bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparative study of the hyperfine fields in ferromagnetic GdRh and GdZn
Authors: Dormann E. , Buschow K. H. J.
Published: February 2003

The zero-field nuclear resonance of Gd155, Gd157, Rh103, and La139 were studied in Gd1−xLaxRh. Magnetic measurements performed on GdRh show that this compound has a Curie temperature of 24 K and a magnetization corresponding to 6.6μB/Gd at 4.2 K. These values are low compared with those of GdZn (270 K; 7.5μB/Gd). The NMR results of Gd1−xLaxRh are compared with similar data available for Gd1−xLaxZn. For both series the hyperfine field at the Gd site is separated into its different contributions. The transferred hyperfine field at the Gd site is positive in GdRh but negative in GdZn. It is suggested that the exchange interaction between the 4f moments in GdZn proceeds predominantly via d-electron polarization, whereas the RKKY-type interaction, mediated by s electrons, is relatively weak.
Precise measurement of the thermal expansion of silicon near 40 °C
Authors: Norton M. A. , Berthold J. W. , Jacobs S. F. , Plummer W. A.
Published: February 2003

We report absolute measurements of the thermal-expansion coefficient of single-crystal silicon having a precision of ±0.2%. Five thermal-expansion values have been determined using 1.9 °C temperature measurement intervals within the temperature range 34–44 °C. Our value for the thermal expansion of silicon at 35.22±0.08 °C is 2.683±0.005×10−6 cm/cm °C, which agrees with previous measurements by others and represents an almost fivefold increase in accuracy.
High-temperature thermodynamical studies by mass spectrometry: Use of heat pipe devices of maintain isothermal conditions in effusion cells
Authors: Chatillon C. , Allibert M. , Moracchioli R. , Pattoret A.
Published: February 2003

Various methods have been attempted to resolve the difficult problem of maintaining a uniform temperature in the multiple effusion cells coupled to a mass spectrometer. A heat pipe device in which the cells are housed provides a very reliable solution and practically eliminates the risk of errors due to temperature gradients.
Comparison of the measurement of beam-current densities in an electron microscope using a Faraday cup and solid-state detector
Authors: Howitt D. G. , Thomas G. , Toutolmin W.
Published: February 2003

A Faraday cup has been constructed which is capable of accurately measuring beam-current densities in the image plane of an electron microscope. This device has been employed to calibrate a solid-state detector typical of those often used to measure such small electron intensities. The ability of the solid-state detector to distinguish single electrons was found to be a sensitive function of the incident electron intensity. Important applications of this work include investigations of radiation damage in beam-sensitive materials, e.g., biological specimens.
Self-defocusing of pulsed light beams
Authors: Steverding B.
Published: February 2003

Beam spreading by thermal blooming of intense light pulses is treated by self-similar methods. Scale parameters for the lateral spreading of the beam and the decrease of the maximum intensity are derived. The system of self-similar ordinary differential equations is derived. Estimates are calculated at which beam-energy thermal blooming exceeds linear absorption.
Lasing in a ternary mixture of He-Ne-O2 at pressures up to 200 Torr
Authors: DeYoung R. J. , Wells W. E. , Miley G. H.
Published: February 2003

Addition of large amounts of helium to the Ne-O2 8446-Å laser has used the multiple resonances of helium and neon excited states to improve lasing output by a factor of 3. A lower power supply voltage requirement was also obtained and lasing in a mixture of He-Ne-O2 was found for total pressures well over 200 Torr. Stable pulsed operation for periods of greater than one week are now possible in sealed-off laser cells due to the higher-pressure operation.
Effects of applied voltage on hologram writing in lithium niobate
Authors: Cornish W. D. , Moharam M. G. , Young L.
Published: February 2003

The effects of applying voltages across the crystal during a repeated cycle of hologram writing followed by simultaneous reading and erasure have been studied with care to avoid errors due to multiple reflections. The results are of significance in connection with improving the efficiency in applications of lithium niobate as the hologram storage material in read-write optical memory systems. They also provide information on the physics of the hologram storage process. It was found that large-scale space-charge fields, which are produced by the optically induced redistribution of electrons among traps, play an important role in determining the buildup of the sinusoidal space-charge fields which produce the hologram. The large-scale space-charge fields cause the diffraction efficiency produced by a given exposure to depend on the voltage applied during the previous write-read/erase cycles as well as on the voltage applied during the current cycle. Increased efficiency can be obtained by applying a different voltage during erase and write phases. Also, it is found that the efficiency of hologram writing depends on the fraction of the crystal illuminated. The development of these dc fields is modelled and compared with results from ellipsometric experiments. It is found that the effects of applied voltage are generally in agreement with hologram formation by the combined action of the new bulk photovoltaic effect of Glass et al., drift of photoreleased electrons in applied and space-charge fields, and possibly some diffusion. The term κ1αI (where κ1 depends on the dopant, α is the absorption, and I is the light intensity), which Glass et al. used to describe the contribution to the electron current density provided by the bulk photovoltaic effect, is shown to be equivalent to what would be produced by a ’’virtual’’ built-in field, provided the drift length was small. However, it does not entirely represent the behavior expected for their proposed model, and estimates of the virtual field are rather scattered. Intervalence transfer may occur. It is shown pyroelectric built-in fields may be present under some circumstances but were not observed even under favorable conditions.
Detection of small concentrations of N2+ in the atmosphere by a laser scattering technique
Authors: Solomon Jerry E. , Silva Dennis M.
Published: February 2003

The resonance absorption and emission at atmospheric pressure from the first negative band in N2+ has been investigated by a laser technique. By stimulation with a narrow-bandpass dye laser the cross section for resonance absorption at 3914 Å and subsequent emission at 4278 Å, (0-1) transition, was measured. This cross section was determined to be 3×10−20 cm2/ion. A theoretical estimate for this process places the cross section at 1.8×10−21 cm2/ion. An analysis of both the experiment and the calculation indicates that these numbers represent the upper and lower limits for the actual value of the cross section.
Extinction ratio limitations in GaAlAs electroabsorption light modulators
Authors: Dyment J. C. , Kapron F. P.
Published: February 2003

This paper reports experimental and theoretical results concerning absorption and scattering losses in GaAlAs electroabsorption (EA) light modulators. Light coupled from the outer confining layers into the central guiding layer is shown to limit the extinction ratio. If a is the EA coefficient and l the modulator length, scattering results in a low background level in the detected light which decreases as a−1 for sufficiently large al product rather than as the usual exp(−al) for smaller al. Scattering effects occur in all the layers, with many modulators showing large local increases in the density of scatter centers in the confining layers.
Deep-level distributions near p-n junctions in LPE GaAs
Authors: Lang D. V. , Logan R. A.
Published: February 2003

Deep-level concentrations near p-n junctions in LPE GaAs have been studied by the capacitance spectroscopy method. Two deep levels which are characteristic of LPE growth were measured within a few μm of the junction in both p+n and n+p diodes. The results indicate a uniform concentration of (6–9) ×1014 cm−3 for these levels in n-type GaAs, but an extremely large variation from 3×1013 to 1015 cm−3 within 1 μm of the junction in p-type GaAs. In addition some samples show Cu and Fe contamination in the low 1014-cm−3 range due to diffusion from the LPE-substrate interface.
Study of trapping in mercuric iodide by thermally stimulated current measurements
Authors: Stuck R. , Muller J. C. , Ponpon J. P. , Scharager C. , Schwab C. , Siffert P.
Published: February 2003

Thermally stimulated current measurements have been performed in red mercuric iodide crystals grown by a vapor-phase technique. They reveal the presence of a hole trap at Ev+0.45 eV with a capture cross section of 10−15 cm2. Two additional centers were found when the crystals were cleaved rather than etched.
Scattering of long-wavelength elastic waves by a cylindrical obstacle in a solid
Authors: Lewis Timothy S. , Kraft David W.
Published: February 2003

The scattering of plane shear and compressional waves incident normally upon an infinitely long circular cylindrical obstacle in an isotropic homogeneous elastic solid medium is examined in the case in which the incident wavelength is large compared to the obstacle diameter. The scatterer can be either an empty cavity, a nonviscous-fluid-filled cavity, or an elastic solid cylinder. Explicit approximate expressions for the scattering cross sections are derived from the general theory formulated by White. The cross sections are proportional to (ka)3, where k is the compressional or shear wave-vector amplitude, and a is the cylinder radius.
Formation, structure, and orientation of gold silicide on gold surfaces
Authors: Green A. K. , Bauer E.
Published: February 2003

The formation of gold silicide on Au films evaporated onto Si(111) surfaces is studied by Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). Surface condition, film thickness, deposition temperature, annealing temperature, and heating rate during annealing are varied. Several oriented crystalline silicide layers are observed.
Doping effects upon the ultrasonic attenuation of Bi12SiO20
Authors: Rehwald W. , Frick K. , Lang G. K. , Meier E.
Published: February 2003

Single crystals of bismuth silicon oxide doped with Al, Ga, or B have been grown by the Czochralski method. Doping with Ga and B reduced the previously observed anomalous ultrasonic attenuation at low temperatures considerably, doping with Al removed it completely. In a similar way the additional optical absorption below the intrinsic absorption edge is affected. Numerical comparison of both results gives values for the defect concentrations involved [(2–6) ×1017 cm−3] and for the deformation potential (about 3 eV).
Breakdown mechanisms and electrical properties of triggered vacuum gaps
Authors: Govinda Raju G. R. , Hackam R. , Benson F. A.
Published: February 2003

Some electrical characteristics of a triggered vacuum gap (TVG) having three different dielectric materials have been studied. Silicon carbide which possesses very high resistance (500 MΩ), steatite ceramic of medium resistance (20 MΩ), and boron nitride of very low resistance (50 Ω) have been used. The resistance of the dielectric is found to decrease with increasing trigger current and this is attributed to the deposition of metal vapor on the surface. The minimum trigger voltage and trigger current nessessary for successful operation of the TVG are measured. Deconditioning (reduction) in the minimum trigger voltage, after repeated firings, has been found and is attributed also to the deposition of metal vapor on the dielectric surface. The minimum trigger current for successful firing of the main gap decreases with increasing trigger voltage. The probability of successful firing of the TVG is found to rise rapidly with increasing trigger voltage. The delay time between the application of the trigger pulse to the breakdown of the main gap decreases with increasing trigger current and trigger voltage. A mechanism is suggested for the operation of the TVG.
Amorphous GexH1−x bolometers
Authors: Moustakas T. D. , Connell G. A. N.
Published: February 2003

Selected materials from the amorphous GexH1−x system are evaluated at 300 K as thermistor bolometers operating at photon energies between approximately 0.2 and 2.5 eV. The devices are deposited on glass and sapphire substrates by rf sputtering of polycrystalline Ge in an argon-hydrogen atmosphere. Their current-voltage characteristics, their response times, the frequency and spectral dependence of their responsivities, and the frequency dependence of the noise in a 3-Hz bandwidth are all measured. Response times between 1 and 10 msec and Dλ* (0.633, 13, 1)’s of between 5×106 and 5×107 W−1 Hz1/2 cm are obtained, using a calibrated He-Ne laser (λ=0.633 μm) as an excitation source. (At this wavelength, all nonreflected incident light is absorbed.)
High-pressure Langmuir probe in a weak flowing plasma or a plasma sheath
Authors: Smy P. R. , Noor A. Ibn.
Published: February 2003

A theory is developed for the current to a negatively biased probe in a moving weakly ionized plasma or a stationary ion sheath. It is found that at low ionization densities the current is no longer space-charge limited but is, in fact, limited by the electric field generated by the probe. For a cylindrical probe the current per unit length I=2πμn0eV[log(I/n0evfrp)−1/2] −1, where μ is the mobility of the ion, e is the electronic charge, V is the probe potential (negative), I is the probe current, vf is the plasma flow velocity, n0 is the plasma ionization density, and rp is the probe radius. For a spherical probe the current I=4πμn0erpV. Measurements with a cylindrical probe at densities down to 1012/m3 show good agreement with theory.
Growth of fine holes in polyethylenenaphthalate film irradiated by fission fragments
Authors: Komaki Yoshihide , Tsujimura Shigeo
Published: February 2003

Growth of fine holes by chemical etching in polyethylenenaphthalate films exposed to fission fragments were examined by measuring gas flow through the films. The etching rate along tracks, the radial etching rate, and the bulk etching rate were determined at effective hole diameters of 100–1 000 Å and hole densities of approximately 108 cm−2. The effects of ethanol and surfactants on the etching rates were studied from the viewpoint of attaining less-tapered holes.
Electromigration in thin aluminum films on titanium nitride
Authors: Blech I. A.
Published: February 2003

The aluminum electromigration drift velocity was measured at the temperature range 250–400 °C. A threshold current density was found inversely proportional to the stripe length. An activation energy of 0.65 eV was found for the drift velocity. The occurrence of the threshold is explained by opposing chemical gradients created by the atom pile-up and depletion at the stripe ends. The threshold may explain several observations reported previously. The threshold is increased by decreasing the temperature or by enclosing the aluminum in silicon nitride. Virtually no electromigration is seen for very short aluminum stripes even at current densities above 106 A/cm2.
Surface-wave nonlinearities: Nonlinear bulk-wave generation by two oppositely directed collinear surface waves
Authors: Padmore T. C. , Stegeman G. I.
Published: February 2003

The nonlinear interaction between two oppositely directed surface acoustic waves (SAW) of frequencies ω1 and ω2 and wave vectors κ1 and κ2 is analyzed theoretically. It is shown from the general theory of thermoelasticity that nonlinear volume forces and surface stresses are created at the frequencies ω1±ω2 and wave vectors κ1∓κ2, respectively. For the difference frequency case the forces and stresses are relieved by evanescent SAW. In the sum frequency case, up to three bulk waves are generated depending on the value of κ2/κ1. The nonlinear interaction is characterized by normalized surface displacement and bulk-wave power parameters. The upshift case is examined as a function of κ2/κ1 for fused quartz, yz sapphire, and zx sapphire and the cross sections for bulk-wave generation are discussed in detail. Numerical calculations are presented (with ω1=ω2) for the (001), (110), and (111) planes of gallium arsenide, the principal planes of sapphire, and for some cuts of piezoelectric α-quartz and lithium niobate (in the quasi-static approximation). The quantity and type of bulk modes generated is discussed in light of SAW propagation plane reflection symmetry, rotational symmetry, and confinement of SAW displacements to the saggital plane.
Charging of insulators by ion bombardment and its minimization for secondary ion mass spectrometry (SIMS) measurements
Authors: Werner H. W. , Morgan A. E.
Published: February 2003

The generation of charge build-up, caused by bombardment of insulating samples with energetic particles, and its role in altering the relative secondary-ion currents and reducing their absolute values, sometimes even to zero, are discussed. Proposed methods for charge reduction by bombardment with negative ions or with neutral particles, or by use of an auxiliary electron beam or spray gun, are shown to be not useful in every experimental situation. A further method involving introduction of an auxiliary conducting electrode when using negative primary ions is considered mechanistically, and tested by placing tantalum diaphragms onto the surface of yttrium iron garnet (YIG). The final charging values and mass spectra thus obtained are compared to those measured when using bare and metallic grid-covered surfaces of the same YIG sample. The satisfactory results achieved with the diaphragm show that SIMS analyses of insulators can be performed in a simple, quick, and inexpensive manner.
Acoustic-surface-wave scattering at a region with material perturbation
Authors: Tuan Hang-Sheng
Published: February 2003

Acoustic surface waves (ASW) scattered at a region with density and elastic parameter variations are studied in view of the newly developed techniques to fabricate ASW reflectors by ion implantation and metal impurity diffusion. The scattering problem is formulated in a perturbation theory. The first-order vector equation and the solution are obtained in terms of a source which is due to the interaction of the incident wave and the material perturbation. An example is given to illustrate the application of the theory. Results are found to agree closely with experimental observation.
Propagation characteristics of helical instabilities in semiconductors
Authors: Chen Pin-Wei , Chen Wen S.
Published: February 2003

A general theory of helical instabilities with different azimuthal propagation modes in an injected electron-hole plasma is given by extending Holter’s theory. The theory can explain the following features of the recent helical instability measurement in p-type InSb obtained by the launching technique: (i) threshold condition of the instability for different azimuthal modes, (ii) frequency dependence of the spatial amplification associated with different propagation modes, and (iii) characteristics of the carrier temperature.
Electron current injected into SiO2 from p-type Si depletion regions
Authors: Young D. R.
Published: February 2003

Electron currents injected into SiO2 from p-type Si depletion regions have been measured as a function of the oxide field strength and of the silicon surface potential. These measurements have been made at room temperature and at liquid-N2 temperatures. The oxide field dependence has been compared with a Schottky-emission model suggested by Ning and it has been found that this model must be corrected for oxide scattering. The barrier lowering effect enables us to probe the electron energy distribution from 2.55 to 2.9 eV. The surface potential dependence is not in agreement with Verwey’s model but has the form suggested by Pepper; however, Pepper’s theory does not give the correct impurity doping dependence. A large increase in oxide current is observed as the temperature is decreased from room temperature to liquid-N2 temperatures.
Monte Carlo studies of hot-electron energy distribution in thin insulating films. I. Constant mean free path and a one-dimensional simulation
Authors: Baidyaroy S. , Lampert M. A. , Zee B. , Martinelli Ramon U.
Published: February 2003

The hot-electron energy distribution produced in a high electric field F across a thin insulating film is studied by Monte Carlo calculations on a digital computer. The dominant electron collisions are assumed to be those with the lattice, producing single optical-phonon emissions of energy εph. The mean free path λ is taken as a constant independent of energy, and both isotropic and anisotropic scattering are studied. A scaling law for the average electron energy Eave,ss in the steady-state distribution, previously found analytically for isotropic scattering, namely, Eave,ss=k (Fλ)2ε/ph, is found to hold also for anisotropic scattering, k being a numerical constant determined by the detailed nature of the scattering law. Forward scattering produces larger values of k, backward scattering smaller values. No matter how strongly peaked the forward scattering, short of exact (ϑ=0) forward scattering, there is a finite steady-state distribution. An analogous scaling law is found for the development distance D require to achieve the steady-state distribution, namely, D=k′ (Fλ2)/εph. Since the study of anisotropic scattering is costly, an extensive computer study was made of a highly simplified simulation, namely, a one-dimensional random walk (fixed path length between collisions) in a force field. The salient features of the three-dimensional energy distribution are reproduced by the one-dimensional simulation, and the computer running time is reduced by a full order of magnitude.
A model for Schottky-barrier solar cell analysis
Authors: McOuat R. F. , Pulfrey D. L.
Published: February 2003

A general model for the analysis of metal-semiconductor solar cells is presented. The model takes into account the cell optical properties, carrier recombination effects, semiconductor minority-carrier properties, series resistance, cell thickness, and active surface area. Numerical methods are used to solve the appropriate continuity equations and hence compute the photocurrent density under AMO conditions. The operation of the model is demonstrated using p- and n-type Si and GaAs with Au being taken as the barrier metal. Calculations are presented showing the effect on solar energy conversion efficiency of surface recombination velocity, barrier height, minority-carrier lifetime, barrier metal thickness, collecting grid configuration, and cell thickness. A comparison of practical and computed data for the Au/n-GaAs system yields good agreement.
Mechanism of laser-induced metal-semiconductor electrical connections in MOS structures
Authors: Platakis Nicolaos S.
Published: February 2003

This paper describes in detail an experimental study of the laser-induced metal-semiconductor connections in MOS structures. Quantitative results concerning these connections, and their dependence on pulse width, pulse power, and the number of pulses are given. This information is valuable when the laser is used for interconnecting integrated circuits and similar devices.
Inhomogeneities in superconducting niobium surfaces
Authors: Das Gupta A. , Gey W. , Halbritter J. , Küpfer H. , Yasaitis J. A.
Published: February 2003

Inhomogeneities in superconducting Nb have considerable influence on ac losses in cables; they also give bad rf results. To study inhomogeneities near Nb surfaces, the magnetic induction profile B (x) and hence the critical current density jc(x) were determined as a function of distance x from the surface in samples which were machined, annealed, and chemically polished or electro-polished and anodized. With identical samples the magnetization and 18-kHz penetration depths were also measured as a function of dc magnetic field, applied parallel to the surface. These measurements on Nb samples, which were all exposed to air, indicate that two superconducting phases exist near the surface. One of them has an Hc2 much higher (50%) and the other somewhat higher (10%) than Hc2 in the bulk. In addition, strong pinning exists near the surface as evidenced by jc higher than 106 A/cm2. These effects were found, although to a somewhat lesser extent, even after UHV annealing. The high Hc2 values and strong pinning near the surface, even above the bulk Hc2, can be explained by the presence of inhomogeneities there.
Heat balance and flow conditions for electron beam and laser welding
Authors: Klemens P. G.
Published: February 2003

The conditions of energy and material flow during beam welding are investigated theoretically to determine the factors which govern the shape of the vapor cavity and of the molten zone. Flow conditions in the horizontal plane determine the dimensions of the weld. Material is moved around the advancing vapor cavity mainly by liquid flow, but there is some vapor flow across the cavity, providing the pressure which drives the liquid. The pressure inside the vapor cavity and its variation with depth is governed by surface tension, by the hydrostatic pressure in the liquid, and by the viscous forces acting on the vapor stream. These factors govern the radius of the cavity as a function of depth. The penetration is limited by the beam power or by the absorption of the beam. For the laser beam, absorption is decreased in the hot center, and beam penetration increases with power, but is insensitive to collimation. For electrons, absorption occurs mainly near the walls of the cavity, and the beam penetration depends on collimation and power. The balance between beam power and power dissipated by conduction, melting, and vaporization is discussed, and a self-consistent description is given of cavity formation and beam penetration.
Multiple elastic scattering of slow electrons: Parametric study for H2
Authors: Kutcher G. J. , Green A. E. S.
Published: February 2003

The spatial pattern of energy deposition about charged particle tracks is of great interest in radiation physics. Secondary electrons with energies of tens of eV play a prominent—and sometimes dominant—role in the energy deposition. Due to the large number of elastic scatterings suffered by the secondaries, the cost of Monte Carlo solutions for the spatial patterns proves prohibitive. The method of condensed case histories facilitates a solution to the problem, but use of the method implies knowledge of the multiple elastic scattering. Since such distributions are not available in the energy regime of interest, we have obtained the distribution of slow electrons diffusing through an infinite medium of gaseous H2 by a Monte Carlo solution to the one-energy time-dependent Boltzmann equation. The equation is solved for five values, between 2 and 50 eV, of the energy parameter E which was used to fit the H2 differential elastic cross sections. The single scattering law in this energy regime is distinguished by a moderate forward peak and a significant backscattering component. The cumulative multiple scattering distributions for pairs of independent variables are fitted by two- and three-parameter analytic functions. The generality of these distributions should make them useful for many other gases.
Ultrafine metal particles
Authors: Granqvist C. G. , Buhrman R. A.
Published: February 2003

In this paper we present a novel and versatile technique for the production of ultrafine metal particles by evaporation from a temperature-regulated oven containing a reduced atmosphere of an inert gas. An extensive investigation of particles of oxidized Al, with diameters of 3 to 6 nm, has been performed. We have also studied ultrafine particles of Mg, Zn, and Sn produced in the same manner. A supplementing investigation has been carried out for particles of Cr, Fe, Co, Ni, Cu, and Ga, as well as larger Al particles, produced by ’’conventional’’ inert-gas evaporation from a resistive filament. Diameter as a function of evaporation rate, inert-gas pressure, and the kind of inert gas are reported. Crystalline particles smaller than 20 nm look almost spherical in the electron microscope, while larger ones often display pronounced crystal habit. Size distributions have been investigated in detail, and consistently the logarithm of the particle diameter has a Gaussian distribution to a high precision for the smallest sizes, whereas larger particles deviate from such a simple behavior. A statistical growth model, based on the Central Limit Theorem, has been formulated for liquidlike coalescence of particles; this theory accounts satisfactorily for all our data, as well as for most size distributions published in the literature. Applications of the model to colloids, discontinuous films, and supported catalysts are discussed. By comparing size distributions for particles produced by a variety of techniques we found a number of empirical rules for the width of the distributions, as defined by a (geometric) standard deviation σ. For crystalline inert-gas- evaporated particles we obtained consistently 1.36?σ?1.60; for coalescing islands in discontinuous films we found 1.22?σ?1.34; and similar rules are applicable to colloids, supported catalysts, and to ultrafine droplets.
Room-temperature gamma spectroscopy of 137Cs using HgI2 detectors
Authors: Whited R. C. , Schieber M. M. , Randtke P. T.
Published: February 2003

Gamma rays from 137Cs have been resolved using room-temperature HgI2 detectors in three different configurations. The methods used were (i) single charge collection in a thick quasihemispherical-shaped detector (ii) a thin HgI2 detector irradiated edge-on, and (iii) pulse rise-time discrimination with a thin detector irradiated face-on.
Easy axis of amorphous ferromagnet Fe40Ni40P14B6
Authors: Chien C. L. , Hasegawa R.
Published: February 2003

The easy axis of magnetization of amorphous Fe40Ni40P14B6 has been measured by 57Fe Mössbauer spectroscopy in zero external field. For T≳240 K, we find the easy axis to lie in the plane of the ribbon and to be predominantly along the long edge. At T<240 K, the easy axis, on the average, first tilts out of the ribbon plane, changing continuously with temperature, and then tilts back toward the ribbon plane at 100 K. This behavior is attributed to stresses produced thermally.
Permeability effects on the magnetization of thin Permalloy I bars
Authors: Dove D. B. , Watson J. K. , Ma H. R. , Huijer E.
Published: February 2003

Calculations and measurements on thin Permalloy bubble circuit elements show effects arising from finite material permeability. A new method is used to directly calculate the magnetization profile in a thin isolated I bar, in quantitative comparison with recent measurements and with a previously reported indirect calculation. The scale factor used in the indirect calculation is found to be about 8% high for the limiting case of infinite susceptibility, with poorer agreement for lower values. New measurements are reported for sparse arrays of I bars using a large-area magneto-optic probe and are compared with SFS and other calculations.
Decreases in intensity of exoelectron emission by heavy gamma irradiations
Authors: Sasaki T.
Published: February 2003

Two peaks of thermally stimulated exoelectron emission (TSEE) from powdered Li2SO4 were observed at 250 and 440 °C. Their intensities become maximum around 2×105 and 6×107 rad, respectively, and decrease in the further irradiations. The decreases are probably due to structural defects of the crystal lattice in the surface layer.
Mobility changes in PbSnTe due to low-temperature electron irradiation
Authors: Green Barry A.
Published: February 2003

Electron irradiations of PbSnTe at 10 °K are found to produce mobility increases in n-type material, while mobility decreases are observed in p-type material. This behavior is shown to be directly related to the carrier addition which occurs during irradiation in n-type samples and the carrier removal which occurs in p-type samples, and is also shown to be dependent on the carrier degeneracy and heavily compensated state of the samples.
Self-interaction of the upper hybrid wave
Authors: Chan V. S. , Seshadri S. R.
Published: February 2003

The self-interaction of the extraordinary mode propagating across the magnetostatic field in an electron plasma is investigated with particular attention to the range of frequencies close to the upper hybrid resonant frequency. The slowly varying amplitude of the upper hybrid wave satisfies a cubic Schrödinger equation which is deduced using the method of Kakutani and Sugimoto. The analysis of the Schrödinger equation shows that the extraordinary mode, in the neighborhood of the upper hybrid resonant frequency, is modulationally stable or unstable according to whether the wave number is below or above a critical value which is controlled only by the dispersive properties of the wave and which corresponds to frequencies slightly below the upper hybrid resonant frequency.
Structure and optical conductivity of thin lithium deposits prepared at 6 K
Authors: Rasigni M. , Rasigni G. , Gasparini J. P. , Fraisse R.
Published: February 2003

A replication technique is used to determine, in situ, the structure of thin lithium deposits prepared at 6 K. It is shown that perfectly smooth deposits are not always obtained. It follows, as in the case of deposits prepared at room temperature, that optical conductivity is not perfectly described by the sum of an intraband term and an interband term, but must take into account a supplementary term that characterizes an absorption due to granular structure of the deposit or to surface roughness defects. It is shown that certain deposits of lithium, prepared at low temperature, are made up of a two-dimensional distribution of grains on a continuous layer of metal. In this case the supplementary term results from collective oscillations of conduction electrons in the metallic grains. From this, it can be concluded that most of the optical measurements made on the thin deposits of lithium (and on alkali metals in general) in all likelihood involve systematic errors, and should be corrected before being collated with theory.
Electron-microscope study of 10.6-μm laser damage in GaAs
Authors: Comer J. J.
Published: February 2003

The nature of the damage to GaAs caused by exposure to a 10.6-μm laser beam at power densities of 1130, 2260, and 5650 W/cm2 was determined by transmission electron microscopy. At 5650 W/cm2 damage was observed at the surface in the form of craters of 80 μm or larger in diameter. Within the craters were found concentric zones spreading out from the center and consisting of (1) an amorphous region, (2) a region showing striations and skeletal crystalline walls in an amorphous matrix, and (3) a mixed amorphous-crystalline region containing small rounded clusters of dislocations, some of which were helical. In one case crystalline arsenic was found near the central zone. The results observed at this power level indicate that thermal effects have caused melting, evaporation, and decomposition. It is suggested that the skeletal walls and the striations parallel to {110} planes are caused by preferential evaporation or decomposition and may be related to the presence of small precipitates or chemical inhomogeneities along {110} planes of GaAs as observed by others. Damage near the entrance surface at low power densities, and at the exit surface for the highest power density, consisted of unique clusters of dislocations spreading out along orthogonal 〈110〉 directions up to 3 μm. Although the direct cause of these dislocations could not be determined, it suggested that they result from cracking or cleavage of the crystal due to stresses caused by localized heating at sites of precipitates, occlusions, or other faults in the crystal.
Si depth profile and contaminants in Si-doped Al film
Authors: Chang C. C. , Sheng T. T. , Speeney D. V. , Fraser D. B.
Published: February 2003

Si depth profiles and contaminants in Si-doped Al films deposited on SiO2 by electron-gun evaporation at different base pressures have been measured. The experimental techniques employed were Auger electron spectroscopy combined with ion milling for chemical analysis and depth profiling, and transmission electron microscopy for film structure studies. Auger analysis showed that at intended doping levels of 1 and 2 at.% (previously calibrated using atomic absorption spectrometry) the Al films contained 0.9 and 1.9 at.% Si, if the total Si content was averaged over the entire film thickness. However, most of the Si had migrated to the Al/SiO2 interface after deposition at 300 °C and formed precipitates which nucleated at or near the Al/SiO2 interface. The major film contaminants were C and O, whose concentrations were directly related to the pressure during deposition. The lowest detection limits with the Auger technique were ∼0.01 at.% (100 ppm) for both C and O, attained using a 50-μA incident electron beam current and a scan time of <30 sec per element.
Scattering of elastic waves by a cylindrical cavity in a solid
Authors: Lewis Timothy S. , Kraft David W. , Hom Norbert
Published: February 2003

Numerical computations of scattering cross sections are made for plane compressional and shear waves incident normally upon an infinitely long circular cylindrical cavity in a homogeneous isotropic elastic solid. Dependencies of the cross sections upon the variables ka and κa (k and κ are the compressional and shear wave vector amplitudes, respectively, and a is the cylinder radius) and upon the material parameter κ/k are discussed, along with the relative contributions of the various components of the total cross sections. Computations are made over the range 0⩽ka⩽6 for incident compressional waves, and 0⩽κa⩽10 for incident shear waves. Both sets of computations are done for a number of values of κ/k corresponding to various host materials.
Integral formalism for surface waves in piezoelectric crystals. Existence considerations
Authors: Lothe J. , Barnett D. M.
Published: February 2003

An integral formalism for surface waves in piezoelectric half-infinite solids valid up to the critical velocity is developed. Various boundary conditions are considered and, in particular, the problem of which boundary conditions allow surface-wave solutions for velocities below the limiting velocity vL is discussed in detail. It is proved that (a) with a mechanically free surface and zero dielectric constant for adjoining medium, at most one solution is possible for v<vL, (b) with a mechanically clamped surface and zero dielectric constant for adjoining medium, no solution is possible for v<vL, (c) with a mechanically clamped surface and an infinitely conducting adjoining medium, no solution is possible for v<vL, and (d) with a mechanically free surface and an infinitely conducting adjoining medium, at least one and at most two solutions are possible for v<vL. When two solutions are possible, one solution is of the Bluestein-Gulyaev type.
Dielectric breakdown of Ag2S in the Au-Ag2S-Ag system
Authors: Sharma S. P. , Thomas III J. H.
Published: February 2003

Electrical breakdown of tarnish films (Ag2S) on silver has been investigated in the Au-Ag2S-Ag system. Dielectric breakdown in the Au-Ag2S-Ag system is polarity sensitive and depends on the rate of application of voltage to the film. Breakdown is consistent with multiple electron avalanche processes. Data indicate intrinsic breakdown fields greater than 3×105 V/cm (for fast rise time voltages). For slow rise time voltages, breakdown is strongly affected by silver ion mobility and becomes polarity dependent. The conductivity ratio (σAgrich/σSrich) has been obtained as a function of time and the average Ag ion mobility (2×10−8 cm2/V sec) has been determined.
Tunneling characteristics of thin epitaxial Bi-film–SiO2–Pb junctions
Authors: Asahi Hajime , Kinbara Akira
Published: February 2003

The tunneling characteristics in thin epitaxial Bi films (thickness: 400–1200 Å) were investigated. Bi-SiO2-Pb tunnel junctions were prepared by vacuum deposition onto freshly cleaved mica substrates in an ultrahigh vacuum system. The dI/dV-V curve has a large peak at the Bi positive voltage range (150–250 mV) which can be attributed to the band structure of Bi. In the low voltage range (‖V‖<25 mV), d2I/dV2-V curves show the peaks or dips reflecting the state density of superconducting lead. The phonon-assisted tunneling peaks or dips in the normal state were also observed. For medium voltage range (‖V‖≳25 mV), there are several peaks or dips due to phonons of SiO2. The subband edges generated by quantum size effects were not observed, probably because the electron bands and the hole band of Bi overlap each other, located at the L and T points in the Brillouin zone, respectively.
Cracks and energy—Criteria for brittle fracture
Authors: Doremus R. H.
Published: February 2003

The energies of cracks are considered in terms of the first and second laws of thermodynamics, and it is concluded that the Griffith criterion provides a necessary but not sufficient condition for crack propagation. Fracture occurs only when the crack tip radius is larger than a critical value that is several times the interatomic spacing. Surface energies calculated from fracture experiments probably give only an upper bound to the true surface energies of solids. The radius of the crack tip is a parameter that cannot be ignored in fracture experiments.
Some aspects of the performance of refrigerating thermojunctions with radial flow of current
Authors: Landecker K.
Published: February 2003

An expression for the maximum temperature difference ΔTmax produced between the hot and cold junctions of a thermocouple is derived when the arms are disks of thermoelectric material. In these disks the flow of current is in a direction radially inwards or radially outwards. No assumptions have been made about the distribution of the Joule heat over the hot and cold junctions. The solution as a function of the ratio (ro/ri) of the outer to inner radii of the N and P disks constituting the couple exhibits an interesting singularity at one particular value of this ratio. If ro/ri approaches the numerical value 4.5, the maximum temperature difference ΔTmax appears to have no limit. However, its growth is finally arrested by the temperature dependence of the figure of merit Z. It is then found experimentally that the current through the junction may be increased to large values without causing ΔT to pass through a maximum. The coefficient of performance tends to unity at the critical ratio ro/ri=4.5. Finally, it is pointed out that junctions whose arms are in the form of rotationally symmetrical bodies with lateral surfaces generated by hyperbolae are a more perfect approach to the mathematical model adopted than are flat disks. Such junctions produced temperatures lower than junctions with arms of any other shape.
Photoelectronic properties of high-resistivity GaAs : Cr
Authors: Lin Alice L. , Bube Richard H.
Published: February 2003

The photoelectronic properties of high-resistivity n-type GaAs : Cr are quite similar to those of high-resistivity n-type GaAs : O described in the preceding paper. In the low-temperature region, intrinsic photoconductivity is n type, increases exponentially with 1/T, and can be consistently described by a simple one-level Shockley-Read recombination model with a level lying 0.66 eV below the conduction band and a density that is remarkably constant over a variety of different materials. Two levels characteristic of the Cr doping lie at 0.86 eV below the conduction band and at 0.9 eV above the valence band. Low-frequency photocurrent oscillations are associated with levels at 0.86 and 1.25 eV below the conduction band. The extrinsic photoconductivity at 0.86 eV is produced via two steps: (i) electrons are photoexcited from the ground state to the excited state of Cr+2 (d4) center, and (ii) they are then thermally excited to the conduction band.
Experimental investigation of high-current relativistic electron flow in diodes
Authors: Di Capua M. , Creedon J. , Huff R.
Published: February 2003

Various aspects of the magnetically self-pinched electron flow patterns in megavolt megampere diodes have been investigated. The onset of pinching has been correlated with a transition from Child-Langmuir to parapotential voltage-current characteristics. The average velocity at which the pinch sweeps towards the axis has been measured and is found to be ∼2 mm/nsec. The invariance of the current under geometrical scaling is demonstrated, and the connection between this invariance and plasma motion is discussed. Measurements of total diode current are compared with existing theories and agreement is found with the parapotential model.
Observations of collective ion acceleration with drifting intense relativistic electron beams
Authors: Miller Robert B. , Straw David C.
Published: February 2003

In this paper we report several observations related to the acceleration of positive ions when an intense relativistic electron beam is injected into a low-pressure neutral gas. In addition to varying the type and pressure of the neutral gas, we have varied a number of geometrical parameters including the radius of both the beam and the guide tube, the length of the guide tube (endplate effects), and dielectric constant of the guide tube. We find that ion acceleration occurs only if the peak electron-beam current I0 exceeds the space-charge-limiting current, Il0, for the cavity. Maximum average ion energies are obtained when I0/Il0≳3: the ion (proton) energy spectrum is rather broad with the spectrum peak occurring at 3/2Ee, and the maximum energy cutoff at approximately 3Ee, where Ee is the electron-beam kinetic energy.
Photoconductivity of amorphous compound semiconductors involving elements from groups IV, V, and VI
Authors: Shiah Ralph T.-S. , Bube Richard H.
Published: February 2003

Photoconductivity measurements as a function of excitation intensity and temperature are analyzed for 20 amorphous compound semiconductors of V-VI, IV-V, IV-VI, and IV-V-VI type. Two principal types of photoconductivity are distinguishable; in type I, the photoconductivity exhibits a maximum at a particular temperature and is comparable to or greater than the dark conductivity, whereas in type II, the photoconductivity exhibits no maximum and is much less than the dark conductivity. Indications of localized state energies, densities, and recombination coefficients are obtained by analyzing the photoconductivity data according to the model of Arnoldussen et al. Basic trends, in which the various parameters scale with the optical absorption gap, are discernible for many of the materials. Additional data are supplied on the effects of annealing and crystallization, and photoductivity decay measurements are interpreted to provide indications of the density of localized states near the Fermi level.
A quasi-phase-matching technique for efficient optical mixing and frequency doubling
Authors: Szilagyi A. , Hordvik A. , Schlossberg H.
Published: February 2003

A detailed theory is presented of the second-order nonlinear optical interaction in a sequence of crystal lamellae oriented to give quasi-phase-matching. The efficiency of second-harmonic and sum-frequency generation is analyzed with respect to the orientation of the crystal axes, plate thickness, input intensities, transmission coefficients, dispersion in the intervening medium, and number of lamellae. An energy conserving modification of the small-signal approximation is introduced. To overcome the Fresnel reflection losses the use of antireflection coatings, optical contacting, and Brewster-angle incidence is considered with the latter approach emerging as the most promising. A series of experiments are described where 10.6-μ laser radiation is frequency doubled in a sequence of GaAs plates using Brewster-angle incidence. The conversion efficiency is investigated as a function of crystal orientation, intensity, and number of plates, and good agreement is found between theory and experiment.