bluuebunny/crossref_metadata_2025 huggingface dataset:
Comments on ``A study of compressed spatially non-Gaussian optical pulses from mode-locked lasers''
Authors: Treacy E. B.
Published: February 2004

The above paper by Kim et al. states that part of the nonlinearity of frequency sweep that we measured in picosecond pulses by dynamic spectroscopy techniques is caused by instrumental effects in a grating pair due to the presence of transverse modes. We would like to make the following comments: (i) The measurements were made with a fast spectrometer rather than with a pair of diffraction gratings. (ii) Transverse modes affect our spectrometer measurements only to the extent of reducing the resolving power by 2%. (iii) The frequency-dependent group delay in the fast spectrometer has been properly accounted for in our earlier publications. (iv) In deriving their prediction of an instrumental contribution to apparent nonlinearity of frequency sweep, Kim et al. use an incorrect equation that describes a pulse crossing its time-reversed image, which is not experimentally realizable. (v) The tilted wave packets that we studied with two-photon fluorescence techniques are unrelated to the tilted wave packets discussed by Kim et al. Those described by Kim et al. would be difficult to observe experimentally. (vi) In our pulse compression experiments that used a pair of gratings, transverse mode effects were rendered negligible by the optical design. We assert that our measurements of average chirp characteristics of trains of mode-locked pulses have been properly interpreted by us.
Observation of dark-line degradation sites in AlGaAs/GaAs DH laser material by etching and phase-contrast microscopy
Authors: Johnston W. D. , Callahan W. M. , Miller B. I.
Published: February 2004

We have observed precise geometrical correlation between ``dark-line''-type defects characteristic of the rapid degradation mode of (optically pumped) AlGaAs DH laser material with etch pit features in the vicinity of the GaAs/p-Alx Ga1−x As heteroboundary. The patterns observed strongly suggest that the degradation is associated with creation or possibly decoration of dislocation lines inclined to the {100} junction plane, and that the commonly observed 〈100〉 orientation of the dark lines is due to statistical aggregation of such inclined lines.
Surface stress distribution due to an array of 60° dislocations on an oblique glide plane
Authors: Taliaferro D. A. , Mitchell J. W.
Published: February 2004

When single crystals of Cu-7.5 at.% Al alloys with the [331] {1̄10} {1̄1̄6} orientation are deformed in tension, narrow slip bands are introduced in which only one or the other of the two equivalent {1̄1̄1} 〈101〉 and {1̄1̄1} 〈011〉 glide systems is activated. Along the gauge length, bands due to the activation of the two glide systems appear in equal numbers. To facilitate the interpretation of these results a model for the relaxation process has been set up and analyzed. The stress distributions at and near the surface due to a single 60° dislocation and to a group of uniformly spaced 60° dislocations on an oblique (1̄1̄1) glide plane have been calculated. The results lead to an interpretation of the experimental observations and suggest that a stress difference of 0.038–0.083 kg mm−2 in a resultant resolved shear stress of 1.34–1.54 kg mm−2 is sufficient to cause preferential activation of one of the two equivalent glide systems. They provide a clear and equivocal demonstration of the role of internal stresses in dislocation generation processes in single crystals of α-phase Cu–Al alloys with this orientation.
Anomalous x-ray transmission evidence for clustering in the annealing stage of neutron-irradiated copper
Authors: Gruber E. E. , Blewitt T. H. , Baldwin T. O.
Published: February 2004

Low-dislocation-density copper crystals have been neutron irradiated at low temperatures (T≲50∘K) and transferred to an x-ray diffractometer at temperatures less than 25°K. Simultaneous measurements of anomalously diffracted x-ray intensities, the lattice parameter, and the electrical resistivity were made at 4.2°K after successively higher annealing temperatures in an isochronal annealing program; x-ray measurements were made on approximately 1 × 1 × 0.15-cm samples, and resistivity measurements were made on wire specimens. The anomalous x-ray absorption, which is most sentitive to clustering of defects, showed a steady increase beginning at the end of stage I and continuing to about 225°K, the end of stage II. During stage III a small decrease in the absorption was observed. A rather pronounced increase in the absorption occurred in stage IV at about 375°K. The ``clustering peaks'' at 225 and 375°K have been compared with electrical resistivity data, and the results are interpreted in terms of existing annealing models.
Elastic constants of nonmetamict zirconium silicate
Authors: Özkan H. , Cartz L. , Jamieson J. C.
Published: February 2004

Two independent reports in the literature for the elastic constants of zircon (zirconium silicate) are in disagreement by an order of magnitude and are reported without specifying the conditions of the mineralogical specimens. However, natural zircon crystals frequently contain uranium and thorium atoms as an impurity so that zircon can exist in a metamict (radiation damaged) condition. A redetermination of the elastic constants has been carried out on small synthetic crystals and on high-purity natural single crystals of nonmetamict zircon of lattice parameters ao = 6.606(2) Å, co = 5.980(2) Å by ultrasonic pulse superposition and also by phase comparison methods. The values in 1012 dyn/cm2 are c11 = 4.237, c33 = 4.900, c44 = 1.136, c66 = 0.485, c12 = 0.703, and c13 = 1.495. The estimated uncertainty in the measurements are 0.4% for c11, c33, c44, and c66, and 3% for c12 and c13. Wave velocity measurements have also been carried out on a metamict zircon crystal (density 4.531 g/cm3) and it is shown that the velocities are reduced by about one-fifth the normal values. The compressibility coefficients calculated from the new elastic constants data differ from those determined by diffraction data, though this may be part of a general discrepancy between such measurements.
Mechanism of the passage of crystal dislocations through tilt boundaries
Authors: Das E. S. P. , Dwarakadasa E. S.
Published: February 2004

The concept of special grain boundary dislocations (as distinct from crystal dislocations) has been used to study the mechanism of the passage of crystal dislocations through tilt boundaries in the simple cubic and bcc systems. It is shown that the Burgers vector of a grain boundary dislocation is not arbitrary but should be a vector belonging to a restricted set defined in terms of the translation vectors of the two grains separated by the grain boundary. It is next shown that a grain boundary dislocation can be constructed in a bicrystal in the same manner as a crystal dislocation in a single crystal. The properties of these dislocations in a bicrystal are studied. It is shown that a crystal dislocation can pass through a tilt boundary without altering its over-all structure by first dissociating into partials whose Burgers vectors are integral units of those of the grain boundary dislocations defined for the bicrystal. The principles involved are illustrated by means of an example each in the simple cubic and bcc systems.
Tilt moiré patterns
Authors: White J. R.
Published: February 2004

Consideration is given to the image formed in the electron microscope of two crystals stacked one above the other when these show a relative rotation about an axis perpendicular to the electron beam. Dark-field moiré fringe patterns are predicted when certain conditions relating to the relative proximity to the Bragg condition of the two crystals are fulfilled. The limits of these conditions and the spacings of the fringes are formulated in terms of the angle of tilt and the direction of the tilt axis.
Particle growth in flowing inert gases
Authors: Hogg E. O. , Silbernagel B. G.
Published: February 2004

Fine particles of Zn, Mn, and Se are produced in a flowing system of argon gas. The experimental geometry is described, and the effect of experimental parameters (metal vapor pressure, gas flow rate, and oxidants) is characterized. These particles are studied using a transmission electron microscope in both imaging and electron diffraction modes. Mn and Zn formed well-defined crystals as verified by electron diffraction, while Se did not. Even small amounts of oxygen inhibited the proper crystal growth.
CO2 laser-driven absorption waves in underdense hydrogen
Authors: Burnett N. H. , Offenberger A. A.
Published: February 2004

A 600-MW CO2 laser oscillator has been used to induce breakdown in hydrogen with filling pressures in the range 10–20 Torr. The breakdown region is observed to undergo a transition from an optically thin symmetric expansion at laser fluxes in excess of ∼ 108 W/cm2 to an optically thick undirectional expansion at laser intensities below this.
Electrical and optical properties of single crystals in the FeO–MnO systems
Authors: Goodwin C. A. , Bowen H. K. , Adler D.
Published: February 2004

The electrical conductivity of FeyMn1−yO1+x single crystals in equilibrium with various partial pressures of oxygen was measured in the temperature range 900–1150°C. When the conductivity data were plotted as functions of x or y, sigmoidally shaped curves were obtained. This composition dependence is consistent with a region of solid-solid immiscibility within the (Fe,Mn)O phase field. The visible and near-infrared absorption spectra of (Fe,Mn)O crystals exhibited crystal-field peaks characteristic of both the Mn2+ and Fe2+ cations. The position of Fe2+ peaks was found to shift with MnO content although the peaks corresponding to the Mn2+ ion did not shift. It was concluded that the manganese ions are located on undistorted lattice sites which may be grouped into phase-separated regions. Thus, both the electrical and optical results reflect a miscibility gap in the pseudobinary phase field.
Thermoelectric and photothermoelectric effects in semiconductors: Cadmium sulfide films
Authors: Wu Chen-ho , Bube Richard H.
Published: February 2004

Techniques of thermoelectric and photothermoelectric analysis have been applied to investigate the electrical transport properties of both solution-sprayed and evaporated polycrystalline CdS films. Dark electron densities are independent of temperature between 200 and 330°K because of shallow donors; dark electron mobilities are thermally activated with energies between 0.09 and 0.23 eV. Photoconductivity of solution-sprayed films is caused primarily by an increase in electron mobility. Other effects investigated are the adsorption and desorption of oxygen, the diffusion of Cu acceptors, and field-assisted drift of Cu impurities in the film at a slightly elevated temperature (100°C). The structure and characteristics of intergrain boundaries dominate the transport processes in these polycrystalline films.
Field ion microscopic study of electric contact phenomena
Authors: Nishikawa Osamu , Utsumi Takao
Published: February 2004

Electrical contacts of W–Ga and Re–Ga were studied using a field ion microscope in which the emitter tips of the microscope were contacted with liquid gallium in vacuum. Threshold values of the closing voltage and opening current needed to create an amorphous state of the surface atoms of the emitter were obtained for W–Ga contacts. Similar characteristics were noted for the Re–Ga contact although a clear determination of the threshold values was overshadowed by a Re–Ga reaction. The observed threshold closing voltages are significantly lower than known values for short arcs. The cause of amorphism on a tip surface at these low closing voltages, therefore, is explained to be the result of the field emission from the Ga cathode in the case of positive tip and of the bombardment by the field-ionized gallium ions in the case of the negative tip. The threshold values for closing and opening contacts were dependent on tip radius.
Observation of a Bernstein wave propagating obliquely to the magnetic field in a streaming plasma
Authors: Idehara T. , Takeda M. , Ishida Y.
Published: February 2004

A Bernstein wave propagating obliquely to the magnetic field is excited by a coaxial antenna in a streaming plasma and detected by an interferometer system, which shows that the dispersion relation for the wave is consistent with the theoretical result. Another wavelike signal with a shorter ``wavelength'' is observed downstream only of the exciting antenna, and its ``phase velocity'' is approximately equal to the velocity of the plasma stream calculated from the Doppler shifts of Bernstein waves in both upstream and downstream regions, which may show that the signal does not propagate as the wave but floats down on the plasma stream as the modulation of plasma particles.
Interpretation of electrostatic probe data taken in a flowing plasma
Authors: Huggins Raymond W.
Published: February 2004

Electrostatic probe measurements taken under continuum conditions in a flowing ionized gas can overestimate the charged-particle density by several orders of magnitude if the convection of charged particles into the plasma sheath is not included in the analysis. A simple physical model which includes both diffusion and convection currents is described, together with an experiment in which charged-particle densities inferred from spherical and disk probes were compared to microwave electron density measurements. The experiment was performed in a room-temperature flowing afterglow plasma over a Reynolds number range 0.4–70 under thick-plasma-sheath conditions. The agreement between the microwave and the spherical probes' ion current measurements was within 30%, and the ion current-voltage characteristic was described to better than 10% at both a high and low Reynolds numbers. The interpretation of electron current data is also discussed.
Nonlinear density-matrix equation for electrons in a weakly ionized plasma
Authors: Willett Joseph E. , Gorham James W.
Published: February 2004

A derivation of a density-matrix equation of motion exact to all orders in the driving field is presented for a system of dynamically independent electrons interacting with a set of randomly distributed static scattering centers. Nonlinear ``driving'', ``collision'', and ``interference'' terms are exhibited. An expansion of the equation of motion through second order in the field is readily obtained from the exact nonlinear equation.
A zero-current electrometer method and its application to charge-decay measurements
Authors: Dreyfus G. , Lewiner J.
Published: February 2004

A zero-current electrometer method is presented. It allows static charge measurements with a precision comparable to that of classical electrometers and current measurements without any current flow in the external circuit. The advantages of this technique are pointed out. The apparatus is used in the investigation of a new charge-decay process due to the interaction of the electret with molecules of a solvent. The observed effects are interpreted in terms of hopping conduction stimulated by chain motion.
Energy transfer and cavity formation in liquid-drop collisions
Authors: van de Sande E. , Smith John M. , van Oord J. J. J.
Published: February 2004

The impact of drops with target liquids has been investigated. A description of the cavity growth after the impact of a single droplet is presented and a theoretical model has been derived which gives the time dependency of the cavity depth. Experimental verification with water shows good agreement between theory and experiment.
Bubble pulsation and cavitation in viscoelastic liquids
Authors: Yang Wen-Jei , Lawson M. L.
Published: February 2004

An analysis is performed to investigate free and forced oscillation of a gas bubble and cavitation in viscoelastic liquids of a three-parameter Oldroyd model. The first-order perturbation method for small amplitudes has been employed to obtain periodic solutions to the bubble dynamics equation. Consideration is given to the influence of surface tension, vapor pressure, and thermodynamic behavior of the gas inside the bubble. It is disclosed that transient behavior of the bubble in viscoelastic liquids is governed by five dimensionless parameters. Conditions for stable bubbles are obtained. Free oscillation consists of a decaying exponential component and a damped sinusoidal oscillation associated with the natural frequency of the bubble-liquid system. The effects of the five governing parameters on the natural frequency are determined. The radial motion of the bubble in an oscillating pressure field includes a sinusoidal oscillation associated with the forcing frequency, a decaying exponential component, and a damped sinusoidal oscillation associated with the natural frequency. Criteria for the onset of incipient cavitation are determined when a bubble is suddenly released into the liquid or is situated in an oscillating pressure field.
Classification of steady-profile shocks in liquids
Authors: Horie Yasuyuki
Published: February 2004

The stability and classification of steady-profile plane shocks in liquids are studied by hydrodynamic equations which include the relaxational properties of momentum and heat fluxes. The thermodynamic behavior during shock deformation is shown to be equivalent to the dissipative motion of a particle described by a generalized Liénard equation. The stability condition produces relations for the relaxation times for momentum and heat fluxes. These relations are in agreement with acoustic data and other theoretical calculations which produce the relaxation times of 10−13−10−14 sec.
Electron distributions in gas lasers
Authors: Allis W. P. , Haus H. A.
Published: February 2004

Simplified models of collision processes are introduced which make possible closed-form analyses of electron distributions in molecular gases. In particular, models are considered that approximate the collision processes in a diatomic gas and in a gas mixture resembling the He : N2 : CO2 laser. Expressions are obtained for the rates of excitation of the vibrational modes which include the effect of superelastic collisions. The results are illustrated by evaluating the V-I characteristic and the efficiency of an E-beam CO2 laser.
Recombination transitions in Zn–N-doped GaAs1−xPx in the direct and indirect composition regions
Authors: Campbell J. C. , Holonyak N. , Lee M. H. , Ludowise M. J. , Craford M. G. , Finn D. , Groves W. O.
Published: February 2004

The behavior of the Zn acceptor in conjunction with the N isoelectronic trap in GaAs1−xPx is studied. The photoluminescence spectra of GaAs1−xPx : N : Zn, doped p type by dilute Zn diffusion, are shifted to lower energy by an amount EZn≃30 meV (x < xc≃0.46, 77°K) for recombination transitions involving the Γ band edge, the A line, or NN pairs. For transitions involving the A line or NN pairs and crystal composition beyond the direct-indirect transition (x > xc), the spectral shift due to the Zn acceptor weakens with increasing x, which is in accord with the relative weakening of k = 0 recombination components as EΓ increases relative to Eχ. Photopumped laser operation of GaAs1−xPx : N : Zn (x < 0.46) platelets is demonstrated on Zn–N transitions. No effect is observed attributable to Zn–N complexes.
Eccentric-core glass optical waveguide
Authors: Miyashita T. , Edahiro T. , Takahashi S. , Horiguchi M. , Masuno K.
Published: February 2004

A new form of glass fiber is investigated. The core of the fiber is eccentrically positioned and contacts only a very small part of the inner surface of the outer tube with a lower index of refraction than that of the core. The total loss measured was 10 dB/km at a 0.80-μm wavelength and the pulse broadening measured on a 55-m section was 0.11 ns, which is much smaller than the value expected for the unclad fiber. Thus, it is shown that the part making contact between the core and tube dominates the transmission characteristics.
Diluent cooling of a vacuum-ultraviolet high-pressure xenon laser
Authors: Johnson A. Wayne , Gerardo J. B.
Published: February 2004

Experimental results are presented on the effect of diluent cooling of a 1721-Å high-pressure xenon laser produced with a pulsed beam of high-energy electrons. Both helium and argon were used as diluents in order to limit the rise in the gas temperature that occurs when the electron beam is stopped in the gas. In the Xe–He mixtures the chemistry was not significantly altered by the presence of He; but in the Xe–Ar mixtures, argon was very important in the absorption and transfer of internal electronic energy. The results demonstrate that both diluents improve the operational characteristics of the laser. Only helium is found to improve the efficiency of conversion of electron-beam energy into stored laser energy.
hFE degradation in the presence of intense magnetic fields
Authors: Saleh N.
Published: February 2004

A theory was worked out to analyze the effect of intense magnetic fields on the forward current gain hFE. The quantum splitting of energy levels (Landau levels) was utilized. The theory is in very good agreement with available experimental data.
Epitaxial PbSe and Pb1−xSnxSe: Growth and electrical properties
Authors: Hohnke D. K. , Kaiser S. W.
Published: February 2004

Epitaxial layers of PbSe and Pb1−xSnxSe have been grown on cleaved BaF2 and SrF2 single-crystal substrates by vacuum deposition of the evaporated binary compounds. The influence of the effusion conditions on the stoichiometry of the molecular beam is considered and it is shown that evaporation of PbSe results in two-phase layers that contain precipitated lead. Coevaporation of selenium compensated the excess lead and permitted the control of n- or p-type carrier concentrations in epitaxial layers in the range 3×1016−6×1017 cm−3. Structural studies indicate that the layers are single crystals with about the same concentration of low-angle grain boundaries as observed on the substrates. Low-temperature Hall mobilities were measured that are as large as those obtained with annealed bulk crystals. The value 4.8×105 cm2/V sec for a PbSe layer with 9.2×1016 hole cm−3 is the largest mobility measured for this material. Below 77°K the mobilities depend markedly on carrier concentration and thermal history of the specimens.
Optical second-harmonic generation coefficients for guanidinium aluminum sulfate hexahydrate
Authors: Miller Robert C. , Nordland W. A.
Published: February 2004

The absolute signs and magnitudes of all the optical second-harmonic generation coefficients dij for ferroelectric guanidinium aluminum sulfate hexahydrate (GASH) have been obtained by using single-domain crystals and a 1.06-μm Nd laser. It is found that in esu units d22 = − 0.25 × 10−9, d31 = d15 = + 0.020 × 10−9, and d33 = + 0.047 × 10−9, where the absolute directions are defined in the usual manner. The magnitudes of d22 and d31 are consistent with values estimated from data previously reported by others. The vector part of the δ form of the d tensor is δν = 2δ31 + δ33 = + 1.2 × 10−7 esu. The value δν/Ps = + 3.4 × 10−7 and is about −5 times the value characteristic of a number of oxide-type ferroelectrics. Upon polarization reversal all the dij coefficients change sign with respect to a fixed coordinate system, which is consistent with structure data and symmetry considerations.
Effects of dislocation density on the properties of liquid phase epitaxial GaAs
Authors: Ettenberg M.
Published: February 2004

A study has been made of the effect of dislocation density on the properties of p-type GaAs (Ge-doped, p = 1 × 1019 cm−3) grown homoepitaxially on GaAs and heteroepitaxially on GaP. It has been found that dislocation densities > 5 × 106 cm−2 reduce the minority-carrier diffusion length in the p-type material and, consistent with this reduction, degrade the junction electroluminescence and p-layer photoluminescence. At high dislocation densities (> 5 × 106 cm−2), it is also found that subgrains form in the GaAs epitaxial layers grown either heteroepitaxially on GaP or homoepitaxially on GaAs. It is surmised that the dislocations polygonize during growth to form subgrain boundaries rather than form due to nucleation at the substrate. Finally, the results indicate that the electron diffusion length is limited to the average dislocation spacing with the dislocations acting as nonradiative recombination centers for electrons.
ac losses in superconducting magnets at low excitation levels
Authors: Hunt T. K.
Published: February 2004

Levitation of high-speed transportation vehicles carrying superconducting magnets may be achieved by repulsion from the currents induced in a conducting guideway. The vertical accelerations of such vehicles moving over a guideway of finite roughness will lead to alternating currents in the superconducting magnets and thus to power dissipation in the cryogenic system. Previous investigators have concluded that the resulting contribution to the cryogenic heat load may be as great as that from all other sources and thus impose serious weight and space penalties on the over-all system design. These investigators have quite generally assumed that the alternating fields will completely penetrate the superconducting wire at all field levels and that the use of twisted multifilament composite wire is thus essential if ac losses are to be minimized. We show that this assumption is incorrect and that it results in a significant overestimate of the loss in multicore wire at the low alternating field levels appropriate for the full-scale vehicle-guideway system. Our analysis further predicts, and our experiments confirm, that an order-of-magnitude improvement in low-level ac loss performance can be achieved merely by the substitution of single-core superconducting wire for the multicore wire ususally proposed. This should reduce the ac loss to about 1.3 W/vehicle from the 14 W for a typical multicore wire. We find a cubic dependence of the loss rate on the alternating field level, and this implies that an additional loss reduction would accrue if the coil bundle could be expanded to reduce the average current density while preserving the total current and lift force. By these means the ac loss contribution to the cryogenic heat load of a levitated vehicle could be made quite negligible.
Interaction energy of dislocations with magnetization in evaporated films
Authors: Srivastava R. S.
Published: February 2004

A simple theory for interaction energy of dislocations with magnetization through magnetostriction is developed for Permalloy films with varying composition. It is found that the inclusion of the dislocation energy in the total anisotropic energy in the pair-strain model gives a better fit with experimental results.
Growth-induced magnetic anisotropy in variously oriented epitaxial films of Sm-YIGG
Authors: Hagedorn F. B. , Hewitt B. S.
Published: February 2004

Epitaxial films of Sm0.4Y2.6Ga1.2Fe3.8O12 have been grown under carefully controlled and essentially identical conditions on Gd3Ga5O12 substrates cut in four different orientations: {112}, {111}, {110}, and {100}. It is found that the two-parameter model for growth-induced anisotropy is inadequate to describe the anisotropies experimentally determined from this group of films. In the context of the preferential site occupation mechanism for growth-induced anisotropy, these results indicate that the site-preference factors for the yttrium and samarium ions depend on the orientations of the growth faces in a more complicated way than has heretofore been considered.
Reduction in switching thresholds of chalcogenide films with polymeric coatings
Authors: Welber B. , Taylor R. C.
Published: February 2004

Polymeric coatings have been deposited on amorphous chalcogenide films used in laser writing. The coatings are shown to be consistently effective in reducing the power required for crystallization. They are less effective in reducing the amorphising energy.
Production of treeing in insulators at damage tracks
Authors: Tommasino Luigi , Armellini Claudio
Published: February 2004

In most insulators heavy ions produce tracks of radiation-damaged material which give rise to microscopic channels after appropriate chemical etching. By applying high-voltage pulses through the irradiated insulator kept between two electrolyte cells containing the etching reagent, these damage tracks cause treeing phenomena. Preliminary results are shown dealing with the treeing production around fission fragment and α-particle tracks in some organic insulators. Treeing at damage tracks provides a new method for initiating treeing processes and enables us to enlarge damage tracks considerably.
Simple model for the slope change of C-V curves of irradiated MOS capacitors
Authors: Galloway K. F.
Published: February 2004

A simple model based on the concept of ionic clustering at the oxide-semiconductor interface of an MOS device can qualitatively account for the observed slope change in the capacitance versus voltage characteristic of irradiated MOS capacitors.
Comment on ``The epitaxial growth of sphalerite and wurtzite ZnSe on a (111) Ge surface''
Authors: Holt D. B.
Published: February 2004

Vacuum evaporation has been employed to obtain reproducible (invariable) epitaxial growth over wide ranges of substrate temperature in the cases of 15 combinations of group II-VI compounds with various substrate surfaces. In all these cases only one basic structure was found in the films. Reproducible epitaxy could not be obtained in the case of ZnSe on (111) Ge. It is suggested that Aung San's variable structures represent scatter arising from growth conditions that do not result in reproducible epitaxial growth. It is pointed out that the interpretations suggested by Aung San for the electron diffraction patterns that he published in two cases do not correspond to his observation, and in the third case, it is not the only interpretation that is consistent with the diffraction pattern. Tilting and dark-field microscopy experiments are necessary to identify these film structures.
Reply to ``Comment on `The epitaxial growth of sphalerite and wurtzite ZnSe on a (111) Ge surface' ''
Authors: San Aung
Published: February 2004

This reply is to establish that the data and the interpretation of the results of the paper commented upon are reliable. Practical details of the crucial factors that influenced the repeatable growth of epitaxial ZnSe on a (111) Ge are given.
Lead telluride-germanium heterojunction properties
Authors: Perfetti P. , Cerrina F. , Coluzza C. , Margaritondo G.
Published: February 2004

PbTe–Ge p-n heterojunctions were formed by evaporating PbTe layers on Ge substrates kept at constant temperature. The electrical characteristics are discussed, indicating that the static potential drop is essentially supported by the Ge side in all diodes. This causes a peaking of the spectral photoresponse near the Ge energy gap.
Photoluminescence of nitrogen-implanted GaAs1−xPx
Authors: Streetman B. G. , Anderson R. E. , Wolford D. J.
Published: February 2004

Nitrogen has been implanted in GaAs1−xPx crystals of direct (x=0.37) and indirect (x=0.50) compositions. Photoluminescence spectra for the implanted material are consistent with previously reported results for GaAs1−xPx with N incorporated during growth. Implantations were performed at 200 keV with fluences sufficient to produce calculated peak N concentrations in the range 1017−1019 cm−3. Samples heated to 200 °C during implantation exhibit improved annealing properties above 800 °C compared with room-temperature implantations.
Dipole reorientation in polyvinylidene fluoride
Authors: Pfister G. , Abkowitz M. A.
Published: February 2004

The thermally stimulated current (TSC) from polarized polyvinylidene fluoride is studied below room temperature. The experimental results indicate that the maximum of the TSC observed at ∼ −50°C is due to reorientation of dipoles in a process associated with the glass transition. The TSC peak is inhomogeneously broadened by a distribution in relaxation frequencies. The results are analyzed in terms of both Arrhenius, and Williams-Landel-Ferry descriptions of the temperature dependence of the relaxation processes and the distribution function for the relaxation frequencies is calculated from the temperature dependence of the TSC. It is shown that a distribution in preexponential factors or in activation energies can account for the observed width of the TSC peak. For the latter case a distribution varying exponentially with activation energy seems most likely. From the data we obtain (3.6±0.4)×104 °K for the apparent activation energy and ∼2×10−3 sec−1 for the relaxation frequency of the dominant realignment process. The glass transition temperature is determined as Tg ∼ −51°C.
Infrared absorption of mixed silicon isotope pairs in gallium arsenide
Authors: Leung P. C. , Fredrickson J. , Spitzer W. G. , Kahan A. , Bouthillette L.
Published: February 2004

The infrared absorption of GaAs doped with 28Si, 30Si, or 28Si + 30Si and compensated by 6Li diffusion or electron irradiation is reported. Isotopic shifts close to those predicted from local-mode theory are observed for all the silicon defect bands in 30Si-doped GaAs from frequencies previously reported for 28Si-doped material. a new band is observed at 456 cm−1 for the sample containing both 28Si and 30Si, and is attributed to (28Si–30Si) pairs. The frequency of the new band is in accord with simple theory, and its presence confirms the observation of the nearest-neighbor silicon pairs. The results indicate, however, that the indentification of one of the three absorption bands previously attributed to the 28Si pairs is questionable. The experimental result also indicates that an absorption band at 369 cm−1 previously observed in electron-irradiated samples in indeed due to a silicon-related defect.
Minimization of conductor surface heating by a pulsed magnetic field
Authors: Rosenbluth M. N. , Furth H. P. , Case K. M.
Published: February 2004

The heat deposition on the surface of a semi-infinite conductor is obtained for a magnetic field pulse of arbitrary time dependence but finite duration. Given a specified ``flat-top'' period for the magnetic field strength at the surface, the rise and decay of the field pulse for minimal surface heating are derived.
Radiation-limited model for a plasma conduction layer in magnetic flux compression systems
Authors: Turchi Peter J.
Published: February 2004

The nature of a high-temperature plasma layer adjacent to a vaporizing conductor surface in multimegagauss flux compression systems is of interest in terms of the maximum field levels attainable and the extent to which high-Z conductor impurities will contaminate plasmas confined by ultrahigh magnetic fields. A model has been developed for such a conductor plasma layer, based on the assumption of a steady balance between resistive heating and radiation loss at any location within the plasma layer. A general analytical solution is found for the magnetic field distribution through the layer in terms of plasma and conductor properties and a nondimensionalized profile integral. Criteria are derived emphasizing the need for proper dynamic operation if plasma conduction layers are to have any importance in high-field flux compression systems.
On the generalized Brewster's law for a moving dielectric medium
Authors: Chuang C. W. , Ko H. C.
Published: February 2004

The Brewster-angle phenomenon for a dielectric half-space moving uniformly parallel to its surface is investigated. A general case is treated in which the polarization of the incident wave and the orientation of the plane of incidence with respect to the velocity vector are arbitrary. The generalized Brewster's law is derived which defines the angle of incidence as well as the required polarization for the electric field of incident wave in order to experience total transmission at the interface. It is shown that in general there are two unequal Brewster angles which are located on the opposite sides of the surface normal. However, when the velocity exceeds a certain value, these two angles occur in the same quadrant. The required polarization is linear, and it is in general not parallel to the plane of incidence.
On the interaction of a transient electromagnetic plane wave and a lossy half-space
Authors: Dudley D. G. , Papazoglou T. M. , White R. C.
Published: February 2004

The problem of a causal transient plane wave incident at an arbitrary angle on a lossy half-space is considered. The classical frequency domain reflection coefficients are inverted to the time domain through a detailed analysis of the singularities in the complex frequency plane. Numerical results are included for a lossy earth. Some peculiarities associated with Brewster's angle are discussed.
Electrical properties of metal-polymer (polysterene) silicon devices
Authors: Sanchez D. , Carchano M. , Bui A.
Published: February 2004

The electrical properties of metal-polymer-silicon (MPS) structures have been investigated. Polymer films have been deposited on silicon substrates by using polymerization of a styrene monomer vapor in an ac glow discharge. A close examination of the hysteresis shown in the C(V) curves of the MPS capacitors has been made. The sense of this hysteresis reverses when the bias-sweep frequency is reduced. The variation of the flat-band voltage shift when the polarizing voltage varies with regular steps between symmetrical extremes is determined with respect to hysteresis. It is shown that the effect of temperature is very important in the variation of the flat-band voltage shift. This variation is appreciably symmetrical when a polarizing voltage step is applied to the structure and when it is short circuited. It may be concluded that the charge variations leading to the hysteresis effect of the dynamic capacitance curve are due to injection of carriers in the polymer film from both the metal and the silicon over the potential barrier present at these interfaces. A model is proposed to express the method of carrier injection.
Image force interactions at the interface between an insulator and a semiconductor
Authors: Williams R.
Published: February 2004

A simplified classical analysis is made of the image force interactions of ions in an insulator near an interface with a semiconductor. The ions induce a countercharge of electrons in the semiconductor, and these screen the field due to the ions. With respect to the image force, the semiconductor may behave like either a metal or a dielectric, depending on the magnitude of Debye screening length relative to the distance of the ions from the interface. An approximate solution of the problem for intermediate cases gives a lateral interaction potential that describes an effective lateral attraction among the components of the system. A numerical example is given for the SiO2–Si interface, and possible applications to other systems are discussed.
Properties of Schottky barriers and p-n junctions prepared with GaAs and Alx Ga1−x As molecular beam epitaxial layers
Authors: Cho A. Y. , Casey H. C.
Published: February 2004

The properties of molecular beam epitaxy (MBE) that are relevant to device applications have been investigated. Precise control of layer thickness is one of the most attractive features of MBE, and layers from a few hundred angstroms to 10 μ may readily be grown. Unintentionally doped GaAs layers grown on 〈100〉-oriented substrates are n type, and room-temperature carrier concentrations of ∼2 × 1015 cm−3 with a mobility of ∼6000 cm2/V sec have been obtained. Schottky barriers on MBE n-type GaAs layers demonstrate that defect-free devices with uniform properties may be prepared at the present time. Junctions of p- and n-type MBE have also been fabricated and have been found to compare favorably with p-n junctions prepared by other techniques. Heterojunctions of GaAs and Alx Ga1−xAs have also been prepared and evaluated. The p-type Alx Ga1−xAs layers are suitable for heterostructure applications, while n-type Alx Ga1−xAs layers tend to be high resistivity at the present time.
Properties of Zn-doped GaN. I. Photoluminescence
Authors: Pankove J. I. , Berkeyheiser J. E. , Miller E. A.
Published: February 2004

Zinc in GaN forms an efficient radiative center emitting blue light at 2.86±0.02 eV and acts as a deep acceptor which can make the crystal insulating. A systematic variation of growth conditions shows that an optimization of the photoluminescence efficiency is possible. Under nonoptimal conditions, lower photon energy emission is obtained. A temperature-dependent competing nonradiative process has an activation energy of 0.33±0.15 eV. The emission peak exhibits a negligible spectral shift with temperature. The response time of the blue photoluminescence is several orders of magnitude slower than the near-gap transition. It is suggested that the photoluminescence is due to a radiative transition from the conduction band tail to the Zn acceptor levels.
Mode-locking dynamics of homogeneously broadened lasers
Authors: Barnes N. P.
Published: February 2004

The dynamics of the mode-locking process for homogeneously broadened lasers are investigated. The investigation focuses attention primarily on the temporal development of the pulse width. However, the other parameters characterizing the mode-locked laser pulse can also be determined in a similar manner. The temporal development of the pulse width is determined for amplitude-modulated and frequency-modulated mode-locked lasers both without and with finite detuning. An important result of this investigation is the determination of the threshold for the mode-locking process. An estimate of the modulation index required to achieve mode locking is given for amplitude and frequency mode-locking processes. The effect of detuning on the required modulation index is also determined for both cases.
High cw output power in stripe-geometry PbS diode lasers
Authors: Ralston R. W. , Walpole J. N. , Calawa A. R. , Harman T. C. , McVittie J. P.
Published: February 2004

Stripe-geometry PbS diode lasers have been developed with cw output powers of about 1/3 W in the 4.3-μm wavelength region. A maximum cw output power in a single longitudinal mode of about 50 mW, over-all external quantum efficiencies as high as 27%, and incremental internal quantum efficiencies near 60% have been observed. The improved performance has been achieved through a number of significant developments in device technology.
Calculation of the minority-carrier confinement properties of III-V semiconductor heterojunctions (applied to transmission-mode photocathodes)
Authors: James L. W.
Published: February 2004

For electro-optical device applications, the principal properties desired of a heterojunctions are minority-carrier confinement and a change in optical parameters. It is shown that for III-V materials with heavily doped junctions the minority-carrier confinement properties may be approximately calculated from the materials parameters by using a simple relationship. The critical parameters are shown to be the minority-carrier diffusion length, the device operating temperature, and the rate at which the band gap of a materials system varies with lattice constant. The effective interfacial recombination velocity into the high-band-gap side of a heterojunction is calculated from these parameters, and is in turn used to calculate the properties of transmission-mode III-V photocathode devices. Some materials systems such as GaAs–AlGaAs and InP–InGaAsP demonstrate near-ideal performance as photocathodes, while other commonly used materials systems such as GaAs–GaAsP are shown to be fundamentally incapable of good performance. A difference in electrical properties is demonstrated between liquid-phase-epitaxially grown heterojunctions and vapor-phase-epitaxially grown heterojunctions.
Low-current-density LED-pumped Nd: YAG laser using a solid cylindrical reflector
Authors: Farmer G. I. , Kiang Y. C.
Published: February 2004

Results of a development program for light-emitting-diode (LED)-pumped neodymium-doped yttrium aluminum garnet (Nd: YAG) lasers highlight a significant design feature: an index-matching method to increase the coupling efficiency of the laser. A solid-glass half-cylinder measuring 5.0×5.6 cm was used for index matching and also as a pumping cavity reflector. An array of twenty 0.034×0.254-cm GaAlAs diodes, connected in series, aligned such that the emission area formed a straight line, was used to excite a 1.5×56-mm laser rod. The interfaces between the diode array, glass half-cylinder, and laser rod were filled with viscous fluid of refractive index n = 1.55. Experiments performed with both the glass half-cylinder and a gold-coated stainless steel reflector under the same operating conditions indicated that the index-matching half-cylinder gave 160–200% improvement of coupling efficiency over the metal reflector at various operating temperatures. For a 207-A/cm2 driving current density the laser produced cw output power of 27 mW.
Self-induced interaction of magnetic domains and bubbles with a neighboring current
Authors: Emtage P. R.
Published: February 2004

It was recently pointed out that magnetic domains tend to move parallel with the current in a nearby conductor; the motion is due to Hall currents set up in the conductor by the domain field and is independent of any field gradients due to the unperturbed current. The magnitude of the force that produces this drift is here calculated for the cases of a single straight domain wall and of a circular magnetic bubble. The force is found to be strong enough to produce controlled motion of a magnetic bubble, provided that the magnetic material is optically flat and the current carriers in the conductor have a high mobility.
Narrow-band variance noise
Authors: Strasilla U. J. , Strutt M. J. O.
Published: February 2004

The variance of the variance of current noise of a type 741 operational amplifier is examined in the frequency region where the 1/f noise is predominant. By using a Fourier analyzer the variance is measured for the relatively small bandwidths, 0.155 and 0.31 Hz, in the frequency region 0.31–10 Hz. The variance of the variance of 1/f noise in a constant narrow band is found to be greater than that predicted for white noise, and increases at lower frequencies. The probability distribution of the variance is found to change from an almost Gaussian shape at frequencies higher than 4 Hz to a positive skewed shape at lower frequencies. The difference of the variance of the variance for 1/f noise from that of white noise, the frequency dependence of the variance of the variance, and the skewness of the probability distribution of the variance are explained with a computer model.
Particle detection with superheated superconducting grains
Authors: Blot J. , Pellan Y. , Pineau J. C. , Rosenblatt J.
Published: February 2004

Electrons having kinetic energy of the order of a few hundred keV can induce superconducting-to-normal transitions in an assembly of metallic spheres in a superheated state. We study this phenomenon in several type I superconductors (In, Hg, Sn, and Sn–Pb alloy) at different electron energies. Experiments show that the transition cross section is strongly dependent upon grain size and thermal properties of the superconductor. We develop a phenomenological model which qualitatively describes the above features, as well as the field and temperature dependence of the transition probability. Possible application to particle detection, particularly of low-energy charged particles and heavy ions, are discussed.