Tunable Nanoresonators Constructed from Telescoping Nanotubes

We have created a tunable mechanical nanoscale resonator with potential applications in precise mass, force, position, and frequency measurement. The device consists of a specially prepared multiwalled carbon nanotube (MWNT) suspended between a metal electrode and a mobile, piezo-controlled contact. By exploiting the unique telescoping ability of MWNTs, we controllably slide an inner nanotube core from its outer nanotube casing, effectively changing its length and tuning its flexural resonance frequency.

Figure 1

(a) Schematic drawing of our tunable resonator. A specially prepared MWNT is suspended between a stationary contact and mobile, piezo-controlled electrode. Varying the length of the nanotube beam through the controlled telescoping of the inner nanotube core from the outer nanotube shell tunes its resonant frequency. Operating the device in an external magnetic field, B, allows actuation with alternating current via the Lorentz force. (b) TEM micrographs show the device in action. The dark region on the right is the mobile contact, while the stationary clamp is more than 200 nm off the image to the left (the bulge pictured at the left of the image is actually the beginning of a MWNT bundle). The top two images show the nanotube at one extension off resonance (sharp) and on resonance (blurred) with a resonant frequency $f=225.0\mathrm{MHz}$. The bottom two images show an extended nanotube with a lowered resonant frequency (192.7 MHz).

Figure 2

Tuning curves for four nanoresonator devices. A theoretical model provides a good fit to the data and yields reasonable values for the effective Young’s modulus of each device. The inset shows a typical resonance peak with a Lorentzian fit.

Figure 3

Dissipation as a function of nanotube beam length for one device. A linear regression indicating a significant positive correlation provides evidence for length-dependent dissipation.