Structural and electronic properties of the metal-metal intramoleular junctions of single-walled carbon nanotubes

Several intramolecular junctions (IMJs) connecting two metallic (11, 8) and (9, 6) carbon nanotubes along their common axis have been realized by using a layer-divided technique to the nanotubes and introducing the topological defects. The atomic structure of each IMJ configuration is optimized with a combination of density-functional theory (DFT) and the universal force field (UFF) method, based upon which a four-orbital tight-binding calculation is made on its electronic properties. Different topological defect structures and their distributions on the IMJ interfaces have been found, showing decisive effects on the localized density of states, while the $\sigma -\pi$ coupling effect is negligible near Fermi energy $\left(E_{\mathrm{F}}\right)$. Finally, a new IMJ model has been proposed, which probably reflects a real atomic structure of the M-M IMJ observed in the experiment [Science 291, 97 (2001)].

Figure 1

(Color online) Selected several optimized geometrical structures for the $\left(11,8\right)∕\left(9,6\right)$ IMJ with different topological defect configurations, in which the carbon atoms of the pentagons and heptagons are indicated by solid balls. The structures I, II, and III contain a joint section with two, three, and four pairs of pentagons and heptagons, respectively. Each of them may have different isomers, such as indicated by (a), (b), or (c).

Figure 2

(Color online) Four-orbital TB calculated LDOS for the junctions shown in Fig. 1, which are averaged over a section with its length of $3\mathrm{\AA }$. The horizontal lines indicate the zero-density levels, while the broken vertical lines indicate the positions of the localized defect states in the interface region. The dashed curves in the top and bottom of the figure correspond to the calculated bulk DOS of the pure (11, 8) and (9, 6) tubes, respectively. The middle panel shows the considered sections schematically.

Figure 3

(Color online) Transmission coefficient vs energy for the model III (c) and those pure (11, 8) and (9,6) tubes. The inset shows the $\pi$-only TB calculation results.