N 1s photoemission spectra acquired after intercalation of different metals under N-graphene, followed by prolonged annealing; and concentrations of pyridinic and graphitic N impurities in each system. The peaks are marked as follows: NP, pyridinic; NG, graphitic. In the initial N-graphene/ Ni(111) system, the pyridinic peak is formed by the two components “1” and “2”, corresponding to different environments of pyridinic N; also two additional peaks can be identified: NA, atomic nitrogen bonded to the Ni substrate (0.16%) and NO, other types of nitrogen (0.15%).
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