Selective sensing characteristics of Fe doped and (Fe, N, O) co-doped molybdenum disulfide toward CO, CO2, and NH3 gases: a first-principles investigation

Abstract

This work investigates the effect of supercell size and effective dopant concentration on Fe-doped and Fe–N/Fe–O co-doped MoS₂ systems toward CO, CO₂, NH₃ adsorption using first-principles calculations. The results show that supercell size is a key physical factor governing the predicted properties of these systems. As the supercell expands from a 2 × 2 × 1 supercell to a 4 × 4 × 1 supercell, the effective dopant concentration decreases markedly, leading to substantial changes in the electronic structure, while the magnetic character remains largely preserved. In particular, Fe–MoS₂, Fe–N–MoS₂, and Fe–O–MoS₂ systems evolve from metallic or half-metallic behavior in smaller supercells toward semiconducting states in the 4 × 4 × 1 model. Adsorption energies also vary with supercell size, although less systematically than the electronic properties. Among the studied systems, Fe–N–MoS₂ shows the most noticeable response toward NH₃ in the high-concentration 2 × 2 × 1 regime, with an adsorption energy of −0.264 eV, an adsorption distance of 1.5267 Å, evident Fe-3d/N-2p hybridization, and stronger charge transfer. In addition, the calculated sensing descriptors indicate a measurable NH₃ response, including a maximum selectivity of 2.24%, an electronic sensitivity of 98.9% at the Fermi level, and a recovery time on the order of 10⁻⁸ s at 300 K. Overall, these results demonstrate that the predicted sensing behavior of doped MoS₂ is strongly dependent on supercell size, with the effective dopant concentration governing both the electronic structure and adsorption characteristics of these two-dimensional systems.