Interface-Protected Subsurface Vacancies for Room-Temperature Sub-ppm SO2 and NO2 Detection in MoS2, MoSe2, and MoTe2 via 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.