CO, H₂S, and NH₃ gas sensing on Mn-doped WSe₂ monolayers: a DFT and machine learning study

The structural, electronic, magnetic, optical, and thermo-mechanical properties of Mn-doped WSe₂ (WSe₂Mn) monolayers and their CO-, H₂S-, and NH₃-adsorbed counterparts were systematically investigated using density functional theory and machine learning techniques. All systems exhibited spin-resolved semimetallic behavior, characterized by metallic spin-up and semiconducting spin-down channels. Magnetic ordering was maintained upon gas adsorption, with a slight enhancement in magnetic moment observed for the H₂S-adsorbed configuration. Thermo-mechanical analysis revealed that gas adsorption increases the bulk modulus and heat capacities while preserving the shear modulus, suggesting enhanced compressive stiffness without compromising shear resistance. The thermal expansion coefficient and Debye temperature showed gas-dependent variations, particularly under NH₃ exposure, indicating strong vibrational coupling. Optical calculations demonstrated strong absorption in the ultraviolet and partial visible range. These findings underscore the potential of WSe₂Mn monolayers for multifunctional applications in nanoelectronics, gas sensing, and thermally responsive devices.