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碳纳米管场致发射中的空间电荷效应 总被引:1,自引:0,他引:1
采用微波等离子体化学气相沉积(MWPCVD)方法成功制备以碳纳米管束为单元的场致发射阵列,获得很好的场致发射电流发射特性,在电流密度较大时,发现I-V特性偏离由Fowler-Nordheim公式计算出的结果。采用Electron Beam Simulation(EBS)软件进行模拟分析发现:在电流密度较低时,I-V特性能很好与F-N公式吻合。但碳纳米管尖端电流密度大于106A/cm2时,碳纳米管尖端处的有效电场强度受空间电荷的影响比较明显,进而对碳纳米管的场致发射特性显现出不可忽略的影响,此时碳纳米管的发射电流密度开始受到空间电荷的限制。 相似文献
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为了研究二极管爆炸电子发射初始阶段阴极表面复杂的物理现象及规律, 建立了由场致电子发射阴极构成的一维平板真空二极管物理模型,通过自行编程数值求解泊松方程, 考虑了发射出的电子对阴极表面电场的非线性影响,自洽模拟得到了阴极表面电场随时间的变化情况. 模拟结果表明,爆炸电子发射初期,阴极表面电场随时间的增加而呈现出不断振荡的规律, 且振荡幅度越来越小,最终到达一个稳态的值,二极管两极板之间的外加电场越大, 阴极表面稳态电场的绝对值越大;电场增强系数越大,阴极表面稳态电场的绝对值越大. 在整个时间演变过程中,阴极表面的实际电场强度决定着阴极发射的电流密度大小, 反过来阴极发射的电流密度又会影响到阴极表面的电场. 相似文献
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热场致发射阴极所产生的强流电子束具有很强的空间电荷效应,为研究该效应对热场致发射过程中诺廷汉(Nottingham)效应的影响机理,在理论分析的基础上,用数值方法研究了不同逸出功和多个外加电场条件下考虑空间电荷效应对诺廷汉效应结果的影响,并与不考虑空间电荷效应时的情形进行了对比. 结果表明:空间电荷效应的强弱会显著影响到阴极表面的稳态电场,进而对诺廷汉效应产生不可忽略的影响;当逸出功在3.0–4.52 eV、外加电场在3×109–9×109 V/m范围内时,考虑空间电荷效应的影响后,热场致发射电子所带走的平均能量较不考虑空间电荷效应时增加0–2.5 eV,且温度越高或外加电场越大时,该增加值越大;考虑空间电荷效应对诺廷汉效应的影响后,热场致发射电子从阴极带走的平均能量随外加电场的增加呈非线性下降规律;当阴极表面温度较高时,诺廷汉效应中的冷却效应随二极管间隙距离的变大而增强.
关键词:
热场致发射
诺廷汉效应
空间电荷效应
阴极表面电场 相似文献
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D. I. Vaisburd S. I. Tverdokhlebov T. A. Tukhfatullin 《Russian Physics Journal》1997,40(11):1064-1082
A dense pulsed electron beam and nanosecond pulse length has been used to inject negative electric charge into various dielectric
materials (single crystals, glasses, composites, plastics) for initiation of electron field emission from the dielectric into
a vacuum. It has been shown that upon reaching a critical electric field in the bulk and at the dielectric surface there is
intense critical electron emission. The local current density from the emission centers reaches a record value (for dielectrics)
of the order of 106 A/cm2. The emission occurs in the form of a single gigantic pulse. The measured amplitude of the emission current averaged over
the emitting surface is the same order of magnitude as the injected electron current: 10–1000 A. the emission current pulse
lages behind the current pulse of the primary electron beam injected into the sample. The delay time is in the range 1–20
nsec and decreases with increasing current density of the injected beam. Direct experimental evidence is found for intense
generation of carriers (band or quasifree electrons) in the near-surface layer of the dielectric in a strong electric field
due to the Frenkel-Poole effect and collisional ionization of traps, usually various donor levels. This process greatly strengthens
the field emission from the dielectric. It has been shown experimentally that the emission is nonuniform and is accompanied
by “point bursts” at the surface of the dielectric and ionized plasma spikes in the vacuum interval. These spikes are the
main reason that the transition of the field emission into “bursts” is critical, similar to the current which has been previously
observed in metals and semiconductors. However there are a number of substantial differences. For example the critical field
emission current density needed for the transition into “bursts” is three orders of magnitude less than for metals. If we
provide sufficient electron current at the surface or from the bulk of the dielectric to the emission centers, then the critical
emission is always accompanied by a vacuum discharge between the surface of the dielectric and a metallic collector. A detailed
computer model of the processes in the dielectric during injection of a high-density electron beam has been developed which
allows one to understand the complex physical pattern of the phenomenon.
Tomsk Polytechnic University. Institute of High-Current Electronics, Siberian Section, Russian Academy of Sciences. Translated
from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 45–67, November, 1997. 相似文献
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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
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Ultrashort laser-gas interaction is a promising candidate for the intense broad band far-infrared radiation in which the gas ionization and the resultant plasma formation occur consequently. The electron current produced in the process is the most important influential parameter which affects the far-infrared radiation generation. Although the interacting forces of the process are the space charge electric and the laser electromagnetic forces, the effect of the former one, has not been investigated on the gas-plasma THz generation. It is noteworthy that the space charge electric force, due to its effect on the electron distribution, has potential influence on the produced electron current and its consequent emission. Here, a 2D relativistic fluid model is presented in which the ions and the resultant space charge field are incorporated. The model investigates the air ionization, electron-ion plasma formation, and the system's evolution, spatiotemporally. Moreover, as the model is based on the transient electron current, as the source for the electromagnetic pulse radiation, it gives the temporal profile of the radiated field in which the space charge effects are observable. Our results show that the space charge field affects the electron velocity and its resultant current. Therefore, the temporal profiles and amplitudes of the radiated field components are affected and their resemblance to the experimental data is enhanced. The results indicate that the amplitude of the radiated field increases in the presence of the space charge field. In addition, it is shown that the space charge effects become more pronounced with the laser intensity. 相似文献
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We have measured the chemical potential and capacitance in a disordered organic semiconductor by electric force microscopy, following the electric field and interfacial charge density microscopically as the semiconductor undergoes a transition from Ohmic to space-charge limited conduction. Electric field and charge density at the metal-organic interface are inferred from the chemical potential and current. The charge density at this interface increases with electric field much faster than is predicted by the standard diffusion-limited thermionic emission theories. 相似文献
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Standstill Electric Charge Generates Magnetostatic Field under Born-Infeld Electrodynamics 总被引:1,自引:1,他引:0
S. O. Vellozo J. A. Helayël Neto A. W. Smith L. P. G. De Assis 《International Journal of Theoretical Physics》2008,47(11):2934-2944
The Abelian Born-Infeld classical non-linear Electrodynamic has been used to investigate the electric and magnetostatic fields
generated by a point-like electric charge at rest in an inertial frame. The results show a rich internal structure for the
charge. Analytical solutions have also been found. Such fields configurations have been interpreted in terms of vacuum polarization
and magnetic-like charges produced by the very high strengths of the electric field considered. Apparently non-linearity is
responsible for the emergence of an anomalous magnetostatic field suggesting a possible connection to that created by a magnetic
dipole composed of two magnetic charges with opposite signs. Consistently in situations where the Born-Infeld field strength
parameter is free to become infinite, Maxwell’s regime takes over, the magnetic sector vanishes and the electric field assumes
a Coulomb behavior with no trace of a magnetic component. The connection to other monopole solutions, like Dirac’s and ’tHooft’s
Poliakov’s types are also discussed. Finally, some speculative remarks are presented in an attempt to explain such fields. 相似文献
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气体中空间电荷的分布与电晕放电的机理紧密相关, 获取电晕放电过程中空间电荷分布对深入研究电晕放电起始、自持过程有着重要作用, 但是如何准确获得电晕放电过程中的空间电荷分布一直是国际上尚未解决的难题. 本文基于声脉冲法提出一种电场信号解耦算法, 推导了空间电荷在声场中被调制产生的电场信号与声脉冲信号和空间电荷密度之间的数值关系, 讨论了不同测量情况下声发射系统的设计要求; 搭建了一套可用于实时测量针板电极电晕放电空间电荷分布的非接触式测量系统, 该系统主要包括声脉冲发生模块、空间电荷模块及电场信号解耦算法模块. 运用该系统实现了声脉冲激发作用下电场信号的测量, 通过提出的电场信号解耦算法得到了空间电荷密度, 对其测量结果与电晕电流法测量结果进行比较, 验证了电场信号解耦算法的有效性. 该算法可以应用于空间电荷一维、二维和三维测量系统中. 相似文献
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Field-emission displays (FEDs) have been studied intensively in recent years as a candidate for flat-display panels in the future. In a FED, electrons emit from field emitters. Some electrons may impinge on the insulator surface between cathode and gate electrodes and cause charging of that surface because the yield of secondary electron emission is usually not equal to one. The charging of the insulator walls between cathode and gate electrodes is one of the important factors influencing the performance of a FED. In this paper, a simulation program is used to calculate this charge deposition, electric field distribution and electron trajectories. From the change of the electric field upon charge deposition in the triode region, it is shown that the insulator surface is negatively charged at a low gate voltage, e.g. 20 V. However, positive charge is deposited when the gate voltage is high, e.g. 100 V. The simulations also show that the emission current will increase even further after coating the dielectric with a thin film of a material with a high-secondary emission coefficient such as MgO. If a cone-shaped dielectric aperture is used in a triode, the emission current will decrease after charge deposition. However, the focus performance of the electron beam is improving in this case. 相似文献
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Alexandre A. Martins Mario J. Pinheiro 《International Journal of Theoretical Physics》2008,47(10):2706-2715
We address the problem of inertial property of matter through analysis of the motion of an extended charged particle. Our
approach is based on the continuity equation for momentum (Newton’s second law) taking due account of the vector potential
and its convective derivative. We obtain a development in terms of retarded potentials allowing an intuitive physical interpretation
of its main terms. The inertial property of matter is then discussed in terms of a kind of induction law related to the extended
charged particle’s own vector potential. Moreover, it is obtained a force term that represents a drag force acting on the
charged particle when in motion relatively to its own vector potential field lines. The time rate of variation of the particle’s
vector potential leads to the acceleration inertia reaction force, equivalent to the Schott term responsible for the source
of the radiation field. We also show that the velocity dependent term of the particle’s vector potential is connected with
the relativistic increase of mass with velocity and generates a longitudinal stress force that is the source of electric field
lines deformation. In the framework of classical electrodynamics, we have shown that the electron mass has possibly a complete
electromagnetic origin and the obtained covariant equation solves the “4/3 mass paradox” for a spherical charge distribution. 相似文献
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Field emission in diamond and graphite-like polycrystalline films is investigated experimentally. It is shown that the emission
efficiency increases as the nondiamond carbon phase increases; for graphite-like films the threshold electric field is less
than 1.5 V/μm, and at 4 V/μm the emission current reaches 1 mA/cm2, while the density of emission centers exceeds 106 cm−2. A general mechanism explaining the phenomenon of electron field emission from materials containing graphite-like carbon
is proposed.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 56–60 (10 July 1998) 相似文献
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研究了电子回旋共振等离子体技术沉积的氟化非晶碳 (a_C :F)薄膜的电学性质 .发现对于不同C_Fx 含量的薄膜 ,CC含量的增大对薄膜的导电行为具有不同的影响 .薄膜的直流I_V特性呈现I =aV bVn规律 ,是低场强区的欧姆导电和高场强区的空间电荷限流 (SCLC)组成的导电过程 .由于非晶材料的空间电荷限流与带尾态密度的分布密切相关 ,而a_C :F薄膜中CC的含量决定带尾态密度的分布 ,因此a_C :F薄膜在高场下的空间电荷限流是由薄膜中 CC 决定的导电过程 . 相似文献
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A stochastic-deterministic model is presented for the propagation of a downward-moving leader. Lightning formation is described
by a stochastic growth of branching discharge channels which is determined by the electrostatic field. The dynamics of the
electric field and of the charge distribution over the lightning structure are calculated deterministically. The model includes
the initiation of lightning, a preliminary discharge in a cloud, the propagation of a downwardmoving stepped leader toward
the earth, and the initiation and upward motion of a return stroke from the earth’s surface. Numerical execution of the model
yields a dynamic picture of the development of the downward-moving leader and of the intracloud discharge structure. The effect
of the charge density in the cloud and the parameters of the developing channels on the spatial-temporal, current, and charge
characteristics of the stepped leader’s propagation are studied. The effect of free-standing structures on the distribution
of points on the earth’s surface where lightning strikes is examined.
Zh. Tekh. Fiz. 69, 48–53 (April 1999) 相似文献
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变像管相机中空间电荷效应的统计动力学分析 总被引:1,自引:1,他引:0
从Boltzmann积分微分方程出发推出了保守势场中电子数密度按势能的分布规律,即Boltzmann统计分布。以此为基础,从统计动力学的角度详细分析了变像管相机中超短电子脉冲内部的空间电荷效应,通过求解Poisson方程得出了表征空间电荷效应的两个特征参量:空间电荷密度分布函数和速度分布函数,并对其按电位的动态变化规律进行了定性讨论。结果表明,限制变像管中的低电位区域和其中光电子脉冲从高电位向低电位传输的区域都将有助于优化整个变像管的性能。同时也重新讨论了光电阴极附近强加速场对光电子脉冲时间弥散的抑制作用,最终确定了其物理机制为不等位区间中电子脉冲空间分布的高度集中性。 相似文献
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Exact partial solutions are found for the electric field distribution in the outer region of a stationary unipolar corona discharge from an ideal conical needle in the space-charge-limited current mode with allowance for the electric field dependence of the ion mobility. It is assumed that only the very tip of the cone is responsible for the discharge, i.e., that the ionization zone is a point. The solutions are obtained by joining the spherically symmetric potential distribution in the drift space and the self-similar potential distribution in the space-charge-free region. Such solutions are outside the framework of the conventional Deutsch approximation, according to which the space charge insignificantly influences the shape of equipotential surfaces and electric lines of force. The dependence is derived of the corona discharge saturation current on the apex angle of the conical electrode and applied potential difference. A simple analytical model is suggested that describes drift in the point-plane electrode geometry under saturation as a superposition of two exact solutions for the field potential. In terms of this model, the angular distribution of the current density over the massive plane electrode is derived, which agrees well with Warburg??s empirical law. 相似文献
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The approximation of electron motion along electric field force lines is used to calculate current in diodes with knife-edge and point emitters. The diode current is limited by space charge, with each current tube considered as a diode element with electrodes in the form of coaxial cylinders or concentric spheres. The effect of the cathode cavity in which the emitter is installed upon current magnitude is considered by limiting beam dimensions at the anode.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–6, February, 1992. 相似文献