A. A. Shokri - Department of Physics, Payame Noor University (PNU), ۱۹۳۹۵-۳۶۹۷, Tehran, Iran.
Z. Karimi - Department of Physics, Islamic Azad University North Tehran Branch, Tehran, Iran.

By employing the theoretical method based on tight-binding, we study electronic band structure of single-wall carbon nanotube (CNT) superlattices, which the system is the made of the junction between the zigzag and armchair carbon nanotubes. Exactly at the place of connection, it is appeared the pentagon–heptagon pairs as topological defect in carbon hexagonal network. The calculations are based on the tight binding model in the nearest-neighbor approximation. We seek to describe electronic band structure in the presence of the pentagon-heptagon pairs. Our calculation  show  that the pentagon–heptagon  pairs  defect  in  the  nanotube  structures is not only responsible  for  a  change  in  a  nanotube  diameter,  but  also governs  the  electronic  behaviour  around  Fermi  level.  Also, we obtain the Fermi energy of the system via integration of the density of states and matching it to the number of electron in the unit cell. The numerical results may be useful to design of electronic devices based on CNTs.

Carbon Nanotube, Tight–binding model, Pentagon-heptagon pair defect, Band Structure, SW defect