Carbon Nanotubes with Catalyst Controlled Chiral Angle.

The control of the structure of carbon nanotubes remains a central issue in rapidly developing science and technology. Of the various structural parameters of nanotubes, namely, diameters, number of walls, length, and chirality, it is the control of chirality which presents significant challenges as well as opportunities. It is known from our earlier work that the addition of nitrogen as a heterocyclic compound in the hydrocarbon feedstock leads to the growth of carpets of multiwall nanotubes in which all the walls are either of the armchair or zigzag structure. The research here shows the role of nitrogen in stabilizing iron carbide catalyst particles, the belt nucleation of the nanotubes, the orientational relationship between particle and nanotube structure, and the reconstruction of the surface layers of the carbide in contact with the growing ends of the tubes. By combining the various pieces of new experimental evidence it has proved possible to suggest why such unique types of nanotubes should form and thus lay the basis for future strategies for the synthesis of different types of nanotube with controlled chirality. [ABSTRACT FROM AUTHOR]