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Medium energy ion scattering (MEIS)
Surface structure
Epitaxy
Vanadium sesquioxide
Abstract:
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.
