In-plane heteroatom substitution of graphene is a promising strategy to modify
its properties. The ability to dope graphene with electron-donor nitrogen
heteroatoms is highly important for modulating electrical properties of graphene.
Here we demonstrate a transfer-free method to directly grow large area quasi
free-standing N-doped graphene bilayers on an insulating substrate (Si3N4).
Electron-bombardment heating under nitrogen flux results in simultaneous
growth of N-doped graphene and a Si3N4 layer on the SiC surface. The decoupling
of N-doped graphene from the substrate and the presence of Si3N4 are identified
by X-ray photoemission spectroscopy and low-energy electron diffraction. The
substitution of nitrogen atoms in the graphene planes was confirmed using
high resolution X-ray photoemission spectroscopy which reveals several atomic
configurations for the nitrogen atoms: Graphitic-like, pyridine-like, and pyrroliclike.
Furthermore, we demonstrated for the first time that N-doped graphene
could be used to efficiently probe oxygen molecules via nitrogen atom defects.