Experimental study on the coalescence process of SiO2 supported colloidal Au nanoparticles

We report on an experimental study of the coalescence-driven grow process of colloidal Au nanoparticles on SiO₂ surface. Nanoparticles with 30, 50, 80, 100 nm nominal diameters on a SiO₂ substrate were deposited, from solutions, by the drop-casting method. Then, annealing processes, in the 573–1173 K temperature range and 900–3600 s time range, were performed. Using scanning electron microscopy analyses, the temporal evolution of the nanoparticles sizes has been studied. In particular, for all classes of nanoparticles, the experimental-obtained diameters distributions evidenced double-peak shapes (i. e. bimodal distributions): a first peak centered (and unchanged changing the annealing temperature and/or time) at the nominal diameter of the as-deposited nanoparticles, 〈D₀〉, and a second peak shifting at higher mean diameters, 〈D_C〉, increasing the annealing temperature and/or time. This observation suggested us a coalescence-driven growth process of a nanoparticles sub-population. As a consequence, the temporal evolution of 〈D_C〉 (for each class of nanoparticles and each annealing temperature), within the well-established particles coalescence theoretical framework, has been analyzed. In particular, by the analyses of the experimental data using relations as prescribed by the theoretical model, a characteristic size-dependent activation energy for the Au nanoparticles coalescence process has been evaluated.