Characterization of thin silicon overlayers on rutile TiO2(110)-(1x1)

Silicon thin films for coverages (theta) between 0.3 and 3 monolayers have been grown on rutile TiO2(110)-(1x1) at room temperature and studied by x-ray and ultraviolet photoelectron spectroscopies, and low-energy electron diffraction (LEED). A clear evidence of a strong Si/TiO2 interaction consistent with the high affinity of O for Si has been found. The Ti cations on the substrate are reduced while the Si film is oxidized, yielding SiO2 and a mixture of silicon suboxides. Neutral Si atoms are observed at a coverage of 3 monolayers. At the interface region we observe the formation of cross- linking Ti-O-Si bonds. The thin Si overlayer strongly attenuates the (1x1) LEED pattern from the substrate. Finally, thermal annealing results in the improvement of the SiO2 stoichiometry but the surface order is not recovered. Using ab initio densityfunctional theory we have obtained optimum geometrical configurations and corresponding density of states for 1/3 <=theta <= 1 monolayers of Si adsorbed on the 1x1 two-dimensional unit cell.