Dependence of the In-Plane Thermal Conductivity of Graphene on Grain Misorientation

The thermal transport across the grain boundary (GB) is inevitably encountered for large-area polycrystalline graphene. However, the influence of GB configuration on thermal transport is not well understood. Here we investigated the effect of grain misorientation angle on the in-plane thermal conductivity (κ) of suspended graphene by using the optothermal Raman technique. Graphene with well-defined grain orientation was synthesized on an electropolished, annealed, and oxygen plasma-treated single-crystalline Cu(111) substrate by low-pressure chemical vapor deposition. The κ was primarily dependent on the grain size of single-, bi-, and polycrystalline graphene, consistent with the Boltzmann transport model. Surprisingly, κ of bicrystalline graphene dramatically decreased with a slight misorientation (<4°) between two neighboring grains. This phonon-boundary scattering was successfully simulated by the GB misorientation model. The GB length or shape also affected κ as a tertiary parameter. The GB misorientation angle and length, in addition to the grain size, were determining factors of κ, which may be applicable for other two-dimensional materials.