Theory of surface phonons in amorphous silica

A new theoretical approach to studying surface vibrations in amorphous solids is applied to silicon dioxide. The method entails modeling the surface as a Bethe lattice with a dangling bond, and treating the two-dimensional nature of the surface and the surface topography as small perturbations. The theory successfully describes the nature and origin of the surface states, as well as their relative intensities as observed in recent infrared-reflectivity and Raman-scattering experiments. Both intrinsic surface effects and those caused by the presence of adsorbates are discussed.