bluuebunny/crossref_metadata_2025 huggingface dataset:
A model of secondary electron yields from atomic and polyatomic ion impacts on copper and tungsten surfaces based upon stopping-power calculations
Authors: Beuhler R. J. , Friedman L.
Published: February 2003

The calculation of the velocity dependence and magnitude of the kinetic secondary electron yield for atomic and polyatomic ions, denoted by γ̄a and γ̄m, respectively, is modeled on stopping-power equations and compared to experimental results from the dynode materials copper and tungsten. From the experimental data, the relationship γ̄m=Σγ̄a is verified, which is necessary to the model calculation of γ̄m. The fundamental assumption of this model is that γ̄a is proportional (even at low ion velocities) to the electronic stopping power (dE/dx)e of that projectile in the target. This fundamental assumption of γ̄a∝ (dE/dx)e has been previously used by Sternglass for calculation of γ̄a’s at ion velocities above 4×108 cm/sec. Example calculations are performed for the velocity dependence of γ̄a for hydrogen, carbon, and fluorine striking copper, and from these results the predicted γ̄m curves for polyatomic ions are in close agreement with experiment. Analogous calculations for a tungsten surface are outlined and the final results are compared with experiment. The model’s utility is shown by illustrating that the measurement of γ̄ can provide not only a relative measurement of (dE/dx)e for different ion atomic numbers on the same target, but can also provide a means of determining the nuclear stopping power (dE/dx)n at low ion velocities where range measurements are difficult to perform. Values of (dE/dx)n derived from measurements for fluorine and carbon striking copper are the same as values predicted by Lindhard and Scharff; for a tungsten target the experimental (dE/dx)n values are a factor of 2 larger than theoretical. The relationship of the stopping power values derived from γ̄ measurements with this model are compared to the values derived from ion range measurements. In addition, the model’s relationship to the secondary electron emission model of Parilis and Kishinevskii is discussed.
Homogeneous excitation of infrared active molecules by laser pulses
Authors: Steverding B. , Dudel H. P.
Published: February 2003

Experiments with focused laser pulses in BCl3 and other infrared active molecules can be arranged in such a way that the vibrational excitation level of the molecule is everywhere the same in the focal conus. The system of differential equations leading to this situation is solved and a few tables are presented indicating the results.
Multifilamentary superconductor with alternating twist in a transverse pulsed field
Authors: Jüngst K. P. , Ries G.
Published: February 2003

A multifilamentary superconductor with alternating twist, proposed earlier in order to reduce coupling losses in longitudinal fields, is investigated in a transverse pulsed field. The induced currents are calculated and a formula for the coupling loss is derived. Magnetization measurements on samples with ordinary and alternating twist have been performed and good agreement with the theory is obtained. The frequency-dependent coupling losses are enhanced by a factor of 2, independent of the alternation rate of twist.
Power spectrum of pulse sequences with correlation between pulse shape and pulse separation time
Authors: Celasco M. , Stepanescu A.
Published: February 2003

A general expression for the power spectrum of a sequence of pulses having time intervals distributed according to an arbitrary probability function and presenting a correlation between pulse shape and pulse intervals is given. Such a correlation is described by means of another arbitrary distribution function giving the joint probability of the parameters that characterize the shape of each pulse in terms of the time interval between that pulse and the preceding one. The expression that has been found is suitable for direct numerical computation and could be applied to many processes of physical interest, some of which are described in the paper.
A technique for measuring optical fiber transmission using the time dispersion of Cerenkov radiation
Authors: Franks L. A. , Nelson M. A. , Davies T. J. , Lyons P. , Golob J.
Published: February 2003

A technique based on measurement of time dispersion in a δ-function Cerenkov pulse has been developed for determining the attenuation coefficient α (λ) of low-loss optical fibers. The time domain amplitude distribution of the transmitted polychromatic pulse is transformed to the wavelength domain by accurate measurement of the differences in arrival times of spectral bands isolated by interference filters. Since the Cerenkov pulses are generated in the fiber by a short burst of relativistic electrons, α (λ) can be measured over a wide and continuous range of path lengths without breaking the fiber. The technique has been demonstrated over the 500–800-nm spectral region for fiber lengths up to 800 m.
Line-tunable CO2 laser operating in the region 2280–2360 cm−1 pumped by energy transfer from Br(42P1/2)
Authors: Petersen Alan B. , Wittig Curt
Published: February 2003

A line-tunable CO2 laser operating in the region 2280–2360 cm−1 is described. The laser is pumped by electronic-to-vibrational energy transfer from Br(42P1/2) atoms, which are produced directly by the pulsed photolysis of Br2, to CO2 molecules. The energy-transfer process is shown to be mode specific, populating the (10°1) state of CO2 directly and thereby providing for stimulated emission on the (10°1) - (10°0) band near 4.3 μm. The experimental arrangement provides a simple line-tunable source of laser radiation in this, as well as other, ir spectral regions. Further, the arrangement is quite convenient and easy to use since the technology involved is derived from that of flash-pumped dye and Nd lasers, and the laser gas samples do not degrade with use, allowing the system to be operated in a sealed-off mode.
Soft x-ray laser pumped by charge exchange between C VII and Ar III in expanding laser-produced plasma
Authors: Seely John F. , McKnight William B.
Published: February 2003

A soft x-ray laser with wavelength 182 Å is proposed. The pumping mechanism is charge exchange between C VII and Ar III which occurs when a laser-produced carbon plasma expands into an argon background gas. Electron pickup is primarily into the n=3 level of C VI, and the laser transition is the Balmer-α line. Nd-glass radiation is converted into 182 Å radiation with efficiency of order 1%.
Discharge studies of the Ne-Cu laser
Authors: de Hoog F. J. , McNeil J. R. , Collins G. J. , Persson K. B.
Published: February 2003

Spontaneous-emission and absorption studies of the Ne-Cu hollow-cathode laser are summarized. The major discharge processes operative in the Ne-Cu laser are outlined and the qualitative aspects of a proposed model of the Ne-Cu laser are discussed. Emphasis is placed on cathode sputtering as a source of copper atoms, and we demonstrate that copper densities of 1014 atoms/cm3 are created via discharge sputtering.
Operation of a plasma-focus device with D2 and He3
Authors: Gullickson R. L. , Luce J. S. , Sahlin H. L.
Published: February 2003

Two plasma-focus devices at the Lawrence Livermore Laboratory, the B Division device (BDPF), with a stored energy of 73 kJ at 18 kV, and the Physics Department device (PDPF), with a stored energy of 67 kJ at 20 kV, were operated with various mixtures of D2 and He3. The purpose of the experiments was to evaluate the D-D/D-He3 yield ratio as a diagnostic tool for determining the plasma ion temperature. Measurements were made in the high-pressure mode (total pressure of 4.0 Torr for the BDPF, 7.5 Torr for the PDPF), where previous measurements using carbon activation showed no significant ion acceleration to energies above the 330-keV carbon (d,n) reaction threshold. The yield from the D(d,n)He3 reaction was determined from measurements of the total neutron yield using the standard silver-activation technique. The yield from the He3(d,p) He4 reaction was determined by measuring the reaction-product protons by copper activation. The Cu anode insert from the center electrode was analyzed for γ activity following each series of shots to measure the presence of Zn63 from the 4.21-MeV-threshold Cu63(p,n)Zn63 reaction. The thick-target yield for this reaction at the proton energy of 14.6 MeV was calculated from cross-section data, giving a value of 7.5×10−4 Zn63 atoms per incident proton. In operation with 50/50 atomic or molecular mixtures of D2 and He3, the D-D/D-He3 yield ratio varied from a minimum of 13.6 to a maximum of 60.5. This corresponds to a plasma temperature range from 4.0 to 6.5 keV, or if a beam-target model is assumed, to a deuteron beam ranging in energy from 28 to 47 keV incident upon stationary He3 ions. Operating with fractions of He3 ranging from 0.053 to 1.0 at a total pressure of 4 Torr, the D-D neutron yield showed the expected dependence on the square of the deuterium fraction [f (D)].
Backscatter and beam refraction in underdense gas breakdown with nanosecond CO2 laser
Authors: Burnett N. H. , Baldis H. A. , Enright G. D. , Richardson M. C. , Corkum P. B.
Published: February 2003

A 50-J 2-ns FWHM CO2 laser pulse focused to intensities in excess of 1014 W/cm2 has been used to induce breakdown in underdense He gas. The laser radiation scattered from these plasmas has been temporally and spectrally analyzed. It is observed that ion wave scattering can result in reflectivities in excess of 50% of the incident intensity. At filling pressures above 30 Torr the incident laser radiation is explosively refracted around the focal region by plasma formed a few mm upstream from focus thus quenching the high-intensity laser plasma interaction less than 1 ns subsequent to breakdown. A weak but well-defined line at 7.06 μm (ω=3/2 ω0) was observed in the backscatter at filling pressures above 40 Torr.
High-pressure sodium lamp arc tube temperature and alumina sublimation
Authors: Rickman James D.
Published: February 2003

The arc tube temperature of a high-pressure sodium lamp is determined from the luminance in the sodium D line and compared with infrared temperature measurements. Good agreement is found after correction for the inside to outside wall temperature difference. The luminance method is used to determine the arc tube temperature in an experiment in which nine lamps are burned for 524 h, after which the normal transmissions of the glass outer jackets are measured. Greater than expected darkening of the outer jackets from standard unground polycrystalline alumina arc tubes is observed when compared with the theory for alumina sublimation from smooth-ground polycrystalline alumina. Little darkening was observed from smooth sapphire (single-crystal alumina) arc tubes. It is suggested that surface irregularities may enhance alumina sublimation from the standard unground alumina.
The influence of electric stress on morphological changes occurring by surface diffusion on a body with anisotropic surface energy
Authors: Brailsford A. D. , Gjostein N. A.
Published: February 2003

The time evolution of the surface morphology of a long single-crystal (initially cylindrical) wire which forms the central electrode of a coaxial capacitor is discussed for mass transport by (isotropic) surface diffusion but allowing for anisotropic surface energy γ. Radial changes in the shape of the wire are shown to be retarded by the electric stress when the γ anisotropy is small. As Nichols and Mullins have shown, the wire is unstable to longitudinal perturbations; their treatment is generalized to incorporate both γ anisotropy and electric stress. The dominant wavelength in the evolving unstable axial profile is related to a γ anisotropy factor involving an out-of-plane second derivative of γ averaged over directions in the radial plane. The electric stress enhances or inhibits the instability depending upon the magnitude of this anisotropy factor. Some tentative remarks, based upon a conjectured extrapolation of the perturbation treatment developed here, are addressed to the problem of the ovulation of a semi-infinite cylinder.
Structure and properties of vacuum-deposited thin films: A new basic relationship
Authors: Vincett P. S. , Barlow W. A. , Roberts G. G.
Published: February 2003

We show that a wide range of vacuum-deposited materials exhibits sharply optimized properties and, in some cases, unusual crystal structures when the temperatures at which the materials are condensed (the substrate temperatures) are in a narrow range near 0.33 of their respective normal boiling points. This generalization applies to essentially all the really sharp optima we can find (for nonmetals) in the recent literature. The materials include organics (our own data on anthracene, phthalocyanine, and pyrene) and inorganics (Se, ZnO, SnTe, and most of the sulphides, selenides, and tellurides of lead, cadmium, and zinc). Both polycrystalline and epitaxial films are involved. The properties optimized include charge-carrier mobility, smoothness, epitaxial order, electrophotographic performance, and photo-emf. We propose a possible explanation for these effects which gives good numerical agreement the experiment; our main postulate is that the optimum properties occur when the rate of reevaporation from well-defined, but disordered, regions of the growing films (probably glassy areas) is just sufficient to exceed the deposition rate.
Tellurium-induced defects in LPE Al0.36Ga0.64As
Authors: Wagner W. R.
Published: February 2003

The effect of Te doping on the growth of Al0.36Ga0.64As films has been studied. Variables investigated were Te concentration, growth rate, growth temperature, and heat treatment of the resultant films. Structural defects occur in Te-doped films grown from 772 °C with a free-carrier concentration as low as n=4×1017/cm3. A free-carrier plateau is reached at n?2×1018/cm3. Surprisingly, electrically active Te is incorporated in Al0.36Ga0.64As at three distinct distribution coefficients. Focusing on the same variables in the temperature regime from 772 to 836 °C, transmission electron microscopy shows that high Te doping causes very high concentrations (109/cm2) of small dislocation loops. These loops occur both over a wide range of growth solution doping at growth rates of 12 and 120 Å/sec. After heat treatment of these films at 820, 860, and 920 °C, substantially larger loops are observed. These loops are found to be extrinsic. In addition, the larger of these loops have small particles attached to them. The nature of the attached particles could not be determined. During heat treatment at 930 °C, dislocation loops could not be nucleated. Since Al2Te3 melts at 895 °C, it is assumed that below 895 °C Al2Te3 is the principal nucleating agent for the observed loops.
Dislocation-defect dragging in electron-irradiated copper over the temperature range 4.2–350°K
Authors: Sosin A. , Simpson H. M.
Published: February 2003

The effects of electron irradiation on the Bordoni peak and on dislocation drag were investigated by means of internal friction and modulus defect measurements over the temperature range 4.2–350 °K. These measurements were made during dynamic irradiations as a function of time and prior to and following irradiation as a function of temperature. It was found that (1) with a moderate dose irradiation the Bordoni peak height decreased 100-fold and (2) that a well-defined defect-dragging peak evolved during electron irradiation at 4.2 °K. This peak is similar but somewhat subdued in height in comparison to the peak previously observed at room temperature by the authors. The reduction in the Bordoni peak height following irradiation is examined in terms of several existing kink models, as well as in terms of stress-assisted defect drag.
On the ultimate yield strength of solids
Authors: Ruoff Arthur L.
Published: February 2003

A method is presented for obtaining the ultimate strength of solids in the absence of defect motion. The procedure which involves finite elasticity theory and measured higher-order elastic coefficients is utilized to compute the ultimate tensile and compressive yield stress of germanium and silicon crystals loaded in the [100] direction. These results are used as the basis for estimating the ultimate compressive strength of diamond.
Temperature dependence of ultrasonic attenuation and nonlinearity constant D for germanium
Authors: Pandey H. C. , Pandey J. D.
Published: February 2003

Values of the nonlinearity constant D which determines the coupling of acoustic phonons with the thermal phonons have been evaluated for the semiconducting material germanium in the temperature range 297–78.9 °K using the experimental data of second- and third-order elastic constants of this material. The temperature-dependent behavior of this constant has thus been tested for the first time on a theoretical basis through ultrasonic attenuation evaluated for high-frequency compressional waves, propagating along the 〈100〉 direction in single-crystal germanium. The results obtained are found to be in excellent agreement with the experimental values observed previously.
Grüneisen γ and other thermodynamic properties of cesium halide crystals at zero and elevated pressures
Authors: Bijanki Sudhir , Hardy Robert J.
Published: February 2003

The quasiharmonic approximation is used to calculate the Helmholtz free energy F. The interionic forces are represented by a deformation-dipole model, which is parameterized self-consistently. We give parameterized expressions for F that can be used to predict the temperature and volume dependence of the thermodynamic properties of CsCl, CsBr, and CsI. These expressions for F are tested by comparing our predicted values for the heat capacity CP and the thermal expansion α with experimental atmospheric-pressure values. Good agreement is obtained. Predicted values for CV, α, BT, the compression −ΔV/V0, and the Grüneisen γ at elevated pressures are given, as are zero-pressure values for the logarithmic derivative qT= (∂lnγ/∂lnV)T and the Anderson-Grüneisen parameters δS and δT.
Ionization and attachment coefficients in CO2 : N2 : He and pure CO2
Authors: Davies D. Kenneth
Published: February 2003

Values of the ionization (α/N) and attachment (η/N) coefficients have been determined from spatial current growth measurements in uniform fields E for a CO2 : N2 : He (1 : 2 : 3) mixture and for pure CO2 over the ranges 4.66×10−16⩽E/N⩽8.48×10−16 V cm2 and 7.63×10−16⩽E/N⩽9.89×10−16 V cm2, respectively, where N is the gas density. The limiting values of E/N, at which α=η, are found to be (4.66±0.14) ×10−16 V cm2 and (8.20±0.16) ×10−16 V cm2 for the CO2 : N2 : He mixture and for CO2, respectively. The present values of the coefficients are in reasonably good agreement with those calculated from a solution of the Boltzmann equation using electron-collision cross sections. Nevertheless, the present results indicate that even closer agreement would be obtained if the attachment cross section used in the calculations is reduced by about 15%.
On the effect of a partial sink in binary diffusion in thin films
Authors: Tompkins H. G.
Published: February 2003

A theoretical treatment is given of ’’partial’’ sinks, i.e., those in which the amount of a diffusing species removed through a surface is proportional to its concentration there. The effect of the existence of a partial sink on the concentration profiles and on the amount of material which accumulates on the surface is treated. Diffusion coefficients calculated from measured data will be in error if a perfect sink is assumed when a partial sink actually exists. The magnitude of this error is considered.
The diffusion and solubility of iron in copper
Authors: Salje G. , Feller-Kniepmeier M.
Published: February 2003

The chemical diffusion coefficients and the solubility limits of iron in copper were determined in the temperature range 650–1050 °C by electron probe microanalysis. Specimens were 99.999% copper single crystals. The diffusion is best described by two regression lines: DFe-Cu=0.504 exp(−49740/RT) cm2/s for the temperature interval 1050–800 °C and DFe-Cu=0.091 exp(−46140/RT) cm2/s for the temperature interval 800–650 °C. The solubility of iron in copper is given to logC=2.951−3357(1/T °K) wt% in the temperature range 1050–650 °C.
The interaction between electrical discharges and gas flow
Authors: Wasserstrom E. , Crispin Y. , Rom J. , Shwartz J.
Published: February 2003

The limitations of high-power electrical lasers due to heating of the gas and the instability of the glow discharge can be alleviated by the flow of the lasing medium. We describe here the results of two experiments which combine glow discharges with gas flow. In the first experiment we study the effects of supersonic flow and shock waves on glow discharges. The results of some numerical calculations of the variation of the gas properties along the discharge tube are then described. In the second experiment the influence of a highly swirled and turbulent flow on electrical discharges is studied. It is observed that both flows have a favorable effect on the discharge stability.
Direct measurement of cesium absorption isobars on polycrystalline tantalum
Authors: Collier R. K. , Backus C. E. , Jacobson D. L.
Published: February 2003

A direct quantitative measurement of cesium adsorbed into polycrystalline tantalum has been made by a new technique involving radioactive cesium. Cesium vapor was admitted into a known control volume and adsorbed onto two adjacent parallel tantalum disk faces. The amount of adsorbed radioactive cesium was monitored with a sodium iodide crystal γ detector. The surface and cesium reservoir temperatures were independently controlled. Tantalum surface temperatures of 500–1700 °K and cesium arrival rates of 1015–1021 atoms/cm2 have been investigated. Atom concentration is plotted as a function of temperature for various constant cesium arrival rates. The results follow theoretical predictions up to 0.5–0.75% of a monolayer. At higher coverages, the cesium adsorption increases rapidly to well over one monolayer. The cause of this rapid increase is determined to be the formation of cesium oxide on the surfaces resulting from a calculable diffusion of oxygen through the tantalum test chamber. Although the oxygen content is not measured, the qualitative behavior of the Cs-O system is shown. Surfaces with coadsorbed cesium and oxygen have a particular usefulness in improving performance of thermionic energy converters.
Power-scaling effects in dye lasers under high-power laser excitation
Authors: Moore C. A. , Decker C. David
Published: February 2003

Eight laser dyes emitting in the spectral region from 550 to 915 nm were investigated to determine their power scalability under excitation by Q-switched frequency-doubled Nd : YAG lasers possessing up to 480 mJ pulse energy at 10 Hz pulse repetition frequency (PRF). Conversion efficiencies for some dyes begin to be limited at pump-power densities as low as 14 MW/cm2 due to excited-state absorption of the pumping radiation. The dependence on resonator length of dye spectral emission, conversion efficiency, and temporal modulation are reported. Divergence of the beam emerging from the dye laser was found to be adversely affected by measures taken to avoid output power saturation at high pump-power densities.
Analysis of bunching of an electron beam at optical wavelengths
Authors: Chen C. K. , Sheppard J. C. , Piestrup M. A. , Pantell R. H.
Published: February 2003

This paper presents an analysis of the bunching of an electron beam at optical wavelengths by means of the inverse Cerenkov effect. A laser light beam is used to modulate the velocity of the electrons, and this velocity modulation becomes charge-density modulation after an appropriate drift distance. The effects of energy and angular spread of the electrons are included, as well as the impact of scatterings in the index-matching medium. Bunching can occur with reasonable parameter values and the drift distance is on the order of several centimeters.
Phase studies, crystal growth, and optical properties of CdGe(As1−xPx)2 and AgGa(Se1−xSx)2 solid solutions
Authors: Mikkelsen J. C. , Kildal H.
Published: February 2003

We report lattice constants, pseudobinary phase diagrams, crystal growth, and optical properties of the chalcopyrite CdGe(As1−xPx)2 and AgGa(Se1−xSx)2 solid solutions. The type-II phase-matching angle for frequency doubling of 10.6-μm radiation has been measured for CdGe(As1−xPx)2 crystals with x=0, 0.13, and 0.19. On the basis of the results, it is estimated that 90° phase matching would be obtained for x∼0.3.
Transferred electron photoemission to 1.65 μ from an InGaAsP heterojunction cathode
Authors: Escher J. S. , Gregory P. E. , Antypas G. A. , Sankaran R. , Houng Y. M.
Published: February 2003

Photoemission to 1.65 μ from a field-assisted heterojunction cathode has been achieved for the first time. The all-LPE-grown cathode consists of a p-type InGaAs photon-absorbing electron-generating layer, lattice matched to a p-type InGaAsP transferred-electron photoelectron-emitting layer. Reflection-mode quantum yield of ∼0.1% at 1.55 μ has been measured at 125 K.
Ge-doped GaxIn1−xAs LED’s in 1-μm wavelength region
Authors: Nagai Haruo , Noguchi Yoshio
Published: February 2003

GaxIn1−xAs light-emitting diodes which utilize Ge as a p-type impurity were fabricated from LPE crystals. Use of a GaAs (111) A surface as a substrate and reduction of dislocation density by a continuous grading technique yield LED’s of 0.48% external quantum efficiency at 1.02-μm wavelength. The electroluminescent response time of these diodes is the same order as that of GaAs LED’s which utilize Zn as a p-type impurity.
Emission of rf radiation from laser-produced plasmas
Authors: Pearlman J. S. , Dahlbacka G. H.
Published: February 2003

Radio-frequency emission from laser-produced plasmas has been observed from 1 to 330 MHz. The emission is found to be dependent on plasma and vacuum-chamber conditions. The low-frequency (1 MHz) oscillations appear characteristic of large-scale charge oscillations in the plasma.
Diagnostics of an rf induction plasma torch with the aid of a magnetic probe
Authors: Shamim A. , Wooding E. R.
Published: February 2003

Estimates of a plasma temperature, electrical conductivity, and torch efficiency have been made from simple measurements made on the plasma and on the rf supply. Measurements were made with the aid of a simple magnetic probe and a pickup coil. Estimates are also made of the heating-coil constants.
Correlation between elastic constants and flow behavior in metallic glasses
Authors: Chen H. S.
Published: February 2003

The addition of glass formers, B and P, raises not only the shear stiffness but also the tensile yield strain (εy) of Fe- and Co-based glasses. εy increases by a factor of 2 from 1.23×10−2 for Pt–Ni–P glasses to 2.45×10−2 for Fe–B glasses as the Poisson’s ratio decreases from 0.42 to 0.32. The Vickers hardness of a Fe75B25 glass attains 1300 kg/mm2 which is the highest value reported for metallic glasses. The directionality of interatomic forces either due to atomic ordering or s-d hybrid bonding in transition metals is proposed to be responsible for this behavior.
Electronic structure of gadolinium-doped EuSe
Authors: Nettel S. J. , Johnson E. J. , Lempicki A.
Published: February 2003

It is suggested that a temperature-dependent gap in Gd-doped EuSe, similar to a suggestion of Oliver for EuO, will reconcile RKKY magnetism and localized magnetic polarons as dominant phenomena.
Photocapacitance effects of deep traps in n-type InP
Authors: Chiao S. H. , Antypas G. A.
Published: February 2003

Deep trapping centers in n-type InP samples grown by the liquid-encapsulated Czochralski, liquid-phase-epitaxial, and vapor-phase-epitaxial processes have been studied by photocapacitance techniques. Photocapacitance effects for Schottky barriers formed on these samples indicate four levels at 0.58, 0.78, 0.89, and 1.15 eV below the conduction band. Estimated trap concentration in various samples range from low-1014 cm−3 to the high-1012 cm−3. The broad increase in photocapacitance near 1.15 eV for all the samples may be associated with an intrinsic defect or phosphorus vacancy/impurity complexes. This result is consistent with the broadband present between 1.08 and 1.25 eV in photoluminescence experiments. The comparison between O2-doped and undoped VPE samples suggests the presence of oxygen located at about 0.78 eV below the conduction band in VPE material.
High-field magnetoresistance in p-type PbTe
Authors: Gupta S. C. , Rajwanshi K. N. S. , Sreedhar A. K.
Published: February 2003

Longitudinal and transverse magnetoresistances have been measured in single-crystal p-type PbTe of hole concentration p=1.3×1019 cm−3 at 4.2 K up to a magnetic field of 68 kG. These magnetoresistances vary linearly with magnetic field. The effective mass anisotropy K of the crystal has been estimated from the magnetoresistance measurements in the classical field region, using the theory of Gold and Roth. The value of K is 3.5.
A slab waveguide laser formed of glass-clad LiNdP4O12
Authors: Kubodera Ken’ichi , Nakano Jun’ichi , Otsuka Kenju , Miyazawa Shintaro
Published: February 2003

A 60-μm-thick and 0.5-mm-long LiNdP4O12 slab waveguide laser clad by sputtered SK12 glass was fabricated. Single TE0-mode pulse and quasi-cw laser oscillations at 1.047 μm were obtained by longitudinal pumping with a rhodamine 6G laser and an argon laser, respectively. The round-trip waveguide loss was evaluated from the threshold pump pulse energy to be 0.035 for TE0-mode oscillation.
Further assignments for the far-infrared laser transitions of HCN and HC15N
Authors: Maki Arthur G.
Published: February 2003

Assignments are given for the 13 H12C14N and 4 H12C15N laser transitions that have not yet been identified. Although 10 different vibrational systems give rise to 27 laser transitions for H12C14N and H12C15N combined, all follow the same basic pattern involving a particular Coriolis interaction and a population inversion between stretching and bending vibrational manifolds. The laser transitions involve rotational states up to J=48, which is higher than has been observed in room-temperature spectra.
Internal friction of vacuum-deposited silver films
Authors: Uozumi K. , Honda H. , Kinbara A.
Published: February 2003

Internal friction of vacuum-deposited silver films 2–4 μm thick was measured using the vibrating-reed method below room temperature in the frequency range 100–400 Hz. Two distinct relaxation peaks were observed, one at around 50 K and the other at around 140 K. The former has been identified as the Bordoni peak, which was very stable against annealing at temperatures as high as 500 °C. The latter is considered as one of the Hasiguti peaks, which completely disappeared through annealing at 400 °C.
Guided-wave measurement of the 1.06-μm two-photon absorption coefficient in GaAs epitaxial layers
Authors: Azema A. , Botineau J. , Gires F. , Saïssy A.
Published: February 2003

The optical perturbation of an infrared wave guided in a GaAs epitaxial layer allows us to measure the two-photon absorption coefficient β for the wavelength λ=1.06 μm. The use of optical properties of free carriers induced by the two-photon effect and of guided optical wave techniques strongly enhances method accuracy. The result (β=0.06 cm MW−1) is in good agreement with the most recent bulk measurements and the theoretical values.
Liquid-phase epitaxial growth of smooth and thin layers of GaAs on nominally oriented substrates
Authors: Subramanian S. , Arora B. M.
Published: February 2003

A method of liquid-phase epitaxial growth of smooth thin layers on nominally oriented GaAs substrates is described. It utilizes a rapid etch-back of the substrate by an undersaturated solution, followed by growth from the same solution as it cools. The technique overcomes the requirement of an exactly oriented substrate for growth of smooth layers, and simultaneously produces a clean interface between the epi-layer and the substrate.
Photoelectronic properties of LPE GaAs : Cu
Authors: Chiao Sun-hai S. , Mattes Brenton L. , Bube Richard H.
Published: February 2003

The photoelectronic properties of liquid-phase epitaxial GaAs : Cu, either grown from a Ga melt with Cu impurity added or with incorporation of Cu by diffusion after growth, have been investigated through measurements of photocapacitance; conductivity in light and dark as a function of photon energy, light intensity, and temperature; thermal and optical quenching of photoconductivity; thermally stimulated conductivity; and photoluminescence. When Cu is present in the growth melt, the electron density in the resulting LPE GaAs layer is increased; when Cu is diffused into a grown layer, it behaves as a conventional acceptor and converts the layers to high-resistivity p-type conductivity. A Cu-related center with energy level about 0.43 eV above the valence band, electron-capture cross section of 10−21 cm2, and hole-capture cross section of 10−16 cm2 is observed in the layers produced with Cu in the melt by spectral response of photocapacitance and photocapacitance decay, and in the layers with diffused Cu by thermal and optical quenching of photoconductivity, spectral response of photoconductivity, and thermally stimulated conductivity. Six other levels, three of them electron traps and three of them hole traps, are also observed and described.
61Ni Mössbauer-effect studies of the hyperfine interaction in the magnetic spinel NiCr2O4
Authors: Göring J. , Wurtinger W. , Link R.
Published: February 2003

Using the Mössbauer technique, we have measured the electric quadrupole and magnetic dipole hyperfine interaction of 61Ni in NiCr2O4. The magnetic transition temperature and the saturation magnetic hyperfine field were determined to be 69±2 K and 442±3 kOe, respectively. The temperature dependence of the reduced field can be reproduced by a Brillouin function with S=1. With the onset of the magnetic ordering, the electric quadrupole interaction parameter changes by a factor of about −2, which indicates that the spin of the Ni2+ ion is parallel to the [a,b] plane of the crystal.
Hole transport in binary solid solutions of triphenylamine and bisphenol-A-polycarbonate
Authors: Borsenberger P. M. , Mey W. , Chowdry A.
Published: February 2003

By means of potential discharge techniques, hole transport has been investigated in binary solid solutions of triphenylamine and bisphenol-A-polycarbonate. Charge was injected from a photoemitting electrode of amorphous selenium. Under space-charge-limited conditions, hole transport can be described by a drift mobility that is linearly dependent upon the electric field. For fields of 105 V/cm, values of the mobility were between 10−7 and 10−5 cm2/V s, depending upon the temperature and concentration. The variation with concentration suggests that hole transport occurs by phonon-assisted hopping between triphenylamine molecules with a charge localization radius of approximately 1.8 Å.
Electron mobility in vapor-grown GaAs films
Authors: Poth H. , Bruch H. , Heyen M. , Balk P.
Published: February 2003

A systematic experimental study shows that the Hall mobilities of electrons at 77 K over the entire accessible range of electron densities in VPE GaAs films grown under high-purity conditions are below the theoretically predicted values. At a given electron concentration the experimental mobilities are independent of the preparation parameters (As/Ga ratio, dopant element, dopant pressure, growth temperature). Most of the literature data, not only on VPE but also on LPE and MBE films, appear to be in good agreement with these results. This finding casts some doubt on the idea that all such layers are electrically compensated.
Transient determinations of thermal diffusivities and emissivities of metal foils
Authors: Canada C. E. , Zinke O. H.
Published: February 2003

Diffusivities and emissivities are measured through the use of the transient technique for five metals. Diffusivity values for Al, Ag, Cu, Fe, and Ni are found to be 0.89, 1.73, 1.14, 0.216, and 0.176 cm2/sec, and respective emissivity values are found to be 0.23, 0.031, 0.038, 0.046, and 0.054. These diffusivities agree well with other values in literature and differ from values previously obtained through use of this technique because of corrections for heat reflection and possibly better heat input techniques.
Spontaneous current emission from PVC
Authors: Radhakrishna S. , Haridoss S.
Published: February 2003

Spontaneous current emission has been observed while heating polyvinyl chloride (PVC) above room temperature. The dependence of this current on various factors including the effects of different metal electrodes have been investigated. Possible mechanisms for such spontaneous currents are discussed.
Solid-state (bronze process) V3Ga from a V-Al alloy core
Authors: Dew-Hughes D.
Published: February 2003

V3Ga has been prepared as a single-filament wire by the solid-state reaction of a composite consisting of a vanadium 10.1 at.% aluminum alloy core in a bronze matrix of copper 16.7 at.% gallium. Reaction temperatures varied from 525 to 750 °C. Reacted layer thicknesses are found to increase as (reaction time)1/2. Rates of layer growth and activation energies are compared for a variety of starting composites. The addition of Al to the core enhances the rate of growth of the V3Ga layer, particularly at temperatures below 600 °C. Aluminum is incorporated within the V3Ga layer to the extent of 2–7.5 at.%. The superconducting transitions have onset temperatures of 15.0–15.3 K, with midpoints of 14.0–14.6 K. The (paramagnetically limited) upper critical fields at 4.2 K are 21–22 T. Critical-current densities were measured up to the critical field and approach those of Howe and Weinmann for material with gallium in the core. The form of the dependence of pinning force on field differs from that of Howe and Weinmann’s specimens in which a different pinning mechanism must operate.
Effect of the uniaxial stress on the dielectric properties of antiferroelectric cupric formate tetrahydrate
Authors: Yasuda Naohiko , Shimizu Hiroyasu , Fujimoto Sanji , Inuishi Yoshio , Yoshino Katsumi
Published: February 2003

The real and imaginary parts of complex relative permittivity along the b axis of antiferroelectric Cu(HCOO)24H2O single crystals were measured at 1 kHz over a temperature range −10 to −45 °C under various uniaxial stresses. The antiferroelectric phase transition temperatures (ϑc) under uniaxial stress along the c axis (σ3) and the a′ axis (σ1) vary linearly with the stress coefficients of dϑc/dσ3=3.3×10−8 K/(N/m2) and dϑc/dσ1=2.6×10−8 K/(N/m2), respectively, and these values agree well with the values calculated by the Clausius-Clapeyron equation. The temperature dependence of the real part of complex permittivity in the paraelectric phase under various uniaxial stresses obeys the Curie-Weiss law. The characteristic temperatures (ϑ0) under σ3 and σ1 vary linearly with the stress coefficients of dϑ0/dσ3=−6.7×10−7 K/(N/m2) and dϑ0/dσ1=−10.8×10−7 K/(N/m2), respectively. The dielectric properties under uniaxial stresses are elucidated by the phenomenological theory for the antiferroelectrics under uniaxial stresses, and the electrostrictive coefficients are estimated from the stress dependence of ϑc and ϑ0. The activation energy for the flip-flop of the dipole (Δφ) is found to increase with applied stresses, and γ which stands for the stress dependence of Δφ has a large anisotropy and its values are 1.1×10−9/(N/m2) along the c axis and 60.0×10−9/(N/m2) along the a′ axis.
A new light-modulated liquid-crystal light valve
Authors: Jost Steven R.
Published: February 2003

A novel light-sensitive large-area double heterojunction provides voltage modulation across the liquid-crystal layer on a prototype-imaging light valve. Preliminary results are reported.
Donor-acceptor-type complex in GaAs
Authors: Reynolds D. C. , Almassy R. J. , Litton C. W. , Nam S. B. , McCoy G. L.
Published: February 2003

A sharp emission line at 1.51165 eV has been observed in the photoluminescent spectra of certain high-quality GaAs crystals. From the analyses of crystals containing residual strain, it is concluded that the transition results from a bound-to-bound transition involving a donor-acceptor-type complex. Two such complexes—namely, the double-acceptor–neutral-donor complex, in which only the initial J=1/2 state is active, or the double-donor–neutral-acceptor complex—can explain the experimental data. From the magnetic field splitting of the line, the effective g values of the hole and electron are determined to be K=2.01±0.11 and ge=−0.35±0.15, respectively.
Determination of temperature and plasma composition in a high-pressure CsI-Hg-Ar discharge
Authors: Waszink J. H. , de Greef L. G. M.
Published: February 2003

A high-pressure CsI-Hg-Ar discharge is investigated (mercury pressure 6 atm, ac current 3.5 A rms, diameter 16 mm). The electron density is derived from the profile of the Stark-broadened Cs 5F-5D line at 802 nm. The axis temperature is derived from the intensity of the self-reversed Hg 7 3S-6 3P lines at 546 and 436 nm. An average density of atomic Cs is obtained from optical absorption of the Cs 7P-6S line at 459 nm. Furthermore, a simple model is made which calculates the density of the various species present from the temperature. Combination of the model calculation with the experimental results yields the plasma composition and the temperature distribution.
New electrostatic probe for measuring the energy anisotropy of ions in a magnetized plasma
Authors: Mase H. , Honzawa T. , Miyamoto G.
Published: February 2003

The possibility of measuring the anisotropic temperature of plasma ions by means of a new probe is described. The probe consists of an analyzing grid having a pinhole and an ion collector. Both ion temperatures parallel and perpendicular to a magnetic field, Ti∥ Ti⊥, respectively, are directly obtained from the semilogarithmic characteristics of the probe, performing the same procedure as in the case of a Langmuir probe. The plasma potential can be easily estimated from the point of inflexion of the probe characteristics.
Multilayered encapsulation of GaAs
Authors: Lidow A. , Gibbons J. F. , Magee T. , Peng J.
Published: February 2003

A method is described by which GaAs may be encapsulated to withstand annealing temperatures over 1100 °C using a double−layered encapsulant consisting of arsenic-doped silicon dioxide on top of plasma-deposited silcion nitride. Samples encapsulated in such a manner and annealed show no signs of mechanical failure and yield higher electrical activation of ion-implanted Se when compared to samples annealed with Si3N4 only. In addition, there is no detectable out-diffusion of Ga or As and no detectable in-diffusion of Si. Peak electrical activation of ion-implanted Se has been measured as 1×1019 carriers/cm3 for samples annealed at 1100 °C. A first-order strain analysis of general multilayered systems is also presented, indicating possible improvements on such an encapsulating procedure for GaAs as well as other compound semiconductors.
Crystallographic textures in diffusion-processed superconducting tapes
Authors: Togano K. , Tachikawa K. , Rose R. M.
Published: February 2003

X-ray pole figures were determined for the bcc and A15 layers in surface-diffusion-processed V3Ga superconducting tapes. Both layers were strongly textured, the A15 layer appearing similar (but not identical) to the bcc layer, which was (112)[11̄0]+(100)[011]. An orientation relationship based on (001)bcc∥ (001)A15, [120]bcc∥[110]A15 is suggested.
Observations of pretransformation lattice instability in near-equiatomic NiTi alloy
Authors: Aboelfotoh M. O. , Aboelfotoh H. A. , Washburn J.
Published: February 2003

Observations were made on the pretransformation effects in near-equiatomic NiTi alloy using the technique of transmission electron microscopy and diffraction. The pretransformation effects are discussed in terms of lattice displacement waves arising from the instability of the B2 lattice.
X-ray Brillouin scattering and electrical measurements of acoustoelectric gain and lattice attenuation in semidegenerate n-GaAs
Authors: Eizenberg M. , Fisher B.
Published: February 2003

Combined x-ray Brillouin scattering and electrical measurements were used to study acoustoelectric interactions in semidegenerate n-GaAs at 100 K. The measurements provided the frequency dependence of the lattice-loss parameter and a set of data for the acoustoelectric gain parameter for the [110] fast transverse acoustic wave in the range of frequencies of tens of GHz. The lattice-loss parameter was found to follow an ω1.1–1.3 dependence which is close to the linear dependence expected in the Landau-Rumer regime. The numerical values of the experimental lattice attenuation could not be approached by the usual approximations in this regime, a fact that stresses the need for a more complete calculation of this parameter in the hypersonic regime. Comparison of the experimental small-signal spectra and the acoustoelectric parameters with their theoretical predictions show that although quite good agreement is obtained in narrow frequency ranges for each concentration, discrepancies are noted in the high-frequency regime. These discrepancies are smaller when the spectra are calculated according to Mosekilde’s quantum theory which takes into account carrier degeneracy. They are exceedingly higher when the semiclassical theory, based on Maxwell-Boltzmann statistics, is used. Although the studies in this paper were mostly confined to the small-signal regime, some results obtained in the large-signal regime are also presented. In this regime, the structure of the acoustic spectra exhibit the up- and down-conversion to high harmonics and subharmonics of the central amplified frequencies. The saturated spectra which could be measured only in several cases were broad, had no pronounced structure, and their maxima were downshifted from the small-signal peak frequency by only 30%.
On the role of interface states in MOS solar cells
Authors: Kar S.
Published: February 2003

The various ways in which the interface states can affect the operation of the MOS solar cell has been discussed. Interface states affect the oxide voltage and the silicon band bending and cause an excess diode current to flow by recombination tunneling via interface states. It has been shown that the open-circuit voltage of an MOS solar cell is determined by the zero-voltage silicon band bending φoi, the oxide tunneling transmission factor at open circuit TocT, and the change in the oxide voltage between short and open circuit δVox. The dependence of Voc on the oxide thickness tox is therefore dictated by the change in the above three parameters with increasing tox. The most advantageous situation is that in which the interface-state density Nis as well as the product Nistox decrease with increasing oxide thickness. Experimental data obtained so far indicate that this is what happens in reality if the oxide is grown under suitable conditions, and the decrease in state density accounts partially for the increase in Voc with tox.
Preparation and compositional analysis of sputtered TaN films
Authors: Reichelt K. , Nellen W. , Mair G.
Published: February 2003

TaNx films have been prepared by reactive sputtering at substrate temperatures of 20, 250, 500, and 750 °C. The structure of the films has been studied by x-ray diffraction. The nitrogen portion of the compound has been determined by the nuclear reaction 14N(d,α)12C, whereas the amount of tantalum has been measured by Rutherford ion backscattering. Depending on the preparation conditions, superconductivity transition temperatures up to 10.8 °K have been observed. The ratio Ta/N of the superconducting films has been found to be between 0.9 and 1.1 and will be attributed to the fcc TaN phase.