ELECTROCHEMISTRY OF MULTILAYER COLLOIDS - PREPARATION AND ABSORPTION-SPECTRUM OF GOLD-COATED SILVER PARTICLES

Gold was deposited onto colloidal silver (mean particle size 76 angstrom) in aqueous solution, and the composite particles were studied by spectrophotometry and electron microscopy. The deposition took place via electron transfer onto the silver particles by radiolytically generated free radicals and subsequent reduction of dissolved Au(CN)2- by the stored electrons. The method allows one to control the coating thickness. The optical spectra were also calculated using Mie theory and the optical constants of the pure metals. It was found that one monolayer of gold should be sufficient to mask the silver resonance band completely and that the gold plasmon band should develop more quickly than observed. The differences between the calculated and observed spectra are explained by possible alloying of the surface layer.