Effect of oxygen and nitrogen functionalization on the physical and electronic structure of graphene

Graphene was grown on low-cost copper foils (99.5% purity, 0.025 mm thick, Alfa Aesar product number 46365) using low pressure chemical vapour deposition. The foils were cleaned by electropolishing (10 s at 5 V, ~1.5 A) in an electrolyte containing orthophosphoric acid and urea, followed by rinsing in acetone and isopropanol. The growth was conducted inside a 1 inch diameter quartz tube under vacuum (10–1 mbar) with 20 sccm hydrogen flowing throughout. After 20 min annealing at 1,000 °C, 2 sccm methane was introduced for 10 min. The methane was kept on while the sample cooled to 600 °C, after which the flow was stopped. Basic characterization is shown in Fig. S1 below. SEM, df-TEM and Raman spectroscopy are all consistent with the sample consisting of predominantly monolayer graphene. The df-TEM shows that the typical graphene grain size is ~5 μm. The large background in the Raman spectra is due to the copper foil; the relative intensities of the 2D and G, their narrow width, and the fact that they can be well fit by single Lorentzians, are all consistent with monolayer graphene. For the pristine graphene, no D peak is found.