Nitrogen-containing carbon nanotubes and Y junctions by floating catalytic chemical vapor deposition

Well-aligned nitrogen-doped multiwalled carbon nanotubes have been synthesized by pyrolysis of acetonitrile and ferrocene mixtures at relative low temperatures (from 500°C to 850°C), which has potential field-emission applications. The effects of chemical vapor deposition parameters such as reaction temperatures and carrier gas on the derived nanotube yield, morphology, and doped N have been systematically studied by scanning electron microscopy and transmission electron microscopy coupled with electron energy-loss spectroscopy (EELS). It is found that the nanotube yield, average length, and diameter increase with reaction temperatures. However, higher reaction temperature (above 800°C) reduces the doped-N concentration resulting in gaseous nitrogen encapsulated within nanotube cores. Using N₂ carriage gas instead of Ar promotes the formation of Y junctions at 800°C, whereas the introduction of 10% H₂ results in the promotion of uniform small-diameter nanotubes with a higher nanotube yield. Spatially resolved EELS studies reveal a higher pyridine-like N concentration in the tube core region and a lower N doping at the tube wall, which is because of dangling bonds at the open fringes in the tube inner cores.