Unoccupied electronic states in graphite oxides

Unoccupied electronic states of graphite oxides with different oxidation times have been investigated using X-ray absorption spectroscopy (XAS) in total electron yield (TEY) and total fluorescence yield (TFY) modes. The graphite oxides exhibit graphite-like sp2 states with additional electronic states originating from functional groups. The intensity of the π* state decreases as the atomic ratio O:C increases. The intensity ratio of carboxyl to π* states in XAS TEY mode corresponds to the area ratio of carboxyl to sp2 carbon in X-ray photoelectron spectroscopy. In addition, the two modes in XAS can identify electronic states of functional groups originating from surface or bulk regions.