Structural study of nitrogen-doping effects in bamboo-shaped multiwalled carbon nanotubes

We have investigated nitrogen doping effects on the structure and crystallinity of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) by means of x-ray photoemission spectroscopy (XPS) and transmission electron microscopy. By controlling the ${\mathrm{NH}}_3/{\mathrm{C}}_2{\mathrm{H}}_2$ flow ratio during the chemical vapor deposition, the nitrogen concentrations of 0.4% to 2.4% were obtained. According to the XPS measurements, the increasing nitrogen concentration gave rise to an increase of the $\mathrm{N}{\mathrm{-sp}}^3$ C bonds as well as the deterioration of the crystallinity of the BS-MWNTs. Besides, the $\mathrm{N}{\mathrm{-sp}}^3$ C bonds were found to prevail over the $\mathrm{N}{\mathrm{-sp}}^2$ C bonds above 5% nitrogen concentration. At higher nitrogen concentrations, the BS-MWNTs showed shorter compartment distances, presumably due to the suppressed surface diffusion of carbon on the catalyst particles.