V2O3(0 0 0 1) surface terminations: from oxygen- to vanadium-rich

Well-ordered epitaxial V2O3(0 0 0 1) films (thickness > 80 Å) have been prepared on the clean Rh(1 1 1) surface and investigated with scanning tunnelling microscopy, low-energy electron diffraction, high-resolution electron energy loss spectroscopy and high-resolution X-ray photoelectron spectroscopy with synchrotron radiation. Atomically flat V2O3(0 0 0 1) surfaces, terminated by vanadyl (VO) groups, have been obtained after the reactive oxide deposition and subsequent annealing in vacuum to 600 °C. Annealing the VO termination in oxygen atmosphere (500 °C, 5 × 10−6 mbar) results in the partial removal of the vanadyl groups and in the formation of an oxygen-richer surface termination, exhibiting a (√3×√3)R30° structure. Structure models for this oxygen-rich termination are proposed, which are characterised by (OV)0.66–O3–V–V⋯ and (OV)0.33–O3–V–V⋯ stacking sequences. Conversely, deposition of submonolayer V coverages onto the VO surface leads to the formation of a metal-rich V2O3(0 0 0 1) surface, terminated by a close-packed V3 layer on top of the bulk-type O3 plane. Such a VO(1 1 1)-layer is only metastable and oxidises back readily upon annealing in vacuum to the vanadyl-terminated V2O3(0 0 0 1) surface.