▎ 摘　　要

Graphene based sensor to gas molecules should be ultrasensitive and ultrafast because of the single-atomic thickness of graphene, while the response is not fast. Usually, the measured response time for many molecules, such as CO, NH3, SO2 and CO2 and so on, is on the scale of minutes or longer. In the present work, we found via ab initio calculations there exists a potential barrier larger than 0.7 eV for the above molecules. It is the barrier that hinders the gas molecules to land directly at the defective sites of graphene, which retards the response. An efficient approach to this problem is suggested as modifying the graphene sheet with other molecules to reduce the adsorption barrier and was demonstrated by a graphene sheet modified by Fe2O3 molecule and the calculated response time is about only 15 mu s, which coincides qualitatively with the previous experimental observation. (C) 2019 Elsevier B.V. All rights reserved.