bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Humidity on the Surface Oxidation of UC Single Crystals at Room Temperature
Authors: Matzke Hj.
Published: February 2004

The formation of oxide layers on fresh {100} cleavage faces of uranium monocarbide (UC) single crystals during exposure to air at room temperature is studied using the channeling technique and Rutherford backscattering of 1-MeV He+ ions. The thickness of the layers increases with humidity and, for exposure times of about 1 week, ranges between 20 and 80 Å.
Thermal Oxidation of Sputtered Tantalum Thin Films between 100° and 525°C
Authors: Steidel C. A. , Gerstenberg D.
Published: February 2004

Results are presented for the thermal oxidation behavior of four types of sputtered tantalum films between 100° and 525°C. These films are bcc tantalum, β-tantalum, a porous β-tantalum, and tantalum nitride (Ta2N). All four types of films show parabolic oxidation kinetics and the formation of adherent Ta2O5 (tantalum oxy-nitride for Ta2N films) with bright interference colors. The first three types of films dissolve about 12 at.% oxygen, which is much higher than the oxygen solubility found in bulk tantalum, and the films show a different degree of suboxide formation than bulk tantalum. The activation energies for oxygen diffusion in the metal and for oxide growth are 1.2 and 1.4 eV, respectively. The dielectric properties of the thermal oxide are discussed in terms of the defects in the oxide.
Thermocouples in Magnetic Fields
Authors: Richards D. B. , Edwards L. R. , Legvold S.
Published: February 2004

It is shown that in a cryostat the use of an isothermal path leading out of an applied magnetic field will ensure insensitivity of thermocouples to the magnetic field. Tests in liquid helium in such a cryostat were conducted on a number of thermocouples with the applied field ranging up to 100 kG. The results showed that Cu-constantan, Cu–Au 0.03 at.% Fe, and Cu–Au 2.1 at.% Co thermocouples are not affected by magnetic fields. In subsequent work up to 300 K the first two thermocouples listed were still insensitive to magnetic fields. The third thermocouple was not tested at the higher temperatures.
Gamma Response of Semi-insulating Material in the Presence of Trapping and Detrapping
Authors: Akutagawa W. , Zanio K.
Published: February 2004

The photoelectric and Compton response to γ rays for a detector made from semi-insulating material (i.e., a monocrystalline semiconductor containing trapping centers) was calculated for the case of charge transport by one type of carrier (electron or hole), and also for the case of two-carrier transport (electron and hole) with each carrier having the same mean free path. Approximate expressions were then derived for the observable γ-ray efficiency of the detector as a function of material parameters for CdTe crystals used in the fabrication of surface barrier detectors; this efficiency is dependent upon temperature and electric field intensity for specified values of the carrier mobility-trapping time product and the threshold used in the recording of spectra. Spectra and values for efficiency were determined at room temperature for γ rays at energy values from 0.393 to 1.33 MeV, and also as a function of temperature over the range 24° to 68°C for γ rays from a 60Co source. The observations show behavior corresponding to a trap-limited response, and the presence of charge detrapping.
Exploding Wire Particle Size by Light Scattering Measurement
Authors: Weber F. N. , Shear D. D.
Published: February 2004

The reddish color seen in photographs of exploding copper wires was assumed to be due in part to the scattering of the blue and green wavelengths of the BH6 mercury lamp used. Accordingly, this scattered light was used to measure particle size by the dissymmetry method. The average value of the predominant particle dimension was found to be time dependent with a value of (12±3)×102 Å occurring 0.6 μsec before the voltage peak.
Ion Sampling from the Positive Column of dc Discharges in He–Ar Mixtures
Authors: Gaur J. P. , Chanin L. M.
Published: February 2004

Measurements have been made of the ion species present in the positive column of dc discharges of 0.05% and 0.5% argon in helium, by sampling through a 35-μ-diam orifice in the wall of the discharge tube. Data for 0.05% argon has been obtained over a current range of 15–90 mA and for pressures from 3 to 30 Torr. The main ion species observed were Ar+, He+, and He2+. Theoretical analysis combined with measurements of the variation of Ar+ with distance from the cathode, enable estimates to be made of the degree of ionization of Ar, and also an upper limit for the helium metastable particle densities present in the discharge. Metastable density values are, in general, an order-of-magnitude larger than the electron densities.
Structural Investigation of Noncrystalline Nickel-Phosphorus Alloys
Authors: Cargill G. S.
Published: February 2004

The structure of noncrystalline electrodeposited Ni–P alloys, 73.8–81.4 at.% Ni, has been investigated by x-ray scattering and by physical density measurements. The x-ray interference functions, I(k), are qualitatively inconsistent with those calculated for fcc-, hcp-, and Ni3P-type crystallites. Calculated radial distribution functions RDF(r) indicate that the alloys have a better defined short-range order than that observed in liquid noble metals above their melting points. The observed I(k) are very similar to the I(k) calculated by Dixmier, Doi, and Guinier [in Physics of Noncrystalline Solids, J. A. Prins, Ed. (North-Holland Publ. Co., Amsterdam, 1965), p. 67] from their model. However, the parameters needed to fit the experimental results are inconsistent with the atomic sizes expected for nickel and phosphorus. The noncrystalline alloys are between 0.6% and 1.4% less dense than the corresponding mixtures of fcc Ni and Ni3P, both of which are essentially close packed. A grain boundary density deficit model has been developed which relates the fractional density difference between the microcrystalline and macrocrystalline forms of a close-packed metal to the minimum average microcrystal grain size. The fractional density differences of between 0.6% and 1.4% observed for the noncrystalline Ni–P alloys would correspond to minimum average microcrystal grain sizes D of between 133 and 57 Å. Stored elastic energy calculations indicate that rms strains 〈ε2〉1/2 greater than 0.03 and due to simple compressive and dilatory stresses are inconsistent with the reported energy of transformation of noncrystalline Ni–P to crystalline nickel and Ni3P. Crystallite size broadening with D≥57 Å and strain broadening with 〈ε2〉1/2≤0.03 are insufficient to produce fcc, hcp, or Ni3P model I(k) consistent with the observed Ni–P I(k). The high densities of the noncrystalline Ni–P alloys suggest that the alloys have a continuous structure rather than one in which internal boundaries separate small well-ordered regions. These limitations on structural models for noncrystalline Ni–P alloys may apply to the other noncrystalline metallic alloys with similar diffraction patterns.
Axial Pressure Distribution in Solidified Argon and Methane
Authors: Hettwer Paul F. , Stajdohar Ralph E. , McCann Donald R.
Published: February 2004

High-pressure experiments at 77°K indicate an axial pressure distribution in solid argon and methane for pressures in the range of 2.0–9.0 kbar. The normalized resistivities of a separated pair of bismuth crystals were measured as a function of pressure in a piston-in-cylinder apparatus using these solidified gases as the pressure transmitters. At an applied pressure of 8.0 kbar, average pressure gradients of 1.3 kbar per cm and 1.1 kbar per cm were measured for initial compressions of argon and methane respectively. Subsequent second and third compressions of these solids to 8.0 kbar reduced the average pressure gradient to 0.8 kbar per cm for both materials. The gradients in each solid were found to depend primarily on the applied pressure, and the increase of shear strength with pressure. Shear strength parameters were determined for each solid from an analysis of second and third compression data. The increase of shear strength with pressure was within 5% of that determined for argon of similar purity obtained by independent extrusion techniques, but was high when compared to methane of considerably higher purity.
Microwave Behavior of Partially Magnetized Ferrites
Authors: Schlömann Ernst
Published: February 2004

The high frequency permeability of partially magnetized ferrites is calculated for some simple domain configurations, comprising only ``up'' and ``down'' domains. The method used is based upon the magnetostatic approximation and neglects exchange effects, but is otherwise substantially rigorous. The components of the effective permeability tensor (ratio of average induction to average magnetic field) in general depend upon details of the domain configuration in addition to the net dc magnetization. When the dc magnetization is cycled between the two states of complete magnetization the high frequency permeability, considered as a function of the dc magnetization, in general shows hysteresis. Detailed calculations of the high frequency permeability have been carried out for the case in which the domain configuration is cylindrically symmetric, i.e., invariant under rotation around the direction of magnetization. For any such domain configuration the two relevant components μeff and κeff of the effective permeability tensor obey the relation μeff2−κeff2=const, regardless of the number of domains and their relative size. This general theorem allows a simple derivation of the (isotropic) permeability in the completely demagnetized state, giving μeff=23{[(ω/γ)2−(Ha+4πM0)2]⧸[(ω/γ)2−Ha2]}1/2+13,where ω is the frequency, Ha the anisotropy field, and M0 the saturation magnetization.
Aspects of Bloch-Wave Channeling in High-Voltage Electron Microscopy
Authors: Humphreys C. J. , Lally J. S.
Published: February 2004

It is shown that the crystal orientation which maximizes the electron transmission for high-energy electrons incident upon medium and heavy atomic-weight materials is the symmetry position. This is contrary to the generally held view that the symmetry position is an orientation of particularly poor penetration. A simple explanation of the effect in terms of Bloch-wave channeling is given. (The term Bloch-wave channeling denotes the wave model analog of particle channeling as it refers to the enhanced transmission of Bloch waves, or of particles in a particle representation, due to their channeling between the atomic planes, thus minimizing inelastic scattering.) It is shown that considerably thicker specimens of heavy materials in particular may be studied in a 1-MV microscope by using the symmetry position rather than the Bragg position.
Observation of Energetic Ions from a Beam-Generated Plasma
Authors: Graybill S. E. , Uglum J. R.
Published: February 2004

Experiments are described which show that pulsed high intensity electron beams can accelerate light ions to high energies. A set of time-of-flight measurements shows proton and deuteron energies of 5 MeV, helium ion energies of 9 MeV, and nitrogen ion energies of about 20 MeV, produced by an electron beam with a maximum electron energy of 1.6 MeV. These measurements are confirmed by Be9 (x, n) reactions for protons, deuterons, and helium ions. Further confirmation is made with an absorber measurement for the protons.
X-Ray Diffraction from Neutron Irradiated Vitreous Silica
Authors: Bale Harold D. , Shepler Robert E. , Gibbs Garry W.
Published: February 2004

Both large-angle and small-angle diffraction studies have been made on pile irradiated silica glass. The radial distribution curves obtained from the large-angle scattering were in essential agreement with the earlier work of Simon. The small-angle scattering from samples irradiated with a relatively low fast neutron dose showed a noticeable rise in the scattering at the smallest angles. Two possible causes of this scattering are suggested. In addition, all irradiated samples showed a general increase in the scattering over the entire small-angle region. This scattering which showed little angular dependence was attributed to increased density fluctuations within the sample after irradiation. The irradiation induced scattering was almost completely removed by annealing the glass at 1300°C.
Some Properties of the Quaternary System PbxSn1 −xTeySe1−y
Authors: Kennedy C. A. , Linden K. J.
Published: February 2004

The Quaternary system PbxSn1−xTeySe1−y can be visualized as either a mixture of the two pseudobinary systems lead-tin telluride and lead-tin selenide or as a mixture of the four binary compounds PbTe, PbSe, SnTe, and SnSe. The liquidus surface of the quaternary system has been experimentally determined from cooling curves. Liquid compositions which fall on this continuous surface are shown to form single-phase cubic crystals, while melt compositions high in SnSe content are shown to crystallize into single-phase orthorhombic material. A region of melt compositions is outlined, which results in two-phase solid material.
Zn-Diffusion-Induced Damage in InSb Diodes
Authors: Mozzi R. L. , Lavine J. M.
Published: February 2004

Relatively shallow (2–10 μ) Zn diffusions into(1̄1̄1̄) Sb surfaces of undoped n-type InSb with Zn surface concentration exceeding 1020/cm3 exhibit lattice contractions of the order of 0.12%, high dislocation densities and mosaic structure in the diffused region. X-ray double-crystal spectrometer rocking curves suggest that preferential tilt of the(1̄1̄1̄) diffused planes by about 0.05° relative to the substrate occurs when the substrate is about 5° off(1̄1̄1̄) orientation. High-concentration Zn diffusions have yielded low quality diodes with zero bias impedances of only a few hundred ohms and poor photoresponse. On the other hand, surface concentrations less than 1019/cm3 have produced rocking curves characteristic of nearly perfect crystals and diodes having zero bias impedance values of the order of 104 Ω and good photoresponse.
Space-Charge-Limited Currents in Solids with Nonuniform Spatial Trap Distribution
Authors: Sworakowski Juliusz
Published: February 2004

Space-charge-limited currents (SCLC) in insulators with a nonuniform spatial distribution of traps have been discussed. General solutions for SCLC controlled by shallow or ``deep'' traps are derived for distribution of traps in energy and in space of the form f(E) g(x). In general data on the spatial distribution of traps cannot be obtained from the current-voltage or current-temperature dependences.
Low-Density Injected Plasma in p-Type Indium Antimonide
Authors: Heinrich H. , Kuchar F. , Merinsky K.
Published: February 2004

Properties of low-density injected plasma in p-InSb have been studied. Measurements have been made on n+-p-p+ diodes biased in the forward direction at 77°K. The time dependent behavior of the I-V characteristics has been measured by application of dc pulses, with and without a transverse magnetic field present. At short periods after applying the pulses, or at low injection levels, the current is carried mainly by holes in the major part of the sample. At long periods after applying the pulses and at high injection levels the shape of the I-V characteristics is governed by the injected plasma, and a steady state is reached within about 10 μsec. In a transverse magnetic field the plasma is deflected by the Suhl effect towards the surface. There the electrons and holes recombine at a high rate. This mechanism reduces the number of carriers which contribute to conduction. At a magnetic field of about 300 G the I-V curves have a similar shape as the ones measured at a short period after applying the pulse. Trapping and recombination mechanisms which are very important for a low-density plasma in p-type InSb have been studied by measuring the conductivity modulation after the end of the injecting pulse. The occurrence of an S-shaped I-V characteristic is due to the filling of the traps with injected electrons. The measurement of the conductivity modulation in connection with fourpoint probe measurements show that already at low currents, below the NDR region, traps are filled within a small channel. Its cross section decreases with increasing distance from the injecting contact. With increasing current the channel grows and reaches a maximum of about half of the sample cross section in the region above negative differential resistivity.
Analysis of In Situ Electron Microscopy Studies of Heterogeneous Nucleation
Authors: Lewis B.
Published: February 2004

Discrepancies with theory revealed by recent nucleation experiments have been examined. It is suggested that a minor deviation between experimental nucleation rate and the atomistic theoretical model, may be ascribed to a value between 1 and 5×1011 sec−1 (instead of 1013 sec−1) for the desorption rate pre-exponential. The much larger deviation with the spherical cap classical model is shown to be due to inability of the model to adequately evaluate the Gibb's free energy of formation from the monomer, ΔGn′, for nuclei in the range n = 1–3 atoms, which is the actual critical size in these experiments. If, for Bi on C, the surface energy term is chosen to give the observed values of n*, then evaluating ΔGn′ for n = 1 gives ΔG1′ = −20 kcal/mole, whereas it should be zero. If the surface energy is chosen to make ΔG1′ = 0, then the calculated values of n* and the nucleation rate do not agree with experiments. A modified form of the monolayer disc classical model gives good agreement between theory and experiment but is less satisfactory than the atomistic model. The experimental temperature variation of the maximum number density of nuclei disagrees with that expected as a result of depletion of single atoms. The results can be explained by depletion of mobile nuclei by mutual capture.
Planar Shock Initiation of Porous Tetryl
Authors: Lindstrom I. E.
Published: February 2004

The plane-wave shock initiation of a large particle size tetryl has been studied at five pressing densities between 1.30 and 1.70 g/cc. The explosive wedge technique was used to observe shock buildup to detonation for a number of initial shock strengths, obtaining shock position data as a function of time. Single-curve buildup was assumed to determine values of the initial shock velocity in the explosive and these were used in the impedance-match solution to compute the initial shock parameters in the explosive. Quantitative expression of the measured time of shock run in terms of the computed shock strength leads to a set of initiation relations characteristic of the test explosive. Comparison of these initiation curves for different densities of tetryl suggests that at least two initiation mechanisms are effective in low-density tetryl. This interpretation is illustrated by discussing the data in terms of two theories of initiation which have appeared in the literature.
Observations of Extrinsic-Intrinsic Faulting in Ag Platelets by High-Voltage Electron Microscopy
Authors: Snyman H. C. , Wilsdorf H. G. F.
Published: February 2004

Thin, chemically grown (111) Ag platelets were deformed and studied by high-voltage electron microscopy. Dislocation networks of two kinds were found to form in the plane of the foil. The first type was the usual disclocation network of contracted and extended nodes and was usually observed in regions of light deformation. After heavier deformation a new, more complex dislocation configuration, which divides the crystal into intrinsically and extrinsically faulted regions, was observed. In some instances these dislocations form a very regular pattern. A formation mechanism for such networks is discussed in terms of present theories.
Low-Stress Shock and Release Wave Behavior of Porous Carbon
Authors: Lysne P. C.
Published: February 2004

Shock-reverberation techniques and transmitted-wave experiments were used to determine multiple shock states and release adiabats from shock-induced states for a 0.68-g/cm3 graphite foam and a 1.37 g/cm3 carbon felt. These experiments indicated that the samples were not compacted to solid density in the 1–3 μsec duration of the stress pulse, even though the peak pressures were well in excess of the quasistatic yield strength of the materials. For the very low-density graphite foam, release adiabats centered at initial shock states between 0.7 and 3.2 kbar were found to be indistinguishable from the principal Hugoniot; whereas for the more dense material, release adiabats centered between 0 and 25 kbar were substantially different from the principal Hugoniot. This seemingly anomalous behavior of the graphite foam is likely due to a separation of the solid portions of the sample from the gauge. A prediction of the distance at which a short stress pulse is overtaken by trailing relief waves is given for the carbon felt.
Small-Angle Electron Diffraction of Very Thin Growing Films
Authors: Heritage M. B. , Tompsett M. F.
Published: February 2004

A new method for studying the structure of thin films during the earliest stages of growth has been developed. Direct measurements of energy filtered, small-angle electron diffraction intensities enables structural information of early stages in the growth of a vapor deposited thin film to be derived with greater accuracy than is possible by conventional electron microscopy. A quantitative theory is developed and curve fitting on the experimentally measured intensities enables the values of island size and the density of islands on the substrate to be obtained. The method is applied to observations of silver evaporated onto carbon and the results correlated with those of electron microscopy.
Internal Friction Studies in Nickel Crystals from 77° to 298°K
Authors: Venkatesan P. S. , Beshers D. N.
Published: February 2004

The deformation-induced damping spectrum has been studied in nickel single crystals from 77° to 290°K. There is a strong correlation between the peaks observed and the stages of deformation. Peak X (Bordoni) rises linearly with resolved shear stress in Stages I and II, the slope in Stage I being probably higher than in Stage II, and then falls in Stage III. The orientation dependence in Stages I and II is consistent with the hypothesis that dislocations in the primary glide system are responsible for it. This linear rise is shown to follow, with the aid of well-known relations, from Paré's version of Seeger's double-kink theory, which predicts that the damping should be proportional to ρl, where ρ is the dislocation density and l the average loop length. Other theories (Brailsford, Seeger) give other powers of l (l2, l0 respectively). The fall of Peak X in Stage III, and its behavior on annealing, are shown to be consistent with pinning (or unpinning) by point defects. Peak Y, which we no longer believe to be the Niblett-Wilks Peak, is associated almost entirely with Stage III, and has an orientation dependence for which there is no immediate explanation.
Examination of Imperfect Muscovite Crystals by X-Ray Diffraction Methods
Authors: Caslavsky J. L. , Vedam K.
Published: February 2004

Single crystals of muscovite have been studied by x-ray Berg-Barrett topography. Remarkably sharp contrasting stripes exhibiting anomalous x-ray contrast were observed. From a detailed study of these as well as rocking curve experiments, it is concluded that the contrast is due to the corrugation of basal planes of mica, as a consequence of irregularity in the slip. The relation between the corrugations and the elastic properties of muscovite is discussed.
Electrical Relaxation in Saline Ice
Authors: Addison J. R.
Published: February 2004

The experimentally observed frequency dispersions of the complex dielectric coefficient for some samples of artificial saline ice (of a type similar to natural sea ice) are examined with a view to identifying major contributing mechanisms. The simultaneous integral equations describing the linear superposition of relaxation processes having a continuum of relaxation times were inverted numerically to yield histogram representations of the relaxation time distribution function between 10−9 and 10−1 sec. These functions exhibited three main features: (1) an abrupt peak near 10−9 sec, responsible in part for the high frequency dispersion (above 1 MHz), and which is attributed to polarization of the elongated conductive brine cells within the ice (Maxwell-Wagner-Sillars dispersion); (2) a hump between 10−6 and 10−4 sec which shifts towards shorter relaxation times at higher temperatures, showing an activation energy similar to that of protons in pure ice—this mechanism is seen at midfrequencies (1 KHz-1 MHz); and (3) a wide mass at longer relaxation times commencing between 10−4 and 10−3 sec which is probably associated with space-charge polarization arising from movement of the ions within continuous brine channels reaching from one electrode to the other.
Acoustic Loss of Vitreous Silica at Elevated Temperatures
Authors: Fraser David B.
Published: February 2004

The resonant sphere technique has been used to measure the temperature variation of the acoustic shear loss of vitreous silica up to 1100°C. The acoustic loss near room temperature, which is on the high temperature end of the 50°K loss peak, was found to be dependent upon fictive temperature, the state of oxidation, and, through the state of oxidation, may be dependent upon the OH or Cl content. A minimum loss occurs above room temperature and for synthesized silicas the loss level is comparable to single-crystal materials. Above the minimum loss, the loss process appears to be thermally activated with an approximate activation energy of 0.5 eV. This low activation energy suggests the diffusion of a network modifier such as hydrogen as a possible cause of the high temperature loss.
Multineedle Field Emission from the Ni–W Eutectic
Authors: Cline H. E.
Published: February 2004

A composite structure consisting of an array of parallel 2 μ wires was produced by directionally solidifying the Ni–W eutectic. A multineedle field-emission cathode was then made by selectively etching and pointing the filament tips. The voltage characteristics of a simple diode constructed from this cold cathode were measured and found to follow the Fowler-Nordheim field-emission equation. At a macroscopic current density of 2×10−4A/cm2 and an electric field of 4×104V/cm a vacuum arc occurred that damaged the multineedle cathode. A field-emission microscope was constructed using a multineedle cathode to observe the emission distribution and the pattern was compared with scanning electron micrographs of the cathode before and after emission. It was concluded that the current was not uniformly distributed over the filaments and that failure was accompanied by local melting.
Nonlinear Effects in Surface Acoustic Waves
Authors: Lean E. G. , Tseng C. C.
Published: February 2004

Experimental results on harmonic generation and parametric mixing of surface acoustic waves are reported. Harmonics of signals at 615 MHz and 1.69 GHz propagating on YZ LiNbO3 substrates were observed: the experiments on parametric mixing used two surface acoustic waves at f1=490 MHz and f2=1.09 GHz. Optical probing technique was used to observe directly the spatial variations of the harmonics, the sum, and difference frequency signals. It will be shown that the nonlinear interactions can be phenomenologically described by coupled amplitude equations. The nonlinear coupling constants are determined by comparing the experimental results with the calculations.
Optical Properties of LiIO3 in the Far Infrared
Authors: Becker C. R. , Nath G.
Published: February 2004

The absorption coefficient of LiIO3 has been measured at 300°, 80°, and 7°K for the ordinary and extra-ordinary ray. The corresponding indices of refraction at 300°, 80°, and 17°K were also determined. Upon cooling from 300° to 7°K, the absorption coefficients decrease drastically in the 10–150-cm−1 spectral region. At 7°K the absorption coefficient is less than 1 cm−1 for frequencies up to 80 and 90 cm−1 for E ∥ c and E ⊥ c, respectively. This characteristic is important for far-infrared generation by mixing of two laser frequencies.
Elastic Field of a Point Defect in a Cubic Medium and its Interaction with Defects
Authors: Masumura R. A. , Sines George
Published: February 2004

Three equal orthogonal double forces without moment aligned along the cubic axes are used as a model for a point defect in a cubic medium. The method of Fourier transforms is used to obtain the solution for the displacement and stress fields. The solution is presented in a polynomial form. The elastic interaction between a point defect and an edge dislocation is computed for copper by making the displacement of the edge dislocation against the stress field of the defect. The interaction with the physically significant [112̄] edge dislocation on the (111) plane in copper is presented. The computer program was verified by the agreement of its results with those for the hypothetical [001] edge dislocation on the (010) plane, for which the stresses can be calculated in closed form. Near the slip plane, the calculated anisotropic interaction was almost twice that of a corresponding isotropic one. The elastic interaction between two point defects in copper is calculated, indicating regions of attraction of like defects along the cube axes and repulsion along the cube diagonals. Eshelby's perturbation analysis for materials with slight anisotropy predicts qualitatively similar effects, but the repulsion is much greater than that predicted by his approximate analysis.
Measurement of the Piezoelectric Coefficient of Quartz Using the Fabry-Perot Dilatometer
Authors: Bottom Virgil E.
Published: February 2004

The piezoelectric strain coefficient d11 has been determined in alpha quartz using a Fabry-Perot dilatometer to measure the strain. The results obtained with eight specimens of Brazilian quartz give an average value of (6.81±0.03) ×10−8 cm/statvolt or (2.27±0.01) ×10−12 m/V. This value is compared with those reported in the literature which range from 5.5 to 7.1×10−8 esu.
Defocusing for the Schulz Technique of Determining Preferred Orientation
Authors: Tenckhoff E.
Published: February 2004

During measurement of preferred crystallographic orientation with the Schulz x-ray diffraction technique, several factors can cause defocusing. Earlier investigations showed that tilt of the specimen in Φ, the angle between the normal to the sample surface and the normal to the diffracting plane, is the most severe limitation for the Schulz reflection technique. The present study shows that this defocusing effect is strongly dependent on the size of the Bragg diffraction angle θ: The greater the Bragg angle, the smaller the decrease in intensity for a given tilt angle of Φ. On the other hand, the absorption coefficient μ of the sample has no influence on the decrease in intensity with increasing tilt in Φ, and its effect is negligibly small for most metals. Correction factors for the loss of intensity can be derived and have a general analytic form, but different coefficients are required for each goniometer setting.
Dependence of Electromigration-Induced Failure Time on Length and Width of Aluminum Thin-Film Conductors
Authors: Agarwala B. N. , Attardo M. J. , Ingraham A. P.
Published: February 2004

Experiments have been undertaken to determine the length and width dependence of electromigration-induced failure time in aluminum thin-film conductors. A statistical model is presented and compared to the experimental data. The significance of the experimental data and the statistical model are discussed in terms of randomly distributed structural defects which produce flux divergences during electromigration.
Alternating Current Distribution Between Planar Conductors
Authors: Luquire J. W. , Deeds W. E. , Dodd C. V.
Published: February 2004

The general theory for the vector potential produced by a sinusoidal current of finite cross section has been developed in a preceding paper.1 In the present work, this theory is applied to a coil between a number of plates of finite electrical conductivities and permeabilities. Linear, isotropic, and homogeneous media are assumed throughout. The Green's function solution is first obtained, and the principle of superposition is then used to effect the desired result. A number of physically observable phenomena, such as the impedance, the power loss due to the presence of the conductors, and the time-averaged electromagnetic force on the conductors are subsequently calculated from the vector potential. The treatment is sufficiently general to allow the solution of a number of difficult electromagnetic induction problems, while each of the expressions obtained for the physically observable phenomena is in terms of an infinite integral that may readily be evaluated on a computer. In all cases for which experimental measurements have been made, the agreement between calculated and observed values is within the limits of experimental error. Preliminary investigations of other cases tend to support the validity of the corresponding theoretical expressions.
Pressure Dependence of the Elastic Constants of NaCl at Low Temperatures
Authors: Ghafelehbashi M. , Koliwad K. M.
Published: February 2004

The paper presents the pressure derivatives of single-crystal NaCl in the temperature range of 180°–300°K. The data have been used to calculate the mode Grüneisen parameters. We have also predicted the shock-velocity and the particle-velocity relationship using the ultrasonic data at 300°K.
Low-Frequency Dynamics of Homogeneous Four-Level cw Lasers
Authors: Danielmeyer H. G.
Published: February 2004

The response of homogeneously broadened four-level lasers to known pertubations is investigated theoretically and experimentally with a Nd:YAG laser. Considered are cavity loss modulations in the low-frequency range including the relaxation-oscillation regime separately from shifts of the cavity frequency. The experiments are carried out in such a way that the population inversion is also spatially homogeneous. This allows us to simplify the theories. Good agreement is obtained between experimental and theoretical results. In the case of loss modulation the laser response exhibits one sharp peak in the vicinity of relaxation oscillations. Regular pulses of high peak intensity are obtained which are controllable with very small loss modulations. In the case of a continuous shift of the cavity frequency the laser output consists of similar pulses. They occur at the relaxation-oscillation frequency independent of the rate of change of the cavity frequency. The laser frequency is shifted away from line center proportional to the third root of the rate of change of the cavity frequency. Mode locking was not found.
Mechanism of Inclusion Damage in Laser Glass
Authors: Hopper R. W. , Uhlmann D. R.
Published: February 2004

The mechanism of inclusion damage in laser glass is associated with the temperature rise of particles, or surface regions of particles, relative to the surrounding glass. The particles of greatest concern are metallic, although at very high-power levels ceramic inclusions containing large concentrations of highly absorbing ions can likewise result in failure. Solutions to the heat-flow problems of a perfectly conducting sphere in a medium of finite conductivity and of the infinite composite solid indicate that temperatures of metal particles subject to a 20-J/cm−2, 30-nsec laser pulse can exceed 10 000°K for a range of particle sizes. These high temperatures produce stresses in the glass adjacent to the particles which can exceed the theoretical strength of the glass, and result in failure. The effects on the breakdown condition of flux level and pulse time, as well as the size, shape, thermal expansivity, and spectral emissivity of the particle, and the heat capacity and thermal conductivity of particle and glass are specified. Observations of damage morphologies are reported and related to the results of the calculations. A fatigue phenomenon is anticipated under certain conditions, and the phenomenon of phase separation is not expected to affect significantly the process of inclusion damage. Likely sources of metallic inclusion particles in laser glasses are considered, and melting conditions most suitable for their avoidance are discussed.
Low-Temperature Luminescence of GaN
Authors: Grimmeiss H. G. , Monemar B.
Published: February 2004

Photoluminescent properties of GaN at low temperatures (1.5°–150°K) have been studied mostly in powder samples. The near-uv emissions at 4.2°K consist of one peak at 3.476 eV, another at about 3.43 eV (dependent on doping), and further a repetitive pattern of emissions in the region 3.0–3.3 eV (so-called satellite emissions). The emission with the highest peak energy is probably due to the recombination of a free exciton. Thus the bandgap of GaN is estimated to 3.48 eV at 4.2°K in good agreement with excitation spectra. The second peak around 3.43 eV is apparently of extrinsic origin. The satellite emissions show at least four peaks at approximately 3.27, 3.18, 3.09, and 3.00 eV. The origin of these emissions is discussed.
Magnetic Properties of some Cubic Rare-Earth-Iron Compounds of the Type RFe2 and RxY1−xFe2
Authors: Buschow K. H. J. , van Stapele R. P.
Published: February 2004

Magnetic measurements in fields up to 30 kOe and for temperatures between 4.2° and 1000°K have been performed for cubic Laves phase compounds RFe2 (R=Gd, Tb, Dy, Ho, Er, and Y) and RxY1−xFe2 (R=Gd, Tb, and Er). The Curie temperatures and saturation moments at 4.2°K are given. A compensation in the temperature dependence of the magnetization is only observed for the various compounds in a certain range of x values. Conditions for the occurrence of a compensation point are derived. For the compounds RxY1−xFe2 the iron moment remains constant for 0≤x≤0.8. Above x=0.8 the iron moment increases strongly. The variation of the Fe moments with x is discussed in terms of a nonlocalized moment associated with the iron ions. The moments shown by Er and Tb in ErFe2 and TbFe2 are both 8.3 μB. For most of the compounds RFe2 the lattice constants are given.
Orthogonal Susceptibility of Permalloy Films
Authors: Greene F. S. , Yarbrough R. B.
Published: February 2004

The switching response of uniaxial 1000-Å nonmagnetostrictive permalloy films in the orthogonal-drive-field mode has been studied. The orthogonal susceptibility is defined as the ratio of the change in the easy-axis (longitudinal) magnetization to the change in easy-axis field. The susceptibility is derived for two cases: first, with only angular dispersion, and second, with both angular and magnitude dispersion. These derivations show that the orthogonal susceptibility is primarily determined by the angular dispersion for well-oriented films. Experimental results are given which confirm these derivations. This analysis was stimulated by the need for a better quantitative analysis of the films used in low-field (∼10−5 Oe) magnetometers.
Ultrasonic Study of Creep in Sodium Chloride
Authors: de Rosset W. S. , Granato A. V.
Published: February 2004

The attenuation and velocity change of a 10-MHz sound wave and the shear strain ε have been measured simultaneously during transient creep in single crystals of sodium chloride. Quantitative determinations of the dislocation den ity A and average dislocation segment length L were obtained from the ultrasonic measurements. A was found to be approximately proportional to ε, and during a given run, L went through a maximum several minutes after a run was started. A model which meets all the limitations imposed by the simultaneous ultrasonic and strain measurements is proposed, according to which transient creep in sodium chloride proceeds by a two-step process. First, edge dislocations move quickly away from the dislocation source, giving an elongated loop composed primarily of two screw segments. The slower screw portions of the loop then move to give the observed strain. The velocity of the screw dislocation thus determines the strain rate ε̇. This model is supported by an interpretation of directly observed shapes of dislocation loops in alkali halide crystals. As the increase in the internal stress σG, determined from the increase in A during a run, was found insufficient to account for the decrease in ε̇, the mobile screw-segment length Ls must decrease. An atomistic theory of transient (logarithmic) creep was developed from this finding. From the theory, the screw-dislocation-segment length Ls was found to be the same order-of-magnitude as that found ultrasonically, and the derived screw-dislocation velocity was found to be in good agreement with that determined independently from an etch-pit study.
Interferometric Determination of the Quadratic Electro-Optic Coefficients in SrTiO3 Crystal
Authors: Fujii Y. , Sakudo T.
Published: February 2004

Quadratic electro-optic coefficients in single crystal SrTiO3 were measured using a Mach-Zehnder interferometer and employing a special phase-modulation technique to find g11=+0.15 m4/C2, g12=+0.04 m4/C2, and g44=+0.08 m4/C2 at room temperature. This result is discussed in connection with DiDomenico-Wemple's theory of nonlinear optical effects in oxygen-octahedra ferroelectrics and also with the induced SHG effect of the crystal.
Effects of Momentum Mismatch on Parametric Gain
Authors: Smith R. G.
Published: February 2004

Solutions to the equations describing traveling-wave parametric amplification are presented. These results extend previous work by including the effects of momentum mismatch and general initial conditions (nonzero pump, signal, and idler fields) on the gain expressions. In contrast to statements found in some earlier published results it is shown that exponential growth is not required to achieve useful parametric gain. This fact is particularly important in the operation of continuously pumped optical parametric oscillators which operate with very small gain coefficients. The equations for the parametric gain are presented in general as well as for a number of limiting cases, and an optimum phase relation between the three waves giving maximum gain is found.
Field of Negative Point, Line or Plane Charges in an n-Type Semiconductor
Authors: Lewis J. A. , McKenna J. , Wasserstrom E.
Published: February 2004

In this paper we study the simplest solutions of the nonlinear differential equation which under certain conditions governs the quasielectrostatic field in a current-free, n-type semiconductor with a negative ``point'' charge in one, two, and three dimensions. Approximate solutions, valid for both large and small charges, are derived and compared with exact solutions, obtained by numerical integration. For small charge the approximation provides a useful estimate of the range of validity of the linear Debye-Hückel theory, while for large charge it yields asymptotic expressions for the potential and the depletion layer radius.
Conduction Bands in In1−xAlxP
Authors: Onton A. , Chicotka R. J.
Published: February 2004

Cathodoluminescence (CL) and x-ray emission excited by an electron microprobe in In1−xAlxP at ∼300°K have been monitored simultaneously to yield conduction band structure and alloy composition, respectively. Efficient single-line CL, characteristic of direct bandgap recombination, is observed for x between 0.0 and almost 0.5. Elsewhere, the CL, characteristic of recombination in indirect bandgap semiconductors, is weak. The direct bandgap CL peak has a composition dependence given by hv=1.34+2.23x (eV). The bandgap in the alloy is direct for 0.00≤x<0.44 with a maximum gap of 2.33 eV.
Structure and Electrical Properties of Sputtered Films of Hafnium and Hafnium Compounds
Authors: Smith F. T. J.
Published: February 2004

The electrical properties of 2000–3000-Å-thick films of hafnium, hafnium nitrides, and hafnium dioxide have been studied. The properties of these films can be related to film structure and composition. Conditions were established under which hafnium films can be prepared by dc sputtering in pure argon with density and resistivity approaching that of pure bulk hafnium. Additions of low concentrations of nitrogen to the argon sputtering atmosphere result in the deposition of films consisting of a solid solution of nitrogen in hafnium. At intermediate nitrogen concentrations films of HfN, a compound with metallic properties, are obtained. Higher nitrogen concentrations in the sputtering atmosphere result in films of nonstoichiometric HfN containing excess nitrogen and finally of films of a higher nitride of hafnium having semiconducting properties. Sputtering in argon-oxygen mixtures above a critical oxygen concentration results in the deposition of HfO2 films with insulating properties.
Piezoresistance in Organometallic Crystals
Authors: Ballard L. F. , Wortman J. J.
Published: February 2004

Several organometallic compounds have been studied to determine the influence of hydrostatic and anisotropic strains on the electrical resistance. Large pressure related changes in resistivity were observed in square planar d8 complexes of iridium and platinum in which a metal-metal interaction is postulated. Compounds not having adjacent metal symmetry show significantly less piezoresistance.
Ortho-Positronium Annihilation in Nitric Acid Treated Polypropylene
Authors: Ogata A. , Tao S. J.
Published: February 2004

The mean lives of positrons annihilating in nitric acid treated polypropylene were determined. A long-lifetime component with a mean life of about 50 nsec appeared when the polypropylene was treated in hot nitric acid for more than three hours. This was obviously due to the annihilation of ortho-positronium in the microcavities in the polypropylene etched by the action of nitric acid. It is suggested that nitric acid attacks the amorphous part of polypropylene first and leaves a skeleton of crystalline form filled with microcavities. The change of the mean life and the intensity of the long lifetime component with the change of the nitric acid treatment time is discussed. The value of the o-Ps diffusion coefficient in polypropylene is estimated to be D>4.5×10−4 cm2 sec−1 and the potential of the barrier surrounding the o-Ps in the cavity is estimated to be less than 1 eV.
Polyoxymethlene Crystals Grown Within Irradiated Trioxane Crystals
Authors: Colson James P. , Reneker Darrell H.
Published: February 2004

The morphological development of polyoxymethylene crystals polymerized from and grown within trioxane crystals was observed following irradiation of the trioxane with alpha particles and a subsequent heat treatment. A novel method of sample preparation enabled the morphology to be observed in detail and resulted in the discovery of new forms of polyoxymethylene crystals as well as an improved description of previously reported forms. A solid-gas-solid crystal growth mechanism was postulated to account for the predominantly acicular habit of the polyoxymethylene crystals.
Thermoelastic Behavior of Rubber-Like Materials at Large Deformations
Authors: Shen Mitchel
Published: February 2004

The statistical theory of rubber-like elasticity requires the energy contribution (fe/f) to be independent of the applied strain. We have in recent publications demonstrated that this stipulation is satisfied within the framework of the statistical theory. However, since this theory is only valid up to moderate strains (∼30%), the question then arises as to how fe/f behaves at large deformations. In this paper we have examined this problem in the context of phenomenological theories of finite elasticity. It is shown that only for neo-Hookean strain energy function, which is equivalent to the statistical-theory free-energy function, is the value of fe/f a constant. For other strain energy functions, such as the Mooney-Rivlin and Valanis-Landel functions, fe/f must decrease with increasing strain. The implication is that in the elasticity of most real rubbers the intermolecular energies play a more important role than previously realized.