Well-Ordered V₂O₅(001) Thin Films on Au(111): Growth and Thermal Stability

Abstract

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 (∼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(001) 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 °C, and they start sublimating above this temperature. Significant thermally induced reduction of the films only occurs above 560 °C. Comparison between these results and published studies emphasizes the influence of surface contamination and beam damage on the thermal reduction of V2O5.

Relating methanol oxidation to the structure of ceria-supported vanadia monolayer catalysts

“…2a). This binding energy agrees well with results previously obtained for a V 2 O 5 (001) film grown on a Au(111) crystal [64].…”

“…3a. Based on C-H stretching vibrations observed in the IR spectrum (not shown) and comparison to similar IR spectra for methanol adsorption on partially reduced V 2 O 3 (001) thin films [64] , this peak is assigned to the C-O stretch of methoxy bound to vanadia, although there also may be a contribution to the peak intensity from vanadyl groups that remain on the surface and have only slightly differing frequencies (see Fig. 3a).…”

Composition-dependent structure of polycrystalline magnetron-sputtered V–Al–C–N hard coatings studied by XRD, XPS, XANES and EXAFS

“…The peak position is in between the expected O1s peak of V 2 O 5 at about 530.0 eV (Mendialdua et al, 1995;Guimond et al, 2008;Zou et al, 2009) and the reported O1s positions of Al 2 O 3 , which are typically in the range 531-533 eV (Hinnen et al, 1994;van den Brand et al, 2004;Snijders et al, 2005). For the V-Al-C-N samples discussed here, the O1s and V2p spectra are similar (see Fig.…”

Loss Mechanisms in High Efficiency Polymer Solar Cells

“…V 2 O 5 is a well-known oxidizing agent, and oxygen vacancies in V 2 O 5 are easily induced [ 12,[33][34][35][36] via annealing [ 35,36 ] and environmental exposure. [ 12,22 ] The reduction of V 5+ to lower oxidation states has been correlated with a decrease in the work function of V 2 O 5 fi lms, [ 22 ] which would represent an extraction barrier for holes from the solar cell.…”