Sep 30, 2009

The motion of nanotubes is ultra-sensitive to electrons passing through them

A research team from Centro de Investigación en Nanotecnología y Nanociencia, CIN2 (CSIC-ICN), in Barcelona, has shown that the oscillating motion of a suspended nanotube can be controlled in an unprecedented manner. The results are published in the last issue of Science. The authors are B. Lassagne, D. García Sanchez, and A. Bachtold, who is the team leader of the Quantum Nanoelectronics Group at CIN2 (CSIC-ICN). They worked in collaboration with Y. Tarakanov and J. Kinaret from Sweden.

The device is based on a carbon nanotube that is suspended and clamped at the extremities to two gold pieces. The nanotube acts as guitar string: It oscillates at specific frequencies. Besides, the nanotube also acts as a transistor. That is, electrons flow through the nanotube from one gold piece to the other one. The finding in the work of Barcelona is that the mechanical motion and the electrons are highly coupled.

This coupling is very useful to harness the oscillating motion of the nanotube. The displacement can be as low as 10 pm (10 ^-11 m) so it is very difficult to detect and to control. In contrast to mechanical oscillators made of other materials, the dynamical motion of nanotubes can be widely tuned by an external electric means, which is very convenient for practical use. Specifically, the resonance frequency, the quality factor and the nonlinear dynamic of the motion can be modified by a large amount by sweeping a voltage on a nearby gate. For this, the nanotube has been cooled down to -270 Celsius. Electron transport enters a regime where electrons flow one by one through the nanotube. Each time that an electron jumps onto the nanotube, it gives a kink to the nanotube and displaces it.

The coupling between the mechanics and the electron transport is much stronger than in previously studied mechanical oscillators made of other materials. This difference arises from the much greater mass of these resonators compared with SWNTs, so they are much less sensitive to the motion of individual electrons. The finding offers new opportunities for various scientific and technological applications. Nanotube oscillators are ultrasensitive detectors of mass. The mass sensitivity is likely to be further improved by using these new results.

+ PRESS RELEASE + Press reference: La Vanguardia