Oct. 1, 2002 — A research group headed by IBM scientist Phaedon Avouris has developed a process to make single-wall carbon nanotubes without using a metal catalyst. The method is described in a paper published in the October issue of the journal Nanoletters.
According to Avouris, manager of nanometer scale science and technology at IBM’s T.J. Watson Research Center, scientists could previously only make multiwall nanotubes without metal catalysts.
Avouris said single-wall nanotubes made with metal catalysts cannot be used in electronics without first removing the metal. However, removing the metal can damage the nanotubes and introduce other problems.
The new method, by contrast, uses a crystal of silicon carbide as a starting material and works without any catalyst. When heated at high temperature in a vacuum, the silicon evaporates. Because the silicon they were bonded to is now gone, the carbon atoms bond to each other and form small sheets of graphite.
These graphite sheets, in turn, have broken bonds at their ends which “can curl up and form the seed of a tube,” Avouris said. “As more carbon atoms are produced they can attach to the tubes and grow.” In short, it’s like a sheet of paper that curls up and rolls into a cylinder, then grows at its ends.
Avouris said the method also produces nanotubes that are oriented because at the high temperature of the experiment the nanotubes are mobile and align themselves with the crystallographic structure of the substrate. But, he cautioned, “I want to indicate that this is not, at this point, a method for mass production of nanotubes.”