Suppressed Thermal Conductivity in Polycrystalline Gold Nanofilm: The Effect of Grain Boundary and Substrate

We investigate the electrical conductivity and thermal conductivity of polycrystalline gold nanofilms, with thicknesses ranging from 40.5 nm to 115.8 nm, and identify a thickness-dependent electrical conductivity, which can be explained via the Mayadas and Shatzkes (MS) theory. At the same time, a suppressed thermal conductivity is observed, as compared to that found in the bulk material, together with a weak thickness effect. We compare the thermal conductivity of suspended and supported gold films, finding that the supporting substrate can effectively suppress the in-plane thermal conductivity of the polycrystalline gold nanofilms. Our results indicate that grain boundary scattering and substrate scattering can affect electron and phonon transport in polycrystalline metallic systems.