Edge effect on thermal transport in graphene nanoribbons: A phonon localization mechanism beyond edge roughness scattering

Equilibrium molecular dynamics simulations show that graphene nanoribbons (GNRs) with zigzag edges have higher thermal conductivity (κ) than armchair-edged ones, and the difference diminishes with increasing temperature or ribbon width. The dominant phonon wavelength for thermal transport can be much longer (by orders of magnitude) than the difference between the “roughness” of smooth zigzag and armchair edges. Therefore, the roughness scattering theory is not sufficient to explain the largely different κ of GNRs with different edge chiralities. Cross-sectional decomposition of the steady-state heat flux shows significant suppression of thermal transport at edges, especially in armchair ones. This behavior is explored by phonon spectra analysis. Considerable phonon localization at edges is concluded to underlie the edge-chirality dependent κ of GNRs.