Island Growth in the Seed-Mediated Overgrowth of Monometallic Colloidal Nanostructures

Manipulating the growth mode of colloidal nanocrystals is of both fundamental interest and technological importance because it is often connected to the control of their shape, morphology, and physicochemical properties. In conventional wisdom, island growth during thin-film deposition is restricted to lattice-mismatched materials. Here, we show that deposition of Au on Au nanostructures (e.g., nanoplates, nanorods, and nanospheres) can produce separate Au islands on the seed surface with tunable size and density while preserving the original crystal structure. The island growth in the system is ascribed to the synergistic effect of fast redox kinetics and surface capping of large polymeric ligands. Decreasing the reaction rate or changing the capping ligands could readily transform the deposition of Au on Au nanostructures from island growth to layer-by-layer mode. We further take advantage of the dense hotspots of the islands-on-plate nanostructures and demonstrate their excellence in surface-enhanced Raman scattering detection. Noble-metal nanocrystals find broad application in sensing, imaging, and catalysis, and their performance is heavily dependent on the nanostructures. Until now, general rules of crystal growth have been established and constitute the current wisdom in the structural design of noble-metal nanocrystals. For example, island growth of a metal on nanocrystals of another metal is usually induced by lattice mismatch between the two metals. However, in many cases, great possibilities lie beyond these rules for discovering new nanostructures with intriguing properties and applications. Here, we demonstrate this possibility by establishing a mechanism that allows an unusual island-growth mode of monometallic Au without involving any lattice mismatch. It enables production of a family of Au island structures, which showed superior performance in surface-enhanced Raman scattering. Our findings could inspire further efforts in building sophisticated metal nanostructures. Gold islands, gold colonies: by controlling reaction kinetics and surface chemistry, Yin and colleagues have discovered an unconventional growth mode of Au nanocrystals whereby Au islands are formed. The resulting Au islands showed excellent properties in surface-enhanced Raman scattering. This finding opens great opportunities for building sophisticated structural features of noble metals with intriguing properties and applications.