Role of Remote Interfacial Phonon (RIP) Scattering in Heat Transport Across Graphene/SiO₂ Interfaces.

Abstract

Heat transfer across interfaces of graphene and polar dielectrics (e.g., SiO₂) could be mediated by direct phonon coupling, as well as electronic coupling with remote interfacial phonons (RIPs). To understand the relative contribution of each component, we develop a new pump-probe technique called voltage-modulated thermoreflectance (VMTR) to accurately measure the change of interfacial thermal conductance under an electrostatic field. We employed VMTR on top gates of graphene field-effect transistors and find that the thermal conductance of SiO₂/graphene/SiO₂ interfaces increases by up to ΔG ≈ 0.8 MW m^-2 K^-1 under electrostatic fields of <0.2 V nm^-1. We propose two possible explanations for the small observed ΔG. First, because the applied electrostatic field induces charge carriers in graphene, our VMTR measurements could originate from heat transfer between the charge carriers in graphene and RIPs in SiO₂. Second, the increase in heat conduction could be caused by better conformity of graphene interfaces under electrostatic pressure exerted by the induced charge carriers. Regardless of the origins of the observed ΔG, our VMTR measurements establish an upper limit for heat transfer from unbiased graphene to SiO₂ substrates via RIP scattering; for example, only <2% of the interfacial heat transport is facilitated by RIP scattering even at a carrier concentration of ∼4 × 10¹² cm^-2.