Ab initio study of stability and migration of point defects in copper-graphene layered composite

Ab initio calculations based on density functional theory have been performed to determine the relative stabilities and migration of point defects in a copper-graphene layered composite (a single graphene layer is inserted between multi Cu(111) layers, Cu/gr/Cu for short). The results indicate that the total trapping region around the graphene layer for point defects is about 15 Å, i.e. the interface in the composite consists of the graphene layer and three Cu layers on each side of the graphene. The interface reduces the formation of C vacancies with a lower formation energy than that in pristine graphene, but slightly affects the formation of C interstitials. However, the formation energies of Cu point defects near the graphene significantly decrease, compared to these in bulk Cu. The migration energy barrier of a C vacancy in the graphene layer of the composite is lower than that in the pristine graphene without full relaxation, while the migration energy barriers of Cu vacancies near the graphene are much smaller than that in the bulk. The Cu vacancies prefer to jump toward the interface center through the nearest neighbor Cu layers rather than jumping within the same Cu layer. The C and Cu interstitials favorably jump between the two nearest fcc sites by passing through a hollow site, and the migration of Cu interstitials in the interface is also easier than in bulk Cu. These results suggest that the interface in the Cu/gr/Cu composite provides a strong sink for trapping defects and preferring sites for their recombination.