Surface electronic structure of silicon dioxide

By using the empirical tight-binding method, we have investigated the surface electronic structure of silicon dioxide. The two-center energy parameters of the tight-binding Hamiltonian are obtained from the first-principles band calculations and the surfaces of silicon dioxide are represented by the ideal (111), (100), and (110) surfaces of $\beta$ crystobalite. For Si-terminated ${\mathrm{SiO}}_2$ surfaces we find surface states in the optical gap and conduction band. Depending upon the degree of oxygen coverage the localized state in the optical gap may be half-filled or empty. In the case of the full oxygen coverage (i.e., the O-terminated ${\mathrm{SiO}}_2$ surface) these surface states are removed and new surface states originating from the oxygen atoms attached to the surface silicons are created in the valence band. Recent experimental data related to the ${\mathrm{SiO}}_2$ surface are outlined. We note that the dangling-bond surface states near the conduction-band edge are also observed experimentally. Furthermore, we examine the ultraviolet photoelectron spectroscopy and electron energy-loss spectroscopy (ELS). Our calculations favor the existence of Si — Si bonds near the ${\mathrm{SiO}}_2$ surface which account for the features lying in the lower part of the ELS spectrum.