bluuebunny/crossref_metadata_2025 huggingface dataset:
On the optimization of magnetic field sources in electromechanical energy conversion
Authors: Biedinger Jean-Marie , Kant Michel
Published: February 2003

This paper describes a numerical approach for the optimization of magnetic field sources, current distribution, and permanent magnets. The developments, based on the finite element method, consider two-dimensional, unsaturated models. As the criteria of optimization, the parameters representing the relationship existing between two Hermitian matrixes are used. An application of this method, in the case of a single-sided, linear motor, permits a number of conclusions to be made concerning the shape of the windings and their power supply. This work may prove useful in the optimization of devices with nonconventional geometry and/or supplied by power electronics.
Comment on ‘‘Ultraviolet light amplification by cool green phosphorous chemiluminescence flame’’
Authors: Benard D. J.
Published: February 2003

Van Zee and Khan have reported a measurement of broadband amplification in the 200–400 nm region of the spectrum upon passage of light through a series of small phosphorous-air flames. This paper shows that the rate of chemical reaction in the reported flame system is several orders of magnitude too small to support even the spontaneous loss rate that would be associated with the claimed amplification, and that focusing phenomena rather than stimulated emission provide a more quantitatively acceptable explanation of the data.
Reply to ‘‘Comment on ‘Ultraviolet light amplification by cool green phosphorus chemiluminescence flame’ ’’
Authors: VanZee Richard J. , Khan Ahsan U.
Published: February 2003

A recent report of ultraviolet light amplification by the cool green phosphorus chemiluminescence flame in the 200–400 nm region, interpreted as an optical gain phenomenon via stimulated emission, has been critized by Benard. Claiming that the rate of chemical reaction is several orders of magnitude too small to support the observed amplification, he has interpreted our result as a focusing phenomenon. In this communication, we point out that an improper spectral parameter was used to evaluate the rate of chemical reaction, and that his claim that focusing is responsible for our observation is inconsistent with our experiments. Nonrecognition of the broadened multilevel inversion in the ambient atmospheric flame is the probable source of his erroneous conclusion.
Radial distribution studies in a diamond anvil pressure cell
Authors: Munro R. G. , Block S. , Mauer F. A. , Piermarini G. J.
Published: February 2003

High pressure radial distribution studies using energy dispersive x-ray diffraction were performed for the first time in a diamond anvil pressure cell. The differential radial distribution functions were determined for the amorphous metal Fe-W (56 wt.% W) at room temperature and at pressures of 0, 0.3, 3.6, 7.3, and 10.5 GPa. An approximately linear compression of the Fe-W sample was observed, and the isothermal bulk modulus was estimated to be 170 GPa.
Intermixing of an AlAs-GaAs superlattice by Zn diffusion
Authors: Van Vechten J. A.
Published: February 2003

The dramatic increase in the intermixing of AlAs and GaAs induced by Zn diffusion is shown to be a natural consequence of the previously predicted and verified dominance of diffusion of As vacancies by nearest-neighbor hopping and the interaction of Zn interstitials with the concomitant antisite defect complexes. Depending on the relative importance of single vacancy or divacancy diffusion, the intermixing on the anion sublattice will be nearly as great or almost nil. Determination of this anion sublattice intermixing is suggested as a means to estimate sample stoichiometry.
Grain boundary effects on ionic conductivity of superionic conductors
Authors: Dube D. C. , Saraswat A. K.
Published: February 2003

Real and imaginary parts of permittivity have been measured at 10 GHz for unsintered pellets of silver iodide in the high ionic conductivity phase (T>146 °C). It has been found that grain boundaries do not affect the dielectric constant whereas the conductivity is reduced by about one order of magnitude.
Energy gap versus alloy composition and temperature in Hg1−xCdxTe
Authors: Hansen G. L. , Schmit J. L. , Casselman T. N.
Published: February 2003

We have used the data from 22 different studies to derive a new empirical expression for the energy band gap (Eg) of Hg1−xCdxTe: Eg =−0.302+1.93x+5.35(10−4)T(1−2x) −0.810x2+0.832x3. This expression is valid over the full composition range and for temperatures from 4.2 to 300 K. The standard error of estimate is 0.013 eV, which is at least 15% better than that of previously reported expressions.
Effects of gate metals on interface effects in metal oxide semiconductor systems after electron trapping
Authors: Lai S. K.
Published: February 2003

In the study of electron trapping in silicon dioxide, a turn-around effect in the flatband voltage shift as a function of injected electrons has been reported. Most of the reported work was on capacitors with aluminum gates. When polycrystalline silicon gates were used, very little electron trapping and turn-around effect was observed. The difference was explained by the decrease in the density of water related traps after the additional high temperature process in polycrystalline silicon deposition and doping. In the present experiment, gate metals other than aluminum were used. It was shown that even though the density of electron traps was not changed significantly, a large turn-around effect was only observed when the aluminum gate was used. This result seems to imply that aluminum is mostly responsible for the slow state generation and turn-around effect.
GaxIn1−xP liquid phase epitaxial growth on (100) GaAs substrates
Authors: Asai Hiromitsu , Oe Kunishige
Published: February 2003

We have performed Gax In1−xP liquid phase epitaxial (LPE) growth on (100) GaAs substrates at a growth temperature of 785 °C. The P atom fraction in the growth melts was kept constant every LPE growth run. The lattice mismatch Δa⊥/a0 between the Gax In1−xP layer and GaAs substrate normal to the wafer surface and photoluminescence (PL) of the alloy layer were measured. It was found that Δa⊥/a0 and the PL peak energy vary linearly from +0.47 to −0.13% and from 1.869 to 1.921 eV at room temperature, depending on the Ga atom fraction in the growth melts, respectively. This means that the so-called composition pulling phenomenon does not occur in LPE growth of Gax In1−xP on (100) GaAs substrates.
Formation and Schottky behavior of manganese silicides on n-type silicon
Authors: Eizenberg M. , Tu K. N.
Published: February 2003

The formation of manganese silicides on Si has been studied by using Rutherford backscattering spectroscopy and glancing-incidence x-ray diffraction; electrical properties of these silicides on n-Si have been studied by current-voltage measurement of Schottky barrier height and four-probe measurement of sheet resistivity. Two silicides have been identified: MnSi formed at 400 °C and MnSi1.7 at 500 °C. The former obeys a parabolic growth in layer form with an activation energy of 1.9 eV, yet the latter grows in patches and is governed by a linear growth. The values of Schottky barrier height on n-type Si of these two silicides are very close: 0.65 and 0.67 eV, respectively, but their sheet resistivities differ significantly: 220 μΩ cm for MnSi and 4100 μΩ cm for MnSi1.7.
Hydrogenated amorphous silicon/electrolyte contacts: Band bending and photoresponse dependence on surface reactions
Authors: Ayers W. M.
Published: February 2003

Aqueous electrolyte contacts do not form Schottky barriers with amorphous silicon electrodes. In the dark, silicon oxidation and electrolyte reduction at a counter electrode produce a battery voltage in series with the depletion-region potential. Illuminating the cell substantially decreases the amorphous silicon electrode series resistance and increases the hole concentration at the surface. This enhances the battery reaction rate and increases the current through the cell. Interpreting this current as a traditional photocurrent (due solely to a Schottky junction) overestimates the magnitude of the barrier height.
A model for field-sensitive interface states
Authors: Crowley J. L. , Hoffman H. J. , Stultz T. J.
Published: February 2003

Oxygen derived point defects called Intimate-Valence-Alternation-Pairs (IVAP) apear to be able to account for the time, temperature, and field dependence of the generation of field-sensitive interface states. The theory and properties of IVAP defects in SiO2 are described. A model for the observed changes in the capacitance voltage characteristics of Metal-Oxide-Semiconductor structures based on the existence of these defects is proposed. Finally the model is compared to existing data from the literature on the buildup of interface states caused by charge injection or ionizing radiation.
Heteronuclear molecular ion model of pairs of unlike impurity acceptors in silicon and germanium
Authors: Vail J. M. , Lagowski J. , Hall N. G.
Published: February 2003

Compensated pairs of unlike group III impurities in silicon or germanium, binding a single hole, are described by pairs of point charges derived empirically from a hydrogenic model of isolated single impurities embedded in a dielectric continuum. The ground and first excited states of the corresponding heteronuclear molecular ion are estimated variationally as a function of impurity separation, and the results are compared with some experimental infrared absorption data.
Spin-coated amorphous chalcogenide films
Authors: Chern G. C. , Lauks I.
Published: February 2003

Preliminary investigations have shown that a family of chalcogenides may be deposited in technologically useful thin film form by an inexpensive technique of spin deposition from solution. The materials which are amorphous and microstructure free retain many of the properties of the solute (e.g., As2S3, As2S2, As2Se3, As2Te3, or GeSe) from which they are prepared. Some of the materials have been demonstrated to be potentially useful for high resolution pattern replication in particular for microlithography.
Electrical and optical properties of magnesium-diffused silicon
Authors: Lin Alice L.
Published: February 2003

The electrical and optical properties of Mg-diffused Si, both as-diffused and post-diffuse heat treated, have been investigated through measurements of dark conductivity and Hall effect, optical absorption, and photoconductivity. Complicated properties are observed which can be described consistently by a five-level model, a major level at 0.107 eV associated with an interstitial neutral magnesium donor plus four shallower donor levels at 0.04, 0.055, 0.08, and 0.093 eV below the conduction band.
Bandwidth, field distribution, and optimal electrode design for waveguide modulators
Authors: Liu Pao-Lo
Published: February 2003

The bandwidth of lumped electro-optic waveguide devices is shown to be limited by the intrinsic inductance as well as the capacitance of the electrodes. Under the optimal design the bandwidth-length product is calculated to be 1.8 GHz cm for LiNbO3. The electric field distribution, the overlap of the electric and optical fields, and the gap-width dependence of the switching voltage are also discussed.
Friction in capillary systems
Authors: Tenan M. A. , Hackwood S. , Beni G.
Published: February 2003

A new macroscopic one-parameter model of static solid-liquid friction in capillary systems is developed. The basic idea is a generalization of the phenomenology of solid-solid friction. The theory considers that the shear frictional force is created by an increase in work of adhesion caused by the deformation of the liquid meniscus just before the onset of liquid motion. The theory contains only one parameter, the ‘‘frictional angle’’ ξ, characteristic of a given solid surface and independent of the nature of the liquid. We have derived a functional relationship, parametrized by ξ, between friction and equilibrium contact angle. The model is in excellent agreement with experiments.
Self-focusing of ion cyclotron waves in a plasma
Authors: Sharma O. P.
Published: February 2003

A high amplitude electromagnetic ion cyclotron wave (shear Alfvén branch) having Gaussian distribution of intensity along its wavefront exerts a transverse ponderomotive force on the plasma and causes a reduction in the local magnetic pressure. This gives rise to a refractive index profile suitable for the self-focusing of the wave. On a longer time scale (greater than the transverse diffusion time), the plasma density is redistributed along the wavefront; however, the refractive index profile thus created causes divergence of the wave. The compressional Alfvén waves show exactly opposite behavior.
Electromagnetic projectile acceleration utilizing distributed energy sources
Authors: Parker Jerald V.
Published: February 2003

Circuit equations are derived for an electromagnetic projectile accelerator (railgun) powered by a large number of capacitive discharge circuits distributed along its length. The circuit equations are put into dimensionless form and the parameters governing the solutions derived. After specializing the equations to constant spacing between circuits, the case of lossless rails and negligible drag is analyzed to show that the electrical to kinetic energy transfer efficiency is equal to σ/2, where σ=2mS/ℒq20 and m is the projectile mass, S the distance between discharge circuit, ℒthe rail inductance per unit length, and q0 the charge on the first stage capacitor. For σ=2 complete transfer of electrical to kinetic energy is predicted while for σ>2 the projective-discharge circuit system is unstable. Numerical solutions are presented for both lossless rails and for finite rail resistance. When rail resistance is included, >70% transfer is calculated for accelerators of arbitrary length. The problem of projectile startup is considered and a simple modification of the first two stages is described which provides proper startup. Finally, the results of the numerical solutions are applied to a practical railgun design. A research railgun designed for repeated operation at 50 km/sec is described. It would have an overall length of 77 m, an electrical efficiency of 81%, a stored energy per stage of 105 kJ, and a charge transfer of <50 C per stage. A railgun of this design appears to be practicable with current pulsed power technology.
Absorption effects of the Cd II 4416 Å line in a cadmium vacuum-arc plasma
Authors: Shalev S. , Goldsmith S. , Boxman R. L.
Published: February 2003

The absorption of the 4416 Å He-Cd laser line (a2D5/2 →5p 2P3/2) by a cadmium vacuum-arc plasma, and its dependence on time from arc initiation, spatial position in the interelectrode region, electrode separation, and the peak of current waveform, were determined. The arc was sustained between two cylindrical electrodes of 12 mm diameter. The current pulse lasted for 1.7 ms with peak current at 0.3 ms. The derived relative absorption of the laser line is found to be as high as 70% for electrode separation of 4 mm and peak current of 1.2 kA. We find that the time to peak absorption does not coincide with time to peak current. Furthermore, the absorption increases with increasing peak current or decreasing electrode separation. The measured optical depth of the vacuum-arc plasma is used for the calculation of the arc plasma self-absorption at 4416 Å, the absorption-corrected population density of the a2D5/2 level, and the estimation of the Cadmium ions velocity spread parallel to the optical observation axis. The estimated full width half-amplitude (FWHA) of the ion velocity distribution is in the region of 0.7–33×103 m/s.
On the determination of liquid crystal-to-wall anchoring anisotropy by the surface-plasmon polariton technique
Authors: Yang K. H.
Published: February 2003

Based on the Oseen and Frank elastic continuum theory of nematic liquid crystals, and on a generalized torque balance equation at the interface, the magnitude and the gradient of the tilt angle of liquid crystal molecules at the interface have been calculated in a homogeneous cell as a function of applied voltage and liquid crystal-to-wall anchoring anisotropy C. Consequently, the reflectivities associated with the excitation of the surface-plasmon polariton propagating along the liquid crystal-to-wall interface can be evaluated for comparison with experimental results to determine a value for C. Numerical computations of reflectivities have been shown to fit the experimental results of Sprokel, Santo, and Swalen [Mol. Cryst. Liq. Cryst. 68, 29 (1981)]. An average value of 0.11±0.05 ergs/cm2 for C has been deduced.
Electron energy loss spectroscopy of carbon in dissociated dislocations in tantalum carbide
Authors: Allison Craig , Hoffman Mark , Williams Wendell S.
Published: February 2003

The carbon concentration in individual stacking faults in dissociated dislocations in tantalum carbide (TaCx) was analyzed using electron energy loss spectroscopy. Although the faulted region is less than 10 nm wide, the small diameter electron beam (0.5 nm) of a dedicated scanning transmission electron microscope allowed the carbon K x-ray excitation edge from the faulted region to be distinguished from the corresponding signal from the unfaulted region. The 50-nm thick foil was prepared by grinding, polishing, and ion milling a specimen sawed from a single crystal of TaC0.78. The analysis showed a significantly lower value for the carbon concentration in the fault, in accordance with crystallographic and energy considerations. The stacking fault in NaCl-structure TaCx must exhibit hcp symmetry, but the appropriate hcp phase, Ta2C, contains less carbon. Hence diffusion of carbon away from the moving dislocation must accompany plastic deformation. However, in view of the high melting point and high activation energy for carbon migration, diffusion is slow below approximately 1600 °C. This temperature corresponds approximately with the brittle-ductile transition for TaC. The isomorphic compound TiC does not exhibit dissociated dislocations, and hence this form of Suzuki hardening should not occur. Indeed, gross plastic deformation in TiC can occur at temperatures as low as 800 °C.
X-ray topographic study of antiphase domain boundaries in ferroelectric ferroelastic GdDy(MoO4)3 crystals. I. Geometry of antiphase domain boundaries
Authors: Capelle B. , Malgrange C.
Published: February 2003

Antiphase domain boundaries (APB’s) in ferroelastic-ferroelectric GdDy(MoO4)3 crystals present an unexpected contrast on x-ray topographic images which leads to introduce a correction vector Δf, in addition to the expected translation vector 1/2(a+b) between two neighboring antiphase domains. The geometry of some APB’s is determined with the help of different traverse topographic images and etch patterns. Emphasis is put on two different geometries which will be studied in more detail in a separate paper.
X-ray topographic study of antiphase domain boundaries in ferroelectric ferroelastic GdDy(MoO4)3 crystals. II. Evaluation of the additional translation vector
Authors: Capelle B. , Epelboin Y. , Malgrange C.
Published: February 2003

Antiphase domain boundaries (APB’s) can be considered as planar defects introducing a phase shift between the structure factors of both domains. Two different geometries of APB’s are considered here, corresponding respectively to Laue–Bragg and Laue–Laue cases for x-ray propagation. Comparison between experimental and computer simulated x-ray topographic sections in both cases leads to an evaluation of the additional translation vector Δf at the APB of the order of a/30 resulting from a local expansion of the lattice. A simple interpretation for this result is given.
Competing processes of Si molecular beam reactive etching and simultaneous deposition on film and bulk SiO2
Authors: Yonehara Takao , Yoshioka Seishiro , Miyazawa Seiichi
Published: February 2003

The Si molecular beam reactive etching of thick thermally grown SiO2 and bulk SiO2 has been studied. In situ observations by Auger electron spectroscopy and reflection high energy electron diffraction reveal that Si films grow epitaxially on Si (100) substrates at 1000 °C after removal of 0.5 μm thermally grown SiO2 by a Si molecular beam. It is found that simultaneous deposition of polycrystalline Si films containing many oxygen atoms occurs on etched SiO2 at 900 °C. Surface morphology of the etched bulk SiO2 and the Si over layers caused by simultaneous deposition is observed by scanning electron microscopy.
Polymeric character of coal
Authors: Wert Charles A. , Weller Manfred
Published: February 2003

We have measured the internal friction spectrum of a number of coals through the range bituminous to anthracite. Damping peaks are seen which bear great similarity in position and height to those found for many polymers. This manifestation of polymer-like character adds to our understanding of the macromolecular character of the coal structure.
Theoretical calculation of conformational energies of polytetrafluoroethylene
Authors: Banerjea Amitava , Taylor P. L.
Published: February 2003

The predictions of three sets of nonbonded steric energy parameters for the low-temperature structure of polytetrafluoroethylene (PTFE) are compared. The free energy and the distribution of torsional angles are also calculated for all three sets using the transfer-matrix (TM) method. The two-near-neighbor approximation normally used is found to be inadequate, and the TM method is modified to include interactions out to four near neighbors. All three parameter sets are found to predict helical conformations at low temperature, but the predicted pitch does not agree with the experimentally determined pitch. Some comments are presented on the applicability of the parameter sets for an investigation of the interchain interactions and the solid-state phase transitions in PTFE.
Thermoelastic temperature changes in poly(methyl methacrylate) at high hydrostatic pressure: Experimental
Authors: Rodriquez E. L. , Filisko F. E.
Published: February 2003

Temperature changes as a result of large rapid hydrostatic pressure changes were measured for poly(methyl methacrylate) at various temperatures from ambient to 95 °C and for various pressure increments from 14 to 207 MN/m2. We observe complete reversibility of the measurements over the pressure range studied. The value of the incremental ratio ΔT/ΔP was a function of both temperature and pressure, ranging from 0.04 to 0.09 K/MNm−2 from 298 to 368 K at low pressures, and 0.03–0.05 at 200 MN/m2 over the same temperature range. The largest variation of ΔT/ΔP with pressure was at low pressures, the ratio becoming nearly constant above about 200 MN/M2.
The pressure and temperature dependence of piezoelectric and pyroelectric response of poled unoriented phase I poly(vinylidene fluoride)
Authors: Chung K. T. , Newman B. A. , Scheinbeim J. I.
Published: February 2003

The hydrostatic piezoelectric coefficient dp and the pyroelectric coefficient py of poled unoriented phase I films were measured at pressures up to 7.0 Kbar and at temperatures from −84 to +48 °C. The pressure dependence of the glasstransition temperature over the same pressure range was also determined. The results obtained for these unoriented films are compared with results obtained previously for oriented films. The effect of the glass transition temperature (Tg) and another transition occurring in the range of pressure and temperature used (Tt) on the piezoelectric and pyroelectric response for both oriented and unoriented films are discussed. At temperatures below Tg,py decreased with increased temperature, while dp showed a shallow maximum so that for both types of response minimum values were obtained at the Tg.
Structural recovery of quenched and annealed glasses
Authors: Chow T. S. , Prest W. M.
Published: February 2003

A continuous approach to the multiordering parameter equations for glass transition phenomena is presented which leads to the unification of two successful phenomenological models. The nature of distribution functions, the temperature-structural dependence of relaxation times, the experimental rate and the state of nonequilibrium during quenching, annealing, and heating are the essential parameters. The effect of distribution function of relaxation times on the enthalpy and heat capacity of glasses, and the sensitivity and convergence of the numerical calculation, are discussed. The theoretical calculation is then compared with the calorimetric measurements of polystyrene.
Floating wire measurement of transverse magnetic field errors in a planar free-electron laser wiggler
Authors: Quimby David C.
Published: February 2003

The first use of a floating wire technique for measurement of erroneous magnetic fields perpendicular to both the electron beam and the alternating field of a planar free-electron laser wiggler is reported. The magnitude of the measured error fields compares favorably with independent measurements made using a Hall effect probe. The accuracy obtained appears to be sufficient to allow the wiggler to be tuned to eliminate the error fields, and thereby to suppress deleterious large amplitude betatron orbits of the e beam.
Heavy-ion source using a laser-generated plasma transported through an axial magnetic field
Authors: Gray L. G. , Hughes R. H. , Anderson R. J.
Published: February 2003

Results of transporting a laser-generated plasma through magnetic fields are reported. Plasma plumes have been generated in strong magnetic fields, in directions both transverse and parallel to the field. Collective effects are demonstrated by the plasma while in the high-density state near the laser target. The formation of the plasma and its transport through an axial magnetic field enhances the relative amount of highest charge states and the lowest charge states. The focusing properties of the magnetic field near the extractor gap can prove useful in enhancing ion density at the anode aperture of the extractor gap. It is suggested that the duty cycle of laser ion sources can be extended by simply increasing the ion flight time through the magnetic field from the laser target to the extractor gap without appreciable loss of ions. Further, it is suggested that energy spread in a given ion species can be made small by using an extractor potential programmed to increase in time relative to the laser fire time.
Molecular-orbital model for metal-sapphire interfacial strength
Authors: Johnson K. H. , Pepper S. V.
Published: February 2003

Self-consistent-field X-Alpha scattered-wave cluster molecular-orbital models have been constructed for transition and noble metals (Fe, Ni, Cu, and Ag) in contact with a sapphire (Al2O3) surface. It is found that a chemical bond is established between the metal d-orbital electrons and the nonbonding 2p-orbital electrons of the oxygen anions on the Al2O3 surface. An increasing number of occupied metal-sapphire antibonding molecular orbitals explains qualitatively the observed decrease of contact shear strength through the series Fe, Ni, Cu, and Ag.
Study of an ‘‘applied-Bθ ’’ magnetically insulated ion diode
Authors: Pal R. , Hammer D. A. , Greenspan M. A.
Published: February 2003

We report parametric studies of an ‘‘applied-Bθ ’’ magnetically insulated ion diode, and the properties of the ion beam obtained from it. The typically 250-keV ion beam extracted from this annular diode is focused by the diode field to a current density of up to 800 A/cm2 on axis 20 cm from the diode. Anomalously rapid dispersion of the beam beyond the focal region in vacuum is eliminated by puffing gas into the drift chamber.
Diffusion of tellurium dopant in silicon
Authors: Janzén E. , Grimmeiss H. G. , Lodding A. , Deline Ch.
Published: February 2003

The diffusion of tellurium in silicon has been investigated by means of secondary ion mass spectrometry. In the temperature interval between 900 and 1250 °C the diffusion coefficient has been found to range from ∼2×10−15 to 6×10−12 cm2/s, i.e., several orders of magnitude lower than the diffusion coefficients of the other chalcogens S and Se. In units of cm2/s and eV, the results may be expressed as DTe=0.50 exp(−3.34/kT), suggestive of a predominantly substitutional mechanism of diffusion.
Mechanical stability of reactive ion-etched poly (methylmethacrylate) and polyimide microstructures in trilevel electron beam lithography
Authors: Oro James A. , Wolfe J. C.
Published: February 2003

Isolation layers are used in trilevel electron beam lithography to planarize wafer topography, reduce electron scattering effects, and increase the effective sensitivity and contrast of the lithographic process. The mechanical stability of the isolation layer structures may limit the overall resolution of the process. We have studied the resolution limits imposed by the mechanical stability of reactive ion-etched poly (methylmethacrylate) and polyimide isolation layer structures in trilevel electron beam lithography. We show that processes can be designed with 50-nm resolution.
Barrier voltage and its effect on stability of ZnO varistor
Authors: Gupta T. K. , Carlson W. G.
Published: February 2003

The major voltage drop in ZnO varistors occurs across the grain boundaries, which behave generally as Schottky barriers supporting a barrier voltage Vg. This voltage is proportional to the device voltage. Experimental evidence shows that there is a time-dependent reduction in the barrier voltage combined with an increase in resistive current iR when the varistor is subjected to a continuous ac voltage stress. The phenomena is reversed when the applied voltage is removed, showing nearly complete recovery. Instabilities of the resistive current and of the barrier voltage are shown to be manifestations of the same phenomenon and are attributed to a metastable component in the Schottky barriers. It is proposed that this metastable component is due to interstitial zinc ions that are capable of migration under thermal and electrical driving forces. When these ions are removed or stabilized by a suitable heat treatment, the instability of the device is reduced. This paper presents experimental data and analysis to support this hypothesis.
Low temperature microwave Hall mobility measurements on copper phthalocyanine single crystals
Authors: Caverly Robert H. , Westgate Charles R.
Published: February 2003

The Hall mobility of copper phthalocyanine as a function of temperature has been measured using a microwave technique at 10 GHz. The mobility increases from 40 cm2/Vsec at 300 K to 200 cm2/Vsec at 100 K. The Hall mobility shows a negative sign, in agreement with other observations, and displays a T−1.5 temperature dependence, in fair agreement with theory. A new instrument for measuring low temperature Hall mobilities, which allows simpler tuning by keeping the cavity at room temperature, is presented.
Material reactions in Al/Pd2Si/Si junctions. I. Phase stability
Authors: Köster U. , Ho P. S. , Lewis J. E.
Published: February 2003

The phase reactions in Al/Pd2Si/Si junctions caused by thermal annealing have been investigated. Combining x-ray diffraction, transmission electron microscopy, and Auger sputter profiling techniques, a ternary phase diagram for Al-Pd-Si at about 400 °C has been qualitatively established for predicting phase changes during reaction. To correlate the present study to junction structures, thin-film layered samples were utilized for exploring the phase fields connecting Al to Pd2Si. Formation of the Al3Pd4Si compound has been observed and is found to be an important intermediate phase in controlling the reaction kinetics. The effectiveness of Pd2Si in preventing Al penetration into Si is attributed to the stability between the Al3Pd4Si and Pd2Si phases. The phase reactions during the initial, intermediate, and final stages of the junction degradation are qualitatively discussed.
Material reactions Al/Pd2Si/Si junctions. II. Kinetic rates
Authors: Ho P. S. , Lewis J. E. , Köster U.
Published: February 2003

The rates of material reactions in Al/Pd2Si/Si junctions have been measured as a function of time between 200 to 350 °C. Using an Auger sputter profiling technique, the kinetics and activation energies for Pd and Si diffusing into Al and the penetration of Al into Pd2Si were determined. The results can be correlated to the overall phase stability of the system and to the changes in the electrical characteristics of the Schottky junction. The mechanism of junction degradation and the role of Pd2Si are discussed. The present results reveal some basic limitations on the stability of this junction at elevated temperatures.
Electronic simulation of Josephson tunneling, including the effects of frequency, temperature, and the superconducting energy gap
Authors: Jablonski Daniel G.
Published: February 2003

An electronic device which simulates the Werthamer theory of Josephson tunneling is described. The simulator includes the effects of frequency, temperature, and the superconducting energy gap. The nonlinear quasi-particle resistance, and the related reactive term, are also modeled. Current-voltage characteristics obtained with the simulator are presented for a variety of temperatures under both current and voltage bias conditions. Phenomena such as subgap structure, the Riedel peak, and photon-assisted tunneling are also illustrated. Finally, brief evidence of a new form of oscillatory behavior associated with the Riedel peak is presented.
Application of intense relativistic electron beams to the switching of high currents in high power electrical networks
Authors: Mayergoyz I. D. , Destler W. W. , Emad F. P.
Published: February 2003

A new concept of switching of high currents using intense relativistic electron beams propagating in vacuum drift tubes is presented. Some possible applications of this concept for the design of current switches are discussed. Supporting analytical one-dimensional theory of an electron beam switch is given. Electron beam hysteresis phenomenon associated with the switching mechanism is briefly discussed.
Preparation of (AlxGa1−x)yIn1−yAs (0≤x≤0.5,y=0.47) lattice matched to InP substrates by molecular beam epitaxy
Authors: Masu Kazuya , Mishima Tomoyoshi , Hiroi Shin-ichiro , Konagai Makoto , Takahashi Kiyoshi
Published: February 2003

The preparation of (AlxGa1−x)yIn1−yAs lattice matched to InP substrates (0≤x≤0.5, y=0.47) by molecular beam epitaxy has been studied. It was found that this quaternary alloy has direct energy band gap wavelengths in the 1.0 –1.65-μm range, as determined from the absorption edges and photoluminescence measurements at 77 K. The dependence of the energy band gap on the Al composition indicated that there is little bowing effect; i.e., the observed energy band gaps agree well with the values interpolated from the end ternaries of GaInAs (0.73 eV) and AlInAs (1.55 eV). Undoped (Al0.1Ga0.9)0.47In0.53As layers showed high resistivities with 50 Ω cm as typical. A beryllium doping level of about 2×1018 cm−3 was obtained and the corresponding Hall mobility μ300 K was 25 cm2 V−1 s−1.
Simple phenomenological modeling of transition-region capacitance of forward-biased p-n junction diodes and transistor diodes
Authors: Lindholm Fredrik A.
Published: February 2003

Phenomenological modeling used here yields simple expressions for the capacitance C(V) of the transition (or space-charge) region of a forward-biased p-n junction diode or transistor diode. Predictions are in general accord with results of previous detailed analytic modeling and of numerical solution of the finite-difference counterparts of the standard (Shockley) equations underlying p-n junction theory. For the capacitance treated, two components exist: the dielectric capacitance CD, from changes in majority carrier concentration near the edges of the space-charge region, and the component CF from free hole and electron accumulation in the space-charge region. The modeling involves picturing the space-charge region as the i (intrinsic) region of an n-i-p structure for a space-charge region markedly wider than the extrinsic Debye lengths at its edges. This i region is excited in the sense that the forward bias creates hole and electron densities orders of magnitude larger than those in equilibrium. The recent Shirts–Gordon modeling of the space-charge region using a dielectric response function is contrasted with the more conventional Schottky–Shockley modeling. Various uses of expressions for C(V) are discussed.
Zero-field ‘‘Fiske’’ steps in small Josephson junctions
Authors: Camerlingo C. , Russo M. , Vaglio R.
Published: February 2003

The theory of Fiske steps in Josephson tunnel junctions is extended to include the presence of structural fluctuations in the barrier. The possibility of excitation of zero-field steps in this case, is discussed. Experimental evidence for the occurrence of zero-field resonances, due to both regular and randomly distributed nonuniformities in ‘‘small’’ Josephson junctions, is reported.
Annealing effects in stretched polyvinylidene difluoride
Authors: DeMattei R. C. , Route R. K. , Feigelson R. S.
Published: February 2003

Annealing has been used as a means of relieving stress after stretching polyvinylidene difluoride films. It has been shown that such post-stretch heat treatment decreases the activity of transducers when compared to transducers made from unannealed films. A study of unannealed films and films annealed under various conditions showed a decrease in the ‘‘β’’ phase unit cell parameters in the annealed films which leads to changes in the coulombic and van der Waals interactions. The hindered molecular rotation leads to decreased polarization and reduced transducer performance.
Stopping ratios for 30–330 keV ions with 1≤Z1≤5
Authors: Mertens P. , Krist Th.
Published: February 2003

By means of a magnetic spectrometer the energy losses of light 30–330 keV ions in C, V, Cr, Fe, Ni, and Zn were measured. As the same target foils were used for different ions, the ratios of stopping cross sections simply became the quotient of energy losses with an error ≤3%. Due to this accuracy, the applicability of a factorization of the electronic stopping cross section Se, i.e., the applicability of the ‘‘simplified stopping function’’ [J. F. Ziegler, Stopping Power and Ranges in All Elements (Pergamon, New York, 1977)] could be checked. This factorization is theoretically not established. It was found by the experiments that the simplified stopping function Se(Z1, Z2, v)=P(Z1, v)×T(Z2, v) (Se: electronic stopping cross section; Z1, Z2: nuclear charge of projectile and target; v: projectile velocity) in most the cases is valid within ±10%. The ratios of stopping cross sections applicable to scale Se from one ion to another ion or from one material to another material were determined.
Anisotropy energy of C
uMn spin glasses
Authors: Hippert F. , Alloul H. , Fert A.
Published: February 2003

We have investigated the angular dependence of the anisotropy energy of a CuMn 4.7 at. % glass alloy at T<Tg by susceptibility and torque measurements. In our experiments the remanent magnetization σ↘ is initially along z↘ and is then rotated by an angle θ in the yz plane by a magnetic field. We measure the ac susceptibility along y↘ and the torque needed to prevent the sample from rotating as a function of θ. Our measurements show that the anisotropy energy is purely unidirectional (EA=−K cos θ) as long as the spin system rotates bodily (θ≲40°). For larger values of θ we observe irreversible and time dependent effects which reveal rearrangements of the spins. Such rearrangements stabilize the states around θ=π and explain previous results on the anisotropy around π(apparent uniaxial anisotropy).
Amorphous structures: A local analysis
Authors: Lévy J. C. S. , Mercier D.
Published: February 2003

After a short review of different ways of building amorphous structures, a new way, derived from the minimization of the total free energy is described. The comparison between different structures is made by means of the analysis of several parameters: pair distribution function, radial distribution function, planar cuts, and density. Our results confirm the quality of this new model and its tractibility. This enables us to study local atomic symmetries of amorphous structures by numbering the holes of this network as a function of their sizes and by classifying the calculated crystalline fields and elasticity coefficients according to the ‘‘strength’’ of their symmetries. Large holes of diameter 0.85 and 0.72 atomic diameter are found and are shown to be responsible for low energy hopping levels, which are characteristic of glassy structures. The analysis of the local symmetry shows a nearly continuous variation and the abundance of strong dissymmetries, i.e., a distribution of low energy electronic levels as well as strong magnetic anisotropies.
Effect of anisotropy strength on phase transitions in random anisotropy magnets
Authors: O’Shea M. J. , Sellmyer D. J.
Published: February 2003

ac susceptibility and magnetization measurements are reported for a number of Gd and Tb based glasses. Raman magnetic anisotropy effects are observed in both the Gd and Tb glasses. The Gd glasses show a transition to an infinite susceptibility state and in some cases a further transition to an hysteretic state at low temperatures in which field-cooling and magnetic viscosity effects are observed. The Tb glass shows only a small speromagnetic peak at low temperatures. The ratio of anisotropy strength to exchange was varied in the Gd glasses by alloying, and the effect of this on the resulting magnetic states is discussed.
About the onset of magnetic order in CoxSn1−x amorphous alloys
Authors: Teirlinck D. , Piecuch M. , Geny J. F. , Marchal G. , Janot Chr. , Mangin Ph.
Published: February 2003

Amorphous alloys of the cobalt–tin system have been obtained by the vapor quenching technique. Bulk magnetization data have been measured up to high field condition (150 kOe). On the basis of these experimental observations, magnetism in CoxSn1−x alloys can be understood by assuming that magnetic cobalt atoms appear (for x≳0.5) in a stoichiometric nonmagnetic Co Sn matrix. Then, depending on the composition, a variety of magnetic behavior can be observed, ranging from PAULI paramagnetism (x<0.5) to cluster glass regime (0.5<x<0.6), weak intinerant ferromagnetism (0.6<xm%0.65) and strong ferromagnetism (x≳0.65).
Laser-induced magneto-optical transitions from deep levels in n-InSb
Authors: Seiler D. G. , Goodwin M. W.
Published: February 2003

We present a novel means for detecting and studying deep levels in high purity n-InSb with extremely sensitive magneto-optical techniques, combining sampling oscilloscope and lock-in amplifier methods. Oscillatory photoconductivity behavior in InSb has been investigated previously under a variety of conditions and in both n- and p-type samples. However, to our knowledge, no evidence has ever been presented for oscillatory magnetophotoconductivity (MPC) in n-InSb (or in any other semiconductor) caused by electron transitions from deep levels to the conduction band Landau levels. These studies allow a more precise determination and sensitive detection of deep levels through a more direct means than has been previously possible. We observe a resonant structure in the CO2 laser-induced MPC at liquid helium temperatures in n-InSb which is periodic in the inverse magnetic field and whose amplitude increases with the magnetic field. This behavior is typical for resonances involving Landau levels. The effect of lattice temperature, laser intensity, photon energy, and light polarization on the MPC is studied. The amplitude of this resonant structure saturates at moderate intensities (∼30 W/cm2) and shows no polarization dependence (for e⊥B and e∥B). These and other results indicate the presence of a deep level ≂74 meV below the conduction band edge (Eg ≂235 meV). Using a CO laser, a resonant structure is also observed from another deep level, ≂170 meV below the band edge. These deep levels could be caused by either lattice defects or residual impurities. Other structures observed with the CO2 laser are identified with LO phonon-assisted cyclotron resonance harmonic transitions within the conduction band, and two-photon magnetoabsorption interband transitions. ufoff
Fluorescence excitation efficiencies for high pressure and liquid xenon excited by electrons, alpha particles, and fission fragments
Authors: Williams J. R. , Gaiser J. E. , Dodhy A. , Miller T. G. , Womack D. R.
Published: February 2003

Relative excitation efficiencies are reported for the fluorescence at 173 nm in liquid xenon excited by 0.5 MeV electrons (β particle), 6 MeV alpha particles (α particle), and 90 MeV fission fragments (ff). Efficiencies at 173 nm are also reported for alpha particle and fission fragment excitation of high pressure xenon. Results are presented in the form of ratios which compare the fluorescent output per unit energy for excitation by the different particles. The β/α and α/ff ratios for liquid xenon are 1.25±0.5 and 3.5±1.2, respectively. For xenon at 2000, 3000, and 4000 Torr, the α/ff ratios are 0.60±0.25, 0.61±0.23, and 0.63±0.24, respectively.
Fourier photo-admittance spectroscopy
Authors: Janzén E. , Larsson K. , Stedman R. , Grimmeiss H. G.
Published: February 2003

A new method of measurement is described in which Fourier technique is applied to diodes. It has the high signal-to-noise ratio and resolution of Fourier spectroscopy, as applied previously to photoconductors, as well as the thin-layer sensitivity of junction techniques. It extends the usefulness of junction techniques to spectral regions where, with a conventional monochromator, room-temperature radiation dominates over the incident monochromatic light. The method is exemplified by measurements on a level 0.3 eV below the conduction band in selenium-doped silicon.
Cathodoluminescence and optical absorption in deformed MgO single crystals
Authors: Gonzalez R. , Piqueras J. , Llopis J.
Published: February 2003

Optical absorption at 220 nm (5.7 eV) and cathodoluminescence emission at 410 nm (3.0 eV) have been measured in deformed MgO single crystals with different geometries. Whereas previous studies indicate that a luminescence band at 430 nm (2.9 eV) is due to photoexcitation of the absorption band at 220 nm, there appears to be no direct correlation between the cathodoluminescence and the absorption band.
Influence of H2 addition on the perpendicular magnetic anisotropy of Gd–Co amorphous films deposited by ion beam sputtering
Authors: Naoe M. , Hoshi Y. , Ishiwatari T. , Yamanaka S.
Published: February 2003

The influence of the addition of hydrogen H2 on the penpendicular magnetic anisotropy of the Gd–Co films deposited by ion beam sputtering has been investigated precisely. Specimen film about 5000 Å thick were deposited on glass slide and rock salt substrates under the strict control of hydrogen partial pressure. The incorporation of H2 into Gd–Co films, as that of O2 and N2, leads to shift of compensation composition at room temperature from the Gd content of 18 at. % to higher Gd content. The Gd–Co:H films show perpendicular magnetization within very wide region of the composition, from about 55 at. % Co to 75 at. %. Besides, the incorporation of H2 increases the K⊥ of the films with Co content less than 75 at. %; however, it decreases that of the films with Co content more than 75 at. %. The electron diffraction pattern of the films changes from broad ring to two separated rings with the incorporation of H2, which indicates that the incorporation of hydrogen causes a phase separation of gadolinium hydrides and cobalt alloys in the Gd–Co:H films.