Comparison of surface structures of corundum Cr2O3(0001) and V2O3(0001) ultrathin films by x-ray photoelectron diffraction

Thin Cr2O3(0 0 0 1) layers are formed by oxidation of a Cr(1 1 0) single crystal. This surface is further modified by growing an epitaxial ultrathin V2O3(0 0 0 1) film by reactive vapor deposition. Synchrotron based soft-x-ray photoemission spectroscopy and x-ray photoelectron diffraction are used to characterize the surface layers of these two corundum-structured oxides. By comparison of experimental XPD patterns with simulated electron multiple scattering calculations, two distinctively different surface terminations are extracted for the two oxides. While for V2O3 we confirm the previously proposed vanadyl-terminated surface structure, we propose a new surface structure for Cr2O3 that consists of excess chromium atoms occupying interstitial sub-surface sites.