Five Orders of Magnitude Reduction in Energy Coupling across Corrugated Graphene/Substrate Interfaces

A normal full-contact graphene/substrate interface has been reported to have a thermal conductance in the order of 10(8) Wm(-2)K(-1). The reported work used a sandwiched structure to probe the interface energy coupling, and the phonon behavior in graphene was significantly altered in an undesirable way. Here, we report an intriguing study of energy coupling across unconstrained graphene/substrate interfaces. Using novel Raman-based dual thermal probing, we directly measured the temperature drop across the few nm gap interface that is subjected to a local heat flow induced by a second laser beam heating. The thermal conductance (G(t)) for graphene/Si and graphene/SiO2 interfaces is determined as 183 +/- 10 and 266 +/- 10 Wm(-2)K(-1). At the graphene/Si interface, G(t), is 5 orders of magnitude smaller than that of full interface contact. It reveals the remarkable effect of graphene corrugation on interface energy coupling. The measurement result is elucidated by atomistic modeling of local corrugation and energy exchange. By decoupling of graphene's thermal and mechanical behavior, we obtained the stress-induced Raman shift of graphene at around 0.1 cm(-1) or less, suggesting extremely loose interface mechanical coupling. The interface gap variation is evaluated quantitatively on the basis of corrugation-induced Raman enhancement. The interface gap could change as much as 1.8 nm when the local thermal equilibrium is destroyed.