Full-dispersion Monte Carlo simulation of phonon transport in micron-sized graphene nanoribbons

• Published in: Journal of applied physics 2014-10, Vol.116 (16)
• Main Authors: Mei, S., Maurer, L. N., Aksamija, Z., Knezevic, I.
• Format: Article
• Language: English
• Subjects: Applied physics; Boltzmann transport equation; Computer simulation; Crossovers; Grain boundaries; Graphene; Heat conductivity; Heat transfer; Mathematical analysis; Monte Carlo simulation; Nanoribbons; Scattering; Thermal conductivity
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4899235

We simulate phonon transport in suspended graphene nanoribbons (GNRs) with real-space edges and experimentally relevant widths and lengths (from submicron to hundreds of microns). The full-dispersion phonon Monte Carlo simulation technique, which we describe in detail, involves a stochastic solution to the phonon Boltzmann transport equation with the relevant scattering mechanisms (edge, three-phonon, isotope, and grain boundary scattering) while accounting for the dispersion of all three acoustic phonon branches, calculated from the fourth-nearest-neighbor dynamical matrix. We accurately reproduce the results of several experimental measurements on pure and isotopically modified samples [S. Chen et al., ACS Nano 5, 321 (2011);S. Chen et al., Nature Mater. 11, 203 (2012); X. Xu et al., Nat. Commun. 5, 3689 (2014)]. We capture the ballistic-to-diffusive crossover in wide GNRs: room-temperature thermal conductivity increases with increasing length up to roughly 100 μm, where it saturates at a value of 5800 W/m K. This finding indicates that most experiments are carried out in the quasiballistic rather than the diffusive regime, and we calculate the diffusive upper-limit thermal conductivities up to 600 K. Furthermore, we demonstrate that calculations with isotropic dispersions overestimate the GNR thermal conductivity. Zigzag GNRs have higher thermal conductivity than same-size armchair GNRs, in agreement with atomistic calculations.