bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Properties of Silicon Films Grown Epitaxially on Sapphire
Authors: Dumin D. J.
Published: January 2005

The resistivity and mobility of p-type and n-type silicon films grown epitaxially on (0001) and (11̄02) sapphire have been measured as a function of substrate prefiring, growth parameters, and film postfiring. Sapphire preheated in hydrogen produced the highest mobility silicon films. Preheating the substrate in helium resulted in films with low mobility. The growth temperature at which the maximum mobility was obtained was found to be about 1200°C on the (0001) sapphire and about 1115°C on the (11̄02) sapphire. The electrical properties were found to be relatively insensitive to growth rate in the range between 0.3 μ/min and 3 μ/min except that slower growth rates and longer growth times lead to relatively more auto-doping from the substrate. The auto-doping was linked to the hydrogen reduction of sapphire (Al2O3) resulting in aluminum-doped silicon. Postfiring of the films below 1250°C resulted in no gross crystal changes but could result in appreciable electrical changes. Postfiring in hydrogen introduced aluminum into the films and postfiring in oxygen removed aluminum. Postfiring in helium resulted in little change in the doping of the films.
Transient and Steady-State Absorption of Microwave Power under Parallel Pumping. Theory
Authors: Joseph R. I. , Schlömann E.
Published: January 2005

The transient growth of the spin-wave population in a microwave magnetic field applied parallel to the dc field is investigated. It is assumed that the sample is in thermal equilibrium before the initiation of the microwave pulse, and that the rf field amplitude remains constant during the pulse. According to the theory the absorption coefficient approaches a steady-state value below threshold, and grows indefinitely (as long as the field amplitude remains constant) above the threshold. The results of detailed calculations concerning the steady-state and the transient absorption are described. Above threshold the time dependence of the absorption coefficient is characterized by a very fast initial rise to an intermediate plateau or hump, a subsequent more gradual rise, and an approximately exponential rise at later times. As the absorption coefficient increases, the field amplitude in the cavity decreases (assuming that the incident power remains constant). This reaction of the sample upon the field amplitude is taken into account in an approximate fashion. Because of this reaction the absorption coefficient approaches a new steady state above the threshold.
Damping of Dislocations in Lead Single Crystals
Authors: Mason Warren P. , Rosenberg Arthur
Published: January 2005

Measurements have been made of the attenuation of longitudinal waves along the 〈110〉 direction in a lead single crystal over a frequency range from 30 to 150 Mc/sec and in a temperature range from 60° to 300°K. The attenuation can be divided into a square-law frequency term and a term consistent with the theoretical form of dislocation attenuation at high frequencies. By determining the high-frequency asymptote of the dislocation internal friction and by assuming a reasonable dislocation density, the drag coefficient for the dislocations can be evaluated. The measurements are consistent with the sum of a phonon scattering term and a phonon viscosity term. The square-law attenuation is about twice as large as the thermoelastic loss and over a temperature range is in agreement with the sum of a thermoelastic loss plus a phonon viscosity loss.
Electrical Characteristics of Sputter-Ion Pumps
Authors: Wear Kenneth B.
Published: January 2005

Ultra-high vacuum pumps of the sputter-ion pattern have been investigated from the standpoint of origin and destination of electrically charged particles constituting pump current. It has been found that secondary electron emission is responsible for a large portion of total current, that ion energies range from 0.50 to 0.80 of applied pump potential, and that needle crystals (whiskers) that grow progressively from pump electrodes cause pump current to depart from its linear dependence on pressure.
Refractive Index as a Function of Temperature in LiNbO3
Authors: Boyd G. D. , Bond W. L. , Carter H. L.
Published: January 2005

The refractive index vs wavelength of LiNbO3 has been measured between 0.42 μ and 4.0 μ at 25°C and 80°C. The measured values have been expanded in a three-term polynomial by a least-squares best fit and the temperature dependence of the polynomial coefficients determined. The results are used to calculate the phase-matching temperatures normal to the optic axis in nonlinear optical second-harmonic generation and parametric experiments. The calculated results are compared with experimentally measured values.
Coupled Molecular Flow and Surface Diffusion. Application to Cesium Transport
Authors: Bates T. R. , Forrester A. T.
Published: January 2005

The mechanisms of cesium transport through a cylindrical tungsten tube are now understood to consist of surface diffusion, molecular flow and ionic flow under the influence of electric fields which exist in the tube. In this paper an exact transport equation is developed for the idealized case of pure molecular flow coupled with surface diffusion. This takes the intractable form of a nonlinear integrodifferential equation of second degree. This is analytically reduced to a nonlinear form of Fredholm's integral equation suitable for solution by numerical iteration.

The Langmuir adsorption and diffusion data for cesium on tungsten are introduced and the approximate domain of convergence for the integral equation is found by the use of an appropriate existence theorem. Sample solutions are shown including one which satisfies required boundary conditions at the orifices.
High-Frequency Surface Waves on Inhomogeneous Plasma Columns
Authors: Granatstein V. L. , Korn P. , Ojo A. , Schlesinger S. P.
Published: January 2005

Dipolar waves are launched onto the surface of a positive column afterglow. Dispersion characteristics are obtained over a more extensive range of parameters than previously examined; phase velocity, ω/kz, ranged from 0.94c to 0.27c and signal frequency is high (λ0≈2πR). The waves are forward near the light line (ω/kz≈c), but become backward waves as ω/kz decreases. Experimental results are compared with an analysis that uses the full set of Maxwell's equations (nonquasistatic) but which adopts a dielectric-clad homogeneous plasma cylinder as a model of the discharge tube. This analysis qualitatively predicts the major dispersive features. In particular, as circumference to free space wavelength ratio, 2πR/λ0, increases, the magnitude of group velocity in the backward wave region decreases; also the peak in the dispersion curve becomes less sharp and its position recedes farther from the light line. However, lack of quantitative fit between experimental results and analytical predictions indicates the need for a theoretical model which accounts for plasma inhomogeneity.
Periodic Dislocation Distributions in a Half-Space
Authors: Owen D. R. J. , Mura T.
Published: January 2005

A solution is given to the stress field produced by an arbitrary periodic distribution of dislocations (or plastic distortion) in a half-space. It is shown how the known results for discrete dislocations are obtained quite simply from this. The solution to the problem of a Frank dislocation network near a free surface is given and its stability examined. The whole-space stress field decreases exponentially with the distance from the plane of the network, as do the stress terms due to the free surface which decrease exponentially with the distance from this surface. It is shown that the network always experiences a force attracting it to the free surface.
The Elastic Anisotropy of Crystals
Authors: Chung D. H. , Buessem W. R.
Published: January 2005

Essentially, the elastic properties of all the known crystals are anisotropic. This paper presents a convenient method to describe the degree of the elastic anisotropy in a given cubic crystal and then discusses its practical values. On the basis of the well-known Voigt and Reuss schemes to average the single-crystal elastic constants for polycrystalline behavior, the degree of elastic anisotropy has been defined as A* = [3(A−1)2]/[3(A−1)2+25A], where A is the usual anisotropy factor given by A = 2c44/(c11−c12). It is shown that the present A* has the folowing properties of practical importance: (a) A* is zero for the crystals of the elastic isotropy, i.e., A = 1. (b) For an anisotropic crystal, A* is a single-valued measure of the elastic anisotropy regardless of whether A < 1 or A > 1. (c) A* gives a relative magnitude of the actual elastic anisotropy possessed by a crystal.
Intrinsic Brittle Strength of Magnesium Oxide Bicrystals
Authors: Lange F. F. , Buessem W. R.
Published: January 2005

The intrinsic brittle strength (i.e., without dislocation motion) was obtained for MgO bicrystals of various misorientations. Bicrystal fracture always occurred at the grain boundary. Strength values ranged between 70 000 psi and 370 000 psi. Two modes of fracture were observed: intergranular and intragranular fracture. The latter occurred only at high strain energies. Secondary cracks, believed to originate from flaws on the grain-boundary surface, were observed for all bicrystal specimens that fractured in a brittle manner.

Tensile stresses as high as 400 000 psi were obtained on single crystals of MgO before ductile fracture occurred.
Pulsed Flashover in Vacuum
Authors: Watson Alan
Published: January 2005

Experiments on the vacuum flashover of dielectric frusta subjected to 35 and 75 nsec pulses show the strong influence of cone angle on insulation strength. A theory is presented to explain the formative process leading to flashover for one polarity. It is proposed that positive surface charge grows by emission of hot electrons during the application of the electric field. When the surface field intensity is sufficient to draw other electrons into it, they will multiply by secondary emission until the critical breakdown condition is achieved. Flashover is thus initiated by secondary emission, but the formative time lag is governed by thermionic emission of electrons. The experimental data are analyzed and interpreted in the light of this theory.
Formation of Dislocation Networks in Gallium Single Crystals
Authors: McFarlane S. H. , Elbaum C.
Published: January 2005

The development of dislocation networks in gallium crystals, initially free of detectable dislocations, has been studied at room temperature by an x-ray diffraction topographic technique. The condition required for the development of these networks is the existence of spatial periodic fluctuations in impurity content. The networks develop, in the absence of an external stress, from individual loops which are first detected 3 to 10 days after the crystal has been grown. These loops grow for days at a uniform rate of 10−8 cm/sec and reach a size of a few hundred microns. No specific nucleation mechanism for these loops has been identified. It it is assumed that the loops expand by climb (by the addition of vacancies), their rate of growth and observed densities are consistent with a formation energy for vacancies Uf in the range 0.2 to 0.3 eV and a migration energy for vacancies Um in the range 0.4 to 0.7 eV. No values of Uf, Um, or Uf+Um determined from other experiments have been reported and a comparison is not possible at the present time. The change of initially straight dislocation lines into jagged lines has been observed and is interpreted as the climb of screw dislocations into irregular helical dislocations. A marked anisotropy in the growth of the loops and helices was observed and is attributed to an anisotropic coefficient of self-diffusion.
Dependence of 50- and 100-keV Bremsstrahlung on Target Thickness, Atomic Number, and Geometric Factors
Authors: Placious R. C.
Published: January 2005

Experimental data have been obtained for the bremsstrahlung spectra produced with 50- and 100-keV electrons incident on different targets. The spectrum per unit solid angle per incident electron is measured for photon emission angles of 30, 70, and 110 deg, for normal and oblique incidence of the electrons on the targets having atomic numbers of 13, 50, and 79, and for four target thicknesses equal to different fractions of the electron range in the given material. Also, results are given for the bremsstrahlung production efficiencies per unit solid angle at a given emission angle. The experimental results at normal incidence show good agreement with the theoretical predictions of Berger and Seltzer, which are based on thin-target bremsstrahlung cross sections and which employ Monte Carlo calculations to account for multiple scattering and energy-loss effects. Similar calculations for other geometries should produce reliable estimates of the emitted bremsstrahlung spectra in this same energy region.
Effect of Stress on the Hall Coefficient of Chromium Films
Authors: Lu Chih-shun , Milgram Alvin A.
Published: January 2005

Hall-coefficient measurements have been made on vapor-deposited chromium films in the temperature range from −195° to 150°C. The stress in the chromium films was estimated by the shift of Néel temperature and the differential thermal-expansion coefficients between the substrate and the film. It was observed that compressive stress reduces the Hall coefficient of chromium and tensile stress increases it. A suggestion is made concerning the similarity between the effects of pressure and the effects of changing the number of 3d electrons in chromium.
New Phase Transformation in InSb at High Pressure and High Temperature
Authors: Banus M. D. , Lavine Mary C.
Published: January 2005

A new phase transformation at high pressure and elevated temperature has been found in the InSb pressure-temperature phase diagram. This transformation to a new phase designated as InSb-III has been established by measurements of superconducting transition temperature (Tc) as a function of annealing temperature at several pressures and by x-ray determinations on the new phase, both retained at one atmosphere and at high pressure and temperature. The higher Tc for InSb-III (Tc = 4.1°±0.1°K) and the x-ray results lead to the conclusion that InSb-III is a new phase different from the orthorhombic phase (Tc = 3.5°K).
Etching Phenomena in the {111} Plane of Niobium
Authors: Zedler E.
Published: January 2005

For single- and polycrystalline niobium the relation between etch figures and dislocations is qualitatively demonstrated. Repeated etching allows investigation of the movement and multiplication of dislocations. Besides triangular etch hillocks there often occur etch traces or walls, respectively, and networks that may be interpreted as dislocations lying nearly parallel to the observation plane. Etch figures of helical dislocations have been found too.
Thermally Engraved Gratings using a Giant-Pulse Laser
Authors: Gerritsen H. J. , Heller M. E.
Published: January 2005

Previous investigators have demonstrated the efficient and cataclysmal removal of material from surfaces hit by a giant-pulse laser. Experimental evidence is presented here that very fine patterns, defined to 0.1 μ, can be engraved directly in metals or insulators by using the interference from two beams. Besides possible practical uses, the study of the structure of such patterns is expected to further our understanding of the mechanisms involved in damage by giant-pulse laser impact.
Ferroelectric Rare-Earth Molybdates
Authors: Borchardt Hans J. , Bierstedt Paul E.
Published: January 2005

The molybdates of Sm, Eu, Tb, and Dy are isotypic with ferroelectric Gd2(MoO4)3. Other compositions of this structure occur in the pseudoternary system Gd–La–Y-molybdate and in the pseudobinary system Gd2(MoO4)3–Gd2(WO4)3. A representative number of these compositions were grown as single crystals and tested for ferroelectricity. Each was found to be ferroelectric as evidenced by a ferroelectric hysteresis loop and by visual observation of domains. The Curie temperatures (TC), spontaneous polarizations (Ps), and coercive fields (Ec) were determined, with values ranging as follows: TC, 148°–190°C; Ps, 0.14–0.23 μC/cm2 at 25°C; Ec, 5.0–14.5 kV/cm at 25°C.
Boron Detection in Metals by Alpha-Particle Tracking
Authors: Armijo J. S. , Rosenbaum H. S.
Published: January 2005

Track-etching techniques were used to detect boron in austenitic steels. The technique involved placing polymers which were known to be sensitive to alpha particles in intimate contact with the polished metal surface, exposing the specimen to neutrons, and then etching the polymer detector. Alpha tracks that result from the 10B(n, α)7Li reaction were developed in the polymer by etching in an aqueous NaOH solution. The boron concentration in the steels was quantitatively determined and the results compared with more conventional analytical techniques. It is seen that in addition to measuring the total boron content, the track-etch method allows one to map the distribution of boron within the microstructure of the metal alloy. The detector materials used were cellulose nitrate and cellulose acetate butyrate. The technique is useful for measuring boron concentrations in the parts-per-million range.
Elastic Deformation of Field-Ion-Microscope Tips
Authors: Rendulic Klaus D. , Müller Erwin W.
Published: January 2005

During the imaging process the specimen in a field ion microscope is subject to a stress of 105 kg/cm2. The extent to which the elastic deformation caused by this stress appears in the image of W, Ta, and Mo specimens is investigated. Depending on the tip shape one observes an increase or a decrease in local magnification. When the electric field is increased from 220 MV/cm to 450 MV/cm the change in the projection angle does not exceed ±1.5°.
Dislocation Pile-Ups against a Locked Dislocation of a Different Burgers Vector
Authors: Chou Y. T.
Published: January 2005

The classical analysis of Eshelby, Frank, and Nabarro of a linear dislocation pile-up is generalized to include the case in which the locked dislocation may have a Burgers vector of mb, where b is the Burgers vector of free dislocations and m is a positive real number. The equilibrium positions of (n−1) free dislocations piled up against the locked dislocation under a uniform applied stress are given by the roots of the Laguerre polynomial Ln−1(2m−1). Simple expressions for the distance between the locked and nearest free dislocation, x1, the length of the pile-up, L, and the stress at its tip, σtip, are obtained. Increasing m will increase x1 and decrease σtip, while L is only slightly extended. For large n the stress field within a certain distance range around the tip is found to be independent of m.

Based on the Petch model of yielding it is shown that increasing m increases the Hall-Petch slope by a factor of (m)1/2. The effect of m on the coalescence of leading dislocations leads to a higher-fracture stress if m is increased.
Method for Determining Molecular-Attachment Kinetics during Crystal Growth. Theory
Authors: Tarshis L. A. , O'Hara S.
Published: January 2005

The phenomenon of planar faceting of an otherwise curved interface is re-examined and shown to provide an experimental means of determining crystal-growth laws and magnitude of kinetic constants. Facets are often observed to form during crystal growth as a result of the large driving force required to generate new layer sources. This driving force is shown to be orders of magnitude larger than that required for layer-edge passage. As a result, the interface must depart from its equilibrium morphology and facet in those crystallographic directions requiring source generation. This nonequilibrium departure is related to the actual interfacial undercooling through the temperature gradient at the interface. The effect of the non-regular morphology on the steady-state temperature gradient is considered. Pertinent experiments are described in detail and exemplary cases are cited.
Effect of Alloying on Aluminum K and Copper L X-Ray Emission Spectra in the Aluminum-Copper System
Authors: Baun William L. , Fischer David W.
Published: January 2005

Data for the Al K emission band, Al Kα satellites and Cu LIII band in Al-Cu alloys (10%–100% Al) are presented. Significant changes in the spectra are noted with changes in composition. The Al K emission band is split and the long-wavelength component shifts to longer wavelengths and becomes dominant with a decrease in Al concentration. The short-wavelength component shifts only slightly and maintains the typical sharp, short wavelength-emission edge seen in pure aluminum. Separation between high- and low-energy components in the Al K band is as much as 4 eV (10% Al) and extrapolates to about 4.5 eV for very dilute alloys, which is nearly the calculated excitation energy of 3s2→3s3p in Al+. The Al K satellites Kα3 and Kα4 show corresponding intensity changes with alloy composition. The intensity ratio Kα4/Kα3 changes linearly (for 6-kV excitation) from 0.48 in Al to 0.70 in 10 Al-90 Cu.

The Cu LIII band also shows changes in shape with alloying but the changes are not as large as observed for the Al K band. The copper band shifts linearly to lower energy as more and more aluminum is added.
Infrared Absorption of the Gamma-Induced Surface Layer on Germanium
Authors: Lin K. C. , Lee L.
Published: January 2005

A thin layer on the surface of single-crystal germanium produced by 60Co-gamma irradiation has been found. This layer can only be produced on specimens which were irradiated in air. Several infrared absorption bands with peak absorptions at 3, 6, 6.85, 11.5, and 12.7 μ are associated with the layer. Of these bands, only the 11.5-μ band has been identified as resulting from germanium dioxide which was formed on the surface by chemical reaction of germanium with oxygen and/or ozone. The origins of other bands as well as the layer remain unknown.
Thermoluminescence and Color Centers in LiF
Authors: Christy R. W. , Johnson N. M. , Wilbarg R. R.
Published: January 2005

Thermoluminescence emission above room temperature and optical absorption have been studied in LiF crystals irradiated by gamma rays, with emphasis on conditions which are of greatest interest for applications to radiation dosimetry. The specimens were Harshaw crystals of differing purity, and the purpose was to correlate the electron and hole traps and recombination centers involved in the thermoluminescence with optical-absorption bands produced by the trapped carriers. The dominant glow peak in suitably treated crystals occurs at about 200°C, and this is correlated with an absorption band at 310 mμ, through thermal and optical bleaching of the thermoluminescence and optical absorption. A smaller glow peak at 100°C is correlated with an absorption band at 380 mμ. The F center absorbing at 250 mμ appears to be the electron trap associated with both glow peaks. It is concluded that the 310- and 380-mμ centers are trapped-hole centers, and the thermoluminescence occurs after they are thermally ionized. The recombination center which produces the visible-light emission is believed to be not the F center, however, but an impurity center which absorbs at 196 mμ. An energy-level diagram is suggested, which can account for the observed optical and thermal transitions. It depends on electron tunneling from the F center to the 196-mμ center. Available evidence indicates that the 310- and 380-mμ centers involve Mg; the impurity responsible for the 196-mμ center may be Al.
Wave Interactions with Moving Boundaries
Authors: Tsai C. S. , Auld B. A.
Published: January 2005

The general theory of the double Doppler effect is reviewed for both vacuum and material media. Frequency and amplitude changes in the reflected and transmitted waves at a partially reflecting moving interface are calculated for cases in which the medium behind the interface: (a) moves at a different velocity than the interface; (b) moves at the interface velocity; (c) is stationary. The advantages of case (c) for practical frequency conversion are discussed.

Multiple moving interfaces in a stationary medium are also considered. On the basis of this theory, Doppler shifts at moving, tapered transition regions are analyzed as a series of discrete, closely spaced steps. This shows that the frequency conversion of the transmitted wave is independent of the slope of the taper. By use of a transmission line model, a simple physical explanation is given for the double Doppler effect in a moving taper.
Ultrasonic Attenuation in Aluminum Ammonium Alum and Aluminum Potassium Alum
Authors: Marshall B. J. , Pederson D. O. , Bailey W. E.
Published: January 2005

The attenuation of 10-Mc/sec sound waves in AlNH4(SO4)2·12H2O and AlK (SO4)2·12H2O over a temperature range of 300° to 4.2°K has been measured. Results, which are available for both longitudinal and transverse waves propagated in the [111], [110], and [100] directions show that there are some very large absorption peaks occurring in the temperature range between 80° and 120°K.

The complex dielectric constants of these alums have also been measured using the same frequency and directional dependence as that used in the ultrasonic attenuation measurements. The results, presented in this paper, show that the real and imaginary parts exhibit peaks in the same temperature region as that for the ultrasonic attenuation peaks.

It is believed that these results might be associated with a Debye type of relaxation in solids.
Dissolution Spirals on Gamma-Irradiated Lithium Fluoride
Authors: Ives M. B. , Ramachandran T. R.
Published: January 2005

Double-spiral features have been observed at high resolution on lithium fluoride {100} surfaces etched in distilled water containing from 0.1 to 9 ppm ferric ions. The models proposed for similar features on other materials are reviewed, and suggestions are made regarding the lattice-defect configurations responsible for the spirals. Radiation-induced climb of segments of dislocations which are parallel to the surface is introduced as a possibility.
Behavior of Passing Dislocations in Superlattices
Authors: Marcinkowski M. J. , Lakso G.
Published: January 2005

A detailed computer analysis has been made of the behavior associated with the passage of pairs of superlattice dislocations on neighboring parallel slip planes for the specific case of the Fe3Si alloy. The treatment has been carried out for superlattice screw and edge dislocations of like and unlike sign for a series of vertical passing distances. In particular, the equilibrium separation between the individual ordinary dislocations constituting the superlattice dislocation has been determined as a function of distance between the pair of superlattice dislocations. In addition, the passing forces as well as the cross slip and climb forces associated with the dislocations have been calculated.

It has been found that cross slip of superlattice screw dislocations with mutual annihilation, if they are of unlike sign, will occur for passing separations of 100 Å or less. Superlattice edge dislocations can, however, be passed by one another at much closer distances, which results in the uncoupling of the superlattice dislocation. Furthermore, the extension of the superlattice dislocations oscillates strongly as they pass one another. All of these results are in general agreement with observations obtained with the Fe3Si superlattice.
Effect of Pressure on the Mössbauer Effect of 57Fe in Nickel Metal
Authors: Raimondi D. L. , Jura G.
Published: January 2005

The Mössbauer spectrum of 57Fe in nickel metal was studied to a pressure of 80 kbar. A peak in the internal field at the 57Fe nucleus was observed at 10 kbar, followed by a slow decrease up to 80 kbar. The initial increase of the internal field with pressure is given by d lnH/dP=10.2×10−4 kbar−1. The isomer shift over the entire pressure range is given by d(IS)/dP=−4.15×10−5 cm/sec/kbar. These results are discussed as they relate to other pressure studies on the properties of pure nickel and iron.
Secondary Emission Studies on Ge and Na-Covered Ge
Authors: Palmberg P. W.
Published: January 2005

The influence of work-function reduction and variation of the incident-beam angle on the secondary-electron yield and secondary-electron energy distribution from the (111) face of Ge have been studied. Reduction of the work function from 4.79 to 2.3 eV by deposition of Na increased the maximum yield from 1.2 to a value near 3.6, while the primary energy at which the maximum yield occurred increased from 700 to 2000 eV. The energy width of the slow secondary-electron energy distribution function decreased strongly both with increasing primary energy and decreasing work function. An investigation of the energy of secondary electrons involved in the yield variation with incident beam angle suggests that this variation in yield is a direct result of variation in the primary-electron backscattering coefficient. A bulk plasma loss of 16.7 eV is manifested in the total secondary-electron energy distribution function by a series of peaks lying at multiples of 16.7 eV below the elastic peak. In addition, a shoulder on the first 16.7 eV loss peak indicates the existence of an 11 eV surface plasma loss. An overlayer of Na does not seriously affect the bulk plasma loss spectrum, but shifts the 11-eV surface loss to about 13 eV and causes the appearance of a second 3.5-eV surface loss peak.
Pressure Effects on Charge Transport in Nickel and Chromium Oxides
Authors: Vaišnys J. Rimas
Published: January 2005

The effects of pressure on charge transport in NiO are given by dE/dP=−1.0×10−6 eV/bar and d |QT|/dP= −0.5×10−6 eV/bar; in Cr2O3, dE/dP= −0.8×10−6 eV/bar and d |QT|/dP= −0.2×10−6 eV/bar, where E is the activation energy for conduction and QT is the thermoelectric energy. No evidence is found for energy-band broadening with pressure in chromium oxide.
Analysis of Electron Current Extraction from Synthesized Plasmas
Authors: Sobol H. , Eichenbaum A. L.
Published: January 2005

The extraction of electron beams from plasma cathodes (common and separate emitter type) has been treated theoretically by space-charge analyses. Stability data for simple space-charge mode potential distributions and extracted current as a function of extractor potential has been computed. The theory when applied to the separate-emitter cathode gives results that agree fairly well with experiments. More definitive experiments must be carried out with common-emitter cathodes before comparisons with theory are possible.
Preparation of Pure Alkali Halide Crystals and Some of Their Properties
Authors: Peech J. M. , Bower D. A. , Pohl R. O.
Published: January 2005

This paper describes some of the techniques that have been used successfully in this laboratory for the purification and preparation of a number of alkali halide crystals, particularly KCl. Measurements of the optical absorption, ionic conductivity, and thermal conductivity, are employed to test the purity of the crystals. Surface contamination of the zone-refined salt upon exposure to air, during handling between the different steps of preparation, appears to be a major source of contamination as judged by the ionic conductivity. A special apparatus has, therefore, been designed to permit both zone refining and subsequent seed pulling of the crystal to be carried out without changing the protective atmosphere.
Higher-Order Modes of the Two-Stream Instability in Bounded and/or Inhomogeneous Plasmas
Authors: Lee Kai Fong
Published: January 2005

The higher-order modes of electrostatic oscillations in transversely bounded and/or inhomogeneous Vlasov plasmas are studied using the generalized formulas and stability criteria reported in a recent paper. While modes higher than the lowest are unimportant in stationary warm plasmas because they are strongly damped, it is found that in counterstreaming plasmas, there are in general several unstable modes, the number of which depends on geometry and streaming velocity. For a given plasma temperature and density, it is possible to excite only the lowest mode and suppress all others either by operating at certain ranges of streaming velocities or by suitably choosing the ratio of plasma diameter to that of the surrounding conducting shield. The relevance of these results on the design of double-stream amplifiers is discussed.
Solutions to Some Steady- and Transient-Flow Problems Relevant to Flow Birefringence and Dichroism of Suspensions
Authors: Hollingsworth C. A. , Poppe Wassily
Published: January 2005

Hydrodynamic equations are solved giving the flow velocity for the types of transient and steady flow that exists in various apparatus used in the study of flow birefringence and dichroism of suspensions. The time involved in starting and stopping the apparatus is taken into account. Formal solutions are given for general cases, and these are worked out in detail for the special cases of constant rate of change of boundary velocity or pressure gradient.
Porosity Effects in the Ionization of Cesium on Tungsten
Authors: Berman David
Published: January 2005

The ionization characteristics of cesium on a porous tungsten substrate may be much different from those of solid tungsten. Cesium vapor diffuses through a porous structure en route to the ionizing surface, creating gradients in the surface concentration of atoms. Therefore, some regions experience increased surface coverage, over and above that corresponding to ionization on solid tungsten. Increased surface concentration diminishes ionization efficiency, producing a higher level of neutral emission. These increased concentrations are calculated by equating mass flow of atoms into the pore to mass flow diffusing to the surface and evaporating directly from the pore. Ionization characteristics as a function of local surface coverage is available from established results for solid substrate tungsten. The parameters used in this study are those of interest in cesium-contact ion rockets: ion emission current densities on the order of 10 mA/cm2, with ionization efficiency of about 99%. The results indicate that porosities of less than 106 pores/cm2 will appreciably decrease ionization efficiency; but with higher porosities, ionization characteristics can approach those of solid tungsten.
Ionization Waves in Semiconductors and Gaseous Plasmas
Authors: Weissglas Peter , Andersson Bengt
Published: January 2005

A theory for ionization waves in plasmas is developed. If the ionization rate depends strongly on carrier temperature such waves may propagate and an instability, which in some cases is absolute, can occur. The wave has a phase velocity opposite the electron drift and can have either positive or negative group velocity. The theory agrees qualitatively, but not in detail with that previously developed by Pekarek for striations in gasous discharges.

In particular, the theory is applied to InSb, which is a favorable solid-state material for observations of ionization waves. Instabilities are predicted for thin layers of intrinsic material.

It is also shown that the temperature dependence of the ambipolar diffusion coefficient can give rise to an instability which is independent of the ionization phenomena.
Localized Doping of Epitaxial Ferrite Films
Authors: Pulliam G. R. , Warren R. G. , Holmes R. E. , Archer J. L.
Published: January 2005

Films of Ni0.6Mn0.4Fe2O4 epitaxially grown on the cube plane of magnesium oxide crystals have been diffusion-doped with cobalt to change the direction of magnetization from the [111] to either the [110] or the [100]. The change in the magnetic vector direction with the small cobalt additions is a result of the extremely strong preference of cobalt ferrite to adopt a [100] easy direction while other ferrites prefer the [111]. An expression is also derived defining the critical film thickness at which the magnetic vector will move from a position making a large angle to the plane to one where the vector will lie completely in the plane.
Threshold for Magnetoelastic Instability in the Subsidiary Absorption Region in YIG
Authors: Thomas G. , Wang S.
Published: January 2005

The Suhl theory for ferromagnetic instability is extended to include the coupling between the magnetization and strain. The threshold for magnetoelastic instability is found to be nearly the same as that for subsidiary absorption in YIG. The experimental threshold is found to agree with the predicted curves; however, the threshold field is found to be about 10% higher than that obtained in the usual manner for subsidiary absorption threshold. This raises some questions about the extension of the linear region of the susceptibility plot to intersect the saturation value of susceptibility in order to obtain the critical field. Explanations are given for the ``beating'' of magnetoacoustic oscillations and for the necessity of long pulse lengths of microwave power in order to produce magnetoacoustic instabilities.
Atomic Mating of Germanium Surfaces
Authors: Haneman D. , Roots W. D. , Grant J. T. P.
Published: January 2005

Single crystals of germanium have been partially split in ultrahigh vacuum (∼10−9 Torr), and the surfaces of the split recontacted with high precision. Initially, an internal n-p-n structure appears about the mated split in n-type specimens, indicating that the surfaces, although in intimate, possibly atomic, contact, retain their new surface structures sufficiently to trap electrons. Subsequently, portion of the junction disappears to an extent which varies from specimen to specimen. This is interpreted as due to the occurrence of atomic bonding across portion of the contacted region, and suggests that cleaved and annealed surface structures are not drastically different from ideal surfaces. When irradiated with a light spot the remaining junction region causes a photovoltage to appear which reverses in sign as the spot traverses the mated region. Due to the narrowness of the latter, applications as light detectors of high positional sensitivity are indicated. The p-type specimens show no junctions when surfaces are mated, confirming that clean cleaved surfaces remain p type. Specimens (n or p) containing surfaces mated in air show no photovoltage. Specimens containing surfaces mated above 200°C, the cleaved-to-annealed surface transition temperature, appear to have higher photovoltages than those mated at room temperature.
Self-Locking of Modes in Lasers
Authors: Statz H. , DeMars G. A. , Tang C. L.
Published: January 2005

We investigated phase-locking effects between longitudinal modes in lasers. In order to show the general trend to be expected for a large number of oscillating modes, we treat three-, four-, and five-mode oscillations. The expected phases depend in a complicated manner upon the relaxation times T1 and T2 of the medium, on the degree of inhomogeneous broadening, the mode separation and location of the medium in the cavity. Simple formation of sharp output spikes at the fundamental frequency are expected where crystals like ruby or YAG are placed near the edges of the cavity. Sharp spikes at twice the fundamental frequency are expected when these solids are placed in the center of a cavity. Certain filters, when placed near the edge or center of the cavity are expected to cause similar locking effects. Gases and solids are expected to act quite differently. The calculations are based on the maximum-emission principle. This principle will be discussed in a later publication. Some experimental results are also presented.
Behavior of Ultrathin Zirconium Films upon Exposure to Oxygen
Authors: Fehlner Francis P.
Published: January 2005

Discontinuous films of zirconium, having surface resistivities between 104 and 106 Ω sq−1, were deposited on glass substrates in ultrahigh vacuum and then exposed to oxygen pressures in the range of 5×10−7 to 4×10−8 Torr at temperatures of 25° and −196°C. The change in film resistance with time was monitored and a plot of logR vs logt was constructed. This graph was initially concave upwards, but became linear after a time which was characteristic of monolayer formation.

An interpretation of the film behavior was based on the transport of electrons by tunneling through gaps separating the metal islands. The initial change in film resistance was caused by an increase in the zirconium work function. This increase was due to oxygen monolayer formation. The subsequent linear log-log behavior was caused by an increase in the tunneling distance which resulted from oxidation of the metal islands.

Values for both the interisland spacing and the room-temperature oxidation rate constant have been calculated from the experimental data. Both impurities and the heat of adsorption interfered with determining a value for the interisland spacing, but when these interferences were eliminated, a distance of 6.9 Å was found for a 104 Ω sq−1 film. The oxidation rate constant for a comparable film at 25°C was 4×10−9 cm with an activation energy of 0.3 kcal mole−1.

Pumping speeds also were determined. Zirconium initially pumped oxygen at ≈1500 ml·sec−1·cm−2. The sticking coefficient for oxygen on a partially oxygen covered zirconium surface was approximately 0.05.
Method for Pulsewidth Measurement of Ultrashort Light Pulses Generated by Phase-Locked Lasers using Nonlinear Optics
Authors: Weber H. P.
Published: January 2005

A nonlinear optics experimental arrangement is proposed for the measurement of the pulsewidth of ultrashort light pulses. The experiment consists of a Michelson-like arrangement in which each light pulse is split into two pulses which are delayed and polarized orthogonally to one another. The two pulses are propagated as ordinary and extraordinary rays through a nonlinear crystal whose orientation is chosen so that the second harmonic is only generated by the interaction arising from the superposition of these two pulses. The pulsewidth is obtained from the dependence of the intensity of the second harmonic upon the relative delay of the pulses. This method suggests itself for coincidence measurements of pulse delays including those due to optical path variations.

The experimental arrangement is given and an analysis for light pulses from an ideal phase locked laser is carried out. The resolution time of the coincidence method as limited by phase matching considerations is calculated. For the example of a phase-locked Nd laser and a 1-mm-thick KDP crystal the numerical value of the resolution time is about 1 psec.
Low-Temperature Anomaly in Ferrimagnetic Resonance of Ytterbium-Doped Yttrium Iron Garnet
Authors: Dillon J. F. , Remeika J. P. , Walker L. R.
Published: January 2005

The field for ferrimagnetic resonance at helium temperatures of YIG in which small amounts of ytterbium have been substituted for yttrium is known to show sharp excursions as a function of applied field direction. These are inconsistent with the accepted energy-level scheme of Yb3+ ions in such a system. It is shown here on the basis of extended resonance studies and of a study of the dependence of the effect on sample preparation and heat treatment that the evidence is consistent with the assumption that some added Yb3+ ions are situated on octahedral sites normally occupied by Fe3+ ions.
Discrepancies from a Perfect Match in the Etch Patterns on the Opposite Cleavage Faces in Bi2Te3
Authors: Sagar A. , Faust J. W.
Published: January 2005

Experimental evidence has been obtained, establishing that the deviations from a perfect one-to-one correspondence between etch pits on the opposite cleavage faces in Bi2Te3 are often due to bending and branching of the dislocations at the cleavage. It is suggested that the observation of deviations from the identical etch patterns on the opposite cleavage faces of a crystal does not necessarily imply the unreliability of an etch for revealing dislocations in that crystal.
Conductance and Capacitance of 6-deg Tilt Boundaries in p-Type InSb
Authors: Mueller R. K. , Jacobson R. L.
Published: January 2005

Conductance and capacitance measurements on α and β grain boundaries in p-type indium antimonide are discussed. It is found that the grain boundary barrier is of the order of the band gap, which implies that an inversion layer exists at the boundary. It is further found that the predominant current transport across the boundary is minority carrier flow, in agreement with a model described in a previous publication.
Noise Spectrum of a Stationary Current with Fluctuating Mean
Authors: Byrne J.
Published: January 2005

An analysis of the noise generated in an emission current which is governed by a compound Poisson law gives the result that the usual shot-noise term is supplemented by a singular low-frequency flicker-noise component. It is shown that the close mathematical relationship between the two noise sources, disclosed by the analysis, may be of value for the description of flicker noise as observed in real systems.
Magnetostatically Coupled Néel Walls
Authors: Aharoni Amikam
Published: January 2005

The energy of Néel walls between ferromagnetic domains in double films is calculated for a two-dimensional model, for which the various energy terms can be calculated analytically. Minimization of the energy with respect to the wall-width parameter is carried out by an approximation which is shown to be within a few percent of the correct minimum for all practical cases. The energy thus turns out to be close to the Slonczewski approximation, and can be (for adequate film thicknesses) smaller by an order of magnitude than previous, one-dimensional estimations.
Superconducting Hc-Jc and Tc Measurements in the Nb–Ti–N, Nb–Hf–N, and Nb–V–N Ternary Systems
Authors: Yen C. M. , Toth L. E. , Shy Y. M. , Anderson D. E. , Rosner L. G.
Published: January 2005

Superconducting critical fields, current densities and temperatures have been measured as a function of composition in the Nb–Ti–N, Nb–Hf–N and Nb–V–N ternary systems. In the Nb–Ti–N system the upper critical fields increase sharply and monotonically with increasing NbN concentration to over 130 kOe at about 90 mole % NbN. In the Nb–Hf–N system the highest upper critical-field value observed was 130 kOe for the composition Nb0.92Hf0.08N. In the Nb–Hf–N system the Tc increases monotonically with NbN concentration, in the Nb–Ti–N system a maximum in Tc exists at about 65 mole % NbN and in the Nb–V–N system a broad minimum exists between 30 and 50 mole % VN.
High Potentials in Electron-Irradiated Dielectrics
Authors: Gross Bernhard , Nablo Sam V.
Published: January 2005

Bombardment of high-resistivity solid dielectrics with energetic electrons leads to electron trapping and space-charge buildup. The space-charge field in the dielectric can become high enough to reduce significantly the range of the incident electrons. A simple mathematical model gives a semiquantitative picture of the effect. It confirms previous suggestions that the potential in the dielectric might exceed the accelerating potential of the electrons.
Large Electric Power Pulses by Explosive Magnetic-Field Compression
Authors: Conger Robert L.
Published: January 2005

A cylinder of high explosive 1 in. in diameter produces about 1010 W of power during detonation. 10% of this energy can be converted to magnetic field energy by using the explosive to implode a conducting cylinder which contains an initial magnetic field. This energy can be transferred to a resistive load, but if the load is constant, the maximum energy transferred is equal to only the initial field energy times the logarithm of the compression ratio. Computer calculations show that if the load is designed so that its resistance increases by resistive heating during explosive compression, the maximum energy transfer can be much larger.