Intrinsic and defect surface states on single‐crystal metal oxides

The electronic properties of the surfaces of several single-crystal metal oxides were studied by electron spectroscopic techniques, yielding information on both intrinsic and extrinsic (defect) surface states. SrTiO//3 and TiO//2 have no intrinsic band-gap surface states, while nearly perfect MgO(100) surfaces exhibit a cation-derived empty surface state about 2 eV below the bulk conduction band edge. Defect surface states generally involve 0 vacancies, with attendant change transfer to surface cations that results in occupied states in the band-gap region.