Carbon nanotubes are tubular carbon molecules that have properties that make them potentially useful in nanotechnology. They exhibit unusual strength and unique electrical properties, and are extremely efficient conductors of heat.
A nanotube is a structure similar to a fullerene, only the carbon atoms are rolled into a cylinder instead of a sphere; each end is capped with half a fullerene molecule. They are only one nanometre wide (on the order of one ten-thousandth the width of a human hair), and their length can be millions of times greater than their width.
In 1889, two British men received a US patent on producing 'hair-like carbon filaments' from methane. In the 1960s and 1970s, groups at the National Carbon company in Parma, Ohio, United States and the University of Canterbury in Christchurch, New Zealand, produced and identified the tubes.
Nanotubes were rediscovered in 1991 by Sumio Iijima. It has since been discovered how nanotubes can be produced in large quantities. The price of nanotubes are still in the US$100 dollar per gram range which prohibits any large scale use of them; when large-scale nanotube production is implemented, however, it is assumed that prices would be far lower, to around five cents per gram or so.
Nanotubes can be opened and filled with materials such as biological molecules, raising the possibility of applications in biotechnology. They can be used to dissipate heat from tiny computer chips. The strength and flexibility of carbon nanotubes makes them of potential use in controlling other nanoscale structures, which suggests they will have an important role in nanotechnology engineering. If nanotube composites can be fabricated that exhibit macroscale strength properties approaching theoretical models of individual nanotubes, they will make possible a huge variety of technical innovations, notably the space elevator.
One use for nanotubes that has already been developed is as extremely fine electron guns, which could be used as miniature cathode ray tubes in thin high-brightness low-energy low-weight displays. In this type of display, a group of many tiny CRTs would provide the electrons to hit the phosphors of one pixel, instead of having one giant CRT whose electrons are aimed using electric and magnetic fields. These displays are known as Field Emission Displays (FEDs). A nanotube formed by joining nanotubes of two different diameters end to end can act as a diode, suggesting the possibility of constructing electronic computer circuits entirely out of nanotubes. Nanotubes have been shown to be superconducting at low temperatures.