bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron transfer in the Hf1Co6 magnetic alloy
Authors: Orehotsky J. , Wahl T.
Published: February 2003

The cobalt atomic magnetic moment in Hf1Co6 was determined from the measured saturation magnetization and compared with predictions of an electron transfer model. Good agreement was found when hafnium contributes only two of its four valence electrons to the empty states in the minority spin band of cobalt.
Electric field line bending limited elastomer deformation in an a-Se type deformographic light valve
Authors: Lakatos A. I.
Published: February 2003

The time development of elastomer deformation under the influence of exposure to light in the a-Se-type RUTICON has been characterized as a function of applied bias and light intensity. The deformation was observed to initially increase linearly while the transverse currents decrease linearly as a function of exposure time. The deformation reaches a maximum Dm at time tm, which is always ?1/2tr, the photoelectric response time for the devices tested. Also, Dm∝V2 and tm∝tr∝F−1, the latter proportionality ensures exposure intensity versus time reciprocity for the device. These features are analyzed using the characteristic photoelectric properties of a-Se, first in terms of a simple parallel field lines model which is successful in explaining all the observed characteristics with the exception of the difference between tm and tr. The second revised model takes into account the bending of the field lines in the photoconductor during exposure to light, and it successfully describes the observed relationship between tm and tr. The results, therefore, give a very clear illustration of the phenomenon of charge modulation on the surface of a photoconductor that is limited by the bending of the field lines in the photoconductor.
Temperature profiles of targets bombarded by electron beams
Authors: El-Kareh A. B. , Moravan K. Y. , Smither M. A.
Published: February 2003

A calculation technique is presented which relates electron-beam power and the physical properties of a target to the size and temperature of the irradiated spot. The technique permits the selection of target materials which are suitable for use in electron-beam-addressed mass-storage systems. The electron-beam-induced heating within the target is determined by assuming that the beam energy is uniformly deposited within a hemispherical volume of radius rE. This effective radius is determined from Monte Carlo simulation of the beam-target interaction. The thermal calculations can be used to identify the required properties of suitable targets. The steady-state temperature must exceed the boiling temperature of the target material. This requirement places an upper limit on the thermal conductivity of the material. A relationship among thermal conductivity, heat capacity, and mass density is similarly obtained by requiring that the heating is to be done in an acceptably short time. A set of normalized curves is presented which shows the spatial and temporal behavior of the temperature in the target. The denormalization parameters for several materials and beam powers are presented for use with the curves.
Rectification effects based on the p-n junction of poly[γ- (β-N-carbazolylethyl) -L-glutamate]— 2,4,7-trinitrofluorenone systems
Authors: Tanikawa Kiyoshi , Okuno Zenjiro , Iwaoka Takehiko , Hatano Masahiro
Published: February 2003

In the dark and under illumination, it has been found that rectification effects in an organic photoconductor system are attributable to a p-n junction barrier. This junction was accomplished by a doping process similar to one used in inorganic semiconductors. The p-n junction barrier was made by immersing a poly[γ- (β-N-carbazolylethyl) -L-glutamate] (PCLG) film in either benzene or a methylethylketone solution of 2,4,7-trinitrofluorenone (TNF), since both benzene and methylethylketone are poor solvents for PCLG and are suitable solvents for TNF. PCLG and PCLG doped with TNF behave as p-type and n-type organic semiconductors, respectively, and a p-n junction with a continuous interface can be accomplished in the sandwich structure system of In2O3//PCLG/PCLG-TNF complex//Au. In this sample, rectification effects both in the dark and under illumination have been observed to be in good agreement with a theoretical equation of the p-n junction for inorganic semiconductors. However, the potential drop across the p-n junction barrier is depressed, being much smaller than the voltage applied externally to the photocell because of the remarkably high electrical resistivities of PCLG and the PCLG-TNF complex. Furthermore, even without an applied field—that is, with a short circuit—the photovoltaic current has been observed and attributed to the junction barrier. On the other hand, in the In2O3//PCLG//Au and In2O3//PCLG-TNF complex//Au systems it has been found that neither dark currents nor photocurrents attributable to a p-n junction are observed.
Thermomigration of molten Ga in Si and GaAs
Authors: Cline H. E. , Anthony T. R.
Published: February 2003

Molten zones of Ga have been migrated through Si and GaAs in thermal gradients between 6 and 92 °C/cm and over a temperature range between 300 and 1000 °C. The observed migration rate is larger in Si than GaAs. In both cases the droplets are faceted on (111) planes. An expression for the migration rate V is derived in terms of the solid’s heat of fusion and its solubility in the liquid. For large liquid zones, the calculated rate agrees with experiments for Ga-Si, Al-Si, and Au-Si systems. In contrast, the observed rate for the Ga-GaAs system is lower than calculated because of interface kinetics. In all systems, small liquid zones migrate slower than large liquid zones. Migration rates are also calculated for the Ag-Si, Sn-Si, Sb-Si, and In-Si systems. The general criteria for applying thermomigration in various metal-semiconductor systems are discussed.
Weak-shock transmission coefficient via harmonic generation
Authors: Harris Paul
Published: February 2003

The problem of stress transmission across a boundary separating acoustically linear and nonlinear media is treated to the first order in the nonlinearity (third-order elastic constant). The study is carried out by considering the role of harmonic generation in the nonlinear medium. An application considered is that of extending low- (but finite) amplitude ultrasonic measurements to the high-pressure regime (e.g., 10 kbar) in sensitive materials such as explosives.
A mathematical model for calculating electrical conditions in wire-duct electrostatic precipitation devices
Authors: McDonald Jack R. , Smith Wallace B. , Spencer III Herbert W. , Sparks Leslie E.
Published: February 2003

A new method is developed which can be used to calculate electrical conditions in wire-duct electrostatic precipitation devices. The method, based upon a numerical solution to the governing differential equations under a suitable choice of boundary conditions, accounts for the effect of space charge and is applicable over the entire range of current and voltage before sparkover. The procedure yields voltage-current characteristics and determines the electric potential and electric field strength as functions of position for each current and applied voltage. Predictions of the theory are compared with existing experimental data and the agreement is excellent.
Time-dependent plasma temperature measurements of the high-pressure sodium arc
Authors: Rautenberg T. H. , Johnson P. D.
Published: February 2003

The plasma temperature of the high-pressure sodium arc has been measured as a function of time and power input on 60-Hz sine-wave operation. A maximum temperature of 4370 °K is found at power input above about 100 W/cm3 of arc tube volume. At zero current the temperature falls to 3300 ° K. Square-wave operation indicates that temperature decay to this value occurs in 0.3 msec. Since local thermodynamic equilibrium (LTE) exists in the hot central core of the plasma, the electron density can be calculated using the Saha equation to decay from 1016 to 1015 cm−3 during this period. This decay in electron density is accompanied by an increase of arc reignition voltage of more than a factor of 4.
Auger profiling of ’’abrupt’’ LPE AlxGa1−xAs-GaAs heterojunctions
Authors: Garner C. M. , Shen Y. D. , Kim J. S. , Pearso G. L. , Spicer F W. E. , Harris J. S. , Edwall D. D.
Published: February 2003

Ion milling–Auger electron spectroscopy has been used to study, for the first time, the chemical widths of ’’abrupt’’ LPE AlxGa1−xAs-GaAs heterojunctions with composition x=0.43, 0.60, and 0.85. ’’Abrupt’’ LPE junctions were found to have chemical interface widths of <90–130 Å.
Detailed calculation of energy relaxation time of hot electrons in InSb
Authors: Kobayashi Toshihiko
Published: February 2003

The electron temperature T0 and the energy relaxation time τε in n-InSb at 78 K have been quantitatively determined from the microwave complex conductivity measured in the presence of a dc heating field. The well-known assumptions such as ωτm≪1 and (T0−TL)/τε(dτε/dT0) ≪1 are not included in the present calculation, where ω is the angular frequency of microwave field, τm is the momentum relaxation time, and TL is the lattice temperature. The electron temperature increases monotonously as the field increases and reaches about 140 K at 150 V/cm. The energy relaxation time is found to be (1.3–2) ×10−12 sec and to be almost constant for field values above 50 V/cm. The quantity ωτε is large enough to cause strong relaxation effects.
The validity of the extrapolation technique for measuring wall widths in asymmetric domain walls
Authors: Marti J. , Lewis W. F.
Published: February 2003

We have analyzed numerically the validity of the extrapolation procedure of Reimer and Kappert for measuring the width of asymmetric ferromagnetic domain walls. It has been found that applying this technique blindly will result in extrapolated wall widths that are either too large or too small. Two alternate image widths are proposed which extrapolate correctly to the corresponding wall widths.
CuInS2 thin-film homojunction solar cells
Authors: Kazmerski L. L. , Sanborn G. A.
Published: February 2003

The fabrication and characteristics of n,p-CuInS2 thin-film homojunction solar cells are presented. Dark and light I-V characteristics are reported for a 0.124-cm2 device with η=3.33%, Voc=0.41 V, Isc=2.34 mA, and FF=0.43. A best efficiency of 3.62% is cited. An examination of the forward dark lnJ-vs-V characteristics indicates that the recombination-generation mechanism at the junction dominates the device operation. The spectral characteristics are presented and indicate a maximum near the wavelength (λ=0.8 μ) corresponding to the energy gap of CuInS2, with a relatively low quantum efficiency (<0.45). The stability and limitations of this photovoltaic device are discussed.
Upper limit of efficiency for photovoltaic solar cells
Authors: Mathers C. D.
Published: February 2003

A theoretical upper limit of efficiency is obtained for a photovoltaic solar cell which uses a semiconductor with a single energy gap. This limit is not based on a particular material or type of device and may be used with any solar or absorption spectrum.
Elastic constants of the bcc phase in niobium-zirconium alloys between 4.2 and 300 K
Authors: Walker E. , Peter M.
Published: February 2003

The adiabatic elastic constants have been determined for quenched single crystals of niobium-zirconium alloys of the following nominal compositions: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, and 70 at.% Zr. The c11, c12, and c44 constants as well as the shear constant C′= (1/2) (c11−c12) and the bulk modulus are given between 4.2 and 300 K. We observe for the whole range of compositions an anomalous temperature behavior for c44 similar to that found in pure Nb, but here the amplitude of the effect disappears progressively with increasing Zr concentration. The Debye temperatures were computed from the constants at 4.2 K.
Equivalent circuit approach to long magnetically insulated transmission lines
Authors: Bergeron Kenneth D.
Published: February 2003

When a magnetically insulated vacuum transmission line is longer than the voltage pulse (or the rising portion thereof), steady-state treatments are not adequate and some account of the time-dependent terms in Maxwell’s equations must be taken to describe the propagation of the pulse. As a first step in studying this problem, an equivalent circuit model of the line is considered. Time-dependent computer solutions are obtained and favorable comparison is made with both experiment and a recent analytic prediction for the front velocity.
Photoelectrolysis with YFeO3 electrodes
Authors: Butler M. A. , Ginley D. S. , Eibschutz M.
Published: February 2003

YFeO3 is shown to work as a photoanode for photoelectrolysis of water. Conduction is n type as indicated by its use as an anode. The optical band gap is an indirect transition of 2.6 eV, somewhat larger than in Fe2O3. However, the smaller electron affinity of YFeO3 means that it requires less bias for photoelectrolysis than Fe2O3.
New infrared laser transitions in neutral sulfur
Authors: Hocker L. O.
Published: February 2003

Pulsed laser emission at 1.046, 1.543, 1.655, and 2.438 μm in dilute mixtures of SF6 in helium is attributed to neutral sulfur transitions fed by recombination of ionized sulfur.
Elastic and piezoelectric properties of Ba2Si2TiO8
Authors: Kimura Masakazu
Published: February 2003

All the elastic constants, temperature coefficients of elastic constants, and thermal-expansion coefficients in Ba2Si2TiO8 were measured. Signs of the piezoelectric constants d31 and d15 were determined to be positive. From the calculations of the orientational dependences on the electromechanical coupling factors k′31 and k′15 and the temperature coefficient of resonance frequency [Tfr]L in the length-extensional mode, it was found that the largest values of k′31 and k′15 are 0.13 and 0.28, respectively, and the minimum value of [Tfr]L is −47 ppm/°C. Surface-acoustic-wave analysis for the crystal showed that the SH-mode piezoelectric surface wave has a piezoelectric coupling constant, k2=0.0053, larger than that of quartz, and a temperature coefficient of delay Tτ=+38 ppm/°C for the Y-propagation direction on the X-cut surface, smaller than that of LiNbO3.
Theory of surface polariton generation through grating couplers
Authors: Mills D. L.
Published: February 2003

We discuss the theory of surface polariton generation by grating couplers. The emphasis is on an analysis of the manner in which the grating may modify the frequency spectrum of a shaped incident pulse. If L is the length of the portion of the grating illuminated by the incident beam, then we find that the frequency spectrum of the incident pulse can be transmitted to the surface polariton undistorted if the criterion L<Vg/σ is satisfied, where Vg is the group velocity of the surface polariton and σ is a measure of the spread of frequencies in the incident beam used to excite the surface polaritons. If this criterion is not satisfied, the frequency spectrum of the transmitted pulse will be narrower than that in the incident pulse. The treatment here provides expressions for the absolute amplitude and shape of the transmitted signal, within the framework of a method that assumes the height of the grating is small.
The influence of sample shape on microwave magnetoplasma and heliconlike resonances in n-type InSb
Authors: Brazis R. S. , Furdyna J. K.
Published: February 2003

Magnetoplasma and heliconlike dimensional resonances are investigated in small samples of n-type InSb interacting with 8-mm wave radiation at 77 K, in order to determine the influence of sample geometry on the interaction, particularly the shift of the resonance condition. Special attention is paid to the disk geometry because of its practical importance. The results are compared with mathematically tractable, but experimentally less practical, geometries: the sphere, the ellipsoid of revolution, and the infinite slab. It is found that, in analogy with ellipsoids, the magnetoplasma resonance in disk samples is determined by an empirical effective depolarizing factor, which is surprisingly close to the depolarizing factor of an ellipsoid of the same axial ratio as the disk. By using very thin disks, magnetoplasma resonance can be shifted to significantly lower magnetic fields than the resonance field observed in spheres. This is of importance for determining the lattice dielectric constant in materials containing a high concentration of carriers, for which magnetoplasma resonance in spheres occurs at inaccessibly high fields. We also observe a sequence of heliconlike dimensional resonances in disks. These resonances form a series of electric dipole and magnetic dipole excitations, as in the case of spheres. However, the resonance conditions for the disk samples are close to the Fabry-Perot resonances in an infinite plate.
Antiferromagnetism of fcc Fe thin films
Authors: Keune W. , Halbauer R. , Gonser U. , Lauer J. , Williamson D. L.
Published: February 2003

Thin iron films (∼18 Å and 90% enriched in Fe57) were prepared on (001) Cu single-crystal substrates. The fcc structure was verified by electron microscopy. By Mössbauer spectroscopy it was found that antiferromagnetic ordering begins at around 80±10 K with hyperfine fields of about 16–20 kOe. Additional proof for the existence of anitferromagnetism has been obtained by measuring the films in a longitudinal (parallel to the γ-ray direction) external magnetic field. The apparent discrepancy in the literature of ferromagnetic and antiferromagnetic ordering in fcc films might be resolved by taking into account the differences concerning the film orientations.
Dislocations and the piezoelectric effect in III-V crystals
Authors: Booyens H. , Vermaak J. S. , Proto G. R.
Published: February 2003

It is shown that 60° and 90° α and β dislocations give rise to piezoelectrically induced charge distributions and electric fields in the surrounding crystal. The general features of the charge distributions are discussed with special references to the relation between the nature of the distributions and the symmetry of the crystal. Finally, it is shown that the dislocation reaction (a0/2)[101̄]+(a0/2)[011]= (a0/2)[110] is self-consistent as regards electrical properties.
Output power and intensity distribution of a transverse-flow CO2 laser
Authors: Eidelman O. , Bin-Nun E. , Rokni M.
Published: February 2003

We have measured the intensity distribution of a transverse-flow CO2 laser along the flow direction and the dependence of its output power on the cavity width. The experiments were performed with a transverse-flow CO2:N2 laser chemically excited by the reaction of nitric oxide with atomic nitrogen. The intensity distribution is found to be of a multimode structure, fairly symmetrical about the optical axis. The overall output power for a given flow velocity and gas mixture is found to increase with increasing cavity width, up to a maximum value, and then it diminishes with any further increase of the cavity width. These results do not agree with those expected from a simple geometric-ray model. On the ohter hand, our results conform qualitatively with those expected from a coupled multimode approach. The main differences between the two approaches are discussed, and simple arguments are presented to illustrate the limitations of these two approaches.
Extraction and propagation of rotating intense proton beams from a magnetically insulated diode
Authors: Humphries S. , Eichenberger C. , Sudan R. N.
Published: February 2003

A magnetically insulated parallel-plate geometry was used to produce intense rotating beams of protons. It is shown that even though the diode is not in equilibrium with respect to the drifting electrons, a decrease in the perveance by more than a factor of 40 could be produced by the application of the field. Operation of the diode is accompanied by strong bursts of microwave radiation. Efficiencies over 50% were achieved in accordance with theory. Ion current-density enhancements above the Child-Langmuir limit that appear directly attributable to drifting electron space-charge effects were observed. Typically, more than 3×1015 protons were extracted per pulse. Space-charge neutralization of the extracted beam appears complete and inductive electron backcurrents were not detected. The beam propagates in accordance with geometric predictions and at least 67% of the beam completes one revolution. A field reversal factor of 1.5% (ΔB=140 G) was obtained. It is shown that this injector can easily be scaled to the parameters needed to produce a self-contained ion ring.
Analytic solutions of a model for radiation-induced conductivity in insulators
Authors: Weaver L. , Shultis J. Kenneth , Faw R. E.
Published: February 2003

A model for radiation-induced bulk electrical conductivity in insulators is developed and discussed. The characteristic equations are coupled nonlinear stiff differential equations for which analytical solutions are presented. Solutions are given for the buildup of conductivity during constant irradiation and the decay of conductivity following interruption of irradiation. The long-time asymptotic results agree favorably with previous experimental data.
X-ray-sensitive vidicon tube for low-level radiation imaging
Authors: Haque Promod , Jacobs J. E.
Published: February 2003

A new type of imaging tube for x rays and γ rays in the 80-keV and higher energy range is described. The tube has the ability to image low flux levels of incident radiation by the process of charge integration in the target plate while the reading electron beam is turned off. The target plate consists of a layer of lead deposited on a substrate. The lead layer converts a portion of the incident radiation into photoelectrons. These photoelectrons travel through a low-density layer of cesium iodide deposited on the lead layer and create secondary electrons. An electric field maintained across the cesium iodide layer causes the secondary electrons to be collected by the conductive backing of the target plate, thereby leaving a charge pattern on the surface. A scanning electron beam neutralizes this charge pattern, resulting in the flow of signal current. The technique of obtaining maximum signal current for a given radiation energy is one of optimizing the thickness of the lead layer and the thickness and density of the cesium iodide layer. Experiments designed to determine the optimal values of these parameters are described. Imaging studies carried out using an x-ray machine as well as a 133Xe radioactive source are described.
Atomic fluorescence of sodium under continuous-wave laser excitation
Authors: Smith B. , Winefordner J. D. , Omenetto N.
Published: February 2003

The tunable continuous-wave (cw) dye laser has been shown to be capable of producing saturation conditions for sodium in an air-acetylene flame. The experimental evidence indicates that the sodium doublet is a reasonably good approximation of a two-level system. Saturation of the sodium 589.6-nm line was observed at laser spectral irradiances of 1013 erg s−1 cm−2 nm−1 and greater. Measurements of the absolute-maximum fluorescence radiance under saturation conditions have been used to measure sodium concentration profiles in air-hydrogen and air-acetylene flames with spatial resolution on the order of 0.01 cm.
Formal aspects of the theory of the scattering of ultrasound by flaws in elastic materials
Authors: Gubernatis J. E. , Domany E. , Krumhansl J. A.
Published: February 2003

An integral equation is used to derive formal expressions for the scattering of a plane wave from a single homogeneous flaw embedded in an isotropic elastic medium. Expressions are found for the scattered amplitudes and differential cross sections. An optical theorem is also derived.
The Born approximation in the theory of the scattering of elastic waves by flaws
Authors: Gubernatis J. E. , Domany E. , Krumhansl J. A. , Huberman M.
Published: February 2003

We used the integral equation formulation of the scattering of elastic waves to generate an approximate solution analogous to the Born approximation in quantum mechanics. This solution is attractive because of the ease with which it may be applied to scatterers of complicated shapes. We investigated the validity of the approximation by comparing it with exact results for spherical scatterers. Our conclusion for voids in elastic media is that the approximation describes well the scattering when the wavelength of the incident wave is approximately an order of magnitude larger than the scatterer and when the scattering is viewed in the backscattered directions. For many applications this range of validity is experimentally accessible. For elastic inclusions, however, where the properties of defect and host differed by 20–40%, the Born approximation is surprisingly good for all angles and even at short wavelengths.
Electronic and orientational contributions to the optical Kerr constant determined by coherent Raman techniques
Authors: Song J. J. , Levenson M. D.
Published: February 2003

We have used the Raman-induced Kerr effect to normalize the optical Kerr constants of several liquids to their corresponding Raman matrix elements. The electronic contribution to the Kerr constant was similarly normalized using three-wave mixing.
The dynamics of a particle attracted by a magnetized wire
Authors: Lawson William F. , Simons William H. , Treat Richard P.
Published: February 2003

The dynamics of a particle attracted by a magnetized wire is studied for nonvanishing gravitational forces and a broad range of Stokes number K. The Newtonian equation of motion for the particle is integrated for 10−2⩽K⩽102, a range which includes conditions where the particle inertia cannot be ignored. Families of trajectories, typical of low and high K, reveal the dominance of viscous forces at low K, as expected, and show oscillatory approach to capture for high K, where inertia is significant. Capture distances in the interval 1⩽Xc⩽8 are given as a function of three independent dimensionless parameters which measure the strengths of the magnetic, viscous, and gravitational forces. The range of conditions is established for which it is permissible to neglect, for the purpose of computing capture distances, both the inertia and the radially attractive short-range part of the magnetic force. The equation of motion in which the inertia and the short-range term are neglected is studied. An integral of this equation is found which extends the trajectory equations of Zebel and Luborsky to include the gravitational force. A general approach to the construction of the integral of motion shows how to find the trajectory equation for a particle moving in a more complicated incompressible viscous flow with higher multipole contributions to the magnetic field of force.
Quantitative study of a photoacoustic system for powdered samples
Authors: Monahan E. M. , Nolle A. W.
Published: February 2003

The absorption edge of powdered amorphous As2S3 of average particle size 0.0066 cm is explored by the photoacoustic method. The output signal varies significantly with changes in the absorption coefficient β of As2S3 over a range of β from less than 10 cm−1 to more than 104 cm−1, at a chopping frequency of 510 Hz. The saturation behavior of the system at the upper end of this range of β, where both optical and thermal penetration depths are less than the particle diameter, is well approximated by the theory of Rosencwaig and Gersho for homogeneous samples. The behavior for small β is explained in terms of Melamed’s analysis of diffuse reflection and absorption by a powder. The behavior of the photoacoustic cell in the limiting case of a charcoal sample, and the absolute sensitivity, are also investigated and related to theory.
Field-emission and field-ion microscopy of lanthanum hexaboride
Authors: Futamoto M. , Hosoki S. , Okano H. , Kawabe U.
Published: February 2003

Field-emission and field-ion microscopy studies are carried out on (001) -oriented LaB6 single-crystal tips. Surface states and some field-emission characteristics are examined. The facet of low-index planes, (001), {011}, and {111}, is observed after heating a tip at high temperatures. The field-emission current fluctuations from thermally cleaned LaB6 tips are larger than those of W field emitters. Field-emission patterns are found to depend on the local curvatures of the tip surface. The surface states are discussed by considering the effects of surface diffusion and evaporation for LaB6 during high-temperature heat treatment.
Production of neutral atoms by pulsed laser heating
Authors: Prengel A. T. , Dehaven J. , Johnson E. J. , Davidovits P.
Published: February 2003

Sodium and thallium surfaces were heated in vacuum by a short intense pulse from a CO2 TEA laser. The time-dependent emission of neutral atoms following the laser pulse was measured in the density range 1011–1012 atoms/cm3 by monitoring the absorption from a beam of resonance light. The temperature of the metal surface and the depth of heating after the laser pulse were obtained using a theoretical model. The results show that at the end of the laser pulse the temperature of the surface is close to the boiling point for the metal independent of laser energy in the range 106–109 W/cm2. The surface temperatures were 593 and 934 °K for sodium and thallium, respectively. The depth of heating is greater than can be explained by heat conduction alone. It is suggested that during the laser pulse the metal is heated by a shock wave. The results also point out the limitations of pulsed laser vaporization in the production of neutral atoms from refractory materials.
Theory for thermal microwave emission from a bounded medium containing spherical scatterers
Authors: Tsang L. , Kong J. A.
Published: February 2003

The theory of thermal microwave emission from a bounded medium containing spherical scatterers is developed with a radiative transfer approach using Mie-scattering functions. Since the boundary of the bounded medium predetermines a preferred direction, the scattering phase functions that are more general than those commonly used have to be developed. Brightness temperatures are calculated and compared with Rayleigh results. Resonance phenomena that are characteristics of Mie scattering are revealed. Results computed from an iterative approach which accounts for single scattering are compared with that obtained from a numerical approach which accounts for multiple scattering. The multiple-scattering results display less oscillatory behavior and are also more accurate. The brightness temperatures as functions of observation angles and frequencies are also examined for the vertical and horizontal polarizations and for particle size distributions.
Comment on ’’Comparison of experimental and theoretical carrier concentrations in heavily doped n-type silicon’’
Authors: Neumark G. F.
Published: February 2003

It is shown that screening effects account for most of the reduction in impurity activation energy given by recent measuremments of the Hall effect and conductivity in n-type Si.
Formation of superconducting A-15 V3Ge compound by a composite-diffusion process
Authors: Tachikawa K. , Burt R. J. , Hartwig K. T.
Published: February 2003

Superconducting A-15 V3Ge is formed by the V/Cu-Ge composite-diffusion process. Copper from the Cu-Ge alloy matrix enhances the formation of V3Ge but does not dissolve in the V3Ge. The highest transition temperature obtained, 7.1 K, is slightly higher than the value reported for arc-melted V3Ge. An off-stoichiometric composition of about 21.7 at.% Ge was found in the A-15 layer, indicating the possibility of Tc enhancement in V3Ge, as in the case of Nb3Ge.
Ultrasonic wave propagation in fiber-reinforced solids containing voids
Authors: Martin B. G.
Published: February 2003

Calculated results are presented for ultrasonic wave propagation in fiber-reinforced composite material containing voids, where the fiber reinforcement is unidirectional. Both elastically isotropic and anisotropic fibers are considered. The propagation direction is taken as normal to the fiber length and expressions are obtained for the longitudinal- and shear-wave velocities as a function of composite void and fiber volume fraction. The results exhibit reasonable behavior and a comparison of calculated data and such experimental data as are available shows fair agreement.
Molecular diffusion and solubility of hydrogen isotopes in vitreous silica
Authors: Shelby J. E.
Published: February 2003

Deuterium permeation, diffusion, and solubility measurements have been made for several types of vitreous silica at temperatures ranging from 0 to 800 °C. The activation energies for permeation and diffusion were found to be somewhat temperature dependent. Isotope exchange between structural hydroxyl and the diffusing deuterium was found to occur at temperatures ?300 °C. Certain types of vitreous silica also react with the diffusing gas to form metastable deuteroxyl at ?600 °C. Isothermal hydrogen-isotope solubility was shown to be described by the Langmuir adsorption isotherm at pressures up to 1400 atm, whereas the temperature dependence of hydrogen-isotope solubility was adequately described by a statistical-mechanics model. Combination of these two models leads to a universal expression for hydrogen solubility from 0 to 800 °C and from 0 to 1400 atm.
Acceptor dopants in silicon molecular-beam epitaxy
Authors: Becker G. E. , Bean J. C.
Published: February 2003

Epitaxial silicon films have been grown on single-crystal Si (100) substrates by evaporation from an e-gun source in ultrahigh vacuum and have been doped with gallium and with aluminum from separate oven sources. Gallium doping profiles have been controlled accurately for substrate temperatures in the range 600–800 °C and for carrier densities in the range 1014–5×1017 cm−3. Examples are given of abrupt changes in doping level. Measured drift mobilities in the films are within 15% of values for bulk silicon. Crystallographic properties of the films are comparable to those of the substrates and are suitable for device applications. Films doped with aluminum exhibit comparable electrical and crystallographic properties, but good control of the doping profile has not been achieved for the range of parameters studied.
Theory of isothermal current-time characteristics and determination of trap parameters
Authors: Gupta H. M.
Published: February 2003

A detailed theoretical study is made of the effect of dielectric relaxation on the isothermal I-t characteristics of metal-insulator-metal structures in which the electrodes make blocking contacts with the insulator in the ’’growth of the cathodic depletion region’’ approach. We have developed a method to plot nonsteady isothermal characteristics starting from the basic parameters and to obtain analytic expressions to directly determine the trap density, the dielectric constant, and the difference between the metal and the insulator work function, (ψm−ψi). It turns out that knowing the initial currents I (0) and the total charges collected in the depletion region Q for any two applied voltages, we can determine the dielectric constant, ψm−ψi, and the trap density without using any other parameter. Furthermore complete I-t characteristics can be plotted without using any adjustable or uncertain parameter. Thus, the comparison of the theoretical results with the experimental results can provide a definite and quantitative proof of the validity and limitations of the assumptions of the theory of dielectric relaxation for metal-insulator-metal or similar structures. Finally, we discuss the effects of various parameters on the I-t characteristics under the present theory for MIM structures.
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u measurement of Hall effect, magnetoresistance, resistivity, and TCR of bismuth films
Authors: Chaudhuri S. , Pal A. K.
Published: February 2003

I n situ measurements of Hall effect, magnetoresistance, resistivity, and temperature coefficient of resistivity of bismuth films (700–2600 Å) were carried out in a specially designed evacuation chamber. The films were deposited on a glass substrate at 150°C and at a pressure of ∼10−6 Torr. The values of the mean free path and specular scattering parameter obtained were 14100 Å and 0.5, respectively. The effect of the grain boundary on the electrical resistivity was also accounted for in the light of the Mayadas-Shatzkes theory.
Determination of the Fe2+ and Fe3+ concentration in MgO
Authors: Modine F. A. , Sonder E. , Weeks R. A.
Published: February 2003

Crystals of MgO containing 140 ppm iron were reduced in CO or oxidized in air at 1150 °C and the iron concentration in different valences was determined by optical and magnetic techniques. Optical density, electron spin resonance, and magnetic circular dichroism measurements gave self-consistent results that yield calibration constants for determining the Fe2+ and Fe3+ concentrations by optical means. Oscillator strengths of the absorption bands at 1000 and 285 nm were calculated from this knowledge of the iron concentration. At low concentrations more than 90% of the iron is unassociated, Fe2+ or Fe3+. Alternate oxidation and reduction converted 80% of this iron between these valence states, while the other 20% remained as Fe2+.
Measurements of copper ground-state and metastable level population densities in a copper-chloride laser
Authors: Nerheim Noble M.
Published: February 2003

The population densities of both the ground and 2D5/2 metastable states of copper atoms in a double-pulsed copper-chloride laser are correlated with the laser energy as a function of time after the dissociation current pulse. Time-resolved density variations of the ground and excited copper atoms were derived from measurements of the optical absorption at 324.7 and 510.6 nm, respectively, over a wide range of operating conditions in laser tubes with diameters from 4 to 40 mm. The minimum delay between the two current pulses at which lasing was observed is shown to be a function of the initial density and subsequent decay of the metastable state. Similarly, the maximum delay is shown to be a function of the initial density and decay of the ground state.
Statistics of the strength of optical fibers
Authors: Helfand Eugene , Wasserman Z. R.
Published: February 2003

A discussion is presented of means of depicting statistical data on the strength of optical fibers (or other fibers) both graphically and in terms of analytic statistical models. Emphasis is placed on the cumulative hazard which may be interpreted as the density of flaws along a fiber which lead to breaks below a given strength. A portion of the data seems to be fit well by a Weibull distribution. Failures at high strength which do not fit the Weibull plot are to be censored. The applicability of this Weibull distribution at very low strengths is still open to question. Quantitative proof testing, and/or an identification of failure modes, would help clarify the issue.
The influence of mass loading outside the electrode area on the resonant frequencies of a quartz-crystal microbalance
Authors: van der Steen C. , Boersma F. , van Ballegooyen E. C.
Published: February 2003

In the present paper the influence of mass loading outside the electrode area on the resonant frequencies of a quartz-crystal microbalance is treated. To investigate this influence a theoretical model has been developed and several experiments have been performed. From both experiment and theory it is concluded that this influence cannot be neglected in high-precision measurements as has been assumed until now.
Kinetic temperature measurement of the front surface of a target exposed to an intense pulsed electron beam
Authors: Peugnet C.
Published: February 2003

A measurement of surface temperature has been developed for pulsed radiation dose levels such that vaporization of the material under investigation is obtained. This method, which has been successfully used, is based on the kinetic definition of temperature, and can be used for temperatures above the vaporization threshold and beyond without changing the physical phenomena. A detector located at a distance l from the target establishes the speed distribution of atoms ejected, from which we deduce the temperature. The rise time of the leading portion of the signal obtained depends on the temperature. Compared to optical methods, this method has the advantage of being unaffected by the electromagnetic and bremsstrahlung noises inherent to electron generators. Moreover, the hydrodynamic expansion velocity can be calculated and the blowoff density estimated. This method can also be used in the case of other pulsed energy sources such as photons or ions.
Metallic glass resistance thermometers
Authors: Hasegawa R. , Tanner L. E.
Published: February 2003

Glassy Ti-Be-Zr base alloys exhibit large negative temperature coefficients of resistivity. The observed values are larger than those previously observed for Pd-Si base noncrystalline alloys. These properties suggest the use of Ti-Be-Zr alloy ribbons as the active elements in resistance thermometers.
Threshold characteristics and extended wavelength operation of GaAs1−x′Sbx′/ AlyGa1−yAs1−xSbx double-heterostructure lasers
Authors: Nahory R. E. , Pollack M. A. , Abrokwah J. K.
Published: February 2003

A normalized threshold current density Jth/d = 4.0 kA cm−2 μm−1 has been determined for pulsed broad-area room-temperature GaAs1−x′Sbx′/AlyGa1−yAs1−xSb x DH lasers of length 380 μm over a range of active-layer thicknesses d. Thresholds as low as 1.2 kA cm−2 and differential efficiencies up to 35% have been obtained in the wavelength range 0.99–1.06 μm. cw operation of stripe-geometry lasers is also described.
Analytical determination of the exact primary beam direction from Kikuchi patterns
Authors: Helfmeier Heinrich , Feller-Kniepmeier Monika
Published: February 2003

An exact analytical solution for the beam direction is derived using two indexed Kikuchi line pairs. The method allows for a rapid analysis of Kikuchi patterns.
Oxidation of silicon without the formation of stacking faults
Authors: Murarka S. P. , Levinstein H. J. , Marcus R. B. , Wagner R. S.
Published: February 2003

A new technique of eliminating oxidation-induced surface stacking faults has been developed. It involves heating clean silicon wafers in an inert or HCl-inert ambient in the same furnace where subsequent oxidation—wet or dry—will be carried out. Typical fault densities after oxidation without in situ cleaning are 1000–5000 and 50–500/cm2 for n- and p-type wafers; these numbers are reduced to ∼10–100 and 0, respectively, when in situ cleaning is used.
The adsorption and early stages of condensation of Ag and Au on W single-crystal surfaces
Authors: Bauer E. , Poppa H. , Todd G. , Davis P. R.
Published: February 2003

Silver and gold were evaporated up to several monolayers in thickness onto W {110} and {100} single-crystal surfaces in the temperature range between 300 and 1300 °K. The mode of growth and the structure of the layers were studied by Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The results are compared with thermal desorption spectroscopy (TDS) data and work-function change (Δφ) measurements. They show certain similarities but also some striking differences between the two systems Ag/W and Au/W, and a strong crystallographic anisotropy of adsorption and condensation.
Extraordinary Hall effect in rare-earth–cobalt amorphous films
Authors: Asomoza R. , Campbell I. A. , Jouve H. , Meyer R.
Published: February 2003

Experiments on the extraordinary Hall effect in sputtered amorphous rare-earth–cobalt films show that the effect is due to the cobalt magnetization rather than that of the rare earth.
The Schottky barriers produced by polymeric sulfur nitride on compound semiconductors
Authors: Scranton R. A.
Published: February 2003

Schottky barriers produced by polymeric sulfur nitride, (SN)x, on nine common III-V and II-VI compound semiconductors are compared to barriers formed by Au. The conductor (SN)x produces significantly higher barriers to n-type semiconductors and lower barriers to p-type semiconductors than Au, the most electronegative elemental metal. The barrier height improvement, defined as ‖φ (SN)x−φ (Au) ‖, is smaller on covalent semiconductors than on ionic semiconductors; (SN)x barriers follow the ionic-covalent transition. Details of (SN)x film deposition, sample preparation, and barrier height measurements are described.
Structural and magnetic disorder effects on electron transport properties of Cu-Ni films
Authors: Thakoor A. P. , Chopra K. L.
Published: February 2003

The resistivity and thermoelectric power of CuxNi1-x films containing 0, 15, 20, and 25 at.% of Cu have been studied in the temperature range 300–675 K. The effect of postdeposition annealing on the microstructure and the transport properties of the alloy films deposited at 100 and 300 K have been studied in detail. The contributions to the resistivity of the alloy films of different compositions due to the structural, thermal, alloying, and magnetic disorder present in the films have been established. The thermoelectric power has been separated into two terms, one corresponding to the structural disorder and the other to the rest of the disorder effects. The presence of structural disorder has been shown to enhance the spin-disorder-induced effects on electron transport properties. The observed concentration and temperature dependence of the transport properties and their anomalous behavior at the Curie temperature can be understood in terms of the thermal and structure-induced spin-disorder scattering in the alloy films.
Enhancement of the critical current of multifilamentary Nb3Sn conductors by tensile stress
Authors: Rupp G.
Published: February 2003

The critical current Ic and the strain ε within multifilamentary Nb3Sn conductors subjected to a uniaxial tensile stress were measured. Ic increases with increasing ε and passes through a maximum Icm at a strain εm. The ratio Icm/Ic is a function of ε−εm only and independent of conductor type. As the ratio γ of the cross-sectional area of the conductor taken up by Nb3Sn to that of bronze decreases, εm increases. For γ=0.06, the smallest value used, εm=0.9% and Icm/Ic0=1.4 at 4.4 T (Ic0: initial value of Ic). This effect occurs because the coefficient of thermal expansion is greater for bronze than for Nb3Sn. The resulting pressure to which the Nb3Sn is subjected at 4.2 K reduces Ic. Initially, an externally applied axial stress reduces the pressure upon the Nb3Sn and produces an increase in Ic. Further increase of the stress exerts a resultant tensile stress upon the Nb3Sn and brings about a reduction in Ic. The technical applicability of the conductor is improved by the internal compressive stress since less degradation in Ic occurs at high tensile loads when compared to the case of a stress-free conductor.
(ErEu)3 (FeGa)5O12 garnet films for magnetic writing and magneto-optic displays
Authors: Antonini Bruno , Borghese Camillo , Menegalli Stefano , Paroli Paolo , Tappa Remo , Toni Mauro
Published: February 2003

Thin films of (ErEu)3 (FeGa)5O12 garnet have been grown by liquid-phase epitaxy onto (111) -oriented GGG substrates, by increasing in steps the Ga2O3 concentration in the melt. For the molar ratio Fe2O3/Ga2O3 ranging from 8.3 to 7.6, the films show large ’’rag’’ domains rather than the usual strip-domain pattern. These ’’rag’’ domains can be given any predetermined shape under the drive of external magnetic fields, the obtained figures being stable without need of any bias field. These features make rag-domain films suitable for magnetic writing and magneto-optic displays. Measurements of the relevant parameters of a number of such films show that reasonable material performances are obtainable.