bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Dislocations on the Thermal Conductivity of Lithium Fluoride
Authors: Sproull R. L. , Moss M. , Weinstock H.
Published: April 2005

Measurements of the thermal conductivity K of Harshaw LiF crystals were made over the temperature range 2°–100°K. A freshly cleaved crystal exhibited K values in agreement with the measurements of Berman, Foster, and Ziman (1956). Annealing raised the maximum K by a factor of two. Dislocations were added by compression, and the dislocation density was determined by the methods of Gilman and Johnston. The K values below 30°K for the deformed specimens were approximately proportional to T2, in agreement with Klemens' theory, but the reduction in K by introduction of dislocations was much larger than Klemens' predictions. The phonon mean free path when limited by dislocation scattering was found to be approximately (4×106)/DT, where D is the number of dislocation lines/cm2 and T is the absolute temperature.
Thermal Expansion of Ice
Authors: Butkovich T. R.
Published: April 2005

Linear thermal expansion coefficients of natural and artificial single ice crystals, commercial ice, and snow ice were determined in the temperature range near 0 to −30°C. There was no measurable difference in the coefficients of linear thermal expansion parallel and normal to the c axis of single crystals or polycrystalline ice. However a steady decrease of expansion coefficients with each succeeding measurement on the same ice specimen was observed. The total decrease was of the order of 2×10−6, while an estimated error calculation yielded a value of about 4×10−7. An entirely satisfactory explanation of this phenomenon cannot be given at this time, and further investigation on this point would be desirable. Values of Cv, the specific heat at constant volume, were calculated from thermodynamic relationships. Average Cp/Cv values were 1.030. Gruneisen's constant was found to average 0.78, and essentially independent of temperature between 0°C and −30°C.
Impurity Compensation and Magnetoresistance in p-Type Silicon
Authors: Long Donald , Motchenbacher C. D. , Myers John
Published: April 2005

A new method is proposed for determining the separate concentrations of acceptor and donor impurities in crystals of p-type silicon, and thereby the degree of compensation of acceptors by donors. The method involves finding the total concentration of impurities in a sample from a measurement of the weak-field transverse magnetoresistance at 77°K and combining this result with the excess of acceptors over donors determined from a room-temperature resistivity or Hall effect measurement. An empirical ``master curve'' of magnetoresistance vs impurity density has been constructed for this purpose. The impurity densities for the master curve were measured by the usual method of fitting a theoretical carrier concentration vs temperature equation to an experimental curve obtained from Hall effect data.
Line Widths in Polycrystalline Yttrium Iron Garnet
Authors: Van Uitert L. G. , Swanekamp F. W. , Haszko S. E.
Published: April 2005

The line widths at the half-power point for ferromagnetic resonance in a number of polycrystalline yttrium iron garnet samples have been measured at 16 kmc.

It has been determined that, starting with mixtures of Y2O3 and Fe2O3, sound parts with small grain size and having line widths as low as 35 to 40 oersteds can be obtained on the iron-rich side of stoichiometry in Y3Fe5O12. However, narrower line widths (∼20 oersteds) in large grained materials are obtained by using less than the stoichiometric amount of iron and firing at temperatures higher than 1450°C. This is due to minimizing the disrupting influences of oxygen loss in iron-rich areas at high temperatures.

Line widths do not appear to be broadened by the addition of small amounts of nickel, cobalt, or manganese to convert excess iron to high resistance forms of spinel in the iron-rich compositions.
Sputtering Yield of Germanium in Rare Gases
Authors: Laegreid N. , Wehner G. , Meckel B.
Published: April 2005

Sputtering yields of germanium bombarded by Xe+, Kr+, A+, Ne+, and He+-ions under normal incidence at energies up to 400 ev have been determined. Yield vs ion energy curves consist of three parts; (1) a low-energy tail (possibly caused by a process of stepwise sputtering), (2) a region in which yield rises proportionally with ion energy, and above ion velocities of ∼3×106 cm/sec, (3) a region in which the yield rises less than proportionally with ion energy.

The slope in the proportional region is largely determined by the energy transfer factor, η=4m1m2/ (m1+m2)2. Surprisingly, the ``cut in'' energies do not follow V0∼H/η (H=heat of sublimation) but are found to be much lower than expected for the lighter gases. The empirical result, V0∼H(m1)½/η (m1=atomic weight of ion), is not yet understood.
Experimental Method for Developing Minute Flaw Patterns in Glass
Authors: Levengood W. C.
Published: April 2005

A new chemical etching technique was used to study minute flaw patterns in glass. The etched structure disclosed that the minute defects react to the chemical treatment in a different manner than ordinary fissures. Flaw patterns formed at the tips of slow-moving internal cracks were analogous to dislocation phenomena in crystals.

Oriented and repeating flaw groupings were observed in various types of glass. These patterns are produced above the ``strain point'' and were shown to be influenced by permanently induced stresses and internal homogeneity.

Fracturing by localized stresses created flaw patterns radiating from the point of origin with shapes similar in appearance to shock wave phenomena. The impact breaking strength of glass containers was directly influenced by the number of flaws. The flaw distribution decreased rapidly with decreasing diameter of glass fibers.
Domain Boundary Configurations during Magnetization Reversals
Authors: Becker J. J.
Published: April 2005

The signal resulting from the application of an alternating field while a magnetization reversal is taking place yields information about the total domain boundary area contributing to the reversal at each moment. This technique is used to show that the variation in rate during a reversal in a 65 Permalloy tape core corresponds to changes in the area of moving domain boundary, whereas in a 3¼% silicon-iron single crystal picture frame specimen the area of moving domain boundary remains approximately constant, and variations in reversal rate therefore correspond to variations in velocity.
Water Waves Produced by Explosions
Authors: Kranzer Herbert C. , Keller Joseph B.
Published: April 2005

Explicit formulas are found for the height of the water waves produced by an arbitrary axially symmetric initial disturbance in water of finite depth. The initial disturbance can be either a distribution of impulse or an elevation or depression of the surface or a combination of these. Upper bounds on the wave height are given to be used when the approximate size of the initial disturbance is known, but not its detailed shape. These results are applied to determine the wave resulting from the explosion of a typical large bomb above the surface. The corresponding formulas for waves in a one-dimensional channel are also derived and are compared with experimental results.
Double Bragg X-Ray Scattering from Cold-Worked Metals
Authors: Ogier W. T. , Wild R. L. , Nickel J. C.
Published: April 2005

The average small angle double Bragg scattering from moderately cold-worked polycrystalline metals has been calculated ignoring extinction. The predicted scattering is of the correct order of magnitude. Tests involving dependence on grain size prior to cold work, density of the metal, degree of plastic deformation, and anisotropy have been made and appear to agree with the calculation.
Secondary Electron Emission from MgO Thin Films
Authors: Whetten N. Rey , Laponsky A. B.
Published: April 2005

MgO thin films have been prepared and their secondary electron emission properties examined using both single pulse and dc measurement methods. High yields in the range of 15–20 are observed. The films are crystalline with an average crystal diameter of 100–500 A, comparable to the escape depth of the secondaries. The high yields are found to result primarily from the properties of bulk crystalline MgO rather than from thin film phenomena. Field enhanced emission is however observed and has been found to enhance the yield under some conditions by as much as 20%. The most probable energy of emission of the secondaries is about 1 ev. The yield of the films decreases upon exposure to water vapor and carbon dioxide. The films are found to be fairly stable under electron bombardment.
Proposed Microwave Mixer Diode of Improved Conversion Efficiency
Authors: Valdes L. B.
Published: April 2005

By using convergent spherically symmetrical flow of minority carriers in a semiconductor it is possible to improve the conversion efficiency of microwave mixer diodes. The proposed structure utilizes a hemispherical p-n junction with a sink for minority carriers in the center. The admittance of such a structure remains small up to fairly high frequencies. Over a limited frequency range, it may be possible to obtain a negative conductance.
Internal Double Reflection in a Perfect Crystal
Authors: Guinier A. , Guyon E.
Published: April 2005

The theory of double Bragg reflections in single crystals is derived on both a kinematical and dynamical basis. Experiments are reported using single crystals of LiF, diamond, aluminum-copper, pentaerithritol, and stilbene, and comparisons made with the theory.
Small Angle Scattering from Dislocations in Deformed Single Crystals
Authors: Seeger Alfred K.
Published: April 2005

It is shown that in spite of the occurrence of double Bragg scattering effects small angle scattering of x-rays from dislocations in cold-worked crystals should be observable, provided face-centered cubic crystals deformed in tension at low temperature are used. In stage II of the stress-strain curve the dislocation arrangement is essentially that of piled-up groups. The small angle scattering from such groups has been worked out, treating both the first-order (linear elastic theory) and second-order (nonlinear elastic theory) effects. The first-order effect dominates if the scattering vector g is normal to the glide-plane, whereas the second-order effect dominates if g lies in the glide-plane. If both effects can be observed, interesting information on the density and the arrangement of dislocations can be derived.
On the Theory of the Peltier Heat Pump
Authors: Rittner E. S.
Published: April 2005

The figure of merit for a single stage Peltier heat pump is optimized in the region of partial Fermi degeneracy. A more rigorous treatment is presented of the properties of a cascade operating at maximum coefficient of performance. Finally, the heat leak in the absence of current flow is called to attention as a serious problem in devices with excess capacity.
Mechanism of Cratering in Ultra-High Velocity Impact
Authors: Cook Melvin A.
Published: April 2005

The equations of the hydrodynamic theory of penetration of targets by shaped charge jets are presented first in general form. These equations are then expressed in the ideal form and examined by experimental observations. Then a nonideal theory is presented that takes into account heat losses by compression, shock heating, and radiated shock waves. The conditions for impact explosions of targets are then discussed and a theory extended to cover the entire velocity range of impact from the plastic deformation threshold vσ to well above the impact explosion threshold vc. Some experimental evidence relating to this more general theory is also presented.
On the Mechanism for Carrier Excitation in CdS
Authors: Snyder D. D. , Bleil C. E.
Published: April 2005

Induced conductivity in CdS crystals produced by electron bombardment (cathodoconductivity) and the associated x-ray production have been studied employing electrons in the 30- to 60-kev range. The conductivity induced solely by these x-rays has been studied. Using classical x-ray theory, the production and absorption of x-rays in the experimental crystals have been calculated. Some confirmatory data are presented. From calculated excitation rates and observed conductivities the x-rays produced by impinging electrons are shown to be sufficient to explain the effects observed in cathodoconductivity, and may be significant in cathodoluminescence.
Stress Waves and Fracture Surfaces
Authors: Andrews E. H.
Published: April 2005

Surface markings observed in the brittle fracture of certain frozen rubbers display striking wave-like characteristics. They have been identified as ``Wallner'' lines, caused by the interaction of the fracture front with stress waves emanating from the region of the fracture front itself. These oscillations are possibly caused by the supply of excess energy to the fracture tip.

A value of approximately 1:2 is obtained for the ratio of fracture velocity to wave velocity.
Space Charge in Semiconductors Resulting from Low Level Injection
Authors: Green Milton
Published: April 2005

A solution of the continuity equations is obtained for the space charge distribution by assuming (1) that deviations from neutrality are small, and (2) that the space charge fields, which are a consequence of the terms containing ▿·E in these equations give rise to pure diffusion and pure ``drift-wave'' terms with time dependent coefficients. It is, for equal numbers of holes and electrons initially injected, e[(p−p0)−(n−n0)]=−τρ∇ lim E·J[1−exp(−t/τρ)], where τρ equals K/4πσ, the relaxation time, J is the total current density including diffusion, as well as drift, and ∇ lim E means that the divergence does not operate on E (the electric field is held constant). In the differentiation ∂n/∂x and ∂p/∂x are considered to be equal, as are ∂2n/∂x2 and ∂2p/∂x2.

Working independently, H. Brooks and W. van Roosbroeck arrived at expressions for both the ambipolar diffusion coefficient and the ``group mobility'' of the drift of a pulse of excess carriers. This theory yields the same results, and, in addition, transient expressions are gotten for each.
Indium Antimonide Photoelectromagnetic Infrared Detector
Authors: Kruse Paul W.
Published: April 2005

The theory of operation, construction, and performance data of an infrared detector based upon the PEM effect in InSb are presented. Theoretical derivations of the spectral noise equivalent input, noise equivalent power, and responsivity are made which show the dependence of these figures of merit upon the electrical properties of the semiconductor, sample thickness, surface area, front and back surface recombination velocities, and magnetic induction. Performance of the detector operating at room temperature shows a spectral response extending to 7.5 microns and a response time of less than 1 microsecond. The noise equivalent input of a detector having a 0.71-mm2 sensitive area has a minimum value at 6.6 microns of 6.7×10−10 w.
Shock Waves Reflected by Magnetic Fields
Authors: Atkinson William R. , Holden William R. , Fowler Richard G.
Published: April 2005

Fast moving plasmas encountering transverse magnetic fields of order 104 gauss are decelerated so rapidly as to produce reflected shock waves. Observations in hydrogen at gas pressures of 1 to about 10 mm Hg are analyzed. There are critical conditions of magnetic field for the onset of the reflection. The velocities of the advancing and reflected waves are recorded as a function of pressure and field.
Single Crystal Anisotropy and Magnetostriction Constants of Several Ferromagnetic Materials Including Alloys of NiFe, SiFe, AlFe, CoNi, and CoFe
Authors: Hall R. C.
Published: April 2005

The anisotropy and magnetostriction of single crystals of several ferromagnetic materials have been determined experimentally. The materials include the metals iron and nickel, binary alloys of nickel iron, silicon iron, aluminum iron, cobalt nickel, and cobalt iron, ternary alloys of molybdenum nickel iron, nickel cobalt iron, and molybdenum aluminum iron, and magnetite. The effect of the order-disorder reaction on these properties was measured for several of the alloys.

The present data for the nickel iron and silicon iron systems agree well with recently published values. Ordering generally raises the magnetostriction and lowers the anisotropy of the aluminum iron alloys near the Fe3Al composition. The first anisotropy constant, K1, for the cobalt nickel system as derived from torque curves is similar to old data derived from magnetization curves. However, K1 for cobalt iron (30, 35, and 45% cobalt) appears to be considerably larger than previously reported. In general, the addition of cobalt to nickel and to iron changes the magnetostriction constants (λ100 and λ111) toward large positive values. Thus, λ100 increases to 100×10−6 for 50% cobalt nickel and to 130×10−6 for 45% cobalt iron; λ111 increases to 30×10−6 for 45% cobalt iron but remains approximately constant for the cobalt nickel alloys.
On the Crystal Perfection of Iron Whiskers
Authors: Gorsuch Paul D.
Published: April 2005

The density and distribution of dislocations in tip grown iron whiskers produced by the hydrogen reduction of liquid iron halide salts has been measured by means of x-ray rocking curves. The data show that the more perfect whiskers have dislocation densities below 106 dislocation lines per cm2. Thus, many of these whiskers which are less than 10 μ in diameter would contain, at most, only a small number of dislocations and should behave as perfect crystals. No evidence of a large elastic twist was found in any of the whiskers as would be expected for a whisker grown by a screw dislocation mechanism. This did not completely prove that iron whiskers must grow, therefore, by a mechanism based on coherent two-dimensional nucleation as there are combinations of specific types of screw dislocations which will not produce elastic twists in the whiskers.
Drift Velocity Saturation in p-Type Germanium
Authors: Larrabee Robert D.
Published: April 2005

A method of making an ohmic contact to a semiconductor that does not inject minority carriers at high current densities has been found. This surmounts difficulties and limitations of previously reported experiments. Utilizing this technique, the high field current-voltage characteristic of p-type germanium was measured at several temperatures from room temperature to liquid helium temperatures, a wider range than previously reported. From these data, one can compute the drift velocity (and drift mobility) as a function of electric field and also estimate the amount of heating that will occur when a square pulse of current is passed through a p-type germanium sample immersed in liquid helium.
Axially Symmetric Electron Beams of Uniform Axial Velocity
Authors: Cook Edward J.
Published: April 2005

Since the initial work of Brillouin, interest in long, dense electrom beams with a uniform velocity profile has increased steadily. Notable contributions have been made by Samuel and Harris. In this paper, the general member of this class of beams is derived. Various special cases become the equilibrium systems of current interest. In addition to these known systems, the analysis leads to new possibilities. One of these is of particular interest in that it is the first of this group of beams in which the axial velocity is important to the balance of forces on the electrons. The new beam has properties ideal for M-type interaction and should be of considerable future importance.
X-Ray Measurement of Microstrains in Germanium Single Crystals
Authors: Hunter L. P.
Published: April 2005

The high intensity of the anomalously transmitted x-ray beam depends upon the coincidence of the nodal planes of the x-ray wave field with one set of atomic planes within the crystal when the crystal is set for Laue diffraction. If there is any structural defect within the crystal which causes some of the atoms of the crystal to deviate from their normal location in perfect planes, these atoms will no longer be at the nodes of the x-ray wave field and by their absorption they will reduce the transmitted intensity.

The present paper shows how this effect may be employed to measure the amount of microstrain present in nearly perfect germanium crystals. It is found that some apparently dislocation free crystals show a greater degree of crystalline imperfection than crystals with a finite dislocation count.
Stress-Assisted Precipitation on Dislocations
Authors: Ham Frank S.
Published: April 2005

The kinetic theory for the rate of stress-assisted precipitation on dislocations is re-examined in order to extend the work of Cottrell and Bilby. Two approximate expressions are used for the elastic interaction between a solute atom and edge and screw dislocations: V=−A sinθ/r and V=−B/r, respectively. The resulting partial differential diffusion equations are integrated numerically to get the time-dependent rate of precipitation on an isolated dislocation. These results are used to calculate the short-time part of the precipitation curve for an array of dislocations. Exact steady-state solutions to the diffusion equations are derived for both interactions and are used with a variational procedure to establish the long-time part of the curve for a regular array. For very short times the precipitated fraction W is proportional to t⅔ as derived by Cottrell and Bilby, but this result is not accurate over the range of t during which most of the precipitation occurs. The long-time part of the curve is given accurately by W=1−exp(−t/τ), where τ can be calculated by replacing each dislocation and its stress field by a cylinder with an ``effective capture radius,'' the value of which is calculated for each form of interaction. Complete precipitation curves are obtained for a regular array by combining the short- and long-time results, and it is shown that these are changed but slightly if the array is random. These results differ significantly from a formula suggested by Harper to extend Cottrell and Bilby's work, and they thereby indicate that the interpretation of the precipitation process for carbon in alpha-iron is not yet entirely established.
Flux Reversal in Soft Ferromagnetics
Authors: Humphrey F. B. , Gyorgy E. M.
Published: April 2005

To describe the flux reversal process in soft ferromagnetics, at least three mechanisms are required. A domain wall motion process is satisfactory only when the drive field is slightly larger than the coercive force. In the intermediate drive region, a nonuniform rotation model is necessary to be consistent with the experimental observations. In particular such a model predicts the observed linear relationship between drive and the inverse of the reversal time, the observed shape of the flux reversal transient and the observed value of the switching coefficient. In the high drive region with a transverse field applied, a coherent rotation model provides the best explanation of the experimental observations. The three regions can be demonstrated with a single sample in the case of the thin film.
Infrared Absorption and Photoconductivity in Irradiated Silicon
Authors: Fan H. Y. , Ramdas A. K.
Published: April 2005

The effects of irradiation on the infrared absorption and photoconductivity in silicon are reported. The absorption near the intrinsic edge is increased and drops off more gradually toward longer wavelengths. Several absorption bands are introduced by neutron irradiation with peak absorptions at 1.8, 3.3, 3.9, 5.5, and 6.0 μ, respectively. The observation of each band depends upon the position of the Fermi level. The 1.8-μ band has also been studied for deuteron irradiated and electron irradiated silicon, and the 3.3-μ band has been observed in electron irradiated samples. The absorption bands arise from electronic excitations of various types of defects and associated photoconductivity has been observed for the 3.9-μ and 5.5-μ bands. In addition absorption bands have been observed at long wavelengths: 20.5, 27.0, and 30.1 μ, which are associated with lattice vibration. The significance of these results is discussed.
Mechanism and Defect Responsible for Edge Emission in CdS
Authors: Collins R. J.
Published: April 2005

The nature of the green and blue emission at 78°K in CdS has been investigated. On the basis of the wavelengths of absorption and emission lines the blue component is assigned as exciton decay. Measurement of the decay of the blue luminescence, following excitation by a 10−8 sec pulse of 1-Mev electrons, gave an exciton lifetime <10−8 sec. Similar measurements have shown that the green component has a slower decay with emission occurring as long as 20 μsec after the excitation has ended. These results have been used to support the recombination of a free electron with a trapped hole as the mechanism for green edge emission. Heating in sulfur vapor quenches the green luminescence in a controllable fashion. From the infrared reflection spectra of CdS in the region 10 to 50 μ the optical phonon frequencies were determined. The value of 305 cm−1 for the longitudinal phonon is in good agreement with the prediction of Kröger and Meyer from edge emission measurements, showing that the emission is coupled to the lattice through the longitudinal optical phonon. Based on an analysis of the effects on edge emission produced by heat treatment in sulfur vapor and electron irradiation with 0.20 and 1.0-Mev electrons, a sulfur vacancy is suggested as the recombination center associated with the green edge emission.
Electron-Bombardment Induced Recombination Centers in Germanium
Authors: Loferski J. J. , Rappaport P.
Published: April 2005

The rate of change of minority carrier lifetime in germanium crystals bombarded by 1-Mev electrons has been studied experimentally as a function of the initial resistivity of the material. Analysis of the data leads to the conclusion that a single recombination center controls lifetime in both n- and p-type material, that this level is located at either 0.21±0.005 ev from the conduction band or else at 0.26±0.005 ev from the valence band, and that the ratio of the cross section for capture of minority holes is 18 times the cross section for capture of minority electrons. The absolute value of the hole capture cross section is 4.5×10−15 cm2 if one uses the best available data for the probability of producing a Frenkel defect by a 1-Mev electron. This large value is compared to the findings of other authors in similar experiments.
Paramagnetic Resonance in Electron Irradiated Silicon
Authors: Bemski G.
Published: April 2005

Electron spin resonance has been observed in n-type silicon irradiated with 0.5-Mev electrons. The particular resonance lines discussed here appear only in pulled crystals which contain about 1018 oxygen atoms per cm3. The lines do not appear in floating zone crystals (<1017 oxygen per cm3). The pattern is anisotropic with respect to the field orientation and can be fitted with a g tensor with components g[100]=2.0029, g[110]=2.0019, g[11̄0]=2.0096.

Hyperfine structure due to interactions with Si29 nuclei is also observed. The hyperfine structure tensor exhibits a [111] symmetry indicating that the electron is not centered on the silicon nucleus with which it is interacting. A model is suggested, consistent with the observed symmetries, according to which vacancies produced during irradiation diffuse to the distorted regions around oxygen atoms.
Spin Resonance in Electron Irradiated Silicon
Authors: Watkins G. D. , Corbett J. W. , Walker R. M.
Published: April 2005

The spin resonance behavior in room temperature irradiated n-type silicon is observed to be significantly different for silicon grown in quartz crucibles from that grown by the floating zone method. The dominant spectrum in each is discussed. The defects giving rise to the spectra are interpreted as containing impurity atoms and as having formed when the impurities trap mobile interstitials and/or vacancies. In quartz crucible grown silicon, the impurity may be oxygen. In the floating zone material, the impurity appears to be the phosphorus used in the doping. A 20°K irradiation and anneal is described which suggests the temperatures at which this defect motion is occurring. Features of the spin resonance spectra suggest that the vacancy may be the mobile effect.
Disordered Regions in Semiconductors Bombarded by Fast Neutrons
Authors: Gossick B. R.
Published: April 2005

The width and depth of the potential wells surrounding disordered regions in neutron irradiated n-type germanium and extrinsic silicon are estimated. Numerical examples of well dimensions for a wide range of sample characteristics are presented. Some effects of disordered regions, e.g., (a) scattering of conduction electrons, (b) absorption of holes, and (c) polarizability, are discussed.
Radiation-Induced Energy Levels in Silicon
Authors: Klein Claude A.
Published: April 2005

Radiation-induced energy levels in silicon have been detected, positioned, and evaluated with the help of many techniques. In this paper, the presently available body of information has been organized, summarized, and analyzed. A short historical review precedes a critical discussion of evidence recently reported for electron-, deuteron-, and neutron-irradiated silicon. Three conclusions emerge from such a confrontation: (1) the energy level pattern is essentially independent of the damaging agent; (2) the pattern seems to present a remarkable symmetry with respect to the middle of the gap; (3) shallow levels close to the band edges are introduced in similar concentrations and at higher rates than the deep traps. On this basis, an attempt is made to interpret the infrared absorption and photoconductivity data of Fan and Ramdas. Problems such as those associated with the charge state of radiation-induced defect centers are examined in the light of a novel experimental approach.
Electron-Bombardment Damage in Oxygen-Free Silicon
Authors: Wertheim G. K. , Buchanan D. N. E.
Published: April 2005

Electron-bombardment damage in oxygen-free silicon is compared with that found in pulled crystals which have been previously reported. It is found, in agreement with conclusions drawn from spin resonance experiments, that the level 0.16 ev below the conduction band is associated with oxygen. In oxygen-free silicon a deep level, 0.38 ev below the conduction band is produced in dominant density, and a broad shallow level in lesser concentration. The 0.16-ev level is not produced. The difference between this level scheme and that found in pulled crystals which contain oxygen points up the hitherto unsuspected importance of impurities in the formation of the stable defects, during the rearrangement of the vacancies and interstitials produced by the primary displacement.
Radiation-Produced Energy Levels in Compound Semiconductors
Authors: Aukerman L. W.
Published: April 2005

The effects of high-energy radiation on the electrical properties of compound semiconductors are reviewed. Emphasis is placed on those effects which can be interpreted in terms of energy levels. The following compounds are discussed: InSb, InAs, GaSb, AlSb, GaAs, InP, CdTe, and SiC. The implications of bombardment-produced changes in carrier concentration on possible energy levels are considered. Of the compound semiconductors, only InSb, irradiated at 200°K with electrons, has been sufficiently studied to enable a determination of the positions of the energy levels and their rates of generation. The annealing behavior of both InSb and GaSb is complex. A possible interpretation of these annealing characteristics in terms of shifting energy levels is discussed.
Precipitation in Semiconductors
Authors: Tweet A. G.
Published: April 2005

A brief review is given of the present status of precipitation phenomena in semiconductors. Recent theoretical advances in the analysis of diffusion-limited precipitation are described. The precipitation of Li and Si is discussed as an example of diffusion-limited precipitation in which metastable centers are observed, and the precipitation of Cu as an example to which formal nucleation theory appears to apply. A recent theory of the clustering of oxygen in Si is described and its significance in terms of the nucleation process is indicated. It is emphasized that a number of techniques are now available for the observation of tiny aggregates of impurities in semiconductors, and the need for a consistently microscopic theory of nucleation is pointed out.
X-Ray and Expansion Effects Produced by Imperfections in Solids: Deuteron-Irradiated Germanium
Authors: Simmons R. O. , Balluffi R. W.
Published: April 2005

Important information concerning atomic models of the defects in damaged crystals can be obtained from measurements of bulk length changes, ΔL/L, and x-ray lattice parameter changes, Δa/a, during irradiation and subsequent recovery. These quantities are not necessarily equal, and their magnitudes and signs may serve to discriminate between possible models. A detailed description of the ΔL/L and Δa/a effects to be expected from models consisting of point imperfections (either uniformly distributed or clustered), displacement spike regions, and dislocation loops is given. Additional discussion is given of the effects expected in measurements of low-angle x-ray scattering, Laue-Bragg reflection broadening, Laue-Bragg reflection intensities, and x-ray diffuse scattering. The currently available experimental results on irradiated germanium are discussed in an attempt to discriminate between the various models. Comparatively simple models consisting of clusters of vacancies and clusters of interstitials are probably consistent with present experiment. No information is available regarding the shapes of these regions. More complicated models are not excluded, of course. The aforementioned techniques are compared with electrical measurements in semiconductors, and some of the strengths and weaknesses of the various methods are assessed. The need for further measurements of all types is emphasized.
Irradiation Damage in Germanium and Silicon due to Electrons and Gamma Rays
Authors: Cahn Julius H.
Published: April 2005

The simple model for atomic displacements by electrons of Seitz and Koehler is used to calculate the total number of displaced atoms in germanium and silicon due to electrons and gamma rays of energies up to 7 Mev. The calculations are compared to reported experiments in the literature. Electron damage at energies below 1 Mev requires the assumption of threshold energies less than 30 ev, while the higher energy electron damage data are fairly well explained by a 30-ev threshold. The measured gamma-ray cross sections for atomic displacements are an order of magnitude smaller than the calculated cross sections, even for a 30-ev threshold both for silicon and germanium.
Neutron Diffraction Techniques and Their Applications to Some Problems in Physics
Authors: Sidhu S. S. , Heaton LeRoy , Mueller M. H.
Published: April 2005

Neutron transmission and diffraction techniques are described with application to problems in nuclear physics, crystallography, magnetic scattering, physical structure of materials, and the liquid state. Experimental results for nuclear scattering amplitudes, positions of light atoms among heavy atoms, magnetic moment alignments in antiferromagnetic structures, and diffraction of neutrons by alkali metals in the liquid state are reported. The main features of the design and operation of the neutron diffraction spectrometer and the auxiliary equipment are given.
Measurement of Thermal Conductivity by Utilization of the Peltier Effect
Authors: Harman T. C. , Cahn J. H. , Logan M. J.
Published: April 2005

A special technique for the accurate measurement of thermal conductivity is discussed. The method involves use of the Peltier heat to maintain a temperature gradient along the specimen. Straightforward measurements allow calculation of the absolute value of the thermoelectric power, thermal conductivity, and electrical resistivity. An especially useful feature of the method is that the thermoelectric figure of merit is given in terms of the ratio of two voltages. The theory is presented for the case in which the radiative heat transfer is important. The method has been tested experimentally at 300°K only, but analysis suggests that accurate measurements of thermal conductivity can be made by this technique on low thermal conductivity materials of small dimensions up to 1000°K.
Relationship between Signal-to-Noise Ratio and Threshold of Response of Infrared Photoconductors Limited by Generation-Recombination Noise
Authors: Spicer W. E.
Published: April 2005

For photoconductors in which the dominant noise is generation-recombination noise, it is shown that the signal-to-noise ratio is proportional to expβEi/2kTD, where Ei is the threshold response of the photoconductor, TD is its temperature, and β is a constant between unity and one-half. If longer wavelength response is desired (smaller Ei) without sacrificing signal-to-noise ratio, this can only be achieved by lowering TD. Similarly, for any given Ei, the generation-recombination noise can be reduced to an arbitrarily low level by lowering TD sufficiently. Expressions are obtained for the optimum value of Ei under typical operating conditions.
Microwave Conductivity of Slightly Ionized Air
Authors: Margenau Henry , Stillinger Dorothea
Published: April 2005

The conductivity of air ionized by injection of electrons at different altitudes is computed with the use of experimentally established collision cross sections of electrons in oxygen and nitrogen. The results, in the form of graphs, are compared with the usual, simpler formulas based upon the assumptions of (a) a constant collision frequency and (b) a constant mean free path. The departures are in excess of the experimental error in good conductivity measurements.
New Method for Range Measurements of Low-Energy Electrons in Solids
Authors: Holliday J. E. , Sternglass E. J.
Published: April 2005

A new method for determining the range of low-energy electrons in solids is described and compared with older techniques. In the new method, the material under study is deposited on a thick layer of greatly different electron backscattering characteristics. When the incident electrons have just sufficient energy to penetrate to the support and return to the surface, a marked change in the backscattered fraction occurs. In this manner, the need for very thin organic supporting films of unknown stopping power is avoided. Range-energy data from 1 to 15 kev for films of aluminum on a gold substrate obtained by this technique are found to agree with the data obtained by the use of cathode luminescence to detect electron penetration. The technique was applied to thin films of gold in the energy region from 2 to 15 kev. It was found that the practical ranges in mg/cm2 for gold and aluminum were the same below 10 kev, unlike the situation in the mev region where the effective penetration into Al is about twice that for Au due to the importance of nuclear scattering in a high Z element. Good agreement is found with the Bohr-Bethe theory for aluminum at all energies and for Au below ∼10 kev.
Effect of Pressure on the Spectra of Olivine and Garnet
Authors: Balchan A. S. , Drickamer H. G.
Published: April 2005

The effect of pressure has been measured on the absorption edge of olivine and on the Fe++ peak of garnet to over 150 000 atmos. The absorption edge of olivine shifts red by about 9% of the gap in this pressure range. The Fe++ peak in garnet shifts to higher energies by 700 cm−1 in 170 000 atmos, due to increased splitting of the d levels by the ligand field. This is consistent with previous experimental work on transition metals, and with available theory. The temperature coefficient of the absorption edge of olivine was also measured at atmospheric pressure to 327°C. It exhibited a linear red shift of 4.21×10−4 ev/°C over this range.
Thermoelectric Properties of Ag2Te
Authors: Taylor P. F. , Wood C.
Published: April 2005

The Seebeck coefficient α, electrical conductivity σ, and thermal conductivity K data are given for a number of Ag2Te specimens measured at room temperature. The maximum value observed for the figure of merit α2σ/K was 1.3×10−3°C−1. The relationship between K and σ was linear, and Kel could be expressed approximately by (π2/3) (k/e)2σT. Kph was found to be 0.72×10−2 w cm−1°C−1. There was no evidence of an ambipolar diffusion contribution to K. It is suggested that the small energy gap (0.02 ev) previously determined in this compound could account for the absence of a measurable ambipolar diffusion effect, the degeneracylike behavior of Kel, and the relatively low values of the Seebeck coefficient.
Elastic Constants of Single Crystals of the bcc Transition Elements V, Nb, and Ta
Authors: Bolef D. I.
Published: April 2005

Values of the elastic constants of single crystals of the bcc transition elements V, Nb, and Ta, are reported at T=27°C. They are, in units of 1011 d/cm2: c11c12c44V22.811.94.26Nb24.613.42.87Ta26.716.18.25Comparisons are made of the values obtained for two crystals each of V and Ta. A high-frequency cw resonance technique was used in these measurements. The shear anisotropies A=2c44/(c11–c12) are anomalously small for these elements as compared to other cubic system elements. An analysis of the shear anisotropy, based on Fuchs' model, is given. It is found essential in this analysis to take into account next-nearest as well as nearest-neighbor ion-ion interactions.
Space Charge Instabilities in Synthesized Plasmas
Authors: Eichenbaum A. L. , Hernqvist K. G.
Published: April 2005

A theoretical and experimental investigation of instability phenomena in synthesized plasmas is carried out. In the theoretical analysis the space charge and potential distributions are obtained for an idealized one-dimensional model. The model consists of two face-to-face electrodes each emitting ions and electrons in any ratio and with a Maxwellian velocity distribution. The calculations show that no stable zero-field solution is possible; instead, distributions with either a potential maximum or minimum in the center are obtained. For a range of values of the ratio β of injected ion to electron space-charge density near unity (0.81 ≤β<1.235), double-valued solutions to the problem are obtained. The actual solution into which the system settles depends on whether this range of β values is approached from above or below. Transitions from one such state to the other can occur at the limits of this β range. In the experimental investigation of a synthesized plasma, these instabilities, or state-to-state transitions, were found to be in good agreement with the theory. Oscillations triggered by state-to-state transitions were observed with a frequency corresponding to the ion transit time through the interelectrode space. These oscillations are not described by the steady-state analysis.
On the Question of Ball Lightning
Authors: Silberg Paul A.
Published: April 2005

The hypothetical model of ball lightning first suggested by P. L. Kapitza [Doklady Akad. Nauk S.S.S.R. 101, No. 2, 245 (1955)] is considered in some detail in an attempt to uncover evidence which will substantiate or contradict the theory. Observers' reports of the phenomenon are summarized briefly. Pro and con arguments concerning Kapitza's scheme are given. A theoretical model in an ideal environment is examined. The radio-frequency field suggested by Kapitza is considered, and the interference effects resulting from the reflection of a discrete band spectrum of linearly polarized waves from a perfect reflector are presented. The gaseous discharge is discussed, under the assumption that the ball lightning phenomenon is analogous to a point-to-plane corona discharge. It is determined that, given a sufficiently intense electric field, a horizontal discharge along one of the electric field antinodes, suggestive of horizontal lightning, can result. It is concluded that this exploratory work supports Kapitza's hypothesis, but that much more must be done before the theory is fully substantiated.
Direct Observation in the Electron Microscope of Oxide Layers on Aluminum
Authors: Thomas K. , Roberts M. W.
Published: April 2005

Using a modified technique of transmission electron microscopy, the properties of oxide films formed on aluminum foil by heat treatment in various oxidizing atmospheres at temperatures from 400 to 600°C have been studied. Above 400°C crystalline oxide forms by nucleation and growth, and has a basically fcc lattice of parameter 7.9±0.15 A.
Thermionic and Photoelectric Emission from Magnesium Oxide
Authors: Stevenson James R. , Hensley Eugene B.
Published: April 2005

Measurements of the thermionic emission as a function of temperature and the photoelectric yield as a function of the photon energy in the range from 2.5 ev to 11.5 ev have been made on magnesium oxide in the form of thin films, powders, and single crystals. The thermionic emission measurements indicate that the position of the Fermi energy in most samples of MgO is controlled primarily by the electrons in a donor level located approximately 3.4 ev below the vacuum level. Measurements of the enhancement of the photoelectric yield in the impurity sensitive region gives evidence for impurity levels slightly greater than 2.4 ev and 5 ev below the bottom of the conduction band. A sharp rise in yield at 7.5 ev in active samples coincides with the optical absorption edge associated with exciton formation. Heating the samples in oxygen greatly reduces the rise at 7.5 ev but has little effect on the yield at energies greater than 10 ev. From this it is concluded that the energy difference from the top of the filled band to the vacuum level is less than 10 ev.
Theory of LASER Oscillations in Fabry-Perot Resonators
Authors: Kotik J. , Newstein M. C.
Published: April 2005

The Fabry-Perot interferometer has been suggested for use as a high-mode LASER (light amplification by stimulated emission of radiation) resonator. The oscillation condition for a Fabry-Perot LASER is derived from an integral equation for the angular spectrum of the field. The kernel of the integral equation involves the scattering matrices of the end mirrors. This integral equation leads to a stationary expression. The use of physically reasonable trial spectra allows one to estimate the effect of ``walkoff,'' diffraction, reflector curvature, and reflector tilt in terms of an ``effective'' reflection coefficient for the infinite-aperture Fabry-Perot. Taking into account the effect of ``walkoff,'' an approximate necessary and sufficient condition for oscillation normal to the reflectors is derived.
Theoretical Bound on the Thermoelectric Figure of Merit from Irreversible Thermodynamics
Authors: Littman Howard , Davidson Burton
Published: April 2005

The principles of irreversible thermodynamics have been used with an idealized model to independently derive Joffe's dimensionless ``figure of merit,'' Tα2σ/(κ)J2=0, and a theoretical upper bound of infinity.
Analytical Solutions for Some Zone Melting Problems
Authors: Reiss H. , Helfand E.
Published: April 2005

Analytical solutions to the zone melting problem are obtained for any initial distribution of solute for the case of two geometries. One is the infinite straight bar and the other the re-entrant annular ring. The former is particularly interesting because under certain conditions the semi-infinite bar may be treated as infinite. The annular ring calculation provides, among other applications, a means of giving quantitative answers to questions arising in the zone leveling process.