Energy distribution of post-accelerated electrons field-emitted from carbon fibres

An electron gun system with post-acceleration is described suitable to operation with a carbon fibre field-emission tip. The system was tested in an electron optical bench with a vacuum pressure of about 10⁻⁶ torr. The electron current was most stable if the current to the extraction electrode was minimized. The half width of the energy distribution of the electrons accelerated up to 30 keV was 215 meV for small currents (≈10⁻⁹A). The half width of the distribution increases with growing emission current. This increase may be attributed to instabilities in the surface structure due to ion bombardment and to the circumstance that more than one emission centre contributes to the electron current.     

Transmission coefficient and energy distribution of electrons emitted from M-I-M thin film structures

A simple model of the electron emission from M-I-M structures with insulator thickness >10 nm has been developed. The electric field distribution inside the insulator is supposed to be inhomogeneous with a region of a high field intensity near the cathode. The dependence of the transmission coefficient and of the parameters of the energy distribution on the applied voltage and on the insulator thickness is calculated. It is shown that features obtained experimentally, which contradict earlier theories, can be explained.     

Discrete levels in the energy distribution of secondary electrons emitted by palladium crystals

Low-energy peaks are detected in the secondary electron spectrum of Pd crystals. They correlate with maxima in the density of empty states calculated for Pd. Their sensitivity to sputter-induced damage, to thermal-induced disorder and to surface contamination is demonstrated.     

Attenuation length of monoenergetic electrons photoinjected into the NaCl layer

A new, precise photoelectric method of electron attenuation length measurement in alkali halides is proposed and experimentally verified. The obtained results confirm the Llacer-Garwin theory of electron-phonon interactions in these substances.     

The angular distribution of electrons emitted from traps in MIM systems

Experimental results give evidence that the angular distribution of electrons emitted from sandwich cathodes at low temperatures is mostly formed by electrons which were absorbed by traps in the dielectric forbidden band during the transfer through the dielectric layer and then again liberated. For this reason the thermal as well as the field-assisted excitation is analyzed in detail in this paper. In both cases angular distributions (in case of the thermal excitation only in the numerical way) and approximate expressions for the height and the half-width of these distributions are obtained. The derived expressions contain cathode parameters (temperature, voltage used, mean free path and depth of traps) and they are usable for evaluation of these parameters from experimental characteristics.     

Field emission of monoenergetic spin-polarized electrons

Field emission from a tungsten tip, covered by a layer of crystallized ferromagnetic europium sulfide, leads to an electron beam with a current of 10⁻⁸ A, an energy width of less than 100 meV, and a spin polarization of about 0.85 at a tip temperature of 9 K. Proper annealing of the EuS layer is crucial.     

Energy distribution of electrons emitted from Al-Al2O3-Al system

On sandwich cathodes of the Al-Al₂O₃-Al structure were measured both the VA characteristics of leakage and emission currents and the distribution of emitted electrons according to a normal energy componentN(W _x ) for various voltages thicknesses of dielectric and upper metal films, and various voltages superimposed on cathode (leakage voltage). On the basis of experimental dependences obtained, the influence of single parts of the system on the transported electrons has been discussed. Three groups of distribution ofN(W _x ) were found differing in their form on the one hand and in their position in the energy band diagram of the studied system, on the other one. The dependence of the distribution width and the position of its maximum on the thickness of the dielectric layer and electric field intensity was followed. To describe the processes in a dielectric layer a model assuming the random collision processes has been applied. All three groups of measured distributions may be expressed by a single equation of the typeN(W _x )=N ₀(W _x ). P(z). D(W), except a small number of cases where the influence of the upper electrode barrier due to higher voltages on cathode is not taken into account and thus theD(W) term need not be considered.     

Energy distribution of electrons field-emitted from carbon nanoemitters

The height of an extra low-energy maximum in the energy distribution of electrons tunneling from crystalline carbon fibers and carbon nanotubes is studied as a function of emitter heating and emitter rotation relative to the energy analyzer axis. The relationships found are related to emission from electron states on the surface of the reconstructed nanocrystals and nanotubes.     

A new approach for the determination of the C ls binding energy

The binding energy of the C 1s-level of clean pyrolytic graphite and amorphous carbon has been measured by means of the excitation-curve technique. Values ofE _{C 1s} ^B =284.31±0.2 eV for graphite and amorphous carbon have been found.     

超短脉冲激光与乙醇微滴相互作用中超热电子的双叶状角分布

测量了聚焦光强为1016W/cm2的超短脉冲激光与乙醇微滴相互作用中产生的能量大于50?keV的超热电子的角分布和电子能谱.观察到的超热电子角分布明显依赖于激光的偏振特性，在与激光偏振平面平行的平面上超热电子相对于激光入射方向呈对称的双叶状分布.超热电子的能谱显示超热电子的最大能量大于750?keV.以上超热电子的角分布可用一个基于共振吸收机制的模型加以解释. 关键词： 超短脉冲激光 超热电子 微滴 共振吸收     

Energy distributions of field emitted electrons from carbon nanosheets: Manifestation of the quantum size effect

We emphasize the importance of experiments with voltage dependent field emission energy distribution analysis in carbon nanosheets. Our analysis shows the crucial influence of the band structure on the energy distribution of field emitted electrons in few-layer graphene. In addition to the main peak we found characteristic sub-peaks in the energy distribution. Their positions strongly depend on the number of layers and the interlayer interaction. The discovery of these peaks in field emission experiments from carbon nanosheets would be a clear manifestation of the quantum size effect in these new materials.     

Energy distribution of field emission electrons from carbon nanocrystals

Using a field electron microscope and a field electron dispersion energy analyzer, carbon nanocrystals contained in polyacrylonitrile (PAN) fibers are studied. Transition of the emitting nanocrystals into the second stable state has been discovered, corresponding to an emission current and field electron energy distribution of magnitudes lower by nearly an order of magnitude, with an additional low-energy peak. Heating the samples at 750° C restores the initial characteristics of the field electron energy distribution and current-voltage characteristics of the nanocrystals. The forbidden bandwidth of the nanocrystals has been determined.     

Flux and energy distribution of axial protons emitted from the hydrogen plasma focus

Experimental results and theoretical studies show that protons from the hydrogen plasma focus are emitted predominantly in the axial direction. In this work the results of the flux and energy distribution measurements of the axial protons using CR-39 detector are presented. The main purpose of the experiment is to test the suitability of a plasma focus device as a source for (p,) nuclear reactions, especially and .     

Surface spin-exchange-scattering of polarized electrons emitted from magnetic materials

It is known that a paramagnetic surface sheet persists far below the Curie temperature in the ferromagnetic semiconductors EuO and EuS. We show that the observed spin-polarization of the photo- and field-emitted electrons is largely determined by spin-exchange collisions in the surface sheet. A single paramagnetic atomic layer may have a depolarizing effect of up to 50 per cent. Other circumstances in which the proposed model might apply are suggested.     

Spin polarization of secondary electrons emitted from a nonmagnetic metal

We present the first angle-, energy-, and spin-resolved measurements of secondary electrons emitted from a Au(110) surface bombarded with unpolarized electrons. Both transversal components normal to and in the scattering plane, of the spin polarization vector exist. A simple two-step scattering process explains the observations, where the polarization is created via spin-orbit coupling in collisions of secondary electrons with ion-cores.     

Structure of the spin polarization spectrum of secondary electrons emitted from nickel

The main features of the structure observed in the energy resolved spin polarization of secondary electrons emitted from Ni are interpreted in terms of surface and bulk plasmon assisted emission. The model also predicts a measurable shift of the main polarization peak of about 0.3 eV to lower energies as the temperature is raised from room temperature to closely below the Curie temperature.     

Thermal emission of electrons from highly excited sodium clusters

Positively charged sodium clusters can be easily ionized by a fs laser pulse of relatively low intensity (<10¹⁰ W/cm²), if the laser is in resonance with the plasmon excitation of the cluster. This ionization process was investigated in detail by measuring the kinetic energy distribution of electrons emitted from a size-selected Na₉₃ ⁺ as a function of the fs laser intensity. In all cases pure Boltzmann-like energy distributions were observed. A comparison with statistical theory shows that the emission is a purely thermal process. It is different to normal thermionic emission insofar as the electrons are emitted from a hot electron system which is only weakly coupled to a cold ionic background. The results demonstrate purely statistical behaviour of a small fermionic system even for very high excitation energy. Received: 25 May 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001     

Variational treatment of continuum orbitals for Auger electrons emitted from neon

A variational method is applied to obtain the wave function of the continuum Auger electron emitted from an ionized neon atom. The trial function is taken to depend on several adjustable parameters, and the wave function of the electrons in different orbitals, such that all possible virtual states of the quantum mechanical system composed of the Auger electron and the ion are represented. The continuum wave function is improved iteratively by increasing the number of terms.Auger transition rates are then calculated applying the angular momentum average scheme, and are compared with other theoretical and experimental results. Agreement with the latest experiment is achieved.