bluuebunny/crossref_metadata_2025 huggingface dataset:
Noncoherent Switching in Permalloy Films
Authors: Smith D. O. , Harte K. J.
Published: April 2005

High resolution Bitter pattern studies of the domain structure of permalloy films, with uniaxial anisotropy Hk and under the influence of applied fields in the film plane, are reported, and from these studies are inferred some aspects of noncoherent flux reversal processes. The threshold field for irreversible domain propagation across the film is measured for a variety of films differing in thickness (150 to 1100 A), rate of deposition (30 to 1100 A/min), substrate temperature (100 to 350°C), and composition (80 to 83.5% Ni), as a function of the angle α between the reversing field and the easy axis, after saturating along the opposite easy direction. For α<αc, where αc depends on thickness and preparation variables and varies from 0° to about 60°, reversal takes place by parallel wall displacement, with a wall coercive force Hw characteristic of the film. Two principal structural features have been identified as affecting Hw: Nonmagnetic inclusions, and local easy axes in the film plane normal to the main easy axis (negative Hk). In films thin enough to support Néel-type walls, long perturbation walls are generated when a domain wall collides with an inclusion (or hole); these perturbation walls, which appear to be some form of 360° (or 720°, etc.) wall separating head-on parallel domains, require several hundred oersteds for removal. Negative Hk, which is demonstrated by high-angle buckling combined with low angular anisotropy dispersion, is readily found in films with hw=Hw/Hk>1, and is believed to be directly correlated with hw. For α>αc, reversal takes place by labyrinth propagation, in which the walls remain relatively fixed, and long, slender domains develop from the tip leaving behind regions of unswitched material, resulting in a labyrinth-like flux pattern. The labyrinth threshold is nearly parallel to the threshold for coherent rotation, but below it by an amount which increases with decreasing film thickness. A model for labyrinth propagation, which treats the film as being composed of regions of differing Hk, with magnetostatic interactions coupling a region undergoing switching to unswitched and previously switched regions, predicts the direction of propagation and its thickness dependence in reasonable agreement with experiment, and is partially successful in explaining the labyrinth threshold. It is suggested that labyrinth propagation is the primary mechanism of intermediate-speed pulse switching (switching time ≳0.1 μsec); the correlation between intermediate- and high-speed threshold fields, and angular and amplitude anisotropy dispersion, is examined. Finally, the high-speed switching mode (τ<0.1 μsec) is considered; the intrinsic damping for this mode is found to be about four times the damping deduced from ferro-magnetic resonance linewidth or from free oscillations of the magnetization, indicating that even for switching times approaching 1 mμsec reversal does not take place by a completely coherent rotation.
Reduction of Contamination in Reflection Electron Diffraction
Authors: Yoda Eiji , Siegel Benjamin M.
Published: April 2005

The rate at which contamination forms on surfaces exposed to electron beams in reflection electron diffraction has been investigated for electropolished single crystals of copper and cleavage faces of alkali halide crystals by observing the decrease of the intensity in the diffraction pattern. It was found that a cold chamber at liquid nitrogen temperatures surrounding the specimen reduces the contamination rate on copper by an amount directly proportional to the solid angle through which the specimen is exposed to the vacuum system, and at the smallest aperture lowers the rate by as much as 2 orders of magnitude. Color centers were produced in the alkali halide crystals exposed to the electron beam. The resultant imperfections in the crystal lattice apparently affected the diffraction spot intensity, making measurement of contamination rates by this method unsatisfactory.
Analysis of the Preferred Orientation of a Small Sample of Crystals with Applications to Sodium Single Crystals
Authors: Weymouth John W. , Soepono Raden
Published: April 2005

A method is presented for a statistical analysis of the preferred orientation of a small sample of single crystals. The growth axes of the crystals, as plotted in stereographic projection, are grouped into cells subdividing the standard stereographic triangle and are analyzed in terms of a multinomial distribution subjected to a goodness-of-fit test with respect to an assumed distribution. The method is applied to a sample of 31 single crystals of sodium grown in small glass capillaries with a thermal gradient along the capillary axis. An assumed random distribution is subjected to a chi-square test with the conclusion that it is not random, but has a 〈111〉 preferred orientation. The analysis of a smaller sample is exemplified by that of six sodium crystals taken from the literature. A random distribution hypothesis is subjected to a likelihood-ratio test and is accepted in this case, although visual inspection might lead one to infer a 〈100〉 preference. The importance of the orientation of bcc sodium with respect to data on the orientation of fcc lead is also discussed.
Current Voltage Characteristics of Germanium Tunnel Diodes
Authors: Nathan Marshall I.
Published: April 2005

The current-voltage characteristics of germanium tunnel diodes with phonon assisted current predominant have been measured for reverse biases at 297°K. The tunneling exponent is deduced from the data and found to be in agreement with that obtained from high pressure experiments. The value of the pre-exponential factor obtained from both experiments is much larger than predicted by theory. Calculations of the tunneling current which take into account nonparabolic effects of the energy band structure and the electric field variation with position in the junction are presented and compared with experiment. The results of current-voltage measurements on germanium diodes with non-phonon current predominant are also presented and discussed.
Re-Emission of Ionically Pumped Helium by Helium Ion Bombardment
Authors: Carmichael J. H. , Waters P. M.
Published: April 2005

Measurements have been made of the release of ionically pumped helium gas when the metal is bombarded with helium ions. The re-emitted helium is distinguished from the bombarding helium by the use of a mass spectrometer and by using either He3 as the bombarding atom and He4 as the trapped atom, or vice versa. The data are presented as a function of: (1) the amount of gas initially trapped, (2) the number of bombarding ions, (3) the initial kinetic energy of the trapped atoms, and (4) the kinetic energy of the bombarding ions. Comparison of these data with those obtained using krypton as the bombarding ion is made and indicates quite different behavior in the two cases. A replacement mechanism is more consistent with the data where helium is the bombarding ion. The corresponding data using krypton had been satisfactorily explained by sputtering of the metal target.
Landau Damping of Space-Charge Waves
Authors: Berghammer J.
Published: April 2005

The current modulation excited by a sinusoidal voltage across a narrow-gap resonator on an electron beam with a Maxwellian distribution of velocities is treated on the basis of the linearized Boltzmann equation without collisions. The numerical part of the analysis reveals that the current modulation as function of distance has the form of a damped sinusoid, with finite minima, and approaches a constant level at large distances. These results are in qualitative agreement with experimental observations reported elsewhere. The analytical results show that the fast space-charge wave of monovelocity theory is replaced by a continuum of waves (for ωp<ω). This fast-wave packet decays with distance because of phase mixing, so that only the slow space-charge wave survives at large distances. The spatial decay of the fast-wave packet is the equivalent in multivelocity beams of temporal Landau damping in stationary plasmas.
Oriented Tungsten Deposition
Authors: Barnett Gordon D. , Miller Arnold
Published: April 2005

This report describes a series of reaction deposition studies directed toward the formation of oriented or epitaxial tungsten films on single-crystal tungsten by the hydrogen reduction of tungsten hexafluoride at low pressure. In addition, a novel method for controlled etching of tungsten by tungsten hexafluoride for surface pretreatment and as a tool for elucidating metallurgical structure is given. The use of this hexafluoride etching technique for surface pretreatment does not insure oriented deposition, but with the proper control of other factors such as system cleanliness, reactant material purity, deposition rates, etc., oriented or epitaxial deposits have been formed.
Activation of Thermionic and Photoelectric Cathodes
Authors: Klemperer D. F.
Published: April 2005

Thermal regeneration of an adsorptive capacity in oxidized metals and semiconductors is identified with a nonspecific tendency for oxygen atoms to bury themselves. This process, which often occurs at room temperature, leads to a positive surface potential, and the thermionic or photoelectric emission of electrons is enhanced. Photoelectric measurements which are in line with this view are presented for titanium undergoing interaction with oxygen. The emission value of the clean metal was doubled after thermally regenerating the surface at 400°C.

Activation of the electron emission of surfaces bearing thin skins of foreign oxides is ascribed to a surface configuration which is essentially similar to that of thermally regenerated metals and semiconductors. The emission from oxide-coated cathodes (thick layers of foreign oxides), is regarded as a maintained form of exoelectron emission which arises from innumerable donor centers produced during the activation process; electrons which have been emitted are replaced from the underlying metal.

Attention is finally drawn to the use of electronegative elements other than oxygen for increasing the electron emission of metal surfaces.
Stacking Faults in Epitaxial Silicon
Authors: Queisser H. J. , Finch R. H. , Washburn J.
Published: April 2005

Stacking faults have been detected in etched thin foils of epitaxially grown silicon by means of optical and electron microscope transmission techniques. The faults lie in (111) planes and either form closed figures or are bounded by dislocations.
A Qualitative Model for Amplitude Dependent Dislocation Damping
Authors: Gelli D.
Published: April 2005

A two-mechanism model for dislocation damping, which should be valid in the cases of rather dense Cottrell atmospheres, is proposed. The first mechanism arises from the movement of the vibrating dislocation inside the most dense (axial) region of the atmosphere, while the second one, which can be identified with the well-known mechanism by Granato and Lücke, takes place at higher amplitudes of vibration, arising from the movement of the dislocation in the (external) low-density region of the atmosphere. Both mechanisms involve an amplitude dependent and an amplitude independent component of the decrement. A butterfly-shaped hysteresis loop is obtained which is the synthesis of one loop of the type proposed by Nowick and by Weertmann and Salkowitz with two loops of the type proposed by Granato and Lücke. In addition, the results of some experimental measurements, carried out on 99.995% aluminium for checking the qualitative features of the model, have been reported.
Rf Current Behavior in Electron Beams with dc Velocity Spread
Authors: Mihran T. G.
Published: April 2005

This paper presents experimental and theoretical work on the behavior of rf currents in electron beams which possess a spread of dc velocity. Experimentally an attenuation or damping of rf current with distance is noted. This attenuation is studied as a function of both velocity spread and space charge. Simple ballistic theory suffices to explain the damping rate for the first half space-charge wavelength. A more exact distribution function analysis fails to give agreement much beyond this point. Qualitative disagreement with the exact theory occurs at a distance of one space-charge wavelength. Here distribution function theory predicts a recovery of the current maximum over its previous value whereas experimentally monatonic damping is found. The failure of distribution function analysis to explain the observed current behavior in this simple case makes the validity of its application to the noise problem in microwave tubes somewhat questionable.
Theory of Noise in Magnetic Recording Tape Coated with Magnetic Particles
Authors: Mikami Itsuo
Published: April 2005

A theoretical investigation is made on the mechanism of noise in magnetic recording tape coated with magnetic particles. It is shown that, for the tape in saturated remanence, noise does not originate from the finite size of particles, but from other factors such as finite concentration of particles, voids, aggregation of particles, and periodic imperfection. For demagnetized tape, however, those factors give a negligible noise. Hence, the origin of noise in the magnetized tape differs from that in the demagnetized one.

It is also shown that the theoretical results agree with the experiments by taking into account the fact that the true volume of single particles is smaller than the apparent volume. The theoretical signal-to-wideband-demagnetized-tape-noise ratio is independent of tape velocity and is about 56 db for the commercial audio tape of ¼-in. track width.
Heat Intensity and Current Density Distributions at the Anode of High Current, Inert Gas Arcs
Authors: Nestor O. H.
Published: April 2005

Heat transfer intensity and current density distributions at the anode of high current arcs in predominantly inert gas atmospheres were determined experimentally. Measurements were made for stable, axially symmetric arcs having a small diameter refractory metal cathode and a plane, cooled copper anode. The experimental method consisted of splitting the anode, measuring the heat flux and the current to one of the sections as a function of arc position relative to the splitting plane, and calculating therefrom the distribution functions. The work encompassed the effects of gas pressure (195–790 mm Hg), cathode geometry and material (tungsten and W-1% ThO2), electrode separation (1.6–12.7 mm), arc current (100–300 amp), gas composition (argon, helium, and diatomic gas-argon mixtures), and localized constriction of the plasma column. Peak heat transfer intensities ranged from 1.0 to 20 kw/cm2 and peak current densities from 100 to 2500 amp/cm2. The heat and current distribution curves were of similar shape and were generally sharper than Gaussian. The heat distributions were partially resolved according to transfer mechanism. An upper limit was set on the average kinetic energy of electrons arriving on axis at the anode. This was used to specify limits on gas heat transfer intensities for certain conditions. The space charge sheath at the anode was estimated to be 10−4 to 10−3 cm thick at the arc axis.
Charge Multiplication in GaP p-n Junctions
Authors: Logan R. A. , Chynoweth A. G.
Published: April 2005

Charge multiplication arising from carriers injected into p-n junctions in gallium phosphide has been studied as a function of applied bias. From these and capacitance studies, the carrier ionization rate as a function of field has been determined. It is found to be very similar, both qualitatively and quantitatively, to the behavior in silicon. In particular, the mean free path for hot carriers between collisions involving optical phonon emission is of the order of 100 A. An additional result obtained from simple analysis of the photoresponse and capacitance behavior of the junctions is that the dominant carrier lifetime is 10−10 sec.
Diffusion of Al26 and Mn54 in Aluminum
Authors: Lundy T. S. , Murdock J. F.
Published: April 2005

Diffusion coefficients of Al26 and Mn54 in aluminum have been determined between 450° and 650°C. Low specific activities of the isotopes necessitated use of a thick layer technique. The exact solution to Fick's second law for the appropriate boundary conditions was used in treating the data. Temperature dependence of the diffusion coefficients may be expressed by the following equations: DAl26=1.71 exp−(34 000/RT)DMn54=0.22 exp−(28 800/RT).
Energy Bands in Semiconductors
Authors: Long Donald
Published: April 2005

A review is given of the energy band structures in a number of relatively well understood semiconductors, including Si and Ge, the Group III–V compounds, the IV–VI compounds (lead salts), CdAs2, and Bi2Te3, and of the experimental methods which have been used in determining these band structures. This review is directed particularly toward the interests of those engaged in applied research and development of semiconductor devices which depend more or less specifically on band structure properties for their operation. It is also meant to provide a single source of the latest available energy band information for those engaged in basic research on semiconductors and for students.
Ferroelectric Harmonic Generator and the Large-Signal Microwave Characteristics of a Ferroelectric Ceramic
Authors: DiDomenico M. , Johnson D. A. , Pantell R. H.
Published: April 2005

At microwave frequencies, ferroelectric ceramics behave as nonlinear dielectrics and exhibit large signal scalar nonlinear characteristics in both the dielectric constant and the rf conductivity. The nonlinear behavior of a ceramic of 73% BaTiO3-27% SrTiO3 has been used to construct a harmonic generator operating from 3 kMc to 9 kMc. An efficiency of 8.5% for a peak input power of 2200 w was attained. In addition, a new measurement technique has been developed for measuring the large signal properties of this ceramic as well as for other nonlinear materials. This technique makes explicit use of the anharmonic response of a resonant system that contains a nonlinear element. The analysis of both the harmonic generator and the nonlinear resonant system takes into account nonlinear reactance as well as nonlinear resistance. For temperatures about 30°C above the Curie temperature (the Curie temperature for the ceramic composed of 73% BaTiO3-27% SrTiO3 is approximately 20°C) the large signal dielectric constant and rf conductivity were found to be given by the expressions ε′(|E|)=ε0[2200−7.5×10−11|E |2] farad/m, and σ(|E|) =ωε0[160+29×10−12|E|2] mhos/m, where |E| is in volts per meter. These results were obtained at 3 kMc and are valid up to field strengths of 20 kv/cm.
Solution of the Space Charge Problem for a Pulsed Townsend Discharge
Authors: Morrison J. A. , Edelson D.
Published: April 2005

The pulsed Townsend discharge technique for the determination of electron attachment coefficients of electronegative gases is examined for situations where the ion density is sufficiently high that space charge effects must be considered. The equations of motion for the ions are solved to yield a first-order differential equation for a parametric function, in terms of which the current and boundary position may be expressed. For the particular case of interest, an initial distribution which decays exponentially from the cathode, an exact solution for the current is obtained by numerical evaluation of this function. Comparison with experiment shows excellent qualitative and fair quantitative agreement.
Fission Fragment Tracks in Metal Films
Authors: Noggle T. S. , Stiegler J. O.
Published: April 2005

Fission fragment tracks observed in electron microscope studies of platinum and palladium films are interpreted in terms of thermal processes involving melting and vaporization. The results require that the energy lost by the fragment be converted into thermal energy over the entire volume of the track in a time short enough that little of it is conducted away. A model in which free electrons disperse the energy over this volume is used to account for the width and structures of the tracks.
Dislocation Mobility and Damping in LiF
Authors: Baker George S.
Published: April 2005

Amplitude dependent dislocation damping was measured in LiF. It was found that average dislocation velocities comparable to those present during plastic deformation occur under periodic stresses more than an order of magnitude below the macroscopic yield stress. This implies that the impediments to dislocation motion effective in plastic deformation are localized at widely separated points along the dislocation.
Trap Density Determination by Space-Charge-Limited Currents
Authors: Bube Richard H.
Published: April 2005

Trap depths and densities can be determined from the analysis of the dependence of space-charge-limited currents on applied electric field in insulators. Values obtained from space-charge-limited current measurements are compared with those obtained from thermally stimulated currents and from photocurrent decay on the same crystal of cadmium sulfide. The results indicate that gross errors in trap depth and density can be made if it is simply assumed that the rapid rise in current toward the trap-free curve with increasing applied voltage always occurs when the traps are filled. Although this may sometimes be true, it is also possible for such a rapid rise to result from field ionization of the traps, or even in certain cases from the onset of double injection. Even if the latter effects occur, however, proper analysis of the space-charge-limited current data permits an evaluation of trap depth and density which is completely consistent with independent measurements of thermally stimulated current and photocurrent decay.
High-Angle Limit in Low-Angle Scattering and Its Effect on the Determination of Surface Area
Authors: Caulfield Daniel , Ullman Robert
Published: April 2005

The initial slope of the correlation function γ(r) is proportional to the specific surface of the scattering sample in principle, and is equal to zero in practice. In this paper, a simple model is investigated which illustrates the problem. Calculations are carried out to show how surface areas may be obtained from scattering data.
A Simplified Cylindrical Distribution Function
Authors: Milberg M. E.
Published: April 2005

A simplified cylindrical distribution function is proposed, which yields a considerable amount of structural information concerning moderately oriented noncrystalline fibers. This function can be obtained with only a small fraction of the labor required for the complete cylindrical distribution function. It is the transform of the difference between the scattered intensity and its average over the polar angle in reciprocal space, and is calculated by means of an expansion of the Fourier-Bessel integral in spherical harmonics. Because all isotropic contributions to the scattered intensity are automatically omitted from the calculation, no consideration need be given to independent scattering, air scattering or, as a rule, the contribution of extraneous wavelengths. The resulting function is the difference between the cylindrical and radial distribution functions on an arbitrary scale, measured from an unknown baseline. Although these features limit the information obtained, that which is obtained is of considerable use in elucidating fiber structures.
Determination of the Anisotropy in Thin Permalloy Films
Authors: Doyle W. D.
Published: April 2005

Four types of measurement on thin Permalloy films are discussed which in the coherent-rotation theory yield equivalent values for the anisotropy field Hk: (A) Hysteresis loop; (B) high field torque; (C) rotational hysteresis; (D) torque 90° to the easy axis. Results reported for several films show that the values obtained from (A) and (B) agree reasonably well, while the values from (C) and (D) are found to be too high and too low, respectively. These discrepancies are explained in terms of a dispersion in both the magnitude and direction of the anisotropy. A torque method to determine an effective dispersion is outlined and illustrated for a particular case.
Fatigue Crack Propagation in Aluminum Single Crystals
Authors: Grosskreutz J. C.
Published: April 2005

Single crystals of commercially pure (2S) aluminum were stressed in push-pull and the development of surface fatigue cracks observed continuously with a specially mounted 300× optical microscope. Time-lapse photographic sequences were used to measure the propagation rate and to determine the relation between surface slip markings and crack propagation mechanisms. Cross-sectional views of the internal disposition of the crack were obtained by sectioning in a microtome. Back reflection x-ray photographs were used to gather evidence concerning the deformation substructure near the fatigue crack. The data thus assembled allow the mechanism of fatigue crack propagation to be described in terms of surface slip bands, the stress concentration at the edges of these bands, and subgrain formation which occurs in the vicinity of the crack tip. The linear relationship between the logarithm of the instantaneous crack length and the number of stress cycles was confirmed and the proportionality between the crack length and the plastic zone immediately ahead of the tip was demonstrated.
Critical Field Measurements of Thin Superconducting Sn Films
Authors: Blumberg R. H.
Published: April 2005

Sn films varying in thickness from 200 to 4500 Å have been prepared by vacuum deposition. The surface roughness has been held to a minimum and the grain size restricted to approximately 1000 Å by cooling the substrate to 80°K and depositing the film at an evaporation rate of 100 Å per sec. The film purities have been calculated from residual resistance data. The mean free paths are in the range of 1000 to 5000 Å. Critical fields for films in this thickness and purity range are reported. The London and Ginzburg-Landau models have been used to calculate from experiment the penetration depth, which has been found to be in general agreement with Ittner's effective penetration depth concept. The temperature dependence of the penetration depth lies between the two temperature-dependence predictions of the Bardeen, Cooper, Schrieffer (BCS) theory.
Thermoelectric Figure of Merit of Two-Band Semiconductors
Authors: Simon R.
Published: April 2005

The locus of points on the (α,κ/σT) plane for a two-band (electrons and holes) semiconductor as the concentration of doping agent is changed, is a curve that forms a closed loop, where α is the Seebeck coefficient, κ the thermal conductivity, σ the electrical conductivity, and T the absolute temperature. The value of the dimensionless thermoelectric figure of merit ZT=α2/(κ/σT) has, in general, two maxima on this loop, either or both of whose values are determinable, in principle, from measurements of α, κ, and σ on a few specimens with different amounts of doping. The shape and size of the loop and its position on the (α,κ/σT) plane depend upon the values of two dimensionless material parameters of the Chasmar and Stratton type, one for each band, the scattering parameters for the charge carriers in each band, and the value of the band gap in kT units. The effects of these parameters on the values of the ZT maxima are considered and approximate empirical relationships for Z(max)T as a function of these parameters are developed to aid in the quantitative evaluation of these effects. The relationships between these parameters and the pertinent physical properties of the material are discussed from the viewpoints of the requirements for improved thermoelectric materials and of the possible existence of an upper limit to the thermoelectric figure of merit.
Heterodyne Properties of a Three-Level Quantum System
Authors: Wells Willard H.
Published: April 2005

It is well known that a three-level system functions as a mixer for radiation at its three resonant frequencies. Here the topic is treated in detail by analogy to a three terminal-pair circuit element, one pair for each frequency. To one pair, fixed power is applied from a local oscillator, or ``pump.'' Attention is then centered on the other two pairs to determine their small-signal response and transfer characteristics. A slight generalization of the impedance concept takes account of the frequency changes and allows the results to be expressed as self-impedance at each terminal pair, and a transfer impedance between pairs. The damping effect of molecular surroundings is taken into account. The three-level maser is a special case in which the terminal pair for the idle frequency is open, and the self-impedance at the signal terminals has a negative resistive part.

Quantization of the radiation field is included by expressing quantum uncertainties in the same form as classical noise, i.e., correlation functions and power spectra. The means for doing this comes from a formalism which connects noise theory to quantum theory through the fact that the Wigner density of linear systems, such as modes of the radiation field, varies with time exactly like a classical probability density. The rules for using this technique are stated as needed without proof. The photon concept is not used.

The method is extended to include a system pumped by broad-band noise.
Experimental Determination of the Current Density-Electric Field Relationship of Silicon Field Emitters
Authors: Perry R. L.
Published: April 2005

The field-emission projection microscope has been used to study the field-emission characteristics of several silicon cold cathodes. The current-voltage data from nine of these field-emitter tips were reduced to the more fundamental current density - electric field values after the tip geometry was determined in an electron microscope. Comparison of these results with the available theory by Stratton has shown only limited agreement. Two distinct forms have been found for the relationship between the field-emitted current I and the applied voltage V when plotted as log10 I vs 104/V. One form is ``nonlinear'' while the other is ``linear,'' and the difference between these appears related to the relative strength of a p layer present on the surface of the silicon field-emitter. A dependence of the field-emitted current on the temperature of the silicon tip has been observed.
Conducting Thin Films Formed by Electron Bombardment of Substrate
Authors: Christy R. W.
Published: April 2005

A new technique for depositing thin films has been investigated. The method consists in decomposing molecules on a substrate by bombarding them with electrons, leaving metal atoms on the substrate. The film is formed selectively on the area of the substrate struck by the electrons. Stannous chloride was decomposed to metallic tin by electrons of about 200 ev energy. Tetrabutyltin was also studied. With the current densities available, tetrabutyltin was only partially decomposed, to form a semiconducting polymer film. Theoretical considerations suggest that the method should be applicable to a wide variety of metals.
Note on Coincidence-Detection Optimal Thresholds
Authors: Sponsler G. C.
Published: April 2005

Precise definitions of coincidence-detection probability and false-alarm ratio are given and their relations explained. The dependence of the false-alarm ratio expression upon certain formulas of Rice pertaining to zero crossings is noted. A pair of simultaneous nonlinear equations is derived which determine optimal thresholds exactly for Gaussian noise and approximately for small signals. Illustrative numerical solutions are displayed.
Comparison of the Size of Spherical Particles of Iron, Cobalt, and Alloys of Iron-Cobalt in Mercury as Determined by Various Methods
Authors: Luborsky F. E.
Published: April 2005

The sizes of particles prepared in mercury with diameters less than about 3000 Å were determined by electron microscope examination, analysis of the magnetization curve, calculation from the temperature dependence of magnetic remanence, tin adsorption, and analysis of their growth kinetics. The results of the various methods were found to be in reasonable agreement.
Scattering of Light by Polymer Films Possessing Correlated Orientation Fluctuations
Authors: Stein Richard S. , Wilson Philip R.
Published: April 2005

A theory for the scattering of light from a film of a polymer possessing randomly correlated oriented fluctuations of anisotropic elements is presented. The case for the film possessing both density and orientation fluctuations is considered. It is shown that one can separate these contributions from measurements obtained using polarized light. The consequences of non-randomly correlated fluctuations are qualitatively considered.
Diffraction of Spherical Scalar and Vector Waves at Axial Points of a Circular Aperture and Disk
Authors: McDonald Keith Leon
Published: April 2005

The following work treats Kottler's saltus problem of diffraction of electromagnetic waves emitted by a Hertzian oscillator source and the analogous Kirchhoff's scalar problem of waves emitted by a point source. The medium is a homogeneous isotropic dielectric. In the vector case a new exact solution of the basic integrals is presented, at axial points only, (a) behind a circular aperture in a ``black'' screen, and (b) behind its complementary ``black'' disk. The relative time-averaged intensity of energy flow is plotted for the disk only. It is shown that the scalar theory predicts considerably larger values than the electromagnetic theory for identical geometrical dispositions.
On the Theory of Monolayer Evaporation
Authors: Danforth W. E.
Published: April 2005

A theory of evaporation of a monolayer is here presented in which the evaporation of individual atoms, without interaction, is treated by statistical methods and in which the effect of interactions between atoms when the coverage is finite is treated by the thermodynamic reasoning developed by Langmuir. By combining these two approaches an expression is obtained which has, formally, only one adjustable constant, namely, the binding energy at zero coverage. The types of interactions taken into account are (following Langmuir): (a) finite size of surface atoms, and (b) dipole repulsion. Values of dipole moment are derived from thermionic emission. Assumptions have to be made regarding the partition functions relating to a surface atom. On the assumption that the only energy states available to a surface atom are those of translation parallel to the surface, agreement within the spread of currently available data for thorium on tungsten is obtained by using a binding energy at zero coverage of 7.61 ev. More precise data are required for determination of whether there must be some other and more complete specification of the partition functions for surface atoms.
Filamentary Standing-Wave Pattern in a Solid-State Maser
Authors: Tonks Lewi
Published: April 2005

The filamentary maser action in a ruby is explained as caused by minute randomly distributed variations in index of refraction. Relations are derived for the density of filaments and their size in terms of a Fourier resolution of the inhomogeneities. These are so small that it seemed that thermal motion might play a part, but this is shown to be orders of magnitude too small at room temperature.
Etch-Tunnels in Lithium Fluoride Crystals
Authors: Westwood A. R. C. , Rubin H.
Published: April 2005

The dissolution and growth behavior of lithium fluoride crystals in aqueous solutions containing long-chain fatty acids as step-poisons has been investigated. Both positive crystals (whiskers and platelets) and negative crystals (etch-tunnels) can be grown, respectively, from supersaturated and undersaturated solutions of lithium fluoride containing identical concentrations of stearic acid (∼2×10−6N). Dissolution behavior in stagnant environments is of particular interest for etch-tunnels some 0.5 μ in diameter and more than 100 μ in length (negative whiskers) have been observed. Two types of etch-tunnel can be distinguished; those nucleated at a surface defect—such as a cleavage step or the point of emergence of a dislocation (D type)—and those nucleated at apparently random points on the crystal surface (R type). Metallographic observations reveal that dislocations are not essential to negative crystal growth and it is proposed that tunnels grow simply because dissolution is less efficiently inhibited at the end of a tunnel than at the external surface of the crystal. This is a consequence of the reduced number of poison molecules available to inhibit kink and step motion at the end of a tunnel because of their slow rate of diffusion in a stagnant environment. Vigorous agitation of the environment suppresses etch-tunnel formation.
Behavior of Manganese in GaAs
Authors: Vieland L. J.
Published: April 2005

Hall measurements on manganese-doped gallium arsenide reveal a single acceptor level for this impurity with an ionization energy of 0.1 ev. The ionization energy and segregation coefficient, ks=0.05, appear to be independent of concentration over the range NA=6×1017−1×1020/cm3.
Electron Microscope Investigation of Extinction Line Contours in Copper Oxide Whiskers
Authors: Lasko William R. , Tice Warren K.
Published: April 2005

Oxide whiskers were grown in dry air on pre-worked and pre-annealed copper and studied by high-magnification transmission electron microscopy. Examinations of individual whiskers at high magnifications revealed a complex array of lines of strong contrast within some of the crystals. Stereoscopic examinations of single whiskers revealed that the lines were not associated with any thickness variation within the crystal. The application of diffraction contrast and dark field techniques indicated that the lines in most cases were a result of loss of illumination due to Bragg reflections, perhaps as a result of bending or elastic buckling of the whisker. Only in a few isolated cases, when line contrast reversals were obtained in the dark field images, was it possible to associate these lines with an inherent strain field in the whisker. The extinction bend contours observed in the broader whiskers formed on pre-worked copper were normally more complex than those exhibited by the thinner whiskers formed on the pre-annealed specimens.
Determination of Twin Fault Probabilities from the Diffraction Patterns of fcc Metals and Alloys
Authors: Cohen J. B. , Wagner C. N. J.
Published: April 2005

Twin faults may be detected from diffraction patterns of fcc metals and alloys by two existing methods: (1) from the sine coefficients of a one-dimensional Fourier series representing the peak, and (2) from the excess intensity between two peaks which are asymmetric in opposite directions, such as the 111 and 200. However, the contribution of twin faults to the particle size measured by Fourier analysis appears too large when the fault probabilities are determined by these methods.

A third technique has been developed based on the displacement of the center of gravity of a peak from the peak maximum, ΔC.G. The displacements for the 111 and 200 peaks are related to the twin fault probability β: ΔC.G. (∘2θ)111=+11β tanθ111ΔC.G. (∘2θ)200=−14.6β tanθ200. By using two peaks, such as the 111 and 200, the difficult choice of background and instrumental effects can be minimized. A comparison of the three techniques is presented.

As a consequence of the new method, it is clear that the probability of deformation stacking faults (α) should be measured from the displacements of peak maxima from those of an annealed specimen; if the C.G. is used and twin faults are present, a large error is possible.
Mechanism of the Penning Discharge at Low Pressures
Authors: Knauer W.
Published: April 2005

Experiments have been conducted with a cold cathode Penning discharge in which the sputtering patterns, the direction of ion motion, the energy distribution of the ions, and the E×B electron rotation were studied. It is concluded that below 10−4 mm Hg the discharge consists essentially of a pronounced, rotating plasma sheath close to the anode, while most of the center portion of the discharge is depressed to near-cathode potential. At 3000 v and 2500 gauss, an average rotation frequency of the sheath of 70 Mc has been observed. This corresponds to an average field strength in the sheath of 8800 v/cm. An approximate computation indicates that in the presence of fields of this magnitude, classical cross-field mobility can well account for the anode currents observed. This result differs from the findings of Backus and of Chen and Bingham at higher pressures, where random-field-enhanced diffusion according to Bohm had to be postulated to explain the large anode currents.
Direct Observations of Grain-Boundary Sliding in Bi-Crystals of Sodium Chloride and Magnesia
Authors: Adams M. A. , Murray G. T.
Published: April 2005

A study has been made of the grain-boundary behavior in bi-crystals of sodium chloride and magnesia held under load at elevated temperatures. Grain-boundary sliding was observed in both materials, of a form similar to that found in metals. The sliding occurred not smoothly, but in discreet jumps followed by periods of zero movement. In sodium chloride the over-all sliding rate was found to depend upon four variables examined: stress, temperature, atmosphere, and boundary misorientation. Two variables examined, stress and boundary misorientation, were found to influence the over-all boundary sliding rate in magnesia. Void formation as a result of sliding was observed in a sodium chloride sample which contained a well-defined jog in its boundary. Implications that the present results bring to bear upon general considerations of the high temperature deformation and fracture behavior of polycrystalline nonmetallic materials are discussed.
Crystal Nucleation in a Glass Containing Titania
Authors: Maurer R. D.
Published: April 2005

The mechanism of crystal nucleation in a titania-magnesia-alumina-silica glass has been studied by light scattering. Predominantly isotropic scattering centers become anisotropic during the initial crystallization process. This is interpreted as crystal nucleation within glassy concentrations fluctuation of titania. Titania-containing glasses nucleate readily because of the tendency of titania to segregate in amorphous regions which are more unstable toward crystallization than the original homogeneous glass. The data can be described by a model of scattering by a center surrounded by a region of polarizability of opposite sign. This model is utilized to obtain measurements of the crystallization rate and average crystal size.
Alternating-Current Generation with Moving Conducting Fluids
Authors: Haus H. A.
Published: April 2005

A one-dimensional, small-amplitude analysis is presented of alternating-current generation by a stationary electromagnetic circuit coupling to waves in a moving, perfectly conducting fluid. In a uniform applied dc magnetic field the waves in the fluid are either compressional waves if the time-average velocity v̄0 is transverse to the dc magnetic field, or Alfvén waves if it is along the dc magnetic field. It is shown that, for velocities v0 greater than the velocity of propagation c of the compressional or Alfvén waves, self-excited oscillations may be produced in a resistively loaded coil coupling to the fluid. In a traveling-wave circuit and in a resistively loaded distributed circuit coupling to the fluid, growing waves are found which result from a transformation of the fluid energy into electromagnetic energy. There is a close analogy between these power-generation mechanisms and those employed in microwave electron-beam tubes.

The results of two- and three-dimensional analyses are summarized in order to show that the phenomena predicted by the simplified one-dimensional analysis occur in less idealized geometries. Possible applications are briefly discussed with reference to ac power generation by using combustion gases or a flow of a high-temperature plasma.
Role of Surfaces in Plastic Flow of NaCl Single Crystals. II
Authors: Mendelson S.
Published: April 2005

The effects of surface sources, ozonized surface films, and surface dissolution, on the nature of plastic flow in NaCl single crystals were studied using etch pit and birefringence techniques. Slip steps increase in depth and become rounded as the slip band broadens. This is also often accompanied by a bending of the steps as much as 3° off 〈100〉. These effects are explained in terms of both internal and surface cross-slip mechanisms. Ozonization of NaCl for short periods restricts the action of surface sources and for longer times provides barriers to the egress of dislocations. The ``Suzuki effect'' (formation of a work-hardened surface layer) is found to depend upon the existence of a multiplicity of surface sources such as is produced by polishing on wet silk. Cross-slip of screw dislocations at the surface is found to be greater and flow more homogeneous when the surface is dissolved during deformation. This is proposed as a likely mechanism to explain the ``Joffe effect'' when atmospheric variables are eliminated.
Some Properties of Dirty Contacts on Semiconductors and Resistivity Measurements by a Two-Terminal Method
Authors: Harman George G. , Higier Theodore
Published: April 2005

The surface and bulk properties of semiconductors have been studied by a two-terminal method using dirty contacts. These contacts are defined as ones that are easily applied and removed and that are separated from the bulk by surface states, oxides, adhered gasses, and chemical films. The method essentially involves measuring the resistance-voltage (R-V) characteristics from the millivolt range up to about 100 V, and from these data the sample resistivity can be obtained directly. The effect of work damaging or etching the semiconductor surface can be readily evaluated. By observation of the shape of the R-V curves it is possible to separate the bulk from the surface effects, calculate the surface barrier height and thickness from tunneling equations, and determine whether the barrier is a surface film or due to metal-semiconductor contact potential difference. An application of the theory of electric field tunneling of Holm to the data of silicon carbide gives values of about 2.4 eV for the barrier height and 13 Å for the barrier width of the film on the surface. Sufficient information is included on electrode techniques and pitfalls so that the experimentalist can readily make the measurements. Efforts were concentrated on silicon carbide and silicon, but the techniques are applicable to all types of semiconductors.
Fluctuations in Bistable Tunnel Diode Circuits
Authors: Landauer R.
Published: April 2005

In a series of preceding papers connection has been made between the physics of the activated jump over a static potential barrier and related computing devices. This paper treats a more complicated system, namely, the tunnel diode, which stores information in one of two possible dissipative states. The activated jump between dissipative states is analyzed. An idealized physical model is used to find which of the two states is the really preferred one, and to also evaluate the rate at which fluctuations bring about an approach to this preferred distribution. To simplify the analysis, the case where the tunnel diode is in series with a vacuum diode, rather than a resistor, is emphasized. For typical germanium Esaki diodes, activated jumps are improbable if the junction cross section exceeds 10−11 cm2.
Critical Currents of Superconducting Nb 25 at.% Zr in High Magnetic Fields
Authors: Aron Paul R. , Hitchcock Harley C.
Published: April 2005

Measurements of critical current as a function of applied magnetic field were made on wire samples of Nb 25% at. Zr alloy at 4.22°K and 2.24°K. Curves are plotted for the cases for which the applied magnetic field is parallel to or perpendicular to the current direction. At 4.22°K, Hc(I → 0) for H perpendicular to I is found to be 70 kG, while for H parallel to I, it is found to be 82 kG. Reduction of the temperature to 2.24°K results in an increase of 13 kG in both cases. For H perpendicular to I, current densities of 4.4×104 A/cm2 are observed at 60 kG and 4.22°K, and at 73 kG and 2.24°K. The effective demagnetization factor of the current carrying elements is 0.6 π. All measurements were made in a dc magnetic field with quasidirect currents by observation of the first resistive voltage to appear across the sample.