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 A1g 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.