bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidation of lead films by rf sputter etching in an oxygen plasma
Authors: Greiner J. H.
Published: February 2004

The method of forming thin oxide layers by sputter etching in a low-power rf oxygen discharge (rf oxidation) was investigated. Use of the method for oxide formation on Pb films was studied using in situ ellipsometry. A steady-state oxide thickness was observed that depended on the oxidation and sputtering parameters. For oxygen pressures of (5–40) × 10−3 Torr and cathode voltages of 175–450 V, the steady-state oxide thickness was in the 60–90-Å range. The oxide layers grown in the rf oxygen discharge had the orthorhombic form of PbO similar to that formed by thermal oxidation. However, the PbO layers were found to be nonstoichiometric due to excess oxygen; ellipsometric measurements indicated values of 2.6–2.8 and about 0.1, respectively, for their index of refraction and extinction coefficient.
Magnetostatic wave propagation losses in an anisotropic insulator
Authors: Vittoria C. , Wilsey N. D.
Published: February 2004

Propagation losses are calculated for magnetostatic surface waves in slabs of YIG and LiFe5O8. A phenomenological (Gilbert) magnetic damping is assumed and known magnetic parameters are used. The propagation loss factor L (dB/μsec) is calculated as a function of frequency. At high frequencies we find that L is proportional to frequency with a slope of 4π(76.4λ/γ2M), where λ is the damping parameter, γ is the gyromagnetic ratio, and M is the magnetization. At low frequencies, L approaches a limiting value of 4π(76.4λ/γ). The quantity L is independent of slab thickness, although both loss and delay time are functions of thickness for a given slab length. Our calculated L is in reasonable agreement with recent measurements. As expected, magnetic anisotropy has a greater effect on L for LiFe5O8 than for YIG.
Superconductivity in some new metastable film phases
Authors: Testardi L. R. , Wernick J. H. , Royer W. A. , Bacon D. D. , Storm A. R.
Published: February 2004

The occurrence of new metallurgical phases and enhanced superconductivity in a number of sputtered transition-metal alloy films has been studied as a function of substrate temperature during deposition. Results indicate that such new phases are readily produced in the temperature range 200–1000°C by this technique and that these new phases are accompanied by marked changes in the superconducting transition temperature. The findings show how easily the more complex transition-metal alloys, particularly σ phase, can be modified at low temperatures, and demonstrate the importance of structural instability, vis-à-vis composition, in determining the superconducting transition temperature.
Nyquist's theorem and 1/f noise
Authors: Tunaley J. K. E.
Published: February 2004

The spectral density of the current fluctuations in a resistor is derived under conditions where the time between collisions or traps has a finite variance. When the variance is infinite, a 1/f type of spectral density can result. It is shown that in both cases a term appears which is given by Nyquist's theorem: in the presence of an applied field the noise intensity is increased at all frequencies. The effect is particularly pronounced if the variance of the intertrapping time is infinite, and the intensity of the current fluctuations is virtually the same as that predicted by a model involving carrier motion in one direction only.
Noise spectrum analysis of a Markov process vs random walk computer solutions simulating 1/f noise spectra
Authors: Bird J. F.
Published: February 2004

Analytical solution is effected for the noise-power spectrum of a Markoffian random walk, which generalizes some computer models that have been claimed to give 1/f noise spectra (as observed in semiconductors and nerves). The analysis demonstrates the erroneous basis of those claims and illustrates the care needed in computer simulation to avoid such error.
Relationship between single-crystal and polycrystal elastic constants
Authors: Ledbetter H. M. , Naimon E. R.
Published: February 2004

A new method is given for computing effective polycrystalline elastic constants from single-crystal elastic coefficients. Agreement with observation is good. The method is based on the assumed equivalence of the lattice-vibrational properties of single crystals and polycrystals of the same material; single-crystal and polycrystal Debye temperatures are equated. Present predictions of polycrystal elastic moduli differ significantly from those of most other averaging methods by being lower than the familiar Voigt-Reuss-Hill results.
Ion-energy distribution in a plasma under a diverging magnetic field
Authors: Hatakeyama R. , Sato N. , Tsunoda Y. , Sugai H. , Hatta Y.
Published: February 2004

A distribution function of ion energy parallel to a magnetic field is measured to be deformed along a diverging magnetic field in a single-ended Q machine. The deformation is well explained by the orbit theory for a collisionless plasma.
Cell dimensions of hydrocarbon crystals: Surface effects
Authors: Davis G. T. , Weeks J. J. , Martin G. M. , Eby R. K.
Published: February 2004

The unit-cell dimensions of a given polyethylene have previously been shown to vary nearly linearly with the reciprocal of lamella thickness. Data obtained at 153.2 and 296.2°K are presented to show that the slope of this dependence is different for crystals of orthorhombic n -paraffins, melt-crystallized polyethylene, and solution-crystallized polyethylene. Within the limits of error, all extrapolate to the same basal area at infinite lamella thickness, and this agrees with the measured value for a sample crystallized from the melt under high pressure to yield a long period of about 3500 Å. Since the effect is a surface one, it is proposed that these differences result from the differences between methyl interactions, fold interactions, different fold planes, domains, etc. It is shown that the variation of cell dimension with lamella thickness leads to a quadratic term in the variation of macroscopic density. This term permits the separation of the thickness and density of a lower-density surface layer in a two-phase model.
Hillock growth in thin films
Authors: Chaudhari P.
Published: February 2004

A model for hillock growth in thin films such as those of lead and tin is developed. It is proposed that hillock growth is a form of stress relaxation in which atomic species diffuse along the film-substrate interface to the base of the hillock. The latter extrudes out along the grain boundaries connecting it to the rest of the film. The stability and kinetics of this process are considered. Taking into account Nabarro-Herring diffusion creep as a parallel stress relaxation mechanism observations such as an incubation period for hillock growth and the effects of film thickness on hillock density are accounted for. In addition, observations on lateral growth of hillocks and unusually tall hillocks (whiskers) are interpreted within the framework of the present model.
Liquid-crystal thermo-optic effects and two new information display devices
Authors: Sasaki Akio , Kurahashi Keizo , Takagi Toshinori
Published: February 2004

Thermo-optic effects have been studied with changing temperature of a part of the liquid crystal in a cell. The light transmission through the liquid crystal is subject to hysteresis. The experiments show that the mesophase barely coexists with the solid phase, and that there are transparent, semitransparent, and opaque states in the solid phase. Two new information display devices have been made in experiments on the basis of the display characteristics of the liquid crystal and the hysteresis phenomena in the thermo-optic effects. The display device in which the mesophase and opaque solid phase are used shows three functions: memory of entry information; variations of the memory state corresponding to a linear analogue value; and temporary erasure of information. The display device in which the transparent and opaque solid phases are used shows such functions that entry and permanent erasure can be done alternately, and that linear analogue information can be stored.
Effects of divalent cation impurities on surface space charge in thin AgBr films
Authors: Hoyen H. A. , Tan Y. T.
Published: February 2004

A model for the surface space-charge layer in thin ionic films has been extended to include the effects of divalent cation impurities and the association of impurity-cation vacancy complexes. The potential, electrostatic field, and defect distributions are shown to be dependent on film thickness. The fate of photogenerated electrons and holes is discussed relative to the field and defect distributions.
Shock-induced melting in bismuth
Authors: Asay J. R.
Published: February 2004

Polycrystalline bismuth specimens were impacted in plane-wave experiments at stresses of 2.3–2.9 GPa (29 kbar) and for initial temperatures ranging from room temperature to 523 °K. These impact stresses are sufficient to produce final states in the solid II phase of bismuth. For initial temperatures below 435 °K, the Hugoniot in the solid I phase of bismuth intersects the solid I-solid II phase boundary; the dynamic measurements of the solid I-solid II transition pressure over this temperature range and the quasistatic measurements of the phase boundary are in good agreement. For initial temperatures above 435 °K, the Hugoniot intersects the melt boundary and melting can occur during shock compression. It is found that there are no discontinuities in the wave profiles, as expected from hydrodynamic predictions for instantaneous melting. Instead, the wave profiles are highly dispersive for initial temperatures near melt. Nevertheless, melting is inferred from the present measurements by comparing the stress states attained during the shock compression with the known phase diagram for bismuth. The present data also show that deviatoric stresses are present for initial states within 20 °K of ambient melt.
Mechanism of formation of Ohmic contacts to ZnSe, ZnS, and mixed crystals ZnSXSe1−X
Authors: Kaufman R. Gilbert , Dowbor Peter
Published: February 2004

The temperature range of Ohmic contact formation to ZnSe, ZnS0.5 Se0.5, and ZnS is presented. New experiments show contacts are formed by cooldown rather than by heatup and that contacts can be formed and removed reversibly by cyclic cooling and heating. This and other evidence suggest contact formation by liquid-phase epitaxy, as had been shown in group-IV and -III-V semiconductors, rather than diffusion. The role of wetting, which is necessary but not equivalent to contact formation, is discussed.
Luminescent properties of CuGaS2 doped with Cd or Zn
Authors: Shay J. L. , Bridenbaugh P. M. , Kasper H. M.
Published: February 2004

The photoluminescence spectra of CuGaS2 crystals doped with Cd or Zn vary continuously from a green emission (0.51 μ) to an orange emission (∼ 0.59 μ) depending upon the concentrations of Cd and Zn. The room-temperature internal quantum efficiency is reproducibly 0.2%. The electroluminescent efficiencies of CuGaS2: CdS heterojunction LEDs fabricated by using these substrates are not appreciably higher than the best efficiencies reported earlier.
Submicrometer resolution replication of relief patterns for integrated optics
Authors: Aumiller G. D. , Chandross E. A. , Tomlinson W. J. , Weber H. P.
Published: February 2004

We report on three techniques for replicating relief patterns in dielectric materials for use as substrates for planar integrated optical circuits: embossing with a metal die; casting from a metal die; and casting from a rubber mold. Techniques for overcoating the substrates with light-guiding films and filling of grooves are also described. Measured losses in sheet film guides were ≤0.5 dB/cm. Guiding was also observed in narrow light guides fabricated by each technique. Embossing is the simplest process, but for small-scale production the casting processes are simpler to implement.
The effect of gas mixture on the electron kinetics in the electrical CO2 gas laser
Authors: Judd O. P.
Published: February 2004

Detailed numerical calculations of electron transport coefficients and vibrational excitation rates in a He:N2:CO2 gas laser discharge have been carried out over a range 1×10−16≤E/N≤5×10−16 V cm2 for several gas mixtures. Comparison of the results indicate that the vibrational excitation processes in the CO2 molecule scale with the average electron energy and are approximately invariant with respect to gas mixture. At a fixed value of electron energy, the dominant effect of gas mixture variation is to modify the vibrational excitation rate into the nitrogen. The effect of gas mixture variation on electron drift velocity is greatest in CO2–He mixtures, but is substantially reduced when a small fraction of N2 is added.
Effect of misorientation on growth anisotropy in [111]-oriented garnet films
Authors: Malozemoff A. P. , DeLuca J. C.
Published: February 2004

Phenomenological anisotropy constants have been measured in three garnet bubble films with their surface normal slightly misoriented from the crystallographic [111] direction. A tilted magnetic easy axis is found from measurements of homogeneous nucleation and bubble collapse in the presence of in-plane fields. An in-plane anisotropy is also found whose axes do not in general lie either normal to or in the easy-axis tilt plane. These results are shown to be consistent with a phenomenological growth anisotropy model which includes the film plane misorientation.
Cleavage surface energy of the ((111)) plane of strontium fluoride
Authors: Kraatz P. , Zoltai T.
Published: February 2004

Due to its excellent optical transmission in the 2–6-μm wavelength region, SrF2 is an attractive candidate window material for high-energy CO and chemical lasers. Fracture strength, an essential parameter used to evaluate window materials, is largely controlled by the specific surface energy of potential cleavage planes in brittle ionic crystals such as SrF2. This quantity has been measured previously for the ((111)) plane of CaF2 and BaF2, but not for SrF2. In order to obtain this information, a modification of the Obreimov-Gilman cleavage technique has been used to determine the specific surface energy of SrF2 ((111)) under a variety of conditions and two methods of calculation of the experimental value have been examined and compared. An intrinsic value of 260±10 erg/cm2 deduced from the data at 298°K is below theoretical estimates, but corresponds most closely to surface energies calculated using Pauling's ionic radii. An intrinsic value of 430±75 erg/cm2, obtained by an alternative method of calculation, is in excellent agreement with surface energies deduced from a Born-Mayer potential and Huggins radii. However, this alternaive method of calculation markedly increases the apparent scatter of the data, rendering its validity questionable. The apparent surface energy of annealed SrF2 decreases linearly with the longarithm of crosshead speed from 0.002 in./min to 2.0 in./min. This effect is attributable, at least qualitatively, to energy dissipation through dislocation multiplication by the multiple cross glide mechanism in the region of the crack tip. While vacuum (10−6 Torr) annealing at 800°C and variation in the direction of crack propagation are found to have a negligible effect on γ, cleavage at 77°K or in the presence of a DMF/DMSO solution leads to significant increases in γ. These increases may be attributed, respectively, to crack blunting and energy dissipation by dislocation multiplication and step formation.
Measurement of subsonic laser absorption wave propagation characteristics at 10.6 μm
Authors: Klosterman Elliot L. , Byron Stanley R.
Published: February 2004

An experimental study of subsonic laser absorption waves arising from the interaction of 10.6-μm radiation with metal and insulator target materials is described. A shock-tube-driven gas-dynamic laser operating up to 400 kW for 4 msec was used as the radiation source. Instrumentation included streak photography to determine wave speed, holographic interferometry to determine the gas density field, time-integrated visible spectroscopy to determine the principal radiating species, and CO2 laser attenuation measurements to determine the plasma absorption coefficient. The results reported here emphasize the characteristics of waves in free and clean air, far from the influence of the target. The measured wave speeds in air at 1 atm pressure ranged from Mach 0.05 to 0.2 for CO2 laser intensities ranging from 1×105 to 5×105 W/cm2. The wave speeds were also found to depend on the laser beam diameter. The spectral emission and CO2 laser absorption measurements showed that the air plasma reaches a temperature of 15 000–20 000°K and is essentially fully ionized. From an analysis of the results, it is concluded that radiation transport in the plasma plays a dominant role as a wave propagation mechanism, and that radial flow ahead of and within the wave is a dominant feature of the wave structure.
Ionic conduction of silver bromide emulsion grains as affected by dye adsorption
Authors: Takada Shunji , Tani Tadaaki
Published: February 2004

The effects of various dyes upon the electrical conductivity of cubic silver bromide grains with edge lengths of 0.9 μm in a photographic emulsion have been studied with the aid of dielectric loss measurements. The conductivity of the grains was increased by 3,3′-diethyl-9-methylthiacarbocyanine bromide (dye 1) and 1,1′-diethyl–2,2′-quinocyanine iodide (dye 2), and decreased by erythrosin (dye 3) and a merocyanine (dye 4). Based on the knowledge that dyes 1 and 2 are tightly attached to positively charged surface sites composed of silver ions, and that dyes 3 and 4 to negatively charged surface sites, the results are considered to provide evidence for the view on the formation of interstitial silver ions through the positively charged surface sites on silver bromide microcrystals.
GaAs–Ga1−xAlxAs buried-heterostructure injection lasers
Authors: Tsukada Toshihisa
Published: February 2004

Buried-heterostructure injection lasers which have the filamentary GaAs active regions completely surrounded by Ga1−xAlxAs are proposed and have been successfully fabricated by using two-step liquid-phase-epitaxial techniques. The active regions of these lasers can be made extremely small and do not have dimensional unbalances encountered in conventional injection lasers. The threshold current has been reduced to a value as low as 15 mA by applying current-confining geometry to this laser. A study of optical characteristics has revealed such improvements over ordinary lasers as Gaussian beam profile, fundamental mode (TE00) operation, mode reproducibility, and mode stability. Due to the superior thermal properties of these lasers cw operation was easily obtained.
Simultaneous two-wavelength output from multiple-dye pulsed tunable dye lasers
Authors: Hilborn Robert C. , Brayman Howard C.
Published: February 2004

We report the observation of simultaneous two-wavelength output from nitrogen-laser-pumped multiple-dye lasers. Rhodamine 6G-cresyl violet mixtures and coumarin-rhodamine 6G mixtures were studied. An analysis of the spatial distribution and time dependence of the two wavelengths indicates that in the range of dye concentrations used, radiative transfer is the dominant excitation transfer process.
Annealing behavior of unimplanted and zinc-implanted GaAs
Authors: Itoh Tadatsugu , Kasahara Jiro
Published: February 2004

The annealing behavior of photoluminescence spectra of silicon-doped n-type (100) GaAs specimens and zinc-ion-implanted specimens at room temperature has been investigated at 77 K. Several energy levels associated with Ga or As vacancies have been observed in unimplanted specimens during the anneal stage between 200 and 900 °C. It has been also observed that dopant silicon atoms migrate from Ga sites to As sites in the unimplanted specimen which was annealed above 600 °C. The irradiated damage in the Zn-implanted specimen was removed by annealing at 600 °C for 20 min. The maximum intensity of total emission due to the Zn-acceptor level was obtained after annealing at 850 °C, and the total emission intensity decreased above this temperature.
Equilibrium-to-nonequilibrium transition in MOS (surface oxide) tunnel diode
Authors: Temple V. A. K. , Green M. A. , Shewchun J.
Published: February 2004

When the insulator barrier in a tunneling MIS diode is less than a certain critical thickness (approximately 30 Å for Al–SiO2–Si at 300 °K), the semiconductor departs from thermal equilibrium and a new type of ``nonequilibrium'' current-voltage characteristic results. Such nonequilibrium diodes have been found to possses current multiplication properties and have been used as the basis of the tunnel surface oxide transistor (SOT) reported by Shewchun and Clarke. They have also been applied to direct energy conversion employing the electron-voltaic and photovoltaic effects. The transition of the MIS tunnel diode from the equilibrium to this nonequilibrium mode is investigated as a function of insulator thickness, metal work function, and temperature as well as a number of semiconductor parameters. A nomograph is presented to assist in determining when the MIS tunnel diode is in the nonequilibrium mode. Surface-state tunneling is seen to play an important role in determining part of the nonequilibrium current-voltage characteristic.
Photoelectromagnetic effect in n-GaSe
Authors: Adduci F. , Cingolani A. , Ferrara M. , Minafra A. , Tantalo P.
Published: February 2004

Photoelectromagnetic (PEM) and photoconductivity (PC) measurements in n-type GaSe monocrystals are reported. The PEM and PC currents are calculated taking into account the anisotropy of the samples. From the analysis of spectral dependence the ambipolar diffusion parameters along the c axis are calculated. Estimates of lifetime and mobilities are also obtained.
Effects of ionizing radiation on cleavage surface energy of SrF2
Authors: Kraatz P. , Zoltai T.
Published: February 2004

Exposure to ionizing radiation is known to alter the mechanical behavior of ionic crystals by impeding the motion of dislocations, leading to increases in such parameters as yield strength and hardness. The influence of irradiation upon fracture strength is not as well understood, particulary for the alkaline earth fluorides, which find important technological use as ir laser windows. In order to better assess these effects, changes in the apparent specific surface energy of the ((111)) planes of SrF2 at 298 °K induced by Co60 γ-gamma irradiation, as determined by a modified Obreimov-Gilman cleavage technique, have been measured. The apparent surface energy is found to increase approximately linearly with the logarithm of total exposure to Co60 γ irradiation in the range from 9.6×105 to 4.3×107 R. This effect is consistent with the decreased dislocation mobility and size of the loops generated at the crack tip, the increased concentration of dislocation sources, and the lengthening of the easy-glide region of the stress-strain curve.
Frequency-dependent absorption efficiency and neutron production in low-energy laser irradiation of slab targets
Authors: Goldman Edward B.
Published: February 2004

A series of numerical experiments have been performed to examine the efficiency of the coupling of laser energy into a plasma target. Classical inverse bremsstrahlung absorption is considered in both the weak- and strong-field limits at laser intensities from ∼ 1015 to ∼ 1016 W cm−2 at the fundamental and first harmonic neodymium laser frequencies. Frequency multiplication from the fundamental to the harmonic is shown to lead to desirable results even if the conversion efficiency is low. The computed absorption, x-ray generation, and neutron production are compared with experimental results. Nonthermal mechanisms are discussed to account for the result that much larger neutron production is found experimentally than can be accounted for in a numerical model.
Magnetostrictive properties of Hox Tb1 −x Fe2 intermetallic compounds
Authors: Koon N. C. , Schindler A. I. , Williams C. M. , Carter F. L.
Published: February 2004

The magnetostriction of several polycrystalline compounds in the Hox Tb1−x Fe2 series have been measured from 77–300°K using magnetic fields up to 17.5 kOe. The extrapolated saturation magnetostriction at room temperature varies linearly with x between 80 × 10−6 for HoFe2 and 1720 × 10−6 for TbFe2, in good agreement with the single-ion model. At the composition x =0.85, where the lowest-order anisotropy constant K1 is very small, the saturation magnetostriction is 325 × 10−6, suggesting that this material might be useful in magnetostrictive device applications.
Effect of strong magnetic fields on superconducting transition of single-crystal NbSe2
Authors: Leupold H. A. , Rothwarf F. , Winter J. J. , Breslin J. T. , Ross R. L. , AuCoin T. R. , Dubeck L. W.
Published: February 2004

The transition temperature of a composite of five single crystals of NbSe2 was measured as a function of magnetic field with the crystal layers in both the parallel and perpendicular orientations with respect to the applied field. Plots of Hc2 versus T for both orientations yielded straight lines up to the largest applied fields of approximately 90 kOe. Linear extrapolation of these lines to T = 0 results in intercepts of the Hc2 axis at 167 and 57.7 kOe for the parallel and perpendicular orientation, repectively. The respective slopes for the parallel and perpendicular orientation are 23.3 and 7.82 kOe/K. The transition temperature in zero applied field was found to be 7.27 K. The transition curves in applied fields exhibited long ``tails'' due to microscopic and macroscopic misalignments of parts of the layer structure with respect to the field. Transverse magnetization measurements near Tc yielded Hc and (d Hc/d t)t = 1 as well as the Ginzburg-Landau parameters κ1(Tc)≃10.6±10% and κ2(Tc)≃11.2±4% for 6 K < T < Tc. Using the tunneling data for the transverse energy gap Δ(0) in the Toxen relation Δ(0)/k Tc = [Hc (0)]−1(dHc/dt)t = 1, Hc(0) was found to be 2.04 kOe±10%. This agreed well with extrapolations of Hc versus t2 plots which yielded Hc(0)=1.95 kOe±10%. Comparisons are made for high-field data obtained on other samples from our laboratory and others. There is evidence for a slight positive curvature in the Hc2 versus T characteristic near Tc for the parallel field orientation of our samples.
Vapor-phase epitaxial growth of GaAs in a nitrogen atmosphere
Authors: Ihara M. , Dazai K. , Ryuzan O.
Published: February 2004

GaAs epitaxial growth by the open-tube AsCl3–Ga–N2 vapor-transport technique was thoroughly examined as to its growth conditions, with some discussion on an optimum condition supplemented. The results of Hall, impurity profile, and photoluminescence studies for both the epitaxial layers grown in the nitrogen carrier gas and in the hydrogen carrier gas were described for the sake of comparison. A number of experiments successfully revealed a residual impurity in an undoped epitaxial layer. It was found that the present method exceeds the conventional one in many respects when preparing high-purity uniform epitaxial layers.
Improved transducer correction for standing-wave ultrasonic velocity measurements
Authors: Ringermacher H. I. , Moerner W. E. , Miller J. G.
Published: February 2004

Determination of acoustic phase velocity in liquid or solid specimens using standing-wave (i.e., continuous wave) ultrasonic techniques requires the use of a transducer correction formula. Previous approximations for the transducer correction in the case of a one-dimensional (planar) composite resonator are considered explicitly and their accuracy and range of validity are quantitatively examined. An improved transducer correction formula is derived which is shown to be substantially more accurate than previous approximations. Quantitative evaluation of the accuracy of this improved transducer correction is presented for simulated velocity measurements in a typical liquid and a typical solid specimen.
Specific heats of ZnTe, ZnSe, and GaP
Authors: Irwin J. C. , LaCombe J.
Published: February 2004

The specific heats of ZnTe, ZnSe, and GaP have been measured to ±3% in the temperature region from 15 to 150°K. The experimental results agree, within the experimental error, with the available previous measurements. The measurements were performed primarily to obtain values of the specific heat for comparison with values calculated from a lattice dynamics model. The parameters used in the theoretical model were determined from second-order Raman spectra. The comparison thus provides a test of the reliability of acoustic-phonon dispersion curves obtained from second-order Raman spectra.
Electron microscopy of size distribution and growth of small zinc crystals formed by homogeneous nucleation in a flowing inert-gas system
Authors: Eversole J. D. , Broida H. P.
Published: February 2004

Homogeneous nucleation of small Zn particles has been observed in a flowing inert-gas system. Zn vapor was produced by heating the bulk metal near 700 K in flowing N2 at pressures near 15 Torr. Nucleation of small Zn particles took place in a cooler region downstream from the furnace. Cooling occurred by gas conduction to room-temperature walls. Particle sizes measured by electron microscopy were from 5 to 5000 nm. Samples were obtained with varying metal temperature, gas flow rate, pressure, and position in the collection chamber. Particles grew with time and had a predominant shape characterized as a regular hexagonal prism.
Measurement of Rayleigh phase velocity and estimates of shear speed by schlieren visualization
Authors: Neubauer Werner G. , Dragonette Louis R.
Published: February 2004

A schlieren technique is used to give a direct accurate measurement of Rayleigh phase velocity on various materials. Plane solid interfaces underwater are insonified by finite acoustic beams. Sound incident at the Rayleigh angle produces a null strip in the radiated field which uniquely identifies the Rayleigh angle. This null strip is caused by the mutual cancellation of equal amplitude specular and Rayleigh radiations which are 180° out of phase. Rayleigh phase velocity is then calculated from the measured Rayleigh angle by a simple equation. The measured Rayleigh velocities are used to give estimates of shear velocity, and these estimates are compared with direct shear velocity measurements. The attenuation of the Rayleigh wave in the low-MHz region is due to radiation into the water and is found to be directly proportional to frequency and inversely proportional to material density as predicted by theory.
Turbulence effects on an ambient pressure discharge
Authors: Biblarz Oscar , Nelson Robert E.
Published: February 2004

This work reports on observations of a diffuse discharge in a turbulent air flow. The discharge power was monitored as a function of velocity and turbulence spectrum in a fixed electrode configuration. The flow direction was also reversed to check on the effect of convection. The flow increased the sparking voltage, and turbulence made the current distribution considerably more homogeneous; the discharge power increased from about 1 W with no flow to about 250 W with 60-m/sec grid-generated turbulent flow. This turbulence was most intense in the range between 1 and 10 kHz.
High-power electromagnetic transmission characteristics of a diffusing reentry plasma
Authors: Papa Robert J. , Taylor Richard L.
Published: February 2004

Antenna voltage breakdown arising from the transmission of high-power microwave radiation may be suppressed on a reentry vehicle by injecting electrophilic chemicals into the flow field. This paper describes numerical procedures for calculating the amount of high-power microwave radiation that can be transmitted through a plasma chemically seeded with an electron-attaching substance. The power incident on a reentry plasma slab may be sufficient to induce electron temperature changes, resulting in variations in time of the electron density and effective collision frequency. The plasma properties are determined as a function of time by numerically integrating the two continuity equations for the electron and positive-ion densities. The processes of electron impact ionization, electron attachment, detachment, and recombination are taken into consideration. The diffusion of the electrons and positive ions in the ambipolar limit is influenced by the presence of negative ions. Runge-Kutta numerical integration of Maxwell's equations together with the above set of plasma transport equations yield the time-dependent plane-wave transmission and reflection coefficients as a function of incident power level for a very wide range of reentry plasma conditions. For one particular set of reentry conditions, graphs are presented of the electron density profile, reflection coefficient, and transmission coefficient as functions of time.
Investigation of kilovolt electron energy dissipation in solids
Authors: Matsukawa T. , Shimizu R. , Harada K. , Kato T.
Published: February 2004

A new technique to determine the depth distribution of energy loss, the so-called depth-dose function, is described for electrons whose energies ranged from 15 to 30 keV at normal and 45° incident angles. This method is based on a series of measurements of currents induced by the penetration of energetic electrons through a metal-oxide-semiconductor-structure (Al–SiO2–Si) specimen whose metal electrode is formed by an aluminum layer deposited in a stepwise manner. The experimental depth-dose function and range-energy relation are compared with other experimental and theoretical results. A particular interest was taken in the comparison of the experimental results with those predicted by our Monte Carlo calculations to confirm the good agreement between them. Furthermore, the ratio of the product of mobility and lifetime to the mean electron excitation energy in SiO2 was also determined to be μτ/EA = 0.10 × 10−11 cm/V2, which may be ranked between the values reported by Everhart and Hoff and by Goodman. The effects of space charge in SiO2 are also discussed.
Switching in copper oxide
Authors: Zarabi M. J. , Satyam M.
Published: February 2004

This paper presents the results of an investigation conducted on the switching behavior of copper oxide. The filamentary nature of the current and also the formation of a copper channel have been observed to be associated with the process of switching. The experiments and the analysis carried out by the authors show that the formation of copper channel is due only to a secondary process and is not responsible for the actual switching of the device to the low-voltage mode. The switching, as is clear from the analysis, seems to be the result of a purely electrothermal process. The effect of the dimensions of the device on the V-I characteristics is also discussed. It has further been shown that it is possible to prevent the formation of copper channel to obtain a monoshot type of switching transition.
Sharp-line and broad-band emission in AgGaS2 crystals
Authors: Yu Phil Won , Park Y. S.
Published: February 2004

The low-temperature photoluminescence spectra of AgGaS2 are investigated in this work. At 4.2°K, the luminescence spectra are dominated by many sharp lines as well as broad emission bands. A series of emission lines was found to be superimposed on the broad band peaking at ∼ 5000 Å. The series of emission lines are attributed to phonon-assisted transitions involving an unidentified impurity or defect. Two basic phonons with energies of 5.4 and 7.2 meV are identified from the phonon structure. The 7.2-meV mode is also seen in the Raman spectrum. They are tentatively identified as the lattice modes.
New intermediate gain laser material: Y3(Al1−xGax)5O12 : Nd
Authors: Watts R. K. , Holton W. C.
Published: February 2004

Optical spectra of rare-earth impurity ions in crystalline solids are inhomogeneously broadened in mixed crystal systems. This principle has been used in Y3(Al1−xGax)O12 : Nd to lower the cross section of the 1.06-μm laser transition by 3.3 relative to Y3Al5O12 : Nd, while not substantially altering the thermal conductivity, thereby providing a host for Nd with improved Q-switched laser performance. Spectroscopic and paramagnetic resonance studies are reported to elucidate the detailed nature of the broadening.
Evidence for surface-state-enhanced field emission in rf superconducting cavities
Authors: Schwettman H. A. , Turneaure J. P. , Waites R. F.
Published: February 2004

Measurements of the x radiation and the electron loading in a niobium cavity resonant in the TM010 mode at 1208 MHz have been made in order to study enhanced electron field emission in superconducting cavities. Measurements have also been made of the low-temperature dc electron field emission from bismuth, niobium, copper, and tungsten utilizing a configuration which approximates the point-to-plane geometry. In the rf cavity measurements, it is found that the x-radiation count rate data follow a modified Fowler-Nordheim equation, which takes into account the time-dependent rf fields, the electron dynamics in the rf fields, the emission of secondary electrons, and the production and absorption of x radiation. Further, it is found that the x radiation from the cavity can be reduced by a factor of 104−106 by helium-ion sputter processing at low temperature. From x-radiation data and electron loading data interpreted with the modified Fowler-Nordheim equation, it has been shown that, after helium-ion sputter processing at low temperature, the electron field emission process can be consistently described by ordinary Fowler-Nordheim electron field emission from geometrical projections at which the electric field is enhanced. Before processing, the electron field emission process cannot be consistently described by ordinary Fowler-Nordheim electron field emission. A point of view which is consistent with the data is that before helium-ion sputter processing the electron field emission is enhanced by resonant tunneling through surface states due to adsorbed atoms, and that as a result of processing, the adsorbed atoms are removed. This point of view is supported by calculated sputtering rates during the processing. In the dc measurements, it is found that the low-temperature electron field emission is consistent with the Fowler-Nordheim theory for an emission tip that has been cleaned by reverse field desorption. However, it is found that the dc electron field emission increases slowly with time, presumably as a result of adsorption of material ejected by electron bombardment of the anode. The resulting changes in the dc electron field emission characteristics are of just the type expected for resonant tunneling through adsorbate surface states, and are remarkably similar to the differences in x-radiation count rate data observed for a superconducting cavity before and after helium-ion sputter processing.
The mechanics of elastic contact with film-covered surfaces
Authors: Leveson Richard C.
Published: February 2004

Solutions to the Hertz problem, which predict the contact area between cylindrical or spherical bodies elastically loaded against one another, have frequently been applied to situations in which one of the bodies is coated with a thin film of different material, notably in the analysis of bearings lubricated with thin solid films. In reality the film may often exert a profound influence on the contact area and the Hertzian assumption will be inappropriate. The present work offers approximate analytical solutions for film-coated cylindrical and spherical contacts, that are valid provided the contact dimensions are large compared to the film thickness and provided also that the Young's modulus of the film material is less than that of the surfaces with which it interacts. It is hoped that the expressions derived here will prove to be particularly useful in the study of lubricant films deposited by such processes as sputtering and ion plating, where a knowledge of the true area of contact is a crucial factor in the understanding of the mechanics involved.
Transverse heating of a cold dense helium plasma by a pulsed CO2 laser beam
Authors: Décoste R. , Engelhardt A. G. , Fuchs V. , Neufeld C. R.
Published: February 2004

We present experimental evidence for the transverse heating of a dense (3.2 × 1017 cm−3) cold (≃4 eV) helium θ-pinch plasma by the focused beam of a TEA CO2 laser having a pulse duration of 180 nsec and a peak power of approximately 5 MW. The laser light was incident on the plasma during the first pinch compression, when streak photographs taken with a high-speed camera indicate a stable quiescent plasma lasting about 1.5 μsec. Time-resolved spectroscopic measurements were made to determine the plasma density and temperature before and after irradiation by the CO2 laser. Maximum temperature increases of 0.8 eV and density increases of 0.5 × 1017 cm−3 were observed for a laser energy of 0.7 J incident on the plasma. The theoretical description of the interaction considers the quasistatic temporal response of the plasma to the absorption of laser energy by inverse bremsstrahlung, and includes deviations from local thermodynamic equilibrium (LTE) before, during, and after irradiation. The absorbed energy is consumed in expansion, heating, and further ionization of the plasma. Highly excited atomic or ionic states are assumed to be in Saha equilibrium with each other and with the ionization continuum, whereas the ground states of successive ionization stages are assumed to be in coronal equilibrium. Thermal conduction losses are negligible. The theory correctly predicts the observed temperature increases but not the observed density changes, since inertial effects are neglected in order to render the model tractable.
Evidence of a precipitatelike zone in as-grown GaAs and its influence on optical absorptivity
Authors: Sande J. B. Vander , Peters E. T.
Published: February 2004

A defect structure, consisting of very small roughly cylindrical zones, was found in as-grown GaAs during observation by transmission electron microscopy. The zones are one atomic plane thick and 10–20 Å in length, lying parallel to 〈110〉. The density of defects in all samples observed was uniform at approximately 1017 cm−3. By using the results of a calculation of the optical absorptivity attributable to these defects and by assuming intermediate metallic conductivity, excellent agreement between theoretical and observed absorptivity was obtained.
Low-energy cathodoluminescence of ZnO: The ZnO-plasma display
Authors: Pennebaker W. B. , Hanlon J. F. O'
Published: February 2004

A ZnO-plasma display has recently been reported consisting of a ZnO phosphor excited by slow electrons drawn from a He plasma. This paper is concerned with the fabrication techniques and operating characteristics of the ZnO-plasma device and with the life and efficiency of the ZnO phosphor. Operating life well in excess of 10 000 h has been achieved with a brightness decay of only a factor of 2. The total charge density passed through the phosphor during this test was 50 000 C/cm2. Phosphor efficiency was found to be strongly influenced by exposure to atomic hydrogen and atomic oxygen generated in the plasma. By following exposure to atomic hydrogen, phosphor efficiencies as high as 25 lm/W were observed at about 5-eV excitation energy. Conversely, exposure to atomic oxygen reduced the efficiency by as much as two orders of magnitude. A physical model for these effects is presented.
Magnetic properties of amorphous Co–P alloys
Authors: Pan D. , Turnbull D.
Published: February 2004

Amorphous Co–P alloys with compositions ranging between 18–25 at.% P were prepared by electrodeposition. Their magnetic properties were measured with a vibrating sample magnetometer between 4 and 520 °K in fields up to 8 kOe. The coercive force Hc and the ratio of remanence to saturation magnetization, σr / σs, of the alloys were several hundred times lower for the amorphous than for their as-crystallized states. Earlier results indicating sharp increases in initial permeability with annealing, short of crystallization, were confirmed. The magnetic moment per atom, n, from low-temperature measurements, decreases with increasing P content. In particular, the results at low P content indicate the transfer of four P valence electrons at the dilute limit, while those at >23 at.% P indicate a more rapid decrease of n than was expected from the rigid band model and suggest that n→0 at 32 at.% P. Both Tc and the spontaneous magnetization in the vicinity of Tc were determined by the method of thermodynamic parameters. The spontaneous magnetizations on the reduced scale, σs(T) / σs(0), were flatter over the entire temperature range 0≤T/Tc≤1 than was predicted by a recent model for amorphous ferromagnets based on MFT. Tc drops rapidly with increasing P content at high concentrations, and apparently it would vanish at a content well below 33 at.% P.
Tests of Bragg rule for energy loss of 4He ions in solid compounds
Authors: Baglin J. E. E. , Ziegler J. F.
Published: February 2004

We have measured energy loss cross sections for 2000-keV 4He ions in a number of elements and in their solid compounds. Observed compound values were compared with those predicted by linear combination of elemental values by using Bragg's rule. Within an experimental uncertainty of ∼2%, we report agreement in each case for RhSi, HfSi2, SiO2, Al2O3, Si3N4, AlN, W2N3, SiC (3C, 6H, and polycrystalline forms), and for melamine and adenine.
Extension of the unified theory of grain boundaries. II. Deformation of the boundaries
Authors: Sadananda K. , Marcinkowski M. J.
Published: February 2004

The deformation of grain boundaries by crystal lattice dislocations is discussed in detail for the case of symmetric boundaries in simple cubic structures. In particular, It is shown that the motion of grain boundary dislocations that are generated as a result of various combinations of crystal lattice dislocations gives rise to either grain boundary sliding or grain boundary migration or both. The structure and motion of various types of ledges such as glide ledges, climb ledges, and compensated and uncompensated ledges are considered in this analysis. Although the analysis is done for simple cubic structures, the concepts developed are quite general and can be applied to more complex crystal structures. It is also shown that some of the grain boundary dislocation arrays can be suitably described as disclination dipoles, and such a dualistic representation is used to interpret the shape changes associated with the grain boundary deformation.
X-ray diffraction in crystals of intermediate perfection. II. A treatment of LiF in symmetrical Bragg geometry
Authors: Brown D. B. , Fatemi M. , Birks L. S.
Published: February 2004

In part I of this series we presented a method for the calculation of the integral diffracting power applicable to flat and curved crystals in symmetrical Bragg geometry. In the present paper we report a test of the above method. The integral reflection coefficient vs wavelength has been measured and calculated for an unusually perfect crystal of LiF and for a crystal of LiF rendered relatively imperfect by ``flexing''. Agreement was good. The mean mosaic block size and misorientation used in the calculation were deduced by using dislocation etch pitting. It is concluded that LiF is of Zachariasen's type I (i.e., extinction is primarily controlled by the mosaic block misorientation).
Numerical studies of exploding-wire plasmas
Authors: Chapin David L. , Duderstadt James J. , Bach David R.
Published: February 2004

A plasma created by exploding a thin lithium wire in a vacuum is analyzed using a magnetohydrodynamic (MHD) model. The two-temperature MHD equations including finite thermal conductivity and electrical resistivity are derived in one-dimensional cylindrical geometry. The resulting system of six coupled nonlinear partial differential equations in six unknowns is then solved numerically. Results of the calculation including spatial dependence of density, temperature, and magnetic field and time dependence of the radial profile and average temperature are given. These calculated properties are compared to available experimental results, giving favorable agreement.