bluuebunny/crossref_metadata_2025 huggingface dataset:
Damping of Dislocations in Niobium by Phonon Viscosity
Authors: Mason Warren P. , MacDonald Douglas E.
Published: February 2004

Attenuation measurements have been made of the body-centered crystal niobium for three waves along the 〈110〉 direction. The room-temperature measurements are consistent with dislocations lying in the (110) planes with glide directions along the 〈100〉 axes. The fast shear has the largest attenuation and it has been measured over a temperature range from 30° to 300°K with frequencies from 10 to 150 MHz. The attenuation can be divided into a square-law attenuation and a dislocation component. The dislocation component can be used to evaluate a drag coefficient which is nearly constant down to 78°K. It rises at low temperatures indicating an electron drag effect. The constant region is consistent with a phonon viscosity damping with a crystal having a peak in the thermal conductivity. The electron drag confirms a theoretical calculation giving a drag inversely proportional to the electrical resistivity.
Propagation in a Rectangular Waveguide Partially and Completely Filled with an Isotropic Inhomogeneous Plasma
Authors: Gonzalez Guillermo
Published: February 2004

Series form solutions are given for both the TEl0 and the LSM mode in a rectangular waveguide partially and completely filled with an isotropic inhomogeneous plasma. The inhomogeneity of the plasma is represented by a polynomial profile and assumed to occur in the direction transverse to the direction of propagation in the waveguide. Numerical calculations showing the variations of cutoff frequency vs the thickness of the plasma are given.
Dispersion of Transient Electromagnetic Signals Propagating along a Coaxial Gas Discharge
Authors: McIntosh Robert E. , Andrews Robert G.
Published: February 2004

Measurements of an rf Gaussian pulse propagating along a coaxial gas discharge indicate that the dispersion suffered by the pulse can be attributed to the anode glow region of the discharge. The signal's group velocity agrees with an approximate theory in which the region between the two conductors is filled with a homogeneous plasma. Large amounts of signal spreading and attenuation are observed near the average electron plasma frequency and are ascribed to collision and intermode coupling losses in the system.
Propagation of an Intense Relativistic Electron Beam Through a Plasma Background
Authors: Levine L. S. , Vitkovitsky I. M. , Hammer D. A. , Andrews M. L.
Published: February 2004

Experiments have been performed to study the propagation of an intense relativistic electron beam [input (ν/γ)≃2.5] in a drift tube filled with either neutral gas or preexisting plasma. Beam front velocity, magnetic neutralization, and energy transport are measured. Results for propagation into neutral gas confirm previous work. Propagation into a preionized background is characterized by nearly complete magnetic neutralization. However, the beam front velocity never exceeds 60% of its potential value, and a two-stream instability is suggested as a possible explanation. The efficiency of beam energy propagation through the plasma is found to depend on the neutral background density, and a possible cause of this effect is suggested. Hollow beam profiles are observed under suitable conditions.
Shot Noise in Platinum-Gallium Arsenide Schottky Barrier Diodes
Authors: Minniti R. J. , Neudeck Gerold W. , Anderson R. M.
Published: February 2004

The high-frequency shot noise of Pt–GaAs Schottky barrier diodes has been measured at 60 MHz for both guard-ring and non-guard-ring structures. The measured equivalent noise temperature agrees well with the shot-noise theory of semiconductor junctions at relatively high forward currents where the metal-semiconductor interface effects can be neglected. At low levels of forward bias the measured noise is greater than that predicted by conventional theory. A measured excess-leakage conductance showing full thermal noise is added to the model and accounts for part of the difference between theory and experiment. The requirements for low-noise diodes are outlined.
Effects of High Pressure on Amorphous Polymers. II. Annealing of Densified Polymethyl Methacrylate
Authors: Kimmel R. M. , Uhlmann D. R.
Published: February 2004

The annealing at atmospheric pressure of polymethyl methacrylate (PMMA) densified in various pressure-temperature-time cycles has been examined in the temperature range 25°–90°C. PMMA densified in the glassy state was found to be less stable than that densified by cooling through the glass transition under pressure, in agreement with previous results on inorganic glasses. Moreover, the relative stability of densified PMMA depended on the sample residence time in the glass transition region at pressure. In the one case where an energy spectrum for annealing could be calculated, the data indicated a multiplicity of molecular processes with activation energies in the range 14–19 kcal/mole.
Axial Yield Strengths and Two Successive Phase Transition Stresses for Crystalline Silicon
Authors: Gust W. H. , Royce E. B.
Published: February 2004

Shock wave experiments with inclined prisms have been used to determine the compression for shocks propagated along three axes of single-crystal Si. At stresses less than about 200 kbar, the shocks along the 〈110〉 and 〈1111〉 axes exhibited four wave structures. The first three waves were taken to be related to the Hugoniot Elastic Limit and to two succeeding polymorphic phase transitions. Scatter in the magnitude of the HEL along the 〈100〉 axis may indicate mixing between the elastic wave and the first phase transition wave.
Stimulated Emission of Bremsstrahlung in a Periodic Magnetic Field
Authors: Madey John M. J.
Published: February 2004

The Weizsäcker-Williams method is used to calculate the gain due to the induced emission of radiation into a single electromagnetic mode parallel to the motion of a relativistic electron through a periodic transverse dc magnetic field. Finite gain is available from the far-infrared through the visible region raising the possibility of continuously tunable amplifiers and oscillators at these frequencies with the further possibility of partially coherent radiation sources in the ultraviolet and x-ray regions to beyond 10 keV. Several numerical examples are considered.
Interferometric Measurements of Time-Dependent Electron Density in the Xenon ``Pinched'' Plasma Laser
Authors: Papayoanou A. , Gumeiner I.
Published: February 2004

Spectroscopic measurements have indicated that laser lines obtained with a xenon ``pinch'' laser arise from transitions in triply ionized species. Measurements of the time-dependent electron density and of the plasma dynamics indicate that this is indeed the case.
Neutron Damage in Epitaxial GaAs Laser Diodes
Authors: Barnes C. E.
Published: February 2004

The effects of neutron irradiation on the radiative, nonradiative, and threshold currents in epitaxial GaAs laser diodes have been studied at room temperature and 76°K. At 300°K for currents below the threshold, most of the current flows by recombination in the space-charge layer, but the radiative current is due to minority carriers thermally injected into the p-type region. Neutron irradiation does not significantly affect these current flow mechanisms. However, it does lead to a reduction in light intensity and an increase in total current through the introduction of nonradiative recombination centers which reduce the lifetime in both the space-charge and neutral regions. Neutron irradiation has less of an effect on the diode properties at 76°K. The radiative current, which is apparently due to tunneling, is rather insensitive to irradiation when the voltage is held constant. However, at constant current the light intensity decreases with neutron fluence although not as rapidly as in the constant current case at 300°K. Similar to the results at 300°K, the total current increases with irradiation; the additive current being due to space-charge recombination and nonradiative tunneling. The laser threshold current increases with neutron irradiation by a multiplication factor which is approximately independent of temperature. The changes in JT can be accounted for by assuming that the neutron-induced nonradiative recombination centers lead to a decrease in the internal stimulated quantum efficiency. Very little annealing of the light degradation was observed between 19° and 550°K. No neutron-induced time delay in laser turn on was detected.
Negative Anhysteretic Susceptibility, Internal Fields, and Domain Wall Interaction in Tape-Wound Cores of 50%–50% NiFe
Authors: Baldwin John A. , Calkins T. R.
Published: February 2004

Tape-wound cores of grain-oriented 50%–50% NiFe were studied in this investigation. The internal field generated by the sample was measured by means of anhysteretic magnetization curves. It was found that, in some cases, the internal field was regenerative, i.e., of the same polarity as the average magnetization. In some cases both a regenerative field and a degenerative demagnetizing field could be separately observed. The demagnetizing field is not a linear function of flux. If the internal field is regenerative, the anhysteretic susceptibility is negative. In order to measure negative anhysteretic susceptibility it is necessary to control the flux of the sample and measure the required magnetomotive force rather than vice versa. Otherwise one measures a spurious infinite susceptibility. A regenerative internal field explains the tendency of minor loops, for some cores, to drift away from the center of the major loop and into plus or minus saturation (``minor loop drift''). This is shown to be a case of positive feedback in which the loop gain exceeds unity and the system is unstable. The regenerative internal field is shown to be the result of magnetostatic interaction between pole-bearing domain walls. The internal field is not a single-valued function of flux, but depends on the detailed magnetization pattern of the sample. The characteristic field of the interaction is of the order of several A/m. The characteristic length is of the order of 10 m.
Wall Stability of Cylindrical (Bubble) Domains in Thin Films and Platelets
Authors: Schuldt S. , Chen D.
Published: February 2004

The stability in an applied magnetic field of a domain of reversed magnetization in an otherwise uniformly magnetized thin-film medium, has been investigated experimentally and theoretically. From a free energy point of view, a field applied antiparallel to the magnetization of the reversed domain tends to affect the size of the domain based on energy minimization. Assuming a cylindrical domain, we have: (1) calculated the total energy due to the domain wall, the magnetostatic field, and the applied field; (2) compared the inward force on the domain wall derived from this total energy with a coercivity or retarding force to establish a threshold applied field for domain motion; and (3) compared theoretical predictions with experimental results in both MnBi films and an orthoferrite platelet. Comparisons were based on values of saturation magnetization and domain-wall energy density which are believed typical or have been reported elsewhere. Agreement of the data with calculation is considered satisfactory for both media. The requirement of accurately measuring MnBi spots of the order of 1 μ in size was met using an automatic Faraday modulation polarimeter. A detailed description of this novel instrument is included.
Diffusion-Controlled Growth of an Array of Plates
Authors: Atkinson C.
Published: February 2004

A simple model for dendritic and Widmanstätten plate growth is considered. This model is applied to an array of plates and a relation obtained between the speed, tip radius of curvature, and spacing of the plates. An expression is found for the ratio of the flux at the tip of one of an array of plates to that at the tip of an isolated plate. This expression is tabulated as a function of bV/2D, where b is the spacing, V the velocity of the plates, and D the diffusion coefficient in the matrix.
Quantum Kinetic Equation for Electron Oscillations in a Weakly Ionized Plasma
Authors: Willett Joseph E. , Warner David C. , Fisher David M.
Published: February 2004

A quantum kinetic equation is derived for the free electrons of a weakly ionized plasma in the presence of a space—time-dependent longitudinal electric field. The derivation is based on a one-electron density matrix formalism with scattering by neutral particles treated in the first Born approximation. A systematic procedure for averaging over the random distribution of fixed scattering centers is employed to avoid the criticism of previous methods. The collisional damping decrement for electron electrostatic oscillations is obtained in the classical limit to second order in the wave number.
Gamma Irradiation of Lithium-Drifted Silicon
Authors: Kool W. H. , Goedbloed J. J. , Ammerlaan C. A. J.
Published: February 2004

Boron-doped silicon, compensated by the lithium ion drift method, was irradiated at room temperature with 60Co gamma rays. Resistivity and Hall-effect measurements show the samples to be p type immediately after irradiation. Kept near room temperature the p-type conductivity of the samples spontaneously increases because lithium donors are lost by precipitation on irradiation-produced defects. Also other defects are introduced which have an electron energy level at Ev+(0.25±0.03) eV in float zone and at Ev+(0.30±0.03) eV in oxygen-rich silicon. The latter level is ascribed to the association of oxygen with an interstitial silicon atom.
Optical Phase-Shift Measurement of Carrier Decay Times (77°K) on Lightly Doped Double-Surface and Surface-Free Epitaxial GaAs
Authors: Keune D. L. , Holonyak N. , Burnham R. D. , Scifres D. R. , Zwicker H. R. , Burd J. W. , Craford M. G. , Dickus D. L. , Fox M. J.
Published: February 2004

By the optical phase-shift technique measurements are made (77°K) of excess carrier lifetimes on ``surface-free'' thin layers of lightly doped n- and p-type GaAs, and on damage-free vapor-grown thin blades. The nonradiative losses due to surface recombination are minimized by selectively photoexciting the center layer of a GaAlAs(n+)/GaAs(n or p)/GaAs(n+) structure through the first layer, which acts as a window and as a confining barrier of excess carriers. The spontaneous carrier lifetime (δn∼1016/cm3) for surface-free epitaxial layers of n-type GaAs (ND-NA=2.42×1015 cm−3) and for p-type GaAs (NA-ND=4.64× 1016 cm−3) at 77°K is 4.1 and 4.3 nsec, respectively, which is to be compared with a value of 1.9 nsec for a thin damage-free vapor-grown blade not seeded on a substrate.
Piezoresistance in Quantized Conduction Bands in Silicon Inversion Layers
Authors: Dorda G.
Published: February 2004

Piezoresistance measurements have been carried out on n-type inversion layers on (100), (110), and (111) silicon at room temperature as a function of the gate voltage (perpendicular electric field). It has been shown that the values of the piezoresistance coefficients depend not only on the surface orientation but also on the magnitude of the gate voltage. The strongest surface field influence was observed in the (100) plane whereas no gate voltage dependence could be detected on (111) surfaces. The data obtained have been interpreted in terms of the quantization of energy levels in inversion layers. This quantization causes generally an occupation anisotropy of the valleys mostly pronounced for an electric field in the [100] direction and disappearing for a [111] direction of the field. Theoretical expressions for the (100) piezoresistance coefficients π11 and π12 have been derived taking into account the field dependences of the population effect and of the intervally scattering contribution, both affected by the valley anisotropy. Experimental data have been fitted to the theory. From this fit numerical values of the occupation anisotropy of the valleys and of the anisotropy of the relaxation times relating to the intervalley scattering have been obtained.
Properties of the Ternary Compound ZnIn2S4 at High Electric Field
Authors: Mora S. , Paorici C. , Romeo N.
Published: February 2004

ZnIn2S4 single crystals, grown from the vapor phase by iodine transport, display interesting current-voltage characteristics at high electric fields. Some crystals under illumination show an n-type negative-resistance effect. However, in other crystals which do not show such an effect, current oscillations occur whose frequency is strongly dependent on the applied electric field and the intensity of the light by which the crystal is illuminated. Furthermore at still higher electric fields, a permanent transformation of the crystals takes place; in these new conditions the crystals display an s-type negative-resistance effect.
Transient Optical Double Injection in Insulators
Authors: Gill W. D. , Batra I. P.
Published: February 2004

The transient analysis for optical double injection into a perfect insulator is presented for arbitrary levels of pulsed injection. Exact solutions, in the absence of trapping and neglecting diffusion, are obtained for the transient behavior of the total current density, the electric field distribution, the space-charge distribution, and the conduction current density. The results are valid up to the meeting time of the leading fronts of the injected carrier pulses. Numerical solutions of the transcendental equation for the meeting time are obtained for several values of carrier injection level and relative mobilities. Some of the analytic results have been verified experimentally in anthracene crystals using pulsed light to simultaneously inject carriers at both electrodes. The total current density for step-function illumination under space-charge-limited double-injection conditions is also obtained.
Electronic Structure of Cubic Refractory Carbides
Authors: Ramqvist Lars
Published: February 2004

Recent electron (ESCA) and x-ray emission and absorption spectra for the cubic refractory carbides of Group IVb (TiC, ZrC, HfC) and Group Vb (VC, NbC, TaC) are summarized. Based on an interpretation of the experimental data by using self-consistent-field calculations on free atoms and ions and supported by an approximately self-consistent augmented-plane-wave calculation on TiC, a model of the electronic structure is presented. The metal atoms are positive and the carbon atoms negative in the refractory carbide. The electrostatic (Madelung) energy of a cubic carbide is less than one-third of the total binding energy and equals the heat of formation of the carbide.
Roughness of the Crystal-Vapor Interface
Authors: Leamy H. J. , Jackson K. A.
Published: February 2004

The equilibrium structure of the interface between a Kossel crystal and its vapor has been investigated by Monte Carlo simulation techniques, and by statistical mechanical analysis in zeroth- and first-order approximation. The interface structure depends on L/kTe, where L is the latent heat, k is the Boltzmann constant, and Te is the equilibrium temperature. The results differ significantly from earlier calculations based on single level models of the interface or on simpler statistical models of the interface. The roughness of the surface R, which is defined as the energy of the surface relative to the energy of a smooth boundary, was found to increase with kTe/L and to be almost the same for each model. The extent of the surface S defined as the number of surface molecules per unit area also increases with kTe/L and is also almost independent of the model. The distribution of atoms amongst the various energy levels has been calculated, and again is similar for the three models. The interface profile is similar for all three models for large and small values of L/kTe, but the Monte Carlo calculations differ from the other two models for intermediate values of L/kTe. Calculations using the zeroth-order model for (110) and (111) faces shows that the surfaces are somewhat rougher than the (100) surface and also have greater extent.
Ultraviolet Laser-Excited Fluorescence Decay Measurements by Convolution Techniques
Authors: Kashnow R. A. , Sousa J. A.
Published: February 2004

Convolution techniques are employed to extract fluorescence decay times, in the nanosecond regime, where the fluorescence is excited by a pulsed uv laser. Data are reported for several organic dyes which are useful in dye lasers.
Physical Properties of Lead Molybdate Relevant to Acousto-Optic Device Applications
Authors: Coquin G. A. , Pinnow D. A. , Warner A. W.
Published: February 2004

All of the elastic and photoelastic constants of crystalline lead molybdate (PbMoO4) and various optical and thermal properties of the material have been measured. This information has been used to evaluate the material for a number of practical acousto-optic device applications. The high figure of merit found in earlier preliminary studies is only 10% smaller than the maximum figure of merit of the material. Thus the material is well suited for acousto-optic modulator and deflector applications. However, the material is not particularly useful for tunable acousto-optic filters because the relevant elasto-optic coefficient is small. Acoustic and optical losses, and changes in sound velocity and index of refraction with temperature, can cause operating limitations in practical devices, and these are discussed.
Experimental Hydroacoustic Imaging System
Authors: Knollman G. C. , Brown A. E. , Weaver J. L. , Bellin J. L. S.
Published: February 2004

An underwater acoustic imaging system is described which has been developed especially for close-range, high-resolution (on the order of millimeters) viewing in very turbid water. The system operates at nominal 2.5-MHz frequency and has a range up to 10 m in water of suspended ocean sediment concentration as high as several thousand parts per million. Larger range capability is possible with lower sediment concentration. Real-time kinescope displays are presented by the system of the acoustic field of view, which is that insonified by a high-intensity sound transmitter of total beamwidth variable up to 30° in 10° increments. The sensitive (better than 10−10 W/cm2) piezoelectric image converter is augmented by a mechanical scanning system to provide in effect a 10 000-element pickup matrix. A Plexiglas lens moved by remote-control drive is employed for focusing. System parameters and performance are discussed, and some typical hydroacoustic images are displayed.
Temperature Variation of Susceptibility of Some Amorphous Antiferromagnetic Oxides
Authors: Simpson A. W. , Lucas J. M.
Published: February 2004

The temperature dependence of the susceptibilities of amorphous magnetic oxides with various iron/yttrium and iron/gadolinium stoichiometries have been studied between 4.2° and 320°K. The reciprocal susceptibilities of the iron/yttrium oxides exhibited an unusual downward curvature at low temperatures. These measurements are interpreted by means of a simple effective field model for amorphous antiferromagnetic materials recently proposed by one of the authors. Good agreement between the experimental results and the theory is obtained. The analysis enables certain broad conclusions to be drawn about the number and distribution of interacting pairs of magnetic atoms.
Temperature Gradient Induced Migration of Gas-Filled Bubbles in KCl
Authors: Carter R. E. , Rosolowski J. H. , Nadeau J. S.
Published: February 2004

The temperature gradient induced migration of gas bubbles has been studied in KCl. This material was selected because of its high vapor pressure and transparency. The experimental variables of temperature, temperature gradient, and diffusion coefficient of the vapor species were investigated and the observed velocities were shown to agree with those expected from the theoretically derived model. The ratio of the temperature difference across a bubble of low thermal conductivity to that across an equal length of the surrounding solid was determined from analogue experiments.
Cell-Wall Dislocation Damping in Single-Crystal Cu
Authors: Akita H. , Fiore N. F.
Published: February 2004

The dislocation substructure of 〈111〉 Cu single crystals has been controlled by varying crystal growth rates from 1.57 to 109 cm/h. Etch-pitting and x-ray studies reveal that the substructure consists of a random dislocation network, with density 1×106/cm1 independent of growth rate, and dislocation cells whose size and intercell misorientation angle increase with decreasing growth rate. Longitudinal resonance bar and ultrasonic pulse-echo damping measurements at frequencies from 25 kHz to 100 MHz show that the larger the cell size, the higher the damping over the entire frequency range. There is strong evidence that damping from cell-wall dislocations overshadows that due to the random network. The results are interpreted in terms of a modification of the Granato-Lücke damping theory, which treats cell walls as pseudomembranes vibrating under the action of the applied stress.
Reflection and Refraction of Plane Waves from Plane Ferrite Surfaces
Authors: Mueller R. S.
Published: February 2004

Wave vector surfaces, phase velocity surfaces, and ray velocity surfaces have been evaluated for electromagnetic waves traveling through magnetized ferrite. These surfaces are shown to have unique shapes depending upon the precessional, magnetization, and excitation frequencies. Double refraction of the waves occur at the interface between different ferrites. A transcendental equation for determining the angle of transmission is presented and a discussion is made on the possibility of total reflection. Since the direction of propagation, boundary surface normal, and direction of magnetization each present a degree of freedom to the incident plane wave problem a general set of coordinates is introduced that takes into account their relative orientation. The two cases for which the static magnetization is parallel and perpendicular to the plane of incidence is solved in detail and expressions are given for the reflection and transmission coefficients. It is shown that for the parallel magnetic polarization case the reflected component of the electric vector can be eliminated if the incident wave strikes the boundary plane at a magnetically dependent Brewster angle.
Simple Model for Internal Photoemission
Authors: Dalal Vikram L.
Published: February 2004

We have studied the influence of film thickness and collision processes upon the internal photoemission process in metal-semiconductor systems. A simple, one-dimensional random walk model has been used. The analysis shows that significantly larger yields may be expected for film thicknesses of the order of or less than electron-phonon mean free paths. The influence of energy dependent mean free paths has also been studied. The results are in qualitative agreement with the results of Fermi-age theory, but are somewhat different quantitatively.
Analysis of Photoemissive Schottky Barrier Photodetectors
Authors: Dalal Vikram L.
Published: February 2004

The performance of Schottky barrier photodetectors employing internal photoemission process is studied. Background-photon-noise limited detectivities Dλ* have been calculated for typical operating conditions. The use of cooled optical filters has also been investigated. The analysis shows that the detectivities may be considerably less (by about an order of magnitude) than those realized for the more conventional quantum detectors employing photovoltaic or photoconductive effects.
Domain Wall and Magnetoelastic Resonances in Hematite
Authors: Maartense I. , Searle C. W.
Published: February 2004

The rf susceptibility of synthetic hematite (α-Fe2O3) has been recorded as a function of applied field for frequencies between 80 kHz and 80 MHz at 300°K. Above 25 MHz, a notch about 11-Oe wide appears in the susceptibility near zero field, with a maximum depth at 42 MHz. Analysis of the data in terms of domain wall resonance dispersion leads to the following parameters for mobile walls: resonance frequency ν0=25 MHz, effective wall mass μ=3.0×10−13 g/cm2, wall stiffness constant α=7.4×103 g/cm2 sec2, and damping constant β≈8.5×10−5 g/cm2 sec. The presence of a large number of strongly pinned domain walls is also confirmed by the data. In the 80–500-kHz region strong narrow resonance dispersions have been found at fields up to the experimental limit of ±500 Oe. These resonances are magnetically tuneable over a 2:1 frequency range, and have a magnetoelastic nature; they are also dependent upon the quality of the crystal's annealed state. A preliminary interpretation is based on the coupling of the crystal's acoustic resonance modes with low-lying spin-wave modes excited near local crystal strains, resulting in magnetoelastic standing waves.
NMR Studies of 1H and 3He Contained in Gold Films
Authors: Weaver H. T.
Published: February 2004

Transient nuclear magnetic resonance (NMR) measurements are presented for 1H and 3He in the systems Au–H and Au–He, respectively. Solute content values of 31 at.% H in Au–H and 18 at.% He in Au–He were obtained by spin counting procedures. Spin-spin relaxation times (T2) of 30, 24, and 0.008 msec and spin-lattice relaxation times (T1) of 0.25, 0.18, and 0.37 sec at 300, 77, and 4 K, respectively, were found for 1H in Au–H. For helium, T1 was found to be 0.7, 0.7, and 53 sec and T2 was 2, 1.1, and 0.8 msec at the above temperatures. The hydrogen data indicate that high-pressure gas pockets are present within the metal whereas the helium situation is not as straightforward. Data from both systems are analyzed regarding possible placement of the hydrogen and helium in the gold lattice.
Improved Phase-Sensitive Detection by Optical Equivalent of Hard Limiting
Authors: Stone J.
Published: February 2004

A method is described for improving the sensitivity of an optical interferometer. The method is to divide the electrical output of the interferometer by a voltage proportional to the incoming light intensity. The resultant ratio is independent of incoming light intensity and also suppresses fluctuations in the interferometer output due to fluctuations in the incoming light. Using this technique, noise suppression by a factor of 50 has been obtained in a Mach-Zehnder type interferometer. Larger factors should be obtainable. It is shown how the same technique can be applied to other types of interferometers.
Analytical and Experimental Study on Landau Damping of Surface Wave along a Plasma Column
Authors: Ida Yoshio , Hayashi Kenichi
Published: February 2004

A resonator method is used to demonstrate Landau-damping of surface waves along a plasma column. As a method of plasma diagnostics, an open plasma resonator utilizing longitudinal resonance of the surface wave has been proposed by one of us. This work presents an analysis of anomalous damping in terms of the Q factor observed in the open plasma resonator. In the analysis, the effect of energy absorption by the thermal electrons travelling across the side boundaries of the resonator is accounted for. A method of single-mode excitation which is convenient for experimental determination of the Q factor is also described. The results of Q measurements are compared with the computer solutions; the Landau-damping mechanism which is responsible for the anomalous damping in the Q factor is examined.
Photoluminescence of Ion-Implanted Oxygen in ZnTe
Authors: Merz J. L.
Published: February 2004

Photoluminescence from the oxygen isoelectronic trap implanted into ZnTe is investigated for various ion doses and annealing conditions. The characteristic oxygen spectrum is observed after annealing either in zinc vapor or in vacuum. The anticipated isotope shift is observed in the spectrum for samples implanted with 18O without the usual 16O contamination found in conventionally doped samples. In isochronal anneal studies the intensity of the oxygen luminescence peaks at 300°–400°C. For samples annealed in Zn vapor the anneal curves show a slight dip at higher temperatures, whereas for vacuum anneals the curves fall off rapidly. The dose for maximum luminescence is found to be a function of the anneal temperature. Much of the gross lattice damage is annealed at 500°C; at this temperature the luminescence peaks at a dose of ∼1014 ions/cm2, corresponding to an implanted concentration of ∼2×1018/cm3. Although reasonable luminescence intensities have been achieved, compared with conventionally doped samples, only ∼5% of the light intensity anticipated on the basis of the implant dose is actually observed as emission from the oxygen isoelectronic trap.
Electron Microscope Study of Radiation Damage in Bismuth Ion-Implanted Cds
Authors: Govind P. K. , Fraikor F. J.
Published: February 2004

Electron microscopy has been used to study the ion-fluence dependence of structural disorder in CdS single-crystal platelets following 25-keV bismuth implantations at room temperature in the dose range of 7×1015−3.2×1016 ions/cm2. Bright-field photomicrographs revealed ``black spots'' ∼100 Å in diameter in the CdS microstructure. The contrast behavior of the strain field surrounding these spots indicated that the majority of spots were interstitial clusters or unresolvable interstitial dislocation loops. The electron diffraction patterns did not show any evidence of amorphous zones in the implanted specimens and there was no indication of a second-phase precipitate.
Materials Problems in Lithium-Drifted Germanium Radiation Detectors II
Authors: Jindal G. R. , Faust J. W.
Published: February 2004

This paper describes materials problems involved in the preparation of lithium-drifted germanium gamma-ray detectors. A comparison is made of gallium- and indium-doped germanium (both good and bad drifters). Furthermore, heat-treated gallium-doped material is compared with heat-treated material with lithium present.
Field-Gradient Voltage in III-V Compounds
Authors: Sharma Satish K. , Dubey P. K.
Published: February 2004

A theoretical study of the field-gradient voltage (FGV) has been made in III-V nonparabolic semiconductors at low and high (k0T<ℏωl, k0T>ℏωl; ωl is the limiting frequency of an optical phonon) temperatures. It is seen that FGV increases with decreasing lattice temperature for the same value of the electric field and electron concentration. FGV at low temperatures is larger by two orders-of-magnitude than the value at high temperatures. In the warm electron region it is seen that FGV is proportional to the square of the electric field in both the temperature ranges, in agreement with earlier results. Some numerical results are presented for n-InSb.
Carrier Mobilities in Pb1−xSnxTe Alloys
Authors: Wagner John W. , Thompson Alan G. , Willardson Robert K.
Published: February 2004

Experimental measurements on the transport properties in Pb1−xSnxTe single-crystal alloys at 77°K have been made as a function of both carrier concentration and composition. The measurements were made on p-type materials, primary interest being in the carrier concentration range where impurity scattering was clearly dominant (p≥1×1019 cm−3). The entire compositional range has been studied and the results reveal the following compositional regions with differing transport characteristics: (1) the region containing from 2- to 5-mol% SnTe, where there is a rapid decrease in hole mobility at any given carrier concentration, (2) the region from 5- to 37-mol%, where the hole mobilities are essentially independent of composition, (3) the region from 37- to 40-mol% SnTe, where a distinct discontinuity in the hole mobility occurs, and (4) the region from 40- to 100-mol% SnTe, where the hole mobility gradually increases with tin content.
Reactions of Silicon with Surfaces of Close-Packed Metals: Silicon on Aluminum
Authors: Jona F.
Published: February 2004

The reactions of silicon with the principal surfaces of aluminum, viz., Al {100}, Al {110}, and Al {111} in their clean state, are investigated by means of the low-energy electron diffraction (LEED) technique. On Al {100}, silicon is disordered; on Al {110}, it forms an 8×2 superstructure; on Al {111}, it forms a 3×3 superstructure. The experiments prove that, upon heating, silicon diffuses into the bulk aluminum lattice very rapidly at temperatures slightly higher than ambient. Structural models are proposed for the ordered structures which lead to the prediction of a √3−30° structure of Si on Ni {111} and Be {0001}.
Specific Heat of CsBr at Low Temperature
Authors: Robbins R. A. , Marshall B. J.
Published: February 2004

Measurement of the specific heat from 1.136° to 5.623°K have been made on a single crystal of CsBr. The Debye temperature at 0°K was calculated to be θ0=150.9°K.
Deformation Potential and Piezoelectric Ultrasonic Phonon-Charge Carrier Coupling in Indium Antimonide
Authors: Smith W. D. , Miller J. G. , Sundfors R. K. , Bolef D. I.
Published: February 2004

The interaction of ultrasonic phonons with charge carriers in nearly intrinsic InSb via deformation potential and piezoelectric coupling mechanisms has been investigated at 296 K in magnetic fields of 0 to 11 kOe and over a frequency range of 10 to 200 MHz. The single crystal InSb was p type with an average acceptor concentration of (1.45±0.05)×1016 cm−3. The experiment permitted an ultrasonic determination of the electron and hole mobilities. The values obtained were μn0 = (58 000±4000) cm2 V−1 sec−1 and μp0 = (720±80) cm2 V−1 sec−1. Values of the deformation potential and piezoelectric coupling constants obtained were | Cn+Cp | = (5.8±0.4) eV and e14 = | 0.076±0.010 | C/m2.
Electron and Nuclear Magnetic Resonance in Semiconducting Phosphate Glasses
Authors: Lynch G. F. , Sayer M. , Segel S. L. , Rosenblatt G.
Published: February 2004

Paramagnetic vanadium-phosphate and molybdenum-phosphate glasses have been studied using electron-spin resonance and nuclear magnetic resonance. These glasses were nominally 80% MO:20% P2O5, where MO denotes the transition-metal oxide. The electron-spin-resonance results showed a strongly exchanged, narrowed interaction with V4+/V5+ and Mo5+/Mo6+ ratios and line shapes which were independent of temperature over the range 77°–300°K. Since the conductivity is nonlinear in this temperature range, the result is direct evidence that the mobility is temperature dependent and that the average paramagnetic-site is unchanged over this temperature range. The nuclear magnetic resonance of 51V and 31P in the glasses verifies the assumption of exchange narrowing. The 51V quadrupole coupling (1.5 MHz) and spin-lattice relaxation time (T1<500 μsec) were temperature independent over the 77°–300°K range. The 31P resonances in each of the glasses also had temperature-independent properties. For the molybdenum glass the linewidth was 0.45 G and T1=300 msec. For the vanadium glass the corresponding numbers were 1.4 G and <500 μsec. The results are compared in part with previously published values.
Effects of Contact Placement and Sample Shape in the Measurement of Electrical Resistivity
Authors: Stephens A. E. , Mackey H. J. , Sybert J. R.
Published: February 2004

The resistivity of a sample is given by ρ=VI−12πsF, where V is the voltage, I is the current, s is the voltage contact separation, and F is a correction factor appropriate to the sample geometry. Correction factors are found for the cases of parallelepiped samples with (1) nonequidistant point contacts symmetrically located on the top face, and (2) point voltage contacts symmetrically located on the top face and point current contacts centered on the end faces. In studies of these cases, curves are given for determining the geometries which give, between the voltage contacts, current densities directed parallel to the sample length. Although in the development it is assumed that the resistivity is homogeneous and isotropic and that there is no magnetic field present, a discussion is given on the applicability to anisotropic resistivity and low magnetic fields. Experimental verification is given.
Calculations of the Energy of Subgrains in a Lattice-Parameter Gradient
Authors: Winchell P. G. , Boah John , Ayres P. S.
Published: February 2004

The dislocation-associated energy of subgrains in a lattice-parameter (concentration) gradient is calculated using two-dimensional isotropic elasticity and neglecting almost all subgrain-subgrain interactions. The subgrains are rectangular and are bounded by regular arrays of pure edge dislocations with Burgers vector normal to the gradient. These boundaries are either lattice-parameter step boundaries or tilt boundaries. The energy per unit volume normalized by μ/4π(1−ν) is R−1[2α−1+ln(b/2πρ0)−α lnα−(1−α)ln(1−α)−α ln(QH/R)−(1−α)ln(H/R)]+(H2/12R2){8(1−α)tan−1Q+(1−4α)Q+[(3−6α+3α2)Q−(1−4α+3α2)Q3]ln(1+Q−2)+[3α2Q+(9α2−6α)Q−1]ln(1+Q2)},where ρ0 is the dislocation core radius, b is its Burgers vector, α is the fraction of dislocations in tilt boundaries, bH is the height of the subgrain (parallel to the concentration gradient), Q is its length to height ratio, bR is its relaxed radius of curvature due to its lattice parameter gradient, μ is the shear modulus, and ν is Poisson's ratio. Two low-energy regimes are identified: first at low H, high Q, and α=0, the lattice-step boundary regime; second at high H, low Q, and α=1, the tilt boundary regime. The latter appears to be slightly lower in energy.
Exact Positions Occupied by Dislocations in a Planar Array
Authors: Smith E.
Published: February 2004

For a very restricted range of situations, earlier work has shown that the exact equilibrium positions of discrete dislocations in a planar array may be obtained analytically, in the sense that they are given by the zeros of classic polynomial functions satisfying certain second-order differential equations; at the same time analytic expressions have been derived for the stresses acting on obstacle dislocations. This paper explores the various models that evolve as a consequence of applying an appropriate coordinate transformation to the most general situation hitherto considered, and the range of application of the analytical approach is thereby extended.
Electromigration Damage in Thin Films due to Grain Boundary Grooving Processes
Authors: Ohring Milton
Published: February 2004

A theory of electromigration damage in thin films by grain boundary grooving processes is presented. A bicrystal film configuration is assumed and profile changes caused by the applied electric field are calculated. The grain boundary constraint converts mass transport along the surface into equivalent thinning changes normal to this direction. Grooving processes are consistent with damage manifestations, such as grain boundary cracks and voids, as well as thinning; specific grooving mechanisms due to the effects of the variable surface curvature and temperature are considered separately and the kinetics of these damage modes are derived. While the latter mechanism yields damage times in agreement with experiment, the effects of variable surface curvature considerably overestimate the film lifetime. This suggests that accelerated thinning due to localized heating, lack of adhesion, and locally enhanced current densities, may be quite important in cases where gross heating effects and temperature gradients are small. The kinetics of the resistance variation in a piecewise straight conductor, grooving by surface curvature effects, is derived and compared with experiment.
Inhomogeneous Plasmas: On the Reflection and Transmission of Fields of Arbitrary Polarization
Authors: Taylor Clayborne D. , Harrison Charles W.
Published: February 2004

One objective of this paper is to develop a simple numerical procedure to determine the electromagnetic field penetration through a slab many hundreds of wavelengths in thickness of cold plasma with collisions. The electron-density-collision frequency profiles may be arbitrary but must contain only a finite number of discontinuities. The solution of this problem leads to a differential equation of the Riccati type. Other objectives are to evaluate exactly the transmission loss through the aforementioned inhomogeneous plasma and to determine the field variation within the plasma slab when the incident field is of arbitrary polarization. This is accomplished by solving the E and H plane incidence problems separately and then employing superposition. The results are in the form of an integral involving the reflection coefficient. The differential equations for the reflection coefficient and the transmission integrals are easily evaluated to practically any desired degree of accuracy by computer. Analytical and numerical results are presented for a plasma half-space with an exponential electron-density distribution.
Effects of Boundary Layers upon Current Distribution and Internal Resistance in Segmented Magnetohydrodynamic Channels
Authors: Taylor R. E. , Wu Y. C. L. , Denzel D. L.
Published: February 2004

The effects of nonuniform properties of an equilibrium plasma in a segmented magnetohydrodynamic generator are investigated. The current distribution is distorted more for laminar flow than for turbulent flow. The shape of the current streamlines depends strongly on wall temperature, free stream Mach number, and boundary layer thickness. For fine segmentation ratio (s/h≈0.1), the current densities are uniform at distances 10% of the channel height away from the walls. Since the two-dimensional effects are confined to this narrow region, the changes of the current distribution outside this region are due to changes in flow properties. The current distribution on the electrode is most sensitive to the electrode temperature. For hot walls, current shorting between adjacent electrodes is important and is significantly affected by the boundary layer type and free stream Mach number. Boundary layer thickness is of minor importance. Shorting decreases as the wall temperature decreases and eventually disappears when the walls are sufficiently cold. The internal resistance of the channel is within 70% of its uniform property value for hot wall (2700°K) conditions for both laminar and turbulent flows. In the cold wall case (1500°K), the internal resistance increases about 3 times over its constant property value for turbulent flow but as high as 350 times for laminar flow. For cold-wall laminar flow, the internal resistance increases almost linearly with boundary layer thickness. The comparison with experiments is favorable.
Rock Fracture Measurements: A New Use for Time-Domain Reflectometry
Authors: Sisemore Clyde J. , Stefani Ray E.
Published: February 2004

The cliper system is a real-time instrument for locating fractures in the rock surrounding a nuclear explosion. An array of transducer cables is emplaced in the region surrounding the nuclear explosive, and their lengths are continuously monitored for a period of time after the nuclear detonation. After detonation, the cables are shortened by the action of the explosive phenomenology of vaporization, plastic deformation, rock fracture, and finally chimney formation. Time-domain reflectometry is used to measure the changes in cable length. A record of these changes in length is used to correlate the explosive phenomenology with time, and thus generate an on-line picture, above ground, of the underground activity as it develops. Typical applications of the cliper system are demonstrated with rock-fracture data and chimney formation data.
Dependence of Delayed Fluorescence on the Velocity of a Moving Pattern of Light
Authors: Ern V. , Suna A. , Merrifield R. E.
Published: February 2004

The dependence of the phase and intensity of delayed fluorescence due to triplet-triplet exciton annihilation on the velocity of a moving periodic intensity distribution of light has been studied. Experimental results with anthracene crystals are in agreement with the low-density triplet exciton diffusion equation for a moving source excitation, and they establish the feasibility of detecting the speed of a spatially inhomogeneous light distribution with delayed fluorescence from a molecular crystal.