An ARPEFS study of the structure of an epitaxial VO2 monolayer at the TiO2(110) surface

In the present communication, we discuss the results of an angle resolved photoemission extended fine structure (ARPEFS) study of a VO2 monolayer (ML) grown on the TiO2 (110) surface by successive cycles of sub-ML vanadium metal deposition followed by annealing at 473 K in 2×10−6 mbar O2. The V 3p photoemission peak shows two distinct components chemically shifted by 1.3 eV. While the higher binding energy (BE) component produces a rather flat ARPEFS curve, the lower BE signal, associated with the VO2 phase, shows well defined intensity modulations whose main features are similar to the ARPEFS scan on the Ti 3p signal of the substrate. This observation demonstrates that the ordered VO2 phase grows epitaxially to the substrate, with a rutile type structure. However, some oxide is present in a more highly oxidized and less-ordered phase. In order to investigate the actual arrangement of the ML with respect to the question related to the possible formation of an intermixed VO2/TiO2 layer, the ARPEFS data have been interpreted by means of single-scattering spherical wave (SSC-SW) simulations. They are compatible with the hypothesis that the deposited ML evolves toward an intermixed VO2/TiO2 double layer where the vanadium atoms occupy the six-fold oxygen-coordinated sites. In addition, our data are in good agreement with a surface relaxation similar to that found by surface XRD on the stoichiometric TiO2(110) surface.