Single-walled carbon nanotubes (SWNTs) are promising building blocks for nano-electromechanical systems because they have a low mass, are easily scalable through their length and have a high Young’s modulus of 1.25 TPa, which is almost an order of magnitude higher than that of silicon. At room temperature, we have used a suspended, semiconducting carbon nanotube as a frequency mixer to detect its own mechanical motion. In the range of 200 MHz, a single gate-dependent resonance is observed, which we attribute to the bending mode vibration of suspended carbon nanotubes [1]. A continuum model [2] describes the gate-dependence of the resonance frequency very well and the analysis shows that the nanotube can be tuned from a regime without strain to a regime where it behaves as a vibrating string under tension. At low temperatures, the suspended nanotubes act as quantum dots. Vibrational modes then become visible as harmonic excitation spectra in single-electron tunneling. Phonon-assisted tunneling mediated by (long-wavelength) longitudinal vibration modes has been observed [3] and comparison with a Franck-Condon model indicates a rather strong electron-phonon coupling factor of order unity. Issues that are currently investigated include mechanisms for electron-vibron coupling, mechanical relaxation, mechanical modes in higher-order tunneling and “distortion blockade of current” in ultra-short (< 100 nm) nanotube segments.

[1] B. Witkamp, M. Poot and H.S.J. van der Zant, Nano Lett. 6 (2006) 2904.

[2] S. Sapmaz, Ya. M. Blanter, L. Gurevich, and H.S.J. van der Zant, Phys. Rev. B. 67 (2003) 235414.

[3] S. Sapmaz, P. Jarillo-Herrero, Ya. M. Blanter, C. Dekker and H.S.J. van der Zant, Phys. Rev. Lett. 96 (2006) 026801.

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1. Vibrational modes in suspended carbon nanotubes probed by transport measurements