Annealing induced electrical conduction and band gap variation in thermally reduced graphene oxide films with different sp2/sp3 fraction

Abstract

Temperature dependent electrical conductivity of as prepared and thermally reduced graphene oxide (GO) thin films was measured in the range 300–520K. As prepared GO films show very low conductivity ∼6.8×10−6S/cm at 300K, which increases slowly till 370K. A sharp increase in conductivity is observed in the temperature range 370–440K, beyond which conductivity is thermally activated with activation energy 0.26eV. Reduced GO films show an increase in conductivity at 300K with increase in reduction temperature. GO films reduced at 400°C exhibit high conductivity ∼40S/cm at 300K, with very low activation energy 0.05eV in the measured temperature range 300–520K. The increase in conductivity after thermal reduction is due to an increase in the ratio sp2/sp3 bonded carbon atoms. The band gap of as prepared GO is 3.20eV and it is decreased by approximately 0.4eV in the case of thermally reduced GO at 400°C in comparison to as prepared GO.