bluuebunny/crossref_metadata_2025 huggingface dataset:
A Thermodynamic Analysis of Ferroelectricity in Bismuth Titanate
Authors: Cross L. E. , Pohanka R. C.
Published: February 2004

The elastic Gibbs function at zero stress has been derived for ferroelectric crystals with point symmetry 4/mmm in the paraelectric phase, and the possible ferroelectric states have been examined. For the special case of bismuth titanate, recent optical data are used to derive the absolute orientation and the temperature dependence of the polarization in the monoclinic ferroelectric state. The optical anisotropies are shown to be consistent with a simple temperature-independent quadratic electro-optic effect.
Thin-Film Technique for the Experimental Determination of the Elastic Strain on the Electron Mean Free Path and on the Free-Electron Density in Bulk Metals
Authors: Meiksin Z. H.
Published: February 2004

A thin-film procedure is suggested for the experimental determination of the changes in the electron mean free path and the free-electron density under applied strain in bulk metals. The method is based on the characteristics of uniform continuous thin films whose conductivity is given by Fuchs' equation. An experimental demonstration is included.
Thermal Conductivities of Polyethylene and Nylon from 1.2° to 20°K
Authors: Kolouch R. J. , Brown R. G.
Published: February 2004

The thermal conductivities of four samples of polyethylene whose densities lie between 0.914 g/cc and 0.971 g/cc have been determined from 1.2° to 20°K. An empirical fit to the data between 1.2° and 4.0°K is effected for longitudinal phonons in terms of ``structure scattering'' and a frequency-independent scattering mechanism. However, the average spherulite sizes as observed with the optical microscope do not agree with the size parameters extracted from the frequency-independent scattering term which gives a best fit to the data. An excellent empirical fit to the data has been obtained up to 20°K by assuming that transverse phonons make an additional contribution to the thermal conductivity. The mechanisms which scatter these waves are chosen to be the same as those scattering the longitudinal phonons at the lower temperatures. The temperature-independent size parameter extracted from this portion of the fit to the data increases with increasing lamella thickness determined from small-angle x-ray scattering measurements, and is in order-of-magnitude agreement with this periodicity. The thermal conductivity of a sample of nylon has been measured and found to be in agreement with previously published data. An analysis similar to that effected for polyethylene failed to reveal consistency between spherulite or lamella dimensions with size parameters extracted from the data.
Propagation of Plastic Strain Pulses in Cylindrical Lead Bars
Authors: Shea James H.
Published: February 2004

The behavior of an elastic-plastic deformation pulse, produced in a cylindrical lead bar by reflection of an air shock from one end, has been studied experimentally by measuring the time variation of stress, as well as strain, at several locations along the length of the bar. To determine whether reasonable predictions of the observed time-dependent behavior could be made within the uniaxial stress approximation from a knowledge only of the properties of the material, the geometry of the specimens, and the known loading conditions, computer solutions were generated using equations of various degrees of complexity. It was found that a set of equations which takes into account work-hardening of the material, longitudinal inertia, an approximate correction for lateral inertia, and a possible rapid relaxation of the material was successful in predicting all the observed features of the pulse.
Radiography of Platinum by Means of Channeled Alpha Particles
Authors: Quéré Y. , Couve H.
Published: February 2004

Alpha particles emitted from a radioactive source and traversing a metallic foil of adequate thickness emerge only if they are channeled in the metal. They produce an image on a collector. It is shown that this image is strongly affected by lattice defects existing in the foil. Recrystallization of platinum is observed. The activation energy is measured: E=(2.85±0.15) eV. Zones of enhanced channeling exist in the metal along {111} and {100} planes, producing geometrical patterns on the image.
LEED Observations of Epitaxially Grown Thorium on (100) Tantalum
Authors: Pollard J. H. , Danforth W. E.
Published: February 2004

The growth of thorium overlayers on (100) tantalum at 950°C has been studied to an equivalent depth of 20 monolayers by LEED. The thorium intinally forms an incomplete c (2×2) structure, in `island,' up to a density of 3×1014 atoms/sq cm. Thereafter the 2D LEED pattern shows that the thorium has apparent (1×1) registry with the tantalum substrate up to a density of 1.8×1015 atoms/sq cm. The possibility of pseudomorphism is discussed. Recent electron micrographs of the surface show that thorium agglomerates in random islands after completion of the first 2D psendomorphic monolayer.
Flux-Line Arrangement in Superconductors as Revealed by Direct Observation
Authors: Träuble Hermann , Essmann Uwe
Published: February 2004

The flux-line lattice in a type-II superconductor in the remanent state is investigated by means of a decoration method. The triangular lattice contains various kinds of defects, the most important of which are flux-line dislocations. A critical lattice parameter dc exists such that for lattice parameters d>dc the flux lines form no longer a lattice but a ``flux-line fluid.'' A belt directly underneath the specimen surface is free from flux lines. The transition from the ``fluid'' to the flux-free region has been utilized to estimate in a fairly direct way the pinning forces acting on the flux lines.
Luminescence due to Ge Acceptors in GaAs
Authors: Kressel H. , Hawrylo F. Z. , LeFur P.
Published: February 2004

A study was made of photoluminescence in n- and p-type Ge-doped GaAs grown by liquid-phase epitaxy and of electroluminescence of Ge-compensated diodes. It is shown that two radiative emission bands are observed at 77°K, which are due to acceptor levels at Eν+0.03 eV and Eν+0.07 eV introduced by Ge. The shallow level is attributed to isolated Ge atoms on As sites, while the deeper level is believed to consist of an atomic complex involving Ge. The density of the deeper centers relative to the shallower ones depends on the growth conditions. In the samples studied, the deep center density is 102 to 103 smaller than the shallow center density. A detailed investigation has been made of the density-of-states distribution of the deeper acceptor levels and the experimental data have been compared to the theory of Morgan. This model considered the effect of the screened Coulomb potential due to charged impurities on the density-of-states distribution of deep recombination centers. The present materials are of particular interest in this respect because the recombination band involving the same set of deep impurity states may be observed in nearly compensated n- and p-type material and the relative effects of screening by either electrons or holes may, in principle, be determined. The experimental results support some of the predictions of Morgan's theory.
Numerical Analysis of Deformation Twin Behavior. Large Dynamic Twins
Authors: Marcinkowski M. J.
Published: February 2004

A numerical analysis has been carried out with respect to the equilibrium configuration of the partial dislocations constituting both screw-type and edge-type twins moving at velocities close to the transverse sound velocity. It is shown that the degree of oblateness of the twin decreases as either the stacking-fault energy or the twin velocity is increased. The partials comprising the edge-type twin become vertically aligned at the Rayleigh wave velocity whereas for the screw-type twins this vertical alignment takes place at the transverse sound velocity. A detailed analysis of the stress field in the vicinity of the twin front shows that shear stresses are such as to favor spontaneous dislocation loop nucleation in a plane normal to the propagation direction of the twin. On the other hand, the normal components of stress in the vicinity of the leading edge of a moving twin are such as to hamper crack propagation. This crack impedance however, is lost as soon as the twin becomes blocked.
Delayed Elasticity in Inorganic Glasses
Authors: Argon A. S.
Published: February 2004

The kinetics of the delayed elasticity in inorganic glasses is explained by a molecular rearrangement mechanism with a distribution of activation energies. An experimental method is described by means of which the spectrum of activation energies for the recovery creep process can be determined. Two such spectra, for a soda-lime-silica glass, and for fused silica are presented. The distributions are strongly skewed toward the high-energy side with peaks at 61 and 42.5 kcal/mole for these two glasses, respectively. In soda-lime-silica the rearranging regions are of ionic size, while in fused silica they contain a large number of ions.
Liquid Lasers: Stimulated Emission of Nd3+ in Liquid Selenium Oxychloride Solutions in the 4F3/2→4I13/2 Transition
Authors: Heller A. , Brophy V.
Published: February 2004

Laser action has been obtained at room temperature in liquid Nd3+–SeOCl2 solutions in the 4F3/2→4I13/2 transition of Nd3+ at 1330 nm. The cross section for stimulated emission at this wavelength is ∼7×10−21 cm2, about elevenfold less than the cross section for stimulated emission at 1056 nm. Correspondingly the thresholds for stimulated emission at 1330 nm exceed those for 1056 nm emission by one order of magnitude.
Some Physical Properties of Single Crystals of Normal and Deuterated Potassium Dihydrogen Arsenate. I. Piezoelectric and Elastic Properties
Authors: Adhav R. S.
Published: February 2004

The elastic and piezoelectric constants of single crystals of potassium dihydrogen arsenate, grown in H2O, and of potassium dideuterium arsenate, grown in D2O, have been measured in the temperature range of 20°–80°C. The shear elastic constants S44 and S66 increase, while the extensional elastic constants S11 and S33 decrease on deuteration. The piezoelectric constants d14 and d36 increase on deuteration. Since the temperature coefficients of frequency of useful cuts are in excess of −100 ppm/°C, these crystals are not useful for electromechanical application.
Laser Frequency Shifting and Modulating System
Authors: Singer J. R.
Published: February 2004

Gaseous ion lasers can provide the feature of tunability through a frequency range limited by the power available. Tuning can be accomplished by accelerating the excited ions through a potential V which, in the nonrelativistic formulation, provides an ion velocity ν proportional to the square root of the potential. The moving ion then can be tuned through a range Δν in a conventional laser configuration (using the Doppler shift) of Δν=±(ν0/c) (2eV/M)1/2,where c is the velocity of light, ν0 is the center of the normal laser transition for ions of velocity zero, e is the charge on the ion, and M is the mass of the ion. The excitation of the ions can be either by ionic collision or by uv optical excitation using intense sources. Up until now there has been no great incentive to optically pump ion lasers in view of the ease of electron excitation, but the present proposal does provide considerable incentive to optically pump ion lasers. Suitable ions are hydrogen molecules, the rare gases, mercury, oxygen, nitrogen, metals, etc. A detailed evaluation of a tunable argon ion laser is discussed.
Solid-Solution Hardening in Concentrated Solutions
Authors: Riddhagni B. R. , Asimow R. M.
Published: February 2004

The stress required to move a dislocation in a solid-solution alloy is considered. The analysis is based on a model which is particularly applicable to concentrated solid solutions. The energy fluctuations a dislocation segment encounters on moving through a crystal due to random composition fluctuations are calculated. In this paper it is assumed that only the elastic constants are affected by the variations in composition. As a result of these energy fluctuations, the dislocation line becomes slightly kinky. It is possible to calculate the mean energy barrier for motion of a double kink and also the average dimension of the double kink. The shear stress at 0°K is then determined. The results are compared to experimental data available for Au–Ag alloys and to other hardening theories.
The Deposition of Niobium Thin Films by dc Diode and Substrate Bias Sputtering
Authors: Sosniak J.
Published: February 2004

The room-temperature properties of sputtered niobium films can be made to approach those of the bulk metal either by deposition after extensive presputtering on substrates heated to ∼700°C, or by the application of a small negative bias to unheated substrates. The effectiveness of the former method is associated with the crystallization of the films in the bcc form of bulk niobium and the absence of the high-resistivity tetragonal form found in sputtered tantalum films (β-Ta). High substrate temperature is a critical factor in both the purity and degree of orientation of the film. Bias sputtering reduces the impurity content of the films both as a result of low-energy ion bombardment and considerable enhancement of the deposition rate with increasing negative bias.
A Mode-Locked Nd:YAG Laser
Authors: Osterink L. M. , Foster J. D.
Published: February 2004

A mode-locked Nd:YAG laser is described which produces pulses 30 psec in duration at a 2.6 nsec repetition rate. The locking range extends over ≈35 GHz, although the free-running oscillating linewidth is only about 10 GHz. Also discussed is the behavior of the phase of the pulsetrain with changing cavity length. The measured phase shifts provide a means for frequency stabilizing the mode-locked laser. A technique for inducing nondamped relaxation oscillations which modulate the mode-locked pulsetrain is described.
The Effect of Hydrostatic Pressure on the Cleavage Fracture of Polycrystalline Materials
Authors: Francois D. , Wilshaw T. R.
Published: February 2004

The dislocation pileup model of Stroh and the wall splitting model of Stroh and Friedel have been used to calculate the effects of hydrostatic pressure on the fracture stress of polycrystalline metals. For each model, the three critical stages of fracture, nucleation, propagation through a grain, and the propagation across a grain boundary have been considered in turn. The variation of the critical cleavage-crack orientation with respect to the tensile axis has been shown to be a function of the hydrostatic pressure. The fracture stress depends upon the grain size and at high pressures where grain boundary propagation is the critical stage, a d−1/2 dependence was found. This analysis both predicts and provides a physical interpretation of the ductility-transition curve.
Recording and Analysis of Pole Figures by Computer
Authors: Alty J. L.
Published: February 2004

A computer program has been written to produce pole figures using the data from an x-ray texture goniometer. The data are corrected for background and absorption. The pole figure is also stored on magnetic or paper tape in a form suitable for quantitative calculations. As an example, the Hall coefficient of a poly-crystalline sample of a close-packed hexagonal material is computed from the pole figure of the sample in terms of the single-crystal components of the Hall tensor.
Effects of Photon Bunching on Shot Noise in Photoelectric Detection
Authors: Lachs Gerard
Published: February 2004

The shot noise which occurs in photoelectric detection is calculated utilizing fully quantum mechanical procedures. The results which are obtained in this paper include the effects of photon bunching and they differ considerably from classical results which are obtained on the assumption of Poisson statistics. In some cases the Poisson-based classical results lead to shot-noise powers that are in error by as much as an order of magnitude. The results reveal the existence of a relative minimum in the plot of shot noise vs input signal to noise ratio. This suggests the possibility of optimum input signal to noise ratios within certain restricted ranges of the input signal to noise ratio. A plot of the shot noise which is in excess of that predicted by Poisson-based statistics vs input signal to noise ratio reveals a maximum at an input signal to noise ratio of approximately 1.5. This suggests that the enhancement of the Hanbury-Brown and Twiss effect that is obtained when coherent radiation is superposed upon chaotic radiation will be maximized at a coherent-to-chaotic ratio of approximately 1.5.
A Two-Body Model for Calorimeters with Constant-Temperature Environment
Authors: West Estal D. , Churney Kenneth L.
Published: February 2004

Equations are derived describing a model of an isoperibol calorimeter in which the calorimeter proper consists of two parts thermally connected, one surrounding the other and exchanging heat with the constant-temperature environment. These solutions provide insights into the behavior of real calorimeters. Inferences are drawn relative to the effect of the locations of the thermometer and heat source on the energy equivalent of the calorimeter and some possible errors are pointed out. Macleod's application of the two-body theory of King and Grover to high-temperature enthalpy measurements is discussed and weaknesses in theory and experiment are pointed out. Procedures having a better theoretical basis are outlined.
Some Observations of the Acceleration in a Coaxial Plasma Gun
Authors: Pert G. J.
Published: February 2004

The current distribution in the plasma behind the luminous front is investigated by means of magnetic probes. It is found that a standing arc is established at the insulator backplate late in the discharge, which effectively crowbars the current in the gun. The motion of the front under these conditions is compared with the model due to Fishman-Petschek.
Electrical and Structural Properties of Mixed Chromium and Silicon Monoxide Films
Authors: Milgram Alvin A. , Lu Chih-Shun
Published: February 2004

Films containing a mixture of chromium and silicon monoxide were prepared on glass substrates by vacuum deposition. The significance of various deposition parameters was determined. The films were examined by x-ray diffraction, electron microscopy, and ir reflectance and transmission. The electrical conductivity was measured as a function of temperature and applied electrical field. A relationship between film structure and electrical conductivity was found for film compositions which were almost metallic to almost insulating.
Constitutional and Thermal Structure Defects in NiGa
Authors: Wasilewski R. J. , Butler S. R. , Hanlon J. E.
Published: February 2004

The structure defects due to deviation from the equiatomic composition within the structure stability range of NiGa consists of Ni antistructure atoms or Ga-site vacancies, depending on the composition. Large concentrations of thermal vacancies form on heating and can be readily retained by quenching. The effective formation and mobility activation energies have been determined throughout a range of compositions. The ordered B2 structure was found in stoichiometric NiGa to temperatures of about 1000°C. It is shown that in ordered compound lattices thermal defects other than single vacancies must also form. The interaction of the constitutional and thermal defects is qualitatively discussed. Because of possibly complex defect relaxation, the conventional mobility measurements cannot be interpreted as corresponding to simple vacancy relaxation. It is concluded that observations on any single composition cannot be considered representative of the compound throughout its stable structure composition range. Similar considerations apply to other B2 compounds, and the relevance to reported observations in AuCd is discussed.
Intrinsic Resistivity and Electron Mean Free Path in Aluminum Films
Authors: Mayadas A. F.
Published: February 2004

Measurements of the electrical resistivity at 296° and 4.2°K in aluminum films, evaporated both in an ion-pumped ultrahigh-vacuum system and in conventional oil-pumped systems onto unheated glass substrates, are presented and used to calculate the intrinsic mean free path and intrinsic electrical resistivity at 4.2°K. It is shown that the UHV films are characterized by a maximum mean free path of the order of 1 μ and by smaller residual resistances than other films. While the mean free path so obtained is still several orders of magnitude smaller than the published value for high-purity foils of bulk aluminum, it is nevertheless not small enough to appreciably influence the resistivity at 296°K which is measured to be ≈60% higher than the bulk value. This discrepancy, which may be due to structural effects, emphasizes the view that the sample artifact of adding the bulk thermal resistivity to a residual resistivity can be misleading in the case of thin films, even when surface scattering is accounted for.
Microwave Emission from Indium Antimonide Stimulated by Acoustic Wave Amplification
Authors: Turner C. W.
Published: February 2004

A small-signal theory is presented for the emission of microwave noise, stimulated by acoustic wave amplification, from n-type InSb at 77°K in a transverse magnetic field, for electric drift fields below 25 V/cm. The acoustic gain at frequencies different from ω0, the frequency of maximum acoustic gain, is greatest at drift fields exceeding that required for highest gain at ω0. At these fields the gain becomes an extremely broad band phenomenon with substantial amplification occurring at frequencies an order of magnitude greater than ω0. The presence of a transverse magnetic field has been shown to enhance the acoustic gain of a high mobility piezoelectric semiconductor, over a certain range of drift fields, by effectively reducing the rf mobility by the factor 1/[1+(μB)2]. Experimental results obtained from 700 MHz to 12 GHz have shown good agreement with the small-signal theory, which takes into account the electric field distribution within the crystal. In particular, the threshold curves obtained at X-band indicate that a constant value of acoustic gain is required for the production of the emission. Receivers of sensitivities around − 105 dBm were used and could detect emission only for magnetic fields exceeding 1kG, oriented close to the exactly transverse direction. Threshold fields as low as 1 V/cm were measured for the inch-long crystals used, for which μ=500 000 and n=1014 cm−3 at 77°K. The conclusions drawn are that this ``low field'' emission is acoustic in origin, requires the presence of a transverse magnetic field and is a one-carrier type phenomenon.
Closed-Form Solution for a Symmetrically Doped Steady-State p-n Junction
Authors: Fekete D.
Published: February 2004

This paper presents an exact closed-form solution for a symmetrically doped steady-state p-n junction. The solution, based on an assumed form for the charge density, concurs with Shockley's space-charge approximation for linear impurity densities near the junction, and also agrees with computer solutions of the linearly graded junction in the asymptotic region. Applied to germanium and silicon p-n junctions, the method reveals an unexpected concentration of the impurity ion density at the junction for moderately large doping gradients.
Interactions in Sequential Diffusion Processes in Semiconductors
Authors: Hu S. M. , Schmidt S.
Published: February 2004

The effect of an internal electric field and the variation of equilibrium lattice vacancy concentration was incorporated into the continuity equations for the treatment of impurity diffusion in semiconductors. After the explanation of dominant mechanisms involved in the interactions, formulations of the sequential diffusion process and its solution are outlined and numerical results are given. It is shown that the base impurity profile generally experiences a strong retardation by the internal field, resulting in a profile much different from what is generally conceived. Important physical and process parameters of this effect are the extrinsicity factor α (defined as the ratio of impurity surface concentration to twice the intrinsic carrier concentration), the base to emitter diffusivity ratio, and the relative diffusion distance of the base initial profile and the emitter profile. Effect of interaction on the emitter profile is mainly due to the variation of vacancy concentration with doping concentration. In the cases considered, comparisons are made between interacting and noninteracting impurity profiles. One implication particularly emphasized is that sequentially diffused transistor profiles constructed by the superposition method can involve large errors even with accurate experimental data on the single diffused emitter and base profiles. The computed transistor profiles from a boron-arsenic sequential diffusion process, based on the model combining the effect of internal field and vacancy concentration variation, agreed well with the experimental results.
Experimental Investigation of the Low-Voltage Arc in Noble Gases
Authors: Martin R. J. , Rowe J. E.
Published: February 2004

An experimental investigation of the low-voltage arc mode of the hot-cathode discharge has been carried out in a diode utilizing planar electrode geometry. The investigation consisted predominantly of Langmuir-probe measurements of the discharge in a neon atmosphere. Measurements were also obtained in argon, xenon, and hydrogen and hydrogen-neon and argon-neon mixtures. The probes were of planar, guard-ringed geometry. The volt-ampere characteristic of the hot-cathode discharge in the Torr range of gas pressure was investigated to further define the low-voltage arc. For ample electron emission at the cathode there are two stable high-current, low-voltage discharge modes that occur in the noble gases; these are termed the low-voltage arc and the ball-of-fire modes of the hot-cathode discharge. No low-voltage discharge modes were obtained in hydrogen. The steady-state characteristics obtained for the low-voltage arc indicated peak plasma potentials of approximately 14, 6, and 4.5 V for neon, argon, and xenon, respectively, considerably lower than the first excitation level of the respective gases. There is a minimum value of the product of pressure and electrode spacing for the existence of the low-voltage arc; this condition also yields a minimum value of discharge voltage. The discharge voltage and peak electron densities increase with increasing pressure- spacing product, while the peak plasma potential decreases gradually. Measurements on the discharge in neon atmospheres containing small admixtures of hydrogen indicated that cumulative ionization is important for the generation of the low-voltage arc. It was not possible to detect in the measurements on pure noble gas experimental atmospheres any effects due to the presence of impurities. The study of the Penning impurity effect in the low-voltage arc was limited, but showed that mixtures of less than 0.06% argon in neon do affect the discharge.
Effect of Heat Treatment on the 1.370 eV Photoluminescence Emission Band in Zn-Doped GaAs
Authors: Hwang C. J.
Published: February 2004

A number of changes in the 1.370 eV photoluminescence band are observed in Zn-doped GaAs after heat treatment in molten KCN, Ga, or diffusion with Cu at temperatures ranging from 235° to 1100°C. The band is replaced by a CuGa− band at 1.356 eV after Cu diffusion under intrinsic conditions and can be eliminated or preserved, respectively, by heat treating the crystal in molten KCN or Ga above 650°C. Emission of a broad band near 1.37 eV with a sharp-line structure appears after saturation with Cu at temperatures between 550° and 370°C. The structure has a zero-phonon line at 1.429 eV and additional lines separated by about 0.011 eV. No change in the shape of the 1.370 eV band is seen for heat treatment below 550°C in the absence of copper. It is proposed that the centers associated with the 1.370 eV band are VAsZnGa or DAsZnGa pairs, where VAs and DAs denote an As vacancy and a donor impurity occupying an As site, and that the centers responsible for the band with sharp-line structure are VAsCuGa or DAsCuGa pairs. The sharp-line structure probably involves emission of local-mode phonons resulting from the pair substituting for a Ga–As pair in the crystal.
Photoluminescence Study of Defect Formation during Copper Diffusion in Zn-Doped GaAs
Authors: Hwang C. J.
Published: February 2004

A new defect center model is proposed to explain the photoluminescence spectra of Zn-doped GaAs after copper diffusion under extrinsic conditions. These centers introduce a broad band which is located at about 1.37 eV and shows a sharp-line structure. Photoluminescence data taken from samples Cu-diffused at different temperatures for different lengths of time are analyzed to obtain the kinetics of the formation of the defect. It is found that the formation kinetics is of first-order with an activation energy of 1.65 eV. The defects are suggested to be VAsCuGa or DAsCuGa pairs, where VAs and DAs denote, respectively, an arsenic vacancy and a donor impurity occupying an arsenic site.
Search for Forbidden Directions of Elastic Surface-Wave Propagation in Anisotropic Crystals
Authors: Lim T. C. , Farnell G. W.
Published: February 2004

A detailed study of elastic surface-wave propagation on a variety of free surfaces on many anisotropic crystals has been made. Included in the search were cases of propagation on nonsymmetry as well as symmetry planes. To date, no combination of surface, direction of progagation, and crystal has been found for which an unattenuated surface wave satisfying the traction-free boundary conditions cannot be propagated. Solutions are shown for examples which occur within previously reported ``forbidden'' ranges and for cases in which the free surface is a nonsymmetry plane. The ``forbidden'' ranges appear now to be those in which the penetration of the surface wave becomes relatively deep. A fast and general computer program has been developed for this study to allow arbitrary choice of propagation conditions. The direction of energy flow is computed in the general case by effectively constructing the normal to an appropriate segment of the slowness surface. Solutions have been found for pseudo-surface waves in various ranges of directions. These are second surface-type waves which can propagate almost unattenuated.
Analytical Methods for Representing Complex Textures by Biaxial Pole Figures
Authors: Williams R. O.
Published: February 2004

Three angular variables which give the relative orientation between two sets of axes have been defined and their angular range specified for important classes of symmetry. All possible orientations are contained within this angular volume. Continuous ranges of orientations require a continuous density function defined over this volume; this representation is termed a biaxial pole figure. Such figures are a complete representation of the texture since the population of all possible orientations are given. The intensity of diffraction of x rays from any plane is equal to the average density over a defined path through the volume. The problem is one of transforming the x-ray data into the biaxial pole figure. Those methods which have been used for the fiber case are directly extendable to the biaxial case but the increased complexity restricts their usefulness. An iterative method which directly relates the density at any point to only those values of intensity to which it can contribute has been defined and implemented. The method converges to a minimum variance solution for positive values of density. Otherwise the density is zero since negative values are physically inadmissible. A comparison shows this method to give superior results.
Experimental Evidence for the Long-Range Interaction of Domains in Ferroelectric KH2PO4
Authors: Bornarel Jean , Lajzerowicz Joseph
Published: February 2004

Detailed optical observations of domain configurations, together with simultaneous electrical measurements, have been made on ferroelectric KH2PO4. These experiments demonstrate the important variation of the dielectric constant with the lateral domain-wall surface, and also provide evidence of the long-range interaction between domain tips, as well as between domain tips and defects.
Electrical Properties of Xenon-Filled Thermionic Diodes in the Radiation Field of a Nuclear Reactor
Authors: Forman Ralph
Published: February 2004

The properties of xenon-filled thermionic diodes exposed to nuclear radiation in the core of a 5.0 MW nuclear reactor are described. Characteristic curves of current vs voltage are obtained as a function of various parametric changes in the radiation-induced plasma between electrodes. The parameters, which are separately varied, are electrode spacing, xenon pressure, nuclear radiation intensity, and electrode temperatures. Electrical discharge phenomena in the radiation-induced plasma were extensively studied. Breakdown at voltages much lower than the first excitation potential are described and this breakdown effect was studied as a function of the pressure of gas and the distance between electrodes. Results are also reported showing that the electrical discharge in the nuclear irradiated xenon plasma can be sustained with applied voltages as low as 1 V.
Theory of Double Charge Ejection from a Dielectric
Authors: O'Dwyer J. J.
Published: February 2004

A new possibility is explored for steady-state current flow at high field strength in a dielectric with blocking electrode contacts. Solutions are given in dimensionless form for a steady state in which the charge carriers arise solely by collision ionization within the dielectric, injection from the electrodes being negligible. This mechanism is referred to as double charge ejection. If electrode emission becomes significant, it is then not possible to give a solution in universal dimensionless form, but a special case is analyzed to show the effect of the space charge on the electrode emission.
Space-Charge Conduction in Insulators
Authors: Lilly A. C. , Lowitz D. A. , Schug John C.
Published: February 2004

The O'Dwyer theory of emission-limited conduction in insulators has been extensively explored. The current-voltage relations based on two types of charge injection were calculated and compared with experimental data for Mylar insulating films. The fit to the data appears reasonable in a general sense; however, although the values of the parameters needed to obtain the fit are physically realistic, they are definitely different from values obtained in other studies. In addition, the experimental data exhibit ``pure'' Schottky characteristics in the region of high-field strength and this cannot be explained on the basis of the O'Dwyer theory. For both processes of Schottky emission and Fowler-Nordheim emission the theory is limited to a current density above some minimum value, but for different reasons. It is very interesting that in every one of our calculations the space charge according to the O'Dwyer theory was found to persist throughout the entire thickness of the sample.
Effect of Carbon on the Lattice Parameter of Silicon
Authors: Baker J. A. , Tucker T. N. , Moyer N. E. , Buschert R. C.
Published: February 2004

A correlation between the lattice parameter and the carbon concentration in otherwise pure samples of silicon has been observed. Carbon content has been determined by mass spectrometry, infrared, and lattice parameter measurements. Typical values of the carbon concentration are given for some float-zoned silicon crystals and for a series of intentionally carbon-doped crystals.
Dynamics of a Repetitively Pump-Pulsed Nd:YAG Laser
Authors: Carlson D. G.
Published: February 2004

Laser pulse dynamics in a repetitively pump-pulsed Nd:YAG laser are examined. Analytic expressions for the laser pulse height and pulse width for a pump-pulsed laser are given, and the variation of the pulse height and width with pump power, cavity length, and cavity loss in the pump-pulsed mode is compared to the variation in the Q-switched mode. By pulsing a xenon pump lamp (with the lamp discharge maintained at a subthreshold value between pulses), 200 W, 200 nsec laser pulses were generated at repetition rates of several hundred per second. The predicted variation of the laser pulse height, width, and delay with pulsed pump power was verified. Using currently available YAG material and pump cavities, it is shown that 3600 W, 200 nsec laser pulses should be available at 50 kW pulsed pump powers.
Analysis of Alkali Surface Ionization on Porous Substrates
Authors: Husmann Otto K.
Published: February 2004

The evaporation of alkali atoms and ions from porous substrates is analyzed, making the basic assumption that the transport of alkali material occurs only by surface flow of densely packed alkali atoms close to the emitter surface. The alkali efflux velocity to the emitter surface depends on the flow rate per pore and the minimum pore radius within the surface-flow range. A concentration gradient exists radial to the pore exit which causes the neutral efflux and threshold temperature for surface ionization to be larger than the values characteristic of ionizers coated with vapor-deposited alkali. Alkali emission originates from an area surrounding and including the pore exit. The diameter of the emitting region depends on the alkali flow velocity from the pore and the atom and ion desorption energies. The emission region is divided into an inner zone that emits atoms and an outer zone which predominantly emits ions. This analysis predicts that the neutral efflux from the inner zone is inversely proportional to the pore density N and gives numerical values in good agreement with measured data. The neutral efflux from the outer zone follows the Saha-Langmuir equation, the total neutral efflux being the sum of both. The analysis leads to the conclusion that the threshold temperature depends on the minimum pore radius within the surface-flow range. The threshold temperature is also related to the pore density. This analysis may not be applicable to short straight capillaries because it depends on surface flow in the vicinity of the emitter.
Microwave Surface Resistance of Superconducting Niobium
Authors: Turneaure J. P. , Weissman Ira
Published: February 2004

The unloaded Q's of pure Nb cavities in the TE011 mode at 11.2 GHz and in the TM010 mode at 8.4 GHz were measured between 1.2° and 4.2°K to determine whether the residual surface losses in Nb could be made sufficiently low to make it a useful material for practical microwave devices. Three forms of reactor grade Nb were evaluated: recrystallized fully wrought, arc melted, and electron-beam melted. Each of these materials was subjected to additional metallurgical processing including high-temperature vacuum firing and polishing to determine their effects on surface losses. In the TE011 mode, a residual Q of 3.8×1010 was achieved. Also in the TE011 mode, the unloaded Q was observed to be essentially a constant up to the ac critical magnetic field Hcae, where it abruptly decreased by a factor of 100 or more. An Hcae as large as 436 Oe was observed for unstrained Nb. In the TM010 mode, which has electric fields terminating on the surface of the Nb, a residual Q of 2×109 was achieved, the limitation on the maximum field level in the cavity was Hcae, and no power loss associated with electric-field emission was observed up to an electric field of 2.1×105 V/cm, which was the maximum field level obtained in the cavity. The Mattis and Bardeen theoretical expression for the superconducting surface resistance fits the data very well, and the value of the energy gap 2Δ(0) obtained from the fitting procedure is (3.72±0.01) kBTc, which agrees with values of 2Δ(0) obtained by other methods. The surface resistance data are not inconsistent with a double energy-gap model, which has been used to explain specific heat data; however, it was not possible using the data to distinguish between a double energy-gap model and a single energy-gap model with a residual surface resistance. It would be expected that Hcae would be about Hc1 where magnetic flux starts penetrating a type-II superconductor; however, the largest measured Hcae (436 Oe) was in fact about Hc1/4.
A Theory of the Hysteretic Contribution to Internal Friction; Thermomechanical Unpinning of Dislocations
Authors: Peguin P. , Birnbaum H. K.
Published: February 2004

The thermomechanical unpinning and repinning of dislocation lines pinned at equidistant points are analyzed. The hysteretic type of internal friction which results from this unpinning is calculated using a computer program which allows an examination of the effects of stress, temperature, frequency, dislocation-pin interaction energy, dislocation loop length, and density of pinning points. It is shown that the internal friction due to thermomechanical unpinning is a function of the above variables. The hysteretic damping exhibits a maximum as a function of temperature, frequency, and stress, and the characteristics of these peaks are examined. A brief comparison of the calculated damping with the experimental results is made and it is shown that the theory can qualitatively account for the features of deformation produced damping peaks such as the Bordoni and Hasiguti peaks.
The Transmission of Electromagnetic Waves and Pulses into the Earth
Authors: King Ronold W. P. , Harrison Charles W.
Published: February 2004

The transmission into the earth of an electromagnetic transient, such as might be generated by a nuclear explosion, is of interest from the point of view of determining the shielding properties of the earth. A plane electromagnetic pulse normally incident on a plane earth is studied as a convenient model. The steady-state transfer function is first evaluated and its properties analyzed for dry, moist, and wet earth over the complete frequency spectrum. The transmission of an incident pulse of Gaussian shape in air is formulated and its shape determined as it enters and advances into the earth. The numerical results determined by a high-speed computer are analyzed and discussed.
Magnetic Anisotropy of MnSb–Sb Aligned Eutectic
Authors: Jackson M. R. , Tauber R. N. , Kraft R. W.
Published: February 2004

Unidirectional solidification of melts of MnSb–Sb eutectic at 2 cm/h has produced an aligned structure. The ferromagnetic MnSb phase exists in the eutectic as rods 2 μ in diameter and several millimeters in length in an Sb matrix. X-ray examination has shown the fibers to be single crystals all having the same orientation relative to the single-crystal matrix. Both as-cast and aligned structures were found to have the same saturation magnetization as bulk MnSb samples. Magnetic anisotropy was studied at room temperature with a magnetic torque technique and correlated with crystallographic data. The measured easy directions for specimens cut at various angles to the growth direction were all in a plane defined by the fiber axis and the normal to the (011̄1) plane of MnSb. The normal to the (011̄1) plane lies in a cone 60 deg from the c axis; this cone has been previously reported to be the cone of easy magnetization for bulk MnSb. The observation that only one direction in the cone is operative for the eutectic is attributed to the interaction of shape and crystalline anisotropies in the aligned eutectic. Another factor that may determine the behavior is strain anisotropy.
Analysis of Thermal Desorption Spectra
Authors: McCarroll Bruce
Published: February 2004

The behavior of detector signals corresponding to the thermal desorption of gas from a solid surface for integral-order kinetics is investigated with respect to variations of the parameters describing (1) the kinetics of the desorption process itself, and (2) the interaction of the desorbed gas with the vacuum system. A computational approach is used because the equations describing the simple model used are, generally, analytically intractable. A computer-driven display and a data-logging system facilitate not only the analysis indicated above, but also curve fitting so that the kinetic parameters can be extracted from experimental desorption data containing distortions caused by gas scattering from structures in the vacuum system.
Transverse Magnetoresistance in Thin Epitaxial Films of PbS: Evidence for a Layered Distribution of Charge Carriers
Authors: Brodsky M. H. , Schoolar R. B.
Published: February 2004

Room-temperature transverse magnetoresistance measurements on n-type PbS films are reported. The results are different for magnetic fields perpendicular and parallel to the film faces. This anisotropy is sensitive to ambient and is understandable in terms of a model consisting of an n-type bulk region and p-type surface space-charge layer.
Conductivity, Thermoelectric Power, and Valence-Band Structure of Thallium Selenide
Authors: Nayar P. S. , Verma J. K. D. , Nag B. D.
Published: February 2004

Electrical conductivity and thermoelectric power of lead-doped thallium selenide (TlSe) of various doping concentrations have been measured. It is found that the material always remains p type. At room temperature, thermoelectric power shows a maximum for a certain value of conductivity and thereafter decreases with increase of conductivity. A qualitative discussion of the applicability of the two-valence-band model is also presented.
The Orientation of Domain Walls in Twinned Ferroelectric Crystals
Authors: Fousek Jan , Janovec Václav
Published: February 2004

Due to the spontaneous deformations of ferroelectric crystals in their ferroelectric phases, twins (domains) may be separated only by those composition planes (domain walls) which satisfy the mechanical compatibility conditions; such planes are in an infinite crystal called permissible walls. A mathematical treatment is proposed which makes it possible to find all permissible walls in any ferroelectric species. It is shown that different types of permissible walls exist: W∞ walls with arbitrary orientation, crystallographically prominent Wf walls, and S walls whose indices depend on PS and the electromechanical coefficients. The orientations of such S walls are necessarily temperature dependent. Two particular domains may be separated by a W∞ wall or by one of two mutually perpendicular permissible walls of Wf and/or S type. In a number of species, however, there are pairs of domains between which no wall is permissible. It is shown that the occurrence of W∞ and Wf walls can be predicted from the symmetry properties of the paraelectric phase. The properties of S walls are discussed in detail. Among the known ferroelectrics, S walls are most likely to exist in MASD and in boracites. The available data on nickel-chlorine boracite suggest that S walls have been observed in this material.
Effect of Hydrostatic and Shock-Wave Compressions on the Magnetization of a 31.4 at.% Ni–Fe Alloy
Authors: Wayne R. C.
Published: February 2004

The saturation magnetization of a 31.4 at.% Ni–Fe alloy has been measured as a function of hydrostatic pressure between 0 and 26 kbar, and as a function of shock-wave compression between 2.5 and 112 kbar. From the hydrostatic pressure measurements, a zero-pressure value of the pressure derivative of the saturation magnetization (∂lnσs/∂P) = −3.15×10−2 kbar−1 is found. A marked departure from linearity of σs(P) is seen at higher pressures. This is considered to be due to the slope of σs(T) becoming steeper and steeper at the ambient temperature as the Curie temperature is depressed by pressure. The shock-wave compression experiments yield a value of (∂ lnσs/∂P) = −2.8×10−2 kbar−1 in the 15–40 kbar stress range.