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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Thermal transport measurements through the charge density wave transition in CsV 3 Sb 5

We study thermal transport and thermalization in single crystals of CsV 3 Sb 5 through the CDW transition by directly measuring thermal diffusivity (D), thermal conductivity (κ), specific heat (c), and resistivity (ρ). Commensurate with previous reports, we observe a sharp, narrow anomaly in specific heat associated with a first-order transition that results in a CDW state below ~94 K. While a corresponding sharp anomaly in thermal diffusivity is also observed, resistivity and thermal conductivity only exhibit small steps at the transition, where the feature is sharp for resistivity and broader for thermal conductivity. Scrutinizing the thermal Einstein relation κ = cD, we find that this relation is generally satisfied, except in the narrow two-phase regime of the putative first-order transition. Here, the Wiedemann-Franz law as well seems to work outside the two-phase regime, where strong resemblance between the specific heat and the resistivity derivative below the transition may point to a concurrent emergence of a secondary electronic order parameter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Measurements of Aerosols, Radiation, and Clouds over the Southern Oceans (MARCUS) Science Plan

The Southern Ocean (SO) is the stormiest place on earth, buffeted by winds and waves that circle the ice of Antarctica, and sheathed in clouds that mantle a dynamic ocean with rich ecosystems. The remote and usually pristine environment, typically removed from anthropogenic and natural continental aerosol sources, makes the SO unique for examining cloud-aerosol interactions for liquid and ice clouds, and the role of primary and secondary marine biogenic aerosols and sea salt. There is strong seasonality in aerosol sources and sinks over the SO that are poorly understood. Weather and climate models are challenged by uncertainties and biases in the simulation of SO clouds, aerosols, and air-sea exchanges that trace to poor physical understanding of these processes, and by cloud feedbacks (e.g., phase changes) in response to warming. Models almost universally underestimate sunlight reflected by near surface cloud, particularly in the cold sector of cyclonic storm systems, and this may be due to difficulties in representing pervasive supercooled and mixed-phase boundary-layer (BL) clouds. Motivated by these issues, a large international multi-agency effort called the Southern Ocean Clouds Radiation Transport Aerosol Transport Experimental Study (SOCRATES) has been proposed to improve our understanding of clouds, aerosols, air-sea exchanges and their interactions over the SO. Coincident with SOCRATES, the Measurements of Aerosols, Radiation and CloUds over the Southern Oceans (MARCUS) experiment will be conducted where the second U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility’s Mobile Facility (AMF2) will be installed on the Australian Antarctic supply vessel Aurora Australis (AA) as it makes routine transits between Hobart, Australia and the Antarctic, visiting the Australian Antarctic stations Mawson, Davis, and Casey, as well as Macquarie Island. During MARCUS, the AMF-2 will acquire comprehensive observations of aerosols (including cloud condensation nuclei [CCN] and ice nucleating particles [INP]) in the BL, vertical distributions of macrophysical and microphysical properties of liquid and mixed-phase clouds, and downwelling radiative fluxes over the SO during a 7-month period (September 2017 to April 2018) centered upon the Austral summer. The MARCUS observations will be self-standing and unique in that they will capture the variability in aerosol and cloud properties across the SO from spring to autumn, especially in cold waters at latitudes poleward 55° S, where supercooled and mixed-phase BL clouds in the cold sector of cyclones are frequent and where past and planned SO observations are most sparse.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

FIRST CONNECTION BETWEEN COLD GAS IN EMISSION AND ABSORPTION: CO EMISSION FROM A GALAXY–QUASAR PAIR

We present the first detection of molecular emission from a galaxy selected to be near a projected background quasar using the Atacama Large Millimeter/submillimeter Array (ALMA). The ALMA detection of CO(1−0) emission from the z = 0.101 galaxy toward quasar PKS 0439–433 is coincident with its stellar disk and yields a molecular gas mass of M{sub mol} ≈ 4.2 × 10{sup 9} M{sub ⊙} (for a Galactic CO-to-H{sub 2} conversion factor), larger than the upper limit on its atomic gas mass. We resolve the CO velocity field, obtaining a rotational velocity of 134 ± 11 km s{sup −1} and a resultant dynamical mass of ≥4 × 10{sup 10} M{sub ⊙}. Despite its high metallicity and large molecular mass, the z = 0.101 galaxy has a low star formation rate, implying a large gas consumption timescale, larger than that typical of late-type galaxies. Most of the molecular gas is hence likely to be in a diffuse extended phase, rather than in dense molecular clouds. By combining the results of emission and absorption studies, we find that the strongest molecular absorption component toward the quasar cannot arise from the molecular disk, but is likely to arise from diffuse gas in the galaxy’s circumgalactic medium. Our results emphasize the potential of combining molecular and stellar emission line studies with optical absorption line studies to achieve a more complete picture of the gas within and surrounding high-redshift galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Suppressing proximity effects during rapid serial two-photon lithography through tuning of reaction–diffusion kinetics

The ability of two-photon lithography (TPL) to print deterministic nanoporous 3D structures is highly valuable for many applications. However, it is challenging to print such structures rapidly due to the proximity effects that cause closely spaced features to enlarge and merge. A key challenge is the limited understanding of the origins and spatiotemporal dynamics of the long-range proximity effects that extend beyond the optical focal spot. Here, we empirically investigate these proximity effects in serial TPL using custom-made acrylate-based photoresists. We demonstrate that the complex spatiotemporal dynamics of the proximity effects can be explained through the kinetics of the reaction–diffusion photopolymerization mechanisms that underlie the curing process. Specifically, we show that the proximity effects arise due to comparable timescales of reaction and diffusion of oxygen. Furthermore, we demonstrate that long-range proximity effects can be suppressed by introducing phenolic inhibitors, which reduce oxygen consumption through non-inhibiting side reactions and promote faster termination of curing reactions. These insights enabled improving the linewidths from >400 to 260 nm during printing of nanoporous 3D woodpiles at scanning speeds of 50 mm s −1 . Thus, the knowledge generated here can be applied to deterministically tune the proximity effects and enable rapid printing of high-resolution nanoporous 3D structures.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Optically Transparent Thin-Film Electrode Chip for Spectroelectrochemical Sensing

The electrochemical and spectroelectrochemical applications of an optically transparent thin film electrode chip are investigated. The working electrode is composed of indium tin oxide (ITO); the counter and quasi-reference electrodes are composed of platinum. The stability of the platinum quasi-reference electrode is modified by coating it with a planar, solid state Ag/AgCl layer. The Ag/AgCl reference is characterized with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Open circuit potential measurements indicate that the potential of the planar Ag/AgCl electrode varies a maximum of 20 mV over four days. Cyclic voltammetry measurements show that the electrode chip is comparable to a standard electrochemical cell. Randles-Sevcik analysis of 10 mM K3[Fe(CN)6] in 0.1 M KCl using the electrode chip shows a diffusion coefficient of 1.59 × 10-6 cm2/s, in comparison to the standard electrochemical cell value of 2.38 × 10-6 cm2/s. By using the electrode chip in an optically transparent thin layer electrode (OTTLE), the spectroelectrochemical modulation of [Ru(bpy)3]2+ florescence was demonstrated, achieving a detection limit of 36 nM.

Ag/AgCl↗
DOE OSTI2016

Structural and Rotational Dynamics of Carbon Dioxide in 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids: The Effect of Chain Length

Ionic liquids (ILs) have been proposed as possible carbon dioxide (CO 2 ) carbon capture media, and so it is useful to understand the dynamics of both the dissolved gas and its IL environment as well as how altering the IL affects these dynamics. With increasing alkyl chain length, it is well established that ILs obtain a mesoscopic structural feature assigned to polarapolar segregation, and the change in structure with chain length affects dynamics. In this work, the dynamics of CO 2 in a series of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs), where alkyl is ethyl, butyl, hexyl, or decyl, were investigated using ultrafast infrared spectroscopy by measuring the reorientation and spectral diffusion of carbon dioxide in the ILs. It was found that reorientation of the carbon dioxide occurs on 3 timescales, which correspond to 2 different timescales of restricted wobbling-in-a-cone motions and a long time complete diffusive reorientation. The complete reorientation slows with increasing chain length but less than the increases in viscosity of the bulk liquids. Spectral diffusion, measured with 2D IR spectroscopy, is caused by a combination of the liquids’ structural fluctuations and reorientation of the CO 2 . The data were analyzed using recent theory that takes into account both contributions to spectral diffusion and extracts the structural spectral diffusion. Different components of the structural fluctuations have distinct dependences on the alkyl chain length. All of the dynamics are fast compared to the complete orientational randomization of the bulk ILs, as measured with optical heterodyne detected optical Kerr effect measurements. The results indicate a hierarchy of constraint releases in the liquids that give rise to increasingly slower dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Comparing optical four-flux model results with experimental data obtained by integrating sphere measurements

Four-flux theory is a way to model scattering through multiple layers of a system based on diffuse and collimated properties. When compared with measurement results obtained using an integrating sphere or a goniophotometer, an approximation is often made as the physical instrument cannot separate the collimated component from the diffuse light scattered in the forward direction. This paper tries to clarify the meaning of the word diffuse for the different cases and outlines simple corrections to improve the accuracy when comparing four-flux models and measured data based on sample haze and the geometry of the integrating sphere.

Bilokur, Maryna (ORCID:0000000191839650)↗
DOE OSTI2017

Ray tracing and Hubble diagrams in post-Newtonian cosmology

On small scales the observable Universe is highly inhomogeneous, with galaxies and clusters forming a complex web of voids and filaments. The optical properties of such configurations can be quite different from the perfectly smooth Friedmann-Lemaȋtre-Robertson-Walker (FLRW) solutions that are frequently used in cosmology, and must be well understood if we are to make precise inferences about fundamental physics from cosmological observations. We investigate this problem by calculating redshifts and luminosity distances within a class of cosmological models that are constructed explicitly in order to allow for large density contrasts on small scales. Our study of optics is then achieved by propagating one hundred thousand null geodesics through such space-times, with matter arranged in either compact opaque objects or diffuse transparent haloes. We find that in the absence of opaque objects, the mean of our ray tracing results faithfully reproduces the expectations from FLRW cosmology. When opaque objects with sizes similar to those of galactic bulges are introduced, however, we find that the mean of distance measures can be shifted up from FLRW predictions by as much as 10%. This bias is due to the viable photon trajectories being restricted by the presence of the opaque objects, which means that they cannot probe the regions of space-time with the highest curvature. It corresponds to a positive bias of order 10% in the estimation of Ω{sub Λ} and highlights the important consequences that astronomical selection effects can have on cosmological observables.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Effect of nanotube coupling on exciton transport in polymer-free monochiral semiconducting carbon nanotube networks

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are attractive light-harvesting components for solar photoconversion schemes and architectures, and selective polymer extraction has emerged as a powerful route to obtain highly pure s-SWCNT samples for electronic applications. Here we demonstrate a novel method for producing electronically coupled thin films of near-monochiral s-SWCNTs without wrapping polymer. Detailed steady-state and transient optical studies on such samples provide new insights into the role of the wrapping polymer on controlling intra-bundle nanotube–nanotube interactions and exciton energy transfer within and between bundles. Complete removal of polymer from the networks results in rapid exciton trapping within nanotube bundles, limiting long-range exciton transport. The results suggest that intertube electronic coupling and associated exciton delocalization across multiple tubes can limit diffusive exciton transport. Here, the complex relationship observed here between exciton delocalization, trapping, and long-range transport, helps to inform the design, preparation, and implementation of carbon nanotube networks as active elements for optical and electronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High sensitivity pump–probe measurements of magnetic, thermal, and acoustic phenomena with a spectrally tunable oscillator

We describe an optical pump/probe system for sensitive measurements of time-resolved optical measurements of material dynamics. The instrument design is optimized for time-resolved magneto-optic Kerr effect (TR-MOKE) measurements of dynamics in magnetic materials. The system also allows for time-domain thermoreflectance (TDTR) measurements of thermal transport properties and picosecond acoustic measurements of film thickness and/or elastic constants. The system has several advantages over the conventional designs for TRMOKE and/or TDTR systems. Measurements of pump-induced changes to the probe beam intensity are shot-noise limited. The system’s design allows for MOKE and/or thermoreflectance measurements of both sides of a sample. Pumping and probing the sample on opposite sides allows nanoscale flash diffusivity measurements of transport properties. The wavelengths of the pump and probe beams are straightforward to tune between 350–525 nm and 690–1050 nm. A tunable wavelength allows for optical resonances in a wide array of materials to be excited and/or probed. Finally, the setup is calibrated to allow for the real and imaginary components of Kerr signals to be separately quantified.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Structural, morphological, optical and magnetic properties of Ag3(2+x)InxNb4-xO11+δ (0.25 ≤ x ≤ 1.0) nanoparticles synthesized by sol–gel method

Highlights: • Novel Ag{sub 3 (2+x)} In{sub x}Nb{sub 4-x}O{sub 11+δ} nanoparticles were synthesized by sol-gel method and studied their optical magnetic properties. • XRD studies confirm the single-phase monoclinic lattice structure with P2/m space group. • Morphology, purity and homogeneity of samples were confirmed by SEM images, EDX and X-ray mapping. • The absorption spectra and tauc plots confirms the semiconductor nature of the samples. • Magnetic studies reveals the ferromagnetic behavior of the samples at room temperature. - Abstract: Herein, we report the structure, morphology, optical and magnetic properties of novel Ag{sub 3 (2+x)} In{sub x}Nb{sub 4-x}O{sub 11+δ} (0.25 ≤ × ≤ 1.0; A1–A4) nanoparticles prepared by sol-gel technique. The samples were studied using X-ray diffraction, electron microscopy, diffuse reflectance spectroscopy, vibrating sample magnetometer, and electron spin resonance. X-ray diffraction studies confirm the formation of monoclinic lattice type with P2/m space group. Purity and homogeneity of the samples were confirmed by X-ray mapping. The semiconductor nature of the samples was identified by optical absorption spectra which indicate an inter-band transition from the oxygen 2p to niobium 4d electronic states. The magnetization plots reveal the room temperature ferromagnetic behavior of the samples.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

One-Dimensional Quaternary and Penternary Alkali Rare Earth Thiophosphates Obtained via Alkali Halide Flux Crystal Growth

Single crystals of nine new quaternary and penternary rare earth containing thiophosphates, Cs 2 KLn(PS 4 ) 2 , Rb 3-x Na x Ln(PS 4 ) 2 (Ln = La, Nd), Rb 2 NaNd(PS 4 ) 2 , Cs 3 La(PS 4 ) 2 , Rb 3 Gd(PS 4 ) 2 , and Cs 5 NaLn 2 (PS 4 ) 4 (Ln = Gd, Tb), were grown in alkali halide eutectic fluxes. All title compounds were structurally characterized by single crystal X-ray diffraction and were found to crystallize in pseudo-one-dimensional structure types, reminiscent of those found for other known alkali rare earth thiophosphates, in a variety of space groups including monoclinic P2 1 /c, P2 1 /m, P2 1 , and orthorhombic Ccca. The crystal structures of the reported compounds are characterized by the formation of complex one-dimensional [(Ln(PS 4 ) 2 )3–] and [(Ln 2 (PS 4 ) 4 ) 6– ] anionic chains that run along the crystallographic α-axis in Cs 2 KLn(PS 4 ) 2 , Rb 3-x NaxLn(PS 4 ) 2 (Ln = La, Nd) and Rb 2 NaNd(PS 4 ) 2 , b-axis in Cs 3 La(PS 4 ) 2 and Rb 3 Gd(PS 4 ) 2 , and c-axis in Cs 5 NaLn 2 (PS 4 ) 4 (Ln = Gd, Tb). Cs 2 KLn(PS 4 ) 2 , Rb 3-x Na x Ln(PS 4 ) 2 (Ln = La, Nd), Rb 2 NaNd(PS 4 ) 2 , Rb 3 Gd(PS 4 ) 2 , and Cs 3 La(PS 4 ) 2 feature two crystallographically unique thiophosphate tetrahedra that face- and edge-share with the LnS x polyhedra forming infinite one-dimensional zigzag-like chains. This unusual face-sharing or face-grafting coordination mode of the thiophosphate group is however absent in Cs 5 NaLn 2 (PS 4 ) 4 (Ln = Gd, Tb), which exhibit only one unique phosphorus site. The magnetic susceptibility and the field-dependent magnetization were measured for Rb 2 NaNd(PS 4 ) 2 and Cs 2 KNd(PS 4 ) 2 which were found to be paramagnetic over the entire 2–300 K temperature range. Finally, optical properties of Cs 2 KNd(PS 4 ) 2 and Rb 2.65 Na 0.35 La(PS 4 ) 2 were measured by UV–vis diffuse reflectance spectrometry which revealed numerous weak absorption bands in the 300–900 nm range characteristic of the f–f electronic transitions in Nd 3+ ; Rb 2.65 Na 0.35 La(PS 4 ) 2 was found to be a semiconductor with a direct band gap of 3.60 eV.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Supernova PTF 12glz: A Possible Shock Breakout Driven through an Aspherical Wind

We present visible-light and ultraviolet (UV) observations of the supernova PTF 12glz. The SN was discovered and monitored in the near-UV and R bands as part of a joint GALEX and Palomar Transient Factory campaign. It is among the most energetic SNe IIn observed to date (≈1051 erg). If the radiated energy mainly came from the thermalization of the shock kinetic energy, we show that PTF 12glz was surrounded by ~1 M ⊙ of circumstellar material (CSM) prior to its explosive death. PTF 12glz shows a puzzling peculiarity: at early times, while the freely expanding ejecta are presumably masked by the optically thick CSM, the radius of the blackbody that best fits the observations grows at ≈7000 km s –1 . Such a velocity is characteristic of fast moving ejecta rather than optically thick CSM. This phase of radial expansion takes place before any spectroscopic signature of expanding ejecta appears in the spectrum and while both the spectroscopic data and the bolometric luminosity seem to indicate that the CSM is optically thick. We propose a geometrical solution to this puzzle, involving an aspherical structure of the CSM around PTF 12glz. By modeling radiative diffusion through a slab of CSM, we show that an aspherical geometry of the CSM can result in a growing effective radius. Furthermore, this simple model also allows us to recover the decreasing blackbody temperature of PTF 12glz. SLAB-Diffusion, the code we wrote to model the radiative diffusion of photons through a slab of CSM and evaluate the observed radius and temperature, is made available online.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Analysis of cell-based diffusion acceleration for the slice balance approach

In this work, we perform analysis on the use of cell-based diffusion acceleration methodologies to accelerate the convergence of transport solutions discretized with the slice balance approach (SBA) on unstructured polygonal grids.We investigated both linear diffusion synthetic acceleration (DSA) and non linear diffusion acceleration (NDA), including its partial-current variant (pNDA). DSA and NDA were both shown to diverge for intermediate ranges of mesh optical thicknesses. However, pNDA and Krylov methods like GMRES and Broyden stabilized the acceleration schemes, including problems with degenerate cells formed by mesh refinement. (author)

42 ENGINEERING↗
DOE OSTI2016

Surface- vs Diffusion-Limited Mechanisms of Anion Exchange in CsPbBr 3 Nanocrystal Cubes Revealed through Kinetic Studies

Ion-exchange transformations allow access to nanocrystalline materials with compositions that are inaccessible via direct synthetic routes. However, additional mechanistic insight into the processes that govern these reactions is needed. We present evidence for the presence of two distinct mechanisms of exchange during anion exchange in CsPbX 3 nanocrystals (NCs), ranging in size from 6.5 to 11.5 nm, for transformations from CsPbBr 3 to CsPbCl 3 or CsPbI 3 . These NCs exhibit bright luminescence throughout the exchange, allowing their optical properties to be observed in real time, in situ. The iodine exchange presents surface-reaction-limited exchanges allowing all anionic sites within the NC to appear chemically identical, whereas the chlorine exchange presents diffusion-limited exchanges proceeding through a more complicated exchange mechanism. Furthermore, our results represent the first steps toward developing a microkinetic description of the anion exchange, with implications not only for understanding the lead halide perovskites but also for nanoscale ion exchange in general.

Koscher, Brent A.↗
DOE OSTI2021

Optimization of four terminal rear heterojunction GaAs on Si interdigitated back contact tandem solar cells

High-efficiency, four-terminal tandem solar cells composed of thin GaAs films mechanically stacked onto interdigitated back contact silicon solar cells with a glass interlayer are demonstrated. The optimal thickness of the absorber layer of a rear heterojunction GaAs subcell for use in four terminal tandem solar cells was studied. GaAs top cells with absorber layer thicknesses of 1.5, 1.9, 2.3, 2.8, and 3.5 µm were fabricated on glass and mechanically stacked onto interdigitated back-contact Si bottom cells. All tandem cells were found to have efficiencies above 30% under the AM1.5 G spectrum demonstrating a relatively weak sensitivity to thickness in the four-terminal configuration. We found the 2.8 µm absorber layer cell to have the highest top cell and tandem cell efficiency at 26.38% and 32.57%, respectively. Optical modeling with transfer matrix method for the planar top cell and Lambertian light trapping in the textured Si subcell, along with drift-diffusion Hovel equations, were used to show photon recycling enhancement to the effective diffusion length and VOC of the top cell as a result of the low-index glass interlayer.

14 SOLAR ENERGY↗
DOE OSTI2022

Proton damage in (Y,Lu,Gd) 3 (Al,Ga) 5 O 12 :Ce mixed garnet scintillators

Scintillators are vital components for nuclear instrumentation and its applications, including plasma diagnostics and imaging. As yields in controlled fusion experiments increase, the radiation tolerance of scintillator candidates for use in instrumentation is of particular importance. High radiation exposure can damage scintillating materials and alter the optical properties. The effects of radiation damage in Ce-doped mixed garnet ceramics over the compositional range (Y,Gd,Lu) 3 (Al,Ga) 5 O 12 are investigated using optical techniques. The samples were exposed to 200 keV protons to an accumulated fluence of 10 16 protons per square centimeter, then characterized using diffuse reflectance spectroscopy (DRS). DRS with visible light can assess the radiation tolerance of opaque poly-crystalline samples, which can be easily sintered from powders and thus offer distinct advantages in characterization compared to single crystals. Qualitative trends in induced absorption are presented as a function of composition, and the ideal cerium dopant concentration for Y 2 LuAl 5 O 12 is determined to be 0.60–0.75 mol.%.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Spatially-resolved measurements of spin valley polarization in MOCVD-grown monolayer WSe 2

Time-resolved Kerr rotation microscopy is used to generate and measure spin valley polarization in MOCVD-grown monolayer tungsten diselenide (WSe 2 ). The Kerr signal reveals bi-exponential decay with time constants of 100 ps and 3 ns. Measurements are performed on several triangular flakes from the same growth cycle and reveal larger spin valley polarization near the edges of the flakes. This spatial dependence is observed across multiple WSe 2 flakes in the Kerr rotation measurements but not in the spatially resolved reflectivity or microphotoluminescence data. Time-resolved pump-probe overlap measurements further reveal that the Kerr signal’s spatial dependence is not due to spin diffusion on the nanosecond timescale.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗