▎ 摘　　要

The evolution of Cu hills beneath graphene grains during the growth of millimeter scale single crystal graphene using low pressure chemical vapor deposition (LPCVD) was investigated. We observed a Cu hill slope decreasing behavior as the graphene grain size increased. It indicated a hill self-flattening process under the growth temperature close to copper melting point. Especially the hill was almost completely flattened once the graphene grains merged. The evolution of the dendritic structure of the graphene grains was also studied. It was found that with a stepwise increased flow of CH4, the interbranch boundaries in the dendritic structure can be healed. The blueshift of the Raman 2D band with the Raman sampling spot moving from the grain center to the edge confirmed the improvement of the crystal quality due to the healing of the interbranch boundaries.