SURFACE ELECTRONIC-STRUCTURE OF V2O5(001) - DEFECT STATES AND CHEMISORPTION

We have studied the electronic structure and gas adsorption properties of both UHV-cleaved and reduced V2O5(001) surfaces by means of ultraviolet and X-ray photoelectron spectroscopies and Auger-electron spectroscopy. The surface band structure of the UHV-cleaved V2O5(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 V2O5(001) to CO leads to a slight reduction of the surface, while the Ar+-ion bombarded (reduced) surface is inert to CO. SO2 does not adsorb on the cleaved V2O5 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 V2O5 at room temperature leads to a partial re-oxidation of the surface.