Gas-Sensing Properties of the SiC Monolayer and Bilayer: A Density Functional Theory Study

Using density functional theory calculations, the adsorption of gaseous molecules (NO, NO₂, NH₃, SO₂, CO, HCN, O₂, H₂, N₂, CO₂, and H₂O) on the graphitic SiC monolayer and bilayer has been investigated to explore the possibilities in gas sensors for NO, NO₂, and NH₃ detection. The strong adsorption of NO₂ and SO₂ on the SiC monolayer precludes its applications in nitride gas sensors. The nitride gases (NO, NO₂, and NH₃) 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 NO₂ and SO₂ molecules, that is, NO₂ molecules are only weakly chemisorbed on the SiC bilayer with an E _ads of -0.62 eV, while SO₂ are physisorbed on the bilayer. These results indicate that the SiC bilayer can serve as a gas sensor to detect NO, NO₂, and NH₃ gases with excellent performance (high sensitivity, high selectivity, and rapid recovery time). Moreover, compared with other molecular adsorptions, the adsorption of NH₃ molecules significantly changes the work function of the SiC monolayer and bilayer, indicating that they can be used as optical gas sensors for NH₃ detection.