Publications

Abstract not provided.

This set of view graphs outline the simulation of the behavior of polyelectrolytes.

We are conducting a comprehensive experimental study of the electromechanical behavior of poled PZT 95/5 (lead zirconate titattate). As part of this study, eight plane-wave tests have been conducted on axially poled PZT 95/5 at stress levels ranging from 0.9 to 4.6 GPa, using VISAR and electrical diagnos- tics. Observed wave velocities were slightly decreased from ultrasonic vahtes, by contrast' with unpoled samples. Compression waveforms show a step at 0.6 GPa more marked than for normally poled or unpoled samples; this may correspond to a poling effect on the ferroelectric/antiferroelectric transition. A similar step is observed on release. The released charge upon loading to 0.9 GPa is consistent with nearly complete depoling. Loading to higher stresses gave lower currents (factor of 10), suggesting shock-induced conduc- tivity or electrical breakdown.

A new mold material has been developed for use in making rare-earth permanent magnet components with precise dimensions in the 10 to 1000 µm range by hot-forging. These molds are made from molds poly(methyl)methacrylate (PMMA) made by deep x-ray lithography (DXRL). An alumina bonded with colloidal silica has been developed for use in these molds. This material can be heated to 950°C without changing dimensions where it develops the strength needed to withstand the hot-fmging conditions (750°C, 100 MPa). In addition, it disintegrates in HF so that parts can be easily removed after forging.

Magnetic field-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.

Composites of carbon black particles in polyethylene are known to exhibit an unusually rapid increase in resistivity as the applied field is increased, making this material useful in automatically resettable fuses. In this application the composite is in series with the circuit it is protecting: at low applied voltages this circuit is the load, but at high applied voltages the composite becomes the load, limiting the current to the circuit. We present a simple model of this behavior in terms of a network of nonlinear conductors. Each conductor has a conductance that depends on its instantaneous Joule heating. It is shown that in the fusing regime, where the current through the composite decreases with increasing voltage, an plate-like dissipation instability develops normal to the applied field. Experimental evidence of this phenomena is described.

Abstract not provided.

Abstract not provided.

Iron catalysts are particularly useful for Fischer-Tropsch (FT) synthesis when the H2 to CO ratio of the synthesis gas is low since iron exhibits water gas shift as well as FT activity. Iron catalysts are active for Fischer Tropsch synthesis only when in the carbide state. The active iron carbide catalyst has a 1-3 nm carbonaceous layer, which can only be found on the carbided iron catalyst (no carbonaceous material is found on iron oxide particles that maybe present). This paper will address the nature of the carbonaceous material that is required for product formation. The carbonaceous material is amorphous, does not require hydrogen to form, and is the starting material for FT products.

Hydrogen was regarded as a harmful impurity in many alloys and particularly in steels where it gives rise to a specific type of embrittlement and forms various discontinuities like flakes and blowholes. For this reason, the researcher efforts were mainly focused on eliminating hydrogen's negative impacts and explaining its uncommonly high diffusivity in condensed phases. Meanwhile, positive characteristics of hydrogen as an alloying element remained unknown for quite a long time. Initial reports in this field did not appear before the early 1970s. Data on new phase diagrams are given for metal-hydrogen systems where the metal may or may not form hydrides. Various kinds of hydrogen impact on structure formation in solidification, melting and solid-solid transformations are covered. Special attention is given to the most popular alloys based on iron, aluminum, copper, nickel, magnesium and titanium. Detailed is what is called gas-eutectic reaction resulting in a special type of gas-solid structure named gasarite. Properties and applications of gasars - gasaritic porous materials - are dealt with. Various versions of solid-state alloying with hydrogen are discussed that change physical properties and fabrication characteristics of metals. Details are given on a unique phenomenon of anomalous spontaneous deformation due to combination of hydrogen environment and polymorphic transformation. All currently known versions of alloying with hydrogen are categorized for both hydride-forming and non-hydrid forming metals.

Particles are inevitably generated in physical vapor deposition (PVD) systems due to the delamination of deposited films on various process chamber parts and shielding. Non-collimated (blanket) and collimated PVD Titanium Nitride (TiN) deposition processes are used for metal ARC (anti-reflective coating) and underlayers, and for the "contact liner" deposition steps (TiN adhesion layers before plug formation). Probe yield analysis and SRAM bit failure analysis, using conventional failure analysis, have shown that particles at these process steps can have a significant impact on wafer yields. In many typical semiconductor wafer fabs, particles generated by TiN film deposition rank consistently at or near the top of the defect pareto. This paper summarizes the results of defect reduction experiments conducted on an Applied Materials Endura Physical Vapor Deposition (PVD) system and various off-line experiments examining film and adhesion characteristics. It includes the results of film adhesion and shield temperature control experiments aimed at reducing defect levels. Key fidings, particle reduction results, and recommended defect reduction measures are presented. The reduction in particles not only can improve yields, but also result in substantial cost savings through the extension of chamber kit end-of-life (EOL).

The pressure-induced phase transition in CdS was investigated using picosecond time-resolved electronic spectroscopy in plate impact shock wave experiments. Real-time changes in the electronic spectra were observed, with 100 ps time resolution, in single crystals of CdS shocked along the c and a axes to peak stresses between 35 and 90 kbar (above the phase transition stress of approximately 30 kbar measured in continuum studies). When shocked to stresses above approximately 50 kbar along the crystal c axis and 60 to 70 kbar along the crystal a axis, the crystals undergo a very rapid change in electronic structure, indicating that significant structural changes occur within the first 100 ps. These results, along with previous ns continuum measurements, make a strong case for a metastable state during the phase transition in shocked CdS. Ab-initio periodic Hartree-Fock calculations (with DFT correlation corrections) were employed to examine the compression of CdS and to determine a possible lattice structure for the proposed metastable structure. These results, along with details of the transformation kinetics and orientational dependence, will be discussed. Work supported by ONR.

In previous studies, ruby R-line shifts under shock compression and tension have been measured using the spontaneous luminescence from optically pumped samples. Signal intensities obtained through the use of this method are limited by the short time duration of the experiments (100 ns to several ps) in comparison to the long lifetime of the luminescence (approximately 3 ins). We have investigated the use of stimulated emission as a technique for measuring R-line shifts in shocked ruby crystals. Feasibility experiments were performed both at ambient conditions and under shock compression to 60 kbar using an experimental configuration similar to that used for time resolved ruby luminescence measurements in previous shock wave studies. Signal gain due to stimulated emission was observed, with gains ranging from 1.1 to 3.4, in agreement with calculations performed for the particular experimental configuration used. The present results make a good case for incorporating this technique to measure shock induced R-line shifts in ruby. Work supported by DSWA.

A series of two-dimensional hydrodynamic calculations using the two-dimensional Second- order Hydrodynamic Automated Mesh Refinement Code (SHAMRC) developed by Applied Research Associates, Inc. (ARA), was made with the objective of understanding the behavior of aqueous foams in the presence of a C4-generated blast wave. A full three-phase water equation-of-state was incorporated in the first calculation. Comparison of the results of the first calculation with experimental data collected by Sandia National Laboratories (SNL) indicated that the interaction was much more complicated than could be represented by a mixture of detonation products, air, and water in local temperature and pressure equilibrium. Other models were incorporated in the code to examine the effects of thermal non-equilibrium between water and the gases and allowed for two-phase flow. The water droplets were allowed to slip relative to the gas velocity, providing non-equilibrium for the velocity distribution. These models permitted heated liquid droplets to be accelerated at high pressures and transported through and ahead of the decaying shock front. The droplets then exchanged momentum and energy with the foam ahead of the shock and preconditioned the medium through which the shock was propagating. This process had the effect of diffusing the shock front and its associated energy. These relatively high resolution calculations develop numerical representations of the Rayleigh-Taylor instabilities at the detonation products/foam interface. This unstable interface plays in important role in understanding the behavior of the interaction of the detonation products with the foam. Figure 4 clearly shows the developing instabilities at the interface and an inward facing shock at a radius of 25 cm. The results of the calculations using the various models can be edited to provide the total energy exchanged between materials, the fraction of water vaporized, and the extent of detonation products as a function of time.

This section reviews physical processes involved in the implantation of energetic hydrogen into plasma facing materials and its subsequent diffusion, release, or immobilization by trapping or precipitation within the material. These topics have also been discussed in previous reviews. The term hydrogen or H is used here generically to refer to protium, deuterium or tritium.

Multi-kilojoule repetitive pulsed power technology moved from a laboratory environment into its first commercial application in 1997 as a driver for ion beam surface treatment. Sandia's RHEPP II, a repetitive 2.5 kJ/pulse electron beam accelerator, has supported the development of radiation treatment processes for polymers and elastomers, food products, and high dose- rate effects testing for defense programs since early 1996. Dos Lineas, an all solid-state testbed, has demonstrated synchronization techniques for parallel magnetic modulator systems and is continuing the development of design standards for long lifetime magnetic switches and voltage adders at a shot rate capability that exceeds 5x10⁶ pulses per day. This paper will describe progress in multi-kilojoule class repetitive pulsed power technology development, limitations of magnetic switching technology for accelerator and modulator applications, and future research and development directions.

Experimental results are presented that provide design guidelines for high repetition rate, long-life pulsed power magnetic modulators. Fault mechanisms that occurred during a series of 32 million shots at 100 pps, with continuous runs of up to 5.7 million shots (~16 hours) on the Dos Lineas magnetic modulator are described. An effort to explain the fault mechanisms and how to avoid them is made. Factors that limit the long life performance of a variety of components including switches, cables and oil are encountered. The high reliability of the magnetic switch technology is demonstrated.

The laser glass for the National Ignition Facility (NIF) Main Amplifier system is pumped by a system of 192 pulsed power/flash lamp assemblies. Each of these 192 assemblies consists of a 1.6 MJ (nominal) capacitor bank working with a Pre-Ionization/Lamp Check (PILC) pulser to drive an array of 40 flash lamps. This paper describes the predicted performance of these Power Conditioning System (PCS) modules in concert with flashlamp assemblies in NIF. Each flashlamp assembly consists of 20 parallel sets of lamps in series pairs. The sensitivity of system performance to various design parameters of the PILC pulser and the main capacitor bank is described. Results of circuit models are compared to sub-scale flashlamp tests and to measurements taken in tests of a PCS module driving a flashlamp assembly in the First Article NIF Test Module facility at Sandia National Laboratories. Also included are predictions from a physics-based, semi-empirical amplifier gain code.

Long range substituent effects on the ²⁹Si NMR chemical shifts in a series of alkylene and arylene-bridged triethoxysilanes were observed over as many as 11 bonds. The hydrolysis reaction of an ethoxide caused the resonance of the silicon on the opposing end of the bridging unit to move downfield. The alkylene bridging units ranged from ethylene to octylene while the arylene bridging units included phenyl and biphenyl. Resonance assignments were confirmed by the absence of these shifts for the triethoxysilyl in l-triphenylsilyl-2-triethoxysilylethane. The magnitude of the downfield shift decreased as the length of the bridging unit between silicon atoms increased. Transmission of the substituent effect along a polyethylene chain was successfully modeled by a through-bond mechanism with an attenuation factor of 1.88 for each methylene unit.

The Laser Engineered Net Shaping (LENSm) process is a laser assisted, direct metal manufacturing process under development at Sandia National Laboratories. The process incorporates features from stereo lithography and laser surfacing, using CAD file cross-sections to control the forming process. Powder metal particles (less than 150 micrometers) are delivered in a gas stream into the focus of a NdYAG laser to form a molten pool. The part is then driven on an x/y stage to generate a three-dimensional part by layer wise, additive processing. In an effort to understand the thermal behavior of the LENS process, in-situ high-speed thermal imaging has been coupled with microstructural analysis and finite element modeling. Cooling of the melt is accomplished primarily by conduction of heat through the part and substrate, and depending on the substrate temperature and laser input energy, cooling rates can be varied from 10 sup2; to 10 sup3; K s^-l. This flexibility allows control of the microstructure and properties in the part. The experiments reported herein were conducted on 316 stainless steel, using two different particle size distributions with two different average particle sizes. Thermal images of the molten pool were analyzed to determine temperature gradients and cooling rates in the vicinity of the molten pool, and this information was correlated to the microstructure and properties of the part. Some preliminary finite element modeling of the LENS process is also presented.

A new semiconductor alloy system, InGaAsN, has been identified as a can- didate material for multi junction solar cells having efficiencies greater than 40%. The introduction of small amounts of nitrogen ( 2%) into the InGaAs alloy system greatly reduces the band gap energy, with reductions approaching 0.4 eV for 2% nitrogen content With the appropriate ratio of indium to nitrogen concentrations, InGaAsN can be lattice matched to GaAs.

The angle of ion incidence at the etched wafer location during RIBE and IBE using Cl₂, Ar and O₂ ion beams has been characterized using an ion energy and angle analyzer. Effects of beam current and accelerator grid bias on beam divergence and the spatial uniformity of the spread of incident angles are measured. It is observed that increased total beam current can lead to reduced current density at the sample stage due to enhanced beam divergence at high currents. Results are related to preferred etch system design for uniform high-aspect-ratio etching across semiconductor wafers.

In the world of computer-based data acquisition and control, the graphical interface program LabVIEW from National Instruments is so ubiquitous that in many ways it has almost become the laboratory standard. To date, there have been approximately fifteen books concerning LabVIEW, but Professor Essick's treatise takes on a completely different tack than all of the previous discussions. In the more standard treatments of the ways and wherefores of LabVIEW such as LabVIEW Graphical Programming: Practical Applications in Instrumentation and Control by Gary W. Johnson (McGraw Hill, NY 1997), the emphasis has been instructing the reader how to program LabVIEW to create a Virtual Instrument (VI) on the computer for interfacing to a particular instruments. LabVIEW is written in G a graphical programming language developed by National Instruments. In the past the emphasis has been on training the experimenter to learn G . Without going into details here, G incorporates the usual loops, arithmetic expressions, etc., found in many programming languages, but in an icon (graphical) environment. The net result being that LabVIEW contains all of the standard methods needed for interfacing to instruments, data acquisition, data analysis, graphics, and also methodology to incorporate programs written in other languages into LabVIEW. Historically, according to Professor Essick, he developed a series of experiments for an upper division laboratory course for computer-based instrumentation. His observation was that while many students had the necessary background in computer programming languages, there were students who had virtually no concept about writing a computer program let alone a computer- based interfacing program. Thus the beginnings of a concept for not only teaching computer- based instrumentation techniques, but aiso a method for the beginner to experience writing a com- puter program. Professor Essick saw LabVIEW as the perfect environment in which to teach computer-based research skills. With this goal in mind, he has succeeded admirably. Advanced LabVIEW Labs presents a series of chapters devoted to not only introducing the reader to LabVIEW, but also to the concepts necessary for writing a successful computer pro- gram. Each chapter is an assignment for the student and is suitable for a ten week course. The first topic introduces the while loop and waveform chart VI'S. After learning how to launch LabVIEW, the student then leans how to use LabVIEW functions such as sine and cosine. The beauty of thk and subsequent chapters, the student is introduced immediately to computer-based instruction by learning how to display the results in graph form on the screen. At each point along the way, the student is not only introduced to another LabVIEW operation, but also to such subjects as spread sheets for data storage, numerical integration, Fourier transformations', curve fitting algorithms, etc. The last few chapters conclude with the purpose of the learning module, and that is, com- puter-based instrumentation. Computer-based laboratory projects such as analog-to-digital con- version, digitizing oscilloscopes treated. Advanced Lab VIEW Labs finishes with a treatment on GPIB interfacing and finally, the student is asked to create an operating VI for temperature con- trol. This is an excellent text, not only as an treatise on LabVIEW but also as an introduction to computer programming logic. All programmers, who are struggling to not only learning how interface computers to instruments, but also trying understand top down programming and other programming language techniques, should add Advanced Lab-VIEW Labs to their computer library.

Our data suggest a correlation between near-interface strain in SiO{sub 2} and the ratio of fixed vs. mobile positive charge generated at the interface during forming gas annealing. A model based on first-principles quantum mechanical calculations supports this correlation.

This paper will focus on the methodology of using a 2D plasma Direct Simulation Monte Carlo technique to simulate the species transport in an inductively coupled, low pressure, chemically reacting plasma system. The pressure in these systems is typically less than 20 mtorr with plasma densities of approximately 10{sup 17} {number_sign}/m{sup 3} and an ionization level of only 0.1%. This low ionization level tightly couples the neutral, ion, and electron chemistries and interactions in a system where the flow is subsonic. We present our strategy and compare simulation results to experimental data for Cl{sub 2} in a Gaseous Electronics Conference (GEC) reference cell modified with an inductive coil.