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Journal of Applied Physics

Issue 12 • Date Dec 1982

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Displaying Results 1 - 25 of 124
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Target design of an archival electron beam memory

    Page(s): 8429 - 8436
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    A new concept for archival electron beam accessed memory has recently been proposed. In the write mode, a high intensity electron beam selectively melts columnar bits in a two‐dimensional lattice which is supported by a thin membrane. The force of surface tension transforms the melted columns into droplets. In the read mode, a low intensity beam interrogates the bits. Transmission contrast is generated by the difference in cross‐sectional area of the columnar and spherical bits. We study the relationship between physical target parameters and system performance of such a memory. Monte‐Carlo simulation of the electron beam‐target interaction has been used to design a target consistent with the following system performance goals: (a) 107 bit/sec data rate, (b) 1010 bit/cm2 data density, and (c) 10-9 error rate. View full abstract»

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  • Theory of magnetic leakage fields from prolate and oblate spheroidal inclusions

    Page(s): 8437 - 8450
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    Magnetic leakage fields from nonspherical inclusions in magnetic materials are discussed using classical electromagnetic theory. The model used is that of a prolate or oblate spheroidal inclusion embedded in an infinite medium. Deviations from the leakage field behavior of a spherical inclusion are discussed and procedures are suggested whereby one can test for inclusion shape. View full abstract»

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  • Threshold of a thallium‐iodide photodissociation laser operated at low pressure

    Page(s): 8451 - 8453
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    The emission intensity of the 535‐nm line of a thallium‐iodide photodissociation laser excited with 193‐nm ultraviolet radiation is measured as a function of pump energy and vapor pressure. Pressure was varied between 4×10-5 and 0.13 Torr. No threshold for positive gain has been found experimentally. The measurements and computer simulation indicate a possibility of constructing lasers with extremely low excitation energy. View full abstract»

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  • Stark effect of SiOH and SiH molecules in SiO2

    Page(s): 8454 - 8461
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    Hydrogen has been implanted into an SiO2 film grown on a Si trapezoid substrate to form SiH and SiOH bonds. Utilizing internal reflection spectroscopy in the near infrared spectral region, we have directly observed the vibration bands of these ‘‘molecules.’’ With the application of a large electric field across this metal‐oxide‐semiconductor structure, the Stark effect of these vibration bands has been observed. The dependence of line intensity and line shape on the applied voltage has been studied. The sharing of voltage between the oxide film and the depletion layer in the Si is seen by its effect on the Stark intensity. These results suggest the feasibility of seeing natural hydrogen molecularly bonded in thermal oxides. View full abstract»

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  • Deposition of chromium films by multiphoton dissociation of chromium hexacarbonyl

    Page(s): 8462 - 8469
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    Focused, pulsed, tunable dye lasers have been used to deposit chromium films by multiphoton dissociation of Cr(CO)6. The multiphoton dissociation of Cr(CO)6 is strongly wavelength dependent. Large increases in deposition rate occur below 350 nm, where the threshold between initial 1 and 2 photon absorption to the lowest lying dissociative state are reached in Cr(CO)6. Lack of correlation of deposition rate with multiphoton ionization (MPI) resonances, and polarity of a biased electrode in the cell, suggests multiphoton absorption leads to decomposition to Cr atoms followed by ionization. Power dependence of the deposition rates and MPI signals indicate saturation in the focal region for wavelengths 280≪λ≪340, for pulse energies 0.02–0.2 mJ. Deposition on cell windows not in the focal region also appears saturated at the shorter wavelengths. Films deposited on silicon and quartz substrates appear uniform, with visible evidence of melting and regrowth in the center of the deposits due to heating by subsequent pulses. Isotropic deposition of Cr atoms on the substrate from the gas phase, away from the irradiated spot, was also observed. Auger analysis of films deposited in the focal region suggest that significant quantities of carbon are present in the film. Alloying of the Cr with the underlying Si by laser heating of the substrate is also suggested. View full abstract»

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  • The shape factor of the capacitance of a conductor

    Page(s): 8470 - 8475
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    This paper shows, analytically and numerically, that the capacitance is a slowly changing function of the conductor shape. This slow change can be monitored by a ‘‘shape factor’’ which is independent of the conductor size. Because of this slow change, from the tabulation of the shape factor, the capacitance of many conductors of arbitrary sizes and shapes with both convex and concave surfaces, can be estimated to an error of 5% or less. View full abstract»

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  • New formulas for the electromagnetic field of a vertical electric dipole in a dielectric or conducting half‐space near its horizontal interface

    Page(s): 8476 - 8482
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    New formulas are derived for the electromagnetic field of a vertical electric dipole in a conducting or dielectric half‐space. These continuously approximate in accuracy the general complex integrals over the entire practical range, yet are quite simple. They supplement similar formulas for the horizontal electric dipole with which they are compared, and provide the means for studying the interference patterns between the direct and lateral components of the waves and the reflection and transmission of lateral waves at boundaries. View full abstract»

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  • Properties of the electromagnetic wave propagation in a helix‐loaded waveguide

    Page(s): 8483 - 8488
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    Properties of the electromagnetic waves propagating through a helix‐loaded waveguide are investigated, including the important influence of the outer conducting wall on the dispersion properties. A closed algebraic dispersion relation for the eigenfrequency ω and the axial wave number k is obtained for arbitrary azimuthal harmonic number. It is shown that in the limiting case, where the outer conducting wall approaches close to the helix, this dispersion relation is reduced to three distinctive modes. These are the transverse electric mode, the transverse magnetic mode, and the helix mode, which can be further simplified to straight lines in the (ω, k) parameter space. Numerical investigation of the dispersion relation is also presented. View full abstract»

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  • Relativistic electron‐beam transport in curved channels

    Page(s): 8489 - 8496
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    Collisionless single particle trajectories are modeled for a single plasma channel having one section curved in a circular arc. The magnetic field is developed by superposition of straight and curved channel segments. The plasma density gives charge and beam‐current neutralization. High transport efficiencies are found for turning a relativistic electron beam 90° under reasonable conditions of plasma current, beam energy, arc radius, channel radius, and injection distributions in velocity and in position at the channel entrance. Channel exit distributions in velocity and position are found consistent with those for a straight plasma channel of equivalent length. Such transport problems are important in any charged particle‐beam application constrained by large diode‐to‐target distance or by requirements of maximum power deposition in a confined area. View full abstract»

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  • Thermal changes of optical properties observed in some suboxide thin films

    Page(s): 8497 - 8500
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    Suboxide thin films of SbOx, TeOx, MoOx, and GeOx (x is smaller than the stoichiometric value for each component) were found to have the property of showing a critical change in their absorption coefficients and refractive indices at elevated temperatures. The thin‐film samples were prepared by evaporating a mixture of the stoichiometric oxide powder and a deoxidization metal powder such as tungsten. The critical temperatures of these thin films are 150, 120, 150, and 280 °C, respectively. The absorption coefficients before and after the heat treatment are 2.5×104 (before) and 6.1×104 (after), 8×104 and 1.0×105, 5.6×103 and 1.1×104, and 4.9×104 and 1.8×105 cm-1, respectively. Their refractive indices are 1.8 (before) and 1.9 (after), 3.1 and 3.5, 1.8 and 2.1, and 2.5 and 2.8, respectively. As determined by x‐ray diffraction analysis, these thin films are composed of very small metal grains and stoichiometric oxide grains. The thermal changes accompanied by the optical constant changes are mainly due to structural changes in the metal grains. These thin films are concluded to have the feasibility of application to optical disk memories of the laser heat‐mode type. View full abstract»

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  • Theory of rotating mirror Q‐switching in a helical transversely excited CO2 laser

    Page(s): 8501 - 8507
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    In a rotating mirror Q‐switching scheme under suitable experimental conditions an effect termed ‘‘mode sweeping’’ can play an important role in the buildup of the laser pulse. A theoretical model has been developed which takes into account this effect and also considers the nonuniform gain distribution resulting from the helical arrangement of the discharge pins. A number of approximations simplify the computation. The agreement between theory and experiment is excellent. The basic limitation of the theory is discussed. The discrepancies between theory and experiment can be attributed to the neglect of the ‘‘thermal lensing’’ in the gas medium, that normally occur in such discharges. View full abstract»

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  • Gain, saturation, and optimization of the XeF discharge laser

    Page(s): 8508 - 8515
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    In this work a xenon‐F2 plasma diluted in helium has been operated as a pulsed amplifier for the B→X transition of XeF. Two synchronously excited plasmas were produced by preionized discharges in atmospheric electrical avalanche devices switched by hydrogen thyratrons. The principle output obtained at 352 nm from the tube serving as an oscillator was optically delayed and then was threaded through the second discharge. Calibrated attenuation of this beam injected into the amplifier provided data on the overall amplification ratio. From these data effective saturation intensities of 620 and 860 kW/cm2 were found for operation at pressures of 2.7 and 3.7 atmospheres, respectively. Corresponding small signal gains were found to be moderately high, reaching 0.11 and 0.13 cm-1, for the two conditions, respectively. Based upon these results for the gain and saturation parameters, a self‐excited oscillator was designed to be optimized simultaneously for energy density and efficiency. By matching the ringing time of the driving circuit to the characteristic time of the discharge a XeF device was realized which produced 10‐ns output pulses representing an energy density of 2.7 J/liter and an efficiency relative to storage of 1.6%. View full abstract»

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  • Second‐harmonic diffraction field in nonlinear propagation of transversely limited surface acoustic wave beams

    Page(s): 8516 - 8524
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    The study of the Fresnel field of the second harmonic of a finite width surface acoustic wave, parametrically generated through the nonlinear interaction on a LiNbO3 substrate, is performed both theoretically and experimentally. Theoretically, a model has been developed which computes the acoustic field at each point as given by the sum of all the second‐harmonic plane wave fronts nonlinearly generated by the interaction of any two plane wave fronts present in the fundamental wave angular spectrum. Experimentally, a phase contrast optical probing technique has been used, which permits separating the contributions of the second‐harmonic field from that of the fundamental wave. Theoretical and experimental transversal amplitude profiles of the surface acoustic wave second‐harmonic field are presented, relative to the case of an acoustic beam launched from a 24‐wavelength‐wide transducer on the free surface of a LiNbO2 sample, at the fundamental frequency of 34.5 MHz. View full abstract»

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  • Investigation of gaseous heat transfer between surfaces by photoacoustic effect

    Page(s): 8525 - 8528
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    The heat transfer, by the interstitial gas, between two metallic surfaces in contact has been investigated by photoacoustic effect. The thermal conductance is determined by interpreting the phase data obtained by varying the laser source modulation frequency. Our experimental results confirm the hypothesis, implicit in most theoretical formulations of the photoacoustic effect, that the surface thermal resistance is generally negligible. View full abstract»

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  • Electronic effects on the elastic constants of n‐type gallium antimonide

    Page(s): 8529 - 8531
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    The second‐order elastic stiffness constants of three n‐type Te‐doped GaSb single crystals were measured by the ultrasonic pulse interference method at 25 °C. Carrier concentrations of the samples are: 1.9×1017, 7.7×1017, and 1.2×1018 per cm3. The largest electronic effect was found in C44: a decrease of 0.32% for the highest doped sample compared with the lowest doped sample. The experimental results were interpreted in terms of Keyes’ theory, which is based on the consideration of electronic free energy. The shear deformation potential Ξ(111)u of the (111) band was found to be 16.5±1.8 eV. The longitudinal deformation potential Ξ(111)d was also estimated. View full abstract»

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  • Metastable atom density in helium, neon, and argon glow discharges

    Page(s): 8532 - 8536
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    A theoretical model of the positive column of a rare gas glow discharge is used to calculate metastable atom densities in the pressure x radius range from 0.01 to 1.0 Torr cm. Two body quenching is shown to be an important loss process for metastables in neon and argon discharges above 0.1 Torr cm. Measurements of metastable atom flux from an anode slit are reported for the title gases and shown to represent the metastable density in the anode fall region of the discharges. View full abstract»

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  • On the determination of particle concentrations in multitemperature plasmas

    Page(s): 8537 - 8542
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    The use of the multitemperature Saha equation (MSE) of Prigogine1 and Patapov2 for calculating particle concentrations in plasmas is shown to be an invalid procedure. Errors greater than one order of magnitude in the electron density in high‐pressure argon and nitrogen electric arc plasmas can be easily incurred by using the multitemperature Saha equation. The alternative kinetic method for calculating concentrations is shown to be based on firm concepts. Simpliying procedures and computational techniques for calculating concentrations with the kinetic method are illustrated with examples. View full abstract»

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  • Pinched‐beam ion‐diode scaling on the Aurora pulser

    Page(s): 8543 - 8548
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    A pinched‐beam ion diode has been operated on the Aurora pulser in positive polarity at impedances ranging from 10 to 35 Ω. Ion generation efficiencies of 20% were observed with ion energies ranging from 2.5 to 5 MeV. The ion current scaled inversely with the anode‐cathode gap, and a peak value of 65 kA was measured for the smallest gap. A plasma erosion switch was used to decrease prepulse voltage and gap closure in the diode. View full abstract»

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  • A technique for inferring outward displacement of magnetic flux surfaces in toroidal plasmas, using multichord interferometry

    Page(s): 8549 - 8553
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    When flow can be neglected and when heat conduction parallel to the magnetic field is sufficiently strong, a confined plasma’s surfaces of constant magnetic flux are also surfaces of constant plasma density. Thus, in principle, measurements of the internal density asymmetries can also determine the internal profile of flux‐surface displacement along major radius caused by toroidal effects. This paper develops a simple algorithm for doing this with multichord interferometer data in toroidal plasmas having circular minor cross section and illustrates the technique with data from the ZT‐40M reversed‐field pinch. View full abstract»

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  • Forbidden line emission from highly ionized atoms in tokamak plasmas

    Page(s): 8554 - 8561
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    Collisional excitation rate coefficients and radiative decay rates are interpolated for ions of elements between calcium and krypton and for levels of the 2s22pk, 2s2pk+1, and 2pk+2 configurations, and for the O I, N I, C I, B I, and Be I isoelectronic sequences. With the use of these interpolated atomic data, level populations and relative line intensities can be calculated for ions of these sequences, for levels of the stated configurations. Relative line intensities for transitions between the 2s22pk ground configurations are considered specifically. These transitions are forbidden, e.g., magnetic dipole transitions, and are strong in XUV spectra of tokamak plasmas. The forbidden lines provide important plasma diagnostic information, such as the ion temperature which can be derived from forbidden line profiles. The relative line intensities are presented graphically, in order that they can be used easily by tokamak researchers. Results are given for three values of electron density: 2.5×1013; 1.6×1014; 1015 cm-3, and two values of electron temperature: the ionization equilibrium temperature and twice this temperature. The behavior of the line intensities along the isoelectronic sequences is discussed and the relative importance of excitations into different intermediate levels for populating the upper level of the forbidden line of the B I sequence by cascade is discussed in detail. View full abstract»

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  • Measurement of ionization and attachment coefficients in SF6 and SF6+N2

    Page(s): 8562 - 8567
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    Prebreakdown ionization currents have been measured in SF6, N2, and SF6+N2 mixtures by the Townsend method over the E/p range 100–450 V cm-1 Torr-1. A digital computer analysis is used for evaluation of the ionization and attachment coefficients. The variation of (α-η)/p in SF6 and N2 mixtures is found to be nonlinear with the percentage mixture ratio. Sparkover voltage measurements are carried out for SF6, N2, and SF6+N2 mixtures in the pd interval of 3.5≤pd≤25 Torr cm. Furthermore, the apparent secondary ionization coefficients have been deduced in SF6+N2 mixtures. They decrease significantly with increasing partial pressure of SF6. The reduction observed in this coefficient is attributed to the increased photon absorption coefficient. View full abstract»

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  • Spectroscopic measurements on discharges along a dielectric surface

    Page(s): 8568 - 8576
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    Spectroscopic measurements have been made on quasilinear surface discharges over dielectric slabs. The first time‐resolved spectra in the range 200–800 nm have been obtained; we define the light emitting centers (N2 molecular bands in a first period and atomic lines in a second one) and the dielectric substrate effect. We give the form of the rotational temperature variations and the upper value of the electron temperature (5 eV) in the first period. The spatial dimension of this phase seems to be constant at about 23 mm. In the second period the electron densities calculated from the Stark broadening width of the Hα and Hβ lines vary in 8×10-7 s from 7×1017 to 2×1016 cm-3. In the same period, the temperature which is obtained by Saha’s law using the intensity ratios of ionized atomic and neutral lines (oxygen O+,O) and nitrogen (N+,N) decreases from 24 000 to 15 000 K. Using these results we estimate the cross‐sectional area of the discharge to be ≂65 000 μm2. View full abstract»

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  • A high‐current magnetically stabilized plasma column for fast current‐reversal and penetration studies

    Page(s): 8577 - 8582
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    A magnetically stabilized He‐plasma column with a diameter of about 40 mm is operated in the electron density and temperature range of 1021 m-3 and 5 eV, respectively. The temperature is inferred through spectroscopy from the He line‐to‐line ratio, and the density profile at a given time is obtained on a single shot from interferometry with a large cross‐section Mach‐Zehnder. At equilibrium a simple balance between ohmic heating and dominant longitudinal conduction losses predicts a core temperature in relatively good agreement with the measurements. At a given time during the long lasting discharge (milliseconds), the 10‐kA current can be completely reversed on a time scale (microseconds) much shorter than the classical time for current penetration toward the center of the column. This plasma device is useful for studying basic energy transport and anomalous current‐penetration mechanisms involved in hot and relatively dense plasmas. View full abstract»

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  • Filamentary breakdown of gases in the presence of dielectric surfaces

    Page(s): 8583 - 8588
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    The effect of dielectric surfaces on the breakdown voltage of gas spark gaps were investigated both theoretically and experimentally. Experiments have been carried out using N2 and other gases at pressures ranging from one to five atmospheres. Several different dielectric materials were used as substrates, having plain and cylindrical surface geometries. The observed results were interpreted by a physical model which was developed for this purpose. In the model, the major physical processes, i.e., electron production and electron loss due to diffusion, were treated in the presence of the dielectric surface. In addition, electron loss due to electron traps on the dielectric surface has also been taken into consideration. The model yields an analytical expression for the breakdown voltage of a given gas spark gap. For the cases studied, the model predictions fit the observed results reasonably well. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory