The structure of vanadia ultrathin films grown on TiO2 (110) in an oxygen ambient

Vanadium oxide has been deposited on TiO2 (1 1 0) by means of e-beam metal evaporation in an oxygen atmosphere at room temperature, following a procedure that has already been adopted by several groups. After an electronic structure characterisation based on XPS, X-ray excited Auger electron spectroscopy and valence band spectra, we have determined the lattice structure of ultrathin vanadia ®lms approximately 5 and 18 monolayers thick by means of anglescanned 2p photoelectron (XPD) measurements. While the electronic structure of the layers is close to that expected for V2O3, as judged from electron spectroscopies, XPD shows in a clear and direct way that the vanadia ultrathin ®lms, instead of having the bulk-like corundum structure typical of V2O3, are characterised by a rutile lattice isomorphic to the substrate. This important di€erence with respect to vanadia ultrathin ®lms grown on other substrates (e.g. Al2O3 (0 0 0 1) and Pd(1 1 1)), where the corundum structure is retained by the overlayer, could be a key to understanding the catalytic speci®city and selectivity of titania-supported vanadia catalysts in many important chemical reactions. copyright 2000 Elsevier Science B.V. All rights reserved.
Keyword: Titanium oxide,Surface structure,Photoelectron diffraction,Roughness,Morphology,Vanadium oxide,Single crystal epitaxy,Topography