How do you make a carbon nanotube? One way is by chemical vapor deposition in a tube furnace. Metal catalyst particles such as iron, cobalt, or nickle, or a combination are heated in the furnace to 700°C (1300°F). A process gas such as hydrogen or ammonia is passed across the particles along with a carbon containing gas, e.g., acetylene, ethylene, methane. . . The nanotubes grow at the site of the metal catalyst particles.
Much research has been done to find a way to deposit carbon nanotubes on various substrates. Recently researchers at MIT found an elegant and simple method. The carbon nanotubes are compressed into lead for a pencil. Carbon nanotubes can be deposited on a substrate merely by drawing a line with the pencil. One application is a portable compact gas sensor. A gas sensor can be devised by drawing a carbon nanotube line on paper imprinted with tiny gold electrodes; the line of carbon nanotubes act as a resistor. If the current across the carbon nanotube pencil line changes it means a gas has bound to the nanotubes. The sensors give consistent results even when the lines drawn are not regular.
Massachusetts Institute of Technology. “Drawing a line, with carbon nanotubes: New low-cost, durable carbon nanotube sensors can be etched with mechanical pencils.” ScienceDaily, 9 Oct. 2012. Web. 10 Oct. 2012.