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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Low-frequency Carbon Radio Recombination Lines. II. The Diffuse Interstellar Medium

In the second paper of the series, we have modeled low-frequency carbon radio recombination lines (CRRLs) from the interstellar medium. Anticipating the Low Frequency Array survey of Galactic CRRLs, we focus our study on the physical conditions of the diffuse, cold neutral medium. We have used the improved departure coefficients computed in the first paper of the series to calculate line-to-continuum ratios. The results show that the line width and integrated optical depths of CRRLs are sensitive probes of the electron density, gas temperature, and emission measure of the cloud. Furthermore, the ratio of CRRL to the [C ii] at the 158 μ m line is a strong function of the temperature and density of diffuse clouds. Guided by our calculations, we analyze CRRL observations and illustrate their use with data from the literature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Catalyst layer formulations for slot-die coating of PEM fuel cell electrodes

The series of electrodes were fabricated by the scalable and manufacturable slot-die coating method for proton exchange membrane fuel cell (PEMFC) application. The inks with different amounts of solids were studied by rheological methods in order to establish a coating window with minimum manufacturing defects. The obtained electrodes were characterized by SEM, AFM, and optical microscopy, which showed that they were uniform and homogeneous with minimum defects. The electrochemical evaluation of the manufactured gas diffusion electrodes (GDE) showed that the main characteristics of the electrodes, like electrochemical surface area, proton resistivity, and double layer capacitance, were found to be close for all samples confirming the reproducibility of the slot-die process. Additionally, we studied the effects of membrane thickness on the performance of the GDE membrane electrode assemblies and determined that a decrease in membrane thickness favored the performance. Furthermore, the obtained results clearly demonstrated the applicability and feasibility of the approach for the Manufacturing of catalyst layers for the fuel cell application with potential for future mass production.

08 HYDROGEN↗
DOE OSTI2025

Optimizing energy yield of monolithic perovskite/silicon tandem solar cells in real-world Conditions: The impact of luminescent coupling

Efficient light management is key to maximizing power conversion efficiency (PCE) in monolithic perovskite/silicon tandem solar cells. Achieving peak efficiency requires closely matched current generation in all junctions, especially in integrated configurations. However, real-world conditions vary significantly due to factors such as sunlight spectrum, diffuse-to-direct sunlight ratio, angular distribution of light, subcell temperature coefficients, and ground reflection. This study introduces a comprehensive optical and device simulation to optimize perovskite/silicon tandem cells, considering experimental luminescent coupling (LC) efficiency and its dependence on working conditions, alongside variations in radiative recombination, effect of temperature on absorptivity spectra, and cloud cover. Our results show potential energy yield improvements of up to 1.4 % with LC, based on current perovskite radiative recombination records, and up to 4 % with direct bandgap materials. Although radiative recombination's dependence on excitation intensity reduces output power and requires thicker absorbers, LC compensates for these losses. LC also lowers the optimized bandgap for the perovskite top cell from 1.72 eV to 1.64–1.68 eV, or even lower in regions with redshifted irradiance. Additionally, optimization revealed that thinner silicon bottom cells require a higher perovskite top cell bandgap, impacting the balance between fabrication cost and cell stability.

14 SOLAR ENERGY↗
DOE OSTI2024

Plasmonic Diamond Membranes for Ultrafast Silicon Vacancy Emission

Silicon vacancy centers (SiVs) in diamond have emerged as a promising platform for quantum sciences due to their excellent photostability, minimal spectral diffusion, and substantial zero-phonon line emission. However, enhancing their slow nanosecond excited-state lifetime by coupling to optical cavities remains an outstanding challenge, as current demonstrations are limited to ~10-fold. Here, we couple negatively charged SiVs to sub-diffraction-limited plasmonic cavities and achieve an instrument-limited ≤8 ps lifetime, corresponding to a 135-fold spontaneous emission rate enhancement and a 19-fold photoluminescence enhancement. Nanoparticles are printed on ultrathin diamond membranes on gold films which create arrays of plasmonic nanogap cavities with ultrasmall volumes. SiVs implanted at 5 and 10 nm depths are examined to elucidate surface effects on their lifetime and brightness. The interplay between cavity, implantation depth, and ultrathin diamond membranes provides insights into generating ultrafast, bright SiV emission for next-generation diamond devices.

Purcell enhancement↗
DOE OSTI2022

Understanding the Effect of Lead Iodide Excess on the Performance of Methylammonium Lead Iodide Perovskite Solar Cells

The presence of unreacted lead iodide in organic-inorganic lead halide perovskite solar cells is widely correlated with an increase in power conversion efficiency. We investigate the mechanism for this increase by identifying the role of surfaces and interfaces present between methylammonium lead iodide perovskite films and excess lead iodide. We show how type I and II band alignments arising under different conditions result in either passivation of surface defects or hole injection. Through first-principles simulations of solid-solid interfaces, we find that lead iodide captures holes from methylammonium lead iodide and modulates the formation of defects in the perovskite, affecting recombination. Using surface-sensitive optical spectroscopy techniques, such as transient reflectance and time-resolved photoluminescence, we show how excess lead iodide affects the diffusion and surface recombination velocity of charge carriers in methylammonium lead iodide films. Our coupled experimental and theoretical results elucidate the role of excess lead iodide in perovskite solar cells.

14 SOLAR ENERGY↗
DOE OSTI2021

Optical magnons with dominant bond-directional exchange interactions in the honeycomb lattice iridate α — Li 2 IrO 3

We have used resonant inelastic x-ray scattering to reveal optical magnons in a honeycomb lattice iridate α - Li 2 IrO 3 . The spectrum in the energy region 20–25 meV exhibits momentum dependence, of which energy is highest at the location of the magnetic Bragg peak, ( h , k ) = ( ± 0.32 , 0 ) , and lowered toward ( 0 , 0 ) and ( ± 1 , 0 ) . We compare our data with a linear spin-wave theory based on a generic nearest-neighbor spin model. We find that a dominant bond-directional Kitaev interaction of order 20 meV is required to explain the energy scale observed in our study. The observed excitations are understood as stemming from optical magnon modes whose intensity is modulated by a structure factor, resulting in the apparent momentum dependence. We also observed diffuse magnetic scattering arising from the short-range magnetic correlation well above T N . In contrast to Na 2 IrO 3 , this diffuse scattering lacks the C 3 rotational symmetry of the honeycomb lattice, suggesting that the bond anisotropy is far from negligible in α - Li 2 IrO 3 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Improvement of Short-Circuit Current Density in GaInP Solar Cells Grown by Dynamic Hydride Vapor Phase Epitaxy

We demonstrate GaInP solar cells grown by dynamic hydride vapor phase epitaxy with improved efficiency through elimination of nonradiative recombination centers. We redesigned our reactor to eliminate unintentional impurities, which led to a reduction of nearly 30 x in dark current. This improvement led to a significantly improved open-circuit voltage of 1.41 V and a band gap-voltage offset of 0.47 V in a device with a rear reflector, achieved without front surface passivation. We demonstrate that the limiting factor toward achieving higher efficiency is control over the emitter thickness. Recombination is high in the unpassivated emitter, but losses can be minimized by designing it to be thin. We show that Se diffusion from the GaAs contact layer into the base is responsible for unintentional thickening of the emitter. Use of reduced contact doping reduces the penetration of Se into the p-GaInP base layer. With improved control of Se diffusion, we achieve 13.0 mA/cm 2 and 15.2% certified efficiency in a single-junction GaInP cell structure that is optically equivalent to the top cell in a GaInP/GaAs tandem.

14 SOLAR ENERGY↗
DOE OSTI2018

Gas Jet Profile Monitor for Use in IOTA Proton Beam

The Integrable Optics Test Accelerator (IOTA) at the Fermilab Accelerator Science and Technology (FAST) Facility will attempt to demonstrate novel techniques for high current accelerators. An electron beam of 150 MeV/c momentum and a proton beam of 70 MeV/c momentum will be used for a number of experiments, including nonlinear focusing integrable optics, space charge compensation, and optical stochastic cooling. The low energy proton beam will provide a space charge dominated regime with which to investigate Hamiltonian diffusion and chaos. A non-invasive beam instrumentation device is needed to study emittance evolution and halo formation without destroying the beam. A supersonic gas jet curtain can be injected perpendicular to the proton beam, which will preserve the integrity of the beam and provide a two-dimensional turn-by-turn profile measurement. Currently, IOTA and the gas jet monitor are being built and commissioned at Fermilab.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Crystal Growth of Quaternary Rare Earth Selenosilicates by Using the Flux-Assisted Boron Chalcogen Mixture Method: Investigation of Their Magnetic and Optical Properties

A series of rare earth magnesium selenosilicates, RE3Mg 0.5 SiSe 7 (RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy) were obtained as single crystal using the flux assisted boron chalcogen mixture (BCM) method. The structures of the crystals were determined by single-crystal X-ray diffraction. The RE3Mg 0.5 SiSe 7 series crystallizes in the hexagonal crystal system in the space group P6 3 . Polycrystalline powders were synthesized to perform physical property measurements. Magnetic measurements over the 2–300 K temperature range reveal that Ce 3 Mg 0.5 SiSe 7 and Gd 3 Mg 0.5 SiSe 7 exhibit paramagnetic behavior with negative Weiss constants (θ W = −14.50, θ W = −6.13 K, respectively). The optical properties of RE 3 Mg 0.5 SiSe 7 (RE = Ce, Pr, Nd, Sm, Gd) were measured by ultraviolet–visible (UV–vis) diffuse reflectance. Density functional theory (DFT) electronic structure calculations were performed. Furthermore, a second harmonic generation measurement was performed on a polycrystalline powder of Ce 3 Mg 0.5 SiSe 7 and was found to be SHG active with an efficiency of 0.11 times the standard potassium dihydrogen phosphate (KDP).

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

Nonlinear processes upon two-photon interband picosecond excitation of PbWO{sub 4} crystal

A new experimental method is proposed to study the dynamics of nonlinear processes occurring upon two-photon interband picosecond excitation of a lead tungstate crystal and upon its excitation by cw probe radiation in a temporal range from several nanoseconds to several seconds. The method is applied to the case of crystal excitation by a sequence of 25 high-power picosecond pulses with a wavelength of 523.5 nm and 633-nm cw probe radiation. Measuring the probe beam transmittance during crystal excitation, one can investigate the influence of two-photon interband absorption and the thermal nonlinearity of the refractive index on the dynamics of nonlinear processes in a wide range of times (from several nanoseconds to several seconds). The time resolution of the measuring system makes it possible to distinguish fast and slow nonlinear processes of electronic or thermal nature, including the generation of a thermal lens and thermal diffusion. An alternative method is proposed to study the dynamics of induced absorption transformation and, therefore, the dynamics of the development of nonlinear rocesses upon degenerate two-photon excitation of the crystal in the absence of external probe radiation. (nonlinear-optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

GAMA/DEVILS: constraining the cosmic star formation history from improved measurements of the 0.3–2.2 μm extragalactic background light

We present a revised measurement of the optical extragalactic background light (EBL), based on the contribution of resolved galaxies to the integrated galaxy light (IGL). The cosmic optical background radiation (COB), encodes the light generated by star formation, and provides a wealth of information about the cosmic star formation history (CSFH). We combine wide and deep galaxy number counts from the Galaxy And Mass Assembly survey (GAMA) and Deep Extragalactic VIsible Legacy Survey (DEVILS), along with the Hubble Space Telescope (HST) archive and other deep survey data sets, in nine multiwavelength filters to measure the COB in the range from 0.35 μm to 2.2 μm. We derive the luminosity density in each band independently and show good agreement with recent and complementary estimates of the optical-EBL from very high-energy (VHE) experiments. Our error analysis suggests that the IGL and γ-ray measurements are now fully consistent to within $\sim 10{{\ \rm per\ cent}}$, suggesting little need for any additional source of diffuse light beyond the known galaxy population. We use our revised IGL measurements to constrain the CSFH, and place amplitude constraints on a number of recent estimates. As a consistency check, we can now demonstrate convincingly, that the CSFH, stellar mass growth, and the optical-EBL provide a fully consistent picture of galaxy evolution. Here, we conclude that the peak of star formation rate lies in the range 0.066–0.076 M ⊙ yr -1 Mpc -3 at a lookback time of 9.1 to 10.9 Gyr.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Vertical Advection Effects on Hyper-accretion Disks and Potential Link between Gamma-Ray Bursts and Kilonovae

Recent simulations on super-Eddington accretion flows have shown that, apart from the diffusion process, the vertical advection based on magnetic buoyancy can be a more efficient process to release the trapped photons in the optically thick disk. As a consequence, the radiative luminosity from the accretion disk can be far beyond the Eddington value. Following this spirit, we revisit the structure and radiation of hyper-accretion disks with mass accretion rates in the range of 10{sup −3}∼10 M{sub ⊙} s{sup −1}. Our results show that, due to the strong cooling through the vertical advection, the disk temperature becomes lower than that in the classic model without the vertical advection process, and therefore the neutrino luminosity from the disk is lower. On the other hand, the gamma-ray photons released through the vertical advection can be extremely super-Eddington. We argue that the large amount of escaped gamma-ray photons may have more significant contribution to the primordial fireball than the neutrino annihilation, and may hint at a link between gamma-ray bursts and kilonovae in the black hole hyper-accretion scenario.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Epitaxial growth and atomic arrangement in Fe2CrO4 on crystal symmetry matched (001) MgAl2O4

We report on the chemical, structural, and optical properties of molecular beam epitaxy (MBE) synthesized thin films of multifunctional Fe2CrO4 on (001)-oriented MgAl2O4 (MAO). Substrate temperatures near 500 °C are required to obtain smooth films with the expected out-of-plane (OOP) lattice parameter. Mg diffusion from the MAO substrate is kinetically suppressed up to 500 °C. We discuss anti-phase boundaries in symmetry matched epitaxial systems. This research provides new insight into the epitaxial growth and crystalline properties of crystal-symmetry-matched Fe2CrO4/MAO(001) heterostructures.

Scafetta, Mark↗
DOE OSTI2017

Radiation Hydrodynamic Simulations of Dust-driven Winds

We study dusty winds driven by radiation pressure in the atmosphere of a rapidly star-forming environment. We apply the variable Eddington tensor algorithm to re-examine the two-dimensional radiation hydrodynamic problem of a column of gas that is accelerated by a constant infrared radiation flux. In the absence of gravity, the system is primarily characterized by the initial optical depth of the gas. We perform several runs with different initial optical depths and resolutions. We find that the gas spreads out along the vertical direction, as its mean velocity and velocity dispersion increase. In contrast to previous work using the flux-limited diffusion algorithm, we find little evolution in the trapping factor. The momentum coupling between radiation and gas in the absence of gravity is similar to that with gravity. For Eddington ratio increasing with the height in the system, the momentum transfer from the radiation to the gas is not merely ∼L/c, but amplified by a factor of 1+ητ{sub IR}, where τ{sub IR} is the integrated infrared optical depth through the system, and η∼0.5--0.9, decreasing with the optical depth. We apply our results to the atmosphere of galaxies and conclude that radiation pressure may be an important mechanism for driving winds in the most rapidly star-forming galaxies and starbursts.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Synthesis of (Ga 1– x Zn x )(N 1– x O x ) with Enhanced Visible-Light Absorption and Reduced Defects by Suppressing Zn Volatilization

(Ga 1– x )(N 1– x O x ) (GZNO) particles with enhanced optical absorption were synthesized by topotactic transformation of Zn 2+ /Ga 3+ layered double hydroxides. This outcome was achieved by suppressing Zn volatilization during nitridation by maintaining a low partial pressure of O 2 (p O2 ). Zn-rich (x > 1/3) variants of GZNO were achieved and compared to those prepared by conventional ammonoylsis conditions. The optical absorption and structural properties of these samples were compared to those prepared in the absence of O 2 by diffuse-reflectance spectroscopy and powder X-ray diffraction methods. Notably, suppression of Zn volatilization leads to smaller-band-gap materials (2.30 eV for x = 0.42 versus 2.71 eV for x = 0.21) and reduced structural defects. This synthetic route and set of characterizations provide useful structure–property studies of GZNO and potentially other oxynitrides of interest as photocatalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Insights on the Synthesis, Crystal and Electronic Structures, and Optical and Thermoelectric Properties of Sr 1– x Sb x HfSe 3 Orthorhombic Perovskite

We report single-phase polycrystalline powders of Sr 1–x Sb x HfSe 3 (x = 0, 0.005, 0.01), a new member of the chalcogenide perovskites, were synthesized using a combination of high temperature solid-state reaction and mechanical alloying approaches. Structural analysis using single-crystal as well as powder X-ray diffraction revealed that the synthesized materials are isostructural with SrZrSe 3 , crystallizing in the orthorhombic space group Pnma (#62) with lattice parameters a = 8.901(2) Å; b = 3.943(1) Å; c = 14.480(3) Å; and Z = 4 for the x = 0 composition. Thermal conductivity data of SrHfSe 3 revealed low values ranging from 0.9 to 1.3 W m –1 K –1 from 300 to 700 K, which is further lowered to 0.77 W m –1 K –1 by doping with 1 mol % Sb for Sr. Electronic property measurements indicate that the compound is quite insulating with an electrical conductivity of 2.9 S/cm at 873 K, which was improved to 6.7 S/cm by 0.5 mol % Sb doping. Thermopower data revealed that SrHfSe 3 is a p-type semiconductor with thermopower values reaching a maximum of 287 μV/K at 873 K for the 1.0 mol % Sb sample. The optical band gap of Sr 1–x Sb x HfSe 3 samples, as determined by density functional theory calculations and the diffuse reflectance method, is ~1.00 eV and increases with Sb concentration to 1.15 eV. Careful analysis of the partial densities of states (PDOS) indicates that the band gap in SrHfSe 3 is essentially determined by the Se-4p and Hf-5d orbitals with little to no contribution from Sr atoms. Typically, band edges of p- and d-character are a good indication of potentially strong absorption coefficient due to the high density of states of the localized p and d orbitals. This points to potential application of SrHfSe3 as absorbing layer in photovoltaic devices.

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

Nonlocal, Pattern-Aware Response and Feedback Framework for Regional Climate Response

We devise a pattern-aware feedback framework for representing the forced climate response using a suite of Green’s function experiments with solar radiation perturbations. By considering the column energy balance, a comprehensive linear response function (CLRF) for important climate variables and feedback quantities such as moist static energy, sea surface temperature, albedo, cloud optical depth, and lapse rate is learned from Green’s function data. The learned CLRF delineates the effects of the energy diffusion in both the ocean and atmosphere and the pattern-aware feedbacks from the aforementioned radiatively active processes. The CLRF can then be decomposed into forcing–response mode pairs, which are in turn used to construct a reduced-order model describing the dominant dynamics of climate responses. These mode pairs capture nonlocal effects and teleconnections in the climate and thus make the reduced-order model apt for capturing regional features of climate response. A key observation is that the CLRF captures the polar-amplified response as the most excitable mode of the climate system, and this mode is explainable in the data-learned pattern-aware feedback framework. The reduced-order model can be used for predicting the response for a given forcing and for reconstructing the forcing from a given response; we demonstrate these capabilities for multiple independent forcing scenarios.

Feedback↗
DOE OSTI2020

An Investigation of Liquefaction in Irradiated TRIGA Fuel Exposed to Relatively High Temperatures

This report presents the findings of an investigation into high temperature fuel cladding chemical interactions (FCCI) in Training, Research, Isotopes, General Atomics (TRIGA) fuel rods. A TRIGA fuel-rod core or meat is principally composed of uranium (U) particles dispersed in a zirconium hydride (Zr H) matrix. The fuel is clad in sealed 304SS or Incoloy 800 tubes. At high temperatures, the fuel will interact with the cladding, resulting in FCCI. To investigate the FCCI (in this case, liquefaction), irradiated TRIGA fuel rods were exposed to relatively high temperatures in furnace tests. The tests were performed at different temperatures using segments from an irradiated TRIGA fuel rod at the Hot Fuel Examination Facility located at Idaho National Laboratory (INL). The data from this study is important for developing a better understanding of the performance of U-ZrH fuel type during transient events (e.g., a Loss of Coolant Accident (LOCA) event) that may result in high temperatures while operating a TRIGA reactor. Furnace tests were run for 6 hours at 730, 800, 900, 950, and 1,000°C. One test was run for 12 hours at 950°C. Post-test microstructural characterization was performed on the heat-treated samples using optical metallography to look for evidence of liquefaction. Additionally, microstructural characterization was performed using scanning electron microscopy to investigate the microstructure of the as-irradiated fuel before heat treatment and the microstructural changes that occurred after heat treating for the 730 and 950°C heat treatments for 6 hours. Results of the analysis were compared to those produced during diffusion studies performed using unirradiated TRIGA fuel meat and type 304 stainless steel. A gap is typically present in as-irradiated fuel that limits any possibility for chemical interaction between the fuel and cladding. Optical metallography (OM) was used to identify areas in the specimens heat treated at 950 and 1000°C where fuel and cladding contact was satisfactory for the FCCI to transpire. The bulk of the interaction zones that form due to FCCI developed in the fuel meat and not as much in the cladding. Even in the sample tested at 1,000°C, no evidence was found that gross fuel meat or cladding melting had occurred. Only limited porosity was found in the fuel meat that possibly could have been due to melting of a particular precipitate phase or phases that had formed during FCCI. These results agreed with those reported for the unirradiated diffusion couple studies.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗