bluuebunny/crossref_metadata_2025 huggingface dataset:
Operation of a Traveling-Wave Maser in a Transverse Field Superconducting Electromagnet
Authors: Nilsen W. G.
Published: April 2005

A 6-Gc traveling-wave maser has been operated in a novel transverse field superconducting magnet. The magnet produces a uniform field in excess of 4000 Oe over a volume of 1.2×1.5×6 in. The field is directed across the shortest dimension (perpendicular to the direction of propagation) which permits nonreciprocal gain and attenuation. The TWM exhibited net gain in excess of 30 dB with 3-dB bandwidths of about 20 Mc. Gain and bandwidth characteristics were the same as those measured on the same traveling-wave maser in the field of a large laboratory magnet. This indicates a field homogeneity of about ±1 Oe or better in the superconducting magnet over the ruby volume of the maser since greater deviations would result in decreased gain and increased bandwidth.
Statistical Tables for Testing Random Orientations of Cubic Crystals
Authors: Weymouth John W. , Epstein Jean H.
Published: April 2005

Critical regions at the level of significance α=1, 5, 10, and 20% are presented in tabular and graphical form for testing whether or not a sample of single, cubic crystals is randomly oriented. The reasoning behind the statistical test is briefly discussed. The use of the tables is illustrated with a sample from the literature.
Conditions Pertinent to the Occurrence of Fiber Orientation in Iron Films <1000 Å Thick Deposited onto Amorphous Substrates
Authors: Clapp Roger W.
Published: April 2005

Iron films having thicknesses of 20, 100, and 250 Å were deposited from the vapor in a vacuum of about 2×10−5 mm Hg at a rate of deposition of approximately 8 Å/sec onto Formvar substrates initially at room temperature and onto silica substrates initially at 50°C. Prior to deposition the latter were baked-out at 500°C for 1 h. Transmission electron diffraction patterns of the specimens were examined with a microphotometer and no evidence of fiber orientation was found. These experiments were repeated with films being deposited at pressures of 10−2 and 10−1 mm Hg of helium introduced into the system after initial evacuation of the system to about 2×10−5 mm Hg. Again random orientation was observed for both the Formvar and silica-backed films. Comparison of the conditions characterizing this work with those describing similar work in which a fiber texture did occur leads to the formulation of the hypothesis that if the experimental technique does not include at least one of two conditions (high deposition rate, high substrate/deposit surface temperature), then fiber orientation is not likely to occur in thin (<1000 Å) iron films deposited onto amorphous substrates, but only in thick films for which prolonged exposure to the radiant source eventually sufficiently elevates the surface temperature. A qualitative description of the processes involved is suggested.
Amplification of Ultrasonic Waves in Piezoelectric Semiconductors
Authors: White D. L.
Published: April 2005

An ultrasonic wave traveling in certain directions in a piezoelectric semiconductor such as cadmium sulfide can be amplified or attenuated by application of a dc electric field. The direct current flowing through the medium in the presence of an ultrasonic wave creates a traveling ac field which interacts with the ultrasonic wave. Amplification occurs when the drift velocity of the electrons exceeds the velocity of sound. For strongly piezoelectric semiconductors, amplification of as much as several percent per wavelength of path is obtainable. Calculations show that for properly prepared material, significant amplification is expected up to the microwave frequencies. At high frequencies, gain is reduced because electron diffusion smooths out the electron bunching necessary for amplification. The dc power required increases rapidly with frequency, and at frequencies above one or two thousand megacycles only pulsed operation seems feasible. Applications as a tool in ultrasonic studies, and for devices such as delay lines and amplifiers, are also discussed.
Effect of the Temperature of Formation on the Crystallinity and Electrical Properties of Germanium Films on Fluorite
Authors: Schalla R. L. , Thaller L. H. , Potter A. E.
Published: April 2005

Crystalline germanium films were grown epitaxially by vacuum evaporation of germanium onto heated fluorite substrates. In the work reported here, the effect of substrate temperature during film evaporation on the crystallinity and electrical properties of the films has been explored. Thirty Ω-cm p-type germanium was evaporated in a conventional bell jar at pressures between 10−5 and 10−4 mm Hg. The germanium was evaporated from a resistance-heated tantalum boat onto a fluorite plate. Substrate temperatures varied from 470° to 915°C, while the rate and duration of evaporation was held constant at about 1500 Å/minute and two minutes, respectively.

The crystalline nature of the films was studied by electron diffraction. The transition from a nearly amorphous film at 470°C to a nearly single-crystal film at 915°C was observed. Hall coefficients and electrical conductivities were measured for the films, which were p type as was the starting material. These results are presented along with the mobilities and carrier concentrations calculated from them. The mobilities increase rapidly with film evaporation temperature. Carrier lifetimes were found to be less than 1 μsec in the most crystalline film, whereas the original germanium had a carrier lifetime of about 12 μsec.
1/f Noise from Vacuum-Cleaned Silicon
Authors: MacRae A. U.
Published: April 2005

The removal of the adsorbed gases and the surface oxide on single-crystal, 100 Ω-cm silicon filaments by ion bombardment and annealing does not have an appreciable effect on either the magnitude or the frequency dependence of the 1/f noise from the filament. Since the slow surface states are commonly associated with gases adsorbed on the oxide, charge transfer between these states and the bulk cannot be the primary source of 1/f noise in semiconductors. The changes in the 1/f noise that were observed during the surface cleaning procedure can be correlated with the presence or absence of an inversion layer at the surface.
Thermal Noise in Linear, Lossy, Electromagnetic Media
Authors: Vanwormhoudt Marc , Haus H. A.
Published: April 2005

The thermal radiation of lossy media is described by a random current-source term that is introduced into Maxwell's equations. The media treated are linear, in general anisotropic, nonuniform, and such that the constituent relations are not local relations, but are described in terms of a Green's operator. For such media, in thermodynamic equilibrium, it is shown that simple relations exist between the correlation and spectral density matrices of the random current-source field and the Green's conductivity operator. These relations are analogous to Nyquist's theorem of lumped circuits.
Etch Pits and Polarity in CdTe Crystals
Authors: Inoue Morio , Teramoto Iwao , Takayanagi Shigetoshi
Published: April 2005

Two types of etch pits in cadmium telluride have been observed. The etchants used are nitric acid solutions of potassium bichromate which also contain silver ions of various concentrations. The etch pits resulting from etch (EAg-1) grow into a tetrahedral shape bounded by the crystallographic habit planes and reveal geometrical polarity on the (111) and (1̄1̄1̄) surfaces. Another type of etch pit is formed at a different point from that of the pit with EAg-1 by the modified etch (EAg-2), which has increased content of Ag+ ion. The two types of etch pits, with EAg-1 and with EAg-2, are believed to be associated with Cd and Te edge dislocations. The dissolution rate and its selectivity to the constituent elements in cadmium telluride is controlled electrochemically by the variation of the Ag+ ion concentration of the etching solution. The structure of the twin boundary is also studied by etching and back Laue techniques.
Numerical Evaluation of X-Ray Absorption Factors for Cylindrical Samples and Annular Sample Cells
Authors: Paalman H. H. , Pings C. J.
Published: April 2005

An analysis is presented for the absorption corrections necessary for the x-ray analysis of diffraction data from a liquid sample confined within a cylindrical sample cell. The evaluation of necessary absorption integrals has been formulated in a numerical calculus procedure appropriate for a digital computer. The procedure has been verified against previous graphical computations.
NMR and Dilatometric Studies of Polyethylene Recrystallization
Authors: Peterlin Anton , Roeckl Ernst
Published: April 2005

Polyethylene samples with different thermal history were annealed at temperatures slightly below melting point. The chain immobilization as revealed by NMR shows first a decrease corresponding to a partial melting and a subsequent slow continuous increase as a consequence of progressive recrystallization. Dilatometric measurements demonstrate two different mechanisms of crystal growth. Primary crystallization with an Avrami coefficient n=3 and a long induction period for nuclei formation characterizes the initial solidification from melt during which the bulk of the sample crystallizes. The volume reduction at subsequent crystallization of the remaining amorphous areas completely blocked by spherulites produces a negative pressure and hence a local melting point depression strongly hampering further crystal growth. This effect is still enhanced by increased concentration of rejected impurities, e.g., short chain or branched macromolecules contained in the sample, which being intrinsically noncrystallizable at a given temperature also reduce the maximum attainable crystallinity. After this transition period during which n drastically drops and soon loses any physical meaning the secondary crystallization begins, where the change in density is no longer due to an increase in crystal-to-total-volume ratio but only to the increasing thickness of the initially formed crystals accompanied by a reduction of the surface-to-volume ratio. The slow density increase with annealing time is fully accounted for by the better order and density in the growing core of lamellar crystals as compared with the less dense surface layers, and by the time dependence of lamellar thickness at the annealing temperature.
Crystal Interfaces. Part II. Finite Overgrowths
Authors: Van Der Merwe J. H.
Published: April 2005

A calculation of the interfacial energy between a crystalline film and a crystalline substrate of a different substance for the simple case in which the lattice parameters differ in one direction only, is presented. The results are expressed in terms of film thickness h, interfacial misfit η, interfacial bonding, and relative hardness of film and substrate. A parabolic interfacial potential has been used to investigate the effect of h showing that it is only a significant factor when either or both h and η are small. It is further shown that, in the minimum energy configuration of the system, the film is homogeneously strained. According to the calculations, a critical value of misfit ηc exists below which the film is strained to fit the substrate exactly and above which the required strain is an order of magnitude less than ηc. The misfit ηc is estimated to vary from as much as 13% for a ``soft'' monatomic layer which is tightly bound down to practically zero for thick films which are loosely bound. It is shown that the interfacial energy associated with an infinitely thick film as calculated with a Peierls-Nabarro type of interfacial force, is a useful approximation for many purposes. Approximate expressions for the strains in terms of the relevant parameters are deduced from this result.
Diffusion of Gases in Polyethylene Terephthalate
Authors: Michaels Alan S. , Vieth Wolf R. , Barrie James A.
Published: April 2005

Diffusion of helium, oxygen, nitrogen, argon, carbon dioxide, and methane in glassy and rubbery polythylene terephthalate has been studied in the range 25° to 130°C. Despite the abnormal solution behavior of these gases in the glassy polymer, the diffusion process is evidently normal and Fickian: Correlation of solubility constants for oxygen and nitrogen, obtained by the time-lag method, with data obtained by a static sorption method, indicates that glassy crystalline polyethylene terephthalate may be considered an isotropic diffusion medium. Diffusion is impeded purely geometrically by the presence of the crystallites, and the impedance factor is equal to the reciprocal of the amorphous volume fraction. In the rubbery crystalline state of the polymer, diffusion is Fickian and apparent activation energies for diffusion are larger than those in the glassy crystalline polymer. A model for diffusion in the glassy amorphous and crystalline polymers is proposed, assuming that the driving force for diffusion is the concentration gradient of dissolved molecules which are assumed to be in local equilibrium with molecules in the ``holes.'' The model predicts that actual diffusion constants and activation energies are larger than those experimentally measured. Thus, part of the observed difference between values of EDa in the glassy and rubbery states may be reconciled. Correlations of D and EDa with the square of gas molecular diameters are obtained in both the glassy and rubbery states. In the latter plots, the helium data fall above the correlations, showing evidence of partially non-activated diffusion in both states of the polymer.
Transport Properties of Bismuth Single Crystals
Authors: Gallo C. F. , Chandrasekhar B. S. , Sutter P. H.
Published: April 2005

The absolute Seebeck coefficient, electrical resistivity, and thermal resistivity were simultaneously measured on pure bismuth single crystals of various orientations between approximately 80° and 300°K. Using an overlapping two-band many-valley model, numerical values for the temperature dependence and anisotropy (where appropriate) of the following parameters have been calculated: (1) the overlap energy and the Fermi energy of the electrons and of the holes, (2) the density of states effective mass of the electrons and of the holes, (3) the separate electronic and lattice thermal conductivities, (4) the actual index of thermo-electric efficiency, and (5) the hypothetical ``optimum'' index of thermoelectric efficiency. The calculated electronic thermal conductivity includes a new term due to bipolar diffusion.
Surface Ionization of Potassium on Tungsten
Authors: Wendt John F. , Cambel Ali Bulent
Published: April 2005

Potassium ion current densities produced by the surface ionization of potassium on a tungsten filament were measured as a function of the filament temperature, applied potential, and potassium vapor density. The current densities, which were two orders of magnitude larger than previously measured values, compared qualitatively with the results predicted by the Saha-Langmuir equation and quantitatively with the results predicted by Child's space-charge law. The extrapolation of previously measured values of the ionic current density by two orders of magnitude agreed with the values measured by the author. The range of measured saturation current densities was from 38 to 83 mA/cm2 with field strengths on the order of 104 V/cm.
Recombination Radiation in GaAs
Authors: Black J. , Lockwood H. , Mayburg S.
Published: April 2005

Recombination radiation in GaAs diodes has been found proportional to the forward diode current at current levels where the recombination radiation is dominant, implying an efficient conversion from injected electrons to band-edge photons. A visible red radiation has been observed from these diodes at high forward diode currents.
Approximate Formulas for Coaxial Two-Cylinder Lenses
Authors: Morikawa Minoru
Published: April 2005

The approximate formulas of cardinal elements of strong coaxial two-cylinder lenses are given by modifying the methods of Grivet et al. and of Félici. The basic idea used by them is to approximate the function T(z) in the path equation by the one which has the same area and abscissa of the center of gravity as T, and which gives exact solutions. Various modified methods of approximating this function, by a proper choice of the width of the replacing function, are given. New formulas are applied to several cases and it is shown that certain modifications, such as replacing T with a rectangular variation and making its width equal to the width at 1/4 the height of T, results in rather small errors. For example, the errors of the average focal length and the locations of the focal points in a two-cylinder lens are smaller than 0.01 in units of the diameter of the cylinder for φ2/φ1≲20.
Preparation of Crystalline Germanium Films on Metals
Authors: Weinreich O. A. , Dermit G.
Published: April 2005

Two methods of obtaining Ge films on tungsten having single-crystalline regions up to 1 mm large are described. One consists in melting a quasi-amorphous Ge film prepared by thermal evaporation with a scanning-electron beam. In a second procedure a tungsten sheet is pulled from a Ge melt. Films prepared by both methods were used to form p-n junctions. The I-V characteristic of a tunnel diode, made by using a Ge film on tungsten is shown. The Ge films on tungsten, after melting and solidifying, are different from thermally evaporated epitaxial Ge films. The latter contain a high concentration of defects which makes junction formation difficult.
Application of the Theory of Paracrystals to the Crystal Structure Analysis of Polyacrylonitrile
Authors: Lindenmeyer P. H. , Hosemann R.
Published: April 2005

X-ray diffraction from single crystals of polyacrylonitrile shows that the diffuse nature of the nonequatorial scattering maxima cannot be accounted for by crystal size. The theory of paracrystals may be used to set both an upper and a lower limit to the amount of lattice distortion and yields a plausible explanation for the absence or extreme weakness of higher-order reflections. Finally, it is shown why the diffuse maxima cannot be used directly in measuring lattice parameters and the method which must be used to obtain a more definite crystal structure for polyacrylonitrile is indicated.
Wide-Line Nuclear Magnetic Resonance Studies of Poly (Ethylene Terephthalate)
Authors: Boye C. A. , Goodlett V. Wilson
Published: April 2005

Wide-line nuclear magnetic resonance (NMR) studies have been made as a function of temperature and the angle between the stretch direction and the magnetic field on one-way stretched poly (ethylene terephthalate) film. The data obtained were consistent with a structural model, the important features of which are the directions of the lines between interacting methylene and aromatic protons relative to the stretch direction. Evidence for planar orientation in one-way stretched poly (ethylene terephthalate) film was obtained from wide-line NMR data which were taken as a function of the angle between the normal to the film surface and the magnetic field. A difference of approximately 25°C has been observed in the temperature at which the sharp component appears in annealed, unoriented poly (ethylene terephthalate) film and powder phase material from the solid-phase buildup reaction. This difference is explained as being due to a difference in the degree of crystalline perfection.
Crystal Habits and Morphology of n-Tetranonacontane (n-C94H190)
Authors: Khoury F.
Published: April 2005

The electron microscope has been used to study (i) the growth habits of orthorhombic (a=7.4Å, b=4.95 Å, c=122 Å) crystals of n-tetranonacontane grown by cooling hot dilute solutions of this n-alkane in xylene to room temperature and (ii) to examine by means of a replicating technique the surface morphology of monoclinic (a=9.0 Å, b=4.95 Å, c=122 Å, β=123°) n-tetranonacontane crystallized from the melt in polycrystalline form. The general habit characteristics of orthorhombic solution grown single crystals, {110} twinned crystals, multiple {110} twins, as well as {310} twinned crystals are described. In addition, the observed dependence of the habit of {110} twinned crystals on screw dislocations situated within the constituent twin lattices as well as the twin boundary in such crystals, is considered in some detail. Polycrystalline monoclinic n-tetranonacontane is shown to possess a distinctly stepped surface structure. The steps are of the order of 100 Å in thickness. It is deduced that the interstep surfaces are {001} faces of the constituent molecular layers and that these layers are bound peripherally by {hko} faces. Although no distinct spiral growth patterns associated with screw dislocations have been observed, the apparent presence of such dislocations in these polycrystalline samples is indicated.
Specific Heat of Atactic and Isotactic Polypropylene and the Entropy of the Glass
Authors: Passaglia Elio , Kevorkian Hagop K.
Published: April 2005

The specific heat of atactic and isotactic polypropylene has been measured from 80° to 490°K. The isotactic sample was 64.9% crystalline, as determined by specific volume, and the atactic sample was 2–3% crystalline, as determined by the specific heat measurements. Below the glass temperature, which was found to be 259°K, and above the melting point, which was found to be 447°K, the specific heats are very nearly the same. From the data, the entropy, enthalpy, and free energy referred to absolute zero were computed. The heat of fusion of pure isotactic polypropylene crystal was found to be 45 cal/g. On the basis that the thermodynamic functions for the two materials above the melting point are the same, the residual entropy of the glass at absolute zero is calculated to be 0.62±0.2 eu/mole. The behavior of the thermodynamic functions is such that a lowering of the glass temperature by 53±20°K would produce a glass of zero configurational entropy. A lowering of 150±15°K is necessary to make the enthalpy of the glass equal that of the crystal. It is deduced that underlying the observed glass transition is a second-order transition in which the entropy of the supercooled liquid is a primary factor.
Response of Photoconducting Imaging Devices with Floating Electrodes
Authors: Sommers H. S.
Published: April 2005

A simplified charge control type of analysis is made of the response of photoconducting imaging devices with a floating electrode. The change of electrode potential with discharge of the device is found to have an importance not previously recognized. The results are relevant for a variety of electrostatic photographic devices and show the dependence of the performance on certain details of the image development process.

The floating electrode limits the gain during exposure to light to one charge pair per quantum absorbed. For the Vidicon TV camera picture tube, a detailed study of the process of reading the stored information demonstrates that net gain exceeding unity can be achieved. The upper limit to the gain is the ratio of the time for the scanning beam to traverse a picture element to the transit time of a free carrier through the layer. This conclusion holds when the time required to trap a free carrier exceeds its recombination lifetime. None of the gain-bandwidth relations yet deduced for photoconductors is applicable to this case. Earlier studies which led to a maximum gain of approximately unity for the Vidicon assumed fast trapping of free carriers.

For the Vidicon, the conditions for gains greater than unity with full frame storage and small lag are developed, including the characteristics of the scanning beam and of the trapping and recombination centers. Suitable targets with only one free carrier should have a low sensitivity photoconductor with a significant density of slow trapping states. Discussion of the similarity between the performance of a homogeneous target with one free carrier and an npn structure shows that the slow trapping states in the uniform layer play the role of the donors and acceptors in the junction device.
Electromagnetic Shock Waves in Gyromagnetic Media
Authors: Hatfield W. B. , Auld B. A.
Published: April 2005

The propagation of finite amplitude electromagnetic waves in a gyromagnetic medium is discussed. It is shown, using the method of characteristics, that in the quasistatic or low frequency limit a wave propagating parallel to the external dc magnetic field distorts continuously until a discontinuity or electromagnetic shock wave appears in the wave profile. When higher-order effects are taken into account, the shock front is found to have a finite width which is reached by a balance between the nonlinear wave-steepening torque term and the wave-broadening loss term. The calculated shock-front width is found to be independent of crystalline anisotropy and exchange and magnetoelastic effects. The theoretical results are compared with numerical calculations and the possibility of using electromagnetic shock waves in pulse sharpening networks and microwave devices is discussed.
Space-Charge Instabilities in Electron Diodes. II
Authors: Bridges William B. , Birdsall Charles K.
Published: April 2005

A detailed analysis of space-charge instabilities in diodes is presented. The oscillation when the input current exceeds the ``limiting input current'' (from an earlier analysis for a short circuited diode with a zero temperature stream) persists with the addition of a diode resistance, or with a two-velocity input or a Maxwellian velocity distribution input, or with streams of finite diameter. The time-averaged value of the minimum potential is nearly zero, as in the classical solution; however, the time-averaged minimum position and transmitted current differ considerably from the classical values. The recovery of the stable state is by a jump rather than gradually as in the classical solution. A small-signal prediction of time growth of all first-order variables (potential, current, velocity) at the point of limiting is given. An energy argument using the zero-order variables is presented showing the onset of instability. Experiments agreed with some parts of the analysis but did not show oscillations with amplitudes as large as expected.
Effect of Hydrostatic Pressure on the Emission from Gallium Arsenide Lasers
Authors: Fenner G. E.
Published: April 2005

The pressure shift of both the coherent and the incoherent emission of GaAs junction lasers has been measured at about 200°K. The peak of the spontaneous emission shifts by +1.09×10−5 eV/atm, which is in agreement with the pressure coefficient of the band gap in GaAs determined by experiments based on the change of resistance under pressure. The shift of the coherent modes is much smaller, namely, +2.96×10−6 eV/atm. The effect of the compressibility on the latter shift is shown to be negligible. It is concluded from considerations of a simple model that the shift of the coherent radiation is primarily due to a change of the dielectric constant with pressure.
Fluorescent Yield in the Phosphor NE-102 for X Rays from 4 to 17 keV
Authors: Bailey L. Evan
Published: April 2005

The measured light output per absorbed x-ray photon of the plastic phosphor NE-102 in the 4- to 17-keV range of x-ray energy fits a straight line with a positive intercept of 1.44 keV.
Effect of Pressure on the Electrical Resistance of some Transition-Metal Oxides and Sulfides
Authors: Minomura S. , Drickamer H. G.
Published: April 2005

The effect of pressure has been measured on the electrical resistance of fourteen oxides and five sulfides of transition metal ions, as well as on four ferrites. In general, the resistance decreased with increasing pressure at a faster rate for compounds with a high oxygen-to-metal ratio than for those with a lower ratio. For the semiconducting compounds the temperature coefficient of resistivity decreased with increasing pressure, but at a rate which would give metallic conduction only at very high pressures (0.7–2.0 Mbars). V2O5 and CrO3 exhibited phase transitions, but remained semiconducting in the high-pressure phase. The sulfides showed markedly larger pressure coefficient of resistance than did the oxides.
An Investigation of the Constant-Current Characteristics of Materials Having a Positive Temperature Coefficient of Resistance
Authors: Wilson G. W. , Schomberg S.
Published: April 2005

Ferroelectric ceramic compounds doped to make them electrically conducting show a marked increase in resistance over a limited temperature rise. They also show good current regulation over a wide range of applied voltages.

The current regulation is dependent upon the shape of the resistance/temperature curve and also upon the mode of heat dissipation from the ceramic. In particular, the magnitude of the constant current obtained is governed by the minimum resistance of the material used. Experimental investigation of these characteristics revealed that the resistance of the material was affected by the voltage applied to it, decreasing as this potential was increased. This led to the variation in the resistance of the pellet with temperature (determined from current and applied voltage measurements) becoming linear, and considerably reduced the positive temperature coefficient of resistance from that obtained when a low constant voltage was used.

This voltage dependence of resistance can probably be explained on the basis of traps at the grain boundaries forming potential barriers through which electrons taking part in the conduction processes have to tunnel.
Surface Energy of {100} Potassium Chloride
Authors: Westwood A. R. C. , Hitch T. T.
Published: April 2005

A modified Obreimov-Gilman cleavage technique utilizing the apparent variation of cleavage surface energy with crack length and specimen dimensions has been used to determine the true surface energy γ0 of the {100} planes of potassium chloride at room temperature. γ0 {100} KCl was found to be 110±5 ergs/cm2, in good agreement with Born and Stern's theoretical estimate of γ0 (108 ergs/cm2) but not with more recent estimates of this quantity (160–185 ergs/cm2). Possible causes for this discrepancy are discussed.

Other experiments revealed that the presence of a solvent environment at the crack tip increased the cleavage fracture energy only some two or three times. This suggests that the Gurney-Pulliam phenomenon of precipitation at a crack tip is not primarily responsible for the increased strength and ductility of ionic crystals tested in solvent environments (Joffe's effect).
Tracks in Fission-Fragment-Bombarded Lead Iodide
Authors: Chadderton L. T. , Montagu-Pollock H. M. , Torrens I. McC.
Published: April 2005

The nature of fission-fragment tracks in crystals of lead iodide is sensitively dependent on the thickness of the crystal as well as on the energy, mass, and direction of the incident particle. As the thickness of the specimen is increased the white contrast tracks seen in the electron microscope become discontinuous, and with diffraction contrast they change to tracks that are dark on a lighter ground. At even greater thicknesses no tracks are visible, but only a random array of inclined dislocation loops.

Tracks formed from fission fragments arising from thick pieces of uranium foil show branching that is interpreted as due to the registration of knocked-on atoms. Calculations of the rate of energy loss for fragments in lead iodide, made on the basis of a treatment first given by Bohr, are in qualitative agreement with the observations.
Point-Defect Relaxation in Rutile Single Crystals
Authors: Carnahan R. D. , Brittain J. O.
Published: April 2005

The existence of a well-defined relaxation process was established in internal friction studies of nonstoichiometric rutile, TiO2, crystals. The peak was observed only in crystals which were vacuum reduced to a room-temperature-resistivity value of 21 Ω-cm or less and oriented so that the principle vibrational strain coincided with an ``a'' crystallographic axis. All resistivity measurements were made with the current flowing parallel to the longitudinal specimen axis. For measurements in the frequency range 3 to 10 cps, the peak temperature varied from ≃60 to 85°C and exhibited a dependence on the degree of reduction, i.e., the peak temperature increased with increasing reduction. The average activation energy for the process obtained from peak shift and peak shape determinations was 24 kcal/mole. Crystallographic considerations coupled with the orientation dependence of the peak suggest that the nonstoichiometric defect in vacuum-reduced rutile is the titanium interstitial.
Prismatic Dislocation Loops in Cold-Worked and Annealed MgO Crystals
Authors: Groves G. W. , Kelly A.
Published: April 2005

Plastic deformation introduces elongated edge-dislocation loops into MgO crystals. Annealing at 1200° to 1500°C does not entirely remove this damage, even close to a free surface. Instead, relatively large circular vacancy loops are derived from the elongated loops. Successive anneals increase the mean diameter of the loops and reduce their number. In crystals which had been heavily strained by repeated bending the mean diameter increased linearly with total annealing time, within the limits 500 to 2000 Å. Loop growth is interpreted as being due to the production of vacancies by plastic flow, in a concentration of at least 10−6 for each 1% strain.
Dislocations and Glide in Lead Sulfide as a Function of Deviations from Stoichiometry and Doping Additions
Authors: Franklin Wilbur M. , Wagner J. Bruce
Published: April 2005

Point defects induced in PbS by slight deviations in chemical composition about the stoichiometric ratio were shown in a qualitative experimental study to affect dislocation density and strength. A very small but reproducible increase in dislocation density was observed by an etch-pit method in single crystals of PbS and in silver-doped PbS having excess sulfur or excess lead as compared with the stoichiometric composition. With a prismatic punching technique to obtain a measure of the yield strength, a slight increase in strength was found to correlate with an increase in point defect concentration in PbS. An etch-pit and slip-line analysis of glide in stoichiometric PbS verified the single primary glide system {100}〈110〉.
X-Ray Analysis of Stacking Fault Structures in Epitaxially Grown Silicon
Authors: Schwuttke G. H. , Sils V.
Published: April 2005

X-ray diffraction microscopy measurements were made on epitaxial silicon. The diffraction contrast produced by different stacking fault combinations was investigated. Fault structures were deduced from changes in diffraction contrast that occur in topographs recorded by different Bragg reflections. It was found that diffraction contrast of single-bend and multibend faults is in agreement with the occurrence of stair-rod dislocations at each bend. Diffraction contrast due to line defects is not consistent with the idea of simple stacking faults. The x-ray measurements indicate that the line defects are also traces of bent stacking faults. The bend must be parallel to the substrate-layer interface. It is concluded that line defects are generated by a stress relief mechanism.
Colloid Absorption Band in CsBr
Authors: Jensen Richard E.
Published: April 2005

An optical extinction band in colored CsBr at 1050 mμ is attributed to colloidal cesium precipitates. The peak wavelength may be closely predicted by assuming the extinction is due to a plasma resonance of conduction electrons in the cesium particles. The band is relatively insensitive to temperature change. The bandwidth decreases as the particle size increases. The shape of the extinction curve is distorted at low temperatures, indicating a distortion of the particle shape. The band resists bleaching.
Analysis of Exo-Electron Glow Curves
Authors: Young Joseph F. , Williams David J.
Published: April 2005

Exo-electron glow curves for an oxide surface on aluminum have two principal peaks. The analysis supports the theory of thermostimulated exo-electrons originating in traps below the conduction band. The aluminum oxide surface had two types of traps, both approximately one electron volt below the conduction band, and attempt-to-escape frequencies of 4×1010 sec−1 and 4×109sec−1.
A Photomultiplier and Electronic Study of Geiger Counter Pulses in Air
Authors: Herreman Harold M. , Loeb Leonard B.
Published: April 2005

A quantitative analysis of pulse sizes recorded in an air Geiger counter at 200 Torr was made, relating counting rates of various pulse types at different sensitivities and potentials along the counting plateau. Using this information and a determination of the onset of the self-counting potential, data concerning counts, pulse size, distance of pulse propagation down the tube, and pulse velocities were obtained for pressures of 100, 200, 300, and 400 Torr. Triggering on the steep rise of the electrical pulse stimulated by α particles at one end of the counter, the time of passage of the luminous pulse from one photomultiplier located at the α particle gun, and a second viewing of the counter at a given distance along the axis could be recorded on an oscillograph screen. Large fluctuations of number of ions per pulse, distance of propagation down the tube, and velocities were noted. All these quantities increased with potential as the onset of steady corona was approached. There was a close correlation between pulse size, distance of propagation, and velocity. These are readily accounted for by the number of ions and photoionizing photons created in the avalanches produced by the initial triggering event.
Photoconductive Mixing in CdSe Single Crystals
Authors: Svelto O. , Coleman P. D. , DiDomenico M. , Pantell R. H.
Published: April 2005

The mixing of the first four axial-mode frequencies of a ruby laser in a bulk, room temperature, CdSe crystal to obtain microwave beat frequencies in the 1–5 Gc/sec range is described. A photoconductive mixing analysis based on a monomolecular recombination process is found to give excellent agreement with the experimental data. The beat frequency power was found to vary as the square of the dc bias voltage applied across the crystal, the square of the incident light power, and inversely as the square of the beat frequency. A minimum lifetime of 10−9 sec, a cross section of 1.3×10−16 cm2, a modulation index of 0.2, and a maximum beat frequency power of 0.2 mW were obtained in the experiments.
Polarization Phenomena in Electrical Tests on Hexane
Authors: Zaky A. A. , House H.
Published: April 2005

Discharge currents which flow in carefully distilled hexane on the removal of the applied potential were investigated for predischarge stresses ranging from 10–750 kV/cm. The duration and shape of the discharge characteristics were found to depend on the electrode material, on the surface state of the cathode, and on the predischarge stress. It is believed that the discharge currents are the result of a redistribution of charges in the gap in the absence of an external field. Using a model based on the theory of simple diffusion within a liquid bulk, an equation is developed which shows good agreement with the experimental results.
Spatial Distribution of Radiation from GaAs Lasers
Authors: Fenner G. E. , Kingsley J. D.
Published: April 2005

The spatial distribution of the energy emitted by GaAs lasers having Fabry-Perot resonators was investigated. In general, the diodes emit several fan-shaped beams of comparable magnitude at angles up to 10° with respect to the normal of the mirrors in the junction plane. These beams have widths from ¾° to several degrees in the plane of the junction and about 10° in the plane perpendicular to the junction. The radiation patterns are usually asymmetric about the normal to the polished faces of the diode and this asymmetry is mirrored on the opposite side of the diode. We conclude that because our Fabry-Perot mirrors are not perfectly parallel, the most prevalent modes of our diodes illuminate the radiating surface with phase and intensity distributions which vary strongly along the junction. This variation is frequently nearly periodic.
Inductive Behavior of Superconducting Magnets
Authors: Hempstead C. F. , Kim Y. B. , Strnad A. R.
Published: April 2005

The inductive behavior of a closed system of superconductors is investigated with the purpose of attaining high magnetic fields. High-field superconductors do not exhibit the Meissner effect, and the inductive behavior of a system formed of these materials can be predicted fairly accurately from the conservation law of flux linkage which follows from the zero resistivity. Simple flux shielding or trapping is quantitatively analyzed for a tubular geometry. The flux concentration scheme is discussed for several practical configurations. In this scheme, a low field over a large volume (externally applied field) is compressed into a smaller volume to achieve the desired intensification in field strength. The energy of the external magnetic field can be utilized more effectively by flux pumping, but this requires intricate switching sequences.
Dielectric Constant of Lead Titanate Zirconate Ceramics at High Frequency
Authors: Gerson R. , Peterson J. M. , Rote D. R.
Published: April 2005

A region of dielectric dispersion has been found in ferroelectric lead titanate zirconate ceramics at frequencies about 1Gc/sec. The losses associated with the dispersion are quite high, the dissipation factor rising to about 0.4 at 2Gc/sec. The magnitude of the dispersion is halved in the measured frequency range (500 Mc/sec to 2 Gc/sec) by electrical orientation (poling) of the ceramic. Two mechanisms which may account for the effect, inertial clamping of the piezoelectric response of ferroelectric domains and clamping of domain-wall motion, are discussed.
Sputtering Yields of Single Crystals Bombarded by 1- to 10-keV Ar+ Ions
Authors: Magnuson G. D. , Carlston C. E.
Published: April 2005

The sputtering yield S, in atoms/ion, has been measured for Cu and Ag single crystals bombarded at normal incidence by 1- to 10-keV Ar+ ions. Yields of the three low-index planes (110), (100), and (111) for Cu and Ag crystals were measured as well as that of a Cu (311) plane. In addition a yield curve of a Cu (100) crystal bombarded in a [111] direction was measured. The yields were obtained by a weight loss method using ion beam techniques. The yields are strongly dependent on crystalline orientation showing a steep rise with energy, a maximum, which appears at an energy depending on the plane being bombarded, and a slow decrease with ion energy above the maximum. A simple theory is presented which accounts reasonably well for the energy dependence of the sputtering yield in terms of crystalline opacity and the momentum of the incident ion.
Reflection and Refraction of Mechanical Waves at Solid-Liquid Boundaries. II
Authors: Mayer Walter G.
Published: April 2005

The energy ratios of reflected and refracted waves at various solid-liquid boundaries are calculated as a function of the angle of incidence in the solid. The influence of density and wave velocities on the general shape of the resulting curves is discussed.
Absorption Measurements of Ultrasonic Waves in Plastic Sheets
Authors: Nakamura Yosio
Published: April 2005

Absorption coefficients of ultrasonic compressional waves in polystyrene and Plexiglas sheets were measured for use in model experiments of elastic wave propagation. A pulsed sinusoidal wave of variable frequency was used. In the frequency range of 30 to 200 kc/sec, the relations between the absorption coefficient α (Np/cm) and frequency f (kc/sec) were found to be approximated by α=7.3×10−5 f1.4 for polystyrene, and α=0.054 log f−0.080 for Plexiglas.
Electrical Properties of Heavily Doped Silicon
Authors: Chapman P. W. , Tufte O. N. , Zook J. David , Long Donald
Published: April 2005

Measurements have been made of the temperature dependences of the electrical resistivity and Hall coefficient in samples of n- and p-type silicon having impurity concentrations in the 1018 to 1020 cm−3 range. The resistivity data extend from 4° to 900°K, and the Hall data from 4° to 300°K. The results exhibit two noteworthy features: viz., (1) a hump or maximum in the resistivity vs temperature curves at or slightly below the degeneracy temperature in each sample, which is most pronounced in the least heavily doped samples and gradually fades out as the impurity concentration increases, and (2) an extension of the positive dependence of resistivity on temperature below the hump or degeneracy temperature to surprisingly low temperatures in each sample.
Gamma Irradiation of Silicon. II. Levels in n-Type Float-Zone Material
Authors: Sonder E. , Templeton L. C.
Published: April 2005

Measurements of the electrical properties of gamma-irradiated float-zone silicon have been used to locate a number of net acceptor levels in the upper half of the forbidden gap. In material doped with less than 1016 donors, a level due to a vacancy-oxygen atom pair located 0.17 eV below the conduction band is introduced at a rate comparable to its introduction in oxygen-containing material. However, in addition there is introduced a level located 0.47 eV below the conduction band in phosphorus-doped and 0.43 eV below the conduction band in antimony-doped float-zone silicon. This latter level is presumably due to vacancy-donor complexes. Annealing above 150°C removes the deep level; further irradiation and annealing causes the reappearance of a deep net acceptor level at 0.47 eV. In irradiated and annealed silicon and additional net acceptor level at 0.21 eV below the conduction band was observed.
Effect of Temperature on the Deformation of KCl-KBr Alloys
Authors: Stoloff N. S. , Lezius D. K. , Johnston T. L.
Published: April 2005

At low temperatures, ionic solids of the rock-salt structure deform by planar {110} slip and are brittle; at higher temperatures slip can occur on any plane of the <110> zone and fully ductile behavior is observed. The effect of alloying on this pattern of behavior has been studied for the KCl-KBr system. Pure polycrystalline KCl and a 0.6% KBr alloy are shown to be ductile at temperatures above 250°C, but a 1.3% alloy polycrystal remains brittle up to 350°C. Associated with this brittleness is the persistence of planar slip to much higher temperatures. More concentrated KBr additions suppress wavy glide in single crystals to temperatures approaching the melting point of the alloys. Data are presented to demonstrate the effect of KBr additions on the yield strength, work-hardening rate, and fracture stress of polycrystalline KCl and two dilute alloys. Small solute additions appear to influence work-hardening behavior much more than the yield strength, but more concentrated additions increase both significantly. The effect of KBr additions on glide behavior appears to be associated with changes in the core energies of dislocations of the <110> zone. Although the glide behavior of pure ionic crystals can be related to the polarizability of the constituent ions, a similar correlation is invalid for ionic solid solution alloys.
A Method for Growing Rare-Earth Single Crystals
Authors: Nigh H. E.
Published: April 2005

Single crystals of yttrium and the heavy rare-earth elements from Gd to Tm were prepared by the annealing of arc-melted buttons. This method resulted in crystals as large as 2.5×2.5×0.8 cm.
Work Hardening and Dislocation Arrangement of fcc Single Crystals. I. Plastic Deformation and Slip Line Studies of Nickel Single Crystals
Authors: Mader Siegfried , Seeger Alfred , Leitz Christoph
Published: April 2005

The work hardening of nickel single crystals and its temperature dependence are investigated. The results are discussed in terms of the long-range stress theory of work hardening. From an analysis of the temperature dependence of the stress τIII at the onset of stage III, we deduce the stacking fault energy of nickel and the magnitude of the stress concentrations in the deformed crystals.

Particular attention is given to the question: Which of the hardening parameters are structure sensitive and which are insensitive to the differences in the microstructure of the crystals?

Simultaneous determinations of the length and height of individual slip lines are carried out. They check with the information on the stress concentrations and agree well with the predictions of the work-hardening theory.