bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrostatic Probe Determination of Electron Density in Medium Pressure (0.2–28 Torr) Discharge Plasma of Argon
Authors: Chen Sin-Li , Chang Jen-Shih , Matsumura S.
Published: February 2004

The validity of electron-density determinations using spherical probe in medium pressure discharge plasmas (rp/λe∼0.3 to 40, where rp=probe radius, λe=electron mean-free path) are examined for density range Ne=109−1011 cm−3. Various collision-dominated probe theories are used to obtain Ne from both electron and ion saturation currents (Ie and Ii). Ne determined from Ie coincide reasonably with those determined from microwave measurement, while Ne from Ii are always greater than those from microwave measurement by a factor of 2 to 100. The discrepancy increases with increasing gas pressure and total discharge current, and Ii can not be used for Ne determinations. There is ``break'' on the ion current characteristics which is the same as that reported in the measurement of very low-density flowing afterglow plasmas (Ne<108 cm−3). Explanation is offered in connection with the unusual increase of ion current caused by the release of electrons from the probe surface by collisions of metastables and the decrease of regular thermal-motion current because of the short mean-free path condition (λ6<rp).
Proton Sputtering of Gold
Authors: Furr A. Keith , Finfgeld C. R.
Published: February 2004

Sputtering of gold by normally incident protons of energies between 500 eV and 8 keV has been studied. An ion source system delivering a magnetically analyzed proton beam to a target at a pressure of 5×10−8 Torr was utilized, and neutron activation established the quantities of sputtered material. The gold targets, consisting of microcrystals with preferred orientation, were sputtered predominantly on (100) and (110) planes, and the yields were not observed to depend perceptibly on the crystal orientation. The yield was a maximum of 0.022 atoms/proton at a proton energy of 4 to 5 keV, dropping off gradually at higher energies and sharply at lower ones. Analysis of the sputtered deposit spot patterns, using autoradiographs, indicated that focused collision sequences were of greater importance in proton sputtering than in sputtering by heavier ions. A readily detectable yield for sputtering by 500-eV protons suggests a minimum atomic ejection energy of less than 10 eV for sputtering of gold.
Field-Induced Photoelectron Emission from p-Type Silicon Aluminum Surface-Barrier Diodes
Authors: Itoh T. , Matsuda I. , Hasegawa K.
Published: February 2004

The diode bias dependence and the spectral response of the external emission of photo-induced conduction electrons have been investigated experimentally and analytically for reverse-biased surface-barrier diodes. An anisotropy has been observed in the diode bias dependence. Variation of the mean-free path of hot electrons with impurity densities in silicon is suggested by comparing the experimental result with the analytical one.
Fracture Surface Energies and Dislocation Processes during Dynamical Cleavage of LiF. II. Experiments
Authors: Burns S. J. , Webb W. W.
Published: February 2004

The dynamics of cleavage of long slender single crystals of LiF has been observed with high-speed ciné-photography in order to measure the surface energy and the dislocation processes in a propagating semiplastic crack. The fracture surface energy deduced from these observations could be separated into two parts, a reversible thermodynamic surface energy and a contribution due to dissipative plastic deformation, using the theoretical analysis given in Part I of this series. A specific reversible surface energy of 480±50 erg/cm2 was obtained and the plastic contribution was found to persist to fracture velocities > 104 cm/sec. Dislocation mechanisms of dissipation persisting to very high crack velocities and to temperatures as low as 90°K were deduced from studies of etch-pit patterns and atomic step structures on the cleaved surfaces. The atomic step structures were observed by imaging in the electron microscope replicas of eptiaxial metal deposits grown from the vapor at the step sites. The plastic flow processes were found to be consistent with the theory of Part I and the observed magnitude of the plastic contribution to the surface energy.
Radio-Frequency Floating Double Probe as a Plasma Diagnostic
Authors: Oliver B. M. , Clements R. M. , Smy P. R.
Published: February 2004

A floating double probe operating at radio frequencies in the MHz range has been developed to the point where measurements of sheath capacitance and resistance yield values for plasma ionization density and electron temperature with an accuracy of ≈8% and ≈16%, respectively. The experimental technique used supersedes previous methods in that it enables sheath capacities as low as 10−2 pF to be measured. The analysis of the results has been extended to cover the important nonplanar (cylindrical) sheath case. As a result of these two developments, the technique is now applicable to small diameter probes which are essential for measurements in most gas discharge plasmas. The performance of the probes has been checked over a range of plasma densities and working frequencies and has been found to give results which are in good agreement with microwave cavity and dc probe measurements. This type of measurement has various advantages over the usual dc probe methods in terms of complete isolation, but it is expected that its main application will be in situations where the use of the dc probe is suspect due to probe surface contamination effects.
Trapping and Thermal Release of Noble Gases at a Nickel Surface
Authors: Truhlar John F. , Donaldson E. E. , Horne D. E.
Published: February 2004

The trapping and thermal reemission of 100–300-eV Ar+ and Kr+ ions at a polycrystalline nickel target have been studied. For Ar+ and Kr+ the trapping probabilities are, respectively, 0.020 and 0.015 at 100 eV and 0.46 and 0.33 at 300 eV. A continuous temperature increase of the target releases trapped argon discontinuously by thermally activated processes at temperatures corresponding to activation energies of 1.12, 1.31, 1.48, 1.67, 1.83, and 2.13 eV. These energies are compared with activation energies which are determined by others for the removal of defects resulting from radiation damage or cold working of nickel. The lowest three energies are believed to be correlated, respectively, with interstitial migration, vacancy formation, and vacancy migration near the surface. The highest energy may be due to surface recrystallization from dislocations produced by the ion bombardment. The intermediate energies probably correspond to the motion of nickel surface atoms along the ridges of facets formed during the bombardment.
Nucleation of Gold on Muscovite Mica
Authors: Morris W. L. , Hines R. L.
Published: February 2004

The nucleation rate of gold on the cleavage face of muscovite mica in UHV was studied as a function of substrate temperature for 403°–515°K and of impinging flux for 0.6–1.8×1013 cm−2 sec−1. This range of substrate temperature and flux values was selected to yield growth conditions consistent with analysis of the nucleation rate data in terms of the atomistic nucleation theory of Walton. Gold was evaporated from a wire maintained at a temperature below the gold melting point and positioned near the mica substrate so that various regions on the mica were exposed to different fluxes with accurately known relative values. The mica was subsequently thinned and examined by transmission electron microscopy to determine the initial nucleation rate. The low-temperature nucleation rate data gree reasonably well with the atomistic nucleation theory of Walton, while the high-temperature data show two peaks in nucleation rate.
Neutron Diffraction Study of the Pseudobinary System ErCo2–ErAl2
Authors: Oesterreicher H. , Corliss L. M. , Hastings J. M.
Published: February 2004

Results obtained by neutron diffraction indicate that the magnetic moment of the ferromagnetic sublattice in the Laves phase structures, C15 (ErCo2, ErAl2) and C14 (ErCoAl), varies with composition while the ordering temperatures stay approximately constant. Low values of the aligned moment, however, are accompanied by high values of the disorder scattering at low temperatures. Co carries no moment from 30 mole % ErAl2 on. Results are discussed in terms of tendencies toward antiferromagnetism at certain values for the valence electron concentration.
Effect of Pressure on Work Hardening of OFHC Copper
Authors: Abey A. E.
Published: February 2004

In this work OFHC copper disks were sheared under pressures of 21.4, 36.7, 50.5, and 62.6 kbar. Torque strain curves were taken for strains from 0.10 to about 18.0. The flow stress was noted to increase approximately as the strain to the one-half power. The yield stress at zero pressure was determined, as was the pressure derivative of the yield stress. The effect of pressure on work hardening was measured by determining how the change in slope of the work hardening curves varies with pressure. A qualitative explanation is given for one possible process which could give the experimental results.
Dependence of Second Harmonic Generation on Crystal Inhomogeneity
Authors: Tsuya Hideki , Fujino Yoshio , Sugibuchi Kiyoshi
Published: February 2004

Effect of the nonuniformity of the natural birefringence in a nonlinear crystal on second harmonic generation (SHG) is theoretically and experimentally studied. The second harmonic power at the phase-matching temperature, the second harmonic power vs temperature, and the temperature bandwidth are calculated in terms of the gradient of the natural birefringence and compared with those from the SHG experiment using a cw Nd:YAG laser and Ba2NaNb5O15 single crystal. It is found that the second harmonic peak power is much depressed by the nonuniformity of the natural birefringence in a crystal. The oscillations in the second harmonic power vs temperature curve become broad and the temperature bandwidth increases with decreasing crystal homogeneity. Satisfactory agreement was obtained between theory and experiment. By analytical calculation the dependence of SH power on crystal length l, is expressed in terms of the inhomogeneity length li, which is defined as a measure of the length beyond which SHG is limited by the crystal inhomogeneity. It is found that in an inhomogeneous crystal the SH power does not vary with length as l2 but decreases by the factor (1−l2/6li2).
Collisional Damping of Plasma Oscillations
Authors: Bogdanor John L. , Willett Joseph E.
Published: February 2004

An analysis of electrostatic oscillations in a weakly ionized plasma is based on the Boltzmann-Vlasov (BV) equation with electron-neutral collisions accounted for by a simplified form of the Lorentz-gas Boltzmann-collision integral. The isotropic scattering contribution to the collision integral is treated exactly while the anisotropic scattering contribution is approximated by assuming a weakly anisotropic electron velocity distribution. The collisional damping decrement is found to be equal to −ν1/2+3ν1k2v t2/ωp2− (11/3)ν2k2vt2/ ωp2 to second order in the wave number k where vt is the electron thermal velocity, ωp is the plasma frequency, and ν1 and ν2 are precisely defined averages of the collision frequency for momentum transfer. An alternative method of analysis based on the simultaneous used of the BV equation and the moment equations is also illustrated.
Long Lifetime (Laser) States in p-Type Si-Doped GaAs
Authors: Craford M. G. , Herzog A. H. , Holonyak N. , Keune D. L.
Published: February 2004

Recombination lifetime measurements on Si-doped GaAs light-emitting diodes and on similarly doped p-type thin platelets are presented. These data, in conjunction with earlier work, show that radiative recombination transitions with lifetimes as long as 10–100 nsec can be made to lase.
Low-Frequency Variance Noise
Authors: Brophy James J.
Published: February 2004

Variance fluctuations in 1/f noise examined with apparatus capable of responding to zero frequency signals are found to have the same magnitude as those in band-limited 1/f noise signals. The distribution of variances in identical sample lengths is skewed to small values in the case of current noise in a carbon resistor and is symmetrical in the case of current noise in a germanium p-n junction. The probability amplitude is normally distributed in all samples investigated, from 10 to 2400 sec long. Both the average variance and the variance of the variance are found to increase as the logarithm of the sample duration.
Anisotropy of the Microwave Conductivity in Polar Semiconductors
Authors: Huber F. , Kopetz H.
Published: February 2004

The disturbance of the distribution function of hot electrons due to a microwave field directed parallel or perpendicular to a steady electric field is calculated considering the interaction of electrons with electrons, polar optical phonons, and impurities. The small-signal microwave conductivity of n-InSb is calculated and compared with experiments at 33 GHz as well as with results obtained by a previously published simpler approach.
Deformation and Fracture of Zinc Oxide Whiskers
Authors: Sharma Ram Bilas
Published: February 2004

Deformation and fracture behaviors of ZnO whiskers were investigated by the performance of tensile, compressive, and bending tests. The whiskers could be elastically strained to as much as 15% in bending without undergoing fracture or plastic deformation. They are generally brittle, except in a few cases. Results of compression tests show that slip may take place on the basal plane as well as on the prism plane. In a tensile test a specimen is found to undergo shear along pyramidal planes. Besides the usual planar fracture, a specimen, when failed in tension, showed cup-and-cone fracture, which is a feature of ductile materials. On the basis of the available evidence it is suggested that cup-and-cone fracture may not be a feature of ductile materials only; it may occur, as in the present case, in brittle materials, with perhaps a different mechanism.
Crystallographic Study of the Low-Temperature Phase Transformation in V3Si and Nb3Sn
Authors: Wanagel J. , Batterman B. W.
Published: February 2004

The cubic-tetragonal phase transformation in V3Si and Nb3Sn has been investigated dynamically with optical and x-ray techniques. For Nb3Sn a simple shear on the {110} 〈11̄0〉 completely describes the lamellar morphology in the tetragonal state. The lamellar structure and associated shear are concluded to arise from an accommodation of internal stresses and are a result of, not a mechanism for, the transformation. All our observations are consistent with a continuous transformation from the cubic to tetragonal state with no evidence of hysteresis or the coexistence of the two phases.
Fingero-Imbibition in Slightly Dipping Porous Medium
Authors: Verma A. P.
Published: February 2004

An analytical discussion of a theoretical model of Fingero-imbibition in a cracked porous medium, of small inclination, is presented in this paper. The phenomenon is assumed to occur in a double-phase displacement process involving two immiscible liquids of small viscosity difference in which the injection is initiated by imbibition and the consequential displacement of the relatively more viscous native liquid produces fingers. The nonlinear differential system governing this phenomenon is mathematically formulated and an approximate solution, using a perturbation technique, has been obtained.
Frequency Shifting of a Gaussian Light Beam by Ultrasonic Surface Waves
Authors: Hallermeier Robert J. , Mayer Walter G.
Published: February 2004

A theoretical treatment of the diffraction of a monochromatic Gaussian light beam by reflection off a single-frequency ultrasonic surface wave is presented. With a suitable incident-light-beam diameter a discrete diffraction pattern is formed. The form and the frequency spectrum of the light in the pattern are stated in detail for the limiting case of small-sound-beam intensity. A description is given of experiments which verify the theoretical predictions.
Effects of Size, Shape, and Frequency on the Antiferromagnetic Resonance Linewidth of MnF2
Authors: O'Brien Kevin C.
Published: February 2004

Experimental measurements of the antiferromagnetic resonance in MnF2 at 4.2°K have been made as a function of microwave frequency and sample size and shape. Measurement frequencies ranged from 100 to 305 GHz. The experimental data have been analyzed with the aid of a newly derived electrodynamic treatment of the experimental arrangement combined with a molecular field theoretic calculation of the rf permeability tensor for MnF2. Agreement between experiment and theory is good using only a one-parameter fit. It was found that the linewidth is not strongly frequency dependent in very good samples except at frequencies very near to or very far from the zero-field resonance frequency. The effect of sample size on observed linewidth is very significant. A value of 90 Oe is given for the residual size-independent linewidth. Experimental aspects are emphasized due to the extremely high frequencies employed.
Noise Analysis for Amplifiers with Superconducting Input
Authors: Radhakrishnan V. , Newhouse V. L.
Published: February 2004

A method is developed to adapt the conventional definition of the noise temperature to amplifiers with superconducting inputs. In particular this method is applied to a crossed-film cryotron amplifier with a superconducting input to calculate its noise temperature. We then compare it with that of other amplifiers and masers. In addition to the noise temperature, a new criterion is evolved here: to estimate the figure of merit of amplifiers and detectors. This involves a new parameter called herein the action factor, which is the product of the smallest energy measurable by a device, with its smallest possible response time. The action factor and the noise temperature are worked out for the cryotron and a few other amplifiers and detectors for comparison. The advantage of the cryotron amplifier is brought out.
Design Features of ac Superconducting Cables
Authors: Long H. M. , Notaro J.
Published: February 2004

Alternating current superconducting cables which can be readily integrated into utility systems require both a superconductor with low characteristic ac losses and a high-performance cryogenic system to minimize the cost of heat pumping the thermal losses to the atmosphere. Moreover, the resulting cable systems must operate with the long-term reliability expected of utility systems. Recent publication have treated the measurement of the superconducting material properties and the conceptual electrical and cryogenic design for a superconducting cable. This paper will discuss a cable configuration and examine its electrical and cryogenic design features with principal emphasis placed upon the relationship of these features with present technological capabilities. Fabrication and installation feasibility and the expected levels of performance and reliability can be inferred from the practical operating cryogenic systems which are used as a guide for the selection and design of the cryogenic enclosure for the cable.
Precipitation and Hardening Behavior of Czochralski Star Sapphire
Authors: Bratton R. J.
Published: February 2004

Sapphire with 0.11-wt% titania in solution (mainly as TiO1.5) was aged isothermally in air up to 21 days at 1100°–1600°C. Optical studies showed that the solubility limit of the titania was exceeded at 1400°C in air, and consequently needle-shaped precipitates were developed. For aging temperature between 1100° and 1300°C, precipitation initiated at grown-in dislocations and at subboundaries. This phenomenon was attributed to rapid oxidation along these defects. Following this initial stage, precipitates formed uniformly throughout the crystals, and they coarsened with time. The variation of average needle length with time was measured. Knoop microhardness measurements showed that Ti4+ ions plus the attendant defects in solution caused measurable hardening of sapphire, but the greatest changes resulted from precipitation. Significant hardening resulted from aging at 1300°C for 13 days. The hardness anisotropy in the basal plane of sapphire, i.e., KH〈101̄0〉>KH〈112̄0〉, was not altered by precipitation.
Tracer Diffusion of Lead in Lead Telluride
Authors: George T. D. , Wagner J. B.
Published: February 2004

Using radio-tracer 210Pb, the diffusion of lead has been studied in PbTe at 700°C as a function of composition and doping level. The results indicate that the predominant cation defect is of the Frenkel type.
Distribution Patterns of Strain and Dislocations Around Indented Areas in Germanium Crystals as Observed by X-Ray Topography
Authors: Wagatsuma Ryugo , Sumino Koji , Uchida Wakio , Yamamoto Soichi
Published: February 2004

Three-dimensional distribution patterns of the strain and dislocations developed around indented areas in germanium crystals are observed as a function of the deformation temperature between 20° and 700°C by use of x-ray diffraction topography. The size of the deformed region around an indented area is found to have a relationship with the hardness value, i.e., the former begins to increase abruptly at the temperature where the latter begins to decrease abruptly as the deformation temperature is raised. The areas indented at high temperatures are subjected to two kinds of treatments: One group of areas is brought to room temperature after indentation while an indenter load is applied, and the other is cooled after an indenter load has been removed. Rearrangement of dislocations takes place during annealing of specimens. Annealing brings about a configuration of dislocations lying parallel to 〈110〉 directions.
Short-Range Interactions Between Two Parallel Dislocations
Authors: Haviland G. P. , Ono Kanji
Published: February 2004

An analytical model of the dislocation core is proposed. The center of a crystal dislocation in this model is represented by a continuous distribution of infinitesimal dislocations, whose distribution function incorporates the atomic configurations of dislocations as determined by Cotterill and Doyama using a many-body-crystal model of copper. The distribution functions used have the same form as the Peierls model except the width parameter, which is about twice that of the original Peierls model. Using the present model and methods of the continuum theory of dislocations, numerical calculations are made for the interaction energies between two parallel screw and two parallel edge dislocations. The results are significantly different from those predicted by the classical theory when the separation distance is less than ten atomic distances. Approximate expressions for the interaction energy between two coplanar edge dislocations and for that between two coplanar screw dislocations are obtained. The magnitudes of both the interaction energy and interaction force remain finite in the present model, enabling the unique determination of the self-energies of single dislocations and edge dislocation dipoles. Dislocation splitting in fcc metals is also discussed.
Detonation of Explosive Slabs of Finite Dimensions
Authors: Crouch Margaret R. , Hoskin N. E.
Published: February 2004

Results of two-dimensional calculations on the detonation of slabs of high explosive of finite dimensions are presented graphically. The effect of the side rarefactions from the free surfaces are shown and two methods of amelioration of these effects are demonstrated. In particular it is shown that the inclusion of metal fences suitably angled to the direction of detonation produces a large reduction in the side effects.
Reduced Hugoniots
Authors: Prieto F. E. , Renero C.
Published: February 2004

Complex variable methods are used to make a further exploration of the consequences of a quadratic fit to shock wave data in the velocity plane on the form of the Hugoniot. When complex pressures and compressions are introduced, the Hugoniot has three branch points. One of them is a critical point of multiplicity two and defines the separation between two branches of the Hugoniot. The other two are complex conjugates and their positions depend on a parameter involving the three coefficients of the quadratic fit. Reduced Hugoniots are defined for each material introducing reduced coordinates referred to the pressure and relative compression at the critical point; the form of these curves depends only on the parameter that determines the positions of the conjugate branch points. It is suggested that this parameter might probably be interpreted as a new property of all materials in solid and liquid phases. Polyurethane, cesium, water, and corundum are used as examples to show the agreement with experimental data. Some experiments are needed to test the validity of results at pressures higher than those available in the literature.
Multilayer Targets as a Diagnostic Tool for Laser-Produced Plasmas
Authors: Seka W. , Schwob J.-L. , Breton C.
Published: February 2004

A novel experimental method employing multilayer targets has been developed permitting a more detailed study of laser-produced plasmas through analysis of the spectrum emitted by a given layer as a function of its location. This method allows us to study the progression of the interaction phenomena into the interior of the target and to examine the plasma expansion phase. It could thus be demonstrated that the plasma produced at different depths within the target has essentially the same characteristic parameters and that the hot plasma region is delimited by very sharp gradients towards the interior of the target. In the expansion phase the importance of recombination phenomena has been well established up to certain limits beyond which our observations are compatible with the notion of freezing of the degree of ionization at closed-shell electron configurations in carbon and aluminum plasmas. A comparison of our experimental results with simple theoretical models is included.
Transition-Field Enhancement and Shape Effects Due to Magnetic Inclusions in a Superconductor
Authors: Lebeau C. , Pinel J. , Rosenblatt J.
Published: February 2004

Magnetization curves of spherical and cylindrical superconductors made of a fine suspension of Fe grains in Hg, have been measured. The experiments show strong effects on the transition field depending both on the magnetization of the ferromagnetic system and on the shape of the sample.
Mössbauer Studies of BiFeO3-PbTiO3 Perovskite-Type Solid Solutions
Authors: Yagnik C. M. , Gerson R. , James W. J.
Published: February 2004

The Mössbauer spectra of the ferroelectric solid solutions (BiFeO3)x(PbTiO3)1−x have been studied as a function of temperature, mainly between room temperature and 600°C, using 57Fe in the solutions as an absorber. The quadrupole splitting increased and the isomer shift decreased between x=0.05 and x=0.70, a range in which the solutions are tetragonal and paramagnetic, and in which the unit cell volume increases with increasing x. The isomer shift, in particular, was primarily determined by the unit cell volume. Data are presented on the internal magnetic field of the antiferromagnetic solutions in the rhombohedral phase between x=0.7 and x=1.0. The results demonstrate the similarity and continuity in internal structure between the ferroelectrics PbTiO3 and BiFeO3.
Electron Effective Mass in PbS Single Crystals by Infrared Reflectivity Measurements
Authors: Barton Claude F.
Published: February 2004

Infrared reflectivity measurements have been performed on a series of PbS single crystals. The temperature dependence of conductivity effective mass ms has been evaluated and used to compute the free-carrier mobilities. Results show how ms decreases as the crystal temperature decreases. Further results show how ms decreases as the carrier concentration decreases. The influence of crystal preparation on reflectivity properties has been studied. It has been determined that lead precipitates up to 1019 atoms/cm3 do not affect the minimum of the reflectivity curve but the homogeneity of the crystals does have a significant effect. Our determinations of conductivity effective mass of free carriers at each temperature have been used to compute the mobilities according to the two alternative theories of thermal vibration scattering, namely by acoustical and optical modes. Results show that the acoustical theory may not be used to predict temperature dependence of the mobilities, but that the optical polaron theory does give good predictions.
High-Field Superconductivity of Alloys in Porous Glass
Authors: Watson J. H. P.
Published: February 2004

Superconductors have been prepared by impregnating porous glass with low-melting-point alloys such as those in the Pb–Bi–Sb system. The critical fields of many alloys in porous glass with a pore diameter of 32 Å are in excess of 100 kOe at 4.2°K. Samples have been prepared having critical current densities near 105 A/cm2 in low (< 10 kOe) magnetic fields.
Density Sensor Utilizing Positrons
Authors: Gibson G. , Jennings B. , Johnston A. S. , Rowland J. W.
Published: February 2004

A positron source and detector of annihilation quanta are shown to form a fast response system that senses changes in its environment. Experimental results are presented to demonstrate that such a sensor can be used to measure gas densities. A particular densitometer design has been calibrated for air at room temperature over the pressure range 100-mm Hg<p<760-mm Hg, the particular pressure range being determined by the limitations of the vacuum chamber used in the calibration. The counting rate has been observed to vary linearly with pressure. Expressions are given for the sensitivity and the statistical uncertainty as a function of source strength, counting interval, and thickness of beryllium covering the source. Experimental results are also presented which demonstrate that the presence of a solid in the field of the positrons can be detected. The observed counting rate is a function of the distance of the solid from the sensor.
Asymmetric Light Diffraction from Nonsinusoidal Ultrasonic Surface Waves
Authors: Neighbors Thomas H. , Mayer Walter G.
Published: February 2004

The diffraction pattern produced by reflection of monochromatic light from an ultrasonic surface wave composed of a fundamental and higher harmonic frequencies is calculated for a Gaussian and a uniform light surface illumination. The diffraction pattern is found to be asymmetric with respect to the central order. This asymmetry is calculated from available diffraction data on LiNbO3.
Theory of Steady-State Evaporation of Alloys
Authors: Dale E. Brock
Published: February 2004

The theory of steady-state evaporation, which produces a vapor having the same composition as the alloy to be evaporated, is given. Equations are derived showing the composition of the evaporant, which is physically separated from the alloy feed, during the approach to steady state. The general case of N components is treated, and closed solutions are given for various special cases involving two, three, and N components with different vapor pressures. Illustrative numerical examples are given.
Phenomenological Model of Electret State in Carnauba Wax Inferred from Electrical Conduction Measurements
Authors: Caserta G. , Serra A.
Published: February 2004

Measurements of current-voltage charactristics, isothermal discharge currents, and thermally stimulated current have been used to clarify the mechanism of formation of electret state in Carnauba wax. The results of such measurements are interpreted with the aid of an energy band model in which a set of localized energy levels, located in the gap of energy bands, acts as charge carrier traps. The gap is about 7.4 eV wide. In the neighborhood of electrode contact the traps have a uniform energy distribution which extends as far as 0.3 eV from the edge of the bands. In the bulk of the material the energy distribution of trapping states becomes exponential and extends all over the gap. The charges (electrons and holes) have a double origin: the injection from the electrodes and a thermally activated process in which electron-hole pairs are produced. The homocharges arise because of trapping of the injected charges near the electrodes and the heterocharge because of trapping of electron-hole pairs in the bulk of the material.
Effect of Colloids on the Thermal Conductivity of γ-Irradiated KCl
Authors: Guenther R. A. , Weinstock H.
Published: February 2004

The influence of γ irradiation at 300 and 77 K on the thermal conductivity of KCl in the range 0.4–4 K has been investigated. The results have been interpreted on the basis of the scattering of phonons by localized defects of both the point and extended varieties. The analysis is consistent with a defect model proposed for irradiated KCl by Sonder et al. This model postulates the formation of interstitial chlorine atoms which aggregate to form (colloid) clusters whose size and number depend on the irradiation temperature of the crystal. Evidence of aggregates with an effective radius of 70 ± 5 Å has been found for three different single crystals (from two sources of supply) irradiated at 300 K. For a sample crystal irradiated at 77 K and measured after direct cooling to 4 K, there was a significantly larger decrease in conductivity suggesting the possibility of extended defects which disappear after a short annealing period at 300 K.
Thickness Dependence of Surface Coercivity in Polished Magnetic Oxide Platelets
Authors: Luff P. P. , Brosselard E.
Published: February 2004

Magnetic oxide platelets which have been prepared using abrasive polishing techniques can possess a high domain wall coercivity, Hc > 5 Oe, which renders them useless for device applications. The coercivity can be reduced by ion milling the platelet surfaces. The problem arises of how much material to remove to provide a useful device for a particular application. This paper describes the application of ion milling to investigate the thickness dependence of coercivity in Sm0.55 Tb0.45 FeO3 and YbFeO3 platelets. The etching rate used was 0.5μ /h/side and coercivities as low as 0.08 Oe for Sm0.55Tb0.45FeO3 and 0.4 Oe for YbFeO3 have been obtained after removal of a total of 9 μ of material from the platelet surfaces. A method for producing a guide channel for bubble domains is also described.
Comments on Homogeneous Nucleation Theory
Authors: Nishioka Kazumi , Pound G. M. , Lothe Jens , Hirth J. P.
Published: February 2004

Reiss, Katz, and Cohen's theory for homogeneous nucleation of liquid from vapor is reformulated by using the criticism of Lothe and Pound. It is concluded that P(0) in Reiss, Katz, and Cohen's result has to be replaced by 1/vcell. This gives a metastable equilibrium concentration of critical clusters 102–105 times larger than that predicted by Reiss, Katz, and Cohen for a typical case. The effect described has to do only with translation; the contribution from rotation of the cluster is still wholly ignored.
Properties of Gallium Arsenide Double-Injection Devices
Authors: Ferro Armand P. , Ghandhi Sorab K.
Published: February 2004

The characteristics of identically fabricated double-injection devices made from oxygen-doped and chromium-doped bulk gallium arsenide are investigated. All these devices exhibit a current-controlled negative resistance once a threshold voltage is reached. The oxygen-doped devices and the thin chromium-doped devices (less than 3 mil) exhibit an abrupt current-controlled negative resistance followed by filamentary current conduction; this behavior is caused by double-injection transit-time effects. The thick chromium-doped devices (greater than 3 mil) exhibit a gradual, current-controlled negative resistance unaccompanied by filament formation; this behavior is due to excessive power dissipation resulting from high threshold voltages. The characteristics of the double-injection oxygen-doped devices show that a current saturation occurs in the prebreakdown region under certain conditions. The characteristics of the chromium-doped devices exhibit no such current saturation, only superlinear behavior. It is established that the oxygen devices have a threshold voltage for breakdown which is proportional to device length squared and that the chromium devices generally follow a similar law. Other evidence supporting the trapping barrier postulated by Lampert is also given. Filamentary conduction in the postbreakdown region is investigated by direct recording of the recombination radiation on infrared film. It is established that impedance variations and secondary breakdowns observed on the voltage-current characteristic are caused by movement of the filament position between the two injecting contacts. Filament position instabilities under cyclic excitation are observed and these effects are linked to a localized increase in the trapping barrier caused by heating along the filament site. Photographs of the recombination radiation emanating from both contacts establish the two-carrier nature of the postbreakdown filamentary state.
Discussion of the Transmitted Waveforms in a Periodic Laminated Composite
Authors: Lundergan C. D.
Published: February 2004

The response of a periodic plate-laminated composite to finite, dilatational stress waves has been investigated both experimentally and analytically. The composite was constructed of ten bilaminates oriented so that the stress wave propagated normal to the plane of the plates. The experimental results were compared to the results of a previous study, to the calculations of two wave-propagation computer programs, and with a model in which the composite was treated as a homogeneous medium for which a stress-relaxation relation was assumed. From these comparisons, the effects which influence the form of the stress wave were deduced. For the composite configuration used in this study and at a stress level of less than 12 kbar, the effects are geometric dispersion which includes the resonance resulting from the periodicity of the configuration, debonding, material nonlinearities, and viscosity.
Lateral Growth in Solid-Solid Phase Transformations
Authors: Jones G. J. , Trivedi R. K.
Published: February 2004

The problem of step motion during lateral growth in solid-solid phase transformations is considered. The present model is concerned with the case in which volume diffusion in the parent phase is the predominant contribution to the growth rate, and it is assumed that the steps do not interact appreciably. The relationships between growth rate and supersaturation are obtained from an approximate solution of the diffusion equation in a moving coordinate system. The predictions of the model are then tested against the observed behavior of steps in Al-15 wt.% Ag as reported by Laird and Aaronson, and good agreement is found.
Method for Determining Composition Profiles and Diffusion-Generated Substructure in Small Diffusion Zones
Authors: Carpenter J. A. , Tenney D. R. , Houska C. R.
Published: February 2004

An x-ray diffraction technique is described which may be used to determine the composition profile of small diffusion zones as well as the diffusion-generated substructure. Thus far, this technique is restricted to volume diffusion and has been applied in the case of a single-phase solid solution; however, the methods may be readily applied to volume diffusion in multiphase systems. Data are presented for a system containing an 8-μ deposit of Ni on a [111] oriented single crystal of Cu. This composite was diffused at 900 °C for 45 min, 2 h, and 5 h. A Matano-Boltzmann analysis of the composition profile gave good agreement with recently obtained diffusion coefficients. The degree of diffusion-generated subgrain misorientation increased with annealing time and zone size up to the maximum time for our experiments. There was no evidence for the existence of nonuniform strain, and the distribution of subgrain misorientation was found to be Gaussian. Also, the widths of the Gaussian misorientation functions appear to be proportional to the lattice-parameter gradient, although this relationship is not exact.
Preparation of High-Crystallinity Polyethylene at Low Pressures. II.
Authors: Hara K. , Schonhorn H.
Published: February 2004

The preparation of highly crystalline polyethylene at low pressure is reported. We demonstrate that with careful control of the substrate, melting and crystallization schedule, and physical state of the specimen (film thickness), it is possible to prepare polyethylene having a density in excess of 0.999 g cm−3, a melting temperature of ∼140°C, and a heat of fusion in excess of 70 cal/g. The approach appears to be general and should be applicable to a wide variety of polymers. An analysis of the heat-of-fusion data suggests a value of 79 cal g−1 for the infinitely extended chain crystal.
New Electrostatic Refraction Probe for Measuring Plasma Parameters
Authors: Kuswa Glenn W.
Published: February 2004

A new probe, employing the refraction of charged particles as they cross the potential interface from a plasma to the screened end of a pipe, containing a single-collection electrode, is described. It is capable of determining Te, Ti, n, and the plasma potential φp of Maxwellian plasmas by straightforward techniques using two simple expressions. Experiments were performed to compare refraction probe measurements with data obtained by Langmuir probe and electrostatic curved-plate energy-analyzer techniques.
Time-Dependent Critical Damping of a Capacitor-Discharge Circuit
Authors: Piller H. , Archibald P. C. , Johnson J. H.
Published: February 2004

Optimal design of a heat-sensitive variable resistor in the circuit of a pulsed capacitor discharge provides a physically simple method of damping without the ringing currents which may shorten capacitor life. Computer simulation is utilized to determine the optimum design parameters and materials of the variable resistor.
Dependence on Crystalline Face of the Band Bending in Cs2 O-Activated GaAs
Authors: James L. W. , Antypas G. A. , Edgecumbe J. , Moon R. L. , Bell R. L.
Published: February 2004

Electron energy loss in the band-bending region of the p-type III–V semiconductor in a III–V photocathode is an important factor in determining the escape probability and the optimum doping. From measurements of photoelectric yield near threshold from Cs2O-activated n-type GaAs, the position of the Fermi level at the GaAs–Cs2O interface was determined for {110}, {100}, {111A}, and {111B} surfaces. Assuming the Fermi-level position at the GaAs surface to be independent of doping, the band bending for p-type GaAs is greatest for the {111A} face and least for the {111B} face. The measured escape probabilities of photoexcited electrons from different crystalline faces of optimally activated 5 × 1018/cm3 Zn-doped liquid epitaxial GaAs correlate well with the band-bending measurements. The {111B} sample has an escape probability of 0.489 and a luminous sensitivity of 1837 μA/lm.
Anomalous X-Ray Transmission Studies in Indium Antimonide: Surface Damage
Authors: Kiss L. T. , Miller D. C. , Gatos H. C. , Witt A. F.
Published: February 2004

Nearly perfect indium antimonide single crystals were studied by x-ray anomalous transmission using silver Kα radiation and {220} reflections. The depth of abrasion-induced surface damage was determined using the diffracted integrated intensities. The depth of damage was found to be greater on the B than on the A surfaces for the same amount of abrasion. For unidirectional abrasion the direction of the strain corresponded to the direction of abrasion, but some directional strain was also present when the abrasion was not unidirectional. The measured rocking curve half-widths were not affected by severe surface abrasion. The effective absorption coefficient was measured to be 10.3 ± 1 cm−1.
Magnetoelastic Love-Wave Propagation in Metal-Coated Layered Substrates
Authors: van de Vaart H.
Published: February 2004

The effect of a perfectly conducting infinitely thin metal coating on the properties of magnetoelastic surface waves is discussed. Dispersion relations are derived for magnetoelastic Love waves propagating in the following structures: (i) metal-coated nonmagnetic-layered magnetic substrate, (ii) nonmagnetic-layered metal-coated magnetic substrate, (iii) metal-coated thin magnetic plate, and (iv) metal-coated magnetic-layered nonmagnetic substrate.
Nonlinear Response of a Weakly Ionized Plasma to a Pulsed Electric Field
Authors: Sodha M. S. , Kaw P. K.
Published: February 2004

The nonlinear response of a weakly ionized gas to a moderately strong pulsed electric field (with arbitrary time dependence) has been analytically investigated using the elementary theory of electrical conduction in gases. Explicit expressions have been obtained for the linear and nonlinear parts of the transient current density; these have been used to compute the absorption of energy in the plasma due to the pulse.
Extension of Maximum Anisotropy Approximation to Examine Warm-Electron Distributions
Authors: Chen Peter C. Y. , Lee Charles A.
Published: February 2004

The maximum anisotropy truncation (MAT) scheme of Baraff is applied to the problem of calculating the electron distribution function in the ``warm''-electron range. The solutions of a Laplace-transformed difference-differential equation governing the symmetrical part of the distribution function are simpler than those of the integral equations derived in a similar context by Baraff and by Budd. With a view to obtaining more physical insight the limiting distributions within the MAT scheme have been derived for very low and very high electric fields; for very low fields a Maxwell-Boltzmann distribution is obtained when both emission and absorption processes are included, and no cooling effects are observed. In addition, the streaming character of the distribution is investigated by comparing the ratio of the first two components of the spherical harmonic expansion of the distribution function. A nearly isotropic distribution occurs when r, the acoustic-to-optical-phonon mean free paths or εR/kT, the ratio of optical phonon energy to kT, is much less than one, while a ``spiked'' distribution is found when εR/kT≫1. Further, the streaming character becomes less pronounced when the electric field increases.
Electrical Conductivity and Tensile Strength of Dispersion-Strengthened Copper
Authors: Fuschillo N. , Gimpl M. L.
Published: February 2004

Dispersion-strengthened alloys of copper containing 2.2 and 5.0 vol% ThO2 were made by precipitating copper from a stirred solution of copper acetate containing a suspension of submicron-sized ThO2 particles. This procedure produced alloys of good oxide particle homogeneity in the metallic matrix. Mechanical properties and electrical resistivities were measured as a function of temperature. The dispersion strengthening caused small increases in the resistivity and large improvements in mechanical properties of the alloy compared to copper at elevated temperatures.
Comparison of High-Energy Gas Flow Experiments
Authors: Glenn H. D. , Crowley B. K.
Published: February 2004

The results of three experiments which used Voitenko compressors to produce high-energy gas jets of Ne, O2, and CO2 are described here. Velocities of various components of the jets were obtained by monitoring the luminosity of the jets as they passed through evacuated outlet pipes. The slight velocity attenuation observed in these jets is briefly compared with other high-energy gas flow experiments that used outlet pipes containing atmospheric air.
Shock Compression of Teflon from 2.5 to 25 kbar-Evidence for a Shock-Induced Transition
Authors: Champion A. R.
Published: February 2004

Uniaxial shock-compression studies were conducted on Teflon in the stress region between 2.5 and 25 kbar using a compressed-gas gun and quartz-gauge instrumentation. Measurements of stress and particle velocity at the impact surface show that a transition occurs at 5.0 ± 0.2 kbar with an associated volume change of approximately 2.2 ± 0.2%. Measurements of the stress wave profiles after transmission through the samples show an attenuation of peak stresses and suggest a visoelastic behavior of Teflon.