Showing papers on "Field electron emission published in 1979"

On the physics of dust grains in hot gas.

Abstract: Charging of dust grains in hot (10/sup 4/--10/sup 9/ K) plasma is studied, including photoelectron and secondary electron emission, field emission, and transmission of electrons and ions through the grain; resulting grain potentials are (for T > or approx. = 10/sup 5/ K) considerably smaller in magnitude than found by Burke and Silk. Even so, large electrostatic stresses can cause ion field emission and rapid destruction of small grains in very hot gas. Rapid rotation can also disrupt small grains, but damping (by microwave emission) usually limits the centrifugal stress to acceptable values for plasma densities n/sub H/< or approx. =1 cm/sup -3/. Sputtering rates are estimated for grains in hot gas, based upon a semiempirical fit to experimental data. Predicted sputtering rates for possible grain constituents are similar to estimates by Barlow, but in some cases differ significantly. Useful approximation formulae are given for the drag forces acting on a grain with arbitrary Mach number.

Soft-x-ray-induced secondary-electron emission from semiconductors and insulators: Models and measurements

Abstract: Secondary-electron energy distribution curves (EDC's) and the total secondary-electron yields relative to such for gold have been measured for seven semiconductors for which electron-electron scattering losses within the emitter were considered dominant and for nine insulators (alkali halides) for which electron-phonon scattering losses were expected to be dominant in the transport process. The secondary-electron spectra were excited by Al-$K\ensuremath{\alpha}$ (1487 eV) photons and were measured from evaporated dielectric films (of about 0.3 \ensuremath{\mu} thickness) on conducting substrates with an electrostatic hemispherical analyzer of about 0.03-eV resolution. Some of the dielectric photoemitters have appreciably narrower energy distributions and higher yields than has gold; CuI and CsI have EDC widths at half-maximum of about one-third of that for gold, and yield values of 11 and 30 times greater. The FWHM and secondary-electron yield for gold were measured to be about 4 eV and 0.50 electrons per normally incident photon, respectively. The shapes of the EDC's were found to be essentially unchanged for photon excitation in the 0.1-10-keV region. Strong structural features appear only in the alkali halide EDC's, and it is proposed that these are mainly the result of single-electron promotion of secondaries from the valence band by plasmon deexcitation. A relatively simple model for x-ray photoemission has been developed which assumes that direct excitation of secondaries by photoelectron and Auger-electron "primaries" is the dominant excitation mechanism, and accounts for both electron-electron and electron-phonon scattering in the transport process. Free-electron conduction-band descriptions are assumed. The theoretical and experimental curves are in satisfactory agreement.

Liquid gold ion source

Abstract: The fabrication procedure for a liquid gold ion source is described. The source consists of a tungsten needle wetted with liquid gold. Stable gold ion currents of 1 to 100 μA have been reliably obtained. Factors affecting the ion emission characteristics including needle geometry, surface structure, and temperature are discussed.

Development of a Field Emission Electron Microscope

Abstract: A field emission electron microscope with highly stabilized gun and illuminating system was developed. Several experiments were made to demonstrate the high performance of the microscope. The brightness of the beam was more than that of the conventional ones, which feature was demonstrated by taking 300 Fresnel fringes and 3,000 bi-prism fringes. Furthermore, monochromatic feature of the microscope makes the effect of chromatic aberration smaller and the half-spacing fringes of nickel {220} planes (1/2 d2:o=O.62A) were observed. Key )tw

Phonon assisted tunnel emission of electrons from deep levels in GaAs

Abstract: A theory is developed for the electric field emission of electrons from deep levels in GaAs taking into account quantum mechanical tunneling and electron phonon interaction. Using this theory, a numerical model is developed simulating capacitive DLTS and capacitive transient experiments. The parameters of the model for the electron irradiation induced defect E3 are extracted by fitting an experimental DLTS spectrum and an experimental transient capacitance curve. In particular, an estimate is given for the Franck-Condon shift. This estimate is found to be consistent with that obtained by another method based on the measured activation energy of the capture cross-section. With the parameters thus found, the model is shown to reproduce correctly several other experimental results over a wide range of temperatures and electric field intensities.

H2 and rare gas field ion source with high angular current

Abstract: We have built and carried out initial tests on a field ion source that has been designed to operate at very low temperatures with a physisorbed surface supply to the ionization region. This mode has been found to give beams of high angular current density and is expected to have low energy spread in the beam. Presently we have measured dI/dΩ?10 to 60/sr with a probable energy spread of ?l eV. The UHV system allows processing of the field emitter under clean, high vacuum conditions. A liquid He cooled finger maintains the tip at controlled temperatures from that of liquid He to room temperature. The tip is mounted on a sapphire block to provide both excellent thermal conduction and electrical insulation to ?30 kV. Differential pumping allows a high supply pressure of H2, He, Ar, etc. in the region of the tip (≳ 10−2 Torr) and a low pressure in the rest of the system. Observation on the characteristics of the field ionization pattern are made under varying conditions of pressure, temperature, field and tip ...

Microwave emission from pulsed, relativistic e‐beam diodes. I. The smooth‐bore magnetron

Abstract: Measurements of intense magnetron oscillations in pulsed, field‐emission diodes (∼350 kV, 30 nsec) subjected to crossed externally applied fields (≲16 kG) are reported. The oscillations set in as soon as the magnetic field exceeds the critical field necessary for cutting off the diode current. The oscilations are diagnosed by the microwave emission which is studied in the range from 7 to 40 GHz. The radiation is emitted in broad frequency bands, it is strongly polarized, and can be tuned by the magnetic field; the power levels are typically 1 to 5 kW. The observations are consistent with the onset of the slipping stream instability in the Brillouin space charge flow of the electron cloud.

Field emission electron gun

Abstract: A field emission electron gun including a cathode, a control electrode which is disposed in the vicinity of the cathode, an anode which is disposed for accelerating electrons emitted from the cathode, and a source of a D.C. voltage to be applied between the cathode and the anode. Also, there is provided a switching arrangement capable of changing-over a potential of the control electrode between ground potential and a potential of the cathode, and an arrangement capable of varying relative positions of the cathode and the control electrode.

The source of high- beta electron emission sites on broad-area high-voltage alloy electrodes

Abstract: Two recently developed techniques have been used sequentially in an attempt to define the nature of high- beta field emission sites on a commercial-alloy, broad-area, electrode surface. The techniques involved were: (i) an in-situ electron optical method for locating and examining the emission site; and (ii) a high-resolution spectrometer for determining the energy spectra of the electrons field emitted from this site. Furthermore, following these measurements, the elemental composition of the emission area was determined by electron microprobe X-ray analysis. Observations, which cast further doubt upon the traditional concept of field-enhancing microprojections, indicate that the sites are non-metallic and probably consist of impurities located at cracks or grain boundaries in the surface. Tentative hypotheses are proposed for the emission mechanism and include provision for an unstable situation caused by the effects of adsorbed gas atoms.

Gallium‐field‐ion emission from liquid point anodes

Abstract: The principal processes controlling the emission of charged and neutral particles and complexes from positive liquid‐gallium points for voltages at or above ∼5 kV are briefly summarized. The components of the extractor and collector current and the fluctuations of the latter are investigated as well as the dependence of the currents on retarding and accelerating potentials that are applied to the collector. The effect of secondary electrons released from the collector by the impact of fast positive ions is examined as well as the suppression of these electrons by means of reversing or deflecting electric or magnetic fields of moderate magnitude. Feeble emission of visible light is observed at the collector surface when condensed gallium evaporates under bombardment of fast particles. The formation and life of protrusions and of the flow of neutral atoms and droplets are discussed.

Application of a thermal field emission source for high resolution, high current e‐beam microprobes

Abstract: A thermal field emission electron source has been incorporated into a microprobe with two magnetic lenses to produce a 0.10 μm beam spot with 0.11 μA current at 12 kV and a working distance of 13 cm, in agreement with calculated performance assuming a source angular intensity of 1 mA sr−1. The power density and brightness of the beam on the target were 1.6×107 W cm−2 and 5.5×107 A cm−2 sr−1 respectively. The emitter used was 〈100〉 oriented W coated with Zr, operated at 1800 K. Probe current fluctuations (〈ΔI2〉)1/2/IP =0.23% in the frequency interval 1–5000 Hz were measured at the target with I=30 nA. The microprobe was used to construct a scanning Auger microscope which produced submicron resolution Auger elemental maps with scan times of 5 min or less.

Measurements on Niobium superconductings C band cavities for linear accelerators applications

Abstract: Superconductings cavities for linear accelerators applications at 4.5 GHz (C Band) have been constructed and tested. The Niobium cavities were obtained by electron beam welding of half cavities previously formed pressing Niobium sheets in a hydraulic press. In such cavities, operating in TM 010 mode, accelerating field of 26.5 MV/m and peak surface field of 50 MV/m were obtained at a power level of 30 W/m. The best quality factor obtained at this field level is Q 0 = 2 × 109at a temperature of 1.8d (2) limitations on accelerating fields are related only to R.F. induced magnetic field. The electron loading due to field emission does not limit the maximum achievable field.

High Resolution Electron Holography with Field Emission Electron Microscope

Abstract: An experimental study of electron holography was carried out with a newly developed field emission electron microscope. Off-axis holograms were formed with a Mollenstedt-type biprism, both in Fresnel holography and image holography. The resolution of reconstructed images was higher in image holography. The obtained image hologram of an evaporated gold particle was shown to contain the Bragg-reflected waves from its {111} planes. The holograms were optically reconstructed and lattice images under arbitrary focusing conditions were observed by adjusting the focus of the optical system. The maximum line resolution in reconstructed images was 0.12 nm, which is the half spacing of gold {111} planes.

Emitter for field emission and method of making same

Abstract: A field emitter consists of a metal carrier wire coated with crystals of an oxide having a metallic luster and which is a compound of a transition metal selected from the group consisting of tungsten, molybdenum, niobium, vanadium and titanium.

Field emission cathode and its manufacture

Abstract: PURPOSE:To take out large probe current stably by adsorbing a particular metal through oxygen within the depth of mono atomic layer on the surface of area where electrons are emitted from a needle cathode. CONSTITUTION:In a vacuum container ambient where the field emission can be performed, at least one metal selected from Cr, Al, Ce, Mg, Ti, Si is deposited on the surface of area where at least the electron is emitted from a needle electrode 1 with the depth approximately same with that of mono atomic layer. Thereafter proper amount of oxygen gas is provided into the vacuum ambient to adsorb the oxygen gas with the depth approximately same with that of monomolecular layer on the metallic monomolecular layer, then the oxygen gas is evacuated to return to the ambient where the field emission can be performed. Thereafter the needle cathode 1 is heated for 10-60sec under the temperature range of 1,300-1,500 deg.C.

Photon enhanced field ionization on semiconductor surfaces

Abstract: The results of experiments reported in Ref. 1 are questioned. It is claimed that the results do not show a photon enhancement of field ionization of metal surfaces. (AIP)