Structure of ultrathin crystallineSiO2films on Mo(112)

The geometrical and electronic structures of a thin ${\mathrm{SiO}}_2$ film epitaxially grown on a Mo(112) substrate have been determined by first-principles density-functional theory calculations. β-cristobalite, β-tridymite, α-quartz, and β-quartz phases were considered. The film grows initially with an OH-terminated β-cristobalite structure which provides the strongest adhesion energy to the Mo substrate. High-temperature annealing results in a complete dehydroxylation and reconstruction of the top layer of the cristobalite film with the formation of two-membered silica rings. This accounts for a specific band at 795 ${\mathrm{cm}}^{\mathrm{-}1}$ observed in the Fourier transform infra-red (FTIR) spectrum of the annealed epilayer.