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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Enhanced Optical Contrast and Switching in Near‐Infrared Electrochromic Devices by Optimizing Conjugated Polymer Oligo(Ethylene Glycol) Sidechain Content and Gel Electrolyte Composition

Abstract A detailed investigation addressing the effects of functionalizing conjugated polymers with oligo(ethylene glycol) (EG n ) sidechains on the performance and polymer‐electrolyte compatibility of electrochromic devices (ECDs) is reported. The electrochemistry for a series of donor‐acceptor copolymers having near‐infrared (NIR)‐optical absorption, where the donor fragment is 3,4‐ethylenedioxythiophene (EDOT) or an EG n functionalized bithiophene (g2T) and the acceptor fragment is diketopyrrolopyrrole (DPP) functionalized with branched alkyl or EG n sidechains, is extensively probed. ECDs are next fabricated and it is found that EG n sidechain incorporation must be finely balanced to promote polymer‐electrolyte compatibility and provide efficient ion exchange. Proper electrolyte‐cation pairing and polymer structural tuning affords a 2x increase in optical contrast (from 12% to 24%) and >60x reduction in switching time (from 20 to 0.3 s). Atomic force microscopy (AFM)/grazing incidence wide‐angle X‐ray scattering (GIWAXS) characterization of the polymer film morphology/microstructure reveals that an over‐abundance of EG n sidechains generates large polymer crystallites, which can suppress ion exchange. Lastly, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) indicates sidechain/electrolyte identity does not influence the electrolyte penetration depth into the films, and EG n sidechain inclusion increases electrolyte cation uptake. The material structural design insight and guidelines regarding the polymer‐electrolyte ion insertion/expulsion dynamics reported here should be of significant utility for developing next‐generation mixed ionic‐electronic conducting materials.

Chemistry↗
DOE OSTI2025

Density Functional Tight-Binding Enables Tractable Studies of Quantum Plasmonics

Routine investigations of plasmonic phenomena at the quantum level present a formidable computational challenge due to the large system sizes and ultrafast time scales involved. This Feature Article highlights the use of density functional tight-binding (DFTB), particularly its real-time time-dependent formulation (RT-TDDFTB), as a tractable approach to study plasmonic nanostructures from a quantum mechanical purview. We begin by outlining the theoretical framework and limitations of DFTB, emphasizing its efficiency in modeling systems with thousands of atoms over picosecond time scales. Applications of RT-TDDFTB are then explored in the context of optical absorption, nonlinear harmonic generation, and plasmon-mediated photocatalysis. We demonstrate how DFTB can reconcile classical and quantum descriptions of plasmonic behavior, capturing key phenomena such as size-dependent plasmon shifts and plasmon coupling in nanoparticle assemblies. Lastly, we showcase DFTB’s ability to model hot carrier generation and reaction dynamics in plasmon-driven H2 dissociation, underscoring its potential to model photocatalytic processes. Collectively, these studies establish DFTB as a powerful, yet computationally efficient tool to probe the emergent physics of materials at the limits of space and time.

Electrical energy↗
DOE OSTI2026

Ultrafast Relaxation of MLCT Excited States in Manganese Tricarbonyl Complexes: Insights from Polarization-Resolved Femtosecond X-ray Absorption Spectroscopy at the Mn and Br K-Edges

Optical absorption features that are often described as metal-to-ligand charge transfer (MLCT) bands underlie the utility of many metal coordination complexes by harnessing the energy of light to drive otherwise inaccessible chemical reactions. Excitation of these bands triggers rapid electronic dynamics that can be challenging to understand, due to complicated potential energy landscapes and highly correlated electronic and nuclear degrees of freedom in metal-containing compounds. The lowest-energy absorption bands in Mn complexes containing alpha-diimine, carbonyl, and halide ligands are particularly interesting, due to the delocalized nature of charge transfer upon excitation. Here, in this study, we report experimental ultrafast dynamics measurements for the series of compounds Mn­(CO) 3 ( R bpy)Br ( R bpy = 4,4′-disubstituted-2,2′-bipyridine; R = H, CF 3 , or NO 2 ) using polarization-resolved, femtosecond X-ray absorption spectroscopy (XAS) at both the Mn and Br K edges. The appearance of a new absorption feature in the Br pre-edge spectrum upon optical excitation reveals the instantaneous formation of an electronic hole that is partially localized on the Br atom and has a lifetime that depends on the electron withdrawing character of the R bpy ligand. For two of the complexes (R = H or CF 3 ), a large expansion of the Mn–Br distance results in a rapid redistribution of the hole and a corresponding decrease in anisotropy of the absorption feature within 50 fs, after which the absorption into the hole disappears on a time scale shorter than 300 fs. We observe a different result for the NO 2 substituted compound, for which the Mn–Br bond contracts and the absorption into the Br-centered hole persists beyond the 2 ps time scale of our measurement. The Mn pre-edge spectrum also reveals structural changes for these three complexes, but the new Mn absorption features become evident only after the nuclei respond to the initial excitation, which allows mixing of Mn 3d and 4p orbitals. The combined use of ultrafast Mn and Br K-edge spectroscopy provides unique insight into the ways in which bipyridine substitution alters the excited-state dynamics, including a very different structural response for the most strongly electron withdrawing substituent.

Otolski, Christopher J. [Univ. of Kansas, Lawrence↗
DOE OSTI2024

Physics and chemistry from parsimonious representations: image analysis via invariant variational autoencoders

Electron, optical, and scanning probe microscopy methods are generating ever increasing volume of image data containing information on atomic and mesoscale structures and functionalities. This necessitates the development of the machine learning methods for discovery of physical and chemical phenomena from the data, such as manifestations of symmetry breaking phenomena in electron and scanning tunneling microscopy images, or variability of the nanoparticles. Variational autoencoders (VAEs) are emerging as a powerful paradigm for the unsupervised data analysis, allowing to disentangle the factors of variability and discover optimal parsimonious representation. Here, we summarize recent developments in VAEs, covering the basic principles and intuition behind the VAEs. The invariant VAEs are introduced as an approach to accommodate scale and translation invariances present in imaging data and separate known factors of variations from the ones to be discovered. We further describe the opportunities enabled by the control over VAE architecture, including conditional, semi-supervised, and joint VAEs. Several case studies of VAE applications for toy models and experimental datasets in Scanning Transmission Electron Microscopy are discussed, emphasizing the deep connection between VAE and basic physical principles. Python codes and datasets discussed in this article are available at https://github.com/saimani5/VAE-tutorials and can be used by researchers as an application guide when applying these to their own datasets.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Band-gap reduction and band alignments of dilute bismide III–V alloys

Adding a few atomic percent of Bi to III–V semiconductors leads to significant changes in their electronic structure and optical properties. Bismuth substitution on the pnictogen site leads to a large increase in spin-orbit splitting Δ SO at the top of the valence band (Γ 8⁢𝑣 −Γ 7⁢𝑣 ) and a large reduction in the band gap, creating unique opportunities in semiconductor device applications. Quantifying these changes is key to the design and simulation of electronic and optoelectronic devices. Using hybrid functional calculations, we predict the band gap of III–Vs (III = Al, Ga, In and V = As, Sb) with low concentrations of Bi (3.125% and 6.25%), the effects of adding Bi on the valence- and conduction-band edges, and the band offset between these dilute alloys and their III–V parent compounds. As expected, adding Bi raises the valence-band maximum (VBM). However, contrary to previous assumptions, the conduction-band minimum (CBM) is also significantly lowered, and both effects contribute to the sizable band-gap reduction. Changes in band gap and Δ SO are notably larger in the arsenides than in the antimonides. In conclusion, we also predict cases of band-gap inversion (Γ 6⁢𝑐 below Γ 8⁢𝑣 ), and Δ SO larger than the band gap, which are key parameters for designing topological materials and for minimizing losses due to Auger recombination in infrared lasers.

Saboor, Abdul [Univ. of Delaware, Newark, DE (Unit↗
DOE OSTI2021

SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The “standard” EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neutral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Optimization and Prediction of Spectral Response of Metasurfaces Using Artificial Intelligence

Hot-electron generation has been a topic of intense research for decades for numerous applications ranging from photodetection and photochemistry to biosensing. Recently, the technique of hot-electron generation using non-radiative decay of surface plasmons excited by metallic nanoantennas, or meta-atoms, in a metasurface has attracted attention. These metasurfaces can be designed with thicknesses on the order of the hot-electron diffusion length. The plasmonic resonances of these ultrathin metasurfaces can be tailored by changing the shape and size of the meta-atoms. One of the fundamental mechanisms leading to generation of hot-electrons in such systems is optical absorption, therefore, optimization of absorption is a key step in enhancing the performance of any metasurface based hot-electron device. Here we utilized an artificial intelligence-based approach, the genetic algorithm, to optimize absorption spectra of plasmonic metasurfaces. Using genetic algorithm optimization strategies, we designed a polarization insensitive plasmonic metasurface with 90% absorption at 1550 nm that does not require an optically thick ground plane. We fabricated and optically characterized the metasurface and our experimental results agree with simulations. Finally, we present a convolutional neural network that can predict the absorption spectra of metasurfaces never seen by the network, thereby eliminating the need for computationally expensive simulations. Our results suggest a new direction for optimizing hot-electron based photodetectors and sensors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1981

Scattering of waves from periodic surfaces

In order to study the scattering of waves from periodic surfaces, the basic grating equations are reviewed, and a general approach for scattering from impenetrable and penetrable media is formulated. Three analytical methods for scattering on a conducting sinusoidal surface for both TE and TM polarized waves are compared. In The Masel, Merrill, and Miller (MMM) method for quantum scattering of atoms (1975, 1976), the surface field expansions are expressed in terms of Fourier series. The Modified Physical Optics (MPO) method (DeSanto, 1975; Whitman and Schwering, 1977) uses surface field expansions consisting of a leading term proportional to the physical optics approximation multiplied by a Fourier series expansion. The Waterman's Plane Harmonics (WPH) approach (1975) makes use of basis functions which are downward plane harmonics evaluated on the surface. The MMM method proved to be the most efficient one in terms of rate and range of convergence. For dielectric media with periodic rough surfaces, an improved method is developed for calculating the reflected and transmitted powers, and the results are compared with experimental data obtained at optical frequencies.

Chuang, S.-L.↗
NASA NTRS1982

The far-infrared disk of M51

Far-infrared maps and multifrequency photometry are presented for M51 and its companion galaxy NGC 5195. Dust reradiates about half the starlight of the M51 + NGC 5195 system to produce the observed far-infrared (80-200 microns) luminosity of 3 x 10 to the 10th solar luminosities. Observed with 49-arcsec resolution and covering 37 arcmin-squared, the maps show that roughly 70% of this luminosity is produced by the 5 arcmin (approximately 15 kpc) wide far-infrared disk of M51. Comparable luminosities emitted from the central regions (diameters = 49 arcsec or 2.3 kpc) of M51 and NGC 5195 contribute the remaining 30% (approximately 1 x 10 to the 10th solar luminosities). The photometry reveals a difference in energetics at the galactic scale; dust producing the central luminosity of NGC 5195 classified as Ip-Ep, Irr II or SBa(r) is much less abundant and considerably warmer than the approximately 20 K dust producing the central luminosity of M51 (Sc I). Far-infrared properties are given for several galactic scale complexes of star formation in M51. Relationships are discussed for selected maps of optical starlight and emissions from these components of M51's interstellar medium: dust grains, CO molecules, hydrogen atoms, electrons, and H II regions.

Smith, J.↗
NASA NTRS1982

Comparison of Venusian lightning observations

Spacecraft observations of Venusian lightning are reviewed to determine the energy dissipation rate. Optical sensors provide data on the total energy dissipated per flash, so long as the contributions of atomic oxygen and ionized carbon are accounted for. Radio probes yield information on the total lightning occurrences. Venera 9-12 radio surveys are reviewed, and event rates of 20-30/sec for Venera 11 are mentioned. Venera 9 observed a sole, 70 sec event period on the Venusian nightside. Comparisons are made between the recorded electromagnetic energy levels and terrestrial lightning data. The nightside occurrence rate is calculated to be 0.08 strokes/sq km per year, while the dayside exhibits 85 flashes/sq km per sec. Energy dissipation rates ranging from 0.0012-0.25 W/sq m are calculated for various flash durations. It is suggested that the lightning occurs in the clouds as part of an organized meteorological system.

Borucki, W. J.↗
NASA NTRS1983

Spectrophotometric studies of the Io Torus

A toroidal volume near Io's orbit is made luminous by multiple optical and ultraviolet line emissions excited by resonant scattering of sunlight and by electron collisions. These emitting atoms and ions have been lost from Io. The spectrophotometric measurements of these emissions and their physical interpretation are considered. It is now known that the flow of material from Io dominates the particle and energy budgets of the Jovian magnetosphere. The observed emitting species in the Io torus are examined, and the atomic clouds are discussed, taking into account morphology and kinematics, atomic cloud supply rates, ion-atom collisions, and charge-exchange collisions. Observations and studies concerning the plasma torus are reported, giving attention to the forbidden lines, the extreme ultraviolet lines, and aspects of ion temperature and spatial distribution. Two types of radial transport in the Io torus include the ballistic motion of neutrals escaping from Io and the cross-L transport of ions.

Brown, R. A.↗
NASA NTRS1986

Dendritic microstructure in argon atomized superalloy powders

The dendritic microstructure of atomized nickel base superalloy powders (Ni-20 pct Cr, NIMONIC-80A, ASTROALOY, and ZHS6-K) was studied. Prealloyed vacuum induction melted ingots were argon-atomized, the powders were cooled to room temperature, and various powder-size fractions were examined by optical metallography. Linear correlations were obtained for the powder size dependence of the secondary dendrite arm spacing, following the expected d-alpha (R) to the m power dependence on the particle size for all four superalloy compositions. However, the Ni-20 pct Cr alloy, which had much coarser arm spacing as compared to the other three alloys, had a much larger value of m.

Tewari, S. N.↗
NASA NTRS1988

Soft X-ray spectrographs for solar observations

Recent advances in soft X-ray spectrometery are reviewed, with emphasis on techniques for studying the windowless region from roughly 1-100 A. Recent technological developments considered include multilayer mirrors, large-format CCD detectors which are sensitive to X-rays, position-sensitive photon counting detectors, new kinds of X-ray films, and optical systems based on gratings with nonuniform ruling spacings. Improvements in the extent and accuracy of the atomic physics data sets on which the analysis of spectroscopic observatons depend are also discussed.

Bruner, M. E.↗
NASA NTRS1991

Ellipsometric study of metal samples

Exposed and unexposed (shielded) portions of the surfaces of six different metal samples (Al, Cu, Ni, Ta, W, and Zr) that had been mounted on LDEF were studied by variable angle spectroscopic ellipsometry. The change in the optical constants of the metals caused by exposure to the space environment was measured. The measured optical constants reflect changes in the morphology and stoichiometry of a surface layer to a depth of this order of magnitude. For all the samples examined in this manner the exposed and unexposed portions exhibited dramatically different optical properties. In order to determine whether the observed changes were caused by the impact of oxygen atoms encountered in flight an experiment was set up in which samples identical to the original metal samples are exposed to a low-energy oxygen plasma in a microwave discharge chamber. Results of this experiment are reported, as well as an analysis of the observed data in terms of surface layers of different composition.

Franzen, W.↗
NASA NTRS1991

Results from analysis of Boeing composite specimens flown on LDEF experiment M0003

Specimens of three selected organic/graphite fiber composite materials were flown on both the leading and trailing edges of LDEF. Additional sets of compression, tension, flexure, and lap shear specimens were flown on the trailing edge. A large T300/934 panel was flown on the leading edge. One quarter of this specimen was directly exposed to a near ram environment; each of the other three quarters were covered with a different thermal control paint. Results of mechanical, optical, and chemical analysis of the specimens are presented. Recession rates of the fiber and resin under atomic oxygen exposure were estimated and are reported.

Hill, Sylvester G.↗
NASA NTRS1992

Long Duration Exposure Facility experiment M0003: Deintegration/findings and impacts

The Long Duration Exposure Facility (LDEF) Experiment M0003 consists of 19 subexperiments from laboratories and contractor organizations and was designed to study the effects of the space environment on a large variety of spacecraft materials and components, both current and developmental. The experiment was housed in four LDEF trays and contained over 1250 specimens, two data systems, and two environment exposure control canisters. Nearly identical pairs of trays were located on the leading and trailing edges of LDEF. The materials in these trays span nearly all generic functions in spacecraft such as optics, thermal control, composites, solar power, and electronics. Effects of the space environment, such as vacuum, ultraviolet, atomic oxygen, meteoroids and debris, thermal cycling, and synergistic effects on various samples, will be described. Summaries of the on-board data will be presented.

Meshishnek, M. J.↗
NASA NTRS1994

The fluorescence-dominated X-ray spectrum of the spiral galaxy NGC 6552

A hard X-ray source with a 2-10 keV flux of approximately 6 x 10(exp -13) ergs/sec/sq cm was detected with ASCA in the north ecliptic pole region. It is identified with the spiral galaxy NGC 6552 at a redshift of z = 0.026, which is optically classified as a Seyfert 2 galaxy. The X-ray spectrum consists of a series of atomic K-emission lines from (nearly-) neutral species of at least seven abundant elements, and a heavily absorbed (N(sub H) approx. = 6 x 10(exp 23)/sq cm) hard continuum. The iron line has an equivalent width as large as approximately 0.9 keV. Our results show that NGC 6552 is an extreme type 2 Seyfert galaxy, in which the fluorescent lines are produced when hard X-rays from a hidden active nucleus are reflected off thick cool matter into our line of sight. The intrinsic 2-10 keV luminosity of the nucleus is estimated to be at least 6 x 10(exp 42) ergs/s.

Fukazawa, Yasushi↗