How Nanoparticles Coalesce: An in Situ Study of Au Nanoparticle Aggregation and Grain Growth

The processes of aggregation and subsequent grain growth of highly twinned, surfactant stabilized gold nanoparticles have been followed in real time using synchrotron X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS). This gives insight into the overall coalescence mechanism of metal nanocrystals. First, the capping ligands melt or desorb, which enables the nanocrystals to aggregate and join together. At longer times, grain growth is observed, and the stacking fault densities decrease. The time scale of the grain growth process is significantly longer than that of the particle aggregation. We contrast the behavior we observe to that of other nanoparticles and discuss the implications of our results on device fabrication.