bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the Transition of Small Niobium—Zirconium Superconducting Solenoids to the Normal State
Authors: Boom Roger W. , Roberts Louis D.
Published: April 2005

A preliminary study has been made of the transition of small superconducting coils to the normal state. This transition was found to be fast compared with velocities found from measurements on short sample lengths of wire. The mode of dissipation of the field energy was studied; a relation between this and the critical current is indicated.
Beam-Generated Beam—Plasma System
Authors: Hopson James E.
Published: April 2005

The generation of a plasma as a result of passing a magnetically focused cylindrical electron beam thorugh a neutral gas is treated. It is theoretically shown on the basis of a particle diffusion model and has been experimentally verified that a certain minimum critical pressure is required for the beam to generate a plasma. For gas pressures in excess of this critical pressure, the equilibrium plasma density is greater than would be expected only from ionizing collisions between primary beam electrons and neutral gas molecules. This increased plasma density is associated with the generation of microwave noise.
Electron Emission Preceding Electrical Breakdown in Vacuum
Authors: Little R. P. , Whitney W. T.
Published: April 2005

An applied field of 105 V/cm produces electron emission from apparently smooth surfaces at room temperature. It is found experimentally that this prebreakdown emission is independent of emitter temperature up to 1000°K. Using a shadow electron microscope, projections about 2 μ high capable of producing field enhancements on the order of 100 have been found on optically polished cathodes at prebreakdown emission sites. This, with other evidence, strongly indicates that prebreakdown emission is Fowler—Nordheim field emission, due to a geometrical field enhancement.
Optical Observation of Pressure Induced Transitions in Polymers
Authors: Van Valkenburg A. , Powers J.
Published: April 2005

Pressure induced transitions in polytetrafluoro—ethylene, nylon 6, natural rubber, and polyethylene were observed optically between diamond anvils. In all polymers examined, the decreases in thickness and in birefringence are irreversible, at least on the time scale of a few months.
Upper and Lower Bounds for the Nucleation Field in an Infinite Rectangular Ferromagnetic Cylinder
Authors: Aharoni Amikam
Published: April 2005

The results of Brown for the nucleation fields of an infinitely long ferromagnetic prism with a square cross section, are generalized for a rectangular cross section, using practically the same techniques used by Brown: lower bounds are found by replacing the (positive) self-magnetostatic energy by a smaller quantity. Upper bounds are obtained by considering only certain types of functions in the variational problem. The upper and lower bounds thus found are reasonably close to each other to give a sufficient estimation for the nucleation field, for rotation in quasiunison. For the curling modes the bounds are very close to each other when the deviation from a square is not too large, but the distance between them increases when the rectangle is more elongated, giving just an order of magnitude estimation for breadth to length ratio of 1:10.
Studies of the Longitudinal Development of Electron—Photon Cascade Showers
Authors: Zerby C. D. , Moran H. S.
Published: April 2005

Numerical results of the track lengths of photons and charged particles and the energy deposition as a function of depth out to 10 radiation lengths in copper are presented for the case of electron-initiated electron—photon cascade showers. The incident energy varied from 50 to 45 000 MeV in these cases.

Monte Carlo methods were used to calculate the longitudinal development of the showers in order to obtain the data that are presented. The Bethe—Heitler cross sections which include screening and the correct energy dependence were used from bremsstrahlung and pair production events. The Klein—Nishina formula was used for Compton scattering. Energy losses by ionization collisions were treated as a continuous energy degradation process.
Temperature Transients in Oxide-Coated Cathodes during Pulsed Operation
Authors: Campbell D. A. , Shepherd W. G.
Published: April 2005

Experimental results presented demonstrate that transient changes in the thermionic emission of oxidecoated cathodes which occur during heavy pulse current drain depend upon the anode material and its past history. When an anode is used which has not been suitably processed a decay characterized by a 100-μsec time constant occurs similar to that described by Sproull, and by Matheson and Nergaard. When a Ti anode which has been suitably processed is used the emission decay no longer occurs and contrariwise an emission enhancement is observed. An experimental study of the emission enhancement leads to the postulate that the effect is a consequence of a temperature increase at the emitting surface.

A solution to the heat equation subject to boundary conditions appropriate to an oxide-coated cathode during pulsed current drain is obtained taking into account the Joule heating (J2ρ), emission cooling (Jχ), and radiation at the emitting surface. The analysis shows that for active cathodes significant temperature changes can develop at the surface of the oxide coating during single pulses of microseconds duration. The temperature changes inferred from experimental results presented are in agreement with the predictions of the theory. A numerical solution appropriate for conditions during temperature limited current drain has been obtained for the nonlinear heat equation which shows that a thermal instability can develop in active cathodes passing high current densities. It is proposed that this thermal instability can account for the phenomenon of cathode sparking.
Growth of Highly Perfect Fluoride Single Crystals for Optical Masers
Authors: Guggenheim H.
Published: April 2005

A technique is described by which highly perfect single crystals of CaF2, SrF2, BaF2, CdF2, LaF2, CeF2, PrF2, TbF2, MgF2, and ZnF2 have been prepared in a hydrogen fluoride atmosphere. Rare-earth-doped CaF2, and SrF2, LaF2, cobalt-doped ZnF2 and MgF2, and nickel-doped MgF2 have been successfully used as optical masers. These crystals were free of light scattering and revealed no strain pattern when viewed through crossed polarizers.
High Photovoltages in Silicon and Silicon Carbide Films and Their Origin from a Trap-Induced Space Charge
Authors: Brandhorst H. W. , Potter A. E.
Published: April 2005

Photovoltages were observed in thin films of silicon and silicon carbide which were not uniform in thickness. In some cases, the photovoltages exceeded the band gap. The photovoltages were retained by the film after removal of the light and decayed exponentially with time constants of the order of tens of seconds. The films were capable of acquiring persistent space charges upon application of an external voltage. The space charges decayed exponentially after removal of the applied voltage with time constants similar to that of the decay of the photovoltages. The photovoltages seemed related to the nonuniformity of the film, increasing with increasing nonuniformity. These results were interpreted to mean that the photovoltage is due to a space charge produced by a nonuniform distribution of trapped minority carriers, and a mathematical formulation was given to this concept. The temperature, light intensity, and carrier lifetime dependence of the photovoltage were in qualitative agreement with this concept. The temperature dependence of the decay constants of the photovoltage could also be interpreted satisfactorily in terms of this theory. A remarkable correlation between the photovoltage and the apparent resistance of the films was noted. It is suggested that the high photovoltages observed in films of other materials may have an origin similar to that discussed here.
Slow Waves in Ferrites and Their Interactions with Electron Streams
Authors: Spector J. , Trivelpiece A. W.
Published: April 2005

The slow waves that propagate in longitudinally magnetized ferrite rods enclosed in cylindrical wave-guides are investigated theoretically. The backward, azimuthally symmetric volume waves that propagate in a lossy ferrite rod are studied with the quasistatic analysis and the lossy permeability tensor derived from the Bloch-Bloembergen phenomenological formulation. The attenuation constant is proportional to the linewidth, and for polycrystalline yttrium iron garnet (YIG) (ΔH ≈ 50 Oe), the loss is approximately 30 dB/cm. The interaction of these waves with an electron stream which passes longitudinally through a hole in the center of the ferrite rod is studied; for normal values of beam perveance (∼10−6 A/V3/2), backward-wave oscillations should occur only for rods having a linewidth less than several oersteds and a length greater than a few centimeters. When the ratio of rod radius to beam hole radius is 1.5, the interaction parameter C is reduced by about 25% of the value when this ratio approaches infinity.

Brillouin diagrams are shown for the azimuthally dependent volume and surface waves in a lossless ferrite. Also, the results of a dynamic analysis are shown demonstrating the relationship between the magnetostatic modes and the waveguide modes. The quasistatic analysis is shown to give a close approximation to the correct dispersion relation even in the limit of fast waves, provided the radius is sufficiently small.
Flicker Noise in Oxide Cathodes Arising from Diffusion and Drift of Ionized Donors
Authors: Van Vliet K. M. , Johnson R. R.
Published: April 2005

A theory is presented which investigates the emission fluctuations arising from random arrival of barium at the surface of the grains followed by donor migration through the effective emitting part of the grains. The basic causes for the noise are diffusion of donor centers and electrolysis in the coating, processes which are known to be vital in cathode operation. The computed spectra are characterized by a diffusion relaxation time, a diffusion-conduction time constant, and a parameter involving the electric field in the coating surface layer. Three different types of spectra result from this.

Experimental data are reported, mainly on 2×2 diodes which support various aspects of the theory. The dependence of the turnover frequencies on temperature, activation, and current is in good agreement with the predicted results. The magnitude of the noise is close to Poissonian, contrary to previous claims. Recommendations for attaining low flicker noise are given.
Magnetization Reversal of Almost Perfect Whiskers
Authors: Luborsky F. E. , Morelock C. R.
Published: April 2005

Single-crystal whiskers of iron and iron-cobalt alloys with diameters from 250 to 4000 Å were prepared by evaporation of the metal in a vacuum. Larger diameter whiskers, from 0.2 to 200 μ, were made by hydrogen reduction of iron bromide. Electron microscopic examination of the vacuum-grown small whiskers showed them to be perfect appearing rods of uniform diameter. Electron diffraction indicated that they were all single crystals with a thin oxide layer. The whisker axes of the small whiskers were all along the 〈100〉 direction, but some of the large whiskers had a 〈111〉 orientation. Magnetic and chemical analysis indicated that the oxide thickness increased with increasing diameter from about 30 Å for 300-Å whiskers to about 100 Å for 1000-Å whiskers. New calculations were carried out for the remanence curves, the intrinsic coercive force and the remanent coercive force of arrays of infinite cylinders with random orientation in either two or three dimensions reversing their magnetization by curling, by fanning, or coherently. The dependence of coercive force, remanence, and rotational hysteresis of the randomly oriented whiskers as a function of diameter correlates well with the curling mode of magnetization reversal for diameters less than about 1000 Å. These results provide the first clear experimental evidence for magnetization curling. This is in sharp contrast to the size-independent behavior of bumpy, irregular, electrodeposited ESD particles, whose properties are described by a fanning mode. The results for alloy whiskers, with up to 60% cobalt and with various crystallographic orientations, were the same as for pure iron. Since the only difference between the alloy and the pure iron whiskers is the crystal anisotropy energy, it is concluded that the crystal anisotropy contribution is negligible. The results suggest a gradual transition from the uniform curling mode below about 1000 Å to some sort of heterogeneous reversal process propagating from one or more nucleation centers in each whisker with increasing diameter.
Electrical Properties of the MoTe2−WTe2 and MoSe2−WSe2 Systems
Authors: Revolinsky E. , Beerntsen D.
Published: April 2005

Electrical resistivity and Seebeck coefficient values were measured on compact polycrystalline samples from the MoSe2−WSe2 and MoTe2−WTe2 systems. In the telluride system the resistivity versus temperature data indicated a number of activation energies from room temperature to the dissociation temperature. In the selenide system there was little divergence from the semiconducting properties of the isomorphic binary compounds. Only one activation energy was found for each of the samples from this system.
Analysis of the Depletion Layer Transducer
Authors: Strauss Walter
Published: April 2005

Some aspects of the radiation of plane elastic waves from a depletion layer in a piezoelectric semiconductor are examined. A formula, relating sonic output flux to frequency, drive amplitude, and junction characteristics, is developed for the case of small electromechanical coupling. The production of elastic energy by the depletion layer transducer is nonlinear. Harmonic production and suppression of selected harmonics is discussed. A half-power bandwidth of 73% is possible for fundamental operation.
Composition Dependence of Photoelectric Characteristics of Cs−Sb Compounds
Authors: Hagino Minoru , Takahashi Tadashi , Wada Masanobu
Published: April 2005

Cesium antimonide photocathodes having various compositions can be prepared. The changes in the photoemissive yield and the resistance correspond reversibly to the changes in the amount of Cs. The maximum yield is attained in a composition Cs3−δSb, which is a p-type material (δ is a positive fraction). If the formation of a Cs−Sb photocathode is carried out under a Cs pressure about 10−5 Torr at 170°C, the photocathode maintains the most suitable composition for photoemissive yield. By flowing a Cs ion current through the Cs−Sb film, a p-n junction is formed in it. The mobility of Cs ions is responsible for the change in photoemissive yield during the operation.
Impurity Conduction and Negative Resistance in Thin Oxide Films
Authors: Hickmott T. W.
Published: April 2005

The conductivity of Al-Al2O3-metal diodes that show low-frequency negative resistance in their current—voltage characteristics depends on impurities in the oxide and on the metal used as counterelectrode. For heavily doped Al2O3, development of diode conductivity by application of voltages occurs at ∼4 V, independent of oxide thickness. For oxide films that are not deliberately doped, the field in the insulator is more important than voltage in developing conductivity. Al-Al2O3-metal diodes have been constructed with Ag, Au, Cu, Co, Sn, In, Bi, Pb, Al, and Mg counterelectrodes. The current—voltage characteristics which develop depend on the metal and on polarity of the diode voltage during development of conductivity. With Ag as counterelectrode, most diodes were initially shorted; with Mg as counterelectrode, no diode conductivity could be developed. Other metals fall in between and give peak currents in the current—voltage characteristics in the sequence Au, Cu, Co, Pb, Sn, Bi, In, Al. There is no correlation between Al-Al2O3-metal diode conductivity and metal radius or work function.
Structural Defects in GaP Crystals and Their Electrical and Optical Effects
Authors: Gershenzon M. , Mikulyak R. M.
Published: April 2005

Oriented single crystals of GaP were plastically deformed and the active slip planes and the individual dislocations lying in them have been identified by etching, by preferential precipitation (decoration), by observations of surface irregularities, and from strain birefringence singularities. Evidence of polygonization is presented and the nodes of planar intersecting dislocation networks can be seen by decoration. Crystals grown by the floating-zone technique contain 105–106 dislocations/cm2 which result from a quench—anneal cycle during the growth process. These dislocations as well as a high degree of residual elastic strain cannot be moved by annealing. This is not true of epitaxial crystals grown from the vapor phase on GaAs seeds. Some indications of growth from active Frank—Read sources have been obtained for these epitaxial crystals.

Precipitation, often unintentional, can be detected optically from Rayleigh scattering. Because minority carrier diffusion lengths in GaP are very short, dislocations and a dispersed second phase generally do not perturb the electrical properties. This is not true of some alloyed p-n junctions.
Experimental Analysis of the Schottky Barrier Layer Model for Reduced Rutile Diodes
Authors: Bechtel Richard
Published: April 2005

Experimental evidence is presented which favors the Schottky barrier layer model for reduced rutile diodes. The experiments involved chemical treatment of the oxide surface layer under the test electrode. The necessary thin insulating barrier layer was formed by regrowth of oxide, either by exposure to the atmosphere or chemical reagent treatment using H2O2 on a surface that had been reduced by treatment with HCl. The desired diode characteristics can be preserved by keeping the diode in an inert atmosphere.
Dielectric Parametric Amplifier
Authors: Billeter T. Roger , Giarola A. J. , Bjorkstam John L.
Published: April 2005

Gain conditions are obtained for a microwave parametric amplifier in which the resonant structure is filled with a nonlinear dielectric material. The gain equation is applied to the case of a toroidal resonator of strontium titanate dielectric. At a signal frequency of 10 Gc/sec, the gain threshold is at a pump power of 7.5 W. If efficient energy transfer is to be realized between pump and signal, resonant modes of the dielectric amplifier must be chosen appropriately. The necessary conditions on mode geometry have been illustrated.
Surface Structures and Epitaxial Growths on AgBr Microcrystals
Authors: Berry C. R. , Skillman D. C.
Published: April 2005

Crystals of AgBr, cubes bounded by {200} surfaces or octahedra bounded by {111} surfaces, can be readily produced. All other shapes may be considered as built up from these two stable faces. Although flat surfaces of cubes are electrically neutral, flat surfaces of octahedra have a large unbalance of charge. The supposition that the electrical neutrality of an octahedral crystal bounded by bromide ions is maintained by a large excess of interstitial ions rather than by certain other surface structures is supported by the amount of lattice expansion observed for the octahedra relative to cubes. Growth hillocks of AgCl on AgBr were produced which mark surface sites of enhanced reactivity. In no case were the growths twinned relative to the substrate crystals, even though both AgCl and AgBr often twin on {111} planes during growth. Preferred reaction sites on the cubes were corners and edges, but the octahedral surfaces were generally reactive. With octahedra also present, the cubes were almost inert. The surfaces of twinned tabular crystals often had linear arrays of growths along 〈211〉 directions before mechanical deformation but along 〈110〉 directions after deformation. Points of enhanced reactivity corresponded to points where the most rapid etching would be expected.
Structure of Anodic Layers on the (100) Face of Aluminum
Authors: Grosskreutz J. C. , Shaw G. G.
Published: April 2005

The structure of coherent anodic layers grown on the {100} faces of aluminum in tartaric acid—ammonia electrolytes has been studied by replicas and transmission electron microscopy. At pH 5.5 these layers are pore-free to the limit of our sensitivity (10–15 Å) and faithfully replicate the original surface formed during electropolishing. The hillock structure, characteristic of perchloric acid polishing baths, can be considerably reduced by electropolishing in a nitric acid—methanol bath at −20°C. The metal—oxide interface in this instance is featureless to within 20 Å. Anodic layers grown at pH 2.0 or 10.5 are highly porous and an electropolishing action takes place. An ultrastructure with characteristic spacing 50 Å is observed on surfaces polished in perchloric acid mixtures. The structure is also seen on the electrolyte interface of the anodic layer. It is proposed that this structure is not an artifact of the shadowing, and that it may correspond to particles of aluminum hydroxide formed during growth of the anodic layer.
Primary Damage State in Neutron-Irradiated Iron
Authors: Beeler J. R.
Published: April 2005

An attempt was made to characterize the primary damage state produced in finite bcc iron samples by neutron irradiation at 0°K, in a series of computer studies. Distributed neutron spectra appropriate to graphite-moderated reactors, water-moderated reactors, and fission neutrons, together with monoenergetic neutron sources with energies up to 10 MeV, were used. The number of primary knock-on atoms displaced by neutron collisions and their energy spectrum were computed using the Monte Carlo method. Anisotropic neutron scattering as a function of energy was described using tabulated experimental data. Damage states produced by these primary knock-on atoms, as a function of their energy, were computed by tracing out elastic atomic collision cascades in the bcc iron lattice. A damage state was described in terms of the displacement spike volume distribution produced, the total number of displaced atoms, and the size distribution of vacancy and interstitial atom clusters in a displacement spike. A description of how the damage state depends upon sample geometry and shape, the incident neutron energy spectrum, and the incident neutron angular distribution is given. It is shown that the damage state produced in samples of different size and shape can be significantly different and the irradiation conditions required to produce equivalent damage states in different sample sizes are defined. The principal content of the article pertains to the primary basis for the change in mechanical properties caused by neutron irradiation, as indicated by current theories.
Light Scattering from Oriented Polymer Films
Authors: Stein R. S. , Hotta T.
Published: April 2005

A theory of scattering of light by oriented films of crystalline high polymers is developed. This describes the variation in the dependence of scattering upon the angle between the incident and scattered beam, the film tilt and azimuthal angles, and the orientation directions of polarizers in the incident and scattered beams upon sample parameters. These are the sizes of the density and orientation fluctuations, correlation distances for each, and parameters describing the average orientation of the optic axes of the scattering elements of the film. Methods for experimentally evaluating these parameters are proposed and are illustrated for polyethylene films of differing degree of biaxial orientation.
Solution and Theoretical Evaluation of Steady-State Equations in Continuous Zone Refining
Authors: Kennedy John K. , Parke N. Grier
Published: April 2005

The classical theory of continuous zone refining is re-examined in light of alternate boundary conditions taking special care to account systematically for density changes due to melting. The new boundary conditions are applied to the zone-void and matter transport systems. Nondimensional parameters are introduced, leading to universal relations that have made it feasible to use an IBM 7090 computer to compute curves for a set of universal charts. These charts make it possible to explore for and choose rapidly optimum parameters for the design of continuous zone refiners for new materials and to evaluate existing proposals.
Large-Amplitude Solutions of the Rate Equations for the Ruby Laser
Authors: Clendenin W. W.
Published: April 2005

Large-amplitude solutions of the rate equations for the ruby laser have been obtained corresponding to the initial low value of photon density. The damping rate for these oscillations increases with optical pump rate in contrast to the decrease found experimentally by Walsh and Kemeny.

Variation of the damping rate with loss rate is also examined; the damping rate becomes the same order as that of the usual flash lamp (∼103 sec−1) for a loss rate corresponding to a rod.
Effect of Temperature on Photo-Exoemission
Authors: Young Joseph F. , Williams David J.
Published: April 2005

Measurements have been made with a Geiger counter of photo-exoemission from aluminum. The effects of time, temperature, and various adsorbates on the electron emission rate were measured. Adsorption reduces the electron emission rate; ion bombardment within the counter is shown to remove the effects of adsorbed gases. Adsorption of atmospheric gases can explain previously reported decay in emission and temperature effects.
Production of Metastable Hg Atoms by Charge Exchange
Authors: Rostron Robert W.
Published: April 2005

Neutral mercury atoms, formed by charge exchange processes between positive mercury ions and mercury vapor atoms, were found to liberate a copious yield of secondary electrons from a metal surface. Values of γ as high as 0.40 were observed. The source of positive ions was the plasma of a mercury arc discharge. Since such a high yield of secondary electrons is not indicative of ground state neutral atoms, the atoms were assumed to be metastable. To test this hypothesis the neutrals were allowed to decay in their flight to the target. A second method of quenching the supposed metastable atoms consisted of admitting minute quantities of H2 and Ar gas into their flight path. In both cases the secondary emission was reduced by several orders of magnitude thus verifying the metastability hypothesis. The 4.66-, 5.43-, and 9.0-eV metastable states were observed along with a long-lived state having a mean lifetime of 6.0 μsec. As an experimental side light of great importance, it was observed that Hg− ions were formed in the collimated beam of excited neutral atoms.
Response of Parallel-Plate Ion Chambers to Radiation Pulses
Authors: Livingston Peter M.
Published: April 2005

A procedure for uncoupling the charge transport and electric field equations under certain restrictions of dose-rate limitation and no recombination in a parallel-plate ion chamber is given. A solution to the first uncoupled transport equation for a flat-topped ionization pulse, including diffusion, is obtained by finding the appropriate Green's function, and the subsequent current densities and external circuit current are derived. The usual assumption of neglecting diffusion is shown to be valid for most cases involving ion transport by an examination of the general form of the external chamber current. Variations of the external circuit current with the radiation pulse width and the ratio of negative to positive ion mobilities are given. An attempt to ``fit'' an observed record shows marked deviation of the decreasing portion of the signal from the calculated one. This is probably due to the cessation of an appreciable free electron current after irradiation not taken into account by the calculation.
Photosensitive Liquid used as a Nondestructive Passive Q-Switch in a Ruby Laser
Authors: Kafalas P. , Masters J. I. , Murray E. M. E.
Published: April 2005

A solution of cryptocyanine in methanol has been used as a self-synchronizing, nondestructive, passive Q-switch in a ruby laser. A symmetric giant pulse of ∼10 nsec width and 5–10 MW peak power is produced with a standard ruby laser system. This pulse is comparable with pulses generated by other Q-switching techniques.
Plasma Experiments with a 570-kJ Theta-Pinch
Authors: Jahoda F. C. , Little E. M. , Quinn W. E. , Ribe F. L. , Sawyer G. A.
Published: April 2005

Initial measurements on the plasma produced in the Scylla IV theta-pinch of its electron density, soft x-ray emission, neutron emission, plasma shape and motion have been carried out as a function of the initial deuterium pressure and bias magnetic field. Interferograms establish electron densities in the range 4 to 7×1016 cm−3 for the plasma at peak compression and give azimuthally symmetric plasma shapes, which show the absence of the ``rotating flute'' instability as well as the absence of large trapped magnetic fields at peak compression. Streak photographs also indicate gross plasma stability. Shadowgraphs in conjunction with deflection mapping of a grid pattern show sharp plasma boundaries. Soft x-ray absorption measurements yield plasma electron temperatures in the range 400 to 1200 eV, which are dependent on the magnitude of the reversed bias field and have a gross correlation with the neutron emission. Neutron emissions in the range 107 to 2×109 per discharge are observed and depend upon the magnitude of the reversed bias field. Neutron collimation experiments yield a plasma length of approximately 70 cm in the 1-m mirrorless compression coil. The observed electron temperature, neutron emission, and electron density as functions of the bias magnetic field and filling pressure are consistent with the product of the plasma particle energy and the plasma density being a constant, as required for a β=1 plasma.
Dielectric Loss due to Impurity Cation Migration in α Quartz
Authors: Snow E. H. , Gibbs P.
Published: April 2005

The dielectric constant and loss factor of natural quartz single crystals have been measured in the temperature range from room temperature to 573°C, and in the frequency range from 50 cps to 100 kc/sec. Parallel to the c axis a large dispersion in the dielectric constant of the order of εs-ε∞ = 500 was observed. Associated with this dispersion is a peak in the loss factor of the order of ε″max = 250. The data were analyzed in terms of the Debye equations with a single thermally activated relaxation time. The activation energy is about 16.7 kcal/mole. Perpendicular to the c axis no peak in ε″ was observed, but both ε′ and ε″ begin to increase at low frequencies and high temperatures.

The loss peak parallel to the c axis was substantially reduced when impurities were removed by electrolysis. The introduction of Ag, Cu, or Na gave rise to new peaks while Li tended to reproduce the original peak. It is concluded that the original loss was due to the motion of Li+ ions along structural channels parallel to the c axis. From the charge transported in electrolysis experiments, it can be inferred that the number of ions involved was about 5×1017 per cm3. The observed activation energy is believed to be the Coulomb binding energy between a substitutional Al3+ ion and an interstitial Li+ ion.
Influence of Ferromagnetic Elastic Modulus Relaxation on the Determination of Magnetic Specific Heat of Fe, Ni, and Co
Authors: Lytton Jack L.
Published: April 2005

Data are presented for Young's modulus of (110) [001] oriented Fe-3.1% Si up to 1200°C for various angles to the rolling direction. These data exhibit a strong decrease in Young's modulus with increasing temperature during the ferromagnetic transformation so that the Young's modulus of the paramagnetic state is lower than for the ferromagnetic state. This effect also exists for Ni and Co, and is attributed to a decrease in interatomic forces accompanying the decrease of the exchange interaction between 3d electrons. This ferromagnetic modulus relaxation leads to a new specific heat term CΔθ which represents the energy absorbed in decreasing the mean frequency of the vibrational spectrum. The value of CΔθ, calculated from Young's modulus data, remains appreciable above the Curie temperature, thus accounting for the apparent excess specific heat of the ferromagnetic metals above that temperature. Separation of the total electronic specific heat suggests that three-fourths of the low-temperature electronic specific heat of Fe, Ni, and Co is of magnetic origin and that the magnetic specific heat Cm increases linearly with temperature up to 0.7 Tc and then increases rapidly to a peak at Tc, the Curie temperature. Well above Tc, a residual electronic term of nonmagnetic origin is found. The calculated values of magnetic entropy and energy derived from Cm for Fe, Ni, and Co are in reasonable agreement with Heisenberg theory using s=½.
Oscillations of Ferroelectric Bodies
Authors: Callaby D. R. , Fatuzzo E.
Published: April 2005

When a ferroelectric body attached to one end of a springy rod is switched with an alternating electric field, it oscillates with the frequency of the applied field. This effect was originally reported by Zheludew and he proposed that it might originate in a manner formally analogous to the classical magnetomechanical experiments of Einstein and de Haas. It is shown here as a result of a theoretical and experimental investigation that this is not the case, but that the oscillations are caused by a shearing of the crystal due to a polarization-induced strain.
Electric Field Excitation of Electrons From Shallow Traps in CdSe Thin-Film Triodes
Authors: Poehler T. O. , Abraham David
Published: April 2005

An investigation of the electrical properties of CdSe thin-film triodes has demonstrated the existence of shallow trapping levels distributed from 0.02 to 0.06 eV below the edge of the conduction band. These values have been experimentally determined by a combination of optical and field effect techniques. The investigation also indicates that field excitation of electrons from such levels is a fundamental mechanism of operation in the thin-film field-effect triode. Close correlation has been obtained between the dependence of device current on applied gate potential and the probability of field excitation of carriers with the field strengths achieved with these values of potential.
Ruby-Laser-Induced Photocurrents and Luminescence in ZnO
Authors: Hotchkiss Donald R.
Published: April 2005

A photoconductive signal has been observed in ZnO single crystals at 300°K upon illumination with the 6935-Å laser light from a ruby rod. With a dark current of 2 mA, a typical peak increase in current was 7 μA.

Green luminescence (centered at 5250 Å) excited by the laser light was also detected. The fluorescent intensity showed an approximately second-power dependence on incident intensity at lower intensities. At higher intensities an approximately fourth-power dependence was noted. A plausible model is given to account for the second- and fourth-power dependencies in terms of a two-photon absorption mechanism. Since the absorption coefficient of ZnO for light of wavelength 6935 Å is quite small, the observed photoconductivity and luminescence are very likely associated with the bulk rather than with the surface.
Simple Physical Model for the Space-Charge Capacitance of Metal-Oxide-Semiconductor Structures
Authors: Grove A. S. , Snow E. H. , Deal B. E. , Sah C. T.
Published: April 2005

A simple physical model is presented which gives the capacitance-voltage characteristics of a metal-oxide-semiconductor structure at high measurement frequencies in excellent agreement with the experimental observations. The model is based on the concept that at high frequencies the minority carriers within the inversion region act as `fixed charges' and so do not contribute to the ac variation of charge within the semiconductor. However, their presence determines the size of the depletion region under the given dc bias and hence the space-charge capacitance.
Electrical Measurements and X-Ray Lattice Parameter Measurements of GaAs Doped with Se, Te, Zn, and Cd and the Stress Effects of These Elements as Diffusants in GaAs
Authors: Black J. , Lublin P.
Published: April 2005

The room-temperature lattice parameter of GaAs doped with Zn, Cd, Te, and Se has been measured with a precision of ±3 parts in 105 using an x-ray powder diffraction technique. Electrical measurements and microscopic examination of samples were used to qualify the measured lattice parameters and allow limits of the solute lattice dilation coefficient (β) to be calculated. For Zn in GaAs, β[equal to or less-than]1.2×10−25 cm3/atom, for Cd in GaAs, β[equal to or less-than]1.1×10−24 cm3/atom; for Se, β>1.3×10−24 cm3/atom; and for Te, β >1.7×10−24 cm3/atom. Limits of the stresses that could be generated at the onset of the diffusion of Zn, Cd, Te, or Se into GaAs are derived from these β values. It appears likely that these stresses will be sufficient to cause plastic flow and the generation of large numbers of dislocations for diffusion of any of these elements into GaAs under conditions of high diffusant surface concentration and high temperature. Preliminary experiments show that the diffusion of zinc into GaAs at 1100°C can generate a high dislocation density in the diffused layer.
Thermoelectric Properties of Uranium Monosulfide, Thorium Monosulfide, and US-ThS Solid Solutions
Authors: Tetenbaum Marvin
Published: April 2005

The measurements on the temperature dependency of the Seebeck coefficient and resistivity of sintered specimens of uranium monosulfide, thorium monosulfide, and US-ThS solid solutions indicate semimetallic and metallic behavior for US and ThS, respectively. The thermoelectric power of US exhibits a weak dependence on temperature and decreases with increasing ThS content; except for initial disordering effects, the resistivity of US shows a similar dependence on temperature and composition. The presence of higher sulfides in US results in a considerable lowering of the Seebeck coefficient with increasing temperature. The figures of merit for US are too low for useful high-temperature power generation by a factor of approximately ten.
Ionic Conductivity in LiF Grain Boundaries
Authors: Moment Roger L. , Gordon Robert B.
Published: April 2005

Tilt boundaries in LiF bicrystals have been doped with Na+ ions and the resulting enhanced ionic conductivity measured. The activation energy associated with this conductivity is found to be 0.32 eV and is a constant, independent of the grain misorientation. This activation energy is the same as for the enhanced conductivity observed in Na+-ion doped edge dislocations in LiF. The results are interpreted in terms of a disordered boundary structure containing a high vacancy concentration.
Dislocation Structure and Growth Mechanism of Cadmium Sulfide Crystals
Authors: Chikawa Jun-ichi , Nakayama Tadahisa
Published: April 2005

Crystals, needles, ribbons, and platelets, grown from pure and impurity-added CdS vapor, have been studied morphologically. Needles grow parallel to the [0001], [101̄0], and [21̄1̄0] axes of the hexagonal system. Ribbons grow parallel to the [101̄0] and [21̄1̄0] axes and their surfaces are parallel to the (12̄10) and (01̄10) planes, respectively. The surfaces of the platelets are parallel to the (12̄10) planes.

The dislocation structures of grown crystals have been observed by x-ray diffraction microscopy and chemical and thermal etch techniques. In order to hinder the dislocations from slipping out of the crystals, some impurity atoms have been put in the crystals.

From the observations of growth manners and dislocation structures of the platelets, ribbons, and needles, it is concluded that whiskers grow in the initial growth stages of every crystal, and when the whiskers contain two parallel dislocations along the axis, the platelets are formed by the thickness increase of the whiskers in a direction perpendicular to the axis. One of the dislocations in the whisker has a Burgers vector 1/3[21̄1̄0] and the other is an edge dislocation with a Burgers vector [0001]. Behaviors of these two dislocations during the growth process of the crystal are inferred as follows: The dislocation with a Burgers vector 1/3[21̄1̄0] is responsible for the axial growth of the whisker and is easy to slip out of the whisker, leaving some dislocation half-loops on one of its side surfaces. The edge dislocation with the Burgers vector [0001] is also easy to slip out of the whisker, leaving many dislocation half-loops on another surface. The ends of these dislocation half-loops act as new sites of crystal growth in the direction perpendicular to its axis and a platelet is formed. Some observations which justify the above inference are illustrated.

It is discussed theoretically that the two parallel axial dislocations are much more stable than any single axial dislocation in a whisker.
Effect of Collision Focusing on Monocrystalline Sputtering Yield Theory
Authors: Smith Harold P.
Published: April 2005

An improvement is offered to the theoretical model of monocyrstalline sputtering yield proposed by Southern, Willis, and Robinson. The collision focusing effect, not considered in the original model, is included by multiplication of a momentum conductance factor which removes the dependence upon first collision depth and substitutes the effect of momentum propagation along the close-packed directions from the point of the first collision to the crystal surface. The inclusion of this factor yields better agreement with the data.
Form for the Relation Between Stress and Finite Elastic and Plastic Strains under Impulsive Loading
Authors: Backman Marvin E.
Published: April 2005

This paper derives a form for the relation between stress and finite elastic and plastic strains. The finite elastic and plastic contributions to large deformation are defined assuming that these arise from distinct elastic and plastic mechanisms of deformation. This assumption is mathematically represented by distinct relations between the elastic and plastic deformations and the state of stress. The choices for these relations are based on the theory of perfect elasticity and on the theory of quasistatic plasticity, but with modifications that permit the application to large strains and to dynamic situations. The expression for the dependence of the plastic deformation on the stress is explicitly strain-rate dependent. For simplicity the material is assumed to be isotropic. Constitutive relations are developed for the problem of one-dimensional stress-wave propagation.
Growth Spirals on Glass
Authors: Tichane Robert M. , Wilson Linda B.
Published: April 2005

Spiral patterns have been observed on a soda-lime glass surface after etching with a frost producing slurry. These patterns are throught to be replicas, etched on the glass during surface crystal growth, of precipitating salts.

The unique conditions required to produce these spirals make it appear that they result from a crystal growth process and thus the glass surface functions only as a substrate.
Growth Spirals on NiBr2 Platelets
Authors: Sickafus Edward N. , Winder Dale R.
Published: April 2005

Platelets of NiBr2 have been grown by sublimation and crystallization in an atmosphere of water vapor and helium. Several crystal habits were observed, including dendrites, platelets, and whiskers. Platelets and dendrites grow in the region of substrate temperatures greater than 500°C and although these crystals are anhydrous, water vapor greatly enhances the growth rate. The crystals are deliquescent. In the early stages of water adsorption the surface is not wetted, but water droplets form at surface imperfections. The resultant decoration of surface morphology exhibits an anisotropy related to the surface structure. Photomicrographs are presented of concentric growth spirals on the isolated faces of the same crystal platelet. These structures are demonstrated via direct observation of the opposite sides of the crystal, superposition of the opposite sides in thin regions of growth, and with the aid of Fizeau interferograms.
Some Mechanical Properties of Vitreous Selenium Near Its Glass Transition
Authors: Graham L. J. , Chang R.
Published: April 2005

The elastic and anelastic properties (in the megacycle frequency range), viscosity, and electrical resistivity of vitreous selenium near its glass transition temperature were measured as a function of the quench (or melt) temperature between 540° and 720°K. The measurements reveal a correlation between the various properties and the internal molecular structure of the material at the quench temperature. Ultrasonic attenuation below the glass transition temperature of vitreous selenium cannot originate from simple mechanical losses due to viscous flow. A phonon-phonon scattering mechanism is suggested.
Initiation of Spherulite Growth: The Case of Concurrent Homogeneous and Heterogeneous Nucleation
Authors: Gornick Fred
Published: April 2005

Direct determination of the rate of homogeneous spherulite initiation requires the subdivision of the melt into a large enough number of droplets so that all undesired nucleation catalysts (heterogeneities, motes, etc.) will be confined to a relatively small number of them. If the undesired heterogeneities nucleate very rapidly, the droplets free of them will freeze at a rate proportional to their volumes and the inherent (homogeneous) nucleation frequency per unit volune. In many cases, however, the time-dependent freezing process is pseudohomogeneous, i.e., the result of concurrent homogeneous and heterogeneous (but sporadic or nearly sporadic) nucleation. A method is presented for analyzing data corresponding to this case and for determining the limits within which the droplet nucleation experiment can be expected to yield fruitful results.
Morphology of Solution-Grown Polypropylene Crystal Aggregates
Authors: Sauer J. A. , Morrow D. R. , Richardson G. C.
Published: April 2005

Polypropylene aggregates, consisting of interwoven arrays of single-crystal lamellae, have been obtained by crystallization of samples of isotactic polypropylene from dilute solutions held at constant temperatures between 85° and 115°C. The solvent used was α-chloronaphthalene with polymer concentrations ranging from 0.4% to 0.01% by weight. The resulting crystalline aggregates were examined by means of phase contrast and electron microscopy. Similar crystal aggregates have been studied by Khoury and found to be incipient spherulites. These aggregates tend to occur in the form of open weave structures, with characteristic cusps. Lath-like lamellar crystals, with well-defined faces, are found at the edges of these structures. These edge lamellae produce a single-crystal electron-diffraction pattern corresponding to the monoclinic structural form of isotactic polypropylene. On the basis of the experimental findings, it is suggested that folding occurs in monoclinic polypropylene only along a given set of parallel fold planes, viz. {010}. Preliminary results of a study of the fracture characteristics of the crystal lamellae tend to support the suggested hypothesis.