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Posted: May 26, 2006
Electromechanical switches based on telescoping carbon nanotubes
(Nanowerk Spotlight) Researchers in China are proposing a nanoelectronic switch based on telescoping double-walled carbon nanotubes (TDWCNT). By varying the overlapping length at the junction, one could control the conducting states and change it between "on" (high conductance state) and "off" (low conductance state).
It has been previously demonstrated that individual concentric carbon nanotubes in a double- or multi-wall nanotube can "telescope" with minimal resistance, much like a greased radio antenna. The possibility of using telescoped nanotubes as really small and incredibly fast electromechanical switches arose when it was found that a fully extended core tube would snap back into its jacket in less than ten billionths of a second.
The scheme of the TDWCNT composed of two coaxial open single-walled carbon nanotubes. One tip of each tube at the junction is open, while the other is assumed to be connected to the external electrode (Reprinted with permission from the American Institute of Physics)
Professor Wenhui Duan of the Department of Physics at Tsinghua University in PR China, together with members of his group, has published a paper describing the possibility of a nanoelectronic switch based on TDWCNTs. The article, titled "Mechanism of nanoelectronic switch based on telescoping carbon nanotubes" was published in the April 24, 2006 edition of Applied Physics Letters.
Professor Duan explained the core of his findings to Nanowerk: "Our ab initio study reveals that the conductance of TDWCNTs is mainly dependent upon the coupling effect of delocalized electronic states between two shells. Based on the change of the delocalized frontier molecular orbitals, an intershell electron transport mechanism i.e., resonant tunneling at the delocalized quantized energy levels is proposed to explain the "on/off" phenomenon in TDWCNTs with different overlapping lengths."
"Intershell electronic transport in TMWNTs is similar to electronic transport through molecules from the view that both of them occur in the finite region" Duan says. "Thus it is very interesting to investigate the electron transport mechanism and characteristics in TMWNTs for future applications in nanoelectronic switches just like molecules."
Duan explains how in the tunneling model of nanotube junction, the electrons could hop from the outmost shell to the inner shell by two different ways: "1) by any position in the bodies of outmost and inner tubes; and 2) by the open ends of outmost and inner tubes, separately. To better design the potential electronic switch, it is important to make clear the effects of electronic states of different parts i.e., the open end and tube body of telescoping tubes on intershell electron transport in the telescoping procedure."
The researchers found that the transport property of telescoping system is mainly determined by the overlapping length while less affected by the rotation effect, and further confirms that the experimental realization of this switch is feasible and stable under nonperfect alignment conditions. The ideal nanoelectronic switch by TDWCNTs therefore could be switched from one state to the other by the relative motion of tubes along the tube axis.