Authors: B.K. Agrawal, A. Pathak
Affilation: Allahabad University, India
Pages: 82 - 85
Keywords: nanotube heterojunction, electronic structures, optical absorption, oscillatory behaviour
The physical properties of the (n,n)/(2n,0); n = 3 and 6 superlattices of the carbon nanotubes (CN’s) has been studied by employing the first–principle pseudopotential method. The curvature effects on the various properties are also investigated. The heterojuction of the small diameter n(3,3)/n(6,0) superlattice which possesses a three-fold rotational symmetry exhibits an oscillatory behavior in terms of the fundamental energy band gap which vanishes whenever the integer ‘n’ is a multiple of 3. A similar behaviour having a periodicity of six may be observed in the case of the large diameter n(6,6)/n(12,0) superlattice whose heterojunction reveals a six-fold symmetry. The electronic structure and optical absorption of a superlattice are quite different from those of its constituent carbon nanotubes. The present results obtained after employing all the s-, p- and d-orbitals of the atoms are quite different from the findings of the earlier workers who have employed a phenomenological tight binding formulation considering only one p orbital or four orbitals. We find that most of the states are extended resonance states and are quite delocalized in contrast to the earlier finding of the occurrence of the completely localized states in the sections of the constituent nanotube. The metallic superlattices exhibit a high DOS at the Fermi level (EF). For the large diameter n(6,6)/n(12,0) superlattices, the electron energy gap vanishes for n=1 and 2 but for n=3 increases up to a maximum value and decreases thereafter for larger ‘n’, a result which is in disagreement with the earlier workers. These new facts have not been reported in the literature.