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An Open Analysis Platform with In-Situ Machine Vision for Electron Microscopy Final Technical Report
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Deep generative modeling for volume reconstruction in cryo-electron microscopy
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Quantum theory of electronic excitation and sputtering by transmission electron microscopy
Combining quantum electrodynamics with density functional theory, we model electronic excitation and sputtering by beam electrons in two-dimensional materials. Electronic excitations can drastically increase the sputtering rates in these materials.
Atomic to Nanoscale Origin of Vinylene Carbonate Enhanced Cycling Stability of Lithium Metal Anode Revealed by Cryo-Transmission Electron Microscopy
Batteries using lithium (Li) metal as anode are considered promising energy storage systems because of their high specific energy densities. The crucial bottlenecks for Li-metal anode are Li dendrites growth and side reactions with electrolyte inducing low Coulombic efficiency (CE) and short cycle life. Vinylene carbonate (VC), as an effective electrolyte additive in Li-ion batteries, has been noticed to significantly enhance the CE, while the origin of such an additive remains unclear. Here we use cryo-TEM imaging combing with EDS elemental and EELS electronic structure analyses to reveal the role of VC additive. We discovered that the electrochemically deposited Li metal (EDLi) in VC-containing electrolyte is slightly oxidized with the SEI being a nanoscale-mosaic like structure comprised of organic species, Li 2 O and Li 2 CO 3 ; while the EDLi formed in VC-free electrolyte is featured by a combination of fully oxidized Li with Li 2 O SEI layer and pure Li metal with multilayer nano-structured SEI. These results highlight the possible tuning of crucial structural and chemical features of EDLi and SEI through additives and consequently direct correlation with electrochemical performance, providing valuable guidelines to rational selection, design and synthesis of additives for new battery chemistries.
Surprisingly high irradiation-induced defect mobility in Fe 3 O 4 as revealed through in situ transmission electron microscopy
Radiation-induced defects are expected to change the corrosion kinetics when a material is exposed to a corrosive environment. Characterization of the defects forming under irradiation and their ability to move/diffuse is therefore key to understanding how they impact the corrosion kinetics and possibly mechanisms. For that matter, Fe/Fe 3 O 4 interfaces were irradiated using 1 MeV Kr 2+ at temperatures of 273 K (25 °C), 573 K (300 °C) and 773 K (500 °C) to a maximum dose of 10 dpa (as measured in the Fe matrix) in situ in a transmission electron microscope. The evolution of the microstructure was followed as a function of the dose and temperature. The formation of defects was followed in the metal and the oxide as well as at the metal/oxide interface and characterized in terms of size and density. Additionally, the dynamic observation of the spatial distribution of the defects allowed for a qualitative assessment of the mobility of defects in the oxide as a function of temperature, revealing evidence for enhanced mobility even more so than in the Fe matrix. Mechanisms of induced defect mobility in the spinel are discussed to account for the observations.
Advanced Electron Microscopy of TRISO coated Particles: FY2021 Overview
Objectives: Understanding Effects of Irradiation on TRISO layers Fission product chemistry and behavior in UCO kernel Identify and Understand Fission Product Transport Mechanisms in TRISO Coated Particles
Tracking Nanoparticle Degradation across Fuel Cell Electrodes by Automated Analytical Electron Microscopy
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A High Brightness Source of Femtosecond Polarized Electrons for Electron Microscopy
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Nanoscale imaging of phonon dynamics by electron microscopy
Spatially resolved vibrational mapping of nanostructures is indispensable to the development and understanding of thermal nanodevices, modulation of thermal transport and novel nanostructured thermoelectric materials. Through the engineering of complex structures, such as alloys, nanostructures and superlattice interfaces, one can significantly alter the propagation of phonons and suppress material thermal conductivity while maintaining electrical conductivity. There have been no correlative experiments that spatially track the modulation of phonon properties in and around nanostructures due to spatial resolution limitations of conventional optical phonon detection techniques. Here we demonstrate two-dimensional spatial mapping of phonons in a single silicon–germanium (SiGe) quantum dot (QD) using monochromated electron energy loss spectroscopy in the transmission electron microscope. Tracking the variation of the Si optical mode in and around the QD, we observe the nanoscale modification of the composition-induced red shift. We observe non-equilibrium phonons that only exist near the interface and, furthermore, develop a novel technique to differentially map phonon momenta, providing direct evidence that the interplay between diffuse and specular reflection largely depends on the detailed atomistic structure: a major advancement in the field. Our work unveils the non-equilibrium phonon dynamics at nanoscale interfaces and can be used to study actual nanodevices and aid in the understanding of heat dissipation near nanoscale hotspots, which is crucial for future high-performance nanoelectronics.
Exploring electron-beam induced modifications of materials with machine-learning assisted high temporal resolution electron microscopy
Directed atomic fabrication using an aberration-corrected scanning transmission electron microscope (STEM) opens new pathways for atomic engineering of functional materials. In this approach, the electron beam is used to actively alter the atomic structure through electron beam induced irradiation processes. One of the impediments that has limited widespread use thus far has been the ability to understand the fundamental mechanisms of atomic transformation pathways at high spatiotemporal resolution. Here, we develop a workflow for obtaining and analyzing high-speed spiral scan STEM data, up to 100 fps, to track the atomic fabrication process during nanopore milling in monolayer MoS 2 . An automated feedback-controlled electron beam positioning system combined with deep convolution neural network (DCNN) was used to decipher fast but low signal-to-noise datasets and classify time-resolved atom positions and nature of their evolving atomic defect configurations. Through this automated decoding, the initial atomic disordering and reordering processes leading to nanopore formation was able to be studied across various timescales. Using these experimental workflows a greater degree of speed and information can be extracted from small datasets without compromising spatial resolution. This approach can be adapted to other 2D materials systems to gain further insights into the defect formation necessary to inform future automated fabrication techniques utilizing the STEM electron beam.
Cation Migration and LSCF/SDC Decomposition Related to Long-Term Operation Mode as Revealed by Electron Microscopy
This study utilized energy dispersive spectroscopy (EDS) in a scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM) in order to track cation migration and related particle decomposition for air electrode components of solid oxide cells. The influence of a Sm-doped ceria (SDC) barrier layers was assessed for three operation modes (fuel cell, electrolysis, reversible) over long time periods (1000-1500 hours). Composition profiles across air electrode/electrolyte interfaces indicated negligible accumulation of La/Sr cations to the yttria-stabilized zirconia (YSZ) electrolyte during operation. Instead, air electrode particles composed of SDC and/or La-Sr-Co-Fe-oxides (LSCF) exhibited decomposition by Sr evaporation and Sm migration to LSCF particle edges.
Reshaping of Truncated Pd Nanocubes: Energetic and Kinetic Analysis Integrating Transmission Electron Microscopy with Atomistic-Level and Coarse-Grained Modeling
Stability against reshaping of metallic fcc nanocrystals synthesized with tailored far-from-equilibrium shapes is key to maintaining optimal properties for applications such as catalysis. Yet Arrhenius analysis of experimental reshaping kinetics, and appropriate theory and simulation, is lacking. As such, we use TEM to monitor the reshaping of Pd nanocubes of ~25 nm side length between 410 °C (over ~4.5 h) and 440 °C (over ~0.25 h), extracting a high effective energy barrier of E eff ≈ 4.6 eV. We also provide an analytic determination of the energy variation along the optimal pathway for reshaping that involves transfer of atoms across the nanocube surface from edges or corners to form new layers on side {100} facets. The effective barrier from this analysis is shown to increase strongly with the degree of truncation of edges and corners in the synthesized nanocube. Theory matches experiment for the appropriate degree of truncation. In addition, we perform simulations of a stochastic atomistic-level model incorporating a realistic description of diffusive hopping for undercoordinated surface atoms, thereby providing a visualization of the initial reshaping process.
An in situ ambient and cryogenic transmission electron microscopy study of the effects of temperature on dislocation behavior in CrCoNi-based high-entropy alloys with low stacking-fault energy
Temperature is known to affect deformation mechanisms in metallic alloys. As temperature decreases, the stacking-fault energy in many face-centered cubic (fcc) alloys decreases, resulting in a change of deformation mode from dislocation slip to deformation twinning. Such an impact of temperature can be more complex in compositionally heterogeneous microstructures that exhibit, for example, local concentration fluctuation such as that in multi-principal element alloys. In this work, we compare the dislocation behavior and mechanical properties of a fcc Cr 20 Mn 10 Fe 30 Co 30 Ni 10 high-entropy alloy at ambient and liquid-nitrogen temperatures. We find that a network of stacking faults is formed by uniformly extended dislocations at ambient temperatures with low stacking-fault energy, whereas at lower temperatures, uneven dissociation of dislocations becomes significant, which results in severe dislocation pile-ups together with their pronounced entanglement. Our findings indicate that as the stacking-fault energy decreases with decreasing temperature, the heterogeneity of the distribution of elements becomes more dominant in tuning the local variation of lattice resistance. As a result, the change in dislocation behavior at low temperatures strongly affects microstructural evolution and consequently leads to significantly more pronounced work hardening.
Investigating the failure behavior of cast Al-11Ce-0.4Mg alloys using in-situ scanning electron microscopy tensile testing
Within the last decade, research on Al-Ce-Mg alloys has reported promising results for use in cast part applications. In this paper, the failure behavior of cast Al-11Ce-0.4Mg (wt%) was investigated experimentally with focus on the effect the matrix and intermetallic phases have on the fracture propagation behavior at failure. For the first time, in-situ SEM tensile testing was used to study the failure behavior of cast Al-Ce alloys, reporting results for uniaxial, DIC, and single edge notch tensile tests. The results of the in-situ SEM tensile testing were compared with the materials characterization experiments, which included serial sectioning, EBSD, EDS, and fractography. Analysis of EBSD and EDS mapping of cast Al-11Ce-0.4Mg showed that the cast microstructure was a hypereutectic two phase Al-Ce alloy with grains encompassing large complex colonies of laminar eutectic Al 11 Ce 3 intermetallic. The uniaxial tensile results reported the effect casting defects have on the strength and ductility of the alloy, and DIC in-situ testing showed that the eutectic colonies plastically deform less than the matrix phase. In-situ SEM single edge notch tensile testing displayed how the strength of an individual phase affected the crack propagation direction in the alloy. The results of both the materials characterization and in-situ tensile testing experiments on the failure of this alloy revealed further directions for future alloy development that can improve both the strength and fracture toughness of Al-Ce-Mg alloys.