Heat transfer mechanism across few-layer graphene by molecular dynamics

We use nonequilibrium molecular dynamics to study heat transfer across structures consisting of a few layers of graphene sandwiched between silicon crystals. We find that when heat transfers from a silicon lead on one side across the graphene layers to a silicon lead on the other side, the interfacial conductance is essentially independent of the number of layers, in agreement with recent experimental findings. By contrast, wave-packet simulations show that the transmission coefficient of individual vibrational modes depends strongly on frequency and the number of graphene layers, indicating significant interference effects. This apparent contradiction is resolved by a theoretical calculation, which shows that the integrated contribution of the phonons to the interfacial thermal conductance is essentially independent of the number of layers. When one atomic layer of graphene is heated directly, the effective interfacial conductance associated with heat dissipation to the silicon substrate is much smaller. We attribute this to the resistance associated with heat transfer between high and low frequency modes within heated graphene.