bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Insulating-Film-Thickness Nonuniformity on Tunnel Characteristics
Authors: Chow C. K.
Published: April 2005

In all theoretical investigations of the electric-tunnel effect through a thin insulating film between two electrodes, it is commonly assumed that the insulating film is of uniform thickness. In practice, it is reasonable to expect that this assumption is not always valid. The present paper demonstrates that nonuniformity in film thickness can have an important effect upon the terminal current—voltage characteristics of tunneling devices. This effect can, at least in part, account for the discrepancy between calculated and measured values of tunnel current.
Noise Picked Up by External Probes in Electrodeless Gas Discharges
Authors: Huang C. H. , Chenette E. R. , Van Der Ziel A.
Published: April 2005

Noise and impedance measurements are reported for external electrodes wrapped around electrodeless discharges. For frequencies between 0.5 and 10 Mc/sec the equivalent noise temperature Tn of the probe noise lies between ½Te and Te, where Te is the electron temperature; this is attributed to the space-charge suppression of the ion shot noise flowing to the wall under the electrodes. At higher frequencies the noise temperature Tn increases because of a high frequency noise mechanism that is also present in dc discharges. The observed data can be fully interpreted in terms of what is known about the noise and impedance properties of floating probes in dc discharges.
Effect of Electromagnetic Propagation on the Magnetostatic Modes
Authors: Ribbens W. B.
Published: April 2005

The second-order effect of electromagnetic propagation on the essentially static-field distribution of the magnetostatic modes of a ferromagnetic sample is obtained by an iteration-type technique. The magnetostatic potential constitutes the source in a mathematical sense for a second-order correct field distribution. The internal sample fields are investigated for a ferrite cylinder enclosed between parallel conducting plates and they are found to consist of resonant modes whose frequencies are determined from a characteristic equation. These frequencies reduce to those of the magnetostatic modes in the limit of vanishingly small wavenumbers. For a nonzero wavenumber the frequencies differ from the corresponding magnetostatic limits by an amount which depends on the sample shape. These resonant frequencies are size-dependent as contrasted to the size-independent magnetostatic modes. No resonant frequencies are possible above a critical value that depends on the spacing between the plates. A sample mode, whose resonant frequency is in a region forbidden to the magnetostatic modes, can exist if the sample size exceeds a critical value.
Ripple Hysteresis in Thin Magnetic Films
Authors: Feldtkeller Ernst
Published: April 2005

Hysteresis measurements and electron micrographs have shown that the rotation in films with uniaxial anisotropy in low fields is not reversible, in contradiction to the single domain theory. A film with Hc/HK=2.3, for instance, has a remanence of 0.04 Ms in an alternating field of the amplitude Ĥ=0.4 HK parallel to the hard axis. The remanence depends on Hc/HK, on the dispersion of the anisotropy, and on the amplitude and the direction of the applied field.

This irreversibility is caused by the magnetization ripple. If the magnetization is rotated, the ripple small-angle walls rearrange themselves by wall motion normal to the new magnetization direction. This wall motion requires a certain excess of energy which results in hysteretic losses even if the applied field strength is lower than the Stoner-Wohlfarth critical field for irreversible rotations.
Preparation, Phase-Boundary Energies, and Thermoelectric Properties of InSb-Sb Eutectic Alloys with Ordered Microstructures
Authors: Liebmann W. K. , Miller E. A.
Published: April 2005

Two-phase solids, single-crystal rods of Sb in a matrix of single-crystal InSb, have been prepared by eutectic crystallization. The size of the Sb rods decreases with increasing crystallization velocity, in quantitative agreement with the theory of eutectic crystallization.

The boundary energy between the InSb and the Sb phases was determined both from the parameters of the crystallization and from a dislocation model. Both values agree, indicating that the strain energy of the dislocations at the phase boundary is the chief contributor to the interfacial energy.

The electrical resistivity ρ, the thermoelectric power Q, and the thermal conductivity K have been measured as a function of the structural arrangement of the two phases in the alloys. The magnitudes of ρ and Q have been explained by simple electrical analogs of the eutectic structure.

A characteristic decrease of the thermal conductivity of the eutectic alloys has been observed. The reduction in K is probably caused by interaction of phonons with the phase boundaries.
Photoelectric and Thermionic Schottky Deviations for Tungsten Single Crystals
Authors: Stafford D. F. , Weber A. H.
Published: April 2005

The periodic Schottky deviations have been obtained for photoelectric and thermionic emission in the [111] direction from a tungsten single crystal in a dual experiment. The thermionic deviations, compared with well-established experimental results and theory, serve as a check on the photoelectric work. The photoelectric deviations, not previously established experimentally in detail, are compared with theory. A composite theory, using Cutler-Gibbons thermionic parameters in Juenker's photoelectric analysis, is in best agreement with the experimental photoelectric results.

The photoelectric deviations are in fair agreement in period and phase with the thermionic deviations, the agreement being better at the larger applied electric fields (corresponding to the earlier time of a run) than at the smaller field values. The photoelectric deviation amplitude is 1.7% at E½=350 (V/cm)½.
Ferromagnetic Domain Structures in Cementite
Authors: Keh Alfred S. , Johnson Charles A.
Published: April 2005

By means of transmission electron microscopy, ferromagnetic domain structures have been studied in thin cementite (Fe3C) particles embedded in a ferrite matrix. In general, the domain structure was found to consist of parallel strips alternately magnetized along the positive and negative direction of the easy axis of magnetization [001]. By means of selected-area electron diffraction the orientation of the cementite particles relative to the foil surface was determined. The domain walls lie in the (100) plane of the cementite lattice, and the width of the domains, as a function of angle between easy axis and normal to foil, agrees very well with the model of Malek and Kambersky. At the cementite-ferrite interface domains of closure frequently occurred in the ferrite, but were never found in the cementite. The width of the (Bloch) domain walls is roughly 100 Å, in reasonable agreement with the theoretical width computed for bulk cementite.
Elastic Properties of Semiconducting Crystals belonging to the Diamond, Blende, and Wurtzite Types
Authors: Touchard L. J.
Published: April 2005

When a face-centered crystal is referred to axes bound to a close-packed plane, its elastic moduli possess the C3v type of symmetry. They differ from the elastic moduli in the axes of the cube by a multiple of the quantity C=C11–C12–2C44. The reduced value of C is nearly the same for Ge and the four III–V semiconducting compounds whose elastic moduli have been measured. A comparison between the cells of blende and wurtzite suggests, for crystals of the latter type, a simple relation which appears to be well satisfied in the case of CdS.
Association in Melted Semiconductors
Authors: Hamilton D. R. , Seidensticker R. G.
Published: April 2005

The melting process of semiconductors has been studied by two techniques. First, the electrical conductivity about the melting point was carefully measured for InSb and Ge. There was no evidence of any hysteresis connected with a two-stage melting process, or with persistence of rigid, directed bonds in the liquid. The average conductivities obtained were 9.4×103 and 1.4×104 (Ω cm)−1 for liquid InSb and Ge at their respective melting points. Secondly, dendrites were grown from undercooled Ge, which had been either melted but not heated much above the melting point, or melted, superheated, and finally undercooled. There was no difference in velocities or tip radii among such dendrites, confirming that molten Ge has at all times a simple metallic character.
Electrical Resistance-Strain Characteristics of Thin Evaporated Metal Films
Authors: Parker R. L. , Krinsky A.
Published: April 2005

The electrical resistance-strain coefficients of thin evaporated films of aluminum, gold, cobalt, nickel, palladium, platinum, antimony, and tellurium have been measured. The coefficients (strain-sensitivity coefficient or ``gauge-factor'' γ) depend on the specific resistance Rs of the films. For relatively thick films (small Rs), γ tends to approach the bulk value γb; for relatively thin films (large Rs), γ may be many times greater than γb; for films of intermediate thickness γ has a minimum value. The resistance change was found to be proportional to strain for all the above films except those of Ni and Sb. Some possible mechanisms for the observed behavior are discussed; it is suggested that free-path effects are predominant in films of intermediate thickness, and that the tunneling conduction mechanism plays an important role in producing the high strain sensitivity of very thin (high Rs) films of separated particles.
Variation of Coercivity of Magnetic Materials with Driving Field
Authors: Hoffman G. R. , Turner J. A. , Lachowicz H. K.
Published: April 2005

The use of a low-frequency sinusoidal driving field to measure the B–H characteristics of magnetic materials is now a well-known technique. An increase in amplitude of this field is generally accompanied by an increase in coercivity. Ferrite cores, tape cores, and thin magnetic films have been investigated—all of which exhibit similar characteristics. Both coercivity and saturation field are shown to depend upon the rate of rise of the applied magnetic field, thus enabling a mathematical analysis to be made which is in good agreement with the experimental results. Pulse techniques are also used in the case of anisotropic, thin magnetic films to confirm the view that changes of magnetic state are by domain-wall motion.
Impurity Clustering Effects on the Anomalous Transmission of X Rays in Silicon
Authors: Patel J. R. , Batterman B. W.
Published: April 2005

The phenomenon of the anomalous transmission of x rays in perfect crystals has been used to follow the perfection of dislocation-free crystals of silicon heat-treated at 1000°C. The heat treatment gives rise to impurity clustering or the formation of strain centers, which results in a decrease of x-ray intensity of over two orders of magnitude. Upon heating at 1350°C, the clusters are dissolved and the original perfection of the crystal is restored. There is strong evidence that the impurity is oxygen, since the kinetics of the intensity decrease depends on the oxygen concentration of the crystals and is slowest for floating-zone crystals, which presumably contain less than 5×1016/cm3 of oxygen. All of the x-ray changes appear to occur before the infrared absorption band at 9 μ (which is a measure of the dissolved oxygen) begins to decrease. Thus the x-ray anomalous transmission method appears to be measuring changes that occur in the early stages of impurity clustering. The anomalous transmission method should, therefore, be an important tool for the investigation of preprecipitation phenomena that may occur in crystals of high initial perfection.
Elastic Constants of Pyrite
Authors: Simmons Gene , Birch Francis
Published: April 2005

Elastic constants, derived from measured velocities of pulsed ultrasonic waves (10 to 20 Mc/sec) are given for three specimens of natural pyrite. For all specimens, the constant C12 is positive. The values for the crystal of best quality are: C11=3.818, C12=+0.310, C44=1.094, in units of 1012 dyn/cm2. An explanation for the negative values of C12 found by some observers is advanced. Ultrasonic double refraction for shear waves was also observed.
Generation—Recombination Noise in an Impurity Semiconductor
Authors: Teitler S.
Published: April 2005

Generation—recombination (G—R) fluctuations are related to fluctuations in the number normalization (Fermi level) of the free carrier distribution function. G—R current noise is calculated without making the usual assumption of the same scattering time τs for all carriers. To define a carrier distribution function without considering the localized levels one assumes τs is much shorter than the carrier lifetime. The fluctuations in the Fermi level are assumed small compared to kT. The autocorrelation function of the current is calculated using the Boltzmann equation. If the equilibrium distribution function is a Boltzmann distribution or if τs is energy independent, the present procedure reduces to the usual one. When τs is energy-dependent and the distribution function is the Fermi function, the usual result for the autocorrelation function is multiplied by a numerical factor dependent on the equilibrium Fermi level.
Surface Structures Resulting from Fission-Fragment Damage in LiF Crystals
Authors: Knorr T. G.
Published: April 2005

Electron microscopic observation of cleaved LiF crystals bombarded with fission fragments shows that rounded mounds are formed on the surface and have diameters ranging from a few hundred angstroms to 1 micron. Thorough statistical analysis confirms that these mounds are somehow produced as a consequence of the fission fragments that penetrate the crystal; however, ready explanations of their formation are not possible. The mounds have a size distribution that is generally exponential, and contain from 106 to as many as 109 atoms above the surface of the crystal; neither fact can be explained by current theories of radiation damage. A theory combining mechanical deformation, radiation hardening, and volume diffusion of radiation-produced defects is suggested.
Growth of Manganous Oxide Whiskers
Authors: Dixon Thomas E. , Kane Richard A.
Published: April 2005

Manganous oxide (MnO) whiskers have been grown by heating manganous chloride (MnCl2) in a stream of hydrogen for 1½ h at about 900°C. These whiskers have very unusual growth structures consisting of spirals, twists, and prisms. MnO whiskers have a high degree of structural perfection as judged by their stability in air. Unlike ordinary crystals of MnO, these whiskers do not absorb oxygen unless they are fractured. It is proposed that MnCl2 diffuses to the whisker growth sites where it reacts with water vapor to form a higher oxide of manganese which is subsequently reduced by the hydrogen to MnO. The MnO then migrates to growth steps provided by the intersections of axial screw dislocations with the surfaces at the tips of the growing whiskers.
Discrepancy in Energy Transfer between Medium Energy Noble-Gas Ions and Neutral Atoms Bombarding Metal Surfaces
Authors: Mahadevan P. , Layton J. K. , Comeaux A. R. , Medved D. B.
Published: April 2005

Experiments using thermoelectric detectors for neutral particles have shown differences in the energy transfer properties of noble-gas ions and neutral atoms. The focused and collimated beams of ions and atoms bombard a platinum-receiving disk spot welded to the thermojunction, formed of Chromel and Constantan wires. Neutral atoms and ions of Ne and Ar have been studied in the energy range 500 to 2500 eV. For ions, the fraction of the kinetic energy used to generate thermo-emf in the detector was observed to be independent of their incident kinetic energy. However, for the neutral atoms, the energy transfer coefficient was found to be a monotonically increasing function of kinetic energy always less than that for ions. No attempt has been made to measure the absolute energy transfer coefficients. This discrepancy has been qualitatively explained by the experimental observation that energetic neutral atoms are specularly reflected more than ions of the same species and kinetic energy from the platinum disk of the detector.
Quenched-In Defects in CsCl-Type Alloys. I
Authors: Wayman C. M. , Thein K. M. , Nakanishi N.
Published: April 2005

CsCl-type Au-Cd binary alloys and Au-Cd-Cu ternary alloys were quenched from various elevated temperatures to determine the activation energy for defect formation. Except at high temperatures, Arrhenius linearity was observed when the logarithm of the excess quenched-in resistivity increment was plotted vs reciprocal temperature. The corresponding activation energies were ∼0.4 eV, considerably smaller than that expected theoretically. The effects of specimen size and possible quenching strains were also investigated.
Annealing of Quenched-In Defects in CsCl-Type Alloys. II
Authors: Nakanishi N. , Thein K. M. , Wayman C. M.
Published: April 2005

Au-Cd and Au-Cd-Cu alloys having the CsCl structure were annealed after quenching from various temperatures in order to determine the activation energy for migration of the quenched-in defects. Both isothermal annealing and alternate annealing between two temperature baths (change-in-slope method) were employed to calculate the activation energy Em. The activation energies were generally higher than would be expected theoretically, depended on the method of calculation, and were strongly dependent upon the quenching temperature. The order of the kinetics was also found to be dependent upon the quenching temperature. The higher-than-anticipated activation energies may be associated with the movement of divacancies.
Crystallographic Orientation and Oxidation of Submicron Whiskers of Iron, Iron—Cobalt, and Cobalt
Authors: Luborsky F. E. , Koch E. F. , Morelock C. R.
Published: April 2005

Individual single-crystal iron, iron—cobalt, and cobalt whiskers with diameters from 250 to 7000 Å have been studied by selected area electron diffraction. All of the iron and iron—cobalt diffraction patterns showed a normal bcc structure with the 〈100〉 direction along the long axis of the whisker. All but one of the cobalt whiskers were hexagonal with the 〈11.0〉 along the whisker axis. This one was a smaller whisker which was fcc. Most of the diffraction patterns also showed a second pattern due to the oxide film on the whisker surfaces coherent with the base metal, but many of the patterns from whiskers smaller than about 700 Å contained no oxide spots. The absence of oxide reflections in the diffraction pattern can be attributed to an increasing degree of crystal perfection with decreasing whisker size. In the case of iron, the oxide was identified as Fe3O4 (or γ-Fe2O3) with its 〈110〉 direction coincident with the 〈100〉 of the iron. The (100) plane of iron was parallel to the (100) of the oxide. The iron—cobalt alloy whiskers had cobalt ferrite spots with the same orientation relationship. The cobalt whiskers had their 〈11.0〉 direction and (00.1) plane coincident with the 〈110〉 and (111) of the CoO. Oxidation at temperatures up to 120°C was followed by the changes in magnetic moment and coercive force. Electron diffraction indicated the formation of α-Fe2O3 accompanied by the loss of the single-crystal structure.
Secondary Positive Ion Emission from Metal Surfaces
Authors: Bradley Richard C.
Published: April 2005

Secondary positive ions ejected from surfaces of Mo, Ta, and Pt under bombardment by inert gas ions of low energy (<1000 ev) have been studied in high vacuum (≤10−8 mm of Hg of background gases) using a 60° sector field mass spectrometer with a 6-in. radius of curvature, the object being to explore this as a technique for investigating solid surfaces in general. Ion species characteristic of the base metal, of surface compounds, and of a few bulk impurities were found. Quantitative analyses based on abundance ratios of the ions are unreliable, however owing to the enormous and essentially unknown differences in ionization efficiencies for the various species. Application of the technique to the investigation of surface kinetics seems highly promising, and as an illustration certain observations on the formation of PtO3 on a Pt surface and its desorption at high temperatures are presented. Another possible application is to the study of sputtering, although some of the properties of secondary ions are shown to be quite different from those of sputtered particles in general. The secondary ions characteristic of the base metal comprise only a small fraction (0.01% for Pt) of the total sputtering yield, are principally singly charged and monatomic, have a low average energy (4–5 ev) and energy spread, and may result either from physical sputtering of the base metal or from the dissociation of surface compounds or both.
Motion of a Satellite Around an Unsymmetrical Central Body
Authors: Newton Robert R.
Published: April 2005

If a central body does not have an inversion center, the eccentricity of a satellite orbit varies periodically, with low frequency and large amplitude. Thus, unless the satellite is initially in a large enough orbit, it may strike the central body, even in the absence of dissipative forces. Details are worked out for a central body composed of a large spherical mass and a small point mass contained somewhere within it. Application is made to satellites of the moon.
Collisions of Metastable Atoms
Authors: Hasted J. B.
Published: April 2005

Collision experiments with He 23S and Ne 3P metastable atoms are described, giving the total collision cross sections of these atoms with He, Ne, A at thermal energies, also the absorption cross sections of resonance photons from the He, Ne discharges.

The secondary electron yields from He metastable atoms and from resonance photons incident upon W, Mo, Pt surfaces flashed to 1700°C are compared with the yields from an unflashed Au surface, previously determined absolutely. The rate of rise of yield due to gas contamination is examined. The yields from the flashed surfaces are found to be distinctly smaller than Hagstrum's yields for low-energy positive ions.
Inelastic Atomic Collision Processes
Authors: Gerjuoy E.
Published: April 2005

At nonrelativistic energies, for arbitrarily complicated collisions of distinguishable or indistinguishable particles, with or without rearrangement, correct formal expressions for the cross sections are known and well established. Nonetheless, all inelastic collision cross sections must be estimated, rather than predicted accurately, because even with present high spread computers there is no three-or-more particle collision for which it is practical to solve the Schroedinger equation exactly. The validity of the customary Born approximation, and of other more elaborate approximate calculations, are discussed, mainly with reference to electron excitation cross sections. The evidence suggests that a ``compound ion model'' of excitation, which is contrasted with the more usual ``direct interaction model,'' may prove helpful in understanding the sharp peaks and other anomalous features in some excitation cross sections near threshold. It is argued briefly that (i) there are reasons to think that at high energies Born approximation is not valid for exchange amplitudes, which are the only amplitudes appearing in excitation involving change of spin multiplicity; (ii) there are circumstances when Born approximation becomes increasingly valid as the incident electron energy is decreased.
Three-Level Solid State Maser
Authors: Bergmann Saul M.
Published: April 2005

The maximum values of the real and imaginary components of the paramagnetic susceptibility of a three-level solid state maser are calculated. For the case of K3Co(CN)6 paramagnetic salt with 0.5% Cr, the values χmax′=2.5×10−4 and χmax″=5×10−4 are obtained. General expressions for the gain and band width of a traveling wave maser are given. An analogy is brought up between the quality factor Q per unit length of wave guide in the traveling wave maser and the Q in the cavity maser.
Elastic Constants of Thorium Single Crystals in the Range 77–400°K
Authors: Armstrong P. E. , Carlson O. N. , Smith J. F.
Published: April 2005

The elastic constants of thorium single crystals have been determined at ultrasonic frequencies employing both resonance and pulse-echo techniques. The values at 300°K in units of 1011 dyne/cm2 are, C11=7.53, C12=4.89, and C44=4.78. The constants C11 and C44 increase and C12 decreases with decreasing temperature and extrapolate to 7.79, 4.82, and 5.13, respectively, at 0°K. The Cauchy relation C12=C44 occurs, quite probably fortuitously, at 271°K. The anisotropy factor 2C44/(C11–C12) at room temperature is 3.6 which is comparable to the values for lead and gold. Calculated Poisson's ratios, σ100 and σ111, indicate a much stronger resistance to contraction in the close-packed planes than in the less densely packed (100) planes.
Electrical Breakdown between Close Electrodes in Air
Authors: Germer L. H.
Published: April 2005

Prebreakdown electron current between electrodes closing at voltages below the minimum which can give breakdown by successive ionization of air molecules has been measured by two different methods. This field emission current varies widely in successive experiments, increasing in general with decreasing voltage, with maximum values of the order of 10−7 amp. At the small electrode separations characteristic of breakdown at voltages below 300, it is shown that the ions necessary for breakdown come from the anode surface. The number of ions in the space at one time is so small that they cannot cooperate to enhance the gross field at the cathode, which is a conclusion having important consequences for the theory of breakdown.
Factors Affecting Separations of Suspensions in Nonuniform Electric Fields
Authors: Pohl H. A. , Schwar J. P.
Published: April 2005

A study of the more quantitative aspects of the behavior of suspended polymer particles in a real dielectric is presented. While it is recognized that nonuniform fields exert an attractive force of appreciable magnitude upon particles of high dielectric constant suspended in a liquid medium of lower dielectric constant, the limits of such behavior are not precisely known. This report presents some quantitative data on the subject. The results show that in real dielectrics there is an appreciable effect due to the very small currents, about 1013 amperes at applied voltages in the kilovolt range [R. Coelho, Progress Report No. 22, pp. 13–17, Laboratory for Insulation Research, Massachusetts Institute of Technology (December, 1957)] which even a good liquid insulator supports.

It is shown that the initial attraction to the central electrode due to the nonuniform field and its polarizing induction is gradually overcome by the repulsive effects of charge accumulated on the particles resulting from ionic conduction and related events in the liquid. The experimental observations include the study of the effects of field strength, electrode size, cell size, and particle size. Field strength, electrode size, and particle size show criticality. At certain upper limiting voltages, smaller central electrode diameters and small particle sizes, all precipitation appears to be prohibited. Use of the newly discovered ``sluff-off'' voltage for making particle size separations is discussed.
Driving Point and Input Admittance of Linear Antennas
Authors: Wu Tai Tsun , King Ronold W. P.
Published: April 2005

An infinity in the input admittance of linear antennas owing to the use of an idealized delta-function generator is investigated. It is shown that the infinity may be interpreted in terms of an infinite capacitance between the two halves of the antenna. The conclusion is reached that conventionally used iterative procedures are not invalidated by difficulties with respect to the driving point.
Flattening of a Nearly Plane Solid Surface due to Capillarity
Authors: Mullins William W.
Published: April 2005

The relaxation of a nearly plane surface to flatness is discussed under the assumption that all surface properties are independent of orientation. A general solution is obtained for the combined action of the transport processes of viscous flow, evaporation-condensation (in a closed system), volume diffusion, and surface diffusion. Green's function solutions are developed for each of the transport processes separately, and criteria are obtained to decide which process dominates. The initial forms of these solutions represent point concentrations (particles), or line concentrations (wires) of material set upon an infinite plane. The progressive topographical developments described by the formulas are idealized representations of the latter stages of the sintering of small wires and particles to a plane.
Effect of Spin on Natural Convection in Mercury Heated from Below
Authors: Dropkin David , Globe Samuel
Published: April 2005

In the absence of spin, natural convection between two horizontal surfaces in mercury heated from below is found to be given by the formula N=0.051R⅓ where N is the Nusselt number and R the Rayleigh number. Spinning the mercury about a vertical axis reduces the amount of convection after a certain value of the spin (Taylor number) is exceeded. This value of the Taylor number increases with increasing heat flux.

Turbulent fluctuation of the temperatures of the bounding surfaces are observed and under some circumstances periodic oscillations of the temperature of the bounding surface are also noted.
Molecular Motion in Some Glassy Polymers
Authors: Slichter W. P. , Mandell Elaine R.
Published: April 2005

Molecular motion in several glassy polymers has been examined by proton resonance methods in the temperature range 77–425°K, and has been interpreted in terms of the detailed behavior of molecular chains and substituents. Comparisons are made between transitions seen by proton resonance and glass transitions seen by other methods. Powles' observations on poly(methyl methacrylate) are qualitatively borne out. The influence of thermal history and polymerization conditions is considered. Motion has been examined also in several polymeric methacrylates, including the ethyl, n-butyl, isobutyl, n-hexyl, n-octyl, lauryl. docosyl, and cyclohexyl esters. Some details of molecular configuration are considered for the ethyl ester. In poly(methyl alpha-chloroacrylate) the low-temperature values of the second moment are much smaller than expected. These depressed values are ascribed to rotation of all of the methyl groups about the threefold axis.
Evidence for a Second Crystal Form of Polypropylene
Authors: Keith H. D. , Padden F. J. , Walter N. M. , Wyckoff H. W.
Published: April 2005

An attempt is made to account for the observed birefringence of the various types of polypropylene spherulite in terms of preferred crystalline orientation. Evidence is also presented showing that some of these spherulites crystallize with a new metastable crystal structure, not previously described.
Nuclear Magnetic Resonance and Thermal Expansion in Partially Crystalline Polypropylene, Poly(Butene-1), and Poly(Pentene-1)
Authors: Sauer J. A. , Woodward A. E. , Fuschillo N.
Published: April 2005

The specific volume of partially crystalline specimens of polypropylene, poly(butene-1), and poly(pentene-1) from about 160°K to above the melting point has been studied. In addition, proton spin magnetic resonance of a partially crystalline poly(butene-1) specimen has been observed over the 77°K to 320°K temperature range. Percent crystallinities as functions of temperature for polypropylene and poly(butene-1) calculated from the specific volume data are compared. The poly(butene-1) specimens show higher densities than the polypropylene samples at 170–180°K although the crystalliniites of the former are 25–40% lower than the latter. In addition, the temperature dependence of the specific volume from 160–280°K is greater for poly(butene-1) than for polypropylene. Somewhat similar trends are noted in a comparison of the NMR (nuclear magnetic resonance) second moment versus temperature curves for these two materials.
Stress-Strain Isotherm for Polymer Networks
Authors: Ciferri A. , Flory P. J.
Published: April 2005

According to the molecular theory of rubber elasticity, the stress τ is related to the relative length α in simple extension according to τ=kT(ν/V)<α>2(α−1/α2), where (ν/V)<α>2 is a parameter of the network structure. Improved agreement with experiment has been claimed through use of the relation τ=(2C1+2C2/α) (α−1/α2) which contains the additional parameter C2. In order to explore factors affecting this theoretically inexplicable term, stress-elongation measurements were performed on networks prepared from natural rubber, Butyl rubber, poly-(dimethylsiloxane), poly-(ethyl acrylate), and poly-(methyl methacrylate) under a wide range of experimental conditions. Results may be summarized as follows: (1) the C2 term offers improved agreement over the extension phase of an elongation cycle, but not for the subsequent retraction phase; (2) apparent values of C2 (determined on extension) vary widely from one polymer to another, increasing with hysteresis and with proximity to the glass transition temperature; (3) they are insensitive to the degree of cross linking; (4) C2 is markedly reduced by permanently swelling the network with a diluent, or by swelling and deswelling the sample at each tension; (5) incorporation of diluent prior to establishing a network by cross linking with gamma radiation likewise lowers C2, the value characteristic of the unswollen polymer being restored upon removal of the diluent. The results demonstrate that the controversial C2 term arises from the difficulty of attaining elastic equilibrium; under ideal experimental conditions the value of this parameter becomes negligible. An alleged limitation of the theory of rubber elasticity is thus refuted.
Improved Semiautomatic Histogram Plotter
Authors: Kelsey R. H. , Hanson E. E.
Published: April 2005

An improved instrument for constructing particle size distribution diagrams from electron micrographs is described. Its use permits the measurement of large numbers of particles rapidly, and with low observer fatigue. The magnification of the image to be measured may be chosen to make the instrument error less than the resolution of the electron microscope.

The device consists of a measuring unit in the form of a pair of dividers, controlling a servo system which automatically classifies the particles and plots the histogram as an array of steel balls in a slotted matrix.

Adjustments for zero and span are provided, and the total number of particles measured is recorded.
Direct Approach to Quantitative Autoradiography
Authors: Poddar R. K.
Published: April 2005

Several physical factors which influence an autoradiographic image produced by radioactive inclusions in thin experimental specimens have been correlated through a semiempirical formula. The latter may be used to estimate the concentration of a radioisotope in a specimen from microscopic measurement of grain density in its autoradiograph, if the period of exposure, sensitivity of the photographic emulsion, and the actual geometrical arrangements of the experiment are known.
Experimental Determination of Atomic Scattering Factors
Authors: Roof R. B.
Published: April 2005

The atomic scattering factor for aluminum has been experimentally re-examined. First-order corrections for the effect of temperature, surface roughness, primary extinction, secondary extinction, and anomalous dispersion were applied to experimental absolute intensity measurements made on a powder slab of aluminum.

The average deviation between the experimentally determined and the theoretical atomic scattering factor for aluminum is 0.16 electron. The slightly different shape of the experimental curve, as compared to the theoretical curve, is interpreted as evidence for a greater contraction in the 3p shell of aluminum than had been heretofore assumed.
Diffusion of Oxygen in Silicon
Authors: Logan R. A. , Peters A. J.
Published: April 2005

Oxygen has been diffused into silicon at temperatures above 1250°C. The diffused layers have been detected by subjecting the samples to a second heat treatment at 450°C. The donors, which then form from the oxygen, cause the layer to convert to n type. The relationship between donor and oxygen concentrations was established by studying donor formation in crystals of known oxygen concentration. From these results and the electrical properties of the layers, the diffusivity and solubility of oxygen in silicon has been measured. For silicon, in contact with SiO2 (glass), the heat of solution is (2.3±0.3) ev and the diffusivity is given by D=135exp(−3.5 ev/kT).
Infrared Studies of Birefringence in Silicon
Authors: Lederhandler S. R.
Published: April 2005

Permanent and elastic strains in silicon crystals grown by the Czochralski technique have been studied by observing the crystal birefringence. These studies reveal that the presence of birefringence is related to (a) plastic deformation caused by severe thermal gradients which produce forces exceeding the crystal yield force and (b) work damage or externally applied forces. The first source of birefringence has been termed permanent strain since this appears in the crystal as grown and the birefringence pattern cannot be altered by changes in sample geometry. This characteristic is typical of a ``frozen-in'' strain. A strain-free sample may also be made birefringent, however, by a work damage such as surface abrasion or sand blasting. Such a birefringent pattern can be altered if the sample geometry is changed. This characteristic, of course, is typical of elastic strain.

Studies made of samples both parallel and perpendicular to the direction of crystal growth revealed birefringence patterns similar to those of naturally anisotropic crystals such as calcite. The patterns indicate the formation of a pseudo-optic axis in silicon coincident with the growth direction and is caused by the uneven temperature distribution which results in perdominantly uniaxial stress.

Regions of tension and compression have been discovered and their respective magnitudes determined. The calculation of the ``frozen-in'' tension and compression stresses are based upon experimental determination of the stress-optic coefficient of silicon. Satisfactory agreement was obtained between frozen-in stress calculations and measurements of yield stress at elevated temperatures.
Asymmetric Hysteresis Loops and the Pyroelectric Effect in Triglycine Sulfate
Authors: Savage Albert , Miller Robert C.
Published: April 2005

Dynamic pyroelectric techniques have been used to study single crystal triglycine sulfate hysteresis loops at room temperature. An apparent polarization bias is observed and is similar to that reported earlier for BaTiO3. The apparent polarization bias can be shifted with the application of a dc electric field. When precautions are taken to eliminate electrode-edge effects, the pyroelectric hysteresis loops are always symmetric. The apparent polarization bias is ascribed to electrode-edge effects as in the case of BaTiO3.
Measurement of the Linear Magnetostriction of Hard-Worked Nickel
Authors: Stauss H. E.
Published: April 2005

The influence of plastic deformation upon the linear magnetostriction of hard-worked nickel has been determined by use of direct measurements of strain in three normal directions and then by measurement of magnetostriction in the same three directions using the method of rotating the specimen 90° for each measurement. This combination of measurements appears to have advantages for the interpretation of magnetostriction in nonisotropic bodies.

The value of magnetostriction at saturation for grade A nickel plastically deformed with an 84% reduction of cross-sectional area was found to be −33.5±1×10−6. This compares with −35±1×10−6 for annealed nickel of the same quality. The hard-worked nickel was free of volume magnetostriction of determinable magnitude. It showed inappreciable preferred domain orientation. It did appear to have a small amount of preferred crystalline orientation.
On the Dependence of the Switching Time of Barium Titanate Crystals on Their Thickness
Authors: Drougard M. E. , Landauer R.
Published: April 2005

The dependence of switching rate on the crystal thickness has been measured by Merz and explained by him in terms of a surface layer which has a low dielectric constant, and is about 10−4 cm thick. While not explicitly stated in Merz' original arguments, the layer must have a reversible polarization. If a layer without a reversible polarization is assumed, instead, and the discontinuity of the normal component of polarization at the interface between the layer and the bulk is taken into account, then a much thinner layer (∼1 atomic thickness) will explain the thickness dependence. This layer can be taken to be very lossy, so that it has a relaxation time (for the disappearance of electric fields) short compared to the switching time, and yet the layer will still be completely effective in slowing down domain wall motion.
Electromotive Force in a Highly Ionized Plasma Moving Across a Magnetic Field
Authors: Sakuntala M. , Clotfelter B. E. , Edwards W. B. , Fowler R. G.
Published: April 2005

When a cloud of highly ionized gas flows across a magnetic field, an emf is produced in the gas which is proportional to the speed of flow. Oscillographic probe measurements have been carried out giving the flow speed as a function of position. By drawing currents from the probes the plasma resistance can be found at various distances from the plasma generator. The resistance is shown to be due to the motion of positive ions.
Diffraction by an Infinite Slit
Authors: Levine Harold
Published: April 2005

The diffraction of plane waves by an infinite slit is investigated, with attention drawn to the case of grazing incidence and for wavelengths short compared to the slit width. The wave pattern is time harmonic and two dimensional, with identical behavior in all planes normal to the slit axis. At the coplanar screens bordering the slit, the normal derivative of the wave function is assumed to vanish, for this boundary condition provides a problem with calculable diffraction even at grazing incidence. A useful formulation (Sec. 2) of the boundary value problem involves Fourier transforms of field distributions in the plane of the screens, and enables the transmission cross section of the slit to be directly inferred (Sec. 3). The screen distributions are characterized by a pair of integral equations which allow systematic approximation (Sec. 4) at short wavelengths for arbitrary angle of incidence. A few terms in the asymptotic development of the cross section at oblique incidence are obtained explicitly, and since this development fails at grazing incidence, the analogous terms for the latter case are derived by a limiting process. Lastly (Sec. 5), in the related problem of planewave scattering by an infinite strip, a comparison is made with the variational results based on strip distributions of primary or unperturbed form.
Temperature Dependence and Lifetime in Semiconductor Junctions
Authors: Jenny D. A. , Wysocki J. J.
Published: April 2005

The temperature dependence of a semiconductor p-n junction over a given temperature range can be held to a minimum by using material with a minority carrier lifetime below a certain maximum value. The first-order temperature dependence of the junction currents is then iαe−Eg/2kT, rather than iαe−Eg/kT, over the entire operating temperature range. Calculations applied to gallium arsenide in monograph form show that an optimum lifetime should be practically attainable by controlled doping with recombination-center impurities. The maximum-lifetime condition fixes the last remaining degree of freedom in the choice of semiconductor material properties for junction device design. The upper operating temperature limit of junction devices is calculated for germanium, silicon, indium phosphide, and gallium arsenide.
Rolling Friction of a Hard Cylinder over a Viscoelastic Material
Authors: May W. D. , Morris E. L. , Atack D.
Published: April 2005

The rolling friction of a hard cylinder over a viscoelastic material is worked out in terms of the bulk properties of the material. It is found that the rolling friction has a maximum at a velocity corresponding to the peak of the relaxation time distribution. Both the load required to maintain the cylinder at constant depth of indentation and the coefficient of friction are dependent on the velocity of rolling. The shape of the rolling friction versus velocity curve is a first approximation to the distribution curve of relaxation times, indicating that rolling friction measurements can be used to determine the distribution experimentally.
Sintering Reactions of Zinc Oxide
Authors: Lee V. J. , Parravano G.
Published: April 2005

The sintering of zinc oxide spheres has been studied in the temperature range 700 to 900°C in air, oxygen, helium, and hydrogen. Fresh zinc oxide sinters rapidly in air and oxygen, but it does not sinter appreciably in helium in the same temperature range. Zinc oxide spheres annealed separately in air may not be sintered in air at temperatures as high as 1100°C. On the other end, fresh spheres, separately air annealed and subsequently treated in an hydrogen atmosphere, do sinter in the temperature range 700 to 900°C. These facts are explained on the basis of a mechanism involving the diffusional transfer of stoichiometric excess of zinc ions. The diffusion equation for zinc ions is derived, and the experimental points fit the equation satisfactorily. The treatment shows that the relationship between the width of bridges connecting sintering spheres and time varies with extent of sintering. This fact invalidates the use of this relationship as a unequivocal diagnostic criterium for the sintering mechanism in nonstoichiometric oxides.
Note on the Scratching of Diamond
Authors: Wentorf R. H.
Published: April 2005

The resistance of diamond to wear is a strong function of its orientation. The observed facts can be explained by assuming that a scratched diamond surface fails in tension behind the scratching particle. The octahedral cleavage planes are most easily pulled apart and give rise to the strong dependence of wear on crystal orientation.
Useful Approximations in Wiener-Hopf Problems
Authors: Carrier G. F.
Published: April 2005

Frequently, the only serious obstacle which prevents one from obtaining a physically interpretable solution to a Wiener-Hopf problem is the explicit factorization of the ``kernel'' of that problem. A technique whereby an easily factored kernel replaces the original without serious loss of accuracy is illustrated by several examples.
Domain Processes in Lead Titanate Zirconate and Barium Titanate Ceramics
Authors: Berlincourt Don , Krueger Helmut H. A.
Published: April 2005

The amount of 90° reorientation during poling was determined from mechanical strains measured during the poling process. With tetragonal lead titanate zirconate 53% of the possible 90° reorientation occurred during poling, but this figure dropped to 44% upon removal of the poling field. With barium titanate the figures are only 17% and 12%, respectively. Comparison of the polarization of poled polycrystalline barium titanate with that for single crystals indicates that 180° reorientation is virtually perfect. Application of very high compressive stress parallel to the polar axis causes 90° switching of nearly all aligned domains, and, therefore, removes virtually all polarization. Curves of released charge as function of mechanical strain are nearly linear, but curves of released charge as function of stress are strongly nonlinear. Application of high compressive stress perpendicular to the polar axis also causes 90° domain reorientation and a reduction in the total polarization of the ceramic. This domain reorientation may be interpreted as a shift of the polar axes of some domains into a position more closely corresponding to the plane of cross expansion, and typically the total electric moment is reduced by less than 10%. High electric stress causes 180° as well as 90° domain reorientation. With prepoled specimens dc fields in the same direction as the poling field cause 90° switching, while reverse dc fields cause both 90° and 180° reorientation, with the latter predominating.