Comparison of surface structures of corundum CrO(0 0 0 1) and VO(0 0 0 1) ultrathin films by x-ray photoelectron diffraction.

Thin CrO(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 VO(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 VO we confirm the previously proposed vanadyl-terminated surface structure, we propose a new surface structure for CrO that consists of excess chromium atoms occupying interstitial sub-surface sites.