bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Defects in GaP Crystals and Their Electrical and Optical Effects
Authors: Gershenzon M. , Mikulyak R. M. 
Published: April 2005

Oriented single crystals of GaP were plastically deformed and the active slip planes and the individual dislocations lying in them have been identified by etching, by preferential precipitation (decoration), by observations of surface irregularities, and from strain birefringence singularities. Evidence of polygonization is presented and the nodes of planar intersecting dislocation networks can be seen by decoration. Crystals grown by the floating-zone technique contain 105–106 dislocations/cm2 which result from a quench—anneal cycle during the growth process. These dislocations as well as a high degree of residual elastic strain cannot be moved by annealing. This is not true of epitaxial crystals grown from the vapor phase on GaAs seeds. Some indications of growth from active Frank—Read sources have been obtained for these epitaxial crystals.
Precipitation, often unintentional, can be detected optically from Rayleigh scattering. Because minority carrier diffusion lengths in GaP are very short, dislocations and a dispersed second phase generally do not perturb the electrical properties. This is not true of some alloyed p-n junctions.
Large-Amplitude Solutions of the Rate Equations for the Ruby Laser
Authors: Clendenin W. W. 
Published: April 2005

Large-amplitude solutions of the rate equations for the ruby laser have been obtained corresponding to the initial low value of photon density. The damping rate for these oscillations increases with optical pump rate in contrast to the decrease found experimentally by Walsh and Kemeny.
Variation of the damping rate with loss rate is also examined; the damping rate becomes the same order as that of the usual flash lamp (∼103 sec−1) for a loss rate corresponding to a rod.
Dielectric Loss due to Impurity Cation Migration in α Quartz
Authors: Snow E. H. , Gibbs P. 
Published: April 2005

The dielectric constant and loss factor of natural quartz single crystals have been measured in the temperature range from room temperature to 573°C, and in the frequency range from 50 cps to 100 kc/sec. Parallel to the c axis a large dispersion in the dielectric constant of the order of εs-ε∞ = 500 was observed. Associated with this dispersion is a peak in the loss factor of the order of ε″max = 250. The data were analyzed in terms of the Debye equations with a single thermally activated relaxation time. The activation energy is about 16.7 kcal/mole. Perpendicular to the c axis no peak in ε″ was observed, but both ε′ and ε″ begin to increase at low frequencies and high temperatures.
The loss peak parallel to the c axis was substantially reduced when impurities were removed by electrolysis. The introduction of Ag, Cu, or Na gave rise to new peaks while Li tended to reproduce the original peak. It is concluded that the original loss was due to the motion of Li+ ions along structural channels parallel to the c axis. From the charge transported in electrolysis experiments, it can be inferred that the number of ions involved was about 5×1017 per cm3. The observed activation energy is believed to be the Coulomb binding energy between a substitutional Al3+ ion and an interstitial Li+ ion.
Ruby-Laser-Induced Photocurrents and Luminescence in ZnO
Authors: Hotchkiss Donald R. 
Published: April 2005

A photoconductive signal has been observed in ZnO single crystals at 300°K upon illumination with the 6935-Å laser light from a ruby rod. With a dark current of 2 mA, a typical peak increase in current was 7 μA.
Green luminescence (centered at 5250 Å) excited by the laser light was also detected. The fluorescent intensity showed an approximately second-power dependence on incident intensity at lower intensities. At higher intensities an approximately fourth-power dependence was noted. A plausible model is given to account for the second- and fourth-power dependencies in terms of a two-photon absorption mechanism. Since the absorption coefficient of ZnO for light of wavelength 6935 Å is quite small, the observed photoconductivity and luminescence are very likely associated with the bulk rather than with the surface.
Dislocation Structure and Growth Mechanism of Cadmium Sulfide Crystals
Authors: Chikawa Jun-ichi , Nakayama Tadahisa 
Published: April 2005

Crystals, needles, ribbons, and platelets, grown from pure and impurity-added CdS vapor, have been studied morphologically. Needles grow parallel to the [0001], [101̄0], and [21̄1̄0] axes of the hexagonal system. Ribbons grow parallel to the [101̄0] and [21̄1̄0] axes and their surfaces are parallel to the (12̄10) and (01̄10) planes, respectively. The surfaces of the platelets are parallel to the (12̄10) planes.
The dislocation structures of grown crystals have been observed by x-ray diffraction microscopy and chemical and thermal etch techniques. In order to hinder the dislocations from slipping out of the crystals, some impurity atoms have been put in the crystals.
From the observations of growth manners and dislocation structures of the platelets, ribbons, and needles, it is concluded that whiskers grow in the initial growth stages of every crystal, and when the whiskers contain two parallel dislocations along the axis, the platelets are formed by the thickness increase of the whiskers in a direction perpendicular to the axis. One of the dislocations in the whisker has a Burgers vector 1/3[21̄1̄0] and the other is an edge dislocation with a Burgers vector [0001]. Behaviors of these two dislocations during the growth process of the crystal are inferred as follows: The dislocation with a Burgers vector 1/3[21̄1̄0] is responsible for the axial growth of the whisker and is easy to slip out of the whisker, leaving some dislocation half-loops on one of its side surfaces. The edge dislocation with the Burgers vector [0001] is also easy to slip out of the whisker, leaving many dislocation half-loops on another surface. The ends of these dislocation half-loops act as new sites of crystal growth in the direction perpendicular to its axis and a platelet is formed. Some observations which justify the above inference are illustrated.
It is discussed theoretically that the two parallel axial dislocations are much more stable than any single axial dislocation in a whisker.
Growth Spirals on Glass
Authors: Tichane Robert M. , Wilson Linda B. 
Published: April 2005

Spiral patterns have been observed on a soda-lime glass surface after etching with a frost producing slurry. These patterns are throught to be replicas, etched on the glass during surface crystal growth, of precipitating salts.
The unique conditions required to produce these spirals make it appear that they result from a crystal growth process and thus the glass surface functions only as a substrate.
Correlation of the Elastic Properties in Steady-State Flow and Vibrational Experiments
Authors: Philippoff W. 
Published: April 2005

A comparison between steady-state and vibrational techniques for measuring the elastic properties of polymer solutions has shown an unexpected anomaly at high frequencies. The steady-state technique used was flow birefringence which relates elasticity (recoverable shear, s) to the extinction angle χ: s=2 cot 2χ. The vibrational technique used, both the ultrasonic crystal and the Birnboim instruments, relates elasticity to the loss angle, δ′: cot δm′=η2/(η1−η solv). The solutions investigated included a monodisperse polystyrene, S111, at concentrations of 2% and 4% in a chlorinated biphenyl (Aroclor 1248), a polydisperse polystyrene, PF-139 and polyisobutylenes in oil. The same solutions were used in both kinds of instruments.
In the lower range of frequencies (taken as equivalent to low shear rates) the steady-state and dynamic instruments showed excellent agreement for the monodisperse polystyrene. In this range the curve agreed with the Zimm theory. But at higher frequencies the results from the two techniques diverged rapidly. The steady-state measurements showed s to increase continually, whereas the dynamic measurements showed cot δm′ to pass through a flat maximum and then decrease slowly out to 2×106 sec−1. This lack of agreement was unexpected and is unexplained. It does show that steady-state elasticity cannot always be predicted from high-frequency dynamic experiments. The steady-state viscosity could be satisfactorily predicted from η1 using Pao's theory, but only for the monodisperse polymers.
Dislocation Mobility in Crystals
Authors: Gilman J. J. 
Published: April 2005

Reaction-rate theory is applied to dislocation motion and it is shown that when the activated complex is allowed two degrees of freedom, the activation energy is inversely proportional to the applied stress, so the dislocation velocity, vd is related to the applied shear stress, τ by a relation of the form: v=v0e−D/τ, where v0 is the terminal velocity and D is called the characteristic drag stress. This relation is obeyed by LiF, Ge, NaCl, W, and possibly Fe−3% Si.
The observed dependences of dislocation velocities on point defect concentrations and temperature are also predicted.
Two classes of crystals are considered. Those in which drag is caused mainly by point defects; and those in which the intrinsic structure (chemical bonds) causes the drag.
Surface States and Barrier Height of Metal-Semiconductor Systems
Authors: Cowley A. M. , Sze S. M. 
Published: April 2005

The dependence of the barrier height of metal-semiconductor systems upon the metal work function is derived based on the following assumptions: (1) the contact between the metal and the semiconductor has an interfacial layer of the order of atomic dimensions; it is further assumed that this layer is transparent to electrons with energy greater than the potential barrier but can withstand potential across it. (2) The surface state density (per unit area per electron volt) at the interface is a property only of the semiconductor surface and is independent of the metal. The barrier height φBn is defined here as the energy needed by an electron at the Fermi level in the metal to enter the conduction band of the semiconductor.
With the above assumptions, the barrier height for n-type semiconductor-metal contacts is found to be a linear combination of the metal work function φm and a quantity φ0 which is defined as the energy below which the surface states must be filled for charge neutrality at the semiconductor surface. The energy φ0 is measured from the edge of the valence band. For constant surface state density the theoretical expression obtained is φBn=γ(φm−χ)+(1−γ)(Eg−φ0)−Δφn,where χ and Eg are electron affinity and the band gap of the semiconductor, respectively, Δφn is the image force barrier lowering, and γ is a weighting factor which depends mainly on the surface state density and the thickness of the interfacial layer.
The theoretical expression is compared to the presently available φBn VS φm data for Si, GaP, GaAs, and CdS, by fitting the data to straight lines using the method of least squares. The best straight-line fit was obtained for the GaP data, with probable error limits on the slope and intercept of ±0.03 and ±0.13 eV, respectively.
The parameter γ in the theoretical expression is found to range from 0.07 for GaAs to almost unity for the CdS data reported by Goodman indicating weak and strong dependence of the surface barrier height on the metal work function, respectively.
The value of φ0 is roughly a third of the respective band gap energies for Si, GaP, and GaAs, and the surface state density for these semiconductors is found to be in the range 1013−1014 states/cm2/eV, for the experiments cited.
Excessive scatter in the data points for the CdS data of Mead and Spitzer casts doubt on the significance of a straight-line fit for this case. The data of Goodman for CdS obey the Schottky theory for a metal-semiconductor barrier, but this agreement requires a value of the electron affinity χ which is different from the vacuum-photothreshold value measured by other authors.
Superconducting Coil Degradation
Authors: Taquet B. 
Published: April 2005

This paper describes experiments carried out to try to explain the degradation phenomenon of superconducting coils.
It is established that flux jumps occurring in a low-field zone cause a sudden decrease in the series current, which in turn causes a disturbance of field throughout the coil and thus probably results in a quench in a high-field zone.
Degradation of short samples is obtained by following a peculiar cycle of magnetization similar to that observed in a coil. An explanation is given to explain the difference of degradation observed between a short sample and a coil.
A measurement of the apparent resistance of a superconducting wire under changing field conditions gives an equivalent resistivity of 10−14 Ω·cm for dB/dt = 200 G/sec.
Effect of Processing History on the Superconducting Properties and Long-Range Order of Ta3Sn
Authors: Courtney T. H. , Pearsall G. W. , Wulff J. 
Published: April 2005

Variations of the transition temperature and long-range order parameter of Ta3Sn compacts were studied as functions of sintering time and temperature. Reacting the compacts for 4 days at 900°C produced a maximum in the order parameter (0.68) and the maximum transition temperature observed (8.35°K).
Transition temperatures could be lowered to less than 4.2°K by vacuum heat treating presintered compacts at elevated temperatures.
Ta3Sn was the only intermediate phase observed to form in the Ta-Sn system between 700° and 1450°C.
Crystal Imperfections in Magnesium Fluoride
Authors: Barber D. J. 
Published: April 2005

Single crystals of magnesium fluoride, grown by the Czochralski technique, have been examined by means of chemical etching, and optical and electron microscopy. Dislocations in as-grown crystals are found to be decorated with precipitates; the nature of the precipitates has been investigated. Grown-in dislocations and undecorated dislocations introduced by slip can be etched in hot sulfuric acid. Etch pits at grown-in dislocations often exhibit characteristic ``beaks'' or ``tails.'' Chemical etching has been used to establish the existence of three slip systems, namely {110}〈001〉, {001}〈100〉, and {101̄}〈101〉.
Specimens for examination by transmission electron microscopy were prepared by chemical dissolution after mechanical shaping. Grown-in dislocations are normally removed by unavoidable selective etching. In the microscope the samples are damaged by the electron beam. Point defects are produced which aggregate and result in both dislocation loops and precipitate platelets.
Effects of High Electric Fields on Dielectric Liquids of High and Low Viscosity
Authors: Schott Hans , Kaghan W. S. 
Published: April 2005

When a portion of a liquid dielectric was subjected to an electric dc field of high intensity, the level rose locally. The maximum rise attained by different liquids above the liquid level outside the field increased with their dielectric constant and polarizability.
The following observations indicate that electrostriction rather than electrophoresis was the cause of the observed rise in liquid level. (a) Molten polymers, which have such high viscosities that electrophoretic motion of ions or charged particles is virtually suppressed, rose to the same heights as fluid liquids. (b) Neither inverting the direction of the field nor (c) adding 0.05% finely dispersed aluminum or 0.15% ultramarine powder to molten polyethylene affected the rise in the dc field qualitatively or quantitatively.
Repulsion occurred in very high fields, producing a slight depression in the liquid level.
Numerical Computations of Elastic Scattering Cross Sections
Authors: Johnson Gregert , Truell Rohn 
Published: April 2005

A brief review is given of the calculation of cross section expressions for the scattering of an elastic wave in an elastic medium. With scatterers that are elastic and spherical in shape, numerical calculations are carried out for non-Rayleigh conditions of scattering. Comparisons of such cross sections are made with those obtained from the Rayleigh approximation.
The deviation from Rayleigh behavior becomes pronounced, for the elastic scatterer, beyond ka≅0.5. In addition a ``peaking'' and ``fluctuating'' of the cross section occurs beyond this point.
Elastic Stiffness Coefficients of Iron from 77° to 673°K
Authors: Lord Arthur E. , Beshers Daniel N. 
Published: April 2005

The elastic stiffness coefficients of single-crystal iron have been measured at room (300°K) and liquid-nitrogen (77°K) temperatures using the ultrasonic pulse-echo technique. The three coefficients were determined from a total of seven independent modes. The values at 300°K are C11=2.28±0.02, C12=1.32 ±0.04, and C44=1.165±0.01, in units of 1012 dyn/cm2; the corresponding values at 77°K are 2.36±0.02, 1.34±0.04, and 1.19±0.01.
The coefficients C11, (C11+C12+2C44)/2, and (C11+2C12+4C44)/3 of iron have been measured from 77° to about 673°K. C11 and (C11+2C12+4C44)/3, as well as the polycrystalline stiffness λ+2μ, depart from a linear dependence on temperature above about 300°C. It was not possible to say whether the same effect occurred in (C11+C12+2C44)/2 because of significant scatter in the data.
The Debye temperature Θ0 was found from the stiffnesses extrapolated to 0°K, to be 471.5°K.
Ion Transport Phenomena in Insulating Films
Authors: Snow E. H. , Grove A. S. , Deal B. E. , Sah C. T. 
Published: April 2005

It is shown that changes in the capacitance-voltage characteristic of a metal-insulator-semiconductor structure provide a powerful tool for the observation of ion motion in thin insulating films. Using this method, a detailed study of the kinetics of alkali ion migration in thermally grown silicon dioxide films has been made. Alkali ions were initially deposited at the metal-oxide interface and their transport through the oxide was studied as a function of time, temperature and applied voltage. When the metal is biased positively the number of ions accumulated at the oxide-silicon interface is initially proportional to the square root of time and then approaches a saturation value. The temperature dependence is exponential and leads to an activation energy for the diffusion coefficient of 32 kcal/mole for Na and 22 kcal/mole for Li.
A simple model is developed which is based on the division of the insulator into two regions: a thin boundary layer near the metal-insulator interface in which ion transport is by diffusion, and the remainder of the insulator where field transport dominates. It is shown that most features of this model are in excellent agreement with the experimental results.
Dislocation-Interstitial Interactions in Single-Crystal Tantalum
Authors: Carpenter S. H. , Baker G. S. 
Published: April 2005

Dislocation-interstitial interactions have been investigated in zone-melted single-crystal tantalum by means of internal friction measurements. A Marx piezoelectric composite oscillator resonating at 50 kc/sec was used to measure the logarithmic decrement as a function of time, temperature, and strain amplitude.
Damping measurements indicate that two separate pinning processes occur in the 0°–100°C temperature range. In the 0°–25°C range the amplitude-independent damping measured immediately following deformation (∼1%) has been found to decrease with time. No change in the amplitude dependence has been detected. This has been called stage-one pinning. The relaxation time for stage-one pinning has been found to be too short to allow for the long-range diffusion of interstitials required for Cottrell-type pinning. The pinning mechanism is believed to be the reorientation of solute interstitial oxygen atoms in the dislocation strain field as proposed by Schoeck. The activation energy for the stage-one process has been found to be 23 500±3000 cal/mole. This value is consistent with the diffusional energy of oxygen in tantalum.
An increase in test temperature to the 75°–100°C range has been found to cause a further reduction of the amplitude-independent damping with time. A decrease in the amplitude dependence has also been observed. This reduction in the damping has been called stage-two pinning. Stage-two pinning is explained satisfactorily by the Cottrell-type pinning of the dislocation lines by solute interstitial oxygen atoms.
Fatigue Hardening of Polycrystalline Copper, Nickel, and Aluminum
Authors: Hartmann R. J. 
Published: April 2005

Fatigue hardening of polycrystalline copper, nickel, and aluminum has been determined by measuring the changes in the area of the hysteresis loop. It can be described as a superposition of two types of hardening, called VI and VII. These two types can far better be resolved by the specific irreversible work of deformation than by the increment of subsequent stress amplitudes.
Hardening VI occurs mainly at high strain amplitudes and is not peculiar to fatigue. Saturation (I) is reached between N=10 and N=104, depending on strain amplitude and stacking fault energy.
Hardening VII is effective only at low and medium strain amplitudes. It is characterized by a very low hardening coefficient. Saturation (II) is reached between N=104 and N=106.
Intermediate overloading during saturation (II) results in a pronounced softening, indicating that hardening VII is caused by the production of small-scale obstacles.
Interaction between a Dislocation and an Assembly of Dislocation Arrays
Authors: Johnson H. H. , Webster L. D. 
Published: April 2005

The force exerted upon a lone dislocation by an assembly of dislocation arrays is discussed in the continuum approximation. The arrays are parallel and in equilibrium with a constant applied stress, but no further restrictions are imposed.
For both edge and screw dislocation arrays, the force parallel to the glide planes can exhibit absolute maxima and minima only at the glide planes, and the sign of the force throughout the medium is governed by the distribution functions evaluated at the glide plane ends. Some numerical results in agreement with the analysis are given for screw dislocations upon two parallel glide planes; a ``shadow effect'' is also demonstrated for this case. The analysis is also valid for the interaction between a dislocation and an assembly of parallel cracks.
Giant-Pulse Laser Activity in Neodymium-Doped Silicate Glass: The Energy Conversion Process
Authors: Wenzel J. H. 
Published: April 2005

An experiment is reported which relates the gain characteristics of the pulsed mode in a neodymium-doped silicate glass laser to the giant-pulse laser energy output. In this experiment optical pumping of both the pulsed and giant-pulse mode occur in a time short compared to laser atom metastable lifetime.
An analysis of the experimental data shows that pulsed-mode gain characteristics can be related to the giant pulse energy output through the use of a model for the giant-pulse laser similar to that derived by Wagner and Lengyel provided that corrections are included to account for the effects of resonator standing waves and gain variations across the radius of the laser rod.
Demagnetizing and Stray Fields of Elliptical Films
Authors: Chang H. , Burns J. 
Published: April 2005

The magnetostatic fields inside and outside of a ferromagnetic thin film, called demagnetizing and stray fields, respectively, are known to be calculable from the model of a uniformly magnetized flat ellipsoid. In this paper, these fields are plotted as functions of the spatial coordinates with the aspect ratios b/a and c/a as parameters. The information is applied to a number of magnetic thin-film device and physics problems.
Demagnetizing fields influence wall motion threshold, shape anisotropy, and the stability of domain configuration. Stray fields affect the creeping and switching thresholds of memory elements in an array. The effectiveness of demagnetizing field reduction in a film pair dictates the drive line configuration. In films coupled magnetostatically or by exchange force, the planar components of stray field are important in determining both the quasistatic and dynamic magnetization reversals. However, the normal component of stray field, being much smaller than the normal component of demagnetizing field, has no significant effect on switching.