Transparent and highly conductive liquid-phase exfoliated graphite films treated with low-temperature air-annealing

This article presents a novel and simple method of liquid-phase exfoliation to fabricate graphene films that possess high conductivity and good light transparency. Graphite was exfoliated in water-ethanol mixture, with the aid of Nafion, to give highly stable graphene dispersion. Transparent graphene thin films were easily deposited by vacuum filtration from the Nafion-stabilized graphene dispersion. More important, low-temperature air-annealing (at 250 °C for 2 h) was employed to treat freshly-prepared graphene films for the first time. It demonstrates that the technique is advantageous and quite efficient for the fabrication of exfoliated graphite films with defect-free structure and high purity, confirmed by TEM, SEM, FTIR, XPS, and Raman spectra. The resulting graphene films possess a sheet resistance lower than 2.86 kΩ sq−1 and optical transmittance over 84% at a typical wavelength of 550 nm.