The effect of oxygen functional groups on the electrical transport behavior of a single piece multi-layered graphene oxide

To investigate the electronic transport mechanisms in multi-layered graphene oxide (MGO), the temperature-dependent electrical conductivity (σ(T)) has been measured as a function of the annealing temperature (Ta). An individual MGO flake was gradually reduced by thermal annealing at Ta from 88 to 300 °C, with the reduction process confirmed at each stage by X-ray photoelectron spectroscopy. As Ta increases, the σ(T) of the MGO also increases. We found that the σ(T) is well interpreted by variable-range hopping in disordered regions in series through activated conduction across small barriers. We associate the localized states for hopping with the oxygen functional groups in GO, as well as the small activation barriers with the domain boundaries between the clustered oxygen functional groups and the graphitic region. Both the hopping and activation barrier resistances decrease systematically as the Ta increases.