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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Computer simulation of the Farley-Buneman instability and anomalous electron heating in the auroral ionosphere

The nonlinear saturation of the Farley-Buneman instability in a collisional plasma is studied by a 2 1/2 dimensional electrostatic particle simulation which includes inelastic and elastic collisions of electrons and elastic collision of ions with neutrals. In the simulation, a uniform convection electric field is applied externally so that the relative velocity between the electrons and ions is greater than the ion sound speed and destabilizes the instability. A nonlinear frequency shift from higher to lower frequencies and diffusion of the wave spectrum in two dimensional wave number space are found. It is found that the dominant mechanism for electron heating is due to an enhanced effective electron collision frequency and hence enhanced resistive heating as suggested by Primdahl (1986) and not due to the heating of electrons by the electric field of the waves parallel to the magnetic field. For the ionospheric conditions discussed by Schlegel and St.-Maurice (1981)an anomalous heating rate of about 4 x 10 to the 7th W/cu cm is found.

Machida, S.↗
DOE OSTI2023

Effect of Molecular Weight on the Morphology of a Polymer Semiconductor–Thermoplastic Elastomer Blend

Abstract Polymer semiconductors (PSCs) are essential active materials in mechanically stretchable electronic devices. However, many exhibit low fracture strain due to their rigid chain conformation and the presence of large crystalline domains. Here, a PSC/elastomer blend, poly[((2,6‐bis(thiophen‐2‐yl)‐3,7‐bis(9‐octylnonadecyl)thieno[3,2‐b]thieno[2′,3′:4,5]thieno[2,3‐d]thiophene)‐5,5′‐diyl)(2,5‐bis(8‐octyloctadecyl)‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione)‐5,5′‐diyl]] (P2TDPP2TFT4) and polystyrene‐ block ‐poly(ethylene‐ran‐butylene)‐ block ‐polystyrene (SEBS) are systematically investigated. Specifically, the effects of molecular weight of both SEBS and P2TDPP2TFT4 on the resulting blend morphology, mechanical, and electrical properties are explored. In addition to commonly used techniques, atomic force microscopy‐based nanomechanical images are used to provide additional insights into the blend film morphology. Opposing trends in SEBS‐induced aggregation are observed for the different P2TDPP2TFT4 molecular weights upon increasing the SEBS molecular weight from 87 to 276 kDa. Furthermore, these trends are seen in device performance trends for both molecular weights of P2TDPP2TFT4. SEBS molecular weight also has a substantial influence on the mesoscale phase separation. Strain at fracture increases dramatically upon blending, reaching a maximum value of 640% ± 20% in the blended films measured with film‐on‐water method. These results highlight the importance of molecular weight for electronic devices. In addition, this study provides valuable insights into appropriate polymer selections for stretchable semiconducting thin films that simultaneously possess excellent mechanical and electrical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Aromatic Amide Foldamers Show Conformation‐Dependent Electronic Properties

Electron transport in organic molecules and biomolecules is governed by electronic structure and molecular conformations. Despite recent progress, key challenges remain in understanding the role of intramolecular interactions and three-dimensional (3D) conformations on the electron transport behavior of organic molecules. In this work, the electronic properties of aromatic amide foldamers are characterized that organize into distinct 3D structures, including an extended secondary amide that adopts a trans-conformation and a folded N-methylated tertiary amide that adopts a cis-conformation. Results from single-molecule electronic experiments show that the extended secondary amide exhibits a fourfold enhancement in molecular conductance compared to the folded N-methylated tertiary amide, despite a longer contour length. The results show that extended amide molecules are governed by a through-bond electron transport mechanism, whereas folded amide molecules are dominated by through-space transport. Bulk spectroscopic characterization and density functional theory calculations further reveal that extended amides have a smaller HOMO–LUMO gap and larger transmission values compared to folded amides, consistent with single-molecule electronic experiments. Overall, this work shows that 3D molecular conformations significantly influence the electronic properties of single-molecule junctions.

electron transport↗
DOE OSTI2024

Dynamic mode decomposition of nonequilibrium electron-phonon dynamics: accelerating the first-principles real-time Boltzmann equation

Abstract Nonequilibrium dynamics governed by electron–phonon ( e -ph) interactions plays a key role in electronic devices and spectroscopies and is central to understanding electronic excitations in materials. The real-time Boltzmann transport equation (rt-BTE) with collision processes computed from first principles can describe the coupled dynamics of electrons and atomic vibrations (phonons). Yet, a bottleneck of these simulations is the calculation of e –ph scattering integrals on dense momentum grids at each time step. Here we show a data-driven approach based on dynamic mode decomposition (DMD) that can accelerate the time propagation of the rt-BTE and identify dominant electronic processes. We apply this approach to two case studies, high-field charge transport and ultrafast excited electron relaxation. In both cases, simulating only a short time window of ~10% of the dynamics suffices to predict the dynamics from initial excitation to steady state using DMD extrapolation. Analysis of the momentum-space modes extracted from DMD sheds light on the microscopic mechanisms governing electron relaxation to a steady state or equilibrium. The combination of accuracy and efficiency makes our DMD-based method a valuable tool for investigating ultrafast dynamics in a wide range of materials.

36 MATERIALS SCIENCE↗
NASA NTRS1993

A comprehensive analysis of electron conical distributions from multi-satellite databases

This report consists of a copy of a paper that has been submitted to the 'Journal of Geophysical Research', entitled 'DE 1 and Viking Observations Associated With Electron Conical Distributions,' and an abstract of another paper (included as an appendix to the report) that is about to be submitted to the same journal entitled 'Perpendicular Electron Heating by Absorption of Auroral Kilometric Radiation.' A bibliography of other papers that have been published as a result of this project follows. The purpose of this project was to use the DE 1 and Viking particle and wave data to better understand the source mechanism of electron conical distributions. We have shown that electron conics are often associated with upper hybrid waves in the nightside auroral region. We have also shown that electron conics are observed near auroral kilometric radiation (AKR) source regions and may be the result of perpendicular heating due to waves. We have completed a statistical study of electron conics observed by DE-l and Viking. The study shows the occurrence frequency and location of electron conical distributions; there are some differences between the results of DE and Viking perhaps due to different regions sampled.

Menietti, J. Douglas↗
NASA NTRS2018

Achieving Improved Reliability with Failure Analysis

Reliability is the ability of a product to properly function, within specified performance limits, for a specified period of time, under the life cycle application conditions. Failure analysis is a vital tool in the effort to ensure reliability of electronic products and systems throughout their product lifecycle. Today, organizations involved in activities within the electronics supply chain are facing new challenges, not just from complex assembly styles, harsher lifecycle environments, and sophisticated supply chains, but also from customers who are demanding a quicker turn-around. Unfortunately, root cause failure analysis is often performed incompletely, leading to a poor understanding of failure mechanisms and causes and, customer dissatisfaction due to recurring failures. The PDC starts with an introduction to reliability concepts, physics of failure and an overview of failure mechanisms that affect PCBs, PCBAs and components. The PDC then dives into root cause hypothesizing techniques (Pareto, FMEA, fishbone, FTA), non-destructive and destructive analysis and, materials characterization will be discussed. Numerous failure analysis case studies will be used to illustrate the techniques and analysis principles to arrive at the root cause(s) of field failures on printed circuit boards, active components, and assemblies. What Will You Learn: Topics include: Overview of Reliability Concepts Failure mechanisms of electronic products Root cause analysis Failure analysis techniques -Non-destructive techniques (optical, CSAM etc.) -Destructive analysis (DPA, Decap, FIB etc.) -Materials characterization (XRF, EDS, TMA/DSC etc.) Who Will Benefit: Reliability engineers, failure analysis engineers, engineering managers, design engineers, component engineers, quality assurance functions and, personnel involved with reliability activities within their company.

non-destructive techniques↗
NASA NTRS1979

Characteristics of the inverted-V event

An attempt is made to determine the origin of the inverted-V precipitating electrons and mechanisms that could create the inverted-V structure. The energy and pitch angle structures are compared with predictions from several theories that have been proposed to explain the origin of inverted-V events. Data from the AE-D satellite indicate that the origin of the inverted-V precipitating electrons is in the magnetosphere, the most probable regions being the plasma sheet and the neutral sheet. The energy and pitch angle distributions show that electrons are trapped between the mirror points and the electric field potential. The observations suggest that field-aligned precipitating electrons have been heated, probably when they were accelerated by the parallel electric field. Qualitatively, the detailed structures of the inverted-V events favor the theory of anomalous resistivity.

Lin, C. S.↗
NASA NTRS1983

Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

Kashkarov, P. K.↗
DOE OSTI2020

Quaternary Charge-Transfer Complex Enables Photoenzymatic Intermolecular Hydroalkylation of Olefins

Intermolecular C–C bond-forming reactions are underdeveloped transformations in the field of biocatalysis. Here we report a photoenzymatic intermolecular hydroalkylation of olefins catalyzed by flavin-dependent ‘ene’-reductases. Radical initiation occurs via photoexcitation of a rare high-order enzyme-templated charge-transfer complex that forms between an alkene, α-chloroamide, and flavin hydroquinone. This unique mechanism ensures that radical formation only occurs when both substrates are present within the protein active site. Here, this active site can control the radical terminating hydrogen atom transfer, enabling the synthesis of enantioenriched γ-stereogenic amides. This work highlights the potential for photoenzymatic catalysis to enable new biocatalytic transformations via previously unknown electron transfer mechanisms.

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

High strain rate nanoindentation testing: Recent advancements, challenges and opportunities

Recent advancements in electronics have renewed the interest in high strain rate nanoindentation testing, resulting in the development of new high strain rate nanoindentation test equipment and test methodologies. Here, in this work, the current state-of-the-art in high strain rate nanoindentation testing is critically reviewed, with focus on three key aspects - the testing equipment's dynamic mechanical and electronic response, test methodology, and post-processing of raw data to obtain hardness and strain rate. The challenges in instrument hardware design and post-test data analysis are discussed, along with optimal strain rate window for accurate high strain rate measurements. Specific focus will be on instrumented high strain rate testing using self-similar indenters at strain rates in excess of 100 s -1 , wherein load and depth of penetration into the sample are both measured or applied.

36 MATERIALS SCIENCE↗
NASA NTRS2010

Smart materials: strain sensing and stress determination by means of nanotube sensing systems, composites, and devices

The present invention is directed toward devices comprising carbon nanotubes that are capable of detecting displacement, impact, stress, and/or strain in materials, methods of making such devices, methods for sensing/detecting/monitoring displacement, impact, stress, and/or strain via carbon nanotubes, and various applications for such methods and devices. The devices and methods of the present invention all rely on mechanically-induced electronic perturbations within the carbon nanotubes to detect and quantify such stress/strain. Such detection and quantification can rely on techniques which include, but are not limited to, electrical conductivity/conductance and/or resistivity/resistance detection/measurements, thermal conductivity detection/measurements, electroluminescence detection/measurements, photoluminescence detection/measurements, and combinations thereof. All such techniques rely on an understanding of how such properties change in response to mechanical stress and/or strain.

Barrera, Enrique V.↗
DOE OSTI2022

Developing a Chemical and Structural Understanding of the Surface Oxide in a Niobium Superconducting Qubit

We report superconducting thin films of niobium have been extensively employed in transmon qubit architectures. Although these architectures have demonstrated remarkable improvements in recent years, further improvements in performance through materials engineering will aid in large-scale deployment. Here, we use information retrieved from secondary ion mass spectrometry and electron microscopy to conduct a detailed assessment of the surface oxide that forms in ambient conditions for transmon test qubit devices patterned from a niobium film. We observe that this oxide exhibits a varying stoichiometry with NbO and NbO 2 found closer to the niobium film and Nb 2 O 5 found closer to the surface. In terms of structural analysis, we find that the Nb 2 O 5 region is semicrystalline in nature and exhibits randomly oriented grains on the order of 1-2 nm corresponding to monoclinic N-Nb 2 O 5 that are dispersed throughout an amorphous matrix. Using fluctuation electron microscopy, we are able to map the relative crystallinity in the Nb 2 O 5 region with nanometer spatial resolution. Through this correlative method, we observe that amorphous regions are more likely to contain oxygen vacancies and exhibit weaker bonds between the niobium and oxygen atoms. Based on these findings, we expect that oxygen vacancies likely serve as a decoherence mechanism in quantum systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Influence of Electronic Polarization on the Spectral Density

Accurate spectral densities are necessary for computing realistic exciton dynamics and nonlinear optical spectra of chromophores in condensed-phase environments, including multichromophore pigment–protein systems. However, due to the significant computational cost of computing spectral densities from first principles, requiring many thousands of excited-state calculations, most simulations of realistic systems rely on treating the environment as fixed-point charges. In this work, using a number of representative systems ranging from solvated chromophores to the photoactive yellow protein (PYP), we demonstrate that the quantum mechanical (QM) electronic polarization of the environment is key to obtaining accurate spectral densities and line shapes within the cumulant framework. We show that the QM environment can enhance or depress the coupling of fast chromophore degrees of freedom to the energy gap, altering the electronic–vibrational coupling and the resulting vibronic progressions in the absorption spectrum. In analyzing the physical origin of peaks in the spectral density, we identify vibrational modes that couple the electron and the hole as being particularly sensitive to the QM screening of the environment. For PYP, we reveal the need for careful determination of the appropriate QM region to obtain reliable spectral densities. Our findings suggest that the QM polarization of the environment can be crucial not just for excitation energies but also for electronic–vibrational coupling in complex systems with implications for the correct modeling of linear and nonlinear optical spectroscopy in the condensed phase as well as energy transfer in pigment–protein complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1989

Characterization of quantum well structures using a photocathode electron microscope

Present day integrated circuits pose a challenge to conventional electronic and mechanical test methods. Feature sizes in the submicron and nanometric regime require radical approaches in order to facilitate electrical contact to circuits and devices being tested. In addition, microwave operating frequencies require careful attention to distributed effects when considering the electrical signal paths within and external to the device under test. An alternative testing approach which combines the best of electrical and optical time domain testing is presented, namely photocathode electron microscope quantitative voltage contrast (PEMQVC).

Spencer, Michael G.↗
DOE OSTI2022

Bandgap analysis and carrier localization in cation-disordered ZnGeN 2

The bandgap of ZnGeN 2 changes with the degree of cation site disorder and is sought in light emitting diodes for emission at green to amber wavelengths. By combining the perspectives of carrier localization and defect states, we analyze the impact of different degrees of disorder on electronic properties in ZnGeN 2 , addressing a gap in current studies, which largely focus on dilute or fully disordered systems. The present study demonstrates changes in the density of states and localization of carriers in ZnGeN 2 calculated using bandgap-corrected density functional theory and hybrid calculations on partially disordered supercells generated using the Monte Carlo method. We use localization and density of states to discuss the ill-defined nature of a bandgap in a disordered material and identify site disorder and its impact on the structure as a mechanism controlling electronic properties and potential device performance. Decreasing the order parameter results in a large reduction of the bandgap. The reduction in bandgap is due, in part, to isolated, localized states that form above the valence band continuum associated with nitrogen coordinated by more zinc than germanium. The prevalence of defect states in all but the perfectly ordered structure creates challenges for incorporating disordered ZnGeN 2 into optical devices, but the localization associated with these defects provides insight into the mechanisms of electron/hole recombination in the material.

36 MATERIALS SCIENCE↗
NASA NTRS2007

Fabrication in Space - What Materials are Needed?

In order to sustain life on the moon, and especially on Mars, the inhabitants must be self-sufficient. As on Earth, electronic and mechanical systems will break down and must be repaired. It is not realistic to "send" parts to the moon or Mars in an effort to replace failed ones or have spares for all components. It will be important to have spares on hand and even better would be to have the capability to fabricate parts in situ. The In Situ Fabrication and Repair (ISFR) team is working to develop the Arcam Electron Beam Melting (EBM) machine as the manufacturing process that will have the capability to produce repair parts, as well as new designs, and tooling on the lunar surface and eventually on Mars. What materials will be available for the inhabitants to use? What materials would be most useful? The EBM process is versatile and can handle a multitude of materials. These include titanium, stainless steels, aluminums, inconels, and copper alloys. Research has shown what parts have failed during past space missions and this data has been compiled and assessed. The EBM machine is fully capable of processing these materials of choice. Additionally, the long-term goal is to use the lunar regolith as a viable feedstock. Preliminary work has been performed to assess the feasibility of using raw lunar regolith as a material source or use a binder combined with the regolith to achieve a good melt.

Good, J↗
DOE OSTI2022

Skyrmion superconductivity: DMRG evidence for a topological route to superconductivity

It was recently suggested that the topology of magic-angle twisted bilayer graphene's (MATBG) flat bands could provide a novel mechanism for superconductivity distinct from both weakly coupled BCS theory and the d-wave phenomenology of the high-T c cuprates. In this work, we examine this possibility using a density matrix renormalization group (DMRG) study of a model which captures the essential features of MATBG's symmetry and topology. Here, using large-scale cylinder-DMRG calculations to obtain the ground state and its excitations as a function of the electron doping, we find clear evidence for superconductivity driven by the binding of electrons into charge-2e skyrmions. Remarkably, this binding is observed even in the regime where the unscreened Coulomb repulsion is by far the largest energy scale, demonstrating the robustness of this topological, all-electronic pairing mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗