Electromechanical Instability in Suspended Carbon Nanotubes (original) (raw)
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New Journal of Physics, 2010
We have theoretically investigated the electromechanical properties of a freely suspended carbon nanotube that is connected to a constant-current source and subjected to an external magnetic field. We show that self-excitation of mechanical vibrations of the nanotube can occur if the magnetic field H exceeds a dissipation-dependent critical value Hc, which we find to be of the order of 10-100 mT for realistic parameters. The instability develops into a stationary regime characterized by time periodic oscillations in the fundamental bending mode amplitude. We find that for nanotubes with large quality factors and a magnetic-field strength just above Hc the frequency of the stationary vibrations is very close to the eigenfrequency of the fundamental mode. We also demonstrate that the magnetic field dependence of the time averaged voltage drop across the nanotube has a singularity at H = Hc. We discuss the possibility of using this phenomenon for the detection of nanotube vibrations.
Signatures of the Current Blockade Instability in Suspended Carbon Nanotubes
2015
Transport measurements allow sensitive detection of nanomechanical motion of suspended carbon nanotubes. It has been predicted that when the electro-mechanical coupling is sufficiently large a bistability with a current blockade appears. Unambiguous observation of this transition by current measurements may be difficult. Instead, we investigate the mechanical response of the system, namely the displacement spectral function; the linear response to a driving; and the ring-down behavior. We find that by increasing the electro-mechanical coupling the peak in the spectral function broadens and shifts at low frequencies while the oscillator dephasing time shortens. These effects are maximum at the transition where non-linearities dominate the dynamics. These strong signatures open the way to detect the blockade transition in devices currently studied by several groups.
Journal of Micromechanics and Microengineering, 2011
We characterize the nanoelectromechanical response of suspended individual carbon nanotubes under 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 nanotube, 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 L/L ≈ −2 × 10 −5 at a bias voltage of 1 V.
Magnetic effects on nonlinear mechanical properties of a suspended carbon nanotube
We propose a microscopic model for a nanoelectromechanical system made by a radio-frequency driven suspended carbon nanotube (CNT) in the presence of an external magnetic field perpendicular to the current. As a main result, we show that, when the device is driven far from equilibrium, one can tune the CNT mechanical properties by varying the external magnetic field. Indeed, the magnetic field affects the CNT bending mode dynamics inducing an enhanced damping as well as a noise term due to the electronic phase fluctuations. The quality factor, as observed experimentally, exhibits a quadratic dependence on external magnetic field strength. Finally, CNT resonance frequencies as a function of gate voltage acquire, increasing the magnetic field strength, a peculiar dip-peak structure that should be experimentally observed. arXiv:1212.0267v3 [cond-mat.mes-hall]
Applied Physics Letters, 2002
A synthetic strategy is devised for reliable integration of long suspended single-walled carbon nanotubes into electrically addressable devices. The method involves patterned growth of nanotubes to bridge predefined molybdenum electrodes, and is versatile in yielding various microstructures comprised of suspended nanotubes that are electrically wired up. The approach affords single-walled nanotube devices without any postgrowth processing, and will find applications in scalable nanotube transistors ͑mobility up to 10 000 cm 2 /V s͒ and nanoelectromechanical systems based on nanowires.
Journal of Applied Physics
With continuous downscaling of resonators, clamping is expected to significantly impact the mechanical stability as well as the energy dissipation mechanisms, especially at the nanoscale. To understand the clamping effects at the nanoscale, we here report on an experimental investigation of a same nanotube based resonator subjected to two different clamping configurations. We investigate clamping associated stability and damping mechanisms by pushing the resonator into the nonlinear regime. The nanotube was first dry-transferred and suspended between source-drain palladium electrodes resulting in a bottom clamped configuration. A selective top-metallization process by platinum atomic layer deposition applied later resulted in a top-bottom clamped configuration. Large nanotube motional amplitude leading to a nonlinear Duffing response initiated small slippage of the nanotube. This instability in clamping was seen in both clamping configurations and was measured as an irreversible resonance frequency downshift. For the measured resonator devices, a gate induced nanotube tension in the range of 58-71 pN was estimated to overcome clamping forces and initiate slipping. In terms of energy dissipation, the topmetallization process was accompanied by a reduction in amplitude dependent nonlinear damping and Q-factor enhancement. Subjecting the same nanotube to both clamping configurations allowed for a direct comparison of clamping and quantification of nonlinear damping. In the present case, nonlinear damping was observed at an estimated nanotube motional amplitude of 11 nm (and higher), being dominant in bottom clamped configuration, suggesting the origin of this nonlinear damping to partially stem from external mechanisms in addition to other possible internal dissipation paths reported such as viscoelastic effects.