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

Area of Science:

• Materials Science
• Nanotechnology
• Surface Chemistry

Background:

• Monolayer molybdenum disulfide (ML-MoS2) is a promising material for sensing applications.
• Surface-enhanced Raman scattering (SERS) performance is highly dependent on the material's surface properties.
• Sulfur vacancies (S_v) are known to influence the electronic and chemical properties of 2D materials.

Purpose of the Study:

• To investigate the impact of chemical etching time on sulfur vacancy formation in ML-MoS2.
• To correlate S_v density with the surface-enhanced Raman scattering (SERS) activity of ML-MoS2.
• To explore the role of S_v in enhancing the sensing capabilities of ML-MoS2.

Main Methods:

• Controlled chemical etching of ML-MoS2 using hydrogen peroxide (H2O2).
• Characterization of sulfur vacancy concentration by varying etching duration.
• Evaluation of SERS performance using the modified ML-MoS2 as a substrate.
• Computational simulations to confirm the donor-like behavior of S_v sites.

Main Results:

• An optimal etching time of approximately 3 minutes with 20% H2O2 was identified for high S_v density.
• The optimized ML-MoS2 exhibited an ~80-fold increase in enhancement factor and a ~100-fold improvement in detection limit for SERS.
• Prolonged etching led to oxygen substitution, reducing SERS performance by decreasing adsorption capacity and surface activity.

Conclusions:

• Controlled sulfur vacancy engineering is a critical factor in enhancing the SERS activity of ML-MoS2.
• Etching duration precisely modulates S_v defects, tuning the opto-chemical properties for improved sensing.
• This work provides a pathway for developing advanced chemical mechanism-based SERS sensing platforms using ML-MoS2.