bluuebunny/crossref_metadata_2025 huggingface dataset:
Angular Variation of Coercive Force in Barium Ferrite
Authors: Ratnam D. V. , Buessem W. R.
Published: February 2004

Magnetization reversals in high magnetocrystalline anisotropy materials like barium ferrite are believed to take place by coherent rotation or by reverse-domain nucleation. The former mechanism gives rise to a Stoner-Wohlfarth type of angular variation of coercive force and the latter mechanism gives rise to Kondorsky-type behavior. Angular variation of coercive force was measured in several oriented particle assemblies with the average particle size ranging from 0.4 to 200 μ. The results were interpreted by a simple model incorporating SW and Kondorsky behavior.
Electrical Properties of Carbon-Doped Gallium Phosphide
Authors: Bortfeld D. P. , Curtis B. J. , Meier H.
Published: February 2004

Carbon-doped platelets of GaP have been grown from gallium solution using a propane doping source. Acceptor concentrations of up to about 4×1017 cm−3 were obtained. The ionization energy was found to be 41±3 meV and 79 K mobilities up to 1786 cm2/V sec were observed.
Mg and Be Ion Implanted GaAs
Authors: Hunsperger R. G. , Wilson R. G. , Jamba D. M.
Published: February 2004

p-type layers have been produced in GaAs by implantation of either Mg or Be ions, with the substrate at room temperature, followed by annealing at higher temperatures. The ion source in both cases was a hot-cathode electron-bombardment type. The Mg ions were generated by placing metallic Mg in an axial probe inserted into the source, while the Be ions were produced by placing BeCl2 in the probe. n-type 〈111〉 substrates were implanted with 45-keV Mg or 40-keV Be ions, and were subsequently annealed for 15 min at temperatures up to 900°C. The dependence of surface carrier concentration and mobility on ion dose and on postimplantation anneal temperatures was determined using the van der Pauw-Hall technique.
Lattice Constants for KMg(1−x)MnxF3 Crystals
Authors: Vehse W. E. , Sherrill F. A. , Riley C. R.
Published: February 2004

The preparation of crystals of the form KMg(1−x)MnxF3 spanning the entire range of composition is reported. Crystal growth parameters are given. Lattice constants for nine crystals of different compositions were measured at room temperature using the Debye-Scherrer x-ray powder patterns. Measured values of the lattice constants conform to Vegard's law within experimental error.
Special Unpaired Dipolar Mode in Plasma-Filled Waveguides and Quasistatic Approximation
Authors: Vassallo Charles
Published: February 2004

An asymptotical development of the fields of the special unpaired dipolar mode of a plasma-filled waveguide with axial magnetization is given. The transverse wave vector is shown to tend towards zero, which explains why this mode cannot be found by the quasistatic approximation, for the nature of which a new theory is proposed, based on the decomposition of a guided field into plane waves.
Gas Analysis in Films by Laser-Induced Flash Evaporation Followed by Mass Spectrometry
Authors: Winters Harold F. , Kay Eric
Published: February 2004

A new technique for determining the concentration of gases in films has been developed which utilizes laser-induced flash evaporation followed by mass-spectrometric analysis of the released gas. It is shown that this technique can be used to perform quantitative analysis for the noble gases and nitrogen in most thin-film materials on a wide variety of substrates. Under ideal conditions, gas concentrations of a few parts per billion can be detected. Qualitative results have been obtained for other chemically active gases such as oxygen and hydrogen. Approaches are suggested which may also allow quantitative measurements to be made for these gases. Several phenomena which could lead to inaccurate or erroneous measurements are evaluated and methods suggested for minimizing their effect.
Surface Elastic-Wave Velocity and Second-Harmonic Generation in an Elastically Nonlinear Medium
Authors: Ljamov V. E. , Hsu Tzu-Hwa , White R. M.
Published: February 2004

We report the derivation of a closed-form expression for the acoustic surface-wave velocity in an isotropic medium which is elastically nonlinear. An expression is given for the particle displacement of the second harmonic generated, and its variation with distance is shown. The amplitude of the harmonic is proportional to the power density of the fundamental frequency input. Numerical results are given for fused quartz.
Thermal Damping of Dislocations in Copper and Lead
Authors: Fate W. A.
Published: February 2004

Ultrasonic attenuation measurements were used to study the thermal part of the dislocation damping factor in copper and lead at frequencies between 10 and 90 MHz in the temperature range 1–180°K. With the assumption that the Granato-Lücke theory is correct in the limits of small and large dislocation damping, it was found that the Lothe expression for the dislocation damping factor well describes the temperature variation of the measured attenuation. The frequency dependence of the attenuation was found to be in serious disagreement with the Granato-Lücke prediction.
Short-Circuit Currents in Charged Dielectrics and Motion of Zero-Field Planes
Authors: Gross Bernhard , Perlman Martin M.
Published: February 2004

When a previously charged dielectric is short circuited, discharge currents result due to the movement of charge carriers in the field of the space charge. It is shown for plane-parallel geometry that the discharge current is given by the product of charge density at, and velocity of, the zero-field plane. The resulting expression includes the displacement current. It can also be applied to the case where the dielectric is exposed to a beam of penetrating radiation; it then allows one to evaluate the effect of space charge on the external current.
Energy Distribution of Transmitted Secondary Electrons from Porous KCl Films
Authors: Akagi M. , Yoshida S.
Published: February 2004

Energy distribution of secondary electrons from three types of porous films (porous KCl films, porous KCl films with intermediate thin Al layer, porous KCl films containing small amount of amorphous Al) was measured by an ac retarding-field method. The half-width of each energy distribution curve was found to be about 10–20 eV. The surface potential of these films was also obtained from the rising point of the energy distribution curve. A single relationship between surface potential and yield and independent of collector voltage was found for constant primary energy. Decay characteristics of the surface potential of three films after ceasing the primary electron bombardment were similar to each other. Secondary currents from a porous KCl film containing a small amount of amorphous Al were found to be considerably more stable compared to those from two other films. A secondary electron emission mechanism is proposed using a channel electron multiplier model.
Effective Dielectric Tensor for Electromagnetic Waves in Weakly Inhomogeneous Media
Authors: Vassallo C.
Published: February 2004

This paper presents a study of the effect of small fluctuations of the permittivity or conductivity of an anisotropic medium on the propagation of electromagnetic waves. There is no restriction on the scale of the inhomogeneities compared with the wavelength. An equivalent homogeneous medium is defined, with a constant effective dielectric tensor, and where the fields are derived from the actual fluctuating fields by a described regularizing process. The difference between this tensor and the mean dielectric tensor is of second order in the inhomogeneity and it generally depends on the wave vector. The effective conductivity tensor calculated by Herring in dc conditions may be used only if the scale of the fluctuations is small enough and if the fluctuations are not too anisotropic. Then there is an enhancement of the damping of helicon waves. The theory shows another kind of damping due to a resonant scattering of the incident wave on inhomogeneities; this effect, which causes a damping of the wave even in a lossless medium, is attenuated when the medium becomes lossy.
Production of High Quasipermanent Charge Densities on Polymer Foils by Application of Breakdown Fields
Authors: Sessler G. M. , West J. E.
Published: February 2004

Charge deposition on 2–25-μ m polyethylene terephthalate (PET), polyfluoroethylenepropylene (FEP), and polycarbonate (PC) foils by application of fields up to, and exceeding breakdown strength in the polymers is reported. The greatest negative or positive charge densities on PET foils metalized on one side are in excess of 10−6 C/cm2, corresponding to full-trap densities of about 4×1016 cm−3 and are thus considerably greater than the largest densities obtained previously on polymer foils with a variety of charging methods. The charge decay is nonexponential with time ``constants'' on PET and FEP in dry atmosphere exceeding 10 years at charge levels of 10−7 C/cm2. Analysis of thermally stimulated currents indicates that electrons in PET are subject to considerable retrapping.
Growth of Smooth Uniform Epitaxial Layers by Liquid-Phase-Epitaxial Method
Authors: Blum J. M. , Shih K. K.
Published: February 2004

The liquid-phase-epitaxial (LPE) process has proven to be a very effective technique for the formation of high-quality III-V semiconductor layers. It has found widespread use because devices made by this method produce high-efficiency LED's and low-threshold lasers. A limitation of this method has been the difficulty of making smooth high-quality surfaces. It will be shown that the use of a specially designed LPE growth apparatus makes possible the growth of reproducible uniform economical and, above all, smooth photolithographic processable layers. This process has made possible the formation of planar monolithic AlxGa1−xAs LED's with luminance characteristics as high as 104 ft L at a current density of ∼40 A/cm2.
Elastic Field and Strain Energy of a Circular Wedge Disclination
Authors: Kuo H. H. , Mura T.
Published: February 2004

The displacement and stress fields for a circular wedge disclination loop are derived by the Fourier integral method, and expressed in terms of tabulated functions. The associated elastic-strain energy is also derived.
Contribution of the Space-Charge Layer to the Dielectric Constant of Silver Halides
Authors: Fatuzzo E. , Coppo S.
Published: February 2004

Electric fields associated with the space-charge layer at the surface of silver halide grains are expected to have a marked effect on the photographic properties of emulsions. The purpose of this paper is to describe a new method based on dielectric measurements to obtain information on the surface layers. It is shown that the surface layers have a strong effect on the low-frequency dielectric constant so that it is possible to derive the properties of the former from measurements made on the latter. Formulas connecting the layer properties to the dielectric constant of the crystal are derived. The experimental results, obtained with the method described here, will be the subject of a separate paper.
Thermal Conditions When Dislocations Are Generated in Silicon
Authors: Porter W. A. , Drew D. D. , Linder J. S.
Published: February 2004

Dislocations in device silicon have been thermally generated. The thermal conditions of the wafer while being cycled in a diffusion furnace have been numerically modeled. These numerical results form the basis for establishing the thermal conditions of the wafer when dislocations are induced during thermal cycling.
Diffusion Cooling of Electrons in Afterglow Plasmas
Authors: Bhattacharya A. K. , Ingold J. H.
Published: February 2004

The results of mass-identified measurements of the decay of positive atomic ion number densities in low-pressure rare-gas afterglow plasmas are reported. At high gas pressure, the loss of atomic ions is due to conversion into molecular ions and by ambipolar diffusion to the wall of the container. At low pressures, the loss of atomic ions is only by diffusion to the wall but at a slower rate than that of ambipolar diffusion; this slow loss rate is interpreted as a manifestation of electron diffusion cooling in heavy rare gases. A semi-quantitative theoretical explanation of diffusion cooling is offered and shown to be in good agreement with the results of measurements of electron decay rates in Ne and Ar afterglows and of ion decay rates in Ne afterglows. Comparison with ion decay measurements in Ar, Kr, and Xe are also given.
Production of High Pressures by a Capacitor Discharge-Powered Linear Magnetic Pinch
Authors: Bless S. J.
Published: February 2004

A capacitor discharge-powered magnetic pinch has been used to produce pressures up to 300 kbar in solid rods. Observed high-pressure effects include the decomposition of mullite and formation under high pressure of polymorphs of boron nitride, carbon, and iron.
Saturable Optical Resonator
Authors: Spiller Eberhard
Published: February 2004

The nonlinear characteristics of saturable optical resonators (resonators containing saturable absorbers) are derived from a two-level model of the absorber. Steady-state and transient responses are given. The influence of incomplete bleaching of the absorber and of detuning of the resonator is discussed. Experiments are performed with a ruby and a neodymium laser as light source and solutions of organic dyes as saturable absorbers. The experimental results can be described by the theory.
Magnetocapacitance Effect in a Metal-CdCr2Se4 Junction
Authors: Toda Minoru , Tosima Soitiro
Published: February 2004

The change in capacitance, due to an applied magnetic field, of a metal-CdCr2Se4 junction, made by evaporating silver onto an In-doped CdCr2Se4 single-crystal surface, has been studied. It was found that the capacitance increased with increasing magnetic field and the rate of increase was found to increase with increasing temperature. On application of a magnetic field of 6 kOe, the capacitance C was increased by 1% at 77°K and by 20% at 98°K. Observation of the C vs bias voltage V characteristics in the presence and absence of the magnetic field showed that C−2 increased linearly with V and that the increase in capacitance is ascribed to the decrease in barrier height of the junction. A theoretical expression for the relative change of capacitance ΔC/C due to an applied magnetic field was derived taking into account the exchange interaction of electrons in the conduction band and donor levels with localized spins, which contributes to the magnetic properties of the material. Agreement between theory and experiment was fairly good, when the average exchange integral J̄ was assumed to be 0.38 eV.
Laser-Heating Studies of Composite Materials
Authors: Anderholm N. C. , Anderson Philip D.
Published: February 2004

Experiments on laser heating of carbon-methacrylate composite materials are described and compared to a theoretical model. The model assumes hydrodynamic response and uses the Mie-Grüneisen equation of state. The laser experiments are carried out on samples with carbon fibers (10-μ diam and 250 μ long) uniformly dispersed in a polymethylmethacrylate (PMMA) matrix. The samples irradiated had a carbon to PMMA mass ratio of 1:1000. The fluence range was from 0.12 to 2.0 J/cm2 and the resulting pressure ranged from 0.3 to 30 bar. By assuming that rapid energy transfer is accomplished by vaporized carbon penetrating cracks in the matrix, the results are in accord with the theory.
Experimental Evidence of Hot-Electron Transport through Thin Metal Films
Authors: Antula J.
Published: February 2004

The metal-base triode sandwich was used to measure the current transfer ratio in a Schottky barrier structure. The transfer ratio is discussed considering two distinct current types—that through base metal and that through pinholes. An electron-phonon mean free path of 125 Å and an electron-electron mean free path of 230 Å (at 0.7 eV) were measured. An investigation of the structure of very thin Al and Au films deposited on Al2O3 was made by transmission electron microscopy. Al films were found to be more continuous than Au films of comparable thickness.
Numerical Modelling of Pulsed Electric CO2 Lasers
Authors: Vlases George C. , Moeny William M.
Published: February 2004

A simple four-level kinetics model is combined with a cavity intensity model to predict the output pulse characteristics of pulsed electric discharge CO2 lasers for pressures ranging from 0.1 to 10 atm. Both free-running (gain-switched) and Q-switched cases are studied. Particular emphasis is placed on peak intensity and energy content of the initial spike as a function of pumping rate, gain at time of Q swithcing, mixture, and pressure.
Nd Ion Site Distribution and Spectral Line Broadening in YA1G: Lu, Nd Laser Materials
Authors: Riseberg L. A. , Holton W. C
Published: February 2004

High-resolution optical spectroscopy at low temperatures has been used to study spectral line broadening in Lu-compensated YA1G: Nd laser materials. The splitting and broadening that is observed is ascribed to a nonrandom distribution of rare-earth sites. The implications of these observations in laser performance are discussed.
Ultrasensitive Magnetic Field Measurements in the Presence of High Ambient Noise Levels-Application to Magnetocardiography
Authors: Rosen A. , Inouye G. T. , Morse A. L. , Judge D. L.
Published: February 2004

A two-junction superconducting Josephson tunneling magnetometer has been developed for the measurement of magnetic field strengths of the order of 10−9 G/Hz1/2 in an unshielded environment. The application of the device to the measurement of the heart's magnetic signature, the magnetocardiogram, and the problems associated with the measurement techniques are discussed. It is demonstrated that the fine details of the heart's magnetic signature (the magnetocardiogram) can be resolved in real time in an unshielded environment.
Electrical and Magnetic Properties of Paramagnetic Vanadium-Iron Alloys
Authors: Nellis W. J. , Brodsky M. B.
Published: February 2004

The low-temperature electrical resistivities, magnetoresistances, and magnetic susceptibilities of VFe alloys have been measured in the range 18–28% iron, the range in which VFe undergoes a transition from Pauli paramagnetism to ferromagnetism. The measurements were repeated after plastic deformation to determine the effects the effects of short-range atomic order on the CsCl-like crystal structure of these alloys. The onset of a magnetic scattering mechanism is observed at 22% iron by the appearance of minima in the resistivity-temperature curves, by an increase in (dρ/dc), and by a negative magnetoresistance. The field dependences of the susceptibilities indicate interactions between ferromagnetic clusters. The electrical properties are interpreted in terms of spin-flip scattering from ferromagnetic clusters. The increases in magnetic susceptibility and in the magnitude of the negative magnetoresistance with plastic deformation are interpreted in terms of a defect structure which increases the number of iron-iron nearest neighbors. The data for V(24% Fe) yield an estimated average cluster moment of 40 μB and an effective cluster concentration of 0.01%.
The Behavior of Input-Power Density in Exploding-Wire Restrikes
Authors: Vlastós Antonios E.
Published: February 2004

The input power per unit volume of the restrike channel of thin exploding wires reaches its maximum slightly before the electrical conductivity has reached its maximum. In its turn, the electrical conductivity reaches its maximum before the current and the total power input, ui, have reached their maxima but slightly after the ledge observed on the voltage oscillograms. The reason why the input power per unit volume and the electrical conductivity reach their maxima much earlier than the current and the total power input reach theirs seems to be closely connected with the magnetogasdynamics of the restrike channel, which have not yet been satisfactorily treated because of the complexity of the problem.
The Resistance of Sparks
Authors: Vlastós Antonios E.
Published: February 2004

A relation describing the temporal variation of the channel resistance of the sparks was derived, using Spitzer's formula for the resistivity of a fully and singly ionized plasma, on the assumption that the current was homogeneously distributed over the cross section of the spark channel. The relation predicts values of the resistance similar to those obtained by the relation of Rompe and Weizel. The reason for the difference between theory and experiment may be due to the fact that the electron density of the channel, which was assumed to be constant in the derivation of the relation, is time dependent.
Epitaxy and Fiber Texture of Pb Films on Mica and Glass
Authors: Wyatt P. W. , Yelon A.
Published: February 2004

We report the production of (111) epitaxial Pb films on mica and (111) textured Pb films on mica and glass. Film structure is studied by reflection electron diffraction and by etching and optical microscopy. Thin epitaxial films (∼1000 Å) are found to be doubly positioned. Reorientation during growth of thicker films leads to single positioning in areas several tenths of a millimeter across.
Negligible Effect of Negative Ions on the Constriction of Arcs in SF6
Authors: Lowke J. J. , Liebermann R. W.
Published: February 2004

From material functions calculated with and without the presence of negative ions, temperature profiles have been calculated for arcs in sulfur hexafluoride. Account is taken of the influence of the negative ions on both the electrical conductivity and the radiation emission coefficient. Results indicate that negative ions have a negligible effect on arc temperature profiles, it being assumed that local thermal equilibrium exists. The constricted arc profiles that are obtained at low currents are due to the reactive peak in the thermal conductivity.
Electrical Properties of Silicon Layers Implanted with BF2 Molecules
Authors: Müller H. , Ryssel H. , Schmid K.
Published: February 2004

The annealing behavior of boron in silicon, implanted as BF2 molecules, has been evaluated using Hall-effect and sheet resistivity measurements. For a dose of 1015 cm−2 at room temperature and an anneal at 650°C, the number of carriers/cm2 is increased by a factor of 20 compared to a boron implant. This indicates that an amorphous layer has been formed with this dose, whereas for boron a dose of≥2×1016 cm−2 is required. For doses ≤1014 cm−2, there is no marked difference in the annealing of BF2 and boron implants concerning majority carriers characteristics of the implanted layers.
Electrically Controlled Birefringence of Thin Nematic Films
Authors: Soref R. A. , Rafuse M. J.
Published: February 2004

This paper reports field-induced realignment of a nematic liquid crystal. A thin nematic film, which has a negative dielectric anisotropy, is initially homeotropic. Application of a threshold field parallel to the optic axis distorts the nematic ordering and increases the film's birefringence in certain light-propagation directions. Experimental results are given for threshold voltage, threshold width, optical contrast ratio, frequency response, angular field of view, electrical power consumption, and transient response. Light-valve applications are described.
Effect of Electron Irradiation on Diffusion in Gold-Silver Alloys
Authors: Spreng D. T. , Hilliard J. E. , Kauffman J. W.
Published: February 2004

The effect of electron irradiation on diffusion in gold-silver alloys at -196°C was determined from the decrease in amplitude of short wavelength (11–20 Å) composition modulations produced by vapor deposition. It was found that (i) mixing occurred during irradiation. For an electron current of 2 μA cm−2 at 2 MeV the effective interdiffusivity was approximately 1 × 10−22 cm2 sec−1. (ii) The interdiffusivity was directly proportional to the electron current and increased with increasing electron energy. (iii) During warm-up to room temperature after irradiation a single stage of mixing was observed above −70°C. The mixing during irradiation is attributed to the migration of interstitialcies to sinks and that during warm-up to the migration of vacancies to sinks. These results support the hypothesis that annealing stages around 0°C in pure fcc metals are due to vacancy migration.
Nonresonant Energy Transfer from Er3+ to Yb3+ in LaF3
Authors: Okamoto Eichi , Masui Hiromitsu , Muto Katsutoshi , Awazu Kenzo
Published: February 2004

Energy transfer in LaF3; Er, Yb is studied by observing the lifetimes of Er3+ in excited states and the excitation spectra both at room temperature and at 77 °K. It is found that the energy transfer from Er3+ (4S3/2→4I13/2) to Yb3+ (2F7/2→2F5/2) is associated with the emission of three phonons of about 350 cm−1, and that the energy transfer from Er3+ (2H9/2→4F9/2) to Yb3+ accompanied by the absorption of phonons takes place.
Effects of Point Defects on Elastic Precursor Decay in LiF
Authors: Asay J. R. , Fowles G. R. , Durall G. E. , Miles M. H. , Tinder R. F.
Published: February 2004

Experimental data for shock propagation along a 〈100〉 direction in single-crystal LiF show that elastic precursor decay is critically dependent on the origin of the sample. The most obvious differences among samples used are in their concentrations of impurities. It is suggested that divalent cation impurities are responsible for variations in precursor decay, and this is supported by results from a set of samples irradiated with γ rays to produce F centers. For the observed range of defect concentrations, quasistatic yield stresses varied monotonically with concentration from 0.02 kbar for pure crystals to 1.0 kbar for the hardest material studied. In the shock loading experiments both hard and soft crystals showed an initial rapid decay of the precursor to near-equilibrium values of about 2 kbar for the softest crystals and about 6 kbar for the hardest. For crystals of intermediate hardness the decay was much slower. From observed effects of annealing before shocking it is inferred that dislocation mechanisms in shock differ from those believed to operate at low strain rates. Impact stress for all experiments was about 28.6 kbar and sample thicknesses ranged from 0.27 to 15.44 mm.
Production of High-Energy Ions in Laser-Produced Plasmas
Authors: Allen F. J.
Published: February 2004

Several reported experiments are analyzed to show that acceleration in transient electric fields is an unlikely means of production of the highly energetic ions observed in laser-produced plasmas. Alternative mechanisms which appear capable of accounting for the observed results are proposed and discussed.
Electroluminescence and Photoluminescence of Thin Films of ZnS Doped with Rare-Earth Metals
Authors: Krupka D. C. , Mahoney D. M.
Published: February 2004

It has been shown recently that efficient electroluminescence may be obtained from thin films formed by the coevaporation of ZnS and rare-earth fluorides. In order to assess the importance of the fluorine ions in such systems, films have been produced by coevaporating ZnS and rare-earth metals (Tb, Sm, Nd). It is shown that large concentrations of well-dispersed rare-earth ions may also be obtained by this method. For ZnS: (Tb metal) the concentration which optimizes the electroluminescence power efficiency has about the same value as that for ZnS : TbF3 (2 at. % Tb), and the peak electroluminescence power efficiency is slightly lower than that obtained for ZnS : TbF3. In general, the metal-doped systems yield electroluminescence spectra which differ from their fluoride-doped counterparts at a similar concentration. This is taken as evidence that the fluorine ions remain in the vicinity of the rare-earth ion. In the case of ZnS : EuF3, it is further suggested that the fluorine ions may help to control the valence of the rare-earth ion to yield Eu3+ since independent evidence indicates that in ZnS crystals only Eu2+ is stable. Absolute photoluminescent power efficiency measurements on films of ZnS : (Tb metal) are used to show that a mechanism for electroluminescence based on electron-hole pair formation with subsequent transfer of this energy to the Tb3+ ion may be effectively ruled out; indirect evidence for direct impact excitation of the active ion is thus obtained. For purposes of application, it appears that systems in which the rare-earth ions are introduced by evaporation of the fluorides are superior, since the evaporation of these is simpler and the electroluminescence spectra of such devices are more reproducible.
Stimulated Emission and Laser Operation (cw, 77°K) of Direct and Indirect GaAs1−xPx on Nitrogen Isoelectronic Trap Transitions
Authors: Scifres D. R. , Holonyak N. , Macksey H. M. , Dupuis R. D. , Zack G. W. , Craford M. G. , Groves W. O. , Keune D. L.
Published: February 2004

The various factors governing the laser operation of direct and indirect semiconductors on isoelectronic trap transitions are considered. A detailed description is given of the operation of optically pumped GaAs1−xPx:N lasers, and the simple and compound optical cavities used for this purpose. The laser operation (cw, 77°K) of direct and indirect GaAs1−xPx:N (0.32≤x≤0.60) on nitrogen-trap transitions is described. Stimulated emission characteristic of an inhomogeneously broadened line is shown to occur on NN pair transitions, both in direct and indirect crystals. Laser operation more characteristic of a homogeneously broadened line is observed on nitrogen A-line transitions, depending to some extent, however, on the crystal composition and the depth of the trap relative to the conduction band.
Design and High-Frequency Response of Resistive SQUID Frequency Converters
Authors: Fife A. A. , Gygax Suso
Published: February 2004

Several resistive SQUID frequency converters (R-SQUID) have been constructed and their properties studied in the frequency regimes 26.5–40 and 67–73 GHz. A brief outline of the theory of the device is presented together with constructional details for a Nb–Nb point-contact version. The device response is complicated by the effects on the ac Josephson current of distributed circuit elements, and a broad range of complex behavior is presented which is only partially understood. A useful amplification effect for the detected signal has been discovered, which gives the device good broad range sensitivity (∼ 10−7–∼ 10−12 W/Hz1/2) and reasonably narrow linewidths (Q-values of ∼ 104 at 70 GHz).
Direction of Chemical Transport of Tungsten in Tungsten-Bromine Lamps
Authors: Yannopoulos L. N. , Pebler A.
Published: February 2004

Computer aided thermodynamic equilibrium calculations were used to predict the direction of tungsten transport in the temperature gradient of a tungsten-bromine lamp in the presence of hydrogen, carbon, and oxygen. The calculations were performed in the temperature range 500–3500 °K. Similar calculations for incandescent lamps without either bromine or carbon were found to be in agreement with experimental observations and support a thermodynamic model to explain chemical tungsten transport in tungsten-bromine lamps.
TEA Laser Power E/p for Atmospheric and Higher Pressures
Authors: Rink John P.
Published: February 2004

The energy output from a CO2 TEA laser was measured at pressures from 585 to 1185 Torr with initial values of E/p from 7 to 17 V/cm Torr. The energy out increased linearly with pressure at a given E/p.
Shock Melting and Vaporization of Metals
Authors: Ahrens Thomas J.
Published: February 2004

The effect of initial porosity on shock induction of melting and vaporization is investigated for Ba, Sr, Li, Fe, Al, U, and Th. For the less compressible of these metals, it is found that for a given strong shock-generation system (explosive in contact, or flyer-plate impact) an optimum initial specific volume exists such that the total entropy production, and hence the amount of metal liquid or vapor, is a maximum. Initial volumes from 1.4 to 2.0 times crystal volumes, depending on the metal sample and shock-inducing system, will result in optimum postshock entropies.
Long-Range Interaction between a Screw Dislocation and a Spherical Inclusion
Authors: Comninou Maria , Dundurs J.
Published: February 2004

The long-range interaction between a screw dislocation and a spherical inclusion is investigated by considering the Peach-Koehler force. The main features of the interaction are determined by the mismatch in the shear moduli. Thus the inclusion repels the dislocation if its shear modulus is higher than that of the matrix. However, the distribution of the force along the dislocation is strongly affected by Poisson's ratio of the matrix. For values of this ratio above 1/4, the distribution ceases to be bell shaped, and the maximum value of the Peach-Koehler force occurs at some distance from the point nearest the inclusion.
Gas Mixture Losses through an Ion-Sampling Orifice
Authors: Tombers Reid B. , Chanin L. M.
Published: February 2004

The compensation of gas losses through an ion-sampling orifice is considered for dc discharges in He–N2 mixtures. Measurements are made under conditions such that the nitrogen concentration is axially dependent due to cataphoretic effects.
On the Signal-to-Noise Ratio for Optical Heterodyne Detection
Authors: Teich M. C. , Yen R. Y.
Published: February 2004

The conventional result for the signal-to-noise ratio in an optical heterodyne detector is shown to apply to the mixing of a stable local oscillator with any radiation field which gives rise to a stationary narrow-band i.f. signal. The result is explicitly demonstrated for radiation scattered from a diffuse target, which may be represented as a narrow-band Gaussian random process.
Effect of Large Vacancy Thermal Expansion on the Pressure Variation of Activation Enthalpy in Pure Metals
Authors: Chhabildas Lalit C. , Gilder H. Michael
Published: February 2004

The pressure derivative of the activation enthalpy for diffusion, (∂ΔH/∂p)T, is a function of the thermal coefficient of expansion αv of an activated vacancy, where αv=(1/ΔV) (∂ΔV/∂T)p and ΔV is the vacancy activation volume. Recent measurements of αv for zinc and cadmium indicate that αv ≫ α0, where α0 is the ideal lattice thermal-expansion co-efficient. The magnitude and functional form of αv indicate a value of (∂ΔH/∂p)T ≪ ΔV, contrary to previous estimates of (∂ΔH/∂p)T ≈ ΔV based on αv=α0.
Transverse-Flow Transverse-Pulsed Chemical CO Laser
Authors: Ahlborn B. , Gensel P. , Kompa K. L.
Published: February 2004

A transverse-pulsed multispark discharge provides O atoms inside the laser cavity to start the chemical reaction of CS2 and oxygen. Transverse flow through 100 tube-shaped ground electrodes facilitates high-pulse repetition rates. Simultaneous laser emission is observed in about 50 P-branch lines. Typical pulse duration is 50 μsec. The multiline power reached 6 W at 70 Torr pressure. The efficiency is about 0.05%. Q switching with rotating mirror increases the power by only a factor of 5 indicating that chemical deactivation processes are important.
Excitation of Shear Elastic Waves by an Interdigital Transducer Operated at Its Surface-Wave Center Frequency
Authors: Schmidt R. V.
Published: February 2004

The excitation of shear elastic waves by an interdigital transducer operated at its surface-wave center frequency is discussed. It is shown experimentally for the high-coupling orientation of LiNbO3 that the shear-wave power radiated by an interdigital transducer may be an appreciable part of the input electrical power even at the surface-wave center frequency. The mode conversion of surface waves to shear waves at a receiving transducer is also considered. It is shown that the shear-wave radiation pattern of an electrically driven interdigital transducer is well described by treating the transducer as a phased-array antenna.
Photoplastic Behavior of CdTe
Authors: Carlsson Lennart , Ahlquist C. N.
Published: February 2004

Single crystals of CdTe have been grown by the Bridgman technique with boric oxide as liquid encapsulation. The nonstoichiometry of these p-type crystals was changed by heat treating in Cd vapor of different partial pressures. Mechanical measurements performed in compression on the n- and p-type crystals in darkness and during illumination showed that high-resistivity crystals had the lowest yield stress; at the same time, only a very small influence of illumination on the yield stress could be detected. The yield stress of low-resistivity samples, however, could be increased as much as 70% by illumination with light corresponding to the band-gap energy. Strain-rate cycling tests have been performed in compression on as-grown crystals. The Johnson-Gilman velocity-stress relationship was used to evaluate the dislocation velocity effective stress exponent and the long-range internal stresses built up during deformation in light and darkness, respectively. The observed increase in flow stress during illumination is consistent with a semiphenomenological model, which assumes a light-induced decrease in the mobile dislocation density by pinning of charged dislocations by oppositely charged native defects.
Method of Simultaneous Measurement of Radiative and Lattice Thermal Conductivity
Authors: Schatz John F. , Simmons Gene
Published: February 2004

A new technique of high-temperature thermal-conductivity measurement is described. A CO2 gas laser is used to generate a low-frequency temperature wave at one face of a small disk-shaped sample, and an infrared detector views the opposite face to detect the phase of the emerging radiation. A mathematical expression is derived which enables phase data at several frequencies to be used for the simultaneous determination of thermal diffusivity and mean extinction coefficient. Lattice and radiative thermal conductivities are then calculated. Test results for sintered aluminum oxide at temperatures from 530 to 1924 °K are within the range of error of previously existing data.
Electromigration Failure at Aluminum-Silicon Contacts
Authors: Prokop G. S. , Joseph R. R.
Published: February 2004

Previous experiments to measure electromigration properties of Al–Si contacts were conducted at high current densities. Failures resulted from a combination of electromigration damage and diffusion of silicon into the aluminum lands. At low current densities, the silicon diffusion is significantly reduced and the median time to failure is inversely related to the current density. In addition, contacts ranging from 10×5 μ to 25×15 μ were tested to determine the dependence of median time to failure on contact size.
Possibility of Switching and Steering Surface Waves by Nonlinear Mixing in Anisotropic Media
Authors: Newhouse V. L. , Chen C. L. , Davis K. L.
Published: February 2004

It is known that when two acoustic surface-wave beams intersect in a suitably anisotropic medium, sum and difference frequency beams are generated parametrically if both frequency and phase velocity are matched. Using coupled-mode theory we show that this effect can occur even in the presence of imperfect phase matching. In consequence it should be possible to produce sum and/or difference frequency beams over a continuous range of angles, with the direction controlled by the ratio of the input beam frequencies. Computed input and output beam angles are presented for a number of materials and device applications are discussed.
Principles Underlying the Behavior of Passing Dislocations
Authors: Sadananda K. , Marcinkowski M. J.
Published: February 2004

The equilibrium configurations of passing dislocations on parallel slip planes are analyzed in terms of their stability. It was found that some of the solutions obtained in the literature correspond to unstable force equilibria and they can be recognized as such from the positive slopes in the force-distance curves. Frictional forces make such equilibrium positions stable, and the extent of the stability depends on the magnitude of the frictional forces. With the requirement that a dislocation moves with zero acceleration and with a constant potential energy, the external stress is continuously monitored while the dislocation continuously moves through the stable and unstable equilibrium configurations. The behavior of two and four dislocations on parallel slip planes is analyzed, but the results can be extended to more complex arrays.
ac Electrical Breakdown of Neon with External Electrodes
Authors: Veron Harry , Wang Chao C.
Published: February 2004

Results are presented of an experimental and theoretical investigation of ac electrical breakdown of neon in glass cells with external electrodes. The calculations are based upon a Townsend avalanche model that takes into account the effect of both the space charge and the surface charge on the glass walls that separate the electrodes from the gas. The experimental and theoretical results give a discharge current pulse in each half-cycle of the applied sine wave that are in agreement. Profiles are calculated of the electric field-to-pressure ratio as a function of position in the discharge gap with time as a parameter. These profiles exhibit a linear dependence on distance from the cathode wall as the discharge current reaches its peak, a behavior similar to that which occurs in the cathode-fall region of dc glow discharges. The calculated propagating luminous fronts associated with the electric field buildup in the cathode region also compare well with experiment. Under the present set of operating conditions, the Townsend avalanche model including space-charge effects adequately accounts for the discharge mechanism. These results are also shown to account for the behavior of the ac plasma display panel.
Dual Magnetic Probe System for Phase Measurements in Thermal Induction Plasmas
Authors: Eckert H. U.
Published: February 2004

Previously reported measurements of rf magnetic field distributions in thermal induction plasmas by a water-cooled coil probe have been extended to phase measurements through the use of a second identical probe placed at a fixed position near the plasma boundary. From measurements of the vector sum and/or difference in addition to the individual signals from both probes, data for the variation of the phase angle with radius were obtained. The reliability of the method was checked with an electrolyte of known conductivity. Tests conducted at 2.6 MHz in a 14-cm-wide argon-plasma column at ambient pressure yielded a change in phase angle of 285 deg over the radius. The variations in phase and magnitude of the magnetic field were used to derive those of the induced electric field, the current density, the electrical conductivity, and the real part of the Poynting vector. From the latter a specific power input of about 1500 W/cm was obtained. A correlation of the conductivity data with temperatures derived from absolute line and continuum intensities is in good agreement with predictions from an equilibrium theory.
Electrical Properties of Silicon Films on Sapphire Using the MOS Hall Technique
Authors: Ipri A. C.
Published: February 2004

An experimental technique is described for determining the electrical properties of thin semiconducting films as a function of distance from the surface. The method is applied to silicon on sapphire films nominally 1 μ thick and doped n and p type on the order of (2–6)×1016/cm3, and the variation in average mobility and carrier concentration with depth into the layer is determined. A physical model for the variation of these parameters in the films is proposed which fits the experimental data and it consists of linearly decreasing mobility and constant impurity profile. The existance of a significantly wide nonconducting sublayer within the film is also suggested. It is found that the postulated model is successful in accurately predicting the actual surface concentration.
Spectral Dependence of Photoconductivity in Indium-Doped Silicon
Authors: Mason Howard J. , Blakemore J. S.
Published: February 2004

The spectral dependence of extrinsic photoconductivity over the range 130–700 meV has been measured (mostly at 80°K, with light chopped at 270 Hz) for a variety of indium-doped silicon crystals. The various samples were characterized by 70–400°K Hall and conductivity measurements, and had indium densities ranging from 7 × 1015 cm−3 to 7 × 1017 cm−3. Crystals of moderately large and extremely small compensation were used. The data were converted into the response per incident photon and per absorbed photon (using, for the latter, data on the photoionization cross section measured on the same group of crystals). The response per absorbed photon is approximately constant from the 150-meV threshold through the spectral range studied, with no visible evidence of an oscillatory component. The data for one sample were Fourier analyzed in order to detect any latent periodicity in the photoresponse, and a weak periodic component at meV intervals was found and tentatively associated with localized phonon modes.
Reproducible Liquid-Phase-Epitaxial Growth of Double Heterostructure GaAs–AlxGa1−xAs Laser Diodes
Authors: Miller B. I. , Pinkas E. , Hayashi I. , Capik R. J.
Published: February 2004

Highly uniform GaAs–AlxGa1−xAs double heterostructure (DH) wafers have been reproducibly grown, and when fabricated into DH laser diodes yield diodes whose current threshold densities Jth lie within ±5% of each other. Other laser parameters such as lasing wavelength and external differential quantum efficiency ηD also show the same uniformity. The DH wafers can be reproducibly grown so that these parameters lie within ±10% from wafer to wafer. The methods used to achieve these results employ a well-designed sample holder, minimization of contaminants into the system, reproduction of oven gradients from run to run, and careful temperature control and temperature reproducibility. Using these techniques, we have been able to grow DH wafers, whose active layers are as thin as 0.14 μm. When fabricated into laser diodes, 200 mW of continuous power output has been obtained at room temperature.
Influence of Oxide Layers on the Determination of the Optical Properties of Silicon
Authors: Philipp Herbert R.
Published: February 2004

Experimental reflectance data for silicon are corrected for the presence of a surface oxide layer and analyzed using the Kramers-Kronig relation to yield a set of optical constants for oxide-free silicon. For etched silicon samples exposed to the atmosphere for ∼ 1 h, this layer is 12–15 Å thick and has the approximate composition SiO. Absorption data are also given for epitaxial silicon on spinel and used as an aid in the analysis.
Photocapacitance Effects at a Cu2S–CdS Heterojunction
Authors: Lindquist P. F. , Bube R. H.
Published: February 2004

The influence of trapped charge on the photovoltaic properties of an efficient Cu2S–CdS single-crystal heterojunction has been studied by a photocapacitance technique. For the non-heat-treated cell, a persistent increment in capacitance as high as 70% of the dark capacitance remained after illumination of the junction by band-gap light at 100°K. The additional capacitance is due to holes trapped in deep levels in the CdS depletion region near the interface. The trapped holes enhanced the 100°K photocurrent spectrum uniformly by a factor of 3 before heat treatment. After a 200°C heat treatment in air, the maximum trapped charge at 100°K enhanced the photocurrent by two orders of magnitude. The results are interpreted in terms of the tunneling through a conduction band spike of electrons photoexcited in the Cu2S. The width of the spike, and thus the tunneling probability, is controlled by the magnitude of the trapped charge. The spike height is estimated to be in the range 13–60 meV.