Photoemission studies of ion bombardment effect on SnO ₂ surfaces

Polycrystalline SnO ₂ surfaces have been studied by X-ray and He I photoelectron spectroscopies (XPS and UPS). To examine ion bombardment effects, SnO ₂ surfaces were sputtered by Ar ⁺ , He ⁺ and H ⁺ ions, after they had been cleaned by heating at 1300 K for 5 h. Surface stoichiometry was determined by the O(1s)/Sn(3d _{5 2} ) XPS peak ratio. UPS probes directly the density of occupied valence bands. Instead of a minimum in the O/Sn ratio for sputtering energies on SnO ₂ (110) surfaces [7] we observed that the preferential sputtering effect in favour of oxygen increases with sputtering energy and ion mass. Electronic properties such as Sn ²⁺ defect states, O(2p)-Sn(5p) hybridized electrons, O(2p) lone pair orbitals, work function changes and the bending of the valence band edge toward the Fermi level were demonstrated to have a strong correlation with oxygen loss under ion bombardment.