Electronic structure of Pt overlayers on (1x3) reconstructed TiO2(100) surfaces

The effect of Pt atoms on the Ti 3d emission of Ti3+ states at (1 x 3) reconstructed TiO2(100) surfaces was studied by means of valence band photoemission spectroscopy using synchrotron radiation with excitation energies between 30 and 120 eV. A clean (1 x 3) reconstructed TiO2(100) surface was prepared by Ar+ sputtering and annealing at T = 870 K as checked with low energy electron diffraction. Subsequently, Pt was evaporated in situ using a resistively heated Pt filament. Evaporation was performed stepwise up to a nominal coverage of 1.8 monolayers (ML) as checked with Auger electron spectroscopy (AES), The Pt 4f core levels are shifted to higher binding energies with respect to Pt metal, indicating the presence of small Pt clusters, Difference spectra show a dublet between the TiO2 valence band maximum and the Fermi energy which is attributed to Pt 5d states. We found that the position and the intensity of the Ti 3d band gap emission were not significantly altered upon evaporation of Pt, In addition, the valence band maximum of TiO2 remains unchanged. These findings indicate the absence of an electronic charge transfer due to the high work function of TiO2(100)-(1 x 3) of 5.4 eV, in line with a simple metal-semiconductor contact theory. (C) 1997 Elsevier Science B.V.