Designer nanoplasmonics with self-assembled metal-dielectric colloidal clusters

Subwavelength metallic nanostructures enable the broad manipulation of electromagnetic fields due to their ability to support surface plasmons, which are oscillations of free electrons in metal that couple with the electromagnetic field. The optical properties of these structures depend sensitively on their geometry, making it possible to engineer their electric and magnetic responses over a broad range. Their fabrication traditionally involves top-down processing such as lithography, which is effective but yields planar, thin-film architectures with limited spatial resolution. The self assembly of colloids is an alternative to top-down processing that offers a flexible and low cost route to nanofabrication. In this thesis, packed clusters of spherical metallic nanoparticles are studied as the basis for a new class of nanophotonic structures. Clusters are assembled using capillary forces, and interparticle separations are controlled with 2nm-thick dielectric spacers, ensuring strong plasmonic mode coupling between nanoparticles. Two types of optical resonances are studied here, magnetic dipole and Fano-like resonances. These types of chemically synthesized colloidal clusters can be generalized to a broad range of other two- and three-dimensional structures, and their assembly from solution supports their integration into various material platforms.