Unveiling Intrinsic Edges and Local Modifications in CVD‐Grown Monolayer TMDCs via Multimodal Optical Probing

ABSTRACT

Edge terminations and localized modulations in monolayer molybdenum disulfide (1L‐MoS ₂ ) are of interest for optoelectronic applications, necessitating precise, non‐destructive characterization. This study extensively investigates intrinsic edges and local modifications in chemical vapor deposition (CVD)‐grown 1L‐MoS ₂ using multimodal optical methods. For the first time, a uniaxial compressive strain gradient perpendicular to the edges of CVD 1L‐MoS ₂ is revealed, evidenced by early hardening of the in‐plane phonon mode and the six‐petal deformation in second‐harmonic generation (SHG) polar plots. We propose that line defects parallel to the edges release CVD‐induced strain, creating anisotropic strain fields. Intriguingly, co‐polarized SHG under zigzag‐direction excitation exhibits pronounced strain contrast, facilitating delicate strain orientation analysis. On the other hand, laser modification induces simultaneous p ‐type doping and strain relief, as evidenced by exciton–trion photoluminescence (PL) behavior and phonon frequency shifts. Notably, SHG measurements operate 100 times faster than Raman spectroscopy and can directly observe laser‐induced modifications, highlighting its utility for in‐line inspection. An increase in SHG depolarization from 6.92% to 7.53% after laser irradiation indicates enhanced structural disorder. This research not only advances understanding of defect engineering in CVD 1L‐MoS ₂ but also emphasizes the viability of nonlinear optical techniques for quality evaluation in non‐centrosymmetric two‐dimensional (2D) materials.