SURFACE STUDIES OF TIO2-SIO2 GLASSES BY X-RAY PHOTOELECTRON-SPECTROSCOPY

The near-surface chemistry of titania-doped silicate glasses using X-ray photoelectron spectroscopy (XPS) has been investigated. It has been found that the Ti(2p) photoelectrons from these glasses have distinctly higher binding energy than those from pure titania (rutile) even though Ti has the same oxidation state in both solids. This difference has been attributed to differing oxygen co-ordinations, as previously shown by X-ray, infrared and Raman spectroscopic studies. This finding will be useful for future analysis of Ti-O systems. The oxygen 1s peak has been successfully resolved into two components: one from Si-O-Si as in fused silica and the other from Si-O-Ti, based on a four-coordinated Ti model. Silicon was found to be preferentially etched by ion bombardment, leaving a Ti-rich surface. High temperature annealing of both ion-etched and freshly cut samples led to substantial depletion of Ti from the near-surface region indicating that at the surface where the network is disrupted, occupancy by Ti is energetically less favored than Si. This surface segregation phenomenon may have a major effect on the surface properties of these glasses.