Monolayer Sc₂CF₂ as a Potential Selective and Sensitive NO₂ Sensor: Insight from First-Principles Calculations

Two-dimensional materials with excellent surface-volume ratios and massive reaction sites recently have been receiving attention for gas sensing. With first-principles calculations, we explored the performance of monolayer Sc₂CF₂ as a gas sensor. We investigated how molecule adsorption affects its electronic structure and optical properties. It is found that a large charge transfer quantity happens between Sc₂CF₂ and NO₂, which results from the fact that the lowest unoccupied molecular orbital (LUMO) of NO₂ is below the valence band maximum (VBM) of Sc₂CF₂. Moreover, the MD simulation shows that NO₂ can adsorb on the Sc₂CF₂ surface stably at room temperature. We explored the effect of biaxial strain on the adsorption energy and charge transfer quantity of each system, and the results show that the biaxial strain can enhance both the adsorption energy and charge transfer quantity of the NO₂ system and thus can improve the sensitivity of Sc₂CF₂ in detecting the NO₂ molecule. Furthermore, we investigated the adsorption behavior and charge transfer of polar polyatomic molecules at the Sc₂CF₂ surface with h-BN as a substrate, and the results demonstrate that the h-BN substrate can hardly modify the main results. Our result predicts that Sc₂CF₂ can be a promising selective and sensitive sensor to detect the NO₂ molecule, and could also give a theoretical guide for other terminated MXenes used for gas sensors or detectors.