Growth of Vertically Aligned Nitrogen-Doped Carbon Nanotubes:  Control of the Nitrogen Content over the Temperature Range 900−1100 °C

Abstract

Nitrogen-doped carbon nanotubes were grown vertically aligned on the iron nanoparticles deposited on silicon substrates, by thermal chemical vapor deposition of methane/ammonia and acetylene/ammonia mixtures in the temperature range 900−1100 °C. The concentration of the nitrogen atoms has been controlled in the range 2−6 atomic %, by the flow rate of ammonia. All nanotubes exhibit a bamboo-like structure over this temperature range. The growth rate is insensitive to this nitrogen content, but the structure is strongly dependent on it. As the nitrogen content increases, the thicker compartment layers form uniformly at a regular distance and the relative amount of crystalline graphitic sheets is notably reduced. Electron energy-loss spectroscopy reveals the higher nitrogen concentration and the lower crystallinity for the compartment layers compared to the wall. The growth of nitrogen-doped carbon nanotubes has been explained using a base growth mechanism proposed for carbon nanotubes. We suggest that the nitrogen doping would produce more flexible compartment layers connecting the wall under a less strain.