Graphene to graphene, and substrate to substrate: How to reliably differentiate supported graphene from polycrystalline substrates using SEM?

Electron channeling contrast (ECC) for the polycrystalline substrate is commenly observed in a SEM image for graphene supported on polycrystalline substrates, making it challenge to differentiate graphene from substrate and determine the layer-numbers of graphene using SEM. Two feasible methods that allow accurate determination of layer-numbers of graphene using SEM were proposed and clearly demonstrated. The first method is to adjust the brightness of local grain in an SEM image with image-processing software, making the gray-scale values of different grains equal to each other. The second method is to tilt the sample stage to a certain angle during imaging process, giving rise to the identical orientation between neighboring grains relative to the incident electron beam. The findings reported here will have important implications for unambiguous differentiation graphene and other 2D materials from the supported polycrystalline substrate.