51 research outputs found
Frequency modulated self-oscillation and phase inertia in a synchronized nanowire mechanical resonator
Synchronization has been reported for a wide range of self-oscillating
systems. However, even though it has been predicted theoretically for several
decades, the experimental realization of phase self-oscillation, sometimes
called phase trapping, in the high driving regime has been studied only
recently. We explored in detail the phase dynamics in a synchronized field
emission SiC nanoelectromechanical system with intrinsic feedback. A richer
variety of phase behavior has been unambiguously identified, implying phase
modulation and inertia. This synchronization regime is expected to have
implications for the comprehension of the dynamics of interacting
self-oscillating networks and for the generation of frequency modulated signals
at the nanoscal
Role of fluctuations and nonlinearities on field emission nanomechanical self-oscillators
A theoretical and experimental description of the threshold, amplitude, and
stability of a self-oscillating nanowire in a field emission configuration is
presented. Two thresholds for the onset of self-oscillation are identified, one
induced by fluctuations of the electromagnetic environment and a second
revealed by these fluctuations by measuring the probability density function of
the current. The ac and dc components of the current and the phase stability
are quantified. An ac to dc ratio above 100% and an Allan deviation of 1.3x10-5
at room temperature can be attained. Finally, it is shown that a simple
nonlinear model cannot describe the equilibrium effective potential in the
self-oscillating regime due to the high amplitude of oscillations
Protective Alumina Coatings by Low Temperature Metalorganic Chemical Vapour Deposition
Alumina thin films were processed from aluminium tri-iso-propoxide in a horizontal, with N2 as a carrier gas, occasional addition of water in the gas phase, deposition temperature in the range 350-700°C, total pressure 0.67 kPa (2 kPa when water was used). The films do not diffract X-ray when prepared below 700°C. At 700°C, they start to crystallize as γ-alumina. EDS, EPMA, ERDA, RBS, FTIR and TGA revealed that films prepared in the range 350-
415°C, without water in the gas phase, have an overall composition Al2O3-x(OH)2x, with x tending to 0 with increasing temperature. Al2O3 is obtained above 415°C. When water is added in the vapour phase, the film composition is Al2O3, even below 415°C. Coatings deposited in these conditions show promising protection properties
Simple modeling of self-oscillation in Nano-electro-mechanical systems
We present here a simple analytical model for self-oscillations in
nano-electro-mechanical systems. We show that a field emission self-oscillator
can be described by a lumped electrical circuit and that this approach is
generalizable to other electromechanical oscillator devices. The analytical
model is supported by dynamical simulations where the electrostatic parameters
are obtained by finite element computations.Comment: accepted in AP
Self-oscillations in field emission nanowire mechanical resonators: a nanometric DC-AC conversion
We report the observation of self-oscillations in a bottom-up
nanoelectromechanical system (NEMS) during field emission driven by a constant
applied voltage. An electromechanical model is explored that explains the
phenomenon and that can be directly used to develop integrated devices. In this
first study we have already achieved ~50% DC/AC (direct to alternative current)
conversion. Electrical self-oscillations in NEMS open up a new path for the
development of high speed, autonomous nanoresonators, and signal generators and
show that field emission (FE) is a powerful tool for building new
nano-components
Sensing and cooling of a nanomechanical resonator with an electron beam stimulated internal feedback and a capacitive force
A model for the cooling properties of a nanocantilever by a free electron
beam is presented for a capacitive interaction. The optimal parameters for
position sensing and cooling applications are estimated from previous
experimental conditions. In particular , we demonstrate that a purely
capacitive force and an electron beam stimulated internal feedback can lower
the temperature of a nanocantilever by several orders of magnitude in striking
contrast with the conventional electrostatic damping regime. We propose a step
by step protocol to extract the interdependent parameters of the experiments.
This work will aid future developments of ultra sensitive force sensors in
electron microscopes
Performance of field-emitting resonating carbon nanotubes as radio-frequency demodulators
International audienceWe report on a systematic study of the use of resonating nanotubes in a field emission (FE) configuration to demodulate radio frequency signals. We particularly concentrate on how the demodulation depends on the variation of the field amplification factor during resonance. Analytical formulas describing the demodulation are derived as functions of the system parameters. Experiments using AM and FM demodulations in a transmission electron microscope are also presented with a determination of all the pertinent experimental parameters. Finally we discuss the use of CNTs undergoing FE as nanoantennae and the different geometries that could be used for optimization and implementation. © 2011 American Physical Society
Ultra Low Power Consumption for Self-Oscillating Nanoelectromechanical Systems Constructed by Contacting Two Nanowires
International audienceWe report here the observation of a new self-oscillation mechanism in nanoelectromechanical systems (NEMS). A highly resistive nanowire was positioned to form a point-contact at a chosen vibration node of a silicon carbide nanowire resonator. Spontaneous and robust mechanical oscillations arise when a sufficient DC voltage is applied between the two nanowires. An original model predicting the threshold voltage is used to estimate the piezoresistivity of the point-contact in agreement with the observations. The measured input power is in the pW-range which is the lowest reported value for such systems. The simplicity of the contacting procedure and the low power consumption open a new route for integrable and low-loss self-excited NEMS devices
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