  N-doped single/multi-walled carbon nanotubes (CNTs) were studied for long
time from synthesis to properties. However, the stability of N in the CNT
lattice still needs further developments. In this work, to obtain more stable
N-doped CNTs, concentric double-walled (DW) CNTs with more N were synthesized
using benzylamine as C and N source. In order to test the stability of N-doped
DWCNTs, high-temperature annealing in vacuum was performed. By XPS and Raman
spectroscopic measurements, we found that the N-doped DWCNTs are still stable
under 1500 $\,^{\circ}\mathrm{C}$: the graphitic N does not change at all, the
molecular N is partly removed, and the pyridinic N ratio greatly increases by
more than two times. The reason could be that the N atoms from the surrounded
N-contained materials combine into the CNT lattice during the annealing.
Compared with the undoped DWCNTs, no Raman frequency shift was observed for the
RBM, the G-band, and the G'-band of the N-doped DWCNTs.
