bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Emission from Single Crystals of LiF and KCl
Authors: Sedgwick R. T.
Published: February 2004

Single crystals of LiF and KCl were subjected to incremental compressive stress along a [100] direction. A continuous record of stress and strain was kept, together with data from ultrasonic damping and acoustic emission measurements. The experimental techniques and the electronic equipment used are discussed in detail. It was found that specimens of LiF exhibited acoustic emission peaks in the macroscopic elastic range having their maximums at a strain of approximately ε0=10−3 and skewed toward larger values of ε. The analysis of this acoustic emission distribution forms the basis for a microscopic deformation model for LiF. It is hypothesized that this distribution should be identical to the distribution of dislocation-source inverse loop-lengths. An expression for the probability of observing N acoustic emission bursts while the crystal is being strained from ε to ε+dε is written in terms of inverse loop-length and used to calculate average values of ε, ρM, and (A1/A2), the dislocation strain, mobile dislocation density, and ratio of successive ultrasonic wave amplitudes, respectively. Since no such peak was observed for KCl, the differences in the microscopic deformation mechanisms for that material are emphasized.
Absorption Spectrum of a Magnetoplasma Dielectric in a Resonant Cavity
Authors: Kent Gordon , Heintz Roger
Published: February 2004

A simple theory based on plane waves in a cold magnetoplasma is proposed to account for experimentally observed absorption bands for transverse electric waves impinging on a microwave cavity. When the cyclotron frequency is equal to the resonant frequency of the TE111 mode of a cylindrical cavity, the data show a three-fold split of the resonance. The outer frequencies are separated by the plasma frequency, and their geometric mean is the cyclotron frequency. The third resonance is shifted by an amount proportional to the square of the plasma frequency, and it occurs only when the cyclotron frequency is very nearly equal to the empty cavity resonance. The simple theory accounts quantitatively for these three absorption bands, and it is in qualitative agreement with other observations. The experiments were performed on a microwave discharge in argon at a pressure of 150 μ and for a range of plasma frequencies from 1.00 to 2.25 GHz.
Measurements on the Stimulated Raman Effect in H2 in Terms of Laser Oscillator and Amplifier Theories
Authors: Avizonis P. V. , Jungling K. C. , Guenther A. H. , Heimlich R. M. , Glass A. J.
Published: February 2004

The growth of Raman-shifted Stokes radiation as a function of various parameters, (such as laser pump power, cavity reflectivity, etc.) has been studied in H2, a nonbeam trapping medium. It is demonstrated that growth of the Stokes converted output follows normal laser-oscillator dynamics. On this basis the previously observed ``anomalous'' gain which is not associated with beam trapping can be explained. If a strong external Stokes signal is injected, the Raman converting medium acts as an amplifier until the laser pump power achieves an intensity sufficient to produce oscillations at the Stokes frequency. The growth of Stokes radiation was examined under dispersive conditions such that anti-Stokes radiation was not produced, thus lending itself to a straightforward rate-theory type of analysis.
Dislocation Velocity in Single and Polycrystalline Silicon-Iron
Authors: Moon D. W. , Vreeland T.
Published: February 2004

The stress dependence of screw-dislocation velocity in single and polycrystalline specimens of an iron-3.14% silicon alloy was measured by observation of slip-band growth. An electrolytic etching technique was used to reveal dislocation intersections with the specimen surface, and slip bands were observed to form from fresh scratches and from grain boundaries as a result of pulse loading. Screw dislocation velocity on the {110} 〈111〉 system in single crystals at room temperature followed the relation ν = (τ/τ0)n, where n = 30.1. A plot of screw-dislocation velocity vs nominal resolved shear stress in individual grains of polycrystalline specimens shows considerable scatter which is attributed to the effects of stress variations due to elastic anisotropy. Observation of slip-band growth in scatched and unscratched grains indicates that the stress required to activate grain boundary sources is greater than the stress required to propagate fresh dislocations.
Properties of Finite Circular Dislocation Glide Loops
Authors: Marcinkowski M. J. , Harsha K. S. Sree
Published: February 2004

A detailed re-analysis has been made of the equations first derived by Kröner and Keller which give exact expressions for the stress field of a circular-glide dislocation in an infinite isotropic material. A number of important errors in these equations have been corrected and the resulting complex expressions solved using a digital computer. The stress fields obtained therefrom have been plotted for various important planar sections passing through the origin of the loop. In addition, a similar treatment has been made pertaining to the interaction energy between a pair of coaxial circular-glide dislocation loops of differing radii but same Burgers vector in an isotropic material. These results show a profound difference between the properites of dislocation loops and those associated with infinite straight dislocations.
The Interaction between Oxygen and Boron in Liquid Germanium
Authors: Edwards W. D.
Published: February 2004

Germanium crystals containing oxygen and boron concentrations up to approximately 6×1017 atoms/cc have been grown by the Czochralski method. Electrical conductivity, Hall voltage, and infrared absorption measurements have been made. It is shown that an interaction takes place between boron and oxygen in a germanium melt. In the subsequently grown crystal the oxidized boron is incorporated in a neutral state that neither provides nor measurably scatters charge carriers. The distribution coefficient of the boron in the oxidized state was found to be much less than K = 7, the value that is applicable to elemental boron at the growth rate used. The reaction is reversible in the melt. On dissociation of the boron-oxygen compound, the initial rate of dissociation and reappearance of the boron as a p-type dope depended on the rate of removal of the oxygen from the melt. Boron-doped crystals of essentially constant resistivity were grown from melts containing boron and oxygen. In ``as-grown'' oxygen-doped crystals less than 0.03% of the oxygen present gave rise to donor levels when α, the optical absorption coefficient at 11.7 μ, was <1 cm−1. As α increased, the fraction of oxygen that gave donor levels increased rapidly and, for α>4 cm−1, the error involved in the measurement of the oxygen concentration by the absorption at 11.7 μ became significant.
Monte Carlo Calculations of Internal Photoemission Yields in M-I-M Thin-Film Structures
Authors: Schuermeyer Fritz L. , Young Charles R. , Blasingame John M.
Published: February 2004

Photomeasurements on Al–Al2O3–Au thin-film sandwiches revealed a very asymmetric barrier shape, Φ1 and Φ2 being 1.8 and 4 eV, respectively. The image-force lowering of the barrier can be explained by the high-frequency dielectric constant. When photoemission measurements are performed only in the visible region, the Au electrode will not emit photoelectrons because of the large Φ2 value. The Al electrode, however, will emit photoelectrons if the Au electrode is sufficiently positively biased. The existence of only one source for photoelectrons facilitates the interpretation of photomeasurements. Monte Carlo calculations were performed to determine the scattering of hot electrons within these films. Electron-optical phonon scattering was assumed and a mean free path of 10 Å was found. The method to determine scattering by photoemission gives values on scattering within the image-force region.
Crystal Orientation and Lattice Parameters from Kossel Lines
Authors: Morris William G.
Published: February 2004

A Kossel x-ray diffraction pattern of a single crystal contains information concerning crystal orientation, structure, and lattice parameters. Procedures have been developed for determining orientations to within ±0.5°, identifying conics and calculating d spacings to within ±0.5%, and determining lattice parameters in any crystal system with errors as small as 10 ppm. Orientation and structure calculations can be made starting with position measurements taken directly from a Kossel pattern. Precision parameter determinations require that suitable intersections of conics appear in the Kossel pattern. This can be assured by selection of appropriate conics and wavelengths and the aid of a stereographic projection of the pattern. Computer programs handle the bulk of the calculations.
Effects of Annealing and Irradiation on the Stacking-Fault Energy of Cu–Al Solid Solutions
Authors: Kamada Koji
Published: February 2004

Annealing and irradiation effects of the stacking-fault energies of Cu–Al were observed by measuring the curvatures and dimensions of dislocation nodes with an electron microscope. For Cu-10 at.% Al alloy, the expansion of the dislocation nodes was observed on annealing at 150°C. For Cu-14 at.% alloy, the annealing at 150°C does not produce any detectable change in the dislocation nodes. For this alloy, the nodes contract on annealing at 300°C and the subsequent electron irradiation at room temperature produces the expansion of the nodes. These annealing and subsequent irradiation effects are due to the departure of the already segregated solute atoms and their resegregation. Slipping on the (111) plane due to the recovery of dislocation networks at 400°C annealing is also observed.
Ray-Theory Analysis of Magnetoelastic Delay Lines
Authors: Addison R. C. , Auld B. A. , Collins J. H.
Published: February 2004

Magnetoelastic wave propagation at microwave frequencies in single-crystal yttrium iron garnet, of various nonellipsoidal geometries, has been intensively investigated experimentally in recent years in connection with delay-line applications. However, two important features, namely the detailed nature of the energy paths and the magnetic excitation mechanisms, have received scant attention. This paper examines these features from the viewpoint of geometrical ray theory. Attention is first directed to two basic phenomena: magnetoelastic wave anisotropy, which gives rise to deflection of the group velocity from the phase velocity vector, and refraction, which arises from the inhomogeneous internal magnetic field. Consideration is then given to justifiable approximations for the wave behavior and magnetic field, and guidelines which enable a specification of the launching surface to be made. Ray plots are presented for the axially magnetized rod, which is found to be strongly focusing, and for the complementary geometry where the demagnetizing field everywhere is reversed in sign, which is found to be strongly defocusing. The field shape for minimum refraction is determined and certain delay-frequency characteristics of practical importance are investigated to assess their lens character. Finally, consideration is given to the excitation probem. It is concluded that in the axially magnetized rod magnetostatic waves are excited at the end face, transforming to spin waves and ultimately to elastic waves. This mechanism is consistent with experimental observations.
Pendellösung Measurement of the Atomic Scattering Factor of Germanium
Authors: Batterman B. W. , Patel J. R.
Published: February 2004

The atomic scattering factor of the (111) and (220) reflections of germanium were determined by two independent dynamical measurements: (a) from the absolute integrated intensities of Bragg reflections, and (b) from a determination of the Pendellösung period. The Pendellösung measurements show that for a relatively highly absorbing material such as germanium the scattering factor can be determined to about ±1% only for the low-order reflections. The resulting scattering factors from the two types of measurements disagree sufficiently outside of experimental uncertainty to conclude that the difference is real. Dynamical theory in its present state offers no explanation why the results should be different.
Plastic Deformation Bands in Glassy Polystyrene
Authors: Argon A. S. , Andrews R. D. , Godrick J. A. , Whitney W.
Published: February 2004

Plastic deformation bands nearly parallel to planes of maximum shear stress have been observed in unoriented glassy polystryene in compression and in preoriented polystyrene in tension and torsion. In the temperature range 77°–375°K, the shear stress for homogeneous nucleation of deformation bands is of the order of a few percent of the shear modulus, and while this shear stress is only moderately dependent on temperature and independent of strain rate, it shows considerable pressure dependence compared to metals. The shear strain of order unity inside the bands, the positive dilatation observed during deformation, and the stress and temperature conditions of band nucleation and propagation suggest a model in which ``rough'' molecules slide through each other in an initially unordered but closely packed molecular tangle.
Microwave Phonon Attenuation in Yttrium Iron Garnet
Authors: Lewis M. F. , Patterson E.
Published: February 2004

We report some microwave ultrasonic attenuation measurements at 9155 MHz on pure single-crystal yttrium iron garnet (YIG) which we believe determine the intrinsic attenuation in this material. Previous measurements on YIG by other workers were complicated by spurious effects. Our measurements are compared with current theories of attenuation by phonon-phonon interactions using the recently measured third-order elastic constants of YIG. The agreement found is about the same as in many other materials, which suggests that the intrinsic attenuation in YIG is understood and is caused by interactions with thermal phonons.
Determination of the Total Emittance of a Nongray Surface
Authors: Wittenberg A. M.
Published: February 2004

It is shown that the usual calorimetric methods for determining total hemispherical emittances, which assume that the test surface absorbs radiation as a gray body, can produce significant errors when the surface is nongray and the temperature of the surface approaches that of its surroundings. A procedure is described for calculating total emittances of nongray surfaces. The equations which are derived are shown to be applicable, with little or no modification, to most total-emittance-measuring methods. It is experimentally verified that equivalent accuracy can be achieved with a considerably simpler experimental technique than has normally been used in the past.
Second-Harmonic Generation in Plasmas by Nonuniform Microwave Fields
Authors: Kaw P. K. , Mittal R. S.
Published: February 2004

In this paper the authors give a Boltzmann-equation analysis of the nonlinear generation of the second harmonic in the current density in a slightly ionized plasma, arising because of the nonuniform nature of the applied microwave field. Under suitable approximations, the expression derived for the second-harmonic component in the current density reduces to the one derived on the basis of an elementary theory by Krenz and Kino. Some numerical results, illustrating the effect of collisions on the harmonic generation process, have also been presented.
Lorentz Microscopy Determination of Domain-Wall Width in Thick Ferromagnetic Films
Authors: Suzuki T. , Wilts C. H. , Patton C. E.
Published: February 2004

Width of the 180° domain wall in Ni–Fe alloy films as a function of film thickness up to 1800 Å was measured using the defocused mode of Lorentz microscopy. For the thinner films, the measured wall widths are in good agreement with earlier data obtained by Fuchs. For films thicker than 800 Å, the wall width increases with film thickness to about 9000 Å at 1800 Å film thickness. The validity of the classical determination of wall width is discussed.
The Shape of a Sessile Drop
Authors: Robertson W. M. , Lehman G. W.
Published: February 2004

A new analysis is presented of the shape of a liquid drop under the influence of gravity and surface tension. A variational method is used to minimize the total energy of the drop and the resulting expressions for the drop shape are evaluated numerically. The new treatment makes more direct use of the accurately measurable drop width than do the classical treatments based on the analysis of Bashforth and Adams.
Hall Measurements of Te-Doped Gallium Phosphide of Improved Homogeneity
Authors: Montgomery H. C.
Published: February 2004

Recent Hall measurements of GaP crystals doped with Te give more consistent values of donor binding energy and effective mass than our earlier work attributable we think to improved homogeneity in the crystals. The Hall coefficient, over the temperature range 80°–350°K, gives an excellent fit to the customary simple theoretical model. Hall mobilities in various samples ranged from 40–105 cm2/V·sec at room temperature and from 19–435 at 80°K. As a donor, Te has a binding energy of 80±5 meV at a concentration ND∼3×1017 cm−3, falling rapidly as ND increases. Extrapolation to low ND gives close agreement with the binding energy 93 meV reported from luminescent spectra. Estimates of the effective electron mass are discussed.
Luminescence in Silicon-Doped GaAs Grown by Liquid-Phase Epitaxy
Authors: Kressel H. , Dunse J. U. , Nelson H. , Hawrylo F. Z.
Published: February 2004

The radiative processes in closely compensated GaAs doped with Si (p-type) and Si+Te (n-type) have been studied by photoluminescence between 300° and 77°K. These materials were grown by liquid-phase epitaxy. The results strongly suggest that Si introduces two acceptor levels in GaAs with ionization energies of approximately 30 meV and ∼100 meV. In the n-type material containing Si and Te only the radiative transition involving the deeper acceptor is observed (hvp∼1.44 eV at 77°K). In moderately Si-doped, p-type material (∼1018 cm−3 range), transitions involving both levels are observed. The apparent ionization energy of the deeper level moves to higher energies with increasing Si concentration while the shallow acceptor band appears to merge with the valence band. In the p-type material, the electron transitions are assumed to originate at deep states (>40 meV) in the ``tail'' of states below the conduction band introduced by the high Si donor concentration. An intense broad emission band centered in the range 1.26 to 1.23 eV at 77°K is observed in some p-type specimens. This band is attributed to an acceptor level 230±20 meV above the valence band. It is tentatively suggested that it involves an As vacancy or As vacancy complex.
A New Technique for the Study of Electronic Transport in Insulators
Authors: Tantraporn W.
Published: February 2004

To avoid the barrier limitation at the injecting electrode and the effect of imperfections in the insulator, a low-energy (<30 eV) electron beam is used for the study of the bulk properties of insulator films. The voltage drop across the insulator is determined by comparing the current-voltage characteristic of the collector before and after the insulator film deposition. Quantities studied are the hot electron absorption coefficient as a function of the kinetic energy and the effective mobility of the thermalized electrons. Polymerized silicone oil films of thicknesses up to 670 Å were used. Under dc condition the absorption coefficient is ≈4×10−3 Å and the effective mobility is ≈10−11 cm2/V sec. Both are nearly independent of the incident energy. Pulse measurements indicate larger absorption coefficient values, especially for kinetic energies >2 eV.
Bandgap Dependence and Related Features of Radiation Ionization Energies in Semiconductors
Authors: Klein Claude A.
Published: February 2004

The problems dealt with concern the production of electron-hole pairs in a semiconductor exposed to high-energy radiation. The goal is to develop a simple phenomenological model capable of describing the present experimental situation from the standpoint of yield, variance, and bandgap dependence. We proceed on the premise that ε, the average amount of radiation energy consumed per pair, can be accounted for by a sum of three contributions: the intrinsic bandgap (EG), optical phonon losses r(ℏωR), and the residual kinetic energy (9/5) EG. The approach differs from prior treatments in the sense that the residual kinetic energy relates to a threshold for impact ionization taken to be 32EG in accordance with indications stemming from studies of avalanching in p-n junctions. This model is subjected to three quantitative tests: (a) Fano-factor variations are found to reflect the relative weight of phonon losses [K=r(ℏωR)/EG], but residual energy fluctuations govern the statistical behavior for K2 ≲0.3. An application to Ge yields good agreement with the best measurements available (F=0.13±0.02 at 77°K). (b) The bandgap dependence of pair-creation energies conforms to the model [ε= (14/5) EG+r(ℏωR)] and suggests that optical phonon losses remain essentially constant [0.5≤r(ℏωR)≤1.0 eV]. This would imply that the mean-free-path ratio for pair production and phonon emission (r=λ̄I/λR) is of the order of 10 or 20 for most semiconductors. (c) A detailed assessment of the situation in Si leads to the conclusion that, in this material, λ̄I is approx 400 Å. The figure accords, roughly, with inferences made from the spectral distribution of hot electrons emitted by shallow junctions and thus points to ``average'' impacts occurring at about 5 eV; by the same token, it substantiates the conception of pairs originating either through plasmon decay or in the final stages of a branching process.
Domain-Wall Mobility in High-Uniaxial-Anisotropy Ferrites
Authors: Asti G. , Conti F. , Maggi C. M.
Published: February 2004

The dynamics of 180° domain walls has been studied in three hexagonal ferrite single crystals with a high uniaxial anisotropy. By means of an improved pulsed magnetic-field technique and by analysis of the experimental method, we can observe the single-wall mobility η just from the initial domain-wall motion, i.e., for the lowest values of the internal field Hi. In the examined ferrimagnetic oxides the initial domain-wall motion shows, as in cubic ferrites, a constant mobility η of the order of 102 cm/sec/Oe. Such a dynamical situation is followed by a more complex one, characterized by mobilities at least one order of magnitude lower. Moreover, we have indications that the domain-wall apparent mass increases with increasing wall acceleration. We discuss the above-mentioned phenomena in connection with the possible spin-wave excitation during the wall movement.
Electrical and Optical Properties of Lead Oxide Single Crystals
Authors: Keezer R. C. , Bowman D. L. , Becker J. H.
Published: February 2004

Single-crystal platelets (3×3×0.1 mm) of both tetragonal and orthorhombic lead oxide have been grown from dilute NaOH solutions at high pressures using conventional hydrothermal techniques. The predominant yield of the two phases was varied in accord with the P-T phase diagram of PbO. Electrical measurements include the Hall coefficient and electrical conductivity as a function of temperature, while the corresponding photoeffects and optical absorption with monochromatic radiation were also studied. ``As-grown'' tetragonal crystals were highly conducting n-type with σ(300°K) ∼10−3 to 1.0Ω−1 cm−1, and had Hall mobilities of about 100 cm2V−1 sec−1. In constrast the ``as-grown'' orthorhombic crystals were rather insulating with σ(300°K) ∼10−5Ω−1 cm−1 and a Hall mobility μe∼50 cm2V−1 sec−1. Heat treatment in air altered both the electrical and optical properties. Photoconductivity was observed in both crystalline forms. The optical measurements indicate band transitions at 1.90 eV and 2.75 eV for the tetragonal form and 2.67 eV for the orthorhombic modification.
Effects of Solid Strength on the Propagation and Attenuation of Spherical and Plane Shock Waves
Authors: Mok Chi-Hung
Published: February 2004

To demonstrate the titled effects, basic equations in Lagrangian coordinates are derived for spherical and plane waves in an elastic-perfectly-plastic solid. The solution is first discussed qualitatively on the basis of the method of characteristics and then is obtained numerically by using a finite difference method for a shock wave induced by a square stress pulse in time at a boundary. In agreement with Frasier's preliminary conclusions from the results of hypervelocity impact experiments in wax, the present results show that the effects of solid strength are significant when the strength of the shock wave is within two orders of magnitude of the yield stress of the material. It is also indicated that precise control of the loading process is necessary in detecting experimentally the possible effects of solid strength on the attenuation of shock waves.
Plasma Transient Response and the Determination of Collision Data
Authors: Bruce R. L. , Crawford F. W. , Harp R. S.
Published: February 2004

This paper discusses the transient response of a magnetoplasma subjected to a short pulse at the electron gyrofrequency, which is applied with its electric field perpendicular to the static magnetic field. Experimental parameters are readily realized in which the decay of the transient-response envelope is influenced most strongly by collisions. Under these conditions, fundamental collision data may be derived from observations of the decay rate. Experiments are described in which elastic electron-neutral collisions have been studied in argon. The results of these experiments, made in a far from ideal system, are sufficiently close to accepted data to warrant the conclusion that, with further development, magnetoplasma transient-response studies would provide a valuable new technique for obtaining collision data. They should be particularly useful in the low energy range (≲1 eV). Suggestions are made for appropriate improvements and further applications of the method.
Normal Freezing with Cubic Liquidus and Solidus Lines
Authors: Li C. H.
Published: February 2004

This paper gives the derivation of an equation for the normal freezing of binary systems which have cubic or higher-order, liquidus and solidus curves. An example of the use of this equation in the cubic case shows that, at least in the Au–Ag system, the cubic normal freezing equation represents a distinct improvement over the linear or even quadratic normal freezing equation.
Existence of Two Types of Electron-Plasma-Oscillation Resonant Modes as a Function of Changes in Initial Electron Distributions and Temperature
Authors: Farrow L. A.
Published: February 2004

Starting with the hydrodynamic equations for the motion of electrons in a plasma, the electron-plasma-oscillation resonances in a slab geometry have been calculated for various spatial distributions of the initial electron densities and for different electron temperatures. The eigenstates for the perturbed electric field and the electron fluctuation density as well as the resonance frequencies have been computed for the lowest frequency mode and the next-higher frequency mode. Two kinds of mode exist, one having the resonance frequency higher than the maximum local plasma frequency, so that the wave can propagate throughout the entire body of the plasma, and the other having resonance frequencies lower than the maximum local plasma frequency, so that the wave propagation is limited to part of the plasma, and is excluded from a cutoff region. The relationship between the two types of mode is demonstrated.
Explosive-Driven Magnetic-Field Compression Generators
Authors: Shearer J. W. , Abraham F. F. , Aplin C. M. , Benham B. P. , Faulkner J. E. , Ford F. C. , Hill M. M. , McDonald C. A. , Stephens W. H. , Steinberg D. J. , Wilson J. R.
Published: February 2004

An explosive-driven magnetic-field compression device can be used as a source of a large pulse of electrical energy. We describe a number of such systems, showing how their measured output currents compare with theoretical calculations. Both large-inductance coil geometries and low-inductance coaxial geometries are discussed. Energy losses due to resistive heating, wall compression, electrical breakdown, and gas compression are considered. A numerical calculation procedure for coaxial generators is also described. We have built and tested coaxial generators whose measured output current can be accounted for by calculations of resistive heating and wall compression. Coil geometry generators are measured to be less efficient than calculated. Our results also show that further investigations of electrical breakdown and gas compression effects are needed.
Diffusion of Minority Carriers in the Base Region of an Alloy Junction Transistor in the Presence of a Magnetic Field
Authors: Misra Maheshwar , Srivastava G. P.
Published: February 2004

This paper reports the study of the nature of diffusion of minority carriers in the base region of an alloy junction transistor in the presence of a magnetic field. It has been experimentally observed that the diffusion constant of minority-carrier holes in a p-n-p type transistor is decreased in magnetic field and the magnitude of the decrement varies with the injected carrier density, being larger at higher injection levels. The relative change in diffusion constant shows a linear variation with the magnetic field intensity, contrary to the quadratic theory for isotropic semiconductor. The results have been explained by taking into consideration the effect of inhomogeneities due to concentration gradients and Hall perturbation effect given by Landauer and Swanson on the diffusion of carriers in the presence of magnetic field.
Field-Ion Microscopy of Graphite
Authors: Williams Wendell S.
Published: February 2004

Streaks in FIM images from graphite are shown to be transverse to the layer planes. Hence, the streaks are not images of layer-plane edges but distorted point images. Streaking is thus an intrinsic feature of the field-ion microscopy of graphite, resulting from its two-dimensional crystal structure. Therefore, structural studies of graphite by this technique are not feasible with the present methods of sample preparation.
Transport Processes of Photoinduced Carriers in Bismuth Germanium Oxide (Bi12GeO20)
Authors: Douglas G. G. , Zitter R. N.
Published: February 2004

This paper describes some investigations aimed at understanding the transport processes of excess carriers in bismuth germanium oxide (Bi12GeO20). Spectral photoconductive response, photoconductive decay, and optical absorption were measured. Photoconductivity exists over a relatively narrow wavelength range with a peak at 0.5 μ, which coincides with a peak in optical rotary power. Apparently the same set of transitions is involved in these effects. When the metallic-end contacts of the sample are illuminated, additional photoconductivity appears at shorter wavelengths. Photoconductive decay times of 1.2×10−2, 6×10−4, and 1.9×10−4 sec have been observed; the first we attribute to free carriers and the remaining two to spacecharge effects. There are strong indications that only a very small portion of absorbed photons contributes to photoconductivity.
A Theory for Microwave Instabilities in InSb
Authors: Gueret P.
Published: February 2004

This paper derives and analyzes the dispersion relation for wave propagation along a drifted electron-hole plasma in a semiconductor in the presence of a transverse magnetic field. In short samples of high-mobility semiconductors (InSb, in particular), this transverse magnetic field and the boundary condition at the sample contacts (vanishing of the tangential electric field) introduce a strong magnetoresistive effect. This effect is shown to result in a plasma instability when the applied fields exceed certain threshold values. The instability is found to have many features in common with the experimental results on microwave emission from InSb and it is proposed here as a possible explanation of this phenomenon.
The Irreversible Critical Range in the TiNi Transition
Authors: Wang Frederick E. , DeSavage Bernard F. , Buehler William J. , Hosler William R.
Published: February 2004

Through an investigation of the transport and related thermodynamic properties of TiNi at and around its ``martensitic'' transition temperature, the existence of a critical range extending over a 60°C interval is established. Within this critical range, the phase transition is second order. Irreversibility of various properties within the critical range is interpreted in terms of irreversible shear movement of atoms. On the basis of transport data, the band structure of TiNi is inferred to be a single or ``nearly'' single positive band within the temperature range investigated. The postulate that some of the valence electrons undergo a ``covalent''→``conduction'' electronic transformation in the course of the second-order transition is consistent in large measure with experimental data.
Observations of Thin Crystals of TiNi in Premartensitic States
Authors: Chandra K. , Purdy G. R.
Published: February 2004

Thin films of TiNi have been examined in the temperature range 0°–200°C, using transmission electron microscopy and selected-area diffraction. The CsCl diffraction patterns are accompanied by strong localized diffuse scattering, which becomes more pronounced as the temperature is reduced, approaching that of a phase transformation. A series of experiments designed to determine the directions of maximum diffusely scattered intensity suggest that these are 〈210〉 and 〈321〉, and that scattering is largely confined to reciprocal lattice directions subtending small angles with the incident electron beam. Since the phase transformation is thought to be of the second kind, and diffusionless, the results are interpreted in terms of large-amplitude, short-wavelength atomic displacements, reflecting incipient mechanical instability. Several diffraction patterns and dark-field photomicrographs are presented to indicate the scale of the domain structure of the transformation product.
Shape-Memory Effect and the Martensitic Transformation of TiNi
Authors: de Lange R. G. , Zijderveld J. A.
Published: February 2004

The object of this investigation is to provide an explanation of the shape-memory effect in TiNi with an equiatomic composition. After a plastic deformation at room temperature of a wire or plate of TiNi, this material appears to remember its undeformed shape when it is heated above 90°C. It is well accepted that a reversible martensitic transformation takes place below 90°C. At room temperature this transformation is not completed but can proceed by mechanical stress. It is assumed that the plastic deformation at room temperature is realized by martensitic transformation. This transformation takes place in a preferred orientation which depends on the direction and the sign of mechanical stress. On heating, the oriented low-temperature phase retransforms to the original structure and annihilates the plastic deformation. X-ray texture measurements of reflections of the low-temperature phase have shown the existence of a relation between an applied stress and the texture. The results have shown a marked difference in texture of martensite formed by tension and martensite formed by compression. Although the crystal structure of the low-temperature phase is unknown, these results give an explanation of the memory effect and any proposed crystal structure or orientation relation should fulfill the relations between stress and texture.
Dependence of the Transport Properties of Transition Metal Alloys and Compounds on the Electron Number
Authors: Goff J. F.
Published: February 2004

A comparison of the transport properties of the elements, compounds, and alloys of the first long period shows many similarities if the electron number is taken as a parameter, although the substances may differ magnetically. This result suggests that their transport band structures are similar. A model for the dependence on electron number of this structure is deduced from the transport properties of some of the nonmagnetic compounds. It is suggested that the model applies to the magnetic substances when they are in their magnetically ordered state.
Neutron-Diffraction Study of TiFexCo1−x Alloys
Authors: Pickart S. J. , Nathans R. , Menzinger F.
Published: February 2004

Neutron-diffraction measurements indicate that TiFexCo1−x alloys with x=0.45, 0.50, and 0.55 are completely ordered in the CsCl lattice. Polarized neutron measurements on alloys with x=0.45 and 0.55 suggest that the observed magnetization arises primarily from the Co and Fe atoms, and is fairly well localized.
Study of the Solubility Limits of the Compound TiCo Using High-Temperature X-Ray Diffractometry
Authors: Iannucci A. , Johnson A. A. , Hughes E. J. , Barton P. W.
Published: February 2004

An experimental study of the TiCo/TiCo+Ti2Co and TiCo/TiCo+TiCo2 phase boundaries has been carried out using high-temperature x-ray diffractometry. The results, together with the result of an approximate mp determination, have been used to delineate the TiCo phase field. By combining this information with the results of other work reported in the literature, a complete TiCo phase diagram has been constructed for the first time.
Spherical-Wave Theory of Dynamical X-Ray Diffraction for Absorbing Perfect Crystals. I. The Crystal Wave Fields
Authors: Kato N.
Published: February 2004

The x-ray wave fields due to a spherical wave are obtained in transmission (Laue) cases for absorbing perfect crystals on the basis of the dynamical diffraction theory. The conventional approximations assuming small absorption compared with extinction due to the Bragg reflection are eliminated. The formulas obtained are the same in form as those obtained previously for nonabsorbing crystals [N. Kato, Acta Cryst. 14, 627 (1961)], provided that the polarizability of the absorbing crystals is assumed to be complex. The intensity fields, the effective absorption coefficients, and the deviation of the positions of the Pendellösung fringes are discussed.
Ultrasonic Attenuation in Carbon Steel and Stainless Steel at Elevated Temperatures
Authors: Darbari G. S. , Singh R. P. , Verma G. S.
Published: February 2004

A pulse-echo method using shouldered samples has been used for the first time to determine the ultrasonic attenuation at room and elevated temperatures. The theory of the method has been worked out and the method is applied to carbon and stainless steels at 5 MHz in the temperature range 20°–800°C. It is observed that the attenuation due to grain scattering of ultrasonic waves according to Bhatia's theory together with Papadakis's refinements is not sufficient to explain the entire temperature dependence of attenuation. A maximum in the attenuation is observed in carbon steels at 200°C, which is the Curie temperature of the ferromagnetic cementite structure. In nonmagnetic stainless steel (18/8) the acoustic attenuation in the sample heated at 800°C for 1 h remains practically constant with respect to temperature.
Use of the Nuclear Reaction O16(d, p)O17 to Study Oxygen Diffusion in Solids and its Application to Zirconium
Authors: Amsel G. , Béranger G. , de Gélas B. , Lacombe P.
Published: February 2004

A method for the determination of oxygen diffusion in metals, making use of the O16(d, p)O17* nuclear reaction, is described in the case of oxygen dissolved in zirconium after oxidation. Energy spectra of protons obtained experimentally have been compared to spectra calculated on a theoretical basis. The oxygen-concentration profile in zirconium and in a zirconium copper alloy, after an oxidizing treatment at 750°C, was measured. The results are compared with microhardness measurements and show that the microhardness oxygen-content relation is not linear. Furthermore, the determined oxygen-concentration profile suggests that the diffusion coefficient of oxygen in zirconium is concentration dependent. The experimental technique described is expected to have great future for studies of oxygen diffusion in metals and oxides.
Thermoelectric Cyclotron Resonance in Germanium
Authors: Fisher P. David , Wagner Peter E.
Published: February 2004

A novel method for observing cyclotron resonance in semiconductors has been predicted and observed. The measured parameter is a dc thermoelectric current generated by carriers which are heated by means of cyclotron resonance absorption in a spatially varying electromagnetic field. Measurements are reported for n- and p-type Ge at 4°K and 70 GHz. The thermoelectric current at resonance is found roughly to be proportional to the logarithm of the microwave power. The line shape also depends on power and, at power levels approaching the values for impact ionization, displays certain peculiarities. The power dependence of conductivity modulation by cyclotron absorption is also reported.
Microwave Mixing by Hot Electrons in Homogeneous Semiconductors
Authors: Nimtz Günter , Seeger Karlheinz
Published: February 2004

A new type of microwave emission from homogeneous semiconductors with nonlinear characteristics is observed when two waves of frequencies ω and ω+Δω are incidental: The emitted waves have frequencies ω−N·Δω and ω+(N+1)·Δω, N=1, 2, 3, ⋯. For medium field amplitudes, the frequency dependence of the emission is calculated taking energy relaxation of the carriers into account.
Electrical and Optical Properties of Ferroelectric Bi4Ti3O12 Single Crystals
Authors: Cummins S. E. , Cross L. E.
Published: February 2004

The symmetry of ferroelectric Bi4Ti3O12 is shown to be monoclinic point group m. The spontaneous polarization PS is approx 50 μC/cm2 at 25°C and lies in the monoclinic a-c plane at an angle of less than 5 deg from the plane of the crystal sheets. A complete determination of the optical indicatrix as a function of temperature is given. Switching for fields along the c axis occurs by a unique ``rocking'' of the large PS vector and leads to interesting electrical-optical behavior. The domain structure is quite complex, and observed wall orientations are compared with those predicted theoretically.
Small-Angle X-Ray-Scattering Determination of Diameter Distributions
Authors: Brill Orville L. , Schmidt Paul W.
Published: February 2004

Test calculations have been carried out to develop a practical method of using small-angle x-ray-scattering data to determine the particle-diameter distribution in polydisperse suspensions of noninteracting spherical particles. A new method has been developed for extrapolating the scattering curve for scattering angles beyond the largest angles at which data can be obtained. This extrapolation technique is shown to be an improvement over an earlier method [J. H. Letcher and P. W. Schmidt, J. Appl. Phys. 37, 649 (1966)] by being less sensitive to uncertainties in the data and to choices of the constants used in the extrapolation.
Hall Coefficient of Tantalum Carbide as a Function of Carbon Content and Temperature
Authors: Santoro G. , Dolloff R. T.
Published: February 2004

The Hall coefficient and the electrical resistivity of tantalum carbide were investigated along the entire cubic phase region at room temperature and at −196°C. At both temperatures the Hall coefficient was found to be negative and to decrease in magnitude with decreasing carbon content. Near the stoichiometric composition the magnitude of the Hall coefficient was lower at −196°C than at room temperature, but approached the room temperature value at about TaC0.8. The electrical resistivity increased with decreasing carbon content at both temperatures. The magnetoresistivity was too small to be detected.
Electron and Ion Emission from Surfaces Originally of TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2 in Cesium Vapor
Authors: Wilson R. G.
Published: February 2004

Full-temperature-range electron- and ion-emission data from six refractory metal compounds in cesium vapor were obtained in the range of cesium arrival flux between 1013 and 1016 atoms/cm2·sec. Data are shown for ZrC and Mo2C; the boride and the three silicides were thermally unstable at emission temperatures, resulting in nonreproducible emission in some cases. Electron-emission S curves and the cesium surface-ionization critical-temperature envelopes are shown.
Effect of Internal Stress Distribution on Magnetomechanical Damping
Authors: Smith George W. , Birchak J. R.
Published: February 2004

Magnetomechanical damping in ferromagnetic materials has its source in stress-driven irreversible movement of magnetic domain boundaries. The maximum damping is proportional to λsE/σi, where λs is the saturation magnetostriction, E is Young's modulus, and σi is the average internal stress opposing domain boundary motion. In order to obtain the stress dependence of the damping, we include a distribution of internal stresses over a range ±Δσi about the average value. Inclusion of this distribution yields a theory in good quantitative agreement with experimental results for samples of 4% Si–Fe and cast iron.
An Improved Model for the Structure of a Néel Wall
Authors: Aharoni Amikam
Published: February 2004

A one-dimensional model is given for the structure of the inter-domain wall in thin ferromagnetic films. The self-consistency parameter for this wall model has a peak value of 3.6, and this peak is considerably narrower than in previous Néel wall models. The model can also be applied to double films, for which it yields a somewhat improved self-consistency parameter and a slightly lower energy than in previous calculations.
Formative Time for Breakdown in Strong Crossed Fields
Authors: Sherwood Arthur R. , Kunkel Wulf B.
Published: February 2004

The formative time of electric breakdown in low-pressure (0.2–2.0 Torr) hydrogen across a strong magnetic field (10<ωbτ<350; maximum B of 18 kG) has been measured in a coaxial cylindrical geometry. Attention was centered on the region of breakdown that occurs with a formative time less than the time required for an electron to drift across the electrode gap in the applied fields. This crossing time was inferred by extrapolations of previous measurements by Bernstein. These formative time measurements are compared with a simplified theory that assumes a constant number of e-folding times until breakdown and neglects electron losses as well as secondary production at the cathode. This model predicts that the formative time is inversely porportional to the gas pressure and otherwise a function of only the ratio E/B and not of either field separately. The predicted pressure dependence is confirmed, but some deviations from the predicted functional dependence on E/B are found. These deviations are attributed to electron losses along the magnetic field. A prediction of the magnitude of the formative time based on this simplified theory must necessarily involve extrapolation of certain previously obtained results. Such a prediction is found to be in reasonable agreement with the experimental values.
Transport Properties of Sputtered Vanadium Dioxide Thin Films
Authors: Hensler D. H.
Published: February 2004

Change-transport phenomena in thin films of vanadium dioxide have been investigated. This paper presents conductivity, Hall coefficient, and thermoelectric power data for reactively sputtered vanadium dioxide thin films both above and below the metal-semiconductor transition. Measurements were made both on single-crystal films and highly oriented polycrystalline films. For temperatures below the transition, the data are interpreted in terms of a two-band model of a semiconductor having a conduction band and an impurity band in which conduction takes place among interacting impurity levels.
Helical Instability of a Hollow Plasma Column in a Magnetic Field with Shear
Authors: Reynolds J. F. , Holt E. H.
Published: February 2004

The theory of the helical instability of the positive column has been generalized to include the case of a magnetic field with shear. The resultant stability criterion has been evaluated numerically. It predicts stabilization when the sense of the helical magnetic field opposes that of the helical density perturbation of the instability. This has been verified by an experiment in a hollow plasma column. The radial form of the density of the unperturbed plasma is required for the calculation and has been obtained by both theoretical and experimental methods.