Impact of N-Doping on MoSe₂ Monolayer for PH₃, C₂N_2, and HN₃ Gas Sensing: A DFT Study

In this research, the different characteristics of MoSe₂ and N-doped MoSe₂ monolayers were studied using density functional theory calculations. The negative cohesive energy (-5.216 eV for MoSe₂ and -5.333 eV for N-MoSe₂) verified their energetical stability. The variation of structural, electronic, and optical properties of MoSe₂ and N-MoSe₂ via adsorption of PH₃, C₂N₂, and HN₃ gases are studied. The N-doping results in a stronger adsorbent-gas interaction, resulting in maximum adsorption energy of -0.036, -0.033, and -0.198 eV for the selected gases. The MoSe₂ and N-MoSe₂ monolayers showed a direct band gap of 1.48 eV and 1.09 eV, respectively. However, upon interaction with the gases, a notable shift in the band gap of both adsorbents is observed. N-MoSe₂ showed semiconductor-to-conductor transition via C₂N₂ and HN₃ adsorption. The sensitivity of MoSe₂ for the selected gases has improved remarkably via N-doping. Also, HN₃ gas can be easily detected by the N-MoSe₂ monolayer due to the greater changes in work function (0.45 eV). The absorption coefficient of both adsorbents is over 10⁵ cm^-1 order in the UV region, which suffers a mild peak shifting due to gas adsorption. This study suggests that N-MoSe₂ can be a potential candidate for selected gas sensing.