bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress and Dilatation Fields of the 〈111〉 Dislocation in Cubic Crystals
Authors: Chou Y. T. , Mitchell T. E.
Published: January 2005

Exact expressions of the stress components and dilatation of a straight dislocation, lying in a 〈111〉 direction in a cubic crystal, have been obtained analytically. The transitions in the contours of stress and dilatation fields are found to be controlled by an elastic anisotropy parameter R. For bcc crystals, the transition of σ23 contours of a screw dislocation takes place atR=(32)1/2 and that of σ13 contours at R=3 (for W, Ta, V, Cr, Mo, Nb, and Fe,R<(32)1/2; for Na, K, Li, (32)1/2<R<3). The results of the stress analysis are useful in treating the dissociation of screw dislocations in the bcc lattice.

The dilatation contours of a [111] dislocation of the mixed type with Burgers vector a/2[111̄] are illustrated. The differences in shape of the contours for the anisotropic and isotropic cases are greater for the pure edge dislocation than for the mixed-type dislocation.
A Shock-Induced Phase Transformation in Bismuth
Authors: Larson Donald B.
Published: January 2005

A study was made of the shock-induced phase transformation in bismuth at 25 kbar. A quartz pressure-gauge technique was used to obtain the experimental data. A previously reported disagreement between the dynamic and the static transition pressure is due in part to a strength-of-material correction. The remaining discrepancy is probably due to a systematic error in the earlier dynamic study. The observed dynamic transition pressures corrected for strength-of-material effects and corrected to 25°C were 25.4 kbar for isotropic bismuth, and 25.9 kbar for cast bismuth. These values agree nicely with the value 25.4 kbar obtained by static compression. Hugoniot elastic limits of 2.4 to 3.1 kbar were observed for the different types of samples.
Diffusion Currents in Large Electric Fields for Discrete Lattices
Authors: Fromhold A. T. , Cook Earl L.
Published: January 2005

A derivation for the steady-state current J produced by a large homogeneous electric field E0 in the presence of a concentration gradient is presented which includes explicitly the effects due to lattice discreteness. The resulting equation is J=4aν exp(−W/kBT) sinh(ZeE0a/kBT)[C(L)−C(0) exp(ZeE0L/kBT)]/[1−exp(ZeE0L/kBT)],where C(0) and C(L) are the boundary concentrations of the diffusing species at the interfaces of the planar film at positions x=0 and x=L; e, the electronic-charge magnitude; Ze, the charge per particle of the diffusing species; 2a, the distance between adjacent potential minima; v, the frequency at which the ion attempts energy barriers which have height W in zero field; kB, the Boltzmann constant; and T, the absolute temperature. A derivation valid in the limit of a continuum model is also presented, and the results are compared numerically. The equations for the discrete and continuum models reduce to the results predicted by the ordinary linear diffusion equation for electric fields below approximately 105 V/cm. The relevance of the equations to the phenomena of anodic and thermal oxidation and to thin-film current-voltage devices is briefly described.
Defects in Silicon Crystals Grown by the VLS Technique
Authors: Wagner R. S.
Published: January 2005

Crystalline defects have been studied in silicon crystals grown by the vapor-liquid-solid (VLS) technique. Most of these crystals are highly perfect. However, some crystals contain defects such as dislocations, stacking faults, and second-phase regions. An elastic stress field, resulting from differential thermal contraction was found near the tip of every crystal. The formation and prevention of these defects and their relation to the VLS growth mechanism are discussed in detail. The morphology of the prismatic side faces of the crystals depends on deposition temperature, and is primarily due to vapor-solid deposit. This deposit is perfect even at deposition temperatures as low as 700°C.
An Arbitrary Current Source in a Homogeneous Anisotropic Plasma
Authors: Van Hulsteyn David B.
Published: January 2005

In analogy with the free-space solution of Maxwell's equations, the excitations which are set up in an anisotropic, macroscopically neutral plasma by an arbitrary current can be described by potentials. The equations which the one vector and two scalar potentials must satisfy are first obtained for a relatively general physical situation. Due to the complexity of the mathematics, however, one cannot expect to obtain analytic solutions to this set of coupled equations without first making some realistic simplifications. One particular case that can be solved without an inordinate amount of difficulty is that of the point charge moving with uniform velocity parallel to a strong magnetic field. It is shown that the propagating waves which arise in this situation are electroacoustic in nature but very different from those created by a moving charge in an isotropic plasma.
Microtwin and Tri-Pyramid Formation in Epitaxial Silicon Films
Authors: Mendelson S.
Published: January 2005

Microtwin lamellae and tri-pyramid defects often form in {111} silicon epitaxial films and these are affected by impurities within the substrate and system. The tri-pyramids, which are doubly twinned with respect to the substrate surface, result when three oblique pyramids sprout from a triangular twinned deposit which forms on the (111) substrate surface. Twinning enhanced by adsorbed impurities could account for the initial twinning, but since it is a random process, cannot explain the second twinning operation for all three pyramids. The results also show that SiC platelets are not unique or necessary for tri-pyramid formation. A reentrant twin mechanism is proposed to account for this as the twinned islands join up with correct ones. This mechanism can also account for the formation of microtwin lamellae which often accompany the tri-pyramids. It is also shown that oblique microtwin lamellae can propagate directly from the twinned deposits and that multiple twin lamellae can result when the twinned deposit has steps in it.
Investigation of Precursor Decay in Iron by the Artificial Viscosity Method
Authors: Johnson James N. , Band William
Published: January 2005

The artificial viscosity method of von Neumann and Richtmyer is used to calculate the flow field for a shocked, elastic-plastic-relaxing solid; particular material parameters are chosen to represent the rate-dependent behavior of iron. The constitutive relation is based on the dislocation model for plastic flow. Dislocation velocity is assumed to be a unique function of shear stress as given by Gilman and Johnston. Two models for dislocation multiplication are studied. The first is the multiple-cross-glide model discussed by Gilman, and the second is one in which pinned dislocations become sources of new mobile dislocations in the sense of the Frank-Read multiplication process. Artificial viscosity calculations yield precursor amplitudes which are sometimes considerably different from those obtained from characteristic theory of precursor decay. These differences are believed to be due to the finite width of the elastic wave front provided by the viscosity. With proper choice of mesh size in the artificial viscosity calculations, a decrease in stress can be seen immediately behind the elastic precursor. This agrees qualitatively with experimentally determined shock profiles in iron.
Diffusion Charging of Aerosol Particles at Low Pressures
Authors: Liu Benjamin Y. H. , Whitby Kenneth T. , Yu Henry H. S.
Published: January 2005

The diffusion charging of aerosol particles by unipolar ions has been studied experimentally over the pressure range, 0.0311 to 0.960 atm, using monodispersed aerosols of di-octyl phthalate. The ratio, a/λ, of the particle radius to the mean free path of ions has been varied over the range from 1.0 to 66. Within the accuracy of the experiments, the particle charge has been found to be independent of the ratio, a/λ, and well represented by the equation, np=9.00Dp ln (1+1.02×10−5N0tDp), where np is the number of elementary units of charge acquired by the particle, Dp is the diameter of the particle in microns, N0 is the number concentration of the ions to which the particle has been exposed in ions/cc, and t is the charging time in seconds. This equation agrees with a theoretical equation derived by White when the molecular weights of the positive ions used in the charging experiments are assumed to be equal to 16 times that of air or 460.
Thermal Conductivity, Thermal Diffusivity, and Specific Heat of Solids from a Single Experiment, with Application to Y1.98Nd0.02O3
Authors: Klein Philipp H.
Published: January 2005

In the absolute method for determining thermal conductivity K, the difference in temperature between two points along a rod is measured under conditions of steady-state flow of heat. The thermal diffusivity κ may also be determined from measurements of the time required for this temperature difference to decrease to half the steady-state value when the source of heat is removed. From K and κ data, the specific heat may be calculated, using the general relationship C=K/κρ, where ρ is the density. The technique permits determination of K, κ, and C with a single, small specimen having a wide range of K and κ. By observing simple experimental precautions, agreement to within 5%–10% has been obtained, for neodymium-doped yttrium oxide, between C values calculated from K and κ data and those derived from calorimetric data.
Thermal Conductivity, Diffusivity, and Expansion of Y2O3, Y3 Al5O12, and LaF3 in the Range 77°–300°K
Authors: Klein Philipp H. , Croft William J.
Published: January 2005

The thermal conductivities of Y2O3, Y2O3:Nd3+, Y3Al5O12:Nd3+, and LaF3 have been measured from 77°–300°K by a steady-heat-flow method. The densities of these crystals and of LaF3:Nd3+ have been determined in the same temperature range, using x-ray methods. Using this information and specific heat data from a variety of sources, the thermal diffusivities of these materials have been calculated. Although the diffusivity of pure yttrium oxide is somewhat higher than that of pure yttrium aluminum garnet, introduction of about 1 mole % of neodymium into both these compounds leads to crystals with diffusivities approximating that of undoped YAG. The diffusivity of doped yttrium oxide and YAG (about 0.05–0.06 cm2/sec at room temperature) is about three times that found for undoped lanthanum fluoride. The relative ease with which heat may be removed from Nd-doped Y2O3 and YAG suggests their use in lasers to diminish time variations in the width of the beam.
Low-Energy Sputtering Yields of Ge Single Crystals as a Function of Temperature
Authors: Anderson G. S.
Published: January 2005

The temperature dependence of the relative sputtering yields of Ge (100), (110), and (111) surfaces for various kinds of noble gas bombarding ions, bombarding ion energies, and bombarding ion fluxes has been investigated. Instantaneous relative yields were obtained by using the spectroscopic emission technique. The dependence of the annealing temperature on the bombarding ion energy and flux can be interpreted in terms of a simplified model where the rate of defect production equals the rate of defect annealing at the annealing temperature. The width of the transition region increases with decreasing bombarding ion energy and mass.
Lithium Tantalate Light Modulators
Authors: Denton R. T. , Chen F. S. , Ballman A. A.
Published: January 2005

Light intensity modulators have been developed using single-domain lithium tantalate as the electro-optic material. A broadband transistor amplifier which can develop 0.2-W output power drives the modulator sample which presents a capacitive load of 5 pF. Approximately 80% modulation is achieved from dc to 220 Mc/sec, when the light is made to traverse the sample twice. The modulation bandwidth is limited by the transistor amplifier. Very little acoustic ringing is observed when the modulator is used as a fast light switch.
Lattice Defects in Shock-Deformed and Cold-Worked Nickel
Authors: Kressel H. , Brown N.
Published: January 2005

For equivalent values of plastic strain, the dislocation density and point-defect concentration following deformation by the propagation of high-amplitude shock waves (70 to 330 kbar) through high-purity polycrystalline nickel are appreciably larger than as a result of cold rolling near 0°C. Based on the electrical-resistivity change in recovery state III and IV, it is concluded that vacancies rather than interstitials are the predominant point defects formed. The ratio of the two types of defects that are formed appears to be essentially strain-rate independent. The dominant point-defect formation mechanism is believed to consist of the nonconservative motion of jogs on screw (or mixed-character) dislocations. The observed enhanced formation of point defects as a result of shock deformation is explained as the result of the increasing efficiency of this process with increasing dislocation velocity.
Recombination Centers in InSb
Authors: Hollis J. E. L. , Choo S. C. , Heasell E. L.
Published: January 2005

A study has been made of the temperature dependence of the lifetime and Hall coefficient in p- and n-type InSb with extrinsic carrier concentrations ranging respectively from 1×1013 to 4×1015 cm–3 and from 2×1012 to 5×1014 cm–3, the lifetime having been measured by means of the phase-shift method. The lifetime data confirm that the interband Auger process is the limiting recombination process in InSb for temperatures above 150°K. Below 150°K both the lifetime and Hall data are generally consistent with a model consisting of two sets of single-level, donor-like recombination centers, rather than with a model of a single set of divalent, donor-like centers as used in a previous work. The energy levels of these centers are located at 0.071 eV and 0.11 eV above the valence band. Subsequent bombardment of a p-type and an n-type sample with 11-Mev electrons produced an increase in the number of recombination centers having the same properties as those occurring before bombardment. It is concluded that the recombination centers in as-grown crystals are lattice defects of a simple nature, and that there are grounds for believing that associated with the two energy levels are two different sets of defects rather than a single set.
Thermal Expansion of Crystals with KH2PO4 Structure
Authors: Cook William R.
Published: January 2005

The thermal-expansion and room-temperature lattice constants were determined for several phosphates and arsenates isomorphous to KH2PO4. From these data, the lattice constants were calculated at the ferroelectric antiferroelectric temperature. They show a nearly identical c/a ratio for the compounds of any given alkali ion and a change of c/a ratio with the ionic radius of the alkali ion. The size of the expansion anomalies at the transition are markedly affected by deuteration. The anomalies in the ammonium compounds are larger by an order of magnitude than those for the ferroelectric alkali compounds. Temperature hysteresis measurements indicate that the transition in KD2PO4 is probably second order.
Oscillatory Modes Associated with One Carrier Transient Space-Charge-Limited Currents
Authors: Schilling Ronald B. , Schachter Harry
Published: January 2005

The transient response of the current to an applied voltage step is analyzed for the range of time approaching equilibrium, using a perturbation scheme applied to the steady-state equations. A modal equation is developed from which an infinite set of decaying, oscillatory modes are shown to exist. The time constant for the system is shown to be approximately one-fourth of the transit time associated with one-carrier space-charge-limited currents.
Magneto-Optic Scattering from Thin Solid Films
Authors: Hunt Robert P.
Published: January 2005

A general theory for treating magneto-optic scattering (reflection and transmission) from multilayer structures comprised of magneto-optic and dielectric materials is presented. The two principle assumptions are: (1) Only terms linear in the off-diagonal element of the permittivity tensor are important. (2) The magnetic medium is optically lossy. The theory is cast in terms of the Fresnel reflection coefficients and the corresponding magneto-optic reflection coefficients, rsp and rps. The theory is illustrated by consideration of a dielectrically enhanced, thick magnetic film. Finally, a general formulation for scattering from a magneto-optic medium with arbitrary orientation of the magnetization is also presented.
Polarization Reversal in Ferroelectric KNO3
Authors: Schubring Norman W. , Dork Ronald A. , Nolta James P.
Published: January 2005

Ferroelectric potassium nitrate has been found, by a pulse-testing technique, to show a threshold electric field, essentially invariant with duration, below which KNO3 behaves as a completely elastic dielectric. Test results on several ferroelectric materials, all single crystals, are shown and compared to the results obtained from fused layers of KNO3. The technique for the detection of a threshold is described and the test circuit for obtaining the required data on change in charge vs applied step voltage is included. Finally, a precise time-independent description of KNO3 polarization reversal over the entire range of applied step fields is given by two empirically derived equations, each covering one side of threshold.
Effect of Grain Boundaries on the Electrical Resistivity of High-Purity Iron at 4.2°K
Authors: Arajs Sigurds , Oliver B. F. , Michalak J. T.
Published: January 2005

Electrical resistivity (ρ) of samples with different grain sizes, made from iron of three different purities (containing a maximum of 34, 79, and 2150 atomic ppm impurities, respectively), has been studied at 4.2°K in the presence of applied longitudinal magnetic fields up to 60 kOe. It has been found that the resistivity is influenced not only by impurities and magnetic domain arrangements but also by the grain-boundary area per unit volume. The ratio R=ρ(300.0°K)/ρmin (4.2°K) varies from 2875 to 528 for the interfacial grain area range of 0 (single crystal) to 7.0 mm−1 in the highest purity iron. (ρmin is the minimum in the resistivity measured as a function of the applied field at 4.2°K.) Due consideration of these large magnetic and grain-boundary effects discloses a clearer correlation between R and purity.
Striations on Copper Single Crystals Subjected to Torsional Fatigue. I. A Test of the Relation of Cross Slip to Fatigue Striation Formation
Authors: Nine Harmon D.
Published: January 2005

The formation of fatgiue striations has been investigated by cycling oriented, cylindrical copper single crystals in torsion. Since in torsion of single crystals the applied stresses resolved on the slip systems vary as a function of azimuth, the stress on the cross-slip system relative to that on the primary system varies with azimuthal position. The importance of cross slip to the formation of fatigue striations is tested by correlating the azimuthal position of fatigue striations with the stresses. It is concluded that a repeated cross slip mechanism will not account for fatigue striation formation.
Phase Stability and Stacking Faults in Cerium Alloys
Authors: Clinard Frank W.
Published: January 2005

Electrical resistivity and x-ray studies were performed on a series of cerium samples, each of which contained in solution a 2-at.% addition of one of the other rare earths (except promethium and ytterbium). The resistivity measurements showed that the amount of double hcp β phase formed at low temperatures varied in accord with the solute species present, the maximum amounts of β being associated with the solutes at the ends of the rare-earth series and the minimum with those near the center of the series. The anomalously strong β-forming tendency of the europium solute is explainable on the basis of atomic-size and valence effects. The x-ray studies revealed a varying tendency toward extrinsic stacking-fault formation, which correlates with the trend in β-phase formation. This correlation is attributed to the fact that both β cerium and extrinsic faults in fcc γ cerium exhibit ABAC stacking of close-packed planes. It is proposed that the observed trends in ABAC stacking stability are dependent on the number of unpaired 4f electrons of the solute atoms, with the stability being least when the number of these magnetic electrons is greatest.
Optical Properties of Magnesium Fluoride in the Vacuum Ultraviolet
Authors: Williams M. W. , MacRae R. A. , Arakawa E. T.
Published: January 2005

The room temperature optical properties of single crystal MgF2 were determined in the 4.1 eV–10.9 eV energy range, from transmission and near-normal-incidence reflectance measurements, and in the 11.0 eV–27.5 eV range, from reflectance measurements made at various angles of incidence. Sharp structure in the reflectance spectra of single crystal MgF2 is associated with an exciton transition at 11.8 eV. Broader structure at higher energies is associated with an interband transition at 20.8 eV. The energy-loss function for volume plasmons has a maximum at 24.5 eV which agrees well with the theoretical value. In addition, the optical properties of an evaporated film were determined in the range 11.0 eV to 29.5 eV, but structure in the reflectance spectrum is not as well defined. However, there is fair agreement with previously published optical constants of evaporated MgF2.
Statistical Model for the Size Effect in Electrical Conduction
Authors: Soffer Stephen B.
Published: January 2005

A statistical model for the reflection of scalar plane waves from a rough surface leads to a plane wave in the direction of specular reflection and to a contribution with a finite angular spread about that direction, depending on the tangential correlation of the surface asperities. Based upon on this result, a new semiclassical model, which satisfies the requirement of flux conservation, is proposed for the boundary condition for the distribution function of the size effect in the electrical conductivity. In the absence of correlation, the resultant expression replaces the constant specularity parameter p of Fuchs by the function exp[−(4π(h/λ) cosθ0)2] with θ0 the angle of the electron wave vector with the surface normal. Correlation produces an additional forward component within the diffuse contribution. Numerical results of the size effect for zero correlation are compared to the Fuchs model as well as a more recent model, and show a different thickness dependence for thin samples. The effect of correlation is to add to the conductivity, as a result of the diffuse contribution whose velocity has a finite expectation value in the direction of the current.
Solid-State Infrared-Wavelength Converter Employing High-Quantum-Efficiency Ge-GaAs Heterojunction
Authors: Kruse P. W. , Pribble F. C. , Schulze R. G.
Published: January 2005

An n-p-n heterojunction structure, formed by the epitaxial growth of n-Ge on a p-GaAs substrate having a diffused n-GaAs region on the opposite face, has been employed to convert 1.5-μ radiation incident on the n-Ge face to 0.9-μ radiation emitted from the n-GaAs face. The internal quantum efficiency of the n-Ge, p-GaAs heterojunction is 0.62; the spectral response of the heterojunction is typical of photon effects in Ge. The internal wavelength conversion efficiency is 2.8×10−5, limited principally by the low electroluminescent quantum efficiency of the GaAs p-n junction at low injection current densities.
Transient Approach to Current Saturation in Photoconductive CdS
Authors: McFee J. H. , Tien P. K. , Hodges H. L.
Published: January 2005

Current saturation and the accompanying current oscillation in CdS are studied by measuring the spatial electric-field distribution as the current decays from its initial Ohmic value to its final saturated value. The initial saturation of the current and subsequent damped oscillation are found to be caused by the presence of moving high-field domains which propagate at the acoustic-wave velocity. The detailed behavior of these domains indicates that they are packets of high acoustic-energy density. As the oscillations damp and the current saturates, the moving domains apparently give way to a competing process. In the current-saturated condition, only a stationary high-field region remains. The field distribution in CdS crystals having the drift-current parallel to the hexagonal axis is also explored in some detail. The results indicate that in these samples the current saturation is caused by the amplification of shear waves which propagate predominantly at an angle of ∼30° with respect to the hexagonal axis.
Plasma Temperatures Generated by Focused Laser Giant Pulses
Authors: Gregg David W. , Thomas Scott J.
Published: January 2005

Plasma temperatures generated by focusing ruby-laser giant pulses on surfaces of Be, Al, and Pb in a vacuum were measured as a function of time and giant-pulse intensity. The monochromatic emission intensities of the plasmas (relative to those obtained with a standard source) were measured at wavelengths ranging from 4000 to 10 500 Å, and the temperatures were then calculated from the Planck function. It was found that the plasma temperatures achieved with the lighter elements were hotter and had greater rates of increase with laser intensity. However, the rates of increase were proportional to only the 0.5 power of the laser intensity or less, and the difference in temperatures between target materials was not very great. Temperatures as high as 8×105 °K were achieved with beryllium.
Electrical Properties of a Degenerate Intrinsic Semiconductor
Authors: Dalven Richard
Published: January 2005

Intrinsic degeneracy occurs in semiconductors in which (ΔE/kT) is sufficiently small that the Fermi level is close to one or both band edges. Since studies of the Hall coefficient R and the conductivity σ are often used to investigate such semiconductors, R, σ, and their variation with temperature have been calculated for a simplified model of a degenerate intrinsic semiconductor. This model included spherical energy surfaces, a parabolic density of states, predominance of acoustic phonon scattering, and a linear variation ΔE=E0+αT of the energy gap with temperature. It was found that R and σ differ significantly from R0 and σ0, the values predicted by classical statistics. (R/R0) and (σ/σ0) are shown as functions of T for several values of the parameters α and (mp/mn), where mp and mn are the hole and electron effective masses. It is also shown that plots of ln | R | T3/2 and of lnσ vs (1/T) are nonlinear in the degenerate case and do not have the constant slope, equal to (±E0/2k), respectively, predicted by classical statistics. The results and their bearing on the analysis of experimental data are discussed in terms of the degeneracy of the semiconductor.
Widths of Kikuchi Lines in Germanium
Authors: Fowler H. A. , Marton L.
Published: January 2005

Transmission Kikuchi patterns at 80 keV from wedges of germanium have been measured with high angular resolution. Linewidths are compared with the Fourier potential calculated from a simple coherent-elastic-amplitude model. Germanium shows a higher experimental curve of scattering amplitude per unit cell volume than silicon, as may be expected from its greater atomic scattering potential. Suppressed contrast is found for the (111) reflection; this is interpreted as an overlap between the halves of the line-pair or band.
Diffusion Widening of p-n Junctions in Semiconductors
Authors: Chakraverty B. K. , Deneuville A.
Published: January 2005

The widening of the p-n junction of a semiconductor is viewed as due to simultaneous diffusion and drift of the impurities. Rigorous first-order differential equations for the variation of the space-charge width with time are given. The equations are only dependent, except for an integral term, on the concentrations at the edges of the space-charge region. Exact solution of the system is always possible for short time if the initial concentration profile is known. This has been done for a few cases.
Radiation Damage in Cadmium Sulfide and Cadmium Telluride
Authors: Chester R. O.
Published: January 2005

The effects of irradiation with 1.17- and 1.33-MeV 60Co gamma rays, 0.662-MeV 137Cs gamma rays, and thermal neutrons on the carrier concentration in n-type CdS and CdTe have been studied by means of Hall-effect measurements. Irradiation of these materials at room temperature did not introduce any new energy levels in the range from 0.02 to 0.2 eV below the conduction band (the range accessible by experiment), although the density of levels initially present in this interval was altered and, under certain conditions, deep-lying acceptor states were produced. The most significant observation was the change in the nature of the effect as the energy of the incident gamma rays was changed. For example, 137Cs photons introduce acceptors in CdS and donors in CdTe, while 60Co photons produce the inverse effect. Atomic displacement calculations indicate that the lower-energy 137Cs photons should preferentially displace sulfur atoms in CdS and cadmium atoms in CdTe; the opposite is calculated for 60Co. Hence, these studies suggest that the net result of displacement of a chalcogenide atom is acceptor introduction, with donor introduction resulting from displacement of the cadmium atom. Thermal neutron irradiation of both materials introduces acceptors.
The Effect of Metal Contacts on Acoustic Generation in CdS Thin Films
Authors: Pizzarello F. A.
Published: January 2005

The relationship of the electrical contact between metal and CdS to the piezoelectric properties was investigated. The influence of the base metal on the crystallographic orientation of the CdS film and the nature of the electrical contact is demonstrated. By measurements of capacitance and I–V characteristics, gold is shown to produce a Schottky barrier and aluminum an Ohmic electrical contact with CdS thin films. The effect of the depletion layer generated by the Schottky barrier on the acoustical output of CdS transducers is shown.
Thermal Neutron Transmutation Effects on W/W-26Re Thermocouples
Authors: Wood Van E.
Published: January 2005

A theoretical estimate is made of the change in output voltage to be expected when a W/W-26Re thermocouple is exposed to thermal neutrons, causing some of the rhenium to be transmuted to osmium. The estimated drift may be fairly large: as much as 9.1% when ⅓% of the rhenium atoms are transmuted for a couple measuring a nominal temperature of 1800°C.
Microwave Interferometer Measurements in Shocked Air
Authors: Tevelow Frank L.
Published: January 2005

Microwave transmission measurements of the electrical properties of shock-ionized air in the range 8≤Ms≤12 and initial pressures of 1, 2, 5, 10, and 20 Torr are presented. The test arm of the microwave transmission bridge is X band waveguide, which passes through the shock tube and has an affixed nozzle to section out a portion of the shocked gas. This gas is constrained to a rectangular cross section and passes through the waveguide where it interacts with the microwave signal. An 0.5-in. and a 1.5-in. nozzle are used, and it is shown that nozzle length has a negligible effect on both the ionization rate and the level. The data are presented in terms of dielectric constant, electron density, collision frequency, conductivity, attenuation, and reflection coefficient. The data are compared with results obtained from other experimental methods and discrepancies are noted. Values of Ne and ν are calculated initially from the Lorentz relation with ν independent of velocity; these data are then recalculated by use of Hochstim's correction factors. Ionization profiles obtained from the microwave measurements at 1 Torr agree below Ms=11 with theoretical values obtained from the rate program of Garr and Marrone. Evaluation of ionization profiles in terms of rate constants is complicated at all pressures by the effects of accelerating shocks.
The Auerbach Range in the Hertzian Fracture of Glass
Authors: Fisher George M. C.
Published: January 2005

Several workers have reported the somewhat curious phenomenon that in ball-indentation fracture experiments on glass plates, the average fracture load is directly proportional to the indenter radius for a wide range of small indenters. As a part of the present investigation, similar experiments have been performed and confirm these observations. That such a definite relation (known as Auerbach's Law) should exist serves as one of the more puzzling barriers to nearly universal acceptance of statistical theories of glass fracture. This paper discusses such behavior from a probabilistic view in the content of the Hertz solution of classical elasticity. In particular a statistical solution is demonstrated, which, based on the hypothesis that there is a distribution of flaws with a density which varies inversely as the cube of the flaw severity, not only yields the linear range for average fracture loads, but also gives good agreement with other detailed characteristics of experimental fracture load-frequency data.
Parametric Interactions Involving Multiple Elementary Scattering Processes
Authors: Hsu H.
Published: January 2005

In the application of lasers in such fields as nonlinear optics, one is often faced with the problem of limitation in the highest available laser power. A potential solution to this situation is to achieve higher power by adding separate lasers in parallel. However, whether such schemes would have an inherent limitation imposed by the lack of coherence of separate lasers is not so obvious. We have found that separate lasers can indeed be used as uncorrelated pump sources for parametric interactions. For optical parametric oscillations, each additional pump for amplification (with Stokes radiation) would enhance the exponential gain and reduce the oscillation threshold. Conversely, each additional pump for up-conversion (with anti-Stokes radiation) would reduce the exponential gain and raise the oscillation threshold. The contribution of each elementary scattering process can be evaluated individually allowing the net effect to be summed together in simple expressions.
Structure and Energy of the Periodic Bloch Wall
Authors: Janak J. F.
Published: January 2005

A variational study of the periodic Bloch wall is carried out. It is found that the periodic Bloch wall is energetically favorable only if the anisotropy constant of the material is smaller than a critical value; otherwise, the ordinary Bloch wall is energetically favored. Computations of the appropriate lengths are carried out, and the results agree fairly well with those obtained by Shtrikman and Treves for small values of the anisotropy constant.
Diffusion of Carbon through Zirconium Monocarbide
Authors: Sarian S. , Criscione J. M.
Published: January 2005

The diffusion coefficients of carbon in single and polycrystalline ZrC have been measured in the temperature range 1350°–2150°C, using radioactive tracer techniques. Volume and short-circuit enhanced tracer diffusion coefficients are represented by the expressions D*=1.32×102 exp (−113 200/RT) cm2/sec and D*=1.6 exp (−90 000/RT) cm2/sec, respectively. The results are compared with apparent diffusion coefficients determined from existing carburization and high-temperature creep data.
Optical Lever Observation of Hypervelocity Impact Shock Waves
Authors: Gregson Victor G.
Published: January 2005

An optical lever system was used to observe the impact shock wave arrival and free-surface motion at the rear surface of a 2.54-cm-thick 2024-T4 aluminum target plate. The projectile was a 0.636-cm-diam. steel ball and struck the target at a velocity of 5.28±0.11 mm/μsec. The shock-wave data, in the range 30–1 kbar, extend data by Fowles to lower pressures. The measured elastic shock velocity of 6.23±3% agrees with ultrasonic values and with elastic shock values by other investigators.

Elastic shock amplitudes do not maintain a constant value as in one-dimensional experiments, but decay at a rate faster than predicted for spherical elastic waves.
Radiation-Field-Dependent Frequency Shifts of Atomic Beam Resonances
Authors: Harrach Robert J.
Published: January 2005

Radiation-field-dependent frequency shifts arising in atomic-beam spectroscopy are treated theoretically and experimentally. Shifts due to fundamental and unavoidable interactions between the radiation field and the atoms comprising the beam are distinguished from those due to various ``apparatus effects.'' Precise measurements of frequency shifts are made for a cesium beam experiencing Ramsey-type excitation. For the magnetic-field-sensitive transitions (F, MF) = (4, ±1) ↔ (3, ±1), the magnitude of the shifts is about 1 part in 1010 of the resonance frequency value, per milliwatt variation of input power to the radiation field. The shifts vary with input intensity in a nonmonotonic fashion and are shown to result from nonuniformity in the static magnetic c-field of the apparatus. Much smaller shifts of about 5 parts in 1013 per milliwatt are observed for the magnetic-field-insensitive transition (F, MF) = (4, 0) ↔ (3, 0). The major features of these shifts are shown to arise from spectral impurities in the radiation exciting the transition and a small phase difference between the pair of separated radiation fields. The bearing these results have on evaluating the accuracy of an atomic beam frequency standard is discussed.
Enhancement of Metal to Insulator Tunneling by Optical Phonons
Authors: Emtage P. R.
Published: January 2005

The interaction between longitudinal optical phonons in an insulator and electrons tunneling through the insulator is investigated on the basis of a simple one-dimensional model. This interaction is found to alter the mechanism of metal-insulator tunneling drastically, the tunneling current being constant at low temperatures and highly temperature-dependent at room temperature. The low-field (≲106V/cm) current-voltage relationship has an algebraic form similar to that for thermionic emission but differs from it in magnitude and temperature dependence. It is concluded that the high- and low-temperature regions of charge transfer from metal to insulator are continuous, representing the evolution of the electron-phonon interaction with temperature.
Square-Wave Phase Modulation in Ramsey-Type Molecular Beam Resonance Experiments
Authors: Kukolich S. G. , Billman K. W.
Published: January 2005

Square-wave phase modulation of the microwave signal which induces transitions allows one to measure velocity-dependent frequency shifts in Ramsey resonance experiments. The output signal from the molecular beam apparatus is demodulated by a synchronous detector operating in phase with the modulation. This output is proportional to the derivative of the transition probability and provides the usual resonance signal which is used in a servo loop to keep a harmonic of a voltage tunable crystal oscillator on the central peak of the resonance. A quadrature synchronous detector operating 90° out of phase with the modulating signal provides a measure of any velocity-dependent frequency shifts. Such shifts arise when there is a phase difference between the oscillating fields or when an electric field applied to a magnetic system produces a v×ε shift. We have theoretically and experimentally demonstrated that this quadrature signal is proportional to the phase difference between the microwave cavities of a Ramsey apparatus with the in-phase signal constrained at zero. We have also shown that the sensitivity of the quadrature system depends on the width of the available velocity distribution.
Nucleation of Polymer Droplets
Authors: Koutsky J. A. , Walton A. G. , Baer Eric
Published: January 2005

The nucleation of droplets of polyethylene, polyethylene oxide, polyoxymethylene, nylon 6, poly (3,3-bis-chloromethyloxacyclobutane), isotactic polypropylene, and isotactic polystyrene, suspended in silicone oil, has been investigated. Under conditions of slow cooling (0.1°C/min), two different phenomena were observed; occasional droplet solidification at low degrees of subcooling, the number of droplets solidified and the temperature at which nucleation occurred being a function of the thermal melt history; and a sudden catastrophic, history-independent, nucleation phenomenon at large subcooling. The latter event may be identified as a critical phenomenon occurring at a subcooling ΔTc which is only slightly dependent upon the rate of cooling.

For polyethylene and isotactic polypropylene, the ΔTc's correspond closely with values obtained by other authors using different suspending media and have been identified with homogeneous nucleation. Homogeneous nucleation may also be explored by the method of kinetic-rate measurements, with the advantage that rate constants can be evaluated directly rather than by theoretical derivation. Interfacial energies calculated from nucleation theory using the first (slow-cooling) method, have been compared in this work with those obtained from the second (isothermal) method. Such comparison shows that the isothermal method gives values of the same order as, but somewhat lower than, the slow-cooling method.

For the other polymers, most of which are glass-forming, it is not entirely clear that the catastrophic event corresponds with homogeneous nucleation. Whereas critical supercooling and solidification rates resemble those for homogeneous nucleation, there is evidence that the interfacial energies recovered are too low and the circumstances surrounding the catastrophic event suggest that the suspending medium may be catalyzing nucleation.
Damping of Waves in Electron Beams
Authors: Caulton Martin
Published: January 2005

The damping of plasma oscillations in velocity-modulated electron beams with large-velocity spreads has been analyzed. It is shown that the observed spatial decay of rf current along the beam (a loss of the fundamental interference pattern) can be characterized by the exponential decay of one of the space-charge waves. The exponential-decay rates for this wave are extracted from the data of over 50 experiments which exhibited a spatial damping. The parameters of the measured ``near-Maxwellian'' distribution of velocities (cutoff with a slow ``tail'') associated with each decay lead to the characterization of an equivalent temperature for the beam condition of each experiment. This is used to calculate the damping-determining parameters (ratio of plasma wavenumber to Debye wavenumber, k/kD, or equivalent). The experimentally observed damping rates for a variety of beam conditions are found to vary with k/kD in a consistent fashion and are also comparable with rates extracted from electron-beam theories. This is interpreted as a demonstration of a damping mechanism without collisions, and leads to the ascription of the decay as Landau damping in electron beams. Further experiments, in which the decay is observed as a function of the driving amplitude of the electron-beam plasma oscillations, are studied as possible evidence of Landau damping in electron beams.
Large Volume Degausser with Gradient Compensation
Authors: Freedman Melvin S. , Wagner F. , Porter F. T. , Day Paul
Published: January 2005

A solution is presented to the practical problem of adapting known theoretical multicoil magnetic field generators for compensation of slightly inhomogeneous fields. Three concentric orthogonal sets of coils are used as uniform field generators. The two sets used to compensate the strong field components are each an array of four parallel, equal-size square coils, separated by ⅓ of a side length, i.e., uniformly spaced on the surface of a cube. Each of these sets generates a magnetic field uniform to 2×10−4 within the central sphere of diameter equal to 0.2 of the side length of a coil. The outer pair of coils (22 turns each) and the inner pair (13 turns each) are series connected to a single current supply. By shunting small fractions of the current from one-half of two of the three coil sets, and by appropriate location of two pairs of small coils near the main degausser coils (also series connected), field gradients that result in variations of the order of 2×10−3 of the uncompensated field over the central sphere can be compensated. Construction and performance specifications are given.
On the Visibility of Bitter Powder Patterns on Ferromagnetic Films with Bloch and Néel-Type Domain Walls
Authors: Olson A. L.
Published: January 2005

It is known that in ferromagnetic films, the Bitter powder pattern of a Néel-type domain wall is much more visible than that of a Bloch wall. The Bitter powder particles are held in place by the magnitude of the stray fields from the domain walls. Calculations on the basis of the simplest wall models show that the magnitude of the component of the Néel wall stray field parallel to the film surface is identical with the magnitude of the Bloch wall stray field perpendicular to the film surface. This is not found to be true if the calculations are made using a theoretical Bloch wall model proposed by Brown and LaBonte and an empirical Néel wall model as measured with Lorentz microscopy techniques by Fuchs. These calculations show that the ratio of the magnitude of the Néel wall stray field component parallel to the film surface to the magnitude of the Bloch wall stray field component perpendicular to the film surface as a function of the distance above the film surface increases almost linearly to a value of 29 at 10 000 Å.
Preparation of K- and L-Edge X-Ray Foil Filters
Authors: Halliday F. O. , Keast A. K. , Kelman J. F. , Passell T. O.
Published: January 2005

Pack-rolling has been utilized to roll foils of Mg, Al, Sc, Ti, V, Mn, Fe, Y, Zr, Mo, Ag, In, Nd, Gd, and Dy for use as K- and LIII-edge filters in x-ray experiments in the 1–15 keV range. Sc, V, Y, Zr, Ag were readily rolled to 0.5–1.0 μ thickness; Mg, Ti, Mn, Gd, and Dy to 1.8–4.5 μ; and Mo and In to about 6.0 μ. Details of the rolling procedures for producing 10–20 cm2 foils for monochromatizing x-ray beams are given. The thickness uniformity of the pack-rolled foils was found to vary from ±10% at >4 μ to ±30% at <1 μ, as measured by 241Am alpha transmission. The successful fabrication of thin, pigmented, plastic films for Ge, SrF2, and Sc2O3 K-edge filters is briefly described.
Electrical Magnetoresistivity of Chromium-Iron Alloys
Authors: Arajs Sigurds , Dunmyre G. R.
Published: January 2005

The effect of longitudinal magnetic fields up to 60 kOe on the electrical resistivity of chromium-iron alloys containing 0.9, 2.3, 3.3, 4.9, 9.5, and 11.2 at. % iron, have been studied at 4.2°K. All these alloys, except that with 0.9 at. % iron, exhibit negative total magnetoresistivity. The role of temperatures on the transverse magnetoresistivity at 12 kOe has been explored using the chromium-9.5-at. %-iron alloy. The change in the magnetic component of the total magnetoresistivity has been calculated from the experimental data. This quantity is discussed from the viewpoint of a localized-magnetic-moment model.
Effects of Sulfates on the Properties of Strontium Ferrite Magnets
Authors: Cochardt A.
Published: January 2005

Up to 6.0 wt % SrSO4, CaSO4, and BaSO4 were added to strontium ferrite magnets consisting of the magnetoplumbite phase SrO·6 Fe2O3. The hysteresis loop, density, saturation moment per gram, and the degree of orientation were measured. The magnets were analyzed by standard chemical methods and by x-ray diffraction techniques. The microstructures of the magnets were examined with a light microscope and with an electron-beam microanalyzer. It was found that approximately 0.1 to 2.0 wt % SrSO4, CaSO4, or BaSO4 are extremely beneficial in activating the ferrite magnet formation and in improving the magnet properties. SrSO4 is particularly effective. With only 0.22 wt % SrSO4 and at a sintering temperature of 2250°F, the remanence is increased from 3425 to 4150 G, the saturation moment from 65.2 to 69.1 G·cm3/g, the density from 4.21 to 4.86 g/cm3, and the degree of orientation from 81% to 87%. X-ray scanning micrographs show that the solubility of SrSO4 in SrO·6 Fe2O3 is greater than 0.22 and less than 1.1 wt % at 2250°F.