Local band gap modulations in non-stoichiometricV2O3films probed by scanning tunneling spectroscopy

Abstract

Scanning tunneling microscopy and spectroscopy have been used to investigate the electronic structure of non-stoichiometric V 2 O 3 islands with a vanadyl termination grown on Au͑111͒. The spectroscopic measurements reveal the correlation gap of bulk V 2 O 3 that varies between 0.2 and 0.75 eV for different sample preparations. In addition, gap modulations of roughly 0.2 eV are observed at different locations within the oxide islands. The changes in gap size are attributed to local deviations from the ideal V 2 O 3 stoichiometry in films produced at more oxidizing or reducing conditions. By evaluating the position of the Fermi level with respect to the band edges, a p-type conductance characteristic is dominantly observed for the V 2 O 3 islands, indicative of an efficient hole doping of the V 3d band.

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

“…194 This experimental finding is compatible with a local switching between p-type and ntype conductance behavior of the oxide film, being triggered by the dominances of either vanadium or oxygen defects within spatially-confined regions of the oxide lattice. The resulting defect states in the gap are filled via electron/hole transfer from the Au support and introduce a bending of the oxide bands in response to the charging effect.…”

“…194 Closely related to polarization interactions and charge exchange is the bending of oxide bands at the interface, a behavior commonly known as Schottky response ( Fig. 3.6).…”

“…The resulting defect states in the gap are filled via electron/hole transfer from the Au support and introduce a bending of the oxide bands in response to the charging effect. 194 From evaluating the position of the band edges with respect to the Au Fermi level, the amount of nonstoichiometry and the charge exchange across the interface can be approximated. A similar band bending effect has been found for alumina films on NiAl(110).…”

Selectivity in Methanol Oxidation as Studied on Model Systems Involving Vanadium Oxides

“…The results presented in the following have been obtained on thin V 2 O 3 films grown on Au(111). Figure 4a shows an area at 5 K where a few vanadyl oxygen atoms have been removed (dark spots) [30]. Figure 4b shows scanning tunneling spectra taken within an area where full vanadyl coverage is observed as opposed to a position where apparently an individual vanadyl oxygen atom is missing.…”

“…Note that the band gap referred to here is the band gap in the surface region which may be different from the bulk band gap. There are indications that even defects within the material influence the band gap at the surface, and that this band gap varies across the surface [30]. The band gap is believed to be important in oxidation reactions where redox processes involve electron transfer and intermediate storage [4].…”