Thermal properties of nanoporous gold

We measured the thermal expansion coefficient and Debye temperature of nanoporous gold (NPG) using the extended x-ray absorption fine structure technique. Reduction of the nearest-neighbor distances in NPG by ca. 0.01 Å compared to the bulk gold was attributed to the surface tension caused, in turn, by the finite-size effect of the NPG ligaments. We also demonstrated that the Debye temperature in NPG is 5% lower than in bulk gold. We interpreted these observations in the framework of a bimodal distribution of surface and bulk bonds with different values of Debye temperature. The surface bonds with low Debye temperature extend within ca. four layers of Au atoms located on the pore surface, in a good agreement with prior resistivity measurements and theoretical predictions.