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Journal of Applied Physics

Issue 13 • Date Dec 1971

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Displaying Results 1 - 25 of 125
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Pyroelectric Properties of Polyvinylidene Flouride and Its Use for Infrared Detection

    Page(s): 5219 - 5222
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    It has recently been discovered that the pyroelectric and nonlinear optical properties of polyvinylidene fluoride (PVF2) closely resemble those of a ferroelectric. In this work, we investigate more fully the ``ferroelectric'' behavior of PVF2. Measurements of the pyroelectric properties and polarization reversal are described. Commercially available PVF2 films have been used for radiation detection at 10.6 μm with responsivities of 17 V/W and noise equivalent power (NEP) of 15×10-9 W/Hz1/2 at 100 Hz (0.02‐cm2 detector area). Although this NEP is considerably higher than that for other pyroelectric materials, this polymer seems particularly attractive in applications where ultimate detectivity is not required because of the great ease and low cost with which detector films can be constructed in any shape or size. View full abstract»

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  • Infrared Localized‐Vibrational‐Mode Absorption of Ion‐Implanted Aluminum and Phosphorous in Gallium Arsenide

    Page(s): 5223 - 5229
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    The localized‐vibrational‐mode absorption of ion‐implanted Al and P in GaAs is observed. The implants were done at room temperature with a flux of ∼3×1012 ion/cm2 sec and fluences of 2.0×1016, 2.8×1016, and 3.7×1016/cm2 at 1 MeV. The Δn=1 transition of Al substitutional on the Ga sublattice and P substitutional on the As sublattice are observed, and liquid‐nitrogen‐temperature absorption measurements are made for isochronal anneals from 200 to 900°C. The Al‐implanted GaAs shows an AlGa local mode near 362 cm-1 and GaAs implanted with P shows a band near 355 cm-1 similar to melt‐doped crystals, but with increased linewidths. From the integrated absorption, it is estimated that nearly all of the Al and P is AlGa and PAs after 900°C anneal, and the site symmetry is approximately tetrahedral. View full abstract»

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  • Localized Vibrational Modes of Boron‐Lithium Pairs in Si‐Rich GeSi Alloys

    Page(s): 5230 - 5240
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    Localized vibrational modes of boron‐lithium pairs have previously been observed in silicon; the 10B(11B) localized mode is split into an axial mode at 584(564) cm-1 and a doubly degenerate transverse mode at 681(655) cm-1. In this work the infrared absorption bands of these modes were observed in boron‐doped lithium‐compensated GexSi1-x for 0≤x≤0.12. The bands were slightly lowered in frequency and asymmetrically broadened by the addition of the germanium. The asymmetric shape results from the superposition of the absorption from boron atoms with different second‐neighbor configurations; the line shape is fit well by a simple model for interactions between the boron and Ge second neighbors and the assumption of random distribution of Ge throughout the crystal. The broadening is attributed primarily to lattice strain, the effect of the mass change being calculated to be far too small, and to modification of the LiB interaction. It is found that the LiB pairing distance must be smaller then the previously reported values of 2.4–2.9 Å. New bands at 553 and 651 cm-1, attributed to boron with a Ge first neighbor, are split off from the previously observed boron localized modes in the sample with 12% Ge. These are weaker than would be predicted by a random distribution of Ge, indicating that boron and Ge tend to avoid first‐neighbor pairs, or that the oscillator strength of the boron mode is lessened by a Ge first neighbor. View full abstract»

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  • Infrared Absorption of Lattice Modes and the Silicon Local Mode in GexSi1-x Alloys

    Page(s): 5241 - 5249
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    Measurements have been made of the infrared absorption of GexSi1-x alloys for x≤0.12 and x≥0.88. The measurements were made in the range 100–700 cm-1 at temperatures from 10 to 300°K. In Si‐rich alloys (x≤0.12) absorption bands are seen near 485, 400, and 125 cm-1 which are essentially temperature independent, indicating a single‐phonon process. The bands do not correspond well with the predictions of simple models for resonance mode absorption, but are more nearly characteristic of the single‐phonon density of states for Si. In the Ge‐rich alloys (x≥0.88) the Si localized mode is observed as an absorption band at 389 cm-1 for x=0.99, increasing to 394 cm-1 at x=0.88. The absorption cross section αpeak/[Si] is only 4×10-21 cm2, smaller by 102-103 than observations for other local modes in semiconductors. Two‐phonon absorption bands at about 200 and 290 cm-1 in Ge are enhanced by the addition of Si. The over‐all temperature dependence of the absorption strength is large enough that it is not obvious whether the observed enhancement is temperature dependent or is a temperature‐independent absorption, caused by the Si, superposed on a temperature‐dependent background. View full abstract»

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  • Mössbauer Study of BiF3‐Type Ordering in Metastable FeGa Alloys

    Page(s): 5250 - 5253
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    Metastable Fe alloys containing up to 25 at.% Ga, obtained by rapidly quenching from the liquid state, have been studied using the Mössbauer effect. A least‐squares analysis of the data has allowed identification of individual configurations of atoms surrounding each Fe atom and the comparison of these configurations with various ordered and disordered states. Partial ordering of the BiF3 type has been definitely observed at 25 at.% Ga, and the results suggest that is may extend to compositions as low as 20 at.% Ga. View full abstract»

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  • Effect of X‐Ray Diffractometer Geometrical Factors on the Centroid Shift of a Diffraction Line for Stress Measurement

    Page(s): 5254 - 5260
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    Expressions for the centroid shift of a diffraction line due to geometrical factors have been deduced for a diffractometer case in which the specimen surface is inclined to the x‐ray beam at an arbitrary angle. Such a geometry is encountered in the determination of residual stress using a diffractometer. The effects of the centroid shift of a diffraction line due to geometrical factors on the stress derived from the diffractometer measurements have been discussed. View full abstract»

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  • Experimental Study of Scattering of Longitudinal Elastic Waves from Cavities in a Solid Medium

    Page(s): 5261 - 5262
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    Measurements of ultrasonic attenuation due to the scattering of longitudinal elastic waves from a distribution of cavities in a solid medium are found to be consistent with theoretical predictions. Under certain conditions such measurements can be utilized to nondestructively characterize the size and number density of such a collection of scatterers. View full abstract»

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  • Light and Current Pulses from X‐Rayed Potassium Di‐Hydrogen Phosphate Crystals

    Page(s): 5263 - 5266
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    Short‐duration light pulses accompanied by current pulses have been observed on warming KDP crystals x‐ray irradiated at 77°K. The pulses start a few degrees above the transition temperature (TC=123°K) and continue until about 200°K. The pulses appear only under ambient gas pressures above about 0.1 Torr. Warming of the irradiated crystal to an intermediate temperature between TC and 200°K causes only a partial exhaustion of the pulses, and after cooling and reheating pulses appear only above the temperature reached in the former cycle. The pulses originate from discharges into the surrounding atmosphere. A simple model is given to account for the experimental results. View full abstract»

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  • Phase Transitions in CsPbCl3

    Page(s): 5267 - 5272
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    Measurements of dielectric properties, pyroelectricity, and the electron paramagnetic resonance spectrum of Gd3+ as a function of temperature have been used to examine the phase transitions in CsPbCl3. The results indicate the presence of five phase transitions and the loss of a center of symmetry at 194 K. The results together with the apparent order of the transitions, and published data, enable the Landau criterion to be used so that the point group of each phase may be identified. A reasonable choice of space group is also made. View full abstract»

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  • Motion of a Dislocation Acted on by a Viscous Drag through an Array of Discrete Obstacles

    Page(s): 5273 - 5279
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    A computer model was used to calculate the shape and average velocity v of a dislocation acted on by a viscous drag, and moving through a field of point obstacles. As a special case, the operation of a Frank‐Read source was computed also. At sufficiently low velocities (and stress levels), the behavior is governed entirely by the obstacle spacing and strength; conventional tensile testing probably falls in this regime. At sufficiently high velocities (and stress levels), the behavior is governed entirely by the viscous drag; shock deformation falls in this regime. In between lies a wide range in which the two effects superimpose, each contributing measurably to the flow stress. The strain rate sensitivity m = (∂lnv/∂lnσ)T, where σ is the stress, reflects this behavior. At low and high velocities, respectively, m characterizes the obstacles and the drag. But in between m is characteristic of neither, and in fact reflects the change in the contributions of the two strengthening mechanisms when the applied stress is changed. View full abstract»

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  • Photoelectronic Properties of Defects in CdSe Single Crystals

    Page(s): 5280 - 5295
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    The properties of electronically active imperfections in CdSe single crystals have been investigated through measurements of dark conductivity, Hall effect, photoconductivity, and optical absorption. The same apparent photoconductivity sensitizing centers with an energy level 0.6 eV above the valence band were found in all photosensitive crystals, regardless of the method of heat treatment. Various procedures for producing high‐resistivity photosensitive crystals from high‐conductivity nonstoichiometric crystals introduce characteristic recombination centers that compete with the sensitizing centers in determining the magnitude and temperature dependence of the photoconductivity. The diffusion of silver acceptors results in a much lower photosensitivity than diffusion of copper acceptors. Annealing in selenium introduces sensitizinglike recombination centers with levels closer to the valence band than 0.6 eV, which dominate the temperature dependence of the photosensitivity, so that the highest sensitivity is found only below liquid‐nitrogen temperature. Subsequent vacuum annealing at an elevated temperature or room‐temperature annealing for several months removes the influence of these centers. The only center definitely associated with Cu impurity has a level 1.05 eV above the valence band. No evidence was obtained associating Cu or Ag impurity with the sensitizing center at 0.6 eV. A defect involving native acceptors, such as Cd vacancies, provides the most consistent explanation for the sensitizing center. View full abstract»

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  • Anomalous X‐Ray Transmission Studies in Indium Antimonide: Surface Damage

    Page(s): 5296 - 5301
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    Nearly perfect indium antimonide single crystals were studied by x‐ray anomalous transmission using silver Kα radiation and {220} reflections. The depth of abrasion‐induced surface damage was determined using the diffracted integrated intensities. The depth of damage was found to be greater on the B than on the A surfaces for the same amount of abrasion. For unidirectional abrasion the direction of the strain corresponded to the direction of abrasion, but some directional strain was also present when the abrasion was not unidirectional. The measured rocking curve half‐widths were not affected by severe surface abrasion. The effective absorption coefficient was measured to be 10.3 ± 1 cm-1. View full abstract»

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  • Growth of ZnO Whiskers, Platelets, and Dendrites

    Page(s): 5302 - 5304
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    Zinc oxide whiskers, platelets, and dendrites have been grown on the ZnO substrate by a simplified and modified vapor phase technique which involves the production of zinc vapor at the growth temperatures itself. By this method, whiskers‐a few mm in length and a fraction of a mm in diameter‐have been obtained at growth temperatures ranging from 960 to 980°C. Change in growth habit from whiskers to platelets has also been observed. Various growth mechanisms have been discussed. It appears that the growth of these crystals takes place at supersaturations higher than those usually required for whisker growth. The dendrites have been observed to grow at about 930°C. View full abstract»

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  • Magnetoelastic Love‐Wave Propagation in Metal‐Coated Layered Substrates

    Page(s): 5305 - 5312
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    The effect of a perfectly conducting infinitely thin metal coating on the properties of magnetoelastic surface waves is discussed. Dispersion relations are derived for magnetoelastic Love waves propagating in the following structures: (i) metal‐coated nonmagnetic‐layered magnetic substrate, (ii) nonmagnetic‐layered metal‐coated magnetic substrate, (iii) metal‐coated thin magnetic plate, and (iv) metal‐coated magnetic‐layered nonmagnetic substrate. View full abstract»

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  • Effects of the Addition of Cholesterics on Nematic Liquid Crystal Properties

    Page(s): 5313 - 5315
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    The influence of different contents of cholesteryl nonanoate (NC) on the properties of liquid nematic crystals is reported. The transmission spectra are recorded with and without dc field. When the quantity of NC is higher, the conductivity is lower and the voltage threshold of dynamic scattering increases. The decay of transmission with increasing voltage is accelerated in the presence of small quantities of NC, compared to that of pure nematic substance. View full abstract»

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  • Diffusion of Silver into Nickel Single Crystals

    Page(s): 5316 - 5320
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    Lattice diffusion of radioactove silver Ag110 into high‐purity nickel single crystals is measured over the temperature range 507–782°C. The lattice diffusion coefficient (DL)Ag/Ni, obtained by Gruzin's residual activity method, is given by (DL)Ag/Ni=0.025 exp(-47 200/RT) cm2/sec. The activation energy QAg/Ni=47 200 cal/mole for silver diffusion in nickel is much smaller than QNi/Ni for self‐diffusion in nickel (66 800 cal/mole) but is about equal to QAg/Ag for self‐diffusion in silver (46 000 cal/mole. View full abstract»

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  • Improved Atomistic Model of a bcc Dislocation Core

    Page(s): 5321 - 5329
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    It is shown that the strain field of a straight dislocation in an anisotropic elastic continuum includes an infinite series of terms of order 2 and higher in inverse distance from the dislocation line. These terms are determined by the nature of the core. A method is developed of finding these terms for a given dislocation while determining the core structure atomistically, using a digital computer. The equilibrium configuration of the core and the higher-order-term values are found rapidly by a method involving atomic force constants, which requires few calculations of interatomic forces. The model is applied to determine the core structure and near-strain field of a <100> edge dislocation in α iron using potentials developed by Johnson and by Chang and Graham. Core structure in agreement with that found by Gehlen et al. is obtained. The results are independent of model size over a wide range, and there is agreement between strain-energy distribution calculated atomistically and from elastic constants, for all three potentials used. The method may be useful in calculation of Peierls stress and of dislocation-point-defect interaction. View full abstract»

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  • Mixing of Noncollinear Elastic Surface Waves on LiNbO3

    Page(s): 5330 - 5332
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    The decrease in a 0.5‐ to 1‐GHz surface wave signal due to its interaction with a noncollinear 1.13‐GHz pump has been observed to be as large as 1.7 dB. The selection rules for the nonlinear elastic interaction show the possibility of single‐sideband mixing and beam deflection of the idler. View full abstract»

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  • Interference Effect on Annealing Temperature of A and E Centers in Silicon

    Page(s): 5333 - 5334
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    Experimental observation of the anomalous annealing temperatures of A and E centers and their impurity concentration dependence is explained by an interference between E and A centers. View full abstract»

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  • Lattice Theory of Second‐ and Third‐Order Elastic Constants of Aluminum, Copper, and Nickel

    Page(s): 5335 - 5342
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    Lattice theory has been used to obtain the expressions for the second‐ and third‐order elastic constants for face‐centered‐cubic lattices in terms of the second‐ and third‐order coupling parameters, considering the general interaction between the nearest‐neighbor atoms. The number of constants have been reduced by expressing the third‐order coupling parameters in terms of the coupling parameters of second order and second‐order elastic constants. The general expressions of the elastic constants have been evaluated for Al, Cu, and Ni in a special case of central forces. The force constants involved in the expressions have been determined by representing the central interaction between the pair of atoms by the Morse potential function. It is found that the Cauchy relations for second‐order elastic contants C12C44 and for third‐order elastic constants C112C166 and C123C456C144 are satisfied in the case of central forces. It is also seen that the values of C111 for all the three metals are the largest and C112 is approximately half as that of C111 and almost all the values of C123 are negative and small compared with the other third‐order elastic constants. The pressure derivatives of second‐order elastic constants, the anisotropy factor, and the Debye temperatures have also been calculated for these metals. The values obtained are in good agreement with the experimental values available in the literature. View full abstract»

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  • Acoustic Surface‐Wave Beam Diffraction on Anisotropic Substrates

    Page(s): 5343 - 5351
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    The diffraction of any distribution can be discussed in terms of its constituent Gaussian modes. Simple design formulas are developed from a two‐dimensional diffraction theory in order to characterize Gaussian beam diffraction in terms of three readily determined anisotropic propagation coefficients. The relationship between these coefficients and known anisotropic propagation phenomena is explored. Beam steering, diffraction, and focusing effects are discussed in some detail. Attention is drawn to two particular effects: autocollimation and ``negative'' phase front curvature. Situations in which both occur in practice are discussed. The former should play a significant role in acoustic matched filter design. A cylindrical transducer is shown, within limits, to be an optimum structure for obtaining a single acoustic beam convergence, even in the presence of beam scattering. The parabolic diffraction theory is applied to the design of an experimental anisotropic focusing system. View full abstract»

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  • Space‐Charge‐Limited Current in Gas Diodes

    Page(s): 5352 - 5357
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    Measured current‐voltage characteristics of space‐charge‐limited cylindrical gas diodes filled with helium, neon, and nitrogen up to pressures of 350 Torr are presented. The data are compared with current‐voltage characteristics calculated from published values of the electron drift velocity as a function of electric field to pressure ratio. While the space‐charge‐limited diode current is always found to be larger than the calculated value, very good agreement exists between the shapes of the experimental and theoretical curves. View full abstract»

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  • Determination of Electron Density Profiles from Tonks‐Dattner Resonance Data in Plasmas

    Page(s): 5358 - 5361
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    A technique is described for deducing an unknown electron density profile from observed Tonks‐Dattner resonance frequencies, which uses a simple resonance condition derived from the WKB approximation. The density profile is approximated by a step model, piecewise‐linear model, step‐piecewise‐linear model, and polynomial model in both active and after‐glow plasmas in plane‐parallel and cylindrical geometries. Good agreement is obtained between the profile determined by this technique and one obtained theoretically. View full abstract»

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  • Comparison of Various Microwave Breakdown Prediction Models

    Page(s): 5362 - 5369
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    This paper is concerned with presenting a comparison of various microwave breakdown prediction models when applied to predicting breakdown of a practical antenna system located in a partially ionized environment. Solutions for the breakdown conditions are obtained numerically, allowing for the field and environment properties to have arbitrary spatial variation. The models are applied to predictions of breakdown for an S‐band slot radiating from a reentry vehicle, and the enviroment properties are taken from aerodynamic conditions existing along the descent trajectory. The three models compared consist of a linear model, a variational model, and a nonlinear model. The models are based on the electron‐continuity equation and allow for the effects of diffusion (including the transition from ambipolar to free diffusion), high‐temperature effects, and recombination, which, to our knowledge, have not been treated previously in a single model. 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