Papers by Author: Katsuyuki Matsunaga

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Authors: Takeo Sasaki, Teruyasu Mizoguchi, Katsuyuki Matsunaga, Shingo Tanaka, Takahisa Yamamoto, Masanori Kohyama, Yuichi Ikuhara
Abstract: Interfacial atomic and electronic structures of Cu/Al2O3(0001) and Cu/Al2O3(11 _ ,20) prepared by a pulsed-laser deposition technique were characterized by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). It was found that both systems have O-terminated interfaces, irrespective of different substrate orientations. This indicates that Cu-O interactions across the interface play an important role for the Cu/Al2O3 systems.
Authors: Hidehiro Yoshida, Katsuyuki Matsunaga, Takahisa Yamamoto, Yuichi Ikuhara
Authors: Katsuyuki Matsunaga, Teruyasu Mizoguchi, Atsutomo Nakamura, Takahisa Yamamoto, Yuichi Ikuhara
Abstract: First-principles pseudopotential calculations were performed to investigate atomic and electronic structures of titanium (Ti) dopants in alumina (Al2O3). It was found that a substitutional Ti3+ defect induced an extra level occupied by one electron within the band gap of Al2O3. When two or more substitutional Ti3+ defects were located closely to each other, the defect-induced levels exhibited strong bonding interactions, and their formation energies decreased with increasing numbers of Ti3+ defects. This indicates that association and clustering of substitutional Ti3+ defects in Al2O3 can take place due to the interaction of the defect-induced levels.
Authors: M. Tanaka, Shouichi Ochiai, M. Hojo, Takashi Ishikawa, Shinji Kajii, Katsuyuki Matsunaga, T. Yamamura
Authors: Yuichi Ikuhara, Katsuyuki Matsunaga, Takahisa Yamamoto, Taketo Sakuma
Authors: H. Ishikawa, Shinji Kajii, T. Hisayuki, Katsuyuki Matsunaga, T. Hogami, Y. Kohtoku
Authors: Tsubasa Nakagawa, Isao Sakaguchi, Katsuyuki Matsunaga, Takahisa Yamamoto, Hajime Haneda, Yuichi Ikuhara
Abstract: Grain boundary diffusion coefficients of oxygen (δDgb) at 1793K in high purity α-alumina bicrystals with Σ7{2 _ ,310}/[0001] and Σ31{7 _ ,1140}/[0001] symmetric tilt grain boundaries were measured by means of the isotopic exchange and diffusion depth profiling using SIMS. δDgb of both grain boundaries were determined to be 7.1x10-24 [m3/sec] for Σ7 grain boundary and 5.3 x10-24 [m3/sec] for Σ31 grain boundary, respectively. These results indicate that Σ values do not directly relate to grain boundary diffusion properties.
Authors: Teruyasu Mizoguchi, Masaki Sakurai, Atsutomo Nakamura, Takeo Sasaki, Yukio Sato, Katsuyuki Matsunaga, Takahisa Yamamoto, Yuichi Ikuhara
Abstract: Near-edge structure of X-ray absorption spectrum (NEXAFS) of various Ti-oxides were investigated by combined with first principles orthogonalized linear combinations of atomic orbitals (OLCAO) method. From experimental and theoretical studies on the NEXAFS of the tetravalent and trivalent Ti-oxides, including rutile, anatase, brookite, columbite, and Ti2O3, it was found that the valence state of Ti can be identified by regarding the positions of the spectral onset and the shoulder in the main-peak of Ti-K NEXAFS.
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