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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Nature of electronic excitations in small nonstoichiometric quantum dots

Colloidal quantum dots (QDs) have emerged as nanocrystalline semiconductors with tunable optoelectronic properties that have attracted attention for numerous commercial applications. While a significant amount of computational research has focused on understanding the stoichiometric QDs, most of the experimental synthesis techniques lead to non-stoichiometry in QD composition. In this work, we utilize time-dependent density functional theory to investigate the nature of electronic excitations in experimentally relevant non-stoichiometric cadmium selenide (CdSe) nanoclusters in a dielectric medium. Contrary to the stoichiometric QDs, we find a distinct charge transfer character for low-energy electronic excitations in non-stoichiometric QDs. This partial charge transfer occurs between the core and surface of QDs due to the charge imbalance originating from the inequivalent number of anionic and cationic atoms in these regions. This general phenomenon, accompanied with charge localization, results in optically dark low-energy transitions that would potentially hamper emissions in non-stoichiometric QDs, especially in anion-rich QDs. We report the insights from this study establish relationships between the optical properties and charge distributions in non-stoichiometric QDs that would facilitate their tunability for various applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Raman spectroscopic study of anhydrous and hydrous REE phosphates, oxides, and hydroxides

Rare earth elements (REE) include the lanthanides (La–Lu), Y, and Sc which are critical elements for the green energy transition. The REE show a decrease in ionic radii with increased atomic numbers, which results in a so-called lanthanide contraction systematically affecting crystal structures and mineral properties. Here we present a compilation of reference Raman spectra of ten REE sesquioxides (A-, B- and C-type), five REE hydroxides, eight xenotime-structured REE phosphate endmembers and two solid solutions, seven monazite-structured REE phosphate endmembers and two solid solutions and seven rhabdophane endmembers with up to five Ce 1–x LREE x rhabdophane solid solutions (LREE = La–Gd). Raman mode assignment is based on a detailed literature review summarizing existing analytical work and theoretical calculations and systematic trends observed in this study by analyzing different REE-bearing solids. Here, the wavenumbers of the main REE-O Raman band systematically increase with decreasing ionic radii forming discrete linear trends within isostructural mineral groups, that can be used to estimate the REE-O mode in other solids with known REE-O coordination numbers. Photoluminescence using 266 nm, 532 nm and 633 nm excitation laser wavelengths for REE-bearing oxides, hydroxides, anhydrous and hydrous phosphates is also presented providing a new framework for identifying REE-phases in phosphate-bearing natural mineral deposits.

58 GEOSCIENCES↗
DOE OSTI2024

Statistical data analysis of x-ray spectroscopy data enabled by neural network accelerated Bayesian inference

Bayesian inference applied to x-ray spectroscopy data analysis enables uncertainty quantification necessary to rigorously test theoretical models. However, when comparing to data, detailed atomic physics and radiation transfer calculations of x-ray emission from non-uniform plasma conditions are typically too slow to be performed in line with statistical sampling methods, such as Markov Chain Monte Carlo sampling. Furthermore, differences in transition energies and x-ray opacities often make direct comparisons between simulated and measured spectra unreliable. Here, we present a spectral decomposition method that allows for corrections to line positions and bound–bound opacities to best fit experimental data, with the goal of providing quantitative feedback to improve the underlying theoretical models and guide future experiments. In this work, we use a neural network (NN) surrogate model to replace spectral calculations of isobaric hot-spots created in Kr-doped implosions at the National Ignition Facility. The NN was trained on calculations of x-ray spectra using an isobaric hot-spot model post-processed with Cretin, a multi-species atomic kinetics and radiation code. The speedup provided by the NN model to generate x-ray emission spectra enables statistical analysis of parameterized models with sufficient detail to accurately represent the physical system and extract the plasma parameters of interest.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Origin of proton irradiation-induced deep acceptors in Al 0.70 Ga 0.30 N

Deep level defect introduction and carrier removal were characterized using steady-state photocapacitance (SSPC), deep level transient spectroscopy (DLTS) and lighted capacitance–voltage for proton irradiated n-type Al 0.70 Ga 0.30 N Schottky diodes grown by metal-organic vapor phase epitaxy on AlN-on-sapphire templates. SSPC observed deep levels in the as-grown diode with zero-phonon transition energies of 2.20, 2.65, 3.10, 3.40, and 4.65 eV relative to the conduction band minimum (E c ), and an additional deep level emerged at 1.20 eV with irradiation. Lighted capacitance–voltage measurements quantified the deep level concentration (N t ) of states detected by SSPC, and it was observed that N t increased with proton fluence only for the 1.2 and 4.65 eV levels. Carrier removal was much larger than the increase in N t of the 1.2 and 4.65 eV deep levels, suggesting that radiation-induced deep level compensators existed beyond what was detected with SSPC. DLTS detected additional, proton-induced deep acceptors at E c —0.55, 0.82, and 1.16 eV, the latter of which is likely the same 1.20 eV deep state observed by SSPC. The concentration of the E c —0.82 eV defect state was large enough to reconcile carrier removal with total deep level introduction. Comparing the E c —0.82 and 1.16 eV deep acceptor levels to previous experimental and theoretical reports suggests that their atomistic origins could be the nitrogen vacancy (V N ) and oxygen substituting on the nitrogen sub-lattice (O N ), respectively. This defect behavior contrasts starkly with GaN, where V N and O N are shallow donors, and demonstrates that the electronic properties of defects can evolve drastically within the AlGaN alloy system ranging from wide bandgap GaN to ultra-wide bandgap AlN.

Armstrong, Andrew Michael [Sandia National Laborat↗
DOE OSTI2020

Measurements of inner-shell excited levels of Na-, Mg-, and Al-like europium on the LLNL EBIT

We report on a measurement of several n = 3 → n = 2 inner-shell transitions in sodiumlike, magnesiumlike, and aluminumlike europium, performed at the EBIT-I electron beam ion trap facility at the Lawrence Livermore National Laboratory using an x-ray calorimeter. Although the inner-shell x-ray lines of such M-shell ions are typically dominated by electric dipole allowed transitions, we have also identified a weak feature that appears to be the result of electric quadrupole decay in sodiumlike Eu 52+ . Here, we compare the measured transitions energies to the calculated values obtained using the flexible atomic code. We find agreement in most cases within 2 eV or better.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Muon-induced fission of actinide nuclei

A negative muon captured by an actinide cascades down through the muonic atomic levels; deeply bound transitions can proceed via inverse internal conversion, depositing the muonic transition energy directly into the nucleus and, when the deposited energy exceeds the fission barrier, inducing prompt fission. Because the muon mean lifetime exceeds the saddle-to-scission timescale by orders of magnitude, the muon can survive the entire fission event as a 1⁢𝑠 spectator and ultimately attach to one or both of the emerging fragments. Its postscission attachment probability to the light fragment, 𝑃 𝐿 , can be used as a direct electromagnetic probe of fission dynamics on a timescale of 10 −21 s. In previous work, we introduced a three-dimensional lattice solution of the time-dependent Dirac equation coupled to the electromagnetic field generated by a fissioning nucleus and reported 𝑃 𝐿 for several actinides at a single dissipation strength. In this work, we extend that framework to a systematic survey of 232 Th , 238 U , and 240 Pu and implement a more realistic fission model which incorporates dynamic pairing correlations. We find that 𝑃 𝐿 falls steeply with the fragment charge asymmetry, a robust structural fingerprint of the fissioning system, while its dependence on nuclear dissipation is secondary and sensitive to the phenomenological friction prescription. These results establish 𝑃 𝐿 as a clean electromagnetic probe of fragment charge asymmetry and motivate a self-consistent, coordinate- and time-dependent treatment of nuclear dissipation as the natural next step.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Giant spin-selective bandgap renormalization in CsPbBr 3 colloidal nanocrystals

The spin-dependence of the strongly correlated phenomena and many-body interactions play an important role in quantum information science. In particular, it is quite interesting but unclear how the spin degree of freedom ramifies the bandgap renormalization, one of the fundamental many-body phenomena. We report the first room-temperature observation of giant spin-selective bandgap renormalization (SS-BGR) in CsPbBr 3 colloidal nanocrystals using time-resolved circularly polarized femtosecond pump-probe spectroscopy. The SS-BGR results from many-body interactions among carriers with the same spin that renormalize their joint density of states by 57+/- 1 meV, visualized here as photoinduced absorption (PIA) below band-edge transition energy when the pump and probe are co-polarized. The hallmark result of spectrally resolved SS-BGR is in stark contrast to the usually submerged signal in II-VI and III-V semiconductors and is 3 orders of magnitude larger than that observed in Ge/SiGe quantum wells, highlighting the unique and beneficial band structure of the metal-halide semiconductors. We propose that the PIA, due to SS-BGR, can be used to describe the spin-polarization and spin-relaxation dynamics. The experimental and theoretical findings open up new possibilities for optical manipulation of spin degrees of freedom and their many-body interactions in metal-halide perovskite nanocrystals for potential room-temperature applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Anomalous neutron yields confirmed for Ba-Mo and newly observed for Ce-Zr from spontaneous fission of Cf 252

We reinvestigated the neutron multiplicity yields of Ba-Mo, Ce-Zr, Te-Pd, and Nd-Sr from the spontaneous fission of 252 Cf by (i) using both γ -γ -γ -γ and γ -γ -γ coincidence data, (ii) using up to date level scheme structures, and (iii) crosschecking analogous energy transitions in multiple isotopes, we have achieved higher precision than previous analyses. Particular attention was given to the Ba-Mo pairs where our results clearly confirm that the Ba-Mo yield data have a second hot fission mode where 8–10, and now 11 neutron evaporation channels are observed. These are the first observations of the 11 neutron channel. These 8–11 neutron channels are observed for the first time in the Ce-Zr pairs, but are not observed in other fission pairs. The measured intensities of the second mode in Ba-Mo and Ce-Zr pairs are ~1.5(4)% and ~1.0(3)%, respectively. These high neutron number evaporation modes can be an indication of hyperdeformation and/or octupole deformation in 143-145 Ba and in 146,148 Ce at scission to give rise to such high neutron multiplicities.

252-Cf↗
DOE OSTI2025

Determination of nuclear charge radius by extreme-ultraviolet spectroscopy of Na-like ions

We report on a method for determining the absolute nuclear charge radius of high-𝑍 elements using extreme-ultraviolet spectroscopy of highly charged Na-like ions in tandem with highly accurate atomic structure calculations of transition energy differences. The application of this method has reduced the nuclear charge radius uncertainty of 191 Ir by a factor of 8 from the currently accepted literature value, with a recently reported charge radius of 5.435(12) fm. The result reduces the charge radius uncertainty along the full Ir isotopic chain when combined with prior optical isotope shift measurements. The technique utilizes only a few million ions stored in an ion trap, which should apply to measurements with small quantities of radioactive nuclei.

Atom & ion trapping & guiding↗
DOE OSTI2025

Full complex amplitude control of second-harmonic generation via electrically tunable intersubband polaritonic metasurfaces

Nonlinear intersubband polaritonic metasurfaces based on coupling of the intersubband nonlinear optical response of quantum-engineered semiconductor heterostructures and electromagnetic modes of nanoresonators provide efficient frequency mixing with moderate pump intensities. The resonant nonlinear optical response, represented as a complex function, can be modulated via Stark tuning of intersubband transition energies under applied voltages. However, achieving full complex amplitude control (both phase and magnitude) remains challenging. In this work, we present and experimentally validate electrically tunable nonlinear intersubband polaritonic metasurfaces that achieve complete complex amplitude control for second-harmonic generation (SHG). Through a design featuring two in-plane flipped meta-atoms per unit cell, we achieve complete electrical control of both the amplitude and phase of the metasurface second-order nonlinear susceptibility, with a tuning range of 0 to 30 nm V −1 for the magnitude and 0-2π for the phase of the nonlinear optical response. Using these properties, we achieve complete on-off SHG modulation and beam diffraction tuning through electrically controlled amplitude and phase gratings.

Science & Technology - Other Topics↗
DOE OSTI2023

Cobalt mineralogy at the Iron Creek deposit, Idaho cobalt belt, USA: Implications for domestic critical mineral production

Current U.S. policies aim to establish domestic supply chains of critical minerals for the energy transition. The Iron Creek deposit in the Idaho cobalt belt (ICB) is one of the most promising cobalt (Co) targets. Our case study illustrates the importance of mineralogy in strategic evaluations of critical mineral potential. Most of the Co at Iron Creek occurs as Fe substitution in pyrite, with lattice-bound and inclusion-hosted Ag, As, Bi, Ni, Pb, Se, Te ± trace Au and Sb. Cobalt also occurs in minor cattierite-vaesite. The Co minerals are intergrown with Co-poor chalcopyrite hosting Cu ± minor In and Zn. Worldwide, most Co is recovered from deposits mineralogically distinct from the ICB, and the United States currently lacks infrastructure to recover this Co and its associated metals. ICB ore minerals could be processed by autoclave, roaster, smelter, bioleach, or heap leach. Recovery of the Ag, As, Au, Bi, In, Pb, Se, Te, and Zn would be costly by autoclave, and construction of a custom smelter for ICB ores is likely uneconomic, so these elements would become waste irrespective of criticality. The Co-Fe and Co-As sulfide minerals are most suitable for Co and Ni recovery by a hydrometallurgical autoclave process, with potential pretreatment of cobaltiferous pyrite/arsenopyrite in an inert-atmosphere roaster, in new domestic or anticipated international facilities. The ICB is the second largest known Co resource in the United States. Consideration of ore mineralogy in the ICB is essential in strategies for domestic production.

58 GEOSCIENCES↗
DOE OSTI2022

California Consumers’ Beliefs and Trust in Electric Utilities

The authors use survey and interview data from California homeowners to understand customers’ trust in their utility company. The authors find that customers’ beliefs about the reliability of electricity do not predict trust. Instead, what matters are beliefs that the utility company does a bad job managing customer service, costs, and wildfires. Distrust among survey respondents aligns with interview participants’ descriptions of utility companies as powerful, greedy monopolies that benefit themselves at the expense of helpless consumers. These results have implications for the energy transition and, more generally, understanding potential challenges experienced by technocratic institutions.

Horne, Christine↗
DOE OSTI2024

GDB-9-Ex_EOM-CCSD: Dataset containing Equation of Motion Coupled Cluster (EOM-CCSD) calculations for organic molecules of the GDB-9-Ex dataset.

This dataset contains data-intensive quantum chemical electronic structure calculations for 80,593 organic molecules of the GDB-9-Ex dataset. Calculations were performed using the Equation of Motion Coupled Cluster (EOM-CCSD) first principles method using the ORCA software. It provides UV-vis spectra calculations of molecules with a high level of accuracy. The optical spectra behavior was collected based on the optimized molecular geometries in the DFTB method with 3ob parameters. All calculations utilized the def2-TZVP basis sets with the auxiliary def2/J and def2-TZVP/C basis sets. The similarity-transformed EOM-CCSD method that used domain-based local pair natural orbitals (DLPNO) approximation which constitutes the STEOM-DLPNO-CCSD method was used. This method is based on the STEOM approach and was found to make accurate predictions of transition energies for organic molecules. For the excitation energy calculations, the lowest 50 excitation states were calculated.

AI dataset↗
DOE OSTI2022

Recent advances in the global rare-earth supply chain

The current global rare-earth element (REE) supply chain is highly imbalanced and tightly controlled by just a few countries. Such an imbalance of the critical metals supply chain poses a significant challenge to the energy-transition strategies and the national security of many countries. As such, this issue of MRS Bulletin delves into the materials science aspects of the REE supply chain, including fundamental REE mineralogy, REE separation and extraction, REE mining economics, the environmental impacts of REE mining and processing, and circular economy potential for REEs. This issue of MRS Bulletin is meant to inform the materials science community of some of the constraints on REE production from the mining of ore deposits, through processing technologies, and then finally, the possibility of recycling.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2022

Appalachian Hydrogen Infrastructure Analysis

As large-scale efforts to decarbonize the global economy ramp up in earnest, hydrogen is being positioned as a critical solution for numerous sectors. Hydrogen produced from fossil energy resources with carbon capture and storage (CCS) is viewed as a bridge in the clean energy transition, enabling the development of midstream infrastructure and downstream demand. This report highlights the potential for the Appalachian region to develop a hydrogen economy with fossil-derived hydrogen with CCS production (hydrogen from natural gas with carbon capture and storage). Specifically, the report provides hydrogen transport and storage infrastructure pathways in support of a broader hydrogen economy. These pathways are consistent with existing and potential technologies and regulations and provide valuable guidance for the investment and research and development potential for transportation and storage of hydrogen in Appalachia.

08 HYDROGEN↗
DOE OSTI2022

Carbon Electrodes from Powder River Basin Coal Development of Competitive Supercapacitor Electrodes of Diverse Compositions from Coal Extract

Recent demand for coal as a thermal energy source has decreased significantly and will likely continue to decrease as renewable sources of energy become more available and environmental concern and cost from burning coal makes it more costly than renewables. Given that Powder River Basin (PRB) coal in Wyoming has relatively low thermal energy, it is critical for Wyoming to employ coal in other capacities at the current energy transition period in history. Among many potential non-thermal applications, PRB coal can be utilized for membrane and electrode applications through the formation of carbon fibers. Coal-derived membranes can become low-cost, conductive membranes for use in electrodialysis separation processes. Carbon fiber derived electrodes have been shown be a cost-effective alternative to typical electrode materials that can meet or exceed the performance of current carbon electrode materials. In this talk, we demonstrate the manufacture of supercapacitor electrodes from Powder River Basin (PRB) coal-derived precursors. Specifically, PRB coal was treated in cheap solvents, partitioned into liquid extract and solid residue. An electropinning process has been developed that can convert either the liquid extract or the solid residue into carbon fiber mats. The electrospinning process is versatile with many tunable process parameters to achieve desirable physiochemical properties. For example, the coal residue can be manipulated by additional heat treatment, or by adding binders, salts, or surfactants to create a solution that can be electrospun into advanced carbon electrodes with desirable structural and surface properties. Similarly, some of the liquid extract (tar fraction) can be subsequently reacted with toluene diisocyanate to create resinous coal-derived polyurethane (PUs) as a spinnable ink. Carbon nanofiber mats made from our proprietary electrospinning process were further carbonized at temperature ranging from 700°C to 900°C before they are used as electrodes in supercapacitors. Galvanostatic charge-discharge (GCD) results show that the best performing PU fiber mats can deliver a specific capacitance of 604 F g -1 at the current density of 1 A g -1 . A carbon fiber mat from a different solvent extraction residue also delivered the specific capacitance of 508 F g -1 . These specific capacitance values are comparable to or better than commercial activated carbons, demonstrating the viability of manufacturing carbon nanofiber electrodes from coal without the use of a commercial polymer as binder in the spinning ink.

Cincotta, Robert↗
DOE OSTI2023

Front-End Engineering Design for Carbon Capture from Shell's Deer Park Chemical Complex (Final Scientific/Technical Report)

This is the final scientific/technical report for a Front-End Engineering and Design (FEED) whose objective was to separate and capture over 820,000 tonnes per year (tpy) CO2 emissions from the commercially operated Shell Chemicals Complex located in Deer Park, Texas, USA reducing the overall facility CO2 emissions by 95% while providing energy transition jobs in a commercial area with a high concentration of refinery and chemical facilities producing CO2 emissions. The emission sources at the facility that were in scope were a total of Sixteen Furnaces – 8 OP3 furnaces and 8 OP3/HT2 Furnaces. Other minor sources were out of scope.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2024

Deploying a Publicly Available and Living National Oil and Gas Well Geodatabase: CO2-Locate: A Dynamic Database & Tool

Emission mitigation and safe geologic carbon storage require an understanding of local wellbore infrastructure, yet well data are siloed across many entities. Addressing this challenge, the National Energy Technology Laboratory published CO2-Locate, an integrated and dynamic national wellbore geodatabase. CO2-Locate offers up to date well data spanning more than 40 federal, state, and tribal entities, as well as spatially summarized insights designed to support commercial, regulatory, and research communities as they strive to curb climate change through a national energy transition.

Pfander, Isabelle↗