bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion of Cobalt, Silver, and Gold in Praseodymium
Authors: Dariel M. P. , Erez G. , Schmidt G. M. J.
Published: February 2004

The thin-layer lathe-sectioning technique has been used to measure the solute diffusivities of cobalt, silver, and gold in dhcp and bcc praseodymium. The diffusivities in the bcc phase can be described DAg=3.2×10−2 exp(−21 500/RT) and DAu=3.3×10−2 exp(−20 100/RT) cm2/sec. In polycrystalline samples the average of the diffusivities along the two axes of dhcp praseodymium can be expressed by DCo=4.7×10−2 exp(−16 400/RT), DAg=1.4×10−1 exp(−25 400/RT), and DAu=4.3×10−2 exp(−19 700/RT) cm2/sec. These diffusivities are substantially higher than the self-diffusion coefficients of praseodymium. The change in the crystalline structure of the matrix affects only slightly the solute diffusivities, contrary to its effect on the self-diffusion coefficients. The remarkable similarity of these results with those concerning the solute diffusion of noble metals in Group III-B and IV-B metals, suggests that the same diffusion mechanism by interstitials operates in both cases.
Electromagnetic Propagation through Materials Possessing Both Faraday Rotation and Birefringence: Experiments with Ytterbium Orthoferrite
Authors: Tabor W. J. , Chen F. S.
Published: February 2004

Electromagnetic wave propagation through materials that possess both Faraday rotation and birefringence is analyzed. A matrix equation is developed which relates the amplitude and relative phase of the electric vectors between any two points along the propagation direction. It is shown that the presence of birefringence can drastically affect the behavior of wave propagation and that it is considerably different from pure Faraday rotation. Methods of measuring the material parameters are also described. Criteria for viewing domains in this type of material are established. It is shown that the thickness of the sample plays a great role in determining the contrast between domains and at some thicknesses no contrast at all can be obtained. It is also shown that the method using elliptical analyzers gives greater contrast over the plane analyzers. Photographs of domain patterns in a wedge of ytterbium orthoferrite are presented and they verify the calculated results.
Electron-Phonon Interaction in Alkali Halides. I. The Transport of Secondary Electrons with Energies between 0.25 and 7.5 eV
Authors: Llacer J. , Garwin E. L.
Published: February 2004

The interaction between conduction electrons with energies from 0.25 to 7.5 eV and longitudinal optical phonons in alkali halides is studied in detail by time-dependent perturbation theory. Expressions for the rate and angular distribution of scattering are obtained. The electron-transport problem is then solved with the exact quantum mechanical scattering results by a direct simulation Monte Carlo method. Probabilities of escape and average energy losses for electrons generated isotropically at a certain depth in the material, with a given initial energy, are computed for CsI, KCl, NaF, and LiF. A simple theory shows the effective mass and temperature dependence. The effect of including scattering to angles other than forward is quite apparent in the results.
Electron-Phonon Interaction in Alkali Halides. II. Transmission Secondary Emission from Alkali Halides
Authors: Llacer J. , Garwin E. L.
Published: February 2004

The phenomenon of secondary emission from alkali halides is studied in transmission. This allows the variation of one more parameter (thickness) than in conventional reflection studies. An empirical method based on published results of scattering by thin foils is used to determine the spatial dependence of the internal electron excitation function. The results of the Monte Carlo calculations presented in the previous paper (Part I) are used to generate a mathematical model of secondary emission. Measurements of pulsed secondary yield and of energy distribution of secondary electrons from uncharged films of CsI, KCl, NaF, and LiF are carried out at various film thicknesses and primary energies. By matching one single experimental point to the mathematical model, complete theoretical curves of yield for each material are generated. The results show that the spatial dependence of the excitation function taken together with the secondary escape results of Part I are sufficient to account for the variations of yield of different materials as a function of thickness and primary energy. An absorption attributed to d-like conduction bands is experimentally observed in KCl. The energy dependence of the internal excitation function is obtained and it is also shown that it is incorrect to characterize the probability of escape of all internal secondaries by a single exponential. The implications and shortcomings of the experiments are discussed.
Magnetic Relaxations and the Koops Inhomogeneity in Ferrites
Authors: Haberey F.
Published: February 2004

Conductivity measurements in various polycrystalline ferrites have shown that the temperature dependence of the conductivity has to be described by two different activation energies, one which is attributed to the bulk material and the other which is due to the poorly conducting layers introduced by Koops. Activation energies as derived from the results of magnetic relaxation measurements of the initial permeability for samples of the BaFe12−2δ3+Fe2δ2+O19−δ system are compared with those determined from the conductivity measurements. It appears that the activation energy as derived from the dc conductivity should not always be related to those determined from the magnetic relaxation. Both the high-frequency conductivity and the magnetic relaxation losses are related to an electron transfer between Fe2+ and Fe3+ ions. The activation energies depend on the Fe2+ content of the sample.
Theory for the First-Order Spin-Wave Instability Threshold in Ferromagnetic Insulators of Ellipsoidal Shape with an Arbitrary Pumping Configuration
Authors: Patton Carl E.
Published: February 2004

The spin-wave instability theory of nonlinear effects in ferromagnetic insulators developed by Suhl for perpendicular pumping and by Schlömann for parallel pumping has been extended to include pumping with an arbitrary microwave field configuration. The theory is applicable to samples of ellipsoidal shape, magnetized to saturation along one principal axis, but not necessarily an axis of rotational symmetry as in the Suhl theory. The theory, in its present form, is quite versatile and applicable to a large variety of situations which are not accessible on the basis of the earlier calculations. Equations are developed specifically for first-order processes. Several examples are considered to demonstrate the versatility of the theory: (1) Perpendicular pumping with a linearly polarized microwave field; (2) oblique pumping with a linearly polarized field at an angle between 0° and 90° to the static field; (3) perpendicular pumping with a circularly polarized field rotating in the anti-Larmor sense.
New Nonlinear Optical Materials: Metal Oxides with Nonbonded Electrons
Authors: Bergman J. G. , Boyd G. D. , Ashkin A. , Kurtz S. K.
Published: February 2004

Molecules or ions of the form BOx−n lack a center of symmetry whenever the B atom has a nonbonded pair of electrons. The problem of generating an acentric crystal can be approached by using these acentric oxygen polyhedrons as building blocks. A very high incidence of acentricity is found in compounds based on distorted BO3−n octahedra, such as XeO3, AIO3 (A=H, Li, Na, K, Rb, Cs, NH4, and Tl), and MTeO3 (M=Ca, Sr, Ba, Zn, Cd, Hg, Pb, Ni). Since these materials also have large indices of refraction, the concept of acentricity via nonbonded electrons provides a new and important guideline in the search for nonlinear optical materials.
Vibration Phase Measurement by Rotation-Strobe Holography
Authors: Mayer Gerald M.
Published: February 2004

A new holography technique that permits direct visual observation of the relative phases of all parts of a vibrating surface is described. A small rotation is introduced between exposures of a stroboscopic hologram of a vibrating surface to produce a series of vertical fringes on the surface. The vertical fringes are distorted to the right or left by the surface deformation of the object under observation; the distortions form a record of the relative phases of all parts of the surface. The ambiguities existing in the interpretation of the shape of nonclassical modes from a conventional time-averaged hologram are, thereby, resolved.
Structural Effects of Fast Neutrons in Germanium
Authors: Wittels M. C.
Published: February 2004

X-ray diffraction studies and volumetric measurements in nearly perfect crystals of germanium are reported for samples exposed to successive fast-neutron fluences above 1020 neutrons/cm2 at approximately 85°C. Volume expansions greater than 7×10−3 were found and complementary lattice parameter results indicate the formation of defect regions having an average density which is considerably lower than that of the ordered structure. Anomalous fast-neutron dose rate effects were observed by varying this parameter from 2.8×1013 neutrons/cm2/sec to 3.5×1014 neutrons/cm2/sec.
Alternating-Current Method for Separating the Contact Influence from Bulk Properties of Semiconductors
Authors: Wagner H. P. , Besocke K. H.
Published: February 2004

An ac test method is described which allows separation of contact influences from the bulk resistance of semiconductors and the measurement of their properties simultaneously. As an example, this method is applied to thin CdS films with different metal electrodes. Examples are given for the light and voltage dependence of both bulk and contact resistance, the true rise and decay curves, and the separation of changes in contact and bulk resistance with time or by post deposition treatments.
Dynamic Compaction of Porous Iron
Authors: Butcher B. M. , Karnes C. H.
Published: February 2004

The dynamic compaction properties of 1.3-, 2.2-, 3.3-, 4.7-, 5.8-, and 7.0-g/cc porous iron as determined from air gun plate impact experiments are described. The data indicate that the final pressure-particle velocity states produced by impacting the three lower density materials are well approximated by a simple locking-type model, neglecting elastic response of the material. In contrast, the higher density materials exhibit definite yield points and well-defined states of partial compaction below about 26 kbar. These states are described in terms of the measured yield points and the properties of solid iron. At pressures above the 26 kbar necessary for complete compaction, agreement was observed between the data and the predictions using Hugoniot theory with the Gruneisen equation of state.
Proposed Model for the Composition of Sputtered Multicomponent Thin Films
Authors: Winters H. F. , Raimondi D. L. , Horne D. E.
Published: February 2004

A simple model is proposed which predicts the composition of sputtered multicomponent thin films. The model is applied to such problems as alloy sputtering, gas incorporation into thin films, and compound formation. Several practical systems are considered such as the sputtering of Gd3Fe5 and Ni4Fe alloys and the incorporation of argon, oxygen, and nitrogen into tungsten films. The results of these studies suggest that the film composition is a strong function of vapor pressure, sputtering rate, atomic size, system geometry, sticking probabilities, and sputtering coefficients.
Electrophoretic Development of Electrostatic Charge Images from Colloidal Suspensions of Carbon
Authors: Dahlquist J. A. , Brodie I.
Published: February 2004

The physical parameters of colloidal carbon particles in an insulating liquid have been measured by several independent techniques. The particle size and charge, the Debye screening distance, and the interparticle distance are found and are used to interpret the electrographic development process (toning). The nature of the developed image depends upon the magnitude of the initial surface charge density and upon the time in the toning bath. The optical density for full development of an electrostatic charge image is shown to be proportional to the charge density in the image indicating that arriving particles overlap in a random manner. Measurements on the development process as a function of time shows that particles are being drawn out of the colloid in the intermediate range where both diffusion and mobility must be considered in determining the motion of the particles.
Finite Slit-Length Correction in Positron Annihilation Experiments
Authors: Mijnarends P. E.
Published: February 2004

The effect of the detector slit length in measurements of the angular correlation of annihilation radiation is treated theoretically. A general formula is derived, which expresses the coincidence rate from a single crystal in terms of the anisotropic momentum distribution, and its behavior is investigated in the limits of very long and very short slits. The result for the special case of an isotropic momentum distribution is compared with an earlier result of Arifov, Gol'danskii, and Sayasov. It is further concluded that line slits are to be preferred to point slits for the measurement of strongly anisotropic momentum distributions, about which no a priori information is available.
Misfit Dislocations in Bicrystals of Epitaxially Grown Silicon on Boron-Doped Silicon Substrates
Authors: Sugita Yoshimitsu , Tamura Masao , Sugawara Katsuro
Published: February 2004

The generation of misfit dislocations has been investigated on epitaxial silicon wafers with boron-doped substrates, as a function of the film thickness and the misfit resulting from the difference in lattice parameters between the film and the substrate. Critical values of the film thickness hc and of the misfit fc required to form misfit dislocations were found to be hc=2.4–-2.9 μ for the interfacial misfit of 0.019% and fc=0.003–0.006% for relatively large film thickness, where the interfacial energy approaches that of infinitely thick film. These results were analyzed in terms of van der Merwe's theory and a good agreement was found between the experiment and the theory. The density of misfit dislocations was observed to increase with the interfacial misfit or with the film thickness. The relation between bending of the specimens associated with the misfit and the film thickness was studied. Some properties of misfit dislocations are described.
Temperature and Pressure Dependence of Dielectric Constant of Cadmium Fluoride
Authors: Young K. F. , Frederikse H. P. R.
Published: February 2004

The temperature and pressure dependence of the dielectric constant ε′ of CdF2 has been measured for T=4°−300° K (at atmospheric pressure) and P=1–2000 bar (at room temperature). The frequency dependence of the real and imaginary parts (ε′ and ε″) has been investigated up to 100 MHz.
Table of Solenoids with Sixth-Order Error and Near-Maximum Power Efficiency
Authors: Garrett Milan Wayne
Published: February 2004

In a sixth-order solenoid of type I (or II), the field errors of second and fourth orders are compensated by a notch in the outer (or inner) cylindrical surface. The power efficiency EF≡G/0.1792, where the Fabry factor G is defined in the same way as for an uncompensated cylindrical coil with the same least radius, and 0.1792 is the largest possible value of G for any such coil. The efficiency of a sixth-order solenoid is defined to be ``near maximum'' when EF has a value no less than 98% of the maximum for any compensated coil of the same type and normalized volume V. The 2% tolerance permits the choice of an experimental coil to be influenced by properties that may be more sensitive to changes in geometry than is EF. Coils of type I are relatively long, with a maximum EF of 0.692 at V≅200. In type II coils, the diameter often exceeds the length, and the maximum EF is 0.884 at V≅300. Separate tables with V1/2 as argument list 100 solenoids of each type, with geometry, field strength, EF, and axial limits for field variations of 0.1% and 1.0%. All radial depths are so adjusted that the layer counts for the midplane and end sections are proportional to a pair of small integers. Though the 0.03% limits of a typical coil of type I could enclose the 1.0% limits of a type II coil of the same volume, the field error of the type II coil is less than 0.02% at the axial 1.0% limit of the same coil without the correcting notch.
Influence of Trivalent Rare-Earth Oxide Layer on Kerr Effects in EuO Films
Authors: Ahn K. Y.
Published: February 2004

The effects of a dielectric overlayer on Kerr magneto-optic properties in thick EuO films were examined. The dielectric film serves not only as a passivation layer, but also to increase the Kerr effects. A series of thin Eu2O3 films were vacuum deposited on a thick EuO film, followed by in situ measurements of the reflectivity and the transverse Kerr effects using a polarized light (with the electric field vector in the plane of incidence) at 45° angle of incidence in the wavelength region from 0.4 to 0.8 μ. As the dielectric (Eu2O3) thickness increases the characteristic reflectance minimum of EuO shifts toward longer wavelengths, accompanied by decreasing reflectivity. This shift agrees well with calculated reflectances using optical constants of Eu2O3 film and EuO. The minimum reflectance of ∼0.04% occurs at 0.675 μ for a dielectric thickness of ∼500 Å. The transverse Kerr effects also depend strongly upon the dielectric thickness. The maximum Kerr effects occur at the wavelength of minimum reflectance For example, corresponding to the minimum reflectance of ∼0.04%, a maximum transverse Kerr effect of ∼+140% occurs at this wavelength. This value can be compared with ∼25% in bulk crystal at 0.575 μ and ∼80% in thin EuO film on a mirror substrate at 0.525 μ, which is the largest value reported in the literature. Preparations and optical properties of several other rare-earth oxide films are also presented.
Bulk Space Charge and Transient Photoconductivity in Amorphous Selenium
Authors: Scharfe Merlin E. , Tabak Mark D.
Published: February 2004

The drift of a small photoinjected sheet of free carriers can be used as a probe of the space charge and internal field distributions in the bulk of amorphous selenium films. We have found that unneutralized space charge can exist for long periods of time and can significantly affect the measurement of both drift mobility and deep trapping lifetimes. By deliberately creating bulk space charge, we can also examine some of the fatigue effects that arise when a selenium photoreceptor is not allowed to relax between large variations in applied field and exposure.
Nonlinear Interaction Between Extraordinary Waves in a Cold Plasma
Authors: Harker K. J. , Crawford F. W.
Published: February 2004

This paper presents an analysis of nonlinear interaction between extraordinary waves propagating perpendicular to the static magnetic field in a cold homogeneous magnetoplasma. It is first shown that the synchronism conditions for wave/wave interaction can be met over wide ranges of parameters. A theory of the interaction based on cold plasma theory is then described which yields a closed-form solution for signal growth by the mechanism of parametric amplification. Numerical solutions are presented for the growth rate, and associated frequencies and wavenumbers, over a range of magnetoplasma parameters. The relevance of these results to laboratory and space plasma experimentation, and to verification of the theory, is discussed.
Infrared Absorption in Neutron-Irradiated GaAs
Authors: Burkig V. C. , McNichols J. L. , Ginell W. S.
Published: February 2004

The effect of fast-neutron irradiation on infrared attenuation in single-crystal GaAs has been investigated. Both n- and p-type materials of several dopant concentrations were exposed to seven fluences of fast neutrons (> 10 keV) from 5×1014 to 1.5×1018 neutrons/cm2. Infrared transmission was measured before and after exposure. At low fluences, the free-carrier absorption of all samples was reduced by neutron irradiation. At the higher neutron fluences, an absorption process which showed no structure and varied approximately as the square of the photon energy was observed to dominate the free-carrier absorption. This absorption increased linearly with fast neutron fluence and was the same for all samples studied independent of impurity type and initial concentration. The results are in agreement with a neutron-produced spike absorption mechanism proposed by McNichols and Ginell.
Effect of a GaAsxP1−x Transition Zone on the Perfection of GaP Crystals Grown by Deposition onto GaAs Substrates
Authors: Saul Robert H.
Published: February 2004

The effect of a mixed crystal transition zone (grading) on the perfection of crystals grown by epitaxial deposition onto substrates of differing lattice parameter and expansion coefficient is considered. The number of misfit dislocations required to compensate lattice mismatch at the growth temperature and magnitude of bending stresses which develop during subsequent cooling have been computed as a function of the width of the transition zone δ. These results have been applied to the case of GaP grown onto GaAs seeds. Using a simple model for lattice displacements, it is predicted that grading does not reduce the number of misfit dislocations but merely distributes them over the width δ so that the density is reduced in proportion to δ−1. The bending stresses in the grown layer are shown to be highly dependent on the width of the transition zone and thickness of the grown layer. Moreover, for a given seed thickness and zone width there is an optimum thickness for the growth layer for which the bending stress is smallest.
Preparation and Optical Properties of InAs1−xPx Alloys
Authors: Thompson Alan G. , Rowe J. E. , Rubenstein M.
Published: February 2004

Homogeneous polycrystalline InAs1−xPx alloys have been prepared by a halogen vapor-transport closed-tube technique over the entire range of composition. Electroreflectance measurements were made at room temperature by the electrolyte method which showed that the E1 and E1+Δ1 transition energies vary in a concave upwards manner, while the E0′, E2, and E2+δ transition energies vary linearly with composition. Wavelength-modulated reflectance measurements on semiconducting alloys above the fundamental edge are reported for the first time. These data, taken at room and liquid-nitrogen temperatures, confirm the interpretation placed on the variation of the electroreflectance E1 peaks. The E1 spin-orbit splitting (Δ1) remains almost constant in energy as x is increased from InAs and then falls rapidly to the InP value. A similar shape is obtained for Δ1 from a k·p calculation for the alloy band structure, which shows that a movement of the transitions in k space is probably responsible for this behavior.
Laser Transitions in p-Type GaAs:Si
Authors: Rossi J. A. , Holonyak N. , Dapkus P. D. , Burnham R. D. , Williams F. V.
Published: February 2004

Data are presented which show that three distinct optical recombination transitions occur in p-type GaAs:Si. These recombination transitions are band to band, conduction band to shallow acceptor, and conduction band to deep acceptor. With adequate pumping, as shown on ultrathin platelets, laser emission due to any of these transitions is possible, depending upon the cavity resonator gain profile and the crystal doping concentration. The effect of compensating Si donors in the crystal upon the wavelength of emission is illustrated. The unusually broad spontaneous linewidth of p-type GaAs:Si demonstrated here, along with the very large spatial spread of injected carriers in a GaAs:Si solution-grown p-n junction, is argued as being the limiting factors to stimulated emission in junction structures.
Anomalous Transverse Magnetoresistance of InSb Films
Authors: Wieder H. H.
Published: February 2004

The room-temperature Corbino magnetoresistance (ΔR/R0)c of electron beam zone-recrystallized n-type InSb films tends toward saturation in magnetic fields greater than 3 kOe. This fact as well as the presence of a large magnetoresistance (Δρ/ρ0)P observed on long rectangular specimens (l/w>3) are interpreted in terms of a surface layer having a higher impurity concentration and lower electron mobility than the rest of the film. The experimental observations on zone-recrystallized as well as dendritic InSb films is shown to be consistent with a model of two superposed layers, one with surface-like and the other with bulk-like electrical and galvanomagnetic properties.
Electron Affinities of the Barium Chalcogenides
Authors: Hu Chien-Yuan , Hensley Eugene B.
Published: February 2004

Measurements of the thermionic emission and electrical conductivity as a function of the temperature for fixed states of activation were obtained for each of the four barium chalcogenides. From the temperature dependences of these quantities the electron affinities were determined. The values obtained were 0.57 for BaO, 0.84 for BaS, 0.95 for BaSe, and 1.43 for BaTe. These values were found to be essentially independent of the state of activation of the samples.
Heat-Pipe Oven: A New, Well-Defined Metal Vapor Device for Spectroscopic Measurements
Authors: Vidal C. R. , Cooper J.
Published: February 2004

A new, well-defined metal vapor device called the heat-pipe oven has been developed on the basis of the heat pipe, a heat conductive element designed by Grover and his co-workers in Los Alamos. It continuously generates homogeneous vapors of well-defined temperature, pressure, and optical path length. The vapor is confined by inert gas boundaries which remove the window problem and allow a direct pressure measurement without relying on vapor pressure curves. Due to the continuous evaporation and condensation the vapor purifies itself during operation.
Display of the 8521-Å Cesium Hyperfine Lines Using a Swept GaAs Laser
Authors: Hochuli U. , Haldemann P. , Siahatgar S.
Published: February 2004

A gallium arsenide laser was used as an optical sweep generator to display the 8521-Å hyperfine lines of an atomic cesium beam. The largest contribution to the displayed over-all linewidths of about 60 MHz is due to the atomic beam divergence of the order of 5°.
Autometric Gyro for Satellite Relativity Experiments
Authors: Frisch D. H. , Kasper J. F.
Published: February 2004

An ``autometric'' gyro is proposed for use in satellite general relativity experiments. The readout for this gyro does not use any intermediate reference, and therefore promises some advantage over other techniques.
Optically Induced Change of Refractive Indices in LiNbO3 and LiTaO3
Authors: Chen F. S.
Published: February 2004

Local changes of indices of refraction observed in poled single crystals of ferroelectric LiNbO3 and LiTaO3 when illuminated by focused light have been studied. The extraordinary index of refraction was observed to decrease as much as 10−3 with a focused Ar laser light of 20 mW intensity as λ=0.488 μ, while the change of ordinary index was much smaller. The effect is attributed to the drifting of photoexcited electrons out of the illuminated region followed by their retrapping near the beam periphery. The space-charge field between these retrapped electrons and the positive ionized centers in the illuminated region causes the observed change of refractive indices via the electro-optic effect of the samples.
Radiative Cooling of an Electrodynamically Contained Proton Gas
Authors: Church D. A. , Dehmelt H. G.
Published: February 2004

On a gas of ∼104 protons, contained at ∼10−11 Torr in a parabolic rf trap of depth D̄ between 2.6 and 10.4 V, equilibrium temperatures kTi≃0.1 eD̄ and storage times T≃100 sec were measured ordinarily, both apparently determined by ``evaporation'' processes. When cooling the ions by coupling their disordered oscillatory heat motion to an LC circuit at room temperature, Ti dropped another factor of 3 to as low as 900°K and T increased to ∼3000 sec.
Strengthening Sapphire by Compressive Surface Layers
Authors: Kirchner H. P. , Gruver R. M. , Walker R. E.
Published: February 2004

Compressive surface layers were formed on sapphire rods. The methods included glazing and quenching, formation of Al2O3–Cr2O3 solid solution surface layers, and formation of mullite and calcium aluminate surface layers. The presence of the compressive stresses was demonstrated by slotted rod tests. Substantial improvements in flexural strength and thermal shock resistance were observed. The highest average flexural strength was obtained by glazing and quenching and was 340 000 psi. The strengths were measured in the ``as-treated'' and ``as-treated and abraded'' conditions. The abraded samples retain a substantial portion of the improved strength.
Grain-Boundary Contribution to the Electrical Resistivity of Iron
Authors: Braunovic M. , Haworth C. W.
Published: February 2004

The electrical resistivity of irons containing different levels of impurity have been measured at 77° and 293°K for a range of grain sizes. The resistivity of a given iron is found to vary with the grain diameter (d mm) as ρ = A+B log(1/d). A and B are both temperature dependent, increasing with increasing temperature. With increasing impurity content, the parameter A increases and B decreases. Thus the purer iron shows a larger variation of resistivity with grain size than the less pure material. The observed relationship can only be explained in terms of a grain-boundary scattering process if the effective width of the boundaries is much greater than is usually believed.
Transition Between Stage I and Stage II Modes of Fatigue Crack Growth
Authors: Swenson D. O.
Published: February 2004

Fatigue crack propagation in metals may exhibit two consecutive modes: an initial crystallographic shear mode (Stage I) followed by a noncrystallographic tensile mode (Stage II). The mode of cracking is assumed to be governed by the character of slip in the vicinity of the crack tip, i.e., Stage I is the result of co-planar reversible slip, while Stage II is associated with homogeneous, ``wavy'' slip. The slip character is, in turn, assumed to depend upon the likelihood of screw dislocations to cross slip out of the primary slip planes, which requires recombination of the Shockley partials. Thus the transition from Stage I to Stage II is postulated to occur when the separation of the partials, influenced by the crack-tip stress field and the material's stacking-fault energy, is reduced to the order of the Burger's vector. A continuous dislocation distribution representing the crack and plastic zones is used to analyze the transition from Stage I to Stage II. In the model, the closest screw dislocation in the plastic zone adjacent to the crack tip is dissociated into discrete partial dislocations, while the dislocations representing the crack and remaining plastic zone are presented as a continuous distribution of dislocations. Although it was found that the separation of partials is very sensitive to the ratio of the applied stress to the yield stress and the stacking-fault energy, the separation is not significantly reduced as the crack length increases. It is therefore concluded that strong obstacles to dislocation movement or dislocation entanglements would be required ahead of the crack to effect recombination of the partials. This result implies that a transition in the mode of crack growth should not be observed in single crystals of metals which display planar slip characteristics.
Viscous Drag on Dislocations at High Strain Rates in Copper
Authors: Kumar A. , Kumble R. G.
Published: February 2004

The mechanical behavior of OFHC copper at strain rates from 10−3 to 103 sec−1 at 300°, 420°, and 590°K was investigated. The strain rate behavior of copper can be divided into two regions. Below 10 sec−1 the dislocation motion is thermally activated over forest dislocation barriers. Above 103 sec−1, a linear relationship between stress and strain rate was observed indicating the presence of a viscous damping mechanism. The stress level τB that must be exceeded in order to obtain viscous behavior depends on the work-hardened state of the copper. The mobile dislocation density in the viscous damping region was found to be (1) independent of strain rate, (b) only a small fraction (10−5) of the total dislocation density, (c) independent of strain, and (d) increased with increasing temperature. These deductions are discussed in terms of the dislocation multiplication and annihilation mechanism.
Effects of Explosive Loading on the Structure of a Magnesium Single Crystal
Authors: Ma Ching H. , Mitchell David W. , Daga Raman
Published: February 2004

The structural changes caused by explosive loading of a magnesium single crystal were investigated by using x-ray Laue patterns, diffractometric measurements, and Fourier analysis of line profiles of x-ray reflections. The results show that the magnesium single crystal was converted to polycrystalline metal with a high order of preferred orientation by explosive-loading. The explosively loaded magnesium specimen consists of very small subgrains having an average size of about 500 Å. Experimental evidence tends to suggest that these subgrains are probably the result of instantaneous polygonization of an once highly strained, bent, and rotated lattice in the course of explosive-loading. The residual strain associated with the subgrain structure is not as great as might be expected in view of the nature of loading.
High-Frequency Fields in Solenoidal Coils
Authors: Contaxes N. , Hatch Albert J.
Published: February 2004

A little-known result of Townsend and Donaldson is extended to show that, for a solenoid carrying ac or rf current, the ratio of the average applied longitudinal field Ez to the induced azimuthal field Eθ at the periphery of the solenoid is equal to the ratio of the circumference of the solenoid to its pitch. For conventional solenoidal coils such as are used to excite electrodeless rf discharges, this ratio is typically ≳15–30. Applicability of the Ez/Eθ ratio to the design of coils and shields is discussed.
Power and Gain Characteristics of High Speed Flow Lasers
Authors: Cool Terrill A.
Published: February 2004

Output power and gain saturation characteristics are analyzed for a class of high speed flowing gas molecular lasers. Those flow lasers are treated for which laser action occurs within an optical cavity with an axis transverse to the flow direction, during the vibrational relaxation period following an initial excitation process that takes place upstream of the cavity. Performance predictions for an electrically excited fluid mixing CO2 laser based upon recent experimental measurements are presented. The concept of an ``equivalent nonflow laser'' is introduced which facilitates flow laser performance analysis in certain cases.
Superconductivity in Niobium Containing Ferromagnetic Gadolinium or Paramagnetic Yttrium Dispersions
Authors: Koch C. C. , Love G. R.
Published: February 2004

Gadolinium and yttrium dispersions were prepared in pure niobium by solidification from the melt; the size, shape, and distribution of the particles were determined metallographically. The superconducting critical temperature and critical field of niobium were unaltered by the presence of the dispersions indicating that neither gadolinium nor yttrium have measurable solubility in solid niobium. Both gadolinium and yttrium dispersions produced large hysteresis in magnetization and large critical current densities. The degree of magnetic hysteresis produced in niobium by these dispersions has only been exceeded in niobium by fast neutron irradiation. Ferromagnetic gadolinium and weakly paramagnetic yttrium appear equally effective as flux pins. It is suggested that the nature of the particle superconducting matrix interface is more important for flux pinning than the bulk magnetic properties of the dispersed phases.
Effect of Inhomogeneity on Magnetic Properties, X-Ray Diffraction and 31P NMR Linewidths in UP1−xSx Powders
Authors: Kuznietz Moshe , Campos F. P. , Baskin Y.
Published: February 2004

The wide temperature range at which transitions occur between magnetic structures, and the coexistence of magnetic structures in the UP1−xSx system are attributed to the incomplete homogeneity of the powder samples. The inhomogeneity affects the linewidths of the x-ray diffractometer traces, the 31P nuclear magnetic resonance (NMR) lines in the paramagnetic state, and the magnetic properties of UP1−xSx. The firing treatment of UP broadens the x-ray lines, while a second homogenization of UP0.72S0.28 sharpens the x-ray and 31P NMR lines and decreases the portion of the antiferromagnetic structure that coexists with the major ferromagnetic phase at low temperatures. The composition ranges (inhomogeneity widths) deduced from the x-ray line broadening are about 0.1x0, where x0 is the mean sulfur concentration. The upper limits of the inhomogeneity widths obtained from the excessive 31P NMR linewidths and the widths of the magnetic transitions are in fair agreement with the inhomogeneity widths based on the x-ray data.
Pulse Shape of Stimulated Raman Emission from an Oscillator Cavity
Authors: Avizonis P. V. , Heimlich R. M.
Published: February 2004

The time behavior of a pulse emitted by the stimulated Raman process (first vibration Stokes level in H2) is examined as a function of the Raman oscillator cavity parameter τ, the photon life time. Theoretical calculations of the Raman pulse shape, including laser depletion, using a linearized model of a standing wave are provided. Experimental comparisons to the calculations demonstrate satisfactory agreement for most measurements. The experiments were performed at 100 atm of H2, in order that antistokes be suppressed and calculations simplified.
Electrical and Optical Properties of n-Type Si-Compensated GaAs Prepared by Liquid-Phase Epitaxy
Authors: Kressel H. , Nelson H.
Published: February 2004

The radiative processes in Si-compensated, n-type GaAs prepared by liquid-phase epitaxy have been studied by photoluminescence between 300° and 4.2°K. The data are consistent with the previous hypothesis of the formation under certain growth conditions of two types of acceptor levels by Si in GaAs (in addition to the shallow donor level) with ionization energies of ∼0.03 and ∼0.1 eV. Three basic radiative processes dominate at various temperatures: (a) Band-to-band recombination at 300°K, (b) conduction band (or possibly conduction-band tail states) to shallow acceptor transitions at 4.2°K, and (c) conduction band to the deeper acceptor transitions at 77°K. The half-width of the third emission band and its peak position depends on the Si and free-carrier densities. The degree of compensation of these materials is a function of the substrate orientation. Of the three planes investigated, (100), (111)-Ga, and (111)-As, growth on the (111)-As face results in the lowest degree of compensation. The present study shows that n-type material with mobilities in excess of 1000 cm2/V·sec and electron concentration in the 2–4×1018 cm−3 range can be prepared by growth at 1060°C with the advantage over Te- or Se-doped GaAs that the formation of precipitates of Ga2Se3 or Ga2Te3 is eliminated. Such precipitates were previously shown to seriously degrade the radiative efficiency and hence the performance of injection lasers and spontaneous emitters.
Surface State and Interface Effects on the Capacitance-Voltage Relationship in Schottky Barriers
Authors: Crowell C. R. , Roberts G. I.
Published: February 2004

In the presence of an interfacial layer and semiconductor surface states, a Schottky barrier height φb decreases with increasing electric field E at the surface of the semiconductor. If the semiconductor doping concentration Nd is uniform throughout the depletion region and if [ (qNd/ε) (dφb/dE)−E] [ (d2φb/dE2) (dE/dV) ]≪1,where V is the applied voltage and ε is the semiconductor permittivity, the slope of the (capacitance)−2 vs voltage relationship is constant and can be interpreted to give Nd. The voltage intercept of the relationship yields an apparent barrier height φa related to the true barrier φb by φa=φb−E (dφb/dE) + (qNd/2ε) (dφb/dE)2, where q is the electron charge. From the measured variation of φa with Nd and one absolute measure of φb at one value of Nd, φb(E), and dφb(E)/dE may be deduced. From dφb(E)/dE the surface state density as a function of energy in the bandgap and the minimum value of interface thickness divided by relative interface permittivity can be obtained. Using the data of Archer and Atalla for vacuum cleaved Au-Si diodes to illustrate our method, the surface state density is found to peak at a value of ∼2×1014 cm−2·eV−1 at about 0.83 below the conduction band and the minimum value of interface thickness divided by relative dielectric constant is found to be of the order of 5 Å. Criteria are given which show how Schottky diode capacitance-voltage data may be further used, in conjunction with photoelectric barrier measurements, to detect the presence of deep lying impurities or the penetration of surface state charge into the body of the semiconductor.
Mobility and Infrared Absorption in n-Type Gallium Arsenide
Authors: Perkowitz S.
Published: February 2004

The relation between infrared absorption and mobility in gallium arsenide has been examined. The absorption theory of Haga and Kimura was used, as suggested by Vakulenko and Lisitsa, to calculate a theoretical drift mobility vs concentration curve for n-type gallium arsenide at 300°K. For concentrations above 1×1017 cm−3, this curve agrees well with that obtained from the Ehrenreich variational calculation. The Haga-Kimura theory was used also to predict that at temperatures between 77° and 300°K and concentrations above 1×1017 cm−3, the free-carrier absorption coefficient α in the far infrared (50–500 μm) takes the simple classical form α ∝Nλ2/μ, where N is the carrier concentration, λ the wavelength, and μ the drift mobility. This result suggests that far infrared absorption data may be used to directly calculate drift mobilities.
Stresses in Heteroepitaxial Layers: GaAs1−xPx on GaAs
Authors: Abrahams M. S. , Weisberg L. R. , Tietjen J. J.
Published: February 2004

A model is presented showing that there is a previously unrecognized source of stress in epitaxially grown heterojunction structures, specifically caused by a set of inclined dislocations formed by misfit dislocations which turn upwards at the heterojunction. This stress is indirectly related to the lattice mismatch at the heterojunction. For small lattice mismatch, the inclined dislocations are in an ordered array and cause the layer to bend upon removal from the substrate. For large lattice mismatch, the inclined dislocations are random so that there are only localized stresses and no net bending stress. A series of heterojunctions of GaAs1−xPx vapor grown onto GaAs were prepared, and the GaAs1−xPx constant-composition layers were removed from the substrate. The bending of the layers observed and the dislocation morphologies revealed in the layers by transmission electron microscopy, demonstrate the validity of the above model. In GaAs0.8P0.2 grown on GaAs, the stress due to lattice mismatch exceeds that due to differential thermal contraction.
Steady Shock Profile in a One-Dimensional Lattice
Authors: Duvall George E. , Manvi R. , Lowell Sherman C.
Published: February 2004

The equations of motion of a one-dimensional lattice of mass points connected by nonlinear springs are set forth and compared with the equations of the corresponding continuum. A permanent regime for the damped lattice is obtained by series approximation and shown to agree with that of the continuum. A higher approximation leads to a permanent regime profile for the undamped lattice which oscillates steadily after shock arrival. This is shown to be in qualitative accord with the results of numerical integrations of the transient problem. However, comparison of periods of steady oscillation with those obtained in the transient problem indicate that the series approximation to the permanent regime is quantitatively unsatisfactory, though qualitatively correct. Scaling of the problem with a parameter u1α is noted, where u1 is steady particle velocity behind the shock and α is a parameter of nonlinearity.
Dynamic Compression of Porous Tungsten
Authors: Boade R. R.
Published: February 2004

Data are presented from a study conducted to examine the shock-loading behavior of a sintered porous tungsten with a density of 12.64 g/cm3 (corresponding to 65.3% of the density of solid tungsten). The experiments were performed by using a gas gun and high explosives. Hugoniot data obtained in the stress range between about 12 kbar and 1 Mbar indicate that compression of the porous material to a fully compacted state is essentially complete at 50 kbar. Above this level, a predicted Hugoniot, calculated from the Hugoniot of solid tungsten by using the Mie-Grüneisen equation of state, agrees well with experimental data. Below 50 kbar the Hugoniot of the porous tungsten deviates from the predicted Hugoniot increasingly with decreasing stress. Propagated wave profiles at lower stresses are characterized by two precursor waves, the faster being a low-level wave (∼0.2 kbar) traveling at about sonic velocity in the porous tungsten (∼3.04 mm/μsec). The slower precursor has an amplitude of 2.73 kbar and travels at 2.02 mm/μsec. The behavior of this porous tungsten is analogous to the behavior of sintered porous copper previously studied.
Shock Deformation of Inconel 600 Alloy: Effect of Fine Coherent Precipitates on Explosive-Shock Hardening
Authors: Murr L. E. , Foltz J. V.
Published: February 2004

Sheet samples of pure nickel and Inconel 600 alloy (76% Ni, 16% Cr, 7% Fe) containing a fine precipitate were simultaneously shock loaded in sandwich assemblies at pressures of 50, 100, 150, 200, and 370 kbar by a planar pulse of roughly 2-μsec duration explosively initiated by a flying plate. The residual microhardness of the nickel was observed to saturate above 300 kbar while that for Inconel continued to increase steadily. Examination of the nickel substructures by transmission electron microscopy revealed a steadily decreasing cell size with increasing shock pressure; with almost no evidence of deformation twins at 370 kbar. The Inconel substructure was characterized by planar dislocation arrays which included an increasing concentration of dipoles and elongated loops to 200 kbar; while at 370 kbar deformation twins having an average thickness of 150 Å and occupying 19% of the volume were observed. The coherent precipitates in the Inconel matrix were observed to become incoherent at pressures above 50 kbar, with the concomitant production of dislocation tangles and loops at the particle-matrix interface. The precipitates were observed to enhance shock hardening by acting as sources for dislocation dipoles and elongated loops.
Vaporization of Solid Silver. I. Kinetic Influence of Surface Orientation, Degree of Vapor Phase Undersaturation, and Gaseous Contaminants
Authors: Winterbottom W. L.
Published: February 2004

A vaporization experiment is described in which both vaporization and condensation coefficients can be accurately determined. The technique involves rate measurements under various degrees of undersaturation and supersaturation and shows that for silver both the vaporization and growth processes are ideal and independent of surface orientations. Low pressures of vapor phase reactants, p<10−5 Torr of O2, CO2, N2, H2S, Cl2, acetone vapor, or CH4, were found to have no influence upon the kinetics of the process. Through the process of adsorption several of these gases markedly influenced the surface morphology of the specimens without appreciably disturbing the concentration of the desorbing silver species. Mechanistically, these results imply that there is a free interchange of silver between surface and bulk sites and that the desorption of silver from the surface is the controlling step in the vaporization process. In a similar way, the gas results show that the absorption or desorption of surface impurities characteristic of normal vacuum environments maintains the surface concentration of all impurities below a value where they could impede the vaporization process.