Breakthroughs in the shape engineering of metallic nanostructures have led to the elucidation of some very fundamental atomic-scale mechanisms. The study of such fundamental events is typically carried out using solution-dispersed metallic nanostructures which act as seeds for additive processes reliant on homo/heterogeneous nucleation (HN) or subtractive processes, such as galvanic replacement reactions (GRRs). While much is understood, mechanistic insights are often difficult to attain from reactions carried out on solution-dispersed templates. Here, we present an alternative platform for investigating these fundamental chemical processes whereby surfactant-free templates are immobilized on a substrate. The platform gives rise to a new set of substrate-based nanostructures while allowing for growth modes which are far less convoluted than current modalities. It combines substrate-based techniques with solution-based synthetic procedures in a manner which allows an impressive colloidal chemistry to occur directly at the substrate surface. Kinetically controlled heterogeneous nucleation of Ag onto Au is shown to modulate crystal growth modes. Synergistic protocols, involving both HN and GRRs, are shown to form periodic arrays of (i) nanoshells with tunable composition, (ii) nanoframes and (iii) structures with a particle-in-a-shell geometry exhibiting tunable gaps. The resulting photonic surfaces formed from these arrayed nanostructures have compositions and shapes engineered to realize the plasmonic resonances and near-fields as predicted by FDTD (finite difference time domain) simulations. These studies aim to establish the mechanistic framework and synthetic protocols required to place shape-engineered substrate-based plasmonic nanostructures at site-specific locations, a capability which will enable the fabrication of advanced sensing devices with plasmonic elements as the active component.

Shape engineering substrate-based plasmonic nanostructures

249th National Meeting (2015)

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