bluuebunny/crossref_metadata_2025 huggingface dataset:
Nature of transient currents in polymers
Authors: Vanderschueren J. , Linkens A.
Published: February 2003

Transient charging and discharging currents were measured in several polymers from room temperature to the glass transition temperature, and the effect of varying parameters such as field strength, electrode material, sample thickness, method of polymer preparation, and addition of impurities was investigated in some of them. Some limited comparative studies of the isochronal characteristics (i.e., current-temperature plots at fixed times) with the thermally stimulated depolarization and polarization currents were also carried out in order to test possible correlations between the phenomena observed by the different methods. All the results suggested that, at temperatures lower than the glass transition temperature and in low to moderate fields, the transient currents are essentially governed by dipolar mechanisms and are thus critically dependent on the position of the measuring temperature with respect to the temperature ranges of the various molecular relaxation processes characteristic of the material investigated.
Refractive indices of YAlO3 : Nd
Authors: Kuwano Yasuhiko
Published: February 2003

Refractive indices of YAlO3 : Nd (containing 1.0 at.% Nd) were determined in the 0.5–1.1-μm wavelength range. The single-term Sellmeier dispersion relation could be applied in the wavelength region between approximately 0.6 and 0.9 μm.
Plasma and conduction resonance dispersion for bulk and aggregated metals
Authors: Marton J. P. , Jordan B. D.
Published: February 2003

Interaction between plasmons and electrons in bulk metals may alter the character of the plasmons and may shift their frequency from the free-electron value h/ωpf. In aggregated metals, both the plasmons and the optical conduction resonance (OCR) may be similarly affected. In this work, a model system consisting of free electrons and a single Lorentzian oscillator is used to study the plasma and OCR dispersion in terms of the oscillator frequency. The results predict quantitatively the way interband transitions can hybridize plasma and OCR resonance in bulk and aggregated metals, and the way they can shift the resonace frequencies in both directions from their free-electron value. These predictions are compared with experimental results on some real metals.
The effect of oxide thickness on photostimulated exoelectron emission from aluminum
Authors: Baxter William J. , Rouze Stanley R.
Published: February 2003

The development of photostimulated exoelectron emission (PSEE) was observed directly in a photoelectron microscope during plastic deformation of anodized aluminum. The PSEE defines the mode of fracture of the oxide as well as the tensile strain required to initiate fracture. Thick oxides (280 nm) develop cracks perpendicular to the stress direction which propagate independently of the underlying microstructure of the metal. Oxides ?70 nm thick fracture at the slip steps in the same manner as the very thin natural oxide. Contrary to the results of previous observers of PSEE, the tensile strain required for the onset of emission actually decreases slightly with increasing oxide thickness.
A self-consistent technique for estimating the dynamic yield strength of a shock-loaded material
Authors: Asay J. R. , Lipkin J.
Published: February 2003

A technique is described for estimating the dynamic yield stress in a shocked material. This method employs reloading and unloading data from a shocked state along with a general assumption of yield and hardening behavior to estimate the yield stress in the precompressed state. No other data are necessary for this evaluation, and, therefore, the method has general applicability at high shock pressures and in materials undergoing phase transitions. In some special cases, it is also possible to estimate the complete state of stress in a shocked state. Using this method, the dynamic yield strength of aluminum at 2.06 GPa has been estimated to be 0.26 GPa. This value agrees reasonably well with previous estimates.
Arrays of Josephson tunnel junctions as parametric amplifiers
Authors: Wahlsten S. , Rudner S. , Claeson T.
Published: February 2003

Arrays of 10 or 40 series-connected small densely packed Josephson tunnel junctions were successfully operated as parametric amplifiers at 10 GHz. Between 50 and 90% of the junctions in an array were observed to work coherently in the amplification process. Signal gain exceeding 24 dB was achieved with a pump power as low as −50 to −70 dBm. A power width (i.e., the range of the pump power for a gain within 3 dB of the peak gain) of 0.25 dB and a bandwidth of 15 MHz were measured for 20-dB gain. The power width was in accordance with theory but the bandwidth was reduced, probably due to noise saturation effects. The latter effects can be reduced by lowering the input noise temperature or by including an external band limitation. The noise temperature was also increased by saturation; however, with an external bandwidth of 60 MHz, a noise temperature of 30±20 K was measured. The application of a magnetic field has proved extremely useful as a means of tuning the amplifiers to stable high-gain operating points. This tuning was also utilized in evaluating the amplifier parameters, and the theory by Feldman, Parrish, and Chiao has been verified. The upper frequency limit for a lead tunnel junction amplifier ought to be well above 300 GHz.
Pulsating ion laser action observed in a magnetically confined plasma
Authors: Lin Shao-Chi , Lischer David W.
Published: February 2003

Pulsating laser emission from the strong blue-green lines of Ar II at a self-repetition frequency up to 15 kHz has been observed in a magnetically confined argon plasma during a quasisteady low-pressure discharge. The laser output power and pulsation frequency are found to vary sensitively with the magnetic field strength, gas pressure, and discharge current. The phenomenon is interpreted as being caused by self-excited radial oscillations of the confined plasma which drives the population inversion density of the Ar+ ions within the prealigned optical cavity to rise and fall periodically above and below the lasing threshold.
The sensitivity of strain gauges
Authors: Arlt G.
Published: February 2003

The familiar formula for the K factor of strain gauges contains a term which is based on geometrical effects and a term containing the change of resistivity by strain. The latter term can be shown to include a geometrical part too. If this is split off, K becomes independent of Poisson’s ratio and K=2, if the material properties remain unchanged by strain.
The erosion of copper cathodes from vacuum to atmospheric-pressure arcs
Authors: Guile A. E. , Hitchcock A. H.
Published: February 2003

The erosion rates of cathodes of copper for arcing conditions ranging from vacuum to atmospheric pressure are examined in the light of very recent scanning-electron-microscope studies made by the authors. These have revealed details of cathode crater sizes and distributions, surface densities, and the numbers produced per second. These results explain the ways in which erosion rates vary with such parameters as arc current, arc duration, and gas pressure. Static arcs as well as arcs having cathode roots moved magnetically are considered.
Multiplexing for the guest-host mode using a nematic cholesteric mixture with a long pitch
Authors: Nara Y. , Kobayashi S. , Miyaji A.
Published: February 2003

Response characteristics of two different kinds of guest-host–type liquid-crystal devices were investigated as a function of d/p, where d and p are the liquid-crystal layer thickness and the physical pitch of a nematic-cholesteric mixture, respectively. Multiplexing was examined using a guest-host device containing optimized concentration of a cholesteric giving rise to a minimum response time; a good result was obtained compared with twisted nematic devices with respect to response times by a factor of 3.
The Anderson-Grüneisen parameter for 16 crystals of cubic symmetry
Authors: Tripathi N. D. , Shanker Kiran , Khare R. P.
Published: February 2003

Using second- and third-order elastic modulii (SOEM and TOEM) data, the Anderson-Grüneisen parameter δ has been evaluated at room temperature for 16 crystals of cubic symmetry.
Comments on ’’On the step structures of alkali halide surfaces’’
Authors: Serna C. R. , Serna J.
Published: February 2003

A recent paper studies some characteristics of the alkali halide cleaved surfaces. It mainly tends to demonstrate that the steps appearing on a new surface are biatomics. Arguments are given together with experimental data that show that these steps can be monoatomics as well. At the same time, some other conclusions are amended.
Reply to ’’Comments on ’On the step structure of alkali halide surfaces’ ’’
Authors: Yacamán M. José , Ocaña T.
Published: February 2003

A discussion about the conditions in which V-shaped structures are obtained is presented. It is shown that the results of our paper are not related to surface contamination, and some clarification about the nucleation sites in our surfaces is made.
Electrical response of a slim-loop-ferroelectric ceramic compressed by shock waves
Authors: Lysne P. C.
Published: February 2003

Shock reverberation experiments were performed on electrically biased specimens of the slim-loop-ferroelectric ceramic (Pb0.715Ba0.285)0.991(Zr0.707Ti0.293) 0.981Bi0.019O3, and a simple model was fitted to the observed electrical response. It was found that the material could be described as a linear reversible dielectric and that the reciprocal of the permittivity is linearly related to the shock stress.
Characteristics of resist films produced by spinning
Authors: Meyerhofer Dietrich
Published: February 2003

A model is presented for the description of thin films prepared from solution by spinning. Using only the centrifugal force, linear shear forces, and uniform evaporation of the solvent, the thickness of the film and the time of drying can be calculated as functions of the various processing parameters. The model is compared with experimental results obtained on positive photoresists and excellent agreement is obtained. When adequate care are is taken, the liquid forms a level surface during spinning, and the film thickness becomes uniform and independent of the size of the substrate. The film thickness h shows the following dependence on spin speed f, initial viscosity ν0, and evaporation rate e:h∝f−2/3νo1/3e1/3, and e is proportional to f1/2.
Interactions in the Co/Si thin-film system. I. Kinetics
Authors: Lau S. S. , Mayer J. W. , Tu K. N.
Published: February 2003

Interactions in the Co/Si thin-film system were investigated by MeV backscattering and x-ray-diffraction techniques. It was found that Si diffuses through the Co layer and accumulates at the sample surface at about 300 °C. Increasing the temperature causes the growth of the Co2Si phase, followed by the simultaneous growth of the CoSi phase. The growth rates for both phases have a square root of time dependence. The activation energies of growth are 1.5 and 1.9 eV for the Co2Si and CoSi phase, respectively. A model for the growth of multiple phases is suggested. The transformation between CoSi2 and CoSi is found to be a reversible reaction.
Interactions in the Co/Si thin-film system. II. Diffusion-marker experiments
Authors: van Gurp G. J. , van der Weg W. F. , Sigurd D.
Published: February 2003

The Kirkendall effect in thin-film Co/Si couples is investigated by He backscattering using diffusion markers. The couples contain the compounds Co2Si and CoSi. The markers used are Xe implanted into Si, C, or Co2Si and a discontinuous W film between Si and Co. In the case of Xe implantation into Co, the experiments can be explained by dragging of Xe bubbles by the moving Co/Co2Si phase boundary. Xe implanted into Si is located at the Si/CoSi interface after the reaction and W is found at the Co/Co2Si interface after the reaction. The same applies to Xe implanted through Co into Co2Si. The results are evidence for predominant Co diffusion in Co2Si growth and Si diffusion in CoSi growth. Grain-size measurements suggest that grain-boundary diffusion plays a role in the growth of the silicide layers. The results of a Xe implantation into Co2Si without Co suggests that at the Co2Si/CoSi interface both Si and Co diffusion currents flow.
Diatomic-complex donor and acceptor model for Ge-doped vapor-grown GaAs
Authors: Kasano Hiroyuki
Published: February 2003

On the basis of thermochemical equilibria considering interactions between dopants and vacancies, the carrier concentration, electron mobility, minority-carrier lifetime, and luminescence intensity, which have been measured as a function of the Ge concentration in a solid, are analyzed for Ge-doped vapor-grown GaAs. The quadratic dependence of the carrier concentration on dopant partial pressure is observed in Ge- and Sn-doped GaAs and is reasonably explained by the hypothesis that the dominant donor is the diatomic complex formed between Ge or Sn substitutionals incorporated in the nearest-neighbor Ga sites. For Ge-doped GaAs, considering that the diatomic Ge donor and monoatomic Ge acceptor are dominant charged species in the extrinsic doping range, the measured electrical and optical properties are uncontradictorily explained with quantitative agreement. Using this double-donor–double-acceptor model, the origin of the space charges which significantly decrease electron mobility and the origin of minority-carrier killer centers which cause concentration quenching of luminescence in the extrinsic doping range are speculated to be VGa-GeAs complexes and VGa- (GeGa)2 complexes, respectively. The self-compensation ratio of Ge, N−A/N+D, reduces to the minimum value (∼0.1) near the boundary between the intrinsic and the extrinsic regions.
Hole photogeneration in poly(N-vinylcarbazole)
Authors: Borsenberger P. M. , Ateya A. I.
Published: February 2003

The photogeneration of holes in poly(N-vinylcarbazole) has been investigated as a function of applied electric field, wavelength, and temperature. For fields above 3.0×104 V/cm, the field and temperature dependences of the photogeneration efficiency are in good agreement with predictions based on the Onsager theory of geminate recombination. The quantum efficiency can be described by a thermalization distance which varies from 26 to 30 Å as a function of wavelength and a primary quantum yield which varies between 0.20 and 0.03 as a function of temperature. The photogeneration efficiency increases in steps with decreasing wavelength. Transitions occur between the ground state and the first, second, and third excited singlet states. For a given transition, the efficiency is constant and depends only upon the electric field and temperature. The increase in efficiency which occurs with decreasing wavelength can be explained by an increase in the thermalization distance. The primary quantum yield shows an exponential dependence on reciprocal temperature with an activation energy of 0.05 eV. The thermalization distance is independent of temperature and determined only by the excitation wavelength.
Transport of minority- carriers in graded-composition semiconductors and its impact on graded-band-gap base transistors operated at high currents
Authors: Hutchby James A.
Published: February 2003

A comprehensive model for minority-carrier transport due to a quasi-electric-field in graded-composition semiconductor materials is developed including effects due to nondegenerate high-level injection of excess electrons and holes. For low-level injection, equivalent to a one-sun photoexcitation of uniformly doped direct- or indirect-band-gap material the total quasifield is given by the standard gradient of band-gap energy. High-level injection asymptotically reduces quasifield components due to band-gap and effective-mass gradients to lower values, and essentially eliminates components due to equilibrium- and excess-carrier concentration gradients. The impact of these results on performance of p-n-p and n-p-n graded-band-gap base transistors operated at high currents is examined.
Electron trapping in SiO2 due to electron-beam deposition of aluminum
Authors: Ning Tak H.
Published: February 2003

Electron trapping in the SiO2 layer of n-channel polycrystalline silicon-SiO2-silicon field-effect transistors with electron-beam-evaporated aluminum was studied. The increased electron trapping was attributed to the x rays generated when the electron beam impinged on the aluminum target. Traps with low-field capture cross sections greater than 10−13 cm2 are associated with the x-ray-induced positively charged centers, while traps with low-field capture cross sections of about 1×10−15 cm2 are associated with the x-ray-induced neutral centers. For the silicon-gate devices, both traps could be effectively reduced by annealing in dry forming gas at 550 °C for 20 min. As reported earlier, the capture cross section of the positively charged traps has a strong field dependence of approximately E−3ox and is approximately independent of temperature. The field dependence of the capture cross section of the neutral traps is much weaker, with roughly a σ  =σ0 exp(−bEox) dependence, where σ0=1.6×10−15 cm2 and b=7.35×10−7 cm/V. A possible origin of these neutral traps is displaced bonds forming polarization potential wells.
Intermetallic compounds of Al and transitions metals: Effect of electromigration in 1–2-μm-wide lines
Authors: Howard J. K. , White J. F. , Ho P. S.
Published: February 2003

This paper describes a method to improve the electromigration capacity of Al-Cu or Al thin-film interconnection metallurgy by incorporating a layer of intermetallic compounds of Al and transition metals. The improvement in lifetime can be 100 times greater than comparable Al-Cu structures tested under the same conditions. Certain structural properties of the intermetallic compounds have been related qualitatively to the failure mode and electromigration lifetime. Results are discussed in an attempt to clarify the mechanisms by which an ordered phase (compound layer) can improve electromigration lifetime. Life-test data obtained from the thin-film metallurgy with Al–transition-metal compound structures indicate that improvements can be achieved by one or a combination of the following factors: (a) blocking void propagation through the film, (b) reducing the rate of mass transport by electromigration, and (c) eliminating divergent damage sites by increasing the degree of preferred grain orientation. In many cases, the thickness of the intermetallic layer can be adjusted to yield a significant improvement in lifetime with only a small increase in stripe resistance.
Time-dependent magnetization in a SmCo3.5Cu1.5 single crystal
Authors: Uehara M.
Published: February 2003

Magnetization reversal in a SmCo3.5Cu1.5 single crystal has been observed as a functon of the field sweep rate in the range 10−5–104 Oe/sec. The reciprocal coercive force varies linearly with the logarithm sweep rate over a wide range, but lowers abruptly above a certain sweep rate. This seems to suggest that the rate controlling process of magnetization reversal changes from elementary nucleations on the parent domain walls to the domain growth resulting from wall migration.
Magnetic properties of amorphous Co-Gd-Mo-Ar thin films
Authors: Gangulee A. , Kobliska R. J.
Published: February 2003

The temperature dependences of the saturation magnetization of amorphous ferrimagnetic Co-Gd-Mo-Ar thin films have been analyzed in terms of the mean-field theory. This analysis yields the spin values of Co and the effective exchange interaction energies between Co-Co and Co-Gd atom pairs, which are then correlated with the film composition. Examples of the calculation of various magnetic properties from these mean-field parameters are given. The magnitude of the anisotropy energy in these films depends both on the composition and on the fabrication parameters; the temperature dependence of the anisotropy energy can be described in terms of a dipolar model.
Plasma etching of Si and SiO2—The effect of oxygen additions to CF4 plasmas
Authors: Mogab C. J. , Adams A. C. , Flamm D. L.
Published: February 2003

The plasma etching of silicon and silicon dioxide in CF4-O2 mixtures has been studied as a function of feed-gas composition in a 13.56-MHz plasma generated in a radial-flow reactor at 200 W and 0.35 Torr. Conversion of CF4 to stable products (CO, CO2, COF2, and SiF4) and the concentration of free F atoms ([F]) in the plasma were measured using a number of different diagnostics. The rate of etching, the concentration of F atoms, and the intensity of emission from electronically excited F atoms (3s2P–3p2P° transition at 703.7 nm) each exhibit a maximum value as a function of feed-gas composition ([O2]); these respective maxima occur at distinct oxygen concentrations. For SiO2, the variation in etching rate with [O2] is accounted for by a proportional variation in [F], the active etchant. The etching of silicon also occurs by a reaction with F atoms, but oxygen competes with F for active surface sites. A quantitative model which takes oxygen adsorption into account is used to relate the etch rate to [F]. The initial increase of [F] with [O2] is accounted for by a sequence of reactions initiating with the production of CF3 radicals by electron impact and followed by a reaction of CF3 with oxygen. When [O2] exceeds ∼23% (under the present discharge conditions), [F] decreases due, probably, to a decrease in electron energy with an increase of oxygen in the feed gas.
Plasma x-ray emission produced by ruby lasers at 1012 W/cm2
Authors: Bleach R. D. , Nagel D. J.
Published: February 2003

Q-switched 20-nsec ruby-laser pulses (∼0.5 GW) were focused to about 1012 W/cm2 on targets containing elements in the range 6⩽Z⩽68. Time- and space-integrated x-ray emission from plasmas 200 μm in diameter with lifetimes near 12 nsec was measured with four active detectors at energies between 0.1 and 5 keV. Maxima in x-ray intensity measured by each detector occurred when binding energies of core electrons in target atoms were 20–30 times the electron plasma temperature. Calculated detector response functions together with coronal-model plasma emission computations were used to analyze the atomic-number dependence of the detector signals. A plasma electron temperature of 70 eV and an electron density of about 4×1020 cm−3 gave the best fit to the ratios of signals. Computed spectra for this temperature showed that the peaks in the low-energy detector (an x-ray diode most sensitive near 0.15 keV) were due in part to line radiation. Peaks in the three detectors sensitive above 1 keV (two silicon PIN diodes and an ionization chamber) were primarily due to recombination radiation. The results of this work augment an earlier similar, but limited, study at 1012 W/cm2.
A theory for the cathode mechanism in low-current vacuum arcs, with application to the calculation of erosion rate
Authors: Kubono Takayoshi
Published: February 2003

A theory has been proposed which seeks to explain the cathode mechanism in low-current vacuum arcs. It is shown that the high current density at the cathode surface has been successfully discussed by relating the energy-balance equation, space-charge equation, electron-emission equation, current equation, MHD equation of motion, and the minimum principle of joule heating. When four equations and two limiting conditions combine the five dependent variables, which are temperature of the arc root, electric field at the cathode, total current density, current density carried by electrons, and the radius of the arc root, the current density and temperature at the arc root are obtained as a function of the arc current with the cathode-fall voltage as a parameter. It is also shown that the relationship between the arc current and the evaporation rate from the arc cathode root can be calculated. The theoretical results are in good qualitative agreement with the experimental data of the current density and the erosion rate.
Substrate-orientation dependence of the epitaxial regrowth rate from Si-implanted amorphous Si
Authors: Csepregi L. , Kennedy E. F. , Mayer J. W. , Sigmon T. W.
Published: February 2003

Amorphous layers, approximately 4000 Å thick, were formed on single-crystal Si samples by implantation of 28Si ions at LN2 substrate temperature. Channeling-effect measurements with MeV 4He ions were used to measure the thickness of the amorphous layers and to measure the subsequent epitaxial regrowth on the underlying crystalline substrates. For annealing temperatures between 450 and 575 °C, the growth rate showed a strong dependence on the substrate orientation with 〈100〉-oriented samples exhibiting about a 25 times higher growth rate than 〈111〉-oriented samples. Measurements of the growth rate on a series of samples cut in 5° angular increments show that there is a monotonic decrease from the 〈100〉 to the 〈111〉 orientation. A simple model is proposed to explain the observed orientation dependence.
Properties of consecutive energy barriers and the associated behavior in plastic flow
Authors: Faucher B. , Krausz A. S.
Published: February 2003

The properties of consecutive energy-barrier systems are derived from the basic principles of deformation kinetics and from the rate theory as applied to plastic flow. It is shown that these properties are functions of well-defined relations between the activation energy and volumes of the different barriers. In particular, for a system of two consecutive energy barriers, it is shown that the usual equation used to calculate the strain rate ?=ε0/(t1+t2), where t1 and t2 are two waiting times, is only an approximation valid when backward activations are negligible. The behavior of materials, in which plastic flow is controlled by a system of two consecutive energy barriers, was determined rigorously for various experimental conditions. It is shown that the calculated temperature dependence of the flow stress as well as the stress and temperature dependence of the experimental activation volume and strain-rate sensitivity that follow from the properties of consecutive energy barriers are in agreement with experimental observations.
Modified lattice-statics approach to dislocation calculations I. Formalism
Authors: Esterling Donald M.
Published: February 2003

A modified lattice-statics method to calculate the atomic displacements associated with a screw dislocation is outlined. The model incorporates an anharmonic region wherein the forces are derived from a pair potential. Appropriate energy and force expressions are derived. The modifications necessary for the implementation of the conjugate-gradient function minimization method are also derived.
Self-focusing and defocusing of pump radiation in a far-infrared laser
Authors: Siegrist M. R. , Morgan P. D. , Green M. R.
Published: February 2003

For optically pumped FIR lasers the frequency of the pump beam is in close coincidence with an absorbing transition of the active medium. Saturable absorption results in an intensity-dependent local refractive index, leading to self-focusing or defocusing. The latter effect has been demonstrated experimentally in CH3F, in which a beam divergence of the order of several mrad was measured, in agreement with theoretical predictions. This phenomenon has important consequences in the design of high-power FIR amplifiers.
Relationship between fiber tension and drawing velocity and their influence on the ultimate strength of laser-drawn silica fibers
Authors: Schonhorn H. , Vazirani H. N. , Frisch H. L.
Published: February 2003

The ultimate strength of laser-drawn silica fibers has been found to be related to the velocity of drawing and the tension in the fiber required to maintain it. We find that when the uncoated pristine fiber tension during drawing exceeds about 80 g for a 110-μm fiber there is a dramatic decrease in strength (coated fiber). Dimensional analysis of the laser-drawing process indicates that for this particular system the fiber tension should be proportional to the cube of the drawing velocity. This is confirmed experimentally for fibers drawn at a variety of tensions and speeds of 0.4 and 1.0 m/s.
Gain measurements on the sequence bands in a TEA-CO2 amplifier
Authors: Lavigne P. , Lachambre J.-L. , Otis G.
Published: February 2003

Small-signal gains as high as 1.5% cm−1 have been measured in a TEA-CO2 amplifier on the 00°2- (1001, 0201)I,II sequence bands. The ratio of the gain coefficient of the sequence bands over the gain coefficient of the regular bands has been observed to be independent of either the CO2 or He proportion in the gas mixture. It has also been found to increase with the electrical energy dumped into the active medium and to reach a value of 1/3 at an excitation density of 140 J/l. Gain on the sequence bands has been found to be responsible for the anomalously high gain coefficient that is measured at low J values of the R branch of the regular 9.4-μm transition in TEA amplifiers.
Prediction of catastrophes in bistable systems using externally applied random force
Authors: Agu Masahiro , Teramachi Yasuaki
Published: February 2003

A method is proposed to forecast the catastrophic changes of the states of bistable systems with the use of externally applied Gaussian random force. The prediction is based on the fact that the probability distribution function of the states of a bistable system under the influence of Gaussian random force becomes far from Gaussian in the vicinity of its catastrophe. In other words, the anomalous increase of the variance of the probability distribution function in the vicinity of the catastrophe can be utilized as a precursory phenomenon to predict the catastrophe. The anomaly of the probability distribution function is caused by the nonlinear property of the bistable system.
Transfer of energy from charged transmission lines with applications to pulsed high-current accelerators
Authors: Eccleshall D. , Temperley J. K.
Published: February 2003

An analysis has been performed of charged transmission-line configurations for use in high-current electron accelerators. Conditions for maximum efficiency and maximum energy transfer to the beam load are derived for ideal constant-impedance lines. It is shown that, in the lossless-line approximation, asymmetric line-pair configurations exist with which both a high accelerating voltage and nominal 100% efficiency can be achieved. The configurations would also have application as a pulse-forming network for use with other switched loads.
Neutral-beam divergence due to imperfect magnetic shielding
Authors: Conrad J. R.
Published: February 2003

The divergence of a neutral beam due to imperfect magnetic shielding of the gas-cell neutralizer is considered. Coupled kinetic equations for the ion and neutral velocity distribution functions are solved. The deflection and divergence of the neutral beam are obtained from moments of the neutral distribution function.
Electrical characterization of heterostructure lasers
Authors: Joyce W. B. , Dixon R. W.
Published: February 2003

An improved phenomenological model of the electrical and optical characteristics of semiconductor heterostructure injection lasers is analyzed with emphasis on the nonlasing-to-lasing phase transition. The model includes both radiative and nonradiative carrier recombination, as well as electron-photon coupling. Recently developed approximations of the Fermi-Dirac integral are used, and they allow closed-form solutions of the electron and photon rate equations to be obtained—even though the carrier populations are highly degenerate near lasing threshold. Because of the detailed information which harmonic-voltage amplitudes provide, calculation of the functional forms of the voltage derivatives of the devices is emphasized, and expressions for the height and width of the second-derivative peak, and for the slope at threshold of the first derivative, are obtained. The effects of carrier degeneracy and of nonradiative recombination are explicitly displayed, and both are found to be important in modifying the values of the parameters entering the traditional form, i=ir exp(qV/mkT), of the forward-conduction current-voltage relation. In (Al,Ga)As stripe-geometry lasers values of m?2 are found to be reasonable.
Single-crystal CdTe with low absorption at 10.6 μm for use as ir laser windows
Authors: Selim F. A. , Kroger F. A.
Published: February 2003

Optimum conditions for the preparation of CdTe with minimum absorption at 10.6 μm are determined, paying attention both to type and concentration of dopants and the conditions of annealing. Doping with indium and annealing at 700 °C followed by quenching led to material with the smallest absorption coefficient at 10.6 μm of 8×10−4 cm−1.
Studies of a small-gap multiatmospheric-pressure CO2 laser
Authors: Carman T. , Dyer P. E.
Published: February 2003

A 4-mm gap uv preionized CO2 laser has been developed, which operates at pressures ≲ 12 atm using relatively low voltages. Studies of the small-signal gain and laser-performance characteristics are reported.
Enhancement of NF(b1Σ+) by iodine laser pumping
Authors: Herbelin J. M. , Kwok M. A. , Spencer D. J.
Published: February 2003

A peak density of electronically excited free radical NF(b1Σ+) of 5.6×10−10 mol/cm3 has been produced in a subsonic flow by means of intracavity pulsed iodine laser pumping of ground-state iodine atoms and subsequent energy transfer of this electronic energy to NF(a1Δ) free radicals. This concentration represents a 30-fold increase over previously reported steady-state concentrations and supports the promise of the NF(b1Σ+) species as a potential laser candidate.
A model for multitrack nonperiodic multistrip couplers
Authors: Datta Supriyo , Hunsinger Bill J.
Published: February 2003

A simple circuit model for the multistrip coupler is presented. The transmission matrix of a single strip relating the output- and input-wave amplitudes in different tracks is obtained from circuit theory. The overall transmission matrix of the coupler is obtained by cascading the transmission matrices of successive strips. The model is shown to yield the correct results for common coupler configurations. This model because of its strip-by-strip approach makes it straightforward to analyze nonperiodic couplers which are difficult to analyze by usual techniques. Numerical solutions for a strip-coupled UDT are presented in agreement with previous experimental results.
Time-dependent crack propagation in linear-elastic solids
Authors: Krausz A. S.
Published: February 2003

Simple rigid crack-front propagation and the mechanism of double-kink nucleation and spreading are analyzed in a periodic crystallographic potential-energy field. For the analysis the classical Griffith model for crack propagation is superposed on the periodic energy field of the crystal lattice. The energy-condition theory of the time-dependent crack propagation is developed in terms of the absolute rate theory. A complete kinetics analysis is carried out for the description of the rigid and kinked crack-front propagation rate over the consecutive energy-barrier system of the crystal lattice. The rate is expressed as a function of the applied stress, temperature, the free energy of fracture, and the lattice parameters.
In-plane anisotropy induced by rare gases in RE-Co amorphous films
Authors: Krishnan R. , Suran G. , Sztern J. , Jouve H. , Meyer R.
Published: February 2003

Postdeposition annealing of some sputtered rare-earth–cobalt (YCo3, GdCo, and HoCo) amorphous films in an atmosphere of rare gases Ne, Ar, Kr, and Xe has been shown to induce a strong in-plane anisotropy Ku?−5×105 erg/cm3. Also, after the rare-gas anneal, the coercive force and the resonance linewidth are remarkably reduced and one observes in YCo3 films a well-defined spin-wave spectra which obeys well the quadratic-dispersion law. The presence of in-plane anisotropy in the annealed films is tentatively attributed to the formation of Co-Co pairs along the thickness.
The evidence of structural relaxation as the origin of Curie temperature aging in metallic glass
Authors: Chen H. S.
Published: February 2003

Kinetics of both isothermal Curie temperature aging and enthalpy recovery of a metallic glass (Fe0.5Ni0.5)75P16B6Al3 near the glass temperature obey approximately a logt law, where t is the annealing time. The frequency factors ke of the first-order rate reaction were obtained by assuming the configurational entropy as the rate determining factor. ke’s obtained agree reasonably with the temperature dependence of viscous flow. This is evidence that Curie temperature aging and thermal heat recovery of metallic glasses have the same origin, associated with structural relaxation, and can be described by the entropy model of viscous flow.
A 125Te Mössbauer study of amorphous and crystalline phases of As2Te3−xSex
Authors: Jones Colin H. W. , Tse Anthony
Published: February 2003

The 125Te Mössbauer data for crystalline and amorphous samples of As2Te3−xSex (x=0 to 2.9) are reported. The quadrupole splitting provides a useful probe for changes in the local environment about the tellurium with changes in phase and composition.
Ionization rates for electrons and holes in GaAs
Authors: Ito Masanori , Kagawa Shuzo , Kaneda Takao , Yamaoka Toyoshi
Published: February 2003

Ionization rates in GaAs are determined from the measurement of photocarrier multiplication. Pure electron and hole initiations are achieved by using the novel crater mesa structure and appropriate optical-injection wavelengths. The ionization rates for holes are greater than that for electrons except at highest fields. This agrees with the studies of Stillman et al., except for the individual values. The ionization rates for electrons and holes are expressed as α=5.6×106 exp(−2.41×106/E) and β=1.5×106 exp(−1.57×106/E), respectively.
Stress splitting of the 0.84-eV luminescence in GaAs : Cr
Authors: Schmidt Martin , Stocker H. J.
Published: February 2003

The photoluminescence spectra of Cr-doped GaAs at 4.2 K exhibits a narrow zero-phonon line (linewidth 1.1 meV) at 0.838 eV, accompanied by a broad phonon structure. The zero-phonon line is split by uniaxial stress. The splitting pattern and the line polarization are explained in terms of transitions to spin-orbit split states of the d shell of Cr2+. Transitions to bound-hole states and the existence of Cr as a complex can be excluded. The results are consistent with an internal transition between an excited state 5E of Cr2+ and the spin-orbit split state(s) 5T2 of Cr2+.
An electron tunneling study of the chemisorption of formic acid on different surfaces
Authors: Magno R. , Adler J. G.
Published: February 2003

A comparison is made of inelastic electron tunneling spectroscopy results for the chemisorption of formic acid into into two different surfaces. Details of the spectra are used to confirm that one surface is alumina and the other aluminum. A formate ion spectrum is obtained in both instances but the aluminum surface shows both greater spectral intensity and a slight shift to higher energies for the peaks. In the case of the aluminum surface the peak intensities are the same for both bias polarities as expected in the case of a single homogeneous barrier. For the alumina surface, on the other hand, there is an asymmetry in peak intensity due to the two insulator barriers.
Interaction of magnetostatic waves with a current
Authors: Emtage P. R.
Published: February 2003

It is shown that the interaction of magnetostatic waves with a current can be characterized by a coupling constant analogous to, but much greater than, the piezoelectric coupling constant. The theory is applied both to surface and forward-traveling volume magnetostatic waves, and the problems of excitation, reflection, and absorption by a single microstrip and by a narrow-band interdigital transducer are treated. It is found that the coupling constant is close to 0.5 for any reciprocal wave, and is greater for any nonreciprocal wave, when the transducer is in contact with the magnetic medium. These values are too large to allow effective signal processing, since the emitted waves react strongly on the transducer; narrow-band transducers must be lifted above the surface so as to weaken the coupling.
Dielectric losses in ferroelectric ceramics produced by domain-wall motion
Authors: Gentner J. O. , Gerthsen P. , Schmidt N. A. , Send R. E.
Published: February 2003

The oscillation of domain walls caused by alternating fields is often thought to be the origin of dielectric losses. In this paper the physical nature of losses is explained by the damping of moving 90° domain walls. For frequencies up to 108 Hz the origin of damping of the wall motion is ascribed to point defects within the 90° domain wall. At high frequencies damping results from the reflection of thermal-lattice waves impinging on a moving 90° domain wall.
The transient penetration of an electric field into a weakly conducting layer with an induced conductivity gradient
Authors: Lonngren K. E. , Reddy S. M.
Published: February 2003

The transient penetration of electric field into a weakly conducting material is calculated. Both numerical and a fairly simple and accurate analytical approximation are obtained using a Frenkel conductivity model for the material.
Dielectric constants of the alkaline-earth chalcogenides
Authors: Goyal S. C.
Published: February 2003

In the present study, the correlation between fractional ionic character and dielectric constants is applied to predict the magnitudes of the static dielectric constant ε0 of the several alkaline-earth-chalcogenide solids. The calculated values of ε0, together with the other known experimental data of these solids, are used as input data to evaluate the model parameter of the suitably modified simple shell model. The determined model parameters are utilized to obtain the values of the ionic polarizability, vibrational frequencies, and effective ionic charge which are found in good agreement with the available experimental values for the alkaline-earth oxides. It is also pointed out that the value of the Szigeti effective charge is larger than 0.5 in all the sixfold coordinated solids.
Edge emission in melt-grown ZnSexS1−x
Authors: Ohmori Kenzo , Ohishi Masakazu , Okuda Tsuyoshi , Hiramatsu Makoto
Published: February 2003

Zinc sulfo-selenide single crystals which have zinc-blende structure are grown from the melt by the Bridgman method under a high-pressure argon atmosphere. It is confirmed that lattice constants vary linearly with the composition of ZnSexS1−x according to Vegard’s law after crystallization. At 10 K, the near-band-edge emission spectrum is observed for ZnSe, ZnSe0.8S0.2, ZnSe0.6S0.4, and ZnSe0.5S0.5 single crystals fired in molten zinc. It is also confirmed that the band gap obtained from the emission peak due to the excitonic transition near the band edge varies monotonic curvilinearly with the composition of ZnSexS1−x, 0.5⩽x⩽1, showing the intermediate values of band-gap energies of ZnSe and ZnS.
Optical-absorption edge in cadmium stannate selective coatings
Authors: Agnihotri O. P. , Gupta B. K. , Sharma A. K.
Published: February 2003

Cadmium stannate selective coatings have been prepared by a pyrolytic method in which two parts of 0.2M CdCl2⋅5H2O solution in ethyl alcohol and one part 0.2M solution of SnCl4⋅3H2O in acetic acid has been sprayed onto a heated substrate of glass and quartz. The films were transparent in the visible portion of the spectrum and exhibited interference colors. The absorption data is interpreted as being due to an allowed direct transition of energy gap of 2.8 eV and an indirect interband transition of energy gap of 2.2 eV. The absorption coefficient reaches values exceeding 105 cm−1 at the higher photon energies, which is expected for direct allowed transitions.
Resonances in semiconductor-barrier Josephson junctions
Authors: Lum W. Y. , Van Duzer T.
Published: February 2003

An analysis is made of the cavity resonances in Josephson junctions with semiconductor barriers. The quality factor Q is evaluated for Pb-Te-Pb junctions and it is found to be typically on the order of unity. Agreement with experiment is shown. The lower Q constitutes an advantage over oxide-barrier junctions for digital applications where cavity resonances can lead to unpredictable switching behavior.
Flux and fluence dependence of implantation disorder in GaAs substrates
Authors: Anderson Wayne J. , Park Y. S.
Published: February 2003

A previously presented technique of measuring radiation damage using electroreflectance (ER) measurement is used to detect disorder dependencies for light and heavy ions as a function of flux and fluence. Lighter-mass ions (Ne, N, and O) cause increasing damage with increasing flux for fluences less than 5×1013 cm−2 because of the decrease in radiation-enhanced annealing. At higher fluences, the damage decreases with increasing flux probably because of thermal annealing. Heavy ions (Cd, Te, and Xe) exhibit the same type of behavior but at lower fluences because of the smaller penetration depths. The ER measurements of damage in ion-implanted GaAs show clearly that the radiation-enhanced and thermal-annealing processes depend upon the energy density and damage concentration in the crystal.
Difference in the transformation processes of pressed and vibro-milled γ-Fe2O3 to α-Fe2O3
Authors: Senna Mamoru
Published: February 2003

Transformation processes of γ-Fe2O3, preliminary treated either through pressing or vibro-milling, to α-Fe2O3 was studied. Although the rate of transformation increased through both treatments, the shape of the reaction isotherms, and accordingly the rate processes, were quite different due to the differences in nature of applied forces and stored energy, as revealed from differential scanning calorimetry (DSC) thermograms.
Surface-wave generation in crystals with high dielectric constant
Authors: Singh Shri Pal , Kabelka H. , Kuzmany H.
Published: February 2003

The generation of surface acoustic waves by interdigital transducers in materials with high and strain-dependent dielectric constants, which are not necessarily piezoelectric, was studied theoretically using Lamb’s integral-solution method and the flat-field approximation of Tseng for the solutions of the wave equation. The influence of the dependence of the dielectric constant on the strain was considered in the approximation given by Pekar and Ogg. As a result, a transducer gain proportional to an applied dc field has been obtained. With respect to the frequency responses, an increased output at higher odd harmonics as compared to transducers on piezoelectric crystals was found. The transducers are shown to be tunable because of a stiffening of the surface-wave velocity by the applied field. Thus, amplitude modulation and frequency modulation should be possible in a simple manner.
Temperature and stresses in a cylindrical conductor with an alternating current
Authors: Rolicz P.
Published: February 2003

Steady periodic temperature, transient temperature, and stresses produced in an isotropic cylindrical conductor carrying an electric alternating current are calculated. The investigations are made for the small skin effect when the current density is homogeneous.
rf electric fields in an inhomogeneous magnetized plasma column
Authors: Skipping C. R. , Oakes M. E.
Published: February 2003

A perturbation method for determining electric fields in an inhomogeneous magnetized plasma column is given that removes restrictions on the wavelengths present in previous treatments. The method is also applicable to finite-amplitude wave problems.
Nonuniform mesh diode simulation code
Authors: Quintenz J. P.
Published: February 2003

A new version of a diode simulation code has been written which allows for nonuniform zoning in both the r and z directions. This new flexibility enables more accurate treatment of crucial areas in the diode such as near emission surfaces and in target regions. The new code also has the ability to treat slanted surfaces such as that found in a tapered cathode diode. An interesting result of the new code is that a ’’parapotential’’ cathode pinches better than the corresponding flat cathode at the same total current.