共查询到20条相似文献,搜索用时 0 毫秒
1.
Browning J. Meassick S. Xia Z. Chan C. McGruer N. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(2):259-260
In previous work (1992), the authors studied the characteristics of gated field emitter failures and developed a theory to explain failure initiation. During a failure, the voltage between the emitter tip and gate (spaced 1 μm apart) was found to drop from -140 V to ≈-10 V. The current density was found to be ~1012 A/m2 during the failure, and plumes of ions and electrons were injected into vacuum. The ratio of ion current to electron current was found to be 10%. Those results indicated that the failures were similar to cathodic vacuum arcs. In the present study the energies of the ions and electrons are measured using a retarding potential energy analyzer. The results show that there are ions with energies as high as 80 eV and electrons with energies of 6 eV. The high-energy ions confirm that emitter failures are cathodic vacuum arcs 相似文献
2.
Sominskii G. G. Taradaev E. P. Tumareva T. A. Mishin M. V. Kornishin S. Yu. 《Technical Physics》2015,60(7):1079-1081
We investigate multitip field emitters prepared by electroerosion treatment of the surface of molybdenum samples. Their characteristics are determined for operation with a protecting activated fullerene coating. Our experiments indicate that such cathodes are promising for high-voltage electron devices operating in technical vacuum.
相似文献3.
基于射线理论分析了在典型深海情况下声源与接收水听器位于海水表层时声场频率-距离干涉结构,给出了直达声作用区与影区情况下声场频率-距离干涉结构的近似理论表达式。数值仿真与实验结果表明:在直达声作用区内,由直达声与海面一次反射声形成声场干涉结构,频率域干涉周期为该两条声线到达时间差的倒数;在影区内,由声源-海底-接收器、声源-海面-海底-接收器、声源-海底-海面-接收器和声源-海面-海底-海面-接收器四条声线形成声场干涉结构,声强随着频率具有两种干涉周期,分别随着声源深度、接收水听器深度的增大而减小,并与收发距离有关。本文给出的理论表达式可以较好的解释实验观测到的声场频率-距离干涉结构。 相似文献
4.
The field evaporation of nickel, nichrome alloy, and tungsten carbide at different temperatures is studied with a time-of-flight atomic probe and a field emission microscope. The charge of evaporating ions does not depend on the emitter temperature: it decreases with decreasing evaporating field F ev. If F ev does not vary with temperature, so does the charge of the ions. In the case of multicomponent emitters with different ionization potentials of the components, the components evaporate at the same values of F ev in the form of atoms and ionized clusters. The reason for such behavior is that the initial evaporation of the easily ionizable component decreases the binding energy of harder-to-ionize ones to the point where they can evaporate at the same field. 相似文献
5.
Increasing computer power and the development of user-friendly, yet highly sophisticated bandstructure programs have made
it possible that theoretical EFG calculations can nowadays be performed for fairly complex materials science problems. We
show that a combination of these theoretical calculations with experimentally obtained quadrupole splittings can lead to new
insight into various interesting problems. This is illustrated for the determination of nuclear quadrupole moments, investigations
of samples containing impurities or other imperfections and for Na2[Fe(CN)5NO], a promising material for holographic storage applications.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
V.L. Kalashnikov E. Podivilov A. Chernykh A. Apolonski 《Applied physics. B, Lasers and optics》2006,83(4):503-510
Theory of chirped-pulse oscillators operating in the positive dispersion regime is presented. It is found that the chirped pulses can be described analytically as solitary pulse solutions of the nonlinear cubic-quintic complex Ginzburg–Landau equation. Due to the closed form of the solution, basic characteristics of the regime under consideration are easily traceable. Numerical simulations validate the analytical technique and the chirped-pulse stability. Experiments with 10 MHz Ti:Sa oscillator providing up to 150 nJ chirped pulses, which are compressible down to 30 fs, are in agreement with the theory. PACS 42.65.Re; 42.65.Tg; 42.55.Rz 相似文献
7.
The properties of steps in thermal equilibrium are described in the context of prediction of the stability and evolution of nanostructures on surfaces. Experimental techniques for measuring the appropriate step parameters are described, and simple lattice models for interpreting the observations are reviewed. The concept of the step chemical potential and its application to the prediction of step motion (and therefore surface mass transport) is presented in depth. Examples of the application of this step-continuum approach to experimental observations of evolution of surface morphology are presented for morphological phase transitions, the decay of metastable structures, and the spontaneous evolution of metastable structure due to kinetic instabilities. 相似文献
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9.
K. A. Nikiforov N. V. Egorov Che-Chou Shen 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2009,3(5):833-839
The surface and emission images of a metal field’s electron cathode in the form of a tip are simulated. The surface structure
is calculated in the thin-shell and broken-bond (local-environment) models for the perfect crystal lattice. The cathode shape
and macroscopic electric field are represented by the sphere-on-cone model. The amplification of a local electric field is
the adjustable parameter of the model. The method of determination of the emitter tip’s crystal faces based on the analysis
of the surface atoms’ environment geometry is proposed. It is shown that it is enough to restrict the consideration of geometric
environment by the fifth order of the nearest neighbors for the emitter radius of 100–1000 lattice parameters (31.6–316 nm
for the tungsten). The crystallographic model of work function anisotropy in the broken-bond approach is used: the local work
function’s value is set in accordance with Miller indices of the face containing this area. The model adequacy is corroborated
by the comparison of current-voltage characteristics and emission images with the data of the natural experiment. 相似文献
10.
Anjan S. Joshipura 《Pramana》1995,45(1):173-182
Possible hints on neutrino masses are reviewed. They come from the deficits in the solar as well as atmospheric neutrinos and from need of a significant amount of hot component in the dark matter of the universe. The role of three generation mixing in simultaneously solving the solar and atmospheric neutrino problem is discussed. All the three hints can be reconciled if three neutrinos are almost degenerate. Models for neutrino masses and mixing implied by the above hints are briefly discussed. 相似文献
11.
Locally periodic Timoshenko rod: experiment and theory 总被引:2,自引:0,他引:2
Díaz-de-Anda A Pimentel A Flores J Morales A Gutiérrez L Méndez-Sánchez RA 《The Journal of the Acoustical Society of America》2005,117(5):2814-2819
The flexural vibrations of a locally periodic rod, which consists of N unit cells, are discussed both from the experimental and theoretical points of view. Timoshenko's beam theory and the transfer matrix method are used to calculate the normal-mode frequencies and amplitudes. The theoretical values are then compared with the experimental ones, which are obtained using an electromagnetic acoustic transducer (EMAT). Good agreement between the numerical results and the experimental measurements is obtained. It is shown that as N grows, a band spectrum emerges. 相似文献
12.
Berrah N Bozek JD Turri G Akerman G Rude B Zhou HL Manson ST 《Physical review letters》2002,88(9):093001
High-resolution K-shell photodetachment measurements of He- giving rise to He+ ions have been performed using a merged synchrotron vacuum ultraviolet photon-ion beam technique. The measurements on this fundamental negative ion display dramatic structure differing substantially, qualitatively and quantitatively, from the corresponding process in neutral atoms and positive ions, owing to the dominance of correlation in both initial and final states of He-. In addition, this experimental investigation provides an unambiguous test of two independent theoretical calculations that report serious discrepancies and shows excellent agreement with one of them. 相似文献
13.
F. Claeyssens G.M. Fuge N.L. Allan P.W. May S.R.J. Pearce M.N.R. Ashfold 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1237-1241
The recent finding that radio frequency plasma activation of CH4/PH3 gas mixtures [7] could lead to films with P:C ratios 3 (which also contain 10% hydrogen, distributed evenly throughout the bulk) has served to trigger further research into new amorphous phosphorus carbide materials. New theoretical and experimental results relating to these materials are presented here. The electronic structure and stability of different crystalline phosphorus carbide PxCy phases have been studied using first-principles density-functional theory methods. Calculations have been carried out for both P4C3 and PC and a range of the more likely periodic structures examined. The lowest energy pseudocubic P4C3 and GaSe PC phases have been further investigated as templates to discover the stability and the electronic and structural properties of these phosphorus carbide materials. Recent experimental studies have involved use of pulsed laser ablation (PLA) methods to produce hydrogen-free phosphorus carbide thin films. Mechanically hard, electrically conducting diamond-like carbon films containing 0-26 at.% P have been deposited on both Si and quartz substrates by 193 nm PLA of graphite/phosphorus targets (containing varying percentages of phosphorus), at a range of substrate temperatures (Tsub=25–400 °C), in vacuum, and analysed via laser Raman and X-ray photoelectron spectroscopy. PACS 68.55.Jk; 71.15.Nc; 81.15.Fg 相似文献
14.
We report the observation of a periodic electric-field-dependent component in the photo-current from a tungsten field emitter illuminated by the focused beam of a krypton ion laser tuned to a photon energy of ~3.51 eV. Over the field range we have investigated, the phase φ of the oscillations in the photocurrent can be related to the electric field strength F by the power law φ ∝ Fα, where . In this preliminary study, we describe the frequency, amplitude, and harmonic structure of oscillations detected with the probe hole centred over the (510) region of the field emission pattern. A Fowler-Nordheim plot of the photocurrent is presented, and the nonoscillatory component is analysed on the basis of a simple theory of barrier penetration. The origin of the oscillatory component of the photocurrent is discussed. 相似文献
15.
《Surface science》1994,318(3):L1211-L1218
16.
Received: 30 May 1997/ 27 August 1997 相似文献
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18.
An electron field emitter based on a carbon nanotube is considered as a frequency converter of the voltage applied to its
electrodes. This property of the emitter relates to the nonlinear form of the current-voltage characteristic described by
the classical Fowler-Nordheim expression. Calculations show that the number of higher harmonics in the spectrum of the emission
current increases upon a decrease in the applied voltage and with increasing relative amplitude of the ac signal. 相似文献
19.
A correction to the electric field strength linear in magnetic field H was found by computations for a two-dimensional disordered system. This correction was used to calculate and graphically tabulate two two-parameter functions present in the equation describing magnetoresistance in a wide range of parameter variations. This correction was also used to determine and tabulate the derivative of the function present in the equation for the effective Hall coefficient with respect to one of its arguments. The data obtained in this work combined with the earlier results of these authors allow the magnetoresistance of binary (composite) media to be completely described in the spirit of the similarity hypothesis. 相似文献