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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Dynamics and resilience of the unconventional charge density wave in ScV 6 Sn 6 bilayer kagome metal

Long-range electronic ordering descending from a metallic parent state constitutes a rich playground to study the interplay of structural and electronic degrees of freedom. In this framework, kagome metals are in the most interesting regime where both phonon and electronically mediated couplings are significant. Several of these systems undergo a charge density wave transition. However, to date, the origin and the main driving force behind this charge order is elusive. Here, we use the kagome metal ScV 6 Sn 6 as a platform to investigate this problem, since it features both a kagome-derived nested Fermi surface and van-Hove singularities near the Fermi level, and a charge-ordered phase that strongly affects its physical properties. By combining time-resolved reflectivity, first principles calculations and photo-emission experiments, we identify the structural degrees of freedom to play a fundamental role in the stabilization of charge order, indicating that ScV 6 Sn 6 features an instance of charge order predominantly originating from phonons.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Low temperature hydrogenation of pyrolytic lignin over Ru/TiO 2 : 2D HSQC and 13 C NMR study of reactants and products

In this paper, pyrolytic lignin and hydrogenated pyrolytic lignin were characterized by 2D 1 H– 13 C HSQC and quantitative 13 C NMR techniques. The pyrolytic lignin was produced from a mixed maple wood feedstock and separated from the bio-oil by water extraction. p-Hydroxyphenyl (H), guaiacyl (G), and syringyl (S) aromatics were the basic units of pyrolytic lignin. The native lignin β-aryl ether, phenylcoumaran and resinol structures were not present in the pyrolytic lignin. The hydrogenation was conducted with a Ru/TiO 2 catalyst at temperatures ranging from 25–150 °C with higher temperatures exhibiting higher levels of hydrogenation. Solid coke formed on the catalyst surface (1% coke yield) even for hydrogenation at 25 °C. The carbon yield of pyrolytic lignin to coke increased from 1% to 5% as the hydrogenation temperature increased from 25 to 150 °C. A single-step hydrogenation at 150 °C resulted in a reduction from 65% to 39% aromatic carbons. A three-step hydrogenation scheme at this same temperature resulted in a reduction of aromatic carbons from 65% to 17%. The decrease in the aromatic carbon corresponded with an increase in the aliphatic carbon. Coke formation reduced from a 5% carbon yield of pyrolytic lignin in the first hydrogenation step to a 1% carbon yield in each of the second and third hydrogenation steps. The pyrolytic lignin could be separated into a high and low molecular weight fraction. Finally, the coke yield from the high molecular weight fraction was twice as much as that from the low molecular weight fraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The ortho-to-para ratio of H 2 Cl + : Quasi-classical trajectory calculations and new simulations in light of new observations

Multi-hydrogenated species with proper symmetry properties can present different spin configurations, and thus exist under different spin symmetry forms, labeled as para and ortho for two-hydrogen molecules. We investigated here the ortho-to-para ratio (OPR) of H 2 Cl + in the light of new observations performed in the z = 0.89 absorber toward the lensed quasar PKS 1830-211 with the Atacama Large Millimeter/submillimeter Array (ALMA). Two independent lines of sight were observed, to the southwest (SW) and northeast (NE) images of the quasar, with OPR values found to be 3.15 ± 0.13 and 3.1 ± 0.5 in each region, respectively, in agreement with a spin statistical weight of 3:1. An OPR of 3:1 for a molecule containing two identical hydrogen nuclei can refer to either a statistical result or a high-temperature limit depending on the reaction mechanism leading to its formation. It is thus crucial to identify rigorously how OPRs are produced in order to constrain the information that these probes can provide. To understand the production of the H 2 Cl + OPR, we undertook a careful theoretical study of the reaction mechanisms involved with the aid of quasi-classical trajectory calculations on a new global potential energy surface fit to a large number of high-level ab initio data. Our study shows that the major formation reaction for HH 2 Cl + produces this ion via a hydrogen abstraction rather than a scrambling mechanism. Finally, such a mechanism leads to a 3:1 OPR, which is not changed by destruction and possible thermalization reactions for H 2 Cl + and is thus likely to be the cause of observed 3:1 OPR ratios, contrary to the normal assumption of scrambling.

211↗
DOE OSTI2011

Adhesion of tungsten carbide reinforced amorphous hydrocarbon thin films (WC/a-C:H) to steel substrates for tribological applications

We have explored the adhesive interlayer structure for a tungsten carbide reinforced amorphous hydrocarbon thin film coating (WC/a-C:H) that demonstrated excellent coating adhesion under highly stressed tribological contact. Transmission electron microscopy (TEM) analysis including cross-sectional imaging, electron diffraction, and energy dispersive spectroscopy was performed on abrupt and gradient interfaces within the multilayer film architecture. Interpretation of these results is aided by quantum mechanical calculations that were performed to investigate bonding interactions of the Cr adhesive interlayer to the Fe substrate surface within a - 3 nm thick interfacial region. Low levels of oxygen present in the coating deposition chamber during deposition were found at the Fe-Cr interface using high-resolution TEM. Molecular orbital calculations for a linear three-atom molecular model Fe-O-Cr demonstrate the role of O in strengthening Fe to Cr bonding within that interfacial region.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Communication: The origin of rotational enhancement effect for the reaction of H{sub 2}O{sup +} + H{sub 2} (D{sub 2})

We have measured the absolute integral cross sections (σ’s) for H{sub 3}O{sup +} formed by the reaction of rovibrationally selected H{sub 2}O{sup +}(X{sup 2}B{sub 1}; v{sub 1}{sup +}v{sub 2}{sup +}v{sub 3}{sup +} = 000; N{sup +}{sub Ka}{sup +}{sub Kc}{sup +} = 0{sub 00}, 1{sub 11}, and 2{sub 11}) ion with H{sub 2} at the center-of-mass collision energy (E{sub cm}) range of 0.03–10.00 eV. The σ(0{sub 00}), σ(1{sub 11}), and σ(2{sub 11}) values thus obtained reveal rotational enhancements at low E{sub cm} < 0.50 eV, in agreement with the observation of the previous study of the H{sub 2}O{sup +}(X{sup 2}B{sub 1}) + D{sub 2} reaction. This Communication presents important progress concerning the high-level ab initio quantum calculation of the potential energy surface for the H{sub 2}O{sup +}(X{sup 2}B{sub 1}) + H{sub 2} (D{sub 2}) reactions, which has provided valuable insight into the origin of the rotational enhancement effect. Governed by the charge and dipole-induced-multipole interactions, the calculation shows that H{sub 2} (D{sub 2}) approaches the H end of H{sub 2}O{sup +}(X{sup 2}B{sub 1}) in the long range, whereas chemical force in the short range favors the orientation of H{sub 2} (D{sub 2}) toward the O side of H{sub 2}O{sup +}. The reorientation of H{sub 2}O{sup +} reactant ion facilitated by rotational excitation thus promotes the H{sub 2}O{sup +} + H{sub 2} (D{sub 2}) reaction along the minimum energy pathway, rendering the observed rotational enhancement effects. The occurrence of this effect at low E{sub cm} indicates that the long range charge and dipole-induced-multipole interactions of the colliding pair play a significant role in the dynamics of the exothermic H{sub 2}O{sup +} + H{sub 2} (D{sub 2}) reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Product fine-structure resolved photodissociation dynamics: The A band of H{sub 2}O

The photodissociation dynamics of H{sub 2}O in its first absorption band is investigated on an accurate potential energy surface based on a large number of high-level ab initio points. Several ro-vibrational states of the parent molecule are considered. Different from most previous theoretical studies, the spin-orbit and Λ-doublet populations of the open-shell OH fragment are reported from full-dimensional wave packet calculations. The populations of the two spin-orbit manifolds are in most cases close to the statistical limit, but the Λ-doublet is dominated by the A{sup ″} component, thanks largely to the fast in-plane dissociation of H{sub 2}O(A{sup ~1}A{sup ′′}). Comparisons with experimental data and a Franck-Condon model are generally very good, although some discrepancies exist.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

A combined experimental and computational study of the molecular interactions between anionic ibuprofen and water

In this work, we report a detailed study of the microsolvation of anionic ibuprofen, Ibu{sup −}. Stochastic explorations of the configurational spaces for the interactions of Ibu{sup −} with up to three water molecules at the DFT level lead to very rich and complex potential energy surfaces. Our results suggest that instead of only one preponderant structure, a collection of isomers with very similar energies would have significant contributions to the properties of the solvated drug. One of these properties is the shift on the vibrational frequencies of the asymmetric stretching band of the carboxylate group in hydrated Ibu{sup −} with respect to the anhydrous drug, whose experimental values are nicely reproduced using the weighted contribution of the structures. We found at least three types of stabilizing interactions, including conventional CO {sub 2}{sup −}⋯H{sub 2}O, H{sub 2}O⋯H{sub 2}O charge assisted hydrogen bonds (HBs), and less common H{sub 2}O⋯H–C and H{sub 2}O⋯π interactions. Biological water molecules, those in direct contact with Ibu{sup −}, prefer to cluster around the carboxylate oxygen atoms via cyclic or bridged charge assisted hydrogen bonds. Many of those interactions are strongly affected by the formal carboxylate charge, resulting in “enhanced” HBs with increased strengths and degree of covalency. We found striking similarities between this case and the microsolvation of dymethylphosphate, which lead us to hypothesize that since microsolvation of phosphatidylcholine depends mainly on the formal charge of its ionic PO {sub 2}{sup −} group in the polar head, then microsolvation of anionic ibuprofen and interactions of water molecules with eukaryotic cell membranes are governed by the same types of physical interactions.

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

Structural, electronic structure, and band alignment properties at epitaxial NiO/Al{sub 2}O{sub 3} heterojunction evaluated from synchrotron based X-ray techniques

The valence band offset value of 2.3 ± 0.2 eV at epitaxial NiO/Al{sub 2}O{sub 3} heterojunction is determined from photoelectron spectroscopy experiments. Pulsed laser deposited thin film of NiO on Al{sub 2}O{sub 3} substrate is epitaxially grown along [111] direction with two domain structures, which are in-plane rotated by 60° with respect to each other. Observation of Pendellosung oscillations around Bragg peak confirms high interfacial and crystalline quality of NiO layer deposited on Al{sub 2}O{sub 3} substrate. Surface related feature in Ni 2p{sub 3/2} core level spectra along with oxygen K-edge soft X-ray absorption spectroscopy results indicates that the initial growth of NiO on Al{sub 2}O{sub 3} substrate is in the form of islands, which merge to form NiO layer for the larger coverage. The value of conduction band offset is also evaluated from the measured values of band gaps of NiO and Al{sub 2}O{sub 3} layers. A type-I band alignment at NiO and Al{sub 2}O{sub 3} heterojunction is also obtained. The determined values of band offsets can be useful in heterojunction based light emitting devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Quantum oscillations in the type-II Dirac semi-metal candidate PtSe 2

Three-dimensional topological semi-metals carry quasiparticle states that mimic massless relativistic Dirac fermions, elusive particles that have never been observed in nature. As they appear in the solid body, they are not bound to the usual symmetries of space-time and thus new types of fermionic excitations that explicitly violate Lorentz-invariance have been proposed, the so-called type-II Dirac fermions. Here, we investigate the electronic spectrum of the transition-metal dichalcogenide PtSe 2 by means of quantum oscillation measurements in fields up to 65 T. The observed Fermi surfaces agree well with the expectations from band structure calculations, that recently predicted a type-II Dirac node to occur in this material. A hole- and an electron-like Fermi surface dominate the semi-metal at the Fermi level. The quasiparticle mass is significantly enhanced over the bare band mass value, likely by phonon renormalization. Our work is consistent with the existence of type-II Dirac nodes in PtSe 2 , yet the Dirac node is too far below the Fermi level to support free Dirac–fermion excitations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas

The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. Here, this study explores mechanisms affecting the formation of flattened density profiles, so-called 'density shoulders', in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces—and subsequent erosion. There is evidence against local enhancement of ionization inducing shoulder formation. We find that increases in SOL parallel resistivity, Λ div (=[ L || ν ei Ω i ]/ c s Ω e ), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A s , but only under a subset of conditions (D 2 -fuelled L-mode density scans with outer strike point on the horizontal target). Λ div fails to correlate with A s for cases of N 2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λ div and A s is also found for H-mode discharges. Thus, while it may be necessary for Λ div to be above a threshold of ~1 for shoulder formation and/or growth, another mechanism is required. More significantly, we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer D α emission, I – D α , does scale with A s where Λ div does and even where Λ div does not. Divertor recycling could lead to SOL density shoulder formation through: (a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and (b) changes in radial electric fields which lead to E &#x00d7; B poloidal flows as well as potentially affecting SOL turbulence birth characteristics. Therefore, changes in divertor recycling may be the sole process involved in bringing about SOL density shoulders or it may be that it acts in tandem with parallel resistivity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Aridity changes in the Tibetan Plateau in a warming climate

Desertification in the Tibetan Plateau (TP) has drawn increasing attention in the recent decades. It has been postulated as a consequence of climate aridity due to the observed warming. This study quantifies the aridity changes in the TP and attributes the changes to different climatic factors. Using the ratio of P/PET (precipitation to potential evapotranspiration) as an aridity index to indicate changes in dryness and wetness in a given area, P/PET was calculated using observed records at 83 stations in the TP, with PET calculated using the Penman–Monteith (PM) algorithm. Spatial and temporal changes of P/PET in 1979-2011 are analyzed. Results show that stations located in the arid and semi-arid northwestern TP are becoming significantly wetter and stations in the semi-humid southeastern TP are becoming drier, though not significantly, in the recent three decades. The aridity change patterns are significantly correlated with precipitation, sunshine duration and diurnal temperature range changes at confidence level of 99.9% from two-tail t-test. Temporal correlations also confirm the significant correlation between aridity changes with the three variables, with precipitation being the most dominant driver of P/PET changes at interannual time scale. PET changes are insignificant but negatively correlated with P/PET in the cold season. In the warm season, however, correlation between PET changes and P/PET changes are significant at confidence level of 99.9% when the cryosphere melts near the surface. Significant correlation between wind speed changes and aridity changes occurs in limited locations and months. Consistency in the climatology pattern and linear trends in surface air temperature and precipitation calculated using station data, gridded data, and nearest grid-to-stations for the TP average and across sub-basins indicate the robustness of the trends despite the large spatial heterogeneity in the TP that challenge climate monitoring.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Discrete quantum geometry and intrinsic spin Hall effect

We show that the quantum geometry of the Fermi surface can be numerically described by a three-dimensional discrete quantum manifold. This approach not only avoids singularities in the Fermi sea, but it also enables the precise computation of the intrinsic Hall conductivity resolved in spin, as well as any other local properties of the Fermi surface. The method assures numerical accuracy when the Fermi level is arbitrarily close to singularities, and it remains robust when Kramers degeneracy is protected by symmetry. Furthermore, the approach is demonstrated by calculating the anomalous Hall and spin Hall conductivities of a two-band lattice model of a Weyl semimetal and a full-band ab initio model of zinc-blende GaAs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Origin of metal-insulator transitions in the parent compounds of ruthenium-pnictide superconductors

Here we study the interplay of the structural phase transition, flat electronic band dispersion, and metal-to-insulator transition (MIT) in the parent compounds of the Ru-pnictide superconductors by using first-principles calculations. Our electron and phonon calculations reveal that Ru(P,As) undergo MIT accompanied by orthorhombic to monoclinic distortion at low temperature, but RuSb stays orthorhombic and metallic in agreement with the experimental findings. It is demonstrated that electronic correlation, as treated in DFT + U, DFT + Gutzwiller, and dynamical mean-field theory (DMFT), cannot induce MIT in the undistorted crystal structure. We find that, although small monoclinic distortion can remove the van Hove singularity at the Fermi level, it does not immediately gap out the Fermi surface and a large value of monoclinic distortion is necessary for a clear MIT, suggesting the possibility of an intermediate pseudogapped monoclinic metallic phase. Furthermore, we predict a light-induced two-step insulator-to-metal and structural transitions in the monoclinic phases of RuP and RuAs, which can be tested in future ultrafast pump-probe experiments as an alternative ideal playground to VO 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Two-stage proximity-induced gap opening in topological-insulator–insulating-ferromagnet ( Bi x Sb 1 - x ) 2 Te 3 – EuS bilayers

To further investigate the interplay between ferromagnetism and topological insulators, thin films of the low-carrier topological insulator (Bi x Sb 1 - x ) 2 Te 3 were deposited on the insulating ferromagnet EuS (100) in situ. AC susceptibility indicates magnetic anomalies between T ≈ 30 K and T ≈ 60 K , well above the Curie temperature T C ≈ 15 K of EuS. When the Fermi level is close to the Dirac point and the surface state dominates the electric conduction, sharp increases in resistance with decreasing temperatures were observed concurrently with the magnetic anomalies. Positive-negative magnetoresistance crossovers were observed at the Curie temperature, which seem only to appear when the sheet resistance exceeds the Mott-Ioffe-Regel limit h/e 2 . Finally, a two-stage gap-opening process due to magnetic proximity is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Data-driven background model for the CUORE experiment

Here, we present the model we developed to reconstruct the CUORE radioactive background based on the analysis of an experimental exposure of 1038.4 kg yr. The data reconstruction relies on a simultaneous Bayesian fit applied to energy spectra over a broad energy range. The high granularity of the CUORE detector, together with the large exposure and extended stable operations, allow for an in-depth exploration of both spatial and time dependence of backgrounds. We achieve high sensitivity to both bulk and surface activities of the materials of the setup, detecting levels as low as 10 nBq kg −1 and 0.1 nBq cm −2 , respectively. We compare the contamination levels we extract from the background model with prior radio-assay data, which informs future background risk mitigation strategies. The results of this background model play a crucial role in constructing the background budget for the CUPID experiment as it will exploit the same CUORE infrastructure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Influence of soil depth, irrigation, and plant genotype on the soil microbiome, metaphenome, and carbon chemistry

ABSTRACT Climate change is causing an increase in drought in many soil ecosystems and a loss of soil organic carbon. Calcareous soils may partially mitigate these losses via carbon capture and storage. Here, we aimed to determine how irrigation-supplied soil moisture and perennial plants impact biotic and abiotic soil properties that underpin deep soil carbon chemistry in an unfertilized calcareous soil. Soil was sampled up to 1 m in depth from irrigated and planted field treatments and was analyzed using a suite of omics and chemical analyses. The soil microbial community composition was impacted more by irrigation and plant cover treatments than by soil depth. By contrast, metabolomes, lipidomes, and proteomes differed more with soil depth than treatments. Deep soil (>50 cm) had higher soil pH and calcium concentrations and higher levels of organic acids, bicarbonate, and triacylglycerides. By contrast, surface soil (0–5 cm) had higher concentrations of soil organic matter, organic carbon, oxidizable carbon, and total nitrogen. Surface soils also had higher amounts of sugars, sugar alcohols, phosphocholines, and proteins that reflect osmotic and oxidative stress responses. The lipidome was more responsive to perennial tall wheatgrass treatments compared to the metabolome or proteome, with a striking change in diacylglyceride composition. Permanganate oxidizable carbon was more consistently correlated to metabolites and proteins than soil organic and inorganic carbon and soil organic matter. This study reveals specific compounds that reflect differences in organic, inorganic, and oxidizable soil carbon fractions that are impacted by interactions between irrigation-supplied moisture and plant cover in calcareous soil profiles. IMPORTANCE Carbon is cycled through the air, plants, and belowground environment. Understanding soil carbon cycling in deep soil profiles will be important to mitigate climate change. Soil carbon cycling is impacted by water, plants, and soil microorganisms, in addition to soil mineralogy. Measuring biotic and abiotic soil properties provides a perspective of how soil microorganisms interact with the surrounding chemical environment. This study emphasizes the importance of considering biotic interactions with inorganic and oxidizable soil carbon in addition to total organic carbon in carbonate-containing soils for better informing soil carbon management decisions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Electronic States of Nanosystems Based on Cadmium Sulfide in the Zinc-Blende Form

The electronic structure of nanosystems based on cadmium sulfide in the zinc-blende form (zb-CdS) is investigated using the method of density functional theory with the application of pseudopotentials. It is shown that this approach makes it possible to adequately describe the electronic states of this material. It is found that the (100)-zb-CdS surface is characterized by a metal-like electronic-state density, while the (110)-zb-CdS surface corresponds to the band gap at the Fermi level and nanofilms with this orientation can be used as a material for semiconductor devices. Epitaxial layered (110)-zb-CdS–Si nanosystems also manifest semiconductor properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗