Exploring and rationalising effective n-doping of large area CVD-graphene by NH3

Despite the large number of papers on the NH doping of graphene, the achievement of stable n-doped large area CVD (chemical vapor deposition) graphene, which is intrinsically p-doped, is still challenging. A control of the NH chemisorption and of the N-bond configuration is still needed. The feasibility of a room temperature high pressure NH treatment of CVD graphene to achieve n-type doping is shown here. We use and correlate data for (a) sheet resistance, R, and the Hall coefficient, R, in van der Pauw configuration, acquired in real time during the NH doping of CVD-graphene on a glass substrate, (b) optical measurements of the effect of doping on the graphene Van Hove singularity point at 4.6 eV in the dielectric function spectra by spectroscopic ellipsometry, and of (c) N-bond configuration by XPS to better understand and, finally, control the NH doping of graphene. The discussion is focused on the thermal and time stability of the n-doping after air exposure. A chemical rationale is provided for the NH n-doping based on the interaction of (i) NH with intrinsic oxygen functionalities and defects of CVD graphene and of (ii) C-NH doping centers with acceptor species present in the air. © 2014 the Owner Societies.