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Journal of Applied Physics

Issue 2 • Date Jul 1986

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Displaying Results 1 - 25 of 67
  • Electrical circuit modeling of conductors with skin effect

    Page(s): 475 - 481
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    The electrical impedance of a lossy conductor is a complicated function of time (or frequency) because of the skin effect. By solving the diffusion equation for magnetic fields in conductors of several prototypical shapes, the impedance can be calculated as a function of time for a step function of current. The solution suggests an electrical circuit representation that allows calculation of time‐dependent voltages and currents of arbitrary waveforms. A technique using an operational amplifier to determine the current in such a conductor by measuring some external voltage is described. Useful analytical approximations to the results are derived. View full abstract»

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  • Zinc‐oxide thin‐film ammonia gas sensors with high sensitivity and excellent selectivity

    Page(s): 482 - 484
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    A sensor with a high sensitivity and an excellent selectivity for ammonia gas was prepared by using sputtered ZnO thin films. The sensor exhibited an increase of resistance for exposure to ammonia gas whereas it exhibited a decrease of resistance for exposure to many other gases such as inflammable and organic gases. The resistance change and the selectivity of the sensor were enhanced by doping group III metal impurities such as Al, In, and Ga. The lower limit of the detection for ammonia gas was about 1 ppm at a working temperature of 350 °C. View full abstract»

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  • Measurements of thermal conductivity of materials using a transient technique. I. Theoretical background

    Page(s): 485 - 492
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    A method of measuring the thermal conductivity of materials during transient heating or cooling is proposed based on the continuous recording of the temperature difference between sample surfaces when known heat flux is supplied to one of the sample surfaces by a heater. The analysis of the solution of the heat conduction equation for a measuring system consisting of two platelike samples separated by a heater shows that the transient heating or cooling significantly influences the temperature distribution within the samples. It follows from the theoretical consideration that this effect as well as the effects resulting from heat generation or absorption in the samples during phase transitions can be eliminated by subtracting the results of two measurements conducted with different powers supplied by the heater. The condition for validity of this procedure is the small temperature difference between sample surfaces which can be achieved by the selection of appropriate temperature change rate or sample thickness. View full abstract»

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  • Measurements of thermal conductivity of materials using a transient technique. II. Description of the apparatus

    Page(s): 493 - 498
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    In this paper, an apparatus for measurements of the thermal conductivity of materials as a continuous function of the temperature is described. It works on the principle of continuous recording of the temperature difference between the surfaces of the sample caused by the flux of heat while the ambient temperature is linearily changed. The theoretical background described in the preceding paper by E. Piorkowska and A. Galeski [J. Appl. Phys. 60, ∎∎∎∎ (1986)] showed that the utilization of the results of two continuous measurements with different heat fluxes makes it possible to eliminate all components of the thermal response of the sample except the one depending on the heat flux and the thermal conductivity only. Testing measurements were conducted on samples of several nonmetalic materials. The results obtained indicate high precision of the method and the apparatus and reveal new possibilities of studying the thermal conductivity of materials during phase transitions. View full abstract»

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  • Studies of total ionization in gases/mixtures of interest to pulsed power applications

    Page(s): 499 - 508
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    The energy required to produce an electron‐ion pair (i.p.), W, for the α‐particle irradiated gases CF4, C2F6, C3F8, and n‐C4F10 has been measured and found to be 34.3, 34.5, 34.4, and 34.2 eV/ i.p., respectively. The large values of W for these perfluorocarbons (PFCs) are attributed to their large cross sections for electron impact‐induced dissociation. The constancy of W for this group of molecules is discussed with respect to the constancy of the ratio (∼0.68) of the respective (energy integrated) total ionization cross section to the total (energy integrated) inelastic scattering cross section. W values are also reported for the binary gas mixtures Ar/CF4, Ar/C2F6, Ar/C3F8, and CH4/CF4 which have conduction and insulation properties suitable for use in diffuse discharge opening switches. The W values for these binary mixtures (and for C2H2/CF4, C2H2/C2F6, and C2H2/C3F8) increase with the amount of PFCs in the mixture and (contrary to the Ar/C2H2 mixture) exhibit no Jesse effect. The ternary gas mixtures Ar/C2H2/PFC (=CF4, C2F6, C3F8) containing ≲10% PFC were found to exhibit a pronounced Jesse effect which is a function of the content of the PFC in the mixture and the electron scattering cross section of the PFC itself. Substantial increases in ionization can be achieved by adding to the Ar/PFC binaries 1–3% of C2H2. An analysis of the W data yielded information on the partition of the α particle’s energy among the gas components and indicated that the rate constant for energy transfer f- rom excited argon atoms (Ar*) to the PFC is smaller than that from Ar* to C2H2; it showed, also, that the rate constant for energy transfer from Ar* to C2H2 is ∼104 larger than that for collisional deexcitation of Ar* by ground‐state Ar atoms. The quantitative measurements reported herewith and the parameters deduced from a simple modeling of the data permit the tailoring of ternary gas mixtures with substantial current increases over those achieved in the binary Ar/PFC (=CF4, C2F6, C3F8) mixtures which possess the desirable conduction and insulation characteristics for pulsed power opening switches. View full abstract»

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  • Formation of primary metal particles in evaporation chambers

    Page(s): 509 - 513
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    Experimental and theoretical studies are reported on formation of primary particles during evaporation of metals into a host gas in an evaporation chamber. The developed theory explains present and previous experimental observations of this process. The dependence of primary particle size on host gas pressure, host‐gas molecular weight and source temperature has been explained. Particle thermophoresis has been shown to cause formation of the so‐called ‘‘smoke shell’’ observed surrounding the vapor source. Coalescence of primary particles has been shown not to be an important growth process for the primary particles, although for longer times primary particle coagulation produces the chains of primary particles observed experimentally. View full abstract»

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  • Fields from a uniform current source: Instantaneous switch‐on

    Page(s): 514 - 517
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    Electromagnetic fields from switching on and off a constant current distributed over a plate of finite extent are studied. Such current distribution will set up a magnetostatic field and an electric dipole field behind the initial transient pulse. Over an area equal to that of the plate, there is a finite volume in which the strengths of the E and H fields of the transient pulse do not decrease with distance. This finite volume decreases as the inverse of the distance from the source so that the energy contained in this volume also decreases as the inverse of the distance traveled. View full abstract»

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  • Observation of microwave Cerenkov radiation as a diffraction pattern

    Page(s): 518 - 520
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    Measurement of microwave Cerenkov radiation in air exhibits the diffraction pattern predicted in earlier work. The radiation appears only at harmonics of the frequency of periodic electron bunches. Angular distribution power measurements are presented for frequencies of 2.86, 5.71, 8.57, and 11.42 GHz corresponding to the fundamental and the first three harmonics of an S‐band rf linac. View full abstract»

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  • Near‐millimeter free electron laser designs based on measured characteristics of small‐period electromagnet wigglers

    Page(s): 521 - 528
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    The performance characteristics of small‐period electromagnet wigglers of novel design are measured and compared with theoretical expectations. Field measurements for wigglers driven by dc, ac, and short‐pulse current sources are reported. Fields as high as 1 kG have been readily obtained in a double‐sided 3.9‐mm‐period wiggler. These performance capabilities allow the design of high‐power free electron laser oscillators and ‘‘optical klystron’’ amplifiers in the near‐millimeter regime using modest electron beam energies in the range 200–400 keV. Oscillator and amplifier designs for operation at 150 and 300 GHz are presented. The generation of 1.2 MW of 150‐GHz radiation with ≫50% efficiency is predicted. View full abstract»

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  • A chemical and mechanistic view of reaction profiles in laser direct‐write metallization in metallo‐organic films. Gold.

    Page(s): 529 - 533
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    Laser direct‐write metallization in metallo‐organic films involves complex thermal profiles and changes in optical properties that affect the spatial resolution, chemical purity, and electrical properties of the resulting features. Compositional profiles of the metal features, determined by scanning Auger electron spectroscopy, are reported and correlated with the chemistry of the laser‐initiated thermal reaction and the observed feature structure. Studies of the changes in optical properties of the films by conventional thermal decomposition offer important insights into the reaction mechanisms. We also report an optimized development procedure for the laser‐exposed samples. View full abstract»

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  • Effect of device parameters on bistable semiconductor laser

    Page(s): 534 - 537
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    The effect of device parameters on static and dynamic properties of inhomogeneously current‐injected bistable semiconductor lasers has been analyzed. It is shown that in addition to the fraction of current injection region in the cavity, the device parameters, such as dopant concentration in active layer, facet reflectivity, and cavity length, affect the hysteresis width and threshold current. The mechanism of transition between lasing and nonlasing states is discussed, in which a new interpretation is given about the bias dependence of switch‐on delay time and the driving condition for switching off is clarified. The carrier increasing rates due to the bias current and dopant concentration in the active layer are dominant factors for the switching on and switching off, respectively. View full abstract»

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  • Acoustic waves in random discrete media via a differential scheme

    Page(s): 538 - 540
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    The concept of differential effective media is extended to the dynamic case by imposing the condition of causality. The dispersion of acoustic waves in such media is treated and results are compared with those following from alternative models. View full abstract»

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  • Use of eigenfunctions for solving radiation transfer in anisotropically scattering, plane‐parallel media

    Page(s): 541 - 551
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    Radiation transfer in an absorbing, emitting, gray, anisotropically scattering, plane‐parallel medium is solved by using the naturally occurring eigenfunctions, and expressions for the forward and backward radiation intensities, the incident radiation, and forward and backward radiation heat fluxes are presented. To illustrate the method of solution, the situation involving an externally incident isotropic radiation at the boundary surface x=0 and no energy sources in the medium is considered for the cases of four different scattering phase functions. It is shown that the convergence to the exact results is fast, and that lower order approximations are accurate. In addition, the present method of solution has an excellent potential for generalization to problems of plane‐parallel media without azimuthal symmetry and to problems in cylindrical and spherical geometries. View full abstract»

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  • Electron swarm properties of CCl2F2/SF6 mixtures

    Page(s): 552 - 558
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    The ionization and attachment coefficients for CCl2F2/SF6 mixtures were determined from measurements of prebreakdown ionization currents in a steady‐state Townsend discharge at a pressure p25=4 Torr and temperature of 25 °C. The curves representing the ionization coefficient (α) for reduced fields in the range from 110 to 180 V cm-1 Torr-1 exhibit a small maximum at about 15% of CCl2F2, while those representing the attachment coefficient (η) flatten out between 0% and 50% CCl2F2 and decrease at higher partial densities. The limit field obtained using the condition α=η shows two extrema, i.e., a minimum at approximately 20% and a maximum at 75% of CCl2F2, while the curves obtained from the breakdown‐potential measurements available in the literature show only a maximum, at roughly the same position. Theoretical values of the transport coefficients were obtained by numerically solving the Boltzmann equation using previously determined effective sets of electron collision cross sections [J. P. Novak and M. F. Fréchette, J. Appl. Phys. 55, 107 (1984); 57, 4368 (1985)]. The good agreement between the calculated and the experimental values provides supporting evidence for the applicability of the present calculation method and collisional cross sections to analyze electron swarms in the range of fields comparable in magnitude to the limit field. View full abstract»

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  • The Orbitron as a stimulated‐bremsstrahlung glow‐discharge maser

    Page(s): 559 - 562
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    A new physical explanation for the operation of the Orbitron maser is presented. The Orbitron experimental results are shown to be in agreement with the prediction of the theory of amplification by stimulated emission of bremsstrahlung. View full abstract»

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  • A model of radial variations in the low‐pressure mercury–argon positive column

    Page(s): 563 - 570
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    The low‐pressure Hg–Ar positive column is studied with a model which accounts for radial transport mechanisms. The model calculates, not assumes, the radial density distribution for each of the species and the radial temperature distributions for the electron and the neutral gases. Solutions to the discharge equations are found for specified values of the wall (Hg reservoir) temperature, electric current, Ar pressure, and tube diameter. These solutions compare favorably with available parametric data for 3.6‐ and 1.4‐cm‐diam. discharge tubes. The model is used to investigate effects such as radial cataphoresis, the effect of radiation trapping on radial distributions, and deviations from a radially uniform electron temperature. The work supports some of the simplifying assumptions often made in modeling the discharge at the standard fluorescent lamp operating condition, such as a radially invariant electron temperature, the use of a constant escape factor to describe radiation trapping, and negligible radial cataphoresis. Under conditions of high Ar pressure, the assumption of a radially invariant electron temperature is found to be less valid. View full abstract»

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  • Measurement of high Rydberg 1P spectra of atomic helium and its application to glow‐discharge diagnostics

    Page(s): 571 - 576
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    The high Rydberg spectra of atomic helium np 1P states were measured up to n=46 in the negative glow region of a discharge, with mJ=±1 polarization, by optogalvanic spectroscopy. The net electric field values in the negative glow region, in the transition region between the negative glow and the positive column, and also on the radial axis of the positive column were determined from series‐termination measurements. The spatial variations of the ion density in the negative glow region were also obtained from the net‐field measurements. View full abstract»

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  • Resistive filamentation of self‐pinched electron beams

    Page(s): 577 - 584
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    A model for resistive filamentation of a self‐pinched slab electron beam is presented. The lowest‐order modes are found to consist of a body mode which leads to bunching of the beam, and a surface mode which leads to rigid rippling of the beam. The dispersion relations for these modes are compared to results from a linearized particle simulation code. The analytic model and simulation code are applied to the interpretation of a recent experiment in which filamentation was observed in a self‐pinched annular electron beam propagating in low‐pressure air. View full abstract»

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  • A ferrite‐loaded autoaccelerator

    Page(s): 585 - 590
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    An account is presented of the performance of an autoaccelerator in which energy is extracted from the front portion of a relativistic electron beam, via a ferrite‐loaded cavity, and stored in an oil‐filled transmission line. The extracted energy is returned to augment the energy of the electrons in the latter half of the beam. An increase of up to 33% in the electron beam energy is reported. The device was also used to investigate beam energy recovery. In this application the line was terminated in a matched load and up to 60% of the beam energy recovered. The autoaccelerator performance was limited by current pulse rise time degradation in the ferrite and by the formation of virtual cathodes during the deceleration phase. The latter process also limits the energy recovery. View full abstract»

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  • Vacancy interactions in GaAs

    Page(s): 591 - 594
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    Isochronal annealing of zinc‐ or silicon‐doped GaAs as well as undoped semi‐insulating or low‐resistivity materials has been investigated by positron lifetime measurements. For impurity concentrations larger than 4.5×1017 cm-3, only monovacancy complexes such as ZnGaVAs,  SiAsVGa, or AsGaVGa are observed and they yield a positron lifetime of 265±5 ps. For impurity concentrations less than 1×1017 cm-3, divacancies dominate and yield a lifetime of 295±5 ps. The concentrations of grown‐in vacancies, either VAs or VGa, are both estimated to be in the range of (1–4)×1017 cm-3. View full abstract»

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  • A model of deep center formation and reactions in electron irradiated InP

    Page(s): 595 - 601
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    We present a model of the production of deep centers and their reactions following electron irradiations in InP. We propose that the dominant hole traps in p‐InP and electron traps in p+n InP junctions are complexes between shallow acceptors and a common intrinsic entity, the phosphorus interstitial or vacancy. The reactions observed below and above room temperature are then due to a local mobility of this entity, which can be obtained as well by thermal as by electronic stimulation of the reactions. This model implies the long‐range migration (at least down to 16 K) of this entity, and explains the strongly different behavior of n‐InP compared to p‐InP samples. View full abstract»

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  • The local structure of amorphous SnO2 by electron microscope techniques

    Page(s): 602 - 606
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    Electron microscopy/diffraction and electron energy‐loss spectroscopy, including low‐loss and core‐edge structures, were used to characterize and study the atomic arrangement in amorphous SnO2 prepared by reactive sputtering. The gross features in the energy‐loss spectra are the same as for crystalline SnO2, whereas the fine structures are smeared out. The diffraction pattern of amorphous SnO2 is qualitatively well described by assuming each tin atom to be surrounded by six oxygen atoms at a distance of 2.05 Å, two tin atoms at 3.19 Å, and eight tin atoms at 3.71 Å, which suggests the same local atomic arrangement as in crystalline SnO2. View full abstract»

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  • Thermal properties of pure and varistor ZnO at low temperatures

    Page(s): 607 - 611
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    Specific heat data are reported on pure and varistor ZnO, 1.7–25 K, and thermal conductivity data are reported on varistor ZnO, 1.7–15 K. In pure ZnO interstitials give rise to an Einstein contribution (ωE=84 cm-1) to the specific heat above 10 K and to a Schottky contribution (δ≂10-5 eV) below 4 K due possibly to ordering. The calorimetric Debye temperature is 399.5 K. In varistor ZnO the specific heat is dominated below 20 K by compensating charge densities (∼1018 cm-3) on the interfacial barriers which give rise to two Schottky terms (δ=7×10-4 and 3×10-3 eV). All of these non‐Debye excitations are localized (do not carry heat). No evidence is seen in the thermal conductivity for Kapitza‐resistance effects at the heavily doped grain boundaries. View full abstract»

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  • Thermal expansion of the hexagonal (4H) polytype of SiC

    Page(s): 612 - 614
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    Thermal expansion of the hexagonal (4H) polytype of SiC was measured from 20 to 1000 °C by the x‐ray diffraction technique. The principal axial coefficients of thermal expansion are expressed by the second‐order polynomials: α11=3.21×10-6+3.56×10-9T-1.62×10-12T2, and  α33=3.09×10-6+2.63×10-9T-1.08×10-12T2 (°C-1). The α11 is larger than the α33 over the entire temperature range, yielding a thermal expansion anisotropy ‘‘A’’ of 0.04 at room temperature which increases to 0.11 at 1000 °C. The thermal expansion of the (4H) structure is compared with previously published results for the cubic (3C) and the hexagonal (6H) SiC polytypes. View full abstract»

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  • New intrinsic gettering process in silicon based on interactions of silicon interstitials

    Page(s): 615 - 621
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    A new intrinsic gettering process was found in silicon crystals subjected to a three‐step annealing sequence. The process involves native point defects (silicon interstitials) rather than residual oxygen impurity, and thus it can be realized in crystals with low or virtually zero oxygen concentration. The key characteristics of the process (i.e., denuding and gettering efficiency and the role of annealing ambient) are discussed in conjunction with a kinetic model involving diffusion of silicon interstitials. The identity of the intrinsic gettering centers was pursued by transmission electron microscopy. 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