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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Direct Observation of Transient Structural Dynamics of Atomically Thin Halide Perovskite Nanowires

Halide perovskite is a unique dynamical system, whose structural and chemical processes happening across different timescales have significant impact on its physical properties and device-level performance. However, due to its intrinsic instability, real-time investigation of the structure dynamics of halide perovskite is challenging, which hinders the systematic understanding of the chemical processes in the synthesis, phase transition, and degradation of halide perovskite. Here, we show that atomically thin carbon materials can stabilize ultrathin halide perovskite nanostructures against otherwise detrimental conditions. Moreover, the protective carbon shells enable atomic-level visualization of the vibrational, rotational, and translational movement of halide perovskite unit cells. Albeit atomically thin, protected halide perovskite nanostructures can maintain their structural integrity up to an electron dose rate of 10,000 e – /Å 2 ·s while exhibiting unusual dynamical behaviors pertaining to the lattice anharmonicity and nanoscale confinement. Here, our work demonstrates an effective method to protect beam-sensitive materials during in situ observation, unlocking new solutions to study new modes of structure dynamics of nanomaterials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2005

A Survey of the Rapidly Emerging Field of Nanotechnology: Potential Applications for Scientific Instruments and Technologies for Atmospheric Entry Probes

The field of Nanotechnology is well funded worldwide and innovations applicable to Solar System Exploration are emerging much more rapidly than thought possible just a few years ago. This presentation will survey recent innovations from nanotechnololgy with a focus on novel applications to atmospheric entry science and probe technology, in a fashion similar to that presented by Arnold and Venkatapathy at the previous workshop forum at Lisbon Portugal, October 6-9, 2003. Nanotechnology is a rapidly emerging field that builds systems, devices and materials from the bottom up, atom by atom, and in so doing provides them with novel and remarkable macro-scale performance. This technology has the potential to revolutionize space exploration by reducing mass and simultaneously increasing capability. Thermal, Radiation, Impact Protective Shields: Atmospheric probes and humans on long duration deep space missions involved in Solar System Exploration must safely endure 3 significant hazards: (i) atmospheric entry; (ii) radiation; and (iii) micrometeorite or debris impact. Nanostructured materials could be developed to address all three hazards with a single protective shield, which would involve much less mass than a traditional approach. The concept can be ready in time for incorporation into NASA s Crew Exploration Vehicle, and possible entry probes to fly on the Jupiter Icy Moons

Meyyappan, M.↗
DOE OSTI2026

Metal Identity and Coordination Environment Modulate Single-Atom Catalyst Stability During Electrocatalysis

A major hurdle to the implementation of single-atom catalysts (SACs) in real-world systems is a poor understanding of their stability under operating conditions, which is particularly relevant due to the high surface free energy of SACs. Here, we evaluated the aggregation behavior of a suite of SACs varied by metal identity (Fe, Co, Ni, and Cu) during electrocatalytic nitrate reduction using in situ X-ray absorption spectroscopy. The metal center had significant influence on reconstruction, where under identical applied reductive potentials, SACs underwent varying levels of reconstruction, ranging from no discernible change to complete reduction into metallic nanoparticles. Such in situ experiments revealed Cu SACs to be the most susceptible to aggregation, prompting a deeper investigation into how coordination environment (O-, B-, and N-graphene) affected Cu SAC aggregation. We further conducted density functional theory calculations to elucidate the relationship between Cu SAC structure and stability. This work deconvolutes the relationship between SAC architecture and stability, which is essential to evaluate and explain for the realization of SACs for electrocatalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Evaluation of the beam-induced depolarization of the HJET target at the EIC

The Polarized Atomic Hydrogen Gas Jet Target (HJET) has played a central role in the absolute calibration of proton beam polarization at RHIC and is foreseen as a key component of the hadron polarimetry program at the future Electron–Ion Collider (EIC). The substantially higher beam current, reduced bunch spacing, and shorter bunch length planned for EIC operation motivate a careful reassessment of possible beam-induced depolarization of the jet target. In this paper, the depolarization of ground-state hydrogen atoms caused by the time-dependent magnetic field of the circulating polarized proton beam is quantitatively evaluated. The hydrogen atom is treated as a four-level hyperfine system in a holding magnetic field, and transitions driven by harmonic components of the bunch-induced magnetic field are analyzed using time-dependent quantum-mechanical evolution along atomic trajectories. Numerical tracking of hydrogen atoms through the beam region is performed using nominal EIC beam parameters. It is shown that, for a holding field of 120 mT (as used at RHIC), the resulting depolarization of the jet target at the EIC is negligibly small, ≲ 0.01 %, and well below the level relevant for EIC polarization accuracy requirements. The stability of this result with respect to plausible variations of the EIC proton beam parameters is also evaluated. In addition, possible effects under alternative experimental conditions are also examined.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1975

Mass transfer in binary X-ray systems

The influence of X-ray heating on gas flows in binary X-ray systems is examined. A simple estimate is obtained for the evaporative wind flux from a stellar atmosphere due to X-ray heating which agrees with numerical calculations by Alme and Wilson (1974) but disagrees with calculations by Arons (1973) and by Basko and Sunyaev (1974) for the Her X-1/HZ Her system. The wind flux is sensitive to the soft X-ray spectrum. The self-excited wind mechanism does not work. Mass transfer in the Hercules system probably occurs by flow of the atmosphere of HZ Her through the gravitational saddle point of the system. The accretion gas stream is probably opaque with atomic density of not less than 10 to the 15th power per cu cm and is confined to a small fraction of 4(pi) steradians. Other binary X-ray systems are briefly discussed.

Mccray, R.↗
DOE OSTI2024

Atom-by-atom imaging of moiré transformations in 2D transition metal dichalcogenides

Understanding the atomic-scale mechanisms that govern the structure of interfaces is critical across materials systems but particularly so for two-dimensional (2D) moiré materials. Here, we image, atom-by-atom, the thermally induced structural evolution of twisted bilayer transition metal dichalcogenides using in situ transmission electron microscopy. We observe low-temperature, local conversion of moiré superlattice into nanoscale aligned domains. Unexpectedly, this process occurs by nucleating a new grain within one monolayer, whose crystal orientation is templated by the other. The aligned domains grow through collective rotation of moiré supercells and hopping of 5|7 defect pairs at moiré boundaries. This provides mechanistic insight into the atomic-scale interactions controlling moiré structures and illustrates the potential to pattern interfacial structure and properties of 2D materials at the nanoscale.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Towards a quantum fluid theory of correlated many-fermion systems from first principles

Correlated many-fermion systems emerge in a broad range of phenomena in warm dense matter, plasmonics, and ultracold atoms. Quantum hydrodynamics (QHD) complements first-principles methods for many-fermion systems at larger scales. We illustrate the failure of the standard Bohm potential central to QHD for strong perturbations when the density perturbation is larger than about 10^{-3} 10 − 3 of the mean density. We then extend QHD to this regime via the many-fermion Bohm potential from first-principles. This may lead to more accurate QHD simulations beyond their common application domain in the presence of strong perturbations at scales unattainable with first-principles methods.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1997

Spacecraft Tests of General Relativity

Current spacecraft tests of general relativity depend on coherent radio tracking referred to atomic frequency standards at the ground stations. This paper addresses the possibility of improved tests using essentially the current system, but with the added possibility of a space-borne atomic clock. Outside of the obvious measurement of the gravitational frequency shift of the spacecraft clock, a successor to the suborbital flight of a Scout D rocket in 1976 (GP-A Project), other metric tests would benefit most directly by a possible improved sensitivity for the reduced coherent data. For purposes of illustration, two possible missions are discussed. The first is a highly eccentric Earth orbiter, and the second a solar-conjunction experiment to measure the Shapiro time delay using coherent Doppler data instead of the conventional ranging modulation.

Anderson, John D.↗
DOE OSTI2022

Universality of Dicke superradiance in arrays of quantum emitters

Abstract Dicke superradiance is an example of emergence of macroscopic quantum coherence via correlated dissipation. Starting from an initially incoherent state, a collection of excited atoms synchronizes as they decay, generating a macroscopic dipole moment and emitting a short and intense pulse of light. While well understood in cavities, superradiance remains an open problem in extended systems due to the exponential growth of complexity with atom number. Here we show that Dicke superradiance is a universal phenomenon in ordered arrays. We present a theoretical framework – which circumvents the exponential complexity of the problem – that allows us to predict the critical distance beyond which Dicke superradiance disappears. This critical distance is highly dependent on the dimensionality and atom number. Our predictions can be tested in state of the art experiments with arrays of neutral atoms, molecules, and solid-state emitters and pave the way towards understanding the role of many-body decay in quantum simulation, metrology, and lasing.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Insights into factors that affect non-Arrhenius migration of a simulated incoherent Σ3 grain boundary

Non-Arrhenius grain boundary migration, sometimes referred to as antithermal migration where temperature and GB velocity values are inversely related to each other, is examined in an incoherent twin Σ3 [111] 60° (11 8 5) nickel grain boundary. Molecular dynamics is used to simulate migration and examine the effect of various factors on the migration, including interatomic potential, system size, driving force, and variation of atomic grain boundary structure. A classical model for grain boundary migration, in its unsimplified form, is used to analyze the results. The grain boundaries exhibit migration mechanisms with very low apparent barrier heights to migration. As a result, the boundaries migrate quickly but exhibit a velocity saturation similar to that of dislocations. Furthermore, the various interatomic potentials exhibit different migration velocities, but their similarities suggest they all predict similar overall behaviors of migration. The variation of atomic structure in the same incoherent twin grain boundary leads to diverse behaviors with barrier heights that vary from non-Arrhenius to Arrhenius migration. Facet nucleation is confirmed not to be a requirement for this boundary based on an examination of simulation cell size; however, the presence and/or interaction between numerous facets does suggest a slowing and increased barrier height to migration for larger boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2022

TTDFT: A GPU accelerated Tucker tensor DFT code for large-scale Kohn-Sham DFT calculations

We present the Tucker tensor DFT (TTDFT) code which uses a tensor-structured algorithm with graphic processing unit (GPU) acceleration for conducting ground-state DFT calculations on large-scale systems. The Tucker tensor DFT algorithm uses a localized Tucker tensor basis computed from an additive separable approximation to the Kohn-Sham Hamiltonian. The discrete Kohn-Sham problem is solved using Chebyshev filtered subspace iteration method that relies on matrix-matrix multiplications of a sparse symmetric Hamiltonian matrix and a dense wavefunction matrix, expressed in the localized Tucker tensor basis. These matrix-matrix multiplication operations, which constitute the most computationally intensive step of the solution procedure, are GPU accelerated providing ~8-fold GPU-CPU speedup for these operations on the largest systems studied. In conclusion, the computational performance of the TTDFT code is presented using benchmark studies on aluminum nano-particles and silicon quantum dots with system sizes ranging up to ~7,000 atoms.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Impact of Cr and Co on 99Tc retention in magnetite: A combined study of ab initio molecular dynamics and experiments

This work explores the effect of co-mingled dopants, Co(II) and Cr(III), on Tc(IV) incorporation and retention in magnetite when heat treated to 625 or 700 °C. Key trends in Tc retention in the high temperature regime were identified using a combination of density-functional-theory based ab initio molecular dynamics (AIMD) simulations, and batch experiments including solid phase characterization techniques, e.g. X-ray absorption spectroscopy. A stabilizing effect on Tc(IV) was observed when the number of Tc and Cr atoms are equal or when the magnetite surface is oversaturated with Tc and Cr inclusions. Here, oversaturation is hypothesized to force Cr from the magnetite surface to form a Cr2O3 phase, which may act as a protective layer that prevents Tc release. With the addition of Co, Tc(IV) is stabilized via redox processes. The presence of Cr in low concentrations interferes with this redox stabilization and Cr is preferentially stabilized as opposed to Tc. As a result, using Co as a stabilizing dopant for Tc may be compromised in the presence of Cr. When the relative concentration of Tc, Cr and Co is the same, or more Co atoms are added to high Cr incorporated systems, the formation of the Cr2O3 phase may be suppressed. Although waste streams with co-mingled Tc and Cr potentially may benefit from a Co dopant, since the formation of a Cr2O3 passivation layer may protect incorporated Tc from being released, the relative concentration of the three elements will be a critical parameter for maximizing effectiveness of this strategy.

Lee, Mal Soon↗
DOE OSTI2023

Ab initio study of the structure and properties of amorphous silicon hydride from accelerated molecular dynamics simulations

This paper presents a large-scale ab initio simulation study of amorphous silicon hydride (a-Si 1-x H x ) with an emphasis on the structure and properties of the material across a range of hydrogen concentration by combining accelerated molecular dynamics (MD) simulations with first-principles density-functional calculations. The accelerated MD scheme relied on classical metadynamics, which enabled the development of 2500+ high-quality structural models of a-Si 1-x H x , with system sizes ranging from 150 to 6000 atoms and hydrogen concentrations vary from 6 to 20 at. %. The resulting amorphous networks were found to be completely free from any coordination defects and that they all exhibited a pristine band-gap in their electronic spectrum. The microstructural properties of hydrogen distributions were examined with an emphasis on the presence of isolated and clustered environments of hydrogen atoms. The results were compared with experimental data obtained from X-ray diffraction, infrared spectroscopy and nuclear magnetic resonance studies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Exploring the composition, phase separation and structure of AgFe alloys for magneto-optical applications

Bimetallic alloys with large discrepancies in atomic radii and crystal structure typically yield systems that are highly immiscible, even at high temperatures. The Ag x Fe 1−x binary system has limited solid and liquid solubility and thus phase separated Ag + Fe alloys should result. Furthermore, Ag has interesting plasmonic properties and Fe is a strong ferromagnet, thus magneto-plasmonic nanoparticles/films should result due to their phase separation. We have leveraged a combinatorial sputter deposition to synthesize thin films with a large Ag x Fe 1−x (0.19 < x < 0.84) phase space to correlate the composition and structure to the optical and magnetic properties for both as-deposited and annealed compositions.

Bimetallic alloys↗
DOE OSTI2025

Alpha-decay width of a near proton-threshold resonance in the 7 Li( α, α ) channel

We investigate the alpha-decay width of a near proton-threshold resonance in 11 B by the excitation functions of 7 Li(α, α) and 7 Li(α, α’) reactions. This resonance is an example of loosely bound atomic nuclei, understood as small open quantum systems, that exhibit properties significantly influenced by their coupling to the continuum. The present experiment focuses on the formation of a specific state in 11 B at excitation energy in the region near 11.4 MeV by bombarding a 7 Li target with a 4 He beam at energies ranging from 3.92 to 4.56 MeV in the laboratory frame. The study provides data complementary to previous observations of the proton emission in the β-decay of the neutron-rich halo nucleus 11 Be. An R-matrix fit to the data provides resonance energy and partial widths consistent with J π =1/2 + for a narrow near-threshold state in 11 B at 11.400(20) MeV, that is 171(20) keV above the proton emission threshold, with partial α-decay width Γ α =2.5$^{+3.5}_{–1.5}$ keV in elastic scattering and Γ α' =15.8$^{+1.9}_{–0.4}$ keV in inelastic scattering. These findings contribute to the understanding of the structure of this open quantum system resonance.

11B↗
DOE OSTI2024

Proposed crystal structure of carbadox, C 11 H 10 N 4 O 4

A model for the crystal structure of carbadox has been generated and refined using synchrotron X-ray powder diffraction data and optimized using density functional theory techniques. Carbadox crystallizes in space groupP2 1 (#4) witha= 13.8155(3),b= 21.4662(1),c= 16.3297(3) Å,β= 110.0931(7)°,V= 4548.10(3) Å 3 , andZ= 16. The crystal structure is characterized by approximately parallel stacking of the eight independent carbadox molecules parallel to thebc-plane. There are two different molecular configurations of the eight carbadox molecules; five are in the lower-energy configuration and three are in a ~10% higher-energy configuration. This arrangement likely achieves the lowest-energy crystalline packing via hydrogen bonding. Hydrogen bonds link the molecules both within and between the planes. Each of the amino groups forms a N–H⋯O hydrogen bond to an oxygen atom of the 1,4-dioxidoquinoxaline ring system of another molecule. The result is four pairs of hydrogen-bonded molecules, which form rings with graph setR2,2(14). Variation in specimen preparation can affect the preferred orientation of particles considerably. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

Materials Science↗
DOE OSTI2024

Association Kinetics for Perfluorinated n -Alkyl Radicals

Radical-radical reaction channels are important in the pyrolysis and oxidation chemistry of perfluoroalkyl substances (PFAS). In particular, unimolecular dissociation reactions within unbranched n-perfluoroalkyl chains, and their corresponding reverse barrierless association reactions, are expected to be significant contributors to the gas-phase thermal decomposition of families of species such as perfluorinated carboxylic acids and perfluorinated sulfonic acids. Unfortunately, experimental data for these reactions are scarce and uncertain. Furthermore, obtaining reliable theoretical predictions for such reactions is a laborious and computationally intensive task. Here, in this work, the chemical kinetics of the various association/decomposition reactions producing/decomposing the C 2 -C 4 series of unbranched n-perfluoroalkanes (C 2 F 6 , C 3 F 8 , and C 4 F 10 ) are examined using state-of-the-art ab initio transition-state-theory-based master-equation calculations. The variable-reaction-coordinate transition-state theory (VRC-TST) formalism is employed in computing the microcanonical and canonical rates for the association reactions. Reaction thermochemistry is obtained via composite quantum chemistry calculations and the laddering of error-canceling reaction schemes via a connectivity-based hierarchy approach employing ANL1/ANL0-style reference energies. Lennard-Jones collision model parameters for the considered systems were estimated by a direct dynamics approach, and collisional energy transfer parameters were obtained from analogies to systems of similar size and heavy-atom connectivity. A one-dimensional master equation approach was used to convert the microcanonical rate coefficients from the VRC-TST analysis into temperature- and pressure-dependent rate constants for the association reactions and the reverse dissociation reactions. The data are reported in standardized formats for usage in comprehensive chemical kinetic models for PFAS thermal destruction.

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

Parsimonious Potential Energy Surface Expansions Using Dictionary Learning with Multipass Greedy Selection

Potential energy surfaces fit with basis set expansions have been shown to provide accurate representations of electronic energies and have enabled a variety of high-accuracy dynamics, kinetics, and spectroscopy applications. The number of terms in these expansions scales poorly with system size, a drawback that challenges their use for systems with more than similar to 10 atoms. A solution is presented here using dictionary learning. Subsets of the full set of conventional basis functions are optimized using a newly developed multipass greedy regression method inspired by forward and backward selection methods from the statistics, signal processing, and machine learning literatures. Here, the optimized representations have accuracies comparable to the full set but are 1 or more orders of magnitude smaller, and notably, the number of terms in the optimized multipass greedy expansions scales approximately linearly with the number of atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗