The addition of Nitrogen as a dopant in monolayer graphene is a flexible approach to tune the electronic properties of graphene as required for applications. Here, we investigate the impact of the doping process that adds N-dopants and defects on the key electronic properties, such as the mobility, the effective mass, the Berry phase and the scattering times of the charge carriers. Measurements at low temperatures and magnetic fields up to 9 T show a decrease of the mobility with increasing defect density due to elastic, short-range scattering. At low magnetic fields weak localization indicates an inelastic contribution depending on both defects and dopants. Analysis of the effective mass shows that the N-dopants decrease the slope of the linear bands, which are characteristic for the band structure of graphene around the Dirac point. The Berry phase, however, remains unaffected by the modifications induced through defects and dopants, showing that the overall band structure of the samples is still exhibiting the key properties as expected for Dirac fermions in graphene.
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M.-L.B. thanks Libor Smejkal and Thomas Gauntlett Saunderson for stimulating discussions on the band structure and Berry phase, Leon Prädel for XPS measurements, and Nils-Eike Weber for developing experimental procedures for preparing doped graphene. M.G. acknowledges the visiting professorship program of the Centre for Dynamics and Topology and Johannes Gutenberg-University Mainz. This work was financially supported by the DFG primarily through the Priority Program Graphene SPP 1459 (Grant No. 130170629), SFB TRR 173 Spin + X, Projects A01 and B02 (Grant 268565370), and the Forschungsinitiative Rheinland-Pfalz through the Center for Dynamics and Topology (TopDyn).
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