bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of particle species evolution in neutral-beam injection lines
Authors: Kim J. , Haselton H. H.
Published: February 2003

Analytic solutions to the rate equations describing the species evolution of a multispecies positive ion beam of hydrogen due to charge exchange and molecular dissociation are derived as a function of the background gas (H2) line density in the neutralizing gas cell and in the drift tube. Using the solutions, calculations are presented for the relative abundance of each species as a function of the gas-cell thickness, the reionization loss in the drift tube, and the neutral-beam power as a function of the beam energy and the species composition of the original ion beam.
Studies in electromagnetic fields and phase constants of a concentric line having a helical inner conductor
Authors: Chiba Jiro , Sato Risaburo , Nimura Tadamoto
Published: February 2003

This paper describes a wire helix which has a coaxial shielding cylinder since in practice a wire helix is often used with a shielding cylinder. Analyses are done by wire theory. The electromagnetic field, phase constant, characteristic impedance, and attenuation constant of the shielded wire helix are necessary in the engineering field, and the first two of them are dealt with in this paper. As for the phase constant, we present the concrete results of calculations using the numerical solution by a computer.
Planar one-dimensional magnetically insulated electron flow for arbitrary canonical-momentum distribution
Authors: Mendel C. W.
Published: February 2003

Equations are derived for finding the current and voltage profiles of electron flows from their momentum distributions. It is found that many of the features of the flow are independent or quasi-independent of the distribution functions. For this reason, it is concluded that the potential difference across the flow can usually be found from the line-current measurements.
Frequency stabilization of HF lasers by means of beat signals and anomalous dispersion
Authors: Wang C. P. , Varwig R. L.
Published: February 2003

A cw HF chemical laser was frequency stabilized by a scheme in which beat signals between adjacent longitudinal modes and the anomalous dispersion of the gain medium were used. The basic theory and the feedback loop are described. Using this scheme, a frequency stability of 350 kHz (3.5×10−9) was achieved.
Generation of 16-μm radiation in 14NH3 by two-quantum excitation of the 2ν−2(7,5) state
Authors: Eggleston J. , Dallarosa J. , Bischel W. K. , Boko J. , Rhodes F C. K.
Published: February 2003

Stimulated emission at 15.82 and 15.91 μm has been obtained in 14NH3 following two-photon excitation of the 2ν−2(7,5) state. Total output energies on the order of 3 mJ have been observed in a simple experimental arrangement. A discussion of the experimental findings concerning the laser output spectrum, the pressure dependence, the utilization of the optical Stark effect, and the influence of the spectral width and spatial profiles of the CO2 radiation providing the nonlinear excitation is given.
Novel neutral atomic fluorine laser lines in a high-pressure mixture of F2 and He
Authors: Sumida Shin , Obara Minoru , Fujioka Tomoo
Published: February 2003

Many intense neutral atomic fluorine laser lines in the visible (λ=7037.5–7552.2 Å) have been obtained from a gas mixture of F2 and He at total pressures up to 3 atm, driven by a fast Blumlein discharge. At high pressures, three new laser lines have been found and were assigned to the quartet manifold: 7425.7 Å (3p4P01/2→3s4P3/2), 7482.7 Å (3p4P03/2→3s4P3/2), and 7515.0 Å (3p4P01/2→3s4P1/2). The number of lines observed and their relative intensities were found to depend strongly on the pressue of the F2/He gas mixture.
Superthermal x-ray emission from CO2-laser-produced plasmas
Authors: Enright G. D. , Richardson M. C. , Burnett N. H.
Published: February 2003

The high-energy continuum x-ray emission from plasma created by intense (1014 W cm−2) nanosecond 10-μm laser pulses has been characterized. The temperature of the superthermal electron component deduced from this emission was found to be strongly dependent on focus position, while displaying a weaker dependence on irradiation angle, beam polarization, and target composition. The variation of the hot-electron temperature as a function of Iλ2 has been examined in detail in a range of Iλ2 from 1015 to 2×1016 W μm2 cm−2 for various target materials and has been found to be in qualitative agreement with the predictions of current theories of hot-electron production based on resonance absorption.
Thermal wave propagation and shock formation in ultrashort optical breakdown
Authors: Griesemann J. C. , Decroisette M.
Published: February 2003

Space-time evolution of a spark produced by ultrashort (25 psec) optical gas breakdown is reported. Experimental evidence is given for the consecutive occurrences of an electron thermal wave and an hydrodynamical shock as leading mechanisms for the plasma expansion. A theoretical model involving ionization of the medium is developed for the first process; it appears that the time dependence of the ionization has to be taken into account for a correct description of the early states of the plasma.
Optical analysis of the interface between a moving arc and air at atmospheric pressure
Authors: Mai H. H. , Dimoff K. , Jean B.
Published: February 2003

The passage of a short magnetically driven arc in air has been recorded simultaneously by means of differential interferometry and phase-contrast photography. Correlation of these results with conventional high-speed photographs reveals an abrupt change in refractive index in the gas preceding the visibly luminous region of the subsonic arc. Midchannel flow calculations and scaling trends indicate the refractive change is due to a front of high-pressure air sustained primarily by molecular heat conduction from the arc core.
Reduction of interface recombination velocity with decreasing lattice-parameter mismatch in PbSnTe heterojunctions
Authors: Kasemset Dumrong , Fonstad Clifton G.
Published: February 2003

We report the first measurements demonstrating and quantifying the systematic reduction of the interface recombination velocity at the (Pb,Sn)Te/PbTe heterojunction interface with decreasing lattice-parameter mismatch. The relation between the degree of lattice-parameter mismatch and the interface recombination velocity is found to be sv = (2.9±0.3) ×107Δε/ε cm/sec. In conjunction with these measurements, we have also observed very low threshold current densities in laser devices fabricated with a small degree of lattice-parameter mimismatch. The lowest threshold current density observed was 15 A/cm2 in a Pb0.96Sn0.04Te/PbTe single-heterostructure laser with a 20-μm active-region width. This is the lowest current density ever reported in (Pb,Sn)Te-diode lasers.
Predicted electron transport coefficients at high E/N values. II. Nitrogen
Authors: Brunet H. , Vincent P.
Published: February 2003

Transport coefficients of electrons in nitrogen are calculated over the range 10−16⩽E/N⩽7.3×10−15 V cm2 by solving the Boltzmann equation using the classical two-term expansion in spherical harmonics. However, as in the case of H2 treated in a previous paper, the sources of new electrons produced by ionization has been accounted for in the Boltzmann equation. It is shown that the release of these new electrons has an effect on the distribution function starting from E/N≃2×10−15 V cm2, which increases rapidly as E/N increases. The recently available cross sections for the excitation of the electronic states of N2 have been used along with the total-momentum-transfer cross section derived by Cartwright. The predicted values of the ionization coefficient are in very good agreement with the experimentally measured values except at low E/N values, for which our predicted ionization coefficients are slightly less than the experimental ones. The agreement is also good for the drift velocities over the entire E/N range, while for the characteristic energies the agreement becomes less satisfactory for E/N≳2.5×10−15 V cm2. The electron excitation rates for the first eight vibrational levels, the A 3Σ+u, B 3Πg, W 3Δu, and C 3Πu electronic states are presented as a function of E/N. The ionization rate and the total dissociation rate (including the dissociative ionization process) are also given as a function of E/N. The percentage of the input power which is delivered to the elastic and the various inelastic processes are presented as a function of E/N.
Nb-Si  A15 compounds produced by liquid quenching
Authors: Waterstrat R. M. , Haenssler F. , Müller J.
Published: February 2003

A metastable A15-type structure has been obtained in binary Nb-Si alloys containing 18.8±0.5 at.% Si by very rapid quenching (splat cooling) from the liquid state. Superconducting onset temperatures (Tc) of about 4 K were measured on these samples. The relatively low Tc values can be a result of the nonstoichiometric (Nb-rich) composition, residual antisite disorder, or other types of defect structures. Ternary additions such as Sn, Pt, or Ir seem to improve the stoichiometry of the A15 phase and a Tc of 13 K was obtained for the analyzed composition Nb75Si16Sn9.
Stability of lamellar eutectics
Authors: Cline H. E.
Published: February 2003

The stability of the growth of lamellar eutectics with respect to variations in the widths of the phases was determined by solving the diffusion in the liquid ahead of the irregular geometry and matching the boundary conditions at the interface. At spacings larger than a critical value corresponding to the minimum undercooling, the growth is stable. Long-wavelength variations in the spacing were found to control the spacing by a mechanism that involves the formation of faults in the structure.
A study of silicide formation by laser irradiation
Authors: Wittmer M. , von Allmen M.
Published: February 2003

We have studied the formation of palladium-silicide and platinum-silicide by laser irradiation of a thin metal film evaporated on single-crystal silicon. The laser-induced silicide layers are very smooth and uniform as found by SEM analysis. The thickness of the reacted metal film has been measured as a function of applied laser fluence. X-ray diffractometry showed that the reacted layers are a mixture of different metal-silicon compounds. This fact is explained by describing the process through which silicides are formed by laser irradiation.
Direct observation of LaB6(001) surface at high temperatures by x-ray and ultraviolet photoelectron spectroscopy, low-energy electron diffraction, Auger electron spectroscopy, and work-function measurements
Authors: Aono M. , Nishitani R. , Oshima C. , Tanaka T. , Bannai E. , Kawai S.
Published: February 2003

The properties of the LaB6(001) surface which is in equilibrium with oxygen (ultrahigh vacuum—10−6 Torr) at high temperatures (room temperature ∼1500 °C) have been investigated by XPS, UPS, LEED, AES, work-function measurements, and so on. In the case of the clean surface (experiments under ultrahigh vacuum), the chemical composition of the surface does not change up to ∼1500 °C, although lanthanum ions which form the outermost layer of the surface begin vigorous thermal motion at ∼1100 °C. A surface electronic state observed at room temperature undergoes no essential change even at ∼1400 °C. Under an oxygen atmosphere, the surface is covered by an oxide and has a high work function below a critical temperature Tc which depends on the oxygen pressure PO2. Above Tc, the surface oxide, which is rich in lanthanum content, evaporates (the activation energy of the evaporation is 7.8 eV), and the chemical composition and work function of the surface become identical to those of the clean surface under ultrahigh vacuum. When PO2 is 1×10−6 Torr, for example, Tc is 1325 °C.
On the mobility of potassium ions in SiO2
Authors: Hillen M. W. , Greeuw G. , Verweij J. F.
Published: February 2003

A new method to measure the mobility of K+ ions in SiO2 is proposed. The method is based on the TVS (triangular voltage sweep) technique at temperatures above 300 °C. The dependence of the voltage at which the current maximum occurs on the sweep rate provides the mobility at a particular temperature. Measurements at different temperatures show that the mobility of K+ ions in SiO2 can be described by μ (T) = (17.46/T)  exp(−1.09/kT) cm2 V−1 s−1 in the temperature region 300–450 °C.
Electronic profile of n-InAs on semi-insulating GaAs
Authors: Washburn H. A. , Sites J. R. , Wieder H. H.
Published: February 2003

The electron density and mobility of VPE-grown 15-μm n-type indium arsenide epilayers have been determined as a function of distance from the gallium arsenide substrate. Both epilayer surfaces show significant increases in density and decreases in mobility from the bulk values (1015–1016 cm−3 and 105 cm2/V sec at 77 °K). The interfacial, or back, surface is apparently dominated by defects to a depth of about 3 μm. The density and mobility profiles are roughly exponential; integrated values are 1.6×1013 cm−2 and 2×103 cm2/V sec. The front surface, highly dependent on applied gate bias, has a density range in accumulation from zero to 5×1012 cm−2 and mobility from 2.5×104 to 3×103 cm2/V sec. The parameters for both surfaces are essentially temperature independent below 80 °K. The front-surface effective mass increases with electron density from its band-edge value of 0.0215me to nearly 0.06 me.
A dual-current-feed magnetically insulated light-ion diode
Authors: Johnson D. J. , Farnsworth A. V. , Fehl D. L. , Leeper R. J. , Kuswa G. W.
Published: February 2003

A 3×1011-W modular magnetically insulated ion diode for inertial-confinement fusion studies is described. Power is supplied to the diode, which is centered in an elongated solenoidal B-field coil structure, by two self-magnetically insulated transmission lines. A circular ion beam is emitted preferentially from one surface of the curved anode plate and extracted through a 13-cm-diam virtual cathode and exposed B-field coils. The virtual cathode is formed by electrons which spiral along the B-field lines that conform to the anode surface. The ion beam converges onto a planar target, located 13-cm from the anode, through a 1-Torr air plume which allows space-charge and partial current neutralization of the beam. The beam is initially primarily composed of protons, but later carbon ions dominate. The proton beam has a divergence of 2.1°±0.3° and peak focused proton-current density of 60 kA/cm2.
X-ray spectra from a gas-puff z-pinch device
Authors: Burkhalter P. G. , Shiloh J. , Fisher A. , Cowan Robert D.
Published: February 2003

X-ray emission was used to diagnose the plasma formation in a gas-puff pulsed-discharge device. X-ray pinhole images were collected simultaneously with x-ray spectra from Ar and Kr gases. X rays were emitted from z-pinched regions (50–100 μm in diameter) along a collinear track formed by the plasma implosion of a hollow gas jet. Spectral analysis indicated Ar plasma formation with electron densities of ∼2×1021 cm−3. The Ar plasma temperature was ∼1 keV, based on a collisional-radiative transport model. Li-like satellite lines were classified in Ar XVI with atomic structure calculations. The Kr x-ray spectrum (6–8-Å region) was dominated by Ne-like Kr XXVII lines. New spectral transitions were classified in Na-like Kr XXVI and F-like Kr XXVIII. The wavelength calibrations in the Kr spectrum were obtained from exploded-Al-wire plasma generated in coincidence with the plasma implosion formed in the puff gas.
Reducing the sensitivity of a free-electron laser to electron energy
Authors: Smith T. I. , Madey J. M. J. , Elias L. R. , Deacon D. A. G.
Published: February 2003

A technique is described which allows a free-electron laser to utilize an electron beam with a wide energy spread. A laser using this technique can be powered by a greater variety of electron sources than would otherwise be possible. In addition, the techniques ease some of the problems encountered when designing a laser to operate in conjunction with a storage ring.
Formation of metallic silver on silver-halide surfaces: Flash-photolysis experiments on silver-halide photochromic glasses
Authors: Marquardt C. L. , Gliemeroth G.
Published: February 2003

Optical and TEM measurements are reported on a series of well-characterized photochromic glasses containing silver-halide microparticles. The growth rate for formation of photolytic silver is found to vary inversely as some fractional power of the silver-halide particle diameter. Comparison with simple models suggests that in these experiments silver cluster growth is being limited by the motion of surface ions. This type of experiment may provide a model system for studying the mechanism of photographic latent-image formation.
Pulsations and absorbing defects in (Al,Ga)As injection lasers
Authors: Hartman R. L. , Logan R. A. , Koszi L. A. , Tsang W. T.
Published: February 2003

Forty-seven strip-buried-heterostructure (Al,Ga)As lasers have been examined for pulsations and absorbing defects in the active volume. All 18 pulsating lasers were found to have defects while only one of the 29 nonpulsating lasers had a visible defect. These results show conclusively that absorbing defects can cause pulsations in double-heterostructure injection lasers and support a recently published model for the origin of these pulsations. The presence of absorbing defects and pulsations also correlates with structure in the functional dependence of −I2 d2V/dI2 upon I above threshold. Lasers not exhibiting pulsations were aged, and the same correlation was found between the development of defects (particularly mirror darkening), the change in −I d2V/dI2, and the development of pulsations.
Numerical evaluation of modal resonances in the echoes of compressional waves scattered from fluid-filled spherical cavities in solids
Authors: Gaunaurd Guillermo C. , Überall Herbert
Published: February 2003

We extend our previous resonance formalism for the scattering of compressional waves by fluid-filled spherical cavities in sound-absorbing media by analyzing the resonances in the partial-wave amplitudes both as functions of frequency for a given mode number, or as a function of (continuous) mode number n, at a given frequency. In both cases we isolate the resonances by subtracting an appropriate smooth nonresonant background. The frequency analysis leads to a unique identification of the resonances in the summed backscattering amplitudes. This finding can be used to decipher the scattering code contained in the cavity’s echo, since with it we can identify the material composition of the cavity’s filler. The frequency analysis also leads to a study of the resonance-decay phenomenon of ’’ringing’’. The mode-number analysis leads to an interpretation of the scattering process taking place around the cavity in terms of Regge poles representing creeping waves, whose trajectories in the complex n plane and associated dispersion curves for the phase velocities are obtained and displayed. We exhibit the curves for the angular amplitude decay parameter of the waves. We find a condition on the wavelength of the surface waves at each resonance which allows us to physically interpret the resonances as a phase-match reinforcement of the creeping waves with themselves; we verify the results of our resonance theory via the Watson-Sommerfeld method and display numerous plots of the resonances in the scattering amplitudes (some in three dimensions for the modular surfaces) for various combinations of materials in the filler and in the matrix.
Predicted electron-transport coefficients at high E/N values. I. Hydrogen
Authors: Brunet H. , Vincent P.
Published: February 2003

Transport coefficients of electrons in hydrogen are calculated over the range 10−16⩽E/N⩽2.9×10−15 V cm2 by solving the Boltzmann equation using a two-term spherical-harmonic expansion which takes into account the effect of the source of new electrons produced by ionization. Recently reported electron cross-section data, both experimental and theoretical, have been used in the calculation. It is shown that the release of new electrons in ionizing collisions has a noticeable effect on the electron distribution function starting from E/N≃1.2×10−15 V cm2. The predicted values of the first Townsend ionization coefficient are in excellent agreement with experimental results over the entire range of E/N values considered without using unrealistically large momentum-transfer cross sections at high electron energies. The calculated values for the drift velocity vd are in good agreement with the measured values. For the characteristic energy DT/μ, the agreement is good up to E/N=2×10−15 V cm2, while for higher E/N it becomes less satisfactory. The electron excitation rates for the vibration, the excitation of the B 1Σ+u and C 1Πu electronic states, and the rate of H-atom production are presented as a function of E/N. Results are also given for the fraction of the input power that is transfered to the various inelastic processes.
The effect of radiation on the OH− infrared absorption of quartz crystals
Authors: Sibley W. A. , Martin J. J. , Wintersgill M. C. , Brown J. D.
Published: February 2003

The effect of 1.6-MeV-electron irradiation on the infrared properties of high-purity quartz crystals has been studied. The infrared bands assciated with OH− impurities in SiO2 crystals are strongly temperature dependent and must be studied at 77 K or below. Prolonged electron irradiation at low temperature suppresses all of the OH− bands, but these bands recover when the crystals are annealed to approximately 740 K. If as-grown crystals are irradiated at 300 K, the intensity of the OH− bands decreases and two new bands appear at 3367 and 3306 cm−1. The relative absorption intensity of these two bands depends on radiation temperature and dose.
Electric field effect on the thermal emission of traps in semiconductor junctions
Authors: Vincent G. , Chantre A. , Bois D.
Published: February 2003

Electric field effects on the thermal emission of traps in a diode have been studied. Calculations were performed and compared with experimental data on deep centers in GaAs. The results are consistent with a thermal equivalent of the optical Franz-Keldysh effect.
Radiation-induced isotope exchange in vitreous silica
Authors: Shelby J. E. , Mattern P. L. , Ottesen D. K.
Published: February 2003

Irradiation of vitreous silica containing dissolved deuterium gas results in the isotope exchange of hydrogen and deuterium at hydroxyl sites in the glass. This exchange process was studied as a function of dose, dissolved deuterium concentration, and the initial hydroxyl concentration of the specimen. Vitreous silica which did not initially contain any hydroxyl was observed to form considerable quantities of deuteroxyl during irradiation.
The effects of the recoil-implanted oxygen in Si on the electrical activation of As after through-oxide implantation
Authors: Hirao T. , Fuse G. , Inoue K. , Takayanagi S. , Yaegashi Y. , Ichikawa S.
Published: February 2003

The effects of the recoil-implanted oxygen resulting from high-dose As implantations into (111) Si through a thin SiO2 film on the electrical activation have been studied in the dose range 1015–1016 ions/cm2. The concentration profiles of total electrically active As and recoil-implanted oxygen have been measured and compared with each other. It was found that the electrically active As profiles derived from the measured resistivity by assuming published data of mobility which are characteristic of defect-free silicon show an apparent fall-off in the surface region for the implantation with doses above 5×1015 ions/cm2. It is shown that the apparent fall-off in the profiles is caused by both the reduction of the mobility and net carrier concentration in the case of 800 °C anneal, while the former is the main cause in case of 1000 °C anneal. By comparing the mobility profiles with the measured concentration profiles of the recoil-implanted oxygen, the marked reduction of the mobility is shown to occur in the region where the oxygen concentration exceeds ∼1020/cm3. From the analysis of the depth distribution of the defects remaining in Si after annealing, it was demonstrated that the region is confined to the thin layer where the anomalous high-density defects are present. For the As implantation with a dose less than 1015 ions/cm2, however, the recoil-implanted oxygen is likely to have little influence on the electrical activation of the implanted As in the temperature range studied.
Growth and dissolution kinetics of III-V heterostructures formed by LPE
Authors: Small M. B. , Ghez R.
Published: February 2003

When a new layer of a heterostructure begins to form by LPE, conditions of nonequilibrium exist between the existing layer and the new solution. This process has been analyzed for a ternary system in terms of matter transport in both phases and the equilibrium phase diagram. The analysis has been applied to conditions under which the second wave-guiding layer of a double-heterostructure laser may be grown in the (GaAl)As system. It is shown that the active layer tends to dissolve in the subsequent solution. Conditions under which this may be prevented are illustrated. Also illustrated are the forms of the compositional profiles at the heterojunction as a function of growth conditions.
Interface recombination of charge carriers in bicrystals
Authors: Leong John Y. , Yee Jick H.
Published: February 2003

A standard photoconductance measurement is suggested for determining the intergrain recombination velocity of excess charge carriers in a bicrystal. Analysis of the bicrystal photoconductance shows two important effects: First, if the grain size is much larger than the diffusion length, the excess-carrier lifetime in a polycrystalline material will be indistinguishable from that in a single crystal with the same bulk and surface properties. Second, as the intergrain recombination velocity increases, its effect tends to saturate.
The physics of solar cells
Authors: Böer K. W.
Published: February 2003

The photovoltaic mechanism is analyzed with special attention to the boundary conditions between emitter and junction. In frontwall cells, these boundary conditions are rather simple and permit a transparent analysis. They connect the current, determined by the emitter/junction boundary, with the potential drop in the junction, determined by the same condition, and yield the current-voltage characteristic without invoking the superposition principle. The chemistry of the interlayer between the emitter and the junction may modify this characteristic when causing major interface recombination, resulting in a potential deformation. Such behavior is analyzed in more detail for the example of CdS/Cu2S and CdzZn1−zS/Cu2S solar cells. Substantially improved agreement between the results of this theory and experiment is reached.
Critical-state model for the determination of critical currents in disk-shaped superconductors
Authors: Frankel David J.
Published: February 2003

A series of experiments has been carried out on the flux trapping and shielding capabilities of a flat strip of Nb-Ti/Cu composite material. A circular piece of material from the strip was tested in a uniform field directed perpendicularly to the surface of the sample. Profiles of the normal component of the field along the sample diameter were measured. The critical-state model was adapted for this geometry and proved capable of reproducing the measured field profiles. Model curves agreed well with experimental field profiles generated when the full sample was in the critical state, when only a portion of the sample was in the critical state, and when profiles were obtained after the direction of the rate change of the magnetic field was reversed. The adaption of the critical-state model to disk geometry provides a possible method either to derive values of the critical current from measurements of field profiles above thin flat samples, or to predict the trapping and shielding behavior of such samples if the critical current is already known. This method of determining critical currents does not require that samples be formed into narrow strips or wires, as is required for direct measurements of Jc, or into tubes or cylinders, as is usually required for magnetization-type measurements. Only a relatively small approximately circular piece of material is needed. The method relies on induced currents, so there is no need to pass large currents into the sample. The field-profile measurements are easily performed with expensive Hall probes and do not require detection of the resistive transition of the superconductor.
Magnetic instability of (Fe0.06Co0.94) -B amorphous alloy system
Authors: Shiiki Kazuo , Watanabe Takehiko , Kudo Mitsuhiro
Published: February 2003

The causes of magnetic instability, which is a change in magnetic properties at temperatures well below the crystallization temperature, are clarified experimentally for the (Fe0.06Co0.94) -B amorphous ferromagnetic alloy system. This instability is found not to be caused by crystallization or relaxation of residual stress. The induction field applied when the alloy is molten and solidified into the amorphous state is shown to influence the structure of the amorphous state resulting in magnetic instability. A model of the mechanism for this instability is proposed. This model can explain experimental results.
EPR investigations of the defect chemistry of semi-insulating GaAs : Cr
Authors: Goltzené A. , Poiblaud G. , Schwab C.
Published: February 2003

The effects of some heat treatments under various atmospheres (vacuum, As, Ga2O3, or H2) on GaAs : Cr samples have been investigated by EPR. The equilibria between the two valence states Cr+ and Cr2+ seem to depend on various parameters such as the total amount of Cr, and other defects such as the iron contaminant. A new paramagnetic defect, occurring at g=2.002±0.001 has been identified, whose intensity is highest after the H2 anneal.
Multiwavelength GaAs rib waveguide directional-coupler switch with ’’stepped Δβ’’ Schottky electrodes
Authors: Carenco A. , Menigaux L. , Delpech Ph.
Published: February 2003

An electro-optic waveguide directional-coupler switch has been fabricated in GaAs by liquid-phase epitaxy, photolithography, chemical etching, and electroplating. The Schottky electrodes, overlaying each single-mode rib waveguide, are cut midway along the device length to allow the electrical optimization of each switching state (’’stepped Δβ’’ configuration) in a wavelength range (1.0–1.3 μm) useful for optical-fiber communications. The device exhibits good power isolation for both states (at least 19 dB and up to 32 dB) with reverse driving voltages of less than 30 V, at 1.06, 1.15, and 1.32 μm. Both states have been obtained at 1.06 μm by switching one single voltage, a convenient way in spite of some power penalty to take full advantage of the large potential bandwidth (1 GHz) of the switch.
Stimulated Raman scattering by an intense relativistic electron beam subjected to a rippled electric field
Authors: Bekefi G. , Shefer R. E.
Published: February 2003

Generation of submillimeter radiation by stimulated Raman scattering in an intense relativistic electron beam subjected to a spatially periodic transverse electric field is examined. The requisite electric field modulation can be obtained by rippling the wall of the conducting drift tube. When the electron beam is subjected to a periodic longitudinal electric field, short-wavelength plasmons, rather than photons, are generated. The growth rate and other parameters related to this instability are discussed.
Channeled-substrate-planar-structure semiconductor lasers with lateral-evanescent-field distributed feedback
Authors: Tsang W. T. , Logan R. A. , Johnson L. F.
Published: February 2003

GaAs-AlxGa1−xAs channeled-substrate-planar-structure lasers with lateral-evanescent-field distributed feedback are fabricated by using one-step liquid-phase epitaxy. The diodes operate stably in single-transverse (fundamental) and longitudinal modes at room temperature under pulsed operation.
Electrical and laser diagnostics of an 80-kW supersonic cw CO electric laser
Authors: Klosterman E. L. , Byron S. R.
Published: February 2003

Detailed spatial and time-dependent measurements of the electrical parameters and the gas properties have been made on a high-average-power quasisteady supersonic cw carbon monoxide electron-beam-stabilized electric-discharge laser. The electrical and optical measurements show that there are major changes in the current-density distribution and in the supersonic flow field due to the high electric-discharge power input to the gas. A multipin resistor-ballasted electrode has been used to make the current density much more uniform, resulting in a factor-of-2 increase in electrical energy input and in laser power output. Small-signal gain measurements were made on the J=7 to J=13 rotational lines of the V=7 to V=6 CO vibrational transition at various locations in the electrical discharge. The measured rotational temperature showed that only 12% of the discharge power went into gas heating in the supersonic free-stream region. The measured small-signal gain was as high as 0.08 cm−1, the maximum electrical energy density input was 430 J/l amagat, and the maximum laser power density extracted was 120 kW/l.
A velocity interferometer technique to determine shear-wave particle velocity in shock-loaded solids
Authors: Chhabildas L. C. , Sutherland H. J. , Asay J. R.
Published: February 2003

An optical technique is described which uses velocity interferometers to determine the large particle velocity changes associated with plane shear-wave propagation. In this technique two velocity interferometers are used to monitor different diffracted laser beams from a surface which undergoes both longitudinal and shear motion. Fringes produced in the interferometer are proportional to a linear combination of both the longitudinal and shear components of the free-surface velocity. The technique has been used successfully to monitor the free-surface velocity of a Y-cut quartz specimen impacted by an X-cut quartz plate. Although the present shear-wave velocity profiles are limited to an accuracy of ±10%, the accuracy can be easily increased by an order of magnitude by using longer delay legs and larger diffraction angles.
Deep-level-transient spectroscopy: System effects and data analysis
Authors: Day D. S. , Tsai M. Y. , Streetman B. G. , Lang D. V.
Published: February 2003

Studies of typical DLTS systems using either the dual-channel boxcar averager or the lock-in amplifier techniques are presented. The effects of nonzero gate width for the boxcar averager, phase angle adjustment for the lock-in amplifier, and response time of a typical commercial capacitance meter are investigated. Errors introduced in the measurements by these effects are calculated for typical cases. Measurements of the gold donor level in silicon are presented, along with calculated corrections. We find the corrections to be minimal in the boxcar-averager method, but significant in the lock-in amplifier approach.
Enhanced HCl laser power through the addition of CO2
Authors: Menard J. , Delaporte T. , Menard-Bourcin F.
Published: February 2003

The HCl multiline output power of a TE helical laser is enhanced by adding CO2 to the H2+Cl2 mixture. In single-line operation, the output powers on the vibration-rotation lines of the (1→0) band can be increased by a factor of 3 as CO2 is added.
Observation of electron beam damage in thin-film SiO2 on Si with scanning Auger electron microscope
Authors: Ichimura S. , Shimizu R.
Published: February 2003

Electron beam damage to thin-film SiO2 was observed with a scanning Auger electron microscope. After a certain degree of electron beam exposure, changes in both the surface topography and chemical composition were investigated. The result suggested that there is a close relationship between the beam damage and the dissipation of incident energy in thin-film SiO2.
Angular intensity of a gas-phase field ionization source
Authors: Orloff J. , Swanson L. W.
Published: February 2003

Angular intensities of 1 μA sr−1 have been measured for a gas-phase field ionization source in an optical column under practical operating conditions. The source, which was differentially pumped and cooled to 77 K, utilized a 〈110〉-oriented iridium emitter and precooled hydrogen gas at 10−2 Torr. The ion beam was collimated with an electrostatic lens and detected below an aperture subtending 0.164 msr. A transmitted current of ∼10−10 A was measured at voltages corresponding to a field of ?2.2 V/Å at the emitter.
Brillouin scattering from rapidly quenched ferromagnetic metallic glasses
Authors: Malozemoff A. P. , Chang P. H. , Grimsditch M.
Published: February 2003

We report on Brillouin-scattering measurements of thermally excited surface acoustic phonons, and bulk and surface magnons, in quenched ribbons of ferromagnetic metallic glasses with compositions Fe100−xBx (x=14–28), Fe76Mo4B20, FexNi80−xB20 (x=20–60), and Co75−xFexSi15B10 (x=0–6). Room-temperature surface-phonon velocity is found to increase monotonically with increasing B in FeB, and with increasing Fe in FeNiB. The velocity is almost 10% less in Fe76Mo4B20 than in Fe80B20. The phonon velocity is not field dependent, even in compositions where large ΔE effects occur. The g factor, determined from the slope of surface-magnon frequency with field, is 2.09±0.02 for Fe100−xBx. The intensity of surface- and bulk-magnon scattering is independent of magnetostriction in CoFeSiB.
The effect of eddy currents on the nuclear magnetic resonance in wires
Authors: Butterworth M. A. , Engardt R. D.
Published: February 2003

The effects of eddy currents on the nuclear magnetic resonance of Al27 wires was determined for specimens with three significantly different diameters. The absorption and dispersion line-shape derivatives, obtained at room temperature using a saturation factor (γ2H21T1T2) much less than unity, were in agreement with theory.
The effect of electron bombardment on the secondary electron emission from Na3AlF6
Authors: Knapp A. G.
Published: February 2003

The secondary emission coefficient δ of evaporated Na3AlF6 films is found to decrease from about 5.0 to 1.8 and then to increase again to between 5.0 and 6.0 under the influence of electron bombardment with 300-eV electrons. These changes are associated with a decrease of over 2 eV in the surface work function. The initial decrease in δ is caused by loss of fluorine, producing a surface consisting of metallic sodium and aluminum. During this period the Na and Al KLL Auger peaks shift to higher energy. The subsequent increase in δ is associated with oxidation of the metallic sodium, the final surface composition being close to Na2O. This oxidation can be caused by CO2, O2, or H2O. Electron bombardment of the final oxidized surface produces a small reversible increase in δ and a decrease in the work function. Initial experiments on films of other metal halides indicate that electron bombardment causes similar changes in δ and surface composition.
Elastic constants of tourmaline
Authors: Özkan Hüsnü
Published: February 2003

Elastic constants of tourmaline crystals of known chemical composition have been measured by the ultrasonic phase-comparison method. The values in 1012 dyn/cm2 are C11=3.050, C33=1.764, C44=0.648, C66=0.984, C14=−0.06, and C13=0.51. The Debye temperature of the tourmaline derived from the elastic constants is 785 °K.
Dislocation etch pits in LPE-grown Pb1−xSnxTe (LTT) heterostructures
Authors: Tamari N. , Shtrikman H.
Published: February 2003

Heterostructures of Pb1−xSnxTe grown by LPE were studied by an etch technique. A consistent pattern appeared in which the lattice-mismatched heterostructure exhibits a high etch-pit density (?1×107 cm−2) at the interface and in the heteroepitaxial layer. The greater the lattice mismatch, the higher is the defect density. A mismatch as small as ∼2×10−4 is already sufficient to generate defects at the interface. A low-etch-pit-density substrate does not moderate the defect performance in the interface and the epilayer. Homostructures show preservation of dislocation etch-pit density throughout the whole thickness of the epilayer without a substantial decrease, contrary to other reported results. Some differences were found with respect to the opposite heterostructures Pb1−xSnxTe/Pb1−ySnyTe and Pb1−ySnyTe/Pb1−xSnxTe. A high growth temperature (?600 °C) causes a decrease in etch-pit density and the disappearance of some defects. Enhanced nucleation, annealing of dislocations, and bulk diffusion are believed to take place at the high temperature. Some defects disappear and others diminish upon slow cooling, but the basic mismatch character remains.
The extremum condition for the rate of cellular phase separation
Authors: Shingu Paul Hideo
Published: February 2003

An examination was carried out on the physical basis for the so-called ’’extremum condition’’ which determines the dimension of transformed phases during the steady-state cellular phase-separation reaction. The concept of the ’’balance of forces’’ which employs the balancing of various forces at the moving phase-separation boundary as the condition for the steady-state cellular phase-separation reaction is proposed. The magnitude and the direction of these forces are given by the partial derivatives of the total free-energy reduction due to the phase change at an undercooled condition in terms of the relevant reaction parameters such as the size of the microstructure and the reaction velocity. A simple model of lamellar formation by the eutectic or eutectoid reaction is used to demonstrate the meaning of the extremum condition and also to show the usefulness of the balance-of-forces concept.
Kinetics and thermodynamics of the shape-memory effect in martensitic NiTi and (Ni1−xCux)Ti alloys
Authors: Mercier O. , Melton K. N.
Published: February 2003

By rapid pulse heating of NiTi-based shape-memory wires, both with and without an applied load, the details of the recovery process have been studied. It is shown that, contrary to existing theories, the temperature of the reverse transformation is relatively independent of applied load. A modified hypothesis for the motion is proposed, taking into account internal stresses present in polycrystalline material. Without applied load, the reverse-phase transformation on heating is measured to occur within 3 ms, and motion under load is shown to be largely governed by the mechanical time needed to move the weight.
The pulse-degradation characteristic of ZnO varistors
Authors: Shirley C. G. , Paulson W. M.
Published: February 2003

We find that two factors bear on the high-energy pulse degradation of a varistor’s electronic characteristic. First, the electronic structure of active grain-boundary segments depends solely on the peak temperature occurring there during a pulse, and second, this peak temperature is determined by the thermal transport properties of the microstructure. We find that the intrinsic electronic structure can be modified without changing the microstructure to greatly improve the pulse-degradation performance of a varistor by an anneal at low temperature (600 °C) in oxygen. The influence of microstructure is embodied in the grain-boundary temperature-magnification factor Zgb which is defined, measured, and studied theoretically. Theory shows that there are three regimes: (i) a long-pulse-width regime where Zgb=1, (ii) a short-pulse-width regime where Zgb∼ (pulse width)−1/2, independent of pulse energy, and (iii) a very-short-pulse-width (or high-energy-density) regime where Zgb∼ (pulse energy)−1/2, independent of the pulse width. The theory contains one microstructural parameter. Our data encompasses the first two regimes and agrees well with theory for a value of the microstructural parameter which is in good agreemet with earlier work.
Thermal conductivity and electrical properties of 6H silicon carbide
Authors: Burgemeister E. A. , von Muench W. , Pettenpaul E.
Published: February 2003

Thermal conductivity measurements of 6H SiC crystals were done in the 300–500 K range by means of radiation thermometry. Both p- and n-type crystals with carrier concentrations in the 8×1015 to 1020 cm−3 range were used. For the purest samples it was found that the thermal conductivity normal to the c axis is proportional to T−1.49, the room-temperature value being 3.87 W/cm deg. It was also found that the thermal conductivity parallel to the c axis is about 30% lower than that normal to the c axis. Electrical data in the 100–1000 K range are also presented.
Silicide formation with Pd-V alloys and bilayers
Authors: Mayer J. W. , Lau S. S. , Tu K. N.
Published: February 2003

Solid phase reactions in the temperature range between 250 and 600 °C between Si and V-Pd bilayers as well as alloy layers have been studied by MeV 4He+ backscattering and x-ray diffraction techniques. When a Pd layer is interposed between Si and V, the bilayer system starts to react at <300 °C with the formation of Pd2Si. Annealing at higher temperatures (∼600 °C) leads to a uniform layer of VSi2 formed on top of the Pd2Si. Reversing the bilayer sequence (Si/V/Pd) raises the reaction temperature of the system to ∼500 °C with V mixing into the Pd layer. Annealing at higher temperature leads to the formation and accumulation of Pd2Si at the interface and a mixed (nonuniform) structure of Pd2Si and VSi2 in the outer surface region. For a Pd-rich alloy (Pd80V20), a reaction started at about 300 °C and produced Pd2Si by depleting Pd from the alloy. This resulted in a mixed structure of Pd2Si and VSi2 in the outer region, similar to the final stage of the Si/V/Pd system. For a V-rich alloy (Pd90V10), the formation temperature of Pd2Si is raised to ∼500 °C and again leads to a mixed structure. The amount of accumulation of Pd2Si at the substrate-silicide interface increases with the Pd content in the alloy.
Instabilities in output of injection lasers
Authors: Hakki B. W.
Published: February 2003

A type of sustained oscillations that can occur in the output of semiconductor injection lasers are studied analytically. The frequency of oscillations and the conditions of instability are deduced from the nonlinear differential rate equations. This model raises the possibility that, at least in some if not many cases, the stability of a laser above threshold is determined by the degree of saturation of the optical gain. If the gain saturates, the laser is stable, and disturbances become damped oscillations. If the gain increases above the standard value, there will be some current level above threshold at which oscillations become sustained. Furthermore, the condition for critically damping the transient ringing in laser output is also derived analytically. The results of the analysis are compared with the limited experimental results available and the agreement is reasonable. The analysis also provides general guidelines for the design of injection lasers that will be less susceptible to instabilities in their optical output.
Three-photon absorption coefficient determination by means of nonlinear luminescence experiments
Authors: Catalano I. M. , Cingolani A.
Published: February 2003

By means of two- and three-photon comparative luminescence measurements, carried out utilizing a ruby and neodymium laser, we show how the γ3 three-photon absorption coefficient can be determined. The technique used is presented and applied for the CdS and PbI2. The γ3 experimental values obtained are compared with the theoretical predictions and with previous experimental data.