Efficient and low-damage nitrogen doping of graphene via plasma-based methods

We investigate the nitrogen doping of mono- and bi-layer graphene on 6H-SiC(0001) using two plasma-based methods: a lab-scale microwave plasma gun and an industrial-scale plasma-based implanter. As revealed by X-ray photoemission spectroscopy, the thickness of the pristine graphene significantly influences the bonding configuration of the incorporated nitrogen atoms. Using the plasma gun, a high concentration of graphitic-nitrogen (3 at%) is obtained in N-doped bilayer graphene, while only 0.2 at% of pyridinic-nitrogen is incorporated. By contrast, a comparable amount of each nitrogen doping configuration is found with monolayer graphene. The integrity of the bilayer graphene is also better preserved than its monolayer counterpart after nitrogen plasma exposure, as evidenced by their inverse photoemission spectra. It is attributed to a better stability and a lower vacancy creation rate in bilayer graphene during plasma exposure. In addition, the N-doped bilayer graphene shows an efficient n-type doping, with a Dirac point brought 0.45 ± 0.1 eV away from the Fermi energy. In brief, this study reports an efficient method for tailoring the electronic properties of graphene using industry-suited techniques, thereby promoting future graphene-based applications.