Showing papers on "Field electron emission published in 1977"

Contact adhesion between solids in vacuum. I. Single-asperity experiments

Abstract: A new technique is described for measuring the adhesion between a sharply curved metal point (platinum, tungsten, titanium, nickel or gold, with a radius of curvature typically 300 nm) and a flat surface (platinum, tungsten, cobalt, silicon or graphite). Adhesion forces as small as 100 nN can be measured with a sensitivity (limited by friction and vibration) of 20 nN, and the electrical resistance of the contact region is measured as a function of positive and negative load. Any plastic deformation of the metal point, as well as its cleanliness, is monitored by current and voltage measurements on electrons drawn by field emission from the point before and after contact.

Field calibration using the energy distribution of a free‐space field ionization

Abstract: Utilizing free‐space field ionization, a new method of field calibration for field ion emitters has been developed. Plotting the differences of relative energy deficits of free‐space ionized H2, D2, or Kr for sets of various applied voltages V against the logarithm of the voltage ratios yields a field factor k from which the surface field F0=V/krtip is obtained with 3% accuracy. Refinement of this method also enabled us to determine the local radii of the specimen tip. In addition to new and more reliable data of evaporation fields of various materials, such as W, Mo, Rh, Ir, Pt, and Ni, it has revealed several significant facts on the geometrical shape of the emitter.

Field-emission sites on unpolished stainless steel

Abstract: An electron-beam tracking technique has been used to locate the sources of field-emitted electrons for subsequent in situ examination with a scanning electron microscope. The electrical characteristics of individual emitters were measured and used to estimate their physical size assuming simple geometric models. Micrographs of two of the locations are shown both before and after the application of an electric field sufficiently large to destroy the emission source.

Field-emission and field-ion microscopy of lanthanum hexaboride

Abstract: Field‐emission and field‐ion microscopy studies are carried out on (001) ‐oriented LaB6 single‐crystal tips Surface states and some field‐emission characteristics are examined The facet of low‐index planes, (001), {011}, and {111}, is observed after heating a tip at high temperatures The field‐emission current fluctuations from thermally cleaned LaB6 tips are larger than those of W field emitters Field‐emission patterns are found to depend on the local curvatures of the tip surface The surface states are discussed by considering the effects of surface diffusion and evaporation for LaB6 during high‐temperature heat treatment

Field Emission of Monoenergetic Spin-Polarized Electrons

Abstract: Field emission from a tungsten tip, covered by a layer of crystallized ferromagnetic europium sulfide, leads to an electron beam with a current of 10 -8 A, an energy width of less than 100 meV, and a spin polarization of about 0.85 at a tip temperature of 9 K. Proper annealing of the EuS layer is crucial.

Interface state density in Au-nGaAs Schottky diodes

Abstract: A method for determining the surface state density in Schottky diodes taking into account both I–V and C–V data while considering the presence of a deep donor level is presented. The model assumes that the barrier height is controlled by the energy distribution of surface states in equilibrium with the metal and the applied potential and does not include, explicitly, an interfacial layer. The model was applied to extract interface state densities of Au- n GaAs guarded Schottky diodes fabricated from bulk and VPE (100) GaAs with carrier conentrations between 3 × 10 15 and 8 × 10 16 cm −3 . These diodes exhibited ideality ( n ) factors of approximately 1.02 and room temperature saturation current densities ∼10 −8 A/cm 2 . This model is in substantial agreement with forward bias measurements over the 77–360°K temperature range investigated, in that a temperature-independent energy distribution of interface states was obtained. In reverse bias the interface state model is most valid with the higher carrier concentration material and at high temperature and low bias voltage. Typical interface state densities from 0.07 eV above the zero bias Fermi level to 0.01 eV below the Fermi level were 2 × 10 13 cm −2 eV −1 . The validity of the model under reverse bias is restricted by a non-thermionic reverse current, thought to be enhance field emission from traps.

Understanding and using field emission sources

Abstract: Field emission tips are growing in popularity due to their high brightness, small source size, minimal energy spread and potentialy long lifetime Disadvantages include the necessity of a moderate ultrahigh vacuum, beam current that fluctuates 2-5% and additional maintenance of the source such as processing or flashing Several practical modes of operation have evolved including cold (room temperature) operation, oxygen processing and thermal (heated) use Stability and lifetime depend on vacuum, tip current, first anode outgassing and temperature Anyone using an instrument with a field emission should be aware of how field emission tips operate and how to optimize their performance (51 references)

Thermionic-field emission through silicon Schottky barriers at room temperature

Abstract: Current transport via thermionic-field emission through Ni-Si diodes having implanted surface layers has been studied for surface fields between 107 and 108 V m−1. The well defined potential profile in these structures enables a close comparison to be made between the calculated and measured thermionic-field emission currents and it is shown that the change of reverse current with field can be accurately predicted using the appropriate electron effective mass in the direction of current flow. For typical barrier heights, the field dependence of the electron current through a triangular barrier with image force correction is very nearly exponential with an effective tunnelling distance between 25 and 30 A at 300K.

Energy distribution of post-accelerated electrons field-emitted from carbon fibres

Abstract: An electron gun system with post-acceleration is described suitable to operation with a carbon fibre field-emission tip. The system was tested in an electron optical bench with a vacuum pressure of about 10−6 torr. The electron current was most stable if the current to the extraction electrode was minimized. The half width of the energy distribution of the electrons accelerated up to 30 keV was 215 meV for small currents (≈10−9A). The half width of the distribution increases with growing emission current. This increase may be attributed to instabilities in the surface structure due to ion bombardment and to the circumstance that more than one emission centre contributes to the electron current.

Electron Tunneling in Chemistry and Biology

Abstract: Electron tunneling is well recognized in physics. It was first proposed by Nordheim (1) in 1927 and was quickly applied to electron movements by many early theorists. For example, Nordheim (1) applied it to thermal emission of electrons. Oppenheimer (2) applied it to the problem of field emission of electrons in 192R. Nordheim (3), Frenkel & Joffe (4), and Wilson (5) applied it to rectifying barriers in 1932. Zener (6) used it to explain avalanche breakdown in semiconductor junctions in 1934. Giaever (7) first observed tunneling currents from superconducting metals separated through oxide barriers. Josephson (8) predicted, and it has been confirmed ex­ perimentally, that electrons tunneling through junctions in superconducting rings ex­ hibit ccrtain quantum-mechanical oscillatory phenomena. Mead and co-workers (9) have studied electron tunneling through barriers nearly 100 A thick and confirmed the quantum-mechanical relationships. Practical appliances have resulted such as tunnel diodes [Esaki (10) 1958], and numerous devices (11) for accurately measuring small voltages or magnetic fields, or detecting infrared radiation that use the Josephson effect. Still being developed are computer memories (12) that use the Josephson effect, and a method of spec­ troscopy of minute amounts of organic or biological materials embedded in a tunnel barrier (13). In chemistry, the tunneling of electrons is also well recognized. Gurney (14) proposed in 1931 that electrolysis involved electron tunneling through the electrode surface and showed how the necessity to match energy levels could produce the phenomenon of overvoltage. His theory was extended by Horiuti & Polanyi (15) in 1935. In 1939 Mott (16) suggested that the oxidation of aluminum is controlled by electrons tunneling through the oxide layer from the metal to adsorbed O2, In 1940 Libby (17a) suggested electron tunneling to explain the rapid exchange between MnO';and MnO�in solution. In 1952 (17b), Libby used tunneling, along with a requirement of solvent rearrangement, to satisfy the Franck-Condon principle and explain such facts as that ferriand ferrocyanide ions exchange electrons much more rapidly than ferric and ferrous ions. R. A. Marcus (18), in a series of papers,

Contribution to the general analysis of field emission

Abstract: The theory of thermionic‐field emission of electrons from metal surfaces with planar geometry has appeared in various publications. Specifically, the functional dependence of the normal, tangential, and total energy distributions of the emitted electrons and of their current density upon work function, temperature, and appied electric field has been established. In this paper, we present, graphically, a numerical analysis of these functions for several work functions, temperatures, and field strengths of experimental interest.

Photon assisted field ionization

Abstract: An enhancement of the field ionization current was observed when the tungsten tip was illuminated by an external light source. Enhanced ionization occurs for photon energies of lower value than the work function of tungsten. Results indicated that holes are created below the Fermi level by the interaction of photons with the tungsten tip. Hence, the critical distance for which field ionization can occur is reduced. This study provides a method which is complementary to photon assisted field emission to study the electronic states at a metal surface.

Comments on nonlinearity, response time and polarity reversal in a thermal field emission metal whisker diode

Abstract: In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region (μm) using a metal-metal point contact diode for the generation, frequency mixing and detection. At present there are two models which attempt to explain the rectification mechanism of the diode: 1) Tunneling of electrons through an intermediate oxide film from whisker to the metal base, i.e., configuration is considered to be a metal-oxide-metal (MOM) tunneling junction. 2) Rectification and nonlinear processes are the result of a thermal enchanced field emission. Such emission is a consequence of the immersion of the whisker in the laser radiation which results in conduction induced thermionic emission and/or generation of an electric field at the tip necessary for electron tunneling by field emission. The purpose of this comment is: a) to discuss qualitatively the basic difference between MOM and TFE theories as regards the origin of the nonlinearity and rectification properties of the metal point contact junction; b) to review the analyses describing the ultimate frequency response of the device; and 3) to provide a possible explanation for polarity reversal consistent with the TFE mechanism describing the operation of the whisker diode.

A field-emission retarding-potential device for absolute work function measurements

Abstract: A field-emission retarding-potential device is described which has been specifically designed to fit typical UHV surface research systems. The design and construction of the lens system are fully described. Its performance is demonstrated, both as an energy analyser for the field-emitted electrons and in the determination of the absolute, area-averaged work function of UHV-evaporated films of aluminium, copper, gold and silver. The values obtained for these metals are 4.26+or-0.02, 4.64+or-0.02, 5.37+or-0.02 and 4.46+or-0.02 eV respectively. In view of (i) the clean conditions of film growth, (ii) the proven purity of the films (by Auger electron spectroscopy), and (iii) the demonstrated reproducibility of the technique, it is claimed that these measurements have yielded the most reliable work function values yet available for thin films of the four metals studied.

On the theory of field emission from p‐type semiconductors

Abstract: The field emission of semiconductors of p-type is investigated and the essential role of recombination processes in cathode is demonstrated. It is also shown that surface states on the emitting surface do not alter the value of the saturation current, while the volume traps may change its temperature dependence. [Russian Text Ignored.]

Hot-electron emission currents in N-channel IGFET's

Abstract: Short-channel effects and the theory of scaling require proportionally increased doping concentrations in the surface channel and/or the bulk substrate regions of Si IGFET's of short channel lengths. Unless the applied voltages are reduced accordingly, appreciable emission of hot electrons from the Si substrate into the gate SiO 2 layer may occur. The emission processes can be studied by measuring the gate current directly in the case of channel electron emission, or the optically induced hot-electron emission current in the case of emission of thermally generated leakage electrons. Absolute emission probabilities as well as relative emission characteristics can be determined. These emission characteristics are useful not only for designing Si devices but also for quantitative testing of theoretical models of the emission process. Important physical mechanisms and device parameters in the emission process are discussed.

Ion impact on field emitter crystals

Abstract: 2014 The hypothesis is introduced that the ions impact distribution on a crystal surface is anisotropic, in the case where the crystal is a field emitter tip, and the ions are produced by field electrons collisions with the residual gas. This anisotropy is a result of the fact that nearly all the ions which bombard the tip hemisphere are produced very near the surface, where the electron current is highly anisotropic. The energetical and geometrical distributions of the bombarding ions (as well as absolute ion currents) are determined theoretically on the basis of electron and ion trajectories calculated by Vernickel and Welter. The geometrical ion distribution at the surface should form an image similar to the field electron microscope image. This image should be visualisable by an observation of the bombardment defects in a field emission microscope. Preliminary experiments have been made with a tungsten tip bombarded by hydrogen ions. These experiments as well as an evaluation of known field emission micrographs seems to confirm the anisotropy hypothesis and indicate the existence of the ion impact image. REVUE DE PHYSIQUE APPLIQUÉE TOME 12, OCTOBRE 1977, PAGE Classification Physics Abstracts 61.80J

Some Investigations on Vacuum-Evaporated Al–CdSe Thin Film Diodes

Abstract: The Schottky barrier formed by deposition of CdSe on Al has been examined by temperature-dependence measurements of the current-voltage (I-V) characteristics and capacitance-voltage (C-V) characteristics. The failure to determine the built–in potential Vd from the simple Schottky approximation can be remedied by assuming two regions of donor concentration in the space-charged region. The value of Vd is 0.2 V. The current transport mechanism is due to the tunneling current arising from field emission.

Field emission from oxidised niobium electrodes at 295 and 4.2K

Abstract: Among the various methods proposed to reduce the electron field emission in Nb superconducting cavities, the authors have investigated oxidisation and compared the DC field emission current from bare Nb plane surfaces with that from oxidised ones. The thickness of the Nb2O5 layer (from 0 to 160 nm), temperature (normal and superconducting states) and previous electronic bombardment were considered. Experiments show that threshold and breakdown DC voltages increase with the thickness of the oxide layer up to 160 nm. The improvement seems to be independent of the temperature and of previous electronic bombardment.

New tunneling experiments from strong ferromagnets and predictions of the band theory: Resolution of a controversy?

Abstract: The positive sign (magnetic moment parallel to the magnetization) of the electron spin polarization P in superconducting tunneling from Ni and Co has been reported to be in condlict with predictions of the band theory of ferromagnetism We have mainly observed positive P also in field emission from single‐crystal Ni(100) and (110) tips, with probe hole selecting emission from high‐index, low‐work‐function planes Using band‐structure calculations we can show that, assuming s tunneling only includng s‐d hybridization, very large positive P can be expected Further inclusion of d contribution is considered and found to bring reasonable agreement with experiment An approach to the matching problem for high‐index crystallographic faces is proposed by using a surface‐scattering formulation

Displacement of Field Emitters by Vacuum Discharges

Abstract: The location of field emitting micro-points, produced by nanosecond discharges in UHV, has been investigated by field emission microscopy. Weak discharges (duration < 5 ns, current < 10 A) caused a displacement of the field emission over the cathode by a distance that corresponds to average crater diameters (4–6 μm). Thus new emitters are produced at the boundary of discharge craters. More intense discharges show sometimes a far higher displacement. This can be explained by the formation of micro-points by splashes of molten metal that fly out of the discharge craters. The results support the model of the development of micro-points, as it was published in [1]. They show furthermore that the motion of arc cathode spots can be related to the displacement of microscopic field emitters.

Feald emission type electron gun

Abstract: PURPOSE:To clean the pointed area of a cathode through evaporation by applying positive voltage potential to the cathode relative to the anode but not using flashing, with the use of carbon or boron compound material for the field emission cathode in a field emission type electron gun