The effect of heat-treatment on morphology and mobility of Au nanoparticles

In the present paper we investigate the effect of heat-treatment on geometry and mobility of Au nanoparticles (NPs) on Si substrate. Chemically synthesized Au nanoparticles with median diameter of 14 nm were annealed at 200°C, 400°C, 600°C and 800°C for 1 hour. Geometry changes from faceted towards more rounded shapes were observed already for 200oC and increased further for higher temperatures. According to KCM simulations NPs become rounded through the minimization of the surface area and transitioning to lower energy surface types {111} and {100}. Next, NPs were manipulated with AFM and it was found that the higher is annealing temperature, the less energy was required to displace the particle. However, after treatment at 800°C particles became immovable. We attributed this surprising effect to diffusion of gold into Si and to the growth of SiO2.