NANOTUBES

They are stronger than steel and as flexible as plastic, conduct energy better than almost any material ever discovered and can be made from unexotic raw materials such as methane gas.
. . Within a decade, nanotubes could replace silicon as the transistors inside processors and memory chips. Tubes could also be used to convey light through optical fibers and, further out, to deliver medicines to specific cells inside a body or even restructure the nation's power grid.
. . Mass production of nanotubes, however, remains a challenge. CNI plans to increase its manufacturing capacity to the point where the company can make 1,000 pounds of nanotubes a day by 2005. Right now, it can make only about a pound or two daily. This cumbersome process makes the technology too costly for wide use. The going price on the company's Web site is $500 a gram.
. . Electrons can travel ballistically on them --that is, barring obstacles or flaws in the material, electrons don't get scattered or lost. Such confined dimensionality means that nanotubes can conduct heat better than any other material ever discovered, including diamonds, and could even be used to transfer energy in homes or between power stations. Tubes can also be used to carry light, enhancing or replacing optical fiber. Engineers can replace wires in airplanes with tubes --strengthen parts and reduce weight.
. . Nanotube monitors would be thinner than LCDs and far cheaper to make. The tubes can be mixed into a paste and printed onto glass. "You put nanotubes in ink and print them down."
. . Nanotubes "heal" themselves by shifting to replace atoms that get removed.
. . Carbon is also good for exploiting van der Waals forces, which cause different types of atoms to bond spontaneously.

. . Today, carbon nanotubes are made in two ways. The first, known as the laser ablation method, was pioneered by CNI and involves blasting graphite with a laser. The second, the modified gas method, involves spraying a hydrocarbon gas like methane or CO2 over a molten metal catalyst. Removing impurities, such as metallic catalyst particles, is a challenge in both.
. . "Chirality", a measure of the arrangement of the hexagons on the surface of a tube. If the carbon hexagons run in parallel vertical lines on the surface of the tube, they will act like a metal and can't be used in electronics. If the rows of tubes are slightly swirled (think of the cardboard on a paper towel roll), they will act like semiconductors, and can be used as transistors.
. . Chips, however, will require that individual nanotubes be placed between specific contacts.
. . Silicon compatibility could tip the balance toward silicon nanowires. These are made by siphoning molecules of SiH4 (a single silicon atom surrounded by four hydrogen atoms) through a gold particle. The gold strips off the hydrogen atoms and allows the naked silicon atoms to form into a wire.
. . Although nanowires may not exhibit the same electrical properties as nanotubes, silicon nanowires may be easier to grow on the wafer itself.