bluuebunny/crossref_metadata_2025 huggingface dataset:
Young’s modulus of polycrystalline Nb3Sn between 4.2 and 300 K
Authors: Bussiere J. F. , Welch D. O. , Suenaga M.
Published: February 2003

Ultrasonic measurements show that the shear modulus 1/2 (C11−C12) softens dramatically as single crystals of Nb3Sn approach the martensitic transition near 50 K. It is expected that Young’s modulus of polycrystals will also soften, but previous ultrasonic measurements, which suffer from severe damping, fail to show the expected effect. We have measured Young’s Modulus of polycrystalline Nb3Sn between 4.2 and 300 K by static beam-deflection methods and observe marked softening. A value of 1.32×1012 dyn cm−2 was obtained at 300 K by the deflection of thin Nb3Sn-Nb-Nb3Sn composite strips by external stress. The variation of the modulus with T was obtained from the change in the radius of curvature of internally stressed Nb3Sn-Nb composite strips. (This method is made possible by the near-perfect match between the thermal expansion coefficients of Nb and Nb3Sn.) The modulus is found to be proportional to lnT between 50 and 300 K and is temperature independent below the superconducting Tc, resulting in a decrease by a factor of ∼2 between 300 and 18 K. The observed softening is somewhat less than that predicted by a polycrystalline average of the experimental single-crystal elastic constants,but is much larger than that observed with ultrasonic measurements.
Optical determination of mobility and carrier concentration in heavily doped polycrystalline silicon
Authors: Mishima Y. , Hirose M. , Osaka Y.
Published: February 2003

Optical absorption of phosphorus-doped polycrystalline Si films observed at photon energies below the energy gap has been interpreted in terms of free-carrier absorption, which obeys the Drude theory. As a result, we can simultaneously determine conductivity, electron mobility, and carrier concentration of heavily doped polycrystalline Si films from their optical transmission spectra alone. The new technique offers a contactless measurement of electrical properties for heavily doped polycrystalline Si thin films.
The emissivity of carburized rhenium
Authors: Pallmer P. G. , Gordon R. L. , Dresser M. J.
Published: February 2003

Reflection techniques were used to measure the spectral emissivity at a wavelength of 0.65 μm of 30-μm-thick Re foils containing 5 at.% C. When heated to a temperature above that for saturated solubility (1900 K) so that all carbon was in solution, the emissivity was 0.420.04, the same as that of pure Re. Heating at a lower temperature caused growth of a graphitic film on the surface and the emissivity increased to 0.700.10. When subjected to intermediate temperatures, the ribbon exhibited emissivity patches, and the average emissivity under these conditions was estimated to be 0.620.04.
New equivalent circuit model for electrographic discharge to dielectric paper
Authors: Landheer D.
Published: February 2003

A new equivalent circuit model for electrographic recording on dielectric paper with a backing electrode is presented. It is shown that the conductivity of a thin layer between the dielectric layer and basepaper is more important than bulk conductivity in the basepaper.
Single-crystal elastic constants of the equiatomic NiTi alloy near the martensitic transformation
Authors: Mercier O. , Melton K. N. , Gremaud G. , Hägi J.
Published: February 2003

The elastic constants measurements have been made for the first time on a single crystal of the near-equiatomic NiTi alloy. The results show that the elastic constants C′ and C44 both have a low value and a positive slope with temperature; this behavior makes NiTi unique in the class of alloys showing a martensitic transition.
Temperature dependence of high-frequency electron mobility in Ga0.47In0.53As
Authors: Chattopadhyay D.
Published: February 2003

Frequency and temperature dependences of the real and the imaginary parts of the high-frequency electron mobility in Ga0.47In0.53As are theoretically studied by an iterative solution of the Boltzmann equation. The high-frequency effects are found to be described by the Drude model unless a high accuracy is desired. The calculated results are sensitive to the value of the alloy scattering potential.
The spectral response of a front surface field solar cell
Authors: von Roos Oldwig
Published: February 2003

A calculation of the short-circuit current Isc as a function of wavelength of the incident light, induced in a front surface field solar cell, is presented. The cell consists of a P+-P-N+ junction. The electric field present in the P+ layer situated at the front surface (the surface exposed to the sun) boosts the minority carrier collection at the P-N+ junction sufficiently to make this structure a viable alternative to ordinary solar cells. A distinct advantage derives from the placement of all Ohmic contacts on the back-surface facilitating array assemblage.
Computer simulation of SEM electron beam induced current images of dislocations and stacking faults
Authors: Donolato C. , Klann H.
Published: February 2003

Images of dislocations and stacking faults as obtained in the scanning electron microscope operating in the electron beam induced current (EBIC) mode are produced by computer simulation on a cathode ray tube plotter. The calculations are based on a model describing charge-collection by a surface barrier in presence of a defect and assume that the minority-carrier diffusion length L in the bulk semiconductor is infinite. It is shown that the approximation L=∞ is valid when L≫Rp (Rp is the range of the electron beam) and is suitable for studying the EBIC images of defects in silicon. Simulations of dislocation images illustrate the influence of the inclination angle of a dislocation with respect to the surface on the shape of its EBIC image. Computed images of stacking faults in (100) and (111) Si are used to investigate the dependence of the contrast distribution of the image on the energy of the electron beam. Comparison with some experimental micrographs indicates that the model gives a satisfactory description of observed images. Limitations and possible improvements of the model are also discussed.
Theory of the flicker noise in homogeneous nondegenerate semiconductors with single-level SRH recombination centers
Authors: Min Hong S.
Published: February 2003

A theoretical flicker noise model for the homogeneous nondegenerate semiconductors with single-level Shockley-Read-Hall recombination centers with no spread in carrier lifetimes is presented where the dominance of the interband scattering over the intraband scattering (equivalent to the mobility fluctuations of free-charge carriers) is shown to be responsible for the flicker noise. The newly derived short-circuited excess noise spectra show all the essential features of the flicker noise in homogeneous semiconductors, i.e., in contrast to McWhorter’s model the noise spectra have no flattening at the low-frequency limit and have a frequency dependence of 1/ωγ with 1/2?γ?3/2, and as in Hooge’s empirical relation the spectra are proportional to the square of the magnitude of dc current and inversely proportional to the total number of free-charge carriers. When γ=1, the noise spectrum is independent of temperature. It is shown that γ depends strongly on the functional form of the electron capture probability cn(εc) in n-type semiconductors. It is also shown that the flicker noise in nondegenerate semiconductors with Shockley-Read-Hall recombination centers is a majority-carrier effect.
Thermoelectric power of tantalum-tungsten alloys
Authors: Lin A. C. , Brotzen F. R.
Published: February 2003

The absolute thermoelectric power of a series of Ta-W alloy crystals was measured between 4.2 and 300 K. The diffusion component of the thermopower as a function of composition would be expected to be proportional to the change of the density of states at the Fermi level with respect to composition. This could not be confirmed unequivocally in this investigation because of the difficulty of differentiating between phonon-drag and diffusion components. The derivative of the diffusion component of the thermopower with respect to temperature has a minimum near the electron/atom ratio of 5.5. The phonon-drag component of the thermopower is positive for all of these alloys and is strongly attenuated by the addition of alloying elements to Ta. The phonon-drag component of W is particularly sensitive to small alloy additions.
Shallow silicide contact
Authors: Tu K. N. , Hammer W. N. , Olowolafe J. O.
Published: February 2003

Device miniaturization requires dimensional shrinkage not only in the lateral directions but also in the vertical direction. A silicide contact in a shallow junction Si device has to be shallow, which means that in forming the silicide it may not consume more than a few hundred angstroms of Si from the substrate. A general scheme of making such a shallow silicide contact is reported here. The scheme utilizes the effect of alloying to dilute the contact reaction, and it produces a shallow contact and a protective diffusion barrier at the same time. Results of Pt-Cr alloys are presented for illustration.
Polarity-dependent tunneling conductance of Ta/Ta2O5/Ag junctions
Authors: Ekrut Horst , Hahn Artur
Published: February 2003

Conductance-voltage characteristics measured on Ta/Ta2O5/Ag tunneling junctions are strongly asymmetric. A similar result is known for Al/Al2O3/Pb junctions. In the Ta/Ta2O5/Ag case the results are fully consistent with the two-band model for the κ (E) dependence in the oxide barrier. A value of 2 V is obtained for the ’’contact potential’’ describing the barrier asymmetry. This value is well understood on the basis of known electrochemical data for Ta2O5 surface films on Ta. The same mechanism is suggested to apply to Al/Al2O3/Pb junctions.
Hysteresis losses and magnetic phenomena in rotating disks of type-II superconductors
Authors: Boyer R. , Fillion G. , LeBlanc M. A. R.
Published: February 2003

Hysteresis losses and the evolution of the magnetic flux threading disks of V and VTi rotating slowly in various static magnetic fields H0 directed perpendicular to the axis of rotation have been investigated by continuously monitoring 〈Bz 〉 and 〈By 〉, the average components of the magnetic induction, in the plane of the disk, parallel and perpendicular to H0. A simple model is developed which satisfactorily accounts for the hysteresis losses and the magnetic behavior during the initial changes and in the subsequent quasi-steady-state as the rotation progresses. The analysis indicates that dψ/dx=±k′Jc (B) describes the change of orientation of the sheets of flux lines with respect to H0 with distance from the flat surfaces. Jc (B) is the critical current density and k′ (T) is the shearing inclination parameter of the flux lattice in the sample. Our results confirm the hypothesis that, regardless of the initial magnetic state of the disk, in regions where ψ (x) varies with depth, the critical slope of the B profile (i) is diamagnetic and (ii) is not shallower than for the situations where the sheets of flux lines are parallel. We stress that point (i) requires that the rotation causes flux to escape from the disk against the gradient of B near the surface when the initial magnetic configuration is uniform or paramagnetic.
Superconducting properties of i
n s
i
t
u–processed Nb3/Sn-Cu composites
Authors: Finnemore D. K. , Ostenson J. E. , Verhoeven J. D. , Gibson E. D.
Published: February 2003

Performance characteristics for a family of Nb3Sn-Cu superconducting composites have been studied to determine the optimum value of various fabrication variables such as the Cu-to-Nb ratio, Sn content, reaction temperature, reaction time, and dendrite size in the original casting. Basic superconducting properties such as the critical current and effective upper critical field are found to change in a very regular way as these parameters change and there are clear design tradeoffs which can be made depending on the wire specifications needed. A typical high-performance wire is made from a Cu70Nb30 casting with 2–8-μm dendrite size reacted with a stoichiometric amount of Sn at 550 °C for 6 days. In this study there has been a special emphasis on materials made from casting of a Cu–20 wt% Nb dendritic alloy. Critical currents of this alloy are smaller than for the 30% Nb samples, but the wire can withstand about 3% bending strain at the outer surface of the wire with only modest degradation of the Jc values.
Evidence that helium irradiation blisters contain high-pressure gas
Authors: Terreault B. , Ross G. , St.-Jacques R. G. , Veilleux G.
Published: February 2003

Trapping of ∼20-keV helium in Be, Cu, and Nb at fluences near the blistering threshold has been investigated by proton backscattering and by elastic recoil detection. Blister cavities at a depth close to the mean range contain up to 2.3×1017 He/cm2 (or more), corresponding to pressures in kbars, in agreement with gas pressure models. Depending on the metal, and its condition (annealing, stresses), the blisters may or may not rupture and release a large burst of helium. The re-emission data of Bauer et al. agrees qualitatively with these trapping data.
A constitutive model for metals applicable at high-strain rate
Authors: Steinberg D. J. , Cochran S. G. , Guinan M. W.
Published: February 2003

A model, applicable at high-strain rate, is presented for the shear modulus and yield strength as functions of equivalent plastic strain, pressure, and internal energy (temperature). The parameters needed to implement the model have been determined for 14 metals. Using this model, hydrodynamic computer simulations have been successful in reproducing measured stress and free-surface-velocity–vs–time data for a number of shock-wave experiments.
Hashin-Shtrikman bounds on the effective elastic moduli of polycrystals with monoclinic symmetry
Authors: Watt J. Peter
Published: February 2003

Bounds on the effective elastic moduli of randomly oriented aggregates of monoclinic crystals are derived using the variational principles of Hashin and Shtrikman. The bounds are considerably narrower than the widely used Voigt and Reuss bounds. The Voigt-Reuss-Hill average lies within the Hashin-Shtrikman bounds in nearly all cases.
Growth and phase stability of epitaxial metastable InSb1−xBix films on GaAs. II. Phase stability
Authors: Zilko J. L. , Greene J. E.
Published: February 2003

Single-crystal metastable InSb1−xBix films have been grown on GaAs substrates by multitarget sputtering. The films were metastable in two directions on the In-Sb-Bi ternary phase diagram—the solid solubility of tetragonal InBi in zinc blende structure InSb was increased by more than a factor of 4, and the width of the InSb-InBi pseudobinary phase field was increased from ∼10−3% to ?0.5%. The transition from the single-phase metastable state M1 to the equilibrium state occurred through the intermediate metastable state M2. The thermal stability of single-phase films was found by high-temperature growth and post-annealing experiments to depend on film orientation in the following order: (110), (111), and (100). The metastable phase diagram was established for (110) oriented films in which it was found that the transition temperature from the M1 state to the M2 state ranged from 150 to 300 °C, depending on film composition, above the equilibrium eutectic temperature at ∼100 °C and to be only about 125 °C less than the liquidus temperature.
Growth and dissolution kinetics of III-V heterostructures formed by LPE. II. Comparison between thermodynamic and kinetic models
Authors: Small M. B. , Ghez R.
Published: February 2003

In a previous paper, we presented both thermodynamic and kinetic models to describe the nonequilibrium state which occurs naturally when growing heterostructures in the Ga1−xAlxAs system by LPE. In this paper we both develop these two models and show them to be mutually compatible as applied to both the GaAs1−xPx and the Ga1−xAlxAs systems.
I
n s
i
t
u monitoring by ellipsometry of metalorganic epitaxy of GaAlAs-GaAs superlattice
Authors: Hottier F. , Hallais J. , Simondet F.
Published: February 2003

I n situ ellipsometry has been used to monitor the growth of GaAs-GaAlAs superlattices by a metalorganic VPE process. The thickness and the regularity of the successive layers can thus be determined. Analysis of transition widths between successive layers is made and compared with results obtained by SIMS depth profiling.
Photoionization cross sections, electron-impact inverse mean free paths, and stopping powers for each subshell of silvera)
Authors: Lin D. L. , Strickland D. J.
Published: February 2003

Using the Herman-Skillman potentials and bound wave functions for each subshell of silver, we have computed the continuum wave functions, and subshell-by-subshell photoionization cross sections with photoelectron energies up to 10 keV. Applying a relationship between photoionization and electron impact ionization, we have obtained inverse mean free paths and stopping powers, again by subshell, for electrons penetrating through silver. The maximum electron energy considered is 100 keV. For the total photoionization cross section, comparison of our work with experiment shows excellent agreement for photon energies down to 100 eV, below which solid-state effects should be included. Theoretical total inverse mean free paths, being strongly dominated by contributions from 4d electrons, are in good agreement with data around 1 keV, but about a factor of 2 larger at energies below 100eV. Our stopping power is in good agreement with other theoretical work above 400 eV and approaches the relativistic Bethe formula above 10 keV. Range is also computed and is in good agreement with other theoretical work.
Simultaneous HF and DF laser excited by a ferroelectric ceramic capacitively coupled discharge
Authors: Brandelik J. E. , Breaux O. P.
Published: February 2003

With ferroelectric ceramic, principally BaTiO3 dielectric capacitive coupling electrodes, simultaneous HF and DF pulsed laser action has been obtained as a function of [H2]/([H2]+[D2]) in H2+D2+SF6 mixtures. The laser had a multiline output of 30 μJ for an efficiency of 5.4×10−4 at 120 pps. After 107 pulses there has been no degradation of electrodes or decrease in laser performance. Alternate H-source gases of CH4, C2H6, and C3H8 had lower HF laser output than H2.
Pulsed laser heating profile width and changes in total coupling with pulse length and pressure
Authors: Maher W. E. , Hall R. B.
Published: February 2003

Thermal coupling involves the heat absorbed by a surface in air under irradiation by a laser beam. At high incident intensities plasmas are ignited and there is an enhancement of total thermal coupling. Part of this occurs as some energy is transferred to the region outside of the laser beam spot because of plasma growth with increasing energy. The diameter of disk-shaped targets was used as a parameter in one set of experiments in order to determine the width of the radial heating profile. Second, when the axial temperatures of thin targets were measured as a function of time, there was a relationship for those and the assumed radial heating profiles which allowed the use of the Laplace inversion technique to obtain their widths. When the laser pulse length was varied over the range 1–25 μsec, the thermal coupling peak and threshold showed only small changes. No real optimization was seen when an initial spike was present. Thermal coupling at 0.1 Torr air pressure was found to lack the normal 1-atm enhanced regime. No abrupt intensity or fluence threshold was seen for either aluminum or titanium and the variation of thermal coupling with fluence was material dependent. Total thermal coupling maxima at 0.1 Torr were lower than those seen at 1 atm.
Vibrational kinetics in CO electric discharge lasers: Modeling and experiments
Authors: Stanton A. C. , Hanson R. K. , Mitchner M.
Published: February 2003

Numerous models have been developed to predict the performance of CO electric discharge lasers. Although many comparisons of predicted and observed laser power have been made, few comparisons exist at the more fundamental level of predicted and measured CO vibrational population distributions. Such comparisons provide a critical test of the vibrational kinetic mechanisms assumed in the models and may help explain discrepancies between predicted and measured laser output. In the present study, a model of CO laser vibrational kinetics is developed, and predicted vibrational distributions are compared with measurements. The experimental distributions were obtained at various flow locations in a transverse cw discharge in supersonic (M=3) flow. Good qualitative agreement is obtained in the comparisons, including the prediction of a total inversion at low discharge current densities. The major area of discrepancy is an observed loss in vibrational energy downstream of the discharge which is not predicted by the model. This discrepancy may be due to three-dimensional effects in the experiment which are not included in the model. Possible kinetic effects which may contribute to vibrational energy loss are also examined.
Growth of Gaussian instabilities in Gaussian laser beams
Authors: Abbi S. C. , Kothari Nitin C.
Published: February 2003

We present a theory for the growth of a Gaussian perturbation superimposed on a Gaussian profile laser beam. This theory gives an exponential growth of the perturbation for small distances z traveled inside the nonlinear medium. For larger values of z, the growth is not exponential. The growth parameter α is defined and an analytical expression for this parameter is obtained. Our theory gives a smooth matching between the exponential growth of perturbations in a linearized instability theory and the sharp self-focusing thresholds expected for smooth Gaussian profile laser beams propagating in nonlinear media.
Magnetostrictive effects in evaporated nickel films
Authors: Vittoria C. , Lubitz P.
Published: February 2003

We have made Ni films by electron beam evaporation for use as a variable delay surface acoustic wave (SAW) device. The films have been characterized by static magnetization and magnetostriction measurements as well as by measurements of SAW phase shift attenuation in applied magnetic fields. A unified theoretical treatment of the field dependence of all the measured quantities is developed, based on a free-energy expression containing Zeeman, demagnetization, anisotropy, magnetoelastic, and elastic energy terms. We introduce an analytical technique by which a quantitative measure of a film inhomogeneity such as the variance of the uniaxial magnetic anisotropy field may be deduced from static field experiments. The dynamic field analysis establishes basic analytical expressions for phase shift and attenuation of SAW devices which may serve as a useful guidance to the design of practical surface acoustic wave devices. Reasonable agreement between experiments and theoretical predictions of these calculations is obstained.
Mechanism of pulsed surface flashover involving electron-stimulated desorption
Authors: Anderson R. A. , Brainard J. P.
Published: February 2003

A simple model is proposed to explain how a breakdown avalanche of secondary emission electrons can lead to surface flashover when an insulator in vacuum breaks down a few nanoseconds after high voltage is applied. The case of a plane insulator–vacuum interface perpendicular to parallel electrodes is considered. Positive surface charging is assumed to occur almost immediately upon application of the voltage, and the attendent secondary emission avalanche is assumed to be maintained at saturation throughout the prebreakdown time delay by field emission from the cathode electrode. Bombardment of the insulator by avalanche electrons desorbs a cloud of gas, which is partially ionized as it drifts through the swarm of electrons in the avalanche. The electric field at the cathode end of the insulator becomes enhanced as positive ions accumulate, which in turn increases the field emission and the rates of gas desorption and ionization. This and other regenerative processes rapidly lead to breakdown. Field enhancement at the cathode end of the insulator and increased field emission are individually considered in determining the prebreakdown time delay, with very similar results. The model predicts a time delay of the order of 10 ns at E=10 MV/m, which is in reasonable agreement with experimental observations. The proportionality we have observed between the time delay and the inverse square of the applied voltage is also predicted, as well as a dependence of the time delay on the insulator length. The model may also account for the improved performance of insulators coated with certain metal oxides.
Simulation of the burst phase of exploding wires
Authors: Baker Louis
Published: February 2003

A one-dimensional magnetohydrodynamic code is used to simulate the explosion of a wire caused by the passage of a large electric current. Comparison with experimental results shows good agreement is achieved for a variety of wire materials and diameters until the time of ’’burst’’ or vaporization of the wire.
Observation of expanding gas bubbles from a pinched electron beam by fast photography
Authors: Wei P. S. P. , Beymer J. R. , Adamski J. L.
Published: February 2003

A self-focused electron beam produces a string of hot spots along its path in 0.35 Torr of air. In this communication we report some interesting snap shots on the luminous gas bubbles expanding from the pinched hot spots. The radial speed of expansion is measured to be ∼9 mm/μsec, which corresponds to ∼6 eV of kinetic energy per N+ ion.
Effect of resonance linewidth on the insertion loss of a periodically corrugated YIG film
Authors: Tsai Ming-Chi , Seshadri S. R.
Published: February 2003

The insertion loss for the magnetic waves on a periodically corrugated YIG film magnetized normal to the film surface is deduced from the solution of the full magnetostatic boundary-value problem taking into account the effect of the finite linewidth of the ferromagnetic resonance. It is found that the contribution to the insertion loss due to the distributed reflection and the mode conversion caused by the periodic surface corrugation is decreased as the resonance linewidth is increased.
The diagonal elastic constants of CsMnCl3⋅2H2O
Authors: Kwaaitaal Th. , Potters F. A. J. A.
Published: February 2003

The six diagonal adiabatic elastic constants of the compound CsMnCl3⋅2H2O have been determined by an ultrasonic pulse-echo technique. The ultrasonic velocities have been measured in the temperature range from 80 to 300 K. The thermal expansion coefficients have been determined in this temperature range to correct for changes in mass density and length of the ultrasonic path. The mass density has been determined from pycnometer measurements and from the lattice constants. The error in the elastic constants is 5×10−3 at room temperature.
Hot carrier injection at semiconductor-electrolyte junctions
Authors: Boudreaux D. S. , Williams F. , Nozik A. J.
Published: February 2003

It is shown that the energy of electronic minority charge carriers injected into an electrolyte from an illuminated semiconductor electrode may be significantly greater than that predicted by previous models. The time constants for tunneling from the semiconductor states in the depletion region are evaluated by two methods: approximating the final states as a continuum resulting from strong electron-vibration interaction in the electrolyte, and calculating the oscillation time between semiconductor states and the discrete electrolyte states before vibrational relaxation. Comparisons are made with the time constants for intraband electronic relaxation in the semiconductor, including the effects of quantization due to confinement in the depletion region, and with those for the vibrational relaxation in the electrolyte. The general conditions for the injection of hot carriers from semiconductors into electrolytes are specified.
Hydrogen content of amorphous silicon carbide prepared by reactive sputtering: Effects on films properties
Authors: Guivarc’h A. , Richard J. , LeContellec M. , Ligeon E. , Fontenille J.
Published: February 2003

Nearly ’’stoichiometric’’ amorphous silicon carbide films were prepared by the reactive sputtering of a silicon target in a gaseous mixture of Ar, CH4, and H2 (or D2). The use of the 1H (11B, α)αα nuclear reaction and infrared transmission measurements shows that controlled amounts of hydrogen can be incorporated in the films during deposition. The hydrogen content has a dominant effect on the density of the films, its optical gap, and its refractive index. The films could be well described as a polycarbosilane, made of CHn, SiH, and SiC groups. Moreover, 11B bombardment induces a decrease of the hydrogen content and a drastic change in the bonds of the polycarbosilane. In conclusion, we show that reactive sputtering is an alternative to the glow discharge technique previously described by W.E. Spear to obtain amorphous silicon carbide.
Sputtered indium-tin oxide/cadmium telluride junctions and cadmium telluride surfaces
Authors: Courreges Francis G. , Fahrenbruch Alan L. , Bube Richard H.
Published: February 2003

The properties of indium-tin oxide (ITO)/CdTe junction solar cells prepared by rf sputtering of ITO on P-doped CdTe single-crystal substrates have been investigated through measurements of the electrical and photovoltaic properties of ITO/CdTe and In/CdTe junctions, and of electron beam induced currents (EBIC) in ITO/CdTe junctions. In addition, surface properties of CdTe related to the sputtering process were investigated as a function of sputter etching and thermal oxidation using the techniques of surface photovoltage and photoluminescence. ITO/CdTe cells prepared by this sputtering method consist of an n+-ITO/n-CdTe/p-CdTe buried homojunction with about a 1-μm-thick n-type CdTe layer formed by heating of the surface of the CdTe during sputtering. Solar efficiencies up to 8% have been observed with V0c=0.82 V and Jsc=14.5 mA/cm2. The chief degradation mechanism involves a decrease in V0c with a transformation of the buried homojunction structure to an actual ITO/CdTe heterojunction.
The effect of strain upon the scaling law for flux pinning in bronze process Nb3Sn
Authors: Kroeger D. M. , Easton D. S. , DasGupta A. , Koch C. C. , Scarbrough J. O.
Published: February 2003

The semiempirical scaling law for flux pinning, Fp=ABnc2bl (1−b)m has been tested for bronze process Nb3Sn conductors under uniaxial tension. The dependences of the bulk pinning force Fp on the upper critical field Bc2 and the reduced field, b=B/Bc2, were weakly affected by strain. However, the factor A, which depends on the number and strength of the pinning centers, and on the Ginzburg-Landau parameter κ decreased by more than a factor of 20 when the compressive prestrain on the Nb3Sn was removed by application of external stress. The variations of Tc and Bc2 with strain suggest that the change in κ is not sufficient to account for the change in A. Therefore, it is probable that strain induces microstructural changes which affect the number and/or strength of the pinning centers.
Production and postacceleration of intense ion beams in magnetically insulated gaps
Authors: Humphries S. , Freeman J. R. , Greenly J. , Kuswa G. W. , Mendel C. W. , Poukey J. W. , Woodall D. M.
Published: February 2003

Experiments are described pertaining to the development of very high-current pulsed linear ion accelerators utilizing electron neutralization. A novel magnetically insulated gap using radial magnetic fields has been tested. It provides stable electron cloud confinement over microsecond time scales with no detectable leakage current. The gap can act as an ion injector when used in conjunction with a plasma source. Control of the electron cloud dynamics allows the injector to operate in an enhanced current density mode (10–50 times the Child-Langmuir limit) with high efficiency and with plasma source control of the current flow. Currents up to 20 kA at 100 kV applied voltage resulted when using a light-ion flashboard plasma source. Carbon beams were produced by extraction from a flowing plasma from a gun array. A 3-kA beam with equal fractions of C+ and C++ was extracted over a microsecond time scale with little proton contamination. The use of active plasma injection into the high-intensity magnetically insulated diode had the advantages of ion species control, reduction of gap damage, operation at constant impedance, elimination of plasma closure effects, and a demonstrated ability to control the extracted beam optics. Observations were also made of beam propagation and compared to fast neutralization models. Agreement was good, and an upper limit of 0.2% was calculated for the imbalance of ion and electron space charge. When using the carbon injector, two-thirds of the beam reached a second magnetically insulated gap where it was postaccelerated. The second gap had an applied voltage in the range 150 –200 kV with beam currents typically 2 kA. Observations were made of electrostatic focusing in the postacceleration gap. These were in good agreement with theory based on the concept of virtual electrodes determined by the neutralizing electron dynamics.
Conditions for soft x-ray lasing action in a confined plasma column
Authors: Suckewer S. , Fishman H.
Published: February 2003

The idea of using a multi-Z (e.g., carbon, oxygen) thin plasma column as a medium for soft x-ray lasing action is presented. A plasma confined by a strong magnetic field is first heated by a CO2 laser, and then cools rapidly by radiation losses. This leads to a level population inversion of hydrogen-like carbon or oxygen ions. Two computational models are presented. One uses given electron temperature Te(t) evolutions. The other uses Te(t) calculated from an energy balance equation with CO2 laser beam power as a parameter. According to calculations, a total gain of G≳100 is expected for 3→2 and G≳10 for 4→2 transitions (λ=182 Å and λ=135 Å, respectively) for C VI ions using a CO2 laser beam with power ∼5×1010 W for plasma column heating.
Experimental and computer analysis of P+-ion penetration tails in a SIO2-Si two-layer system
Authors: Desalvo A. , Galloni R. , Rosa R. , Zignani F.
Published: February 2003

Penetration profiles of P+ ions with energy between 70 and 150 keV incident 7.5° off the 〈100〉 axis on silicon covered with a SiO2 layer of thicknesses ranging from 0.05 to 0.20 μm were studied both experimentally and by computer simulation. Electrical measurements were routinely performed, but occasionally CAMECA ion-probe measurements were carried out to obtain chemical profiles. For a given energy of implantation, maximum penetration occurs when the oxide thickness produces an angular spreading of the misaligned incident beam with maximum transmitted intensity along the crystallographic direction. This suggests that the tails are due to a channeling process, in agreement with the finding by Blood et al. in bare silicon. It is also shown that diffusion occurs after 1/2-h annealing at 900 °C, implying the presence of a high-diffusivity region around the penetration tail.
Cathodoluminescence studies of anomalous ion implantation defect introduction in ZnTe
Authors: Norris C. B.
Published: February 2003

Depth-resolved cathodoluminescence was employed in conjunction with layer removal by chemical etching in an investigation of the anomalous postrange damage introduction which accompanies shallow ion implantations in ZnTe. 200-keV Xe+ implantations were performed at substrate temperatures of 300 or 80 K; the latter implant was postannealed at 300 K. The calculated projected range of these implants was 0.05 μm. However, 10- to 1000-fold quenching of the incumbent extrinsic and intrinsic ZnTe luminescence was found at depths of 1–2 μm following both implants. In comparison to the 300 K implant, the 80 K implant and subsequent 300 K anneal introduces postrange defects at a higher concentration and the highly damaged region extends to a greater depth. Injection level dependence measurements show that the predominant effect of the postrange defects is to introduce independent nonradiative recombination centers rather than to react with the incumbent luminescence centers. However, we presently have no clue to the identity of the defect species introduced. In conclusion, we discuss the implications of the anomalous defect introduction for the device technology of ZnTe.
X-ray rocking curves for silicon-on-sapphire characterization
Authors: Trilhe J. , Borel J. , Gonchond J. P.
Published: February 2003

An analysis of the double-crystal x-ray rocking-curve technique applied to silicon-on-sapphire technology is presented. Using the proposed model, it is possible to obtain a more accurate characterization of the silicon layer on the sapphire substrate.
Structure of electrodeposited equiatomic tin-nickel alloy
Authors: Lo C. C.
Published: February 2003

Theoretical diffraction intensities were calculated for electrodeposited tin-nickel alloy by assuming a unit cell of Ni3Sn2. They agreed very well with the observed intensities obtained from both x-ray and electon diffractions. The grain size for the tin-nickel plate was measured from transmission electron micrographs, and the grain boundary layer was evaluated by fracturing the sample inside an AES. By considering the grain interior as Ni3Sn2 and the grain boundary layer as tin and gaseous impurities, the combined density and the gross tin-to-nickel ratio agreed very well with the directly measured values.
Oxygen diffusion in silicon and the influence of different dopants
Authors: Gass J. , Müller H. H. , Stüssi H. , Schweitzer S.
Published: February 2003

The diffusion of oxygen in silicon is an important process with respect to the planar technology of semiconductor devices. A sensitive method was developed to measure oxygen concentration profiles in silicon by means of the nuclear reaction 18O( p,n) 18F. By this activation technique oxygen concentrations as low as 1015 atoms cm−3 can be registered in a silicon layer of 5 μ thickness. In a subsection we discuss the difficulties and limitations caused by the always present natural oxide layer on the surface of the sample. The temperature dependence of the diffusion constant has been determined between 1000 and 1280 °C. An activation energy for the diffusion of oxygen in silicon of 3.15 eV has been extracted from these data. In addition, the influence of other dopants as Ga, Al, B, and P to the oxygen diffusion has been investigated. The deviations we found in the oxygen concentrations appear to be produced by the preparation techniques of the samples rather than by a direct influence of the different dopants.
Energy dependence of deep level introduction in electron irradiated GaAs
Authors: Pons D. , Mooney P. M. , Bourgoin J. C.
Published: February 2003

The energy dependence of the introduction rates of the E2–E5 traps which are created by electron irradiation at room temperature has been studied and found to correspond to a threshold energy for production of 10 eV. A comparison is given between these results and other published results dealing with defects introduced by irradiation at 77 K.
Electron mobility and free-carrier absorption in InP; determination of the compensation ratio
Authors: Walukiewicz W. , Lagowski J. , Jastrzebski L. , Rava P. , Lichtensteiger M. , Gatos C. H. , Gatos H. C.
Published: February 2003

Theoretical and experimental studies of the electron mobility and the free-carrier absorption of n-type InP were carried out in the temperature range 77–300 °K. All major scattering processes and screening effects were taken into consideration. It was found that the experimental dependence of electron mobility and free-carrier absorption on temperature and/or on carrier concentration can be consistently explained only when the effect of compensation is quantitatively taken into account. Convenient procedures are presented for the determination of the compensation ratio from the values of electron mobility and from the free-carrier absorption coefficient. The high contribution of optical-phonon scattering in InP limits the applicability of the free-carrier absorption approach to electron concentration n≳1017 cm−3. Electron mobility, however, can be reliably employed for the determination of the compensation ratio for n≳1017 cm−3 at 300 °K and n≳1015 cm−3 at 77 °K.
A study of alloy scattering in Ga1−xAlxAs
Authors: Chandra Amitabh , Eastman Lester F.
Published: February 2003

The temperature dependence of electron mobility of high-purity LPE Ga1−xAlxAs layers (x<0.18) has been studied in the range 25–110 °K to measure the extents of alloylike and ionized impurity scattering. Values of the alloy scattering parameter EB (which may include a contribution from space-charge scattering) determined for these samples were found to lie in the range 0.36–0.51 eV, the average being 0.44 eV. The compensation ratio was found to be about 2, and independent of x.
Degradation mechanism of non-Ohmic zinc oxide ceramics
Authors: Eda Kazuo , Iga Atsushi , Matsuoka Michio
Published: February 2003

The degradation phenomena caused by dc and ac biasing in non-Ohmic ZnO ceramics are studied from the viewpoints of voltage (V)-current (I) characteristics, dielectric properties, and thermally stimulated current (TSC). As a result, it is concluded that the degradation caused by dc biasing is attributed to the asymmetrical deformation of Schottky barriers, due to ion migrations in Bi2O3-rich intergranular layers and in the depletion layers of the Schottky barriers; and that the degradation caused by ac biasing is attributed to the symmetrical deformation of the Schottky barriers, due to ion migration in the depletion layers of the Schottky barriers. Also, the relationship between the thermal runaway life of non-Ohmic ZnO ceramics and biasing conditions, such as biasing temperature and bias voltage, is obtained.
Carrier mobilities and breakdown in halogen doped polymers
Authors: Yoshino K. , Harada S. , Kyokane J. , Iwakawa S. , Inuishi Y.
Published: February 2003

Carrier mobilities in polyethylene (PE) and polystyrene (PS) doped with halogens such as iodine or bromine, were studied using a short electron beam pulse (100 ns time width). Both the hole and the electron signals induced by the electron bombardment in PE and PS increase with doping of halogens but the former is more affected. A logarithmic plot (Scher-Montroll plot) of the induced current versus time gives a knee at a time Tr, which is interpreted as the transit time of the carrier front between electrodes. Hole and electron mobilities in Br2 doped PE are about 2×10−5 cm2/V sec and 1×10−5 cm2/V sec, repectively, at room temperature, which are higher than those of undoped PE by more than two orders of magnitude. The activation energy of the mobilities also decreases from 0.330.01 eV for both electron and hole in undoped PE to 0.270.01 eV in doped PE. Similar effects are also observed in PS. Although hole mobilitiy is much smaller than electron mobility in undoped PS, these two become comparable after halogen doping. The electric breakdown strength of PE (about 6 MV/cm at room temperature) decreases after the doping of halogen (about 2.5 MV/cm in I2 doped PE at room temperature) and becomes temperature insensitive between 10 and 60 °C.
Feasibility of hybrid Josephson field effect transistors
Authors: Clark T. D. , Prance R. J. , Grassie A. D. C.
Published: February 2003

We consider the feasibility of fabricating planar superconductor-semiconductor-superconductor Josephson junctions in which the junction supercurrent is controlled by a gate electrode isolated from the junction by either a dielectric film (MOS-JOFET) or a Schottky barrier (MES-JOFET). We find that device critical currents between ∼1 and 100 μA and critical temperatures approximately a few K appear possible. We discuss the circuit applications of such devices.
Critical conditions of flux flow in long Josephson tunnel junctions
Authors: Rajeevakumar T. V. , Geppert L. M. , Chen J. T.
Published: February 2003

We have investigated several critical conditions for flux flow in long Sn–Sn-oxide–Sn tunnel junctions. These critical conditions are a temperature-dependent threshold magnetic field, a minimum current determined by the critical magnetic field Bc1, and a maximum voltage related to ?, the speed of the electromagnetic waves in the junction. In addition, we have also observed the two dimensionality of the k vector associated with flux flow in a magnetic field which was applied perpendicular to the axes of the vortices.
Magnetic properties of amorphous rare-earth–cobalt alloys
Authors: Buschow K. H. J.
Published: February 2003

The magnetic properties of several amorphous alloys prepared by melt spinning have been studied. These comprise alloys of the series Tb1−xCox, Y1−xCox (0.25⩽x⩽0.60), and R69Co31 (R=La, Nd, Sm, Gd, Tb, Dy, Ho, and Er). Most of the alloys in which the R component has an orbital momentum were found to exhibit large intrinsic coercive forces at low temperatures. The thermomagnetic history effects studied on several of these alloys have been interpreted in terms of a thermally activated magnetization process. The magnetic ordering temperatures of the series R69Co31 scale to the deGennes factor (g−1)2J(J+1) only approximatley. The systematic deviations suggest that the indirect magnetic coupling between the localized 4 f moments involves a term proportional to Si⋅Lj in addition to the main term, proportional to Si⋅Sj .
Permittivity and attenuation of wet snow between 4 and 12 GHz
Authors: Linlor William I.
Published: February 2003

The permittivity and attenuation of prepared samples of wet snow are measured and curves presented showing the dependence of these quantities on snow wetness and frequency. Equations are given that express the experimentally determined relation between attenuation per unit length and volume-percent wetness at any frequency between 4 and 12 GHz. Additional equations are given for the calculation of permittivity from the snow density, attenuation per unit length, and frequency. Water retention characteristics of snow are described. Some applications of the techniques, such as runoff forecasting from mountain snowpacks, are proposed.
Angular distribution of Si atoms sputtered by keV Ar+ ions
Authors: Okutani T. , Shikata M. , Ichimura S. , Shimizu R.
Published: February 2003

Angular distributions of sputtered Si atoms from polycrystalline Si targets were measured for Ar+ ions of 3 and 10 keV, at angles of incidence of 0° (normal incidence) and 60°. The results were compared with the theoretical ones obtained from Monte Carlo calculations by Kang et al. Theory describes qualitatively the experimental results fairly well. Some discrepancy between the theoretical and experimental results was, however, found in the preferred ejection angles. The preferred ejection angle of the experimental results for 10 keV at angle of incidence of 60° agrees very well with that suggested by the universal curve of the correlation between the preferred ejection angle and sputtering yield, which has been proposed by Betz et al.
Auger spectra induced by 100-keV Ar+ impact on Be, Al, and Si
Authors: Metz W. A. , Legg K. O. , Thomas E. W.
Published: February 2003

The Auger electron spectrum induced by the impact of 100-keV Ar+ on metallic aluminum is shown to be consistent with the source of Auger electrons being ejected target particles. The principal spectral line has been identified as being due to ejected Al atoms with a single 2p vacancy. Subsidiary peaks are due to ejected atoms and Al+ ions with one or two 2p vacancies. The ion-induced Auger spectrum of silicon is similar. By contrast the spectrum induced by Ar+ impact on Be exhibits a rather broad peak characteristic of a K-shell vacancy and is similar to that induced by the impact of electrons. By considering the lifetime of the Be K-shell vacancy we conclude that the Auger decay occurs while the Be atoms are either in the solid or interacting with the surface.