Properties of CNT

Carbon nanotubes hold great promise due to their extraordinary properties. Carbon nanotubes come in many different forms and purities. They range from flexible, thin, few-walled or single-walled nanotubes (SWNTs) to rigid, long, thick, multi-walled nanotubes (MWNTs), with a spectrum of characteristics and properties in-between. Carbon nanotubes can be one, two or more tubular fullerenes nested inside one another and due to the perfection of their sidewalls, these endotopic structures also form ropes.

There are currently at least five methods for producing carbon nanotubes: (1) Chemical Vapor Deposition (CVD), (2) arc discharge, (3) laser ablation, (4) HIPCO, and (5) surface mediated growth of vertically-aligned tubes by Plasma Enhanced Chemical Vapor Deposition (PECVD).

Properties

High Electrical Conductivity

Carbon nanotubes are the best conductors of electricity of any organic molecule ever discovered with a current carrying capacity per unit area that is 100 times greater than copper. Varying structures of carbon nanotubes can be defined by two indices, typically labeled n and m which specify uniquely the chirality by the ordered pair (n,m). Electronically, carbon nanotubes can be either semiconducting or metallic, depending on the value of (n-m).Tubes in which (n-m) is either zero or a multiple of 3, have electrons in their conduction bands at room temperature, conduct electricity very well, and are called metallic nanotubes. All other structures produce nanotubes that are true semiconductors, with a band gap typically between 0.5 and 3.5 electron-Volts. The band gap varies inversely with the diameter of the tube, and for a tube of 1 nm diameter, the band gap is about 1 eV. Their conductivity has been shown to be a function of their chirality (degree of twist), as well as their diameter.

Electron mobility

Carbon nanotube transistors can have a mobility that is 70 times higher than silicon.

High thermal conductivity

The thermal conductivity along the carbon nanotube is twice that of diamond (which was the best thermal conductor until the discovery of CNTs) and has a thermal conductivity of about 3000 Watts per meter-degree Kelvin. Thermal conductivity is very high along its axis because vibrations of the carbon atoms propagate easily down the tube.

Very high mechanical strength

The tensile strength of carbon nanotubes is 100 times greater than steel, but CNTs are less dense than aluminum. Nanotubes are the stiffest, strongest, and toughest molecule known, Young's modulus is up to 1.4 TPa and tensile strength is well above 100 GPa,