Optical Characterization of Defects in 2D Materials

This thesis presents an optical study of defects in two-dimensional (2D) materials, also known as van der Waals materials, and larger defect based processes which allow structural engineering of metal surfaces via plasma treatment. The primary focus of this study is the optical characterization of defects as quantum emitters in hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDCs). The research encompasses a comprehensive investigation of the fundamental optical properties and fabrication strategies employed for defect engineering in these materials. The key results of this thesis are divided into four sections. The first part demonstrates enhanced Raman signal intensity in hBN through transfer matrix calculations and experimental verification. This enhancement enables improved identification and optimization of van der Waals heterostructures for spectroscopy and quantum photonic applications. The second part systematically explores the creation of optically active defect centers in hBN by remote plasma treatment with various gases, providing statistical analysis of emitter creation yields for argon, nitrogen, and oxygen plasmas. It identifies argon plasma as the most selective and efficient route for producing single emitters at room temperature with plasma treatment. The third part investigates site- and strain-controlled quantum emitters in TMDC-based heterostructures. The use of nanopillar substrates to induce localized strain, in conjunction with the introduction of defects via electron beam irradiation, demonstrates the deterministic formation of single-photon emitters in WSe2 monolayers. The optical properties of these emitters are characterized by applying photoluminescence spectroscopy, with focus on examining emission properties, gate voltage tunability, phonon coupling, and exploring potential mechanisms to understand the emitter behavior. The fourth part extends beyond quantum photonics in 2D materials and investigates scalable plasma processing of nickel surfaces for hydrogen electrolyzer applications. This study elucidates the critical role of defect-facilitated diffusion and surface structure formation during remote nitrogen plasma treatment. Collectively, this thesis aims to advance the understanding and practical engineering of optically active defects in 2D materials, while establishing routes for the deterministic fabrication of quantum emitters. Furthermore, it demonstrates the broader relevance of defect control for future quantum technologies as well as energy conversion applications.