From nanorods to nanostars: Tuning the optical properties of gold nanoparticles

Seed mediated growth assisted by surfactant is used to grow nanoparticles. The choice of seed particle, i.e. single crystal or multi-twinned, enables growth of nanorods and multi-branched nanoparticles. The latter are generally referred to as nanostars. The shape and size of the nanoparticles can be tuned by varying the solution composition and relative reactant concentrations. The optical properties of nanorods and nanostars are described and discussed in relation to their shape. For nanorods, the aspect ratio is a key parameter determining the plasmon resonance, while the absolute size has a much less pronounced effect. With the nanostars, the length of the branches turns out to be relevant. The optical properties of the multi-branched nanoparticles are discussed in terms of plasmon hybridization.