Electronic structures of an extra Si atom diffusing in the Si(1 1 1)(7 × 7) surface

The potential energy surface and the electronic properties for the migration of an extra Si atom in the Si(1 1 1)(7 × 7) surface are studied by performing tight-binding calculations. Our predicted diffusion region and the lowest energy barrier of an extra Si atom hopping across the cell boundary in the (7 × 7) reconstructed surface match the experimental observations and previous theoretical results very well. Based on our calculated electronic structures of the system, we find that the extra Si atom diffusing along the favored paths in the Si(1 1 1)(7 × 7) surface is driven by decreasing the density of occupied states at/nearby the fermi energy level as much as possible. Furthermore, we point out the fact that the calculated local density of states at/below the fermi energy level can significantly reflect the different local bonding features of the diffused Si atom at different sites in the surface is strongly associated with the covalent bonding character in the system in nature. In addition, we suggest that the observed brighter spot in the STM image from experiment most probably corresponds to the adsorption of an extra Si atom nearby the center adatom in the Si(1 1 1)(7 × 7) surface yet.