Engineering the Optical Properties of Semiconducting Two-Dimensional Materials

Over the last two decades, two-dimensional (2D) materials have emerged as a promising platform for photonic and optoelectronic applications. Especially, transition metal dichalcogenides (TMDs) have gained huge attention due to their exceptional properties, including strong photoluminescence, strong spin–orbit coupling, high optical non-linearity and unique valley physics. Combining these properties with the atomical thickness and tuneable band gap makes TMDs an attractive platform for various applications. Furthermore, TMD-based single photon emitters (SPEs) are of special significance for quantum photonic technologies. However, addressing the coherence limitations of the SPEs in TMDs has remained elusive, necessitating a deeper understanding of them. This doctoral thesis explores methods to engineer the optical properties of 2D TMDs using optical modification and atomic layer deposition (ALD). The optical modification involves femtosecond pulsed light illumination of monolayer TMDs in an inert environment, resulting in altered physical and optical properties. ALD of TiO2 on 2D TMDs induces intensity reduction and spectral shifts in their photoluminescence (PL) and Raman responses, and increased exciton state lifetimes. The effects arise from chemical interactions, dielectric screening, and mechanical strain. Notably, the chemical effects, such as doping and oxidation, could be significantly mitigated by depositing a protective hBN layer on top of TMDs. The results presented here shed light on the physical properties of 2D TMDs and their potential for diverse applications (e.g., single photon emission). This thesis contributes essential knowledge to the rapidly developing field of 2D materials and quantum photonic research, serving as a foundation for future investigations and advancements.