In this study, we report a facile method to obtain air-stable n-type graphene by plasma-enhanced chemical vapor depositing Si-3 N4 film on the surface of graphene. We have demonstrated that the overlying Si3N4 film can not only act as the penetration-barrier against H2O and O-2 adsorbed on the graphene surface, but also cause an effective n-type doping due to the amine groups at the interface of graphene/Si3N4. Furthermore, the studies reveal that the Dirac point of graphene can be modulated by the thickness of Si-3 N-4 film, which is due to competing effects of Si3N4-induced doping (n-type) and penetrating H2O (O-2)-induced doping (p-type). We expect this method to be used for obtaining stable n-type graphene field-effect transistors in air, which will be widely used in graphene electronic devices. (C) 2014 Elsevier B.V. All rights reserved.