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X-ray and ultraviolet photo electron spectroscopy have been used to investigate nitrogen doping in single walled carbon nanotubes using 300 eV N2+ ion irradiation. N 1s core level photoemission spectra show three main peaks at 398, 399.3, and 400.5 eV with the last one being assigned to N atoms bonded to three C sp2 atoms in a graphitic network. Annealing to high temperatures results in preferential nitrogen substitutional doping and at 1000°C this is the only stable bonding configuration and the valence band spectra show a well developed Fermi edge. |