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Using density functional theory calculations, the adsorption of gaseous molecules (NO, NO 2 , NH 3 , SO 2 , CO, HCN, O 2 , H 2 , N 2 , CO 2 , and H 2 O) on the graphitic SiC monolayer and bilayer has been investigated to explore the possibilities in gas sensors for NO, NO 2 , and NH 3 detection. The strong adsorption of NO 2 and SO 2 on the SiC monolayer precludes its applications in nitride gas sensors. The nitride gases (NO, NO 2 , and NH 3 ) are chemisorbed on the SiC bilayer with moderate adsorption energies and apparent charge transfer, while the other molecules are all physisorbed. Further, the bilayer can effectively weaken the adsorption strength of NO 2 and SO 2 molecules, that is, NO 2 molecules are only weakly chemisorbed on the SiC bilayer with an E ads of −0.62 eV, while SO 2 are physisorbed on the bilayer. These results indicate that the SiC bilayer can serve as a gas sensor to detect NO, NO 2 , and NH 3 gases with excellent performance (high sensitivity, high selectivity, and rapid recovery time). Moreover, compared with other molecular adsorptions, the adsorption of NH 3 molecules significantly changes the work function of the SiC monolayer and bilayer, indicating that they can be used as optical gas sensors for NH 3 detection.

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Recent reports have raised exciting prospects for the use of C3N monolayers exhibiting excellent adsorptive properties in nanodevice applications. In this study, we carried out first-principle calculations to investigate the adsorption of NO2, NO, CO, HCN, NH3, CO2, H2, N2, CH4, H2O, O2, and N2O gas molecules on a C3N monolayer as well as its potential applications in gas sensor devices. Our results reveal that the chemisorption of NO2 can significantly influence the electronic properties of the C3N monolayer (e.g., changing semiconducting behavior to conducting behavior). In contrast, physisorption of the other gas molecules had little effect on the electronic properties of the C3N monolayer. These results suggest that the C3N monolayer is much more sensitive and selective to NO2 than to the other gases. The recovery time of NO2 at T = 300 K is only 0.62 s. Moreover, the optical properties of the C3N monolayer can be modified as a result of the adsorption of different molecules, especially the NO2 molecule. Thus, the C3N monolayer is a promising and desirable candidate for use as a suitable material in gas sensors for NO2 detection.

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