Thermal conductivity and scattering models for graphene: From intrinsic scattering of pristine graphene to strong extrinsic scattering of functionalized graphene

The present study used various scattering models in a Callaway framework to elucidate the relationship between the scattering mechanisms and thermal conductivity of graphene. As well as intrinsic scattering, the scattering caused by external conditions was constructed using a combination of boundary, imperfection, and interface scattering. The effect of each type of scattering on the length-dependent thermal conductivity of graphene, which is a subject of fundamental importance, was evaluated. The change in specularity shifted the logarithmic length-dependent regime from the micrometer scale for a diffuse boundary to the submicrometer scale for high specularity. Imperfection scattering had little effect on the intrinsically determined length dependence of thermal conductivity. Substrate scattering, that is, interface scattering by van der Waals interaction, caused large decreases of both the thermal conductivity and length scale. A rough model for functionalized graphene was constructed by considering both impurity and interface scattering. The spring constant in interface scattering with functionalizing bond was nearly 40 times larger than that for substrate scattering, in combination with an imperfection source, explained the length-independent low thermal conductivity of functionalized graphene. This model was extended to nonsubstitutionally functionalized graphene, for which imperfection scattering strength was proportional to the mass of the adatom.