Resonance Raman Spectroscopy of Plasma-Treated Monolayer MoS₂

Molybdenum disulfide (MoS₂) is a highly promising two-dimensional (2D) material, with applications in diverse fields such as optoelectronics and high-performance Li-S batteries. Defect engineering plays a pivotal role in fine-tuning the optical and electrical properties of 2D materials. This study investigates the controlled introduction of defects into MoS₂ monolayers through plasma treatments utilizing nitrogen and helium gases, enabling tailored properties for specific applications. We utilize resonance Raman spectroscopy, photoluminescence spectroscopy, and atomic force microscopy to investigate and characterize these defects. The samples are grown via Chemical Vapor Deposition (CVD).<br/><br/>Photoluminescence spectroscopy is utilized to investigate the optical properties of the MoS₂ monolayers. The main excitons change their intensity ratio for different treatment times, which is another defect-related phenomenon. Furthermore, atomic force microscopy enables detailed morphological analysis, contributing to the comprehensive characterization of the samples.<br/><br/>Resonance Raman spectroscopy reveals gradual changes in the MoS₂ monolayer's Raman spectra as the nitrogen plasma treatment time increases. We employ longitudinal acoustic LA(M) intensity, second-order 2LA(M) and 2LA(K) intensity, and full-width at half-maximum variations as quantitative figures of merit to assess defect density. This is particularly useful in heavily doped samples where photoluminescence is not present.<br/><br/>Additionally, we conducted plasma treatment with helium ions to further expand our understanding of defect engineering in MoS2. Comparing the effects of different plasma sources provides valuable insights into defect formation and properties tuning.