PNNL

Abstract

Although there has been considerable debate in the solid state literature regarding oxygen vacancy versus titanium interstitial models for point defect diffusion in rutile TiO2, ultrahigh vaccum (UHV) surface scientists have all but unanimously adopted the oxygen vacancy model in explaining mass transport phenomena occurring between the bulk and surface. This unanimity, however, has not arisen from detailed mechanistic studies, but from a general misunderstanding that surface oxygen and titanium concentration changes measured by techniques like XPS and AES can be interpreted mechanistically. This thinking is especially pervasive in investigations of the bulk-assisted reoxidation of ion sputtered TiO2 surfaces. It is will known that ion sputtering TiO2 preferentially depletes the surface of oxygen until a steady-state level of surface reduction has been established. The surface stoichiometry of the sputtered TiO2 surface can be restored when annealing in UHV by transport of sputter damage to the bulk.