Theoretical studies of pentagon-heptagon pair defects in carbon nanotube junctions

The electronic and energetic properties of topological defect in single-walled carbon nanotube junctions (SWCNTJ) were studied theoretically. The interfacial junction geometries can be constructed by fusing two zigzag tubes having different helicities and diameters. One segment of the fused nanotube is kept constant by using the (5,0) nanotube, while varying another segment from (6,0) to (10,0). Practically, the junctions are composed of one or more pentagon-heptagon pairs as defect in the perfect hexagonal lattice. The study shows that the electronic structures of SWCNTJ are dependent on the variation of diameter and length of carbon nanotubes. The HOMO and LUMO levels exhibit the even-odd iquestquantum sizeiquest oscillation of nanotube chiralities, even with increasing length of nanotubes. The energy gap that indicates metallic or semi-conducting behavior depends on correlation between the tubes indices and tubule length. The energy of formation gently changes with the variation of tubular length and not diameter. The straight pair defect (5,0)//(6,0) SWCNTJ is more stable than other SWCNTJs. Comparison between the pair defect and the point defect structures shows that the straight SWCNTJ with topological pair defect has no affect by the alteration of numbers of pair defect structure around tube circumference. The outcome of this study would be of help as a knowledge base in the field of carbon nanotube molecular electronics.