Grain Boundary Energy and Grain Size Dependences of Thermal Conductivity of Polycrystalline Graphene

We investigate with molecular dynamics simulations the dependence of thermal conductivity (k) of polycrystalline graphene on grain boundary (GB) energy and grain size. Hexagonal grains and grains with random shapes and sizes are explored, and their thermal properties and phonon densities of states are characterized. It is found that k decreases exponentially with increasing GB energy, and decreasing grain size reduces k. GB-induced phonon softening and scattering, as well as reduction in the number of heat conducting phonons, contribute to the decrease in thermal conductivity.