Akio Yoshimori

Electronic structure of the DAS model for the Si(111)7 × 7 reconstructed surface by energy band calculations

Abstract Electronic structure of the dimers adatoms and stacking fault (DAS) model for the Si(111)7 × 7 reconstructed surface is theoretically investigated. A standard scheme with norm-conserving pseudopotential and local density approximation is applied in the repeated slab geometry. Surface states due to three kinds of dangling bonds are obtained: (1) of the adatoms, (2) of the first layer atoms, and (3) of the corner hole atoms. The local densities of states have been calculated at these dangling bond sites. For the adatom dangling bond states, pronounced asymmetry is found between the faulted and unfaulted parts of the unit cell. The obtained local densities of states are compared with the measured scanning tunneling spectroscopy (STS) data and with the photoemission spectra. Qualitative agreement has been obtained between the experimental results and the theory.

Theory of the transition to the incommensurate reconstructed surface of W(001) induced by H-adsorption

Abstract Pairwise interactions between adsorbed H and surface W-atoms, competing with the intrinsic displacive surface instability, are shown to be able to account for the transition to the W(001) surface incommensurate reconstruction. Analysis is made by the mean field approximation on these interactions with an assumed free energy of a clean surface in terms of W-displacements. Results are qualitatively in accord with the observed data.

Charge Transfer in Hartree-Fock Approximation of Time-Dependent Anderson Model

The effect of the intraatomic Coulomb interaction on the charge transfer is treated in the Hartree-Fock approximation with use of the time-dependent Anderson model which has been widely employed in gas-surface collision without the intraatomic interaction so far. The charge state of the scattered ion from the metal surface is calculated numerically for a case of simple time-dependence in a surface-adatom interaction within the wide band approximation. The total number of electrons transferred to the adatom-orbital is found to saturate in a rather short time interval. The spin polarisation grows exponentially, dependent on the spin splitting of the adatom level. Also shown is an oscillatory behaviour of spin polarisation near its equilibrium value after the exponential growth.

Electronic structure of the DAS model for Si(111)7 × 7 by energy band calculations — simplified models

Abstract Ab initio band calculations are made to investigate the electronic structure of the DAS model for the 7 × 7 reconstructed surface of Si(111). A standard scheme with a norm conserving Pseudopotential is applied to simplified model structures with 2 × 2 or 3 × 3 periodicity. Surface states due to three kinds of dangling bonds are obtained. A remarkably large value for the effective transfer is found between the adatom dangling bonds neighboring the dimer structure, leading to wide bands associated with them. The calculated results are then used to predict the electronic structure of the real surface with 7 × 7 periodicity.

Theoretical analysis of effects of hydrogen adsorption on the W(001) reconstructed surface

The system of the W(001) reconstructed surface with adsorbed hydrogen is theoretically analyzed. A phenomenological Ginzburg-Landau type free energy is assumed for the clean surface, and the interaction between adsorbed H atoms and “displaced” surface W atoms is taken into account. Fluctuation effects of dislacive order parameter are considered by means of a variational method for the partition function of functional integral form. The thermal desorption spectra and the coverage dependence of the symmetric vibrational mode frequency of adsorbed H atoms are calculated from the free energy.

Electronic‐structure theory of the dimers adatoms and stacking fault model on Si(111) reconstructed surface—comparison with scanning tunneling spectroscopy

The electronic structure of the Si(111) 5×5 dimers adatoms and stacking (DAS) model has been calculated in the slab geometry, using the local density approximation (LDA) and norm‐conserving pseudopotential method. Surface states due to three kinds of dangling bonds are obtained, i.e., of the adatoms, the first layer atoms, and in the corner holes. The local densities of states have been calculated on these dangling bond sites. Since those of 5×5 are expected to be different from those of 7×7, a qualitative comparison of these results with the measured scanning tunneling spectroscopy (STS) of 7×7 has been made. In general, qualitative features agree well with the observed ones.

Singlet-triplet conversion of He∗(1s2s) by metal surfaces

Abstract The singlet-triplet conversion of the excited He(1s2s) metastable atom, approaching the metal surface with relatively low work function, is delt with on the basis of an extended Newns-Anderson model allowing the atom to have spin singlet and triplet states. After a canonical transformation, we show that a virtual process through the ionic states, of both the positive and the negative ions, makes the conversion possible. The numerical results show that in a certain range of parameters, the conversion possibly takes place in a region rather far from the surface.

Interpolation formula for the Auger neutralization probability

Abstract The higher order perturbation terms of the Auger neutralization process are examined with use of the Keldysh Green function method. An explicit condition is found to guarantee the Hagstrum equation. With the aid of numerical analyses, an interpolation formula is proposed for the Auger neutralization of an ion with an arbitrary velocity.

Oscillation of the Spin Polarization in the Time-Dependent Newns-Anderson Model

The oscillatory approach in time to the equilibrium value of the spin polarization of moving atoms near metal surfaces is analyzed in detail, which appears in the Hartree-Fock approximation for the time-dependent Newns-Anderson model. The approximate asymptotic solution is obtained for the long time behavior of the spin polarization and also the detailed analytic property of the exact solution for long time is discussed.

Theoretical study of the electronic structure of the dimer—adatom-stacking-fault model for the Si(111) surface

Abstract The electronic structure of the Si(111)7 × 7 dimer—adatom-stacking-fault (DAS) model has been calculated in the slab geometry, using the local density approximation (LDA) and the norm-conserving pseudopotential. Surface states and resonance states are obtained in the whole energy range for valence electrons. The dependence of one-electron energies on the cut-off values in the plane wave expansion is examined for the 1 × 1 truncated surface, and the result is utilized for the interpretation of the calculated result of the 7 × 7 surface. The obtained results for the 7 × 7 DAS model are found to agree well with the experimental ones for the 7 × 7 reconstructed surface.