Enhanced and stable field emission from in situ nitrogen-doped few-layered graphene nanoflakes

Vertically aligned few-layered graphene (FLG) nanoflakes were synthesized on bare silicon (Si) substrates by a microwave plasma enhanced chemical vapor deposition method. In situ nitrogen (N2) plasma treatment was carried out using electron cyclotron resonance plasma, resulting in various nitrogen functionalities being grafted to the FLG surface. Compared with pristine FLGs, the N2 plasma-treated FLGs showed significant improvement in field emission characteristics by lowering the turn-on field (defined at 10 μA/cm2) from 1.94 to 1.0 V/μm. Accordingly, the field emission current increased from 17 μA/cm2 at 2.16 V/μm for pristine FLGs to about 103 μA/cm2 at 1.45 V/μm for N-doped FLGs. Furthermore, N-doped FLG samples retained 94% of the starting current over a period of 10 000 s, during which the fluctuations were of the order of ±10.7% only. The field emission behavior of pristine and N2 plasma-treated FLGs is explained in terms of change in the effective microstructure as well as a reduction in the work function as probed by X-ray photoelectron valence band spectroscopy