Joshua Daniel Sugar

Using EELS to Determine He Pressure Inside Nanometer-Scale Bubbles

He bubbles are a common form of radiation damage that degrade mechanical and electrical properties. They occur during ion implantation in Si [1, 2], nuclear waste disposal [3], in nuclear reactors [4, 5], and in tritium storage materials [6]. Knowledge of the mechanisms of the initial bubble formation and their evolution is critical to predicting long-term performance of materials subjected to these harsh environments. The use of the TEM and EELS provides a unique way to characterize the spatial distribution and properties of these individual bubbles because the TEM’s high-spatial resolution can reveal bubbles even at the nanoscale, and EELS’ low-energy sensitivity enables He concentration measurements of the 21 eV He K absorption line that can be directly converted to bubble pressure [5, 7]. The ability to investigate correlations between bubble size and pressure is critical to testing theories of the mechanisms of the initial nucleation and eventual growth of these bubbles.

Crystallographic Orientation Image Mapping with Multiple Detector Configurations at 30 - 300 kV

The acquisition of 2D diffraction patterns from an array of 2D points in a scanning electron beam experiment is a 4D experiment that can be used to map local crystallographic orientations. The automated acquisition and analysis of these Kikuchi diffraction patterns [1, 2] has enabled orientation mapping of crystals with a large range of length scales. For example, commercially available electron back-scattered diffraction (EBSD) systems for an SEM are capable of measuring micronand submicron–scale features over length scales of 1 cm using automated montaging techniques. However, the pursuit of crystallographic features that are 10 nm or smaller requires the use of transmission-based techniques available in both SEM and TEM. There have been several advancements in automated analysis of diffraction patterns that have enabled the ability to perform automated Kikuchi diffraction experiments in a variety of microscope configurations [3-6]. At accelerating voltages of 30 kV and lower, it is now possible to perform transmission Kikuchi diffraction (TKD) experiments using a conventional EBSD detector and an SEM to study features 10 nm and smaller. In addition, the use of scanning precession electron diffraction (PED) has enabled experiments with similar spatial resolutions for spot diffraction patterns in TEMs at accelerating voltages of hundreds of kV.

Strong Photothermoelectric Response and Contact Reactivity of the Dirac Semimetal ZrTe5

The family of three-dimensional topological insulators opens new avenues to discover novel photophysics and to develop novel types of photodetectors. ZrTe5 has been shown to be a Dirac semimetal possessing unique topological, electronic, and optical properties. Here, we present spatially resolved photocurrent measurements on devices made of nanoplatelets of ZrTe5, demonstrating the photothermoelectric origin of the photoresponse. Because of the high electrical conductivity and good Seebeck coefficient, we obtain noise-equivalent powers as low as 42 pW/Hz1/2, at room temperature for visible light illumination, at zero bias. We also show that these devices suffer from significant ambient reactivity, such as the formation of a Te-rich surface region driven by Zr oxidation as well as severe reactions with the metal contacts. This reactivity results in significant stresses in the devices, leading to unusual geometries that are useful for gaining insight into the photocurrent mechanisms. Our results indicate that both the large photothermoelectric response and reactivity must be considered when designing or interpreting photocurrent measurements in these systems.

Hydrogen Assisted Fracture of Stainless Steels

The Enhanced Surveillance Sub-program has an annual NNSA requirement to submit a comprehensive report on all our fiscal year activities right after the start of the next calendar year. As most of you know, we collate all of our PI task submissions into a single volume that we send to NNSA, our customers, and use for other programmatic purposes. The functional objective of this report is to formally document the purpose, status, and accomplishments and impacts of all our work. For your specific submission, please follow the instructions described below and use the template provided. These are essentially the same as was used last year. We recognize this report may also include information on specific age-related findings that you will provide again in a few months as input to the Stockpile Annual Assessment process (e.g., in the submittal of your Component Assessment Report). However, the related content of your ES AR input should provide an excellent foundation that can simply be updated as needed for your Annual Assessment input.

Using Energy-Filtered TEM to Solve Practical Materials Problems with Inspirations from Gareth Thomas

1 Sandia National Laboratories, Livermore, CA, USA 2 Materials Science and Engineering, Stanford University, Stanford, CA, USA 3 Sandia National Laboratories, Albuquerque, NM, USA 4 Lawrence Livermore National Laboratory, Livermore, CA, USA 5 Materials Science and Engineering, University of CA, Berkeley, CA, USA 6 Nanotechnology and Functional Materials Center, University of Belgrade, Belgrade, Serbia

Measuring relative performance of an EDS detector using a NiO standard.

A method for measuring the relative performance of energy dispersive spectrometers (EDS) on a TEM is discussed. A NiO thin-film standard fabricated at Sandia CA is used. A performance parameter,, is measured and compared to values on several TEM systems.

Spatially confined alloy single crystals for model studies of volumetrically constrained phase transformations

The authors present a method to fabricate confined, oriented, single crystals of ternary alloys within an inert ceramic matrix. Pulsed-laser deposition of a polycrystalline CuNiFe film fills lithographically defined surface cavities in a sapphire single crystal. Solid-state diffusion bonding to a second sapphire crystal internalizes the metal-filled cavities. Electron microscopy verifies that subsequent heat treatment converts the thin, fully constrained films into single crystals of specific orientation by nucleation-controlled liquid-phase epitaxy during cooling from above the alloy melting temperature. The resulting films provide an ideal medium for fundamental studies of a wide range of volumetrically constrained phase transformations.

Mechanisms of microstructure development at metallic-interlayer/ceramic interfaces during liquid-film-assisted bonding

Alumina has been bonded via copper/niobium/copper interlayers, and correlations have been made between various processing conditions (applied load, processing temperature, copper film thickness, surface roughness, etc.) and strength. Four-point bend strengths and micrographs of fracture surfaces have been used to determine the relationship between processing, microstructure, and properties. Transparent sapphire substrates bonded with copper/niobium/copper interlayers were used in model experiments to track the microstructural development of these ceramic/metal interfaces and to identify the important mechanisms that contribute. High interfacial strengths were generally associated with small unbonded regions, extensive breakup of the copper film into isolated particles, ceramic pullout, and regions of niobium/alumina contact where the grain boundary grooves of the alumina are visible on both sides of the fracture surface. Experiments with sapphire substrates showed that asperities in the niobium and grain boundary grooves in the niobium play an important role in the initiation and growth of sapphire/niobium contact. The presence of a liquid film can enhance the kinetics of sapphire/niobium contact and growth by providing a low-temperature high-diffusivity path. The breakup of the copper film was described using two models that were in fairly close agreement. The breakup of the copper film depended on the asperity density in themorexa0» niobium, niobium grain boundary density, liquid film redistribution, and the breakup of liquid patches via Rayleigh instabilities. The redistribution of the liquid was affected by defect geometry, local film thickness, and local interfacial crystallography. Thermal grooving effects of liquid copper on alumina and niobium were studied using conventional sessile drop experiments. The thermal grooving of one particular grain boundary in alumina when in contact with copper and niobium was studied using a fabricated bicrystal. Both diffusion mechanisms and the dissolution-precipitation reaction of alumina in niobium limited the kinetics of thermal grooving.«xa0less