Well-ordered V2O5(001) thin films on Au(111):: Growth and thermal stability

Vanadium oxide thin films were grown on Au(111) by the oxidation of vapor-deposited V layers with 50 mbar of oxygen. The structure, composition, and thermal stability of the films have been investigated with scanning tunneling microscopy, low energy electron diffraction, photoemission spectroscopy, near-edge X-ray absorption fine structure, and temperature-programmed desorption. Well-ordered V2O5(001) thin films containing very few point defects have been obtained. Although the films have the tendency to grow in large crystallites and "dewet" the interface layer, growth by multiple steps of V deposition and oxidation precludes this problem and leads to flat films having a surface with a low density of steps. The films are composed of rather large (similar to 20 nm), single crystalline, and (001)-oriented V2O5 domains which show some azimuthal disorder between themselves. The X-ray-induced surface reduction of the V2O5(000 films was investigated with STM. O vacancies do not form randomly on the surface but rather appear as pairs or rows, indicating a concerted reduction process. Upon heating in UHV, the films are stable up to 500 degrees C, and they start sublimating above this temperature. Significant thermally induced reduction of the films only occurs above 560 degrees C. Comparison between these results and published studies emphasizes the influence of surface contamination and beam damage on the thermal reduction Of V2O5.