Surface morphology changes on silica-coated gold colloids

Coating gold colloids with a well controllable silica shell is finding many applications in the fields of bioconjugation and photonic crystals. In this work, we report on ravine-structured surface morphology changes on silica-coated gold (Au@SiO2) colloids as observed using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) characterizations. These Au@SiO2 colloids were prepared in the direct Stöber synthetic route and the silica-shell thickness was varied between 20 to 100 nm. An aggregation mechanism is proposed to successfully model the silica-shell growth on the gold nanoparticles (NPs) and explain the formation of the ravine-structured surface of the Au@SiO2 colloids. Furthermore, it is found that the ravine-structured surface strongly influences the formation of the Au@SiO2 colloidal crystal films. The improved understanding of the surface morphology changes provides a suitable methodology for tailoring the growth of the core–shell structured colloids and assembling them into highly ordered colloidal crystal films.