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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.

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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Deactivation of Cu-Exchanged Automotive-Emission NH 3 -SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X-ray Microscopy

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NO x with an ammonia reductant, we employed scanning transmission X-ray microscopy (STXM) to study Cu-exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000-mile aging. X-ray absorption near-edge structure (XANES) measurements were performed at the Al K- and Cu L-edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi-factor-induced catalytic deactivation. In Cu-exchanged MFI, a transformation of Cu II to Cu I and Cu x O y was observed. We also found a spatial correlation between extra-framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of CuI and tri-coordinated Al. By inspecting both Al and Cu in fresh and aged Cu-exchanged zeolites, we conclude that the importance of the preservation of isolated Cu II sites trumps that of Brønsted acid sites for NH 3 -SCR activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The Role of Gas in Determining Image Quality and Resolution During In Situ Scanning Transmission Electron Microscopy Experiments

As gas-solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomic scale characterization under realistic operating conditions. While atomic resolution imaging has become a routine in modern high-vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade when reaction gases are introduced. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelastic scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. We demonstrate the application of the ESTEM with atomic resolution images of a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Micro‐ and Nanoscale Heterogeneities in Zeolite Beta as Measured by Atom Probe Tomography and Confocal Fluorescence Microscopy

Micro- and nanoscale information on the activating and deactivating coking behaviour of zeolite catalyst materials increases our current understanding of many industrially applied processes, such as the methanol-to-hydrocarbon (MTH) reaction. Atom probe tomography (APT) was used to reveal the link between framework and coke elemental distributions in 3D with sub-nanometre resolution. APT revealed 10–20 nanometre-sized Al-rich regions and short-range ordering (within nanometres) between Al atoms. With confocal fluorescence microscopy, it was found that the morphology of the zeolite crystal as well as the secondary mesoporous structures have a great effect on the microscale coke distribution throughout individual zeolite crystals over time. Additionally, a nanoscale heterogeneous distribution of carbon as residue from the MTH reaction was determined with carbon-rich areas of tens of nanometres within the zeolite crystals. Finally, a short length-scale affinity between C and Al atoms, as revealed by APT, indicates the formation of carbon-containing molecules next to the acidic sites in the zeolite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

In-Situ Characterization of Dynamic Morphological and Phase Changes of Selenium-doped Germanium Using a Single Particle Cell and Synchrotron Transmission X-ray Microscopy

The dynamic information of lithium-ion battery active materials obtained from coin cell-based in-situ characterizations might not represent the properties of the active material itself because many other factors in the cell could have impacts on the cell performance. To address this problem, a single particle cell was developed to perform the in-situ characterization without the interference of inactive materials in the battery electrode as well as the X-ray-induced damage. In this study, the dynamic morphological and phase changes of selenium-doped germanium (Ge 0.9 Se 0.1 ) at the single particle level were investigated via synchrotron-based in-situ transmission X-ray microscopy. The results demonstrate the good reversibility of Ge 0.9 Se 0.1 at high cycling rate that helps understand its good cycling performance and rate capability. This in-situ and operando technique based on a single particle battery cell provides an approach to understanding the dynamic electrochemical processes of battery materials during charging and discharging at the particle level.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Nanoscale properties of lead halide perovskites by scanning tunneling microscopy

Since the introduction of lead halide perovskites, tremendous progress has been made regarding their stability, reproducibility and durability. However, one of the issues that remains is related to the interfacial atomic structure arrangement and structure-property relationship under optical and electrical stimuli. In this critical review, we highlight the recent progress using scanning tunneling microscopy (STM) to understand the nanoscale properties and dynamic processes occurring in these halide perovskite materials. STM is known to be a very challenging technique, which is reflected by the low number of relevant publications in the last years. These initial reports mirror the unique potential of STM to give Ångstrom-scale insight into the (opto)-electronic properties, morphology and underlying electronic structure and provide a path toward harnessing the full potential of these materials. However, care must be taken to understand the effects of the perturbations caused by STM and tailor the measurement conditions accordingly.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Measuring the dynamic response of the thylakoid architecture in plant leaves by electron microscopy

The performance of the photosynthesis machinery in plants, including light harvesting, electron transport, and protein repair is controlled by structural changes of the thylakoid membrane system inside the chloroplasts. In particular, the structure of the stacked grana area of thylakoid membranes is highly dynamic, changing in response to different environmental cues such as light intensity. For example, the aqueous thylakoid lumen enclosed by thylakoid membranes in grana has been documented to swell in the presence of light. However, light-induced alteration of the stromal gap in the stacked grana (partition gap) and of the unstacked stroma lamellae have not been well characterized. Light-induced changes of the entire thylakoid membrane system including the lumen in both stacked and unstacked domains as well as the partition gap are presented here, and the functional implications are discussed. This structural analysis was made possible by development of a robust semi-automated image analysis method combined with optimized plant tissue fixation techniques for transmission electron microscopy generating quantitative structural results for the analysis of thylakoid ultrastructure.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Signal Origin of Electrochemical Strain Microscopy and Link to Local Chemical Distribution in Solid State Electrolytes

Electrochemical strain microscopy (ESM) is a distinguished method to characterize Li-ion mobility in energy materials with extremely high spatial resolution. The exact origin of the cantilever deflection when the technique is applied on solid state electrolytes (SSEs) is currently discussed in the literature. Under-standing local properties and influences on ion mobility in SSEs is of utmost importance to improve such materials for next generation batteries. Here, the exact signal formation process of ESM when applied on sodium super ionic conductor (NASICON)-type SSE containing Na- and Li-ions is investigated. Changes in the dielectric properties, which are linked to the local chemical composition, are found to be responsible for the observed contrast in the deflection of the cantilever instead of a physical volume change as a result of Vegard´s Law. The cantilever response is strongly reduced in areas of high sodium content which is attributed to a reduction of the tip-sample capacitance in comparison to areas with high lithium content. This is the first time a direct link between electrostatic forces in contact mode and local chemical information is demonstrated on SSEs. Furthermore, the results open up new possibilities in information gain since dielectric proper-ties are sensitive to subtle changes in local chemical composition.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing the Mechanical Properties of 2D Materials via Atomic‐Force‐Microscopy‐Based Modulated Nanoindentation

Abstract As the field of low‐dimensional materials (1D or 2D) grows and more complex and intriguing structures are continuing to be found, there is an emerging need for techniques to characterize the nanoscale mechanical properties of all kinds of 1D/2D materials, in particular in their most practical state: sitting on an underlying substrate. While traditional nanoindentation techniques cannot accurately determine the transverse Young's modulus at the necessary scale without large indentations depths and effects to and from the substrate, herein an atomic‐force‐microscopy‐based modulated nanomechanical measurement technique with Angstrom‐level resolution (MoNI/ÅI) is presented. This technique enables non‐destructive measurements of the out‐of‐plane elasticity of ultra‐thin materials with resolution sufficient to eliminate any contributions from the substrate. This method is used to elucidate the multi‐layer stiffness dependence of graphene deposited via chemical vapor deposition and discover a peak transverse modulus in two‐layer graphene. While MoNI/ÅI has been used toward great findings in the recent past, here all aspects of the implementation of the technique as well as the unique challenges in performing measurements at such small resolutions are encompassed.

2D materials↗
DOE OSTI2025

Correlated X‐Ray and Electron Microscopies of a Single Biphasic GaAs Nanowire

Engineering the properties of semiconductors by changing their crystalline phase is a technologically and economically relevant alternative to doping using foreign elements, with strong potential for photonic and electronic applications. Although major advances have been reported recently for crystal‐phase engineering of III‐V and group IV semiconductor nanowires, interfacing two mismatched crystalline phases in a nanostructure induces several deformation mechanisms, which remain largely unexplored. Here, using state‐of‐the‐art synchrotron X‐ray nanobeam diffraction and transmission electron microscopy, subtle twisting and bending is unveiled within an individual GaAs nanowire containing cubic and hexagonal segments. Their role is discussed in accommodating the inter‐reticular spacing fluctuations, and their variations are correlated to the nanoscale phase distribution and to the effect of the NW support. This study brings direct evidence of a complex combination of deformation mechanisms in biphasic nanowires, which opens a new path to tune the nanowire properties with appealing perspectives for device engineering in nanophotonics and nanomechanics.

III-V semiconductors↗
DOE OSTI2024

A Machine Learning Approach to Quantitative Analysis of Enamel Microstructure from Scanning Electron Microscopy Images

Dental enamel, the outermost tissue of mammalian teeth, must withstand a lifetime of wear and cyclic contact. To meet this demand, enamel possesses a combination of high hardness and resistance to fracture, properties that are typically mutually exclusive. The impressive damage tolerance has been attributed largely to decussation of the enamel rods, the principal unit of its microstructure. As such, enamel is inspiring the design of next‐generation structural materials. However, quantitative descriptions of the decussated enamel rod microstructure remain limited due to challenges encountered in applying computed tomography and in acquiring quality images appropriate for traditional digital processing methods. Here, a machine learning segmentation method is applied to images of the enamel obtained using scanning electron microscopy to support quantitative analysis of the microstructure. A pretrained convolutional neural network is used to expand the input training image dataset to allow the training of a random forest classifier, which ultimately segments the image with a very small training set ( n = 3 images). A validation of this segmentation method is presented, in addition to its application to calculate relevant microstructural parameters for images of tooth enamel from selected mammalian species. The methodology applied here is equally applicable to other hard tissues.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High-Resolution Imaging of Cellulose Organization in Cell Walls by Field Emission Scanning Electron Microscopy

Field emission scanning electron microscopy (FESEM) is a powerful tool for analyzing surface structures of biological and nonbiological samples. However, when it is used to study fine structures of nanometer-sized microfibrils of epidermal cell walls, one often encounters tremendous challenges to acquire clear and undistorted images because of two major issues: (1) Preparation of samples suitable for high resolution imaging; due to the delicateness of some plant materials, such as onion epidermal cell walls, many things can happen during sample processing, which subsequently result in damaged samples or introduce artifacts. (2) Difficulties to acquire clear images of samples which are electron-beam sensitive and prone to charging artifacts at magnifications over 100,000×. In this chapter we described detailed procedures for sample preparation and conditions for high-resolution FESEM imaging of onion epidermal cell walls. Lastly, the methods can be readily adapted for other wall materials.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Characterizing the Number of Kinesin Motors Bound to Microtubules in the Gliding Motility Assay Using FLIC Microscopy [Book Chapter]

Intracellular transport by kinesin motors moving along their associated cytoskeletal filaments, microtubules, is essential to many biological processes. This active transport system can be reconstituted in vitro with the surface-adhered motors transporting the microtubules across a planar surface. In this geometry, the kinesin-microtubule system has been used to study active self-assembly, to power microdevices, and to perform analyte detection. Fundamental to these applications is the ability to characterize the interactions between the surface tethered motors and microtubules. Further, Fluorescence Interference Contrast (FLIC) microscopy can illuminate the height of the microtubule above a surface, which, at sufficiently low surface densities of kinesin, also reveals the number, locations, and dynamics of the bound motors.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Analytical methods for superresolution dislocation identification in dark-field X-ray microscopy

In this work, we develop several inference methods to estimate the position of dislocations from images generated using dark-field X-ray microscopy (DFXM)—achieving superresolution accuracy and principled uncertainty quantification. Using the framework of Bayesian inference, we incorporate models of the DFXM contrast mechanism and detector measurement noise, along with initial position estimates, into a statistical model coupling DFXM images with the dislocation position of interest. We motivate several position estimation and uncertainty quantification algorithms based on this model. We then demonstrate the accuracy of our primary estimation algorithm on synthetic realistic DFXM images of edge dislocations in single-crystal aluminum. We conclude with a discussion of our methods’ impact on future dislocation studies and possible future research avenues.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Characterization of Two Fast-Turnaround Dry Dilution Refrigerators for Scanning Probe Microscopy

Low-temperature scanning probe microscopes (SPMs) are critical for the study of quantum materials and quantum information science. Due to the rising costs of helium, cryogen-free cryostats have become increasingly desirable. However, they typically suffer from comparatively worse vibrations than cryogen-based systems, necessitating the understanding and mitigation of vibrations for SPM applications. Here, in this work, we demonstrate the construction of two cryogen-free dilution refrigerator SPMs with minimal modifications to the factory default and we systematically characterize their vibrational performance. We measure the absolute vibrations at the microscope stage with geophones and use both microwave impedance microscopy and a scanning single-electron transistor to independently measure tip-sample vibrations. Additionally, we implement customized filtering and thermal anchoring schemes and characterize the cooling power at the scanning stage and the tip electron temperature. This work serves as a reference to researchers interested in cryogen-free SPMs, as such characterization is not standardized in the literature or available from manufacturers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

3D Microscopy to Assess the Effect of High Temperature Cyclic Oxidation on the Deformation of Cast and ODS FeCrAlY Alloys

Specimen deformation, oxide scale growth, and scale cracking were monitored for cyclic oxidation exposures at 1200 °C of three cast FeCrAlY(Hf) alloys and two oxide dispersion strengthened (ODS) FeCrAl alloys. Evolution of both the specimen geometry and surface deformation was quantified using 3D optical microscopy. The stress in the alumina scale was also measured using photo-stimulated luminescence piezospectroscopy. The goal was to examine the effect of stress generation and stress relaxation on scale spallation for FeCrAl materials with drastic differences in terms of high temperature strengths. After 1000, 1-h cycles, the cast alloys exhibited significant deformation with a convoluted oxide scale, leading for the two Hf-free FeCrAlY alloys to undergo crack formation and spallation. For the Hf-containing FeCrAlY, limited spallation was observed due to the localization of spallation at grain boundaries, the large grain structure, and the beneficial effect of Hf on scale adhesion. On the other hand, limited deformation was measured for the ODS FeCrAl alloys, with minimal cracking and scale spallation for alloy PM2000 after 1000 h. A higher spallation rate was observed for ODS MA956, which was attributed to a high defect concentration in the alumina scale that formed. The mechanisms leading to spallation during cyclic oxidation for the cast and ODS FeCrAlY alloys are described.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structure of polystyrene latex particles determined by electron microscopy

The structures of individual polystyrene microspheres obtained in the presence of organosilicon surfactants were studied by transmission electron microscopy. The density of the macro-molecule distribution over the cross section of particles was determined. The synthesized latex particles have a core—shell structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

High-Resolution Electron Microscopy Investigations of Structure and Morphology of Cadmium Selenide Nanocrystals

The paper presents high-resolution electron microscopy investigations of the structure and morphology of cadmium selenide nanocrystals and nanoplatelets, and nanoplatelets having cadmium selenide core/crown nanostructure. These nanocrystals and nanoplatelets are obtained by the colloid technology and are deposited onto carbon substrates using the Langmuir–Blodgett method. It is shown that two-dimensional structures of nanocrystals and nanoplatelets can be formed on carbon substrates. The quantity specifications of these structures are determined in this paper.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Direct Observation of Pure Cu and Cu-Ag Anode Passivation in H{sub 2}SO{sub 4}-CuSO{sub 4} Aqueous Solution by Channel Flow Double Electrode and Optical Microscopy

The dissolution and passivation of pure Cu and Cu-5 wt pct Ag anodes in H{sub 2}SO{sub 4}-CuSO{sub 4} electrolyte were investigated by a direct observation method that combined the techniques of optical microscopy and channel flow double electrode. Linear sweep voltammetry of the anodes showed that the dissolution of Cu transited from the charge transfer-controlled reaction to the mass transfer-controlled reaction, followed by the passivation of the electrodes. The direct observation of the pure Cu anode revealed that Cu particles were generated on the surface and the particles fell away during passivation. On the other hand, a slime layer of Ag particles that adhered to the surface was generated during the dissolution of the Cu-5 wt pct Ag anode. The Cu-5 wt pct Ag anode was passivated with a lower current density than the pure Cu anode, which suggested that the morphology and adhesive characteristics of the slime on the anode affected the passivation. The direct observation method described herein is useful for understanding reactions on electrodes that undergo drastic changes in their surface morphology. Information obtained from this method can help with the development of new processes for the effective utilization of limited natural resources and energy, such as the recycling of Cu by electrorefining.

36 MATERIALS SCIENCE↗