Electrons In Vacuum Research Articles

Electron transition probabilities in elementary electron-phonon scattering processes using electron-energy-loss spectroscopy: Application to graphite

We have investigated coupling constants in elementary electron-phonon scattering processes on a graphite surface by the combined use of high-resolution electron-energy-loss spectroscopy (HREELS) and very low-energy electron diffraction (VLEED). HREELS is used to measure the modulations of electron transition probabilities from incoming electrons in vacuum to outgoing electrons in vacuum where the transition includes one-phonon scattering processes inside a solid. Determining the electronic band structures of graphite with VLEED, we defined electronic states of the solid surface that electrons entered before and after scattering off phonons. Thus, we observed that the measured electron transition probabilities significantly depended on whether the electrons were in a bulk Bloch state or an evanescent state before scattering off the phonons. This result clearly indicates that the measured electron transition probabilities reflect the strength of the coupling constants in the solid.

All-Electric Spin Control in Interference Single Electron Transistors

Single particle interference lies at the heart of quantum mechanics. The archetypal double-slit experiment(1) has been repeated with electrons in vacuum(2,3) up to the more massive C(60) molecules.(4) Mesoscopic rings threaded by a magnetic flux provide the solid-state analogues.(5,6) Intramolecular interference has been recently discussed in molecular junctions.(7-11) Here we propose to exploit interference to achieve all-electrical control of a single electron spin in quantum dots, a highly desirable property for spintronics(12-14) and spin-qubit applications.(15-19) The device consists of an interference single electron transistor,(10,11) where destructive interference between orbitally degenerate electronic states produces current blocking at specific bias voltages. We show that in the presence of parallel polarized ferromagnetic leads the interplay between interference and the exchange interaction on the system generates an effective energy renormalization yielding different blocking biases for majority and minority spins. Hence, by tuning the bias voltage full control over the spin of the trapped electron is achieved.

Field emission studies of amorphous carbon deposited on copper nanowires grown by cathodic arc plasma deposition

The field emission properties of amorphous carbon/copper nanowire (CuNW)/Si composites have been investigated. The CuNWs (50–80 nm in diameters) were deposited anodically within the pores of a porous anodic aluminum oxide (AAO) nano-template by electrolysis of a CuSO 4-H 2SO 4 solution at room temperature using DC current. Two kinds of structure, amorphous carbon/Si and amorphous carbon/CuNWs/Si, were used. Both of them can emit electrons in vacuum towards an anode at a very low turn-on field. Field emission from the amorphous carbon/CuNWs/Si shows a fourfold decrease in turn-on field compared with the amorphous carbon/Si. Results indicated that the electrons were emitted under the effect of an enhanced field because of the geometry of the amorphous carbon sample.

Combined effect of tight-focusing and frequency-chirping on laser acceleration of an electron in vacuum

The investigation [Gupta et al., Appl. Phys. Lett. 91, 211101 (2007)] for electron acceleration by a tightly focused laser beam is revisited by including the effect of laser frequency chirping. The frequency chirping plays an important role to enhance the electron energy if the laser is tightly focused. Due to the combined effect of frequency chirping and tight focusing of a laser beam, an electron can be accelerated for a longer time in vacuum. As a result, from the proposed investigation, the electron energy gain during the laser acceleration is found to be considerably higher.

Efficient high-harmonic radiations by chirped laser-pulse interactions with electrons in the presence of a magnetic field

We present numerical investigations for high-order harmonic generations by a high-intensity chirped-laser interaction with vacuum electrons in the presence of an axial static magnetic field. Combined role of frequency chirp of the laser and a magnetic field enhances the electron acceleration and leads electron energy gain after passing of the laser pulse that generates high-harmonic radiations until the magnetic field diminishes. The result shows that high-harmonic radiations in the range of soft x-rays up to about 10 nm can be generated with common experimental parameters by the proposed scheme of this paper.

Structure of C60 polymer coatings deposited via electron-beam dispersion of fullerite

The structure and surface of thin coatings deposited via electron-beam dispersion of the C60 fullerite have been investigated using IR and Raman spectroscopy, mass spectroscopy, and atomic-force microscopy. It has been demonstrated that layers with different contents of the polymerized phase, crystals of the tetragonal polymer phase, and three-dimensional polymeric forms of the C60 fullerene are formed under the conditions providing for irradiation by secondary electrons in vacuum at a substrate temperature of 300 K.

A cause of energy exchange between light and electron

According to the electron-cloud-conductor model, there should exist interaction of electromagnetic induction between light and electron when they meet, and this interaction may result in the energy exchange between them. Energy exchange between light and free electron in vacuum is analyzed with the model, and the result consists with that of the existing theory. The model can also be used to explain the experimental result of ionization rate of N2 molecules by short laser pulses and the behavior of ionization of molecules by X-ray. It is concluded that one of the root causes for energy exchange between light and an electron is electromagnetic induction between them.

Generation of a Picosecond Runaway Electron Beam in a Gas Gap With a Nonuniform Field

The formation of a picosecond beam of runaway electrons in a gas-filled acceleration gap with a cold cathode and a strongly nonuniform electric field was investigated. The experimental data obtained were compared to those characteristic of the mode of generation and acceleration of electrons in vacuum. Voltage pulses of amplitudes up to -300 kV (in a traveling wave) whose minimum rise time and FWHM did not exceed 100-150 ps were applied to the cathode. The duration and amplitude of the current pulse of the picosecond runaway electron beam behind the anode foil were measured with high time resolution. The emission region of the beam in a gas-filled diode was determined experimentally. The time-of-flight method was used to investigate the acceleration mode of particles in the gap. Information about the part played by field emission in the initiation of the runaway electron beam has been obtained. It has been demonstrated that the point within the rise time of the accelerating voltage pulse at which the beam is injected into the gap correlates with the magnitude of the macroscopic electric field at the cathode emitting edge.

High Speed HPD for Photon Counting

We have succeeded in the development of a highspeed Hybrid-Photodetector (HPD), by using reduced electron lens and newly developed avalanche diode (AD) with very low capacitance. The HPD shows fast time response of less than 400 ps in both rise and fall times, and good timing resolution of 23 ps in sigma for single photons at full illumination on photocathode of Phi 8 mm, after deducting the waveform of the input light pulse. Limiting factor of the timing resolution was further investigated, and clarified to be the transit time difference of electrons in vacuum along the photocathode. The timing resolution was estimated to be less than 10 ps for the spot illumination of Phi 1 mm on the central part of the photocathode, where small transit time difference was expected by the simulation. This resolution is the world highest in the HPD, and matches for those of MCP-PMTs. Both GaAsP photocathode having close to 50% quantum efficiency in visible region and bialkali photocathode having 34% in UV region were fabricated in view of various applications. In this paper, we report the results of the evaluation including discussion about the limiting factors of the timing resolution for the new HPD.

Electron avalanche model of dielectric-vacuum surface breakdown

The model assumes that an “initiating event” results in positive ions on the surface near the anode and reverses the direction of the normal component of electric field so that electrons in vacuum are attracted to the dielectric locally. A sequence of surface electron avalanches progresses in steps from the anode to the cathode. For 200kV across 1cm, the spacing of avalanches is predicted to be about 13μm. The time for avalanches to step from the anode to the cathode is predicted to be about a nanosecond.

Hamiltonian formulation of direct laser acceleration in vacuum

AbstractWe present a new formulation for the direct laser acceleration of electrons in vacuum based on the Hamiltonian theory. Two different regimes for the snow-plowed, accelerated electrons are identified and characterized, the first pertaining to high-intensity and the second to low-intensity pulses, both leading to efficient electron acceleration. Particle energy yields are shown to be independent of the exact shape of the laser pulse and energy gains are estimated.

What is spin-magnetic moment of electron?

We investigate the problem about what the spin-magnetic moment is. The magnetic moment of the Dirac electron in the frame along z-axis is evaluated. This is identified with the spin-magnetic moment of the electron, because there is not any z-component of magnetic moment caused by orbital angular momentum in our frame. The correct value of the spin-magnetic moment and the correct ratio of the spin-magnetic moment to the spin (i.e. g=2) are obtained explicitly. In deriving them, the negative energy solutions of the Dirac equation perform essential roles. We find that the transition current from a positive energy state to a negative energy state causes spin-magnetic moment of the electrons in vacuum. This fact implies that the ratio of the spin-magnetic moment to the spin may change depending on the environments. For example, it may have different values in materials.

Amorphous Diamond for Generating Cold Cathode Fluorescence Light

Amorphous diamond can emit electrons in vacuum when applied with an electrical field of only a few volts per micron. It is also extremely thermionic so the emitted current can increase millions times when heated to only a few hundreds degrees centigrade. As a result, amorphous diamond can be a thermal generator or a solar cell. The energy conversion efficiency can have much higher (e.g. 50%) than that (e.g. 15%) of silicon based solar cells that can absorb only a narrow spectrum of sun light. As a solar cell, amorphous diamond has another advantage that its radiation hardness is the highest of all materials, hence, its thermal electricity efficiency will not attenuate as does the solar cell based on photo electric semiconductorls. An immediate application of amorphous diamond is to coat it on electron emitting electrodes, such as that used as cold cathode fluorescence lamps (CCFL) that illuminate liquid crystal displays (LCD) for fornote books and television sets. Amorphous diamond can dramatically reduce the turn-on voltage to lit CCFL so the lamp life can be greatly extended. Moreover, the electrical current can be increased to enhance the brightness of the light.

Subfemtosecond electron bunch generation by a tightly focused laser pulse

Three-dimensional electron motion in a linearly polarized tightly focused laser field is numerically calculated. A high-intensity laser pulse focused on the free electrons in vacuum generates relativistic electron bunches whose length is shorter than the laser wavelength. The extremely short electron bunches with low-energy spread less than 1% are generated for a wide range of the laser parameters.

One-dimensional semirelativity for electrons in carbon nanotubes

It is shown that the band structure of single-wall semiconducting carbon nanotubes (CNT) is analogous to relativistic description of electrons in vacuum, with the maximum velocity $u={10}^{8}\phantom{\rule{0.3em}{0ex}}\mathrm{cm}∕\mathrm{s}$ replacing the light velocity. One-dimensional semirelativistic kinematics and dynamics of electrons in CNT is formulated. Two-band $\mathbf{k}∙\mathbf{p}$ Hamiltonian is employed to demonstrate that electrons in CNT experience a zitterbewegung (trembling motion) in absence of external fields. This zitterbewegung should be observable much more easily in CNT than its analogue for free relativistic electrons in vacuum. It is argued that in the lowest subband of metallic CNT, where the rest effective mass of electrons vanishes, the zitterbewegung should not occur.

Angular and energy dependences of the surface excitation parameter for electrons crossing a solid surface

When fast electrons cross a solid surface, surface plasmons may be generated. Surface plasmon excitations induced by electrons moving in the vacuum are generally characterized by the surface excitation parameter. This parameter was calculated for 200–1000 eV electrons crossing the surfaces of Au, Cu, Ag, Fe, Si, Ni, Pd, MgO and SiO 2 with various crossing angles. Such calculations were performed based on the dielectric response theory for both incident (from vacuum to solid) and escaping (from solid to vacuum) electrons. Calculated results showed that the surface excitation parameter increased with crossing angle but decreased with electron energy. This was due to the longer time for electron–surface interaction by glancing incident or escaping electrons and by slow moving electrons. The results were fitted very well to a simple formula, i.e. P s = aE - b ( cos α ) c , where P s is the surface excitation parameter, E is the electron energy, α is the angle between the electron trajectory and the surface normal, and a, b and c are material dependent constants.

Investigation of p‐Type MOS Structure Irradiated with 23 MeV Electrons

AbstractSummary: p‐type silicon MOS structures were irradiated with 23 MeV electrons in vacuum for different durations. Capacitance‐voltage (C/V), current‐voltage (I/V) and conductance‐voltage (G/V) methods were used to investigate the changes in the electrical characteristic of the MOS structures after electron irradiation. Our results show that high‐energy electron irradiation generates positive charges in the oxide and at the SiSiO2 interface, which are frequency dependent. After electron irradiation, two kinds of interface traps are determined. The traps energy position evaluated by these three independent methods is very close to Ev + 0.16 eV and Ev + 0.36 eV. As these results are in a very good agreement with our earlier results, obtained by TSC and DLTS methods, the observed traps can be attributed to the boron‐ (V/B) and oxygen (V/O) vacancies complexes.I/V characteristics of a reference and of a MOS structures, the latter being irradiated by 23 MeV electrons.imageI/V characteristics of a reference and of a MOS structures, the latter being irradiated by 23 MeV electrons.

Proof-of-principle experiment for laser-driven acceleration of relativistic electrons in a semi-infinite vacuum

We recently achieved the first experimental observation of laser-driven particle acceleration of relativistic electrons from a single Gaussian near-infrared laser beam in a semi-infinite vacuum. This article presents an in-depth account of key aspects of the experiment. An analysis of the transverse and longitudinal forces acting on the electron beam is included. A comparison of the observed data to the acceleration viewed as an inverse transition radiation process is presented. This is followed by a detailed description of the components of the experiment and a discussion of future measurements.

High energy electron bunch generation by using a plasma separator

In this paper, we propose an electron acceleration by using an intense short pulse laser and a thin slab plasma separator. When an intense short pulse laser illuminates electrons in vacuum, the electrons are accelerated by the ponderomotive force at the front of laser pulse and the electrons accelerated loose their energies at the tail of laser pulse. This is one of serious problems in the ponderomotive electron acceleration. In order to suppress the energy loss, we propose an overdense plasma separator to extract the electrons before entering the deceleration region of laser pulse. In our electron acceleration mechanism, only the laser is reflected by the overdense plasma separator and the electrons pass through the plasma separator. Consequently, the electrons can obtain a net energy after the interaction with the laser pulse.

Visible-Laser Acceleration of Relativistic Electrons in a Semi-Infinite Vacuum

We demonstrate a new particle acceleration mechanism using 800 nm laser radiation to accelerate relativistic electrons in a semi-infinite vacuum. The experimental demonstration is the first of its kind and is a proof of principle for the concept of laser-driven particle acceleration in a structure loaded vacuum. We observed up to 30 keV energy modulation over a distance of 1000 lambda, corresponding to a 40 MeV/m peak gradient. The energy modulation was observed to scale linearly with the laser electric field and showed the expected laser-polarization dependence. Furthermore, as expected, laser acceleration occurred only in the presence of a boundary that limited the laser-electron interaction to a finite distance.