TOWARD RELIABLE IDENTIFICATION OF 2D MONOLAYER VS MULTILAYER: OPTICAL AND AFM ANALYSIS OF MOS₂ OBTAINED WITH CVD AND MECHANICAL EXFOLIATION METHODS

Abstract

This thesis presents a comprehensive study on the fabrication and reliable identification of monolayer molybdenum disulfide (MoS₂) using two distinct methods: face-to-face chemical vapor deposition (CVD) and mechanical exfoliation. The CVD growth process was based on an established methodology within our research group, and efforts in this work focused on fine-tuning growth parameters and characterization. In parallel, mechanical exfoliation was introduced as a new technique, with this thesis being the first to develop and optimize it within the group for producing monolayer MoS₂. Comprehensive characterization of the resulting flakes from both methods was carried out using atomic force microscopy (AFM), Raman spectroscopy, photoluminescence (PL), and a co-localized approach. One exfoliated flake displayed excellent agreement across all techniques, confirming it as a high-quality monolayer (strong PL at ~1.85 eV, ~16 cm⁻¹ Raman mode separation, and ~0.8 nm AFM height). Another flake showed monolayer-like optical features but a significantly larger AFM thickness (~5.5–7.6 nm), highlighting the necessity of multi-modal analysis. The thesis also details the development and verification of a custom mini-probe station for upcoming low-temperature optical and electrical experiments. Although optical access constraints prevented cryogenic PL, the technology was successfully tested using TiN thin films. The findings provide a robust reference for assessing CVD-grown monolayers and contribute to improving both fabrication and verification techniques for 2D materials.