Defect-Engineered Monolayer MoS₂ via Chemical Etching: A Facile Route to Study SERS Sensitivity

Controlled sulfur vacancies (S_v) engineering in monolayer molybdenum disulfide (ML-MoS₂) has emerged as a powerful strategy to enhance its surface-enhanced Raman scattering (SERS) performance. In this study, we investigate the effect of chemical (H₂O₂) etching time on S_v formation in ML-MoS₂ and its subsequent impact on SERS activity. An optimal etching time (∼3 min for 20% H₂O₂) yields a high density of S_v sites that act as active adsorption centers and localized donor states, resulting in an ∼80-fold increase in enhancement factor (EF) and a ∼100-fold improvement in the detection limit (2.35 × 10⁻¹⁰ m) compared to pristine MoS₂ (1 × 10⁻⁸ m), while performing SERS measurements. In addition, donor-like behavior of the S_v sites is confirmed by computational simulations. However, prolonged etching beyond the optimal S_v concentration results in oxygen substitution at S_v sites, significantly reducing the adsorption capacity and surface chemical activity of ML-MoS₂, ultimately impairing its SERS performance. This study highlights the critical role of the etching duration in modulating S_v-defects to tune the opto-chemical properties of ML-MoS₂, offering a promising strategy for the development of chemical mechanism-based SERS sensing platforms.