Effects of grain dimensions and edge states on the thermal conductivity of graphene ribbons

Abstract

Phonons are of paramount importance to the thermal conductivity of a graphene-based material. To analyze the nanoscale thermal transport phenomena occurring within the material efficiently and accurately, the most important factors affecting the physical process of phonon transport need to be identified. Computational simulations were carried out using non-equilibrium molecular dynamics to investigate the effects of grain dimensions and edge states on the thermal properties of graphene ribbons so as to understand the heat transport phenomena occurring within the two-dimensional carbon-based material. Particular focus was placed on the physical factors limiting heat conduction in graphene ribbons. The dimensional phenomena of heat conduction in finite-size graphene ribbons were studied to better understand the applied physics of thermal transport at the nanoscale. The intrinsic thermal conductivity of graphene ribbons was determined, and the mechanism of phonon transport in the carbon-based material was discussed. The results indicated that grain dimensions and edge states are the primary factors influencing the thermal conductivity of graphene ribbons. The intrinsic thermal conductivity of graphene ribbons is about 2020–2200 W/m·K at room temperature. Quantitative predictions of the thermal conductivity are in good agreement with experiments. The thermal transport within a graphene ribbon with 5.4 nm in width and 40 nm in length is dominated by the mechanism of diffusive-ballistic heat conduction. Graphene ribbons must be of sufficient size to enhance their phonon transport properties and reduce the probability of phonon-boundary scattering. Rough edges can lead to thermal performance degradation due to the increased probability of phonon scattering from grain boundaries. Hydrogen termination or passivation will lead to a significant decrease in the thermal conductivity of graphene ribbons. The difference in thermal conductivity is insignificant between zigzag-edged and armchair-edged graphene ribbons.