Publications

This report describes the research accomplishments achieved under the LDRD Project ``Electron Phase Coherent Effects in Nanostructures and Coupled 2D Systems.`` The goal of this project was to discover and characterize novel quantum transport phenomena in small semiconductor structures at low temperatures. Included is a description of the purpose of the research, the various approaches used, and a detailed qualitative description of the numerous new results obtained. The first appendix gives a detailed listing of publications, presentations, patent applications, awards received, and various other measures of the LDRD project success. Subsequent appendices consist of reprinted versions of several specific,`` scientific journal publications resulting from this LDRD project.

An integral part of the licensing procedure for the potential nuclear waste repository at Yucca Mountain, Nevada, involves prediction of the in situ rheology for the design and construction of the facility and the emplacement of canisters containing radioactive waste. The data used to model the thermal and mechanical behavior of the repository and surrounding lithologies include dry and saturated bulk densities, average grain density, porosity, compressional and shear wave velocities, elastic moduli, and compressional and tensional fracture strengths. In this study, a suite of experiments was performed on cores recovered from the USW NRG-717A borehole drilled in support of the Exploratory Studies Facility (ESF) at Yucca Mountain. USW NRG-7/7A was drilled to a depth of 1,513.4 feet through five thermal/mechanical units of Paintbrush tuff and terminating in the tuffaceous beds of the Calico IEUS. The thermal/mechanical stratigraphy was defined by Orfiz et al. to group rock horizons of similar properties for the purpose of simplifying modeling efforts. The relationship between the geologic stratigraphy and the thermal/mechanical stratigraphy is presented. The tuff samples in this study have a wide range of welding characteristics, and a smaller range of mineralogy and petrology characteristics. Generally, the samples are silicic, ash-fall tuffs that exhibit large variability in their elastic and strength properties.

Relationships between countries generally exist somewhere in the grey area between war and peace. Crisis prevention activities are important in this area, and should have two goals: stabilizing tense situations that could push countries toward war, and supporting or reinforcing efforts to move countries toward peace. A Crisis Prevention Center (CPC) should facilitate efforts to achieve these goals. Its functions can be grouped into three broad, interrelated categories: establishing and facilitating communication among participating countries; supporting negotiations and consensus-building on regional security issues; and supporting implementation of agreed confidence and security building measures. Technology will play a critical role in a CPC. Technology is required for establishing communication systems to ensure the timely flow of information between countries and to provide the means for organizing and analyzing this information. Technically-based cooperative monitoring can provide an objective source of information on mutually agreed issues, thereby supporting the implementation of confidence building measures and treaties. Technology can be a neutral subject of interaction and collaboration between technical communities from different countries, thereby providing an important channel for improving relationships. Potential first steps for a CPC in the Middle Ease could include establishing communication channels and a dedicated communications center in each country, together with an agreement to use the system as a ``Hot Line` in bilateral and multilateral-lateral emergency situations. Bilateral cooperative monitoring centers could be established to assist with implementation of agreements. A centrally located CPC could serve as a regional communications hub, coordinating a number of functions aimed at stabilizing regional tensions and supporting confidence building activities. Specific recommendations for confidence building activities are discussed.

A novel multi-chip module (MCM) design and manufacturing methodology which utilizes active CMOS circuits in what is normally a passive substrate realizes the `smart substrate` for use in highly testable, high reliability MCMS. The active devices are used to test the bare substrate, diagnose assembly errors or integrated circuit (IC) failures that require rework, and improve the testability of the final MCM assembly. A static random access memory (SRAM) MCM has been designed and fabricated in Sandia Microelectronics Development Laboratory in order to demonstrate the technical feasibility of this concept and to examine design and manufacturing issues which will ultimately determine the economic viability of this approach. The smart substrate memory MCM represents a first in MCM packaging. At the time the first modules were fabricated, no other company or MCM vendor had incorporated active devices in the substrate to improve manufacturability and testability, and thereby improve MCM reliability and reduce cost.

Sandia National Laboratories and the Institute for Global Conflict and Cooperation hosted a workshop on the application of cooperative monitoring to the Middle East. The workshop, held in Albuquerque, New Mexico, from July 17 through 21, 1994, was sponsored by the US Department of Energy, the Arms Control and Disarmament Agency, and the US Department of State. The meeting, which focused on use of technical monitoring tools and sharing of collected information to facilitate regional agreements, included participants from five regional countries as well as from American universities, the US government, and US National Laboratories. Some attendees previously participated in meetings of the Arms Control and Regional Security working group of the Middle East Multilateral Peace Talks. The workshop combined presentations, demonstrations and hands-on experimentation with monitoring hardware and software. An exercise was conducted to evaluate and recommend cooperative monitoring options for a model agreement between two hypothetical countries. Historical precedents were reviewed and the role of environmental and natural resource conflicts explored. These activities were supplemented by roundtable discussions covering Middle East security issues, the relationship of ``national means`` to cooperative monitoring, and cooperative monitoring of ballistic missiles in the Middle East.

This report presents the results of an experimental study of the aerosol produced by the combustion of high-velocity molten-uranium droplets produced by the simultaneous heating and electromagnetic launch of uranium wires. These tests are intended to simulate the reduction of high-velocity fragments into aerosol in high-explosive detonations or reactor accidents involving nuclear materials. As reported earlier, the resulting aerosol consists mainly of web-like chain agglomerates. A condensation nucleus counter was used to investigate the decay of the total particle concentration due to coagulation and losses. Number size distributions based on mobility equivalent diameter obtained soon after launch with a Differential Mobility Particle Sizer showed lognormal distributions with an initial count median diameter (CMD) of 0.3 {mu}m and a geometric standard deviation, {sigma}{sub g} of about 2; the CMD was found to increase and {sigma}{sub g} decrease with time due to coagulation. Mass size distributions based on aerodynamic diameter were obtained for the first time with a Microorifice Uniform Deposit Impactor, which showed lognormal distributions with mass median aerodynamic diameters of about 0.5 {mu}m and an aerodynamic geometric standard deviation of about 2. Approximate methods for converting between number and mass distributions and between mobility and aerodynamic equivalent diameters are presented.

This contribution proposes the format of the {open_quotes}Algorithm-Specific Information{close_quotes} and {open_quotes}Signature{close_quotes} fields within the {open_quotes}Proposed Generic Authentication Information Element{close_quotes} for authentication IEs based on the Digital Signature Standard (DSS). These fields are designed to allow various levels of authentication {open_quotes}strength{close_quotes} (or robustness), and many of these fields may be omitted in systems that optimize authentication performance by sharing common (public) Digital Signature Algorithm (DSA) parameters. This allows users and site security officers to design their authenicated signaling according to site security and performance requirements.

A natural and basic problem in scheduling theory is to provide good average quality of service to a stream of jobs that arrive over time. In this paper we consider the problem of scheduling n jobs that are released over time in order to minimize the average completion time of the set of jobs. In contrast to the problem of minimizing average completion time when all jobs are available at time 0, all the problems that we consider are NP-hard, and essentially nothing was known about constructing good approximations in polynomial time. We give the first constant-factor approximation algorithms for several variants of the single and parallel machine model. Many of the algorithms are based on interesting algorithmic and structural relationships between preemptive and nonpreemptive schedules and linear programming relaxations of both. Many of the algorithms generalize to the minimization of average weighted completion time as well.

The cryogenic thermometers used in superconducting accelerators must function in very adverse environments. Typical conditions are a temperature range of 1.5--300 K, high irradiation doses and magnetic fields which must be endured for the 20 to 50 year life of the accelerator. The authors determined the principal requirements for cryogenic thermometers in accelerator installations and for industrial applications. Some constructions of the thermometer mounting fixtures used in the ``Nuclotron`` (Dubna, Russia) and the SSCL (Dallas, USA) accelerator installations are described. The experimental results for long-term stability of the cryogenic thermometers applied are presented. The basic recommendations on the application technology of the cryogenic thermometers in large superconducting accelerator systems are given.

Numerous Federal facilities within the US involve multiple government agencies that face overlapping environmental concerns. This paper highlights the benefits of looking beyond the strict letter of environmental regulations that might affect a single tenant or environmental site to cooperative environmental efforts that focus on the entire facility, consistent with the missions of participating agencies. Using Kirtland Air Force Base (AFB) as a model, seven areas of Department of Defense (DoD) and Department of Energy (DOE) environmental cooperation are discussed that span technical, regulatory compliance, and administrative issues.

Detailed simulations have been performed for the TEVES (Thermal Enhanced Vapor Extraction System) Project using the TOUGH2 code considering air, water, and a single-component NAPL. A critical parameter varied in the simulations is the borehole vacuum which directly affects air flow through the system and indirectly influences soil temperatures and water and NAPL fluid masses. Contaminant migration from the heated zone into the unheated soil can occur if the borehole vacuum, or borehole flow rate, is not sufficient. Under these conditions, evaporation of liquids (water and NAPL) due to the heating can cause flow from the heated zone into the unheated soil. Insufficient air sweep may be indicated by a vapor dominated mass flow rate into the borehole, at least for the present configuration. Sufficient air flow through the heated zone must be provided to contain the contaminants within the heated zone.

The DOE requires that sensitive unclassified data be protected while being transmitted electronically. On most large networks it is difficult and expensive to provide the required level of physical protection. At Sandia National Laboratories, we are assembling the structure necessary to protect sensitive unclassified data using software-based encryption. This approach has the advantage that the data can be protected after arrival at its destination without additional investment While Sandia has expertise in cryptography, we had not used cryptography in this field. This discussion deals with the client-server model of file-based data exchange and interactive access to on-line data bases using Unix workstations, Macs and PCs.

The goal of the Offsite Demonstration Project for Mixed Waste Landfill Integrated Demonstration (MWLID)-developed environmental site characterization and remediation technologies is to facilitate the transfer, use, and commercialization of these technologies to the public and private sector. The meet this goal, the project identified environmental restoration needs of mixed waste and/or hazardous waste landfill owners (Native American, municipal, DOE, and DoD); documenting potential demonstration sites and the contaminants present at each site; assessing the environmental regulations that would effect demonstration activities; and evaluating site suitability for demonstrating MWLID technologies at the tribal and municipal sites identified. Eighteen landfill sites within a 40.2-km radius of Sandia National Laboratories are listed on the CERCLIS Site/Event Listing for the state of New Mexico. Seventeen are not located within DOE or DoD facilities and are potential offsite MWLID technology demonstration sites. Two of the seventeen CERCLIS sites, one on Native American land and one on municipal land, were evaluated and identified as potential candidates for off-site demonstrations of MWLID-developed technologies. Contaminants potentially present on site include chromium waste, household/commercial hazardous waste, volatile organic compounds, and petroleum products. MWLID characterization technologies applicable to these sites include Magnetometer Towed Array, Cross-borehole Electromagnetic Imaging, SitePlanner {trademark}/PLUME, Hybrid Directional Drilling, Seamist{trademark}/Vadose Zone Monitoring, Stripping Analyses, and x-ray Fluorescence Spectroscopy for Heavy Metals.

The industrial sector is the most complex and diverse segment of the US economy. There are more than 360,000 industrial facilities in the US, using tens of thousands of processes with millions of different pieces of equipment and employing nearly 30 million people to make hundreds of thousands of products. These facilities consume large quantities of raw materials and energy resources every year. Their waste streams, as well as the technology options for preventing them, are very specific not only to individual industries, but even to plants within the same industry that produce similar products. On October 24, 1992, President Bush signed the Energy Policy Act of 1992 (EPAct) into law as Public Law 102-486. Section 2108 of the Act requires the DOE to identify opportunities to demonstrate energy efficient pollution prevention technologies and processes. As a first step in DOE`s response to congress, Sandia National Laboratories lead a fast tracked project to compile information from the open literature, and pilot a process for identifying and prioritizing opportunity areas from industrial and federal experts. Approximately 300 documents were collected and reviewed, and knowledgeable individuals in government, universities, and trade associations were interviewed. A panel of experts from petroleum industry was assembled for the future opportunity assessments pilot These activities were conducted between May and August, 1993. Project background and results are summarized.

Human intrusion scenarios at the Waste Isolation Pilot Plant (WIPP) involve penetration of the repository and an underlying brine reservoir by a future borehole. Brine and gas from the brine reservoir and the repository may flow up the borehole and into the overlying Culebra formation, which is saturated with water containing different amounts of dissolved `solids resulting in a spatially varying density. Current modeling approaches involve perturbing a steady-state Culebra flow field by inflow of gas and/or brine from a breach borehole that has passed through the repository. Previous studies simulating steady-state flow in the Culebra have been done. One specific study by LaVenue et al. (1990) used the SWIFT 2 code, a single-phase flow and transport code, to develop the steady-state flow field. Because gas may also be present in the fluids from the intrusion borehole, a two-phase code such as TOUGH2 can be used to determine the effect that emitted fluids may have on the steady-state Culebra flow field. Thus a comparison between TOUGH2 and SWIFT2 was prompted. In order to compare the two codes and to evaluate the influence of gas on flow in the Culebra, modifications were made to TOUGH2. Modifications were performed by the authors to allow for element-specific values of permeability, porosity, and elevation. The analysis also used a new equation of state module for a water-brine-air mixture, EOS7 (Pruess, 1991), which was developed to simulate variable water densities by assuming a miscible mixture of water and brine phases and allows for element-specific brine concentration in the INCON file.

The Waste Isolation Pilot Plant (WIPP) is a US Department of Energy (DOE) research and development facility for the underground disposal of transuranic waste in southeastern New Mexico. The WIPP repository is located 655 m below the land surface in the lower portion of the Salado Formation, which is comprised of beds of pure and impure halite with thin interbeds of anhydrite and related clay seams. The regional dip of the Salado Formation is approximately 1{degree} southeast in the vicinity of the repository. The proposed waste storage area has eight waste disposal panels, each of which will contain seven rooms. The repository is designed to follow a single stratigraphic horizon. Due to the dip, the north end of the repository will be about 10 meters higher than the south end. Waste that is emplaced in the disposal rooms will generate gas due to microbial degradation, anoxic corrosion, and radiolysis. Brine inflow to the rooms from the surrounding Salado Formation may significantly influence the gas generation rate and the total amount of gas generated. The salt surrounding the repository will creep in response to the excavation, reducing the room volume. Gas generation in the room may increase the pressure sufficiently to drive brine and gas into the surrounding Salado Formation. Migration of gas and brine in the Salado is an important factor in evaluating the performance of the repository. The studies summarized in this paper have. been performed to evaluate brine and gas flow processes in the WIPP disposal system and to identify some of the important processes. These studies are done in support of, but are not part of, the formal Performance Assessment (PA) effort. Because of probabilistic and system-scale requirements, the PA effort uses the Sandia-developed BRAGFLO (BRine And Gas FLOw) code for multiphase flow calculations.

The Waste Isolation Pilot Plant (WIPP) is a US Department of Energy facility designed to demonstrate the safe underground disposal of transuranic waste. Following waste emplacement, each room will be backfilled with crushed salt. Due to deviatoric stress introduced by excavation, the walls of the waste disposal rooms in the repository will deform over time, consolidating waste containers and salt backfill, thereby decreasing the void volume of the repository. Long-term repository assessment must consider the processes of gas generation, room closure and expansion due to salt creep, and multiphase (brine and gas) fluid flow, as well as the complex coupling between these three processes. Stone (1992) used the mechanical creep closure code SANCHO to simulate the closure of a single, perfectly sealed disposal room filled with waste and backfill. The results of the SANCHO f-series simulations provide a relationship between gas generation, room closure, and room pressure. Several methods for coupling this relationship with multiphase fluid flow into and out of a room were examined by Freeze et al. TOUGH2 was employed to couple the processes of gas generation, room closure/consolidation, and multiphase brine and gas flow. Two empirically-based methods for approximating salt creep and room consolidation were implemented in TOUGH2: the pressure-time-porosity line interpolation approach and the fluid-phase-salt approach. Both approaches utilized links to the SANCHO f-series simulation results to calculate room-void-volume changes with time during a simulation.

The Waste Isolation Pilot Plant (WIPP) is a US Department of Energy research and development facility for the underground disposal of transuranic waste from US defense-related activities. The WIPP repository is located within the Salado Formation, which is comprised of beds of pure and impure halite with thin interbeds of anhydrite and related clay seams. This formation is brine saturated with a pore pressure of approximately 12.5 MPa at the repository horizon. The Salado Formation dips gently southeast, on the average approximately 1{degree}, with steeper dips locally. Elevated repository pressures, caused by gas generated as emplaced waste corrodes and degrades, may drive brine and gas out of the repository into the surrounding formation. Stratigraphic dip may cause increased brine inflow to the repository through countercurrent flow in the interbeds and enhanced gas migration distances in the updip direction due to buoyancy. Two-dimensional simulations of isolated WIPP repository room have been performed using TOUGH2 for horizontal and 1{degree} dipping stratigraphy. The impact of dip on multiphase flow at the WIPP may be significant. With dip, an additional mechanism for brine inflow may occur, namely the formation of a cell of countercurrent brine and gas flow in the interbeds. The additional volume of brine inflow resulting from the countercurrent flow cell may be of similar magnitude to brine inflow without dip. Therefore, dip must be included in any repository model to include the countercurrent brine inflow mechanism. Gas migration may also be significantly influenced due to dip. Gas migration distances may increase dramatically with preferential migration updip.

MELCOR models the progression of severe accidents in light water reactor nuclear power plants. Recent efforts in MELCOR development to incorporate CORCON-Mod3 models for core-concrete interactions, new models for advanced reactors, and improvements to several other existing models have resulted in release of MELCOR 1.8.3. In addition, continuing efforts to expand the code assessment database have filled in many of the gaps in phenomenological coverage. Efforts are now under way to develop models for chemical interactions of fission products with structural surfaces and for reactions of iodine in the presence of water, and work is also in progress to improve models for the scrubbing of fission products by water pools, the chemical reactions of boron carbide with steam, and the coupling of flow blockages with the hydrodynamics. Several code assessment analyses are in progress, and more are planned.

Sandia National Laboratories performs R and D in structural dynamics and vibration suppression for precision applications in weapon systems, space, underwater, transportation and civil structures. Over the last decade these efforts have expanded into the areas of active vibration control and ``smart`` structures and material systems. In addition, Sandia has focused major resources towards technology to support weapon product development and agile manufacturing capability for defense and industrial applications. This paper will briefly describe the structural dynamics modeling and verification process currently in place at Sandia that supports vibration control and some specific applications of these techniques to manufacturing in the areas of lithography, machine tools and flexible robotics.

To improve process reliability and deposition methods, it is essential to identify the rate-limiting step in TEOS-based SiO{sub 2} CVD and its dependence on process conditions. For this purpose, experiments designed to evaluate by-product inhibition effects and to identify the rate-limiting step in TEOS decomposition have been carried out in a research reactor using GCMS and FTIR. By repetitively sampling a series of reactions in which TEOS was first mixed with ethylene, ethanol, and water in the gas-phase, GCMS was used to show clearly that these reaction by-products do not inhibit the heterogeneous reaction step on SiO{sub 2} at 1,000K. FTIR was used to determine that ethoxy groups from TEOS dissociative chemisorption have a significant lifetime on the SiO{sub 2} surface at CVD temperatures and have an activation energy for decomposition of 16kcal/mol{+-}4kcal/mol. This is much higher than the activation energy of 6 kcal/mol reported for the initial chemisorption step and is near the 22 kcal/mol reported for the overall activation energy for SiO{sub 2} deposition in a cold-wall reactor. These results suggest that, whether or not surface ethoxy groups inhibit TEOS reactions, their decomposition may be directly related to the rate-limiting step in SiO{sub 2} deposition.

If current plans are realized, within the next few years, an extraordinary set of coordinated research efforts focusing on energy flows in the Arctic will be implemented. All are motivated by the prospect of global climate change. SHEBA (Surface Energy Budget of the Arctic Ocean), led by the National Science Foundation (NSF) and the Office of Naval Research (ONR), involves instrumenting an ice camp in the perennial Arctic ice pack, and taking data for 12--18 months. The ARM (Atmospheric Radiation Measurement) North Slope of Alaska and Adjacent Arctic Ocean (NSA/AAO) Cloud and Radiation Testbed (CART) focuses on atmospheric radiative transport, especially in the presence of clouds. The NSA/AAO CART involves instrumenting a sizeable area on the North Slope of Alaska and adjacent waters in the vicinity of Barrow, and acquiring data over a period of about 10 years. FIRE (First ISCCP [International Satellite Cloud Climatology Program] Regional Experiment) Phase 3 is a program led by the National Aeronautics and Space Administration (NASA) which focuses on Arctic clouds, and which is coordinated with SHEBA and ARM. FIRE has historically emphasized data from airborne and satellite platforms. All three program anticipate initiating Arctic data acquisition during spring, 1997. In light of his historic opportunity, the authors discuss a strawman atmospheric radiative transfer experimental plan that identifies which features of the radiative transport models they think should be tested, what experimental data are required for each type of test, the platforms and instrumentation necessary to acquire those data, and in general terms, how the experiments could be conducted. Aspects of the plan are applicable to all three programs.

This paper describes an application of Sandia`s non-contact capacitive sensing technology for collision avoidance during the manufacturing of rocket engine thrust chambers. The collision avoidance system consists of an octagon shaped collar with a capacitive proximity sensor mounted on each face. The sensors produced electric fields which extend several inches from the face of the collar and detect potential collisions between the robot and the workpiece. A signal conditioning system processes the sensor output and provides varying voltage signals to the robot controller for stopping the robot.

The introduction of alternative, non-lead bearing solders into electronic assemblies requires a thorough investigation of product manufacturability and reliability. Both of these attributes can be impacted by the excessive growth of intermetallic compound (IMC) layers at the solder/substrate interface. An extensive study has documented the stoichiometry and solid state growth kinetics of IMC layers formed between copper and the lead-free solders: 96.5Sn-3.5Ag (wt.%), 95Sn-5Sb, 100Sn, and 58Bi-42Sn. Aging temperatures were 70--205 C for the Sn-based solders and 55--120 C for the Bi-rich solder. Time periods were 1--400 days for all of the alloys. The Sn/Cu, Sn-Ag/Cu, and Sn-Sb/Cu IMC layers exhibited sub-layers of Cu{sub 6}Sn{sub 5} and Cu{sub 3}Sn; the latter composition was present only following prolonged aging times or higher temperatures. The total layer growth exhibited a time exponent of n = 0.5 at low temperatures and a value of n = 0.42 at higher temperatures in each of the solder/Cu systems. Similar growth kinetics were observed with the low temperature 58Bi-42Sn solder; however, a considerably more complex sub-layer structure was observed. The kinetic data will be discussed with respect to predicting IMC layer growth based upon solder composition.

Switchable polarization can be significantly suppressed in ferroelectric (FE) materials by optical, thermal, and electrical processes. The thermal process can occur by either annealing the FE in a reducing environment or by heating it in air to 100 C while impressing a bias near the switching threshold. The optical process occurs while biasing the FE near the switching threshold and illuminating with bandgap light. And the electrical suppression effect occurs by subjecting the FE to repeated polarization reversals. Using electron paramagnetic resonance, polarization-voltage measurements, and charge injection scenarios, the authors have been able to elucidate both electronic and ionic trapping effects that lead to a suppression in the amount of switchable polarization in FE materials. The relative roles of electronic and ionic effects in the same material can depend on the stress condition. For instance, in oxidized BaTiO3 crystals, optical and thermal suppressions occur by electronic domain pinning; electrical fatigue in the BaTiO{sub 3} crystals also appears to involve electronic charge trapping, however, it is suggested that these electronic traps are further stabilized by nearby ionic defects. In sol-gel PZT thin films with either Pt, RuO{sub 2}, or La-Sr-Co-O electrodes it appears that the polarization suppression induced by electrical fatigue, a temperature/bias combination, or a light/bias combination are all primarily due to the trapping of electronic charge carriers to first order.