Showing papers on "Field electron emission published in 1969"

Fowler‐Nordheim Tunneling into Thermally Grown SiO2

Abstract: Electronic conduction in thermally grown SiO2 has been shown to be limited by Fowler‐Nordheim emission, i.e., tunneling of electrons from the vicinity of the electrode Fermi level through the forbidden energy gap into the conduction band of the oxide. Fowler‐Nordheim characteristics have been observed over more than five decades of current for emission from Si, Al, and Mg. If previously measured values of the barrier heights are used, the slopes of the Fowler‐Nordheim characteristics (log J/E2 vs 1/E) imply values of the relative effective mass in the forbidden band of about 0.4. These values take into account corrections for image‐force barrier lowering and for temperature effects. The absolute values of the currents are lower by a factor of five to ten than the theoretically expected values, probably due to trapping effects. The temperature dependence of the current was found to follow the theoretical curve from 80°–420°K. However, an inconsistent relative effective mass of about 0.95 had to be assumed....

Normalized thermionic-field (T-F) emission in metal-semiconductor (Schottky) barriers

Abstract: Thermionic field (T-F) emission in uniformly doped metal-semiconductor (Schottky) barriers is analyzed to yield a normalized solution in closed form for the forward and reverse current (I)-voltage (V) relationship. A quasi one-dimensional approach and Maxwell-Boltzmann statistics are used. The formulation is expressed in terms of the ‘flat-band’ current density Im, the band bending Eb in the semiconductor depletion region, the materials constant E0 0 ( ln [ I I m ] = − E b E 0 0 at 0°K in the WKB approximation), and kT. The kinetic energy in units of Eb at which the maximum injection of carriers occurs in the semiconductor is shown to be cosh -2(kT/E0 0). Current flow in the temperature range between pure thermionic emission (kT/E0 0 ⪢ 1) and pure field emission (kT/E0 0 ⪡ 1) is analyzed and criteria for the transition of T-F emission to thermionic and to field emission are given. Computer solutions for the energy distribution of the injected carriers and for the normalized I-V characteristic are presented in graphical form. The results permit a straightforward calculation of the barrier height and the impurity concentration in the semiconductor from measurements of current density and differential resistance at a single applied bias. Application of these results explains a reported discrepancy between barrier heights deduced from photothreshold, C-V and I-V characteristics of WGaAs and AuGaAs Schottky barriers. A relatively constant excess temperature T0 (i.e., ln I ∝ (T + T0) when V ⪢ kT/q) is predicted in the case of large Eb/E0 0 in the higher kT/E0 0 range where thermionic emission is nearly predominant. I ∝ [exp(qV/kT) − 1] is shown to be a general expectation for all Schottky barriers near zero bias when the I-V characteristic is dominated by either thermionic or thermionic-field emission. The assumption of a Gaussian energy distribution of carriers leads to values for the slope of ln I vs. V in reasonable agreement with the results of the computer analysis, but the prediction of the absolute value of the current density deviates rapidly from the computed value when kT/E0 0 departs appreciably from unity. The Gaussian distribution also does not provide the smooth transition from T-F to thermionic emission characteristic of the computer solution.

Electrohydrodynamic Ion Source

Abstract: An electrohydrodynamic (EHD) technique is used to generate ions from liquid metals. Liquid metal is fed to the tip of a capillary needle emitter with a voltage difference applied between the emitter and an extractor electrode to produce an intense electric field at the liquid surface. Electrostatic forces overcome surface tension forces to produce ions by field emission. When using liquid cesium, time‐of‐flight mass analysis showed the ion current to be primarily Cs+ with a small percentage of Cs2+ and Cs3+. Electron currents of over 1 mA have been produced by operating the emitter at 2 kV negative. Besides cesium, alkali ion beams have been generated using NaK/cesium alloy and sodium. Calculations show that liquid metals of low work functions appear more suitable for production of atomic ions while higher work functions metals may produce multiatomic ions and charged droplets in addition to atomic ions.

Adsorption of CO on Tungsten: Field Emission from Single Planes

Abstract: Work‐function and Fowler–Nordheim pre‐exponential changes for incremental oxygen adsorption at 20 and 100°K have been measured on the (120), (111), (100), (211), and (110) planes of a tungsten field emitter. On the (110) plane Δφ = 0.6 eV at full coverage, while Δφ = 1.2–1.4 eV on most other planes. A model of O adsorption based on the partial filling of an affinity band is presented to account for this and other features of the results. Diffusion into various planes was also investigated. It was found that low‐temperature boundary diffusion at 25°K leaves the (110) plane bare. Diffusion in the chemisorbed layer starts at 400°K on (110) with an activation energy of 15 kcal, and on other planes at temperatures of ∼ 500°K.

Theory of Dielectric Breakdown in Solids

Abstract: A short review is given of current trends in research on the theory of dielectric breakdown in solids; in particular the theory of thermal breakdown is discussed for the case in which the dielectric conductivity is explicitly field dependent. A new possibility for avalanche breakdown is also examined. The field in the dielectric is considered to be nonuniform because of the space charges created by collision ionization, and the enhanced field adjacent to the cathode causes field emission which is many orders of magnitude greater than would be expected from a mean field calculation.

Schottky Barriers on GaAs

Abstract: The forward current of Schottky barriers on n-type GaAs is investigated as a function of electron concentration in the range of 8×10^17 to 8×10^18 cm^−3 at temperatures 297-4.2°K. Both vacuum-cleaved and chemically polished surfaces are used. The majority of the junctions studied are gold Schottky barriers, but tin and lead contacts are also examined. The predominant current mechanism is field emission at liquid-nitrogen temperature and below for the range of electron concentrations used. These data are in excellent quantitative agreement at 77°K with the field-emission analysis of Padovani and Stratton if one uses a two-band model for the imaginary wave number kn. At 297°K, thermionic field emission predominates, but for an electron density above 3×1018 cm−3 the field-emission mechanism with a two-band model still gives reasonable agreement.

Field emission from metal particles in a vacuum gap

Abstract: The motion of a charged metal particle which is itself a source of field emission has been investigated. It will be shown that the effect of electron emission from a particle may significantly affect its behaviour and may even reverse its direction of motion in the electric field within a vacuum gap. Cathode-directed particles have their energies increased by this process, while the reverse is true for anode-directed particles. These findings are in accord with the results of other investigators who have suggested that particle impact on the cathode of a vacuum gap is most likely to initiate vacuum breakdown.

Field emission cathode with metallic boride coating

Abstract: A field emission cathode comprises a hairpin rhenium filament coated with lanthanum boride and with a fine tungsten tip attached to the rhenium filament serves as an efficient source of electrons. The presence of free lanthanum atoms at the tungsten surface lowers the work function and enhances the field emission from the tungsten tip.

Field Emission from p-Type Si

Abstract: The nonlinear field emission behaviour in dependence on temperature and light intensity was studied in p-type silicon crystals, whose surfaces were prepared by high-field evaporation in vacuo. The voltage drop along the emitter measured by the retarding potential technique and the size of the emission pattern were determined for every point of the Fowler-Nordheim plot. The curvature of the current—voltage curves for Si has more distinct character than it was observed earlier for Ge. The region of “absolute field emission saturation”, which extends over a wide range of applied voltage variation was found in the Fowler-Nordheim plots. The emission current—voltage behaviour appreciably depends on sample history and especially on temperature treatments. Sample heating to 400 to 450 °C during bake-out fully distorts the field emission data in Si. Light and temperature produce the same effect on the field emission current. [Russian Text Ignored]

Tunneling in Schottky Barrier Rectifiers

Abstract: When a metal is brought into intimate contact with a semiconductor there sometimes arises a potential barrier within the semiconductor which impedes the flow of electrons between it and the metal. The formation of such Schottky barriers will be described by Professor Mead and this chapter will be mainly concerned with the tunneling of electrons through them. Clearly, if a bias is applied between a metal and a semiconductor, current will flow. If the barriers are sufficiently thin and the temperature is sufficiently low, then the current flow will be primarily by electron tunneling. Conversely, for thicker barriers and higher temperatures the current flow will be due to thermionic emission over the barrier. We will also consider intermediate ranges of thickness and temperature, where the current is primarily due to tunneling of thermally excited carriers. This is the socalled TF emission first introduced by Dolan and Dyke (1) in connection with field emission from a metal tip.

Field emission from wires

Abstract: This paper discusses the field emission of electrons from a wire surrounded by a coaxial cylindrical shell at a very high potential with respect to the wire. It is seen that, for many cases of interest, the results are at considerable variance with the plane surface case.

Field Emission through Hydrogen and Helium Layers

Abstract: Field emission through multilayers of H2, D2, HD, and He adsorbed on tungsten field emitters has been studied at 4.2–1.6°K and pressures of 10−5–10−7 torr of these gases under ultrahigh‐vacuum conditions. In the case of H2, HD, or D2, small work function increases relative to the chemisorbed layer were obtained, indicating a barrier to the solution of free electrons in these layers. In the case of He an apparent decrease in work function was observed for vacuum work functions of 5–3.5 eV (obtained by Ba or O2 adsorption). The effect is explained in terms of a second‐order resonance transition in which a He electron makes a virtual transition from the ground state to the 2p level, and then tunnels; an electron from the metal then fills the He ground state. In this way horizontal tunneling occurs, but avoids the strong repulsive He potential which would be seen by a metal electron tunneling normally. The mechanism fails when the work function is too low, or when the broadened He 2p level is raised above the...

Near-surface electron temperature of weakly ionized plasma according to kinetic theory.

Abstract: Properties of electrons near absorbing and emitting surfaces are studied for weakly ionized plasmas by analyzing the Boltzmann equation governing the electrons. For simplicity, it is assumed that the electric field intensity is given a priori. It is shown that there exists a “nonequilibrium absorption layer,” near the surface, wherein the kinetic distribution of electrons is completely out of equilibrium for all values of the mean free path, when the surface is highly absorbent with small or no electron emission. This layer is responsible for the large electron temperature jump at the surface, and it governs the electron temperature profile through the continuum as well as the rarefied plasmas. From the analysis it is found that the simple surface boundary condition for the continuum electron energy equation previously employed by the present author is correct when there is no surface emission. A similar simple surface boundary condition is deduced for surfaces with given finite emission rates.

Field Emission from Oxidized Metal Films

Abstract: If a sufficient voltage is applied to a thin-film system of sandwich-type (metal-oxide-metal), an electron emission can be observed under certain conditions. This emission is connected with the presence of a strong electric field within the dielectric and can be considered as a special type of field emission. It is strongly influenced by the properties and the structure of the layers, mainly the dielectric layer and the upper metal layer. The interactions of electrons in these layers are not known exactly enough and the measurement of the mentioned emission properties can considerably contribute to the solution of this problem, In this paper, a survey of the most important experimental data is given—I–V characteristics, temperature dependence, transfer ratio, energy and angular distribution—and a simple theoretical model is proposed, in which the interaction of the traversing electrons with phonons and traps in the dielectric, and with conduction electrons and phonons in the upper metal electrode, is concerned. On the basis of comparison of this theory with experimental evidence, conclusions about the role of single kinds of interactions are drawn.

A Novel Diode Sputter-Ion Pump

Abstract: A new diode sputter-ion pump employing cathode posts which protrude within the anode cell is described. For suitable post geometry and material, stable pumping of argon at equilibrium speeds in excess of 25% of the nitrogen speed of the pump has been demonstrated. Effects of post geometry and material are explored with respect to optimizing argon speed. Pumping of noble gases is analyzed in terms of the “high-energy neutrals” hypothesis. Memory effects are shown to be reduced due to the enhancement of permanent pumping mechanisms. Field emission from the post results in greatly enhanced starting at extreme high vacuum.

Electron Emission from Core and Valence States of Some Semiconductors

Abstract: Abstract Measurements of the energy distributions of emitted electrons from Si, GaP, and ZnS allowed the determination of the relative positions of some core levels of these materials and the optical density of states of the valence band in Si. These energy levels were determined relative to the Fermi level. The electron emission was induced by monochromatic X-rays (AlKα). These results are compared with values obtained from OPW calculations for the valence bands and selfconsistent Hartree-Fock-Slater calculations for the core states.

Erhöhung der Feldelektronen-Emission von Wolframspitzen durch Aufdampfen von Beryllium

Abstract: The mean work function of tungsten determined from Fowler-Nordheim plots can be reduced from 4.5 to 2.5 eV by depositing a thin layer of evaporated beryllium and subsequent thermal treatment at 800 °C in a vacuum of 10−7 to 10−10 Torr. Electron and ion field emission patterns of tungsten tips with and without beryllium demonstrate the effect of the beryllium deposit. For an application of the tungsten tips with beryllium, the excellent stability and the high emissivity at low voltages are of interest.

The brightness of electron emission systems

Abstract: Expressions are derived for the brightness and directional beam intensity of an electron beam at a general point and direction in space, in terms of the tangential velocity of emission at the cathode, for Schottky emission and field emission. An expression for the directional beam intensity at the cross-over position of an electron gun is given, in terms of the magnification of the gun, the radius of the cathode tip, the potential at the cross-over and the temperature, or applied field, at the cathode.

The Electrical Breakdown of Vacuum Insulated Electrodes under Radio Frequency Stress

Abstract: The electronic and ionic theories of vacuum breakdown under the influence of RF fields are discussed. Theoretical calculations indicate that phenomena involving electrode ions in gaps of 0.2 cmandlargerare strongly influencedby time varying fields in the frequency range of 20 to 120 MHz. Similar gap conditions do not significantly alter breakdown when only field emission electrons are considered. Experimental equipment which can compare breakdown at RF to that at 60 Hz has been constructed. The results of experiments at 21. 4 MHz are best predicted by the electron theories of vacuum breakdown.

Secondary Electron Detection in a Field Emission Scanning Microscope

Abstract: Operation of a field emission scanning microscope in a secondary electron mode is described The microscope uses only a field emission electron gun without auxiliary lenses and a silicon surface barrier detector to detect the secondary electron current Resolution of 100 to 200 A with beam currents of 10−11 to 10−10 A is reported Micrographs of a variety of specimens are shown