bluuebunny/crossref_metadata_2025 huggingface dataset:
Pyroelectric Voltage Response to Rectangular Infrared Signals in Triglycine Sulphate and Strontium-Barium Niobate
Authors: Shaulov A. , Simhony M.
Published: February 2004

The pyroelectric voltage response to rectangular signals of infrared radiation is derived using our recent analysis of the response to a step signal. The response is symmetrical with respect to the electronic and thermal time constants, τe and τT of the samples, and with respect to the times T1 and T2 of irradiation and darkening. When τe differs appreciably from τT, the rise of the response at the onset of irradiation and its fall at the beginning of darkening are exponentials with the same time constant, which is the smaller one from among τe and τT. A rectangular response is obtained when τe ≪ (T1, T2) ≪ τT. In this case the peak-to-peak value Vptp of the response is proportional to τe and independent of the pulse frequency, as well as of the ratio T1/T2. When T1 and T2 are each less than the smaller one from among τe and τT, triangular responses are obtained, for which Vptp is independent of τe and inversely proportional to the pulse frequency. Pyroelectric responses obtained in triglycine sulphate and strontium-barium niobate samples of different τT were found to follow the derived expression, and plots of the measured parameters of the response vs τe, T1/T2, and pulse frequency show good agreement with the analysis.
Detection Efficiency of Electron Multipliers for Low-Energy Electrons
Authors: Bunting W. D. , Tarstrup J. , Heikkila W. J.
Published: February 2004

Pulse-height spectra have been obtained for electron multipliers with discrete dynodes of CuBe. A peak in the spectrum shows up at low pulse heights (≈ 0.1 pC for a multiplier with a dc gain of about 106), but a long tail extends out to very large pulses. These observations can be understood in terms of secondary emission processes. They have provided a good basis for the design and calibration of a soft particle spectrometer for the ISIS-2 satellite. The detection efficiency for 300-eV electrons, with a 14-stage venetian blind multiplier having a total gain of 106, is about 80%. Below 100 eV the detection efficiency falls off, but in practice this can be overcome by postacceleration. At higher energies it also decreases to about 30% at 4 keV. This efficiency is reduced at very high counting rates, above 107 sec−1, owing partly to amplifier bandwidth limitations related to noise immunity requirements, and partly to the finite rise time of the multiplier pulses.
Molecular Dynamic Simulations of Shock Waves in a Three-Dimensional Solid
Authors: Paskin Arthur , Dienes G. J.
Published: February 2004

Molecular dynamic techniques were used to simulate the motion of a one-dimensional shock wave in a three-dimensional solid. A Lennard-Jones potential was used to simulate a rare-gas solid. The pressure, volume and temperature were monitored. The pressure and volume were found to agree with dynamic calculations using the Hugoniot relations. A large temperature increase was found, probably the result of kinetic energy transfer by direct collisions with atoms in the shock-wave front. Reasonable agreement was found between the computer simulation results and static high-pressure measurements on neon. The general results establish the value of applying molecular dynamic techniques to shock-wave problems.
Solubility of Gases in Glass. II. He, Ne, and H2 in Fused Silica
Authors: Shackelford James F. , Studt Perry L. , Fulrath Richard M.
Published: February 2004

The statistical thermodynamics of the gas-in-glass system provides a basic model of both physical and chemical solubility. The physical solubility result is essentially equivalent to that for monatomic solubility. The chemical solubility result is dependent upon the specific system involved. The model was compared with experiment for a variety of systems. Helium and neon in fused silica were examples of the physical solubility of monatomic gases. Variations of the thermal history of the fused silica did not appear to have a measurable effect on physical solubility as evidenced in the helium data. Hydrogen in fused silica was an example of the physical solubility of polyatomic gases. Physical solubility was measured by a modified Seiverts technique and was characterized by a linear dependence on pressure. Binding energies for the physically dissolved species were of the order expected for van der Waals bonding. Vibrational frequencies were on the order of 1013 sec−1 with the heavier species having the lower frequencies. Hydrogen in fused silica was also an example of the chemical solubility of polyatomic gases. The literature gave data for the chemical solution of hydrogen in fused silica, but the fused silica of this study did not, perhaps because of the presence of water-produced hydroxyls. Comparison of the model with the literature data showed a p1/2 pressure dependence for the solubility (indicative of dissociation) and a binding energy of about 63 kcal/mole (indicative of chemical bonding).
Frequency Response of Gold Impurity Centers in the Depletion Layer of Reverse-Biased Silicon p+n Junctions
Authors: Zohta Yasuhito
Published: February 2004

The frequency dependence of ΔV/Δ(Crf−2), which is closely related to the space-charge density of a reverse-biased p+n junction containing deep impurities, is discussed by using Goodman's model. In order to measure the variation of ΔV/Δ(Crf−2) with frequency, a special technique has been developed. The experimental result on a gold-doped silicon p+n junction shows that frequency dispersion of gold acceptors is well explained by assuming a single deep level, whose charging and discharging time constant is 8.0 × 10−4 sec at room temperature. A value of 1.25 × 103 sec−1 is obtained for the thermal emission rate of electrons from the gold acceptors, which agrees well with the data obtained from the photo and dark junction current and capacitance experiments. This result differs from that determined by capture rate measurements. The disagreement is removed by taking into account an electron capture process through the excited states of the gold acceptors under non-equilibrium conditions.
Techniques for Obtaining Recombination-Center Parameters from Carrier Lifetime Studies
Authors: Srour J. R. , Curtis O. L.
Published: February 2004

Relationships useful in the determination of semiconductor recombination properties are presented. Expressions appropriate for both one- and two-recombination-level behavior are considered, with emphasis being placed on techniques for obtaining the following parameters: recombination-center energy-level positions, temperature dependences of the electron and hole capture probabilities associated with these levels, magnitudes and temperature dependences of hole-to-electron capture-probability ratios. Analysis is based on knowledge of both the temperature and injection-level dependences of minority-carrier lifetime. An experimental example is given to illustrate the application of the relationships presented in the determination of recombination parameters associated with radiation-induced defects in silicon.
Spectral Output Properties of the Nd–POCl3 Inorganic Liquid Laser
Authors: Brinkschulte H. , Fill E. , Lang R.
Published: February 2004

The spectral behavior of the neodymium inorganic liquid laser was investigated in detail. It has been found that the width of the line strongly depends on the mode of operation. In the spiking mode the half-width is 6 Å and increases by approximately one order of magnitude under mode-locked conditions. The experiments prove that the line of the Nd liquid laser is essentially homogeneously broadened.
Magnetoelastic YIG Delay Lines with Linear Dispersion
Authors: Dötsch H.
Published: February 2004

The internal magnetic field in YIG cones and pyramids has been calculated. With a ratio of the height to the base diameter between 0.7 and 1, constant slopes of the axial fields and hence linear dispersion curves for the magnetoelastic echoes are obtained. The useful frequency range is estimated in terms of the focusing condition for spin waves which requires H(off axis) > H(on axis). Experimentally a nearly linear dispersion curve was obtained with a cone of 4.5-mm height and equal base diameter over a frequency range from 1 to 2 GHz; the dispersion rate was 1.7 nsec/MHz. When the turning surface approaches the region in the crystal where the focusing condition is violated, the echoes are cut off. Measured cutoff lengths and demagnetizing fields agree well with calculations. Similar results have been obtained for pyramids and truncated cones.
Shock-Induced Anisotropy in Ferromagnetic Material. I. Domain-Theory Analysis of Single-Crystal Behavior
Authors: Grady D. E.
Published: February 2004

Shock-induced demagnetization produced by strain-induced anisotropy is considered in cubic single-crystal ferromagnetic material. Equilibrium thermodynamics, along with established methods of ferromagnetic domain theory, are used to predict energy expressions, magnetization curves, and domain structure in the magnetic material behind the shock wave. In particular, specific expressions for the exchange energy and magnetic self-energy are obtained. They are predicted to increase as the fourth root of the strain and are small compared to the induced anisotropy energy in the region of large elastic and plastic strain. Calculations are made for yttrium iron garnet.
Shock-Induced Anisotropy in Ferromagnetic Material. II. Polycrystalline Behavior and Experimental Results for YIG
Authors: Grady D. E. , Duvall G. E. , Royce E. B.
Published: February 2004

The theory of shock-induced demagnetization produced by strain-induced magnetic anisotropy is considered in cubic polycrystalline ferromagnetic material. Analysis of the averaging procedure required to predict the polycrystalline behavior reveals the importance of magnetic grain interaction. Magnetization curves for extreme assumptions of interacting grains and independent grains are determined. Experimental shock demagnetization data are obtained for polycrystalline yttrium iron garnet in the region of large elastic strain (approximately ⅓ and ⅔ of the Hugoniot elastic limit). Results support the independent grain assumption.
Dependence of Barrier Height of Metal Semiconductor Contact (Au–GaAs) on Thickness of Semiconductor Surface Layer
Authors: Pruniaux B. R. , Adams A. C.
Published: February 2004

In this work it is experimentally shown that the apparent potential barrier height at a metal-semiconductor interface (Au–GaAs) is related to the thickness of the semiconductor surface ``oxide films''. The barrier height was measured by capacitance-voltage and photoelectric techniques. The surface layer seems to behave approximately as described by Cowley and Sze, and can account for a variation from 0.82 to 1.08 eV in measured effective barrier height. However, for a more complete explanation of the experimental results it seems likely that additional parameters, such as charge, surface states, and band structure in the surface layer, will have to be taken into account.
Comments on the Correlation between Parameters for Melting and Diffusion and on the Relaxion Mechanism
Authors: Rothman S. J. , Mundy J. N.
Published: February 2004

This paper points out that the correlation between parameters for diffusion and melting is rather less accurate than the experimental data and that it fails to predict some interesting effects. It also shows that the ``relaxion'' model, which is based on the melting-diffusion correlation, cannot explain experimental results on the mass effect in diffusion.
Influence of Microwave Radiation on Current-Voltage Characteristic of Superconducting Weak Links
Authors: Russer P.
Published: February 2004

The current-voltage characteristics of microwave-irradiated superconducting weak links have been calculated on the analog computer. Experimental results of several authors can be interpreted correctly by taking into consideration the resistive feedback.
Calculation of Plane-Wave Propagation in Anisotropic Elastic-Plastic Solids
Authors: Johnson J. N.
Published: February 2004

Wave-propagation effects induced in isotropic materials by either explosive or impact loading uniformly over a planar surface are much simpler than those produced in anisotropic solids in which significant transverse particle motion may occur. Such behavior in linearly elastic anisotropic solids has been investigated previously, and in the present work the analysis has been extended to include elastic-plastic behavior. A general mathematical description of both elastically and plastically anisotropic materials is presented, and then several specific applications are considered in detail. For the case of an elastically isotropic solid that is plastically anisotropic with a single slip plane and direction, it is found that for certain orientations two plastic waves can be propagated, one of which is quasilongitudinal and the other is quasitransverse. For more general orientations there may be two quasitransverse waves and a single quasilongitudinal disturbance. These results approximate the behavior of a single-crystal material of hexagonal symmetry, such as beryllium, for which effects of elastic anisotropy are small and slip occurs predominantly on the basal plane. Since there is a single spatial coordinate involved in planar wave propagation, the general equations describing elastic-plastic wave propagation can be written in one-dimensional finite-difference form and solved numerically for arbitrary crystal structure and orientation. A number of specific examples are considered and compared with analytical solutions.
Mixed Dislocations in Anisotropic Cubic Crystals: Interaction with Point-Defect Stress Fields
Authors: Goodman J. W. , Sines George
Published: February 2004

A method is presented to calculate point-defect-dislocation interaction for dislocations of any orientation in anisotropic crystals. The interaction energy is obtained by consideration of the stress field from the point defect acting against the displacements defining the dislocation. A computer program for stresses around a symmetric point defect in a cubic anisotropic crystal was prepared and successfully employed to calculate the elastic interaction between a symmetric point defect and a number of real mixed dislocations on known slip planes in fcc, bcc, and NaCl-type crystals. The calculated interactions for the mixed dislocations, considering the anisotropic nature of the crystal, deviate substantially from those based on isotropy, and the deviation is greatest for mixed dislocations near the screw orientation.
Determination of Dislocation Velocities and Densities from the Deformation Waves of Discontinuous Yielding
Authors: Bodner S. R. , Baruch J.
Published: February 2004

The deformation waves that accompany the repeated discontinuous yielding of metals are analyzed with respect to utilizing their characteristics to determine dislocation velocities and densities as functions of stress and strain. Repeated yielding experiments were performed on an annealed 2024 aluminum alloy and an α-brass using a ``dead-weight'' loading apparatus. Measurements were taken of deformation wave velocities and widths and the associated plastic strain increments and strain rates. The calculated dislocation velocities and densities appear to be reasonable and consistent.
Dislocation Dissociations and Dislocation Mobility in Diamond Lattice Crystals
Authors: Mendelson S.
Published: February 2004

Dislocation dissociations are derived for AB-type dislocations in the diamond lattice which slip on {111}, {001}, {110}, and {113} planes with stacking faults on planes of the 〈11̄0〉 and 〈112̄〉 zones. Atomic shuffling, necessary for the Shockley dissociation as atom pairs rotate to form the intrinsic twin stacking fault on {111}, is not required for nonplanar dissociations when type IIφ faults develop by rotation of one atomic bond through φ° while maintaining the closest atomic approach and coordination number. The nonplanar dissociations apply to all tetrahedrally coordinated layer structures, and are described for the ice I wurtzite structure, which shows similar plastic flow behavior as that in Ge and Si. Activation energies are evaluated for motion of dissociated dislocations and dissociated kinks and compared with existing data for dislocation velocities and internal friction effects. The effects of doping with donor and acceptor elements on the mobility of dissociated dislocations is found to be consistent with common-ion and elastic modulus effects. The partialized dislocations give a consistent description of various phenomena, many of which cannot be explained by the Peierls barrier model.
Effect of Impurity Clustering on Elastic Precursor Decay in LiF
Authors: Asay J. R. , Gupta Y. M.
Published: February 2004

Experimental data are presented for shock propagation along a 〈100〉 crystallographic direction in single-crystal LiF. The initial impact stress for these measurements was 29 kbar. For crystals containing two different divalent impurity concentrations, elastic precursor amplitudes were measured as a function of propagation distance. In agreement with quasistatic yield stresses, it was found that the degree of impurity clustering strongly influences dynamic yielding. For crystals containing 130 ppm of Mg++ ions, the precursor amplitude at a propagation distance of 2 mm decreased from 17.3 kbar for annealed specimens to 5.6 kbar for samples air quenched from a high temperature. For crystals containing 270 ppm of Mg++, a smaller change in precursor amplitudes occurred upon quenching. The dislocation density remained unchanged for the heat treatments mentioned here. From these measurements, it is concluded that the rate of attenuation of high-amplitude elastic waves is reduced for a given defect concentration if the defects are clustered.
Dense Plasma Driver
Authors: Kuswa G.W. , Freiwald D.A.
Published: February 2004

Plasma from a short coaxial accelerator operated in 5-Torr deuterium was channeled through a conical section into a 5-cm-diam Pyrex expansion section where dense (ni∼1018/cm3) high-velocity (∼ 8.5 cm/μsec) plasmas were observed, as determined from difference holograms and streak camera photos.
Force on a Coil Moving over a Conducting Surface Including Edge and Channel Effects
Authors: Borcherts R. H. , Davis L. C.
Published: February 2004

The lift force FL and the drag force FD on small conducting coils placed near a large rotating conducting cylinder have been measured as functions of velocity, height, and coil geometry. These data are compared with exact calculations based upon Fourier transforms for coils moving over infinitely wide flat plates. By placing the coil near the edge of the cylinder, the effect of the edge on FL and FD and the transverse force FT were studied. A channel was then cut in the cylinder, and the properties of a U-shaped guideway were examined. Both the edge effects and channel effects were compared with approximate calculations. Agreement was generally good, substantiating a variety of predictions for the large magnets proposed for the suspension of high-speed ground vehicles.
Superconductivity in Cubic and Monoclinic ``TiO''
Authors: Reed T. B. , Banus M. D. , Sjöstrand M. , Keesom P. H.
Published: February 2004

The cubic metallic oxide ``TiOx'' exists over the wide homogeneity range 0.8<x<1.30. Though the compound was previously reported to be superconducting above 0.08°K only over the center portion of this range, measurements on well-characterized samples show that the transition temperature is relatively independent of composition and lies between 0.6 and 0.9°K for the whole range. Transition temperatures are reported for several compositions annealed at 60 kbar that had not been measured previously, and the superconductivity of the monoclinic ordered structure TiO1.0 is discussed. Some scatter in the data is attributed to the tendency of other compositions to form ordered structures on cooling.
Comment on ``Temperature Dependence of Hole Velocity in p GaAs''
Authors: Stirn Richard J.
Published: February 2004

A comparison of magnetoresistance mobility values and their temperature dependence with theoretical values of the conductivity mobility was made in a recent publication. Reasons are discussed why such a comparison is unwarranted, particularly when multiple-carrier conduction is present.
Spherical Particles Formed in the Fretting of Silver
Authors: Stowers I. F. , Rabinowicz E.
Published: February 2004

Examination of wear debris formed during the low-speed fretting of silver reveals spherically and cylindrically shaped particles. A decrease in the coefficient of friction with time and a low wear coefficient may be attributed to the rolling action of this spherical debris.
Study of Cyclic Fatigue Damage in Copper-Aluminum Alloys by Thermal Conductivity Measurements
Authors: Chu T. K. , Lipschultz F. P.
Published: February 2004

Low-temperature (4–70 °K)thermal-conductivity measurements have been carried out on two copper-aluminum alloys (copper plus 1 at.% aluminum) which have undergone various stages of fatiguing. From the temperature variation of the lattice component of the measured thermal conductivity, the dominant lattice imperfections introduced by fatiguing were determined. It is found that in the copper plus 1 at.% aluminum alloy, the damage is in the form of dislocation pile-ups. In the copper plus 15 at.% aluminum alloy, the damage is a random distribution of dislocations. This damage is of the same nature as that induced by uniaxial tensile deformation.
Transmission Electron Microscopy of Granular Nickel/SiO2 Cermet Films
Authors: Abrahams M. S. , Buiocchi C. J. , Rayl M. , Wojtowicz P. J.
Published: February 2004

Granular nickel films have been prepared by co-sputtering nickel and silica onto glass substrates at room temperature. Seven films of (Ni)1−x(SiO2)x, where x is the volume fraction of silica, were examined by transmission electron microscopy. For all samples, the microstructure consisted of nickel grains embedded in a matrix of silica. The grain size is observed to decrease linearly with x; the distribution of grain sizes varies from 170 to 310 Å for x≃0.1 and from 40 to 55 Å for x≃0.75. The thickness of the intergranular silica is about 22 Å and is independent of composition. The nickel lattice is observed to expand with increasing x; the fractional expansion is inversely proportional to grain size and attains values as large as 10% for large x. These results will prove useful in the interpretation of the magnetic, electrical, and optical properties of granular metal films. In particular, these results have been applied to the interpretation of the depression in magnetic Curie temperature observed in the (Ni)1−x(SiO2)x system.
Derivation of the Critical Rayleigh Number for Convection in Crystalline Solids
Authors: Hughes T.
Published: February 2004

The classical theory of thermal convection applies to viscous materials whose linear flow behavior can be described by a Newtonian coefficient of viscosity. When applied to the earth's mantle and polar ice sheets, this theory should be modified so that it holds for viscoplastic materials whose nonlinear flow behavior is described by a non-Newtonian coefficient of effective viscosity. When this is done, the critical Rayleigh number for nonlinear convection flow depends on the thermal stress driving convection and on the parameters of the flow law which describes creep deformation of the viscoplastic material.
Effect of Saturated Frequency Chirping on Mode-Locked Laser Pulses
Authors: Kim Dae M. , Tittel F. K. , Rabson T. A.
Published: February 2004

A dye-induced nonlinear frequency chirping is analytically shown to have significant modifications on the nature of the output mode-locked lasers. It is shown that the saturated frequency sweeping is responsible for substantial pulse broadening as well as substructures.
Use of a Fine-Wire Thermocouple to Measure Total Temperature in Shock-Tube Lasers
Authors: Mullaney George J. , Christiansen Walter H.
Published: February 2004

The use of a fine-wire thermocouple probe to measure the total temperature of shock-tunnel flows is described. It is concluded that the probe has a satisfactory response time for this application and can accurately measure temperatures in the range 600–1300 °K.
Defect Studies of GaP Crystals Pulled from Nonstoichiometric Melts: Dislocation and ``Saucer'' Etch Pits
Authors: Rozgonyi G. A. , Von Neida A. R. , Iizuka T. , Haszko S. E.
Published: February 2004

It has recently been shown that the occurrence of flat-bottomed saucer-shaped etch pits (S-pits) in GaP grown by the liquid-encapsulated-Czochralski (LEC) technique can be correlated with reduced photoluminescence (PL) and electroluminescence (EL) efficiencies. At the same time a new class of LEC crystals pulled from nonstoichiometric melts (LEC/NSM) have become available which show much improved PL efficiencies (η). A study of the etchpit densities in LEC/NSM crystals was therefore carried out. Both p- and n-type material were examined. In n-type material the S-pit density is reduced by at least 4 orders of magnitude for all LEC/NSM crystals compared with LEC material. Similar reductions in S-pit density are observed in p-type material, but only for crystals pulled from melts containing less than 30 at. % phosphorus. This correlates well with those p-type crystals showing major improvements in PL η. However, crystals pulled from 20 and 10 a/o P melts are small in size and have a strong tendency to entrain pockets of gallium. The most promising LEC/NSM samples are the low or zero S-pit density n-type crystals pulled from 36 and 30 a/o P melts. Since these crystals have no Ga inclusions, are very low in dislocation density, and can be grown to reasonably large diameters (greater than 15 mm), they are expected to be quite useful as substrates for diffused or single-tipped LPE p/n junction EL devices. In fact, preliminary measurements have shown that the EL η of red-emitting diodes fabricated on LEC/NSM substrates equals the best reported values (∼2%) at 10 mA for single-tipped 0.015-in.-square LPE devices.
X-ray study of interdiffusion in bimetallic Cu–Au films
Authors: Tu K.N. , Berry B.S.
Published: February 2004

Bimetallic films prepared by consecutive evaporation of Cu and Au onto fused quartz substrates have been annealed for up to 500 h at 160–220°C. The interdiffusion behavior was studied by x rays, using a Seeman-Bohlin diffractometer. The first changes observed were the appearance of Cu3Au reflections, followed by those from CuAu3. As time progressed, these lines increased in intensity, while those from the parent films decreased without, however, either broadening or changing position. Metallographic observations support the conclusion that interdiffusion produces the layered-structure Cu/Cu3Au/CuAu3/Au with sharp steps in composition between the different phases. Data on relative integrated intensities were used to determine the thicknesses of the new phases as a function of time and temperature. In general, the thickness of CuAu3 was about twice that of Cu3Au, and both phases were found to thicken nearly linearly with time. An activation energy of 1.65 ± 0.17 eV was obtained from the temperature dependence of the thickening rate. The observed kinetics are consistent with a model in which atomic transport through a growing layer occurs rapidly by boundary diffusion, and the rate-limiting step is provided instead by the local atom movements that take place in the crystal lattice behind the advancing interface to secure order and stoichiometry in the new phase.
Argon laser quenching, dark spaces, and deexcitation mechanisms
Authors: Skurnick Eugene , Schacter Harry
Published: February 2004

A model for quenching of the ArII laser oscillation is presented that compares collisional and radiative deexcitation processes. High electron densities (1015 cm−3) in the quenching regime indicate that collisional effects mask the radiation-trapping mechanisms in a radially dependent way. An analytic solution to the radiation-trapping model is found and estimates of the hole or dark space radius indicated.
Pulser/sustainer electric-discharge laser
Authors: Reilly James P.
Published: February 2004

An electric-discharge concept is discussed which uncouples electron density from electron temperature to allow production of stable uniform electric laser discharges at higher pressure and in larger volumes than those stabilized by surface effects. Experimental results from both small- and large-scale devices prove both pressure and volume scaling of electric power input and laser power output. Focusing experiments with the large device indicate laser medium homogeneity sufficiently good to support better than 90% of theoretical diffraction-limited focal-power densities.
Laser action of Nd3+ in a crystal Ba2ZnGe2O7
Authors: Horowitz D.J. , Gillespie L.F. , Miller J.E. , Sharp E.J.
Published: February 2004

Stimulated emission at 1054.4 nm has been observed from Nd3+ in a crystal of Ba2ZnGe2O7. The threshold for laser action at room temperature was 4.5 J. The crystalline Stark levels determined from the absorption and fluorescence spectra of Ba2ZnGe2O7 are reported and compared to those of Ba2MgGe2O7 : Nd3+. The fluorescence lifetimes are reported and the laser transition cross sections have been calculated.
Critical current periodicity of Josephson junction interferometers
Authors: Stuehm D.L. , Wilmsen C.W.
Published: February 2004

The critical current through a Josephson junction interferometer has been numerically computed taking into consideration the effect of applied and self-induced magnetic fields on the junctions and in the interference loop. The periodicity of the interference pattern is shown to be less than the flux quantum φ0 = hc/2e. Quantitative results are given illustrating the degree of deviation in periodicity from the flux quantum.
Time and spatial distribution of amplified acoustic flux in n-InSb
Authors: Fisher B. , Pratt B. , Gorelik J. , Feingold I. , Many A.
Published: February 2004

The growth process of amplified acoustic flux in n-InSb under an applied constant-current pulse is analyzed in detail, taking into account flux blocking and reflection at the contact-semiconductor interfaces. The analysis accounts well for the observed time and spatial distribution of the amplified flux, provided spurious effects associated with current feedback and hole injection is eliminated. The measurements provide conclusive evidence that the predominant source of the amplified flux in n-InSb is the thermal-equilibrium phonon distribution; the piezoelectric shock produced at the contact boundaries by the onset of the applied pulse plays no role in this respect. The information derived here on the detailed mechanism governing the flux growth is utilized in measurements of the gain parameters in InSb to be described in the following paper.
Nucleation of moving acoustoelectric domains
Authors: Zold T.
Published: February 2004

A recent report on acoustoelectric domain nucleation suggests shock-wave generation as the only cause of domain nucleation in homogeneous samples. In this paper we show both experimentally and with simple physical arguments that, although the effect of shock-wave generation is appreciable on moving domain nucleation when the drift field and its rate of increase are large, acoustoelectric domains nucleate as well, both in homogeneous and inhomogeneous samples, from the spatially nonuniformly amplified thermal vibrations of the piezoelectric semiconductor when the drift field or its rate of increase is small. The detailed mathematical work on the latter type of domain nucleation will be reported elsewhere.
High-field current transients in KCl
Authors: Moore E. J. , Hanscomb J. R.
Published: February 2004

Current transients which are anomalously large compared with steady state current are reported for KCl for the temperature range 100–340 °C at field strengths between 0.3 and 0.8 MV cm−1. The form of the transients is discussed, and a model which quantitatively fits the experimental data is developed. It is proposed that the observed currents contain a time-independent part which is probably ionic, and a transient part which is probably electronic. The electronic current appears to be due to hopping of electrons between shallow localized levels. The time dependence of the current is explained by excitation of electrons into these conducting levels from shallow localized nonconducting levels, followed by bimolecular recombination at deeper levels.
Nonlinear variation of the induced birefringence of vitreous silica with uniaxial stress to 7 kbar
Authors: Shull H. Eugene , Vedam K.
Published: February 2004

The induced birefringence of vitreous silica for λ 5893 Å was measured at uniaxial stress to about 7 kbar with a Babinet compensator. Nonlinear elasticity was used to account for specimen dimension changes. The variation of birefringence with stress is linear within the limits of experimental error, whereas its relation to Lagrangean strain is nonlinear. This is in contrast to the nonlinear piezo-optic but linear strain-optic behavior observed in vitreous silica under hydrostatic stress. The difference p- q of the Neumann strain-optic constants and its stress and strain derivatives is also presented.
Luminescence of Zn- and Cd-doped GaN
Authors: Ilegems M. , Dingle R. , Logan R. A.
Published: February 2004

The luminescence of epitaxial GaN layers doped with Zn or Cd during growth is characterized, at low doping levels, by the presence of an I1-type line at 3.455 eV at 4.2 K which is attributed to the decay of excitons bound to neutral [inverted lazy s] 190-meV deep Zn or Cd acceptors on Ga sites. In addition, a broad and very efficient (> 12% at 300 K) band centered around 2.85 eV is observed in both vapor- and solution-grown samples and completely dominates the spectrum at high doping levels. Contrary to the usual band-gap dependence, this ``blue'' emission band shifts to slightly higher energies with increasing temperature.
A physical process for 1/f noise in thin metallic films
Authors: Tunaley J. K. E.
Published: February 2004

The concept of power spectra for nonstationary stochastic processes is examined and a definition of ``expected power spectrum'' is employed. This allows a derivation of the spectrum for a simple process where the current arises in a conductor consisting of a collection of sites by virtue of carrier jumps. If the noise may be described by a series of noise generators associated with each volume element of the conductor we are led to a spectrum essentially in accord with the experimental observations of noise in thin films subject to a certain condition. It is shown that this condition can be satisfied if a stochastic model is chosen in which the conduction takes place by a tunnelling mechanism between small islands of conductivity.
Electro-osmotic energy conversion in the glass/n-propanol system
Authors: Phillips R. W. , Mastrangelo S. V. R.
Published: February 2004

A cascade electro-osmotic cell utilizing an organic working fluid, n-propanol, in combination with Pyrex glass sinter produced pressures proportional to the number of stages and to the applied voltage. Pressures as high as 0.84 atm were recorded. Flow rates, however, were directly proportional to the applied voltage and were independent of the number of stages. Positive-ion mobilities were calculated to be in the range 0.45–2.2×10−5 cm2V−1 sec−1 which are in the accepted range for ion mobilities in organic media. The electromechanical coupling efficiency was 0.31±0.03%.
A method to determine the thickness and magnetization of thin uniaxial magnetic films
Authors: Schreurs J. W. H. , Borrelli N. F.
Published: February 2004

A method is described whereby the thickness and magnetization of thin epitaxial magnetic films can be estimated from a measurement of the initial slope of the magnetic flux vs magnetic field curve and the zero-field domain period, respectively. The method is based on an analysis of the parallel-stripe-domain configuration as an approximation to the real domain configuration. Data is shown comparing the calculated thickness to that obtained by optically observing edge polished specimens, for a number of films.
(d,n) thick-target yields and total cross sections between 1 and 40 MeV
Authors: Lucas Larry L. , Root John W.
Published: February 2004

New results are reported for (d,n) neutron yields, total cross sections, and zero-degree energy spectra for Li, Be, C, and Al targets and for bombarding energies ranging from 15 to 40 MeV. Semiempirical equations have been derived from the available (d,n) thick-target total cross section and total yield data.
Quantitative theory of retarded base diffusion in silicon n-p-n structures with arsenic emitters
Authors: Fair Richard B.
Published: February 2004

When As is sequentially diffused into Ga or B-doped Si, a retardation of the p -type base layer is generally observed. This is in contrast to the ``emitter-push'' effect associated with sequential phosphorus diffusions. In order to simulate transistor profiles it is necessary to be able to quantitatively describe the emmiter-base interactions during diffusion. In this study, the way in which the internal electric field, the equilibrium vacancy density, ion pairing, and the rate of [VSiAS2] complex formation affect the redistribution of the base layer during sequential processing was investigated. Numerical solutions to coupled diffusion equations indicate that the electric field and ion-pairing effects only cause localized retardation of a B profile during the As emitter diffusion. However, the formation of [VSiAs2] complexes causes a vacancy undersaturation in the Si to a distance in the crystal well beyond most practical collector-base junction depths. Since the local-base diffusivity depends upon the vacancy density, this extrinsic vacancy undersaturation effect causes the expected retarded base diffusion. Experimental verification of the correctness of the theory present is given as a function of emitter- and base-surface concentrations, initial base depths, and times and temperatures.
Experimental study of 1/f noise stationarity by digital techniques
Authors: Dell R. A. , Epstein M. , Kannewurf C. R.
Published: February 2004

Electronic noise measurements in carbon resistors, germanium, cadmium sulfide, and thermionic devices over the frequency range 2 Hz to 2 kHz are presented, using a real-time computer-controlled instrumentation system. The reproducibility and resolution of this system were sufficient to identify small but significant statistical differences between 1/f- and Nyquist-type noise sources which have not been observed in previous investigations.
Relations between electrostatic contributions to elastic constants
Authors: Fuller E. R. , Granato A. V.
Published: February 2004

Some useful relations are given between the electrostatic contributions to elastic constants for different structures for any order including the energy density. Also, relationships are given for intermediate metallic structures with arbitrary (not necessarily integer) charges, with applications to alloys.
Solid-state electronic structure effects of silicon Kβ x-ray spectra produced in α-particle excitation
Authors: Moore C. Fred , McWherter Joseph , Olsen David K. , Richard Patrick
Published: February 2004

Both Si and SiO2 crystals were bombarded by a 3.2-MeV α-particle beam and the subsequent Si K x-ray yield was measured. The Kα x-ray spectra show fairly close agreement; however, the structure in the Kβ x-ray spectra is quite different for Si and SiO2. These results are interpreted as effects due to the chemical bonding of the oxygen atoms to silicon.
Interpretation of shift of relaxation time with deformation in glassy polymers in terms of excess enthalpy
Authors: Matsuoka S. , Aloisio C. J. , Bair H. E.
Published: February 2004

The mechanical relaxation time in a glassy polymer depends on the magnitude of strain. The stress relaxation modulus of a styrene acrylonitrile and polybutadiene composite system (ABS) was measured at strains ranging from 0.005 to 0.10. The relaxation time was observed to shorten by up to four orders of magnitude. In addition, there was observed a decrease in the elastic contribution to the modulus. These two aspects of nonlinear viscoelasticity are interpreted in terms of the excess enthalpy associated with dilatation under strain, a crucial factor for ductile behavior and the formation of crazes. Up to 0.9 cal/g of the excess enthalpy associated with the stress-induced dilatation is obtained from the differential scanning calorimetry study.
Sorption of benzene by biaxially oriented polystyrene
Authors: Kwei T. K.
Published: February 2004

The sorption of benzene vapor by a biaxially oriented polystyrene film was studied in the temperature range 30–70°C. A comparison of the sorption isotherms for the oriented and the unoriented materials allowed the calculation of the enthalpy and entropy of orientation. The enthalpy of orientation is about − 1 to − 1.4 cal/g and the entropy change is about − 2.6 to − 4.3 cal/g. It was also concluded that the clustering tendency for benzene molecules was greater in the oriented specimen.
Deformation of polytetrafluoroethylene from 78 to 298 °K and the effects of environmental crazing
Authors: Fischer Solomon , Brown Norman
Published: February 2004

The tensile mechanical properties of PTFE were measured as a function of crystallinity, temperature, strain rate, and the environment. All prior investigations had unknowingly included the environmental effect produced by N2 and acetone. The intrinsic low-temperature mechanical properties were displayed for the first time by using helium as the inert environment. It was found that all drops in the load at yield point were caused by environmental craze yielding. For the first time crazes were observed in PTFE. At 78 °K, the effects of crystallinity on the intrinsic mechanical behavior could be simply understood by viewing the PTFE as a polycrystalline material with different grain sizes where the rigid grain boundaries impede the deformation within the grains. At 200 °K grain boundary and grain deformation occur easily. The yield behavior was found to be entirely consistent with the internal friction and morphological results from other investigations.
Growth of ZnO needles from molten hydrous KOH solutions
Authors: Kashyap Subhash C.
Published: February 2004

Thin needles of ZnO have been grown at 480 °C, employing hydrous KOH melt as a solvent. Unlike other molten salt solvent methods, in the present case supersaturation is promoted by the decomposition of zincate ions. Laser Raman spectroscopic investigation made on molten hydrous KOH–ZnO system by employing a single—crystalline KCl cell has confirmed the presence of the zincate ion (ZnO22−) with a linear structure.
Nonlinear sound amplification in zinc oxide
Authors: Kuzmany H.
Published: February 2004

The generation and propagation of acoustoelectric domains in ZnO is studied by Brillouin scattering. Special attention is paid to the nonlinear region of sound amplification; it is shown how such experiments can be compared with existing nonlinear theories for the acoustoelectric effect. In particular, the experiments are compared with the parametric theory of Conwell et al. and a theory based on strong bunching effects of Tien and Wonneberger. It is found that at the beginning of gain saturation, the theory of Tien and Wonneberger gives a better fit to the experimental results. However, at slightly increased domain intensities, the parametric processes become dominating before a complete saturation due to carrier bunching has occurred.
Plastic relaxation of a shear crack near a planar interface
Authors: Jagannadham K. , Raghavan K. S.
Published: February 2004

The plastic relaxation of a shear crack near a planar interface of a two-phase system composed of two welded elastic half-planes is considered. Using the models suggested by Bilby, Cottrell, and Swinden, and by Atkinson and Kay, expressions relating the applied stress, the yield stress, and the width of the plastic zone are obtained. The relative displacement of the crack faces is also obtained and the behavior of the plastic zone is discussed.
Upper and lower bounds on gas breakdown in inhomogeneous fields
Authors: Hayes Dallas T.
Published: February 2004

The prediction of the electric field strength at which gas breakdown will take place is a difficult and crucial problem for many applications. In the case of microwave antennas, breakdown in the gas or plasma surrounding the antenna first occurs in the inhomogeneous near-field region close to the antenna surface. Recently, variational techniques have been used to estimate breakdown field strengths in such cases. These techniques have one drawback in that only upper bounds are provided, i.e., a field strength above which breakdown definitely takes place. Depending upon the accuracy of a particular calculation, breakdown may occur for an appreciable range below the estimated field strength. What is needed is a lower bound upon the breakdown field strength. In this paper a formulation of variational theory is used which allows lower bounds to be calculated. In addition, a variational-iterative technique is presented by which it is possible to systematically improve upon a calculated lower bound should this be necessary. These techniques are then applied to breakdown problems already considered by other authors to demonstrate the upper-bound calculations.
Experimental investigation of the low-frequency capacitive response of a plasma sheath
Authors: Oliver B. M. , Clements R. M. , Smy P. R.
Published: February 2004

Several theoretical models are examined for the low-frequency capacitive response of the ion sheath surrounding both planar and cylindrical Langmuir probes in a collisionless plasma. It is found that a recent theoretical approach by Shkarofsky, based on the total probe surface charge derived from Gauss's law, predicts values for both the low-frequency, capacitance and the transient charge flow which are as much as an order of magnitude smaller than that predicted based on the electron current flow caused by the motion of the sheath edge, e.g., Kamke and Rose. This discrepancy is attributed to the neglect by Shkarofsky of the transient ion conduction current through the sheath. Additionally, a recent theory by Rosa for the complex impedance of a planar sheath is seen, in the limit of low frequency, to be in agreement with that predicted following Kamke and Rose. Experimental measurements have been made, for both pulsed and rf-driven probes, of the transient charge flow to the probe and the effective low-frequency sheath capacitance. These measurements show good agreement with the theoretical approach of Kamke and Rose, and Rosa. The plasma was formed in the positive column of a low-pressure helium dc discharge with plasma electron densities and temperatures in the ranges 5 × 1015 −3 × 1016 m−3 and 5 × 105 −7 × 105 °K, respectively. The pulsed probe measurements were made by integrating the probe current response to both small- and large-amplitude negative voltage pulses. The rf measurements were made using a tunnel diode oscillator circuit whose resonant frequency was chosen somewhat below the ion plasma frequency.
Throughput limit in mass spectrograph-type isotope separators
Authors: Alexeff I.
Published: February 2004

A fundamental limit to the throughput of heavy ions (U235, U238) is shown to exist for a mass spectrograph-type isotope separator. It is due simply to multiple scattering caused by the particulate nature of the ion beam, and does not depend on any plasma instabilities or waves whatever.