bluuebunny/crossref_metadata_2025 huggingface dataset:
Equilibrium Charge, Field, and Potential Distributions in Semiconductors
Authors: Lindmayer J. , Wrigley C. , Schoeni K.
Published: April 2005

Space-charge, field, and potential distributions in inhomogeneously doped crystals are determined by a nonlinear differential equation which requires numerical computation in order to be solved. By means of numerical computation an attempt is made to obtain the potential, field, and space charge throughout the crystal. For exponential impurity distributions bounding curves can be obtained which allow one to obtain the complete distributions. A few examples are computed which demonstrate the difficulties encountered in obtaining solutions.
Gamma-Ray Induced Conductivity in Polyethylene and Teflon under Radiation at High Dose Rate
Authors: Yahagi Kichinosuke , Danno Akibumi
Published: April 2005

The conductivity induced by gamma radiation from Co60 has been measured for polyethylene and Teflon as functions of temperature, dose rate, and applied voltage. The range of dose rates was from about 103 to 105 R/h and of the temperature from 190° to 300°K. The value of Δ, which shows the dependence of the induced current i on the dose rate R, i.e., i ∝ RΔ, varies from 1 (characteristic of the monomolecular recombination) to ½ (characteristic of the bimolecular recombination) with decreasing temperature. In both polymers, below about 240°K the induced current at a thermal equilibrium was independent of temperature, although it was slightly increased with decreasing temperature. From the investigation of temperature and dose-rate dependences, it is considered that the thermal electrons are dominant as charge carriers above 230°K, but fast electrons at below that temperature.
Absorption Spectrum of Germanium and Zinc-Blende-Type Materials at Energies Higher than the Fundamental Absorption Edge
Authors: Cardona Manuel , Harbeke Günther
Published: April 2005

Thin films of several III–V and II–VI zinc-blende-type semiconductors were prepared by vacuum evaporation. Germanium thin films were prepared by epitaxial vacuum evaporation onto CaF2 substrates. The absorption spectra of these films reveal, besides the fundamental absorption edge and its spin-orbit splitting, additional structure at higher energies. This structure has been interpreted along the lines followed in the interpretation of the reflection spectra of these materials. The agreement between the values for the various energy gaps derived from absorption and from reflection spectra is excellent.
Interrelationship of Substrate Temperature and Angle of Incidence Effects upon Anisotropy Variations in Evaporated Nickel-Iron Thin Films
Authors: Hardwick Albert J.
Published: April 2005

The dependence of magnetic anisotropy in Permalloy thin films upon the substrate temperature and angle of incidence is demonstrated, and the critical substrate temperature above which the angle of incidence no longer affects the magnetic anisotropy is discussed. Experiments indicate, also, that the increase in grain size with increased substrate temperature influences the value of the magnetic anisotropy attained. By rigid control of these parameters during the evaporation of thin films, the magnetic anisotropy may be made to have almost any desired value; hence, usable magnetic properties may be achieved.
New Technique for Identifying Particles Observed by a Scintillation Counter
Authors: Gersch W.
Published: April 2005

A new technique is offered to determine the quantity of radioactive particles observed by a scintillation or proportional counter when the distribution of the source particles vs particle energy is immersed in the distribution of the background particles.

The particle identification problem is interpreted from the point of view of a parameter estimation problem in mathematical statistics in the following way: Assume there are M events, where an event is the occurrence of a scintillation counter pulse. M is a known number, N of these events are associated with the desired source particles and the scintillation counter output is source plus background. The remaining (M-N) events consist of background alone. The background statistics are assumed known and the source pulse amplitude distribution is assumed known to within K distribution parameters. One number, the amplitude of the counter response, is observed for each of the M events. The problem is to estimate N.

There are (K+1) unknown parameters: the number N and the K unknown parameters of the source pulse distribution. The problem is solved by what is essentially a method of moments technique. The estimation procedure has desirable statistical properties for large N and M in that the estimate of N is asymptotically unbiased and that the relative variance of the estimate of N asymptotically goes to zero.

Implementation of this technique supplants the conventional multichannel pulse-height analyzer with digital recording of the individual pulse count amplitudes and subsequent data processing by a modest size digital computer.
Rectifying Action and the Electromotive Forces of the Films of Ta2O5 and SiO2 at High Temperatures
Authors: Ishikawa Yoshioki , Sasaki Yozo , Seki Yasuo , Inowaki Shûichi
Published: April 2005

When the anodic films of Ta2O5 or of SiO2, each having the thickness 100∼2500 Å, are heated at high temperatures in contact with MnO2 layers, they exhibit rectifying actions of p-i-n junction type as well as large electromotive forces in the direction of easy flow resulting from the ion flow through the films. The short-circuit ion current increases greatly with increasing temperature, while the open-circuit voltage increases rapidly at first with increasing temperature, reaches a maximum, and then decreases gradually at higher temperatures.

The results obtained are analyzed in the light of a p-i-n junction structure in the film. In the steady states the observed current through the external circuit is equal to the sum of the ion current, the generation, and recombination current, and the leakage current of the junction. Theoretical expressions having an explicit form are given for Iion and If, by making the assumptions that (a) the built-in voltage in the junction is equal to the free-energy change in the reaction of film formation and (b) If is of the Sah-Noyce-Shockley type. Agreement between the theory and experiments is excellent. We believe that the present method of investigation could also be applied in the elucidation of the growth mechanism as well as of the electric properties of films formed on other metals or semiconductors.
Schottky Field Emission Through Insulating Layers
Authors: Pollack S. R.
Published: April 2005

Pb–Al2O3–Pb structures have been fabricated by vacuum evaporation. For oxide thickness of approximately 300 Å, a forming process was noted. This forming process resulted in large electron transfer currents which were described as the sum of a temperature-independent current plus a current with a voltage and temperature dependence appropriate to Schottky field emission into a solid. The forming process is assumed to be due to the establishment of a positive ion space charge which increases the field at the cathode.
Resolution Study of Photographic Thermal Neutron Image Detectors
Authors: Berger Harold
Published: April 2005

The high contrast resolving power of several photographic thermal neutron image detection methods has been experimentally determined. For the most part, the comparisons between the different imaging techniques were made after optimizing each technique for resolution capabilities. The resolution was studied by determining the minimum hole separation in an almost totally absorbing object which could be resolved by a number of observers on neutron radiographs made by each method. From the standpoint of resolution, the best methods employed thin gadolinium metal screens, compressed Li-6F powder, and a thin B-10 layer covered with a vapor deposited ZnS (Ag) phosphor in techniques in which the photographic film and screen were exposed together to the low gamma content, 1.05 Å monochromatic neutron beam. A transfer of an image carrying radioactive gold screen to film also yielded resolution values in the order of 0.001 in. Evidence is presented to explain many of the observed resolution comparisons on the basis of the average penetrating power of the photographically effective radiation emitted from the converter screen. A technique for measuring this property on a comparative basis is described.
Photographic Observations of a Prebreakdown Discharge Transition between Metal Electrodes in Vacuum
Authors: DeGeeter Dale J.
Published: April 2005

Photomicrographs were made of the electrode gap between a spherical molybdenum anode and a like stainless steel cathode at voltages near the breakdown limit. At a discrete voltage for a particular gap, ionized patches of about 0.05 mm in diameter appeared on the anode surface. These ionized areas increased in luminosity and number with voltage until one or more degenerated into a highly unstable incandescent spot undergoing severe localized heating. Both of these events lead to breakdown at these sites, providing evidence for a complex vacuum breakdown process related to the prebreakdown discharges observed.
Flow Configurations in Colliding Plates: Explosive Bonding
Authors: Cowan George R. , Holtzman Arnold H.
Published: April 2005

The collision of plates at high velocity sometimes causes them to be metallurgically bonded. A study has been made of the nature of the bonds and of the conditions required to produce bonding. A necessary requirement is the formation of a jet in the space ahead of the region of impact. When the collision region moves along the plates at a velocity which exceeds the bulk sound velocity of both materials, the relative velocity of the plates must exceed a critical value for jetting. Clarification of these critical conditions in symmetric collisions, and a correct extension to asymmetric collisions have been obtained by consideration of the effect of downstream boundary conditions on the configuration of the shock waves attached to the collision line in the jetless case. When the velocity of the collision is subsonic, bonding is obtained when the elastic strength of the material is exceeded. Metallographic examination shows that three types of bond may be formed: (1) a direct bond, (2) a uniform layer of solidified melt, and (3) a wavy interface with discrete regions of solidified melt alternating with regions of direct bond. Consideration of the flow indicates the following: (1) the direct bond results from the removal of the surface layers as part of the jet, (2) the alloy results from the melting caused by entrapment of the high-velocity jet between the plates, and (3) the wavy interface is caused by an oscillation in the jet flow which produces the mixed type of bonding. The thickness of the continuous alloy layer, which greatly exceeds the calculated jet thickness, indicates that entrapment of the jet dissipates most of the kinetic energy lost in the collision. Analysis of the layer indicates a composition and structure which is expected from the rapid quenching of a well-mixed melt.
Unresolved Fine Structure of the Nitric Oxide γ 0–0 Band for the Determination of Temperature
Authors: Levine David
Published: April 2005

An experimental program was conducted to investigate the properties of the unresolved rotational fine structure of the NO γ00 band. The experimental values were taken spectroscopically in absorption at controlled temperatures.

An analytic expression representing the unresolved fine structure is utilized to compute absorption coefficients and absorption intensities for the experimental temperatures. A doublet model and a singlet model of the band are investigated.

From the experimental absorption coefficients, temperatures are determined to within 6% of the directly measured values. The rotational constants of the upper and lower states are determined to accuracies of 13 and 6%, respectively, of the known values.
Laser Operation Without Spikes in a Ruby Ring
Authors: Walsh Peter , Kemeny G.
Published: April 2005

Pulsed laser operation has been produced by complete internal reflection in a ruby ring at room temperature. The linearized equations of Statz and de Mars give a good description of the steady state laser operation. The lifetime of the excited Cr3+ ions is found to be ∼1 μsec under operating conditions. We have observed short-lived transient oscillations rather than spikes in the laser output. This result can be tentatively explained by assuming a cavity Q of 108–109.
Diffraction Studies with Plane-Parallel Maser Interferometer
Authors: Rigrod W. W. , Rustako A. J.
Published: April 2005

A helium-neon optical maser tube with high-quality fused quartz windows at the Brewster angle supports oscillations between external plane mirrors at 6328 Å, 1.15 μ, and 3.39 μ, producing over 40 mW at 1.15 μ and 28 mW at 3.39 μ in the dominant TEM00 mode. Calculations of Fox and Li are verified by means of apertures inside the resonator. Patterns made with various obstacles in the resonator bear a blurred resemblance to those made with the same obstacles in the 1-cm beam outside the resonator.
Use of Cataphoresis to Determine Discharge Parameters
Authors: Muller Walter , Tubbs Eldred F.
Published: April 2005

The balance between diffusion and ion migration in dc discharges in certain mixtures of metal vapors and rare gases produces a very sharp line of demarcation between the region containing only the rare gas and the region containing both the rare gas and metal vapor. Although the formation of such a sharp boundary depends in a complex way upon the elastic and inelastic cross sections for electron-atom collisions, it can be used in a simple way for the determination of certain discharge parameters.

If a cold spot with a well-defined location is provided near the cathode end of the positive column, the distance from the cold spot to the line of demarcation and the potential drop across the tube are, at a given current and rare gas pressure, accurately reproducible functions of the cold-spot temperature. If these functions are determined, and if the neutral-atom diffusion coefficient and positive ion mobility are known for the metal vapor in the rare gas, a simple theory yields values for electron concentration, electron mobility, and the ratio of electron to ion current as a function of pressure of the metal vapor.

Detailed application has been made to a hot-cathode neon-mercury discharge over a range of mercury pressure from 2.5 to 25μ and for a neon pressure of 3 Torr. For a 500-mA discharge n− is about 3.5×1011 cm−3, μ− ranges from 1.4 to 2.5×106 cm2/V sec, and μ−/μ+, from 800 to 1800.
Thermal Expansion and Pyroelectricity in Lead Titanate Zirconate and Barium Titanate
Authors: Cook W. R. , Berlincourt D. A. , Scholz F. J.
Published: April 2005

Curves of thermal expansion parallel and perpendicular to the polar axis are shown for poled barium titanate and lead titanate zirconate ceramics. Anistropy is remarkably higher in the latter due to greater alignment by 90° switching during poling. The anisotropy disappears after heating through the Curie point, and is also virtually eliminated within a given temperature range below the Curie point after exposure to a temperature only slightly above this range. The contraction in the polar direction upon first heating is due largely to a decrease in the alignment of domains originally reoriented by 90° during poling. The reversible expansion on repeated heating is due to a combination of domain anisotropy and a reversible increase in nonpolar alignment during heating. The pyroelectric effect is also greatly reduced in subsequent heating, although piezoelectric constants are reduced only slightly. The pyroelectric effect is found to be largely primary in both barium titanate and lead titanate zirconate ceramics. The increase in nonpolar 90° domain alignment on second heating of the lead titanate zirconate causes the primary and secondary pyroelectricity to be of opposite sign near room temperature.
Properties of Bi2Te3-Bi2Se3 Alloys
Authors: Miller G. R. , Li Che-Yu , Spencer C. W.
Published: April 2005

Lattice parameters and distribution coefficients for the Bi2Te3-Bi2Se3 pseudobinary alloy system have been determined for several compositions across the phase diagram. The c lattice constant (based on a hexagonal lattice) shows deviation from Vegard's law between 33% Bi2Se3 and pure Bi2Se3 with maximum deviation at 67% Bi2Se3. Thermal energy gap as a function of composition shows a maximum near 33% Bi2Se3 and a minimum near 67% Bi2Se3. It is postulated that at least two sets of energy band minima are present in this alloy system.
Investigations on Constriction of the Positive Column Using Glow Discharges of Limited Duration
Authors: Fowler R. G. , Jones L. W.
Published: April 2005

An experimental method is presented, for the study of glow discharges, that can provide data suitable for analysis in terms of the diffusion of a ternary mixture. Particular emphasis is given to the constriction of flow discharges in neon with increasing gas density. It is found that quantitative estimates of the onset of this phenomenon are now possible.
Injection of High Velocity Charged Particles into Strong Magnetic Fields
Authors: MacLeod Malcolm A. , Waniek Ralph W.
Published: April 2005

Strong magnetic fields are useful in work with high velocity charged particles by virtue of their ability to rotate the particle momentum vector. The degree of usefulness is measured by the extent to which the desired rotations can be produced at the proper positions in the field. It is frequently necessary to inject charged particles into magnetic fields at points remote from these proper positions, in which case the injection parameters which enable the particles to reach these positions must be specified. For the production of gyromagnetic radiation in axially symmetric magnetostatic fields the proper positions correspond to the high field regions near the symmetry axis. The present introductory study is concerned with delineating approximate injection parameter ranges which allow the particles to attain the regions of high magnetic field strength in the field whose axial variation is bell-shaped. The single-particle model is adopted, and the results of both qualitative and quantitative investigations are presented.

A general formulation of the axially symmetric, magnetostatic field, forbidden-zone theory is given and the useful concept of the paraxial forbidden zones is introduced. This theory is then applied to obtain qualitative answers to the injection problem for the bell-shaped field for both zero and nonzero values of the angular momentum constant. Quantitative relations for the zero angular momentum constant case are obtained using the bell-shaped field paraxial trajectories. A discussion of the limitations of the approximations employed is included.
Error in Hall Cell Angle Measurement Due to Magnet Edge Effects
Authors: Gold E. Mark
Published: April 2005

The magnetic field in the vicinity of the center of a magnet gap is analyzed. In measuring an angle by means of a Hall cell in the magnetic field of the gap, the inhomogeneity of the magnetic field due to the influence of the edge of the gap leads to an error. The maximum error of the Hall voltage due to this cause is shown to be (5/16)Ww2/R3, where W is gap spacing, R is magnet face radius, and w is Hall cell width in direction across which VH is measured.
Effect of Fast-Neutron Irradiation on the Pressure and Temperature Dependence of the Elastic Moduli of SiO2 Glass
Authors: Strakna R. E. , Clark A. E. , Bradley D. L. , Slie W. M.
Published: April 2005

The low-temperature ultransonic attenuation, the elastic moduli, and the temperature and pressure dependence of the moduli of SiO2 glass are modified by heavy fast-neutron irradiation. A sample of Amersil optical-grade fused silica was irradiated to an integrated flux density in excess of 5×1019 neutrons/cm2. In this sample the ultrasonic loss is decreased by about 85%, the shear modulus increased less than 2%, and the compressibility decreased by about 20%. The anomalous temperature dependence of the compressibility changed from −3.3×10−2% per °K before irradiation to −9.5×10−3% per °K after irradiation over a temperature range of from 100°K to 300°K. The anomalous pressure dependence of the compressibility changed from 7.35×10−2% per atm before irradiation to 2.86×10−2% per atm after irradiation over a pressure range from atmospheric pressure to 5×104 psi. Similar effects were found in the pressure and temperature dependence of the shear modulus. The effect of γ irradiation on the low-temperature ultrasonic loss and on the temperature dependence of the sound velocity in this glass was also studied. No change in the ultrasonic attenuation was detected at an irradiation level several orders of magnitude larger than that required to eliminate effectively the comparable 50°K loss peak in synthetic quartz.
Thermal Diffusivity by Electron Bombardment Heating
Authors: Cerceo M. , Childers H. M.
Published: April 2005

A method is developed for determining the thermal diffusivity of materials by heating with an electron beam. A solution of the heat transfer equation is obtained for the case of a finitely thick, infinitely wide slab, and the expression for the temperature-wave phase shift is given. Using an experimental measurement of the temperature-wave phase shift, values of diffusivity in Al2O3 and carbon were determined. The accuracy of the method should be within ±10%.
Growth Mechanisms of Germanium Dendrites: Kinetics and the Nonisothermal Interface
Authors: Hamilton D. R. , Seidensticker R. G.
Published: April 2005

The growth of germanium dendrites containing two twin planes has been investigated. The solution of the heat flow problem in the stem of a growing dendrite being pulled from a melt permitted the design of experiments suitable for testing theory. The limiting growth velocity was determined as a function of melt undercooling for a number of twin spacings. Tip radii were measured on decanted interfaces, many of which were found to have parabolic sections. The data for these could be fitted with the theory for dendritic growth assuming a layer flow mechanism with a rate constant ≥3 cm/sec-°C. The only adjustable parameter is the average interfacial energy which may be as little as 15% less than the expected value, although lower values result in a somewhat more satisfactory fit. All the dendrites observed appear to grow under the condition that the magnitude of the tip radii is determined by the presence and spacing of the twins, and not under the condition of maximum velocity.
Role of Oxygen in Reducing Silicon Contamination of GaAs during Crystal Growth
Authors: Woods J. F. , Ainslie N. G.
Published: April 2005

GaAs grown in a horizontal Bridgman crystal growth apparatus to which oxygen has been added exhibits lower silicon content than that grown without oxygen. Material grown under oxygen additions of 10–20 Torr exhibits, at room temperature, carrier densities in the 2–4×1015 cm−3 range and mobilities between 7500–8650 cm2 V−1 sec−1.

Silicon concentrations computed from the reaction 4Ga+SiO2 → 2Ga2O+Si are compared with electrical determinations of donor densities and spectroscopic determinations of silicon concentrations with reasonably good agreement. It is concluded that suppression of SiO2 dissociation at the walls of the silica reaction tube is the most important action of oxygen on GaAs properties although oxygen doping may play a role in the production of high resistivity GaAs.
Apparatus for Measuring Relative Roughness Factors of Inert Metals by the Adsorption of Radioactive Iodine
Authors: Testerman M. K. , Hartman R. D.
Published: April 2005

A description is given of an empirical method of determining relative surface roughness factors for inert metallic surfaces by radioactive gas adsorption. I131 was used as the adsorbate. The apparatus and experimental procedure are described. Roughness factors were determined for gold surfaces of varying degrees of roughness. Polished gold foil, of high purity, was used as the reference surface. Aluminum and brass were also tested as adsorbents. The technique appears to be applicable to gold and aluminum, but not brass.
Dependence of Recombination Radiation on Current in GaAs Diodes
Authors: Mayburg S. , Black J.
Published: April 2005

The ``band-edge'' radiation in a GaAs diode is calculated to be proportional to the diode current at high forward current, while at low currents it is proportional to the square of the current. The impurity radiation in a GaAs diode is shown to vary at high current at a rate smaller than the square root of the current. For efficient conversion of electrical energy into ``edge'' radiation, diodes should be operated at as high currents as possible compatible with no diode heating.
Ion Drift Equilibrium in a Semiconductor
Authors: Bockemuehl Robert R. , Eddy David S.
Published: April 2005

If the impurity ions in a semiconductor are subjected to an electric field, an equilibrium distribution can result when the sum of drift and diffusion fluxes are balanced throughout the system. A simple solution for this distribution results for a one-ion system in which intrinsic carriers are neglected. The solution agrees with experimental results for indium ions in cadmium sulfide based on capacitance-voltage measurements.
Ultrasonic Amplification and Non-Ohmic Behavior in CdS and ZnO
Authors: McFee J. H.
Published: April 2005

This paper presents observations of ultrasonic flux buildup and the accompanying departures from Ohmic behavior in CdS and ZnO (piezoelectric semiconductor) crystals. The results give strong support to a model which connects this non-Ohmic behavior with the amplification of ultrasonic waves.

The behavior of an ultrasonic signal in the presence of varying amounts of ultrasonic flux is also studied experimentally. It is found that the signal gain is substantially reduced by interaction with the flux. The results also lend support to Hutson's theory which ascribes the non-Ohmic behavior of piezoelectric semiconductors to the acoustoelectric current accompanying the ultrasonic flux.
Anomalous Discharges in Ferroelectrics
Authors: Huey R. M. , Taylor R. McK.
Published: April 2005

The phenomenon of anomalous polarization is described, previous work is summarized, and some further observations reported. The double exponential form of discharge current with time observed by Northrip is confirmed for (Sr0.76Ca0.24) (Ti0.76Sn0.24)O3 and Ba0.97Pb0.03TiO3. The association of crystal structure with the phenomenon and equivalent circuits to account for the form of discharge are discussed.
Strain-Enhanced Diffusion in Metals. II. Dislocation and Grain-Boundary Short-Circuiting Models
Authors: Ruoff A. L. , Balluffi R. W.
Published: April 2005

Rapid diffusion along dislocation cores generally enhances the average bulk diffusion in a dislocated crystal. If each diffusing atom has at least several opportunities to make rapid excursions along various dislocation cores, Hart has shown that DT/DT0 = 1+fDP/DT0. DT is the average bulk diffusivity, DT0 is the diffusivity in the dislocation-free lattice, f is the fraction of atoms in dislocation pipes, and DP is the diffusivity along dislocation pipes. Under these conditions, the diffusion-penetration is increased by the short-circuiting but the general shape of the penetration curve is unaffected. When the dislocations are static, each diffusing atom must visit a number of dislocations, and a necessary condition for the Hart relation to hold is 2(DT0t)½>ld, where t is the diffusion time, and ld is the dislocation spacing. When this condition fails (for example, at lower temperatures), and when the dislocations are static, it is demonstrated that the amount of short-circuiting is greatly reduced and that the dislocations become essentially ``clogged.'' However, if the dislocations move through the crystal, as they do in plastic deformation, the situation is quite different, since in this case the dislocations may visit the diffusing atoms rather than vice versa. In such cases, the short-circuiting may again be randomized and the enhancement can be as large as (but no larger than) the result given by Hart, even if 2(DT0t)½<ld. In certain cases, this type of short-circuiting can produce very large relative enhancements.

A parallel development is given for short-circuiting due to grain boundaries. In particular, it is shown that grain boundary migration and recrystallization, which occurs repeatedly during deformation of metals with low stacking fault energy, can, for temperatures equal to or less than about half the melting temperature, lead to a greatly increased diffusion coefficient without altering the general shape of the penetration curve.

A number of the results established in this work (Part II) are used in Part III (to be published) where a comprehensive interpretation of recent experimental work in the field is carried out. Part I consists of an analysis of point defect models for strain-enhanced diffusion.
Dislocation Behavior and the Yield Stress in Neutron-Irradiated MgO
Authors: Stablein Paul F.
Published: April 2005

Mechanical property measurements on neutron-irradiated MgO single crystals show that hardening is caused by fast neutrons exclusively. Microhardness measurements, followed by etching to reveal dislocation distribution, permit an analysis of plastic flow even on samples which are so embrittled by the irradiation (with a dose of 1019 nvt) that it has not been possible to bend them. As determined from 3-point bending experiments on samples annealed at temperatures up to 1200°C, it does require an increasingly higher stress to form a dislocation (source hardening) as well as to move it through the damaged lattice (friction hardening). The type of defects responsible for such behavior are discussed.
Observations on Work-Hardening and Fracture of Pure Polycrystalline Zinc in Tension
Authors: Kamel R. , Bessa F. A.
Published: April 2005

High-purity zinc wires of different grain sizes were subjected to increasing tensile loading at different temperatures, and the associated changes in length, internal friction, and shear modulus were simultaneously measured. The work-hardening coefficient was found to be parabolic and to decrease with increase of grain size and temperature. This was interpreted in terms of the associated variations of the dislocation slip distance. An internal friction peak was observed at low stresses before excessive slip took place, and was attributed to the freeing and subsequent locking of the loosely pinned dislocations under the action of the applied stress. In fine-grained samples, a rise in the shear modulus was also observed and was attributed to the dislocations created by activated Frank—Read sources, which pile up against grain boundaries. The grain-boundary fracture surface energy, calculated from the observed dependence of the fracture and yield stresses on grain size, amounted to 1280 ergs/cm2 at room temperature.
Relation of Equilibrium Phase-Transition Pressure to Ionic Radii
Authors: Stubican V. S. , Roy Rustum
Published: April 2005

Pressure-temperature equilibria curves for a series of some 20 rare-earth arsenates and rare-earth vanadates which undergo the reconstructive transition zircon (Zr SiO4) ⇆ scheelite (CaWO4) type structure in the region 10 000–60 000 atm were obtained. From these curves, a set of data were extracted representing (with a fair approximation to corresponding states) the change of equilibrium pressure for a transition as a function of the radius of the rare-earth ion. The result is a V-shaped curve for both vanadates and arsenates showing a minimum transformation pressure near Dy3+ or Ho3+. An interesting even-odd effect is noted.
Fluctuations in Hot Tungsten Filaments
Authors: Brophy James J.
Published: April 2005

The high-frequency spectral noise voltage appearing across a metallic conductor electrically heated to high temperatures is experimentally found to be in agreement with the Nyquist theorem even though the conductor is far from thermodynamic equilibrium. Furthermore, because of the thermal origin of the nonlinearities in the current-voltage characteristic the proper value of resistance to use in the Nyquist expression corresponds to the voltage/current ratio, rather than the differential resistance at the operating point. At frequencies below that corresponding to the thermal time constant of the conductor, an additional noise voltage caused by temperature fluctuations is detected. The observed magnitude and spectrum of this noise voltage is in very good agreement with a simple calculation of temperature fluctuations due to heat conduction.
Modulated Langmuir Probe Characteristics
Authors: Crawford F. W.
Published: April 2005

The presence of fluctuations in the discharge parameters introduces errors into Langmuir probe measurements. Previous work by Garscadden and Emeleus considered the effects of fluctuations in the individual parameters. In this paper a generalized small-amplitude theory of the effects of these fluctuations is given and also a large signal theory for single-frequency oscillations. The results of Garscadden and Emeleus can be deduced from these, but additional terms are predicted due to cross modulation occurring when the various fluctuations are correlated. The large signal theory has been checked experimentally in a mercury-vapor discharge at a pressure of about 1 μ. Further experimental measurements with injected broadband noise signals confirm certain features of the generalized theory. The errors caused by fluctuations are discussed and it is concluded that although electron temperatures may still be measured accurately in their presence, serious errors can be incurred in the measurement of electron saturation current and number density.
Temperature and Finite Pulse-Time Effects in the Flash Method for Measuring Thermal Diffusivity
Authors: Cape J. A. , Lehman G. W.
Published: April 2005

The flash technique for measuring thermal diffusivity is analyzed for the case of a cylindrical-shaped specimen of radius r0 and thickness a to determine the effects of radiation at high temperatures, finite duration of the heat pulse, and the feasibility of low temperature measurements. It is found that the flash diffusivity method is useful in two complementary limits: (1) pulse time τ short compared to the characteristic thermal response time tc, (2) τ/tc of the order 1 to 10. The former case corresponds to the original description of Parker, Jenkins, and Abbott, while the latter case is suitable at very low temperatures. Moreover, it is shown that there is an optimum specimen thickness a for a given material and pulse time τ, in the sense that a higher temperature can be reached before any corrections have to be made to the Parker et al. analysis.
Acceptors in Donor-Doped GaAs Resulting from Li Diffusion
Authors: Fuller C. S. , Wolfstirn K. B.
Published: April 2005

Experiments have been carried out on Te-doped (∼1–3×1018 cm−3) GaAs crystals in which changes in n are measured when Li is introduced by diffusion and again after the Li is removed. The amounts of Li removed are determined by chemical analyses. It is found that two Li atoms introduced cause a loss of one electron, corresponding to a (Li+Li=) pair. Acceptors remain during the removal of Li which are postulated to be Ga vacancies. The kinetics of the disappearance of the ``vacancies'' have been investigated. The process appears to be diffusion controlled with an activation energy corresponding to 5–6 eV. The equilibria reached show an increasing ``vacancy'' solubility with decreasing temperature. A model in which Ga vacancies form stable pairs with Te atoms is discussed.
Dynamics of a Viscoelastic Wear Particle between Sliding Surfaces
Authors: May W. D. , Morris E. L. , Atack D.
Published: April 2005

It is predicted theoretically that because of its time-dependent mechanical properties, the rolling behavior of a wear fragment of viscoelastic material trapped between two moving surfaces is complex. If the moving surfaces are smooth and unlubricated, the fragment may either roll with a velocity equal to half the relative velocity between the surfaces, or it may reach a terminal rolling velocity beyond which increases in surface speed cannot drive it. If the surfaces are lubricated, the tractive force tending to roll the fragments arises from the friction of surface asperities sliding through the fragment. The rolling behavior then depends on the ratio of the size of the asperity to the size of the fragment. A critical value of this ratio exists. Above it, the fragment rolls at a velocity always slightly less than half that of the surfaces because of slip. Below the critical ratio, the fragment cannot be driven beyond a certain maximum velocity. Slip always takes place between the fragment and the surface, and increases with increasing surface velocity. Beyond the maximum rolling velocity, an increase of surface velocity leads to a decrease in the rolling velocity of the fragment.
Analysis of Noise from Magnetic Storage Media
Authors: Stein Irving
Published: April 2005

Noise arising from the transduction of a storage medium, such as a magnetic tape, is analyzed for the case where the storage elements (magnetic domains) are noninteracting and the magnetic tape, except where otherwise specified, is homogeneous. Since the fields arising from the tape are uniquely determined only if the boundary conditions (established by the presence of the reproduce head) are given, the broadband signal-to-noise ratio is a function not of the tape alone but of the tape-head system. It is found that the signal-to-noise ratio is proportional to the square root of the ``effective'' number of particles detected by the head. Thus, the signal-to-noise ratio is proportional to the square root of a length of tape, which is a measure of the tape-head resolution. The noise itself can be considered to arise from sources which add, in circuit terminology, serieswise across the width and along the length of the tape.

The essential source of what we call the ``no-signal'' tape noise is not in the surface roughness (assuming an otherwise homogeneous tape) or the physical distribution of the particles, but in the random orientation of the magnetic moments. Furthermore, a distribution in either the particle magnetization or the particle volume increases the noise. These conclusions are derived from purely statistical considerations.

Although the basic concepts of tape-head noise can be established without considering interaction of the tape particles, the formulas for dc and ac signal-to-noise and accurate quantitative results for the no-signal noise can only be obtained if the effect of particle interaction is included in the analysis. An externally applied field divides the particles into two groups: ``unflipped'' particles, which strongly interact, and ``flipped'' particles, which weakly interact. Using this distinction, it is possible to derive the signal-to-noise ratio for dc- and ac-magnetized tapes with no further reference to particle interaction. The formula for signal-to-dc noise is found; for small magnetizations it is seen that the noise voltage is proportional to the square root of the magnetization level. Alternating current noise is found to be purely a modulation of dc noise. Obtaining quantitative results, of course, involves interaction theory, a subject not treated here.
GaP Surface-Barrier Diodes
Authors: White H. G. , Logan R. A.
Published: April 2005

Surface-barrier diodes have been formed by depositing vaporized metals onto chemically cleaned GaP. Detailed studies of diodes made with gold on p-type GaP show that current flow is by the Schottky emission of hot holes from the gold over the barrier at the metal-semiconductor interface. The barrier properties deduced from the current-voltage properties were checked by capacitance-voltage and photoresponse studies. With the junction biased in avalanche breakdown, electrons were emitted through the gold film into vacuum, and were studied as a function of junction bias, film thickness, and retarding potential. It was found that the distribution of hot electrons in GaP has a Maxwellian temperature of 0.8 V, and that the attenuation length for 4.7- to 9-V electrons in gold is 130±40 Å.
A Diffractometer Study of Long-Range Ordering in Ni3Fe and Associated Permalloys
Authors: Treuting R. G. , Batterman B. W.
Published: April 2005

The long-range order in heat treated Permalloys near the composition Ni3Fe was determined from x-ray measurements of the (100) superstructure reflection. Comparing heat treatments previously shown to stabilize magnetic anisotropy and magnetic saturation with those producing order, it can be concluded that long-range order is not a significant factor in affecting the magnetic properties of the usual compositions of Permalloys. From the breadth of the (100) reflection, an antiphase domain size of 60 Å was estimated for ordered Ni3Fe.
Space-Charge-Wave Decay Along a Signal-Current-Excited Multivelocity Beam
Authors: Bloom S. , Vural B.
Published: April 2005

A previous analysis of noise propagation along a drifting electron beam with a half-Maxwellian distribution of velocities is specialized here to apply to the case of excitation by a signal current. The computed wave patterns that result are shown to be in quantitative agreement with those measured by Mihran.
Streaming Potentials at very High Differential Pressures
Authors: Tuman V. S.
Published: April 2005

Experiments were conducted to examine the electrokinetic phenomenon in porous media due to the flow of water. It was observed that the streaming potential developed across a given porous plug at high pressure did not vary directly with the pressure drop as predicted by the Helmholtz model. Although deviation from linearity is to be expected in the non-Darcy flow, this in itself is not sufficient to account for the observed variation of the streaming potential. Since this investigation is preliminary in nature the data obtained are insufficient to permit a thorough explanation of the phenomenon observed. It is, however, speculated that the variation in streaming potential observed at high pressure differentials may be due in part to relaxation. This phenomenon is discussed, and two possible functions which could describe the streaming potential at very high differential pressure are proposed. More specific experiments are desirable to clarify the exact mechanism which prevails at very high differential pressure.
Interdiffusion of Gases in a Low-Permeability Graphite. II. Influence of Pressure Gradients
Authors: Evans R. B. , Watson G. M. , Truitt J.
Published: April 2005

A previous experimental investigation of the interdiffusion behavior of two unlike gases within a porous medium at uniform pressure has been extended. The extended studies were focused on interdiffusion under the influence of pressure gradients which, in turn, give rise to both viscous and diffusive components of the experimentally determined fluxes. The fact that the diffusion processes investigated occurred within the region bounded by the normal and Knudsen regimes (the transition region), constituted one of the most important features of these studies. The experimentally observed flux phenomena could be readily explained within the framework of a ``dust-gas'' model. The flux equations exhibited only one major weakness and this involved the absence of viscous flow contributions resulting from the pressure gradients. However, it was possible to use these and related equations and, with associated parameters, to reconstruct the experimental curves via computations. It was found that the range of applicability of the equations was limited and that none of the parameters could be predicted beforehand. This was partially the result of the internal-pore geometry of the graphite. Nevertheless, the applicability of the existing dust-gas equations to nonuniform pressure conditions has been established for the transition region insofar as is possible with a medium such as graphite.
Polarization of Dielectrics by Nuclear Radiation. I. Release of Space Charge in Electron Irradiated Dielectrics
Authors: Murphy Preston V. , Ribeiro Sergio Costa
Published: April 2005

Irradiation of solid dielectrics with high-energy electrons produces a region of negative space charge which may persist for a long time. The capacity of various dielectrics for charge storage and the characteristics of thermal and photoelectric charge release are discussed. Charge storage capacity is highest in electret forming materials and in materials with a high density of deep ``traps.''
Theoretical Bound on the Thermoelectric Figure of Merit of Two-Band Semiconductors
Authors: Rittner E. S. , Neumark G. F.
Published: April 2005

The Simon two-band semiconductor model is investigated further theoretically to determine whether a finite upper bound can be imposed on the thermoelectric figure of merit. It is shown that limitations on the adjustability of the Fermi level and use of reasonable physical values for the band parameters do lead to a finite upper bound for the two-band model which is of the same order of magnitude as that derived earlier by Rittner for a one-band model. The former can be severalfold higher than the latter but only at pathologically high values of the effective mass ratio mh/me. Other factors which favor a high value of the upper bound are discussed.
Diffusion of a Magnetic Field Into a Conductor, with a Moving Boundary Condition
Authors: Oddson J. K.
Published: April 2005

An exact analysis of the diffusion of a magnetic field into a finite length conducting slab as the slab passes through a field region is presented. The problem is characterized by a parabolic differential equation with boundary conditions at a prescribed moving interface. The solution is obtained as a combination of two functions, the first of which satisfies the conditions at the moving boundary but not the differential equation; and the second, obtained by standard transform methods, which completes the requirements. Results are presented in terms of the magnetic Reynolds number of the system.
Kα Satellite Interference in X-Ray Diffractometer Line Profiles
Authors: Parrish W. , Mack M. , Taylor J.
Published: April 2005

The Kα satellites occur as a group of weak, unresolved lines superimposed on the short wavelength tail of the Kα1 line. Satellite data obtained experimentally with a single-crystal diffractometer are reported and compared with the results of two-crystal spectrometer measurements by previous investigators. It is calculated from spectral data that the addition of the satellite group to the Kα1,2 lines shifts the Cu centroid 0.031 xu and the Fe centroid 0.061 xu to shorter wavelengths. The satellites occur superimposed on the short wavelength tail of the Kα1 line in back-reflection powder line profiles and appear as a low intensity ``plateau'' which may cause difficulties in precision measurements. The effect of the satellite group on the value of the centroid obtained by various methods of truncating the profile is described. The angular separation of the satellites from the Kα1 component increases with increasing diffraction angles and may cause an error of the order of 1% in the relative integrated line intensities if the integration limits do not consistently include or exclude the satellites.
Electric Tunnel Effect between Dissimilar Electrodes Separated by a Thin Insulating Film
Authors: Simmons John G.
Published: April 2005

The theory of the electric tunnel effect has been extended to asymmetric junctions—i.e., junctions having electrodes of different materials. It is found that the J—V characteristic is polarity-dependent. At lower voltages, the greater current flows when the electrode of lower work function is positively biased, in agreement with observations on junctions having one aluminum electrode. At higher voltages, there is a change in direction of rectification; i.e., greater current flows when the electrode of lower work function is negatively biased. This effect has also been experimentally observed.