Rigorous Modeling of the Radiative Properties of Micro/Nanostructures and Comparisons with Measurements of Fabricated Gratings and Slit Arrays
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Radiative properties of a material is the core of thermal science and optics, which play critical roles in modern technologies, including microelectronics, energy conversion, and nanotechnology. The key to modify or enhance radiative properties is employing one-, two-, and three-dimensional (1, 2, and 3D) periodic micro/nanostructures. Since their applications are not fully uncovered and very few comprehensive studies are available, the objective of this dissertation is to explore applications of periodic micro/nanostructures with modified radiative properties in modern technologies through both numerically and experimentally investigations. Theses representative applications include the thermal control in rapid thermal processing, the design of a wavelength-selective radiator for thermophotovoltaic systems, and the nanothermal manufacturing. The theoretical foundation of the study is built on the rigorous coupled-wave analysis (RCWA) for numerical calculation of the far-field radiative properties and the electromagnetic field distribution in the near-field regime. Measurements of diffraction efficiencies are conducted on fabricated 1D and 2D periodic silicon microstructures with a laser scatterometer/diffractometer with high angular resolution. The diffraction efficiency can be employed for non-contact surface profile inspection tool because it strongly depends on structure patterns. For better temperature control during rapid thermal processing, the dissertation performs a parametric study on radiation absorption of a generic CMOS device together with its simplified nanoscale structures. The applicability of approximation models, which homogenize micro/nanostructures into a film, is also evaluated. Next, a new concept of complex gratings is proposed for actively tailoring the radiative properties and serving as a thermophotovoltaic (TPV) radiator. The radiator exhibits a wide-band and angle-independent high transverse magnetic wave emittance matching the bandgap of TPV cells so that the energy conversion efficiency can be improved. Furthermore, the nanoscale metallic slit arrays show polarization-dependant enhanced transmission and highly localized electromagnetic energy density, which hold promising potentials in nanothermal manufacturing. Three submicrometer metallic slit arrays are fabricated on top of a silicon substrate. Their spectral transmittance is measured with a Fourier-transform infrared spectrometer and largely agrees with RCWA modeling results. In short, the dissertation clearly demonstrates that precise control and tuning of radiative properties using micro/nanofabrication are not only feasible but also may have numerous technological impacts.