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林 好一*; Lederer, M.*; 福本 陽平*; 後藤 雅司*; 山本 裕太*; 八方 直久*; 原田 正英; 稲村 泰弘; 及川 健一; 大山 研司*; et al.
Applied Physics Letters, 120(13), p.132101_1 - 132101_6, 2022/03
被引用回数：4 パーセンタイル：33.23(Physics, Applied)The local structure around boron doped in a 6H-type silicon carbide (SiC) was investigated using neutron holography. Three dimensional atomic images reconstructed from multiple-wavelength holograms revealed the boron substitution for both silicon and carbon. To determine the boron locations accurately, we calculated holograms with varying occupancies of six different sites and fitted the image intensities with those obtained from the experimental holograms by the steepest descent method. As a result, it was found that boron atoms were selectively located at the Si-C-cubic site layer. Furthermore, boundaries right above the boron locations were suggested from the absence of atomic images in the upper region of the reconstruction.
Si single crystals林 慶*; 齋藤 亘*; 杉本 和哉*; 大山 研司*; 林 好一*; 八方 直久*; 原田 正英; 及川 健一; 稲村 泰弘; 宮崎 譲*
AIP Advances (Internet), 10(3), p.035115_1 - 035115_7, 2020/03
被引用回数：19 パーセンタイル：68.77(Nanoscience & Nanotechnology)MgSi is a potential thermoelectric (TE) material that can directly convert waste energy into electricity. In expectation of improving its TE performance by increasing electron carrier concentration, the element boron (B) is doped in MgSi single crystals (SCs). Their detailed crystal structures are definitely determined by using white neutron holography and single-crystal X-ray diffraction (SC-XRD) measurements. The white neutron holography measurement proves that the doped B atom successfully substitutes for the Mg site. The SC-XRD measurement confirms the B-doping site and also reveals the presence of the defect of Si vacancy (VSi) in the B-doped MgSi SCs. Regarding TE properties, the electrical conductivity, 
, and the Seebeck coefficient, S, decreases and increases, respectively, due to the decrease in the electron carrier concentration, contrary to the expectation. The power factor of the B-doped MgSi SCs evaluated from and S does not increase but rather decreases by the B-doping.
林 好一*; 大山 研司*; 八方 直久*; 松下 智裕*; 細川 伸也*; 原田 正英; 稲村 泰弘; 仁谷 浩明*; 宍戸 統悦*; 湯葢 邦夫*
Science Advances (Internet), 3(8), p.e1700294_1 - e1700294_7, 2017/08
Local structures around impurities in solids provide important information for understanding the mechanisms of material functions, because most of them are controlled by dopants. For this purpose, the X-ray absorption fine structure method, which provides radial distribution functions around specific elements, is most widely used. However, a similar method using neutron techniques has not yet been developed. If one can establish a method of local structural analysis with neutrons, then a new frontier of materials science can be explored owing to the specific nature of neutron scattering-that is, its high sensitivity to light elements and magnetic moments. Multiple-wavelength neutron holography using the time-of-flight technique with pulsed neutrons has great potential to realize this. We demonstrated multiple-wavelength neutron holography using a Eu-doped CaF single crystal and obtained a clear three-dimensional atomic image around trivalent Eu substituted for divalent Ca, revealing an interesting feature of the local structure that allows it to maintain charge neutrality. The new holography technique is expected to provide new information on local structures using the neutron technique.
松下 智裕*; 安居院 あかね; 吉越 章隆
Europhysics Letters, 65(2), p.207 - 213, 2004/01
被引用回数：32 パーセンタイル：76.07(Physics, Multidisciplinary)一般に光電子ホログラムから3次元的な原子配列を再構成する方法としてフーリエ変換を中心とした計算法が用いられてきた。しかし現実的には原子で散乱された電子波は理想的なs波ではないために単純なフーリエ変換で3次元空間を再構成するのは難しい。われわれはフーリエ変換を用いずに原子の立体配列を再構成するアルゴリズム(scattering pattern matrix)を見いだした。単一エネルギーのホログラムからでも再構成が可能である。
伊藤 智義*; H.Eldeib*; 吉田 賢司*; 高橋 伸弥*; 矢部 孝*; 功刀 資彰
Computer Physics Communications, 93, p.13 - 20, 1996/00
被引用回数：35 パーセンタイル：83.31(Computer Science, Interdisciplinary Applications)核融合炉の事故時には、真空容器の破断口等から、トリチウムを含む放射化ダスト等が自然対流(置換流)に同伴して炉外へ移送されることが考えられる。この置換流は非定常的な対向流動を伴うことから、この流れに同伴されるダストの粒径分布、流束分布等の測定は極めて難しい。そこで、本研究では置換流全体を一挙に捕捉し、これを高速に処理して粒径分布や速度分布を求める方法としてホログラフィを利用することとした。しかし、多数のホログラムを高速に処理する必要があり、群馬大学と協力してホログラフィ専用計算機HORN-2を開発することに成功した。HORN-2(HOlographic ReconstructioN,#2)は32bit浮動少数点演算で1ボート当たり0.3Gflopsの速度をもち、光の強度計算を実行することが出来る。今回は3ボード用いて、並列操作することで1Gflopsの高速演算を達成した。
