Identification of Copper Surface Index by Optical Contrast

With the rise of 2D materials, copper (Cu) is revealed as good surface catalyst, especially in the self-limited growth of graphene. In the regime of surface catalyst, the catalytic activities and functionalities of Cu should be highly dependent on its surface type. Traditional methods to determine the surface index are mainly high-vacuum based surface science techniques and are typically of low throughput and in small scale. A method to fast detect the surface index of Cu in large scale is still lacking. Here, the authors report an effective optical contrast method to identify the Cu surface index in large area. This method is based on the Cu₂O-thickness dependent color of Cu surface after a mild oxidation in hot air. It is revealed that different Cu surfaces (Cu(111), Cu(100), and Cu(110) as examples) have various oxidation barriers and would exhibit distinct color evolution with heating time. It is also showed that graphene grown on Cu surfaces with varied orientations has totally different growth behaviors. The results would greatly facilitate the high-throughput determination of Cu surface index and accelerate the large-scale facet-dependent catalytic research of Cu, such as in single-crystal graphene growth.