Probing Voltage Drop Variations in Graphene with Photoelectron Spectroscopy

We use X-ray photoelectron spectroscopy (XPS) for characterization of voltage drop variations of large area single-layer graphene on quartz substrates, by application of a voltage bias across two gold electrodes deposited on top. By monitoring the spatial variation of the kinetic energies of emitted C1s photoelectrons, we extract voltage variations in the graphene layer in a chemically specific format. The potential drop is uniform across the entire layer in the pristine sample but is not uniform in the oxidized one, due to cracks and/or morphological defects created during the oxidation process. This new way of data gathering reintroduces XPS as a major analytical tool for extracting electrical as well as chemical information about surface and/or nanostructured materials