bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron-Diffraction Study of Magnetic Ordering in K2ReCl6
Authors: Smith H. G. , Bacon G. E.
Published: April 2005

Neutron-diffraction measurements have been made on single-crystal and powder specimens of K2ReCl6 at temperatures from 295° to 4.2°K. This compound is fcc at room temperature but becomes primitive cubic below 76°K. In both structures the Re ions are in an fcc arrangement, and, although the over-all symmetry is reduced at low temperatures, the immediate environment of the Re ion (i.e., the six bonding Cl ions) has essentially octahedral symmetry. Previous specific heat and magnetic susceptibility measurements have indicated an antiferromagnetic transition at 11.9°K, and the neutron-diffraction patterns confirm that an ordered antiferromagnetic structure exists at 4.2°K. Because of the rapid decrease of the magnetic form factor associated with the 5d electrons, only four antiferromagnetic reflections could be measured. These reflections indicate magnetic ordering of the first kind, i.e., the moments are ferromagnetically aligned in (001) planes and adjacent planes are oriented antiparallel. Both the moment value of 2.6±0.5 Bohr magnetons and the magnetic form factor are consistent with a spin-only value for the magnetic moment.
Internal Magnetic Field Analysis and Synthesis for Prescribed Magnetoelastic Delay Characteristics
Authors: Auld B. A. , Strauss W.
Published: April 2005

A systematic procedure is given for synthesizing the internal magnetic field required to realize prescribed magnetoelastic delay characteristics. The method is based on the expression Tr = (2/c) {y+ω[γHi′(y, He)]−1} for the transit time of magnetoelastic waves in ferromagnetic insulators. Here Hi′(y, He) is the gradient of the internal magnetic field at the turning point, and He is the external magnetic field. Some necessary conditions for physical realizability are discussed and a delay-bandwidth invariant is demonstrated. Field distributions are obtained having the characteristics: (a) ∂Tr/∂ω = 0, independent of ω at specified Hi(0, He), and (b) ∂Tr/∂ω = 0, independent of Hi(0, He) at specified ω. The last case is used as a basis for evaluating the bandwidth capabilities of magnetoelastic variable delay lines. Limitations on the bandwidth, delay variation, and delay distortion are discussed.

Realization of a desired internal magnetic field is greatly simplified by a method for determining the field from measurements of the transit time Tr(ω, He) of magnetoelastic pulses and the separation Sm(ω, He) in magnetic field between adjacent standing-wave modes. The relation Hi′ = ωSm/πc gives y = Φ(ω/γ, He) = (c/2)[Tr−2π/γSm] in terms of measurable quantities; inversion of the function Φ at constant He recovers the internal field in the form ω/γ = Hi(y, He). This method has been applied to data from an yttrium iron garnet rod immersed in a steady, uniform, axial field He; a comparison of the measured results with existing theory is presented.
General Method of Treating Instrumental Distortion of Spectral Data with Applications to X-Ray Physics
Authors: Sauder William C.
Published: April 2005

Experimental profiles such as those obtained in spectroscopic measurements often can be represented by a mathematical expression that is dominated by a convolution of an incident spectrum and an apparatus window function. It is shown that replacing this convolution integral by an infinite series allows an ``unfolding'' of the observed spectrum that does not involve the use of the functional form for the true spectrum and requires only a relatively crude knowledge of the window. As a result, a general solution for the instrumental ``shift'' in any characteristic abscissa of the profile is obtained. The theory thus developed is then applied to four problems of current interest: (1) unfolding of spectral data, (2) correction of double crystal x-ray spectrometer measurements, (3) truncation errors in centroid lattice parameter determinations, and (4) errors in x-ray grating experiments. Finally, suggestions for further work are given.
Influence of Statistical Time Lags upon Electric Breakdown in Electronegative Gases
Authors: Crowe Robert W.
Published: April 2005

Measurement of the electric strength of SF6 and a number of other electronegative gases has provided direct evidence that an unusually long statistical time lag is associated with the breakdown process in such gases under certain experimental conditions. For example, time lags in excess of one minute have been reported for the breakdown of SF6. The reason for the difference in breakdown behavior of such gases, when compared with the behavior of the more common gases, is not well understood.

The intent in writing this paper was not merely to verify the fact that the time required for breakdown is completely random, although evidence of this plays an important role in the theories and equations developed here. The paper represents an attempt to provide an explanation of the role that these statistical time lags can often play in yielding misleading experimental values of the electric breakdown voltage, when measured under certain standard test conditions. A number of cases are discussed and evaluated by combining accurate experimental data with theories involving the occurance of random events. It is concluded that the ``apparent'' value of the electric breakdown voltage in electronegative gases ought to be strongly dependent upon the mean statistical time lag, the nature of voltage application, and the electrode configuration. The experimentally observed appearance of field emission from the cathode surface at voltages considerably in excess of the threshold value, can be used to derive theoretical relationships which indicate that rather significant ``apparent'' deviations from Paschen's law are to be expected under certain experimental conditions. The latter inconsistency and the method of avoiding it are described in the paper.
Laser-Induced Perturbations of Excited-State Populations in a He-Ne Discharge
Authors: Weaver L. A. , Freiberg R. J.
Published: April 2005

Radiative cascade patterns in noble gases are described by an idealized theoretical model. Assuming a pure j-l coupling of angular momenta, branching ratios for spontaneous decays are computed using the Coulomb approximation of Bates and Damgaard. The computations are compared with the results of experiments on He-Ne gas lasers, in which oscillation serves as a selective perturbation of excited state populations in the active laser medium. Populations can be monitored spectroscopically through radiative transition rates, and good agreement with predicted decay patterns is found for the 3.39-μ, 6328-Å, and 1.15-μ transitions in neon. Observed deviations from idealized j-l coupling behavior indicate that population distributions are substantially altered by the collisional mixing of excited neon levels. Furthermore, electron impact with Ne(3s2) atoms is shown to be an important excitation mechanism for high-lying neon levels, since they are quenched by up to 3.7% during lasering. When collisional processes are considered, the j-l coupling model adequately explains observed changes in line intensity. It is suggested that infrared lasers can be aligned conveniently by monitoring visible sidelight, and that noble-gas laser transitions of doubtful term assignment can be identified accurately by observing laser-induced decay patterns.
Molecular Beams Formed by Arrays of 3–40 μ Diameter Tubes
Authors: Johnson John C. , Stair A. T. , Pritchard James L.
Published: April 2005

The results of an experimental investigation of molecular beams formed by a closely packed array of glass tubes of uniform diameter are presented. The sets of tubes used (which are commercially available) ranged in diameter from 3 to 40 μ with length-to-diameter ratios of 12 to 100, and were driven by pressures extending from 0.025 to 15 Torr. The experimentally determined functional variations for flux density, on-axis intensity, and beam half-width (conditions L≥λ and a «L) are: Q/A=32(2/3π)(ν̄/σ2)(L/λ)(ε/L)(a/L),Ic/A=(1/8π32)(ν̄/σ2)(L/λ)12(ε/L)(a/a0)13,θ12=(4/√π)(L/λ)12(a/L).L is the length of the tubes, a is the tube radius, and ε is the percent transparency of the area A of the array. It is found experimentally that the flux is approximately ⅔ of that predicted theoretically, the beam width is twice that predicted theoretically, and the prediction for center line intensity is modified by (a/a.)⅓ The dependence of the beam intensity on the tube radius is attributed to self-scattering due to the dense packing of many tubes.
Onset of Instability Patterns between Miscible Fluids in Porous Media
Authors: Heller J. P.
Published: April 2005

A theoretical treatment of the stability of isoconcentration surfaces in a porous sample saturated with a single-phase liquid of variable density and viscosity is presented. In a rectangular system with horizontal displacement front the early growth or decay of Fourier perturbation components is exponential with time. Dependence of growth exponent on wavenumber is presented, including effect of dispersion. Regions of stability with respect to nondimensionalized flow rate, viscosity gradient, and density gradient are shown.
Analysis of High-Velocity Projectile Penetration Mechanics
Authors: Christman D. R. , Gehring J. W.
Published: April 2005

The process of cratering in materials is described in terms of four phases: transient, primary, secondary, and recovery. Rod projectiles were used in an experimental study of the relative importance of each phase and its influence on final crater dimensions. Aluminum and steel rods with aspect ratios of 1/6 to 25 were impacted into metallic and nonmetallic target materials at impact velocities of 0.3 to 6.7 km/sec. During the primary penetration phase, rod deformation was found to be comparable to that observed for shaped-charge liner collapse, and measured rod penetration rates showed good agreement with rates calculated on the basis of incompressible fluid flow considerations. Empirically developed equations are presented for predicting crater penetration and volume in metal targets.
Electrical Conduction between Metallic Microparticles
Authors: Herman D. S. , Rhodin T. N.
Published: April 2005

Electrical conduction in very thin metal films deposited onto single-crystal sodium chloride substrates has been investigated. The conduction for annealed films is found to be thermally activated with a negative temperature coefficient of resistance. Inspection of the films in an electron microscope shows them to consist of separated microparticles. Electron tunneling through the vacuum between microparticles is generally assumed to be the mechanism of electrical conduction. In this work an attempt has been made to show that conduction can occur in the substrate surface. The conduction is believed to be electron tunneling between regions in the substrate surface immediately under the metallic particles. The current carriers can be contributed to the insulator surface regions by the metallic microparticles. In addition, an activation energy is thought to be necessary before tunneling can occur. This energy is electrostatic in nature and is dependent upon the average size and separation of the microparticle regions.
Skin Effect in Anisotropic Plasmas and Resonance Excitation of Electron-Cyclotron Waves. II. Experiments
Authors: Pfeiffer B.
Published: April 2005

The high-frequency magnetic fields within a homogeneous plasma sheath were measured as a function of the plasma parameters and a perpendicularly superimposed static magnetic field. These fields are compared with those calculated taking collision into account. A theoretically predicted resonance of the electron cyclotron wave is observed. Investigations on an electrodeless ring discharge with a superimposed static magnetic field perpendicular to the axis of the discharge also exhibit a similar resonance behavior which in the literature was first reported in 1948. However a valid physical explanation has not been previously established thus far. The phenomenon is widely used to optimize the carrier production in inductively coupled high-frequency ion sources.
X-Ray Photoeffect Cross Sections in Low- and Medium-Z Absorbers for the Energy Range 852 eV to 40 keV
Authors: Bearden Alan J.
Published: April 2005

Experimental determinations of the mass-attenuation coefficient (μm) using both a two-crystal (quartz) and single-crystal (beryl) monochromator for Be, C, N, O, Ne, Al, Ar, Cu, and Sn at selected photon energies between 852 eV and 40 keV are presented. The experimental precautions necessary to ensure freedom from effects such as small angle scattering, x-ray fluorescence, and the Borrmann effect guarantee that the measured values of μm are characteristic of atomic absorbers. Values of the photoelectric cross section (σpe) for these elements are determined by subtraction of the contribution of coherent (Thomson) and incoherent (Compton) scattering to enable direct comparison with calculated values of σpe based on modified Coulomb wavefunctions (Stobbe theory). Modification of inner screening constants gives calculated values of σpe in fair agreement with experiment, whereas fully screened calculations or calculations made with no screening underestimate or overesimate, respectively, the cross section. The use of nonrelativistic sum rules and the precaution necessary when using Hartree-Fock wavefunctions for the determination of σpe are discussed.
Energy Echoes
Authors: White Robert M.
Published: April 2005

It is proposed that nonlinearity can lead to coherent echoes in time just as it leads to harmonic frequency generation. In particular, it is shown how photon echoes, magnetostatic mode echoes, and cyclotron resonance echoes all involve nonlinearity.
Wave Propagation in a Three-Element Linear Spring and Dashpot Model Filament
Authors: Smith Jack C.
Published: April 2005

Mathematical expressions are derived for the particle velocity, stress, and strain distributions in the wave that results when a semi-infinite viscoelastic filament is subjected at one end to constant velocity tensile impact. The equations governing the stress-strain-time behavior of the filament are assumed to be those for a linear model consisting of a spring coupled in parallel with a spring and dashpot in series. These equations are so formulated that by changing a single parameter λ either the spring branch or spring and dashpot branch can be made to dominate. The general solution expressed as a series in λ is obtained. This solution is especially convenient for making calculations. Special solutions describing the behavior at the wavefront and at the point of impact are also derived. The application of these solutions in the interpretation of experimental data is discussed.
High-Frequency Dielectric Resonance Probe for the Measurement of Plasma Densities
Authors: Messiaen A. M. , Vandenplas P. E.
Published: April 2005

Recent theory and experiments show that the resonance value of the high-frequency signal of a metallic probe can only be used to measure the plasma density accurately if the detailed structure of the sheath is known. This paper describes a new resonance probe which makes use of the fact that a system consisting of a vacuum cylinder embedded in an infinite plasma has an eigenfrequency equal to ωe/√2 and independent of the radius of the cylinder. It is shown that the resonance frequency of the probe-and thus the plasma density found-depends only slightly on the sheath. There is very good agreement between theory and experiments when the density obtained by this method is compared to the values measured by the electron and ion characteristics of the Langmuir probe. Plasma densities can be measured over a wide range by this method. General considerations on the difference between the resonant (or antiresonant) behavior of a metallic probe and that of a dielectric structure are given.
Frictional Electrification of Belts of Insulating Materials. II. Relation between Charge Density and Work Done Against Friction
Authors: Cunningham R. G.
Published: April 2005

For large values of work done against friction, the charge density on an insulating belt slipping on a metal roller exponentially approaches a limiting value. This limiting value increases as the pressure between the belt and roller is increased.

A triboelectric series can be formed for the two belt materials and the two roller materials used in these experiments. The positions of the rollers in this series are qualitatively related to their contact potential differences.
Characteristics of the Möllenstedt Electron Velocity Analyzer
Authors: Metherell A. J. F. , Whelan M. J.
Published: April 2005

The performance of the Möllenstedt electron velocity analyzer has been investigated by numerical trajectory tracing by digital computer. Two methods of calculating a field distribution have been employed, namely (a) relaxation for an actual case of interest with cylindrical electrodes, and (b) an analytical solution for a system of two line charges between earthed plates. Suitable equipotential surfaces for this system can be chosen to simulate the cylindrical electrodes of a practical analyzer. The latter system is a reasonable approximation to the actual case, and in practice is much simpler to use in numerical calculations than (a). Using (a) one electrode system has been studied in detail; using (b) several geometries have been investigated. The dispersion of the instrument and the effects of slit width and angular divergence on resolution have been investigated for various electrode geometries. A simple rule for slit width resolution is given.
Wave Propagation along Warm Plasma Columns
Authors: Diament Paul , Granatstein Victor L. , Schlesinger S. Perry
Published: April 2005

Dispersion relations for waves propagating along homogeneous, isotropic, warm plasma columns surrounded by a dielectric medium are obtained. A steady-state linearized model with temperature introduced through a scalar pressure is analyzed both quasistatically and more rigorously from Maxwell's equations. The results show effects of temperature on the cold plasma surface wave and predict a new series of propagating modes above the plasma frequency related to the Tonks-Dattner scattering resonances near cutoff and to the Bohm-Gross longitudinal plasma waves for large wave numbers. Warm and cold plasmas, large and small columns, and quasistatic and rigorous predictions are contrasted. Regions of the Brillouin diagram corresponding to different bound and radiating wave types are delineated and related to their physical properties.
Arc-Transfer Method of Crystal Growth
Authors: Drabble J. R. , Palmer A. W.
Published: April 2005

A new method of crystal growing is reported. It consists essentially of striking a dc arc between two electrodes. The growing crystal acts as the anode and a sintered feed rod as the cathode. The establishment of the arc results in cathode material being transferred to a molten zone on the anode where crystallization takes place. Crystal growth in this manner is particularly suited to certain high-melting-point materials. Crystals which have been successfully grown by the method include the oxides of cobalt, iron, nickel, titanium, and vanadium. The arc-transfer method and its advantages over existing high-temperature techniques are illustrated by describing the production of single crystals of nickel oxide.
Evaluation and Interpretation of Threshold Displacement Energy Measurements
Authors: Bauer Walter , Sosin A.
Published: April 2005

We present a discussion of the inherent limitations imposed by experimental and theoretical considerations on a precise determination of the threshold displacement energy. The recently varying deductions of the threshold energy in copper, 9 eV to 30 eV, are discussed in detail. Upon consideration of the available experimental data and using theoretical estimates only as a guide, we conclude that currently the best value of the threshold energy in copper is 16 to 19 eV.
The 1.0- and 1.28-eV Emission from GaAs Diodes
Authors: Millea M. F. , Aukerman L. W.
Published: April 2005

The 1.0- and 1.28-eV emission bands observed in the electroluminescence from GaAs diodes are investigated. The intensity of these bands at low voltages is proportional to exp(qV/kT). The intensity at high voltages is proportional to exp(qV/nkT), where n is an increasing function of voltage. At high current levels, the intensity as a function of diode current is sublinear (i.e., tends to saturate). Radiation damage decreases the intensity of these emission bands at a constant voltage, indicating that the 1.0- and 1.28-eV recombination is occurring outside the space-charge region. The intensity at 1.28 eV at a constant current decreases with increasing temperature as exp(ΔE/kT), where ΔE∼0.1 eV. Copper doping increases the quantum efficiency of these emission bands while decreasing the quantum efficiency of the near-edge emission band. All three emission bands are decreased by nickel doping. A donor-acceptor pair model is proposed for the 1.28-eV emission band.
Low-Temperature Internal Friction Peak in Rutile
Authors: Carnahan R. D. , Brittain J. O.
Published: April 2005

A relaxation peak has been observed in rutile at 229°K at a frequency of 9 cps. Deviations from stoichiometry and a low-temperature prestrain in the amplitude-dependent region of internal friction are necessary conditions for observing the peak. This relaxation in nonstoichiometric rutile appears to fit the category of low-temperature relaxation phenomena reported in the literature for prestrained crystalline solids.
Electrostatic and Magnetic Pinch Effects in Beam-Generated Plasmas
Authors: Halsted A. S. , Dunn D. A.
Published: April 2005

A kilovolt electron beam of a few mm diameter passing through a gas at pressures of 10−2 Torr or lower is not significantly scattered by collisions with neutrals in distances of many beam diameters. The beam will ionize the gas and generate a plasma that has a potential distribution that will cause the beam to be pinched toward its axis. This electrostatic pinch effect is compared with the magnetic pinch and the electrostatic pinch is found to be the dominant effect at low voltages and currents. Experimental results confirming the results of early experiments at a few hundred volts demonstrate that the electrostatic pinch exists at higher voltages and can be more important than the magnetic pinch at voltages up to the order of 100 kV for typical plasma electron temperatures and beam currents. Computer studies of beam trajectories in a simulated beam-generated plasma provide an explanation for the detailed structure of the beam profiles that have been observed.
Ionic Conductivity, Dielectric Constant, and Optical Properties of Anodic Oxide Films on Two Types of Sputtered Tantalum Films
Authors: Mills D. , Young L. , Zobel F. G. R.
Published: April 2005

The growth of anodic oxide films on sputtered tantalum films in dilute sulfuric acid has been studied by in situ ellipsometry. Two types of tantalum film were used which had been deposited onto substrates at different temperatures giving two structural forms of tantalum (``β'' and bcc). The optical properties of the metal films differed from each other and from those of the bulk metal but the refractive index and dielectric constant of the oxides were nevertheless very similar to those for the oxide on bulk tantalum. However, the field E in the oxide required to produce a given ionic current density I was about 4% higher than for the oxide on the bulk metal and ∂ logI/∂E was slightly less than for the bulk metal. This appears to show an effect of the metal/oxide interface as predicted by Mott and Cabrera.
Experimental Characteristics of Crossed-Field Space-Charge Flows
Authors: Masnari N. A. , Rowe J. E.
Published: April 2005

An experimental method is described for determining the characteristics of space-charge flow in crossed electric and magnetic fields. A beam-intercepting system, which consists of a movable grid of wires biased at appropriate potentials, is inserted across the space-charge flow. The currents intercepted by the wires provide a description of the beam profile at each cross section of the electron beam. Evaluation of the data indicated that in no case did the beam assume a scalloped configuration. In general, it was found that the entire beam undulates in a serpentine manner and has variable thickness throughout the region of interest. The experimental undulation is observed to be in good agreement with the theoretical cycloidal wavelength for electron motion in a crossed-field environment. Calculations of space-charge density indicate that the average value is generally between 0.5 and 1.5 times the Brillouin space-charge density in each case.
Extended Dislocation Nodes in a Silver-Tin Alloy
Authors: Ives L. K. , Ruff A. W.
Published: April 2005

A study of dislocation nodes formed in silver-tin solid solution alloys has been conducted using transmission electron microscopy. In alloys of 6 and 8 at.% Sn, both extrinsic and intrinsic stacking faults were observed at threefold dislocation nodes. Burgers' vector data obtained from diffraction contrast studies were in agreement with predictions based on geometric considerations. From a qualitative comparison of the node extensions, the extrinsic fault energy appears to be greater than the intrinsic fault energy. Both fault energies were observed to decrease with increasing solute concentration. At many of the nodes containing extrinsic faults, the partial dislocations were bowed outward; at the intrinsically faulted nodes, inward curvatures were always observed. It is believed that the dislocation constrictions or cross-linking dislocations required at the extrinsically faulted nodes were responsible for this difference. Motion under stress of the extrinsically faulted nodes was observed, consistent with the coplanar Burgers' vector geomtery. The observations lead us to suggest the general occurrence of both types of faults in low stacking-fault energy fcc materials.
Temperature Variation of the Magnetization Curve of Superparamagnetic Alloys
Authors: Kneller E. , Wolff M. , Egger E.
Published: April 2005

Thermodynamical considerations suggest that in precipitation alloys there will, in general, be a gradual transition of composition between precipitate and matrix over at least a few atom layers. Since the Curie temperature of solutions is a continuous function of composition, this implies that the magnetically effective volume of ferromagnetic precipitates in a nonferromagnetic matrix depends on temperature. This interface effect may be rather large, especially for small particles.

It is shown that characteristic deviations of the magnetic behavior of superparamagnetic alloys from that predicted by current theory of superparamagnetism, which assumes temperature-independent particle volumes, can be explained quantitatively by the interface effect. In particular, a corresponding analysis of initial susceptibility data taken on 2 Fe-24 Ni-74 Cu as aged at 873°K yields for the interface thickness Δρ of spherical precipitates, in the size range between 19 and 45 Å in radius, the value Δρ≃12.3 Å.

It is suggested that the analysis of magnetic data, as outlined in this paper, may be utilized to determine concentration profiles of precipitates in suitable alloy systems.
Optical Inhomogeneities in Gallium Arsenide
Authors: Drougard M. E.
Published: April 2005

Slices of pulled, n-type gallium arsenide crystals containing the growth axis have been examined in transmission using an infrared image converter. Under conditions of parallel illumination some samples exhibit a pattern of alternating dark and bright lines, whose spacing is sometimes equal to the length of crystal pulled during a rotation of the crucible and generally smaller. The visibility of these growth striations is shown to be due to periodic variations of the real part of the refractive index, arising from periodic variations of the width of the optical energy gap or of the free-carrier concentration. In very highly doped samples the band-gap changes are associated with a varying Burstein shift, largely compensated by a corresponding shrinking of the gap. In undoped crystals contaminated by silicon, carbon, or aluminum the band-gap changes can be ascribed to an alloy effect.

Other inhomogeneities seen in transmission include strains (using polarized light), p-n and n-n junctions, a mottled appearance in boat-grown crystals and unidentified defects in epitaxially deposited layers.
Discharge Figures in Dielectrics by Electron Irradiation
Authors: Furuta Junichiro , Hiraoka Eiichi , Okamoto Shinichi
Published: April 2005

The electrical breakage of glass shielding windows by intense gamma irradiation presents a severe problem for hot caves. To understand this phenomenon the authors studied the discharge conditions, their natures, and the decay of the accumulated electric charge by electron irradiation. The samples used were lead glass F62-R, nonbrowning lead glass F36-N, nonbrowning glass C-N, common window glass, polymethylmethacrylate (PMMA) and polyvinylchloride (PVC). Their specific gravities were 6.2, 3.6, 2.7, 2.5, 1.2, and 1.4 respectively. The samples were discharged by a steel needle pricking the surface prior to, or after, irradiation. The 2-MeV Van de Graaff generator and 15-MeV Linac were used in these experiments. The relation between irradiation doses and the largeness of discharge pattern in the samples and the decay of the discharge pattern after irradiation are described. The times in which the initial stored charge became its half-value were 30 min for PMMA, 70 h for PVC, 8 h for C-N and 90 h for F36-N.
Germanium Films as Thermal Elements in Heat-Transfer Gauges
Authors: Moeller C. E. , Metz F. I.
Published: April 2005

The results of Seebeck coefficient determinations on germanium film vacuum-deposited on a Vycor substrate are given. The apparatus for the determinations is described. The structure and orientation as obtained by a diffractometer is indicated for each of several films of various thicknesses.
Effect of the Thermal Population of the (000) and (100) Conduction Bands on the Elastic Constants of Heavily Doped n-Type Germanium
Authors: Csavinszky P.
Published: April 2005

The effect of the thermal population of the (000) and (100) conduction bands on the elastic constants of heavily doped n-type Ge is investigated. The theory predicts changes with doping (relative to pure Ge) in all three elastic constants: c44, C′=(1/2) (c11−c12), and B=(1/3) (c11+2c12). The changes in the shear elastic constant C′ and bulk modulus B gradually disappear when the temperature becomes low enough to allow the depopulation of the higher lying bands while the change in c44 becomes identical with that predicted theoretically and verified experimentally by others. The magnitude of C′ as a function of temperature is estimated and found to be within the range of sensitivity of present day ultrasonic techniques. From measurements of the changes in C′ at different temperatures it is possible to determine the effective mass and the magnitude of the shear deformation potential constant associated with the six (100) minima. Measurements of the changes in B at different temperatures lead to two sets of dilatational-compressional deformation potential constants associated with the (000) and (100) minima depending on what sign is assumed for the shear deformation potential constant of the (100) band.
Generation-Recombination Noise in Ge Single Crystals under Fast-Neutron Irradiation
Authors: Bilger H. R. , McCarter E. R.
Published: April 2005

Experimental results are reported on the Fourier spectra of generation-recombination (g-r) noise of Ge single crystals, using a reversible technique to vary the noise parameters. Namely, a comparison is made with the noise before irradiation, after irradiation with 14.7-MeV neutrons, and after annealing. Reasonable agreement was obtained with the theory based on a three-level recombination with a single (Shockley-Read) level in the forbidden band.
Yield-Point Phenomenon in Impact-Loaded 1060 Aluminum
Authors: Barker L. M. , Butcher B. M. , Karnes C. H.
Published: April 2005

Experiments are described in which flat plates of 1060 aluminum were impact loaded by similar plates at velocities up to 36 m/sec. The resulting elastic and plastic wave shapes were observed after they had traveled 25 mm through the material. It was found that the stress in the so-called elastic wave rose to a peak and then unexpectedly decreased before the following plastic wave again increased the stress toward its maximum value. The relation of the overshoot in stress to dislocation motion is discussed.
Photovoltage Measurements on an Al-Al2O3-Al Thin-Film Sandwich
Authors: Schuermeyer Fritz L.
Published: April 2005

The photovoltage of an Al-Al2O3-Al thin-film sandwich with an Al2O3 layer of 60 Å was measured as a function of wavelength and incident light intensity; a potentiometer-type technique was used to eliminate the distortion of the photovoltage by the dark current. Photocurrent measurements were performed using chopped light and synchronous detection. From these measurements barrier height and barrier shape of the Al2O3 insulating film were determined. The measurements indicate that photocurrents flow simultaneously in both directions between the electrodes and, in addition, that the attenuation of the hot electrons in the insulating film used is not less than 60 Å.
Inhomogeneities in Optical Crystals Resulting from Nonplanar Solid-Melt Interface during Growth
Authors: Nester James F.
Published: April 2005

An approximate two-dimensional model is presented which shows that nonunique growth directions along a nonplanar interface can lead to significant variations in the actual growth rates along the interface. Such growth-rate variations can be the source of appreciable chemical inhomogeneity in directions normal to the mechanically imposed crystal growth direction. Numerical estimates are made for the magnitude of this radial chemical gradient in CaWO4:Nd3+ crystals under typical growth conditions and with hemispherically shaped solid-melt interfaces during growth. These estimates are in good agreement with the measured optical quality of typical CaWO4:Nd3+ crystals in which laser beam divergences of at least 10 times the diffraction limit for a 7-mm aperture are common.
Giant Pulse Shortening by Resonator Transients
Authors: Roess Dieter
Published: April 2005

A method for giant pulse shortening by oscillator transients is proposed, where giant pulses are used to pump a secondary laser oscillator with suitable absorption bands. Further shortening is possible by combination with a saturated amplifier, which too is pumped by the primary pulse. Materials of high transition probability are favorable for this scheme; ruby-YAG:Nd3+ seems well suited.
Electrical Oscillations in Silicon Compensated with Deep Levels
Authors: Moore J. S. , Penchina Claude M. , Holonyak Nick , Sirkis M. D. , Yamada T.
Published: April 2005

Recent studies of electrical oscillations in silicon compensated with deep lying impurity levels are described. Factors affecting these oscillations such as sample resistivities and geometrical configurations, field strengths, current densities, and illumination are discussed. It is found that there are two possible oscillation mechanisms.
X-ray Study of Ternary Ordering of the Noble Metals in AgAuZn2 and CuAuZn2
Authors: Muldawer L.
Published: April 2005

X-ray measurements of the ternary long-range order (LRO) of noble metals in AgAuZn2 and CuAuZn2 have been obtained using a high-temperature diffraction camera. The behavior of the LRO parameter S as a function of temperature is similar to that in β brass; the order disappears gradually as the temperature is raised. However, S lies above that obtained for β brass when plotted as a function of T/Tc, Tc being the critical temperature for disordering. X-ray Debye temperatures of 210°K for CuAuZn2 and 200°K for AgAuZn2 were obtained; these are in good agreement with expected values. The ratio Tc/Tm (Tm is the temperature of melting) was found to range from 0.56 to 0.58 in agreement with the correlation observed by Oriani. A simple distance dependence of the interaction energy between the noble-metal atoms cannot be used to explain the observed Tc's. Data for Tc and Tm of AgAuCd2 are also included.
Space-Charge Polarization in Glass Films
Authors: Snow E. H. , Dumesnil M. E.
Published: April 2005

It is shown that electrical polarization effects in glass films can be conveniently studied using a metal-glass-silicon dioxide-silicon double-layer capacitor. The buildup of a polarization in the glass layer under the application of a voltage at elevated temperatures can be detected from the resulting shift ΔV in the capacitance-voltage characteristic. Equations are derived on the basis of a simple model which gives ΔV as a function of time, temperature, applied voltage, and the glass and oxide thicknesses.

Experimental data for a lead borosilicate glass are presented and shown to be in excellent agreement with this model. The time constant for polarization of the glass has an activation energy of 1.05 eV and is of the order of weeks at room temperature and minutes at 100°C. The diffusion coefficient calculated from this time constant is in agreement with that for lead in glasses of similar composition and hence it is concluded that in this glass the major mobile ion is Pb++.

Additional long-term polarization effects are observed when the metal is biased positively and these are related to the diffusion of sodium contaminant out of the glass layer into the underlying silicon dioxide.
Some Efficiency Measurements of the Theta-Pinch
Authors: Silberg P. A.
Published: April 2005

A calorimeter technique has been developed to measure the transfer efficiency of the theta-pinch in converting capacitively stored electrical energy to plasma energy. Circuit-decay measurements show that the efficient theta-pinch circuit decay consists of a two-stage circuit decay and that the inefficient theta-pinch consists of a three-stage decay. With the use of the circuit decay data, a modified transfer efficiency measurement technique has been developed for a two-stage decay which is approximately as accurate as the calorimeter technique and very much quicker and easier to make. Measurements have been made to evaluate the transfer efficiency of the theta-pinch in argon at pressures of 2 and 5 Torr with different tube sizes and with different coupling impedances. These measurements show that within the present range of parameter values a transfer efficiency as high as 59% is possible.
Effect of Thermal-Neutron Irradiation on the Superconducting Properties of Nb3Al and V3Si Doped with Fissionable Impurities
Authors: Bean C. P. , Fleischer R. L. , Swartz P. S. , Hart H. R.
Published: April 2005

The superconducting critical temperatures and current carrying capacities of Nb3Al and V3Si doped with small amounts of uranium and boron and subsequently irradiated with thermal neutrons are reported. While the critical temperatures are substantially unaffected, the critical current densities are dramatically increased by the internal fission of uranium in both materials. Samples of Nb3Al containing 0.321 at.% uranium and V3Si containing 0.19 at.% uranium irradiated with 1.7×1018 neutrons/cm2 give superconducting critical current densities over 106 A/cm2 at 30 kOe. The boron-doped samples, however, showed no effects arising from fission of boron. Two new experimental techniques have been used in this investigation. First, uranium and boron analyses as well as information on homogeneity were determined by use of the Price-Walker nuclear track detectors. Secondly, the critical current measurements were made on 50-mg samples of 70-μ powders by a technique that measures the generation of odd-harmonic voltages caused by small alternating magnetic fields applied to the sample.
Strain in Thin Metal Films on Quartz
Authors: Haruta K. , Spencer W. J.
Published: April 2005

From x-ray diffraction intensity measurements it is possible to evaluate strain gradient in a single crystal. Transmission diffraction techniques were applied to investigate strain in the film evaporated on a quartz plate. Topographs showed qualitatively the locations of high strain gradient. Quantitative measurements were made through the thickness of the plate with a narrow well-collimated x-ray beam and a scintillation counter. It was found that the strain gradient was high at the film edge on the surface of the crystal plate.
Influence of Electric Field on the Growth of Thin Metal Films
Authors: Chopra K. L.
Published: April 2005

It has been found that an electric field applied in the plane of a metal film during deposition induces coalescence of the three-dimensional island-like structure at an earlier stage of the film growth than is obtained without the field. The surface area of the three dimensional islands is increased under applied electric field. The critical thickness, at which the electrically continuous film is obtained, decreases with the increase of electric field. The decrease is more rapid at higher substrate temperatures. Enhanced orientation effects and fewer structural defects have been observed in films deposited under applied field and are attributed to the recrystallization during induced coalescence.

The observed short range order in the coalescence pattern indicates that the applied field transfers and redistributes the electrostatic charges on the islands. It is shown that the presence of a small number of electrostatic charges increases the surface energy and thus the surface area considerably. The electrostatic forces between two islands which either come very close to each other or carry significantly different charges of either polarity are predominantly attractive and are of sufficient magnitude to account for the physical merger. Coalescence as well as breakup of metal islands due to the presence of electrostatic charges on them have been observed on suitably prepared single-crystal lead films irradiated with the imaging electron beam inside an electron microscope.
Mechanism of Electron Trapping in Silver Bromide Photographic Grains
Authors: Brady L. E. , Hamilton J. F.
Published: April 2005

The temperature dependence of the electron lifetime and of the time for decay of an internal applied electric field in the silver bromide microcrystals of a simple photographic emulsion has been measured by the technique employing flash exposure of the emulsion in pulsed electric fields. Activation energies were found to be 0.236±0.012 eV for the electron lifetime and 0.245±0.008 for the field-decay time. The agreement of the temperature dependence of the two processes, together with the observation that the room-temperature values of these two times are, without exception, nearly equal in measurements made on a variety of other emulsions, supports the hypothesis that the mechanism of permanent electron-trapping involves the motion of the silver ion to a temporarily trapped electron to form a stable center. These results are not consistent with the alternative suggestion, namely, that the electron is captured at a preexisting deep trap consisting of a silver ion associated with a crystal imperfection.
Vacuum Evaporation of β Ag2Te
Authors: Dalven Richard
Published: April 2005

The evaporation of β Ag2Te in vacuum has been studied. It is concluded that β Ag2Te dissociates on heating and that deposits of this compound produced by evaporation are formed by diffusion and reaction on the substrate.
Large Wavelength Changes with Cavity Q in Injection Lasers
Authors: Dousmanis G. C. , Staebler D. L.
Published: April 2005

Changes in the cavity Q of GaAs lasers, aside from changing the threshold, cause large changes in the laser wavelength. The wavelength changes by about ±0.6 percent when the threshold is varied by a factor of two to three by changing the surface reflectivity. For comparable fractional changes in Q (or threshold) the wavelength changes are larger at 300°K than at lower temperatures. The wavelength dependence on Q is specific to semiconductor lasers and is based on the continuous nature of the energy levels involved in stimulated emission. The wavelength shifts are theoretically related to the changes in Q using the ``band-filling'' model and an expotential density in ``tail'' states. Fair agreement with the data is obtained at low temperature as well as at 300°K. The wavelength shift with Q in conjunction with changes in the shape of the threshold vs temperature curve, leads to a correction to the usual relation between threshold and losses. The wavelength dependence on Q can be used for frequency control and possibly for frequency modulation.
Internal Fracture Caused by Focusing of Explosive Waves
Authors: Hsiao C. C. , Moghe S. R. , Soong C. K. , Yin W. L.
Published: April 2005

Experimental success in reflecting and focusing explosive waves and thus fracturing the neighborhood of a focus in a prolate spheroid is obtained. The shape and size of the internal fracture is essentially spherical whose volume ranges from a pinpoint to several millimeters in diameter. On the basis of a simple consideration of the transmission of elastic strain energy, corresponding sizes of fracture can be analyzed and estimated. Comparison of the theoretical results with experimental data indicates that the strain energy transmitted is directly proportional to the amount of explosive charge used.
Elastic Explosions in Solids Caused by Radiation
Authors: Bullough R. , Gilman J. J.
Published: April 2005

If intense radiation (coherent light, secondary ionization, or sustained fission) is put into a solid in a time δ short compared with the elastic relaxation time, a resulting internal ``explosion'' may cause multiple fracturing and other damage. We postulate that at t=δ≃0, the radiation causes a uniform dilation within a cylindrical region of radius a. Solution of the relevant wave equation (continuity preserved at r=a) indicates that a rarefaction wave of increasing amplitude moves inward from a with velocity v during the time interval, 0<t<a/v. The transient pressure variation at the center demonstrates a negative divergence at t=a/v. The pressure field at various times has been found by numerical integration. This model accounts for some features of the damage caused by laser beams and other damage processes.
Low-Energy Electron Diffraction Study of the Cleaved Surfaces of PbS, PbSe, and PbTe
Authors: Johnson D. C. , Rae A. U. Mac
Published: April 2005

Low-energy electron diffraction was used to study the cleaved surfaces of PbS, PbSe, and PbTe for the purpose of obtaining information about the factors that influence the intensities of the diffracted beams. The addition of the successively heavier anion in the three compounds produced no significant changes in the intensities that could be attributed to the atomic scattering factors of the anions. Prominent features in the dependence of the intensity of the diffracted beams on the energy of the incident electrons are attributed to multiple scattering. The structure of the surfaces in two dimensions parallel to the surface is the same as the (001) substrate planes. A complete analysis of structure normal to the surface is prevented by strong multiple scattering. Single scattering events are identified at low energies by measurements on the angular dependence of the intensities.
Velocity Measurement of a Magnetically Induced Arc ``Wind''
Authors: Weichel Hugo
Published: April 2005

In agreement with earlier observations, an arc discharge in a transverse magnetic field was found to be always accompanied by a high-velocity gas flow in the j×B̄ direction. By means of a temperature probe and a calibrated dragmeter the velocity of this arc wind was measured for several magnetic fields and various distances above the arc path. The maximum velocity was found to be between 3.5×103 and 7.0×103 cm/sec for magnetic fields of 520 and 2000 G, respectively.