Effects of Different Phonon Scattering Factors on the Heat Transport Properties of Graphene Ribbons.

Understanding the effect of phonon scattering is of primary significance in the study of the thermal transport properties of graphene. While phonon scattering negatively affects the thermal conductivity, the exact effect of microscopic phonon scattering is still poorly understood when full phonon dispersions are taken into account. The heat transport properties of graphene ribbons were investigated theoretically by taking into account different polarization branches with different frequencies in order to understand the physical mechanism of the thermal transport phenomenon at the nanoscale. The effects of grain size, chiral angle, Grüneisen anharmonicity parameter, specularity parameter, and mass-fluctuation-scattering parameter were evaluated, taking into account of the restrictions imposed by boundary, Umklapp, and isotope scattering mechanisms. The contribution from each phonon branch was estimated, and the anisotropic coefficients were determined accordingly. The results indicated that the graphene ribbons are very efficient at conducting heat in all the cases studied. All the acoustical branches contribute significantly to the heat transport properties, and the temperature strongly affects the relative contribution of the phonon branches. The lattice thermal conductivity varies periodically with the chiral angle. The maximum thermal conductivity is achieved in the zigzag direction, and the minimum thermal conductivity is obtained in the armchair direction. The lattice thermal conductivity and anisotropic coefficient depend heavily upon the roughness of the edges and the width of the ribbons. The specularity parameter and mass-fluctuation-scattering parameter significantly affect the lattice thermal conductivity, and the effect arising from isotope scattering is significant in the context of natural isotopic abundance. The dependence of the Grüneisen anharmonicity parameter on phonon branches must be taken into account when making predictions. The results have significant implications for the understanding of the relations between phonon scattering and thermal properties.