Unidym uses a chemical vapor deposition method to grow the material. A mixture of carbon-containing gas and a metal-catalyst-coated substrate is heated at a high temperature. The carbon atoms from the gas attach to the substrate and form nanotubes. Then the company uses purification processes, including oxidation and acid treatment, to remove unwanted nanotubes and contaminants, such as other forms of carbon.
Unidym has also patented a process to disperse the nanotubes in a liquid. It uses a roll-to-roll technique akin to printing on paper to deposit the nanotube ink on plastic. The company can print at speeds up to 50 meters a minute. Olson won’t divulge any more information but says that the company has “optimized these techniques to get the best transparent, conductive film performance.”
At least one other ITO replacement is already being sold. Fujitsu is using a transparent, conducting organic polymer to make touch screens. However, the polymer degrades over time when exposed to heat or light, and its conductivity is not high enough for use in LCDs or electronic-paper displays.
Other potential ITO replacements are currently being worked on in various labs. Many research groups are making advances with the carbon material graphene. University of Michigan electrical-engineering and computer-science professor L. Jay Guo has made grids of extremely thin metal wires. He says that these would be more suitable than carbon nanotubes for making electrodes on thin-film solar cells because they would enhance light absorption. “Think of it as concentrating incoming sunlight energy into a very thin layer,” Guo says.
But Unidym’s carbon-nanotube films could be the first viable ITO replacement for touch screens, flexible displays, and thin-film solar cells. Unidym is also developing printable thin-film transistors and fuel-cell electrodes using carbon nanotubes.