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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Interfacial magnetic characteristics of nearly compensated gadolinium iron garnet

Reports on spin Hall magnetoresistance, magnonic spin currents from thermal gradients, and spin transfertorque magnetic random-access memory using compensated ferrimagnets largely discuss bulk magnetization but lack consideration of depth profiles or interfacial characteristics. Here, magnetic and structural characterization of profiles and interfaces was performed for nearly compensated gadolinium iron garnet (GdIG) thin films. X-ray diffraction and reciprocal space maps show that sputter deposited GdIG on Si is polycrystalline with the desired cubic garnet phase, and GdIG on gadolinium gallium garnet (GGG) is epitaxial with <0.06% compressive strain. Temperature-dependent magnetometry confirms the compensation temperatures of GGG/GdIG and Si/GdIG to be 285 and 260 K, respectively, both near room temperature. Interestingly, these measurements suggest the presence of unsaturated rare-earth moments, which result in a characteristic hysteresis between heating and cooling sequences in the magnetization-temperature curves at zero field. Depth-profile measurements from polarized neutron reflectometry (PNR) indicate up to 91% volume fraction in GdIG on Si. At the interface, PNR reveals a region containing magnetized Fe-doped GGG, a low-density GdIG at the GGG/GdIG interface, and a thin magnetically dead layer at the Si/GdIG interface. Cross-sectional transmission electron microscopy and energy dispersive x-ray spectroscopy confirm the assessment of PNR. In conclusion, the magnetic characteristics of interfacial regions are attributed to intermixing of Fe-Ga at the GGG/GdIG interface and the presence of amorphous Fe-Si at the Si/GdIG interface.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Synthesis and characterization of electron beam irradiation-induced damage in polycrystalline metal thin films

High-energy physics research, industrial sterilizing, and material processing depend extensively on electron beam accelerators. Exit windows are crucial components of such electron accelerator systems, maintaining vacuum integrity inside the machine while providing mechanical strength, thermal stability, and radiation resistance at the beam-target interface. In this study, thin metallic films of Ni, Ti, Cr, and V were explored for use in electron beam exit windows, and their properties were compared with the properties of their bulk counterparts. Simulation results of metal foils predicted Ti to exhibit less beam power dissipation compared to Ni. However, Ni possesses superior mechanical and structural properties compared to Ti. The performance of these films under electron beam irradiation was examined by depositing thin layers of these films on silicon and metallic substrates using magnetron sputtering and exposing them to e-beam irradiation in a controlled setup. The deposited films were subjected to a dose of approximately 66 kGy at a beam energy of 10 MeV and characterized prior to and postexposure to the beam using field emission scanning electron microscopy, atomic force microscopy, x-ray diffraction (XRD), and nanoindentation. Particular emphasis was given to characteristics like the grain structure, surface morphology, dislocation density, and hardness. XRD patterns revealed irradiation-induced changes in peak intensities, while the crystallinity remained largely unchanged. Nanoindentation results showed that the pristine and irradiated Ti and Ni films were twice as hard when compared to bulk Ti and Ni samples, regardless of the substrate type used (Si or bulk Ti, or Ni). These results emphasize the superior mechanical properties of thin metal films compared to their bulk counterparts. In conclusion, this study advances the optimization of thin film materials for robust and efficient e-beam applications, ensuring improved durability and operational reliability.

AFM↗
DOE OSTI2023

Tuning Self-Assembly of Gold Nanoparticles Grafted with Charged Polymers by Varying Temperature and Electrolytes

Here, we report on the assembly of gold nanoparticles (AuNPs, 5 and 10 nm core diameters) grafted with poly(ethylene glycol) (PEG) terminated with either positively (–NH 2 ) or negatively charged (–COOH) end groups. We employ synchrotron-based small-angle X-ray scattering (SAXS) techniques to investigate the effect of electrolytes and temperature on the assembly and crystallization behavior of these grafted AuNPs. Our studies reveal that –NH 2 -grafted AuNPs spontaneously assemble into a layered hexagonal structure that deteriorates upon adding K 2 CO 3 to the suspension. The hexagonal structure recovers after heating the same suspension above 60 °C. On the other hand, the COOH-terminated AuNPs remain dispersed in the suspensions and assemble and crystallize into a face-centered cubic structure only in the presence of K 2 CO 3 at temperatures above 60 °C. Varying the pH of the –NH 2 -terminated AuNP suspensions induces short-range order (SRO) structures with a single characteristic length scale that shrinks upon heating. Similarly, SRO for the –COOH-terminated AuNP is realized only by lowering the pH. This study demonstrates the use of electrolytes and temperature on the surface charge of grafted AuNPs as knobs to tune self-assembly and crystallization.

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

Chemo–mechanical properties of carbon fiber reinforced geopolymer interphase

Geopolymers, as a potentially environmentally friendly alternative to Portland cement, are increasingly attracting attention in the construction industry. Various methods have been applied for customizing the properties of geopolymers and improving their commercial viability. One of the promising methods for refining the properties of geopolymers such as their toughness is the use of short fibers. The effectiveness of a high-strength short fiber in the geopolymer matrix is largely dependent on the interfacial bonding between the fiber and its surrounding matrix. While the importance of this interfacial chemistry is highlighted in the literature, the characteristics of this bonding structure have not been fully understood. In this paper, we aim to investigate the bonding mechanism between the carbon fiber and metakaolin-based geopolymer matrix. For the first time, the existence and nature of the chemical bonding at the interfacial region (interphase) between carbon fiber and geopolymer matrix has been revealed. X-ray pair distribution function computed tomography (PDF-CT), field emission-scanning electron microscopy imaging, and nanoindentation techniques are employed to discern the chemo-mechanical properties of the interphase. PDF-CT results show the emergence of a new atom-atom correlation at the interfacial region (around 1.82 angstrom). This correlation is a characteristic of interfacial bonding between the fiber and its surrounding matrix, where the existence of chemical linkages (potentially Al-V-O-C) between fibers and the matrix contributes to the adhesion between the two constituents making up the composite. Due to such chemical bonding, the nanomechanical properties of the interfacial region fall between that of the carbon fiber and geopolymer. The combination of advanced techniques is proved useful for enhancing our understanding of the interfacial chemistry between fibers and the binding matrix. This level of knowledge facilitates the engineering of composite systems through the manipulation of their nanostructure.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Gallidation assisted impurity doping

In one embodiment, a product includes a structure comprising a material of a Group-III-nitride having a dopant, where a concentration of the dopant in the structure has a concentration gradient characteristic of diffusion of the dopant inward from at least a portion of a surface of the structure in a direction substantially normal to the portion of the surface. The structure has less than 1% decomposition of the Group-III-nitride at the surface of the structure.

Voss, Lars↗
DOE OSTI2021

Conceptual Designs of the Structure of Inflatable Blades for Enabling Larger Turbines

Over the last couple of decades, increasingly larger rotor diameters have enabled significant reductions in the levelized cost of energy for wind through higher energy capture and improved capacity factors. But for onshore turbines, this has been met with manufacturing and transportation challenges. To enable larger onshore rotors, an innovative inflatable blade concept is investigated that employs both traditional and onsite manufacturing. The design architecture consists primarily of an inflatable aerodynamic shell attached to a factory-manufactured primary structure. Multiple architectures, cross-sectional topologies, and material combinations for the primary structure are investigated, as well as multiple skin materials. Structural cross-sectional characteristics are compared to a traditional blade, and inflatability and cost evaluations are presented. Results show that a box-beam architecture using only composite materials yields significant mass reduction with mature technologies/processes and modest cost decrease compared to traditional blade construction. This low-TRL study demonstrates the inflatable blade concept's techno-economic potential.

49 EE - Wind and Water Power Program - Wind (EE-4W↗
DOE OSTI2022

Exploring the sensitivity of charge-exchange ( p , n ) reactions to the neutron density distribution

The determination of the nuclear neutron properties suffers from uncontrolled uncertainties, which have attracted considerable attention recently, such as in the context of the PREX experiment. Our aim is to analyze the sensitivity of charge-exchange (p,n) reactions to the neutron density distribution ρ n and constrain the neutron characteristics in the nuclear structure models. Method: By combing the folding and the mean-field models, the nucleon-nucleus (N,A) potential can be obtained from the nuclear density distribution. Further, the (p,p) and (p,n) cross sections for 48 Ca and 208 Pb are calculated following the distorted-wave Born approximation method. As a result, compared with the (p,p) cross section, the effects of ρ n variation on the (p,n) cross section are significant, which is due to the impact of isovector properties. Based on the global folding model analyses of data, it is found that 48 Ca and 208 Pb have relatively large neutron skin thickness ΔR np . Results illustrate that the charge-exchange (p,n) reaction is a sensitive probe of ρ n . The results in this paper can offer useful guides for future experiments of neutron characteristics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Unlikelihood of a phonon mechanism for the high-temperature superconductivity in La 3 Ni 2 O 7

The discovery of ~80 K superconductivity in nickelate La 3 Ni 2 O 7 under pressure has ignited intense interest. Here, we present a comprehensive first-principles study of the electron-phonon (e-ph) coupling in La 3 Ni 2 O 7 and its implications on the observed superconductivity. Our results conclude that the e-ph coupling is too weak (with a coupling constant λ ≲ 0.5) to account for the high T c , albeit interesting many-electron correlation effects exist. While Coulomb interactions (via GW self-energy and Hubbard U) enhance the e-ph coupling strength, electron doping (oxygen vacancies) introduces no major changes. Additionally, different structural phases display varying characteristics near the Fermi level, but do not alter the conclusion. The e-ph coupling landscape of La 3 Ni 2 O 7 is intrinsically different from that of infinite-layer nickelates. These findings suggest that a phonon-mediated mechanism is unlikely to be responsible for the observed superconductivity in La 3 Ni 2 O 7 , pointing instead to an unconventional nature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Chemical Kinetics Underlying the Sooting Tendency and Auto-Ignition Characteristics of Linear, Branched, and Cyclic Ether Compounds

Biofuels present opportunities for improving the performance and reducing emissions from internal combustion engines by incorporating oxygenated functional groups to the fuels. Among various oxygenates, ethers have been recognized as promising candidates for an alternative to conventional diesel fuel owing to their higher reactivity and lower sooting tendency. The detailed guidelines for designing ethers, however, have not been fully discussed, even though their combustion characteristics are sensitive to the molecular structure. This study was devoted to exploring the structure-property relationships, particularly focusing on the cetane number and yield sooting index, using five linear, branched, and cyclic ethers: di-amyl-ether, 4-butoxy-heptane, 3,3-dimethyl-oxetane, 2-ethyl-4-methyl-1,3-dioxolane, and 2-isopropyl-4-methyl-1,3-dioxolane. First, we examined the chemical kinetics underlying the sooting tendency of the test fuels. The combustion product distribution was measured from flow reactor experiments at 750-1100 K, F=3, at atmospheric pressure. As a result, it was revealed that the sooting tendency is closely related to the size of hydrocarbon intermediates in the high-temperature regime (>1000 K); that is, larger hydrocarbons lead to more soot precursor formation. The underlying chemistry determining the size of the hydrocarbons from the tested fuels was analyzed using reaction pathway analysis and quantum mechanics calculations, which showed that the branched and cyclic ether structures form abundant C3-C4 compounds. Moreover, the auto-ignition characteristics of the test fuels were studied using the flow reactor at low-temperature (400-700 K) and F=1. We found a clear difference in the combustion-product distribution from high and low reactivity fuels, which was then correlated to the systematic analysis of the key reaction energy barriers with the varying molecular structure.

BIOMASS FUELS,INORGANIC, ORGANIC, PHYSICAL, AND AN↗
DOE OSTI2021

Geometric deep learning of RNA structure

RNA molecules adopt three-dimensional structures that are critical to their function and of interest in drug discovery. Few RNA structures are known, however, and predicting them computationally has proven challenging. We introduce a machine learning approach that enables identification of accurate structural models without assumptions about their defining characteristics, despite being trained with only 18 known RNA structures. The resulting scoring function, the Atomic Rotationally Equivariant Scorer (ARES), substantially outperforms previous methods and consistently produces the best results in community-wide blind RNA structure prediction challenges. By learning effectively even from a small amount of data, our approach overcomes a major limitation of standard deep neural networks. Because it uses only atomic coordinates as inputs and incorporates no RNA-specific information, this approach is applicable to diverse problems in structural biology, chemistry, materials science, and beyond.

Townshend, Raphael J. L.↗
DOE OSTI2021

Evolution of global and local deformation in additively manufactured octet truss lattice structures

Additively manufactured lattice truss structures, often referred to as architected cellular materials, present significant advantages over conventional structures due to their unique characteristics such as high strength-to-weight ratios and surface area-to-volume ratios. These geometrically complex structures, however, come with concomitant challenges for qualification and inspection. In this study, compression testing interrupted with micro-computed tomography inspection was conducted to monitor the evolution of global and local deformation throughout the loading process of 304L stainless steel octet truss lattice structures. Both two- and three-dimensional image analysis techniques were leveraged to characterize geometric heterogeneities resulting from the laser powder bed fusion manufacturing process as well as track the structure throughout deformation. Variations from model-predicted behavior resulting from these heterogeneities are considered relative to the predicted and actual responses of the structures during compression to better understand, model, and predict the octet truss lattice structure compression response.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Advanced Modeling and Simulation Methods for Evaluation of Thermal Neutron Scattering Materials

With the rise of interest in thermal neutron scattering data for advanced reactor, criticality safety, and shielding applications, new experimental data are required for evaluation of new materials or for re-evaluation (or validations) of previously evaluated materials. New experimental data are evaluated in a three-step process: (1) computing the phonon characteristics, (2) computing the dynamic structure factor (DSF) from the data, and (3) using the experimental setup to simulate the experimental data. All three steps have challenges, ranging from the need for a sufficiently general material simulation code—a processing code that can compute the corresponding DSF—to having a detailed layout of the instrument/beamline/facility where the data were measured. Whereas phonon characteristics of materials can be computed using various methods (molecular dynamics, density functional theory, etc.), a high-fidelity computation of the DSF and the simulation of the experiment based on the DSF is vital to the accuracy of the evaluation. The latter two steps can be achieved by using the two corresponding code systems developed by instrument scientists at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory: (1) OCLIMAX, a program that calculates the dynamic structure factor from DFT and MD simulation results, and (2) MCViNE, a Monte Carlo neutron ray-tracing program designed to simulate neutron scattering experiments. Recently, polyethylene and yttrium hydride were measured at the Wide Angular-Range Chopper (ARCS) and SEQUOIA instrument stations of the SNS. These experiments are simulated using the density functional theory code, the Cambridge Serial Total Energy Package (CASTEP), to compute its phonon characteristics (eigenvalues/vectors and PDOS), which is then processed using OCLIMAX to yield the DSF, and finally the data at each instrument station are simulated by the MCViNE for comparison to the measured data for evaluation. For comparison to conventional evaluation methods, the scattering data processed from OCLIMAX are compared against those processed from the LEAPR module of NJOY, and the results from MCViNE simulations are compared against previously used simplified beamline models implemented in the Monte Carlo N-Particle (MCNP) code.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

AIMD‐Based Protocols for Modeling Exciplex Fluorescence Spectra and Inter‐System Crossing in Photocatalytic Chromophores

ABSTRACT This study introduces a computational protocol for modeling the emission spectra of exciplexes using excited‐state ab initio molecular dynamics (AIMD) simulations. The protocol is applied to a model exciplex formed by oligo‐p‐phenylenes (OPPs) and triethylamine (TEA), which is of interest in the context of photocatalytic reduction of . AIMD facilitates efficient sampling of the conformational space of OPP3 and OPP4 exciplexes with TEA, offering a dynamic alternative to previously employed static methods. The AIMD‐based protocol successfully reproduces experimental emission spectra for OPP‐TEA exciplexes, agreeing with previous computational and experimental findings. The results show that AIMD simulations provide an efficient means of sampling the conformational space of these exciplexes, requiring less user input and, in some instances, fewer computational resources than multiple excited‐state optimizations initiated from user‐specified initial structures. The study also evaluates the yield of intersystem crossing (ISC) using AIMD and Landau‐Zener probability. The results suggest that ISC is a minor decay channel for OPP3 and OPP4. This work provides new insights into the structural flexibility and emission characteristics of OPP‐TEA photoredox catalyst systems, potentially contributing to improved design strategies for organic chromophores in reduction applications.

Giudetti, Goran [Department of Chemistry Universit↗
DOE OSTI2021

Corrosion integrity of oil cement modified by environment responsive microspheres for CO2 geologic sequestration wells

In order to ensure the safe and effectiveness of CO{sub 2} geological storage, an environmental responsive polymer microspheres (ERPM) was prepared to improve the corrosion resistance of cement stone. The structure and environmental response characteristics of ERPM were characterized, and then the anti-corrosion performance and anti-corrosion mechanism for ERPM were discussed. The results shown that ERPM had good environmental response characteristics and temperature resistance. ERPM could effectively suppressed the corrosion rate and the damage degree of mechanical properties of cement stone. The corrosion integrity of cement stone was improved due to the acidic response characteristic and form polymer films of ERPM, which effectively shield the direct contact between corrosion medium and hydration products.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Quinonoid versus Aromatic π-Conjugated Oligomers and Polymers and Their Diradical Characters

Quinonoid elements in π-conjugated oligomers and polymers have promising characteristics by providing unique structures and electronic properties, including varying degrees of ground state open shell diradical character and small band gaps. So far, quinonoid ground state polymers were rarely identified, and one of the goals of this work was to expand the portfolio of such systems in which over 17 different repeat units were considered, about half preferred a quinonoid and half preferred aromatic structures plus several with the alternating A-Q composition were also included. The dependency of the diradical character as a function of size and composition opens a rich space to discover trends affecting the aromaticity and diradical character. Herein, we show that the diradical character is a useful parameter to classify a wide variety of polymers based on their ground states in a systematic study of a large number of homo- and heterosystems. Homo-polymers with quinonoid ground states show a high diradical character, while those with the aromatic ground state behave as closed-shell systems with no or a very small diradical character. The diradical character of quinonoid systems depends strongly on the size, which increases with the size of the oligomer. Here, we found a correlation between the diradical character and the interring C–C distance as well as the singlet–triplet energy gaps. In alternating copolymers mixing quinonoid and aromatic subunits, we found open-shell hetero-polymers with moderate to high diradical characters.

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

Depletion-Driven Assembly of Polymer-Coated Nanocrystals

Depletion-driven assembly has been widely studied for micron-sized colloids, but questions remain at the nanoscale where the governing physics are impacted by stabilizing surface ligands or wrapping polymers, whose dimensions are similar to those of the colloidal core and the depletant. Here, we probe how wrapping colloidal tin-doped indium oxide nanocrystals with polymers affects their depletion-induced interactions and assembly in solutions of polyethylene glycol. Copolymers of polyacrylic acid grafted with polyethylene oxide provide nanocrystal wrappings with different effective polymer graft densities and molecular weights. (Ultra) small angle X-ray scattering, coarse-grained molecular dynamics simulation, and molecular thermodynamic theory were combined to analyze how depletant size and polymer wrapping characteristics affect depletion interactions, structure, and phase behavior. The results show how depletant molecular weight, as well as surface density and molecular weight of polymer grafts, set thresholds for assembly. These signatures are unique to depletion-driven assembly of nanoscale colloids and mirror phase behaviors of grafted nanoparticle–polymer composites. Optical and rheological responses of depletion-driven assemblies of nanocrystals with different polymer shell architectures were probed to learn how their structural differences impact properties. Finally, we discuss how these wrinkles for depletion-driven assembly at the nanoscale may provide fresh opportunities for designing responsive depletion interactions and dynamically reconfigurable materials.

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

Origin, nature, and the dynamic behavior of nanoscale vacancy clusters in Ni-rich layered oxide cathodes

Oxygen and transition metal (TM) vacancies in transition metal oxides (TMOs) play an important role in materials functionalities. For TMO cathodes of Li-ion batteries, vacancies can be introduced, either deliberately or inevitably, during materials synthesis or upon electrochemical cycling. Effects of vacancies on the electrochemical properties of cathodes critically depend on the dynamic characteristics of vacancies during the battery cycling. However, a fundamental understanding of such characteristics in the layer structured cathode remains elusive. Here, using scanning transmission electron microscopy (STEM), we reveal a cycling-induced aggregation behavior of oxygen and TM vacancies in a Ni-rich layer structured cathode of secondary particles. We discover that during the initial charging, vacancies aggregate to form visible vacancy-rich nanoregions (vacancy clusters) firstly at the outer layer of the secondary particle, and then the vacancy-cluster populated region extends to the inner part of particle upon fully charged. The spatial distinction of preferential nucleation of vacancy clusters at the outer layer indicates that the vacancy migration and clustering is associated with Li migration flux, which is larger at the outer layer, as all the Li from the inner part has to go through the outer layer. With extended cycling (> 50), these vacancy clusters become immobilized. We further reveal that the generation of these vacancy clusters is correlated to the material-synthesis conditions. Our findings solve a long-standing puzzle on the origin, nature, and behavior of the commonly visible vacancy clusters in the NMC cathode, providing insights on correlation between properties and dynamic behaviors of atomic-scale defects in layered oxide cathodes.

Li-ion batteries, layered oxide cathodes, NMC, cat↗
DOE OSTI2026

Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO 2 /Fe Bilayer Heterostructures

Initially identified as a promising altermagnetic (AM) candidate, rutile RuO 2 has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk nonmagnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patterned RuO 2 Hall bars and film heterostructures display magnetotransport signatures of magnetic ordering. Among the characteristics routinely cited as evidence for AM is the observation of exchange bias (EB) in an intimately contacted Fe-based ferromagnetic (FM) layer, which can arise due to interfacial coupling with a compensated antiferromagnet. Here, within this work, the origins of this EB coupling in Ru-capped RuO 2 /Fe bilayers are investigated using polarized neutron diffraction, polarized neutron reflectometry, cross-sectional transmission electron microscopy, and super conducting quantum interference device measurements. These experiments reveal that the EB behavior is driven by the formation of an iron oxide interlayer containing Fe 3 O 4 that undergoes a magnetic transition and pins interfacial moments within Fe at low temperature. These findings are confirmed by comparable measurements of Ni-based heterostructures, which do not display EB coupling, as well as magnetometry of additional Fe/Ru bilayers that display oxide-driven EB coupling despite the absence of the epitaxial RuO 2 layer. While these results do not directly refute the possibility of AM ordering in RuO 2 thin films, they reveal that EB, and related magnetotransport phenomena, cannot alone be considered evidence of this characteristic in the rutile structure due to interfacial chemical disorder.

RuO2↗