Oxygen vacancies and defect electronic states on the SnO2(110)-1 x 1 surface.

Abstract

The ${\mathrm{SnO}}_{2}$(110)-1\ifmmode\times\else\texttimes\fi{}1 surface, a surface which is structurally similar to the more studied ${\mathrm{TiO}}_{2}$(110) surface, has been found to be an ideal system of study for the identification and characterization of surface oxygen vacancies. Heating a well-oxidized, nearly perfect (110) surface in UHV removes large amounts of surface lattice oxygen. Ion-scattering spectroscopy (ISS) and ultraviolet photoelectron spectroscopy (UPS) have shown conclusively that defect electronic states which appear low in the band gap for annealing temperatures less than 800 K arise from ``bridging'' oxygen vacancies [i.e., from the removal of oxygen anions from the terminal layer of an ideal, rutile-structure (110) surface]. UPS and four-point conductivity measurements indicate that heating at 800 K or above causes the formation of a second type of surface defect. It is argued that this second defect is an ``in-plane'' oxygen vacancy [i.e., the result of removing an oxygen anion from what is normally the second, tin-containing, atomic plane of an ideal (110) surface]. The in-plane oxygen vacancy is characterized by occupied states higher in the band gap which extend to the Fermi level.