Graphene Growth across the Twin Boundaries of Copper Substrate

Twin crystals, the formation energy of which is much smaller than that of ordinary grain boundaries, widely exist in the annealed copper and are hard to eliminate. The study of the effects of twin boundaries on graphene growth is of great significance to the understanding of graphene epitaxy. However, there are few studies on the effects of twin boundaries on the graphene growth process. Here, this article experimentally demonstrates that graphene islands are subjected to different compressive strains from the opposite copper crystal plane after growing across the twin boundary. Further results reveal that graphene can grow across different twin boundaries, such as atom steps, narrow valleys, and even micron-scale ridges, without forming linear defect. Therefore, strain-induced graphene doping can be manipulated with the type of twin boundaries and the location on the twin crystals. The transition region where the degree of doping changes monotonically across the twin boundary further confirms the different spatial doping phenomena of graphene islands. This work provides a new perspective for understanding the effect of twin boundaries on the graphene epitaxy, which is expected to have a potential impact on growing high-quality graphene on twinned copper substrates.