(285d) Quantifying the Surface Generation Rate for Bulk Point Defects In TiO2

Pangan-Okimoto, K., University of Illinois
Hollister, A., University of Illinois
Gorai, P., University of Illinois

The defect and surface properties of titania have been well-studied for its potential use in memory resistors and nanoelectronic gas sensors but the control of these properties in such fields has still not been fully realized. Such control of defect mobility and concentration in titania is essential for improving the operation of these technologies. Previous work in our research group has found that controlling the rutile (110) surface has opened up a new pathway for oxygen self-diffusion via an oxygen-interstitial mechanism in conditions where oxygen vacancies and titanium interstitials are thought to dominate. The present work models the detailed diffusion-reaction network of point defects in rutile to simulate interstitial-mediated self-diffusion of oxygen and to calculate a generation rate of bulk point defects at the surface. The model explicitly incorporates gas adsorption onto the (110) surface, interstitial generation at the surface/near surface, and diffusion of the oxygen in an interstitial-mediated mechanism through the bulk. In addition, the model employs techniques drawn from systems engineering to estimate the key kinetic parameters. Simulated diffusion profiles were compared to experimental profiles obtained by exposing annealing single-crystal rutile titania to isotopically labeled oxygen gas and then measuring isotopic oxygen concentration with secondary ion mass spectrometry. The simulated diffusion profiles matched experimental results, verifying that oxygen interstitials do indeed mediate oxygen self-diffusion. More importantly, our model allows us to calculate the oxygen interstitial generation rate at the (110) surface, a first for titania.