Sensing mechanism of the nano-confined space constructed by graphene

Multilayer graphene with dense interlayer space is the most explored two-dimensional material (2DMs) in high performance gas sensor. Herein, the insertion and the diffusion behaviors of NO, NO₂, NH₃and H₂S in the nano-confined space of graphene are investigated using density functional theory calculations. The optimum interlayer distance is found to be 6-7 Å, in which the interaction strength is enhanced by 2 -3 times compared to monolayer graphene. Based on the optimum interlayer spacing, a barrierless diffusion process is observed due to the negligible influence of adsorption sites on the adsorption energy. Besides, an enhanced adsorption of NO₂is found at the edge, which leads to a small barrier (<0.15 eV) during the its inserting into graphene layers, while the barrierless process is observed for NO, NH₃and H₂S. As for sensing performance, an increased sensitivity is observed for NO and NO₂at the edge because of the significant energy level shift and charge transfer. Meanwhile, multilayer graphene shows good selectivity towards NO₂gas. Therefore, modulating the interlayer spacing of graphene layers is a promising strategy for fabricating practical low-cost gas sensors, which may facilitate future exploration of high performance gas sensor using multilayer 2DMs.