| Description |
Surface polariton mediated near-field radiative transfer exceeds the blackbody limit by orders of magnitude and is quasimonochromatic. Thermophotovoltaic (TPV) power generation consists of converting thermal radiation into useful electrical energy and exhibits a peak performance near the TPV cell bandgap, which is typically located within the near infrared bandwidth. Therefore, an ideal emission source for a nanoscale gap TPV device, in which the emitter and cell are separated by no more than one peak emitted wavelength, will sustain surface polariton resonance at or near the TPV cell bandgap in the near infrared. To date, few materials have been identified that satisfy this requirement. The first objective of this dissertation is to theoretically explore dielectric Mie resonance-based (DMRB) electromagnetic metamaterials for the potential to sustain near infrared surface polariton resonance. Electromagnetic metamaterials are composite media, consisting of subwavelength, repeating unit structures called “meta-atoms.†The microscopic configuration of the meta-atom can be engineered, dictating the effective macroscale electromagnetic properties of the bulk metamaterial, including the surface polariton resonance wavelength. DMRB metamaterials consist of dielectric nanoparticles within a host medium and are analyzed using an effective medium theory. The local density of electromagnetic states, an indicator of possibly harvestable energy near an emitting surface, is calculated for two DMRB metamaterials: spherical nanoparticles of 1) silicon carbide, and 2) silicon embedded in a host medium. Results show that the surface polariton resonance of these metamaterials is tunable and, for the silicon metamaterial only, is found in the near infrared bandwidth, making it a viable candidate for use in a nano-TPV device. In order to demonstrate the practicality thereof, the second objective is to fabricate and characterize DMRB metamaterials. Specimens are fabricated by hand mixing and sonicating nanoparticles with two part epoxy resins. Transmission measurements of the specimens reveal divergence from the theoretical predictions. Microscopic inspection suggests insufficient nanoparticle dispersion within the host resin medium. All results indicate that enhanced fabrication techniques must be developed to improve nanoparticle dispersion in DMRB metamaterials prior to further electromagnetic characterization. The lack of success with the second objective drives a third: theoretically explore various forms of indium tin oxide (ITO) for the potential to sustain near infrared surface polariton resonance. ITO is an electron doped metallic oxide, the electromagnetic properties of which depend highly on the fabrication process, that has been shown to exhibit surface polariton resonance in the near infrared. Analyses similar to those performed under the first objective are performed on ITO. Results indicate that ITO indeed exhibits near infrared surface polariton resonance, making it a viable candidate for use in a nano-TPV device. |
