bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Magnetoelastic Conversion Efficiency
Authors: Kirchner E. K. , Donaghey L. F. , Olson F. A. , Auld B. A.
Published: April 2005

Coupling of spin waves and elastic waves in ferrimagnetic materials is investigated theoretically. The magnetoelastic equations are transformed into coupled equations for fast and slow hybrid waves; the magnetoelastic coupling mechanism is then treated as a distributed directional coupler where the velocities of quasinormal modes are slowly tapered over the coupling length. Solution of the hybrid wave equations using a computerized numerical integration yielded conversion efficiencies versus magnetic field gradient. Over the efficiency range from 10% to 99.4% the conversion efficiency is equal to 1 − exp (−H′crit/ |H′|), to within one-half of one percent. The results provide a complete curve of conversion efficiency versus field gradient, and at the limits agree with Schlömann's strong and weak coupling approximations.
Nondegenerate Parallel Pumping of Magnetoelastic Waves
Authors: Comstock R. L.
Published: April 2005

An analysis is presented of a model of a nondegenerate parallel-pumped magnetoelastic wave amplifier. The instability involves two waves propagating in opposite directions and in contrast to previous analysis of lossless parametric systems, the unequal loss of the two waves leads to exponential growth. The amplifier gain is evaluated for the case that the magnetoelastic waves are near the crossover of the uncoupled spin and elastic wave spectra. The spin wave losses away from the crossover are evaluated for arbitrary angles of propagation with respect to the dc saturating field. Amplifier performance characteristics are evaluated for several ferrimagnets.
Gain and Saturation Characteristics of Parametrically Amplified Elastic Waves in YIG
Authors: Sparks R. A. , Higgins E. L.
Published: April 2005

The classification of transversely pumped magnetoelastic instabilities in a saturated ferrimagnetic insulator such as YIG suggests the availability of a number of parametric processes that may be useful for amplification purposes. In this paper the results of an experimental investigation of the transient mode of quasidegenerate parametric amplification of elastic waves are described and the gain and saturation effects over a wide range of input signal levels and pump powers are presented. These results are compared with the nonlinear limiting behavior of the unpumped case of YIG delay line operation.
Second-Order Magnetoelastic Properties of Yttrium Iron Garnet
Authors: Eastman D. E.
Published: April 2005

Second-order (in strain) magnetoelastic properties of yttrium iron garnet (YIG) have been studied using an ultrasonic technique. The group velocity of selected small-amplitude magnetoelastic (dominantly elastic) modes in single-crystal specimens has been measured at a frequency of 30 Mc/sec as a function of magnetic field strength and magnetization orientation. In this manner, first-order and second-order magnetoelastic constants and second-order ``morphic'' constants have been completely determined for YIG. This work reports the first evaluation of second-order magnetoelastic constants and morphic constants. All results have been interpreted using finite deformation magnetoelastic theory. Small strain magnetoelastic theory, valid only to first order in small quantities, leads to incorrect results in the treatment of second-order effects.
Interaction of Ultrasound with Magnetic Domains and Dislocations
Authors: Langenecker B.
Published: April 2005

Ultrasonic stress waves influence the state-of-magnetization; this effect can be used (up to the Curie temperature) to observe the energy distribution of ultrasonic fields for energy densities up to 1010 erg/cm3.1 Application of intense ultrasound reveals relations between magnetostriction and Young's modulus, while the inverse magnetostrictive effect detects phase transitions and certain phenomena associated with the internal structure of metal crystals. By using ferromagnetic thin films, one may investigate these relations and phenomena in situ in an electron microscope. At the same time, thin-film techniques extend the range of materials to nonferromagnetics and it is possible to combine direct microscopy of such internal structures as dislocations with the observation of damping of ultrasound at substructures. Results from these in situ observations carried out in a Siemens Elmiskop I are discussed in the light of acoustic energy conversion at dislocations, and transformation of mechanical energy into magnetic energy.
Photoemission of Electrons from Silicon into Silicon Dioxide. Effects of Ion Migration in the Oxide
Authors: Williams Richard
Published: April 2005

Photoemission of electrons from silicon into SiO2 has been used as a tool to study changes at the silicon-SiO2 interface which result from the application of high electric fields at elevated temperature. Before treatment the photoemission threshold energy for electrons from silicon into SiO2 is 4.22 eV. After applying a dc voltage across the oxide at elevated temperature, with polarity such that the silicon is negative, there are significant changes in the photoemission spectrum. A new low-energy branch appears which gives a threshold energy around 3.05 eV. This is believed to be due to the formation of a degenerate n-type surface. Light absorption by electrons in the conduction band becomes important, and there is a corresponding contribution to the photoemission current. Semiquantitative arguments are advanced to show what the charge distribution in the oxide must be to account for the experimental results.
Structural and Optical Characteristics of Thin GaAs Films. II
Authors: Pankey Titus , Davey John E.
Published: April 2005

Free carrier absorption measurements have been carried out on GaAs films which exhibit an absorption edge shift to lower energies; acceptor concentrations of >1019/cm3 are associated with this shift and causally related to it according to a model proposed by Stern. Absorption measurements on films deposited on a number of substrates and at different temperatures eliminate strain as a major cause in the shift of the edge for polycrystalline films. Reflectivity measurements show a marked dependence on both substrate temperature and thickness. The fall off in reflectivity values for very thick films is associated with the growth of microcrystals in the surface of the films. Examination of these surfaces by electron microscope shows extensive lamellar growth for deposition at temperatures above 350°C; this lamellar growth is explained on the basis of a twin-plane re-entrant growth mechanism. Examination of the films by electron and x-ray diffraction has shown the existence of extra reflections which can be indexed as due to a hcp phase; the existence of these reflections is associated with the lamellar growth in the films.
Role of Surface Diffusion in Stabilizing the Surface of a Solid Growing from Solution or Vapor
Authors: Coriell S. R. , Parker R. L.
Published: April 2005

The effect of surface diffusion on the stability of shape of a solid growing by diffusion in a supersaturated solution or vapor is considered. Cylindrical and spherical shapes are treated. It is found that under some conditions, for example, vapor-phase growth of metals in the presence of an inert gas, surface diffusion can provide a significant enhancement of the stability.
Thermal Dependence of Ruby Laser Emission
Authors: Izatt Jerald R. , Mitchell Robert C. , Daw Harold A.
Published: April 2005

The temperature shift of ruby laser emission has been measured interferometrically for temperatures between 66° and 210°K. Representative values of the temperature shift coefficient are 0.004 Å/K° at 66°K, 0.014 Å/K° at 100°K, and 0.046 Å/K° at 200°K. These results are in excellent agreement with calculations by McCumber and Sturge which were based on Raman scattering of Debye-model phonons. The experimental technique for measuring the wavelength shifts is described in detail, and the results are compared with earlier measurements of the temperature dependence of ruby R1 absorption and ruby laser emission.
Epitaxial Growth of Silicon on Hexagonal Silicon Carbide
Authors: Tallman R. L. , Chu T. L. , Gruber G. A. , Oberly J. J. , Wolley E. D.
Published: April 2005

The epitaxial growth of silicon on the basal plane of hexagonal silicon carbide substrates has been studied using the pyrolysis of silane in a flow system. The effects of deposition variables on the properties of grown films were evaluated using chemical etching and optical microscope techniques. The films were found to have almost exclusively {111} and {110} orientations and were found to be different in appearance on the carbon and silicon faces of the substrate. The epitaxial orientations were confirmed by reflection electron diffraction. The device quality of these films was established by preparing small diffused and epitaxial p-n junctions and MOS transistors.
Depths of Low-Energy Ion Bombardment Damage in Germanium
Authors: MacDonald R. J. , Haneman D.
Published: April 2005

The depth of the damage induced in thin films (≈10 μ) of germanium by bombardment with low-energy (≤1000 eV) argon ions has been measured by a new technique. The method is based on the differences in sputtering yield for a given energy, between material previously damaged by a higher-energy bombardment and material previously undamaged. The change in yield when the previously damaged material is eroded away marks the depth of this region. The sputtering yield was obtained from changes in the resonant frequency of a piezoelectric quartz crystal on which the thin germanium films were deposited and annealed. The detector was sensitive to mass changes of 4×10−10 g/cm2. The depth of the damaged region was found to be eight atomic layers when the damaging ions were of 400-eV energy increasing up to 25 atomic layers for damage induced by 1-keV argon ions. The extent of the damage induced by 1-keV argon ions was measured as a function of damaging ion dosage and found to saturate at doses of 1×1017 ions/cm2 and greater. Analysis indicates the damage could be accounted for in part by embedded argon atoms. The depth of the damage was found also to depend on the film thickness in the case of very thin films. Effects of annealing treatments during film deposition are described.
Imaging of Single Atoms with the Electron Microscope by Phase Contrast
Authors: Eisenhandler Claire B. , Siegel Benjamin M.
Published: April 2005

Calculations have been made on image contrast by computing the Kirchhoff diffraction integral assuming the amplitudes of elastic scattering from single atoms and linear chains of atoms given by the first Born approximation using either the Hartree-Fock or Thomas-Fermi atomic models. Phase shifts occur due to diffraction, spherical aberration, and defocusing which can be optimized by suitable choices of defocus and aperture size. Balancing of phase shifts due to defocus and spherical aberration produces a relatively uniform phase shift over a considerable part of the objective aperture and allows maximum contrast in the image which does not depend critically on atomic spacing. For atoms with Z>10 image contrasts of at least 5%−10% are indicated with presently available objective lenses. Resolutions down to ∼2.5 Å may be achieved at 100 kV and as low as ∼1.5 Å at 750 kV if spherical aberration sets the ultimate limit.
Ruby Whisker Growth and Characteristics
Authors: Schuster D. M. , Teich M. C. , Scala E.
Published: April 2005

Chromium-doped α-Al2O3 (ruby) whiskers have been grown by a vapor phase reaction. The ruby whisker growth morphologies were studied by means of optical and x-ray microscopy. Neutron activation analysis was employed to determine the chromium concentrations. Several unusual whisker shapes and surface configurations were observed and are discussed.
Nuclear Magnetic Resonance Study of Dislocation Effects and Elastic Axial Compression Effects in Sodium Iodide Single Crystals
Authors: Hooper H. O. , Bray P. J.
Published: April 2005

The nuclear magnetic resonance (NMR) intensity and line shape for 127I in NaI single crystals have been examined as a function of the orientation of the crystals relative to the external magnetic field. The intensity of the 127I NMR varied as the crystals were rotated about 〈110〉 and 〈100〉 directions perpendicular to the magnetic field. Full intensity of the NMR line is observed when H0 is along a 〈100〉 direction. This variation in intensity cannot be explained by nuclear magnetic dipole-dipole interaction alone and is thus termed anomalous. The intensity anomaly has been found to be due to the changing amount of first-order quadrupolar broadening of the 127I NMR line as a crystal is rotated in the magnetic field; the quadrupole effects are attributed to oriented dislocations in these previously unstrained crystals. A theoretical treatment of the effects of oriented dislocations has been carried out. The angular dependence of the frequency splittings was calculated for the cases of H0 varying in a (100) or (110) plane, assuming that the dislocations were oriented preferentially along either 〈100〉 or 〈110〉 directions. A comparison of the calculated angular dependence and the experimental angular dependence was made to determine which was the preferred orientation of both screw and edge dislocations. It was found that the best agreement with experiment is obtained if the screw dislocations are oriented with their axis along 〈100〉 directions and edge dislocation lines are oriented along 〈110〉 directions. Since the total intensity of the 127I NMR line is observed when H0 is along a 〈100〉 direction, it was possible to compress NaI crystals while a 〈100〉 direction was parallel to H0 and introduce quadrupolar broadening due to the strain-induced electric field gradients. The NMR lines were examined as the crystals were compressed up to about 3.5 × 107 dyn/cm2. With small pressure the NMR lines broadened and then returned to their original width when the weights were removed. Such compression experiments were continued to higher pressures at which the crystals obtained a permanent change as measured by the fact that the NMR line did not return to its original height or width. No width change was noticed if the magnetic field was along any crystal direction departing significantly from a 〈100〉 direction. From these compression experiments, the value (∼4) of the electrical polarizability of the iodine ion has been estimated.
Dynamically Determined Pressure-Volume Relationships for Aluminum, Copper, and Lead
Authors: Munson D. E. , Barker L. M.
Published: April 2005

This work presents experimentally determined pressure-volume data for copper to 116 kbars, lead to 78 kbars, and 1060 aluminum to 39 kbars. At these low stresses, the shear strength cannot be ignored; therefore, the dynamic stress-strain curves are reduced to Hugoniot form for further correction to ``shock hydrostats.'' These data may be compared to either isothermal hydrostatic data or to ultrasonic and very high-pressure dynamic data. In the former, polynomial pressure-volume data fits are corrected thermodynamically to isothermal conditions through the Grüneisen equation of state. Copper and aluminum dynamic curves are in reasonable agreement with the Bridgman curves; lead, on the other hand, shows marked discrepancies. In the latter comparison, the pressure-volume data are reduced to a bulk shock velocity and particle velocity plot. These data fit smoothly with the very high dynamic pressure data. Copper gives a linear fit, aluminum a quadratic fit, and lead does not permit distinction between a linear or quadratic fit. Agreement between dynamic and ultrasonic data is extremely good and suggests high accuracy for the dynamic data.
Ge-Epitaxial-PbS Heterojunctions
Authors: Davis John L. , Norr Marriner K.
Published: April 2005

Films of lead sulfide have been grown on single-crystal germanium substrates from a water solution of reacting chemicals. The details of the preparation method are described. Lauè back reflection and diffractometer measurements indicate that the films are single crystal with the same orientation as the substrate. Measurements were made of the photovoltage generated between the germanium and the lead sulfide as a function of wavelength between 1 and 4 μ at room temperature and at 77°K. At 77°K all samples showed a peak in photovoltage at 1.5 μ. In addition, samples grown on n-type germanium show a response out to 3.3 μ. Finally, the time constant of the photovoltage was measured. At room temperature it was less than 10 μsec for all samples while at 77°K it was 25 μsec for the samples grown on n-type germanium and less than 10 μsec for the remaining samples.
Excitation of Waves in Hot-Plasma Waveguides with Infinite Magnetostatic Fields
Authors: Kuehl H. H. , Stewart G. E.
Published: April 2005

The expressions for the electric field in a hot-plasma-filled waveguide with an infinite axial magnetostatic field due to a harmonically varying slot and double-grid excitation are given. Ion motion and collisions are not included. Asymptotic expressions for large distances from the excitation are given which consist of pole and saddle-point contributions. It is shown that for typical experimental parameters, the saddle-point contribution is negligible.
Determination of Absolute Concentrations by Gas-Phase Electron Spin Resonance Spectroscopy
Authors: Ultee C. J.
Published: April 2005

Absolute concentration measurements by ESR spectroscopy require the determination of integrated intensities. It is shown that the commonly employed first moment method can lead to serious errors when applied to Lorentzian lines. These errors result from neglecting the area in the wings of these lines. A general correction curve for modulation-distorted lines is presented. The use of oxygen for the calibration of ESR spectrometers is discussed.
Phenomenological Theory of Polarization Reversal in Ferrielectric Bi4Ti3O12 Single Crystals
Authors: Pulvari Charles F. , De La Paz Antonio S.
Published: April 2005

A theory describing polarization reversal in Bi4Ti3O12 single domain crystals based on observed time and field dependence of polarization P=f(E,t) is presented. The existence of a threshold switching field and a strong transverse dipole-dipole coupling is not only experimentally but also theoretically verified. The activation field α as well as mobility μ are related to the constants appearing in the basic equation. The theory gives time and field dependence of the switching current at constant temperature. Although the theory does not imply restriction on the applied field E(t), results are given only for pulsed and sinusoidal fields. Dependence of coercive field on applied field and frequency are presented. Switching resistance is calculated.
Crater Depth in Fluid Impacts
Authors: Engel Olive G.
Published: April 2005

A theoretical analysis of cavity depth for impacts of waterdrops against water is made and an equation for cavity depth is derived. Experimental crater-depth data, collected for the purpose of testing the equation, are tabulated. The agreement found is considered good.
Photoelectric Response of Metal Surfaces in Ambient Atmospheres
Authors: Howling D. H.
Published: April 2005

Experiments are described which examine variations in the photoelectric response of metal surfaces immersed in gas atmospheres. Work-function changes have been produced by gas bombardment, electrode heating, and the deposition of small amounts of K onto the surface. By operating the electrode under study as the cathode of a Geiger-Mueller photon counter, photocurrents as low as 10−21 A could be measured. Variations in the spectral tail could be observed with great sensitivity. Factors which influence the well-known irreversible changes in work function have been explored. A less well-known increase in the work function, which is reversible and thermally activated, has been demonstrated. Emphasis is given to the W/H2 system, but similar phenomena were observed for Ni, Fe, Pt, Pd, and Re in atmospheres of H2, N2, Ne, Ar, and NH3.
Growth Faults in β Silicon Carbide Whiskers
Authors: Van Torne L. I.
Published: April 2005

Silicon carbide whiskers grown from the vapor were examined by transmission electron microscopy and electron diffraction. Nearly 95% of the whiskers examined were of the β (cubic) crystalline form and contained stacking faults on {111}. The stacking faults form microtwins of the order of a few lattice parameters thick.
Recoil Gold Atoms from Fast-Neutron Bombardment
Authors: Keller Keaton , Lee R. V.
Published: April 2005

Gold foils were irradiated with fast neutrons from a Pu-Be neutron source and the gold atoms knocked out of these foils were collected on aluminum foils. Sets of Au-Al foils were placed at various angles around the Pu-Be source. Some foil sets had the gold foil nearer the neutron source; some had the aluminum foil nearer. In this way, both the ejection of gold atoms from open-ended displacement spikes and the sputtering of gold atoms by fast neutrons could be studied. As was expected, no 198Au was detected on the Al foils because of the small (n,γ) cross section of 197Au. After neutron activation in a nuclear reactor, all the Al foils emitted the 0.412-MeV gamma ray of 198Au. Calculations showed that each Al foil had approximately 1012 197Au atoms on it. Since the Pu-Be neutron source strength was known, the number of gold atoms ejected per open-ended displacement spike was calculated and found to be of the order of magnitude of 106. Focusing collisions may account for the large number of Au atoms per open-ended displacement spike. The sputtering ratio was found to be about 0.5 gold atoms sputtered per incident neutron.
Anisotropy and Annealing Behavior in Extrinsic Single-Crystal Tellurium
Authors: Skadron P. , Johnson V. A.
Published: April 2005

Electrical resistivity and Hall coefficient measurements have been made on tellurium specimens to determine anisotropy characteristics. Single-crystal boules of differing impurity contents were cut into rectangular samples with one edge parallel to the c axis of the parent crystal. For each sample, the electrical resistivity was measured in the temperature range 78°K to about 300°K, first with the current flow parallel to the c axis (ρ∥) and then with the current flow perpendicular to the c axis (ρ∥). The Hall coefficient was similarly measured, first with the magnetic field perpendicular to the c axis (R∥) and then with the magnetic field parallel to the c axis (R∥). For samples not given special heat treatment prior to measurement, the anisotropy ratios ρ∥/ρ∥ and R∥/R∥ at a fixed temperature tended to increase as the carrier concentration (R∥e)−1 decreased. Annealing at 350°C in helium at 0.5 atm pressure for 60 to 160 h caused initially different anisotropy ratios to approach the values: ρ∥/ρ∥=1.41±0.11, R∥/R∥=1.29±0.04. Annealing also produced a trend toward a common mobility, R∥/ρ∥=5700±400 cm2 V−1 sec−1 at 78°K, for samples with (R∥e)−1 ranging from 1.8×1015 cm−3 to 1.9×1017 cm−3 at 78°K.
Relationship between Creep and Stress Relaxation
Authors: Aklonis J. J. , Tobolsky A. V.
Published: April 2005

The relationship between creep and stress relaxation is investigated. It is found that large changes in the slope of stress-relaxation master curves are reflected as minute slope changes in creep master curves under some conditions. It is pointed out that while a system with a narrow distribution of relaxation times and a Maxwell body are almost identical in creep, they should be easily distinguishable in stress relaxation.
Thermoelasticity, Chain Conformation, and the Equation of State for Rubber Networks
Authors: Tobolsky Arthur V. , Shen Mitchel C.
Published: April 2005

A new semiempirical equation of state for rubber elasticity is proposed which postulates a volume dependence of the front factor due to intermolecular forces. The thermoelastic consequences of this equation are presented and compared with experiment. The theory is couched in terms of a single parameter which is readily obtainable from experiment. If this parameter is zero, the new equation reduces to previous equations. Experimental data on hand suggest that the parameter is not zero. If this result is confirmed, it would indicate that present equations relating thermoelastic experiments to chain conformation in free space or in solution must be reconsidered.
Dislocations and Precipitates in GaAs Injection Lasers
Authors: Abrahams M. S. , Buiocchi C. J.
Published: April 2005

The new A-B etchant has been employed to reveal interfacial dislocations near the junctions of GaAs injection lasers. Injection lasers were examined parallel and perpendicular to the junction region. Dislocations are seen predominantly in the junction region, lying in the (001) plane, and in only two directions, the [110] and [11̄0]. Their source is ascribed to the lattice mismatch between the substrate and grown layer. Decoration of the dislocations parallel to [110] is observed, but very little decoration of the [11̄0] dislocations is seen. The decorating impurity is believed to be Zn. The difference in decoration of the [110] and [11̄0] dislocations is accounted for by a difference in the structure of these two dislocations. A direct correlation between lasing filaments and decorated interfacial dislocations was found in the [110] direction. This is believed to be due to the local distortion of the current lines near the defects.
Preparation and Characterization of Evaporated Boron Films
Authors: McElligott P. E. , Roberts R. W.
Published: April 2005

A method of preparing high purity, evaporated boron films by direct Ohmic heating of elemental boron filaments in ultrahigh vacuum is described. Electron micrography, electron diffraction, and B.E.T. (Brunauer-Emmett-Teller) surface area measurements yield some insight on the nature of these films.
Lattice Vibrational Properties of Hexagonal CdSe
Authors: Geick R. , Perry C. H. , Mitra S. S.
Published: April 2005

The reflectivity of single-crystalline CdSe was studied with linearly polarized light at room temperature and at liquid-nitrogen temperature. The characteristic data of the fundamental lattice vibration were determined by means of a classical oscillator fit. A shift of 6 cm−1 or 3.5% in the infrared eigenfrequency was found, due to anisotropy splitting. Transmission measurements yielded several multiphonon peaks and an impurity band. The multiphonon peaks are interpreted in terms of a set of four representative phonon energies for the edge of the Brillouin zone.
Deposition of Permalloy Films on Organic-Polymer-Coated Substrates
Authors: Medernach J. W. , Bobb L. J. , Hunter N. A.
Published: April 2005

Imperfections, inhomogeneities, and roughness of the surface of thin glass substrates, commonly used in the deposition of Permalloy thin films, can produce variations in the magnetic parameters of these films. Attempts to prepare smooth substrate surfaces for film deposition have been tried using various chemical cleaning techniques. These techniques can reduce the effects of surface contamination and surface roughness, but never eliminate them. Permalloy films that have been electrodeposited on an organic polymer (OP) coating on metal substrate were found to have a decrease in the coercive force Hc, while the anisotropy field Hk remained constant, and were easily reproducible. This decrease in the coercive force is attributed to a lesser degree of surface roughness and waviness of the OP-coated substrate as compared to a thin glass substrate.
Use of Thin Single Crystals as Reference Standards for Precision Electron Diffraction
Authors: Corbett J. M. , Boswell F. W.
Published: April 2005

The use of thin single crystals of layer structures as internal standards for precision lattice-parameter determinations in limited-area electron diffraction is examined. Under suitable conditions it is shown experimentally that the lattice parameter of a polycrystalline material can be determined in terms of a single-crystal standard with an accuracy of ±0.05%. It is concluded that lattice-parameter determinations in limited-area electron diffraction can be made in terms of single-crystal internal standards with an accuracy comparable to that which can be obtained using polycrystalline standards.
Elimination of Solute Banding in Indium Antimonide Crystals by Growth in a Magnetic Field
Authors: Utech Harvey P. , Flemings Merton C.
Published: April 2005

Samples of tellurium-doped indium antimonide that exhibited solute banding when solidified in a horizontal boat under ordinary conditions showed no bands when solidified in the presence of a vertical dc magnetic field. The effect of the field was to damp the thermal convection in the molten sample to the point of suppressing turbulence, thereby eliminating the temperature fluctuations in the liquid that cause the bands.
Effect of a Temperature Gradient on Thermionic Emission
Authors: Bowers Harold C. , Wolga George J.
Published: April 2005

The effect of a temperature gradient at the surface of a metal on the thermionic emission current is calculated. The calculation is motivated by current research in which metal surfaces are exposed to high-intensity optical maser beams with a consequent heating of the surface. A Sommerfeld free-electron model of a metal is used in which the temperature of the metal is allowed to be a function of position. A modified distribution function for the electrons is calculated using the Boltzmann transport equation from which the thermionic current is obtained. Approximations are made that limit the theory to small changes in the distribution function but the results are valid for realizable experimental conditions. It is shown in an example that for Q-switched laser intensities observable effects can be expected.
Anomalous Surface Heating Rates
Authors: Harrington R. E.
Published: April 2005

Metals, semiconductors, and insulators, when exposed to the high irradiance produced by an arc image furnace, appear hot much sooner than predicted by heat theory. For an irradiance of 1500 W/cm2, the surface of the samples tested reached a temperature of 2000°K or more in a few milliseconds whereas the mathematical theory of heat conduction suggests that several seconds should be required. The existence of anomalously fast heating is confirmed by a variety of experiments. The observations are consistent with the results expected for a surface region of very low thermal conductivity.

Tests using a high-brightness flash tube (to obtain higher irradiances) show a ``saturation'' of reflectivity for smoked MgO, tantalum, and water-cooled platinum samples. The ``saturation'' can be qualitatively explained on the basis of thermal equilibrium of the surface region with the irradiance.
Effect of Local Pressure on Germanium p-n Junctions
Authors: Bulthuis K.
Published: April 2005

Pressure is applied locally, with a small round diamond point on the flat surface of germanium mesa diodes. The pressure dependence of the forward and reverse currents is interpreted in terms of a change of the energy gap by introducing a simplified pressure pattern. For the pressure dependence of the energy gap for 〈111〉 germanium is found ∂EG/∂P≈−9×10−6 eV kg−1 cm2.
Inversion of Pole Figures for Materials Having Cubic Crystal Symmetry
Authors: Roe Ryong-Joon
Published: April 2005

X-ray diffraction measurements on anisotropic polycrystalline samples give a set of functions (pole-figures) describing the orientation distribution of individual plane-normals. From the set of these plane-normal distributions it is possible to deduce the orientation distribution of all crystallites in the sample (inversion of pole-figures) by a procedure described in a previous paper, in which the crystallite distribution function is expanded in a series of generalized Legendre functions. The expansion coefficients Wlmn which characterize the crystallite distribution have to satisfy restrictions imposed by the crystallographic and statistical symmetry elements existing in the sample. When the crystallites belong to the cubic crystal class, it is required not only that some of Wlmn be identically equal to zero but also that the remaining nonzero Wlmn be linearly related to each other (for given l and m). The matrix equation expressing the linear dependence among Wlmn is solved numerically by a computer and the result is presented in a table.
Positive Impurity Ion Emission from α Quartz
Authors: Hills R. G. , Gibbs P.
Published: April 2005

Positive ion emission from single-crystal α quartz has been studied in the temperature range 435°–560°C. For low voltages, current was proportional to the 3/2-power of the applied voltage, and attributed to the limiting of emission by the space charge in the vacuum. For higher voltages, observed values of current density J as a function of temperature were fitted to the equation J = A0T⅓ exp (−H/kT), where A0 = 220 A·cm−2 deg−½. The activation enthalpy H decreased with applied electric field, the zero-field value being 2.56 eV (59 kcal/mole). Etching with HF increased the emission current approximately 100 times over that of surfaces lapped to an optical finish. The primary species of emitted ion was identified as Li+ by magnetic deflection. Surmounting of the electrostatic barrier due to image forces in the vacuum (102−104 A from the quartz-vacuum interface) was concluded to be the rate-limiting step. A similar interpretation is also in reasonable agreement with published data for Li+ emission from aluminosilicates.
Electrical Resistivity of Equiatomic Rare-Earth-Noble-Metal Compounds
Authors: Chao Chang-Chih
Published: April 2005

The electrical resistivity of twenty CsCl type intermediate phases of Gd, Tb, Dy, Ho, Er, and Tm with Cu, Ag, and Au and of Y and Nd with Ag were measured from 4.2°K to about 250°K. All of the resistivity-temperature curves, except that of YAg, show anomalies at temperatures which are in good agreement with the available antiferromagnetic-paramagnetic transition temperatures obtained by either neutron diffraction studies or magnetic susceptibility measurements. The spin disordering part of the resistivity of the CsCl phases were deduced and any attempt to apply the theory of de Gennes and Friedel which was used by Rocher for pure rare-earth elements, was not successful.
Effects of Annealing on Thin Gold Films
Authors: Kane Walter M. , Spratt James P. , Hershinger Lincoln W.
Published: April 2005

As a part of a thin-film device study, an investigation was conducted of the conditions under which thin metal films cease to be continuous. This paper discusses the effects of annealing on thin gold films that were sandwiched between two evaporated layers of zinc sulfide.

The electrical resistance of films in the 60- to 80-Å thickness range was monitored during constant-temperature anneals in a helium atmosphere. A portion of the resistance-time curve is found to follow the relationship R=R0eαt, where α depends on the temperature according to the equation α=α0e−E/kT. Electron micrographs show that the resistance increase is due to the agglomeration of the films, and it is suggested that the latter equation defines an activation energy for migration of gold atoms. A value of E∼1.8 eV is obtained for this gold-zinc sulfide system.
Linewidth and Saturation Parameters for the 6328-Å Transition in a He–Ne Laser
Authors: Smith P. W.
Published: April 2005

Experimental measurements of the collision-broadened linewidth and saturation parameters for the 6328-Å transition of Ne in a He–Ne laser are reported as a function of total gas pressure in the laser tube. The measurements are made from observations of the single-mode output power of a laser as a function of frequency. The experimental results are found to fit well a form of Lamb's theory for single-mode operation which has been modified to include gas-collision effects. A theoretical calculation of the saturation parameter is made and the result is found to be in fair agreement with the experimental measurements.
Annealing and Arsenic Overpressure Experiments on Defects in Gallium Arsenide
Authors: Potts H. R. , Pearson G. L.
Published: April 2005

Previous experiments reported by the authors revealed a measurable expansion in the lattice constant of GaAs single crystals quenched from temperatures above 1000°C. These results led to the conclusion that a defect structure consisting of both Frenkel pairs and Schottky vacancies was produced in these crystals. In this paper we report experiments in which an arsenic overpressure, obtained by including metallic arsenic along with the GaAs crystal, depresses the defect concentration. These results are used to identify the primary defect species as arsenic monovacancies. Subsequent heat treatments at both room temperature and high temperature show that annealing proceeds in two stages. The first stage is quite rapid but does not have a well-defined activation energy. The second stage is slower and has an activation energy of 1.0 eV. These results are interpreted to include the presence of arsenic interstitial atoms. A physical model is proposed to describe the defect structure as well as the annealing behavior and the effect of excess arsenic pressure.
Lateral Traveling Solvent Growth in Indium Arsenide
Authors: Kleinknecht Hans P.
Published: April 2005

A new type of traveling solvent technique has been developed for making p-n-p or n-p-n semiconductor structures with a highly doped middle layer. It is demonstrated on indium arsenide p-n-p structures. The process involves the fabrication of perfectly wetted semiconductor-metal-semiconductor sandwiches by a ``saturated dot'' technique and a traveling solvent process in a temperature gradient parallel to the sandwich plane. Over areas of about 1 mm×1 mm, middle layers as thin as 12 μ were obtained. An analysis is given describing the essential features of the process and giving limits for process temperature and temperature gradient. Some process data are obtained by experiments of normal traveling solvent growth carried out in the same system.
Properties of Single-Crystal CoO Films on MgO
Authors: Greiner J. H. , Berkowitz A. E. , Weidenborner J. E.
Published: April 2005

Single-crystal CoO films, 3 to 30 μ thick, were grown epitaxially on MgO by halide decomposition. Optical, x-ray, and magnetic torque measurements were made on the as-grown samples, i.e., with the CoO attached to the MgO. Films with (001) and (111) orientations had a spiral growth structure. Twinning in the CoO films below the Néel temperature was investigated by optical and x-ray techniques. Antiferromagnetic twin domains were observed in (001) CoO films at 77°K by transmitted polarized light. The tetragonal distortion in CoO was measured down to 83°K and had bulk values with a c/a ratio of 0.9880 at 83°K. Magnetic torque measurements were made from 77° to 296°K in fields up to 22 kOe. The symmetry and amplitude of the torque varied when the sample was cooled from room temperature in a field. Cooling in a field altered the spin axes distribution to favor those spin axes most perpendicular to the cooling field direction. The torque data for the (111) orientation were consistent with a single- and a multi-spin-axis model. However, the torque data for the (001) orientation were consistent only with a single-spin-axis model.
Magnetic Shielding by Superconducting Niobium Tin Plates
Authors: Benaroya R. , Mogensen H. P.
Published: April 2005

This work experimentally explores the effectiveness of magnetic shielding between superconducting Nb3Sn plates at 4.2°K in transverse magnetic fields up to 19.6 kG. At 19.6 kG the field exclusion obtained in the center between two 3.0×2.5×0.3-cm thick plates, separated from each other by 1.0 cm, was 17.9 kG. It has been found that flux jumps not only degrade the shielding capability of the plates but also give rise to nonsymmetrical field distributions. A relationship has been established between the applied field B1 and its critical rate of increase (dB1/dt)c, below which flux jumps do not occur for pairs of plates of various thicknesses. Flux jumps have been completely eliminated by keeping dB1/dt<(dB1/dt)c.

Bean's model of current penetration into a high-field superconductor and the assumption of induced rectangular current loops have been successfully applied in calculating field distributions between the plates at medium and high applied fields. This model is not as successful at the early stages of plate magnetization where the current penetration is a small fraction of the total depth of the superconductor and the surface currents are appreciable. It has been found that the condition of field reversal external to the shielding volume can be minimized by the use of shunt iron in close proximity to the superconducting plates. Such a feature is desirable for the application of superconductor plate shields to a deflector system for a high-intensity variable-energy cyclotron.
Hall Effect in a Collision-Dominated Gaseous Plasma
Authors: Chen C. L.
Published: April 2005

A theoretical treatment of the Hall voltage developed in a gaseous plasma immersed in a uniform magnetic field is presented. The plasma considered is collision dominated and is confined by parallel planes with insulating walls. The Hall voltage is found to depend on electron-ion volume recombination and on the tensor character of the electron mobility. The cases to be discussed are: (i) negligible diffusion, (ii) negligible electron-ion volume recombination, and (iii) diffusion with small but not negligible volume recombination.
Computer Solution for Time-Invariant Electric Fields
Authors: Rush Stanley , Turner A. H. , Cherin A. H.
Published: April 2005

A general method suitable for computerized solution is described for finding the electric and/or current density fields due to time-invariant sources. A charge distribution satisfying the boundary conditions is specified as the solution of an integral equation. The latter is approximated as a system of linear algebraic equations and solved by the computer. The field at any point is then obtained by Coulomb's law and superposition from the boundary charge distribution and any impressed fields that exist. The method will, within the practical restrictions imposed by the computer's capacity to solve simultaneous equations, solve any inhomogeneous, linear, isotropic, steady current flow and/or static field problem with any of the various boundary conditions which uniquely define a field. While the derivation is given here in terms of electric field quantities, it applies as well to the several analogous fields of engineering and physics. In addition to the theoretical formulation, data are given to guide in the selection of the most efficient and accurate formulas with which to approximate the integral equation. Several examples and results are presented together with data bearing on questions of accuracy and convergence. Two example results are combined to derive a quasi-empirical formula for the capacitance of widely spaced square parallel plates.
Accuracy in the Use of Electron-Diffraction Spot Patterns for Determining Crystal Orientations
Authors: Laird C. , Eichen E. , Bitler W. R.
Published: April 2005

It has long been known that transmission electron-diffraction patterns appropriate to low-index zone axes in thin crystals exist over several degrees of tilt from the exact orientations. In this work the magnitude of the errors in determining crystal orientation from spot patterns has been investigated using precisely oriented crystals prepared by vapor deposition and an electron microscope equipped with a goniometer specimen stage. It was observed that patterns of low-index orientations existed over ranges as high as 20° tilt, and were insensitive to the size of the area diffracted. Tilt ranges were observed to increase noticeably when the foils were plastically deformed. However, orientations accurate to 0.5° may be determined by weighting the pattern according to the intensities of the diffraction spots.

Elastic bending of the foils and ``polygonization'' bending due to dislocations help to explain why the relrods are so much ``longer'' than predicted on the basis of relaxation of the Laue conditions, using kinematic theory.
Nonuniform Emission of Thermionic Cathodes
Authors: Jansen C. G. J. , Venema A. , Weekers Th. H.
Published: April 2005

The nonuniform emission of thermionic cathodes has been studied with an anode-hole scanning technique by means of which ``effective'' work-function distributions could be obtained. Using these ``effective'' work-function distributions, information has been gained about the fraction of the total cathode surface that actually determines the saturated emission. The knowledge of this fraction facilitates the physical interpretation of the emission constant AR, appearing when the experimental Richardson formula is used.

It is proved that different types of practical cathodes show marked differences in emission uniformity under space charge as well as under saturated emission conditions and as a function of their lifetime.

At several hundred hours of life, approximated values of the fraction of the surface area that determines the saturated emission and of its work function were found to be 0.35 and 1.81 V at 1350°K for an L cathode, 0.18 and 1.72 V at 1350°K for an impregnated cathode, 0.067 and 1.26 V at 1025°K for a (BaSr)O cathode.
Spectroscopic Investigations of the Helium Short Arc
Authors: Simon D. R. , Rogers K. C.
Published: April 2005

A short (5 mm) helium arc between a ⅜-in.-diam thoriated tungsten cathode and a 1-in.-diam copper anode was examined spectroscopically. Electron densities were determined from the Inglis-Teller relation for a range of gas pressures and arc currents from 500 Torr, 50 A to 5000 Torr, 250 A. At 850 Torr, 100 A, the electron density was 1.2(+2.1/−0.2)×1016 per cm3. At 850 Torr, 100 A (2.4-kW power level) the atomic excitation temperature was measured using a line intensity ratio technique. Self-absorption corrections were determined experimentally using a tandem arc arrangement and were found to be significant. A numerical computational technique was solved for the spatial dependence of emission and absorption of the HeI 23S-N3P series. The state populations followed a Boltzmann distribution with an excitation temperature of 4800°K. A best straight line fit to the data was obtained with spontaneous decay coefficients computed by Bates and Damgaard and by Schiff and Perkeris. This excitation temperature is too low to account for the observed electron density assuming equilibrium so that local thermodynamic equilibrium (LTE) does not exist in the arc at this power level.
Measurement of Third-Order Elastic Moduli of Yttrium Iron Garnet
Authors: Eastman D. E.
Published: April 2005

The third-order elastic moduli of yttrium iron garnet (YIG) have been determined from measurements of ultrasonic velocity. A pulsed ultrasonic system which uses a phase comparison principle to measure velocity versus applied stress is described. In units of 1012 dyn/cm2 and for 28°C, the third-order moduli are: C111=−23.3±0.8C112=−7.17±0.6C123=−0.33±1.3C144=−1.48±0.29C155=−3.06±0.14C456=−0.97±0.16.Thermodynamic definitions for the moduli [K. Brugger, Phys. Rev. 133, A1611 (1964)] have been used.
Propagation of Bragg-Reflected Neutrons in Bounded Mosaic Crystals
Authors: Werner S. A. , Arrott Anthony , King J. S. , Kendrick H.
Published: April 2005

The analysis of the multiple Bragg reflection of a neutron beam of finite size in a semi-infinite mosaic crystal given in a recent paper by Werner and Arrott is generalized to include bounded crystals. The coupled differential equations describing secondary extinction given by Hamilton are solved in general, and a method of piecewise solution, or solution by regions, is given.

A discussion is given of experiments on the spatial distribution of the diffracted current from slab-shaped crystals. Various methods for measuring the probability for Bragg scattering per unit path are compared and found not to agree. It is felt that the discrepancies are basic to the mosaic structure of crystals in general.