Electronic structure and growth of vanadium on TiO 2(110)

Abstract

The electronic structure, morphology, and thermal stability of vanadium deposits on TiO 2(110) were studied in the submonolayer-to-multilayer coverage regime. The deposition of vanadium was performed at 300 K by evaporation of metallic vanadium in UHV. The electronic structure of both the filled and the empty states was investigated by means of X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and near-edge X-ray absorption fine structure (NEXAFS) measurements, respectively. The growth of vanadium particles on this surface of TiO 2 was also studied with scanning tunneling microscopy (STM). At submonolayer coverage a charge transfer from vanadium to TiO 2 leads to the formation of V 2+/3+ and Ti 3+ cations. STM revealed the appearance of features with a typical diameter of 10–15 Å and a thickness corresponding to both one and two monolayers (ML) due to vanadium deposition. The density of these particles increases with vanadium exposure, whereas the size remains nearly constant. For coverages exceeding 1 ML a two-dimensional, granular, metallic vanadium film forms without any long-range order. Upon annealing above 600 K, reduced titanium cations are reoxidized and vanadium diffuses into the TiO 2 bulk, where V 2+/3+ cations seem to occupy substitutional sites.