Interface-protected subsurface vacancies for room-temperature sub-ppm SO ₂ and NO ₂ detection in MoS ₂ , MoSe ₂ , and MoTe ₂ <i>via</i> electron irradiation

Transition metal dichalcogenides (TMDs) are promising candidates for room-temperature gas sensing, but limited intrinsic adsorption hampers trace-level detection. Here, we introduce a scalable defect-engineering route that creates subsurface chalcogen vacancies-selectively generated in the bottom chalcogen layer by tunable electron irradiation-yielding chemically clean, stable, and interface-protected active sites. Density functional theory (DFT) and statistical thermodynamics calculations reveal adsorption, charge transfer, and carrier modulation in MoS₂, MoSe₂, and MoTe₂ for key air pollutants over 0.01-1000 ppm at 300 K. The impact of these buried vacancies is found to be highly material- and analyte-dependent: for N₂, O₂, CH₄, NH₃, H₂S, and CO₂, vacancy effects are negligible across all substrates, whereas for SO₂ and NO₂ the enhancements are substantial and strongly TMD-specific. At only 2% vacancy density, MoS₂ and MoSe₂ exhibit modest (<15%) carrier modulation gains, while MoTe₂ shows exceptional improvements-exceeding 50% for SO₂ and reaching up to 350% for NO₂ in the sub-ppm regime-driven by markedly increased adsorption coverage at defect sites. These results position subsurface vacancy engineering as a targeted and scalable route to selective, high-sensitivity TMD gas sensors, identifying MoTe₂ as a particularly compelling platform for ultra-trace detection.