bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation of the Elastic Properties in Steady-State Flow and Vibrational Experiments
Authors: Philippoff W.
Published: April 2005

A comparison between steady-state and vibrational techniques for measuring the elastic properties of polymer solutions has shown an unexpected anomaly at high frequencies. The steady-state technique used was flow birefringence which relates elasticity (recoverable shear, s) to the extinction angle χ: s=2 cot 2χ. The vibrational technique used, both the ultrasonic crystal and the Birnboim instruments, relates elasticity to the loss angle, δ′: cot δm′=η2/(η1−η solv). The solutions investigated included a monodisperse polystyrene, S111, at concentrations of 2% and 4% in a chlorinated biphenyl (Aroclor 1248), a polydisperse polystyrene, PF-139 and polyisobutylenes in oil. The same solutions were used in both kinds of instruments.

In the lower range of frequencies (taken as equivalent to low shear rates) the steady-state and dynamic instruments showed excellent agreement for the monodisperse polystyrene. In this range the curve agreed with the Zimm theory. But at higher frequencies the results from the two techniques diverged rapidly. The steady-state measurements showed s to increase continually, whereas the dynamic measurements showed cot δm′ to pass through a flat maximum and then decrease slowly out to 2×106 sec−1. This lack of agreement was unexpected and is unexplained. It does show that steady-state elasticity cannot always be predicted from high-frequency dynamic experiments. The steady-state viscosity could be satisfactorily predicted from η1 using Pao's theory, but only for the monodisperse polymers.
Direct Observation of Dislocations in Silicon Web Crystals
Authors: Jungbluth E. D.
Published: April 2005

Dislocations in web silicon have been observed by x-ray diffraction microscopy. Numerous sources of dislocations originate in the dendrite and form low-angle grain boundaries within the web. Dislocations propagating along the growth direction have [01̄1] and [101] or [110] Burgers vectors, and dislocations aligned along the [11̄0] and [101̄] directions are product dislocations of a Lomer-Cottrell reaction. Interactions between the two sets of dislocations are often observed.
Optimization of the Cross-Sectional Geometry of Nernst—Ettingshausen Devices
Authors: Guthrie G. L.
Published: April 2005

The cross-sectional geometry of Nernst—Ettingshausen generators and refrigerators is optimized for essentially rectangular geometry and also for Norwood's spiral screw thread configuration. The magnetic field, heat flow, and electrical current flow are assumed to be mutually perpendicular. The derivation is carried out without any restrictive assumptions concerning electric current distribution. There are no restrictive assumptions about the temperature dependence of κ, σ, or the Nernst coefficient. The expressions for the boundary of the device are given in parametric form with temperature as the parameter. Formulas are given for use in estimating the effect of incomplete optimization.
Pyroelectric Effect in Crystals of Salicylideneanilines
Authors: Lang Sidney B. , Cohen M. D. , Steckel F.
Published: April 2005

Measurements were made of the pyroelectric coefficient in three salicylideneanilines (``anils''). The nonpolar salicylidene-3-toluidine was found to be nonpyroelectric as expected. Pyroelectric coefficients of 3 to 6×10−10 and 2 to 3×10−10 C·cm−2·°C−1 were found for salicylidene-4-bromoaniline and 5-chlorosalicy-lideneaniline, respectively, over the temperature range of 25° to 60°C. Anomalous pyroelectric behavior, possibly due to a structure change, was found in the 5-chloro-anil between 50° and 95°C.
Absorption of Resonance Radiation and Formation of Molecular Ions in Cesium Vapor
Authors: Pollock D. H. , Jensen A. O.
Published: April 2005

The results of resonance absorption measurements in cesium vapor are reported. It is shown that the half-height width of the absorption (γ) is directly proportional to the neutral cesium density. Over the reduced pressure range of 0.2 to 10 Torr, γk=10−22 cm3, where k is the photon-atom absorption cross section. Ionization measurements are reported describing the effect of the absorption of resonance radiation in cesium vapor. On the basis of the results presented, an ionization mechanism has been hypothesized for the production of the cesium molecular ion (Cs2+) as the dominant ionic species in high-pressure, low-energy cesium vapor thermionic plasmas. The mechanism is based on the collision of two cesium atoms excited to the resonance level (1.45 or 1.38 eV). The excitation mechanism shifts from nearly complete photon-induced excitation at a cathode temperature of 2000°K to equal contributions of photon induced and electron induced excitation at a cathode temperature of 1550°K. At lower cathode temperatures, the excitation is accomplished primarily by electron impact processes. Single impact electron ionization processes are shown to be inadequate for neutralization in the plasma of low-energy discharges such as those found in cesium vapor thermionic converters. It is shown that for a condition of space charge neutralization in the plasma of low-energy cesium vapor discharges the ratio of excited state population density to ion population should be between 2.5 and 5 to 1.
Dislocation Mobility in Crystals
Authors: Gilman J. J.
Published: April 2005

Reaction-rate theory is applied to dislocation motion and it is shown that when the activated complex is allowed two degrees of freedom, the activation energy is inversely proportional to the applied stress, so the dislocation velocity, vd is related to the applied shear stress, τ by a relation of the form: v=v0e−D/τ, where v0 is the terminal velocity and D is called the characteristic drag stress. This relation is obeyed by LiF, Ge, NaCl, W, and possibly Fe−3% Si.

The observed dependences of dislocation velocities on point defect concentrations and temperature are also predicted.

Two classes of crystals are considered. Those in which drag is caused mainly by point defects; and those in which the intrinsic structure (chemical bonds) causes the drag.
Surface States and Barrier Height of Metal-Semiconductor Systems
Authors: Cowley A. M. , Sze S. M.
Published: April 2005

The dependence of the barrier height of metal-semiconductor systems upon the metal work function is derived based on the following assumptions: (1) the contact between the metal and the semiconductor has an interfacial layer of the order of atomic dimensions; it is further assumed that this layer is transparent to electrons with energy greater than the potential barrier but can withstand potential across it. (2) The surface state density (per unit area per electron volt) at the interface is a property only of the semiconductor surface and is independent of the metal. The barrier height φBn is defined here as the energy needed by an electron at the Fermi level in the metal to enter the conduction band of the semiconductor.

With the above assumptions, the barrier height for n-type semiconductor-metal contacts is found to be a linear combination of the metal work function φm and a quantity φ0 which is defined as the energy below which the surface states must be filled for charge neutrality at the semiconductor surface. The energy φ0 is measured from the edge of the valence band. For constant surface state density the theoretical expression obtained is φBn=γ(φm−χ)+(1−γ)(Eg−φ0)−Δφn,where χ and Eg are electron affinity and the band gap of the semiconductor, respectively, Δφn is the image force barrier lowering, and γ is a weighting factor which depends mainly on the surface state density and the thickness of the interfacial layer.

The theoretical expression is compared to the presently available φBn VS φm data for Si, GaP, GaAs, and CdS, by fitting the data to straight lines using the method of least squares. The best straight-line fit was obtained for the GaP data, with probable error limits on the slope and intercept of ±0.03 and ±0.13 eV, respectively.

The parameter γ in the theoretical expression is found to range from 0.07 for GaAs to almost unity for the CdS data reported by Goodman indicating weak and strong dependence of the surface barrier height on the metal work function, respectively.

The value of φ0 is roughly a third of the respective band gap energies for Si, GaP, and GaAs, and the surface state density for these semiconductors is found to be in the range 1013−1014 states/cm2/eV, for the experiments cited.

Excessive scatter in the data points for the CdS data of Mead and Spitzer casts doubt on the significance of a straight-line fit for this case. The data of Goodman for CdS obey the Schottky theory for a metal-semiconductor barrier, but this agreement requires a value of the electron affinity χ which is different from the vacuum-photothreshold value measured by other authors.
Photosensitive Field Emission from p-Type Germanium
Authors: Arthur John R.
Published: April 2005

The field-emission current-voltage behavior was examined for germanium crystals ranging from 0.001-Ωcm n to 0.0006-Ωcm p type, whose surfaces were prepared by high-field evaporation. In contrast to the emission from n-type crystals from which linear Fowler-Nordheim data were always obtained, the emission from p-type crystals produced nonlinear F-N curves which were strongly influenced by temperature and illumination. This behavior was caused by the presence of a narrow, high-resistance region near the emitting surface of the p-type crystals. It is proposed that this depletion region was produced by surface inversion due to field penetration. Supporting evidence for this hypothesis was obtained from the spectral response and quantum efficiency of photoenhanced field emission and from measurements of the resistance and spatial profile of the depletion region. There was also evidence for carrier multiplication at high fields, leading to avalanche breakdown of the depletion region.
Superconducting Coil Degradation
Authors: Taquet B.
Published: April 2005

This paper describes experiments carried out to try to explain the degradation phenomenon of superconducting coils.

It is established that flux jumps occurring in a low-field zone cause a sudden decrease in the series current, which in turn causes a disturbance of field throughout the coil and thus probably results in a quench in a high-field zone.

Degradation of short samples is obtained by following a peculiar cycle of magnetization similar to that observed in a coil. An explanation is given to explain the difference of degradation observed between a short sample and a coil.

A measurement of the apparent resistance of a superconducting wire under changing field conditions gives an equivalent resistivity of 10−14 Ω·cm for dB/dt = 200 G/sec.
Effect of Processing History on the Superconducting Properties and Long-Range Order of Ta3Sn
Authors: Courtney T. H. , Pearsall G. W. , Wulff J.
Published: April 2005

Variations of the transition temperature and long-range order parameter of Ta3Sn compacts were studied as functions of sintering time and temperature. Reacting the compacts for 4 days at 900°C produced a maximum in the order parameter (0.68) and the maximum transition temperature observed (8.35°K).

Transition temperatures could be lowered to less than 4.2°K by vacuum heat treating presintered compacts at elevated temperatures.

Ta3Sn was the only intermediate phase observed to form in the Ta-Sn system between 700° and 1450°C.
Energy Spectrum of the Electron Beam in a Racetrack Microtron
Authors: Sells V. , Froelich H. , Brannen Eric
Published: April 2005

The energy spectrum of the beam of a four-sector racetrack microtron has been measured here, using a high-resolution double focusing beta-ray spectrometer. For an energy gain per orbit of 750 keV, it was found that 50% of the integrated current in the eighth orbit (6 MeV) was contained in an energy interval of 34 keV and 90% of the beam current in a 73-keV interval. This narrow energy spread (±0.3%) is of particular interest in the generation of submillimeter radiation and in the use of the microtron as an injector for high-energy synchrotrons.
Growth of Rutile of Controlled Composition from Borate Fluxes
Authors: Berkes John S. , White William B. , Roy Rustum
Published: April 2005

Rutile crystals of controlled composition have been grown from Na2O·3B2O3 and K2O·3B2O3 fluxes. The compositions were controlled by the use of various atmospheres of known oxygen activity as the equilibrium vapor phase. The crystals are prisms 2 to 10 mm in length and 0.1 to 0.3 mm in thickness. The morphology of the crystals and their response to changes in temperature, oxygen activity, and flux composition are described. The average dislocation density is 4×104 cm−2, but dislocation-free areas can be found.
Hydromagnetic Wave in a Toroidal Discharge with Longitudinal Magnetic Field
Authors: Itoh Satoshi , Fujisawa Noboru , Miyajima Shigeki , Yamamoto Kenzo
Published: April 2005

A regular hydromagnetic oscillation in a simple toroidal discharge has been found for the first time. The externally applied longitudinal magnetic field and high degree of ionization are essential to generation of the oscillation. The observation by magnetic probes and streak camera shows that a plasma column of the m=1 helix rotates in the direction of right-handed screw to the applied magnetic field. The wavelength of helix and rotational frequency depend on the pressure, ion mass, and applied magnetic field. The phase velocity of the plasma helix coincides with the Alfvén velocity.
Static Response Characteristics for a Carbon Bolometer
Authors: Shephard Glenn G.
Published: April 2005

The electrical resistivity of carbon resistor material has been experimentally determined as a function of temperature and has been used to calculate the static response characteristics of a particular carbon bolometer element without making use of the usual isothermality and constant thermal conductivity assumptions.
Effect of Plastic Deformation on the Thermal Conductivity of Calcium Fluoride and Lithium Fluoride
Authors: Moss Marvin
Published: April 2005

Measurements of the thermal conductivity of plastically deformed CaF2 and LiF between 1.3° and 80°K indicate the presence of a phonon scattering mechanism which does not display the frequency dependence normally associated with dislocations. Instead of a reciprocal relaxation time τ−1∝ω, which is characteristic of scattering due to individual dislocations, it is found that a stronger frequency dependence is indicated. Furthermore, a large anisotropy in the conductivity of CaF2 is evident from the results obtained when the temperature gradient is parallel to the strongly oriented edge dislocations, as contrasted to when the gradient is perpendicular to them. It is suggested that dislocation dipoles, composed of pairs of edge dislocations of opposite sign and of dipole spacing comparable to the dominant phonon wavelength, are the cause of the observed effects. There is strong evidence for cross-glide in these materials, and an examination of the etched surface of deformed CaF2 reveals many etch pits which are sufficiently close together to indicate that, as a mode of dislocation multiplication, cross-glide produces dipoles which could be responsible for the observed departure from normal dislocation scattering.
Crystal Imperfections in Magnesium Fluoride
Authors: Barber D. J.
Published: April 2005

Single crystals of magnesium fluoride, grown by the Czochralski technique, have been examined by means of chemical etching, and optical and electron microscopy. Dislocations in as-grown crystals are found to be decorated with precipitates; the nature of the precipitates has been investigated. Grown-in dislocations and undecorated dislocations introduced by slip can be etched in hot sulfuric acid. Etch pits at grown-in dislocations often exhibit characteristic ``beaks'' or ``tails.'' Chemical etching has been used to establish the existence of three slip systems, namely {110}〈001〉, {001}〈100〉, and {101̄}〈101〉.

Specimens for examination by transmission electron microscopy were prepared by chemical dissolution after mechanical shaping. Grown-in dislocations are normally removed by unavoidable selective etching. In the microscope the samples are damaged by the electron beam. Point defects are produced which aggregate and result in both dislocation loops and precipitate platelets.
Influence of Hall Effect on Faraday Rotation
Authors: Engineer M. H. , Nag B. R.
Published: April 2005

The method of analysis developed by the authors for the study of Faraday rotation in terms of the conduction-current Hall field has been extended to include the effect of the Hall field due to dielectric current. The expression for the angle of rotation derived in this paper is different from that given by Barlow. The contribution of the dielectric-current Hall field to rotation is found to be smaller than that obtained from Barlow's expressions.
Experimental Observation of Faraday Rotation in Artificial Dielectrics
Authors: Nag B. R. , Engineer M. H.
Published: April 2005

An experimental investigation of the Faraday rotation at 3 cm in artificial dielectrics composed of paraffin wax and powdered indium antimonide is described. It is found that a rotation which can be ascribed to the dielectric properties of the medium does indeed occur. The experimental results are found to be in reasonable agreement with theoretical predictions made earlier.
Dynamics of Semiconductor ``Web'' Growth
Authors: Dermatis S. N.
Published: April 2005

The dynamics of ``web'' growth have been investigated, with particular emphasis on the meniscus. The meniscus deflections have been expressed as a function of surface tension, and pulling force. An effort is being made to describe the parameters which influence surface tension, and its reflection on the process of web growth, and the properties of the material. The degree of supercooling, crucible design, and the control of thermal gradients have profound effects on the quality of the crystal and its physical dimensions.
Effects of High Electric Fields on Dielectric Liquids of High and Low Viscosity
Authors: Schott Hans , Kaghan W. S.
Published: April 2005

When a portion of a liquid dielectric was subjected to an electric dc field of high intensity, the level rose locally. The maximum rise attained by different liquids above the liquid level outside the field increased with their dielectric constant and polarizability.

The following observations indicate that electrostriction rather than electrophoresis was the cause of the observed rise in liquid level. (a) Molten polymers, which have such high viscosities that electrophoretic motion of ions or charged particles is virtually suppressed, rose to the same heights as fluid liquids. (b) Neither inverting the direction of the field nor (c) adding 0.05% finely dispersed aluminum or 0.15% ultramarine powder to molten polyethylene affected the rise in the dc field qualitatively or quantitatively.

Repulsion occurred in very high fields, producing a slight depression in the liquid level.
Properties of Gallium Arsenide Diodes between 4.2° and 300°K
Authors: Dumin D. J. , Pearson G. L.
Published: April 2005

The current-voltage characteristics of zinc-diffused gallium arsenide diodes have been measured between 4.2° and 300°K, with carrier concentrations in the n-type region varying from 6×1015 to 9×1018 cm−3. In the forward direction it is shown that the current is due to tunneling at low temperatures and high carrier concentrations whereas it arises from thermal processes involving recombination in the space-charge region at higher temperatures and low carrier concentrations. The temperature at which the current changes from predominantly tunneling to predominantly thermal in origin has been determined as a function of the n-type carrier concentration. In the reverse direction the current in these diodes appears to be dominated by tunneling at all temperatures and doping densities tested.
Determination of Relative Intensity in X-Ray Reflection Study
Authors: Feng C.
Published: April 2005

An analysis is made of the loss of x-ray intensity for the reflection technique with respect to geometric arrangement of the specimen. Good agreement has been obtained between the analysis and experimental data from various materials of different lattice structures. The relative loss of intensity was found decreasing with higher index planes, i.e., shorter d spacings. This is considered advantageous in comparison with the transmission techniques of which the loss of intensity is greater for higher index planes.
Electrical Properties and Resonance Scattering in Heavily Doped n-Type GaSb and Related Semiconductors
Authors: Long Donald , Hager Robert J.
Published: April 2005

Data are presented of the resistivity ρ and Hall coefficient RH vs temperature T from 4.2°K to room temperature for seven n-type moderately heavily Te-doped samples of GaSb. The ρ-vs-T curve shapes are similar at low temperatures to those previously measured on n-GaAs and n-InAs, and they are presumably caused by the same near-resonance scattering mechanism as proposed earlier to explain the n-GaAs and n-InAs results. An unusual rise in the low-temperature mobility with increasing carrier concentration in the n-GaSb samples can also apparently be understood on the basis of the near-resonance scattering model.
Numerical Computations of Elastic Scattering Cross Sections
Authors: Johnson Gregert , Truell Rohn
Published: April 2005

A brief review is given of the calculation of cross section expressions for the scattering of an elastic wave in an elastic medium. With scatterers that are elastic and spherical in shape, numerical calculations are carried out for non-Rayleigh conditions of scattering. Comparisons of such cross sections are made with those obtained from the Rayleigh approximation.

The deviation from Rayleigh behavior becomes pronounced, for the elastic scatterer, beyond ka≅0.5. In addition a ``peaking'' and ``fluctuating'' of the cross section occurs beyond this point.
Thermoelectric and Electrical Measurements in the Er-Se System
Authors: Haase D. J. , Steinfink H.
Published: April 2005

An evaluation of the electrical conductivity and thermoelectric power for compounds in the Er-Se system shows that they are degenerate semiconductors. In order to explain the observations in the intrinsic region the number of carriers must be considered as a function of the concentration of the erbium atoms in the compound. Two temperature-dependent processes take place; the activation of impurity levels and the high-temperature activation of localized energy levels associated with the number of erbium atoms present.
X-Ray Topographic Observation of Dislocation Contrast in Thin CdS Crystals
Authors: Chikawa Jun-ichi
Published: April 2005

Dislocations in thin CdS crystals have been observed by x-ray diffraction topography (Laue case). A method with a divergent beam from a point focus has been used for the study of dislocation contrast. Images of individual dislocations observed by this method consist of two lines which seem to be located on either side of their core. The observation shows that dislocation contrast is formed by x rays which are so deviated from the Bragg condition that the x rays are hardly diffracted by the perfect region of the crystal, and that one of the two lines is formed by the incident x rays with larger glancing angles than the Bragg angle and the other with smaller ones. From the comparison of the observed dislocation images and the elastical distortion near the dislocation core, it is inferred that, when a dislocation is observed by a beam deviated from the Bragg condition for the perfect region, an intensity enhancement of diffracted beam is produced at the place near the core where the beam satisfies the Bragg condition. By using a simple model based on this inference, the dislocation contrast and its variation with the dislocation depth are discussed. The signs of Burgers vectors can be determined from the dislocation contrast.
Observation of Nonquasistatic Plasma Surface Waves
Authors: Granatstein V. L. , Schlesinger S. P.
Published: April 2005

Surface waves have been launched from a waveguide onto a glass-clad plasma column of moderate size (2πR≈λ0) in order to test the validity of quasistatic analysis when the small-column condition (2πR≈λ0) is not satisfied. Resonances were observed in an open microwave cavity, and dispersion of both the circularly symmetric surface wave and the dipole surface wave has been determined from experimental data. The two waves exhibit regions of backward-wave and forward-wave propagation. The observed positive slope of the dipole mode dispersion curve near ω/kz=c is contrary to the predictions of quasistatic analysis and is shown to agree quantitatively with the results of a more rigorous analysis.
Signal Amplitudes of Modulation-Broadened Lorentz and Gaussian Magnetic Resonances
Authors: Wilson G. V. H.
Published: April 2005

For a given ratio of modulation amplitude to linewidth at half-height, the signal amplitudes of modulation-broadened Lorentz and Gaussian dispersion resonances detected at the modulation frequency are similar. It is pointed out that, after correction of an error in a previous calculation of signal amplitudes of Gaussian absorption line shapes, the signal amplitudes of Gaussian and Lorentz absorption resonances are also approximately equal.
Effect of Surface Pinning on the Magnetization of Thin Films
Authors: Davis James A.
Published: April 2005

The effect of surface pinning, as manifested by a surface anisotropy field, on the magnetization of thin films is examined in detail for a simple cubic lattice of atoms having spin ½ coupled by pure exchange. The magnetization-versus-temperature curve is found to lie above that obtained in the absence of pinning. For very weak pinning (surface anisotropy field much less than surface exchange field), the magnetization is sensitive to film thickness falling off more rapidly than for bulk, in qualitative agreement with some experiments. For intermediate pinning, the magnetization is essentially independent of film thickness, following the bulk behavior, in qualitative agreement with other experiments. For very strong pinning (surface anisotropy field on the order of or greater than surface exchange field), the magnetization falls off slower than for bulk, again with a thickness dependence. As a consequence, one may interpret experimental results in terms of the degree of surface spin pinning. Physically it is not yet clear why the degree of pinning should behave in the required fashion.
Enhancement of Plasma Density in an Arc Discharge
Authors: Singh A. , Rowe J. E.
Published: April 2005

The amplification or generation of coherent signals by electron-beam—plasma interactions requires the creation of a high-density stable plasma. A plasma density of approximately 1015 particles/cm3 is required to produce a plasma resonance frequency of 300 Gc/sec. The density in an arc-discharge plasma has been increased using mechanical and magnetic constriction methods with the result that np=7.5×1014 particles/cm3 is realized at a discharge current of 4 A in argon. Double Langmuir probe measurements on density and temperature in the plasma are presented and interpreted for zero and finite magnetic-field conditions.
Incorporation of a Laser into the Arm of an Interferometer for Measurement of Transient Phase Changes
Authors: Thornton Edward
Published: April 2005

An interferometer is described in which a He—Ne laser has been introduced into one of the arms to act as a coherent light source, eliminating the use of a beam splitter and making more efficient use of available light. The interferometer has been used with 0.63-μ laser light to observe the fringe shift produced in a small transient plasma with submicrosecond time resolution. Electron densities of the order of 1015/cm3 over a path length of 15 cm were measured, close to the sensitivity limit for the unrefined experimental setup. The use of a laser source with long light paths and narrow beam width gave good discrimination against plasma light.
Electron Emission from Aluminum after Low-Temperature Deformation
Authors: Claytor R. N. , Brotzen F. R.
Published: April 2005

Emission of electrons (``exo-electrons'') was observed by means of an open-window Geiger—Müller counter during annealing of aluminum wire subsequent to low-temperature deformation. A mathematical model was developed based on the concept that the emission is controlled by the diffusion of point defects to the surface. Interpretation of the experimental data yielded an activation energy of 0.44±0.03 eV for the migration of the point defects. Electrical resistivity measurements made at 4.2°K on aluminum deformed at a low temperature revealed that defects anneal out in the general temperature range in which emission is observed.
Temperature Dependence of Orientation Birefringence of Polymers in the Glassy and Rubbery States. II
Authors: Hammack T. J. , Andrews R. D.
Published: April 2005

The variation of orientation birefringence with temperature has been investigated for a group of five crosslinked amorphous polymers—natural rubber, butyl rubber, polystyrene, silicone rubber, and poly(methyl methacrylate)—in measurements covering both the glassy and rubbery states. The hydrocarbon polymers (natural rubber, butyl rubber, and polystyrene) show nearly ideal behavior in both the glassy and rubbery states, where ideality is defined as birefringence independent of temperature in the glassy state, and in the rubbery state conforming to the rubber elasiticity theory of birefringence. Silicone rubber under constant dead load shows a nonideal increase of birefringence with temperature in the rubbery region; in addition, partial crystallization occurs during cooling at around −70°C, and a strong temperature dependence of birefringence is observed in the semicrystalline-glassy state at lower temperatures. Irreversible changes of birefringence are observed in PMMA above 175°C, and nonideal reversible behavior is observed in both the glassy and rubbery states. It is proposed that the changes of birefringence with temperature in both glassy and rubbery PMMA are a result of progressive breakdown with increasing temperature of an intermolecular dipole-dipole association between the ester side groups.
Lattice and Grain Boundary Self-Diffusion in Nickel
Authors: Wazzan Ahmed Rassem
Published: April 2005

Lattice and grain boundary self-diffusion coefficients of radioactive nickel 63 into high purity nickel have been measured over the temperature range 650°–475°C. The lattice diffusion coefficients, measured by radioactive counting of the surface, are given by DL=1.9 exp(−66 800/RT) cm2sec−1in agreement with previous measurements at higher temperatures. The grain boundary diffusion coefficients, determined from activity-penetration data, are similarly given by DB=0.07 exp(−27 400/RT) cm2sec−1and found to be independent of grain diameter in the range of about 0.03 to 0.07 mm.
Equivalence of Stress- and Radiation-Induced Defects in Degenerate p-n Junctions
Authors: Rindner W. , Roth H. , Bernard W.
Published: April 2005

Excess current, irreversibly introduced by inhomogeneous stress in germanium tunnel diodes, has been found to be annealable by the application of suitable forward bias in a manner analogous to that in the case of electron-irradiated tunnel diodes. Thermal and voltage-anneal characteristics of radiation- and stress-induced excess currents have been studied over a temperature range from 4.2° to 300°K. Strong similarities in the voltage-anneal characteristics, as well as certain common features of the thermal anneals, suggest that the electrically active defects introduced by electron-irradiation and by inhomogeneous stress may be of a similar nature.
Initial Oxidation of Tantalum Observed in a Field Ion Microscope
Authors: Nakamura Shogo , Müller Erwin W.
Published: April 2005

The distribution of oxygen atoms diffused into a tantalum crystal as a function of temperature, oxygen pressure, and time has been observed in a field ion microscope. Light oxidation below 450°K causes corrosion of the first atomic layer only, while there is no diffusion into the matrix. The distribution of oxygen interstitials occuring at higher temperature with an activation energy of 1.1 eV is measured by direct counting of surface concentration of interstitials using the field evaporation sectioning technique. Heavy oxidation causes a breakup of the lattice and homogeneously dispersed nuclei of oxide. Tantalum with 1% oxygen content only shows the statistically expected number of interstitial pairs when quenched from 1100°K. In situ annealing between 395° and 360°K causes up to 14.5% of the interstitials to associate in pairs or clusters.
Microwave Plasma Density Measurements
Authors: Thomassen K. I.
Published: April 2005

To make plasma density measurements on a cylindrical column with a microwave cavity requires a precise curve of cavity frequency versus density. In practice, one uses the measured cavity frequency (without a plasma) and the initial slope of this curve. An analysis is made for the TM010 mode to determine the effects of nonuniformity (a parabolic density) and of the holes in the cavity where the plasma column is admitted. It is shown that both effects result in a smaller slope so that one underestimates the density if they are not taken into account.
Ion Explosion Spike Mechanism for Formation of Charged-Particle Tracks in Solids
Authors: Fleischer R. L. , Price P. B. , Walker R. M.
Published: April 2005

Massive charged particles create regions of intense damage (tracks) by passing through bulk samples of insulating materials. These tracks are shown to result from the positively charged region created by ionization. An approximate model of an ``ion explosion spike'' is proposed in which the mutual repulsion of the positive ions ejects them into the surrounding lattice. This model is shown to be generally consistent with a wide range of experimental fact. An additional damage mechanism appears to apply to polymers, in some of which tracks are produced by light projectiles such as α particles. The data here are shown to be consistent with tracks consisting primarily of broken bonds caused by decay of directly excited electrons.
Effective Polarizing Field in Ionic Crystals
Authors: Theimer O. , Paul R.
Published: April 2005

The polarizing field E in ionic crystals is calculated from a ``rigid-ion'' model in which the spherical charge cloud of the valence electrons is displaced rigidly against the ionic core under the influence of an electrical field. It is shown that overlap between neighboring charge clouds affects the Lorentz field (4π/3)Pγ (P=macroscopic polarization) in such a fashion that the Lorentz factor γ becomes equal to 1+δ even in crystals with tetrahedral symmetry where it is generally assumed equal to unity. The overlap correction δ is calculated on the assumption that the wavefunctions of the valence electrons may be approximated by Slater functions, i.e., hydrogenlike wavefunctions with effective, nonintegral atomic numbers Z* and quantum number n*. Using Slater's empirical values for Z* and n*, δ is found of the order 0.1 for crystals with large anions and small cations such as sodium bromide and lithium iodide. For most other crystals δ is found of the order 0.01.
Theory of Laser Giant Pulsing by a Saturable Absorber
Authors: Szabo A. , Stein R. A.
Published: April 2005

Several experimental demonstrations of laser giant pulsing using a saturable absorber inside the laser cavity as a fast switch have recently been reported. In the present work giant pulse parameters such as pulse rise and fall times and peak power are calculated as a function of σ, the ratio of absorber to laser ion cross sections; nai, the normalized inversion prior to switching; and the laser mirror transmission Tr. It is shown that there is an optimum Tr for the extraction of maximum peak power. A criterion for the minimum σ for giant pulsing to occur is derived. The largest output occurs when σ → ∞ in which case the theory approaches that of Wagner and Lengyel. Some numerical examples are presented as well as a discussion of the range of validity of the theory.
Effect of Temperature on the Mechanical Properties of Solid Pressure-Transmitting Media. II. Pyrophyllite
Authors: Hulse C. O. , Graf R. B.
Published: April 2005

The high-temperature compressive strength of block pyrophyllite is not significantly less than the room-temperature strength at temperatures below 1200° and it is noticeably greater at 600° and 1100°C. The major increase in strength occurs above 1050°C and is associated with the decomposition of the pyrophyllite to mullite and silica phases. This increase in ultimate strength is time dependent and may amount to as much as five times the room-temperature strength. Because pyrophyllite is also used as a thermal insulator in high-temperature high-pressure applications, a shell of this stronger material will be present around samples heated for long times above 1050°C. This may adversely affect its efficiency as a solid pressure-transmitting medium. Pyrophyllite is superior to talc for similar high-temperature applications because it can be dehydrated prior to use without increasing its strength, and it develops its high-temperature strength more slowly.
Elastic Stiffness Coefficients of Iron from 77° to 673°K
Authors: Lord Arthur E. , Beshers Daniel N.
Published: April 2005

The elastic stiffness coefficients of single-crystal iron have been measured at room (300°K) and liquid-nitrogen (77°K) temperatures using the ultrasonic pulse-echo technique. The three coefficients were determined from a total of seven independent modes. The values at 300°K are C11=2.28±0.02, C12=1.32 ±0.04, and C44=1.165±0.01, in units of 1012 dyn/cm2; the corresponding values at 77°K are 2.36±0.02, 1.34±0.04, and 1.19±0.01.

The coefficients C11, (C11+C12+2C44)/2, and (C11+2C12+4C44)/3 of iron have been measured from 77° to about 673°K. C11 and (C11+2C12+4C44)/3, as well as the polycrystalline stiffness λ+2μ, depart from a linear dependence on temperature above about 300°C. It was not possible to say whether the same effect occurred in (C11+C12+2C44)/2 because of significant scatter in the data.

The Debye temperature Θ0 was found from the stiffnesses extrapolated to 0°K, to be 471.5°K.
Electrical Conductivity of Thin Metallic Films with Unlike Surfaces
Authors: Lucas M. S. P.
Published: April 2005

A theoretical analysis, based on the Fuchs-Sondheimer formalism, is given of the conductivity of single-layer, thin metallic films in which the scattering of the conduction electrons is different at each surface. The electron-surface scattering is described by the parameters P and Q which represent the fractions of conduction electrons specularly scattered at each surface. Tables of normalized resistivity as a function of thickness divided by mean free path are given for various combinations of P and Q.
Ion Beam Profiles in Three-Dimensional Magnetic Fields
Authors: Lilly A. C. , Weismann T. J.
Published: April 2005

A practical numerical method for the determination of ion trajectories in the midplane of nonhomogeneous magnetic fields utilizing a computer program has been extended to include x and y components of the field both on and off the median plane. The method permits calculation of beam shape and the effects of z focusing. Practical implications in attaining maximum efficiency in the design of collector slits for mass spectrometry are pointed out.
Ion Transport Phenomena in Insulating Films
Authors: Snow E. H. , Grove A. S. , Deal B. E. , Sah C. T.
Published: April 2005

It is shown that changes in the capacitance-voltage characteristic of a metal-insulator-semiconductor structure provide a powerful tool for the observation of ion motion in thin insulating films. Using this method, a detailed study of the kinetics of alkali ion migration in thermally grown silicon dioxide films has been made. Alkali ions were initially deposited at the metal-oxide interface and their transport through the oxide was studied as a function of time, temperature and applied voltage. When the metal is biased positively the number of ions accumulated at the oxide-silicon interface is initially proportional to the square root of time and then approaches a saturation value. The temperature dependence is exponential and leads to an activation energy for the diffusion coefficient of 32 kcal/mole for Na and 22 kcal/mole for Li.

A simple model is developed which is based on the division of the insulator into two regions: a thin boundary layer near the metal-insulator interface in which ion transport is by diffusion, and the remainder of the insulator where field transport dominates. It is shown that most features of this model are in excellent agreement with the experimental results.
Sputtering of Single-Crystal Copper and Aluminum with 20–600 eV Argon Ions
Authors: Zdanuk E. J. , Wolsky S. P.
Published: April 2005

Absolute measurement of the sputtering yield of (100) and (111) copper and of (111) aluminum single-crystal targets bombarded with 20–600 eV argon ions was performed employing a sensitive quartz micro-balance in an ultrahigh-vacuum system. The threshold energies for copper and aluminum targets were less than 20 eV. The sputtering yield values in the threshold region were dependent upon the detailed nature of the target surfaces. The threshold region orientation dependence of the sputtering yield for copper was different from that in the higher energy regions.
Formation of Dislocations Around Precipitates in Single Crystals of (Zn,Cd)S:Er
Authors: Abrahams M. S. , Dreeben A.
Published: April 2005

As-grown single crystals of (Zn,Cd)S doped with Er were examined microscopically. Unique precipitation patterns were found in which essentially spherical precipitates were surrounded by six arms, each oriented parallel to a <101̄0> direction. The structure of these arms was comprised of decorated dislocation loops and helices. The process responsible for the formation of these arms is thought to be prismatic punching, which occurs to relieve the stresses arising from differential thermal contraction during the cooling of the crystal. Evidence is presented indicating that the central precipitate of an asterisk nucleates at sites along grown-in dislocations. Also observed was an increase in loop diameter with distance from the central precipitate indicating that dislocation climb occurred as the crystal was cooled.
Field-Enhanced Secondary-Electron Emission from Polar Crystals
Authors: Khokley W. S. , Van Vliet K. M.
Published: April 2005

A calculation is given of the effect of an electric field on the migration to the surface of secondary electrons produced in polar crystals. As in a previous paper, the scattering with the optical polar modes is accounted for by an approximate treatment of the Boltzmann transport equation. The effect of the field on the secondary emission coefficient is obtained from a perturbation treatment and evaluated for a planar source and a ``constant loss'' production function. The results are compared with experimental data on MgO and agree as to order of magnitude.
Calorimetric Investigation of the Cu3Au Alloy Above the Critical Temperature
Authors: Guarini G. , Schiavini G. M.
Published: April 2005

The amount of heat released in a Cu3Au sample, while undergoing an incremental decrease of 50°C in temperature, has been measured at several temperatures. Apart from the sharp maximum at the critical temperature, the heat release does not decrease monotonically with increasing temperature, as predicted by the theory of the short-range order: it goes up to a maximum at about 600°C. The heat release at the maximum is 1% of the value obtained at the critical temperature.
Anisotropy in Nickel-Iron Films: The Pair-Strain Model
Authors: Siegle W. T. , Beam W. R.
Published: April 2005

A systematic investigation has been made of magnetically induced uniaxial planar anisotropy in a series of 27 Ni–Fe normal incidence, vapor-deposited films spanning the composition range 65% Ni to 100% Ni. The small experimental data scatter permits an unambiguous presentation of the compositional dependence. A series of magnetic annealing treatments was applied under various temperature and field conditions; each produced changes in the compositional dependence of anisotropy. The data can be closely fitted to a theoretical model (for the compositional dependence) based on mechanisms of magnetostrictively induced anisotropic strain and short-range iron-pair order. The component of anisotropy associated with strain is in good agreement with theoretical predictions for its magnitude, and is found to be characterized by the deposition substrate temperature, or (after long anneal) the anneal temperature. An activation energy of around 0.9 eV (for the films in this study) fits the annealing behavior of the strain component. The remaining anisotropy, although well represented in its compositional form by the c2(1−c)2 form expected for pair order, does not respond to annealing treatment with a discrete relaxation time. Two possible explanations are considered.
Statistics of Jogs on Dislocations at Equilibrium
Authors: Ardell Alan J. , Reiss Howard , Nix William D.
Published: April 2005

A statistical treatment is presented for the distribution of jogs on dislocations at complete thermodynamic equilibrium. General expressions for the density and average height of jogs are derived. Specific formulas for the jog density and average jog height are obtained for two separate models of the jog energy. It is found that the jog density is not given by a simple Boltzmann formula as has often been assumed. It is also found that the assumption by others that the average jog height is one atom distance, while not strictly valid, is very nearly true for reasonable values of the jog energy. The distribution of jog spacings is found and is identified with the distribution known in statistics as the geometric distribution. Some implications of these results are discussed.
Dislocation-Interstitial Interactions in Single-Crystal Tantalum
Authors: Carpenter S. H. , Baker G. S.
Published: April 2005

Dislocation-interstitial interactions have been investigated in zone-melted single-crystal tantalum by means of internal friction measurements. A Marx piezoelectric composite oscillator resonating at 50 kc/sec was used to measure the logarithmic decrement as a function of time, temperature, and strain amplitude.

Damping measurements indicate that two separate pinning processes occur in the 0°–100°C temperature range. In the 0°–25°C range the amplitude-independent damping measured immediately following deformation (∼1%) has been found to decrease with time. No change in the amplitude dependence has been detected. This has been called stage-one pinning. The relaxation time for stage-one pinning has been found to be too short to allow for the long-range diffusion of interstitials required for Cottrell-type pinning. The pinning mechanism is believed to be the reorientation of solute interstitial oxygen atoms in the dislocation strain field as proposed by Schoeck. The activation energy for the stage-one process has been found to be 23 500±3000 cal/mole. This value is consistent with the diffusional energy of oxygen in tantalum.

An increase in test temperature to the 75°–100°C range has been found to cause a further reduction of the amplitude-independent damping with time. A decrease in the amplitude dependence has also been observed. This reduction in the damping has been called stage-two pinning. Stage-two pinning is explained satisfactorily by the Cottrell-type pinning of the dislocation lines by solute interstitial oxygen atoms.