Nitrogen doped graphene sheets, have attracted much attention due to their exceptional performance as parts of fuel cells, lithium-ion batteries and supercapacitors. Free-standing Nitrogen-doped graphene sheets where produced in a low pressure microwave N₂-Ar plasma. Graphene sheets were treated by plasma at different exposure times and doped with nitrogen atoms, which incorporated the hexagonal carbon lattice, mainly, in pyridinic, pyrrolic and quaternary functional groups. Optical emission spectroscopy were applied to monitor the nitrogen atoms, gas temperature and electron density at the substrate position. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques were applied to characterize the produced N-graphene, along with transmission electron microscopy (TEM) to study the morphology and structure of the samples. Doping levels as high as 5.6 % were achieved and an increase in the sp²/sp³ratio was observed for a relatively short exposure times. This study shows that by incorporating nitrogen atoms into graphene, its physico-chemical properties are considerably altered.

Acknowledgements: This work was supported by Fundação para a Ciência e a Tecnologia, under Project Pest-OE/UID/FIS/50010/2013 and grant SFRH/BD/52413 (PD-F APPLAuSE) .