bluuebunny/crossref_metadata_2025 huggingface dataset:
Longitudinal χ″ of polycrystalline and impurity-doped YIG in strong rf fields
Authors: Borghese Camillo
Published: February 2004

The imaginary longitudinal susceptibility χ″ of polycrystalline YIG in a strong rf magnetic field with amplitude h behaves according to the average size x̄ of the grain size distribution p(x), to its standard deviation σ, and to the impurities' concentration c. The threshold field h̄c increases with c and with decreasing x̄. The slope of the tangent to χ″ through h̄c decreases with increasing h̄c while, if h̄c is constant, it increases with the impurity content. Taking into account Schlömann's expression for χ″ for a single crystal and a modification of Patton's transit-time-limited spin-wave lifetime model, formulas for χ″ and h̄c for an impurity-doped polycrystalline aggregate of spheres having lognormally distributed diameters are worked out. A graphical method to infer the relevant parameters from the experiment is presented. Experimental data and theory are compared on two pairs of compositions; the first one exhibiting a moderate h̄c (∼ 15 Oe) and a second one, a high h̄c ([inverted lazy s] 40 Oe). Each pair consists of a fine-grained YIG and an impurity-doped YIG. The agreement is qualitatively satisfactory. The modifications resulting from Scotter's inclusion/porosity scattering model are also briefly treated.
Surface charge and infrared absorption characteristics of polyethylene terephthalate electrets
Authors: Pillai P. K. C. , Goel Malti
Published: February 2004

In this paper a study of surface charge decay has been made on polyethylene terephthalate thermoelectrets prepared from foils of thicknesses 6, 25, 75,and 250 μ under various conditions of polarization. Initially, heterocharges have been observed on both the surfaces, while final charges one month after preparation were homo- on the cathode surface and hetero- on the anode surface. Infrared absorption characteristics have also been studied. Experimental evidence is given for dipolar alignment during polarization in this polymer. Dipole alignment and space charge trapping are shown to be the main causes of electret polarization in polyethylene terephthalate. Relaxations of dipoles and trap hopping processes are responsible for the charge decay.
Calculation of radial magnetic fields for axisymmetric solenoids with rectangular cross section
Authors: Walstrom P. L. , Lubell M. S.
Published: February 2004

The ratio of maximum radial field to maximum axial field has been calculated numerically for axisymmetric solenoids of rectangular cross section and constant current density over a wide range of coil configurations. It is also shown that for a certain range of coil shapes the maximum modulus of the magnetic field occurs on the end faces of the windings. These considerations are pertinent in the design of superconducting magnets for two reasons: (i) Many superconductors have lower critical current in a field normal to the wide surface than in a field parallel to the surface, and (ii) large radial fields can cause catastrophic flux jumps.
Injection dependence of the excess carrier lifetimes in Cr-doped n-type GaAs
Authors: Huang C. I. , Li S. S.
Published: February 2004

The dependence of excess carrier lifetimes on the photoinjected carrier densities has been investigated for Cr-doped GaAs at 300 and 80°K, using photomagnetoelectric (PME) and photoconductive (PC) methods. The result shows three distinct injection ranges covering five orders of magnitude change in photoconductance. The lifetimes are constant at low and high injection ranges while showing injection dependence at intermediate injection range. A theory is given to explain the observed results.
Variable pulse-length electron beam CO2 laser
Authors: Marcus S. , Kleiman H. , O'Neil R. W. , Pettingill L. C.
Published: February 2004

A longitudinal electron beam was used to provide the preionization for a TEA-type CO2 laser. Single-line energy in excess of 10 J/liter at 10.6 μm can be obtained from this laser in approximately 2 μsec. This device may be simply converted to one previously reported which uses the electron beam to provide the total ionization required for laser excitation and emits 20–120-μsec pulses of comparable energy.
Kinetic effects in drilling with the CO2 laser
Authors: Duley W. W. , Young W. A.
Published: February 2004

The time evolution of holes drilled in fused quartz with a cw CO2 laser has been determined. It is shown that drilling proceeds by a complex balance between absorption and channeling of incident radiation. During drilling, the tip of the hole is often far removed from the optical axis and appears to propagate along a helical path on moving into the target.
Theory of optical-waveguide distributed lasers with nonuniform gain and coupling
Authors: Shubert Richard
Published: February 2004

Coupled-mode theory is applied to distributed feedback lasers having step variations in the longitudinal distributions of both the gain and the coupling. Threshold solutions for the required laser gain and the longitudinal mode spectra are presented for the modified geometries. Numerical computations show that these modifications on the uniform structures considered heretofore allow for optimization of the laser characteristics such as lowering the threshold gains and providing controllable higher-order-mode rejection, as well as unidirectional operation.
Domain walls in bubble films. III. Wall structure of stripe domains
Authors: Schlömann Ernst
Published: February 2004

The internal structure of domain walls in bubble films, their energy, and their velocity-momentum relationship are calculated for stripe domains of arbitrary period. The results are similar to those derived previously for films containing a single straight wall, provided that the film thickness is in the range preferred for device applications. For thicker films, however, the theoretically calculated properties of stripe-domain walls differ considerably from those derived on the assumption that only a single straight wall is present in the film.
Tunneling in lead-lead oxide-lead junctions
Authors: Basavaiah S. , Eldridge J. M. , Matisoo J.
Published: February 2004

A detailed investigation of tunneling in Pb/PbO/Pb junctions has been carried out, in an attempt to independently measure several of the parameters known to enter the tunneling problem. In particular, the thickness of the tunnel barrier (orthorhombic PbO thermally grown in situ in an ultraclean vacuum system) has been measured ellipsometrically, and barrier heights of 1.15 ± 0.15 eV at both metal-oxide interfaces have been deduced from Fowler-Nordheim plots and logarithmic conductivity measurements. The junctions are of high quality (less than 0.1% nontunneling currents) and cover a Josephson current density range of from 10−4 to 103A/cm2. From the dependence of the current density on the barrier thickness, an effective mass ratio, m*/m of 0.5 ± 0.1 has been deduced for electrons in the barrier. Comparison of experimental results with the tunneling theory shows that to obtain an agreement between them, image-force corrections must be neglected. Reasonable quantitative agreement has been obtained with a small correction of 4–5 Å to the ellipsometric thickness values in the range 19–31 Å; no other adjustments are found necessary. This discrepancy might be attributed to a difference between ellipsometric and tunneling thickness values.
Space charge in silver halides—Theory of surface charge and electrode charge
Authors: Macdonald J. Ross
Published: February 2004

It is suggested that the recent space-charge theory of Fatuzzo and Coppo omits consideration of several effects important in general space-charge situations and probably also important in these authors' experimental studies of silver halides. These effects are discussed in some depth and may explain, at least in part, why Fatuzzo and Coppo's theoretical analysis does not apply well to their experimental results. A detailed discussion is given of the diffusion potential and of surface and electrode charge in blocking and nonblocking electrode situations. Although a careful distinction between electrode and surface (absorbed) charge is usually made in the ideally polarized electrode (completely blocking) electrolyte case, the need for this necessary separation has apparently not been well recognized heretofore for situations where a solid material of interest is assumed to be contained between electrodes which are completely blocking for some or all types of mobile charge carriers in the solid. When this distinction is made for the problem considered by Fatuzzo and Coppo, quite different results than theirs are obtained. Three important improvements over the Fatuzzo-Coppo work are the present use of more appropriate general expressions for static and differential dielectric constants (or capacitances), the avoidance of their implicit assumption that surface charge is independent of total applied potential difference, and the avoidance of their assumption that the applied potential difference divides equally between the left and right crystal-electrode regions. The new analysis, appropriate for intrinsic materials with completely blocking electrodes, leads to expressions for the differential capacitance of such a system for a specific situation where surface charge may depend on the applied potential difference.
Amorphous structure heat: Molecular structure from solution heats of polymethylmethacrylate in orthodichlorobenzene
Authors: Raghava Ram S. , Filisko F. E.
Published: February 2004

The heats of solution in orthodichlorobenzene were measured as a function of temperature for both as-reprecipitated and quenched atactic polymethylmethacrylate. The as-reprecipitated curve decreases linearly with a slope of 0.096 cal/g°C from room temperature to 90°C, and above 110°C has a constant value of +1.5 cal/g. The quenched material data decreases linearly with a slope of 0.12 cal/g°C from room temperature to 55°C, jumps +2 cal/g at 55°C, and continues the linear decrease with a slope of 0.096 cal/g°C from 55 to 90°C. The data suggests that isotactic stereochemical impurities in the atactic material are able to crystallize at 55°C which is the Tg of i-PMMA, and therefore must be associated as i-PMMA islands in a rigid atactic-syndiotactic PMMA matrix. This also suggests that the β transition in PMMA may be associated with the isotactic impurities
A model for the Magill-Li viscosity-temperature relation
Authors: Breitling S. M. , Magill J. H.
Published: February 2004

A simple model has been developed to account for the viscosity-temperature dependence of liquids. It is predicated upon the valid assumption that the activation energy for flow is Arrhenius-like at sufficiently high temperatures, and that this activation energy varies inversely as the probability of finding sufficient local volume for transport at lower temperatures. The model yields a viscosity reducing equation very similar to the Magill-Li empirical equation for the zero shear viscosity η as the function of temperature T. The relation is ln(ηηs)=A(exp [B (x+φ−1)−1]x−exp(B/2 φ)1+φ),where A = 2.68, B = 0.432, φ = 0.238, x = T/Tg, ηS is the reference viscosity at the reference temperature Ts, and Tg is the glass temperature. This relation has been successful in reducing data for several viscous materials unto a single master curve which extends over about 16 orders of magnitude in viscosity and encompasses a broad temperature range extending from Tg to about 2.5Tg in some instances.
Towards a theory of viscosity for glass-forming liquids
Authors: Sanchez Isaac C.
Published: February 2004

A theoretical relationship has been obtained between viscosity and the PVT properties of a glass-forming liquid. First an equation of state is determined for the liquid by using a hole model of the liquid state. This equation of state is then combined in a unique way with the Cohen-Turnbull theory of self-diffusion and an important result from Brownian motion theory to obtain what is essentially an equation of state for viscosity. The principal results of the theory are as follow: (i) The change in the thermal expansion coefficient Δα that occurs at the glass transition temperature Tg can be predicted from the WLF C2 constant (T∞ ≡ Tg − C2), Tg Δα = 2(T∞/Tg) × [exp (1 + 2T∞/Tg)−1]−1. Except for the polyakylmethacrylates, good agreement is obtained between observed and theoretical Δα values for many polymers. (ii) A theoretical upper bound for Tg Δα has been found and is equal to 0.159. To within the experimental uncertainties in measured Δα values, there are no known violations of this bound. (iii) The hole energy Eh required to form a hole in a glass-forming liquid is equal to 2RT∞. (iv) A glass-forming liquid tends to an isofree volume state at T∞. The calculated hole fraction equals e−3 = 0.0498. (v) A correlation has been found between the hole energy and a viscosity parameter. This correlation is sensitive to the chemical structure of a polymer chain backbone. (vi) Both WLF constants, C1 and C2, can be predicted from the observed Δα and viscosity-temperature behavior. Excellent agreement has been obtained for polyvinyl acetate and a nonpolymeric glass-forming liquid, tri-α-naphtyhl benzene. (vii) Even though the theory is a free-volume theory, the temperature derivative of the viscosity at constant volume is nonzero when we identify T∞ with the second-order phase transition temperature of the Gibbs-DiMarzio theory.
Si-defect concentrations in heavily Si-doped GaAs: Changes induced by annealing
Authors: Kung J. K. , Spitzer W. G.
Published: February 2004

Previously reported annealing effects on the carrier density and free-carrier absorption are correlated with photoluminescence and localized vibrational mode infrared absorption measurements of annealed samples of heavily doped GaAs: Si. Annealing in the range 400≤TA≤750 °C produces the following qualitative changes: (i) a major reduction in the free-carrier concentration ne, (ii) an increase in the carrier absorption cross section, (iii) a reduction of the SiGa localized mode absorption band, and (iv) the introduction of a new photoluminescence band at 0.98 eV. A defect model is proposed which is consistent with the observed changes. There is a major reduction in [SiGa], the Si donor concentration, which is a function of the anneal temperature between 400 and 750 °C. The reduction is probably through the formation of (SiGa − VGa) pairs. There is little change if any in [SiAs] the Si acceptor concentration. When TA = 400°C the ne = [SiGa] −[SiAs]. When TA = 600 and 750°C, a new acceptor is formed having concentrations ≃3 to 4×1018 cm−3, in samples having [Si]≃4×1019 cm−3, and ne≠[SiGa] − [SiAs]. The new acceptor defect is a Si complex with an acceptor state ≃0.54 eV above the valence band. There is no evidence for SiGa → SiAs site transfer after annealing at any TA in the 400–750°C range. Annealing at 1100 °C removes all the lower-temperature annealing effects including the new acceptors and again ne =[SiGa] − [SiAs].
Implant dose profile dependence of electrical characteristics of ion-implanted MOS transistors
Authors: Kudoh Osamu , Nakamura Kunio , Kamoshida Mototaka
Published: February 2004

Ion-implanted MOS transistors were fabricated and their electrical characteristics, such as threshold voltage, effective mobility, etc., were measured. In the 11B+-implanted p-channel case, threshold voltage VT can be shifted linearly with implant dose. These shifts ΔVT were entirely determined by the net dose entering silicon. On the other hand, in the 11B+-implanted n-channel case, threshold voltage shift ΔVT varied sublinearly with dose and showed strong dose profile dependence. The profiles were varied with changing implantation energies and annealing times. These results can be interpreted in accordance with the rapid decrease of the maximum surface depletion layer Xd max with the implant dose increase. Numerical calculations of threshold voltage shifts accounting for nonuniformly implanted profiles were compared with observed results. Good agreement was obtained. Effective mobilities μeff of 11B+-implanted p - and n -channel MOS transistors also showed different dose dependences. In the low-dose region, effective mobilities of 11B+-implanted p -channel MOSFET remained almost unchanged, but those of the n -channel case decreased monotonically with dose increase. Qualitative arguments, taking into account surface scattering and impurity scattering effects, and rough calculations are presented.
Comments on ``Luminescence from electron-irradiated silicon''
Authors: Walker John
Published: February 2004

Zero-phonon transitions at 0.79 and 0.97 eV observed in electron-irradiated silicon have been ascribed by previous workers to the K center and the divacancy, respectively, on the basis of their production and annealing behavior. This paper shows that, contrary to the original interpretation, the uniaxial stress results on these lines indicate monoclinic symmetry, which is consistent with the proposed models. The stress results on a third zero-phonon line at 1.045 eV are reinterpreted.
Low-temperature frequency effect in nickel ferrous ferrites
Authors: Poplawsky R. P. , Duvvury C. , Michel R. E.
Published: February 2004

Low-temperature values of the magnetocrystalline anisotropy constant K1 for several nickel ferrous ferrites were measured using the torque method. These were compared to existing microwave K1 values for the same crystals. The incremental ΔK1=K1 (torque)-K1 (microwave) were found to increase to well-defined maxima below 77°K and then to decrease toward zero at 4.2°K. The temperature at which the maximum value of ΔK1 occurred increased with increasing Fe2+ concentration. The low-temperature maxima and subsequent sharp decreases in ΔK1 cannot be fit to earlier theory which was successful above 77°K. This indicates the loss mechanism responsible for ΔK1 at higher temperatures becomes inoperative at liquid-helium temperatures. The maximum value of ΔK1 is found to depend on the Ni2+ concentration as well as Fe2+ concentration. This suggests that the Ni2+ ions may also be involved in the relaxation mechanism responsible for ΔK1.
Magnetostatic wave propagation in double layers of magnetically anisotropic slabs
Authors: Ganguly A. K. , Vittoria C.
Published: February 2004

Magnetostatic wave propagations in parallel layers of magnetic slabs have been considered. The dispersion characteristics depend strongly on the separation between slabs and their respective crystal plane orientations. The frequency range for nondispersive magnetostatic wave propagation can be extended as compared to the range obtained from the single slab. Magnetic interactions between magnetostatic waves can be studied directly in this configuration.
Propagation along a dielectric-coated cylinder immersed in plasma
Authors: Basu J. , Maiti J. N.
Published: February 2004

The dispersion relation for propagation in the TM01 mode along a dielectric-coated perfectly conducting cylinder immersed in plasma is studied. The dispersion characteristics reveal some interesting and novel features for negative values of the dielectric constant of the plasma.
Room-temperature deep-state emission spectra, radiative efficiency, and lifetime of some GaP:Te,N crystals
Authors: Bachrach R. Z. , Dapkus P. D. , Lorimor O. G.
Published: February 2004

Photoluminescent spectral measurements are presented on a series of GaP:Te,N crystals with varying net donor concentration. The maximum near-bandedge emission internal quantum efficiency in these crystals had been shown to be 0.6% at 1017 cm−3 net donor concentration. We show that the radiative deep-state recombination component above 1.2 eV accounts for only 3% of the total recombination in the material with the highest green efficiency. Two infrared emission bands are observed in our Te- and S-doped LPE material at ∼1.2 and ∼1.6 eV. The relative and absolute strength of these two bands vary with both ND−NA and nitrogen concentration [N]. Simplified analysis of the saturation behavior of one of the infrared bands and the green emission showed that at low-excitation levels where this center is unsaturated, 42% of the total recombination was flowing through the responsible center. Thus the dominant recombination proceeds nonradiatively. However, at normal LED operation currents these centers should be saturated and thus responsible for only a small amount of the recombination.
Spin-flip Raman laser as a tunable infrared source
Authors: Ganley J. T. , Harrison F. B. , Leland W. T.
Published: February 2004

The output of a spin-flip Raman laser, pumped by a Q-switched CO2 laser, has been examined with a Fabry-Perot interferometer. It was found to consist of discrete lines, separated by the longitudinal-mode spacing of the spin-flip crystal. These lines do not move as the magnetic field is varied. As a result, the usefulness of a laser operated under these conditions as a spectroscopic tool is much reduced.
Electrical effects in laser-damaged phototransistors
Authors: Giuliani J. F. , Marquardt C. L.
Published: February 2004

Current-voltage behavior of the dark current and photocurrent, photocurrent frequency response, and light spot profiles have been measured for silicon phototransistors irradiated by short pulses from a neodymium glass laser above energy densities of 10 J/cm2. The principal bulk damage effects observed were the generation of an Ohmic dark current, the formation of localized conduction paths, and the narrowing of the base layer of the device. An empirical model was used to account for these results and was shown to be consistent with previous predictions based upon the migration of phosphorus across the detector by laser-induced melting and subsequent refreezing.
Surface roughness interpretation of ellipsometer measurements using the generalized Maxwell Garnett theory
Authors: Marton J. P. , Chan E. C.
Published: February 2004

The generalized Maxwell Garnett theory developed in the preceding paper is utilized here to specify the state of roughness of a surface. Both thick and thin metal samples are measured on the ellipsometer. In the interpretation, the surface roughness layer is replaced by a smooth but anisotropic medium whose optical behavior is assumed to be governed by the generalized Maxwell Garnett theory which specifies a roughness layer by two parameters d and q. Success of the interpretation is judged according to the degree of independence existing between the two parameters d and q and the angle of incidence. Experimental results on several metals indicate that in many cases the surface roughness and not an oxide layer is responsible for the variation of ellipsometer parameters ψ and Δ from that of a truly smooth bulk material surface.
Holographic interferograms of side-by-side exploding wires
Authors: Seftor J. Laurence
Published: February 2004

Holographic interferograms have been made of two aluminum wires exploding side by side in a vacuum environment. The resulting refractivity data demonstrates the relevant character of the event for a laser interaction experiment. In addition, lower bound values of specie density have been estimated.
Interference of electromagnetic waves in inhomogeneous dielectric media
Authors: Geiger F. E. , Kyle H. Lee
Published: February 2004

Calculations are made of the plane-wave reflection coefficient of a semi-infinite inhomogeneous lossy dielectric medium with dielectric constant ε(z)=ε′(0)(1 + az)−iε″(0)(1 + bz), a, b ≥0, ε′(0)/ε0≥1.0, ε″(0)/ε0≥0. The reflection coefficient decreases to a minimum as a function of the parameter b for a given a, despite the increasing absolute value of ε(z). This phenomenon is a direct confirmation of the interference of coherent scattering reflections in the inhomogeneous medium with constant gradient ∇ε(z). Solutions are discussed in terms of Hankel and Airy integral functions.
Domain-impurities interaction in KNbO3 single crystals
Authors: Mishra M. B. , Ingle S. G.
Published: February 2004

Impurity segregations and their interactions with domains and dislocations in KNbO3 single crystals have been studied. In the technique used, impurity structures in the bulk are first brought to the surface by removing layers of crystal without stress by methyl alcohol. The domain structure in the crystal remains completely undisturbed in this process. The dislocation pattern is then revealed by etch pits produced with an etchant such as a mixture of a concentrated solution of ammonium acetate in water and hydrogen peroxide (30% wt/vol) in the volume ratio 1 : 2. It has been found that impurity segregations interfere quite appreciably with domain formation. Segregations around arrays of edge dislocations form surprisingly straight lines parallel to pseudocubic 〈100〉 directions, appearing very similar to 60° domain lines under reflected light. Under these conditions, they prevent the formation of a 60° domain. Domain walls terminate at such lines, and may also be bent as a result of segregation-dislocation interactions, occupying crystallographically irregular positions. These and other observations are discussed, providing the necessary microscopic and interferometric evidence.
Optoacoustic testing of microsound devices
Authors: Bridoux E. , Rouvaen J. M. , Moriamez M. , Torguet R. , Hartemann P.
Published: February 2004

Acoustic surface wave (ASW) components have been tested by visualizing the acoustic field amplitude and phase distribution in real time in the 15–25-MHz frequency range. The properties of some useful devices are reported here.
Auger spectroscopy of silicones
Authors: Stupian Gary W.
Published: February 2004

Silicon LMM Auger spectra arising from a variety of silicon compounds, mostly silicones, have been studied. Silicones may be regarded, in a sense, as compounds intermediate between elemental silicon and silicon dioxide. The observed silicon Auger peak energies of silicones are found to lie between the Si (LMM) peak energies of Si and SiO2, and are correlated with the net electronic charge on silicon as estimated from a very simple model of charge transfer based on Pauling electronegativities.
Photovoltaic effects at the interface between amorphous selenium and organic polymers
Authors: Okumura Koji
Published: February 2004

Band bending in the surface layer of amorphous selenium induced by contact with an insulating organic polymer was detected by photoelectric signals generated at the interface under no external bias. The magnitudes and polarities of the signal varied among samples involving different polymers, and also among samples involving the same polymer with and without doping by an electropositive organic impurity. Details of this behavior, along with the observation that the polarity of the signal was reversed when the method of making the contact between selenium and polymer was altered, indicate that the preferred orientation of polymer molecules containing dipole moments on the selenium surface is the principal cause of the surface potential gradient in the selenium.
Physics of the MOS electron-beam memory
Authors: Cohen M. S. , Moore J. S.
Published: February 2004

The physics of a novel write-read random-access memory for a digital computer is described. The memory employs an electron beam for accessing the information for both the write and read operations, while the data storage medium, an MOS capacitor, forms the target of the electron-optical systems. Information is stored in the memory in the form of a pattern of positive charge in the oxide near the oxide-semiconductor interface; the presence of such charge is said to correspond to a binary ONE, while its absence corresponds to a binary ZERO. The positive charge can be introduced (written) or removed (erased) from this interface when the gate bias during irradiation by the beam is made positive or negative, respectively. These processes have been described previously by workers in the field of ``radiation damage'' of MOS devices; the status of present knowledge is reviewed, and the role in the writing and erasing processes of localized electron states in the oxide is discussed. While the information storage mechanisms are primarily properties of the oxide, the readout mechanisms are associated with the semiconductor. Positive charge in the oxide at a ONE causes inversion of the underlying surface of the p-type semiconductor; during readout, the lateral propagation of electrons in this inversion layer ensures the separation of electron-hole pairs which are generated by the read beam in the space-charge region, so that a large signal is externally detected. By these processes, which are inherent in the target, the signal current is greatly increased above the original beam current. On the other hand, in a ZERO these processes are suppressed because of poor inversion-layer conductivity, and the resulting signal is small. Equivalent circuits for the readout processes are discussed.
Shape correction by ion-beam milling with an interferometer
Authors: Yasuda Hiroshi
Published: February 2004

A shape-correction technique has been developed to flatten a waved surface by ion-beam milling with an interferometer. The local area on a silicon surface was selectively removed by bombardment of a 10-keV argon ion beam which was electrostatically scanned in a programmed manner. After using the shape-correction procedures several times, a flat surface was successfully produced under interferometrical observation during the milling operation.
Surface stress distribution due to a group of edge dislocations on an oblique glide plane
Authors: Taliaferro D. A. , Henry L. F. , Mitchell J. W.
Published: February 2004

The stress distributions at and near the surface due to a single edge dislocation and to a group of uniformly spaced edge dislocations on an oblique glide plane have been calculated. For the evaluation of the stress an Airy stress function, previously derived, was used after a change in sign of one of the terms. The shear stress at the surface develops an increasingly sharp maximum at the acute angle between the surface and the glide plane as the single dislocation or the leading dislocation of the array approaches the trace of the glide plane. This stress is superimposed additively on the applied stress. Over the region of the stress maximum the probability for the generation of dislocations with a Burgers vector of opposite sign on parallel glide planes is increased compared with that for their generation elsewhere at the same surface. This leads to a possible explanation of the frequent occurrence of clusters of activated glide planes in close-spaced pairs.
Breakdown phenomena in high-speed dislocations
Authors: Earmme Y. Y. , Weiner J. H.
Published: February 2004

An analytical solution is presented for the atomic displacements in the steady motion of a dislocation in a modified Frenkel-Kontorova model of the form treated previously by Atkinson and Cabrera. It is found that at a critical dislocation velocity, here termed the breakdown velocity, ν B, the regular dislocation motion postulated a priori breaks down, so that the analytical solution is not valid for dislocation velocities ν ≥ ν B. Furthermore, ν B is less than the corresponding macroscopic sound velocity for this model. The results of computer-simulation studies of the behavior of the model at stress levels greater than those which cause dislocation breakdown are also presented.
Identity and interactions of ions from relay break arcs
Authors: Gray E. W. , McKnight L. G. , Sawina J. M.
Published: February 2004

The ion chemistry of the ions derived from wire spring relays has been found to be dominated by the presence of diethylphthalate (DEP), C12H14O4, derived from the cellulose acetate around the relay coil. Under our experimental conditions, using 0.5-A resistive break arcs in air and in pure gases at a pressure of about 1 Torr, the positive ion current extracted from the arc was found to consist almost exclusively of this compound and its derivatives; with both air and contact metal ions present as minority species if at all. This indicates that the characteristics of DEP are such that charge-exchange and clustering mechanisms operate to selectively transfer the charge to the organic material. Minute amounts (< 10−5 Torr) of DEP will accomplish this transformation in less than 1 msec. DEP has been found to activate relay contacts when present in air in part per million quantities. There are indications that the reactions of diethylphthalate are not unique and that other organic materials will similarly affect the ion species derived from the relay arc.
Theoretical and experimental study of the effect of the sheath on an antenna immersed in a warm isotropic plasma
Authors: Meyer P. , Vernet N. , Lassudrie-Duchesne P.
Published: February 2004

A new approach to the problem of electromagnetic wave propagation through a vacuum-plasma interface is formulated and used to solve two simple antenna problems. First, the impedance of a spherical body covered by a vacuum sheath and immersed in a plasma is calculated. The result is found to coincide with the empirical formula commonly used so far. Second, a cylindrical antenna also isolated from the plasma by a sheath is studied. The antenna can support guided modes whose dispersion relation is derived. An experiment has been performed in order to verify this dispersion relation. Experimental results are found to be in favor of the present approach.
Steady-state recombination in semiconductors containing two or more trapping levels
Authors: Curtis O. L. , Srour J. R.
Published: February 2004

This paper presents an analysis of lifetime versus excess density or photoconductivity versus excitation intensity for a semiconductor when two or more trapping levels are present. As an example, data for a p-type (boron-doped vacuum-float-zone grown) silicon sample which had been irradiated with Co60 γ rays are considered. Measurements covered seven orders of magnitude in photoconductivity, and the lowest excess electron concentration was ∼ 10−8 times the equilibrium hole concentration. Two trap levels were identified at Ec−(0.56±0.01) eV and Ec−(0.71±0.02) eV. Introduction rates for these levels were ∼ 10−6 and ∼ 10−8 (photon cm)−1, respectively.
Optical spectra and relaxation of Cr3+ ions in YAlO3
Authors: Weber M.J. , Varitimos T.E.
Published: February 2004

Optical absorption and emission spectra of Cr3+ ions in YAlO3 have been investigated at 300 and 77°K. In the cubic field approximation, the spectra can be fitted by the parameters Dq = 1800 cm−1, B = 590 cm−1, C = 2980 cm−1. An intense vibronic spectrum is associated with 2E → 4A2 fluorescence transitions. Measurements of absorption cross sections and oscillator strengths, thermal broadening and shifts of the R-line fluorescence, and lifetimes of the 2E fluorescence and Cr3+-Cr3+ pair lines are reported. At low temperatures and chromium concentrations, the radiative quantum efficiency of the 2E state is approximately unity. Other relaxation processes become important at temperatures > 400°K. The possibility of observing stimulated emission from YAlO3:Cr3+ is discussed.
ac loss in a twisted filamentary superconducting wire. II
Authors: Carr W. J.
Published: February 2004

Hysteresis losses in a twisted filamentary superconducting wire are calculated for various cases corresponding to complete penetration of the magnetic field into the wire, shielding of the field by the supercurrents, and shielding due to eddy currents. In general, the wire may be divided into two regions; an outer saturated layer which tends to behave at the higher frequencies like a solid superconductor and the interior where the average parallel electric field vanishes and the wire behaves like a collection of individual filaments.
Magnetic bubble mobility in epitaxial Sm0.4Y2.6Ga1.2Fe3.8O12 films
Authors: Vella-Coleiro G. P. , Hagedorn F. B. , Chen Y. S. , Hewitt B. S. , Blank S. L. , Zappulla R.
Published: February 2004

Extensive measurements of magnetic bubble mobility in epitaxial Sm0.4Y2.6Ga1.2Fe3.8O12 films have shown that is is possible to obtain a uniformity of better than ± 15% over a 1.1 × 1.1-cm area and an average mobility of 270 cm/sec Oe. This uniformity was obtained in films which were grown under carefully controlled conditions, whereas a variation in the mobility from 170 to 510 cm/sec Oe was observed in other films where the growth parameters were not as carefully controlled. The possibility that the growth rate and growth temperature might influence the mobility was investigated, but no correlation was observed. However, annealing at 1200°C was found to have a beneficial effect on the mobility when the mobility was abnormally low in the as-grown state. The mobility was also observed to increase by a factor of ∼ 2 over the temperature range 25–80°C, and proton implantation at a dosage sufficient to suppress hard bubbles did not materially affect the mobility. The value of the damping parameter obtained from measurements of wall mobility was found to be in good agreement with the value obtained from measurements of the microwave resonance linewidth.
Comments on ``Dependence of barrier height of metal-semiconductor contact (Au–GaAs) on thickness of semiconductor surface layer''
Authors: Wei C. H. , Yee S. S.
Published: February 2004

Experimental results on the dependence of the Au–GaAs barrier height on the thickness d of the oxide film reported by Pruniaux and Adams indicate that ΦB=Φi+Ad. This communication shows that neglecting the effect of surface states in the Cowley-Sze model predicts a linear decrease of barrier height with increasing oxide thickness. The observed increase of barrier height with increasing oxide thickness may be partly due to surface states at the oxide-semiconductor interface. A model that includes the effects of surface states and of screening on the metal side is proposed to explain the various values for Φi.
Defect centers in oxygen-deficient rf-sputtered SiO2 films. I. Electron spin resonance
Authors: Hickmott T. W.
Published: February 2004

Two new defect centers have been observed by electron spin resonance (ESR) in rf-sputtered SiO2 films with low metallic impurity content. At 77°K, as-sputtered films have three ESR centers, two HX centers, and an HY center. The HY center, a hole center, has g = 2.008–2.009. The HX center has two components, the HXa center with axial symmetry and with ga∥ = 2.022 and ga⊥ = 2.037; the HXb center with gb = 1.984 which is split by hyperfine interaction with hydrogen. The hydrogen hyperfine interaction has axial symmetry, Ab∥ = 30.2 G and Ab⊥ = 63.6 G. Both the HX and HY centers show hyperfine splitting due to interaction with Si29. Annealing of as-sputtered films in hydrogen-containing atmospheres at 350°C eliminates the HY center, leaving the HX center. Annealing in N2 or O2 at 550°C also eliminates the HY center; the resulting HX resonance is identical to that obtained after hydrogen anneal. The activation energy for the appearance of the HX center is 0.036 eV when samples are cooled to 77°K. From similarities in hyperfine interactions, activation energies, and g values, it is suggested that the HY center is the silicon analog of the Al center in SiO2. It occurs in oxygen-deficient SiO2 and is due to removal of a nonbonding electron from an oxygen which bonds Si+3 to Si+4. The HY center is converted to the HX center by bonding with hydrogen which can be provided by H2 from the annealing ambient or by the H atom in Si–OH incorporated in SiO2 films.
Flat guidance schemes for magnetically levitated high-speed guided ground transport
Authors: Atherton David L. , Eastham A. R.
Published: February 2004

A magnetically levitated high-speed vehicle requires a noncontact guidance system. Guideway configurations are discussed, and the possibility of achieving guidance from a flat surface is investigated. A vehicle with electrodynamic suspension and linear synchronous motor propulsion carries superconducting magnets which may be used for guidance purposes. Eight possible ``flat'' guidance mechanisms are examined. It is shown that the interaction between vehicle-borne magnets and levitation strips or linear synchronous motor (LSM) windings cannot provide adequate restoring forces. Additional conductors are therefore required for guidance. The use of either vertically mounted rectangular loops or horizontally mounted null-flux (NF) loops under either the levitation magnets or propulsion magnets is therefore examined. The most promising system involves the interaction between propulsion magnets and horizontal NF loops, with the interaction between propulsion magnets and the edges of the levitation strips providing backup guidance. The guidance characteristics are analyzed and checked by model impedance measurements, and it is shown that, for this system a lateral stiffness of 106 N/m can be achieved.
On the inverse formulation of the problem of brittle fracture statistics
Authors: Rao C. V. S. Kameswara
Published: February 2004

A new formulation of the problem of brittle fracture statistics is presented. It is shown that it is possible to devise a mathematical approach by which a strength distribution function corresponding to a given form of a size-mean-strength relationship can be obtained rather than by fitting test data to an a priori assumed form of strength distribution function. The problem in effect is shown to reduce to the solution of a nonlinear integral equation, and a method of its solution is presented. To illustrate the feasibility of the method, the well-known distribution function due to Weibull is derived.
Generation of thickness-twist modes in a piezoceramic plate
Authors: de Jong G.
Published: February 2004

In the present paper we investigate theoretically the generation of thickness-twist modes in a plate of piezoceramic material. The poling axis is chosen parallel to the plane boundaries of the plate. On one of the faces of the plate a finite number of cylindrical strip electrodes of vanishing thickness is present. If an electric generator is connected to the electrodes, piezoelectric thickness-twist modes are generated. Our problem is to calculate the amplitudes of the different modes and the input impedance of the transducer. To this aim we employ our integral equation formulation of piezoelectric diffraction problems that has been presented in an earlier paper. Once the resulting system of integral equations has been solved, the field distribution on the electrodes is obtained. Then the input impedance of the transducer can be calculated, and with the aid of appropriate integral representations the amplitudes of the different modes are obtained.
Wavefront visualization of bulk acoustic waves
Authors: Torguet R. , Carles C. , Rouvaen J. M. , Bridoux E. , Moriamez M.
Published: February 2004

Bulk acoustic waves at frequencies up to several hundred megahertz and acoustic powers down to the nanowatt range have been visualized via acousto-optic Bragg diffraction. Using double-optical and electrical-heterodyne mixing, the acoustic wavefronts have been displayed over several wavelengths along the propagation path. Possible applications of the reported experiments are briefly reviewed.
Differential thermal analysis of ferroelectric and ferroelastic transitions in barium sodium niobate
Authors: Toledano J. C. , Pateau L.
Published: February 2004

Differential thermal analysis has been performed on barium sodium niobate single crystals. A thermal effect is detected for the first time at the 260°C ferroelastic transition. A large thermal peak is also observed at the 570°C Curie point. For both transitions an estimate of the latent heat is obtained by comparison with thermal effects recorded in gadolinium molybdate and quartz single crystals. The results for the first-order 570°C transition is in good agreement with existing dielectric data. First order is also assigned to the lower ferroelastic transition whose features are discussed in the framework of the available thermodynamic theory.
Action of an electrostatic field on photoelectric effect of thin films of iron
Authors: Garron Roger , Gaudart Louis , Testard Denise
Published: February 2004

We have studied the effects of a constant external electrostatic field on the photoemissive characteristics of thin films of iron. The thin films were obtained by thermal evaporation and condensation on a silica substrate. Thickness was between 0.5 and 110 nm. The direction of the field is perpendicular to the surface of the film; its intensity varies by a few V m−1 at 510 000 V m−1. With all the films, the greater the field is, the lower the work function is. The value of this lowering depends on the thickness and structure of the film. It is maximum in absolute value and equal to about 0.07 eV for a thickness of about 2 nm. When the field varies, the photoionization coefficient remains constant within measurement precision for the same film. A possible interpretation, based on the variations of the electrostatic double layer on the surface, is suggested.
Electron effective mass and conduction-band effective density of states in Bi12SiO20
Authors: Lauer R. B.
Published: February 2004

The photocurrent kinetic response and the photocurrent spectral response at 300 K are reported for Bi12SiO20 in the optical range 1.0–2.0 eV. In this range trap occupancy dominates the response. The kinetic response of the transient-trap-filled photocurrent provides values of the electron trap density and the optical absorption coefficient for the photoionization of the electron trap. The optical ionization energies of the traps are provided from the trap-filled spectral response. Combining these quantities with previously determined thermal ionization energies of the electron traps provides a value for the electron effective mass of m*=14 m and a value for the effective density of states in the conduction band of Nc=1×1017T3/2. Using this value for the effective mass, an optical absorption coefficient for the photoionization process is calculated, and found to be in good agreement with the experimentally observed value.
Superconducting microwave cavities and Josephson junctions
Authors: Smith Todd I.
Published: February 2004

The possibility of using very-high-Q superconducting microwave cavities to obtain a strong coupling between the electromagnetic field and a Josephson junction has prompted a study of such systems. Expressions have been obtained describing the dc I-V characteristic of a junction biased so that the Josephson radiation frequency is near a resonance of the cavity in which it is located. The rf power coupled into an X-band (10 GHz) TE011 mode cavity from a weakly coupled junction is approximately 3×10−13 I02 Q W, where I0 is the critical current of the junction and Q is the cavity Q. When the coupling between the junction and cavity is large enough, the I-V characteristic becomes multiple valued and the power coupled to the cavity depends on the state of the system. The maximum power which can be coupled to the cavity is approximately 0.58I0Vdc, where Vdc is the voltage required to bias the junction to the resonant frequency of the cavity.
Representation of random noise by random pulses
Authors: Bell T. H.
Published: February 2004

The problem of modeling random noise by a sequence of random pulses that result from the random occurrence of similar events of randomly varying duration and strength is considered. It is illustrated how the statistical properties of the distribution of noise-producing events may be inferred from a knowledge of the power spectrum of the noise and the characteristic shape of the pulses.
X-ray microscopy of single-crystal potassium dideuterium phosphate
Authors: Farabaugh E. N.
Published: February 2004

Examination of solution-grown KD*P single crystals by the Lang technique has shown that the crystals are free from growth veils, impurity segregation, and subgrain boundaries. The density of dislocations varies throughout the volume of the crystals, some areas being nearly dislocation free. One Burgers vector identified as being parallel to 〈100〉 is common to the similar KDP and ADP single crystals.