Monolayer ScCF as a Potential Selective and Sensitive NO 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 ScCF 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 ScCF and NO, which results from the fact that the lowest unoccupied molecular orbital (LUMO) of NO is below the valence band maximum (VBM) of ScCF. Moreover, the MD simulation shows that NO can adsorb on the ScCF 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 NO system and thus can improve the sensitivity of ScCF in detecting the NO molecule. Furthermore, we investigated the adsorption behavior and charge transfer of polar polyatomic molecules at the ScCF surface with -BN as a substrate, and the results demonstrate that the -BN substrate can hardly modify the main results. Our result predicts that ScCF can be a promising selective and sensitive sensor to detect the NO molecule, and could also give a theoretical guide for other terminated MXenes used for gas sensors or detectors.