|AAPT Winter Meeting 2006|
A nanotube is a very small wire. It is another form of carbon, like graphite, diamond and fullerenes. The diameter can be as small as 0.7 nm, and the length up to 4 cm. One way to imagine the formation of a nanotube is to roll up a sheet of graphite. Since the graphite can be rolled among various angles, different kinds of nanotubes are possible. Applications include nanowires, transistors, computer memory, chemical sensing, biomedicine, displays, hydrogen storage, composite materials, nano-tweezers, and the construction of a space elevator.
There are several ways to make nanotubes, each with advantages and disadvantages: arc discharge, laser ablation, chemical vapour deposition, and high pressure carbon monoxide. The cable for a space elevator must get thicker with altitude, since it must support the part of the cable hanging below it. A steel cable requires a taper ratio of 1.7 x 1033, a Kevlar cable 2.6 x 109, and a nanotube cable 1.5. A company called LiftPort was established in 2003 to develop a space elevator. Projected liftoff date is April 12, 2018. Visit www.liftport.com for more information.
Nanoelectric circuits offer the possibility of constructing field effect transistors with greater ON conductance than silicon, and faster switching at lower voltages. Motorola plans to market a 40" HDTV less than an inch thick, costing about $400. Nanotubes will make it possible. Absorption of chemicals change the resistance of nanotubes, making them sensitive chemical detectors.