Negligible Electronic Contribution to Heat Transfer across Intrinsic Metal/Graphene Interfaces

Despite the importance of high thermal conductance (G) of metal/graphene interfaces to thermal management of graphene devices, prior reported G of graphene interfaces is all relatively low. One possible route to improve G of metal/graphene interfaces is through additional heat conduction by electrons, since graphene can be easily doped by metals. In this study, we evaluate the electronic heat conduction across metal/graphene interfaces by measuring G of palladium (Pd)/transferred graphene (trG)/Pd interfaces, prepared by either thermal evaporation or magnetron sputtering. It is found that, for Pd/trG/Pd samples prepared by thermal evaporation, G = 42 MW m(-2) K-1 and G only weakly depends on temperature, suggesting that heat is predominantly carried by phonons. However, for Pd/trG/Pd samples prepared by sputtering, a significant increment of G is observed. G = 300 MW m(-2) K-1, and is roughly proportional to temperature. We attribute the enhancement of G to an additional channel of heat transport by electrons via atomic-scale pinholes generated in the graphene by ion bombardment during magetron sputtering. Thus, it is concluded that electrons play a negligible role in heat conduction across intrinsic metal/graphene interfaces, and the contribution of electrons is only substantial if graphene is damaged.