New insights into the density of states of graphene oxide using capacitive photocurrent spectroscopy

Capacitive photocurrent spectroscopy is used to probe the electronic states of graphene-oxide, and reduced graphene-oxide. Three peaks are observed whose intensities scale with the oxygen coverage. The energy of these peaks correlate with the luminescence spectra reported for graphene-oxide. Using a fitting procedure, the density of states for graphene oxide is extracted from the data. It consists of the π/π∗ states along with a distribution of mid-gap states centered at three different energies near the Dirac point. X-ray photoelectron spectroscopy measurements are used to identify the oxygen functional groups corresponding to the observed state distribution.