Surface Lattice Resonances in Self-Assembled Arrays of Monodisperse Ag Cuboctahedra

Plasmonic metal nanoparticles arranged in periodic arrays can generate surface lattice plasmon resonances (SLRs) with high Q-factors. These collective resonances are interesting because the associated electromagnetic field is delocalized throughout the plane of the array, enabling applications such as biosensing and nanolasing. In most cases such periodic nanostructures are created via top-down nanofabrication processes. Here we describe a capillary-force-assisted particle assembly method (CAPA) to assemble monodisperse single-crystal colloidal Ag cuboctahedra into nearly defect-free >1 cm² hexagonal lattices. These arrays are large enough to be measured with conventional ultraviolet-visible spectroscopy, which revealed an extinction peak with a Q-factor of 30 at orthogonal illumination and up to 80 at oblique illumination angles. We explain how the experimental extinction changes with different light polarizations and angles of incidence, and compare the evolution of the peaks with computational models based on the coupled dipole approximation and the finite element method. These arrays can support high Q-factors even when exposed to air, because of the high aspect ratio of the single-crystal nanoparticles. The observation of SLRs in a self-assembled system demonstrates that a high level of long-range positional control can be achieved at the single-particle level.