Carbon nanotubes, (a.k.a. buckytubes), are cylindrical molecules of carbon with novel properties that are potentially useful in a wide variety of applications including nano-electronics, optics, materials applications, etc. They exhibit extraordinary tensile strength, a unique range of electrical properties, and are efficient thermal conductors.
Most single-walled nanotubes (SWNT) are close to 1 nanometer in diameter, with a tube length that can be many millions of times longer. The structure of a SWNT can be thought of as a one-atom-thick layer of graphite, called graphene, wrapped into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of indices.
Single-walled nanotubes are still very expensive to produce, around $1500 per gram as of 2000. Several suppliers offer as-produced arc discharge SWNTs for ~$50–100 per gram as of 2007.
Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphene. The interlayer distance in multi-walled nanotubes is close to the distance between graphene layers in graphite, approximately 3.3 Å (330 pm).
Inorganic nanotubes have also been synthesized. A nanotube is a member of the fullerene structural family, which also includes buckyballs. Whereas buckyballs are spherical in shape, a nanotube is cylindrical, with at least one end typically capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers or less (approximately 50,000 times smaller than the width of a human hair), while they can be up to several centimeters in length. There are two main types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).