Metal Nanoparticle Ensembles: Collective Optical Properties
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Ensembles of gold and silver nanoparticles in the 10- to 100-nm size range exhibit collective electromagnetic properties, which can be tuned according to particle size and interparticle spacing. Self-assembly is a critical enabling mechanism for organizing nanoparticles into ensembles with well-defined lattice structures or geometries, if particle dispersion forces can be adequately controlled. Presented here are several recent theoretical and experimental studies on metal nanoparticle assemblies with novel and technologically appealing optical properties. For example, gold nanoparticles with intense plasmon resonances can be organized into planar arrays or spherical ensembles around dielectric cores, and serve as substrates for surface-enhanced Raman scattering (SERS). Recent theoretical developments indicate that the electromagnetic field factors responsible for such enhancements can be further tuned by adjusting the diameter–spacing ratio, enabling the optimization of metal nanoparticle ensembles for various applications in sensing and nanophotonics.