bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoemission and electron scattering in Cs3Bi and Cs3Sb
Authors: Wooten F. , Hernandez J. P. , Spicer W. E.
Published: February 2004

Photoemission studies of Cs3Bi and Cs3Sb have been made for the spectral region from 5 to 11.5 eV. Structure in the energy distribution as a result of structure in the valence-band density of states is the same as that measured previously at lower energies. As the photon energy is increased, this structure moves to higher energy by an amount equal to the increase of h ν. This further supports the argument that conservation of k is an unimportant selection rule for these materials. Monte Carlo calculations of photoemission from these materials have made possible a determination of the scattering parameters and density of states. Photoemission from Cs3Sb can be understood quantitatively only by including scattering of electrons at acceptor sites. For both Cs3Sb and Cs3Bi, the higher lying valence-band peak has an area twice that of the lower lying peak. However, the electron-electron scattering cross section happens to increase with increasing electron energy so as to reduce the magnitude of the higher lying peak in the photoelectron energy distribution in a particular way; the higher energy peak is of smaller magnitude than the lower peak but has nearly the same relative height at all photon energies. This shows that one must be careful in interpreting structure in the energy distribution as a being a replica of the density of states.
Resonance behavior of the ion-sheath capacitance near the plasma ion frequency
Authors: Oliver B. M. , Clements R. M.
Published: February 2004

A slight minimum in the measured rf capacitance of the ion sheath surrounding negatively biased planar and cylindrical Langmuir probes in a collisionless plasma has been observed. The position of the minimum, which is near the plasma ion frequency ωi, and which closely agrees with that predicted on the basis of simple physical arguments, is studied both as a function of plasma density and probe potential. The experimental results, for the planar probe, are compared with a recent theory by Rosa. The plasma was formed in the positive column of a helium dc discharge at a pressure of 0.3–0.5 Torr, with plasma electron densities and temperatures ranging between 1015 and 1016 m−3 and between 5×105 and 7×105°K, respectively. Measurements of the sheath capacitance were made using a tunnel-diode oscillator circuit whose frequency could be adjusted approximately an order of magnitude above or below ωi.
Multipole induction: a novel formulation of multiple scattering of scalar waves
Authors: Howarth B. A. , Pavlasek T. J. F.
Published: February 2004

A novel method of formulating and solving two-dimensional multiple scattering problems is described. The formalism is based on the concept of the ``induction'' of multipoles in a scatterer by an incident wave, and the subsequent coupling of multiple scattering obstacles through such ``induction''. This model is applied to the formulation of the matrix equations describing the multiple scattering of scalar waves by two- and three-cylinder configurations. Predictions for the latter case are compared with detailed near-field measurements at 23.5 GHz of the intensity and phase of the diffracted wave behind three 1.0λ-diam conducting cylinders.
Absolute Seebeck coefficient of platinum from 80 to 340 K and the thermal and electrical conductivities of lead from 80 to 400 K
Authors: Moore J. P. , Graves R. S.
Published: February 2004

The absolute Seebeck coefficient of platinum was determined from 80 to 340 K by direct comparsion to lead. Results of this comparison disagree with previous results which have been used for the calculation of absolute values for other materials. The thermal conductivity λ and electrical resistivity ρ of the lead standard were also determined. The electrical resistivity could be described with a modified Gruneisen-Bloch equation which allows for the effect of thermal expansion on the Debye temperature ΘD. The ratio λρ/T was within 1% of the Sommerfeld value of 2.443×10−8 (V/K)2 from 1.0 to 5.0 ΘD.
Low-temperature thermal properties of nylon and polyethylene
Authors: Scott Terry A. , de Bruin Johannes , Giles Monte M. , Terry Colin
Published: February 2004

The thermal conductivity and heat capacity of polyethylene and nylon samples have been measured in the temperature range 0.15–4°K. A good theoretical fit is obtained for the thermal conductivity above 1°K by using a Debye ω2 phonon frequency distribution with constant mean free path internal boundary scattering and amorphous structure scattering. Below 1°K the experimental results show a lower power dependence on temperature than would be predicted by the above theory. The theory can be modified to fit the low-temperature data by the addition of a term containing a frequency distribution proportional to ω, corresponding to two-dimensional vibrations due to the platelike nature of the individual crystallites. At temperatures below 1°K the heat-capacity data show a lower power dependence on temperature than that predicted by the Debye model. The proposed phonon frequency distribution also provides a satisfactory explanation for this behavior.
Photoeffects in potassium tantalate
Authors: Petersen P. E.
Published: February 2004

Photoeffects in high-resistivity samples of potassium tantalate having blocking metallic electrical contacts have been measured. We have observed photoconductive gains greater than unity and a rather broad spectral response. Examination of the photocurrent-voltage characteristic and the results of a series of photomasking experiments reveals that the photocurrent is limited by the junction resistance at low bias, and that a transition to bulk- (surface) limited conduction occurs as the bias is increased. We have evidence that multiple photomechanisms exist in this material. In the bulk-limited (high bias) regime, photodesorption of the surface is a contributing photomechanism.
Torque studies performed on an anisotropic superconductor: vanadium
Authors: Genberg R. W.
Published: February 2004

Null-deflection torque magnetometer measurements reveal that the torque on a vanadium single crystal in the Meissner region is consistent with, however in the mixed state is at variance with, that predicted from shape anisotropy considerations. This suggests that in the mixed state for T somewhat near Tc nonlocal effects must be considered and may be the dominant factor in determining the torque on such a specimen. In addition this study reveals a new and sensitive technique for determining the upper critical field and indicates that for T near Tc the torque in the mixed state near Hc2 is approximately proportional to Ho(Hc2−H).
Nucleation and growth of stacking faults in epitaxial silicon during thermal oxidation
Authors: Hsieh C. M. , Maher D. M.
Published: February 2004

An optical and electron microscopy study of the nucleation and growth of stacking faults in {001}-oriented epitaxial silicon has been carried out following pretreatment of the crystal in hydrofluoric acid and thermal oxidation in steam at 1050°C. A direct correlation of the etched surface structure as revealed by interference contrast optical and scanning electron microscopy with substructural defects as revealed by transmission electron microscopy has been established for times ≥1 min. The observations are divided into five stages which, taking the TEM observations as a reference, are (i) formation of a needle-shaped precipitate at the Si–SiO2 interface; (ii) nucleation of an interfacial Frank dislocation; (iii) climb of the Frank dislocation into the silicon substrate; (iv) formation of an equilibrium-shaped stacking fault; and (v) stacking-fault interactions.
Annealing studies of PbTe and Pb1−xSnxTe
Authors: Hewes C. Robert , Adler Michael S. , Senturia Stephen D.
Published: February 2004

The results of single-zone annealing of 76 samples of Pb1−xSnxTe are reported, covering the entire composition range from pure PbTe to pure SnTe. Some of the sample preparation work overlapped and improved on the work of others, while some of the results, particularly in the alloy samples, are new. Annealing times, temperatures, source ingot preparation, resulting carrier concentrations, and 77 °K Hall mobilities are reported. The Knight shift of the Pb207 nuclear magnetic resonance and the NMR line shape were used for additional sample characterization. This interesting technique was applied most successfully in the pure PbTe samples with carrier concentrations below 1018 cm−3. It was discovered from NMR studies on powders that strain damage introduced by powdering could completely compensate p-type PbTe. No corresponding effect was noted in n-type PbTe, suggesting the presence of damage-induced levels in the gap.
Residual microwave surface resistance of superconducting lead
Authors: Pierce John M.
Published: February 2004

An extensive experimental investigation aimed at minimizing the residual microwave surface resistance of superconducting lead is described. X-band cavities were made by electroplating lead on copper which had a residual Q as high as 3.7×1010, corresponding to an average residual surface resistance of 3.1×10−8 Ω. Electroplating techniques and surface preparation are discussed in detail. Residual resistance due to magnetic flux trapped through the surface was found to have frequency and flux dependence consistent with losses in normal metal exposed at the ends of the flux tubes. It was not necessary to consider flux motion. Loss identified with adsorbed material and surface protrusions was observed as well. Under the best conditions in cavities cooled in ambient magnetic field <10−4 Oe, residual resistance of 10−8–10−7 Ω remains which varies a factor of 2 or more on temperature cycling. A hypothesis involving thermoelectrically generated trapped magnetic flux is advanced to explain part of this loss, and it is argued that direct phonon generation as suggested by Halbritter and Passow cannot fully explain it.
An evidence of glide motion up to upper yield point on copper whiskers
Authors: Gotoh Yoshihiko
Published: February 2004

The surface structure of copper whiskers strained in the preyield region has been observed with a differential interference-contrast microscope. The results show that microslip occurs in this region. The deviation from Hooke's law can be explained by both the nonlinear elasticity and the motion of dislocations.
Refractive index behavior of garnets
Authors: Wemple S. H. , Tabor W. J.
Published: February 2004

Refractive index dispersion data are reported for the iron garnets Gd2.3Tb0.7Fe5O12, Eu2Er1Ga0.7Fe4.3O12, and Eu2Er1Al0.7Fe4.3O12. Using a Sellmeier oscillator formulation these data are compared with results for several iron-free garnets, and the relative importance of optical transitions involving Fe, Ga, and Al are briefly discussed. Finally, dispersion curves are presented for the effective refractive index n̄ to be used in the computation of film thickness from optical interference fringe count data.
Variation of the properties of chemically deposited lead sulfide film with the use of an oxidant
Authors: Blount G. H. , Schreiber P. J. , Smith D. K. , Yamada R. T.
Published: February 2004

The structural, chemical, and photoelectronic properties are compared for three types of chemically deposited lead sulfide film. The film types differ in the use of an oxidant during the deposition. The films are grainy in structure and show a decrease in grain compaction as the concentration of the oxidant is increased. Nominal chemical composition, including the concentration of oxygen, is not significantly dependent on the use of the oxidant. Photosensitive films may be described in terms of sensitizing centers which are present only when an oxidant is used but which are not dependent solely on the presence of oxygen. The physical identification of the sensitizing centers has not been determined but may be associated with film structure.
Thermal diffusivity measuring technique for hazardous materials
Authors: Murray R. C. , Cooper T. E.
Published: February 2004

A technique is presented for measuring the thermal diffusivity of solids. This technique differs from others in that boundary conditions are obtained by use of a well-stirred constant-temperature bath. By varying the bath temperature and the initial temperature of the specimen, thermal diffusivity values may be determined as a function of temperature. Accuracies within ±5% may be obtained and the major sources of error in the technique may be isolated and controlled. The method lends itself to remote-control testing of hazardous materials such as high explosives and solid propellants. In the present studies thermal diffusivities ranging from 0.005 to 0.010 ft2/h were measured between −65 and 165°F on a typical high explosive material.
Nonlinear heat flow in anisotropic media with property variations and nonlinear heat generation
Authors: Campo A. , Wolko H. S.
Published: February 2004

A method based upon the use of two algebraic transformations is applied to the equation of heat conduction in anisotropic media having nonlinear generation. The feasibility of the method is manifested when the principal conductivities together with the volumetric heat capacity vary with temperature in a power fashion. Also, the conductivities are taken parallel to the principal axes. Except for the unsteady term, the transformed equation reduces to its counterpart in isotropic media with constant properties. Applicable boundary and initial conditions of general type are analyzed.
High-velocity dislocation damping in aluminum
Authors: Dharan C. K. H. , Hauser F. E.
Published: February 2004

High-velocity compression tests were conducted on pure polycrystalline aluminum. Data obtained at compressive strain rates ranging from 0.4×104 to 12×104 sec−1 could be divided into two regions of interest. For strain rates from 0.7×104 to 1.4×104 sec−1 a linear relationship was found to exist between the applied stress and the strain rate, indicating that the moving dislocations are viscously damped in this region. The values of the damping constant B obtained in this region ranged from 1.9×10−4 to 3.0×104 dyn sec/cm2 and showed good agreement with B determined by other investigators. Beyond these strain rates, the damping reduced at first and then increased, with very high stresses being obtained at the highest strain rates reached. The drop in the damping has been attributed to the reduction in the volume around the cores of the moving dislocations that can exchange energy with the lattice phonons. The rise in the damping at the higher strain rates may be due to relativistic effects as the moving dislocations approach the velocity of sound. Using the expression for the strain field around a fast-moving dislocation in the phonon viscosity theory and the general expression for dislocation damping due to phonon scattering, an expression for the damping constant was obtained embodying these effects. This was found to show good agreement with the data.
Study of ion-nitriding
Authors: Hudis Martin
Published: February 2004

A study of ion nitriding has been conducted in a nitrogen-hydrogen-argon gas mixture with emphasis on the mechanism and the active plasma ingredients which cause nitriding. The study is based on mass and energy data of ions sampled through a 4-mil hole in the cathode, metallurgical data, and gas-absorption data. The results of the experiment demonstrate that ion nitriding is not a gas-absorption process. Ion nitriding requires ionic bombardment. Nitrogen ions and nitrogen-hydrogen molecular ions are the active plasma ingredients. Nitrogen-hydrogen molecular ions are responsible for the superior nitriding properties produced by a nitrogen-hydrogen plasma compared to the properties produced by a nitrogen or nitrogen-noble gas mixture.
Parametric excitaiton of ultrasonic waves in piezoelectric semiconductors
Authors: Kaw Predhiman K.
Published: February 2004

We have investigated the parametric excitation of ultrasonic waves in piezoelectric semiconductors by the application of a high-frequency electric field, near the electron-plasma frequency. The high-frequency field produces a nonlinear coupling between the ultrasonic waves and electron-plasma waves and leads to an instability when a critical value is exceeded.
Dielectric behavior of ceramic grain boundaries by electron-beam scanning
Authors: Mountvala A. J. , Marks H. R.
Published: February 2004

The use of the electron-beam-scanning technique to study the dielectric properties of material interfaces, such as grain boundaries is described and results obtained on potassium chloride and barium titanate boundaries discussed. The results indicate that grain boundaries in ionic materials such as KCl have electrical conductivities differing from those of the grain depending upon their misorientation and degree of hydration. For twist boundaries, the grain-boundary conductivity is higher than that of the grains and this difference increases with increasing twist. No such conductivity difference was evident for a high-angle tilt boundary. In BaTiO3 ceramics, the permittivity values in the grain-boundary regions were specifically different from those in the grains.
Interpretation of ultrasonic measurements of hot-pressed polycrystalline specimens of MgO
Authors: Fancher D. L. , Spetzler H. A.
Published: February 2004

A model has been developed to interpret the anomalous behavior in the elastic properties of hot-pressed MgO samples as observed by ultrasonic measurements. The present model, by including distortion of individual crystallites within the polycrystalline samples, extends the Kröner theory which calculates longitudinal and shear moduli and their pressure derivatives. In this ``distorted'' Kröner theory, a distortion factor proportional to Young's modulus is used. The results obtained from the present theory agree quite well with the observed change in the shear and longitudinal moduli in polycrystalline MgO samples which have been simultaneously subjected to pressure and temperature changes subsequent to hot pressing.
Long-range elastic interaction between a dislocation and an ellipsoidal inclusion in cubic crystals
Authors: Lin S. C. , Mura T.
Published: February 2004

By using the stress field of 〈110〉 dislocation in cubic crystals and the solutions of eigen-strain problem in anisotropic media, the long-range interaction energy between 〈110〉 dislocation and an ellipsoidal inclusion in cubic crystals is derived. Also, the Peach-Koehler force on the dislocation is calculated. The explicit expressions of the interaction are shown for spherical, disk-shaped, and rod-shaped inclusions interacting with screw, glide-edge, and climb-edge dislocations. When the material is isotropic and the inclusion is spherical, the results agree with the result obtained by Comninou and Dundurs, and Weeks, Pati, Ashby, and Barrand. The numerical results are shown for the void interacting with a screw dislocation. It can be seen that the results are qualitatively the same as those of the isotropic case, but quantitatively different, due to anisotropy of the materials.
Filter method and silicon detectors to measure the temperature of a hot dense thermal deuterium plasma from its quantum bremsstrahlung
Authors: Robouch B.V. , Rager J.P.
Published: February 2004

The filter method, used to measure the temperature of a hot (T> 1 keV) deuterium plasma through its bremsstrahlung emission, is studied taking into account two new features: (i) the bremsstrahlung emission (accounted for, up until now, by its classical approximation) is described by its quantum expression, (ii) real solid-state silicon detectors are considered, instead of ideal ones. Deductions are made concerning the best choice of the detector and the corresponding adequate filter for different temperature ranges; the limits of the temperature ranges are established considering the minimum number of points necessary to identify the shape of the spectrum curve, as well as the loss of efficiency of the detectors at high energies. An upper bound is set to the measurable temperature. Neutron radiation damages to the Si detectors, at current and foreseen levels, are considered and shown to impose no serious limitation to the practical applicability of the method.
Observation of radially propagating collisionless-drift-wave instability
Authors: Nishida Y. , Dodo T. , Kuroda T. , Horikoshi G.
Published: February 2004

The radially traveling drift-wave instability is observed in a fully ionized collisionless plasma. The observed radial wave number is larger than the azimuthal wave number. The observed frequency, in the frame of ErBz plasma rotation, is in good agreement with the calculated frequency of the drift instability after the correction of finite ion inertia including the radial wave number, where Er is a radial electric field and Bz is an axial magnetic field.
Photopolarization studies of the CdS:S system as an electrophotographic layer
Authors: Pillai P. K. C. , Arya S. K.
Published: February 2004

A mixed CdS:S system has been investigated for its use in photoelectret electrophotographic layers. High photosensitivity (102) and high resistivity ([inverted lazy s]1010 Ω cm) are characteristics of this system. The photoelectret effect in this system exhibits high charge density ([inverted lazy s]10−8C/cm2), long persistence of the latent electrostatic charge pattern, and fast speed for the formation of an electrostatic image. Further, it is shown that this layer is useful for both the positive-to-positive and positive-to-negative mode of electrophotography.
Torques and forces on a moving coil due to eddy currents
Authors: Langerholc J.
Published: February 2004

The steady-state forces and torques acting on a planar current-carrying winding, moving at constant velocity parallel to a conducting permeable slab of finite thickness and infinite extent are calculated from exact solutions of Maxwell's equations. These calculations are extended to apply to an arbitrary coil consisting of a superposition of planar windings. The special cases of solenoidal coils of finite and infinite height are discussed as approximations to bar, iron core, and horseshoe magnets, and the limiting cases of magnetic monopoles and dipoles are considered. The relativistically exact formulas are simplified for the practical case of a magnetically suspended train, and similarity laws are derived relating the forces measured on scaled-down models to those on their prototypes. These calculations are valid for levitation over nonpermeable conducting media as well as for the reduction due to eddy currents of the attractive force in the alternatively proposed ferromagnetic suspension systems. Aside from the infinite length and width of the track, the only physical approximations made consist in linearity assumptions in the track: constancy of the permeability and conductivity (Ohm's law).
Explosively driven deuterium arcs as an energy source
Authors: Cowan M. , Freeman J. R.
Published: February 2004

A cylindrical arc in deuterium plasma was imploded with high explosive into its own magnetic flux to form a powerful source of pulsed energy. Joule heat produced during flux compression appeared to be radiated about as fast as it was generated by the conducting plasma, consistent with the release of about 106 J of radiant energy with peak power about 1012 W. During implosion, the magnetic field increased to about 102 Wb/m2 and supported a current density of 3×1011 A/m2. The plasma arc was estimated to have a density of 1027 m−3 and to reach a temperature of 2×105 °K. Calculations are made using a one-dimensional time-dependent hydromagnetic model which includes thermal conduction, radiant heat transfer, self-consistent magnetic fields, and temperature-dependent transport properties. The finite difference solution predicts arc currents, plasma properties, and radiation losses consistent with the experimental observations. A simplified analytical theory is derived to provide convenient scaling information.
Performance comparison of pulsed discharge and E-beam controlled CO2 lasers
Authors: Kast Steven J. , Cason Charles
Published: February 2004

A pulsed CO2 laser model for axial pulse and TEA lasers is developed based on combining electric excitation with vibrational energy level kinetics and a laser cavity intensity model. The model is applied to electron-beam-controlled lasers by adding an electron-beam plasma generation component. Calculated results show the electron-beam laser has a maximum output energy efficiency approaching 20% if the input energy is sufficient to rapidly heat the gas to the self-terminating temperature, about 600 °K. Efficiencies higher than 20% have been achieved with pulsed discharge lasers but with a consequent penalty in output energy, because the state-of-the-art limits the amount of electrical energy input to less than that necessary to reach the self-terminating temperature in axial pulsed or TEA lasers. Results of kinetics studies suggested several approximations that permit analysis of laser performance for the self-terminating temperature condition. These approximations lead to a set of transcendental but closed form coupled expressions which yield solutions in good agreement with those obtained by exact kinetics treatment. Contour plots for a 1 mA/cm2 electron-beam laser, obtained from the closed form treatment, make it possible to determine the maximum laser energy output and efficiency for any given gas mixture. The upper bound on laser energy output was found to be 100 J/liter atmosphere.
Properties of Sn-doped GaAs
Authors: Nishizawa Jun-ichi , Shinozaki Satoshi , Ishida Katsuhiko
Published: February 2004

The defect properties of GaAs have been investigated through a process of crystal growth, especially in relation to the change in electrical and luminescence properties and lattice constant due to the deviation from stoichiometry. GaAs crystals were grown from Sn solutions by the temperature gradient method under controlled As pressure from 8.5×10−-6 to 4.3×10 Torr. From the photoluminescence measurements, the level which is associated with the As vacancy and Sn is found at 1.34 eV in the low As pressure region. With increasing As pressure, the concentration of the Ga vacancies which behave as acceptors increases and carrier compensation proceeds. The lattice constant is increased by the incorporation of Sn. It also is a function of the As pressure, that is, the Ga vacancy is found to make the lattice constant increase. It can be said that GaAs crystals which deviate from stoichiometry can be obtained when they are grown from Sn solutions under controlled As pressure.
Recombination mechanisms in 8–14-μ HgCdTe
Authors: Kinch M. A. , Brau M. J. , Simmons A.
Published: February 2004

Photoconductive measurements on n-type Hg1−xCdxTe, for compositions of 0.195 < x < 0.210, have been carried out in the temperature range 65–300°K. A comparison of the experimental data with simple band-to-band recombination theory indicates that the lifetime in the intrinsic range of temperatures is determined by an Auger limited process. The measured variation of lifetime with temperature can be used to predict values for the Auger limited lifetime in intrinsic material, τAi, over the entire temperature range 65–300°K. Calculations, using these values of τAi, for the extrinsic temperature range (<100°K) indicate that for our purer material (ND−NA≳4×1014 cm−3;μ77≳1.5×105 cm2 V−1 sec−1), the lifetime is still determined by an Auger limited band-to-band process. In somewhat more compensated material (ND−NA<4×1014 cm−3;μ77≲1.5×105 cm2 V−1 sec−1), Shockley-Read limited lifetimes are observed, although in the majority of samples measured the electron lifetime is independent of temperature. However, in some extremely highly compensated material (ND − NA < 2×1014 cm−3; μ77 < 105 cm2 V−1 sec−1), temperature-dependent lifetimes are observed below 100°K, indicating a Shockley-Read center approximately 30 meV above the valence band. Spectral response measurements indicate values of surface recombination velocity∼280 cm/sec for carefully prepared surfaces on this material.
Eigenfunction analysis of mode-locking process
Authors: Kim Dae M. , Marathe S. , Rabson T. A.
Published: February 2004

An active mode-locking process in a homogeneously broadened medium is discussed by using an eigenfunction analysis of a time-varying strongly interacting closed-loop system. This direct time domain analysis is shown to yield a complete set of eigenfunctions or supermodes for steady-state pulse configurations. The kinetics of generated pulses is described in this eigenvector space. The result shows that, depending on the buildup time, the string of detected pulses can differ substantially among themselves. Also, the possibility of using this time domain approach to analyze time-tailoring pulse envelopes is pointed out.
Influence of CO on the population inversion in CO2 lasers
Authors: Avivi P. , Dothan-Deutsch F. , Friedland L. , Keren H.
Published: February 2004

The population inversion in a CO2–He glow discharge has been calculated, taking into account CO produced by dissociation in the discharge. The calculation was based on experimentally determined electron energy distribution functions and the measured effective relaxation constant of the CO2 (001) level. It is shown that the population inversion is negligible in the absence of CO. The importance of excitation and relaxation of CO2 (001) by electrons is stressed.
Monte Carlo simulation of response of a semiconductor to periodic perturbations
Authors: Lebwohl Paul A.
Published: February 2004

Monte Carlo simulation, as it is usually applied to carriers in semiconductors, has been extended to permit the calculation of the periodic response of the carriers to periodic external fields of any strength. To illustrate this extension the frequency-dependent differential mobility of GaAs is calculated for frequencies of 1010 to 1013 rad/sec. A second illustration is the response of GaAs to a constant electric field of 10 kV/cm and a sinusoidal electric field of 8 kV/cm and of frequency 1.88×1011 rad/sec.
Direct comparison of thermal and magnetic profiles in ``Curie point'' writing on MnGaGe films
Authors: Wieder Harold , Burn Robert A.
Published: February 2004

Measurements have been made of both the real-time temperature profile and the steady-state magnetization profile achieved in a film of MnGaGe as a result of ``Curie point'' writing with a GaAs laser pulse. A HeNe laser probe having a half-power diameter of 1 μ was used to measure both profiles. Temperature was measured during and after application of the heat pulse by relating the time-dependent transmission change of the heated area of the film to the temperature-calibrated shift of the absorption edge of MnGaGe. Magnetization information was obtained by measuring the Faraday rotation within the written area after the film had cooled to ambient. A comparison of the two profiles indicates that (a) magnetization reversal occurs at temperatures well below the Curie point, even in the absence of an external bias field, and (b) the critical temperature required for reversal increases with an increase in the size of the heated area. Both results can be explained qualitatively by local demagnetization effects.
Application of difference equations to a square Hall plate with finite interior driving and Hall electrodes
Authors: White D. J. , Knotek M. L. , Ritchie M. H.
Published: February 2004

The Hall potential, geometrical correction factor, and magnetoresistance of a square Hall plate were computed for values of Hall tangent up to 0.5. The computations were carried out by a ``difference-equation'' method utilizing a standard computer matrix inversion subroutine. Various square electrode arrays are considered. Point driving electrodes and Hall electrodes at diagonally opposite corners yield computed results essentially identical to a theoretically ideal infinitely long Hall plate. Point interior driving and Hall electrodes, however, show increased magnetoresistance and a Hall voltage decreased from the ideal. Interior finite-area driving electrodes accentuate this trend. The further addition of finite-area interior Hall electrodes did not appreciably alter the necessary Hall voltage correction, or increase the computed magnetoresistance.
Interpretation of scanning high-energy electron diffraction measurements with application to GaAs surfaces
Authors: Dove D. B. , Ludeke R. , Chang L. L.
Published: February 2004

SHEED measurements have been made on the surface of GaAs crystals during in situ epitaxial deposition. The (bulk) spot pattern changes to a streak pattern as deposition proceeds, as noted by other workers. An interpretation of these patterns is given in terms of simple kinematic scatttering from flat surface regions. This leads to a straightforward interpretation of the observed specular reflection phenomenon, enables the area of coherent scattering to be estimated (0.16 μ2 in the present experiments), and should permit a more detailed analysis of ordered surface structures.
Stimulated emission cross section of H2 dissociation transition
Authors: Cohn Arthur , Marcucci Michael
Published: February 2004

The stimulated emission section of the a-b dissociation transition in H2 is calculated for the 0–9 vibrational levels of the a state. This includes the region of wavelengths longer than 4000 Å not investigated by James and Coolidge. It is found that the average cross section has a broad peak near 4000 Å, only dropping to half-maximum near 6000 Å wavelength.
Mössbauer studies on the superparamagnetic behavior of 69–31 at.% FeNi fine particles
Authors: Ok Hang Nam , Han Moon Shik
Published: February 2004

The Mössbauer effect is used to study the superparamagnetic behavior of fine particles of 69–31 at.% FeNi alloy. The Mössbauer spectrum of the alloy consists of a central single line and a six-line magnetic hyperfine pattern for fine particles; but the single line disappears for larger particles, which is in disagreement with the previously reported interpretation that the central single line originates from the paramagnetic state of the antiferromagnetic regions in the ferromagnetic alloy. It is suggested that the central line originates from the superparamagnetic behavior of the ferromagnetic or antiferromagnetic fine particles.
Measured and calculated Cs excited-state densities in Cs–Ar low-pressure discharges
Authors: Bleekrode R. , van Tongeren H.
Published: February 2004

Radial distributions of the 62P excited-state density of Cs in low-pressure Cs–Ar discharges have been measured by means of absorption from a continuum in the 876.1- and 917.2-nm lines of Cs. The variation of the excited-state densities with the discharge current has also been studied. The experimental data are compared with results of calculations based on a model of the positive column of the Cs–Ar discharge in which radiation trapping is taken into account.
Statistical calculation of dislocation movements in thin films
Authors: Gangulee A. , Basu A. P.
Published: February 2004

A statistical method for calculating the effects of dislocation movements is described; the method is based on a realistic model although the effects of cross slip are not included. The long-range interactions between dislocations are considered to be limited by large intrinsic stresses and image stresses. The numerical results indicate that with sufficient time, about half of the dislocations are annihilated while the other half are bound in dipoles. The maximum strain is found to be almost independent of either the initial dislocation density or the initial dipole density. The calculated maximum strains are in fair agreement with the experimental data published by other investigators.
Elastic surface waves guided by curved thin films
Authors: Tiersten H. F. , Davis R. C.
Published: February 2004

An approximation technique previously developed for straight elastic surface wave guides utilizing thin films is extended and applied to curved guides with large radius-to-guide-width ratios. The dispersion curves for the circular guides are obtained by employing approximate bound modes in place of the actual wave functions, which are not fully bound. This procedure is quite accurate for the determination of dispersion curves in the propagation range of interest. Nevertheless, since the actual wave functions are not fully bound, some radiation is always present in a curved guide. This radiation loss accompanying the approximate bound modes is evaluated. A critical radius-to-guide-width ratio, beyond which a calculation cannot be performed by the method employed, is defined, and it is shown that the radiation attenuation becomes prohibitively large even before this limiting ratio is reached. The problem of the lowest symmetric guided elastic surface wave in a straight guide incident on a curved guide in the shape of a quarter-circle is treated and the transmitted and reflected waves are determined, including in the calculation only the two lowest modes in each region and the radiation attenuation associated with each mode.
Shape of cathode dark space of a sputtering plasma determined from probe measurements
Authors: Larsen W. R. , Wilmsen C. W. , Chan P. W.
Published: February 2004

This paper reports measurements of the shape of the cathode dark space (CDS) of a dc sputtering system. Special attention was given the CDS enveloping the cathode since this region influences the sputtering of the cathode periphery. A Langmuir probe was used to map the CDS negative glow boundary which was found to remain unchanged with cathode-anode spacing until the anode neared the CDS boundary. Glass substrates placed on the anode also influenced the CDS shape. The Langmuir probe current-voltage characteristic changed with time until the probe was completely coated with metal sputtered from the cathode. The coated probe gave reproducible results over a long period of time.
Stimulated Compton scattering as a radiation source—theoretical limitations
Authors: Sukhatme Vikas P. , Wolff P. A.
Published: February 2004

Several authors have considered the possibility of using stimulated Compton scattering for obtaining laser action. To date, all gain calculations for these devices have assumed an infinite interaction region. The purpose of this paper is to consider the effect of a finite geometry on the gain. We find that in most experimental situations the gain is significantly reduced, to the point where stimulated Compton scattering seems unlikely.
The superleak as a gyroscope
Authors: Galas David J.
Published: February 2004

This paper introduces the possibility of using the metastable persistent-current quantum states of liquid helium II observed in superleaks as the principal element of an extremely stable gyroscope. It is suggested that combining the advantages of the nondecaying angular momentum inherent in the superleak with the suspension technique devised by Ensley could result in unprecedented stability and accuracy. An idealized system is described and two simple physical situations are analyzed. An interesting effect peculiar to this system is predicted. We find that temperature fluctuations, by transferring angular momentum in and out of the supercurrent state, drive the float containing the superleak into rotation. This rotation depends only on the nature of the fluctuations and the persistent current state. On the basis of the analysis of the simplified system described we conclude that a supercurrent gyroscope is quite feasible with existing technology.
Effect of metallurgical history on critical current density in NbTi alloys
Authors: McInturff A. D. , Chase G. G.
Published: February 2004

Data are presented describing critical current density Jc as a function of Ha, applied magnetic field, for NbTi alloys containing between 22 and 38 at.% Nb. The effect on Jc(Ha) of precipitation heat treatments between 275 and 565°C was studied in conjunction with cold area reductions up to 99.9%. The highest critical current densities, Jc(Ha), were in the range 1.0 to 3.6×105 A/cm2 at 3.0 T where most of the data were obtained. Critical temperature data are presented as a function of alloy composition and metallurgical preparation.
Analysis of a method for measuring the magnetocrystalline anisotropy of bubble materials
Authors: Druyvesteyn W. F. , Dorleijn J. W. F. , Rijnierse P. J.
Published: February 2004

A method of measuring the uniaxial anisotropy of bubble materials is analyzed. The method consists of observing the in-plane field H∥* at which a stripe domain pattern disappears. Calculations, based on a model with uniaxial anisotropy, are presented which give a relation between H∥* and the uniaxial anisotropy field HK for different values of the characteristic magnetic length. It is shown that H∥* is always smaller than HK owing to the influence of the wall energy and the demagnetizing energy. The calculations are verified experimentally.
Time-resolved gain of a volume-excited TEA CO2 laser amplifier
Authors: Dyer P. E. , James D. J. , Ramsden S. A.
Published: February 2004

An investigation of the time-resolved gain of a volume-excited TEA CO2 laser amplifier is described. The amplitude and decay time of the small-signal gain are obtained as a function of molecular gas flow ratio and input energy density.
Discussion on ``Comment on `Habit and morphology of copper precipitates in silicon'''
Authors: Hu S. M. , Poponiak M. R.
Published: February 2004

The dislocation climb mechanism for the growth and morphology of copper precipitates in silicon, as proposed by Fiermans and Vennik, is questioned on a number of points. In particular, the regularity of the geometry of precipitate colonies, the variation in precipitate density within a colony, and the different morphologies of precipitates of various interstitial impurities in silicon are cited against the suitability of the mechanism.
High-density image-storage holograms by sampling and random phase shifter method
Authors: Tsunoda Y. , Takeda Y.
Published: February 2004

As a new method of making high-quality and high-storage-density holograms capable of storing such image information as pictures and portraits, combination of the sampling method and random phase shifter method is proposed. This method reduces the concentrations of information light energy on the hologram plane which are located evenly in the just Fourier-transformed plane. As an experimental result, the light waves passing through 106 sampling points on a frame information with random phases were focused into a spot to make a hologram of 2.0-mm diameter. The reconstructed image from the hologram showed high quality without speckle and high efficiency.
Reflection and transmission of electromagnetic waves obliquely incident on a relativistically moving isotropic plasma slab
Authors: Kalluri Dikshitulu , Shrivastava R. K.
Published: February 2004

The oscillations in the power reflection coefficient as a function of the normalized incident wave frequency and slab velocity are shown for electromagnetic waves obliquely incident on an isotropic plasma slab relativistically moving along the slab interface. Both parallel and perpendicular polarizations of the wave are considered.
Pressure dependence of elastic moduli of tungsten carbide cermet
Authors: Day J. Paul , Ruoff Arthur L.
Published: February 2004

The elastic constants of a commercial tungsten carbide cermet (3% cobalt binder) were measured as a function of pressure at room temperature. As pointed out in a recent publication by Ruoff, the pressure dependence of the elastic constants affects the maximum possible pressure which a vessel can contain. This dependence is discussed in light of the present data.
Measurement of the anisotropy of resistivity due to screw dislocations in aluminium
Authors: Hamdani A. J.
Published: February 2004

The anisotrpic resistivity of dislocations produced by deformation is measured in high-purity Al single crystals at liquid-helium temperature. A network of screw dislocations is produced by twisting a single-crystal cylindrical Al bar about the [111] direction which was along the axis of the bar. Resistivity parallel to the slip plane is measured by a mutual inductance method and along the crystal axis by a dc potentiometric method using Josephson junctions. Resistivities perpendicular to the specimen axis are found to be greater than those parallel to the specimen axis. The ratio Δρac/Δρdc (where Δρac and Δρdc are the resistivity increments along the directions perpendicular and parallel to specimen axis, respectively) is approximately equal to 1.29.
Electromigration and metalization lifetimes
Authors: Sigsbee R. A.
Published: February 2004

A model has been developed to predict the lifetime τf of integrated circuit metalizations which operate at high dc densities Je. Grain-boundary electromigration, internal heat generation, and current crowding at growing voids dominate the rate processes that lead to failure. Joule heating of the stripe causes an initial temperature rise ΔT0 and heat flow into the substrate. If this rise is appreciable an instability exists in the stripe. When vacancies electromigrate down grain boundaries and precipitate on a suitable boundary, forming an elongated void, the electric current will be diverted. This is serious if the crack has a substantial length component perpendicular to the current flow which increases vacancy currents to the crack tip and the local heating. An analytical model considering these effects and the time for a crack to propagate across the stripe width yields a stripe lifetime integral which fits the form Pn =(1/2)(1+0.265γΔT0). Here γ=ΔH/kT2 is the temperature coefficient of the diffusion constant. Pn, the crack width, and the initial electromigration grain boundary flux then largely determine the stripe lifetime. The self-heating contribution ΔT0 is shown to be an important term in the interpretation of accelerated test data and for proper extrapolation to lower temperature-and-current stress levels. The stripe temperature coefficient of resistance and melting point are shown to have only secondary effects on lifetime. Lifetimes have a Je−n dependence with n varying from unity at low ΔT0 levels to 15+ for high ΔT0 levels and are determined by the stripe and heat-sink temperatures. For maximum stripe lifetimes, wide stripes with good thermal coupling to the heat sink are desirable.
Observation of aspherical particle rotation in Poiseuille flow via the resistance pulse technique. II. Application to fused sphere ``dumbbells''
Authors: Golibersuch D. C.
Published: February 2004

The presence of an insulating particle in an electrolyte-filled pore causes a fractional resistance change, ΔR / R = fv / V, where v / V is the ratio of particle to pore volume. The shape factor f is a function of particle shape and orientation. While traversing the pore, the particles will rotate in the shear of Poiseuille flow. As a result aspherical particles will exhibit periodic resistance variations and this effect has been observed directly using fused sphere ``dumbbells'' as test particles. The particle dynamics are found to be in agreement with simple hydrodynamic theory. The resistance effects for the dumbbells can be described in terms of an equivalent ellipsoid with an axis of symmetry to equatorial axis ratio of 1.25. On the other hand, the dumbbells are hydrodynamically well described in terms of an ellipsoid with an axis ratio of 2.4. The data indicate that strong orientation effects occur in the convergent entrance flow.