Fabrication of hollow gold nanoparticles by dewetting, dealloying and coarsening

A sequence of diffusion-controlled processes, namely, thin film dewetting, dealloying and thermal coarsening was employed for producing of hollow gold nanoparticles. The porous gold nanoparticles on silica substrate were obtained by solid state dewetting of Au-Ag bi-layers followed by selective dealloying of Ag. We studied in detail the last stage of the proposed method enabling the transformation of porous nanoparticles into hollow ones due to curvature-driven surface diffusion. The porous nanoparticles were annealed at 350 °C in air and in vacuum and characterized by high-resolution scanning electron microscopy. The microstructure evolution of the particles during thermal treatment was studied by in-situ X-ray diffraction. The observed decrease of compressive strain in the particles during coarsening was discussed in terms of Weissmüller-Cahn model. Annealing in ambient air resulted in faster coarsening of gold nanoparticles compared to annealing in vacuum. The isolated pores trapped in the particle bulk as well as the pores located at the particle/substrate interface were observed in the particles annealed in air. A qualitative model illustrating the observed coarsening behavior is proposed.