bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical and Electrical Properties of Single-Crystal GaP Vapor-Grown on GaAs Substrate
Authors: Flicker Herbert , Goldstein Bernard , Hoss Paul-Andre
Published: April 2005

Single-crystal GaP has been grown at rates up to 13 mils (330 μ) per hour onto a GaAs substrate by using a close-spaced vapor transport technique. The as-grown layers are invariably n type. Thin layers (3–6 mils, or 75 to 150 μ) grown at slow rates are essentially strain-free, while thicker layers grown more rapidly exhibit considerable strain. Hall measurements were made and show that the dominant donor has an activation energy of 0.089 eV. Mobilities as high as 120 cm2/V-sec and carrier concentrations as low as 4×1015/cm3 have been measured. The Hall data imply an effective mass of 0.25m. The decay of pulse-injected excess carriers indicate a lifetime of about 1 μsec and the presence of several deep traps. Photovoltaic measurements were made and are discussed.
Thin-Film Thickness from Theoretical Expressions for Conductivity and Isothermal Hall Effect
Authors: Leonard W. F. , Ramey R. L.
Published: April 2005

Expressions for the electrical conductivity σ and the isothermal Hall coefficient AH are transcendental equations in terms of film thickness and are solved graphically for film thickness. Measurements on vacuum-deposited gold films in the thickness range 150–500 Å are compared with thickness measurements based upon the multiple beam interferometer methods of Tolansky and upon thickness calculations from microgram weighings. The deviations in measured film thickness are relatively constant, having a value of 30 Å for films greater than 300 Å. This constant deviation can be eliminated if the electron mean free path in bulk material is 370 Å in place of the value given in the literature (410 Å).
Theory of One-Carrier, Space-Charge-Limited Currents Including Diffusion and Trapping
Authors: Lampert Murray A. , Edelman Franz
Published: April 2005

The theoretical problem of one-carrier, space-charge-limited current flow is beyond the reach of analytical solutions when trapping and diffusion are included in the analysis. Nonetheless, the problem for the semiinfinite solid very generally lends itself to rather simple numerical solution on a digital computer. An interesting feature of the machine solution is that it is based on a universal geometric property of the one dimensional, planar current flow. Detailed solutions are obtained for several special cases of the trap-filled insulator problem which plays a fundamental role in the space-charge-limited current measurement of trap densities in insulators. A comparison of these exact solutions with the analytical solutions neglecting diffusion indicates that an error of a factor of two might be made in a trap density determination for the typical case which is completely studied. A brief discussion of the problem of extending the technique to the finite solid with an anode constraint is given. Also a few computer results for the Ohm's law problem are given.
Interaction Between Particles and a Solid-Liquid Interface
Authors: Uhlmann D. R. , Chalmers B. , Jackson K. A.
Published: April 2005

The interaction between particles and an advancing solid-liquid interface has been investigated both experimentally and theoretically. For each particular type of particle, a ``critical velocity'' was observed, below which the particles are rejected by the interface, and above which they are trapped in the solid. The dependence of the critical velocity on various properties of matrix and particle was investigated. A theory has been developed, based on the assumption that a very short-range repulsion exists between the particle and the solid. This repulsion occurs when the particle-solid interfacial free energy is greater than the sum of the particle-liquid and liquid-solid interfacial free energies. The particle is pushed along ahead of the advancing interface and becomes incorporated into the solid if liquid cannot diffuse sufficiently rapidly to the growing solid behind the particle. Reasonable agreement was obtained between the calculated and experimentally observed critical velocities.
Effect of Vacancy Distributions Caused by Elastic Interaction on the Growth of Guinier-Preston Zones
Authors: Grupen W. B. , Sines G.
Published: April 2005

The effect of elastic interaction on the distribution of vacancies around Guinier-Preston zones of the first kind (GP [1]) is investigated. The elastic interaction between a small disk-shaped GP [1] zone and an initially uniform distribution of quenched-in vacancies causes the rapid formation of a vacancy atmosphere surrounding the zone. This atmosphere has an appreciable effect on the early rate of growth of the zone.
Self-Diffusion in Antimony
Authors: Huntington H. B. , Ghate P. B. , Rosolowski J. H.
Published: April 2005

The self-diffusion of antimony has been measured in single crystals with the tracer 124Sb. The least-squares fit to the data gives in the direction of the trigonal axis Q‖=47.1±1.2 kcal/mole and ln(D0 in cm2/sec)=3.1±0.7, and in the plane perpendicular to the trigonal axis Q‖=44.4±4.9 kcal/mole and ln(D0 in cm2/sec)=2.81±2.8. The standard sectioning technique was used except that the very friable nature of the semimetal complicated the procedure at practically every step of the operation. The greatest source for the inaccuracy arose from the ``tails'' on the deep penetration side, noticable for D‖ and strongly prominent for D‖. Correlation considerations in the Sb lattice are considered in detail in the Appendix.
NMR Observations of Drawn Polymers. IV. Molecular Orientation and Mobility in Drawn Polyethylene and Polyoxymethylene
Authors: Olf Heinz G. , Peterlin Anton
Published: April 2005

The linewidth and second moment of oriented samples of drawn PE and POM were measured as a function of temperature. from −196° to 160°C, and of the angle between draw direction and magnetic field H0, mostly at 0°, 45°, and 90°. Much detail in the temperature behavior of these quantities is resolved which cannot be observed with unoriented samples. On the basis of linewidth measurements of drawn PE, an interpretation of the high-temperature narrowing of the broad line observed with PE single crystals and PE crystallized from the melt is given. The anisotropy of the decrease in second moment with rising temperature which is related to anisotropic molecular motion was determined for PE, subtracting the contribution due to lattice expansion from the total decrease measured. The ``mobile fraction'' was determined for the two polymers as a function of temperature. In both cases a reduction of mobile fraction upon drawing is observed.
Relationship between Morphology and Deformation Mechanisms of Polyolefins. II
Authors: Sasaguri K. , Yamada R. , Stein R. S.
Published: April 2005

The deformation of polybutene-1 spherulites is studied by measuring the variation of their birefringence with strain at differing angular positions within the spherulite. Results are compared with a phenomenological model for the deformation process. It is concluded that the deformation process depends upon the angular orientation within the spherulite with respect to the strain direction. In order to simplify the resolution of these processes, uniaxially crystallized films are prepared in which the lamellas are believed to be arranged parallel to each other rather than radially. The results of x-ray, birefringence, and mechanical experiments on such films are described.
Reduction of Dielectric Loss in Polyethylene
Authors: Conklin Glenn E.
Published: April 2005

A mechanism contributing to the dielectric loss at 55.2 Gc/sec in highly crystalline polyethylene has been identified. The manufacturing process introduces imperfections in the form of vinyl unsaturation which can orient in the presence of a microwave field. Hinderance to orientation, in similar cases, by neighboring atoms is known to produce losses. The dielectric loss tangent of the polyethylene was found to decrease by a factor of 1.5 from 4.5×10−5 when the vinyl groups were destroyed with a small amount of gamma irradiation. Furthermore, the dielectric loss attributable to the vinyl unsaturation was found to vary linearly with the vinyl concentration as indicated by the associated infrared absorption coefficient of the 11.0-μ vinyl line, and to be consistent with the view that the unsaturation is homogeneously distributed in the polyethylene.

A technique for the measurement of the complex dielectric constant of isotropic solids at millimeter wave frequencies is described which utilizes a unique property of the TEono modes in circular waveguide. For these modes the tangential electric field vanishes at all points on the waveguide wall. This gives rise to the important results that wall loss corrections to the complex dielectric constant are relatively minor and that the effects of the air space at the junction between sections of waveguide are also minor provided the length of the space is less than about λ/6.
Dislocations in Polyethylene Single Crystals
Authors: Holland V. F.
Published: April 2005

Dislocations have been observed and characterized in polyethylene single crystals by means of moiré patterns produced by superimposed lamellas. Analysis of the dislocations by dark and bright field electron microscopy has revealed that they are partial (imperfect) dislocations. The partials were shown to involve terminating {110} planes and to have Burgers vectors of 〈½a, ½b, γc〉. Most of the dislocations involved {110} planes containing chain folds. The occurrence of the dislocations as isolated partials rather than paired ones implies a low stacking fault energy for the polyethylene lattice. This conclusion is not surprising when one considers that the ``faults'' consist mostly of chains which simply have been rotated from their normal positions.

Annealing of single crystals increased approximately one-thousand fold the dislocation density, and in addition produced, in dark field, bands parallel to the long diagonals of the crystals. These bands were found predominantly at the crystal edges. Selected area electron diffraction of the annealed crystals revealed that a monoclinic crystal phase, previously observed in stressed polyethylene, was concentrated near the crystal edges. The fact that the reported chain packing in the monoclinic phase is similar to that of a possible stacking fault in the orthorhombic lattice implies a definite relationship between the formation of partial dislocations and the occurrence of the monoclinic phase. These results suggest that dislocations play an important part in the annealing of polyethylene single crystals and perhaps of other polymers as well.
Nature of Spontaneous Oscillations in a Cesium Diode Energy Converter
Authors: Norris W. T.
Published: April 2005

In an attempt to understand the nature of the oscillations that are observed in plasma diodes the usual collision-free model is examined. The equations describing the model are simplified by neglecting the time-dependent term in the Boltzmann equation for the electrons. Even this simplification does not readily yield quantitative predictions about the frequency or form of the oscillations, or even about the conditions under which they are likely to occur.

However we introduce a criterion of stability which allows us to predict a possible instability in the steady-state condition which arises because the electrons can redistribute their charge more rapidly than the ions. The simplified equations and the criterion together lead to a good qualitative and a partial quantitative understanding of a particular case. The particular case can be regarded as the epitome of the general case, and the arguments used in it seem capable of the necessary extension to cover all instances of this sort of spontaneous oscillation.
Cleavage in High Vacuums of Alkali Halide Single Crystals—Secondary Electron Emission
Authors: Whetten N. Rey
Published: April 2005

Alkali halide single crystals were cleaved along the (100) plane in a high vacuum so that the monolayer adsorption time following cleavage was many hours. Secondary electron emission measurements were made on surfaces clean to within less than 1/100 of a monolayer. Single pulse measurement techniques minimized charging and electron bombardment damage of the surface. Maximum secondary electron emission yields for the cleaved crystals were generally very high, and include NaBr(23), KBr(14), KI(11), KCl(13), NaCl(14), and LiF(7). The maximum yield of a BaF2 single crystal with the surface scraped in the vacuum (but not cleaved) was 6. The most probable energy of the secondary electrons emitted from KCl was close to 1 eV. The yield of these crystals did not deteriorate rapidly with adsorption of gases in the vacuum system, lending support to the conclusion that only certain gases with a small partial pressure (or low accommodation coefficient) degrade their yield. Some reasons for the high yields of these materials are presented.
Tunneling Through Asymmetric Barriers
Authors: Hartman Thomas E.
Published: April 2005

Two alternative analytical approaches to the problem of tunneling through asymmetric barriers are applied to the case of the trapezoidal barrier for comparison. Stratton's method, representative of one approach, predicts somewhat smaller magnitudes and asymmetries in the current density as a function of voltage than does a modified version of Simmons' method. By using the temperature dependence, experimental data may be readily analyzed by means of Stratton's method to give the apparent barrier heights as well as the effective zero applied voltage barrier parameters. Simmons' method, representative of the other approach, when corrected also predicts asymmetry in the current density or junction resistance even for small applied voltages, i.e., V < φ/q. Excellent agreement is obtained between the modified version of Simmons' method and the numerical evaluation of the WKB approximation for the current density or junction resistance as a function of voltage. The agreement with Stratton's method, though acceptable, is not as good. Results of measurements on the Al-Al2O3-Al system show that the trapezoidal barrier shape is inadequate in accounting for the details of the observations.
Shape and Energy of Néel Walls in Very Thin Ferromagnetic Films
Authors: Collette René
Published: April 2005

The so-called Néel walls separating antiparallel domains in very thin ferromagnetic films are found, on the basis of a precise treatment, to have a shape differing significantly from the linear rotation model used by Néel. In this 180° rotation, three regions can be distinguished: a central one where the magnetization M rotates rapidly and where the demagnetizing energy is positive, and two adjacent regions extending in the neighboring domains where the rotation is very much slower and the magnetostatic energy negative. In these ``tail'' portions of the curve the direction of M is determined mostly by the balance between the anisotropy torque and the torque due to the internal demagnetizing field. The calculations have been performed for Permalloy films with thicknesses ranging from 0 to 200 Å. The walls extend up to several microns in each of the adjacent domains (of the order of 15 μ at a thickness of 200 Å). The energy stored inside the wall is calculated for this new configuration and found to be less than previous approximate results.
Ultrasonic Determination of the Superconducting Energy Gap in In2Bi
Authors: Saunders G. A. , Lawson A. W.
Published: April 2005

The attenuation of longitudinal ultrasonic waves in the superconducting and normal states of the indium-bismuth alloy of composition equivalent to the In2Bi was measured at 60 Mc/sec by the double-ended pulse-echo technique. The decrease in attenuation below the superconducting critical temperature (5.6±0.1°K) and the temperature dependence of the superconducting energy gap were in reasonable agreement with the predictions of the BCS theory. The limiting energy gap at 0°K, 2 Δ (0), was determined as (3.4±0.2)kTc. These results provide confirmation of Anderson's theory of dirty superconductors. The limiting critical field at 0°K was 870±10 G.
MAFCO—A Magnetic Field Code for Handling General Current Elements in Three Dimensions
Authors: Perkins W. A. , Brown J. C.
Published: April 2005

MAFCO, which is written in FORTRAN language, can be used on the IBM 7094 and other similar computers which will compile a machine language code from a FORTRAN deck. The purpose of this code is to take a given set of current-carrying elements of arbitrary geometry and calculate the magnetic field B at any point in space and also the continuation of the magnetic field line (line of force) passing through any desired point in space. In practice, however, computer memory and available machine time usually require that most of the current-carrying conductors be approximated by straight lines and circular loops.
Fluorescence of GaAs Under Intense Electron Excitation
Authors: Babcock R. V.
Published: April 2005

Fluorescent emission from Te or Zn-doped GaAs was examined under electron beam excitation sufficient to generate electron-hole pairs at rates ranging from 3×1022 to 4×1025cm−3sec−1, and over the temperature range 77° to 300°K. Peak emission frequencies were constant in this intensity range, and the spectrum from Zn-doped samples agreed qualitatively with transitions between acceptor states and a Boltzmann population in the conduction band. Te-doped samples showed strong emission at 1.494 eV. An unsuccessful attempt was made to excite coherent emission with excitation intensities exceeding 8×1025cm−3sec−1. No spectrum narrowing or shift in emission frequency was seen; this is consistent with a recombination lifetime of 6×10−10 sec or less.
Strain and Precision Lattice Parameter Measurements by the X-Ray Divergent Beam Method. I
Authors: Ellis T. , Nanni L. F. , Shrier A. , Weissmann S. , Padawer G. E. , Hosokawa N.
Published: April 2005

An X-ray method is described which permits a precise determination of the interplanar spacings in a crystal. The method is capable of disclosing small differences in interplanar spacings even between various sets of (hkl) planes of the same form and, therefore, serves as a basis for a stress-strain analysis. An error analysis of this method shows that the minimum measurable strains in the lattice, expressed as Δd/d, are a function of the diffraction angle θ. For θ varying from 35° to 65°, the minimum measurable strains vary from 0.03% to 0.009%.

A precision determination of the lattice parameter of a zone-refined tungsten crystal yielded a0=3.16566±0.00002 Å. Limitations and possible applications of the method to problems in physical metallurgy and solid state physics are presented.
Stress-Strain Analysis of Single Cubic Crystals and Its Application to the Ordering of CuAu I. Paper II
Authors: Slade J. J. , Weissmann S. , Nakajima K. , Hirabayashi M.
Published: April 2005

A stress-strain analysis of single cubic crystals is developed which utilizes the strain data supplied by the x-ray back-reflection divergent beam method. The principal strains and their directions are determined and from the principal strains and the known elastic constants the complete stress-strain configuration is obtained. Thus the maximum magnitude and the direction of the shearing strain on a given set of crystallographic planes are obtained and the set of planes on which the maximum value of the shearing maxima occurs is also determined. From a knowledge of the stress-strain configuration, the stored elastic energy of the crystal is deduced; it can be partitioned into two components, that due to shearing strains and that due to a mixture of normal and shearing strains.

The conditions under which the principal stress system coincides with the principal strain system are also investigated. Furthermore, a number is constructed that measures the distortion of the crystal in terms of the energy increments associated with the elastic constants.

The stress-strain analysis applied to the ordering of a CuAu crystal at 125°C corroborates quantitatively the qualitative results previously obtained by transmission electron microscopy. The dependence of stored elastic energy on annealing time is determined and it is shown that the first maximum and decline are associated with the maximum and decline of coherency strains set up between the ordered CuAu I nuclei and the disordered matrix. Upon increasing the annealing time, twinning occurs to relieve the tetragonality strains introduced by the ordered CuAu I domains. The second maximum is compounded by twinning on certain (110) planes and delayed ordering on other (110) planes of the matrix. The subsequent decline of the stored elastic energy is associated with twinning on all (110) planes. The shearing stress necessary to initiate microtwinning does not exceed 7×108 dyn/cm2.
Plasma Temperature Measurement for the Hollow Cathode Discharge
Authors: Roberts A. S. , Bennett W. H.
Published: April 2005

A retarding potential technique has been employed in determining the velocity spread of electrons emerging through an aperture in the anode of a hollow cathode discharge device which is to serve as an electron source. Estimates of electron temperature for the sample stream emerging into a high-vacuum drift space were inferred by assuming a Maxwellian distribution. Electron temperatures of ∼1 eV were obtained in this manner, and the assumption of a Maxwellian energy distribution was justified experimentally. Characteristics of the emergent beam are interpreted as being indicative of discharge properties. It was further found that the kinetic energy of the sample stream was consistently several electron-volts greater than that corresponding to the total voltage applied across the arc.
Characteristics of the Plasma Resonance Probe
Authors: Harp R. S. , Crawford F. W.
Published: April 2005

The plasma resonance probe was first studied by Takayama and his co-workers in 1960. Since that time several attempts have been made to determine precisely the experimental and theoretical behavior of the resonance. This paper reviews the various contributions made so far, and develops further the explanation advanced in 1963 by Harp. Detailed experiments have been carried out to confirm the predictions: (i) that the resonance frequency lies below the local electron plasma frequency, (ii) that it is dependent on probe potential and probe size and, (iii) that the resonance should be highly damped when probe dimensions are smaller than a few electronic Debye lengths. If the resonance probe is to be of great practical importance, a simplified theoretical model describing its behavior is desirable. The theory of such a model is presented and compared to experimental results. The paper concludes with a discussion of improved methods of applying the resonance probe, and suggests a ringing technique which provides electron density measurements in laboratory discharges in times of the order of a few cycles at the electron plasma frequency.
Mode-Selecting Prism Reflectors for Optical Masers
Authors: Giordmaine J. A. , Kaiser W.
Published: April 2005

A prism reflector is described which has high reflectivity for only a very narrow angular range (∼1′). The prism makes use of multiple internal reflections near the critical angle, where the dependence of reflectivity on angle is extremely sharp. It is shown experimentally that such a prism can be used to suppress unwanted off-axis modes in an optical maser. With a typical ruby optical maser a substantial reduction in beam width, as well as an increase in emission near the beam center, is observed. Applications to various optical masers and use as a modulator are discussed.
Effects of Metal Defects on Positive Ion Emission from Heated Iron Filaments
Authors: Tinder R. F. , Antypas G. A. , Donaldson E. E.
Published: April 2005

The positive ion current emitted by heated filaments of high-purity Fe displayed sharp maxima when the metal passed through the structural transformation temperature. The height of the maxima varied with previous flashing temperatures and with the direction of approach to the transformation. Plastic deformation also produced maxima in the positive ion current after a temperature-dependent time delay; the peak height was approximately proportional to strain. Electron emission from the same filaments was unaffected by these factors. The results suggest that the positive ion emission from flash-cleaned Fe filaments is not surface controlled and they seem to require internal rate controlling mechanisms which involve diffusion of the impurity species to the surface along high diffusivity paths.
Thermal Conductivity of Pure and Impure Silicon, Silicon Carbide, and Diamond
Authors: Slack Glen A.
Published: April 2005

Thermal conductivity measurements on high-purity SiC and impure Si and SiC have been made over the temperature range from 3° to 300°K. These results show that the thermal conductivity K, of the highest purity SiC is intermediate between those of pure Si and pure diamond, and at 300°K is greater than that of copper. The heat transport in SiC is produced by phonons and these are scattered by other phonons, isotopes, and the crystal boundaries in the pure material.

In impure SiC the phonons are also scattered by the electrically active impurities Al and N. These impurities reduce the K of SiC in much the same way that B and P impurities do in Si. The N impurities in natural diamonds also reduce their K below that of ideally pure diamond, but the effect is rather different since N is not electrically active.
Injection Luminescence in Germanium
Authors: Muss D. R.
Published: April 2005

The possibility of obtaining appreciable injection luminescence from a germanium device was investigated experimentally. In a p-n-p structure electrons tunnel and holes are injected into the n base region; a weak optical line was observed at 300°, 77°, and 4°K arising from indirect band gap transitions and no evidence of direct transitions was seen.
Carrier Lifetime Studies in Electron-(10–55 MeV) and Proton-(25–110 MeV) Irradiated Germanium
Authors: Fischer J. E. , Corelli J. C.
Published: April 2005

Samples of single-crystal germanium were irradiated at room temperature with electrons of energies from 12 to 55 MeV and with protons of energies from 25 to 109 MeV. Measurements of the minority carrier lifetime as a function of flux and initial carrier concentration suggest that: (1) More than one recombination level, active at room temperature, is introduced in the forbidden gap by the defects created during electron and proton bombardment, with the multilevel effect being greater for the proton-irradiated specimens. (2) The carrier lifetime change with increasing proton energy does not decrease as sharply as predicted by Rutherford scattering and the Kinchin-Pease model. This indicates that nuclear elastic and inelastic processes must be included in computing the number of primary knockons created by protons of energies above at least 50 MeV. (3) The energy dependence of carrier lifetime change in the case of electron bombardment is complicated by a non-constant contribution of multiple levels to the recombination process in the electron energy range studied. At 12 MeV the behavior is adequately represented by single-level theory and a value of 15.4 displacements/cm is obtained.
Etch-Pit Observations Concerning Twins in Iron and Iron Alloys
Authors: Spreadborough J. , Langheinrich D. , Anderson E. , Brandon D.
Published: April 2005

Etch-pit procedures may be used to gain qualitative information about processes involving twins in samples deformed to strains of the order of 10%; a visual representation of the local strain fields may be obtained together with evidence which may be interpreted in favor of the emissary dislocation model for twin growth. The etch-pit procedure reveals about 10% of the dislocations thought to be present and indicates local stresses around twin/twin or twin/grain boundary intersections at least 20% higher than the over-all stresses at distances of about 10 μ or five times the width of the twins.
Solid Solution and Precipitation Hardening in Mg-Fe-O Alloys
Authors: Groves G. W. , Fine M. E.
Published: April 2005

Iron was introduced into single crystals of MgO by diffusion to produce thin homogeneous slices of alloy crystals containing up to ∼4% Fe/(Mg+Fe). When the iron is present as Fe2+ the MgO crystal is not appreciably strengthened but 1% Fe3+ retained in solution by quenching approximately doubles the flow stress of the original crystal. The strengthening due to Fe3+ can be enhanced slightly by aging the crystal in air at 700° to 1000°C. This causes a precipitate of magnesioferrite to form as octahedra which are perfectly oriented within the MgO, the faces of the octahedra being parallel to {111} in the MgO. The fracture process is not greatly affected by the presence of this ``coherent'' precipitate. Continued aging reduces the strength and coarsens the precipitate without change in shape over a size range of 100 Å to 1 μ.
Low-Energy Electron Diffraction Study of Graphite
Authors: Lander J. J. , Morrison J.
Published: April 2005

A low-energy electron diffraction study of surface properties of single-crystal graphite revealed that unlike silicon, germanium, or diamond, the basal plane at the surface was not reconstructed nor did it chemisorb H2O, O2, CO, Br2, or I2 in monolayer quantities at low pressures and moderate or high temperatures.

Elastic and inelastic electron scattering factors for graphite and their contributions to diffraction effects have also been evaluated. The layered structure serves to simplify certain analytical problems and, in particular, results in an energy region from about 10 to 70 V where one-dimensional analysis provides first-order estimates of these scattering factors. But it is also seen that from the point of view of complete and precise quantitative analysis, the elastic and inelastic scattering amplitudes, phase effects, three-dimensional effects, and dynamic factors are almost inextricably entangled in the energy region below about 70 V. Above this region the diffraction effects are largely kinematic and analysis is much simpler.
Capacitance of Thin Dielectric Structures
Authors: Ku H. Y. , Ullman F. G.
Published: April 2005

The capacitance contribution from the space charge and associated potential distribution in the metal electrodes of a parallel-plane capacitor has been estimated by a classical, electrostatic calculation. The electron density is assumed to be given by the absolute zero temperature, Fermi-Dirac distribution function. The first integration of Poisson's equation and application of the boundary conditions for the electric field at the metal-dielectric interfaces result in two nonlinear, algebraic equations (one for each electrode) for the potential distribution as a function of the dielectric thickness and applied voltage. These equations were solved numerically. The results show that for reasonable electric fields in the dielectric (<108 V/cm) the lumped-series capacitance of the electrodes is practically constant and independent of applied voltage and dielectric thickness, in good, qualitative agreement with previously reported experimental results. The total capacitance is the series combination of the capacitances of the dielectric and the electrodes. The electrodes are effectively a capacitor with a thickness 2.3 L, where L is a length characteristic of the metal. This electrode series capacitance for metals such as gold is of the order of 1 μF/cm2.
Microwave Reflection by Nonuniform Plasmas with Exponential Electron Distribution
Authors: Yen K. T.
Published: April 2005

Microwave reflection is considered for nonuniform plasmas with an exponential electron distribution that approaches an equilibrium value far downstream. Several approximate formulas for the reflection coefficient and phase-shift angle and the graphical results of some numerical calculations are presented. Comparison of the results with those for ``ramped'' electron distributions shows an interesting point; when piecewise linear segments are used to represent a continuous electron distribution, the wave interactions may affect the reflection and transmission of electromagnetic waves.
Limiting-Current Densities in the Presence of a Magnetic Field
Authors: Ash E. A.
Published: April 2005

The limiting value of the current density in a beam compressed by an arbitrarily large magnetic field has been derived from Liouville's theorem and the adiabatic invariance theorem. For sufficiently large compression ratios the limiting values are (1+eV/kt), as a result expected from the Langmuir-Pierce expression. Some of the effects due to the use of a finite magnetic field have been examined with particular reference to the current density obtainable at the planes where cathode images are formed. The transit time scatter imposes an upper limit on the maximum compression ratio for which these cathode images can be utilized.
Ion Acoustic Oscillations in Plasma Thermionic Energy Converters
Authors: Chivian Jay S.
Published: April 2005

The oscillations in low-pressure plasma thermionic energy converters are ion acoustic oscillations that may be explained on the basis of an electron beam-plasma interaction. A low-energy beam is formed by the acceleration of electrons through an ion sheath at the emitting surface. The ion acoustic oscillations are observed as expected when the ordered beam velocity is greater than the phase velocity of the wave and less than the plasma electron thermal velocity. Their frequency is f=λ−1(γekTe/mi)12 where the emitter to collector spacing is a multiple of the half-wavelength. Langmuir probes indicate high effective electron temperatures, and the agreement between calculated and measured frequencies is good if γe=3 is used, whether or not the electron-electron collision frequency is higher than the frequency of the observed oscillations.
Origin of the Induced Magnetic Anisotropy in Nickel Ferrite
Authors: Schnettler F. J. , Gyorgy E. M.
Published: April 2005

The magnetic anisotropy induced in nickel ferrite at room temperature by an applied field has been investigated as a function of composition. The magnitude and time rate of change, or relaxation, of this anisotropy has been studied by measuring the torque produced by an applied magnetic field. Disaccommodation, or the change of permeability with time of multidomain materials, is a direct result of this relaxation. The relaxation times are independent of composition and the magnitude of the anisotropy is not simply related to the concentration of cation vacancies or Fe2+ ions; this behavior of the induced anisotropy cannot be explained by either electron or cation migration. A model, consistant with the experimental results, is suggested in which the induced anisotropy is the result of preferentially oriented, localized Jahn-Teller distortions. The distortions arise from Ni2+ ions on the tetrahedral (A) sites of the spinel lattice.
Optical Absorption and Diffuse Reflectance of Powders
Authors: Johnson Peter D.
Published: April 2005

Two different models for the dependence of diffuse reflectance of powders on optical absorption coefficient, particle size, and index of refraction are discussed. For particles large compared to the wavelength of incident radiation a model in which the path of this radiation is controlled mainly by specular internal and external reflections and refraction is preferable to one in which path deviation by Lambert law scattering dominates.
Fourth-Order Elastic Coefficients
Authors: Ghate P. B.
Published: April 2005

The fourth-order elastic coefficients form an eighth-order tensor containing 6561 components of which 126 are independent for a triclinic system. From symmetry arguments it is shown that there are only eleven independent fourth-order elastic coefficients for a crystal with full cubic symmetry.
Large-Signal Photoconductive Effect
Authors: Beattie Alan R. , Cunningham R. W.
Published: April 2005

The theory of the photoconductive effect in semiconductors is extended to include nonlinear recombination rates. A method for determining the excess majority-carrier density and lifetime (defined by the non-linear recombination rate) as functions of the excess minority-carrier concentration is developed from this theory and applied to experimental measurements on a p-type sample of InSb at 80°K. After an initial sharp decrease from its small signal value of 5.2×10−6 sec the hole lifetime becomes constant at a value ∼3.05×10−6 sec when the excess electron concentration increases from 6.0×109 cm−3 to the maximum value investigated, 15.5×109 cm−3. The monotonic increase of the excess hole concentration Δp with excess electron concentration shows a tendency to flatten off at the higher densities (Δp=6.2×1013 cm−3 when Δn=15.5×109 cm−3). A previous theory for the large-signal photomagnetoelectric effect by the present authors is modified by the removal of the assumption that the excess majority-carrier concentration be much smaller than the corresponding thermal equilibrium concentration. The resulting corrections (∼15%) to the graphs of electron lifetime and electron surface recombination velocity as functions of excess electron density, for the same sample of p-type InSb that was used in the present investigation, are also presented.
Noise in Single-Crystal Tellurium from Thermal or Optical Excitation
Authors: Vis Vincent A.
Published: April 2005

The electrical noise of carefully prepared single-crystal tellurium samples was measured in the extrinsic temperature range. The effect of temperature variations on the noise power spectrum is interpreted quantitatively as the result of transitions between the valence band and four species of traps lying ∼0.045 eV above it. The additional noise due to steady optical excitation at 77°K is attributed to transverse carrier density gradients which result from nonuniform excitation.
Double Injection in Deep-Lying Impurity Semiconductors
Authors: Ashley K. L. , Milnes A. G.
Published: April 2005

The analysis of double injection for a semi-insulator model with a single recombination center extends previous treatments by varying the ratio of occupied and unoccupied centers. The voltage-current characteristic of the model consists of an Ohm's-law region followed by a square-law region that terminates into a vertically rising current (threshold of double injection). Expressions for the Ohm's-law-square-law intersection voltage and the threshold (breakdown) voltages represent experimental results better than expressions derived from earlier models. Together with experimental voltages from Au-doped Ge devices at low temperature, these expressions give the electron- and hole-capture-cross section of the recombination center.
Diffusion and Solubility of Zinc in Gallium Phosphide Single Crystals
Authors: Chang L. L. , Pearson G. L.
Published: April 2005

Radiotracer Zn65 has been diffused into 0.2-Ω cm sulfur-doped GaP single crystals from constant pressure vapor sources. Solid solubilities have been measured at temperatures between 800° and 1100°C, the diffusion profiles have been obtained and these have been analyzed by the Matano method. Although retrograde solid solubility is expected at higher temperatures, the data below 1100°C are an excellent fit to the relation C=2.6×1023 exp(−0.85/kT). The diffusion coefficient is found to be concentration-dependent. At temperatures below 900°C the diffusion coefficient can be represented by the empirical expression D=7.5×10−8 C0.45 exp(−2.50/kT). Above 900°C the profiles are similar to those of Zn in GaAs and the diffusion coefficient varies approximately as the square of the zinc concentration. The results are interpreted and the diffusion mechanism is discussed in terms of parallel-mode diffusion of interstitial and substitutional zinc.
Diffusion and Solubility of Copper in Extrinsic and Intrinsic Germanium, Silicon, and Gallium Arsenide
Authors: Hall R. N. , Racette J. H.
Published: April 2005

The solubilities of substitutional and interstitial copper (Cus and Cui) have been measured in intrinsic and extrinsic n- and p-type Ge, Si, and GaAs, using Cu64. These measurements show that Cus is a triple acceptor in both Ge and Si, and that Cui is a single donor in all three semiconductors. Charge compensation experiments show that Cus is a double acceptor in GaAs. In intrinsic semiconductor near 700°C the ratios of substitutional to interstitial solubilities are 6, ∼10−4, and 30, respectively. Electrically active donors due to Cui have been observed in Si by Hall-effect measurements. Pairing between Cus and donors is pronounced in n-type Ge but relatively unimportant above 600°C in Si. There is no evidence for pairing between Cui and acceptors in any of these semiconductors.

The interstitial diffusion coefficient Di is independent of doping in extrinsic p-type material. At 500°C, Di=2.8, 0.76, and 1.0×10−5 cm2/sec with activation energies of 0.33, 0.43, and 0.53 (±10% in each case) eV, respectively. Di and the single positive charge of Cui in p-type GaAs have been confirmed by drift experiments.

The decrease in energy gap with acceptor doping is 0.28 eV in Ge and 0.14 eV in Si at 4×1020 cm−3 acceptors, as deduced from Cui solubility data.

KCN solutions remove Cu effectively from surfaces and from liquid Ga. Ga is much more effective than molten KCN in extracting Cu from the interior of semiconductors. KCN contains Cu and may actually introduce Cu instead of removing it.
Preparation of Peritectic-Type Intermetallic Compounds by a Modified Čzochralski Method
Authors: Barber D. J.
Published: April 2005

The growth of single crystals of peritectic-type intermetallic compounds has been investigated for binary aluminium-rich systems. Single crystals of MnAl6 and NiAl3 have been grown in this way.

In principle, the method is suitable for the extraction of high-temperature phases which transform peritectically at lower temperatures and thus cannot easily be obtained in bulk form (e.g., MnAl4, which can transform into MnAl6). In practice, preliminary work indicates that the experimental requirements are difficult to realize.
Spiral Copper Whiskers
Authors: Edwards P. L. , Svager A.
Published: April 2005

Spiral copper whiskers from the hydrogen reduction of copper halides grow with two to three times as many in an [001] axial direction as in either the [011] or [111] direction, whereas for straight copper whiskers the latter directions predominate. Well-defined faces, usually with low Miller indices, were found on the whiskers. The pitch, even of the most perfectly formed spirals, varied from turn to turn. We conclude that the pitch is not completely determined by crystallographic properties, but infer from the abrupt pitch changes that they play a part.
Theory of the Interaction of Vacancies with Stress Fields in Metals. I. Derivation of Basic Equations
Authors: Girifalco L. A. , Kuhlmann-Wilsdorf D.
Published: April 2005

A theory for the effect of stresses on vacancy concentration in simple metals is presented in which the variation of mechanical energy, electronic energy, and vibration frequencies with stress is taken into account. The vacancy is treated as a point of dilatation and a local soft spot in the crystal with the result that the mechanical energy consists of a term representing the work done by the volume of relaxation against the internal pressure, plus an additional term which is quadratic in the stresses. The electronic energy term is computed from the quasifree electron model based on phase-shift analysis, giving a term proportional to the dilatation. The variation of atomic frequencies with strain is treated by a generalized Gruneisen model which shows that the entropy of vacancy formation is proportional to the dilatation.

The internal work and electronic terms in the energy of interaction of a vacancy with a stress field decreases the vacancy concentration in dilated regions and increases it in compressed regions relative to the concentration in unstrained metal. The quadratic part of the mechanical energy, which comes from the softening of the crystal by the vacancy, always acts to increase the vacancy concentration in regions of high stress, regardless of the sign of the stress field. The entropic contribution, arising from the vibration frequencies, opposes the internal work and electronic terms, decreasing the vacancy concentration in compressed regions and increasing it in dilated regions. The final result is that the interaction energy of a vacancy with a stress field is a function whose magnitude decreases linearly with temperature.
Stability of a Planar Interface During Solidification of a Dilute Binary Alloy
Authors: Mullins W. W. , Sekerka R. F.
Published: April 2005

The stability of the shape of a moving planar liquid-solid interface during the unidirectional freezing of a dilute binary alloy is theoretically investigated by calculating the time dependence of the amplitude of a sinusoidal perturbation of infinitesimal amplitude introduced into the planar shape. The calculation is accomplished by using gradients of the steady-state thermal and diffusion fields satisfying the perturbed boundary conditions (capillarity included) to determine the velocity of each element of interface, a procedure justified in some detail. Instability occurs if any Fourier component of an arbitrary perturbation grows; stability occurs if all components decay. A stability criterion expressed in terms of growth parameters and system characteristics is thereby deduced and is compared with the currently used stability criterion of constitutional supercooling; some very marked differences are discussed.
Sublattice Magnetization and Lattice Distortions in MnO and NiO
Authors: Rodbell D. S. , Owen J.
Published: April 2005

If in the Heisenberg interaction J (S̄a·S̄b), J is separation dependent and the lattice is distortable, then an extended system of arbitrary angular momentum yields more long-range order at a given temperature than the molecular field predicts for the ``clamped crystal.'' Both MnO and NiO show such departures from molecular field prediction and earlier estimates based on isotropic deformations could not account for the observed behavior. Anisotropic deformations have not previously been considered in this regard. The form of these anisotropic distortions is a contraction along the [111] crystallographic direction perpendicular to the sublattice magnetization. In NiO this trigonal deformation corresponds to a change in angle of the original cubic cell from 90° to 90°06′. This distortion accounts for only a small part of the sublattice magnetization's deviation from molecular field prediction. For MnO, on the other hand, neutron diffraction data indicate that this angle is as large as 90°26′, a distortion that would account for about a third of the observed estimate. We have made a direct x-ray diffraction measurement of this deformation and fully confirm this value. The x-ray data supply additional evidence that the disordering transition in MnO is thermodynamically of first order.
Crystal Growth and Magnetic Susceptibilities of Some Rare-Earth Sodium Molybdenum Scheelites
Authors: Schieber M. , Holmes L.
Published: April 2005

The composition range for growing tetragonal scheelite-type single crystals, was investigated and located on the ternary diagram Gd2O3–MoO3–Na2O. Single crystals, the largest one weighing more than 1.2 g, and having a composition of R0.5Na0.5MoO4, with R=Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb, were grown by slowly cooling the ternary melts from 1000°C with rates between 1.1°–3.2°C/h. The crystals were leached out of the flux by boiling them with NH4OH. The various colored transparent pyramidal crystals have their tetragonal ``c'' axis perpendicular to the pyramidal base. The unit cell dimensions of the individual crystals are given. The magnetic susceptibilities of the scheelites of Gd and Dy are reported between 3° and 300°K. Dy or Gd scheelite did not show an ordinary ordering temperature above 1.8°K.