bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic Harmonic Generation in Piezoelectric Semiconductors
Authors: Wu Chhi-Chong , Spector Harold N.
Published: February 2004

Second-harmonic generation of ultrasound in piezoelectric semiconductors is investigated using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The effects of collisions are neglected so that our treatment is valid only for ql≫1. It is shown that the amplitude of the second harmonic can be expressed in terms of the fundamental using the linear and nonlinear conductivity tensors. The latter quantities are related to the current densities which are linear and nonlinear in the piezoelectric fields generated by the ultrasound. The linear and nonlinear conductivities are calculated using the parabolic and nonparabolic models for the energy bands of a semiconductor. It is found that only those sound waves which induce longitudinal electric fields will contribute appreciably to second-harmonic generation. For waves propagating parallel to a magnetic field, we find that the amplitude of the second harmonic is independent of the magnetic field for the parabolic model. It is also found that the acoustic flux in the second harmonic will peak at sound wave vectors of the order of the Debye wave vector. In contrast, for the nonparabolic model it is found that the amplitude of the second harmonic depends upon magnetic field. The results of the calculation are applied to n-type InSb, and the magnitude of the second-harmonic generation is estimated for ultrasonic frequencies in the microwave region. It is found that the magnitude of the second harmonic is considerably enhanced using the nonparabolic model over what would be predicted using the parabolic model.
Cesium Adsorption on W: Ellipsometry, Auger Spectroscopy, and Surface Potential Difference Studies
Authors: Smith Tennyson
Published: February 2004

A study has been made of cesium adsorption of W and Ti using the combined measurements of ellipsometry, Auger spectroscopy, and surface potential difference measurements. The single and polycrystals of W have been cleaned in ultrahigh vacuum (∼2×10−10 Torr) and the cesium deposited as an ion beam at low voltages (5–30 V). The deposition of Cs+ did not occur unless some oxygen was detected on the sample by Auger spectroscopy. The sticking coefficient for Cs/W proved to be directly proportional to the concentration of oxygen on the W in the range 0–0.1 fraction of a monolayer oxygen coverage. The optical constants of bulk Cs can be used to interpret ellipsometric results for the adsorption of Cs on W and Ti in the region above, at and below monolayer coverage. The coverage obtained for the work-function minimum is consistent with earlier work by Taylor and Langmuir.
Voltage Dependence of Cathode-Ray Efficiency of Phosphors: Phosphor Particles with Nonluminescent Coatings
Authors: Kingsley J.D. , Prener J.S.
Published: February 2004

The cathodoluminescence intensity as a function of the accelerating potential was measured for a number of powdered ZnS:Cu phosphors, each of which had a thin nonluminescent ZnS coating of known thickness deposited upon every grain. The luminescence efficiency is dominated by the power loss of the electron beam in the nonluminescent coating. The efficiency-voltage curves were analyzed in terms of the electron power loss function proposed by Makhov. Very good agreement with the experimental results was achieved after correcting for the nonplanar surface of the phosphor particles and the intrinsic surface deexcitation.
Thermal Conductivity of Bone at Low Temperatures
Authors: Chu T.K.
Published: February 2004

The thermal conductivity of a bone sample at cryogenic temperatures has been measured. Interpretation of the result was made in terms of the phonon mean free path. It is found that the phonon mean free path is related to the size and the gross structure of the hydroxyapatite crystallites in bone.
Magnetic properties of sputtered Ni–Fe and Fe–Co alloy lasers
Authors: Philipp H.R. , Tiemann J.J.
Published: February 2004

The initial permeability, the position and magnitude of the maximum permeability, the intrinsic magnetization, the coercivity and the remanence are given for 21 different compositions in the Ni–Fe and Fe–Co alloy system. The B-H loop tracer used in these measurements is described.
A note on the bandwidths of electromagnetic ion cyclotron harmonic waves in plasmas
Authors: Lee Kai Fong
Published: February 2004

It is shown that the propagation bandwidths of electromagnetic ion cyclotron harmonic waves in hot and collisionless plasmas are of the order (T∥ime / T⊥imi)Ωi, where T∥i/T⊥i is the ratio of parallel to perpendicular ion temperatures, Ωi is the ion cyclotron frequency, and me/mi is the electron-to-ion-mass ratio.
An azimuthally symmetric unidirectional ion cyclotron wave exciter
Authors: Hipp J.E. , Kristiansen M. , Hagler M.O.
Published: February 2004

A unidirectional device for excitation of azimuthally symmetric (m = 0) ion cyclotron waves is proposed. This work is related to the m = ± 1 traveling wave coupler which was described by Hipp, Kristiansen, and Hagler (Ref. 4). The m = 0 coupler is analyzed theoretically and numerical calculations are made of maximum loading resistance and directivities as functions of plasma density. Directivities of better than 0.99 are found.
Combination of a power transmission line and an active track for a magnetically suspended high-speed train
Authors: Clark Alan F.
Published: February 2004

The idea of utilizing proposed cryogenic power transmission lines as an active track for magnetically suspended high-speed ground transportation is briefly explored. The advantages of transporting both people and power on the same right of way are many, and proposed transmission current levels are more than adequate for suspension.
A linear stability analysis of an interface in an isothermal phase transformation with a concentration-dependent diffusion coefficient
Authors: Wollkind David J.
Published: February 2004

A linear stability analysis of a moving planar interface between the liquid and solid phases in an isothermal phase transformation is carried out with the diffusion coefficient assumed to be a slowly varying function of concentration. The results of this analysis show that for the precipitation system under consideration (one in which the distribution coefficient, a ratio of the equilibrium concentration of solute on the solid side of the interface to that on the liquid side, is greater than unity), there is a destabilizing influence if the diffusion coefficient is an increasing function of concentration and a stabilizing one if it is a decreasing function.
Cerenkov and transition radiation in space-time periodic media
Authors: Elachi Charles
Published: February 2004

The solution to the problem of determining the radiation emitted by a uniformly moving charged particle in a sinusoidally space-time periodic medium is obtained. The space-time periodicity can be considered as due to a strong pump wave and is expressed as a traveling-wave-type change in the dielectric constant or the plasma density. The solution covers also the limiting case of sinusoidally stratified media. The expression and spectrum of the radiated electromagnetic field are determined for different media: dielectric, isotropic and uniaxial plasma. Depending on the nature of the medium and the velocity of the particle, the radiated field is of the Cerenkov and/or transition type. The Brillouin diagram is used extensively in understanding and determining the nature, extent, and spectrum of the different modes of radiation, and a focusing effect is also studied.
ac electrical properties and I-V characteristics of MoO3 film under dc bias
Authors: Nadkarni G. S. , Simmons J. G.
Published: February 2004

The ac electrical properties and the I-V Δ characteristics of Au–MoO3–Au thin-film sandwiches were measured under dc voltage bias. The capacitance of the samples is a strong function of the temperature and dc voltage bias. It increases as much as a factor of 20 for a 2900-Å-thick sample as the temperature is increased; this variation is reduced with increasing voltage bias. At 325 °K the capacitance is a strong function of the dc voltage bias, decreasing from its zero-bias value by about 50% at V = 1.5 V. The voltage dependence of the capacitance decreases with decreasing temperature, and at T = 77 °K it is essentially voltage independent. The conductance is also observed to be strongly dependent on temperature and dc voltage bias. For V≲0.6 V, it initially increases strongly with increasing temperature and reaches a maximum value at about 310 °K. With further increase in temperature, it decreases to a minimum value and then increases monotonically. For V≳0.6 V, the conductance increases monotonically with increasing temperature. The I-V characteristics under dc bias are essentially thickness independent for V≲0.6 V and thickness dependent for V≳0.6 V. All the results are interpreted in terms of a self-consistent model that incorporates Schottky barriers at the two metal-insulator interfaces and a conduction process that exhibits an electrode-limited to bulk-limited transition occurring at V ≅ 0.6 V.
Magneto-microwave free-carrier absorption in germanium in the Faraday configuration
Authors: Srivastava G. P. , Sethi B. R. , Agarwal S. K.
Published: February 2004

The variation of the transmitted amplitude ratio in ln[E(B)/E(0)] and its correlation with Faraday rotation, i.e., (1/γ)ln[E(B)/E(0)] have been studied as a function of magnetic field in the Faraday configuration in a series of n- and p-type germanium samples, (111) and (110) oriented, with resistivity lying in the range 30–1.5 Ω cm at 24.0 and 31.9 GHz at room temperature. From the measured data, the values of the Hall mobility and scattering parameter 〈τ3〉/〈τ2〉 〈τ〉 in the n-type samples and the light-hole mobility in the p-type samples have been evaluated using the expressions of Furdyna and Brodwin. The values of the Hall mobility have been compared with the directly measured values by the van der Pauw technique.
Calculated efficiency of dye lasers as a function of pump parameters and triplet lifetime
Authors: Pappalardo R. , Samelson H. , Lempicki A.
Published: February 2004

The rate equations governing pulsed laser operation in dyes have been solved numerically and the results discussed for a variety of material parameters and pump conditions, especially for pulses in excess of 1 μsec. The resulting laser parameters have been considered as a function of the triplet lifetime and the pump peak power. Calculated values of the efficiency in the conversion of pump light into laser light have been derived in general, and applied specifically to the case of Rhodamine 6G. The calculated efficiencies have been compared with known experimental results on Rhodamine 6G under laser and flashlamp excitation. The agreement is generally good. Since the predicted efficiencies for laser operation in excess of a few hundred nanoseconds depend critically on the values of the triplet lifetime τp in solution, especially for τp in the range 100–300 nsec, the results of the calculations can be reliably compared to experiment only when precise values of the triplet lifetimes become experimentally available.
Bulk effects in photoluminescence measurements
Authors: Fabre E.
Published: February 2004

It is shown that in some particular cases, photoluminescence measurements may involve not only the thin superficial layer of a semiconductor, but also the bulk of the material. This is the case with a p-type or highly compensated n-type GaAs epitaxial layer deposited on a GaAs substrate. A model of ``secondary luminescence effects'' is given to explain the observed anomalies.
Laser desorption of submonolayers of Na and Cs from Ge substrates
Authors: Chen J. M. , Chang C. C.
Published: February 2004

Laser-pulse desorption of submonolayers of Na and Cs from Ge (100) substrates has been studied. It is found that fractional amounts of Na and Cs adsorbates can be desorbed without mechanical damage of the substrate. The fraction of alkali desorbed increases with increasing alkali coverage. The amount of desorption reaches saturation, however, with increasing number of laser-pulse bombardment. Contrary to the results of thermal-desorption experiments, Cs is desorbed more readily than Na.
Application of Monte Carlo calculations to quantitative microanalysis of alloy systems
Authors: Nishigori N. , Shimizu R. , Murata K.
Published: February 2004

The Monte Carlo technique based on the multiple-scattering theory of Lewis was extended to enable the simulation of electron scattering in a compound. The accuracy of this Monte Carlo simulation was assessed by applying it to the electron probe microanalysis of Cu–Al and Fe–Al binary systems. The results were compared with those obtained by the other quantitative correction methods to conclude that this approach is comparable to the others in accuracy, and is applicable in the cases of much wider experimental conditions, e.g., tilting incidence, etc.
Laser shock-induced microstructural and mechanical property changes in 7075 aluminum
Authors: Fairand B. P. , Wilcox B. A. , Gallagher W. J. , Williams D. N.
Published: February 2004

Stress waves generated by a giant pulsed laser were used to change the in-depth microstructural and mechanical properties of 7075 aluminum. The 0.2% offset yield strengths of 7075-T73 and unaged 7075 aluminum were increased as much as 30% over unshocked values. Microstructural analyses showed that laser shocking induced a tangled dislocation substructure similar to explosively shocked aluminum.
Simple model of soft x-ray photoemission
Authors: Schaefer R. R.
Published: February 2004

A simple model of the photoelectric yield is proposed and predictions of the yield and yield spectrum based upon this model are compared with published experimental data for aluminum. Furthermore, simple expressions for the electron emission current for arbitrary incident photon fluxes are derived for the higher-energy components of the photoelectric yield. Since the electrons are assumed to propagate isotropically, no distinction is made between forward and backward scatter.
Spectroscopic analysis of high-current free-burning ac arcs between copper contacts in argon and air
Authors: Slade P. G. , Schulz-Gulde E.
Published: February 2004

A technique has been developed to take short-time-exposure photographic spectra of ac arcs between separating electric contacts. In these experiments the arc was formed in both argon and air between copper electrodes which separated a total of 0.96 cm. Side-on spectra were taken for five axial positions at ±500 μsec around the current maximum (1100 A). In order to obtain a symmetrical arc with less than 0.01% copper vapor impurity, freshly polished electrodes had to be used each time the arc was formed. The spectra were used to calculate the arc temperature and the arc radius. The argon arc had a maximum temperature of 16 000 K and a diameter of 1.6 cm. The air arc had a temperature of 21 000 K and a diameter of 0.7 cm. The assumption of LTE (local thermodynamic equilibrium) which was used in the analysis of these arcs, was shown to be a reasonable assumption for the argon arc. The random introduction of a small percentage of zinc vapor into the argon arc was analyzed and found not to affect the assumptions made in this investigation.
Radiation blistering of polycrystalline niobium by helium-ion implantation
Authors: Das S. K. , Kaminsky M.
Published: February 2004

The radiation blistering of polycrystalline niobium surfaces at room temperature has been investigated for different doses of helium ions implanted at 0.5 MeV and for different amounts of initial defect structure in the samples. The cold-worked samples show large blisters (up to 500 μm in diameter), many of which are ruptured. In samples annealed before irradiation, the blistering at low doses (0.1 C/cm2) was lower than in the cold-worked sample, but at a higher dose (1.0 C/cm2) the blistering was even greater. The observation of interconnecting bubbles offers a possible explanation for the formation of such large blisters at low temperatures.
Relationship between resistivity and total arsenic concentration in heavily doped n - and p -type silicon
Authors: Fair Richard B. , Weber Gary R.
Published: February 2004

It has been observed that considerable discrepancy occurs between total As in Si diffusion profiles obtained by Irvin's curve and those determined by neutron-activation analysis. This discripancy can be explained in terms of the formation of inactive [VSiAs2] complexes. Under conditions of equilibrium between As+ ions and [VSiAs2] complexes, it is possible to derive the relation-relationship between total As, CT, and bulk resistivity, ρ, by using Irvin's curve as a standard. It is shown that a single CT-vs-ρ curve is not sufficient because of the temperature and initial Si substrate dopant dependence of [VSiAs2] complex formation. Equilibrated near-Si-surface As data obtained by activation analysis and resistivity measurements are presented to verify the theory. Excellent agreement is obtained. The important result of this study is that it is now possible to determine partially the As CT(x) diffusion profile from four-point probe measurements and anodic sectioning of the Si. While this technique can only be used over approximately the first 50% of the diffused layer, the rest of the CT(x) profile can be estimated from the electrically active As profile, CA(x) (determined by Irvin's curve) and an equation relating CT(x) to CA(x).
Thermal switching in thin glass films triggered by a control electrode
Authors: Schuöcker Dieter
Published: February 2004

A new three-electrode glass switch device is described that shows performance like a thyrister. The planar electrodes are obtained by dividing a chromium layer by two perpendicular gaps in four parts. Two of these parts are connected and form the common electrode. The two remaining parts are used as control electrode and load electrode. The device is in the on state, if the load electrode is connected by a conducting filament to the common electrode. Investigations of the performance of the new device show that the load diode can be triggered by a voltage pulse supplied to the control electrode if the control diode is in the off state. It can also be triggered by a current pulse supplied to the control electrode, if the control diode is in the on state and operated by a dc current. The measured performance of the new device is explained under the assumption that in both diodes a thermal-switching mechanism takes place.
New method of improving the stability of superconductors against flux jumping
Authors: Sutton J.
Published: February 2004

The threshold magnetic field for flux jumping in a bulk irreversible type-II superconductor is known to be independent of its bulk critical current density. The present analysis shows that the flux jump field should be enhanced in a laminated superconductor in which the surface layer has a lower critical current density than the underlayer. For very large critical current density ratios, the limiting enhancement is 41%; for a 1:4 ratio the improvement is 32%. Experiments on laminated samples of Nb–48 wt% Ti alloys demonstrate an improvement in stability which is in good agreement with the theory. The technique may be useful in increasing the overload current rating of an ac superconducting power cable.
Ultrasonic reflection of a bounded beam at Rayleigh and critical angles for a plane liquid-solid interface
Authors: Neubauer Werner G.
Published: February 2004

Limited beams of low MHz ultrasound are directed at plane interfaces between water and different solids. Reradiated energy is observed by means of schlieren visualization outside the region predicted by Schoch for incidence at the Rayleigh angle. Some of the solids have properties that would cause prediction of a beam displacement many times that for aluminum. Previous thoery would predict the reflected beam to emerge totally separated from the incident beam for several of the materials used, but no such separation is observed. It is concluded that the reradiated field is composed of specular reflection and Rayleigh-wave radiation at and near the Rayleigh angle. These two radiations are out of phase at low MHz frequencies, and where they coexist and are of equal amplitude, which occurs within the specular region, a null strip occurs. This strip is sharply defined at exactly the Rayleigh angle. Surface waves (sometimes called pseudosurface waves) are also generated at the longitudinal and shear critical angles. These are also shown to radiate into the fluid but are generated to a much lesser degree and are difficult to demonstrate by schlieren visualization.
Use of oblique shock waves in high-temperature shock-tube studies
Authors: Sandeman R. J. , Stalker R. J. , Benneworth R. L. , Boreham B. W.
Published: February 2004

The use of the oblique shock wave generated by a wedge, as a means of increasing the gas thermodynamic energy per unit mass available in a shock tube, is considered. In experiments with argon, a homogeneous sample of test gas was produced at energies of 20 eV per atom.
Improved methods for measurement of thermal neutron dose by the fission track technique
Authors: Seitz M. G. , Walker R. M. , Carpenter B. S.
Published: February 2004

We describe scanning electron microscope and reflected light observations of fission tracks that lead to highly reproducible track density measurements for different observers. These new observational techniques are used to calibrate two uranium-doped glasses for neutron dose measurements. The glasses are available to other investigators.
The epitaxial growth of sphalerite and wurzite ZnSe on a (111)Ge surface
Authors: San Aung
Published: February 2004

Epitaxial ZnSe/(111)Ge has been obtained for substrate temperatures from about 180°C to beyond 450°C by the sublimation of a ZnSe source in a vacuum of 1×10−6 Torr during growth. The predominantly sphaleriteor wurzite-structure epitaxial films obtained were found to be dependent on the substrate temperature and their epitaxial perfection to the deposition rate.
Measurement of high-temperature thermal conductivity of Lucalox (Al2O3) using a heat pipe technique
Authors: Forman Ralph
Published: February 2004

The thermal conductivity of Lucalox, a high-purity form of aluminum oxide, has been measured over the temperature range 870–1400°C. The technique employed is a novel one using a lithium-filled heat pipe in series with a gas gap variable heat conductance unit as a heat source. The procedure enables one to measure heat flux through the sample directly. The measurements indicate that the thermal conductivity of high-purity aluminum oxide has a minimum value of about 0.05 W/cm°C at 950°C and increases with higher temperatures to values in the range of 0.3 W/cm°C at 1400°C.
Scattering of microwaves by a stratified overdense plasma at high collision frequencies
Authors: Klein Milton M.
Published: February 2004

A study has been conducted, for several electron-density distributions, of the reflection of electromagnetic waves from stratified overdense plasmas in which the rate of collision frequency to incident frequency is large and the transmission negligible. With positive power profiles where the density changes slowly near the turning point, the reflection coefficient is small, whereas for inverse power profiles where the density gradient is large near the turning point, the reflection is large. In the case of a symmetric type of profile where the maximum density is finite, the results are dependent upon profile type. In an inverse profile type, the reflection is fairly sensitive to maximum density, decreasing with it. With a Gaussian distribution, reflection increases slowly with maximum density, whereas for a sech2 model, the reflection is, for the most part, independent of this parameter.
Microbial degradation of polymer solids: Effect of pretreatments on degradability of cellophane
Authors: Bradley S. A. , Carr S. H.
Published: February 2004

Specimens of regenerated cellulose films (cellophane) have been subjected to a pretreatment followed by microbial degradation. Pretreatments included mechanical deformation, acid hydrolysis, and alkaline degradation, and the subsequent fungal deterioration process was monitored by x-ray diffraction, infrared spectroscopy, and tensile property tests. Longitudinal prestraining of films, which produces small surface cracks, caused accelerated weakening due to action of cellulase enzymes; transverse prestraining of films, which produces internal reorganization but no surface cracks did not lead to any significant change in degradation rate. Nonenzymatic hydrolysis appeared to cause recrystallization of cellulose chain segments cleaved in disordered regions, and subsequent fungal degradation was found to remove these recrystallized regions preferentially.
Steady waves in ductile porous solids
Authors: Carroll M. M. , Holt A. C.
Published: February 2004

A porous material is idealized as a suspension of voids in an incompressible ductile matrix. A constitutive equation for this ideal material is based on a rate-dependent pore-collapse relation obtained previously from a spherical model calculation. This theory is used to study the propagation of steady waves; closed-form expressions are obtained for the Hugoniots and the differential equation for the steady wave profiles is integrated numerically. A feature of the theory is prediction of a finite compaction pressure Pc such that shocking to pressure P* causes partial compaction if P* < Pc and total compaction if P* ≥ Pc. We also discuss a qualitative difference in the behavior of the rate-dependent energy for these two situations.
Photostimulated exoelectron emission from slip lines: A new microscopy of metal deformation
Authors: Baxter William J. , Rouze Stanley R.
Published: February 2004

In this paper we show that photostimulated exoelectron emission resulting from the plastic deformation of a metal originates solely from the slip lines produced on the surface. Conclusive evidence is provided by micrographs formed by direct electron optical imaging of the exoelectrons. The exoelectrons are emitted only from bare metal revealed by a localized rupturing of the natural surface oxide during the formation of the slip step. This contrast mechanism is unique and offers a new form of electron microscopy for the study of plastic deformation of metals.
Concentration contours in regions with both normal and enhanced diffusion coefficients
Authors: Cherednichenco D.I. , LePage W.R. , Anderson R.L.
Published: February 2004

Formulas are obtained for impurity concentration where diffusion is from a surface, and the diffusion coefficient is a step function across a plane boundary normal to the surface. Asymptotic expressions are obtained for the case in which the ratio of the diffusion coefficients is large. The results are applicable to diffusion in materials having regions of enhanced diffusion coefficient, such as irradiated semiconductors.
Extension of the double resonator technique
Authors: EerNisse E. P.
Published: February 2004

The application possibilities of the double resonator technique for simultaneous thin-film areal mass density and integrated lateral stress measurements have been expanded by removing the requirement of equal film thicknesses on both resonators. Several situations with either or both of the integrated stress or the areal mass density being proportional to film thickness are treated. The new equations are tested with Er metal film deposition and hydriding results.
Resistivity study of single-crystal silver films from 4.2 to 56°K
Authors: Nagpal V. P. , Duggal V. P.
Published: February 2004

An analysis of the results of electrical resistivity measurements from 4.2 to 56 °K for single-crystal Ag films shows the nature of the temperature variation as predicted by the theory of Azbel and Gurzhi based on the Olsen effect.
Transient ion neutralization by electrons
Authors: Wilhelm H. E.
Published: February 2004

The nonlinear initial-boundary-value problems describing the lateral neutralization of ion beams for the cases that (i) an auxiliary electric field accelerates the electrons into the ion space, and (ii) the electrons are injected into the ion space at a prescribed current density are treated. Analytical solutions are derived which give the position and speed of the neutralization front as a function of time, and the temporal development of the electron density, velocity, and electric fields during the neutralization process.
Double injection in cylindrical germanium structures
Authors: Lee D. H.
Published: February 2004

Current-voltage characteristics and electric field distributions have been measured on large hollow-core coaxial germanium devices operating in the double-injection semiconductor regime. The I-V characteristics obey an I α V2 relationship and the magnitude of the current is predicted to within a factor of 2 by I = δqμpμnτ (p0−n0)V2, where the term δ is a constant scaling factor dependent upon the concentric cylindrical geometry. The shape of the electric field is obtained from potential probe measurements taken along the radius r of a p+ − π − n+ structure with the current density directed radially outward. In this case the field follows an E α [(r2/r)2 − 1]1/2 dependence over the central portion of the device and diffusion effects are present at the inner (r1) and outer (r2) injecting boundaries. A first-order correction for diffusion at the contacts is made by the application of an effective radii difference r2eff − r1eff = r2 − r1 − 2QLa, where La is the ambipolar diffusion length and Q is a constant with values ≈ 0.5. A small-signal equivalent circuit representation for double injection in the concentric cylindrical geometry is established from impedance measurements over the frequency range 103≲ω≲106. Field and charge carrier distributions for cylindrical double injection in the diffusion-dominated regime are also discussed.
Evolution of steady shock waves in polymethyl methacrylate
Authors: Nunziato Jace W. , Schuler Karl W.
Published: February 2004

The observation of steady shock wave profiles plays an important role in the characterization of the dynamic response of viscoelastic solids. Here we consider the evolution of such wave profiles in polymethyl methacrylate (PMMA) in plate-impact experiments. On the basis of some experimental observations, we determine a lower bound on the propagation distance required for the development of a steady wave for a given impact velocity. This result can then be used to estimate the minimum sample thickness required for the observation of steady shock waves in PMMA and in other polymers with similar structure.
A new electric field effect in silicon solar cells
Authors: Mandelkorn Joseph , Lamneck John H.
Published: February 2004

The phenomenon of high-resistivity silicon solar cells manifesting high open-circuit voltages previously observed only for cells made from low-resistivity silicon is shown to be caused by the presence of a shallow diffused region at the back surface of the cell. The basic cell structure is either n+, p, p+ or p+, n, n+. The high open-circuit voltage arises from the injection and accumulation of excess majority carriers in the bulk upon illumination or application of forward bias to the structure. A working model for the cell, designated a back surface field (BSF) cell, is described, and recent developments are cited.
Isochronal annealing studies of a plastically deformed ferromagnetic metal using magnetic hysteresis measurements
Authors: Milstein Frederick , Baldwin John A. , James Timothy W.
Published: February 2004

An experimental study has been made of magnetic hysteresis in plastically deformed and annealed gadolinium (Gd) metal as a function of annealing temperature. Seven plastically deformed samples were annealed at temperatures ranging from 155° to 916°C; major and minor magnetic hysteresis loops of these seven samples plus one as-deformed sample were examined. The results are discussed in terms of the recovery and recrystallization processes. The measurements of magnetic parameters clearly show three distinct regions of behavior, viz., the regions of annealing temperature Ta<300°C, 300<Ta<500°C, and Ta<500°C. These regions are identified as regions of recovery, recrystallization, and completed recrystallization plus additional grain growth, respectively. Two distinct advantages of the magnetic measurements are (i) using the magnetic measurements, it was found possible to distinguish between metallurgical processes which are not easily detectable using traditional measuring techniques, and (ii) the weak-field magnetic parameters were found to be extremely sensitive to changes in microstructure resulting from the isochronal anneals. The weak-field (or Rayleigh) hysteresis-loop data are analyzed in terms of a spring model of domain-wall pinning by defects. Good qualitative agreement is found between experimental results and predictions based upon this model.
Eddy current measurements on ultrapure molybdenum and rhenium
Authors: Riherd M. C. , Schreiber R.
Published: February 2004

An extension of the well-known eddy current method for measuring the resistivity ρ of low-resistivity specimens is described. The induced voltage in a pickup coil around a cylindrical sample is given, for a sudden field change, as V(t)∝∑n=1∞exp[−λn2α(ρ)t]. The usual procedure requires the measurement of V(t) for values of the time t such that only the first term in the sum need be considered. For low-resistivity metals, this method requires a long observation time (several seconds) and a low-noise high-gain amplifier. By including the first M terms in this expansion, the amplifier requirements and the observation time may be reduced. Resistivity data with an estimated error of less than 5% have been obtained for several ultrapure samples of Mo and Re at 4.2 K.
Plasma-resonance scattering studies of the formation of alkali metal particles in inert gases
Authors: Mann D. M. , Broida H. P.
Published: February 2004

Plasma-resonance light scattering has been observed from alkali metal particles condensed from atoms in a flowing inert gas. Lithium, sodium, potassium, rubidium, and cesium vapors were found to spontaneously form particles from 0.5 to more than 200 Torr inert gas pressure. Wavelengths of observed resonances agree with those calculated for spherical particles of 5–50 nm diameter. Using the resonance peak position as an indication of particle size, it has been possible to study the growth of the particles in situ. . Particle size was found to be a function of the metal, metal vapor pressure, inert gas, inert gas flow rate, and total pressure, with prime factors being the transit time from the furnace to the observation region and metal vapor concentration.
Grüneisen parameter implied by maximum free-surface velocity
Authors: Heyda James F.
Published: February 2004

Using the Walsh-Christian formulation for the isentropes of a solid having the property of maximum free-surface velocity, we obtain the first three terms in the expansion of the Grüneisen parameter in terms of the compression. In addition, we determine the coefficients of the quadratic and cubic terms in the expansion of the shock velocity in terms of the particle velocity. Finally, we show that the Grüneisen parameter for a maximum free-surface velocity solid furnishes an upper bound to the Grüneisen parameter for a given solid. Calculations are given for aluminum and copper by way of illustration.
Avalanche injection and local breakdown in n-type InSb
Authors: Löschner H.
Published: February 2004

If In(3%Te) current contacts are applied to n-type InSb samples, no injection of holes is found up to average electric fields of 70–110 V/cm. Above a certain threshold field, however, intensive hole injection becomes apparent which causes a marked time dependence of the dc conduction characteristic and of the potential distribution even below the threshold field of 250 V/cm for impact ionization in the bulk of the samples. Additionally, accurate ac measurements were performed at 134 GHz, utilizing the small size of the 2-mm rectangular waveguide. These ac measurements help to distinguish a second time-dependent phenomenon caused by local breakdown in regions of high electric field at inhomogeneities in the samples. The method of measurement is very suitable for studying the quality and the properties of the current contacts and the homogeneity of n-type InSb samples.
Ion mass spectrum of borazine (B3N3H6)
Authors: Wilson R. G.
Published: February 2004

Borazine (BH · NH · BH · NH · BH · NH) was ionized in an electron discharge ionization source with a cathode-anode potential of 100 V; however, the energy distribution of the ionizing electrons in the plasma was shown to be less than about 25 eV. The extracted ion beam was momentum analyzed with a 6-in. magnet. The measured masses and intensities are reported; every mass from 1 to 108 amu was recorded, with intensities varying from 0.41 to 10−7 of the total ion beam. As a result of analyzing the ion mass distribution, tentative conclusions are drawn concerning the dissociation reactions and relative probabilities for the breakup of the parent molecules. The strongest components in the spectrum are assigned to hydrogen-type species (masses 1, 2, 3, 4) totaling 14.5%, nitrogen (14, 15, 28, 29, 30, including some hydride) totaling [inverted lazy s]47.5%, the parent group B3N3Hn(6) (75–81) totaling 19%, and the parent grouping less one N2 molecule, B3NHn(6) (47–54) totaling 8.5%. The third element B is only weakly present in the uncombined form (10, 11) at 0.85%. The observed masses heavier than the expected parent molecule B3N3H6 are interpreted to be derived from a small amount of B4N4H8 (masses 100–108); the total intensity of masses 86–108 is [inverted lazy s]0.014%. N2 and NH3 or NH4 are probably easily dissociated from B3N3H6. H2, N2, B2Hn(6), and BHn(6) are probably the strong volatile final products, and B and BN are probably the strong nonvolatile final products of all of the dissociation reactions.
Bubble lattice formation in a magnetic uniaxial single-crystal thin plate
Authors: Shimada Yutaka , Kojima Hiroshi
Published: February 2004

Experimental evidence which may give a solution to the puzzling problem of the contradiction between micromagnetic predictions and experiments on the domain nucleation mode in a thin plate with uniaxial easy axis perpendicular to the plane is reported. It is very likely that a honeycomb structure or a bubble lattice in a remanent state is a result of stripe domain pinching, not an indication of a domain nucleation mode as has generally been speculated. The behavior of domains near saturation when a field is inclined at an arbitrary angle was observed in detail. It was found that a bubble lattice was formed near saturation through a stripe domain pinching for a wide range of the angle between the applied field and the easy axis. Only in a narrow range of this angle do the bubbles survive into a demagnetized state to form a lattice. Furthermore, the domain structures that appear first during demagnetization are not like those of micromagnetic predictions at any intermediate angle of the field between the easy axis and the plane of the sample. They seem rather a result of the initial domain formation at the edges of the sample.
Comments on ``Dielectric relaxation of ZnF2 : LiF''
Authors: Nowick A. S.
Published: February 2004

In recent papers, Roth has presented experimental results on dielectric relaxation in ZnF2 doped with LiF and has discussed the origin in terms of an interstitial defect pair mechanism. This communication points out some errors in Roth's considerations and then discusses the observed relaxation in terms of Li+-fluorine vacancy pairs. Suggestions for further experiments are made.
Switching speed of electrically controlled scattering in PLZT
Authors: Ready J. F. , Brinda R. J.
Published: February 2004

We have measured the speed of switching of PLZT (composition 7/65/35) in the electrically controlled scattering mode of operation. This material may be switched between maximum and minimum transmission within times of a few microseconds. As the pulse duration decreases, the required field increases, reaching approximately 75 kV/cm for 5-μsec pulses.
Strain electricity
Authors: Zaharia C.
Published: February 2004

A potential difference has been observed between two points in a metallic sample in the presence of a strain field gradient. The strain-induced emf is of a transient nature, and we believe that it arises from a time-dependent density gradient in the charge carrier distribution caused by the application of stress. The local charge density change is due to the unit cell deformation and the consequent change in the number of electrons per unit cell. The potential difference is of such direction and magnitude as to reestablish uniform charge density on the surface of the metal specimen. The results reported here are qualitative and relate to two basic deformations, compression and tension. They are also consistent with shear, bending, and twisting, and these effects will be reported elsewhere.
Influence of microstructure on the dynamic high-temperature elastic moduli of aluminum
Authors: Swearengen J. C. , Lipkin J. , Percival C. M.
Published: February 2004

The dynamic elevated temperature elastic properties of single-crystal and polycrystalline aluminum have been studied by employing a laser pulse technique to produce propagating stress pulses in slender rods. The behavior at temperatures between 25 and 500°C of monocrystals and slender polycrystalline specimens having a cold work texture is described. Experimental results are presented for the polycrystals as a function of thermomechanical history and compared to the results for single crystals of known orientation. The results are evaluated in terms of dislocation dynamics and anisotropy of the lattice in single crystals and polycrystals. Results show that the longitudinal wave velocity increases with the annealing of dislocations and then decreases with the disappearance of texture in polycrystals.
Annealing kinetics of sputtered gold-tungsten and gold-molybdenum films
Authors: Christou Aristotelis , Day Howard M.
Published: February 2004

The annealing kinetics of sputtered Au–W and Au–Mo films have been investigated as a function of temperature up to 500°C. The electrical resistivity of the gold layer after deposition was measured to be 1.25 times the bulk resistivity. The excess resistivity was attributed to structural defects such as vacancies, interstitials, twins, dislocations, and impurities which were quenched in during deposition. Particle size changes in Au–W and Au–Mo occur in two stages, with an activation energy for gold of 0.4 eV below 200°C and 0.7 eV above 200°C. The activation energy for the refractory layer particle growth was 1.8 eV up to 500°C. The kinetics of dislocation (Nd) annealing at 500°C was determined to follow an equation of the form Q(Nd) = − A(Nd)m, with m = 3. Annealing the films up to 500°C resulted in a decrease of internal stress in gold from 2.5 × 109 dyn/cm2. The observed results are discussed in terms of microstructural changes and the dependence of internal stress on film thickness.
Electromagnetic surface fields of an inclined buried cable of finite length
Authors: Hill David A.
Published: February 2004

The magnetic fields on the surface produced by a buried current-carrying cable of finite length are considered. A homogeneous half-space model of the earth and quasistatic conditions are assumed. The cable is grounded at its end points and oriented at an arbitrary angle to the interface. While, in general, numerical integration is required, the low-frequency limit may be treated analytically. Small cable tilts are shown to modify the direction of the surface field but not the magnitude. The results have possible application to uplink communication and radio location of trapped miners.
Wave amplification of electromagnetic surface waves supported by a plasma-beam half-space
Authors: Ha K. W. , Seshadri S. R.
Published: February 2004

The characteristics of electromagnetic surface waves supported by a plane interface separating a semi-infinite region of free space from another semi-infinite region consisting of a background plasma permeated by a neutralized beam streaming parallel to the interface are investigated for the case in which the wave is progressing either in, or opposite to, the direction of the beam. As compared to the case of a stationary plasma, the surface wave has new branches and drastically different characteristics. For the case of waves progressing opposite to the direction of the beam, there are backward-wave regions as well as regions of instability if the beam is sufficiently strong. These regions of instability occur below the plasma frequency. In general, there are two frequency ranges of instability in which the surface wave undergoes traveling wave amplification in the direction of the stream. The wave amplification characteristics are studied and their dependence on the number density of the beam relative to the background plasma is examined.
Positive ion ratio measurements in Ar, Kr, and Xe glow discharges
Authors: Fitzwilson R. L. , Chanin L. M.
Published: February 2004

Results are presented of an experimental study of the relative concentration of ions in the positive column of small-diameter noble-gas discharges. The ratio of the molecular ion concentration to the atomic ion concentration has been measured as a function of discharge pressure and current for dc discharges in argon, krypton, and xenon. Discharge pressures and currents were varied from 0.1 to 10 Torr and 15 to 40 mA. A simple theoretical model of the positive column was developed and the pressure dependence of the ion concentration ratio was calculated. By parametrically fitting the predicted ion ratio equation to the experimental data, estimates of several reaction rate coefficients could be derived. Where possible, the ion ratio data and the derived rate coefficients have been compared to previously published data.
Shear strength and friction of copolymers of tetrafluoroethylene with ethylene and hexafluoropropylene under high pressure
Authors: Towle Laird C.
Published: February 2004

A rotating-anvil shear press was used to measure the friction coefficient and shear strength of thin layers of copolymers of tetrafluoroethylene with ethylene and hexafluoropropylene at room temperature at pressures up to 5 kbar. The friction coefficient of both copolymers decreased monotonically, approaching a small asymptotic value at high pressure. The shear strength of both materials increased approximately linearly with pressure. The ethylene copolymer exhibited a small discontinuity suggestive of a polymorphic transformation.
Luminescence of Bi4 Ge3 O12 : Spectral and decay properties
Authors: Weber M. J. , Monchamp R. R.
Published: February 2004

Intense broadband emission in the visible is observed from crystals of Bi4Ge3O12 under optical and x-ray excitation. From measurements of absorption, reflection, fluorescence, and excitation spectra, the emission is assigned to 3P1 → 1S0 transitions of Bi3+. The Stokes shift is large, [inverted lazy s]14 000 cm−1. The temperature dependences of the fluorescence intensity and lifetime in the range 77–400 °K establish that nonradiative decay becomes significant at temperatures ⪞250°K. Comparison of the properties of Bi4Ge3O12 with those of Bi12GeO20 and other bismuth-activated materials demonstrates the importance of the Stokes shift and the 1S-3P energy difference in determining the luminescence behavior. The use of Bi4Ge3O12 as a laser host crystal for rare-earth and iron group activator ions, and as a scintillator material is discussed briefly.
Optical anisotropy effects in magneto-optic memory materials
Authors: Jacobs J. T. , Treves D.
Published: February 2004

The effect of birefringence and dichroism in materials for magneto-optic memory applications is analyzed. The optical constants of MnAlGe and MnGaGe have been measured. The birefringence and dichroism are approximately equal and are an order of magnitude larger than the magneto-optic effect. A statistical analysis of the effect of orientation and grain size on noise due to optical anisotropy is also carried out.