium ions produced a radiation-enhanced precipitation with Fe-rich composition and the radiation-induced amorphization in the B4C matrix, but the irradiation by 100keV helium did not make amorphization. This result suggests that the inelastic scattering (electron excitation), rather than elastic scattering, plays an important role in amorphization of B4C. The annealing of ion irradiated B4C above 1000 degrees C indicated incineration of precipitated crystals and a formation of a small numbers of helium bubbles.
  • S Watanabe, T Koike, T Suda, S Ohnuki, H Takahashi, NQ Lam
    MATERIALS TRANSACTIONS 45 1 24 - 28 2004年01月 [査読有り][通常論文]
     
    Chemical and topological disorderings in the NiTi intermetallic compound during electron irradiation were studied using a combination of in situ irradiation inside a high-resolution high-voltage electron microscope and image analyses of molecular-dynamics-simulated atom configurations. It was found that metastable defect clusters formed during the chemical-disordering phase prior to topological disordering leading to amorphization. These planar defect clusters contributed to the characteristic diffuse scattering were also observed in selected-area diffraction patterns.
  • S. Watanabe, M. Hoshino, T. Koike, T. Suda, S. Ohnuki, H. Takahashi, N. Q. Lam
    Philosophical Magazine 83 22 2599 - 2619 2003年08月01日 [査読有り][通常論文]
     
    Temporal nanostructural fluctuations brought about by transient metastable atom-cluster formation during radiation-induced amorphizing transformation in the intermetallic compound NiTi, observed using a combination of high-resolution high-voltage electron microscopy and molecular dynamics simulation, were characterized in terms of power-law responses of non-equilibrium energy-dissipative systems. Within the framework of the multi-Lorentzian picture, the resultant power law also describes the multirelaxation time (i.e. cluster lifetime) distribution. In addition, a unified relation for the autocorrelation functions for such fluctuation phenomena is discussed.
  • S Watanabe, M Hoshino, T Koike, T Suda, S Ohnuki, H Takahashi, NQ Lam
    PHILOSOPHICAL MAGAZINE 83 22 2599 - 2619 2003年08月 [査読有り][通常論文]
     
    Temporal nanostructural fluctuations brought about by transient metastable atom-cluster formation during radiation-induced amorphizing transformation in the intermetallic compound NiTi, observed using a combination of high-resolution high-voltage electron microscopy and molecular dynamics simulation, were characterized in terms of power-law responses of non-equilibrium energy-dissipative systems. Within the framework of the multi-Lorentzian picture, the resultant power law also describes the multirelaxation time (i.e. cluster lifetime) distribution. In addition, a unified relation for the autocorrelation functions for such fluctuation phenomena is discussed.
  • S Watanabe, K Kawata, T Kokie, T Suda, S Ohnuki, H Takahashi, Y Matsukawa, M Kiritani
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 350 1-2 145 - 149 2003年06月 [査読有り][通常論文]
     
    Materials responses under non-equilibrium conditions, especially in the state far-from-equilibrium, have been attracting great interest. Although of limited use, there are some tools available for investigating the phenomena, e.g. theoretical approaches such as non-equilibrium thermodynamics or atomistic computer simulation. The present study centers on high-resolution TEM of ordered NiTi specimens subjected to ultra-high-speed plastic deformation at Hiroshima Institute of Technology. Various local nonequilibrium nano-phases were observed to form due to high-speed deformation. Image analysis using high-resolution electron microscopy (HREM) simulation and the FFT technique revealed that those meta-stable phases in the Ni-Ti system were R-phases (Ni4Ti3), O-phases (Ni3Ti2) and amorphous phases. The current study also elaborates on the formation and nature of deformation-induced lattice invariant shear bands. Our results suggest that ultra-high-speed deformation is a promising tool to study the material responses in far-from-equilibrium states. (C) 2002 Elsevier Science B.V. All rights reserved.
  • S Watanabe, M Hoshino, T Koike, T Suda, S Ohnuki, H Takahashi, NQ Lam
    JOURNAL OF ELECTRON MICROSCOPY 52 1 33 - 40 2003年 [査読有り][通常論文]
     
    We performed a dynamic-atomistic study of radiation-induced amorphization in the NiTi intermetallic compound using in situ high-resolution high-voltage electron microscopy and molecular dynamics simulations in connection with image simulation. Spatio-temporal fluctuations as non-equilibrium fluctuations in an energy-dissipative system, due to transient atom-cluster formation during amorphization, were revealed by the present spatial autocorrelation analysis.
  • P Torres, K Aoyagi, T Suda, S Watanabe, S Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 307 625 - 629 2002年12月 [査読有り][通常論文]
     
    The effects of hydrogen in vanadium, V-5Cr and V-5Ti have been evaluated by the change in surface and in microstructure and by the aspect of fractured surfaces. Hydrogen accumulation promotes local concentration of hydrides and assists the generation of stacking faults. Under increased stress, crack propagation occurs by the successive formation of crack fronts. (C) 2002 Elsevier Science B.V. All rights reserved.
  • T Suda, M Ohkawa, S Sawada, S Watanabe, S Ohnuki, S Nagata
    MATERIALS TRANSACTIONS 43 11 2703 - 2705 2002年11月 [査読有り][通常論文]
     
    In order to improve initial activation properties of TiFe alloy, simple ion implantation and ion mixing with the deposition of LaNi5 were carried out at room temperature. The results show that argon-ion mixing caused extensive improvement of initial activation, wherein hydrogenation was easily effected at 373 K and 1 MPa. Those results are related to several irradiation effects; the re-crystallization of amorphous film of LaNi5 and the local segregation of composed elements. Both of these irradiation effects greatly improve the initial hydrogenation process of TiFe alloy.
  • T Koike, S Watanabe, M Hoshino, T Suda, S Ohnuki, H Takahashi, NQ Lam
    MATERIALS TRANSACTIONS 43 7 1716 - 1718 2002年07月 [査読有り][通常論文]
     
    We have studied nanostructural fluctuations during electron irradiation in the ordered intermetallic compound NiTi by performing irradiation experiments with a high-resolution high-voltage electron microscope (HVEM) and molecular dynamics (MD) simulations. It was observed that atom clusters formed and disappeared repeatedly during irradiation, which results in the structural fluctuation. Comparing the experimental results with the MD simulations, we conclude that such spatio-temporal structural fluctuations under irradiation can be accounted for the evolution of metastable nanoclusters. The present study demonstrates the usefulness of high-resolution HVEM for in situ studies of dynamic, nanoscale fluctuation phenomena.
  • M Ishino, O Yoda, Y Haishi, F Arimoto, M Takeda, S Watanabe, S Ohnuki, H Abe
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 5A 3052 - 3056 2002年05月 [査読有り][通常論文]
     
    Characterizations of Mo/Si multilayers for soft X-ray mirrors have been carried out by high-resolution transmission electron microscopy (TEM) and X-ray scatterings. The crystallite size of oriented Mo in the direction normal to the (110) plane has been found to be approximately equal to the designed thickness of the Mo layer below 8 nm. However, when the Mo layer thickness becomes greater than 8 nm, the crystallite size deviates from the designed thickness and saturates at about 10 nm. The Si layer thickness is smaller than the expected one, which is calculated from the periodic length and the Mo layer thickness, indicating that the mixed layer at the inter-face is formed in the Si layer. The thickness and density of the mixed layer at the Mo-on-Si inter-face are larger than those at the Si-on-Mo interface. The sum of the thicknesses of the mixed layer is about 1.4 nm, irrespective of the Mo/Si composition. Moreover, the density of the mixed layer at the Mo-on-Si interface becomes larger with the increase of the Mo content.
  • Y Masumoto, M Takeda, T Suda, S Watanabe, S Ohnuki, T Ohtsuka, K Ikezawa
    MATERIALS TRANSACTIONS 43 4 638 - 640 2002年04月 [査読有り][通常論文]
     
    High-energy ion-beam mixing technique was applied for the surface modification of austenitic stainless steel. followed by electrochemical characterization and microstructural obeservation, The co-mixing of silicon and chromium resisted the passivation current to 1/1000 relative to the un-modified condition. The corrosion resistance improved remarkably. Microstructural observation revealed that the enhanced diffusion and induced amorphous structure introduced by the co-mixing of silicon and chromium, which played a very important role in the improvement of electrochemical behavior at surface.
  • E Shioya, T Suda, S Watanabe, S Ohnuki, M Ishino, O Yoda, H Abe, F Phillips
    MATERIALS TRANSACTIONS 43 4 650 - 653 2002年04月 [査読有り][通常論文]
     
    In the Mo-Si system, there are three typical intermetallic compounds, In order to get insight into the phase stability under irradiation, interface structure and non-equilibrium phase formation in multilayer materials with several nanometers scale were investigated by means of high-voltage electron microscope. The initial structure was composed of crystalline Mo and amorphous Si layers. and transition layer existed at the interfaces. The thickness of transition layers is thicker at the Mo-on-Si than at the Si-on-Mo interface, While those structures were basically stable after thermal annealing up to 773 K, two types of amorphous layers developed during electron irradiation at room temperature: one is an amorphous-Si layer and the other is a Mo-Si mixing layer. And the radiation-induced amorphization was accompanied by anomalous shrinkage in the thickness of layers. It is suggested that those phenomena are related to non-equilibrium phase formation and biased diffusion process during irradiation.
  • S Watanabe, Y Haishi, T Suda, S Ohnuki, H Takahashi, M Kiritani
    RADIATION EFFECTS AND DEFECTS IN SOLIDS 157 1-2 101 - 108 2002年01月 [査読有り][通常論文]
     
    In situ tensile straining experiments have been carried out on thin films of the ordered intermetallic compound NiTi (B2 structure) in a high-voltage electron microscope. Real-time observations of stress-induced local amorphization of moving crack tips were followed by high-resolution transmission electron microscopy examination of nanocrystalline regions formed near the crack tip and in the region between the amorphous and crystalline regions. We have also independently confirmed the occurrence of local amorphization by ultra-high speed deformation at an atomistic level in bulk samples of the same NiTi sample. A fast Fourier transformation (FFT) image analysis technique was used to determine the root mean square displacement (RMSD) parameter within the nanocrystalline regions. The RMSD parameter increases to a critical fraction of the nearest neighbor distance of 0.12 +/- 0.01 as the amorphous region is approached, and this finding agrees with the generalized Lindemann melting criterion for amorphization proposed by Okamoto and Lam [1,2]. The present study shows that FFT-real-space analysis technique can provide local measurements of the RMSD parameter in an inhomogeneous system.
  • S Watanabe, T Koike, T Suda, S Ohnuki, H Takahashi, NQ Lam
    PHILOSOPHICAL MAGAZINE LETTERS 81 11 789 - 794 2001年11月 [査読有り][通常論文]
     
    We have carried out an atomistic study of electron-induced amorphization of an ordered intermetallic compound NiTi by means of in-situ high-resolution high-voltage electron microscopy observations and molecular dynamics simulations. Both theoretical and experimental results show that metastable nanometre-size atomic clusters form and disappear during irradiation, so that a spatiotemporal fluctuation under amorphization is induced. Mean-lifetime measurements of these clusters demonstrate that high-energy particle irradiation provides a useful tool to study dynamic fluctuations of the local atomic structure in the non-equilibrium open systems.
  • N Sakaguchi, S Watanabe, H Takahashi
    ACTA MATERIALIA 49 7 1129 - 1137 2001年04月 [査読有り][通常論文]
     
    We investigated the radiation-induced segregation (RIS) near grain boundaries in austenitic stainless steel under electron irradiation, taking into account the simultaneous evolution of faulted dislocation loops and network dislocations. The formation of a dislocation-free zone (DLFZ) in the vicinity of the grain boundary due to in situ irradiation was observed using a high-voltage electron microscope (HVEM). Predicted temperature and dose dependencies of DLFZ formation agreed with the experimental results. The relationship between RIS and DLFZ formation near a grain boundary has been substantially clarified. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
  • E Shioya, T Suda, S Watanabe, S Ohnuki, M Ishino, O Yoda, H Abe, F Phillip
    PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II 1351 - 1353 2001年 [査読有り][通常論文]
     
    Interface structure and non-equilibrium phase formation in multilayer materials with several nanometers scale were investigated by means of high-voltage electron microscopy. The initial structure was composed of crystalline Mo and amorphous Si layers, and transition layer existed at the interfaces. Those structures were basically stable after thermal annealing up to 773 K. Whereas, two types of amorphous layers developed during electron-irradiation at room temperature, and the radiation-induced amorphization was accompanied by anomalous shrinkage in the thickness of layers. It is suggested that those phenomena are related to non-equilibrium phase formation and biased diffusion process during irradiation.
  • M Ohkawa, S Sawada, T Suda, S Watanabe, S Ohnuki, S Nagata
    PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II 481 - 484 2001年 [査読有り][通常論文]
     
    For the improvement of initial activation properties in TiFe alloy, simple ion-implantation and ion-mixing with the deposition of LaNi5 were carried out at room temperature. As the result, extensive improvement of the initial activation was achieved by Argon ion-mixing, where the hydrogenation took place easily at 373 K and 1 MPa. Those results are related to several irradiation effects; the re-crystallization of amorphous film of LaNi5, the local segregation of composed elements and large amount of lattice defects. All of those factors may affect on the hydrogen dissolution on the surface and the diffusion in sub-surfaces area.
  • M Takeda, T Suda, S Watanabe, S Ohnuki, H Abe
    PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II 2539 - 2542 2001年 [査読有り][通常論文]
     
    Silicon thin film that was 200 nm in thickness was produced on the silicon oxide (SiO2) by Low Pressure Chemical Vapor Deposition (LPCVD). Heat treatment was given at 1223 K for 4 h under Ar atmosphere. Grain size of polycrystalline silicon (poly-Si) film was about 230 am in diameter. Transmission Electron Microscopy (TEM) specimen was prepared by supporting poly-Si film by Mo grid. In-situ TEM observation was performed under ion-irradiation with 100similar to300 keV C+, N+ and Ar+ at temperature range from 104 K to 773 K. Ion flux was 3.5+/-0.5x10(17) m(2)s(-1). Poly-Si irradiated at 343 K with 100 keV C+ was amorphization in the neighborhood of grain boundaries (GB). This preferential amorphization was recognized in the other irradiation condition. The amorphous phase was grown by the crystal-amorphous interface (C-A interface) migration. On the other hands, at above preferential amorphization temperature, the C-A interface migration in preferential amorphous phase was enhanced crystallization. The migration rate was depended on the mass and the energy of the incident ion. The obtained results are discussed in relation to damage energy from the incident ion.
  • S Ohnuki, F Arimoto, S Watanabe, PR Okamoto, NQ Lam, H Abe
    PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II 1331 - 1333 2001年 [査読有り][通常論文]
     
    We focused on the non-equilibrium phase formation and diffusion in multi-layers in several nanometers scale by using "in-situ" observation of ion irradiation. In the samples deposited on Si substrate, the initial structure is composed of crystalline Mo and amorphous Si layers. The mixing layers with amorphous structure were formed immediately after the ion-irradiation at room temperature. Diffusion-assisted tiny voids (<1 nm) developed at the interface and then line up at the center of the a-Si layer. This is a result of a Kikrendall effect, suggesting an intensive diffusion of Si toward c-Mo at room temperature. These phenomena are discussed from non-equilibrium phase formation and biased diffusion process, which can be induced irradiation.
  • T Koike, S Watanabe, T Suda, S Ohnuki, H Takahashi
    PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II 1347 - 1349 2001年 [査読有り][通常論文]
     
    The irradiation of energetic particles often induces chemical disordering, and subsequent amorphization of a variety of ordered intermetallic compounds. An implicit assumption of current theories of the phenomenon is that a critical degree of chemical disorder is necessary to initiate the crystal-to-amorphous transition and that once formed the amorphous phase grows monotonously with irradiation time. The development of high resolution-high-voltage electron microscopy (HR-HVEM) has made it possible to carry out in situ real-dine studies of radiation-induced structural changes on the atomic-scale. MM X structure) samples were irradiated with 1.25 MeV electrons (dose rate 1.0x10(24) e m(-2)sec(-1)) at 300, 323,373 and 523 K in HR-HVEM (JEM-ARM1300). In situ atomistic observations of electron-induced amorphization show that metastable nanometer-size atomic dusters form and disappear during irradiation. This clustering behavior induces a fluctuation in radiation-induced amorphization process. Molecular dynamics simulations also support to observe this phenomenon.
  • T Suda, R Kobayashi, S Watanabe, S Ohnuki
    PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II 489 - 492 2001年 [査読有り][通常論文]
     
    The hydride formation on the surface of ZrCo and ZrNi under hydrogen exposure was investigated at 423-473 K by means of Hot-Stage Microscope. In the case of ZrCo, hydrides formed with and without ion-implanted area, the ion-mixing of Co and Ni enhanced the growth rate of hydrides by 2-3 times. The activation energy for the growth was 40 kJ/mol for the non-treated sample, and it was 32 kJ/mol for the Co ion-mixing sample. In the case of ZrNi, after implantation was 28-40 kJ/mol and depended on the ion dose. The process of the hydrogenation was different in the nucleation, growth and cracking of both alloys, Those results indicate the ion-implantation drastically activate initial stage of hydrogenation.
  • S Watanabe, T Koike, M Hoshino, T Suda, S Ohnuki, H Takahashi, NQ Lam
    PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II 1339 - 1341 2001年 [査読有り][通常論文]
     
    We studied nanostructural fluctuations during electron irradiation of the ordered intermetallic compound NiII by means of molecular dynamics (MD) simulations and irradiation experiments with a high resolution high-voltage electron microscope (HVEM). It was observed that metastable, nanosized atom clusters formed and disappeared during irradiation. Comparing the experimental results with the MD simulations, we interpret the spatio-temporal fluctuations of the irradiated structure in terms of evolution of these nanoclusters. The present study demonstrates that the dynamic; atomic-scale structural fluctuation phenomenon can be studied in situ using irradiation inside a high resolution HVEM.
  • S Watanabe, Y Takamatsu, N Sakaguchi, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 283 152 - 156 2000年12月 [査読有り][通常論文]
     
    We have investigated the orientation dependence of grain boundaries in radiation-induced segregation (RIS) in an austenitic stainless steel under irradiation using a high-voltage electron microscope (HVEM) at the Hokkaido University HVEM facility and a new rate equation model for RIS, which incorporates the grain boundary sink strength for point defects. The [110] tilt grain boundaries were chosen for the present study. It was observed that, after electron irradiation at a dose rate of 2.0 x 10(-3) dpa s(-1) to 10 dpa at temperatures of either 623 or 723 K, RIS was enhanced as the tilt angle increased but was suppressed at coincidence grain boundaries (Sigma9 and Sigma3). The present result indicates that one needs to explicitly consider the grain boundary sink strength as an important factor affecting radiation-induced grain boundary phenomena (RIGBPH). This work can be thought as a study of the radiation-induced grain boundary phenomena associated with grain boundary engineering related to non-equilibrium phenomena. (C) 2000 Elsevier Science B.V. All rights reserved.
  • S Yamashita, S Watanabe, S Ohnuki, H Takahashi, N Akasaka, S Ukai
    JOURNAL OF NUCLEAR MATERIALS 283 647 - 651 2000年12月 [査読有り][通常論文]
     
    Issues for developing oxide dispersion strengthened (ODS) steel are anisotropic mechanical properties due to the bamboo-like structure, impurity pick up during the mechanical alloying (MA) process, stability of oxide particles, heat-treatment condition and chemical composition. Several ODS steels were fabricated with a changing gas environment during MA, heat-treatment condition and chemical composition, and were electron-irradiated to 12 dpa at 673-748 K in a high-voltage electron microscope. An ODS martensitic steel (M-Ar) with high dislocation density showed very good swelling resistance. Swelling levels of ODS ferritic steels depended on the gas environment during MA and the recrystallization condition. These indicated that a helium gas environment during MA was more effective to suppress swelling than an argon gas environment and that cold working after recrystallization reduced void formation and swelling. The effect of MA parameters, such as the gas environment, heat-treat condition and cold working on the swelling behavior was evaluated. (C) 2000 Elsevier Science B.V. All rights reserved.
  • S Watanabe, Y Takamatsu, N Sakaguchi, H Takahashi
    JOURNAL DE PHYSIQUE IV 10 P6 173 - 178 2000年04月 [査読有り][通常論文]
     
    The effect of grain boundary misorientation on intergranular Radiation-Induced Segregation (RIS) in an Fe-15Cr-20Ni alloy was studied using a high voltage electron microscope (HVEM) at Hokkaido University HVEM facility and a rate equation model for RIS which incorporated grain boundary sink strength. The < 110 > tilt grain boundaries were chosen for the present study. It was observed that after electron irradiation with 3x10(-3) dpa/s to 3 dpa at both temperatures of 623 K and 723 K, RIS was enhanced as the tilt angle increases but was suppressed at coincidence grain boundaries (Sigma 9 and Sigma 3). The present result indicates that one needs explicitly to consider the grain boundary sink strength for point defects as an important factor affecting radiation induced grain boundary phenomena.
  • Y Matsukawa, Y Sumita, S Ohnuki, S Watanabe, C Namba, H Takahashi
    EFFECTS OF RADIATION ON MATERIALS: 19TH INTERNATIONAL SYMPOSIUM 1366 1147 - 1158 2000年 [査読有り][通常論文]
     
    Ion-irradiation induced amorphization and crystallization processes in TiNi shape memory alloys have been investigated. The primary concern is to clarify the relationship between the critical temperature for irradiation-induced amorphization and the thermal crystallization temperature. The critical temperature for irradiation-induced amorphization was 673K, however, the edge of the foil specimen crystallized during the irradiation at a lower temperature. The crystallization temperature of the specimen edge during irradiation decreased with increasing of incident ion energy. Thermal annealing experiments revealed that the thermal crystallization preferentially occurred at the specimen edge and the crystalline-amorphous (C-A) interface; The crystallization temperature of the preferential sites were 573K and 623K, respectively. These preferential nucleation indicate that the nucleation barrier dominates the thermal crystallization temperature; the critical temperature for amorphization is higher than the thermal crystallization temperature with no nucleation barrier.
  • S Watanabe, N Sakaguchi, H Takahashi, S Ohnuki
    EFFECTS OF RADIATION ON MATERIALS: 19TH INTERNATIONAL SYMPOSIUM 1366 919 - 931 2000年 [査読有り][通常論文]
     
    We have investigated radiation-induced segregation (RIS) near a grain boundary in an austenitic stainless steel under electron irradiation taking into account the simultaneous evolution of faulted dislocation loops and network dislocations by a composite model. It has been found that dislocation free zones (DLFZ) formed in the vicinity of the grain boundary by the irradiation, and we carried out direct observation of the DLFZ formation by in-situ irradiation in a high-voltage electron microscope (HVEM). Prediction of temperature and dose dependence of DLFZ formation agreed with experimental results. The inter-relationship between RIS and DLFZ formation near a grain boundary has been substantially clarified. RIS and DLFZ were understood considering point defect and solute flow associated with the excess defect to the grain boundary.
  • N Sakaguchi, S Watanabe, H Takahashi
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 153 1-4 142 - 146 1999年06月 [査読有り][通常論文]
     
    Radiation-induced segregation (RIS) influences the chemical and mechanical properties of structural materials of fission and fusion reactors. In the present study, we investigated the effect of minor alloying elements on RIS in austenitic stainless steel on the basis of the rate theory at or near grain boundaries. It was assumed that the additional minor elements interacted with vacancies and formed additive-vacancy complexes. The effects of additional element concentration and the binding energy between additives and vacancies on solute segregation at the grain boundary were clarified by the present calculations, and the results were compared with recent electron irradiation experiments using a high-voltage electron microscope (HVEM). (C) 1999 Published by Elsevier Science B.V. All rights reserved.
  • 須田 孝徳, 小林 良一, 渡辺 精一, 大貫 惣明, 高橋 平七郎, 荒島 裕信, 兜森 俊樹
    日本金屬學會誌 63 5 601 - 604 公益社団法人 日本金属学会 1999年05月 [査読有り][通常論文]
     
    Most of hydrogen storage alloys show decrepitation during hydriding-dehydriding cycles. The decrepitation assists initial activity and reaction rate. However, it causes lowering of thermal conductivity, difficulties of handling, degradation and others. In this work, the decrepitation process was examined with regard to mechanical properties and microstructure.
    Four types of alloys; LaNi5, TiMn1.5, TiFe0.8C0.1 and ZrNi are used for this work. Compression test, Vickers hardness measurement and high-resolution electron microscopy observation were carried out before and after hydrogenation. Ductile alloys did not show remarkable decrepitation. Brittle alloys showed typical decrepitation, in which the nano crystal grains were observed by use of high-resolution microscopy. These results emphasize that the decrepitation process is different each other’s, depending on the ductility or brittleness of the alloys.
  • F Arimoto, M Takeda, T Suda, S Watanabe, S Ohnuki, H Takahashi, H Abe, H Naramoto
    MATERIALS TRANSACTIONS JIM 40 5 408 - 411 1999年05月 [査読有り][通常論文]
     
    In order to form the silicide at relatively low temperature, ion-beam-mixing was applied to Mo/Si and Ti/Si systems in a temperature range from room temperature to 473 K. After the irradiation of 1 MeV Si+, the cross-sectional specimens were examined by transmission electron microscopy and X-ray microanalysis. Crystalline silicide formation was achieved only in Mo/Si system irradiated to high dose at each temperature. The evaluation of interdiffusion coefficient indicated that the diffusion is predominant in the ion-beam-mixing process. The nucleation process of silicide and the phase stability are discussed.
  • S Watanabe, N Sakaguchi, S Mochizuki, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 271 184 - 188 1999年05月 [査読有り][通常論文]
     
    The authors investigated radiation-induced segregation (RIS) at a grain boundary in an Fe-Cr-Ni alloy under irradiation taking account of the evolution of faulted dislocation loops and network dislocations. Electron irradiation with a high voltage electron microscope (1000 kV) at Hokkaido University, Japan, was performed to study radiation-induced solute segregation and point defect flow in a typical austenitic Fe-Cr-Ni alloy. The theoretical analysis was conducted by solving the coupled rate equations for solute and defect concentrations near a grain boundary sink. The experimental solute redistribution profiles predicted by the theory were explained qualitatively. The formation of dislocation free zone (DLFZ) in the vicinity of a grain boundary was also observed during in situ observation under electron irradiation. The temperature dependence of the segregation width and that of DLFZ zone width show similar trends. It is thus suggested that RIS and DLFZ formation should be explained by the defect-flow-induced phenomenon under irradiation. The inter-relationship between RIS and such heterogeneous defect clustering near a grain boundary was also clarified substantially. (C) 1999 Elsevier Science Inc. All rights reserved.
  • M Takeda, S Ohnuki, S Watanabe, H Abe, H Naramoto, PR Okamoto, NQ Lam
    MICROSTRUCTURAL PROCESSES IN IRRADIATED MATERIALS 540 37 - 42 1999年 [査読有り][通常論文]
     
    Clarifying the local amorphization on the grain boundaries, the in-situ observation during ion-irradiation was carried out for poly-crystalline Si film. The critical dose of amorphous formation increased exponentially with increasing temperature, where the local amorphization was developed at middle temperature. The critical dose was affected by the doped impurity and the grain size. The preferential amorphization on and near grain boundaries had two processes; first stage with rapid growth rate and second stage with almost constant growth rate. The importance of stress was demonstrated from the acceleration due to the stress on the first stage of amorphization.
  • H Takahashi, H Tsuchida, Y Hidaka, H Kinoshita, S Watanabe
    EFFECTS OF RADIATION ON MATERIALS: 18TH INTERNATIONAL SYMPOSIUM 1325 701 - 709 1999年 [査読有り][通常論文]
     
    The effect of helium on microstructural development during dual beam irradiation with electrons/He+ ions was examined for Fe-16wt%Cr-14wt%Ni-xwt%P-ywt%Ti (x=0, 0.1, y=0, 0.1) model alloys. Irradiation was carried out using a high voltage electron microscope (1000kv) connecting with 300 keV ion accelerator. The simultaneous ion injection rate was 20 at.ppm He/dpa at 70KeV and irradiation temperatures were 723 X and 773K. In the phosphorus containing alloy, vacancy type dislocation loops were nucleated in the early irradiation stage with electrons beam irradiation, Voids were nucleated from lower dose during electrons/He+ ions dual beam irradiations. In the titanium contained alloy, under electrons/He+ ions dual irradiation, void nucleation was lower comparing to phosphorus containing alloy under electron beam. Furthermore, structural development in alloy containing both titanium and phosphorous was similar to that of alloy with phosphorus and dislocation density was very high. From these results it was clarified that helium strongly influences void nucleation in each alloy as a result of interaction between phosphorus and interstitials.
  • N Sakaguchi, S Watanabe, H Takahashi
    MULTISCALE MODELLING OF MATERIALS 538 169 - 178 1999年 [査読有り][通常論文]
     
    We have investigated the solute segregation and simultaneous evolution of extended defects in an Fe-Cr-Ni alloy during irradiation by computer simulation. It sheds a light on the accomplishment of performing "the combined total calculation" or "the muliscale modeling" which deals with both radiation-induced segregation and various kinds of internal sink evolution. The formation of dislocation-free zone (DLFZ) was predicted in the vicinity of a grain boundary. It indicated that DLFZ formation is controlled by solute diffusional process via point defects diffusion near the grain boundary and the activation energy obtained by the width of DLFZ corresponds to the half of the value of the radiation-enhanced solute diffusivity.
  • K Tozawa, Y Haishi, Y Matsukawa, S Watanabe, S Ohnuki, H Takahashi
    JOURNAL OF ELECTRON MICROSCOPY 48 5 613 - 616 1999年 [査読有り][通常論文]
     
    Although the local stress intensification in the immediate vicinity of a crack is known to be the primary driving force for material fracture, the mechanism of crack propagation is not well understood. In the present study in-situ microscopic observations have been carried out on thin films of NiTi intermetallic compounds under tensile loading conditions in a high-voltage electron microscope, followed by high-resolution TEM (HREM) observation. In addition to HREM, observation of the specimen fractured outside HVEM at room temperature was also carried out. Local stress-induced amorphization at moving crack tips has been observed. The HREM observation with a 200 kV FE-TEM revealed nano-crystalline formation in the intermediate region between the amorphous region and the crystalline region.
  • S Watanabe, N Sakaguchi, K Kurome, M Nakamura, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 240 3 251 - 253 1997年02月 [査読有り][通常論文]
  • Composition and microstructural changes near grain boundary in an austenitic stainless steel under electron irradiation
    N. Sakaguchi, S. Watanabe, H. Takahashi
    Annales De Physique 22 C2-147 - C2-153 1997年 [査読有り][通常論文]
  • S Watanabe, J Satou, N Sakaguchi, H Takahashi, C Namba
    JOURNAL OF NUCLEAR MATERIALS 239 1-3 200 - 204 1996年12月 [査読有り][通常論文]
     
    The effect of temperature variation during electron irradiation by high-voltage electron microscope (HVEM) on radiation-induced segregation (RIS) at a grain boundary in an austenitic stainless steel was investigated by means of a computer simulation. The calculation was carried out by solving the coupled rate equations for solute and defect concentrations which depend on the Kirkendall effect. The evolution of dislocation sink strength during the temperature variation was also investigated. It turned out that the effect of temperature variation on RIS was very weak and, thus, a high spatial resolution or a high sensitivity detector would be necessary to detect the phenomenon. Moreover, a retardation phenomenon in the sink strength during the temperature variation was found.
  • H Takahashi, FA Garner, A Kohyama, S Watanabe
    JOURNAL OF NUCLEAR MATERIALS 239 1-3 R7 - R7 1996年12月 [査読有り][通常論文]
  • H Kinoshita, S Watanabe, S Mochizuki, N Sakaguchi, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 239 1-3 205 - 209 1996年12月 [査読有り][通常論文]
     
    Fe-Cr-Ni austenitic alloys were irradiated to investigate the dependence of radiation induced grain boundary segregation on the initial composition of alloying elements. Electron irradiations were performed at grain boundary by using HVEM with 00 keV accelerating voltage. The irradiation temperature was 723 K and the dose was up to 7 dpa. Measurements of grain boundary composition were made using 200 keV TEM with EDS analysis device. Typical grain boundary segregation, such as Ni enrichment and Cr depletion, was recognized in all specimens. The amounts of segregation varied with the contents of alloying elements. For constant bulk Cr (15 wt% Cr) concentration and for increasing bull; Ni concentration, from 15 to 40 wt%, the highest amount of Ni segregation was observed in the range of 25 to 30 wt% Ni specimens, and Cr concentration at grain boundaries was of almost the same level. For constant bulk Ni (20 wt% Ni) content and for increasing bulk Cr content, from 15 to 35 wt%, the amount of Cr segregation at grain boundaries increased with greater Cr bulk content and the amount of Ni segregation was almost the same over the range of 15 to 35 wt% Cr. These tendencies of segregation which depend on the alloying composition were consistent with the computer simulation results of the grain boundary segregation.
  • N Sakaguchi, S Watanabe, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 239 1-3 176 - 179 1996年12月 [査読有り][通常論文]
     
    Radiation-induced segregation (RIS) influences the chemical and mechanical properties of the structural materials of fusion and fission reactors. In this study, such RIS and dislocation sink strength evolution were investigated on the basis of computer simulation for solute segregation at and near a grain boundary. A new continuity equation model for RIS, based on the rate theory which includes the simultaneous evolution of faulted dislocation loops and network dislocations, has been developed. A di-interstitial was assumed to be the nucleus of a dislocation loop in the present work, and we calculated dislocation evolution due to absorption of interstitials and vacancies. The dependencies of irradiation temperature, irradiation rate and dose on the RIS at a grain boundary under electron irradiation in high-voltage electron microscope (HVEM were clarified. We also considered the effect of probe size used in TEM-EDS analysis in order to satisfy the relationship with measured compositional profiles. The present work sheds a light on the accomplishment of performing 'combined calculation' which deals with both RIS and various kinds of internal sink evolution.
  • S Watanabe, N Sakaguchi, S Mochizuki, H Takahashi
    PHILOSOPHICAL MAGAZINE LETTERS 74 5 351 - 356 1996年11月 [査読有り][通常論文]
     
    We have investigated the radiation-induced segregation (RIS) near a grain boundary in an Fe-Cr-Ni alloy under electron irradiation taking account of the evolution of faulted dislocation loops and network dislocations. First, we predicted, on the basis of the rate theory, the formation dislocation-free zone (DLFZ) in the vicinity (about 30 nm) of a grain boundary and then carried out direct observation of the DLFZ by in-situ irradiation with high-voltage electron microscopy. The inter-relationship between RIS and heterogeneous defect clustering near a grain boundary has been substantially clarified.
  • S Watanabe, H Tsuchida, Y Hidaka, N Sakaguchi, S Ohnuki, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 233 177 - 182 1996年10月 [査読有り][通常論文]
     
    The synergistic effect of helium and the addition of the minor elements phosphorus and titanium on void formation in austenitic stainless steels has been studied using a HVEM connected with an ion accelerator. The specimens used were pure Fe-16Cr-14Ni and the same alloy containing either 0.1% P or 0.1% Ti. The electron-induced damage rate was 2 x 10(-3) dpa/s and the helium injection rate was 20 at.ppm/dpa at 70 keV. Dislocation loops of vacancy type were nucleated in the early stage of the electron-only irradiation in the specimen containing phosphorus, but under dual beam irradiation many voids were nucleated and the dislocation loops grew rapidly. When the specimen with titanium was electron-irradiated, void nucleation tended to be reduced but significant void formation occurred due to dual-beam irradiation. In order to explain the result, the free defect concentration has been calculated using a kinetic model based on binding between interstitial and the minor element.
  • S Watanabe, N Sakaguchi, N Hashimoto, M Nakamura, H Takahashi, C Namba, NQ Lam
    JOURNAL OF NUCLEAR MATERIALS 232 2-3 113 - 118 1996年09月 [査読有り][通常論文]
     
    A computer simulation and an electron irradiation in a high voltage electron microscope (1000 kV) were used to study radiation-induced solute segregation and point defect flow in typical austenitic Fe-Cr-Ni alloys. The calculation was conducted by solving the coupled rate equations for solute and defect concentrations considering the Kirkendall effect at a moving grain boundary sink. The experimental solute redistribution profiles were explained qualitatively. Redistribution of nickel and chromium solutes near the grain boundaries and simultaneously grain boundary migration occurred during irradiation. The amount of nickel enrichment at a grain boundary was especially remarkable, comparing to the amount of chromium depletion. It is suggested that grain boundary migration may contribute to the flow of under-sized nickel solute toward the boundary. The influence of the probe size on EDS analysis of compositional profiles was investigated, with some experimental data.
  • H Takahashi, N Sakaguchi, N Hashimoto, S Watanabe
    INTERGRANULAR AND INTERPHASE BOUNDARIES IN MATERIALS, PT 2 207- 561 - 564 1996年 [査読有り][通常論文]
     
    Fe-Cr-Ni,Ni-Si and Ni-Al alloys were electron-irradiated using a high voltage electronmicroscopy (1000kV),and in situ observation on structural evolution and microchemical analysis were carried out. When the Fe-Cr-Ni alloy was irradiated, there occurred the nucleation of dislocation loops followed by voids and at the same time grain boundary migration occurred. The compositional analysis after irradiation of an area including the migrated grain boundary indicated nickel enrichment and chromium depletion. Furthermore the grain boundary tended to migrate toward a coarser facing boundary plane. The same grain boundary migration and compositional change at the boundary was recognized in Ni-Si alloy. These results suggested that boundary migration and solutes redistribution are closely related to irradiation-introduced point defects flow, especially interstitial atoms and the direction of the boundary migration depends on the relationship between the two grains.
  • S WATANABE, H KINOSHITA, N SAKAGUCHI, H TAKAHASHI
    JOURNAL OF NUCLEAR MATERIALS 226 3 330 - 331 1995年11月 [査読有り][通常論文]
  • S WATANABE, N SAKAGUCHI, N HASHIMOTO, H TAKAHASHI
    JOURNAL OF NUCLEAR MATERIALS 224 2 158 - 168 1995年08月 [査読有り][通常論文]
     
    An irradiation-induced phenomenon was studied on account of solute segregation and concurrent grain boundary migration in a model Fe-Cr-Ni alloy during electron irradiation with a high voltage electron microscope (1000 kV) and also by computer simulation. The calculation was conducted by solving the coupled rate equations for solute and defect concentrations, which involve the Kirkendall effects at a grain boundary sink, so that the solute redistribution profiles experimentally obtained were quantitatively explained. We also extensively studied the effects of the probe size in the EDS analysis on composition profiles, the Gibbsian segregation in the vicinity of a grain boundary and the discriminant of segregation under irradiation, as well as other important factors that influence the phenomenon.
  • H Takahashi, T Kato, S Watanabe, N Sakaguchi
    ANNALES DE PHYSIQUE 20 3 109 - 116 1995年06月 [査読有り][通常論文]
     
    Solute redistribution and microstructural development in the vicinity of grain boundaries in Fe-19Cr-XMn-3Al (X=5,10,15) alloys were studied under electron irradiation to about 10 dpa at 725 K in a high voltage electron microscope in order to simulate the segregation behavior during neutron irradiation. The oversized solute atoms, manganese and aluminum, were depleted at grain boundaries, whereas the concentration of chromium increased even though it is an oversized one. The segregation behavior of aluminum and manganese was related to size effect. However,with increasing manganese concentration the size factor decreased and then the amount of depletion of the solutes decreased with manganese concentration. The enrichment of chromium seemed to be related to chromium-rich precipitate formation at the boundary.
  • H TAKAHASHI, N HASHIMOTO, S WATANABE
    ULTRAMICROSCOPY 56 1-3 193 - 199 1994年11月 [査読有り][通常論文]
     
    An Fe-Cr-Ni alloy was electron-irradiated using a high voltage electron microscope (1 MV), and in situ observations on the structural evolution and microchemical analysis were carried out. The compositional analysis showed that under irradiation an area near a grain boundary was nickel-enriched and chromium-depleted, and that, simultaneously, grain boundary migration occurred. Moreover, the distance of the grain boundary migration increased almost linearly with the degree of segregation, and the migration occurred predominantly in the direction perpendicular to close-packed crystal planes. Underpinned with computer calculations, it is suggested that when the radiation-induced point defects flow into the grain boundary, boundary migration and solute redistribution occur. Furthermore, the magnitude of the effects depends on the net point defect flow, especially that of interstitial atoms.
  • Y HIDAKA, S OHNUKI, H TAKAHASHI, S WATANABE
    JOURNAL OF NUCLEAR MATERIALS 212 330 - 335 1994年09月 [査読有り][通常論文]
     
    To investigate the effect of helium on void formation and radiation-induced segregation, dual-beam irradiation with electrons and helium ions has been carried out for an Fe-Cr-Ni alloy by using a 1000 keV HVEM and a 300 keV ion-accelerator. From the measurement of dislocation loop growth, the vacancy migration energy was estimated at different injection rates of helium. The value increased with increasing injection rate of helium, which means strong trapping between vacancies and helium atoms. As a result the mutual recombination of point defects is retarded and the formation of secondary defects can be enhanced. Namely, on increase the densities of voids and dislocations was observed, as compared with the result without helium. With respect to the radiation-induced segregation, depletion of Ni and enrichment of Cr in the irradiated area were detected. The segregation of Ni and Cr was suppressed with increasing helium. From these results the role of helium on radiation-induced segregation is discussed on the basis of vacancy trapping and internal sinks.
  • 渡辺 精一
    まてりあ 33 3 261 - 267 The Japan Institute of Metals and Materials 1994年
  • Theoretical and Experimental Studies of Irradiation-Induced Grain Boundary Migration and Segregation
    H. Takahashi, N. Hashimoto, S. Watanabe, N.Q. Lam
    The 1994 Gordon Res. Conf. on Particle Solid Interactions 1994年 [査読有り][通常論文]
  • S WATANABE, H TAKAHASHI
    JOURNAL OF NUCLEAR MATERIALS 208 1-2 191 - 194 1994年01月 [査読有り][通常論文]
  • Mechanical Properties in B2 FeAl without Frozen-in Vacancies
    K. Yoshimi, N. Matsumoto, S. Hanada, S. Watanabe
    Proceedings of the 3rd Japan International SAMPE Symposium 2 1404 - 1409 1993年12月 [査読有り][通常論文]
  • S FUJITA, S WATANABE
    JOURNAL OF SUPERCONDUCTIVITY 6 2 75 - 79 1993年04月 [査読有り][通常論文]
     
    The relationship between superconductivity and band structures of electrons and phonons is established on the basis of a generalized Bardeen-Cooper-Schrieffer model in which the interaction strengths (V11, V12, V22) among and between ''electron'' (1) and ''hole'' (2) Cooper pairs are differentiated. Elemental superconductors must have local hyperboloidal Fermi surfaces called ''necks'' or ''inverted double caps.''
  • S WATANABE, H TAKAHASHI, S FUJITA
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 54 3 325 - 329 1993年03月 [査読有り][通常論文]
     
    The angular dependence of the Azbel'-Kaner cyclotron resonance peaks in lead is analyzed. All of the anisotropies in the cyclotron resonance peaks originating from the [110] arms of the Fermi surface in the third band are shown to be characterized by a set of three effective masses with one negative, corresponding to a hyperboloidal shape of the Fermi surface. The splitting of the cyclotron resonance peaks found by Khaikin and Mina [Sov. Phys.-JETP 15, 24 (1962)] is also explained by the set of masses in terms of the approximately 3.2 degree misalignment of the (001) sample surface.
  • S FUJITA, S WATANABE
    JOURNAL OF SUPERCONDUCTIVITY 5 3 219 - 237 1992年06月 [査読有り][通常論文]
     
    A general theory of superconductivity is developed, starting with a BCS Hamiltonian in which the interaction strengths (V11, V22, V12) among and between "electron" (1) and "hole" (2) Cooper pairs arc differentiated, and identifying "electrons" ("holes") with positive (negative) masses as those Bloch electrons moving on the empty (filled) side of the Fermi surface. The supercondensate is shown to be composed of equal numbers of "electron" and "hole" ground (zero-momentum) Cooper pairs with charges +/-2e and different masses. This picture of a neutral supercondensate naturally explains the London rigidity and the meta-stability of the supercurrent ring. It is proposed that for a compound conductor the supercondensate is formed between "electron" and "hole" Fermi energy sheets with the aid of optical phonons having momenta greater than the minimum distance (momentum) between the two sheets. The proposed model can account for the relatively short coherence lengths xi observed for the compound superconductors including intermetallic compound, organic, and cuprous superconductors. In particular, the model can explain why these compounds are type 11 superconductors in contrast with type I elemental superconductors whose condensate is mediated by acoustic phonons. A cuprous superconductor has 2D conduction bands due to its layered perovskite lattice structure. Excited (nonzero momentum) Cooper pairs (bound by the exchange of optical phonons) above T(c) are shown to move like free bosons with the energy-momentum relation epsilon = 1.2v(F)q. They undergo a Bose-Einstein condensation at T(c)= 0.977hv(F)k(B)-1n1/2BAR, where n is the number density of the Cooper pairs. The relatively high value of T(c) (approximately 100 K) arises from the fact that the density n is high: n1/2 approximately xi-1 approximately 10(7) cm-1. The phase transition is of the third order, and the heat capacity has a reversed lambda (lambda)-like peak at T(c).
  • S WATANABE, S FUJITA
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 52 8 985 - 989 1991年 [査読有り][通常論文]
     
    The angular dependence of the Azbel'-Kaner cyclotron resonance peaks in lead is analyzed in terms of Shockley's formula. All of the anisotropies in the cyclotron resonance peaks originating from the <110> cylindrical arms of the Fermi surface measured in the four parallel field geometries by O triple-overdot nuki et al. [J. Phys. Chem. Solids 38, 419 (1977)] are shown to be characterized by the set of the effective masses (m1, m2, m3) = (1.18, 0.244, -8.71)m along the crystal directions ([001], [110BAR], [110]) and their equivalents. This means that the cyclotronic motion in the {110} planes is electron-like and its orbits are elliptic in k-space characterized by masses (m1, m2) while the heli-axial motion is hole-like. The physical origins of this unusual behavior are discussed in direct-lattice space.
  • S FUJITA, S WATANABE
    PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 158 1 K69 - K73 1990年03月 [査読有り][通常論文]
  • S FUJITA, S WATANABE
    SOLID STATE COMMUNICATIONS 72 6 581 - 583 1989年11月 [査読有り][通常論文]
  • S FUJITA, A GARCIA, D OLEYAR, S WATANABE, T BURNETT
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 50 1 27 - 31 1989年 [査読有り][通常論文]
  • 渡邊 精一
    日本水産学会誌 54 2 183 - 186 日本水産學會 1988年 
    The simple logistic model with time lag control is employed to consider the constant rate stocking effects. Stocking increases the equilibrium level of the population. The stability of the equilibrium depends on all parameters employed in the model. The equilibrium becomes unstable and the limit cycle arises under the sufficient level of stocking although the product of the increasing rate and time lag is less than π/2. Stocking produces the increase of the amplitude and the decrease of the period of the population's fluctuation. Careful stocking is desired in controlling natural populations.

書籍

講演・口頭発表等

その他活動・業績

特許

受賞

  • 2022年07月 物質・デバイス領域共同研究拠点 第4回 物質・デバイス共同研究賞
     光・ 電子デバイ ス応用に向けたガルバニック水中結晶光合成法による表面ナノパターン作製 
    受賞者: 髙橋 優樹;塚村 順平;村上 俊太郎;渡辺 精一;張 麗華;岡本 一将
  • 2021年09月 日本金属学会 日本金属学会 第37回 優秀ポスター賞
     鉄腐食を利用したヒドロゲル中アクアイオン拡散係数定量評価 
    受賞者: 高井 智史、村上 俊太郎、張 麗華、渡辺精一
  • 2021年09月 日本金属学会 日本金属学会 第37回 優秀ポスター賞
     G-SPSCを用いた欠陥制御による色調表面パターニング 
    受賞者: 塚村 順平、高橋 優樹、張 麗華、ジェーム メルバート、岡本 一将、渡辺精一
  • 2021年08月 The Water and Environment Technology Conference Online 2021 Excellent Presentation Award
     Nanostructured ZnO/CuO Composite Photocatalyst for Valuable Products Synthesis 
    受賞者: Ryosuke MATSUO;Chhunhong KAING;Yuki TAKAHASHI;Seiichi WATANABE;SatoshiOKABE
  • 2020年09月 日本金属学会 (第35回)優秀ポスター賞
     異種金属接触水中光合成法による機能性ヘテロナノ構造体の作製 
    受賞者: 高橋 優樹;ジェーム メルバート;渡辺 精一
  • 2019年03月 日本金属学会 第32回 優秀ポスター賞
     水中結晶光合成法における光の効果と表面パターニング応用 
    受賞者: 水野潤一;Melbert JEEM;高橋 優樹;渡辺精一
  • 2017年12月 日本顕微鏡学会北海道支部 Excellent Presentation Award
     Tuning ZnO nanorods opto-electrical properties and their evaluation by STEM-VEELS 
    受賞者: Melbert JEEM;Seiichi Watanabe
  • 2016年03月 日本金属学会 第26回 優秀ポスター賞
     水中結晶光合成法による酸化銅表面ナノ構造の形成機構 
    受賞者: 西野史香;Melbert JEEM;西山賢;張麗華;岡本一将;渡辺精一
  • 2015年12月 日本顕微鏡学会北海道支部 奨励賞
     イオン液体中ZnO ナノ結晶のレーザー照射誘起光腐食のTEM 内その場観察 
    受賞者: 大藤功将;石岡準也;小暮一馬;河口楓;五十嵐直也;メルバートジェーム;谷津茂男;渡辺精一;柴山環樹
  • 2013年09月 日本磁気学会学 学術奨励賞
     ナノ秒パルスレーザー照射したFe52Al48表面の磁気特性 
    受賞者: 海住 英生;吉田 裕;大澤 和也;渡辺 精一;近藤 憲治;石橋 晃;吉見 享 祐
  • 2011年12月 日本顕微鏡学会北海道支部 奨励賞
     HRTEM および EELS に基づくシリコン対応粒界の原子構造・電子状態評価 
    受賞者: 三宅牧人;坂口紀史;渡辺精一
  • 2010年09月 日本金属学会 第15回 優秀ポスター賞
     HRTEM および EELS によるΣ3 対応粒界ファセットの原子構造・電子状態評価 
    受賞者: 三宅牧人;坂口紀史;渡辺精一
  • 2010年09月 日本金属学会 第15回 優秀ポスター賞-2
     シリコン表面レーザー誘起ナノドットの微細構造解析 
    受賞者: 吉田 裕;渡辺精一;谷津茂男;坂口紀史;柴山環樹;大久保賢二;高橋平七郎;加藤隆彦;川合將義
  • 2010年07月 日本金属学会北海道支部 夏季サマーセッション優秀ポスター賞
     シリコンΣ3 対応粒界ファセットにおける電子状態のEELS による評価 
    受賞者: 三宅牧人;坂口紀史;渡辺精一
  • 2009年09月 日本金属学会 第13回 優秀ポスター賞
     W/SiC接合界面に形成した反応相の微細構造解析とクラック進展のその場観察 
    受賞者: 松尾元一郎;荻津健;柴山環樹;浜田弘一;渡辺精一;岸本弘立;香山晃
  • 2009年09月 日本金属学会 第13回 優秀ポスター賞-2
     液中プラズマ放電によるナノ粒子の生成 
    受賞者: 齊藤元貴;吉田壮貴;谷津茂男;渡辺精一;秋山友宏
  • 2009年03月 日本金属学会 第12回 優秀ポスター賞-2
     Pd-Zn合金中に内部酸化で析出したZnO粒子の形態と結晶構造 
    受賞者: 渡辺圭;鈴木義典;坂口紀史;渡辺精一
  • 2009年03月 日本金属学会 第12回 優秀ポスター賞
     オーステナイト系ステンレス鋼における照射効果ならびに腐食挙動に及ぼす粒界性質依存性 
    受賞者: 遠藤正樹;坂口紀史;木下博嗣;渡辺精一;粉川博之;山下真一郎;矢野康英;川合將義
  • 2007年03月 日本金属学会 第8回 優秀ポスター賞
     イオン照射したシリコン多結晶粒界の高分解能電子顕微鏡解析 
    受賞者: 落合章裕;米塚健大郎;小門礼;坂口紀史;渡辺精一;市野瀬英喜
  • 2007年03月 日本金属学会 第65回 功績賞 (物性部門)
     『量子エネルギービーム照射による開放系の材料研究と強非平衡性に基づく材料創製』 
    受賞者: 渡辺精一
  • 2007年03月 プラズマ応用科学会 論文賞
     β-Ni(Al,Cr)合金に形成されるAl2O3酸化皮膜の耐剥離性に及ぼすZr添加の影響 
    受賞者: 東本英哲;山内啓;柴山環樹;渡辺精一;黒川一哉;成田敏夫
  • 2007年 Meritorious Award, Japan Institute of Metals
  • 1997年03月 平成9年度風戸奨励賞
     『マルチビーム超高圧電子顕微鏡を用いた照射下微細欠陥クラスター形成挙動』 
    受賞者: 渡辺精一
  • 1993年03月 日本金属学会 第3回日本金属学会奨励賞・物性部門
     『金属中の電子輸送に関する研究』 
    受賞者: 渡辺精一
  • 1993年 1993 Young Scientist Award (Div. of Solid State Physics), Japan Institute of Metals1995 Monbusho Visiting Fellowship, Japan Society for the Promotion of Science (Japanese Government)

共同研究・競争的資金等の研究課題

  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 渡辺 精一
  • 非生物・生物ハイブリッド人工光合成システムの構築:持続可能な酢酸生成拠点の創出
    日本学術振興会:科学研究費助成事業 挑戦的研究(開拓)
    研究期間 : 2019年06月 -2022年03月 
    代表者 : 岡部 聡, 渡辺 精一, 佐藤 久
  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2012年04月 -2016年03月 
    代表者 : 連川 貞弘, 渡辺 精一, 柴山 環樹, 森園 靖浩, 山室 賢輝
     
    本研究課題では,優れた環境耐久性を有するフェライト系耐熱鋼の開発を行うことを目的として,ラスマルテンサイト組織を有する9-12Cr系耐熱鋼の粒界制御を試みた。ラスマルテンサイト鋼における特性劣化の優先的なサイトとなる旧オーステナイト粒界の対応粒界頻度を飛躍的に高めることができた。また,粒界制御熱処理によりサブブロック組織が微細化し,その後の焼戻し処理により,M23C6炭化物が微細に分散することを見出した。このような粒界制御材料に対して,高温クリープ試験,高温水蒸気酸化試験,液体金属腐食試験を行ったところ,いずれの特性も粒界制御により著しく向上することが明らかとなった。
  • 日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 中村 孝, 柴山 環樹, 塩澤 大輝, 中井 善一, 上杉 健太朗, 小熊 博幸, 渡辺 精一
     
    超高サイクル域における軸荷重疲労試験が行われ,放射光μCTイメージングにより材料内部に発生する微小き裂が観察された.内部き裂周囲の環境がき裂進展に及ぼす影響を明らかにするため,da/dNと応力拡大係数範囲の関係が測定され,真空中表面き裂のそれと比較された.その結果,内部き裂は1.0E-10m/cycleの極めて低速で進展するのに対し,表面に到達した後のき裂は1.0E-7m/cycle 程度の高速で進展することがわかった.内部き裂の進展速度は真空中表面き裂の進展速度に一致し,内部き裂周囲の真空に類似した環境が超高サイクル疲労における内部き裂進展過程に大きな影響を与えることが明らかとなった.
  • 文部科学省:科学研究費補助金(新学術領域研究(研究領域提案型))
    研究期間 : 2012年 -2013年 
    代表者 : 渡辺 精一
  • 文部科学省:科学研究費補助金(挑戦的萌芽研究)
    研究期間 : 2011年 -2012年 
    代表者 : 渡辺 精一, 谷津 茂男
     
    ステンレス合金のナノボール(ナノメートルサイズの球状粒子)に関して,申請者らが開発した液中グロー放電法を利用して極小化ナノボールを作製するための基礎技術を確立し,最小のステンレス合金ナノボールを得た。また、このステンレス合金ナノボールがデバイス化への応用面の期待ができる光触媒効果を有することを見出した。
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2009年 -2011年 
    代表者 : 柴山 環樹, 渡辺 精一, 谷津 茂男, 伊藤 芳浩, 富岡 智, 西山 修輔, 坂口 紀史
     
    本研究は、これまで透過電子顕微鏡で唯一の課題となっていた画像記録の高速化と長時間化についてピコ秒の現象であるレーザー核融合のターゲット計測に実績がある各種高速カメラを組み合わせたナノ時空間ダイナミクスその場観察システムの技術開発を行うことを目的として平成21年度から平成23年度まで3年計画で実施した。この新しく開発した装置を現有の透過電子顕微鏡に取り付けて、電子線やイオン照射下での接合界面における破壊の起点やマルチクラックの進展経路をこれまでは困難だったナノ時空間で記録しその場観察すると共に高速で発生し進展するマルチクラックとナノサイズ欠陥との相互作用を明らかにした。
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2008年 -2011年 
    代表者 : 渡辺 精一, 保田 英洋, 庭瀬 敬右, 西口 規彦, 大笹 憲一, 三浦 誠司, 谷津 茂男, 安住 和久, 坂口 紀史, 黒川 一哉, 秋山 友宏
     
    本研究は, 申請代表者らが開発したグロー放電による液中プラズマ利用の新規金属ナノボールの製法を活用し,各種金属と合金材料を出発原料としたナノボール創製研究と機能物性発現の物性解析評価,および作製したナノ粒子を利用した新規機能デバイス材料の開発基礎のための材料設計を行なった.
  • 文部科学省:科学研究費補助金(基盤研究(S))
    研究期間 : 2007年 -2010年 
    代表者 : 川合 將義, 菊地 賢司, 川崎 亮, 義家 敏正, 渡辺 精一, 栗下 裕明, 粉川 博之, 菊地 賢司, 川崎 亮, 長谷川 晃, 神山 崇, 原 信義, 山村 力, 二川 正敏, 深堀 智生, 斎藤 滋, 前川 克廣, 伊藤 高啓, 後藤 琢也, 佐藤 紘一, 橋本 敏, 寺澤 倫孝, 渡辺 幸信, 徐 超男, 石野 栞, 柴山 環樹, 坂口 紀史, 島川 聡司, 直江 崇, 岩瀬 宏, 兼子 佳久, 岸田 逸平, 竹中 信幸, 仲井 清眞
     
    高エネルギー高強度陽子ビーム場の材料は、強烈な熱衝撃や放射線によって損傷を受ける。衝撃損傷過程と影響を実験的に調べ、その緩和法を導いた。また放射線損傷を理論的に評価するコードを開発した。さらに、損傷に強い材料として従来の材料に比べて強度の4倍高く室温で延性を持つタングステン材と耐食性が4倍高いステンレス鋼を開発した。衝撃実験における応力発光材を用いた定量的な方法を考案し、実用化の目処を得た。
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2007年 -2009年 
    代表者 : 三浦 誠司, 木村 好里, 毛利 哲夫, 渡辺 精一, 大笹 憲一, 三島 良直, 滝沢 聡, 木村 好里
     
    凝固速度1500mm/hで高速一方向凝固したNb-18.1Si-1.5Zr合金を熱処理したところ、所期の金属組織が得られた。Nb相の3Dイメージングより、高温材料として有利な巨大サイズNb結晶粒実現が示唆された。この試料は室温で2%の圧縮塑性変形能を示し、50kgでダイヤモンド圧子を押し込んでも、脆い強化相Nb_5Si_3の破壊は周囲の延性Nb母相が抑制する。高温変形特性を決めるNb相の高温強度を向上させるMo、W添加は、Ta添加と組み合わせると組織制御と高強度化を同時に達成できる。
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2004年 -2006年 
    代表者 : 川合 將義, 菊地 賢司, 神山 崇, 山村 力, 川崎 亮, 義家 敏正, 原 信義, 粉川 博之, 二川 正敏, 栗下 裕明, 渡辺 精一, 菊地 賢司
     
    核破砕場と宇宙を対象として、耐衝撃特性と耐放射線損傷の強い材料の開発研究を行った。主要な結果は以下の通りである。(1)核破砕中性子源の固体ターゲット材用に炭化チタン分散型の高靭性タングステンをメカニカルアロイング法により開発し、タングステン材料では世界で初めて超塑性を実現できた。(2)ターゲット等の構造材として重要なステンレス鋼について、耐放射線特性を向上させるため、加工熱処理により多数の焼鈍双晶を導入することによって低エネルギー構造粒界(対応粒界)を高頻度かつ均一分散させた粒界制御したステンレス鋼を創出した。(3)タングステンの腐食と放射化の問題を解決すべく、イオンプレーティングでのPVD法および2重ビーム法、電気化学法によってタングステン板の周囲に安定してCrNの薄膜層を形成できた。(4)水銀ターゲット容器壁やビーム窓のピッティング対策として、高速度ビデオによってバブル形成の機構を明らかにするとともに、(5)ステンレス鋼の表面改質効果を調べ、とりわけ窒化および侵炭法の複合的な表面処理によって、ピッテング損傷の進展を一桁送らせることができた。(6)宇宙材料として、アルミニウム-チタン系の高靭性複合セラミックスを開発した。(7)宇宙塵が衝突した際の亀裂伝播を防止する機能を付与したニオブ-アルミ系の合金を開発した。上記の材料について機械試験や腐食試験を行い、所定の機能を持っていることを評価した。(8)MW級の固体ターゲット用にHIP法(熱間静水圧加圧法)によって開発したタンタル被覆のタングステン薄板を高温からの急冷試験を行い、破損が生じず、冷却水の喪失事故時に対応可能なことが確認できた。(9)陽電子消滅法により、粒界制御の工程がステンレス鋼に損傷を与えない事、材料試験炉での中性子照射損傷効果を明確にした。(10)超高圧電子顕微鏡の電子線および陽子ビームを用いた照射シミューション実験にて、粒界制御材が普通材に比べて放射線損傷に強そうだというデータ、さらにニオブ-アルミ系の合金が期待した中間金属を形成し、亀裂伝播の防止機能を持っていそうだという結果を得た。(11)さらに材料の放射線損傷試験として、スイスの核破砕中性子源施設に送って放射した材料の照射後試験を行った。その結果、日本のステンレス鋼JPCAが、3dpa以上の照射でも伸び特性を持っている事、生成ガスの保持量を明らかにできた。以上で、損傷研究の基礎的な手法が得られた。今後、損傷データの一層の採取と理論的研究を通じてさらなる材料開発研究に展開したい。
  • 文部科学省:科学研究費補助金(基盤研究(C))
    研究期間 : 2003年 -2005年 
    代表者 : 渡辺 精一
     
    研究の目的本研究では、エネルギービーム照射およびアニール過程におけるアモルファス合金中の多様体クラスターの遷移挙動を明らかにし、揺らぎ特性(b:0〜2)を制御した機能性アモルファス材料の開発設計を行うために1/f^α型揺らぎ応答発現の機構解明を行うことを目的とする。研究実施事項:《非晶質(アモルファス)化過程の原子レベル構造評価》高分解能型超高圧電子顕微鏡(1.25MV:分解能0.117nm)による電子線照射誘起アモルファス化過程の原子レベルその場観察を行いデジタル録画。画像処理解析による画像解析(FFTパターンと画像マスク処理、多様体原子クラスター情報の抽出)。照射温度等を変え同様実験。アモルファス化過程における長距離秩序の消滅と短範囲秩序クラスター形成とその時間発展を詳細調査。今年度は、特に揺らぎの原因となる原子オーダーリングの構造変化について調査を行なった。《照射過程と非晶質化各段階でのアニールの分子動力学計算》分子動力学計算は、原子挿入法(EAM)をもちいて既に開発したEAMポテンシャルを用いて、フレンケル欠陥を逐次ランダムに所定照射量になるまで導入する方法を用いる。固有クラスターはボロノイ多面体解析により調査。また原子緩和を計算中に行ない、最後に体積やエネルギー等の系のプロパティーを評価する。各照射量段階での動径分布関数、原子間結合長変化と体積、トータルポテンシャルエネルギー増加評価,電子顕微鏡画像計算、FFT2次元画像処理、電子回折パターン像解析と回折強度分布定量評価。揺らぎの多変量相関性の評価を行なった。
  • 時空間マルチスケール構造解析に基づく非平衡系材料科学とナノ材料創製 i)非平衡断熱系および非平衡開放系:弱非平衡から強非平衡までの材料統計科学 ii)材料中の照射効果および機能物性に関する微細構造解析研究
    研究期間 : 2004年
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1999年 -2000年 
    代表者 : 渡辺 精一
     
    オーステナイト系ステンレス鋼における照射誘起偏析の速度論による定量化・モデリング照射誘起粒界偏析および促進拡散に関し速度論によるモデル化をおこない、定量化に成功した。照射誘起の粒界応答反応、特に照射誘起による偏析が粒界性質(方位とS値)によってどの様に依存性を調べることができ、傾角粒界の場合には明確な依存性があることを確認した。また、粒界性格を境界条件として取り入れた速度論による定量化にも成功した。照射誘起粒界応答反応の粒界性質依存性の実験的確認と定量化モデリングに成功することができた。これらの研究成果をふまえ今後は、各種合金(オーステナイトステンレス鋼、フェライト鋼、ODSフェライト鋼、および結合形式の異なる化合物系合金)における非平衡粒界応答効果に関して電子線照射その場観察実験を行い原子レベルの欠陥形成初期過程から巨視的現象(本研究では数マイクロメータ程度を対象とする)に至るまでの現象の総合的解明を行う。現在まで行ってきた速度論手法はそのままでは原子レベルの実験解析には不向きであるため、離散型の計算手法を取り込みこれと速度論を結合させ、原子レベルから巨視的レベルまでの空間的・時間的マルチスケーリングモデリングによる総合的定量化支援プログラミングを行なう。原子レベルから巨視的レベルまでの空間的・時間的マルチスケーリングモデリングによる総合的定量化支援プログラミングを行なう。当該研究は従来型の照射効果の研究に対して、原子レベル動的観察、マルチスケーリングによる定量化といった新たな視点からの息吹を注入するものであり、非平衡粒界挙動を利用した材料創製に貢献するところ大であると考えられる。
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1994年 -1994年 
    代表者 : 渡辺 精一
     
    高速増殖炉、軽水炉などの核分裂型原子炉や、将来実用化が期待される核融合炉における照射損傷は、炉材料の使用にあたり主要な問題点である。特に相安定性に関わる照射誘起偏析現象は、結晶粒界の溶質の偏析を通して照射脆化に結び付き、またボイド表面での偏析、母相での溶質濃度の変化からボイド形成に影響する可能性が指摘されている。現在までいくつかの偏析モデルが提唱されてきたが、実用材料を念頭とした照射研究に応用された例は少ない。本研究では計算コードを開発し、ステンレス鋼の粒界近傍における過剰点欠陥の容質拡散として照射誘起偏析の定量的予測を行なった。具体的には、本研究室所有の超電圧電子顕微鏡による1MeV電子線照射をおこない材料中(Fe-Cr-Ni)の2次欠陥の密度測定、粒界近傍の濃度分布分析、拡散係数等必要な物性値を見積もる。i)拡散方程式による計算照射下での連立した拡散方程式をたて、これを解くことにより各場所での元素の濃度の経時変化を調べる。この時各元素とさらに点欠陥(原子空孔と格子間原子)の濃度も併せて調べる。非線形の連立微分方程式を数値計算により解く。(逆)カ-ケンドール効果を取り入れた連立速度式によりFe-Cr-Ni合金の粒界近傍での照射誘起偏析のモデル計算を行った。本計算結果は超高圧電子顕微鏡(1MeV)を用いたシュミレーション実験より得られた照射量、温度、損傷速度の変化に伴う誘起偏析の変化と、濃度分布を概ね説明している。中性子照射などの高エネルギー粒子による照射でも、照射誘起偏析によりステンレス鋼の粒子近傍(<〜10^<-1>μm)でNiの濃度とCrの枯渇が起こると考えられる。より確実な相関則を得るためには,実験等による各種パラメータの確認が必要であることを明らかにした。

教育活動情報

主要な担当授業

  • 光熱エネルギー変換材料特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : 光および熱エネルギーと材料物性,光物性、固体中の電子・原子拡散
  • 光熱エネルギー変換材料特論
    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : 光および熱エネルギーと材料物性,光物性、固体中の電子・原子拡散
  • 材料デザイン工学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 金属材料、電子、原子、結晶構造、機能性、構造材、表面、反応プロセス
  • 材料工学概論
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 金属材料、電子、原子、結晶構造、機能性、構造材、表面、反応プロセス
  • 環境と人間
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : マテリアル製造、製造プロセス、省エネルギー、地球環境、持続的発展
  • エネルギー材料工学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : エネルギー,エネルギー変換材料,発電材料,光エネルギー変換材料,エネルギーシステム設計
  • セラミック材料学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 構造用セラミックス,電気用材料としてのセラミックス,材料学的特性
  • 半導体材料学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 固体電子論、電子のエネルギー帯、電気伝導、半導体素子

大学運営

学内役職歴

  • 2019年4月1日 - 2021年3月31日 大学院工学研究院附属エネルギー・マテリアル融合領域研究センター長
  • 2021年4月1日 - 2023年3月31日 大学院工学研究院附属エネルギー・マテリアル融合領域研究センター長

委員歴

  • 2017年04月 - 現在   日本金属学会北海道支部   幹事
  • 2017年05月 - 2019年05月   日本顕微鏡学会   理事
  • 2017年04月 - 2019年03月   日本顕微鏡学会北海道支部   支部長
  • 2015年 - 2017年   日本顕微鏡学会 北海道支部   副支部長
  • 2008年 - 2009年   日本金属学会   評議員   日本金属学会
  • 2006年 - 2008年   日本金属学会   分科会委員   日本金属学会
  • 2005年 - 2008年   日本金属学会   欧文誌編集委員   日本金属学会
  • 2005年 - 2008年   日本原子力学会   原子力計算科学専門部会委員   日本原子力学会
  • 2005年 - 2008年   日本原子力学会   北海道支部評議委員   日本原子力学会
  • 2005年 - 2008年   日本金属学会   北海道支部評議委員   日本金属学会
  • 2005年 - 2008年   日本顕微鏡学会   評議委員   日本顕微鏡学会
  • 2005年 - 2008年   日本顕微鏡学会   北海道支部評議委員   日本顕微鏡学会
  • 2004年 - 2006年   日本原子力学会   専門委員(材料関係)   日本原子力学会
  • 2004年 - 2006年   日本金属学会   編集委員   日本金属学会
  • 2004年 - 2006年   日本顕微鏡学会   評議委員   日本顕微鏡学会
  • 日本顕微鏡学会   照射効果研究部会責任者(2001~2003)   日本顕微鏡学会
  • 日本顕微鏡学会   評議委員(2001~)   日本顕微鏡学会
  • 日本金属学会   会報編集委員(1997~1999   日本金属学会
  • 日本金属学会   欧文誌編集委員(2001~)   日本金属学会
  • 日本金属学会   分科会委員(1999~2004)   日本金属学会
  • 日本金属学会   北海道支部幹事(1997~1999)   日本金属学会
  • 日本金属学会   北海道支部幹事(1997~1999)   日本金属学会
  • 日本金属学会   会報編集委員(1997~1999   日本金属学会
  • 日本金属学会   欧文誌編集委員(2001~)   日本金属学会
  • 日本金属学会   分科会委員(1999~2004)   日本金属学会
  • 原子力コード研究委員会   専門委員 (2003~)   原子力コード研究委員会
  • 日本顕微鏡学会   評議委員(2001~)   日本顕微鏡学会
  • 日本顕微鏡学会   照射効果研究部会責任者(2001~2003)   日本顕微鏡学会
  • 日本金属学会   会報編集委員(1997~1999   日本金属学会
  • 日本金属学会   欧文誌編集委員(2001~)   日本金属学会
  • 日本金属学会   分科会委員(1999~2004)   日本金属学会
  • 日本金属学会   北海道支部幹事(1997~1999)   日本金属学会
  • 日本原子力学会   照射材料専門委員(1999~)   日本原子力学会
  • 日本金属学会   会報編集委員(1997~1999   日本金属学会
  • 日本金属学会   欧文誌編集委員(2001~)   日本金属学会
  • 日本金属学会   分科会委員(1999~2004)   日本金属学会
  • 日本金属学会   北海道支部幹事(1997~1999)   日本金属学会


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