Assignment of a photoemission feature in the O-2s-O-2p band gaps of TiO2 and V2O5.

Abstract

A photoemission feature is observed in the O-2[ital s]--O-2[ital p] band gap of both UHV-cleaved single-crystal V[sub 2]O[sub 5](001) and UHV-fractured single-crystal TiO[sub 2]. There are three possible origins of this feature: (1) the ground states of V[sub 2]O[sub 5] and TiO[sub 2] may contain electron-energy levels with binding energies that correspond to the observed feature; (2) many-body effects may result in electrons that are photoexcited to energies other than [h bar][omega][sub 0] above their ground-state energies; or (3) the band-gap feature may result from the inelastic energy losses suffered by the electrons after photoexcitation. Band-structure and energy-level calculations performed by others eliminate possibility (1). We have performed photoemission, resonant photoemission, and electron-energy-loss measurements in order to discuss the remaining two possibilities. By removing the inelastic backgrounds from the photoemission spectra of V[sub 2]O[sub 5](001) and TiO[sub 2] using experimentally measured electron-energy-loss spectra, we have shown that the band-gap feature is at least partially due to the inelastic energy losses suffered by the photoexcited O 2[ital p] electrons during transport through the crystal.