bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Superconducting Lenses for a 500-kV Electron-Microscope Column
Authors: Worsham R. E.
Published: February 2004

The advantages of using superconducting windings and cryogenic temperatures in transmission electron microscopes have been recognized for some time but not fully achieved; they are: improved resolution because of higher fields and shorter focal lengths, reduced size, better vacuum, improved mechanical stability, and greater electrical stability with persistent mode of operation of lens field. At ORNL, a 500-kV microscope is being developed with the goal of 1-Å point-to-point resolution in biological specimens. All lenses will use superconducting windings operated in the persistent mode. A quadrupole-octupole lens system will correct the primary spherical aberration of the objective. Over-all in-instrument magnification will be 5 ×106X. An investigation of round-lens fields shaped primarily by currents showed that low aberrations could not be attained. Lenses using pole pieces of 1010 steel, Armco iron, and Hiperco 50 were evaluated in magnetic field tests. Typical figures are an uncorrected resolution limited by spherical aberration of 1.21-Å in an Armco iron lens with a 7.6-mm bore and 32-kG field. Further work with Hiperco 50 and dysprosium pole pieces at fields above 30 kG is in progress.
Direct Measurement of the Effect of Strain on Tc in Thin Films
Authors: Friday B. W. , Mundy J. L.
Published: February 2004

Direct measurements have been made of the effect of strain on the critical temperature of tin, aluminum, and indium films. The films (<1000 Å) were vacuum deposited onto glass and mylar substrates at room temperature and were then strained by mechanically bending the substrate in liquid helium. Tc depended linearly on the strain over the range of observation, ∼10−3, for both tensile and compressive bending. The slopes of the Tc vs strain curves were 8.7° and 9.1°K per unit strain, respectively for tin and aluminum films on glass substrates and 4.9° and 3.8°K per unit strain for tin and indium films on mylar substrates. Earlier measurements1,2 have indicated considerable variation in the Tc dependence on strain from film to film, but our data are quite reproducible and do not seem to depend markedly on the evaporation conditions. For an isotropic material or an anisotropic material for which the relative orientation of the strain axis and the axes of crystal symmetry are known it is possible to relate the change in Tc to a corresponding volume change. On this basis one can compare the results on thin films with strain and pressure measurements on bulk samples. Comparing d ln Tc/d ln V for thin films and bulk samples3 we find that the values for aluminum agree within five percent, those for tin films on glass are lower by thirty percent, and those for indium films are higher by a factor of three. The change in Tc due solely to a change in sample volume can be calculated as a function of the Debye temperature on the basis of the McMillan theory1 by using the Gruneisen relation and taking λ, the phonon-mediated electron interaction, to be inversely proportional to the square of the Debye temperature. Comparing experimental results with these calculations we find that the experimental results for dTc/dθD lie within the limits imposed by μ* = 0.1 to 0.2 for bulk aluminum, tin, and indium and thin-film aluminum and tin. (Materials for which the Coulomb pseudopotential, μ*, has been measured lie within these limits.)
Resistivity Minimum in an Amorphous Ferromagnetic Alloy
Authors: Lin S. C. H.
Published: February 2004

The electrical resistance-vs-temperature curve of an amorphous Fe80P13C7 alloy, obtained by rapid quenching from the liquid state, has a minimum at low temperature. Because the quenching conditions cannot be accurately controlled, the temperature at which the minimum occurs varies from specimen to specimen and covers a range from 10° to 50°K. A study of 14 different specimens shows a correlation between this temperature and the ratio of the resistances at helium temperature to that at room temperature. This correlation is interpreted in terms of the existence of regions of short range order, or small amounts of crystalline phases in imperfectly quenched specimens.
Grain-Boundary Fine Structure in an Iron Alloy
Authors: Ishida Y. , Hasegawa T. , Nagata F.
Published: February 2004

Regular substructures were observed in grain boundaries of an annealed Fe-0.75% Mn alloy by transmission electron microscopy. A detailed analysis was made on one of the grain boundaries. The result indicates that the analyzed grain boundary may be considered as a coincidence site grain boundary.
Resistance of Tantalum in the Intermediate (Superconducting-Normal) State
Authors: Smith Frank T. J. , Gatos Harry C.
Published: February 2004

Tantalum may be converted from a type I to a type II superconductor when small amounts of interstitial impurities are present. The resistance of type I and type II wire specimens was measured in a transverse magnetic field during the superconducting to normal transition. It was found that for both types carrying a transport current, the resistance for the major portion of the transition region is a function of the Lorentz force acting on the normal domains of the intermediate state or on the flux filaments of the mixed state. The effects of strain and impurity were also studied and were interpreted in terms of their influence in retarding the motion or pinning of normal domains in the material.
Constitutive Relation for Rate-Dependent Plastic Flow in Polycrystalline Metals
Authors: Johnson James N.
Published: February 2004

The rate-dependent constitutive relation developed by Taylor, which considers dislocation motion only in glide directions and on glide planes for which the shear stress is maximum, is extended to include dislocation motion in all glide directions on all glide planes. The theory requires that grain orientation be random, that expanding dislocation loops be rectangular, and that the velocity of edge dislocations be much greater than the velocity of screw dislocations. The velocity of screw dislocations is assumed to be given by vs=vm exp (-B/τ), where τ is the applied shear stress, B is a constant, and vm is the elastic shear wave velocity. On the basis of this theory, elastic wave attenuation in Armco iron is calculated and compared with the experimental data of Taylor and Rice. It is found that the mobile dislocation density necessary for the theoretical calculation to agree with experimental data is five times greater than that obtained by Taylor on the basis of the simpler theory. Likewise, for a given shear stress, it is found that the dislocation velocity is greater than that determined previously. This indicates that the results obtained on the basis of the simpler theory may significantly underestimate the velocity of individual dislocations as well as the mobile dislocation density.
Experimental and Theoretical Eigenmodes of a Spherical Cavity Partially Filled with Plasma
Authors: Boyen H. L. , Messiaen A. M. , Vandenplas P. E.
Published: February 2004

A complete experimental and theoretical account is given of the eigenmodes (cold and hot) which exist at low power in a cavity partially filled with a plasma. The cavity modes which are perturbed by the plasma together with the basic cold-plasma modes are studied theoretically using uniform cold-plasma theory. The hot-plasma modes of the system are investigated on the basis of a WKB approximation of the relevant equations of a nonuniform hot plasma. Experiments performed with a spherical discharge tube and also with a spherical afterglow plasma give results which are in satisfactory agreement with theoretical predictions. The measured Q factor of the resonances also agrees with theoretical calculations.
Single-Specimen FEM-LEED Studies: Carbon on Tungsten
Authors: Melmed Allan J.
Published: February 2004

Field-electron microscopy and low-energy-electron diffraction can be used in a complementary manner. A method of making such a direct combination on a single specimen is described and applied to a study of the problem of carbon contamination of tungsten surfaces. It is shown that, within the sensitivity of the apparatus used, carbon may be present and remain undetected by the display mode of LEED on a (nonperfect) (011)-oriented W LEED specimen.
Microwave Magnetoresistance Measurements
Authors: Friedberg Charles B. , Strandberg M. W. P.
Published: February 2004

The magnetoresistance of a conducting solid has been measured at high frequencies through the techniques of microwave spectroscopy. The measurement is based on the detection of electromagnetic power absorbed by conduction electrons under the conditions imposed by a resonant cavity and an external magnetic field. The magnetic field dependence of this power absorption is calculated and verified experimentally within one order-of-magnitude for a thin copper film. The method developed has potential application to the measurement of mobility of charge carriers in organic substances. In certain biomolecules, particularly those that are important in life processes, mobility measurements should be useful in distinguishing electronic and protonic conduction processes.
Ellipsometric Analysis of Radiation Damage in Dielectrics
Authors: Schroeder J. B. , Dieselman H. D.
Published: February 2004

The reflectivities have been calculated by the matrix method using a digital computer for light polarized parallel (P) and perpendicular (S) to the plane of incidence for dielectric materials with continuously varying index of refraction profiles. Assuming various index of refraction profiles up to the computed penetration depth for positive ions, it was found that the phase difference between the P- and S-waves is sensitive to the magnitude and shape of the index perturbation. Results for 150 keV Ar+ bombardments of transparent vitreous silica are presented which show that implanted argon increases the refractive index of the solid by 0.02. The implanted ions appear to out diffuse between 200° and 600°C.
Experimental Investigation of the Nucleation of Silver on Molybdenite
Authors: Corbett J. M. , Boswell F. W.
Published: February 2004

An experimental investigation has been made of the nucleation of Ag on single-crystal MoS2 for deposition rates in the range 8×1011−7×1013 atoms/cm2·sec and at two substrate temperatures, 30 and 200°C. At the lower deposition rates employed, the Ag deposits were found to be very highly oriented with Ag (111) parallel to MoS2 (0001) and Ag [11̄0] parallel to MoS2 [21̄1̄0]. The smallest Ag clusters detected by transmission electron microscopy were approximately 20 Å in diameter. Nucleation rates were determined for various deposition rates and it was found that the nucleation rate varied linearly with the deposition rate at each temperature. Attempts were made to fit both the capillarity and atomistic theories of thin-film nucleation to the experimental results, and it was found that neither theory could be fitted in a completely consistent manner. Explanations for the differences between theory and experiment are discussed.
Magnetization Studies on Superconducting Vanadium-Gallium
Authors: Decker D. L. , Laquer H. L.
Published: February 2004

The temperature dependence of the critical fields of V3Ga has been measured up to 70 kOe using ac and dc magnetization techniques. For a material with a transition width of 26 mdeg at a transition temperature, Tc, of 14.19°K, one calculates from the slope (dHc2/dT=−43.2 kOe/deg) and curvature of the Hc2 vs T curve, the Ginzburg—Landau parameter, κ=40±2, the Pauli paramagnetism parameter α=2.28±0.04, and the spin—orbit scattering constant λso=0.6±0.1. No evidence for Hc3 was detected and the experimentally difficult upper limit to Hc1 appears to be about three times as large as calculated from the theories.
Wall-Pinning Model of Magnetic Hysteresis
Authors: Baldwin John A. , Culler Glen J.
Published: February 2004

A simple model for the motion of a domain wall in most magnetic materials is presented. The real flexible wall is represented by an equivalent rigid plane wall. The motion of the plane is impeded by springs which are attached to the wall and to defects in the material in the wake of the plane. A spring breaks when the force it exerts on the wall reaches a value characteristic of the defect, and the energy stored in it is lost to the motion. The model is similar to one developed earlier but is based on a more plausible view of the interaction of a wall with a defect. In common with the earlier model, it describes both reversible and irreversible flux changes; it predicts a small-signal hysteresis loop which is similar to, but significantly different from, the Rayleigh loop; it explains the frictional nature of magnetic hysteresis without invoking any ad hoc energy-loss mechanisms. It is sufficiently simple to be applied to complex problems. It agrees with the results of exact dynamic calculations to good accuracy and is exact when applied to quasistatic problems. The model is derived by considering the motion of an anisotropic flexible wall pinned by a periodic array of defects. The springs of the model represent the distortions of the wall in the vicinity of the defects. It is shown that the force f exerted by the defect on the wall and the energy W per defect stored in wall distortions are related approximately to the average displacement z̄ of the wall from the defect by the equations f(t)=kz̄(t),   W(t)=kz̄2(t)/2,where k is a spring constant associated with wall deformation. These relations justify the spring model. Finally, a comparison is made among f, W, and z̄ calculated as functions of time for a step of applied field from both the exact equations and from the spring model. The agreement is, in all cases, better than 10% of the final values. After the wall breaks free from a defect the energy stored in distortion is dissipated in viscous damping. It does not affect the average wall position and is thus lost to the motion in agreement with the model.
Magnetic-Field Computation for a Plated-Wire Memory Utilizing an Integral/Matrix-Equation Technique
Authors: Lotsch Helmut K. V.
Published: February 2004

An integral/matrix-equation technique for the calculation of a magnetic field produced by stationary current in the presence of permeable material is presented. Utilizing this technique, magnetic fields are computed on the basis of a two-dimensional model for the plated-wire memory element. This model essentially represents a planar-memory element since the plated wire is simulated by a slab of permeable material. Numerical results are presented for different permeabilities of the keepers and the simulated wire. These results show quantitatively how the keepers enhance the magnetic field between the current straps, where the information is to be stored, and how they reduce the fringing fields outside. The field enhancement can be interpreted as reduction in current or power for a given field at the center due to the use of keepers. The technique presented is sufficiently simple and efficient to be a useful tool in designing magnetic memories, as well as in determining the effect of mechanical tolerances on their performance.
Thermal Release of Inert Gases from (110) and (211) Tungsten Surfaces
Authors: Kornelsen E. V. , Sinha M. K.
Published: February 2004

Clean (211) and (110) surfaces of tungsten have been bombarded with inert-gas-ion beams in the energy range 40 eV–5 keV. Thermal desorption spectra of the trapped gas show patterns of peaks characteristic of the ion and the face bombarded. The results are comparable to those obtained previously for a (100) tungsten surface. In particular, all peaks below 1650°K are associated with desorption from sites within about 10 Å of the crystal surfaces, while the single peak above 1700°K is the result of isotropic diffusion of ions which have penetrated more than 10Å. Evidence is presented to support the hypothesis that the trapping sites consist of substitutional gas atoms and associated point defects.
Direct-Current Measurement of the Hall Effect in Trigonal Selenium Single Crystal
Authors: Heleskivi J. , Stubb T. , Suntola T.
Published: February 2004

The Hall effect in trigonal selenium single crystals has been measured by a dc method. The measurements give a carrier concentration of 0.5×1015 cm−3 at room temperature and 1015 cm−3 at 100°K. The conductivity is of p type within the entire temperature range. By illumination with extrinsic light the carrier concentration has to a certain extent turned out to be independent of the intensity of light. The mobility calculated from a barrier model is about 260 cm2/V sec at room temperature in the direction of the c axis. The value is considerably higher than earlier reported values.
Deposition of Silicon by Electron Irradiation of Tetramethylsilane
Authors: Faber E. S. , Tauber R. N. , Broyde Barret
Published: February 2004

The deposition of thin silicon films by the electron beam dissociation of adsorbed tetramethylsilane has been investigated. Growth rate was studied as a function of P the vapor pressure of tetramethylsilane, T the substrate temperature, and J the current density. It was found that there is a region where the value of the growth rate can be calculated from the expression r=KPJ expa/T, where K and a are constants. Assuming a model in which a=Q/R and K=cσ, where R is the gas constant and c is a calculable constant, Q, the heat of adsorption, was found to be 11.6 kcal/mole and σ, the collision cross section, was determined to have the unexpectedly high value of 3.86×103 Å2 for 300-V electrons. Electron diffraction and transmission electron microscopy showed the as-deposited films to be amorphous. The resistivity of these films varied with thickness and showed a minimum value of approximately 5×104Ω·cm when the film thickness was between 1000 and 1500 Å. Thinner films were less conductive because the high amount of stress in the film increased scattering. Thicker films were less conductive because the impurity content of the films increased with film thickness. Heat treating at 800°C produced extensive grain growth and resistivities dropped by a factor of 103. Annealing at 300°C for a few hours decreased the resistivity by about a factor of two although no grain growth occurred at this temperature.
Electron-Microscope Study of Thermal Recovery Processes in Explosion-Shocked Nickel
Authors: Trueb Lucien F.
Published: February 2004

A study by transmission electron microscopy was made of the microstructure of pure polycrystalline nickel foil after explosive-shock loading and subsequent heat treatments between 600° and 780°C. In the instance of specimens shocked at 70 and 320 kbar, the deformation substructures resemble those normally caused by cold work, but the recovery process consists mainly in dislocation migration and recombination; no polygonization, nucleation, or grain growth are observed. Nickel shocked at 1000 kbar on the other hand, exhibits an extremely high density of dislocations, point defect clusters, and microtwins arranged in complex patterns. In this instance, heat treatment causes nonuniform polygonization, nucleation, and grain-boundary migration. This results in a significantly lower dislocation density after annealing, particularly at the higher temperatures, and considerably more extensive softening than is the case for nickel shocked at lower pressures.
Electrostatic Contribution to Powder-Particle Adhesion
Authors: Donald D. K.
Published: February 2004

Experiments are described which examine the electrostatic contribution to the adhesion of powder particles to substrates. The fine powder in these experiments was dispensed over the large surface area of an assembly of glass beads and the adhesion of the particles to the larger beads was measured with a centrifuge. Complementing the adhesion measurements were charge measurements where the average charge density and also the incremental charge density were measured by gradually blowing the powder from the beads. A purely electrostatic point-charge model for the adhesion of the particles was consistent with the observations in most cases. In some situations, however, an additional term was needed to better describe the adhesion, and this may have been either an electrostatic multipole phenomenon or a van der Waals contribution.
Internal Friction of Single Crystal U4O9
Authors: Doi H.
Published: February 2004

Measurements of internal friction and Young's modulus between −210° and 700°C have been carried out at frequencies 130–185 kHz on U4O9 single crystals. Two pronounced internal friction peaks were observed, one at 60° and the other at −175°C. The peak at the higher temperature seems to be due to a phase transition of U4O9. The factors affecting the peak suggest that it is not caused by a relaxation process. It is suggested that some cooperative movements of interstitial oxygen ions in some lattice planes cause such a transition. The peak at the lower temperature is due to a relaxation effect. A rough calculation of the activation energy gave 0.034 eV. In addition, the results of the electrical conductivity measurements at low temperatures (25°–−160°C) gave the activation energy of 0.057 eV, in an approximate agreement with the one derived from the internal friction measurements. This indicates that the relaxation process involves activated charge transfer between U5+ and U4+ ions (hopping motion of electronic holes). It is tentatively proposed that stress-induced ordering of a defect complex involving U5+ ion and some oxygen ion(s), which produces a 〈111〉 elastic distortion in the lattice, gives rise to the relaxation effect.
Electrical Properties of Saline Ice
Authors: Addison J. R.
Published: February 2004

Results are presented of a study of the (normalized) complex dielectric coefficient, and related parameters, of unidirectionally frozen artificial sea ice having salinities from 4 to 20‰. The frequency dispersion was investigated between 20 Hz and 100 MHz at temperatures from −35° to −12.5°C. An unusual measurement cell, which becomes incorporated into the ice as it forms, is described and justification offered for its use. The frequency dispersion of the real part of the dielectric coefficient may be considered in three parts. Large values (105 to 106 at −15°C, and 103 to 104 at −35°C) were observed at 20 Hz, falling slightly more rapidly than (frequency)−1 up to 5 kHz. Between 5 and 500 KHz most curves exhibited a distinct downward concavity (which was more prominent at lower temperatures), values dropping from between 103 and 104 to the order of 102 over this range. At higher frequencies the rate of decrease was smaller, values of 10 or less being observed at 100 MHz. Loss factors (values at 20 Hz: 106 to 107 at −15°C, and 104 to 105 at −35°C) in most cases decreased approximately as (frequency)−1 over most of the frequency range. Loss tangents, which were slightly larger at higher temperatures, were of order 10 below 1 MHz, dropping to less than 1 above 10 MHz. The curves for this parameter exhibited two temperature-dependent maxima. The electrical properties changed most rapidly with temperatures near −23°C, the NaCl deposition temperature.
Low-Frequency, Electrostatic Oscillations of a Tenuous, Hot E Layer
Authors: D'Ambrogio Enos , Nocentini Aldo
Published: February 2004

The stability against low-frequency, electrostatic, flute-like oscillations of a tenuous, hot, plane layer of charged particles embedded in a uniform and constant magnetic field is considered. It is shown that finite Larmor radius effects do not modify essentially the diocotron modes. It is also shown that a layer of particles whose guiding centers are located on a thin (with respect to the thickness of the layer) sheet around the midplane of the layer, is unstable: more precisely it has, for long (with respect to the thickness of the layer) waves, the same dispersion relation which holds for the diocotron modes. This strongly supports the conclusion that the diocotron instability of a charged, tenuous, plane layer is essentially independent from its kinetic structure.
Electrets, Semipermanently Charged Capacitors
Authors: Roos J.
Published: February 2004

Electret theory is briefly summarized and discussed. The electret strength as usually measured is shown to depend on the measuring method, the electret thickness, and the storage conditions. This is caused by charge leakage and sparking. The maximum charge density as a function of electret thickness is calculated; the thicker the electret the lower the maximum charge density. Our electrets are thin (5 μm) polymer membranes, provided with evaporated gold electrodes. They do not have to be stored in a short-circuited condition.
Potential Distributions and Topography of npn-Type Junctions in Photosensitive Epitaxial PbS Films
Authors: English F. L. , Parsons M. K. , Schoolar R. B. , Riedl H. R.
Published: February 2004

The electron-mirror microscope (EMM) has been used to study photosensitive npn-type junctions in heat-treated epitaxial PbS films. The EMM indicated variations in junction symmetry and strength on a much smaller scale than previously observed with a light-spot scanning technique. In addition, the variations observed were found to correlate with surface topography. Regions of high junction density that have nearly zero photovoltaic response due to cancellation effects, were clearly resolved with the EMM.
Stress-Induced Desorption from Aluminum, Magnesium, and Molybdenum
Authors: Feuerstein S. , John I. W.
Published: February 2004

Room-temperature tensile deformation experiments were performed on aluminum, magnesium, and molybdenum at 10−10 Torr; at the same time, chamber pressure and residual gas species were monitored. Pressure increases noted during the deformations were attributed to specimen desorption resulting from imposed stresses and their concomitant lattice distortions. Hydrogen and methane were evolved from all three metals. The extent of desorption, however, was different for each material.
Preparation of Free Surface Mercury Single Crystals
Authors: Fickett F. R.
Published: February 2004

A simple method for the preparation of free surface single crystals of mercury is presented. X-ray orientation determination and formation of electrical contacts are discussed.
Influence of Dissolved Oxygen upon Point Defect Mobility in Copper
Authors: Heiple C. R. , Thompson D. O.
Published: February 2004

The results of measurements of the rate of arrival of defects at dislocations in copper doped with varying amounts of oxygen are presented. The defects were created continuously during the measurement by gamma-irradiation, and the arrival of defects at the dislocations was detected by measuring the dislocation damping. The rate of arrival of the stage III defect at the dislocations was not affected by the oxygen content of the copper. This result indicates that the binding energy between oxygen and the stage III defect is considerably less than the motion energy of the defect. Some evidence for a significant binding between oxygen and another defect (presumably the vacancy) created by the irradiation is presented.
Orientation Dependence of Dislocation Damping in Hexagonal Metals
Authors: Henneke Edmund G. , Green Robert E.
Published: February 2004

The orientation dependence of dislocation damping in the five hexagonal metals Mg, Cd, Be, Zn, and Ti has been predicted by calculation of the appropriate factors relating the stress field of the elastic waves to the slip systems in which the dislocations are moving. The four metals having basal slip systems have very similar qualitative behavior of the orientation factors. Titanium, with prismatic slip systems, has a quite different behavior and the orientation factors are smaller for all orientations than the values for the basal slip metals. For Zn, Cd, Mg, and Ti, the values of the orientation factors for standing waves (resonance technique) are larger than the corresponding values for the traveling waves (pulse-echo technique). For Be, the orientation factors for both types of waves are nearly equal. Crystal orientations and wave types of particular interest for experimental study are delineated.
Experimental Investigation of the Normal Modes in a Warm Cylindrical Plasma
Authors: Ben-Yosef N.
Published: February 2004

Experimental observations of the normal modes in a cylindrical plasma without external excitation is presented. The experimental results compare favorably with theory. Measurement of the high-frequency electromagnetic field outside of the plasma and its spectrum lead to a method of measuring the electrostatic oscillations spectrum in a plasma without perturbing it in any way. Exact measurement of the emission profile at the plasma frequency can give information about the mean thermal speed of the electrons without any assumption about their distribution function.
Magneto-optical Effects of Hot Electrons
Authors: Wood Van E.
Published: February 2004

The effect of a large static electric field on the Faraday and Voigt free-carrier magneto-optical effects in semiconductors is calculated for a parabolic band, for acoustic scattering, and for both high and low frequencies and low losses. It is shown that the electric field produces a larger relative change in the Voigt effect than in the Faraday, and that sizable effects may occur in all cases. Only the effect of the electric field on heating up the charge carrier distribution is considered, specifically directional effects being neglected. Comparison is made with experiments on indium antimonide.
Vaporization of Solid Silver. II. Macroscopic Surface Roughening
Authors: Winterbottom W. L.
Published: February 2004

Certain morphological features developed during the vaporization of solid silver have been found to correlate with crystallography and environment. Through the results obtained in related kinetic measurements, capillarity forces are shown to be responsible for the hill and valley roughness that is developed. On the basis of the deduced origin, a model for the roughening process is developed. An orientation dependence of the surface morphology, vaporization faceting, is shown to demonstrate the presence of cusped minima in the surface-energy-orientation relationship for silver at the {111} and {100} orientations. Evidence for the adsorption of O2, acetone, CH3, H2S, and Cl2 on Ag during vaporization was obtained. The results indicate that a C impurity is deposited on the surface by the interaction between carbon-bearing gases and the vaporizing silver and that the C impurity adsorbs preferentially at surface defects and tends to blunt the surface-energy cusps at the low-index orientations. Absorbed oxygen was found to react with other impurities to form desorbable surface species.
Effect of Temperature on the Work-Function Minimum of Cesiated Tungsten Surfaces
Authors: Lee T. J. , Hopkins B. J. , Blott B. H.
Published: February 2004

Work-function changes during the desorption of cesium from three tungsten surfaces, polycrystalline foil, (100), and (110) oriented single crystals, have been measured in the region of the work function minimum. A modification of the vibrating capacitor technique which made contact-potential difference on electron emitting surfaces possible was developed for these experiments. For different arrival rates of cesium, the minimum work function occurred at different temperatures and decreased in magnitude with temperature. Values at 295°K were 1.78 eV for polycrystalline foil, 1.795 eV for the (100), and 1.955 eV for the (110). For all specimens the decrease in magnitude with temperature was of the order of 10−3 eV·K0−1. These data were compared with thermionic values for the work function minimum and with theoretical predictions. We note especially that the sign of the variation is opposite to that predicted by the Rasor-Warner theory in every case.
Structure and Energy of a Néel Wall by a Four-Parameter Ritz Method
Authors: Aharoni Amikam
Published: February 2004

A one-dimensional model with four adjustable parameters is assumed for the Néel wall separating two oppositely magnetized domains in a thin ferromagnetic film. It yields an energy which is somewhat lower than in any of the published models. Its self-consistency parameter S is not very sensitive to changes in the anisotropy constant; and, for the parameters usually used for Permalloy films, this S varies between 0.94 and 1.23, which is a necessary condition that the wall energy thus calculated is reasonably close to the true, three-dimensional minimum. It turns out that almost the same results can be obtained by choosing convenient values for two of the four parameters, and adjusting only two.
Electronic Properties of Silicon Doped with Silver
Authors: Thiel Frank L. , Ghandhi Sorab K.
Published: February 2004

A study of the electronic properties of bulk silicon doped with silver is described. It is shown that silver has a singly ionizable donor level 0.26 eV above the valence band edge, and a singly ionizable acceptor level 0.29 eV below the conduction band edge, in variance with previously published data. The effects of large concentrations of silver upon carrier mobilities are also explored. Measurements of the capture probabilities of the various silver charge states are described and the results compared to those for gold in silicon.
Dependence of Schottky Barrier Height on Donor Concentration
Authors: Archer R. J. , Yep T. O.
Published: February 2004

Schottky barrier heights of Au contacts to n-type Si with either etch-polished or vacuum-cleaved interfaces are independent of donor concentration within an experimental uncertainty of about ±0.05 eV for 1014 cm−3≤ND≤1019 cm−3. Within the same uncertainty and over the same doping range, barrier heights determined from capacitance using the standard formula are equal to those determined from photoemission thresholds. A theory for deducing barrier heights from photoemission thresholds that includes the effects of tunneling and image force is presented. The results are interpreted in terms of a simple model for the interface, which is characterized by the thickness d and dielectric constant κ′ of the interfacial film and the density nss of interface states. The insensitivity of the barrier height to the quantity of space charge leads to the following limit on the interfacial parameters: (k′/d)+1.8×10−6nss≥3.8×108 cm−1for d in cm, and nss in cm−2 eV−1.
Misfit Accommodation by Imperfect Dislocations in Epitaxial fcc Films
Authors: Jesser W. A.
Published: February 2004

Expressions are derived for the equilibrium elastic strain of an overgrowth film in terms of the Burgers vectors of imperfect misfit dislocations and their associated stacking faults. It is shown that under most experimentally encountered conditions, the effect of the stacking fault on the equilibrium spacing of the dislocations is unimportant.
Electronic Effect on the Solubility of Interstitials in Transition Metal Alloys
Authors: Chao K. A. , Ansell G. S.
Published: February 2004

A theoretical analysis of the solubility of interstitials in transition metal alloys is given. The change-of-system free energy as the interstitials are formed from the atomic state to the ionized state during the dissolving process is found to be dominated by the electronic interaction. This electronic interaction energy is characterized by the energy band structure, a rigid band model being used for the case of these bcc alloys. The minimum exhibited in the density-of-states curve, caused by the overlapping of subbands, gives rise to an unusual free energy change. Numerical calculations predict the interstitial solubilities in good agreement with Jones' experimental result. By comparing the solubilities of hydrogen and oxygen, oxygen should be singly ionized as an interstitial in these alloys.
Beam Loading in a High-Current Standing-Wave Electron Accelerator
Authors: Stapleton R. E. , Gritzo L. A. , Venable Douglas
Published: February 2004

Electron-beam loading of a single-cavity standing-wave accelerator has been investigated experimentally and theoretically for the case of continuous injection over ten cycles. The particular cavity used was a 2.4-m long right-circular cylinder excited at 50 MHz in its TM010 mode with an unloaded Q of 1.2×105. Beam currents were varied from 40 to 210 A, field strengths from 0.2 to 6 MV/m, and the energy of the ejected beam from 1 to 10 MeV. During beam injection the energy supplied per cycle to the accelerator by its power amplifiers was negligibly small compared to the energy absorbed per cycle by the injected electron beam. The energy extracted by the electrons was determined from cycle-to-cycle oscilloscopic observations of the decay of the accelerating field. Energy extraction per cycle was as great as 8% of that residing in the electromagnetic field at the time of beam injection. The results agree with predictions over most of the range of the experimental parameters when assuming paraxial trajectories. Disagreement with calculations, when using the same assumption, arose when there were serious departures from paraxial flow. The special case of injection of a sharply bunched relativistic electron beam is also reported. Here each 18-MeV bunch contained about 1.7 μC and was about 6-nsec long. When in an accelerative mode the electric field was degraded and energy flowed from the field into the beam bunches at a rate of about 0.6 BW. However, when the phase of the field was reversed to establish a decelerative configuration the electric field was enhanced, energy flowed coherently from the beam bunches into the field at a rate of about 0.6 BW. Within experimental uncertainties, these values agree with predictions.
Origin of Striations Due to Mechanical Effects in Fast Wire Explosions
Authors: Smith Stanley H.
Published: February 2004

The suggestion that mechanical oscillations in the solid wire are in part responsible for the production of striations observed in a class of wire explosions is investigated using the dispersion relation for elastic waves in isotropic solid cylinders. It is proposed that these oscillations arise due to the transient nature of the electrical energy deposition and that axial waves originate at points of discontinuities such as impurities and grain boundaries. Numerical solutions are obtained using the first shear- and dilatationalmode cutoff frequencies, and the wave numbers of these and standing waves are presented as a function of Poisson's ratio. Experimental data on the average distance between striations and new data are found to lie within the range predicted by the theoretical analysis.
Pressure Enhancement of the Net Acoustic Gain in Piezoelectric Semiconductors
Authors: Zemon S. , Zucker J. , Adler P. N.
Published: February 2004

Hydrostatic pressures of up to 16 kbar are shown to increase the net acoustoelectric gain in semiconducting CdS and CdSe. Decreasing conductivity with pressure in CdS is attributed to a decrease in both mobility and carrier concentration whereas no significant changes were observed in CdSe. The frequency of maximum gain, as calculated from linear theory, decreases with pressure in CdS.
Dynamic Annealing of Magnetic Films
Authors: Tan S. I. , Mayadas A. F.
Published: February 2004

A dynamic technique using a rotating field has been developed for studying the uniaxial anisotropy of magnetic thin films. It is shown that reversible time-dependent contributions to the anisotropy can be revealed as peaks in a skew versus temperature curve at constant frequency, or in a skew versus frequency curve at constant temperature. Compared to the use of static isothermal annealing, the dynamic technique offers an improvement in the resolution of the components of the anisotropy spectrum. The method has been applied to 900 Å permalloy films prepared by evaporation onto substrates held at 300°C. Measurements conducted from room temperature to 200°C yielded reproducible results, and revealed one rotatable time-dependent contribution governed by an activation energy of 1.2 eV and a period factor of 10−13 sec. The data conform quite well to the formal theory developed for the case of a contribution possessing a single relaxation time. The rotatable contribution accounts for 11% of the total room-temperature anisotropy, and has an absolute magnitude KR∞ of 0.2×103 erg/cm3. The effect can be accounted for by the ordering of iron atom-vacancy pairs.
Effect of Electric Charge on the Evaporation of Naphthalene Single Crystals
Authors: Williams R. , Campos M.
Published: February 2004

An electrically charged crystal of naphthalene shows characteristic evaporation etch pits not found on evaporation of an uncharged crystal. The charge is deposited on the crystal from a corona discharge in air. The effect of the charge is apparently to nucleate evaporation at sites where nucleation is unlikely in the absence of charge.
Computer Models of Polyethylene Spherulites
Authors: Thornton A. W. , Predecki Paul
Published: February 2004

In order to account for the morphology observed in surface replicas of polyethylene spherulites, two possible mathematical models are proposed. These are based on the requirement that lamellae with a given twist angle about the radius vector of the lamella form continuous surfaces. It was found possible to arrange the lamellae in such a way that the locus of all points of given lamellar twist within the spherulite was a continuous surface of three-dimensional spiral form. A computer was used to plot out the ring structure to be expected on sections through the models, and these were compared with the actual ring structures observed on surface replicas of polyethylene spherulites. On all sections not passing through the spherulite center, both models show a double-armed spiral form in keeping with observed structures. Sections passing through the centers of the models do not always give double-armed spirals, depending on the model.
Time Dependence of Dislocation Damping
Authors: Trott B. D. , Birnbaum H. K.
Published: February 2004

The behavior of pinning points at dislocations during internal friction measurements is discussed. Diffusion of pins along the dislocation prior to breakaway of the dislocation from the pinning points and in the lattice subsequent to breakaway is qualitatively considered. Both types of motion lead to time dependence of the internal friction and the variation of this time dependence with temperature and strain amplitude is discussed. It is shown that a study of these effects can lead to an understanding of the contribution of the amplitude-dependent viscous damping and of the amplitude-dependent hysteretic damping to the total specimen damping. An experimental technique is described which allows a separation of these two contributions. This technique is applied to Al and Al–Mg alloys at high and low temperatures and the existence of these two damping contributions is demonstrated.
Analysis of Asymptotic Small-Angle X-Ray Scattering Curves
Authors: Rothwell W. S.
Published: February 2004

The extent to which various factors contribute to smoothing of the classical small-angle x-ray scattering curve in the subsidiary peak region is examined. The effects of finite chromatic and angular resolutions and of shape and size distribution of heterogeneities are determined and discussed. Two methods of obtaining quantitative size data from curves exhibiting asymptotic behavior are discussed. An analysis is presented to show the validity of a method first suggested by Bragg from an empirical evaluation. A new method using an intercept of the extrapolated asymptotic curve is described. The significance of the effective mean heterogeneity dimensions found is discussed. It is shown how correlation with analysis of data for the Guinier region can be used to estimate the spread of heterogeneity size distributions.
Temperature Dependence of γ-Irradiation Hardening in NaCl
Authors: Lerma I. S. , Agulló-López F.
Published: February 2004

It has been shown that the γ-radiation-induced hardening of NaCl is strongly dependent on temperature [between liquid-nitrogen temperature (LNT) and room temperature (RT)] for low irradiation doses, but it is essentially independent of it for doses ≳6×106 R. For very low doses ≲1×106 R the experimental data can be analyzed in terms of a rapid solution hardening mechanism of the type proposed by Fleischer. For higher doses this model is not adequate and one should think of a precipitation (Orowan) hardening mechanism.
Effect of a Magnetic Field on Steady-State Charge Carrier Distribution
Authors: Green Milton
Published: February 2004

The carrier distribution, space charge, and related quantities in a nondegenerate semiconductor are examined theoretically in rectangular Hall geometry with an applied magnetic field, and in cylindrical geometry with the self-magnetic field only. Solutions in rectangular geometry are found for the special cases of zero and infinite recombination coefficient and for space-charge conditions giving rise to constant and quadratic electric field configurations (symmetric recombination conditions). Solutions in cylindrical geometry are of zero order in the radius, i.e., n and p are constant, but not the equilibrium values; the recombination coefficient is variable. The pinch gain, np/ni2, is determined essentially by the product of the transport numbers, the sum of the carrier mobilities, the magnetic permeability, the square of the axial current density, and the reciprocal of the recombination coefficient.
Approximate Step-Function Response of a Horizontally Polarized Electromagnetic Wave Reflected at an Imperfectly Conducting Surface
Authors: Monroe Richard L.
Published: February 2004

A two-term expression consisting of a constant plus the product of an exponential and complementary error function is given for the transient reflected field of a horizontally polarized (E field normal to the plane of incidence) plane wave in free space with a step-function time variation incident obliquely on a plane imperfectly conducting surface. Curves computed with this expression are shown to be in good agreement with corresponding curves obtained numerically for all values of the time. Asymptotic expressions valid in early and late time are also given.
Effect of Surface Protrusions on the Current Distribution in a London Superconductor
Authors: Appel J.
Published: February 2004

The current density and the magnetic field strength are calculated in a type-I superconductor which has the form of a long cylinder with a sinusoidal surface contour. London's and Maxwell's equations are solved with a straightforward perturbation calculation. The amplitude of a protrusion Δ is assumed to be small compared with the penetration depth λ. The results show a sizable variation of current and field near the surface when Δ/λ and λ/L (L=wavelength of protrusion) are both ≥0.1.
Low-Energy Ar+ Sputtering Yields of Solid and Liquid Tin
Authors: Krutenat R. C. , Panzera C.
Published: February 2004

Low-energy Ar+ sputtering yields have been obtained for solid and liquid tin from threshold to 1200 eV. The solid yield at 200 eV is twice that for the liquid but a crossover occurs at 375 eV above which liquid yields are 15% higher. The liquid-yield curve exhibits a linear dependence up to E=475 eV and breaks sharply to a lower dependence on ion energy. Yields of remelted solid were intermediate between the curves for liquid and solid, demonstrating the effect of surface roughness on the yield for polycrystalline targets. This work confirms experimentally the theory of Sigmund for yield of amorphous targets particularly in the low-energy range near threshold where surface effects predominate.
Directional Langmuir Probe
Authors: Hudis Martin , Lidsky L. M.
Published: February 2004

The theory for an asymmetric Langmuir probe is developed for the case of a collisionless streaming high-density (ai>Rp>30λd) plasma with Ti<Te. The results are used to analyze the response of the probe to a mildly turbulent drifting plasma. Ion saturation current is a function of the angle between the streaming direction and the probe asymmetry axis and has the form Vdi=(Te/Ti)1/2(Vs/4)(ΔIsi/Isi). The operation of the probe is verified by measurements of a known plasma-drift velocity and found to be accurate within a factor of three.