Photo-Induced Unpinning of Fermi Level in WO(3)

Atomic force and high resolution scanning tunneling analyses were carried out on nanostructured WO(3) films. It turned out that the band gap measured by scanning tunneling spectroscopy at surface is lower than the band gap reported in the literature. This effect is attributed to the high density of surface states in this material, which allows tunneling into these states. Such a high density of surface states pins the Fermi level resulting in modest surface activity at room temperature. Photo activation of WO(3) results in unpinning of the Fermi level and thereby in higher chemical activity at surface.