Highly nitrogen-doped carbon nanotube (${\mathrm{CN}}_x\mathrm{NT}$, $x=12\mathrm{at.}\%$) was synthesized by the pyrolysis of acetonitrile on Co-Mo catalysts. The electronic structures and chemical bondings of ${\mathrm{CN}}_x\mathrm{NT}$ were studied using various spectroscopic techniques: Raman, photoelectron and x-ray absorption spectroscopies. The ultrafast pump-probe measurements of ${\mathrm{CN}}_x\mathrm{NT}$ exhibited a larger third-order susceptibility ${\chi }^{\left(3\right)}$, a relaxation time of ${\tau }_2=1\mathrm{ps}$ and improved saturable absorption, as compared with undoped multiple-walled carbon nanotubes, which indicate that N-doping can improve all-optical switching properties of carbon nanotubes.

• Received 19 June 2005

DOI:https://doi.org/10.1103/PhysRevB.73.045402