bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoelectric Power and Resistivity of Chromium-Rich CrFe Alloys between 25° and 1000°C
Authors: Cox John E. , Lucke William H.
Published: January 2005

A study has been made of the thermoelectric powers (S) and electrical resistivities (ρ) of CrFe alloys over the concentration range 0 to 48.2 at. % Fe and temperature (T) range from 25° to 1000°C. The plots of S vs T and ρ vs T move in an orderly progression from that of pure Cr to the curve for the Cr51.8Fe48.2 alloy with no anomalies occurring. One might think that S should change sign as the alloy concentration passed through the region where Beck et al. observed their ``spike'' in the electronic specific heat, but no such phenomenon was observed.
The Splash of a Liquid Drop
Authors: Harlow Francis H. , Shannon John P.
Published: January 2005

The full Navier-Stokes equations are solved numerically in cylindrical coordinates in order to investigate the splash of a liquid drop onto a flat plate, into a shallow pool, or into a deep pool. Solution is accomplished with the Marker-and-Cell technique using a high-speed computer. Results include data on pressures, velocities, oscillations, droplet rupture, and the effects of compressibility. They also show how the technique can be applied to a wide variety of other complicated fluid flow problems involving the transient behavior of a free surface.
Photoconductivity Oscillations in Semiconducting Diamonds
Authors: Krumme J. B. , Leivo W. J.
Published: January 2005

The photoconductive response of several semiconducting diamonds was measured in the spectral range 0.8 to 4.7 μ with crystal temperatures of 4.2° and 77°K. Photoconductive minima, most of which are not observed in the optical absorption spectrum of these diamonds, were recorded at 3.6, 3.5, 2.72, 2.65, 2.48, 2.41, 2.38, 2.35, 1.97, 1.87, 1.83, 1.78, 1.56, 1.44, 1.21, 1.05, 0.92, and 0.83 μ, and minor features were recorded at 2.44, 2.25, 2.02, 1.33, and 1.13 μ. Five activation energies, 0.21, 0.30, 0.37, 0.52, and 0.7 eV, for semiconducting diamonds have been observed. Good correlation is found between the photoconductive minima and the five activation energies EAi(i=1,⋯, 5) through the terms En = EAi+nEph wherein Eph = 0.165 eV, the energy of a Raman-frequency phonon, and n takes integral values from 1 though 8. The minima may be explained as follows. Holes are excited to the valence band by the incident radiation. They lose energy mainly through the emission of Raman-frequency phonons. When the energy relations are proper, holes are left in excited bound states at acceptor sites and do not contribute to the conduction process.
Heterogeneous Nucleation of Bi and Ag on Amorphous Substrates (In Situ Electron Microscopy Studies)
Authors: Poppa Helmut
Published: January 2005

Quantitative measurements of the kinetics of nucleation in some simple substrate-overgrowth systems have been made using improved in situ electron microscopy techniques. The nucleation of bismuth and silver on evaporated carbon and the nucleation of bismuth on evaporated SiO substrates were studied as a function of substrate temperature and impinging flux. The results were analyzed in terms of the phenomeno-logical theory of nucleation and in terms of Walton's atomistic model of condensation from the vapor phase. Both theoretical concepts led to specific conclusions concerning such nucleation parameters as the number of atoms in the critical nucleus n* and the free energy of desorption ΔGdes. The substrate temperature and impingement flux dependence of the maximum number of deposit particles that can be accommodated on the substrate surface were determined and tentatively interpreted on the basis of nucleation-limited surface migration. Some nucleation induction time observations were made and were related to the clustering kinetics of adatoms, the growth process of individual nuclei, and the instrumental limitations of the detection method.
Recovery Processes and Ordering in Ni3Al
Authors: Corey Clark L. , Potter Donald I.
Published: January 2005

Isothermal changes in long-range order S, x-ray line shifts due to stacking faults Δ, and x-ray particle size from Fourier analysis of line shapes D were measured for filed samples of Ni3Al. Recovery temperatures between 200° and 270°C were investigated. The recovery of all three measured properties appeared to depend upon the mobility of vacancies in this temperature range. The evaporation of vacancies from faulted loops appeared to supply the vacancy flux for ordering and particle-size changes. Fault shrinkage was found to cease quite abruptly between 215° and 200°C; at 200°C faulting initially increased, during which ordering did not occur, but after some 20 h the faulting began to anneal out and somewhat later ordering proceeded. An activation energy of 1.65 eV was found for the ordering reaction; this compares with a value of 1.5 eV for Emv in nickel.
Secondary Stresses in a Stress-Pulse-Activated Piezoelectric Element
Authors: Stuetzer O. M.
Published: January 2005

Previous treatments of stress-pulse-activated piezoelectric and ferroelectric stress gauges and power generators neglect the secondary stresses produced by circuit-enforced fields in not-directly-stressed parts of the transducer. It is pointed out that under short-circuit conditions these secondary stresses generate strong effects in materials with high electromechanical coupling factors. To demonstrate this, a thin plate activated by a plane rectangular low-amplitude stress front is considered. A rigorous theoretical analysis is sketched for this configuration. It is found that short-circuit current pulses generated by the stress-front transit are not rectangular, but vary exponentially in time. The exponent is proportional to the square of the electromechanical coupling factor and depends on the mechanical boundary conditions. Supporting experiments are reported.
Some Characteristics of Lithium-Drifted Silicon Structures
Authors: Baily N. A. , Akutagawa W. M. , Andres R. J. , Montano H. L.
Published: January 2005

Collection efficiency for carriers generated by visible light and potential path distributions have been studied in p-i-n structures formed from p-type silicon after compensation by the lithium drift method. The experimental results show that the characteristics of the resultant devices are similar to those expected when an excess donor concentration excists in the compensated region. The effects of high-field, reverse-bias, room-temperature storage indicate that a reduction in the donor concentration takes place under these conditions, resulting in a device behaving more like a p-i-n structure.
Computer-Oriented Procedures for Dimensional Analysis
Authors: Happ William W.
Published: January 2005

A fortran program has been developed for the IBM 1620 computer in order to calculate Buckingham or B-numbers, dimensionless products of variables, from the laws of physics. For a given set of physical quantities, the corresponding set of B-numbers is invariant under changes of the reference set of dimensions, such as length, mass, time, charge, and temperature. Complete and nonredundant sets of B-numbers are obtained for 35 formulas from a representative branch of physics (solid-state). A systematic procedure is established for coding and cataloguing these formulas in terms of B-numbers. It is anticipated that decoding techniques can be applied to this catalogue to yield information on the interrelationships among and redundancy in the laws governing physical phenomena.
Initial Pressure, Initial Flow Velocity, and the Time Dependence of Crater Depth in Fluid Impacts
Authors: Engel Olive G.
Published: January 2005

An explicit expression for the velocity potential governing the flow produced by impact of a liquid drop against a liquid is given. With use of this velocity potential, an equation is derived from which the cavity depth and the velocity of the cavity wall, for various times after the instant of impact, can be obtained. With use of this velocity potential an expression for the initial pressure in the fluid is also obtained. Good agreement is found between calculated and observed values of cavity depth at various times after the instant of impact and between the calculated initial pressure and the water-hammer pressure.
Investigation of Strong Guiding Effects in Helicon Propagation
Authors: Wisseman W. R. , Davies E. J.
Published: January 2005

Measurements were made of the phase, attenuation, and coupling constants of circularly polarized m=±1 traveling helicons in n-type InSb cylinders at 54.2 MHz. Values of kHa between 0.25 and 3.0 were achieved by varying the temperature from 81° to 373°K and the magnetic field from 0 to 11 kG. The quantity kH is the infinite-medium phase constant and a is the cylinder radius. Theoretical calculations were made extending earlier work to the values of kHa and ωcτ covered experimentally, where ωc is the cyclotron frequency and τ is the collision time. The results differ from the earlier work, and in particular, it is found that the m=×1 modes do not have the same polarization near the cylinder axis. Transverse magnetoresistance and Hall measurements were made to determine kHa and ωcτ. The agreement between experiment and guided theory was found to be relatively good. Both of the guided helicon modes excited had higher phase velocities and much larger attenuation constants than the values calculated from infinite-medium theory. These results indicate difficulty in achieving the conditions necessary for predicted two-stream helicon instabilities.
Comparison of X-Ray Topography and Infrared Birefringence for Investigating Thermal Stresses in Silicon
Authors: Carron Gene J. , Walford L. K.
Published: January 2005

The objective of this work has been to correlate x-ray and infrared experimental scattering phenomena. X-ray topography and polarized infrared radiation have been used to study the stresses induced in single-crystal silicon wafers by electron-beam heating. The results of this work are discussed in relation to previous results of various investigators for stresses produced by several mechanisms. X-ray topographs showing four-lobed rosette patterns are presented together with an infrared birefringence pattern of the same electron-beam-spot area. Also illustrated and discussed is a triangular macrodefect observed by x-ray topography. The results presented herein have led to the conclusion that x-ray rosette patterns and infrared birefringence occur together and are due to thermally induced residual stress surrounding the electron-beam-spot areas. The results also indicate the need for additional experimental and theoretical work on the relation between scattering phenomena observed for electromagnetic radiations of different wavelengths.
Constriction of the Thermally Inhomogeneous Positive Column with Volume Recombination
Authors: Lynch Robert H.
Published: January 2005

The effect of gas heating and volume recombination on the constriction in the positive column in glow discharges is analyzed theoretically. Specific results are obtained for helium by solving conservation and diffusion equations for the case where energy balance is dominated by elastic collisions. The degree of constriction is found to be an increasing function of the two parameters Rp and Ip, where R, I, and p are the tube radius, tube current, and gas pressure, respectively. In helium the constriction is predicted to set in at a value of Rp of about 750 cm·Torr. This value is much larger than the value (≈30 cm·Torr) at which elastic collisions gain control of the energy balance in helium. Some results calculated for neon gas indicate that volume recombination in the heavier inert gases becomes effective before elastic collisions gain control of the energy balance.
Work-Function Distribution Studies of Pressed Matrix Cathodes
Authors: Haas George A. , Thomas Richard E.
Published: January 2005

The work-function distribution of commercial pressed matrix cathodes has been investigated from room temperature to 1300°K. The measurements were obtained by probing the surface with a beam of electrons in the retarding field region. The beam, which was of the order of 2 μ in diameter, sampled the work function of 30 000 regions of the surface during the 3 sec. required for one scan. The results show that the emitter exhibits a very patchy behavior at low temperatures, while a relatively uniform temperature insensitive region exists from ∼900° to 1400°K. Above this temperature, activation and poisoning effects are dominant. Patch field distribution measurements show that surface fields as high as 1500 V/cm exist in the patchy state, whereas a well activated pressed matrix cathode would have surface fields only of the order of 100 V/cm. The measurement of thermionically emitted electrons is in good agreement with results obtained by the incident electron beam. These data as well as work-function and conductivity measurements from various microregions are discussed in terms of a thin semiconductor surface layer.
Studies of Magnetic Hardness in Vicalloy using the Mössbauer Effect
Authors: Gorodetsky G. , Shtrikman S.
Published: January 2005

Mössbauer spectra were taken at room temperature on rolled Vicalloy samples in (i) a state obtained by quenching the sample from 950°C; (ii) a state obtained by annealing for optimum permanent magnet properties. Annealing results in a narrowing of the absorption peaks, an increase in hyperfine field, and the appearance of an additional absorption peak indicative of a paramagnetic phase. These results are interpreted in terms of the known phase diagram of Fe–Co–V, and lend support to the description of Vicalloy magnets as fine-particle magnets.
Internal Quantum Efficiency of GaP Diodes
Authors: Lorenz M. R. , Pettit G. D.
Published: January 2005

The internal quantum efficiencies of red (∼7000 Å) emitting diodes have been evaluated from measurements of external efficiencies by the method of indices of refraction matching. The internal efficiencies of the diodes are on the average about a factor of five larger than the external efficiencies. The highest internal quantum efficiency was 3.85×10−2. Free carriers account for the absorption losses of the emitted radiation, but nonradiative recombination processes are responsible for the low values of the internal efficiency.
Changes in Conductor Shape during ``Wire Explosions''
Authors: Chace W. G. , Fish C. V.
Published: January 2005

The explosion of ovoid conductors (noncylindrical exploding wires) is observed with pulsed x-rays and is shown to occur only after the original ovoid shape is severely distorted, toward cylindrical symmetry.
An Axial Form of the Sampling Theorem and its Application to Optical Diffraction
Authors: Arsenault Henri , Boivin Albéric
Published: January 2005

The sampling theorem is used to obtain expressions for the diffracted amplitude G(y, z) at any point in space, once the distribution along the axis G(y, 0) is known at the sampling points. In the case of a circular symmetrical pupil, G(y, 0) is simply the Fourier transform of the pupil function. The real or imaginary parts of G(y, z) may be obtained either from the real or from the imaginary part of G(y, 0). By suitable oversampling, the real part of G(y, z) may be found from its imaginary part, and vice versa. A technique for the synthesis of antenna patterns is suggested.
Application of the Dynamical Theory of X-Ray Diffraction to Holography
Authors: Saccocio Edward J.
Published: January 2005

The concepts of the dynamical theory of x-ray diffraction are applied to optical holography. A plane-grating hologram is the assumed diffraction element and its behavior is shown to be consistent with that of its x-ray counterpart, namely a thin, one-dimensionally periodic structure. Evidence is cited which corroborates the theory. In particular, an anomalous transmission of light through the plane-grating structure, at the Bragg angle, is reported-referred to as the Borrmann effect in the x-ray-crystal situation-which in x-ray optics is taken as prima facie evidence for the dynamical theory. The usually observed subsidiary maxima about the Bragg peak and their reported asymmetry are explainable in terms of the dynamical theory as effects due to a finite lattice. The minimum angle of deviation found in holograms, so familiar to prisms and line gratings, is described as a finite-lattice effect.

It is concluded that the dynamical approach in holography is a useful one for the thick emulsion, whereas the simple kinematic theory is more adequate for thin emulsions. However, attention is drawn to the use of the dynamical theory even for the case of thin emulsions to help provide some physical insight into the diffraction of light by holograms.
Mobility of Edge Dislocations in the Basal-Slip System of Zinc
Authors: Pope D. P. , Vreeland T. , Wood D. S.
Published: January 2005

This paper presents the results of measurements of the velocities of 〈12̄10〉 (0001) edge dislocations in zinc as a function of applied shear stress. All tests were conducted at room temperature on 99.999% pure zinc monocrystals. Dislocations were revealed by means of the Berg-Barrett x-ray technique. Stress pulses of microsecond duration were applied to the test specimens by means of a torsion testing machine. Applied resolved shear stresses ranged from 0 to 17.2×106 dyn/cm2 and measured dislocation velocities ranged from 40–700 cm/sec.

The results of this study indicate that the velocity of edge dislocations in the basal slip system of zinc is linearly proportional to the applied resolved shear stress. These results are analyzed in terms of the phonondrag theory. Agreement between this theory and the results reported here is quite good.
Adsorption and Desorption of O2 on GaAs {111} Surfaces
Authors: Arthur J. R.
Published: January 2005

A quadrupole mass spectrometer was used to measure the desorption rate of oxides produced by adsorption of oxygen on GaAs polar {111} crystal planes. The results suggest that oxygen is adsorbed dissociatively at Ga surface atoms and is desorbed as Ga2O in a first-order process with an activation energy of 54±4 kcal/mole from the (111) face and 42±4 kcal/mole from the (1̄1̄1̄) face. In agreement with previous work, O2 sticking probability was∼10−4 at low coverage; however, no activation energy for adsorption was detected for the (111) face. Desorption of Ga2O from the (1̄1̄1̄) surface showed evidence of an additional, weaker binding state not present on the (111) surface.
X-Ray K Absorption Edges of Alloys. III. Copper-Zinc and Nickel-Zinc Systems
Authors: Yeh H. C. , Azároff Leonid V.
Published: January 2005

A comparison of the fine structures at the K absorption edges of copper, nickel, and zinc in several alloys demonstrates that the rigid-band model is strictly obeyed by copper-zinc and nickel-zinc solid solutions. The density of 3d holes in nickel declines progressively with increasing zinc concentration, vanishing at 30 at.% Zn according to a plot of the integrated absorptions in the corresponding energy region of the Ni K edge. A similar systematic decline in the 4s hole density at copper atoms takes place with increasing zinc content. A shift to lower energies of the initial rise in the Zn K edge in both alloy systems is ascribed to the emergence of 4s holes at zinc atoms. Although the initial rise of the copper K edge does not shift with alloying, the rest of the absorption spectrum shifts to lower energies with increasing zinc content. No shifts in the fine structure at the nickel K edge are observed.
Phase Transformation of As2Se3 and Sb2Se3 Films
Authors: Coutts M. D. , Levin E. R.
Published: January 2005

Films of As2Se3 and Sb2Se3 and their mixtures have been studied by electron microscopy and diffraction. On heating amorphous As2Se3 films no change occurs, but the Sb2Se3 films and mixtures of Sb2Se3 and As2Se3 transform to give small single crystals. These crystals have their c axes parallel to the substrate and give mainly (010) and (100) planes normal to the beam. Rate of nucleation is independent of temperature, indicating nucleation from predetermined nucleation centers. Growth rate increases with increasing temperature, but involves very little migration of material, implying that surface migration is very slow.
Helicon-Type Solutions for an Anisotropic Magnetoresistivity Tensor
Authors: Penz P. Andrew
Published: January 2005

The propagation of an electromagnetic wave in an anisotropic conductor in the presence of a static magnetic field is discussed. The medium is described by a general tensor relation between the current density and the electric field. In the isotropic, uncompensated limit the wave is known as the helicon. The infiniteslab boundary-value problem is solved and the resistivity tensor elements are related to experimentally measurable quantities.
Power Output and Efficiency of Continuous Ruby Lasers
Authors: Evtuhov V. , Neeland J. K.
Published: January 2005

This paper reports recent observations on the performance of continuous ruby lasers and compares them with theoretical computations of threshold, power output, and efficiency. The theoretical model includes effects due to scattering, temperature, 2E level splitting, and excited-state absorption. It is used to compute numerically the optimized output coupling for various pump levels and the corresponding power outputs. Experimentally, power outputs of up to 2.4 W and incremental (above threshold) efficiencies of ∼0.11% were observed. Some experiments on the effects of differing crystal diameters and cooling water temperatures and flow rates were performed. Good agreement was obtained between the observed and computed dependence of power output and efficiency on various laser parameters. The agreement is of significance primarily because it implies that the theoretical model can be used in optimizing the design of continuous ruby lasers, and in predicting their performance. Results of rough calculations of projected performance are given.
Molecular Orientation in Poly-p-Xylylene Films
Authors: Niegisch W. D.
Published: January 2005

An electron diffraction study of thin (100–200 Å) vapor-deposited films of poly-p-xylylene which had been annealed to the beta modification reveals that the majority of crystallites are very specifically oriented with (10·0) prism faces in the plane of the film. Since the polymer chains are aligned in the c-axis direction [00·1], it follows that the molecules within oriented crystallites are lying in the film plane. A smaller number of crystallites are randomly oriented in these films. These conclusions are qualitatively extended on the basis of x-ray diffraction data to include films as thick as 4 mil. This study corroborates the hexagonal assignment to the beta cell, with a=20.52 and c=6.581 Å. The level of orientation is essentially independent of the nature of the crystalline and amorphous substrates upon which the films were deposited, but is inversely proportional to the partial pressure of the p-xylylene monomer in the vapor phase above the substrate.
Rheo-optical Properties of Polyvinyl Chloride Films: Unplasticized Homopolymer
Authors: Andrews R. D. , Kazama Y.
Published: January 2005

The rheo-optical properties of PVC homopolymer films, prepared by solvent casting, were studied by measuring length and birefringence changes during creep experiments at constant load. Both temperature and stress level were varied in these experiments; however, the effects of stress level were particularly emphasized. Temperature was varied in the range of 30°–140°C. An unusual phenomenon of stepwise extension was sometimes observed, particularly in the case of unannealed films. There seems to be a unique relation between birefringence and strain over a wide range of experimental conditions, and this relation is significantly different from that corresponding to a rubbery network. Cold drawing is observed at high stress levels. A pattern of curves very similar to that obtained for different temperatures at a constant load, is produced by varying the stress level at a constant temperature. However, the curves at different stress levels and different temperatures do not superpose when shifted vs log time. Optical-creep compliance (birefringence/stress ratio) shows two stages of increase in creep experiments at different stress levels at a single temperature, indicating two birefringence mechanisms. The second mechanism appears to be associated with whitening of the sample. This second-stage process is less clearly visible in the mechanical compliance curves. Annealing conditions seem to have very important effects on the film properties observed. A three-dimensional isothermal surface can be used to describe the relation of strain to stress and log time conveniently. The linear relation between yield stress and temperature, which extrapolates to zero stress near the glass transition temperature, was investigated in more detail by use of these creep experiments. A stress-temperature equivalence of 6.79 kg/cm2 (or 6.66×106 dyn/cm2) tensile stress per degree centigrade was obtained. From the results, it appears that the cold-drawing phenomenon can be described as a stress-induced glass transition. The glass transition must, therefore, be regarded not simply as a temperature, but as a phenomenon which is a function of temperature, stress level, and time.
A Dislocation Mechanism for Deformation in Polyethylene
Authors: Predecki Paul , Statton W. O.
Published: January 2005

A mechanism is proposed for transverse slip on {100} 〈010〉 in polyethylene, in terms of the motion and multiplication of dislocations caused by chain ends. Some of these defects, the jogged dislocations, are able to move at stresses somewhat below the yield stress. However, the extent of transverse slip and of the resulting transverse textures is limited by chain folds and the requirement of chain continuity. Slip displacements parallel to the chain direction are then favored.

The mismatch requirements for dislocations with Burgers vectors having components in the chain direction are determined. The Burgers vectors are 〈0, b, nc〉 on {100} and 〈a, b, nc〉 on {110}; the latter can dissociate into two types of partials with Burgers vectors 〈a/2, b/2, nc〉 or 〈a/2, b/2, (n−½)c〉, where n=1, 2⋯. Such defects can act in pairs [u, v, w] and [ū, v̄, w] producing displacements parallel to the chain direction.
Plastic-Flow Rates in Nylon Interpreted in Terms of Dislocation Motion
Authors: Dey B. N.
Published: January 2005

Observations of the propagation of plastic band fronts in nonoriented Nylon 6–10 monofilaments have been made as a function of load and temperature, and analyzed in terms of dislocation dynamics. From the shapes and the velocities of the band fronts, dislocation velocities are estimated and found to have a stress dependence similar to that found for nonpolymeric crystalline materials. The measurements yield the following quantities: characteristic drag parameter (3×109 dyn/cm2), dislocation density (105/cm2), dislocation multiplication coefficient (20/cm), length of propagating front (10−2 cm), and activation energy for the dislocation motion (0.3 eV). The maximum strain required to initiate flow in Nylon is about 40%, independent of the load and strain rate, and in agreement with previous experiments of Milkowitz, and of Williams and Bender. Measurements by Williams and Bender for Nylon 66 have also been analyzed. From the stress dependence of creep incubation times, reasonable values for the mean dislocation velocity in Nylon 66, and the associated activation energy, have been obtained. It is tentatively concluded that the rate of breaking of hydrogen bonds limits dislocation mobility in Nylons 6–10 and 66. The glide system appears to be (100) [001] within the crystallites.
Coherence and Deformation of Lamellar Crystals after Annealing
Authors: Statton W. O.
Published: January 2005

A striking change in coherence is obtained when single-crystal platelets of linear polyethylene are recrystallized by annealing at temperatures between 120°C and the melting point, 137°C. Instead of showing micaceous cleavage, the sintered crystal mat is ductile and malleable in shear, yet still will not flow under compression.

Annealing provides enough toughness to the crystal mat to allow a deformation which elongates it several-fold. Hot calendering allows a much greater elongation than cold rolling and produces a tough, crackly, clear film. The sintered aggregate can be easily hand drawn hot to extremely high draw ratios, often above ×40. The product has very good tensile properties when tested as a fiber. A two-way hot calendering operation produces a film with outstanding tear strength and poor puncture and impact strengths.

The coherence caused by the annealing of the platelets is analogous to the coherence developed in powder metallurgy or in sintering of ceramic bodies. In polymer crystals, annealing has been shown to cause the molecules to refold into longer fold periods, leaving holes. These holes provide the growing room for the refolding of chains from adjacent platelets; a cooperative intermeshing of chains occurs. This creates one large crystal aggregate which has a homogeneous distribution of sites of weakness. It is proposed that many annealing treatments of bulk crystalline polymers cause this intermeshing to occur, and a new interpretation is at hand for the well-known relationship of strength vs annealing temperature.
Surface Replicas of Drawn Polyethylene. III. The Morphology of Drawing with Neck Formation
Authors: Peterlin A. , Sakaoku K.
Published: January 2005

During the first stage of plastic deformation before the neck formation the crystal lamellae are rotated into the position of maximum compliance to applied stress that causes the stress-strain curve to drop to the plateau characteristic for deformation with neck propagation. The plastic-flow pattern in the neck results in an asymmetry of strain momentum imposed on tie molecules which during annealing lets the lamellae on the sample surface rotate about an axis parallel to the surface and perpendicular to the draw direction. The temperature at which such a rotation starts increases with the draw ratio. Concurrently the c axis moves away from the draw direction. The rotation of lamellae in the surface layer is nearly prevented by keeping the sample at constant length during annealing and in the interior of the sample by the surrounding lamellae even if the sample is free to shrink. The difference in long period which depends on the temperature of drawing in bulk samples and on the thickness of original crystals in extremely thin films is most probably a consequence of different geometry of heat dissipation in both cases.
Neck Geometry during Cold drawing of Glassy PMMA
Authors: Allison S. W. , Andrews R. D.
Published: January 2005

Experiments have been carried out to characterize the geometry of the neck which forms during the cold drawing of poly (methyl methacrylate). Sequence photography was used in conjunction with tensile stress-strain measurements. A series of tests were carried out at various temperatures, strain rates, and amounts of molecular preorientation to determine the effect of each of these variables on neck geometry. It was found that: (1) The neck geometry does not stabilize at the point where the load first reaches its steady-state value, but at an elongation much beyond this point. (2) As the applied strain rate is increased, the steepness of the neck shoulder passes through a maximum. Further increase in the strain rate causes the neck to become more diffuse. (3) A similar maximum in neck sharpness is observed vs temperature. (4) Preorientation drastically reduces the tendency for yielding to become localized in a well-defined neck. By combining neck-profile photographs and load-extension curves during drawing, it was possible to construct a series of ``true'' stress-strain curves for poly (methyl methacrylate) at various temperatures, strain rates, and degrees of molecular preorientation, which should represent very closely the homogeneous stress-strain characteristics of the material itself.
Polytetrafluoroethylene Fibril Structure
Authors: O'Leary K. , Geil P. H.
Published: January 2005

The fine-scale structure that exists in polytetrafluoroethylene fibers produced by different methods was investigated by electron microscopy and electron diffraction. These fibers were formed by mechanically abrading the surface and by fracture of compacted granular grade PTFE, and by stripping the fibers from the surface of Teflon-coated aluminum foil. Bright-field electron microscope observations indicate that the fibers are composed of microfibers or fibrils with a nearly uniform diameter of 450 Å. These fibrils are composed of platelet-like units 60 Å thick, oriented normal to the fiber axis, and are organized into blocks on the order of 475 Å in length. Electron diffraction from unshadowed individual fibers indicates that the crystal size must be fairly large, with few defects. These observations are well supported by the dark-field micrographs of the fibers. The dark-field photographs show crystalline regions along these fibrisl, which appear to be multiples of the fundamental 450-Å fibrill diameter, with a range in lnegth of 160–7000 Å. Additional observations of the fibrils indicate that these molecular packets can slide past one another, either individually or in groups. Examples of slip or shear, bowing, rotation, and kinking of the platelet-like structures have been observed.
Intercluster Links—A Mechanism for Flow-Induced Crystallization of Polymer Melts
Authors: Williamson R. B. , Busse W. F.
Published: January 2005

An experimental study and review of the literature on the oriented crystallization of high polymers was made to develop an understanding of how ``row-nucleated'' or shishkebab microstructures and the fibrillar links between lamellar crystals may be formed. A new mechanism is proposed for the formation of the fiber nuclei in flowing melts, based on the mechanical alignment and extension of molecules that are entangled with, and extend between, two or more rotating clusters in the melt. Similar alignment of molecules can occur when entangled clusters are pulled to different lamellar crystals during crystallization, producing intercrystallic links.
Effect of Chain Twisting on the Effective Barrier to Reorientation for a Hindered Rotator
Authors: Williams Graham , Lauritzen John I. , Hoffman John D.
Published: January 2005

The effective barrier to reorientation is calculated for a chain which may occupy two equivalent energy states, 180° apart for the case where the chain is allowed to twist during the reorientation process. Results are obtained for (I) a ``parabola-antiparabola'' and (II) a cosine form for the intermolecular energy. The results for (I) and (II) are similar, but differ both in form and magnitude from that obtained earlier using a cusplike barrier. Both (I) and (II) lead to the conclusion that a chain will behave as a rigid rod up to a critical chain length, and then exhibit twisting for all lengths exceeding this critical value.
Strain-Wave Propagation in Strips of Natural Rubber Subjected to High-Velocity Transverse Impact
Authors: Smith Jack C. , Fenstermaker Carl A.
Published: January 2005

If a flexible filament marked at intervals along its length is struck transversely by a flying projectile, high-speed photography reveals a shifting of the marks caused by passage of a strain wave, and analysis of these shifts provides data on the strain and average strain velocity in the wave. Tests were performed on strips of lightly vulcanized natural rubber at transverse impact velocities up to 65 m/sec, and the resulting strain-velocity distributions analyzed for viscoelastic effects. The analysis showed that although creep effects were small in the observation time interval of 1–8 msec after impact, significant creep must have occurred at the point of impact within the first millisecond, and additional significant creep occurs at times greater than 8 msec. The strain-wave-front velocity calculated from the quasistatic stress-strain curve was 35.2 m/sec, but a value of approximately 60 m/sec was observed in the tests. The strain at the wave front, however, tended to attenuate as the wave propagated causing a progressive decrease in the observed value of the strain-wave-front velocity.
Mathematics of the Polarized-Fluorescence Experiment
Authors: Desper C. Richard , Kimura I.
Published: January 2005

The polarized-fluorescence experiment for measurement of preferred orientation is analyzed mathematically. The intensity is dependent upon P and A, unit vectors describing the positions of the polarizer and analyzer, and upon the orientation distribution N(α, δ) of the chromophoric group of the polymer. In the case of biaxial or uniaxial symmetry, the intensity IPA for any combination of P and A vectors is expressed as linear combination of nine fundamental intensities characteristic of a given sample. These intensities form a 3×3 matrix, each entry Iij being the intensity obtained with P and A parallel to the ith and jth principal axes of the sample. Of the nine components of I, only five are independent for a biaxially oriented sample; two for uniaxial orientation. Each Iij is proportional to 〈xi2xj2〉Av, where xi and xj are the components of the chromophore vector along the corresponding principal axes. Calculated matrices are shown for several model distributions. Nishijima's P function is related to the Iij's, and the problem of measuring biaxial orientation is discussed. The Iij's are also shown to be directly related to the second-and fourth-order coefficients in the spherical harmonic expansion of N(α, δ). These coefficients can be measured directly by a few simple experiments involving spinning the sample between crossed or parallel polarizers. Thus, the experimental error in their determination can be minimized.
Grüneisen Numbers for Polymeric Solids
Authors: Barker R. E.
Published: January 2005

Recent considerations by Wada make it appropriate to extend a previous discussion of Grüneisen ``numbers'' for polymers and other molecular solids. Wada hypothesized that the proper Grüneisen constant for polymers is γG=αV/βCvb, where Cvb is the interchain contribution to the heat capacity at constant volume; α, β, and V are the volumetric thermal expansivity, the compressibility, and the volume. To the extent that a polymer can be treated as a vibrational lattice, the hypothesis appears to be consistent with γG=Σγiε(xi)/Σε(xi), averaged over Einstein oscillator functions ε(xi) with xi=hvi/kT. At low temperatures, ε(xi) is much larger for the low-frequency modes, so that they tend to determine γG below the Debye −θ. Since γi=−∂ lnνi/∂ lnV and since low νi are likely to be more sensitive to changes in V, it is expected that γG will be larger for molecular solids than for metallic, ionic, or covalent crystals. Earlier predictions and Wada's calculations agree that γG≈4 might be typical for polymers and suggest that ∂γ/∂T>0. The correlation, Eαl2≈15 N/m2°K2, between modulus E and linear expansivity αl led to the prediction, now verified, that there should be relations between the harmonic and anharmonic moduli. The anharmonic coefficients in the relation ΔV/V0=a1p+a2p2+a3p3+⋯are a2=C1a12 and a3=C3a13, where for metals C2=−2.5±0.5, and for polymers C2=−4.0±0.1 and C3=8.8±0.2. A phenomenological theory based on a ``bundle of tubes'' model is developed which is in good agreement with data and according to which γG=−C2 and dγG/dT∼αC2. The relation of γG to intermolecular potential functions also is discussed and some qualtitatively encouraging results are obtained.
Dislocations, Slip, and Fracture in BeO Single Crystals
Authors: Bentle G. G. , Miller K. T.
Published: January 2005

Dislocations formed during the growth and deformation of BeO single crystals were studied with x-ray and electron microscopy. The stresses for slip on the systems (0001) 〈112̄0〉, {101̄0} [0001], {101̄0} 〈112̄0〉, and {112̄2} 〈112̄3〉 are approximately 3.5×108, 1.1×109, 4.9×108, and >2.5×109 dyn/cm2, respectively, at 1000°C. Slip directions in deformed specimens were shown with x-ray microscopy. Defects in the specimens were shown to interfere with slip. Dislocation pinning and elastic interactions were observed in electron micrographs. These observations are correlated with theory.
Experiments with Quadrupole Lenses in a Scanning Microscope
Authors: Crewe A. V. , Eggenberger D. N. , Welter L. M. , Wall J.
Published: January 2005

A scanning electron microscope using a quadrupole doublet as the focusing lens is described. The optical properties of an unsymmetrical, ``pseudostigmatic'' (unequal magnifications in perpendicular planes) doublet are summarized, and rotational misalignment of the elements is discussed. Experimental studies were made to determine the dependence of the final image size on lens aberrations and construction defects. A computer was used to fit the experimental data to a generalized spot size equation. Separate experiments were made on both magnetic and electrostatic doublets, and the smallest experimental image size (which appears to be limited by astigmatism) was 150 by 450 Å using either quadrupole system. Experimental results agree with recent computer predictions for these doublets, and further calculations indicate that the use of quadrupoles and octupoles in a scanning microscope may be advantageous.
Noise and Multiplication Measurements in InSb Avalanche Photodiodes
Authors: Baertsch R. D.
Published: January 2005

Multiplication and noise measurements on InSb avalanche photodiodes have been made from 77° to 125°K. For the diodes studied, the electron ionization rate is much larger than the hole ionization rate and depends only weakly on the field for fields between 5×103 and 104 V/cm. The electron ionization rate increases and the breakdown voltage decreases with increasing temperature. The dependence of the ionization rate on field and temperature is explained by the weak dependence of the distribution function on field for high fields. The noise measurements are consistent with McIntyre's theory providing that the electron ionization rate is much greater than the hole ionization rate. A current-controlled negative resistance is observed in InSb avalanche diodes at breakdown.
Propagation of Piezoelectric and Elastic Surface Waves on the Basal Plane of Hexagonal Piezoelectric Crystals
Authors: Tseng Chin-Chong , White R. M.
Published: January 2005

Propagation of piezoelectric and elastic surface waves on the basal plane of hexagonal piezoelectric crystals has been investigated theoretically. Variations of the piezoelectric field and the particle displacement with the distance from the surface have been derived and compared with Stoneley's result for nonpiezoelectric crystals.

The results are applied to hexagonal CdSe, CdS, and ZnO. For CdSe and CdS, the surface waves are pure Rayleigh modes. However, for ZnO which has relatively large piezoelectric coupling coefficients, the surface waves are found to have the form of a general surface wave defined by Synge. Velocities of surface waves propagating on the basal plane of CdSe, CdS, and ZnO are computed to be 1.470×105, 1.7306×105, and 2.70×105 cm/sec, respectively, which are in good agreement with measured values.
Elastic Surface Waves on Free Surface and Metallized Surface of CdS, ZnO, and PZT-4
Authors: Tseng Chin-Chong
Published: January 2005

Velocities, particle displacement, and piezoelectric field associated with surface elastic waves in CdS, ZnO, and lead-titanate zirconate (PZT-4) have been computed for two cases, with and without metallic coating on the surface. Compiled are data for CdS, ZnO, with their c axis normal to the surface, and PZT-4, poled in the direction normal to the surface. The velocity of propagation is found to be slightly lowered by the presence of metallic coating. Such change in velocity is applied to conduct an experiment which shows strong Bragg's reflection of elastic surface waves by metallic thin-film gratings. It has been pointed out that the previously reported surface wave velocities inferred from the response of interdigital transducer are believed to be slightly lower than the actual velocity of propagation.
Effect of Hydrostatic Pressure on Dislocation Mobility in Lithium Fluoride
Authors: Hanafee J. E. , Radcliffe S. V.
Published: January 2005

The effects of hydrostatic pressures up to 13 kbar on the stress dependence of the velocity of screw dislocations in single crystals of lithium fluoride at room temperature have been determined. The shear stresses to move the dislocations were introduced by means of a three-point bending device incorporating a load-cell and operated entirely within a fluid medium at constant pressure and temperature. The range of velocities observed was from 10−5 to 10−2 cm/sec. Both high-purity and impurity-doped crystals were studied.

At all the pressures examined, the dislocation velocity was found to vary with the applied shear stress τ in accordance with the empirical relationship v = v*·e−A/τ (where v* is a terminal velocity and A is a drag stress) suggested by Gilman for one-atmosphere behavior. However, the stress required to move a dislocation at a given velocity in increases rapidly with pressure, by a factor of approximately 3 at 10 kbar. Correspondingly, the dislocation velocity at constant applied shear stress decreases by several orders of magnitude. Based on the magnitudes of the activation volume measured for the high-purity and doped crystals, the effects are interpreted in terms o the mobility of jogs as the mechanism controlling dislocation velocity at pressure.

The measured decrease in dislocation mobility has been used to compute the expected change in stress—strain behavior in LiF as a function of pressure.
Secondary-Electron Emission from Glycerol-Coated Copper Surfaces
Authors: Gill J. J. , Hendricks C. D.
Published: January 2005

This paper reports the results of an experimental determination of the secondary-emission characteristics of glycerol layers on copper surfaces. This work has as its motivation the use of glycerol as a working fluid in electric thrustors for spacecraft.

Secondary-emission coefficients for glycerol are reported as a function of incident primary-electron energy. Primary-electron energy was varied from 200–900 eV and glycerol secondary-emission coefficients were found to vary from 2.5 to about 1.0. These results are compared with values for clean copper surfaces found by using the same apparatus.
Slip Modes of Hexagonal-Close-Packed Metals
Authors: Yoo M. H. , Wei C. T.
Published: January 2005

The effective shear moduli, dislocation line energies, dislocation widths, and relative ease of gliding have been calculated for the (0001) [112̄0], (11̄00) [112̄0], (11̄01) [112̄0], (112̄2) [112̄3̄], and (hk.0) [0001] slip systems in each of the hexagonal close-packed metals Cd, Zn, Mg, Co, Zr, Ti, and Be by applying anisotropic elasticity theory of dislocations. Except for the case of Be, the results correctly explain the choice of prevailing slip systems among the three with a common slip vector ⅓ [112̄0]. The second-order pyramidal slip, frequently observed in Cd and Zn, cannot be accounted for in terms of its calculated relative ease of gliding. It seems that the extended nature of a dislocation, hence the stacking-fault energy, may affect the ease of gliding of the dislocation.
Silicon Oxide Films Grown in a Microwave Discharge
Authors: Kraitchman J.
Published: January 2005

The growth of silicon dioxide in a microwave discharge was investigated. The oxide growth can be characterized by a rate-limiting diffusion process modified by sputtering effects produced by the discharge. Analysis of the growth behavior leads to the conclusion that a limiting oxide thickness is obtained at infinite time. The growth process provides a technique for rapidly oxidizing silicon at temperatures estimated to be 500°C or lower. At these low temperatures, growth rates corresponding to steam-oxidization rates at 1100°C can be obtained. Films about 2000 Å thick can be grown in five minutes, and about 6000 Å thick in sixty minutes. High-quality oxides are produced by this process with properties which are for the most part indistinguishable from those of thermally grown oxides. MOS capacitance—voltage measurements indicate that these oxides are essentially free of mobile ions.