Publications

As a result of an Environmental Impact Statement (EIS) recently issued by the Department of Energy, Sandia National Laboratories (SNL) has been selected as the {open_quotes}most appropriate facility{close_quotes} for the production of {sup 99}Mo. The daughter product of {sup 99}Mo is {sup 99m}Tc, a radioisotope used in 36,000 medical procedures per day in the U.S.{close_quote} At SNL, the {sup 99}Mo would be created by the fission process in UO{sub 2} coated {open_quotes}targets{close_quotes} and chemically separated in the SNL Hot Cell Facility (HCF). SNL has recently completed the irradiation of five production targets at its Annular Core Research Reactor (ACRR). Following irradiation, four of the targets were chemically processed in the HCF using the Cintichem process.

The simulation of mechanical system random vibrations is important in structural dynamics, but it is particularly difficult when the system under consideration is nonlinear. Artificial neural networks provide a useful tool for the modeling of nonlinear systems, however, such modeling may be inefficient or insufficiently accurate when the system under consideration is complex. This paper shows that there are several transformations that can be used to uncouple and simplify the components of motion of a complex nonlinear system, thereby making its modeling and random vibration simulation, via component modeling with artificial neural networks, a much simpler problem. A numerical example is presented.

Environmental and health concerns pertaining to lead have encouraged research into low-lead alloys for electronic soldering. The development of solder alloys containing lower amounts of lead than Sn/Pb eutectic (37 wt.% lead), but possessing similar properties, is an industry-wide goal. To determine the wettability of low-lead solders, 21 alloys each of Sn/Ag and Sn/Cu eutectic (containing 0 to 10 wt.% lead and/or indium) were tested on as-received copper-clad FR-4. Contact angles for the alloys ranged from 12.5 to 38.9{degrees} and area of spread measurements ranged from 5.2 to 17.3 mm{sup 2} compared with 5 to 150 and {approximately}19 mm{sup 2}, respectively, for Sn/Pb eutectic. Alloys with 8 to 10 wt.% lead showed contact angles and areas of spread similar to Sn/Pb eutectic under similar conditions. The best results on the as-received substrates, compared to the Sn/Pb eutectic, were obtained from the Sn/Ag eutectic with 10 wt.% lead. The very low-lead (less than 10 wt.% lead) and lead-free alloys, however, failed to achieve the performance level of eutectic Sn/Pb solders. A desire to improve the spreading of very low-lead and lead-free solders provided the impetus for these efforts to produce {open_quotes}engineered{close_quotes} rough surfaces. In an attempt to improve the wettability and spreading behavior of very low-lead and lead-free alloys, the very low-lead and lead-free members of the Sn/Ag system were tested on roughened copper-clad FR-4. Every alloy in the test suite demonstrated improvement in area of spread on the roughened substrates. The best results on the roughened substrates, compared to the Sn/Pb eutectic, were obtained from the Sn/Ag eutectic with 8 wt.% lead. The effects of surface roughness on the wettability and flow behavior of solder alloys has provided insight into surface morphologies that lead to improved solderability.

This paper presents a convergence theory for evolutionary pattern search algorithms (EPSAs). EPSAs are self-adapting evolutionary algorithms that modify the step size of the mutation operator in response to the success of previous optimization steps. Previously, the authors have proven a stationary point convergence theory for EPSAs for which the step size is not allowed to increase. The present analysis generalizes this analysis to prove a convergence theory for EPSAs that are allowed to both increase and decrease the step size. This convergence theory is based on an extension of the convergence theory for generalized pattern search methods.

A microstructurally-based computational simulation is presented that predicts the behavior and lifetime of solder interconnects for electronic applications. This finite element simulation is based on an internal state variable constitutive model that captures both creep and plasticity, and accounts for microstructural evolution. The basis of the microstructural evolution is a simple model that captures the grain size and microstructural defects in the solder. The mechanical behavior of the solder is incorporated into the model in the form of time-dependent viscoplastic equations derived from experimental creep tests. The unique aspect of this methodology is that the constants in the constitutive relations of the model are determined from experimental tests. This paper presents the constitutive relations and the experimental means by which the constants in the equations are determined. The fatigue lifetime of the solder interconnects is predicted using a damage parameter (or grain size) that is an output of the computer simulation. This damage parameter methodology is discussed and experimentally validated.

New soldering materials and processes have been developed over the last several years to address a variety of environmental issues. One of the primary efforts by the electronics industry has involved the development of alternative solders to replace the traditional lead-containing alloys. Sandia National Laboratories is developing such alternative solder materials for printed circuit board and hybrid microcircuit (HMC) applications. This paper describes the work associated with low residue, lead-free soldering of thick film HMC`s. The response of the different materials to wetting, aging, and mechanical test conditions was investigated. Hybrid test vehicles were designed and fabricated with a variety of chip capacitors and leadless ceramic chip carriers to conduct thermal, electrical continuity, and mechanical evaluations of prototype joints. Microstructural development along the solder and thick film interface, after isothermal solid state aging over a range of elevated temperatures and times, was quantified using microanalytical techniques. Flux residues on soldered samples were stressed (temperature-humidity aged) to identify potential corrosion problems. Mechanical tests also supported the development of a solder joint lifetime prediction model. Progress of this effort is summarized.

Cost and schedule overruns are often caused by poor requirements that are produced by people who do not understand the requirement process. This paper provides a high-level overview of the requirements discovery process.

This paper presents an experimental evaluation of evolutionary pattern search algorithms (EPSAs). Our experimental evaluation of EPSAs indicates that EPSAs can achieve similar performance to EAs on challenging global optimization problems. Additionally, we describe a stopping rule for EPSAs that reliably terminated them near a stationary point of the objective function. The ability for EPSAs to reliably terminate near stationary points offers a practical advantage over other EAs, which are typically stopped by heuristic stopping rules or simple bounds on the number of iterations. Our experiments also illustrate how the rate of the crossover operator can influence the tradeoff between the number of iterations before termination and the quality of the solution found by an EPSA.

The Waste Isolation Pilot Plant (WIPP), located in a salt bed in southern New Mexico, is designed by US Department of Energy to demonstrate the safe and permanent disposal of design-basis transuranic waste. WIPP performance assessment requires consideration of radionuclide release in brines in the event of inadvertent human intrusion. The mobility of radionuclides depends on chemical factors such as brine pmH (-log molality of H{sup +}) and CO{sub 2} fugacity. According to current waste inventory estimates, a large quantity ({approximately} 10{sup 9} moles C) of organic materials will be emplaced in the WIPP. Those organic material will potentially be degraded by halophilic or halotolerant microorganisms in the presence of liquid water in the repository, especially if a large volume of brine is introduced into the repository by human intrusions. Organic material biodegradation will produce a large amount of CO{sub 2}, which will acidify the WIPP brine and thus significantly increase the mobility of actinides. This communication addresses (1) the rate of organic material biodegradation and the quantity of CO{sub 2} to be possibly generated, (2) the effect of microbial CO{sub 2} production on overall WIPP performance, and (3) the mechanism of using MgO to mitigate this effect.

The authors have demonstrated room-temperature CW operation of type-II quantum cascade (QC) light emitting diodes at 4.2 {micro}m using InAs/InGaSb/InAlSb type-II quantum wells. The type-II QC configuration utilizes sequential multiple photon emissions in a staircase of coupled type-II quantum wells. The device was grown by molecular beam epitaxy on a p-type GaSb substrate and was compared of 20 periods of active regions separated by digitally graded quantum well injection regions. The maximum average output power is about 250 {micro}W at 80 K, and 140 {micro}W at 300 K at a repetition rate of 1 kHz with a duty cycle of 50%.

The electrochemical properties of LiMn2O4 and LiAlxMn2-xO4 (where x = 0.125, 0.25, 0.375) were studied for variations in lithium-ion diffusion. The largest diffusion coefficient was shown for the undoped material, DLi+=2.7×10-11 cm2/s. As the level of dopant was increased a concurrent decrease in diffusion coefficient is shown. This effect was attributed to a decrease in the lattice parameter caused by dopant addition. © 1997 Published by Elsevier Science S.A.

Solid and annular silicon aerogel and agar foams were imploded on the SATURN accelerator to study plasma initiation, acceleration, and stagnation. SATURN delivers 7 MA with a 50 ns rise time to these foam loads. We fielded several spectroscopic diagnostics to measure plasma parameters throughout the z-pinch discharge. A spatially resolved single frame time-gated extreme ultraviolet spectrometer measured the extent of plasma ablation off the surface of the foam. A time integrated crystal spectrometer showed that characteristic K shell radiation of silicon in the aerogel and of sulfur and sodium impurities in the agar were attenuated when the foam loads were coated with a conductive layer of gold. A time-resolved pinhole camera showed that in general the quality of the pinch implosions was poor but improved with increasing efforts to improve current continuity such as prepulse and conductive coatings. © 1997 American Institute of Physics.

A pulsed Na atomic beam source developed for spectroscopic diagnosis of a high-power ion diode is described. The goal is to produce a ∼1012-cm-3-density Na atomic beam that can be injected into the diode acceleration gap to measure electric and magnetic fields from the Stark and Zeeman effects through laser-induced fluorescence or absorption spectroscopy. A ∼10 ns full width at half-maximum (FWHM), 1.06 μm, 0.6 J/cm2 laser incident through a glass slide heats a Na-bearing thin film, creating a plasma that generates a sodium vapor plume. A ∼1 μs FWHM dye laser beam tuned to 5890 Å is used for absorption measurement of the Na I resonant doublet by viewing parallel to the film surface. The dye laser light is coupled through a fiber to a spectrograph with a time-integrated charge-coupled-device camera. A two-dimensional mapping of the Na vapor density is obtained through absorption measurements at different spatial locations. Time-of-flight and Doppler broadening of the absorption with ∼0.1 Å spectral resolution indicate that the Na neutral vapor temperature is about 0.5-2 eV. Laser-induced fluorescence from ∼1×1012 cm-3 Na I 3s-3p lines observed with a streaked spectrograph provides a signal level sufficient for ∼±0.06 Å wavelength shift measurements in a mock-up of an ion diode experiment. © 1997 American Institute of Physics.

We find that significant polarization fatigue (> 90%) can be induced in SrBi2Ta2O9 (SET) thin films using (a) broad-band optical illumination combined with a bias near the switching threshold and (b) electric field cycling under broadband optical illumination. In the latter case, the extent of polarization fatigue increases with decreasing cycling voltage. In either case, the optically fatigued SET capacitors can be fully rejuvenated by applying a saturating dc bias with light or by electric field cycling without light, which suggests a field-assisted recovery mechanism. A similar behavior was observed in Pb(Zr,Ti)O3 (PZT) films with LSCO electrodes. Based on these results, we suggest that polarization fatigue in ferroelectrics is essentially a dynamic competition between domain wall pinning due to electronic charge trapping, and field-assisted unpinning of the domain walls. Thus, domain wall pinning is not necessarily absent in nominally fatigue-free systems. Instead, these systems are ones in which domain wall unpinning occurs at least as rapidly as any pinning. Factors which may affect the pinning and unpinning rates will be discussed.

We describe the application of the techniques of high pressure liquid chromatography (HPLC) to analyze and characterize various types of inorganic nanoclusters. Both metal and semiconductor nanoclusters were grown in inverse micelles and we demonstrate how the nanoclusters can be separated from the surfactants and other byproducts of the reaction by using a variety of HPLC columns. We also discuss passivation of the cluster surface to prevent aggregation. The HPLC columns separate the clusters based upon a combination of size exclusion and chemical affinity mechanisms and the optical properties of the purified clusters are determined on-line using a variety of detectors. These include a photodiode array for collecting absorbance spectra, a fluorescence detector to monitor luminesence, and a conductivity detector to monitor surface charge on the nanoclusters. We illustrate the analysis of nanoclusters using HPLC by showing data from semiconductor Si, MoS2 nanoclusters and Au nanoclusters. An extremely novel luminesence was observed from very small metal nanoclusters. © 1997 Acta Metallurgica Inc.

We have grown AlSb and AlAsxSb1 - x epitaxial layers by metal-organic chemical vapor deposition (MOCVD) using trimethylamine alane or ethyldimethylamine alane, triethylantimony, and arsine. These layers were successfully doped p-or n-type using diethylzinc or tetraethyltin, respectively. We examined the growth of AlAsxSb1 - x using temperatures of 500-600°C, pressures of 65-630 Torr, V/III ratios of 1-17, and growth rates of 0.3-2.7 μm/h in a horizontal quartz reactor. We have also fabricated gain-guided, injection lasers using AlAsxSb1 - x for optical confinement and a strained InAsSb/InAs multi-quantum well active region grown using MOCVD. In pulsed mode, the laser operated up to 210 K with an emission wavelength of 3.8-3.9 μm.

Micro-Electrical Mechanical Systems (MEMS) is an emerging technology with demonstrated potential for a wide range of applications including sensors and actuators for medical, industrial, consumer, military, automotive and instrumentation products. Failure analysis (FA) of MEMS is critically needed for the successful design, fabrication, performance analysis and reliability assurance of this new technology. Many devices have been examined using techniques developed for integrated circuit analysis, including optical inspection, scanning laser microscopy (SLM), scanning electron microscopy (SEM), focused ion beam (FIB) techniques, atomic force microscopy (AFM), infrared (lR) microscopy, light emission (LE) microscopy, acoustic microscopy and acoustic emission analysis. For example, the FIB was used to microsection microengines that developed poor performance characteristics. Subsequent SEM analysis clearly demonstrated the absence of wear on gear, hub, and pin joint bearing surfaces, contrary to expectations. Another example involved the use of infrared microscopy for thermal analysis of operating microengines. Hot spots were located, which did not involve the gear or hub, but indicated contact between comb structures which drive microengines. Voltage contrast imaging proved useful on static and operating MEMS in both the SEM and the FIB and identified electrostatic clamping as a potentially significant contributor to failure mechanisms in microengines. This work describes MEMS devices, FA techniques, failure modes, and examples of FA of MEMS.

We studied whether plasma-etching techniques can use standard screen-printed gridlines as etch masks to form self-aligned, patterned-emitter profiles on multicrystalline-silicon (mc-Si) cells from Solarex. We conducted an investigation of plasma deposition and etching processes on full-size mc-Si cells processed in commercial production lines, so that any improvements obtained would be immediately relevant to the PV industry. This investigation determined that reactive ion etching (RIE) is compatible with using standard, commercial, screen-printed gridlines as etch masks to form self-aligned, selectively doped emitter profiles. This process results in reduced gridline contact resistance when followed by plasma-enhanced chemical vapor deposition (PECVD) treatments, an undamaged emitter surface easily passivated by plasma-nitride, and a less heavily doped emitter between gridlines for reduced emitter recombination. This allows for heavier doping beneath the gridlines for even lower contact resistance, reduced contact recombination, and better bulk defect gettering. Our initial results found a statistically significant improvement of about half an absolute percentage point in cell efficiency when the self-aligned emitter etchback was combined with a PECVD-nitride surface passivation treatment. Some additional improvement in bulk diffusion length was observed when a hydrogen passivation treatment was used in the process. We attempted to gain additional benefits from using an extra-heavy phosphorus emitter diffusion before the gridlines were deposited. However, this required a higher plasma-etch power to etch back the deeper diffusion and keep the etch time reasonably short. The higher power etch may have damaged the surface and the gridlines so that improvement due to surface passivation and reduced gridline contact resistance was inhibited.

This paper is concerned with describing a damage mechanics formulation which provides for non-isotropic effects using a scalar damage variable. An investigation has been in progress for establishing the constitutive behavior of rock salt at long times and low to moderate confining pressures in relation to the possible use of excavated rooms in rock salt formations as repositories for nuclear waste. An important consideration is the effect of damage manifested principally by the formation of shear induced wing cracks which have a stress dependent orientation. The analytical formulation utilizes a scalar damage parameter, but is capable of indicating the non-isotropic dependence of inelastic straining on the stress state and the confining pressure. Also, the equations indicate the possibility of volumetric expansions leading to the onset of tertiary creep and eventually rupture if the damage variable reaches a critical value.

The interactions of CP-Ti and Ti-6Al-4V with investment molds containing alumina/silica and yttria/silica face coat systems were studied. "Containerless" melting in argon was employed and small test samples were made by drop casting into the molds. The effects of the face coat material and mold preheat temperatures on the thickness of the alpha case in the drop castings were evaluated with microhardness and microprobe measurements. It was found that the thickness of the alpha case was the same, whether a yttria/silica or alumina/silica face coat was used, indicating that the silica binder can reduce the apparent inertness of a more stable refractory, such as yttria. It was also found that the alloyed titanium castings had a thinner alpha case than those produced from CP-Ti, which suggests that the thickness of the alpha case depends on the crystal structure of the alloy during cooling from high temperatures. Furthermore, the small drop castings made in small yttria crucibles used as molds exhibited little or no alpha case.

The nuclear microprobe has proven to be a useful tool in radiation testing of integrated circuits. This paper reviews single event upset and ion beam induced charge collection imaging techniques, with special attention to damage-dependent effects. Comparisons of charge collection measurements with three-dimensional charge transport simulations of charge collection are then presented for isolated p-channel field effect transistors under conducting and non-conducting bias conditions.

Mid-infrared lasers grown by MOCVD with AlAsSb claddings and strained InAsSb active regions are reported. A 3.8-3.9 μm injection laser with a pseudomorphic InAsSb multiple quantum well active region lased at 210 K under pulsed operation. A semi-metal layer acts as an internal electron source for the injection laser. An optically pumped laser with an InAsSb/InAsP strained-layer superlattice active region was demonstrated at 3.7 μm, 240 K.

The wide band gap group-III nitride materials continue to generate interest in the semiconductor community with the fabrication of green, blue, and ultraviolet light emitting diodes (LEDs), blue lasers, and high temperature transistors. Realization of more advanced devices requires pattern transfer processes which are well controlled, smooth, highly anisotropic and have etch rates exceeding 0.5 μm/min. The utilization of high-density chlorine-based plasmas including electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) systems has resulted in improved etch quality of the group-III nitrides over more conventional reactive ion etch (RIE) systems.

Many applications of high temperature superconductors, HTS, require the presence of lattice defects in the material structure to suppress the motion of magnetic vortices and enhance the critical current density, Jc. The microstructure of Tl2Ba2CaCu2O8-δ (Tl-2212) thin films which have extended defects induced by high energy Au and Cu ion irradiation is studied using high resolution transmission electron microscopy, HRTEM, with slow scan digital imaging. In order to optimize the HTS properties and better analyze the consequent microstructural modification, the fluence is varied. At moderate fluences, resulting in approximately 4% reduction of the superconducting transition, large enhancements of Jc and vortex pinning potential are observed. The density and microstructure of isolated defects and surrounding structure will be discussed and compared to damage profiles calculated using the TRIM code. Correlation will be made between the HRTEM results and the changes in HTS properties.

Optically targeted, ion microbeams provide a useful means of exposing individual structures within an integrated circuit to ionizing radiation. With this tool, calibrated, low damage, charge collection spectra can be measured from specific circuit structures without preceding ion damage to the structure or surrounding circuitry. This paper presents comparisons of calibrated, low damage, ion microbeam-based charge collection measurements and three-dimensional, charge transport simulations of charge collection for isolated n-and p-channel field effect transistors under conducting and non-conducting bias conditions.

Vector network analyzers provide a convenient way to measure scattering parameters of a variety of microwave devices. However, these instruments, unlike oscilloscopes for example, require a relatively high degree of user knowledge and expertise. Due to the complexity of the instrument and of the calibration process, there are many ways in which an incorrect measurement may be produced. We routinely use check standards to verify that the network analyzer is operating properly. In the past, these measurements were recorded manually and, sometimes, interpretation of the results was problematic. To aid our measurement assurance, a software program was developed to automatically measure a check standard and compare the new measurements with an historical database of measurements of the same device. The program acquires new measurement data from selected check standards, plots the new data against the mean and standard deviation of prior data for the check standard, and updates the database files for the check standard. The program is entirely menu-driven requiring little additional work by the user. This paper describes the function of the software, including a discussion of its capabilities, and the way in which the software is used in our lab. Finally, some examples are given showing how the software can detect potential measurement problems.

VRaptor, a VR system for situational training that uses trainer-defined scenarios is described. The trainee is represented by an avatar; the rest of the virtual world is populated by virtual actors, which are under the control of trainer-defined scripts. The scripts allow reactive behaviors, but the trainer can control the overall scenario. This type of training system may be very useful in supplementing physical training.

The design of complex systems is difficult at best, but as a design becomes intensively dependent on the computer processing of external and internal information, the design process quickly borders chaos. This situation is exacerbated with the requirement that these systems operate with a minimal quantity of information, generally corrupted by noise, regarding the current state of the system. Establishing performance requirements for such systems is particularly difficult. This paper briefly sketches a general systems design approach with emphasis on the design of computer based decision processing systems subject to parameter and environmental variation. The approach will be demonstrated with application to an on-board diagnostic (OBD) system for automotive emissions systems now mandated by the state of California and the Federal Clean Air Act. The emphasis is on developing approach for establishing probabilistically based performance requirements for computer based systems.

The goal is to provide a high level of confidence that critical software driven event sequences are maintained in the face of hardware failures and harsh or unstable operating environments. The technical approach includes in-situ (embedded in the software) dynamic (run-time) fault management for ensuring critical event sequences in high consequence software. Our method is based on deriving a mathematical description of the critical software controlled event sequence, embedding check points and update points around the critical events into the target code, and adding a module that implements the functionality of the underlying mathematical model. This methodology is inspired by previous work in path expressions. This paper discusses the perceived problems, a brief overview of path expressions, the proposed methods, and a discussion of the differences between the proposed methods and traditional path expression usage and implementation.

The Downhole Dynamometer Database is a compilation of test data collected with a set of five downhole tools built by Albert Engineering under contract to Sandia National Laboratories. The downhole dynamometer tools are memory tools deployed in the sucker rod string with sensors to measure pressure, temperature, load, and acceleration. The acceleration data is processed to yield position, so that a load vs. position dynagraph can be generated using data collected downhole. With five tools in the hole at one time, all measured data and computed dynagraphs from five different positions in the rod string are available. The purpose of the Database is to provide industry with a complete and high quality measurement of downhole sucker rod pumping dynamics. To facilitate use of the database, Sandia has developed a Microsoft Windows-based interface that functions as a visualizer and browser to the more than 40 MBytes of data. The interface also includes a data export feature to allow users to extract data from the database for use in their own programs. This paper includes a description of the downhole dynamometer tools, data collection program, database content, and a few illustrations of the data contained in the downhole dynamometer database.

We discuss the integration of the SANDROS path planner into a general robot simulation and control package with the inclusion of a fast geometry engine for distance calculations. This creates a single system that allows the path to be computed, simulated, and then executed on the physical robot. The architecture and usage procedures are presented. Also, we present examples of its usage in typical environments found in our organization. The resulting system is as easy to use as the general simulation system (which is in common use here) and is fast enough (example problems are solved in seconds) to be used interactively on an everyday basis.

A compact optoelectronic integrated circuit (OEIC) for generation of millimeter-wave frequencies was demonstrated. It integrates a passively modelocked semiconductor ring laser, optical amplifier and high-speed photodiode for generation, amplification and detection of an optical pulse train with 30 to 90 GHz pulse-repetition frequency. This OEIC concept can be used in a wide variety of applications that require a very compact, light weight millimeter-wave source.

Microfluidic chips have the potential to be useful in bioanalytical tools for DNA, protein, and cellular studies. To realize this potential, means for introducing fluids, separating their components, and detection must be integrated in onto the chip. Semiconductor laser microcavity spectroscopy is investigated as a means for ultrasensitive detection of various fluids, cells, and particulates. Two methods for implementing this laser device, the spectra for four different types of cells, and how the transverse mode spacings can be used to caliper the cell dimensions are discussed. The current investigations of different methods for pumping fluids through the microactivity space using mechanical or electromotive forces are also discussed.

Sandia National Laboratories has developed a chip scale packaging technology called mini Ball Grid Array (mBGA). The mBGA is a flip chip die, obtained by redistributing peripheral pads in existing dies to an area array of pads 10 mils or larger in diameter with a minimum pitch of 20 mils. The peripheral pads are redistributed to area array pads using two polyimide dielectric and two metal conductor layers. mBGA can be closely tiled together on a substrate to yield a very high circuit density. In an earlier report, we presented the results on the reliability and thermal performance of mBGA on silicon and ceramic substrates. In this report, we present an mBGA cost analysis, improvement in the mBGA bump adhesion, and reliability and thermal performance of mBGA assemblies on FR-4 boards.

VRaptor, a VR system for situational training that uses trainer-defined scenarios is described. The trainee is represented by an avatar; the rest of the virtual world is populated by virtual actors, which are under the control of trainer-defined scripts. The scripts allow reactive behaviors, but the trainer can control the overall scenario. This type of training system may be very useful in supplementing physical training.

Gamma-densitometry tomography (GDT) and electrical-impedance tomography (EIT) have both been applied to a liquid-solid flow for comparison purposes. The experiment consisted of a cylinder (19 cm diameter) filled with water, in which 80 μm glass spheres were suspended by a mixer to achieve solid volume fractions of 0.01, 0.02, and 0.03. Both GDT and EIT revealed a relatively uniform distribution of solids in the measurement plane, and the average solid volume fractions from both techniques were in good agreement.

Hot electron induced degradation in 0.25 μm n-channel MOSFETs annealed in H2 or D2 containing atmospheres is reported. Threshold voltage and channel transconductance variations correlate with the growth of the interface state density evidenced by charge pumping measurements. The transistor lifetime (for a given transconductance variation) is ∼ 10-40 times shorter for H2 as opposed to D2 annealed devices.

It is shown analytically and experimentally that, when significant densities of positive and/or negative charge are trapped in the bulk of the oxide, standard thermally stimulated current (TSC) measurements at negative gate bias may not provide accurate estimates of MOS oxide-trap charge densities. Combining TSC measurements at negative bias with capacitance-voltage (C-V) measurements allows useful, self-consistent estimates of trapped electron densities in the oxide to be obtained. However, unless one can determine whether most of the trapped electrons lie in the bulk of the oxide or in border traps, unambiguous estimates of trapped positive charge densities cannot be obtained with negative or positive bias TSC, with or without C-V measurements. Implications are discussed for charge trapping in radiation-hardened thermal oxides, SIMOX buried oxides, and bipolar base oxides. © 1997 IEEE.

The dependence of single event gate rupture (SEGR) critical field on oxide thickness is examined for gate oxides from 6 to 18 nm. Capacitor data are compared to SEGR data from full integrated circuits. A I/ECR dependence is found for critical field to rupture as a function of ion linear energy transfer (LET), consistent with earlier work for power MOSFETS with oxide thicknesses from 30 to 150 nm. More importantly, critical field to rupture increases with decreasing oxide thickness, consistent with increasing oxide breakdown field prior to heavy-ion exposure. This suggests that SEGR need not be a limiting factor as future technologies scale into the deep submicron region. However, there is a great deal of uncertainty in how voltage may scale with decreasing oxide thickness, and SEGR may continue to be a concern for devices that operate at electric fields significantly higher than 5 MV/cm. © 1997 IEEE.

Radiation-induced gain degradation is compared in two types of lateral PNP bipolar devices that are identical except for the emitter doping. The devices with heavily-doped emitters (1×1020 cm-3) degrade less than the devices with lightly-doped emitters (1×1018 cm-3). Both device types are sensitive to interface-trap formation in the oxide above the emitter-base junction and the neutral base region. In addition, the devices with lightly-doped emitters experience spreading of the depletion region into the emitter, increasing their sensitivity to total-dose irradiation. The gain degradation in both device types is due to a combination of increased base current and decreased collector current. The radiation-induced decrease in collector current is more significant for devices from this technology than for other devices studied previously. Increased gain degradation is observed in heavily-doped devices irradiated at low dose rates, but the enhanced degradation appears to be due to time-dependent effects rather than true dose-rate effects. The lightly-doped devices do not exhibit a clear dose-rate trend and the gain of these devices improves during post-irradiation annealing. © 1997 IEEE.

In large scale 3D EM inverse problems it may not be possible to directly invert a full least-squares system matrix involving model sensitivity elements. Thus iterative methods must be employed. For the inverse problem, we favor either a linear or non-linear (NL) CG scheme, depending on the application. In a NL CG scheme, the gradient of the objective function is required at each relaxation step along with a univariate line search needed to determine the optimum model update. Solution examples based on both approaches will be presented.

The method of finite differences has been employed to solve a variety of 3D electromagnetic (EM) forward problems arising in geophysical applications. Specific sources considered include dipolar and magnetotelluric (MT) field excitation in the frequency domain. In the forward problem, the EM fields are simulated using a vector Helmholtz equation for the electric field, which are approximated using finite differences on a staggered grid. To obtain the fields, a complex-symmetric matrix system of equations is assembled and iteratively solved using the quasi-minimum method (QMR) method. Perfectly matched layer (PML) absorbing boundary conditions are included in the solution and are necessary to accurately simulate fields in propagation regime (frequencies>10 MHz). For frequencies approaching the static limit (<10 KHz), the solution also includes a static-divergence correction, which is necessary to accurately simulate MT source fields and can be used to accelerate convergence for the dipolar source problem.

Light induced electron transfer (ET) from nanosize semiconductors of MoS2 to organic electron acceptors such as 2,2′-bipyridine (bpy) and methyl substituted 4,4′,5,5′-tetramethyl-2,2′-bipyridine (tmb) was studied by static and time resolved photoluminescence spectroscopy. The kinetics of ET were varied by changing the nanocluster size (the band gap), the electron acceptor, and the polarity of the solvent. MoS2 is an especially interesting semiconductor material as it is an indirect semiconductor in bulk form, and has a layered covalent bonding arrangement which is highly resistant to photocorrosion.

A miniature solid-propellant rocket motor has been developed to impart a specific motion to an object deployed in space. This rocket motor effectively eliminated the need for a cold-gas thruster system or mechanical spin-up system. A low-energy igniter, an XMC4397, employing a semiconductor bridge was used to ignite the rocket motor. The rocket motor was ground-tested in a vacuum tank to verify predicted space performance and successfully flown in a Sandia National Laboratories flight vehicle program.

The thermal stability of fluorinated SiO2 films (SiOF) was found to be dependent on F content and the type of substrate upon which the film was deposited. SiOF films with a range of F concentrations were deposited using an electron cyclotron resonance (ECR) plasma upon Si, Al/Si, TiN/Al/Si, and Al/SiO2/Si substrates. Following deposition, the films were deliberately hydrated and/or annealed and their stability assessed. Hydration was found to only affect the high F content films. Capacitance changes with annealing in the high F content films were found to occur beginning at 200 °C. These changes, which were independent of substrate type, likely occurred due to desorption of H2O in the films. After annealing of the high F content films up to 400 °C, a reduction in F content was found for SiOF films on some substrates. Significant reductions were found for SiOF films on Al/Si substrates, while little or no change was found for films on TiN/Al/Si, Al/SiO2/Si, or Si substrates. Local chemical analysis of those films which showed F reduction indicated that the F profile was approximately uniform throughout the layer and did not pile-up at the interface. The substrate-dependent thermal instability exhibited by these films suggests the chemical nature or qualities of the substrate may play a role in the F reduction reaction.

An acousto-optic (AO) deflector composed of PbMoO4 was exposed to 4 MeV protons while operating under Bragg angle conditions. An ion beam in air of 1 mm width was directed normal to the crystal face and laser beam. Between exposures, the approximately 13 mm × 8.5 mm AO deflector was mechanically translated in two dimensions in front of the fixed ion beam. The AO diffraction efficiency was mapped and was observed to change as a function of ion beam location and dose rate. These effects are attributed to the induced change in the temperature distribution of the crystal, which changed the sonic velocity and refractive index. Similar effects were observed when the ion beam was directed at the acoustic transducer.

Charge collection and SEU from angled ion strikes are studied using three-dimensional simulation. The physics of charge collection in unloaded diodes and transistors is explored, as is the angular dependence of upset threshold in CMOS SRAMs. The simulation results are compared to analytical models for charge collection. Modeling fundamental transport in SRAMs, the true effective LET relationship is computed and used to analyze experimental heavy-ion data. Impacts on SEU test methodology are discussed. © 1997, IEEE. All rights reserved.

A room Co-60 source was characterized using thermoluminescent dosimeters (TLDs) and pMOS RADFETs. Measurements were made over a range of dose rates between 0.8 and 100 mrad(Si)/s. Dose enhancement (DE) was measured using RADFETs with and without gold-flashed kovar lids. DE factors ranged from 1.05 to 2.35. A method was developed to predict dose enhancement as a function of position and test configuration. This method involves separation of direct and scattered gamma dose rate contributions. ©1997 IEEE.

Finite-difference, prestack depth migrations offers significant improvements over Kirchhoff methods in imaging near or under salt structures. We have implemented a finite-difference prestack depth migration algorithm for use on massively parallel computers which is discussed. The image quality of the finite-difference scheme has been investigated and suggested improvements are discussed.

A key to reducing the risks and costs of associated with oil and gas exploration is the fast, accurate imaging of complex geologies, such as salt domes in the Gulf of Mexico and overthrust regions in U.S. onshore regions. Pre-stack depth migration generally yields the most accurate images, and one approach to this is to solve the scalar-wave equation using finite differences. Current industry computational capabilities are insufficient for the application of finite-difference, 3-D, prestack, depth-migration algorithms. High performance computers and state-of-the-art algorithms and software are required to meet this need. As part of an ongoing ACT1 project funded by the U.S. Department of Energy, we have developed a finite-difference, 3-D prestack, depth-migration code for massively parallel computer systems. The goal of this work is to demonstrate that massively parallel computers (thousands of processors) can be used efficiently for seismic imaging, and that sufficient computing power exists (or soon will exist) to make finite-difference, prestack, depth migration practical for oil and gas exploration.