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

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