Homogeneous films of Au@SiO 2 particles have been deposited on glass as a prototype 3D "artificial solid" using the LBL method. The film thickness is controlled by the number of dipping cycles and is measured by AFM. Each cycle results in approximately one monolayer of particles being deposited. The particle films are dense, but disordered. The optical properties of the resulting thin films have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness. We find that the surface plasmon peak position in films with volume fractions up to φ > 0.5 is accurately predicted by the MaxwellGarnett model. The films exhibit remarkably uniform, transmitted colors and display metallic reflection at low angles of incidence, even at low volume fractions. The films can be annealed at T > 500 K to provide extremely stable, optical films.

The preparation and chemical reactivity of Ag@SiO2 particles have been investigated using UV−vis spectroscopy, laser Doppler electrophoresis, and electron microscopy. The factors governing the deposition of silica onto silane-primed silver particles have been investigated and the deposition conditions (pH and reagent concentrations) optimized. It is demonstrated that the thin silica shells deposited from aqueous/ethanolic sodium silicate solutions are porous. Silver cores dissolve in alkaline cyanide solutions, with the rate depending on the shell thickness. Ag2S@SiO2 can be prepared following exposure to sulfide ion, while silica-coated alloys of silver and gold can be prepared by reaction of Ag@SiO2 with AuCl4 -. The kinetics of these core reactions with solution reagents is governed by their rate of diffusion through the shell. A diffusion coefficient of 10-12 cm2 s-1 is estimated for cyanide ion diffusing through non-heat-treated silica shells.

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