Hauge’s group started playing with making nanotubes using the same machinery the U.S. Treasury uses to embed special anti-counterfeiting materials and markings in paper currency. The group used this specialized printing process to lay down a three-part surface on a Mylar roll. One layer was made up of iron particles. A layer of flakes of alumina is then spread over the iron. The iron and alumina act as a catalyst for nanotube growth. The bottom layer is a release layer that can be activated by acetylene.
Next, the film is put in a furnace with an acetylene-hydrogen atmosphere. As the temperature increases, the alumina flakes lift in the chemical vapor while arrays of nanotubes grew vertically in tight, forest-like formations atop the iron particles. They say that under a microscope, the bundles of tubes looked the pile of a carpet.
Hauge’s group says the flakes look like they are “flying” in the vapor and “pulling up” the nanotubes. They call the product made using this process “odako” SWNTs, named for the huge, multistringed traditional Japanese kites they resemble.
The team has also grown odako on pure carbon, Grafoil (a flexible graphite material) and carbon fiber that has been woven into a material.
So far they have been able to make SWNTs measured in centimeters, and, he said, the process could eventually yield tubes of unlimited length. They also believe that odako-type growth may be possible on such other materials as quartz fibers and some metals.