bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetization distribution in an ideally soft sphere
Authors: Aharoni Amikam
Published: February 2003

The magnetization in a perfect, small ferromagnetic sphere with no anisotropy is calculated for a modified Ritz model that allows a central, spherical domain to remain completely saturated. Such a domain is found to be formed at a magnetic field which is about 1/2 of that which is required to saturate the sphere, but it causes only a small change in the total energy, and in the average magnetization. The latter is, thus, still saturating well below the rigorous nucleation field.
Variational approach to analysis of propagation of magnetostatic waves in highly inhomogeneously magnetized media
Authors: Sawado E. , Chang N. S.
Published: February 2003

Effects of highly inhomogeneously magnetized ferrite on propagative characteristics of magnetostatic waves are analyzed by the variational method. Dispersion characteristics and energy trap phenomena of magnetostatic waves in a ferrite slab are given in the microwave frequency region. Representative calculated curves show that, for the extermely high nonuniformity of the saturation magnetization distribution, the dispersion shows a backward nature. In connection with the calculation of the dispersion relation, power flow density of magnetostatic waves is obtained for several branch lines of the dispersion, which demonstrate the energy concentration phenomena in a highly inhomogeneously magnetized ferrite slab. The boundary conditions over ferrite surfaces of discontinuity are also discussed.
Crystallization and magnetic properties of amorphous Fe-Sn-B-Si alloys
Authors: Dunlap R. A. , Stroink G.
Published: February 2003

Amorphous alloys of the form Fe79SnB20−xSix (x=0,2,5,9,12) were prepared by quenching from the melt. The crystallization was characterized by differential thermal analysis (DTA) measurements. Alloys with x=0 and x=2 show single DTA peaks at 450°and 475 °C, respectively. Alloys with x≥5 show two DTA peaks corresponding to the crystallization of Fe–Si phases at a lower temperature and Fe–B phases at a higher temperature. Magnetization measurements yield magnetic moments on the Fe ions which increase from 1.87μB in Fe79SnB20 to 1.97μB in Fe79SnB8Si12. Mössbauer effect measurements give values of the Fe and Sn hyperfine fields of approximately 285 k and +29 kOe, respectively, which are essentially independent of x. The width of the field distribution for both sites is found to remain nearly constant across the series as well.
Tunneling of domain walls in ferromagnetic materials
Authors: Riehemann Werner , Nembach Eckhard
Published: February 2003

For picture-frame-type specimens of various ferromagnetic alloys, the dependence of the domain wall velocity v on the external magnetic field H and on temperature T has been experimentally investigated. T ranged from 1.4 to 5 K and v from 1 to 106 μm/s. For four alloys, v varied exponentially with H and T. A model has been developed which describes the function v(H,T) found experimentally. The basic assumptions of this model are: (i) v is governed by the interaction of the domain wall with small obstacles present in the specimen. (ii) These obstacles can be overcome by a combination of two processes: thermal activation and tunneling. The experimental data are in excellent agreement with this model. Below 2.0 K, v is nearly exclusively governed by tunneling. The obstacles, which pin the domain walls, are probably small clusters of atoms.
Electrical properties of n-amorphous/p-crystalline silicon heterojunctions
Authors: Matsuura Hideharu , Okuno Tetsuhiro , Okushi Hideyo , Tanaka Kazunobu
Published: February 2003

We have measured C-V characteristics and temperature dependence of J-V characteristics of undoped hydrogenated amorphous silicon (a-Si:H) heterojunctions formed on p-type crystalline silicon ( p c-Si) substrates with different resistivities. It has been found that an abrupt heterojunction model is valid for a-Si:H/p c-Si heterojunctions, and the electron affinity of a-Si:H has been estimated as 3.93±0.07 eV from C-V characteristics. The forward current of all the junctions studied shows voltage and temperature dependence expressed as exp(−ΔEa f/kT) exp(AV), where ΔEa f and A are constants independent of voltage and temperature, being successfully explained by a multitunneling capture-emission model. The reverse current is proportional to exp(−ΔEar/kT)(VD−V)1/2, where VD is the diffusion voltage and ΔEar is a constant. This current is probably limited by generation-recombination process.
Numerical and analytical studies of mutual locking of Josephson tunnel junctions
Authors: Lee G. S. , Schwarz S. E.
Published: February 2003

Mutual locking of Josephson tunnel junctions in a simple resistive circuit has been studied numerically. Locking is found to exist over voltage ranges of considerable size, on the order of 20%–30%. The voltage–locking range depends on random parameter variations; however, it increases as the number of junctions N increases, nearly becoming constant for large N. Available output power is expected to be proportional to frequency and to the number of junctions. New locking effects are described, the most unusual of which is a sequence of period-doubling bifurcations leading to a chaotic state in which the junctions’ phases vary aperiodically, while their time-averaged voltages remain equal. The effect of noise is considered, as well as operation at frequencies of the order of the gap frequency.
The polar magneto-optical Kerr effect and the dielectric tensor elements of CoFe2−xAlxO4 0.1≤x≤1 in the photon energy range 0.65≤hν≤4.5 eV
Authors: Martens J. W. D. , Peeters W. L. , Nederpel P. Q. J. , Erman M.
Published: February 2003

The polar magneto-optical Kerr rotation and ellipticity have been determined for ceramic CoFe2−xA1xO4 samples (0.1≤x≤1.0) in the photon energy range 0.65≤hν≤4.5 eV. In the same energy range spectroscopic ellipsometry has been used to determine the optical properties. The results have been combined in the calculation of the complete dielectric tensor. Two diamagnetic crystal field transitions of Co2+ (Td) at 0.8 and 2.0 eV have been identified as well as a broad paramagnetic transition also at ∼2.0 eV. This last transition is assigned to a Co2+→Fe3+ charge transfer transition on octahedral lattice sites.
Excimer laser annealing of ion-implanted silicon
Authors: Narayan J. , Holland O. W. , White C. W. , Young R. T.
Published: February 2003

We have studied pulsed excimer laser (xenon chloride, wavelength 0.308 μm) annealing of boron, arsenic, and self-ion-implanted silicon specimens that contained dislocation loops and/or amorphous layers. Microstructural changes as a function of laser parameters were investigated by cross-section transmission electron microscopy and concomitant changes in dopant profiles were monitored by Rutherford backscattering spectroscopy. The depth of the annealed or melted regions was found to increase linearly with pulse energy density and inversely with pulse duration. While dopant redistribution can provide information on total melt-life time and depth of melting, a gross underestimate of depth of melting in amorphous layers may be obtained, particularly near the threshold, if the dopant redistribution is less than 100 Å. We found that transmission electron microscopy techniques were more reliable for accurate determination of melt depths. A minimum thickness of defect-free annealed or melted region of 400 Å was achieved in the case of boron-implanted specimens. A maximum depth of melting up to 1 μ in these specimens could be achieved by 2.5 J cm−2 (25 ns) pulses. The quality of excimer laser annealing in terms of residual point defects and spatial inhomogeneity was found to be better than that achieved by pulsed ruby laser annealing.
Potential improvement of polysilicon solar cells by grain boundary and intragrain diffusion of aluminum
Authors: Sundaresan R. , Burk D. E. , Fossum J. G.
Published: February 2003

Experimental results are presented that imply potential improvements afforded by aluminum diffusion in both bulk and thin-film polysilicon solar cells. For bulk cells, a high-temperature aluminum diffusion (alloying) is shown to increase the minority-carrier diffusion length by gettering intragrain impurities. The role of the grain boundaries in this process and the influence of a light bias on the carrier lifetime are discussed. For thin-film cells, a low-temperature aluminum diffusion is shown to substantially passivate grain boundaries and hence decrease the recombination velocity. The decrease is evaluated using electron-beam-induced-current (EBIC) measurements interpreted via numerical analysis of the underlying carrier-transport problem. The actual benefit of the grain-boundary passivation to the open-circuit voltage of a thin-film cell is discussed.
Fundamental noise limits of thermal detectors
Authors: Garn Lynn E.
Published: February 2003

This paper examines the fundamental noise limit in arrays of uncooled thermal detectors which must change temperature to produce signals. This limit is shown to be the statistical fluctuations of the temperature of the detectors (temperature noise). The noise spectrum associated with these temperature fluctuations is derived. The spectrum’s strong dependence on thermal coupling between the detectors and their environment is also shown. This spectrum explicitly accounts for lateral heat conduction which occurs when detectors in the array are thermally coupled to each other. The detectivity is also derived which is shown to depend strongly on the spatial frequency of the signal being detected. In the ideal limit when the thermal coupling is radiation only, the detectivity of these thermal detectors is shown to be D*=1.8×1010 cm Hz1/2 W−1. This closely approaches the maximum D* of a cooled photoconductive detector when its limiting noise is also the noise in the photons from 300 K background radiation. Using the autocorrelation function in both space and time, an expression is derived for the mean square noise-induced temperature change that occurs during the time interval between two samplings of signal and noise. Finally, it is shown that the signal-to-noise ratio, as derived in this paper, may be a better measure of thermal detector performance than the often-used detectivity.
Development of an atom buncher
Authors: Hurst G. S. , Payne M. G. , Phillips R. C. , Dabbs J. W. T. , Lehmann B. E.
Published: February 2003

An ‘‘atom buncher’’ for controlling the concentration of gaseous samples has been conceptualized, evaluated theoretically, fabricated, and tested with excellent results. In effect, the atom buncher greatly increases the probability that a free atom will be in a small detector volume at a desired time. This was accomplished by using cryogenic techniques to condense atoms on a small spot and a pulsed laser to momentarily heat the spot to release the atoms at the desired time. Our work on noble gas atom counting by using resonance ionization spectroscopy is discussed as one example of the applications of the atom buncher.
Resonant helically distorted relativistic electron beam equilibria for free electron laser applications
Authors: Johnston George L. , Davidson Ronald C.
Published: February 2003

This paper extends the development of a self-consistent kinetic description of helically distorted relativistic electron beam equilibria for free electron laser applications to include particular conditions of beam propagation, not treated heretofore, which are of considerable practical interest. Radially confined equilibria are considered for a helically distorted electron beam propagating in the combined transverse wiggler and uniform axial guide fields described by B0=B0êz +δB=B0êz−δB cos k0z êx −δB sin k0zêy, where B0=const., δB=const., and λ0=2π/k0=const. is the axial wavelength of the wiggler field. It is assumed that the beam density and current are sufficiently small that the equilibrium self fields can be neglected in comparison with B0. In this context, it is found that there are three useful (and exact) invariants (C⊥, Ch, Cz) associated with single-particle motion in the equilibrium field B0êz +δB. These invariants are used to construct radially confined Vlasov equilibria F0b (C⊥, Ch, Cz) for an intense relativistic electron beam propagating in the z direction. Examples of both solid and hollow beam equilibria are considered, and it is shown that the transverse wiggler field can have a large modulational influence on the beam envelope, depending on the size of δB/B0 and other parameters. In the present work, no a priori assumption is made that the gyrofrequency (ωc=eB0/γbmc) of electron motion in the guide field and the frequency of axial electron motion (ω0=k0Vb) in the wiggler field are well separated. Thus the condition of beam-cyclotron resonance with ω0≂ωc can be treated. Numerical procedures for the determination of boundaries of both solid and hollow beam equilibria are developed, and calculations of solid and hollow beam boundaries at resonance are presented.
Chemical modification of near-surface charge trapping in polymers
Authors: Haridoss S. , Perlman M. M.
Published: February 2003

The surfaces of three polyolefin films, low-density polyethylene, high-density polyethylene, and polypropylene, were chemically modified by etching with permanganic acid, and low-density polyethylene by etching with chromic acid and by staining with chlorosulphonic acid. Polytetrafluoroethylene (Teflon) was treated with a sodium naphthalene complex in glycol ether. The surfaces were examined with a scanning electron microscope, and chemical groups identified by attenuated total reflectance infrared measurements. The surfaces were then corona charged, and the charge stability and trap distributions determined by the methods of thermally stimulated charge decay and thermally stimulated current, respectively. Scanning electron micrographs revealed a nodular surface structure in polyolefins etched with permanganic acid, a rough surface without nodules in low-density polyethylene etched with chromic acid, isolated corroded surface spots in low-density polyethylene stained with chlorosulphonic acid, and a web-like surface in etched Teflon. Permanganic acid removed amorphous and defective regions of the polymer surfaces, exposing more crystalline regions and crystalline-amorphous boundaries, both of which provided trapping sites, producing better charge storers than the virgin equivalents. Lifetimes, and hence usable temperatures in device application, were increased for both negative and positive charge. The other acids reduced the lifetimes in low-density polyethylene. Etching made Teflon as good a positive charge storer as the virgin negatively charged material, a result important to practical applications. While attenuated total reflectance measurements showed the presence of various chemical groups, charge stability seemed to depend more on surface morphology than on which active groups were added to the polymers by the etchants and staining agent.
Deformation-induced work function changes in Cu single crystals. II. Theory
Authors: Chow Robert , Tiller William A.
Published: February 2003

The jellium model of work function change with elastic deformation has been compared to the cellular and electronegativity models and was found to give the best fit to the experimental data. A point and patch effect model has been developed to account for the work function change with plastic deformation. The single slip variant of the model provides a better fit to the experimental data than the equal cross slip variant of the model.
Temperature dependence of 1/f noise in thin bismuth films
Authors: Bisschop J. , de Kuijper A. H.
Published: February 2003

We have measured the 1/f noise in thin bismuth films in the temperature range of 80–300 K. The experimental results are described in terms of mobility fluctuations. The influence of several scattering mechanisms on the noise is discussed.
Optically pumped GaSb/Al0.6Ga0.4Sb multiquantum well lasers operating in the λ=1.5–1.6 μm region
Authors: Temkin H. , Tsang W. T.
Published: February 2003

Multiquantum well structures of GaSb/Al0.6Ga0.4Sb were grown by molecular beam epitaxy and their spontaneous and stimulated emission properties were studied. The luminescence spectra exhibited high efficiency with the upward energy shift from λ=1.72  μm of GaSb up to λ=1.31  μm for the well width of ∼40 Å. Optically induced lasing has been obtained at the wavelength as short as λ=1.207  μm at 80 K and in the spectral region of λ=1.5–1.6  μm at temperatures as high as 80 °C. The optical thresholds of the quantum well lasers are similar to that of the more conventional GaSb/AlGaSb heterostructures.
Magneto-optic observation of Bloch lines
Authors: Argyle B. E. , Terrenzio E.
Published: February 2003

We report the first visual observation of Bloch lines in thin garnet films without the perturbing influence of magnetic particles in suspension (Bitter solution). A second-order magneto-optic effect reveals the Bloch line position and the signs and positions of the domain wall segments lying adjacent to it. The present study is limited to Neel walls that separate in-plane domains aligned along [110] ‘‘easy’’ magnetic axes in a (100) garnet film 0.8 μm thick with large in-plane uniaxial anisotropy (Ku≪0). Images are viewed using normally incident laser illumination and crossed polarizers in a polarizing microscope also having an adjustable optical phase compensator. The contrast image for 180° walls with incident light vector E∥ polarized parallel to the wall is an adjacent pair of dark and light stripes. The usual first-order Faraday effect (magnetic circular birefringence) is excluded because all components of M are perpendicular to the beam. The quadratic dependence on M is verified, outside the wall at least, in domain contrast studies, e.g., by the lack of contrast between two opposing 180° domains. Within the wall magnetic linear birefringence would cause incident light E∥ to emerge as right- or left-handed elliptically polarized light according to the quadrants of the orientation of M wall in the E∥−E⊥ plane. Thus, the observed ordering of black/white or white/black stripes in the image reflects the sign of twist in M wall when the transmitted light is viewed through a compensator and analyser. The Bloch-line position is delineated by a discontinuous reversal in the black/white ordering.
Dependence on drive fields of bubbles wall state conversion
Authors: Arnaud L. , Jouve H.
Published: February 2003

Investigation is presented on dynamic conversion of magnetic bubbles in a (Y Gd Yb)3 (Fe Ga Mn)5 O12 epitaxial film. This material is characterized by small bubbles (∼1.5 μm), small Q factor (∼2.7) and a rather high wall mobility μω=1500 cm s−1 Oe−1. S=0 bubbles transform into S=+1.5 bubbles when they are displaced by sufficient drive fields in a gradient propagation experiment. A linear law is found for the drive field dependence versus the reciprocal of drive field duration needed for conversion. Experimental results are interpreted by using a model where a horizontal Bloch line stacking phenomenon occurs before state conversion.
Magnetic and Mössbauer study of metal-zeolite interaction in catalysts
Authors: Pannaparayil Thomas , Oskooie-Tabrizi M. , Lo C. , Mulay L. N. , Melson G. A. , Rao V. U. S.
Published: February 2003

Molecular sieve aluminosilicates, such as ZSM-5 and mordenite, when impregnated with highly dispersed Fe, yield catalysts for the selective conversion of coal-derived syngas (CO+H2) to liquid hydrocarbon fuels. Fe performs the primary Fischer-Tropsch (FT) syngas to yield light olefins which are converted by the acidic (H+) and shape-selective function of the zeolite to high octane gasoline components. The physical aspects of the Fe-mordenite interaction studied by magnetic measurements, Mössbauer, and IR spectroscopy are reported and correlations with the catalytic properties are drawn. Mordenite samples with [SiO2/Al2O3] ratio in the range 12 – 60 were impregnated with 15 wt. % Fe using Fe3(CO)12; decarbonylation yielded superparamagmetic dispersions of γ-Fe2O3, in the range 1.4–5.0 nm; the smallest particles were obtained for a ratio=17. Hydrogen chemisorption also revealed a similar trend in Fe dispersions. No samples, other than the one with a ratio=60 and containing the largest particles could be carbided under usual conditions. The acidity of the mordenite and the aromatics fraction in liquid hydrocarbons from syngas conversion also showed maxima at a ratio=17. The presence of a strong metal-support interaction between Fe and mordenite was thus influenced by the varying ratios in the mordenite in a manner that paralleled the acidity and catalytic activity.
Effects of magnetic fields and flow applied to single electrodes on electrolytic cell potentials
Authors: Dash J. , Takeo M.
Published: February 2003

The effects of a uniform magnetic field applied to one of the electrodes in a flow cell were investigated. It was found that the cell potential is either increased or decreased, depending on the relative orientations of the magnetic field, the electric field, and the flow. The change of the cell potential is directly proportional to the magnetic field strength and the flow velocity. The proportionality constant, however, depends on the relative orientation of the fields, contrary to expectation from magnetohydrodynamic theory on laminar flow. The orientation dependence is explained in terms of a turbulent boundary layer. The conductivity of this boundary layer is calculated.
The effect of magnetic fields applied during aqueous electrolysis on circulation and on electrode processes
Authors: Cousins C. A. , Dash J. , Gorg C.
Published: February 2003

The effects of a magnetic field on electrolyte motion and on the gases produced during electrolysis of water were recorded on motion picture film. Measurements of the volume of hydrogen gas collected showed that a magnetic field reduced the amount collected during electrolysis of water and to a greater extent during chromium plating. A magnetic field also produced significant effects on the compactness of chromium deposits.
Ferromagnetic fluid applications in some rotating electrical equipment (abstract)
Authors: Farkas J.
Published: February 2003

The incorporation of ferromagnetic fluid (FMF) in the air gaps of electrical current generators to reduce the losses by using a higher than air permeability medium was tested in the laboratory. The investigation was performed by using a highly instrumented and modified alternator through which FMF of saturation magnetization ranging from 0.01–0.04 T was circulated. Theoretical calculations predicted that the air-gap losses could be reduced by as much as 40% by substitution of higher than air permeability medium, i.e., FMF. The results obtained showed that a current generating efficiency improvement of about 10% was possible with the 0.04 T FMF at 1300 rpm. Less improvement was obtained with lower saturation fluids and higher speeds. These were partly due to parasitic forces such as viscous and magnetic drags, the not too good compatibility of the alternator with FMF containment and some beneficial cooling obtained by the circulating fluid. This contributed about 3% improvement. Therefore, a more appropriate investigation of this phenomenon should be made with properly designed equipment to take advantage of the FMF’s 40% higher than air magnetic permeability.
Ferrite plating in aqueous solution: New technique for preparing magnetic thin film
Authors: Abe Masanori , Tamaura Yutaka
Published: February 2003

This paper describes the principle and performance of a new technique which facilitates the formation of crystalline spinel film at low temperature (T<80 °C) without a heat treatment. For a substrate, not only a metal but also oxides and organic compounds can be used. Various transition metals (M=Ni, Co, Mn, Cu, Zn, etc.) are incorporated into the spinel. Hydrolyzed metal ions FeOH+ and MOH(n−1)+ in an aqueous solution (pH=6∼11,T=40∼80 °C) are adsorbed on a substrate surface which react into spinel film associated with anodic or air oxidation of the FeOH+ ion. We have plated Fe3O4 and CoFe2O4 films on a substrate of Cu, polyethylene terephthalate, and stainless steel. They are polycrystalline with no preferred orientation, and exhibit no magnetic anisotropy. The polar Kerr rotation of these films has been measured.
A magnetic chain reaction and its application to digital pickup heads
Authors: Schwee L. J. , Shephard M. T. , Hunter P. E. , Salton F. G.
Published: February 2003

When crosstie domain walls in 81–19 Ni–Fe films are brought to within 10 μm of each other, there is a tendency for the crossties on one wall to couple to the Bloch lines on the other wall, and vice versa. If a 400-Å-thick film is etched into a zig-zag column of proper proportions, conditions for crosstie-Bloch line coupling can be achieved. The zig-zag pattern runs along the hard axis of the film. After a large field is applied along the zig-zag column, Néel walls form between the inner and outer points. A field in the opposite direction will create a crosstie-Bloch line pair which makes conditions favorable for neighboring pairs to be generated. Like dominoes, neighboring crossties generate neighboring crossties along the column. The resistance of the column changes due to the magnetoresistance effect when crossties generate. So if a current flows through the column, a large signal can be obtained. Likewise, a resistance change occurs when crossties annihilate. Imagine, then, a pickup head where the bottom wall is in close proximity to a disk. The vertical component of a bit being read can generate or annihilate a crosstie-Bloch line pair on the bottom wall triggering a chain reaction and a consequent large signal. The zig-zag column can then be set to await the arrival of the next field of opposite polarity.
Nondestructive inspection of kinetic bonding by eddy current method
Authors: Palanisamy R.
Published: February 2003

Kinetic bonding is a welding procedure in which two metals are joined together by forcing them to collide under high pressure and at high velocity by explosive detonation. Applied to steam condenser tube/tube-sheet welding, this method has demonstrated considerable reduction in cost and improvement in welding speed and effectiveness. Presented in this paper is the result of a theoretical study conducted to determine the suitability of ‘‘eddy current method’’ for nondestructively testing the kinetically bonded tube/tube-sheet region. The study shows that an eddy current probe is sensitive enough for this application and an advanced state-of-the-art instrumentation may be needed for quantitative evaluation.
Mather-type dense plasma focus as a new optical pump for short-wavelength high-power lasers
Authors: Fanning James J. , Kim Kyekyoon
Published: February 2003

For the first time, a Mather-type dense plasma focus (MDPF) is successfully operated as an optical pump for lasers. Rhodamine-6G dye is optically pumped using the MDPF fluorescence, producing a laser pulse 1 μs in duration and more than 50 kW in output power. No optimization is attempted either of the laser cavity or of the lasing medium concentration and volume. A brief description of the experimental setup is presented, along with a summary and discussion of the results. The advantages of the present optical pump source and, in particular, their implications for the pumping of short-wavelength lasers are discussed.
Thermal-anneal wavelength modification of multiple-well p-n AlxGa1−x As-GaAs quantum-well lasers
Authors: Meehan K. , Brown J. M. , Gavrilovic P. , Holonyak N. , Burnham R. D. , Paoli T. L. , Streifer W.
Published: February 2003

Data are presented showing that ordinary thermal annealing can be used to modify GaAs square wells into rounded AlxGa1−xAs quantum wells and shift the continuous 300-K laser operation of a p-n multiple-well AlxGa1−xAs–GaAs heterostructure laser to higher energy. Transmission electron microscopy is used to show that thermal annealing at 900 °C for 10-h changes, for example, well sizes from 85 to 105 Å and coupling barriers from 95 to 75 Å, which results in a change of laser photon energy of Δℏω∼50 meV. Bandfilling is minimal in multiple quantum-well lasers, thus making thermal annealing a useful method to ‘‘tune’’ a continuous 300-K quantum-well laser to shorter wavelength as shown here. These thermal annealing experiments indicate that the Al-Ga interdiffusion coefficient at a heterointerface is D(900)∼10−18 cm2/s.
The effect of material strength on determining pressures ‘‘on’’ and ‘‘off’’ the Hugoniot
Authors: Moss William C.
Published: February 2003

It has been traditional to use the fluid approximation when using solid Hugoniot data to construct a constitutive equation for the pressure as a function of volume and energy. The tradition rests on the assumption that material strength is negligible at large pressures, and the unavailability of Hugoniot shear stress data. However, material strength may be non-negligible, even at large Hugoniot stresses, and a method for calculating shear stresses along the Hugoniot has been developed, so that in principle, P(V,E) can be constructed without making the fluid approximation. Using beryllium as an example, we show how to construct P(V,E), taking material strength into account. We also show that the calculated shear stresses along the Hugoniot are less than the actual values, due to assumptions that are made to reduce the data. Thus, the resulting ratios of the Hugoniot shear stress to the Hugoniot pressure underestimate the actual values. In beryllium, this ratio varies from 0.07 at 5 GPa to 0.015 at 35 GPa.
Stabilization of positive charge in fluorinated ethylene propylene copolymer
Authors: von Seggern H. , West J. E.
Published: February 2003

Stabilization of positive charge in fluorinated ethylene propylene copolymer (Teflon FEP) is demonstrated using corona charging through a controlling grid at elevated temperatures. The extrapolated lifetime of the equivalent surface potential is 800 yr for samples charged at 150 °C and deteriorates for lower charging temperatures. Obtained results for the trap structure confirm published data on the same material. Activation energies, determined by the initial rise of thermally stimulated current measuremnts, are 0.63, 1.16, 1.43, and 1.5 eV for samples charged at 30, 60, 90, and 150 °C, respectively. A uniform charge distribution throughout the bulk of the material is found in samples charged above 100 °C. The total density of occupied traps decreases from 2.2×1014 cm−3 to 1.0×1014 cm−3 when charging at temperatures ranging from 100 to 180 °C.
Propagation properties of fluxons in a well-damped Josephson transmission line
Authors: Nitta J. , Matsuda A. , Kawakami T.
Published: February 2003

Fluxon threshold properties and propagation velocities have been studied with regard to Josephson transmission line (JTL) having an external shunt resistance parallel to the Nb/Nb-oxide/Pb junction. Stable and separated multifluxon waveforms have been observed in the well damped JTL. Experimentally obtained thresholds for the number of propagated fluxons and interval times between each respective fluxon agree with numerical simulations. The dependence of fluxon propagation velocities on the bias current level can be interpreted in terms of the McLaughlin–Scott theory.
Investigation of piezoelectricity distributions in poly(vinylidene fluoride) by means of quartz- or laser-generated pressure pulses
Authors: Gerhard-Multhaupt R. , Sessler G. M. , West J. E. , Holdik K. , Haardt M. , Eisenmenger W.
Published: February 2003

The direct determination of charge, polarization, or piezoelectricity profiles in thin dielectrics is now possible if piezoelectrically generated pressure steps or pulses and laser-induced pressure pulses are employed. These recently developed high-resolution methods were applied to the same piezoelectric poly(vinylidene fluoride) (PVDF) samples. Comparison of the respective results demonstrates the feasibility, the advantages, and the limitations of the new techniques for the study of piezoelectricity distributions. It is confirmed that, for relatively low poling fields, the piezoelectric activity of thermopoled PVDF foils is often confined to a layer near the positively biased surface. The same effect is found for poling with a positive corona discharge. For high-field corona poling, the piezoelectric activity extends throughout the PVDF film.
Photocalorimetric spectroscopy and ac calorimetry of thin surface films
Authors: Geraghty P. , Wixom M. , Francis A. H.
Published: February 2003

Photocalorimetric spectroscopy is demonstrated as a sensitive technique for recording the vibrational and electronic spectra of weakly absorbing films on surfaces. The method employs a low-temperature microcalorimeter which may also be used to monitor enthalpy changes associated with processes in surface films. The calorimeter is sufficiently sensitive to determine growth rates during film deposition, enthalpies of surface adsorption, and the heat capacity of the surface film. Therefore, it becomes possible to correlate spectroscopic data from surface films with thermodynamic information from the same sample. Preliminary results from studies of pyridine films on evaporated metal films are reported.
Enhanced conduction and minimized charge trapping in electrically alterable read-only memories using off-stoichiometric silicon dioxide films
Authors: DiMaria D. J. , Dong D. W. , Pesavento F. L. , Lam C. , Brorson S. D.
Published: February 2003

An electrically alterable read-only memory using silicon dioxide and silicon-rich silicon dioxide layers capable of being cycled ≳107 times by minimizing electron charge trapping in the SiO2 layers of the device by incorporation of small amounts of silicon is discussed in detail. Charge transfer to and from a floating polycrystalline silicon layer from a control gate electrode is accomplished by means of a modified dual-electron-injector-structure stack. This modified stack has the intervening silicon dioxide layer, which is sandwiched between silicon-rich silicon dioxide injectors, replaced by a slightly off-stoichiometric oxide containing between 1 and 6% excess atomic silicon above the normal 33% found in silicon dioxide. The operation of the electrically alterable device structures in terms of write/erase voltages, cyclability, breakdown, and retention is related to current-voltage characteristics obtained from capacitors. A physical model based on direct tunneling between Si islands in the off-stoichiometric oxide layer is proposed to account for the observed increase in the moderate electric field conductance and decrease in charge trapping in these oxide layers incorporated into devices and capacitors. This model and the observed current-voltage characteristics are used to predict device operation for a variety of conditions.
Stress-induced anisotropy and permeability of magnetostrictive Co-based amorphous alloys
Authors: Hayashi K. , Hayakawa M. , Ochiai Y. , Matsuda H. , Ishikawa W. , Aso K.
Published: February 2003

Effects of stress-induced uniaxial anisotropy Ku on initial permeability μ of magnetostrictive Co-based amorphous alloys were investigated over a wide frequency region by potting ribbons of the material in epoxy resin. Anisotropy in plane caused the low frequency (kHz) permeability to change as μ∝K−l/2u due to domain wall displacements and, therefore, resulted in large eddy current losses due to wall movements which decreased the permeability in the high frequency (MHz) region. Anisotropy normal to the plane caused the low frequency permeability to change as μ∝K−1u due to magnetization rotation and the permeability in the high frequency region took higher values than for the case of in-planed anisotropy because the eddy current losses were smaller.
Permeability and field-induced anisotropy in zero magnetostrictive amorphous alloy Fe5Co75Si4B16
Authors: Ochiai Y. , Hayashi K. , Aso K. , Hayakawa M. , Matsuda H.
Published: February 2003

Zero magnetostrictive high saturation magnetic induction material Fe5Co75Si4B16 was studied to relate the induced anisotropy Ku with the permeability μ′, for both strip and ring specimens with induced anisotropy KSu and KRu , respectively. A simple model gives the ratio of KSu/KRu=π/2 . The results show that the permeability is well expressed by μ′KRu=2πM2s derived from the reversible rotational magnetization process at higher driving field. A distinct deviation from the above relation was found at a lower field.
Absorption of infrared radiation in silicon
Authors: Boyd I. W. , Binnie T. D. , Wilson J. I. B. , Colles M. J.
Published: February 2003

The absorption of 9–11 μm radiation by thin wafers of lightly doped, n-type Si has been measured at several lattice temperatures from 300 to 800 K. The temperature dependence of the absorption coefficient at λ=10.6 μm is extracted from the data and compared with previous measurements and also with recent theoretical models. A novel processing technique is described in which coupling of the CO2 laser radiation to the Si lattice is significantly enhanced by the simultaneous absorption of radiation from an argon laser.
Infrared spectroscopic study of hydrogenated and deuterated silicon nitride films prepared from plasma-enhanced deposition
Authors: Maeda Masahiko , Nakamura Hiroaki
Published: February 2003

The infrared spectroscopic studies were carried out for plasma-enhanced chemical vapor deposition amorphous silicon nitride films prepared from gas systems which contain deuterosilane (SiD4) or deuteroammonia (ND3). The stretch-mode frequencies of N–H, N–D, Si–H, and Si–D bonds were observed at 3340, 2480, 2180, and 1585 cm−1, respectively. The absorption cross section of Si–D bond has been determined considering ratios of reduced masses and dipole moment derivatives for Si–H and Si–D bonds. As a result of the calculation of Si–H and Si–D bond concentrations using the respective absorption cross sections, the isotope effect on introduction ratio of H and D atoms bonded to Si atoms was not observed. Assuming that the isotope effect does not also affect the introduction ratio between N–H and N–D bond concentrations, the absorption cross section of N–D bonds is determined. It is also found that 80–90% of the total hydrogen atoms in the films are introduced from ammonia gas.
A study of zinc doping in metallo-organic chemical vapor deposition of InP
Authors: Nelson A. W. , Westbrook L. D.
Published: February 2003

Zn-doped InP epitaxial layers, grown by atmospheric pressure metallo-organic chemical vapor deposition using the adduct process, have been characterized by Hall effect, secondary ion mass spectroscopy, and electrochemical profilling techniques. From the results of these measurements the dopant vapor concentration dependence of the room temperature carrier density, net acceptor density, and total Zn atomic density in the layers has been ascertained and the activation energy of the main acceptor level has been measured as 30 meV. A novel technique for measuring the extent of dopant diffusion is described and this has been used to determine diffusion coefficients of Zn of 1–6×10−13 cm2 s−1, values which are much lower than those previously reported. p-n homojunction devices have also been fabricated and these were evaluated by I-V and C-V measurements. The classical diode equation was obeyed over large ranges of current, and ideality factors for the diodes were found to be 1.2–1.5. These results, together with the C-V measurements, show that high quality InP homojunctions can be produced by the adduct technique and the successful use of the material in advanced devices indicates that this is a valuable process for the future.
Annealing effects and charge compensation mechanism in calcium-doped Y3Fe5O12 films
Authors: de Roode W. H. , van de Pavert C. A. P. W.
Published: February 2003

A large series of calcium-doped Y3Fe5O12 (YIG) films were investigated to determine their behaviour upon annealing in air at temperatures between 100 and 700 °C, and upon treatment with reducing and oxidizing solutions at 100 °C. On the basis of the observed changes in the mismatch, and of the optical and electrical properties of the films, it was concluded that for the as-grown Ca, YIG films in which the calcium content is smaller than the sum of the platinum and lead content the charge compensation is accomplished by the self-compensating ability of the lead ions. For the samples in which the calcium content is larger than the sum of the platinum and lead content the charge compensation is performed by electron holes on the oxygen ions rather than by the introduction of Fe4+ ions. Treatment of the samples with a FeCl2 solution or annealing at 250 °C results in a reduction of the Pb4+ ions and as a consequence in the creation of oxygen vacancies. Reoxidation of the reduced samples can be accomplished by treating the samples in a KMnO4 solution or by annealing at 600 °C. Magnetic measurements showed that the saturation magnetization is not affected by annealing or treatment with oxidizing or reducing solutions. The small changes observed in the uniaxial anisotropy on reduction of the samples could well be explained by the changes in the lattice constant resulting in changes in the stress-induced anisotropy. The reaction rate of the reduction of Ca,YIG films is determined by the relative reaction rates of the surface process and the oxygen diffusion process of the film. In the case where the surface process is much faster than the oxygen diffusion, a diffusion rate of 7.4 μm/h at 100 °C was observed.
Effect of thermal annealing on optical and electrical properties of rf sputtered amorphous silicon
Authors: Sunatori G. S. , Berezin A. A.
Published: February 2003

The effect of thermal annealing on the optical and electrical properties of amorphous silicon (a-Si) was studied on the samples prepared by radio-frequency sputtering. Hydrogen evolution is likely responsible for the change in optical absorption, while oxygen incorporation during sputtering is probably responsible for the change in electrical conductivity after thermal annealing. Our data indicate the possibility of the variable range hopping in unhydrogenated a-Si films.
Reactive ion etching of GaAs in CCl4/H2 and CCl4/O2
Authors: Semura Shigeru , Saitoh Hiroshi , Asakawa Kiyoshi
Published: February 2003

The effect of CCl4/H2 on the etched shape and morphology of GaAs crystals compared with that of CCl4/O2 has been studied. Anisotropic etching with a residue-free and smooth surface is obtained in CCl4/H2. Etching in CCl4/H2 shows an anisotropic shape for H2 ratios above 0.5 at 1.5 Pa. The etched surfaces are smooth for H2 ratios above 0.6, and Auger electron spectroscopy analysis shows that the surface is contaminated to a depth of 10 Å by CCl4. Raman spectra indicate that the surface is free from damage. CCl4/O2 etching rates show a maximum (1.7 μm/min) with an O2 ratio of 0.1 at 1.5 Pa, and etching profiles are isotropic The surfaces are seriously roughened in the case of O2 addition.
Correlation of the fine structure of InM4.5N4.5N4.5 Auger spectrum and thermal degradation at InP surfaces
Authors: Massies J. , Lemaire-Dezaly F.
Published: February 2003

The study of differently prepared InP surfaces by Auger electron spectroscopy (AES) shows that, contrary to previous reports, this technique can distinguish metallic In from In bonded to P in InP. Chemical shifts are indeed observed in the fine structure of InM4.5N4.5N4.5 Auger transitions when InP surface decomposes, leading to the formation of In microinclusions. A chemical shift of 2.2 eV is determined between metallic In and In in InP. Therefore, it is shown that AES can be used to detect InP surface decomposition and is suitable for controlling thermal cleaning generally performed before epitaxial growth of overlayers in molecular beam epitaxy or other vacuum deposition techniques.
Photogenerated current improvement by optimization of amorphous solar cell optical parameters
Authors: Demichelis F. , Minetti-Mezzetti E. , Tagliaferro A. , Tresso E.
Published: February 2003

An analysis of the optical parameters of amorphous solar cells to maximize the absorption of photons in the active region of the cell and then the short circuit current is presented. The model applied to several kinds of amorphous structures indicates that total optical losses of only 9% and short circuit currents up to 24.5 mA/cm2 can be achieved.
Internal friction and viscosity associated with mobile interstitials in the presence of a kink harmonically or uniformly moving in anisotropic body-centered cubic metals
Authors: Ogurtani Tarik Ö. , Seeger Alfred K.
Published: February 2003

The power dissipation (internal friction) due to mobile octahedral interstitials in the stress field of a harmonically oscillating or uniformly moving rigid kink of a dislocation line is derived for anisotropic body-centered -cubic metals using the discrete Fourier k-space transformation of the elastic Green’s function in connection with the general linear-response theory of inhomogeneous interactive fields. The viscosity and the drag force acting on the kink moving rigidly and uniformly along the dislocation line are formulated which show strong velocity and the temperature dependent behavior. A discrete Debye relaxation spectrum, the first term of which is identical in form to the ordinary Snoek peak, is found to represent the anelastic behavior associated with the kink enhancement. The inverse relaxation time spectrum of octahedral interstitials which has three distrinct branches, one acoustic and two optical in the first Brillouin zone, is also presented and discussed.
Properties of amorphous hydrogenated silicon-tin alloys prepared by radio frequency sputtering
Authors: Williamson D. L. , Kerns Ralph C. , Deb S. K.
Published: February 2003

Amorphous Si1−xSnx and Si1−xSnx :H (0≤x≤0.3) alloy films have been prepared by radio frequency sputtering from composite Si–Sn targets in Ar or Ar-10% H2 mixtures at dynamic pressures of 4 or 20 mTorr. The structural characteristics of the alloys have been probed with 119Sn conversion electron Mössbauer spectroscopy, x-ray diffraction, and infrared absorption. Most of the tin goes into tetrahedral substitutional Si sites at 4 mTorr whereas significant fractions of crystalline β-Sn are produced at 20 mTorr. The substitutional Sn Mössbauer resonance is systematically characterized with a Lorentzian doublet line shape. Oxygen contamination increases with increasing Sn content in the 20-mTorr films but is attributed to postdeposition oxidation. No evidence is found for Sn–H bonds or interstitial (nonbonded) Sn. The optical band-gap decreases at a rate of −0.056 eV/at. % Sn for alloys containing little or no β-Sn and for x up to 0.13. Both the optical band gap and the Mössbauer isomer shift extrapolate to α-Sn (grey tin) behavior at x≂0.3–0.4. The electrical conductivity increases with x at a rate which is not consistent with the measured reduction in band gap and a fixed relative Fermi level. This and the temperature dependence of the conductivity suggest a transition from extended state free-carrier conduction to localized state hopping conduction. Annealing experiments show that the films are stable at 300 °C but that at 400 °C β-Sn precipitation occurs concurrently with hydrogen evolution and with partial crystallization of the amorphous silicon matrix.