bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic and stationary charging of heavy metallic and dielectric particles against a conducting wall in the presence of a dc applied electric field
Authors: Colver G. M.
Published: February 2003

Dielectric and metallic paricles (both spherical and irregular in shape) in the range 29−4760 μm in diameter are electrically charged while in dynamic or stationary contact with either wall of a charged parallel-plate capacitor. The charge distribution received tends to remove any particle from the wall. Particles larger than 127 μm are studied individually with dc electric field strengths of 2−15 kV/cm. Smaller particles are studied mainly in the form of clouds. In the presence of gravity and standard atmosphereic air, the particle motion, once initiated, is continuous between the parallel plates both dynamic and stationary charging and the resulting particle motion are experimentally and theoretically studied considering the particles as capacitors in themselves. For copper particles a single formula of the form Q= (πε) a2EK applies 2EK applies with K=1.64 whether or not charging is dynamically or statically acquired. The presence of an oxide film does not alter K. Dielectric particles followed a similar equation (K<1.64) when contact (triboelectric) charging was assumed small and surface electrical conductivity was sufficiently large. K for dielectrics is dependent on surface conductivity, permittivity, diameter, and contact time. Induced average particle velocities in atmospheric air were tested from 40 to 105 cm/s. Inelastic particle-wall collisions and a conservative body force such as gravity resulted in a critical lower limit electric field strength for sustained particle motion. Gaseous discharge from a particle to a wall of opposite sign can occur with sufficient particle size and electric field strength.
Halide composition profiles in silver halide microcrystals
Authors: Kelly T. M. , Mason M. G.
Published: February 2003

We investigated the halide composition depth profile in micron-size silver halide microcrystals using x-ray photoelectron spectroscopy in conjunction with ion etching. Using a double-jet technique, intentionally mixed halide microcrystals were precipitated such that the thermodynamic equlibrium of the solution-solid interface was maintained. Microcrystals precipitated using halide-conversion techniques showed a compositional variation. In bromide-converted silver chloride microcrystals, after an initial decrease from the surface value, the chloride ion concentration increased smoothly with depth, leveling off (at about 100 nm below the original surface) to a value about 10% higher than in the surface region. X-ray diffraction patterns from these microcrystals show a skewed line shape for the halide-converted materials. A graded-band-gap model is proposed which may account for the tendency of the halide-converted crystals to form an internal latent image.
Multitarget sputtering using decoupled plasmas
Authors: Wickersham C. E. , Greene J. E.
Published: February 2003

A method is developed for quantitatively predicting the chemical composition and thickness distributions of alloy films deposited by decoupled-plasma multitarget rf sputtering in which the substrates rotate at a variable rate through separate glow discharges. The film thickness distributions deposited from each target are expressed in terms of deposition variables such as applied target voltage, target radius, sputtering pressure, substrate rotation radius, rotation rate, and target-substrate separation. Predicted films thickness distributions were found to be in agreement with experimental results in which β backscattering was used to measure the thickness of InSb films deposited on both stationary and rotating substrates. Using deposition parameters determined from the model presented in this paper, single-phase In1−xGaxSb alloy films were grown whose experimentally determined compositions agreed with predicted values. Intercalated films with layer thicknesses of less than 100 Å and films which were chemically graded in the lateral and in-depth directions were also grown.
Interstitial trapping during stage I
E recovery of electron-irradiated pure aluminum and its dilute alloys with Ag and Mg
Authors: Rizk R. , Vajda P. , Maury F. , Lucasson A. , Lucasson P. , Dimitrov C. , Dimitrov O.
Published: February 2003

Recent experimental data on the influence of additional vacancies and Frenkel pairs upon the stage IE recovery of electron-irradiated Al and Al-15 ppm Ag and newly obtained results on the dilute alloy system Al- (5–65) ppm Mg are analyzed in terms of the chemical reaction rate theory. The corresponding rate equations are solved numerically yielding the following quantitative results: the capture radius of a vacancy for an Al self-interstitial, rAlv=2.1a0; the capture radii of an Mg and of an Ag atom, respectively, rMg=0.33rv, rAg=0.6rv; the electrical resistivity of a unit concentration of vacancies, ρv=2.0×10−4 Ω cm/unit concentration. The best fit has been obtained with a value of Em=112 meV for the migration energy of la self-interstitial and a frequency factor of 3×1014 sec−1.
Kinetics of carbon deposition on diamond powder
Authors: Chauhan Satya P. , Angus John C. , Gardner Nelson C.
Published: February 2003

The rate of carbon deposition on 0–1-μm diamond seed crystals was investigated in the temperature range 1140–1475 °C, methane partial pressures form 10−3 to 44.4 Torr and hydrogen partial pressures from 0 to 16.4 Torr. Two distinct kinetic regimes were found. A relatively rapid initial rate of diamond growth decayed exponentially to a final slow constant rate as graphitic carbon was codeposited and covered the surface. A maximum initial diamond growth rate of 1.06×10−7 g cm−2 min−1, which corresponded to a nominal linear growth rate of only 0.45 μm per day, was observed. Dilution of methane with hydrogen decreased the nucleation rate of graphitic carbon relative to that of diamond resulting in a increase in the diamond yield. The activation energy for diamond deposition from pure methane was 55 kcal mole−1. The dependence of the initial rate data on methane partial pressure could be described by a Langmuir-type equation. The deposits were identified by chemical etching, chemical analysis, density measurements, x-ray and electron diffraction, transmission electron microscopy, and optical measurements. The crystalline quality of the diamond was not determined and could be highly defective.
Transmission electron microscopy determinations of dislocation Burgers vectors in plastically deformed yttrium iron garnet single crystals
Authors: Rabier J. , Garem H. , Veyssière P.
Published: February 2003

Dislocations have been studied in YIG by transmission electron microscopy. Loops are found to have (a/2) 〈111〉 Burgers vectors whereas dislocation segments may have (a/2) 〈111〉 or a 〈001〉 ones, the latter resulting from the attractive reaction of dislocations with (a/2) 〈111〉 Burgers vectors. Owing to the large unit cell of YIG, experimental imaging conditions prevented from concluding on the possibility of dislocation dissociation.
Electrical responses of nonlinear piezoelectric materials to plane waves of uniaxial strain
Authors: Chen Peter J. , Davison Lee , McCarthy Matthew F.
Published: February 2003

In this paper we consider propagation of finite-amplitude plane waves of uniaxial strain in piezoelectric disks exhibiting fully coupled nonlinear response. In particular, we derive explicit expressions for determination of the electric current in external circuits consisting of resistors, inductors, or capacitors connecting the electrodes on the faces of a disk. The formulation of a specific-boundary initial-value problem is discussed and a discussion of how the fully coupled electromechanical problem may be solved numerically is given.
New method for the measurement of hydrogen diffusion in metals
Authors: Zeilinger A. , Pochman W. A.
Published: February 2003

Neutron radiography is established as a method to measure hydrogen diffusion in metals. Measurements on β-Ti are reported.
Acoustic phase technique for measuring stress region in materials
Authors: Souquet J. , Kino G. S.
Published: February 2003

This paper describes an acoustic phase measurement by which a phase shift by a fraction of a degree can be detected. This method enables us to measure stress in a fatique-cracked double-cantilever steel sample in the region around the crack. The results give an indication of the size of the plastic region in the neighborhood of the crack.
Noise-equivalent power in highly doped infrared Schottky-barrier diodes without substrate
Authors: van der Ziel A.
Published: February 2003

The noise-equivalent power of heavily doped infrared silicon Schottky-barrier diodes is calculated for the case in which the substrate has been eliminated. Assuming an antenna radiation resistance Ra=100 Ω and minimizing Peq at λ=10 μm for an impurity concentration of 1019/cm3 yields Peq=10−12 W/Hz1/2 for the detector and Peq=4.8×10−17 W/Hz for the mixer.
Diamagnetic studies on as-processed carbon fibers
Authors: Scott C. B. , Fischbach D. B.
Published: February 2003

The diamagnetic susceptibilities of a wide range of commercially available carbon fiber types have been investigated in the as-processed condition by the Faraday method at room temperature using small bundles of aligned fibers. The tensor trace (total) susceptibility χT varies systematically over the range 0.8–20 (in units of −10−6 emu/g) as a function of precursor type and processing history. In general, χT increases with increasing nominal treatment temperature and hot stretching, and with increasing tensile elastic modulus E; but there are significant differences in the behavior of fibers from rayon or isotropic pitch and those from polyacrylonitrile (PAN). However, the anisotropy ratio χradial/χaxial increases approximately linearly with E for all fibers (from ∼1 for E?70 GN/m2 to ∼22 at 700 GN/m2 in air); and is quantitatively consistent with the layer-plane orientation textures determined by x-ray diffraction when appropriate values of the ’’crystallite’’ principal susceptibilities χa and χc are used. These are determined by setting χa=0.32, the graphite value, and computing the structure-dependent χc value from the observed χT. The dependence of χT on apparent layer size La is similar to that of glassy carbons. The significance of these results is discussed in relation to the characterization of carbon fibers and the structure dependence of the diamagnetism of disordered carbons.
Reflection of nonlinear shock waves in a lattice
Authors: Tasi James
Published: February 2003

An analysis is made of the longitudinal shock response of a finite one-dimensional elastic lattice with a step jump in velocity applied at one end and the remaining end free. For linearly elastic interactions between nearest-neighbor particles, an exact solution is obtained using transform theory. For nonlinear elastic interactions, an asymptotic solution is obtained for the head of the pulse response near the free end, in terms of incident compression wave and reflected tension wave contributions. Nonlinear solutions for particle velocity and strain response near the free end are presented and discussed when the incident shock wave that has evolved in a lattice is of oscillatory form or is a sequence of solitary waves. On reflection of an incident shock wave at a free end, the strain response of a lattice behind the reflected wave rapidly alternates between compression and tension rather than behaving as an elastic continuum with a strain-free response. The cumulative effect of nonlinear elastic interaction is to accentuate these changes near the free end and noticeably increase the difference between lattice and continuum responses.
High-resolution spectroscopy with a tunable dye laser
Authors: Zeltmann A. H. , Wampler F. B.
Published: February 2003

Two high-resolution spectra taken at SO2 pressures of 40 and 122 Torr illustrate results obtained using a tunable dye-laser spectrometer. The spectra taken in the 3880-Å region with an intracavity etalon inserted to narrow the bandwidth to 0.015 Å were used to obtain a measurement of the self-broadening of SO2 for the spin-forbidden singlet-triplet transition, 3B1(0,0,0) ←1A1(0,0,0).
Calculated spectral dependence of gain in excited GaAs
Authors: Stern Frank
Published: February 2003

The calculated dependence of the gain coefficient on photon energy and excitation level in GaAs is given for 297 and 77 K. The curves of gain versus excitation rate generally have downward curvature for photon energies near the gain peak, while the envelope of these curves generally has upward curvature except at high excitation rates. Results are also given for the calculated dependence of the radiative recombination rate coefficient and of the photon energy at the gain peak on excitation rate. The qualitative behavior of the results is in agreement with experiment.
Investigation of the structure of ferroelectric domain boundaries by transmission electron microscopy
Authors: Malis T. , Gleiter H.
Published: February 2003

A transmission electron microscopy investigation has been conducted on the structure of 90° and 180° domain boundaries in polycrystalline BaTiO3. When such boundaries were imaged with a continuous set of lattice planes, fringes were observed, indicating a stacking-fault-type displacement of the crystal lattices on either side of the boundaries. For a 90° domain boundary, this displacement most likely consists of both a dilatation and shear of {110} planes parallel to the boundary plane. The displacement for a 180° boundary lies approximately parallel to [101̄] and is of a greater magnitude. Structural models of both types of boundaries are derived from the observed displacements. The models suggest a distortion of the crystal structure in the boundary region. This distortion allows the polarization vector to simultaneously rotate and decrease in magnitude to zero at the center of the boundary, resulting in the required 90° or 180° rotation of the vector. The presence of the displacement associated with the 180° boundary suggests a substantial boundary thickness, in contradiction to previous models.
Tait equation for inorganic solids with applications to the pressure dependence of melting temperature
Authors: Couchman P. R. , Reynolds C. L.
Published: February 2003

The original version of the Tait equation is proposed to represent the compression of certain inorganic solids and has been applied to a derivation of the pressure dependence of melting temperature.
First-order treatment of combined effect of space-charge and external fields on plane-symmetric finite-emittance beams of charged particles
Authors: Bosi G.
Published: February 2003

An earlier treatment, which proved useful when dealing with zero-emittance beams, is suitably modified to describe the space-charge spread of finite-emittance charged-particle beams. The actual beam shape is obtained as a function of the initial shape by integrating first-order motion and field equations, which are listed explicitly. Formulas applying to elliptically shaped beams are worked out and numerical results are given for a circular-cross-section drifting beam.
Limitations of power outputs from continuously operating GaAs-Ga1−xAlxAs double-heterostructure lasers
Authors: Chinone N. , Ito R. , Nakada O.
Published: February 2003

Reported here are the results of measurements of several factors limiting the maximum output from GaAs-Ga1−xAlxAs double-heterostructure injection lasers under continuous operation at room temperature. The factors are (i) catastrophic damage to the mirror facets and (ii) saturation of the output power due to self-heating. Threshold optical density for catastrophic damage is 1.1 MW/cm2, and 390 mW is obtained from one mirror of a DH laser with a 80-μ-wide stripe under continuous operation. It is emphasized that DH lasers with a very thin active layer are attractive in order to achieve high-power operation.
Preparation and properties of InP/CdS solar cells
Authors: Shay J. L. , Wagner Sigurd. , Bachmann K. J. , Buehler E.
Published: February 2003

We describe the preparation and properties of the recently reported InP/CdS single-crystal solar cells having a solar power conversion efficiency of 12.5%. We also describe a process for increasing the efficiency of these and inadvertently inferior cells to 14%. The ultimate efficiency achievable with InP/CdS using state-of-the-art liquid-encapsulated Czochralski p-type InP substrates is calculated to be 17.2% for AM2 conditions and 14.0% for AM0 conditions.
Photovoltaic properties of Cu2Se-AgInSe2 heterojunctions
Authors: Tell B. , Bridenbaugh P. M. , Kasper H. M.
Published: February 2003

p-type Cu2Se/n-type AgInSe2 heterodiodes were fabricated by annealing Cu-plated AgInSe2 samples in Se at temperatures between 200 and 500°C. When operated as photovoltaic detectors, the diodes exhibit a peak quantum efficiency of 0.18 near 1.15 μ.
Noise and electrical transport properties of polycrystalline InSb thin films
Authors: Shigeta Junji , Kotera Nobuo , Oi Tetsu
Published: February 2003

Both noise and electrical transport properties of polycrystalline InSb thin films are measured and analyzed for the same potential model. Films are prepared by evaporation upon sputtered SiO2 glass and annealed in an Ar atmosphere. Films are inhomogeneously compensated and show what appears to be p- and n-type conduction at low temperatures. It is found that the n-type films actually contain p-n junctions because the measured barrier heights reach the energy of the band gap. Between 150 and 77°K, low conducting sheets along grain boundaries with notch-type barriers exist. Current noise of 1/f type observed at room temperature is well correlated with this notch-type barrier. A higher notch-type barrier leads to lower mobility as well as higher noise voltage. This indicates that the noise originates in the bulk effect of the films.
Depth-resolved cathodoluminescence of ion-implanted layers in zinc oxide
Authors: Pierce B. J. , Hengehold R. L.
Published: February 2003

Single-crystal substrates of ZnO prepared from a large boule of hydrothermally grown material were implanted with ions of Li, Na, N, P, and Ne using energies in the range 30 keV–1 MeV and doses of 1×1011–1×1016 ions/cm2 using substrates maintained at either room temperature or 475 °C. These implanted layers were studied using depth-resolved cathodoluminescence. The spectra obtained agreed well with those expected based on a comparison of theoretical electron-hole pair profiles and computer-generated ion implantation profiles. The spectra of all samples implanted at 475 °C exhibited a peak near 6500 Å, and a series of previously unreported phonon-coupled peaks analogous to the well-known CdS ’’edge’’ emission was observed to some extent in all the implanted samples, independent of implant species. The luminescence could be quenched by annealing above 600 °C and is probably a result of the formation of damage centers.
The emission coefficient of silicon coated with Si3N4 or SiO2 layers
Authors: van der Meer P. L. A. Chr. M. , Giling L. J. , Kroon S. G.
Published: February 2003

When temperatures are measured on silicon coated with Si3N4 or SiO2 layers using an infrared radiation pyrometer, large differences in temperature have been observed on slices with the same true temperature. Analysis of this phenomenon reveals that the emission coefficient of the combined silicon-layer system is determined by the thickness of the Si3N4 or SiO2 layer and the angle of observation. From calculations it follows that the value of the emission coefficient of coated Si may vary from 0.66 to 1.0. The variation of the emissivity as a function of the thickness of the dielectric layer is represented in a graph, by means of which the observed temperature readings can be converted into true temperatures. Good correlation with experiment is obtained. On the other hand, when the emissivity is calculated for the epitaxial system Si/Si3N4/Si or Si/SiO2/Si the maximum value of the emission coefficient is 0.5, independent of the dielectric coating (Si3N4 or SiO2).
Radiative recombination in melt-grown and Cd-implanted CuInSe2
Authors: Yu Phil Won
Published: February 2003

The behavior of the low-temperature emission spectra of melt-grown p-type and Cd-implanted n-type CuInSe2 with changes in temperature and excitation intensity have been investigated. Broad-band emission was dominant in the melt-grown crystals grown under an excess Se atmosphere. Generally, the broad-band peak was observed to occur at ∼0.94–0.95 eV, all peaks lying in the broad range of energy of ∼0.87–0.95 eV at 4.2 °K. The band was observed to shift to higher energy as the excitation intensity or temperature was increased, which implies that the band is due to a donor-acceptor pair mechanism. The spectral characteristics are explained by the presence of an acceptor level (EA=85±2 meV) and a donor level (ED=65±2 meV) and by compensation-dependent band shift in the p-type crystals. Acceptors and donors responsible for the pair band appear to be Cu and Se vacancies. The change in the peak energy of the band per decade of excitation intensity was found to be in the range 4–25 meV at 4.2 °K. The shift of the broad-band peak to lower energies and the increase in the magnitude of the energy shift due to the excitation intensity are consistent with high doping and compensation. A broad emission band was also observed in Cd-implanted crystals at low temperatures. The temperature dependence of the broad band in these crystals was opposite to that of the p-type crystals, the peak shifting to lower energy with an increase in temperature.
Quantum efficiency of the internal photoelectric effect in silicon and germanium
Authors: Christensen Ove
Published: February 2003

The quantum efficiency of silicon and germanium has been measured for photon energies up to 6 eV for Si and 5.3 eV for Ge. Diodes have been constructed with unity collection coefficient in this spectral range. The observed quantum efficieny of silicon in the ultraviolet is much smaller than hitherto believed, i.e., a value of 1.50 is found at 6 eV. The results for Ge accidentally agree with Vavilov and Britsyn’s measurements. An analysis of sources of error in quantum-efficiency measurements is given.
Effect of acoustic generation on the residual surface impedance of superconductors
Authors: Kartheuser E. , Rodriguez Sergio
Published: February 2003

A study is given of the effect of ultrasonic generation on the residual surface impedance of superconductors at microwave frequencies. We present an exact solution of the problem for London superconductors and give also general expressions for the residual surface resistance at zero temperature. Universal curves of the residual resistance as a function of the frequency and of the ratio of the correlation length to the electron mean free path are given using the Pippard and BCS kernels. Our investigation yields a lower limit to the surface impedance within the limits of the use of the free-electon model. A comparison is given with experimental data available in the literature for niobium, lead, and indium as well as a critical analysis of previous theoretical work. For indium and lead our results are one or two orders of magnitude below selected experimental results. For niobium, the lowest experimental results agree fairly well with those estimated in the present work.
New wet-replication technique. I. Replication of water droplets
Authors: Basu S. , Parsons D. F.
Published: February 2003

This paper concerns condensation of submicroscopic water droplets on hydrophobic substrates in a hydration chamber and then replication of water droplets by SiO vapor. In the first approach, the water-vapor pressure was adjusted in relation to the temperature of the carbon substrate. At or below the relevant equilibrium saturation vapor pressure, no replicas of droplets were seen in low magnification fields. Above the saturation value many replicas of water drops were seen at a similar magnification. The number and distribution of the droplets increased with increasing level of supersaturation. In the second approach, the water droplets were labeled by the addition of 120-Å diam ferritin molecules or 880-Å polystyrene latex spheres. These droplets were deposited by spraying labeled water. Alternatively, droplets were settled on grids from sonicated emulsions of iso-octane and labeled water. The iso-octane was allowed to evaporate off in a saturated water-vapor atmosphere leaving the labeled droplets on the grid. One grid was replicated by SiO in the wet state and the other was allowed to dry to show a circle of the droplet markers corresponding to each water droplet. The comparison at low magnification of the replicated droplet distribution and the circumscribed deposits of label clearly showed that it was water droplets that were being replicated. The mechanism of formation of a film of SiO on a low-viscosity liquid-water surface has been explained on the bases of current theories of solid-state nucleation.
New wet-replication technique. II. Replication of various wet specimens
Authors: Basu S. , Hausner G. , Parsons D. F.
Published: February 2003

The physical ability of a differentially pumped hydration chamber to replicate water surfaces and droplets has been proven in the preceding report. This has provided a new approach to tackle some questions of solid-state nucleation, aerosol science, and fluid dynamics. In this report, the physical aspects of the wet-replication technique have been described with particular attention to the flow of evaporating gases through saturated water vapor in a hydration chamber. The reasons for selecting SiO as the replicating material when biological specimens are used are explained. At low water-vapor pressure the outward SiO beam is diffracted by the streaming water vapor. At higher vapor pressures the flow pattern changes to an effusive type and cross-beam collision predominates near the axis of the inner aperture. The penetrating central SiO beam is thus involved in random collisions until it is thermalized in the water vapor. Some SiO molecules are dragged or diffused toward the cooler specimen surface to produce a replica of all lateral and reentrant surfaces of the specimen. This shape-replication ability of the present technique has been demonstrated using objects of various sizes in the range 100 Å–10 μm and of different degrees of rigidity. The technique at hand may have some limitations when applied on delicate processes and to soft biological materials, and some modifications of the technique are suggested accordingly.
Lattice theory of three-dimensional cracks
Authors: Esterling Donald M.
Published: February 2003

The problem of the stability of a three-dimensional crack will be analyzed within a lattice-statics approximation. Hsieh and Thomson employed a similar approach for a two-dimensional crack. In that work the force was taken to be linear up to an arbitrary displacement and set equal to zero for larger displacements. This paper will investigate the consequence of introducing a jog into the crack face as well as the effects of various nonlinear-force laws. The phenomenon of lattice trapping (upper and lower bounds on the applied stress for an equilibrium crack of given length) is again obtained. By looking at various force laws, it is possible to obtain some physical insight into which aspects of the force law are critical for crack stability. In particular, the inadequacy of a thermodynamic approach (which relates the critical stress to a surface energy corresponding to the area under the cohesive-force–vs–displacement curve) will be demonstrated. Surface energy is a global property of the cohesive-force law. Crack stability is sensitive to much more refined aspects of the cohesive-force law. Crack healing is sensitive to the long-range portion of the cohesive force. It occurs when an applied load leads to a pair of atoms, whose bond had been broken, acquiring a net displacement such that the cohesive force is non-negligible (about 5% of peak value) and increasing with decreasing displacment. Crack expansion normally occurs when an increment in a net atomic displacement leads to a change in slope in the cohesive-force law: a positive spring constant becoming negative. Hence crack expansion is sensitive to the position of the maximum in the cohesive-force relation.
Linear instabilities of a cylindrical plasma column in the guiding-center approximation
Authors: Shoucri Magdi
Published: February 2003

The linearized three-dimensional guiding-center equations for a plasma of cold ions and thermal electrons are solved in a cylindrical geometry. Conditions under which solutions of the disperion relation with complex frequencies can exist are determined. The consequences on the possibility of developing a ’’plasma magnetron’’, where the electron fluid of a classical magnetron is substituted by a guiding-center plasma, are discussed.
Inhibition of chemical sputtering of organics and C by trace amounts of Cu surface contamination
Authors: Vossen J. L.
Published: February 2003

Chemical sputtering is the reaction of an excited reactive gas with a solid surface to form a volatile compound. In rf sputter-etching processes, in which an oxygen glow discharge is often used to remove organic masking materials, the presence of 5–6% surface coverage of organic materials by Cu reduces the chemical sputter-etch rate of the organic material by several orders of magnitude. The physical sputter-etch rate of such surfaces is reduced by a factor of about 10. The effect occurs both in glow discharge and ion-beam sputtering. The Cu clusters apparently have a very low sputtering yield, resulting in local masking and the formation of cones. It is postulated that local field enhancement at the tips of the cones diverts incoming oxygen ions toward the tips and away from exposed organic material, leading to a lower chemical sputter-etch rate.
The depletion layer collection efficiency for p-n junction, Schottky diode, and surface insulator solar cells
Authors: Green Martin A.
Published: February 2003

The collection efficiency for carriers optically generated in the depletion region of photovoltaic solar cells is analyzed. For p-n junction devices, it is shown that virtually all these carriers are collected provided the minority carrier diffusion lengths are larger than the width of the depletion layer, and that a reasonable percentage will be collected even when the diffusion lengths are much smaller than this. For Schottky diode devices, the collection efficiency for carriers optically generated near the metal-semiconductor interface is shown to be small and to depend critically upon the exact model of the contact used. As a consequence the spectral response of Schottky diodes at short wavelengths is shown to contain considerable information regarding the physics of the metal-semiconductor contact. New surface insulator devices are shown to have a short-wavelength response superior to that of Schottky diodes.
An x-ray diffraction study of lattice imperfections in cold-worked silver-gallium (α-phase) alloys
Authors: Chatterjee S. K. , Halder S. K. , Sen Gupta S. P.
Published: February 2003

X-ray diffraction profiles from four compositions of α-phase Ag-Ga alloys containing 3.55, 9.45, 13.05, and 15.90 at.% of solute gallium have been recorded in a Geiger-counter x-ray diffractometer for both the cold-worked and fully annealed states of the samples, and a detailed analysis of the line shifts, line asymmetry, and Fourier line shapes has been performed considering recent improvements made in such studies. The line-shift analysis from 111, 200, 220, and 311 reflections has shown the prominent effect of net stacking-fault density α=α′−α″ (α′ and α″ being intrinsic and extrinsic fault densities, respectively) over the residual stresses and this has also been observed from the shifts in the lattice parameter values (Δahkl). The logarithmic dependence of α with the solute concentration X has been examined using the semiempirical expressions of the forms logα=logα0+K ‖ΔZ‖ X and logα=logα0+Kα[C/(1+C)]. Combining the results of all the methods of analysis, the individual stacking-fault densities α′, α″, and β (twin-fault density) have been evaluated, which indicates the increased presence of intrinsic fault with a total absence of twin fault in the deformed structures. An over-all analysis suggests that the extrinsic fault may also occur in very small concentrations in the these alloys. The values of the dislocation density ρ and the parameter γ/μ (γ is the stacking-fault energy and μ is the shear modulus) have also been calculated for these alloy compositions. From the logarithmic dependence of γ/μ with solute concentrations, γ0, the stacking-fault energy for pure silver has further been estimated.
Detection of surface acoustic waves using acoustoelectric streaming of charge carriers
Authors: Duracz A.
Published: February 2003

The Weinreich relation expressed in differential form is used as the basis for determining the dc electric field set up along the acoustic path of a piezoelectric semiconductor. This field results from the streaming of the charge carriers as they are carried along in the direction of a propagating surface wave by the electric fields associated with that wave. Two nonlinear effects are considered. The first is the saturation of the charge modulation or bunching. The second is the change in the surface wave attenuation coefficient due to the acoustoelectric current. The return loop for this current may be through the substrate or through an external resistor connected to electrodes on the surface. The output dc voltage as detected by these two electrodes is calculated as a function of the input rf signal. Experimental results obtained on CdS agree with the theoretical predictions in both the linear and nonlinear regions.
Bounds for effective permittivities of lossy dielectric composites
Authors: Schulgasser Kalman , Hashin Zvi
Published: February 2003

A statistically homogeneous and iostropic two-phase composite is considered. The constituents are dielectrics with low loss factors. Bounds are found on the dielectric behavior of the composite utilizing the fact that the imaginary part of the complex permittivity is small compared to the real part. The bounds on loss factor are found generally (with one exception) to be the best possible based only on volume fractions and constituent properties. Further, it is shown that for dielectric constituents whose dielectric constants are nearly unvarying with frequency, the loss factor of the aggregate is simply a linear combination of the loss factors of the constituents.
Pressure derivatives of the elastic moduli of niobium and tantalum
Authors: Katahara K. W. , Manghnani M. H. , Fisher E. S.
Published: February 2003

The pressure derivatives of the adiabatic elastic moduli of single-crystal Nb and Ta have been measured ultrasonically at 25 °C. The results are in good agreement with shock compression data but differ, particularly for Nb, with previous ultrasonic work. Experimental evidence is presented which indicates that the discrepancy in results may be due to nonideal specimen-transducer geometries which cause an apparent dependence of the observed pressure derivatives on the ultrasonic carrier frequency.
Atomistic calculation of the core structure and Peierls energy of an (a/2) [110] edge dislocation in MgO
Authors: Puls M. P. , Norgett M. J.
Published: February 2003

The core configuration and energies of the two symmetric configurations of an (a/2) [110] edge dislocation in a model MgO crystal were calculated atomistically using a point-ion or shell model with a rigid boundary region. Two short-range potentials and one set of shell-model parameters used in the present calculation were developed by Catlow, Faux, and Norgett who employed them to calculate Schottky defect energies and volumes of formation in MgO. The two symmetric dislocation configurations investigated turned out to have unequal energies, but which dislocation configuration had the higher energy depended on the particular version of the short-range potential. The shell model yielded dislocation strain energies which were approximately 0.24 eV/repeat distance lower than the corresponding strain energies for the point-ion model. The atomistically calculated energy factors derived from a strain-energy–vs–lnr plot were, in all cases, larger than the corresponding values derived from anisotropic elasticity theory. The Peierls energy barrier separating two equal-energy dislocation configurations was calculated using a linear interpolation technique. These calculations showed that the higher-energy symmetric dislocation configuration was situated either in a small local minimum or on top of a very flat-topped ’’Peierls hill’’. The maximum value of the Peierls barrier varied between 0.012 and 0.042 eV/repeat distance, depending on the method and the potential used to calculate it. The Peierls stress derived from the Peierls energy calculations ranged between 162 and 383 MPa.
Localized vibrational modes of Al paried with Cu, Ag, or Au in ZnSe
Authors: Dutt B. V. , Spitzer W. G.
Published: February 2003

Infrared absorption bands attributable to the localized vibrational modes of pair defects of Al with the elements Cu, Ag, and Au in ZnSe have been observed. A comparison with CdTe containing these same impurities shows some major similarities in the defect structures. The proposed defects for ZnSe, their point-group symmetries, and the vibrational frequencies in cm−1 at 80 °K are as follows: AlZn, Td, 359; AlZn-CuZn, Cs, 348, 351.5, 377; AlZn-Agi or AlZn-AgSe, C3v, 349.5, 381; AlZn-AuZn, Cs, 345, 348, 381. The dopants Cu, Ag, and Au were introduced by saturation diffusions into ZnSe:Al.
Characteristics of a large-volume rf-grid discharge plasma
Authors: Schumacher R. W. , Hershkowitz N. , MacKenzie K. R.
Published: February 2003

The properties of a large-volume rf (75 MHz) -grid discharge plasma have been determined. Measurements in the steady state and in the afterglow indicate that the rf grid produces a plasma with two electron components—a secondary Maxwellian component of density 2×1010 electrons/cm3 and temperature 4.5 eV and a ’’primary’’ component of density 1×1010 electrons/cm3 and temperature approximately 15 eV. The ion temperature is ?0.3 eV. A useful 35-liter argon plasma with a noise level on the order of 1% is easily produced in neutral pressure backgrounds as low as 4×10−5 Torr.
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u observation of microparticles in a vacuum-insulated gap using a scanning electron microscope
Authors: Theophilus G. D. , Srivastava K. D. , van Heeswijk R. G.
Published: February 2003

Results are presented of an investigation into microparticle activity in a vacuum-insulated 1-mm electrode gap. The experiments were conducted in situ in the specimen stage of a scanning electron microscope (SEM) and confirm microparticle activity at voltages well below breakdown. The most common size of the microparticles observed was 3 μm and very few particles above 10 μm were detected.
Magnetohydrodynamic instability of a cylindrical liquid-metal brush
Authors: Hong S. H. , Wilhelm H. E.
Published: February 2003

The stability of a homopolar generator brush, consisting of a liquid-metal-filled cavity between rotating (rotor) and fixed (stator) cylinder electrodes, is analyzed in the presence of radial current transport and an axial homogeneous magnetic field. Within the frame of linear magnetohydrodynamics, it is shown that the liquid-metal flow in the brush is always unstable if the brush transports current. In the absence of current flow (infinite load) the axial magnetic field stabilizes the liquid-metal flow in the brush if the magnetic energy density is larger than a certain fraction of the energy density of the rotating fluid.
Vibration and stability of a set of superconducting toroidal magnets
Authors: Moon F. C. , Swanson C.
Published: February 2003

The vibration and elastic stability of a set of discrete superconducting magnets arranged to form a ’’bumpy’’ toroidal field is examined. The mutual destabilizing magnetic forces between magnet pairs are calculated using a numerical differential inductance technique. It is shown that the mutual attractive magnetic forces can produce elastic buckling of the entire toroidal set. Using the theory of periodic structures, the vibration modes of the set are found as functions of the coil current. The response of the set of magnets to an earthquake-type motion of the toroidal base is also calculated.
Electromechanical properties of polarized polyvinylidene fluoride films as studied by the piezoelectric resonance method
Authors: Ohigashi Hiroji
Published: February 2003

The piezoelectric resonance was observed in free vibrators of uniaxially oriented and biaxially oriented polyvinylidene fluoride films polarized at high electric fields. Using the piezoelectric resonance method, piezoelectric and elastic constants, and electromechanical coupling factors of such films were determined at high frequencies (20 kHz–30 MHz) in the temperature range −170–100 °C. For the uniaxially oriented films, the coupling factors k33 and k32 are independent of temperature, while k31 increases noticeably above the primary dispersion temperature. The value of k33 is about 0.2, one of the largest values ever reported for piezoelectric polymers. Similar results were obtained for the biaxially oriented films. The temperature dependence of elastic and piezoelectric constants of the uniaxially oriented films is interpreted by a model in which the crystalline and amorphous phases are combined in series along the stretching direction and in parallel along the perpendicular directions. The origin of the strong piezoelectric effect in polyvinylidene fluoride is discussed on the basis that the spontaneous polarization depends on applied stress.
Defect centers in a pure-silica-core borosilicate-clad optical fiber: ESR studies
Authors: Griscom D. L. , Sigel G. H. , Ginther R. J.
Published: February 2003

An electron-spin-resonance (ESR) study has been carried out on γ-ray-induced color centers in a pure-SiO2-core B2O3⋅3SiO2-clad prototype optical fiber and in bulk glasses of the core and cladding compositions. Defects in the core material included the familiar silicon E′ center and other centers tentatively attributed to oxygen-associated structures. Approximately 102 times more centers per unit mass and unit γ-ray dose were created in the cladding material than in the core glass; these comprised just three defect types: the boron-oxygen hole center (BOHC), the silicon E′ center, and a boron analog of the latter, the boron E′ center. These same defects were also observed in the irradiated prototype fiber in concentrations comparable to those attained in the bulk glass of the cladding composition. The unexpectedly high radiation sensitivity of the fiber, therefore, would appear to be due to the efficient production of (intrinsic) boron-related defects in the cladding. Considerable insight has been gained into the electronic structures of the BOHC and the boron E′ center, by means of careful computer simulations of their ESR line shapes in B2O3⋅SiO2 glasses, as functions of both frequency and boron isotopic enrichment.
Properties of PbS-PbO crystalline films. II. Electrical and photoelectronic properties
Authors: Said M. Sameh , Zemel Jay N.
Published: February 2003

Electrical, optical, and photoconductive studies were carried out PbS-PbO codeposited films. The segregated PbO microcrystallites had an increasingly profound effect on these properties. Some traces of the excess oxygen appear to enter the PbS single-crystal matrix. Oxygen vacancies in the PbO crystallites produces a peak in the photoconductivity of p-type PbS-PbO films but not in n-type films. By a detailed study of these properties, a band diagram is suggested for the PbS-PbO heterostructure that accounts for our observations.
Magnetic, corrosion, and surface properties of Ni-Fe-Cr thin films
Authors: Rice D. W. , Suits J. C. , Lewis S. J.
Published: February 2003

Films in the Ni-Fe-Cr ternary system were evaporated and examined with regard to magnetic properties, resistance to atmospheric corrosion, and surface chemistry. It was found that films with relatively high magnetization and low coercive force could be made which at the same time exhibited good corrosion resistance. The corrosion occurred predominately by pitting for the low chromium concentration films. The surface chemistry was studied by Auger and XPS techniques which indicated that addition of Cr to Ni-Fe caused replacement of a nonpassivating iron-rich oxide surface layer by a passivating Cr-rich oxide layer.
Superconducting tunable-diaphragm transducer for sensitive acceleration measurements
Authors: Paik Ho Jung
Published: February 2003

A very sensitive resonant superconducting accelerometer has been developed as a component of a cryogenic gravitational-radiation detector. The device consists of a superconducting test mass and superconducting coils carrying a persistent current. The displacement of the test mass modulates the inductances of the coils and generates an ac magnetic field which is detected by a Josephson-junction magnetometer. The restoring force provided by the magnetic field is used to tune the resonant frequency of the transducer. The expected sensitivity of the system is better than 10−12gE/Hz1/2 (gE=9.8 m/s2) when used to detect accelerations at frequencies lower than 50 Hz. The system has been thoroughly tested and is being used to detect small accelerations of a gravitational-wave antenna caused by the Brownian motion and other external disturbances. When used as a resonant displacement sensor in a gravitational-wave detector cooled to 3 mK, this transducer is capable of converting a displacement of 4×10−20 m at 1 kHz into an electrical signal detectable with unity signal-to-noise ratio for 1-Hz bandwidth. The gravitational-radiation-flux sensitivity implied by this is 0.1 erg/cm2 Hz. This will make not only the observation of expected galactic events possible, but will allow one to extend the scope of observation beyond the Milky Way. The system can be modified to make a sensitive gravity gradiometer. When two accelerometers are coupled to the same Josephson-junction magnetometer with their transformer coils wound in the opposite sense, direct subtraction of acceleration signals can be accomplished. The system will be easy to build and mechanically rugged. The device in various applications is discussed and the theory of transducer energy coupling, frequency tuning, and parameter optimization is presented. Some experimental results confirming the theory are reported. Included are data showing the temperature dependence of the Q of a niobium diaphragm and the measurement of the low-frequency background acceleration of a magnetically levitated gravitational-wave antenna.
Attenuated-total-reflection measurements of Si-SiO2 interfaces
Authors: Haas G. A. , Pankey T. , Holm R. T.
Published: February 2003

Preliminary experiments involving attenuated-total-reflection (ATR) spectroscopy at the Si-SiO2 interface of thermally grown oxides showed discrepancies in structure from standard SiO2 transmission data. Absorption coefficients calculated from SiC and SiO2 transmission data were included in a computer program which theoretically generated the ATR results showing effects of the presence of a SiC layer at the Si-SiO2 interface. The computed results were similar to the experimental results, thus corroborating earlier Auger-electron-spectroscopy measurements which indicated that residual graphitic carbon on the Si surface changed to a carbide form after oxidation and remained at the Si-SiO2 interface.
Temperature dependence of the silicon work function by means of a retarding potential technique
Authors: Burton L. C.
Published: February 2003

The temperature dependence of the work function of a (111) silicon surface has been measured at temperatures from 1335 to 1638 °K. The work function over this temperature can be expressed as φ (T) =4.18+3.3×10−4T eV. A Richardson A value of 2.05 A/cm2 °K2 and a mean electron reflection coefficient of ?=0.213 were also determined.