Alan Dozier

Crack Pattern Formation in Thin Film Lithium-Ion Battery Electrodes

Cracking of electrodes caused by large volume change and the associated lithium diffusion-induced stress during electrochemical cycling is one of the main reasons for the short cycle life of lithium-ion batteries using high capacity anode materials, such as Si and Sn. In this work, we study the fracture behavior and cracking patterns in amorphous Si thin film electrodes as a result of electrochemical cycling. A modified spring-block model is shown to capture the essential features of cracking patterns of electrode materials, including self-similarity. It is shown that cracks are straight in thick films, but show more wiggles in thin films. As the thickness of film decreases, the average size of islands separated by cracks decreases. A critical thickness bellow which material would not crack is found for amorphous Si films. The experimental and simulation results of this work provide guidelines for designing crack free thin-film lithium ion battery electrodes during cycling by patterning the electrode and reducing the film thickness.

From Dose to Response: In Vivo Nanoparticle Processing and Potential Toxicity

Adverse human health impacts due to occupational and environmental exposures to manufactured nanoparticles are of concern and pose a potential threat to the continued industrial use and integration of nanomaterials into commercial products. This chapter addresses the inter-relationship between dose and response and will elucidate on how the dynamic chemical and physical transformation and breakdown of the nanoparticles at the cellular and subcellular levels can lead to the in vivo formation of new reaction products. The dose-response relationship is complicated by the continuous physicochemical transformations in the nanoparticles induced by the dynamics of the biological system, where dose, bio-processing, and response are related in a non-linear manner. Nanoscale alterations are monitored using high-resolution imaging combined with in situ elemental analysis and emphasis is placed on the importance of the precision of characterization. The result is an in-depth understanding of the starting particles, the particle transformation in a biological environment, and the physiological response.

Eels-Stem Investigation of the Formation of Nano-Zones in Iron Catalysts for Fischer-Tropsch Synthesis

This chapter studies Iron Fischer-Tropsch (Fe-FTS) catalyst particles using high resolution transmission electron microscopy (HR-TEM) and electron energy loss spectroscopy (EELS) as well as energy filtered TEM (EFTEM) with spectrum imaging spectral analysis and mapping capabilities. These studies have independently demonstrated the formation of various nanozones within iron catalyst particles. By this studys classification schema, nanozones comprises of nm-wide layers that host a dense array of either iron carbide or iron oxide crystallites and multiple carbon-rich nano-layers that occur both on the exterior of the Fe-FTS catalyst grains and also further inwards. The precursor catalyst material that underwent phase transformations leads to the formation of the reported nanozones during the FT-experiments was a precipitated unsupported iron oxide and the materials under investigation were derived from slurry-bed reactor runs that were sampled after exposure to increasing length of synthesis time. It discusses that the presence of a carbon-rich layer closer to the core was a surprise, while the amorphous carbon zone that occurs at the rim of the catalyst grains had already been known. The chapter explores the carbon-rich layer located closer to the core in fact has carbon EELS signatures that are different from those of the carbide carbon that is concentrated in the core region and also those of the exterior amorphous carbon layer. It suggests that the inner carbon nanozone was derived either from the carbide core after some phase transformations of the iron carbide crystallites that caused a spatial repositioning of extra carbon outside of the iron carbide nanozone, or that the carbon was independently deposited onto the inner core during the reactor runs.

Workplace Monitoring of Airborne Carbon Nanomaterials by HRTEM

Growing production and use of carbon nanomaterials may pose health risks for exposed workers. The National Institute for Occupational Safety and Health (NIOSH) set a recommended exposure limit (REL) for carbon nanotubes and nanofibers (CNT and CNF): an 8-hr time weighted average (TWA) of 1 μg/m as respirable elemental carbon (EC) [1]. As other EC sources may interfere, complementary techniques (e.g., metals, organics, and microscopy analyses) have been used to better characterize exposure [1-4]. High resolution transmission electron microscopy (HRTEM) is especially useful because it provides visualization of particle size, shape, structure, and agglomeration state.

Automated generation and ensemble-learned matching of X-ray absorption spectra

X-ray absorption spectroscopy (XAS) is a widely used materials characterization technique to determine oxidation states, coordination environment, and other local atomic structure information. Analysis of XAS relies on comparison of measured spectra to reliable reference spectra. However, existing databases of XAS spectra are highly limited both in terms of the number of reference spectra available as well as the breadth of chemistry coverage. In this work, we report the development of XASdb, a large database of computed reference XAS, and an Ensemble-Learned Spectra IdEntification (ELSIE) algorithm for the matching of spectra. XASdb currently hosts more than 800,000 K-edge X-ray absorption near-edge spectra (XANES) for over 40,000 materials from the open-science Materials Project database. We discuss a high-throughput automation framework for FEFF calculations, built on robust, rigorously benchmarked parameters. FEFF is a computer program uses a real-space Green’s function approach to calculate X-ray absorption spectra. We will demonstrate that the ELSIE algorithm, which combines 33 weak “learners” comprising a set of preprocessing steps and a similarity metric, can achieve up to 84.2% accuracy in identifying the correct oxidation state and coordination environment of a test set of 19 K-edge XANES spectra encompassing a diverse range of chemistries and crystal structures. The XASdb with the ELSIE algorithm has been integrated into a web application in the Materials Project, providing an important new public resource for the analysis of XAS to all materials researchers. Finally, the ELSIE algorithm itself has been made available as part of veidt, an open source machine-learning library for materials science.Machine learning: Web application for matching X-ray absorption spectraAnalyzing X-ray absorption spectra (XAS) just became easier thanks to a publically-available database and spectra matching web tool. Interpreting XAS data is currently hindered by a lack of reference spectra, which are laborious to obtain as they require finely tunable X-rays only accessible at synchrotron facilities. Here, a collaboration led by Kristin Persson at the University of California Berkeley, and Shyu Ping Ong at the University of California San Diego developed a ‘high-throughput’ approach generating a large database of computed XAS data, along with a machine-learning algorithm matching unknown spectra with ones in the database. The program correctly identified the oxidation states and coordination environments of a diverse test set of materials with high accuracy. The authors hope their web app will provide a valuable public resource for materials science researchers.

Creation of an XAS and EELS Spectroscopy Resource within the Materials Project using FEFF9

We describe the development of an X-ray Absorption Spectroscopy (XAS) and Electron Energy Loss Spectroscopy (EELS) resource in the Materials Project (MP) [1] database as part of the Local Spectroscopy Data Infrastructure Project [2]. This integration within the MP allows material properties and the associated spectroscopies to be calculated using NERSC (National Energy Research Scientific Computing Center) computing facilities and retrieved through either the user portal or the Representational State Transfer (REST) interface [1]. This ability to search the MP database through its REST interface and carry out a comparative analysis with experimental spectra introduces an efficiency in characterization that will aid in understanding material functionality in various technologically important areas such as semi-conductors, batteries, reactions, etc.

In vivo formation of Ce-phosphate Nanoparticles following Intratracheal Instillation of CeCl3: Subcellular sites, Nanostructures, Precipitation Mechanisms and Nanoparticle 3D-Alignment

We demonstrate the in vivo formation of nano-particulate Ce-containing structures in lungs instilled with 5 mg/kg CeCl3 using high resolution electron microscopy (HRTEM), energy loss spectroscopy (EELS), and elemental mapping (EDS). The observed high lung retention of Ce after instillation of CeCl3 (75-92% retained at 28 days) is unexpected since metal ions are usually readily transported across the air-blood barrier. The binding of cerium ions to lung constituents has been suggested [1], and the formation of cerium phosphate has been shown previously, but without discussions on the mechanisms involved in nanoparticle nucleation and growth [2]. Determining the form of Ce after lung exposure to CeCl3 has been challenging due to the difficulties in distinguishing ions from particulate forms when using radioactivity or ICP-MS. We have identified cerium nanoparticles at the sub-cellular level in lung macrophages after CeCl3 instillation. This observation provides insights on the cell structures and components that will help distinguish which cellular areas are the sites of in vivo nanoparticle formation.

Analytical High-resolution Electron Microscopy Reveals Organ-specific Nanoceria Bioprocessing

This is the first utilization of advanced analytical electron microscopy methods, including high-resolution transmission electron microscopy, high-angle annular dark field scanning transmission electron microscopy, electron energy loss spectroscopy, and energy-dispersive X-ray spectroscopy mapping to characterize the organ-specific bioprocessing of a relatively inert nanomaterial (nanoceria). Liver and spleen samples from rats given a single intravenous infusion of nanoceria were obtained after prolonged (90 days) in vivo exposure. These advanced analytical electron microscopy methods were applied to elucidate the organ-specific cellular and subcellular fate of nanoceria after its uptake. Nanoceria is bioprocessed differently in the spleen than in the liver.

Calcium co-Localization with in vivo Cerium Phosphate Nanoparticle Formation after Intratracheal Instillation Dosing with CeCl3 or CeO2 NPs

The bioprocessing of CeO2 nanoparticles after uptake in lung tissues is compared with the formation of nanoparticles after inhalation of CeCl3 aerosols. In both cases, high-resolution TEM/STEM analyses indicate that cerium phosphate nanoparticles (NPs) had precipitated in phagolysosomal regions within macrophages. Importantly, the primary particle size, morphology, and agglomeration tendencies of the NPs were strikingly similar. Formation of cerium phosphate NPs after bioprocessing of inhaled CeO2 crystals proceeds via dissolution, ion transport, followed by nucleation and growth [1]. Application of 2D and 3D elemental maps of the NP bioprocessing stages and corresponding tissue interactions provide insights on the breakdown mechanisms, formation of new precipitates, size, and morphology changes of the original delivered NPs, and ion transport phenomena that result in secondary particle formation. Particle size and morphology are very similar for all of the cerium phosphate NPs, suggesting a common underlying precipitation mechanism independent of whether the metal ions are derived from dissolution of nanoparticles (CeO2) or from instilled metal ions (CeCl3).

Analysis of erionites from volcaniclastic sedimentary rocks and possible implications for toxicological research

Abstract Erionite occurs in volcaniclastic rocks and soils; in some villages in Turkey the presence of erionite in local rocks is associated with mesothelioma, a disease also associated with inhalation of airborne asbestos. Since volcaniclastic rocks containing erionite are widely present in the western U.S.A., there is a concern over potential health issues following inhalation of dust particles in these areas and thus there is a need to identify and quantify erionite particles found in air samples during hygienic investigations. Previous attempts to analyze the few micrometer-sized erionite particles found on air sample filters under transmission electron microscope (TEM) encountered difficulties due to electron beam damage. Recommendations are presented for accurate analysis by both energy-dispersive spectroscopy (EDS) and selected-area electron diffraction (SAED). Much of the work previously published to establish the crystal chemistry of erionite has involved the relatively large crystals found in vesicles in extrusive volcanic rocks. Analysis of these crystals gives a weight percent ratio of Si to Al in a narrow range around 2.7 (molar ratio 2.6), consistent with a unit-cell formula Al10Si26. In addition, the cation contents of these crystals generally meet the charge balance error formula for zeolites. However, erionites formed in volcaniclastic sedimentary rocks (tuffs) have very different Si:Al weight percent ratios, around 4.0, which is above the upper range for the analyses of the crystals found in vesicles. Analysis of many particles in samples from different locations reveal two other major differences between the erionites from the sedimentary situations and those found in vesicles. (1) The extra-framework alkali cation (Na, K, Ca) contents are lower than required for a stoichiometric balance with framework Al substitution for Si so that the cation charge balance error formula limits for zeolites are not met. (2) There is a large variability in measured cation contents from particle to particle from the same source as well as substantial differences in average compositions from different sources. However, sedimentary erionites cannot be termed a separate mineral species because the crystallographic data are consistent with erionite and new zeolite names cannot be proposed on the basis of Si:Al ratios alone. In addition to chemical differences between erionite from different sources, there are also morphological differences. By analogy with asbestos minerals, differences in composition and morphology may have implications for relative toxicity, and future research should include consideration of these aspects.