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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Enhancement of reactive oxygen species production by ultra-short electron pulses

The development of laser-driven accelerators-on-chip has provided an opportunity to miniaturize devices for electron radiotherapy delivery. Laser-driven accelerators produce highly time-compressed electron pulses, on the 100 fs to 1 ps scale. This delivers electrons at high peak power yet low average beam current compared with conventional delivery devices, which generate pulses of approximately 3 µs. The biophysical effects of this time structure, however, are unclear. Here, we use a Monte Carlo simulation approach to explore the effects of the electron beam time structure on the production of reactive oxygen species (ROS) in water. Our results show a power law increase in the generation of hydroxyl ions per deposited electron with decreasing pulse length over the pulse length range of 10 µs to 100 fs. Similar trends were observed for hydrogen peroxide, superoxide, hydroperoxyl, hydronium and solvated electrons. In practical terms, this indicates a fourfold increase in the efficiency of free radical production for sub-picosecond pulses, relative to that of conventional microsecond pulses, for the same number of deposited electrons.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2016

Electrical, Electronic, and Electromechanical (EEE) Parts Management and Control Requirements for Space Flight Hardware and Critical Ground Support Equipment...aka... The NASA EEE Parts Standard, NASA-STD 8739.10

Describes development and content of a new NASA Standard for Electrical Electronic and Electromechanical (EEE) parts. This Standard reflects current practices, instead of changing them. Most NASA Centers utilize local documents, but there is minimal consistency across the Agency. A gap analysis clearly shows the differences that exist among the different centers and with respect to the NASA Parts Policy. Once approved, the new standard can be referenced in contracts and agreements with organizations outside of NASA.

Electronic↗
DOE OSTI2025

Actinide 5f Occupations: The Case of PuO 2

In actinide chemistry, the formal number of open-shell 5f electrons, n open , is a well-defined quantity with an integer value. The effective 5f occupation, n f , additionally takes donation and back-donation into account, generally has a non-integer value, and has varying numerical definitions. The present study explores the important distinction between n f and n open in actinide chemistry with the example of PuO2, by using electronic structure methods with a relativistic Hamiltonian in combination with experimental Pu M 5 -edge high-energy-resolution X-ray absorption and emission spectroscopic data. The total donation to the metal in PuO 2 is between 3.1 and 2.4 electrons, depending on the type of calculation, most of which is to the Pu 6d and 5f shells. The donation into 5f is sensitive to the approximations in the electronic structure model but likely amounts to 1.6/0.8 electrons when the diffuse regions of the 5f shell are included/excluded. Valence band resonant inelastic X-ray scattering experiments demonstrate that Pu 5f electron density is present in the valence band; thus, there is a clear experimental signature of covalent bonding in PuO 2 . Pu M 5 -edge and M 3 -edge high-energy-resolution X-ray absorption near-edge structures for Pu 3+ and Pu 4+ in an aqueous solution are compared to PuO 2 , showing that Pu in PuO 2 has an nf closer to Pu 4+ (aq).

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

Real-Time Time-Dependent Electronic Structure Theory

Real-time electronic structure methods provide an unprecedented view of electron dynamics and ultrafast spectroscopy on the atto- and femtosecond time scale with vast potential to yield new insights into the electronic behavior of molecules and materials. Here, we discuss the fundamental theory underlying various real-time electronic structure methods as well as advantages and disadvantages of each. We give an overview of the numerical techniques that are widely used for real-time propagation of the quantum electron dynamics with an emphasis on Gaussian basis set methods. We also showcase many of the chemical applications and scientific advances made by using real-time electronic structure calculations and provide an outlook of possible new directions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Electrolyte-Dependent, “Microscopically Irreversible” H-Atom Transfer Kinetics of Ce-Based Metal–Organic Framework, Ce-MOF-808

Redox reactions at the interface of metal oxides and protic electrolytes almost always involve protons and electrons in equal amounts. Given the stoichiometry, these proton-coupled electron transfer (PCET) reactions are thermochemically equivalent to net H-atom transfer (HAT) reactions. The correlation between the chemical nature of solid catalysts and HAT kinetics has been employed for decades as the design principle for energy-relevant reactions (e.g., reactions of 2H + /H 2 ). More recently, chemists have experimentally determined that a change in liquid electrolytes that alters the microenvironment at the redox-active sites has an equally profound impact on electrocatalysis involving PCET/HAT. Yet, precise correlations between the chemical nature of electrolytes and the PCET kinetics are, to date, rare in the literature. Herein, we report our findings using the Ce-based metal−organic framework, Ce-MOF-808, as a model system. Each Ce 6 (μ 3 −O) 4 (μ 3 − OH) 4 (OH) 6 (H 2 O) 6 node of this MOF undergoes a 1H + /1e − redox reaction. Using chronoamperometry and the Cottrell analysis, we have determined that the PCET hopping kinetics within the pores of Ce-MOF-808 can change by orders of magnitude by altering the buffer species and the proton activity of the electrolyte. Furthermore, in all buffers, reductive reactions were ∼3−10 times faster in kinetics than the reverse oxidative reaction with the same electrochemical driving force, suggesting that the system, at first glance, violates the principle of microscopic reversibility. Isothermal titration calorimetry (ITC) and computational simulations corroborated that the buffer-node binding thermodynamics are quite distinct, depending on the chemical nature of the buffer and the oxidation state of the node. Together, these results suggest that the substrate and the product during the oxidative vs reductive reaction of Ce-MOF-808 are chemically different species, which explains the apparent ‘microscopic irreversibility.’ Thus, the rational modulation of electrolytes can dramatically enhance PCET kinetics, even though the solid electrodes remain identical. Implications of these findings are contrasted with the electrochemical/electrocatalytic behavior of other redox-active MOFs, heterogeneous catalysts, and enzymatic systems at the solid−liquid interface.

Ce-based MOF↗
DOE OSTI2025

Electrochemically Mediated Au–C(sp 2 ) Anchors for Molecular Electronics

Terminal anchor groups play a key role in the stability and electronic properties of molecular junctions. Single molecule junctions typically consist of two preinstalled terminal anchors linking organic molecules to metal electrodes. Here, in this work, we show that p -terphenyl derivatives containing only a single terminal anchor show conductance features similar to junctions with two preinstalled terminal anchors. A set of p -terphenyl derivatives with one terminal anchor was prepared using automated chemical synthesis and characterized using single molecule electronics experiments, molecular dynamics (MD) simulations, bulk electrochemistry and spectroscopy, and nonequilibrium Green’s function-density functional theory (NEGF-DFT) calculations. Our results show that 4-amino- p -terphenyl (PPP) and related analogs exhibit a well-defined high conductance state that is diminished or absent in other p-terphenyl derivatives lacking a preinstalled amine terminal anchor or fluorine or methyl substitutions at the terminal para position. However, a low conductance state is observed in all amino- p -terphenyl derivatives with one preinstalled anchor due to molecular junctions formed by noncovalent dimeric π–π stacking interactions. The observed high conductance state diminishes upon the addition of reducing agents and is restored upon the addition of an oxidizing agent. Our results suggest that the high conductance state arises due to Au–C(sp 2 ) bond formation facilitated by a single electron oxidation event at the electrode surface. A series of control experiments with different anchor groups shows that primary amines play a key role in forming Au–C bonds for molecular junctions. Overall, these results suggest that Au–C bond formation gives rise to high conductance pathways in organic molecules containing only one preinstalled terminal anchor. Insights from this work can be leveraged in the design of molecular electronic devices, particularly in understanding the mechanisms of molecular binding and junction formation.

charge transport↗
DOE OSTI2021

Relativistic coupled‐cluster and equation‐of‐motion coupled‐cluster methods

Abstract The development of relativistic coupled‐cluster (CC) and equation‐of‐motion coupled‐cluster (EOM‐CC) methods is reviewed. An emphasis is placed on recent efforts to improve the computational efficiency of CC and EOM‐CC calculations with non‐perturbative treatments of spin‐orbit coupling (SO‐CC and EOM‐CC) by partially recovering spin symmetry in the formulations. Example calculations of electronic ground state as well as valence‐excited and core‐excited states for molecules containing heavy elements are presented to demonstrate the applicability and usefulness of the SO‐CC and EOM‐CC methods. Future directions for the development of the SO‐CC and EOM‐CC methods are also discussed. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1997

Restoration and Archiving of Data from the Plasma Composition Experiment on the International Sun-Earth Explorer One (ISEE 1)

The objective of this project has been to complete the archiving of energetic (10 eV/epsilon - 18 keV/epsilon) ion composition data from the Lockheed Plasma Composition Experiment on the International Sun-Earth Explorer One (ISEE 1) satellite, using a particular data format that had previously been approved by NASA and the NSSDC. That same format, a combination of ion velocity moments and differential flux spectra, had been used in 1991 to archive, at the NSSDC, the first 28 months (the "Prime" period of ISEE investigations) of data from the Lockheed instrument under NASA Contract NAS5-33047. With the completion of this project, the almost 4 1/2-year time span of these unique data is now covered by a very compact set, approximately 1 gigabyte in total, of electronic files with physical quantities, all in ASCII. The files are organized by data type and time of data acquisition, in Universal Time, and named according to year and day of year. Each calendar day has five separate files (five types of data), the lengths of which vary from day to day, depending on the instrument mode of operation. The data format and file structure are described in detail in appendices 1 and 2. The physical medium consists of high-density (6250 cpi) 9-track magnetic tapes, complemented by a set of hardcopy line plots of certain plasma parameters. In this case there are five tapes, to be added to the six previous ones from 1991, and 25 booklets of plots, one per month, to be added to the previous 28. The tapes, including an extra standard-density (1600 cpi) tape with electronic versions of the Data User's Guide and self-guiding VAX/VMS command files, and the hardcopy plots are being boxed for shipment to the NSSDC.

Lennartsson, O. W.↗
DOE OSTI2020

Electron Paramagnetic Resonance Characteristics and Crystal Structure of a Tutton Salt Analogue: Copper-Doped Cadmium Creatininium Sulfate

Electron paramagnetic resonance and crystallographic studies on copper-doped cadmium creatininium sulfate (CdCrnS) were undertaken to study the characteristics of a copper-hexahydrate complex in an organic analogue of Tutton's salt. X-ray diffraction experiments determined the crystal structure of CdCrnS at both 100 and 298 K. CdCrnS, like Tutton salt, crystallizes in the monoclinic space group P2 1 /n. The unit cell contains two cadmium hexahydrate complexes, four creatininium ions, four sulfates, and four additional solvation waters. Both crystallography and EPR find that the doped copper replaces the cadmium in the structure. Single-crystal EPR measurements at room temperature determined the g and copper hyperfine (A Cu ) tensors (principal values: g = 2.437, 2.134, and 2.080 and A Cu = -327, -84.8, and 7.33 MHz). EPR spectra of the powder at room temperature gave g = 2.448, 2.125, and 2.085 and A Cu = -315, -75.0, and 35.0 MHz and at 110 K gave g = 2.462, 2.116, and 2.077 and A Cu = -340, -30.0, and 35.0 MHz. The room-temperature tensors are close to the "rigid lattice limit" values found in copper-doped Tutton salts but with a higher gmin and weaker A Cu x coupling than average. A small but measurable temperature dependency of the tensors indicated the presence of a dynamic Jahn-Teller (JT) effect. In addition, the EPR line width changed dramatically with temperature, which is like that found in all copper-doped Tutton crystals. Utilizing the model of Silver-Getz for the g-value variation gave an estimate for the energy difference (δ 12 = 640 cm -1 ) between the ground and next highest JT configurations. An empirical correlation appears to exist between δ 12 and g min and A Cu x for the copper hexahydrates studied in similar crystals. Finally, this suggests a relationship between the amount of unpaired spins in the copper d-orbital x lobe and the gap between wells of the adiabatic potential surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Photoluminescence of Cis-Polyacetylene Semiconductor Material

Photoluminescence (PL) is one of the key experimental characterizations of optoelectronic materials, including conjugated polymers (CPs). In this study, a simplified model of an undoped cis-polyacetylene (cis-PA) oligomer was selected and used to explain the mechanism of photoluminescence (PL) of the CPs. Using a combination of the ab initio electronic structure and a time-dependent density matrix methodology, the photo-induced time-dependent excited state dynamics were computed. We explored the phonon-induced relaxation of the photoexcited state for a single oligomer of cis-PA. Here, the dissipative Redfield equation of the motion was used to compute the dissipative excited state dynamics of electronic degrees of freedom. This equation used the nonadiabatic couplings as parameters. The computed excited state dynamics showed that the relaxation rate of the electron is faster than the relaxation rate of the hole. The dissipative excited-state dynamics were combined with radiative recombination channels to predict the PL spectrum. The simulated results showed that the absorption and emission spectra both have a similar transition. The main result is that the computed PL spectrum demonstrates two mechanisms of light emission originating from (i) the inter-band transitions, corresponding to the same range of transition energies as the absorption spectrum and (ii) intra-band transitions not available in the absorption spectra. However, the dissipative Redfield equation of the motion was used to compute the electronic degrees of freedom of the nonadiabatic couplings, which helped to process the time propagation of the excited dynamic state. This excited dynamic state shows that the relaxation rate of the electron is faster than the relaxation rate of the hole, which can be used for improving organic semiconductor materials for photovoltaic and LED applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Characterization of ferredoxins involved in electron transfer pathways for nitrogen fixation implicates differences in electronic structure in tuning 2[4Fe 4S] Fd activity

Ferredoxins (Fds) are small proteins which shuttle electrons to pathways like biological nitrogen fixation. Physical properties tune the reactivity of Fds with different pathways, but knowledge on how these properties can be manipulated to engineer new electron transfer pathways is lacking. Recently, we showed that an evolved strain of Rhodopseudomonas palustris uses a new electron transfer pathway for nitrogen fixation. This pathway involves a variant of the primary Fd of nitrogen fixation in R. palustris, Fer1, in which threonine at position 11 is substituted for isoleucine (Fer1 T11I ). To understand why this substitution in Fer1 enables more efficient electron transfer, we used in vivo and in vitro methods to characterize Fer1 and Fer1 T11I . Electrochemical characterization revealed both Fer1 and Fer1 T11I have similar redox transitions (–480 mV and – 550 mV), indicating the reduction potential was unaffected despite the proximity of T11 to an iron-sulfur (Fe—S) cluster of Fer1. Additionally, disruption of hydrogen bonding around an Fe—S cluster in Fer1 by substituting threonine with alanine (T11A) or valine (T11V) did not increase nitrogenase activity, indicating that disruption of hydrogen bonding does not explain the difference in activity observed for Fer1 T11I . Electron paramagnetic resonance spectroscopy studies revealed key differences in the electronic structure of Fer1 and Fer1 T11I , which indicate changes to the high spin states and/or spin-spin coupling between the Fe—S clusters of Fer1. Finally, our data implicates these electronic structure differences in facilitating electron flow and sets a foundation for further investigations to understand the connection between these properties and intermolecular electron transfer.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Natural formation of linear defect structures in MoS 2

Near surface defects can significantly impact the quality of metallic interconnects and other interfaces necessary to create device structures incorporating two-dimensional materials. Furthermore, the impact of such defects can strongly depend on their organization. In this study, we present scanning tunneling microscopy images and tunneling spectroscopy of point and linear defects near the surface of natural MoS 2 . The point defects share similar structural and electronic characteristics and occur with comparable frequency as subsurface sulfur vacancies observed previously on natural MoS 2 . The linear defects observed here occur less frequently than the point defects but share the same depth profile and electronic structure. These data indicate that the linear defects are actually a one-dimensional organization of subsurface sulfur vacancies. Our density functional calculations agree with this assessment in that, for sufficient local defect concentrations, it is energetically more favorable for the defects to be organized in a linear fashion rather than as clusters or even isolated single point defects. Given these measurements were taken from naturally formed MoS 2 , this organization likely occurs during crystal formation. Considering the impact of one-dimensional organization on the local properties of layered materials, and the potential for them to be introduced purposefully during crystal formation, research into the formation mechanism and properties of these defects could enable new paths for defect engineering in MoS 2 -based systems.

2D materials↗
NASA NTRS1984

Improved charge injection device and a focal plane interface electronics board for stellar tracking

An improved Charge Injection Device (CID) stellar tracking sensor and an operating sensor in a control/readout electronics board were developed. The sensor consists of a shift register scanned, 256x256 CID array organized for readout of 4x4 subarrays. The 4x4 subarrays can be positioned anywhere within the 256x256 array with a 2 pixel resolution. This allows continuous tracking of a number of stars simultaneously since nine pixels (3x3) centered on any star can always be read out. Organization and operation of this sensor and the improvements in design and semiconductor processing are described. A hermetic package incorporating an internal thermoelectric cooler assembled using low temperature solders was developed. The electronics board, which contains the sensor drivers, amplifiers, sample hold circuits, multiplexer, analog to digital converter, and the sensor temperature control circuits, is also described. Packaged sensors were evaluated for readout efficiency, spectral quantum efficiency, temporal noise, fixed pattern noise, and dark current. Eight sensors along with two tracker electronics boards were completed, evaluated, and delivered.

Michon, G. J.↗
DOE OSTI2021

Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

Low-dimensional hybrid organic–inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. In this work, we report a new zero-dimensional hybrid organic–inorganic halide, RInBr 4 , featuring photoemissive trimethyl(4-stilbenyl)methylammonium (R + ) cations and nonemissive InBr 4 – tetrahedral anions. The crystal structure of RInBr 4 is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l’Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In(III) halides for light emission applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

How Thermodynamic, Electronic, and Steric Factors Influence Mesitylcopper Oligomers

Mesitylcopper (CuMes) is a highly versatile organocopper reagent used in both organic and inorganic syntheses. It has previously been shown that CuMes exists as a tetrameric or pentameric cyclic oligomer [CuMes] n (n = 4, 5), both in solution and in the solid state. The bonding arrangement between the [CuMes] units has qualitatively been described as localized three-center twoelectron (3c-2e) bonds. However, the electronic, structural, and thermodynamic forces driving this aggregation are still not well understood. For this reason, we employed density functional theory (DFT) calculations to study mesitylcopper as a monomeric [CuMes] unit and [CuMes]n oligomers with n = 2 to n = 7. We found that there is a strong electronic driving force for aggregation caused by strong mixing between the Cu’s d orbitals and Mes’s π orbitals in oligomers larger than the dimer. This mixing is only optimized in oligomers with n ≥ 3, where the mesityl group is no longer bonded to a single copper center but instead becomes a bridging ligand. Beyond the trimer, steric and entropic factors become relevant for determining the relative stabilities of the different aggregates, with midsized oligomers (n = 4−5) having the optimal balance between the electronic Cu−C bonding character, Cu···Cu attractive forces, entropy, reduced internal ring strain, and reduced steric interactions between the mesityl groups.

Copper↗
DOE OSTI2021

Dynamic interactions at the mineral–organic matter interface

Minerals are widely assumed to protect organic matter (OM) from degradation in the environment, promoting the persistence of carbon in soil and sediments. In this Review, we describe the mechanisms and processes operating at the mineral–organic interface as they relate to OM transformation dynamics. A broad set of interactions occur, with minerals adsorbing organic compounds to their surfaces and/or acting as catalysts for organic reactions. Minerals can serve as redox partners for OM through direct electron transfer or by generating reactive oxygen species, which then oxidize OM. Finally, the compartmentalization of soil and sediment by minerals creates unique microsites that host diverse microbial communities. Acknowledgement of this multiplicity of interactions suggests that the general assumption that the mineral matrix provides a protective function for OM is overly simplistic. Future work must recognize adsorption as a condition for further reactions instead of as a final destination for organic adsorbates, and should consider the spatial and functional complexity that is characteristic of the environments where mineral–OM interactions are observed.

54 ENVIRONMENTAL SCIENCES↗