bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of Oxygen with (110) Nickel
Authors: Park Robert L. , Farnsworth H. E.
Published: April 2005

The interaction of oxygen with a (110) nickel surface has been studied by photoelectric and low-energy electron diffraction techniques. With increasing exposure to O2, a sequence of oxygen—nickel structures is formed terminating in the NiO rocksalt structure which is oriented with the (100) face of the oxide parallel to the surface. It was possible to observe some of these structures in reverse order by heating the oxide-covered crystal in vacuum or subjecting it to brief argon ion bombardment. From the fact that the oxide was decomposed at only 200°C, and from the associated changes in work function and diffraction intensity, it is concluded that oxygen readily penetrates into the nickel lattice, occupying substitutional sites to form three-dimensional oxygen—nickel structures of increasing oxygen content until the composition of NiO is reached. This makes possible the correlation of the two-dimensional oxygen—nickel structures observed on different faces.
Dislocation Damping in Dilute Cu-Ge Alloys
Authors: Fiore Nicholas F. , Bauer Charles L.
Published: April 2005

Internal friction measurements have been performed on copper-germanium single crystals, ranging in composition from 0.005 to 0.5 at.% germanium, in order to test some predictions of dislocation damping theory. The Marx composite piezoelectric oscillator has been used with the specimens driven in their fundamental longitudinal mode of vibration at 80 kc/sec and at temperatures ranging between 200° and 600°C.

Three distinct regions appear when the decrement is plotted vs strain amplitude: an amplitude-independent, an amplitude-dependent, and a plateau region. While the Granato-Lücke theory can adequately account for the results in the amplitude-dependent region, behavior of the decrement in the amplitude-independent and plateau regions is more readily explicable in terms of Rogers' modification of the theory. From the appropriate analysis for each region, values of the average dislocation segment length between nodal pinning points, the average length between impurity pinning points, and the damping constant of a dislocation are obtained. These values are compatible with the physical constraints inherent in dislocation damping theory and are in good agreement with present notions concerning the internal structure of solids. In addition, the decrement exhibits a time dependency which qualitatively can be explained by the fact that the mobility of solute atom pinning points increases with increasing temperature.
Likelihood Detection of a Signal Obscured by First-Order Markovian Noise
Authors: Potter D. S. , Leedham C. D.
Published: April 2005

This paper develops a procedure for the optimum detection of a deterministic, finite length signal obscured by Gaussian-Markovian noise that approximates sea noise by employing the concept of a Likelihood Ratio. For the particular noise model, the optimum procedure is to use a cross-correlation detector. The variables fed to the correlation device are additive combinations of each channel's signal and its derivative. This procedure is equivalent to filtering each channel to render the background noise white and then cross-correlating the filter outputs.
Proposed Lossless Dissociating Plasma for Use with a DCX-Type Device
Authors: Ehler A. W.
Published: April 2005

This paper proposes a novel method for dissociating high-energy molecular ions, such as H2+, which are injected into a magnetic mirror container. The dissociating medium is a highly ionized plasma consisting of protons and high-energy electrons ejected in the decay of dense thermal neutrons which exist within a nuclear research reactor. The plasma is accumulated within a weak magnetic mirror container inside the reactor and then transferred magnetically to the site where the H2+ injection is to take place. Finally the dissociating plasma is compressed magnetically to a density of 1011/cm3 and injection is begun. The plasma provides an efficient means for dissociating the injected H2+ ions, but contributes negligibly to charge exchange losses of trapped high-energy protons.
Photon Emission from Irradiated Dielectric Slabs
Authors: Ashley J. C. , Ritchie R. H.
Published: April 2005

In this paper a simple derivation is given of the distribution of photons emitted when an energetic charged particle passes through a thin layer of dielectric material. This derivation emphasizes the individual microscopic events which occur during such a process. The distribution function is shown to agree with that obtainable from the transition radiation theory of Frank and Ginzburg and from the plasmon decay theory of Ferrell for the case of a thin foil. The special case of a double foil bounded by vacuum is considered in detail, and a general formula is found for the photon distribution function. An approximation analogous to that of Born's in quantum mechanics is developed to treat the case of a general composite foil whose thickness is small compared with λ but which may be large compared with vλ/c, where λ is the wavelength of the light emitted and v is the speed of the charged particle.
Faraday Rotation of Rare-Earth (III) Borate Glasses
Authors: Rubinstein C. B. , Berger S. B. , Van Uitert L. G. , Bonner W. A.
Published: April 2005

Optical Faraday rotation of rare-earth (III) borate glasses has been investigated at room temperature. The rotation is described in terms of an effective transition wavelength λt which is an indicator of the spectral region of the 4fn-4fn−1 5d absorptions mainly responsible for the rotation. An experimental investigation of the magnitude of rotation as a function of rare-earth (III) ion reveals the importance of the transition wavelengths and the electric dipole matrix elements as parameters affecting the rotation. The borate matrix is found to be more effective than many other environments in the realization of higher Verdet constants.
Ag Ion Migration in α Quartz
Authors: Milne E. L. , Gibbs P.
Published: April 2005

Ag ion conduction currents in α quartz were measured at temperatures between 300° and 550°C with 2.5 V dc applied between Ag electrodes on the inner and outer surfaces of a natural quartz tube. The activation energy H for this conduction process depends upon the average electric field intensity according to the equation H=H0-βE½, where H0=38 kcal/mole and β=0.32 kcal/[mole (V/cm)½]. A theory which appears to explain this field dependence postulates the formation of a lattice-bound negative space charge near the Ag anode. This space charge is formed by the migration of mobile impurity cations away from the anode, leaving behind a net charge due to the presence of substitutional ions such as Al+3. This negative space charge creates electrical field intensities of the order of 105 to 107 V/cm at the anode surface. This field lowers the height of the 38-kcal/mole barrier near the anode. Graphs of the available data for Li+ and Na+ migration indicate that the rate-limiting step for these processes might also be the surmounting of a potential barrier near the anode-quartz interface.
Photochemical Reactions in Potassium Chloride Crystals Grown from Reagent Grade KCl
Authors: Grassano U. M. , Jacobs P. W. M.
Published: April 2005

Reagent grade potassium chloride usually contains sufficient water to hydrolyze some of the KCl so that crystals grown from it contain KOH unless they are treated with either HCl or Cl2. Thus crystals grown in platinum without pretreatment show the well-known OH band. Crystals grown in silica do not show this OH band but they nevertheless contain a source of hydrogen as shown by the formation of the U2 band on exposure to ultraviolet light. It is shown that such crystals have an absorption band at 187 mμ and form bands at 193.5 and 360 mμ, in addition to other bands previously recorded, on exposure to uv light. Various possible models for the centers responsible for these absorption bands are discussed, together with the photochemical reactions involved.
Resistivity of Ferromagnetic Alloys
Authors: Sivertsen J. M.
Published: April 2005

A theory is given for the spin-dependent scattering contribution to the resistivity of a ferromagnetic alloy as a function of temperature, composition, and short-range order. A spin-dependent s-d exchange interaction of the Zener-Yosida type is assumed responsible for the major part of the scattering. Steady-state pair correlations between spins in the ferromagnetic alloy are also considered in deriving the resistivity. On ignoring the effect of short-range order on the electronic structure, the short-range order is seen to affect both the temperature-dependent and temperature-independent parts of the scattering. For binary alloys of a monvalent metal solvent with transition element solutes, short-range order tends to increase the resistivity relative to that of a random structure. Clustering tends to decrease it.
Electrical Conductivity of Single-Crystal Cr2O3
Authors: Crawford Julian A. , Vest Robert W.
Published: April 2005

The electrical conductivity of single crystals of Cr2O3 has been measured as a function of temperature from 600° to 1400°C and as a function of oxygen partial pressure from 1 to 10−6 atm. The results show a high-temperature ``intrinsic'' conductivity that is independent of oxygen pressure, and a low-temperature defect-controlled conductivity that varies with oxygen pressure in a manner which cannot be determined from measurements on single crystals. The very low mobility deduced from the intrinsic conductivity suggests an interpretation in terms of the theory of small polarons. Although the possibility of charge transport in very narrow bands cannot be ruled out on the strength of the experimental data, it seems less likely. The model suggested is that of charge formation and transport in localized 3d levels of the cations.
Ferromagnetic-Paramagnetic Transition in Iron
Authors: Arajs Sigurds , Colvin R. V.
Published: April 2005

Magnetization per gram of an iron sphere σ as a function of temperature T has been studied between the ferromagnetic Curie temperature TFC and TFC+30°K with applied magnetic fields between 180 and 1360 Oe. The temperature TFC, appearing as an abrupt decrease in the σ vs T curves, occurs at 1044±2°K. Mass magnetic susceptibility of iron, above the ferromagnetic Curie temperature in small magnetic fields, is proportional to (T-TFC)−4/3, which is the theoretical prediction for a Heisenberg three-dimensional ferromagnet.
Potential Barriers and Emission-Limited Current Flow Between Closely Spaced Parallel Metal Electrodes
Authors: Simmons John G.
Published: April 2005

This paper discusses in detail the shape of the potential barrier existing between two parallel-plane metal electrodes separated by a thin insulating film. The emission-limited current flow between the electrodes is determined for symmetric and asymmetric junctions. The asymmetric J-V (current-voltage) characteristic is of particular interest, as it can be shown that the difference in work function of the two electrodes comprising the junction can be obtained from a perfunctory study of the characteristic. The thermionic J-V characteristic is compared to the tunnel J-V characteristic. For a temperature of 300°K, and for a barrier thickness less than 40 Å, the tunnel J-V characteristic predominates. However, for barrier thickness greater than 40 Å, either the thermionic or the tunnel characteristic can predominate, depending upon the barrier height and the applied voltage. In the case of asymmetric junctions, there may be a reversal of direction of rectification with decreasing temperature. This reversal of rectification may explain the similar effect sometimes observed in tunnel junctions.
Preparation and Semiconducting Properties of Cd3P2
Authors: Haacke G. , Castellion G. A.
Published: April 2005

Single and polycrystalline samples of Cd3P2 have been prepared. Undoped samples are n-type with carrier concentrations between 1017 and 1018 cm−3. The thermoelectric power of these samples goes up to −170 μV/°C at 300°K. Mobility values up to 3000 cm2/V sec at 300°K were measured. The mobility of single crystals varies in the extrinsic range near room temperature proportionally to T−1.1 (T is temperature). Optical measurements indicate an optical band gap of approximately 0.5 eV. The results of annealing experiments support the assumption that the high electron concentration of undoped samples is due to phosphorus vacancies. The doping properties of various elements have been studied. Copper introduces what is probably a deep-lying acceptor level, but p-type samples could not be obtained.
Dislocation Multipoles and Their Role in Strain-Hardening
Authors: Chen H. S. , Gilman J. J. , Head A. K.
Published: April 2005

The stress fields of edge dislocation dipoles are able to trap other edge dislocations that pass nearby. The configurations, energies, and trapping stresses of the resulting tripoles are discussed here in some detail. Dipoles may also interact dynamically with approaching dislocations because they cause fluctuating stresses. The decrease in the average velocity of a moving dislocation is given in terms of the fluctuation amplitude and the dislocation's ``mobility parameter.''

On the basis of these results, linear strain-hardening can be accounted for in terms of edge dislocation dipoles. Since dipoles in real crystals tend to be finite in length and their stress fields attenuate rapidly with distance, they act as particles to impede dislocation motions. Thus hardening is proportional to the dipole concentration which is proportional to the plastic strain, so the hardening will be linear in the strain.

Through interactions with approaching dislocations, dipoles may become tripoles, then quadrupoles, etc., leading to some of the characteristic residual structures in plastically strained crystals, such as slip bands, deformation bands, and bands of secondary slip.

No attempt is made to calculate the strain-hardening coefficients of real crystals because concentrations and distributions of dipoles are not known in sufficient detail.

Finally, it is shown that the asymmetric stress fields of dipoles can account in a natural way for the Bauschinger effect.
Nonlinear Rubberlike Viscoelasticity—A Molecular Approach
Authors: Halpin J. C.
Published: April 2005

The difference between the dynamic and equilibrium tension in a macromolecular chain is expressed as a ``functional'' of the variation of the nonlinear strain function φ(r*) developed in the kinetic theory of elasticity, with respect to time through the interval (0,t) r*≡r/rm where r is the vectorial end-to-end distance of the molecular chain and rm is the maximum separation). The ``functional'' is expanded in an integral series analogous to Taylor's series and higher terms are neglected to obtain a linear integral equation for the viscously retarded response of the network chain. The equation obtained is a generalized one-dimensional Boltzmann's superposition equation. It is then shown that the time-dependent response of the molecular chain is independent of the magnitude of the deformation and, consequently, is of the same analytical form whether the deformation is infinitesimal or finite. From this it necessarily follows that there cannot be an inconsistency at finite stress and strain which is not allowed at infinitesimal excitations. Thus the response at finite excitations can be treated generally by employing the ``generalized'' superposition equation and the same techniques which have been utilized in the linear theories. Employing the usual kinetic theory assumptions, equations are developed for the macroscopic response of a well-vulcanized rubber. Experimental data obtained in creep, stress relaxation, and dynamic stress-strain for three different elastomers are presented which support the approach outlined. Some consequences of the theory are discussed.
Crystalline Morphology of Synthetic Polypeptides
Authors: Padden F. J. , Keith H. D.
Published: April 2005

In an attempt to grow single crystals of synthetic polypeptides, polyglycine, poly-l-alanine, and poly-l-tyrosine have been precipitated from dilute solution and also cast as films by the slow evaporation of solvent. Polyglycine precipitated from solutions containing equal parts of trifluoroacetic acid (TFA) and trifluoroethanol (TFE) by the addition of water, crystallizes with the polyglycine II structure in the form of lamellar platelets with folded molecular chains. In films of polyglycine cast from these solutions, however, sheaves of ribbonlike crystals are produced, also chain folded and having the same structure. Selected-area electron diffraction from these various crystals yields corroborative evidence for some of the structural features of polyglycine II. Poly-l-alanine cast from solution in TFA and TFE, on the other hand, crystallizes to give platelets and sheaves side by side in the same preparations. Both have the crystal structure of the α form of poly-l-alanine, and indirect evidence indicates that chain folding probably occurs in both instances. There is a suggestion that, as grown, the crystals contain solvent complexed chemically with the polymer. Poly-l tyrosine can be precipitated from solution in mixtures of N,N-dimethylformamide (DMF) and n-heptanol in the form of hexagonal platelets and these too probably consist of folded molecules complexed with solvent. A tentative correlation between conformation in solution and crystalline morphology is suggested in the case of poly-l-tyrosine, but no definitive conclusion can be reached without further study of the conformation of the polymer held in solution under the conditions prevailing during crystallization.
Ultimate Tensile Properties of Elastomers. IV. Dependence of the Failure Envelope, Maximum Extensibility, and Equilibrium Stress-Strain Curve on Network Characteristics
Authors: Smith Thor L. , Frederick J. E.
Published: April 2005

Uniaxial tensile data from tests at different rates of extension over a wide temperature range are considered for butyl, silicone, Viton B, SBR, and natural rubber vulcanizates (series A) and for six Viton A-HV vulcanizates (series B) of differing crosslink densities. For series A and for A-6 in series B, equilibrium stress-strain data were obtained at large deformations by an indirect method. The ultimate tensile properties of all vulcanizates were previously characterized by a time- and temperature-independent failure envelope. The failure envelope's maximum extension ratio, (λb)max, is shown to be equal to or less than (λ∞)max, the maximum extension ratio (hypothetical) in the absence of rupture and also the maximum extension ratio of network models. Failure and equilibrium data for series A vulcanizates are represented by a specific function of the equilibrium modulus and the maximum extensibility; except for SBR and possibly Viton B, equilibrium and failure data are sensibly identical; thus, (λb)max≅(λ∞)max. For series B vulcanizates, qualitative considerations indicate that (λ∞)max/(λb)max is greater than unity and possibly dependent on crosslink density. Consideration of network models suggests that (λ∞)max should be directly proportional to Mc½ and inversely proportional to (〈r2〉0/M)½. For series A, no correlation between (λb)max and (〈r2〉0/M)½ was found. For series B, it is shown that (λb)max∝Mcβ, where β is a constant in the neighborhood of 0.7. For all vulcanizates, (σb)max≅104(λb)max−1, where (σb)max is the stress in psi (based on the undeformed cross section) at (λb)max.
Photographic Light Scattering and Photomicroscopy of Deformed Ringed Spherulites
Authors: Moore Robert S. , Gieniewski Chester
Published: April 2005

Polyethylene films were studied by photographic light scattering and photomicroscopy at successive increments of strain, usually 5%. Photomicrographs were taken at times sufficiently long after sample deformation so that the light scattering patterns were constant with respect to intensity and shape. Analysis of such scattering patterns and photomicrographs indicated that upon spherulite deformation, the ring spacing (hence the twist-distance) increased in the direction of tensile strain and decreased at right angles to the strain direction, as noted in earlier experiments on samples subjected to tensile stress. At about 30% strain the wide-angle parallel polarizer scattering pattern (polarization and strain directions horizontal) split into a set of 4 arcs nearly parallel to the meridian. With increasing strain (analyzer and strain directions vertical) the arcs of the 4-arc wide-angle crossed polarizer scattering pattern, originally at 45° to the polarizer and analyzer axes, occurred nearer the meridian and became nearly parallel to the equator. Photomicrographs indicated that at 30% strain the ring spacing at right angles to the strain direction was extremely small or in some cases not resolvable and that discontinuities occurred in the rings. Immediately adjacent to the axis of sample deformation in many spherulites there was a discontinuity in the rings such that they appeared to cross the axis at an angle of 50° to 60°. The relationship between the changes observed by light scattering and the changes observed by microscopy is shown. Photomicrographs and light scattering patterns are presented and a brief analysis of the changes is given in terms of mechanisms of spherulite deformation.
Thermodynamic Properties of Drawn Linear Polyethylene
Authors: Peterlin A. , Meinel G.
Published: April 2005

Measurements of melting curves, density, and long period of undrawn and drawn PE as a function of the draw ratio and the annealing temperature between 118° and 129.8°C for different annealing times were performed. Melting experiments show a linear increase of melting point and a reduction of heat content of the noncrystalline component with increasing draw ratio. As a consequence of plastic deformation during drawing, the tied macromolecules partly incorporated in more than one crystal are under high strain. This reduces not only the entropy but also the intra- (trans instead of gauche conformation) and interchain (aligned extended chains are more closely packed) energy of the amorphous regions. Annealing nearly instantaneously removes the strain on tied chains, restores the enthalpy and entropy to the values in a nearly completely relaxed supercooled melt, and increases crystallinity and long period. Subsequent prolonged annealing produces only slight additional changes.

The variation of enthalpy and entropy rather well explains the observed drastic changes in sorption and diffusion of solvent molecules as a consequence of drawing and annealing.
Superheating of Linear High-Polymer Polyethylene Crystals
Authors: Hellmuth E. , Wunderlich B.
Published: April 2005

The time dependence of melting of morphologically different crystals of polyethylene was investigated. New DTA and calorimeter techniques were developed. A microscope hot stage allowing heating rates of up to 3000°C/min was built for melting-point determinations. The superheating of extended-chain crystals was clearly demonstrated by qualitative DTA and isothermal quantitative calorimetry. Smaller crystals and folded-chain crystals showed decreasingly less superheating. Crystals which are less perfect and have large surfaces show increasing reorganization. A region of approximately zero entropy production melting seems to lie between reorganization at slow heating rates and superheating at faster heating rates.
Direct Observation of Dislocation Networks in Folded-Chain Crystals of Polyethylene
Authors: Holland V. F. , Lindenmeyer P. H.
Published: April 2005

The direct observation of networks of dislocations between platelets of folded-chain polyethylene crystals has been accomplished using diffraction contrast electron microscopy. The networks are composed of dislocations, primarily in their screw orientation, having Burgers vectors [110], [100], and [010]. The [110] dislocations are invariably dissociated into ribbons and there is evidence that the other two also tend to dissociate. Singularities in the networks are interpreted in terms of interactions between the partial edge dislocations previously detected by moiré patterns and glissile screw dislocation ribbons. These observations prove that folded-chain surfaces are sufficiently regular to pack crystallographically and that slip between folded-chain platelets can occur by the motion of dislocations.
Scattering of Light by Two-Dimensional Spherulites
Authors: Clough S. , Van Aartsen J. J. , Stein R. S.
Published: April 2005

The low-angle light scattering for anisotropic disks (representing two-dimensional polymer spherulites) is calculated for the cases of (1) the optic axis lying in the plane of the disk and tilted at the angle β to the radius, (2) the optic axis rotating cylindrically about the radius through the angle ω while making a constant angle β to the radius where (a) ω rotates randomly and (b) ω varies linearly with the distance r from the center of the disk, and (3) affine deformation of the disk to an ellipsoid. For case (1) the scattering pattern is shown to rotate azimuthally through the angle β from that previously described where β=0° in agreement with experimental observations on polytetrafluoroethylene. Case (2) is shown to predict an azimuthal dependence of the wide-angle scattering maxima of a type experimentally observed for banded spherulites. Case (3) predicts a deformation of the scattering pattern of a type observed for deformed polyethylene spherulites.
Brush Cathode Plasma—A Well-Behaved Plasma
Authors: Persson Karl-Birger
Published: April 2005

Results of probe, spectroscopic, and microwave studies are used to describe properties of a novel cold-cathode discharge. The use of a brush cathode allows stable operation in the abnormal glow region where some of the usual cold-cathode mechanisms are greatly exaggerated and determine the features of the produced plasma. The cathode fall is about an order of magnitude larger than for the corresponding normal cold cathode. The brush cathode generates a uniform electron beam in the energy range 1 to 10 kV and a corresponding negative glow with a longitudinal dimension (reaching distance of the beam) one to two orders of magnitude larger than for the normal cathode glow. The large dimensions of the negative glow and the fact that it is well-behaved (no instabilities and no striations) make it ideal for a whole series of investigations in plasma physics and spectroscopy. The electron density in the helium plasma is in the range 1010 to 1014 cm−3, the electron temperature in the range 0.05 to 0.10 eV. The negative glow is beam generated (essentially field free) and recombination dominated making it a practically uniform plasma ideal for the study of rate and transport coefficients. Preliminary measurements of the particle balance give a recombination rate of 5×10−10 cm3 sec−1 at 1100°K and an electron density of 3×1012 cm−3 in agreement with the collisional-radiative recombination theory developed by Bates, Kingston, and McWhirter. The recombination light emitted by the plasma is sufficiently strong to make spectroscopic methods useful for measurements of the electron density and the electron temperature. Lines in the helium series 2s3S—np3P0 are observed up to the quantum level n=30.
Mechanisms Contributing to the Noise Pulse Rate of Avalanche Diodes
Authors: Haitz Roland H.
Published: April 2005

The noise pulse rate of microplasmas and uniform avalanche diodes is determined by carrier generation within the space-charge layer of the breakdown region, and by minority carrier diffusion to the breakdown region. By suppressing the minority carrier diffusion from bulk to breakdown region with a suitable geometry, it is possible to investigate the carrier generation within the space-charge layer of a p-n junction. Three contributions to the carrier generation rate are found: (1) thermal carriers from generation centers, (2) re-emission of carriers trapped during preceding periods of avalanche breakdown, and (3) carrier generation by internal field emission (band-to-band tunneling). For the case of uniform avalanche diodes, these three contributions are investigated separately. The density of generation and trapping centers within the breakdown region could be reduced by several orders of magnitude by driving the diodes into secondary breakdown. During this process the breakdown region is heated to a temperature of the order of 1000°C at which trapping and generation centers are partly annealed.
Structure of the Double Sheath in a Hot-Cathode Plasma
Authors: Crawford F. W. , Cannara A. B.
Published: April 2005

This paper is concerned with the double sheath which is normally present in front of a hot cathode in a low-pressure dc discharge. The authors present a theory of an idealized form of this sheath, under space-charge-limited cathode emission conditions. The discrepancies from this model to be expected in a practical situation are discussed, and comparisons are made with experimental results. To obtain these, an electron beam probing technique was used, and electric field measurements were made directly in the cathode sheath of a low-pressure mercury-vapor discharge. Good agreement was obtained between the simplified theory and the experiments.
Dislocation Dynamics and Dynamic Yielding
Authors: Taylor John W.
Published: April 2005

The dislocation dynamics of Gilman and Johnston are applied to the problem of elastic—plastic flow in Armco iron at very high strain rates. The dislocation velocity is assumed to follow the law v=v∞ exp(−τ0/τ); experimental data support this form of dependence and are used to determine the value of τ0. This value is in reasonable agreement with other measurements taken from Lüders band front velocities. A second quantity which can be evaluated is the initial density of dislocation lines, N0, which is found to be 2.0×108 cm−2.
Growth Morphology of Hexagonal Selenium at High Pressures
Authors: Harrison D. E.
Published: April 2005

Hexagonal selenium can be grown from the melt either in the form of spherulites or as single crystals. At normal pressures, the transition from spherulitic to single-crystal growth habit is usually not seen due to the very slow growth rate of single crystals. At higher pressures, the single-crystal growth rate is enhanced sufficiently to permit observation of this transition. Examination of melt-grown crystals by Weissenberg x-ray techniques disclosed a disorder normal to the ``c'' axis direction. The absence of the disorder in vapor-grown needles produced at 5 kbar indicates that the disorder is built in during growth from the melt.
Computer Studies of Copper Atom Ranges in Copper Lattices
Authors: Harrison D. E. , Leeds R. W. , Gay W. L.
Published: April 2005

We have used an n-body collision computer simulation model with a Gibson #2 potential to examine various ways in which the lattice nature of the slowing down material influences the motion of a medium-energy copper atom. For normal incidence upon a (110) surface, we found that the lattice has a significant effect upon the scattering angle when a 10-keV copper atom strikes an atom of a copper lattice. The channel area, which comprises approximately 40% of the representative area in this orientation, is quite insensitive to the copper atom's energy above 1 keV. Total ranges are significantly longer than those reported by Robinson and Oen from calculations based upon a binary collision model. Below 1 keV, total ranges closely approximate the E32 law reported by Kornelsen et al. Above 1 keV dE/dx=A−B/E appears to describe the motion at all positions in the channel if the values of A and B are specified for the initial point at which the atom enters the channel. This behavior above 1 keV is clearly nonphysical. To be meaningful, even at intermediate energies, computer range studies must include inelastic energy losses. Lattices are known to focus atoms incident near the [110] direction into [110] channels. This mechanism was studied at the center of the channel with 1-keV atoms. The effect is anisotropic in the azimuthal angle, but we found that atoms inside a 10° cone were always focused, and that 20° focusing occured in one orientation. Angular focusing was less effective at higher energies. Transverse oscillations in the channel were also considered. The ``wavelengths'' are proportional to E½, but oscillations are usually not symmetric about the channel axis. Transverse motion is approximately harmonic, but the ``vertical'' and ``horizontal'' frequencies are never commensurable. We have evidence for a skimming mechanism in which high energy atoms are confined between (111) planes, or to a lesser extent between (100) planes. Trajectories of 5-keV knock-on atoms are shorter than 40 Å unless the moving atom skims. One true channel event was found in 120 trials in which the moving atom started from a lattice site.
Formation Conditions and Structure of Ge Films Deposited on Polished (111) CaF2 Substrates in an Ultrahigh-Vacuum System
Authors: Sloope Billy W. , Tiller Calvin O.
Published: April 2005

The structure of Ge films deposited over a wide range of deposition rates and substrate temperatures onto hand-polished (111) CaF2 substrates in a vacuum of 10−9 to 4×10−7 Torr has been characterized. The epitaxial temperature and the amorphous to crystalline transition temperature were found to be rate dependent. The linear relation observed between the logarithm of the deposition rate and the reciprocal of the epitaxial temperature agrees generally with nucleation theory of small clusters and yields an activation energy of 1.43 eV. The observed linear relation between the logarithm of the deposition rate and the reciprocal of the amorphous to crystalline transition temperature has been interpreted in terms of simple surface diffusion theory and leads to an activation energy for surface diffusion of Ge on CaF2 of 1.53 eV.
Aluminum Antimonide Thin Films by Coevaporation of the Elements
Authors: Johnson J. E.
Published: April 2005

Stoichiometric thin films of AlSb have been prepared by coevaporation of the elements onto glass substrates held at 550°C. Conductance activation energies of 0.17 and 0.29 eV were observed. Oxygen adsorption causes a level at 0.24 eV that dominates the conductance in air at room temperature. Space-charge-limited current flow was observed at room- and liquid-nitrogen temperatures. The hole concentration and mobility in the layers are estimated at 1015 cm−3 and 1.5 cm2/V-sec, respectively.
Hall-Effect Measurements of n-Type Gallium Phosphide
Authors: Montgomery H. C. , Feldmann W. L.
Published: April 2005

Hall measurements of GaP crystals grown by several different methods and doped with S, Te, Si, and Ge show n-type behavior with donor concentrations ranging from 1016 to 1019 cm−3. Binding energies for the donor states at concentrations of 1018 cm−3 were estimated at 0.089±0.020 eV for S, 0.076±0.020 eV for Te, and 0.078±0.020 eV for Si. The electron mobility was usually between 60 and 100 cm2/V-sec at room temperature and varied widely with temperature.
Crystal Structure and a Unique ``Martensitic'' Transition of TiNi
Authors: Wang Frederick E. , Buehler William J. , Pickart Stanley J.
Published: April 2005

Through single-crystal x-ray diffraction methods, the crystal structure of TiNi has been determined in the temperature range −70° to 900°C. Contrary to what has been assumed from previous work based on the powder pattern methods, the TiNi crystal structure is not a simple CsCl type. Rather, it has an a0=9Å superlattice and an a0=3Å sublattice with 54 atoms per unit cell complex structure.

The 9Å superlattice undergoes, at about 166°C, a ``martensitic'' pseudo order-disorder transition which is not accompanied by a crystallographic transformation. Through the understanding of this unique transition the apparent contradicting observations made on TiNi by various past investigators can now be reconciled and the unusual physical properties associated with the alloy are explained qualitatively.
High-Stress Low-Temperature Dislocation Kinetics of Ge
Authors: Johnson O. W.
Published: April 2005

Measurements of dislocation velocities in Ge crystals below 325°C are reported, at resolved shear stresses as high as 60kg/mm2. No drastic departures from known behavior at higher temperatures and lower stresses were observed. No statistically significant change in activation energy due to applied stress was detected, suggesting that dislocation motion under these conditions is probably limited by Peierls' forces.
New Excitation Mechanism for Magnetoacoustic Resonance in YIG
Authors: Ikola R. J.
Published: April 2005

Past experiments have shown that standing elastic waves can be excited in an yttrium iron garnet sphere through a parametric interaction with the magnetostatic modes. Lowest thresholds were obtained when the dc magnetic field was adjusted so that the difference between the microwave pump frequency and the acoustic frequency corresponded to the uniform precession frequency. The experiment reported in this paper utilizes a dielectric resonator to couple a high transverse rf magnetic field to the YIG sphere. This system enabled the observation of magnetoacoustic resonance using dc fields which are considerably lower than would be required to bias the idler frequency at the uniform precession. An explanation is offered which invokes a two-step parametric process making use of Suhl's theory of the subsidiary absorption.
Method for the Precise Determination of Orientation from Electron Diffraction Patterns
Authors: Sheinin S. S.
Published: April 2005

A method for the exact determination of orientation from electron diffraction patterns by diffracted beam intensity measurements is presented. The method is applicable to strain-free specimens and results indicate that the accuracy obtained is considerably better than previous techniques.
Diffusion-Controlled Dislocation Damping
Authors: Yamafuji Kaoru , Bauer Charles L.
Published: April 2005

A theory of diffusion-controlled dislocation damping is developed by considering the motion of pinning points within the dislocation core when an oscillating driving stress is applied to a crystal. At low temperatures, the pinning points are immobile and the result is equivalent to that of the Granato-Lücke theory of resonant dislocation damping. At higher temperatures, however, the pinning points migrate under the influence of an externally applied stress σ, if σ exceeds a critical value σc, and the resonant-type loss becomes time dependent. When σ is reduced below σc, the pinning points thermally diffuse to their original equilibrium positions and the time-dependent damping, characterized by a relaxation time τ(0), nearly decays exponentially. In addition, a relaxation-type loss is predicted when the applied frequency approximately equals τ−1(0). The analysis relates τ(0) to the ``pipe'' diffusion coefficient of the pinning species Dp by the expression τ(0)=2l02/Dp, where l0 is the average dislocation loop length, and procedures are suggested that allow the determination of Dp from dislocation damping measurements.
Photoeffects in Lead Telluride p-n Junctions
Authors: Laff Robert A.
Published: April 2005

The direct energy gap in PbTe has been deduced over the range 3.5°≤T≤300°K, from the spectral dependence of short circuit photocurrent in grown p-n junctions. At temperatures above ∼30°K, the deduced absorption in the depletion region is found to be exponential, with the steepness of the edge dominated by thermal broadening. At lower temperatures, the effects of broadening due to the electric field within the junction depletion region have been observed. A third broadening mechanism is observed at low temperatures. At 5.8°K, this mechanism is of approximately equal strength to the thermal broadening. The energy gap, taken from the photon energy at which the photocurrent has fallen to one-half its maximum value, at which point the absorption coefficient α=14 cm−1, is given by Eg=0.173+0.485×10−3T eV for temperatures 30°<T<250°K. Below ∼10°K, the energy gap has a constant value of 0.185±0.002 eV.
Exchange Anisotropy and Strain Interactions in the Ni-NiO System
Authors: Berkowitz A. E. , Greiner J. H.
Published: April 2005

The interactions between Ni and NiO were investigated by examining the magnetic properties of Ni films on single-crystal NiO substrates. The orientations of the NiO substrates were (001) (compensated spin planes), and (111) (parallel spin planes). With (001) NiO the Ni films were strained an amount corresponding approximately to the rhombohedral deformation of NiO below its Néel temperature. The amplitude and symmetry of magnetic torque data were consistent with the magnitude of this strain and the symmetry of the antiferromagnetic domain structure, respectively. Ni films on (111) NiO substrates had a complex field dependence of rotational hysteresis. This behavior was analyzed in terms of exchange anisotropy coupling and the interaction of the field with both the Ni and NiO spin systems. The analysis provided good agreement with the data for an exchange anisotropy energy of 1.75 erg/cm2 of interface, a crystalline anisotropy of NiO in its parallel spin plane of 1.1×103 erg/cc NiO, and a ``flop field'' for NiO in its parallel spin plane of 5 to 10 kOe. The analysis showed that two new regions of rotational hysteresis loss are present in fields ≥ the ``flop field'' of the antiferromagnetic spin system. Some more general features of exchange anisotropy coupling are also discussed.
Internal Quantum Efficiency of GaAs Electroluminescent Diodes
Authors: Hill Dale E.
Published: April 2005

The internal quantum efficiency and spectral distribution of radiation from GaAs electroluminescent diodes is examined with a careful investigation of the optical absorption of both the n-type and p-type layers of the diodes. A group of diodes so fabricated as to allow necessary corrections for internal absorption and reflection has internal quantum efficiencies greater than 50%. These diodes have more than 85% of all photons in the principal peak and the temperature variation of the emission is explainable on the basis of changes of the absorption with temperature. In addition, the shape of the emission can be interpreted in terms of radiation originating in a compensated p-type layer of relatively low carrier concentration.
Coloring of Mixed Crystals of Ca(W1−xMox)O4 by Photolytic and Vacuum Reduction Processes
Authors: Cronemeyer D. C. , Beaubien M. W.
Published: April 2005

Two important effects of the addition of Mo to the laser material CaWO4:Nd have been found and are discussed: (1) an increased susceptibility to photolytic coloring, and (2) a drastic change in the vacuum reduction coloring spectra. Therefore, it is necessary to specify the Mo concentration in CaWO4:Nd crystals in order to understand either photolytic or reduction processes. The Mo content in the crystals has been obtained from x-ray and optical fluorescence analysis. The distribution coefficient of Mo in CaWO4 has been determined to be 0.7 from crystal growth studies. The Nd concentration is obtained in terms of the optical absorption cross sections for the 580 and 740 mμ absorption peaks. For these two wavelengths, the extraordinary ray cross sections are 10 and 2.6×10−20 cm2; the ordinary ray cross sections are 8.0 and 1.6×10−20 cm2.
Field Dependence of Photoresponse in Germanium Bicrystals
Authors: Mataré H. F. , Cho K. S.
Published: April 2005

Measurements of the photoresponse of germanium bicrystals are reported here with two specific results in mind:

(1)The detailed response at higher optical frequencies. The measured transition steps at larger than band gap energies can be associated with the specific band structure of the dislocation plane taking the stress field into consideration.

(2) The detailed bias or field dependence yields a linear law for the photovoltage. It is found that the electronic dislocation model, as used earlier, explains the linear field dependence of the photoresponse.
Twinning in Silicon Epitaxially Deposited on Sapphire
Authors: Nolder R. L. , Klein D. J. , Forbes D. H.
Published: April 2005

By means of x-ray diffraction techniques, the presence of twin relationships in silicon epitaxially deposited on sapphire was demonstrated and the relative amounts determined in a semiquantitative manner. A correlation was made with the surface structure observed by means of replica electron microscopy and the twinning relationships. The minor twin relationships appear to be present as long thin microtwins. Besides the four silicon-sapphire orientation relationships previously reported, a fifth relationship has been found. The density of twins deposited on substrates near the (1̄1̄23) orientation appears to be greatly dependent on the substrate orientation. Possible explanations for this phenomenon are discussed. Discrepancies with the work of other investigators are described.
Determination of the Mean Size of Disordered Regions Induced in Germanium by Fast-Neutron Bombardment at Low Temperature
Authors: Van Dong Nguyen
Published: April 2005

Thermal conductivity measurements have been performed on germanium at 80°K during fast-neutron bombardment. By using Callaway's formula it is established that the change in thermal conductivity can be related to the size of disordered regions by a simple expression. From experimental data, it is found that the mean radius of disordered regions is about 70 Å.
Propagation of Magnetostatic Spin Waves at Microwave Frequencies in a Normally-Magnetized Disk
Authors: Damon R. W. , Van De Vaart H.
Published: April 2005

The theoretical transit time is derived for propagation of spin waves across a normally-magnetized disk. The exchange-free case is described first. The group velocity is obtained for magnetostatic spin waves in an infinite slab. This is combined with the inhomogeneous internal field of a disk to compute the time delay of a wave packet in the disk. The time delay obtained from a computer calculation is compared with an approximate calculation. The dispersion relation is then modified to include exchange effects and the delay time is computed for this case. Experimental observations of microwave pulse-echo behavior in disks of yttrium iron garnet are compared with these theoretical results.
Photoinduced Discharge Characteristics of Cadmium Sulfide Binder Layers in the Xerographic Mode
Authors: Smith M. , Behringer A. J.
Published: April 2005

The photoinduced discharge characteristics of cadmium sulfide-Lucite binder layers with a CdS powder weight concentration of 89% have been studied as a function of the initial potential, layer thickness, and light intensity over the wavelength range 3800 to 6800 Å. The results are well described by the capacitor discharge model previously presented by Li and Regensburger with only a slight extension necessitated by light penetration into the bulk of the layer; this penetration is caused by light scattering due to the particulate nature of the layer. On the basis of this model, the electron trapping range was determined to be 4.5±1×10−7 cm2/V, a result independently confirmed by a light pulse technique. The quantum efficiency for the photoexcitation of carrier pairs was estimated as unity for all wavelengths studied.
Stress Relaxation and Creep Master Curves for Several Monodisperse Polystyrenes
Authors: Aklonis J. J. , Tobolsky A. V.
Published: April 2005

The stress relaxation master curves of five monodisperse polystyrenes are converted to creep master curves using an approximation method. Stress relaxation and creep curves are tabulated with values of the characteristic relaxation time K(T), as a function of temperature.
Ultrasonic Studies of the Nonlinear Behavior of Solids
Authors: Breazeale M. A. , Ford Joseph
Published: April 2005

The non-Hookeian behavior of a solid is studied using the distortion of an initially sinusoidal ultrasonic wave. The nonlinear differential equation describing the propagation of a finite amplitude ultrasonic wave in a cubic crystal is shown to take the same form as that describing a fluid. The propagation distance required for discontinuity in the particle velocity is calculated for various directions in the crystal. It is shown that in a typical experiment the path length can be appreciably less than the discontinuity distance, so that the distortion can be represented as a linear increase of second harmonic content with path length. Experimental results are given for copper single crystals which have been annealed or neutron irradiated.