Carbon nanotube resonance frequencies

Can be tuned by a factor of 10 in a field-emission microscope (FEM). A group of physicists at the University of Lyon, France, grew several multiwall nanotubes (MWNT) on a nickel support tip, then placed the tip in an FEM. With a static voltage applied between the nanotubes and a counter electrode, electrons sprayed out of the MWNTs onto a detection screen. Each MWNT has natural resonant frequencies at which it oscillates with large amplitudes. The vibration is excited by applying an additional sinusoidal voltage of the correct frequency to one of the electrodes. By varying the applied voltage and watching the screen, the researchers not only measured the natural resonances for several MWNTs—permitting a measure of the MWNT stiffness—but also found that the voltage effectively “pulls” on the nanotube, tuning it much like increasing the tension on a guitar string. According to group member Stephen Purcell, carefully excited and tuned MWNTs may act as a core element for future nanometric oscillator circuits, nanobalances, or nanoforce sensors. For more on carbon nanotubes, see articles in Physics Today by Thomas Ebbesen (June 1996, page 26 ) and by Cees Dekker (May 1999, page 22 . (S. T. Purcell et al., Phys. Rev. Lett. 89, 276103, 2002 http://dx.doi.org/10.1103/PhysRevLett.89.276103 ).