Showing papers on "Field electron emission published in 1968"
TL;DR: In this article, a field emission electron source operating at a pressure of 10−9 Torr was used to produce a focused spot having a radius smaller than 50 A and providing 1000 times more intensity than a hot filament system having a similar final spot size.
Abstract: A new electron gun has been built which features mechanical and optical simplicity. Theoretically, it can produce a focused spot having a radius smaller than 50 A and provide 1000 times more intensity than a hot filament system having a similar final spot size. The increase in intensity is made possible by using a field emission electron source operating at a pressure of 10−9 Torr, which is provided (without baking) using commercially available pumps. The small spot is produced by using two properly shaped electrodes which accelerate and focus the electrons from the tip. It would take a hot filament gun and at least two additional lenses to replace this field emission gun when a spot radius less than 100 A is required. Even then the brightness of the conventional source would be too low to make use of the small spot size obtained. The optical properties for the new gun were predicted on a computer and experimentally confirmed in a new scanning electron microscope. The aperture aberration coefficient was measured to be no more than a factor of two greater than the theoretical value of 1.5 cm. A spot radius of 250 A has been measured, and this value is to be compared with the theoretical value of 150 A. Although it was convenient to measure the spot directly only at a relatively large image distance (11.3 cm), calculations imply that the gun can provide a spot radius less than 25 A when very small image distances are used. The gun can be used in pulsed operation because all optical properties are constant for a given voltage ratio so that application of the electrode voltages by means of a voltage divider provides automatic focusing for arbitrary changes in the applied voltage. The methods used to make and operate reliable high field emission tips are reviewed, and a technique is described for changing the required tip voltage to obtain a given emission current.
348 citations
TL;DR: Dense thermonuclear plasma by irradiating liquid or solid T-D target with electrons or ions from intense field emission discharge is discussed in this article, where the authors present a method to generate a dense therminuclear plasma.
Abstract: Dense thermonuclear plasma by irradiating liquid or solid T-D target with electrons or ions from intense field emission discharge
144 citations
TL;DR: In this article, the influence of energy analyzer transmission function on measured field emission energy distributions has been evaluated by folding a Gaussian transmission function into the field emission total energy distribution, and the resulting distributions at 0, 4.2, 20.3, 77, and 300 K are plotted as a function of the field and work function dependent parameter d, and for the special case φ=4.40 eV, F=3.0×107 V/cm.
Abstract: The influence of energy analyzer transmission function on measured field emission energy distributions has been evaluated by folding a Gaussian transmission function into the field emission total energy distribution. The resulting distributions at 0, 4.2, 20.3, 77, and 300 K are plotted as a function of the field‐ and work‐function‐dependent parameter d, and for the special case φ=4.40 eV, F=3.0×107 V/cm. A criterion is established for determining the width of an analyzer transmission function from distributions measured at the above temperatures. It is shown that the slope of the log of the energy distribution is changed by less than 1% when the analyzer width is changed from 0 to 100 mV.
61 citations
TL;DR: In this article, it was shown that the stopping-potential method is unreliable for the measurement of the surface tension of refractory metal surfaces, and the results of this work brought into question the reliability of the stoppingpotential approach for surface tension measurement.
36 citations
TL;DR: Low temperature oxygen adsorption on W single crystal surfaces field emission, discussing desorption by substrate heating was discussed in this paper, where the authors used a single crystal surface field emission detector.
34 citations
TL;DR: In this article, a comparison between the recently developed general theory of thermionic and field emission from metals and the available experimental data related to the dependence of the electron emission current on both temperature and field was made.
Abstract: A comparison is made between the recently developed general theory of thermionic and field emission from metals and the available experimental data related to the dependence of the electron emission current on both temperature and field (Andreev, Dyke et al. , Drechsler, Haag). It is shown that the measurements at relatively strong currents agree well with the theoretical equations in rather wide temperature and field ranges while those at very weak currents are not reliable to be a test of the theory.
30 citations
TL;DR: In this paper, a preliminary experimental study was made of the problems involved in the preparation, imaging, identification and field-evaporation of the deposits of gold on tungsten and of iron on iridium were prepared by vapour deposition in ultra-high vacuum in a liquid nitrogen-cooled helium-ion microscope.
30 citations
25 citations
TL;DR: The effect of heating at temperatures in the range 1000-1500°K on oxygen-covered tungsten surfaces has been studied by field emission and field ion microscopy.
Abstract: The effect of heating at temperatures in the range 1000–1500°K on oxygen-covered tungsten surfaces has been studied by field emission and field ion microscopy. The shape of the tungsten emitter changed from the initial field evaporated form to a more polygonal form, which varied with the oxygen coverage. The form of the field emission patterns was determined by electron emission from the highly curved regions of the surface between the enlarged (211), (100), (310) and (110) facets. The intensity of electron emission and the final shape of the emitter indicated that for sub-monolayer coverages the equilibrium coverage of the (100) region was less than for other surface regions, showing that the binding energy is least for oxygen adsorbed on (100) surfaces. The change in shape of partly oxygen-covered emitters occurred by the same type of surface tungsten atom displacement as rearrangement of clean field-evaporated tungsten emitters. Adsorbed oxygen hindered surface diffusion of tungsten.
21 citations
TL;DR: In this article, the field emission from negatively charged spherical solid particles has been studied analytically, and some numerical results depicting the variation in the number of emitted electrons with the charge, radius and work function of the particle are presented.
Abstract: The field emission from negatively charged spherical solid particles has been studied analytically, and some numerical results depicting the variation in the number of emitted electrons with the charge, radius and work function of the particle are presented.
19 citations
TL;DR: In this paper, a theory for field emission from ferromagnetic solids is given in which the two spin subbands of the conduction band are split by exchange forces using a simple plane wave model.
Abstract: A theory is given for field emission from ferromagnetic solids in which the two spin subbands of the conduction band are split by exchange forces Using a simple plane wave model for the conduction band states it is shown that the familiar WKB approximation for the tunneling probability has to be improved by momentum dependent factors to account for the spin polarization of the emission current observed in a recent experiment which is 8% in the case of Gd The calculations are extended to describe emission from Bloch states Applications of the theory to various ferromagnetic systems are discussed, the use of ferromagnetic Eu1−xGdxS as a source for highly polarized beams is suggested
TL;DR: In this paper, three distinct adsorption states were observed in the temperature ranges corresponding to the bulk metal α, β and γ phases, and the final work functions were found to be 3.60±0.03 eV at 295 ° K, 3.53± 0.03eV at 934°K and 3.43± 0.03 ev at 1042°K.
TL;DR: In this article, the electron field emitter is used as an approximate point source of electrons to produce magnified shadows, or profile images, of small electrically conducting objects in ultrahigh vacuum.
Abstract: An electron field emitter is used as an approximate point source of electrons to produce magnified shadows, or profile images, of small electrically conducting objects in ultrahigh vacuum. Some electrical and electron optical properties of this type of microscopy are described.
TL;DR: A phenomenological model is presented to account for the observed emission pulses in this article, where the dielectric materials are ascribed to laser heating of surface contaminants with subsequent production of high energy photons and thermionic emission of electrons and ions.
Abstract: Positive and negative charged particle currents induced in vacuo by high‐power laser irradiation of transparent dielectric materials below the threshold for physical damage have been investigated. Soft glass, Pyrex, fused quartz, Supracil quartz, CaF2, LiF, and sapphire all show similar behavior. Currents as large as 1010 charged particles per pulse are obtained using ruby laser radiation with normal mode power levels of about 200 kW. For negative particle currents, two distinct signals have been time resolved using Q‐switched pulses. The emission can be correlated qualitatively with that from laser irradiated metal surfaces. A phenomenological model is presented to account for the observed emission pulses. For the dielectric materials, currents are ascribed to laser heating of surface contaminants with subsequent production of high‐energy photons and thermionic emission of electrons and ions. The emission of photons, electrons, and ions can be reduced, but not completely eliminated, by careful precleanin...
01 Jan 1968
TL;DR: Both the field ion and the field emission microscopes are projection microscopes as mentioned in this paper, in which the image is formed by radiation originating from a sharply pointed specimen and diverging from it to strike a fluorescent screen in a vacuum chamber.
Abstract: Both the field-ion microscope and the field-emission microscope are projection microscopes, in which the image is formed by radiation originating from a sharply pointed specimen and diverging from it to strike a fluorescent screen in a vacuum chamber. In the field-emission microscope the image is formed by electrons escaping from the negatively charged specimen by quantum-mechanical tunneling under the influence of an intense electric field. In the field-ion microscope the specimen is positively charged and the vacuum vessel contains a gas at a low pressure; the image is formed by the positive ions produced near the specimen’s surface when electrons tunnel from their parent gas atoms into the specimen.
CERN1
TL;DR: In this article, it is shown that, for small gaps between clean metal electrodes, satisfactory explanations may be found for the initiation and development of electrical discharges in vacuum, based on a detailed analysis of the electron field emission from the cathode and the associated current thermal interaction with either electrode.
TL;DR: In this article, high voltage pulsed field effect experiments were performed on the {111} A and B surfaces of n-type InSb which were previously exposed to a mixture of chlorine and air.
TL;DR: Dense thermonuclear plasma production in Th-D by high energy intense electron beam from pulsed high intensity field emission discharge as mentioned in this paper was shown to be possible in the video.
Abstract: Dense thermonuclear plasma production in Th-D by high energy intense electron beam from pulsed high intensity field emission discharge
01 Jan 1968
TL;DR: In this paper, Brodie et al. performed an experimental search for de Haas-van Alphen-like quantum oscillations in field emission current from bismuth single crystals.
Abstract: approved: (Signature ) Laird C. Brodie An experimental search. based on previous published theoretical work. was made for de Haas-van Alphen~like quantum oscillations in field emission current, The study was motivated by the possible applicability of de Haas-van Alphen measurements to the study of Fermi surfaces near real surfaces, Field emitters were fabricated from bismuth single crystals grown from the melt by a modified Bridgeman technique. Field emission current was measured with the field emitter cooled by contact with a liquid helium bath. Most measurements were made at 4,2 0 K. although a few measurements were made at 2.02°K, Fowler-Nordheim plots of the experimental current-voltage data were linear over several orders of magnitude. The field emission current was measured as a function of magnetic field strength to twenty kilogauss and as a function of direction, with respect to the emitter axis t for a steady field of ten kilogau~s. The results of measurerrents on four'field emitter crystals are reported in this thesis. In most of this work, de Haas-van Alphenlike quantum oscillations were not observed. In one set of data, however, de Haas-van Alphen-like oscillations havin,g a period of -5 -1 0.50 x 10 G appear to be present. The published theoretical work was reevaluated. As a result of a lar~ effective Dingle temperature for field emitters, and because the effective masses of carriers in bismuth are anisotropic, the de Haasvan Alphen effect ,in field emission current could be several times smaller than has been suggested in the literature. The sensitivi ty of the experiments reported in this thesis was not sufficient to allow unambi guous identification of quantum oscillations at the reduced level. An outline of an experimental 'procedure sui table for observation of the de Haas-van Alphen-like effect in field emission current at the reduced level is provided in the final chapter. Search for Quantum Oscillations in Field Emission Current from Bismuth
TL;DR: The theory of the anode sheath for quasineutral collision-dominated arc plasmas is developed in this paper, both for the steady state and for behavior following emission of a burst of ions from the anodes surface.
Abstract: The theory of the anode sheath for quasineutral collision‐dominated arc plasmas is developed, both for the steady state and for behavior following emission of a burst of ions from the anode surface. It is shown that the decay time constant for such a burst is related to the ambipolar diffusion time, τ=Λ2/Da, where Λ is the appropriate diffusion length. The ion burst, a consequence of field emission from the anode surface, causes a local sharp decrease in the electric field strength, followed by a gradual increase as the ion cloud dissipates. A new burst of field‐emitted ions begins another cycle. A summary is given of experimental work on anode‐spot oscillations, some of which supports the predictions of the theory.
Journal Article•
TL;DR: In this article, the field desorption of cesium ions from a positive electrode is formulated for the range of electric field over which an image potential binds the ions to the electrode surface.
Abstract: The field desorption of cesium ions from a positive electrode is formulated for the range of electric field over which an image potential binds the ions to the electrode surface. Recent investigations on the ionization of gas atoms by a metal surface are utilized, in conjunction with steady‐state arguments, to yield an expression for the ion supply at the electrode surface. A tunneling process in the presence of an electric field is then considered, and the ion emission obtained in terms of fundamental constants and pertinent parameters. As part of the over‐all problem, the effect on the emission current of fractional adsorbed atomic layers on the electrode is examined; not surprisingly, the nonuniform properties of a real electrode lead to the same difficulties in the description of ion emission as those met in the case of electron field emission.
Patent•
04 Nov 1968TL;DR: A light detector based on the fact that the field emission from a photoconductive material varies depending on a variation in the intensity of the light to which the material is exposed is presented in this paper.
Abstract: A light detector based on the fact that the field emission from a photoconductive material varies depending on a variation in the intensity of the light to which said photoconductive material is exposed, said detector comprising basically a field emission cathode of a photoconductive semiconductor in the form of a pointed whisker, and an electron collector for collecting the electrons emitted from said cathode, an appropriate accelerating voltage being applied between said cathode and said collector.