Experimental study on the influences of grain boundary scattering on the charge and heat transport in gold and platinum nanofilms

The electrical and thermal conductivities of polycrystalline gold and platinum nanofilms have been measured simultaneously using a direct current heating method from 60 to 300 K. The measured electrical and thermal conductivities are greatly decreased from the corresponding bulk values. And it is found that the reduction increases as the temperature decreases. The deviation from the bulk value is due to the effect of grain boundary scattering. Furthermore, the experimental results indicate that the grain boundary scattering effect imposes greater influence to the charge transport than to the heat transport. Consequentially, the Lorentz number is several times larger than that of bulk materials, leading to the violation of the Wiedemann-Franz law. The reflection coefficient R (0.86 in platinum, 0.42 in gold) at grain boundaries is obtained based on the Mayadas-Shatzkes theory and Matthiessen's rule, which agrees well with the previous experiments.