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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Dynamics of Polymer Nanocapsule Buckling and Collapse Revealed by In Situ Liquid-Phase TEM

Nanocapsules are hollow nanoscale shells that have applications in drug delivery, batteries, self-healing materials, and as model systems for naturally occurring shell geometries. In many applications, nanocapsules are designed to release their cargo as they buckle and collapse, but the details of this transient buckling process have not been directly observed. In this work, we use in situ liquid-phase transmission electron microscopy to record the electron-irradiation-induced buckling in spherical 60-187 nm polymer capsules with ~3.5 nm walls. We observe in real time the release of aqueous cargo from these nanocapsules and their buckling into morphologies with single or multiple indentations. The in situ buckling of nanoscale capsules is compared to ex situ measurements of collapsed and micrometer-sized capsules and to Monte Carlo (MC) simulations. The shape and dynamics of the collapsing nanocapsules are consistent with MC simulations, which reveal that the excessive wrinkling of nanocapsules with ultrathin walls results from their large Föppl-von Kármán numbers around 10 5 . Our experiments suggest design rules for nanocapsules with the desired buckling response based on parameters such as capsule radius, wall thickness, and collapse rate.

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

In Situ TEM Study of Radiation Resistance of Metallic Glass–Metal Core–Shell Nanocubes

Radiation damage can cause significantly more surface damage in metallic nanostructures than bulk materials. Structural changes from displacement damage compromise the performance of nanostructures in radiation environments such as nuclear reactors and outer space, or used in radiation therapy for biomedical treatments. As such, it is important to develop strategies to prevent this from occurring if nanostructures are to be incorporated into these applications. In this work, in situ transmission electron microscope ion irradiation was used to investigate whether a metallic glass (MG) coating mitigates sputtering and morphological changes in metallic nanostructures. Dislocation-free Au nanocubes and Au nanocubes coated with a Ni–B MG were bombarded with 2.8 MeV Au 4+ ions. The formation of internal defects in bare Au nanocubes was observed at a fluence of 7.5 × 10 11 ions/cm 2 (0.008 dpa), and morphological changes such as surface roughening, rounding of corners, and formation of nanofilaments began at 4 × 10 12 ions/cm 2 (0.04 dpa). In contrast, the Ni–B MG-coated Au nanocubes (Au@NiB) showed minimal morphological changes at a fluence of 1.9 × 10 13 ions/cm 2 (0.2 dpa). Finally, the MG coating maintains its amorphous nature under all irradiation conditions investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Facile hermetic TEM grid preparation for molecular imaging of hydrated biological samples at room temperature

Abstract Although structures of vitrified supramolecular complexes have been determined at near-atomic resolution, elucidating in situ molecular structure in living cells remains a challenge. Here, we report a straightforward liquid cell technique, originally developed for real-time visualization of dynamics at a liquid-gas interface using transmission electron microscopy, to image wet biological samples. Due to the scattering effects from the liquid phase, the micrographs display an amplitude contrast comparable to that observed in negatively stained samples. We succeed in resolving subunits within the protein complex GroEL imaged in a buffer solution at room temperature. Additionally, we capture various stages of virus cell entry, a process for which only sparse structural data exists due to their transient nature. To scrutinize the morphological details further, we used individual particle electron tomography for 3D reconstruction of each virus. These findings showcase this approach potential as an efficient, cost-effective complement to other microscopy technique in addressing biological questions at the molecular level.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Platinum nanoparticle compression: Combining in situ TEM and atomistic modeling

The mechanical behavior of nanoparticles governs their performance and stability in many applications. However, the small sizes of technologically relevant nanoparticles, with diameters in the range of 10 nm or less, significantly complicate experimental examination. These small nanoparticles are difficult to manipulate onto commercial test platforms and deform at loads that are below the typical noise floor of the testing instruments. Here, we synthesized small platinum nanoparticles directly onto a mechanical tester and used a modified nanomanipulator to enhance load resolution to the nanonewton scale. We demonstrated the in situ compression of an 11.5-nm platinum nanoparticle with simultaneous high-resolution measurements of load and particle morphology. Molecular dynamics simulations were performed on similarly sized particles to achieve complementary measurements of load and morphology, along with atomic resolution of dislocations. The experimental and simulation results revealed comparable values for the critical resolved shear stress for failure, 1.28 and 1.15 GPa, respectively. Altogether, this investigation demonstrated the promise of, and some initial results from, the combination of atomistic simulations and in situ experiments with an unprecedented combination of high spatial resolution and high load resolution to understand the behavior of metal nanoparticles under compression.

42 ENGINEERING↗
DOE OSTI2024

The self-annealing of irradiation induced defects in magnetite Fe 3 O 4 : Revealing reversible irradiation-induced disorder transformation through in situ TEM

This work reports heavy ion-irradiation effects in polycrystalline Fe 3 O 4 . For this matter, Fe/Fe 3 O 4 heterostructures were irradiated in situ in a transmission electron microscopy with 1 MeV Kr ions at 50 K. Evidence of cubic to monoclinic transformation (a.k.a Verwey transition) was recorded in some magnetite grains upon cooling the sample (around 90 K); however, most of the oxide grains retain their cubic spinel structure. Irradiation effects were analyzed in the cubic phase up to a maximum dose of 38 dpa without the sign of amorphization. The extinction of first-order reflections was recorded at doses below 1 dpa, indicating the formation of a new (metastable) phase with half of the lattice parameters compared to the unirradiated Fe 3 O 4 crystal. The formation of the new crystalline phase, which also presents a high resistance to amorphization, is related to the disordering of the cation lattice and the high mobility of the cation interstitials. The metastable phase readily recovers around 225 K during the natural warming of the sample from 50 K to room temperature.

Atom irradiation effects↗
DOE OSTI2025

Ultracold cryogenic TEM with liquid helium and high stability

Cryogenic transmission electron microscopy has revolutionized structural biology and materials science. To image below liquid nitrogen temperatures, various liquid helium stages have been constructed but have proven to be complex and unstable, making high-resolution imaging challenging. This problem is even more pronounced in side-entry specimen holders common on modern transmission electron microscopes. Here, we introduce an ultracold liquid helium transmission electron microscope side-entry specimen holder, featuring continuous cryogen flow and vibration decoupling. This instrument is compatible with modern aberration-corrected microscopes and achieves sub-25 K base temperature, ±2 mK thermal stability over many hours, and atomic resolution—setting the stage for a new era of cryogenic electron microscopy.

42 ENGINEERING↗
DOE OSTI2025

Tiny Bubbles: Combined HR(S)TEM and 4D-STEM Analysis of Sub-Nanometer He Bubbles in Au

Irradiation produces a distribution of defect sizes in materials, with the smallest defects often below one nanometer in size and approaching the scale of a single unit cell in metals. While high-resolution scanning transmission electron microscopy (STEM)-based imaging can directly image structures at this level, techniques such as four-dimensional STEM (4D-STEM) enable characterization of materials across large fields of view, capturing a more representative volume that can be valuable for quantifying defects, their distributions, and the associated strain fields. Here we present a combined HRSTEM and 4D-STEM approach to study the model system of He bubble implantation in an Au thin film. The present work is of general interest for the study of materials in extreme environments, as it demonstrates an effective way to characterize even the tiniest sub-nanometer sized He bubbles in addition to larger irradiation defects.

atomic-resolution STEM↗
DOE OSTI2023

Lessons Learned Using in-situ TEM Liquid Corrosion of Al Alloys

Al and Al alloys are of interest in energy applications due to their strength and low weight [1] in addition to their electrochemical properties for aluminum-air batteries for energy storage [2]. However, Al alloys also are susceptible to corrosion in a variety of environments including liquid electrolytes and in solar panels [3], which has led to a great deal of research to understand and improve corrosion resistance in these materials. Al metal forms a native, passivating oxide layer in the presence of ambient air, which slows corrosion initiation. However, pitting still occurs as this protective layer breaks down in the presence of electrolytes. Thin metal Al films were used in these experiments to observe initiation and growth of pitting, which can be used as an approximation of corrosion initiation behavior in bulk samples.

alluminum alloys↗