▎ 摘　　要

Due to its huge surface-to-volume ratio, graphene has become one of the most popular materials for sensors. However, H2O molecules in atmospheric environments can cause the instability of graphene devices, which greatly limits the practical applications of graphene devices. The charge transfer between graphene and adsorbed H2O molecules has been proved previously by first-principle studies, but experimental demonstrations are still lacking. Here, gate-polarity-dependent doping behaviors of adsorbed H2O molecules on a graphene/SiO(2)field-effect transistor (GFET) are experimentally investigated. The results indicate that the orientation of the adsorbed H2O can be affected by the gate-voltage polarity due to the dipolar interaction, which leads to the amphoteric doping behavior of adsorbed H2O molecules. With reducing the graphene layer number, the amphoteric doping behavior is more sensitive to the gate voltage polarity. Our results are helpful for constructing high performance graphene-based sensors and enhancing the stability of GFETs.