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論文

Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex, 2; Neutron scattering instruments

中島 健次; 川北 至信; 伊藤 晋一*; 阿部 淳*; 相澤 一也; 青木 裕之; 遠藤 仁*; 藤田 全基*; 舟越 賢一*; Gong, W.*; et al.

Quantum Beam Science (Internet), 1(3), p.9_1 - 9_59, 2017/12

J-PARC物質・生命科学実験施設の中性子実験装置についてのレビューである。物質・生命科学実験施設には23の中性子ビームポートがあり21台の装置が設置されている。それらは、J-PARCの高性能な中性子源と最新の技術を組み合わせた世界屈指の実験装置群である。このレビューでは、装置性能や典型的な成果等について概観する。

論文

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by X-ray diffraction

鈴木 秀俊*; 仲田 侑加*; 高橋 正光; 池田 和磨*; 大下 祥雄*; 諸原 理*; 外賀 寛崇*; 森安 嘉貴*

AIP Advances (Internet), 6(3), p.035303_1 - 035303_6, 2016/03

 被引用回数:3 パーセンタイル:66.57(Nanoscience & Nanotechnology)

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ X-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

論文

Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using ${{it in situ}}$ X-ray diffraction

下村 憲一*; 鈴木 秀俊*; 佐々木 拓生; 高橋 正光; 大下 祥雄*; 神谷 格*

Journal of Applied Physics, 118(18), p.185303_1 - 185303_7, 2015/11

 被引用回数:4 パーセンタイル:67.17(Physics, Applied)

Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by ${{it in situ}}$ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping, attributed to In-Ga intermixing between the QDs and the cap layer. Photoluminescence wavelength can be tuned by controlling the intermixing and the cap layer thickness. It is demonstrated that such information about strain is useful for designing and preparing novel device structures.

論文

Local lattice distortion caused by short-range charge ordering in transition metal oxides

樹神 克明; 井川 直樹; 社本 真一; 池田 一貴*; 大下 英敏*; 金子 直勝*; 大友 季哉*; 鈴谷 賢太郎; 星川 晃範*; 石垣 徹*

JPS Conference Proceedings (Internet), 8, p.034002_1 - 034002_6, 2015/09

Cubic spinel compound LiMn$$_2$$O$$_4$$ with the mixed valence of Mn$$^{3.5+}$$ has non-metallic conductivity. The local structure determined by the PDF analysis has an orthorhombic lattice distortion and includes inequivalent Mn$$^{3+}$$ and Mn$$^{4+}$$ sites. YBaCo$$_2$$O$$_5$$ also exhibits non-metallic conductivity although the Co has the mixed valence of +2.5 above 220 K which corresponds with charge ordering temperature. The PDF obtained at 450 K is not reproduced by the PDF calculated for the averaged structure and can be reproduced by the PDF calculated for the structure model corresponding to the charge ordering state. These results suggest that the valence electrons are localized with short-range periodicity, resulting in the non-metallic conductivities in these materials.

論文

${it In situ}$ three-dimensional X-ray reciprocal-space mapping of InGaAs multilayer structures grown on GaAs(001) by MBE

佐々木 拓生; 高橋 正光; 鈴木 秀俊*; 大下 祥雄*; 山口 真史*

Journal of Crystal Growth, 425, p.13 - 15, 2015/09

 パーセンタイル:100(Crystallography)

${it In situ}$ three-dimensional X-ray reciprocal space mapping (${it in situ}$ 3D-RSM) was employed for studying molecular beam epitaxial (MBE) growth of InGaAs multilayer structures on GaAs(001). Measuring the symmetric 004 diffraction allowed us to separately obtain film properties of individual layers and to track the real-time evolution of both residual strain and lattice tilting. In two- layer growth of InGaAs, significant plastic relaxation was observed during the upper layer growth, and its critical thickness was experimentally determined. At the same thickness, it was found that the direction of lattice tilting drastically changed. We discuss these features based on the Dunstan model and confirm that strain relaxation in the multilayer structure is induced by two kinds of dislocation motion (dislocation multiplication and the generation of dislocation half-loops).

論文

Local structural analysis by using atomic pair distribution function on mixed valence compound LiMn$$_2$$O$$_4$$

樹神 克明; 井川 直樹; 社本 真一; 池田 一貴*; 大下 英敏*; 金子 直勝*; 大友 季哉*; 鈴谷 賢太郎; 星川 晃範*; 石垣 徹*

JPS Conference Proceedings (Internet), 3, p.013012_1 - 013012_6, 2014/06

LiMn$$_2$$O$$_4$$ has a cubic spinel structure with a single Mn site whose valence is +3.5. Below about 260 K, the compound exhibits a charge ordering and has inequivalent Mn sites with valences of +3 and +4. However, even in the cubic phase without the charge ordering, temperature dependence of the electrical conductivity is non-metallic. We have performed PDF (atomic pair distribution function) analysis on powder neutron diffraction data of LiMn$$_2$$O$$_4$$ obtained above 300 K where the compound has cubic structure. The local structure determined by PDF analysis has an orthorhombic lattice distortion and includes the inequivalent Mn sites with valences of +3 and +4 up to, at least, about 450 K. These results indicate that valence electrons are localized at Mn sites with short range periodicity, resulting in the non-metallic electrical conductivity. It can be regarded as a glass state of valence electrons whereas a charge ordering can be regarded as a crystallization of valence electrons.

論文

2D neutron diffraction imaging on an ammonite

社本 真一; 樹神 克明; 伊巻 正*; 中谷 健; 大下 英敏*; 金子 直勝*; 増子 献児*; 坂本 健作; 山口 憲司; 鈴谷 賢太郎; et al.

JPS Conference Proceedings (Internet), 1, p.014011_1 - 014011_5, 2014/03

アンモナイト化石の2次元回折イメージングをJ-PARCにおける高強度全散乱装置NOVAで行った。観測された回折プロファイルはカルサイト,シデライトとアモルファス構造からなっていることがわかった。

論文

Real-time observation of crystallographic tilting InGaAs layers on GaAs offcut substrates

西 俊明*; 佐々木 拓生; 池田 和磨*; 鈴木 秀俊*; 高橋 正光; 下村 憲一*; 小島 信晃*; 大下 祥雄*; 山口 真史*

AIP Conference Proceedings 1556, p.14 - 17, 2013/09

 パーセンタイル:100

${it In situ}$ X-ray reciprocal space mapping during In$$_{x}$$Ga$$_{1-x}$$As/GaAs(001) MBE growth is performed to investigate effects of substrate misorientations on crystallographic tilting. It was found that evolution of the crystallographic tilt for the InGaAs films is strongly dependent on both layer structures and substrate misorientations. We discuss these observations in terms of an asymmetric distribution of dislocations.

論文

In situ three-dimensional X-ray reciprocal-space mapping of GaAs epitaxial films on Si(001)

高橋 正光; 仲田 侑加*; 鈴木 秀俊*; 池田 和磨*; 神津 美和; Hu, W.; 大下 祥雄*

Journal of Crystal Growth, 378, p.34 - 36, 2013/09

 被引用回数:4 パーセンタイル:53.18(Crystallography)

Epitaxial growth of III-V semiconductors on silicon substrates is a longstanding issue in semiconductor technology including optoelectronics, high-mobility devices and solar cells. In addition to a lattice mismatch of 4%, formation of antiphase domain boundaries makes the growth of GaAs/Si(001) more complicated than that of congeneric combinations, such as Ge/Si(001) and InGaAs/GaAs(001). In the present study, defects in GaAs/Si(001) epitaxial films are investigated by three-dimensional X-ray reciprocal-space mapping technique, which we have successfully applied for InGaAs/GaAs(001) growth. Experiments were carried out at a synchrotron beamline 11XU at SPring-8 using a molecular-beam epitaxy chamber integrated with a multi-axis X-ray diffractometer. Streaky scattering extending from the GaAs 022 peak in the $$langle 111rangle$$ directions was observed, indicating development of plane defects, such as facets and stacking faults.

論文

Local lattice distortion caused by short range charge ordering in LiMn$$_2$$O$$_4$$

樹神 克明; 井川 直樹; 社本 真一; 池田 一貴*; 大下 英敏*; 金子 直勝*; 大友 季哉*; 鈴谷 賢太郎

Journal of the Physical Society of Japan, 82(9), p.094601_1 - 094601_6, 2013/09

 被引用回数:6 パーセンタイル:46.59(Physics, Multidisciplinary)

We have performed powder neutron diffraction on $$^7$$LiMn$$_2$$O$$_4$$ at 300 K. The crystal structure determined by Rietveld analysis is a cubic spinel with space group of $$Fdbar{3}m$$ in which all Mn atoms are crystallograghically equivalent, consistent with many preceding studies. However, the atomic pair distribution function (PDF) of this compound cannot be fitted by the cubic structure satisfactorily, and it can be reproduced by the orthorhombic structure with $$Fddd$$. It corresponds with the structure of charge ordered phase below about 260 K, indicating a short range charge ordering. In the local structure determined by PDF analysis, two types of MnO$$_6$$ octahedra with long and short atomic distances between Mn and O atoms exist and their Mn-O distances are almost consistent with the distances in the charge ordered phase. From these results, valence electrons are localized at Mn sites like a glass even in the cubic phase, resulting in the non-metallic electrical conductivity.

論文

高圧力下で形成される岩塩構造ランタン1水素化物; 放射光X線と中性子の利用による新しい希土類金属水素化物の発見

町田 晃彦; 本田 充紀*; 服部 高典; 佐野 亜沙美; 綿貫 徹; 片山 芳則; 青木 勝敏; 大下 英敏*; 池田 一貴*; 大友 季哉*

波紋, 23(2), p.131 - 136, 2013/05

高圧下における放射光及び中性子利用実験により、NaCl型構造の一重水素化物LaDが形成されることを初めて観測した。これまでにランタン2水素化物LaH$$_{2}$$が約11GPaの高圧力下で高水素濃度相と低水素濃度相へ相分離することを放射光X線回折によって示した。今回実施したLaD$$_2$$の高圧下中性子回折実験から、相分離で生成した低水素濃度相がNaCl型構造LaDであることを確認した。このNaCl型構造のLaDの形成は希土類金属水素間物では初めてのことであり、水素-金属間相互作用の水素占有サイト依存性の研究の足がかりとなる。

論文

Formation of NaCl-type monodeuteride LaD by the disproportionation reaction of LaD$$_{2}$$

町田 晃彦; 本田 充紀*; 服部 高典; 佐野 亜沙美; 綿貫 徹; 片山 芳則; 青木 勝敏; 小松 一生*; 有馬 寛*; 大下 英敏*; et al.

Physical Review Letters, 108(20), p.205501_1 - 205501_5, 2012/05

 被引用回数:8 パーセンタイル:42.01(Physics, Multidisciplinary)

希土類金属水素化物ではH/M=2及び3の化学量論比組成が存在する。2水素化物は金属格子がfcc構造でその四面体(T)サイトを水素が占有している。八面体(O)サイトも水素が占有すると3水素化物となる。これまでにLaH$$_{2.3}$$が高圧下、約11GPaで水素の高濃度相と低濃度相へ相分離することを放射光X線回折によって示した。今回実施したLaD$$_2$$の高圧下中性子回折実験から、相分離の生成物としてNaCl型構造の一重水素化物LaDが形成されることを初めて観測した。第一原理計算及び格子ダイナミクス計算からも高圧下でLaDが形成されることが示された。このNaCl型構造のLaHの発見は水素-金属間相互作用の水素占有サイト依存性の研究の足がかりとなる。

論文

Observation of in-plane asymmetric strain relaxation during crystal growth and growth interruption in InGaAs/GaAs(001)

佐々木 拓生*; 下村 憲一*; 鈴木 秀俊*; 高橋 正光; 神谷 格*; 大下 祥雄*; 山口 真史*

Japanese Journal of Applied Physics, 51(2), p.02BP01_1 - 02BP01_3, 2012/02

 被引用回数:2 パーセンタイル:87.32(Physics, Applied)

In-plane asymmetric strain relaxation in lattice-mismatched InGaAs/GaAs(001) heteroepitaxy is studied by ${it in situ}$ three-dimensional X-ray reciprocal space mapping. Repeating crystal growth and growth interruptions during measurements allows us to investigate whether the strain relaxation is limited at a certain thickness or saturated. We find that the degree of relaxation during growth interruption depends on both the film thickness and the in-plane directions. Significant lattice relaxation is observed in rapid relaxation regimes during interruption. This is a clear indication that relaxation is kinetically limited. In addition, relaxation along the [110] direction can saturate more readily than that along the [$${bar 1}$$10] direction. We discuss this result in terms of the interaction between orthogonally aligned dislocations.

論文

Real-time structural analysis of compositionally graded InGaAs/GaAs(001) layers

佐々木 拓生*; 鈴木 秀俊*; 稲垣 充*; 池田 和磨*; 下村 憲一*; 高橋 正光; 神津 美和*; Hu, W.; 神谷 格*; 大下 祥雄*; et al.

IEEE Journal of Photovoltaics, 2(1), p.35 - 40, 2012/01

 被引用回数:5 パーセンタイル:69.24(Energy & Fuels)

Compositionally step-graded InGaAs/GaAs(001) buffers with overshooting (OS) layers were evaluated by several characterization techniques for higher efficiency metamorphic III-V multijunction solar cells. By high-resolution X-ray diffraction, we found that fully relaxed or tensile strained top layers can be obtained by choosing appropriate OS layer thickness. Moreover, from real-time structural analysis using ${it in situ}$ X-ray reciprocal space mapping (${it in situ}$ RSM), it was proved that the top layer is almost strained to the OS layers, and it is independent of the thicknesses of the OS layers. Dislocations in the vicinity of the OS layers were observed by transmission electron microscopy, and the validity of results of ${it in situ}$ RSM was confirmed from the viewpoint of misfit dislocation behavior. Finally, by photoluminescence measurements, we showed that tensile strained top layers may be suitable for the improvement of minority-carrier lifetime.

論文

X-ray reciprocal space mapping of dislocation-mediated strain relaxation during InGaAs/GaAs(001) epitaxial growth

佐々木 拓生*; 鈴木 秀俊*; 高橋 正光; 大下 祥男*; 神谷 格*; 山口 真史*

Journal of Applied Physics, 110(11), p.113502_1 - 113502_7, 2011/12

 被引用回数:8 パーセンタイル:56.54(Physics, Applied)

Dislocation-mediated strain relaxation during lattice-mismatched InGaAs/GaAs(001) heteroepitaxy was studied through ${it in situ}$ X-ray reciprocal space mapping. At the synchrotron radiation facility SPring-8, a hybrid system of molecular beam epitaxy and X-ray diffractometry with a two-dimensional detector enabled us to perform ${it in situ}$ reciprocal space mapping at high-speed and high-resolution. Using this experimental setup, the lattice constants, the diffraction broadenings along in-plane and out-of-plane directions, and the diffuse scattering were investigated. The strain relaxation processes were classified into four thickness ranges with different dislocation behavior. In addition, the existence of transition regimes between the thickness ranges was identified.

論文

Growth temperature dependence of strain relaxation during InGaAs/GaAs(0 0 1) heteroepitaxy

佐々木 拓生*; 鈴木 秀俊*; 崔 炳久*; 高橋 正光; 藤川 誠司; 神谷 格*; 大下 祥雄*; 山口 真史*

Journal of Crystal Growth, 323(1), p.13 - 16, 2011/05

 被引用回数:15 パーセンタイル:16.7(Crystallography)

In$$_{0.12}$$Ga$$_{0.88}$$As/GaAs(001)の分子線エピタキシャル成長中のひずみ緩和の様子をその場X線逆格子マッピングにより解析した。成長温度420, 445, 477$$^{circ}$$Cにおける残留ひずみ・結晶性の変化の様子が測定された。Dodson-Tsaoの運動学的モデルは、実験による残留ひずみの測定結果とよく一致することがわかった。さらにひずみ緩和過程における転位の運動の温度依存性の解析から、転位の運動の熱励起を議論することが可能になった。

論文

Real-time observation of anisotropic strain relaxation by three-dimensional reciprocal space mapping during InGaAs/GaAs(001) growth

鈴木 秀俊*; 佐々木 拓生*; 崔 炳久*; 大下 祥雄*; 神谷 格*; 山口 真史*; 高橋 正光; 藤川 誠司

Applied Physics Letters, 97(4), p.041906_1 - 041906_3, 2010/07

 被引用回数:26 パーセンタイル:22.49(Physics, Applied)

Real-time three-dimensional reciprocal space mapping measurement during In$$_{0.12}$$Ga$$_{0.88}$$As/GaAs(001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes. Anisotropies, strain relaxation, and crystal quality in [110] and [1$$bar{1}$$0] directions were simultaneously evaluated via the position and broadness of 022 diffraction. In the small-thickness region, strain relaxation caused by $$alpha$$-dislocations is higher than that caused by $$beta$$-dislocations, and therefore crystal quality along [110] is worse than that along [1$$bar{1}$$0]. Rapid relaxation along both [110] and [1$$bar{1}$$0] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [1$$bar{1}$$0] direction, presumably due to $$beta$$-dislocations, becomes better that along [110] direction and the ratio does not decay with thickness.

論文

In situ study of strain relaxation mechanisms during lattice-mismatched InGaAs/GaAs growth by X-ray reciprocal space mapping

佐々木 拓生*; 鈴木 秀俊*; 崔 炳久*; 高橋 正光; 藤川 誠司; 大下 祥雄*; 山口 真史*

Materials Research Society Symposium Proceedings, Vol.1268, 6 Pages, 2010/05

 パーセンタイル:100

The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study.

論文

Anionic fluoro complex of element 105, Db

笠松 良崇*; 豊嶋 厚史; 浅井 雅人; 塚田 和明; Li, Z.; 石井 康雄; 當銘 勇人*; 佐藤 哲也; 菊池 貴宏; 西中 一朗; et al.

Chemistry Letters, 38(11), p.1084 - 1085, 2009/10

 被引用回数:13 パーセンタイル:48.46(Chemistry, Multidisciplinary)

105番元素ドブニウム(Db)のフッ化水素酸と硝酸混合水溶液中における陰イオン交換挙動を、新規に開発した迅速イオン交換分離装置を用いて調べた。Dbのフッ化物陰イオン錯体の挙動は、近接の第6周期同族元素タンタル(Ta)の挙動とは大きく異なり、第5周期のニオブ(Nb)の挙動と似ているという特徴的な性質を示すことがわかった。

論文

${it In situ}$ real-time X-Ray reciprocal space mapping during InGaAs/GaAs growth for understanding strain relaxation mechanisms

佐々木 拓生*; 鈴木 秀俊*; 崔 炳久*; Lee, J.-H.*; 高橋 正光; 藤川 誠司; 新船 幸二*; 神谷 格*; 大下 祥雄*; 山口 真史*

Applied Physics Express, 2, p.085501_1 - 085501_3, 2009/07

 被引用回数:30 パーセンタイル:20.41(Physics, Applied)

${it In situ}$ real-time X-ray diffraction measurements during In$$_{0.12}$$Ga$$_{0.88}$$As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-mismatched system. The high resolution reciprocal space maps of 004 diffraction obtained at interval of 6.2 nm thickness enable transient behavior of residual strain and crystal quality to be observed simultaneously as a function of InGaAs film thickness. From the evolution of these data, five thickness ranges with different relaxation processes and these transition points are determined quantitatively, and the dominant dislocation behavior in each phase is deduced.

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