Date of Award
Level of Access Assigned by Author
Doctor of Philosophy (PhD)
Second Committee Member
Carl P. Tripp
Third Committee Member
Additional Committee Members
Thermal emission observed at sub-wavelength distances from the thermal source is referred to as near-field thermal radiation. Thermal radiation in the near-field regime can exceed Planck’s blackbody limit by orders of magnitude and be quasi-monochromatic. Due to these unique properties, near-field thermal radiation is very promising for several thermal management and energy harvesting applications. Many of these applications, such as nanogap thermophotovoltaics and thermal rectification, require near-field spectra that are not found among natural materials. Artificial metamaterials, which are engineered at the sub-wavelength scale, have been theoretically proposed for tuning the spectrum of near-field thermal radiation. However, engineering the near-field spectra using metamaterials has not been experimentally demonstrated mostly due to the complexities associated with guiding the near-field evanescent waves to an FTIR spectrometer located in the far zone. Additionally, the possibility of tuning the near-field spectra by engineering materials at length scales much smaller than the thermal wavelength, i.e., atomic length scales, has not been explored theoretically or experimentally.
In this dissertation, a new technique is proposed and implemented for measuring the near-field thermal spectra. The proposed technique is verified against the theoretical predictions of near-field thermal radiation from natural materials. This technique is then utilized for measuring the near-field spectra thermally emitted by metamaterials made of silicon carbide nanopillars, and the tunability of the near-field thermal spectra by changing the dimensions of the nanopillars at the sub-wavelength scale is demonstrated. Using numerically-exact simulations, it is shown that the effective medium theory, commonly used for theoretical study of the near-field thermal spectra of nanopillar metamaterials, is not valid in the near-field regime. Additionally, the tunability of near-field spectra by using spherically-shaped sub-wavelength particles is theoretically investigated by developing analytical expressions for predicting the energy density emitted by spherical particles. Lastly, near-field thermal radiation from quantum dots, which have a length scale comparable to the atomic scales, is theoretically studied for the first time. It is shown that the near-field thermal radiation is highly impacted by the size-dependent quantum confinement effect that arises at the atomic length scales, thus providing a new mechanism for tuning the near-field thermal emission spectra.
Zare, Saman, "Engineering the Spectrum of Near-Field Thermal Radiation" (2022). Electronic Theses and Dissertations. 3716.