Tailoring Thermal Radiative Propertieswith1d Micro/nanostructures And Their Applications

Nano-microscale thermal radiation has received much attention lately because of its important applications in energy harvesting, nanomanufacturing, biomedical sensing, and thermal imaging and locating heating below the diffraction limit. Radiative heat transfer can be greatly enhanced at nanometer distances. Furthermore, the performance of various devices can be greatly enhanced by the modification of the reflection, transmission, absorption and emission spectra using micro/nanostructures. In this study, we apply one-dimensional (1D) periodic multilayer micro/nanostructures in energy conversion and photonic systems to improve efficiency and enhance the output power by modified radiative properties. The aims and applications which are representative in this dissertation include:(1) Study of the influence of1D periodic multilayer micro/nanostructures on the improvement conversion efficiency and output power in modern technologies such as thermophotovoltaic (TPV) and light emitting diodes systems (LEDs) through both numerically (RCWA) method and experimentally investigations.(2) Manufacture a wavelength selective emitter and filter to be used in applications of TPV systems.(3) Design a TPV system by using a selective emitter and filter.The simulation methods have become an indispensable tool for the study of simulation of the physical phenomena of very complex and nanoscale geometry. They provide with details, in a short time, that can be very expensive in experimental cases. There are methods widely used by the researchers and industry. We found rigorous coupled-wave analysis method (RCWA) to be a suitable and fast compared with other methods. The theoretical foundation of the study is built on the RCWA method used for calculating the radiative properties of periodic micro/nanostructures in thermophotovoltaic (emitter and filter) and light emitting diode systems. Periodic micro/nanostructures are able to tailor thermal radiation based on several different physical mechanisms such as surface plasmon/phonon polaritons (SPPs/SPhPs), cavity resonance (CR), Wood’s anomaly (WA), wave interference and magnetic resonance. Light-emitting diodes (LEDs) systems convert electrical energy directly into electromagnetic radiation. The external quantum efficiency (EQE) for LEDs is very low due to total internal reflection (TIR) at the interface between the light-emitting material and the outside of the LED. The better performance of the LED which has resulted on high external quantum efficiency and light extraction efficiency has been achieved by using top or bottom micro/nanostructures gratings integrated on LED system. Thermophotovoltaic systems are capable of converting thermal infrared radiation directly into electricity by using photovoltaic effect. The most obvious drawbacks are their low throughput and poor conversion efficiency due to a large amount of unusable radiation. Near-field thermal radiation has been proposed to enhance the throughput and conversion efficiency by bringing the emitter and TPV cell in close proximity. Multilayer micro/nanostructures have been studied as a potential selective emitter and filter in TPV system. Selective emitter and filter have demonstrated the enhancement of the conversion efficiency and output power by reducing the amount of unusable radiation and the distance between the emitter and the TPV cell to sub-wavelength dimensions. Selective filter have been used for spectral control of thermal radiation from an emitter to a TPV cell. Based on the parametric study results those obtained from the simulation method, high emittance and transmittance for both of the emitter and filter have been achieved. We have fabricated optimum design for wavelength selective emitter and filter which are used in TPV system to improve the conversion efficiency and electrical output power.The radio frequency magnetron sputtering process has been used to fabricate1D multilayer microstructures design in form of alternating5-layers of (tungsten(W)/silicon dioxide(SiO2)) and1D alternating8-layer (silicon(Si)/silicon dioxide(SiO2) design. The surface topography for these designs is characterized by using a scanning electronic microscope (SEM). Measurements of the spectral radiative properties of the fabricated designs have been conducted by a spectral transmittance and reflectance system. Three-axis automated scatterometer (TAAS) instrument has been used to measure bidirectional reflectance and transmittance distribution function for both of the fabricated designs at room temperature. The emittance of the1D5-layer (W/SiO2) design is obtained indirectly from reflectance based on the Kirchhoff’s law. Both of the experimental and numerical studies reveal the performance of the design which consists of5-layers made of (W/SiO2). It has proved to have high emittance and to be suitable for use as a wavelength selective emitter in our experiment. The design which is composed of8-layers (Si/SiO2) has high transmittance and good performance as selective filter. The selective emitter and filter, with low band gap photovoltaic cell GaSb TPV cell, has shown great enhancement of TPV conversion efficiency and electrical power output compared with the macro-TPV systems.The fundamental understanding and experimental results obtained from the dissertation will facilitate the design and optimization for applications of micro/nanostructures in energy conversion and photonic systems. For future research, other grating matrix, such as conical matrix, cylindrical matrix, triangular matrix, hexagon matrix,8Quasi-periodic Photonic Crystals (QPCs), and12QPCs, should also be investigated as micro/nanostructures in energy conversion and photonic applications. We also recommend the fabrication of the proposed TPV design described in this study and compare the measured results with the predicted results.