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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Study of Interfacial Interactions Using Thing Film Surface Modification: Radiation and Oxidation Effects in Materials

Interfaces play a key role in dictating the long-term stability of materials under the influence of radiation and high temperatures. For example, grain boundaries affect corrosion by way of providing kinetically favorable paths for elemental diffusion, but they can also act as sinks for defects and helium generated during irradiation. Likewise, the retention of high-temperature strength in nanostructured, oxide-dispersion strengthened steels depends strongly on the stoichiometric and physical stability of the (Y, Ti)-oxide particles/matrix interface under radiation and high temperatures. An understanding of these interfacial effects at a fundamental level is important for the development of materials for extreme environments of nuclear reactors. The goal of this project is to develop an understanding stability of interfaces by depositing thin films of materials on substrates followed by ion irradiation of the film-substrate system at elevated temperatures followed by post-irradiation oxidation treatments. Specifically, the research will be performed by depositing thin films of yttrium and titanium (~500 nm) on Fe-12%Cr binary alloy substrate. Y and Ti have been selected as thin-film materials because they form highly stable protective oxides layers. The Fe-12%Cr binary alloy has been selected because it is representative of ferritic steels that are widely used in nuclear systems. The absence of other alloying elements in this binary alloy would allow for a clearer examination of structures and compositions that evolve during high-temperature irradiations and oxidation treatments. The research is divided into four specific tasks: (1) sputter deposition of 500 nm thick films of Y and Ti on Fe-12%Cr alloy substrates, (2) ion irradiation of the film-substrate system with 2MeV protons to a dose of 2 dpa at temperatures of 300°C, 500°C, and 700°C, (3) oxidation of as-deposited and ion-irradiated samples in a controlled oxygen environment at 500°C and 700°C, (4) multi-scale computational modeling involving first- principle molecular dynamics (FPMD) and coarse-grained dissipative particle dynamics (DPD) approaches to develop theories underlying the evolution and stability of structures and phases. Samples from Tasks 1 to 3 (above) will be rigorously characterized and analyzed using scanning electron microscopy, Auger electron microscopy, x-ray diffraction, Rutherford back scatter spectroscopy, and transmission electron microscopy. Expected outcomes of the experimental work include a quantitative understanding film-substrate interface mixing, evolution of defects and other phases at the interface, interaction of interfaces with defects, and the ability of the Y and Ti films to mitigate irradiation-assisted oxidation.The aforementioned experimental work will be closely coupled with multi-scale molecular dynamics (MD) modeling to understand the reactions at the surface, the transport of oxidant through the thin film, and the stabilities of the deposited thin films under radiation and oxidation. Simulations of materials property changes under conditions of radiation and oxidation require multiple size domains and a different simulation scheme for each of these domains. This will be achieved by coupling the FPMD and coarse-grained kinetic Monte Carlo (KMC). This will enable the comparison of the results of each simulation approach with the experimental results.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A self-healing plastic ceramic electrolyte by an aprotic dynamic polymer network for lithium metal batteries

Abstract Oxide ceramic electrolytes (OCEs) have great potential for solid-state lithium metal (Li 0 ) battery applications because, in theory, their high elastic modulus provides better resistance to Li 0 dendrite growth. However, in practice, OCEs can hardly survive critical current densities higher than 1 mA/cm 2 . Key issues that contribute to the breakdown of OCEs include Li 0 penetration promoted by grain boundaries (GBs), uncontrolled side reactions at electrode-OCE interfaces, and, equally importantly, defects evolution (e.g., void growth and crack propagation) that leads to local current concentration and mechanical failure inside and on OCEs. Here, taking advantage of a dynamically crosslinked aprotic polymer with non-covalent –CH 3 ⋯CF 3 bonds, we developed a plastic ceramic electrolyte (PCE) by hybridizing the polymer framework with ionically conductive ceramics. Using in-situ synchrotron X-ray technique and Cryogenic transmission electron microscopy (Cryo-TEM), we uncover that the PCE exhibits self-healing/repairing capability through a two-step dynamic defects removal mechanism. This significantly suppresses the generation of hotspots for Li 0 penetration and chemomechanical degradations, resulting in durability beyond 2000 hours in Li 0 -Li 0 cells at 1 mA/cm 2 . Furthermore, by introducing a polyacrylate buffer layer between PCE and Li 0 -anode, long cycle life >3600 cycles was achieved when paired with a 4.2 V zero-strain cathode, all under near-zero stack pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Machine learning-based multidomain processing for texture-based image segmentation and analysis

Atomic and molecular resolved atomic force microscopy (AFM) images offer unique insights into materials' properties such as local ordering, molecular orientation, and topological defects, which can be used to pinpoint physical and chemical interactions occurring at the surface. Utilizing machine learning for extracting underlying physical parameters increases the throughput of AFM data processing and eliminates inconsistencies intrinsic to manual image analysis, thus enabling the creation of reliable frameworks for qualitative and quantitative evaluation of experimental data. Here, we present a robust and scalable approach to the segmentation of AFM images based on flexible pre-selected classification criteria. The usage of supervised learning and feature extraction allows us to retain the consideration of specific problem-dependent features (such as types of periodical structures observed in the images and the associated numerical parameters: spacing, orientation, etc.). We highlight the applicability of this approach for the segmentation of molecular resolved AFM images based on the crystal orientation of the observed domains, automated selection of boundaries, and collection of relevant statistics. Finally, we outline a general strategy for machine learning-enabled analysis of nanoscale systems exhibiting periodic order that could be applied to any analytical imaging technique

36 MATERIALS SCIENCE↗
DOE OSTI2020

The spore coat is essential for Bacillus subtilis spore resistance to pulsed light, and pulsed light treatment eliminates some spore coat proteins

Microbial surface contamination of equipment or of food contact material is a recurring problem in the food industry. Spore-forming bacteria are far more resistant to a wide variety of treatments than their vegetative forms. Understanding the mechanisms underlying decontamination processes is needed to improve surface decontamination strategies against endospores potentially at the source of foodborne diseases or food-spoilage. Pulsed light (PL) with xenon lamps delivers high-energy short-time pulses of light with wavelengths in the range 200 nm-1100 nm and a high UV-C fraction. Bacillus subtilis spores were exposed to either PL or to continuous UV-C. Gel electrophoresis and western blotting revealed elimination of various proteins of the spore coat, an essential outer structure that protects spores from a wide variety of environmental conditions and inactivation treatments. Proteomic analysis confirmed the elimination of some spore coat proteins after PL treatment. Transmission electron microscopy of PL treated spores revealed a gap between the lamellar inner spore coat and the outer spore coat. Overall, spores of mutant strains with defects in genes coding for spore coat proteins were more sensitive to PL than to continuous UV-C. This study demonstrates that radiations delivered by PL contribute to specific damage to the spore coat, and overall to spore inactivation. Keywords Decontamination, UV, proteins, proteomics, microscopy Journal Pre-proof

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Correlation Between Magnetization and Particle Size of CdS Nanostructures by Solvothermal Method

Micro- and nano-structures of CdS including microrods, nanoparticles, nanorods, microspheres, and nanosheets were prepared by solvothermal method using monoethanolamine (EA), ethylene glycol (EG), and ethylenediamine (EN) to act as a mixed and pure solvent at multiple Cd and S concentrations. X-ray diffraction (XRD) patterns have shown CdS micro- and nano-structures with hexagonal and wurtzite structures. Scanning electron microscopy (SEM) has depicted nanosheet existence, microsphere, and microrods of CdS at various volume ratios. Transmission electron microscopy (TEM) has shown nanorod existence and nanoparticles of CdS at various volume ratios. Optical properties have been investigated using UV-Vis. A vibrating sample magnetometer (VSM) has been used to measure the CdS nanoparticle ferromagnetism at ambient temperature. The saturation magnetization has exhibited 9.109 (10{sup −3} emu/g). The ferromagnetic properties of CdS are referred to their structural defects.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

X-Ray Scattering and Electron Microscopy Characterization

This research added to the understanding of p-type activation in GaN vertical transistors for power applications by identifying key defects which inhibit p-type activation. We also developed an approach to eliminate such defects with the appropriate annealing treatments. Additionally we addressed the limitations of GaN substrates used in the production of these devices and exploited the non-uniform distribution of substrate defects to better understand the relationship between device performance and defect density. Through this work, we also established how irregularities – step bunching and haze formation – during epitaxial growth are related to defects in the underlying substrates. Our charter was to work with several other teams to determine connections between defects and performance of GaN-based vertical transistors and have several presentations and publications as well as manuscripts and follow-up collaborations. The research at UCLA supported two full graduate students, one of whom is graduating this summer as well as three undergraduate students.

36 MATERIALS SCIENCE↗
DOE OSTI2016

I2 basal stacking fault as a degradation mechanism in reverse gate-biased AlGaN/GaN HEMTs

Here, we present the observation of a bias-induced, degradation-enhancing defect process in plasma-assisted molecular beam epitaxy grown reverse gate-biased AlGaN/GaN high electron mobility transistors (HEMTs), which is compatible with the current theoretical framework of HEMT degradation. Specifically, we utilize both conventional transmission electron microscopy and aberration-corrected transmission electron microscopy to analyze microstructural changes in not only high strained regions in degraded AlGaN/GaN HEMTs but also the extended gate-drain access region. We find a complex defect structure containing an I2 basal stacking fault and offer a potential mechanism for device degradation based on this defect structure. This work supports the reality of multiple failure mechanisms during device operation and identifies a defect potentially involved with device degradation.

Lang, A. C.↗
DOE OSTI2025

Molecular-resolution imaging of ice crystallized from liquid water by cryogenic liquid-cell TEM

Despite the ubiquity of ice, a molecular-resolution image of nanoscopic defects or microstructures in ice crystallized from liquid water has never been obtained. This is mainly due to the difficulties in preparing and preserving crystalline ice samples that can survive under high-resolution imaging conditions. Here, we report the stabilization and Å-resolution electron imaging of ice Ih crystallized from liquid water by developing cryogenic liquid-cell transmission electron microscopy (CRYOLIC-TEM). We combine lattice mapping with molecular dynamics simulations to reveal that ice formation is highly tolerant to nanoscale defects such as misoriented subdomains and trapped gas bubbles, which are stabilized by molecular-scale structural motifs. Importantly, bubble surfaces adopt low-energy nanofacets and create negligible strain fields in the surrounding crystal. These bubbles can dynamically nucleate, grow, migrate, dissolve, and coalesce under electron irradiation and be monitored in situ near a steady state. This work improves our understanding of water crystallization behaviors at a molecular spatial resolution.

Materials science↗
DOE OSTI2026

Identifying Decoherence Mechanisms in Superconducting Qubits through Advanced Materials Characterization

Although superconducting qubits have emerged as a leading technology platform for quantum computing through large improvements in device coherence times and gate fidelity in recent years, the presence of defects and impurities at the interfaces and surfaces in the constituent materials continue to limit performance and serve as a critical barrier in achieving scalable quantum systems. Understanding and eliminating these sources of quantum decoherence in superconducting qubit devices requires dedicated studies aimed at establishing robust structure-property relationships that will enable researchers to target and eliminate defects strategically. As part of the Superconducting Materials and Systems (SQMS) center, we have extensively employed state-of-the-art materials characterization techniques, including scanning/transmission electron microscopy, secondary ion mass spectrometry, atom probe tomography, x-ray diffraction, and x-ray photoelectron spectroscopy in conjunction with device measurements to elucidate such relationships. In this talk, I will discuss some of our recent findings, including linking atomic defects to microwave loss in surface oxides, linking impurities in the Josephson Junction to qubit parameters, and linking low temperature precipitates to device performance. By applying these insights, we have been able to strategically develop and implement mitigation strategies for reliable fabrication of high coherence superconducting qubits.

Murthy, A. [Fermilab] (ORCID:0000000176776866)↗
DOE OSTI2026

Identifying Decoherence Mechanisms in Superconducting Qubits through Advanced Materials Characterization

Although superconducting qubits have emerged as a leading technology platform for quantum computing through large improvements in device coherence times and gate fidelity in recent years, the presence of defects and impurities at the interfaces and surfaces in the constituent materials continue to limit performance and serve as a critical barrier in achieving scalable quantum systems. Understanding and eliminating these sources of quantum decoherence in superconducting qubit devices requires dedicated studies aimed at establishing robust structure-property relationships that will enable researchers to target and eliminate defects strategically. As part of the Superconducting Materials and Systems (SQMS) center, we have extensively employed state-of-the-art materials characterization techniques, including scanning/transmission electron microscopy, secondary ion mass spectrometry, atom probe tomography, x-ray diffraction, and x-ray photoelectron spectroscopy in conjunction with device measurements to elucidate such relationships. In this talk, I will discuss some of our recent findings, including linking atomic defects to microwave loss in surface oxides, linking impurities in the Josephson Junction to qubit parameters, and linking low temperature precipitates to device performance. By applying these insights, we have been able to strategically develop and implement mitigation strategies for reliable fabrication of high coherence superconducting qubits.

Murthy, A. [Fermilab] (ORCID:0000000176776866)↗
DOE OSTI2013

First-principles DFT+U modeling of defect behaviors in anti-ferromagnetic uranium mononitride

A series of point defects in uranium mononitride (UN) have been studied by first-principles DFT+U calculations. The influence of intrinsic defects on the properties of UN was explored by considering the anti-ferromagnetic (AFM) order along the [001] direction. Our results show that all the point defects lead to obvious volume swelling of UN crystal. Energetically, the interstitial nitrogen defect is the most favorable one among single-point defects in UN crystal with the formation energy of 4.539 eV, while the N-Frenkel pair becomes the most preferable one among double-point defects. The AFM order induces obvious electron spin polarization of uranium towards neighboring uranium atoms with opposite spin orientations in UN crystal.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Pyrolytic synthesis and characterization of N-doped carbon nanoflakes for electrochemical applications

Highlights: • Carbon nanoflakes doped with nitrogen were produced by a pyrolytic technique. • Quarternary, pyrrolic and pyridinic types of nitrogen are confirmed by XPS. • Nitrogen content depends on precursor used and temperature processed. • Specific surface area values decrease with increasing of synthesis duration. • N-doped carbon nanoflakes may be suitable for electrochemical applications. - Abstract: Nitrogen doped carbon nanoflakes, which are very important for many electrochemical applications, were synthesized by pyrolysis of nitrogen containing organic compounds over metal oxide template. Acetonitrile, pyridine and butylamine, which are of different volatility were tested as N-containing precursors. Morphology, structure and chemical composition of the as-synthesized materials were investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that materials are highly defective and consist of a few malformed graphene layers. X-ray photoelectron spectra reflect the dominant graphitic and pyridinic N-bonding configuration. It was also noted that specific surface area depends on the duration and temperature of the reaction. Increase in duration and temperature led to decrease of the specific surface area from 1000 to 160 m{sup 2}/g, 1170 to 210 m{sup 2}/g and 1180 to 480 m{sup 2}/g for acetonitrile, butylamine and pyridine precursors, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Variation of lattice constant and cluster formation in GaAsBi

We investigate the structural properties of GaAsBi layers grown by molecular beam epitaxy on GaAs at substrate temperatures between 220–315 °C. Irrespective of the growth temperature, the structures exhibited similar Bi compositions, and good overall crystal quality as deduced from X-Ray diffraction measurements. After thermal annealing at temperatures as low as 500 °C, the GaAsBi layers grown at the lowest temperatures exhibited a significant reduction of the lattice constant. The lattice variation was significantly larger for Bi-containing samples than for Bi-free low-temperature GaAs samples grown as a reference. Rutherford backscattering spectrometry gave no evidence of Bi diffusing out of the layer during annealing. However, dark-field and Z-contrast transmission electron microscopy analyses revealed the formation of GaAsBi clusters with a Bi content higher than in the surrounding matrix, as well as the presence of metallic As clusters. The apparent reduction of the lattice constant can be explained by a two-fold process: the diffusion of the excess As incorporated within As{sub Ga} antisites to As clusters, and the reduction of the Bi content in the GaAs matrix due to diffusion of Bi to GaAsBi clusters. Diffusion of both As and Bi are believed to be assisted by the native point defects, which are present in the low-temperature as-grown material.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electrical current leakage and open-core threading dislocations in AlGaN-based deep ultraviolet light-emitting diodes

Electrical current transport through leakage paths in AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) and their effect on LED performance are investigated. Open-core threading dislocations, or nanopipes, are found to conduct current through nominally insulating Al{sub 0.7}Ga{sub 0.3}N layers and limit the performance of DUV-LEDs. A defect-sensitive phosphoric acid etch reveals these open-core threading dislocations in the form of large, micron-scale hexagonal etch pits visible with optical microscopy, while closed-core screw-, edge-, and mixed-type threading dislocations are represented by smaller and more numerous nanometer-scale pits visible by atomic-force microscopy. The electrical and optical performances of DUV-LEDs fabricated on similar Si-doped Al{sub 0.7}Ga{sub 0.3}N templates are found to have a strong correlation to the density of these nanopipes, despite their small fraction (<0.1% in this study) of the total density of threading dislocations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Atomic defects in monolayer titanium carbide (Ti 3 C 2 T x ) MXene

Here, the 2D transition metal carbides or nitrides, or MXenes, are emerging as a group of materials showing great promise in lithium ion batteries and supercapacitors. Until now, characterization and properties of single-layer MXenes have been scarcely reported. Here, using scanning transmission electron microscopy, we determined the atomic structure of freestanding monolayer Ti 3 C 2 T x flakes prepared via the minimally intensive layer delamination method and characterized different point defects that are prevalent in the monolayer flakes. We determine that the Ti vacancy concentration can be controlled by the etchant concentration during preparation. Density function theory-based calculations confirm the defect structures and predict that the defects can influence the surface morphology and termination groups, but do not strongly influence the metallic conductivity. Using devices fabricated from single- and few-layer Ti 3 C 2 T x MXene flakes, the effect of the number of layers in the flake on conductivity has been demonstrated.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Damage buildup in Ar-ion-irradiated 3 C -SiC at elevated temperatures

Above room temperature, the accumulation of radiation damage in 3 C -SiC is strongly influenced by dynamic defect interaction processes and remains poorly understood. Here, we use a combination of ion channeling and transmission electron microscopy to study lattice disorder in 3 C -SiC irradiated with 500 keV Ar ions in the temperature range of 25–250 °C. Results reveal sigmoidal damage buildup for all the temperatures studied. For 150 °C and below, the damage level monotonically increases with ion dose up to amorphization. Starting at 200 °C, the shape of damage–depth profiles becomes anomalous, with the damage peak narrowing and moving to larger depths and an additional shoulder forming close to the ion end of range. As a result, damage buildup curves for 200 and 250 °C exhibit an anomalous two-step shape, with a damage saturation stage followed by rapid amorphization above a critical ion dose, suggesting a nucleation-limited amorphization behavior. Despite their complexity, all damage buildup curves are well described by a phenomenological model based on an assumption of a linear dependence of the effective amorphization cross section on ion dose. Here, in contrast to the results of previous studies, 3 C -SiC can be amorphized by bombardment with 500 keV Ar ions even at 250 °C with a relatively large dose rate of ~2×10 13 cm -2 s -1 , revealing a dominant role of defect interaction dynamics at elevated temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Carrier transport in graphite/Si{sub 3}N{sub 4}-nanobelt/PtIr Schottky barrier diodes

Understanding the roles of contacts and interfaces between metals and semiconductors is critically important for exploring nanostructure-based nanodevices. The present study shed some light on the dominated mechanism of size-dependent carrier transfer in the Schottky barrier diodes configured by the Pt-Ir/Si{sub 3}N{sub 4}-nanobelt/graphite (metal-semiconductor-metal (MSM)) sandwiched structure via a conductive atomic force microscopy using nanobelts with various thicknesses. The observed I-V behaviors suggested that the charge transports under the low and high biases were dominated by the reverse-biased Schottky barrier and space-charge-limited current (SCLC), respectively. The intermediate region between the low and high biases presented the transition between the Ohmic and SCLC behaviors, in which the ≡Si and =N dangling bonds acted as the defects within the Si{sub 3}N{sub 4} nanobelt surface are predominant in the charge transfer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Novel Y doped Bi{sub 2}WO{sub 6} photocatalyst: Hydrothermal fabrication, characterization and enhanced visible-light-driven photocatalytic activity for Rhodamine B degradation and photocurrent generation

Visible-light-driven (VLD) Yttrium (Y) ion doped Bi{sub 2}WO{sub 6} photocatalyst has been synthesized via a facile hydrothermal route. Incorporation of Y{sup 3} {sup +} into Bi{sub 2}WO{sub 6} lattice was successfully confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ICP analysis. The microstructure and optical property of the as-prepared samples have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherm and UV–vis diffuse reflectance spectra (DRS). The photocatalytic experiments indicated that the Y-Bi{sub 2}WO{sub 6} showed a much higher photocatalytic activity than the pristine Bi{sub 2}WO{sub 6} for the degradation of Rhodamine B (RhB) and photocurrent (PC) generation. This enhancement should be ascribed to the slightly increased band gap and the generated defects by Y{sup 3} {sup +} doping, thus resulting in a much lower recombination rate of the photoinduced electrons and holes. Such a process was verified by the photoluminescence (PL) spectroscopy. In addition, the active species trapping experiments indicated that holes (h{sup +}) and superoxide radicals (·O{sub 2}{sup −}) play important roles in the photocatalytic reaction. - Highlights: • Novel Y-Bi{sub 2}WO{sub 6} photocatalyst has been synthesized by a facile hydrothermal route. • Y-Bi{sub 2}WO{sub 6} exhibits a much higher photocatalytic activity than pristine Bi{sub 2}WO{sub 6}. • Holes (h{sup +}) and superoxide radicals (·O{sub 2}{sup −}) are the two main active species. • Y{sup 3} {sup +} ion can result in a low recombination of photogenerated electron and hole.

36 MATERIALS SCIENCE↗