bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of high pressure on electrical relaxation in poly(propylene oxide) and electrical conductivity in poly(propylene oxide) complexed with lithium salts
Authors: Fontanella J. J. , Wintersgill M. C. , Smith M. K. , Semancik J. , Andeen C. G.
Published: July 2002

Audio frequency electrical conductivity and relaxation studies have been carried out on Parel 58 elastomer and Parel 58 elastomer complexed with a variety of lithium salts. The measurements have been carried out in vacuum over the temperature range 5–380 K and at pressures up to 0.65 GPa over the temperature range 230–380 K. Both the electrical conductivity for the complexed material and the electrical relaxation time associated with the α relaxation in the uncomplexed material exhibit VTF or WLF behavior. From a VTF analysis for both the vacuum electrical relaxation time and electrical conductivity, Ea is found to be about 0.09 eV and T0 is found to be about 40 °C below the ‘‘central’’ glass transition temperature. In addition, it is found that the activation volumes for the electrical relaxation time and the electrical conductivity are the same when compared relative to T0. These results imply that the mechanism controlling ionic conductivity is the same as that for the α relaxation, namely large-scale segmental motions of the polymer chain.
Photoacoustic study of surface and bulk nonradiative recombinations in GaAs with two-wavelength excitations
Authors: Yamamoto Hiroaki , Suemune Ikuo , Yamanishi Masamichi
Published: July 2002

A new photoacoustic method for distinguishing the surface nonradiative recombinations from the bulk ones in GaAs is presented. The method is based on the noncontact photoacoustic spectroscopy with a Michelson interferometry. It is shown that the surface contributions in a Cr-doped GaAs are relatively large even with the below-gap excitations. The bulk property is shown to be observed with the simultaneous continuous light irradiation with the photon energy above the energy gap.
Optical behavior of sputter-deposited vanadium pentoxide
Authors: Aita Carolyn Rubin , Liu Ying-Li , Kao Mei Lee , Hansen Steven D.
Published: July 2002

A series of V–O alloy films were sputter deposited on glass substrates using a vanadium target and rf-excited Ar/O2 discharges containing 2%–8% O2. On the basis of x-ray results, the films were nominally identified as vanadium pentoxide. Optical transmission and reflection characteristics were measured by double-beam spectrophotometry in the 390- to 700-nm-wavelength region. From these measurements, the absorption coefficient α was determined as a function of the incident photon energy hν. The absorption edge of all films showed two distinct regions of behavior: a high photon energy region in which α varied linearly with (hν)2 and a low-energy tail. The behavior of α is discussed in terms of the structural and electronic changes in the films due to nonstoichiometry and compared to results obtained for single crystal V2O5.
Fracture of solid state laser slabs
Authors: Marion John E.
Published: July 2002

Fracture due to thermal stress limits the power output potential of modern, high average power slab lasers. Here the criteria for slab fracture and the nature of the surface flaws which constitute the strength-controlling defects are reviewed. Specific fracture data for gadolinium scandium gallium garnet and LHG-5 phosphate glass with different surface finishes are evaluated in the context of assigning appropriate slab operating parameters using Wiebull statistics. These examples illustrate both the danger of design using brittle components without adequate fracture testing, and the inadequacy of design methods which use a fixed safety factor, for this class of materials. Further consideration reveals that operation of slab lasers in contact with an aqueous coolant may lead to strength degradation with time. Finally, the evolution of the failure process in which a characteristic midplane crack forms is outlined, and the pertinent parameters for avoiding slab fracture are identified.
High-resolution electron microscopy study of x-ray multilayer structures
Authors: Petford-Long Amanda K. , Stearns Mary Beth , Chang C.-H. , Nutt S. R. , Stearns D. G. , Ceglio N. M. , Hawryluk A. M.
Published: July 2002

Multilayered structures containing thin (1–12 nm) layers of W or Mo, alternating with C or Si, have been prepared to produce thin cross-sectional specimens, and direct structural information on the atomic scale has been obtained using an ultrahigh resolution electron microscope. Layer thickness and flatness have been analyzed—the average layer thickness varies by up to 0.6 nm from the average value, and the flatness of the layers depends on the quality of the substrate surface. The degree of crystallinity and crystal orientation within the layers has also been examined. This information should enable more accurate theoretical models to be proposed for the multilayer materials and their x-ray optical properties. The results for the Mo/Si multilayers suggest a model for their growth when prepared by sputtering.
Interpretation of capacitance-voltage characteristics of polycrystalline silicon thin-film transistors
Authors: Greve David W. , Hay Valerie R.
Published: July 2002

Measurements of the gate-to-channel capacitance in thin-film transistors are potentially useful for rapid evaluation of insulator and interface quality. In this paper, we develop a transmission line model of the gate-to-channel capacitance. We then compare the model with measurements made on unpassivated polycrystalline silicon thin-film transistors. An excellent fit to the measurements is obtained. Finally, we discuss the influence of semiconductor traps and insulator charge on the measured capacitance.
Gettering of gold in silicon: A tool for understanding the properties of silicon interstitials
Authors: Bronner Gary B. , Plummer James D.
Published: July 2002

The movement of gold in silicon is controlled by the reaction of gold with silicon interstitials, not by the intrinsic diffusion coefficient of gold. This fact is used to understand the role silicon interstitials play during gettering in silicon. An analysis of gold profiles after gettering reveals that high concentration phosphorus diffusion, argon-ion implantation, and mechanical damage of a silicon surface all act as sources of silicon interstitials. This finding is experimentally confirmed by studying the effect of an argon implanted surface layer on the diffusion of both phosphorus and antimony buried layers; only the phosphorus layer shows an enhancement, which is consistent with the injection of silicon interstitials. Studying the enhancement of the phosphorus diffusion versus temperature reveals that the phosphorus-interstitial pair has a migration energy of 1.3 eV. Under the assumption of local equilibrium between silicon interstitials and phosphorus atoms, estimates of the diffusion coefficient and equilibrium concentration of the silicon interstitial are made based on this enhanced diffusion data and the gold gettering profiles. These numbers are compared with other estimates in the literature.
Interaction of deuterium gas with dry SiO2 on Si: An ion-beam study
Authors: Myers S. M.
Published: July 2002

The interaction of deuterium gas (D2) with nominally dry SiO2 on Si was characterized in the temperature range 100–1000 °C using high-sensitivity nuclear-reaction analysis for D. Two trapped configurations were distinguished: one, hypothesized to involve Si–D bonding, produced D uptake at 300 °C and above followed by release at 600 °C; the other, identified as O–H, formed readily at 100 °C and dissociated at about 800 °C. Retained D in the 0.5-μm oxide layer was present at areal densities of about 1014 atoms/cm2 or less, and it was distributed approximately uniformly except for a small surface peak. Prior irradiation with high-energy He ions increased the D uptake by two orders of magnitude through, it is believed, the same trapping mechanisms discussed above. The data on uptake and release were semiquantitatively described by a fitted mathematical model, from which effective activation energies for trapping and detrapping were obtained.
Photoacoustic characterization of photovoltaic cells
Authors: Mello S. M. N. , Ghizoni C. C. , Miranda L. C. M. , Vargas H.
Published: July 2002

The photoacoustic characterization of Si solar-cell samples having distinct internal resistances, both at low and high modulation frequencies, yielded results significantly different from each other. For large samples with very small internal resistances (∼0.1 Ω), the additional contribution of the current dissipation near short-circuit conditions yielded results similar to those obtained with photothermal radiometry or the pyroelectric detection. For small samples, the results for the conversion efficiency, both at low and high modulation frequencies, are similar to ones obtained from the conventional electrical measurements.
On the Preisach function of ferromagnetic hysteresis
Authors: Kádár György
Published: July 2002

In ferromagnetic materials complex hysteresis curves of magnetization processes can be described by the magnetic history dependent calculation of consecutive Everett integrals of the two-variable Preisach function. For the one-dimensional case, when the external magnetic field varies along a fixed direction, an explicit structure of the Preisach function is proposed offering a better insight into the mechanism of the magnetization process. With the proposed form the rate of change of the magnetization with respect to the applied field depends on the magnetization itself, thus emphasizing the intrinsic nonlinearity of the magnetization curves. Specifically, the magnetization dependence is assumed to be separable as a multiplicative factor, namely, (1−m2). The residual field-dependent part of the Preisach function is assumed to be a bilinear form of a single-variable distribution function which may be interpreted as the probability of the switching of magnetic moments between states of opposite direction, thus representing the coercivity character of the material along the direction of the field. Examples of calculated major and minor hysteresis loops and a method of the determination of the coercivity function from the main experimental hysteresis loop are also given.
Steady-state photocarrier grating technique for diffusion-length measurement in semiconductors: Theory and experimental results for amorphous silicon and semi-insulating GaAs
Authors: Ritter D. , Weiser K. , Zeldov E.
Published: July 2002

The theory underlying the steady-state photocarrier grating technique is presented, including the effect of surface recombination. Experimental results for amorphous hydrogenated silicon and semi-insulating GaAs prove that diffusion lengths ranging from 200 Å to 10 μm can be measured with an accuracy of better than 5%.
Investigation of thin-film Ni/single-crystal SiC interface reaction
Authors: Ohdomari I. , Sha S. , Aochi H. , Chikyow T. , Suzuki S.
Published: July 2002

Interface reaction between Ni thin film and bulk SiC during heat treatment was investigated by MeV ion backscattering spectrometry using resonance scattering of helium-carbon, x-ray diffraction, and Auger electron spectroscopy (AES). Polycrystalline nickel-silicide, Ni2Si, was formed by heat treatment at 600 °C in forming gas. Carbon compounds were not detected in the reaction products. Carbon was distributed uniformly with a concentration of about 25 at. % in the reacted film, and the C KLL line shape of AES in the reaction products as similar to that of elementary carbon.
Photoabsorption cross section of XeF2 from 150 to 275 nm by forward-scattering electron energy-loss spectroscopy
Authors: Spence David , Tanaka Hiroshi , Dillon M. A.
Published: July 2002

Using the technique of high-incident-energy forward-scattering electron energy-loss spectroscopy, we have derived the relative photoabsorption cross section of xenon difluoride from 150 to 275 nm. Normalization of our data to two previous measurements which used conventional photoabsorption techniques shows good agreement with an early measurement over the entire spectral range, but significant disagreement with more recent data for wavelengths greater than 175 nm.
Space-charge-limited-current diode model for CuxS/CdS solar cells and their degradation
Authors: Partain Larry D.
Published: July 2002

A space-charge-limited-current diode model for CuxS/CdS solar cells accurately models their current-density-versus-voltage (J-V) curves for a 9.2% efficient device and a 4.1% efficient device that degraded to 0.3% efficiency in hot-moist air. For a 1-μm-thick, high-resistance region of Cu compensated CdS at the interface to the CuxS, all the measured fill factors from 0.54 to 0.71 and the open-circuit voltages from 0.41 to 0.52 V are well fit for steady-state conduction electron concentrations between 1.2×109 and 6.9×1010 cm−3 and for electron trap densities between 7×1014 and 5×1018 cm−3 eV−1 at energies of 0.3–0.5 eV below the conduction-band edge of this high-resistance CdS region. The trap changes that occur with short-circuit current degradation increase the fill factor. A CuxS/CdS configuration is proposed to reduce reproducibility problems and to eliminate all the known modes of degradation with the possible exception of photoinduced degradation. Efficiency increases of 10%–11% are projected.
Enhancement of the superconducting critical current from saturation in Nb-Ti wire. I.
Authors: Matsushita T. , Küpfer H.
Published: July 2002

The flux pinning characteristic of processed Nb-Ti monofilamentary wires was investigated at 4.2 K and higher temperatures by an ac measuring method. Saturation of the global pinning force, as in Nb3Sn, was observed at high fields for specimens heat treated after initial heavy cold work. A transition from the saturation to a strongly pinned nonsaturation occurred after the specimen was finally cold worked. This transition directly demonstrates that the saturation is not caused by a shearing deformation of the fluxoid lattice assumed in Kramer’s model [J. Appl. Phys. 44, 1360 (1973)], because this proposed mechanism primarily depends on intrinsic superconducting properties which are not changed by the final cold working. From the measurements of the elastic and plastic behavior of the fluxoid lattice by using the ac method, it was also found that it was not the shearing deformation of the fluxoid lattice but rather the depinning that occurred in the saturation: The saturation is expected to be caused by a catastrophic avalanching flow of the brittle fluxoid lattice. The transition can be explained by an increase of the elementary pinning force of normal Ti precipitates due to elongation by the cold work. The present result and existing results on various materials suggest that the nonsaturation is attained by increasing the elementary pinning force and/or the pin concentration.
The formation of a continuous amorphous layer by room-temperature implantation of boron into silicon
Authors: Jones K. S. , Sadana D. K. , Prussin S. , Washburn J. , Weber E. R. , Hamilton W. J.
Published: July 2002

Ion implantation of 60 keV boron into {100} silicon at medium beam currents (150 μA) was performed at 300–315 K over the dose range from 1 to 8×1016/cm2. Diffraction contrast and high-resolution phase contrast transmission electron microscopy (TEM) were used on plan-view and 90° cross-section samples to study the formation of a continuous amorphous layer as a function of increasing dose. Our TEM results show that, unlike implantation of Si with heavier ions where amorphization initially occurs at or around the projected range, the amorphization by high dose (>5×1016/cm2) B+-implanted Si first occurs at and/or near the surface. It is proposed that the buildup of a high concentration of vacancies which inevitably occurs near the surface during high-dose B+ implantation is primarily responsible for the observed near-surface amorphization. Based on the results of this investigation and those available in the published literature, it appears that low temperature (slow recombination rate for point defects) and high beam current (high generation rate for point defects) implantation may result in the optimum conditions for amorphous layer formation with boron.
dc surface flashover mechanism along solids in vacuum based on a collision-ionization model
Authors: Jaitly N. C. , Sudarshan T. S.
Published: July 2002

Selected experimental results are presented from an extensive experimental investigation of dc prebreakdown and breakdown processes in vacuum along solid insulators made of a variety of alumina ceramics and polymers. The investigations included measurements of predischarge current, x-ray intensity, insulator surface charge density, breakdown behavior as influenced by insulator surface characteristics and insulator profiles, and the analysis of the spectral characteristics associated with insulator surface luminescence. The prebreakdown and breakdown phenomena were found to be strongly influenced by surface microstructure and the chemical state of the insulator surface. The experimentally observed phenomena in our studies strongly point to a new breakdown model based on collision-ionization by electrons of defect sites and/or traps within the dielectric subsurface at the vacuum interface.
Semiclassical high-field transport equations for nonparabolic heterostructure degenerate semiconductors
Authors: Azoff E. M.
Published: July 2002

High-field transport equations are derived for heterostructure degenerate semiconductors, with the inclusion of first-order nonparabolicity in the energy band structure for diamond and zinc-blende semiconductors. The model is based on the first four moments of the relaxation time approximation Boltzmann transport equation. Cubic symmetry has been assumed, although field orientation effects may be included in the relaxation time function. The model is valid up to a hot carrier energy condition satisfying 2αW<1. The low-field limits of the model are also examined.
Laser instrumentation for one-phonon sensitivity and wide bandwidth with multimode gravitational radiation detectors
Authors: Richard Jean-Paul
Published: July 2002

In a multimode detector of gravitational radiation, the displacements induced in the antenna by the gravitational field can be amplified by many orders at the last resonator. Detection of the displacements of that resonator with a Fabry–Perot interferometer is considered. Quantum and classical sources of noise are analyzed and specifications for laser instrumented massive wideband systems operating at the level of δh=2.6×10−20 and 3×10−22/(Hz)1/2 are given. Three detectors could be used to cover the frequency range ≊400–≊1200 Hz with approximately uniform sensitivity.
An x-ray photoelectron spectroscopy study of the interfacial relations between titanium and cordierite-based ceramic thin films
Authors: Bortz Michael , Ohuchi Fumio S.
Published: July 2002

Interfacial reactions between titanium and cordierite-based (2MgO⋅2Al2O3⋅5SiO2) ceramic thin films are probed using x-ray photoelectron spectroscopy. Upon initial room-temperature submonolayer titanium deposition the SiO substrate bonds begin to dissociate, and subsequent deposition results in AlO bond dissociation with low valency Ti oxide formation at the interface. Upon subsequent annealing in vacuum titanium strongly reduces the SiO and AlO bonds, but no observable reduction of the MgO bond is found. Furthermore, between 600 and 700 °C the metallic Al reduces the remaining SiO bonds, with AlO bonds reforming. These results are in qualitative agreement with bulk thermodynamic considerations and this study represents the first comprehensive treatment of the interfacial reactions in metal-multicomponent ceramic systems.
Characterization of FeMn(N)/FeMn/Permalloy exchange coupled structures
Authors: Howard J. K. , Huang T. C.
Published: July 2002

X-ray diffraction was used to investigate the effect of nitrogen additions on the crystal structure and preferred orientation of FeMn films reactively sputtered in an Ar-N2 ambient. The fcc γ-FeMn phase was stabilized over a range of nitrogen pressures. The fcc FeMn(N) film was then used as a nucleation substrate for the deposition of an FeMn/Permalloy exchange coupled structure. A maximum exchange bias of 60–70 Oe was obtained when the FeMn(N) film was lattice matched to the γ-FeMn structure (a0=3.63 Å).
Thermal stability of multilayer films Pt/Si, W/Si, Mo/Si, and W/C
Authors: Jiang Zuimin , Jiang Xiaoming , Liu Wenhan , Wu Ziqin
Published: July 2002

The thermal stability of multilayer films has been studied by use of small-angle x-ray diffraction. The temperatures at which the periodicities of Pt/Si, W/Si, Mo/Si, and W/C multilayers begin to be worse are 200, 300, 400, 900 °C, respectively. The temperatures of total mixing of Pt/Si, W/Si, Mo/Si, and W/C are 600, 600, 700, and >900 °C, respectively. The periods of Mo/Si and W/Si decrease about 5%, 10%, respectively, after annealing at 400 °C for 0.5 h. The period of W/C increases continuously with the increasing temperatures. After annealing at 1000 °C for 0.5 h the increment of the period of W/C is about 20%. The former may be mainly due to the interfacial reaction between metal and Si and the latter may be due to the expansion of C films in W/C.
Metal drilling with a CO2 laser beam. I. Theory
Authors: Armon E. , Zvirin Y. , Laufer G. , Solan A.
Published: July 2002

The initiation and evolution of a ‘‘keyhole’’ produced with a CO2 laser beam in a metal plate is analyzed, accounting for the following effects either exactly or by estimates of their limiting values: the spatial intensity profile of the beam, the temperature-dependent absorptivity, attenuation of the beam intensity by the metal vapor, the exothermic reaction in the presence of oxygen, evaporative material removal and flushing of molten drops, heat conduction within the workpiece, phase transitions from solid to liquid and from liquid to gas, and heat losses at the workpiece boundaries. A study of the drilling of aluminum plates shows the relative effect of these parameters on the crater shape and penetration time. Simple criteria for initiation, penetration rate, and shift to spontaneous burning are presented. In a companion paper experimental results are analyzed to validate the formalism and to yield estimates of the interaction parameters for a specific exposure condition.
Ultrafast imaging of 0.532-μm laser ablation of polymers: Time evolution of surface damage and blast wave generation
Authors: Zyung Taehyoung , Kim Hackjin , Postlewaite Jay C. , Dlott Dana D.
Published: July 2002

An ultrafast two-color laser spectrometer with image acquisition capability is used to study surface ablation of a transparent polymer, PMMA (polymethyl methacrylate). Surface ablation was produced by 100-ps, 0.532-μm pulses and probed by 2-ps, 0.570-μm pulses. Computer-digitized images were obtained over the time range 10−12 –100 s. The images were analyzed to obtain the time-dependent behavior of the damaged solid, and the blast wave generated at the solid-gas interface. Near the peak of the ablation pulse, self-focusing begins and produces a small-diameter filament lasting for 20 ps. The polymer irradiated by the filament then undergoes explosive thermal decomposition, ejecting particles from a conical volume into the atmosphere above the surface. This ablated matter produces a hemispherical, supersonic blast wave whose kinetic energy is one-fourth of the ablation pulse energy. The evacuated pit produced in the polymer is very hot, and the surrounding solid softens and flows, resolidifying in about 1 s. A mechanism for the ablation process involving nonlinear absorption is proposed. The steeply rising envelope of the ablation pulse simultaneously increases the absorption coefficient and decreases the absorption length, resulting in a runaway heating process with a rate of ≊1013 K/s. The polymer is overheated far beyond the normal decomposition temperature. Thermal decomposition then proceeds with a large, negative free energy.
A comprehensive analysis of surface acoustic wave reflections
Authors: Robinson H. , Hahn Y. , Gau J. N.
Published: July 2002

A thorough study of the perturbative and variational approaches is carried out for the surface acoustic wave reflection problem. We have shown that the perturbation treatment by Datta and Hunsinger and potentially powerful variational formulation by Chen and Haus [IEEE Trans. Sonics Ultrason. SU-32, 395 (1985)] are mutually consistent. In their common region of validity, these two approaches yield nearly identical results for the reflection coefficients and velocity shifts due to metal finger and groove overlays. Term-by-term comparison of the mass- and stress-loading effects, and also the electric shorting effect, is carried out to provide a coherent picture of the reflection phenomena. The on- and off-resonance behavior of the reflection coefficient can be described correctly using either one of these theories, with proper inclusion of the overlay shape dependence. A new term for electric shorting is derived for groove overlays.
Dielectric relaxation and deuteron NMR of water in polyimide films
Authors: Xu Gu , Gryte C. C. , Nowick A. S. , Li S. Z. , Pak Y. S. , Greenbaum S. G.
Published: July 2002

Polyimide films containing up to 3.2 wt. % water (H2 O or D2 O) have been studied by dielectric relaxation (DR) and 2H nuclear magnetic resonance (NMR) spectroscopies. Dielectric loss measurements show the presence of a double peak near 200 K due to water, with two components designated as γ1 and γ2 . The γ2 peak, which appears at the lower temperature, is only present for the interior portion of thick (>25 μm) films and rapidly decreases as the moisture content decreases. Correspondingly, deuteron NMR measurements show the presence of narrow and broad lines, which are correlated, respectively, with the γ1 and γ2 DR peaks. The spin-spin relaxation time T2, is much longer for the narrow line than for the broad line. The γ1 DR peak and the narrow NMR line are attributed to sites where isolated water molecules are only loosely coupled to the polymer chains. The γ2 and broad NMR lines involve small clusters of water molecules with associated nuclear magnetic dipole-dipole coupling. Additional measurements on polyimides containing methanol and acetic acid absorbents are also reported.
Ratio of Balmer line intensities resulting from dissociative excitation of molecular hydrogen in an ionizing plasma
Authors: Fujimoto Takashi , Sawada Keiji , Takahata Kiyoto
Published: July 2002

We have estimated the cross section for the production of excited hydrogen atoms from the emission cross sections for Lyman and Balmer lines when molecular hydrogen is dissociated into excited atoms. We have constructed a collisional-radiative model for the system of ground-state hydrogen molecules, excited hydrogen atoms, and protons, in a plasma and have calculated the population density distribution of the excited states. The resulting emission-line intensity ratios for the Balmer series lines are plotted against electron density. We expect these results to be useful for studies of plasmas containing molecular hydrogen, such as occur in the outer region of tokamak plasmas.
Liquid junctions for characterization of electronic materials. III. Modulation spectroscopies of reactive ion etching of Si
Authors: Shen Wu-mian , Fantini M. C. A. , Pollak Fred H. , Tomkiewicz Micha , Leary Herbert J. , Gambino J. P.
Published: July 2002

Photoreflectance, electrolyte photoreflectance, and electrolyte electroreflectance (EER) were measured for various reactive ion etching (RIE) treatments of 〈100〉 n-Si that include CHF3/Ar, CF4, CClF3/H2, CClF3/H2, followed by O2 ash. For all the RIE-treated samples we observe a shift of the transition energy and splitting or broadening of the peaks. These spectral changes were interpreted in terms of tensile strain of the order of 1% caused by the surface damage. In all the cases except for CClF3/H2 the strain is two dimensional. The potential dependence of the EER shows that the CHF3/Ar and the CF4 treatments result in an accumulation of slow surface states that pin the dc potential but not the ac modulation. The CClF3/H2 results in a much smaller pinning that can be removed by O2 ash.
Studies of excimer-laser-produced copper plasma in the presence of background gas
Authors: Kumar V. , Thareja R. K.
Published: July 2002

Studies on spatial and temporal behavior of the emission spectrum of excimer-laser-produced copper plasma in vacuum and in the presence of argon and neon gas are reported. Intensity of spectral lines increases in presence of background gas. Intensity of spontaneously emitted Cu i transition 4p 2P3/2-4s2 2D5/2 at 510.5 nm shows a strong dependence on pressure of neon gas.
Current from shock-loaded piezoelectric crystals
Authors: Gupta V. , Epstein D. J.
Published: July 2002

Electrical responses of shock-loaded X-cut quartz crystals were studied using laser-produced stress pulses. For acoustic transit times that are long compared to the duration of the stress pulse, two short-circuit current signals were observed. The amplitude of the current signal from the rear electrode is predicted to be twice that obtained from the ground electrode using a one-dimensional analysis of the dynamic piezoelectric effect. Experimental observations confirming such predictions are given.
Basic considerations for scaling Z-pinch x-ray emission with atomic number
Authors: Whitney K. G. , Thornhill J. W. , Apruzese J. P. , Davis J.
Published: July 2002

Two energies are identified that define the x-ray emission characteristics of Z-pinch array implosions. One, the kinetic energy per ion, is intensive, and the other, the kinetic energy per centimeter, is extensive. From a series of one-dimensional axisymmetric hydrodynamic calculations, we have calculated the dependence of the x-ray emission from aluminum implosions above 1 keV on these energies. These calculations are carried out for a specially chosen theoretical case where the kinetic energy that is generated during implosion is converted to thermal energy and x rays during the plasma collision on axis in the absence of current. In this case, we determine the I4 to I2 transition of the scaling of emission with peak current, I, as a parametric function of the kinetic energy per ion. We also determine a functional dependence of the emission on this energy when the mass of the imploded aluminum array is held fixed. It is seen that the ability of the plasma to radiate large amounts of energy in either I4 or I2 regimes is strongly dependent on the mass loading. Finally, some arguments are presented on how the breakpoint between I4 and I2 scaling is expected to scale when the atomic number of the array load is varied.
Swelling and microcracking of boron carbide subjected to fast neutron irradiations
Authors: Stoto T. , Housseau N. , Zuppiroli L. , Kryger B.
Published: July 2002

The neutron absorbing ceramic boron carbide was irradiated in the Phenix fast breeder reactor between 600 and 1500 °C. Selected pellets were observed at different magnifications using optical ceramography, scanning electron microscopy, and transmission electron microscopy. The bulk swelling was measured as a function of the burn-up and compared to a recent model based on microstructural observations. Intergranular microcracking was identified as the main source of troubles in the use of boron carbide at high fluence levels and studied in relation with our recent models.
Néel lines in the Bloch walls of bubble garnets and their dark-field observation
Authors: Thiaville A. , Miltat J.
Published: July 2002

The technique for optical microscopy, [polarized anisotropic dark-field observation (PADO)], of vertical Néel lines (also called vertical Bloch lines) existing inside the Bloch walls separating magnetic domains in thin epitaxial films of ferrimagnetic garnets (bubble garnets) is studied and applied here. Results of experiments investigating the role of the polarization of light impose severe constraints on the theoretical models. The picture emerging from them excludes a contrast due to light diffracted by the usual magneto-optical effects inside the wall. By varying the angle of incidence of the anisotropic dark-field illuminating beam, line contrast inversions can be obtained. It is shown that the sample’s thickness, when well above the wavelength of light, is responsible for that fact. Moreover, to reproduce all line contrast reversals, an effective height which is smaller than the sample’s thickness has to be considered for the line structure. A tempting conclusion from this study may be that lines are seen in PADO by means of a wall deformation, the origin of which has to be found.
All-optical modulation using an n-doped quantum-well structure
Authors: Noda Susumu , Uemura Tetsuya , Yamashita Takao , Sasaki Akio
Published: July 2002

The modulation of interband-resonant light by intersubband-resonant light using an n-doped quantum well is proposed, and results of the theoretical analysis are reported. It is shown that a large change in absorption coefficient from 100 to 3160 cm−1 for interband-resonant light can be obtained by changing the intensity of intersubband-resonant light from 0 to 1 MW/cm2. Very fast modulation speed (∼ps) can be expected.
Chemical sputtering of Al2O3 by fluorine-containing plasmas excited by electron cyclotron resonance
Authors: Lee Y. H. , Zhou Z. H. , Danner D. A. , Fryer P. M. , Harper J. M.
Published: July 2002

Reactive ion etching of aluminum oxide has been studied in CHF3 and SF6 plasmas generated by electron cyclotron resonance in conjunction with in situ ellipsometric measurement for thickness variation. Because of the involatility of etch products associated with aluminum, purely chemical reactions cannot desorb etch products at room temperatures, and ion bombardment is essential to etch Al2O3 through chemically enhanced physical sputtering. The higher the oxygen content in a film, the faster the etch rate, resulting from chemical sputtering due to volatile CO molecules in CHF3 plasmas. This dependence on composition is absent in SF6 plasma. The threshold ion energy for physi-chemical sputtering by fluorine-containing species is estimated to be about 20 eV at room temperature, while the threshold for Ar sputtering is 50 eV. In CHF3 plasmas, however, Al2O3 exhibits a larger threshold energy at a lower temperature due to passivating species which inhibit sputtering. These passivating species have a very weak binding energy of roughly 0.1 eV, which has been deduced from a temperature dependence of the threshold energy. A patterned sample always shows vertical profile without undercuts.
Mechanically alloyed Sm-Co materials
Authors: Wecker J. , Katter M. , Schultz L.
Published: July 2002

The preparation of SmCo5 magnets is based on a high-temperature heat treatment above 800 °C followed by a rapid cooling to room temperature. By mechanical alloying and a subsequent heat treatment, it is possible for the first time to prepare hard magnetic SmCo5 powder at low temperatures. The process involves first the formation of an amorphous precursor during milling, which then is transformed to the 1:5 structure at temperatures above 500 °C. The magnetically isotropic samples show a coercivity of 24 kA/cm and a remanence of 0.52 T. The process is also applicable to Sm2Co17. However, here the coercivity is less than 5 kA/cm and higher values require the formation of a precipitation-hardened microstructure. The stability of SmCo5 below 800 °C questions the eutectoid decomposition into Sm2Co17 and Sm2Co7.
Magnetic coercivity of Fe3O4 particle systems
Authors: Arajs Sigurds , Amin Nurul , Anderson Elmer E.
Published: July 2002

Magnetic coercivity and squareness of various Fe3O4 particle systems have been investigated as a function of particle size and packing density. It has been found that these particle systems, exhibiting considerable deviations from spherical symmetry, have magnetic coercivities and squareness which are almost independent of packing density.
Spin and angle-resolved photoemission studies of one to three monolayer films of p(1×1) Fe on W(100)
Authors: Fink R. L. , Mulhollan G. A. , Andrews A. B. , Erskine J. L. , Walters G. K.
Published: July 2002

The electronic and magnetic properties of thin (one to three monolayer) epitaxial Fe films grown on W(100) are studied using spin-polarized angle-resolved photoemission. Low-energy electron-diffraction studies of a number of samples confirm excellent epitaxy for monolayer films and suggest that two- and three-layer films begin to form strain-relieving dislocations. Submonolayer films manifest no in-plane remanent spin polarization at T=115 K, but effectively quench W(100) surface states and surface resonances. Monolayer and thicker films yield spin-polarized photoelectrons under remanent magnetic conditions. Analysis of spin-polarized electron energy distribution curves (EDCs) corresponding to even-symmetry initial states along the Γ̄-M̄ direction of the two-dimensional Brillouin zone yields a flat majority-spin band at 0.95 eV and an exchange split pair of bands (ΔEexΔEex= 2.15 ± 0.2 eV at Γ̄, 1.2±0.2 eV at M̄) which exhibit significant dispersion. No significant changes in the binding energies of spin-up or -down features in EDCs obtained above the Curie temperature at Γ̄ (normal emission geometry) were detected.
Crystallization of sol-gel derived lead zirconate titanate thin films
Authors: Dana S. S. , Etzold K. F. , Clabes J.
Published: July 2002

Thin films of lead zirconate titanate (PZT) have been prepared by the sol-gel processing method using metal alkoxides. The crystallographic and morphological properties of the films have been analyzed by x-ray diffraction and scanning electron microscopy. The elemental composition of the films was determined by Rutherford backscattering, electron microprobe, and Auger electron spectroscopy, and was compared to that of the precursor solution characterized by inductively coupled plasma spectrophotometry. Results are presented which illustrate the relationships between the properties and the observed structure of the thin films, with the processing conditions. The electrical properties, dielectric constant, and ferroelectric hysterisis response were tested to determine the quality of the films. The experimental observations suggest two competing mechanisms during the PZT formation: lead loss out of the film, and nucleation of the PZT phase with its subsequent crystallization.
Pressure-assisted reaction bonding between W and Si80Ge20 alloy with Ni as the interlayer
Authors: Xu Y. , Laabs F. C. , Beaudry B. J. , Gschneidner K. A.
Published: July 2002

The conditions and reaction mechanism of W/Ni/Si80Ge20 hot-press bonding have been studied. It was found that a Ni/Si80Ge20 bond can be formed using low pressure, 19.6 MPa, in the temperature range between 780 and 900 °C in a short time. The kinetics follows a parabolic pattern, suggesting it is a diffusion-controlled process. The activation energy is 2.7 eV and the parabolic rate constant is given by KP = 4.0 × 1014 exp(−3.2×104/T) (μm2/min). The bonding interface has a multilayered structure. A phenomenological mechanism of the bonding formation has been proposed based on scanning electron microscopy observations and energy dispersive spectroscopy. The cracking problem due to thermal stress is discussed based on Oxx’s equation. It was found that bonds free from cracks in the Si80Ge20 alloy are formed when the Ni consumption (as measured by the thickness of the nickel layer) is sufficiently small (<40–45 μm) and the post-hot-press cooling is slow. On the other hand, tungsten and nickel react during hot pressing at higher temperature, forming WNi4. As an interlayer, nickel can join the tungsten sheet and the Si80Ge20 together. It has been also demonstrated that a thin nickel layer formed by vapor deposition on a tungsten sheet may be used as the interlayer in place of nickel sheet.
Study of silver addition to Y1Ba2Cu3O7−y screen printed thick films
Authors: Dhingra Indu , Padam G. K. , Singh Satbir , Tripathi R. B. , Rao S. U. M. , Suri D. K. , Nagpal K. C. , Das B. K.
Published: July 2002

A study of the effect on the superconducting and microstructural properties of YBa2Cu3O7−x screen printed thick films as a function of silver content (in the form of Ag and Ag2O) from 0 to 40 wt. % by employing different experimental techniques has been carried out. It has been found that silver improves the sinterability and intergrain connectivity and reduces the normal state resistivity. The superconducting transition temperature of the above films was found to be in the range of 82 to 91 K. Our results show that a small addition of silver (Ag or Ag2O) helps in enhancing the superconducting properties. However, large amounts lead to formation of 211 phase as the decomposed product and thereby deteriorate the quality of the superconductor. Silver has been found to remain as metal in the samples for the entire range. Further, in light of our results, it seems that an addition of Ag metal is more beneficial than the addition of Ag2O.
Production of ultrafine aluminum and aluminum nitride particles by plasma–alloy reaction and their microstructure and morphology
Authors: Inoue A. , Kim B. G. , Nosaki K. , Yamaguchi T. , Masumoto T.
Published: July 2002

The preparation condition, microstructure, and morphology of ultrafine Al and AlN particles were examined by a combined technique of nitrogen plasma–aluminum reaction and spray deposition as well as by metallographic techniques. The Al and AlN particles have the morphologies of sphere and hexagonal plate, respectively, and the particle size is 5 to 200 nm for Al and 20 to 120 nm for AlN. The volume ratio of AlN to Al increases continuously with an increase of the mixing gas ratio of nitrogen to argon and the total pressure of nitrogen and reaches about 25% in a nitrogen atmosphere with a pressure of 93 kPa. The composite Al–AlN particles are also observed and have an orientation relationship of (111)Al//(001)AlN, [101̄]Al//[110]AlN, and [12̄1]Al//[11̄0]AlN, in which the lattice misfit is as small as 6.4%, 8.6%, and 8.6%, respectively. The formation of the composite particles is presumed to result from the collision and incorporation of Al particles with the AlN plate adhered to Al particles. The Al and AlN particles produced by the present method are concluded to be small and homogeneous enough to be used as raw materials for the production of nanoscale composites and compositionally gradient materials.
Optical properties of Si partially amorphized by ion implantation
Authors: Adachi Sadao , Aoki Toshiaki
Published: July 2002

Optical properties of Si partially amorphized by As+-ion implantation have been studied by means of the two-phase mixture Bruggeman effective-medium approximation in which the partially amorphized layer is assumed as a physical mixture of fully amorphous Si and crystalline Si. The dielectric functions of the crystalline components deduced from this study differ appreciably from that of the bulk crystalline Si, especially in the vicinity of the sharp critical point (CP) features. We find that the change in the optical properties of the crystalline component is due to the increase in the broadening parameters of the CPs caused by implantation-induced damage. The amorphous volume fraction fa is also found to be simply expressed as fa=([As+]/A)α, where [As+] is the ion fluence (150-keV As+ ions), A (=1×1015 cm−2) is an amorphization-threshold fluence (i.e., the minimum fluence required to form a fully amorphous layer), and α (=0.46) is an amorphization-rate factor of the incident ions. Dielectric-function-related optical data of partially amorphized Si, such as the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity, are also presented as a byproduct of the present analysis.
Alexandrite as a high-temperature pressure calibrant, and implications for the ruby-fluorescence scale
Authors: Jahren A. H. , Kruger M. B. , Jeanloz Raymond
Published: July 2002

The wavelength shifts of the R1 and R2 fluorescence lines of alexandrite (BeAl2O4:Cr+3) have been experimentally calibrated against the ruby-fluorescence scale as a function of both hydrostatic and nonhydrostatic pressures between 0 and 50 GPa, and simultaneously as a function of temperatures between 290 and 550 K. The results can be expressed in nm as λ(R1)=680.26(±0.01)+8.7×10−3 (±0.3) (T−273)+0.292(±0.003)P +1.3(±0.1)×10−3 P2 and λ(R2)=678.63 (±0.01)+7.8×10−3(±0.2)(T−273)+0.031 (±0.003)P+0.8(±0.1)×10−3 P2, with pressure P in GPa and temperature T in K. Notably, we find that the pressure–temperature cross derivative of the fluorescence wavelength shifts are negligible for both ruby and alexandrite.
On the normal acceleration sensitivity of contoured quartz resonators stiffened by quartz cover plates supported by clips
Authors: Zhou Y. S. , Tiersten H. F.
Published: July 2002

Recent work has shown that both the normal and resultant in-plane acceleration sensitivities of contoured quartz resonators vanish for a perfectly symmetric resonator and support system. It has also been shown that any loss of symmetry in the combined resonator plus support configuration results in a significant degradation in the acceleration sensitivity. Since it is essentially impossible to construct a perfectly symmetric resonator plus support configuration in practice, a stiffened structure is considered. The structure consists of the active biconvex quartz resonator attached to identical top and bottom quartz cover plates by means of small sidewalls around the periphery. The mounting clips are attached to the top and bottom cover plates without touching the active plate. An analysis of the normal acceleration sensitivity of this configuration is performed. Results are presented for a mispositioning of either a clip or the mode shape for a range of thickness of cover plates relative to the active plate.
Self-consistent electron cyclotron resonance absorption in a plasma with varying parameters
Authors: Williamson M. C. , Lichtenberg A. J. , Lieberman M. A.
Published: July 2002

A formalism is developed for numerically calculating reflection and absorption of right-hand polarized waves and reflection of left-hand polarized waves propagating into a cyclotron resonance zone in a medium in which both magnetic field and plasma density are varying. The results are shown to agree with previous analytic calculations in the limit of constant density, weak collisionality, and linearly varying magnetic field, where the analytic calculation applies. The formalism is then applied to a plasma with general field and density variations, and arbitrary collisionality. The absorption and reflections are calculated for various boundary conditions along the propagation path, showing that there is an optimum density for power absorption. The collisionless absorption in the resonance zone, calculated from the single particle heating averaged over the flux is shown to be consistent with the linear wave absorption at low absorption and collisionality. At high absorption a prescription for bringing the two calculation methods into agreement is advanced. The results are used to qualitatively explain some previously puzzling experimental observations.