Tuning surface properties of SnO2(1 0 1) by reduction

The SnO2(1 0 1) surface can be prepared with a SnO2 or SnO composition and consequently the surface Sn-atoms are either in a Sn(II) or Sn(IV) charge state. For a Sn(II) surface, Sn-5s derived surface states are identified by resonant, angle resolved photoemission spectroscopy (ARUPS). The differences in the interface properties of the Sn(II) and Sn(IV) surfaces of SnO2(1 0 1) are reviewed on the example of benzene and water adsorption. It is found that the difference in work function of these two surfaces causes a shift of the molecular orbitals of benzene by ∼1 eV with respect to the Fermi-level of the substrate. Density functional theory calculations predict dissociation of water on the stoichiometric (Sn(IV)) surface but only weak molecular adsorption on the reduced Sn(II) surface. These predictions are in agreement with ARUPS measurements that show that at 160 K no water adsorbs on the reduced surface but adsorbs dissociatively on the stoichiometric surface. A strong adsorbate induced band bending is also observed for water adsorption on the stoichiometric surface that is likely associated with the formation of surface hydroxyls.