This review discusses wet processes to synthesize metallic nanoparticles with many surface projections. Such projections can be formed by the aggregation of seed nanoparticles or by anisotropic crystal growth from specific facets on a base nanoparticle. The aggregation process can be controlled by protecting agents, which also play a key role in determining the morphology of the projections and the size of the nanoparticles. The reducing agents used for this purpose are mostly moderate and therefore allow seed aggregation before crystal growth. Some reducing agents act catalytically on specific crystal facets to promote anisotropic crystal growth. Branched nanostructures with high symmetry can be prepared from monocrystalline nanoparticles by site-selective growth and etching. The optical and plasmonic properties of the nanoparticles thus obtained can be used for various applications in surface-enhanced spectroscopy and in plasmon photocatalysts.
Keywords: aggregation; crystal facet; nanoparticle; particle growth; surface plasmon.