First-Principles Design Rules for Selective Room-Temperature Gas Sensing in Transition-Metal-Doped MoS₂

Substitutional doping provides a practical and scalable strategy to tune the surface reactivity of transition-metal dichalcogenides (TMDs) for chemical sensing, yet the underlying relationships between dopant identity and adsorption behavior remain poorly understood. Here, first-principles calculations are employed to examine the effects of substituting molybdenum in monolayer MoS₂ with transition metals from groups 4 (Zr, Hf), 5 (Nb, Ta), 7 (Tc, Re), and 10 (Pd, Pt). These dopants, which themselves form stable TMD monolayers, incorporate effectively into the MoS₂ lattice─consistent with their demonstrated feasibility via chemical vapor deposition (CVD). While the adsorption of NH₃, CO₂, SO₂, and NO₂ remains governed by physisorption, distinct dopant-dependent selectivity emerges. Group 4, 5, and 10 dopants induce negligible modulation of adsorption and charge transfer, whereas group 7 dopants markedly enhance the NO₂ binding and electron exchange. The resulting carrier concentration changes reach up to 4 orders of magnitude higher than in pristine MoS₂ at sub-ppm analyte levels and room temperature, enabling potential ppb-level NO₂ detection with minimal cross-sensitivity to SO₂. These results establish transition-metal substitution as a chemically coherent and experimentally viable route for selectively boosting the sensitivity of MoS₂-based gas sensors toward oxidizing, polar analytes such as NO₂.