Publications

The EPA Environmental Technology Verification (ETV) Site Characterization Pilot is a joint effort between EPA and DOE with the objective of accelerating the acceptance of technologies that reduce the cost and increase the speed of environmental clean-up and monitoring. To date, several technology verifications have already been completed. Typical results from completed field demonstrations are presented to illustrate the verification process and the importance of the program in providing objective information to aid potential users in making informed choices regarding the efficacy of these technologies for their specific characterization and monitoring problems.

Vertical-cavity surface-emitting lasers (VCSELs) are uniquely suited to miniaturized free-space optical systems in which surface-mounting and hybrid assembly techniques can be used to combine different technologies together. Two examples are described of such microsystems that are being developed for sensing applications. The first example is a optical position sensing system for rotating parts. Progress on fabricating similar systems by flip-chip bonding techniques is then discussed. The second example is a chemical sensing/analysis system which uses a miniature fluorescence detection module that is based on surface-mounted VCSELs and diffractive optical elements. The detection module is integrated with a capillary electrochromatography separation system and uses substrate-mode light propagation to focus the VCSEL beam on the capillary channel.

Issues related to the MOCVD growth of AlGaN, specifically the gas-phase parasitic reactions among TMG, TMA, and NH3, are studied using an in-situ optical reflectometer. It is observed that the presence of the well-known gas phase adduct (TMA: NH3) could seriously hinder the incorporation behavior of TMGa. Relatively low reactor pressures (30-50 Torr) are employed to grow an AlGaN/GaN SCH QW p-n diode structure. The UV emission at 360 nm (FWHM ∼ 10 nm) represents the first report of LED operation from an indium-free GaN QW diode.

The Gleeble is an oft-used tool for welding metallurgy research. Besides producing synthetic weld specimens, it is used to determine phase transformation temperatures and kinetics via dilatometry. Experimental data and an FEM model are used to examine measured dilatation errors because of non-uniform heating of the dilatometer and other sources such as sample elastic and plastic deformation. Both isothermal and constant heating/cooling rate scenarios are considered. Further errors which may be introduced when the dilatation is incorrectly assumed to be linearly related to the volume fraction transformed are also discussed.

We report observations of contrasting surface modification behavior of the Au(111) surface in the presence of an electric field and field-emission currents using interfacial force microscopy (IFM) and scanning tunneling microscopy (STM). Our experiments consist of surface modification procedures which allow for large tip-sample gaps, in contrast to fast voltage pulses (applied at tunneling distances) employed by previous STM investigations. Dramatic surface distortions are observed when a 200 nm-radius tip, biased at -100 V, is brought toward the Au surface at a field emission current level of 400 nA and then retracted. In other experiments, we raise the sample voltage to field-emission levels while maintaining a constant current. STM images, measured in a time-resolved manner after each such procedure, show that the presence of a higher electric field (approximately 0.07 V/angstrom) results in step retraction and the disappearance of small islands on the Au(111) surface followed by the formation of vacancy islands in the area directly beneath the apex of the tip where the field is highest. We discuss the implications of these contrasting surface modifications in terms of the various key parameters and in relation to previous studies using voltage pulses in the STM.

The Telemetry Technology Development Department at Sandia National Laboratories actively develops and tests acceleration recorders for penetrating weapons. This new acceleration recorder (MinPen) utilizes a microprocessor-based architecture for operational flexibility while maintaining electronics and packaging techniques developed over years of penetrator testing. MinPen has been demonstrated to function in shock environments up to 20,000 Gs. The MinPen instrumentation development has resulted in a rugged, versatile, miniature acceleration recorder and is a valuable tool for penetrator testing in a wide range of applications.

The monolithic integration of coupled resonators within a vertical cavity laser opens up new possibilities due to the unique ability to tailor the interaction between the cavities. We report the first electrically injected coupled resonator vertical-cavity laser diode and demonstrate novel characteristics arising from the cavity coupling, including methods for external modulation of the laser. A coupled mode theory is used model the output modulation of the coupled resonator vertical cavity laser.

On-heating transformation kinetics were investigated for several steels by using a Gleeble capable of programmable power input as well as programmable temperature cycling. Transformation kinetics determined in both modes are reported. The temperature cycles are significantly different between the two modes due to the latent heat associated with the phase transformations. Both diffusion rates and transformation driving force increase with temperature above the eutectoid temperature, therefore the latent heat can potentially have a significant impact on the transformation kinetics. Experiments with plain carbon steels illustrate that the latent heat of austenite formation causes an appreciable temperature arrest during transformation, and the dilatation response is similarly altered. A kinetic transformation model, based on the decomposition of pearlite and the diffusional growth of austenite, reproduced the transient dilatation data obtained from both control modes reasonably well using the same kinetic parameter values.

Semiconductor processing tools that use a plasma to etch polysilicon or oxides produce residue polymers that build up on the exposed surfaces of the processing chamber. These residues are generally stressed and with time can cause flaking onto wafers resulting in yield loss. Currently, residue buildup is not monitored, and chambers are cleaned at regular intervals resulting in excess downtime for the tool. In addition, knowledge of the residue buildup rate and index of refraction is useful in determining the state of health of the chamber process. We have developed a novel optical fiber-based robust sensor that allows measurements of the residue polymer buildup while not affecting the plasma process.

The establishment of a process to allow planarization of deep x-ray lithography based microfabricated metal components via diamond lapping has enabled examination of three additional microfabrication issues. The areas of improvement that are discussed include materials, microassembly and packaging, and multilevel fabrication. New materials work has centered on magnetic materials including precision micromagnets and surface treatments of electrodeposited materials. Assembly and packaging has been aided by deep silicon etch processing and the use of conventional precision milling equipment combined with press-fit assembly. Diffusion bonding is shown to be a particularly important approach to achieving multilevel metal mechanisms and furthermore shows promise for achieving batch assembled and packaged high aspect-ratio metal micromechanics.

A series of static overpressurization tests of scale models of nuclear containment structures is being conducted by Sandia National Laboratories for the Nuclear Power Engineering Corporation of Japan and the US Nuclear Regulatory Commission. Two tests are being conducted: a test of a model of a steel containment vessel (SCV) and a test of a model of a prestressed concrete containment vessel (PCCV). This paper summarizes the conduct of the high pressure pneumatic test of the SCV model and the results of that test. Results of this test are summarized and are compared with pretest predictions performed by the sponsoring organizations and others who participated in a blind pretest prediction effort. Questions raised by this comparison are identified and plans for posttest analysis are discussed.

The entire current transient induced by single 12-MeV Carbon ions was measured at a 5GHz analog bandwidth. A focused ion micro-beam was used to acquire multiple single ion transients at multiple locations of a single CMOS transistor. The current transients reveal clear and discernible contributions of drift and diffusive charge collection. Transients measured for drain and off-drain ion strikes compare well to 3D DA VINCI calculations. The simulations match the drift charge collection measurements within experimental errors. Estimates are presented for the drift assisted funneling charge collection depth. © 1998 IEEE.

Mechanisms that control the response of MOS and bipolar devices to ionizing radiation in the natural space environment are briefly reviewed. Standard tests based on room-temperature irradiation and elevated temperature annealing are described for MOS devices to bound the effects of oxide and interface-trap charge in space. For bipolar devices that exhibit enhanced low-dose-rate sensitivity, a standard test equivalent to that developed for MOS devices is not available. However, screening techniques based on room temperature and/or elevated temperature irradiations are described which can minimize the risk to spacecraft and satellite electronics from this phenomenon.

The goals of this Laboratory Directed Research and Development (LDRD) effort were to develop and prototype a new molecular simulation method and companion parallel algorithm able to model diffusion of multi-atom molecules through macromolecules under conditions of a chemical potential gradient. At the start of the project no such method existed, thus many important industrial and technological materials problems where gradient driven diffusion of multi-atom molecules is the predominant phenomenon were beyond the reach of molecular simulation (e.g. diffusion in polymers, a fundamental problem underlying polymer degradation in aging weapons).

This report describes how to obtain publication-quality graphics from distorted grid electronic structure codes using the combination of the conversion utility, dgtoexo2, and mustafa, an AVS Express application. dgtoexo2 converts scalar function results from a format applicable to distorted grid codes into the Exodus II unstructured finite element data representation. nmstafa can read Exodus II files and use the AVS Express engine to visualize data on unix and Windows NT platforms. Though not designed for the purpose, the dgtoexo2/EXOdUS II/mustafa combination is sufficiently versatile to provide for the specialized graphics needs of electronic structure codes. The combination also scales well, producing robust performance for problems involving millions of grid points.

This paper presents experimental data and an computational model of the cold spray solid particle impact process. Copper particles impacting onto a polished stainless steel substrate are examined. The high velocity impact causes significant plastic deformation of both the particle and the sub- strate, but no melting is observed. The plastic deformation exposes clean surfaces that, under the high impact pressures, result in significant bond strengths between the particle and substrate. Experimental measurements of the splat and crater sizes compare well with the numerical calculations. It is shown that the crater depth is significant and increases with impact velocity. However, the splat diameter is much less sensitive to the impact velocity. It is also shown that the geometric lengths of the splat and crater scale linearly with the diameter of the impacting particle. It is hoped that the results presented will allow better understanding of the bonding process during cold spray.

A parametric study of the etch characteristics of GaN, AIN and InN has been earned out with IC1/Ar and IBr/Ar chemistries in an Inductively Coupled Plasma discharge. The etch rates of InN and AIN were relatively independent of plasma composition, while GaN showed increased etch rates with interhalogen concentration. Etch rates for all materials increased with increasing rf chuck power, indicating that higher ion bombardment energies are more efficient in enhancing sputter resorption of etch products. The etch rates increased for source powers up to 500 W and remained relatively thereafter for all materials, while GaN and InN showed maximum etch rates with increasing pressure. The etched GaN showed extremely smooth surfaces, which were somewhat better with IBr/Ar than with IC1/Ar. Maximum selectivities of- 14 for InN over GaN and >25 for InN over AIN were obtained with both chemistries.

A new method for measuring the spin of the electrically charged ground state excitations m the Q$j~j quantum Hall effect ia proposed and demonstmted for the tirst time in GaAs/AIGaAs nndtiquantum wells. The method is &sed on the nuclear spin orientation dependence of" the 2D dc conductivity y in the quantum Hall regime due to the nuclear hyperfine interaction. As a demonstration of this method the spin of the electrically charged excitations of the ground state is determined at filling factor v = 1.

For well resolved electrokinetic separation, we L tilize crystalline quartz to micromachine a uniformly packe Q&iKLmnel. Packing features are posts 5 Vm on a side with:} pm spacing and etched 42 Vm deep. In addition to anisotropic wet etch characteristics for micromachining, quartz propmties are compatible with chemical soiutioits, ekctrokinetic high voltage operation, and stationary phase film depositions. To seal these channels, we employ a room temperature silicon-oxynhride deposition to forma membrane, that is subsequently coated for mechanical stability. Using this technique, particulate issues and global warp, that make large area wafer bon ding methods difficult, are avoided, and a room temperature process, in contrast to high temperature bonding techniques, accommodate preprocessing of metal films for electrical interconnect. After sealing channels, a number of macro-assembly steps are required to attach a micro-optical detection system and fluid interconnects. Keywords: microcharmel, integrated channel, micromachined channel, packed channel, electrokinetic channel, eleetrophoretic channel

We are currently evaluating large capacity (20 - 40 Ah) Bluestar (cylindrical) and Yardney (prismatic) Li-ion cells for their electrical and electrochemical performance characteristics at different temperatures. The cell resistance was nearly constant from room temperature to -20{degrees}C but increased by over 10 times at -40{degrees}C. The specific energy and power as well as the energy density and power density are high and didn't reach a plateau even at the highest discharge rates tested. For example, the prismatic Li-ion cells gave close to 280 Wh l{sup -1} at 4-amp discharge and 249 Wh l{sup -1} at 20-amp discharge at room temperature. For the same current range the specific power values are 102 Wh kg{sup -1} and 91 Wh kg{sup -1}. Cycle life and other electrical and electrochemical properties of the cells will be presented.

The nature of this work was to develop the physics and chemistry base for understanding molecular-scale lubricants used to reduce of friction- and adhesion-induced failure in silicon micromachines (MEMS). We acquired this new knowledge by tailoring the molecular properties of the lubricants, applying local probes that can directly monitor the response of lubricants in contact conditions, and evaluating the performance of model lubricants MEMS devices. Model lubricants under investigation were the silane coupling agents that form monolayer films on native oxide silicon surfaces, which is the substrate in MEMS. These molecules bind via strong surface bonds and produce a layer of hydro- or fluoro-carbon chains normal to the substrate. "Tailoring" the lubricants entails modifying the chain length, the chain chemical reactivity (H or F), and the density of chain structures. Thus much effort went into understanding the surface chemistry of silane-silicon oxide coupling. With proximal probes such as atomic force microscopy (AFM), interracial force microscopy (FM), and shear force microscopy in combination with IFM, we examined the frictional and adhesive properties of the silane films with very high spatial resolution (< 100 nm) and sensitivity. MEMS structures are treated with silanes under identical conditions, and examined for friction and adhesion under operating conditions. Proper assessment of the lubricants required quantitative analysis of MEMS performance at high speeds and long operating times. Our proximal probe measurements and WS performance analyses form a very important link for future molecular dynamics simulations, that, in turn, should be able to predict MEMS performance under all conditions.

A new epoxy foam encapsulant, EF-ARIO/20, has been developed at Sandia National Laboratories (SNL) as a replacement for Ablefoam", an epoxy foam encapsulant used in the W76 Arming, Fusing, and Firing (Al%@) system. Since it contained toxic ingredients including a known carcinogen, Ablefoarn" is no longer commercially available. It has been demonstrated by scanning electron microscopy (SEM) that the microstructure of the new epoxy foam is similar to that of Ablefoam@. Mechanical properties of tensile and compressive strength, and tensile and compressive modulus, and thermal properties of glass transition temperature (.TJ, and coefficient of thermal expansion (CTE) have been measured for the new foam. Electrical properties of dielectric constant, dissipation factors, volume resistivity, and dielectric strength were also measured. These property measurements are comparable to those of Ablefoam@. Development and characterization of the new foam will be discusse~ and a comparison of mechanical, thermal, and electrical properties for the new epoxy foam and Ablefoam@ will be reported.

This report examines methods of mobile communications with an emphasis on mobile computing and wireless communications. Many of the advances in communications involve the use of Internet Protocol (IP), Asynchronous Transfer Mode (ATM), and ad hoc network protocols. However, many of the advances in these protocols have been focused on wired communications. Recently much focus has been directed at advancing communication technology in the area of mobile wireless networks. This report discusses various protocols used in mobile communications and proposes a number of extensions to existing protocols. A detailed discussion is also included on desirable protocol characteristics and evaluation criteria. In addition, the report includes a discussion on several network simulation tools that maybe used to evaluate network protocols.

The proposed "catalytic membrane sensor" (CMS) was developed to generate a device which would selectively identify a specific reagent in a complex mixture of gases. This was to be accomplished by modifying an existing Hz sensor with a series of thin films. Through selectively sieving the desired component from a complex mixture and identifying it by decomposing it into Hz (and other by-products), a Hz sensor could then be used to detect the presence of the select component. The proposed "sandwich-type" modifications involved the deposition of a catalyst layered between two size selective sol-gel layers on a Pd/Ni resistive Hz sensor. The role of the catalyst was to convert organic materials to Hz and organic by-products. The role of the membraneo was to impart both chemical specificity by molecukir sieving of the analyte and converted product streams, as well as controlling access to the underlying Pd/Ni sensor. Ultimately, an array of these CMS elements encompassing different catalysts and membranes were to be developed which would enable improved selectivity and specificity from a compiex mixture of organic gases via pattern recognition methodologies. We have successfully generated a CMS device by a series of spin-coat deposited methods; however, it was determined that the high temperature required to activate the catalyst, destroys the sensor.

Abstract not provided.