▎ 摘　　要

Understanding the influence of grain boundaries (GBs) on the electrical and thermal transport properties of graphene films is essentially important for electronic, optoelectronic and thermoelectric applications. Here we report a segregation-adsorption chemical vapour deposition method to grow well-stitched high-quality monolayer graphene films with a tunable uniform grain size from similar to 200 nm to similar to 1 mu m, by using a Pt substrate with medium carbon solubility, which enables the determination of the scaling laws of thermal and electrical conductivities as a function of grain size. We found that the thermal conductivity of graphene films dramatically decreases with decreasing grain size by a small thermal boundary conductance of similar to 3.8 x 10(9) Wm(-2) K-1, while the electrical conductivity slowly decreases with an extraordinarily small GB transport gap of similar to 0.01 eV and resistivity of similar to 0.3 k Omega mu m. Moreover, the changes in both the thermal and electrical conductivities with grain size change are greater than those of typical semiconducting thermoelectric materials.