Showing papers on "Field electron emission published in 1974"

Auroral electron energy derived from ratio of spectroscopic emissions 1. Model computations

Abstract: The relationship between auroral electron fluxes and spectroscopic emission features in aurora is quantitatively explored. The model computations focus on the prominent auroral radiations of atomic oxygen at 6300 A and 5577 A and a vibrational band of ionized molecular nitrogen at 4278 A. The emission rate ratios, 6300/4278, 5577/4278, and 6300/5577, together with the absolute emission rate of the 4278-A radiation, may be used to infer a characteristic energy of the precipitating electron flux. This characteristic energy and the 4278-A intensity then determine the total electron flux and the energy deposition rate. Computational results are presented in easily used curves, and the assumptions made in the model calculations are discussed in the text. At the present time it appears that the ratio 6300/4278 is the most reliable and informative of the set.

Micro-structure field emission electron source

Abstract: A new and improved microminiature field emission electron source and method of manufacturing is described using a single crystal semiconductor substrate. The substrate is processed in accordance with known integrated microelectronic circuit techniques to form a plurality of integral, single crystal semiconductor raised field emitter tips at desired field emission cathode sites on the surface of the substrate in a manner such that the field emitter tips are integral with the single crystal semiconductor substrate. An insulating layer and overlying conductive layer may be formed in the order named over the semiconductor substrate and provided with openings at the field emission site locations to form micro-anode structures for each field emitter tip. By initially appropriately doping the semiconductor substrate to provide opposite conductivity-type regions at each of the field emission sites, and appropriately forming the conductive layer, electrical isolation between the several field emission sites can be obtained.

Plasma‐induced field emission and the characteristics of high‐current relativistic electron flow

Abstract: The results of a comprehensive diode study conducted using a pulsed high‐current electron accelerator are reported Time‐dependent analysis of right‐cylindrical graphite cathodes has shown evidence of the field emission character of the cold‐cathode diode The effects of cathode whiskers or microprojections on the diode response have been observed Within a few nanoseconds after the voltage is applied to the diode, the whiskers explode to form cathode flares The observed diode perveance throughout the remainder of the pulse can be explained in terms of the expansion of the plasma cathode formed by the merger of many cathode flares Cathode plasma velocities ranged from approximately 2 to 3 cm/μsec The observed diode behavior was consistent with that predicted by previous studies of high‐voltage vacuum breakdown

Thermally stimulated field emission from pyroelectric LiNbO3

Abstract: Proximity‐imaging techniques are used to observe thermally stimulated field emission (TSFE) from single‐domain and multidomain single crystals of LiNbO3. Experimental results are reported and the mechanism responsible for this emission is discussed.

Electronic surface states of liquid helium

Abstract: Electrons at the surface of liquid $^{4}\mathrm{He}$ are potentially valuable probes of both static and dynamic properties of the interface. Two species of surface state are discussed. One of these is localized just above the interface, weakly bound by the image force. The existence of this state has been confirmed by direct spectroscopic observation. Measurements of parallel field mobility and life-time on the surface are discussed and compared with predictions. The other surface state is an electron bubble held below the interface with an applied field. A resonance experiment in this geometry determines an effective mass different from the bulk liquid value. Studies of field emission from the bubbles lead to an evaluation of other bubble properties.

Fabrication and some applications of large-area silicon field emission arrays

Abstract: A method of fabricating large-area arrays of sharply-pointed field emitters at densities up to 1·5 × 10 5 per cm 2 from single crystal silicon wafers is described. The point emitters are formed by etch-undercutting a precision oxide pattern which is delineated on the silicon surface by projection photolithography. Observations indicate that emitters with very small tip dimensions in the 200Arange are formed. In the presence of an external electric field, such as produced by a voltage applied to a closely-spaced, planar anode, multiple-emitter arrays are shown to field-emit electrons uniformly over areas up to 3 cm dia. Two important applications currently being explored, are discussed: (1) High resistivity, p -Si has been utilized to develop experimental field emission photocathodes with which field emission imaging has been demonstrated. These photoemitters exhibit very high photo-sensitivities at visible and near i.r. wavelengths. For example, at 0·86 μm, the measured quantum efficiency is 25 per cent which is about five-times higher than the red-sensitive S-20 photocathode and comparable to the highest reported sensitivities of the III–V photosurfaces; (2) N -type emitter arrays show considerable promise as high current, cold cathodes and total emission currents of 1/4 A from 1 cm 2 areas of 100 Ω-cm n -type emitters have been obtained. Measurements were made under pulse conditions because of anode dissipation considerations.

The semiconductor field-emission photocathode

Abstract: The recently developed large-area field-emission photocathode is described. It consists of a finely spaced array of point emitters fabricated by etching of p-type silicon or other semiconductor. Uniform emission over areas of 6-7 cm2have been obtained. For Si, the spectral response extends from 0.4 to 1.1 µm. Quantum yields of 25 percent at 0.86 µm have been measured, which is about five times the value reported for the extended S-20 photocathode and comparable to the best III-V photoemitters. Calculations indicate that quantum yields of up to 40 percent at 0.86 µm and 28 percent at 0.9 µm are attainable with the present photocathode structures. For low dark current densities, photocathode cooling to temperatures approaching 77 K must be employed at present. The dark current is shown to be dominated by surface-generated electrons in the space-chargeregion of the emitters. Effects of phosphorus gettering and annealing treatments on dark current are discussed, and the spatial frequency response of the device is determined. The results of a computer study show that the field intensification factor of p-semiconductor field emitters behaves quite differently from that of metallic emitters.

Evidence for surface‐state‐enhanced field emission in rf superconducting cavities

Abstract: Measurements of the x radiation and the electron loading in a niobium cavity resonant in the TM010 mode at 1208 MHz have been made in order to study enhanced electron field emission in superconducting cavities. Measurements have also been made of the low‐temperature dc electron field emission from bismuth, niobium, copper, and tungsten utilizing a configuration which approximates the point‐to‐plane geometry. In the rf cavity measurements, it is found that the x‐radiation count rate data follow a modified Fowler‐Nordheim equation, which takes into account the time‐dependent rf fields, the electron dynamics in the rf fields, the emission of secondary electrons, and the production and absorption of x radiation. Further, it is found that the x radiation from the cavity can be reduced by a factor of 104−106 by helium‐ion sputter processing at low temperature. From x‐radiation data and electron loading data interpreted with the modified Fowler‐Nordheim equation, it has been shown that, after helium‐ion sputter ...

Energy distributions of field emitted electrons from tungsten in the presence of adsorbed CO

Abstract: Energy distributions were measured on the (110), (100), (111), and (210) planes under various conditions of CO adsorption. Resonances were seen for the low temperature layer at −7 to 7.5 eV below vacuum on all planes except (100). A comparison of the widths and maximum amplitudes of the resonances shows good agreement with the theory of field emission from adsorbate covered surfaces. On heating, the resonances disappeared at ≤350 K corresponding to conversion of the low temperature states to beta‐precursor states. Readsorption on beta or beta‐precursor layers led to resonances at −7 eV on (210) and (111), but not on (110) or (100). The resonances are interpreted as arising from interaction of CO–π* orbitals with tungsten d‐t2g orbitals in adsorption via the C atom on single W atoms. Disappearance of the resonances on heating is interpreted as activated rearrangement to new bonding configurations‐for instance, bridge bonding via C‐sp2 orbitals. The intensity of the resonances increases initially with cover...

Long journey into tunneling

Abstract: N 1923, during the infancy of the quantum theory, de Broglie [ 11 introducted a new fundamental hypothesis that matter may be endowed with a dualistic natureparticles may also have the characteristics of waves. This hypothesis, in the hands of Schrodinger [2] found expression in the definite form now known as the Schrodinger wave equation, whereby an electron or a particle is assumed to be represented by a solution to this equation. The continuous nonzero nature of such solutions, even in classically forbidden regions of negative kinetic energy, implies an ability to penetrate such forbidden regions and a probability of tunneling from one classically allowed region to another. The concept of tunneling, indeed, arises from this quantum-mechanical result. The subsequent experimental manifestations of this concept can be regarded as one of the early triumphs of the quantum theory. In 1928, theoretical physicists believed that tunneling could occur by the distortion, lowering or thinning, of a potential barrier under an externally applied high electric field. Oppenheimer [3] attributed the autoionization of excited states of atomic hydrogen to the tunnel effect: The coulombic potential well which binds an atomic electron could be distorted by a strong electric field so that the electron would see a finite potential barrier through which it could tunnel. Fowler and Nordheim [4] explained, on the basis of electron tunneling, the main features of the phenomenon of electron emission from cold metals by high external electric fields, which had been unexplained since its observation by Lilienfeld [SI in 1922. They proposed a one-dimensional model. Metal electrons are confined by a potential wall whose height is determined by the work function 9 plus the Fermi energy E/, and the wall thickness is substantially decreased with an externally applied high electric field, allowing electrons to tunnel through the potential wall, as shown in Fig. 1. They successfully derived the well-known Fowler-Nordheim formula for the current as a function of electric field F: J = AF* exp [-4(2nr)1'*t$a'*/3kF]. An application of these ideas which followed almost immediately came in the model for a decay as a tunneling process put forth by Gamow [6] and Gurney and Condon [7]. Subsequently, Rice [8] extended this theory to the description of molecular dissociation. The next important development was an attempt to invoke tunneling in order to understand transport properties of electrical contacts between two solid conductors. The problems of metal-to-metal and semiconductor-to-metal contacts are important technically, because they are directly related to electrical switches and rectifiers or detectors.

Theory of surface effect in photoassisted field emission

Abstract: The influence of the surface on the photoassisted field emission from a metal is studied theoretically for two simple models of the solid. First, we consider the model of a half-space square well for the metal, and solve exactly for the current density after ignoring the Schottky effect. Next, we take into account the effect of the image charge, and calculate the current density in the WKB approximation. Numerical results based on the calculations are compared with the recent experimental data on photoassisted field emission from tungsten. Areas of agreement and discrepancy between the theory and experiment are pointed out and discussed.

Some Aspects of the CO-Tungsten System

Abstract: The adsorption of CO on tungsten is discussed in the light of thermal and electron impact desorption, as well as photoemission and field emission spectroscopy. The evidence for the existence of several low and intermediate temperature binding states is discussed, and the nature of the states interpreted in terms of undissociated CO. The high temperature binding modes are also discussed and it is suggested that the present evidence does not permit a distinction between dissociated and undissociated adsorption although both C and O seem to be in contact with W atoms.

Electron beam pattern generator

Abstract: An electron beam pattern generator for the rapid and accurate generation of electron images upon a surface such as a surface coated with an electron sensitive resist material. The pattern generator is comprised of a field emission electron gun, the emission of which is focused and deflected by deflection coils controlled by a computer through digital to analog converters. Blanking of the beam is accomplished by deflection of the beam off range and onto the edge of an aperture plate. A stable high current beam is achieved by heating the field emission electrode. A properly biased device collects the secondary emission from the object on which the electron pattern is focused, and together with the deflection signals for the beam may be used to create a CRT display. A means for achieving step and repeat capability is also disclosed, as is a means for maintaining constant exposure dosage independent of beam current changes.

The Atomic Nature of Polymer-Metal Interactions in Adhesion, Friction, and Wear

Abstract: The polymers PTFE (polytetraf1uoroethylene) and polyimide were studied contacting various metals in adhesion and sliding friction experiments. Field ion microscopy and Auger emission spectroscopy, were used to examine the nature of the polymermetal interactions. Strong adhesion of polymers to all metals in both the clean and oxidized states was observed. Adhesive bonding was sufficiently strong with the cohesively weaker metals such as aluminum that metal transferred to the polymers. Adhesion coefficients measured approach those for clean metals in contact and field ion microscopy indicates that the polymer to metal bonds are chemical in nature. The field ion microscope also indicates that polymer fragments transferred to cohesively strong metals such as tungsten and that these fragments are highly oriented. Auger emission spectroscopy indicates that a single pass of PTFE across a metal surface is sufficient to generate a transfer film. Electron induced desorption of the PTFE from the metal surface indicates that bonding to the metal is via the carbon atom with little to no fluorine to metal interaction.

Field Emission Studies of TiC Single Crystal

Abstract: The work function and emission characteristics of TiC single crystal have been investigated by a field emission microscope. A titanium carbide tip was prepared by electrochemical etching from a crystal bar (1 mm×1 mm×8 mm) oriented in the [100] direction. The work function of TiC has been found to be 2.6 eV for annealed tip at 1600–1700°C and 2.7 eV for annealed one at 1800°C. The clean field emission pattern of TiC single crystal tip showed the fcc like four-fold symmetry having the dark area corresponding to the (001) plane at the center. The stable emission characteristics were obtained at the pressure below 10-6 Torr in a field emission system.

Field emission electron gun having automatic current control

Abstract: An improved field emission type electron gun is automatically controlled so as to generate a stable emission current. The preferred embodiment employs a detecting means for detecting the emission current fluctuation and a control means for controlling the electric field for field emission according to the output signal of said detecting means.