Graphite mediated reduction of graphene oxide monolayer sheets

Large area graphene oxide (GO) monolayer sheets were transferred on Si and SiO2/Si substrates by Langmuir-Blodgett technique and reduced by heat treatment in the presence of graphite powder, inside an evacuated and sealed enclosure. Reduction at 1000 °C results in a decrease of sheet thickness to ∼0.5 nm without any morphological changes, and de-oxygenation (O/C ratio 5%) accompanied by enhancement in sp2-C to 84%. Red-shift of G-peak to ∼1585 cm−1, decrease in I(D)/I(G) ratio and appearance of an intense G′-peak as a single Lorentzian, are indicative of substantial reduction in defects and restoration of graphitic network. Ultraviolet photoelectron spectroscopy (UPS) studies show large increase in density of states (DOS) in the immediate vicinity of Fermi level and decrease in work function after reduction. Bottom gated field effect transistors fabricated with isolated RGO sheets display ambipolar behavior, with charge neutrality point at a positive gate voltage, indicating p-type nature, consistent with UPS results. RGO sheets exhibit conductivity of (2-3) × 103 S/cm and field effect mobility of (20-45) cm2/Vs, which are substantially higher than the values usually reported for RGO sheets, particularly those obtained by chemical reduction followed by heat treatment.