[Show abstract][Hide abstract]ABSTRACT: Field electron emission from the edges of large-area (∼1. cm. ×. 1. cm) graphene films deposited onto quartz wafers was studied. The graphene was previously grown by chemical vapour deposition on copper. An extreme enhancement of electrostatic field at the edge of the films with macroscopically large lateral dimensions and with single atom thickness was achieved. This resulted in the creation of a blade type electron emitter, providing stable field emission at low-voltage with linear current density up to 0.5. mA/cm. A strong hysteresis in current-voltage characteristics and a step-like increase of the emission current during voltage ramp up were observed. These effects were explained by the local mechanical peeling of the graphene edge from the quartz substrate by the ponderomotive force during the field emission process. Specific field emission phenomena exhibited in the experimental study are explained by a unique combination of structural, electronic and mechanical properties of graphene. Various potential applications ranging from linear electron beam sources to microelectromechanical systems are discussed.
[Show abstract][Hide abstract]ABSTRACT: We demonstrate field evaporation of insulating materials, specifically BN nanotubes and undoped Si nanowires, assisted by a convergent electron beam.
Electron irradiation leads to positive charging at the nano-object's apex and to an important increase of the local electric field thus inducing field evaporation. Experiments performed both in a transmission electron microscope and in a scanning electron microscope are presented. This technique permits the selective evaporation of individual nanowires in complex materials. Electron assisted field evaporation could be an interesting alternative or complementary to laser induced field desorption used in atom probe tomography of insulating materials.
Full-text · Article · May 2015 · Applied Physics Letters
[Show abstract][Hide abstract]ABSTRACT: 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.
Full-text · Article · Aug 2014 · New Journal of Physics
[Show abstract][Hide abstract]ABSTRACT: We report ultra-low threshold optically induced self-oscillations of a ultra-low dissipation nanowire. We interpret the asymmetrically observed responses as a signature of the laser shot noise drive, consistent with our system’s parameters
[Show abstract][Hide abstract]ABSTRACT: We present here well-defined Coulomb staircases using an original field-emission experiment on several individual in situ-grown single-wall carbon nanotubes. A unique in situ process was applied nine times to progressively shorten one single-wall carbon nanotube down to ≃10 nm, which increased the oscillations periods from 5.5 to 80 V, the temperature for observable Coulomb staircase to 1100 K and the currents to 1.8 μA. This process led to the brightest electron source ever reported [9×1011 A/(str m2 V)].
Full-text · Article · Mar 2014 · Physical Review Letters
[Show abstract][Hide abstract]ABSTRACT: 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.
[Show abstract][Hide abstract]ABSTRACT: We report here the first realization of top-down silicon nanowires (SiNW) transduced by both junction-less field-effect transistor (FET) and the piezoresistive (PZR) effect. The suspended SiNWs are among the smallest top-down SiNWs reported to date, featuring widths down to ∼20 nm. This has been achieved thanks to a 200 mm-wafer-scale, VLSI process fully amenable to monolithic CMOS co-integration. Thanks to the very small dimensions, the conductance of the silicon nanowire can be controlled by a nearby electrostatic gate. Both the junction-less FET and the previously demonstrated PZR transduction have been performed with the same SiNW. These self-transducing schemes have shown similar signal-to-background ratios, and the PZR transduction has exhibited a relatively higher output signal. Allan deviation (σA) of the same SiNW has been measured with both schemes, and we obtain σA ∼ 20 ppm for the FET detection and σA ∼ 3 ppm for the PZR detection at room temperature and low pressure. Orders of magnitude improvements are expected from tighter electrostatic control via changes in geometry and doping level, as well as from CMOS integration. The compact, simple topology of these elementary SiNW resonators opens up new paths towards ultra-dense arrays for gas and mass sensing, time keeping or logic switching systems on the SiNW-CMOS platform.
[Show abstract][Hide abstract]ABSTRACT: 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.
[Show abstract][Hide abstract]ABSTRACT: New models of fluid transport are expected to emerge from the confinement of liquids at the nanoscale, with potential applications in ultrafiltration, desalination and energy conversion. Nevertheless, advancing our fundamental understanding of fluid transport on the smallest scales requires mass and ion dynamics to be ultimately characterized across an individual channel to avoid averaging over many pores. A major challenge for nanofluidics thus lies in building distinct and well-controlled nanochannels, amenable to the systematic exploration of their properties. Here we describe the fabrication and use of a hierarchical nanofluidic device made of a boron nitride nanotube that pierces an ultrathin membrane and connects two fluid reservoirs. Such a transmembrane geometry allows the detailed study of fluidic transport through a single nanotube under diverse forces, including electric fields, pressure drops and chemical gradients. Using this device, we discover very large, osmotically induced electric currents generated by salinity gradients, exceeding by two orders of magnitude their pressure-driven counterpart. We show that this result originates in the anomalously high surface charge carried by the nanotube's internal surface in water at large pH, which we independently quantify in conductance measurements. The nano-assembly route using nanostructures as building blocks opens the way to studying fluid, ionic and molecule transport on the nanoscale, and may lead to biomimetic functionalities. Our results furthermore suggest that boron nitride nanotubes could be used as membranes for osmotic power harvesting under salinity gradients.
[Show abstract][Hide abstract]ABSTRACT: We present in this paper a study on highly resistive SiC nanowires in a singly clamped geometry. We demonstrate that these field emission nanoelectromechanical systems (NEMS) can be synchronized ton an external AC signal and act as an amplifier.
[Show abstract][Hide abstract]ABSTRACT: This paper explores the field emission (FE) properties of highly crystalline Si nanowires (NWs) with controlled surface passivation. The NWs were batch-grown by the vapor-liquid-solid process using Au catalysts with no intentional doping. The FE current-voltage characteristics showed quasi-ideal current saturation that resembles those predicted by the basic theory for emission from semiconductors, even at room temperature. In the saturation region, the currents were extremely sensitive to temperature and also increased linearly with voltage drop along the nanowire. The latter permits the estimation of the doping concentration and the carrier lifetime, which is limited by surface recombination. The conductivity could be tuned over 2 orders of magnitude by in situ hydrogen passivation/desorption cycles. This work highlights the role of dangling bonds in surface leakage currents and demonstrates the use of hydrogen passivation for optimizing the FE characteristics of Si NWs.
[Show abstract][Hide abstract]ABSTRACT: Silicon Nanowires (SiNWs) are being studied for a wide variety of applications in nanoscience with significant progress in their integration into devices such as transistors, solar cells, photodectors, chemical sensors, etc.. However there has been much less work on field emission (FE) even though their semiconducting properties open distinct possibilities compared to metallic emitters and carbon nanotubes. The few measurements in the literature for SiNW arrays have only shown linear Fowler-Nordheim (FN) behavior as for metallic emitters. In addition to strong current saturation in FE due to the band-gap, their properties could be strongly influenced by surface states because of their large surface-to-volume ratio. As a consequence, there is a clear need for in-depth FE studies of individual NWs in order to understand surface effects and optimize FE characteristics.
[Show abstract][Hide abstract]ABSTRACT: This article presents a study of the poorly understood "shear-force" used in an important class of near-field instruments that use mechanical resonance feedback detection. In the case of a metallic probe near a metallic surface in vacuum, we show that in the 10-60 nm range there is no such a thing as a shear-force in the sense of the nonconservative friction force. Fluctuations of the oscillator resonance frequency, likely induced by local charge variations, could account for the reported effects in the literature without introducing a dissipative force.
[Show abstract][Hide abstract]ABSTRACT: In this article, we explore and compare two distinct configurations of the "nanoradio" concept where individual carbon nanotube resonators are the central electromechanical element permitting signal demodulation. The two configurations of singly-clamped field emitters and doubly-clamped field effect transistors are examined which at first glance are quite different, but in fact involve quite similar physical concepts. Amplitude, frequency and digital demodulation are demonstrated and the analytical formulae describing the demodulation are derived as functions of the system parameters. The crucial role played by the mechanical resonance in demodulation is clearly demonstrated. For the field emission configuration we particularly concentrate on how the demodulation depends on the variation of the field amplification factor during resonance and show that amplitude demodulation results in the best transmitted signal. For the transistor configuration the important aspect is the variation of the nanotube conductance as a function of its distance to the gate. In this case frequency demodulation is much more effective and digital signal processing was achieved. The respective strengths and weaknesses of each configuration are discussed throughout the article.
No preview · Article · Jun 2012 · Comptes Rendus Physique
[Show abstract][Hide abstract]ABSTRACT: High frequency Silicon NanoWire Resonators (SNWR) have been fabricated and their performances for time reference applications have been assessed. The SNWR have been designed to operate at different frequencies going from 55 MHz up to 300 MHz with quality factors higher than 2000 at room temperature under high vacuum. The measured temperature coefficient of frequency (TCF) for different SNWR is about 40 ppm over a range of temperature going from 4 K to 300 K. The evolution of the quality factor as function of temperature has also been measured as well as the Allan deviation for different nanowire lengths.
[Show abstract][Hide abstract]ABSTRACT: We study the contribution of ohmic dissipation to the mechanical damping of nanoresonators. This damping occurs when DC voltage is applied to a resistive resonator, because the mechanical motion modifies the associated capacitance, thus inducing a dissipative current. Silicon carbide nanowire resonators were studied as a function of applied voltage and their geometrical environment. Nanometric positioners were used to control and continuously modify the position of the resonator with respect to counter electrodes. The experimental results are shown to be in agreement with an electromechanical model developed here, which allows for the establishment of a universal formula for the lower dissipation limit of a nanoresonator in its capacitive environment.
No preview · Article · Feb 2012 · Physical review. B, Condensed matter
[Show abstract][Hide abstract]ABSTRACT: This paper deals with an electromechanical model for silicon nanowires with an electrostatic actuation and piezoresistive detection. The model, based on electrical /mechanical equivalencies, is built of elementary electrical equivalent circuit blocks that are constructed as voltage controlled current sources. It takes into account the various electromechanical forces applied on the nanowire to compute its displacement which leads to a change in its resistance (piezoresistive effect). As the model is built of current sources, it can be implemented in commercial circuit simulation softwares in order to predict the dynamic behaviour of nanowires and the current level at the output. The model has been validated by measurements on high frequency resonating silicon nanowires.
[Show abstract][Hide abstract]ABSTRACT: The authors present studies on the field emission (FE) mechanism and the FE-induced transformation of individual anatase TiO2 nanowires (NWs). The NWs were synthesized by electrospinning followed by calcination at 500 °C which produces polycrystalline anatase nanofibers as determined by Raman spectroscopy and transmission electron microscopy (TEM) characterization. Nanowires of ∼100 nm in diameter were individually mounted at the apexes of tungsten tips for further physical characterization. The FE experiments were carried out in a TEM which allows the measurement of the FE current while simultaneously observing structural modifications leading to the NW’s destruction. For low currents (below 100 nA), we observe reproducible FE Fowler-Nordheim I/V characteristics. Higher currents (up to 1 μA) can be obtained but sudden destruction of the NW may take place. Our observations show that a thermally-activated transition occurs and leads to rapid re-crystallization phenomena and a variation of the FE characteristics. If not controlled, this transition leads to thermal runaway and sample destruction. The understanding of the destruction phenomena is a key parameter to further improve the FE performance of such nanowire cathodes.
Full-text · Article · Jan 2012 · Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures
[Show abstract][Hide abstract]ABSTRACT: The fabrication and the electromechanical characterization of top-down silicon nanowire resonators for sensing applications are presented. To date, these are the smallest nanowires reported that can take advantage of compatibility with CMOS fabrication and co-integration. The nanowires are actuated through the electrostatic force and the resonances are transduced by the piezoresistive effect of second order. Their electromechanical characterization is performed with the FM demodulation technique, which has allowed the detection of resonances at frequencies as high as 94.7 MHz. In the future, silicon nanowires could serve as mass sensors with sensitivities as low as 1zg/root Hz. (C) 2011 Published by Elsevier Ltd.
No preview · Article · Dec 2011 · Procedia Engineering