WFU Physics Colloquium

Metamaterials have become an important area of research due to the freedom they can potentially provide in designing the optical response of materials. Engineering of the electromagnetic subunits means that the optical constants of a fabricated medium are not restricted to the limits encountered in nature. Metamaterials operational at visible frequencies require nanofabrication techniques so that the constituent subunits are smaller than the operational wavelength. Silver nanowires are useful as optical electromagnetic subunits because they behave similarly to natural electromagnetic subunits (i.e. atoms and molecules). Small nanowires exhibit particle plasmon resonances, and long nanowires follow the Drude model with a reduced plasma frequency. In each case the behavior can be "tuned" by altering the dimensions of the nanowires.

This dissertation explores the use of plasmonic silver nanowires imbedded in dielectric hosts as metamaterials operational at visible frequencies. Two design strategies are implemented. The first involves dispersion of silver nanowires in a non-ordered way to fabricate a three-dimensional isotropic metamaterial. The second uses electrodeposition of silver into porous anodized aluminum oxide to fabricate a uniaxial medium of aligned nanowires. Uniaxial metamaterials can exhibit a hyperbolic dispersion relation that results in negative refraction of the group velocity.

The fabrication processes are detailed and electron microscopy is used to analyze the morphology. The reflection and refraction behavior is theoretically explored for both isotropic and anisotropic metamaterials. Optical characterization is done by transmission spectroscopy, angle dependent reflectometry, and field mapping of Fresnel diffraction fringes from light passing through the sample.