Optical properties of metal nanoparticle coated silica spheres: A simple effective medium approach

Abstract

The preparation of gold particle coated silica microspheres is described and the optical absorption spectra for various surface coverages of gold particles are presented. Onion-shell particles with the structure silica-gold-silica are also described. An effective medium model is used to quantify the surface plasmon shifts observed in such particles, which predicts the shifts in surface plasmon band for both solvent refractive index and surface coverage. The resultant microspheres exhibit absorption spectra resembling those of the isolated nanocrystals. However they possess extinction cross-sections orders of magnitude higher than the nanocrystals and can be centrifuged and redispersed more e..