Defects such as oxygen vacancies play a crucial role in the surface properties of transition metal oxides. By means of time-resolved, high-resolution scanning tunnelling microscopy, an adsorbate-mediated diffusion mechanism of oxygen vacancies on rutile TiO2(110) was revealed. Adsorbed oxygen molecules mediated vacancy diffusion through the jump of an oxygen atom to a vacancy and the sequential capture of an oxygen atom from a neighboring bridging oxygen row, leading to an anisotropic oxygen vacancy diffusion pathway perpendicular to the bridging oxygen rows.

Oxygen-Mediated Diffusion of Oxygen Vacancies on the TiO2(110) Surface. Schaub, R., Wahlström, E., Rønnau, A., Lægsgaard, E., Stensgaard, I., Besenbacher, F.: Science, 2003, 299[5605], 377-9