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42 results on '"Ohachi, Tadashi"'

5. GaAsエピタキシャル成長における吸着-脱離現象への理論的アプローチ(<小特集>結晶成長理論の最近の動向)

Author

Kangawa, Yoshihiro, Ito, Tomonori, Taguchi, Akihito, Shiraish, Kenji, Hiraoka, Yoshiko S, Irisawa, Toshiharu, and Ohachi, Tadashi

Abstract

A newly developed ab initio-based approach was applied for understanding adsorption-desorption behavior during molecular beam epitaxial growth of GaAs. The ab initiobased approach incorporates free energy of vapor phase; therefore we can calculate how adsorption and desorption depend on growth temperature and beam equivalent pressure (BEP). Versatility of the theoretical approach was confirmed by the calculation of Ga adsorption-desorption transition temperatures and transition BEPs on Ga-rich GaAs (001)-(4×2)β2 surface. Furthermore, in order to check the feasibility of the theoretical approach for prediction of adsorption-desorption behavior of As_2 molecules, the conditions where GaAs(001)-c (4×4) reconstructed structure is stable were investigated by the calculations of stability of As-dimers on the top surface under the various temperatures and BEPs. We also applied the theoretical approach to Ga diffusion length while staying on the GaAs (001)- (2×4)β2 and - (2×4)β1 surfaces and As pressure dependence of GaAs growth rate.

Published
2002

7. GaAsエピタキシャル成長における吸着-脱離現象への理論的アプローチ(<小特集>結晶成長理論の最近の動向)

Author

学習院大学計算機センター, 三重大学工学部物理工学科, NTT物性科学基礎研究所, 筑波大学物理学系, (株)東芝研究開発センター, 同志壮大学工学部電気工学科, Computer Center, Gakushuin University, Department of Physics Engineering, Mie University, NTT Basic Research Laboratories, Institute of Physics, University of Tsukuba, Research and Development Center, Toshiba Corporation, Department of Electrical Engineering, Doshisha University, Kangawa, Yoshihiro, Ito, Tomonori, Taguchi, Akihito, Shiraish, Kenji, Hiraoka, Yoshiko S, Irisawa, Toshiharu, Ohachi, Tadashi, 寒川, 義裕, 伊藤, 智徳, 田口, 明仁, 白石, 賢二, 平岡, 佳子, 入澤, 寿美, 大鉢, 忠, 学習院大学計算機センター, 三重大学工学部物理工学科, NTT物性科学基礎研究所, 筑波大学物理学系, (株)東芝研究開発センター, 同志壮大学工学部電気工学科, Computer Center, Gakushuin University, Department of Physics Engineering, Mie University, NTT Basic Research Laboratories, Institute of Physics, University of Tsukuba, Research and Development Center, Toshiba Corporation, Department of Electrical Engineering, Doshisha University, Kangawa, Yoshihiro, Ito, Tomonori, Taguchi, Akihito, Shiraish, Kenji, Hiraoka, Yoshiko S, Irisawa, Toshiharu, Ohachi, Tadashi, 寒川, 義裕, 伊藤, 智徳, 田口, 明仁, 白石, 賢二, 平岡, 佳子, 入澤, 寿美, and 大鉢, 忠

Abstract

A newly developed ab initio-based approach was applied for understanding adsorption-desorption behavior during molecular beam epitaxial growth of GaAs. The ab initiobased approach incorporates free energy of vapor phase; therefore we can calculate how adsorption and desorption depend on growth temperature and beam equivalent pressure (BEP). Versatility of the theoretical approach was confirmed by the calculation of Ga adsorption-desorption transition temperatures and transition BEPs on Ga-rich GaAs (001)-(4×2)β2 surface. Furthermore, in order to check the feasibility of the theoretical approach for prediction of adsorption-desorption behavior of As_2 molecules, the conditions where GaAs(001)-c (4×4) reconstructed structure is stable were investigated by the calculations of stability of As-dimers on the top surface under the various temperatures and BEPs. We also applied the theoretical approach to Ga diffusion length while staying on the GaAs (001)- (2×4)β2 and - (2×4)β1 surfaces and As pressure dependence of GaAs growth rate.

Published
2008

14. Antisite defect elimination through Mg doping in stoichiometric lithium tantalate powder synthesized via a wet-chemical spray-drying method.

Author

Sun, Dehui, Kang, Xueliang, Yu, Qian, Cui, Kun, Qin, Xiaoyong, Shi, Xuxia, Cai, Huaqiang, Ohachi, Tadashi, Sang, Yuanhua, and Liu, Hong

Subjects
ANTISITE defects, MAGNESIUM, DOPING agents (Chemistry), LITHIUM tantalate, CHEMICAL synthesis, SPRAY drying
Abstract

MgO-doped stoichiometric LiTaO3 (MgO:SLT) is one of the most promising nonlinear materials. However, its industrial application is limited by the poor optical quality caused by the nonhomogeneous distribution of magnesium. Herein, an MgO:SLT polycrystalline powder was synthesized with a homogenous magnesium distribution by a wet-chemical spray-drying method. A comparative investigation of the coordination state of Ta ions in MgO:SLT powders synthesized by this method and by a conventional solid-state reaction method was performed by X-ray photoelectron spectroscopy. It is proved that the Ta-Li antisite was completely eliminated as a result of the homogeneous Mg doping in the SLT lattice using the wet-chemical spray-drying method. However, for MgO:LT powder produced by the solid-state reaction method, element analysis after acid treatment shows that some Mg ions did not enter the LT lattice after high-temperature calcination. Also, scanning electron microscopy and transmission electron microscopy energy dispersive spectroscopy verified that some MgO particles still exist in the as-synthesized MgO:LT powder. This synthesis method can be used for mass production of high-quality polycrystalline powders for doped crystal growth and some other doped oxide powder products with high melt point. [ABSTRACT FROM AUTHOR]

Published
2015
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17. Activity modulation MEE growth of 2H-AlN on Si(111) using double buffer layer grown by PA-MBE.

Author

Ohachi, Tadashi, Yamamoto, Yuka, Ariyada, Osamu, Sato, Yuuki, Yoshikado, Sinzo, and Wada, Motoi

Abstract

As a demonstration of the activity modulation migration enhanced epitaxy (AM-MEE) heteroepitaxial 2H-AlN thin films of 53.8 nm and 171.3 nm thickness on Si(111) on a double buffer layer (DBL) have been grown by the AM-MEE of plasma assisted molecular beam epitaxy (PA-MBE) method. It is a droplet free growth and an atomic layer epitaxy (ALE). The influence of the DBL, which was formed in a MBE chamber before the AM-MEE growth of 2H-AlN thin films on Si(111), was studied to improve the crystallinity of AlN films. For the growth of high quality 2H-AlN on Si(111), the optimization of growth of the DBL. The interface roughness of the DBL as a layer between two layers of AlN and Si, AlN/DBL/Si was characterized by grazing incidence X-ray reflectivity (GIXR) and the surfaces were observed by AFM. Full width at half maximum (FWHM) of ω /2θ for 53.8 nm and 171.3 nm thickness AlN (0002) films were 12.1 arcmin and 7.1 arcmin, respectively. AFM images showed droplet free growth after the AM-MEE and importance of the preparation of initial clean Si surface. Unifrom formation of DBL on a large size wafer of Si was available to use indirect exposure of N radical atoms. By increasing the thickness of the AlN the crystallinity was improved but the surface roughness of AlN did not depend on the thickness of the AlN films obtained by fitting results of GIXR curves. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Published
2013
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26. Ionic conductivity of hollandite type compound at 9.54 and 32.8 GHz

Author

Yoshikado, Shinzo, Fujiki, Yoshinori, Ohachi, Tadashi, and Taniguchi, Ichiro

Abstract

The microwave ionic conductivity σ of single-crystals of K-Mg priderite ( a hollandite type compound ) K1·6Mg0·8Ti7·2O16has been measured using a standing wave method at 9.54 and 32.8 GHz from 83 to 616 K. The results of σT−1Tcharacteristic are divided into two regions, one is the part of higher temperatures I and the other is the part of lower temperatures II. As the ionic conductivity at 32.8 GHz at the region I is interpreted by the configurational model proposed by Bayeler et al., the frequency-independent intrinsic ionic conductivity dominated by the configurational model is predicted to be observed at higher frequencies than 32.8 GHz.

Published
1981
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27. Structural aspects of the new one-dimensional ionic conductors: AxGa8Ga8+xTi16−xO56(A=K, Rb and Cs, x<-2)

Author

Watanabe, Mamoru, Fujiki, Yoshinori, Yoshikado, Shinzo, and Ohachi, Tadashi

Abstract

The title materials, mutually isostructural, have an intergrowth structure of rutile and β-gallia, and the structure contains one-dimensional large channels occupied by alkali ions. The free diameter of these channels is about 3.4 Å at minimum, which is significantly larger than the effective ionic radii of K+and Rb+. Their lattice constants hardly change in spite of a large size difference among K+, Rb+, and Cs+. The electron density distributions show a distinct delocalization of the alkali ions on the channel axis, which is attributed to the large number of energetically quasi-equivalent sites available for the mobile ions due to the disappearance of virtual bottlenecks in the tunnels. Diffuse scatterings, which imply some short-range ordering among the alkali ions, were revealed by X-ray and electron diffraction techniques. They are very weak, but suggest that the ordering is similar to that in K2vMgxTi8−xO16.

Published
1988
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28. NMR study of one-dimensional ionic conductors with hollandite-type structure

Author

Onoda, Yoshito, Fujiki, Yoshinori, Yoshikado, Shinzo, Ohachi, Tadashi, and Taniguchi, Ichiro

Abstract

The motion of K+ion in the one-dimensional ionic conductor, Al-priderite, with hollandite-type structure was investigated using 27Al in the framework as a probe. The temperature dependence of the spin-lattice relaxation time T1showed that it is divided into two regions. In the low temperature region where the motion is dominated by the intrinsic barrier, the frequency dependence of T1is proportional to ω1.5. The slope, δln(T1)/δ(1/T), in the low temperature side gives a small value of 29 meV. In the high temperature region, where T1is influenced by the long range fluctuation of K+ion over the impurity barriers, T1becomes independent of the frequency, and this behavior may be due to the existence of reflecting walls introduced by impurities with high barrier height which K+ion can not pass over.

Published
1983
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29. Frequency-independent ionic conductivity of hollandite type compounds

Author

Yoshikado, Shinzo, Ohachi, Tadashi, Taniguchi, Ichiro, Onoda, Yoshito, Watanabe, Mamoru, and Fujiki, Yoshinori

Abstract

The frequency- and temperature-dependences of a.c. ionic conductivity of one-dimensional superionic conductors K-priderites, K1.6Mg0.8Ti7.2O16(KMTO) and K1.6Al1.6Ti6.4O16(KATO), which were grown by using a flux with high grade purity, were investigated from 100 Hz to 10 MHz. The complex ionic conductivity along a c-axis was analyzed by using an equivalent circuit constructed by considering the frequency-dependent ionic conductivity σmband the frequency-independent ionic conductivity σdcwhich was not observed for samples grown by using a flux with normal grade purity. The σdcwas thermally activated and the activation energies for KMTO and KATO were 0.26 and 0.30 eV respectively. The lateral conductivity was very small.

Published
1983
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42. In situ synthesis of TiH2 layer on metallic titanium foil through gaseous hydrogen free acid-hydrothermal method.

Author

Ren, Na, Wang, Guancong, Liu, Hong, and Ohachi, Tadashi

Subjects
*TITANIUM compounds synthesis, *METAL foils, *HYDROGEN, *THERMAL analysis, *TEMPERATURE effect, *DEHYDROGENATION, *INTERMEDIATES (Chemistry), *ACIDS
Abstract

Highlights: [•] A dense TiH2 layer is synthesized by a hydrogen free acid-hydrothermal method. [•] Hydrogen in a TiH2 layer synthesized can release at low temperature. [•] During the dehydrogenation process, there is no any intermediate phase forming. [•] We report a method of low-cost, low-risk and convenience toward productive TiH2. [Copyright &y& Elsevier]

Published
2014
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