(Sub)surface mobility of oxygen vacancies at the TiO${}_2$ anatase (101) surface

Abstract

Anatase is a metastable polymorph of TiO${}_2$. In contrast to the more widely-studied TiO${}_2$ rutile, O vacancies (V${}_{\mathrm{O}}$'s) are not stable at the anatase (101) surface. Low-temperature STM shows that surface V${}_{\mathrm{O}}$'s, created by electron bombardment at 105 K, start migrating to subsurface sites at temperatures $\ge$ 200 K. After an initial decrease of the V${}_{\mathrm{O}}$ density, a temperature-dependent dynamic equilibrium is established where V${}_{\mathrm{O}}$'s move to subsurface sites and back again, as seen in time-lapse STM images. We estimate that activation energies for subsurface migration lie between 0.6 and 1.2 eV; in comparison, DFT calculations predict a barrier of ca. 0.75 eV. The wide scatter of the experimental values might be attributed to inhomogeneously-distributed subsurface defects in the reduced sample.

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• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Charge Localization Dynamics induced by Oxygen Vacancies on the Titania TiO${}_2$(110) Surface

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