Photoemission study of In2O3 thin films on NiIn(0001): valence bands and indium 4d levels of a model for ITO

Ultraviolet photoemission has been used to study the growth of ultrathin films of In2O3 on NiIn(0001), a model material for technologically important indium–tin–oxide (ITO). He II excited In 4d spectra are shown to be an excellent monitor of the indium oxidation, which allows an interface layer to be discerned between the alloy and In2O3 film. The growth of the second layer begins before the completion of this layer. Valence band spectra show that the electronic structure of the films is consistent with photoemission data from bulk In2O3 and In2O3 grown on Si(111), and with published density of states calculations. From a comparison of He I and He II excited valence band spectra we suggest that the valence band contains a finite contribution from In 4d antibonding states, as seen in the published calculations. With the exception of oxygen plasma treated ITO, which also shows significant differences to the calculations, the In2O3/NiIn(0001) valence band spectra are in good agreement with spectra from differently treated ITO samples.