A detailed Raman study of the photochemical oxidation process of monolayer CVD grown graphene

Although graphene oxide (GO) has emerged as a promising material in the semiconductor industry, optimization of oxidation conditions to meet industrial needs had remained a challenge for researchers. We prepared a monolayer GO sheet by photochemical treatment of CVD graphene within 80 s using UV irradiation. TEM data confirms that there were no structural defects through the optimized oxidation condition with 20% oxygen content. Comparing to conventional GO flakes, this large area GO layer shows higher homogeneity in functional group distribution. Comparison of Amplitude and Area intensity ratios of Raman peaks and XPS data show a correlation between changes in D’ (~1620 cm^-1), G (~1587 cm^-1), and 2D (~2678 cm^-1) peaks with C sp3 (C-O), epoxide (C-O-C), and C sp2 (C=C) bonding. Moreover, although patterned graphene and GO regions are imperceptible by optical illuminance, they are distinguishable by Raman D and/or G-peak mapping. According to AFM data, our GO samples show the average thickness of 0.79 nm in its optimized condition with an ultra-clean surface comparable to that of exfoliated graphene. This work reveals some details about the oxidation process of graphene and sets the ground for transparent flexible optical and electrical applications of functionalized graphene.