SUMMARY

The study of the radiative properties of thin films and near-field radiation transfer in layered thin film structures are very important for many applications in energy, near-field imaging, coherent emission, and aerospace thermal management. This thesis begins with a study of the optical constants of dielectric thin films of tantalum pentoxide (Ta2O5) and hafnium oxide (HfO2) across a broad spectral region from visible to the far infrared using spectroscopic methods. The changes in the film structure and optical constants due to annealing at 2000 K are studied. Both dielectric materials have broad applications in multilayer coatings, anti-reflectance films, and corrosion resistant coatings, as well as devices with potential applications in the near-field, such as metallodielectric structures. Additionally, both materials have melting points above 2000 K and are ideal for high-temperature applications.
This thesis will then progress to a theoretical study of near-field heat transfer and imaging; including a parametric study of near-field TPV performance, the near-field transfer between metallodielectric structures, and the energy streamlines in metallodielectric structures. Currently near-field TPV devices have been shown to have increase power throughput compared to their far-field counterparts, but have performance efficiencies that are lower than desired. This is due to their low quantum efficiency caused by recombination of minority carriers and the waste of sub-bandgap radiation. The currently reported efficiencies can be improved with better design, making near-field TPVs more appealing for waste heat recovery.
Future near-field devices may utilize metallodielectric structures which can exhibit unique properties such as high transmittance over a tunable range of the spectrum and negative refraction due to their hyperbolic nature. Furthermore, the energy streamlines in such structures will be studied for the first time. Energy streamlines illustrate the flow of energy through a structure and are important at a fundamental level. The energy pathways through a multilayer structure will be compared using an effective medium approach and a direct calculation from Maxwell’s equations. This study will expand the current understanding of near-field heat transfer and energy pathways in new structures.