bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Certain Spectral Distributions of Soft X Rays by Theoretical Analysis of Absorption Experiments
Authors: Kerr Nancy A.
Published: April 2005

The temperature of a blackbody source which emits continuous radiation with a spectral peak in the range 0.6 to 8 kev in photon energy (soft x rays) may be determined by analyzing an absorption experiment. The technique employed here may be useful for the analysis of other continuous radiation distributions of soft x rays (e.g., free-free continuum radiation from plasma discharges and deceleration radiation from thick targets). Use is made of the approximation that over a limited energy region the absorption coefficient varies inversely with the cube of the spectral energy. The following equation, I(x)=I0(1+C1x logex+C2x+C3x43),neglecting terms of magnitude C4x5/3 or less for thin absorbers, describes the relative dependence of the transmitted x-ray intensity I(x) on the absorber thickness x for a blackbody spectrum of incident intensity I0. The constants C1 through C3 are related in a known manner to the temperature of the blackbody source for a given absorber material. Similarly, the equation, I(x)=I0D1x7/8(1+D2x−1/4) exp(−D3x1/4),neglecting terms of magnitude D4x−1/2 or less for thick absorbers, describes the transmission of a blackbody spectrum characterized by a source temperature which may be determined from the constants D1 through D3.
Forbidden Reflections in Electron Diffraction Patterns of Evaporated Tin Films
Authors: Vook Richard W.
Published: April 2005

Previous work has shown the existence of some structurally forbidden reflections in the electron diffraction patterns of (100) oriented polycrystalline films. These films were deposited under ultra-high vacuum conditions. A continuation of this work has resulted in the observation of these and other forbidden reflections in the diffraction patterns of two other kinds of films: (001) oriented single crystals containing deformation twins and (100) oriented single crystals. The existence of these strong reflections is probably due to strong dynamic interactions between the electron beam and the crystal lattice.
Analysis of a Nonlinear First-Order System with a White Noise Input
Authors: Caughey T. K. , Dienes J. K.
Published: April 2005

A general technique for computing the power spectrum of nonlinear systems is presented, and the method is applied to the Brownian motion of a particle with idealized Coulomb damping. In this method the transition probability is obtained by solving the appropriate Fokker-Planck equation. Then the autocorrelation function is calculated by an appropriate integration, and finally the power spectrum is found by means of the Wiener-Khintchine relation. Comparison is made with the method of equivalent linearization, which is applicable to a wide class of nonlinear problems.
Radiation from a Modulated Electron Beam with a Plasma Background
Authors: Parzen Philip
Published: April 2005

Expressions are derived for the electromagnetic radiation of current modulated electron beams which emerge from a plasma. Simple expressions are derived in the case where the dielectric constant of the plasma is zero or infinity.
A New Approach to Ionic Character in Solids
Authors: Phillips J. C. , Cohen M. H.
Published: April 2005

If a lattice of point ions is embedded in a free electron gas, the resulting screening can be calculated by first-order perturbation theory. The answer can be expressed in terms of a static wave-number-dependent dielectric function ε(q). Because the plane-wave approximation gives good results for the valence bandwidths in semiconductors, it is interesting to apply the simple idea of dielectric screening to charge distributions in partially ionic zinc-blende and wurtzite semiconductors. To do so one must include the effect of occupied atomic core states. This is easily done in the effective potential representation. One then finds that dielectric screening gives a good approximation to the results of band calculations for the screening of the longest and strongest Fourier component of the lattice potential. Nonlinear effects leading to the formation of covalent bonds will also be discussed.
Nuclear Quadrupole Resonance and Bonding in Solid Layer Type Metal Halides
Authors: Barnes R. G. , Segel S. L. , Jones W. H.
Published: April 2005

Pure nuclear quadrupole resonance spectra have been reported for halogen nuclei in a number of metal halides crystallizing in layer structures of the CdI2 or related types. Because of the extreme smallness of the quadrupole coupling constants, particularly in the case of the dihalides, the possible appropriateness of a purely ionic model to account for the electric field gradients has been investigated. Detailed calculations of the ion-lattice field gradient have been made for a number of compounds representing several types of infinite-layer structure. In no case is the coupling due to the ion-lattice alone sufficient to explain the observed interactions. In fact, comparison with the experimental data suggests that empirical values of the antishielding factor γ∞ about 3–5 times smaller than the theoretical values are appropriate to account for the ion-lattice contribution to the coupling. Covalent bonding between the metal and halogen layers involving only small departures from pure p-bond configurations at the halogens can account for the experimental results. Taking the ion-lattice gradient into account causes in general a small increase in the values of s hybridization needed in the covalent bond model.
Effects of Ionizing Radiations on Alkali Halides Containing Divalent Impurities
Authors: Hayes W.
Published: April 2005

Alkaline earth impurities introduce hole traps into KCl and KBr. Holes of the type X2− (X is a halogen) with 〈100〉 orientation are observed after x-irradiation at 195°K, and are a source of anion vacancies. Iron group ions behave as electron traps in NaF and LiF.
Self-Trapping and Drift Motion of an Electron
Authors: Toyozawa Y.
Published: April 2005

The importance of the acoustical mode lattice vibration for self-trapping of an electron is emphasized in this paper. It is shown that when the coupling constant between the electron and the acoustical vibration exceeds a certain critical value, the effective mass of the electron changes discontinuously to such an enormous value that it is practically allowed to take a localized self-trapping state as an eigenstate, in contrast to the case of polar mode, in which the effective mass changes continuously with coupling constant. This difference is attributed to the different force range of the electron-lattice interaction in the two cases.

The self-trapping state as well as the activated state for the hopping motion are discussed within the framework of adiabatic approximation by making use of Koster-Slater's method. It is pointed out that drift motion is more probable than the hopping motion for the intermediate magnitude of coupling constant.
Spin Resonance of Ion Pairs in Crystal Lattices
Authors: Owen J.
Published: April 2005

Some paramagnetic resonance experiments on pairs of exchange coupled paramagnetic ions in magnetically dilute crystals are described. The exchange parameters found in this way are compared with susceptibility data for the corresponding concentrated salts. For some iridium salts the exchange energy is discussed in terms of a simple model which uses a Morse potential energy curve. The results emphasize the importance in these salts of superexchange through two intermediate nonmagnetic ions and suggest that similar interactions may be important in other antiferromagnetics.
Infrared Spectra of Dilute Solid Solutions
Authors: Morgan H. W. , Staats P. A.
Published: April 2005

The infrared spectra of polyatomic ions in dilute solid solution reflect interactions of the vibrational modes with the lattice environment. The spectra are usually characterized by very narrow bandwidths, and by frequency shifts and changes in absorption intensities which depend upon the host lattice. We have examined the spectra of a number of ions in solid solution in alkali halides. From this data, conclusions have been drawn relative to the symmetries of the ions and the lattice sites which they occupy. The ultimate goal is the use of complex ions as ``probes'' to yield information on crystal lattices. Certain of the ions produced in fused alkali halides are characteristic of chemical equilibria at high temperatures, and have not previously been studied. We have identified several impurities found in the spectra of single crystals from commercial sources. The infrared absorption offers the possibility of determining the types and concentrations of trace impurities in single crystals.
ESR Study of Trapping of Mn Ions along Dislocation Lines in NaCl
Authors: Kawamura Hajimu , Okubo Yoshio
Published: April 2005

There is much evidence that point defects are trapped by dislocation lines. We wished to obtain direct evidence by means of ESR study. Since the structure of the ESR spectrum of manganese ion is quite sensitive to the crystalline field, it is expected to serve as a detector of the local imperfection of the host crystal in which it is dissolved.
Spin Resonance of Transition Metal Ions in Corundum
Authors: Geschwind S. , Remeika J. P.
Published: April 2005

The results of electron spin resonance experiments on a series of transition metal ions in single crystals of corundum are reviewed and interpreted in terms of crystal field theory emphasizing three topics: (1) The strength of the cubic crystal field, (2) the axial field as an indicator of position of the impurity ion, and (3) Jahn-Teller effects in the ground state. The 4d and 5d ions which were examined, i.e., Ru3+, Rh3+, and Ir3+ are found to be strong crystal field cases. In addition, the increased charge of Ni3+(3d7) is shown to be sufficient to drive it to a strong crystal field case (t26e) with S = ½ compared to Co2+ (3d7) which is t25e3 with S = 32. The parameter v which measures the trigonal field potential, was found to be +850 cm−1 in Ru3+ in good agreement with other ions such as Co2+ and V3+ whose cubic field ground states are also orbitally degenerate. In contrast, the determination of v from ESR data on ions with singlet ground states such as Cu3+ and Ni2+ is regarded as less reliable. The Jahn-Teller effect was observed for Pt+ (or Pt3+), Ni3+, and Cu2+.
Polarization of Luminescence
Authors: Clark C. D. , Maycraft G. W. , Mitchell E. W. J.
Published: April 2005

A brief review will be given of the methods of studying the polarization of luminescence and of the theory of the effect in relation to determining the electronic structure of centers. Reference will be made to the work on the alkali halides and diamond.

Detailed experimental results will be presented and discussed of the fluorescence of the 5032 A center in diamond which is formed by heat treatment after irradiation. In these experiments the polarization has been studied as a function of the energy of both the exciting and of the emitted light. Depolarization occurs if the system is excited above the lowest level in the excited electronic state, or decays to a level above the lowest level in the ground electronic state.

A comparison of the results will be given with those expected from centers having various electronic axes.
Electronic Structure of Point Defects in Crystals
Authors: Pryce M. H. L.
Published: April 2005

Impurity ions in insulating crystals can be regarded as isolated electronic systems. Their paramagnetic resonance is determined by their ground state characteristics, which can be derived from application of Hund's rules, together with simple applications of ligand-field theory and consideration of spin-orbit interaction. The paramagnetic resonance is characteristic of the ion and its coordination in the crystal, and furnishes a powerful diagnostic tool. F centers can be regarded as special cases of ions, of particularly simple nature. V centers also can be understood in this way, often in terms of molecular ions. Distortions from the full symmetry of the host crystal site, due to the Jahn-Teller effect, are frequent and predictable. Optical absorption, arising from transitions to higher levels, is closely related to the above properties, and is briefly discussed.
Nonstoichiometry and Lattice Defects in Transition Metal Hydrides
Authors: Libowitz G. G.
Published: April 2005

The relationships between equilibrium hydrogen pressure, hydrogen content, and temperature have been derived for nonstoichiometric transition metal hydrides from both statistical mechanical and thermodynamic considerations. By comparing the derived equations with experimental pressure-composition isotherms, the type of lattice defect causing deviations from stoichiometry as well as the energies of defect formation and interaction can be calculated. This was done for uranium hydride and palladium hydride. The energies obtained were 69 kcal/mole for the vacancy formation energy, and 4.4 kcal/mole for the attractive vacancy interaction energy in uranium hydride. The corresponding energies in palladium hydride were 58.0 kcal/mole and 0.35 kcal/mole. The derived relationships are of general applicability to any nonstoichiometric binary compound which is deficient in the volatile component.
Effect of Added Oxides on p-Conducting Nickel Oxide
Authors: Schwab G.-M. , Schmid H.
Published: April 2005

It is a well-known result of semiconductor physics, that the conductivity of a semiconducting oxide can be shifted in the direction of increased p conductivity or decreased n conductivity by addition of small proportions of oxides of lower cation valency and that the reverse is true in the case of higher valency of the added cation. This effect is understood on the basis of the corpuscular semiconductor theory of Wagner and Schottky and is even used for establishing the nature of the conduction mechanism in certain materials. It is generally supposed that the only necessary condition for this doping effect is solubility in the solid state and that this is granted by a similarity of the cation radii. No importance has been attributed to the chemical nature of the dope, and for this reason we have tried to dope p-conducting nickel oxide with other oxides, differing not only in valence but also in their chemical nature.
On the Structure and Related Properties of the Oxides of Praseodymium
Authors: Eyring L. , Baenziger N. C.
Published: April 2005

The structures of praseodymium oxide phases of composition PrO1.83, PrO1.81, PrO1.78, PrO1.71, and PrO1.69 are discussed in terms of the structures of PrO2.00 and PrO1.50 (C and A types). The way in which the existence of these several stable structures are mirrored in the physical and chemical properties is discussed.
Electrical Properties of Nonstoichiometric Semiconductors
Authors: Becker J. H. , Frederikse H. P. R.
Published: April 2005

The electrical conductivity σ, thermoelectric power Q, and Hall coefficient R are examined as a function of the ratio of hole-to-electron concentrations p/n for a nondegenerate semiconductor at constant temperature. From these relations the fundamental parameters of the material (forbidden band gap, mobilities, and effective masses) can be derived. This approach is particularly applicable to materials whose stoichiometry varies as a function of temperature and vapor pressure of the constituents P. For any model of this equilibrium decomposition, it is easy to transform the calculations in terms of p/n into results as a function of P. As p/n increases, σ passes through a minimum, while Q and R traverse minimum (negative), zero, and maximum (positive) values. These extrema are of special interest. In the simple case of one kind of imperfection, σ, Q, and R become independent of P in a certain pressure range (i.e., when the intrinsic condition n=p has been reached). It is then possible to derive the ratio of mobilities μn/μp and the ratio of the average effective masses mn*/mp* from σ(P) and Q(P) only. Hence, if μn or mn* are known (i.e., from measurements at lower temperatures), one can calculate these parameters for the other charge carrier.
Climb of Dislocations in Magnesium Oxide
Authors: Groves G. W. , Kelly A.
Published: April 2005

Detailed electron microscope observations of plastically deformed and annealed magnesium oxide have been made. After cold work the material contains trails of elongated prismatic dislocation loops, of which the majority corresponds to a sheet of interstitial ions. On annealing at temperatures between 850° and 1600°C these trails break up into circular loops of edge dislocation and the loops then increase in size. The process occurs by the motion of vacant lattice sites along dislocation lines and possibly through the bulk material. The kinetics of the former process is described. A theory of breakup by pipe diffusion has been developed and used to obtain an activation energy for the motion of point defects in the core of a dislocation of ∼3.1 ev.
On the Theory of the Photoadsorptive Effect on Semiconductors
Authors: Wolkenstein Th. , Karpenko I. V.
Published: April 2005

On the basis of the electron theory of chemisorption, a criterion is deduced for the positive and negative photoadsorptive effect on semiconductors (photoadsorption and photodesorption). A relation is established between the sign of the effect and the nature of the adsorbent and adsorbate, the previous treatment of the sample, and the experimental conditions (temperature and pressure). The available experimental material is analyzed and interpreted from the standpoint of the proposed theory.
Defect Structures and Transport of Matter in AgBr
Authors: Lawson A. W.
Published: April 2005

The wide diversity of studies carried out on transport phenomena in AgBr permits a critical evaluation of the success and failures of existing theories of ion kinetics and defect equilibrium. Some unsolved problems relating to polarization, microwave dielectric constant, creep, thermoelectric power, and their relation to mobility and density of defects are discussed.
Disorder and Oxygen Transport in Cadmium Oxide
Authors: Haul R. , Just D.
Published: April 2005

Oxygen-18 exchange between gaseous oxygen and cadmium oxide crystals has been studied in the temperature range 630° to 855°C. Since isotope equilibrium is not instantaneously established at the crystal surface an appropriate solution for this particular diffusion problem has been given. In this way it is possible to evaluate rate constants (K) of the phase boundary reaction as well as lattice diffusion constants (D): D=3.8·106exp(−92±4/RT);  K=1.3·102exp(−49±11/RT). The influence of the ambient oxygen pressure (D∼po2−1/5) indicates that a vacancy mechanism is operative in the diffusion of oxygen. This is substantiated by the finding that diffusion is enhanced by incorporation of Li2O. From experiments with doped crystals the fraction of vacancies can be estimated, e.g., 4.4·10−4 in ``pure'' CdO at 790°C and 0.16 atm O2. On the basis of thermodynamic considerations the energy of formation of defects can be estimated at 29 leaving 63 kcal/mole for the activation energy of the diffusion process proper.

The rate constant of the phase boundary reaction increases with decreasing oxygen pressure (K∼po2−⅓) as well as with increasing Li2O addition. These findings offer a possibility for the suggestion of a mechanism of the surface exchange process.
On the Gyulai-Hartly Effect in Single Crystals of Potassium Iodide at Temperatures between 77° and 297°K
Authors: Hovi V. , Mäntysalo E. , Ketolainen P.
Published: April 2005

The increase of the dark current caused by plastic deformation in potassium iodide crystals has been measured at temperatures between 77° and 297°K. The Gyulai-Hartly effect was not found to be dependent on temperature in this range. The maximum current induced by the deformation decreased in repeated deformation experiments, as has also been observed at higher temperatures. At 77°K a charge flow in the opposite direction to the Gyulai-Hartly effect was found when the load was removed. On further deformation, a charge flow in the above direction was observed, instead of the expected Gyulai-Hartly effect. As a result of successive deformation experiments, saturation currents associated with work hardening were measured. Potassium iodide crystals containing R′ centers did not show any Gyulai-Hartly effect at 297°K.
Magnetic Shielding Factors of a System of Concentric Spherical Shells
Authors: Schweizer Felix
Published: April 2005

General expressions are developed for the shielding factors of concentric spherical shells of linear isotropic magnetic material. Approximate results are given for shells of highly permeable material which are thin compared to their radii.
Vapor Growth of Cadmium Telluride Single Crystals
Authors: Lynch R. T.
Published: April 2005

Single crystals of CdTe have been grown from the vapor. Crystals grown by the methods described grew either as hexagonal rods or dodecahedra. Both types of crystals have been identified, by back-reflection x-ray photographs, as cubic CdTe. The exhagonal rods have extensive micro-twinning.
Ultrasonic Damping at Kilocycle Frequencies in Aluminum at Low Temperatures
Authors: Hutchison T. S. , Rogers D. H.
Published: April 2005

Measurements of 40-kc acoustic damping in well-annealed polycrystalline, 99.996% pure aluminum at temperatures between 4.2° and 273°K are compared with theories of dislocation damping by Granato and Lücke and by Rogers. Two dislocation systems are indicated, both pinned by impurity atoms, with the average loop length of the one greater than that of the other. An amplitude-dependent dynamic loss and an amplitude-dependent breakaway loss for the long-loop system, and the usual amplitude-dependent breakaway loss for the short-loop system are observed. The temperature dependence of various parameters important to the several types of damping is discussed and limits to the values of the types deduced for different temperatures. Electron-lattice damping is observed at temperatures below 60°K and is found to be larger than theory predicts.
Experimental Evidence of Landau Damping in Electron Beams
Authors: Caulton M. , Hershenov B. , Paschke F.
Published: April 2005

Investigations have been made of plasma oscillations by studying space-charge waves in velocity-modulated electron beams. The convection current in a velocity-modulated slowly-drifting electron beam was measured as a function of distance from the modulating cavity. The experiments indicate that in the presence of an appreciable velocity spread, the fast space-charge wave is damped while the slow space-charge wave remains unattenuated. The measurements were made under conditions where the velocity spread is dominated by lens effects in the electron-optical system. The results confirm qualitatively the theory of Berghammer and thus demonstrate the existence of the much disputed Landau damping.
Kinetic Theory of Dislocation Climb. I. General Models for Edge and Screw Dislocations
Authors: Thomson R. M. , Balluffi R. W.
Published: April 2005

General kinetic models are established for the climb of edge and screw dislocations. The climb of a straight unconstrained edge dislocation is considered in terms of the diffusion of nonequilibrium point defects to (or from) the line and their absorption (emission) and destruction (creation) at the line. The climb is nucleated by the formation of short rows of defects which are attached to the edge of the extra plane and are bounded by jog pairs. Climb occurs by the growth of these aggregates until they destroy each other by mutual collisions. No a priori assumptions are made about the ability of either the dislocation or the jogs to maintain local point defect equilibrium during climb, and account is taken of rapid defect diffusion along the core. Effects of nonequilibrium defects in perturbing the jog population are also included. Equations describing this edge dislocation climb are developed but are left in a general form. Complete solutions are worked out in a following paper (Part II). Complications which arise when geometrical constraints and line curvature are present are discussed, and a description of the relationships between curvature, macroscopic line tension, and jog density is given. It is concluded that the results for the unconstrained climb model can be used in many such cases over a considerable range of conditions. The treatment of screw dislocation climb focuses attention on the climb of an initially straight dislocation into a multi-turned helix. The detailed mechanisms are found to depend strongly upon the geometry and mobility of point defects and point defect aggregates on the core, and therefore only a qualitative theory is given. It is suggested that in many crystals vacancies largely dissociate into kinks when they enter the core, and that the helical turns build up rather uniformly along the line by the aggregation of ordered arrangements of these kinks.
Temperature Dependence of Ferromagnetic Uniaxial Anisotropy Coefficients
Authors: Callen Earl R.
Published: April 2005

The problem of a spin one Weiss molecular field Hamiltonian with uniaxial anisotropy is solved exactly. The free energy contains magnetocrystalline anisotropy terms of all even order Legendre polynomials. The P2 coefficient varies as the third power of the magnetization rather well even for fairly large anisotropy, and over the entire temperature range. The higher order terms can be of both signs, and all change sign as the temperature is increased.
Thermoelectric Properties of Bismuth-Antimony Alloys
Authors: Smith G. E. , Wolfe R.
Published: April 2005

The thermoelectric figure of merit (z), resistivity, and Seebeck coefficient have been measured between 20° and 300°K on single crystals of several alloys in the range from 1% to 40% antimony in bismuth. These materials are semimetals (0 to 5% antimony) or small energy gap intrinsic semiconductors (5 to 40% antimony) and all are n type. The Seebeck coefficients and figures of merit are anisotropic, the larger values being those measured parallel to the threefold symmetry axis. In the 12% antimony alloy the larger z rises from 1.0×10−3/°K at 300°K to a maximum of 5.2×10−3/°K at 80°K and falls rapidly at lower temperatures. All of the alloys between 3% and 16% antimony have a maximum z near 5×10−3/°K at a temperature between 70°K and 100°K. The 5% antimony alloy has the highest z at room temperature (z=1.8×10−3/°K). In this material, the Seebeck coefficient is practically constant (S=−110±10 μv/°K) between 77° and 300°K and the ratio of the thermal to electrical conductivities is close to the theoretical Wiedemann-Franz ratio above 100°K. As a result, z is inversely proportional to the absolute temperature (zT=0.52±0.05) between 100° and 300°K. In the 12% antimony alloy, S rises from −110 μv/°K at 300°K to −220 μv/°K at 20°K. A specimen of this material, doped with 0.01% lead, is p type below 42°K. A qualitative explanation of these results is given in terms of mixed conduction by electrons and holes having properties similar to those in pure bismuth. The use of these alloys (and semimetals in general) in thermoelectric refrigeration at low temperatures is discussed.
A Photometric Procedure for Weight Determination of Submicroscopic Particles Quantitative Electron Microscopy
Authors: Zeitler Elmar , Bahr Gunter F.
Published: April 2005

A photometric procedure for rapid determination of weight of isolated particles down to a size of 200 A is described. Under normal conditions of electron microscopy, weights of down to 10−18 g can be determined with an inaccuracy of less than 10%. By lowering the accuracy or using more elaborate measures (such as very low accelerating voltage) one to two orders of magnitude for the lower weight limit can be gained. The method can now be applied to population studies of biologic particles, especially those of inhomogeneous and odd-shaped entities. Individual losses of matter through the action of enzymes and the uptake of specific stains can be measured quantitatively. The method extends the possibilities of individual mass-weight determination to the biologically important region of submicroscopic particles.
Superconducting Film Geometry With Strong Critical Current Asymmetry
Authors: Edwards H. H. , Newhouse V. L.
Published: April 2005

It is shown that film critical current, defined as the maximum current for which a film shows no resistance, can be strongly increased in one direction and strongly decreased in the other by the field from two current carrying conductors placed parallel to the film edges.

The effect is shown to be due to mutual cancellation of the magnetic fields normal to the film created by the wire currents and the film current. It appears to make a flat film superconductive rectifier possible.

It is proved that the symmetrical increase of critical current due to the proximity of a superconducting ``shield'' plane is due to a similar mechanism, and that fields normal to the film surface are largely responsible for the broad current induced transition of flat ``unshielded'' films.

It is also shown that with mutually opposed wire currents the variation of critical current with wire current exhibits a significant hysteresis. This effect may have applications to digital storage.
Approach to the Ideal Magnetic Circuit Concept through Superconductivity
Authors: Cioffi P. P.
Published: April 2005

The ideal magnetic circuit concept in which leakage and fringing flux are absent has not heretofore been realized because of the absence of magnetic insulators under normal conditions. Below the transition temperature, however, a superconductor is a perfect magnetic insulator and a superconducting enclosure of PbBi around the source of mmf and the air gap of an experimental electromagnet operating in liquid helium has been found to reduce leakage flux from 5.1 to 0.39 maxwells per maxwell of air gap flux. The small residual leakage flux observed is accounted for by leakage in the space occupied by the winding. No detectable fringing flux was observed outside the superconducting magnetic insulator surrounding the air gap. The flux within the air gap follows the contour of the superconducting enclosure and the degree of field uniformity within is determined by the precision of alignment of the enclosure surfaces. The large reduction in size and weight possible under ideal magnetic circuit conditions makes operation in liquid helium feasible. In a magnetic circuit for maser application, a reduction in weight of nearly 2 orders of magnitude was possible partly because of the reduction in air gap length resulting from the inclusion of the magnetic circuit in the cryostat and partly because of ideal magnetic circuit operation.
Effect of Noncrystallizable Components on the Crystallization Kinetics of Polymers
Authors: Gornick F. , Mandelkern L.
Published: April 2005

The effects of chain irregularities, treated as randomly introduced copolymeric units and of added monomeric diluents, on the nucleation rate of crystallizing polymeric systems have been calculated. A marked attenuation in the nucleation rate is expected under certain conditions as a consequence of the varying composition of the melt. The decrease in the nucleation rate becomes more pronounced at the lower undercoolings and as the concentration of the noncrystallizing component increases.

The Avrami mathematical formulation for the kinetics of phase changes can be generalized to allow for nucleation and growth rates which vary with the amount of material transformed. The resulting isotherms for copolymers are no longer superposable, superposability being characteristic of crystallization under conditions of constant nucleation and growth. Possible error in the interpretation of crystallization kinetics utilizing the simplified version of Avrami's equation is pointed out, as is the extreme sensitivity of the crystallization process to the presence of small amounts of chain irregularities.
Elasticity and Internal Friction of α-Fe2O3
Authors: Makkay R. W. , Geiger G. H. , Fine M. E.
Published: April 2005

Young's modulus and internal friction of natural crystals of α-Fe2O3 (Congonhas, Brazil) were measured as functions of temperature in the region of the Morin transition with and without a 1570-oe magnetic field. Nonelastic components of strain occur and these, we suggest, are due to stress-induced changes in the directions of the magnetization vectors.
Structure of 〈100〉 Dielectric Breakdown Dendrites
Authors: Pasternak J. , Davisson J. W. , Vaughan W. H.
Published: April 2005

Direct evidence is presented that 〈100〉 dielectric breakdown dendrites on LiF cleavage surfaces are grooved features that are flanked by volume 〈110〉 channels. The dendrite has presumably resulted from disruptive forces attending an electronic breakdown process. No evidence of primary involvement of dislocations in the process of dielectric breakdown was found. Indirect evidence is presented that Y branches and the etch features surrounding random sites represent the surface intersections of 〈110〉 spikes that are associated with submerged electrical breakdown paths. The existence of the 〈110〉 dielectric breakdown dendrite and its relationship to the Y branch is noted.
Precision Determination of the Lattice Constant by the Kossel Line Technique
Authors: Heise B. H.
Published: April 2005

A high accuracy lattice constant determination of a specimen is possible through the analysis of the x-ray diffraction image known as Kossel lines. In the present work general formulas are derived by which the lattice constant can be obtained from the Kossel line picture. The lattice constant of a nickel specimen is then measured to demonstrate the applicability of the method.
Electron Trajectories in a Field Emission Microscope
Authors: Russell Allan M.
Published: April 2005

Trajectories of electrons in a field emission microscope have been calculated for the case of a tip and screen taken as confocal hyperboloids of revolution. The calculations were done in prolate spheroidal coordinates by an iterative method utilizing Hamilton's equations. An IBM digital computer has been programmed to accept values for the initial position and momentum of the electron, the tip and screen radii (each measured at the apex), the tip-to-screen distance and the applied voltage. A calculation yields the final values of position and momentum components at the screen as well as the transit time for the electron. The results of the calculation have been used to predict a field emission pattern which is compared with an experimental pattern. Good agreement is obtained without the use of any adjustable parameters.
Dependance of Power Radiated on Beam Current in a Magnetic Undulator
Authors: Motz H. , Walsh D.
Published: April 2005

It was found that with a particular 10-cm electron linear accelerator power radiated from undulating electrons in the 8-mm band increased as (current)1.7. At higher frequencies there was only an approximately linear increase. A large undulator, designed to radiate in the fundamental mode at 8 mm gave a half-watt power output. This is in general agreement with the theoretical radiation from electrons combined with the experimental power law.
Damage Produced in Ge at Room Temperature by Indentation
Authors: Johnson O. W.
Published: April 2005

Damage produced at room temperature by a spherical indenter on etch-polished Ge surfaces and the effect of subsequent annealing at 550°C was studied with an optical microscope using interference contrast techniques. No evidence for dislocation glide at room temperature was obtained. Dislocation generation and motion during subsequent anneals occurred only in association with microcracks, which were in all cases observable without etching. By using dislocation etch pit counts to infer glide step heights, it was estimated that steps of height less than 15 Å may be detected with interference contrast under favorable conditions. Polished TiO2 and MgO cleavage surfaces were also indented and examined. Clear evidence for dislocation generation and motion was obtained in both cases.
High-Pressure Electrical Behavior and Equation of State of Magnesium Oxide from Shock Wave Measurements
Authors: Ahrens Thomas J.
Published: April 2005

A decrease in resistivity of MgO from >105 to ∼103 Ω·cm is observed when thin single crystals are shocked in the [001] direction to 920±70 kbar. This effect may be produced by several electronic processes, or by ionic transport in which the effective O= or Mg++ diffusion constants are increased by perhaps a factor of 1039 from those calculated at high pressure (according to Zener strain-energy model). Voltages are observed during passage of various-strength (70 to 936 kbar) shock fronts through the specimen. These voltages approximately scale as the inverse of the specimen thickness and may arise from net volume polarization (∼0.2 to ∼9 V/cm). Some Hugoniot data to 660 kbar (including measurement of elastic-shock amplitude varying from 35 to 89 kbar) are presented.
Defects in Natural Quartz
Authors: Spencer W. J. , Smith W. L.
Published: April 2005

X-ray diffraction topographs show at least two types of defects in natural quartz, planar defects which are parallel to the natural quartz faces and needle-like defects. The planar defects color when exposed to γ irradiation, indicating these are sheets of substitutional aluminum, with an interstitial alkali ion nearby for charge compensation. The linear defects are similar to macroscopic needles of TiO2 sometimes found in quartz and have previously been associated with dislocations by Lang. Both types of defects show diffraction contrast when observed from different Bragg planes. There does not seem to be a simple relation between either type of defect density and acoustic loss at 300°K in natural quartz.
Controlled Domain Tip Propagation. Part II
Authors: Spain R. J. , Jauvtis H. I.
Published: April 2005

The controlled propagation of domain tips in appropriately prepared thin magnetic films has been shown to lead to a wide variety of possible thin-film devices. Two particular devices which utilize this technique are discussed. The first is a new type of thin-film shift register the operation of which depends upon the speed and directionality of domain tip propagation. The second is a system of thin-film, all-magnetic logic which utilizes, in addition, the forces of interaction between domain tips brought into proximity. The construction and operation of prototype devices of this sort are described.
Twinning of Iridium in a Field Ion Microscope
Authors: Rendulic Klaus D. , Müller Erwin W.
Published: April 2005

Multiple twinning of [111]-oriented iridium crystals caused by the field stress is observed in a field ion microscope. The twin plane is pure (111) and the direction of shear [112̄]. The twins are formed only at small tip radii. The twins are stable enough to survive annealing to 1000°C and controlled field evaporation of many atomic layers.
Orientation Effect in GaAs Injection Lasers
Authors: Abrahams M. S. , Pankove J. I.
Published: April 2005

An orientation effect was found with regard to the emission patterns observed on GaAs injection lasers. The emission in the [11̄0] direction is considerably more uniform than that in the [110] direction. The beadiness observed on the (110) plane is believed to be due to linear low-resistivity regions parallel to [110]. These result from zinc decoration of the misfit dislocations parallel to [110]. The absence of zinc decoration on the [11̄0] set of misfit dislocations can explain the absence of local bright spots and, thus, the more uniform emission in this direction.
Transient Response of Double Injection in a Semiconductor of Finite Cross Section
Authors: Baron R. , Marsh O. J. , Mayer J. W.
Published: April 2005

The transient response of the current to an applied voltage step is analyzed for a structure exhibiting double-injection behavior, subject to the condition that both initial and final states are describable by the same double-injection regime. The analysis is carried out for both the one-dimensional case (no surface recombination) and the case of a two-dimensional slab (surface recombination included). For the one-dimensional case, the response is an Ohmic current step followed by an exponential decay with a time constant equal to the high level, common lifetime. For the two-dimensional case the response is similar, except that the decay following the current step is described by a sum of exponential decays with time constants determined by the transverse modes of the system. The time constant for the longest lived mode is not equal to the effective lifetime found by Hiroto et al. for the steady-state case, but may differ from it by as much as 23.4%. The high level photoconductive decay is also analyzed for the two-dimensional case. Two types of initial excitation are considered, a steady state excitation abruptly terminated and a brief flash of light abruptly terminated. In both cases the light is allowed to have an arbitrary penetration depth. A comparison of the results shows that the decay from a voltage step invariably gives less interference from the higher modes and in general is a more attractive method of measuring the high level lifetime. Experimental results on a silicon p—π—n structure illustrating the above are also given.
Direct Correlation between Domain Size and Coercive Force in Iron Alloys
Authors: Pesch Joseph A.
Published: April 2005

The Bitter technique was used to observe magnetic domain patterns on specimens of polycrystalline iron and iron containing 2.5 wt % silicon. Domain patterns that appear on grains oriented close to (110) [001] with respect to the specimen surface were observed. A critical domain size indicator S, based on measurements of domain size with the specimen in the demagnetized state, was developed and found to vary inversely with the coercive force. Values of S ranging from 0.23×10−3 cm to 1.2×10−3 cm were measured on iron specimens having coercive force values from 2.75 Oe down to 0.43 Oe. Similar results were obtained for the 2.5% Si-Fe alloy. Domain patterns were also observed under changing applied field conditions. In the region of the coercive force, ``spike'' domains annihilated one another and also joined together to form a continuous volume of reverse magnetization. The domain interactions suggest an unstable condition between domain wall energy and volume energy, followed by the interaction of domains which resulted in a lower wall energy.
Quantum-Mechanical Reflection of Electrons at Metal-Semiconductor Barriers: Electron Transport in Semiconductor-Metal-Semiconductor Structures
Authors: Crowell C. R. , Sze S. M.
Published: April 2005

Numerical methods have been used to solve the Schrödinger equation for the quantum-mechanical reflection coefficient (QMR) of electrons at metal-semiconductor barriers. The calculations were carried out for a ``MacColl'' type barrier and a ``Thomas-Fermi'' type barrier. It was found that for both barrier models the QMR≳50% for an electron incident on a barrier with energy less than 0.05 eV with respect to the barrier maximum. The QMR decreases slowly with increasing energy. On the basis of these calculations and calculations of the effects of electron-phonon scattering in the collector and emitter semiconductors of semiconductor-metal-semiconductor structures, the predicted net current transfer ratio in such structure is less than 0.5 exclusive of base-transport losses.
Hot-Electron Transport in Semiconductor-Metal-Semiconductor Structures
Authors: Sze S. M. , Crowell C. R. , Carey G. P. , LaBate E. E.
Published: April 2005

The low-frequency common-base current transfer ratio α0 for hot-electron transport in semiconductor-metal-semiconductor point-contact-transistor structures has been measured as a function of metal film thickness and temperature. Measurements have been made possible by the use of a cantilever-beam mechanism capable of contact-separation adjustments as low as 10 Å. From these results, the ballistic mean free paths for electron transport in the metal base have been obtained as a function of temperature and electron energy.

Au, Ag, Pd, and Al have been used as the base metals; Ge, Si, GaAs, and GaP as the emitter semiconductors; and Ge, Si, GaAs, GaP, CdSe, and CdS as the collector semiconductors.

The measured values of α0 obey the simple expression α0=α* exp(−W/LB), where α* is the current gain extrapolated to zero metal-base thickness, and LB the ballistic mean free path. Of the structures investigated GaP-Au-Ge exhibits the highest α*, about 0.5. With≈100-Å base thickness, the highest α0 obtained is about 0.3 (for Si–Au/Ag–Ge and GaP–Au/Ag–Ge structures). The ballistic mean free paths for 1-eV electrons at room temperature are 265 Å for Ag, 220 Å for Au, 90 Å for Pd, and ≈100 Å for Al. The results are in reasonable agreement with theoretical expectations.
Formation of Stacking Faults in Single-Crystal Films of Copper Grown on NaCl, KCl, and LiF Substrates
Authors: Rowe A. P. , Brockway L. O.
Published: April 2005

Copper films 700 Å thick deposited on NaCl or KCl at 330°C are preferentially oriented on the (001) plane, and after heating at 630°C they exhibit complex stacking faults of 2 to 3 μ in width. Examination of carbon replicas and of platinum-shadowed copper films shows that straight surface terraces of 50 to 100 Å in elevation occur over the faults and that these terraces are formed in the copper film while on the substrate. Copper deposited on cleaved LiF substrates shows several orientations, and annealing up to 745°C produces no preferential growth among them; no stacking faults appear in the annealed film. On the LiF preheated above 700°C before cleaving, copper films are deposited as single crystals and when annealed at 745°C show complex stacking faults and terraces as observed with the chloride substrates. In all cases the faults are believed to form under compressive stresses in the single crystal of copper as the film on the substrate is cooled from a high temperature.
Plasma Diagnostics using Lasers: Relations between Scattered Spectrum and Electron-Velocity Distribution
Authors: Brown Terrence S. , Rose D. J.
Published: April 2005

Laser light scattered from plasma electrons can be used to determine the electron density and velocity distribution. The process is classical Thomson scattering, and the scattered spectrum is constructed of the Doppler shifts of the electrons. The spectrum I(k), which appears at all angles and over a range of wave-numbers, is uniquely related to the electron velocity distribution f(v). Either can be obtained from the other, and we derive the expressions I(k) = Lf(v) and f(v) = L−1I(k) relativistically correctly. We also discuss the amount of information about f(v) obtainable from a simple measurement of the scattered spectrum. The electron density and mean speed can be measured easily; more subtle features depend upon accurate observation of the low-intensity wings of the spectrum.
Temperature Dependence of Dielectric Breakdown of Potassium Chloride Crystals under dc and Pulse Voltages
Authors: Kaseta Francis W. , Li H. Tung
Published: April 2005

The dielectric breakdown strength of a KCl single crystal in the temperature range 4.2°–425°K and of a mixed crystal (75/25 mole % KCl-RbCl) between 77° and 375°K was measured with dc voltage and with pulses of 1- and 10-μsec risetime. The dc strength lies below the pulse strength over the entire temperature range. Pulse and dc strengths gradually rise from 4° to 77°K. The temperature characteristic of the dc breakdown strength traverses a maximum that vanishes completely for 1-μsec risetime. The dc strength for the mixed crystal lies above that of pure KCl at low temperature and drops more sharply in the high temperature range.

Von Hippel's and Fröhlich's breakdown criteria are re-examined. The former is formulated quantitatively and its necessity demonstrated within the framework of the ``one-electron'' intrinsic breakdown theory. The experimental results are in substantial agreement with theoretical values, based on von Hippel's criterion and Callen's calculation.