bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoelastic Constants of Selected Ultrasonic Delay-Line Crystals
Authors: Reintjes J. , Schulz M. B.
Published: February 2004

All of the photoelastic constants of cubic SrTiO3, yttrium gallium garnet, and sapphire, three of the constants of LiNbO3, and all except p44 of rutile have been measured relative to those of fused quartz. The measurements were made at room temperature using 6328 Å light. The photoelastic tensor of sapphire is unusual because all of the off-diagonal components appear to be very small or zero.
Magnetic Characteristics of 2–17 Lanthanide-Nickel Compounds
Authors: Carfagna Paul D. , Wallace W. E.
Published: February 2004

Magnetic characteristics of nine compounds represented by the formula Ln2Ni17 (Ln=Y or a lanthanide) are reported. The Y, Sm, and Lu compounds are ferromagnetic; the others are ferrimagnetic. Curie temperatures range from 601° to 641°K. The nickel moment is 0.27 μB, which is in very close agreement with 0.25 μB, the value expected if all Ln valence electrons are transferred into the Ni 3d band. Magnetization of the Y2Ni17 and Lu2Ni17 compounds is lost in two stages as temperature is increased. Ferrimagnetism of heavy lanthanide compounds is indicated by the magnitude of their saturation moments and the form of the magnetization-temperature curves. The magnetic coupling is the same as that observed in similar and related Ln–Co and Ln–Fe compounds, i.e., the Ln–Ni coupling is antiferromagnetic and ferromagnetic for heavy and light lanthanides, respectively. From the Curie temperature it is inferred that the Ni–Ni interaction is dominant. This is in contrast with the situation in Ni-containing Laves and Haucke phases, in which the Ln–Ln interaction is dominant.
Temperature Dependence of Magnetic Domain Structure and Wall Energy in Single-Crystal Thulium Orthoferrite
Authors: Rossol F. C.
Published: February 2004

A study has been made of the temperature and field dependence of the magnetic domain structure in thin single-crystal c-axis plates of thulium orthoferrite from room temperature down through the reorientation range (80° to 94°K) where the net magnetization moves from the c axis to the a axis. Visual observation of the domain pattern was achieved by means of Faraday rotation. In the reorientation range the domain pattern consists of stripes bounded by Néel walls parallel to the b axis. A field applied along the c axis causes unconnected domains to collapse into cylindrical domains which are stable within a range of field of about 7 Oe at room temperature and increasing to nearly 20 Oe at the upper end of the reorientation range. Cylindrical domains with diameters as small as 7 μ or 16% of the sample thickness have been observed. The temperature dependence of the domain-wall energy, which decreases by a factor of five from room temperature down to 94°K and faster still in the reorientation range, is deduced from measurements of domain width.
Mechanical Response of Solid Cylindrical Conductors to Axial Electrical Currents
Authors: Smith Stanley H.
Published: February 2004

An analytical investigation has been made of the behavior of long cylindrical conductors which are subjected to the thermal and magnetic stresses arising from the passage of axial, time-dependent, electrical currents. The motion of the medium is assumed to be small, and it is also assumed that the electrical, mechanical, and thermodynamic properties of the medium are constant. Solutions have been obtained to the equations of linear thermoelasticity describing the radial motion induced by stresses of electromagnetic origin both for a medium of finite electrical conductivity and for the limiting case of a perfect conductor. The wavelengths of the axial waves produced by the radial motion are given as solutions of the Pochhammer-Chree equation. Results of the calculations of the axial wavelengths for a Poisson's ratio of ⅓, corresponding to the value for copper and aluminum, are presented.
Ambient-Sensitive Photoelectronic Behavior of CdS Sintered Layers
Authors: Micheletti Frank B. , Mark Peter
Published: February 2004

The temperature dependence of the equilibrium conductivity and the temperature and illumination dependence of the steady-state and transient photoconductivity of Cu and Cl doped sintered CdS layers are strongly affected by atmospheric oxygen. It is shown that the surface state due to chemisorbed oxygen determines the steady-state photoconductivity and the equilibrium dark conductivity in the adsorbate ambient. Further, an oxygen chemisorption surface state, 0.9 eV below the conduction band, together with the associated surface space-charge region cause the photocurrent to undershoot the equilibrium current upon cessation of illumination, and to overshoot the steady-state photocurrent on reillumination.
Electrical Studies of Neutron-Irradiated p-Type Silicon: Defect Structure and Annealing
Authors: Stein H. J.
Published: February 2004

Defects produced in float-zone and crucible-grown p-type silicon by neutron irradiation at 76°K were investigated, using electrical conductivity and Hall-effect measurements. The behavior of the neutron-produced defects is independent of the crystal growth, and exhibits an illumination dependence similar to that previously observed in n-type silicon and attributed to the presence of defect clusters. The neutron-produced changes in the electrical properties of p-type silicon at 76°K are therefore ascribed to defect clusters. The annealing loss of the light-sensitive defects occurs in diffuse stages between 150° and 550°K. The largest stage is observed between 150° and 240°K. A major fraction of the hole-mobility annealing parallels the annealing for the light-sensitive defects, and suggests that the mobility change caused by defect clusters is significantly larger than that caused by isolated defects formed from cluster dissociation. The most apparent crystal-growth-dependent annealing is observed between 540° and 620°K, where a reverse annealing occurs in the hole-removal rate for crucible-grown, but not for float-zone, silicon. The fractions of the neutron-produced decreases in hole concentration and mobility which remain after 700°K annealing are, respectively, ∼0.1 and 0.01 for float-zone, and ∼0.25 and 0.1 for crucible-grown silicon.
Low-Energy Depth Distributions in Pt, Al, and KCl as Obtained by Sputtering
Authors: Kelly Roger
Published: February 2004

Depth-distribution measurements have been made by means of the sputtering technique with Pt, Al, and KCl, in all cases following low-energy labelings with Kr containing 85Kr. The observed values of Rm, the median or 50% range, were with Pt 14 Å at 3 keV and 59 Å at 9 keV; with Al they were 56 Å at 4 keV and 101 Å at 10 keV; and with KCl they were 9 Å for Tesla energies, 38 Å at 2 keV, 67 Å at 4 keV, and 105 Å at 10 keV. It was possible to show that gas sputtering and related effects probably did not play an important role in the experiments. Thus, the ranges (a) were, in general, comparable to those obtained using electrochemical techniques, (b) were independent of the sputtering energy (shown with KCl), and (c) were in a similar proportion to each other as required from dissolution experiments (shown with KCl).
Phonon Scattering by Cottrell Atmospheres Surrounding Dislocations
Authors: Klemens P. G.
Published: February 2004

Cottrell atmospheres modulate the solute concentration of alloys and lead to fluctuations in phonon velocity essentially proportional to the dislocation strain field. Normally one regards point defects as ineffective in scattering phonons at the very low temperatures when the thermal resistance due to dislocations is important. However, the modulation of the impurity concentration about the dislocations increases the phonon scattering by dislocations if heavy impurities are associated with positive dilatation, or light impurities with negative dilatation, and decreases phonon scattering for the opposite combinations. Cottrell atmospheres may thus account for an apparent dependence of phonon scattering by dislocations on the solute content of alloys, as well as changes in the lattice thermal conductivity with aging.
Nuclear Magnetic Resonance Absorption in Metals in the Region of the Doppler-Shifted Cyclotron Edge
Authors: Kaplan J. I.
Published: February 2004

A calculation has been made of the nuclear magnetic resonance lineshape in a semi-infinite metal slab with a magnetic field perpendicular to the sample surface. The range of frequencies has been chosen such that the resonance moves from below the Doppler-shifted cyclotron edge to above it. A discussion of the feasibility of such an experiment is given.
Electrical Properties of n-Type Epitaxial Films of Silicon on Sapphire Formed by Vacuum Evaporation
Authors: Itoh Tadatsugu , Hasegawa Shinichi , Kaminaka Nobuyuki
Published: February 2004

n-type epitaxial films of silicon on sapphire were successfully obtained with a high degree of reproducibility by adding antimony during the evaporation of undoped silicon having the resistivity of 2400 Ω·cm. An attempt to control resistivities of films was made by changing the temperatures of the antimony source. The dependence of the Hall mobilities and the carrier concentrations of the films upon temperatures was measured at temperatures ranging from 77°K to room temperature. The Hall mobility of films grown on (0001) sapphire at a substrate temperature of 900°C was higher than that of films with a similar resistivity grown on(1̄012) sapphire. Effects of the thermal oxidation and the subsequent annealing of these as-grown films upon their electrical properties were investigated. After these treatments a remarkable rise in the Hall mobilities of the films was observed at temperatures ranging from 77°K to room temperature.
Pressure and Temperature Dependences of the Isotropic Elastic Moduli of Polycrystalline Alumina
Authors: Chung D. H. , Simmons Gene
Published: February 2004

The isotropic elastic moduli of polycrystalline alumina have been determined as a function of hydrostatic pressure up to 10 kbar and also as a function of temperature over the range 4.2° to about 1300°K. The pressure dependence of the elastic moduli is linear over this pressure range. The low-temperature limit of the elastic Debye temperature, 1044 (±3) °K, compares very well with thermal Debye temperature. Values of various pressure derivatives evaluated at 298°K are as follows: Pressure derivatives   dL/dp   dG/dp   dB/dp(∂Ms/∂p)T6.57 (6.58)1.79 (1.73)4.19 (4.27)(∂MT/∂p)T6.621.794.23(∂Ms/∂p)s6.521.734.16The quantities in the parentheses are averaged values calculated from the single-crystal second-order elastic constants and their first pressure derivatives. The experimental data are interpreted with respect to (a) the polycrystalline data calculated from the corresponding single-crystal data, (b) the temperature dependence of the isotropic elastic moduli, (c) the acoustic Grüneisen parameters and their comparison with the corresponding quantities evaluated from thermodynamic properties, (d) the equation of state for alumina, and (e) the Debye temperature as a function of temperature and pressure.
Thermodynamics of Nonlinearity and Noise in Diodes
Authors: Gunn J. B.
Published: February 2004

The irreversible thermodynamics of a nonlinear diode are discussed by considering a circuit in which a biased diode exchanges noise power with a linear resistor at a different temperature. By applying the Onsager reciprocity relations to the two cross terms involving the rectification of thermal noise, and the generation of current noise by the diode, respectively, an equation is obtained relating the nonlinearity of the diode and a parameter which specifies its current-noise behavior. The implications of this equation are discussed in relation to the existence of a maximum value of the nonlinearity. The analysis predicts that a reverse current will flow through the diode when the resistor is at a lower temperature, and an experiment to confirm this is reported briefly.
The Diffusion and Solubility of Phosphorus in CdTe and CdSe
Authors: Hall R. B. , Woodbury H. H.
Published: February 2004

Measurements of the solubility and diffusion of P in CdSe from 800°–1000°C and in CdTe at 900° and 950°C as a function of cadmium partial pressure were made using radiotracer techniques. In addition, electrical measurements were made on some P-doped samples of both systems. The phosphorus solubility is highest at a given temperature under maximum cadmium pressure. It is suggested that under these conditions the phosphorus is a substitutional acceptor atom on a chalcogen site that is highly compensated by a donor defect with interstitial Cd donors a likely possibility. The diffusion results are similar to that observed for the chalcogen self-diffusion and are not inconsistent with an interstitial mechanism.
Cathodoluminescence of n-Type GaAs
Authors: Pankove J. I.
Published: February 2004

n-type GaAs specimens with carrier concentration in the range of 4×1016 to 6.8×1018 cm−3 were bombarded with 24-kV electrons at 4.2°K. The emission spectrum indicates that the radiative transition occurs between donors and residual acceptor states. A simple phenomenological model suggests that most of the donor states are located below the Fermi level. Taking the bottom of a parabolic distribution of states in the conduction band as a reference, the maximum density of donor occurs roughly one-third of the way to the Fermi level, this Fermi level being already depressed by the tail of states of the conduction band. The same model indicates that the width of the donor band varies as the one-third power of the donor concentration.
Pressure Effects on the Friction Coefficient of Thin-Film Solid Lubricants
Authors: Bowers R. C. , Zisman W. A.
Published: February 2004

Thin solid films on harder backings are now widely used as dry-film lubricants. An early extension by us of the Bowen-Tabor adhesion theory of friction showed that the coefficient of friction of a coated backing was equal to only a fraction of that of the coating material, and this fraction was simply the ratio of the mean yield pressure of the coating material to that of the backing. However, we pointed out that the effect of pressure on the shear strength of the coating material was neglected. We have since analyzed and applied to this problem the data on the effect of pressure on shear strength of paraffin, gold, and molybdenum disulfide, using the experimental data of Bridgman as well as of Boyd and Robertson. The principal complication in applying these data to the frictional problem is to allow properly for the elastic (or plastic) deformation of the two sliding solids in calculating the pressure exerted on the coating material during sliding. Our calculated coefficients of friction are in good agreement with the recent measurements of Takagi and Liu on gold-coated hard steel and the earlier data by Haltner and Oliver on molybdenum-disulfide-coated steel. Recently we measured coefficients of friction of thin coatings of paraffin on steel and obtained results which were in good agreement with our calculated values. It is concluded that a sound basis now exists for treating the subject of dry film lubricants. Further research on such systems requires more experimental data on the effect of pressure on shear strength in a variety of indicated polymers and inorganic solids.
Magnetic-Field Dependence of Josephson Current Modified by Self-Field
Authors: Yamashita Tsutomu , Kunita Masanori , Onodera Yutaka
Published: February 2004

The magnetic-field dependences of the Josephson critical current were investigated in many high- and low-current Josephson junctions. Our experimental results were different from the theoretically expected Fraunhofer diffraction pattern with respect to its period in magnetic field and the maximum critical current for high-current junctions. It was found that the first period of the magnetic-field dependence increased with the Josephson current and the maximum critical currents were reduced. The differences were interpreted as the influence of the self-field induced by the Josephson current.
Electrical and Optical Properties of Vapor-Grown GaP
Authors: Taylor R. C. , Woods J. F. , Lorenz M. R.
Published: February 2004

GaP, both undoped and Se- or S-doped, has been vapor deposited onto the polar 111A (Ga face) and 111B (P or As face) surfaces of GaAs and GaP substrates by means of a PCl3 chemical-transport method. Hall measurements carried out on the crystals over the temperature range of 77°–500°K and optical spectra taken on as-grown and zinc-diffused samples show a pronounced substrate orientation and substrate material effect. Samples grown on GaAs substrates are less uniform than those grown on GaP, and show both a carrier concentration gradient and arsenic contamination. Samples grown on GaP substrates have given electron mobilities as high as 187 cm2/V·sec at room temperature going to 2130 cm2/V·sec at liquidnitrogen temperature. The residual impurity in undoped crystals grown on 111B substrates is shown to be sulfur at a concentration of 2−3×1016 cm−3. Undoped crystals grown on 111A substrates are high-resistivity p type. Both optical studies and electrical measurements show compensation in the n-type crystals to be of the order of 10%.
The Rice and Walsh Equation of State for Water: Discussion, Limitations, and Extensions
Authors: Papetti R. A. , Fujisaki M.
Published: February 2004

The equations of state of water developed by Rice and Walsh are discussed. Analytic expressions and quadratures are developed for results that were previously obtained by numerical computations. Approximate bounds on the region of validity of the Rice and Walsh relations for water are constructed. Their energy-volume-pressure and enthalpy-volume-pressure relations are extended to 450 kbar, and strips of the energy-volume-pressure and enthalpy-volume-pressure surfaces containing the Hugoniot curve are extrapolated to pressures of approximately 20 Mbar, where the Thomas-Fermi method may be used to obtain thermodynamic relations for water.
Thickness Estimation of Carbon Films by Electron Microscopy of Transverse Sections and Optical Density Measurements
Authors: Moretz R. C. , Johnson H. M. , Parsons D. F.
Published: February 2004

A rapid and convenient method is described for the accurate determination of the thickness of carbon films from their optical density. A linear relationship was found between optical density and film thickness. The optical-density-thickness curve was calibrated by direct measurement of the thickness of transverse sections of carbon films embedded in epoxy resin. The method can probably be extended to thin films of soft metals and other inorganic films having significant optical density and capable of being sectioned with a diamond knife.
Structural and Magnetic Properties of a Bi–MnBi Composite
Authors: van Goor J. M. Noothoven , Zijlstra H.
Published: February 2004

Composites made up of MnBi needles embedded in bismuth single crystals are grown from eutectic melts by both Czochralski and zone-melting techniques. The galvanomagnetic properties of the composite are determined mainly by the bismuth matrix. Magnetic measurements reveal a magnetic phase with an anisotropy field of more than 200 kOe at 77°K and a Curie point of 240°K. This phase is believed to be a modification of MnBi different from the two already known. The solubility of Mn in solid Bi is concluded to be less than 30 wt ppm.
Study of Shapes of Diffracting Planes by X-Ray Laue Technique
Authors: Lal Krishan , Peneva S. K.
Published: February 2004

Various lattice defects have been observed in the whiskers, some of which are fairly complicated compared to a single axial screw dislocation. We have developed a general method of finding out the shapes of the diffracting planes. It is based upon the laws of reflection. The method has been illustrated by analysis of four equatorial Laue spots of a Cd whisker. The corresponding planes were found to be curved.
Shock Compression of Porous Iron in the Region of Incomplete Compaction
Authors: Lysne P. C. , Halpin W. J.
Published: February 2004

Shock loading of 4.44 and 5.32 g/cm3 pressed iron powder has been performed in the pressure region of incomplete compaction to solid density. Quartz gauges mounted in gas gun projectiles provided pressure-particle-velocity measurements at the impacted interface and standard quartz gauge instrumentation was used to record the transmitted waveform. Shock velocities were determined, from which pressure-particle-velocity states at the impact interface were estimated by the use of the Rankine-Hugoniot equations. These states compared favorably with the same states obtained from the projectile quartz gauges. Severe attenuation of the constant-velocity shock front, along with an anomalous behavior of the precursor wave, which did not immediately separate from the main shock, suggest that loading-rate-dependent processes are important for this porous material.
Maser Oscillations with External Gain
Authors: Hellwig H. , Pannaci E.
Published: February 2004

Using external-gain hydrogen-maser oscillations were obtained at cavity Q values and beam intensities far below those required for a conventional hydrogen maser. Frequency-pulling measurements and absolute frequency determinations of the hydrogen maser are reported. It is shown that the long-term frequency stability and accuracy are basically not affected by the use of external gain. The external-gain principle offers new solutions for operation and design of hydrogen masers, however, it is not restricted to the hydrogen maser but can be applied to any other maser.
Effect of 50 MeV Electrons of the Ultimate Fermi Level in Germanium
Authors: Bohlke W. H. , Kalma A. H. , Corelli J. C.
Published: February 2004

p-type Ge doped with Ga and In to resistivities ranging from 0.001 to 30 Ω·cm and n-type Ge doped with Sb and As to resistivities ranging from 0.1 to 30 Ω·cm were irradiated with 50 MeV electrons to various doses up to a maximum total integrated flux of 1.0×1019 electrons/cm2. Electrical measurements were performed to determine the effect of irradiation on the temperature dependence (78° to 320°K) of the conductivity, carrier concentration, and Fermi level. After irradiation to relatively high doses (≳1018 electrons/cm2), both types of Ge reach a saturation in the hole concentration which is accompanied by an ultimate value for the Fermi level at Ev+0.220±0.010 eV for all samples studied. Comparison of this result with studies made using fast neutrons shows that the position of the ultimate Fermi level strongly depends on the damaging or ``disordering'' capabilities of the incident radiation. We find that the ultimate Fermi level is positioned closer to the valence band as a result of irradiation by particles capable of imparting a larger maximum recoil energy to the Ge atom. Finally, a comparison is made with the work of others on the ultimate position of the Fermi level for Ge irradiated by 60Co gamma rays and 4.5 MeV electrons which are not sufficiently energetic to produce disordered regions comparable to what is observed in fast-neutron and 50 MeV electron irradiation of Ge.
Three-Dimensional Orientation Distribution Function of Crystals in Cold-Rolled Copper
Authors: Bunge Hans-Joachim , Haessner Frank
Published: February 2004

The three-dimensional orientation distribution function of crystallites in cold-rolled copper sheets has been calculated from 512 individual selected area electron-diffraction orientation determinations as well as from (111), (200), and (220) pole figures which were determined by x-ray diffraction. In both cases tube-shaped orientation distributions with comparable dispersion were obtained. In case of the electron-diffraction data the orientation density decreases from a value of 15 times the random distribution value at the brass orientation, (101) [1̄2̄1], to a value of only five times the random distribution value at the orientation (112) [4̄6̄5]. A second density maximum appears in the vicinity of the orientation (213) [4̄7̄5]. The width at half-maximum intensity of the spread in the direction perpendicular to the axis of the tube amounts to about 5°. The accuracy and uniqueness of the calculated orientation distribution function are discussed.
Effects of an Electric Field on the Diffusion Flux of Argon-40 from KCl and Microcline Feldspar
Authors: Pronko P. P. , Krouse H. R.
Published: February 2004

It has been determined that an electric field of the order of a few thousand volts per centimeter can increase the diffusion flux of radiogenic argon from the ionic conductors KCl and microcline feldspar. Argon flux vs applied voltage curves are presented. Flux-time relaxation curves, obtained after removing the applied field, are also presented and indicate that the perturbation introduced by the electric field has a rather long-term residual effect (∼1 h).
Domain Structure and the Influence of Growth Defects in Single Crystals of Yttrium Iron Garnet
Authors: Basterfield J.
Published: February 2004

Thin slices of single crystals of yttrium iron garnet were prepared free from mechanical polishing strains by chemical polishing in hot phosphoric acid. The magnetic domain structure was investigated using transmitted polarized light. 180° Bloch walls with a periodic structure of right- and left-hand sections were found to be tilted at the Bloch lines separating the sections. In specimens containing growth defects, for example dislocations or growth striations, the domain structure was markedly changed, in the latter case by the rotation of the magnetization out of the easy direction in the plane of the slice. The significance of the interaction with respect to domain-wall motion experiments using picture frame specimens is discussed.
Formation of Uniaxial Magnetic Anisotropy in Nickel by Plastic Deformation
Authors: Krause R. F. , Cullity B. D.
Published: February 2004

Previous plastic elongation, or compression, of polycrystalline nickel was found to produce a uniaxial anisotropy. The easy axis of magnetization was parallel to the axis of previous elongation and at right angles to the axis of previous compression. The maximum value of the uniaxial anisotropy energy constant Ku was about 2700 erg/cm3 after 2.5% elongation. The observed anisotropy is shown to be due to a particular distribution of residual microstress, in which most of the volume of the specimen is in residual compression, balanced by a small volume in tension, after plastic elongation. These stresses, although balanced, introduce magnetoelastic effects which do not cancel in a nonsaturated specimen, and which thereby cause the observed anisotropy. Evidence for the assumed stress distribution was obtained by x-ray diffraction.
Thermoelastic Stress Production in Solids
Authors: Bushnell J. C. , McCloskey D. J.
Published: February 2004

Theoretical calculations of the consequences of the thermoelastic mechanism for production of stress in solids by pulsed energy input have been performed, and the effect of variations in the acoustic impedance of a transparent backup material and variations in the pulse duration as compared to the acoustic transit time across the penetration depth of the incident energy have been investigated. Experimental verification of the theoretical calculations has been done using a Q-switched ruby laser as an energy source with samples of absorbing glass as targets. It is found that the experimental results give good agreement in the shapes of the stress pulses produced, and fair agreement in the absolute amplitude of the stress, with no adjustable parameters being required. The calculations and experiments demonstrate the validity of the thermoelastic stress-production mechanism in solids when no phase transformation occurs.
Superconductivity in β-Tungsten Films
Authors: Basavaiah S. , Pollack S. R.
Published: February 2004

Evaporated tungsten films were found to have a superconducting transition temperature Tc of 3.2°K as compared to the bulk value of 0.01°K. Structural study of the electron-beam-evaporated W films was carried out by both x-ray and electron diffraction techniques. It was found that films prepared at pressures >10−7 Torr and evaporation rates <30 Å/min are a mixture of both the α and β phases, the β phase being the A15 structure, and the α phase being the bcc structure. It was established that the enhancement in Tc of these films is due to the presence of the β phase. Films prepared at 3×10−9 Torr are pure α-W and they did not superconduct down to 1°K. The superconducting energy gap Δ(T) of the β-W films prepared at 5×10−5 Torr and 25 Å/min was determined by tunneling in W-B-M junctions, where B is the plasma-grown oxide barrier on W and M stands for Sn, Pb, and Au counterelectrodes. The temperature dependence of the energy gap Δ(T)/Δ(0) vs T/Tc followed the BCS curve remarkably well. The ratio 2Δ(0)/KTc varied between 2.32 to 3.64 as against the BCS value of 3.53, corresponding to the variation in Tc between 3.1° to 3.3°K, respectively. The relative amounts of the α and β phases present were estimated from the tunneling experiments. The variations in Tc, 2Δ(0), and 2Δ(0)/KTc are related to the relative amounts of α and β phases present in the composite film and their connectivity.
Motions of a Magnetic Particle in a Viscous Medium
Authors: Newman J. J. , Yarbrough R. B.
Published: February 2004

A solution has been obtained to the problem of the motion of a fine magnetic particle in a viscous medium when subjected to an orienting magnetic field. Orientation and scaling curves are obtained which allow the description of the motion to be obtained for any particle with a given acicularity in a medium of any given viscosity.
Growth Characteristics of AlN Films Pyrolytically Deposited on Si
Authors: Noreika A. J. , Ing D. W.
Published: February 2004

AlN films prepared by the ammonolysis of AlCl3·xNH3 have been studied by transmission electron microscopy. The films are found to be mosaiclike arrays composed of numerous small crystallites. Average linear dimensions of the crystallites are dependent on deposition temperature and follow an inverse relationship, e.g., 1600 Å at 900°C and 150 Å at 1350°C. The number of crystallites per unit area is likened to a saturation density of stable nuclei which have formed according to an ``initially incomplete condensation of nuclei'' model. The refractory nature of AlN prevents extensive recrystallization and preserves a numerical relationship between the saturation number of nuclei and the number of crystallites. An epitaxial component of the AlN films on single-crystal Si substrates is evident over a restricted temperature range, viz., 1100°–1300°C. The orientation relationship is (0001)AlN ∥ (111)Si and [112̄0]AlN ∥ [22̄0]Si.
Fatigue Mechanism in fcc Metals at Ultrasonic Frequencies
Authors: Mason W. P. , Wood W. A.
Published: February 2004

A comparison is made of microstructural changes leading to fatigue of copper and alpha-brass at small strain amplitudes imposed at the normal test frequency of 1700 cpm and at the ultrasonic frequency of 17 000 Hz. A striking difference appears in the distribution of slip. At normal frequency the slip spreads densely over a grain, with no slip-band cracking (stage S of the S-N curve). At ultrasonic frequency the slip concentrates in single isolated bands in only occasional grains and reduces these to microcracks before any general spread of slip can be observed. However, as might be expected, the ultrasonic slip did spread in specimens tested at elevated temperatures, which expedited dislocation climb and diffusion processes; then this spreading of slip prevented the slip-band microcracking at ultrasonic frequency also. The internal friction for the copper was so high that fatigue cracks could not be generated even at room temperature.
Estimate of the Temperature Rise of Micron-Sized Silver Particles in the Electron Microscope due to Electron-Beam Heating
Authors: Gessinger G. H. , Lenel F. V. , Ansell G. S.
Published: February 2004

The temperature rise of micron-sized silver particles on a carbon film due to electron-beam heating was determined semiquantitatively. A heat-balance equation was set up by equating the absorbed kinetic energy of the electron beam to the amount of heat given off by radiation and heat conduction. It was shown that heat loss by radiation does not significantly contribute to the temperature rise at temperatures below the melting point of the particle. The temperature rise is strongly influenced by the distance of the particle from heat sinks, i.e., other metallic particles or the specimen grid. The magnitude of the temperature rise can be kept below 50°C for electron-beam current densities below 10−2 A·cm−2.
Dispersion of the Piezobirefringence of GaAs
Authors: Feldman Albert , Horowitz Deane
Published: February 2004

The piezobirefringence of GaAs shows a large anomalous dispersion near the absorption edge and exhibits a nonlinear stress dependence. The coefficient π11–π12 reverses sign. Lowering the temperature from 298° to 77°K shifts the dispersion curves +0.088 eV, which is approximately equal to the shift of the energy gap with temperature. These effects, which have not been observed previously in GaAs, are related to the stress dependence of transitions associated with the absorption edge and resonance photoelasticity described by Kaplyanskii and Lozovskaya.
The Poole-Frenkel Effect with Compensation Present
Authors: Yeargan J. R. , Taylor H. L.
Published: February 2004

This extended Poole-Frenkel model includes the effects of compensation. The relative densities of donor and acceptor sites control the slope of the log J vs E1/2 plots. With only one type of site present, the slope equals that expected for Schottky emission [slope= (e3/πεε0)1/2/2kT]. When sites of the opposite type compensate, the slope doubles. The degree of compensation must be known to determine the barrier heights separating the emission site from the band edge. Data from metal-silicon nitride-metal devices are consistent with this model with emission occurring from impurity sites approximately 2.0 eV from the conduction band edge.
Charge Phenomena in dc Reactively Sputtered SiO2 Films
Authors: Wu S. Y. , Formigoni N. P.
Published: February 2004

The charge behavior of dc reactively sputtered SiO2 films has been studied. We observed insulator charge of both polarities in the SiO2–Si structure, depending on the sputtering conditions. When the SiO2 layer is deposited under high-cathode-voltage low-gas-pressure conditions, the insulator charge is positive; when the SiO2 layer is deposited under low-cathode-voltage high-gas-pressure conditions, the insulator charge is negative. This, we propose, is attributed to the adsorption of oxygen ions, which are generated in oxygen glow discharges, on the silicon surface, and the deposited SiO2 layer during the oxide deposition. Published work on ion yield under varying plasma conditions can be cited to support this model. These ions appear to exist throughout the bulk of the oxide, but are predominantly found at or near the SiO2–Si interface. After annealing at 800°C in dry oxygen, only ions at or near the interface are observed. Results of bias and temperature stresses on the films deposited under different conditions are also described.
Measurement of the Domain-Wall Energy of the Orthoferrites
Authors: Kurtzig A. J. , Shockley W.
Published: February 2004

A new technique for the direct measurement of the magnetic domain-wall energy per unit area has been developed and applied in the orthoferrites. A previously reported technique to determine the domain-wall energy per unit area from the radii of cylindrical domains has been reinterpreted. The simplest possible domain-wall configuration (a set of planar, parallel, equally spaced domain walls) has been predicted and observed to be stable in properly prepared samples. In the new technique to measure the domain-wall energy per unit area, these planar walls are controllably stretched into sinusoidal corrugations by an applied magnetic field to increase the total wall area and total wall energy within a sample. The increase of wall area has been observed by the Bitter and Faraday techniques. Calculation of the work exerted by the applied and demagnetizing magnetic fields in forcing the controlled increase of wall area yields the new measure of the domain wall energy per unit area; the domain wall energy per unit area of ErFeO3 at 25°C has been measured to be 1.95 erg/cm2±5%. The precision is limited by sample inhomogeneity and experimental uncertainty, not by inherent uncertainty in the technique.
New Deep-Level Luminescence in GaAs:Sn
Authors: Kressel H. , Nelson H. , Hawrylo F. Z.
Published: February 2004

A study has been made of the photoluminescence spectra of Sn-doped GaAs grown by liquid-phase epitaxy, in which, because of growth under As deficient conditions, compensation is expected to occur by the possible occupation by Sn atom of As sites. Hall data suggest that some compensation does take place by the formation of Sn acceptor levels. A broad emission band was found at about 1.26 eV (77°K) whose peak position follows closely the temperature-dependent variation of the bandgap energy. This band was not seen in materials grown from the melt. It is suggested that the band is due to an acceptor 0.2±0.02 eV above the valence band edge. Evidence is inconclusive for the existence of a shallow acceptor due to Sn similar to that introduced by Si and Ge in GaAs. Thus, the deep level may be due to Sn on isolated As sites, rather than to a complex involving Sn atoms. The radiative band due to this deep acceptor exhibits unusual structure below 77°K, which is explained as an electronic transition to a tightly bound hole trapped on the deep acceptor accompanied by phonon emission. This hypothesis is consistent with other experimental observations concerning the properties of the emission band at higher temperatures. It is shown that Pb in GaAs also introduces a deep level (presumably at Ev+0.12 eV), and the resulting emission band similarly exhibits what is believed to be phonon structure.
The Radiation Compaction of Vitreous Silica
Authors: Primak William , Kampwirth Robert
Published: February 2004

The dilatations (negative) caused by neutrons, 40–600 keV electrons, 140 keV H+, D+, He+, and gamma rays are given as a function of dose and are compared. The presaturation dependence is linear for neutrons, He+, and D+, and depends on the 0.5–0.7 power of dose for H+, electrons, and gamma rays. The dilatations are not temperature dependent from about 0°–100°C, hence are not thermally activated. The dilatations are explained as compaction of the silica structure resulting from oxygens moving into some of the ``free volume,'' the structural change being similar to that occurring on pressure, shock, or thermal compaction of vitreous silica. The mechanism given for the neutron-induced compaction involves the state of high vibrational excitation developed in the slowing down of scattered atoms. The compaction by gamma rays, electrons, protons, or deuterons is explained as caused by transient ionization relaxing Si–O binding to permit oxygens to move into the ``free volume'' where they may be locked-in on recombination by similar incidents occurring nearby. The reduced power dependence is explained as a ``hardening'' effect; succeeding events are more difficult to perform or are performed with lower probability. The compaction caused by He+ (140 keV) seems to possess an equal contribution from ionization compaction and that caused by energy transfer to atomic vibrations.
Some Magnetic Properties of Magnetite (Fe3O4) Microcrystals
Authors: McNab T. K. , Fox R. A. , Boyle A. J. F.
Published: February 2004

Single-domain particles of Fe3O4 have been observed to exhibit superparamagnetic behavior with the Mössbauer effect. Using a simple theory for the spin relaxation, it was possible to make an approximate curve fit of the spectra, taking into account the particle-size distribution of the samples. For a sample prepared by a grinding method, the values obtained by the fitting procedure were Ku=(6.0±1.0)×104 erg/cm3 for the energy barrier and τ0=(9.5±1.5) × 10−10 sec for the frequency factor. The value of Ku was interpreted as being due to shape anisotropy; analysis of the hyperfine spectra of both bulk and fine-particle Fe3O4 at T=4.2°K supported this view. The flipping frequencies of the particle moments were altered by the application of a magnetic field, so that the average internal field in a relaxed spectrum could be determined. Other samples of Fe3O4, prepared by a precipitation method, gave the values Ku=6.0×104 and 8.0×104 erg/cm3. The latter value could be partially accounted for by the existence of a small oxygen excess in those particles prepared at temperatures close to 100°C.
Bounds on Field Fluctuations in a Random Medium
Authors: Beran M.
Published: February 2004

We derive here upper and lower bounds on the magnitude of fluctuations for the electric and displacement fields in a random medium. We also point out the type of fluctuation inequalities that may be derived by the procedure used here for stress and strain fields in a random medium.
Orientation Dependence of Pitting and Blistering in Proton-Irradiated Aluminum Crystals
Authors: Milacek Leonard H. , Daniels Raymond D.
Published: February 2004

Pitting and blistering occurred on the surfaces of aluminum crystals bombarded with protons in the 10–100 keV energy range. The extent of pitting and/or blistering was found to be orientation dependent. Surfaces with orientations near {111} were least affected. This was followed by the {100} orientation. {110} and higher indices orientations suffered greatest damage. Blistering is caused by the protons trapped as hydrogen gas, and the orientation dependence of the process is explained by the orientation dependence of penetration of ions in the aluminum lattice.
Magnetothermal Convection in Insulating Paramagnetic Fluids
Authors: Carruthers J. R. , Wolfe R.
Published: February 2004

When an insulating paramagnetic fluid such as gaseous oxygen is subjected to combined thermal and magnetic field gradients, a magnetic body force is shown to exist which is analogous to that of gravity. It is shown both theoretically and experimentally that this magnetic body force can be larger in magnitude than that due to gravity for gaseous oxygen for even modest values of the magnetic field strength-gradient product. The possibility of magnetic control of thermal convection is discussed for several instances. The application of this effect to control thermal convection during crystal growth from paramagnetic liquids is discussed in detail.
Far-Infrared Laser Interferometry for Electron Density Measurements
Authors: Turner R. , Poehler T. O.
Published: February 2004

A far-infrared laser interferometer suitable for use with thin, transient plasmas of densities from 1014 to greater than 1017 cm−3 has been developed. A HCN gas laser operating at 337 and 128 μm and a H2O gas laser operating at 119, 79, and 48 μm are used as sources for a Mach—Zehnder interferometer; fast InSb and Ge:Ga detectors are used to measure the phase shift produced by the plasma. The interferometer has been used to study the output of a plasma gun which produces a plasma 4 cm in diameter and average density greater than 1015 cm−3, a plasma not suitable for microwave or optical interferometry.
Ultrasonic Probing of Plastic Waves
Authors: Wright T. W.
Published: February 2004

With the aid of a theory due to Cauchy this paper examines mathematically the consequences of assuming that small incremental waves propagate independently of plastic or other finite waves in metals. It is found that for sharp transitions or short risetimes in the finite wave there exists the possibility of reflecting a small oscillation off the sharp front. By examining the echo return, one could deduce information concerning the speed and structure of the finite wave.
Interaction of Intense rf Fields with Heated Air
Authors: Mayhan J. T. , DeVore R. V.
Published: February 2004

A model is formulated which predicts the characteristics of a short duration, intense microwave pulse propagating in initially heated, high-temperature air. The temporal and spatial evolution of the electron temperature and density throughout the plasma are specified upon incorporating certain kinetic processes involving N2, NO, and O for 4000°–5000°K air. In conjunction with measurements, field-induced ionization rates of initially heated 4500°K air are presented and found to be substantially greater than room temperature-to-4000°K ionization rates. The post breakdown recombination rate has also been found. The usual constant collision frequency assumption used in predicting rf breakdown levels is shown to be a good approximation.
A Theoretical Model for Gas Separation in a Glow Discharge: Cataphoresis
Authors: Shair Fredrick H. , Remer Donald S.
Published: February 2004

A theoretical model for transient and steady-state cataphoresis is developed starting with the macroscopic equations of continuity. After a brief breakdown period, the impurity ions are assumed to be closely coupled with their neutral counterparts. The basic assumptions in the model are that after breakdown, the level of ionization of the impurity, and the axial electric field remain constant; it is demonstràted that under these conditions a system involving rapid ionization-recombination reactions is equivalent to a system in which no reaction occurs, but in which the ``effective'' ion mobility is a product of the true ion mobility and the fraction of impurity ionization. The influence of endbulbs commonly employed in experiments is analyzed and found to influence greatly the characteristic time required to reach steady state. Agreement is found between the model and available experimental data. Particular emphasis is placed upon mass spectrometer data reported by Matveeva, and by Beckey, Groth, and Welge; these data are for mixtures of rare gases and for mixtures of hydrogen and deuterium, and involve endbulbs. The ordinary diffusion case, associated with the collapse of the steady-state cataphoretic profile, is also analyzed for a system containing endbulbs.
Elastic Constants of Molybdenum-Rich Rhenium Alloys in the Temperature Range −190°C to +100°C
Authors: Davidson D. L. , Brotzen F. R.
Published: February 2004

The adiabatic elastic constants of molybdenum and molybdenum alloyed in solid solution with 7.0, 16.6, and 26.9 at.% rhenium were measured in the temperature range −190°C to +100°C. Rhenium additions decrease (c11−c12)/2 and the twinning shear (c11−c12+c44)/3, and increase the bulk modulus and c44. The 26.9 at.% alloy is elastically isotropic. Alloy additions strengthen nearest-neighbor interactions and weaken second-nearest-neighbor interactions. Debye temperatures calculated from the measured elastic constants agree well with those determined by calorimetry. Thermal expansion of the alloys was found to be essentially the same as for molybdenum in this temperature range.
Beam-Induced Contrast in the Electron-Microscope Images of Polymers as Observed in Ultrathin Sections
Authors: Dlugosz J. , Keller A.
Published: February 2004

Sections of spherulitic polyethylene used as control specimens in the development of cryo-ultramicrotomy were found to display a concentric ring structure under the electron microscope corresponding to the familiar extinction bands revealed by polarizing microscopy. This observation is unexpected as the source of contrast must be quite different in the two cases. The present note deals with the nature and possible origin of this contrast. It was observed that the bands develop during beam irradiation after all Bragg diffraction ceased and that the surface of the section becomes correspondingly undulating at the same time. Transmission and stereoscan micrographs are included which demonstrate these effects. The contrast of beam-induced band structure depends on the relation of the cut to the spherulite center. High dose rates induce additional larger scale movements of the material in the section. Selective etching and material rearrangement are thought to be responsible for the electron-beam-induced changes in the polymeric specimens. The significance of these findings for the understanding of the spherulitic texture and for the interpretation of transmission and scanning micrographs of polymers in general is pointed out.