CONFINED-SPACE CVD GROWTH OF THIN-LAYER WS2 AND MOS2, EFFECT OF MOISTURE (H2O) AND SYSTEMATIC RESPONSE TO PROTON IRRADIATION

Abstract

Monolayer and few layers transition-metal dichalcogenides (TMDs), such as WS2 and MoS2 are 2D materials that combine atomically thin structures with exceptional optoelectronic properties. These properties are highly suitable for a range of applications from fundamental defect engineering to robust optoelectronic devices operating in spaceborne electronics that have to withstand radiation-rich environments. This thesis work presents the synthesis of high-quality WS2 and MoS2 thin layers via a confined-space chemical vapour deposition (CVD) process that provides uniform nucleation, atomically smooth crystal edges, and centimetre-scale reproducibility. Controlled moisture (H2O) introduction during the synthesis was explored, which revealed significant improvements in flake uniformity and morphology. The results highlight moisture as an important factor in optimizing crystal quality. The synthesized samples were irradiated with 200 keV and 400 keV proton beams at six different fluences from 3 × 1012 to 1 × 1015 cm−2. Raman spectra showed a fluence-dependent increase and subsequent decrease in the 2LA/A1g (WS2) and E2g/A1g (MoS2) intensity ratios, marking the onset of mild point-defect accumulation and biaxial tensile strain to lattice disorder and strain relaxation. Complementary photoluminescence analysis of WS2 displayed an exciton conservation at lower f luences, while trion-dominated emission took place at higher fluences, validating the results acquired with Raman spectra analysis. Comparing the effects of irradiation of WS2 and MoS2 shows that WS2 has a wider defect-tolerance window, whereas MoS2 degrades rapidly beyond 1 × 1014 cm−2. These findings present the first extensive, energy-resolved f luence mapping of proton-irradiated WS2/MoS2 monolayers and few layers and establish quantitative thresholds for defects engineering and shielding 2D devices in radiation-rich environments.