Anomalous thermal transport along the grain boundaries of bicrystalline graphene nanoribbons from atomistic simulations

We investigate the thermal transport properties of bicrystalline graphene nanoribbons (bi-GNRs) with different symmetric tilt grain boundaries (GBs) by using the molecular dynamics (MD) simulations. It is found that the bi-GNR with the 10.98° GB (the highest dislocation density) has an anomalously enhanced thermal conductivity for the heat flux along the GB compared to other ribbons with lower dislocation densities. This is in strong contrast to the behavior of thermal conductivity across the GB, which decreases monotonically with increasing the dislocation density. We attribute this counterintuitive phenomenon to its non-folding structure and lower edge stress, which can reduce the phonon scatterings induced by GBs and rough edges. In addition, we also examine the effects of the characteristic length and temperature on the thermal conductivity of the bi-GNRs through the phonon Boltzmann transport equation. At any given temperature and characteristic length, the low-dislocation-density bi-GNR are shown to be much more efficient in suppressing the thermal conductivity, and has a higher tailoring rate. These facts reveal the bi-GNR with a lower dislocation density is more promising to be a high figure of merit thermoelectric material.