V2O3(0001) surface terminations:: from oxygen- to vanadium-rich

Well-ordered epitaxial V2O3(0 0 0 1) films (thickness > 80 Angstrom) 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 degreesC. Annealing the V=O termination in oxygen atmosphere (500 degreesC, 5 x 10(-6) mbar) results in the partial removal of the vanadyl groups and in the formation of an oxygen-richer surface termination, exhibiting a (root3 x root3)R30degrees structure. Structure models for this oxygen-rich termination are proposed, which are characterised by (O=V)(0.66)-O-3-V-V-. . . and (O=V)(0.33)-O-3-V-V (. . .) stacking sequences. Conversely, deposition of sub-monolayer 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 V-3 layer on top of the bulk-type O-3 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. (C) 2004 Elsevier B.V. All rights reserved.