Valence Band Onset and Valence Plasmons of SnO2 and In2-xSnx O3 Thin   Films
  Valence band onset (Ev), valence band tail (VBT) and valence plasmons (VPs) have been studied as a function of sputtering of SnO2 and In2-xSnxO3 (ITO) thin films, using ultraviolet photoemission spectroscopy (UPS). Decrease in Ev with respect to the Fermi level and increase in the density of energy levels of VBT have been observed after 5 minutes of sputtering using Ar+ ions (500V). Bulk and surface components of VPs of Sn, SnO and SnO2 in sputtered SnO2 thin films have been observed in UPS spectra. Similarly, bulk and surface components of VPs of In, Sn and oxygen deficient ITO in sputtered ITO thin films have been observed in UPS spectra. Possible roles of Ev and increase in the density of energy levels of VBT are discussed in the mechanisms of current transport through heterojunctions of SnO2 with semiconductors. 
Shailendra Kumar, C. Mukherjee and D. M. Phase
cond-mat.mtrl-sci