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P. Scheiber, M. Fidler, O. Dulub, M. Schmid, U. Diebold, W. Hou, U. Aschauer, A. Selloni:
"(Sub)Surface Mobility of Oxygen Vacancies at the TiO₂ Anatase (101) Surface";
Physical Review Letters, 109 (2012), 1361031 - 1361035.

Anatase is a metastable polymorph of TiO2. In contrast to the more widely studied TiO2 rutile, O vacancies
(VO´s) are not stable at the anatase (101) surface. Low-temperature STM shows that surface VO´s, created by
electron bombardment at 105 K, start migrating to subsurface sites at temperatures 200 K. After an initial
decrease of the VO density, a temperature-dependent dynamic equilibrium is established where VO´s move to
subsurface sites and back again, as seen in time-lapse STM images. We estimate that activation energies for
subsurfacemigration lie between 0.6 and 1.2eV; in comparison, density functional theory 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.