Oxygen vacancies at the SnO2 (110) and (101) surface and sub-surface sites were studied in the framework of density functional theory by using both all-electron Gaussian and pseudopotential plane-wave methods. The all-electron calculations were performed using the B3LYP exchange-correlation functional with accurate estimations of energy gaps and density of states. It was shown that bulk O vacancies were responsible for the appearance of a fully occupied flat energy level lying at about 1eV above the top valence band, and an empty level resonant with the conduction band. Surface O vacancies strongly modified the surface band structures with the appearance of intra-gap states covering most of the forbidden energy window, or only a small part of it, depending upon the vacancy depth from the surface. Oxygen vacancies could account for electron affinity variations with respect to the stoichiometric surfaces as well. A significant support for the present results was found by comparing them with available experimental data.

Density Functional Study of Oxygen Vacancies at the SnO2 Surface and Subsurface Sites. F.Trani, M.Causà, D.Ninno, G.Cantele, V.Barone: Physical Review B, 2008, 77[24], 245410 (8pp)