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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Solar generation and storage of O2 (a 1 delta g)

An investigation was performed of the technical steps required to design a solar powered oxygen-iodine laser. Singlet delta oxygen is formed upon transfer of energy from selected photoexcited dye molecules to ground state molecular oxygen and then is concentrated and stored as an endoperoxide by reaction with an aromatic hydrocarbon. The endoperoxide, when heated, releases singlet oxygen in high yield thus providing a regenerable source of laser fuel. Energy transfer from dye molecules to molecular oxygen was investigated. When dye molecules were adsorbed to polymer substrates it was observed that the dye became embedded in the polymer matrix. Porphin dyes were incorporated into films of 1,4-dimethyl-2-poly(vinylnaphthalene), 2PVN. An endoperoxide was formed when porphin-doped 2PVN was exposed to visible radiation. This demonstrates the possibility of generating singlet oxygen using solar energy and concentrating and storing it in one simple step. Transport of energy by exciton migration in polycrystalline dye films was also investigated.

Twarowski, Allen J.↗
DOE OSTI2017

Treatment of Magnesium-Thorium Alloy Used in Military Defence Equipment by Separation of Thorium and/or Thermal Oxidation - 17009

Magnesium-alloys doped with thorium (Th, 3% by weight and with a total activity content in the alloy of 120 Bq/g) to improve mechanical properties has been used in, among other applications, military equipment such as in the jet-engines in military aircraft. The material cannot, due to the presence of the radioactive Th, be handled as an ordinary scrap metal. It needs to be treated to render a more stable waste form prior to final disposal in which the amount of disposed metallic magnesium is limited due to the pyrophoric properties of such type of materials. By thermally treating the material it is possible to transform the alloy into oxide form (MgO and ThO{sub 2}) which is a much more stable form than metallic. This itself enables a form suitable for final disposal of the material. The oxidation step does however lead to an increase in volume and is therefore not an optimal treatment method. It is possible to treat the metal oxide powder in order to get a better volume reduction such as by super compaction but a better result can be obtained by separating the Th from the alloy, leaving a much smaller volume for final disposal. One way of separating the Th from the metal is by dissolution of metallic material in acid followed by directed precipitation of Th as Th-oxalate. Several parameters such as the choice of acid, metal concentration in the acid solution, pH prior to precipitation and amount of added oxalic acid have been investigated. Another method to separate Th from Mg is to perform a selective dissolution of MgO from an MgO/ThO{sub 2} mixture with HNO{sub 3} leaving only ThO{sub 2} as a residue. These tests had to be preceded with an oxidation of the alloy. The tests show that it is possible to separate Th from the metal alloy by either dissolution followed by precipitation or selective dissolution of MgO from an MgO/ThO{sub 2} mixture. This leads to very effective volume reduction of the waste. For the direct dissolution and precipitation tests typically > 95% of the magnesium can be found in the acid solution while 99.5 % of the Th is found as a solid in the filters. For the oxide dissolution tests typically 98% of the Th can be separated from the bulk material, leaving the acid solution possible to free release and dispose of in the same way as for the previous method. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2013

Plasmonic transparent conducting metal oxide nanoparticles and nanoparticle films for optical sensing applications

The ability to monitor gas species selectively, sensitively, and reliably in extreme temperatures and harsh conditions is critically important for more efficient energy production using conventional fossil energy based production technologies, enabling advanced technologies for fossil based power plants of the future, and improving efficiency in domestic manufacturing industries. Optical waveguide based sensing platforms have become increasingly important but a need exists for materials that exhibit useful changes in optical properties in response to changing gas atmospheres at high temperatures. In this manuscript, the onset of a near-IR absorption associated with an increase in free carrier density in doped metal oxide nanoparticles to form so-called conducting metal oxides is discussed in the context of results obtained for undoped and Al-doped ZnO nanoparticle based films. Detailed film characterization results are presented along with measured changes in optical absorption resulting from various high temperature treatments in a range of gas atmospheres. Optical property changes are also discussed in the context of a simple model for optical absorption in conducting metal oxide nanoparticles and thin films. The combination of experimental results and theoretical modeling presented here suggests that such materials have potential for high temperature optical gas sensing applications. Simulated sensing experiments were performed at 500 °C and a useful, rapid, and reproducible near-IR optical sensing response to H{sub 2} confirms that this class of materials shows great promise for optical gas sensing.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Spin-dependent vibronic response of a carbon radical ion in two-dimensional WS 2

Atomic spin centers in 2D materials are a highly anticipated building block for quantum technologies. Here, we demonstrate the creation of an effective spin-1/2 system via the atomically controlled generation of magnetic carbon radical ions (CRIs) in synthetic two-dimensional transition metal dichalcogenides. Hydrogenated carbon impurities located at chalcogen sites introduced by chemical doping are activated with atomic precision by hydrogen depassivation using a scanning probe tip. In its anionic state, the carbon impurity is computed to have a magnetic moment of 1 μ B resulting from an unpaired electron populating a spin-polarized in-gap orbital. We show that the CRI defect states couple to a small number of local vibrational modes. The vibronic coupling strength critically depends on the spin state and differs for monolayer and bilayer WS 2 . The carbon radical ion is a surface-bound atomic defect that can be selectively introduced, features a well-understood vibronic spectrum, and is charge state controlled.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Observation of site-controlled localized charged excitons in CrI3/WSe2 heterostructures

Abstract Isolated spins are the focus of intense scientific exploration due to their potential role as qubits for quantum information science. Optical access to single spins, demonstrated in III-V semiconducting quantum dots, has fueled research aimed at realizing quantum networks. More recently, quantum emitters in atomically thin materials such as tungsten diselenide have been demonstrated to host optically addressable single spins by means of electrostatic doping the localized excitons. Electrostatic doping is not the only route to charging localized quantum emitters and another path forward is through band structure engineering using van der Waals heterojunctions. Critical to this second approach is to interface tungsten diselenide with other van der Waals materials with relative band-alignments conducive to the phenomenon of charge transfer. In this work we show that the Type-II band-alignment between tungsten diselenide and chromium triiodide can be exploited to excite localized charged excitons in tungsten diselenide. Leveraging spin-dependent charge transfer in the device, we demonstrate spin selectivity in the preparation of the spin-valley state of localized single holes. Combined with the use of strain-inducing nanopillars to coordinate the spatial location of tungsten diselenide quantum emitters, we uncover the possibility of realizing large-scale deterministic arrays of optically addressable spin-valley holes in a solid state platform.

42 ENGINEERING↗
DOE OSTI2022

Revealing the Structure of Single Cobalt Sites in Carbon Nitride for Photocatalytic CO 2 Reduction

Single Co 2+ sites in graphitic carbon nitride (C 3 N 4 ) have demonstrated excellent activity and selectivity in photocatalytic CO 2 reduction. In this work, we combine computational and spectroscopic tools, including X-ray absorption spectroscopy, to probe the structure of such single Co 2+ sites. Our results indicate that the Co 2+ sites exist in the Co–N 2+2 coordination at the edges of C 3 N 4 flakes. This mode of coordination is further supported by experimental results obtained using single Co 2+ sites in C 3 N 4 materials treated with NH 3 , which contain more edge sites than untreated C 3 N 4 . In our experimental observations, doping C 3 N 4 with carbon is found to be important for the photocatalytic properties of the single Co 2+ sites. Here, a simplified model is proposed to explain the origin of the observed enhancement effect of C doping. In this model, the presence of C dopant near the metal centers results in shorter Co–N bond length and stronger Co–N binding energy. In addition to enhanced light absorption and charge separation in C-doped C 3 N 4 , the stronger Co–N binding upon C doping likely contributes to the improved catalytic properties of the single Co 2+ sites.

14 SOLAR ENERGY↗
DOE OSTI2014

Band offsets of n-type electron-selective contacts on cuprous oxide (Cu{sub 2}O) for photovoltaics

The development of cuprous oxide (Cu{sub 2}O) photovoltaics (PVs) is limited by low device open-circuit voltages. A strong contributing factor to this underperformance is the conduction-band offset between Cu{sub 2}O and its n-type heterojunction partner or electron-selective contact. In the present work, a broad range of possible n-type materials is surveyed, including ZnO, ZnS, Zn(O,S), (Mg,Zn)O, TiO{sub 2}, CdS, and Ga{sub 2}O{sub 3}. Band offsets are determined through X-ray photoelectron spectroscopy and optical bandgap measurements. A majority of these materials is identified as having a negative conduction-band offset with respect to Cu{sub 2}O; the detrimental impact of this on open-circuit voltage (V{sub OC}) is evaluated through 1-D device simulation. These results suggest that doping density of the n-type material is important as well, and that a poorly optimized heterojunction can easily mask changes in bulk minority carrier lifetime. Promising heterojunction candidates identified here include Zn(O,S) with [S]/[Zn] ratios >70%, and Ga{sub 2}O{sub 3}, which both demonstrate slightly positive conduction-band offsets and high V{sub OC} potential. This experimental protocol and modeling may be generalized to evaluate the efficiency potential of candidate heterojunction partners for other PV absorbers, and the materials identified herein may be promising for other absorbers with low electron affinities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Selective mass enhancement close to the quantum critical point in BaFe 2 (As 1-x P x ) 2

A quantum critical point (QCP) is currently being conjectured for the BaFe 2 (As 1-x P x ) 2 system at the critical value x c ≈ 0.3. In the proximity of a QCP, all thermodynamic and transport properties are expected to scale with a single characteristic energy, given by the quantum fluctuations. Such a universal behavior has not, however, been found in the superconducting upper critical field H c2 . Here we report H c2 data for epitaxial thin films extracted from the electrical resistance measured in very high magnetic fields up to 67 Tesla. Using a multi-band analysis we find that H c2 is sensitive to the QCP, implying a significant charge carrier effective mass enhancement at the doping-induced QCP that is essentially band-dependent. Our results point to two qualitatively different groups of electrons in BaFe 2 (As 1-x P x ) 2 . The first one (possibly associated to hot spots or whole Fermi sheets) has a strong mass enhancement at the QCP, and the second one is insensitive to the QCP. The observed duality could also be present in many other quantum critical systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Nanopinhole Passivating Contact Si Solar Cells Fabricated with Metal-Assisted Chemical Etching

Monocrystalline Si (c-Si) solar cells with passivating contacts based on doped polycrystalline Si (poly-Si) on ≈2.0 nm silicon oxide (SiO x ) require >1000 °C thermal processing to create conducting pinholes in the SiO x layer. However, this high thermal budget can induce bulk defects in the Czochralski c-Si wafers used as the cell absorber layer. We demonstrate that pinholes can instead be created using metal-assisted chemical etching on planar or textured morphologies, at room temperature. This wet process creates up to 200 nm wide conducting pinholes that are directly observed with transmission electron and atomic force microscopies. High-performance hole-selective poly-Si/SiN y /SiO x and electron-selective poly-Si/SiO x passivating contacts are fabricated and implemented in laboratory-scale solar cells. This process development significantly broadens the range of passivation layer materials, their thicknesses, and surface morphologies, which enables the design of poly-Si contacts with superior passivating quality.

14 SOLAR ENERGY↗
DOE OSTI2020

Chemical instability at chalcogenide surfaces impacts chalcopyrite devices well beyond the surface

The electrical and optoelectronic properties of materials are determined by the chemical potentials of their constituents. The relative density of point defects is thus controlled, allowing to craft microstructure, trap densities and doping levels. Here, we show that the chemical potentials of chalcogenide materials near the edge of their existence region are not only determined during growth but also at room temperature by post-processing. In particular, we study the generation of anion vacancies, which are critical defects in chalcogenide semiconductors and topological insulators. The example of CuInSe 2 photovoltaic semiconductor reveals that single phase material crosses the phase boundary and forms surface secondary phases upon oxidation, thereby creating anion vacancies. The arising metastable point defect population explains a common root cause of performance losses. This study shows how selective defect annihilation is attained with tailored chemical treatments that mitigate anion vacancy formation and improve the performance of CuInSe 2 solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

Advanced Multi-Component Defect Cluster Oxide Doped Zirconia-Yttria Thermal Barrier Coatings

The advantages of using ceramic thermal barrier coatings in gas turbine engine hot sections include increased fuel efficiency and improved engine reliability. However, current thermal barrier coatings will not have the low thermal conductivity and necessary sintering resistance under higher operating temperatures and thermal gradients required by future advanced ultra efficient and low emission aircraft engines. In this paper, a novel oxide defect cluster design approach is described for achieving low thermal conductivity and excellent thermal stability of the thermal barrier coating systems. This approach utilizes multi-component rare earth and other metal cluster oxide dopants that are incorporated in the zirconia-yttna based systems, thus significantly reducing coating thermal conductivity and sintering resistance by effectively promoting the formation of thermodynamically stable, essentially immobile defect clusters and/or nanoscale phases. The performance of selected plasma-sprayed cluster oxide thermal barrier coating systems has been evaluated. The advanced multi-component thermal barrier coating systems were found to have significantly lower initial and long-term thermal conductivities, and better high temperature stability. The effect of oxide cluster dopants on coating thermal conductivity, sintering resistance, oxide grain growth behavior and durability will be discussed.

Zhu, Dongming↗
DOE OSTI2022

Single-Atomic Site Catalyst Enhanced Lateral Flow Immunoassay for Point-of-Care Detection of Herbicide

Point-of-care (POC) detection of herbicides is of great importance due to their impact on the environment and potential risks to human health. Here, we design a single-atomic site catalyst (SASC) with excellent peroxidase-like (POD-like) catalytic activity, which enhances the detection performance of corresponding lateral flow immunoassay (LFIA). The iron single-atomic site catalyst (Fe-SASC) is synthesized from hemin-doped ZIF-8, creating active sites that mimic the Fe active center coordination environment of natural enzyme and their functions. Due to its atomically dispersed iron active sites that result in maximum utilization of active metal atoms, the Fe-SASC exhibits superior POD-like activity, which has great potential to replace its natural counterparts. Also, the catalytic mechanism of Fe-SASC is systematically investigated. Utilizing its outstanding catalytic activity, the Fe-SASC is used as label to construct LFIA (Fe-SASC-LFIA) for herbicide detection. The 2,4-dichlorophenoxyacetic acid (2,4-D) is selected as a target here, since it is a commonly used herbicide as well as a biomarker for herbicide exposure evaluation. A linear detection range of 1-250 ng/mL with a low limit of detection (LOD) of 0.82 ng/mL has been achieved. Meanwhile, excellent specificity and selectivity towards 2,4-D have been obtained. The outstanding detection performance of the Fe-SASC-LFIA has also been demonstrated in the detection of human urine samples, indicating the practicability of this POC detection platform for analyzing the 2,4-D exposure level of a person. We believe this proposed Fe-SASC-LFIA has potential as a portable, rapid, and high-sensitive POC detection strategy for pesticide exposure evaluation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1990

Advanced Multi-Component Defect Cluster Oxide Doped Zirconia-Yttria Thermal Barrier Coatings

The advantages of using ceramic thermal barrier coatings in gas turbine engine hot sections include increased fuel efficiency and improved engine reliability. However, current thermal barrier coatings will not have the low thermal conductivity and necessary sintering resistance under higher operating temperatures and thermal gradients required by future advanced ultra-efficient and low-emission aircraft engines. In this paper, a novel oxide defect cluster design approach is described for achieving low thermal conductivity and excellent thermal stability of the thermal barrier coating systems. This approach utilizes multi-component rare earth and other metal cluster oxide dopants that are incorporated in the zirconia-yttria based systems, thus significantly reducing coating thermal conductivity and sintering resistance by effectively promoting the formation of thermodynamically stable, essentially immobile defect clusters and/or nanoscale phases. The performance of selected plasma-sprayed cluster oxide thermal barrier coating systems has been evaluated. The advanced multi-component thermal barrier coating systems were found to have significantly lower initial and long-term thermal conductivities, and better high temperature stability. The effect of oxide cluster dopants on coating thermal conductivity, sintering resistance, oxide grain growth behavior and durability will be discussed.

Zhu, Dongming↗
DOE OSTI2015

State-of-the-art Thin Film Electrolytes For Solid Oxide Fuel Cells

State-of-the-Art solid oxide fuel cells (SOFC) are amongst the main candidates for clean energy technology due to their high efficiency, fuel flexibility, low air pollution, and minimal greenhouse gas emission. However, high operational temperature of SOFC is a greater challenge in commercialization these devices for low cost and portable applications. High temperature operation of SOFC degrades its performance with aging, limits the selection of materials for fuel cell components, and increases the fabrication cost. Thus, there have been enormous efforts to improve the properties of existing materials and develop new materials for SOFC components in order to lower the operating temperature of SOFC. Recent advances in thin film technology have also been utilized to develop new materials with improved properties for SOFC. One of the key components in SOFC is the electrolyte and several research groups are working on developing new electrolyte materials. In this chapter, we will discuss the recent advances in thin film SOFC electrolytes. This extensive discussion includes the evolution of doped ceria, doped zirconia, and multilayer hetero-structured thin film electrolytes. The newly developed nanoscale thin films and multi-layer hetero-structures with improved oxygen ionic conductivity will have significant impact on SOFC devices.

Thevuthasan, Suntharampillai↗
DOE OSTI2024

Highly Active Carbon–Platinum-Based Nanozymes: Synthesis, Characterization, and Immunoassay Application

Nanozymes (nanomaterials with intrinsic enzyme-like characteristics) have gained much attention for diagnostics and therapy due to their excellent enzyme-mimicking capability, great stability in environments, and facile and low-cost production. However, developing nanozymes with a high catalytic constant, K cat , has been challenging. Herein, we report a class of nanozyme-mimicking peroxidases, which are formed by depositing ultrasmall platinum nanoparticles (Pt NPs) 1–2 nm in size on the surface of hydrophilic nitrogen-doped carbon nanoparticles (CN NPs). These nanozymes defined as CN-Pt NPs show a high peroxidase-like activity with K cat values of 1.27 M·mL/s·g for 3,3,5,5′-tetramethylbenzidine (TMB) and 1.97 M·mL/s·g for hydrogen peroxide (H 2 O 2 ), respectively, which are at least one or two orders higher than many other reported carbon–noble metal-based nanozymes. Our developed CN-Pt NPs were further utilized in a colorimetric immunoassay as signal amplifiers for the biomarker detection of Burkholderia pseudomallei, a Gram-negative bacterial pathogen classified as a tier 1 select agent by the US CDC. In conclusion, the assay achieved lower limits of detection of 0.11 ng/mL in phosphate-buffered saline (PBS) and 0.16 ng/mL in human serum, when compared to many other assays in detecting the same biomarker.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Controlled Dielectric Breakdown to Form Pinhole Passivating Contacts

This contribution explores an alternate route to forming pinhole-based poly-Si/dielectric/c-Si passivating contacts. The method utilizes controlled dielectric breakdown or electroforming to produce nanoscale pinholes in a thick (non-tunnelling) dielectric which, when annealed, allows dopant atoms to pass from doped poly-Si through the pinholes and into the c-Si wafer, forming conductive pathways. We show that the pinholes lose passivation after electroforming but can be repassivated with a forming gas anneal. N-type contacts show contact resistivities of ~20 mOhm-cm2, but p-type contacts are ~100 mOhm-cm2. Devices show a distinct kink in the J-V curve indicative of a barrier to transport. The method can be expanded to optimized dielectric passivation stacks (not just thin, single layers) and can be formed in parallel over the faces of the wafer in selected areas (pinholes only under the grid lines).

CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SU↗
DOE OSTI2020

Strong crystal field splitting and polarization dependence observed in the emission from Eu3+ ions doped into GaN

Eu-doped GaN is a promising material with a wide array of potential applications in optoelectronics, optogenetics, micro displays and quantum computing. While this system has been the subject of intense investigation for the last two decades, several questions still remain about certain aspects of its optical properties, such as the polarization dependence of the optical transitions, and the coupling between the 4f-electron configuration and bulk phonons, as well and the appearance of local phonon modes. Moreover, the origin of certain emission peaks remains under debate in the literature. In this proceeding, the results of a systematic series of “site-selective” photoluminescence measurements are presented, where the properties of pulsed and continuous-wave laser excitation, such as polarization and intensity, were controlled.

Copelman, S↗
NASA NTRS2018

Physical and Biological Properties of Cobalt- and Copper-Doped Calcium Phosphates as Bone Substitute Materials

Arthritis, osteoporosis, and other bone diseases and defects are common medical issues worldwide. By utilizing ceramic biomaterials as bone substitutes to treat these diseases, bone regeneration can be promoted and toxicity from the substitute material can be limited. Calcium phosphate (CaP) ceramics have become popular as bone substitutes due to their biocompatibility and similarity in composition to natural bone. The purpose of this research was to investigate the physical properties and biological responses of CaP-based bone substitutes, doped with metal ions. Some metal ions are present in natural bone in small amounts, and recent studies show they affect the biological responses of CaPs significantly. Dopants such as magnesium (Mg), strontium (Sr), silicon (Si) and iron (Fe) alter the phase composition, mechanical properties, osteogenesis and angiogenesis properties of CaPs, depending on their concentration and method of addition. In the present study, the effects of cobalt (Co) and copper (Cu) on the physical and biological properties of two main CaP materials, brushite cement (BrC) and tricalcium phosphate (TCP), have been investigated. Different concentrations of dopants in forms of oxide and/or chloride were selected and their effect on phase composition, sintering behavior, density, setting time, compressive strength and in vitro interaction with osteosarcoma and osteoblast cells were studied. Different techniques of sample preparation, challenges during cement preparation and compact sample pressing, sintering, and methods of dopant addition are discussed. The presence of Cu in tricalcium phosphate was found to increase thermal stability of the material and decrease the impact of sintering temperature on porosity. In addition, Cu caused a reduction in expression of inflammatory gene markers by human osteoblast cells and an increased expression at early time points due of osteoinductive markers.The addition of Cu and Co to brushite cement caused an increase in thermal stability of the material, and the addition of Cu caused significant increase in setting time. Small dopant amounts of Co caused decrease in setting time, but higher amounts caused an increase. In addition, Cu dopant in small amounts resulted in an increase of compressive strength. Both Cu and Co led to a decrease in expression of inflammatory gene markers by osteoblast and osteosarcoma cells respectively, and Cu also caused an increase in osteoinductive marker expression. Thus, these results indicate that Cu and Co have a positive impact on the physical, mechanical and biological properties of calcium phosphate biomaterials.

Cummings, Haley V.↗