Nitrogen-doping processes of graphene by a versatile plasma-based method

We present controllable processes to fabricate nitrogen-doped graphene with different doping configurations, in particular pyridinic- or graphitic-nitrogen-rich graphene. Nitrogen-doping is realized by in situ post-growth doping of monolayer graphene on SiC(0 0 0 1) using a tunable hybrid plasma source, which exposes the graphene to a stream of ions and/or to a neutral flow of thermalized species from a precursor nitrogen gas. Using angle-resolved inverse photoemission spectroscopy (ARIPES), we determine the doping level of the graphene through the analysis of the π∗ states dispersion. At a dose of about 1 × 1015 ions cm−2 and an energy of ∼35 eV, the Fermi level of the nitrogen-doped graphene is brought 0.4 eV above its value for the pristine graphene monolayer on SiC(0 0 0 1). This n-type doping is attributed to a 8.7  at.% graphitic-nitrogen as revealed by the core level spectroscopy (XPS). In contrast, exposure to a beam of thermalized nitrogen atoms mainly induces pyridinic-like nitrogen doping of graphene. It is thus possible to control the predominant bonding configuration of the doping nitrogen by choosing either a thermalized atom or a low-energy ion source.