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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Measurements of electron transport in liquid and gas Xenon using a laser-driven photocathode

Measurements of electron drift properties in liquid and gaseous xenon are reported. The electrons are generated by the photoelectric effect in a semitransparent gold photocathode driven in transmission mode with a pulsed ultraviolet laser. The charges drift and diffuse in a small chamber at various electric fields and a fixed drift distance of 2.0 cm. At an electric field of 0.5 kV/cm, the measured drift velocities and corresponding temperature coefficients respectively are 1.97 ± 0.04 mm/µs and (-0.69 ± 0.05)%/K for liquid xenon, and 1.42 ± 0.03 mm/µs and (+0.11 ± 0.01)%/K for gaseous xenon at 1.5 bar. In addition, we measure longitudinal diffusion coefficients of 25.7±4.6 cm2/s and 149±23 cm2/s, for liquid and gas, respectively. The quantum efficiency of the gold photocathode is studied at the photon energy of 4.73 eV in liquid and gaseous xenon, and vacuum. These charge transport properties and the behavior of photocathodes in a xenon environment are important in designing and calibrating future large scale noble liquid detectors.

Njoya, Oumarou↗
DOE OSTI2020

Water-Fed Hydroxide Exchange Membrane Electrolyzer Enabled by a Fluoride-Incorporated Nickel–Iron Oxyhydroxide Oxygen Evolution Electrode

Here, we have developed a dissolved oxygen and galvanic corrosion method to synthesize vertically aligned fluoride-incorporated nickel–iron oxyhydroxide nanosheet arrays on a compressed Ni foam as an efficient self-supported oxygen evolution electrode. It is integrated with poly(aryl piperidinium) hydroxide exchange membrane and ionomers with high ion exchange capacity into a hydroxide exchange membrane electrolyzer fed with pure water, which achieves a performance of 1020 mA cm –2 at 1.8 V and prevents the detachment of catalysts during continuous operation (>160 h at 200 mA cm –2 ). Furthermore, this work provides a potential pathway for massively producing low-cost hydrogen using intermittent renewable energy sources.

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

Enhancing Hydrogen Production from Bioenergy Crops via Photoreforming

Photoreforming perennial bioenergy crops (willow, Miscanthus , and poplar) has the potential to produce H 2 with reduced environmental impacts. To understand the compositional effects of the biomass on the average rate of H 2 production over the first 30 min of reaction ( r H 2 ), the r H 2 values of model biomass component (i.e., cellulose, hemicellulose, and lignin) mixtures were compared with those from the raw biomass. The higher cellulose or hemicellulose content in multicomponent mixtures resulted in higher r H 2 , whereas lignin reduced the hydrogen production rate. However, with raw biomass, the ratio of biomass components alone did not determine the r H 2 via photoreforming, with rates of hydrogen production for different varieties of willow ranging between 1.9 μmol h -1 and 12.3 μmol h -1 , 11.8 μmol h -1 for a poplar, and 6.8 μmol h -1 for a miscanthus biomass. In addition, comparable r H 2 values of raw poplar and its extracted cellulose via an IonoSolv treatment indicated the possibility of using raw biomass materials without delignification for generating H 2 via photoreforming. Importantly, r H 2 was positively correlated with the interaction between water and the biomass, as assessed by NMR relaxation via an examination of the T 1 /T 2 ratio. A stronger water-biomass interaction resulted in a higher r H 2 . Genetic modification of biomass has been suggested as a putative way to improve the r H 2 of biomass with an enhanced interaction with water. This research enhances the understanding of factors influencing H 2 production from lignocellulosic biomass by photoreforming and supports the breeding and management of perennial biomass crops to maximize H 2 yields while minimizing land area requirements.

biomass↗
DOE OSTI2023

Allosteric autoregulation of DNA binding via a DNA-mimicking protein domain: a biophysical study of ZNF410–DNA interaction using small angle X-ray scattering

ZNF410 is a highly-conserved transcription factor, remarkable in that it recognizes a 15-base pair DNA element but has just a single responsive target gene in mammalian erythroid cells. ZNF410 includes a tandem array of five zinc-fingers (ZFs), surrounded by uncharacterized N- and C-terminal regions. Unexpectedly, full-length ZNF410 has reduced DNA binding affinity, compared to that of the isolated DNA binding ZF array, both in vitro and in cells. AlphaFold predicts a partially-folded N-terminal subdomain that includes a 30-residue long helix, preceded by a hairpin loop rich in acidic (aspartate/glutamate) and serine/threonine residues. This hairpin loop is predicted by AlphaFold to lie against the DNA binding interface of the ZF array. In solution, ZNF410 is a monomer and binds to DNA with 1:1 stoichiometry. Surprisingly, the single best-fit model for the experimental small angle X-ray scattering profile, in the absence of DNA, is the original AlphaFold model with the N-terminal long-helix and the hairpin loop occupying the ZF DNA binding surface. For DNA binding, the hairpin loop presumably must be displaced. After combining biophysical, biochemical, bioinformatic and artificial intelligence-based AlphaFold analyses, we suggest that the hairpin loop mimics the structure and electrostatics of DNA, and provides an additional mechanism, supplementary to sequence specificity, of regulating ZNF410 DNA binding.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Chiral kinetic theory of anomalous transport induced by torsion

In Weyl semimetals subjected to torsion, there are two different kinds of chirality: (i) The (coordinate-space) shape of the twisted crystal is chiral and (ii) the momentum space contains chiral quasiparticles. Here we construct a general kinetic theory of anomalous transport using the phase space (coordinate and momentum spaces combined) Berry curvature induced by torsion in Weyl systems. We describe how torsion generates the chiral chemical potential and thus leads to the chiral magnetic effect (CME) in the presence of a background magnetic field. We propose to measure the CME current induced by the torsion as a way to detect the anomalous coupling between the coordinate-space and momentum-space chiralities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2021

Trend Detection of Atmospheric Time Series: Incorporating Appropriate Uncertainty Estimates and Handling Extreme Events

This paper is aimed at atmospheric scientists without formal training in statistical theory. Its goal is to, 1) provide a critical review of the rationale for trend analysis of the time series typically encountered in the field of atmospheric chemistry; 2) describe a range of trend-detection methods; and 3) demonstrate effective means of conveying the results to a general audience. Trend detections in atmospheric chemical composition data are often challenged by a variety of sources of uncertainty, which often behave differently to other environmental phenomena such as temperature, precipitation rate, or stream flow, and may require specific methods depending on the science questions to be addressed. Some sources of uncertainty can be explicitly included in the model specification, such as autocorrelation and seasonality, but some inherent uncertainties are difficult to quantify, such as data heterogeneity and measurement uncertainty due to the combined effect of short- and long-term natural variability, instrumental stability, and aggregation of data from sparse sampling frequency. Failure to account for these uncertainties might result in an inappropriate inference of the trends and their estimation errors. On the other hand, the variation in extreme events might be interesting for different scientific questions, for example, the frequency of extremely high surface ozone events and their relevance to human health. In this study we aim to, 1) review trend detection methods for addressing different levels of data complexity in different chemical species; 2) demonstrate that the incorporation of scientifically interpretable covariates can outperform pure numerical curve fitting techniques in terms of uncertainty reduction and improved predictability; 3) illustrate the study of trends based on extreme quantiles that can provide insight beyond standard mean or median based trend estimates; and 4) present an advanced method of quantifying regional trends based on the inter-site correlations of multi-site data. All demonstrations are based on time series of observed trace gases relevant to atmospheric chemistry, but the methods can be applied to other environmental data sets.

Trace gas↗
DOE OSTI2022

Unravelling the Role of Electron Acceptors for the Universal Enhancement of Charge Transport in Quinoid-Donor-Acceptor Polymers for High-Performance Transistors

The quinoid-donor-acceptor (Q-D-A) strategy has recently emerged as a promising approach for constructing high mobility semiconducting polymers. In order to fully explore the potential of this strategy in improving the charge transport and elucidating the structure-property-performance relationships in Q-D-A polymers, a series of new polymers with different electron acceptor units and backbone coplanarity have been synthesized and characterized. In this work, all of the resulting Q-D-A polymers exhibit much more planar backbone conformations in comparison to their donor-acceptor (D-A) counterparts. Moreover, organic field-effect transistors based on Q-D-A polymers exhibit excellent effective hole mobilities in a range of 0.44 to 3.35 cm 2 V –1 s –1 , most of which are orders of magnitude higher than those of their corresponding D-A polymers. Notably, the hole mobility of 3.35 cm 2 V –1 s –1 is among the highest for the quinoidal-aromatic polymers characterized by conventional spin-coating methods. Furthermore, the role of electron acceptors in Q-D-A polymers has been comprehensively investigated. Polymers with stronger acceptor units are more inclined to deliver edge-on lamellas, high film crystallinity, small effective hole masses, and decent operational stability. The detailed structure-property-device performance relationship will pave the way toward high performance semiconducting polymers using the potent Q-D-A strategy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Superhydrophobic Phosphonium Modified Robust 3D Covalent Organic Framework for Preferential Trapping of Charge Dispersed Oxoanionic Pollutants

Abstract Charge dispersed and less hydrophilic anionic pollutants are often difficult to be preferentially captured by common cationic framework materials. A gamma radiation modification approach is employed to anchor a superhydrophobic phosphonium‐containing coating on a robust crystalline 3D covalent organic framework (COF). By regulating the surface hydrophobicity, the prepared 3DCOF‐ g ‐VBPPh 3 Cl is endowed with a strong affinity for charge dispersed and less hydrophilic oxoanions, such as MnO 4 − , TcO 4 − and ReO 4 − , to surmount the Hofmeister bias, which much favors remediation of oxoanionic pollutants in complex aqueous systems. Batch and column experiments with 3DCOF‐g‐VBPPh 3 Cl in both tap water and simulated groundwater are performed, and rapid sequestration is achieved with removal efficacy up to 99.995%, record‐high distribution coefficient of 1.0 × 10 8 mL g −1 , and desirable priority over competing anions such as Cl − , SO 4 2− , HCO 3 − , and NO 3 − , confirming promise for remediation of charge dispersed anionic pollutants. Theoretical calculations reveal a mechanism of preferential capture based on electrostatic and dispersion interaction between charge dispersed anions and 3DCOF‐g‐VBPPh 3 Cl that effectively competes with solvation of the aqueous anions.

Wang, Yue↗
DOE OSTI2023

Zinc‐Imidazolate Films as an All‐Dry Resist Technology

Here, motivated by the drawbacks of solution phase processing, an all‐dry resist formation process is presented that utilizes amorphous zinc‐imidazolate (aZnMIm) films deposited by atomic/molecular layer deposition (ALD/MLD), patterned with electron beam lithography (EBL), and developed by novel low temperature (120 °C) gas phase etching using 1,1,1,5,5,5‐hexafluoroacetylacetone (hfacH) to achieve well‐resolved 22 nm lines with a pitch of 30 nm. The effects of electron beam irradiation on the chemical structure and hfacH etch resistance of aZnMIm films are investigated, and it is found that electron irradiation degrades the 2‐methylimidazolate ligands and transforms aZnMIm into a more dense material that is resistant to etching by hfacH and has a C:N:Zn ratio effectively identical to that of unmodified aZnMIm. These findings showcase the potential for aZnMIm films to function in a dry resist technology. Sensitivity, contrast, and critical dimensions of the patterns are determined to be 37 mC cm −2 , 0.87, and 29 nm, respectively, for aZnMIm deposited on silicon substrates and patterned at 30 keV. This work introduces a new direction for solvent‐free resist processing, offering the prospect of scalable, high‐resolution patterning techniques for advanced semiconductor fabrication processes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

High‐Pressure Synthesis of Ultra‐Incompressible, Hard and Superconducting Tungsten Nitrides

Abstract Transition metal nitrides, particularly those of 5 d metals, are known for their outstanding properties, often relevant for industrial applications. Among these metal elements, tungsten is especially attractive given its low cost. In this high‐pressure investigation of the W–N system, two novel ultra‐incompressible tungsten nitride superconductors, namely W 2 N 3 and W 3 N 5 , are successfully synthesized at 35 and 56 GPa, respectively, through a direct reaction between N 2 and W in laser‐heated diamond anvil cells. Their crystal structure is determined using synchrotron single‐crystal X‐ray diffraction. While the W 2 N 3 solid's sole constituting nitrogen species are N 3‐ units, W 3 N 5 features both discrete N 3‐ as well as N 2 4‐ pernitride anions. The bulk modulus of W 2 N 3 and W 3 N 5 is experimentally determined to be 380(3) and 406(7) GPa, and their ultra‐incompressible behavior is rationalized by their constituting WN 7 polyhedra and their linkages. Importantly, both W 2 N 3 and W 3 N 5 are recoverable to ambient conditions and stable in air. Density functional theory calculations reveal W 2 N 3 and W 3 N 5 to have a Vickers hardness of 30 and 34 GPa, and superconducting transition temperatures at ambient pressure (50 GPa) of 11.6 K (9.8 K) and 9.4 K (7.2 K), respectively. Additionally, transport measurements performed at 50 GPa on W 2 N 3 corroborate with the calculations.

Chemistry↗
DOE OSTI2024

Impact of Linker Engineering in Core‐Linked Dimeric Acceptors for High‐Performance Organic Solar Cells

Abstract The dimerization of small molecule acceptors (SMAs) is a promising strategy for enhancing the long‐term stability and power conversion efficiency (PCE) of organic solar cells (OSCs). However, the reported DSMAs are primarily limited to end‐linked molecular configurations, highlighting the need for further exploration of various dimer architectures. Herein, the development of two distinct core‐linked dimerized SMAs (DYF‐V and DYF‐E) are reported with tailored linker structures (vinylene and ethynyl, respectively), achieving high‐performance OSCs (PCE = 18.53%). Interestingly, a subtle change in the linker structures results in markedly different molecular properties and photovoltaic performances of the dimer acceptors. DYF‐E with an ethynyl linker exhibits more twisted backbone conformation and mitigated aggregation property compared to DYF‐V, inducing desirable blend morphologies with a polymer donor including high crystallinity, face‐on oriented packing structures, and well‐intermixed domains. Thus, the DYF‐E‐based OSCs exhibit a high PCE (17.02%), which significantly outperforms the DYF‐V‐based OSCs (PCE = 9.98%). Furthermore, the ternary OSCs based on DYF‐E achieve a higher PCE of 18.53%. Thus, this study highlights the significance of selecting an appropriate linker in core‐linked dimerized SMAs for producing high‐performance OSCs.

Oh, Shinbee↗