Crystallographic analysis in the Scanning electron microscope: Electron backscatter diffraction.
Abstract not provided.
Michael, Joseph R.↗
SEARCH · Engineering Papers
Results for “Scanning Electron Microscopes”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Electron Backscatter Diffraction based Strain Analysis in the Scanning Electron Microscope.
Abstract not provided.
Wright, Stuart↗
Effect of nitriding on mechanical and microstructural properties of Direct Metal Laser Sintered 17-4PH stainless steel
In this work, the effect of the nitriding process on microstructure and mechanical properties of additively manufactured (AM) 17-4PH stainless steel is investigated. The nitriding was performed at 530 °C, 560 °C, and 580 °C for 2 h. The nitriding process improves the hardness and surface roughness of the AM 17-4PH steel. Detailed microstructural characterizations of both as-built and nitride samples are performed using an optical microscope, scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction technique. It reveals that the nitride layer thickness increases with nitriding temperature. A distinct transition layer between the substrate and nitride layer is observed in the 560 °C and 580 °C nitride samples. The nitriding process develops almost equiaxed grain microstructure with new secondary phase precipitates, whereas in the as-built material, the grains are primarily columnar along the AM process build direction. Specifically, the nitriding process introduces γ-Fe4N, ε-Fe3N, CrN, and Ni3N precipitates. The increase in Ni- and Cu-rich precipitates with the nitriding temperature explains the observed improvement in the hardness and surface roughness. Furthermore, the nitriding process does not alter the substrate's initial weak crystallographic texture.
17-4PH steel↗
Mineralogy and petrology of fine‐grained samples recovered from the asteroid (162173) Ryugu
Abstract Samples returned from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 mission revealed that Ryugu is composed of materials consistent with CI chondrites and some types of space weathering. We report detailed mineralogy of the fine‐grained Ryugu samples allocated to our “Sand” team and report additional space weathering features found on the grains. The dominant mineralogy is composed of a fine‐grained mixture of Mg‐rich saponite and serpentine, magnetite, pyrrhotite, pentlandite, dolomite, and Fe‐bearing magnesite. These grains have mineralogy comparable to that of CI chondrites, showing severe aqueous alteration but lacking ferrihydrite and sulfate. These results are similar to previous works on large Ryugu grains. In addition to the major minerals, we also find many minerals that are rare or have not been reported among CI chondrites. Accessory minerals identified are hydroxyapatite, Mg‐Na phosphate, olivine, low‐Ca pyroxene, Mg‐Al spinel, chromite, manganochromite, eskolaite, ilmenite, cubanite, polydymite, transjordanite, schreibersite, calcite, moissanite, and poorly crystalline phyllosilicate. We also show scanning transmission electron microscope and scanning electron microscope compositional maps and images of some space‐weathered grains and severely heated and melted grains. Although our mineralogical results are consistent with that of millimeter‐sized grains, the fine‐grained fraction is best suited to investigate impact‐induced space weathering.
Geochemistry & Geophysics↗
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.
Picard, Yoosuf↗
Isotope-Resolved Electron Energy Loss Spectroscopy in a Monochromated Scanning Transmission Electron Microscope
The development and implementation of high-stability monochromators in state-of-the-art aberration-corrected scanning transmission electron microscopes has enabled materials characterization with an energy resolution as good as 3 meV. This allows the vibrational modes, which would otherwise be obscured by the energy spread of the electron beam, to be probed with very high precision in molecular materials. Since the vibrational energies depend on the weight of the atomic nuclei, vibrational spectroscopy can distinguish isotopes whose only difference lies in their neutron content. This opens up isotopic analysis and mapping in transmission electron microscopy as two important new research areas. In this paper, we review the monochromated electron energy loss spectroscopy (EELS) instrumentation, discuss optimal methods for probing beam-sensitive materials without destroying them, and review key nanoscale isotope-resolved results.
47 OTHER INSTRUMENTATION↗
Direct imaging of electron density with a scanning transmission electron microscope
Abstract Recent studies of secondary electron (SE) emission in scanning transmission electron microscopes suggest that material’s properties such as electrical conductivity, connectivity, and work function can be probed with atomic scale resolution using a technique known as secondary electron e-beam-induced current (SEEBIC). Here, we apply the SEEBIC imaging technique to a stacked 2D heterostructure device to reveal the spatially resolved electron density of an encapsulated WSe 2 layer. We find that the double Se lattice site shows higher emission than the W site, which is at odds with first-principles modelling of valence ionization of an isolated WSe 2 cluster. These results illustrate that atomic level SEEBIC contrast within a single material is possible and that an enhanced understanding of atomic scale SE emission is required to account for the observed contrast. In turn, this suggests that, in the future, subtle information about interlayer bonding and the effect on electron orbitals could be directly revealed with this technique.
36 MATERIALS SCIENCE↗
A Platform for Atomic Fabrication and In Situ Synthesis in a Scanning Transmission Electron Microscope
Here, the engineering of quantum materials requires the development of tools able to address various synthesis and characterization challenges. These include the establishment and refinement of growth methods, material manipulation, and defect engineering. Atomic-scale modification will be a key enabling factor for engineering quantum materials where desired phenomena are critically determined by atomic structures. Successful use of scanning transmission electron microscopes (STEMs) for atomic scale material manipulation has opened the door for a transformed view of what can be accomplished using electron-beam-based strategies. However, serious obstacles exist on the pathway from possibility to practical reality. One such obstacle is the in situ delivery of atomized material in the STEM to the region of interest for further fabrication processes. Here, progress on this front is presented with a view toward performing synthesis (deposition and growth) processes in a scanning transmission electron microscope in combination with top-down control over the reaction region. An in situ thermal deposition platform is presented, tested, and deposition and growth processes are demonstrated. In particular, it is shown that isolated Sn atoms can be evaporated from a filament and caught on the nearby sample, demonstrating atomized material delivery. This platform is envisioned to facilitate real-time atomic resolution imaging of growth processes and open new pathways toward atomic fabrication.
36 MATERIALS SCIENCE↗
Advanced Characterization of Fuel-cladding Chemical Interaction between U-10Zr Fuel and HT9 Cladding Tested in Fast Flux Test Facility
Fuel cladding chemical interaction (FCCI) can greatly accelerate the cladding failure. However, due to the limited space in a fuel cladding assembly, it is historically challenging to gain an mechanistical understanding of the formation mechanism of FCCI and its influence on fuel and cladding performance. With the imminent need to qualify U-10Zr based metallic fuel cladded by HT-9 for advanced reactors demonstration project, it is of vital importance to use advanced characterization method to study FCCI in a unprecedent detailed manner and gain better mechanism understanding of FCCI. Mechanistic Fuel Failure (MFF) series of prototypic fuel elements irradiated in FFTF [1, 2] provides the best samples to study FCCI since the MFF-series assemblies had an axial fuel height the same as proposed length by industry partners. Jason et al. [3] has performed preliminary post-irradiation examination on a MFF fuel pin sample, which was extracted from the HT9 cladded U-10at.%Zr MFF-3 pin MFF-3 pin (#193045) at an axial location of X/L = 0.98. This sample has a peak burnup of 5.7 at.% and peak inner cladding temperature (PICT) of around 615 °C during in-core testing. Scanning electron microscope examination has identified visible FCCI region on more than half of the HT9 circumference [3]. The most striking feature are grain boundary attacking by apparently lanthanides (Lns) rich phase. However, SEM cannot provide accurate assessment of phase and concentration of grain boundary phases and prevented a better understanding of the formation mechanism of such attach. This study, by pairing transmission electron microscope (TEM) characterization and atom probe tomography (APT) techniques with in-situ micro-tensile testing in scanning electron microscope (SEM), aims at gaining in-depth understanding on the formed FCCI region. The identified FCCI region roughly consists of multilayers as illustrated in Figure 1 (c). The main findings are: (1) layer-B shows observable lanthanides (Lns) infiltration along grain boundaries and mechanical softening due to FCCI- and irradiation-induced microstructural and microchemistry changes, particularly the recovery of martensitic lath structure and dissolution of pre-existing M23C6 together with the formation of coarsened Laves phases, (Fe, Cr)2(Mo, W); (2) layer-C is Fe depleted but Lns significantly enriched, becoming very brittle; (3) layer-D is mainly composed of UFe2 and Lns; (4) three FCCI-induced intermetallic U-Fe-Zr phases, ? (Fe0.5Zr0.32U0.18), e (Fe0.3Zr0.4U0.3), ? (Fe0.06Zr0.23U0.71), were identified near layer-E; (5) the ? (Fe0.5Zr0.32U0.18) phase was characterized to be a face centered cubic (FCC) crystal structure. These results will help to better understanding the governing mechanism of FCCI and facilitating the development of theoretical model for assessing the performance of metallic fuel and cladding integrity.
36 MATERIALS SCIENCE↗
Isothermal oxidation of zirconium using steam
Oxidation of zirconium and its alloys under any atmosphere is generally characterised by a protective and non-protective stage. During the protective stage, the kinetics of oxidation are quasi-parabolic, while the oxide scale formed on the surface of the metal is black, compact, and protective in nature. For the non-protective stage, the oxidation rate becomes linear, while the protective oxide film turns into a deteriorated white scale. Breakaway is known as the transition point from protective to non-protective stage. The actual mechanism leading to breakaway of zirconium is still a matter of controversy, however some of the most common factors affecting breakaway are the following: - Impurities on the metal (Carbon, Oxygen, Nitrogen); - Oxidizing atmosphere (Presence of H{sub 2}O (g) or N{sub 2} (g)); - Sample preparation (Chemically etched or polished); - Temperature (LWR, LOCA). This research investigates the effect of temperature on 'breakaway' when zirconium is oxidized isothermally in steam for 60 min at 800 and 900 deg. C using thermogravimetric and optical microscopic imaging techniques. 1. Steam isothermal oxidations were performed on zirconium at 800 and 900 deg. C using a Thermogravimetric Analyzer (TGA). 2. Log-log plots of mass gain vs time were obtained from thermogravimetric results to calculate the reaction orders (n) and reaction rate constants (K) during oxidation. 3. Results of the kinetics of reaction were correlated with optical microscopic images form Light Microscope (LM) and Scanning Electron Microscope (SEM). Breakaway depends very strongly on temperature. At 800 deg. C, the weight gain followed a cubic-parabolic behaviour with evidence of a protective oxide film. On the other hand, oxidation at 900 deg. C showed signs of breakaway since the oxide film was cracked and oxidation rate was almost linear throughout the reaction.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
An Automated Scanning Transmission Electron Microscope Guided by Sparse Data Analytics
Abstract Artificial intelligence (AI) promises to reshape scientific inquiry and enable breakthrough discoveries in areas such as energy storage, quantum computing, and biomedicine. Scanning transmission electron microscopy (STEM), a cornerstone of the study of chemical and materials systems, stands to benefit greatly from AI-driven automation. However, present barriers to low-level instrument control, as well as generalizable and interpretable feature detection, make truly automated microscopy impractical. Here, we discuss the design of a closed-loop instrument control platform guided by emerging sparse data analytics. We hypothesize that a centralized controller, informed by machine learning combining limited a priori knowledge and task-based discrimination, could drive on-the-fly experimental decision-making. This platform may unlock practical, automated analysis of a variety of material features, enabling new high-throughput and statistical studies.
47 OTHER INSTRUMENTATION↗
Minimising damage in high resolution scanning transmission electron microscope images of nanoscale structures and processes
Determining the optimum electron dose distribution for damage mitigated scanning transmission electron microscopy imaging using subsampling and image inpainting.
47 OTHER INSTRUMENTATION↗
Origin of organic matter and organic pores in the overmature Ordovician-Silurian Wufeng-Longmaxi Shale of the Sichuan Basin, China
Organic matter (OM)-hosted pores play important roles in controlling the porosity and gas content of gas shales. However, the control of organic pore development and preservation remains poorly understood, partly because of the inability to distinguish OM types under the scanning electron microscope (SEM). In this study, seven over-mature Wufeng-Longmaxi Shale samples (equivalent vitrinite reflectance 1.93%–3.07%) were investigated with organic petrography and scanning electron microscope to study the origin of OM and development of organic pores in this black shale succession. Correlative light and electron microscopy was employed to examine pore development in individual macerals. Organic petrographic observations show that OM in these over-mature black shales is dominated by pyrobitumen and graptolites (> 90 vol.% of total OM based on point counting). Pyrobitumen mainly occurs as matrix bitumen in the fine-grained matrix, and also as a mixture with clay minerals and fossil cavity infillings. Vitrinite-like particles are minor constituents of OM in the Wufeng-Longmaxi Shale, and their average reflectance, reflectance distribution, and morphology suggest that they may be derived from graptolite fragments lacking diagnostic features and acritarchs. OM type critically controls the development of organic pores. Here, organic pores primarily occur in pyrobitumen, whereas other macerals are mostly non-porous when examined under the SEM. Results of this study provided important insights into OM thermal evolution and organic pore development in source-rock reservoirs, calling for a critical appraisal of OM in black shales with organic petrography in addition to SEM.
03 NATURAL GAS↗
An efficient instance segmentation approach for studying fission gas bubbles in irradiated metallic nuclear fuel
Abstract Gaseous fission products from nuclear fission reactions tend to form fission gas bubbles of various shapes and sizes inside nuclear fuel. The behavior of fission gas bubbles dictates nuclear fuel performances, such as fission gas release, grain growth, swelling, and fuel cladding mechanical interaction. Although mechanical understanding of the overall evolution behavior of fission gas bubbles is well known, lacking the quantitative data and high-level correlation between burnup/temperature and microstructure evolution blocks the development of predictive models and reduces the possibility of accelerating the qualification for new fuel forms. Historical characterization of fission gas bubbles in irradiated nuclear fuel relied on a simple threshold method working on low-resolution optical microscopy images. Advanced characterization of fission gas bubbles using scanning electron microscopic images reveals unprecedented details and extensive morphological data, which strains the effectiveness of conventional methods. This paper proposes a hybrid framework, based on digital image processing and deep learning models, to efficiently detect and classify fission gas bubbles from scanning electron microscopic images. The developed bubble annotation tool used a multitask deep learning network that integrates U-Net and ResNet to accomplish instance-level bubble segmentation. With limited annotated data, the model achieves a recall ratio of more than 90%, a leap forward compared to the threshold method. The model has the capability to identify fission gas bubbles with and without lanthanides to better understand the movement of lanthanide fission products and fuel cladding chemical interaction. Lastly, the deep learning model is versatile and applicable to the micro-structure segmentation of similar materials.
36 MATERIALS SCIENCE↗
Enabling the Acquisition of Electron Beam-Induced Current (EBIC) Images in Conventional SEM and STEM Instruments
Electron beam-induced current (EBIC) imaging is a well-established scanning electron microscope (SEM) technique used to analyze the behavior of microelectronic devices including solar cells. Recently, the application of EBIC imaging in an aberration-corrected scanning transmission electron microscope (STEM) has been demonstrated and offers great potential for the in situ study of electronic materials, correlating charge transport properties to atomic structural and elemental information. Here, this work presents two ways to implement EBIC imaging in conventional SEM and STEM systems: one relying on the instrument's inherent scanning and imaging electronics and the other involving third-party systems usually available in electron microscopes. The implementation of lock-in EBIC in systems equipped with a fast beam blanker is also described. In addition, this work shows and discusses the different mechanisms at play in EBIC imaging and their dependence on beam energy, sample impedance, and electrical measurement configuration, providing researchers with the basic information needed to apply the technique to their research.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Transport Simulations on Scanning Transmission Electron Microscope Images of Nanoporous Shale
Digital rock physics is an often-mentioned approach to better understand and model transport processes occurring in tight nanoporous media including the organic and inorganic matrix of shale. Workflows integrating nanometer-scale image data and pore-scale simulations are relatively undeveloped, however. In this paper, a workflow is demonstrated progressing from sample acquisition and preparation, to image acquisition by Scanning Transmission Electron Microscopy (STEM) tomography, to volumetric reconstruction to pore-space discretization to numerical simulation of pore-scale transport. Key aspects of the workflow include (i) STEM tomography in high angle annular dark field (HAADF) mode to image three-dimensional pore networks in µm-sized samples with nanometer resolution and (ii) lattice Boltzmann method (LBM) simulations to describe gas flow in slip, transitional, and Knudsen diffusion regimes. It is shown that STEM tomography with nanoscale resolution yields excellent representation of the size and connectivity of organic nanopore networks. In turn, pore-scale simulation on such networks contributes to understanding of transport and storage properties of nanoporous shale. Interestingly, flow occurs primarily along pore networks with pore dimensions on the order of tens of nanometers. Smaller pores do not form percolating pathways in the sample volume imaged. Apparent gas permeability in the range of 10−19 to 10−16 m2 is computed.
42 ENGINEERING↗
Controlling hydrocarbon transport and electron beam induced deposition on single layer graphene: Toward atomic scale synthesis in the scanning transmission electron microscope
Abstract Focused electron beam induced deposition (FEBID) is a direct write technique for depositing materials on a support substrate akin to 3D printing with an electron beam (e‐beam). Opportunities exist for merging this existing technique with aberration‐corrected scanning transmission electron microscopy to achieve molecular‐ or atomic‐level spatial precision. Several demonstrations have been performed using graphene as the support substrate. A common challenge that arises during this process is e‐beam‐induced hydrocarbon deposition, suggesting greater control over the sample environment is needed. Various strategies exist for cleaning graphene in situ. One of the most effective methods is to rapidly heat to high temperatures, for example, 600℃ or higher. While this can produce large areas of what appears to be atomically clean graphene, mobile hydrocarbons can still be present on the surfaces. Here, we show that these hydrocarbons are primarily limited to surface migration and demonstrate an effective method for interrupting the flow using e‐beam deposition to form corralled hydrocarbon regions. This strategy is effective for maintaining atomically clean graphene at high temperatures where hydrocarbon mobility can lead to substantial accumulation of unwanted e‐beam deposition.
36 MATERIALS SCIENCE↗
Parameters, Properties, and Process: Conditional Neural Generation of Realistic SEM Imagery Toward ML-Assisted Advanced Manufacturing
Abstract The research and development cycle of advanced manufacturing processes traditionally requires a large investment of time and resources. Experiments can be expensive and are hence conducted on relatively small scales. This poses problems for typically data-hungry machine learning tools which could otherwise expedite the development cycle. We build upon prior work by applying conditional generative adversarial networks (GANs) to scanning electron microscope (SEM) imagery from an emerging advanced manufacturing process, shear-assisted processing and extrusion (ShAPE). We generate realistic images conditioned on temper and either experimental parameters or material properties. In doing so, we are able to integrate machine learning into the development cycle, by allowing a user to immediately visualize the microstructure that would arise from particular process parameters or properties. This work forms a technical backbone for a fundamentally new approach for understanding manufacturing processes in the absence of first-principle models. By characterizing microstructure from a topological perspective, we are able to evaluate our models’ ability to capture the breadth and diversity of experimental scanning electron microscope (SEM) samples. Our method is successful in capturing the visual and general microstructural features arising from the considered process, with analysis highlighting directions to further improve the topological realism of our synthetic imagery.
36 MATERIALS SCIENCE↗