Epsilon-Near-Zero Materials based Photonic Architectures for Absorption and Emission Control

Abstract

Engineering optical responses at surfaces, including reflection, absorption, transmission, and emission, is crucial for advanced photonic, energy, thermal-management, and optoelectronic applications. This thesis investigates epsilon-near-zero (ENZ) materials, particularly indium tin oxide (ITO) and titanium nitride (TiN), for controlling light-matter interactions through engineered optical coatings and nanostructures. It also explores the enhancement of optical absorption and emission in two-dimensional (2D) materials such as monolayer molybdenum disulphide (MoS2), whose atomic-scale thickness inherently limits light interaction. The research integrates theoretical analysis, finite-element simulations, nanofabrication, and experimental characterization to develop and validate ENZ-based optical platforms. An ITO-based multilayer coating is demonstrated to provide step-function-like reflectivity, with low reflectance in the visible-to-near-infrared range and high reflectance beyond a tunable cut-in wavelength, offering potential for spectrally selective energy management. Building on this, an ITO-based grating structure is developed to achieve broadband and angularly robust near-infrared absorption, demonstrating its potential for thermal-emission applications. TiN thin films are further demonstrated as an effective platform for enhancing the absorption and emission of monolayer MoS2 without complex nanostructuring. Complementary studies investigate substrate-induced strain and ion-irradiation-induced defects as approaches for tailoring the electronic and optical properties of MoS2. Overall, this work establishes ENZ materials based engineered surfaces as versatile platforms for spectral and light-matter interaction control, contributing to efficient, tunable, thermally stable, and scalable solutions for energy, thermal management, and 2D-material-based optoelectronic applications.