bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Electron Trapping in Alumina Using Thermally Stimulated Electrical Currents
Authors: Pickard Paul S. , Davis Monte V.
Published: February 2004

Electron trapping in alumina was investigated using the methods of thermal stimulation of occupied trapping levels. A constant recombination lifetime energy band model was used to develop a general analysis employing the concept of an ``effective'' thermal emission probability. This analysis was used to relate experimental results to theoretical expressions for arbitrary retrapping rates. Results for polycrystalline alumina revealed several discrete traps in the trapping spectra with trap densities on the order of 1018 cm−3 and capture cross sections varying from 10−21 to 10−15 cm2 for the different trap levels observed. An extension of this analysis yielded an estimate of 0.2 (cm2/V sec) for the carrier mobility at 600°K.
Electrical Properties of High-Resistivity Nickel-Doped Silicon
Authors: Chua W. B. , Rose K.
Published: February 2004

Detailed galvanomagnetic measurements on high-purity, high-resistivity nickel-doped silicon confirm the existence of two acceptor levels lying 0.24±0.01 and 0.37±0.01 eV from the valence and conduction bands, respectively. The electron and hole mobilities are generally in good agreement from sample to sample. Hall mobilities have temperature variations of T−2.2 for electrons and T−3.2 for holes. The conductivity mobilities, obtained in regions of constant carrier concentration, are 1300(T/300)−2.2 for electrons and 500(T/300)−2.7 for holes. A significant degree of compensation was produced when nickel was diffused into both n- and p-type material at elevated temperatures.
Electrical Transport Properties in a Superlattice
Authors: Lebwohl Paul A. , Tsu Raphael
Published: February 2004

Boltzmann's equation is solved for electrons in a one-dimensional superlattice under the influence of a uniform electric field; an energy independent scattering time and nonspherical energy bands are assumed. The current density-electric field characteristic shows negative differential conductivity at fields of 103−104 V/cm independent of the detailed shape of the minibands.
Temperature Dependence of Surface Acoustic Wave Velocity on α Quartz
Authors: Schulz M. B. , Matsinger B. J. , Holland M. G.
Published: February 2004

Measurements of the temperature dependence of surface acoustic wave velocity were performed for propagation on X, Y, AC, AT, and along the x axis of several other rotated Y cuts of quartz over the temperature range −25° to +75°C. A pulsed rf technique was employed. To facilitate the measurement of angular dependence of the temperature coefficient of velocity, surface wave delay lines were constructed in which the waves were excited on the quartz by means of an interdigital electrode structure on a glass substrate which was brought into contact with the quartz. Calculations of the temperature coefficients of velocity and delay time were performed using an iterative computer program based on the work of Coquin and Tiersten. The measurements and calculations are in good agreement in most cases, the largest discrepancy being approximately five percent. It is concluded that the orientation which best combines low-temperature dependence of delay time, high coupling constant, and a minimum of deleterious side effects is 42½° rotated Y-cut quartz with propagation along the x axis.
Molecular Beam Sources Fabricated from Multichannel Arrays. III. The Exit Density Problem
Authors: Olander Donald R. , Kruger Valerie
Published: February 2004

Although the theory of Giordmaine and Wang adequately predicts the centerline intensity of a molecular beam from a channel source, it is less successful in describing the angular distribution. This deficiency has been ascribed to a nonzero number density at the tube exit. The end conditions chosen by previous workers lead to angular distributions which fail to satisfy total flow and average cosine restrictions. A method of choosing the parameters of the linear density profile which satisfies these integral constraints is described. The computed angular distributions according to the theories utilizing different end conditions differ very little from each other, but represent a clear improvement over Giordmaine and Wang's angular distribution.
Solubility of Gases in Glass—A Monatomic Model
Authors: Studt Perry L. , Shackelford James F. , Fulrath Richard M.
Published: February 2004

A statistical mechanical model of gas solubility in glass is presented. For equilibrium, the Gibbs free energy of the free gas is equated to that of the gas in solution. Expressions for the Gibbs energies are obtained from assumptions of the atomic motion in the free gas and dissolved states. The resulting solubility equations express the solubility (in atoms per cubic centimeter of glass) as a function of gas pressure, temperature, fundamental constants, and material parameters. An initial evaluation of the model is made by comparison with literature data for helium and neon in fused silica.
Morphology of Epitaxial Growth of GaAs by a Molecular Beam Method: The Observation of Surface Structures
Authors: Cho A. Y.
Published: February 2004

Homoepitaxial growth of GaAs was studied in situ in an ultrahigh-vacuum high-energy electron diffraction (HEED) system. Two surface structures, GaAs(1̄1̄1̄)−(19)1/2 and GaAs(1̄1̄1̄)−2, were observed during growth. The transition from one surface structure to the other was found to be a function of the deposition rate and the substrate temperature, with the high-temperature structure being the (1̄1̄1̄)−(19)1/2. The film growth morphology was studied by the carbon replication technique. Growth by a step mechanism was observed on a bromine-methanol etched surface while three-dimensional nuclei were observed on a polished or contaminated surface.
Precipitation and Dissolution Potentials
Authors: Rastogi R. P. , Shukla R. D.
Published: February 2004

Precipitation and dissolution potentials for KCl, NaCl, BaCl2, and NH4Cl have been measured with a Lindemann electrometer both in air as well as in nitrogen. The values in the latter case are lower. The electrode on which precipitation and dissolution takes place is found to be negative. The available evidence shows that static potential is developed. In order to assess the relative contributions of (i) diffusion potential, (ii) thermodiffusion potential, and (iii) zeta potential to the overall precipitation and dissolution potential, suitable experiments have been performed. Zeta potential was estimated from measurements of streaming potentials. Phase potentials have also been measured. It appears that the major contribution to the observed precipitation and dissolution potential arises due to unequal mobilities of the two ions being incorporated into or detached from the crystal lattice. The temperature, concentration, and time dependence of the various potentials have also been investigated.
Evidence for Partly Specular Reflection of Electrons in Thin Metal Films Condensed on Amorphous Substrates
Authors: Estermann I. , Schlesinger T.
Published: February 2004

Measurements of the electrical resistivity of thin silver films prepared by evaporation on amorphous substrates in ultrahigh vacuum indicate partial specular reflection of the conduction electrons at the films' surfaces. Some correlation between the electrical resistivity and the structure of the deposited films was observed, and the influence of residual gases during the evaporation process on structure and properties of the films was investigated.
Characteristics of Stress and Dilatation Fields of Straight Dislocations in Anisotropic Crystals
Authors: Yoo M. H. , Loh B. T. M.
Published: February 2004

The stress fields σij and the dilatation field Δ have been obtained in contour plots for a straight dislocation situated perpendicular to a reflection plane in an anisotropic crystal. A common characteristic feature of the results obtained for various metals at room temperature is that no twofold symmetry exists in any of σij or in Δ with respect to any axis normal to the dislocation line. For certain values of the modified elastic compliances S16 and S26, anomalous patterns have been found in the elastic fields that each of the σ11, σ33, and Δ fields is divided into six sectors as compared to the usual cases of two sectors, and either of σ12 and σ22 fields is divided into two sectors in contrast to the normal pattern of six sectors. Some direct effects of the asymmetries and certain anomalies of these elastic fields on deformation processes are discussed.
Morphology of Etch Pits on Germanium Studied by Optical and Scanning Electron Microscopy
Authors: Ehman Michael F. , Jindal G. R. , Faust J. W. , White William B.
Published: February 2004

A comparison is made between optical and scanning electron microscopy techniques on germanium surfaces that have been etched in several common chemical etchants. The morphology of the etch pits due to dislocations and different types of surface preparation are discussed. The high resolution and depth of field of the scanning electron microscope allowed resolution of the fine structure of the etch figures. Due to the manner in which the image is formed on the scanning electron microscope, the limit of resolution is much higher and light interference encountered using standard metallurgical microscopes is eliminated.
Dielectric Relaxation in Strontium Titanates Containing Rare-Earth Ions
Authors: Johnson D. W. , Cross L. E. , Hummel F. A.
Published: February 2004

Ceramic samples of SrTiO3, containing a wide range of solid substitution of trivalent rare-earth ions, have been fabricated and examined in detail. Well-developed dielectric relaxation was observed in samples containing lanthanum, praesodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, but not in samples containing cerium or europium. The relaxation occurs at normal low radio frequencies (102−105 Hz) in the temperature range −150° to +40°C, and there is a systematic variation of the relaxation parameters with both concentration and ionic size of the substituted ion. X-ray and density measurements confirm that as with lanthanum [T. Y. Tien and L. E. Cross, Jap. J. Appl. Phys. 6, 459 (1967)]. and bismuth [G. I. Skanavi, I. A. M. Ksendzov, V. A. Trigubenko, and V. G. Prokhvatilov, Sov. Phys. JETP 6, 250 (1959)] substitutions, two rare-earth ions and an associated vacancy substitute for three strontium ions in the ``A'' sites of the perovskite lattice. Possible explanations for the dielectric behavior are considered and it is shown that the data are consistent with an ionic model proposed earlier by Skanavi. [G. I. Skanavi and E. N. Matveeva, Sov. Phys. JETP 3, 905 (1957)].
Dielectric Properties of Bismuth Titanate
Authors: Fouskova A. , Cross L. E.
Published: February 2004

Three-terminal dielectric measurements of the weak-field permittivity have been carried out on single crystals of bismuth titanate (Bi4Ti3O12), which contained only ``narrow-angle'' twin walls. The pseudo-orthorhombic εa, εb, εc in these twinned monoclinic crystals show strong dispersion in the frequency range 100 Hz-1 mHz, and only above 1 mHz are the data representative of the intrinsic properties. The dispersion is thought to arise from space charge developed through the high conduction current at elevated temperatures and not from domain wall motion or damped piezoelectric resonance.
Analysis of Double-Stream Diffusion with Variable Trapping and Releasing Rates and Variable Diffusion Coefficient
Authors: Boctor S. A. , Watt L. A. K.
Published: February 2004

An analytical method has been developed for solving the partial differential equations that govern double-stream diffusion under very general conditions. The diffusion coefficient of the slow stream is set equal to zero. The trapping and releasing rates and the diffusion coefficient of the fast stream are assumed to be functions of distance and time rather than constants. General solutions of the equations which satisfy the boundary and initial conditions for the two important cases of a thin planar source and a constant surface concentration are obtained in terms of the diffusivity of the fast stream D1(x). The expressions obtained for the trapping and releasing rates are found to be physically realizable. Expressions for the concentration of the diffusing substance N(x, t) are obtained by considering suitable forms of D1(x). By varying the parameters in the expressions for the function N(x, t), concentration profiles are obtained which give a reasonable fit to the experimental data. A method is also developed to define the nominal Fick's diffusivity from the expressions of the apparent diffusivity. The values computed are of the same order-of-magnitude, but not in complete agreement, with those calculated using other methods.
Thermal Diffusion of Argon Isotopes
Authors: Tokuda Taneki , Ando Yasumasa , Fukui Katsunori
Published: February 2004

The optimum conditions in operating a thermal diffusion column have been searched using argon gas. The results obtained were compared with the theoretical values. Two molecular models used for the comparison with the experimental results are the inverse power model and the Lennard-Jones (12–6) potential model. The former showed a little better agreement with our results than the latter. When P4 is plotted as abscissa and P2/ln q as ordinate, the relation P2/lnq = (1/a) (P4+b) gives a straight line using the assumption given by Furry et al. Substituting the experimental results in this equation, the time-course variation of the values ``1/a'' and ``b/a'' from the slope and intercept of these linear plots was obtained. The variation of a and b with time is useful as a clue to see if the system is in equilibrium or not. Minimum values were observed near the optimum pressure in each operating time. Theoretical calculation of the relaxation tr which characterizes the approach to equilibrium was 1.04 h. Employment of direct current to heat the wire was a little better than the alternating current.
Concentration-Dependent Diffusion of Boron and Phosphorus in Silicon
Authors: Thái N. D.
Published: February 2004

A model of enhanced diffusion of boron and phosphorus in silicon is proposed, which includes the effects of plastic deformation and the degeneracy of highly doped silicon. Numerical solutions of the diffusion equation with concentration-dependent diffusion constant are presented, and the average conductivities of typical `anomalously diffused' silicon layers are given as a function of surface concentrations. Also discussed are the effects of background doping levels and surface concentrations on the effective diffusion constant and its measured activation energy.
Intrinsic Carrier Concentration of Hg1−xCdxTe as a Function of x and T Using k·p Calculations
Authors: Schmit J. L.
Published: February 2004

The intrinsic carrier concentration, reduced Fermi energy, electron effective mass, and the Fermi energy with and without doping are calculated for Hg1−xCdxTe with x>0.16 and 50<T<350°K. The calculations take into account the nonparabolicity of the bands by using the k·p method (Kane model) to determine n and by using the most recent linear temperature dependence of the bandgap. By fitting the ni curves calculated for nonparabolic bands to the expression for parabolic bands, the following approximation for the intrinsic carrier concentration was obtained: ni=(1.093−0.296x+0.000442T)5.16(1014)(Eg)3/4(T)3/2exp(−Eg/2kT).
Exact Fields of a Pulsed Dipole in a Homogeneous Cold Plasma
Authors: Wait James R.
Published: February 2004

The well-known time-harmonic field expressions for a dipole in a cold plasma are generalized to the transient or nonsteady situation. Specifically, we consider a Hertzian dipole excited by both a constant and sinusoidal current turned on at t=0. It is found that the early part of the waveform behaves in a manner fundamentally different from the steady-state response. (In spite of the simplicity of the model, it appears that the results are novel.)
Operation of III-V Semiconductor Photocathodes in the Semitransparent Mode
Authors: Antypas G. A. , James L. W. , Uebbing J. J.
Published: February 2004

Calculations show that very nearly bulk quality material is required for high-efficiency semitransparent III-V photocathodes. For narrow-band response, this can be obtained by epitaxially growing a thin layer of a semiconductor whose bandgap is slightly less than that of the substrate. Cathodes made by growing GaAsSb on GaAs have given quantum efficiencies comparable with front surface values, peaking out at 0.54% at 1.35 eV near the onset of absorption in the GaAs substrate. Preliminary results demonstrating semitransparent yield at 1.06 μ of 0.013% are also shown.
Effects of Changes in Ionization and Attachment Coefficients on the Dielectric Recovery of High-Current Air Gaps
Authors: Perkins J. F. , Parker A. B.
Published: February 2004

Earlier experiments have indicated that the rate of dielectric recovery of high-pressure, high-current spark channels is closely related to the fall of gas temperature. Recent experimental measurements of dielectric recovery in air at 1 atm following a critically-damped 190-kA spark discharge of 100-μsec duration have been made. By using measurements of gas temperature and Paschen's law, recovery characteristics have been derived on the assumption that the sole mechanism operative in the post spark channel is the reduction in gas density. It is shown in this paper that temporal variations in the values of the Townsend primary (α), secondary (γ) ionization coefficients, and of the attachment coefficient (a) can account for the detailed discrepancies between measured and derived recovery curves. During the early recovery period, an increase in γ due to the removal of adsorbed gas layers by the high-current discharge is thought to account for the reduction in recovery voltage below that derived from gas temperature measurements. It is concluded that, at later times, γ has decreased to a point near its predischarge value; an overall increase in electron attachment due to the formation of impurity products by the high-current discharge causes an increase in recovery voltage beyond that predicted from gas density considerations.
Microwave Breakdown in Air Plus H2O
Authors: Bandel H. W. , MacDonald A. D.
Published: February 2004

Breakdown electric field strengths have been measured in an S-band microwave cavity for dry air, water vapor, and air plus water vapor. Breakdown field strengths for mixtures of air plus 17.2 Torr of water vapor are up to about 25% greater than for dry air at the same total pressure.
Kinetics of Electrophoretic Development of Electrostatic Charge Patterns
Authors: Stark H. M. , Menchel R. S.
Published: February 2004

A theory of the development of electrostatic images on dielectric surfaces by colloidal suspension is presented. The rate of development is dependent upon the conductivity of the developer and the electric field in the development region. This field depends on the distance of a development electrode above the dielectric surface and the thickness of the dielectric. Measurements are presented which indicate that the developed optical density is proportional to the amount of charge that flows in the external circuit between the development electrode and the conducting substrate of the dielectric. The rate at which development proceeds can be accounted for by the decrease in the electric field due to the discharge of the dielectric, and the decrease of the conductivity of the developer due presumably to toner depletion.
Effects of High Pressure on Amorphous Polymers: Densification of Polymethyl Methacrylate
Authors: Kimmel R. M. , Uhlmann D. R.
Published: February 2004

The densification of polymethyl methacrylate resulting from pressure and temperature treatment in a Bridgman anvil device has been studied at temperatures to 245°C and pressures to 50 kbar. Treatment in the glass transition region at pressure produces samples 1.1%–1.5% more dense than the starting materials, depending on the length of treatment. Treatment in the glassy state produces samples up to 0.7% more dense than the starting material, depending on the temperature and the internal state of the sample immediately prior to the application of pressure. Samples held in the transition region under pressure and then vitrified by rapid application of a high pressure show densifications similar to but somewhat higher than those produced by treatment in the glassy state. The results are compared with thermodynamic theories of the glass transition and with similar data on other polymers and inorganic glasses.
Absolute Frequency of the Hydrogen Maser Using a Flexible Storage Bulb
Authors: Brenner Douglas
Published: February 2004

The hydrogen maser is a very highly stable frequency source having a fractional stability over periods longer than one second of a few parts in 1014. Unfortunately, difficulties in measuring the wall shift of the hydrogen maser cause uncertainties of several parts in 1013 in the absolute frequency of the hydrogen maser. A new technique for measuring the wall shift shows promise for considerably improving the accuracy of wall shift measurements, while greatly decreasing the time required for the measurements. Wall shift measurements are usually performed by making oscillation frequency measurements on two similarly coated storage bulbs which have different volume-to-area ratios, and thus different mean-free paths between wall collisions for the atoms. In the new technique described here a flexible storage bulb is used instead of the usual rigid bulb, and the mean-free path is changed by squeezing the flexible bulb instead of substituting a smaller rigid bulb for the original bulb. Since the same surface is used for both measurements, anomalous wall shifts caused by ``bad spots'' in a coating do not affect the accuracy of the wall shift measurements. This paper reports measurements made with the hydrogen maser on several varieties of flexible storage bulbs. An FEP Teflon bulb, and a polyethylene bulb coated with Fluorolube were the most promising of the flexible storage bulbs used. It is expected that further development of the flexible storage bulb technique will lead to accuracies for the absolute frequency of the hydrogen maser which approach its present frequency stability.
Morphology of Rhenium Metal Dispersed on High Area Oxides
Authors: Lewis R. T.
Published: February 2004

In this paper we present and discuss measurements of magnetic susceptibility, made at temperatures below the superconducting transition of rhenium, on samples made by dispersing rhenium in porous high area oxides by typical catalyst preparative techniques. These measurements show that a significant fraction of the rhenium in these samples is in the form of extensive networks, probably consisting of thin films, which are continuous over distances of the order of 25 μ or more.
Magneto-Optical Observation of the Magnetic Flux Structure in Superconducting Niobium
Authors: Huebener R. P. , Rowe V. A. , Kampwirth R. T.
Published: February 2004

The magnetic flux structure in superconducting niobium has been studied using the high specific Faraday rotation in thin films of a mixture of EuS and EuF2 at low temperatures. The magneto-optical detection system had a resolution of about 20 μm. The specimens were niobium foils 18-μm-thick and vacuum-deposited niobium films. In the foils, after raising the magnetic field and returning it to zero, the trapped flux structure consists of large domains of flux with opposite direction in the specimen. The arrangement of the domains is closely related to the sample shape. As in a ferromagnetic body, the domains are established to reduce the total free energy of the system. The Nb films show a very imhomogeneous magnetic flux distribution consisting of regions with very large local magnetic fields.
Thermoluminescence and Color Center Correlations in Dosimetry LiF
Authors: Mayhugh M. R. , Christy R. W. , Johnson N. M.
Published: February 2004

Dosimetry LiF was γ irradiated up to 10 000 R, and the resulting thermoluminescence was studied above room temperature in conjunction with the optical absorption between 190 and 400 nm. Changes in the glow curves and absorption spectra after various optical and thermal treatments show that the thermoluminescence process begins with thermal release of electrons from centers causing optical absorption in the 310–380-nm region. Moreover, the centers causing the important dosimetry glow peaks near 200°C appear to have two excited states, so that these centers have optical absorption bands at both 310 nm and under the F band at 250 nm. In particular two glow peaks near 200°C are correlated with two 310-nm absorption bands which are distinguished by different optical bleaching rates. For the glow peak usually used for dosimetry, the correlation is supported by an equality of thermal activation energies for the glow peak and 310-nm band. To interpret all the data in terms of these correlations requires assuming a restriction in the availability of luminescence sites. Implications for the photon production mechanisms and the trap structures are discussed. An asymmetry in the F band of LiF, as if a large K band were present, is also found.
Analysis of an Electron Spin Resonance Spectrum in Natural Diamonds
Authors: Klingsporn P. E. , Bell M. D. , Leivo W. J.
Published: February 2004

An anisotropic electron spin resonance spectrum was observed in three natural Type Ib diamonds. The diamonds which exhibit the spectrum also show the spectrum from substitutional nitrogen donors previously observed by others. The spectrum consists of three anisotropic groups of lines. The spectrum is interpreted in terms of a model in which each defect center is characterized by a spin Hamiltonian of the form H=βS·g·H+A·I·S, where S = ½ and I = 1, and in which the tensors g and A each have one component g1 and A1 oriented in a 〈110〉 direction. The spin-one nucleus is believed to be nitrogen. The principal components of g and A have the values g1 = 2.0031±0.0003, g2 = 2.0019±0.0003, g3 = 2.0025±0.0003, A1 = 5.303±0.005×10−4 cm−1, A2 = 7.164±0.005×10−4 cm−1, and A3 = 5.293±0.005×10−4 cm−1. The components g2 and A2 make angles Ψ = 45.2°±0.3° and α = 22.4°±0.1°, respectively, with 〈110〉 directions. The theoretical angular dependencies of the spectra when the magnetic field H is rotated in {100}, {110}, and {111} crystalline planes were calculated on the basis of the above model and are in excellent agreement with the experimentally observed angular behaviors.
Effects of Tensile Stress on Total Loss of Single Crystals of 3% Silicon-Iron
Authors: Yamamoto Takaaki , Nozawa Tadao
Published: February 2004

The variation of total loss under the tensile stress applied along the near [001] direction has been measured on the single crystals with (110) [001] orientation of 3% silicon-iron. It has been found that the total loss was greatly decreased with an application of stress. This effect is more remarkable when the orientation is more perfect or the permeability at 10 Oe is higher. An influence of surface roughness and grain size on this effect was also investigated. The large reduction in total loss with an application of stress can be qualitatively explained by a change of domain structure and a domain wall pinning taking the degree of orientation into account. It is also pointed out that the glass film by which a tensile stress is induced on the materials is very useful in improving the total loss of grain-oriented silicon-iron with high permeability.
Elastic Constants of ZnTe and ZnSe between 77°–300°K
Authors: Lee B. H.
Published: February 2004

The elastic constants of single crystals of ZnTe and ZnSe (zinc-blende type) have been determined over the temperature range 77°–300°K by means of the ultrasonic pulse-echo method. The velocity of the longitudinal and two transverse waves propagated in the [110] direction showed 1%–1.4% increase at 77°K from the room-temperature values and as a result, the elastic constants of both crystals showed 2%–3.5% increase at 77°K from the room-temperature values. From the low-temperature elastic constants, the Debye temperature was calculated to be 225.3°K for ZnTe and 278.5°K for ZnSe, respectively.
Hydrostatic Pressure Derivatives of the Single-Crystal Elastic Moduli of Zirconium
Authors: Fisher E. S. , Manghnani M. H. , Sokolowski T. J.
Published: February 2004

The adiabatic elastic moduli of single-crystal Zr vary linearly with hydrostatic pressures up to 4.7 kbar. The pressure derivatives are dC11/dP=3.93, dC33/dP=5.49, dC44/dP=−0.22, dC66/dP=0.26, dC12/dP=3.42, and dC13/dP=4.25. The average high-temperature Gruneisen mode γ̄H calculated from this data is in wide disagreement with that calculated from the volume thermal expansion coefficient. It is proposed that this disagreement arises because the negative dC44/dP is caused by the change with pressure in the c/a ratio, rather than the volume change.
Third-Order Elastic Constants of Ge at Room and Liquid-Nitrogen Temperatures
Authors: Tripathi R. C. , Verma G. S.
Published: February 2004

Keating's theory is applied to explain the recent experimental data of the third-order elastic moduli for Ge at room and liquid-nitrogen temperatures. The agreement between theory and experiment obtained for the new data at 293°K is better than that obtained by Keating. Also, the theory explains the experimental data at 77°K in an excellent way. It is found that unlike the other anharmonic interactions, the nearest-neighbor central one is further enhanced with the lowering of the temperature. The important parameter in Akhiezer's theory for microwave phonon attenuation in solids, called the nonlinearity constant D, has also been calculated for the said temperatures for 〈100〉 and 〈111〉 directions of ultrasonic longitudinal wave propagation, and in both the cases, it is found to be temperature dependent. The present work represents the first experimental support for our previous prediction, derived on the phonon conductivity data for Si, that D is temperature dependent and decreases at low temperatures.
Influence of a Strain Amplitude Distribution in a Crystal on the Hysteretic Breakaway Loss
Authors: Shimanuki Y. , Doi H.
Published: February 2004

The pattern of a strain amplitude distribution in a crystal in the internal friction measurements affects the strain-amplitude-dependent breakaway loss. On the basis of the Granato and Lücke theory, correct mathematical expressions of the effective breakaway losses for longitudinal, flexural, and torsional vibrations are derived and their strain-amplitude dependence is numerically calculated and examined in detail. An approximate useful expression for the effective breakaway loss, which is independent of the mode of vibration, is proposed. Furthermore, the functional relations between the breakaway losses of a crystal measured by different vibration methods are derived.
Nonlinear Optical Properties of Lithium Gallium Oxide
Authors: Miller Robert C. , Nordland W. A. , Kolb E. D. , Bond W. L.
Published: February 2004

The crystal symmetry (point group mm2) and refractive indices of LiGaO2 show that it can be phase matched for second-harmonic generation (SHG) of laser fundamentals in the near infrared. Furthermore, these data suggest that LiGaO2 might be a useful nonlinear medium for a 1.06-μ pumped near-infrared optical parametric oscillator in which the pump, signal, and idler waves all travel along a principal index direction. The magnitudes and relative signs of the nonlinear optical coefficients that determine SHG and optical parametric interactions in LiGaO2 have been measured using a 1.06-μ fundamental. It is found that these coefficients relative to d36 for KH2PO4 are: d33=±1.45±0.15, d31=±0.17±0.02, and d32=∓0.37±0.04. The small magnitudes of these coefficients would seem to preclude the use of LiGaO2 in efficient nonlinear optical devices. A discussion of a simple experimental method for the determination of the relative signs of the nonlinear optical coefficients of a given crystal is also included.
Calculation of Small Optical Absorption Coefficients from Calorimetric Experimental Data
Authors: Weil Raoul
Published: February 2004

The absorption coefficient α can be calculated from the equation: α=[PStBR2/lPTn(1+rBR2)],where PS and PT are the power lost in the sample and the power transmitted, respectively; n and l are the index of refraction and the length of the material; tBR2/n and rBR2 are the transmittance and reflectance of the exit end of the sample. It is assumed that the light impinges normally, and that the specimen has plane parallel entrance and exit faces.
Effects of Index Inhomogeneities on Optical Second-Harmonic Generation
Authors: Smith R. G.
Published: February 2004

Some nonlinear optical materials useful for optical second-harmonic generation and parametric amplification are troubled with index inhomogeneities, one form of which is striae which are quasiperiodic variations in the indices of refraction. Propagation of a laser beam normal to the plane in which these variations occur results in servere distortion of the wavefront. Propagation along the direction of the striae minimizes the wavefront distortion but introduces variations in the propagation constant of a traveling wave. In optical second-harmonic generation or parametric amplification this results in a quasiperiodic modulation of the momentum mismatch Δk. The effects of this modulation of the momentum mismatch on second-harmonic generation (and hence parametric amplification) are evaluated for the idealized case of periodic index variations. It is found that the shape of the curve of harmonic generated versus average momentum mismatch (produced for example by varying the crystal temperature) has a number of maxima each with the familiar sin2x/x2 shape but with reduced peak intensity. The spacing of these maxima is inversely proportional to the spacing of the striae and the magnitudes of the peaks are determined by the product of the striae spacing and the peak index variations. For minimum reduction of the absolute maximum harmonic produced, closely spaced striae of small index excursions are desired.
Thermo-Optic Effects in Nematic-Cholesteric Mixtures
Authors: Soref R. A.
Published: February 2004

Optical storage is found to be produced thermally in mixtures of nematic and cholesteric liquid crystals. The thin mesophase layer is initially transparent. It is subjected to a heating-cooling cycle that takes it back and forth through one of its phase-transition temperatures. This converts it to a long-lived light scatterer and decreases its optical transmission by 200:1. The initial state can be restored rapidly using electric fields; thus, the optical transition is reversible. Experimental data in the −18°C to 50°C range are presented and discussed.
Homogeneous Nucleation Kinetics of Ice from Water
Authors: Wood G. R. , Walton A. G.
Published: February 2004

Nucleation rates for the formation of ice from water have been calculated from observations of the frequency with which liquid droplets solidify. The stochastic nature of these solidifications has been considered and statistical methods employed for weighting observations and predicting experimental errors. The dependence of the solidification frequency on droplet volume and temperature has also been considered and methods were found for incorporating these dependencies into the rate calculations. The influence of the droplets' environment on the nucleation process was found in most cases to be negligible. The nucleation rates obtained from isothermal and continuous cooling experiments were in good agreement with each other, and their temperature dependence was in accord with the functional relationship predicted by theory. The rate's temperature dependence indicated a transition from a heterogeneous to a homogeneous nucleation mechanism; this finding was supported by the rate's dependence on droplet radius, which indicated a surface catalysis for the heterogeneous data. The average experimental kinetic constant was found to be greater than the theoretical value by a factor of 1015.5. This discrepancy could be explained by invoking a temperature dependent ice-water interfacial free energy.
Elementary Analysis of the Delayed-Emission Theory of the Dark Sheath in rf Plasmoidal Discharges
Authors: Kregel M. D. , Miller A.
Published: February 2004

This paper considers a possible explanation of the dark sheath observed in rf discharges. This theory, termed the delayed-emission theory, accounts for the dark sheath in terms of the finite lifetimes of newly created ions against radiative de-excitation. In addition, simple analytical expressions describing the dark sheath are obtained and comparisons are made with a more detailed calculation. For the form of the electric field used in the calculations it is found that a dark sheath would be detectable for ions with a lifetime against radiative de-excitation as short as 1×10−7 sec.
Instability of the Linearly Polarized Mode in Counterstreaming Electron-Ion Plasmas
Authors: Lee Kai Fong
Published: February 2004

The instability of the linearly polarized mode propagating perpendicular to the magnetic field, considered previously for counterstreaming electron plasmas, is here studied for plasmas with ion streaming using the cold-plasma equations. For two ion beams with velocities +ui and −ui in a neutralizing background of electrons, it is found that instability occurs when ui>cΩi/ωpi, with maximum growth rate (ui2ωpi2/c2 − Ωi2)1/2, when Ωi and ωpi are, respectively, the ion cyclotron and plasma frequencies; c is the velocity of light. The case of two counterstreaming plasmas with both electron and ion streaming is also discussed.
Avalanche Injection of Electrons into Insulating SiO2 Using MOS Structures
Authors: Nicollian E. H. , Berglund C. N.
Published: February 2004

A model is presented to explain the direct current which flows when a metal-SiO2–Si (MOS) capacitor is driven by a large-amplitude ac signal sufficient to produce avalanche breakdown in the silicon. During the portion of each cycle that the silicon is in avalanche breakdown, minority carriers generated by impact ionization are accelerated towards the interface. It is assumed that some of these minority carriers attain sufficient energy to surmount the potential barrier at the interface, enter the SiO2, and result in a dc component of current. Experimental results from MOS structures with p-type silicon substrates (electron injection into the SiO2) are shown to be consistent with this model. If the energy distribution of hot electrons in the Si avalanche plasma is Maxwellian, the data indicate that the effective temperature is 5550°K.
Relationship of Copper Sulfide and Cadmium Sulfide Phases
Authors: Cook William R. , Shiozawa Lee , Augustine Frank
Published: February 2004

Single-crystal CdS can be converted by cation exchange in CuCl solution to single-crystal copper sulfide with the chalcocite, djurletie, and CuxS (with 1.96>x>1.8) structures. The last is a previously undescribed hexagonal or pseudohexagonal phase with a=15.475±0.010 Å and c=13.356±0.010 Å. The structural relationship of the various phases to each other and to CdS is described with reference to two basic sulfur arrangements: hexagonal and cubic close packing. The gradual shift of phase of small crystals from high to lowered copper content is attributed to surface oxidation of copper atoms and strongly suggests that natural chalcocite crystals may also change composition and phase with time.
Transient Analysis of Output Pulse from Lithium-Drifted Detector-Amplifier Combination under Conditions of Carrier Drift, Carrier Diffusion, and Carrier Surface Recombination
Authors: Tuzzolino A. J.
Published: February 2004

A calculation has been made of the output pulse shape obtained from an idealized lithium-drifted detector-amplifier combination under conditions where an incident-charged particle uniformly generates carriers in both the electric-field region and the zero-field region of the detector. The current pulse to the input of the amplifier is calculated by considering the motion of electrons and holes initially generated in the field region, and the motion of holes initially generated in the field-free region which then diffuse into the field region. For the diffusion component of the input current, the finite tranisit time across the field region and loss of carriers at the back surface of the detector are taken into account in the calculation. Numerical results are given for the output pulse shape and ballistic deficit as a function of amplifier time constant, carrier transit time, carrier diffusion time, and surface recombination velocity. When bulk recombination in the field-free region may be neglected, it is shown that for an initial charge distribution which is a general function of position and for given surface recombination velocity at the back surface, one may determine directly: (a) the amplitude of the output pulse resulting from carriers generated in this region for an amplifier with a ``long'' time constant, (b) the total charge ``collected'' resulting from diffusion, and (c) the steady-state diffusion current in a steady-state problem with a charge generation rate in the field-free region equal to the initial charge distribution for the transient case.
Electron Mobility in High-Purity GaAs
Authors: Wolfe C. M. , Stillman G. E. , Lindley W. T.
Published: February 2004

The combination of polar optical phonon, piezoelectric acoustic photon, deformation potential acoustic phonon, ionized impurity, and neutral impurity scattering in the relaxation time approximation is shown to give results which are in good agreement with the temperature and concentration dependence of the electron mobility in high-purity GaAs. For polar optical phonon scattering a relaxation time is defined at each temperature from Ehrenreich's variational calculation. Since most of the parameters are well known, the only adjustable parameter in the calculation is the conduction band deformation potential with the best agreement with experiment given by | E1 | = 7.0 eV. Using this value a 77°K lattice scattering limited mobility of 240 000 cm2/V sec is obtained.
Carrier Diffusion in Semiconductor Avalanches
Authors: Kuvås R. , Lee C. A.
Published: February 2004

The effect of carrier diffusion has been evaluated in a large-signal analysis of semiconductor avalanches in the quasistatic approximation. It is shown that diffusion tends to smooth out the carrier distributions by upstream diffusion against the drift velocities, which causes a change in the carrier induced electric field. The dc solutions of the carrier and current distributions can be used in evaluating the effects of diffusion on the current response of the avalanche. The main effect is to increase the intrinsic response time with the ratio between the characteristic diffusion length D/v and the width of the avalanche region w as a critical parameter. In the effective avalanche width approximation a correction factor for the intrinsic response time due to diffusion is calculated. The results are also presented in curves with α/β and D/wv as parameters. The correction factor is found to increase linearly with D/vw for small values and saturate for large values. A criterion is given for the maximum multiplication factor possible in avalanche photodetectors without significantly reducing the bandwidth. Previously found discrepancies between experimental and theoretical values for the intrinsic response time can be removed by estimating a high-field diffusion constant of 600 cm2/sec for an electric field of 3×105 V/cm in silicon. Diffusion corrections to the carrier transport in the drift regions adjacent to the avalanche region have been considered for a time-harmonic component of the current. As a result, modifications to the usual transport factors (1−cosθ)/θ and sinθ/θ are established.
Analysis of Polar Optical Scattering of Electrons in GaAs
Authors: Fortini A. , Diguet D. , Lugand J.
Published: February 2004

The theory of the scattering of electrons by longitudinal optical phonons in III-V compounds is reconsidered, in the nondegenerate limit, assuming a spherical conduction band. The off-equilibrium part of the distribution function and the Hall-mobility-temperature function are obtained with a numerical resolution of the Boltzmann equation, up to a precision of a few 10−4. The results are compared with previous work due to Sondheimer and Howarth, and Ehrenreich. Application of the theoretical results to high-purity epitaxially grown GaAs layers is in good agreement around 300°K, but there is a strong discrepancy at higher temperatures. It is suggested that such a discrepancy could be explained by further refinements of the present theory (temperature dependence of the dielectric constant, two-phonon process).
Shock Wave from a Four-Meter Spark
Authors: Uman M. A. , Cookson A. H. , Moreland J. B.
Published: February 2004

The shock wave emitted by a 4-m spark of energy 2×104 J has been measured at distances from spark midgap of between 0.34 and 16.5 m. Close to the spark, a single dominant shock wave is observed; farther from the spark, a number of significant shock waves (generally 3 or 4) are observed. For distances less than 2 m, both the shock overpressure and the duration of the overpressure are between a factor of 1.5 to 5 less than predicted by cylindrical shock-wave theory. The discrepancies between the experimental data and cylindrical shock-wave theory are partially explained by consideration of the spark channel tortuosity.
Analysis of Thin Surface Layers by Fe-57 Mössbauer Backscattering Spectrometry
Authors: Swanson K. R. , Spijkerman J. J.
Published: February 2004

Fe-57 Mössbauer spectra for extremely thin surface layers (600–3000 Å) were obtained by detecting internal conversion electrons emitted after resonant absorption. The sample was placed inside a proportional counter specifically designed for Mössbauer backscattering measurements. Helium-10% methane flowgas was used to detect the conversion electrons. It is estimated from the observed spectra that this technique can be used to obtain Mössbauer backscattering spectra for iron-containing surface layers 50–3000-Å thick. Backscattering spectra for thicker surface layers (0.2–0.5 mil) were obtained by merely changing to an argon-10% methane flow-gas mixture and counting the 6.3-keV internal conversion x rays rather than conversion electrons.
Chemical Bonding Studies of Yttrium Compounds by X-Ray K-Emission Spectroscopy
Authors: Bhide V. G. , Bhat N. V.
Published: February 2004

The x-ray K-emission spectrum of yttrium in several compounds has been investigated using 400-mm bent-crystal (mica) spectrograph. The secondary method of excitation (fluorescence) has been employed in order to ensure that the compound under study does not decompose during the investigation. The shifts which occur in the positions of the x-ray diagram lines such as Kα1,2 and Kβ1,3 have been measured. The reasons responsible for producing these chemical shifts have been discussed. An estimation of the shift of Kα1 line has been made using Moseley's law, and it is seen that the agreement with the experimental value is indeed good. The correlation between the x-ray K-absorption and K-emission studies has been pointed out.
Effect of Ultrasonic Cavitation on the Etching Processes on Single Crystals of Aluminum
Authors: Ehman Michael F. , Faust J. W.
Published: February 2004

Single crystals of aluminum were etched under cavitation conditions in a 10% solution of sodium hydroxide. The cavitation processes prevented the buildup of oxide thin films, which, under standard etching condition would stop the etching processes. The etch rate of the aluminum at 60° was 0.460 mg/cm2/min. The experimental activation energy determinations indicate that the rate-controlling step is diffusion with a value of ΔE act=3.9 kcal/mole.