Nano-scale chemical imaging of a single sheet of reduced graphene oxide

Scanning transmission X-ray microscopy (STXM) has been used to chemically image single and multiple layers of a thermally reduced graphene oxide (r-GO) multi-layer sheet of the size of ∼1 μm and a thickness of ∼5 nm. The thickness of individual layers in the single sheet can be identified through quantitative analysis of STXM. The local electronic and chemical structure of interest (edge versus center) in different regions within the single r-GO sheet has been studied by C K-edge X-ray absorption near edge structure spectroscopy (XANES) with 30 nm spatial resolution. High and localized unoccupied densities of states (DOS) of carbon σ* character were observed in r-GO compared to graphite and were interpreted as the lack of strong layer to layer interaction in the former. The azimuthal dependence of C K-edge XANES in selected locations has also been obtained and was used to infer the preferred edge structure. The r-GO sample was also characterized by TEM, AFM and Raman spectroscopy; the findings are in good accord with the STXM results.