bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and optical characterization of grain boundaries in polycrystalline cadmium telluride
Authors: Thorpe Thomas P. , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

The optical and electrical properties of grain boundaries in n- and p-type CdTe have been investigated by analysis of single boundaries within bicrystals and of polycrystalline thin films. The grain-boundary parameters evaluated include the conductivity activation energy, the boundary diffusion potential, the energy distribution of grain-boundary states, the minority-carrier recombination velocity, the majority–carrier capture coefficient, and the optical cross section of grain-boundary states. Passivation experiments indicate that heat treatment in H2 or Li provide effective but temporary passivation in p-type CdTe, and that similar effects are found for heat treatment in air for n-type material.
One-dimensional steady-state model for damage by vaporization and liquid expulsion due to laser-material interaction
Authors: Chan C. L. , Mazumder J.
Published: July 2002

A one-dimensional steady-state model describing the damage caused by materials removal by vaporization and liquid expulsion due to laser-material interaction is developed and presented. When vaporization occurs, there exists a discontinuity across the Knudsen layer of a few molecular mean free paths. This discontinuity is modeled by a Mott–Smith-type solution. The vaporization process creates a recoil pressure that pushes the vapor away from the target and expels the liquid. The materials are, therefore, removed in both vapor and liquid phases. The materials-removal rates are incorporated in the moving boundary immobilization transformation. The vapor phase is assumed to be optically thin so that its absorption of the high-energy beam is negligible. Closed-form analytical solutions are obtained and presented. The effect of heat-source power on removal rates, vaporization rate, liquid-expulsion rate, surface temperature, and Mach number are presented and discussed. Results are obtained for three different materials: aluminum, superalloy, and titanium.
Magnetic properties of electrodeposited Co-W thin films
Authors: Admon U. , Dariel M. P. , Grunbaum E. , Lodder J. C.
Published: July 2002

Thin films of Co-W, 300–500 Å thick, were electrodeposited at various compositions under a wide range of plating conditions. The saturation magnetization, coercivity, and squareness ratio of the films were derived from the parallel (in-plane) and perpendicular hysteresis loops, measured by using a vibrating sample magnetometer. The magnetic properties of the films are strongly related to their microstructure. The nonmagnetic alloying element (W) affects the saturation magnetization via the dilution mechanism. The in-plane coercivity, which increases with increasing content of the hexagonal phase and with decreasing degree of [0001]h texture, is in the range of 100–600 Oe for the crystalline deposits and decreases to a few oersteds for amorphous deposits. The in-plane squareness ratio increases with the fcc or amorphous phase content and with decreasing degree of [0001]h texture. The magnetic measurements suggest that films that appeared amorphous according to their electron diffraction patterns are actually microcrystalline or at least partially crystallized.
Dark discharge in hydrogenated amorphous silicon photoreceptors
Authors: Kakinuma H. , Watanabe T.
Published: July 2002

We have studied the electric field, thickness, and temperature dependencies of dark discharge in corona-charged glow-discharge amorphous silicon (a-Si:H) films. Dark discharge is a basic property for image devices such as photoreceptors. The dark-discharge rate ‖dV/dt‖ is found to be proportional to the square root of the electric field E as in the form log‖dV/dt‖∝√E, and increases nearly proportionally to the thickness of the a-Si:H film, indicating a bulk emission of charges from barriers lowered by electric fields like the Poole–Frenkel emission. It was also found that the contribution of electron injection from the substrate increases significantly in the dark discharge for small film thicknesses. The temperature dependence of dark discharge revealed the barrier height to be approximately 0.9 eV. A discharge mechanism was considered on the basis of these results, and was compared to that of other conventional materials for photoreceptors such as a-Se and a-As2Se3.
Neutron spectra from inertial confinement fusion targets for measurement of fuel areal density and charged particle stopping powers
Authors: Cable M. D. , Hatchett S. P.
Published: July 2002

Measurements of the ratio of dt to dd neutrons from pure deuterium fuel have been used as a method for determination of fuel areal density (〈ρR〉). The relationship between fuel 〈ρR〉 and dt neutron production becomes uncertain for 〈ρR〉 values large enough that the 1.01-MeV tritons from the d(d,t)p reaction lose a significant amount of energy in the fuel. A method based on neutron spectroscopy is described that improves the determination of fuel 〈ρR〉 in the region where tritons lose significant energy but have not yet thermalized. Charged particle stopping powers relevant to inertial confinement fusion ignition conditions may also be determined.
A simplified thermal model for calculating the maximum output power from a 1.3-μm buried heterostructure laser
Authors: Arvind M. , Hsing H. , Figueroa L.
Published: July 2002

A one-dimensional thermal model is presented for calculating the maximum output power from InGaAsP/InP (λ=1.3 μm) buried heterostructure lasers, whose output power is limited by thermal considerations. The effect of Auger recombination and ohmic resistance, which play significant roles in these lasers at high temperatures, is included. We have also incorporated the temperature dependence of efficiency from first principles using experimentally available data for Auger and radiative recombination coefficients. Calculations made on InGaAsP/InP lasers show that a maximum cw power of 57 mW/facet (diamond heat sink) and a maximum operating temperature of up to 132 °C for a geometry similar to the double-channel buried heterostructure laser can be achieved. In addition, the model has been used to determine the maximum achievable power as a function of device geometry (active layer thickness, width, and length of the device). We find that by increasing the length of the laser from 300 to 700 μm we can increase the output power of the laser by 79%. The results obtained agree reasonably well with experiment.
Levitation of a magnet over a flat type II superconductor
Authors: Hellman F. , Gyorgy E. M. , Johnson D. W. , O’Bryan H. M. , Sherwood R. C.
Published: July 2002

Levitation of a magnet over a type II superconductor where the field at the superconductor exceeds Hc1 is described and shown. The penetration and pinning of the flux lines in the superconductor cause the position of the magnet to be stable over a flat disk; a complete Meissner effect would make this position unstable. Furthermore, the observed dependence of the height of levitation on such variables as the thickness of the superconducting disk and the size of the magnet are consistent with a model described in this paper based on the energy cost of flux penetration through vortices and inconsistent with a Meissner effect model.
Preionization electron density and ion decay measurements in an x-ray preionized rare-gas-fluoride laser
Authors: Osborne M. R.
Published: July 2002

Measurements have been made of the preionization electron number density produced by x-ray irradiation of typical rare-gas fluoride laser gas mixtures. The results obtained show significant deviations from predictions made by using the mass absorption coefficients of the individual laser gases. Those deviations are shown to be caused by interactions between the constituent gases of the laser mixture and ionization produced from areas of the laser chamber exposed to the x rays. Measurements of the decay of the ion species produced have also been made, indicating a rate in close agreement with diffusion-limited ion-ion recombination. An unexplained dependence of this rate on initial ion number density has been observed.
Electron energy deposition in atomic oxygen
Authors: Slinker S. P. , Taylor R. D. , Ali A. W.
Published: July 2002

A discrete, time-dependent energy deposition model is developed and applied to the study of high-energy electron-beam (100 eV–10 MeV) deposition in atomic oxygen. Secondary electron distributions are computed and observed to relax to steady-state results. Characteristic relaxation times are shown. The loss function, mean energies per electron-ion pair production, production efficiencies, and distribution functions are presented for a wide range of energies. The model uses the latest experimental and theoretical cross sections as input.
Dielectric breakdown of polymer films containing metal clusters
Authors: Laurent C. , Kay E. , Souag N.
Published: July 2002

Thin films of gold-containing plasma-polymerized tetrafluoroethylene were prepared in an rf glow discharge. The films thus obtained showed a wide range of conductivities from insulating ( ρ>1016 Ω cm) to metallic ( ρ∼3×10−6 Ω cm), depending on plasma conditions during synthesis. The synthesis of the polymer is described in detail since it presents several new aspects. The structure and composition of the films were investigated by x-ray photoelectron spectroscopy and transmission electron microscopy. Studies of current-voltage characteristics in the dielectric regime, i.e., below electrical percolation, show that the conduction is volume limited (Poole–Frenkel effect) in non-gold-containing films, and characterized by a bistable switching behavior for gold-rich films. Dielectric breakdown measurements were realized on self-healing metal-insulator-metal structures. The Weibull analysis of breakdown voltages and a statistical treatment of times to breakdown under constant stress give, respectively, the nominal breakdown field E0 and the specific breakdown field Ec. These two sets of data follow similar functional behavior as a function of metallic volume fraction in the films. Surprisingly, the breakdown-field values remain relativity high up to the percolation concentration.
Studies of surface magnetism using electron and ion beam probes (invited)
Authors: Kirschner J.
Published: July 2002

Spin polarization analysis of electrons from ferromagnets has proven to be a valuable tool for the study of near-surface magnetism. High-resolution imaging of domains and domain walls in the scanning electron microscope is demonstrated. Analysis of the temperature dependence of Stoner excitations in Ni may be carried out in a ‘‘complete’’ inelastic electron scattering experiment with a polarized electron source. Examples for probing the electronic structure of epitaxially grown thin films of Co on Cu(100) by spin-polarized photoemission are given. Two recent applications of ion beam probes are discussed: (i) the analysis of ion-excited spin-polarized secondary electrons and its use for ‘‘magnetic sputter depth profiling,’’ and (ii) the capture of polarized electrons in ion-surface scattering resulting in the emission of circularly polarized light.
PbSnTe double-heterostructure lasers and PbEuTe double-heterostructure lasers by hot-wall epitaxy
Authors: Nishijima Yoshito
Published: July 2002

Pb1−x Snx Te, double-heterostructure (DH) lasers and Pb1−x Eux Te DH lasers produced by hot-wall epitaxy have been studied. The growth temperature for both laser crystals is 300 °C. This is lower than the growth temperatures obtainable by molecular-beam epitaxy and liquid phase epitaxy. By investigating the I-V characteristics of Pb1−x Snx Te DH lasers with x values greater than 0.2, it was confirmed that the band structure of the p-n heterojunction is type 1′. A Pb1−x Snx Te1−y Sey layer, rather than a PbTe1−y Sey layer, should be used for the cladding layer of Pb1−x Snx Te DH lasers with x values greater than 0.2. One of the primary factors preventing an increase in the maximum operating temperature to 200 K is that the carrier density injected into the active layer is not sufficient for laser emissions over 200 K due to the p-n heterojunction of the type 1′ band structure. The band structure of the p-n heterojunction of Pb1−x Eux Te DH lasers is type 1. Therefore, the maximum operating temperatures of the Pb1−x Eux Te DH lasers are expected to be greater than those of Pb1−x Snx Te DH lasers. The maximum operating temperature of Pb1−x Eux Te DH lasers exceeded 200 K. The maximum operating temperature of the laser with a PbTe active layer was 170 K under CW operation and 243 K under pulsed operation. This temperature was nearly 50 K higher than the maximum pulsed operation temperature of Pb1−x Snx Te DH lasers.
Numerical analysis for high-efficiency GaAs solar cells fabricated on Si substrates
Authors: Yamaguchi Masafumi , Amano Chikara , Itoh Yoshio
Published: July 2002

This paper describes some recent developments in GaAs thin-film solar cells fabricated on Si substrates by metalorganic chemical vapor deposition and numerically analyzes them.GaAs solar cells with efficiency of more than 18% are successfully fabricated on Si substrates by reducing the dislocation density. Photovoltaic properties of GaAs/Si cells are analyzed by considering the effect of nonuniform dislocation distribution on recombination properties of GaAs thin films on Si substrates. Numerical analysis shows that the effect of majority-carrier trapping must be considered. High efficiency GaAs solar cells with total-area efficiency of over 20% on Si substrates can be realized if dislocation density can be reduced to less than 5×105 cm−2.
Polarity determination of single-crystal epitaxial layers by x-ray diffraction
Authors: Stevenson Andrew W. , Wilkins Stephen W. , Kwietniak Mark S. , Pain Geoff N.
Published: July 2002

The anomalous scattering of x rays has been used to determine the polarity of single-crystal epitaxial layers, as grown on the substrate material. The method relies on the breakdown of Friedel’s law in noncentrosymmetric structures and is particularly effective when there exists a large difference between the values of the imaginary anomalous dispersion correction, f″, for the respective atomic species. The method is nondestructive and measurements are taken from only one side of the sample (the side with the epitaxial layer).
Wavelength effects in the ultraviolet-laser ablation of polycarbonate and poly(α-methylstyrene) examined by time-of-flight mass spectroscopy
Authors: Hansen S. G.
Published: July 2002

Slow moving material (velocity ≊3×104 cm/s) ejected from polycarbonate and poly(α-methylstyrene) targets by ultraviolet laser photoablation is probed using time-of-flight mass spectroscopy. The product distribution seen from polycarbonate, using resonant-two-photon ionization with 248- or 266-nm light, consists of aromatic species smaller than the monomer. Mass spectra are similar for 355-, 266-, and 193-nm ablation, and the products differ structurally from the starting material; both observations suggest that slow moving species are ejected by a thermal mechanism at all three wavelengths. 248-nm ablation of polycarbonate near the ablation threshold, gives a different product distribution and it is argued that a cooler thermal regime is being sampled or, that photochemical effects are important. The dominant product seen in 266-, 248-, and 193-nm ablation of poly(α-methylstyrene) is the monomer in each case. Subtle differences present in the resulting mass spectra may be due to photochemical effects, but major similarities suggest that slow movers are ejected by a photothermal mechanism.
p-polarized optical properties of aggregated Au films
Authors: Bader Georges , Ashrit P. V. , Girouard Fernand E. , Truong Vo-Van
Published: July 2002

Transmittance with p-polarized light at oblique incidence has been measured for aggregated Au films in the region from 0.40 to 0.65 μm. At large values of the incidence angle, two minima associated with the perpendicular and parallel plasma resonances in the particles were observed. The dependence of these absorption features on film characteristics was accounted for by a simple effective medium model assuming a spheroidal shape for the particles. In this model, the substrate effect has been incorporated by mirror-image contributions of the induced dipoles. A log-normal distribution for the axial ratio was assumed in order to take into account the broadening of the absorption characteristics. Satisfactory agreement between theory and experiment has been obtained using only the optical thickness as a fitting parameter, and assuming a certain standard deviation for the log-normal distribution.
Comparison of YAG:Er and YAlO3:Er laser crystals emitting near 2.9 μm
Authors: Wüthrich S. , Lüthy W. , Weber H. P.
Published: July 2002

Four different erbium laser crystals, two YAG:Er (40 at. %) and two YAlO3:Er (30 at. % and 50 at. %), have been compared with respect to their laser thresholds and slope efficiencies. The performance of these laser crystals was further compared with a YSGG:Cr:Er (Y3Sc2Ga3O12) (3.6 at. % Cr3+ and 4 at. % Er3+). The experimental results are explained with up-conversion processes in the crystals.
Microstructure evolution of newly developed electroless ruthenium deposition on silicon observed by scanning transmission electron microscope
Authors: Chang Y. S. , Chou M. L.
Published: July 2002

Autocatalytic Ruthenium thin films have been successfully deposited on silicon. The deposition reactions were proven to be electroless by the measurement of the electrochemical rest potentials of anodic and cathodic partial reactions and mixed potentials. A new method for direct observation of microstructure and formation at the initial stage of deposition has also been developed. The progressive formation and microstructure of ruthenium thin films during various growth stages have been investigated by scanning transmission electron microscopy. Deposition takes place immediately after the n-type silicon is immersed in the electroless plating solution. The film was identified to be amorphous by the selected area electron diffraction analysis. Cross-sectional transmission electron microscopy method was utilized to explore the uniformity and morphology of the film as well as the Ru/Si interface. Accordingly, the deposition rate was also measured with a high precision nanometer. The microstructure evolution and significance in applications are also discussed.
Skin effect and proximity effect in multiconductor systems with applied currents and voltages
Authors: Bourmanne P. , Delincé F. , Genon A. , Legros W. , Nicolet A.
Published: July 2002

A finite element-boundary element coupling method is used to compute the two-dimensional magnetic field in multiconductor systems with magnetic materials. The terminal voltages and the tangential magnetic field on the boundaries are included in the finite element formulation for conductors. The total current in a conductor is expressed as the line integral of the tangential field around the conductor. One extra condition per conductor is necessary. It can be used to force the total current or, more generally, to couple the magnetic field computation program with circuit equations. Comparison between numerical results and analytical computations (a circular conductor and two rectangular bars in a slot) shows the accuracy of the method.
Suppression of the emitter size effect on the current gain of AlGaAs/GaAs heterojunction bipolar transistor by utilizing (NH4)2Sx treatment
Authors: Shikata S. , Okada H. , Hayashi H.
Published: July 2002

The (NH4)2Sx surface treatment was applied to the AlGaAs/GaAs heterojunction bipolar transistor. The suppression of the emitter size effect on the current gain was observed for up to 4×4 μm2 emitter size devices, and 2.5 times high current gain was obtained with the improvement of the ideality factor. These results indicate that the surface recombination at emitter-base junction area are largely reduced by this treatment. The (NH4)2Sx treatment also proved to be applicable to the conventional device fabrication processes and highly reliable for the heat treatment.
Properties of nitrogen-doped amorphous hydrogenated carbon films
Authors: Amir O. , Kalish R.
Published: July 2002

Nitrogen-containing hydrogenated amorphous carbon (a-C:H(N)) films are grown from a dc plasma of a N2+C6H6 gas mixture. By varying the N2 fraction in this mixture films with different amounts of N are produced. The actual amount of nitrogen in the a-C:H(N) films is determined by nuclear reaction analysis and by Auger electron spectroscopy profiling. The nitrogen concentration in the films grows exponentially with nitrogen content in the gas mixture reaching concentrations as high as 10 at.% for the films grown from a N2-rich gas mixture (N2/(N2+C6H6)=0.75). The electrical and structural properties of the N2-doped films are studied by performing electrical conductivity, thermopower (TP), optical absorption, and electron-paramagnetic resonance measurements. Films with low (<1 at.%) nitrogen content exhibit fairly high resistivities, have an optical gap of 1 eV, are rich with dangling bonds (5×1020 cm−3) and their thermopower is positive and in the mV/K regime, indicating conductivity in the valence band tail. However, with increased N doping, the resistivity decreases and the optical band gap shrinks and reached zero for the highest doped film. The TPs for films containing more than 1 at.% are in the μV/K range, indicating hopping conductivity around the Fermi level. The results of all measurements are consistent with the model of Robertson for the electrical structure of amorphous hydrogenated carbon and for the proposed doping mechanism in this material.
Ensemble Monte Carlo study of electron transport in degenerate bulk GaAs
Authors: Mansour Nabil S. , Diff Karim , Brennan Kevin F.
Published: July 2002

A theoretical investigation is presented of the effect of ionized impurity scattering, electron-electron interaction, and degeneracy, both separately and collectively, on the bulk steady-state transport properties of degenerate GaAs. The calculations are performed using an ensemble Monte Carlo simulation that includes an analytic nonparabolic formulation of the three principal valleys in the conduction band and all of the important phonon scattering mechanisms. It is found that the overall velocity-field characteristic is determined primarily by the action of electron-plasmon scattering at high electric fields (near the intervalley threshold field). At lower fields, below which the electrons are not heated to the threshold energy for plasmon emission, ionized impurity scattering is the most dominant mechanism. In addition the effects of degeneracy are also important throughout. Only the short-range electron-electron interaction has little effect on the velocity-field curve owing to the fact that it does not alter the net momentum or energy of the electron gas in steady-state bulk material.
Midgap states in a-Si:H and a-SiGe:H p-i-n solar cells and Schottky junctions by capacitance techniques
Authors: Hegedus Steven S. , Fagen E. A.
Published: July 2002

The midgap density of states (MGDOS) in a-SiGe:H alloys is investigated by capacitance measurements on p-i-n solar cells. Past work on thick a-Si:H Schottky barriers is extended to thin a-SiGe:H p-i-n cells. Four methods of determining the MGDOS from the measured capacitance are described, and each is applied to two p-i-n devices having 0% and 62% Ge in the i layers, respectively. The first method involves fitting an equivalent circuit model to the measured admittance. Close agreement is found over a wide range of temperature and frequency. The single junction model is shown to apply equally well to p-i-n and Schottky diodes, justifying the neglect of the n-i junction and thin doped layers in the p-i-n admittance analysis. A second method determines g0 from the limiting capacitance at high temperature. The third and fourth methods extract g0 from the dependence of capacitance on voltage bias. One of these is novel, presented here for the first time. Thus, a unique feature of this study is the application of several different capacitance methods to standard p-i-n solar cell devices. Agreement within ±25% is found among the values of the MGDOS from the four methods. The MGDOS increases exponentially from (1–2)×1016 to (3–4)×1017/cm3 eV as the Ge increases from 0% to 62%, in general agreement with results of others.
The elastic moduli of simple two-dimensional isotropic composites: Computer simulation and effective medium theory
Authors: Snyder K. A. , Garboczi E. J. , Day A. R.
Published: July 2002

An algorithm, combining digital-image with spring network techniques, has been developed that enables computation of the elastic moduli of random two-dimensional multiphase composites. This algorithm is used to study the case of isotropic, randomly centered, overlapping circular inclusions in an isotropic elastic matrix. The results of the algorithm for the few-inclusion limit, as well as the case where both phases have the same shear moduli, agree well with the exact results for these two problems. The case where the two phases have the same Poisson’s ratio, but different Young’s moduli, is also studied, and it is shown that the effective medium theory developed by Thorpe and Sen agrees well with the numerical results. A surprising result is that the effective moduli of systems with nonoverlapping circular inclusions are almost identical with the overlapping inclusion case, up to an inclusion area fraction of 50%. Using the validated effective medium theory, we illustrate how the effective Poisson’s ratio ν behaves as a function of ν0, the pure phase Poisson’s ratio, and the stiffness ratio between the two components. Two distinct regions of behavior are found, defined by ν0≳ν* and ν0<ν*, where ν* is approximately 1/3 for the geometry of this model.
One-dimensional diffusion into a multilayer structure: An exact solution for a bilayer
Authors: Goldner R. B. , Wong K. K. , Haas T. E.
Published: July 2002

An exact solution to the problem of time-dependent, one-dimensional diffusion in two parallel layers backed by an impenetrable wall is presented, together with graphical results for some numerical examples. The solution can be generalized to more than two layers, and it is expected to be useful to several areas of applied science. This includes (a) ion diffusion in multilayer thin-film solid-state ionic devices such as electrochromic windows and rechargeable batteries, (b) mass diffusion of neutral species (e.g., dopants) encountered in the fabrication of multilayer thin-film integrated electronics and integrated optics circuits, and (c) heat diffusion through a multiplicity of parallel layers, each of which have different diffusion coefficients.
Metal Schottky barrier contacts to alpha 6H-SiC
Authors: Waldrop J. R. , Grant R. W. , Wang Y. C. , Davis R. F.
Published: July 2002

Formation of Schottky barrier contacts to n-type 6H-SiC for a number of metals chosen to include a variety of physical and chemical properties has been investigated. The metals (Pd, Au, Ag, Tb, Er, Mn, Al, and Mg) were deposited onto room temperature surfaces terminated with a submonolayer coverage of oxygen. The metal/6H-SiC interface chemistry and Schottky barrier height φB during contact formation were obtained with x-ray photoemission spectroscopy; the electrical properties of subsequently formed thick contacts were characterized by current-voltage and capacitance-voltage techniques. The o/B values for these metals extend over a wide 1.3 eV range. To a varying degree φB depends on the 6H-SiC crystal face (Si vs C). Mg and Al (Si face of latter) have φB=0.3 eV, a value which is suitable for nonalloyed ohmic contacts.
Highly selective etching of polycrystalline silicon on silicon dioxide at low wafer temperature, employing magnetron plasma
Authors: Sekine Makoto , Horioka Keiji , Arikado Tsunetoshi , Okano Haruo
Published: July 2002

A mechanism for highly selective etching of phosphorus-doped polycrystalline silicon (n+ poly-Si) on SiO2 by employing a Cl2 magnetron plasma reactor at low wafer temperatures was investigated. Only the SiO2 etch rate drops rapidly in the magnetron plasma at low wafer temperatures below 0 °C. X-ray photoelectron spectroscopy analysis revealed that only the SiO2 surface etched at lower temperatures was covered with silicon chloride or/and oxychloride compounds. The highly dense magnetron plasma decomposes the etched products into unsaturated molecules such as SiCl, SiCl2, and their oxides. These species have a large dipole moment and a higher sticking probability on SiO2 than on Si because the SiO2 bond is also ionic, and thus attracts a dipole molecule by Coulomb force. Thus, only the SiO2 surface was protected by a thin film from chlorine ion bombardment at a certain temperature range in the magnetron plasma. This protection film suppressed SiO2 etching, and a high selectivity of n+ poly-Si/SiO2 has been achieved.
Gas-phase oxidation chemistry during pulsed laser deposition of YBa2Cu3O7−δ films
Authors: Gupta Arunava
Published: July 2002

The gas-phase processes relevant for oxidation during growth of YBa2Cu3O7−δ (YBCO) films by pulsed laser deposition in different oxidizing ambients are discussed using a phenomenological model. The model consists of an accounting for the neutral species generated from the target during laser ablation, and their attenuation due to reactive and elastic scattering during transport, to determine the flux of neutral cation and anion species incident onto the substrate. In particular, the oxygen (O and O2), cation (Y, Ba, and Cu), and diatomic oxide fluxes in the presence of O2, O3, N2O, or NO2 as background oxidizer gases are qualitatively analyzed based on the known photochemical and electron-impact dissociation, and oxidation reactions of these gases. The relative effectiveness of these oxidizing agents, as judged from their propensity to produce diatomic oxides and atomic oxygen in the gas phase, is found to be in qualitative agreement with the previously observed trends in their oxidation behavior as deduced from the superconducting characteristics of YBCO films prepared using these gases.
Collection, measurement, and analysis of airborne magnetic particulates from pollution in the environment (invited)
Authors: Flanders Philip J.
Published: July 2002

Magnetic particulates in the environment, collected from surfaces and directly from the atmosphere, are reported. A significant percentage of magnetic material in many air-borne samples consists of spherical magnetite from coal-burning utilities and from iron/steel manufacturing with particle diameters 2–10 μm which correspond to average coercive fields of ∼100 Oe and remanence to saturation ratios of ∼0.1. The amount of air-borne magnetic material that settles to the ground varies inversely with distance from its source.
Theoretical and experimental investigation of a method for increasing the output power of a microwave tube based on the split-cavity oscillator
Authors: Lemke Raymond W. , Clark M. Collins , Marder Barry M.
Published: July 2002

The split-cavity oscillator (SCO) is a cavity resonator that can be used to produce a high degree of density modulation in an intense relativistic electron beam. The kinetic energy of electrons in the modulated beam can be converted into high-power microwaves. Aspects of the modulated beam that affect the process of converting beam power into microwave power are considered, and a technique is investigated for optimizing the conversion efficiency of a microwave tube based on the SCO. Using a combination of nonlinear theory, numerical simulation, and experiment, it is shown that the most efficient implementation of the SCO is as the modulating component of a klystronlike tube, in which the modulated beam is drifted a relatively short distance to maximize the rf current, which optimizes the efficiency of power extraction.
Bias-enhanced nucleation of diamond during microwave-assisted chemical vapor deposition
Authors: Sheldon Brian W. , Csencsits Roseann , Rankin Janet , Boekenhauer Rachel E. , Shigesato Yuzo
Published: July 2002

Bias-enhanced chemical vapor deposition of diamond was investigated, using cross-sectional transmission electron microscopy and concurrent electron energy-loss spectroscopy to characterize the deposited material. Under the conditions investigated, the negative bias leads to the formation of a thin amorphous carbon layer. The growth rate of this layer is relatively independent of the substrate temperature, which indicates that amorphous carbon is formed by the deposition of positively charged hydrocarbon or carbon ions. Reactive neutral species in the plasma, particularly atomic hydrogen, are also believed to play a role in creating nucleation sites. Higher nucleation densities were observed after longer biased pretreatments, which suggests that nucleation sites form as the amorphous layer is deposited. These sites are probably small clusters of either sp3 or sp2 carbon. Raman spectroscopy shows that the material deposited under biased conditions is a mixture of sp3 and sp2 carbon, compared to the purer diamond that forms at the same temperature, pressure, and gas composition when unbiased growth follows a biased pretreatment. Thus, while the deposition of energetic ions leads to the creation of diamond nucleation sites, it also inhibits diamond growth.
Time delay and phase shift measurements for ultrasonic pulses using autocorrelation methods
Authors: Cutard Thierry , Fargeot Dominique , Gault Christian , Huger Marc
Published: July 2002

At the interface between two media, a monochromatic ultrasonic pulse separates into two waves, a reflected one and a transmitted one. A simple hypothesis is to consider the phase shift, introduced by the reflection, as equal to 0 or π. But, in many cases, it becomes necessary to know the phase shift precisely. This is done by a Fourier analysis of the different signals. This article deals with mathematical methods that can be used for time and/or phase shift measurements. A new method, based on an analysis of the analytic signal of the autocorrelation function, is described and compared to existing phase slope and autocorrelation methods. An application of this method is given in the case of a ‘‘long bar’’ mode propagation at the interface between alumina and glass.
Perpendicular magnetoresistance in magnetic multilayers: Theoretical model and discussion (invited)
Authors: Fert Albert , Valet Thierry , Barnas Jozef
Published: July 2002

After a general introduction describing the mechanisms of the current perpendicular to the layer plane magnetoresistance (CPP-MR), a microscopic model based on the Boltzmann equation is presented and a general expression of the magnetoresistance is derived in which the spin diffusion length appears as the unique scaling length of the problem. In the limit where the spin diffusion lengths are much larger than the layer thicknesses, the expression of the CPP-MR becomes very simple and similar to that already used at Michigan State University for the analysis of experimental results. Out of this limit, the model predicts a dramatic reduction of the CPP-MR if the spin diffusion lengths are shortened sufficiently by paramagnetic impurities or spin-orbit scatterers. Finally, a calculation is presented of the spin-dependent interface resistances involved in the model and related to interface potential steps, and experimental data are compared.
Intermetallic formation in copper/magnesium thin films—kinetics, nucleation and growth, and effect of interfacial oxygen
Authors: Arcot B. , Murarka S. P. , Clevenger L. A. , Hong Q. Z. , Ziegler W. , Harper J. M. E.
Published: July 2002

In situ resistance measurements, x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, isothermal and constant heating rate differential scanning calorimetry and Auger electron spectrometry depth profiles have been used to investigate the interactions in copper and magnesium thin films leading to the growth of Cu2Mg and CuMg2 intermetallics. The effect of exposing the reacting interfaces to controlled exposure of oxygen on the nucleation and growth kinetics of such intermetallics was also investigated. It is found that the first phase to form is CuMg2, at about 200–215 °C. It is determined that the formation of CuMg2 occurs by a two step process consisting of nucleation and growth. The nucleation of CuMg2 takes place in a region composed of a Cu/Mg solid solution. The nuclei form at certain preferred sites and grow in directions both parallel and perpendicular to the surface, eventually leading to a continuous CuMg2 layer. The growth of CuMg2 nuclei in the plane of the original interface occurs at a constant rate, whereas the growth in a direction perpendicular to the original interface is found to be diffusion limited. In the presence of excess copper Cu2Mg forms at higher temperatures, with complete conversion to Cu2Mg occurring at about 380 °C. When the Cu surface is dosed with oxygen prior to Mg deposition, ramp rate differential scanning calorimetry (DSC) shows that the nucleation and growth of CuMg2 as well as the growth of Cu2Mg are not disturbed. Dosing the Mg surface with oxygen results in significant changes in the growth of the two phases. In this case a thin MgO layer is formed at the oxygen dosed surface, lateral growth of CuMg2 is unaffected, but vertical growth of CuMg2 across the oxygen dosed interfaces is delayed by 25–30 °C. The growth of Cu2Mg is also shown to be delayed, by 22–54 °C due to the interfacial oxygen dose.
Characterization and removal of silicon surface residue resulting from CHF3/C2F6 reactive ion etching
Authors: Park Hyung-Ho , Kwon Kwang-Ho , Lee Jong-Lam , Suh Kyung-Soo , Kwon Oh-Joon , Cho Kyoung-Ik , Park Sin-Chong
Published: July 2002

The surface properties of an underlying Si substrate after reactive ion etching of SiO2 in CHF3/C2F6 gas plasmas have been studied using x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, Rutherford backscattering spectroscopy, and high resolution transmission electron microscopy (HRTEM). A 50-nm-thick silicon layer that contains carbon and fluorine and a 4-nm-thick uniform residue layer composed entirely of carbon, fluorine, oxygen, and hydrogen on the silicon surface have been observed. The residue film has nine different kinds of chemical bonds. At the surface, O—F bond is found on C—F polymer that contains C—CFx (x≤3), C—F1, C—F2, and C—F3 bonds. Between the C—F polymer layer and the silicon substrate, C—C/H, Si—C, Si—O, and Si—F bonds exist. Neither point defect clusters nor distinct planar defects are found in cross-sectional HRTEM images of the silicon substrate. The changes of peak shapes for C, Si, O, and F in the residual film have been analyzed through an in situ resistive anneal under ultrahigh vacuum condition. C—F1, C—F2, and C—F3 bonds decompose and form C—CFx bonds above 200 °C. Above 400 °C, C—CFx bonds also decompose to C—C/H bonds. For removal of the silicon surface residue, reactive ion etched specimens have been exposed to O2, NF3, Cl2, and SF6 plasmas. By XPS analysis, NF3 treatment has been revealed to be the most effective. With 10 s exposure to NF3 plasma, the fluorocarbon residue film decomposes and the remaining fluorine is mostly bound to silicon. The fluorine completely disappears after wet cleaning.
Constitutive model of shock-induced chemical reactions in inorganic powder mixtures
Authors: Bennett L. S. , Horie Y. , Hwang M. M.
Published: July 2002

An improved hydrodynamic model has been developed for analysis and interpretation of shock-induced chemical reactions in inorganic powder mixtures. Attention is focused on the interaction of hydrodynamic flow with the thermodynamic changes associated with chemical reactions such as specific volume, specific internal energy, and material properties. Predictive capabilities of the model have been illustrated using experimental shock wave profile data involving Ni-Al and Al-Fe2O3 mixtures.
High pressure study of AlP: Transformation to a metallic NiAs phase
Authors: Greene Raymond G. , Luo Huan , Ruoff Arthur L.
Published: July 2002

The crystal structure and optical reflectivity of AlP has been studied in a diamond anvil cell using energy dispersive x-ray diffraction to 43 GPa and micro-optical reflectance spectroscopy to 36 GPa. AlP undergoes a first order phase transformation from zincblende to a NiAs structure which exhibits metallic reflectivity in the near-infrared. The decrease in volume on transformation is 17%±1%. The transformation is reversible but has large hysteresis. The equilibrium transformation pressure is 9.5±5 GPa.
Low temperature properties of the filled skutterudite CeFe4Sb12
Authors: Morelli Donald T. , Meisner Gregory P.
Published: July 2002

CeFe4Sb12 is a member of a class of advanced thermoelectric materials. In order to evaluate this material’s potential for such applications, we have measured a variety of its properties at low temperature, including thermal conductivity, thermoelectric power, electrical resistivity, Hall coefficient, and magnetic susceptibility.
Growth and optical properties of nanometer-scale GaAs and InAs whiskers
Authors: Hiruma K. , Yazawa M. , Katsuyama T. , Ogawa K. , Haraguchi K. , Koguchi M. , Kakibayashi H.
Published: July 2002

The growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15–40 nm and about 2 μm long are reviewed and discussed. Experimental results for growing whiskers using Au as a growth catalyst during metalorganic vapor phase epitaxy (MOVPE) and the shape and growth direction of whiskers provide new insight into growth control of GaAs and InAs whiskers. The crystal structure of whiskers, Au behavior during MOVPE, and their growth mechanism are reviewed and discussed on the basis of transmission electron microscopic analysis. The photoluminescence spectra of GaAs wires are compared with those of a GaAs epitaxial layer, and the effect of surface treatment on the luminescence peak energy shift is discussed. The time dependent photoluminescence of GaAs wires is also discussed. The application of GaAs whiskers to light emitting devices is reviewed because a semiconductor wire structure employing quantum size effects is a very important element of electronic and optical devices.
Photoplasticity and photonic control of dislocation densities in type II-VI semiconductors
Authors: Garosshen T. J. , Galligan J. M.
Published: July 2002

Crystal defects, such as dislocations, introduce electronic states into semiconductors and thereby degrade the desired electronic behavior of semiconductor devices. Special processing precautions are therefore pursued to minimize dislocation densities in semiconductor materials. When light irradiates a semiconductor, incident photons with appropriate wavelengths excite electrons and holes into traps such as point defects and dislocations. This modification of the population of charged defects can modify the flow stress required to propagate dislocations. This effect manifests itself as an inhibition of dislocation motion in type II-VI compound semiconductors; whereas in type III-V semiconductors light can enhance dislocation mobility. This effect is known as photoplasticity. In this article we report on the basic characteristics of photoplasticity in CdS and show how it can be exploited to reduce dislocation densities in semiconductor materials.
Spectroscopy and laser operation of Pr, Mg:SrAl12O19
Authors: Merkle Larry D. , Zandi Bahram , Moncorgé Richard , Guyot Yannick , Verdun Horacio R. , McIntosh Bruce
Published: July 2002

Pr3+-doped SrAl12O19 has been investigated spectroscopically as a visible laser material. Its 3P0 fluorescence lifetime is rather long for an oxide, about 35 μs. This excited state exhibits only mild concentration and temperature quenching, so that concentrations high enough to give good ground state absorption into the 3P0 and 3P1 manifolds still give strong, long-lived emission. The ground state absorption spectra indicate that excited state absorption into the 4f5d configuration is less likely to be significant at laser wavelengths in this host than in Y3Al5O12. The stimulated emission cross sections of major emission lines have been estimated, and are quite realistic for laser operation. Laser pumped laser operation has been demonstrated in the red (3P0→3F2) at room temperature and in the blue-green (3P0→3H4) at cryogenic temperatures.
Magnetic particle–particle interaction in frozen magnetic fluids
Authors: Morais P. C. , Lara M. C. F. L. , Tronconi A. L. , Tourinho F. A. , Pereira A. R. , Pelegrini F.
Published: July 2002

Magnetic resonance is used to study magnetic dipole particle–particle interaction in ionic water-based iron-manganese magnetic fluids. A set of six samples having particle concentration running from 1.2×1016 to 6.3×1016 particles/cm3 were frozen below room temperature and analyzed in the range of 100–250 K. Average values of magnetic particle–particle interaction energy were obtained from the temperature dependence of the resonance linewidth broadening. At 1.2×1016 particles/cm3 magnetic particle–particle interaction energy is found to be of the order of 1.2 meV. However, at 6.3×1016 particles/cm3 magnetic particle–particle interaction energy goes to 32 meV. The enhancement of the magnetic particle–particle interaction energy far beyond the linearity is associated to cluster structuration. A one-dimensional model for cluster structuration is presented.
Propagation of an intense relativistic electron beam in an annular channel
Authors: Friedman M.
Published: July 2002

The propagation of an annular intense relativistic electron beam inside a cylindrical drift tube is affected by many factors such as external magnetic field, drift tube geometry, the beam self electric and magnetic fields, etc. It is shown, experimentally and theoretically, that the deleterious influence of the self-fields on the electron flow can be reduced when part of the beam return current is allowed to flow on a grounded conductor that is inserted coaxially within the beam. The improvement manifested itself by reducing the axial magnetic field needed to confine the electron beam or alternately by lowering the electron transverse velocities.
Ultraviolet luminescence of CsI and CsCl excited by soft x-ray laser
Authors: Jaeglé P. , Sebban S. , Carillon A. , Jamelot G. , Klisnick A. , Zeitoun P. , Rus B. , Nantel M. , Albert F. , Ros D.
Published: July 2002

We present the observation of solid material luminescence excited by soft x-ray laser. The 21.2 nm photons of the soft x-ray laser of the Laboratoire d’Utilisation des Lasers Intenses (Palaiseau, France) have been used to induce ultraviolet luminescence in CsCl and CsI. The laser supplied up to 6×1012 photons in 80 ps. A single laser shot was sufficient to obtain luminescence spectra with very good resolution. In the case of CsI, the use of two illumination conditions, differing by a factor 150 in intensity, showed the collapse of luminescence efficiency for very strong illumination. The quenching effect is discussed in terms of the large increase of crystal excitation mean density, altering the usual process of luminescence centers production.
Anomalous degradation in silicon solar cells subjected to high-fluence proton and electron irradiations
Authors: Morita Yousuke , Ohshima Takeshi , Nashiyama Isamu , Yamamoto Yasunari , Kawasaki Osamu , Matsuda Sumio
Published: July 2002

Distinct from the well-known logarithmic degradation in electrical performances of a crystalline silicon solar cell, an anomalous degradation of short-circuit current density (Isc) was observed in a cell irradiated by energetic protons and electrons at high fluence. From results of proton irradiations with various energies (0.4–10 MeV) and high frequency (1 MHz) capacitance measurements, the anomalous drop of Isc is found to be caused by (1) the p-type substrate changes into the intrinsiclike layer (Fermi level shift) by the irradiations, followed by an extension of the depletion layer, and (2) the drift length of the minority carrier becomes shorter than the depletion layer.