Radiation from a thermal source, such as an incandescent light bulb, is usually incoherent. However, thermal radiation from plasmonic metamaterials and two-dimensional (2D) materials can be coherent, which has enormous applications in photonic and energy conversion systems. This proposed thesis aims to investigate the thermal radiative properties of micro/nanostructured plasmonic metamaterials and different 2D materials in both far and near field. The work is divided into three tasks.
The first task is to study the coherent far-field radiative properties of plasmonic metamaterials. A 2D grating/thin-film periodic nanostructure is proposed to utilize surface waves and magnetic polaritons (MPs) to create wavelength-selective emission and improve the efficiency of thermophotovoltaics. Deep metallic gratings are to be investigated for its coherent radiative properties due to MPs in different wavelength ranges. The scalability of the MPs will be scrutinized to reveal the role of kinetic inductance for resonances in nano and micro scale. Moreover, the polarization dependence of the radiative properties for anisotropic metamaterials will be examined.
The second task is to explore the possibilities to create unique far-field thermal radiative properties by using the emerging 2D materials as an element to construct hybrid structures with plasmonic metamaterials. A graphene-covered deep metal grating is proposed to couple the MPs with graphene in different wavelength ranges and enable enhanced coherent emission. Also, plasmonic and phononic gratings are proposed to couple with waveguide modes in hyperbolic 2D material, hexagonal boron nitride (hBN), and potentially enable coherent radiative properties.
Finally, the possibility of using 2D materials to enhance near-field radiative heat transfer will be examined. To understand the validity of Kirchhoff’s law for general anisotropic materials from a near-field perspective, it is proposed to predict the far-field emissivity directly from the fluctuation-dissipation theorem based on the Green’s function. The near-field heat transfer between graphene, hBN films, and van der Waals heterostructures assembled by them will also be studied. The results obtained from this thesis will benefit applications such as energy-harvesting, thermal imaging, and radiative cooling.