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Ab initio study of hydrogen adsorption to single-walled carbon nanotubes

Physical Review B 2001年第15期63卷 155405-155405页

作者： K. Tada S. Furuya K. Watanabe Department of Physics Science University of Tokyo 1-3 Kagurazaka Shinjuku-ku Tokyo 162-8601 Japan Frontier Research Center for Computational Sciences Science University of Tokyo 1-3 Kagurazaka Shinjuku-ku Tokyo 162-8601 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Corporation 4-1-8 Honmachi Kawaguchi Saitama 332-0012 Japan

We perform the density-functional and quantum chemical calculations of adsorption of a hydrogen molecule to various kinds of single-walled carbon nanotubes (SWNT’s). The potential energy barrier height (PBH) for the dissociative adsorption of a hydrogen molecule onto the outer wall of a nanotube decreases as the tube diameter decreases. In contrast, the PBH for H2 penetration into an open-ended nanotube increases as the tube diameter decreases, independent of the atomic geometry, i.e., zigzag or armchair structures. H2, however, cannot adsorb to the inner wall of any type of nanotube. These results on the structure-dependent H2 adsorption to SWNT’s are reasonably explained by the sp2−sp3 rehybridization caused by the interaction between the adsorbing hydrogen and carbon atoms of SWNT’s.

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High-Pressure Mssbauer Study of Perovskite Iron Oxide

High-Pressure Mssbauer Study of Perovskite Iron Oxide

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18th International Conference on High Pressure science and technology

作者： T.Kawakami T.Sasaki S.Morimoto S.Nasu S.Endo S.Kawasaki M.Takano Division of Materials Physics Department of Physical Science Graduate School of Engineering Science Osaka 560-8531 Japan Division of Materials Physics Department of Physical Science Graduate School of Engineering Science Osaka 560-8531 Japan Division of Materials Physics Department of Physical Science Graduate School of Engineering Science Osaka 560-8531 Japan Division of Materials Physics Department of Physical Science Graduate School of Engineering Science Osaka 560-8531 Japan Core Research for Evolutional Science and Technology(CREST Research Center for Materials Science at Extreme Conditions Osqka University Toyonaka Osaka 560-8531 Japan Core Research for Evolutional Science and Technology(CREST Institute for Chemical Research Kyoto University Uji Kyoto-fu 611-0011 Japan Institute for Chemical Research Kyoto University Uji Kyoto-fu 611-0011 Japan

High valent states of Fein CaFeO and Fein LaSrFeO of the perovskite iron oxide whichshow a strong hybridization between Fe（3d） andO（2p） play an important role on their magneticordering,electrical conductivity and charge ordering. Using a diamond anvil cell,Fe Mossbauermeasurements have been carried out on theperovskite oxide CaFeO under high pressure up to65 GPa at various *** criticaltemperature of a charge disproportionation(CD:2Fe=Fe+Fe) and a magnetic ordering havebeen determined as a function of *** CD

关键词： High-pressure 57Fe Mossbauer spectro-scopy, charge disproportionation, CaFeO3,La1/3Sr2/3FeO3.

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Dispersion and Damping of a Two-Dimensional Plasmon in a Metallic Surface-State Band

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Physical Review Letters 2001年第25期86卷 5747-5747页

作者： Tadaaki Nagao Torsten Hildebrandt Martin Henzler Shuji Hasegawa Department of Physics Graduate School of Science The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033 Japan Precursory Research for Embryonic Science and Technology (PRESTO) Japan Science and Technology Corporation (JST) 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Corporation (JST) 4-1-8 Honcho Kawaguchi Saitama 332-0012 Japan Institut für Festkörperphysik der Universität Hannover Appelstraße 2 D-30167 Hannover Germany

We have studied, for the first time, the energy and the linewidth dispersion of a plasmon in a dense two-dimensional electron system in a metallic surface-state band on a silicon surface. As expected from the considerably high effective density and long Fermi wavelength of the system, the plasmon energy dispersion exhibited an excellent agreement with the nearly free-electron theory. However, in a small wave number region below the Landau edge, we have observed an anomalous linewidth dispersion which nearly free-electron theories do not predict.

关键词： Plasma theory

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Partitioned Real-Space Density Functional Calculations of Bielectrode Systems under Bias Voltage and Electric Field

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Physical Review Letters 2001年第3期86卷 540-540页

作者： N. Nakaoka K. Tada S. Watanabe H. Fujita K. Watanabe Department of Physics Science University of Tokyo 1-3 Kagurazaka Shinjuku-ku Tokyo 162-8601 Japan Department of Material Science University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Corporation Institute of Industrial Science University of Tokyo 7-22-1 Roppongi Minato-ku Tokyo 106-8558 Japan Frontier Research Center for Computational Sciences Science University of Tokyo 1-3 Kagurazaka Shinjuku-ku Tokyo 162-8601 Japan

We have developed a new partitioned real-space density functional (PRDF) method and applied it to bielectrode systems under bias voltage and electric field. The electronic states, electrostatic potentials, local electric fields, and chemical potentials of biased jelliums and two Si5 clusters are fully self-consistently determined. We overcame an essential difficulty in obtaining the electronic states of biased systems from the conventional density functional method by dividing the entire system into subsystems of each electrode. The PRDF method can be applied to multielectrode systems and enables the investigation of ionic systems with computational efficiency.

关键词： Electronic structure

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Sign reversal of the oxygen isotope effect on Tc in Sr2RuO4

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Physical Review B 2001年第14期63卷 144514-144514页

作者： Z. Q. Mao Y. Maeno Y. Mori S. Sakita S. Nimori M. Udagawa Department of Physics Kyoto University Kyoto 606-8502 Japan Core Research for Evolutional Science and Technology Japan Science and Technology Corporation (CREST-JST) Kawaguchi Saitama 332-0012 Japan Venture Business Laboratory Hiroshima University Higashi-Hiroshima 739-8527 Japan Faculty of Integrated Arts and Sciences Hiroshima University Higashi-Hiroshima 739-8521 Japan

We investigated the oxygen isotope effect (IE) on the transition temperature Tc in the spin-triplet superconductor Sr2RuO4 (with the intrinsic Tc0=1.5K). A clear IE shift in Tc was observed. Moreover, we found that the IE coefficient alpha exhibits an unusual variation with Tc. For lower-Tc crystals containing impurities and defects, α is positive and increases with decreasing Tc; α(Tc) is described well by the universal behavior expected theoretically. However, for crystals with Tc approaching Tc0, α deviates from the universal α(Tc) and becomes negative. We discuss its possible mechanism on the basis of existing models.

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Free GaAs surfaces studied using a back-gated undoped GaAs/AlxGa1−xAs heterostructure

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Physical Review B 2001年第24期63卷 245309-245309页

作者： A. Kawaharazuka T. Saku C. A. Kikuchi Y. Horikoshi Y. Hirayama NTT Basic Research Laboratories 3-1 Morinosato-Wakamiya Atsugi-shi Kanagawa 243-0198 Japan School of Science and Engineering Waseda University 3-4-1 Okubo Shinjuku-ku Tokyo 169-0072 Japan CREST Core Research for Evolutional Science and Technology 4-1-8 Honmachi Kawaguchi-shi Saitama 331-0012 Japan

We study the free GaAs surface by using a back-gated undoped GaAs/AlxGa1−xAs heterostructure. This structure is suitable in investigating the free GaAs surface since a two-dimensional electron gas is induced by the back-gate bias in the undoped heterostructure. We compare the channel depth dependence of the transport characteristics with two different models of the free GaAs. The “midgap pinning model” assumes a constant surface Fermi level and an alternative approach called the “frozen surface model” assumes a constant surface charge density. The experimental results indicate that the frozen surface model appropriately describes free GaAs surfaces at low temperatures although the midgap pinning model is widely accepted. This is because charges cannot be transferred to the free GaAs surface at low temperatures.

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Dynamics of the cantilever in noncontact dynamic force microscopy: The steady-state approximation and beyond

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Physical Review B 2001年第8期64卷 085409-085409页

作者： M. Gauthier N. Sasaki M. Tsukada Department of Physics Graduate School of Science University of Tokyo Hongo 7-3-1 Bunkyo-ku Tokyo 113-0033 Japan Department of Materials Engineering Graduate School of Engineering University of Tokyo Hongo 7-3-1 Bunkyo-ku Tokyo 113-8656 Japan Core Research for Evolutional Science and Technology (CREST) Japan Science and Technology Corporation (JST) 2-1-6 Sengen Tsukuba Ibaraki 305-0047 Japan

A detailed analysis of models that have been used for describing the dynamics of the cantilever in large-amplitude noncontact dynamic force microscopy is presented. For each model, attention is especially paid to the nonlinear nature of the problem and its implication for experiments. In particular, in the steady-state approximation where the equations of motion for an externally and self-driven oscillator are rigorously identical, the theory predicts the existence of unstable solutions whether the interaction force is dissipative or not. The need to go beyond the steady-state approximation by including the finite-time response of the system to a change of tip-surface separation or interaction during the scanning is also discussed.

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Electronic structure of Ag-induced 3×3 and 21×21 superstructures on the Si(111) surface studied by angle-resolved photoemission spectroscopy and scanning tunneling microscopy

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Physical Review B 2001年第20期64卷 205316-205316页

作者： Xiao Tong Satoru Ohuchi Norio Sato Takehiro Tanikawa Tadaaki Nagao Iwao Matsuda Yoshinobu Aoyagi Shuji Hasegawa The Institute of Physical and Chemical Research (RIKEN) 2-1 Hirosawa Wako Saitama 351-0198 Japan Department of Physics University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033 Japan Core Research for Evolutional Science and Technology The Japan Science and Technology Corporation Kawaguchi Center Building Hon-cho 4-1-8 Kawaguchi Saitama 332-0012 Japan Department of Chemistry University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033 Japan

Polarization-dependent angle-resolved photoemission spectroscopy was used to analyze the electronic band structure of the Si(111)−21×21(R±10.89°)−Ag surface induced by adding submonolayer Ag atoms on top of the Si(111)-3×3-Ag surface at 140 K, together with a refinement of the electronic states of the initial 3×3-Ag substrate itself. The surface-state band crossing the Fermi level on the the 3×3-Ag surface was found to have similar dispersions in both Γ¯−K¯ and Γ¯−M¯ directions around the Γ¯ point of the 3×3 surface Brillouin zone, and consist mainly of components parallel to the surface with no measurable polarization dependence. The five intrinsic surface-state bands observed on the 3×3-Ag surface basically remained in the 21×21-Ag structure, but shifted down in energy position from the Fermi level by about 0.4 eV. This is due to electron transfer from the Ag adatoms to the substrate, suggesting that the Ag adatoms in the 21×21-Ag phase sit on a nearly unaltered 3×3-Ag substrate, and do not make any orbital hybridization with the substrate. Only one parabolic band crossing the Fermi level was found on the 21×21-Ag surface, for which distribution in real space is observed by bias-dependent scanning tunneling microscopy. This result is in contrast to two metallic bands on the 21×21 phase induced by Au or Cu adatoms on the 3×3-Ag substrate reported in previous papers.

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Device Grade B-Doped Homoepitaxial Diamond Thin Films

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physica status solidi (a) 2001年第2期186卷

作者： D. Takeuchi S. Yamanaka H. Watanabe H. Okushi Research Center for Advanced Carbon Materials National Institute of Advanced Industrial Science and Technology (AIST) AIST Tsukuba Central 5 1-1-1 Higashi Tsukuba 305-8565 Ibaraki Japan Core Research for Evolutional Science and Technology of Japan Science and Technology Corporation (CREST JST)

We review our recent results on properties of high quality B-doped homoepitaxial diamond thin films grown by chemical vapor deposition (CVD) by using trimethylboron (TMB) as a B source gas. The conventional (one-step) and the two-step growth methods were used for film preparation. The latter realized smooth surface without any non-epitaxial crystallites (UCs). The films showed a sharp Raman shift peak at 1332 cm —1 , a strong free-excitonic emission at room temperature, and high Hall mobility as high as 1000 cm 2 /Vs or more, indicating high-quality diamond. We also successfully realized resistivity control of the films in a wide range from 10 0 to 10 5 Ω cm due to low compensation ratio. Using the two-step growth method, Schottky junctions with the ideality factor n of 1.1 or less and undetectable leakage current could be prepared between various metals such as Al, Zn, Cr, Ni, Au or Pt and oxidized B-doped CVD diamond films. In particular, we successfully made nearly ideal Schottky junctions using highly B-doped films in the order of 10 17 cm —3 , indicating that the quality of the present B-doped films is comparable with or higher than those of conventional semiconductors such as Si and GaAs.

关键词： 73.20.Hb 73.40.Ns 78.66.Db S5

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Drastic effect of Mo on diamond nucleation in the system of MgCO₃-CaCO₃-graphite at 7.7 GPa

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JOURNAL OF CRYSTAL GROWTH 2000年第4期210卷 623-628页

作者： Sato, K Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Corporation (JST) Japan

Drastic effect of additional Mo on diamond nucleation was observed in the system of Mc60Cc40 (mixture of 60 mol% MgCO3 and 40 mol% CaCO3)-graphite at 7.7 GPa, 1700 and 1800 degrees C for 1 h. The decrease of temperature required for nucleation of diamond by addition of Mo is 200 degrees C, compared with the temperature in the system of Mc60Cc40-graphite (Sato et al., Diamond Related Mater. 8 (1999) 1900). These results indicate that a lower energy barrier is expected for the nucleation in the Mc60Cc40-Mo-graphite system. Therefore, this nucleation process in the system of Mc60Cc40-graphite-Mo can be considered to be different from the spontaneous nucleation in the system of Mc60Cc40-graphite. Two probable models for nucleation can be suggested: (1) heterogeneous nucleation in which nucleation is affected by MoC that is formed by the reaction between the carbonate and Mo and (2) achievement of enough concentration of carbon for formation of nuclei by the reaction between the carbonate and Mo. (C) 2000 Elsevier science B.V. All rights reserved.

关键词： diamond carbonate molybdenum nucleation

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