Yanna Chen
National Institute for Materials Science
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Featured researches published by Yanna Chen.
Inorganic Chemistry | 2018
Akhil Tayal; Yanna Chen; Chulho Song; Satoshi Hiroi; L. S. R. Kumara; Natalia Palina; Okkyun Seo; Megumi Mukoyoshi; Hirokazu Kobayashi; Hiroshi Kitagawa; Osami Sakata
Metal-organic frameworks (MOFs) provide highly selective catalytic activity because of their porous crystalline structure. There is particular interest in metal nanoparticle-MOF composites (MNP@MOF) that could take advantage of synergistic effects for enhanced catalytic properties. We present an investigation into the local geometry and electronic properties of thermally decomposed Ni-MOF-74 calcined at different temperatures and time durations. Pair distribution function analysis using high-energy X-ray diffraction reveals the formation of fcc-Ni nanoparticles with a mixture of MOF phase in samples heated at 623 K for 12 h. Elevating the calcination temperature and lengthening the time duration assisted complete precipitation of Ni nanoparticles in the MOF matrix. Local structures and valence states were investigated using X-ray absorption fine structure spectroscopy. Evidence of ligand-to-metal charge transfer and gradual reduction of Ni2+ is apparent for those samples heated above 623 K for 12 h. In addition, the Ni lattice was found to be slightly compressed as a result of surface stresses in the nanosized particles or surface ligand environment. Electronic structure investigation using hard X-ray photoelectron spectroscopy shows a significant narrowing of the valence band and a decrease in the d-band center (toward the Fermi level) when the heating temperature is increased, thus suggesting promising catalytic properties for NiNP@MOF composite.
CrystEngComm | 2018
Yanfang Lou; Chulho Song; Yanna Chen; L. S. R. Kumara; Natalia Palina; Okkyun Seo; Satoshi Hiroi; Kentaro Kajiwara; Masato Hoshino; Kentaro Uesugi; Yoshihiro Irokawa; Toshihide Nabatame; Yasuo Koide; Osami Sakata
The crystallinity of one n-GaN (Si-doped) and two p-GaN (Mg-doped) homoepitaxial thin films selectively grown on GaN substrates was evaluated by using synchrotron X-ray diffraction. A reflection-mode monochromatic X-ray topography image from the n-GaN homoepitaxial thin film shows a mesh-shape structure that is similar to that of the selective-growth GaN substrate. Moreover, transmission-mode white-beam X-ray topography images from the GaN substrate and the n-GaN homoepitaxial thin film show similar regular dot-shape diffraction patterns. This suggests that, following hydride vapor phase epitaxy, the structural characteristics of the selectively grown GaN substrates inherited from their corresponding foreign substrates (dot-patterned sapphire) were inherited by the subsequent n-GaN homoepitaxial thin film, although the crystal quality of the homoepitaxial thin film had been deteriorated. White-beam topography images from two p-GaN homoepitaxial thin films grown on the same GaN substrate wafer and cut from adjacent areas indicate that the p-GaN thin films were non-uniform.
Communications Chemistry | 2018
Yanna Chen; Osami Sakata; Yusuke Nanba; L. S. R. Kumara; Anli Yang; Chulho Song; Michihisa Koyama; Guangqin Li; Hirokazu Kobayashi; Hiroshi Kitagawa
The previously published version of this Article contained an error in Fig. 1. In panel c, the thickness of the HKUST-1 layer (3 nm) was incorrectly labelled. This error has been corrected in both the PDF and HTML versions of the Article.
Applied Physics Letters | 2018
Okkyun Seo; Jaemyung Kim; Satoshi Hiroi; Chulho Song; L. S. R. Kumara; Akhil Tayal; Yanna Chen; Hirokazu Kobayashi; Hiroshi Kitagawa; Osami Sakata
Crystal structure deviations of bimetallic Pd-Pt nanoparticles (NPs) were investigated using synchrotron high-energy X-ray diffraction. The samples comprised Pd NPs and bimetallic Pd-Pt NPs featuring those with a Pd-core/Pt-shell structure as well as PdPt solid-solution NPs with varying diameters of 6.1, 6.7, 8.1, and 11.2 nm. The Rietveld method was used to find the lattice constant of the Pd NPs, which was larger than the bulk value, while reverse Monte Carlo modeling revealed that they possessed a highly disordered structure. The lattice constants of the Pd-Pt bimetallic NPs were found to vary with the Pt content. For Pd-core/Pt-shell structure NPs, the lattice constants decreased with the Pt content owing to lattice relaxation at the core/shell interface. After a reaction process of hydrogen absorption/desorption, the lattice constant of the resulting PdPt solid-solution NPs increased with the NP Pt content, which followed Vegards law. The degree of disorder of the solid-solution NPs was evaluated by the PBOO values (i.e., structural parameters describing the deviation of the local structure from an ideal crystal structure) and was found to decrease with the Pt content. A short-range-order parameter was introduced using a three-dimensional reverse Monte Carlo configuration structure to evaluate the atomic-scale solid solubility of the Pd0.92Pt0.08 and Pd0.79Pt0.21 NPs. The parameter values obtained were close to 0, indicating that the Pd and Pt atoms were essentially randomly dispersed in the solid-solution NPs.
AIP Advances | 2018
Okkyun Seo; Jae Myung Kim; Chulho Song; Yanfang Lou; L. S. R. Kumara; Satoshi Hiroi; Yanna Chen; Yoshio Katsuya; Yoshihiro Irokawa; Toshihide Nabatame; Yasuo Koide; Osami Sakata
We evaluated the lattice curvature, crystallinity, and crystalline homogeneity of a GaN layer on a free standing GaN substrate using lattice orientation measurements, θ rocking curves, and reciprocal space mapping from synchrotron X-ray diffraction topography, and X-ray diffraction. The lattice curvature of the 2-inch GaN homo-epitaxial layer was a concave bend, which had a curvature radius of approximately 20.7 m. The GaN layer was epitaxially grown on the GaN substrate and had good crystallinity with a high homogeneity.
Physical Review B | 2017
Yanna Chen; Osami Sakata; Ryosuke Yamauchi; Anli Yang; L. S. R. Kumara; Chulho Song; Natalia Palina; M. Taguchi; Toshiaki Ina; Yoshio Katsuya; Hiroshi Daimon; Akifumi Matsuda; Mamoru Yoshimoto
Applied Physics Express | 2018
Jaemyung Kim; Okkyun Seo; Chulho Song; Satoshi Hiroi; Yanna Chen; Yoshihiro Irokawa; Toshihide Nabatame; Yasuo Koide; Osami Sakata
Journal of Electronic Materials | 2018
Satoshi Hiroi; Seongho Choi; Shunsuke Nishino; Okkyun Seo; Yanna Chen; Osami Sakata; Tsunehiro Takeuchi
Communications Chemistry | 2018
Yanna Chen; Osami Sakata; Yusuke Nanba; L. S. R. Kumara; Anli Yang; Chulho Song; Michihisa Koyama; Guangqin Li; Hirokazu Kobayashi; Hiroshi Kitagawa
Archive | 2017
Akifumi Matsuda; 松田 晃史; Daishi Shiojiri; 塩尻 大士; Hiroki Uchida; 内田 啓貴; Kisho Nakamura; 中村稀星; Yanna Chen; Osami Sakata; 坂田 修身; Nobuo Tsuchimine; 土嶺 信男; Satoru Kaneko; 智. 金子; Mamoru Yoshimoto; 護. 吉本