STRUCTURAL STUDIES OF TIO2(110) USING SCANNING-TUNNELING-MICROSCOPY

The structure of the (110) plane of TiO2 has been studied as a function of temperature and oxygen coverage using scanning tunneling microscopy. Three stable phases are observed above 700 K at which temperature surface mobility is sufficient to generate long range order. Above 1000 K, oxygen is lost from the sample unless the heating is carried out in an appreciable partial pressure of oxygen. The 1 X 1 phase has the structure expected from a normal termination of the bulk structure. If a surface with this structure is heated in vacuum to temperatures above 1000 K, it will convert to the 1 X 2 phase. This phase differs 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 occurs. We have observed enhanced tunneling through the 1 X 2 phase which makes coplanar 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 generates a long period structure rather than the 1 X 1 phase. This phase is characterized by the formation of crosslinking rows which stabilize the missing row structure. Argon ion bombardment of the surface leads to disorder which is annealed out above 700 K. Annealing to 900 K leads to the formation of a well-ordered 1 X 1 phase through a network of crosslinking elements.