Real-Time Optical Visualization of Graphene Defects and Grain Boundaries by the Thermal Oxidation of a Graphene-Coated Copper Foil

We have constructed a system that can visualize graphene defects in real time by coupling a heater and an optical instrument. In this system, the phenomenon of copper oxidation was used to visualize defects in graphene. When heat is applied to graphene synthesized on a copper foil, oxygen in the atmosphere penetrates through the graphene grain boundaries and oxidizes the copper substrate. This system observes the entire process of copper oxidation in real time and controls the rate of the visualization process by adjusting the temperature and time. A temperature–time graph for graphene defect visualization was plotted based on the experimental data, which indicates that it only requires 5 min at 225 °C for completion of the visualization process. Additionally, through scanning electron microscopy–energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses, it has been confirmed that copper oxidation occurs during the process of visualization of graphene defects. Compared to conventional optical visualization methods, this technique is faster and more convenient. This system is expected to enable easy and fast quality inspection for the mass production of graphene.