Density of the electronic states of graphite: Derivation from differential capacitance measurements

Differential capacitance data for stress-annealed pyrolytic graphite in acetonitrile containing tetrapropylammonium tetrafluoroborate have been measured over an energy range of 3 eV. The data are interpreted within a model which has successfully been applied to semiconductor electrolyte contacts. In this model the overall capacitance is considered as a space charge capacitance inside the solid in series with a Helmholtz double-layer capacitance at the interface. In contrast to normal metals, the relative low density of electronic states of the semimetal graphite results in the measured capacitance being dominated by the space charge contribution of the graphite. From a correlation between the local position of the Fermi level and the local density of excess charge, the density of states around the Fermi surface can be calculated from such data. The result is compared with theoretical calculations of the electronic properties of graphite.