Substrate effects on the thermal conductivity of epitaxial graphene nanoribbons

We study the effect of SiC substrate on thermal conductivity of epitaxial graphene nanoribbons (GNRs) using the nonequilibrium molecular dynamics method. We show that the substrate has strong interaction with single-layer GNRs during the thermal transport, which largely reduces the thermal conductivity. The high thermal conductivity of suspended GNRs is obtained in the second layers of bilayer GNRs, which has a weak van der Waals interaction with the underlying structures. The out-of-plane phonon mode is found to play a critical role on the thermal conductivity variation of the second GNR layer induced by the underlying structures. The effect of disordered edge defects on thermal conductivity is further investigated. The results show that the disordered edge defects can remarkably decrease thermal conductivity of GNRs weakly interacted with substrate, while the effect becomes minor on GNRs strongly interacted with substrate.