ESYCOM, Univ Gustave Eiffel, CNRS, CNAM, ESIEE Paris, F-77454 Marne-la-Vallée, France
Infrared metamaterials are of paramount importance for several applications such as infrared radiation sensing, thermal energy harvesting and management, and radiative cooling and have drawn an increasing scientific attention in the past two decades. They are widely used in gas sensing[1], infrared interferometry[2], optical spectroscopy using chemical analysis[3], as well as in novel thermal energy conversion and management devices such as thermo-photovoltaic converters[4], radiative thermal rectifiers[5], and smart radiative cooling coatings[6]. Some of these applications necessitate the use of wide band emitters, whereas others necessitate the use of narrow band selective spectral emission. A key requirement for obtaining specific and energy-efficient devices is the quality of wavelength-selective emission. Because the devices are expected to operate at temperatures higher than room temperature, the temperature dependence of the radiative properties is a second critical parameter. In the work to be presented, the design, optimization, fabrication and characterization of tunable MEMS-compatible silicon based metamaterials have been done to be employed for both wideband and wavelength-selective emitters for the different above-cited applications. The design optimization of the selective and wide-band emitters have been attempted through numerical electromagnetic simulations using different techniques such as the Transfer Matrix Method(TMM), the Rigorous Coupled Wave Analysis (RCWA) and the Finite Element Method (FEM). The specific materials that have been investigated are heavily doped grated silicon (Si) for selective emission and micro/nano-structured Black Silicon (BSi)[7,8] for broadband emission, thus venturing from periodic to non-periodic nano-structures, highlighting the importance of geometrical asymmetry on the IR absorptance. Particular interest have been taken to evaluate closely through FEM simulations, the dependence of doping, morphological parameters- topographical aspect ratio and the effect of the angle of incidence, on the absorption of BSi. The synergetic effects of a high level of doping on the micro-morphology of black silicon- both volume doping and surface doping(ion-implantation) have been explored in depth, for ascertaining it as one of the most significant parameters for enhancing the radiative optical properties of silicon-based metamaterials. Taking all of the conclusive results in mind; it gives us a fruitful idea about the design rules for making silicon, ultra-black and ultra-broadband. The radiative properties characterization of fabricated samples have been done through direct and indirect acquisition of emissivity and SEM characterization of surface topology have been done to elucidate specific morphological properties of BSi. Following the foundation of an indirect method of extraction of emissivity of BSi, a complete direct emissivity characterization setup designed and developed and results of temperature dependent IR emissivity derived thereof have been discussed. These results will pave way to the formation of a vital temperature dependent radiative properties database of BSi non-existent in literature and of other materials in the future, which will not only yield significant steps towards material applications in a broadband spectrum but also in elucidating physical phenomenon of metamaterials ‘beyond limits’. Reported results eventually pave way for a motley of applications including wide and narrow band emitters, gas sensing, and radiative thermal rectifiers- a case in point, which has been particularly explored.
ABOUT THE PRESENTER: Sreyash Sarkar received his Bachelor of Engineering in Electrical & Electronic Engineering from Visvesvaraya Technological University, India, earning a gold medal for his scholastic achievements. He completed his Masters (Diplome d’ingenieur) from Ecole Supérieure d’Ingénieur en Electronique et Electrotechnique (ESIEE)–Paris, Université Paris-Est with a spécialisation in Micro & Nanotechnology, with honoris: mention très bien. He is currently a PhD student at the Health, Energy & Environment Department, of ESIEE Paris affiliated to the ESYCOM, CNRS lab, where he is an MSTIC fellow. His research interests lie in the intersection of infrared radiation, plasmonics, electromagnetics, optical meta-surfaces, and their light-matter interactions.