Papers by Author: Naoki Ohashi

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Authors: Yutaka Adachi, Naoki Ohashi, Isao Sakaguchi, Takeo Osawa, Haruki Ryoken, Hideki Yoshikawa, Shigenori Ueda, Keisuke Kobayashi, Hajime Haneda
Abstract: (Mg,Zn)O films were grown on Zn- and O-face ZnO single crystal substrates by pulsed laser deposition. The surface morphologies of the films grown on the Zn- and O-face substrates were quite different, indicating that no domain inversion occurred in both films. The films showed markedly different features for valence band spectra obtained by hard X-ray photoemission spectroscopy. This suggests that the effect of film polarity should be considered in X-ray photoemission spectroscopy.
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Authors: Haruki Ryoken, Yutaka Adachi, Isao Sakaguchi, Naoki Ohashi, Hajime Haneda, Tadashi Takenaka
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Authors: Kentaro Morito, Toshimasa Suzuki, Youichi Mizuno, Isao Sakaguchi, Naoki Ohashi, Kenji Matsumoto, Hajime Haneda
Abstract: The behavior of hydrogen in (Ba,Sr)TiO3 (BST) thin film capacitors under electric fields was investigated by performing secondary ion mass spectroscopy (SIMS) analyses. It was clearly observed that the ingress of atmospheric hydrogen into BST thin film capacitors occurred through the anode and that it diffused toward the cathode under electric fields. In addition, it was found that the deterioration of the I-V properties of the BST thin film capacitors can be interpreted in terms of the distribution of hydrogen concentration in the BST thin films.
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Authors: Naoki Ohashi, Takashi Sekiguchi, Hajime Haneda, Yoshihiro Terada, Takeshi Ohgaki, Takaaki Tsurumi, M. Tanaka, O. Fukunaga
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Authors: Takashi Sekiguchi, Naoki Ohashi, Yoshihiro Terada
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Authors: Takashi Sekiguchi, Naoki Ohashi, Hisanori Yamane
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Authors: Haruki Ryoken, Isao Sakaguchi, Naoki Ohashi, Yutaka Adachi, Takeshi Ohgaki, Shunichi Hishita, Hajime Haneda
Abstract: The defect structure of undoped ZnO and (Zn1-x,Mgx)O solid-solution films were deposited on YSZ substrate with pulsed laser deposition (PLD) to investigate defect equilibria in those films. In particular, the effects of thermal treatment on the structures and prosperities of (Zn1-x,Mgx)O solid-solution films were examined. The films with high MgO concentration (x>0.12) decomposed to the wurtzite-type and rock-salt-type phase after thermal treatment, indicating that the solubility limit of Mg was about x=0.12 and the wurtzite-type (Zn,Mg)O films with x>0.12 were indicated to be non-equilibrium ones. The subsequent analyses of oxygen diffusivity in those films revealed that the films under non-equilibrium state, i.e., wurtzite-type (Zn1-x,Mgx)O with x>0.12, contained significantly high concentration of anion defects.
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Authors: Haruki Ryoken, Isao Sakaguchi, Takeshi Ohgaki, Yoshitaka Adachi, Tadashi Takenaka, Naoki Ohashi, Hajime Haneda
Abstract: The defect structure of undoped and Al-doped ZnO films deposited by pulse laser deposition was investigated to understand the charge compensation mechanism in those films. Particularly, the effect of oxidation assist, i.e., O2 gas or oxygen radicals, on the defect structure of the resultant films was examined. The examination indicated that the defect structure of undoped ZnO was not affected by the oxidation assist, whereas the properties of Al-doped ZnO obviously varied with the method of oxidation assist. An analyses of oxygen diffusion in these films revealed that Al-doping enhanced formation of oxygen defects in Al-doped ZnO.
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Authors: Ken Watanabe, Tetsuya Kida, Isao Sakaguchi, Naoki Ohashi, Kengo Shimanoe, Hajime Haneda
Abstract: To determine the effect of the annealing atmosphere on oxygen diffusion through Ba0.95La0.05FeO3-d pellets, 18O2 tracer diffusion and high-resolution secondary ion mapping were performed. When annealing in air, the 18O concentration around the surface up to a depth of 40 µm was almost constant. On the other hand, when annealing in vacuum, the 18O concentration obviously decreased. High-resolution secondary ion mapping indicated that the 18O concentration around the grain boundary was reduced. These results suggested that the grain boundary of BLF annealed in vacuum prevents oxygen diffusion.
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Authors: Takeshi Ohgaki, Tomokazu Nakata, Naoki Ohashi, Satoshi Wada, Takaaki Tsurumi
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