Atomic structures and atomic dynamics on ''1x1'' Si(111) at high temperatures

The Si(111) surface shows a first-order phase transition to the so-called ''1 x 1'' phase above Tc from the (7 x 7) phase. In the (1 x 1) phase, the surface atomic structure and the atomic dynamics were investigated by using empirical Tersoff-Dodson interatomic potential. From the calculation of the surface potential map of a Si adatom, both the surface diffusion coefficient and the evaporation rate of an Si adatom were evaluated. From a Monte Carlo simulation at high temperatures below the bulk melting point, surface melting was found on Si(111) surface above the critical temperature, provided that Si adatoms exist which are greater than the critical coverage. In the melting layers, all Si atoms are moving about with a diffusion coefficient as large as that of a Si adatom on Si(111) below the critical coverage at the same temperature. Below the critical coverage, only adatoms move about by surface diffusion; other surface atoms oscillate around their equilibrium positions, although exchanges among adatoms and surface atoms take place frequently.