bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Magnetostatic and Micromagnetic Properties of the Infinite Rectangular Bar
Authors: Brown William Fuller
Published: April 2005

In estimating the nucleation field of an infinite rectangular bar, Aharoni used a variational method to calculate a lower bound to the magnetostatic energy. He constrained the variable potential to a specified form inside an ellipse circumscribed about the rectangle. In the present article, the method is improved by imposing the constraint only inside the rectangle itself. The resulting potential problem can be reduced to that of a bar of infinite permeability in an applied field of specified form; the final results can be expressed in terms of the demagnetizing factors Dx∞ and Dy∞ of such a bar. Similarly, an upper bound to the energy can be expressed in terms of the demagnetizing factors Dx0 and Dy0 of a bar of zero permeability. For rotation in quasiunison, the new lower bound to the nucleation field is considerably better than the old, but the new upper bound is not as good as that already obtained by constraining the magnetization to uniformity. New tables of Dx∞,Dy∞,Nx∞ (≡4πDx∞), and Ny∞ (≡4πDy∞) as functions of dimension ratio p are included; the demagnetizing factors at infinite and at zero permeabilities satisfy the relations Dx∞+Dy0= Dx0+Dy∞=1.
Effect of Mechanical Stress on p-n Junction Device Characteristics
Authors: Wortman J. J. , Hauser J. R. , Burger R. M.
Published: April 2005

A theoretical model is developed for the effect of mechanical stress on the electrical characteristics of Ge and Si p-n junction devices. This model is based upon the stress-induced variations in energy band structure and their effect on minority carrier densities. The changes in minority carrier densities are shown to depend upon the type of stress applied, with anisotropic stresses causing larger changes than hydrostatic stresses. From the calculated dependence of minority carrier densities upon stress, the equations are developed for the current—voltage characteristics of diodes and transistors under stress.

Following the general analysis several examples are given in which stress is applied to a small section of a junction in a diode or transistor. The results show that at stress levels greater than 1010 dyn/cm2, the device currents can change by several orders of magnitude when stress levels are changed by a factor of 2. The theory is compared with published experimental data and found to be in good agreement.
Electrical Properties of Thin Polymer Films. Part I. Thickness 500–2500 Å
Authors: Mann H. T.
Published: April 2005

The current I through silicone polymer films formed by electron-beam bombardment in the thickness range 500–2500 Å has been measured as a function of voltage and temperature between 4° and 300°K. The electrodes were vapor-deposited films of various metals. The electron transport is nonlinear and depends on voltage and thickness only through the electric field E when the applied voltage is greater than 5 V. At and below five volts, a negative resistance phenomenon similar to that described by Hickmott is sometimes observed which is voltage dependent rather than field dependent. The high-field electron transport depends rather strongly on temperature. The negative resistance phenomenon is not temperature dependent. The field-dependent current changes with time as a result of the diffusion of oxygen into the film, and this change appears to be correlated with a change in electron spin resonance absorption. The effect of free radicals on the electron transport which is thereby suggested, is further confirmed by the increased current observed as a result of a relative increase in the electron beam intensity used in the film formation. A hysteresis observed in the electron transport may be due to high-field polarization of the dielectric. The capacity of the specimens also changes with time, as a result of the diffusion of water into the dielectric. The usual theoretical expressions for field emission or Schottky emission do not completely fit the electron transport data although log I varies as E1/2.
Orientation Determinations of Crystals Using Ejection Patterns Resulting from Ion Bombardment
Authors: Cunningham R. L. , Ng-Yelim Joyce
Published: April 2005

Data on six common metals are presented to indicate the general usefulness of ion bombardment for orientation determinations of fcc and bcc crystals. The accuracy is 3° or better and is attained by the use of hemispherical collectors and a simple optical projection device. No film processing is involved and a complete determination, including all operations, usually takes less than 20 min.
Model for Fission-Fragment Damage in Thin Polycrystalline Metal Films
Authors: Goland Allen N. , Paskin Arthur
Published: April 2005

Fission fragments produce tracks in thin films made up of small crystallites and do not produce tracks in continuous films. This has been difficult to understand on the basis of the spike models where one considers only the energy transmitted directly to the lattice and neglects the energy acquired by the electrons. The energy to evaporate the crystallites must come from the electron gas because it has acquired almost all the energy initially lost by the fission fragment; consequently, in order to explain the evaporation of particles one must understand the subsequent electron energy-transfer processes. Examining the various relaxation times, we find that the energy is transferred first to other electrons via electron—electron collisions. If the electron gas is confined to a small region, as in a film of small crystallites, this immediately leads to a size effect. The largest crystallite that can be evaporated is one in which the total energy of the electron gas just equals the energy required for evaporation. This size estimate is an upper limit because the electrons may simultaneously lose energy via thermionic emission. A comparison of the two rate processes for an isolated particle of a typical metal suggests that electron—phonon energy transfer is the more important process, and that a negligible amount of energy is lost to the environment via escaping electrons. Consequently, almost all of the fission-fragment energy ultimately appears in the lattice. Estimates of the critical size for Au yield a diameter of about 170 Å for a spherical crystallite, in reasonable agreement with experiment. We conclude that thin metal films will exhibit evaporation fission tracks provided that the film is made up of crystallites in poor electrical contact with one another and that the crystallites are smaller than the largest that can be evaporated.
Magnetic and Structural Properties of Metastable Fe-Cu Solid Solutions
Authors: Kneller E. F.
Published: April 2005

Metastable Fe-Cu solid solutions with Cu concentrations up to 80% were obtained by simultaneous vapor deposition of Fe and Cu on cold substrates. Alloys with less than 50% Cu are bcc and ferromagnetic, the average magnetic moment per atom being slightly higher than for simple dilution. The Curie temperature decreases and the spectroscopic g factor increases with Cu concentration. Alloys with more than 70% Cu are fcc and appear to be paramagnetic. At elevated temperatures the alloys decompose into a bcc Ferich and an fcc Cu-rich phase. The kinetics of precipitation were studied by means of coercivity measurements; from these an activation energy Q=29 kcal/mole was determined.
Orientation Distribution Function of Statistical Segments in Deformed Polymer Networks
Authors: Roe R. J. , Krigbaum W R.
Published: April 2005

When a crosslinked network is deformed unidimensionally, the distribution of chain displacement vectors becomes rather well oriented along the stretching direction. It is shown that the distribution function w(cosχ) pertaining to the individual statistical segments comprising the network chains may be expressed in a series of Legendre polynomials. This function should be of value in the theoretical treatment of the kinetics of formation, and of the distribution of orientations, of crystallites formed in stretched networks. Examination of the distribution function indicates that the segmental orientation remains rather poor, even for highly strained networks. An expression is derived for 〈cos2χ〉 from the present treatment, where χ is the angle between a statistical segment and the stretching direction. Finally, expressions applicable only for low relative elongations are presented which relate the distribution function w(cosχ) to the experimentally measurable retractive force or birefringence of a stretched network.
Modification of the Threshold Current and Near-Field Emission Pattern of a GaAs Laser by an Adsorbed Dielectric Layer
Authors: Walker E. J. , Michel A. E.
Published: April 2005

We have observed the near-field emission patterns of a number of GaAs diode lasers. The onset of laser action is accompanied by an abrupt increase in the intensity of light emission at one or several spots along the junction. The adsorption of a dielectric film at a constant rate on one or both surfaces of a laser causes the threshold current to vary periodically with time. The position of the threshold spot did not vary as long as the film was of uniform thickness along the junction; however, the emission pattern could be altered by a suitable nonuniform film. The variation of the threshold current with film thickness can be fitted by a simple model that assumes the gain in the active region is proportional to the current density. Calculated values for the loss and gain factors ranged from 10 to 60 cm−1 and 0.5 to 4×10−2 cm/A, respectively.
Raman Maser Study of Optical Difference Frequency Production
Authors: Davis L. W. , McCall S. L. , Rodgers A. P.
Published: April 2005

Beat-frequency light generation in ammonium dihydrogen phosphate, arising from interaction of 3470-Å ruby maser second harmonic and 7454-Å ruby stimulated Raman scattering from benzene, has been investigated. A single crystal can serve to efficiently produce both the ruby second harmonic and the beat note, since in each process the phase matching condition is satisfied at nearly the same crystal orientation. The phase matching effect is readily observable when the crystal is rotated.
Measurements of Shock Tube Ionization Phenomena by a New Microwave Method
Authors: Brandewie Richard A. , Williams Everard M.
Published: April 2005

Measured values of electron density and collision frequency in shock-heated argon are presented and compared with theoretical equilibrium values. Both parameters are measured as a function of time during a single shock tube experiment. The measured density at 1 and 3 Torr forepressure equals or exceeds the predicted 1016−1017 electrons per cc at high Mach number (15–18); for lower Mach number, measured values fall far below the calculated curve, showing that loss mechanisms dominate thermal electron production over a significant interval of shock wave flow. The measured collision frequency compares well with the predicted value at 1 Torr but is lower by about an order of magnitude at 3 Torr. The experimental configuration comprises a theta pinch driven shock tube designed to drive a shock front into a coaxial waveguide. Two types of interference patterns are observed by transverse sampling of the longitudinal waves: the first, an anomalous pattern, is interpreted as a resonance caused by electrons ahead of the shock; the second, a well-defined interference between incident and reflected waves, yields measurements of the plasma reflection coefficient magnitude and phase.
Control of Laser Radiation with Birefringent Crystals: The Microwave Circuit Viewpoint
Authors: Wohlers M. R. , Leib K. G.
Published: April 2005

Microwave circuit theory is utilized to describe three devices which control coherent optical beams using birefringent crystals. A frequency demodulator uses the difference of the index of refraction along two axes of a birefringent crystal together with a Fabry-Perot interferometer to obtain an ``s'' type frequency discriminator. An optical isolator consists of a crystal and a polarizer that function in such a way that the input of the device is isolated from the reflection which can occur at its output. An optical switch is based on the filter characteristics of a Fabry-Perot interferometer which can be adjusted with an electrically activated birefringent crystal.
New Junction Laser Resonant Structures
Authors: Garfinkel M. , Engeler W. E. , Locke D. J.
Published: April 2005

Two new and related junction laser resonant structures are described together with their unique spatial output patterns. One of these structures emits a coherent beam in only one direction. The other may oscillate in a variety of spatial modes.
Studies of Field Emission and Electrical Breakdown Between Extended Nickel Surfaces in Vacuum
Authors: Brodie I.
Published: April 2005

Experimental studies of field emission and breakdown with nickel cathodes in planar diodes and a cylindrical projection tube are presented. These demonstrate that the currents preceding electrical breakdown are due to field emission from protruding whiskers. An activation of these whiskers can proceed by desorption of gases, and very high electric fields are capable of inducing new intensely emitting whiskers to appear. At critical electrical fields the whiskers disrupt, leaving molten pools at the cathode even in the cylindrical geometry where the anode can play no part in the process. Image disappearance may be caused by the whisker's melting. An estimate of the whisker height can be made from the size of the images in the projection tube. Application of the Fowler-Nordheim equation enables the current emitting area and the field magnification factor of a protuberance to be estimated. Whisker melting may be the origin of Cranberg's clumps for circuit limited breakdown.
Frictional Electrification of Belts of Insulating Materials
Authors: Cunningham R. G.
Published: April 2005

An apparatus has been constructed to introduce known amounts of slip between a belt of an insulating material and a rotating, grounded metal roller over which the belt passes. This slip results in frictional generation of electrostatic charge on the belt. The charge generated has been measured at different belt speeds, tensions, angles of wrap of belt around the roller, and at various amounts of slip on the roller. The charge generated per unit area on the belt is correlated with the work per unit area done against the force of friction. A method is presented for obtaining a value of the coefficient of sliding friction between the belt and the roller by the measurement of the charge generated. In addition, evidence of increased charge transfer as a result of frictional heating is discussed.
Magnetoelastic Damping in Zone-Melted Iron
Authors: Maringer R. E.
Published: April 2005

Ferromagnetic domain walls tend to move in phase with an alternating stress or magnetic field. This movement is opposed by directionally ordered interstitial atoms. When the time associated with the relaxation process is the order of the period of the moving walls, a phase lag between the applied field and the domain-wall movement occurs. This phase lag, coupled with normal hysteresis losses, causes a variety of magnetic and magnetoelastic phenomena, among them a strong temperature dependence of the ac magnetic permeability and a broad internal-friction peak in the temperature range of the Snoek peaks. These phenomena can be interpreted in terms of viscoelastic theory, with a relaxation process (interstitial directional ordering) having a unique activation energy.
Generation of Spin Waves in Nonuniform Magnetic Fields. III. Magnetoelastic Interaction
Authors: Schlömann E. , Joseph R. I.
Published: April 2005

If a spin wave propagates through a region of nonuniform magnetic field in which the effective magnon wavenumber equals the phonon wavenumber, it is partially converted into an elastic wave. The conversion efficiency depends primarily on the field gradient (H′) at the crossover point. Theories have been developed both for the case of weak magnetoelastic coupling and strong magnetoelastic coupling. For weak coupling the magnon-phonon conversion efficiency ηmp is ηmp=H′crit/|H′| (for |H′|>>H′crit), whereas for strong coupling ηmp = 1−π2exp(−H′crit/|H′|) (for |H′|<<H′crit). Here H′crit=πb22 ω/cMμ is a critical field gradient, b2 is one of the magnetoelastic constants, ω/2π the signal frequency, c the velocity of (transverse) sound, M the saturation magnetization, and μ the shear modulus. It has been assumed that the dc magnetic field is applied along a cube edge of a cubic crystal and that the material is elastically isotropic. For yttrium iron garnet (YIG) at room temperature and a signal frequency of 3×109 sec−1, H′crit≃5×104 Oe/cm. The field gradients encountered in practice are usually appreciably smaller. Thus the strong coupling theory applies and the magnon-phonon conversion should be substantially complete. The magnetoelastic interaction also gives rise to a reflected wave which originates in the crossover region. The amplitude of the reflected wave is much smaller than the amplitude of the transmitted wave.
Paramagnetic Susceptibility, Electrical Resistivity, and Lattice Parameters of Nickel-Rich Nickel-Tantalum Alloys
Authors: Chessin Henry , Arajs Sigurds , Colvin R. V.
Published: April 2005

The paramagnetic susceptibility, electrical resistivity, and lattice parameters of nickel-rich nickel-tantalum solid solutions (10 compositions) have been studied. The paramagnetic measurements extend to about 1500°K. The resistivities have been obtained at 4.2°, 77.2,° and 297.0°K. The lattice parameters of samples quenched from 1473°K were determined at 298°K. All these data indicate that the influence of tantalum on the physical properties of nickel is very similar to that of niobium. It is demonstrated by means of the magnetic susceptibility measurements that the generally accepted Curie-Weiss law, with an additive temperature-independent susceptibility term, is not applicable to the solid solutions of tantalum in nickel. The susceptibility and resistivity data are briefly discussed from the viewpoint of recent theoretical and experimental developments. The lattice parameters are analyzed using the previously suggested atomic volume scheme and elasticity theory. The agreement between the experimental values and the predictions is satisfactory.
Parallel Pumping of Magnetoelastic Waves in Ferromagnets
Authors: Comstock R. L.
Published: April 2005

An analysis is presented of the parallel pumping of magnetoelastic waves in ferromagnets. The resulting general threshold expression has as special cases the spin wave and elastic wave limits. The analysis clarifies the nature of the instability near the spin-wave-elastic-wave crossover where the normal modes are magnetoelastic. It is shown that the magnetoelastic notch in the spin-wave threshold curve (hcrit vs Hdc) observed in yttrium iron garnet is not the expected behavior for materials with large magnetoelastic coupling constants, small elastic losses, and low saturation magnetization. Under these conditions and for frequencies above the crossover frequency it is shown that the lowest threshold may result from the elastic-wave instability instead of the spin-wave instability.
Electroluminescent Gallium Arsenide Diodes with Negative Resistance
Authors: Weiser K. , Levitt R. S.
Published: April 2005

Electrical and optical properties of gallium arsenide diodes with a P-P0-N structure were studied between 4.2° and 90°K. The diodes were prepared by first diffusing manganese, and then zinc, into n-type gallium arsenide, keeping the zinc junction depth much shallower than that of the manganese junction. The P0 region, dominated by the manganese, becomes one of high resistivity at these temperatures because of freezeout of holes on the deep-lying manganese centers. The low-resistivity N and P regions on either side serve as electron and hole injecting contacts, respectively. The diodes are electroluminescent and exhibit a negative resistance over a portion of their current-voltage characteristics when a forward bias is applied. At 77°K, a typical voltage for the onset of the negative resistance is 5 V at a current of 5 mA; at about 2.2 V the dynamic resistance becomes positive again. The spectrum of the emitted light indicates recombination through both zinc and manganese centers. It appears that the mechanism responsible for the negative resistance is not the one suggested by Lampert. Possibly, the absorption by the P0 region of light emitted at the P-P0 boundary is responsible for the phenomena observed, as suggested by Dumke. At voltages below the onset of the negative resistance, the current-voltage relation in the P0 region obeys Ohm's law at low injection levels but eventually the current depends on the square of the voltage. This behavior, as well as the spatial origin of the light, is in good agreement with the theory of Ashley and Milnes.
Use of Electron Probes in the Study of Recombination Radiation
Authors: Wittry David B. , Kyser David F.
Published: April 2005

The electron probe microanalyzer has been used to study the local variations in recombination radiation from gallium arsenide. The intensity of recombination radiation from different specimens varies by several orders of magnitude. Local fluctuations are observed which are attributed to surface deformation and to non-uniform distribution of impurities. Within experimental error, the wavelength distribution was indistinguishable from the wavelength distribution from GaAs diodes.
Photothresholds in Mg2Ge
Authors: Mead C. A.
Published: April 2005

Optical absorption and surface barrier photoresponse measurements have been made on cleaved samples of Mg2Ge. The form of the results obtained from both techniques indicates an indirect transition at approximately 0.54 eV followed by a direct transition at approximately 1.8 eV.
Degradation in Zinc-Doped GaAs Tunnel Diodes
Authors: Epstein A. S. , Caldwell J. F.
Published: April 2005

The effects of the voltage swing, peak current-to-capacity ratio (IP/Cjv), zinc concentration, and lithium on the degradation of the peak tunnel current are examined in zinc-doped GaAs tunnel diodes.
Derivation of the Orientation Correlation Function in Semicrystalline Polymers
Authors: Smith K. J.
Published: April 2005

The quantity 〈cos2θij〉r is needed to describe correlations in orientation of ordered regions in semicrystalline polymeric films. The approximate form was found by Stein and Sidham [J. Appl. Phys. 35, 42 (1964)]; here the exact formula in closed form is obtained.
Monte Carlo Range Calculations for a Thomas-Fermi Potential
Authors: Oen Ordean S. , Robinson Mark T.
Published: April 2005

Our earlier Monte Carlo calculations of the ranges of atoms having energies from 1 to 100 keV, slowing down in a random solid through binary elastic collisions, have been extended by using a Thomas-Fermi potential to represent the interaction between the moving atom and a lattice atom. The screening radius of the potential is that derived by Firsov. The calculations have been made for a wide variety of target-to-projectile mass ratios. Except for the highest energies, the calculated ranges are considerably shorter than those found previously using the exponentially screened Coulomb potential. Most of the experimental range data lie between the range curves calculated for these two potentials, although the Thomas-Fermi potential gives somewhat better over-all agreement. The shapes of the calculated range distributions give close agreement with those found by experiment in amorphous solids. Average ranges calculated by integrating the reciprocal of the stopping power agree fairly well with these Monte Carlo calculations, especially when the mass of the slowing-down atom is large compared to that of a lattice atom.
Photoelectric Determination of the Image Force Dielectric Constant For Hot Electrons in Schottky Barriers
Authors: Sze S. M. , Crowell C. R. , Kahng D.
Published: April 2005

Photoelectric measurements of the bias dependence of the potential energy barrier for electrons in gold n-type silicon Schottky diodes show that the image force dielectric constant deduced from direct measurement of the barrier lowering is 12.0±0.5, in close agreement with the infrared dielectric constant of silicion, and independent of the applied field for fields between 104 and 2×105 V/cm. The current-voltage characteristics of these diodes at room temperature cannot be explained on the basis of pure Schottky emission.
Dynamic Birefringence and Mechanical Loss Spectra of Crystalline Polymers
Authors: Yamada Ryo , Stein R. S.
Published: April 2005

The variation of the real parts of the dynamic modulus E′, the dynamic strain-optical coefficient K′, the mechanical loss tangent tan δ, and the optical loss tangent tan α have been measured as a function of temperature between −40° and +120°C at constant frequency of 1 cps for low-density polyethylene, high-density polyethylene, polypropylene, and nylon-6. The results are interpreted in terms of both phenomenological theory and molecular mechanisms. The results for these polymers may be understood in terms of differing contributions by the processes of (a) spherulite or superstructure deformation, (b) delayed crystal reorientation within the deformed superstructure, and (c) relaxation of crystal orientation. For low-density polyethylene, processes (b) and (c) are the principal contributors while for high-density polyethylene, (a) becomes important at the lower temperatures. For polypropylene, (a) dominates and (b) begins to contribute at the higher temperatures, while for nylon-6, (a) gives way to (c) without any appreciable region of important contribution of (b).
Some Comments on the ``Avrami'' Equation
Authors: Price F. P.
Published: April 2005

The ``Avrami'' equation applies rigorously only to a system which does not change volume on transformation and where the developing regions are spheres. The consequences of the impossibility of achieving these conditions in real systems is discussed. It is shown that excessive approximation combined with the use of weight rather than volume fractions can lead to errors in the exponent n of as much as 0.3. It is emphasized that only at very low conversions can meaningful interpretations be made of the exponent.
Extension of Unoriented Nylon 66 Filaments. III. Superposition of Data
Authors: Williams Malcolm L. , Bender Malcolm F.
Published: April 2005

In an effort to understand the molecular mechanism of cold drawing, the tensile creep of unoriented nylon 66 monofilaments as a function of load has been obtained at three different combinations of temperature and moisture content. Qualitatively, an increase in either load, temperature, or moisture content will shift the creep curve to shorter times. These data can be quantitatively correlated by plotting the elongation ε against log t−a+bx+cT+c1σ/(c2+σ). Here t is time, x is % H2O, T is temperature in °K, σ is an average stress in dynes/cm2, and a, b, c, c1, and c2 are constants. The parameters b and c are identical with those previously found to apply to the moisture and temperature dependence of the elastic extension of oriented nylon 66 fibers. The free-volume theory frequently employed for amorphous polymer behavior is shown to be inapplicable since moisture sorption decreases the free volume although it quickens cold drawing. Application of dislocation concepts enables an estimate of the stress dependence of dislocation velocity to be calculated.
Cold Drawing of Glassy Polystyrene under Dead Load
Authors: Ender D. H. , Andrews R. D.
Published: April 2005

The deformation of glassy polystyrene under a fixed tensile dead load can take place in three different modes: (a) drawing by formation and propagation of a neck, (b) drawing by proliferation of deformation bands without necking, and (c) homogeneous creep. Which mode is observed depends primarily on stress level and temperature. In homogeneous creep, deformation bands are not found; however, they are always observed in connection with the two types of drawing. At any given temperature a boundary stress is observed above which drawing takes place and below which only creep is observed. This critical stress decreases with increasing temperature. It is believed that this is the stress necessary either for the formation or propagation of deformation bands. It seems likely that drawing by shear band proliferation is the ideal mode which would be obtained in a perfectly homogeneous and uniform sample; however, drawing usually goes over into the necking mode because of nonuniformities in specimen geometry or uneven temperature. Neck initiation is delayed for a certain time interval after application of the dead load. The logarithm of the delay time is found to be a linear function of stress and, also, an approximately linear function of temperature.
Birefringence Effects in Acrylonitrile Polymers. II. The Nature of the 140°C Transition
Authors: Kimmel R. M. , Andrews R. D.
Published: April 2005

Birefringence measurements on solvent-cast films of polyacrylonitrile homopolymer under dead load are reported as a function of temperature and as a function of time at constant temperature. It is shown that a large positive birefringence effect is associated with the 240°C aromaticization reaction in PAN. The high negative birefringence state produced by temperature cycling and first reported in Part I of the present series is found to require a small dead load on the sample during cooling for its formation, and is observed to form under conditions of almost constant length. From the interaction between the large negative effect and the positive effects of the nitrile conjugation reaction, it is deduced that the magnitude of the large negative effect is directly proportional to the concentration of nitrile groups present. It is proposed that the 140°C transition in PAN is a result of the association-dissociation equilibrium between nitrile dipoles on adjacent chains. The temperature dependence of the equilibrium constant for this association is calculated from the birefringence ``cooling curve,'' giving an enthalpy change of 48 kcal/mole, which suggests that association of dipole multiples is involved. Creep, dynamic mechanical, and dielectric loss data from the literature are correlated on the basis of this proposal concerning the nature of the transition.
Tripyramid and Raised-Triangle (111) Diamond-Lattice Imperfections in Silicon Epitaxial Films
Authors: Lawrence J. E. , Tucker R. N.
Published: April 2005

Two epitaxial defects, the raised triangle and the tripyramid, which appear in silicon and germanium films, are discussed with respect to their origin, crystallography, and electrical characteristics. These crystalline defects propagate from substrate surface contamination, such as refractory particles, and grow more rapidly than the defect-free film. Referred to the substrate lattice, the raised-triangle defect is bound by the inclined {111} planes; the defect lattice is rotated 180° around the [111] direction. The raised-triangle defect provides the conditions necessary for the formation of the tripyramid structure. The three crystallite lattices of the tripyramid are rotated relative to the raised-triangle lattice's [111] direction such that their [1̄1̄1̄] directions are tilted 4° in the [211] direction. The major exposed faces of the tripyramid crystallites are {1̄1̄0} planes. Both the raised triangle and the tripyramid are centers for soft electrical junctions.
Parallel-Pumped Magnon Instabilities in a Two-Sublattice Ferrimagnetic Crystal
Authors: Morgenthaler Frederic R.
Published: April 2005

Instability thresholds for parallel-pumped magnons in a two-sublattice ferrimagnet are derived by means of a perturbation method. Cases are considered in which the pump frequency is twice a particular magnon frequency or else the sum of two distinct magnon frequencies—one belonging to each branch of the spinwave dispersion relation. The calculations are made within the molecular field approximation for a single crystal of ellipsoidal shape, and include the effects of the volume dipolar energy as well as those due to unequal g factors of the sublattices. The thresholds appropriate to an ``unflopped'' antiferromagnet are also given when the dc magnetic field is applied parallel to the anisotropy axis.

The prospects for experimentally reaching the thresholds, particularly those occurring at submillimeter wavelengths, are evaluated insofar as is possible; in such cases the possibility exists of utilizing a laser for the pump.
Effect of Hydrostatic Pressure on Shock Waves from Underwater Explosions
Authors: Vanzant B. W. , DeHart R. C.
Published: April 2005

Techniques for using pressure vessels to study the characteristics of shock waves from high explosives detonated under high hydrostatic pressure have provided empirical observations not previously available in the literature. Results indicate that although peak pressure is not affected by hydrostatic pressure, the duration is shortened and the impulse lowered by increasing the hydrostatic pressure. Also, the negative phase of the pressure pulse appears to increase as the ambient pressure increases.
Beam Probing of rf Beam/Plasma Interactions
Authors: Cannara A. B. , Crawford F. W.
Published: April 2005

Experimental measurement of rf electric fields in electron-beam/plasma interactions requires a non-perturbing probing technique. Such a technique is described in this paper and has been applied to study cathodic electron beam break-up and meniscus formation phenomena observed in a low-pressure mercury-vapor discharge. Experiments are described in which the deflection of a fine electron-beam probe directed parallel to the cathode surface is measured to determine the spatial variations of the low- and high-frequency electric fields. A number of supporting experiments are reported which help to clarify the various phenomena occurring in the beam/plasma interaction region.
Plasma Resonance Probe Characteristics in a Magnetic Field
Authors: Crawford F. W.
Published: April 2005

The operation of the plasma resonance probe in the absence of a magnetic field is now well understood, and the resonant frequency can be interpreted to give the electron density in the plasma. In many potential applications of this diagnostic technique to laboratory and space plasmas, a static magnetic field is present. This paper considers the resulting modifications to the resonance. The analysis is based on the simplified model of the probe behavior that has been validated for the zero magnetic field case by the work of Harp and Crawford. It is concluded that the technique can be applied to obtain the electron plasma frequency ωp and the electron density for ωc2≪ωp2; and the electron cyclotron frequency ωc, and hence the local magnetic field when ωc2≫ωp2. An approximate correction formula is derived for the intermediate range ωc2≈ωp2.
X-Ray Extinction Contrast Topography of Silicon Strained by Thin Surface Films
Authors: Meieran Eugene S. , Blech Ilan A.
Published: April 2005

Diffraction topographs of oxidized silicon wafers made by the extinction contrast technique show extremely high intensity being diffracted from the silicon surface directly under steps etched in the oxide. Edges of metal or dielectric films evaporated on silicon similarly show enhanced intensity. In some cases, a decreased diffracted intensity (less than that diffracted by pure Si) is seen in these regions. These two effects are attributed to elastic strain transmitted to the Si by the step or edge, due to the adherence of the film to the substrate. Enhanced intensity is due to extinction contrast, while decreased intensity is due to a Borrmann anomalous transmission effect. The orientation of the step with respect to the diffraction vector ghkl, the height of the step, and the compositions of substrate and film are shown to be important parameters affecting the diffracted intensity.
Magnetization of Current-Carrying Cold-Worked NbZr Superconducting Wires
Authors: Bergeron C. J. , Williams M. W. , Haubold A. D.
Published: April 2005

Magnetization data have been obtained for Nb−33%Zr 0.010-in.-diam wires carrying a transport current I in a constant external longitudinal magnetic field Hext and with a liquid-helium bath temperature of 4.2°K. The variation of magnetization with I for a constant Hext depends on the relative directions of I and Hext. When I is antiparallel to Hext, the specimens were observed to become paramagnetic at a threshold current less than the experimental critical current and remain paramagnetic up to the critical current. A linear relationship between the threshold current and the external field for Hext<500 G is observed.
Deformation and Fracture of Ivory
Authors: Bonfield W. , Li C. H.
Published: April 2005

Ivory does not deform in a completely elastic manner prior to fracture, but instead plastic microyielding commences at a very small applied stress. The nature of the plastic deformation is determined by the orientation of the test specimen relative to the growth ring structure. Specimens oriented with the tension axis parallel to the tusk length (designated longitudinal) exhibit both a larger microscopic yield stress (the stress to produce a plastic strain of 2×10−6 in./in.) and a higher rate of strain hardening than specimens oriented perpendicular to the tusk length (designated transverse). Prestraining has no effect on the rate of strain hardening of longitudinal specimens, but progressively reduces the measured rate of strain hardening of transverse specimens. A feature common to the deformation of both longitudinal and transverse specimens is the considerable anelastic contraction which occurs after unloading. The fracture characteristics, which are also a function of specimen orientation, are correlated with the relative planes of weakness provided by the interfaces between growth rings.
Space-Charge Capacitance of an Intrinsic Semiconductor Film
Authors: Heiman Fred P. , Warfield George
Published: April 2005

The zero-bias capacitance C of a thin intrinsic semiconductor film sandwiched between identical electron-injecting contacts is computed exactly and compared with the value C0 for noninjecting contacts. The effect of traps and recombination centers is omitted. The curve of normalized capacitance versus film thickness exhibits a bump for an intermediate value of thickness. C/C0 is unity for very thin or very thick films and may reach a maximum value of 1.934 (nominally 2). Contact-dominated conditions disappear for films thicker than four Debye lengths based on the intrinsic carrier concentration.
Curie Temperatures of Thin Nickel Films by Torque Measurements
Authors: Livesay B. R. , Scheibner E. J.
Published: April 2005

The results of torque measurements on thin nickel films were used to determine the saturation magnetization in the neighborhood of the Curie point. The films were deposited by evaporation in high vacuum (10−7 to 10−8 Torr) and protected with a silicon monoxide overcoat. The relative magnetization σ was found to depend upon the temperature according to the power law σ2=ξ(1−T/Tc) for temperatures near but below the Curie point Tc. Curie temperatures determined according to this power law were found to be considerably less than the Curie temperature of bulk nickel below 100Å. In addition, the parameter ξ was found to increase linearly with film thickness, from 20 to 225Å. Details are given on the techniques used for film preparation and for the magnetic measurements.
Dislocations in Quartz Observed by Transmission Electron Microscopy
Authors: McLaren A. C. , Phakey P. P.
Published: April 2005

Arrays and networks of dislocations have been observed by diffraction contrast electron microscopy in crystals of natural milky quartz. These arrays and networks have been analyzed in terms of Burgers vectors suggested from examination of the crystal structure. The relevance of these dislocations to the plastic deformation of quartz is discussed.
Measurement of Microwave Acoustic Attenuation in Sapphire and Rutile using Nickel-Film Transducers
Authors: Wilson R. A. , Shaw H. J. , Winslow D. K.
Published: April 2005

Initial investigations on the room-temperature acoustic attenuation in sapphire and rutile at S band, which were reported earlier, showed the attenuation in both of these materials to be relatively low. These measurements have now been extended to other frequencies, and curves of attenuation are shown for rutile shear waves and sapphire longitudinal waves covering the frequency range from L band to X band, and for sapphire shear waves from L band to S band. The attenuation has a nearly linear variation with frequency at the lower frequencies, and increases monotonically as frequency increases. This behavior may be attributable to Rayleigh scattering from submicron scattering centers within the crystals. Nickel-film magnetostrictive transducers, coupled to dielectric resonators, were used to generate the acoustic waves in the samples under study, and the acoustic attenuation was determined from echo measurements. Conversion efficiencies and certain other observed properties of nickel-film transducers over the above frequency ranges are also discussed.
Oscillations and Noise Generation in a Beam-Generated Plasma
Authors: Dunn D. A. , Nichparenko W. , Simpson J. E. , Thomassen K. I.
Published: April 2005

An electron beam at a few kilovolts is used to generate a plasma in helium or argon at 10−4 to 10−2 Torr in a glass tube aligned with an axial uniform magnetic field of 0.3 to 2 kG. At and above a critical beam current and gas pressure, the discharge changes from a glow region the size of the beam to a glow discharge filling or nearly filling the glass tube (total glow). Measurements of the plasma density, the velocity distribution of the beam, and the spectrum of the rf noise generated in the plasma as functions of beam current, voltage, and gas pressure have been made. These data are consistent with an explanation of the effect involving a convective forward-wave beam-plasma oscillation which has a starting current equal to the measured critical current for the transition to total glow and which is determined by the net gain of the system including reflections at the ends. The oscillation, once started, is not a coherent oscillation, but can have a very wide noise bandwidth extending essentially from zero frequency to near the electron plasma frequency.
Saturation Effects in Second-Harmonic Generation of Light using Unfocused Laser Beams
Authors: Wang Charles C. , Racette George W.
Published: April 2005

The theory of second-harmonic generation of light was examined with particular emphasis on the saturation effects occurring at high laser power levels. The nonlinear coupled Maxwell's equations were solved approximately to yield solutions of simple form. The effect of beam divergence was taken into account by averaging the solution over the entire angular spread of the laser beam. The second harmonic thus generated is seen to be proportional to the32 power of the laser power independently of the length of the crystal in long crystals. Experimental data in good agreement with the theory are presented.
Crystallite Size Distributions from X-Ray Powder Line Profiles
Authors: Smith Vedene H. , Simpson Paul G.
Published: April 2005

The distribution of column lengths, p(n)/Nc, in a strain-free powder sample is given by the relationship p(n)/Nc=k(An+1−2An+An−1)/(A1−Ak+1)among the Fourier coefficients of the x-ray powder diffraction line shape under the assumption that the total number of columns of length 1, 2, …, k unit cells is negligibly small. This eliminates the necessity for use of the experimentally imperfect coefficient A0 and is equivalent to Warren's method for elimination of the ``hook effect.'' It is also shown that the technique of Warren and Averbach is valid for either narrow or broad diffraction lines if the crystallite size distribution is treated as a function of a discrete variable.
Electrical and Spectrographic Study of a Double-Pulsed Flashtube as applied to Laser Pumping
Authors: Avizonis Petras V. , Legato Tony
Published: April 2005

Excitation of ruby lasers by means of double-pumped high-intensity helical flashtubes of approximately 10−4 sec flash duration is described. Electrical discharge parameters for double-pulse operation of the helical flashtubes were correlated experimentally and theoretically with maximum loading possible for such tubes. Time-resolved spectra of such discharges were obtained and plasma temperatures were computed from the xenon continuum. Temperatures thus computed varied from 1 to 2 eV and were correlated with peak discharge currents. The laser energy obtained from such excitation of rubies was found to be the same as that from normal (1 msec or longer) discharges having the same pump energy, but the power in the laser beam was proportionately increased with the decrease in the excitation time.
Solution of Electromagnetic Problems in Anisotropic and Compressible Media
Authors: Chen Hollis H. C. , Cheng David K.
Published: April 2005

It is shown that in the solution of electromagnetic problems the compressibility of a medium can be characterized by a ``compressivity tensor,'' just as a permittivity tensor is used to characterize anisotropy. The effects of a compressible medium can be accounted for by a ``pressure displacement current,'' which depends on the spatial variation in pressure, and by an equivalent volume density of charge, which is proportional to the pressure deviation from the mean. The constitutive parameter tensors are given in both dyadic and matrix forms. With the suggested representations, the solution of electromagnetic problems in an anisotropic and compressible plasma can proceed on a systematic basis. It is also shown that with a constant, externally applied magnetic field, the electromagnetic fields can be decomposed into longitudinal and transverse components. A complete formal solution is given for the case where there is no longitudinal variation.
Conduction Phenomena in Rutile Single Crystals
Authors: Van Raalte John A
Published: April 2005

Application of voltage along the c axis in rutile single crystals produces an increase in conductivity after a ``delay'' period. During this period, which may amount to several days at room temperature, the current decays as a result of trapping. The subsequent rise in current leads to thermal breakdown unless the current is limited externally. The destruction of the insulating properties reflects a change in the bulk, brought about by an injection of positive space charge from the anode. This charge, believed to be holes, is injected by field emission due to a steepening anode fall and allows the electron current to rise exponentially. The anode fall is approximately 10−3 mm wide and sustains fields of 106 V/cm. Trapping of electrons and holes produces two types of color centers, which are distinguishable by their color and migration in the applied field.