Unveiling Defect-Related Raman Mode of Monolayer WS₂ via Tip-Enhanced Resonance Raman Scattering

Monolayer tungsten disulfide (WS₂) has emerged as an active material for optoelectronic devices due to its quantum yield of photoluminescence. Despite the enormous research about physical characteristics of monolayer WS₂, the defect-related Raman scattering has been rarely studied. Here, we report the correlation of topography and Raman scattering in monolayer WS₂ by using tip-enhanced resonance Raman spectroscopy and reveal defect-related Raman modes denoted as D and D' modes. We found that the sulfur vacancies introduce not only the red-shifted A_1g mode but also the D and D' modes by the density functional theory calculations. The observed defect-related Raman modes can be utilized to evaluate the quality of monolayer WS₂ and will be helpful to improve the performance of WS₂ optoelectronic devices.