Carbon nanotube, an  allotrope of carbon  is one of the breakthroughs of nanotechnology. It is a nano-scale tube formed of carbon atoms.There exist a large number of carbon nanotubes with different geometries depend on a parameter known as 'Chirality', is a vector represented by a pair of integers (n,m).

To form a nanotube first you have to mark a nanoribbon on a graphene layer as shown in following figure.

Ch is the chiral vector known as Ch = na1 + ma2 . T is the vector perpendicular to Ch.

To form the nanotube,  nanoribbon should be rolled around an axis parallel to T. If m=n, nanotube is known as an armchair nanotube. If m or n is zero tube is known as zig zag. Otherwise it is said to be a chiral nanotube.

In above figure (a) is a (5,5) armchair nanotube, (b) is a (8,0) zig zag nanotube and (C) is a (5,9) nanotube. You can plot any nanotube using ninithi with different parameters. You can also customize the apperance.

Electrical properties of Carbon Nanotubes (CNT)

Carbon nanotubes exhibit geometry dependent electrical properties. As an example if (m-n) is a multiple of 3, nanotube is metallic.(So all armchair nanotubes are metalic) Otherwise semi-conductive with some band-gap. ninithi can be used to plot band structures of all the nanotubes. So you can understand the band gap and electrical properties of nanotubes using ninithi.

Above image illustrates the band structure of a (5,5) nanotube. You  can see that band gap is zero and material is metalic.