Superior selectivity for NH3 (NO2) gas molecules in In2SSe (Ga2SSe) Janus materials: a first-principles study

Anthropogenic gasses are very detrimental, requiring superior sensitive and selective materials to sense and segregate them. Using first-principles density functional theory (DFT) tools we have explored the sensitivity and selectivity of CO2, CO, NH3, NO2, H2S, and SO2 gases in the promising group-III Janus Ga2SSe and In2SSe nanostructured materials. We have explored all the possible adsorption sites in the Ga2SSe and In2SSe monolayer for sensing the gases and found that all the gasses are physisorbed in the sites with the lowest adsorption energy of −0.392 eV (−0.167 eV) for NH3 (NO2) on top of Indium (on the bridge-3 site) site of In2SSe (Ga2SSe). All adsorbed gasses significantly alter the bandgap of Ga2SSe and In2SSe from their pristine value and NO2-adsorbed M2SSe (M = Ga, In) structure exhibits significant bandgap changes: ∼0.16 eV reduction in Ga2SSe and ∼0.3 eV reduction in In2SSe from the pristine value, signifying substantial increase in conductivity. Additionally, analyzing the total density of states (TDOS), it can be concluded that NH3 at the Indium site of In2SSe and NO2 at the Bridge-3 site of Ga2SSe exhibit the most significant conductivity changes. Considering charge transfer, it is determined that 0.727 e/Å−3 of charge is transferred from In2SSe to NH3, while 1.05 e/Å−3 of charge is transferred from Ga2SSe to NO2 gas molecules, inferring that both NH3 and NO2 act as electron acceptors. Through this analysis, we found that NH3 is very selective on In2SSe while NO2 is selective on Ga2SSe Janus materials among the control gasses. This selectivity toward NH3 (NO2) gas on In2SSe (Ga2SSe) Janus material can open the new possibility of these materials for noxious gas sensing as well as NO2 utilization applications.