One-dimensional coupling of gold nanoparticle plasmons in self-assembled ring superstructures.

Plasmon coupling in ordered metal nanoparticle assemblies leads to tunable collective surface plasmon resonances that strongly depend on the interparticle distance. Here we report on the surface plasmon scattering of polystyrene-functionalized 40 nm gold nanoparticles self-assembled into close-packed rings. Using single particle dark-field scattering spectroscopy, we observed strong near-field coupling between neighboring nanoparticles, which results in red-shifted multipolar plasmon modes highly polarized along the ring circumference. Correlated optical spectroscopy and scanning electron microscopy of individual rings with different diameters revealed that the plasmon coupling is independent of ring curvature and mostly insensitive to the local nanoparticle arrangement. Our results further suggest that a one-dimensional gold nanoparticle assembly yields long-range collective plasmonic properties similar to those of metallic nanowires.