Morphology change of oxygen-restructured TiO2(110) surfaces by UHV annealing:: Formation of a low-temperature (1X2) structure

When reduced TiO2(110) single crystals are oxidized at moderate temperatures (470-660 K), the surfaces restructure. Interstitial Ti atoms from the bulk diffuse to the surface where they react with gaseous oxygen and form new, added TiO2 layers. These are characterized by three structural elements: small (1X1) islands, irregular networks of pseudohexagonal rosettes, and [001]-oriented strands. The strands exhibit the same structural characteristics as the(1X2) surface reconstruction, which forms upon annealing at higher temperatures. Atomic-resolution scanning tunneling microscopy images of the strands are consistent with the added-Ti2O3-row model. UHV annealing of oxygen-restructured surfaces smooths the surfaces and converts the rosette networks into strands and finally into regular (1X1) terraces. The composition of these oxygen-induced phases is quantified using O-18(2) gas in combination with low-energy He+ ion scattering measurements. Dynamic processes for the conversion from rosette networks into (1X2) strands and ultimately into (1X1) terraces are discussed.