Structure of a carbon nanotube

To completely describe the structure of the nanotube, we have to consider the winding operation of the grapheme sheet. This operation amounts to superimpose two hexagons A and B of the network and the result depends entirely and solely the choice of these two hexagons. This choice sets the diameter of the nanotube and the winding angle.
By choosing as reference direction a direction that builds on one side of a hexagon, we define the winding angle as the angle between the axis of the cylinder and the reference direction.
This angle, called elicited  Varies from 0 to 30 ° view of the symmetry of a hexagonal lattice and allows to classify all configurations possible in three categories called 'chair' ('armchair'), 'zigzag' and chiral.
Each tube may be designated by two integers (n, m) values in the vector units of the grapheme system, components of the vector connecting one point along the circumference

The different winding modes of the nanotubes are: