bluuebunny/crossref_metadata_2025 huggingface dataset:
An Electron Transport Model for the Prediction of X-Ray Production and Electron Backscattering in Electron Microanalysis
Authors: Brown D. B. , Ogilvie R. E.
Published: April 2005

An electron transport equation has been applied to the case of electron—specimen interaction, which is associated with the problems in electron microanalysis. It has been solved numerically to predict the distribution in depth of x-ray production [open phi](ρx), the x-ray absorption correction factor f(χ), and the distribution in energy and angle of electrons backscattered. These results are compared with available experimental data for Al, Cu, and Au.
Scaling Underwater Exploding Wires
Authors: McGrath James R.
Published: April 2005

The parameters of peak pressure and decay time constant of the shock wave caused by electrically exploding wires underwater have been compared to TNT data and theory. The wire used was 5-mil, ½-in. Nichrome. Electrical energy up to 100 J was stored in the capacitor.

The results indicate that peak pressure reduces to the same kind of similitude functions as those used for TNT data if losses owing to the circuit and heating of the wire are accounted for. On this basis, an expression for the equivalent weight of TNT (on the order of micropounds) is presented in terms of the electrical parameters and heat of detonation.

The reduced time constant for exploding wires also reduces to the same kind of similitude function as those used for TNT data. The magnitude and behavior of the reduced time constant are comparable to TNT data.
Effect of Deformation-Induced Crystal Imperfections on Magnetocrystalline Anisotropy of Nickel Single Crystals
Authors: Bhattacharyya Arup , Pollack Solomon R. , Maddin Robert
Published: April 2005

The first magnetocrystalline anisotropy constant of plastically deformed nickel single crystals was studied as a function of deformation. Contributions of specific types of imperfection, viz., interstitials, vacancies, and disclocations on the ``effective magnetic anisotropy constant'' K1′ were analyzed from the recovery characteristics of K1′. The dislocation structure of the deformed crystals was investigated by transmission electron microscopy at various stages of recovery.

The absolute value of K1′ increased with deformation. The maximum change occurred at a strain ε≈0.17 with an increase of about 6.5% from the undeformed value of K1 = −5.52×104±0.02×104 erg/cc measured at 21.5°C and at a magnetic field of 8 kOe. Point defects were not found to have a measurable effect on the recovery of K1′. Deformation-induced dislocations were mainly responsible for the observed change. The recovery of K1′ was interpreted in terms of rearrangement and annihilation of disclocations.
Shear Strength of Silver Chloride
Authors: Towle Laird C.
Published: April 2005

The shear strength of silver chloride has been measured in an inverted extrusion apparatus. Over the temperature range from 520° to 77.4°K it varies from about 50 bars to 1000 bars as the temperature is decreased. Because of its reduced plasticity, silver chloride has only a limited usefulness as a pressure transmitter at 77.4°K or below.
Dislocation Etch Pits in Single-Crystal and Poly crystalline Beryllium Oxide
Authors: Vandervoort R. R. , Barmore W. L.
Published: April 2005

An etching solution is reported which can successfully reveal dislocation sites on the basal, first- and second-order prismatic, and the first-order pyramidal planes of beryllium oxide single crystals. Each of these crystallographic surfaces has an uniquely shaped dislocation etch pit which had not previously been reported. Freshly introduced dislocations on all the above planes were mobile at room temperature under high stresses. Dislocation motion was observed in several directions having low indices. The etchant also revealed dislocation sites in as-sintered and plastically deformed polycrystalline specimens.
X-Ray Spectrometer Performance as a Function of Electron Probe Geometry
Authors: Abelmann Ronald A. , Jones Robert
Published: April 2005

Experimental data were gathered to determine the effect of sample orientation and electron beam incidence on x-ray spectrometer performance. Dispersive counting techniques were used to compare results. The nature of the backscattered electron yield and the relationship to emitted x radiation is discussed. A wide selection of samples was used to study several wavelengths, including the ultrasoft x-ray region. Analytical data include line-to-background ratios to show the results of various investigated parameters.
Comparison of Electron-Radiation Damage Thresholds of Silver at Liquid-Helium and Liquid-Nitrogen Temperatures
Authors: Roberts C. Gordon , Rickey W. P. , Shearin Paul E.
Published: April 2005

The threshold for electron-radiation damage in silver at liquid-helium and liquid-nitrogen temperatures was found to be the same to better than 1 eV.
Cation Self-Diffusion and Electrical Conductivity in Polycrystalline Beryllium Oxide
Authors: De Bruin H. J. , Watson G. M. , Blood C. M.
Published: April 2005

Beryllium self-diffusion coefficients were determined in high-density polycrystalline BeO in the temperature range 800° to 1795°C. A precision lapping method using Be as a radiotracer was used in the interval above 1180°C, and electrical conductivity between 800° and 1250°C. Volume diffusion coefficients determined by both methods correlate well between 1100° and 1250°C. The results can be expressed over the temperature range 1100° to 1800°C by the relation D=3.2×10−3 exp(−63.0×103/RT).

Above 1100°C, the agreement between the results obtained by the two techniques supports an ionic drift mechanism for the electrical conductivity of BeO. Below this temperature, however, the transport behavior appears to be considerably influenced by the history of the sample as well as the nature and concentrations of impurities.

Classical volume diffusion was observed in a region near the surface of the specimens; at greater depths, deviations occurred and the magnitude of the deviations increased with decreasing grain size of the BeO. These discrepancies have been explained on the basis of a simultaneous grain-boundary diffusion mechanism.
Creep of Intrinsic and Gallium-Doped Germanium
Authors: Shea M. M. , Hendrickson L. E. , Heldt L. A.
Published: April 2005

The strain-time characteristics of germanium crystals bent by a constant four point load were studied at temperatures between 450° and 550°C. Bar specimens oriented for single slip were prepared from intrinsic crystals and from p-type crystals heavily doped with gallium; dislocation densities of all specimens before bending were <400 cm−2. The heavy gallium doping prolongs the duration of the initial region of the strain-time curve, which is characterized by an increasing strain rate, and retards the stationary strain rate of the second region. The temperature dependence of the stationary strain rate is described by an activation energy of 1.65 eV for the intrinsic and 1.75 eV for the p-type material. Both the temperature dependence of the creep parameters and the retarding effects of gallium doping reflect the characteristics of dislocation velocities in these crystals.
Magnetic Properties of DyAl2 and NdAl2
Authors: Nereson N. , Olsen C. , Arnold G.
Published: April 2005

The magnetic properties of two dialuminides, DyAl2 and NdAl2, have been investigated by neutron diffraction and susceptibility measurements. Both compounds show Curie-Weiss behavior in the paramagnetic region and are basically ferromagnetic below Curie temperatures of 62°K and 65°K, respectively. At low temperatures, the compound NdAl2 is a pure ferromagnet, whereas DyAl2 is almost completely ferromagnetic, but has the additional property of a weak antiferromagnetic ordering. The susceptibility measurements show an effective moment per molecule of 9.7±0.1 and 3.1±0.05 μB for DyAl2 and NdAl2, respectively. The neutron diffraction data show a rare-earth-ordered saturation moment of 9.1±0.4 and 2.5±0.1 μB on the Dy and Nd atom sites, respectively. The Al atom sites exhibit no measureable moment within the limits of experimental detection (0.5 μB). Both compounds show a temperature-dependent magnetic ordering process which obeys a Brillouin function. The experimental magnetic form factor for both the Dy3+ and Nd3+ ions diminishes more rapidly with increasing (sinθ)/λ than present theory postulates.
Stress—Strain Isotherms for Poly-(Dimethylsiloxane) Networks
Authors: Mark J. E. , Flory P. J.
Published: April 2005

Stress—strain isotherms are presented for poly-(dimethylsiloxane) networks of different degrees of cross linking, swollen to various extents by a diluent. Results are interpreted in terms of the equation f*v213V*/(α−α−2)=2C1+2C2α−1, where f* is the tension per unit initial area (unswollen) exhibited by a network when swollen to a polymer volume fraction v2 and elongated to the relative length α, 2C1 is a parameter of the network structure established by the molecular theory of rubber elasticity, and 2C2 is an additional parameter found to give a better representation of experimental data. Values of C2 obtained for networks are found to decrease as the degree of cross linking is decreased, and the degree of swelling is increased.
Thermal Properties of Molecular Crystals. I. Heat Capacity and Thermal Expansion
Authors: Bondi A.
Published: April 2005

The lattice heat capacity Cvs and especially the difference Cps-Cvs of molecular crystals composed of rigid molecules is shown to be well represented by a suitably modified form of the Leibfried and Ludwig theory of anharmonic crystals. Crystals of low packing density (ρ*<0.65) such as benzene require a (fairly large) heat capacity correction for the heat of lattice defect formation. An empirical correction of the theory is proposed to adapt it for the estimation of Cvs of crystals composed of flexible molecules.

The expansion coefficient (αs) of molecular crystals composed of rigid molecules at 0.7Tm<T<0.9Tm is represented by a universal value of the dimensionless number αs*=αsΔHs/Cvs first proposed by Grueneisen and also derivable from Ludwig's theory of anharmonic oscillator crystals. Variants of αs* are discussed also for hydrogen-bonded crystals and for crystals composed of flexible molecules.
Thermal Properties of Molecular Crystals. II. Thermal Conductivity
Authors: Bondi A.
Published: April 2005

A corresponding states type correlation of the thermal conductivity of polycrystalline molecular crystals is presented which requires as input information only the heat of sublimation, the van der Waals volume of the molecules, and the number of external degrees of freedom per molecule.
Improved Surface Ionization Efficiency by High Work Function Refractory Metals and Alloys
Authors: Husmann Otto K.
Published: April 2005

For continuous one-year operation without deterioration of the surface ionization engine characteristic, the neutral efflux should be in the 0.1% range. For the neutral efflux reduction the Saha equation implies the use of high work function metals. Therefore, tungsten-rhenium alloys and iridium filaments were investigated. For completeness, tungsten and rhenium filaments were also studied with regard to their thermionic work function and threshold temperature for cesium surface ionization. The data were measured in an all-metal guard ring diode with directly heated filament under clean surface conditions. The electron work functions and the threshold temperatures of the tungsten-rhenium alloys increase with increasing amount of rhenium in tungsten. For φ-I≤0.5 eV the electron work function governs the surface ionization.

One porous tungsten-25% rhenium pellet and two porous tungsten substrates chemically coated with rhenium and iridium yielded work functions below those measured with the corresponding filaments. At 10-mA/cm2 cesium ion current density, the neutral efflux from the rhenium coated pellet was, with 2×106 pores/cm2 (traverse counting technique), 1%±0.1%. Under clean conditions 0.3% neutral efflux may be expected. The increase of the threshold temperature with electron work function leads to increased grain size and lower pore density for long term stability of the porous structure.
Direct Determination of the Flow Curves of Non-Newtonian Fluids. IV. Parallel-Plane Rotational Viscometer
Authors: Krieger Irvin M. , Woods Martin E.
Published: April 2005

Analysis of the laminar flow of a non-Newtonian fluid between rotating parallel planes permits the viscosity to be calculated as a function of shear rate from data of torque vs angular velocity. Experimental results are presented which show that the non-Newtonian viscosities thus obtained agree with capillary, Couette, and cone-and-plate instruments over a four-decade shear rate range.
Substitutional-Interstitial Interaction and the Anomalous Snoek Peak in Fe-V-N Alloys
Authors: Perry A. J. , Malone M. , Boon M. H.
Published: April 2005

It has been shown that the anomalous Snoek internal friction peaks observed in Fe-V-N alloys by Fast and Meijering2 can be interpreted as being made up of three distinct contributions. From a study of the manner in which these contributions vary with the free nitrogen level in the alloy, a model is proposed and considered in detail in which between one and three nitrogen atoms reside in the six octahedral sites co-ordinated with a vanadium atom. The three contributions then correspond to jumps by the nitrogen atoms for the cases when one, two, and three interstitials are present. The model allows the evaluation of the interaction energy between a nitrogen atom and either a vanadium atom, a vanadium-nitrogen pair, or a vanadium-di-nitrogen group as about 0.3 eV. The calculated variation of the filling of sites with the free nitrogen level in the alloy is in fair agreement with the resolved contributions to the anomalous peak.
Dielectric Breakdown in LiF Crystals Bombarded by Electrons
Authors: Kubo Kazuko
Published: April 2005

Dielectric breakdown phenomena were observed in LiF single crystals bombarded by electrons of 1–2 MeV. The Lichtenberg figures were developed in a layer which included the range plane of the bombarding electrons. The components of the figures lay in the directions 〈221〉, 〈111〉, 〈114〉, and a few 〈100〉, besides dominant 〈110〉, with small angle deviations. Turns and reflections of the path were found at the boundary of the layer. Structural alterations of the crystal, including edge dislocations, were observed around the large paths. These phenomena, which have not been observed in the previous experiments by the conventional method, are suggested to result from the intense ionization and heating due to electronic avalanches occuring in a rather long period of discharge time, superposing on the damage induced by electron bombardment.
Hugoniot Equation of State of Alkali Metals
Authors: Ehrenfeld J. , Krimsky S. , Selvitella J.
Published: April 2005

The Hugoniot equations of state of the alkali metals have not been directly determined because of severe experimental limitations. In this paper the equation of state is calculated by a technique that has yielded results which are in excellent agreement with existing experimental data for other metals. These calculated results are compared with the experimental data for Al, Cu, Sn, Zn, Pb, and W.
Infrared Reflectivity of Heavily Doped Low-Mobility Semiconductors. I. GaAs
Authors: Murray L. A. , Rivera J. J. , Hoss P-A.
Published: April 2005

The disagreement between experimental measurement of the reflectivity minimum of low-mobility semiconductors and simple theory is accounted for by inclusion of the imaginary part of the dielectric constant in deriving the carrier-concentration/plasma-wavelength relationship. Data on the plasma wavelength of p-type gallium arsenide are presented.
Superconducting Transition Temperature of Solid-Solution Ta–Ti Alloys
Authors: Colling D. A. , Ralls K. M. , Wulff J.
Published: April 2005

The composition dependence of the superconducting transition temperature Tc has been measured for the solid-solution range of the system Ta–Ti. Tc values, determined resistively for heavily cold-worked wire specimens, varied smoothly with composition, exhibiting a maximum of 8.8°K corresponding to a valence-electron-to-atom ratio of 4.5. Little sharpening of transitions was found for annealed samples, and lower values of Tc were obtained. The change in Tc of a nominally equiatomic alloy with heat treatments in the range 300° to 1200°C is discussed in terms of the microstructural changes.
Immersed-Foil Method for Measuring Shock Wave Profiles in Solids
Authors: Ahrens Thomas J. , Ruderman M. H.
Published: April 2005

A new technique is described for measuring, essentially directly, a complex shock front profile that is transmitted into a transparent liquid from a solid material. The image of a grid light source, reflected from a Mylar foil immersed within the liquid, is recorded with a streak camera. Index of refraction data for liquids in the high-pressure shocked state (required for calculating particle velocities from image displacements) are reported for glycerol, ethanol, water, and hexane to 220, 135, 58, and 41 kbar, respectively. The increase of index of refraction with density for water agrees with that reported by Zel'dovich, Sinitsyn, and Kormer, but is considerably less (as are also the results for the other liquids) than that predicted by the Lorentz-Lorenz formula. Hugoniot data obtained concurrently with the refractive index data agree closely with those of Rice and Walsh. Applications of the immersed-foil method are discussed for: (a) determining the release adiabats from shock states produced by a double shock front in a solid; (b) the study of shock wave attenuation in solids; and (3) measurement of the adiabatic sound velocity of liquids in the high-pressure shocked state.
Surface Tension of Solid Tin
Authors: Rice C. M. , Eppelsheimer D. S. , McNeil M. B.
Published: April 2005

The surface tension of solid tin was determined as a function of temperature over a small temperature range near the melting point. The results are considered from the standpoint of the present theories of solid surface tension. Extrapolation of the results to the melting point gives a value of 514 erg/cm2.
Influence of Charged Defects on Mechanical Properties of Lead Sulfide
Authors: Seltzer Martin S.
Published: April 2005

A chemical etch, suitable for revealing dislocation etch pits on cleaved crystals of PbS, has been utilized to reveal rosette patterns formed upon indentation of specimens whose charge-carrier concentration had been fixed by high-temperature equilibration in controlled sulfur pressure. Hardness and rosette wing length are nearly independent of concentration of free electrons in the range 2×1017 to 3×1019 cm−3. This is true for n-type material prepared by introduction of an excess of lead or by addition of a high concentration of bismuth donors to the PbS. Similar measurements on p-type, sulfur excess crystals, pure or containing silver as an acceptor addition, reveal a marked dependence of hardness and wing length on concentration of holes. For hole concentrations above 8×1017 cm−3, rapid hardening is observed with an attendant decrease in rosette size. It is suggested that this behavior results from an electrostatic interaction between charged dislocations and acceptor point defects.
Saturation of Absorption and Fluorescence in Solutions of Phthalocyanines
Authors: Kosonocky Walter F. , Harrison Sol E.
Published: April 2005

Lifetimes of the excited states of phthalocyanines are studied by the irradiation of solutions with a Q-switched ruby laser. By detailed measurements of the saturation of fluorescence and absorption with increasing-pulse laser power, the radiative and the nonradiative lifetimes of S1 as well as the time constants for the S1 → T1 and T1 → S0 transitions are determined. The transition between the ground state and the first excited singlet state in the metal-free as well as the metallophthalocyanine saturates at laser pulse flux power densities of 0.1 to 0.15 MW/cm2. A complete transition of the molecular system from a ground state, S0, into a triplet state, T1, is observed in the case of the metal-free phthalocyanine H2Pc. The triplet state has a relaxation time to the ground state of 1.0 μsec at 300°K and 150 μsec at 77°K. The absence of fluorescence in VOPc and CuPc implies that a third state also is involved in the saturation of the absorption of the metallophthalocyanines. In these solutions, the saturation of absorption recovers with a relaxation time of less than 20 nsec. All the data obtained at room temperature is consistent with a three energy-level model. The lifetime of the first excited singlet state, S1, is determined as ∼2.0 nsec for all Pc's. The radiative lifetime of S1 and the S1 → T1 intersystem crossing time for H2Pc are estimated from the measurements to be about 6 and 10 nsec, respectively.
Background Internal Friction of Some Pure Metals at Low Frequencies
Authors: Routbort J. L. , Sack H. S.
Published: April 2005

The background internal friction of Al, Cu, and Mg at 300°K was investigated as a function of plastic deformation, gamma-ray and neutron irradiation, and frequency (1 cps–40 kc/sec). The results suggest that the Granato-Lücke vibrating-string model does not adequately describe the results at low frequencies.
Quantum-Counting Spectroscopy
Authors: Brown M. R. , Strain R. J.
Published: April 2005

Techniques are described for using quantum-counting cycles to extract spectroscopic information about the active media. Experimental results from the near and far-infrared regions are presented, and these illustrate the utility of the method for measuring transition energies, transition linewidths, and lifetimes. Materials studied are Er3+ in various fluoride host lattices and dark ruby.
Effect of Thermal Fluctuations on the Anhysteretic Process in Ferromagnetic Fine-Particle Assemblies
Authors: Kneller E. , Wohlfarth E. P.
Published: April 2005

The temperature dependence of the ``ac melting curve'', introduced in a recent paper, has been estimated theoretically, taking as an example a carbonyl iron powder for which measurements at 77°K and 300°K are presented. The theory is based on considerations of thermal fluctuation phenomena, and the estimated shift of the curves as the temperature is changed is in reasonable agreement with observation. The various approximations involved in the calculation are stated and the implications of the results discussed.
Optical Properties and Color-Center Formation in Thin Films of Molybdenum Trioxide
Authors: Deb S. K. , Chopoorian J. A.
Published: April 2005

The optical absorption spectrum of thin films of MoO3 has been measured over the temperature range from 77° to 290°K. The fundamental absorption edge occurs at 3300 Å with an absorption coefficient of 105 cm−1. A stoichiometric film of MoO3 shows three absorption peaks at 3350, 2880, and 2700 Å, respectively, and these are suggested to be due either to exciton formation or to transitions involving a split valence band.

Values for the refractive index have been measured in the wavelength range 0.42–1.2μ. The low-frequency dielectric constant (18.0±1) has been measured and the comparison with the high-frequency dielectric constant (5.70) indicates that the bonding is predominantly ionic.

The electrical conductivity has been measured on a polycrystalline sample in the temperature range 298° to 900°K and the activation energies of conduction found to be 1.83 eV (intrinsic) and 0.56 eV (impurity).

On irradiating a thin film (0.2μ) of MoO3 with light of wavelength shorter than 3300 Å, three color-center bands having maxima around 5000, 6250, and 7700 Å are formed. The same type of color centers are also formed on heating the film in oxygen in inert atmosphere. The color centers thus formed cannot be bleached optically. However, they can be bleached thermally in oxygen at 300°C. The growth and decay of color centers has been studied in detail.

The formation of color centers is associated with increased dark conductivity of the MoO3. Very weak photoconductivity and photovoltaic effects with threshold energy corresponding to the fundamental absorption edge at 3300 Å have been observed.

An ESR signal characteristic of Mo5+ state has been observed in a film of MoO3. There is a small increase of ESR signal on color-center formation which disappears completely on heating in air at 300°C.

An energy-level diagram has been proposed to account for the optical and electrical properties as well as the color-center formation in MoO3.
Calculation of Upper Bounds to the Small-Angle Scattering from Crystallite Models of Amorphous Materials
Authors: Bienenstock Arthur , Bagley Brian G.
Published: April 2005

The inability of experimentalists to observe small-angle x-ray scattering from single-phase liquids and amorphous solids has been considered, by many workers in the field, to invalidate a crystallite model for these materials. In this work we calculate the intensity of small-angle x-ray scattering from two crystallite models which are designed to yield upper bounds to the actual scattering. The calculated upper bounds are, in general, considerably lower in intensity than the scattering from isolated particles. The results are extremely sensitive to the density and average crystallite size of the sample, so that general conclusions about the observability of such scattering cannot be made. The particular case of vitreous SiO2, which was examined experimentally by Warren and Weinberg, has been studied in detail. For this case, the calculated scattering intensity is of the same order of magnitude as that observed by these authors. Thus, it is concluded that the failure to observe small-angle scattering from vitreous SiO2 does not invalidate a crystallite model for that material. It should be noted that the calculation does not, on the other hand, offer any evidence for the existence of crystallites.
Scanning Electron Microscopy of Graphite Growth in Iron and Nickel Alloys
Authors: Minkoff I. , Nixon W. C.
Published: April 2005

Principles of the scanning electron microscope are outlined, and a description is given of an instrument and techniques which have been employed for high-resolution microscopy of graphite crystals. Growth processes of graphite in iron—carbon and nickel—carbon alloys have been studied, with observations of crystals at magnifications of up to ×20 000. The paper presents an initial summary of some of the observations which have been made. It is shown that an element in solution of the type which spheroidizes graphite adsorbs on the crystal surface and blocks growth. For a limited adsorption of impurity, holes are formed in the crystal surface. The blockage of growth increases in extent as the melt concentration of impurity increases, eventually suppressing normal flake development. Branched crystals are associated with the initial stage of impurity adsorption, and spherulitic crystals with a later stage corresponding to total surface coverage.
Thermal and Optical Energy Gaps in PbTe
Authors: Tauber R. N. , Machonis A. A. , Cadoff I. B.
Published: April 2005

The optical absorption edge (indirect energy gap) for PbTe was determined in the temperature range of 80°–520°K. It was found that dEg/dT had a value of 4.1×10−4 eV/°K in the temperature range from 80°–350°K, while above 400°K, dEg/dT was approximately zero. The low-temperature linear portion extrapolated to 0.19 eV at 0°K while the high-temperature portion extrapolated to 0.36 eV. This behavior is explained by a two-valence band model, one active at low temperatures, the other in the high temperature range.

A thermal energy gap of approximately 0.36eV was obtained from the temperature variation of resistivity and Hall coefficient in the intrinsic range, 500°–900°K. This value agrees with the high temperature optical data extrapolated to 0°K, thus correlating the optical and thermal energy gaps.
Superconducting Properties of Nb6Sn5 and of Multiphase Nb–Sn Alloys
Authors: Enstrom Ronald E.
Published: April 2005

The critical temperature of Nb6Sn5 is less than 2.8°K and the maximum critical field is less than 600 G at 2.1°K. Since NbSn2 also has a transition temperature below 4.2°K, Nb3Sn is the only compound in the Nb—Sn system that is superconducting at 4.2°K. Nb3Sn can be formed at temperatures as low as 600°C, and accounts for the observed high-field superconductivity in multiphase alloys where Nb6Sn5 or NbSn2 may be the predominant phases present.
Selective Etch for New Edge Dislocations in Sodium Fluoride
Authors: Davisson J. W. , Levinson Solomon
Published: April 2005

A simple etch consisting of a dilute aqueous solution containing manganous ions has been found to selectivity etch new edge dislocations in sodium fluoride. With this etch the new edge dislocations produced deep pits based on the icositetrahedral form, whereas all other dislocations yielded shallow cones. The selective etching action was decreased with increase of manganous ion concentration and with increase of the impurity content of the edge dislocation. The selective etching action is attributed to the combined effect of the elastic energy and the core energy of the new edge dislocation.
Carrier Lifetime in Photoconductive InAs
Authors: Borrello S. R.
Published: April 2005

The majority carrier lifetime associated with the photoconductivity of heavily doped n-type InAs has been found to depend exponentially on the reciprocal absolute temperature between 300°K and 140°K. Lifetimes were found to range from 10−8 sec at 300°K to nearly 10−3 sec at 100°K. Measurements indicate that lifetime is determined by recombination centers located 0.23 eV below the conduction band that are probably ionized donors. The temperature dependence of the lifetime above 140°K is interpreted in terms of the temperature variation of the recombination center density. Below 100°K the density of recombination centers is determined by absorption of 300°K background radiation.
Theory of a Plasma Resonance Probe in a Magnetic Field
Authors: Wait James R.
Published: April 2005

An analysis of the spherical probe immersed in a magnetoplasma is presented. A quasistatic theory is used and the electron plasma is assumed to be homogeneous, cold, and lossless. The sheath is idealized as a concentric vacuum layer of constant thickness. By using a special coordinate transformation, it is shown that the condition for probe resonance may be written in uncoupled form. A particularly simple result is obtained for the lowest-order symmetric mode for small sheath thickness.
High-Pressure Phase-Equilibrium Studies of CdS and MnS by Static and Dynamic Methods
Authors: Miller R. O. , Dachille F. , Roy R.
Published: April 2005

The P-T equilibrium of CdS polymorphs was studied in the range to over 50 kbar and 700°C in opposedanvil and hydrothermal pressure apparatuses. Use of CdS of diverse origins revealed important effects of structure, preparations, and mechanical treatment on polymorphic transitions, especially noticeable in electrical resistance discontinuities with pressure or temperature changes. A triple point was located at 425°±5°C and 16.5±0.5 kbar between the phase fields of CdS-I (wurtzite, and also CdS-I′, metastable sphalerite), CdS-II (rocksalt structure) and CdS-III (a new polymorph, presumably of B23 structure). The slopes of the I to II, I to III, and II to III phase boundaries are 130°, −47°, and 1.6°C/kbar, respectively.

Resistivity of the II phase was found not to be ``metallic.'' The large drop in resistance during the I–II reconstructive transformation is attributed to a grain boundary conduction mechanism.

The P-T-X of the system MnS-CdS was determined to 600°C and 40 kbar. A maximum of 80 mol % CdS was found in a quenchable II phase, but the III phase could not be quenched at any composition.
Effects of Saturable Absorber Lifetime on the Performance of Giant-Pulse Lasers
Authors: Erickson L. E. , Szabo A.
Published: April 2005

An earlier paper on the theory of saturable absorber giant-pulse lasers is extended by considering the effects of a finite absorber lifetime ts on the pulse parameters. Digital-computer studies show that for typical systems the giant-pulse energy and peak power are practically unchanged from the case for which ts → ∞. A new result is that the initial cavity photon density or, alternately, the pump power, must exceed a threshold value to proceed from the region of initial normal lasing to giant pulsing. The role of the pump in the pulse buildup from noise is examined, in particular the transition region between the low-level behavior described by Sooy and the onset of absorber saturation. The ratio of photon density in the transition region to the peak density is shown to provide a measure of the product of the ratio of absorber-to-laser cross section times the absorber lifetime. Some possible mechanisms which lead either to mode selection or mode locking in passive Q-switched lasers are discussed.
Kinetics of Wetting of Surfaces by Polymer Melts
Authors: Schonhorn H. , Frisch H. L. , Kwei T. K.
Published: April 2005

The kinetics of wetting of both high-energy (aluminum, mica) and low-energy (FEP Teflon) surfaces by thermostated polyethylene and ethylene-vinyl acetate copolymer melts in air were followed by the rate of approach of the apparent contact angle θ to its final value θ∞ and the change of the radius of the base of the polymer melt drop, r, with time. The volume of the drops studied varied from 0.006 cm3 to 0.028 cm3 and θ could be studied in the interval from about 100°>θ≥θ∞. The melted polymer drops maintain the shape of a spherical segment. The reduced dimension r/r0, where r0 is the value of r when the contact angle is 90°, is a universal function of the reduced time aTt, a dimensionless quantity. The reduced contact angle cosθ/cosθ∞, where cosθ∞ is the value of cosθ at infinite time, can be represented by a function of the same variable aTt. The shift factor aT is given by γ/Lwη, where γ is the surface tension of the liquid, η is the viscosity, and Lw is a length characteristic of the polymer-substrate system.
Ferromagnetic Domain Wall Interactions using Lorenz Electron Microscopy
Authors: Kallor J. , Paul D. I. , Tobin A.
Published: April 2005

We have investigated the interactions of magnetic domain walls with precipitates, dislocations, and grain boundaries in Ferrovac iron foils by means of Lorenz electron microscopy. Our results show that dislocations and grain boundaries do not significantly impede domain wall motion compared to precipitates and holes. Also, our results support the concept of nucleation of spike domains of reverse magnetization from grain boundaries, the nucleation energy being found equal to or less than 1.3-Oe applied field. Photographs are presented of both single-spike and double-spike domain configurations at grain boundaries.
Multiple Source Moiré Patterns
Authors: McCurry R. E.
Published: April 2005

Moiré patterns produced by viewing a large number of spatially periodic light sources through an appropriate grid structure of similar periodicity are sometimes characterized by a spatial location away from the grid structures. This paper gives a simple geometrical obstruction theory of this effect. It also demonstrates that the results predicted are observable.
Multiple Source Moiré Patterns with Photographic Diffraction Gratings
Authors: McCurry R. E.
Published: April 2005

Moiré patterns of the multiple source type can be used in the evaluation of line shape, line spacing, and grating plane separation of two nearly identical gratings. For line spacing analysis, the location of the MP indicates which of the gratings has the greater line spacing in a particular region. A difference in the average spacing of the order of one part in 107 between adjacent lines has been detected.
Pair Spectra Involving Donor and/or Acceptor Germanium in GaP
Authors: Gershenzon M. , Trumbore F. A. , Mikulyak R. M. , Kowalchik M.
Published: April 2005

Photoluminescence spectra were obtained between 20° and 298°K for GaP crystals containing germanium alone or in combination with shallow acceptors (zinc or cadmium), or shallow donors (tellurium or selenium), or a deep donor (oxygen). Emission bands at 77°K at 1.942, 1.907, 1.823, 1.815, 1.38, and 1.59 eV were correlated, respectively, with the simultaneous presence of both germanium and zinc, germanium and cadmium, germanium and tellurium, germanium and selenium, germanium and oxygen, and germanium alone. The shift between the zinc-germanium and the cadmium-germanium bands was just the difference in binding energies between the two shallow acceptors, indicating that the emission was due to donor-acceptor recombination between the shallow acceptor and a deep germanium donor level of binding energy ≤0.36 eV. Similarly the shift between the tellurium-germanium and selenium-germanium bands indicated pair recombination between the shallow donor and a deep germanium acceptor of binding energy ≤0.45 eV. The band associated with germanium alone corresponded to a pair band involving both donor and acceptor germanium, the maximum in the emission corresponding to a much smaller donor-acceptor separation (18 Å) than for the bands involving shallow levels (52 Å) because the carriers are more tightly bound in the former case. The band at 1.38 eV was ascribed to a pair band between oxygen donors and germanium acceptors. Thermal quenching of the emission bands was predominantly due to thermal release of minority carriers after (efficient) capture by the ionized deeper level of the pair in the compensated samples.
Threshold Energy for Avalanche Multiplication in Semiconductors
Authors: Hauser J. R.
Published: April 2005

The threshold energy for carrier multiplication Ei in Ge, Si, and GaAs is calculated theoretically. The theoretical values of Ei are obtained from a consideration of the semiconductor energy band structure along with energy and crystal momentum conservation in the ionization process. Calculated values are found to be consistent with experimental data.
Ion Collection in the Bayard-Alpert Gauge
Authors: Comşa George
Published: April 2005

A collecting factor for ions created at a given distance is computed on the basis of a simplified model and under the assumption of a Maxwell distribution of the initial velocities of ions. The factor is independent of the mass of the ion, but is a function of the temperature and takes values differing substantially from unity for usual dimensions of the collector.

The effect of the collector dimensions on the x-ray-limited pressure may be analyzed by using an approximate expression for the integral collecting factor.

Calculation shows that for very fine collecting wires the collecting factor is affected even by the extremely small momentum transferred to the helium ion from the electron during the ionizing collision. Experiments have confirmed the foregoing considerations, thus opening the way to the measurement of such momenta.
Phase Changes in Mg-Cd Alloys in the Region of Mg3Cd
Authors: Edwards D. A.
Published: April 2005

A magnesium-rich phase and a cadmium-rich phase have been found to coexist for 25 and 30 at.% cadmium over temperature ranges of about 10 and 2 C°, respectively. With changing temperature, x-ray diffractometer tracings of the (004) and (110) reflections showed a pair of peaks associated with each phase, one increasing in intensity while the other decreased. The appearance or disappearance of one pair of peaks established the temperature boundaries of the two-phase region. Lattice parameters, calculated from the positions of these peaks, changed with temperature in a nonrectilinear manner which indicated maximum changes in composition of 2% and 1% for the 25% and 30% alloys, respectively. The sudden increase or decrease in the intensity of the (101) superlattice line confirmed the upper boundary of the region. Relative amounts of the phases, as determined from areas of the peaks, agreed with the relative amounts determined by applying the ``lever law'' to the revised phase diagram. These results suggest an ordinary first-order phase transformation. Moore and Raynor reported two phases of the same composition for Mg3Cd. However, Kamath, Craig, and Wallace found phases of different composition for MgCd3.
Dislocation Damping in Dilute Lead Alloys
Authors: Hinton T. , Rider J. G.
Published: April 2005

Internal friction has been measured at 4 kc/sec on single crystals as a function of strain amplitude, temperature, and composition in a series of Pb-In alloys, and one Pb-Sn alloy. The compositions are in the solid solution range. The results are discussed in terms of the theory of Granato and Lücke. There is a considerable measure of agreement between experiment and theory regarding the functional relationships between the various parameters. The binding energy of a dislocation to both In and Sn solute atoms is found to be 0.10 eV. There is some evidence that thermal unpinning may be playing a part. Some measurements on the effect of etching surface layers and of growth rate are described which demonstrate the structure sensitivity of internal friction.
Partial Switching Behavior in Ferroelectric Triglycine Sulfate
Authors: Taylor G. W.
Published: April 2005

Experimental techniques were developed for measuring t*, the threshold time for stable partial switching in ferroelectrics. Measurements made on triglycine sulfate showed that t* decreases with temperature and applied field, and increases slightly with crystal thickness. Also the ratio of t* to ts, the total switching time, was found to increase sharply with grinding of the crystal surface. The transition in the partial switching properties at t* was observed to be sharp rather than absolute. The t* results seem to be explained satisfactorily by the Fatuzzo-Merz three-stage switching model of surface nucleation, followed by forward and then by sidewise growth. If this interpretation is accepted, then the results indicate that t* is the natural division between forward and sidewise growth. If this is correct, then t* measurements can be used for calculating forward and sidewise wall velocities.
Current-Voltage Characteristics of Dielectric Films
Authors: O'Dwyer J. J.
Published: April 2005

The current-voltage characteristic of insulating films is usually regarded as being due to quantum-mechanical tunneling for very thin films, and as being space-charge-limited for thicker films. Using an electronic model of a dielectric which was first introduced to explain dielectric breakdown, the current-voltage characteristic is derived taking explicit account of field emission from the cathode and space-charge buildup in the body of the dielectric. The characteristic is non-Ohmic and dependent on thickness and temperature.
Sputtering of Polycrystalline Gold by Fast Neutrons
Authors: Norcross D. W. , Fairand B. P. , Anno J. N.
Published: April 2005

The atomic sputtering by fast neutrons incident upon a thin gold foil target was determined by measuring the activity of radioactive gold atoms collected during continuous exposure of the target to a known fast-neutron flux. The sputtering ratio (atoms of gold sputtered per fast-neutron-crossing the surface of the target) was found to be (1.0±0.3)×10−4, assuming an isotropic neutron flux and negligible thermal-neutron contribution to the sputtering.
Anelasticity Due to Intrinsic Defects in GaAs
Authors: Chakraverty B. K. , Dreyfus R. W.
Published: April 2005

Defects in GaAs crystals were studied by internal friction. Measurements (at 10 kc/sec) show a damping peak at 140°C, corresponding to a single activation energy of 0.7 eV. The peak occurs for crystals stressed in both [111] and [100] directions. The fact that the peak height can be varied by treatments in arsenic vapor, but is not related to grown-in impurities, suggests that an intrinsic type of defect causes the peak. A nearest-neighbor pair of Ga vacancies is the simplest defect which can explain the observed peak. The possibility that the damping peak is due to isolated Ga vacancies, or to defects occupying neighboring Ga and As sites, is ruled out.
Small-Angle X-Ray Scattering Determination of Particle-Diameter Distributions in Polydisperse Suspensions of Spherical Particles
Authors: Letcher J. H. , Schmidt P. W.
Published: April 2005

A scheme is developed for using small-angle x-ray-scattering data to find the distribution of the particle diameters in dilute colloidal suspensions of noninteracting spherical particles. No assumptions need to be made about the form of the distribution function. An investigation is made of the errors likely to be introduced in the numerical operations on the data. The method was tested on theoretical scattering curves for which the calculations could be done both numerically and analytically. After these tests showed the feasibility of the calculation, diameter distributions were computed from the x-ray small-angle scattering data from some polydisperse colloidal samples composed of spherical particles. The results suggest that this technique may often be a useful procedure for analysis of small-angle x-ray-scattering data.
Determination of Electron Densities in dc Discharges with the Aid of Probes
Authors: Barnes Bentley T.
Published: April 2005

Oscillation-free arcs were operated at 1.4 or 1.0 A in a tube with a 34 mm i.d. and a filling pressure of 7 Torr for neon, and 1–2 Torr for Ar, Kr, and Xe. Probes, including one moved radially, were used to determine positive column characteristics, particularly the axial electron density n0. In each computation, corrections were made for the radial variation of gas temperature. The electron density distribution, n/n0 vs r, was not determined with the desired accuracy. Disturbance of the discharge made the probe current rise too rapidly as the probe approached the axis. After due allowance for errors, n/n0 in the neon discharge seemed to vary roughly as the Bessel function J0 (2.33 r/R), where R=radius of positive column. With the heavier gases there was some evidence of a slight constriction of the discharge, presumably due to dissociative recombination of molecular ions formed in the cooler regions near the tube wall. Plausible curves for n/n0 vs r can be drawn to make n0 values computed from the ambipolar flow of charge agree roughly with those derived from the current, at space potential, to a very small probe at the axis of the tube. Ion current to this probe gave values that were usually somewhat larger, and depended on the probe voltage. Collisions with ions made the electron mobility calculated for the Ar discharge only 45% of that based on atomic collisions alone. With Kr this value was 60%. Computed arc currents ranged from 0.63 to 1.53 times the actual values.
Sputtering of Single-Crystal Copper
Authors: Snouse T. W. , Haughney Louis C.
Published: April 2005

Sputtering yields from the (111), (100), and (110) planes of copper single crystals were measured as a function of normally incident argon-ion energy over the range from 100 to 200 000 eV. A comparison of the ratios of the yield curves as a function of ion energy reveals that lattice ``transparency'' is apparently not sufficient for a complete theoretical description of the sputtering process.
Precipitation in NaCl-KCl Mixed Crystals
Authors: Wolfson R. G. , Kobes W. , Fine M. E.
Published: April 2005

The mechanical properties of precipitation-hardened dilute mixtures of KCl in NaCl were studied. Two peaks in the flow stress occur. The suggested sequence of events is growth of coherent KCl-rich platelets, loss of coherence, growth of incoherent KCl-rich platelets, and finally recrystallization. The fracture stress is maximum for a long aging time considerably beyond the second hardness peak where the presence of rather coarse precipitates interferes with the cleavage process and increases the energy to propagate a fracture. This is an important principle for increasing the fracture strength of ceramics.