From fundamental to CO 2 and COCl 2 gas sensing properties of pristine and defective Si 2 BN monolayers.

In this work, the capability of Si 2 BN monolayers (Si 2 BN-MLs) to sense CO 2 and COCl 2 molecules was investigated by analyzing the structural, electronic, mechanical and gas sensing properties of defect-free and defective Si 2 BN-ML structures. Electronic property analysis revealed that the Si 2 BN-ML retains its metallicity in the presence of vacancy defects. The computed vacancy formation energies of Si, B and N monovacancies are 3.25 eV, 2.27 eV and 2.55 eV, respectively, which indicate that the B monovacancy is thermodynamically more feasible. Besides, both pristine and defective Si 2 BN-ML structures show good mechanical stability. To validate the gas sensing properties, the adsorption energy and charge transfer were analysed, showing that both pristine and defective Si 2 BN-ML structures receive considerable charges from the CO 2 and COCl 2 molecules via a stable physisorption process. The work function analysis revealed that a minute increase <0.10 eV is responsible for the enhanced selectivity and sensitivity of Si 2 BN-ML structures in detecting CO 2 and COCl 2 molecules. The low adsorption energies of both CO 2 and COCl 2 gas molecules during the interaction with Si 2 BN-ML structures signify the possibility of a large number of adsorption-desorption cycles with an ultra-low recovery time, 0.174 ns for CO 2 and 0.016 ns for COCl 2 , suitable for efficient gas sensing applications.