Direct Identification of Multilayer Graphene Stacks on Copper by Optical Microscopy

Growing graphene on copper (Cu) by chemical vapor deposition (CVD) has emerged as a most promising approach to satisfy its practical requirements, but the fast and large-scale characterization of its grown adlayers remains a challenge. Here we present a facile and inexpensive method to directly identify the multilayer graphene stacks on Cu by optical microscopy, using simple ultraviolet and heating treatments. The sharp optical contrast, originating from the variation in Cu oxide thickness underneath graphene, reproduces the stacking geometry with high fidelity to scanning electron microscopy observation, demonstrating the correspondence among the optical contrast, the oxide thickness variation, and the stack of adlayers. The close correlation roots in the throttling effect of graphene grain with discrete structural defects in controlling the rate-determined Cu oxidizing agent supply. We believe that this approach can enable large-scale evaluation of CVD-derived graphene quality, which are critical for optimizing CVD processing parameters of graphene growth.