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1 Dec 1976

Volume 47, Issue 12, pp. 5133-5494

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Stress produced in a solid by cavitation

B. Vyas and C. M. Preece

J. Appl. Phys. 47, 5133 (1976); http://dx.doi.org/10.1063/1.322584 (6 pages) | Cited 48 times

Online Publication Date: 28 August 2008

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The stresses produced in a solid by cavitation generated in distilled water by 10‐, 20‐, and 30‐kHz vibrations have been determined by a transducer technique. The measured stress pulses are attributed to the concerted collapse of the whole cloud of bubbles created by the pressure changes in the water rather than to the independent effects of individual bubbles. The magnitude and duration of the stress pulses are characteristic of those of a shock wave and can be related directly to the degree and mode of damage which they produce in a solid.
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47.55.dp Cavitation and boiling
62.50.-p High-pressure effects in solids and liquids
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations

Early growth of silicon on sapphire. I. Transmission electron microscopy

M. S. Abrahams, C. J. Buiocchi, R. T. Smith, J. F. Corboy, J. Blanc, and G. W. Cullen

J. Appl. Phys. 47, 5139 (1976); http://dx.doi.org/10.1063/1.322585 (12 pages) | Cited 19 times

Online Publication Date: 28 August 2008

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The early growth of Si on (0112) ‐oriented sapphire has been examined by transmission electron microscopy. The Si was deposited at 1000 °C by pyrolyzing silane in H2. The nominal growth rate was 0.4 μm/min. The morphology of the initial Si growth islands was determined after 0.5, 1.0, 2.5, and 3.5 sec of growth. The basic Si orientation is (100) with [011] Si∥[2110] Al2O3. Extensive faulting and twinning is observed leading to {221} orientations. These defects apparently form at coalescence sites of adjacent islands. Also present are four {110} orientations occuring as twin‐related pairs. The observation of isolated {110} domains indicates that they nucleate on the sapphire independently of the (100) domains. The {110} and (100) domains grow at about the same rate. Eventually, the {110} domains become trapped by the surrounding (100) domains. The volume percentage of the {110} domains is constant with growth time and equals 7% up to coverages of 90%.
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68.55.-a Thin film structure and morphology
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Early growth of silicon on sapphire. II. Models

J. Blanc and M. S. Abrahams

J. Appl. Phys. 47, 5151 (1976); http://dx.doi.org/10.1063/1.322586 (10 pages) | Cited 13 times

Online Publication Date: 28 August 2008

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We analyze data obtained on the morphology of (100) silicon on (0112) sapphire at early stages of growth. For the sake of simplicity and concreteness, we assume, perhaps incorrectly, that isolated growth islands are hemispherical. In order to account for the observation that the rate of increase of deposited silicon has achieved the bulk value at surface coverages of 50% or less, we postulate a ’’collection zone’’ around each growing island. Material falling in this zone is assumed to all diffuse to the growing island. For our experiments, the width of this zone is some tens of angstroms. We show that the growth rate of {110} islands is not significantly different than that of (100) islands. The eventual disappearance of {110} Si for full growths can be ascribed to the tendency to reduce the high‐energy contact area between (100) and {110} Si. The logarithm of (100) island density appears to be proportional to (growth time)1/2. A simple model of island coalescence yields such a dependence, the proportionality constant being essentially equal to the (initial nucleation site density)1/4 multiplied by the (growth rate)1/2. The model for individual island growth in conjunction with the coalescence model yields a satisfactory explanation of the observed time dependence of island density, of surface coverage, and of total deposited volume. We suggest that, under the high effective supersaturations used in the growth of silicon on sapphire, island growth and coalescence are not dominated by surface energies. We speculate that nucleation of silicon on sapphire occurs by a type of homogeneous surface mechanism, rather than being due to either ’’dirt’’ on the substrate or crystallographic defects in the sapphire substrate.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
68.55.-a Thin film structure and morphology

Growth of CdS smoke particles prepared by evaporation in inert gases

Chihiro Kaito, Kazuo Fujita, and Makoto Shiojiri

J. Appl. Phys. 47, 5161 (1976); http://dx.doi.org/10.1063/1.322587 (6 pages) | Cited 18 times

Online Publication Date: 28 August 2008

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Cds particles, which were prepared in He, Ne, Ar, and Xe gases at pressures of 5–150 Torr, were studied by electron microscopy. Crystals with wurtzite structure grew in single hexagonal plates or prisms or in a more complicated form composed of three or more hexagonal prisms. The mean size of the particles was larger if they were prepared in a heavier gas, and increased almost linearly with gas pressure up to a saturation pressure which was lower for heavier gasses. The particle size distributions in the smokes and the temperature distributions in the chamber are presented for various atmospheres, and on these bases the growth of the particles is discussed.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
82.70.-y Disperse systems; complex fluids
81.20.-n Methods of materials synthesis and materials processing

Annealing characteristics of boron‐ and phosphorus‐implanted polycrystalline silicon

John Y. W. Seto

J. Appl. Phys. 47, 5167 (1976); http://dx.doi.org/10.1063/1.322588 (4 pages) | Cited 6 times

Online Publication Date: 28 August 2008

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Polycrystalline silicon films implanted with 1×1012 to 7.8×1015/cm2 doses of boron and phosphorus were isochronally annealed up to 1100 °C. Annealing below 600 °C removes the radiation damage created by the implantation process. For doses higher than 1×1014/cm2 an abrupt decrease in sheet resistance takes place between 650 and 700 °C. Hall measurements show that this decrease is the result of a large increase in both the carrier concentration and mobility. Electron‐reflection diffraction patterns show that recrystallization takes place within this temperature range. Annealing above 700 °C only causes a small further decrease in the sheet resistance.
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61.72.U- Doping and impurity implantation
72.80.Cw Elemental semiconductors

The role of the grain boundaries in hot pressing silicon carbide

Jean‐Marie Bind and James V. Biggers

J. Appl. Phys. 47, 5171 (1976); http://dx.doi.org/10.1063/1.322589 (4 pages) | Cited 4 times

Online Publication Date: 28 August 2008

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Silicon carbide is difficult to sinter without the aid of additives and/or pressure. Additions of boron carbide, boron or alumina were made to obtain dense materials. This is explained in terms of surface free energy modifications taking place in the grain boundaries. An expression of the chemical potential over the grain boundaries is developed to show that there is no theoretical limitation for the sintering of covalent ceramics if the grain size of the starting powder is small enough.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.35.Md Surface thermodynamics, surface energies
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations

Thin‐film interaction in aluminum and platinum

S. P. Murarka, I. A. Blech, and H. J. Levinstein

J. Appl. Phys. 47, 5175 (1976); http://dx.doi.org/10.1063/1.322590 (7 pages) | Cited 23 times

Online Publication Date: 28 August 2008

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The interdiffusion and intermetallic formation in thin‐film sandwiches of platinum on preannealed aluminum has been investigated at temperatures in the range 200–500 °C. X‐ray diffractometer studies, sheet‐resistivity measurements, and microscopic studies were employed to follow the metallurgical reaction. It has been found that Al‐Pt interact very rapidly, leading to the formation of several intermetallics. In heat‐treated samples with thick aluminum (?6000 Å), Pt2Al3, PtAl2, PtAl3, and PtAl4 were present. In others with 4000 Å or less Al, platinum‐rich phases Pt5Al3 and Pt3Al2 were detected. After prolonged or high‐temperature anneals, phases comparatively richer in Al were found to grow at the expense of other phases formed earlier. The Al‐Pt interaction rate was found to be dependent on the annealing ambient, being significantly higher in forming gas, argon, or helium than in vacuum or air. Also, the intermetallic formation resulted in large stress changes in the composite Al‐Pt films due to a volume increase accompanying the formation of Al‐rich phases, which led to the loss of adhesion.
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66.30.-h Diffusion in solids
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
73.61.At Metal and metallic alloys

Formation kinetics of CrSi2 films on Si substrates with and without interposed Pd2Si layer

J. O. Olowolafe, M‐A. Nicolet, and J. W. Mayer

J. Appl. Phys. 47, 5182 (1976); http://dx.doi.org/10.1063/1.322591 (5 pages) | Cited 43 times

Online Publication Date: 28 August 2008

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We have measured the kinetic rate of formation of CrSi2 using 2.0‐MeV 4He+ backscattering spectrometry. CrSi2 was formed on single‐crystal 〈100〉‐ and 〈111〉‐oriented Si and on Pd2Si grown on 〈100〉 Si. For both Si‐Cr and Si‐Pd2Si‐Cr samples the rate of growth of CrSi2 is linear in time with an activation energy of 1.7±0.1 eV and a value of 0.7 Å/sec at 450 °C. For all annealing temperatures, the growth becomes nonlinear at long annealing times. The nonlinearity is attributed to a contaminant, probably oxygen. On Pd2Si, CrSi2 starts to form at about 400 °C, while on Si, CrSi2 formation is observed at 450 °C and above. The difference in formation temperatures is due to contamination at the Si‐Cr interface, quite probably a thin oxide layer. The growth rate of CrSi2 in the Si‐Pd2Si‐Cr samples is independent of the thickness of Pd2Si.
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68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
82.40.Bj Oscillations, chaos, and bifurcations

Basic characteristics of surface‐acoustic‐wave convolver in monolithic MIS structure

Kazuo Tsubouchi, Shoichi Minagawa, and Nobuo Mikoshiba

J. Appl. Phys. 47, 5187 (1976); http://dx.doi.org/10.1063/1.322580 (4 pages) | Cited 7 times

Online Publication Date: 28 August 2008

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We propose a new nonlinear theory including the gate‐voltage dependence and the effect of surface states based on a simple model (low‐frequency limit) of surface‐acoustic‐wave (SAW) convolver in monolithic MIS structure, and we confirm our theory by experiment on the n‐Si/SiO2/ZnO/Al system. Our results show that the convolution signal corresponds to the derivatives of C‐V curves in the ideal MIS structure and the effect of surface states appears in the peak shift.
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43.25.-x Nonlinear acoustics
72.50.+b Acoustoelectric effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
43.60.+d Acoustic signal processing

Time‐dependent crystal‐melt interface shape in Czochralski growth system

J. Arkani‐Hamed, M. J. Heshmati Moulaii, and S. Vojdani

J. Appl. Phys. 47, 5191 (1976); http://dx.doi.org/10.1063/1.322581 (4 pages)

Online Publication Date: 28 August 2008

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The time variations of the shape and position of the crystal‐melt interface in a crystal pulling system, caused by sudden changes of different parameters, are investigated. Zero pull rate and vacuum surroundings are assumed throughout. In particular, the effects of the variation of the after‐heater height and the Peltier current are determined in detail for germanium. It is found that the Peltier current affects the interface more strongly than the after heater.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Investigation of the structure of ferroelectric domain boundaries by transmission electron microscopy

T. Malis and H. Gleiter

J. Appl. Phys. 47, 5195 (1976); http://dx.doi.org/10.1063/1.322582 (6 pages) | Cited 47 times

Online Publication Date: 28 August 2008

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A transmission electron microscopy investigation has been conducted on the structure of 90° and 180° domain boundaries in polycrystalline BaTiO3. When such boundaries were imaged with a continuous set of lattice planes, fringes were observed, indicating a stacking‐fault‐type displacement of the crystal lattices on either side of the boundaries. For a 90° domain boundary, this displacement most likely consists of both a dilatation and shear of {110} planes parallel to the boundary plane. The displacement for a 180° boundary lies approximately parallel to [101] and is of a greater magnitude. Structural models of both types of boundaries are derived from the observed displacements. The models suggest a distortion of the crystal structure in the boundary region. This distortion allows the polarization vector to simultaneously rotate and decrease in magnitude to zero at the center of the boundary, resulting in the required 90° or 180° rotation of the vector. The presence of the displacement associated with the 180° boundary suggests a substantial boundary thickness, in contradiction to previous models.
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77.80.Dj Domain structure; hysteresis
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Tait equation for inorganic solids with applications to the pressure dependence of melting temperature

P. R. Couchman and C. L. Reynolds

J. Appl. Phys. 47, 5201 (1976); http://dx.doi.org/10.1063/1.322583 (5 pages) | Cited 12 times

Online Publication Date: 28 August 2008

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The original version of the Tait equation is proposed to represent the compression of certain inorganic solids and has been applied to a derivation of the pressure dependence of melting temperature.
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64.70.D- Solid-liquid transitions

Off‐axis channeling disorder analysis

G. Foti, P. Baeri, E. Rimini, and S. U. Campisano

J. Appl. Phys. 47, 5206 (1976); http://dx.doi.org/10.1063/1.322592 (8 pages) | Cited 4 times

Online Publication Date: 28 August 2008

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A new method has been developed to obtain, by means of channeling measurements, the distribution of defects in a plane normal to a low‐index axis direction. This method takes advantage of the response of nonsubstitutional atoms to the spatial distribution of the channeled ion flux. It represents then an extention of the flux‐peaking effect used to locate foreign atoms in a single‐crystal lattice. This method has been used to study the disorder introduced by 300‐keV N+ implantations in Si with fluences ranging between 6×1014 and 1016 ions/cm2 and analyzed in situ with 2.0‐MeV He+ backscattering. Flux distributions of channeled ions have been evaluated as a function of the impinging angle for the <111≳ and 〈110〉 crystal directions of a Si lattice. The dechanneling probability has been estimated as a function of the impinging angle and of the total number of scattering centers, on the basis of plural scattering treatment. The analysis of the experimental data indicates a departure from a uniform transverse distribution of scattering centers both along the 〈111〉 and the 〈110〉 directions for low damage levels. The analysis has been detailed together with the main assumptions, and the range of validity of the method has been defined.
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61.72.U- Doping and impurity implantation
81.05.Dz II-VI semiconductors
81.05.Ea III-V semiconductors
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Resolution of electron emission mechanisms in an argon arc with a hot tungsten cathode

Michael M. Chen, Roderick E. Thorne, and Elliot F. Wyner

J. Appl. Phys. 47, 5214 (1976); http://dx.doi.org/10.1063/1.322593 (4 pages) | Cited 1 time

Online Publication Date: 28 August 2008

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The regenerative nature of the interaction between the electron emission processes at the cathode surface and the ion‐, excited‐atom‐, and photon‐production processes in the plasma was examined. Semiquantitative estimates of the thickness of the species production layer, the current partition, and the time constants were made. These results were used to interpret experimental measurements of the current decay of an argon arc at 46.7 kPa, 3.2–7.9 A, and 28–18 V, with a self‐sustained hot tungsten cathode. After the discharge is suddenly connected to a voltage clamp, the disparity of decay rates for different emission processes permits the separation of thermionic emission from the faster‐decaying components. The observed thermionic current constitutes about 30% of the total emission. The high nonthermionic portions of the current could not be explained in terms of the present understanding of the emission processes.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
79.40.+z Thermionic emission
79.20.-m Impact phenomena (including electron spectra and sputtering)

Calculation of reflection and transmission coefficients in one‐dimensional wave propagation problems

G. Mur and A. J. A. Nicia

J. Appl. Phys. 47, 5218 (1976); http://dx.doi.org/10.1063/1.322594 (4 pages) | Cited 2 times

Online Publication Date: 28 August 2008

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One‐dimensional electromagnetic wave propagation problems can be formulated exactly in terms of an integrodifferential equation of the Fredholm type. The numerical solution of this equation is often complicated and time consuming. In this paper a method is described of transforming this equation into an integral equation of the Volterra type. The solution of the latter equation can be carried out easily and within a short time.
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03.50.De Classical electromagnetism, Maxwell equations
41.20.Jb Electromagnetic wave propagation; radiowave propagation
02.70.-c Computational techniques; simulations

Secondary electron emission from beams of polystyrene latex spheres

T. D. Hall and W. W. Beeman

J. Appl. Phys. 47, 5222 (1976); http://dx.doi.org/10.1063/1.322595 (4 pages) | Cited 4 times

Online Publication Date: 28 August 2008

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Polystyrene latex spheres suspended in a carrier gas of nitrogen are accelerated through a nozzle‐skimmer system into a vacuum chamber and ionized in a crossed electron beam. Measurements of the particle beam current as a function of the primary electron energy and current give information on the secondary electron emission yield of the spheres and on the energy distribution of the secondaries. The positively charged spheres provide their own retarding potential for the energy scan of the secondaries. For 260‐eV primaries the distribution in energy of the secondaries from polystyrene peaks between 1 and 2 eV. At 5 eV it has fallen to about 40% of its peak value. The yield per incident primary of secondaries (or scattered primaries) whose energy is greater than 5 eV is unity. Some advantages and limitations of the method are discussed.
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79.20.Hx Electron impact: secondary emission
47.57.E- Suspensions
47.57.J- Colloidal systems

Two‐element array of insulated antennas in a relatively dense medium

R. W. P. King and L. C. Shen

J. Appl. Phys. 47, 5226 (1976); http://dx.doi.org/10.1063/1.322596 (10 pages) | Cited 3 times

Online Publication Date: 28 August 2008

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The applications and the theory of coupled insulated dipoles and monopoles in a relatively dense medium (like water, the earth, a living tissue) are reviewed. Graphs of the distributions of current and the admittances calculated from the theory are displayed for two‐element arrays of air‐insulated monopoles in lake water. A comparison is made with measured data and generally good agreement is observed for the currents. Differences in the admittances due to the effects at the junctions between the monopole and the driving coaxial line and the approximations of the theory are discussed.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
87.85.-d Biomedical engineering
93.85.Pq Remote sensing in exploration geophysics

Diode compression of an intense relativistic electron beam

M. E. Read and John A. Nation

J. Appl. Phys. 47, 5236 (1976); http://dx.doi.org/10.1063/1.322597 (6 pages) | Cited 4 times

Online Publication Date: 28 August 2008

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Experiments are reported on the compression of an intense relativistic electron beam. The compression is aided by an externally driven current flow along the axis of the diode. It is found that the compressions achieved with the externally driven axial ’’wire’’ current are limited by the magnitude of the externally driven current and are substantially less than those obtained from the self‐pinching of an e‐beam from a low‐impedance generator.
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52.30.-q Plasma dynamics and flow
52.27.Ny Relativistic plasmas
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
41.75.Fr Electron and positron beams

Effects of transpiration on MHD boundary layers

Hsing Chuang

J. Appl. Phys. 47, 5242 (1976); http://dx.doi.org/10.1063/1.322598 (3 pages) | Cited 15 times

Online Publication Date: 28 August 2008

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A steady two‐dimensional MHD boundary‐layer flow on a flat plate with a uniform transpiration through the plate is considered. The shearing stress at the wall is found to increase with the magnetic interaction number and the transpiration number. Injection will cause a shearing stress reduction and eventually a flow separation which can be suppressed by increasing the magnetic interaction number. The velocity profile is substantially altered by both magnetic interaction and transpiration.
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52.30.-q Plasma dynamics and flow
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.15.Cb Laminar boundary layers
47.56.+r Flows through porous media

Measurement of the effective mean free paths of primary electrons in a multidipole device

K. N. Leung, R. E. Kribel, and G. R. Taylor

J. Appl. Phys. 47, 5245 (1976); http://dx.doi.org/10.1063/1.322599 (3 pages) | Cited 3 times

Online Publication Date: 28 August 2008

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The effective mean free path of the primary ionizing electrons in a multidipole device is measured by simply inserting a negatively biased electrode into the plasma.
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52.50.Dg Plasma sources
52.55.-s Magnetic confinement and equilibrium
34.80.Dp Atomic excitation and ionization

Physical properties of thin‐film field emission cathodes with molybdenum cones

C. A. Spindt, I. Brodie, L. Humphrey, and E. R. Westerberg

J. Appl. Phys. 47, 5248 (1976); http://dx.doi.org/10.1063/1.322600 (16 pages) | Cited 598 times

Online Publication Date: 28 August 2008

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Field emission cathodes fabricated using thin‐film techniques and electron beam microlithography are described, together with effects obtained by varying the fabrication parameters. The emission originates from the tip of molybdenum cones that are about 1.5 μm tall with a tip radius around 500 Å. Such cathodes have been produced in closely packed arrays containing 100 and 5000 cones as well as singly. Maximum currents in the range 50–150 μA per cone can be drawn with applied voltages in the range 100–300 V when operated in conventional ion‐pumped vacua at pressures of 10−9 Torr or less. In the arrays, current densities (averaged over the array) of above 10 A/cm2 have been demonstrated. Life tests with the 100‐cone arrays drawing 2 mA total emission (or 3 A/cm2) have proceeded in excess of 7000 h with about a 10% drop in emission current. Studies are presented of the emission characteristics and current fluctuation phenomena. It is tentatively concluded that the emission arises from only one or a few atomic sites on the cone tips.
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79.70.+q Field emission, ionization, evaporation, and desorption
29.25.Bx Electron sources
52.80.Vp Discharge in vacuum

Electrostatic metallic spray theory

A. J. Kelly

J. Appl. Phys. 47, 5264 (1976); http://dx.doi.org/10.1063/1.322601 (8 pages) | Cited 19 times

Online Publication Date: 28 August 2008

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A statistical model for the description of an isolated cloud of electrostatically generated droplets is developed. The droplet charging process is assumed independent of droplet population density consistent with high fluid conductivity and maximal charging levels. It is found that charge distribution is describable by Fermi‐Dirac statistics and droplet number distribution by Maxwell‐Boltzmann statistics. Evaluation of molten copper sprays reveals that the smaller the droplet cloud mass the higher the overall charge‐to‐mass ratio will be. Charge‐to‐mass ratio is found to vary approximately as the inverse square of droplet radius. The smaller the droplet the closer it can in general approach the Rayleigh criterion charge limit. The influence of emission‐limited charging was found to be unimportant for the cases studied. The model indicates the possibility that microscopic distributions of charge and mass can be inferred from knowledge of total charge and mass.
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47.55.D- Drops and bubbles
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Surface studies of barium and barium oxide on tungsten and its application to understanding the mechanism of operation of an impregnated tungsten cathode

R. Forman

J. Appl. Phys. 47, 5272 (1976); http://dx.doi.org/10.1063/1.322602 (8 pages) | Cited 26 times

Online Publication Date: 28 August 2008

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Surface studies have been made of multilayer and monolayer films of barium and barium oxide on a tungsten substrate. The purpose of the investigation was to synthesize the surface conditions that exist on an activated impregnated tungsten cathode and obtain a better understanding of the mechanism of operation of such cathodes. The techniques employed in these measurements were Auger spectroscopy and work‐function measurements. The results of this study show that the surface of an impregnated cathode is identical to that observed for a synthesized monolayer or partial monolayer of barium on oxidized tungsten, by evaluating Auger spectra and work‐function measurements. Data obtained from desorption studies of barium monolayers on a tungsten substrate in conjunction with Auger and work‐function results have been interpreted to show that throughout most of its life an impregnated cathode has a partial monolayer, rather than a monolayer, of barium on its surface.
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79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions

Analysis of the voltage drop arising from a collision‐dominated sheath

R. C. Dolson and O. Biblarz

J. Appl. Phys. 47, 5280 (1976); http://dx.doi.org/10.1063/1.322603 (8 pages)

Online Publication Date: 28 August 2008

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Voltage drops associated with the collisional sheath of nonemitting, MHD electrodes are investigated. The problem is described by a set of coupled nonlinear partial differential equations which are solved by finite differencing in a computer. The sheath and ambipolar regions form in a self‐consistent way obviating the need to match boundaries. A two‐dimensional model with periodic active sites on a flat plate is used. The current constricts at these sites in order to satisfy the controlling equations for frozen charge flow. The effects of a magnetic field as well as of Joule heating are included in the model; convection can be shown to be negligible in the sheath. Joule heating is assumed to have no effect on the bulk temperature of the gas. Changes in the current‐voltage characteristics due to Joule heating are small since the effect is extremely localized; the presence of a magnetic field has a slight influence on the size of the sheath but alters noticeably the current‐voltage characteristics.
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52.40.Kh Plasma sheaths
52.30.-q Plasma dynamics and flow
52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes

Extensions of the two‐dimensional constant property arc

Ira M. Cohen

J. Appl. Phys. 47, 5288 (1976); http://dx.doi.org/10.1063/1.322604 (4 pages)

Online Publication Date: 28 August 2008

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Our Galerkin approximate analysis of two‐dimensional arc properties and arc shape has been extended from planar constant property arcs to axisymmetric constant property arcs and to planar arcs with thermal and electrical conductivity variations. Axisymmetric constant property arcs are qualitatively similar to planar constant property arcs. Local temperature maxima occur on the arc axis about halfway between the central plane and the electrodes, and increase in magnitude as the arc slenderness ratio increases. When the electrical conductivity increases as a power of n of the heat flux potential, the arc gets thinner and cooler with increasing n for larger currents, but for small currents the arc gets thicker and hotter with increasing n. Since conductivity increases rapidly with heat flux potential ?, when this is greater than unity, high enough conductivities can be obtained at lower temperatures and with thinner arcs. On the other hand, when current ? is small, ?<1, so larger n corresponds to smaller conductivities. Thus higher temperatures and thicker arcs (as n increases) are required in order to pass small currents.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
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