Breaking plasmonic symmetry through the asymmetric growth of gold nanorods

The optoelectronic properties of asymmetric metal nanostructures are of current interest for applications in photonics, sensing, and catalysis. Here, we break the symmetry of the localized surface plasmon resonance of gold nanorods by selective overgrowth of a single tip via a high-yield ( > 80 % ) wet-chemical method. While optical spectroscopy exhibits a bathochromic shift of the nanoparticle plasmon resonance, cathodoluminescence and electron energy loss spectroscopy measurements reveal a breaking of the symmetry of the associated localized surface plasmon resonance mode, which results in the subwavelength concentration of electromagnetic energy. The simple, one-step postsynthetic modification allows control of nanoparticle structural parameters, and we demonstrate how the asymmetric energy redistribution leads to increases in the surface-enhanced Raman scattering of a model analyte attached to the surface of the nanostructures. The spatial localization of energy in these nanostructures may find applications in nanofocusing, nanoimaging, and light harvesting.