Resolution of the binding configuration in nitrogen-doped carbon nanotubes

Nitrogen-doped carbon nanotubes (N-doped CNTs) were synthesized by exposing CNTs under high input power nitrogen plasma (3.10.3em0exkW), using a microwave plasma enhanced chemical vapor deposition system. In the analysis of high resolution transmission electron microscopy, it was found that graphene layers of the N-doped CNTs became seriously curved, waved, or buckled, and even contained fullerene-like structures, in contrast to the parallel concentric graphene layers in the normal CNTs. X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were combined to resolve the binding configurations of nitrogen and carbon in the N-doped CNTs. In the XPS study, it may be concluded that the N-doped CNTs have three binding configuration types (poly 4-vinylpyridine, poly 9-vinylcarbazole, and poly aniline oligomer) using the method proposed by [F. L. Normand, J. Hommet, T. Sz\"or\'enyi, C. Fuchs, and E. Fogarassy, Phys. Rev. B. 64, 235416 (2001)] EELS results showed that the incorporation of nitrogen into the CNTs would induce sp² binding for carbon atoms, similar to the results in amorphous carbon nitride films [J. Hu, P. Yang, and C. M. Leiber, C. Ronning, H. Feldermann, R. Merk, and H. Hofs\"asPhys. Rev. B 57, 3185 (1998); , Phys. Rev. B 58, 2207 (1998)]. N0.3em0ex1s core-level downshift of ~10.3em0exeV in the XPS analyses was mainly caused by the screening effects of core holes in the π bond around nitrogen atoms.