Formation of hollow gold-silver nanoparticles through the surface diffusion induced bulk intermixing

Hollow nanoparticles with size-controlled internal cavities can be synthesized through a novel mechanism of surface diffusion induced bulk intermixing in a thin polycrystalline film between the particles. Starting with single crystalline silver nanoparticles on sapphire substrate produced by solid state dewetting technique, we show that subsequent deposition of the thin gold layer, followed by annealing at a low homological temperature leads to the outdiffusion of silver into the film and formation of hollow nanoparticles with a single internal cavity. We built a kinetic model of hollowing which identified the surface diffusion induced bulk intermixing as a dominating atomistic mechanism, and provided an excellent fit to experimental data without any adjustable parameters. This process allows sculpturing of internal porosity of the nanoparticles and provides a general route to the synthesis of ordered arrays of hollow nanostructures attached to the substrate.