The structure of the (110) plane of TiO2 was studied as a function of temperature and oxygen coverage using scanning tunnelling microscopy. Three stable phases were observed above 700K at which temperature surface mobility was sufficient to generate long-range order. Above 1000K, oxygen was lost from the sample unless the heating was carried out in an appreciable partial pressure of oxygen. The 1 x 1 phase had the structure expected from a normal termination of the bulk structure. If a surface with this structure was heated in vacuum to temperatures above 1000K, it converted to the 1 x 2 phase. This phase differed from the 1 x 1 phase principally through the elimination of alternate rows of bridging oxygens. Additional relaxation in the plane of the surface also occurred. Enhanced tunnelling through the 1 x 2 phase was observed which made co-planar two-phase regions of 1 x 1 and 1 x 2 appear to have different heights relative to the surface plane. Heating the surface in the 1 x 2 phase to 1000 K in oxygen generated a long period structure rather than the 1 x 1 phase. This phase was characterized by the formation of cross-linking rows which stabilized the missing row structure. Argon ion bombardment of the surface led to disorder which annealed out above 700K. Annealing to 900K led to the formation of a well-ordered 1x1 phase through a network of cross-linking elements.

Structural Studies of TiO2(110) using Scanning Tunneling Microscopy. Szabo, A., Engel, T.: Surface Science, 1995, 329[3], 241-54