bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric Breakdown in Thin Evaporated Films of CaF2, MgF2, NaF, and LiF
Authors: Smith J. Lynn , Budenstein Paul P.
Published: February 2004

Prebreakdown dc conduction and breakdown properties have been studied in thin-film capacitors with dielectrics of CaF2, MgF2, NaF, and LiF. The results are compared mostly with theory developed for electronic breakdown in ionic crystals due to Fröhlich, Callen, and Forlani and Minnaja. Capacitors were formed on glass substrates with dielectric thicknesses from 700 to 30 000 Å and electrodes of Al. Between −200° and 100°C prebreakdown and breakdown conduction appear to be independent. The transition time between prebreakdown and breakdown conduction is 10−8–10−7 sec. Except for some cases where the breakdown field Fmax (≈106 V/cm) displays an initial rise, an increase in temperature from −200 to 100 C is accompanied by a decrease in Fmax. Only the initial rise can be interpreted in terms of theoretical developments by Fröhlich and Callen. An increase in Fmax is observed as the rate of voltage rise varies from 15 to 15 000 V/sec. The breakdown field also varies in most cases as w1/2, where w is dielectric thickness. This behavior is in agreement with the theory of Forlani and Minnaja, implying that impact ionization plays an important role in breakdown. A voltage threshold (≈15 V) for the cessation of breakdown which is independent of thickness and temperature is found for each material studied. This is consistent with the notion that Vmin is the cutoff voltage of a gaseous arc. The above facts attribute an electronic nature to breakdown where, at the onset, the magnitude of current density is not altogether the critical factor. Evidence implies a period devoid of current enhancement just prior to breakdown during which the dielectric accumulates energy necessary to change to a gaseous state. It is the gas which affords the high conductance during breakdown.
Effect of Alpha Irradiation on the X-Ray Diffraction Profiles of Silicon Single Crystals
Authors: Burgeat J. , Colella R.
Published: February 2004

A series of perfect single crystals of silicon have been irradiated with alpha particles from 210Po to a maximum dose of 20.1×1015 α/cm2. The convoluted profiles obtained by means of a double-crystal spectrometer in the (n, −n) arrangement, with a perfect unirradiated crystal on the first axis, exhibit a secondary peak on the low-angle side with half-width and peak intensity comparable to that of the main peak in most cases. The main peak does not seem to be much influenced by irradiation except for a slight depression and broadening. The dynamical theory as developed by Taupin for imperfect crystals has been applied to these results by assuming that the only effect of irradiation is to introduce a uniform change in the lattice constant of the crystal which is function only of depth normal to the crystal surface. The convoluted reflectivity of such an imperfect crystal is computed at the reflecting surface in the symmetrical Bragg case by using a profile for the damage as computed from the simple theory of collision based on Rutherford scattering and on the hard sphere model. A satisfactory agreement is found, on a qualitative basis, between computed and experimental profiles. The fact that the calculated profiles, within the limitations of the approximations involved, can reproduce the essential features of the experimental ones suggest that some coherence is preserved between the diffracted waves. The damaged region of the crystal, having a varying lattice parameter, gives rise to a secondary peak but exerts a negligible absorption effect on the main peak, which originates from the bulk.
Temperature Dependence of Electron Elastic Diffraction by Aluminum Films
Authors: Graczyk J. F.
Published: February 2004

The temperature dependence of elastic-diffracted intensities for polycrystalline Al films has been investigated at 296° and 77°K as a function of crystal thickness in the range 600–2500 Å. A quantitative agreement is found with the predictions of the BJR two-beam approximation of the dynamical theory. This agreement, however, appears to be best for Al in a range of thickness below the anomalous absorption distance or where kinematical theory should apply.
Diffusion of 44Ti in TiCx
Authors: Sarian S.
Published: February 2004

The self-diffusion of titanium-44 in TiCx (0.67≤x≤0.97) was studied in the temperature range 1920°–2215°C. The diffusion coefficients are composition independent and can be described by the expression DTi*=(4.36−2.34+5.02)×104 exp[−(176 400±3600)/RT] cm2/sec; titanium diffuses slower than the non-metal atom by a factor of approximately 104 in the temperature range investigated. The results support the concept of independent diffusion along the respective sublattice of each component.
Effect of Open Orbits on Helicon Propagation in Copper
Authors: Hui S. W.
Published: February 2004

The effect of open orbits on helicon propagation is investigated theoretically and experimentally. At the high field limit, the damping of helicons is found to be very sensitive to the amount of open orbit current, whereas the dispersion is only slightly affected. The low rf surface impedance of a copper single crystal is measured at 4.2°K in a magnetic field up to 55 kG. The field direction is oriented along or within a few degrees of the [001] axis. The result is compared with the calculated rf susceptibility based on the knowledge of several known open orbits. The standing wave pattern is observed when B is parallel to the [001] axis. The ``effective Hall coefficient'' obtained from the dispersion relation agrees with other dc measurements. The attenuation when B tilts away from the [001] axis is interpreted to be the damping effect caused by the two-dimensional open orbit current. The average damping effect is smaller than that calculated from open orbits of known order.
Approximate Step-Function Response of a Vertically Polarized Electromagnetic Plane Wave Reflected at an Imperfectly Conducting Surface
Authors: Monroe Richard L.
Published: February 2004

A three-term expression consisting of a constant plus two exponentials is given for the reflected field of a vertically polarized (E field in the plane of incidence) plane wave in free space with a step-function time variation incident obliquely on a plane imperfectly conducting surface. Curves computed with this expression are shown to be in good agreement with corresponding curves obtained numerically for a time range 0≤t≤10tr, where tr, the relaxation time, is the ratio of permittivity to conductivity in the reflecting medium. Although the exponential time variation is limited to early times, it is shown that the three-term approximation can be extended to times greater than 10tr at the expense of introducing modified Bessel functions of zeroth order. The first approximation to the step-function response is used to investigate the transient reflected field of a rectangular pulse: Explicit expressions are obtained for the reflected field, the energy of the reflected field, and the ratio of reflected to incident energy. The latter indicates that the ratio of reflected to incident energy for incident pulses less than tr in length is approximately equal to α02, where α0 is the Fresnel reflection coefficient for a perfect dielectric.
Plasma-Filled Waveguide with Axial Magnetization. I. Variational Determination of Normal Modes
Authors: Champlin K. S. , Glover G. H. , O'Connor D. E.
Published: February 2004

Propagation coefficients and field configurations of the normal modes of an axially magnetized, plasma-filled waveguide are treated by the Rayleigh-Ritz variational technique. The results are placed in the form of a matrix eigenvalue problem. The eigenvalues are approximations to the propagation coefficients, and the eigenvectors contain Fourier coefficients of the electric fields of the normal modes expanded in terms of fundamental functions. This form is well suited to computer calculation and is used in a following paper to compute reflection and transmission coefficients of waveguide sections of finite length. The axially symmetric normal modes are examined in detail and are found to possess certain interesting properties that have not been fully recognized. First of all, these modes are reciprocal. Furthermore, under certain conditions they can, like ``helicon'' waves, be divided into ``ordinary'' (``cut off'') and ``extraordinary'' (``lossless'') modes. The axially symmetric modes are not circularly polarized, however, but instead change shape in a rather remarkable manner as they propagate.
Plasma-Filled Waveguide with Axial Magnetization. II. Scattering by a Section of Finite Length
Authors: Champlin K. S. , Glover G. H. , Holm-Kennedy J. W.
Published: February 2004

The problem of mode conversion and scattering by a finite-length section of magnetoplasma-filled waveguide is formulated in matrix notation. This formulation becomes increasingly exact as the dimensions of the matrices (i.e., the number of modes considered) increases. The desired reflection- and transmission-coefficient matrices are readily evaluated with a digital computer. Computations of TE010-mode reflection coefficients indicate that good accuracy can be obtained with a fairly small (∼10) number of modes. Large errors result from considering only the incident (TE010) mode, however.
Radiance Amplification by a Fluorescence Radiation Converter
Authors: Keil Günter
Published: February 2004

Radiance amplification has been demonstrated in a two-stage fluorescence radiation converter consisting of fluorescent acrylic glasses and suitably attached reflectors. The experimental results are in agreement with the theory for such systems. Internal absorption of the fluorescence radiation reduces the radiance amplification considerably. Fluorescence converter systems seem to offer some advantages in the detection of diffuse, nondirectional quantum and particle radiation and for the application of small semiconductor detectors with high sensitivity in the long-wavelength region of the visible spectrum.
Variance Fluctuations in Flicker Noise and Current Noise
Authors: Brophy James J.
Published: February 2004

Variance fluctuations in band-limited vacuum-tube flicker noise, current noise in a germanium p-n junction, and current noise in a carbon resistor are measured by determining probability amplitude distributions of the noise signals with a multichannel pulse-height analyzer. The variances of 30 noise specimens, each 100 sec in duration, for the three noise sources are obtained from the width of the probability amplitude distributions, all of which obey a normal-distribution law. Fluctuations in variance are largest in the case of resistor current noise and least for current noise in a p-n junction. Even in the latter case, however, the variations are well in excess of artifacts resulting from sampling errors, as demonstrated by examining Nyquist noise signals. It is concluded that all three 1/f noise sources exhibit variance fluctuations to varying degrees.
Elevated Pressure Study of the Effect of Different Donors on Electron Transfer in n-GaAs
Authors: Adler P. N.
Published: February 2004

The elevated-pressure resistance behavior of differently doped samples suggests that the ratio of mobility in the [000] conduction band to that in the [100] band is constant and independent of initial mobility. A mobility ratio of 39 is indicated at atmospheric pressure. Carrier freeze-out with respect to the [100] band was observed for S- and Si-doped samples but not with Se and Te.
Dispersion Effects in a High-Gain 3.39-μ He–Ne Laser
Authors: Liu C. S. , Cherrington B. E. , Verdeyen J. T.
Published: February 2004

A He–Ne laser heterodyne system was utilized to evaluate the dispersive effect at 3.39 μ in a He–He laser. The dispersion introduced by lasering atoms at 3.39 μ was measured as a function of cavity loss, excitation level, and deviation of the laser frequency from line center. Theoretical and experimental results were compared, and close agreement was obtained if the natural linewidth was taken to be 115 MHz and the Doppler linewidth was taken to be 315 MHz for the 3.39-μ transition.
Study of Saturable Absorber Switching Efficiencies
Authors: Szabo A. , Erickson L. E.
Published: February 2004

Theoretical and experimental studies of absorber switching efficiencies are described for a ruby laser operating at 77°K. The various operating regimes of absorber-switched lasers are reviewed and the importance of inclusion in the theory of nonsaturable losses associated with the laser and absorber media is demonstrated. A particular dye-host combination is found to have a markedly superior switching efficiency, the essential factor being a low residual loss under saturation conditions. The residual loss of vanadium phthalocyanine is shown to be host dependent and some tentative explanations of this are discussed.
Effect of Substrate Imperfections on GaAs Injection Lasers Prepared by Liquid-Phase Epitaxy
Authors: Kressel H. , Nelson H. , McFarlane S. H. , Abrahams M. S. , LeFur P. , Buiocchi C. J.
Published: February 2004

A study was made of the correlation between substrate flaws and the performance of GaAs injection lasers fabricated by liquid-phase epitaxy. These devices are p+/n structures where the p+ region is deposited epitaxially, followed by heat treatment to displace the p-n junction about 1–2 μ into the n-type substrate. The melt-grown substrates were studied with the aid of transmission electron microscopy, infrared transmission, x-ray topography, etching studies, and photoluminescence. It is concluded that the dislocation density of the substrate is not the controlling factor in laser performance unless it exceeds 105 cm−2. A dislocation density of 103–104 cm−2 is not excessive. Precipitates and impurity striations in the substrate are probably the most damaging imperfections. In Te-doped GaAs the presence of Ga2Te3 precipitates is to be avoided. In the case of Si-doped materials, the precipitation problem appears to be less severe. Nevertheless, small clusters have been detected by electron transmission microscopy in the back portion of some melt-grown ingots (furthest from the seed end). Their nature is unknown but they severely degrade laser performance. We show that a good correlation exists between the relative photoluminescence efficiency and laser performance. Thus, photoluminescence measurements are useful in the selection of Si-doped substrates.
Domain Wall Profiles in Magnetic Films
Authors: Cohen M. S. , Harte K. J.
Published: February 2004

An inversion procedure for determining a domain wall profile from the associated Lorentz-microscopy electron-density distribution is discussed. This procedure is verified by application to computer-simulated electron-density distributions derived from assumed wall profiles. The experimental realization of the inversion procedure is demonstrated for high-resolution Lorentz micrographs of films ranging in thickness from 100 to 500 Å; unreliable profiles were obtained for thicker films. The importance of correcting for the effects of nonmagnetically scattered electrons is emphasized; these effects increase with increasing sample thickness and defocussing distance. The experimental domain wall profiles exhibit first a rapid, then a slow increase of wall angle with distance from the wall center. Wall widths derived from these profiles are consistent with theoretical predictions if corrections are made for nonmagnetic scattering; if such corrections are not made, the large widths reported by other authors are obtained.
Stability of Ferromagnetic Domain Structures at Grain Boundaries
Authors: Tobin A. G. , Paul D. I.
Published: February 2004

The magnetic domain structures formed at grain boundaries in recrystallized iron foils have been analyzed using Lorentz electron microscopy. Five basic types of domain structures have been observed at grain boundaries in iron: (1) Domain walls which penetrate through the boundary indicating ``no interaction,'' (2) double spike reverse domains, (3) single spike reverse domains, (4) echelon domains, and (5) domains of closure. Attempts to correlate the stability of the various domain types with the magnetic pole density of the grain boundary led to the following conclusions: (a) Double spike and ``no interaction'' domains appear to be associated with low pole densities while domains of closure appear to be associated with relatively larger pole densities and (b) no clear statement can be made with respect to the relative stabilities of the single spike and echelon domains due to difficulties in determining the magnetization direction within the domains and within the grain itself. They appear to overlap the pole densities of the other structures and each other as well. It is suggested that grain boundaries are important sources of reverse domain nucleation in polycrystalline ferromagnetic materials. The results emphasize the importance of the internal magnetostatic energy in determining the magnetic domain structure of iron.
Magnetic Susceptibility of β′-NiAl
Authors: Brodsky M. B. , Brittain J. O.
Published: February 2004

The magnetic susceptibility has been measured for a number of NiAl compounds, ranging from 46.1 to 59.2 at.% Ni. The results were found to fit the expression, χ = (A/T) + B between 6° and 300°K. Calculations of the temperature independent term fit the observed composition dependence up to 50 at.% Ni, but the composition dependence of that term is much higher for Ni contents above the equiatomic composition. Similarly, the value of A remains close to zero up to 50 at.% Ni and then rises over a small composition range to a large, composition independent value. The results above 50 at.% Ni are attributed to Ni–Ni nearest neighbors, which cause short-range magnetic order.
Magnetostatic Waves in Short, Axially Magnetized YIG Rods
Authors: Lewis M. F. , Scotter D. G.
Published: February 2004

We have performed cw resonance and pulse-echo measurements on magnetostatic waves in short, axially magnetized YIG rods which do, and do not, contain a turning point. The results are compared with a simple theory which includes the effects of the radial variation of the demagnetizing field. The agreement is generally satisfactory except for the magnetostatic mode spacing when the rod contains a turning point. In this latter case the agreement is only qualitative.
Compilation of Elastic Wave Modes in Hexagonal Metals
Authors: Henneke Edmund G. , Green Robert E.
Published: February 2004

Elastic wave velocities, particle displacement vectors, and directions of energy flux have been calculated and are given as a function of the polar angle θ in the five hexagonal metals Be, Cd, Mg, Ti, and Zn. Because of elastic transverse isotropy around the hexagonal axis, the wave characteristics are functions of the angle between the hexagonal axis and the direction of propagation in the crystal only. The results of these calculations are especially useful for experimental investigations utilizing the ultrasonic pulse-echo technique.
Experimental Investigation on the Blurring of Spatial Moiré Fringes
Authors: Theocaris P. S. , Vafiadakis A. P. , Liakopoulos C.
Published: February 2004

An experiment was carried out on the intensity distributions resulting from the superposition of the images formed in the direction of each resultant order to the diffraction and optical interference pattern of a plane amplitude grating viewing a set of slits lying in a parallel plane. The experiment demonstrated the causes of blurring of the moiré fringes formed by two gratings separated by an air gap. From experiments conducted with pairs of identical amplitude gratings the blurring of spatial moiré fringes is demonstrated by microdensity tracings. It was found that the optical effects did not affect the interfringe spacing of the fringes.
Determination of the Low-Frequency Electro-optic Coefficients of NaNO2
Authors: Johnston A. R. , Nakamura T.
Published: February 2004

The unclamped electro-optic coefficients were measured in ferroelectric NaNO2. The following values were obtained at 150°C, in units of 10−10 cm/V: ra = r22 − (n3/n2)3r32 = 4.1; rb = r32 − (n1/n3)3r12 = 4.2; rc = r22 − (n1/n2)3r12 = 0.6; r43 = − 1.9; r61 = − 3.0. The constants ra and rc vary approximately as ε2 does near the Curie temperature, as expected, but rb does not, decreasing toward zero at Tc. No significant temperature dependence was found in r61 or r43. The quantity ra changes sign as a function of temperature at 115°C. The observed behavior can be explained in terms of a temperature-independent response including both second- and fourth-order terms, biased by the spontaneous polarization.
Optical Activity and Birefringence Associated with Elastic and Plastic Deformation of the Alkali Halides
Authors: Chang Roger
Published: February 2004

The optical activity and birefringence associated with elastic and plastic deformation of alkali halide single crystals were studied by means of transmission of monochromatic light in the visible region between crossed Nichols. Below the elastic limit, the optical axis is the direction of stress application. For permanently deformed crystals, the optical axes are the [110] directions regardless of the directions of original stress application, and the associated birefringence is shown to be dependent on the modes of plastic deformation. The origin for optical activity in both elastically and plastically deformed materials is not yet clear and is probably associated with perturbation by local electric or magnetic fields of charged dislocations present in the material under investigation.
Effects of Light on the Charge State of InSb–MOS Devices
Authors: Krag W. E. , Phelan R. J. , Dimmock J. O.
Published: February 2004

We have made a detailed study of the effects of photon radiation in the energy range between 0.5 and 5.0 eV on InSb metal-oxide-semiconductor (MOS) devices. Measurements of the photocurrent through the MOS structures made at several temperatures showed that even at 300°K a photovoltage is developed for photon energies greater than about 1.3 eV. For photon energies above 3 eV the indium-antimony oxide layer became photoconductive. The charging and discharging characteristics of the InSb-oxide interface were investigated by measuring the response of the InSb–MOS structure to modulated long wavelength (3.9 μ) radiation. This radiation acts as a probe for examining the band bending in the InSb at the InSb-oxide interface, which in turn depends on the amount of charge trapped in the oxide or at the interface. When the MOS structure is irradiated with 1.3- to 4-eV photons, the oxide and/or the interface becomes negatively charged. At photon energies above 3.5 eV there is a competition between the mechanism which induces negative charge in the oxide and/or interface region and the mechanism which releases this charge. This competition can be influenced by applied bias, and by properly biasing the device and irradiating with photons having energies greater than 4 eV the charges can be released.
Continuum Electrostatic Probe Theory for Large Sheaths on Spheres and Cylinders
Authors: Kiel R. E.
Published: February 2004

An approximate analysis is presented for spherical and cylindrical electrostatic probe operation under conditions such that large collision-dominated sheaths are obtained. Analytical expressions are given for the sheath growth as a function of experimentally determined parameters. If pressure and temperatures are known, use of these results makes possible the direct interpretation of electron number density from a single probe measurement.
Temperature of a Laser-Heated Carbon Plasma
Authors: David C. D. , Weichel H.
Published: February 2004

The temperature of a laser-heated carbon plasma, formed by the interaction between a Q-switched ruby laser and a pyrolytic graphite slab, has been measured using interferometric, spectroscopic, and energy conservation techniques. Results indicate that the maximum plasma temperature is less than 10 eV. A method of determining whether the plasma is in thermodynamic equilibrium is employed and indicates that at laser fluxes of 109 W/cm2 the plasma is not in LTE with the electron temperature nearly an order-of-magnitude larger than the plasma temperature. For fluxes of 1010 W/cm2, however, the plasma appears to approach a state of thermodynamic equilibrium with a temperature of 2eV.
Characteristics of Rotationally Stabilized Long Plasma Arcs in a Chamber
Authors: Yeh Hsu-Chieh , Yang Wen-Jei
Published: February 2004

An analytical method is developed to determine the gas temperature distribution and the electric field strength-arc length characteristics of a rotationally stabilized long plasma arc in a cylindrical chamber. The application of the method was demonstrated by numerical computations which were carried out for a monatomic hydrogen arc stabilized in a very large chamber. The relationships among the electric field strength, current, arc length, and arc-axis temperature are disclosed.
Length Change of Copper and Aluminum after Electron Irradiation
Authors: Hanada R. , Snead C. L. , Kauffman J. W.
Published: February 2004

With the new application of capacitance-change techniques, length-change measurements were made in conjunction with annealing copper and aluminum specimens above their electron-irradiation temperature of about 15°K. Damage rates at this temperature were also measured. The Stage I recovery of length change is compared with its resistivity counterpart. Remarkable correspondence is obtained to the degree that percentages of recovery of individual substages compare favorably, with the same defect inferred to be responsible for recovery in both cases. The production rate for length change was determined to be +1.8×10−23 cm2/electron for 2.2 MeV electrons. Linear bending with dose was observed. This bending was analyzed as due to electron straggling. The ratio of resistivity change to volume change and to stored energy for electron and heavy-particle bombardment shows good relative agreement. From the results, it was concluded that these physical-property changes do not depend sensitively upon Frenkel pair close-pair separation.
Electrical Behavior of Group III and V Implanted Dopants in Silicon
Authors: Baron R. , Shifrin G. A. , Marsh O. J. , Mayer James W.
Published: February 2004

The anneal behavior of layers implanted with dopants from column III (B, Al, Ga, and Tl) and column V (As, Sb, and Bi) in silicon substrates has been investigated. The ranges of implant conditions were energy 20–50 keV, dose 1013–1015/cm2, and substrate temperature 23°–500°C. Hall-effect and sheet resistivity measurements were used to determine the effective number of carriers/cm2 (Ns)eff and the effective mobility μeff. Analysis of nonuniform distributions of carrier densities and mobilities on these measurements shows that the values of (Ns)eff and μeff can be misleading unless the effect of the depth distributions is allowed for. These distributions have been determined in some cases by the use of layer removal techniques combined with Hall-effect and sheet resistivity measurements. We find in well-annealed implanted samples that the dependence of the mobility on carrier density follows that determined for bulk silicon. In many cases deviation from this relation can be accounted for on the basis of compensation. In the case of aluminum we suggest that this compensation may be accounted for by the presence of interstitial aluminum atoms acting as donors. We have found that interstitial thallium can behave as a donor. The anneal behavior of the implanted layer is influenced by ion species, dose, and substrate temperature. The carrier concentration measured in implantations of column III elements did not exceed the limits of thermal equilibrium solubility as is found for column V elements. In the former case, enhanced diffusion effects are observed. From the known substitutional behavior of column V elements, it is suggested that the anneal behavior in the 600°–800°C range is due to the dissociation of radiation damage complexes.
Optical Properties of n-Type GaAs. I. Determination of Hole Diffusion Length from Optical Absorption and Photoluminescence Measurements
Authors: Hwang C. J.
Published: February 2004

Hole diffusion lengths L were determined for several Te-doped GaAs crystals with electron concentrations ranging from 2×1016 to 6.5×1018 cm−3. The values of L were obtained by fitting experimental photoluminescence spectra to a theoretical expression which contains the measured absorption coefficients. This expression was derived from radiative recombination statistics, taking into account the reabsorption of emitted photons and the diffusion of minority carriers. The idea used by van Roosbroeck and Shockley of introducing the measured absorption coefficient by means of the principle of detailed balance is shown here to be valid for both nondegenerate and degenerate n-type GaAs. It was found that the hole diffusion lengths are nearly independent of electron concentration n for n < 1×1018 cm−3. This result is attributed to a constant total hole lifetime associated with a nearly constant concentration of ``frozen-in'' defects. For n > 2×1018 cm−3 values for diffusion length decrease rapidly with increasing n. This decrease is attributed to the formation of additional defects associated with donor complexes or precipitates, or both. The diffusion lengths determined in this work are in good agreement with those found by Wittry and Kyser from the electron-beam excitation method but are larger than those obtained by Aukerman et al. from short-circuit current measurements on n-type surface barrier diodes subjected to high-energy electron bombardment.
Measurement of Diffusion Lengths in p-Type Gallium Arsenide by Electron Beam Excitation
Authors: Rao-Sahib T. S. , Wittry D. B.
Published: February 2004

Theoretical curves of the voltage dependence of cathodoluminescence have been obtained for the case where the intensity of cathodoluminescence varies superlinearly with the net carrier generation rate. Calculations are based on numerical integration of the distribution of excess carriers assuming a Guassian approximation to the distribution of excitation with depth. The theoretical curves make possible the measurement of diffusion lengths using the method of voltage dependence of cathodoluminescence in specimens where the intensity of cathodoluminescence is not linearly proportional to the specimen current (e.g., p-type GaAs). Experimental results with accelerating voltages of 5–50 kV using a defocused electron beam and selected area technique indicate values of electron diffusion length in p-type GaAs ranging from 3.2 μ at low carrier concentration (6.9×1016 cm−3) to 0.6 μ at high carrier concentration (3.76×1019 cm−3).
Correlation between Surface Structure and Surface States at the Clean Germanium (111) Surface
Authors: Henzler M.
Published: February 2004

A transition from a 2×1 to an 8 structure on the ultrahigh-vacuum-cleaved germanium {111} face during heat treatment below 350°C makes germanium particularly well suited as a material for investigating a possible correlation between surface states and surface structure. Individual studies of either the electrical or structural properties of this surface have been made over a number of years, but the present experiment was designed to make both the structural and electrical measurements ``simultaneously'' on the same surface. In the present experiment both surface state density as calculated from surface conductivity and dc-field effect, and surface structure as characterized by symmetry and spot intensities of the LEED pattern were determined at 30°C as a function of heat treatment over the temperature range 30° to 300°C. The structural changes are accompanied by parallel changes in surface conductivity and field effect mobility. It is concluded that at cleaved germanium surfaces the surface states are essentially determined by the two-dimensional surface structure rather than domain boundaries or surface defects. A model which correlates different surface state distributions with the 2×1 and the 8 germanium superstructures allows the description of the present results. This is the first time that changes in surface state distributions have been directly correlated with changes in the two-dimensional surface structure.
Electrical Response of Anodized Aluminum Layers to Shock-Wave Compression
Authors: Champion A. R.
Published: February 2004

The electrical output which is obtained from an anodized aluminum layer during shock-wave loading has been studied as a function of shock stress, sample area, shock propagation direction, and temperature history. The dependence of the electrical response on these variables is shown to be consistent with an electret-like behavior of the anodized layers. A sample macroscopic model based on this behavior is used to predict the features of the electric output.
Measurement of Elastic and Plastic Unloading Wave Profiles in 2024-T4 Aluminum Alloy
Authors: Kusubov A. S. , van Thiel M.
Published: February 2004

Velocities for one-dimensional release waves in 2024-T4 aluminum alloy have been obtained between 30 and 132 kbar. Stress-time records were obtained with piezoresistive manganin gauges. The release wave clearly showed the existence of two release systems. The leading edge of the release wave was 27% faster than the bulk sound velocity calculated from the ideal fluid model. The second release system was identified by a change in slope of the release wave profile. The peak velocity of this release system did correspond more closely to the hydrodynamic bulk sound velocity. These results imply elastic behavior of aluminum at high pressure. The shape of the release wave, however, cannot be fitted by a perfect elastic-plastic model, thus pointing out the need of a more elaborate description.
Determination of Release Adiabats and Recentered Hugoniot Curves by Shock Reverberation Techniques
Authors: Lysne P. C. , Boade R. R. , Percival C. M. , Jones O. E.
Published: February 2004

Release adiabats and Hugoniot curves centered at shock states can be readily determined by impacting a projectile disk onto a stationary reverberation disk made of a linear elastic material of known shock properties. The reverberation disk may have a free back surface or may be backed by a buffer disk made of the specimen or some other material. The reverberation disk is very thin compared to the thicknesses of the other disks so that many wave reverberations occur in it during the experiment. Depending on the impedance of the reverberation disk relative to the other disks, each reverberation successively unloads, or loads, the projectile disk, thus establishing points on a release adiabat or on recentered Hugoniot curves of the specimen material. The technique is particularly valuable for measurements on compressible nonlinear materials, and it generates a large amount of information in a single experiment. Experiments have been performed with X-cut quartz, Lucalox, and 60° orientation sapphire reverberation disks which illustrate the technique, and results are presented for an epoxy resin and a porous tuff.
Propagation and Amplification of Ultrasonic Waves in a Layered Structure of Quartz-Liquid-CdS
Authors: Wang Wen-Chung
Published: February 2004

Amplification of surface wave has been experimentally observed in a composite structure consisting of a quartz plate, a thin liquid layer, and a piezoelectric semiconductor. An additional time delay is also observed in such a composite structure.
Characteristics of Slender Finite Length Arcs
Authors: Whitman Alan M.
Published: February 2004

A method is presented for extending the theory of wall stabilized arcs to free burning arcs. It is based on accounting for the finite length of the arc column and utilizing the fact that such arcs are normally very thin compared to this length. Detailed calculations are performed for an arc column with constant properties, and an outline is given for incorporating more realistic properties. An interesting result of the analysis is that the axis temperature must increase greatly in front of the electrodes.
Field Fluctuations in a Random Continuum Containing a Spherical Object Inclusion
Authors: Knollman G. C.
Published: February 2004

For planewave propagation in a random continuum, the changes in mean-square amplitude and phase variations are derived due to the presence in the medium of a large spherical object arbitrary in density and refractive index, and positioned on the transmitter-to-receiver line-of-sight. The random continuum is taken as statistically homogeneous and isotropic in space with weak, large-scale refractive-index variations representable by a Gaussian autocorrelation function. Calculations are performed for far-field observation of the forward-scattered fluctuating signal.
Partial Separation of Argon from a Helium-Argon Mixture by Sampling Capillary Flow
Authors: Creutz E.
Published: February 2004

The partial separation of helium and argon in a sample withdrawn through a tube at right angles to a capillary through which the mixture is flowing at high velocity is measured. With a helical capillary the effect is greater by at least a factor of 4 than can be accounted for by the centrifugal field due to the average velocity along the helix, even if no mixing or turbulence is assumed. The effect in a straight capillary is somewhat smaller and is about that expected to be produced by a stable eddy near the entrance to the sampling tube. The helix results depend in sign as well as magnitude on the flow conditions. Separations up to 0.7% are observed. The effect vanishes at small withdrawal rates, indicating an interaction between any possible effect of the helix and the demonstrated effect at the withdrawal hole.
Lock-In and Intensity-Phase Interaction in the Ring Laser
Authors: Aronowitz Frederick , Collins R. J.
Published: February 2004

The lock-in threshold of a single-mode 0.633-μ He–Ne laser was measured. Experiments were performed with a 1:1 mixture of the 20Ne and 22Ne isotope. The lock-in threshold was found to increase with operation of the laser with smaller excess unsaturated gain. Minimum lock-in threshold was found to occur at a higher frequency than the frequency at which the output power was a maximum. A rotational mode competition between the oppositely directed traveling waves was found for rotation rates less than the lock-in threshold. The beam traveling with and against the direction of rotation was found to decrease and increase, respectively, with increasing rotation rate. Analysis showed that the single-mode-ring, laser equations, with mode coupling due to backscattering, satisfactorily explained the experiments.
Laser Interferometry in the Presence of Transverse Plasma Density Gradients
Authors: Medley S. S.
Published: February 2004

A novel laser interferometric technique involving the use of an unstable external resonator is presented. The unstable resonator greatly facilitates electron density measurements in the presence of plasma density gradients transverse to the direction of beam propagation. The technique is used to obtain time-resolved radial electron density distributions in the implosion stage of a linear z-pinch discharge in argon at filling pressures of 0.1 and 1.0 Torr.
GaAs–GaxAl1−xAs Heterostructure Injection Lasers which Exhibit Low Thresholds at Room Temperature
Authors: Hayashi I. , Panish M. B.
Published: February 2004

The electrical and optical properties of GaAs–GaxAl1−xAs injection lasers produced by solution epitaxy are described. These lasers are composed of three layers, n-GaAs, a thin p-GaAs layer, and a p-GaxAl1−xAs layer. In these lasers, the threshold current Jth is a strong function of the width of the p-GaAs layer d, being optimum where d is about 2 μ. The temperature dependence of Jth is comparatively small below some maximum temperature TM, above which it increases very rapidly. The values of Jth obtained near room temperature for these lasers are lower than have previously been reported for injection lasers. Fabry-Perot-type diodes with cavities of about 400 μ may be reproducibly prepared with Jth (300°K) about 10 000 A/cm2. The lowest Jth (300°K) observed for one of these units was 8600 A/cm2. Units with fully internally reflected modes can be reproducibly prepared with Jth (300°K) ≈6000–7000 A/cm2. The low Jth (300°K) of these lasers is attributed primarily to carrier confinement, although improved optical confinement and reduced absorption losses may also play a role. The behavior of Jth at TM and the minimum in Jth as a function d are attributed to hole injection.
Influence of External Noise on Microwave-Induced Josephson Steps
Authors: Kose V. E. , Sullivan D. B.
Published: February 2004

The influence of fluctuations on microwave-induced Josephson steps is treated phenomenologically and it is found that the center voltage of these steps is not shifted by the disturbance. Expressions governing the step shape are obtained for various noise spectra. The theory was checked by subjecting niobium point-contact junctions to several forms of externally generated noise. The theory does not differentiate between internal and external noise sources, so that a number of the conclusions can be extended to intrinsic fluctuations.
Analysis of Energy Transfer and Infrared-to-Visible Conversion in LaF3:Yb, Er
Authors: Kingsley J. D.
Published: February 2004

A model of the energy transfer between Yb3+ and Er3+ in LaF3 which explains the efficiency and time dependence of the conversion of infrared excitation to visible emission in this material is presented and analyzed. It is concluded that in La0.86Yb0.12Er0.02F3 the probability of an excited Yb3+ ion transfering its energy of excitation to an Er3+ ion is at least an order-of-magnitude greater than the probability of the Yb3+ ion decaying with the emission of radiation or phonons. Similarly, an Er3+ excited to its 4I11/2 state is much more likely to lose the energy of excitation by radiationless energy transfer to a Yb3+ ion than by other means. The decay time of the emission from the 4S3/2 state of the Er3+ ion in La0.86Yb0.12Er0.02F3 was measured to be 140±20 μsec if the Er ion is excited directly in the 2H11/2 or 4F7/2 states while the same emission decays with a time constant of 1.1 msec when the phosphor is excited with infrared absorbed by the Yb3+ ions.
Exchange Anisotropy in Thin Cobalt Films Deposited on a CoO Single-Crystal Substrate
Authors: Bransky Judith , Bransky I. , Hirsch A. A.
Published: February 2004

Thin films of cobalt were deposited on annealed CoO single crystal disks having surfaces parallel to (100) and (111) planes. The films were cooled to below the Néel temperature of CoO in a high magnetic field. The magnetization loop and the magnetic torque curves of the film deposited on the (111) plane of the CoO crystal, recorded below the Néel temperature of CoO, showed a unidirectional anisotropy due to the exchange interaction between the ferromagnetic film and the antiferromagnetic substrate. The anisotropy energy related to this coupling was found by two independent methods to be about 4×105 erg/cm3. However, when the film surface was parallel to the (100) plane of the substrate only a slight coupling energy was detected.
Unidirectional Anisotropy in Permalloy Films at 4.2°K
Authors: Bailey Sheila B. , Peterlin Tatjana M. , Richard Roy T. , Mitchell E. N.
Published: February 2004

Studies of the temperature dependence of the unidirectional anisotropy of permalloy films as a function of the oxidation of the surface are reported and correlated with electron diffration studies of the surface oxides. Hematite (α-Fe2O3) is found to correlate with the existence of the anisotropy in films oxidized at 120°C in which the transition temperature is near 40°K. A specimen oxidized at 250°C showed a higher and broader transition though no α-Fe2O3 could be correlated with the existence of the unidirectional anisotropy.
Structure and Magnetic Properties of Au–Co Aligned Eutectic
Authors: Livingston J. D.
Published: February 2004

Directional solidification of Au–Co eutectic produces an aligned array of fcc cobalt rods in a gold matrix. The cobalt becomes finer, but more lamellar, as growth rate increases. Intrinsic coercive force increases with increasing growth rate, reaching 330 Oe at 2.1×10−1 cm/sec. Coercive forces up to 925 Oe are produced by subsequent wire drawing. Analysis of the magnetization curves indicates that deformation transforms the cobalt from fcc to hcp.
Fracture of Bone
Authors: Piekarski K.
Published: February 2004

Fracture of bone is investigated by measuring the energy required to propagate a crack and by observing, microscopically, the mechanism of fracture. At low strain rates bone displays very high resistance to crack propagation comparable even to some metallic materials. The type of fracture is similar to fiber-reinforced composite materials.
Variational Bounds of Transport Properties of Composite Materials
Authors: Yeh Robert H. T.
Published: February 2004

We discuss here the relative merits, physical interpretations, limitations, and generalizations of various bounds of composite materials.
Electrical Properties of Thorium Carbonitrides
Authors: Auskern A. B. , Aronson S.
Published: February 2004

The electrical resistivity, Hall coefficient, and thermoelectric power of thorium carbonitride solid solutions ranging in composition from ThC0.778N0.108 to ThC0.029N0.937 were measured from 4.2°K to about 400°K. A maximum was observed in each property as nitrogen was substituted for carbon. The results were compared with results on nonstoichiometric thorium monocarbide and thorium mononitride.
Optical Reflection Studies of Damage in Ion Implanted Silicon
Authors: McGill T. C. , Kurtin S. L. , Shifrin G. A.
Published: February 2004

Optical (3–6.5 eV) reflection spectra are presented for crystalline Si implanted at room temperature with 40 keV Sb ions to doses of less than 2×1015/cm2. These spectra, and their deviation from the reflection spectrum of crystalline Si, are discussed in terms of a model based on the average dielectric properties of the implanted region. For samples having a high ion dose (>1015/cm2) the observed spectra resemble the spectra of sputtered Si films. Anneal characteristics of the reflection spectra are found to be dose dependent. These observations are compared to, and found to substantiate, the results of other experimental techniques for studying lattice damage in Si.
Germanium-Doped Gallium Arsenide
Authors: Rosztoczy F. E. , Ermanis F. , Hayashi I. , Schwartz B.
Published: February 2004

Germanium-doped GaAs crystals were grown on GaAs seeds from Ga solution. The properties of the Ge-doped GaAs layers were examined by Hall effect measurements from 20° to 400°K and by photoluminescence measurements between 12° and 300°K. It was found that Ge-doped GaAs is always p-type when grown at 900°–875°C from Ga solution containing 56 at.% or less Ge. The temperature dependence of the Hall coefficient and the photoluminescence experiment indicated an acceptor energy level of 0.035 and 0.038 eV respectively. It was also found that at least 85% of the Ge was present as an acceptor in the GaAs crystals when the growth solution contained two atom percent or less Ge.
Surface and Bulk Conductivities of Cu2O Single Crystals
Authors: Kužel R. , Weichman F. L.
Published: February 2004

The surface and bulk conductivities of Cu2O crystals were measured using guard ring techniques on cleaved, polished and etched samples over a temperature range from +200°C to −170°C in air, vacuum, and helium atmosphere. The bulk conductivity followed the simple exponential temperature dependence of the typical semiconductor with a single activation energy of about 0.3 eV over the entire range. The temperature dependence of the surface conductivity appeared to consist of a number of activation energies, ranging from 0.1 to 0.3 eV. Heating to 180°C in air or vacuum can be used to minimize the surface contribution to the conductivity. It was found that polished surfaces are highly deceptive for standard measurements of transport effects.