Defect-Engineering in MoS2 Layers for Surface Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) offers exceptional molecular sensitivity, but the instability and poor reproducibility of noble metal substrates limit its practical use. Here, we investigate low-cost, non-plasmonic alternatives based on two-dimensional molybdenum disulfide (MoS2). We introduce a reagent-free, pulsed-laser irradiation in liquid protocol to controllably engineer defects and induce the metallic 1T phase within MoS2, thereby tailoring its electronic structure through sulfur vacancies. Laser-modified MoS2 displays markedly enhanced SERS activity relative to unmodified 2H-MoS2; the enhancement correlates with increased density of defect sites and the presence of the conducting 1T phase, which together promote more efficient substrate-adsorbate charge transfer. By using 4-mercaptobenzoic acid (4-MBA) as a probe molecule, laser-modified MoS2 shows a SERS enhancement factor of ≈105 compared with pristine 2H-MoS2 under 532 nm excitation. The experimental results were further validated by density functional theory calculations, which show a better match of the energy level of MoS2 1T with our probe molecule, supporting the ongoing research aimed at designing novel SERS substrates. Our results demonstrate that phase and defect engineering in 2D materials provide a robust route to reproducible, non-plasmonic SERS substrates, offering a scalable alternative to noble metals for sensitive chemical and biosensing applications.