bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Heat Treatment upon the Electrical Properties of Indium Arsenide
Authors: Dixon Jack R. , Enright Dorothy P.
Published: April 2005

Large reversible variations in carrier concentration, Hall mobility, and carrier lifetime have been produced in indium arsenide by heat treatment. For material cut from the parent ingot, carrier lifetimes measured by the photoelectromagnetic-photoconductive ratio method increase by a factor of over 20 as a result of slow cooling from 850°C. Heat treatment at temperatures of 450°C and above increases the carrier concentration of n-type material and decreases the carrier concentration of p-type material. Such variations are reversed by heat treatment at temperatures below 350°C. In this way, changes in the carrier concentration of over 1017 cm−3 have been produced, and InAs has been converted from p to n type. Various heat treatment mechanisms are examined. It is shown that the experimental results are consistent with the model proposed by Kurtz and Kulin involving the segregation and dispersion of donor impurities to and from dislocations.
Theory of Creep Limited by Self-Diffusion
Authors: Christy R. W.
Published: April 2005

A theory of steady-state creep at high temperature and stress is based on the climb of dislocations limited by the diffusion of vacancies from them. The creep rate is found to be approximately (MnL3)D0 exp[− (W+E+U−ΔW)/kT], where M is the number of dislocation sources per unit volume, n is the number of dislocations of length L per unit area, and D0 exp (−W/kT) is the coefficient of self-diffusion. The number of jogs in the dislocations is determined by U, and E is an activation energy for formation of vacancies, due to relaxation of the lattice. The reduction in vacancy formation energy near a dislocation ΔW is estimated from the interaction energy of the climbing dislocations. A comparison of experimental data for Zn and AgBr suggests that E is a significant contribution to the activation energy for ionic crystals but not for metals. The predicted increase in vacancy concentration during creep is too small to give observable effects. It is concluded that any observed enhancement of diffusivity during creep is due to increased mobility of defects.
Photoelastic Constants of Vitreous Silica and Its Elastic Coefficient of Refractive Index
Authors: Primak William , Post Daniel
Published: April 2005

The photoelastic constants and their dispersion for visible light were determined for two samples of vitreous silica, Corning and Herasil No. 1. The results for the mercury green line, 546 mμ, are quoted here. The photoelastic constants were 4.22×10−13 (d/cm2)−1 (ordinary ray) and 3.56×10−13 (d/cm2)−1 (extraordinary ray). From the ratio of Poisson's ratio to Young's modulus 0.216×10−12 (d/cm2)−1 and Young's modulus 0.76×1012 (d/cm2), which were also determined, there were calculated the pressure coefficient of refractive index 0.909×10−12 (d/cm2)−1 and the elasticity volume coefficient of refractive index V dN/dV=0.34. Comparison of these results with those reported for other glasses indicates that the oxygen ions of vitreous silica are more deformable then the oxygen ions of other siliceous glasses. In vitreous silica about ⅓ of the volume change accompanying an elastic dilatation arises from the dilatation of the oxygen ions. A comparison is also made with the results reported for corresponding thermally induced effects. It indicates that (a) during a thermal dilatation of a siliceous glass, the oxygen ion undergoes a dilatation which in the case of most siliceous glasses causes an equivalent dilatation of the body, but which in the case of vitreous occurs internally instead, and (b) in crystal quartz no appreciable dilatation of the oxygen ion occurs during a thermal dilatation. The thermal dilatation of the oxygen ion in the glasses would thus seem related to its strained bond configuration.
Experimental Verification of Theoretical Relations between Total Gas Absorptivities and Total Gas Emissivities for CO
Authors: Oppenheim U. P.
Published: April 2005

An experimental study has been carried out for the purpose of verifying theoretical predictions concerning the relations between total absorptivities and total emissivities for transparent gases. The experimental conditions have been designed in such a way as to permit a direct check of theoretical relations derived for (a) nonoverlapping dispersion lines and (b) spectral lines with sufficient pressure broadening to permit neglect of the rotational fine structure. A comparison between the emissivities derived from absorptivity measurements and emissivities calculated from the spectroscopic constants of CO shows a good agreement (within 20% for most of the temperature range).

The apparatus for the measurement of total gas absorptivities is described. Results for total absorptivities of carbon monoxide measured at temperatures between 300 and 500°K are given and total emissivities have been calculated in the temperature range of 300 to 1600°K. The range of total gas pressure is 0 to 515 psia.
Interdiffusion in Binary Ionic Semiconductors
Authors: Brebrick R. F.
Published: April 2005

Interdiffusion in a nondegenerate, exhaustion range, binary ionic semiconductor is investigated using the recently improved theory for the concentrations of defects in crystals and Wagner's phenomenological flow equation. The composition dependence of the interdiffusion constant is found to be determined by the ratio of the ion jump frequencies, the Schottky constant, and the intrinsic concentration of conduction band electrons. The removal of the restriction to an exhaustion range semiconductor and the replacement of the basic assumption of local electroneutrality are discussed.
Anisotropic Mobilities in Plastically Deformed Germanium
Authors: Logan R. A. , Pearson G. L. , Kleinman D. A.
Published: April 2005

We have measured the carrier density as a function of temperature in n-type germanium which has been plastically deformed by bending, and find that it can be accounted for on the basis of Read's theory if the dislocation acceptor level lies 0.18 to 0.20 ev below the conduction band. The analysis indicates that the dislocation density introduced by plastic bending is about 8 times the theoretical equilibrium density that would correspond to zero internal stress. We observe that the mobility for current flow along the bending axis is the normal mobility, which indicates that the dislocations are parallel to the bending axis, although they may zig-zag with line segments along (110) type directions. The mobility perpendicular to the bending axis is in qualitative agreement with the theory given by Read, although the theory tends to underestimate the reduction of mobility below 50°K. We have extended Read's theory to the case where the current flows along the bending axis and the magnetic field is perpendicular to the bending axis.
Effect of Variations in Surface Potential on Junction Characteristics
Authors: Forster J. H. , Veloric H. S.
Published: April 2005

A filamentary structure has been used to compare the electrical properties of a germanium surface with those of an adjacent p-n junction intersecting the same surface. Surface charge is varied by field effect plates in the isolated portion of the filament and near the junction. An orderly relation can be found between surface potential variations and changes in the reverse currents across the junction. At low bias, the junction current varies with surface recombination velocity, and for bias near breakdown, the breakdown voltage varies with induced charge at the surface. For inverted surfaces, the low bias current varies rapidly as expected from channel length variations. With inverted surfaces, channel growth leads to large reverse current variations with surface potential, but breakdown voltage becomes independent of surface charge. These variations are considered in terms of simple theory, and device implications are discussed.
Proportionality between Photoconductance and Time Constant in Lead Sulfide Films
Authors: Spencer H. E.
Published: April 2005

Relative humidity variation, aging, vacuum overcoating, and background light change the signal, the resistance, and the time constant of lead sulfide films at room temperature. Yet the relative change in photoconductance is proportional to the relative change in time constant. This result is taken as evidence that the time constant of photoconductivity is identical to the lifetime of the holes. It is shown that the ratio of signal to the product of resistance and time constant is useful in interpreting data taken on films whose properties are changed by ambient conditions.
InAs and InSb as Thermoelectric Materials
Authors: Bowers R. , Ure R. W. , Bauerle J. E. , Cornish A. J.
Published: April 2005

Measurements of the electrical conductivity, thermal conductivity, and Seebeck coefficient (thermoelectric power) of InSb and InAs have been made at high temperatures. The thermoelectric figure of merit (S2σ/κ) averaged 0.42×10−3 °K−1 between 100 and 500°C for InSb and 0.44×10−3 °K−1 between 500 and 750°C for InAs. Hence n-InAs and InSb in series may be used to generate electrical power with an efficiency of about 6% when used in conjunction with p-type materials of similar characteristics. In neither InSb up to 500° nor InAs up to 800°C did the thermal conductivity show the large high-temperature anomaly previously reported in InSb.
Radiation Effects in Semiconductors: Thermal Conductivity and Thermoelectric Power
Authors: Geballe T. H.
Published: April 2005

The use of thermal conduction and thermoelectric measurements in studying radiation damage effects in semiconductors is discussed. The conclusion is reached that in the present state of knowledge such measurements will probably be more helpful in studying the kinetics of the formation and annealing of radiation-introduced defects than in characterizing the structure of such defects.
Transport Properties in Silicon and Gallium Arsenide
Authors: Willardson R. K.
Published: April 2005

High-purity n- and p-type silicon has been irradiated lightly with Co60 γ rays. Analysis of the Hall mobility and magnetoresistance data indicate the introduction of levels near the conduction and valence bands. The analysis suggests the presence of triply ionized acceptors and singly ionized donors. The third ionization state of the acceptor apparently produces a level above the center of the band gap. Under more extensive irradiation a double ionization of the donors can account for the observed high resistivity. An initial increase in the magnetic field dependence of the Hall coefficient in both n- and p-type silicon may be related to the multiple ionization or to radiation annealing. The Hall mobility and transverse magnetoresistance in n-type gallium arsenide have been studied as a function of impurity concentration and density of defects introduced by fast-neutron irradiation. The change in the mobility and magnetoresistance with fast-neutron bombardment suggests the introduction of levels near the band edges and of multiply ionized levels similar to those in silicon.
Recombination Properties of Bombardment Defects in Semiconductors
Authors: Wertheim G. K.
Published: April 2005

The theory of recombination via defects having energy levels in the forbidden gap is reviewed. Emphasis is given to those aspects which complicate interpretation of lifetime data, such as the inherent difference between steady state and transient measurements, large-signal behavior, competing recombination mechanisms, trapping, the possible existence of strongly temperature-dependent cross sections, and the properties of multilevel defects. A summary of the known recombination properties of bombardment-produced defects is given.
Radiation Effects on Recombination in Germanium
Authors: Curtis Orlie L.
Published: April 2005

The properties of recombination centers in germanium are obtained on the basis of lifetime data in conjunction with other information available. For recombination centers introduced by Co60 gamma rays and fission neutrons, the recombination energy level position is placed at 0.20 ev below the conduction band. The room temperature hole-capture cross sections resulting are 1.1×10−15 cm2 and 6×10−15 cm2 for Co60 gammaray and fission neutron irradiation, respectively. For the case of 14-Mev neutron irradiation the energy level is located 0.32 ev above the valence band. The room temperature hole and electron cross sections are ∼6 ×10−15 cm2 and 2.2×10−17 cm2, respectively. The capture probabilities are assumed to be independent of temperature except for the case of gamma irradiation, for which there is apparently a fairly strong variation corresponding to a change in the activation energy of 0.07 ev. The selection of the values given above is not entirely unique. The assumptions made in their determination are discussed. The values given are directly applicable only in the case of n-type material, the situation in p-type material being more complex.
Magnetic Susceptibility of Solids
Authors: Krumhansl J. A.
Published: April 2005

The magnetic susceptibility of semiconductors depends on electronic properties of the lattice, on the motion of free carriers and on the presence of impurity states. Critical points in the work on Ge and Si are reviewed relative to demands they place on theoretical interpretations. Anomalies in the susceptibility of high-purity specimens, various aspects of valence band carrier susceptibility, and the susceptibility of acceptor states are not as yet explained satisfactorily.
Magnetic and Electrical Properties of Reactor-Irradiated Silicon
Authors: Sonder E.
Published: April 2005

Magnetic susceptibility measurements above 3°K and Hall effect and resistivity determinations between 50 and 300°K are reported for n-type silicon samples irradiated with increasingly higher doses of fission neutrons. The paramagnetism due to electronic states in the forbidden gap shows an initial decrease after short irradiation but a reversal, increase, and final saturation at a value less than that originally contributed to the paramagnetism by the filled donors after longer irradiation.

The Hall coefficient shows evidence of a distribution of irradiation-produced energy levels in the neighborhood of 0.3 ev below the conduction band. The mobility goes through an initial sharp decrease with irradiation but recovers partially after longer irradiations. The results are discussed in terms of several models of radiation damage. It is concluded that a simple model based on uniformly dispersed interstitials and vacancies is not adequate to explain the results and that interactions between centers, and nonuniform distribution of damage will probably have to be taken into consideration.
Nature of Bombardment Damage and Energy Levels in Semiconductors
Authors: Crawford J. H. , Cleland J. W.
Published: April 2005

The different effects of Co60 gamma ray and fast neutron bombardment on the electrical behavior of germanium are discussed in terms of different local distributions of lattice defects expected for these two types of radiation. For the first of these, which is expected to introduce randomly distributed pairs of interstitials and vacancies, the state at 0.20 ev below the conduction band has been found to increase the concentration of ionized scattering centers on becoming occupied with conduction electrons. This state has been ascribed to a mobile interstitial because of its annealing behavior at moderate temperatures. Energy levels in p-type Ge and their annealing behavior are also discussed. In neutron irradiated n-type germanium the behavior of Hall mobility and the apparent energy distribution of defect levels are discussed in terms of a tentative model for the potential distribution around regions of high local lattice disorder expected to result from neutron bombardment. This model postulates that the disordered region is p type and is surrounded by a positive space charge region in the n-type matrix which insulates it from the matrix. This configuration of electrostatic potential around the disordered region in effect produces an insulating region whose radius is ∼10 times that of the disordered region itself. The behavior of Hall mobility in irradiated n-type specimens is consistent with the predictions of this model.
Energy Levels in Irradiated Germanium
Authors: Blount E. I.
Published: April 2005

The energy levels found in germanium irradiated by different particles seem at first to be mutually inconsistent. It is possible tentatively to reconcile the differences by consideration of clustering and association of defects. Four levels are ascribed to single vacancies and interstitials. A crude theory is constructed to explain these levels, particularly their asymmetrical distribution in the energy gap, and to assign each to a definite defect. This theory differs somewhat from a previous one due to James and Lark-Horovitz; some differences in experimental predictions are discussed in particular.
Low-Temperature Annealing Studies in Ge
Authors: MacKay J. W. , Klontz E. E.
Published: April 2005

Irradiation at ∼10°K using 1.10 Mev electrons produces very different changes in the electrical properties of n-type Ge as compared to those produced in p-type Ge. In n-type Ge, more carriers are removed per incident electron at 10°K than at 78°K. However about 50% of the removed carriers are recovered in two stages of annealing, at 34°K and 64°K, after low temperature irradiation. Irradiation at 0.315 Mev, after a 1.10 Mev irradiation, also produces recovery of about 50% of the carriers removed by the 1.10 Mev irradiation. In p-type Ge, low temperature irradiation is at least 100 times less effective in removing carriers than is the case in n type. Annealing of an irradiated p-type sample to 130°K produces no measurable change. It is concluded that the stability of close-vacancy-interstitial pairs against recombination is less in p type than in n-type Ge. A qualitative argument as to the origin of this difference in stability is presented.
Ultrasonic Methods and Radiation Effects in Solids
Authors: Truell Rohn
Published: April 2005

The various mechanisms producing damping of ultrasonic elastic waves in solids are reviewed in this paper. Particular attention is given to the changes in attenuation produced by pinning of dislocation lines. Measurements of ultrasonic attenuation in irradiated single crystals of NaCl are presented and discussed, on the assumption that the dislocation density remains constant while the radiation displaced defects pin the dislocations. The effects on the velocity of propagation are discussed on the basis of the same model.
Displacement Thresholds in Semiconductors
Authors: Loferski J. J. , Rappaport P.
Published: April 2005

The paper reviews the current status of displacement threshold determinations, both theoretical and experimental, in semiconductors. The work of Seitz, Kohn, Klontz, Loferski, and Rappaport, Vavilov, et al., and Brown and Augustyniak on germanium are discussed and compared. Measurements of thresholds in Si and InSb also are discussed briefly.
Energy, Orientation, and Temperature Dependence of Defect Formation in Electron Irradiation of n-Type Germanium
Authors: Brown W. L. , Augustyniak W. M.
Published: April 2005

From measurements of change in conductivity with electron irradiation of thin n-type germanium samples at 79°K, a threshold energy for the formation of stable acceptor centers has been determined. It is found to be 355±5 kev, corresponding to 15.1 ev for the lightest mass germanium isotope at rest. Taking into account the contribution of lattice vibrations to the displacement energy the threshold is ∼16 ev. An orientation dependence has been found in the rate of formation of the centers in agreement with the predictions of Kohn. In order of decreasing rate of center formation the three orientations examined are (111), (110), (100). There is no corresponding orientation dependence in the threshold energy itself. The energy dependence of the rate of acceptor formation suggests the defects are not the closest vacancy-interstitial pairs. A positive temperature dependence of the rate of acceptor formation has been found. This effect is largest at lowest electron energies. It is not explicable by lattice vibrations, although they can contribute to the effect between 79°K and room temperature. The apparent threshold changes by ∼100 kev between 21 and 263°K.
Use of the Principles of Conservation of Energy and Momentum in Connection with the Operation of Wave-Type Parametric Amplifiers
Authors: Pierce J. R.
Published: April 2005

The operation of a wave-type parametric amplifier may be thought of in terms of the force exerted by traveling discontinuities or reflecting elements on the waves present in the device. By invoking the principles of conservation of energy and momentum it is possible to understand in very simple terms certain limitations on the operation of such devices and to arrive very easily at certain general relations governing their behavior, including the Manley-Rowe relation. It is proposed that for a guided wave the momentum per unit distance is the power divided by the product of the group and phase velocities.
Harmonic Current Growth in Velocity-Modulated Electron Beams
Authors: Mihran T. G.
Published: April 2005

Harmonic currents accompanying a fundamental space charge wave of current in a velocity modulated electron beam are found to grow with distance even though the peak amplitude of the fundamental current remains relatively constant.

This effect was first noted in studying the results of a series of disk-electron calculations. Subsequently, second harmonic growth was found experimentally using a sliding cavity setup. A physical explanation of this phenomenon is given.

The harmonic growth can be interpreted as parametric amplification in which the finite electron beam acts as the nonlinear element, with the fundamental current providing the pump power.
High-Temperature Oxidation of Iron Whiskers
Authors: Laukonis J. V. , Coleman R. V.
Published: April 2005

Single crystal α-iron whiskers have been used to study early stages in the oxidation of iron at high temperatures. Well defined oxide patterns are observed on clean iron surfaces and there are characteristic differences between the patterns on {100} and {110} faces. These differences tend to be eliminated if a natural oxide film is present before the high temperature oxidation is performed. Unusual mosaic oxide patterns which form on clean {100} iron surfaces are shown.
Uniform Rotational Flux Reversal of Ferrite Toroids
Authors: Gyorgy E. M. , Hagedorn F. B.
Published: April 2005

A model is presented for the high speed uniform rotational flux reversal of ferrite toroids. The magnetization is uniform in the sense that the components of magnetization in a cylindrical coordinate system are independent of position. Analysis of the model, to a very good approximation, leads to results identical with those obtained from uniform rotation in isotropic thin films. The minimum switching coefficient predicted by this model is 0.005 oe μsec. Experimental confirmation of a high speed switching mode in ferrite toroids is given. A toroid with a wire loop embedded in it was used to induce the proposed flux configuration. The switching coefficient and the extrapolated threshold field associated with the high speed mode have been found to decrease with increasing temperature.
Anomalous Electrical Properties of p-Type Indium Arsenide
Authors: Dixon Jack R.
Published: April 2005

Hall constants and resistivities have been measured as a function of carrier concentration for zinc-doped, single crystal p-type indium arsenide at temperatures ranging from 4.2 to 500°K. For carrier concentrations greater than 2×1017 cm−3 the electrical properties appear to be normal for a material of this type. However, for smaller carrier concentrations anomalies appear which consist of dips and double reversals in the Hall constant-temperature relationship. These results are in agreement with data reported by Folberth and Weiss for polycrystalline material. A mechanism involving inhomogeneities arising from the inclusion of microscopic n-type regions in p-type material is proposed to explain the anomalies. Such small n-type regions could arise from the aggregation of impurities about dislocations. On the basis of this model, it is predicted that the anomalies should be removed by appropriate heat treatment of the material. The prediction is confirmed by experiment. Recent work of Rupprecht suggests that the anomalous behavior of p-type InAs is due to an n-type surface layer which can be introduced by grinding or polishing, and removed by etching. This is consistent with the mechanism we propose.
Nuclear Magnetic Resonance Studies of Dislocations in NaI and KI
Authors: Hon J. F. , Bray P. J.
Published: April 2005

Intensity anomalies have been found in the nuclear magnetic resonance of I127 in NaI and KI single crystals when the magnetic field is along a [1,0,0] type direction. The intensity enhancement in these cases indicates a collapse of the satellite transitions (m → m − 1, m ≠ ½) into the central transition (m = ½ → m = −½). It is concluded that the crystals contain edge and/or screw dislocations which are preferentially oriented along [1,1,0] and [1,0,0] type directions, respectively. The degree of orientation is greater in NaI than in KI.

These studies afford an explanation of anomalous resonance line widths reported for NaI by other observers.
Initial Wedge Impact on a Compressible Fluid
Authors: Borg S. F.
Published: April 2005

A physical model is developed and a solution is obtained for rigid two-dimensional wedge impact on a compressible fluid. The solution is given as a combined compressible flow—elastic viscous body action. The combined solution satisfies the field equations for the physical model assumed for the impact and, approximately, the necessary boundary conditions. It holds for a semicircular wedge, expanding similar to itself with time and entering the fluid at a velocity equal to half the velocity of sound. Hence, it applies best to wedges with pointed noses. Approximate procedures are given for solving noncircular shapes moving with arbitrary velocities. An order-of-magnitude estimate is made for the time of importance of compressibility effects.
Thermoelectric Properties of the Plasma Diode
Authors: Lewis H. W. , Reitz J. R.
Published: April 2005

The thermoelectric properties of a gas-filled diode containing a high density of positive ions are discussed in some detail. The complete circuit of diode and load is treated as a thermocouple, and expressions for both the Seebeck emf and thermoelectric conversion efficiency are obtained as a function of cathode and anode temperatures. The interior of the diode is divided, for convenience, into three regions: (1) the cathode sheath, (2) main body of plasma, and (3) the anode sheath. The anode sheath is the region of large temperature gradient; the approximate temperature distribution in the sheath is obtained by solving a greatly simplified heat-conduction equation. Finally, the results of this analysis are compared with experiments performed by Grover, Roehling, Salmi, and Pidd.
Effect of Residual Gases on Superconducting Characteristics of Tin Films
Authors: Caswell Hollis L.
Published: April 2005

A special oil-free, ultra-high vacuum system has been used to deposit tin films at pressures less than 10−9 mm Hg onto room temperature substrates. These films were found to possess extremely sharp and reproducible magnetic field transitions as compared to films deposited by more conventional techniques. This resulted from breakup of the penumbra of a film deposited through a mask into electrically discontinuous islands leaving a film of uniform thickness. Specific residual gases were found to decrease the surface mobility of the tin atoms which contributed to continuous film edges and higher critical fields. For example, the critical field extrapolated to 0°K increased from 370 oe for a pure film to 490, 590, and 820 oe as the ratio of oxygen molecules to tin atoms striking the substrate increased from 0 to 3, 6, and 9% respectively. For more highly doped films the bulk characteristics were also altered, indicating the presence of oxygen in the film material. Water vapor and carbon dioxide were found also to alter the edge structure, whereas N2, H2, CH4, C3H8, C5H12, A, and CO did not. By analyzing the critical field and residual resistance data of the various films, the vacuum requirements necessary for obtaining high purity films with sharp magnetic transitions occurring at predictable field values were ascertained. An ultra-high vacuum system is not required if the partial pressure of critical gases is maintained below specified values.
Microwave Measurements of the Radiation Temperature of Plasmas
Authors: Bekefi G. , Brown Sanborn C.
Published: April 2005

Radiation-temperature measurements of positive columns of glow discharges in helium, neon, and hydrogen were compared with calculations and with Langmuir probe measurements of the electron temperature. The microwave-noise radiation was detected at a frequency of 3000 Mc. The plasma studied was illuminated by a blackbody source of known variable temperature. The blackbody temperature was adjusted until the received noise power became independent of the presence of the unknown plasma. At this point, the temperature of the two radiators is the same, irrespective of the magnitude of the plasma absorptivity.
Zone Refining of the Silver Halides
Authors: Moser F. , Burnham D. C. , Tippins H. H.
Published: April 2005

The techniques of zone melting have been applied to AgCl and AgBr in an attempt to obtain large crystals of extremely high purity. By measuring distributions in ingots with deliberate impurity additions, both optimum conditions for zoning and distribution coefficients for several impurities were determined. For AgCl, zone melting in a chlorine atmosphere led to near-ultimate distributions for Cu, Pb, Ni, and Fe after passage of 70 zones at a rate of 3 in./hr. The distribution coefficients determined were as follows: Cu, 0.4; Pb, 0.4; Ni, 1.4; and Fe, 0.7. Zone melting in vacuum resulted in similar distributions for Cu, Pb, and Ni, but Fe separated with an effective distribution coefficient slightly greater than one. Under these conditions, Mn and Cd separated in a direction opposite to that of zone travel, and Sn, Al, and Sr separated in the direction of zone travel. Zone refining of nominally pure AgCl resulted in crystals which probably contain less than one part in 109 of Cu and Ni, less than one part in 108 of Pb, and less than five parts in 108 of Fe. Limited data on AgBr indicate that in this case, too, useful purification can be obtained. The dark electrical conductivity of the zoned crystals was found to be intrinsic above 315°K for AgCl and 300°K for AgBr.
Influence of the Cathode Surface on Arc Velocity
Authors: Lewis T. J. , Secker P. E.
Published: April 2005

An arc cathode spot in a transverse magnetic field may move either in the Amperian (forward) direction or in the opposite, i.e., retrograde sense. The rate and direction of movement are dependent on a number of parameters such as arc current, magnetic field strength, and gas pressure at the cathode root. New experiments which demonstrate clearly the effect of cathode oxide layers on arc velocity are described. A simplified model of the cathode root region of the arc which is consistent with the experimental results is proposed. The predictions of this model, which is applicable to both Amperian and retrograde motion, are also in satisfactory agreement with results obtained by previous investigators.
Germanium Saturated with Gallium Antimonide
Authors: McCaldin J. O. , Wittry D. B.
Published: April 2005

Single crystals of Ge saturated with GaSb were prepared by temperature gradient zone melting at 750°C. Electron probe microanalysis indicated 4.83×1020 Ga atoms and 2.36×1020 Sb atoms/cc in the saturated material with an estimated error of about 10%. Thus the solubility of Sb is greatly enhanced by the presence of Ga, though the reverse is not true. Hall measurements were in semiquantitative agreement with the chemical concentration measurements and indicated that carrier mobility is not much affected by the presence of the compensating impurity.
Reflection and Transmission of Electromagnetic Waves at Electron Density Gradients
Authors: Albini Frank A. , Jahn Robert G.
Published: April 2005

Solutions are obtained for the propagation of plane electromagnetic waves parallel to a gradient of free electron density, in the form of complex Airy functions. Reflection and transmission coefficients are derived for normal incidence on a linear ``ramp'' of electron density connecting a uniform dielectric gas with a uniform ionized gas, as functions of ramp length and propagation exponent of the latter. Machine evaluations of typical cases of physical interest are displayed and discussed. Similar study is made of two-stage ramps of variable proportions, intended as second approximations to smooth profile transition zones. In each case, the reflection and transmission coefficients are found to depend strongly on ramp width over a range of several tenths of a wavelength, then to oscillate mildly toward the asymptotic values predicted from a WKB-type approximation. The results are less sensitive to the detailed shape of the electron density profile. Propagation through a finite slab of ionized gas bounded on each side by such linear transition zones is formulated and evaluated for typical cases. Asymptotic approximations for the linear ramp problem are found to be inadequate to cover the entire range of interest. The neglect of variation in collision frequency through the transition is discussed and justified for a broad class of equilibrium profiles.
Theory of Tunneling
Authors: Kane Evan O.
Published: April 2005

The theory of ``direct'' and ``phonon-assisted'' tunneling is reviewed. Theoretical I–V characteristics are calculated using the constant field model. Generalizations to nonconstant field and more complicated band structure models are discussed briefly.
On the Internal Friction of Cold-Worked and Quenched Martensitic Iron and Steel
Authors: Mura T. , Tamura I. , Brittain J. O.
Published: April 2005

A theoretical explanation is given for the internal friction peaks which are observed at 200°∼250°C for cold-worked iron and steels and for steels in the martensitic condition. The theory for the peaks is based upon the addition of a term to the free energy in order to account for the strain energy due to the interaction of an atmosphere and the line imperfections. The standard linear solid was obtained from the model in which dislocations are vibrating with an atmosphere of carbide precipitates.
Clustering in an Alpha Iron-Molybdenum Solid Solution
Authors: Hornbogen Erhard
Published: April 2005

Clustering in alpha iron-molybdenum alloys begins with the formation and growth of dislocation rings from supersaturated vacancies. The rings form on {100} planes and reach a maximum diameter of ∼800 A. Segregation of molybdenum to these rings starts just after their formation. Molybdenum-rich zones grow inside the rings until a disk is formed. After very long periods of aging, particles of the bcc η solid solution form from the clusters at aging temperatures below 500°C.
Determination of Crystallite Size Distributions from X-Ray Line Broadening
Authors: Bienenstock Arthur
Published: April 2005

The broadening of an 00l powder diffraction line caused by a distribution of sizes of crystallites is discussed. A function of the intensity, P(h3) sin2(πh3), is derived. Its cosine transform gives the size distribution directly. The first term of a series expansion of this distribution function corresponds to the expression previously obtained by Warren and Averbach. In addition, this function gives less weight to the extremes of the diffraction line shape.
Etch Pits at Dislocations in Copper
Authors: Young F. W.
Published: April 2005

A possible mechanism for the development of etch pits at dislocations in copper by etching in solution is presented, and experiments are described which may substantiate this mechanism. Etchants which will develop pits at clean dislocations on the (111), (100), and (110) faces of copper are described. These etchants are capable of distinguishing between clean dislocations and dislocations with a ``Cottrell atmosphere'' in 99.999% copper. Clean edge and screw dislocations can also be differentiated with these etchants. Some observations concerning the relation of facet structure, developed by etching, to the dislocation structure of the crystal are reported.
Influence of Tensor Conductivity on Current Distribution in a MHD Generator
Authors: Hurwitz H. , Kilb R. W. , Sutton G. W.
Published: April 2005

Magnetohydrodynamic generators may operate under conditions such that the product of electron cyclotron frequency and mean collision time is not small compared to unity. Accordingly the electrical conductivity is a tensor rather than a scalar quantity. The influence of tensor conductivity on the electrical current distribution has been investigated in two idealized situations, one pertaining to the entrance and exit regions of the generator and the other pertaining to the region near segmented electrodes. The calculations predict modifications of the internal impedance of the generator which can be described in terms of increases in the effective duct length and width.
Ultrasonic Attenuation of Longitudinal Waves in Plastics
Authors: Auberger Michel , Rinehart John S.
Published: April 2005

Hughes' pulse technique for measuring longitudinal velocities has been adapted and extended to measure attenuation of longitudinal waves in the frequency range from 250 to 1,000 kc. Data for attenuation in nepers per wavelength in six different plastics (Plexiglas, polystyrene, nylon 101, Formica XXN, polyethylene, and Teflon) are given for eight different frequencies ranging from 250 to 1000 kc. The results for Plexiglas and polystyrene are compared with results obtained previously by other methods. Attenuation in nepers per wavelength has been found to decrease when frequency increases for all plastics, except for Teflon, which shows a well-defined peak at about 700 kc.
Diffusion in a Ferromagnetic Alloy
Authors: Stanley James , Wert Charles
Published: April 2005

Diffusion constants in an alloy of Fe+ 18%V have been determined over a wide temperature range by a combination of radioactive tracer and anelastic methods. The region of measurement extends over a considerable interval on both sides of the magnetic Curie temperature. The data show a pronounced effect of ferromagnetic spin ordering on diffusion. Diffusion in the well-ordered ferromagnetic state is about 100 times slower than would be expected from extrapolation of data in the paramagnetic region. Part of this retardation appears to be an increase in the activation energy and, part a decrease in D0.
Experimental Study of Anomalous Electron Stream Behavior
Authors: Miller M. H. , Dow W. G.
Published: April 2005

Experimental measurements on the characteristics of the sole current in a rectilinear crossed-field beam are reported. The sole current may be assigned a kinetic temperature on the order of 10 v corresponding to energy in excess of that corresponding to motion in static fields. The energy exchange leading to this excess energy is believed to be associated with multiple-loop trajectories in the low-potential region near the cathode.
Vapor Phase Growth and Properties of Zinc Sulfide Single Crystals
Authors: Samelson Harold
Published: April 2005

The growth of zinc sulfide single crystals by a sealed tube vapor phase method is described. In this system the parameters that are studied are the evaporation temperature, the temperature schedule during a run, the temperature gradient along the length of the tube, and, finally, the ambient pressure of H2S in the tube. The resulting crystals are of a rodlike, distorted rodlike, or platelike habit, and the dominant habit, in any given run, is responsive to variations in the experimental parameters. An altogether different habit is observed in runs performed in a vacuum. The structure of the crystals varies from pure hexagonal to reversed cubic; most of the crystals exhibit stacking faults to various degrees. The structure is a function of the growth temperature.

For crystals grown in an H2S ambient, the mechanism proposed is an initial growth of a fine rod followed by a thickening of the rod and its possible subsequent development into a plate. The whisker growth is probably not a nucleation process and may proceed by a screw dislocation or stepped plane mechanism. The subsequent steps, as well as the growth of crystals in a vacuum are consistent with a surface nucleation mechanism.
Extended Curves of the Space Charge, Electric Field, and Free Carrier Concentration at the Surface of a Semiconductor, and Curves of the Electrostatic Potential Inside a Semiconductor
Authors: Young Charles E.
Published: April 2005

This article is an extension of work begun by R. H. Kingston and S. F. Neustadter [J. Appl. Phys. 26, 718 (1955)]. They calculated the space charge, electric field, and change in free carrier concentration for a semiconductor surface. Their results may be expressed as functions of the deviation for the Fermi energy from its intrinsic value in the bulk and at the surface. Curves calculated from their results may be used for any nondegenerate semiconductor at any temperature, provided that the donor and acceptor levels are completely ionized. The curves presented in the above-mentioned article, however, are extensively applicable only to germanium or semiconductors of similar energy gap. The extended curves presented in this article enable computations to be applied to materials of higher energy gap, such as silicon and gallium arsenide, over a wide resistivity range. Also, in this article several curves of electrostatic potential inside a semiconductor have been computed. A few of these curves were presented previously by G. C. Dousmanis and R. C. Duncan, Jr. [J. Appl. Phys. 29, 1627 (1958)]. The curves presented in this article are intended to supplement those previously presented.
Electron Microscope Observation of Dislocations in Talc
Authors: Amelinckx S. , Delavignette P.
Published: April 2005

Dislocations in talc appear to be dissociated into four partial dislocations separated by their stacking fault ribbons. This phenomenon can easily be interpreted in terms of the known structure of talc. The stacking fault energy can be estimated from the equilibrium condition of the four partials. Complicated networks resulting from the interactions of ribbons are observed. A number of striking contrast effects are also described.
Transformation—Disorder to Order in Ni3Mn
Authors: Marcinkowski M. J. , Brown N.
Published: April 2005

The ordering transformation in the alloy Ni3Mn has been investigated using both magnetic and neutron diffraction techniques. These measurements were made with alloys that were allowed to relax to nearly equilibrium states of order over a range of temperatures above and below the critical ordering temperature. In addition, the manner in which these equilibrium states were approached isothermally was also investigated over a range of temperatures. From these measurements, it has been postulated that the equilibrium configurations of partial order are nonhomogeneous, consisting of long-range ordered domains in a matrix of short-range order. In addition, the isothermal transformation from disorder to long-range order proceeds first by the development of short-range order. Both short- and long-range order have been found to increase the magnetic Curie temperature as well as the magnetization above that of the weakly magnetic disordered alloy. These results support the hypothesis that nearest neighbor magnetic-spin interactions play an important role in determining these magnetic properties, although the importance of more distant neighbor interactions cannot be ruled out.
Calculation of X-Ray Intensities from Electron Probe Specimens
Authors: Birks L. S.
Published: April 2005

Complete calibration curves may be prepared for electron probe specimens of any matrix composition without the aid of known calibration standards. When there is no fluorescent excitation of the desired element by matrix components, the equation for relative x-ray intensity is simply IA/I100 = FAWA/FA100, where IA and I100 are the intensities from weight fraction WA and from 100% of the element, respectively; FA and FA100 are values of an ``intensity variable'' at WA and 100% of the desired element. Values of F for all elements from Ti to Au (and probably from Al to Ti as well) for any takeoff angle ψ, and for any matrix composition, can be obtained from a single intensity-variable curve that will, of course, be valid for any electron probe instrument operated in the 25–30 kev range. When there is fluorescent excitation of the desired element A by characteristic radiation from matrix element B, the equation is the same except for a fluorescent correction term KF, which is evaluated from tabulated values of absorption coefficients and excitation efficiencies. Then IA/I100 = FAWA(1+KF)/FA100. For the NRL electron probe operated in the 25–30 kev range, x-ray intensities calculated from these equations agreed with measured values to within 5% of the amount present even when very strong fluorescence by matrix elements occurred.
Fracture of Brittle Solids. I. Distribution Function for Fragment Size in Single Fracture (Theoretical)
Authors: Gilvarry J. J.
Published: April 2005

For single fracture of a brittle solid, the distribution function for fragment size is obtained on the basis of Griffith's theory of brittle strength (which postulates crack propagation when pre-existent flaws are activated by stress). Three assumptions are made: (a) Fracture proceeds by activation of flaws in the volume of the specimen, in fracture surfaces through the specimen, and in the edges produced by fracture surfaces, (b) the corresponding volume, facial, and edge flaws are distributed independently of each other when activated, and (c) activated flaws of a particular type are distributed at random, individually and collectively, in the sense of Fry. These assumptions yield directly and uniquely the probability dp(l,s,v) of formation of a fragment with total edge length, total face area, and total volume in the ranges l to l+dl, s to s+ds, and v to v+dv, respectively, as e−QdQ in the general case, with Q linear in l, s, and v. The derivation yielding this Poisson form requires no assumption on the shape of a fragment or the type of fracture surface. The number dn(l,s,v) of fragments with total edge length, total face area, and total volume in the ranges l to l+dl, s to s+ds, and v to v+dv, respectively, is evaluated as the product of dp(l,s,v) by the a priori number q of particles with these values of l, s, and v. The distribution function dn(l,s,v) meets the necessary physical requirement that the fracture process conserve volume independently of particle shape. By assuming that all fragments are geometrically similar, one can replace dp(l,s,v) and dn(l,s,v) by forms, p(x)dx and n(x)dx, respectively, which depend only on a mean linear dimension x of a fragment. The resulting expression for y, the cumulative fraction of the initial volume corresponding to fragments of dimension up to x, then yields rigorously forms of the empirical equations of Schuhmann and of Rosin and Rammler for this quantity, as limiting cases for x small. The conclusion follows that activation of edge flaws represents the dominant mode of fragmentation, in general. The moments of the distribution corresponding to the total number, the total edge length, and the total surface of the fragments are divergent; this anomaly is explained as the result of neglect of flaw depletion.