Electromechanical Effects

The coupling between structural distortions and electrical properties of carbon nanotubes represents another possibility for creating nanotube junctions and promises potential applications in nano-electromechanical devices. Earlier on it was realized that nanotubes can be distorted as a result of the van der Waals interaction between the nanotubes and the substrates, and that controlled deformation could be easily induced by the use of the tip of an AFM [48].

The effects of bending on the electronic properties of the nanotubes have been theoretically investigated by a number of authors [8,49,50,51]. In the n-electron approximation, the electronic properties of metallic armchair nano-tubes remain essentially unchanged upon small bending deformation [49]. However, for strongly bent carbon nanotubes, a-n hybridization effects have to be taken into account. Electronic structure calculations involving both s and p electrons showed that strong bending introduces localized density of states [50] that may lead to localization. Further calculations showed that drastic decrease in the conductance of metallic tubes occurs upon buckling [8,51].

Experimentally, Bezryadin et al. [23] found that local bending of a nano-tube near the electrodes causes local barriers and breaks the nanotube into multiple quantum dots at low temperature. AFM proves especially useful in controllably introducing mechanical deformation. Postma et al. [36] measured the transport across a buckled nanotube manipulated from an initially straight nanotube by an AFM. The buckle was found to act as a tunnel barrier and the transport showed end-to-end tunneling behavior between two Luttinger liquids. Recently Tombler et al. [52] conducted in situ transport measurement of suspended nanotubes which were reversibly bent by an AFM tip. They found that conductance of the nanotubes can be decreased by two orders of magnitude upon a bending angle up to 14°. Simulations showed that the large suppression in conductance originates from the highly deformed region near the AFM tip where local bonding is changed from sp2 to nearly sp3 configuration.

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