Papers - YAMAMOTO Masahiro
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First-principles calculations of the surface relaxation and electronic structure of Zr(0001) Reviewed
Masahiro Yamamoto, C. T. Chan, K. M. Ho
Physical Review B 50 ( 11 ) 7932 - 7939 1994
Single Work
Authorship：Lead author
The multilayer relaxations of the Zr(0001) surface and the surface electronic structure are studied using first-principles total-energy and force calculations. The distance between the outermost two layers is 4.44.7 % smaller than the ideal interlayer spacing, while inner layers show oscillatory relaxations. We examined two possible termination sequences for the surface and found that the hcp surface termination is more stable by about 0.06 eV per surface atom as compared to the fcc terminated structure. We observed an increase in the local density of states (LDOS) for the surface atoms around the Fermi level relative to the bulk atoms. The increase in the LDOS is found to be closely related to the existence of surface states and resonances around the Fermi level. © 1994 The American Physical Society.
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EFFECTS OF HYDROGEN AND DEUTERIUM CONCENTRATION ON MEASUREMENTS OF THE SOLUBILITY AND DIFFUSIVITY OF HYDROGEN ISOTOPES IN YTTRIUM Reviewed
T MAEDA, S NAITO, M YAMAMOTO, M MABUCHI
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 90 ( 13 ) 1979 - 1982 1994
Single Work
Publisher：ROYAL SOC CHEMISTRY
The solubility and diffusivity of hydrogen and deuterium in polycrystalline alpha-yttrium have been measured in the temperature range 1073-1273 K and at hydrogen and deuterium concentrations, theta (H:Y and D:Y, atomic ratio), of 0-0.44. The measured solubility obeys the relationship p = k[theta/(1-theta)]2, where p is the hydrogen pressure and k is a constant independent of theta. The measured diffusion coefficients for hydrogen and deuterium increased with theta. The experimental result has been explained by a model in which a hydrogen atom can occupy a pair of two nearest-neighbour tetrahedral sites of the hcp alpha-yttrium lattice and move almost freely between the two sites.
DOI： 10.1039/ft9949001979
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DIFFUSION OF HYDROGEN IN TI3AL Reviewed
S NAITO, O HASHITOMI, M YAMAMOTO, Y BABA, M KIMURA
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 90 ( 16 ) 2423 - 2424 1994
Single Work
Publisher：ROYAL SOC CHEMISTRY
The diffusivity of hydrogen in the intermetallic compound Ti3Al has been measured in the temperature range 973-1323 K. The activation energy for diffusion has been found to be nearly twice those for pure Ti and Al. A possible origin of this large activation energy is the presence of ordered Al atoms in Ti3Al and the difference in the heat of solution of hydrogen between Ti and Al.
DOI： 10.1039/ft9949002423
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AUGER-ELECTRON, ELECTRON-ENERGY-LOSS, SECONDARY-ELECTRON EMISSION AND SECONDARY-ION MASS SPECTROSCOPIC STUDIES ON THE OXIDATION OF HAFNIUM AT ROOM-TEMPERATURE Reviewed
T SATAKE, M YAMAMOTO, S NATIO, M MABUCHI, A KANEDA, M KURAHASHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 89 ( 19 ) 3611 - 3618 1993
Single Work
Publisher：ROYAL SOC CHEMISTRY
Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), secondary electron emission spectroscopy (SES) and secondary ion mass spectrometry (SIMS) have been used to investigate the oxidation of a hafniun surface at room temperature (298 K). The change in the electronic energies of the core and valence levels with the oxidation is discussed on the basis of the comparison between the observed spectra and the electronic structures calculated for a hafnium atom, ion, bulk metal and bulk oxide. The growth of oxide films to a thickness of ca. 1.5 nm is found from the decay in the intensity of Auger electrons emitted by the metal substrate and from the depth profile ot the SIMS spectra.
DOI： 10.1039/ft9938903611
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DIFFUSIVITY AND SOLUBILITY OF HYDROGEN AND DEUTERIUM IN YTTRIUM Reviewed
T MAEDA, S NAITO, M YAMAMOTO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 89 ( 24 ) 4375 - 4379 1993
Single Work
Publisher：ROYAL SOC CHEMISTRY
The diffusivity and solubility of hydrogen and deuterium in polycrystalline alpha-yttrium have been measured in the temperature range 1073-1373 K. The ratios of the measured diffusion coefficient of deuterium to that of hydrogen showed the classical value 1/square-root 2. The activation energy of diffusion has been found to be 510 meV for both hydrogen and deuterium. The differences in the solubility and diffusivity between hydrogen and deuterium have been explained by using rate theory and assuming that hydrogen and deuterium atoms in yttrium are slightly anharmonic oscillators.
DOI： 10.1039/ft9938904375
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ADSORPTION POTENTIAL OF HYDROGEN-ATOM ON ZIRCONIUM Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF PHYSICAL CHEMISTRY 96 ( 8 ) 3409 - 3412 1992
Single Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
The adsorption potential of hydrogen atom on zirconium(0001) surface has been calculated by an effective medium theory. The adsorption energy is found to be -3.0 eV for both the overlayer sites above the tetrahedral site and the octahedral site. The hydrogen vibrational energy and the potential energy including an effect of lattice relaxation at the subsurface tetrahedral site are in good agreement with experiments.
DOI： 10.1021/j100187a042
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RELATIVISTIC SELF-CONSISTENT CALCULATION FOR HAFNIUM ATOMS AND IONS BASED ON A RELATIVISTIC LOCAL DENSITY FUNCTIONAL THEORY Reviewed
M YAMAMOTO, M MABUCHI, S NAITO
JOURNAL OF PHYSICAL CHEMISTRY 96,10784 ( 26 ) 10784 - 10788 1992
Single Work
Authorship：Lead author Publisher：AMER CHEMICAL SOC
The Dirac equation for the spherical symmetrical potential of hafnium atoms and ions with various electron configurations has been calculated numerically by using a relativistic local density functional approximation. Electron binding energies, ionization potential, X-ray emission energies, and Auger electron energies are evaluated by the total energy difference (DELTASCF) method and Slater's transition-state method. The calculated results are in agreement with the experimental results measured by spectroscopies.
DOI： 10.1021/j100205a036
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Mechanism of oxygen absorption by zirconium
Masahiro Yamamoto
1991.3
Single Work
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AUGER-ELECTRON, ELECTRON-ENERGY LOSS AND SECONDARY-ELECTRON EMISSION SPECTROSCOPIC STUDIES ON THE OXIDATION OF ZIRCONIUM AT HIGH-TEMPERATURES AND ROOM-TEMPERATURE Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 87 ( 10 ) 1591 - 1599 1991
Single Work
Authorship：Lead author Publisher：ROYAL SOC CHEMISTRY
Auger electron (AES), electron energy loss (EELS) and secondary electron emission spectroscopy (SES) have been used to investigate the surface oxidation of zirconium at room temperature and high temperatures, 773-973 K, under low oxygen pressures 1.3 x 10(-5)-1.3 x 10(-3) Pa. The kinetic energies of the Auger and the secondary electrons and the electron energy losses by single electron excitations are explained by the electronic structure in the core and the valence states of the metal and the oxide of zirconium. The energy loss by the collective excitation of plasmon is also observed in the EELS measurement for the metal and the oxide surface. The increase in the relative peak-to-peak height of the oxygen Auger transition and of the zirconium Auger transition by oxidation at high temperatures does not depend simply on the oxygen exposure represented by the product of oxygen pressure and exposure time, i.e. exposure in Langmuir, because of the dynamic competition between surface processes and the diffusion process of oxygen into the bulk. The rate of oxide growth is found to be parabolic at high temperature (773 K) and at 1.3 x 10(-5) Pa.
DOI： 10.1039/ft9918701591
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CHANGE IN THE WORK FUNCTION OF ZIRCONIUM BY OXIDATION AT HIGH-TEMPERATURES AND LOW OXYGEN PRESSURES Reviewed
Y MAENO, M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 87 ( 9 ) 1399 - 1403 1991
Single Work
Publisher：ROYAL SOC CHEMISTRY
Changes in the work function of zirconium on oxidation are measured at oxygen pressures of 3.0 x 10(-6)-3.0 x 10(-4) Pa and at temperatures in the range 426-775 K. The work function first decreases then increases until a final saturation stage is reached. Use of secondary-ion mass spectroscopy (SIMS) shows that the changes correspond to oxygen adsorption, oxide nucleation and oxide growth, respectively. The initial decrease in work function is interpreted by the incorporation of oxygen adatoms into the subsurface. The oxygen adsorption potential of zirconium is evaluated by an effective medium theory, and the physical origin of the incorporation of oxygen adatoms is discussed. The positive change in the work function caused by oxide formation and the temperature and pressure dependences of the change in the work function by oxidation are explained qualitatively.
DOI： 10.1039/ft9918701399
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ANOMALY IN THE RATE OF OXYGEN ABSORPTION BY ZIRCONIUM DUE TO THE FORMATION OF OXIDE AT THE SURFACE - AUTOCATALYTIC REACTION MODEL OF OXIDE NUCLEATION Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 86 ( 22 ) 3797 - 3802 1990
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SOLUBILITY AND DIFFUSIVITY OF HYDROGEN AND DEUTERIUM IN ALPHA-HAFNIUM AT HIGH-TEMPERATURES Reviewed
S NAITO, M YAMAMOTO, T HASHINO
JOURNAL OF PHYSICS-CONDENSED MATTER 2 ( 8 ) 1963 - 1970 1990
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INCREASE IN YIELDS OF SECONDARY IONS BY OXIDATION OF ZIRCONIUM AT HIGH-TEMPERATURES AND LOW OXYGEN PRESSURES Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 86 ( 1 ) 157 - 164 1990
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KINETICS OF OXYGEN ABSORPTION BY ALPHA-ZIRCONIUM Reviewed
M YAMAMOTO, S NAITO, M MABUCHI, T HASHINO
JOURNAL OF PHYSICAL CHEMISTRY 93 ( 13 ) 5203 - 5209 1989
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PRESSURE-DEPENDENCE OF OXYGEN ABSORPTION BY METALLIC ZIRCONIUM WITH A CLEAN SURFACE Reviewed
H TAKEUCHI, S NAITO, M YAMAMOTO, T HASHINO
JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS I 84 ( 12 ) 4235 - 4247 1988