bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Turbulence in a Reflex-Arc Plasma
Authors: Hooper E. B. , Girvin Steven M.
Published: February 2004

The spectral characteristics of turbulence in a reflex arc with thermionic cathodes are described. There are two regimes of qualitatively different behavior: (i) As the magnetic field is increased above the range for which the oscillations are coherent (⪝ 250 G) an m=1 and m=2 mode coexist with several beat frequencies. (ii) At higher fields (⪞ 750 G) two frequencies (related by a factor of 2) are observed; different correlation times are associated with each. Present models of plasma turbulence are inadequate to describe the observations.
Experimental Investigation of the Positive Column of a GaI3–Ar Discharge
Authors: Waszink J. H. , Kauffmann M.
Published: February 2004

The radial distribution of the number density of atomic Ga was measured in the positive column of a dc discharge in a mixture of GaI3 vapor and Ar. The GaI3 density was 7.7×1017 m−3, and the Ar density was 3.2×1023 m−3. The measurements were made in the current range between 0.1 mA and 1 A. The atom density was determined by optical absorption. The electric field and the noise temperature were also measured. A dissociation of the iodide by electron impact takes place in the column. At low discharge currents, the Ga density increases with increase in current, and the radial density profile shows a maximum at the tube axis. For a current of 1 mA, the density at this maximum is about 1017 m−3. When the current is further increased, a minimum in the profile develops at the axis and a maximum develops between the axis and the tube wall. At currents above 20 mA, the discharge is carried predominantly by Ar.
Recovery Characteristics of a Triggered-Vacuum Gap at High Currents
Authors: Cobine J. D. , Prescott L. E.
Published: February 2004

A system has been devised for use with a high-current generator whereby the recovery-strength characteristics of a triggered-vacuum gap (TVG) may be determined. Data are presented for an experimental hydrogen-triggered TVG for currents of 2000, 5000, and 10 000 A, the latter value being near the upper limit of the tube studied. The causes of data scattering are discussed.
Determination of Charging Effect in Photoelectron Spectroscopy of Nonconducting Solids
Authors: Hnatowich D. J. , Hudis J. , Perlman M. L. , Ragaini R. C.
Published: February 2004

It is shown by measurements of photoelectron spectra of Ba, Au, and Pd from various samples of BaSO4 coated with microgram quantities of Au or Pd that electron binding energies in Ba are consistent to within 0.1 eV or less when kinetic energy shifts due to surface charging are corrected for by referring the energies of the Au or Pd lines to the same lines measured with conducting metallic samples.
Traveling-Wave Antenna for Exciting Waves in a Cylindrical Anisotropic Plasma
Authors: Hipp Jackie E. , Kristiansen Magne , Hagler Marion O.
Published: February 2004

Several variations of a newly proposed device for exciting ion cyclotron waves in a magnetoplasma are analyzed theoretically and numerically. The results of this analysis are compared with those of a similar analysis of a Stix coil. The new coupler is composed of a set of identical helical straps driven by a multiphase rf source and excites waves that vary azimuthally as ejmθ where m =±1, ±2,…. The analysis reveals that the new coupler offers the following advantages over the Stix coil: (i) a certain degree of control over radial variations of accelerating fields, (ii) a preferred direction of propagation, (iii) more energy coupled into propagating waves (for a given input current), (iv) maximum loading resistance at a higher plasma density, and (v) a slightly wider effective density range for propagating waves.
Analysis of the 3-Tube Asymmetrical Electrostatic Unipotential Lens
Authors: El-Kareh A. B. , Sturans M. A.
Published: February 2004

The 3-tube asymmetrical electrostatic unipotential lens was analyzed as was done with the symmetrical case. A reliable mathematical expression for the axial potential distribution was used to obtain the cardinal points and coefficients of spherical and chromatic aberration. The image and object side properties were obtained in each case. The values of S1/R and S2/R, the separations between the tubes, were taken equal to 0. 25, 0. 375, 0. 5, 0. 75, and 1. 00 and the length of the central electrode L/R was varied from 0. 25 to 2. 00 in steps of 0. 25. A comparison is made between the symmetrical and asymmetrical lens in the accelerating and decelerating modes.
Effects of Pressure on Amorphous Polymers. III. Thermodynamic Properties of Densified Polymethyl Methacrylate
Authors: Kimmel R. M. , Uhlmann D. R.
Published: February 2004

Measurements of the temperature dependence of specific heat are presented for polymethyl methacrylate densified in various pressure-temperature-time cycles. It is found that treatment in the glass transition region produces samples with higher glassy specific heat (0. 38 vs 0. 35 cal/g °C) and lower heat content (difference in enthalpy of 2 to 5 cal/g) than the original material. The change in thermal properties is directly correlated with increased density and increased resistance to annealing. High-pressure treatment in the glassy state is found to produce little change in the thermodynamic properties. Samples vitrified by rapid application of high pressure show complex specific-heat-temperature curves. The results are related to previously reported data on densification and annealing and are discussed in terms of theories of the glassy state and the glass transition.
Anodic Oxides of Ta–Al Alloy Films
Authors: Muth D. G. , Sitarik J. P.
Published: February 2004

The anodic oxides formed on two Ta alloy films with 23 at. % Al and 45 at. % Al are compared with anodic Ta2O5. The alloy films were obtained by cosputtering Ta and Al. A number of the oxide properties investigated depend on the Al concentration. The refractive index and dielectric constant vary as predicted for a homogeneous mixture of Ta2O5 and Al2O3, while the differential field strength and breakdown voltage increase in proportion to the Al2O3 content. For the anodization conditions and the electrolyte used in this study, the refractive index, dielectric constant, and differential field strength are independent of anodization voltage, and the stoichiometry of the two alloy compositions studied is maintained in the oxides.
Equation of State for Porous Metals under Strong Shock Compression
Authors: Naumann Robert J.
Published: February 2004

An equation of state is developed for metals in the high-pressure high-temperature region that can be extended in a thermodynamically consistent manner to the vapor phase. The constants are obtained from observed thermodynamic properties and are specified for Al, Fe, Cu, Ni, Pb, and W. This equation of state was checked against experimental data by computing the Hugoniot curves for normal and porous samples for cases where experimental data are available. Also, the velocity of sound and release isentropes were computed for various shock conditions.
Coefficient of Friction of High Polymers as a Function of Pressure
Authors: Bowers R. C.
Published: February 2004

In a previous paper, we described a method for calculating the coefficient of friction μ for thin solid films deposited on harder substrates. In order to use this method, the shear strength of the film material as a function of pressure must be known. A major limitation of the earlier study was the paucity of such data for materials of interest as dry film lubricants. Recently, data have become available for five high polymers: low-density polyethylene, high-density polyethylene, polypropylene, polyvinylidenefluoride, and polytetrafluoroethylene. The frictional behavior of these same materials in addition to a copolymer of ethylene and tetrafluoroethylene and a copolymer of tetrafluoroethylene and hexafluoropropylene, both in bulk form and as thin films, forms the substance of this report. The experimental values of μ for each polymer agreed well with the values calculated from the pressure-shear-strength data, even when these data were extrapolated to higher or lower pressures. It is concluded that μ as a function of pressure can be determined from shear measurements and, conversely, shear strength as a function of pressure can be estimated from friction measurements of thin films. In general, for thin polymer films, where pressures are usually high, μ will be determined almost entirely by the slope of the shear-strength-vs-pressure curve. For bulk polymer specimens, μ will be greatly influenced by the intercept on the shear axis of that curve and the hardness of the polymer. This has led to an explanation that accounts for the large difference in the frictional properties between bulk specimens of high- and low-density polyethylene.
X-Ray Determinations of the Debye Temperatures and Thermal Expansions for the Pd–Ag–Au System
Authors: Naidu S.V. Nagender , Houska C.R.
Published: February 2004

X-ray measurements of the Debye characteristic temperatures ΘM and the coefficient of thermal expansion for the Pd–Ag–Au ternary-alloy system are presented. The integrated intensities of Bragg reflections and lattice parameters were measured in the temperatures range 80–298°K. For all the alloys, the predominant lattice disturbance was due to thermal vibrations. No significant effect due to static displacements was found. Debye temperatures were found to range from a low of 184°K for gold to a high of 290°K for palladium, with silver intermediate at 226°K. The mean coefficient of thermal expansion was found to range from 9.8×10−6 for palladium to 17.9×10−6 for silver. Grüneisen's relationship between the meansquare atomic-vibration amplitude and the thermal expansion for cubic solids has been found to be valid for these alloys and the constant γZ2 was found to be 0.167. The results suggest that a general weakening of the cohesive forces might be taking place as the smaller palladium atoms are replaced by silver and/or gold in the solid solution.
Theory of Luminescent Efficiency of Ternary Semiconductors
Authors: Hakki B. W.
Published: February 2004

The luminescent efficiency is calculated for a ternary semiconductor, wherein the total electron concentration is divided between the direct and indirect conduction-band minima. In each valley, the rate equations are determined by radiative, nonradiative, and intervalley transfer times. Although such intervalley transfer times are unimportant at 300°K for efficient material, they are found to be important at 300°K when the internal radiative efficiencies are less than 1%. Furthermore, since phonon cooperation is mandatory for transitions between the direct and indirect valleys, the intervalley transfer times become quite long (>10−9 sec in GaAsP) at lattice temperatures below 77°K. In order to compare the analytical expressions of luminescent efficiency with experiment, it was necessary to derive expressions for the external quantum efficiency of a p-n junction in a direct band-gap material. The external electroluminescent efficiency is derived in terms of the junction depth, diffusion length, and absorption coefficient. For the particular case of radiative transitions between free electrons and holes, the predicted ternary electroluminescent efficiencies are in agreement with published experimental results on GaAsP. Furthermore, application of the efficiency expressions to the case of deep impurity emission associated with Si in GaAlAs leads to good agreement with published experimental data on this system. Finally, it is shown that the nonradiative transitions associated with the alloying process are unimportant for most direct band-gap ternaries, as well as inefficent indirect band-gap compositions.
Theoretical Study of Gunn Domains and Domain Avalanching
Authors: Owens J. , Kino G. S.
Published: February 2004

Theoretical studies of the characteristics of Gunn domains have been conducted, using the simplifying assumption that the domain is invariant after its initial formation. This assumption greatly simplifies the calculation, allowing a high degree of accuracy in the solution. The solution involves the use of the most recent experimentally derived velcoity-field and diffusion-field characteristics of the carriers. Calculations in the resistivity range 0.1–10 Ωcm are presented. Using this detailed solution of the domain characteristics and data for the ionization coefficient for avalanching, which are available from experimental and theortical studies the domain potentials required for avalanching have been determined as a function of material characteristics. Two types of calculations have been carried out to predict avalanching within the domain. The first type of calculation is applicable to avalanching occurring in a time comparable to the time required for the domain to drift one domain width. The second type of calculation is directed toward avalanching occurring when a domain drifts for much longer periods of time, including multiple transits through a sample.
Optical Distortion by Heated Windows in High-Power Laser Systems
Authors: Sparks M.
Published: February 2004

In a typical long-focal-length laser system, the distortion of the laser beam by the heated exit window can significantly reduce the intensity at the target at power levels well below those required to melt or fracture the window. The spatially inhomogeneous incident laser intensity causes a temperature gradient which changes the thickness and the index of refraction n of the window, causing it to become a lens having, in general, aberration and birefringence in addition to a finite focal length. Expressions are derived for the thermally induced optical distortion in terms of measurable parameters such as n, dn/dT, the strain-optical coefficients p11 and p12, and the thermal-expansion coefficient α. Since the values of all these parameters are not known for most materials of interest, alternate expressions are derived for use in obtaining rough estimates of the amount of distortion. The temperature differential ΔTcrit across the radius of the window which causes a factor of 1/q reduction in target intensity is derived and tabulated (for the case of q=2). Figures of merit for rating materials are derived and tabulated for various materials. The distortion is smaller in general for ionic crystals than for covalent crystals. The briefringence is expected to be larger for the ionic materials than for the covalent ones. In typical systems, rather large increases, say an order of magnitude, in the value of ΔTcrit can be obtained by changing the focal length of the optical system. Other methods of reducing the optical distortion are discussed briefly. Since the optical distortion is expected to be the factor which determines the limit of the target intensity in long-focal-length systems, a large heat capacity and small values of α, dn/dT, p11, p12, and n are important, while the melting point, tensile strength, and Young's modulus are less important, within obvious limits. Experiments are suggested for studying the thermally induced optical distortion.
Influence of the Specularity Coefficient of Surface Scattering in the Leonard-Ramey Relations for Metallic Thin Films
Authors: Marsocci V. A. , Shue S. S.
Published: February 2004

The research reported herein is a continuation of previous studies concerned with the relationship between the thickness of thin metallic films and the measured data for conductivity and the isothermal Hall voltage. It is demonstrated that the discrepancy between the experimentally determined results, and those which can be theoretically predicted as ideal, may be accounted for if the value of the specularity coefficient of surface scattering is not assumed to be zero, as was the case in previous investigations. The computations, based on the experimental data, would predict a negative value for the coefficient; however, such a value has no physical significance. A similar discrepancy in the computed value of the specularity coefficient has been observed by other investigators and may be accounted for in terms of the enhancement of the thickness dependence of the resistivity due to an additional contribution to the surface-scattering mechanism.
Temperature Profiles in Argon Induction Plasmas: Theory and Experiment
Authors: Eckert H. U. , Pridmore-Brown D. C.
Published: February 2004

A comparison is made between recent temperature measurements of argon induction plasmas which include cases of annular geometry and calculations based on the one-dimensional Elenbaas-Heller equation. Exact numerical solutions, as well as approximate closed-form solutions derived from a two-zone model are used. Good agreement is obtained for the central portion of the plasma column with the exact method for all reported power inputs and with the approximate method for medium power input. Near the walls, however, the experimental temperatures are considerably higher for all geometries and power inputs. It is argued that here electron diffusion causes an overpopulation of electrons and thus an overestimation of gas temperatures when Saha equilibrium is assumed.
Measurement of Relative Minority-Carrier Lifetimes and Luminescence-Center Concentrations in GaP(Zn,O)
Authors: Caruso R.
Published: February 2004

A technique for determining relative minority-carrier lifetimes and relative Zn–O center concentrations in GaP (Zn, O) is presented. This method utilizes relative steady-state measurements of above- and below-gap excited red luminescence. The technique is applied to a series of GaP (Zn, O) crystals and the relative lifetime measurements are correlated with absolute measurements obtained by a different method. Minority-carrier lifetimes varying from 0.5 to 25 nsec were measured.
Stimulated Emission and Excited States of the I6 Donor Electron in ZnO
Authors: Goto Takenari , Langer Dietrich W.
Published: February 2004

Laser-excited luminescence has been measured in ZnO at 1.2°K. Emission due to the annihilation of the I6 bound excition with simultaneous excitation or ionization of the donor electron has been observed in stimulated emission, which was excited by intense N2 laser light. From the hydrogenlike series of these emission lines, the binding energy and the effective mass of the donor electron are estimated to be 40 meV and 0.22m, respectively.
Direct Evidence for Generation of Defect Centers during Forward-Bias Degradation of GaAs1−xPxElectroluminescent Diodes
Authors: Schade H. , Nuese C. J. , Gannon J. J.
Published: February 2004

Direct evidence is presented for the generation of nonradiative defect centers in GaAs1−xPx electroluminescent diodes during forward-bias degradation. The defect centers, which have been observed by thermally stimulated current measurements, have concentrations between 5×1014 and 6×1015 cm−3 and lie 0.2–0.4 eV from either band edge. A qualitative correlation is established between the concentration of the induced defect centers and the extent of the electroluminescence efficiency reduction. In contrast to irradiation-induced defects previously described, defects due to long-term operation cannot be removed by annealing. This difference in annealing behavior is discussed in terms of the nature of defects formed in each case.
Switching and Memory Characteristics of ZnSe - Ge Heterojunctions
Authors: Hovel H. J. , Urgell J. J.
Published: February 2004

Heterojunctions of nZnSe-pGe in which the ZnSe layer is thin and contains a considerable defect density exhibit switching between a high-impedance state of typically 106−107 Ω and low-impedance states three to five orders of magnitude lower, and have the ability to retain either state at zero bias for long periods of time. Switching speeds of 100 nsec or less are observed at repetition rates of 500 KHz, as long as sufficient overdrive is applied to reduce delay times for switching in both directions to negligible values. The effect of temperature on the device parameters is presented, and a model consisting of trap emptying by impact ionization, the formation of current filaments, and the refilling of traps by electron injection is proposed.
Radiative Processes in Direct and Indirect Band Gap In1−xGaxP
Authors: Bachrach R. Z. , Hakki B. W.
Published: February 2004

Using a new technique for measuring time-resolved spectra, the radiative recombination processes have been studied in In1−xGaxP for compositions in the vicinity of the direct-indirect band-gap crossover point. Free-to-free, free-to-bound, and bound-to-bound (donor-acceptor pair) transitions are shown to occur in Zn-doped samples at various temperatures in both direct and indirect band-gap materials close to the crossover composition. Time-decay measurements of the donor-acceptor pair recombination show the effect of the increased recombination transition rate as the lowest conduction-band minimum changes from X to Γ. Optical-absorption measurements have been used to determine the band gap for the Γ valley as a function of composition and temperature and to confirm the presence of free-electron-hole recombination. The measurements in this work support the direct-indirect transition band gap of 2.17 eV at 300 °K determined from pressure experiments. The recombination probability B for direct band-gap compositions of In1−xGaxP has been determined to be 7.5 × 10−10 cm3/sec at 300 °K and band gaps between 2 and 2.2 eV. In1−xGaxP near the direct-indirect transition have a measured index of refraction of 3.46.
uv Microprobe Technique for Measurement of Minority-Carrier Diffusion Length in GaP p-n Junction Material
Authors: Hwang C. J. , Haszko S. E. , Bergh A. A.
Published: February 2004

The minority-carrier diffusion length on either side of a GaP p-n junction have been determined from measurements of the short-circuit current under uv excitation. The uv lines at 3.41 and 3.53 eV are extracted from an Ar laser and are focused to a spot 10 μ in diameter. The uv spot is scanned along the angle-lapped surface of the junction to obtain the variation of short-circuit current as a function of distance normal to the junction from which the diffusion length is derived. The technique provides a determination of diffusion lengths as short as 0.13 μ with an accuracy of 15%. The technique is straightforward and should be useful in the evaluation of GaP and other semiconductor material containing p-n junctions.
Arsenic and Cadmium Implantations into n-Type Gallium Arsenide
Authors: Itoh Tadatsugu , Kushiro Yukitoshi
Published: February 2004

Electrical properties of cadmium-implanted layers in n-type GaAs substrates and effects of arsenic preimplantations have been investigated. The implant conditions were energy 20 keV, dose 1014–1016/cm2, and substrate temperature 500°C for cadmium implants and 25°C for arsenic preimplants. The measured carrier-concentration profile shows that a heavily doped p-type layer exists within 1000 Å of the surface for cadmium-implanted specimens. However, current-voltage and capacitance-voltage characteristics of the diodes fabricated by implantations of 1015 and 1016 Cd/cm2 indicate that these junctions have a p-π-n structure. Thicknesses of the π layers are about 3 μ for the dose of 1016 Cd/cm2 and 1.5 μ for 1015 Cd/cm2. On the other hand, diodes fabricated by arsenic and cadmium implants have characteristics of normal p-n junctions. Arsenic preimplantation reveals the fact that high-dose implantation into a hot substrate produces a large number of arsenic vacancies, which diffuse deeply into the substrate. Arsenic vacancy-donor silicon complex acts as a deep-level compensating center and forms a thick high-resistance layer.
Negative Differential Conductivity Due to Electrothermal Instabilities in Thin Amorphous Films
Authors: Shousha A. H. M.
Published: February 2004

Static, transient, and ac signal characteristics of semiconducting glasses are investigated in terms of electrothermal instabilities. The simple analytical treatment assuming adiabatic conditions is evaluated by comparing its approximate results with the exact computed results. Electrothermal instability could account for the device static characteristics and delay time. However, the conduction mechanism should change during the switching process to account for switching times of the order of 10−9 sec. The possibility of stable dynamic characteristics is discussed.
Enhancement of the Superconducting Transition Temperatures of Ti–Mo (5, 7 at.%) Alloys by Mechanical Deformation
Authors: Ho J. C. , Collings E. W.
Published: February 2004

Low-temperature calorimetric measurements have shown that severe mechanical deformation of Ti–Mo (5 and 7 at. %) alloys, although it has little influence on either the density of states or the Debye temperature, significantly enhances the superconducting transition temperature. The net effect of the deformation is thus to distort the phonon spectrum in such a way as to favor the superconducting electron coupling.
Josephson Tunneling Barriers by rf Sputter Etching in an Oxygen Plasma
Authors: Greiner J. H.
Published: February 2004

A new technique for fabricating Josephson tunneling barriers has been developed. Oxide tunnel barriers with estimated thicknesses from 20 to 50 Å have been formed on lead films with indium underlayers and on niobium films. The technique includes an rf sputter etching step in argon for cleaning followed by an rf sputter etching step in oxygen. During the latter, an oxide film is grown having a steady-state thickness which is attributed to a balance between sputtering and oxidation rates. Different oxide thickness may be obtained by varying process parameters such as oxygen pressure and rf power.
Detection Process in Neutron Radiography
Authors: Garside B. K. , Harms A. A.
Published: February 2004

A model of the imaging process in the direct conversion method for obtaining neutron radiographs is presented. The analysis is aimed at obtaining expressions for the attainable object resolution as a function of system and object parameters. Initially, the analysis is carried out assuming a parallel incident beam of neutrons in order to compute the best possible resolution. The results obtained are subsequently used to elucidate the effect of varying certain detection system parameters on both the resolution function and the relative exposure times for a gadolinium converter. Since the neutron beams used in radiography cannot generally be considered to be sufficiently close to parallel, the model has been extended to allow the incorporation of the effects of neutron beam divergence due to finite source size. Comparisons are presented between the results obtained from this model of the neutron radiographic process and experimental data already reported in the literature.
NMR Study of Water Metabolism in the Olfactory Nerve of Garfish
Authors: Silvidi A. A. , Easton D. M.
Published: February 2004

The proton nuclear magnetic resonance line for H2O in nerve is broadened when the K+ concentration of the physiological solution is increased 30×. The difference between nerve in normal compared to high K+ solution was maintained during an observation period of 100 h. Changes in linewidth are attributed to alteration in viscosity of the H2O associated with a changing contribution of metabolic H2O to the signal.
Cylindrical Magnetic Domain Propagation in Sm0.55 Tb0.45 FeO3 Platelets Possessing High Surface Coercivity
Authors: Luff Peter P. , Lucas John M.
Published: February 2004

Differential domain-wall propagation in the surface layers and interior of single-crystal c-axis-oriented 75-μ-thick Sm0.55 Tb0.45 FeO3 platelets has resulted from high surface coercivity induced by mechanical polishing. Cylindrical magnetic domains with measured wall coer-civities of 0.5 Oe were formed inside the platelets following saturation of the surface magnetizations. The magnetized surfaces imposed a self-biasing effect on the bubbles. These bubbles were propagated at 100 Hz with a Permalloy T-bar shift register.
Thermal Expansion Characteristics of CrVO4 by X-Ray Diffraction
Authors: Riedner R. J. , Cartz L.
Published: February 2004

The anisotropic thermal expansion coefficients for CrVO4 determined by x-ray diffraction studies are αa = 58 ± 11, αb = 68 ± 12, αc = 78 ± 14 (all × 10−7 / °C) over a temperature range 25–700 °C. This anisotropy of CrVO4 is attributed to the relative motion of the vanadium ions towards the positions of the rutile-type structure, which is the structure attained by CrVO4 at high pressures. The small degree of anisotropy is in agreement with the small differences in the cation-oxygen bond lengths of CrVO4.
Coupling to Volume Waves in an Elastic Waveguide
Authors: Ristic V. M.
Published: February 2004

Strong coupling to volume elastic waves is achieved with a pseudoperiodic grating on the plane surface of piezoelectric plate. First the identification of various elastic modes is established by correlating the dispersion equation and the experimental results obtained from swept frequency measurement of the elastic waveguide, and second the enhanced coupling to volume elastic modes is explained in terms of a frequency condition and a phase-matching condition.
Electrical Resistivity and Magnetic Susceptibility of Amorphous Cr–Ni–Pt–P Alloys
Authors: Sinha Ashok K.
Published: February 2004

Amorphous alloys having the composition (CrxNi0.30−xPt0.70) 0.75P0.25, where 0.0 ≤ x ≤ 0.06, were synthesized by rapid quenching of the melt. The base alloy, x=0, is nonmagnetic and its negative temperature dependence of resistivity in the range 4.2 ≤ T ≤ 400 °K was earlier interpreted in terms of Ziman's theory of structural scattering of electrons. Chromium additions to this Ni–Pt–P alloy give rise to an additional temperature-dependent negative-resistivity contribution. This observation may be correlated with the presence of localized magnetic moment on Cr atoms, and consequent Curie-Weiss behavior of the 1/χ-vs-T plots.
Stark Effects in C13H3F: Passive Q Switching of the CO2 Laser Using C13 Enriched Methyl Fluoride
Authors: Weitz Eric , Flynn George , Ronn A. M.
Published: February 2004

Stark modulated absorption of CO2 laser radiation at 1035.462 cm−1 [P(32), 9.6 μ] by methyl fluoride shows that C13H3F is the absorbing species. The approximate absorption coefficient of C13H3F at the laser frequency is 0.25 cm−1 Torr−1. Passive Q switching of the P(32) 9.6-μ laser transition has been achieved using 50% C13 enriched samples and a wide range of CH3F pressures depending on the gain of the laser cavity.
c-Axis Orientation of Sputtered ZnO Films
Authors: Dybwad G. L.
Published: February 2004

Piezoelectric tests on thin polycrystalline films of sputtered ZnO have shown that the c-axis polarity is dependent on the substrate material. Evidence suggests that the heat conductivity of the substrate is the bulk physical property controlling this effect. Two different c-axis polarities might be expected, since it has already been observed that the two polar ends of ZnO have different properties. Correlation of these piezoelectric data with existing crystallographic conventions shows that substrates with large heat conductivity cause the ZnO to grow with the Zn face next to the Au layer evaporated onto each substrate before deposition.
Josephson Effects in a Bulk Granular Superconductor
Authors: Warman J. , Jahn M. T. , Kao Y. H.
Published: February 2004

Experimental results are presented for the dc and ac Josephson effects found in a bulk granular superconductor comprised of about 104 superconducting grains (less than 45 μ in dimension) packed in an insulator capsule. This new type of Josephson weakly coupled superconductor offers high sensitivity in response to microwave radiations with a noise-equivalent power as low as 10−14 W/(Hz)1/2.
Another Look at the Pressure Dependence of Interstitial-Substitutional Dissociative Diffusion
Authors: Weyland J. A.
Published: February 2004

The pressure dependence of the interstitial-substitutional dissociative mechanism of diffusion has been reexamined. It has been predicted previously that for such a mechanism a plot of the logarithm of the diffusion constant D vs the anneal pressure along an isotherm should have negative or zero curvature. A more exact analysis shows that there is no reason why a positive curvature should be prohibited for this mechanism. Before any predictions about the sign of the curvature can be made, it is necessary to look at the factor CsDs/CiDi, where Cs and Ci are the substitutional and interstitial solute concentrations, and Ds and Di are the substitutional and interstitial diffusion constants, respectively.
Effective Rate Coefficients for the Formation of N3+ and N4+ Produced in dc Discharges of He–N2 Mixtures
Authors: Tombers Reid B. , Chanin L. M.
Published: February 2004

Analysis of ion-sampling results obtained for dc discharges containing He–N2 mixtures enables estimates to be made of the rate coefficients for termolecular-association reactions producing N3+ and N4+. The resulting effective rate coefficients are small compared to values obtained from afterglow studies. This result is believed due to losses by dissociation within the discharge.
Pyroelectric Properties of Polyvinylidene Flouride and Its Use for Infrared Detection
Authors: Glass A. M. , McFee J. H. , Bergman J. G.
Published: February 2004

It has recently been discovered that the pyroelectric and nonlinear optical properties of polyvinylidene fluoride (PVF2) closely resemble those of a ferroelectric. In this work, we investigate more fully the ``ferroelectric'' behavior of PVF2. Measurements of the pyroelectric properties and polarization reversal are described. Commercially available PVF2 films have been used for radiation detection at 10.6 μm with responsivities of 17 V/W and noise equivalent power (NEP) of 15×10−9 W/Hz1/2 at 100 Hz (0.02-cm2 detector area). Although this NEP is considerably higher than that for other pyroelectric materials, this polymer seems particularly attractive in applications where ultimate detectivity is not required because of the great ease and low cost with which detector films can be constructed in any shape or size.
Infrared Localized-Vibrational-Mode Absorption of Ion-Implanted Aluminum and Phosphorous in Gallium Arsenide
Authors: Skolnik L. H. , Spitzer W. G. , Kahan A. , Hunsperger R. G.
Published: February 2004

The localized-vibrational-mode absorption of ion-implanted Al and P in GaAs is observed. The implants were done at room temperature with a flux of ∼3×1012 ion/cm2 sec and fluences of 2.0×1016, 2.8×1016, and 3.7×1016/cm2 at 1 MeV. The Δn=1 transition of Al substitutional on the Ga sublattice and P substitutional on the As sublattice are observed, and liquid-nitrogen-temperature absorption measurements are made for isochronal anneals from 200 to 900°C. The Al-implanted GaAs shows an AlGa local mode near 362 cm−1 and GaAs implanted with P shows a band near 355 cm−1 similar to melt-doped crystals, but with increased linewidths. From the integrated absorption, it is estimated that nearly all of the Al and P is AlGa and PAs after 900°C anneal, and the site symmetry is approximately tetrahedral.
Localized Vibrational Modes of Boron-Lithium Pairs in Si-Rich Ge–Si Alloys
Authors: Cosand A. E.
Published: February 2004

Localized vibrational modes of boron-lithium pairs have previously been observed in silicon; the 10B(11B) localized mode is split into an axial mode at 584(564) cm−1 and a doubly degenerate transverse mode at 681(655) cm−1. In this work the infrared absorption bands of these modes were observed in boron-doped lithium-compensated GexSi1−x for 0≤x≤0.12. The bands were slightly lowered in frequency and asymmetrically broadened by the addition of the germanium. The asymmetric shape results from the superposition of the absorption from boron atoms with different second-neighbor configurations; the line shape is fit well by a simple model for interactions between the boron and Ge second neighbors and the assumption of random distribution of Ge throughout the crystal. The broadening is attributed primarily to lattice strain, the effect of the mass change being calculated to be far too small, and to modification of the Li–B interaction. It is found that the Li–B pairing distance must be smaller then the previously reported values of 2.4–2.9 Å. New bands at 553 and 651 cm−1, attributed to boron with a Ge first neighbor, are split off from the previously observed boron localized modes in the sample with 12% Ge. These are weaker than would be predicted by a random distribution of Ge, indicating that boron and Ge tend to avoid first-neighbor pairs, or that the oscillator strength of the boron mode is lessened by a Ge first neighbor.
Infrared Absorption of Lattice Modes and the Silicon Local Mode in GexSi1−x Alloys
Authors: Cosand A. E. , Spitzer W. G.
Published: February 2004

Measurements have been made of the infrared absorption of GexSi1−x alloys for x≤0.12 and x≥0.88. The measurements were made in the range 100–700 cm−1 at temperatures from 10 to 300°K. In Si-rich alloys (x≤0.12) absorption bands are seen near 485, 400, and 125 cm−1 which are essentially temperature independent, indicating a single-phonon process. The bands do not correspond well with the predictions of simple models for resonance mode absorption, but are more nearly characteristic of the single-phonon density of states for Si. In the Ge-rich alloys (x≥0.88) the Si localized mode is observed as an absorption band at 389 cm−1 for x=0.99, increasing to 394 cm−1 at x=0.88. The absorption cross section αpeak/[Si] is only 4×10−21 cm2, smaller by 102−103 than observations for other local modes in semiconductors. Two-phonon absorption bands at about 200 and 290 cm−1 in Ge are enhanced by the addition of Si. The over-all temperature dependence of the absorption strength is large enough that it is not obvious whether the observed enhancement is temperature dependent or is a temperature-independent absorption, caused by the Si, superposed on a temperature-dependent background.
Experimental Study of Scattering of Longitudinal Elastic Waves from Cavities in a Solid Medium
Authors: Franzblau Michael C. , Kraft David W.
Published: February 2004

Measurements of ultrasonic attenuation due to the scattering of longitudinal elastic waves from a distribution of cavities in a solid medium are found to be consistent with theoretical predictions. Under certain conditions such measurements can be utilized to nondestructively characterize the size and number density of such a collection of scatterers.
Phase Transitions in CsPbCl3
Authors: Cohen M. I. , Young K. F. , Chang Te-Tse , Brower W. S.
Published: February 2004

Measurements of dielectric properties, pyroelectricity, and the electron paramagnetic resonance spectrum of Gd3+ as a function of temperature have been used to examine the phase transitions in CsPbCl3. The results indicate the presence of five phase transitions and the loss of a center of symmetry at 194 K. The results together with the apparent order of the transitions, and published data, enable the Landau criterion to be used so that the point group of each phase may be identified. A reasonable choice of space group is also made.
Photoelectronic Properties of Defects in CdSe Single Crystals
Authors: Robinson Arthur L. , Bube Richard H.
Published: February 2004

The properties of electronically active imperfections in CdSe single crystals have been investigated through measurements of dark conductivity, Hall effect, photoconductivity, and optical absorption. The same apparent photoconductivity sensitizing centers with an energy level 0.6 eV above the valence band were found in all photosensitive crystals, regardless of the method of heat treatment. Various procedures for producing high-resistivity photosensitive crystals from high-conductivity nonstoichiometric crystals introduce characteristic recombination centers that compete with the sensitizing centers in determining the magnitude and temperature dependence of the photoconductivity. The diffusion of silver acceptors results in a much lower photosensitivity than diffusion of copper acceptors. Annealing in selenium introduces sensitizinglike recombination centers with levels closer to the valence band than 0.6 eV, which dominate the temperature dependence of the photosensitivity, so that the highest sensitivity is found only below liquid-nitrogen temperature. Subsequent vacuum annealing at an elevated temperature or room-temperature annealing for several months removes the influence of these centers. The only center definitely associated with Cu impurity has a level 1.05 eV above the valence band. No evidence was obtained associating Cu or Ag impurity with the sensitizing center at 0.6 eV. A defect involving native acceptors, such as Cd vacancies, provides the most consistent explanation for the sensitizing center.
Growth of ZnO Whiskers, Platelets, and Dendrites
Authors: Sharma S. D. , Kashyap Subhash C.
Published: February 2004

Zinc oxide whiskers, platelets, and dendrites have been grown on the ZnO substrate by a simplified and modified vapor phase technique which involves the production of zinc vapor at the growth temperatures itself. By this method, whiskers-a few mm in length and a fraction of a mm in diameter-have been obtained at growth temperatures ranging from 960 to 980°C. Change in growth habit from whiskers to platelets has also been observed. Various growth mechanisms have been discussed. It appears that the growth of these crystals takes place at supersaturations higher than those usually required for whisker growth. The dendrites have been observed to grow at about 930°C.
Effects of the Addition of Cholesterics on Nematic Liquid Crystal Properties
Authors: Kerlleñevich Betty , Coche André
Published: February 2004

The influence of different contents of cholesteryl nonanoate (NC) on the properties of liquid nematic crystals is reported. The transmission spectra are recorded with and without dc field. When the quantity of NC is higher, the conductivity is lower and the voltage threshold of dynamic scattering increases. The decay of transmission with increasing voltage is accelerated in the presence of small quantities of NC, compared to that of pure nematic substance.
Diffusion of Silver into Nickel Single Crystals
Authors: Wazzan Ahmed R. , Tung P. , Robinson Lawrence Baylor
Published: February 2004

Lattice diffusion of radioactove silver Ag110 into high-purity nickel single crystals is measured over the temperature range 507–782°C. The lattice diffusion coefficient (DL)Ag/Ni, obtained by Gruzin's residual activity method, is given by (DL)Ag/Ni=0.025 exp(−47 200/RT) cm2/sec. The activation energy QAg/Ni=47 200 cal/mole for silver diffusion in nickel is much smaller than QNi/Ni for self-diffusion in nickel (66 800 cal/mole) but is about equal to QAg/Ag for self-diffusion in silver (46 000 cal/mole.
Mixing of Noncollinear Elastic Surface Waves on LiNbO3
Authors: Carr Paul H.
Published: February 2004

The decrease in a 0.5- to 1-GHz surface wave signal due to its interaction with a noncollinear 1.13-GHz pump has been observed to be as large as 1.7 dB. The selection rules for the nonlinear elastic interaction show the possibility of single-sideband mixing and beam deflection of the idler.
Acoustic Surface-Wave Beam Diffraction on Anisotropic Substrates
Authors: Mason I. M. , Ash E. A.
Published: February 2004

The diffraction of any distribution can be discussed in terms of its constituent Gaussian modes. Simple design formulas are developed from a two-dimensional diffraction theory in order to characterize Gaussian beam diffraction in terms of three readily determined anisotropic propagation coefficients. The relationship between these coefficients and known anisotropic propagation phenomena is explored. Beam steering, diffraction, and focusing effects are discussed in some detail. Attention is drawn to two particular effects: autocollimation and ``negative'' phase front curvature. Situations in which both occur in practice are discussed. The former should play a significant role in acoustic matched filter design. A cylindrical transducer is shown, within limits, to be an optimum structure for obtaining a single acoustic beam convergence, even in the presence of beam scattering. The parabolic diffraction theory is applied to the design of an experimental anisotropic focusing system.
Determination of Electron Density Profiles from Tonks-Dattner Resonance Data in Plasmas
Authors: Baird A. W.
Published: February 2004

A technique is described for deducing an unknown electron density profile from observed Tonks-Dattner resonance frequencies, which uses a simple resonance condition derived from the WKB approximation. The density profile is approximated by a step model, piecewise-linear model, step-piecewise-linear model, and polynomial model in both active and after-glow plasmas in plane-parallel and cylindrical geometries. Good agreement is obtained between the profile determined by this technique and one obtained theoretically.
Comparison of Various Microwave Breakdown Prediction Models
Authors: Mayhan Joseph T. , Fante Ronald L. , O'Keefe Robert , Elkin Richard , Klugerman Jack , Yos J.
Published: February 2004

This paper is concerned with presenting a comparison of various microwave breakdown prediction models when applied to predicting breakdown of a practical antenna system located in a partially ionized environment. Solutions for the breakdown conditions are obtained numerically, allowing for the field and environment properties to have arbitrary spatial variation. The models are applied to predictions of breakdown for an S-band slot radiating from a reentry vehicle, and the enviroment properties are taken from aerodynamic conditions existing along the descent trajectory. The three models compared consist of a linear model, a variational model, and a nonlinear model. The models are based on the electron-continuity equation and allow for the effects of diffusion (including the transition from ambipolar to free diffusion), high-temperature effects, and recombination, which, to our knowledge, have not been treated previously in a single model.
Reduction of Sparking Voltages Due to a Magnetic Field Parallel to the Axis of Rod Electrodes
Authors: Kofoid M. J. , Cleva H. V.
Published: February 2004

Round-rod electrodes with flat ends were aligned with the axis of a glass vacuum chamber. They were completely insulated by close-fitting glass except for the 1.0-cm-diam ends which faced each other to form a 2.5-cm-long spark gap. Sparkover voltage tests were made at 5 and/or 40 μ in Kr, Ne, He, N2, and air. An unexpected dramatic and sudden decrease in sparkover voltage occurred in all gases when a modest steady uniform magnetic field was applied parallel to the axis of the electrodes.
Dynamic Scattering by a Nematic Liquid Crystal Where the Applied Electric Field Is Normal to the Incident Light
Authors: Holloway W. W. , Rafuse M. J.
Published: February 2004

The scattering of light perpendicularly incident to an electric field in a nematic liquid crystal has been investigated. At low electric field strengths, the formation of domains results in the diffraction of the scattered coherent light. This diffraction provides a convenient tool for the study of domain behavior. The formation of the domains depends on the cell thickness and applied electric field. As the electric field is increased, the liquid-crystal domains become narrower and rotate slightly until they are parallel to the applied field. A further increase in field strength leads to the onset of dynamic scattering with the attendant disruption of domain regularity. The scattered light loses the structure of the diffraction patterns but retains a preferential scattering in the direction of the diffraction orders. No appreciable effects due to the polarization of incident radiation have been observed.
Direct-Display of Plasma Density and Temperature
Authors: Kawashima Nobuki , Yamori Akira
Published: February 2004

A direct-display plasma density and temperature meter was developed using a floating double-probe method. A small ac voltage was superposed on the dc voltage, and the third harmonic component of ac current was detected. The phase reversal of the third harmonic component was observed at Vdc = V* = 1.30 kTe, and an experiment was carried out to fix the dc voltage automatically at this voltage V* detecting the phase reversal of the third harmonic component. The plasma density and electron temperature were obtained directly from the dc voltage V* and the dc current corresponding to the voltage V*.