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Journal of Applied Physics

Issue 1 • Date Jan 1961

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Displaying Results 1 - 25 of 35
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Thermoelectric Properties of Ag2Te

    Page(s): 1 - 3
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    The Seebeck coefficient α, electrical conductivity σ, and thermal conductivity K data are given for a number of Ag2Te specimens measured at room temperature. The maximum value observed for the figure of merit α2σ/K was 1.3×10-3°C-1. The relationship between K and σ was linear, and Kel could be expressed approximately by (π2/3) (k/e)2σT. Kph was found to be 0.72×10-2 w cm-1°C-1. There was no evidence of an ambipolar diffusion contribution to K. It is suggested that the small energy gap (0.02 ev) previously determined in this compound could account for the absence of a measurable ambipolar diffusion effect, the degeneracylike behavior of Kel, and the relatively low values of the Seebeck coefficient. View full abstract»

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  • Kinetic and Experimental Basis of Flash Desorption

    Page(s): 4 - 15
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    Techniques are developed for deriving both qualitative and quantitative information on the kinetics of gas desorption from measurements at continuously changing temperature. First‐ and second‐order processes can be distinguished immediately by the constancy of the end point of the former. Quantitative values for activation energy and frequency factors are deduced from the experimental time‐temperature curve and the instantaneous slopes of the evolution curve, even for systems with concentration‐dependent rate parameters. It is shown that for multiple desorption peaks, qualitative detection is simplified by slow heating, but may result in interconversion. The experimental basis of desorption measurements using the Bayard‐Alpert gauge is also analyzed, together with artifacts arising from negative pressures, bistable gauge operation, formation of new species in the gauge, and the delay in sensing density pulses transmitted through tubes. View full abstract»

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  • Space Charge Instabilities in Synthesized Plasmas

    Page(s): 16 - 21
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    A theoretical and experimental investigation of instability phenomena in synthesized plasmas is carried out. In the theoretical analysis the space charge and potential distributions are obtained for an idealized one‐dimensional model. The model consists of two face‐to‐face electrodes each emitting ions and electrons in any ratio and with a Maxwellian velocity distribution. The calculations show that no stable zero‐field solution is possible; instead, distributions with either a potential maximum or minimum in the center are obtained. For a range of values of the ratio β of injected ion to electron space‐charge density near unity (0.81 ≤β≪1.235), double‐valued solutions to the problem are obtained. The actual solution into which the system settles depends on whether this range of β values is approached from above or below. Transitions from one such state to the other can occur at the limits of this β range. In the experimental investigation of a synthesized plasma, these instabilities, or state‐to‐state transitions, were found to be in good agreement with the theory. Oscillations triggered by state‐to‐state transitions were observed with a frequency corresponding to the ion transit time through the interelectrode space. These oscillations are not described by the steady‐state analysis. View full abstract»

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  • Diffusion in a Liquid Indium‐Tin Alloy at the Eutectic Concentration

    Page(s): 22 - 24
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    Self diffusion coefficients for the two tracers In114 and Sn113 in the liquid alloy indium-tin at the eutectic composition have been measured as a function of temperature in the range 200°C–450°C. The customary Arrhenius equation is used to describe the experimental results. For indium as a tracer we obtained

    D=(42.5±5.7) 10-5exp
    -
     2771±158 
     RT 
    cm2/sec
    , and for tin
    D=(11.7±1.7) 10-5exp
    -
     1380±156 
     RT 
    cm2/sec
    . It is possible that the large difference between the two activation energies could be associated with properties of the eutectic composition. View full abstract»

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  • Microwave Measurements of the Radiation Temperature of Plasmas

    Page(s): 25 - 30
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    Radiation‐temperature measurements of positive columns of glow discharges in helium, neon, and hydrogen were compared with calculations and with Langmuir probe measurements of the electron temperature. The microwave‐noise radiation was detected at a frequency of 3000 Mc. The plasma studied was illuminated by a blackbody source of known variable temperature. The blackbody temperature was adjusted until the received noise power became independent of the presence of the unknown plasma. At this point, the temperature of the two radiators is the same, irrespective of the magnitude of the plasma absorptivity. View full abstract»

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  • On the Question of Ball Lightning

    Page(s): 30 - 35
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    The hypothetical model of ball lightning first suggested by P. L. Kapitza [Doklady Akad. Nauk S.S.S.R. 101, No. 2, 245 (1955)] is considered in some detail in an attempt to uncover evidence which will substantiate or contradict the theory. Observers' reports of the phenomenon are summarized briefly. Pro and con arguments concerning Kapitza's scheme are given. A theoretical model in an ideal environment is examined. The radio‐frequency field suggested by Kapitza is considered, and the interference effects resulting from the reflection of a discrete band spectrum of linearly polarized waves from a perfect reflector are presented. The gaseous discharge is discussed, under the assumption that the ball lightning phenomenon is analogous to a point‐to‐plane corona discharge. It is determined that, given a sufficiently intense electric field, a horizontal discharge along one of the electric field antinodes, suggestive of horizontal lightning, can result. It is concluded that this exploratory work supports Kapitza's hypothesis, but that much more must be done before the theory is fully substantiated. View full abstract»

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  • Proposed Fiber Cavities for Optical Masers

    Page(s): 36 - 39
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    The use of dielectric waveguides in the form of small fibers as the mode selector in optical masers is considered. The fibers consist of a core of index of refraction n1 which contains the maser material, surrounded by a cladding of lower index n2. A comparison is made with the Fabry‐Perot interferometer used as a cavity. The principal advantages of the fiber for maser applications are the mode selection and the stronger mode coupling. It is shown that for core diameters just small enough to support only the two HE11 modes, the fraction of spontaneous emissions into the waveguide modes is given approximately by 1.4 (n1-n2)/(n1+n2). This could make maser action possible at much lower power levels. The major disadvantage is the difficulty of pumping into the small volume of the fiber. Schemes to overcome this difficulty are discussed. View full abstract»

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  • Pulse Method for the Measurement of Thermal Diffusivity of Metals

    Page(s): 40 - 45
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    A pulse method for measuring thermal diffusivitity of metals has been developed. The temperature in an effectively infinite rod is zero everywhere up to the time t=0, when a very short heat pulse is introduced in the plane x=0. The subsequent temperature histories of several points at different distances from x=0 are recorded, and from these data the thermal diffusivity may be calculated. Since an experimental run lasts less than one minute, the requirements on the stability of the ambient temperature are not as stringent as in previously reported methods. The present method saves time without sacrificing accuracy, a maximum error of ±4% being estimated. Although this work was all done at room temperature, the specimens were mounted in a vacuum furnace which should permit measurements at elevated temperatures. The method was tested on commercial ``A'' nickel, giving a result in excellent agreement with previous values. Results are reported for four new steels developed by the Bethlehem Steel Company. View full abstract»

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  • Uniformity of Electrical Current Flow in Cylindrical Semiconductor Specimens with Cylindrical Metallic End Caps

    Page(s): 46 - 47
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    The distribution of current is computed in a cylindrical semiconductor specimen provided with cylindrical metallic end caps of the same diameter as that of the specimen and electrical lead wires of much smaller diameter. Nonuniformity of the longitudinal current density of 1% or less can be obtained in specimens with electrical resistivities at least 200 times greater than that of the end caps if the lengths of the specimens are at least equal to their diameters and if the length of each end cap is at least 0.3 diam. View full abstract»

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  • Zone Refining of the Silver Halides

    Page(s): 48 - 54
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    The techniques of zone melting have been applied to AgCl and AgBr in an attempt to obtain large crystals of extremely high purity. By measuring distributions in ingots with deliberate impurity additions, both optimum conditions for zoning and distribution coefficients for several impurities were determined. For AgCl, zone melting in a chlorine atmosphere led to near‐ultimate distributions for Cu, Pb, Ni, and Fe after passage of 70 zones at a rate of 3 in./hr. The distribution coefficients determined were as follows: Cu, 0.4; Pb, 0.4; Ni, 1.4; and Fe, 0.7. Zone melting in vacuum resulted in similar distributions for Cu, Pb, and Ni, but Fe separated with an effective distribution coefficient slightly greater than one. Under these conditions, Mn and Cd separated in a direction opposite to that of zone travel, and Sn, Al, and Sr separated in the direction of zone travel. Zone refining of nominally pure AgCl resulted in crystals which probably contain less than one part in 109 of Cu and Ni, less than one part in 108 of Pb, and less than five parts in 108 of Fe. Limited data on AgBr indicate that in this case, too, useful purification can be obtained. The dark electrical conductivity of the zoned crystals was found to be intrinsic above 315°K for AgCl and 300°K for AgBr. View full abstract»

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  • Influence of the Cathode Surface on Arc Velocity

    Page(s): 54 - 64
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    An arc cathode spot in a transverse magnetic field may move either in the Amperian (forward) direction or in the opposite, i.e., retrograde sense. The rate and direction of movement are dependent on a number of parameters such as arc current, magnetic field strength, and gas pressure at the cathode root. New experiments which demonstrate clearly the effect of cathode oxide layers on arc velocity are described. A simplified model of the cathode root region of the arc which is consistent with the experimental results is proposed. The predictions of this model, which is applicable to both Amperian and retrograde motion, are also in satisfactory agreement with results obtained by previous investigators. View full abstract»

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  • Germanium Saturated with Gallium Antimonide

    Page(s): 65 - 69
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    Single crystals of Ge saturated with GaSb were prepared by temperature gradient zone melting at 750°C. Electron probe microanalysis indicated 4.83×1020 Ga atoms and 2.36×1020 Sb atoms/cc in the saturated material with an estimated error of about 10%. Thus the solubility of Sb is greatly enhanced by the presence of Ga, though the reverse is not true. Hall measurements were in semiquantitative agreement with the chemical concentration measurements and indicated that carrier mobility is not much affected by the presence of the compensating impurity. View full abstract»

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  • Direct Observation in the Electron Microscope of Oxide Layers on Aluminum

    Page(s): 70 - 75
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    Using a modified technique of transmission electron microscopy, the properties of oxide films formed on aluminum foil by heat treatment in various oxidizing atmospheres at temperatures from 400 to 600°C have been studied. Above 400°C crystalline oxide forms by nucleation and growth, and has a basically fcc lattice of parameter 7.9±0.15 A. View full abstract»

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  • Reflection and Transmission of Electromagnetic Waves at Electron Density Gradients

    Page(s): 75 - 82
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    Solutions are obtained for the propagation of plane electromagnetic waves parallel to a gradient of free electron density, in the form of complex Airy functions. Reflection and transmission coefficients are derived for normal incidence on a linear ``ramp'' of electron density connecting a uniform dielectric gas with a uniform ionized gas, as functions of ramp length and propagation exponent of the latter. Machine evaluations of typical cases of physical interest are displayed and discussed. Similar study is made of two‐stage ramps of variable proportions, intended as second approximations to smooth profile transition zones. In each case, the reflection and transmission coefficients are found to depend strongly on ramp width over a range of several tenths of a wavelength, then to oscillate mildly toward the asymptotic values predicted from a WKB‐type approximation. The results are less sensitive to the detailed shape of the electron density profile. Propagation through a finite slab of ionized gas bounded on each side by such linear transition zones is formulated and evaluated for typical cases. Asymptotic approximations for the linear ramp problem are found to be inadequate to cover the entire range of interest. The neglect of variation in collision frequency through the transition is discussed and justified for a broad class of equilibrium profiles. View full abstract»

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  • Theory of Tunneling

    Page(s): 83 - 91
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    The theory of ``direct'' and ``phonon‐assisted'' tunneling is reviewed. Theoretical I–V characteristics are calculated using the constant field model. Generalizations to nonconstant field and more complicated band structure models are discussed briefly. View full abstract»

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  • On the Internal Friction of Cold‐Worked and Quenched Martensitic Iron and Steel

    Page(s): 92 - 96
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    A theoretical explanation is given for the internal friction peaks which are observed at 200°∼250°C for cold‐worked iron and steels and for steels in the martensitic condition. The theory for the peaks is based upon the addition of a term to the free energy in order to account for the strain energy due to the interaction of an atmosphere and the line imperfections. The standard linear solid was obtained from the model in which dislocations are vibrating with an atmosphere of carbide precipitates. View full abstract»

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  • Electrical Resistivities of Nickel‐Niobium Solid Solutions

    Page(s): 97 - 99
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    The electrical resistivities of nickel‐rich nickel‐niobium solid solutions have been determined from liquid‐helium temperatures to 1000°K. The Matthiessen rule is not obeyed at any temperature. The addition of niobium to nickel increases its ideal electrical resistivity when the alloy is in the ferromagnetic state but decreases it in the paramagnetic region. Dissolved niobium in nickel at liquid‐helium temperatures causes considerably larger perturbation for the conduction electron transport than either copper or palladium. View full abstract»

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  • Elastic Constants of Single Crystals of the bcc Transition Elements V, Nb, and Ta

    Page(s): 100 - 105
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    Values of the elastic constants of single crystals of the bcc transition elements V, Nb, and Ta, are reported at T=27°C. They are, in units of 1011 d/cm2: c11 c12 c44 V 22.8 11.9 4.26 Nb 24.6 13.4 2.87 Ta 26.7 16.1 8.25 Comparisons are made of the values obtained for two crystals each of V and Ta. A high-frequency cw resonance technique was used in these measurements. The shear anisotropies A=2c44/(c11–c12) are anomalously small for these elements as compared to other cubic system elements. An analysis of the shear anisotropy, based on Fuchs' model, is given. It is found essential in this analysis to take into account next-nearest as well as nearest-neighbor ion-ion interactions. View full abstract»

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  • Effect of Residual Gases on Superconducting Characteristics of Tin Films

    Page(s): 105 - 114
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    A special oil‐free, ultra‐high vacuum system has been used to deposit tin films at pressures less than 10-9 mm Hg onto room temperature substrates. These films were found to possess extremely sharp and reproducible magnetic field transitions as compared to films deposited by more conventional techniques. This resulted from breakup of the penumbra of a film deposited through a mask into electrically discontinuous islands leaving a film of uniform thickness. Specific residual gases were found to decrease the surface mobility of the tin atoms which contributed to continuous film edges and higher critical fields. For example, the critical field extrapolated to 0°K increased from 370 oe for a pure film to 490, 590, and 820 oe as the ratio of oxygen molecules to tin atoms striking the substrate increased from 0 to 3, 6, and 9% respectively. For more highly doped films the bulk characteristics were also altered, indicating the presence of oxygen in the film material. Water vapor and carbon dioxide were found also to alter the edge structure, whereas N2, H2, CH4, C3H8, C5H12, A, and CO did not. By analyzing the critical field and residual resistance data of the various films, the vacuum requirements necessary for obtaining high purity films with sharp magnetic transitions occurring at predictable field values were ascertained. An ultra‐high vacuum system is not required if the partial pressure of critical gases is maintained below specified values. View full abstract»

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  • Solubility of Oxygen in Germanium

    Page(s): 115 - 118
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    The infrared absorption band at 11.7 μ corresponding to a germanium‐oxygen molecular vibration is quantitatively correlated to the chemically determined oxygen content of germanium crystals. The solid solubility of oxygen is determined as a function of temperature and the precipitation of the second phase GeO2 is observed. Crystals containing about 1017 atoms per cm3 of dissolved oxygen have been prepared. The maximum solubility appears to be 2×1018 atoms/cm2. The heat of solution is 1.2 ev. Silicon in a melt of germanium acts as a getter for oxygen, resulting in the formation of SiO2; this observation is in agreement with thermodynamical considerations. 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