Carbon nanotubes are a novel form of pure carbon. CNTs are formed by roll graphite sheets, with an inner diameter starting from 0.4 nm to several nm and a length of 10-100 ? Tubes formed by only one single graphite layer are called single-wall nanotubes (SWNT). Tubes consisting of multiple concentric graphite layers are called multi-wall nanotubes (MWNT).

Properties of Single-Wall Carbon Nanotubes
The diameter of SWNTs varies from 0.4 to 3 nm. The helicity of the nanotubes is usually described by the Hamada vector, which indicates how the graphene sheet is rolled up along a lattice vector with components (n, m). The values of the integers n and m identify the general geometry of SWNT. Tubes with n=m are named "armchair"; tubes with either n=0 or m=0 are named "zigzag"; all others have chiral symmetry. SWNTs tend to agglomerate and form bundles of several tens of nanotubes. SWNTs are quite stiff and exceptionally strong, which translates to high Young's modulus and high tensile strength.

Properties of Multi-Wall Carbon Nanotubes
The interlayer distance in MWNTs is closer to the interlayer distance in graphite, which is equal to half of the cell parameter c (0.5c=0.3355 nm). MWNTs show typical diameters of 30-50 nm.

Carbon nanotubes exhibit potentials derived from a combination of unique dimensional, structural and topological features. In particular, electronic conductive or semiconductive behavior, excellent mechanical strength, exceptionally high elastic properties, large elastic strain, low density, high thermal conductivity, open pipe framework and relative chemical inertness. These properties render CNTs ideal materials for use in conventional and high technology applications, including sensors, microelectronic and semi-conductor devices, field emission displays, light weight but high-strength composites, scanning probes, hydrogen storage materials, nanoelectrodes, sorbents and membrane materials for separations, catalysts, and energy conversion devices (e.g., fuel cells and batteries).