bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Moisture and High Electric Fields on Conductivity in Alkali-Halide-Doped Cellulose Acetate
Authors: Barker R. E. , Thomas Charles R.
Published: April 2005

Several problems associated with ionic conduction in amorphous hydrophilic polymers have been investigated from a theoretical point of view and then discussed in the light of experiments with alkali-halide-doped cellulose 2.5 acetate. The main ideas emphasized are: (1) The major effects of moisture on conductivity σ in this class of polymers are to increase the dielectric constant ε′ and therefore the concentration of ions by reducing the effective dissociation energy from its maximum U0′ (≈ 140 kcal/mole) to a lower value ≈U0′/ε′ such that σ≈σ1exp(−U0′/2RTε′), where σ1 depends on the square root of salt concentration n0; and (2) departures from Ohm's law in high fields E would occur as a result of activation barrier perturbation even in the absence of thermal and chemical effects. The above equation for σ was checked by starting with ``dry'' disks of CA and simultaneously measuring ε′ and σ (dc) after periods of moisture sorption. The evidence suggests that the micro- and macroscopic values for ε′ are proportional and of the same magnitude and that approximations valid for weak electrolytic solutions are applicable to ionic salts in moist solid polymers. For the C2.5A samples of the present study (≈ 270μ thick), the contribution of barrier perturbation to non-Ohmic behavior is larger than the effects of internal I2R heating or Onsager's theory of field-enhanced dissociation.
Crystallization of Poly-(Tetramethyl-p-Silphenylene)-Siloxane Polymers
Authors: Magill J. H.
Published: April 2005

The kinetics of spherulite growth of TMPS has been measured as a function of the fusion conditions (time of melting and fusion temperature) for different crystallization temperatures. The influence of fusion conditions on nucleation is described. The rates of spherulite growth (G) have been measured through the maximum in the G/T curve over the range 20°–130°C, approximately. Fractionated, unfractionated, and a few mixed polymer fractions were studied. The morphology and growth rates of spherulites from the glassy and molten states are compared. The implications of these results are discussed in relation to chain mobility and to the long-range coil-coil interactions which give rise to a strong dependence of the viscosity or diffusion co-efficients on chain length and dimensions.
Unified Consideration of Wave Amplification in Moving Media
Authors: Musha Toshimitsu
Published: April 2005

By quantization of wave fields in a moving medium we have quanta of negative energy when the velocity of the moving medium exceeds the phase velocity of a wave in the moving medium. Wave amplification phenomena caused by negative quanta are classified in four types, to each of which several kinds of known amplification phenomena or instabilities are attached, e.g. a traveling-wave tube, two-stream instability, ultrasonic wave amplification in a CdS crystal, roton excitation in a superfluid helium, beam-plasma instability, etc. A new type of amplifier, an inverse maser, is proposed.
Measurement of Third-Order Moduli of Silicon and Germanium
Authors: McSkimin H. J. , Andreatch P.
Published: April 2005

Experimental techniques for determining third-order moduli of single crystals by means of ultrasonic wave propagation are described. Results for silicon and germanium demonstrate a good degree of self-consistency among the basic experimental data obtained with both hydrostatic and uniaxial pressure.

In units of 1012 dyn/cm2 and for 25°C, the third-order moduli are: ModulusValue for SiValue for GeC111−8.25±0.10−7.10±0.06C112−4.51±0.05−3.89±0.03C123−0.64±0.10−0.18±0.06C144+0.12±0.25−0.23±0.16C166−3.10±0.10−2.92±0.08C456−0.64±0.20−0.53±0.07Thermodynamic definitions for the moduli (K. Brugger, Phys. Rev. 133, A1611 (1964)] have been used.
Plasticity of Barium Fluoride Single Crystals
Authors: Liu T. S. , Li C. H.
Published: April 2005

Barium fluoride single crystals exhibit considerable plasticity at 200°C. Between room temperature and 200°C, they slip in a (100) plane and in a [110] direction. By using etch pit techniques, it was observed that at 200°C fresh dislocations introduced by sprinkling with hard particles start to move at a stress level considerably lower than that indicated by compressive yielding at the same temperature. Fracture in barium fluoride, induced by microhardness indentation, took place on {111} and on {100} planes; the {111} cleavage fracture was more common than {100} fracture.
Orientation Dependence of the Evaporation Rate of CdS Single Crystals
Authors: Somorjai G. A. , Stemple N. R.
Published: April 2005

The vacuum evaporation characteristics of the (0001), (112̄0), and (101̄0) crystal faces of CdS single crystals have been measured in the temperature range of 680°–760°C. From the temperature dependence of the rate, the activation energy of the surface reaction which controls the vaporization of (0001) and (112̄0) faces has been determined. Semisphere shaped crystals are used to study the evaporation of all the orientations simultaneously. The (101̄0) crystal face is unstable under vacuum evaporation conditions. During vaporization the surface area changes drastically; the crystals develop new orientations. The surface areas of the (0001) and (112̄0) crystal faces do not change throughout the evaporation within the accuracy of the experiments.
Rare Earths in Covalent Semiconductors: the Thulium-Gallium Arsenide System
Authors: Casey H. C. , Pearson G. L.
Published: April 2005

Solutions containing radioactive 170Tm were applied to the surface of GaAs wafers that were heated to 800°, 900°, or 1000°C for times up to 100 h. The solubilities and diffusion coefficients were obtained by fitting the experimental data with complementary error functions. The resulting surface concentration (cm−3) was taken as the equilibrium saturation solubility and is represented below the eutectic temperature of 1150°C by 6.7×1025 exp (−2.3 eV/kT), which gives Cmax=4×1017 cm−3. The atom size, defined as the single-bond radius, was found to be the dominant factor in limiting the solid-solution solubility of the rare earths in GaAs. Diffusion was faster at lower temperatures, and the diffusion coefficient D (cm2/sec) was 2.3×10−16 exp (1.0 eV/kT). This inverse temperature dependence of the diffusion coefficient may be explained by the effective D derived from the concept of simultaneous diffusion and chemical reaction. The resulting diffusion coefficient in intrinsic material is Dei=DiCii+/Cs0, where Di is the interstitial diffusion coefficient and Cii+/Cs0 is the ratio of singly ionized interstitial concentration to neutral substitutional concentration. The inverse temperature dependence of D may be ascribed to the more rapid increase of Cs0 with temperature than that of DiCii+.
Modified Snowplow Model for Coaxial Plasma Accelerators
Authors: Hart Philip J.
Published: April 2005

In order to explain previously observed deviations of measured plasma velocities from velocities predicted by computer solutions based on a snowplow model, the experimental and computer data are here extended over a much wider range of electrode configurations, capacitor potentials, and gas densities in the shock tube. At low densities the experimental velocity curves fall below the predicted curves because of material evaporated from insulation and electrodes. At high gas densities the experimental velocity curve for the largest center electrode coincides with the predicted curve, but for center electrodes of successively smaller diameter the measured curves lie progressively farther above, but parallel to, those predicted, up to a factor of 5.5 times for the smallest electrode used. These results are explainable in terms of a modified snowplow model postulating an effective annular region adjacent to the center electrode, whose thickness is of the same order as the electrode radius, such that the force due to the magnetic pressure inside this annulus acts on only the gas contained within it to produce the measured velocity.
Effect of Temperature on the Mechanical Properties of Solid Pressure-Transmitting Media. I. Talc
Authors: Graf R. B. , Hulse C. O.
Published: April 2005

High-temperature compression tests have revealed unsuspected high-temperature strength in block talc. Analyses by x-ray diffraction indicate that the increase in strength is associated with the transformation of the talc to protoenstatite, silica, and water. The bulk modulus of elasticity also increases with increasing temperature, reaches a maximum at 1100°C and then decreases at higher temperatures. These findings suggest that block talc is not as suitable for a solid pressure-transmitting medium at elevated temperatures as is commonly supposed.
Local Regions with Biaxial Anisotropy in Thin Polycrystalline Ferromagnetic Films with Uniaxial Anisotropy
Authors: Torok E. J. , Oredson H. N. , Olson A. L.
Published: April 2005

Deposited thin ferromagnetic films with uniaxial anisotropy have local regions with admixed biaxial anisotropy, although there is no biaxial component to the average anisotropy field of the whole film. Two methods are presented for measuring the biaxial contribution to the inhomogeneity in the anisotropy field. The effect of this biaxial inhomogeneity is investigated theoretically and found to explain much puzzling data: the various negative anisotropy effects, the relationship between α90 and Δ90 (the inhomogeneity in orientation and in magnitude of the anisotropy, respectively), the internal biasing field, the compositional dependence of the inhomogeneity and negative anisotropy, the deposition substrate temperature dependence of negative anisotropy, the position of the negative anisotropy peak, the shape of the probability density function for films with both large and small inhomogeneities, the ratio of positive to negative anisotropy, and the skew of the Δ90 probability density curves. Theoretical switching threshold curves for complex (biaxial) anisotropy are drawn; theoretical probability density functions are plotted for various values of biaxial inhomogeneity and compared with experimental curves. Local regions of biaxial anisotropy can arise from the interaction of strongly coupled adjacent areas of the film with different anisotropy fields, as well as from magnetocrystalline anisotropy.
Anisotropy Fields in Hexagonal Ferrimagnetic Oxides by Ferrimagnetic Resonance
Authors: De Bitetto D. J.
Published: April 2005

Room-temperature microwave ferrimagnetic resonance measurements of the large uniaxial magnetocrystalline anisotropy fields (Han) of two compositional series of hexagonal ferrimagnetic oxides are reported. Han was found to increase rapidly in the Al-substitution series (SrO·xAl2O3·(6−x)Fe2O3) from 19.3 to 53.4 kOe as x was increased from 0 to 1.7. In the TiCo series (BaO·x[TiCoO3]·(6−x)Fe2O3), Han was found to decrease from 17.5 to 6.6 kOe as x was increased from 0 to 0.78. Experimental plots are given for the variation of Han with x. The linewidths of these oriented polycrystalline compounds were all about 2 kOe. The g value was consistently found to be about 1.9.

Variation with x of the respective saturation magnetizations, anisotropy constants, and anisotropy fields are discussed; relations are presented.
Domain Shape during Magnetization Reversal in Thin Films
Authors: Conger Robert L.
Published: April 2005

High-speed magneto-optical experiments show that when magnetization reversal takes place in a magnetic film in a period of a few microseconds, roughly diamond-shaped domains form with the long axis of the domain parallel to the film easy axis. Calculations show that domains of this shape form because the component of the magnetic field parallel to the easy axis is uniform along the boundary of such a domain.
Prediction of Curie Temperatures in Ternary Fe-Co-Ni Alloys. II
Authors: Pilkington T. C. , Artley J. L. , Wooten F. T.
Published: April 2005

The model (for predicting Curie temperatures of ternary alloys) developed in a previous paper is extended by removing the assumption that the fraction of plus and minus spins contributed by an element in the alloy is directly proportional to the concentration of the element. Empirical data concerning the Curie temperatures of binary Co-Ni, Fe-Ni, and Fe-Co alloys is again used to predict the Curie temperature of ternary fcc Fe-Ni-Co alloys. The predicted temperatures agree with experimental values within 30°C over the range of concentrations where the magnetic moments of the elements in the alloy do not vary with concentration (nickel concentration greater than 0.55 and the cobalt concentration greater than 0.4).
Electrical Conduction in Very Thin Polybutadiene Films Formed in a Glow Discharge
Authors: Bashara N. M. , Doty C. T.
Published: April 2005

Films in the thickness range 100 to 500 Å are studied. Ohmic contacts (gold electrodes) are formed only sporadically. In the best example of Ohmic contact, space-charge-limited current (SCLC) occurs at a field of 3×104 V/cm. SCLC is obtained in this and other specimens at fields great enough for field emission (3 to 5×105 V/cm) where trap densities about 1023/m3 were found, greater by a factor of ten than the lower field case. In less conclusive results and in general agreement with theory, a greater dependence on thickness as compared to voltage is found. The establishing of SCLC at fields great enough for field emission suggests a causative relation, perhaps tunneling through the blocking contact at the electrode-insulator interface. The change in the ac resistivity is lower than that using dc by about three orders of magnitude over the temperature range of 20° to 95°C. Three activation levels are found with transition points at 20° and 110°C. It is necessary to use a layer of SiO at the crossover region of the electrodes to prevent dielectric breakdown in this area. This protective layer is made sufficiently thick not to interfere significantly with the measurements on the polybutadiene.
Superconductivity of Highly Agglomerated Indium Films
Authors: Learn Arthur J. , Spriggs R. Spencer
Published: April 2005

The conductive properties of indium films vacuum deposited at room temperature were examined in a shielded cryotron configuration for thicknesses up to 10 200 Å and temperatures down to 2.90°K. Due to agglomeration, films were conductive only for thicknesses exceeding a thickness tc about 2000 Å for large rates of deposition and 5000 Å for small rates. For thicknesses tb or greater, room-temperature resistivity was independent of thickness and had a value of 9.2±0.3 μΩ-cm. Thickness tb was about 2.5 and 1.5 tc for high and low deposition rates, respectively. The superconductive critical temperature was 3.420°±0.005°K in the thickness range tested, 2200 to 10 200 Å. Critical fields were described by the London theory with penetration depth having the temperature dependence suggested by the Gorter-Casimir theory and value 700 ± 100 Å at 0°K. Film current for first appearance of resistance had a dependence on film thickness markedly different from any previously reported in the literature. This critical current exhibited a distinct peak at a thickness between tc and tb. The peak values agreed quantitatively with the London theory assuming width-independent current density and adopting a critical current density switching hypothesis. It was postulated that structure inhomogeneities served to maintain a uniformly distributed current on a macroscopic scale for certain thicknesses between tc and tb.
Optical Absorption of CdS-CdSe Mixed Crystals Prepared by Solid-State Diffusion
Authors: Handelman E. T. , Kaiser W.
Published: April 2005

Mixed crystals of CdS-CdSe were prepared in a sealed system by solid-state diffusion; by starting with pure CdS crystals, a composition as high as CdS0.6Se0.4 was easily obtained. With increasing Se content, the sharp absorption edge of the compound shifted from approximately 5200 to 6200 Å. The composition of the mixed crystals prepared under equilibrium conditions agrees with values calculated from available thermo-dynamic data and with the assumption that the mixed crystals form ideal solid solutions.
Pyroelectric Response of Triglycine Sulfate to Amplitude-Modulated X-Band Signals
Authors: White David J.
Published: April 2005

The pyroelectric response of single-crystal triglycine sulfate to amplitude-modulated X-band microwave signals was obtained for a range of modulation frequencies, modulation coefficients, and microwave power levels. A first-order theory has been derived which corresponds reasonably well with the experimental results. Most of the departures of experiment from theory are qualitatively explicable in terms of second-order effects involving the increase in the average temperature of the TGS sample owing to the absorption of rf energy.
Effect of Hydrostatic Pressure on Self-Diffusion in Gold-34 Atomic Percent Silver Alloy
Authors: Albrecht E. Daniel , Tomizuka C. T.
Published: April 2005

The diffusion of 110Ag and 198Au in a nominally Au-34 at.% Ag alloy has been measured at 860°, 910°, and 960°C and at hydrostatic pressures from 2070 to 8280 bars. A retarding effect of pressure on the diffusion rate has been observed for both the silver and gold tracers. Temperature determination, uniformity, and reproducibility have been found to be the limiting sources of error in pressure-diffusion studies. Activation volumes are 7.2 cm3 per mole for 110Ag and 7.5 cm3 per mole for 198Au, consistent with the theory of Lawson, Rice, Corneliussen, and Nachtrieb, and with the experimental value of the activation volume of motion of vacancies ΔVm in Au found by Emrick. Changes in activation enthalpy values and frequency factors have been calculated and compared to the experimentally determined values-the agreement is fair. The variation of diffusion rates and activation volumes is explained on the basis of isothermal compressibilities where Ag is much more compressible than Au.
Influence of Interstitial Solutes on Elasticity and Damping of Chromium near Its Néel Temperature
Authors: Klein Mark J. , Clauer A. H.
Published: April 2005

Carbon and nitrogen influence the Young's modulus and the damping behavior of chromium near its Néel temperature; the thermal history is also important. Changes in the modulus and the damping induced by varying the thermal history are attributed to changes in the characteristics of the interstitial dispersions, rather than to variations in the concentration of soluble interstitials. The stress sensitivity of the modulus and damping anomalies in unalloyed chromium suggest that stresses associated with the nitride and carbide dispersions contribute to the changes observed in the alloys.
Amorphous Oxide Layers on Gold and Nickel Films Observed by Electron Microscopy
Authors: Gimpl M. L. , McMaster A. D. , Fuschillo N.
Published: April 2005

Thin films of vapor-deposited nickel and gold, supported only by copper grids, were annealed inside the electron microscope. The microstructures were recorded as a function of temperature. The originally continuous thin films of nickel (150 Å thick) and gold (400 Å thick) form discontinuous islands at temperatures of 700° and 600°C, respectively. The islands of metal are supported by a thin amorphous membrane, in the nickel films identified as NiO, that accounts for the high tensile strengths observed on thin films.
Low-Energy Sputtering Yields by Resonance Absorption and Emission Spectroscopic Methods
Authors: Kreye W. C.
Published: April 2005

Low-energy sputtering yields for a (110)-oriented gold single crystal are determined by means of a resonance or atomic absorption technique wherein the sputtered atoms absorb the resonance radiation from an external gold, hollow cathode source. If the square root of the relative yield is plotted vs target voltage, a linear portion is found between 40 and 70 V. The extrapolation of the linear portion of the curves gives rise to an average intercept energy EE of 29 eV at low pressures.

The discharge chamber is specially designed to permit consecutive measurements of the sputtering yields by the absorption and by a previously employed emission technique under identical chamber geometry and discharge conditions. In the direct comparison of results possible thereby, the average value of EE from the emission curves is 29.5 eV which is approximately equal to the above absorption value of 29 eV. The plasma potential for these experiments is found to be about 12 eV. Moreover, the curves themselves are proportional over the range of 40 to 100 V. These results strongly indicate that EE is an experimental invariant from which reliable threshold energies can be obtained. This coincidence of curves also indicates that the variation of excitation probability of the Au atoms with different ion and correspondingly different atom energies does not affect the emission yield curves.

The sensitivity of the absorption method with the present hollow cathode is slightly poorer than that of the emission method. The observed increase in the slope of the absorption square root yield curve with increased discharge current is attributed to imperfect resonance which may be due to the difference in argon pressures and discharge currents within the gold, hollow cathode source and those within the sputtering single-crystal target chamber.
Etch-Pit Patterns and Crystal Structure of PtSb2
Authors: Miller R. C. , Damon D. H. , Sagar A.
Published: April 2005

The lack of fourfold symmetry about the 〈100〉 axes of PtSb2 (cubic class Th) is revealed by a simple etching technique. The relative intensities of the 102 and 012 spots in a Laue back reflection pattern for a (001) surface are correlated with the etch-pit pattern.
Dislocation Damping in Semiconductors and Abrupt versus Smooth Kinks
Authors: Ninomiya T. , Thomson R. , Garcia—Moliner F.
Published: April 2005

A previous dragging point model of dislocation mobility is modified and applied to the dislocation damping data in Si and Ge. The motion of built-in kinks along a dislocation is considered to be responsible for the damping. In contrast to the abrupt kink model, the free motion of the kinks is impeded by the dragging points. The predictions of this model are compared with those made on the basis of the abrupt kink model, with regard to (a) damping, (b) estimated kink width, and (c) dislocation mobility. The dragging-point model seems to give a more consistent picture, although direct experimental verification of the presence of dragging points is not yet available. An improved table of derived parameters for the dragging-point theory of dislocation mobility is given based on additional information from damping measurements in Ge.
Onset of Breakdown at Voltages below Ionization Potential in High-Pressure Thermionic Diodes
Authors: Forman R.
Published: April 2005

Early breakdown effects have been measured in relatively high-pressure thermionic diodes under given conditions of pressure and anode spacing. Apparent breakdown conditions are obtained at anode voltages considerably lower than the ionization potential of the gas. Measurements on xenon- and mercury-filled thermionic diodes, under space-charge conditions of operation, are presented which show that this breakdown voltage seems to be associated with the first excited state of the gas. Experimentally, early ignition occurs in diodes with a fixed cathode-anode spacing in a limited pressure range only. A theoretical explanation for this behavior is based on the model that, in the limited pressure range, electrons traversing the cathode-anode space can pick up almost all the energy of the applied voltage.

In addition, data are presented showing that early breakdown in an inert gas-filled diode can occur at voltages much lower than the first excited state. This has been accomplished in thermionic diodes exposed to the radiation of a nuclear reactor. A qualitative explanation for this behavior is proposed.
Structural Effects in Thin-Film Sandwich Emitters
Authors: Harris L. A.
Published: April 2005

Direct current measurements have been made of film currents in and emission currents from thin-film sandwiches consisting of beryllium, thermally formed beryllium oxide, and overlayers of silver, barium or a combination of the two.

Silver covered oxide films formed at low temperature yield regular film current characteristics but no electron emission. With high oxidizing temperatures, electron emission can be obtained but the films are subject to frequent breakdown. An intermediate temperature range yields more reproducible film currents and, in many cases, small but steady electron emission. A discontinuous forming process generally precedes the electron emission.

Films with barium overlayers break down and heal repeatedly, accompanied by very irregular emission at film voltages considerably below those for silver covered films. Brief exposure of a silver overlayer to barium vapor induces marked changes. Initially, the film current is irregular as it is for barium alone, but as the current increases the characteristic reverts to that for silver without barium. Electron emission is more frequently obtained in this way, though it occurs in the same voltage range as without barium.

The film-current curve shapes indicate that the current is carried mainly by electrons passing over a voltage-dependent barrier (Schottky effect), but cooling the samples has no effect on these curves, probably because of localized heating.

A tentative model is proposed to account for the particular observations reported here. Work function differences, the porosity of the thin silver films, and cracks or grain boundaries in the oxide layer combine to produce highly localized currents, heating, and structural changes consistent with measurements and observed emission patterns.
Energy Dependence of Extinction Distance and Transmissive Power for Electron Waves in Crystals
Authors: Hashimoto Hatsujiro
Published: April 2005

Quantitative measurements of the energy dependence of the extinction distance and transmissive power for electron waves in crystals have been carried out photographically and electrically with 100-kV and 300-kV electron microscopes. The observations show that the relativistic correction for the mass of the electron must not be disregarded in the dynamical theory of electron diffraction for either the elastic or inelastic scattering. The energy dependence of the visibility of thickness extinction contour fringes and the resolutions of the images of thick films are also discussed. Some of the features observed in electron micrographs of thin metallic films taken at 250–300 kV are illustrated.
Efficiency Measurements on GaAs Electroluminescent Diodes
Authors: Galginaitis S. V.
Published: April 2005

An integrating sphere was adapted to measurement of external efficiencies of GaAs injection lasers. External efficiencies rise rather sharply with current once the laser threshold is reached, attaining ultimate values of about 35% at 77°K for the more efficient diodes, as high as 60% at 20°K. On the basis of a highly simplified model, the observed external efficiencies indicate junction efficiencies near unity.
Efficiency of Production of Characteristic X Radiation from Pure Elements Bombarded by Electrons
Authors: Brown D. B. , Ogilvie R. E.
Published: April 2005

Equations are presented which give the intensity (photons/electron steradian) of K characteristic x radiation produced by pure elements under electron bombardment at normal incidence. For values of φ (the angle between the x-ray beam and the specimen surface) between 0° and 90° the equations may be summarized: νK=(δω/4π)NK,NK=WRf(χ)NQ̄xK+NKf,where vK is the number of K quanta per incident electron radiated into solid angle δω at takeoff angle φ, W is the fluorescence yield factor, R is a correction for loss of ionization due to electron back scattering, f(χ) is Castaing's absorption correction function, N is the number of atoms per unit volume, Q̄ is an average over electron energy of the cross section for K shell ionization, xK is the electron path length at which the energy of the electron drops to that necessary for K shell ionization, and NKf is the contribution due to secondary K shell ionization by high energy continuous x radiation. It is concluded that the predictions of this theory are in general in good agreement with available experimental data; further, that this theory shows certain advantages over those of Archard (1960) and of Green and Cosslett (1961). Values of f(χ) are calculated and compared with the experimental work of Castaing and the calculations of Archard and Mulvey.
Thermal Velocity Limit to Current Density in a Beam
Authors: Lichtenberg A. J.
Published: April 2005

The limiting current density that can be achieved with thermal velocities in the source emission is calculated by phase-space ellipse transformations. The results check those of Pierce, and are applicable to a wider range of problems. Simple lens systems can realize the ellipse transformations which give the limiting density. Under certain conditions the maximum current density is obtained between the object plane and the image plane, a situation analogous to the ``waist'' formation in a beam transport system used with particle accelerators.
Propagation of Microwaves in a Plasma-Filled Waveguide
Authors: Harmon Gerald S. , Eisner Melvin
Published: April 2005

A reasonably homogeneous plasma slab has been produced in a waveguide in order to examine a number of features of the plasma-microwave interaction. The usual linear theory gives expressions for the transmission and reflection coefficients in terms of the electron density and collision frequency for such a slab. Experimental values for the electron density are compared with those found from the shift in the cyclotron resonance absorption peak. In addition, an observed microwave amplification is described.
First Approximation to Magnetization Curling in a Chain of Spheres
Authors: Aharoni Amikam
Published: April 2005

The nucleation field for the magnetization curling mode in an infinite chain of ferromagnetic spheres is calculated as a first-order perturbation on the curling mode in a sphere. To this approximation, the nucleation field dependence on the radius R of the spheres is expressed as a−bR−2 with a, b positive constants. This yields positive nucleation fields for rather small radii (R≥130 Å for iron). To this first approximaton, nucleation by curling is more difficult than by fanning, for R≤100 Å in iron. The packing might influence somewhat the nucleation field, but the dependence is essentially exponential and as such is negligibly small for all practical cases.
Absorption Data of Laser-Type GaAs at 300° and 77°K
Authors: Turner W. J. , Reese W. E.
Published: April 2005

Optical absorption coefficients have been determined at 300° and 77°K for samples of GaAs which were doped to concentrations comparable to those present in the n, p, and p+ regions of the GaAs injection laser. n-type GaAs doped with Te to 3×1017 cm−3 and 9.6×1017 cm−3 have absorption coefficients of 20 cm−1 and 10 cm−1, respectively, at 1.475 eV and 77°K. Free carrier and deep-level absorptions contribute approximately 5 cm−1 to these values. At 77°K, p-type Zn-doped samples with NA−ND equal to 1.6×1018 cm−3 exhibit in the spectral region of laser emission an absorption that increases exponentially with photon energy and probably results from transitions of electrons in acceptor states to levels in the conduction band or conduction band tail. At 1.475 eV and 77°K, the absorption coefficient of this p-type material is 225 cm−1 to which free carrier absorption contributes only 3 cm−1. For heavier Zn-doped p+ material, e.g., 7×1019 cm−3, the value of K at 77°K and 1.475 eV is 250 cm−1 and is entirely due to free carrier absorption. For both n and p materials, a Burstein shift of the edge to higher energies is observed for the heavily doped materials in agreement with the observations of others.
Photoconductivity in Single-Crystal Tellurium
Authors: Vis Vincent A.
Published: April 2005

Measurements of the steady-state and transient photoconductive behavior in the extrinsic range are presented and interpreted in terms of a simple trapping model. The change of electrical conductivity due to steady irradiation by light of 3.5-μ wavelength is proportional to the first power of the intensity of the light for low excitation, becoming proportional to the square root at higher excitation. The small signal responsive time constant is 350 μsec for T<77°K in the dark and decreases with either thermal or optical excitation. A model composed of 0.5×1013 traps/cm3 of energy level 0.072 eV above the top of the valence band and an unspecified recombination mechanism account quantitatively for the observed effects. Details of the sample preparation process are given.
X-Ray Diffraction on Whiskers Grown from Ferrous Chloride in an Argon Atmosphere
Authors: Rambauske Werner , Gruenzel Ronald R.
Published: April 2005

Whiskers grown from ferrous chloride in an atmosphere of argon with 1% hydrogen were investigated by Laue, rotation, and Weissenberg methods. The whiskers exhibit a lattice twist over their length and are face-centered cubic. At least a portion of the whisker appears to be Fe3O4.
Dislocations in Webs of Germanium and Silicon
Authors: O'Hara S.
Published: April 2005

The generation of dislocations in webs of germanium or silicon is discussed. In silicon many of these dislocations intersect the web solid-liquid interface and are propagated during growth; they frequently align themselves into low-angle grain boundaries which tend to lie in the (01̄1) plane and propagate in the [21̄1̄] crystal-growth direction. The dislocations also interact strongly with the twin planes in the web and with each other. The effects of these interactions are made visible by the peculiar etching characteristics of the dislocations involved.
Effect of Long Decay Chains on the Counting Statistics in the Analysis of Radium224 and Radon222
Authors: Lucas H. F. , Woodward D. A.
Published: April 2005

In the counting of long decay chains, it is often necessary to use counting intervals that are long with respect to the half-life of the individual members of the series. With modern instrumentation the geometrical and detection efficiencies may be very nearly 4π and 100%, respectively. Consequently, the approximations normally used for estimating the statistical counting error are not valid. A method has been presented by which the variance of the observed count can be easily calculated for any long decay chain. The effects of the counting interval, the geometrical efficiency, and the delay of start of counting relative to the time of separation of Ra224 and Rn222 from their respective daughters have been determined. The counting interval and the geometrical efficiency were found to produce the most significant effect for both the Ra224 and Rn222 series. A simple and convenient method has been presented to correct for this effect by the use of a quantity J which can be calculated for a given experimental condition.
Fine-Grained Ferrites. III. Ni1−xCoxFe2O4. High-Power Microwave and rf Properties
Authors: Malinofsky W. W. , Babbitt R. W.
Published: April 2005

Dense Ni1−xCoxFe2O4, with x=0, 0.028, 0.030, and 0.067, was prepared with grain sizes down to 0.1 μ by using a previously described technique. This consists of a combination of flame-spraying to obtain the initial fine ferrite particles (down to 0.03 μ), and hot-pressing to sinter these into single-phase bodies of near theoretical density (to 98%).

The high-power microwave properties were measured in a cavity at X band with perpendicular pumping for a series of grain sizes ranging from 0.10 to 0.35 μ. Co=0.027 was used, since the magnetocrystalline anisotropy constant K1 is theoretically zero and thus would be expected to provide minimum linewidth ΔH in this compositional system. Measured values of the microwave magnetic loss susceptibility under perpendicular pumping χ⊥″, the threshold field for the onset of the subsidiary absorption hc, ΔH, 4πMs, and density are given as a function of grain size. hc was found to increase with decreasing grain (or pore) size. This was explained on the basis that spin waves which are important at the subsidiary resonance are longer than the grain size, and therefore interact effectively with such inhomogeneities. This explanation is supported by the finding that [(hc)2000− (hc)1500]/(hc)1500, for Hdc=1500 and 2000 Oe, decreases with decreasing grain size. χ⊥″ passes through a minimum near 0.18 μ in unannealed samples, but in annealed samples it decreases rather linearly with grain size. Of practical concern are the following combinations of hc and χ⊥″ which are obtainable by this method: >105 Oe and 0.6, >75 Oe and 0.15, compared to 16 Oe and 0.03 for a large-grained ferrite. The power ratio between the first and last is over 40.

Radio-frequency properties such as μ′ and μ″ were measured from 0.1 Mc/sec to 7 Gc/sec. In the dispersion curves obtained, the rf resonance frequency compared well with that calculated on the basis of the domain rotation mechanism. The static μ′ had similar values to those in large-grained samples, contrary to the case of NiZn ferrites, where wall motion plays a role. The resonance frequency of the microwave peak also agreed well with that calculated from a previously derived equation.
Magnetostriction of Single-Crystal Dysprosium, Gadolinium Iron Garnet, and Dysprosium Iron Garnet
Authors: Clark A. E. , DeSavage B. F. , Callen E. R.
Published: April 2005

The temperature and field dependences of the magnetostriction of dysprosium single crystals were measured from 78°K to room temperatures. In the paramagnetic region (T>178°K), the six lowest-order coefficients were measured and were found to vary as H2. At lower temperatures, due to the large uniaxial anisotropy, only the basal plane coefficient was measureable. The temperature and field dependences of this coefficient are adequately represented by the single-ion magnetoelastic coupling theory and are given as a function of the moment by λ=8.7×10−3I5/2[L−1(m)].

The temperature dependences of the magnetostriction coefficients of single-crystal GdIG and DyIG were measured from 78° to 400°K and found to be much larger and of opposite sign than that of YIG over most of the temperature range. This is due to the larger magnetoelastic coupling coefficient of the rareearth ions. Among the several interesting features are: the observance of magnetostriction compensation points, the sharp dip (and change of sign) of the apparent saturation magnetostriction at the magnetization compensation points, and the reversal in sign of the forced magnetostriction.
Spiral Structure and Moments in Gd-Dy Alloys
Authors: Bozorth R. M. , Suits J. C.
Published: April 2005

Magnetic moment and electrical resistivity measurements of the Curie (TC) and Néel (TN) points of Gd-Dy alloys show that the region of spiral structure between TC and TN narrows as Gd is added to Dy and disappears at about 50 at. % Gd. Apparently no spiral structure exists in Gd or Gd-rich alloys. The magnetic moments of Dy-rich alloys show the saturation expected when the magnetization is confined to the hexagonal plane (Jgπ/4), but the moments gradually approach the theoretical Jg as the Gd content increases toward 100%. The spin disorder resistivities are not linear in (g-1)2J(J+1); this suggests a variation in the electronic structure of these alloys.
Thermal Conductivity and Lorenz Function of Gadolinium between 5° and 310°K
Authors: Arajs Sigurds , Colvin R. V.
Published: April 2005

The thermal conductivity (λ) of a polycrystalline gadolinium sample, having an electrical resistivity of 2.41 μΩ cm at 4.18°K, has been studied as a function of temperature (T) between 5° and 310°K. The thermal conductivity has a maximum value of 0.333 W cm−1 °K−1 at 16.5°K. Changes in the slope of the λ vs T curve occur at 230° and 270°K. The former is believed due to the rapidly varying easy cone of magnetization. The second anomaly is associated with the ferromagnetic-paramagnetic transformation. The Lorenz function, from measured thermal conductivity and electrical resistivity data on the same sample, has been calculated as a function of temperature. This function clearly indicates that in addition to the electronic thermal conductivity there is considerable phonon and possibly some magnon heat transport.
Superparamagnetism in Magnetically Dilute Systems
Authors: Ishikawa Yoshikazu
Published: April 2005

Superparamagnetic behavior observed in magnetically dilute systems is discussed. The clusters that behave like superparamagnetic fine particles are ferromagnetic or ferrimagnetic regions separated magnetically from the matrix, because these regions are surrounded by nonmagnetic atoms. The magnetic properties of dilute oxide systems such as: 0.9 ZnFe2O4-0.1 NiFe2O4; 0.9 FeTiO3-0.1 Fe2O3; and Y1.5Ca1.5Fe4.5Sn1.5O12 are better understood if we take into account the existence of the superparamagnetic clusters. The Langevin function type magnetization curves observed for the Fe—Cr alloys in the composition range where ferromagnetism just disappears, however, were found not to have the characteristics of superparamagnetism, although superparamagnetic clusters are predicted by the localized model.
Induced Anisotropy in YIG with Si and Mn Additions
Authors: Gyorgy E. M. , Schnettler F. J.
Published: April 2005

The induced anisotropy in YIG (yttrium iron garnet) with Si and Mn additions has been studied. At 300°K the induced anisotropy increases with increasing Mn concentration and is zero for the samples containing Si. At 195°K an induced anisotropy could not be detected in any of the samples. At 77°K the YIG sample as well as the samples containing Si had an induced anisotropy whose magnitude increased with increasing Si. These results are consistent with the model attributing the induced anisotropy to localized Jahn—Teller distortions. They do not, however, invalidate other explanations.
Spinel-Type Ferrites Containing Florine
Authors: Schieber M.
Published: April 2005

Charge compensation by substituting univalent fluorine for divalent oxygen in spinel type ferrites was studied by preparing and analyzing single-phase polycrystalline materials. Starting with a 1:1 molar ratio of divalent fluorides and Fe2O3, charge compensation was mainly achieved by metal vacancies, although some Fe2+ was also present. The preparative method, unit cell dimensions, chemical compositions, magnetic moments at 90°K and Curie points for these compounds are given. Their properties can be interpreted as those of solid solutions of mainly γ-Fe2O3 and a stoichiometric fluorine ferrite M22+Fe3+O32−F−, where M is Mg, Mn, Co, Ni, or Zn.
Internal Fields at Iron in FePd Alloys
Authors: Bemski George , da Silva Ximenes Alexandrino
Published: April 2005

Mössbauer absorption of gamma rays by Fe nuclei in FePd alloys indicates that the internal field at iron is about the same for iron concentrations between 4 and 100 at.%. This field is identical to that in metallic iron. A temperature-dependent isomeric shift has also been observed for temperatures between 120° and 350°K.
Spin Correlations Among Narrow-Band Electrons
Authors: Goodenough John B.
Published: April 2005

In order to study the properties of narrow-band d electrons, it is convenient to study primarily ionic transition-metal compounds in which the broad-band states are separated into a filled valence band, an empty conduction band. A general Hamiltonian for this class of compound is presented. Since there is no analytic expression for the many-body spin-correlation energy of collective electrons, the Heisenberg exchange Hamiltonian for localized electrons is extrapolated continuously to the narrow-band case. In order to test the validity and power of this approach, it is used to construct a schematic energy diagram for orthorhombic MnP. The signs and relative magnitudes of the different exchange interactions follow from this diagram. The interaction along the orthorhombic c axis is predicted to be particularly sensitive to c-axis spacing, and therefore to increase with decreasing temperature and to induce significant exchange striction. The ground-state spin configurations are calculated from the Heisenberg exchange Hamiltonian, given these interactions. The antiferromagnetic⇌ferromagnetic transition found at 50°K and the metamagnetism of the low-temperature phase are found to follow from the model. The low-temperature magnetic phase is predicted to be a simple cycloidal spiral propagating along the orthorhombic c axis with spins in the b-c plane. However, the spiral is distorted by anisotropy and exchange striction, so that the turn angle is not uniform but is modulated with a wavelength half the spiral wavelength. The c-axis spacing is similarly modulated with a strain amplitude ε0∼0.015.
Ferromagnetic Hall Effect at Optical Frequencies and Inner Effective Magnetic Field of Ferromagnetic Metals
Authors: Krinchik G. S.
Published: April 2005

The results of magneto-optical measurements on Fe, Co, and Ni over a wide range of frequencies, varying from infrared to ultraviolet, have been analyzed. It is suggested that the magneto-optical phenomena in ferromagnetic metals are caused by the influence of the inner effective magnetic field Hi (which is responsible for the static ferromagnetic Hall effect) on the motion of the current carriers. The previously detected infrared magneto-optical resonance in Ni is interpreted according to this theory as the cyclotron resonance of the current carriers in the field Hi. A quantitative correlation of the static electrical conductivity and the ferromagnetic Hall constant is obtained by comparison of the magneto-optical data with the results of direct measurements. The conclusion may lead to a change in the commonly accepted point of view of the origin of ferromagnetism in transition metals.
Work Function of the (110) Face of Tantalum in a Cesium Vapor
Authors: Norris W. T.
Published: April 2005

The effective work function of the (110) face of a crystal of tantalum in the presence of cesium was estimated from values of the saturated electron emission deduced from the characteristics of a diode. The temperature of the cesium reservoir ranged from 320° to 380°K and the emitter temperatures were in the range 1100° to 1350°K. Under these conditions the work function of the cesium-covered surface was about 0.3 eV lower than that of polycrystalline material under similar conditions.
Effect of Space Charge upon the Transport of Charge Carriers
Authors: Ward A. L.
Published: April 2005

Numerical machine calculations have been made on the effect that space charge, composed of mobile charge carriers, has on the drift and diffusion of those carriers in an electric field. An apparent diffusion of carriers arises from the difference equations used to solve the transport problem, even though no diffusion term is included in the transport equations. This calculated diffusion is shown to be exact in the absence of space charge and in the limit of infinitely small calculation intervals. Numerical results illustrating the effect of space charge upon apparent diffusion coefficients and drift velocities are given for a fictitious gas. Calculations show good agreement with experimental data taken in two other laboratories to measure attachment coefficients in gases. Exploratory calculations have indicated the usefulness of this model for calculations in solid-state transport.
Field-Enhanced Secondary Electron Emission from Films of Low Density
Authors: Goetze G. W. , Boerio A. H. , Green M.
Published: April 2005

Low-density deposits of KCl showing stable secondary electron gains of 30 to 60 in transmission have been prepared by evaporation in an argon atmosphere. The layers have a fast response, high resistivity, and long life under primary electron bombardment. Measurements of their electrical properties suggest that the emission current consists entirely of true secondary electrons and no avalanche multiplication processes occur in the region of stable operation. Practical application of these layers as dynodes in electron multipliers and image intensifiers and as targets in camera tubes is discussed in some detail.