Negative frequency tuning of a carbon nanotube nano-electromechanical resonator under tension (Phys. Status Solidi B 12/2013)

Abstract

On the back cover, a single wall carbon nanotube is displayed (thin black line in the sketch) that is grown across a trench and contact electrodes (green), cooled to milli-Kelvin temperatures, and then characterized in electronic transport measurements. A quantum dot forms within the suspended segment at these temperatures. The typical Coulomb “diamond” pattern of differential conductance displays distinct signatures of electromechanical feedback and self-excitation (background measurement, yellow arrows). Using a radio-frequency cw source, driven mechanical resonances of the nanotube can be detected in dc transport - as exemplified by the red line, a measurement of time-averaged dc current as a function of the driving frequency. Stiller et al. (pp. 2518–2522) find higher harmonic resonances at integer multiples of the fundamental frequency, indicating that the nanotube is a string under tension. Applying a finite gate voltage to the highly doped chip substrate (light blue), the mechanical resonance strongly shifts to lower frequencies. This can be explained by electrostatic softening of the vibration mode.