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Electromechanical Resonance Behavior Of Suspended Single Walled Carbon Nanotubes Under High Bias Voltages Daniel C. Ralph, Cornell University, ECCS 0335765.

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Electromechanical Resonance Behavior Of Suspended Single Walled Carbon Nanotubes Under High Bias VoltagesDaniel C. Ralph, Cornell University, ECCS 0335765

The fundamental electrical and electro-mechanical properties of carbon nanotubes (CNTs) continue to expose interesting underlying physics. In this work, we characterize the nanoelectromechanical response of suspended individual CNTsunder high voltage biases. An abrupt upshift in the mechanical resonance frequency of approximately 3 MHz is observed at high bias. While several possible mechanisms are discussed, this upshift is attributed to the onset of optical phonon emission, which results in a sudden contraction of the nanotube due to its negative thermal expansion coefficient. This, in turn, causes an increase in the tension in the suspended CNT, which upshifts its mechanical resonance frequency. This upshift is consistent with Raman spectral measurements, which show a sudden downshift of the optical phonon modes at high bias voltages. Using a simple model for oscillations on a string, we estimate the effective change in the length of the nanotube to be ΔL/L ≈ −2 × 10−5 at a bias voltage of 1 V

SEM images of a suspended CNT sample device. The right panel shows a high resolution SEM image of an individual CNT

Aykol, et. al. Cronin Group,

University of Southern California

Partial work performed at UCSB Nano Facility

Bias voltage dependence of the mechanical resonance frequency of two different suspended CNTs. (a) Data taken on different days at a constant gate voltage of VG = −3 V, demonstrating the repeatability of the observed effect. The inset in (a) shows the I–V characteristics of this device, which exhibit metallic behavior. The red solid lines represent the I–VbiasAnd conductance–Vgate characteristics of the device.

This research was supported in part by (ONR) Award No. N000141010511, (DOE) Award No. DE-FG02- 07ER46376, and (NSF) Award No. CBET-0854118.

J. Micromech. Microeng.21085008 (2011)