ELECTRONIC-STRUCTURE OF A DIMER ADATOM STACKING-FAULT MODEL FOR THE SI(111) 7X7 RECONSTRUCTED SURFACE

The electronic structure of a dimer-adatom-stacking-fault (DAS) model for the Si(111)7 x 7 structure was investigated by total energy calculations. Using the density functional theory, the pseudopotential method and the local density approximation, the local density of states of the 7 x 7 reconstructed surface were obtained. Calculation results of the charge densities of the dangling bonds provide an overall explanation of the scanning tunneling microscopy results of Hamers et al. [Surf. Sci. 181 (1987) 346; Phys. Rev. Lett. 56 (1986) 19721. We found that the bonds between adatoms and the atoms just below them, which are characterized by a fivefold coordinate structure, have geometrical dependence, and that those in the faulted unit cell of the 7 x 7 surface are stronger than in the unfaulted unit cell. The charge transfer from adatoms to restatom is also theoretically confirmed.