Growth regimes of the oxygen-deficient TiO2(1 1 0) surface exposed to oxygen

We use low-energy electron microscopy (LEEM) to systematically investigate how the (1 1 0) surfaces of oxygen-deficient rutile crystals grow epitaxially when exposed to oxygen. Distinct growth processes occur, depending primarily on temperature and oxygen pressure. The temperature dependence of these growth regimes has been systematically determined for a slightly reduced crystal of medium-blue color. At high-temperature, TiO2 growth occurs by pure step flow without the nucleation of new islands. At relatively low-temperatures, crystal growth proceeds by two-dimensional islands nucleating and spreading laterally. In this layer-by-layer growth regime, the surface periodically oscillates between structures with 1 × 1 and 1 × 2 periodicity. The threshold temperature above which island nucleation does not occur depends upon the local terrace width. For a range of temperatures around the threshold, nucleation occurs on wide terraces but not on narrow terraces. We demonstrate how to use the different growth regimes to efficiently increase a crystal’s oxygen content, smooth its surface, and synthesize island arrays and stacks.