Oxygen-induced restructuring of the TiO 2(110) surface: a comprehensive study

Abstract

We report a comprehensive experimental and theoretical study of the effect of oxidizing a TiO 2(110) surface at moderate temperatures. The surfaces are investigated with scanning tunneling microscopy (STM), low-energy He + ion scattering (LEIS) and static secondary ion mass spectroscopy (SSIMS). Flat (1×1)-terminated TiO 2(110) surfaces are obtained by sputtering and annealing in UHV at 880 K. These surfaces are exposed to oxygen gas at elevated temperatures in the range 470–830 K. Formation of irregular networks of pseudo-hexagonal rosettes (6.5 Å×6 Å) and small (11̄0] oriented (1×1) islands along with {001}-oriented strands is induced at temperatures from 470 to 660 K. After annealing above 830 K, only regular (1×1) terraces and white strands are observed. The composition of these oxygen-induced phases is quantified using 18O 2 gas in combination with LEIS and SSIMS measurements. The dependence of the restructuring process on annealing time, annealing temperature, and sample history is systematically investigated. Exposure to H 2 18O and air in the same temperature regime fails to induce the restructuring. UHV annealing of restructured, oxygen-enriched TiO 2(110) surface smooths the surfaces and converts the rosette networks into strands and finally into the regular (1×1) terraces. This is reported in an accompanying paper [M. Li, W. Hebenstreit, U. Diebold, Phys. Rev. B (1999), submitted]. The rosette model is supported by first-principles density functional calculations which show a stable structure results, accompanied by significant relaxations from bulk-truncated positions. A mechanism for the dynamic processes of the formation of rosettes and (1×1) islands is presented and the importance of these results for the surface chemistry of TiO 2(110) surfaces is discussed.