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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Discovery of orbital ordering in Bi 2 Sr 2 CaCu 2 O 8+x

The primordial ingredient of cuprate superconductivity is the CuO 2 unit cell. Theories usually concentrate on the intra-atom Coulombic interactions dominating the 3d 9 and 3d 10 configurations of each copper ion. However, if Coulombic interactions also occur between electrons of the 2p 6 orbitals of each planar oxygen atom, spontaneous orbital ordering may split their energy levels. This long-predicted intra-unit-cell symmetry breaking should generate an orbitally ordered phase, for which the charge transfer energy ε separating the 2p 6 and 3d 10 orbitals is distinct for the two oxygen atoms. Here we introduce sublattice-resolved ε(r) imaging to CuO 2 studies and discover intra-unit-cell rotational symmetry breaking of ε(r). Spatially, this state is arranged in disordered Ising domains of orthogonally oriented orbital order bounded by dopant ions, and within whose domain walls low-energy electronic quadrupolar two-level systems occur. Overall, these data reveal a Q = 0 orbitally ordered state that splits the oxygen energy levels by ~50 meV, in underdoped CuO 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

An atomic beam of titanium for ultracold atom experiments

Here we generate an atomic beam of titanium (Ti) using a “Ti-ball” Ti-sublimation pump, which is a common getter pump used in ultrahigh vacuum systems. We show that the sublimated atomic beam can be optically pumped into the metastable 3d 3 ( 4 F)4s a 5 F 5 state, which is the lower energy level in a cycling optical transition that can be used for laser cooling. We measure the atomic density and transverse and longitudinal velocity distributions of the beam through laser fluorescence spectroscopy. We find a metastable atomic flux density of 4.3(2) × 10 9 s -1 cm -2 with a mean forward velocity of 773(8) m/s at 2.55 cm directly downstream of the center of the Ti-ball. Owing to the details of optical pumping, the beam is highly collimated along the transverse axis parallel to the optical pumping beam and the flux density falls off as 1/r. We discuss how this source can be used to load atoms into a magneto-optical trap.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Visualizing and analyzing 3D biomolecular structures using Mol* at RCSB.org: Influenza A H5N1 virus proteome case study

The easiest and often most useful way to work with experimentally determined or computationally predicted structures of biomolecules is by viewing their three-dimensional (3D) shapes using a molecular visualization tool. Mol* was collaboratively developed by RCSB Protein Data Bank (RCSB PDB, RCSB.org) and Protein Data Bank in Europe (PDBe, PDBe.org) as an open-source, web-based, 3D visualization software suite for examination and analyses of biostructures. It is capable of displaying atomic coordinates and related experimental data of biomolecular structures together with a variety of annotations, facilitating basic and applied research, training, education, and information dissemination. Across RCSB.org, the RCSB PDB research-focused web portal, Mol* has been implemented to support single-mouse-click atomic-level visualization of biomolecules (e.g., proteins, nucleic acids, carbohydrates) with bound cofactors, small-molecule ligands, ions, water molecules, or other macromolecules. RCSB.org Mol* can seamlessly display 3D structures from various sources, allowing structure interrogation, superimposition, and comparison. Using influenza A H5N1 virus as a topical case study of an important pathogen, we exemplify how Mol* has been embedded within various RCSB.org tools—allowing users to view polymer sequence and structure-based annotations integrated from trusted bioinformatics data resources, assess patterns and trends in groups of structures, and view structures of any size and compositional complexity. In addition to being linked to every experimentally determined biostructure and Computed Structure Model made available at RCSB.org, Standalone Mol* is freely available for visualizing any atomic-level or multi-scale biostructure at rcsb.org/3d-view.

3D biostructure↗
DOE OSTI2022

RCSB Protein Data Bank 1D3D module: displaying positional features on macromolecular assemblies

Mapping positional features from one-dimensional (1D) sequences onto three-dimensional (3D) structures of biological macromolecules is a powerful tool to show geometric patterns of biochemical annotations and provide a better understanding of the mechanisms underpinning protein and nucleic acid function at the atomic level. We present a new library designed to display fully customizable interactive views between 1D positional features of protein and/or nucleic acid sequences and their 3D structures as isolated chains or components of macromolecular assemblies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Probing the atomically diffuse interfaces in Pd@Pt core-shell nanoparticles in three dimensions

Deciphering the three-dimensional atomic structure of solid-solid interfaces in core-shell nanomaterials is the key to understand their catalytical, optical and electronic properties. Here, we probe the three-dimensional atomic structures of palladium-platinum core-shell nanoparticles at the single-atom level using atomic resolution electron tomography. We quantify the rich structural variety of core-shell nanoparticles with heteroepitaxy in 3D at atomic resolution. Instead of forming an atomically-sharp boundary, the core-shell interface is found to be atomically diffuse with an average thickness of 4.2 Å, irrespective of the particle’s morphology or crystallographic texture. The high concentration of Pd in the diffusive interface is highly related to the free Pd atoms dissolved from the Pd seeds, which is confirmed by atomic images of Pd and Pt single atoms and sub-nanometer clusters using cryogenic electron microscopy. These results advance our understanding of core-shell structures at the fundamental level, providing potential strategies into precise nanomaterial manipulation and chemical property regulation.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1994

Three-dimensional radiative transfer on a massively parallel computer

We perform 3D radiative transfer calculations in non-local thermodynamic equilibrium (NLTE) in the simple two-level atom approximation on the Mas-Par MP-1, which contains 8192 processors and is a single instruction multiple data (SIMD) machine, an example of the new generation of massively parallel computers. On such a machine, all processors execute the same command at a given time, but on different data. To make radiative transfer calculations efficient, we must re-consider the numerical methods and storage of data. To solve the transfer equation, we adopt the short characteristic method and examine different acceleration methods to obtain the source function. We use the ALI method and test local and non-local operators. Furthermore, we compare the Ng and the orthomin methods of acceleration. We also investigate the use of multi-grid methods to get fast solutions for the NLTE case. In order to test these numerical methods, we apply them to two problems with and without periodic boundary conditions.

Vath, H. M.↗
DOE OSTI2022

Chemical order-disorder nanodomains in Fe 3 Pt bulk alloy

Chemical ordering is a common phenomenon and highly correlated with the properties of solid materials. By means of the redistribution of atoms and chemical bonds, it invokes an effective lattice adjustment and tailors corresponding physical properties. To date, however, directly probing the 3D interfacial interactions of chemical ordering remains a big challenge. In this work, we deciphered the interlaced distribution of nanosized domains with chemical order/disorder in Fe 3 Pt bulk alloy. HAADF-STEM images evidence the existence of such nanodomains. The reverse Monte Carlo method with the X-ray pair distribution function data reveal the 3D distribution of local structures and the tensile effect in the disordered domains at the single-atomic level. The chemical bonding around the domain boundary changes the bonding feature in the disordered side and reduces the local magnetic moment of Fe atoms. This results in a suppressed negative thermal expansion and extended temperature range in Fe 3 Pt bulk alloy with nanodomains. Our study demonstrates a local revelation for the chemical order/disorder nanodomains in bulk alloy. The understanding gained from atomic short-range interactions within the domain boundaries provides useful insights with regard to designing new functional compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Atomic structure and Mott nature of the insulating charge density wave phase of 1T-TaS 2

Here, using x-ray pair distribution function (PDF) analysis and computer modeling, we explore structure models for the complex charge density wave (CDW) phases of layered 1T-TaS 2 that both well capture their atomic-level features and are amenable to electronic structure calculations. The models give the most probable position of constituent atoms in terms of 3D repetitive unit cells comprising a minimum number of Ta–S layers. Structure modeling results confirm the emergence of star-of-David (SD) like clusters of Ta atoms in the high-temperature incommensurate (IC) CDW phase and show that, contrary to the suggestions of recent studies, the low-temperature commensurate (C) CDW phase expands upon cooling thus reducing lattice strain. The C-CDW phase is also found to preserve the stacking sequence of Ta–S layers found in the room temperature, nearly commensurate (NC) CDW phase to a large extent. DFT based on the PDF refined model shows that bulk C-CDW 1T-TaS 2 also preserves the insulating state of individual layers of SD clusters, favoring the Mott physics description of the metal-to-insulator (NC-CDW to C-CDW) phase transition in 1T-TaS 2 . Our work highlights the importance of using precise crystal structure models in determining the nature of electronic phases in complex materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1987

Theoretical studies of the potential surface for the F - H2 greater than HF + H reaction

The F + H2 yields HF + H potential energy hypersurface was studied in the saddle point and entrance channel regions. Using a large (5s 5p 3d 2f 1g/4s 3p 2d) atomic natural orbital basis set, a classical barrier height of 1.86 kcal/mole was obtained at the CASSCF/multireference CI level (MRCI) after correcting for basis set superposition error and including a Davidson correction (+Q) for higher excitations. Based upon an analysis of the computed results, the true classical barrier is estimated to be about 1.4 kcal/mole. The location of the bottleneck on the lowest vibrationally adiabatic potential curve was also computed and the translational energy threshold determined from a one-dimensional tunneling calculation. Using the difference between the calculated and experimental threshold to adjust the classical barrier height on the computed surface yields a classical barrier in the range of 1.0 to 1.5 kcal/mole. Combining the results of the direct estimates of the classical barrier height with the empirical values obtained from the approximation calculations of the dynamical threshold, it is predicted that the true classical barrier height is 1.4 + or - 0.4 kcal/mole. Arguments are presented in favor of including the relatively large +Q correction obtained when nine electrons are correlated at the CASSCF/MRCI level.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1988

Multilevel calculation of the Ne IV solar spectrum

A calculation of the atomic parameters of the seven-electron ion Ne IV yields radiative rates A(ki) and distorted-wave collision strengths Omega (ki) between 72 levels of the six configurations 2s2 2p3, 2s2p4, 2p5, 2p2 3s, 2p2 3p, and 2p2 3d. These are used to obtain expected line intensities for quiet, active, and flare solar conditions. Comparisons are made with available solar observations. Good agreement is found, including observed density-sensitivity in the case of the multiplet at 469.8 A. The atomic radiative rates are separately compared with laboratory beam-foil measurements and are shown to be in reasonable agreement with the latter.

Bhatia, A. K.↗
DOE OSTI2024

Plutonium and Cerium Perrhenate/Pertechnetate Coordination Polymers and Frameworks

Spent nuclear fuel (SNF) contains transuranic and lanthanide species, which are sometimes recovered and repurposed. One particularly problematic fission product, 99 TcO 4 – , hampers this recovery via coextraction with high valence metals, perhaps by complexation during aqueous reprocessing of SNF. There is limited molecular-level knowledge concerning the coordination chemistry between TcO 4 – or its well-known surrogate ReO 4 – and transuranic/lanthanide species. In the current study, we investigated the coordination of ReO 4 – /TcO 4 – with plutonium and cerium cations by structural and chemical characterization of a series of isolated extended solids. In this study, Ce represents both trivalent lanthanides and is considered a surrogate for Pu, respectively, in its common trivalent and tetravalent oxidation states. The structural elucidation of the seven isolated crystalline solids revealed that ReO 4 – /TcO 4 – directly connects to Pu IV , Pu VI O 2 2 + , Ce III , and Ce IV in the terminal and bridging coordination modes, leading to 1-, 2-, and 3-dimensional frameworks. For example, ReO 4 – coordination to Pu(IV) formed a 1D chain or 2D framework, isostructural with previously isolated Th(IV) compounds. However, Pu VI O 2 2 + alternating with ReO 4 – led to a unique 1D chain, different from the prior-reported U(VI)/Np(VI)-ReO 4 – /TcO 4 – structures. Coordination of ReO 4 – /TcO 4 – with Ce(III) promotes the assembly of 3D frameworks. Finally, attempted synthesis of a Ce(IV)-ReO 4 – compound resulted in a 2D framework with a mixed-valence Ce III/IV . The highly acidic reaction conditions supported the reduction of both Ce IV and Tc VII , challenging isolation of compounds featuring these species. Only one TcO 4 -containing structure was obtained in this study (Ce III –TcO 4 3D framework), vs the six total Ce/Pu-ReO 4 compounds. Furthermore, our three Pu-ReO 4 crystal structures are the first reported and translated to atomic-level information about Pu-TcO 4 coordination in nuclear fuel reprocessing scenarios, in addition to broadening our knowledge of bonding trends in the early, high-valence actinides.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Controlling hydrocarbon transport and electron beam induced deposition on single layer graphene: Toward atomic scale synthesis in the scanning transmission electron microscope

Abstract Focused electron beam induced deposition (FEBID) is a direct write technique for depositing materials on a support substrate akin to 3D printing with an electron beam (e‐beam). Opportunities exist for merging this existing technique with aberration‐corrected scanning transmission electron microscopy to achieve molecular‐ or atomic‐level spatial precision. Several demonstrations have been performed using graphene as the support substrate. A common challenge that arises during this process is e‐beam‐induced hydrocarbon deposition, suggesting greater control over the sample environment is needed. Various strategies exist for cleaning graphene in situ. One of the most effective methods is to rapidly heat to high temperatures, for example, 600℃ or higher. While this can produce large areas of what appears to be atomically clean graphene, mobile hydrocarbons can still be present on the surfaces. Here, we show that these hydrocarbons are primarily limited to surface migration and demonstrate an effective method for interrupting the flow using e‐beam deposition to form corralled hydrocarbon regions. This strategy is effective for maintaining atomically clean graphene at high temperatures where hydrocarbon mobility can lead to substantial accumulation of unwanted e‐beam deposition.

36 MATERIALS SCIENCE↗
NASA NTRS2010

Atomic Data and Spectral Line Intensities for Ni XI

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ni XI. We include in the calculations the 10 lowest configurations, corresponding to 164 fine structure levels: 3s(sup 2)3p(sup 6), 3s(sup 2)3p(sup 5)3d, 3s(sup 2)3p(sup 4)3d(sup 2), 3s3p(sup 6)3d, 3s(sup 2)3p(sup 5)4l and 3s3p6 4l with l =.s, p, d. Collision strengths are calculated at five incident energies for all transitions: 7.1, 16.8, 30.2, 48.7 and 74.1 Ry above the threshold of each transition. An additional energy, very close to the transition threshold, has been added, whose value is between 0.06 Ry and 0.25 Ry depending on the lower level. Calculations have been carried out using the Flexible Atomic Code and the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, combined with Close Coupling collision excitation rate coefficient available in the literature for the lowest 17 levels, statistical equilibrium equations for level populations are solved at electron densities covering the 10(exp 8)-10(exp 14) cu cm range and at an electron temperature of logT(sub c)(K)=6.1, corresponding to the maximum abundance of Ni XI. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database.

Bhatia, A. K.↗
NASA NTRS1979

Simplified model of a volumetric direct nuclear pumped He-3-Ar laser

A physical model for the volumetric nuclear pumped He-3-Ar laser is described and the source terms arising from the He-3(n, p)H-3 reaction as well as the rate equations are given. Steady state solutions are derived for the densities of the species vs the fraction of argon. The dominant pumping mechanism is found to be collisional radiative recombination of the argon atomic ions and subsequent cascading into the upper laser level. The reactions following recombination are described and an expression is derived for the difference in densities of the argon 3d and 4p levels. Comparison with experiments shows good agreement.

Harries, W. L.↗
DOE OSTI2021

Rapid prototyping of arbitrary 2D and 3D wireframe DNA origami

Wireframe DNA origami assemblies can now be programmed automatically from the top-down using simple wireframe target geometries, or meshes, in 2D and 3D, using either rigid, six-helix bundle (6HB) or more compliant, two-helix bundle (DX) edges. While these assemblies have numerous applications in nanoscale materials fabrication due to their nanoscale spatial addressability and high degree of customization, no easy-to-use graphical user interface software yet exists to deploy these algorithmic approaches within a single, standalone interface. Further, top-down sequence design of 3D DX-based objects previously enabled by DAEDALUS was limited to discrete edge lengths and uniform vertex angles, limiting the scope of objects that can be designed. Here, we introduce the open-source software package ATHENA with a graphical user interface that automatically renders single-stranded DNA scaffold routing and staple strand sequences for any target wireframe DNA origami using DX or 6HB edges, including irregular, asymmetric DX-based polyhedra with variable edge lengths and vertices demonstrated experimentally, which significantly expands the set of possible 3D DNA-based assemblies that can be designed. ATHENA also enables external editing of sequences using caDNAno, demonstrated using asymmetric nanoscale positioning of gold nanoparticles, as well as providing atomic-level models for molecular dynamics, coarse-grained dynamics with oxDNA, and other computational chemistry simulation approaches.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1993

Laser-induced fluorescence detection strategies for sodium atoms and compounds in high-pressure combustors

A variety of laser-induced fluorescence schemes were examined experimentally in atmospheric pressure flames to determine their use for sodium atom and salt detection in high-pressure, optically thick environments. Collisional energy transfer plays a large role in fluorescence detection. Optimum sensitivity, at the parts in 10 exp 9 level for a single laser pulse, was obtained with the excitation of the 4p-3s transition at 330 nm and the detection of the 3d-3p fluorescence at 818 nm. Fluorescence loss processes, such as ionization and amplified spontaneous emission, were examined. A new laser-induced atomization/laser-induced fluorescence detection technique was demonstrated for NaOH and NaCl. A 248-nm excimer laser photodissociates the salt molecules present in the seeded flames prior to atom detection by laser-induced fluorescence.

Weiland, Karen J. R.↗
DOE OSTI2025

Catalytic Promotion of Transition-Metal-Doped Graphene Cathodes in Li-CO 2 Batteries

The Li-CO 2 battery is a promising energy storage system with impressive theoretical specific energy and discharge capacity. Graphene-based single-atom catalysts (SACs) provide high surface area and long-term electrochemical reactivity and stability, making SACs among the most promising cathode catalysts for these batteries. However, current Li-CO 2 systems have high reaction barriers, slowing the reaction and greatly increasing the overpotential. Improvement of the discharge/charge energetics requires atomic-level innovations in cathode design, such as alterations to the catalyst chemical structure. In this paper, we propose enhancing the SAC by using a Ti metal center, which is found to deliver the highest electrochemical Li + CO 2 activity among 3d transition metal candidates. Furthermore, we propose cathode surface coating with ionic liquids, since these environments promote the formation of reaction intermediates in the electrochemical conversion process. Here, our work provides insights to optimize electrode design for high-performance Li-CO 2 batteries, which can open new avenues to recycle greenhouse gases and achieve enhanced renewable energy storage.

25 ENERGY STORAGE↗
NASA NTRS1986

Theoretical dipole moments for the first-row transition metal hydrides

Spectroscopic parameters (D sub e, r sub e, mu) are determined for the first-row transition metal hydrides using better than DZP basis sets at the modified coupled pair functional (MCPF) level. Extensive comparisons between MCPF and complete-active space self-consistent field (CASSCF)/MRCI calculations with natural orbital iterations, and studies with more extensive basis sets, show this level of treatment to supply an accurate and cost-effective treatment of these systems. For the transition metal hydrides, the bonding can arise from either the 3d(n)4s(2) or 3d(n + 1)4s(1) atomic asymptotes, or a mixture of both. Since the dipole moment arising from these two bonding mechanisms is very different, the dipole moment is found to be directly related to the 3d population. Thus, the magnitude of the dipole moments provides a sensitive test of the wave function, and gives insight into the nature of the bonding.

Chong, D. P.↗