Reactive re-oxidation of reduced TiO2(110) surfaces demonstrated by high temperature STM movies

The re-oxidation of slightly reduced TiO2(110) surfaces by exposure to an oxygen pressure of∼ 2× 10−7 mbar in the temperature range 473–1000 K occurs by re-growth of TiO2 overlayers by diffusion of Tin+ interstitials from the bulk. Starting with a (1 × 2) reconstructed surface, scanning tunnelling microscope images of the surface reacting under these conditions show that the (1×1) islands nucleate within the (1×2) layer and grow laterally. As the islands reach a critical size, which is temperature dependent, a new (1× 2) layer begins to nucleate and grow. At both extremes of the temperature range nucleation of the second layer occurs before coalescence of the (1 × 1) islands, however, at temperatures between 673 and 773 K large areas of (1 × 1) surface form before growth of the second layer. The reaction is cyclic and several layers of TiO2 can be grown in this way.