Optical properties of nanoporous gold foams

Abstract

We fabricated and experimentally studied Au nano-foams and Al2O3 scaffolds filled with Au nanoparticles (NPs). We found that while the reflectance spectra of Au nano-foams depended very little on the 8-10 nm Al2O3 ALD coating, the spectra were highly sensitive to annealing, which increased the sizes of voids and ligaments from 50-100 nm to ∼300 nm. The effective dielectric permittivities of the Au nano-foams and Al2O3 scaffolds with Au NPs were extremely high, ∼50. At the same time, Au nano-foams covered with a dielectric (MgF2) featured bright structural colors, calling for the model, which extends beyond the effective medium approximation.