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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Enhancing the photoresponse and photocatalytic properties of TiO 2 by controllably tuning defects across {101} facets

Introducing defects into semiconductors with well-controlled exposed facets offers an effective route for the development of photocatalytic materials with greatly improved properties. Here, we report a facile ethylene glycol reduction procedure to make anatase titanium dioxide (TiO 2 ) with different concentrations of exposed {001} and {101} facets, leading to different surficial defects. TiO 2 with increased concentrations of {101} facets shows a 5-fold improvement in photocurrent generation as well as improved photocatalytic activity towards water splitting under visible light irradiation. Thus, the improved activity is ascribed to the oxygen vacancies as well as the variable surface chemical states, which collectively induce a slower recombination rate of photo-induced electron-hole pairs. This work also highlights a feasible strategy to obtain the defective TiO 2 and explore the synergistic effect of surface defects and different concentrations of exposed {001} and {101} facets for photocurrent and photocatalytic properties under visible light irradiation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Edaphic controls on soil organic carbon stocks in restored grasslands

Cultivation of undisturbed soils dramatically depletes organic carbon stocks at shallow depths, releasing a substantial quantity of stored carbon to the atmosphere. Restoration of native ecosystems can help degraded soils rebuild a portion of the depleted soil organic matter. However, the rate and magnitude of soil carbon accrual can be highly variable from site to site. Thus, a better understanding of the mechanisms controlling soil organic carbon stocks is necessary to improve predictions of soil carbon recovery. We measured soil organic carbon stocks and a suite of edaphic factors in the upper 10 cm of a series of restored tallgrass prairies representing a range of drainage conditions. Our findings suggest that factors related to soil organic matter stabilization mechanisms (texture, polyvalent cations) were key predictors of soil organic carbon, along with variables that influence plant and microbial biomass (available phosphorus, pH) and soil moisture. Exchangeable soil calcium was the strongest single predictor, explaining 74% of the variation in soil organic carbon, followed by clay content,which explained 52% of the variation. Our results demonstrate that the cumulative effects of even relatively small differences in these edaphic properties can have a large impact on soil carbon stocks when integrated over several decades.

Calcium↗
DOE OSTI2011

Scoring Systems to Estimate Intracerebral Control and Survival Rates of Patients Irradiated for Brain Metastases;Brain metastases; Radiation therapy; Local control; Survival; Prognostic scores

Purpose: To create and validate scoring systems for intracerebral control (IC) and overall survival (OS) of patients irradiated for brain metastases. Methods and Materials: In this study, 1,797 patients were randomly assigned to the test (n = 1,198) or the validation group (n = 599). Two scoring systems were developed, one for IC and another for OS. The scores included prognostic factors found significant on multivariate analyses. Age, performance status, extracerebral metastases, interval tumor diagnosis to RT, and number of brain metastases were associated with OS. Tumor type, performance status, interval, and number of brain metastases were associated with IC. The score for each factor was determined by dividing the 6-month IC or OS rate (given in percent) by 10. The total score represented the sum of the scores for each factor. The score groups of the test group were compared with the corresponding score groups of the validation group. Results: In the test group, 6-month IC rates were 17% for 14-18 points, 49% for 19-23 points, and 77% for 24-27 points (p < 0.0001). IC rates in the validation group were 19%, 52%, and 77%, respectively (p < 0.0001). In the test group, 6-month OS rates were 9% for 15-19 points, 41% for 20-25 points, and 78% for 26-30 points (p < 0.0001). OS rates in the validation group were 7%, 39%, and 79%, respectively (p < 0.0001). Conclusions: Patients irradiated for brain metastases can be given scores to estimate OS and IC. IC and OS rates of the validation group were similar to the test group demonstrating the validity and reproducibility of both scores.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Multielectrode Array Sensors to Enable Long-Duration Corrosion Monitoring and Control of Concentrating Solar Power Systems

Molten mixtures of MgCl2-KCl-NaCl are promising heat transfer fluid (HTF) candidates for the next generation of concentrating solar power systems (Gen3 CSP), because of their low cost, high decomposition temperature, and favorable heat transfer characteristics. However, if the chemistry of the salts is not properly controlled, molten chlorides can cause corrosion of high-temperature metal alloys, such as Inconel (R), in CSP systems. Here we demonstrate a corrosion monitoring system that can be used to monitor the health of the structural alloys over long durations. The monitoring system includes a multielectrode array voltammetry sensor that measures the redox potential of molten MgCl2-KCl-NaCl mixture as well as the presence of corrosion products and impurities. The sensors have been successfully operated in static molten salt environments for long durations, and are capable of detecting corrosion products, such as Cr2+ and Fe2+, quantitatively at low concentrations (i.e., approximately 100 ppm) with less than 4% error.

Concentrated solar power↗
DOE OSTI2021

Control of Peptide Amphiphile Supramolecular Nanostructures by Isosteric Replacements

Supramolecular nanostructures with tunable properties can have applications in medicine, pharmacy, and biotechnology. In this work, we show that the self-assembly behavior of peptide amphiphiles (PAs) can be effectively tuned by replacing the carboxylic acids exposed to the aqueous media with isosteres, functionalities that share key physical or chemical properties with another chemical group. Transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering studies indicated that the nanostructure’s morphologies are responsive to the ionization states of the side chains, which are related to their pK a values. Circular dichroism studies revealed the effect of the isosteres on the internal arrangement of the nanostructures. The interactions between diverse surfaces and the nanostructures and the effect of salt concentration and temperature were assessed to further understand the properties of these self-assembled systems. These results indicate that isosteric replacements allow the pH control of supramolecular morphology by manipulating the pK a of the charged groups located on the nanostructure’s surface. Theoretical studies were performed to understand the morphological transitions that the nanostructures underwent in response to pH changes, suggesting that the transitions result from alterations in the Coulomb forces between PA molecules. Furthermore, this work provides a strategy for designing biomaterials that can maintain or change behaviors based on the pH differences found within cells and tissues.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Controlling Infrared Plasmon Resonances in Inverse-Spinel Cadmium Stannate Nanocrystals via Site-Selective Cation-Exchange Reactions

Doped metal oxide nanocrystals (NCs) exhibit tunable localized surface plasmon resonances (LSPRs) in the infrared spectral region. Compared to the binary oxides commonly studied, plasmonic NCs derived from ternary oxides remain far less explored primarily due to the difficulty of controlling NC phase-purity and stoichiometry. Here, we report the synthesis of inverse spinel-type cadmium stannate (Cd 2 SnO 4 ) NCs, for which cation-exchange reactions were developed to tailor their composition and LSPR properties. X-ray absorption spectroscopy studies revealed that the inequivalent tetrahedrally and octahedrally coordinated Cd 2+ can be selectively exchanged for Cu + and In 3+ ions, respectively, enabling broadband tunable LSPR and Cu-mediated cation-exchange with lanthanide ions that are otherwise difficult to incorporate. Here, our work paves the way for systematic compositional engineering to accelerate the design of complex metal oxide NCs with emerging plasmonic, electronic, and magnetic properties.

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

Molecular Structure Controlled Transitions between Free-Charge Generation and Trap Formation in a Conjugated Copolymer Series

Charge transfer copolymers, where each repeating unit has at least one “donor” and one “acceptor” block, have played important roles in recent advances in organic photovoltaic (OPV) devices, however design criteria for these materials are still not completely clear. Here we show that the well-recognized LUMO-LUMO energy off-set design criterion for OPV materials using a fullerene acceptor is challenged in a series of copolymers, PTRn (n = 3, 5, 7 and 9), where n is the number of fused aromatic rings in the “donor” block and thienothiophene is the “acceptor” block in each repeating unit. Photoexcitation dynamics of PTRn copolymers in solution and BHJ (bulk heterojunction) films demonstrated that local push-pull interactions between the “donor” block and the “acceptor” block weakens with increasing n, whereas the LUMO-LUMO off-set between the polymer and PC71BM (Phenyl-C71-butyric acid methyl ester) increases. Such a counter intuitive trend can be explained by local energetics of each repeating unit as a function of n. The energetic changes transform the copolymer with strong local charge transfer character for efficient hole-electron separation to localized hole-electron pairs with low mobility, despite the apparent increase of the polymer/PC71BM LUMO-LUMO off-set. This suggests the importance of local charge transfer character in these copolymers in the initial exciton splitting dynamics, which could ultimately be reflected in the device performance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Controlled Placement of Microparticles at the Water–Liquid Crystal Elastomer Interface

Control of cells behavior through topography of substrates is an important theme in biomedical applications. Among many materials used as substrates, polymers show advantages since they can be tailored by chemical functionalization. Fabrication of polymer substrates with nano- and microscale topography requires processing by lithography, microprinting, etching, etc. In this work, we introduce a different approach based on anisotropic elastic properties of polymerized smectic A (SmA) liquid crystal elastomer (LCE). When the SmA liquid crystal coating is deposited onto a substrate with planar alignment of the molecules, it develops nanogrooves at its free surface. After photopolymerization, these nanogrooves show an excellent ability to align human dermal fibroblasts (hDFs) over large areas. The alignment quality is good for both bare SmA LCE substrates and for substrates coated with fibronectin. The SmA LCE nano-topographies show a high potential for tissue engineering.

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

Nanoscale Control of Intrinsic Magnetic Topological Insulator MnBi 2 Te 4 Using Molecular Beam Epitaxy: Implications for Defect Control

Intrinsic magnetic topological insulators have emerged as a promising platform to study the interplay between the topological surface states and ferromagnetism. This unique interplay can give rise to a variety of exotic quantum phenomena, including the quantum anomalous Hall effect and axion insulating states. Here, in this study, utilizing molecular beam epitaxy (MBE), we present a comprehensive study of the growth of MnBi 2 Te 4 thin films on Si (111), epitaxial graphene, and highly ordered pyrolytic graphite substrates. By combining a suite of in situ characterization techniques, we obtain critical insights into the nanoscale control of MnBi 2 Te 4 epitaxial growth. First, we extract the free energy landscape for the epitaxial relationship as a function of the in-plane angular distribution. Then, by employing an optimized layer-by-layer growth, we determine the chemical potential and Dirac point of the thin film at different thicknesses and how this quantity is manifested by the dopant compensation from different antisite defects. Overall, these results establish a foundation for understanding the growth kinetics of MnBi 2 Te 4 and pave the way for future applications of MBE-grown thin films in emerging topological quantum materials.

36 MATERIALS SCIENCE↗