Thermal radiative properties of micro/nanostructured plasmonic metamaterials including two-dimensional materials
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Micro/nanoscale thermal radiation is of great importance in advanced energy systems, nanomanufacturing, local thermal management, and near-field imaging. It concerns both electromagnetic wave interactions with micro/nanostructured materials that could create unique far-field radiative properties as well as near-field radiative heat transfer between close objects. This dissertation explores the capability of micro/nanostructured plasmonic metamaterials and two-dimensional (2D) materials to control far- and near-field thermal radiation. The major goals are to (1) study the coherent far-field radiative properties of plasmonic metamaterials for thermal radiation control; (2) design unusual far-field thermal radiative properties by using the emerging 2D materials; (3) use 2D materials to enhance photon tunneling and near-field radiative heat transfer. A 2D grating/thin-film periodic nanostructure is studied to utilize magnetic polaritons (MPs) and surface waves, including surface plasmon polaritons and Wood’s anomaly, to create wavelength-selective thermal emission and improve the efficiency of thermophotovoltaics. Deep metallic gratings are investigated for their coherent radiative properties due to MPs in different wavelength ranges. The scalability of the MPs is scrutinized to reveal the role of kinetic inductance for resonances in nanometer and micrometer scale. The polarization dependence of the diffraction efficiency and radiative properties of anisotropic periodic surfaces is examined. A graphene-covered deep metal grating is investigated where MPs in gratings couple with graphene. The coupled resonances are studied in visible and near-infrared range with an emphasis on the enhanced absorption in graphene. The plasmonic coupling between graphene ribbon array and metal gratings is explored in mid- and far-infrared. A natural phononic hyperbolic 2D material, hexagonal boron nitride (hBN), is used with metal gratings to achieve perfect wavelength-selective absorption caused by coupling between hyperbolic phonon polaritons with MPs. Trapezoidal gratings made of hBN is also studied for its ability to support broadband perfect absorption. The directional hyperbolic phonon polaritons are inspected for its capability to create resonance absorption in resonators with different shapes. The near-field heat transfer and photon tunneling between graphene, hBN films, and van der Waals heterostructures assembled by them are studied based on fluctuational electrodynamics. A hybrid polariton in the heterostructure, surface plasmon-phonon polariton, is discussed for its contribution to the near-field heat transfer. The effects of the thickness of hBN film, the chemical potential of graphene, as well as a second layer of graphene on the backside of the heterostructure, are investigated. The results obtained from this thesis provide a better understanding of the radiative properties of various micro/nanostructured plasmonic metamaterials and 2D materials. The insights from combining metamaterials, micro/nanostructures with various 2D materials may open a new route to better control both near- and far-field thermal radiation. This dissertation can benefit a wide spectrum of applications with a desire of thermal radiation control, such as personal thermal management, radiative cooling, thermal imaging, solar energy harvesting, as well as thermophotovoltaics.