[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.
[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)].
[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: 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.
[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.
Electromagnetics in Advanced Applications (ICEAA), 2012 International Conference on; 01/2012
[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: 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.
Frequency Control Symposium (FCS), 2012 IEEE International; 01/2012
[Show abstract][Hide abstract] ABSTRACT: We have recently shown that individual single wall carbon nanotubes (CNTs) can be grown on metallic tips in a field emission microscope (FEM) on which carbon passivation layers and Ni catalysts have been pre-deposited in situ (see Fig. 1). This allows direct observation from the nucleation stage until the end of the growth . In this talk I will review this unique synthesis method and our more recent progress, and discuss the comportment of the as-grown CNTs as field emission sources and nano-mechanical oscillators.
[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: Measurements of the gauge factor of suspended, top-down silicon nanowires are presented. The nanowires are fabricated with a CMOS compatible process and with doping concentrations ranging from 2 × 10(20) down to 5 × 10(17) cm(-3). The extracted gauge factors are compared with results on identical non-suspended nanowires and with state-of-the-art results. An increase of the gauge factor after suspension is demonstrated. For the low doped nanowires a value of 235 is measured. Particular attention was paid throughout the experiments to distinguishing real resistance change due to strain modulation from resistance fluctuations due to charge trapping. Furthermore, a numerical model correlating surface charge density with the gauge factor is presented. Comparison of the simulations with experimental measurements shows the validity of this approach. These results contribute to a deeper understanding of the piezoresistive effect in Si nanowires.
[Show abstract][Hide abstract] ABSTRACT: A simple technique is explored to determine the temporal photo-response, Τ, of individual semiconducting SiC and Si nanowires (NWs), with a high time resolution. Laser-assisted field emission (LAFE) from the NWs is first shown to be highly sensitive to continuous laser illumination. Pulsed illumination is then combined with measurements of the total energy distributions to determine Τ which were rather large, 4–200 μs. The time response scaled roughly with the square of the NWs length and could be attributed to laser-induced heating. LAFE is thus a new tool for quantifying rapid thermo-optical effects in such nano-objects.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: We 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.
[Show abstract][Hide abstract] ABSTRACT: 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. (C) 2011 American Institute of Physics. [doi:10.1063/1.3553779]
[Show abstract][Hide abstract] ABSTRACT: We simulate the nonlinear behaviour of a cantilevered nanowire in field emis-sion to understand and exploit the self-oscillations experimentally observed in this NanoElectroMechanical System. The original coupling taking place in this oscillator is predicted with a low-dimensional model consisting of a bi-articulated cantilevered beam flowing electrons and immersed in an elec-trostatic environment. We propose a simple model to set up the qualitative nonlinear governing equations of the system and also highlight the elaborate equilibrium between the electrostatic field, the nanowire motion and the elec-tric field emission current. A linear stability analysis of the nonlinear static fixed points aims at determining the instability threshold as a function of the applied DC voltage. It is found that instability is mostly due to the competi-tion between the field emission current dependence on the nanowire position and the voltage. As a consequence, the emergence of flutter requires specific external conditions such as an initial angular imperfection, a strong mechani-cal Q factor or a high electrical resistance. Finally, a direct integration of the nonlinear governing equations confirms the presence of high-frequency self-oscillations, i.e. the possibility of DC/AC conversion in this autonomous electromechanical device.
International Journal of Mechanical Sciences 11/2010; 52(11). DOI:10.1016/j.ijmecsci.2010.01.011 · 2.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We explore here the use of field evaporation in a transmission electron microscope for controlled apex modification, opening, and shortening of various types of individual nanotubes and nanowires. The technique works well for conducting carbon nanotubes but also for large bandgap silicon carbide nanowires and insulating boron nitride nanotubes. Since the length reduction does not affect the diameter of the object, we can thus compare mechanical properties at a given diameter for different lengths or, conversely, precisely tune the mechanical resonance frequencies. Opening the nanotubes also creates perspectives for their use as nano-capillaries.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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 APL
[Show abstract][Hide abstract] ABSTRACT: In this article we review our recent experimental inves-tigations of phenomena associated with the mechanical resonances of nanotubes and nanowires (NN) during field emission (FE). The goal is to show how this configuration can be used for measuring the physi-cal parameters of an NN and how it opens interesting perspectives in the emerging field of Nano Electro-Mechanical Systems (NEMS). In the basic experiment the resonances are excited capacitively in ultra high vacuum (UHV) and are detected by either a variation in the FE cur-rent or an increase in the size of the FE pattern. The high electric field also induces a giant tuning of the NN resonance frequency making our NNs tunable oscillators. An image analysis technique has been de-veloped to exploit the FE pattern changes for measuring low vibration amplitudes. High Q-factors of SiC nanowires have been determined as a function of in UHV heating cycles. The effect of the tuning on the resonance frequency has been modelled allowing the extraction of the natural frequency and thus the Young's modulus. Finally, an example of a new NEMS phenomena in the FE configuration is amechanical "self oscillations" observed without any AC drive: it is a nanometric DC/AC conversion device. LPMCN, where he is now an assistant professor since 2007. His actual research field is characterization and modeling of NEMS based on carbon nanotubes or nanowires and more recently on piezomaterials. Pascal Vincent, PhD 2002, Lyon 1 University, on the field emis-sion properties of carbon nanotubes. He did a post doctorate in Thales Research in Technology. Since 2003, he is assistant professor at Uni-versity Lyon 1 where he developed the Nanomecatronics orientation in the LPMCN laboratory. His research interests range from NEMS based on carbon nanotubes or nanowires, self-oscillations, collective effects to field emission NEMS.
International Journal of Nanotechnology 02/2010; 7(4). DOI:10.1504/IJNT.2010.031740 · 0.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report here field-emission (FE) studies of individual single-crystal SiC nanowires that showed several distinct I/V regimes including strong saturation resulting in highly nonlinear Fowler-Nordheim plots. The saturation is due to the formation of a depletion layer near the nanowire ends as predicted for FE from semiconductors and appears after in situ control of the surface cleanliness. This work opens the door to improving the uniformity, stability, and photon control of mass-produced planar nanowire FE cathodes and shows how FE can be used for transport measurements on individual semiconducting nanowires.