Role of Bulk Thermal Defects in the Reconstruction Dynamics of the TiO₂(110) Surface

We use low-energy electron microscopy to show that changing the temperature of oxygen-deficient, rutile-structure crystals causes steps on the (110) surfaces to move. This motion occurs because the concentration of bulk oxygen vacancies changes with temperature, requiring that material be added to or subtracted from the surface. During cooling below a bulk-stoichiometry-dependent temperature, the surface reconstructs into a 1×2 structure in the regions surface steps have swept through, showing that the structural and compositional changes needed to form the 1×2 phase are facilitated by the surface-to-bulk mass flow.