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Journal of Applied Physics

Issue 3 • Date Mar 1976

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Displaying Results 1 - 25 of 76
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Diffusion of vacancies and interstitials to edge dislocations

    Page(s): 791 - 800
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    The steady‐state diffusion of radiation‐produced point defects in the stress field of an edge dislocation is solved by a perturbation method. The drift term entering the diffusion equation includes the size interaction and the inhomogeneity interaction as well as the effects of externally applied loads. By comparing the perturbation solution with the rigorous solution of Ham, we show that the perturbation solution is always adequate provided the drift term is proportional to the gradient of the interaction energy of the point defect with the dislocation. The steady‐state distributions of vacancies and interstitials is such that voids or vacancy clusters preferentially grow on the compressive side of the edge dislocation. The external stresses give rise to an orientation‐dependent bias of the edge dislocation which is shown to provide a possible mechanism for radiation‐induced creep. View full abstract»

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  • Shear strength of metal‐sapphire contacts

    Page(s): 801 - 808
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    The shear strength of polycrystalline Ag, Cu, Ni, and Fe contacts on clean (0001) sapphire has been studied in ultrahigh vacuum. Both clean metal surfaces and surfaces exposed to O2, Cl2, and C2H4 were used. Auger electron spectroscopy was used to assess both the cleanliness of the surfaces and the approximate coverage of O, Cl, and C after exposure to the gases. The results indicate that there are two sources of strength of Al2O3‐metal contacts: an intrinsic one that depends on the particular clean metal in contact with Al2O3 and an additional one due to intermediate films. The shear strength of the clean metal contacts correlated directly with the free energy of oxide formation for the lowest metal oxide, in accord with the hypothesis that a chemical bond is formed between metal cations and oxygen anions in the sapphire surface. Contacts formed by metals exposed to chlorine exhibited uniformly low shear strength indicative of van der Waals bonding between chlorinated metal surfaces and sapphire. Contacts formed by metals exposed to oxygen exhibited enhanced shear strength, in accord with the hypothesis that an intermediate oxide layer increases interfacial strength. It is suggested that the strong oxide‐oxide bond is due to the establishment of interfacial bonds associated with complex oxide (spinel structure) formation. It was also found that C2H4 exposures increased the strength of the Fe contact, but had no effect on the other contacts. View full abstract»

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  • Stage‐I recovery of prequenched and electron‐irradiated pure aluminum and of the alloy Al‐15 ppm Ag

    Page(s): 809 - 816
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    High‐purity Al and the alloy Al‐15 ppm Ag have been irradiated with electrons at liquid‐helium temperatures. The influence of various parameters (electron energy and dose, impurity content and the, presence of excess vacancies introduced by prequenching or irradiation doping) upon the annealing spectra of the radiation‐induced residual electrical resistivity was determined. Besides the usually observed recovery substages in stage I ( IB, IC, ID, and IE), we have found several supplementary structures labelled IA (at 14–15 K), IC (at 26–27 K), ID (at 33 K), ID (at 39 K), and IF (between 53 and 59 K). The observed characteristics are compatible with the attribution of the substages IA, IB, IC′, and IC to close‐pair recombination; ID′, ID, and ID to correlated migration of interstitials; IE to the recombination of freely migrating interstitials; and IF to the migration of diinterstitials. View full abstract»

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  • Mobility of arrays of dissociated and superlattice dislocations in an internally stressed solid

    Page(s): 817 - 821
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    A study is made of the mobility of planar arrays of dislocations of Burgers vector b that are either separated into their component partials or are of the superlattice type and are contained in an internally stressed solid, the stress being generated by a preexisting coplanar obstacle dislocation of Burgers vector mb. The aim here is to estimate the effect of the internal stress and the fault energy on the separation between the components of the first discrete dislocation since the latter plays an important part in a wide range of physical phenomena. All the mobile complete dislocations except the leader are either smeared into a continuous distribution or are replaced by a superdislocation of appropriate Burgers vector. These two approaches, which lead to lower and upper bounds for the separation distance, are shown to give fairly close results for small m. View full abstract»

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  • Particle size and strain broadening in energy‐dispersive x‐ray powder patterns

    Page(s): 822 - 825
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    An energy‐dispersive x‐ray method for a rapid analysis of the broadening of diffraction lines in powder patterns has been developed. Experimental results are given for magnetite powders with sizes in the range 50–200 Å and compared with the results of standard angle‐dispersive diffractometry and electron microscopy. The greatest advantages of the energy‐dispersive method compared with the angle‐dispersive method are the absence of the Kα doublet, the simultaneous recording of a large part of the diffraction pattern, the fast data accumulation, and the adaptability of the technique to in situ studies. The method should be of special advantage for the study of solid‐state reactions and processes such as sintering. View full abstract»

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  • Similarity of Hall‐conductivity integrals for metals and semiconductors

    Page(s): 826 - 829
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    The expressions for the Hall conductivity of a spherical quadratic‐band semiconductor for various power‐law scattering mechanisms are evaluated numerically as functions of the Fermi energy. Comparison of these results to curves based on the simple constant‐τ model shows there is only a slight deviation of geometric form which diminishes as the Fermi energy ϵF approaches the band edge and vanishes as ϵf moves deep into the band. This similarity explains the fact that the τ=const. model can be used to determine conductivity mobility and carrier density from σxy curves with surprising accuracy over a wide temperature range. Application is made to n‐InSb. View full abstract»

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  • Bombardment‐enhanced diffusion of arsenic in silicon

    Page(s): 830 - 836
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    A theoretical model which describes a diffusion process enhanced by ion bombardment has been investigated for the case of arsenic in silicon. The model predicts a spatially variant diffusion coefficient of the form D*f (x,Ld), where Ld is an unknown constant characteristic of the diffusing medium and presumably independent of the diffusing species. An experimental value for Ld was determined which agrees well with the theory, but differs from the value obtained for boron in silicon. View full abstract»

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  • Theory of laser heating of solids: Metals

    Page(s): 837 - 849
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    Calculations of the transient and steady‐state temperature rise T of laser‐irradiated metals indicate that values of the intensity (irradiance) If that cause failure change drastically under different experimental conditions, such as the degree of plasma ignition on the surface and the relative magnitudes of the laser‐beam diameter, sample thickness l, lateral dimension, and thermal diffusion distance. The dependence of If on material parameters such as thermal conductivity and heat capacity is also quite different, depending on the experimental conditions. The results suggest that the highest of the recently measured copper‐damage thresholds of 125–750 J/cm2 for 0.6‐μsec pulses at 10.6 μm are likely to be at or at least quite near the intrinsic limit set by the simple process of melting that results from the intrinsic absorption. The theoretical intensity at which the cavity mirrors of recently developed xenon uv lasers fail is in good agreement with the experimental value. The theoretical value of T of metals irradiated for 20 sec with 10.6‐μm radiation is two orders of magnitude too small to explain recent experimental results. It is suggested that the discrepancy is related to plasma ignition at the sample surface. The steady‐state value of T for metals cooled with a surface‐heat‐transfer coefficient h is not reduced substantially by increasing the cooling efficiency past a certain point (h≳hl≡K/l). For short time t≪τ, where the characteristic time τ depends on both l and h, cooling the metal is not effective is preventing the temperature rise. View full abstract»

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  • Analysis of weak-boundary-coupling effects in liquid-crystal displays

    Page(s): 850 - 857
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    The analysis of Rapini and Papoular for homeotropic and homogeneous geometries is extended to predict the effects of weak boundary coupling on liquid-crystal display performance. An implicit expression for deformation as a function of applied field is derived for the case of equal elastic constants. Steeper transitions with complete saturation at low fields are found, which promise improved optical performance and multiplexing capability. A similar analysis of twisted nematic displays predicts a less pronounced improvement in electro-optic response and indicates a minimum boundary-coupling strength below which spontaneous deformation occurs. View full abstract»

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  • Surface acoustic wave properties of lithium gallium oxide

    Page(s): 858 - 860
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    The surface acoustic wave (SAW) properties of lithium gallium oxide (LiGaO2) are theoretically predicted in order to determine the feasibility of using this material in related SAW devices. The surface wave velocity, the temperature coefficient of delay, an estimate of the electromagnetic to acoustic coupling, and the power flow angle for nine standard crystallographic cuts are obtained. This material is shown to have moderate coupling, low power flow angle, and a temperature coefficient of delay slightly larger than that of LiTaO3. View full abstract»

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  • Photoelectron microscopy of organic surfaces: The effect of substrate reflectivity

    Page(s): 861 - 865
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    Photoelectron measurements of thin organic films deposited on a metal substrate may contain information from deep within the sample, derived from reflected ultraviolet light. This effect depends on the reflectivity of the substrate, the sample thickness and optical absorption coefficient, and the photoelectron escape depth. Calculations are given for phthalocyanine as a specific example. Contrast reversal and apparent see‐through effects resulting from reflection are predicted in overlapping thin films. Photoelectron micrographs of thin films and grid patterns of phthalocyanine show that the reflection model is essentially correct. This effect can be substantially reduced by using a nitrocellulose‐coated carbon substrate. View full abstract»

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  • Properties of PbS‐PbO crystalline films. I. Preparation and physical structure

    Page(s): 866 - 870
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    The physical properties of PbO‐PbS, prepared by vapor codeposition on a heated NaCl substrate, were studied. The PbO did not alloy with the PbS, but, instead, segregated out as a finely dispersed separate phase within a single‐crystal PbS matrix. Electron diffraction data established that trace amounts of PbSO4 and SiO2β also precipitated. The PbS lattice constant did not vary as the amount of PbO was increased, indicating a very low oxygen solubility in PbS. This is in agreement with thermodynamic data on the PbS‐PbO system. View full abstract»

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  • Properties of PbS‐PbO crystalline films. II. Electrical and photoelectronic properties

    Page(s): 871 - 878
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    Electrical, optical, and photoconductive studies were carried out PbS‐PbO codeposited films. The segregated PbO microcrystallites had an increasingly profound effect on these properties. Some traces of the excess oxygen appear to enter the PbS single‐crystal matrix. Oxygen vacancies in the PbO crystallites produces a peak in the photoconductivity of p‐type PbS‐PbO films but not in n‐type films. By a detailed study of these properties, a band diagram is suggested for the PbS‐PbO heterostructure that accounts for our observations. View full abstract»

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  • Plasma diagnostics using laser‐excited coupled and transmission ring resonators

    Page(s): 879 - 885
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    In this paper a simple two‐level laser model is used to investigate the frequency response of coupled‐cavity laser interferometers. It is found that under certain circumstances, often satisfied by molecular gas lasers, the frequency response exhibits a resonant behavior. This behavior severely complicates the interpretation of coupled‐cavity laser interferometer measurements of rapidly varying plasmas. To circumvent this limitation a new type of laser interferometer plasma diagnostic with significantly improved time response was developed. In this interferometer the plasma is located in one arm of a transmission ring resonator cavity that is excited by an externally positioned laser. Thus, the laser is decoupled from the interferometer cavity and the time response of the interferometer is then limited by the Q of the ring resonator cavity. This improved time response is acquired without loss of spatial resolution, but requires a more sensitive signal detector since the laser is no longer used as a detector as it is in conventional coupled‐cavity laser interferometers. Thus, the new technique incorporates the speed of the Mach–Zender interferometer and the sensitivity of the coupled‐cavity laser interferometer. The basic operating principles of this type of interferometer have been verified using a CO2 laser. View full abstract»

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  • Characteristics of a large‐volume rf‐grid discharge plasma

    Page(s): 886 - 893
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    The properties of a large‐volume rf (75 MHz) ‐grid discharge plasma have been determined. Measurements in the steady state and in the afterglow indicate that the rf grid produces a plasma with two electron components—a secondary Maxwellian component of density 2×1010 electrons/cm3 and temperature 4.5 eV and a ’’primary’’ component of density 1×1010 electrons/cm3 and temperature approximately 15 eV. The ion temperature is ?0.3 eV. A useful 35‐liter argon plasma with a noise level on the order of 1% is easily produced in neutral pressure backgrounds as low as 4×10-5 Torr. View full abstract»

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  • Magnetic field effects on the emission law of electron current from cathodes

    Page(s): 894 - 896
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    The Child‐Langmuir emission law is corrected to include magnetic field effects. The treatment is performed in local Cartesian coordinates near the cathode surface and all the terms obtained include first‐order relativistic effects. The effect of space charge flowing back to the cathode is also considered. The importance of using the corrected emission laws in the simulation of relativistic diodes is discussed. View full abstract»

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  • In‐situ observation of microparticles in a vacuum‐insulated gap using a scanning electron microscope

    Page(s): 897 - 898
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    Results are presented of an investigation into microparticle activity in a vacuum‐insulated 1‐mm electrode gap. The experiments were conducted in situ in the specimen stage of a scanning electron microscope (SEM) and confirm microparticle activity at voltages well below breakdown. The most common size of the microparticles observed was 3 μm and very few particles above 10 μm were detected. View full abstract»

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  • Space‐charged limitation of radiation‐induced secondary‐electron emission currents in evacuated diodes

    Page(s): 899 - 905
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    When a diode is bombarded with high‐energy radiation, the current density of low‐energy secondary electrons flowing in the interelectrode gap may experience space‐charge limitation. In this paper an evacuated planar diode is considered in which the two electrodes may be of dissimilar materials, have different saturation emission current densities, and be subjected to an externally applied potential difference. It is shown in detail how Lindsay and Parker’s analysis pertaining to space‐charge effects on thermionic emission in a similar diode configuration can be carried over in its entirety to the present problem with the substitution of just three parameters. Their method is extended so that one can quantitatively specify the threshold conditions at which space‐charge effects just begin to occur, the voltage regimes over which they are valid, and their magnitudes throughout this regime. Generalized solutions are presented and graphed showing how the net current through the diode varies as a function of voltage. Heretofore, such quantitative evaluations have not been available for the planar‐diode case under such generalized conditions. View full abstract»

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  • Magnetohydrodynamic instability of a cylindrical liquid‐metal brush

    Page(s): 906 - 913
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    The stability of a homopolar generator brush, consisting of a liquid‐metal‐filled cavity between rotating (rotor) and fixed (stator) cylinder electrodes, is analyzed in the presence of radial current transport and an axial homogeneous magnetic field. Within the frame of linear magnetohydrodynamics, it is shown that the liquid‐metal flow in the brush is always unstable if the brush transports current. In the absence of current flow (infinite load) the axial magnetic field stabilizes the liquid‐metal flow in the brush if the magnetic energy density is larger than a certain fraction of the energy density of the rotating fluid. View full abstract»

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  • Vibration and stability of a set of superconducting toroidal magnets

    Page(s): 914 - 919
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    The vibration and elastic stability of a set of discrete superconducting magnets arranged to form a ’’bumpy’’ toroidal field is examined. The mutual destabilizing magnetic forces between magnet pairs are calculated using a numerical differential inductance technique. It is shown that the mutual attractive magnetic forces can produce elastic buckling of the entire toroidal set. Using the theory of periodic structures, the vibration modes of the set are found as functions of the coil current. The response of the set of magnets to an earthquake‐type motion of the toroidal base is also calculated. View full abstract»

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  • Buckling of a superconducting coil nested in a three‐coil toroidal segment

    Page(s): 920 - 921
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    Measurements are made of the lateral stiffness of a flexible planar superconducting coil between two rigid coils in series. These tests show a dramatic decrease in the natural bending frequency with subsequent elastic instability or ’’buckling’’ at a critical value of the current in the coils. These observations support a magnetoelastic analysis which shows that proposed designs of toroidal field coils for Tokamak fusion reactors have insufficient lateral support for mechanical stability of the magnets. View full abstract»

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  • Parametric resonance instabilities in argon and neon plasmas

    Page(s): 922 - 929
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    Experimental results, interpreted by a theoretical model based on the first two hydrodynamic equations, concerning parametric resonance instabilities in argon and neon dc discharges are presented. These instabilities were detected by scattered microwaves in the frequency band 2–40 GHz when the plasma positive column was pierced across a rectangular waveguide, by measuring time‐modulation enhancement due to striation eigenmodes built‐up in plasmas. View full abstract»

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  • Charge transfer in metal/atactic polystyrene contacts

    Page(s): 930 - 939
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    Contact charge‐exchange experiments between various metals and atactic polystyrene are utilized to elucidate the electronic structure of the polystyrene. Bulk states present at approximately 1014/cm3 within a 4‐μ‐thick boundary layer, as well as surface states of approximate density 1010/cm2, govern the charge‐exchange characteristics of polystyrene in the metal contacts. It is argued that the carriers are electrons injected from the region of the Fermi level of the metal into the polymer, and that the metal/polymer junction remains indefinitely in a nonequilibrium state. A steady‐state injection level is reached because of differences in injection and transport properties of the surface boundary layer and the deeper bulk material. A significant effect of the substrate metal on the populations of the electronic states at the free surface of the polystyrene films is identified and shown to be long range (at least 15 μ). View full abstract»

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  • The distribution of localized electronic states in atactic polystyrene

    Page(s): 940 - 948
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    The steady‐state charge level reached after repeated contact of a single metal with a film of atactic polystyrene has been interpreted previously in terms of electron injection from the metal into the polymer. The charge level is a function of film thickness, the particular contacting metal, and the particular metallic film substrate. In this study different metals are contacted to the same film until a steady‐state condition is reached for each metal. The net charge level at the end of the contact sequence is found to be approximately equal to the sum of the previously measured single‐metal charge levels for an initially charge‐neutral film and is independent of the order of the metals in the sequence. Therefore, charge injection does not follow a simple energetic relationship between the Fermi level of the metal and the energy of a surface or bulk band or localized level of the polymer. Rather, each metal communicates with a discreet portion of the distribution of localized polymeric electronic states. The energy selective feature of the charge‐injection process converts the contact charge‐exchange experiments into a spectroscopic tool for the study of the localized polymeric states. As a result the localized electronic‐state distribution of the polymer can be derived for a range of electron energies related to that spanned by the Fermi levels of the contacting metals. 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