UC San Diego

This dissertation presents an investigation on the topic by using surface polaritons to assist electromagnetic wave propagation and radiation, thus used for heat transfer and thermal radiation control. Surface polaritons are collective oscillations of surface charge at metal-dielectric interfaces (surface plasmon polaritons, SPP), and the surface of polar materials (surface phonon polaritons, SPhP). The excited surface polaritons can either propagate along the surface or be confined locally as resonance depending on the interface morphology. We investigated the propagation behavior of SPhP on a polar material SiO2. We designed a SiO2 nanoribbon (NR) waveguide to control the mode size of the surface phonon polaritons and its efficient coupling to thermal reservoirs through numerical simulations. An increased thermal conductivity of as much as 34% over its well-known phonon thermal conductivity limit is demonstrated theoretically and experimentally. This could be an additional channel for heat transfer, complementing the three traditional mechanisms: convection, conduction, and radiation. The localized resonance behavior of surface polaritons can be used for radiation spectrum engineering. We designed a 3D singular metasurface by using the idea of compress dimensions with singularity structures and investigated the optical spectrum numerically and experimentally. By exclusively utilizing only SiO2 in the design of singular metasurfaces, we achieved an experimental demonstration of a longwave infrared (LWIR) emittance of 96.5%. The structure only needs to be prepared with dry etching and wet etching on SiO2 wafer, no complex compounds and structures. It’s cheap, stable, and capable of handling harsh environment which makes it a perfect platform for radiative cooling. In addition to singular metasurface, we also introduce a novel approach as molten metamaterial (MMM) for thermal radiation control at high temperatures. With numerical simulations and optimized structural design, a narrowband emissivity peak at λ=1.6 um with a quality factor of ~5.6 and maximum emissivity >98% were observed, well-aligned with the center wavelength of blackbody radiation at T=1500^o C. This demonstrates the effectiveness of utilizing the MMM to tailor thermal emission spectrum solely by geometries. More experimental demonstrations need to be done, but it already has a good start with a great potential.