bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic moduli of filled polymers: The effect of particle shape
Authors: Chow T. S.
Published: February 2003

Eshelby’s theory is known for its simplicity in the treatment of the elastic moduli of a composite filled with spheres. His approach is utilized in this paper to estimate the five elastic constants of a filled polymer containing aligned ellipsoids. The anisotropy-particle-shape effect is characterized by the aspect ratios (ρ) of an ellipsoid. Because Eshelby’s theory is limited to dilute dispersions, we have to confine the present derivation to the intrinsic moduli. The basic definition and method are outlined in the discussion of shear moduli which have the form analogous to that of spherical filler and have also been investigated by several authors relating explicitly to disk- and needle-shaped particles. Equations on the bulk, longitudinal, and transverse Young’s moduli are the new results which are valid for all values of ρ. Orienting fibers (ρ≳1) parallel or disks (ρ<1) perpendicular to the stretch direction has the similar reinforcing effect and is illustrated with data on glass and boron in epoxy resins.
Effects of hydrostatic pressure on shear deformation of polymers
Authors: Silano A. A. , Pae K. D. , Sauer J. A.
Published: February 2003

The effects of hydrostatic pressure on the torsional shear stress-strain behavior of polyoxymethylene (POM) and polypropylene (PP) have been investigated. The experimental data show that the shear modulus of polyoxymethylene increases linearly with pressure while the shear modulus of polypropylene increases bilinearly with pressure with the break, the glass transition pressure, occurring at 2.1 kbar. This value coincides with prior results obtained from Young’s modulus–vs–pressure curve for polypropylene. The linear variation of the shear moduli with pressure is compared with the Birch’s equation which was derived from finite strain theory of elasticity. The shear yield stress (2% offset) has been found to increase linearly with pressure for POM but increase nonlinearly with pressure for PP. The Pae yield criterion (J′2)1/2 =𝒥nk=0αkJk1 predicts accurately both the linear and the nonlinear variation of the shear stresses with hydrostatic pressure. Other proposed yield criteria, however, predict only linear or nonlinear, but not both. A new phenomenon, which is analogous to the necking in a tensile specimen, has been observed on the torsional shear specimens of polyoxymethylene and polypropylene. This phenomenon has been named girdling. Girdling is a constriction or a reduction of a cross-sectional area in a narrow band on the shear specimens.
The work to produce environmental crazing at low temperatures
Authors: Brown Norman , Metzger Bruce D.
Published: February 2003

The work to form a unit area of craze, U, was measured for PCTFE and PMMA which were deformed by creep in nitrogen environments at around 78 K. It was found that the average value of U=60±50% J/m2 for both polymers. The theory for determining U was based on measurements of the parameters that are contained in the equation U=σb=σε/ργA, where σ is the applied tensile stress, b is the average craze opening displacement, ε is the creep strain, ργ is the number of crazes per unit volume, and A is the average area of a craze. Both equations gave the same results. U is not a unique quantity since it appears to depend on the type of site at which the craze nucleated. The relationship of U to the fracture energy as measured by Berry is also discussed.
Longitudinal acoustic mode in polymers: Applications of the general theory to planar zigzag methylene chains
Authors: Hsu S. L. , Krimm S.
Published: February 2003

The general theory of the longitudinal vibrations of a composite perturbed elastic rod has been applied to the observed LAM frequencies of n-paraffins, a cyclic paraffin, and polyethylene. The good agreement obtained between observed and calculated results shows that force and mass perturbations at the chain ends have a significant, and non-negligible, effect on the LAM frequency.
Viscoelastic properties of entangled polymers: The transient network model
Authors: Hong S. D. , Soong D. , Shen M.
Published: February 2003

The viscoelastic behavior of entangled polymers is modeled by a three-dimensional transient network where the entangled points are considered to act as temporary crosslinks. Polymer chains are represented by beads and springs. The effects of entanglements on chain dynamics are introduced by assigning enhanced frictional coefficients to selected beads as well as extra elastic couplings between pairs of the entangled beads. The formation and disengagement of the entanglements can be envisioned to be in a dynamic equilibrium. The strength of elastic coupling is set to decrease with increasing distance between the entangled points. The resulting modified Rouse-Bueche-Zimm matrix is solved for the relaxation times from which the dynamic moduli, relaxation moduli, steady-state shear compliance, and zero-shear viscosity are computed. Results are in excellent agreement with experimental data on monodisperse polystyrene, poly(α-methylstyrene), poly(vinyl acetate) and polybutadiene.
Mechanical property and physical structure changes in highly hot-drawn polycarbonate
Authors: DeRudder J. L. , Filisko F. E.
Published: February 2003

The effect of hot stretching on the structure and properties of bisphenol-A polycarbonate was studied to determine if ordering and conformational changes occur, and their effect on the impact toughness of PC. The mechanical properties of hot-stretched PC were found to follow the same behavior observed for enthalpy changes, which showed (1) a drop at draw ratios between 2 and 5; (2) a plateau region extending out to a draw ratio of 45; (3) a further drop at draw ratios of 57 and 62. The enthalpy decrease at a draw ratio of 62 is comparable to that found for 15% solvent-crystallized PC; yet, wide-angle x-ray diffraction indicates that no crystallinity is present. Annealing of this highly hot-drawn PC increased the enthalpy by 7.5 kJ/kg, indicating that this highly hot-drawn PC must be in an ordered state.
Energetics of defect motion which transports polyethylene molecules along their axis
Authors: Reneker D. H. , Fanconi B. M. , Mazur J.
Published: February 2003

Defect energy was calculated as a function of dihedral angles of the bonds in a point dislocation for sequences of conformations that resulted in motion of the dislocation along the polyethylene chain. Paths that presented low barriers to diffusive motion of the defect were found by incrementing, in a particular sequence, selected dihedral angles around two separated bonds near the opposite ends of the defect as the computer searched for the lowest energy conformation of all the other parts of the defect. Thus, the diffusion of a point dislocation provides a plausible mechanism for diffusion of the chain along its axis.
Conformational specific heat of polymers
Authors: O’Reilly James M.
Published: February 2003

A method to evaluate the conformational specific heat of polymers is proposed. The change in Cv at Tg is identified with the conformational specific heat and calculated from thermodynamic data on 14 polymers. The equation for specific heat of a two-state model yields the energy difference between the two states, ε, from the experimental data for ΔCv(Tg). The basic premise of this work is also shown to be derivable from the Gibbs-DiMarzio theory of glass formation. Derived values of ε are in agreement with results calculated from Tg data and the dependence of Tg upon molecular weight using G-D theory.
The temperature drop in glassy polymers during deformation
Authors: Matsuoka S. , Bair H. E.
Published: February 2003

Mechanical relaxation time in polymeric glass has been previously shown to shift to shorter times under tensile strain, and this phenomenon has been attributed to the increase in free volume accompanying the deformation. To be consistent with this concept, the excess enthalpy associated with free volume must also increase with deformation. The temperature of polycarbonate was measured during deformation and was found to decrease continuously up to a few percent strain in tension as well as in shear. The total increase in enthalpy was calculated from the data to be 0.2 cal/g.
Theory of gain and saturation for collision-induced lasing transitions
Authors: Julienne Paul S.
Published: February 2003

Theoretical expressions are given for the inversion density, small-signal-gain coefficient, and saturation-energy flux which pertain to stimulated collision-induced emission, that is, the free-free and free-bound dipole emission from unbound excited states formed during a collision of an atomic metastable species and another atom. The probability of stimulated emission during a collision is assumed to remain much less than unity so that a Maxwellian velocity distribution of excited atoms is maintained. The gain and saturation are described in terms of a profile function k (ν), a frequency-dependent two-body rate coefficient per unit frequency. The final expressions are analogous to those for a homogeneously broadened two-level atom. The theory is applied to the collision-induced green continuum from oxygen 1S0 in argon.
Electron-beam and photolithographic fabrication of guided-wave optical components
Authors: Aagard R. L. , Shepherd L. T. , Ulmer R. P.
Published: February 2003

Thin-film lenses, mirrors, and diffraction gratings have been fabricated from electon-beam-generated masks. These masks were used to make iron oxide working masks for photolithographic fabrication of these passive components in Nb2O5 optical waveguides. The optical-waveguide characteristics of these components are discussed.
Spark photoionization of CO2 laser gases
Authors: Ceglio N. M. , Lawrence J. D. , George E. V.
Published: February 2003

An experimental investigation at atmospheric pressure of volume photoionization produced by bare sparks in He, CO2, and N2 gas mixtures containing tripropylamine is reported. Measurements were made using a probe and a pair of contoured collector electrodes with an applied dc potential. The variation of photoelectron density with gas mixture, tripropylamine addition, and uv source (spark) energy was investigated. Single-step photoionization of tripropylamine vapor was found to be the dominant ionization mechanism in this experiment. The addition of moderate amounts of tripropylamine vapor to gas mixtures containing CO2 resulted in an increase of photoelectron density by more than an order of magnitude. The effects of gas mixture variation and tripropylamine addition on photoelectron temporal decay was studied and decay rates measured. The addition of tripropylamine to the gas mixtures was found to significantly increase electron decay rates. Measurements with a LiF window and a fused-quartz window were used to estimate the photoionization contributions from different portions of the spark spectrum. Short-wavelength radiation below the LiF cutoff appeared to be much more efficient for photoionization of the tripropylamine than that above the LiF cutoff. Radiation above the fused-quartz cutoff made no measurable contribution to the photoionization.
The stability of shaped-charge jets
Authors: Chou Pei Chi , Carleone Joseph
Published: February 2003

Shaped-charge jets have a tendency to break up into a series of segments along the jet axis, as evidenced by flash radiographs. This paper studies the stability of stretching plastic shaped-charge jets by two approaches. First, a one-dimensional theory is formulated. This theory yields a stability criterion which depends on the instantaneous values of stress and the slope of the stress-strain curve. It also relates the disturbance growth rate to disturbance wavelength, stretching rate, and yield stress to density ratio. In the second approach, two-dimensional finite-difference calculations are performed which substantiate all of the trends indicated by the one-dimensional theory. Also, the two-dimensional calculation shows the existence of a critical wavelength; disturbances of this wavelength grow faster than all others. Other effects such as irregular surface disturbances and elasticity are also studied.
Pump efficiency and saturation effects in waveguide lasers
Authors: Lundgren Lennart
Published: February 2003

The cross-sectional variation of the energy density in a waveguide gas laser results in a transversely varying saturation if the molecules are stationary. At a transversely constant excitation of the upper laser level, the varying saturation reduces the efficiency and power output compared to the case when rapid molecular movements make the saturation constant. Near threshold, the reduction factor is approximately 2. The cross-sectional saturation has, however, little influence on the optimization of the output coupling.
The formation of small sparks
Authors: Barreto E. , Jurenka H. , Reynolds S. I.
Published: February 2003

The formation of a small incendiary spark at atmospheric pressure is identified with the transition from a weakly to a strongly ionized plasma. It is shown that initial gaseous ionization produced by avalanches and/or streamers always creates a high-temperature ideal electron gas that can shield the applied voltage difference and reduce ionization in the volume of the gas. The electron gas is collision dominated but able to maintain its high temperature, for times long compared to discharge events, through long-range Coulomb forces. In fact, electrons in the weakly ionized plasma constitute a collisionless independent fluid with a thermodynamic state that can be affected directly by field or density changes. Accordingly, with metal electrodes, cathode spot emission is always associated with the transition to a strongly ionized plasma. Neutral heating can be accomplished in two different ways. Effective dispersal of the electrons from the cathode leads to electron heating dominated by diffusion effects. Conversely, a fast rate of emission or rapid field changes can produce nonlinear wave propagation. It is shown that solitary waves are possible, and it is suggested that some spark transitions are associated with shock waves in the collisionless electron gas. In either the diffuse or nonlinear regime, neutral gas heating is controlled by collisions of ions with isotropic thermal electrons. This interaction is always subsequent to changes in state of the electron gas population. The basic results obtained should apply to all sparks.
Time- and space-resolved spectroscopic studies of electrical breakdowns in an argon-hydrogen mixture
Authors: Wiese L. L. , Augis J. A.
Published: February 2003

Emission spectra from a 6-A 250-ns cable discharge between gold electrodes in a mixture of 90% Ar+10% H2 at atmospheric pressure have been obtained both with and without time resolution as a function of position in the gap. The Stark broadening of the hydrogen Hβ line and of Ar II lines has been used to estimate the electron density in the gap which is observed to exceed 1018 cm−3 during the first 100 ns of the discharge. A quasi-steady-state is observed after approximately 100 ns until current extinction, during which time the Ar II populations are given by Boltzmann statistics with a temperature of ∼20 000 °K. The results of the time-integrated and time-resolved studies are compared to provide information about the effects of spatial and temporal integrations on measured parameters. The qualitative features of the spectra together with estimates of the plasma equilibration time indicate that it may be possible to use a local thermodynamic equilibrium (LTE) model of the plasma to quantiatively study the electrode erosion process.
Defect clusters and annealing in self-ion-irradiated nickel
Authors: Narayan J. , Larson B. C.
Published: February 2003

Transmission electron microscopy and x-ray diffuse scattering have been used to study defect clusters in 4-MeV self-ion-irradiated (total doses of 2.5×1013 and 5.0×1013 ions/cm2) nickel. The distribution of defect clusters as a function of the ion penetration depth was measured directly in the electron microscope using a transverse sectioning technique. For an ion dose of 2.5×1013 cm−2, the average cluster radius of 32±2 Å at the damage peak depth (0.82 μm) was 20% larger than the average radius near the crystal surface. The fraction of point defects created in the displacement cascades that survived in the form of defect clusters was found to be about 1% for these doses. Annealing at 125, 250, and 450 °C gave a monotonic decrease in the number of point defects stored in the form of loops.
Migration of ion-implanted krypton in silicon during anneal
Authors: Welch J. D. , Davies J. A. , Cobbold R. S. C.
Published: February 2003

Helium backscattering and 85Kr radiotracer techniques have been used to study the movement of implanted krypton in silicon during subsequent vacuum anneal at 650, 750, and 900°C. Doses from 5×1013 to 1×1016 cm−2 and implantation energies of 25, 50, 100, and 500 keV were used in the study. Within the dose range 1014–1015 ions cm−2, a large outward migration of 85Kr is observed during the anneal and, except in the 500-keV case, most of the Kr escapes from the target. At still higher implant doses (i.e.,≳2×1015 cm−2), this outward migration is reduced, and no loss of 85Kr is detected except at 25 keV. In all cases, at implant doses ≲1014 cm−2, no migration or loss of Kr is observed. Helium backscattering measurements on the 500-keV implants indicate that in the dose range 1014–1015 cm−2 reordering of the amorphous silicon formed by the implantation is associated with some outward Kr movement.
Neutralization of electrophotographic developer
Authors: Hays D. A.
Published: February 2003

In many electrophotographic development systems, the developer consists of toner particles (∼10 μ) triboelectrically charged by carrier beads (∼100–250 μ). Since development onto a photoconductor continually removes charged toner from the development system, the carrier-bead charge would continue to increase with use unless, as happens, the developer net charge is limited by some neutralization mechanism. From a series of measurements on typical developer materials, we rule out electrical conduction and air breakdown as straightforward dominant neutralization mechanisms and find that the neutralization of developer is a multistep process. When the net-charged developer is agitated, toner migrates through the developer, reducing the net charge in its bulk and leaving a toner-starved bead layer adhering to any conducting boundary surface. When the developer is further agitated, the surface layer of highly charged adhering beads can be released by either of two charge neutralizing mechanisms. If the beads have conducting cores coated with a polymer, the carrier beads are neutralized by triboelectric charging in the presence of the high electric field due to the net charge on the beads. But if the bead coating integrity is poor, the beads can be neutralized by charge flow from the boundary surface to the conducting bead cores.
A vibrational-bath model for the dynamics of SF6 absorption near 10.4 μm as a function of wavelength and absorbed energy
Authors: Taylor R. S. , Znotins T. A. , Ballik E. A. , Garside B. K.
Published: February 2003

A ’’vibrational-bath’’ model is employed to determine the characteristics of the absorption of pulsed CO2 laser radiation by SF6 at the 10.4-μm band of CO2. This model allows calculation of the absorption of any CO2 P line, other than that of the incident pulse, both during and after the pulse transmission and over a wide range of pulse intensities. Infrared double-resonance experiments, using both short and long pump pulses, demonstrate the appropriateness of the model in predicting the SF6 absorption behavior and the range of SF6 pressures and input pulse durations where such a model applies.
Excitation of highly excited states by collisions between two excited cesium atoms
Authors: Leslie S. G. , Verdeyen J. T. , Millar W. S.
Published: February 2003

Fluorescence from highly excited atomic states has been observed in cesium vapor irradiated by a dye laser tuned to either one of the 62S–72P transitions. The emission originated from levels as high as 1 eV above the state being pumped. The high-lying states are believed to be excited by an electronic energy transfer induced in a collision of two atoms occupying lower excited levels.
Statistical theory of dislocation configurations in a random array of point obstacles
Authors: Labusch R.
Published: February 2003

The stable configurations of a dislocation in an infinite random array of point obstacles are analyzed using the mathematical methods of statistical mechanics. The theory provides exact distribution functions of the forces on pinning points and of the link lengths between points on the line. The expected number of stable configurations is a function of the applied stress. This number drops to zero at the critical stress. Due to a degeneracy problem in the line count, the value of the flow stress cannot be determined rigorously, but we can give a good approximation that is very close to the empirical value.
On the description of crystal defects by point-force arrays
Authors: Hartley Craig S. , Bullough R.
Published: February 2003

A modification to the continuum theory of crystal defects is described in which the interatomic reaction forces developed when a defect is introduced are replaced by point forces in a continuum. The locations of the forces are determined by the atomic positions surrounding the defect, and the magnitudes by the requirement that the force array produce the proper displacement field for the defect. The technique is applied to the construction of primitive prismatic and shear dislocation loops in a hypothetical isotropic simple cubic lattice. A screw dislocation is formed from an array of shear loops, and the displacement field, width, and self-energy are calculated. Applications of the model to other dislocation configurations are suggested.
Resistivity of shock-wave-compressed PZT 95/5
Authors: Lysne P. C.
Published: February 2003

A model is developed that takes into account the finite resistivity of ferroelectric ceramics compressed by shock waves propagating in a direction perpendicular to the remanent polarization vector. This model is fit to data obtained from experiments on Pb0.98Nb0.02(Zr0.95Ti0.05)0.98O3 (referred to as PZT 95/5). The resistivity of this material in the stress range 1.6–3.2 GPa is about 7×104 Ω cm.
Contribution to the general analysis of field emission
Authors: El-Kareh A. B. , Wolfe J. C. , Wolfe J. E.
Published: February 2003

The theory of thermionic-field emission of electrons from metal surfaces with planar geometry has appeared in various publications. Specifically, the functional dependence of the normal, tangential, and total energy distributions of the emitted electrons and of their current density upon work function, temperature, and appied electric field has been established. In this paper, we present, graphically, a numerical analysis of these functions for several work functions, temperatures, and field strengths of experimental interest.
Ion-beam plating using mass-analyzed ions
Authors: Tsukizoe Tadasu , Nakai Tetsuo , Ohmae Nobuo
Published: February 2003

An ion-beam-plating apparatus controlled by mass spectrometry was developed to study the fundamentals of ion plating. A decelerating lens system was fitted to the apparatus and the deposition was carried out at ion energies from 30 to 300 eV. By the elimination of contaminant ions and neutrals and making the kinetic energy of incident ion-beam constant the fundamental deposition mechanism can be discussed. A high-voltage transmission electron microscope at 2000 kV was employed for examining ion-beam-induced dislocations in single-crystal substrates of aluminum and the growth of ion-beam-plated films. The effects of kinetic energy and substrate orientation are discussed. It was found that the higher the ion energy, the higher the dislocation density. A high density of dislocation was observed on the close-packed plane, i.e., (111) of an aluminum single crystal. Stainless steel was also used as a substrate. In this case, a twin deformation was found. The high-voltage transmission electron microscope provided an observation of both growth of film and substrate structure. Coalescence of particles and island formation were observed. Depth profiling was obtained by performing argon ion sputtering at 3 keV while using a secondary ion mass spectrometer and an Auger electron spectrometer for analyzing interfacial composition. When the kinetic energy of the depositing ion is high or when the closepacked plane is chosen as a substrate, the diffused layer was found to be deep. This result corresponds well with the density of dislocation observed by transmission electron microscope. Argon ion sputter cleaning before deposition was found to increase the depth of the diffused layer. These results may indicate the transport of ions through dislocation cores, which were produced by argon ion bombardment.
Study of the LiH-Te reaction using ion backscattering
Authors: Myers S. M.
Published: February 2003

The mechanism and kinetics of the exothermic solid-state reaction between LiH and thin-film Te have been investigated, including the effects of LiOH on the LiH surface. Single-crystal LiH was covered with ?1 μm of vapor-deposited Te, in some cases after a layer of LiOH had formed on the LiH. The reaction 2 LiH+Te→Li2Te +H2↑ was examined by vacuum annealing in the temperature range 473–543 K with the concentration-vs-depth profiles of Te, O, and Li being determined by backscattering analysis. The results are consistent with a two-step process. First, the LiOH layer is converted to Li2O through the thermally activated reaction LiOH+LiH→Li2O +H2↑ which produces open fissures. Second, the LiH-Te reaction occurs through these fissures with vapor transport of Te being the rate-determining step.
Gas temperature and cooling in waveguide CO2 lasers
Authors: Shields H. , Smith A. L. S.
Published: February 2003

Gas temperatures in waveguide laser discharges have been measured. The temperature obeys the scaling laws for similarity with conventional positive column CO2 laser discharges. Beryllia and alumina are equally efficient in cooling the CO2-N2-He gas, but Pyrex is less effective.
Plasma-injection-stabilized discharges in CO and He at low temperatures
Authors: Cohn D. B. , Lim D. G.
Published: February 2003

Pulsed and cw discharges in low-temperature flowing mixtures of CO and He, typical of those required for efficient laser action at 5 μm, are stabilized by convective flow injection of a weakly ionized plasma maintained by an auxiliary discharge adjacent to the main discharge volume. Pulsed input energy densities range from 0.5 kJ/l atm at 300 K to 0.2 kJ/l atm at 80 K for pressures on the order of 50 Torr and discharge pulse lengths of approximately 1 μs. Continuous discharge operation has been demonstrated with specific input powers of 300 W/(g/s) at pressures and temperatures of 40 Torr and 110 K.
Reduction in dislocation density in In-doped GaP LPE layers grown from indium solvent
Authors: Sugiura Toshifumi , Tanaka Akira , Hagino Minoru , Sukegawa Tokuzo
Published: February 2003

A reduction in dislocation density, typically by a factor of 3–8, was observed across the interface between LEC GaP (111)B substrate and an n-type In-doped GaP layer grown from indium solvent by liquid-phase epitaxy. Doping of the epitaxial layer with indium contributed to the reduction in dislocation density in the epitaxial layer.
Temperature dependence of the drift velocity of carbon in α-iron during electromigration
Authors: Nakajima Hideo , Hirano Ken-ichi
Published: February 2003

To confirm the effect of the magnetic transformation on electromigration of carbon in α-iron, the temperature dependence of the drift velocity of carbon in α-iron during electromigration has been determined at 870 and 890 °C in addition to the previous work. The drift velocity of carbon per unit electric current density in the ferromagnetic α-iron is shown to be lower than that expected by an extrapolation from the temperature dependence of it in the paramagnetic range. The results are discussed based on the spin-disorder scattering model.
A quenched-in defect in boron-doped silicon
Authors: Gerson J. D. , Cheng L. J. , Corbett J. W.
Published: February 2003

We observed a majority-carrier trapping level at Ev+0.45 eV in boron-doped silicon with a wide range of resistivities after being quenched from 900 to 1200 °C. The carrier capture cross section was measured to be 4×10−18 cm2. The activation energy for migration and defect formation energy were found to be 0.76±0.05 and 2.8±04 eV, respectively, consistent with that of the interstitial iron in silicon. However, we found a marked boron dependence, indicating that the nature of the defect processes may be complex.
Impurity effects on conduction in heavily doped n-type silicon
Authors: Finetti M. , Mazzone A. M.
Published: February 2003

Conductivity and Hall effect measurements have been performed on n-type silicon samples with phosphorus doping concentrations varying from 4.4×1018 to 8.65×1019 cm−3 and for temperatures ranging from 77 to 300 °K. It is demonstrated that, on the whole, the Bonch-Bruevich theoretical model allows a satisfactory interpretation of the experimental results.
The effect of oxidation-expanded defects upon MOS parameters
Authors: Prussin S. , Li S. P. , Cockrum R. H.
Published: February 2003

Implantation of Ne ions was chosen as a means of introducing a uniformly distributed quantitatively controllable and reproducible amount of microdefects at the silicon surface. Each wafer was ion implanted on one-half of its surface, the other half remaining as a control. Seven implant fluences from 1×1012 to 5×1014 Ne cm−2 were used. The fluences, as well as the concentrations of defects expanded by the subsequent gate oxidation, were correlated with seven different MOS parameters. For implant fluences of 1×1014 cm−2 and above, increasing stacking-fault densities were found. The oxide defect density associated with time-dependent breakdown increased significantly with Ne dose. The presence of oxidation-expanded defects drastically increases the surface-generation velocity and decreases the bulk lifetime. Slight increases in flatband voltage and surface-state density occurred only for the wafers having the greatest defect concentrations. Oxidation of a P-containing damaged silicon surface results in a greater pileup of P at the surface than occurs for the oxidation of a similar but undamaged surface. It appears that the expanding defects restrain the diffusion of P inward from the surface.
Oxidation of lead tunnel barriers in a humidity-controlled oxygen-regulated atmosphere
Authors: Garno J. P.
Published: February 2003

High-quality reproducible Pb oxide tunneling barriers have been grown using thermal oxidation methods. Junctions were made over a conductance range of 104(Ω cm2)−1 by accurately controlling the humidity in a flow of room-temperature oxygen. An inspection of the I-V characteristics in the region eV<2Δ at low temperatures indicates extremely high-quality barriers with no nontunneling processes shunting the tunneling process.
An investigation of the thermal cycling of Pb-alloy Josephson tunneling gates
Authors: Basavaiah S. , Greiner J. H.
Published: February 2003

Thermal cycling stability between room temperature and 4.2 °K of in-line Josephson tunneling gates employing Pb-alloy films was investigated. Pb films containing In and/or Au additions were used for the junction electrodes. Samples containing 19 gates typically had one failure after about 50 cycles, and some of those gates withstood as many as 200 cycles without any measurable change. It was found that the failure rates can be adequately described by a log-normal distribution above the 5% level. It is believed that the stability of the gates resulted from the mechanical strengthening of the Pb films by the alloying additions.
Orthorhombic magnetic anisotropy in garnet epitaxial films containing europium
Authors: Stacy W. T. , Voermans A. B. , Logmans H.
Published: February 2003

We have determined the conditions under which an orthorhombic anisotropy can be induced in epitaxial (Eu, Lu)3Fe5O12 films such that the easy axis is normal to the film surface and the medium and hard axes are in plane. The presence of the in-plane anisotropy has been shown in a previous publication to increase the maximum domain-wall velocity substantially above that of comparable uniaxial materials. Suitable anisotropies have been found in films grown in compression on (110) Gd3Ga5O12 substrates. The resulting anisotropy is shown to be partly stress induced and partly growth induced; a separation of the two components has been obtained by examining films with different misfit strains and by measuring the anisotropy torques, magnetization, and lattice misfit as a function of temperature. Films grown on (111) and (100) substrates have also been examined. The results indicate that a two-parameter model of the growth-induced anisotropy is incapable of describing the magnetic anisotropies measured for the above three orientations. A different functional dependence of the induced anisotropy on the growth direction is needed. For compositions corresponding to small lattice misfit, the temperature dependence of the growth-induced anisotropy parameters is well described by that of the magnetic anisotropy of the Eu3+ ion as calculated by Sturge et al. At larger misfit values (−Δa/a≳2×10−3) the presence of additional mechanisms contributing to the anisotropy can be inferred from the data.
Gradient propagation, overshoot, and creep in magnetic-bubble garnet material
Authors: Ju Kochan , Humphrey F. B.
Published: February 2003

Gradient propagation of free magnetic bubbles has been investigated using high-speed transient photography. Overshoot in the translational motion was confirmed and a new mode of motion, creep, was introduced. Creep is induced translational motion caused by bias-field pulsing after a driven translation and overshoot. It was found that overshoot is bubble-size (bias-field) dependent and that creep and overshoot are complementary with the total motion independent of the bias field. A model is presented that provides that the wall structure at the end of the gradient pulse be dominated by these vertical wall twists, i.e., vertical Bloch line pairs with each having a winding direction opposite the other. This structure is packed by the g forces during translation and relaxes after the termination of the pulse to give overshoot. Creep is the result of annihilating the remaining wall twists by bias-field pulsing as the wall assumes its most stable state.
Measurement of B versus H of Alumel from 25 to 180 °C
Authors: Horton J. L. , Kollie T. G. , Rubin L. G.
Published: February 2003

The relationship between the magnetic induction B and the magnetic field H in Alumel was measured by the ring method for temperatures T between 25 and 180 °C. These data were needed to correct for large temperature measurement errors that occurred when Chromel-vs-Alumel thermocouples were used in a magnetic field. Through application of the Weiss equation, the saturation value of the intrinsic magnetic induction Bs was calculated as a function of T from the experimental B-vs-T data. Weiss’s method was used to determine the Curie temperature of Alumel, Tc?152 °C, from a plot of B2s versus T near Tc. The experimental values of Bs versus T were in good agreement with those obtained from the Brillouin function with quantum number J=1/2.
Nature of injection processes during poling of poly(vinylidene fluoride) and their relationship to pyroelectricity
Authors: Takahashi K. , Lee H. , Salomon R. E. , Labes M. M.
Published: February 2003

By analysis of steady-state current-time-voltage-temperature relationships, it is concluded that a Richardson-Schottky process is dominant at the high fields and temperatures typically employed in poling poly(vinylidene fluoride) to impart pyroelectric and piezoelectric properties. Data on pyroelectric behavior with different layer configurations and with different electrode configurations indicate the primary importance of hole injection.
Anomalous electroconvection in weakly conducting liquids
Authors: Coelho R. , Vanderschueren H.
Published: February 2003

According to the classical treatments given in standard textbooks, the presence of an electric field in an insulating fluid should favor natural convection. The effect of an electric field on thermal convection was reinvestigated with an experimental setup consisting essentially of a thin platinum wire stretched in the axis of a metal ring. Both electrodes were immersed in a cell containing the liquid under investigation. The wire was heated by Joule effect, and a dc voltage up to 5 kV was applied between the wire and the ring. The cell, fitted with optical windows, was placed in the beam of a striograph (Schlieren optics bench) by which the heat front rising above the wire was observed. The heat exchange between the wire and the liquid could also be monitored by estimating the steady temperature of the wire, through the measurement of its resistance. With these techniques, it was found that the electric field may actually impede thermal convection if the liquid contains a sufficient amount of ionizable impurities. The interpretation is based on the space charge which appears wherever a gradient of temperature—hence of conductivity—and an electric field simultaneously exist. A mathematical analysis, made possible by a few simplifying assumptions, shows that an electrostatic attractive force opposes the upward gravitational pull acting on the heated liquid, and satisfactorily predicts the stable position of the heat front above the wire. Other manifestations of this space charge are briefly described.
Cathodoluminescence measurements of the minority-carrier lifetime in semiconductors
Authors: Boulou M. , Bois D.
Published: February 2003

Detailed calculations of the cathodoluminescence decay after an excitation pulse are developed; the generation function, the carrier diffusion, the surface recombination, the self-absorption, and the excitation-pulse duration are taken into account. It is demonstrated that the surface recombination leads to a nonexponential region at the beginning of the decay when short excitation pulses are used. This effect disappears with longer pulses. It can be used in order to determine separately the surface recombination velocity and the true bulk lifetime of the carriers. Nomograms are given which permit this determination without further calculation. The influence of the pulse duration on the form of the cathodoluminescence decay has been experimentally verified in GaP. The surface recombination velocities and the lifetimes in many samples have been deduced. Finally, it appears that this method provides a simple means of determining the minority-carrier lifetime in semiconductors.
Light-ion sputtering yields for molybdenum and gold at low energies
Authors: Bay H. L. , Roth J. , Bohdansky J.
Published: February 2003

The sputtering yields of molybdenum and gold for H+, D+, 3He+, and 4He+ ion irradiation at normal incidence with large irradiation doses have been measured for energies between 150 eV and 20 keV. The yields were determined from the weight loss of the targets. The sputtering yields are strongly influenced by threshold effects for energies below ∼10 keV. It is found that the experimental yields can be described by a yield formula with an energy parameter E′=E/Eth, where Eth is a theoretical threshold energy.
Power spectrum of radiation from a Josephson junction
Authors: Likes Richard S. , Falco Charles M.
Published: February 2003

The harmonic content of the power generated by a Josephson junction is calculated as a function of the applied current. The effect of the pair-quasiparticle interference conductivity is considered, and the limiting form of the power is derived for large driving currents.
Comments on ’’Magnetic domain wall bowing in a perfect metallic crystal’’
Authors: Bishop J. E. L.
Published: February 2003

Carr’s equations governing eddy-current-limited domain-wall motion and bowing are found to be essentially equivalent to Bishop’s. The nature of the wall velocity vector is discussed. The argument used by Carr to show that severely bowed wall shapes (such as those calculated by Bishop) cannot be stable is shown to be unsound. A simple analytic model for extreme bowing is proposed and found to agree well with Bishop’s earlier numerical results.
Wall bowing and stability
Authors: Carr W. J.
Published: February 2003

Domain-wall bowing and stability of a given wall shape are briefly reviewed. It is pointed out that Bishop’s arguments for the stable existence of severe bowing are inconclusive, since in his example, conditions at the extremities of the stretched-out wall were ignored. In contrast to the case of a weakly bowed wall, for an elongated wall, the extremities are the most likely points of instability.
Molecular emissions from laser–solid-target interactions
Authors: Greig J. R.
Published: February 2003

When a high-power Nd/glass laser pulse is incident on a polyethylene target, a bright plasma plume is created. Subsequently, a cloud of un-ionized gas is formed which contains 10–100 times the amount of material in the plasma plume. This gas cloud is cold (expansion velocity ∼105 cm/sec) and dense (n≳1019). It is shown to contain diatomic molecules of carbon C2 by heating the core of the cloud with the pulse from a 1-kJ TEA CO2 laser. Then, the C2 molecules in the cold outer regions of the cloud are seen in absorption on the light emitted by the hot core.
Physical and electrical properties of plasma-grown oxide on Ga0.64Al0.36As
Authors: Chang R. P. H. , Chang C. C. , Coleman J. J. , Kauffman R. L. , Wagner W. R. , Feldman L. C.
Published: February 2003

Auger, Rutherford backscattering, and x-ray-diffraction measurements show that plasma-grown oxide films on Ga0.64Al0.36As are amorphous, uniform in composition with depth, and possess very sharp oxide-semiconductor interfaces. The electrical properties (I-V, C-V) of these films are such that they may be used for surface passivation of optoelectronic devices and as dielectric layers in electronic device fabrication.
A note on the assumption of quasiequilibrium in semiconductor junction devices
Authors: von Roos Oldwig
Published: February 2003

The usual junction relations connecting the number densities of minority and majority carriers across the junction or depletion layer of a p-n junction are only applicable to conditions pertaining to low-level injection. Although this fact has been suspected to be true for a long time, the general consensus has been that only exact numerical calculations will reveal at which injection level the simple junction relations become incorrect. Here we wish to point out that simple algebraic manipulations of the quasiequilibrium equations valid at very low injection levels suffice to show at what injection level the quasiequilibrium theory becomes untenable under a given circumstance. Thus, a new and simple method is provided to ascertain if an extensive numerical calculation is warranted in order to obtain meaningful device characteristics.
Optical and photoconductive properties of discharge-produced amorphous silicon
Authors: Zanzucchi P. J. , Wronski C. R. , Carlson D. E.
Published: February 2003

Optical and photoconductive properties of discharge-produced amorphous silicon (a-Si) of the type used in efficient thin-film solar cells have been studied as a function of a wide range of deposition conditions. The optical absorption, optical band gap, photoconductivity, hydrogen content, and the characteristics of the Si-H vibrational mode in a-Si were determined. Both substrate temperature in the range ∼200–400 °C and the type of discharge used are found to be important factors in determining the measured optical and photoconductive properties of a-Si. For films produced at substrate temperatures near 200 °C, dihydride bonding occurs, and the optical band gap is about 1.7 eV. As the substrate temerature increases, monohydride bonding is favored, the optical band gap decreases, the optical absorption increases, and the photoconductive properties improve. These properties are, in part, associated with the presence of bonded hydrogen. For substrate temperatures between 300 and 400 °C, the photoconductive properties are not strongly affected by changes in the substrate temperature, but are strongly influenced by the deposition technique. The Si-H bond is shown to be stable to thermal treatments at or below the deposition temperature. This is critical for the stability of a-Si properties in the fabrication of solar cells and other devices at elevated temperatures.
Photoluminescence of ZnSe single crystals diffused with a group-III element
Authors: Yamaguchi Masafumi , Yamamoto Akio , Kondo Mamoru
Published: February 2003

Photoluminescence of ZnSe single crystals doped with group-III elements (Al, Ga, In) has been studied in order to obtain both a high blue luminescence quality and suitable conductance for making a luminescence diode. The highest-energy blue emission, which is the strong blue emission in electroluminescence at room temperature, is increased with Zn-Ga diffusion. The free-to-bound blue emission is enhanced and the self-activated orange emission is suppressed with Zn-Ga and Zn-In diffusion. The Zn-Al and Ga diffused crystals exhibit only the self-activated emission. Several characteristics of the recombination centers have been examined, including the temperature dependence of the emission peak energy, half-width, and emission intensity, as well as excitation spectra for these centers. Information gained from these studies concerning impurity levels and luminescence processes in impurity-doped ZnSe crystals is discussed.
Approximate analytical solutions of diffusional boundary-value problems by the method of finite zone continuity
Authors: Reiss H. , Patel J. R. , Jackson K. A.
Published: February 2003

An approximate technique for solving diffusional boundary-value problems is described which has considerable generality and yields analytical results. The main feature of the method involves the relaxation of the pointwise requirement of material conservation while insisting that conservation is established at the boundaries of a finite region of the diffusion field. The main effect of this approach is to allow one to deal with the diffusion equation as though it were an ordinary rather than a partial differential equation. Several applications are discussed, and, in particular, one which has relevance with respect to the following paper on stacking-fault generation in silicon.
Particle-size distribution of NiO in coprecipitated NiO-Al2O3 powders
Authors: Kidron A. , De Angelis R. J. , Reucroft P. J.
Published: February 2003

The particle-size distributions along the [100] and [111] directions of NiO catalyst particles which were coprecipitated with alumina were measured by x-ray diffraction profile analysis. The average particle size is about 20 Å in both directions. The distribution along the [111] direction shows three peaks indicating an anisotropy in the shape of the particles and supports the idea that the particles are platelets with the [111] direction normal to their surface. This study shows beyond doubt that careful x-ray diffraction profiles analysis techniques employing least-squares analysis methods can be used to determine the distribution of particle sizes existing in metal supported catalyst materials.