Pulsed Electron Emission Research Articles

Methods for Research on the Spectra of Pulse X-Ray Radiation and Emission of Micropinched Plasma Electrons

Abstract—The results of experimental studies are presented on the spectral composition of pulsed X-ray radiation and electron emission of a micropinch plasma in a wide 1–300 keV energy range. Studies were conducted on a “low inductive vacuum spark” apparatus at various discharge currents. The results we obtained make it possible to determine the effect of the discharge current on the spectral composition of X-ray radiation and the electron emission of a micropinch plasma.

Photoassisted and multiphoton emission from single-crystal diamond needles.

Practical realization of stable and high brightness sources of ultra-short electron pulses is an important issue in the development of time-resolved electron microscopy for the study of ultra-fast dynamics in materials. Here, we report on the experimental investigation of static (in the dark) and pulsed (under illumination by sub-picosecond laser pulses at 1040 nm) electron emission from single-crystal diamond needles. A significant increase of electron emission current was detected under laser illumination. The nonlinear dependence of the emission current on the laser intensity and on the angle between the needle and the laser beam polarization axis suggests multi-photon emission processes. This interpretation is in agreement with electron spectroscopy measurements performed for electrons emitted at different bias voltages and different laser power levels and repetition rates. The remarkable feature of the diamond emitters is their stability under high average power of laser radiation. This provides a new highly efficient source of photoemitted electrons based on single-crystal diamond.

Vacuum Outgassing Behavior of Carbon Nanotube Cathode with High-Intensity Pulsed Electron Emission

Experimental investigations on the vacuum outgassing of a carbon nanotube (CNT) cathode with high-intensity pulsed electron emission on a 2 MeV linear induction accelerator injector are presented. Under the 1.60 MV diode voltage, the CNT cathode could provide 1.67 kA electron beam with the amount of outgassing of about 0.51 Pa·L. It is found that the amount of outgassing, which determines the cathode emission current, depends on the diode voltage and the vacuum.

Study of the hard component of pulsed X-ray emission of micropinch discharge plasma

A set of spectrometers that allow simultaneous measurements of the spectra of pulsed X-ray and electron emission from a micropinch discharge in a wide energy range (1.5–500 keV) is described. The experimental results of the study of electron and X-ray spectra of micropinch discharge plasma are discussed. The mechanism for the formation of hard X-rays is caused by acceleration processes in micropinch discharge plasma.

Development of a Pulsed Secondary Electron Emission Gun and its Application to VOC Treatment

An electron beam is widely used for various purposes in industry. We have developed a pulsed secondary electron emission gun (SEEG) which uses pulsed discharge and high voltage technology. The device has some inherent advantages, such as compactness in size and generation of a uniform and wide electron beam. The SEEG consists of a wire ion plasma source, a cathode plate in a vacuum chamber and an electron beam irradiation part. In this paper, we improved the SEEG for stable operation. Previously an abnormal electrical discharge in the vacuum chamber disturbed prolonged electron beam irradiation. Therefore, based on the simulation result of an electrical potential distribution, we installed a plate of reducing electric stress in the vacuum chamber. Then the stable operation of the SEEG became possible. In addition, we have conducted experiment on decomposition of toluene using the SEEG in N2 and Air. The decomposition rate in N2 was higher than that in air. The addition of O2 and increase of humidity in N2 decreased the decomposition rate. Reaction products such as benzene and xylene were identified in N2 by means of GC-MS. On the other hand, benzaldehyde and formic acid were identified in Air. It is conceivable that the difference of byproducts is caused by the presence or absence of OH radical.

Picosecond photoassisted electron emission from gated p-silicon high density field emitter array

A 1 mm square array of oxidation sharpened p-type Si field emitter tips (2.4 μm spacing and 1 μm gate aperture) produces 40 ps rise time pulsed electron emission into the vacuum when excited by 110 fs duration optical pulses (λ=0.78 μm). The observed emission quantum yield for pulsed excitation of 0.04% is partially accounted for by gate shadowing and overlap of optical absorption depth and an estimated depletion layer thickness. These results suggest that more efficient photoexcited picosecond time scale electron emission is possible from optimized semiconductor field emitter structures.

Pulsed field emitted current from different commercial samples in the purpose of a free electron laser application

The development of an electron gun with the lowest possible emittance would help reduce the total length and cost of a free electron laser. Recent progress in vacuum microelectronics makes field emitter tips an attractive technology to explore for high brightness electron sources. In order to be a good candidate for a low emittance gun, field emission cathodes must provide at least the peak current, stability, and homogeneity of current state of the art electron sources. In this article, we report on current voltage measurements of commercially available field emitter samples in both continuous and pulsed mode. Pulsed electron emission is of particular interest for a free electron laser application. As mentioned by other authors [F. Charbonnier, Appl. Surf. Sci. 94/95, 26 (1996); P. R. Schwoebol et al., J. Vac. Sci. Technol B 19, 980 (2001)], higher peak current and more stable emission can be achieved when using short square voltage pulses at low frequency. We present maximum peak currents achieved with 100 ns long voltage pulses at low frequency (50 Hz). In such a pulsed mode, the risk of excessive heating and cathode damaging is considerably reduced.

High-Current-Density Electron Emission From Lead Zirconium Titanate Ferroelectric Disc Under Application of Short-Duration High-Voltage Pulses

High-current-density pulsed-electron emission is observed from a poled lead zirconium titanate (PZT, Zr/Ti:53/47) ferroelectric ceramic disc on application of short-duration (/spl sim/6 ns) negative high-voltage (/spl sim/4 kV) pulses. Electron-emission pulses with a peak current density /spl sim/400--450 A/cm/sup 2/ and a full-width at half-maximum (FWHM) duration of /spl sim/200--250 ns were recorded in the presence of a dc extraction field. These are comparable to the various earlier results obtained using excitation pulses of duration comparable to the polarization switching time (/spl ges/100 ns). Self-emission of electrons with a current density of /spl sim/20--30 A/cm/sup 2/ was also observed. The experimental observations indicate occurrence of partial polarization reversal in the ferroelectric sample followed by plasma formation on the surface.

Surfaces, Electron and Ion Emission

By using the method of pulsed field electron emission, it is shown that, as the current density approaches the ultimate value, there appears a bright ring around a normal field-emission image. This effect is frequently observed in the case of planar field-emission cathodes. It is suggested that secondary electrons emitted from the anode return to the anode under the action of the electric field, producing the rings. Field-emission applications based on this effect are discussed.

Laser-driven high-current-density pulsed electron emission from lead zirconium titanate ferroelectric ceramic

Laser driven high current density pulsed electron emission is observed from a lead zirconium titanate (PZT, Zr/Ti: 53/47) ferroelectric ceramic disk using second harmonic of neodium: glass laser (wavelength ∼527 nm, pulse duration ∼3 ns, laser fluence ∼5–40 mJ/cm2) in the presence of a dc extraction field. Apart from electron current pulses of ∼100 A/cm2 [full width at half maximum (FWHM) ∼400 ns] obtained from laser irradiation of the surface towards the positive end of the polarization vector, electron current pulses of ∼30 A/cm2 (FWHM ∼1.1 μs) are also emitted from laser irradiation of the opposite surface. Dependencies of various characteristics of the electron pulse on laser fluence in the two configurations are presented.

In situ cleaning of microfabricated field emitter cathodes

The use of microfabricated field emission cathodes in applications of technological importance has been hindered by difficulties in obtaining acceptable emission characteristics in the vacuum environment of the device. We have investigated in situ surface cleaning and annealing using high pulsed electron emission. Extraction of high current densities provides a reliable means to shape and clean microfabricated field emitter tips, thereby enhancing their temporal stability and emission spatial uniformity.

Electron energy distributions of ferroelectric emission from plzt 8/65/35

Strong pulsed electron emission from ferroelectrics due to fast polarization switching (i.e., ferroelectric emission) has attracted much interest recently. In this paper, electron energy distributions of PLZT 8/65/35 were measured using a double pass cylindrical mirror analyzer (DPCMA) operating in Auger mode. The results showed a very narrow energy distribution (FWHM: 10eV∼20eV), and the emission energy was on the order of the applied pulse potential. In addition, electron emission energy was relatively independent of driving pulse frequency, but increased with driving pulse amplitude, and decreased with sample temperature. At a temperature (200°c) far above the phase transition temperature (≈130°C), strong electron emission was still observed. These results suggest that ferroelectric emission is primarily related to the material polarization switching rate.

Analysis of physical mechanism of field electron emission from ferroelectrics

Pulsed electron emission from ceramic composition PLZT 2/95/5 and x/65/35 (x = 7;8;9;13) has been observed. Three levels of emission are shown and peculiarities of each of them are interpreted.

High-intense pulsed electron emission by fast polarization changes in ferroelectrics

Abstract The phenomenon of high-intensity pulsed electron emission from ferroelectrics, discovered at CERN in 1988, has attracted much interest and is today a subject of investigation all over the word. Applications of this new kind of electron source are manifold, since the emission effect does not rely on the quality of the vacuum, the electrons may have an initial kinetic energy up to several keV, the pulse duration can be varied, and the cross-section of the source may be determined from the electrode geometry. Thus, research and development on the Ferroelectric Electron Beam Source (FEBS) is wide-ranging and comprises pulse generation of femtosecond to microsecond duration, high current cathodes, large area emitters, micro sources, and electron emission from ferroelectric thin films. The phenomenon is initiated by suddenly unbalancing the charge equilibrium of the ferroelectric, and the emission of the pulsed electron beam is part of the relaxation process. A convenient method of achieving the initia...

Plasma-assisted electron emission from (Pb,La)(Zr,Ti)O3 ceramic cathodes

Strong pulsed electron emission has been observed from 12/65/35 lead lanthanum zirconate titanate ceramic composition in two different nonswitched phases at room temperature and at the temperature 100 °C. The electron emission parameters of this composition appear to be independent of phase for the two phases investigated. Fast photography and direct observation show that the strong electron emission occurs from the surface discharge plasma. The new experimental data make it possible to demonstrate the validity of the Child–Langmuir law for this electron emitter. A pulsed plasma lead lanthanum zirconate titanate ceramic cathode with burst frequency up to 100 kHz and collector current density up to 10 A/cm2 is developed.

Heating and failure of niobium tip cathodes due to a high-density pulsed field electron emission currenta)

This article presents the investigative results of pulsed threshold current densities of niobium tip cathodes at temperatures ranging from 4.2 to 300 K. It has been shown that the superconducting-to-normal phase state transition of the cathode has no effect on pulsed threshold current densities. Estimations have been made for the factors limiting the current from a superconducting emitter. The experiments have shown that the cooling of the cathode from 300 to 4.2 K changes the dynamics of cathode heating considerably and leads to a steady increase in the threshold current densities with the delay time range of 10−9–10−6 s. Numerical analysis of thermal processes in the emitter has shown that the above effects are not due to the difference between the electron and the phonon temperatures (the electron–phonon relaxation time does not exceed 10−9 s), but to the more intense heat transfer processes and the reduction of Joule heating, with the cooling of the cathode. It has been shown that the space charge of emitted electrons produces a considerable effect on the temperature and current density distribution in the tip apex. Investigations have shown that the mechanism of the tip cathode failure depends on the delay time range. The simple relationship for estimation of average pulsed threshold emission current density of the tip cathode for a delay time range of 10−9–10−7 s is presented.

First simultaneous observation of electron emission from and switching current transient in PZT ferroelectric ceramics

Abstract Fast ferroelectric switching in PZT has been investigated simultaneously with the characteristic pulsed electron emission. The visible correlation in time directly suggests that the change of polarization inside the ceramic material causes the emission effect. It is shown that the amount of emitted charge is related to the degree of switching while changing the polarization starting from different points at the hysteresis loop. Resetting by an opposite-oriented electrical field between the single emission processes increases the electron beam current, improves the stability and is of practical advantage.

Pulsed laser-induced electron and positive-ion emission from Cu(100) under ultrahigh-vacuum conditions near the threshold for surface damage

Results are presented from an experimental study of pulsed laser-induced electron and positive-ion emission at 590 nm from single-crystal Cu(100) under ultrahigh-vacuum conditions near the threshold for surface damage. Below 60 MW/cm2 the electron emission is consistent with a three-photon photoemission mechanism. Above 60 MW/cm2 thermionic electron emission becomes dominant. Positive ions are produced with a threshold of approximately 60 MW/cm2 and a slope of 9.5 in a log(yield) vs log(power) plot. The kinetic energy distribution of the ions is nonthermal with a maximum at approximately 0.7 eV. Ion production is most likely due to collisions of thermally desorbed atoms with electrons above the surface. Evidence is presented that suggests a critical role of substrate-emitted electrons in the formation of a laser-induced surface plasma near its low power threshold. It is also found that electron and ion yields from a given spot on the surface decrease with the number of laser pulses and spot receives. The yield from a previously unirradiated spot decreases by an order of magnitude over the course of approximately the first 25 laser pulses approaching a constant level for subsequent pulses. Enhanced yields from new spots could be eliminated by additional annealing of the surface prior to laser irradiation. These observations are consistent with enhanced charged particle yield from surface defects which are reduced in number by subsequent annealing by the laser.

Electron and ion emission from liquid metal surfaces

The application of positive or negative electric fields to small-area liquid metal surfaces leads to very high brightness DC ion or pulsed electron emission. The stabilization of a cone-shaped structure by the balance of electrostatic and surface tensions forces is described. Electron and ion emission occurs by field emission and field evaporation mechanisms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electron emission properties of laser pulsed GaAs negative electron affinity photocathodes

The emitted electron energy distribution of a laser pulsed GaAs negative electron affinity (NEA) photocathode was measured with a retarding grid analyzer. The total electron energy distribution was found to depend strongly on laser intensity and cathode thickness. A model based on the separation of the excess photogenerated carriers within the cathode structure has been developed and tested to explain this behavior. Pulsed electron emission patterns were obtained by directing the emitted electrons to a phosphorous screen. The patterns indicate that uniform emission occurs and that the emission develops uniformly as the cathode is activated to a NEA condition. An extrapolated plot of the angular intensity FWHM versus V1/2B indicates that the pulsed cathode possesses a natural semicone angle of approximately 10°. The angular distribution is narrow because of the electron refraction which occurs upon emission due to differences in the effective mass and vacuum rest mass of the electrons.