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 A, 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.