Annealing response of disordered sputter deposited vanadium pentoxide (V2O5)

Abstract

We report the response to isothermal, low temperature (280 °C) annealing in air for up to 60 min, in terms of changes in crystallography and optical absorption coefficient α(E) of two types of sputter deposited, disordered vanadium pentoxide; (1) an amorphous film and (2) a single 〈010〉-crystallographic orientation film in which the interlayer spacing b is slightly greater (0.03%) than b0, the ideal value. It was found that low temperature annealing does not crystallize amorphous vanadium pentoxide, and that no change occurs in α(E) in the charge transfer region E≥∼2.5 eV. The Tauc nondirect optical band gap E′=2.34 eV. However, the low energy absorption tail present in the as-grown amorphous film disappears upon annealing, attributed to the elimination of V+4 sites. On the other hand, annealing crystalline vanadium pentoxide causes crystallographic changes, the interlayer spacing expands, and concurrently, α(E) in the charge transfer region, E≥2.6 eV, increases. In agreement with a recent theoretical band calculation and single crystal data, the indirect optical band gap Ei=2.36 eV for both as-grown and annealed crystalline vanadium pentoxide.