Practicum Abstracts

The project I worked on this summer at Sandia National Laboratories involved using a 3D printer to fabricate alumina samples. The dimensional accuracy of the samples was tracked by manipulating parameters such as printer settings, thermal processes, and ceramic composition. The impact that this has on the DOE is to provide a new manufacturing process for components.

Project #1 Titanium and stainless steel have notoriously been difficult to join due to prevalent formation of brittle intermetallics. The use of interlayers of different materials have been suggested to provide a ‘buffer’ so that the titanium and stainless steel do not negatively interact. Previous work on niobium has revealed it could be a suitable interlayer material. Building off these findings, this project investigated the feasibility of using additively manufactured niobium track deposits as an interlayer material between titanium and stainless steel. The inclusion of additive manufacturing provided many benefits including increased design flexibility and material utilization over conventional manufacturing techniques. Significant cracks and build failures were present in niobium tracks deposited onto stainless steel substrates suggesting the formation of detrimental intermetallics. Successful niobium walls were deposited onto titanium substrates, where post-mortem imaging did not reveal any detrimental cracking. Based on these results, another interlayer material such as vanadium may be better suited for this application. Project #2 Titan 23 is a new titanium alloy, designed by Allegany Technologies Incorporated (ATI), with reported combinations of strength and ductility superior to conventional titanium alloys. These claims have created excitement for titanium users, however the infancy of the alloy means there is still much to be understand in order to obtain the promised properties. To populate the upper limits of both strength and ductility possible with additively manufactured Titan 23, a range of microstructures were desired to achieve varying mechanical responses. Samples were heat treated at various times and temperatures with post-mortem imaging confirming the desired range of microstructures were obtained. Microhardness testing also revealed the microstructures possessed largely different hardness values. Initial results suggest Titan 23 can cover large regions of property space which allows for promising applications of this alloy.

The primary goal of the practicum project was to investigate physical damage, manifested as displacement damage, on memory circuits when exposed to radiation. Such damage can render a circuit block of affected transistors non-functional. With the expectation that electronic systems used in defense applications may be exposed to radiation upon deployment, such a malfunction may cause an unacceptable operational failure. This work investigated displacement damage in state-of-the-art technology (5 nm bulk FinFET technology) through heavy-ions exposure. I used static random-access memory (SRAM) arrays to investigate the displacement damage effects at the circuit-level. SRAM cells are very sensitive to any changes in transistor parameters, especially at reduced supply voltages. When a transistor in an SRAM cell is damaged, the SRAM cell will appear to stay stuck at either a low state or a high state. Previous work has shown the possibility of such a mechanism, but there has been no previous experimental work showing circuit-level failures due to displacement damage for advanced technology nodes. In theory, displacement damage becomes more problematic as feature sizes shrink, so this practicum pioneered the evaluation of this failure mechanism at the 5-nm bulk FinFET technology (the most highly-scaled technology that is currently in mass production). I used the Ion Beam Laboratory (IBL) and ARACOR X-ray source at Sandia National Laboratories (SNL) to thoroughly evaluate custom-designed integrated circuits (fabricated at a 5-nm bulk FinFET technology node) containing SRAMs during the practicum. I investigated the physical mechanisms causing stuck-bit failures in this technology. In addition to experiments on stuck bits, I also had guidance and support from engineers to gain experience in schematic design and layout for a custom test chip design for a 7-nm bulk FinFET technology node.

In the magnetized liner inertial fusion (MagLIF) platform fielded on the Z Machine at Sandia National Laboratories, inertial confinement fusion is pursued using a three-step process: fuel pre-magnetization, fuel preheat, and z-pinch compression. The preheat stage of MagLIF is accomplished by irradiating the fusion fuel with the Z-Beamlet Laser (ZBL), a multi-kJ, TW-class laser operated as part of the Z-Backlighter facility. Preheating the fusion fuel is one of the key components for successfully driving fusion reactions in the MagLIF concept; increasing the initial temperature of the fuel increases the adiabat of the implosion and consequently decreases the compression ratio required to reach fusion-relevant conditions. In my primary practicum project, I worked with members of the Z-Backlighter team to measure 3D profiles of the laser energy deposited by the ZBL in gas cell targets relevant to MagLIF target designs. We irradiated these targets with the ZBL in the Z-Backlighter facility's Conchas target chamber, collecting 2D projections of thermal x-ray emission from the heated gas at various angles that could then be reconstructed into a 3D profile using computed tomography (CT). Using fast multi-frame x-ray cameras developed at Sandia, we collected several images at each angular position separated by approximately 2 ns. After reconstruction using a CT algorithm, these images will yield a "4D CT" that will capture the volumetric time evolution of this plasma. By evaluating how the properties of the laser-generated plasma columns vary with target parameters and magnetization, we can ultimately provide experimental data to benchmark radiation-hydrodynamic codes such as 3D HYDRA and aid in designing advanced MagLIF experiments for improved fusion yields. In a secondary project intended to complement the ZBL shot schedule, I used a Sandia-developed photodiode array and digitizer to perform direct measurements of laser pulse properties on the nanosecond timescale. I measured a variety of pulse profiles throughout the Z-Petawatt frontend, benchmarking the photodiode array and digitizer and investigating a new method for measuring spatiotemporal couplings in nanosecond-duration laser pulses. This work also provides the groundwork for future applications of this instrument to experiments on large-scale facilities active in high energy density science such as the Z Machine or NIF.

This project consists of annealing and straining experiments conducted on 3D interface Cu/Nb nanolaminates (3D Cu/Nb) in the TEM. Annealing experiments were performed in-situ in the TEM to evaluate the thermal stability of 3D Cu/Nb and monitor the order in which microstructural changes occur during thermal degradation. Experiments were conducted at low and high-resolution magnifications to capture phenomena occurring at different length scales. Ongoing straining experiments will be conducted on nanopillars of 3D Cu/Nb to reveal the origins of high strength and deformability in this material. Results from these experiments will determine if a size effect exists in 3D Cu/Nb and where dislocations nucleate in the material.

This project aims to uncover the dynamics of deformation and thermal decomposition of Cu/Nb nanolaminates with nanometer resolution. This project comprises nanopillar compression and laser annealing experiments, with footage of both being taken in a transmission electron microscope to directly observe the progression of nano- and atomic-scale deformation and annealing processes. As Cu/Nb is a model system for controllably studying the effects of heterophase interface structure on the thermomechanical stability of nanostructured alloys, insights from this project can be used to shed light on the underpinnings of how interface structure can be manipulated to achieve record strength and thermal stability in nanocrystalline alloys.

For my practicum, I focused on x-ray spectroscopy of MagLIF experiments. The initial plans for my practicum were to extract the magnetic field from a MagLIF implosion by analyzing the Zeeman splitting in the Lyman alpha emission. We planned on studying previously measured iron spectra generated from iron contaminants in the beryllium liner and then design or adjust an x-ray spectrometer to either improve the spectral resolving power or change the energy range to study a different element. However, the current iron spectra showed differential splitting between the two Lyman alpha emission peaks, showing evidence that we may be able to extract the magnetic field from the current spectra. The primary analysis for my practicum focused on modeling the Lyman alpha emission to constrain the magnetic field. A continuous spectral model, with magnetic field, ion / electron temperature and electron density as free variables, was generated from a spectral grid and used to fit the data with a Bayesian inference routine. Preliminary results indicated a magnetic field of 20 kT. We plan on running additional tests with denser spectral grids as well as fitting additional spectral features, such as the iron helium alpha parent line, to confirm these results. We were also able to perform x-ray spectrometer development and characterization tests using a Manson source. In order to help characterize the energy dispersion relation using absorption edge filters, we performed exposures on a Manson source with multiple source anodes and k-edge filters. Furthermore, to gain an understanding of the spectral resolution of XRS3, we fit the different emission peaks with models based off the intrinsic width of each emission line. Lastly, we performed an extremely high spectral resolution measurement (E/DE > 10,000) to constrain the shape of the intrinsic iron k-alpha emission. These tests characterizing the spectrometer resolution are important for fitting the MagLIF spectra because the spectrometer response must be included in the Bayesian inference fitting routine.

I worked on two projects while at Sandia. They are each summarized in respective paragraphs below. I wrote my practicum proposal on Project 1, and I began Project 2 as a collaborative side project when I arrived at Sandia. Project 1: Zeolites are inorganic, porous, crystalline solids which are some of the most widely used industrial materials, applied in catalysis, separations, and sensing. While there are over two million hypothetical zeolites, only 255 exist. Thus, the synthesis of novel zeolites is a challenging task that is important for their broad commercial usage and for understanding more of their fundamental chemistry. A method to synthesize new zeolites, termed the Assembly-Disassembly-Organization-Reassembly (ADOR) process, has become well established in producing novel zeolites that are not feasible through traditional routes. Typically, ADOR takes a preassembled parent zeolite, selectively breaks it apart, and then pieces it back together to form a new daughter zeolite. I worked to employ ADOR to disassemble two different zeolites and combine their layers into one novel zeolite. By implementing two, rather than one, parent zeolite, additional structural diversity can be integrated. Project 2: While metal nanoparticles show increased catalytic reactivity compared to their bulk metal counterparts, particle migration, aggregation, and subsequent deactivation greatly decrease reactivity. To avoid nanoparticle deactivation, porous framework materials with regular cavities can serve as scaffolds for confining metal nanoparticle catalysts into cages where they prefer not to migrate. Additionally, these cages are connected by channels to other pores within the framework which allow access for reactants, products, and other substrates necessary for the given reaction. Zeolites specifically are crystalline porous materials that have been observed to improve the activity of encapsulated metal nanoparticles for acid gas adsorption (NOx and SOx). However, reported metal impregnation methods typically involve complex metal precursors and lengthy time frames, and the resulting nanoparticle location within the zeolite is not always clear. We have developed a new method to design zeolites with size-restricted, impregnated metal nanoparticles, evenly dispersed throughout zeolite layers. This method requires simple metal salts rather than complex metal precursors, takes place in water (green synthesis), runs for a short length of time (3-6 hours), and involves a facile one-pot procedure. Additionally, we observe diverse kinetics of impregnation for eleven different metal salts. Kinetic analysis using the Avrami-Erofeev model indicates that the coordination ability of the metal salt counterion plays a role in the rate of nanoparticle impregnation. As a result of metal impregnation, NOx adsorption was realized. We anticipate that this impregnation method can be broadly generalized for a variety of other metals and applications.

My practicum project involved investigating the fatigue properties of silicon (Si) thin films using in situ TEM fatigue testing. The overall goal of the project was to conduct the fatigue experiments within the environmental TEM (ETEM) to study the effect moisture has on stress-induced oxide growth (which can influence the fatigue behavior). The project mainly involved preparing the Si specimens on the push-to-pull devices used for the fatigue tests by floating 50nm thick Si film on top of the device using a drop of water followed by focused ion beam (FIB) release of the gauge. The devices were then tested in a conventional vacuum TEM at different stress amplitude and mean levels to obtain information on fatigue failure. I also worked on a few other side projects while I was there. One project involved analyzing in situ heating TEM experiments on gold-silicon samples to study the Au-Si eutectic reaction in depth. I also conducted in situ straining TEM experiments on gold thin films combined with Automated Crystal Orientation Mapping (ACOM) to study the deformation mechanisms relationship to the starting grain orientation, structure, etc.

My project can be divided into two efforts. The first is the study of FeO's strain curve using various Quantum Monte Carlo wave functions and methods to unambiguously determine the shape of the strain curve. The second is the study of LiF's optical properties at extreme pressures/temperatures using DFT/MD methods and kubo-greenwood formula.

This project involves modeling HMX-based polymer bonded explosive misrostructures and how they evolve under shock loading. These 2D simulations were performed using Sandia's Eulerian hydrocode - CTH. The effects of chemistry were modeled and the run-to-detonation distance was calculated as a function of shock pressure.

During this practicum we utilized the versatility of Sandia National Lab’s Thor-64 machine, where a tunable current pulse (80 kV) generates a magnetic drive to isentropically compress a sample of interest. In our case, we were interested in the homogenous phase transition of liquid water to solid ice VII. Previous studies have focused on peak pressure and window material as major factors for the onset of freezing. We took a different approach and looked at the effects of initial temperature and ramp rate. We found that increasing the initial temperature changes the isentropic loading path and results in a much higher phase transition pressure. We also found that decreasing the rap rate, or decreasing the rate of compression, decreased the transition pressure; however, it effected the initial room temperature isentropic loading paths less than the increased initial temperature paths.

For the practicum project I learned to use the Vasp DFT code for ab initio molecular dynamics. Using this tool, I studied hydrogen under high pressure with two different potentials, looking for the critical point in the liquid-liquid insulator-metal transition and doing conductivity calculations. I also studied the forsterite vapor dome to compute the critical point for this material.

The project involved writing 3 codes: a magneto-hydrodynamics (MHD) code, a two-fluid (TF) plasma code, and a particle in cell (PIC) code. With the three working codes, the goal was then to couple PIC to TF in the regime where their traditional applications overlap.

The Pecos test chamber is used to study laser preheat on MagLIF targets for Z, but in an offline environment that is more accessible in terms of shot rate and diagnostics. This allows much more rapid development of new target designs and preheating platforms that can be benchmarked for performance before fielding on Z, which has a much slower shot rate and higher risk.

Designed and built and in situ, laser-based materials diagnostic for the 6 MV tandem accelerator at the Sandia Ion Beam Lab. Experiment will be used to track the thermal and mechanical properties of materials subject to ion beam irradiation in near real time.

Surface laser-irradiation of oxidizing metals such as stainless steel induces a high-temperature chemical reaction between the metal and ambient atmosphere, resulting in the growth of a film composed of elements from the substrate in combination with environmental gasses. Such films are highly colored and may find use as unique authenticity markings in welded components. The practicum research focused on critical experimental studies to develop materials processing methods to ensure sealed components are robust in harsh corrosive and embrittling environments. As it is likely that laser-induced Cr-depletion from stainless steel substrates is the primary cause of corrosion for the oxidized SS 304L, a set of conditions to will control the environmental resistance of alloys subjected to laser processing was predicted. A set of experiments assessed the effectiveness of pre- and post-treatment of SS 304L for reducing Cr dissolution.

For the twelve weeks of my practicum, I was part of Sandia National Laboratories’ Sunshine to Petrol (S2P) project. As the United States seeks to become energy-independent, novel methods for sourcing fuels are required. It is not feasible to have an immediate shift to all renewable energy sources, especially in the area of transportation fuels, and thus, easily implementable, renewable energy sources with shorter time scales are needed. The S2P Program aims to fulfill this need by researching thermochemical fuel production fueled by concentrated solar power. The overarching goal of this project is to find materials that can split carbon dioxide and water. Products from these reactions (carbon monoxide and hydrogen, respectively) can then be used as precursors for the manufacture of hydrocarbon fuels. Current materials which have been successful for this purpose such as ceria have been well-studied but are limited in efficiency; thus the search for better performing, thermodynamically and kinetically favorable redox systems must be expanded.

This project uses Sandia computer systems and simulation tools to study the properties of deuterium under extreme conditions. In particular, MD-DFT simulations were performed and analyzed to compare to recent x-ray scattering experiments that were performed at LLNL.

A fiber coupled streaked spectroscopic system was set up to be fielded on the Z machine at Sandia National Labs. This diagnostic was used to observe light emission by z-pinch wires during the initial ablation stage. It was also used to observe light emission from a photo-ionized neon gas cell. Future experiments that will utilize this diagnostic include observation of the plasma formed in a post-hole convolute and hydrogen/helium gas cell emission/absorption with applications to white dwarf stars.

The National Spherical Torus eXperiment (NSTX) at the Princeton Plasma Physics Laboratory (PPPL) intends to install a novel liquid lithium divertor (LLD) prior to the next run campaign. Before the final divertor can be built, design and materials testing must be completed in order to ascertain the parameters for an optimal device. While design work is underway, Sandia is involved in materials testing. The initial wetting tests are an examination of a unique molybdenum foam and the behavior of lithium in its presence. Thermocouple and IR data are gathered from both bench-top and vacuum heating tests of the foam itself. In addition, lithium foil is melted on to the foam and a variety of both qualitative and quantitative data regarding the manner in which the lithium wets the foam is collected.