Shape evolution of gold nanoparticles

The tetraoctylammonium bromide-stabilized gold nanoparticles have been successfully fabricated. The shape evolution of these nanoparticles under different annealing temperatures has been investigated using high-resolution transmission electron microscopy. After an annealing at 100 °C for 30 min, the average diameters of the gold nanoparticles change a little. However, the shapes of gold nanoparticles change drastically, and facets appear in most nanoparticles. After an annealing at 200 °C for 30 min, not only the size but also the shape changes a lot. After an annealing at 300 °C for 30 min, two or more gold nanoparticles coalesce into bigger ones. In addition, because of the presence of Cu grid during the annealing, some gold particles become the nucleation sites of Cu₂O nanocubes, which possess a microstructure of gold-particle core/Cu₂O shell. These Au/Cu₂O heterostructure nanocubes can only be formed at a relatively high temperature (≥300 °C). The results can provide some insights on controlling the shapes of gold nanoparticles.