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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Growth and characterization of nonlinear optical telluromolybdate CoTeMoO{sub 6} single crystals

Nonlinear optical (NLO) crystals CoTeMoO{sub 6} have been grown from high temperature solution by means of spontaneous crystallization. These crystals have been characterized by temperature-dependent X-ray diffraction, infrared and electron absorption methods. Moreover, polarized Raman spectra have been measured at room temperature. These studies showed that the Mo{sup 6+} and Te{sup 4+} ions are in asymmetric coordination environment, and CoTeMoO{sub 6} has the largest flexibility index among MTeMoO{sub 6} family of telluro-molybdates (M=Zn, Mg, Cd, Mn, Co), making this compound attractive NLO material. Raman and IR studies allowed assigning the observed modes to respective motions of atoms in the unit cell. They have also showed evidence for spin–phonon coupling at low temperatures and suggested that CoTeMoO{sub 6} is prospective material for solid-state Raman laser-frequency converters. Analysis of electron absorption data has shown that Co{sup 2+} ions are located in sites of weak crystal field with the crystal field parameters Dq and B equal to 548 cm{sup −1} and 882 cm{sup −1}, respectively. - Graphical abstract: View of CoTeMoO{sub 6} crystal structure along the b-axis. - Highlights: • Single crystals of nonlinear optical telluromolybdate CoTeMoO{sub 6} were grown. • Crystal structure was solved by means of single crystal X-ray diffraction. • Raman and IR spectra were measured and analyzed. • Crystal field strength acting on Co{sup 2+} ions was established from analysis of electron absorption spectra.

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

High strain-rate compression behavior of polymeric rod and plate Kelvin lattice structures

The compressive high strain-rate behavior of polymeric Kelvin lattice structures with rod-based or plate-based unit cells was investigated through experimental techniques and finite element simulations. Polymeric lattice structures with 5x5x5 unit cell geometries were manufactured on the millimeter scale using vat polymerization additive manufacturing and tested at low (0.001/s) and high (1000/s) strain-rates. High strain-rate experiments were performed and validated for a viscoelastic split-Hopkinson (Kolsky) pressure bar system (SHPB) coupled with high-speed imaging and digital image correlation (DIC). Experimental results at both low and high strain-rates show the formation of a localized deformation band which was more prevalent in low relative density specimens and low strain-rate experiments. Strain-rate effects of lattice specimens strongly correlate with effects of the base polymer material; both bulk polymer and lattice specimen demonstrated strain-rate hardening, strain-rate stiffening, and decreased fracture strain under dynamic loading. Results show mechanical failure properties and energy absorption depended strongly on the relative density of the lattice specimen and exhibited distinct scaling between relative density and geometry type (rod, plate) and loading rate. High relative density plate-lattices demonstrated inferior mechanical properties to rod-lattices; however, there exists a critical relative density for a given mechanical property (17%- 28%) below which plate-lattices outperform rod-lattices of similar mass. As a result, high strain-rate explicit finite element simulations were performed and showed good agreement with the mechanical failure trends and deformation modes observed in the experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Evanescent and inertial-like waves in rigidly rotating odd viscous liquids

Three-dimensional non-rotating odd viscous liquids give rise to Taylor columns and support axisymmetric inertial-like waves ( J. Fluid Mech ., vol. 973, 2023, A30). When an odd viscous liquid is subjected to rigid-body rotation however, there arise in addition a plethora of other phenomena that need to be clarified. In this paper, we show that three-dimensional incompressible or two-dimensional compressible odd viscous liquids, rotating rigidly with angular velocity 𝛺, give rise to both oscillatory and evanescent inertial-like waves or a combination thereof (which we call of mixed type) that can be non-axisymmetric. By evanescent, we mean that along the radial direction, typically when moving away from a solid boundary, the velocity field decreases exponentially. These waves precess in a prograde or retrograde manner with respect to the rotating frame. The oscillatory and evanescent waves resemble respectively the body and wall-modes observed in (non-odd) rotating Rayleigh–Bénard convection ( J. Fluid Mech ., vol. 248, 1993, pp. 583–604). We show that the three types of waves (wall, body or mixed) can be classified with respect to pairs of planar wavenumbers 𝜅 which are complex, real or a combination, respectively. Experimentally, by observing the precession rate of the patterns, it would be possible to determine the largely unknown values of the odd viscosity coefficients. This formulation recovers as special cases recent studies of equatorial or topological waves in two-dimensional odd viscous liquids which provided examples of the bulk–interface correspondence at frequencies 𝜔 < 2⁢𝛺. We finally point out that the two- and three-dimensional problems are formally equivalent. Their difference then lies in the way data propagate along characteristic rays in three dimensions, which we demonstrate by classifying the resulting Poincaré–Cartan equations.

Mechanics↗
DOE OSTI2015

Hydrogen-Bonding Network and OH Stretch Vibration of Cellulose: Comparison of Computational Modeling with Polarized IR and SFG Spectra

Hydrogen bonds play critical roles in noncovalent directional interactions determining the crystal structure of cellulose. Although diffraction studies accurately determined the coordinates of carbon and oxygen atoms in crystalline cellulose, the structural information on hydrogen atoms involved in hydrogen-bonding is still elusive. This could be complemented by vibrational spectroscopy; but the assignment of the OH stretch peaks has been controversial. In this study, we performed calculations using density functional theory with dispersion corrections (DFT-D2) for the cellulose Iβ crystal lattices with the experimentally determined carbon and oxygen coordinates. DFT-D2 calculations revealed that the OH stretch vibrations of cellulose are highly coupled and delocalized through intra- and interchain hydrogen bonds involving all OH groups in the crystal. Additionally, molecular dynamics (MD) simulations of a single cellulose microfibril showed that the conformations of OH groups exposed at the microfibril surface are not well-defined. Finally, comparison of the computation results with the experimentally determined IR dichroism of uniaxially aligned cellulose microfibrils and the peak positions of various cellulose crystals allowed unambiguous identification of OH stretch modes observed in the vibrational spectra of cellulose.

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

Charge ordering and structural transition in the new organic conductor {delta}'-(BEDT-TTF){sub 2}CF{sub 3}CF{sub 2}SO{sub 3}.

We report structural, transport, and optical properties and electronic structure calculations of the delta'-(BEDT-TTF) 2CF3CF2SO3 (BEDT-TTF = bis(ethylenedithio)-tetrathiafulvalene) organic conductor that has been synthesized by electrocrystallization. Electronic structure calculations demonstrate the quasi-one-dimensional Fermi surfaces of the compound, while the optical spectra are characteristic for a dimer-Mott insulator. The single-crystal X-ray diffraction measurements reveal the structural phase transition at 200 K from the ambient-temperature monoclinic P2(1)/m phase to the low-temperature orthorhombic Pca2(1) phase, while the resistivity measurements clearly show the first order semiconductor-semiconductor transition at the same temperature. This transition is accompanied by charge-ordering as it is confirmed by splitting of charge-sensitive vibrational modes observed in the Raman and infrared spectra. The horizontal stripe charge-order pattern is suggested based on the crystal structure, band structure calculations, and optical spectra.

Olejniczak, Iwona↗
DOE OSTI2019

Laguerre–Gauss and Hermite–Gauss soft X-ray states generated using diffractive optics

Light’s capacity to carry angular momentum is integral to our knowledge of physics and ability to probe matter. In addition to spin, photons can occupy free-space orbital angular momentum eigenstates. Visible light orbital angular momentum is used in quantum information experiments, super-resolution microscopy, optical tweezers and angular momentum transfer to atoms in optical lattices. Soft X-ray orbital angular momentum applications, slowed by the lack of suitable optics and the rarity of coherent X-ray sources, could enable the direct alteration of atomic states through orbital angular momentum exchange, and methods to study the electronic properties of quantum materials. We have made soft X-ray diffractive optics that generate single Laguerre–Gauss modes, observed carrying up to 30$\hbar$ angular momentum per photon, or their superpositions. We also present Hermite–Gauss diffractive optics and a soft X-ray orbital angular momentum analyser. Finally, these tools could enable both the manipulation and finer characterization of topologically complex electronic matter, such as magnetic skyrmions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Towards validation of combined-accelerated stress testing through failure analysis of polyamide-based photovoltaic backsheets

Abstract Novel methods for advancing reliability testing of photovoltaic (PV) modules and materials have recently been developed. Combined-accelerated stress testing (C-AST) is one such method which has demonstrated reliable reproduction of some field-failures which were not reproducible by standard certification tests. To increase confidence and assist in the development of C-AST, and other new testing protocols, it is important to validate that the failure modes observed and mechanisms induced are representative of those observed in the field, and not the product of unrealistic stress conditions. Here we outline a method using appropriate materials characterization and modelling to validate the failure mechanisms induced in C-AST such that we can increase confidence in the test protocol. The method is demonstrated by applying it to a known cracking failure of a specific polyamide (PA)-based backsheet material. We found that the failure of the PA-based backsheet was a result of a combination of stress factors. Photo-oxidation from ultra-violet (UV) radiation exposure caused a reduction in fracture toughness, which ultimately lead to the cracking failure. We show that the chemical and structural changes observed in the backsheet following C-AST aging were also observed in field-aged samples. These results increase confidence that the conditions applied in C-AST are representative of the field and demonstrates our approach to validating the failure mechanisms induced.

14 SOLAR ENERGY↗
DOE OSTI2016

Quantifying the binding strength of salicylaldoxime–uranyl complexes relative to competing salicylaldoxime–transition metal ion complexes in aqueous solution: a combined experimental and computational study

Here, the design of new ligands and investigation of UO 2 2+ complexations are an essential aspect of reducing the cost of extracting uranium from seawater, improving the sorption efficiency for uranium and the selectivity for uranium over competing ions (such as the transition metal cations). The binding strengths of salicylaldoxime–UO 2 2+ complexes were quantified for the first time and compared with the binding strengths of salicylic acid–UO 2 2+ and representative amidoxime–UO 2 2+ complexes. We found that the binding strengths of salicylaldoxime–UO 2 2+ complexes are ~2–4 log β 2 units greater in magnitude than their corresponding salicylic acid–UO 2 2+ and representative amidoxime–UO 2 2+ complexes; moreover, the selectivity of salicylaldoxime towards the UO 2 2+ cation over competing Cu 2+ and Fe 3+ cations is far greater than those reported for salicylic acid and glutarimidedioxime in the literature. The higher UO 2 2+ selectivity can likely be attributed to the different coordination modes observed for salicylaldoxime–UO 2 2+ and salicylaldoxime–transition metal complexes. Density functional theory calculations indicate that salicylaldoxime can coordinate with UO 2 2+ as a dianion species formed by η 2 coordination of the aldoximate and monodentate binding of the phenolate group. In contrast, salicylaldoxime coordinates with transition metal cations as a monoanion species via a chelate formed between phenolate and the oxime N; the complexes are stabilized via hydrogen bonding interactions between the oxime OH group and phenolate. By coupling the experimentally determined thermodynamic constants and the results of theoretical computations, we are able to derive a number of ligand design principles to further improve the UO 2 2+ cation affinity, and thus further increase the selectivity of salicylaldoxime derivatives.

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

Planck 2015 results: XV. Gravitational lensing

Here, we present the most significant measurement of the cosmic microwave background (CMB) lensing potential to date (at a level of 40σ), using temperature and polarization data from the Planck 2015 full-mission release. Using a polarization-only estimator, we detect lensing at a significance of 5σ. We cross-check the accuracy of our measurement using the wide frequency coverage and complementarity of the temperature and polarization measurements. Public products based on this measurement include an estimate of the lensing potential over approximately 70% of the sky, an estimate of the lensing potential power spectrum in bandpowers for the multipole range 40 ≤ L ≤ 400, and an associated likelihood for cosmological parameter constraints. We find good agreement between our measurement of the lensing potential power spectrum and that found in the ΛCDM model that best fits the Planck temperature and polarization power spectra. Using the lensing likelihood alone we obtain a percent-level measurement of the parameter combination σ 8 Ω 0.25 m = 0.591 ± 0.021. We combine our determination of the lensing potential with the E-mode polarization, also measured by Planck, to generate an estimate of the lensing B-mode. We show that this lensing B-mode estimate is correlated with the B-modes observed directly by Planck at the expected level and with a statistical significance of 10σ, confirming Planck’s sensitivity to this known sky signal. Finally, we also correlate our lensing potential estimate with the large-scale temperature anisotropies, detecting a cross-correlation at the 3σ level, as expected because of dark energy in the concordance ΛCDM model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Potential measurements with heavy ion beam probe system on LHD

The heavy ion beam probe system in the Large Helical Device (LHD) was improved as follows. At first, the additional new sweeper was installed into the diagnostic port to extend the observable region. By using this sweeper, the potential profile was measured in a wider minor radius range than in previous experiments, in the case of outward shifted magnetic configuration of LHD. Next, the real time control system was installed to control the probe beam orbit for measuring the potential in plasma with large plasma current. In this system, a digital signal processor was used to control the probe beam in real time. The system worked well in the fixed position observation mode. In the sweeping mode for profile measurement, this control system became unstable. The details of this system and the experimental results are reported in this article.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Precursors for Carbon Nitride Synthesis

Nano structured carbon nitride films were prepared by pyrolysis assisted chemical vapour deposition. Pyrrole (C{sub 4}H{sub 5}N), Pyrrolidine (C{sub 4}H{sub 9}N), Azabenzimidazole (C{sub 6}H{sub 5}N{sub 3}) and Triazine (C{sub 6}H{sub 15}N{sub 3}) were used as precursors. The vibrational modes observed for C-N and C = N from FTIR spectra confirms the bonding of nitrogen with carbon. XPS core level spectra of C 1s and N 1s also show the formation of bonding between carbon and nitrogen atoms. The nitrogen content in the prepared samples was found to be around 25 atomic %.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Molecular beam epitaxial growth and characterization of InSb{sub 1-x}N{sub x} on GaAs for long wavelength infrared applications

Recent research progress and findings in InSbN have attracted great attention due to its use in long wavelength infrared applications. A large bandgap reduction in InSb resulting from high N incorporation with minimal crystal defects is challenging due to relatively small atomic size of N. Hence optimization of growth conditions plays an important role in the growth of high-quality InSbN epilayers for device purposes. In this paper, we report on the correlation of structural, vibrational, electrical, and optical properties of molecular beam epitaxially grown InSbN epilayers grown on GaAs substrates, as a function of varying growth temperatures. Two dimensional growths of InSb and InSbN were confirmed from dynamic reflection high energy electron diffraction patterns and growth parameters were optimized. High crystalline quality of the epilayers is attested to by a low full width at half maximum of 200 arcsec from high resolution x-ray diffraction (HRXRD) scans and by the high intensity and well-resolved InSb longitudinal optical (LO) and 2{sup nd} order InSb LO mode observed from micro-Raman spectroscopy. The N incorporation in these InSbN epilayers is estimated to be 1.4% based on HRXRD simulation. X-ray photoelectron spectroscopy (XPS) studies reveal that most of the N present in the layers are in the form of In-N bonding. Variation of the lattice disorder with growth temperature is correlated with the types of N bonding present, the carrier concentration and mobility, observed in the corresponding XPS spectra and Hall measurements, respectively. XPS analysis, HRXRD scans, and Raman spectral analysis indicate that lower growth temperature favors In-N bonding which dictates N incorporation in the substitutional sites and lattice disorder, whereas, high growth temperature promotes the formation of In-N-Sb bonding. The best room temperature and 77 K electrical transport parameters and maximum redshift in the absorption edge have been achieved in the InSbN epilayer grown in the 290 deg. C {approx} 330 deg. C temperature range.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Spin-pseudospin intertwined excitation at the ν = 1 bilayer quantum Hall state investigated by nuclear-spin relaxation

We investigate the electron spin degree of freedom at the imbalanced density bilayer ν = 1 quantum Hall states using the resistively detected nuclear-spin-lattice relaxation rate 1/T{sub 1}. Our measurements reveal a continuous change in 1/T{sub 1} for σ = 1 to 0, suggesting that the balanced density ν = 1 state also exhibits electron-spin fluctuations. Moreover, the value of 1/T{sub 1} in the back layer (the layer from which electrons are transferred to the front layer) increases at intermediate density imbalance states. This indicates that the low-energy electron-spin mode, similar to a mode observed in Skyrmion crystals, might extend across the two layers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Threshold ionization, structural isomers, and electronic states of M{sub 2}O{sub 2} (M = Sc, Y, and La)

M{sub 2}O{sub 2} (M = Sc, Y, and La) were synthesized in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and ab initio calculations. Adiabatic ionization energies (AIEs) and several vibrational frequencies were measured accurately for the first time from the MATI spectra. Six possible structural isomers of M{sub 2}O{sub 2} were considered in the calculations and the three converged structures were used in the spectral analysis. A planar cyclic structure in D{sub 2h} point group was predicted to be the most stable one by the theory and observed by the experiment. The cyclic structure is formed by joining two MO{sub 2} fragments together through two shared oxygen atoms. In forming the ground state clusters, each metal atom loses two (n − 1)d electrons and as a result, has only one ns electron in the metal-based valence orbital. The ground electronic state of Sc{sub 2}O{sub 2} is {sup 1}A{sub g}, and those of Y{sub 2}O{sub 2} and La{sub 2}O{sub 2} are {sup 3}B{sub 1u}. Ionization of both {sup 1}A{sub g} and {sup 3}B{sub 1u} neutral states yields the {sup 2}A{sub g} ion state by removing one of the two ns electrons, and the resultant ion has a similar geometry to the neutral cluster. The AIEs of the clusters are 5.5752 (6), 5.2639 (6), 4.5795 (6) eV for M = Sc, Y, and La, respectively. The vibrational frequencies of the observed modes, including O-M and M-M stretches, are in the range of 200–800 cm{sup −1}.

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

An axially propagating two-stream instability in the Hall thruster plasma

Collective Thomson scattering experiments reveal the presence of high-frequency, axial electron density fluctuations at millimetric wavelengths in the Hall thruster plasma. The properties of these fluctuations are investigated experimentally and via linear kinetic theory. The relative drift of electrons and ions in the axial direction is found to be insufficient to cause excitation of the observed mode. Instead, the mode is determined to be a two-stream instability arising due to the velocity difference between singly and doubly charged ion populations in the plume.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Highly time-resolved evaluation technique of instantaneous amplitude and phase difference using analytic signals for multi-channel diagnostics

A fluctuation analysis technique using analytic signals is proposed. Analytic signals are suitable to characterize a single mode with time-dependent amplitude and frequency, such as an MHD mode observed in fusion plasmas since the technique can evaluate amplitude and frequency at a specific moment without limitations of temporal and frequency resolutions, which is problematic in Fourier-based analyses. Moreover, a concept of instantaneous phase difference is newly introduced, and error of the evaluated phase difference and its error reduction techniques using conditional/ensemble averaging are discussed. These techniques are applied to experimental data of the beam emission spectroscopic measurement in the Heliotron J device, which demonstrates that the technique can describe nonlinear evolution of MHD instabilities. This technique is widely applicable to other diagnostics having necessity to evaluate phase difference.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Temperature dependence of Raman shifts in layered ReSe{sub 2} and SnSe{sub 2} semiconductor nanosheets

Transition metal dichalcogenides (TMDCs) are attractive for variety of nanoscale electronics and optoelectronics devices due to their unique properties. Despite growing progress in the research field of TMDCs, many of their properties are still unknown. In this letter, we report measurements of Raman spectra of rhenium diselenide (ReSe{sub 2}) and tin diselenide (SnSe{sub 2}) layered semiconductor nanosheets as a function of temperature (70–400 K). We analyze the temperature dependence of the positions of eight ReSe{sub 2} modes and SnSe{sub 2} A{sub 1g} mode. All observed Raman mode shifts exhibit nonlinear temperature dependence at low temperatures which is explained by optical phonon decay process into two or three acoustics phonons. The first order temperature coefficients (χ), determined for high temperatures, of rhenium diselenide Raman modes are in the range between −0.0033 and −0.0118 cm{sup −1}/K, whereas χ of tin diselenide A{sub 1g} mode was −0.0129 cm{sup −1}/K. Our findings are useful for further analysis of phonon and thermal properties of these dichalcogenide layered semiconductors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗