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 (N-2) 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 N-2 plasma-treated FLGs showed significant improvement in field emission characteristics by lowering the turn-on field (defined at 10 mu A/cm(2)) from 1.94 to 1.0 V/mu m. Accordingly, the field emission current increased from 17 mu A/cm(2) at 2.16 V/mu m for pristine FLGs to about 103 mu A/cm(2) at 1.45 V/mu m 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 N-2 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.