UPS and UV spectroscopies combined to position energy levels of TiO2 anatase and rutile nanopowders

Abstract

An accurate experimental determination of electronic structure in semi-conductors nanopowders is a challenging task. We propose here to combine UPS and UV-Vis spectroscopies in order to get the full description of electronic bands alignment of powder samples, TiO2 rutile and anatase. For UPS measurements, two preparation methods, namely dropping method and electrophoretic deposition, were used to prepare layers of titania powders on a conducting substrate, ITO or Ag. Both methods lead to comparable results, with a quantitative description of the energy levels from the valence band. Combining these results with the UV-Vis spectra of the same powders, enables to determine the absolute position of the valence band maximum and of the conduction band minimum. Combined UPS--UV-vis spectroscopy provides a better insight into the properties of a powdered material which can differ from single crystal model systems. It can be also used to predict the electronic transfer in mixed phase systems during, in photocatalytic processes.