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 proced ure that has already been adopted by several groups. After an electronic st ructure characterisation based on XPS, X-ray excited Auger electron spectro scopy and valence band spectra, we have determined the lattice structure of ultrathin vanadia films approximately 5 and 18 monolayers thick by means o f angle-scanned 2 pi 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 vana dia ultrathin films, instead of having the bulk-like corundum structure typ ical of V2O3, are characterised by a rutile lattice isomorphic to the subst rate. This important difference with respect to vanadia ultrathin films gro wn on other substrates (e.g. Al2O3; (0 0 0 1) and Pd(1 1 1)), where the cor undum structure is retained by the overlayer, could be a key to understandi ng the catalytic specificity and selectivity of titania-supported vanadia c atalysts in many important chemical reactions. (C) 2000 Elsevier Science B. V. All rights reserved.