Tuning Near Field Radiation by Nanophotonic Materials

Although blackbody radiation described by Planck's law is commonly regarded as the maximum of thermal radiation, thermal energy transfer in the near-field can exceed the blackbody limit due to the contribution from evanescent waves. This novel thermal transport mechanism has important practical implications in a variety of technologies, e.g., thermophotovoltaic energy conversion, radiative cooling, thermal infrared imaging, and heat assisted magnetic recording. In recent years, the underlying physics of this phenomenon has been actively investigated, however, on the experiment side, there is limited progress except several initial demonstrations. During my time as a graduate student, I’ve been focusing on realizing the tuning of the near field radiation experimentally by adjusting the optical properties of materials. For the first project, I investigated theoretically and experimentally the near field radiation properties of doped silicon at different doping concentrations, which provides a scheme for tuning near field radiation. In the second project, the near field radiation properties of hyperbolic metamaterials are investigated. Hyperbolic metamaterials is demonstrated to work as a broad band thermal extractor. At the same gap between an emitter and an absorber, the near field radiation can be enhanced by around one order of magnitude with the thermal extractor added in between. For the third project, the near field radiation properties of ultrathin metallic films are investigated. It is demonstrated both theoretically and experimentally that the near field radiation from metallic films on top of silicon substrate can be tuned to different intensities by changing the thickness of the metallic films. This phenomenon can be explained by the special surface plasmon mode along the thin metallic film and the screening effect of metals.