MF研究者総覧

研究者データベース

詳細
大沼　正人(オオヌマ　マサト)
工学研究院　応用量子科学部門　物質量子工学
教授
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Last Updated :2023/11/02

基本情報

所属

  • 工学研究院　応用量子科学部門　物質量子工学

職名

  • 教授

学位

  • 博士（工学）

ホームページURL

J-Global ID

研究キーワード

  • 食品科学   量子ビーム   小角散乱   誘導磁気異方性   複合材料・物性   中性子散乱   軟磁性材料   安全・安心材料   磁性   酸化物   量子サイズ効果   半導体   複合材料   ナノグラニュラー構造薄膜   ナノ粒子   無機   鉄鋼材料   GHz磁気デバイス   一軸磁気異方性   相変態   中性子小角散乱   薄膜   中性子回折   ナノ結晶   化学量論比化合物   アトムプローブ   Co基薄膜   電子顕微鏡   トンネル型磁気抵抗効果   磁気ナノ結晶   電子・情報材料   

研究分野

  • ライフサイエンス / 食品科学 / 食品構造
  • ナノテク・材料 / 構造材料、機能材料
  • ナノテク・材料 / 材料加工、組織制御
  • ナノテク・材料 / ナノ構造物理
  • ナノテク・材料 / ナノ構造化学
  • ものづくり技術（機械・電気電子・化学工学） / 電気電子材料工学
  • エネルギー / 量子ビーム科学

担当教育組織

職歴

  • 2013年04月 - 現在 北海道大学 大学院工学研究院 量子理工学部門 教授
  • 2012年04月 - 現在 京都大学 構造材料元素戦略研究拠点 拠点教授
  • 2011年07月 - 2013年03月 ワルシャワ工科大学 材料工学科 客員教授
  • 2011年04月 - 2013年03月 物質・材料研究機構 量子ビームユニット 主席研究員
  • 2009年04月 - 2011年03月 物質・材料研究機構 量子ビームセンター 主席研究員
  • 2009年01月 - 2009年12月 東北大学 学際センター 客員教授
  • 2006年04月 - 2009年03月 物質・材料研究機構 量子ビームセンター 主幹研究員
  • 2004年04月 - 2006年03月 物質・材料研究機構 材料研究所 主幹研究員
  • 2001年04月 - 2004年03月 物質・材料研究機構 材料研究所 主任研究員
  • 2000年04月 - 2001年03月 科学技術庁金属材料技術研究所 計算材料研究部 主任研究官
  • 1994年04月 - 2000年03月 科学技術庁金属材料技術研究所 材料設計研究部 研究員
  • 1997年03月 - 1998年02月 デンマークRIso国立研究所 材料研究部 客員研究員

学歴

  • 1991年04月 - 1994年03月   室蘭工業大学   大学院博士後期課程   物質工学専攻
  • 1989年04月 - 1991年03月   室蘭工業大学   大学院修士課程   金属工学専攻
  • 1985年04月 - 1989年03月   室蘭工業大学   工学部   金属工学科

研究活動情報

論文

  • 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]
  • Pawel Kozikowski, Masato Ohnuma, Ryuichi Hashimoto, Kodai Takano, Giselher Herzer, Markus Kuhnt, Christian Polak
    PHYSICAL REVIEW MATERIALS 4 9 2020年09月 [査読有り]
     
    Stress annealing (SA)-induced magnetic anisotropy is known in iron, nickel, and cobalt-based ferromagnetic metallic glass ribbons and it has already been used in commercial processes. Uniaxial elastic strain is introduced by SA and is quenched into the ribbons even after cooling and removing the external stress. The release of the uniaxial quenched strains is clearly observed as an anomaly in the linear thermal-expansion coefficient (LTEC) when the ribbon is reheated without stress. The rate of strain release corresponding to the LTEC anomaly reaches a maximum at the temperature at which the original SA was performed. We have observed this temperature memory effect over the whole temperature range from 280 to 400 degrees C, which is below the crystallization temperature T-x. The observed results are explained well by the existence of a localized "flow unit" embedded in an elastic matrix, which is accepted as the origin of the shear band formation and rejuvenation of metallic glasses with T-g (glass transition temperature) T-x), the results here indicate that the same important structural feature is common to metallic glasses with both T-g < T-x and T-g > T-x. Because magnetization behavior is very sensitive to the existence of residual elastic strain which is difficult to evaluate in most of the metallic glasses, detailed studies and a revival of interest in ferromagnetic ribbons will help us to understand more about the nature of the localized flow unit, as well as nonaffine deformations.
  • Shinya Teramoto, Masahito Imura, Yuki Masuda, Toshinori Ishida, Masato Ohnuma, Yutaka Neishi, Takahisa Suzuki
    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN 106 3 165 - 173 2020年03月 [査読有り]
     
    Using a medium-carbon steel containing 2 mass% Si, we investigated the effect of its tempered martensite microstructure on its mechanical properties. We found that the tensile strength of tempered martensite continuously decreases with increasing tempering temperature and that its yield strength markedly decreases in a tempering temperature range of 673 K to 723 K. To investigate the correlation with the microstructure, we examined the effect of tempering temperature on the microstructure by SEM and TEM and identified Fe carbide phases by TEM nanobeam diffraction pattern analysis and X-ray diffractometry. In the tempering temperature range where the yield strength significantly decreases, the morphology of the epsilon carbide precipitated in martensite blocks changed from platelike to granular and the chi carbide was precipitated in a small amount in the samples tempered at 723 K. SAXS quantitative evaluation of the epsilon carbide revealed that the decrease in the size and volume fraction of the epsilon carbide with the increase in the tempering temperature was far greater than with the samples tempered at 673 K and below. The sharp decrease in the yield strength was suggested to be correlated with the increase in the mobility of dislocations with the decrease in the precipitate volume fraction resulting from the dissolution of epsilon carbide in the transformation process of the Fe carbides.
  • Yuko Nasuda, Masato Ohnuma, Michihiro Furusaka, Kaoru Hara, Toshinori Ishida
    JOURNAL OF THE JAPANESE SOCIETY FOR FOOD SCIENCE AND TECHNOLOGY-NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI 67 6 186 - 192 2020年 [査読有り]
     
    Nanostructures in dairy products were studied using laboratory small-angle X-ray scattering (SAXS). Using a high penetration Mo-K alpha line, both milk and cheese were measured using the same shape and optics. The samples were low- and regular-fat milk, mozzarella cheese and hard cheese with different ripening periods. All samples were used in their "as obtained state" from the supermarket and no pre-treatment was used before SAXS measurements. Most of the SAXS profiles of milk and cheese showed two features. Sharp peaks corresponding to the chain structure of fat appeared in the region of q> 1 nm(-1). The positions of peaks indicate the existence of a 2 L structure in all samples except low-fat milk. In addition, a 3 L structure appeared in the cheese with ripening of 22 months. The second feature was a shoulder observed in log-log plot. The position of the shoulder in milk and mozzarella cheese was about q= 0.7 nm(-1), which has been attributed to colloidal calcium phosphate (CCP) in many papers. Similar shoulders have been observed in hard cheese with ripening of 2 and 6 months, while the position is about 0.3 nm(-1), which is lower than that of milk and mozzarella cheese. This suggests that growth of CCP size may occur during the cheese making process.
  • Takaaki Tanaka, Yuki Toji, Pawel Kozikowski, Masato Ohnuma, Miho Nagano
    ISIJ INTERNATIONAL 60 10 2246 - 2254 2020年 [査読有り]
     
    Transmission electron microscopy (TEM) is a powerful tool for analyzing fine precipitates because it can measure the size of the precipitates directly. In contrast, small angle X-ray scattering (SAXS) can observe much larger volumes and yield statistical quantitative results. However, the consistency between results obtained by SAXS and TEM has not been well investigated, especially in the case of precipitates having anisotropic shapes. In this study, the quantitative capability of SAXS was investigated by comparing SAXS and TEM results for TiC precipitates contained in high-strength steel. Samples with various size distributions of TiC precipitates were prepared. The average size, number density and volume fraction of TiC were obtained by SAXS analysis of these samples using a sphere or a disk form factor. Regardless of the form factor, the average size and volume fraction were almost the same, whereas the number density differed by one order of magnitude. The average size of TiC precipitates measured by SAXS analysis was consistent with that obtained by TEM. Since it is considered that the difference in number density depending on the form factor is attributed to an error due to the overestimation of the size distribution width, the average number density was defined to correct for this. The average number density calculated from the results using both form factors agreed well and were reasonable. It was found that using a sphere form factor with good convergence is effective for obtaining average information concerning the precipitates.
  • Shinya Teramoto, Masahito Imura, Yuki Masuda, Toshinori Ishida, Masato Ohnuma, Yutaka Neishi, Takahisa Suzuki
    ISIJ INTERNATIONAL 60 1 182 - 189 2020年 [査読有り]
     
    Using a medium-carbon steel containing 2 mass% Si, we investigated the effect of its tempered martensite microstructure on its mechanical properties. We found that the tensile strength of tempered martensite continuously decreases with increasing tempering temperature and that its yield strength markedly decreases in a tempering temperature range of 673 K to 723 K. To investigate the correlation with the microstructure, we examined the effect of tempering temperature on the microstructure by SEM and TEM and identified Fe carbide phases by TEM nanobeam diffraction pattern analysis and X-ray diffractometry. In the tempering temperature range where the yield strength significantly decreases, the morphology of the epsilon carbide precipitated in martensite blocks changed from platelike to granular and the chi carbide was precipitated in a small amount in the samples tempered at 723 K. SAXS quantitative evaluation of the e carbide revealed that the decrease in the size and volume fraction of the epsilon carbide with the increase in the tempering temperature was far greater than with the samples tempered at 673 K and below. The sharp decrease in the yield strength was suggested to be correlated with the increase in the mobility of dislocations with the decrease in the precipitate volume fraction resulting from the dissolution of e carbide in the transformation process of the Fe carbides.
  • Y. Matsumoto, K. Watanabe, K. Ohmae, A. Uritani, Y. Kiyanagi, H. Sato, M. Ohnuma, A. H. Pham, S. Morito, T. Ohba, K. Oikawa, T. Shinohara, T. Kai, S. Harjo, M. Ito
    Materials Research Proceedings 15 221 - 226 2020年 [査読有り][通常論文]
  • K. Ohmae, Y. Kiyanagi, H. Sato, K. Oikawa, A. H. Pham, K. Watanabe, Y. Matsumoto, T. Shinohara, T. Kai, S. Harjo, M. Ohnuma, S. Morito, T. Ohba, A. Uritani, M. Ito
    Materials Research Proceedings 15 227 - 232 2020年 [査読有り][通常論文]
  • K. Oikawa, Y. Kiyanagi, H. Sato, K. Ohmae, A. H. Pham, K. Watanabe, Y. Matsumoto, T. Shinohara, T. Kai, S. Harjo, M. Ohnuma, S. Morito, T. Ohba, A. Uritani, M. Ito
    Materials Research Proceedings 15 207 - 213 2020年 [査読有り][通常論文]
  • Yusuke Morikawa, Shin-ichi Nishimura, Ryu-ichi Hashimoto, Masato Ohnuma, Atsuo Yamada
    Advanced Energy Materials 10 3 1903176  Wiley 2019年12月 [査読有り][通常論文]
     
    Hard carbon is a standard anode material for Na-ion batteries. However, its low crystallinity and diverse microstructures make obtaining a full understanding of the sodium storage mechanism challenging. Here, the results of a systematic ex situ small and wide angle X-ray scattering study of a series of nanostructured hard carbons, which reveal clear evidence of sodium storage in the graphene-graphene interlayers and nanopores, are presented. Particularly, an emergence of a broad peak around q approximate to 2.0-2.1 angstrom(-1) in the low voltage region is suggested to be an indicator that sodium is densely confined in the nanopores. Thus, classical X-ray scattering techniques are demonstrated to be effective in elucidating the overall reaction scheme of Na insertion into hard carbon.
  • Takaaki Tanaka, Yuki Tao, Pawel Kozikowski, Masato Ohnuma, Miho Nagano
    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN 105 10 965 - 974 2019年10月 
    Transmission electron microscopy (TEM) is a powerful method for analyzing fine precipitates because it can measure the size of precipitates directly. In contrast, small angle X-ray scattering (SAXS) covers much larger observation volumes and has an advantage in the quantitativity of statistical representative values. However the consistency between results obtained by SAXS and TEM has been less discussed quantitatively, especially in the case of precipitates having anisotropic shapes. In this study, the quantitativity of SAXS was investigated by comparing SAXS and TEM analysis of TiC in high strength steels. Samples with various size distribution of TiC were prepared. The average size, number density and volume fraction of TiC were obtained by SAXS analysis performed on these samples using both sphere and disk form factor. Regardress of the form factor, the average size and volume fraction were almost the same, whereas the number density differed by one order. The average size of TiC measured by SAXS analysis was consistent with that obtained by TEM. Since it is considered that the difference in the number density depending on the form factors is attributed to an error due to the overestimation of size distribution width, the average number density was defined to correct this overestimation. The average number density calculated from the results using both form factors well agreed, which were a reasonable value. It was found that using sphere form factor with good convergence is effective to discuss the average information of the precipitates.
  • Zhang Boyi, Sato Rodrigo, Oyoshi Keiji, Mamiya Hiroaki, Ohnuma Masato, Takeda Yoshihiko
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 447 38 - 42 2019年05月15日 [査読有り][通常論文]
     
    We report on the spectral dependence of nonlinear optical response of Au nanocomposites in a broad photon energy (1.5-3.0 eV). Negative Au ions of 60 keV were implanted into amorphous SiO2 substrates with a total fluence varying from 3 to 9 x 10(16) ion/cm(2) to fabricate nanoparticles. The average size of Au nanoparticles under different total fluence were estimated by small angle X-ray scattering, from which a threshold of size growth was determined at 6 x 10(16) ion/cm(2). Through the combined analysis of spectroscopic ellipsometry and pump and probe spectroscopy, we have evaluated the effective and intrinsic third order susceptibility for the composites and individual Au nanoparticles, respectively. Exhibiting from the measured transient transmission spectra, the effective third order susceptibility simultaneously show saturable absorption and reversed saturable absorption at different photon energy. In order to understand this spectral dependence, we clarified the intraband and interband contributions to the intrinsic third order susceptibility. A different balance between these two contributions was observed in tiny nanoparticles with radius of 1.5 nm.
  • Oba Yojiro, Sasaki Hirokazu, Yamazaki Satoshi, Nakasaki Ryusuke, Ohnuma Masato
    SUPERCONDUCTOR SCIENCE & TECHNOLOGY 32 5 2019年05月 [査読有り][通常論文]
     
    BaZrO3 nanocolumns in (Gd, Y) Ba2Cu3Ox superconductor tapes have been characterized by anomalous small-angle x-ray scattering ( ASAXS). As Zr is distributed only in the nanocolumns, the scattering from the nanocolumns can be separated using ASAXS measurements at the Zr K absorption edge. The ASAXS results showed that the distance between the nanocolumns decreases from 37 to 28 nm with increasing the content of Zr from 15 to 25 mol%. The average diameter of the nanocolumns increases up to Zr content of 20 mol%, while the average diameter of the 25 mol% Zr sample is similar to that of the 20 mol% Zr sample. These results confirm that ASAXS measurements are useful for the characterization of BaZrO3 nanocolumns.
  • Wei Xiaoya, Lan Si, Wu Zhenduo, Ohnuma Masato, Shibayama Tamaki, Watanabe Seiichi, Zhou Jie, Lu Zhaoping, Ren Yang, Wang Xun-Li
    INTERMETALLICS 105 173 - 178 2019年02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.
  • J-PARC物質・生命科学実験施設（MLF）を用いた文化財試料等を対象とする連携研究
    鬼柳善明, 渡辺賢一, 瓜谷章, 及川健一, 篠原武尚, Stefanus Harjo, 甲斐哲也, 二川正敏, 佐藤博隆, 大沼正人, 松本吉弘, Anh Hoang Pham, 森戸茂一, 大庭卓也, 伊藤正和
    東京大学・日本原子力研究開発機構・量子科学技術研究開発機構施設利用共同研究「連携重点研究」2018年度成果報告書 H28-02  2019年 [査読無し][通常論文]
  • Inverse Pole Figure Mapping of Crystalline Grains by Bragg-dip Neutron Transmission Imaging
    H. Sato, Y. Shiota, S. Morooka, Y. Todaka, N. Adachi, S. Sadamatsu, K. Oikawa, M. Harada, S. Y. Zhang, Y. H. Su, T. Kamiyama, M. Ohnuma, M. Furusaka, T. Shinohara, Y. Kiyanagi
    J-PARC Annual Report 2017 Volume 2: Materials and Life Science Experimental Facility (MLF Annual Report 2017) J-PARC 18-04 8 - 10 2019年 [査読無し][招待有り]
  • Kuhnt Markus, Xu Xiandong, Amalraj Marshal, Kozikowski Pawel, Pradeep K. G, Ohkubo Tadakatsu, Marsilius Mie, Strache Thomas, Polak Christian, Ohnuma Masato, Hono Kazuhiro, Herzer Giselher
    JOURNAL OF ALLOYS AND COMPOUNDS 766 686 - 693 2018年10月25日 [査読有り][通常論文]
     
    Magnetic properties of amorphous and nanocrystalline Fe85.2-xCoxSi0.5B9.5P4Cu0.8 (x = 0, 4, 10, 15, 20, 25, 35, 40, 50 and 57 at%) alloys have been investigated and their detailed structural parameters have been quantitatively investigated by X-ray diffraction, transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and three dimensional atom probe (3DAP). The nanocrystalline structure that forms by annealing the melt-spun amorphous ribbon at above 400 degrees C comprises a bcc phase and a residual amorphous phase. Both coercivity and magnetostriction of the nanocrystalline state increase with increasing Co content, from H-c = 4 A m(-1) to 29 A m(-1) and from lambda(s) = 14 ppm-55 ppm, respectively. The saturation polarization J(s) reaches a maximum of about 1.88 T at a Co-content of about 25 at%. The dependence of magnetic properties on the Co content can be explained by the composite rule of the intrinsic magnetic properties of the constituent phases. We also found the grain size dependence of coercivity to change from the well-known D-6 dependence to D-3-dependence in the composition range where the magnetocrystalline anisotropy constant vanishes. (C) 2018 Elsevier B.V. All rights reserved.
  • Xu Yi, Cheng Junye, Yiu Pak Man, Shan Guangcun, Shibayama Tamaki, Watanabe Seiichi, Ohnuma Masato, Shek Chan-Hung
    NANOSCALE 10 39 18846 - 18856 2018年10月21日 [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'.
  • A. Mori, H. Mamaya, M. Ohnuma, J. Ilavsky, K. Ohishi, W. Jaroslaw, A. Olszyna, N. Watanabe, J. Suzuki, H. Kitazawa, M. Lewandowska
    J. Nucl. Mater. 501 72 - 81 2018年 [査読有り][通常論文]
  • Ping Dehai, Singh Alok, Gu Shuqi, Ohmura Takahito, Ohnuma Masato, Abe Taichi, Onodera Hidehiro
    ISIJ INTERNATIONAL 58 1 159 - 164 2018年 [査読有り][通常論文]
     
    In twinned martensite, a metastable hexagonal omega-Fe phase always exists in the twin boundary region of the body-centered cubic (bcc) {112} < 111 >-type twin. The omega-Fe electron diffraction spots at the1/3{112}alpha-Fe and 2/3{112}alpha-Fe positions have been treated as the twinning double diffraction effect previously. The omega-Fe spots fully cover the spots of the bcc matrix, twin and their double diffraction. Due to this, it is difficult to practically distinguish the omega-Fe diffraction spots from the sum of matrix + twin + double diffraction. Here, a simple method for observing the omega-Fe spots is introduced based on the twinning crystallographic analysis.In this method, at first a [011] zone axis is found in twinned martensite, containing the diffraction spots of twin and omega-Fe (previously double diffraction spots). It is then confirmed that the twin plane is inclined to the incident electron beam by means of the dark field observation. The reciprocal < 222 > * direction (containing spots at 1/3{222} and 2/3{222} positions), is noted. A tilting is then performed keeping this direction un-tilted, i.e., tilting about this direction, to < 112 > zone axis. This requires about 30 tilting. If the omega-Fe spots are absent at the 1/3{222} and 2/3{222} positions when the zone axis reaches < 112 >, then an opposite tilt is performed (since there are two tilting directions: clockwise and counter-clockwise), then, the omega-Fe diffraction spots can be seen at the 1/3{222} and 2/3{222} positions. A large twinned martensite at the TEM specimen edge is better for tilting to avoid any overlapping.
  • Xu Yi, Yiu Pak Man, Shan Guangcun, Shibayama Tamaki, Watanabe Seiichi, Ohnuma Masato, Huang Wei, Shek Chan-Hung
    CHEMNANOMAT 4 1 88 - 97 2018年01月 [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 approximate to 31m(2)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 2.14mAcm(-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.
  • Haruo Nakamichi, Katsumi Yamada, Kaneharu Okuda, Toshinori Ishida, Masato Ohnuma
    THERMEC 2018: 10TH INTERNATIONAL CONFERENCE ON PROCESSING AND MANUFACTURING OF ADVANCED MATERIALS 941 141 - 146 2018年 [査読有り][通常論文]
     
    Nano size precipitate morphologies are very important for considering the precipitate hardening mechanism of HSLA steels. Systematic analysis of precipitates from nano scale to bulk scale were carried out using Nb bearing hot rolled steels through transmission electron microscopy (TEM) observations and chemical analysis of precipitates by solvent extraction. A small angle neutron scattering (SANS) experiment was also performed using a Hokkaido Univ. compact neutron source to understand average precipitate size. Results show that both changes in hardness and the amount of precipitates (under 20nm in size) have the same tendency. Precipitate is recognized as NbC plates, which have coherency with the steel matrix by Baker-Nutting orientation relationships. A row of precipitates, formed on the interface between austenite and ferrite during transformation, is also apparent. The SANS profile shows that small size precipitate formation is detected even though the amount of precipitation is small. In addition, the magnetic scattering component of the SANS profile has high sensitivity to NbC precipitates compared with that of the nucleus scattering component. By comparing precipitate data from comprehensive experiments, we consider the relationship between precipitate behavior and the hardening mechanism.
  • Hirotaka Sato, Yoshinori Shiota, Satoshi Morooka, Yoshikazu Todaka, Nozomu Adachi, Sunao Sadamatsu, Kenichi Oikawa, Masahide Harada, Shuoyuan Zhang, Yuhua Su, Takashi Kamiyama, Masato Ohnuma, Michihiro Furusaka, Takenao Shinohara, Yoshiaki Kiyanagi
    Journal of Applied Crystallography 50 1601 - 1610 2017年12月 [査読有り][通常論文]
     
    © International Union of Crystallography, 2017. A new mapping procedure for polycrystals using neutron Bragg-dip transmission is presented. This is expected to be useful as a new materials characterization tool which can simultaneously map the crystallographic direction of grains parallel to the incident beam. The method potentially has a higher spatial resolution than neutron diffraction imaging. As a demonstration, a Bragg-dip neutron transmission experiment was conducted at J-PARC on beamline MLF BL10 NOBORU. A large-grained Si-steel plate was used. Since this specimen included multiple grains along the neutron beam transmission path, it was a challenging task for existing methods to analyse the direction of the crystal lattice of each grain. A new data-analysis method for Bragg-dip transmission measurements was developed based on database matching. As a result, the number of grains and their crystallographic direction along the neutron transmission path have been determined.Pulsed neutron Bragg-dip transmission is an efficient method for determining the crystallographic direction of crystals lying parallel to the incident beam. The method can be used for crystalline grain identification with a spatial resolution higher than that achievable by neutron diffraction imaging.
  • Sato Hirotaka, Shiota Yoshinori, Morooka Satoshi, Todaka Yoshikazu, Adachi Nozomu, Sadamatsu Sunao, Oikawa Kenichi, Harada Masahide, Zhang Shuoyuan, Su Yuhua, Kamiyama Takashi, Ohnuma Masato, Furusaka Michihiro, Shinohara Takenao, Kiyanagi Yoshiaki
    JOURNAL OF APPLIED CRYSTALLOGRAPHY 50 1601 - 1610 2017年12月 [査読有り][通常論文]
     
    A new mapping procedure for polycrystals using neutron Bragg-dip transmission is presented. This is expected to be useful as a new materials characterization tool which can simultaneously map the crystallographic direction of grains parallel to the incident beam. The method potentially has a higher spatial resolution than neutron diffraction imaging. As a demonstration, a Bragg-dip neutron transmission experiment was conducted at J-PARC on beamline MLF BL10 NOBORU. A large-grained Si-steel plate was used. Since this specimen included multiple grains along the neutron beam transmission path, it was a challenging task for existing methods to analyse the direction of the crystal lattice of each grain. A new data-analysis method for Bragg-dip transmission measurements was developed based on database matching. As a result, the number of grains and their crystallographic direction along the neutron transmission path have been determined.
  • Saida Junji, Yamada Rui, Kozikowski Pawel, Imafuku Muneyuki, Sato Shigeo, Ohnuma Masato
    JOURNAL OF ALLOYS AND COMPOUNDS 707 46 - 50 2017年06月15日 [査読有り][通常論文]
     
    The effect of a noble metal (Pd) on the local atomic structure of the glassy state and the transformation behavior of quasicrystal (QC) precipitation in Zr-70(Cu and Ni)(30-x)Pd-x (x = 0, 5, 10, 20) alloys were investigated. A QC phase precipitates in Zr-Cu glassy alloys at Pd concentrations of 5-20 at.% and in Zr-Ni glassy alloys at Pd concentrations of 10-20 at.%. The radial distribution function (RDF) indicates a change in the local atomic structure upon the addition of Pd. The QC phase is abruptly formed from the glassy structure above a certain temperature. The activation energy for nucleation is much larger than that for the precipitation of conventional intermetallic compounds. The QC growth is suddenly suppressed when their diameter reaches approximately 20 nm. The cooperative motion of icosahedral clusters as the precipitation mechanism was discussed. It was assumed that QC nucleus has a Zr-centered icosahedral medium-range order (MRO) as its core, and it grows by the aggregation of surrounding small icosahedral clusters. Noble metals might play a role of stabilizing the individual Zr-centered icosahedral MROs. (C) 2016 Elsevier B.V. All rights reserved.
  • S. Lan, Y. Ren, X. Y. Wei, B. Wang, X. L. Wu, 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]
  • Coakley James, Seong Baek-Seok, Dye David, Ohnuma Masato
    PHILOSOPHICAL MAGAZINE LETTERS 97 3 83 - 91 2017年 [査読有り][通常論文]
     
    Small angle X-ray and neutron scattering provide a non-localised quantitative analysis of nanoscale. precipitates in Ti-7Mo at.% and Gum metal, a Ti-Nb based alloy. The nucleation and coarsening kinetics are more rapid in the Ti-Nb alloy than the Ti-Mo alloy, presumably as Nb diffuses more rapidly than Mo in Ti. Therefore Mo-based beta-Ti alloys are more stable during. ageing than Nb-based beta-Ti alloys. To the authors' knowledge, this represents the first publication quantifying omega size, volume fraction and element partitioning in Gum metal.
  • Ping Dehai, Liu Tianwei, Ohnuma Masato, Ohmura Takahito, Abe Taichi, Onodera Hidehiro
    ISIJ INTERNATIONAL 57 7 1233 - 1240 2017年 [査読有り][通常論文]
     
    Binary Fe-C alloys are basic for various carbon steels in view of chemical compositions, thus, understanding the microstructural evolution in Fe-C alloys is fundamentally necessary. Three Fe-xC (x = 0.02, 0.05 and 0.1 (wt.%)) alloys were selected and the microstructure changes during water-quenching process has been studied using transmission electron microscopy (TEM).Fine carbides with a size of tens of nanometer, mainly theta-Fe3C cementite, are observed in quenched Fe-0.02C and Fe-0.05C samples. Lath martensite has been commonly observed in all the quenched alloys. Body-centered cubic (bcc) {112} < 111 > -type twinning structure with fine omega particles on the twinning boundaries has been frequently observed in the quenched Fe-0.1wt.%C samples; while the fine cementite are absent in the twinned region.A novel formation mechanism for the quenched microstructure has been proposed as follows: austenite twinned martensite (bcc + omega on twinning boundaries) -> lath martensite + carbides on lath boundaries -> carbides + ferrite (alpha-Fe). The first transition corresponds to the martensitic transformation; while the second and third transitions are the auto-tempering results of the first one. In the ultra-low carbon sample (Fe-0.02C), the third transition will be the observed microstructure; Slight high carbon (Fe-0.05C) will result in the second transition, not to the third one. The product of the first transition will be the twinned martensite (Fe-0.1C), and the final microstructure will not experience the second and third transitions. Of course, the quenching condition can also affect the final microstructure.
  • Kamiyama Takashi, Narita Yuki, Sato Hirotaka, Ohnuma Masato, Kiyanagi Yoshiaki
    NEUTRON IMAGING FOR APPLICATIONS IN INDUSTRY AND SCIENCE 88 27 - 33 2017年 [査読有り][通常論文]
     
    Spectroscopic neutron Bragg-edge imaging was performed to study a lithium-ion battery (LIB) product. This non-destructive neutron imaging method is suitable for the evaluation of industrial products, but presents some difficulties for application to multicomponent products. The LIB includes a strong neutron scatterer and an absorber, and is thus a suitable test case for the use of neutron imaging in actual product measurement. In this study, we analyzed the variation of the graphite anode structure with changes in the battery charge level. The experiments were carried out using the compact neutron source at the Hokkaido University neutron source facility (HUNS). To eliminate the effect of scattered neutron contamination, we first determined the distance between the sample and detector required to reduce this effect to under 1 %. Using this separation, the charge level dependence of the anode structure was measured. The graphite {002} Bragg-edge could be recognized on the neutron transmission spectra. The Bragg-edge was shifted and broadened with increasing battery charge. The edge was consistent with the existence of multiple graphite structural stages. The layer spacing distribution images for different charge levels showed the inhomogeneous fluctuation on the LIB lattice plane. Based on the images the fraction of the graphite structural stages were analyzed. The ratio of each stage varied with the charge level, and the ideal intercalation structure, in which the graphite layers are stuffed with Li-ions, was found to be minor in the final charging state. (C) 2017 The Authors. Published by Elsevier B.V.
  • Ishida Toshinori, Ohnuma Masato, Seong Baek Seok, Furusaka Michihiro
    ISIJ INTERNATIONAL 57 10 1831 - 1837 2017年 [査読有り][通常論文]
     
    For characterizing nanostructures embedded in a metallic matrix, a newly designed intermediate-angle neutron scattering (iANS: "irons") instrument has been developed that shortens the distance between the sample and detector and is combined with a time-of-flight (TOF) technique. Since the momentum transfer (Q) resolution can be relaxed to provide an optimum Q-range when we focus on characterizing nanoscale heterogeneity, a much higher neutron flux can be utilized for the measurements than those available in a conventional small-angle neutron scattering (SANS) instrument. Consequently, iANS gives sufficiently high quality profiles for quantitative analysis on an absolute unit scale even using a compact accelerator driven neutron source (CANS). The results obtained at the Hokkaido University Neutron Source (HUNS) are com pared to those obtained in large facilities. Some results obtained by iANS, are compared to those obtained by small angle X-ray scattering (SAXS) with respect to SAXS/SANS contrast variation.
  • Satoh Kozue, Sato Shigeo, Ohnuma Masato, Naruse Tatsuya, Kim Yonghwan, Ebata Takashi, Suzuki Shigeru, Wagatsuma Kazuaki
    ISIJ INTERNATIONAL 57 11 2028 - 2033 2017年 [査読有り][通常論文]
     
    We investigated the effect of alloying elements Ni, AI, and Mo on the mechanical properties of precipitation -hardened soft-magnetic stainless steels, whose aging condition and chemical composition were varied. Thermodynamic calculations suggested that the aging treatments led to precipitation of a beta-NiAI compound with B2 structure and Fe2Mo-type Laves phases. Although coarse precipitates, which are less effective for precipitation hardening, were observed in bright-field images obtained by transmission electron microscopy (TEM), the B2-type precipitates were detected in TEM electron diffraction patterns. By changing the concentration of the alloying elements, the B2-type beta-NiAI precipitates were mainly responsible for the precipitation hardening, and the Vickers hardness was hardly affected by the Mo content. Small-angle X-ray scattering analysis was used to determine the size and number density of the fine P-NiAl precipitates, which contributed to the hardening. The high-density beta-NiAI precipitates grew to a few nano meters in radius after an adequate period of aging, suggesting that the beta-NiAI precipitates were responsible for the precipitation-hardening characteristics. On the other hand, the size of the precipitates was less affected by the amounts of Ni and Al, and the number density decreased with decreasing Ni and Al content. The improvement in hardness resulting from theil-NiAl precipitates had a linear relationship with the square root of the product of the precipitate size and number density.
  • Oka Hiroshi, Tanno Takashi, Ohtsuka Satoshi, Yano Yasuhide, Uwaba Tomoyuki, Kaito Takeji, Ohnuma Masato
    NUCLEAR MATERIALS AND ENERGY 9 346 - 352 2016年12月 [査読有り][通常論文]
     
    The effect of thermo-mechanical treatments (TMTs) on the evolution of nano-structure in an oxide dispersion strengthened (ODS) ferritic/martensitic steel (Fe-9Cr-2W-0.22Ti-0.36Y203) was investigated. TMTs involve hot extruding and subsequent forging, which are expected to be part of a future industrial-scale manufacturing process of the ODS steel. It was shown that the ODS steel was composed of two phases a fine-grained residual ferrite phase and a transformable martensite phase. The number density of the nano-sized particles in the residual ferrite phase was significantly higher than that in the martensite phase. The TMTs did not significantly affect the number density, but slightly affected the size distribution of the nano-sized particles in both ferrite phase and martensite phase. Moreover, the volume fraction of the residual ferrite phase decreased after TMTs. In summary, the TMT conditions could be a parameter which affects the nano-structure of the ODS steel. (C) 2016 The Authors. Published by Elsevier Ltd.
  • Shi Shi, Oono Naoko, Ukai Shigeharu, Ishida Toshinori, Ohnuma Masato
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 658 296 - 300 2016年03月21日 [査読有り][通常論文]
     
    Nano-sized bubble dispersion in copper was achieved by a powder metallurgy method based on ball milling and spark plasma sintering. The microstructure of bubbles was evaluated by using Transmission Electron Microscopy (TEM), and the bubble size and interspacing were further quantitatively determined from small-angle X-ray scattering (SAXS) measurement. From TEM observation, the average radius of bubbles is 2 nm and their interspacing is 75 nm, while according to SAXS measurement, the radius is found to be 1.5 nm and the interspacing is 54 nm. By combining those parameters with the bubble distribution and Vickers hardness, the obstacle strength factor was evaluated as 0.23 by using TEM result, and 0.16 by using SAXS data. This suggested that bubbles could impede dislocation motion. (C) 2016 Elsevier B.V. All rights reserved.
  • Coakley James, Rahman Khandaker M, Vorontsov Vassili A, Ohnuma Masato, Dye David
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 655 399 - 407 2016年02月08日 [査読有り][通常論文]
     
    Tensile testing and cyclic tensile loading measurements were performed on heat-treated samples of annealed Ti-2448 and cold-rolled Ti-2448. Quenching from above the beta-transus produces an alloy that is highly superelastic has ultra-low elastic modulus (10-25 GPa) and exhibits hysteresis on loading-unloading cycles. On repeated cycling the strain energy absorbed in each cycle decreases. Annealed Ti-2448 exhibits a stable hysteresis loop. Peaks from the alpha '' phase are observed in X-ray diffraction (XRD) patterns, thus the material is quite lean in beta-stabilising additions. The alloy is shown to be highly unstable when heat-treated. A combination of small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) was employed to relate the thermally induced microstructural evolution to the change in mechanical properties. A heat-treatment of 80 degrees C to the cold-rolled material precipitated the omega phase causing embrittlement. Increasing the ageing temperature from 80 to 300 degrees C increased the stiffness, made the elastic regime more linear, and further embrittled the alloy. The low temperature heat-treatments precipitate both omega and alpha '' phases. A higher temperature ageing treatment at 450 degrees C increased the yield strength to over 1 GPa and caused embrittlement, indicating co-precipitation of alpha and omega phases. (C) 2015 Elsevier B.V. All rights reserved.
  • Relation between Vickers Hardness and Bragg-edge Broadening in Quenched Steel Rods
    H. Sato, T. Sato, Y. Shiota, T. Kamiyama, M. Ohnuma, Y. Kiyanagi
    J-PARC Annual Report 2014 Volume 2: Materials and Life Science Experimental Facility (MLF Annual Report 2014) J-PARC 16-01 KEK Progress Report 2015-5 6 - 8 2016年 [査読無し][招待有り]
  • Sato Satoru, Takei Toshiaki, Matsushita Yoshitaka, Yasuda Takeshi, Kojima Tatsuhiro, Kawano Masaki, Ohnuma Masato, Tashiro Kentaro
    INORGANIC CHEMISTRY 54 24 11581 - 11583 2015年12月21日 [査読有り][通常論文]
     
    The self-assembly of covalently linked dyad la of cyclometalated organoplatinum(II) complex and fullerene afforded alternating multilayers of electron-rich and -deficient molecular components. On the other hand, the coassembly of la with organoplatinum(II) complex 2 having no fullerene moiety gave an exfoliated form of the multilayers, by inhibiting the interdigitation of organoplatinum(II) complex moieties of la. The coassembled la/2 transports both of the photogenerated holes and electrons, while the self-assembled la allows only the transportation of electrons under the same conditions.
  • Su Yuhua, Morooka Satoshi, Ohnuma Masato, Suzuki Junichi, Tomota Yo
    METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 46A 4 1731 - 1740 2015年04月 [査読有り][通常論文]
     
    Small-angle neutron scattering (SANS) was used to investigate the spheroidization of cementite in pearlite upon annealing. Globally averaged information on the shape and size of cementite particles was collected by using the SANS profile analysis of 0.8 mass pct C pearlitic steel (0.8C) samples annealed at 973 K (700 A degrees C) for 3.6 to 86.4 ks. The change in the total area of the ferrite-cementite interface or aspect ratio determined by ex situ SANS exhibits excellent correspondence with scanning electron microscopy observations. Then, in situ SANS data were collected during isothermal annealing of the 0.8C steel and the commercially available 0.45C carbon steel (JIS-S45C). The shape change of the cementite plate was monitored, and the spheroidization rate of the 0.8C steel was found to be faster than that of the 0.45C steel. (C) The Minerals, Metals & Materials Society and ASM International 2015
  • Sato Rodrigo, Ohnuma Masato, Oyoshi Keiji, Takeda Yoshihiko
    JOURNAL OF APPLIED PHYSICS 117 11 2015年03月21日 [査読有り][通常論文]
     
    The capability of Ag nanoparticles to modulate their optical resonance condition, by optical nonlinearity, without an external feedback system was experimentally demonstrated. These optical nonlinearities were studied in the vicinity of the localized surface plasmon resonance (LSPR), using femtosecond pump-and-probe spectroscopy with a white-light continuum probe. Transient transmission changes Delta T/T exhibited strong photon energy and particle size dependence and showed a complex and non-monotonic change with increasing pump light intensity. Peak position and change of sign redshift with increasing pump light intensity demonstrate the modulation of the LSPR. These features are discussed in terms of the intrinsic feedback via local field enhancement. (C) 2015 AIP Publishing LLC.
  • Coakley James, Vorontsov Vassili A, Littrell Kenneth C, Heenan Richard K, Ohnuma Masato, Jones Nicholas G, Dye David
    JOURNAL OF ALLOYS AND COMPOUNDS 623 146 - 156 2015年02月25日 [査読有り][通常論文]
     
    This paper represents the first application of small angle neutron scattering (SANS) to the study of precipitate nucleation and growth in beta-Ti alloys in an attempt to observe both the precipitation process in-situ and to quantify the evolving microstructure that affects mechanical behaviour. TEM suggests that athermal omega can be induced by cold-rolling Gum metal, a beta-Ti alloy. During thermal exposure at 400 degrees C, isothermal omega particles precipitate at a greater rate in cold-rolled material than in the recovered, hot deformed state. SANS modelling is consistent with disc shaped nanoparticles, with length and radius under 6 nm after thermal exposures up to 16 h. Modelling suggests that the nanoprecipitate volume fraction and extent of Nb partitioning to the beta matrix is greater in the cold-rolled material than the extruded. The results show that nucleation and growth of the nanoprecipitates impart strengthening to the alloy. (C) 2014 Elsevier B.V. All rights reserved.
  • Hirotaka Sato, Yoshinori Shiota, Takenao Shinohara, Takashi Kamiyama, Masato Ohnuma, Michihiro Furusaka, Yoshiaki Kiyanagi
    Physics Procedia 69 349 - 357 2015年01月01日 [査読有り][通常論文]
     
    © 2015 The Authors.The tensor CT algorithm for strain tomography using the Bragg-edge neutron transmission spectroscopy is presented. Crystal lattice strain is not scalar but is a tensorwhich changesdepending on the observation angle. Therefore, since traditional"scalar" CT algorithms cannot be applied to tomography of strain, the development of a "tensor" CT algorithm is needed. Aiming at further developments in the future, we first developed a ML-EM based versatile tensor tomography using ofa simple algorithm withsmall restriction. The basic concept is to simultaneously reconstruct multiple strain-tensor components (scalar quantities of normal strain and shear strain) existing at a certain position. In the actual CT image reconstruction, it is important to consider the angular dependence of each tensor component. Through the simulation studies on axially-symmetric and axially-asymmetric distributionscomposed of two strain components and experimental demonstration using the axially-symmetric VAMAS standard sample, we found some important points for strain-tensor tomography. The angle-dependent back-projection procedure of ML-EM is indispensable fortomography of each tensor component,butsuch function also causes animage distortion which can average each strain value along each strain direction. Also, we found that the optimization of the angle-dependent back-projection procedure is important for further improvements of the tensor CT algorithm.
  • Size distribution of precipitates in age-hardenable electromagnetic stainless steels determined using small angle X-ray scattering
    K. Satoh, S. Sato, M. Ohnuma, T. Naruse, Y. Kim, T. Ebata, S. Suzuki, K. Wagatsuma
    Proceedings of Asia Steel Interanational Conference 2015 572-573  2015年 [査読有り][通常論文]
  • Sato Hirotaka, Sato Tomoya, Shiota Yoshinori, Kamiyama Takashi, Tremsin Anton S, Ohnuma Masato, Kiyanagi Yoshiaki
    MATERIALS TRANSACTIONS 56 8 1147 - 1152 2015年 [査読有り][通常論文]
     
    The width of crystal lattice plane spacing (d-spacing) distribution related to microscopic-strain and crystallite size in a martensite phase in a 2 cm thick quenched-ferritic steel sample was quantitatively mapped in real space by a Bragg-edge broadening analysis of spectral data from a pulsed neutron transmission experiment. This analysis was performed under the condition that the instrumental resolution parameters, determined from the data of ferrite in the same sample without microscopic-strain and crystallite size effects, were unchanged over the sample area, and assuming that the d-spacing was distributed according to a Gaussian function in the martensite area. As a result, the full width at half maximum (FWHM) of the Gaussian d-spacing distribution in the martensite was extracted at each position in a sample. Consequently, it was found that the real-space distribution of the FWHM of the d-spacing distribution is closely correlated with a real-space distribution of the Vickers hardness that corresponds to the quantity of martensite. Furthermore, it was indicated that the Vickers hardness was proportional to the FWHM of the d-spacing distribution. The results suggest that it will be possible to measure the Vickers hardness in the martensite non-destructively by using the Bragg-edge neutron transmission method.
  • Sato Hirotaka, Shiota Yoshinori, Shinohara Takenao, Kamiyama Takashi, Ohnuma Masato, Furusaka Michihiro, Kiyanagi Yoshiaki
    PROCEEDINGS OF THE 10TH WORLD CONFERENCE ON NEUTRON RADIOGRAPHY (WCNR-10) 69 349 - 357 2015年 [査読有り][通常論文]
     
    The tensor CT algorithm for strain tomography using the Bragg-edge neutron transmission spectroscopy is presented. Crystal lattice strain is not scalar but is a tensor which changes depending on the observation angle. Therefore, since traditional "scalar" CT algorithms cannot be applied to tomography of strain, the development of a "tensor" CT algorithm is needed. Aiming at further developments in the future, we first developed a ML-EM based versatile tensor tomography using of a simple algorithm with small restriction. The basic concept is to simultaneously reconstruct multiple strain-tensor components (scalar quantities of normal strain and shear strain) existing at a certain position. In the actual CT image reconstruction, it is important to consider the angular dependence of each tensor component. Through the simulation studies on axially-symmetric and axially-asymmetric distributions composed of two strain components and experimental demonstration using the axially-symmetric VAMAS standard sample, we found some important points for strain-tensor tomography. The angle-dependent back-projection procedure of ML-EM is indispensable for tomography of each tensor component, but such function also causes an image distortion which can average each strain value along each strain direction. Also, we found that the optimization of the angle-dependent back-projection procedure is important for further improvements of the tensor CT algorithm. (C) 2015 The Authors. Published by Elsevier B.V.
  • Oba Yojiro, Abe Seishi, Ohnuma Masato, Sato Nobuhiro, Sugiyama Masaaki
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 47 43 2014年10月29日 [査読有り][通常論文]
     
    The nanostructure of PbSe-ZnSe composite thin films prepared by the hot-wall deposition (HWD) method was investigated using small-angle x-ray (SAXS) scattering. The SAXS profiles indicate the formation of two kinds of nanoparticles: large nanoparticles that vanish and small particles that increase in size with increasing temperature. At high substrate temperatures, the volume fraction of all the nanoparticles estimated from SAXS is consistent with that of PbSe obtained by chemical analysis. This shows that PbSe forms nanoparticles at high substrate temperatures. On the other hand, the same analysis for the volume fraction at low substrate temperatures reveals that the chemical composition of the nanoparticles differs from PbSe. Pb nanoparticles are probably formed at low substrate temperatures and disappear with increasing substrate temperature.
  • Sato Rodrigo, Ohnuma Masato, Oyoshi Keiji, Takeda Yoshihiko
    PHYSICAL REVIEW B 90 12 2014年09月11日 [査読有り][通常論文]
     
    The effects of size quantization on the nonlinear optical response of Ag nanoparticles are experimentally studied by spectroscopic ellipsometry and femtosecond spectroscopic pump-and-probe techniques. In the vicinity of a localized surface-plasmon resonance (2.0-3.5 eV), we have investigated the optical nonlinearity of Ag particles embedded in silica glass for particle diameters ranging from 3.0 to 16 nm. The intrinsic third-order optical susceptibility chi((3))(m) m of Ag particles exhibited significant spectral and size dependences. These results are explained as quantum and dielectric confinements and are compared to the results of theoretical quantum finite-size effects calculation for metallic particles. In light of these results, we discuss the contribution of interband transitions to the size dependence of chi((3))(m) m. Quantum size effects lead to an increase in nonlinearity in small Ag particles.
  • Lewandowska Malgorzata, Wawer Kinga, Kozikowski Pawel, Ohnuma Masato, Kurzydlowski Krzysztof J
    ADVANCED ENGINEERING MATERIALS 16 5 482 - 485 2014年05月 [査読有り][通常論文]
     
    The precipitation phenomena in 7475 nanograined aluminium alloy was analysed by means of microhardness measurements, small angle X-ray scattering and electron microscopy. The nanograined samples were obtained by the hydrostatic extrusion of solution annealed and water quenched samples. It has been established that low temperature ageing causes precipitation processes to occur. However, the precipitation phenomena in nanograined materials proceed differently to those in micrograined materials. Moreover, the particle strengthening is limited by enhanced grain boundary precipitation which does not contribute to an increase in strength (when dislocation slip is the dominant deformation mechanism) and by the smaller size of precipitates.
  • Tran Duy Tap, Sawada Shin-ichi, Hasegawa Shin, Yoshimura Kimio, Oba Yojiro, Ohnuma Masato, Katsumura Yosuke, Maekawa Yasunari
    MACROMOLECULES 47 7 2373 - 2383 2014年04月08日 [査読有り][通常論文]
     
    The hierarchical structures of graft-type poly-(ethylene-co-tetrafluoroethylene) (ETFE)-based polymer electrolyte membranes (ETFE-PEMs) were investigated using small- and ultrasmall-angle X-ray scattering experiments. The ETFE-PEMs with ion exchange capacities (IECs) <2.4 mmol/g possessed conducting graft domains around lamellar crystals, with a d-spacing of 21.8-29.1 nm, and oriented crystallites (lamellar grains) with short and long correlation distances of 218-320 and 903-1124 nm, respectively. The membranes with IECs > 2.7 mmol/g showed a new phase of crystallite network domains with a d-range of 225-256 nm, indicating a phase transition from oriented crystallite to crystallite network structures in the IEC range of 2.4-2.7 mmol/g. Noted that for the ETFE-PEMs with high IECs higher conductivity at 30% RH and compatible tensile strengths at 100% RH and 80 degrees C, compared with Nafion, originated from the well-interconnected ion channels around the crystallites and the remaining lamellar crystals and crystallites, respectively.
  • Hirotaka Sato, Yoshinori Shiota, Yoshikazu Todaka, Takenao Shinohara, Takashi Kamiyama, Masato Ohnuma, Michihiro Furusaka, Yoshiaki Kiyanagi
    Advanced Materials Research 783-786 2109 - 2114 2014年01月01日 [査読無し][通常論文]
     
    Recent status of the technical development of the Bragg-edge neutron transmission imaging and its application to material science is presented. The neutron Bragg imaging has the advantages in measuring large area with reasonable spatial resolution, and it is a non-destructive method capable of looking inside a bulk material. Therefore, various information that are quite different from EBSD, synchrotron microtomography and X-ray/neutron scattering can be obtained by this method. We carried out quantitative imaging to obtain crystalline microstructural information in ultralow-carbon steels that received the high pressure torsion (HPT). The real-space distributions of texture and grain/crystallite size of HPTed steels of four torsion numbers were quantitatively visualized at once. As a result, we could deduce unique distributions of microstructural information depending on each torsion number, and correlated them with real-space distributions of the Vickers hardness. We also successfully developed a versatile strain tomography technique that can obtain tensor values for strain although traditional CT techniques can deal with only scalar values. The new CT algorithm, the tensor CT method, is based on our original algorithm called FBP-EM. The strain tensor tomography using FBP-EM was successfully applied for the experimental measured result obtained with the VAMAS neutron strain analysis international standard sample. © (2014) Trans Tech Publications, Switzerland.
  • High Pressure Torsion加工材の中性子ブラッグイメージング
    佐藤博隆, 戸高義一, 大沼正人, 篠原武尚, 加美山隆, 古坂道弘, 鬼柳善明
    日本鉄鋼協会C型研究会「新世代中性子源を利用した鉄鋼元素機能の解明」最終報告書 65 - 71 2014年 [査読無し][通常論文]
  • Activity of Hokkaido University Neutron Source, HUNS
    M. Furusaka, H. Sato, T. Kamiyama, M. Ohnuma, Y. Kiyanagi
    Physics Procedia 60 167 - 174 2014年 [査読有り][通常論文]
  • Performance of the Bragg-edge Transmission Imaging at a Compact Accelerator-driven Pulsed Neutron Source
    H. Sato, Y. Shiota, T. Kamiyama, M. Ohnuma, M. Furusaka, Y. Kiyanagi
    Physics Procedia 60 254 - 263 2014年 [査読有り][通常論文]
  • Imaging of Crystalline Structural Information of Japanese Swords by Pulsed Neutron Transmission Spectroscopy
    S. Nagashima, Y. Shiota, H. Sato, T. Kamiyama, M. Ohnuma, Y. Kiyanagi
    Physics Procedia 60 327 - 331 2014年 [査読有り][通常論文]
  • SATO Hirotaka, SHIOTA Yoshinori, TODAKA Yoshikazu, SHINOHARA Takenao, KAMIYAMA Takashi, OHNUMA Masato, FURUSAKA Michihiro, KIYANAGI Yoshiaki
    Mater Sci Forum 783/786 Pt.3 2109 - 2114 2014年 [査読無し][通常論文]
  • Tanno Takashi, Ohtsuka Satoshi, Yano Yasuhide, Kaito Takeji, Oba Yojiro, Ohnuma Masato, Koyama Shinichi, Tanaka Kenya
    JOURNAL OF NUCLEAR MATERIALS 440 1-3 568 - 574 2013年09月 [査読有り][通常論文]
     
    This study carried out mechanical tests and microstructural characterizations of several 9Cr and 11Cr-ODS tempered martensitic steels. From those results, the appropriate chemical composition range of 11Cr-ODS tempered martensitic steel was discussed from the viewpoint of high temperature strength improvement. It was shown that the residual a-ferrite fraction in 11Cr-ODS steel was successfully controlled to the same level as the 9Cr-ODS steel, which has excellent high temperature strength, by selecting the chemical compositions on the basis of the multi-component phase diagram. The tensile strength decreased with decreasing W content from 2.0 to 1.4 wt%. On the other hand, creep strength at 973 K did not degrade by the decreasing W content. Both tensile strength and creep strength increased with increasing population of the nano-sized oxide particles. Small angle X-ray scattering analysis revealed that titanium and excess oxygen contents were key parameters in order to improve the dispersion conditions of nano-sized oxide particles. (C) 2013 Elsevier B.V. All rights reserved.
  • Oksiuta Zbigniew, Kozikowski Pawel, Lewandowska Malgorzata, Ohnuma Masato, Suresh Koppoju, Kurzydlowski Krzysztof J
    JOURNAL OF MATERIALS SCIENCE 48 13 4620 - 4625 2013年07月 [査読有り][通常論文]
     
    In this study, the stability of grain size and oxide nanoparticles in the ODS steel upon annealing at high temperature (650-1350 A degrees C) has been evaluated. The ODS Fe-Cr-W-Ti-Y2O3 steel has been manufactured by powder metallurgy, consolidated by hot isostatic pressing and processed by hydrostatic extrusion. Such a processing brings about ultrafine grain structure reinforced with oxide nanoparticles (few nm in diameter) and results in superior mechanical properties. The stability of nano-oxides has been analyzed by small angle X-ray scattering together with transmission electron microscopy. The results obtained revealed excellent thermal stability of ultrafine grained ODS ferritic steel, which was attributed to the resistance of oxides against coarsening.
  • Yoshida Noboru, Yamada Yuki, Nishimura Shin-ichi, Oba Yojiro, Ohnuma Masato, Yamada Atsuo
    JOURNAL OF PHYSICAL CHEMISTRY C 117 23 12003 - 12009 2013年06月13日 [査読有り][通常論文]
     
    Hydrous ruthenium oxide (RuO2 center dot nH(2)O) has inherent proton electron mixed-conductive nature and offers huge pseudocapacitance (>700 F g(-1)), having attracted the attention of many capacitor engineers. However, the origin of the anomalous pseudocapacitance,. exhibiting a strong maximum at a specific narrow optimum annealing temperature of ca. 150 degrees C, has yet to be understood. Here we show a long-awaited explanation for this mystery based on its hierarchical nanostructure unveiled by small-angle X-ray scattering (SAXS). The striking contrast in X-ray atomic scattering factors enables SAXS to exclusively probe heavy RuO2 in subnano-to nanoscale, dispersed in confined water. We demonstrate that the surface area of the first aggregate of subnano primary RuO2 particles dominates the accessible number of proton and hence pseudocapacitance, providing critical insights into the nanoarchitectural design of high-performance electrodes for electrochemical capacitors.
  • Oba Yojiro, Ohnuma Masato, Ohnuma Shigehiro, Furusaka Michihiro, Koppoju Suresh, Takeda Shin
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 334 45 - 51 2013年05月 [査読有り][通常論文]
     
    The nanostructure of a Co-Pd-Si-O nanogranular film was investigated with the combined use of small-angle x-ray (SAXS) and neutron scattering (SANS). Using a new, compact type of SANS instrument, the SANS profiles of individual particles with a diameter of about 2-4 nm were successfully observed. The structures of magnetic regions were found to be the same as the chemical structures of the particles, and a sharp interface was observed between the matrix and the particles. The SAXS to SANS ratio clearly indicates that the particles are a CoPd alloy and the matrix is not pure SiO2. In fact, the matrix is composed of a meaningful amount of Co. (C) 2013 Elsevier B.V. All rights reserved.
  • Hasegawa Shin, Takahashi Shuichi, Iwase Hiroki, Koizumi Satoshi, Ohnuma Masato, Maekawa Yasunari
    POLYMER 54 12 2895 - 2900 2013年05月 [査読有り][通常論文]
     
    The effect of crystal morphology, such as the crystallinity and lamellar structure, on the radiation-induced graft polymerization of styrenesulfonate ethyl ester (E4S) onto poly(ether ether ketone) PEEK films was evaluated. The PEEK films possessing crystallinities ranging from 11 to 32% were irradiated with 30-150 kGy, and the graft polymerization was performed in an E4S/1,4-dioxane solution at 80 degrees C. For the PEEK films with crystallinities between 11 and 26%, the graft polymerization proceeded and reached grafting degrees of up to 70%, whereas for those having crystallinities higher than 26%, the reaction barely proceeded. The concentration of phenoxy radicals that initiated the graft polymerization in the irradiated PEEK films was constant over the entire range of crystallinity (11-32%). On the other hand, in the small-angle X-ray scattering (SAXS) profiles, a discontinuous change in the peak intensity at Q = 0.44 nm(-1), which corresponds to a lamellar spacing of 14 nm, was observed at a crystallinity of approximately 26%; namely, the PEEK films with a crystallinities greater than 26% exhibited prominent anisotropic scattering in the drawing direction. Judging from the above results, it can be concluded that the graft polymerization of styrene derivatives onto the PEEK films was affected by the formation of oriented lamellar structures that inhibited monomer diffusion into the films. (c) 2013 Elsevier Ltd. All rights reserved.
  • Iwase Hiroki, Sawada Shin-ichi, Yamaki Tetsuya, Koizumi Satoshi, Ohnuma Masato, Maekawa Yasunari
    MACROMOLECULES 45 22 9121 - 9127 2012年11月27日 [査読有り][通常論文]
     
    Small-angle scattering in a wide-Q range (4 x 10(-3) to 1.5 nm(-1)) of polymer electrolyte membranes consisting of poly(styrenesulfonic acid) and cross-linked polytetrafluoroethylene (cPTFE-PEM) with various grafting degrees up to 36% was observed by focusing small-angle neutron scattering (FSANS), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS). The hierarchical structure of the PEM was characterized as being composed of conducting layers (graft domains) in lamellar stacks with 48-57 nm spacing on the surfaces of 480 nm diameter crystallites and ultrasmall structures with 1.7 nm correlation distance of the sulfonic acid groups in the conducting layers. The PEMs with grafting degrees less than 15% possessed only grafting domains in the amorphous layers of the lamellar stacks of cPTFE. An increase in the grafting degree up to 5% led to an increase in the lamellar spacing of 20%, while the lamellar spacing remained constant with grafting degrees above 5% because of crystalline restriction. Moreover, with grafting degrees of greater than 15%, grafting domains were phase separated from the cPTFE substrate and covered the crystallites with a diameter of 480 nm (the length of a crystallite is above the observed Q region (>1.6 mu m). The graft domains around the crystallites were connected with the adjoining domains; accordingly, the PEMs with a higher degree of grafting had conductivity higher than that of Nafion. Furthermore, in the SAXS measurement, the nano order internal structure (1.7 nm) corresponded to the distance between the sulfonic acid groups of the graft polymers in the conducting layers of the cPTFE-PEM. The nano order correlation distances of the sulfa groups, which cannot be observed in Nafion, should result in methanol and water crossover levels lower than those in Nafion.
  • Kozikowski Pawel, Ohnuma Masato, Herzer Giselher, Polak Christian, Budinsky Viktoria, Koppoju Suresh, Lewandowska Malgorzata, Kurzydlowski Krzysztof J
    SCRIPTA MATERIALIA 67 9 763 - 766 2012年11月 [査読有り][通常論文]
     
    Amorphous ferromagnetic (Fe,Co,Ni) ribbons of various compositions have been prepared by rapid solidification and annealed with applied tensile stress. This process yields both creep-induced magnetic anisotropy and structural anisotropy. Post-annealing has been done to investigate the relaxation process. X-ray diffraction and thermomechanical analysis measurement of post-annealed samples reveal a clear underlying relaxation process in the material, proving that structural anisotropy corresponds to the elastic strain induced by creep annealing. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • Sato Rodrigo, Momida Hiroyoshi, Ohnuma Masato, Sasase Masato, Ohno Takahisa, Kishimoto Naoki, Takeda Yoshihiko
    JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 29 9 2410 - 2413 2012年09月 [査読有り][通常論文]
     
    We have experimentally investigated the dispersion of the third order optical susceptibility chi((3)) of silver nanoparticles embedded in silica glass in the vicinity of the surface plasmon resonance. The dispersion of the real and imaginary parts of the effective third order optical susceptibility chi((3))(eff) was evaluated from the effective refractive index using a spectroscopic ellipsometry and the transient transmission and reflection changes using a femtosecond pump probe spectroscopy. The Im chi((3))(eff) exhibits a minimum value of -1.3 x 10(-17) m(2)/V-2 at 3.03 eV. The results demonstrate that the local field factor greatly contributes to the dispersion of chi((3))(eff) for Ag nanoparticles. (c) 2012 Optical Society of America
  • Abe Seishi, Ping De Hai, Nakamura Shintaro, Ohnuma Masato, Ohnuma Shigehiro
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 12 6 5087 - 5090 2012年06月 [査読有り][通常論文]
     
    This paper investigates magnetite (Fe3O4) thin film containing a small amount of a metal element. The films are prepared by rf sputtering with a composite target of ceramic iron oxide with metal chips. Low-temperature magnetization of magnetite containing 5.3%Ge reveals that the film contains some magnetically weak coupling grains. The metal element Mg reduces both hematite (alpha-Fe2O3) and magnetite, resulting in single-phase wustite (Fe1-xO). In contrast, adding Ge selectively reduces hematite, while magnetite remains unreactive. According to the free energy of reaction, the element Ge is able to reduce hematite only, whereas the element Mg is capable of reducing both hematite and magnetite. This property is in good agreement with the experiment results.
  • Oba Yojiro, Koppoju Suresh, Ohnuma Masato, Kinjo Yuki, Morooka Satoshi, Tomota Yo, Suzuki Jun-ichi, Yamaguchi Daisuke, Koizumi Satoshi, Sato Masugu, Shiraga Tetsuo
    ISIJ INTERNATIONAL 52 3 457 - 463 2012年 [査読有り][通常論文]
     
    The microstructure of inclusions in low carbon free cutting steel without lead addition was investigated using small-angle X-ray scattering (SAXS) coupled with small-angle neutron scattering (SANS). The two-dimensional (2D) SAXS pattern shows clear scattering due to inclusions composed of large elongated particles aligned along the rolling direction, and small isotropic particles. From a comparison of the simulated and experimental 2D SAXS patterns, the shapes of the inclusions are regarded as ellipsoid for the larger inclusions and spherical for the smaller inclusions. The length of the minor axis in the large inclusion is 6.9 mu m, while the diameter of the small inclusion is 0.50 mu m. The aspect ratio of the large inclusion is estimated to be 3.8 in the lower q region, and is reduced slightly to 3.5 in the higher q region from the azimuthal plots. The results of an alloy contrast variation (ACV) analysis using both the SAXS and SANS data indicate that the chemical composition of the inclusions is almost NaCl-type manganese sulfide, and that the amount of iron sulfide is low. The volume fractions are 1.4% for the large inclusions and 0.2% for the small inclusions. This is consistent with the area fraction estimated using an optical microscope, and indicates that nearly all of the sulfur in the steel sample forms the manganese sulfide inclusions.
  • Abe Seishi, Ping De Hai, Ohnuma Masato, Ohnuma Shigehiro
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 6 2011年06月 [査読有り][通常論文]
     
    In this study, we investigate the transformation mechanism from a phase mixture of magnetite (Fe3O4) and hematite (alpha-Fe2O3) to a single-phase magnetite through the addition of a specific metal element. The thin films were prepared by rf sputtering with a composite target of metal chips set on a ceramic magnetite (or hematite) target in Ar atmosphere. It is revealed that the addition of Ge to the polycrystalline hematite film obviously produces single-phase magnetite, indicating that the hematite is fully transformed to magnetite through an addition of Ge. Such transformation is also seen with slight additions of Mo, W, Cr, and Mg, whereas the addition of Sn does not affect the phase mixture of magnetite and hematite. According to the free energy of the reaction, elements of Ge, Mo, W, Cr, and Mg are capable of reducing hematite, whereas hematite remains unreactive with addition of Sn. This is in good agreement with the experiment results. This unique technique additionally provides the maximum magnetization of 3.9 kG at 8 x 10(5) A-m(-1) (10 kOe) at a Mo concentration of 1.3 at. %. (C) 2011 The Japan Society of Applied Physics
  • Saida Junji, Sanada Takashi, Sato Shigeo, Imafuku Muneyuki, Ohnuma Masato, Ohkubo Tadakatsu, Hono Kazuhiro, Matsubara Eiichiro
    JOURNAL OF PHYSICS-CONDENSED MATTER 23 17 2011年05月04日 [査読有り][通常論文]
     
    The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structure in Zr70Cu30 glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certain temperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization is accompanied by a significant change in the local environment around the Zr atoms and a slight change around the noble metal. However, the local environment around the Cu atoms remains almost the same during QC formation. It is suggested that two types of icosahedral polyhedra exist in the glassy state: one has a relatively perfect icosahedral structure formed around the Zr atoms. The other is in a distorted state around the Cu atoms. We speculate that the medium-range order (i.e. QC nucleus) has a Zr-centered icosahedral cluster as its core, and the QC grows via aggregation of possible clusters in the initial stage. Pd or Pt atoms stabilize and/or connect individual Zr-centered icosahedral clusters, facilitating the formation of the nucleus and growth of the QC phase.
  • Hasegawa Shin, Takahashi Shuichi, Iwase Hiroki, Koizumi Satoshi, Morishita Norio, Sato Ken, Narita Tadashi, Ohnuma Masato, Maekawa Yasunari
    POLYMER 52 1 98 - 106 2011年01月07日 [査読有り][通常論文]
     
    Radiation-induced graft polymerization of sulfo-containing styrene derivatives into crystalline poly(ether ether ketone) (PEEK) substrates was carried out to prepare thermally and mechanically stable polymer electrolyte membranes based on an aromatic hydrocarbon polymer, so-called "super-engineering plastics". Graft polymerization of the sulfo-containing styrene, ethyl 4-styrenesulfonate (E4S) into a high crystalline PEEK substrate (degree of crystallinity: 32%) hardly progressed, whereas graft polymerization into a low crystalline PEEK substrate (degree of crystallinity: 11%) gradually progressed, achieving a grafting degree of more than 50% after 72 h. Oxygen radicals appeared in the ESR spectra of irradiated PEEK films, indicating that graft polymerization initiates from the phenoxy radicals generated by scission of PEEK main chains and proceeds so as to yield block type grafts. The PEEK-based polymer electrolyte membrane (PEM) converted by aqueous hydrolysis of grafted films exhibited mechanical strength (100 MPa), being 88% of the original PEEK substrates. These mechanical properties of PEEK-based PEM are much higher than those of graft-type fluorinated PEM reported previously and almost three times higher than that of Nafion (35 MPa). Wide- and small-angle X-ray scattering (WAXS and SAXS) indicated that the graft polymerization was accompanied with recrystallization of the amorphous phase of PEEK substrate, the well known solvent-induced recrystallization of amorphous PEEK solids, to form a weak lamellar structure with 8 nm spacing. Complementary SAXS and small-angle neutron scattering (SANS) observations clearly showed that the graft-type PEEK membranes possessed ion channel domains with the average distance of 13 nm, being larger than that of Nafion. Furthermore, there was a micro-structure in the ion channels with the average distance of 1.8 nm. (C) 2010 Elsevier Ltd. All rights reserved.
  • El-Safty Sherif A, Shahat Ahmed, Warkocki Wojciech, Ohnuma Masato
    SMALL 7 1 62 - 65 2011年01月03日 [査読有り][通常論文]
  • Atomic structure of nanoscale quasicrystal-forming Zr–noble metal binary metallic glasses
    J. Saida, K. Itoh, T. Sanada, S. Sato, M. Imafuku, M. Ohnuma, A. Inoue
    J. Alloys and Compounds 509S S27-S33  2011年 [査読有り][通常論文]
  • H. Mamiya, H. Hagiya, Y. Oba, M. Ohnuma, T. Oku, J. Suzuki, M. Yokoyama, T. Katayama, Y. Nishihara, H. Awano, T. Koda
    Journal of Physics: Conference Series 266 1 2011年 [査読有り][通常論文]
  • Su Yuhua, Tomota Yo, Suzuki Junichi, Ohnuma Masato
    ISIJ INTERNATIONAL 51 9 1534 - 1538 2011年 [査読有り][通常論文]
     
    The behavior of hydrogen in an ultrafine-grained electrodeposited pure iron with Lankford (r) value larger than 7.0 was studied by small angle neutron scattering (SANS) and thermal desorption spectroscopy (TDS). Nano-sized inhomogeneity consisting of hydrogen bubble exists in the deposited specimen. The bubble size increases a little by 673 K annealing and then all the bubbles disappear after 973 K annealing. With rolling at room temperature (RI), the bubble size and number density are found to decrease, which must be caused by the change in the status of hydrogen location during plastic deformation. Crystal rotation and grain coalescence are revealed to occur after rolling deformation from electron backscattered diffraction (EBSD) results.
  • Oba Yojiro, Koppoju Suresh, Ohnuma Masato, Murakami Toshio, Hatano Hitoshi, Sasakawa Kaoru, Kitahara Amane, Suzuki Jun-ichi
    ISIJ INTERNATIONAL 51 11 1852 - 1858 2011年 [査読有り][通常論文]
     
    The microstructures and chemical composition of nano-precipitates in vanadium (V) steels were investigated by the alloy contrast variation method (ACV) using small-angle X-ray scattering (SAXS) coupled with small-angle neutron scattering (SANS) at holding temperatures ranging between 600 and 700 degrees C. Both the SAXS and SANS profiles exhibited clear scattering, depending on the holding temperature, due to the presence of nano-precipitates. The scattering profiles of the precipitates are characteristic of spherical or disc-like particles. The average diameters of these precipitates increased from 0.5 nm at 600 degrees C to 23 nm at 700 degrees C, whereas the number density of the precipitates decreases with increased holding temperature. Therefore, the increasing holding temperature results in an increase in the growth rate of the precipitates. ACV analysis revealed that the chemical composition of the precipitates corresponds to NaCl-type vanadium carbide (VC) at 675 and 700 degrees C, and as VC0.9 at 625 and 650 degrees C. The formation of a different heterogeneity, non-NaCl type, was found in the sample at a holding temperature of 600 degrees C. This probably corresponds to a precursor of the NaCl phase in the initial process of precipitation.
  • Ohnuma M, Yanai T, Hono K, Nakano M, Fukunaga H, Yoshizawa Y, Herzer G
    Journal of Applied Physics 108 9 2010年11月01日 [査読有り][通常論文]
  • El-Safty Sherif A, Shahat Ahmed, Mekawy Moataz, Nguyen Hoa, Warkocki Wojciech, Ohnuma Masato
    NANOTECHNOLOGY 21 37 2010年09月17日 [査読有り][通常論文]
     
    The development of nanofiltration systems would greatly assist in the production of well-defined particles and biomolecules with unique properties. We report a direct, simple synthesis of hexagonal silica nanotubes (NTs), which vertically aligned inside anodic alumina membranes (AAM) by means of a direct templating method of microemulsion phases with cationic surfactants. The direct approach was used as soft templates for predicting ordered assemblies of surfactant/silica composites through strong interactions within AAM pockets. Thus, densely packed NTs were successfully formed in the entirety of the AAM channels. These silica NTs were coated with layers of organic moieties to create a powerful technique for the ultrafine filtration. The resulting modified-silica NTs were chemically robust and showed affinity toward the transport of small molecular particles. The rigid silica NTs inside AAM channels had a pore diameter of <= 4 nm and were used as ultrafine filtration systems for noble metal nanoparticles (NM NPs) and semiconductor nanocrystals (SC NCs) fabricated with a wide range of sizes (1.0-50 nm) and spherical/pyramidal morphologies. Moreover, the silica NTs hybrid membranes were also found to be suitable for separation of biomolecules such as cytochrome c (CytC). Importantly, this nanofilter design retains high nanofiltration efficiency of NM NPs, SC NCs and biomolecules after a number of reuse cycles. Such retention is crucial in industrial applications.
  • Yasuhara Hisao, Sato Kaoru, Toji Yuki, Ohnuma Masato, Suzuki Jun-ichi, Tomota Yo
    TETSU TO HAGANE-JOURNAL OF THE IRON AND STEEL INSTITUTE OF JAPAN 96 9 B15 - B19 2010年09月 [査読有り][通常論文]
     
    Utilization of nanometer size precipitates in steel is a promising technology for the developing high tensile strength steels, and it is important to analyze the size of the precipitates. Electron microscopy is a powerful method in directly determining the precipitates size, but the area observed is limited and statistical procedure is tedious. Therefore, size analysis of precipitates in steel was conducted by using small-angle neutron scattering method (SANS). Sample (0.045%C-1.8%Mn-0.2%Ti-0.004%N) with different heat treatment was used for the experiments. Size of nanometer size TiC calculated by SANS profiles agreed with that obtained by direct observation of precipitates by transmission electron microscope (TEM). We have succeeded in macroscopic and non-destructive determination of the size of nanometer-sized TiC.
  • Kim Je-Deok, Oba Yojiro, Ohnuma Masato, Mori Toshiyuki, Nishimura Chikashi, Honma Itaru
    SOLID STATE IONICS 181 23-24 1098 - 1102 2010年08月04日 [査読有り][通常論文]
     
    Anhydrous nafion-benzimidazole (bz) blend membranes were prepared by room temperature and autoclave solution processing. The physico-chemical properties of anhydrous nafion-bz blend membranes using different solution processing were investigated by TG-DTA, dynamic elastic modulus, XRD, SAXS, and proton conductivity. The nafion-bz blend membrane using autoclave solution processing improved the properties such as a flexibility, density, homogeneity and dynamic elastic modulus, while the crystalline in a macroscopic crystal structure and proton conductivity was nearly the same. (C) 2010 Elsevier B.V. All rights reserved.
  • Abe Seishi, Ping De Hai, Usui Hiroyuki, Ohnuma Masato, Ohnuma Shigehiro
    THIN SOLID FILMS 518 20 5690 - 5693 2010年08月02日 [査読有り][通常論文]
     
    This study investigated the preparation and particle size control of nanocrystalline magnetite (Fe(3)O(4)) containing a small amount of Ge. Thin films were prepared by radio-frequency sputtering with a composite target of Ge chips set on a Fe(3)O(4) compound target in a mixed atmosphere of Ar and O(2). X-ray diffraction revealed that the diffraction peak of magnetite gradually broadened as the oxygen ratio increased, with the mean grain size ranging from 26 to 2 nm. Transmission electron microscopy also revealed that the magnetite structurally changed from polycrystalline single phase to isolated granular nanocrystals. Magnetization at 8 x 10(5) A/m was monotonically reduced from 0.32 to 0.04T, and coercivity was monotonically reduced from 4.2 x 10(4) to 2.1 x 10(3) A/m with increasing the oxygen ratio from 0 to 0.4%. (C) 2010 Elsevier B.V. All rights reserved.
  • Byrne Cormac J, Eldrup Morten, Ohnuma Masato, Eriksen Rasmus S
    JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 210 11 1419 - 1428 2010年08月01日 [査読有り][通常論文]
     
    Bulk metallic glasses have enormous potential for use in small-scale devices such as MEMS and biomedical components. Thermoplastic forging of free standing components poses challenges unlike those seen when forging crystalline materials. Central to these challenges is the simultaneous advantage/disadvantage that BMGs flow readily into small features and asperities in the dies and molds. Whilst useful for replicating patterned surfaces, this quite often makes non-destructive removal of components quite difficult, with disproportionate extraction forces and specialized tools required to overcome friction and mechanical locking. Several solutions to this extraction problem were explored, including high temperature extraction, lubrication and the use of materials with low coefficients of thermal expansion (CTE) as die/mold materials. We show that the use of appropriately chosen low CTE die materials offers a superior method to remove BMG components from dies/molds at room temperature. The criteria for selecting the appropriate die material, cavity size and extraction temperatures are outlined. (C) 2010 Elsevier B.V. All rights reserved.
  • Pascua Chelo S, Ohnuma Masato, Matsushita Yoshitaka, Tamura Kenji, Yamada Hirohisa, Cuadros Javier, Ye Jinhua
    APPLIED CLAY SCIENCE 48 1-2 55 - 59 2010年03月 [査読有り][通常論文]
     
    The preparation of ultra-thin clay mineral films promises to open novel applications for more sensitive sensors, stronger plastics and other unexpected functionalities. However, most natural and synthetic clay particles necessarily need often tedious preparation procedures to remove crystalline impurities and to obtain completely exfoliated forms. Furthermore, the wide range of particle sizes characteristic of commonly available synthetic and natural clays can lead to variable properties and unexpected reactions. Here we report the synthesis of a homogenous monolayer-thick Zn-smectite that will benefit specific applications requiring ultra-thin and monodispersed layered nanomaterials. Furthermore, the fast and easy preparation overcomes the problems associated with the processing of both currently available synthetic and natural smectites. XRD, FE-SEM, and TEM analyses show the synthetic Zn-smectites to be relatively impurity free. Electron microscopy imaging illustrates its nanometer-sized dimension and very thin sheet-like morphology. Based on light scattering and small angle X-ray scattering measurements, it has a narrow size distribution (ave.similar to 70 nm) and a molecular-level thickness (similar to 0.7 nm), respectively. This nanostructure combined with the interesting properties of Zn is anticipated to yield novel applications as a clay-based nanomaterial. (C) 2009 Elsevier B.V. All rights reserved.
  • Amekura H, Tanaka M, Katsuya Y, Yoshikawa H, Ohnuma M, Matsushita Y, Kobayashi K, Kishimoto N
    Journal of Applied Physics 108 10 2010年 [査読有り][通常論文]
  • Amekura H, Tanaka M, Katsuya Y, Yoshikawa H, Shinotsuka H, Tanuma S, Ohnuma M, Matsushita Y, Kobayashi K, Buchal Ch, Mantl S, Kishimoto N
    Applied Physics Letters 96 2 2010年 [査読有り][通常論文]
  • 安原久雄, 佐藤馨, 田路勇樹, 大沼正人, 鈴木淳市, 友田陽
    鉄と鋼 96 545 - 549 2010年 [査読有り][通常論文]
  • K. Suresh, M. Ohnuma, Y. Oba, N. Kishimoto, P. Das, T.K. Chini
    Journal of Applied Physics 107 7 73504  2010年 [査読有り][通常論文]
  • Kim Je-Deok, Oba Yojiro, Ohnuma Masato, Jun Mun-Suk, Tanaka Yoshinori, Mori Toshiyuki, Choi Young-Woo, Yoon Young-Gi
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 157 12 B1872 - B1877 2010年 [査読有り][通常論文]
     
    Temperature tolerant new anhydrous Nafion-1,2,3-triazole blend membranes were prepared by room temperature (RT) and autoclave (AC) solution processing. Both blend membranes were very flexible and stable up to 260 degrees C. Interestingly, they showed very different physico-chemical properties. In this paper, the properties of both the blend membranes were compared by Fourier transform infrared, thermogravimetric-differential thermal analysis, dynamic elastic modulus, X-ray diffraction, small angle X-ray scattering, atomic force microscopy, and proton conductivity. 1,2,3-Triazole was successfully incorporated into the nanostructure of Nafion. The blend membranes were more conductive than Nafion at 200 degrees C under anhydrous conditions, and the conductivity was about 1 mS/cm. The blend membrane using AC solution processing showed higher thermal stability, density, and conductivity than that of RT solution processing. Therefore, an AC solution processing can be expected as a new synthesis method to get electrolyte membranes. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3503598] All rights reserved.
  • Ohtsuka Satoshi, Kaito Takeji, Kim Sawoong, Inoue Masaki, Asayama Tai, Ohnuma Masato, Suzuki Junichi
    MATERIALS TRANSACTIONS 50 7 1778 - 1784 2009年07月 [査読有り][通常論文]
     
    The effects of chemical compositions on the microstructure and high-temperature creep strength of 9Cr-ODS steel was discussed in the light of quantitative data of delta-ferrite proportion and nano-size oxide particle dispersion, which were evaluated by dilatometric analysis and small angle neutron/X-ray scattering analysis, respectively. These quantitative data are well consistent with the conventional data obtained by transmission electron microscope. Both data indicate that the important microstructural feature for creep strength improvement of the 9Cr-ODS steel is the number density of nano-size oxide particles, and ferrite/martensite (F/M) duplex structure is favorable for high population nano-size oxide particle dispersion. Both optimization of excess oxygen concentration and control of the F/M duplex structure are promising technique for nano-structure control of 9Cr-ODS steel. Tungsten solid solution strengthening appears to be small compared with oxide dispersion strengthening enhanced by duplex microstructure formation. [doi: 10.2320/matertrans.M2009096]
  • Oba Yojiro, Shinohara Takenao, Oku Takayuri, Suzuki Jun-ichi, Ohnuma Masato, Sato Tetsuya
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 4 2009年04月 [査読有り][通常論文]
     
    The small-angle neutron scattering measurement of Pd nanoparticles was performed to investigate their intraparticle magnetic Structures. The magnetic scattering from the magnetization of the samples was observed using the polarized neutron. The nuclear scattering indicated that the Pd nanoparticles can be regarded as spherical particles, and the magnetic scattering is explained based on the shell model that the particle is composed of magnetic core and shell. The magnetic moment of the core was larger than that of the shell. These results suggest that the spontaneous magnetization of the Pit nanoparticles mainly exists in the core region.
  • Kim Sa-Woong, Shobu Takahisa, Ohtsuka Satoshi, Kaito Takeji, Inoue Masaki, Ohnuma Masato
    MATERIALS TRANSACTIONS 50 4 917 - 921 2009年04月 [査読有り][通常論文]
     
    Nanometer size oxide particles in 9Cr-ODS steel are dispersed finely and densely in a matrix by the hot-solidification process. The size and density distribution of dispersed oxide particles is recognized as one of the main issues for ensuring good microstructural stability and high temperature strength in a high temperature (<700 degrees C) and neutron irradiation (250 dpa) environment. However, the behavior of oxide particles in the hot-solidification process has not been determined yet. This study evaluated the correlation between nano-size oxide particles and the heat treatment temperature and time in order to characterize the mechanism of formation and the behavior during growth and coalescence of these particles in 9Cr-ODS steel raw powder. XRD and SAXS measurements were made using high-energy synchrotron radiation X-rays in SPring-8. This is the first report of the oxide complex particles (Y2Ti2O7 and Y2TiO5) being formed from 800 to 960 degrees C, and they were observed to grow and coalesce on increasing both heat-treatment temperature and time. [doi:10.2320/matertrans.MER2008439]
  • Evaluation of Cementite Spheroidizing for a Pearlite Steel by Small Angle Neutron Scattering
    S. Morooka, M. Ohnuma, Y. Adachi, J. Suzuki, Y. Tomota
    Proc. of The 17th IFHTSE Congress 49 466 - 469 2009年 [査読有り][通常論文]
  • M. Ohnuma, J. Suzuki, S. Ohtsuka, S. Kim, M. Inoue, H. Kitazawa
    Acta Materialia 57 5571 - 5581 2009年 [査読有り][通常論文]
  • Kim Je-Deok, Ohnuma Masato, Nishimura Chikashi, Mori Toshiyuki, Kucernak Anthony
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 156 6 B729 - B734 2009年 [査読有り][通常論文]
     
    The small-angle X-ray scattering (SAXS) and proton conductivity of Nafion-benzimidazole (na-bz) blend membranes were investigated at various annealing temperatures. The SAXS data showed that the bz base as a proton source was successfully incorporated in the Nafion nanostructure, and the bz in the nanostructure was stable under both wet and dry conditions at room temperature. The nanostructural stability of the na-bz blend membrane was also investigated at various temperatures and was compared to the X-ray diffraction and proton conductivity data. In the na-bz blend membrane, both the nanostructure and the bz were stable up to 150 degrees C under anhydrous (nonhumidified) conditions. The proton conductivity was also stable over this temperature range. The na-bz blend membrane may be useful as an anhydrous membrane for high temperature polymer electrolyte fuel cells.
  • Tsuchiya Koichi, Ohnuma Masato, Nakajima Kiyomi, Koike Tadahiro, Hada Yasufumi, Todaka Yoshikazu, Umemoto Minoru
    MATERIALS AND DEVICES FOR SMART SYSTEMS III 1129 113 - 124 2009年 [査読有り][通常論文]
     
    Crystalline-to-amorphous transformation and nanostructure formation by severe plastic deformation was investigated for TiNi shape memory alloy by high pressure torsion deformation and cold drawing. Phase transformation and mechanical properties of partially amorphous materials were also investigated. The amorphization and nanocrystallization can be an effective mean to produce materials with high young's modulus and large recovery strain. The amorphous/nanocrystalline TiNi wires after aging exhibit high tensile strength (similar to 2 GPa), high apparent elastic modulus (similar to 71 GPa) and large pseudoelastic recovery (> 5%). Such properties are useful for novel medical devices.
  • Kim Je-Deok, Ohnuma Masato, Nishimura Chikashi, Mori Toshiyuki
    PROTON EXCHANGE MEMBRANE FUEL CELLS 9 25 1 405 - 414 2009年 [査読有り][通常論文]
     
    anhydrous proton conducting electrolytes. Among them, nafion-bz and -triazole blend membranes showed high proton conductivity properties under non-humidified (anhydrous) conditions. The SAXS data showed that the bases as a proton source was successfully incorporated in the nafion nanostructure, and also the bz base in the nanostructure was stable under both wet and dry conditions at room temperature. The nanostructural stability of the nafion-bz blend membrane was also investigated at various temperatures, and was compared to the XRD and proton conductivity data.
  • Abe Seishi, Ohnuma Masato, Ping D. H, Ohnuma Shigehiro
    JOURNAL OF APPLIED PHYSICS 104 10 2008年11月15日 [査読有り][通常論文]
     
    This paper investigates size distribution of Ge nanogranules embedded in Al oxide thin film prepared by rf reactive sputtering method. It is found from the results of x-ray diffraction and small angle x-ray diffraction spectroscopy that their mean sizes distribute bimodally or single dominantly with respect to sputtering process parameter of additional oxygen ratio in Ar and Ge concentrations. Compositional plane of these distribution types reveals that single dominant distribution appears along the line of stoichiometric composition of Al(2)O(3), and deviation from stoichiometry results in bimodal distribution. Thus, size uniformity of Ge nanogranules seems to be enhanced when the Al oxide matrix forms stoichiometric composition.
  • Abe Seishi, Ohnuma Masato, Ping De Hai, Ohnuma Shigehiro
    APPLIED PHYSICS EXPRESS 1 9 2008年09月 [査読有り][通常論文]
     
    This paper investigates the crystal structure and optical absorption of Ge/TiO2 composite thin films for next-generation solar cells. X-ray diffraction patterns reveal that an anatase-dominant structure of TiO2 matrix is successfully obtained by compositional optimization. The optical absorption spectra are obviously shifted to visible- and near-infrared-regions due to the presence of Ge nanogranules, suggesting that Ge/TiO2 composite thin films are therefore capable of converting solar radiation to electrical power. Accordingly, the two valuable properties of anatase-dominant structure and favorable absorption are found to be retained simultaneously in the Ge/TiO2 composite thin films. (C) 2008 The Japan Society of Applied Physics.
  • Takeda Yoshihiko, Momida Hiroyoshi, Ohnuma Masato, Ohno Takahisa, Kishimoto Naoki
    OPTICS EXPRESS 16 10 7471 - 7480 2008年05月12日 [査読有り][通常論文]
     
    The wavelength dispersions of third-order nonlinear optical response for Cu nanoparticle materials have been experimentally evaluated from transient spectra measured with the pump-probe method. The evaluated dispersions were analyzed on hot electron contribution using the Maxwell-Garnett approximation with the Drude model for intraband transition and first principles calculation for interband transition. The wavelength dispersion didn't directly reflect the dispersion of a local electric field factor. The interband transition term in hot electron contribution strongly dominated the dispersion around the surface plasmon resonance by Fermi smearing. Intrinsic interband contribution to the nonlinearity was suggested from the analysis. Particle-size and host-medium dependence of the nonlinearity were also simulated. (C) 2008 Optical Society of America.
  • Kumar G, Ohnuma M, Furubayashi T, Ohkubo T, Hono K
    JOURNAL OF NON-CRYSTALLINE SOLIDS 354 10-11 882 - 888 2008年02月01日 [査読有り][通常論文]
  • M. Ojima, M. Ohnuma, J. Suzuki, S. Ueta, T. Shimizu, Y. Tomota
    Scripta Materialia 59 313 - 316 2008年 [査読有り][通常論文]
  • Ohnuma Masato, Suzuki Jun-Ichi, Wei Fu-Gao, Tsuzaki Kaneaki
    SCRIPTA MATERIALIA 58 2 142 - 145 2008年01月 [査読有り][通常論文]
     
    Small-angle neutron scattering has been measured for 97.62Fe-0.23C-0.25Nb-1.90Ni (at.%) steel with and without hydrogen charging. The intensity of the scattering from nanosized NbC is higher for samples with hydrogen than for those without hydrogen. The enhanced scattering intensity for samples with hydrogen disappears after hydrogen desorption heat treatment. This result provides direct structural evidence for the trapping of hydrogen by NbC. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • Kundig A. A, Ohnuma M, Ohkubo T, Abe T, Hono K
    SCRIPTA MATERIALIA 55 5 449 - 452 2006年09月 [査読有り][通常論文]
  • Kumar G, Nagahama D, Ohnuma M, Ohkubo T, Hono K
    SCRIPTA MATERIALIA 54 5 801 - 805 2006年03月 [査読有り][通常論文]
  • Tian N, Ohnuma M, Ohkubo T, Hono K
    MATERIALS TRANSACTIONS 46 12 2880 - 2885 2005年12月 [査読有り][通常論文]
  • Norio Maruyama, Sachiko Hiromoto, Masato Ohnuma, Takao Hanawa
    MATERIALS TRANSACTIONS 45 4 1233 - 1238 2005年10月17日 [査読有り][通常論文]
     
    市販のZr基バルクアモルファス合金を用いて、大気中と擬似体液中におけるフレッティング疲労特性を比較検討した。 フレッティング損傷が飽和する下限界疲労繰返し数は大気中の場合、全寿命の20%以下であるのに対して、擬似体液中でのそれは約30-50%であり、フレッティングによるき裂発生寿命はPBS(-)中で1桁以上遅れることが明らかになった。その原因として試料表面の酸化皮膜の相違であることを示唆した。
  • Tian N, Ohnuma M, Hono K
    SCRIPTA MATERIALIA 53 6 681 - 685 2005年09月 [査読有り][通常論文]
  • Ohnuma M, Hono K, Yanai T, Nakano M, Fukunaga H, Yoshizawa Y
    APPLIED PHYSICS LETTERS 86 15 2005年04月11日 [査読有り][通常論文]
  • Gopalan R, Kundig AA, Ohnuma M, Kishimoto S, Hono K
    SCRIPTA MATERIALIA 52 8 761 - 765 2005年04月 [査読有り][通常論文]
  • Kundig AA, Ohnuma M, Ohkubo T, Hono K
    ACTA MATERIALIA 53 7 2091 - 2099 2005年04月 [査読有り][通常論文]
  • Ping DH, Ohnuma M, Hirakawa Y, Kadoya Y, Hono K
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 394 1-2 285 - 295 2005年03月15日 [査読有り][通常論文]
  • J. Saida, H. Kato, A. Inoue, M. Ohnuma
    Advanced Engineering Materials 7 39 - 43 2005年02月 [査読有り][招待有り]
  • Tian N, Ohnuma M, Hono K
    Metastable, Mechanically Alloyed and Nanocrystalline Materials 24-25 491 - 494 2005年 [査読有り][通常論文]
  • Novel Nanoctructure and deformation behavior in rapidly quenched Cu-(Zr or Hf)-Ti Alloys
    J. Saida, H. Kato, A. Inoue, M. Ohnuma
    J. Sci. Adv. Eng. Mater. 62 000  2004年12月31日 [査読有り][通常論文]
  • Martin I, Ohkubo T, Ohnuma M, Deconihout B, Hono K
    ACTA MATERIALIA 52 15 4427 - 4435 2004年09月06日 [査読有り][通常論文]
  • Kundig AA, Abe N, Ohnuma M, Ohkubo T, Mamiya H, Hono K
    APPLIED PHYSICS LETTERS 85 5 789 - 791 2004年08月02日 [査読有り][通常論文]
  • Kajiwara K, Ohnuma M, Ohkubo T, Ping DH, Hono K
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 375 738 - 743 2004年07月15日 [査読有り][通常論文]
  • Yoshizawa Y, Fujii S, Ping DH, Ohnuma M, Hono K
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 375 207 - 212 2004年07月15日 [査読有り][通常論文]
  • Kundig AA, Ohnuma M, Ping DH, Ohkubo T, Hono K
    ACTA MATERIALIA 52 8 2441 - 2448 2004年05月03日 [査読有り][通常論文]
  • Takahashi YK, Koyama T, Ohnuma M, Ohkubo T, Hono K
    JOURNAL OF APPLIED PHYSICS 95 5 2690 - 2696 2004年03月01日 [査読有り][通常論文]
  • Ohnuma M, Hono K, Yanai T, Fukunaga H, Yoshizawa Y
    APPLIED PHYSICS LETTERS 83 14 2859 - 2861 2003年10月06日 [査読有り][通常論文]
  • Nagahama D, Ping DH, Ohnuma M, Sasaki H, Kita K, Hono K
    MATERIALS TRANSACTIONS 44 10 1955 - 1961 2003年10月 [査読有り][通常論文]
  • Xiong XY, Ohnuma M, Ohkubo T, Ping DH, Hono K, Ohnuma S, Fujimori H, Masumoto T
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 265 1 83 - 93 2003年09月 [査読有り][通常論文]
  • Ohnuma M, Ping DH, Abe T, Onodera H, Hono K, Yoshizawa Y
    JOURNAL OF APPLIED PHYSICS 93 11 9186 - 9194 2003年06月01日 [査読有り][通常論文]
  • Takahashi YK, Ohkubo T, Ohnuma M, Hono K
    JOURNAL OF APPLIED PHYSICS 93 10 7166 - 7168 2003年05月15日 [査読有り][通常論文]
  • Takahashi YK, Ohnuma M, Hono K
    JOURNAL OF APPLIED PHYSICS 93 10 7580 - 7582 2003年05月15日 [査読有り][通常論文]
  • Yoshizawa Y, Fujii S, Ping DH, Ohnuma M, Hono K
    SCRIPTA MATERIALIA 48 7 863 - 868 2003年04月01日 [査読有り][通常論文]
  • Kajiwara K, Ohnuma M, Ping DH, Haruyama O, Hono K
    INTERMETALLICS 10 11-12 1053 - 1060 2002年11月 [査読有り][通常論文]
  • Takahashi YK, Ohnuma M, Hono K
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 246 1-2 259 - 265 2002年04月 [査読有り][通常論文]
  • Takahashi YK, Ohnuma M, Hono K
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 40 12B L1367 - L1369 2001年12月15日 [査読有り][通常論文]
  • Ping DH, Ohnuma M, Hono K, Watanabe M, Iwasa T, Masumoto T
    JOURNAL OF APPLIED PHYSICS 90 9 4708 - 4716 2001年11月01日 [査読有り][通常論文]
  • Murty BS, Ping DH, Ohnuma M, Hono K
    ACTA MATERIALIA 49 17 3453 - 3462 2001年10月09日 [査読有り][通常論文]
  • Evidence of quantum size effect in nanocrystalline silicon by optical absorption
    T. Matsumoto, J. Suzuki, M. Ohnuma, Y. Kanemitsu, Y. Masumoto
    Phys. Rev. B 63 195322/1 - 5 2001年 [査読有り][通常論文]
  • Nanostructures of hydrogen- and deuterium-terminated porous silicon
    J. Suzuki, M. Ohnuma, T. Matsumoto
    J. Phys. Soc. Jpn. 70, Suppl. A 303 - 305 2001年 [査読有り][通常論文]
  • Mitani S, Fujimori H, Takanashi K, Yakushiji K, Ha JG, Takahashi S, Maekawa S, Ohnuma S, Kobayashi N, Masumoto T, Ohnuma M, Hono K
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 198-99 179 - 184 1999年06月 [査読有り][通常論文]
  • Ha JG, Mitani S, Takanashi K, Ohnuma M, Hono K, Fujimori H
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 198-99 21 - 23 1999年06月 [査読有り][通常論文]
  • M OHNUMA, J SUZUKI, S FUNAHASHI, T ISHIGAKI, H KUWANO, Y HAMAGUCHI
    PHYSICA B 213 582 - 584 1995年08月 [査読有り][通常論文]
     
    The small-angle neutron scattering (SANS) from Fe-Cu-Nb-Si-B nanocrystalline alloys has been measured in magnetic field. The features of nuclear scattering profiles are different from those of the magnetic scattering. The magnetic scattering shows that the distribution of local magnetization is not uniform in a BCC-Fe grain. On the other hand the nuclear scattering shows that the Omstein-Zernike-type fluctuation of concentration exits in nanocrystalline alloys.
  • M. Ohnuma, J. Suzuki, S. Funahashi, T. Ishigaki, H. Kuwano, Y. Hamaguchi
    Mater. Trans. 36 918 - 923 1995年 [査読有り][通常論文]
  • Small angle neutron scattering study on a phase separation in a 3-component microemulsion system
    H. Seto, E. Yokoi, S. Komura, D. Schwahn, K. Mortensen, J. Suzuki, M. Ohnuma, Y. Ito
    J. de Physique I 3 161 - 164 1993年 [査読有り][通常論文]

その他活動・業績

  • Rodrigo Sato, Rodrigo Sato, Keiji Oyoshi, Masato Ohnuma, Yoshihiko Takeda, Yoshihiko Takeda Optics InfoBase Conference Papers 2016年08月29日 [査読無し][通常論文]
     
    © 2016 OSA. We clarified the quantum size effects of the intrinsic nonlinearity and the nonlinear optical modulation of the local-field of an Ag nanoparticle. Understanding the underlying mechanisms in the nonlinear regime is a crucial step for controlling the light at nanoscale.
  • Recent Activity of KUMASANS
    Y. Oba, M. Hino, T. Oda, M. Ohnuma, N. Sato, R. Inoue, M. Sugiyama The 8th Meeting on Collective Action for Nomadic Small Angle Scatterers 2015年04月 [査読無し][通常論文]
  • Rodrigo Sato, Masato Ohnuma, Keiji Oyoshi, Yoshihiko Takeda, Yoshihiko Takeda JSAP-OSA Joint Symposia, JSAP 2014 2014年01月01日 [査読無し][通常論文]
  • Hirotaka Sato, Yoshinori Shiota, Takashi Kamiyama, Masato Ohnuma, Michihiro Furusaka, Yoshiaki Kiyanagi, Yoshiaki Kiyanagi Physics Procedia 60 254 -263 2014年01月01日 [査読無し][通常論文]
     
    © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license. Performances of the Bragg-edge transmission imaging at a compact accelerator-driven pulsed neutron source (pulsed CANS) are presented and evaluated. This technique is expected to be a new material analysis tool that can quantitatively visualize crystalline microstructural information inside a bulk material over large area with reasonable spatial resolution non-destructively. Therefore, it is expected that such new useful instrument should be installed at not only world-leading pulsed spallation neutron sources but also popular-priced CANS. For this reason, we evaluated and discussed the performances of the Bragg-edge transmission imaging at CANS for potential users. A coupled moderator is usually used to gain higher neutron flux at CANS. In such situation, quantitative imaging of crystal lattice strain and crystalline phase is not easy due to the low wavelength resolution. However, according to Monte-Carlo simulation calculation studies, it was found that an experimental setup using a decoupled moderator connected to a supermirror guide tube can solve this problem. On the other hand, in the situation using the coupled moderator, quantitative imaging of crystallographic texture and crystallite size can be carried out, but the Rietveldtype data analysis software, RITS, is necessary to evaluate reasonably low statistics data measured at CANS. Furthermore, it was found that reasonable results can be obtained by the Bragg-edge transmission imaging with the RITS code at CANS, which are consistent with results of a high-performance neutron diffraction experiment with the Rietveld analysis at a world-leading pulsed spallation neutron source. This means the Bragg-edge transmission imaging is expected to be one of the most efficient crystallographic/metallographic analysis tools for CANS.
  • Michihiro Furusaka, Hirotaka Sato, Takashi Kamiyama, Masato Ohnuma, Yoshiaki Kiyanagi, Yoshiaki Kiyanagi Physics Procedia 60 167 -174 2014年01月01日 [査読無し][通常論文]
     
    © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license. Hokkaido University neutron source, HUNS was completed in 1973, and has been used actively for developments of moderators, neutron instruments, neutron devices and new methods for 40 years although its power is not so high. Recently, a pulsed neutron imaging method has been developed and a new type of small angle neutron scattering method has been also developed. The pulsed neutron imaging is a unique method that can give the physical quantities such as crystallographic quantities of materials over wide area of the real space. So far, the small angle neutron scattering (SANS) is considered to be impossible at a neutron source with a power of HUNS. However, mini focusing SANS (mfSANS) was developed and proved to be useful. Here, we present the present activities on the pulsed neutron imaging and mfSANS at HUNS.
  • S. Nagashima, Y. Shiota, H. Sato, T. Kamiyama, M. Ohnuma, Y. Kiyanagi Physics Procedia 60 327 -331 2014年01月01日 [査読無し][通常論文]
     
    © 2014 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license. Japanese swords are peculiar ones forged by a unique method developed in Japan. The forging methods are different each other, depending on age and area. Therefore, the crystalline structure of a Japanese sword depends on the age and the area. In this study, we obtained crystallographic information of Japanese swords and investigated the difference in texture and crystallite size from Japanese swords by using the pulsed neutron transmission spectroscopy. The neutron transmission experiment was carried out at HUNS (Hokkaido University Neutron Source). The samples were two types of Japanese swords. We analyzed the position-dependent neutron transmission spectra and obtained quantitative microstructural information in two-dimensional real space. We found that there were differences of the microstructure between edge and back of each Japanese sword and the microstructure was different between two Japanese swords.
  • Rodrigo Sato, Masato Ohnuma, Takahisa Ohno, Hiroyoshi Momida, Yoshihiko Takeda, Yoshihiko Takeda Optics InfoBase Conference Papers 2013年12月01日 [査読無し][通常論文]
  • Characterization of Nanostructures in Co-Insulator Nanogranular Films Using Small-Angle Neutron and X-ray Scattering
    Y. Oba, M. Ohnuma, S. Ohnuma, K. Ohishi, S. Takata, J. Suzuki, M. Sugiyama The 8th Pacific Rim International Conference on Advanced Materials and Processing, Hawaii, USA 2013年08月 [査読無し][通常論文]
  • Nanostructure and Chemical State of Co-Insulator Soft magnetic Nanogranular Film
    Y. Oba, M. Ohnuma, S. Ohnuma, K. Ohishi, K. Takata, J. Suzuki, M. Sugiyama 15th International Small-Angle Scattering Conference, Sydney, Australia 2012年11月 [査読無し][通常論文]
  • Cluster strengthening of steels ~ Importance of characterization for the heterogeneities with a few nanometer scale ~
    M. Ohnuma, P. Kozikowski, Y. Oba, J. Suzuki, M. Furusaka 15th International Small-Angle Scattering Conference, Sydney, Australia 2012年11月 [査読無し][通常論文]
  • Compact-Accelerator Based laboratory-Neutron Source for Nano-Scale Structure Characterization
    M. Furusaka, T. Miyata, M. Ohnuma, Y. Oba, S. Takeda, A. Homma International Union of Materials Research Societies – International Conference on Electronic Materials 2012, Yokohama, Japan 2012年09月 [査読無し][通常論文]
  • Partitioning State of Co in Co-insulator Soft Magnetic Nanogranular Films Characterized by Small-Angle Scattering
    Y. Oba, M. Ohnuma, S. Ohnuma, M. Furusaka International Union of Materials Research Societies – International Conference on Electronic Materials 2012, Yokohama, Japan 2012年09月 [査読無し][通常論文]
  • Unveiling the Origin of Pseudo-Capacitance at Hydrous RuO2 Nanoparticles by Small-Angle X-Ray Scattering
    N. Yoshida, Y. Yamada, S. Nishimura, Y. Oba, M. Ohnuma, A. Yamada International Union of Materials Research Societies – International Conference on Electronic Materials 2012, Yokohama, Japan 2012年09月 [査読無し][通常論文]
  • Characterization of Nanostructures in Co-Pd-Si-O Soft Magnetic Nanogranular Film Using Compact type Small-Angle Neutron Scattering Spectrometer
    Y. Oba, M. Ohnuma, S. Ohnuma, M. Furusaka 2012 TMS Annual Meeting & Exhibition, Orlando, USA 2012年03月 [査読無し][通常論文]
  • Characterization of Morphology and Chemical Composition of Inclusion in Steel Using Small-Angle X-ray and Neutron Scattering
    Y. Oba, S. Koppoju, M. Ohnuma, Y. Kinjo, S. Morooka, Y. Tomota, J. Suzuki, D. Yamaguchi, S. Koizumi, M. Sato, T. Shiraga 日本MRS学術シンポジウム、2011年12月 (横浜情報文化センター、横浜) 2011年12月 [査読無し][通常論文]
  • Microstructural Analysis of Metallic Materials using Small-Angle X-ray and Neutron Scattering
    Y. Oba, M. Ohnuma, P. Kozikowski 1st Asia-Oceania Conference on Neutron Scattering, Tsukuba, Japan 2011年11月 [査読無し][通常論文]
  • Micellisation of hydrophobic fullerene amphiphiles in alkane solvents
    ホランビー マーティン, 大場 洋次郎, 大沼 正人, 中西 尚志 第63回コロイドおよび界面化学討論会、2011年9月 (京都大、京都) 2011年09月 [査読無し][通常論文]
  • New application of small angle X-ray Scattering: Redox-active nano-RuO2 dispersed in hydrous phase
    N. Yoshida, S. Nishimura, Y. Yamada, Y. Oba, M. Ohnuma, A. Yamada The 62nd Annual Meeting of the International Society of Electrochemistry, Niigata, Japan 2011年09月 [査読無し][通常論文]
  • 大沼 正人 非破壊検査 : journal of N.D.I 60 (2) 86 -92 2011年02月01日 [査読無し][通常論文]
  • 大沼 繁弘, 中村 慎太郎, 大沼 正人 日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan 175 17 -24 2010年12月17日 [査読無し][通常論文]
  • Characterization of Nano-size Heterogeneities by Combining SAXS and SANS
    M. Ohnuma, Y. Oba, K. Suresh, J. Suzuki 日本MRS学術シンポジウム、2010年12月 (横浜市開港記念会館、神奈川) 2010年12月 [査読無し][通常論文]
  • Quantitative Analysis for Vanadium Carbide Precipitates in Microalloyed Steels using Small-Angle X-ray and Neutron Scattering
    Y. Oba, M. Ohnuma, T. Murakami, H. Hatano, J. Suzuki 日本MRS学術シンポジウム、2010年12月 (横浜市開港記念会館、神奈川) 2010年12月 [査読無し][通常論文]
  • robing nano-scale structures in Ar-ion irradiated c-Si by small angle x-ray scattering
    K. Suresh, M. Ohnuma, Y. Oba, N. Kishimoto, P. Das, T. K. Chini 日本MRS学術シンポジウム、2010年12月 (横浜市開港記念会館、神奈川) 2010年12月 [査読無し][通常論文]
  • Nano-Structure of Aggregates Formed by Hydrocarbon–Fluorocarbon Hybrid type Gemini Surfactants in Aqueous Solution
    T. Yoshimura, A. Okuda, H. Iwase, Y. Oba, M. Ohnuma, T. Ogawa, S. Isoda International Conference on Nanoscopic Colloid and Surface Science, Chiba, Japan 2010年09月 [査読無し][通常論文]
  • Aggregation Properties of Amphiphilic Dendrimer in Aqueous Solutions: A Combined Small-Angle Scattering (SANS and SAXS) Study
    H. Iwase, T. Yoshimura, A. Ebihara, Y. Oba, M. Ohnuma, M. Shibayama International Conference on Nanoscopic Colloid and Surface Science, Chiba, Japan 2010年09月 [査読無し][通常論文]
  • Nanostructures and magnetic properties in Co–metal oxide nano-granular films
    Y. Oba, M. Ohnuma, K. Suresh, S. Ohnuma International Symposium on Advanced Magnetic Materials and Applications 2010, Sendai, Japan 2010年07月 [査読無し][通常論文]
  • 萩谷 裕之, 奥 隆之, 鈴木 淳市, 吉良 弘, 篠原 武尚, 加倉井 和久, 横山 淳, 西原 美一, 間宮 広明, 大場 洋次郎, 大沼 正人, 粟野 博之, 神田 哲典, 片山 利一 日本物理学会講演概要集 65 (1) 2010年03月01日 [査読無し][通常論文]
  • Small-angle scattering as a tool for quantitative analysis of precipitates in steels
    M. Ohnuma, J. Suzuki, K. Suresh, Y. Oba XIV International Conference on Small-Angle Scattering, Oxford, United Kingdom 2009年09月 [査読無し][通常論文]
  • Small-Angle Neutron Scattering Study on Ferromagnetic Pd Nanoparticles using Polarised Neutrons
    Y. Oba, T. Shinohara, T. Oku, J. Suzuki, M. Ohnuma, T. Sato XIV International Conference on Small-Angle Scattering, Oxford, United Kingdom 2009年09月 [査読無し][通常論文]
  • 萩谷 裕之, 奥 隆之, 鈴木 淳市, 吉良 弘, 篠原 武尚, 加倉井 和久, 横山 淳, 西原 美一, 間宮 広明, 大場 洋次郎, 大沼 正人, 栗野 博之, 神田 哲典, 片山 利一 日本物理学会講演概要集 64 (2) 2009年08月18日 [査読無し][通常論文]
  • 篠原 武尚, 鈴木 淳市, 大沼 正人, 奥 隆之, 大沼 繁弘 日本物理学会講演概要集 63 (1) 2008年02月29日 [査読無し][通常論文]
  • H. Amekura, M. Ohnuma, N. Kishimoto, Ch. Buchal, S. Mantl J. Appl. Phys. 104 (11) 114309 2008年 [査読無し][通常論文]
  • 大沼 正人, 鈴木 淳市 電気製鋼 79 (3) 217 -227 2008年 [査読無し][通常論文]
     
    Small-angle scattering is one of simplest methods to evaluate the average size and volume fraction of precipitates in the metals and alloys. The accuracy of the evaluated size is higher than 5 % if the analysis is proceeded in the proper way. In comparison with powder diffraction, however, there are some differences in the way to measure and analyze the small-angle scattering although the principle of the phenomena are same in both way. The key issues for measurements and analysis of small-angle scattering are overviewed and the results for high nitrogen martensitic steel are shown as an ex...
  • 間宮 広明, 大沼 正人, 大沼 繋弘, 古林 孝夫, 藤森 啓安 日本物理学会講演概要集 62 (1) 2007年02月28日 [査読無し][通常論文]
  • 間宮 広明, 大沼 正人, 大沼 繁弘, 古林 孝夫, 藤森 啓安 日本物理学会講演概要集 61 (2) 2006年08月18日 [査読無し][通常論文]
  • 大沼 正人, 鈴木 淳市 分析化学 55 (6) 381 -390 2006年06月05日 [査読無し][通常論文]
     
    X線及び中性子小角散乱により,金属-非金属ナノグラニュラ軟磁性膜,析出強化型ステンレス鋼,Al-Mg-Si合金の微細組織評価を行った.小角散乱法ではこれら金属材科の各種特性長(粒径,粒子間隔など)をサブナノメートルスケールの精度で評価可能である.この平均スケールの定量評価結果を基に磁気的/機械的特性の発現機構を検討した結果について報告する.
  • 茂筑 高士, 八巻 和宏, 清水 夏美, Wuernisha Tuerxun, 森 一広, 石垣 徹, 神山 崇, 藤井 宏樹, 大沼 正人, 山田 圭, 伊藤 真二, 門脇 和男, 平田 和人 日本物理学会講演概要集 61 (1) 2006年03月04日 [査読無し][通常論文]
  • 中性子鉄鋼研究への応用-2 中性子およびX線小角散乱によるミクロ組織定量測定
    大沼正人, 鈴木淳市 日本鉄鋼協会誌「ふぇらむ」 11 631 -640 2006年 [査読無し][通常論文]
  • 丸山 典夫, 廣本 祥子, 大沼 正人, 塙 隆夫 日本金屬學會誌 = Journal of the Japan Institute of Metals 69 (6) 481 -487 2005年06月20日 [査読無し][通常論文]
  • 間宮 広明, 中谷 功, 大沼 正人, 古林 孝夫 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 28 2004年09月21日 [査読無し][通常論文]
  • 間宮 広明, 大沼 正人, 中谷 功, 古林 孝夫 日本物理学会講演概要集 59 (1) 2004年03月03日 [査読無し][通常論文]
  • 大沼 正人 金属 74 (1) 79 -86 2004年01月 [査読無し][通常論文]
  • 大沼 正人 金属 73 (12) 1233 -1240 2003年12月 [査読無し][通常論文]
  • 大沼 正人, 鈴木 淳市, 宝野 和博, 三谷 誠司 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 27 12 -13 2003年09月01日 [査読無し][通常論文]
  • 大沼 正人, 宝野 和博, 大沼 繁弘, 小野寺 秀博, 藤森 啓安 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 25 2001年09月01日 [査読無し][通常論文]
  • K. Hono, M. Ohnuma, M. Murayama, S. Nishida, A. Yoshie, T. Takahashi Scripta Materialia 44 (6) 977 -983 2001年04月01日 [査読無し][通常論文]
     
    The microstructures of pearlitic steel wires with cementite is investigated. The wires has a strain of 5.1 and tensile strength of 5,170 MPa. The cementite is present as fragmented nanoscale particles. The evidence for partial dissolution of cementite is analyzed.
  • M. Ohnuma, K. Hono, S. Linderoth, J. S. Pedersen, Y. Yoshizawa, H. Onodera Acta Materialia 48 (20) 4783 -4790 2000年12月04日 [査読無し][通常論文]
     
    The kinetics of copper clustering and primary crystallization of FINEMET type alloys with the compositions Fe74.5-xSi13.5B9Nb3Cux and Fe77Si11B9Nb3-xCux have been studied by small-angle neutron scattering (SANS) and high-sensitivity differential scanning calorimetry (DSC) in order to explain the different optimized Cu contents, x, for obtaining the highest permeability in these two alloys. SANS results have shown that the alloys with the optimized Cu contents have the finest nanocrystalline microstructures. Kinetic analyses of Cu clustering prior to primary crystallization have shown that the number density of Cu clusters becomes highest at the crystallization stage of α-Fe primary crystals in the alloy containing an optimized amount of Cu.
  • M Ohnuma, K Hono, H Onodera, S Ohnuma, H Fujimori, JS Pedersen JOURNAL OF APPLIED PHYSICS 87 (2) 817 -823 2000年01月 [査読無し][通常論文]
     
    The microstructures of Co-Al-O thin films of wide varieties of compositions are studied by transmission electron microscopy and small angle x-ray scattering (SAXS). In the superparamagnetic specimens, high resolution electron microscope images reveal that isolated spherical Co particles are surrounded by an amorphous aluminum oxide matrix. However, in the soft ferromagnetic films, the shape of the Co particles is prolate ellipsoidal. SAXS intensities from the soft magnetic specimens decrease inversely with the wave vector, q, in a low wave-vector region, while an interparticle interference peak is observed for the superparamagnetic specimens. The scattering profiles of the soft magnetic films imply that the Co particles have a cylindrical shape and are randomly oriented. The correlation between the magnetic properties and the microstructures is discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)00802-1].
  • 大沼 正人, 宝野 和博, 小野寺 秀博 まてりあ : 日本金属学会会報 38 (12) 982 -988 1999年12月20日 [査読無し][通常論文]
  • M Ohnuma, K Hono, H Onodera, S Mitani, JG Ha, H Fujimori NANOSTRUCTURED MATERIALS 12 (1-4) 573 -576 1999年07月 [査読無し][通常論文]
     
    We have studied changes in microstructures of Co46Al19O35 granular thin films on annealing by transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS). The as-deposited from exhibits a large magnetoresistance (MR) ratio of approximately 9% at room temperature. The films consist of nearly spherical cobalt particles of a few nanometer in diameter embedded in an amorphous aluminum oxide matrix. Although the MR ratio decreases during annealing at 300 degrees C, no visible changes in the microstructure are evident. However, the interparticle distance of the particles estimated from the peak position in the SAXS data shows apparent increase after 10 min annealing. Upon further annealing, the interparticle distance does not change noticeably, but the MR ratio continues to decrease. Electron diffraction results show that a considerable amount of cobalt oxide appears during long term annealing. Thus the degradation of the MR ratio after long term annealing is attributed to oxidation of the Co particles. (C) 1999 Acta Metallurgica Inc.
  • 大沼 正人, 宝野 和博, 小野寺 秀博, 三谷 誠司, 藤森 啓安 まてりあ : 日本金属学会会報 37 (5) 1998年05月20日 [査読無し][通常論文]
  • 大沼 正人, 宝野 和博, 阿部 英司, 小野寺 秀博 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 21 253 -a-253-b 1997年10月01日 [査読無し][通常論文]
  • 菅原 貴彦, 高梨 弘毅, 藤森 啓安, 宝野 和博, 大沼 正人, 後藤 敦, 安岡 弘志 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan 20 1996年09月01日 [査読無し][通常論文]
  • 小野寺 秀博, 阿部 太一, 大沼 正人, 木村 一弘, 藤田 充苗, 田中 千秋 鐵と鋼 : 日本鐡鋼協會々誌 81 (8) 821 -826 1995年08月01日 [査読無し][通常論文]
     
    One of the present authors has proposed a new concept about the Inherent creep strength determining the long term creep strength of ferritic steels. In the present study, effect of solute elements in the ferrite matrix on the Inherent creep strength of 0.2 and 0.3 mass% carbon steels was studied from a view point of atomic configurations such as atomic pairs. The equilibrium concentrations of solute elements and atomic pairs in the ferrite matrix were estimated by thermodynamic calculations with the sublattice model (Thermo-calc.) and the central atoms model, respectively. The following res...
  • 瀬戸 秀紀, 横井 英司, 長尾 道弘, 好村 滋洋, 今井 正幸, 鈴木 淳市, 大沼 正人, Schwahn D 日本物理学会講演概要集. 年会 49 (3) 1994年03月16日 [査読無し][通常論文]
  • 瀬戸 秀紀, 横井 英司, 好村 滋洋, Schwahn D, Mortensen K, 鈴木 淳市, 大沼 正人, 伊藤 雄而 日本物理学会講演概要集. 秋の分科会 1993 (3) 1993年09月20日 [査読無し][通常論文]
  • 大沼 正人, 桑野 寿, 浜口 由和 日本金属学会誌 56 (3) p238 -246 1992年03月 [査読無し][通常論文]

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委員歴

  • 2009年03月 - 現在   日本鉄鋼協会   評価・分析・解析部会委員
  • 2008年04月 - 2011年03月   日本中性子科学会   波紋編集委員
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