The structure of epitaxial V 2 O 3 films and their surfaces : a medium energy ion scattering study

Medium energy ion scattering (MEIS), using 100 keV H incident ions, has been used to investigate the growth of epitaxial films, up to thicknesses of ~200 Å, of V2O3 on both Pd(111) and Au(111). Scattered-ion energy spectra provide a measure of the average film thickness and the variations in this thickness, and show that, with suitable annealing, the crystalline quality is good. Plots of the scattering yield as a function of scattering angle, so-called blocking curves, have been measured for two different incidence directions and have been used to determine the surface structure. Specifically, VEGAS simulations for a range of different model structures show poor agreement with experiment for half-metal (....V’O3V) and vanadyl (....V’O3V=O) terminations, with and without surface interlayer relaxations. However, good agreement with experiment is found for the modified oxygen-termination structure, first proposed by Kresse et al., in which a subsurface V half-metal layer is moved up into the outermost V buckled metal layer to produce a VO2 overlayer on the underlying V2O3, with an associated layer structure of ....O3VV’’V’O3. This result is consistent with the predictions of thermodynamic equilibrium at the surface 1 Present address: Institüt für Angewandte Physik, TU Wien, 1040 Wien, Austria 2 Also at Fritz-Haber-Institut der MPG, Faradyweg 4-6, 14195 Berlin, Germany ∗ Corresponding author. Email [email protected]