The structure of vanadia ultrathin films grown on TiO 2 (1 1 0) in an oxygen ambient

Abstract

Vanadium oxide has been deposited on TiO 2 (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 films approximately 5 and 18 monolayers thick by means of angle-scanned 2π photoelectron (XPD) measurements. While the electronic structure of the layers is close to that expected for V 2O 3, as judged from electron spectroscopies, XPD shows in a clear and direct way that the vanadia ultrathin films, instead of having the bulk-like corundum structure typical of V 2O 3, are characterised by a rutile lattice isomorphic to the substrate. This important difference with respect to vanadia ultrathin films grown on other substrates (e.g. Al 2O 3 (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 specificity and selectivity of titania-supported vanadia catalysts in many important chemical reactions.