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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Effects of aluminum content on thermoelectric performance of Al x CoCrFeNi high-entropy alloys

Introducing a non-regular distribution in the mass and bonding by including distinctly different elements can reduce the phonon transport even within structurally well-ordered materials. These distributions are a quality of all high-entropy alloys (HEAs), however the inclusion of aluminum in Al x CoCrFeNi is particularly impactful due to the large mismatch in atomic mass with other components. The resultant low phonon conductivity is a requirement for high thermoelectric performance, motivating the investigation of the effects of Al content on phonon transport as well as other thermoelectric properties. This work examines the phonon and electron transport and thermoelectric conversion properties with various Al contents (0 ≤ x Al ≤ 2) in this Cantor alloy using first-principles calculations, molecular dynamics, and semi-classical Boltzmann transport theory. The calculated phonon density of states and thermoelectric properties present reasonable agreements with experiments, including neutron scattering. A large reduction of phonon conductivity (k L ) is observed even with low x Al s, which we attribute to effective phonon scatterings by the large mass mismatch. However, its temperature dependence is not significant, demonstrating a minor contribution of interphonon scattering. In contrast, electrical conductivity (σ) and Seebeck coefficient (S) increase with temperature at higher x Al s with body-centered cubic structures. Therefore, the thermoelectric figure of merit (ZT) of Al x CoCrFeNi HEAs is enhanced by increasing the Al content mainly due to the increase of the thermoelectric power factor (σS 2 ) at high temperatures, while at low temperatures the phonon-scattering enhancement by mass mismatch is also important.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Metallization of colloidal crystals

Colloidal crystals formed by size-asymmetric binary particles coassemble into a wide variety of colloidal compounds with lattices akin to ionic crystals. Recently, a transition from a compound phase with a sublattice of small particles to a metal-like phase in which the small particles are delocalized has been predicted computationally and observed experimentally. In this colloidal metallic phase, the small particles roam the crystal maintaining the integrity of the lattice of large particles, as electrons do in metals. A similar transition also occurs in superionic crystals, termed sublattice melting. Here, we use energetic principles and a generalized molecular dynamics model of a binary system of functionalized nanoparticles to analyze the transition to sublattice delocalization in different coassembled crystal phases as a function of temperature (T), number of grafted chains on the small particles, and number ratio between the small and large particles n s : n l . Here we find that n s : n l is the primary determinant of crystal type due to energetic interactions and interstitial site filling, while the number of grafted chains per small particle determines the stability of these crystals. We observe first-order sublattice delocalization transitions as T increases, in which the host lattice transforms from low- to high-symmetry crystal structures, including A20 → bct → bcc, A d → bct → bcc, and bcc → bcc/fcc → fcc transitions and lattices. Analogous sublattice transitions driven primarily by lattice vibrations have been seen in some atomic materials exhibiting an insulator-metal transition also referred to as metallization. We also find minima in the lattice vibrations and diffusion coefficient of small particles as a function of n s : n l , indicating enhanced stability of certain crystal structures for n s : n l values that form compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enhanced resistance to helium irradiations through unusual interaction between high-entropy-alloy and helium

Finding high performance plasma-facing materials (PFMs) is one of the most important and challenging tasks for realizing the commercial application of fusion reactors. Herein, we found the CrMoTaWV high entropy alloy (HEA) is highly resistant to low-energy and high-flux He plasma exposure. The nanochannel HEA film has 20 times higher initial fluence for the formation of fuzz and a remarkable 8.9 times slower fuzz growth rate than those of W. Combining the in-situ TEM observation and the Molecular dynamics (MD) simulation of the He bubble growth process, a new mechanism for the enhanced radiation resistance in HEA with the unusual interaction between HEA and He is found, where, differing from traditional metal, bubble growth in HEA leads to non-directional emission of interstitial atoms while HEA greatly suppress the growth of He bubbles. Additionally, the special nanochannel structure further rise the radiation resistance through releasing He out of the HEA film and reducing the He concentration. This new nanochannel refractory HEA material presents a promising choice as the PFMs with excellent performance and a much longer serving lifetime for future commercial fusion reactors.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interface structures of inclined ZnO thin film on (0 1 1)-MgO substrate with bulk-like optical properties

Combining different phase structure materials with unique properties to design novel devices plays a significant role in the development of modern electronics. Here, we explore the characteristics of this type of complex interface and epitaxy structures based on the coupling between hexagonal ZnO film and cubic MgO substrate. The ZnO film was prepared by the molecular beam epitaxy technique on the MgO (0 1 1) substrate. The analysis results from the in situ reflection high energy electron diffraction patterns, X-ray diffraction (XRD)-pole figures and high resolution transmission electron microscopy images demonstrate that the film exhibits two-fold symmetry domains with a growth direction deviated from c-axis at about 31º along the [0 1 0] MgO or [0 $\bar{1}$ 0] MgO azimuth. Despite the intertwined diffusion from Zn and Mg atoms in the interface, which is the possible origin of a blue shift of about 0.083 eV in the Photoluminescence (PL) spectrum, the inclined film shows a full width at half maximum value that is close to the reported value from the high quality film. Finally, this work hopefully provides useful insights to the design and exploration of the novel optoelectronic devices that involve the integration of materials with different structure and different properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Gas-Phase Study of the Elementary Reaction of the D1-Ethynyl Radical (C 2 D; X 2 Σ + ) with Propylene (C 3 H 6 ; X 1 A') under Single-Collision Conditions

The bimolecular gas-phase reactions of the D1-ethynyl radical (C 2 D; X 2 Σ + ) with propylene (C 3 H 6 ; X 1 A’) and partially substituted D3-3,3,3-propylene (C 2 H 3 CD 3 ; X 1 A’) were studied under single collision conditions utilizing the crossed molecular beams technique. Combining our laboratory data with electronic structure and statistical calculations, the D1-ethynyl radical is found to add without barrier to the C1 and C2 carbons of the propylene reactant, resulting in doublet C 5 H 6 D intermediate(s) with lifetime(s) longer than their rotational period(s). These intermediates undergo isomerization and unimolecular decomposition via atomic hydrogen loss through tight exit transition states forming predominantly cis/trans-3-penten-1-yne ((HCC)CH=CH(CH 3 )) and to a minor amount 3-methyl-3-buten-1-yne ((HCC)C(CH 3 )=CH 2 ) via overall exoergic reactions. Although the title reaction does not lead to the cyclopentadiene molecule (c-C 5 H 6 , X 1 A 1 ), high temperature environments can convert the identified acyclic C 5 H 6 isomers through hydrogen atom assisted isomerization to cyclopentadiene (c-C 5 H 6 , X 1 A 1 ). Since both the ethynyl radical and propylene reactants have been observed in cold interstellar environments such as TMC-1 and the reaction is exoergic and all barriers lie below the energy of the separated reactants, the these C 5 H 6 product isomers are predicted to form in those low temperature regions.

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

Effect of Solvents on Lignin–Surface Interactions via Molecular Dynamics Simulations

Lignin, an essential building block of lignocellulosic biomass, is a potential abundant source of aromatic monomers for the polymer and chemical industry. Reductive catalytic fractionation (RCF) is one promising process that can produce high yields of phenolic monomers and oligomers from lignin under different catalytic conditions. An important choice in optimizing RCF is the selection of solvent; however, detailed insights into solvent effects on lignin behaviors and interactions remain limited. Here, in this work, we perform all-atom molecular dynamics simulations to study the solvation of lignin, solvent-mediated conformational changes, and the interaction of solvated lignin oligomers with model surfaces. We focus on the behavior of an oligomeric lignin model compound in methanol, ethanol, a binary mixture of ethanol and water, and water at both the RCF reaction temperature (473 K) and room temperature. Analysis of structural features of lignin suggests that these three organic solvent systems favorably solvate lignin, resulting in a more extended conformation suitable for catalytic conversion to valuable chemicals. We further introduce model palladium (Pd) and carbon (C) surfaces to understand how solvent choice impacts adsorption onto a representative catalytic surface and support, and to quantify the competition among the reactant and solvent molecules for the surface. Unbiased simulations suggest strong adsorption of lignin on both Pd and C surfaces at 473 K, with notable solvent-mediated differences in adsorption energies. Additionally, our findings indicate that lignin adsorption is promoted by the entropy change resulting from the displacement of solvent molecules from the surface. This study provides a molecular perspective of adsorption of lignin onto varying surfaces, which is a step towards understanding and optimizing the catalytic conversion of lignin into valuable chemicals.

adsorption↗
DOE OSTI2022

Modular Approach for the Synthesis of Bottlebrush Diblock Copolymers from Poly(Glycidyl Methacrylate)-block-Poly(Vinyldimethylazlactone) Backbones

A strategy that enables the facile synthesis of bottlebrush block copolymers with flexible backbones was developed. A demonstration of the strategy’s utility was carried out by grafting end-functionalized polymethylmethacrylate (PMMA) and polystyrene (PS) to the dually reactive block copolymer, poly(glycidyl methacrylate)-block-poly(vinyldimethylazlactone) (PGMA-b-PVDMA). Five different bottlebrush diblock copolymers were investigated by size-exclusion chromatography (SEC), 1H NMR, Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), X-ray scattering methods, atomic force microscopy (AFM), rheology and computational simulations using molecular dynamics (MD), and self-consistent field theory (SCFT). A relationship between the glass transition temperature and the fraction of chain ends was demonstrated by DSC and highlights the potential of this synthetic method to tailor polymer properties. All five samples were found to be in a disordered phase exhibiting multiscale structures revealed by two broad peaks in small-angle X-ray scattering (SAXS) that can be attributed to graft-to-graft and backbone-to-backbone density correlations using MD simulations. The SCFT-based simulations justify the observation of a disordered phase due to its stabilization by the grafts. Additionally, this modular approach can be easily extended to other grafts, including responsive, conducting, and charged polymers with the prerequisite end groups. The versatility and ease of assembling these functional bottlebrushes constitute a powerful “toolbox” method for the rapid and scalable synthesis of novel bottlebrush block copolymers with desired properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mechanistic insight into the active centers of single/dual-atom Ni/Fe-based oxygen electrocatalysts

Single-atom catalysts with maximum metal utilization efficiency show great potential for sustainable catalytic applications and fundamental mechanistic studies. We here provide a convenient molecular tailoring strategy based on graphitic carbon nitride as support for the rational design of single-site and dual-site single-atom catalysts. Catalysts with single Fe sites exhibit impressive oxygen reduction reaction activity with a half-wave potential of 0.89 V vs. RHE. We find that the single Ni sites are favorable to promote the key structural reconstruction into bridging Ni-O-Fe bonds in dual-site NiFe SAC. Meanwhile, the newly formed Ni-O-Fe bonds create spin channels for electron transfer, resulting in a significant improvement of the oxygen evolution reaction activity with an overpotential of 270 mV at 10 mA cm –2 . We further reveal that the water oxidation reaction follows a dual-site pathway through the deprotonation of *OH at both Ni and Fe sites, leading to the formation of bridging O 2 atop the Ni-O-Fe sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Design, Control and Application of Next Generation Qubits

Design, Control and Application of Next Generation Qubits Arun Bansil, Northeastern University (Principal Investigator) Claudio Chamon, Boston University (Co-Investigator) Adrian Feiguin, Northeastern University (Co-Investigator) Liang Fu, MIT (Co-Investigator) Eduardo Mucciolo, Univ. of Central Florida (Co-Investigator) Qimin Yan, Temple University (Co-Investigator) The quest for developing technologies for manipulating and storing information quantum mechanically is currently led by approaches that include Josephson-junctions, ion-traps, and qubits generated by defect spins in solids. Topological qubits, however, are inherently more robust to decoherence by environmental effects, and should be able to sprint ahead once practical barriers have been overcome. At the present stage of the development of the field, it is important to explore a variety of architectures and materials beyond the conventional paradigms in order to seed breakthroughs toward building a scalable quantum computer. Our comprehensive theoretical research program involved four interconnected thrusts as follows. • A materials discovery effort in two-dimensional compounds in search of materials to support Majorana zero modes and defect structures suitable as qubits. • Exploration of architectures for topological quantum computation by investigating both superconducting Majorana qubits, and robust platforms for braiding with new “meta-materials” built of arrays of Majorana qubits. • Investigation of properties of hybrid metal-organic qubits based on transition-metal centers in graphene, and molecular crystals of polyaromatic complexes with embedded transition-metal atoms. • Development of tensor-network and semiclassical approaches to study decoherence in the presence of random and dispersive spin baths, and NV centers in diamond. The full spectrum of theoretical and numerical approaches was used to address the goals of this project including first-principles, density-matrix-renormalization group, tensor networks, and data-driven high-throughput approaches using materials database and machine-learning.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Supernovae effects on the terrestrial atmosphere

The first effects of a nearby (10 parsec) supernova on the earth's atmosphere will be caused by ultraviolet radiation dissociating molecular oxygen. The event will be of about one month's duration. Several months later nuclear gamma radiation may arrive, causing a decrease in atmospheric ozone. Cosmic radiation from the supernova remnant will not intercept the earth for at least 1000 years at which time ozone will be seriously depleted. Supernova ultraviolet radiation increases column ozone and atomic oxygen. Atmospheric thermal structure is modified with a large temperature increase in the mesosphere and lower thermosphere and a decrease at higher altitudes caused by enhanced heat loss due to atomic oxygen radiation and conduction.

Aikin, A. C.↗
NASA NTRS1981

Morphology of Saturn's aurora

Aurorally-excited emissions of atomic and molecular hydrogen come from a narrow circumpolar band near 80 deg north and south latitude on Saturn. The aurorae, which lie near the edge of the polar cap region, are continuously excited in both the north and south. If the strong variations observed in the auroral intensity are temporal, rather than longitudinal, they may be related to the periodic structure in the Saturn kilometric radiation.

Sandel, B. R.↗
NASA NTRS1987

Submillimeter and far infrared line observations of M17 SW: A clumpy molecular cloud penetrated by UV radiation

Millimeter, submillimeter, and far infrared spectroscopic observations of the M17 SW star formation region are discussed. The results require the molecular cloud near the interface to be clumpy or filamentary. As a consequence, far ultraviolet radiation from the central OB stellar cluster can penetrate into the dense molecular cloud to a depth of several pc, thus creating bright and extended (CII) emission from the photodissociated surfaces of dense atomic and molecular clumps or sheets. The extended (CII) emission throughout the molecular cloud SW of the M17 complex has a level 20 times higher than expected from a single molecular cloud interface exposed to an ultraviolet radiation field typical of the solar neighborhood. This suggests that the molecular cloud as a whole is penetrated by ultraviolet radiation and has a clumpy or filamentary structure. The number of B stars expected to be embedded in the M17 molecular cloud probably can provide the UV radiation necessary for the extended (CII) emission. Alternatively, the UV radiation could be external, if the interstellar radiation in the vicinity of M17 is higher than in the solar neighborhood.

Stutzki, J.↗
NASA NTRS2003

Crystallization Physics in Biomacromolecular Systems

The crystals are built of molecules of protein, nucleic acid and their complexes, like viruses, approx. 5x10(exp 3)+ 3x10(exp 6) Da in weight and 2 + 20 nm in effective diameter. This size strongly exceeds action range of molecular forces and makes a big difference with inorganic crystals. Intermolecular contacts form patches on the biomacromolecular surface. Each patch may occupy only a small percent of the whole surface and vary from polymorph to polymorph of the same protein. Thus, under different conditions (pH, solution chemistry, temperature, any area on the macromolecular surface may form a contact. The crystal Young moduli, E approx. equals 0.1 + 0.5 GPa are more than 10 times lower than that of inorganics and the biomolecules themselves. Water within biocrystals (30-70%) is unable to flow unless typical deformation time is longer than approx. 10(exp -5)s. This explains the discrepancy between light scattering and static measurements of E. Nucleation and Growth requires typically concentrations exceeding the equilibrium ones up to 100 times - because of the new size scale results in 10 - 10(exp 3) times lower kinetic coefficients than that needed for inorganic solution growth. All phenomena observed in the latter occur with protein crystallization and are even better studied by AFM. Crystals are typically facetted. Among unexpected findings of general significance are - net molecular exchange flux at kinks is much lower than that expected from supersaturation, steps with low (< approx. 10(exp -2)) kink density at steps follow Gibbs-Thomson law only at very low supersaturations, step segment growth rate may be independent of step energy. Crystal perfection is a must of biocrystallization to achieve the major goal to find 3-D atomic structure of biomacromolecules by x-ray diffraction. Poor diffraction resolution (> 3Angstrom) makes crystallization a bottleneck for structural biology. All defects typical of small molecule crystals are found in biocrystals, but the defects responsible for poor resolution are not identified. Conformational changes are one of them. Biocrystallization in microgravity reportedly results in 20% cases of better crystals. The mechanism of how lack of convection can do this is still not clear. Lower supersaturation, self-purification &om preferentially trapped homologous impurities and step bunching are viable hypotheses.

Chernov, A. A.↗
NASA NTRS1998

Carbon Nanotube Based Molecular Electronics

Carbon nanotubes and the nanotube heterojunctions have recently emerged as excellent candidates for nanoscale molecular electronic device components. Experimental measurements on the conductivity, rectifying behavior and conductivity-chirality correlation have also been made. While quasi-one dimensional simple heterojunctions between nanotubes with different electronic behavior can be generated by introduction of a pair of heptagon-pentagon defects in an otherwise all hexagon graphene sheet. Other complex 3- and 4-point junctions may require other mechanisms. Structural stability as well as local electronic density of states of various nanotube junctions are investigated using a generalized tight-binding molecular dynamics (GDBMD) scheme that incorporates non-orthogonality of the orbitals. The junctions investigated include straight and small angle heterojunctions of various chiralities and diameters; as well as more complex 'T' and 'Y' junctions which do not always obey the usual pentagon-heptagon pair rule. The study of local density of states (LDOS) reveal many interesting features, most prominent among them being the defect-induced states in the gap. The proposed three and four pointjunctions are one of the smallest possible tunnel junctions made entirely of carbon atoms. Furthermore the electronic behavior of the nanotube based device components can be taylored by doping with group III-V elements such as B and N, and BN nanotubes as a wide band gap semiconductor has also been realized in experiments. Structural properties of heteroatomic nanotubes comprising C, B and N will be discussed.

Srivastava, Deepak↗
DOE OSTI2026

Ferroelectric Fractals: Switching Mechanism of Wurtzite AlN

The advent of wurtzite ferroelectrics is enabling new ferroelectric devices for computer memory that have the potential to bypass the von Neumann bottleneck due to their robust polarization and silicon compatibility. However, the atomistic switching mechanism of wurtzites is still undetermined due to the limitations of density functional theory simulation size and experimental temporal and spatial resolution. Thus, physics-informed materials engineering to reduce coercive field and breakdown in these devices has been limited. In this work, the atomistic mechanism of domain wall migration and domain growth in aluminum nitride-based wurtzites is uncovered using molecular dynamics and Monte Carlo simulations. We reveal the anomalous switching mechanism of fast 1D single columns of atoms propagating from a slow-moving 2D fractallike domain wall. We find that the critical nucleus is a single aluminum ion that breaks its bond with one nitrogen and bonds to another nitrogen; this creates a cascade that flips atoms directly only in the same column, due to the extreme locality (sharpness) of the domain walls in wurtzites. We further show how the fractallike shape of the domain wall in the 2D plane breaks assumptions in the Kolmogorov, Avrami, and Ishibashi (KAI) model and leads to the anomalously fast switching in wurtzite structured ferroelectrics.

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 OSTI2025

Ternary molecular switching in a single-crystal optical actuator with correlated crystal strain

A growing portfolio of single-crystal optical actuators is forging a new class of photonic materials that hold prospects for quantum technologies. Ruthenium-based complexes that exhibit this phenomenon via SO 2 -linkage photoisomerisation are of particular interest since they display multiple metastable states, once induced by green light; yet, complete photoconversion into each SO 2 -isomeric state is rarely achieved. We discover a new complex, trans-[Ru(SO 2 )(NH 3 ) 4 (4-bromopyridine)]tosylate 2 , that produces 100% photoconverted η 1 -OSO isomeric crystal structures at 90 K, which fully transition into η 2 -(OS)O photoisomers upon warming to 100 K, while the dark-state η 1 -SO 2 structure is wholly recovered by heating the crystal to room temperature. Crystal structures and optical-absorption profiles of each state are captured via in-situ light-induced single-crystal X-ray diffraction and optical-absorption spectroscopy. Results show that both photoisomeric species behave as optical switches, but with distinct optical properties. The photoisomerisation process causes thermally-reversible micro- and nanoscopic crystal strain, as characterised by optical microscopy and in-situ light-induced atomic-force microscopy.

actuators↗