(a) Schematics of the resonance frequency measurement of the suspended nanotube resonator. A constant current was passed through the nanotube, while the actuation frequency applied at the substrate was swept from 10 kHz to 50 MHz. The resistance change during the frequency sweep was calculated from the voltage drop across the two contact electrodes bridged by the nanotube. (b) A plot of time-averaged normalized resistance of a typical suspended nanotube device as a function of the actuation frequency. A constant current of 20 nA was passed through the nanotube, while an AC signal with an RMS amplitude of 1 V was applied at the substrate with a DC offset of 10 V.