Carbon nano tube are allotropes of carbon with cylindrical nanostructure.

Nanotubes have been constructed with length-to-diameter ratio upto 132,000,000:1, significantly larger than any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology.

Types of carbon nanotubes:

• Single-walled
• Multi-walled
• Torus
• Three-dimensional carbon nanotube architecture
• Graphenated carbon nanotubes
• Nitrogen-doped carbon nanotubes
• Cup-stacked carbon nanotubes

Electrical properties of carbon nanotubes. Because of the symmetry and unique electric structure of graphene, the structure of a nanotube strongly affects its electrical properties. For a given (n,m) nanotubes, if

• n=m, the nanotube is metallic
• n-m is a multiple of 3, then the nanotube is semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor.

Mechanical Properties:

Carbon nanotubes are one of the strangest materials in nature. On the other hand, there was evidence that in the radial direction they are rather soft.

The first transmission electron microscope observation of radial elasticity suggested that even the van der walls forces can deform two adjacent nanotubes.

Radial direction elasticity of CNTs is important especially for carbon nanotube composites where the embedded tubes are subjected to large deformation in the transverse direction under the applied load on the composite structure.