S. Perisanu

High Q factor for mechanical resonances of batch-fabricated SiC nanowires

The authors present here the measurements of high mechanical Q factors for singly clamped, batch-fabricated SiC nanowires measured by field emission (FE) in ultrahigh vacuum. The resonances of two nanowires, glued to the ends of tungsten support tips, were electrostatically excited and detected by the variation in the FE microscopy (FEM) images. Low amplitude oscillations were measured by numerical analysis of the FEM image blurring during frequency scans through the resonances. This avoided the artificial broadening of the resonances by nonlinear effects. A room temperature Q factor of 159 000 was achieved after high temperature in situ cleaning.

Evidence for Poole-Frenkel conduction in individual SiC nanowires by field emission transport measurements

In this paper we examine carrier transport mechanisms in individual Silicon Carbide nanowires (NWs) by an original use of field emission (FE). Total energy distributions were measured as a function of temperature and extraction voltage allowing us to determine the voltage drops along the NWs and thus the temperature-dependent current-voltage (I-V-T) characteristics. The measurements were analyzed using different transport mechanisms of which only the Poole–Frenkel model gives an excellent fit. The dielectric constant was estimated for several samples at ɛ~10 in excellent agreement with the bulk value. The characteristic trap energies, Ea, were determined from the I-V-T data to be ∼0.3 eV. In general this work shows how FE can be used for transport measurements on individual semiconducting NWs.

Effect of non-ideal clamping shape on the resonance frequencies of silicon nanocantilevers

In this paper, we investigate the effects of non-ideal clamping shapes on the dynamic behavior of silicon nanocantilevers. We fabricated silicon nanocantilevers using silicon on insulator (SOI) wafers by employing stepper ultraviolet (UV) lithography, which permits a resolution of under 100 nm. The nanocantilevers were driven by electrostatic force inside a scanning electron microscope (SEM). Both lateral and out-of-plane resonance frequencies were visually detected with the SEM. Next, we discuss overhanging of the cantilever support and curvature at the clamping point in the silicon nanocantilevers, which generally arises in the fabrication process. We found that the fundamental out-of-plane frequency of a realistically clamped cantilever is always lower than that for a perfectly clamped cantilever, and depends on the cantilever width and the geometry of the clamping point structure. Using simulation with the finite-elements method, we demonstrate that this discrepancy is attributed to the particular geometry of the clamping point (non-zero joining curvatures and a flexible overhanging) that is obtained in the fabrication process. The influence of the material orthotropy is also investigated and is shown to be negligible.

Simple modeling of self-oscillations in nanoelectromechanical systems

We present here a simple analytical model for self-oscillations in nanoelectromechanical 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.

Ultra Low Power Consumption for Self-Oscillating Nanoelectromechanical Systems Constructed by Contacting Two Nanowires

We 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.

The mechanical resonances of electrostatically coupled nanocantilevers

We present here an experimental study of the electrostatic coupling between the mechanical resonances of two nanowires or two nanotubes. This coupling occurs when the eigenfrequencies of the two resonators are matched by electrostatic tuning and it changes from a weak coupling to a strong coupling regime as the distance between the cantilevers is decreased. Linear coupling theory is shown to be in excellent agreement with the experimental data.

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 nanoscale.

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

Quality-Factor Enhancement of Nanoelectromechanical Systems by Capacitive Driving Beyond Resonance

1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}

Fabrication and characterization of 100-nm wide silicon nanocantilevers using top-down approach

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.