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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Microscopic origin of Cooper pairing in the iron-based superconductor Ba 1-x K x Fe 2 As 2

Resolving the microscopic pairing mechanism and its experimental identification in unconventional superconductors is among the most vexing problems of contemporary condensed matter physics. We show that Raman spectroscopy provides an avenue towards this aim by probing the structure of the pairing interaction at play in an unconventional superconductor. As we study the spectra of the prototypical Fe-based superconductor Ba 1-x K x Fe 2 As 2 for 0.22 ≤ x ≤ 0.70 in all symmetry channels, Raman spectroscopy allows us to distill the leading s-wave state. In addition, the spectra collected in the B1g symmetry channel reveal the existence of two collective modes which are indicative of the presence of two competing, yet sub-dominant, pairing tendencies of d x 2 -y 2 symmetry type. A comprehensive functional Renormalization Group and random-phase approximation study on this compound confirms the presence of the two sub-leading channels, and consistently matches the experimental doping dependence of the related modes. In conclusion, the consistency between the experimental observations and the theoretical modeling suggests that spin fluctuations play a significant role in superconducting pairing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Constraining neutron-star matter with microscopic and macroscopic collisions

Interpreting high-energy, astrophysical phenomena, such as supernova explosions or neutron-star collisions, requires a robust understanding of matter at supranuclear densities. However, our knowledge about dense matter explored in the cores of neutron stars remains limited. Fortunately, dense matter is not probed only in astrophysical observations, but also in terrestrial heavy-ion collision experiments. Here we use Bayesian inference to combine data from astrophysical multi-messenger observations of neutron stars and from heavy-ion collisions of gold nuclei at relativistic energies with microscopic nuclear theory calculations to improve our understanding of dense matter. We find that the inclusion of heavy-ion collision data indicates an increase in the pressure in dense matter relative to previous analyses, shifting neutron-star radii towards larger values, consistent with recent observations by the Neutron Star Interior Composition Explorer mission. Our findings show that constraints from heavy-ion collision experiments show a remarkable consistency with multi-messenger observations and provide complementary information on nuclear matter at intermediate densities. This work combines nuclear theory, nuclear experiment and astrophysical observations, and shows how joint analyses can shed light on the properties of neutron-rich supranuclear matter over the density range probed in neutron stars.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Computational scanning tunneling microscope image database

We introduce the systematic database of scanning tunneling microscope (STM) images obtained using density functional theory (DFT) for two-dimensional (2D) materials, calculated using the Tersoff-Hamann method. It currently contains data for 716 exfoliable 2D materials. Examples of the five possible Bravais lattice types for 2D materials and their Fourier-transforms are discussed. All the computational STM images generated in this work are made available on the JARVIS-STM website ( https://jarvis.nist.gov/jarvisstm ). We find excellent qualitative agreement between the computational and experimental STM images for selected materials. As a first example application of this database, we train a convolution neural network model to identify the Bravais lattice from the STM images. We believe the model can aid high-throughput experimental data analysis. These computational STM images can directly aid the identification of phases, analyzing defects and lattice-distortions in experimental STM images, as well as be incorporated in the autonomous experiment workflows.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Microscopic relaxation channels in materials for superconducting qubits

Despite mounting evidence that materials imperfections are a major obstacle to practical applications of superconducting qubits, connections between microscopic material properties and qubit coherence are poorly understood. Here, we combine measurements of transmon qubit relaxation times ( T 1 ) with spectroscopy and microscopy of the polycrystalline niobium films used in qubit fabrication. By comparing films deposited using three different techniques, we reveal correlations between T 1 and intrinsic film properties such as grain size, enhanced oxygen diffusion along grain boundaries, and the concentration of suboxides near the surface. Qubit and resonator measurements show signatures of two-level system defects, which we propose to be hosted in the grain boundaries and surface oxides. We also show that the residual resistance ratio of the polycrystalline niobium films can be used as a figure of merit for qubit lifetime. This comprehensive approach to understanding qubit decoherence charts a pathway for materials-driven improvements of superconducting qubit performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

On the correlation between microscopic structural heterogeneity and embrittlement behavior in metallic glasses

To establish a relationship between microstructure and mechanical properties, we systematically annealed a Zr-based bulk metallic glass (BMG) at 100 ~ 300°C and measured their mechanical and thermal properties. The as-cast BMG exhibits some ductility, while the increase of annealing temperature and time leads to the transition to a brittle behavior that can reach nearly-zero fracture energy. The differential scanning calorimetry did not find any significant changes in crystallization temperature and enthalpy, indicating that the materials still remained fully amorphous. Elastic constants measured by ultrasonic technique vary only slightly with respect to annealing temperature and time, which does obey the empirical relationship between Poisson’s ratio and fracture behavior. Nanoindentation pop-in tests were conducted, from which the pop-in strength mapping provides a “mechanical probe” of the microscopic structural heterogeneities in these metallic glasses. Based on stochastically statistic defect model, we found that the defect density decreases with increasing annealing temperature and annealing time and is exponentially related to the fracture energy. A ductile-versus-brittle behavior (DBB) model based on the structural heterogeneity is developed to identify the physical origins of the embrittlement behavior through the interactions between these defects and crack tip.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Direct observation of electronic-liquid-crystal phase transitions and their microscopic origin in La 1/3 Ca 2/3 MnO 3

The ground-state electronic order in doped manganites is frequently associated with a lattice modulation, contributing to their many interesting properties. However, measuring the thermal evolution of the lattice superstructure with reciprocal-space probes alone can lead to ambiguous results with competing interpretations. Here, we provide direct observations of the evolution of the superstructure in La 1/3 Ca 2/3 MnO 3 in real space, as well as reciprocal space, using transmission electron microscopic (TEM) techniques. We show that the transitions are the consequence of a proliferation of dislocations plus electronic phase separation. The resulting states are well described by the symmetries associated with electronic-liquid-crystal (ELC) phases. Furthermore, our results resolve the long-standing controversy over the origin of the incommensurate superstructure and suggest a new structural model that is consistent with recent theoretical calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Activation of carbon dioxide by a terminal uranium–nitrogen bond in the gas-phase: a demonstration of the principle of microscopic reversibility

Activation of CO 2 is demonstrated by its spontaneous dissociative reaction with the gas-phase anion complex NUOCl 2 - , which can be considered as NUO + coordinated by two chloride anion ligands. This reaction was previously predicted by density functional theory to occur exothermically, without barriers above the reactant energy. In this paper, the present results demonstrate the validity of the prediction of microscopic reversibility, and provide a rare case of spontaneous dissociative addition of CO 2 to a gas-phase complex. The activation of CO 2 by NUOCl 2 - proceeds by conversion of a U[triple bond]N bond to a U[double bond]O bond and creation of an isocyanate ligand to yield the complex UO 2 (NCO)Cl 2 - , in which uranyl, UO 2 2+ , is coordinated by one isocyanate and two chloride anion ligands. This activation of CO 2 by a uranium(VI) nitride complex is distinctive from previous reports of oxidative insertion of CO 2 into lower oxidation state U(III) or U(IV) solid complexes, during which both C–O bonds remain intact. This unusual observation of spontaneous addition and activation of CO 2 by NUOCl 2 - is a result of the high oxophilicity of uranium. If the computed Gibbs free energy of the reaction pathway, rather than the energy, is considered, there are barriers above the reactant asymptotes such that the observed reaction should not proceed under thermal conditions. Finally, this result provides a demonstration that energy rather than Gibbs free energy determines reactivity under low-pressure bimolecular conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Direct-write liquid phase transformations with a scanning transmission electron microscope

The highly energetic electron beam from a scanning transmission electron microscope (STEM) can induce local changes in the state of matter, ranging from local knock-out and atomic movement, to amorphization/crystallization, and chemical/electrochemical reactions occuring at localized liquid-solid and gas-solid interfaces. To date, fundamental studies of e-beam induced phenomena and practical applications have been limited by conventional e-beam rastering modes that allow only for uniform e-beam exposures. Here we develop an automated liquid phase nanolithography method that is capable of directly writing nanometer scaled features within silicon nitride encapsulated liquid cells. An external beam control system, connected to the scan coils of an aberration-corrected STEM, is used to precisely control the position, dwell time, and scan velocity of a sub-nanometer STEM probe. Site-specific locations in a sealed liquid cell containing an aqueous solution of H 2 PdCl 4 are irradiated to controllably deposit palladium onto silicon nitride membranes. We determine the threshold electron dose required for the radiolytic deposition of metallic palladium, explore the influence of electron dose on the feature size and morphology of nanolithographically patterned nanostructures, and propose a feedback-controlled monitoring method for active control of the nanofabricated structures through STEM detector signal monitoring. As a result, this approach enables both fundamental studies of electron beam induced interactions with matter, as well as opens a pathway to fabricate nanostructures with tailored architectures and chemistries via shape-controlled nanolithographic patterning from liquid phase precursors.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Basics of the scanning electrochemical microscope and its application in the characterization of lithium-ion batteries: a brief review

A scanning electrochemical microscope (SECM) can directly monitor electrochemical processes at interfaces of electrodes and electrolytes and has been used as an analytical tool for lithium-ion battery (LIB) studies. Through SECM, we can visualize the electrochemical reactivities of active species in LIBs in-situ during cycling. This review begins with introducing SECM-based LIB research and then summarizes the working mechanism and operating modes of the technique as well as combinations of SECM with other techniques for LIB studies. We review the results with a focus on the interfacial properties, surface reactions and electrochemical activity of different electrode materials for LIBs. The investigations of battery degradation, kinetic parameters and electrolyte swelling by SECM are also discussed. Finally, the current limitations and perspectives are also described regarding future developments.

25 ENERGY STORAGE↗
DOE OSTI2024

Microscopic modeling of direct pre-equilibrium emission: Impact on exclusive and inclusive (n, x n) and fission channels

We report on a microscopic modeling of the first order of multistep direct emission based on one phonon excitations, given by the QRPA model, and an effective in-medium nucleon nucleon interaction, described within the JLM folding model. The results of our coupled channels framework for deformed target are illustrated in the case of low energy discrete state excitations in 152 Sm. Pre-equilibrium predictions and their impact on inclusive and exclusive (n,xn) cross sections and fission cross sections are discussed for actinides. We discuss the importance of i) collective excitations to describe the neutron emission spectra and of ii) spin distribution of the residual nucleus formed after the neutron pre-equilibrium emission, that is a key ingredient to model the residual nucleus decay.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Microscopic evidence for scission neutrons

We discuss the neck rupture stage of fission and the emission of particles afterwards, two extremely rapid and highly non-equilibrium processes. Currently, the neck rupture cannot be directly probed by experiment, highlighting the importance of reliable theoretical predictions for this stage of fission. Time-dependent density functional theory (TDDFT) is used to simulate the spontaneous fission of 252 Cf. In conjunction with statistical models, inputs from microscopic calculations can be used to make predictions for prompt neutron and gamma emission spectra, quantities which can be experimentally measured. Here we characterize the scission mechanism within TDDFT and estimate the number of scission neutrons and their kinetic energies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Microscopic origin of criticality at macroscale in QCD chiral phase transition

We reveal that the criticality of the chiral phase transition in QCD at the macroscale arises from the microscopic energy levels of its fundamental constituents, the quarks. We establish a novel relation between cumulants of the chiral order parameter (i.e., chiral condensate) and correlations among the energy levels of quarks (i.e., eigenspectra of the massless Dirac operator), which naturally leads to a generalization of the Banks-Casher relation. Based on this novel relation and through (2+1)-flavor lattice QCD calculations using the HISQ action with varying light quark masses in the vicinity of the chiral phase transition, we demonstrate that the correlations among the infrared part of the Dirac eigenspectra exhibit same universal scaling behaviors as expected of the cumulants of the chiral condensate. We find that these universal scaling behaviors extend up to the physical values of the up and down quark masses.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Quantifying the Mobility and Energy Benefits of Automated Mobility Districts Using Microscopic Traffic Simulation

Connected and automated vehicles (CAVs) are increasingly being discussed as the basis for shared mobility and on-demand services to replace privately owned vehicles. The rapid growth of transportation networking companies (TNCs) and their increasing investment in automated vehicle (AV) technologies attests to this. Combining the concepts of TNCs, with AV and on-demand transit services, the term 'automated mobility district' (AMD) describes a district-scale implementation of CAV technology to realize the full benefits of a shared, fully automated vehicle service within a confined region. This research effort provides a modeling architecture for AMDs along with a preliminary analysis to quantify the mobility and energy benefits of such districts. A customized open-source microscopic mobility simulation toolkit built on the simulation of urban mobility (SUMO) platform is implemented for AMD performance evaluation. Experimental scenarios are tested with different combinations of operational variables to provide insights on energy and mobility gains that can be realized in AMDs.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2013

A high-stability scanning tunneling microscope achieved by an isolated tiny scanner with low voltage imaging capability

We present a novel homebuilt scanning tunneling microscope (STM) with high quality atomic resolution. It is equipped with a small but powerful GeckoDrive piezoelectric motor which drives a miniature and detachable scanning part to implement coarse approach. The scanning part is a tiny piezoelectric tube scanner (industry type: PZT-8, whose d{sub 31} coefficient is one of the lowest) housed in a slightly bigger polished sapphire tube, which is riding on and spring clamped against the knife edges of a tungsten slot. The STM so constructed shows low back-lashing and drifting and high repeatability and immunity to external vibrations. These are confirmed by its low imaging voltages, low distortions in the spiral scanned images, and high atomic resolution quality even when the STM is placed on the ground of the fifth floor without any external or internal vibration isolation devices.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Microscopic magnetic properties of an oxygen-doped Tb-Fe thin film by magnetic Compton scattering

The magnetic Compton scattering of a Tb{sub 32}Fe{sub 55}O{sub 13} film was measured in order to investigate the microscopic magnetization processes (i.e., the spin moment, orbital moment, and element specific moments). The trend of the spin magnetic moment was the same as that of the total magnetic moment but opposite to the orbital magnetic moment. In the low magnetic field region, the magnetic moments were not perfectly aligned perpendicular to the film surface, and the perpendicular components were found to mainly arise from the magnetic moment of Tb. Oxygen atoms hinder long range magnetic interaction and hence also affect the magnetization process of the magnetic moments of Tb and Fe.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Linear relationship between water wetting behavior and microscopic interactions of super-hydrophilic surfaces

Using molecular dynamics simulations, we show a fine linear relationship between surface energies and microscopic Lennard-Jones parameters of super-hydrophilic surfaces. The linear slope of the super-hydrophilic surfaces is consistent with the linear slope of the super-hydrophobic, hydrophobic, and hydrophilic surfaces where stable water droplets can stand, indicating that there is a universal linear behavior of the surface energies with the water-surface van der Waals interaction that extends from the super-hydrophobic to super-hydrophilic surfaces. Moreover, we find that the linear relationship exists for various substrate types, and the linear slopes of these different types of substrates are dependent on the surface atom density, i.e., higher surface atom densities correspond to larger linear slopes. These results enrich our understanding of water behavior on solid surfaces, especially the water wetting behaviors on uncharged super-hydrophilic metal surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

A 350 mK, 9 T scanning tunneling microscope for the study of superconducting thin films on insulating substrates and single crystals

We report the construction and performance of a low temperature, high field scanning tunneling microscope (STM) operating down to 350 mK and in magnetic fields up to 9 T, with thin film deposition and in situ single crystal cleaving capabilities. The main focus lies on the simple design of STM head and a sample holder design that allows us to get spectroscopic data on superconducting thin films grown in situ on insulating substrates. Other design details on sample transport, sample preparation chamber, and vibration isolation schemes are also described. We demonstrate the capability of our instrument through the atomic resolution imaging and spectroscopy on NbSe{sub 2} single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗