Dispersive Properties of Mesoporous Gold: van der Waals and Near-Field Radiative Heat Interactions

We present a theoretical calculation of the dispersive interaction of mesoporous Au sponges. The ability to manipulate the dielectric function of the sponge by varying its porosity is applied to the calculation of the Hamaker constant using Lifshitz theory and the near radiative heat transfer properties. By using an effective medium approximation the dielectric function of the mesoporous sponge is calculated. As the porosity increases, our calculations show that the Hamaker constant decreases significantly. This is also used to calculate the van der Waals force between a gold nanoparticle and a gold mesoporous sponge as a function of the porosity. Also, using the fluctuating electrodynamics formalism, the change in the local electromagnetic density of states in the near field is calculated. As an application, the near field radiative heat absorbed by a SiC nanoparticle at a fixed distance from a Au sponge is calculated for different values of the porosity. The maximum heat transfer is achieved for high porosities near a metal-insulator percolation transition.