MECHANISM FOR THE BULK-ASSISTED REOXIDATION OF ION SPUTTERED TIO2 SURFACES - DIFFUSION OF OXYGEN TO THE SURFACE OR TITANIUM TO THE BULK

The reoxidation of Ar+ sputtered TiO2 surfaces by thermal annealing in vacuum is shown to result primarily from the diffusion of titanium cations, presumably in reduced oxidation states, from the damaged surface into the bulk, and not from the diffusion of bulk oxygen anions to the surface. Temperature programmed static secondary ion mass spectrometry (SSIMS) measurements indicate that the ratios of O to Ti in the Ar+ sputtered surfaces of TiO2(110) and TiO2(100) increase significantly as the temperature exceeds 700 K. With oxygen-18 incorporated into the Ar+ sputtered surfaces, the ratios of O-16 to O-18 remain constant during this reoxidation process. However, for both surfaces, the ratios of O-16 to Ti and O-18 to Ti increase during the reoxidation process. These ratios increase primarily as a result of a decrease in the surface Ti concentration which is ascribed to the diffusion of reduced Ti cations into the bulk of the oxide.