Surface electronic structure of V 2O 5(001): defect states and chemisorption

Abstract

We have studied the electronic structure and gas adsorption properties of both UHV-cleaved and reduced V 2O 5(001) surfaces by means of ultraviolet and X-ray photoelectron spectroscopies and Auger-electron spectroscopy. The surface band structure of the UHV-cleaved V 2O 5(001) surface is similar to that of the bulk: the V 3d band is unoccupied, and the upper edge of the 6 eV wide O 2p valence band lies about 2.5 eV below E F. Electron or Ar +-ion bombardment results in an oxygen-deficient surface; charge is transferred to surface V cations, producing defect-induced states in the bulk-bandgap region. At room temperature, exposure of UHV-cleaved V 2O 5(001) to CO leads to a slight reduction of the surface, while the Ar + -ion bombarded (reduced) surface is inert to CO. SO 2 does not adsorb on the cleaved V 2O 5 surface at room temperature, but it does adsorb weakly on the reduced surface: both dissociatively and associatively at 300 K, and only dissociatively at 413 and 513 K. The interaction of O 2 with reduced V 2O 5 at room temperature leads to a partial re-oxidation of the surface.