Fractal aggregate of hollow spherical nanoparticles: engineering the absorption spectrum by hollow size

Abstract

We study the optical properties of aggregates of hollow gold nanoparticles: monodisperse and bidisperse random gas particles and fractal cluster-cluster aggregates consisting of 1000 particles. We use the coupled-dipole equations to describe the interaction of the electromagnetic wave with particles. We find that the particle core volume fraction can be tuned to minimize the full width at half-maximum (FWHM) and to considerably shift the peak of the absorption spectrum. We find that the redshift, but not the FWHM of the peak, has a monotonic dependence on the particle core volume fraction. High pass, low pass and band rejection filters can be realized with random and fractal aggregates of hollow particles. In the case of fractal clusters, particle size dispersion has a deep influence on the overall shape of the spectrum. Thus, the aggregates of hollow nanoparticles are superior to the aggregates of solid nanoparticles: their absorption spectrum can be easily engineered by hollow size.