Peculiarities of conductance of carbon nanotube‐based quantum dots

Within the framework of the surface Green's function matching method, we carried out calculations of the differential conductance of symmetrically and asymmetrically connected armchair ( n, n )—zigzag (2 n , 0)—armchair ( n , n ) carbon nanotubes with different lengths of the middle section and infinitely long ends. It is shown that the ( n, n )/(2 n , 0)/( n, n ) segment, when n is not a multiple of 3, behaves as a quantum dot and has a conduction gap even for short middle segments. The position of the conductance peeks closest to the Fermi energy is determined by the interface states of the ( n, n )/(2 n , 0) junction. In addition to conductance peaks originating from the interface states of the ( n, n )/(2 n , 0) heterojunction, for sufficiently long middle zigzag nanotube, there are more conductance peaks in the vicinity of the Fermi energy, and those stem from the electronic structure of an individual finite (2 n , 0) zigzag nanotube. However, positions of the peaks farther away from the Fermi energy cannot be found in such a simple way. Thus, such ( n, n )/(2 n , 0)/( n, n ) quantum dot has singularities in its electronic properties, which may yield the Coulomb blockade effect should those strongly localized discrete levels become occupied. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010