Defect‐Engineered Monolayer MoS ₂ via Chemical Etching: A Facile Route to Study SERS Sensitivity

ABSTRACT Controlled sulfur vacancies (S _v ) engineering in monolayer molybdenum disulfide (ML‐MoS ₂ ) has emerged as a powerful strategy to enhance its surface‐enhanced Raman scattering (SERS) performance. In this study, we investigate the effect of chemical (H ₂ O ₂ ) etching time on S _v formation in ML‐MoS ₂ and its subsequent impact on SERS activity. An optimal etching time (∼3 min for 20% H ₂ O ₂ ) 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 MoS ₂ (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‐MoS ₂ , 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‐MoS ₂ , offering a promising strategy for the development of chemical mechanism‐based SERS sensing platforms.