The carbon's solubility into copper is amazingly reduced and so largely floor diffusion and nucleation of carbon atoms are associated. Because of this and also the growth kinetics, the graphene thickness is restricted to predominantly a monolayer. The massive edge would be that the graphene is often developed on Cu https://www.quora.com/profile/Trevor-Flatcher-2/Thermal-Conductivity-of-Silicon-Carbide-and-Heat-Dissipation-Solutions-for-Electronic-Devices-Thermal-management-is-a-c