The structure of epitaxial V2O3 films and their surfaces: A medium energy ion scattering study

Medium energy ion scattering, 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, scattering 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 under the surface preparation conditions, but is at variance with the conclusions of earlier studies of this system that have favoured the vanadyl termination. The results of these previous studies are re-evaluated in the light of the new result.