Electron Beam Probe Research Articles

Measuring rotationally symmetric potential profiles with an electron-beam probe

An electron-beam probe has been developed to measure the potential profile of a plasma within a spherical grid structure which was designed to trap charged particles. The potential was obtained from observed deflections of a collimated beam of electrons incident upon the device at selected impact parameters. The beam consisted of conversion electrons of 62.2 and 84.2 keV from a Cd109 source. Deflections of the beam through the plasma were measured relative to the beam trajectory without voltage applied to the grids. A movable detector allowed angular resolution to within 0.08 deg for maximum deflections of 7 deg. The inversion of the nonlinear singular integral relating potential and deflection is accomplished in an iterative manner with appropriate series expansions about the singular points. Simulations using postulated potential profiles show this procedure to give accuracy typically better than 4% with 20 deflection samples. Beam deflection measurements in spherical electrostatic systems without plasma show this probe technique to be very accurate. For a variety of experimentally controlled plasma parameters, no measurable departures from electrostatic potential profiles were observed.

Potential well structure in an inertial electrostatic plasma confinement device

Electron beam probing has been used to infer the behavior of potential wells formed by electron injection in a spherical inertial electrostatic plasma containment device. At very low pressures, the electron injection clearly results in the production of a steady state deep negative potential well. When deuterium gas at pressures of up to 10−5 Torr was admitted, the pronounced focusing of the probing electron beam strongly indicated that a steady state positive potential well, due to background ionization, was formed within the negative potential well.

A Simple Correlation for Incipient-Turbulent Boundary-Layer Separation due to a Skewed Shock Wave

References 1 Fingerson, L. M., A Heat Flux Probe for Transient Measurements in High Temperature Gases, Ph.D. thesis, 1961, Univ. of Minnesota, Minneapolis, Minn.; also ARS Journal, Vol. 13, No. 11, Nov. 1962, p. 1709. 2 McCroskey, W. J., Density and Velocity Measurements in HighSpeed Flows, AIAA Journal, Vol. 6, No. 9, Sept. 1968, pp. 1805-1808. 3 Horstman, C. C. and Kussoy, M. I, Viscous Interaction on Slender Cones, AIAA Paper 68-2, New York, 1968. 4 Vas, I. E., An Investigation of the Flow About a Slender Cone at Hypersonic Speeds, Ph.D. thesis, 1970, New York Univ., New York. 5 Becker, M., Papanikas, D. G., and Schweiger, G., Experimental Study of the Flow Field in Front of Hemispheres in the Transition and Shock Formation Regime, presented at the 7th RGDS, July 1970, Deutsche Forschungsurid Versuchsanstalt fur Luftund Raumfahrt, (DFVLR) Porz-Wahn, W. Germany. 6 Harbour, P. J. and Lewis, J. H., Preliminary Measurements of the Hypersonic Rarefield Flow Field on a Sharp Flat Plate Using an Electron Beam Probe, Rarefied Gas Dynamics, Supp. 4, Vol. 1, Academic Press, New York, 1967. 7 Petraites, R. J., An Investigation of the Effects of Three-Dimensionality on the Flow Over a Flat Plate at M ~ 25, MSE thesis, Aug. 1972, Dept. of Aerospace and Mechanical Sciences, Princeton Univ., Princeton, N.J. 8 Dewey, C. F., Jr., A Correlation of Convective Heat Transfer and Recovery Temperature Data for Cylinders in Compressible Flow, International Journal of Heat and Mass Transfer, Vol. 8, 1965, pp. 245-252. 9 Rubin, S. G., Rudman, S., Lin, T. C, and Pierucci, M., Viscous-Inviscid Interaction by a New Type of Analysis, AGARD CP 30, Hypersonic Boundary Layers and Flow Fields, May 1968. 10 Mayne, A. W., Jr., Gilley, G. E., and Lewis, C. H., Binary Boundary Layers on Sharp Cones in Low-Density Supersonic and Hypersonic Flow, AIAA Journal, Vol. 7, No. 4, April 1969, pp. 699-706.

LSI Pattern Generation and Replication by Electron Beams

The combined use of the digitally controlled single electron beam pattern generator to make micron-scale LSI patterns and the 1:1 electron image projection system to replicate these patterns on device substrates represents a practical means for realizing high-density integrated circuits in large volume production. After six years of research and development at Westinghouse, most of the obstacles to successful use of these methods have been removed. Among the problems solved are uniform exposure of points, lines, and areas in a device pattern, fabrication of high-resolution electromasks for the electron image projector, and registration of successive device patterns in both electron beams systems, used in combination. In the most recent work, a 1024-bit random access memory was used as a test vehicle. Eight mask levels were involved, including a buried diffusion. In both machines, alignment of a new pattern with a preexisting pattern on the substrate was obtained through electron beam probing of fiducial mark areas. An automatic alignment system developed for the electron image projection system made possible alignment within a few seconds and subsequent controlled exposure. Including alignment errors originating in the electron beam mask generator, over-all pattern registrations were within ±1.5μ.

Scanning Electron Microdensitometry

Diffraction arid partial coherence cause errors in the measurement of small-scale photographic detail by microdensitometers and projection systems. The optical imaging nonlinearities can be avoided by scanning the silver distribution with a narrow beam of energetic electrons and counting the secondary quanta that are excited. It is found that the number of low energy (secondary) and high energy (backscattered) electrons emitted from various emulsion types as well as the characteristic Ag x-ray fluorescence are measures of the local silver concentration. A mechanism for the secondary electron contrast, which is only in part due to surface relief, is proposed. Spatial frequencies up to 2280 1p/mm have been retrieved by such scanning electron beam probes.

757. Production of electron-beam probes with the aid of an electron field emitter and magneto-optics: I P Zhizhin et al, Izv AN SSSR Ser Fiz, 35 (2), 1971, 302–306 ( in Russian)

757. Production of electron-beam probes with the aid of an electron field emitter and magneto-optics: I P Zhizhin et al, Izv AN SSSR Ser Fiz, 35 (2), 1971, 302–306 ( in Russian)

Rotational Temperature in an Underexpanded Jet

The axial rotational temperature distribution in an underexpanded nitrogen jet emitted from a sonic orifice has been investigated. The expansion is from room temperature and the gas possesses negligible vibrational energy. The observed difference between the rotational temperature measured with an electronbeam probe and the isentropic value can be described by a rotational relaxation analysis. The governing flow equations were integrated numerically by the classical fourth-order Runge-Kutta method. The rotational relaxation time developed by Lordi using Wang Chang and Uhlenbeck's formal kinetic theory and Parker's molecular model was employed. Both the easy and difficult energy transfer cases were investigated and the easy case was shown to underestimate nonequilibrium affects. The numerical solutions were very sensitive to the separation between the repulsive force centers, for both energy transfer cases. The rotational temperature distributions obtained in this study are in general agreement with existing experimental data for nitrogen.

Plasma Resonance and Standing Longitudinal Electron Waves

Using an electron beam probe, the existence of a standing electrostatic wave in the sheath surrounding a planar probe immersed in a plasma when the probe is driven at frequencies near ωp has been demonstrated. The driven probe exhibits two admittance resonances. The larger of these (near 12ωp) is the well documented “resonance probe” resonance. The smaller second resonance at ω≈ωp is associated with the standing wave and its interpretation as a Tonks-Dattner resonance is discussed. The effect of such a standing wave on the usual interpretation of plasma resonance probe data is examined.

Collisionless Sheath—An Experimental Investigation

An electron beam probing technique has been utilized to measure the sheath electric field distribution near a planar floating plate immersed in a low-pressure argon arc discharge plasma. The static sheath field determined by this nonperturbing measurement is compared with the predictions of the collisionless or free-fall model of the sheath. The agreement is found to be so satisfactory that such static sheath field measurements, supplemented by a floating potential measurement, are sufficient to yield accurate values of the plasma electron density and temperature.

Potential Distribution in a Two-emitter Diode

Abstract The existing model of a "collisionless" alkali plasma diode is extended including the case of two incandescent plane electrodes emitting electrons as well as ions with a half-Maxwellian velocity distribution. The potential distributions within the diode space derived from this theory are examined in detail. Physically necessary conditions reduce the well-known ambiguity of solutions to a single one (with uniform plasma potential) at a given set of parameters. Further solutions, cor-responding to spatially oscillatory potential shapes which are consistent with the collisionless theory, disappear if the ion-ion collision probability within the diode plasma exceeds 0.1 per emitter distance. In the experiment the potential distributions are scanned using a new electron beam probing technique. The results agree with theory.

Electron Beam Measurement of Ion Acoustic Wave Propagation

Ion acoustic wave propagation, near the sheath developed at a plasma-wall boundary, has been investigated in a low-pressure (∼ 5 × 10−4 Torr) argon plasma by an electron beam probing technique. Waves propagating into the plasma are found to have velocities ∼ 2 × 105 cm/sec, increasing with distance from the wall. The results are consistent with an analysis in terms of an ion free-fall model of the sheath. The model also makes plausible the observed zero reflection coefficient for small ion acoustic disturbances at the plasma boundary.

A method for measuring plasma arc wind tunnel gas velocity with a position controlled electron beam probe

An electron beam probe has been used in the Micom 8 MW Plasma Facility. Difficulties in applying the probe to measurements of such parameters as gas density were found to be caused by the weak plasma arc-generated magnetic fields producing positional displacements of the beam. This problem was solved by means of a closed-loop electronic controller. Response time of the controller is down 3 dB at 130 Hz; this was found to be sufficiently fast for adequate control. The operation of the controller indicated that 0·26 G magnetic field was induced in the flow stream by the arc jets. Gas velocity in a plasma flow was estimated by observation of the drift rate of pulsed beam-generated plasma cylinders as a phase shift from two observation points. Estimates of gas velocity for an air flow of 156 g s−1 from phase shift measurements gave 3700±400 m s−1 as compared with a machine computed value of 3800 m s−1 for a normalized specific total enthalpy of 150.

Hypersonic turbulent boundary-layer measurements using an electron beam.

Density and density fluctuations in hypersonic turbulent boundary layer on shock tunnel nozzle wall measured using electron beam probe

A low energy scanned electron beam potential probe

Electron beam probe equipment is described that measures the potential of flat conducting or semiconducting surfaces with a resolution of 5 mV and a probe diameter of 10-20 μm. The operation of the probe is, in some ways, similar to that of the Vidicon camera tube and the use of a control loop ensures that the output from the system is an accurate replica of changes in surface potential. The probe can be scanned over an area of more than 2 cm diameter and is suited to the examination of planar semiconductor devices.

Synthesis and some properties of ZnSe: GaAs solid solutions

Four methods for the synthesis of solid ZnSe: GaAs solutions are reported. Crystals of the order of millimeters on an edge were prepared and analyzed for composition by precision lattice parameter determinations as well as by X-ray fluorescence and electron beam probe measurements. Optical determinations of energy gaps show, with the aforementioned data, that mutual solubility is attainable over the entire composition range.

Experimental Studies of a Deep, Negative, Electrostatic Potential Well in Spherical Geometry

Steady electron injection produced a stable, negative electrostatic potential well at the center of a hollow, open, 6.35-cm-diam spherical anode. Even though the primary electron source was localized, electron flow became spherically symmetric at anode currents of the order of 10 mA for anode potentials up to 1.0 kV. Well defined and reproducible oscillations were observed over a lower current range. These oscillations ceased and certain collector characteristics abruptly changed at currents which varied as V32, suggesting space charge saturation. An electron beam probe verified the presence of the well and measured its depth. The data showed correlation with a simple model and demonstrated the ease with which such wells can be produced.

Influence of Secondary Electrons on an Electron-Beam Probe

The flow of secondary electrons, produced by ionization when an electron beam traverses a gas, is retarded by electrostatic fields and their density is higher than has previously been assumed. An experiment indicates that low energy electrons could have important effects on an electron-beam density and temperature probe and that further research is needed.

Temperature and Density Measurements in Free Jets and Shock Waves

The fluorescence stimulated by a 17.5-kV electron beam probe was used to obtain measurements of rotational temperature and gas density in supersonic nitrogen jets expanding from room temperature. The parameter P0d (where P0 is the stagnation pressure in Torricelli and d is the orifice exit diameter in millimeters) was varied from 15 to 480 Torr-mm. Density measurements were made using an interference filter-photomultiplier combination. The experimental density data follow the axial isentropic density distribution in regions of rotational nonequilibrium. Rotational temperature measurements were obtained from rotational spectra of the 0–0 band of the N2+ first negative system. The experimentally determined rotational temperatures, which initially follow the axial isentropic temperature distribution in a free jet, depart from the isentropic curve at low temperatures and freeze at a constant value, indicating a substantial degree of nonequilibrium in the expansion. A shock holder was inserted in the jet and a number of shock waves in the range M = 4 to M = 15 were investigated. Rotational spectra indicate a large departure from a Boltzmann distribution in the rotational levels in the center of a shock front. An apparent non-Boltzmann rotational distribution in the jet expansion was also observed.

Time Resolved Electron Deposition Studies at High Dose Rates in Dielectrics

The grazing electron beam probe technique has been used to study the behavior of the electric field external to planar irradiated samples in vacuo. The trapped charge density can be determined from these data so that its behavior during and subsequent to the irradiation period can be studied with microsecond time resolution. Secondary phenomena associated with high-rate electron deposition of energy in dielectrics at dose rates from 106 to 1010 rads/sec are discussed and include charged particle emission, backscatter, and luminescence. The measurements have been conducted with simultaneous determination of the trapped charge level in the irradiated sample.

Electron hopping transport and trapping phenomena in orthorhombic sulphur crystals

A detailed investigation of the temperature dependence of the electron transport in orthorhombic S crystals has been carried out using drift mobility techniques. The transport is an activated process leading to a drift mobility of (6.2 ± 0.6) × 10 −4 cm 2 sec −1 V −1 at 21°C and an activation energy of 0.167 ± 0.005 eV in all principal directions. The remarkable consistency of the results for about 30 specimens, which is in complete contrast to the hole mobility results, allows us to exclude a trap controlled transport. It is suggested that electron conduction in S is an intermolecular hopping mechanism. The results have been fitted to the small polaron theories of Holstein and of Yamashita and Kurosawa, leading to a polaron binding energy of 0.48 eV. It is likely that the electron interacts predominantly with fundamental vibrational modes of the S-molecule between 151 cm −1 and 236 cm −1. Electron lifetimes with respect to deep centres have been measured by interrupting transits at various depths within the specimen. Bulk lifetimes of up to 17 msec were observed at room temperature. The electron trapping spectrum has been studied by thermally stimulated current measurements and by an electron beam probing technique. Five prominent centres were found and it is shown that the measurements are consistent with the interpretation of electron transport.