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 sp(2) states with additional electronic states originating from functional groups. The intensity of the pi* state decreases as the atomic ratio O:C increases. The intensity ratio of carboxyl to pi* states in XAS TEY mode corresponds to the area ratio of carboxyl to sp(2) 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. (c) 2008 Elsevier B. V. All rights reserved.