bluuebunny/crossref_metadata_2025 huggingface dataset:
Absolute measurement of low-energy H0 fluxes by a secondary emission detector
Authors: Ray J. A. , Barnett C. F. , Van Zyl B.
Published: February 2003

Secondary negative and positive charge emission coefficients for bombardment of a gas-covered Cu surface by H+, H0, and H− have been measured for projectile energies of ∼25–2500 eV. The secondary negative charge yield for H0 impact was found to be 1.15±0.08 times that for H+ impact. For H− impact, the secondary negative charge yield decreased less rapidly with projectile energy than that of H+ and H0 impact, being about an order of magnitude larger at the lowest energies investigated. The secondary positive charge yields were found to be independent of the projectile charge state and were about an order of magnitude smaller than the negative charge yields. The measurement techniques are described, and the results are compared with the data of other investigators.
Deposited profiles and homogeneous alloys from a hexagonal array of point sources
Authors: Dahlgren S. D.
Published: February 2003

Deposition profiles calculated for a hexagonal array of point sources were used to determine the optimum spacing of components in composite sputtering targets. The results showed that smooth deposit-thickness profiles and homogeneous alloys could be expected for a point spacing of one-half the source-to-substrate distance and that deposit-thickness variations had nearly the same spacing dependence as had been calculated earlier for parallel strip sources. A Ag-0.5 at.% Pu sputter deposit made from such a hexagonal-array composite target was found indeed to be homogeneous by autoradiographic analysis of the Pu distribution in the deposit. The results for both point and strip sources suggest that vapor deposition will homogenize any inhomogeneous composite source if the spacing of the inhomogeneity is less than one-half the source-to-substrate distance. Thus, vapor deposition can be used to chemically homogenize alloys.
The semiconductor-insulator-semiconductor (indium tin oxide on silicon) solar cell: Characteristics and loss mechanisms
Authors: Shewchun J. , Burk D. , Singh R. , Spitzer M. , Dubow J.
Published: February 2003

We have reported on the theory of semiconductor-insulator-semiconductor (SIS) solar cells and the experimental characteristics of indium tin oxide (ITO) -SiOx-silicon cells in previous publications. There appear to be no reports in the literature on SIS devices of any type with conversion efficiencies greater than about 12%. Theoretically, 20% efficiency should be possible using 0.2 Ω cm p-type silicon with a 12-Å interfacial layer. This paper seeks to identify the various possible loss mechanisms (and the range of efficiency loss associated with each of them) that seem to be impeding the achievement of the theoretical limit. To determine the losses, the dark I-V characteristics as a function of temperature and performance parameters such as Voc, Jsc, FF, and η as a function of the intensity of illumination (up to 6 suns) have been examined. The intensity measurements reveal in a very distinct way the presence of an interfacial layer and serve to confirm the applicability of the theoretical model.
A calculation of particle size distributions in the break-up of shaped charge jets
Authors: Shelton R. D. , Arbuckle A. L.
Published: February 2003

The break-up of stretching jets created by shaped explosive charges is treated from a dynamic and kinematic viewpoint. By examining the kinetic energy available in an idealized jet as it stretches and breaks and by including some material parameters typical of copper, the maximum permissible length of jet particles after break-up is calculated. By assuming that relief waves propagate from break points in the jet while the process of break-up continues in unrelieved parts of the jet, a distribution of number with respect to length is calculated for the jet particles resulting from break-up, so as to yield a most probable length and a maximum length. The results of two different assumptions for the speed of the relief waves are compared with experimental data for a copper-lined shaped charge.
Study of a rare-gas transverse fast discharge
Authors: Chubb Donald L. , Michels Charles J.
Published: February 2003

Results of an experimental and analytical study of a Blumlein-type transverse fast discharge operating with He and Xe are presented. An electro-optical voltage probe was used to measure the discharge voltage. The measured voltages were in good agreement with the computed voltages. The analytical model was used to predict the dependence of the discharge efficiency for producing metastables and ions on the important plasma and external circuit parameters. In He the ion efficiency is greater than the metastable efficiency, whereas in Xe the opposite is true. Much larger ion efficiencies (η+∼0.12) occur in He than in Xe, whereas much larger metastable efficiencies (η+∼0.20) occur in Xe than in He. The large dissociative recombination rate of Xe compared to He accounts for the differences in performance between Xe and He.
Coherent curvature radiation from an electron beam rotating in a plasma
Authors: Tzach D. , Benford Gregory , Roberson C. W. , Rostoker N.
Published: February 2003

Microwave-radiation bursts at λ∼1 cm are observed when a rotating relativistic electron beam interacts with a plasma. The power level exceeds 1 MW, and the radiation pulse lasts as long as the electron beam pulse for beams up to 1 μsec long. The results are consistent with a model of coherent curvature radiation from electrons bunched due to a two-stream instability. Other mechanisms are ruled out by observations of harmonic splittings and the power spectrum.
Anomalous carrier tail generation mechanism in BF+2 ion-implanted layers of silicon
Authors: Wada Yasuo , Hashimoto Norikazu
Published: February 2003

Anomalous carrier tail generation in BF+2 ion-implanted layers through gas-ion interaction is quantitatively examined by a combination of gas pressure measurements and carrier profile measurements. The collision cross sections of He, Ar, Kr, and N2 gases with BF+2 ions are derived from the relative peak carrier concentrations of the tail and residual gas pressure relationships. Below 10−2 Pa, simple gas-ion interaction occurs and the collision cross section is around 10−14 cm−2. A gas pressure of less than 10−5 Pa in the implanter ion path is necessary to almost completely eliminate the anomalous tail generation. On the other hand, more than 4×10−1 Pa, multiple collisions between the ions and the residual gas atoms/moleculs occur and the tail carrier concentration become saturated. BF3 gas molecules are also foud to generate B+ ions through collisions with BF+2 ions.
Frequency variations in quartz crystal resonators due to internal dissipation
Authors: Theobald G. , Gagnepain J. J.
Published: February 2003

The amplitude-frequency effect in quartz crystal resonators is a consequence of the nonlinear elastic behavior of the crystal. However, dissipation due to internal losses can also induce frequency changes caused by amplitude variations, but in this case with a large time constant. Nonuniform heating introduces thermal stresses and density changes which act on a propagating wave by nonlinear coupling through the third-order elastic constants. Both the heat and wave equations are solved for the quartz crystal, and thermal exchanges with the surrounding medium are considered for several types of mounting. The resonator frequency change due to variation of the driving level, which appears as the indirect amplitude-frequency effect, is calculated. It is shown that the large time constants experimentally observed can be mainly attributed to thermal diffusion through the connection wires.
Silicide formation by high-dose Si+-ion implantation of Pd
Authors: Chapman G. E. , Lau S. S. , Matteson S. , Mayer J. W.
Published: February 2003

The formation of palladium silicide phases by implantation of Si ions into evaporated-palladium films on two different substrates (Si and SiO2) has been investigated. The amount and phase of silicide formed depend on the implantation temperature, substrate type, and the penetration of the ions relative to the substrate depth. Provided the ions do not penetrate to the substrate, it is found that Pd2Si is formed for both types of substrate, even at 150 °K. When the ions just reach the Pd/substrate interface, the sample temperature and substrate type become important. For the SiO2 substrate, the amorphous alloy Pd4Si forms at low temperatures. With the Si substrate Pd2Si forms under all conditions and there is a large incorporation of silicon from the substrate into the palladium, to an extent dependent on the temperature. This effect is explained in terms of radiation-enhanced diffusion, possibly assisted by dynamic cascade mixing. In the SiO2 substrate case, oxygen is thought to play an important role in determining the formation of phases.
The dependence of the piezoelectric response of poly(vinylidene fluoride) on phase-I volume fraction
Authors: Scheinbeim J. I. , Chung K. T. , Pae K. D. , Newman B. A.
Published: February 2003

Investigations of the dynamic piezoelectric response (d*31 and e*31) of unoriented poled poly(vinylidene fluoride) films containing different volume fractions of phase-I and phase-II crystalline materials show a linear relationship between phase-I content and piezoelectric response. Samples were poled under conditions (106 V/cm at 23 °C) which produced no observable changes in x-ray diffraction patterns taken before and after poling. The piezoelectric strain constant of the unoriented phase-II film is d′31=0.48×10−12 C/N, while that of the unoriented phase-I sample is d′31 =6.68×10−12 C/N. The data supports a model in which the piezoelectric activity is primarily due to a bulk polarization of the PVF2 by a 180° dipole switching mechanism in the polar phase-I crystals.
Design of complex electron lenses consisting of two double cylinders
Authors: Saito T. , Kikuchi M. , Sovers O. J.
Published: February 2003

A family of complex electron lenses, consisting of two coaxial double-cylinder elements with unequal diameters, is investigated. It is concluded that the dominant contribution to the spherical aberration of such lenses arises in the accelerating component. Considerable reduction of the shperical aberration coefficient is possible in comparison with the unipotential and bipotential lenses customarily employed in cathode-ray-tube electron-optical systems.
Intense electron-beam propagation in a dielectric guide
Authors: Greenwald Anton C.
Published: February 2003

Intense electron-beam propagation in a dielectric guide, without external magnetic fields, has been studied for 30–100-keV beams with ν/γ?1. The electron beam was injected into an evacuated cavity lined by dielectric materials with a thickness exceeding the electron range. The beam did not propagate until it was charge neutralized by ions removed from the dielectric following surface flashover caused by electron bombardment. The charge transported was a linear function of the cylindrical guide length, and the beam could be focused by a conical guide. Transport efficiency was reduced for dielectrics made of SiO2 compared to various plastics.
Attenuation characteristics of a high-power CO2 laser by an air discharge plasma column
Authors: Kawamura Y. , Matoba M. , Nakai S. , Yamanaka C.
Published: February 2003

It was shown that an electric discharge plasma in air (240 A) highly attenuated a high-power CO2 laser beam. Maximum attenuation of 98% was obtained on the axis of the discharge column at 150 nsec after the start of the discharge.
The effect of molecular weight on glass-transition temperatures (compositional variation of glass-transition temperatures 3)
Authors: Couchman P. R.
Published: February 2003

A predictive equation for the influence of chain ends on glass-transition temperatures is derived from a thermodynamic theory for the compositional variation of Tg. This relation is found to give excellent agreement with results for the effect in polystyrene, and produces a convenient and accurate first approximation. Secondary approximations to the principal equation are formally identical to the Ueberreiter-Kanig and Fox-Flory equations for the variation of Tg with molecular weight.
Modeling of tensile properties of polymer blends: PPO/poly(styrene-c
o-p-chlorostyrene)
Authors: Fried J. R. , MacKnight W. J. , Karasz F. E.
Published: February 2003

Young’s modulus, yield (break) strength, and elongation to yield (break) have been measured for blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) with polystyrene (PS), poly(p-chlorostyrene) (PpClS), and random copolymers of styrene and p-chlorostyrene (pClS). The significant difference between blend compositions is the compatibility of PPO with each styrene polymer. Blends of PPO with PS or copolymers with 67.1 mole% or less pClS are compatible (i.e., one Tg) and show small synergistic maxima in modulus, strength, and elongation as a function of PPO composition. These maxima correspond to observed maxima in packing density as a result of specific interactions contributing to blend compatibility. A rule of mixtures for one-phase systems with an adjustable compatibility parameter gives adequate fit to the observed composition dependence of the modulus. In a narrow composition range between 67.8 and 68.6 mole% pClS, copolymers exhibit partial miscibility with PPO. Two mixed composition phases are present. Moduli of these transitional blends follow the same form of synergistic dependence on blend composition as do the compatible blends but strength and elongation exhibit a sigmoidal relation to blend PPO content. At about 20% PPO, strength (and elongation) reaches a minimum as predicted by a simple composite model for a dispersed phase with good adhesion to the matrix. A maximum is reached at ∼80% PPO at which composition blend test specimens yield prior to failure. Blends of PPO with PpClS and with copolymers of ≳68.6 mole% pClS exhibit a broader minimum in strength (and elongation) but a similar maximum at 80% PPO. Unlike the compatible and transitional blends, moduli follow a nonsynergistic composition dependence adequately represented by the series model for two-phase systems.
Theoretical prediction of the specific heat of polymer glasses
Authors: DiMarzio E. A. , Dowell F.
Published: February 2003

Lattice vibrations are incorporated into the Gibbs-DiMarzio configurational entropy theory of glasses. A comparison is made with data compiled by O’Reilly. The resulting theory predicts the specific-heat discontinuity at the glass transition to within 20%. No adjustable parameters are involved; only the chemical structure need be known. The specific-heat discontinuity has three parts. The formula in customary notation is Δcp=R (Δε/kTg)2 f (1−f) +RTgΔα (4−TgΔα/0.06) +0.5TgΔαcp(Tg−). The first part is a configurational term arising from shape changes of the molecules (?50% of total). The second part is a configurational term arising from volume expansion (?30% of total). Finally there is a vibrational contribution arising from the change of the force constants (or characteristics frequencies) with temperature (?20% of total).
The origin of the optical anisotropy of solvent cast polymeric films
Authors: Prest W. M. , Luca D. J.
Published: February 2003

The optical mode structures of solvent cast films of different polymers have been measured with a single prism film coupler. The allowed modes define the index of refraction for light polarized in and perpendicular to the plane of the film. It is shown that the solvent coating process preferentially aligns the polymeric chain backbone in the plane of the film and that this biaxial orientation may produce birefringent films in optically anisotropic resins. The sign of this birefringence depends upon the orientation of the dominating polarizable group relative to the chain backbone in the plasticized melt. The magnitude of this effect reflects both the optical anisotropy of the group and the steric constraints to its free rotation.
Glass transition temperature of nylon 6—Inorganic salt mixtures
Authors: Kim Hyo-gun , Harget Paul J.
Published: February 2003

The glass transition temperature of nylon 6–inorganic salt mixtures has been investigated. Tg not only increases monotonically with the salt content but the rate of increase depends on the type of salt. Infrared measurements indicate that metal ions form adducts with the amide group, and, as a result, the nylon chains are stiffened. This effect appears to be a major cause of the Tg increase. The adduct formation between the ions and the amide group is very similar to hydration of ions and the observed effect of ions on the Tg of nylon 6 is similar to the effect of the same ions on hydration. The effect is also shown well correlated to Q/R of the ion, the ratio of the oxidation number to ionic radius of the ion.
Viscoelastic properties of entangled polymers: Ternary blends of monodisperse homopolymers
Authors: Soong D. , Shyu S. S. , Shen M. , Hong S. D. , Moacanin J.
Published: February 2003

In a previous publication from this laboratory, the Rouse-Bueche-Zimm molecular theory of viscoelasticity has been extended by using a transient network model to apply to binary blends of monodisperse polymers with chain entanglements. The dynamics of the entanglements were modeled both by the enhanced frictional coefficients and by the additional elastic couplings. It was recognized that entanglements not only may form between chains of the same lengths (intracomponent entanglements) but also between those of different lengths (intercomponent entanglements). At a given intercomponent entanglement, the longer chain was assumed to have the frictional coefficient of the shorter chain. Similarly, for blends consisting of several monodisperse components with different molecular weights, such modifications are also required to predict their linear viscoelastic behavior. The frequency of these interactions is assumed to be proportional to the weight ratio of the respective component chains in the blend. Equations of motion are formulated for each component and solved numerically for the relaxation time spectra. Linear viscoelastic properties such as the dynamic mechanical moduli, stress relaxation moduli, and zero-shear viscosity can then be computed for these systems by linear summation of those of the components. The reduced steady-state shear compliance of the blends can also be computed from the component relaxation times. Results are found to be in good agreement with experimental data on polystyrene ternary blends.
Supercurrent-versus-magnetic field characteristics of two-dimensional Josephson tunnel junctions
Authors: Pace S. , Vaglio R.
Published: February 2003

Detailed measurements have been performed on the magnetic field dependence of ’’large’’ Nb-NbxOy-Pb Josephson junctions in which the junction dimension in the direction parallel to the applied field is several times larger than the Josephson penetration depth. The results are discussed in the framework of an approximate analysis for two-dimensional tunnel junctions, based on the assumption of a linear current-phase relation. A size-reduction technique has been employed for the samples, to allow a consistent comparison betweeen ’’large’’ and ’’small’’ junction behavior.
Basic Josephson tunnel parameters at microwave frequency—Strong temperature variations
Authors: Rudner S. , Claeson T.
Published: February 2003

Unexpected partly dramatic temperature dependences were registered for the basic tunnel parameters used to characterize a Josephson junction. Measurements of the magnetic field variation of the microwave-power reflection, i.e., a mapping of the Josephson plasma resonance, enabled determinations of the rf small-voltage resistance RJ, the cosφ amplitude ζ, and the effective junction capacitance C in both Pb-O-Pb and PbTl-O-Pb junctions. The uncertainties in the parameter values are large, particularly in the low temperature values of ζ, for which we confirm earlier estimates of ζ, but as the superconducting transition temperature Tc is approached, ζ increases rapidly and goes through a positive maximum close to +1 before it decreases towards zero at Tc. Also, RJ displays a pronounced maximum in the same temperature interval; it decreases rapidly within a narrow range below the temperature of the maximum before it again increases slowly well below Tc. The location in temperature for the two maxima depends upon the barrier via the critical current density, but seems to be material independent. Well below Tc, the ratios of RJ to the normal-state tunnel resistance are also affected by the barrier transmission. These latter properties seem hard to explain within a model based only on the relaxation of the order parameters in the superconductors. A considerable decrease in C close to Tc can be explained by temperature-dependent surface losses in the junction electrodes. The Q-value associated with these could be determined as a function of temperature. In accordance with previous measurements, the Josephson current IJ is reduced at low temperature in small high-resistance tunnel junctions. Smaller deviations in IJ from theoretical estimates can be explained by strong coupling effects.
Radial motion of unichiral magnetic bubbles with in-plane field
Authors: Gallagher Timothy J. , Humphrey Floyd B.
Published: February 2003

The radial motion of unichiral magnetic bubbles in an in-plane field has been investigated using transient photography. It is found that when a 20-Oe in-plane field is applied to a unichiral bubble, the wall section whose center spin is opposed to the in-plane field is initially immobile during a bias-field step pulse. This immobility lasts for about 25 nsec, depending on the pulse field. The normal wall section, whose center spin is along the in-plane field, moves with a drive-dependent velocity on the order of 20 m/sec. The velocity difference between the two walls occurs in films of all types, but is particularly prominent in the film with moderate damping (α=0.14) that is used here. Numerical calculations show that the in-plane field produces a different static-spin structure in each of these two wall sections. In the normal wall section, the in-plane field merely reduces the total twist due to the surface stray field. However, in the wall whose center spin is opposed to the in-plane field, a statically stable 2π horizontal Bloch line is nucleated when the in-plane field is above a threshold, which is 12 Oe for the film used here. The velocity of the normal wall is compared with that predicted by a one-dimensional model, and they are found to be in agreement for pulse fields less than 8 Oe. Numerical calculations of the velocity of the wall with the 2π HBL are made using Hubert’s finite-difference method. These calculations confirm that the wall section is essentially immobile until the HBL approaches the film surface. When the pulse field is greater than 8.6 Oe, punch-through of the 2π HBL occurs, leaving two opposite-winding VBL’s. An implanted layer suppresses punch-through.
Magnetic, surface, and corrosion properties of Ni-Fe-Pd thin films
Authors: Rice D. W. , Suits J. , Nepela D. , Tremoureux R.
Published: February 2003

Films in the Ni-Fe-Pd ternary system were evaporated and characterized with regard to magnetic properties, resistance to atmospheric corrosion, and surface composition. It was found that Pd behaves like Ni magnetically and results in little magnetic dilution. High moments can be maintained at high Pd concentrations. Low coercive forces exist in a trough from Ni0.8Fe0.2 to Fe0.7Pd0.3 in the ternary composition field. The magnetoresistance was found to be significantly less than for Ni0.8Fe0.2 (Permalloy) in all other composition regions. Pd addition at low concentrations caused the alloy atmospheric corrosion to increase and then decrease for higher Pd addition. The surface of these alloys is enriched in Fe and O while the oxide-alloy interface shows significant Pd enrichment. The oxide thickness increases with the addition of Fe.
Nitrogen isotope separation by multiphoton dissociation of methylamine
Authors: Chen Hao-Lin , Borzileri C.
Published: February 2003

A selective multiphoton photochemical process has been used to enrich nitrogen-14 isotope in methylamine. A separation factor of 2 has been achieved for irradiation of CH3N14H2/CH3N15H2/NO sample with the P (24) line of the 9.6-μ CO2 laser transition. The threshold laser energy fluence for reaction is roughly 30 J/cm2. The vibrational isotope shift of methylamine at the 9.6-μ region was found to be 12.5 cm−1. The selectivity of the photochemical reaction appears to be limited by the overlap of vibrational-rotational lines of CH3N14H2 and CH3N15H2 molecules due to power broadening under the intense laser field.
Time-resolved spectrometry of i
n v
i
v
o firefly bioluminescence emissions
Authors: Barry J. D. , Heitman J. M. , Lane C. R.
Published: February 2003

The optical emissions of in vivo bioluminescence pulses have been evaluated by time-resolved spectrometry for the first time. The firefly Photinus pyralis (Linnaeus) (Coleoptera: Lampyridae) was used as the test specimen. The time-resolved spectrometry has allowed evaluation of the intrapulse characteristics as well as those of the overall envelope. The light pulses were found to last 0.3–0.4 sec, have a nonsymmetrical wavelength envelope, have an emission peak near 585 nm, have apparently continuous omission over the interval 500–720 nm, emit a power of the order of 1×10−6 W/pulse, and have an intrapulse peak wavelength shift to shorter wavelengths during the pulse period. Time-resolved spectrometry is recommended for intrapulse evaluation of other bioluminescence systems.
Formation and properties of Na smoke particles
Authors: Hecht J.
Published: February 2003

The nucleation and growth of Na smoke particles were studied using light-scattering techniques. Homogeneous nucleation occurred at a rate at least 1011 slower than predicted by Becker-Döring or Lothe-Pound theory. This could be resolved either by assuming that the surface tension of small Na clusters (10 atoms) is larger than the bulk value or by applying a nucleation model which does not rely on macroscopic parameters. Particle growth initially occurred by single-atom accretion and then by particle-particle coagulation. Single-atom accretion was found to have a significant effect on particle size in disagreement with the model of Granqvist and Buhrman. A coagulation constant for a 23-nm-radius Na particle was measured as 3.6×10−9 cm3/s and was found to be in agreement with the free-molecular model of Fuchs.
Hydrogen-diffusion-rate-limited hydriding and dehydriding kinetics
Authors: Rudman P. S.
Published: February 2003

Hydriding and dehydriding kinetics are derived within the framework of the Johnson-Mehl-Avrami equation. Hydriding is considered to be rate limited by hydrogen diffusion through a growing hydride layer, and dehydriding by hydrogen diffusion through a growing metal layer. Incubation time effects due to surface contamination are taken into account by a delayed nucleation function. The dominant composition-dependent terms in the thermodynamics and in the mobility are taken into account to derive normative diffusivity for hydrogen. The temperature dependence of hydriding is defined by an activation energy (QD−ΔH̄H+ΔH12) where QD is the activation energy for diffusion of hydrogen in the hydride, ΔH̄H is the relative partial molar enthalpy of hydrogen in the hydride, and ΔH12 is the enthalpy of the hydrogen-pressure plateau reaction. For dehydriding the activation energy is (QD+ΔH̄H−ΔH12), but now QD and ΔH̄H refer to hydrogen in the metal. The solution thermodynamics contributions to the activation energy are shown to be very important. It is emphasized that in order to determine a meaningful activation energy, it is not the pressure that must be maintained constant but rather a factor T[1−(Pd/P)1/2] in hydriding and a factor [T[1−(P/Pd)1/2] in dehydriding, where Pd is the dissociation pressure of the hydride. Several hydriding studies from the literature are critically disccused in terms of these results.
Hydriding and dehydriding kinetics of Mg in a Mg/Mg2Cu eutectic alloy: Pressure sweep method
Authors: Karty A. , Grunzweig-Genossar J. , Rudman P. S.
Published: February 2003

The hydriding and dehydriding kinetics of Mg were measured by a method which sweeps through the pressure and reacted-fraction variables. However, a new data-analysis method is employed which permits the derivation of the kinetics at constant pressure, in which form they are much more amenable to interpretation. The eutectic alloy Mg/Mg2Cu was studied at hydrogen pressures such that only the Mg phase was hydrided and dehydrided, so that the Mg2Cu phase played a catalyzer role only. By analysis of the time, pressure, and temperature dependence of the kinetics, it is concluded that the hydriding is rate limited by the diffusion of hydrogen through a growing MgH2 layer, and that dehydriding is rate limited by the diffusion of hydrogen through a growing Mg layer. In addition to the Mg2Cu-catalyzed Mg, a vapor-deposited Mg component developed in the reactor. This complicated the analysis somewhat, but a separation and comparison of the kinetics of both Mg components was achieved. It is concluded that the catalytic role of the Mg2Cu phase is that it provides an external surface that can be reduced of hydriding/dehydriding inhibiting oxides or surface adsorbed gases.
A theoretical evaluation and optimization of the radiation resistance of gallium arsenide soar-cell structures
Authors: Debney B. T.
Published: February 2003

Theoretical treatments are used to analyze the performance of Ga1−xAlxAs/GaAs heteroface and graded band-gap solar cells, and to study the radiation resistance of the two types of cell. The optimization of these solar-cell structures to tolerate radiation-induced degradation in electronic properties is discussed and their power-conversion efficiency evaluated. The calculations indicate only a marginally greater output from the graded band-gap cell compared to the conventional heteroface type for optimized structures. A comparison with the performance of a Si space cell under 1-MeV-electron irradiation is made which illustrates a superior performance from GaAs in respect of efficiency and radiation tolerance.
Reflection and transmission in discontinuous cylindrical waveguides
Authors: Wilhelm H. E. , DuBow J. B. , Singh P.
Published: February 2003

Analytical solutions are derived for the electromagnetic E and H modes mn in a cylindrical wave guide of radius a and infinite length which is filled axially with media of different dielectric permittivity (ε) and magnetic permeability (μ) such that ε=ε1, μ=μ1 for −∞?z<−d; ε=ε2, μ=μ2 for −d<z<+d; and ε=ε3, μ=μ3 for +d<z?+∞. The power and the reflection and transmission coefficients of the E and H modes mn are given as functions of their frequency ω and the guide parameters εi, μi, a, and d. It is shown that the reflection and transmission coefficients exhibit a periodic fine structure for frequencies ω above the cutoff frequency ωmn, as a result of the spatial eigenvalue nature of the field solutions.
New profiled silicon photodetector for improved short-wavelength quantum efficiency
Authors: Chamberlain Savvas G.
Published: February 2003

A new silicon-profiled ion-implanted n+-n−-p photodetector structure was developed for improved quantum efficiency in the visible spectrum. This device offers a significantly improved blue color response and it is compatible with CCD and MOSFET technologies. Experimental results show that the new device offers a quantum efficiency of more than 80% at 4000-Å wavelength relative to less than 1% quantum efficiency which a conventional n+-p silicon photodiode offers at the same wavelength. In addition, the present new device offers a flat quantum efficiency of more than 80% in the ultraviolet and entire visible spectrum (3800?λ?8000 Å). Also, the present device can be used as an efficient silicon solar cell.
Elastoresistance-coefficient measurements of p-type silicon on sapphire
Authors: Onga Shinji , Ko Wen H. , Ohmura Yamichi
Published: February 2003

The elastoresistance coefficients are measured for p-type (001) silicon on (1̄012) sapphire substrate at room temperature. The impurity concentration in silicon is 2.4×1017/cm3. The additional strain applied to the SOS cantilever ranges from 5.4×10−5 to 2.1×10−4. The elastoresistance coefficients mij are measured to be m11=18.3, m12=8.5, and m44=188±0.2. These values are 50–80% larger than those of bulk p-type silicon. This can be ascribed to the fact that the energy level of the ground state with the light mass, which is split off under the compressive residual strain in the film of the order of 10−3, depends on the strain significantly more than bulk p-type silicon.
On the rate-controlling step of copper diffusion/oxidation through gold
Authors: Tompkins H. G. , Pinnel M. R.
Published: February 2003

We consider both diffusion of copper through gold via grain boundaries and oxidation, and the factors which cause one or the other to be rate limiting. From published data we conclude that when the surface reaction is oxidation in clean air, after a few hundred seconds the rate-limiting step is oxidation.
Grain-boundary diffusion of Ag through Cu films
Authors: Schoen J. M. , Poate J. M. , Doherty C. J. , Melliar-Smith C. M.
Published: February 2003

The interdiffusion of bimetallic couples consisting of 1850 Å Cu/1550 Å Ag on sapphire substrates has been studied using Rutherford backscattering for anneal temperatures ranging from 225 to 500 °C. The Ag-Cu couple was chosen because it represents a system in which only grain-boundary diffusion as opposed to lattice diffusion should occur. No Ag-Cu intermetallic compounds have been reported and the equilibrium solid solubility of Ag in Cu and Cu in Ag is under 3 at.% for the temperature range of interest. A series of in situ isothermal vacuum anneals established the following mechanism for interdiffusion in these couples. Initially, the Cu grain boundaries saturate with Ag. Then Ag atoms in the Cu grain boundaries diffuse to the Cu surface and spread out. Finally, the diffusion process ceases when about one monolayer of Ag covers the Cu surface. Also, at temperatures exceeding 350 °C, grain growth at the Ag-Cu interface roughens that interface and makes Rutherford-backscattering analysis more difficult. Grain-boundary diffusivity has been calculated employing the model of Hwang and Balluffi. Agreement with published values obtained by radioactive-tracer measurements on foil samples is quite good. A discrepancy was observed between grain size of Cu as estimated by the saturated concentration of Ag in Cu grain boundaries and that determined by TEM measurements. This can be accounted for by assuming that some grain boundaries are blocked by light impurity atoms or that the grain-boundary segregation coefficient of Ag in Cu is not unity. In either case, it is shown that analysis of the Rutherford-backscattering spectra with the Hwang and Balluffi model can take account of these factors.
AES observation of electron-beam-induced layer formation on ZnS in the presence of water vapor
Authors: Okada Akira , Oka Takao
Published: February 2003

Electron-beam-induced formation of a reacted layer was observed on a ZnS (110) cleaved surface. The layer was formed in the presence of 6.7×10−6 Pa of water vapor. The layer was studied by Auger electron spectroscopy (AES) using an electron-beam energy and current density of 3 keV and 1.4×10−2 A/cm2, respectively. An approximately 200-Å-thick reacted layer was grown after 40 min exposure to the electron beam. Oxygen diffusion into the bulk during the formation was found. The oxygen diffused layer was twice as thick as the initially formed layer. The zinc concentration beneath the layer was 3% less than that of the original cleaved surface. The disappearance of characteristic energy loss structures indicated the reduction of ZnS bonds in the layer. The formed layer may play an important role in the surface degradation process of the ZnS phosphors.
Morphology and crystallography of CdS-CdTe double layers on various GaAs surfaces
Authors: Bettini M. , Brandt G.
Published: February 2003

Epitaxial double layers of CdS and CdTe have been grown on GaAs by close-spaced chemical vapor transport, to study the growth of CdTe on various CdS surfaces. Since the [00.1] axis of CdS aligns to one of the 〈111〉A axes of the GaAs substrate, the deposition of CdS on {111̄}A, {110}, and {100} GaAs surfaces yields approximately the {00.1}, {10.3}, and {11̄.1} CdS surfaces. On {111̄}A and slightly inclined substrates the CdS-CdTe layers (2–10 μm thick) grow uniformly thick with smooth surfaces. On the {110} and {100} faces the CdTe layers show a scale structure through the whole layer, which is approximately aligned to one of the 〈111〉 axes of the substrate. X-ray investigations reveal three- and two-dimensional lattice defects in the CdTe layer such as twinning, cubic-hexagonal mixture, stacking faults, fiber texture, and polycrystallinity. The number of defects increases in layers grown on {111̄}A to {110} and to {100}. The most perfect layers on {111}A faces and slightly inclined ones have a cubic structure with twinning about the growth direction. On {110} and {100} faces, the [00.1] and [111̄] stacking axes of the three lattices are slightly tilted to each other. The tilt angle can be explained by an accommodation of the lattice mismatch at the interface in such a way that the stacking planes join together continuously at the boundaries.
Application of the current noise technique to the investigation on dislocations in metals during plastic deformation
Authors: Bertotti G. , Celasco M. , Fiorillo F. , Mazzetti P.
Published: February 2003

A current noise due to dislocation processes in aluminum film samples has been put in evidence during plastic deformation. Burst-type dislocation generation and annihilation processes have been observed, showing the discontinuous character of plastic flow and the presence of strong correlation effects on dislocation dynamics. Noise behavior shows a strong enhancement of the dislocation generation and annihilation events with increasing temperature, a fact which accounts for the material softening at high temperature. The stress-strain behavior of the metal film upon cyclic deformation is obtained from the noise results; in particular it is possible to detect the very beginning of plastic deformation of the metal and the temperature dependence of the elastic limit. The behavior of the dislocation density during cycling can also be obtained. Such a behavior of the dislocation density during cycling can also be obtained. Such a behavior is accounted for by a theoretical model where the competing effects of generation and annihilation of dislocations are evidenced through a balance equation. It can be concluded that current noise yields more detailed information on plastic deformation than usual acoustic noise emission methods and can be easily applied to nondestructive mechanical testing of integrated circuits metallizations.
Ultrasonic parametric amplification effects: Contributions of the nonlinear material coefficients
Authors: Economou John E. , Spector Harold N.
Published: February 2003

This paper presents a theoretical approach to ultrasonic parametric processes in piezoelectric semiconductors that takes into account the contributions of the nonlinear material coefficients to various frequency-mixing phenomena. We have found, in particular, that the coupling coefficients for second-harmonic and subharmonic generation can be dominated by the contributions from the lattice anharmonicity and the nonlinearities in the strain rather than by the contributions arising from the nonlinear currents. Comparison with previous theories and experiments is made and the significance of the results is discussed.
Size effects on the normal-state resistance of long microbridges
Authors: Berchier Jean Luc , Weiss Laura , Sanchez Daniel H.
Published: February 2003

We have calculated, within the Fuchs-Sondheimer approach, the effect on the normal-state resistivity introduced by the width in a long microbridge made in a thin film. It is shown that for bridges having widths smaller than about ten times the film thickness, their resistance increases. This result is in agreement with existing experimental results. We also discuss the role played by the effective bulk mean free path in relation to the film and bridge superconducting properties.
The AI1−y
BIy
CIIIDVI2x
EV I2(1−x) pentenary alloy system and its application to photovoltaic solar energy conversion
Authors: Shewchun J. , Loferski J.J. , Beaulieu R. , Chapman G. H. , Garside B. K.
Published: February 2003

This paper reports work on pentenary alloy systems similar to the quarternary system in In1−xGaxP1−yAsy. Such AI1−yBIyCIIIDVI2xEV I2(1−x) and AII1−yBIIyCIVDV2xE V2(1−x) pentenary alloys are mixtures of ternary chalcopyrites of the I-III-VI2 and II-IV-V2 variety. These materials are of interest because their use can improve the performance of heterojunction electro-optic devices such as solar cells. This improvement arises because the pentenaries can permit different semiconductor layers to be deposited upon each other such that they are lattice and crystallographically matched, but at the same time have independently adjustable band gaps. More specifically, we have focused on the Cu1−yAgyInS2(1−x)Se2x system which appears to have the best potential of all the possible systems for solar energy applications. Samples were prepared by reacting stoichiometric powder mixtures at about 900 °C. X-ray diffractometry indicated complete solid solubility over the whole compositional range. Cathodoluminescence was used to determine band gaps at 300 and 77 °K and the spectra indicate that all alloys are direct-band-gap semiconductors. Isolattice constant and band-gap contour maps for the system have been obtained.
Crystallization in amorphous germanium
Authors: Germain P. , Zellama K. , Squelard S. , Bourgoin J. C. , Gheorghiu A.
Published: February 2003

Crystallization has been studied in amorphous germanium layers produced by evaporation. The crystalline fraction is deduced from conductivity measurements. Depending upon the conditions of evaporation homogeneous or heterogeneous nucleation is observed and the crystallization is induced at the surface or in the bulk. The variations with temperature of the growth rate of crystallization and of the nucleation rate are obtained from the kinetics of the crystallization measured at various temperatures. The results allow to provide orders of magnitude for the thermodynamical parameters which characterize the crystallization.
Crystallization in amorphous silicon
Authors: Zellama K. , Germain P. , Squelard S. , Bourgoin J. C. , Thomas P. A.
Published: February 2003

Crystallization has been studied in amorphous silicon layers produced by evaporation. The crystalline fraction is deduced from conductivity measurements. Depending upon the conditions of evaporation homogeneous or heterogeneous nucleation is observed and the crystallization is induced at the surface or in the bulk. The variations with temperature of the growth rate of crystallization and of the nucleation rate are obtained from the kinetics of the crystallization measured at various temperatures. The results allow one to provide orders of magnitude for the thermodynamical parameters which characterize the crystallization.
Transport processes of electrons in MNOS structures
Authors: Suzuki Eiichi , Hayashi Yutaka , Yanai Hisayoshi
Published: February 2003

The transport processes of electrons in MNOS structures, especially in the SiO2 layer and the surface region of the Si substrate, have been investigated using p-channel MNOS transistors with a relatively thick SiO2 layer to avoid the complexity of two-carrier transport in the system. An induced junction technique utilizing the electron and hole separation properties of the transistor structure was used as a means of analysis. Theoretical derivation of the carrier multiplication factor, i.e., the number of electron-hole pairs produced by an electron entering the Si from the SiO2, is calculated. It is experimentally shown that an electron entering the Si from the SiO2 produces approximately one electron-hole pair in the low negative gate bias voltage range up to a critical voltage, and above this critical voltage the multiplication factor increases with increasing gate bias voltage. The former observation is in good agreement with the prediction of the theory, considering cascaded impact ionization of an electron with high energy in Si. The latter fact reveals that electrons in SiO2 become hot in the high voltage range. The critical voltage coincides with the value theoretically estimated using an LO phonon energy of 0.153 eV and an electron-phonon scattering length of 1.74 Å in SiO2. The mean free path of the electrons between scatterings by defects or other scattering centers in SiO2 is estimated to be about 30 Å by analyzing gate bias dependence of the multiplication phenomena.
Studies of the effect of oxidation time and temperature on the Si-SiO2 interface using Auger sputter profiling
Authors: Helms C. R. , Johnson N. M. , Schwarz S. A. , Spicer W. E.
Published: February 2003

In this paper, we present the results of new studies of the Si-SiO2 interface for thermal oxides using Auger electron spectroscopy with ion etching. We will describe the results obtained from a matrix of samples chosen to study the effect of oxidation time and temperature on the chemistry and morphology of the Si-SiO2 interface. This matrix consists of oxides grown on (100) silicon that have a range of thickness 25–100 nm and growth temperatures 800–1150 °C. In order to assure proper interpretation of the results, we have developed models for electron escape depth and ion knock-on broadening of Auger sputter profiles which will also be described. We find the 10%/90% width of the transition region between SiO2 and Si is independent of oxide thickness over the range of our measurements. The width of this transition region increases slightly between growth temperatures of 800 and 1150 °C. These results will be compared to previous Auger as well as x-ray photoelectron spectroscopy studies on the Si-SiO2 interface.
Flux distribution and hysteresis loss in a round superconducting wire for the complete range of flux penetration
Authors: Ashkin M.
Published: February 2003

Flux distributions are determined numerically for quasistatic conditions within the Bean model. The field penetration ranges from 0 to 100%. The moving boundary of this distribution is calculated using an optimization technique to force the field component on the boundary to vanish, the variables being the parameters describing the boundary curve. The hysteresis loss is found using the flux distribution for a variable field superposed on a constant bias; the two fields are parallel to each other and transverse to the wire axis.
The equivalent circuit of a step discontinuity in surface acoustic wave metallic gratings
Authors: Ristic Velimir M.
Published: February 2003

The equivalent circuit of a step discontinuity in surface acoustic wave metallic gratings is of interest in many surface-wave devices such as resonators and high-frequency filters for signal processing applications. Using the field theory approach several equivalent circuits of a step discontinuity in SAW metallic gratings were derived in the limit of a single-normal-mode approximation for acoustic waveguides. The equivalent circuits clearly demonstrate the contributions of various device parameters to the energy storage and the impedance mismatch at the junction.