bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology of Poly-p-Xylylene Crystallized during Polymerization
Authors: Kubo S. , Wunderlich B.
Published: February 2004

The morphology of as-polymerized poly-p-xylylene grown between −17 and 30 °C is found to consist of lamellar α crystals oriented with the (010) plane parallel to the support surface. The crystallinity decreases with decreasing polymerization temperature. Spherulitic and nonspherulitic portions of the polymer film consist of folded chain lamellas (∼80 Å fold length) with the chain axis parallel to the support surface. The results were obtained by small- and wide-angle x-ray measurements, electron and optical microscopy, and differential thermal analysis.
Diffraction Study of Solid-State Photopolymerization of Trans, Trans-1, 4-bis-[β-pyridyl-(2)-vinyl]-benzene
Authors: Baughman R. H.
Published: February 2004

Single-crystal x-ray diffraction studies of trans, trans-1, 4-bis-[β-pyridyl-(2)-vinyl]-benzene (P2VB) and its solid-state addition photopolymerization to a high-crystallinity nearly three-dimensionally aligned linear polymer are presented. Both P2VB and poly-P2VB are orthorhombic. The lattice parameters are a=21.09±0.16, b=9.61±0.05, and c=7.29±0.03 Å for P2VB, and a=19.16±0.20, b=10.69±0.05, and c=7.45±0.15 Å for poly-P2VB. For both monomer and polymer the unit cell contains four monomer molecules. From systematic absences, the probable space group of P2VB is Pbca. The observed absences for poly-P2VB are also consistent with this space group. The solid-state photopolymerization of P2VB is controlled by the crystal structure of this monomer with the orthorhombic axes of monomer and polymer on the average aligned in the same direction. The slight change in unit cell dimensions, the probably identical unit cell symmetry, and the invariance of average unit cell orientation suggest that minimal molecular rearrangement occurs during polymerization. Models are proposed for the polymerization mechanism and are related to the configuration and lattice structure of the resulting polymer. To obtain more detailed knowledge of the structure of crystalline P2VB and hence of the polymerization mechanism, energy minimization packing calculations have been performed. This monomer was found to deviate appreciably from a planar molecular structure. The present study is compared with recent work on the solid-state photopolymerization of an isomeric compound trans, trans-2, 5-distyrylpyrazine (DSP).
Pressure-Volume-Temperature Properties and Transitions of Amorphous Polymers; Polystyrene and Poly (orthomethylstyrene)
Authors: Quach A. , Simha Robert
Published: February 2004

An apparatus based on Bridgman's bellows method, originally devised for fluids, has been constructed for use with solid samples. Mercury is employed as the confining liquid. The operating range is 0≤t≤200 °C and 1≤P≤2000 bar. Calibration with benzene and mercury shows an accuracy of ±2×10−4 cm3/g in the measurement of the specific volume change. A detailed investigation of two systems, polystyrene and poly(orthomethylstyrene) in the glassy and liquid states is undertaken. The P-V-T results in both states can be well represented by the Tait equation, with the single parameter B as an exponentially decreasing function of T. Similar to the earlier result for polystyrene, a β-relaxation region is observed in terms of the isothermal compressibility of the methylated polymer with Tβ/Tg≃0.70 for both. The pressure coefficients for the two transition temperatures are discussed. For the glass transition, the Ehrenfest-type equation appears to be obeyed by the low-pressure glasses (formed by cooling the liquid at atmospheric pressure) but not the high-pressure glasses (formed by pressurizing the melt isothermally). The experimental compressibility factors, the internal pressures, and the changes in internal energy upon compression are compared with the predictions of the cell theory of the Brussels group and the hole theory of Simha-Somaynsky. The characteristic parameters are evaluated by a superposition of the experimental and theoretical atmospheric-pressure isobars and from the ordinates of one isotherm. In the temperature and pressure range considered here, the performance of the cell theory is quite satisfactory. Very good agreement in respect to the P-V-T function is obtained for the hole theory.
Annealing and Melting of Polyoxymethylene Crystals Polymerized Within Irradiated Trioxane Crystals
Authors: Reneker Darrell H. , Colson James P.
Published: February 2004

Morphological changes produced by the annealing and melting of the polyoxymethylene crystals that polymerize inside irradiated trioxane crystals were observed. The crystals in which the polyoxymethylene chains were oriented parallel to the threefold axis of the trioxane underwent major reorganization when held at 184°C for 30 sec. The polyoxymethylene crystals in which the chain axis was inclined at a large angle with respect to the threefold axis of the trioxane transformed and melted at temperatures approximately 5°C lower.
Deformation of Polyethylene at High Pressure
Authors: Davis L. A. , Pampillo C. A.
Published: February 2004

The influence of pressure, deformation rate, and pressure fluid on the mechanical properties of high-molecular-weight polyethylene is examined. A miniature motor-driven testing machine which operates completely enclosed in a high-pressure vessel is employed. This device allows for the first time in any material measurement of the sensitivity of the flow stress σ to an instantaneous change of strain rate under superposed high hydrostatic pressure. From these data and the pressure dependence of σ it is possible to calculate the activiation volume V* for plastic flow as a function of pressure; it is suggested that V* is the appropriate parameter to describe the pressure dependence of a kinetic process such as plastic deformation. It is found that samples deformed in n-pentane generally exhibit a reduced flow stress relative to those tested in water. In addition, it is observed that V* for specimens tested in pentane is significantly less than for those tested in water (∼230 Å at 1 atm as opposed to ∼266 Å3). In both cases V* is observed to decrease moderately with increasing pressure.
Volume Change during Deformation and Pressure Dependence of Yield Stress
Authors: Pampillo C. A. , Davis L. A.
Published: February 2004

Polymers are distinguished from metals by the considerable pressure dependence of their yield stresses, and one might expect this to be associated with a plastic volume change during yielding. We have measured the macroscopic volume changes during uniaxial compression of PMMA and PC, using a mercury-filled dilatometer. For PMMA a plastic volume change cannot be defined unambiguously because the volume-stress curve is reversible upon unloading to the yield point. For PC the plastic volume change is negative. Hence, if the pressure dependence of yielding is associated with this volume change, one would predict a decrease of the yield stress with increasing pressure. Contrary to this, we find that pressure increases the yield stress of PC. Hence, the plastic volume change is not directly related to the pressure dependence of the yield stress.
Single Crystalline Elastic Constants of AuZn and YZn
Authors: Schiltz R. J. , Prevender T. S. , Smith J. F.
Published: February 2004

The elastic constants of single crystals of cubic AuZn have been determined over the temperature range 85–300 °K and of cubic YZn over the temperature range 4.2–300 °K. The anisotropy ratio of AuZn increases with decreasing temperature and exceeds a value of 9 prior to a martensitic phase transformation which occurs near 60 °K for alloys of this stoichiometry. In contrast, the anisotropy ratio of YZn remains constant at 1.95 independent of temperature. Extrapolation of the elastic constants of YZn to 0 °K allows evaluation of a Debye temperature of Θ0=306.8 °K.
Relationship between Acoustic Emission and Dislocation Kinetics in Crystalline Solids
Authors: James Darrell R. , Carpenter Steve H.
Published: February 2004

The sounds emitted from single crystals of irradiated LiF, annealed LiF, NaCl, and zinc during constant-strain-rate compressive deformation were recorded and analyzed. The acoustic emission consisted of discrete pulses of varying amplitudes, and the rate of pulsing changed with total strain during the continuous deformation experiments. A reasonable correlation between acoustic-emission pulse rate and the rate of change of mobile dislocation density was found and led to the conclusion that the pulses were generated by dislocation breakaway from pinning points. The measured dislocation densities were used to estimate that several thousand centimeters of dislocation line length had been involved in the generation of an individual acoustic pulse. It was suggested that some 105−106 segments of dislocation line were involved in a cumulative fashion due to the stimulating effect of the moving acoustic wave on bowed dislocation segments. The concept of stimulated dislocation breakaway from pinning points appeared to be a reasonable model to explain the acoustic results of this study and may provide the fundamental basis for explaining discontinuous plastic flow, jerky dislocation motion, slip line broadening, and other features of crystal plasticity.
Effect of Domain Structure on the Fluorescence of Cr3+-Doped SrTiO3
Authors: Chang T. S. , Imbusch G. F.
Published: February 2004

The effect of domain structure on the fluorescence of Cr3+-doped SrTiO3 is studied by examining the intensity ratio of the two R lines when the domain structure is changed under application of uniaxial stress. Fluorescence patterns of individual domains are seen to be most consistent with a magnetic dipole optical process. Theoretical Zeeman patterns of individual domains are given and these can be used to analyze experimental Zeeman data.
Mössbauer-Effect Studies of the Phase Transitions in Antiferroelectric PbZrO3 and Ferroelectric PbTi0.02Zr0.8O3
Authors: Canner James P. , Yagnik C. M. , Gerson R. , James W. J.
Published: February 2004

The Mössbauer spectra were studied for the antiferroelectric compound PbZrO3 and for the closely related ferroelectric PbTi0.2Zr0.8O3. In both cases, a substitution of 5-mol% BiFeO3 was made to permit the Mössbauer measurements. Little difference was found in the isomer shift in these compounds, whether they were in the ferroelectric, antiferroelectric, or cubic state, indicating that the bonding character is not affected by the transitions among the states. There was a pronounced and approximately equivalent dip in the recoil-free fraction at the Curie points of both the antiferroelectric and ferroelectric materials, associated with a low-frequency lattice mode at the Brillouin-zone boundary.
Decay of Excess Charge in Dielectrics Having Shorted Electrodes
Authors: Wintle H. J.
Published: February 2004

The flow equations are derived for the discharge of dielectrics having an arbitrary initial charge and shorted electrodes, for the case of rapid shallow trapping. The case of an initial charge distribution which is uniform down to a depth y is considered in detail. Nonisothermal conditions are readily handled. It is shown that only a small fraction f of the initial charge can be observed in the external circuit, and that a significant fraction g ≠ 1-f is retained in the specimen when the external current flow ceases. The calculation is applied to the ionic thermo-current observed in Mylar and is shown to accord well with the experimental measurements.
Observation of Fine Structures in Iron and Chromium Kα1,2 Lines Using a High-Resolution Three-Crystal Spectrometer
Authors: Priest John F.
Published: February 2004

Utilizing the high resolution of the recently developed three-crystal spectrometer in the (1, 2, 2) position, fine structures have been observed in the Kα1 and Kα2 lines of iron. The existence of similar structures was confirmed for chromium Kα1, Kα2 lines.
Variations of the Dislocation Damping Coefficient during Gamma Irradiation of NaCl Single Crystals
Authors: Bielig G. A.
Published: February 2004

Deformed sodium chloride crystals were irradiated by γ rays from spent fuel elements while their ultrasonic properties (resonant frequency and decrement) were being measured. It was found that the damping coefficient associated with the viscous drag on a moving dislocation varied with time during irradiation, and was also a function of the state of deformation of the crystal. The variations in the damping coefficient were interpreted in terms of the model developed by Robinson and Birnbaum for dislocation damping in alkali halides.
Thermal Conduction near an Interface in a Nematic Liquid Crystal Subjected to a Magnetic Field
Authors: Yun C. K. , Picot J. J. C. , Fredrickson A. G.
Published: February 2004

Thermal conductivities of nematic p-n-decyloxybenzoic acid were measured by a transient hot-wire method. A magnetic field was applied in a direction perpendicular to the heat flux. It was found that conductivity of the interfacial layer around the wire is not affected by the field, whereas conductivity of the bulk region decreases toward a saturation value as the field strength is increased. By an extrapolation method, the principal thermal conductivities and the magnetic polarizability of the unit particle of orientation were determined.
Analysis of Motion of Magnetic Levitation Systems: Implications for High-Speed Vehicles
Authors: Davis L. C. , Wilkie Dennis F.
Published: February 2004

To study the motion of a magnetically suspended high-speed vehicle, a simple example (the long wire above a thin conducting plate) is considered in detail. The lift and drag forces on the magnet (long wire) are derived for arbitrary motion above the plate. The stability of the system is analyzed for typical parameters (velocity = 300 mph, height = 0.1 m). By using a Laplace-transform technique, it is shown that two types of modes occur (in the linearized equations of motion). One mode is a vertical oscillation with an amplitude that grows slowly in time. The other mode is an unbounded increase in the horizontal velocity error. This latter instability results from the fact that the drag force decreases with increasing velocity at high speeds. In this connection, an error is pointed out in a recent publication in which it was claimed that the system is stable. Detailed consideration of the effects of horizontal acceleration and vertical velocity on the magnetic forces is given. The effects of aerodynamic drag and the need for active control of the system are also discussed.
Admittance of Coaxially Driven Infinite Monopole
Authors: Kao Cheng C.
Published: February 2004

The apparent admittance of a coaxially driven infinite monopole is reexamined. Systematic procedures are found to derive the higher-order terms. The first-order terms for both the exact admittance Ya∞ and the approximate admittance YTEM∞ are shown to vanish. The slope of (Ya∞ - YTEM∞) with respect to (b/a-1) is therefore zero as b/a→1. This information is important to bridge the heretofore little understood region between (i) the exactly known limiting value for b/a=1 and (ii) the values for b/a>1 which can be calculated numerically.
Spatial Conductivity Measurements in Turbulent Plasmas
Authors: Korn P. , Wharton C. B.
Published: February 2004

The design of an rf conductivity probe for measurements in transient plasmas is described. Calibration is performed using electrolytic solutions of known conductivity determined from a standard cell in a resistance bridge. The spatial resolution of the probe is determined, and conductivity measurements of a high-density plasma in a magnetic mirror prior to and following turbulent heating are presented.
Diagnostics of Non-Neutral Plasmas Using an Induced-Current Electrostatic Probe
Authors: Kapetanakos C. A. , Trivelpiece A. W.
Published: February 2004

The charge induced on an insulated conductor by a nonneutral collection of charged particles furnishes information about the macroscopic motion of such a system. Expressions for the current induced in probe by circular motion of a charged rod are derived and compared with results obtained in a nonneutral plasma confinement experiment to illustrate the usefulness of this technique.
Cataphoresis and Nitrogen-Removal Processes for dc Discharges in He–N2 Mixtures
Authors: Tombers Reid B. , Gaur J. P. , Chanin L. M.
Published: February 2004

Ion-sampling measurements have been made from the positive column of dc discharges in mixtures of 0.05%, 0.10%, and 0.28% nitrogen in helium. The major ions observed were He+, He2+, N+, and N2+. Traces of Ne+, Ar+, N3+, N4+, O+, O2+, NO+, and N2O+ were also detected. The variation of N+ and N2+ with distance from the cathode was measured as a function of gas pressure and discharge current. Using the axial variations, estimates have been made of the average degree of ionization of nitrogen. Measurements using certain types of cathodes for various discharge conditions show the volume removal of nitrogen from the mixture due to processes occurring at the cathode. Conditions which produce the removal of nitrogen are discussed. Considerations for the purification of noble gases contaminated by small concentrations of nitrogen are also mentioned. The result emphasize the difficulty of conducting dc gas-discharge studies, on known small concentrations of a molecular gas such as nitrogen.
Theoretical and Experimental Investigation of Pressure and Flow in Induction Plasmas
Authors: Chase J. D.
Published: February 2004

An investigation of flow in and around an induction plasma is made as a continuation of an earlier theoretical study of magnetic pressure in an induction plasma. The existence of the predicted flow out from both ends of the plasma is confirmed by flow visualization and stagnation pressure measurements in and around an ambient-pressure vortex-free argon plasma in a 28-mm tube. Flow visualization and gas velocities are obtained by photographing injected solid particles. For a 3-kW argon discharge, the velocity at the upstream end of the plasma was 6±0.3 m/sec, and velocity varies linearly with discharge power over the range investigated (up to 4.7 kW). A model of the plasma is devised to enable the maximum velocity of magnetically pumped flow to be calculated from the static magnetic pressure. Pressures in the range of +0.04 in. water, caused by expansion thrust of hot gases from the torch, were measured behind the plasma. The thrust pressure is calculated and is in reasonable agreement with measurements. A consequence of both magnetic and thrust pressures is that material introduced at the back of the torch tends to bypass the plasma.
Internal Photoemission Measurements in a Metal-Al2O3–Si System
Authors: Szydlo N. , Poirier R.
Published: February 2004

The photoelectric threshold energies for electron photoemission from Al, Au, and Si into a thin layer of Al2O3, deposited on Si by pyrolysis of AlCl3 at 850°C, have been measured and found to be, respectively, 3.05±0.1, 4.0±0.1, and 4.1±0.1 eV (from Si valence band). No hole photocurrent, as reported for plasma-anodization-grown Al2O3, was detectable. An approximate energy-band diagram of the Al–Al2O3–Si system is presented.
Photodecomposition of Amorphous As2Se3 and As2S3
Authors: Berkes John S. , Ing Samuel W. , Hillegas William J.
Published: February 2004

Electromagnetic radiation approximately equal to band-gap energy has been established as responsible for the dissociation of amorphous As2Se3 and As2S3. The dissociation is accompanied by an optical densification observable as a ``photographic'' effect in thin films of these materials. The dissociation can be expressed by the following equations: As2Se3→ lim hvxAs+As2−xSe3, 0<x<2 As2S3→ lim hv2As+3S.The densification is reversible by thermal cycling to higher temperatures. A detailed analysis of the experimental results is given and a mechanism is proposed which explains the photodecomposition reactions and the thermally induced reversibility in As2Se3. The photographic cycling characteristics of As2Se3 are discussed in the light of its potential device application.
Activation-Energy Spectra for Retraction of Hot-Stretched Polystyrene and Shear Creep in Polymethyl Methacrylate
Authors: Kimmel R. M. , Uhlmann D. R.
Published: February 2004

The data of Andrews for the retraction kinetics of hot-stretched polystyrene and the data of Thompson for shear creep in polymethyl methacrylate in the glassy state have been analyzed to obtain activation-energy spectra characterizing the kinetic processes. For the retraction data, singly peaked spectra covering the range between 15 and 35 kcal/mole were found. These were virtually independent of widely varying sample history, and the range of activation energies was somewhat higher than that found for volume relaxation in unoriented samples of the same polymer. The energy spectrum for the creep data is similar in shape to the retardation-time spectrum derived by Thompson, and covers the range 6–43 kcal/ mole. This range includes the three energy values previously calculated from the temperature dependence of the shift factor, log10aT. Changes in structure with temperature are easily inferred from the temperature dependence of the shift factor used to derive the energy spectrum.
Elastic Behavior of Disclinations in Nonhomogenous Media
Authors: Chou Tsu-Wei
Published: February 2004

The method of images is shown to be applicable in discussing the elastic field of twist disclinations in nonhomogeneous media. The interaction energies of disclination loops near a phase boundary have been obtained and it is found that the sum of self-energy and interaction energy is a continuous function of loop locations across a phase boundary. Furthermore, the image force on a twist disclination always acts in such a direction as to push the loop away from the more rigid phase. The implications of these findings apply not only to the behavior of grain boundaries of polyphase materials but also to macromolecular solids.
Production, Evaporation, and Measurement of Submicron CsF Particles in a Shock Tube
Authors: Mandl A.
Published: February 2004

Shock-tube experiments have been carried out to determine the size of submicron CsF particles suspended in a carrier gas. The particles are produced in an oven by passing the carrier gas over a melt of CsF, causing the CsF to self-nucleate. The rate of CsF ablation in the incident shock (1700<T<2700 °K) was measured directly by following the CsF gas production by an absorption measurement at 2095 Å. Calculations were carried out to determine the particle size for these observed ablation rates. The technique described provides a useful method for producing and introducing submicron particles into a shock tube and for measuring their evaporation rate and size.
Comparison of the Bismuth I–II Phase Transformations in Liquid and Solid High-Pressure Systems
Authors: Vanfleet H. B. , Zeto Robert J.
Published: February 2004

Bismuth specimens exposed to liquid and to solid pressure-transmitting media were examined simultaneously in a hydrostatic pressure system, and the measured initiation and equilibrium pressures of the I–II and II–I transitions were compared. The hydrostatic pressure-transmitting-medium was an equivolume mixture of normal- and iso-pentane, and the solid pressure transmitting media investigated were AgCl and Epoxy resin. Encapsulation by AgCl and Epoxy resin caused a lower I–II initiation pressure, but did not alter the equilibrium pressure. The bismuth I–II transition initiated near the equilibrium pressure in each of the solid pressure media. In the liquid pressure medium the equilibrium pressure was also found to be asymmetrically located toward the high-pressure side of the initiation pressure hysteresis. The region of indifference was 30 bar wide. The transformation behavior is explained in terms of the strain and kinetic dependences of solid-state nucleation. The solid pressure media accelerate the nucleation kinetics so that the transition initiates at the boundary of the strain hysteresis which is small for the forward transformation. For standard calibration of solid-media systems on increasing pressure, experimental justification is provided for the practice of calibrating the initiation of the I–II transition with the equilibrium pressure. The pressure of initiation is defined, and the importance of the pressurization rate is illustrated. Several common calibration methods used in solid-media systems are shown to be incorrect.
Optical Spectra and Intensities of Nd3+ in YAlO3
Authors: Weber M. J. , Varitimos T. E.
Published: February 2004

The optical absorption and emission spectra, fluorescence kinetics, and radiative and nonradiative transition probabilities of Nd3+ ions in YAlO3 are investigated. Measurements are presented of the energy levels, absorption and emission cross sections, linewidths as a function of temperature and Nd concentration, thermal line shifts, and fluorescence branching ratios. Judd-Ofelt intensity parameters for electric-dipole transition probabilities are derived from measurements of the absorption spectrum. Stimulated emission cross sections, absorption-band intensities, fluorescence quantum efficiency, possible excited-state absorption, and other properties of importance for YAlO3:Nd3+ laser action are discussed.
Experimental Studies of Gunn Domains and Avalanching
Authors: Owens J. , Kino G. S.
Published: February 2004

The characteristics of domains have been observed experimentally through the current-voltage characteristics and by using capacitive probes. Avalanching within the domain has been observed and studied. These studies have involved the use of a capacitive probe and photomultipliers to study the recombination radiation seen after avalanche has occurred. This radiation has been spatially resolved showing that avalanche does occur within the domain and not in the bulk. The characteristics of hole trapping in bulk material after avalanche have been studied. The agreement between theoretical results in the accompanying paper and experimental avalanche studies mainly on bulk material has been good.
Analysis of Pulsed CO Lasers
Authors: Jeffers W. Q. , Wiswall C. E.
Published: February 2004

This paper presents an analysis of pulsed laser emission in carbon monoxide. The excited-state populations are calculated by means of known vibrational excitation cross sections in CO-electron collisions. The time evolution of the excited distribution is described by anharmonic oscillator relaxation based on recent experimental and theoretical results on V–V energy transfer in CO collisions. Calculated results are in excellent agreement with data obtained with a transverse discharge-pulsed CO laser.
A Structural Investigation of the Laser Machining of Thin Bismuth Films
Authors: Sard R. , Maydan D.
Published: February 2004

An experimental investigation of laser matching of thin films of Bi deposited on Mylar substrates has been carried out. Both He–Ne and argon acousto-optical intracavity modulation systems were used to effect the machining. Scanning and transmission electron microscopy were employed to determine the structural changes caused by machining. It was found that the formation of holes several microns in diameter by laser beams requires melting and probably the initiation of evaporation in the center of the illuminated region. Liquid-phase material is then transported from the center resulting in the formation of machined holes bounded by thicker rim structures. Only a few percent of the material removed needs to be in the vapor phase to achieve the maximum spot diameter for a given pulse energy. It was also found that for short optical pulses (≤ 50 nsec), which require lower machining energies to create a machined spot of a given size than with longer pulses, the substrates are undamaged.
Interfacial Barrier of Heterojunction Photocathodes
Authors: Milton A. Fenner , Baer A. D.
Published: February 2004

The theory of N, large band gap; P, small band gap (NLPS) heterojunctions is examined in the case, where EAp-EAn>Egn, and it is shown that the height of the interfacial barrier (from P to N) can be no larger than Egn as measured from the Fermi level. This means that the interfacial barrier of N-type Cs2O deposited on III–V P-type semiconductors can be no greater than ∼2.0 eV. This barrier will be reduced in practice if interfacial states stabilize the Fermi level in the N-type material by providing a depository for electronic charge concentrated right at the surface. These states can be caused by the first layer of Cs deposited on a III–V semiconductor in the fabrication process for a III–V, Cs2O photocathode. In that case, the height of the interfacial barrier can be expected to be Iads-EAn, where Iads is the ionization energy of Cs alone deposited on the III–V semiconductor and EAn is the electron affinity of Cs2O. Good correlation is shown with experiment for GaSb, N-type GaAs, and Ge.
Analytical Expressions for Electric Field and for Capacitances of Symmetrical and Asymmetrical Abrupt p-n Junctions
Authors: Nuyts W. , Van Overstraeten R.
Published: February 2004

Computer calculations carried out for p-n junctions justify the assumption that, to obtain a good approximation for the electric field and for the capacitance, the quasi-Fermi potentials may be considered constant in the depletion region. Making use of this property an analytical method for the calculation of the electric field and of the capacitance is worked out. This method yields for asymmetrical junctions simple results for (1) the explanation of the peak in the electric field distribution near the metallurgical junction; (2) the calculation of the critical voltage at which the inversion layer disappears; (3) a new analytical formula for the capacitance and a simple formula for the calculation of the C−2 vs U intercept. The results of the analytical method completely agree with the results of exact computer calculations, and are in contradiction with earlier publications.
Shallow Hole Levels in Ion-Implanted CdS
Authors: Anderson W. W. , Swanson R. M.
Published: February 2004

Thermally stimulated current measurements have shown the existence of a hole level 0.05 eV above the valence-band edge in P-implanted CdS. The thermally released carrier could be identified as a hole since the measurement was performed on a diode structure. An additional level with an ionization energy of 0.45 eV was also present. Capacitance measurements of space-charge density before and after level emptying indicated that some carrier multiplication mechanism is operative during current flow.
Structural and Magnetic Studies on ErFe2-ErAl2
Authors: Oesterreicher Hans
Published: February 2004

Specimens annealed at 1000 K are of C15 type from ErFe2 to Er0.333Fe0.425Al0.242, of C14 type from Er0.333Fe0.412Al0.255 to Er0.333Fe0.237Al0.430, and of C15 type from Er0.333Fe0.222Al0.445 to ErAl2. Magnetic investigations in the paramagnetic and ordered region show evidence for electron transfer to Fe from the trivalent ligands to the extent that Fe becomes nonmagnetic toward the Al-rich phase boundary of C14 ErFeAl. The materials order ferromagnetically on rare-earth sites, while Fe aligns antiparallel to the lanthanide. The saturation mechanism, however, is complex. Domain-wall effects, anisotropy, and the development of disordered magnetic components may be responsible for depressions in the saturation values of certain concentrations, stepwise increases of magnetization with field, and almost linear increases in magnetic moment in higher fields (10–47 kOe).
Observation of Ferromagnetic Domains with the Scanning Electron Microscope
Authors: Kammlott G. W.
Published: February 2004

It is shown that ferromagnetic domains may be observed using an unmodified scanning electron microscope. Magnetic contrast is due to the Lorentz force acting upon secondary electrons as they pass through magnetic fields near the surface of the sample. The influence of these fields is more marked upon secondary electrons of lower energy, and only these slower electrons contribute significantly to magnetic contrast. The technique described depends upon mounting the specimen in a position such that a straight line between the area under study and the collector is intercepted by a shield or by the bulk of the sample, in order to prevent many of the faster secondary electrons from contributing to the image.
Intracavity Metastable Measurements in He–Ne Lasers
Authors: Arrathoon R.
Published: February 2004

An experimental technique for gas discharges is described that allows the measurement of metastable populations within a laser cavity. The method is applied to a helium-neon laser system in order to evaluate the extent of forward and reverse He 21S ↔ Ne 3S2 resonant transfer coupling. The experimental results indicate that the He 21S level is virtually unaffected by 6328-Å or 3.39-μ laser operation. An associated rate-equation analysis suggests that atom-atom collisional transfer from the neon 3S2 level to adjacent neon levels may constitute a significant 3S2 level relaxation mechanism.
Voltage Sensitivity of the Electron Mirror
Authors: Szentesi O. I.
Published: February 2004

Using an interdigital electrode structure as the specimen, the voltage sensitivity of the electron mirror is studied. A dc voltage difference of 15 mV is detected and it is shown that there is good agreement between experimental and theoretical results.
Laser-Induced Thermal Lensing and Optical Damage in a Dichroic Sheet
Authors: Leib Kenneth G.
Published: February 2004

Light beams propagating through gases and liquids exhibit a developing thermal lensing until equilibrium is reached. Similar results have been observed in the early stages of thermal lensing in cellulose acetate butyrate H-type polarizing laminates containing one absorptive lamina. Stop action of the observed optical aberrations can be effected in these partially transparent laminates by decreasing laser beam power. Further exposure enables various stages of light-scattering damage caused by these materials to be developed and ``frozen'' at the desired levels. Examination and observation can then be conducted in a ``time-independent'' manner. With appropriate control of test conditions, the time history of lensing and damage can also be readily established.
Temperature Dependence of Ionization Rates in Ge
Authors: Dai B. T. , Chang C. Y.
Published: February 2004

The ionization rates of electrons and holes in Ge have been measured from 200 to 300°K and were fit to the Baraff theory, in which the optical-phonon mean free path is verified to be temperature dependent and fits to the formula λ=λ0 tanh(Ep/2KT), where Ep is the average optical-phonon energy. The asymptotic optical-phonon mean free paths deduced from experiments are λ0e=76 Å and λ0h=84 Å for electrons and holes, respectively, which are in good agreement with Miller's data obtained at room temperature. A simplified approach to calculate the ionization rates from the photomultiplication data has also been deduced for the one-sided abrupt junction.
Thermal Expansion of Lead-Tin and Lead-Cadmium Alloys
Authors: Balasundaram L. J. , Sinha A. N.
Published: February 2004

Thermal-expansion coefficients of low-melting lead-tin and lead-cadmium alloys have been measured in the temperature range from room temperature to 125°C. In the two-phase region of the alloys, the simple rule of mixtures is applicable and there is good agreement between calculated and measured values.
Mössbauer Study of BiF3-Type Ordering in Metastable FeGa Alloys
Authors: Newkirk L. R. , Tsuei C. C.
Published: February 2004

Metastable Fe alloys containing up to 25 at.% Ga, obtained by rapidly quenching from the liquid state, have been studied using the Mössbauer effect. A least-squares analysis of the data has allowed identification of individual configurations of atoms surrounding each Fe atom and the comparison of these configurations with various ordered and disordered states. Partial ordering of the BiF3 type has been definitely observed at 25 at.% Ga, and the results suggest that is may extend to compositions as low as 20 at.% Ga.
Effect of X-Ray Diffractometer Geometrical Factors on the Centroid Shift of a Diffraction Line for Stress Measurement
Authors: Singh A. K. , Balasingh C.
Published: February 2004

Expressions for the centroid shift of a diffraction line due to geometrical factors have been deduced for a diffractometer case in which the specimen surface is inclined to the x-ray beam at an arbitrary angle. Such a geometry is encountered in the determination of residual stress using a diffractometer. The effects of the centroid shift of a diffraction line due to geometrical factors on the stress derived from the diffractometer measurements have been discussed.
Light and Current Pulses from X-Rayed Potassium Di-Hydrogen Phosphate Crystals
Authors: Zerem J. Z. , Halperin A.
Published: February 2004

Short-duration light pulses accompanied by current pulses have been observed on warming KDP crystals x-ray irradiated at 77°K. The pulses start a few degrees above the transition temperature (TC=123°K) and continue until about 200°K. The pulses appear only under ambient gas pressures above about 0.1 Torr. Warming of the irradiated crystal to an intermediate temperature between TC and 200°K causes only a partial exhaustion of the pulses, and after cooling and reheating pulses appear only above the temperature reached in the former cycle. The pulses originate from discharges into the surrounding atmosphere. A simple model is given to account for the experimental results.
Motion of a Dislocation Acted on by a Viscous Drag through an Array of Discrete Obstacles
Authors: Frost H. J. , Ashby M. F.
Published: February 2004

A computer model was used to calculate the shape and average velocity v of a dislocation acted on by a viscous drag, and moving through a field of point obstacles. As a special case, the operation of a Frank-Read source was computed also. At sufficiently low velocities (and stress levels), the behavior is governed entirely by the obstacle spacing and strength; conventional tensile testing probably falls in this regime. At sufficiently high velocities (and stress levels), the behavior is governed entirely by the viscous drag; shock deformation falls in this regime. In between lies a wide range in which the two effects superimpose, each contributing measurably to the flow stress. The strain rate sensitivity m = (∂lnv/∂lnσ)T, where σ is the stress, reflects this behavior. At low and high velocities, respectively, m characterizes the obstacles and the drag. But in between m is characteristic of neither, and in fact reflects the change in the contributions of the two strengthening mechanisms when the applied stress is changed.
Improved Atomistic Model of a bcc Dislocation Core
Authors: Sinclair J. E.
Published: February 2004

It is shown that the strain field of a straight dislocation in an anisotropic elastic continuum includes an infinite series of terms of order 2 and higher in inverse distance from the dislocation line. These terms are determined by the nature of the core. A method is developed of finding these terms for a given dislocation while determining the core structure atomistically, using a digital computer. The equilibrium configuration of the core and the higher-order-term values are found rapidly by a method involving atomic force constants, which requires few calculations of interatomic forces. The model is applied to determine the core structure and near-strain field of a 〈100〉 edge dislocation in α iron using potentials developed by Johnson and by Chang and Graham. Core structure in agreement with that found by Gehlen et al. is obtained. The results are independent of model size over a wide range, and there is agreement between strain-energy distribution calculated atomistically and from elastic constants, for all three potentials used. The method may be useful in calculation of Peierls stress and of dislocation-point-defect interaction.
Interference Effect on Annealing Temperature of A and E Centers in Silicon
Authors: Fang P. H. , Tanaka T.
Published: February 2004

Experimental observation of the anomalous annealing temperatures of A and E centers and their impurity concentration dependence is explained by an interference between E and A centers.
Lattice Theory of Second- and Third-Order Elastic Constants of Aluminum, Copper, and Nickel
Authors: Mathur S. S. , Sharma Y. P. , Gupta P. N.
Published: February 2004

Lattice theory has been used to obtain the expressions for the second- and third-order elastic constants for face-centered-cubic lattices in terms of the second- and third-order coupling parameters, considering the general interaction between the nearest-neighbor atoms. The number of constants have been reduced by expressing the third-order coupling parameters in terms of the coupling parameters of second order and second-order elastic constants. The general expressions of the elastic constants have been evaluated for Al, Cu, and Ni in a special case of central forces. The force constants involved in the expressions have been determined by representing the central interaction between the pair of atoms by the Morse potential function. It is found that the Cauchy relations for second-order elastic contants C12=C44 and for third-order elastic constants C112=C166 and C123=C456=C144 are satisfied in the case of central forces. It is also seen that the values of C111 for all the three metals are the largest and C112 is approximately half as that of C111 and almost all the values of C123 are negative and small compared with the other third-order elastic constants. The pressure derivatives of second-order elastic constants, the anisotropy factor, and the Debye temperatures have also been calculated for these metals. The values obtained are in good agreement with the experimental values available in the literature.
Space-Charge-Limited Current in Gas Diodes
Authors: Johnson C. B. , Oskam H. J.
Published: February 2004

Measured current-voltage characteristics of space-charge-limited cylindrical gas diodes filled with helium, neon, and nitrogen up to pressures of 350 Torr are presented. The data are compared with current-voltage characteristics calculated from published values of the electron drift velocity as a function of electric field to pressure ratio. While the space-charge-limited diode current is always found to be larger than the calculated value, very good agreement exists between the shapes of the experimental and theoretical curves.
New Dislocation Etchant for Silver
Authors: Chen C. C. , Hendrickson A. A.
Published: February 2004

A new dislocation etchant for silver reliably reveals etch pits at both grown-in and fresh dislocations without decoration treatments. This etchant and the modified Levinstein-Robinson etchant are compared by detailed examination of the etch-pit morphology and the dislocation distribution patterns around microindentations. This etchant produces conical-shape etch pits and selectively etches only edge dislocations of one sign.
Metastable Densities in Noble-Gas Plasmas Created by Nuclear Radiations
Authors: Guyot J. C. , Miley G. H. , Verdeyen J. T.
Published: February 2004

Optical absorption measurements of metastable densities in plasmas of He, Ne, and He–Ne are reported. The plasmas were created through bombardment of the gases by the products from the boron−10 (n, α) lithium−7 nuclear reaction during irradiation by neutrons from a pulsed nuclear reactor. The experiments covered gas pressures up to 900 Torr, with neutron fluxes from 1012 to 1016 n/cm2sec. The He(21S), He(23S), Ne (1s5), and Ne(1s3) metastable densities were studied in the single gases and in (9/1) He–Ne mixtures. In general, the observed densities increase with pressure up to about 100–200 Torr after which collisional losses, combined with a decrease in the source rate, eventually cause the metastable populations to fall off. The variation with neutron flux typically changes from a linear to a square-root dependence whenever the destruction by electron superelastic collisions is the dominant loss mechanism. Maximum He(23S) and He(21S) densities of the order of 10−2 to 10−3 and 10−4 to 10−5 atom/cm3 unit flux, respectively, were measured; peak Ne(1s5) and Ne(1s3) densities were roughly 10−3 to 10−5 and 10−4 to 10−6 atom/cm3 unit flux, respectively, depending on the flux level. For pressures below 20 Torr, the Ne-metastable densities in the (9/1) He–Ne mixture were as much as ten times the densities in neon (at a pressure corresponding to the Ne partial pressure in the mixture). A theoretical model is presented which predicts the behavior of the metastable densities quite well, the largest discrepancy being for He(23S) in helium.
A Pulsed Source of Fast Hydrogen Atoms
Authors: Barr W. L.
Published: February 2004

A large pulse of energetic H atoms was produced by charge-exchange neutralization of the plasma from a washer-stack plasma gun. The neutral atoms had a broad energy spectrum peaked at about 630 eV. Limiting effects apparently due to the buildup of cold plasma were observed in the pulsed gas neutralizer. No such limiting was observed when a honeycomb collimator was used to produce the gas for charge exchange. Within a half-angle of 0.65 deg, 7×1013 H atoms per pulse were detected. A diagnostic technique using a pulse of fast neutrals is suggested, and ways to increase the mean energy and the total output are discussed.
Dispersion Characteristics of Electromagnetic Cyclotron Harmonic Waves in Warm Plasmas
Authors: Lee Kai Fong
Published: February 2004

A discussion is given on the dispersion properties of the electromagnetic ordinary wave propagating perpendicular to a uniform magnetic field in collisionless warm plasmas. In addition to the cold-plasma prediction that the wave is propagating when its frequency exceeds the plasma frequency, the Vlasov theory predicts the existence of propagation bands in the neighborhoods of the harmonics of the cyclotron frequencies. Detailed results are given for the first three electron cyclotron harmonics. It is found that the bandwidths increase with β∥ and T∥/T⊥, where β∥ is the parallel electron thermal pressure to magnetic pressure and T∥ and T⊥ are the electron temperatures parallel and perpendicular to the field, respectively. For β∥ values of unity or higher, the propagation band around the first harmonic is sensitively dependent on the ratio T∥/T⊥. In the limit of T⊥→0 but T∥ remaining finite, the second and higher harmonics vanish while the first harmonic can extend to a small fraction of the cyclotron frequency.
Surface Charging of Insulators by Ion Irradiation
Authors: Vance Dennis W.
Published: February 2004

The charging of insulating surfaces by irradiation with gaseous ions is discussed from the viewpoint of basic interactions between individual ions and surfaces. Experiments are reported in which mass-selected beams of low-energy positive and negative ions are used to irradiate insulating amorphous selenium films. The surface-charging efficiency (the number of charges retained on the surface per incident ion) is found to be initially equal to 1, independent of the ion species and ion kinetic energy. As charge accumulates on the surface, the charging efficiency decreases, the extent of decrease being a function of species and kinetic energy. The results are shown to be consistent with a model in which the ion injects a hole or electron into the solid and the injected carrier is trapped in a surface state. The deviation of the charging efficiency from unity arises as a result of free carrier generation in the solid by means of a transfer of kinetic and/or potential energy from the neutralized ion. Implications of the selenium results to insulator charging in general are considered.
Anomalous Longitudinal Magnetoresistance in Metals
Authors: Reed W. A. , Blount E. I. , Marcus J. A. , Arko A. J.
Published: February 2004

A theoretical model and experimental data on chromium and tungsten are presented which show that poor lead geometry combined with a highly anisotropic magnetoconductivity can produce a ``zero resistance'' when the magnetic field is parallel to the current.