bluuebunny/crossref_metadata_2025 huggingface dataset:
Microfaceting in a tungsten incoherent twin boundary
Authors: Eato H. C. , Bayuzick R. J.
Published: February 2003

Experiments are described in which the field-ion microscope is used to observe the details of grain-boundary migration in polycrystalline tungsten. Annealing is done in situ and the specimen is observed prior to and after several heating pulses. Microfacets are formed during the process which after analysis are observed to differ from those expected when the coincidence site lattice model is assumed to be valid.
Electron-beam annealing of ion-implantation damage in integrated-circuit devices
Authors: Kamins T. I. , Rose P. H.
Published: February 2003

The use of a large-diameter pulsed electron beam to anneal ion-implantation damage has been studied with application to integrated-circuit structures. The annealing of arsenic-implanted p-n junction diodes shows that properly selected exposure to an electron beam can anneal implant damage and provide nearly ideal device characteristics. Tests on MOS capacitor structures show that the electron beam itself introduces states at the Si-SiO2 interface but that these states can be easily annealed during the low-temperature metal alloy cycle. The practical utilization of the concept requires an electron beam uniform over the entire wafer area.
Contrast of a stacking fault in x-ray section topography study of the Laue-Bragg case
Authors: Epelboin Y.
Published: February 2003

We have studied the contrast of a stacking fault in the Laue-Bragg case, i.e., when the wave fields incident from the defect are reflected from its surface and never propagate into the other part of the crystal. To calculate the contrast of such a defect we have computed the images by a direct integration of Takagi’s equations. We show the influence of different parameters such as the geometry of the fault, the fault vector, and the photoelectric absorption. The results are very similar to those obtained by Authier in the Laue-Laue case and the contrast may be explained in a similar manner.
Electrical profiles of magnesium-ion-implanted GaP
Authors: Lank David J. , Dobbs B. C. , Park Y. S.
Published: February 2003

The first controlled differential etching for profiling magnesium-implanted semi-insulating gallium phosphide is reported. Profiles of surface resistivity, mobility, and carrier concentration versus depth below the substrate surface for 129-keV magnesium-ion implants are obtained. Agreement was obtained with glow-discharge optical spectroscopy data from an unannealed implanted substrate. The non-Gaussian profiles indicate ion diffusion during annealing and possibly during implantation. Optimum procedures and techniques are developed for the substrate capping material, the anneal temperature, the capping method, and the application of Ohmic contacts. The carrier concentration of electrically active implanted magnesium ions in gallium phosphide, for a total magnesium-ion dose of 1.0×1013/cm2, is the highest percent efficiency reported (∼44%).
Measurement of grain-boundary diffusion at low temperatures by the surface accumulation method. I. Method and analysis
Authors: Hwang J. C. M. , Balluffi R. W.
Published: February 2003

An analysis of the measurement of grain-boundary diffusion at low temperatures by the surface-accumulation mehod was carried out. In this method atoms are allowed to diffuse along grain boundaries from a source to a free surface where they spread out, accumulate, and are measured. The diffusion is carried out at low temperatures so that only the grain boundary and surface ’’short-circuit paths’’ are active, and lattice diffusion is frozen out. This method is generally more sensitive than the depth profiling method for measuring grain-boundary diffusion at low temperatures. However, the kinetics of the surface accumulation are strongly dependent on the nature of the source and sink. Treating the surface as a sink of finite capacity with a finite diffusion coefficient, diffusion analyses were developed for either a constant or an instantaneous source. Two dimensionless parameters, G and H, play important roles in determining the form of the solutions. H involves the ratio of grain-boundary capacity to surface capacity. G is proportional to the ratio of the grain-boundary diffusivity to that of the surface. When G⩽1 and H⩽1, conditions for uniform concentration on the surface and quasi-steady-state diffusion in the grain boundary are met, and the general solution becomes relatively simple. For a constant source, the surface concentration then obeys the relation cs=1−exp(−st), where s is a parameter proportional to the boundary diffusivity and t is the time. The application of the analyses to a variety of diffusion systems was discussed. It was concluded that the conditions for the simple solutions to apply are not particularly stringent.
The temperature dependence of threshold current for double-heterojunction lasers
Authors: Ettenberg M. , Nuese C. J. , Kressel H.
Published: February 2003

The temperature dependence of the threshold current has been examined for the double-heterojunction lasers (AlGa)As, (InGa) (AsP)/InP, and (InGaAs)/(InGa)P with emission wavelengths between 0.8 and 1.4 μm. For all lasers studied, the threshold current density was found to follow the exponential relationship Jth(T) ∝ exp(T/T0), where the constant T0 was found to be directly related to the energy-band-gap step, ΔEg, between the recombination region and the adjacent confining layers. The value of T0 was found experimentally to obey the relationship T0=AΔEg, with the constant A having values between 200 and 300 °K/eV for the three types of lasers studied.
The use of spectroscopic measurements to evaluate cataphoretic segregation
Authors: Metze Armin , Kuehn D. G. , Chanin L. M.
Published: February 2003

A study has been made on the influence of neutral end volumes on the segregation rates (time-dependent cataphoresis) in the positive column of a 0.01% Ar-Ne gas mixture. The Ar(4200 Å) and Ne(5882 Å) spectral-line intensities were monitored using optical techniques 5 cm from the anode and cathode. The effectiveness of the segregation as inferred from the Ne(5882 Å) intensity is inconsistent with a 0.01% Ar-Ne gas mixture. It is believed that this inconsistency is due to an axial variation of the electron-energy distribution.
Interferometric characterization of density dynamics of an ultradense Z-pinch plasma
Authors: Ackenhusen John G. , Bach David R.
Published: February 2003

We have measured the spatially and temporally resolved density in a Z-pinch plasma by holographic interferometry. The high electron density (4×1019 e/cm3), short density scale length (100 μm), and low temperature (about 20 eV) make the plasma source suitable for simulation of laser-pellet interaction experiments at 10.6-μm laser wavelengths. A cinema of density evolution, indicating plasma pinching and subsequent relaxation, provides an experimental view of plasma dynamics which is then compared to simple theoretical models.
Positron lifetimes in GaAs
Authors: Cheng L. J. , Karins J. P. , Corbett J. W. , Kimerling L. C.
Published: February 2003

The suitability of the positron-lifetime technique to the study of native vacancies in GaAs is demonstrated. Significant variations in positron lifetime among a variety of as-grown GaAs single crystals were observed. The longest positron lifetime was found in undoped samples. Annealing in vacuum at 300–500 °C reduced the long-lifetime component. The results present strong evidence for the existence of Ga vacancies in the as-grown material.
Repetitive readout effect of a polarization echo
Authors: Kimura T. , Onuki K. , Yoshikawa S.
Published: February 2003

The repetitive readout effect of a polarization echo has been experimentally studied, using LiNbO3 powder. The repetitive reading-pulse application causes the readout echo height to increase and to be saturated at certain repetitive reading times. The effect is affected by the writing-pulse-application repetition times.
Efficiency and humidity dependence of WO3-insulator electrochromic display structures
Authors: Stocker H. J. , Singh S. , VanUitert L. G. , Zydzik G. J.
Published: February 2003

Contrast ratio, optical density, efficiencies, coloration, and bleaching times of WO3-insulator (LiF, MgF2) sandwich display structures have been measured and are compared to the characteristics of WO3-liquid electrochromic cells. The efficiencies of the two are comparable, but it is harder to achieve sufficient contrast in the solid-state structures. Measurements in a controlled-humidity environment demonstrate clearly the crucial role of the presence of water vapor in the operation of these sandwich structures. Transport of protons through the insulator is indicated as the rate-limiting mechanism.
Simultaneous measurement of the temperature and the hydrodynamic speed of a thin foil submitted to an intense electronic energy deposition
Authors: Peugnet C. , Roche M. , Delvaux J.
Published: February 2003

We have determined the temperature and hydrodynamic speed of a thin tantalum anode heated by a pinched relativistic electron beam. These measurements were simultaneously realized by analyzing the speed distribution of thermal ions emitted by the plasma. The plasma ions can be represented by a Maxwellian velocity distribution superposed upon an expansion velocity u. In the particular experimental condition with rapid short circuit, the interaction was realized by electrons of low energy. The maximal temperature obtained with a thin 25-μm tantalum anode was of the order of 20 eV and hydrodynamic speed 1.4 cm/μs. The characteristics of the electron beam generator used were 600 kV, 200 kA, and 60 ns.
Identification of TSC peaks and surface-voltage stability in Teflon FEP
Authors: von Seggern Heinz
Published: February 2003

In this paper we examine the stability of corona- and electron-beam-charged 25-μm FEP-A in open circuit by using thermally stimulated (TSC) measurements. We show that electrets charged with electron beams of 10 keV or higher are more stable than corona-charged foils. The inferior stability of corona-charged samples is due to the filling of surface traps as opposed to volume traps in electron-beam-charged samples. A peak at 155 °C was attributed to surface traps located at a depth of 0–0.5 μm, while a peak at 170 °C is due to charge stored 0.5–1.8 μm beneath the nonmetallized surface. The volume traps yield a peak at 200 °C. The total volume trap density was estimated to 1.4×1014 traps/cm3.
Improved approximate analytic charge distributions for abrupt p-n junctions
Authors: Shirts Randall B. , Gordon Roy G.
Published: February 2003

Poisson’s equation is solved approximately in abrupt nondegenerate semiconductor p-n heterojunctions and homojunctions by using the Thomas-Fermi dielectric function to describe free-carrier (Debye) screening with the approximation of a local screening length function. Analytic forms are presented for the electrostatic charge distribution and electrostatic potential, which illustrate features not predicted by the usual Schottky theory. Charge density and space-charge capacitance are shown to change with applied voltage in agreement with exact numerical calculations.
Schottky barriers at the interface between amorphous silicon and electrolytes
Authors: Williams Richard
Published: February 2003

A Schottky barrier forms at the interface between amorphous silicon and an electrolyte. The barrier height, φB, can be estimated from the open-circuit photovoltage. It depends on the potential-determining ion in solution and is a linear function of the redox potential. The magnitude of φB ranged from 1.0 to 1.7 eV for various electrolyte compositions.
Measurement of the work function of some metals using internal voltage in MIM structures
Authors: Gupta S. K. , Kapil A. K. , Singal C. M. , Srivastava V. K.
Published: February 2003

Work functions of some metals (Mg, Mn, Cr, Bi, Cd, Pb, Te, Zn, and Sn) have been determined by using the zero-bias internal-voltage technique in asymmetric electrodes structures of metal/insulator/metal systems. The built-up Langmuir films of barium-stearate have been used as an insulator in these structures, as the thicknesses of the multilayer Langmuir films are known accurately and the effect of the thickness dependence of the internal voltage can be corrected for when obtaining a work function from internal-voltage measurements. Any contribution arising due to alumina (Al2O3) film on base aluminum electrodes has also been accounted for, to give the correct value of the work function. The measured values of the work function by this technique are found to be in agreement with the known data.
Superconductivity in Nb5Si3
Authors: Willis J. O. , Waterstrat R. M.
Published: February 2003

A sample of the high-temperature (β) phase of Nb5Si3, possessing the tetragonal W5Si3 structure, had a superconducting transition temperature T0 of 0.7 K and a transition width of about 0.25 K. The value of −67 mT/K (670 Oe/K) for the initial slope of the curve of the critical magnetic field versus temperature indicates that β-Nb5Si3 is a type-II superconductor. The dominant structural feature of β-Nb5Si3 is the parallel linear chains of closely spaced Nb atoms which occur along the tetragonal c axis. The Nb-Nb intrachain spacing is 0.254 nm, very close to the Nb-Nb spacing of the mutually orthogonal linear chain atoms in a hypothetical cubic A15-Nb3Si structure. The near-neighbor environment of the Nb chain atoms is virtually identical in A15-Nb3Si and β-Nb5Si3. However, the T0 of A15-Nb3Si is expected to be greater than 20 K, much higher than the T0 of β-Nb5Si3. The presence of closely spaced Nb atoms in linear chains therefore does not appear to be a sufficient condition for a high T0. The low-temperature (α) phase of Nb5Si3 was found to be normal down to 0.01 K.
Critical currents for superconducting composites in the 1000-Å regime
Authors: Finnemore D.K. , Verhoeven J. D. , Ostenson J. E. , Gibson E. D. , Sample H. H.
Published: February 2003

Multifilamentary superconducting composites having Nb3Sn filament sizes in the 200–2000-Å regime have been studied in magnetic fields up to 18 T. The critical currents obey Kramer’s scaling laws, and flux pinning at high fields is governed by the flux-line lattice shear modulus C66. Despite the discontinuous nature of the filaments, the flux pinning at the field approaching Hc2 is very similar to the large-diameter continuous filament case. The upper critical field is somewhat lower than bulk Nb3Sn as expected from the stress imposed by the bronze matrix. With the addition of a few percent Ga, Hc2 can be raised by about 2 T.
Anodization rate and augmentation factor of anodic aluminum oxide films
Authors: Birey H.
Published: February 2003

This paper presents a determination method for both the oxidation rate and the augmentation factor of anodic oxide films. The augmentation factor, which is the ratio of pure oxide thickness to that of its initial metallic thickness, is determined by thickness and optical absorption measurements. The oxidation rate is defined as the ratio of oxide thickness to the forming anodization voltage and it is determined from the dependence of thickness on anodization voltage. The augmentation factor and oxidation rate of anodic aluminum films, oxidized in 3% aqueous ammonium tartrate (pH=5.5) at room temperature (∼25 °C), are determined as 1.5 and 13.2 Å/V, respectively. The thickness of the residual metallic aluminum film corresponding to that of the upper limit of the anodic oxide film is estimated as ∼35 Å.
Energy levels and laser action in Nd : CaY2Ge3O12
Authors: Tucker A. W. , Birnbaum M.
Published: February 2003

Fluorescence studies of Nd : CaY2Ge3O12 at 77 and 300 °K has resulted in new level identifications for several transitions. In particular, the dominant laser transition (lower threshold) corresponds to an R2→Y3 transition (1058 nm). Laser action has also been observed at 1065 nm (R1→Y2) over the temperature range 77–300 °K.
Gas discharges in planar, low-pressure thermionic diodes. II. Plasma regime
Authors: Bromberg L. , Smullin L. D.
Published: February 2003

The theory and experiment of a one-dimensional low-pressure discharge is presented. The discharge current is provided by a thermionic cathode that operates space-charge limited. The primary electrons ionize the background gas and also heat the plasma electrons. The plasma characteristics (plasma density, electron temperature, and ion current density) and the discharge current are computed as functions of the discharge voltage and the neutral pressure. The model is self-consistent and requires no experimentally determined parameters.
Evaluation of electron density profiles in plasmas from integrated measurements
Authors: Gottardi N.
Published: February 2003

Obtaining electron density profiles from integrated measurements (e.g., those made with a multichannel interferometer) in the case of asymmetrical plasma distributions often entails serious difficulties. Here we describe a method applicable when the profiles are shifted along the equatorial plane and also when the relation between phase shift and electron density may not be considered as linear (proximity of the cutoff for the exploring wave).
Variation of measured particle velocity distributions with distance from a finite-size plasma
Authors: DeNeef C. P. , Theiss A. J.
Published: February 2003

The distribution function measured using an ideal planar retarding-field energy analyzer external to a finite-size uniform source of particles depends on the location of the analyzer. The error that occurs when this distribution function is used to infer the temperature inside the source is investigated for a variety of source shapes, locations, and potentials when the distribution is both Maxwellian and anisotropic.
Contactless probing of semiconductor dopant profile parameters by ir spectroscopy
Authors: Wagner Hans H. , Schaefer Rolf R.
Published: February 2003

The optical properties of arsenic-implanted and annealed silicon in the infrared are investigated. A theory is fitted to transmittance and reflectance spectra. The fitted profile parameters are correlated with nonoptical measurement results. It is shown that infrared optical measurements offer the capability of probing nondestructively sheet resistance, electrically active dose, and surface concentration. Thus, it is a promising measurement technique for in-line process control.
Structural characterization of amorphous electrodeposited cobalt-phosphorus alloys
Authors: Chi G. C. , Cargill III G. S.
Published: February 2003

The structure of amorphous electrodeposited Co-P alloy foils has been examined by x-ray scattering techniques. Samples with phosphorus contents from 18 to 26 at.% have been examined with large-angle x-ray scattering. Atomic arrangements in these alloys are described in terms of radial distribution functions. Effects of alloy composition on randomness of short-range order, atomic-pair distances, and strength of long-range order have been observed. Evidence of large-scale (10–104-Å) composition fluctuations has been obtained from small-angle x-ray scattering on amorphous Co77.5P22.5 samples. The composition fluctuation regions are anisotropically shaped (rodlike) with their largest extent (≳2000 Å) perpendicular to the foil plane and their smallest extent (∼60 Å) in the foil plane.
Rise-time measurements of shock transitions in aluminum, copper, and steel
Authors: Chhabildas Lalit C. , Asay James R.
Published: February 2003

Time-resolved measurements of shock-wave rise times have been accomplished for aluminum, copper, and steel to stress levels of 41, 96, and 139 GPa, respectively, using velocity-interferometer techniques. To within the time resolution of the technique, the shock transition is found to occur within 3 ns in all materials. Based on this upper limit for the transition time, limiting viscosity coefficients of 1000, 3000, and 4000 P are obtained for 6061-T6 aluminum, OFHC copper, and 4340 steel, respectively, at strain rates above 108 s−1. It is found that the effective viscosity can be expressed as parameters in a Maxwellian relation for an elastic-plastic solid, in which the viscosity is related to an effective relaxation time. It is also shown that viscosity is inversely proportional to mobile-dislocation density, which implies that the density of mobile dislocations obtained during shock compression in these materials is well over 109/cm2.
Raman spectra of vanadium phosphate glasses
Authors: Anderson Gordon Wood , Verble J. Larry
Published: February 2003

The Raman spectra of 60.0, 70.0, and 87.5 mole% V2O5 vanadium phosphate glasses and of crystalline V2O5 were measured at room temperature. Raman bands were observed at frequency shifts of 340, 480, 750, 945, and 1030 cm−1 for 60.0 mole% V2O5 glasses, of 32, 490, 705, and 1025 cm−1 for 70.0 mole% V2O5 glasses, and of 320, 480, 650, and 1010 cm−1 for 87.5 mole% V2O5 glasses. The bands just above 1000 cm−1 are correlated with bands observed in the infrared and Raman spectra of crystalline V2O5. Previously unreported Raman bands were observed at frequency shifts of about 650 and 1025 cm−1 for crystalline V2O5.
An analysis of the dependence of thermal transport parameters on organic content for Green River oil shales
Authors: Wang Y. , Rajeshwar K. , DuBow J.
Published: February 2003

An analysis of the trends in the variation of the thermal transport parameters with organic content (taking thermal diffusivity as an example) is presented for oil shales of the Green River formation. The Cheng-Vachon model gives good agreement with experimental data, for oil shales of medium grade (100–250 l/ton) and for heat flowing in directions perpendicular to the orientation of the shale bedding planes. The degree of anisotropy experimentally observed for thermal conductivity and thermal diffusivity for these materials is much less than that predicted by theory. The marked discrepancy between the experimental data and the trends predicted by theory for heat flow in directions parallel to the shale stratigraphic planes is explained in terms of departure from a strict parallel configuration and an effective lower value for the thermal diffusivity of the mineral phase. Good agreement with experimental data is shown by the geometric mean model and Maxwell’s equation for the parallel case. Possible reasons for the failure of these models at low levels of shale organic content (<∼35% by volume) are discussed.
Electromigration and diffusion of copper in aluminum thin films
Authors: Reddy K. V. , Beniere F. , Kostopoulos D. , Le Traon J. Y.
Published: February 2003

Using an original radiotracer sectioning technique, we have measured the drift mobility, the diffusion coefficient, and the effective valency of copper in aluminum thin films in the temperature range 100–150 °C. The results are interpreted in view of the considerable increase of the lifetime of the electrical contacts on silicon substrates by doping aluminum with copper.
Fourier-Bessel series solution for potential and intensity field of open electron optical systems with rotational symmetry, in terms of I0 Bessel functions
Authors: van der Merwe J. P.
Published: February 2003

A Fourier-Bessel series representation in terms of I0 Bessel functions is given for the potential distribution in certain open Einzel- or immersion-type electrostatic configurations with rotational symmetry described by φ (A,z) =F (z), 0<z<L; and φ (A,z) =0 for all z<0 and for all z≳L. F (z) is a given function and A and L are constants. The method is a direct one—no iterations or matrix inversions are required—and a superior rate of convergence in the paraxial region is achieved through the elimination of J0 Bessel functions. The precision reached is apparently limited by the computer word length only, programming is of a simple nature, and computer memory requirements are modest enough to allow implementation on small desk-top computers.
A numerical method of determining propagation characteristics of guided waves along inhomogeneous planar waveguides
Authors: Hashimoto Masahiro
Published: February 2003

A simple method is presented of numerically solving inhomogeneous planar waveguide problems. The characteristic mode equation given here to determine rigorous solutions is similar to WKB’s mode equation and is solved by the step-by-step numerical method. Examples are given for the sake of comparison with other results.
Accelerated aging test of Ga1−xAlxAs DH lasers
Authors: Ishikawa H. , Fujiwara T. , Fujiwara K. , Morimoto M. , Takusagawa M.
Published: February 2003

An accelerated aging test is performed at temperatures of 70, 110, and 140 °C to estimate the activation energy. Samples are operated in the LED mode at high temperatures of 110 and 140 °C. At 70 °C samples are operated in lasing mode of optical output 0.27 mW/μm. The laser lifetime is defined to be a time at which the cw threshold current measured at a standard temperature 25 °C reaches 1.5 times the initial value. The activation energy 0.74 eV is obtained. It is shown that the degradation does not depend on the optical output power below the power level of 0.3 mW/μm and that the activation energy is indifferent to the operation mode, LED mode, or lasing mode, at a low power level. The use of the LED mode operation and the definition of the laser lifetime in terms of the characteristics at low standard temperature enable one to perform the accelerated aging test at high temperatures above 110 °C where cw operation is almost impossible. The reliability is examined at 70 °C using 50 samples and an average laser lifetime is obtained. The application of the activation energy gives the average laser lifetime at the junction temperature of 30 °C to be 3×105 h.
High-energy electron acceleration by ponderomotive forces in tenuous plasmas
Authors: Boreham B. W. , Luther-Davies B.
Published: February 2003

The results of an experimental study of electrons produced by multiphoton ionization of helium gas by intense 25-psec-duration pulses from a neodymium laser are reported. Electrons with energies up to 300 eV have been observed and both the maximum electron energy and the measured electron-energy spectra are shown to be characteristic of electron acceleration by ponderomotive forces.
Loss measurement in p-type GaAs dielectric waveguides using Raman scattering
Authors: Sergent A. M. , Merz J. L. , Logan R. A.
Published: February 2003

Raman scattering measurements have been made to determine losses in p-type GaAs slab waveguides cladded by Al0.3Ga0.7As epitaxial layers. For these measurements, 1.064-μm laser light is focused onto a cleaved edge of the waveguide layer and the Raman-scattered photons are detected at 90°. The attenuation of the resulting signal is measured as a function of the propagation distance along the waveguide. Five Ge-doped waveguide layer samples, ranging in concentration from 3×1016 to 3×1018 cm−3, were measured. Results are reported for samples 3–5 mm long having layer thicknesses of ∼5–6 μm. Losses from 0.8 to 12.2 cm−1 have been measured. Comparison is made with earlier results in n-type GaAs.
Radiative transfer theory for scattering by layered media
Authors: Tsang L. , Kong J. A.
Published: February 2003

Remote sensing of brightness temperatures of a scattering medium composed of spherical scatterers beneath a homogeneous surface layer is studied by using Mie scattering functions. We illustrate the effects of a surface layer by plotting the brightness temperatures as functions of frequency and viewing angle for different layer thicknesses, dielectric constants, and fractional scattering volumes. It is found that the brightness temperature increases when the loss tangent of the surface layer is increased and when the fractional volume occupied by the scatterers is decreased. In the absence of a surface layer the brightness temperature is usually decreasing as a function of frequency. The presence of a homogeneous layer may cause the brightness temperature to increase with frequency. At all viewing angles the vertical polarization is brighter than the horizontal polarization.
Structures of an electron beam drifting in vacuum and in low-pressure gases
Authors: Luches A. , Nassisi V. , Perrone A.
Published: February 2003

We performed a series of tests on the propagation of intense electron beams with ν/γ?0.40 and 0.85 in a vacuum (∼10−4 Torr) and in a few gases (nitrogen, helium, and carbon dioxide) at pressures ranging from 50 mTorr to 1 Torr. Beam currents were recorded step by step by a Faraday cup movable along the drift-tube axis up to about (1/2) m from the anode of the field emission diode. Current neutralization and almost complete transport of the electron beam along the drift tube occur at different pressures in different gases. Structures in the transmitted currents appear as a function of the drift distance, markedly at pressures slightly lower than that of complete neutralization of the beam. They are in good agreement with Lawson’s predictions.
Guided-radiation mode interaction in off-axis propagation in anisotropic optical waveguides with application to direct-intensity modulators
Authors: Yamamoto Sadahiko , Okamura Yasuyuki
Published: February 2003

A closed-form solution of the coupled-mode equations is derived for the guided–radiation mode interaction in optical waveguides by using a Lorentzian approximation to the coupling-factor distribution. This solution does not neglect reconversion from radiation to guided modes as did the previous perturbation solution. It is thus more accurate for the case of higher-order guided modes for which the power attenuation due to radiation conversion exhibits an oscillatory form and the ’’effective’’ perturbation assumption that the coupling factor is independent of the phase constant is not valid. Peaks in the mode conversion characteristics at certain eigenvalues of the relevant guided mode can be physically interpreted as the coupling to leaky waves. Illustrative examples and related discussions are given for the polarization-rotated (TE→TM) guided-to-radiation mode conversion in off-axis propagation in an anisotropic LiNbO3 waveguide. Also, an electro-optic direct-intensity modulator is described where the angle of propagation is used instead of a dc field to set a bias point for linear modulation.
Theoretical gain-optimization studies in CO2–N2 gasdynamic lasers. II. Results of parametric study
Authors: Reddy N. M. , Shanmugasundaram V.
Published: February 2003

Based on a method presented in detail in a previous work by the authors, similar solutions have been obtained for the steady inviscid quasi-one-dimensional nonreacting flow in the supersonic nozzle of a CO2–N2 gasdynamic laser system, with either H2O or He as the catalyst. It has been demonstrated how these solutions could be used to optimize the small-signal gain coefficient on a specified vibrational-rotational transition. Results presented for a wide range of mixture compositions include optimum values for the small-signal gain, area ratio, reservoir temperature, and a binary scaling parameter, which is the product of reservoir pressure and nozzle shape factor.
A viscoelastic wave propagation model for tungsten at near-melt conditions (3000K)
Authors: Schmidt R. M.
Published: February 2003

Analysis of dynamic response data for tungsten at 3000 K has confirmed the suitability of a linear viscoelastic constitutive relationship which can be used to model material response due to high-strain-rate loadings. Such uniaxial strain loadings are produced by planar impact energy deposition due to electrons or photons.
Acoustoelastic imaging of stress fields
Authors: Kino G. S. , Hunter J. B. , Johnson G. C. , Selfridge A. R. , Barnett D. M. , Hermann G. , Steele C. R.
Published: February 2003

An acoustic technique for measuring inhomogeneous stress in externally loaded solids is described. This method requires a measurement of transit time of a longitudinal acoustic wave through a stressed thin metal specimen using a small-diameter water-coupled acoustic transducer. The transducer is mechanically scanned over the surface of the sample by a computer-controlled system and transit-time measurements are made at discrete points. Predictions of velocity variation with stress using the theory of nonlinear elasticity are employed to relate the acoustic transit time to stress levels at field points in the specimen. Stress-field contour plots are developed and compared with theoretical results. Samples investigated include uniaxial tension specimens of aluminum and steel, an aluminum plate containing a central hole, and a double edge-notched aluminum panel, both under far-field tension.
Study of an electrically driven jet
Authors: Horning Darrell W. , Hendricks Charles D.
Published: February 2003

This is a study of the charge distribution and the forces on an electrically driven jet. A numerical solution of the charge distribution is presented, based on the measurement of the jet profile and the jet current. The influence of the charge distribution and fluid conductivity on jet length is considered. As a check on the charge distribution calculations, the electric driving forces are compared to the reaction forces.
Laser-driven hydrodynamic perturbation in an overdense Z-pinch plasma
Authors: Ackenhusen John G. , Bach David R.
Published: February 2003

Holographic interferometry of the interaction of a radially incident intense CO2 laser beam (1011 W/cm2, 38-nsec FWHM pulse) with an overdense helium Z-pinch plasma (ne≳1019 e/cm3, Te∼20 eV, L=100 μm) has indicated the presence of a laser-driven shock. The radial dimension of the shock was found to be similar to the electron thermal conduction length, several times larger than the focal-spot dimension. Density structure within the shock was inferred from holographic interferograms. Heuristic considerations of the shock density ratio, the front thickness, and the shock velocity allowed for an estimate of 50–80% energy absorption.
Gas discharges in planar low-pressure thermionic diodes. I. Space-charge regime
Authors: Bromberg L. , Smullin L. D.
Published: February 2003

Current flow in a gas-filled planar thermionic diode is studied for the case when pd is small, i.e., the diode spacing is small compared with the collision mean free path. The fast primary electrons ionize the gas and the positive space charge partially neutralizes the electron space charge. The diode volt-ampere characteristics are computed and compared with experiments in the regime of small pd that produces a monotonic potential distribution between the cathode and the anode. The minimum value of pd necessary for a nonmonotonic distribution is found.
Catastrophic damage of AlxGa1−xAs double-heterostructure laser material
Authors: Henry C. H. , Petroff P. M. , Logan R. A. , Merritt F. R.
Published: February 2003

We carry out a detailed study of catastrophic degradation (CD) in DH laser material from which we reach two conclusions. First, local melting occurs and is due to intense nonradiative recombination of minority carriers at a cleaved surface or at a defect. The minority carriers are generated by absorbed superradiant light. Second, the dark line associated with CD results from propagation of a molten zone confined to the active layer. It is recrystallized epitaxially after the laser pulse but remains highly nonradiative because large numbers of point defects and dislocation loops are quenched into this region during rapid cooling from the molten state. Catastrophic damage was induced by exciting superradiance in the DH material with a cavity-dumped Ar-ion laser. The melting and recrystallization were established by observing a redistribution of Ga and Al in the x=0.08 active layers by TEM studies. The point defects were detected by scanning junction photocurrent measurements, electron-beam-induced current, and cathodoluminescent analysis. Calculations of the power required for thermal runaway at a cleaved surface, melting, and propagation of a molten zone are within twice the observed threshold intensities.
Long-wavelength PbSnTe/PbTe inverted heterostructure mosaics
Authors: Wang C. C. , Kim M. E.
Published: February 2003

Pb0.76Sn0.24Te/PbTe inverted heterostructure mosaics were fabricated from epilayers grown by a liquid-phase-epitaxy technique. At 85 K, the spectral peak of these diodes occurred at 13 μm with a spectral cutoff at 14.2 μm. This response is believed to be one of the longest that has ever been reported for PbSnTe infrared detectors near LN2 temperature. The spectral cutoff, as expected, shifted toward a longer wavelength as the temperature was lowered; however, it reached a maximum at 30 K, beyond which the spectral response exhibited a retrograde characteristic. This behavior is explicable from the combined temperature dependencies of the energy gap, the Fermi level, and the thermal broadening of the optical transitions.
Recombination lifetimes and surface recombination velocities of minority carriers in n-p junctions. A new method for their determination by means of a stationary amplitude-modulated electron beam
Authors: von Roos Oldwig
Published: February 2003

When a well-collimated electron beam of an electron microscope impinges on the free surface of an n-p junction, a short circuit ISC will be generated. If the primary beam current is amplitude modulated sinusoidally in time, the ISC exhibits a characteristic coherent phase shift with respect to the modulated primary beam. This phase shift depends on the minority-carrier lifetime, doping level, and the position of energy levels of recombination centers within the band gap. For solar-grade material with their long lifetimes the influence of energy-level positions is negligible, but for short-lifetime material (switching devices) the dependence of the phase shift on the energy levels of the recombination centers is critical. In this paper it is shown that the measurement of the phase shift at two different beam-modulation frequencies allows for the determination of the lifetime and surface recombination velocity in solar-grade material (solar cells).
High-power-density single-mode operation of GaAs-GaAlAs TJS lasers utilizing Si3N4 plasma deposition for facet coating
Authors: Namizaki H. , Takamiya S. , Ishii M. , Susaki W.
Published: February 2003

A new method of laser diode facet coating, plasma deposition of Si3N4 film, has been developed. Utilizing it, laser diodes which operate at 4 mW/μm power density in single longitudinal and fundamental transverse mode for more than 1000 h have been realized.
Static optoelectronic characteristics of SnO2/V2O5 : P2O5/Si heterojunctions
Authors: Winn O. H. , Franz S. L. , Anderson R. L.
Published: February 2003

The dark and illuminated characteristics of SnO2/V2O5 : P2O5/Si heterojunctions can be explained by considering the cell to consist of a Schottky barrier in the Si at the Si/glass interface in series with the resistance of the bulk V2O5 : P2O5 glass. The series resistance is voltage, temperature, and illumination-intensity dependent. Space-charge-limited currents are found to be an unimportant conduction mechanism. The resistance of the amorphous glass layer precludes the use of these cells as practical solar-energy converters.
Comments on ’’Electrochemical effects as the source of emf in metal(1) -polymer-metal(2)’’
Authors: Crine J.-P. , Piron D. -L. , Yelon A.
Published: February 2003

The model proposed by Vijh of an emf produced by a metal-oxide reaction in metal(1) -polymer-metal(2) cannot explain many experimental observations including the presence of a voltage under a vacuum, the influence of different polymers upon this voltage and its temperature dependence. These observations can be understood if protons are released from residual acid groups in the polymer and not by the electrochemical reaction itself.
Effects of Be alloy additions to the bronze matrix of Nb3Sn monofilament wires
Authors: Luhman Thomas
Published: February 2003

The superconducting parameters Tc, Jc, and Hc2 have been measured on monofilament Nb3Sn wires containing 0.20 wt% Be in a Cu+11.2 wt% Sn matrix. Jc was measured both as a function of applied magnetic fields to 18.0 T and as a function of tensile strain at 4.0 T and 4 K. The Be alloy addition decreases the strain sensitivity of Jc. However, since this improvement results from an increased residual compressive strain in the compound, Tc, Jc, and Hc2 are decreased below corresponding values for a Nb3Sn wire produced from a binary Cu-Sn matrix. The decrease in Jc at 14.0 T is nearly 60%.
Components for a Josephson intracomputer communication system
Authors: Calander N. , Zappe H. H.
Published: February 2003

Josephson interferometers are shown to operate as oscilators (≳1 μW power) and as narrow-band receivers. Their operation is described in the context of a potential intracomputer communications network with an ultimate channel capacity of the order of 100 Gbits/sec.
Enhancement of Pb film thermal-cycling stability by deposition on substrates having a relatively large thermal-expansion coefficient
Authors: Wood Gordon H. , Nadon Lawrence A.
Published: February 2003

A comparative study has been made of the thermal-cycling stability of Pb thin-film tunnel junctions prepared on microscope-slide glass and on a sealing glass with a relatively high thermal-expansion coefficient. Definite improvements in thermal-cycling stability using the latter substrate material were found.
Pyroelectricity due to a space-charge mechanism in a copolymer of acrylonitrile and vinylidene chloride
Authors: Lee H. , Salomon R. E. , Labes M. M.
Published: February 2003

Polarization due to an inhomogeneous space-charge distribution can result in a small pyroelectric coefficient (∼1–10 pC cm−2 K−1) of opposite sign to the large pyroelectric coefficient (∼1–4 nC cm−2 K−1) observed in crystalline poly(vinylidene fluoride) which is largely due to the temperature-dependence dipole orientation. The former effect is reported in an amorphous copolymer of acrylonitrile (20%) and vinylidene chloride (80%).
Plasma region in high-fluence implants of phosphorus in amorphized silicon
Authors: Spitzer W. G. , Ko J. S. , Waddell C. N. , Hubler G. K. , Fredrickson J. E.
Published: February 2003

Phosphorus ions were implanted into silicon previously made amorphous by implantation with neon ions of projected range considerably greater than that of the P+ ions. Comparison of the annealing behavior for this case with that for P+-only implants indicates that free-carrier plasma formation in the region of high phosphorus concentration does not occur until the material has recrystallized.
Superconductivity at 23 K in A15 Nb3(Ge,Si) prepared by CVD
Authors: Païdassi S.
Published: February 2003

High-Tc A15 Nb3(Ge,Si) superconductors have been prepared by chemical vapor deposition. Films obtained after deposition have been examined by x-ray diffraction, chemical analysis, and transmission electron microscopy. Structural and superconducting properties are discussed. Onset of 23 K is obtained. Heat treatments are suggested to improve the order and Tc of inhomogeneous materials.
High-induction low-loss metallic glasses
Authors: O’Handley R. C. , Chou C.-P. , DeCristofaro N.
Published: February 2003

Alloying effects of cobalt metal and the metalloids carbon, silicon, phosphorus, germanium, and aluminum in Fe80B20 glass are considered in terms of magnetization σ and in terms of Curie and crystallization temperatures TC and Tχ, respectively. Silicon additions are reported in detail and are shown to increase both TC and Tχ strongly while only weakly affecting σ (RT). The highest magnetization, Tc, and Tχ are found in the series Fe82B18−xSix. B-H loops and core loss are reported for Fe82B10Si8 glass. dc coercivities under 0.03 Oe, remanences over 12 kG and initial permeabilities of 8000 are obtainable in field-annealed toroids of this composition. Core loss under sine-flux conditions at 60 Hz is 0.24 W/kg at 16 kG compared with 1.3 W/kg for M-4 grade Si/Fe and well below that of Fe80B20 glass. The kinetics of crystallization of Fe82B10Si8 glass (E=2.7±0.1 eV, τ0?3±1×10−17 sec) show it to be slightly more resistant to crystallization than is Fe80B20 glass (E=2.67 eV, τ0=1.75×10−17 sec).
The effect of alumina inclusions on the breakdown and emission properties of copper surfaces in vacuum
Authors: Farrall G. A. , Hudda F. G. , Johnston R. H.
Published: February 2003

We have studied electrical breakdown in vacuum for copper electrodes which have been intentionally contaminated by adding 1/2% by weight of alumina powder having a size of 500, 50, or 5 μm. Electron emission, pulse breakdown, and scanning electron microscopy have been used to evaluate the dielectric characteristics of the surfaces. Comparison of these results with those obtained using a zone-refined copper surface indicate an initial degradation of about 30% for the surface containing 50-μm particles and little effect for the surface containing 500-μm particles. All surfaces conditioned to about the same voltage. Breakdown to all samples containing particles was clearly associated with metal-insulator boundaries.
Infrared quenching of photocapacitance in evaporated ZnS : Ag thin films
Authors: Suda Toshikazu , Matsuzaki Kichie , Kurita Shoichi
Published: February 2003

The deep centers in evaporated ZnS : Ag thin films have been characterized by observation of the infrared quenching of photocapacitance using Schottky barriers. The photoionization energy of holes for transitions from Ag centers to the valence band edge is determined to be 0.56 eV at 300 K. The spectral distribution of the photoionization cross section of holes is obtained theoretically. It has been found that the magnitude of the photocapacitance quenching depends linearly on the intensity of the infrared illumination in the low-intensity range. The concentration profile of Ag impurities has been measured and is almost uniform throughout the depletion layer in the films.
Luminescence studies of the 1.36-eV band and the edge emission in melt-grown GaAs : Cu
Authors: Norris C. B.
Published: February 2003

Using cathodoluminescence at 80–300 K, we have measured the injection-level dependence, frequency response, and temperature dependence of the 1.36-eV band and the 1.50-eV edge emission in melt-grown GaAs : Cu. The overall luminescence is relatively weak and the 1.36-eV band is accompanied by a broad emission in the range 1–1.4 eV. We find no inherent injection-level shift in the shape or peak energy of the 1.36-eV band. With increasing temperature, the 1.36-eV band quenches out with an activation energy of 0.1 eV or greater. The frequency response of the 1.36-eV band is remarkably flat for deep-center luminescence. However, the frequency response of the edge emission is unusually slow in GaAs : Cu, particularly in samples with higher Cu concentration. Variation in injection level causes a strong variation in branching between the 1.36-eV band and the edge emission which is not explicable in terms of occupancy effects related to the relative kinetics of the two bands. It is suggested that the 1.36-eV band results from a conduction-band-to-acceptor transition whose kinetics are dominated by another process such as equilibration of a carrier trapping level in resonance with the conduction-band continuum. The same process also controls the kinetics of the edge emission transition in GaAs : Cu with high Cu concentration.
Thermionic constants determined from retarding-field data
Authors: Medicus G.
Published: February 2003

In the method described here, the intersection point of the ’’Davisson lines’’ determines the emission constant A, the anode work function (wf) φa, and the cathode wf φ (T). The Davisson lines are defined by ln(ir/Tκ) =lnA+e (V−φa)/ kT, where ir is the current density in the retarding-field range, T is the absolute cathode temperature (parameter), κ=2 for metals, κ=5/4 for oxide cathodes, and V is the anode-cathode voltage (independent variable); at the intersection point V−φa=0, ln(i/Tκ) =lnA. At the knees of the i (V) curves, V=Vs(T) =voltage at ir=is0=zero-field saturation current density, such that φ (T) =φa−Vs(T). Shelton’s method [Phys. Rev. 107, 1553 (1957)] is shown to be equivalent to the Davisson-line method. The method is applied to experimental data for a W emitter (κ=2) and for an oxide cathode (κ=5/4). The advantage of the method is that A, φa, and φ (T) result directly and correctly for any φ (T). The large A values resulting for the oxide cathode (A?45 000) remain to be interpreted.