Switching and Rectification in Carbon-Nanotube Junctions

Ames Research Center, Moffett Field, California

Figure 1. Symmetric and Asymmetric Carbon-Nanotube

Multiterminal carbon-nanotube junctions are under investigation as candidate components of nanoscale electronic devices and circuits. Three-terminal "Y" junctions of carbon nanotubes (see Figure 1) have proven to be especially interesting because (1) it is now possible to synthesize them in high yield in a controlled manner and (2) results of preliminary experimental and theoretical studies suggest that such junctions could exhibit switching and rectification properties.

Following the preliminary studies, current-versus-voltage characteristics of a number of different "Y" junctions of single-wall carbon nanotubes connected to metal wires were computed. Both semiconducting and metallic nanotubes of various chiralities were considered. Most of the junctions considered were symmetric. These computations involved modeling of the quantum electrical conductivity of the carbon nanotubes and junctions, taking account of such complicating factors as the topological defects (pentagons, heptagons, and octagons) present in the hexagonal molecular structures at the junctions, and the effects of the nanotube/wire interfaces. A major component of the computational approach was the use of an efficient Green's function embedding scheme.

Figure 2. These Current-Versus-Voltage Characteristics were computed for the three branches of the symmetric junction depicted in the upper left part of Figure 1, with zero potential applied to branches L and R and a potential VS applied to branch S.

The results of these computations showed that symmetric junctions could be expected to support both rectification and switching. The results also showed that rectification and switching properties of a junction could be expected to depend strongly on its symmetry and, to a lesser degree, on the chirality of the nanotubes. In particular, it was found that a zigzag nanotube branching at a symmetric "Y" junction could exhibit either perfect rectification or partial rectification (asymmetric current-versus-voltage characteristic, as in the example of Figure 2). It was also found that an asymmetric "Y" junction would not exhibit rectification.

This work was done by Deepak Srivastava of Ames Research Center; Antonis N. Andriotis of the Institute of Electronic Structure and Laser, Foundation for Research and Technology — Hellas; Madhu Menon of the University of Kentucky; and Leonid Chernozatonskii of the Institute of Biochemical Physics of the Russian Academy of Sciences. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Materials category.

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