ASSIGNMENT OF A PHOTOEMISSION FEATURE IN THE O-2S O-2P BAND-GAPS OF TIO2 AND V2O5

A photoemission feature is observed in the O-2s-O-2p band gap of both UHV-cleaved single-crystal V2O5(001) and UHV-fractured single-crystal TiO2. There are three possible origins of this feature: (1) the ground states of V2O5 and TiO2 may contain electron-energy levels with bindi ng energies that correspond to the observed feature; (2) many-body eff ects may result in electrons that are photoexcited to energies other t han ($) over bar h omega(0) above their ground-state energies; or (3) the band-gap feature may result from the inelastic energy losses suffe red by the electrons after photoexcitation. Band-structure and energy- level calculations performed by others eliminate possibility (1). We h ave performed photoemission, resonant photoemission, and electron-ener gy-loss measurements in order to discuss the remaining two possibiliti es. By removing the inelastic backgrounds from the photoemission spect ra of V2O5(001) and TiO2 using experimentally measured electron-energy -loss spectra, we have shown that the band-gap feature is at least par tially due to the inelastic energy losses suffered by the photoexcited O 2p electrons during transport through the crystal.