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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal–Sulfur and Selenium Batteries

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal–sulfur batteries remain challenged by several factors, including polysulfides’ (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li–S and the emerging Na–S and K–S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li–S are relatively mature, less progress has been made with Na–S and K–S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal–selenium and the metal–selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal–sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li–S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure–battery electrochemical performance interrelations. Finally, throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.

25 ENERGY STORAGE↗
DOE OSTI2026

Ionic-Based Electrochemical Gas Sensors for Low-Cost, High-Sensitivity SO2 Detection

Sulfur dioxide (SO2) is a toxic gas associated with adverse health and environmental effects that necessitate reliable monitoring techniques. Here, we report the development of an all-solid-state electrochemical sensor utilizing a lithium borate (Li3BO3) solid electrolyte capable of subppm of SO2 detection. While subppm of SO2 sensing has been previously demonstrated in other solid-state electrolyte systems─such as stabilized zirconia, natrium super ionic conductors (NASICON) under mixed-potential conditions─here we establish Li3BO3 as an alternative solid electrolyte enabling equilibrium potentiometric sensing in an all-solid architecture. This sensor demonstrates a detection limit of at least 0.25 ppm, surpassing the human-olfactory threshold and meeting the rigorous requirements for industrial and personal monitoring applications. The sensing mechanism relies on the formation of Li2SO4 on the electrode surface, as evidenced by multimodal characterization techniques, including Raman spectroscopy, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM). The strong linear correlation between the open-circuit potential (OCV) and the logarithm of SO2 concentration between 0.25 and 2 ppm indicates that the response is Nernstian in nature.

Lagunas, Francisco (ORCID:000000026377683X)↗
DOE OSTI2023

Two-Dimensional Siloxene Nanosheets: Impact of Morphology and Purity on Electrochemistry

Two-dimensional (2D) siloxene (Si 6 O 3 H 6 ) has shown promise as a negative electrode material for Li-ion batteries due to its high gravimetric capacity and superior mechanical properties under (de)lithiation compared to bulk Si. Here, in this work, we prepare purified siloxene nanosheets through the removal of bulk Si contaminants, use ultrasonication to control the lateral size and thickness of the nanosheets, and probe the effects of the resulting morphology and purity on the electrochemistry. The thin siloxene nanosheets formed after 4 h of ultrasonication deliver an average capacity of 810 mA h/g under a 1000 mA/g rate over 200 cycles with a capacity retention of 76%. Interestingly, the purified siloxene shows lower initial capacity but superior capacity retention over extended cycling. The 2D morphology benefit is illustrated where the parent siloxene nanosheet morphology and structure were largely maintained based on operando optoelectrochemistry, in situ Raman, ex situ scanning electron microscopy, and ex situ transmission electron microscopy. Furthermore, the purified siloxene-based electrode free from crystalline Si impurity experiences the least expansion upon (de)lithiation as visualized by cross-section electron microscopy of samples recovered post-cycling.

25 ENERGY STORAGE↗
DOE OSTI2022

Variable-Temperature Scattering and Spectroscopy Characterizations for Temperature-Dependent Solution Assembly of PffBT4T-Based Conjugated Polymers

The solution structure of conjugated polymers (CPs) from which the films are cast is critical for tailoring the thin-film morphology thus device performance. Here, we used multimodal variable-temperature scattering and spectroscopy tools to fully quantify the solution assembly of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3'''-dialkyl-2,2';5',2'';5'',2'''-quaterthiophen-5,5'''-diyl)] (PffBT4T) polymers with varying side-chain lengths at different assembly temperatures. The conformational and aggregation behaviors for PffBT4T-based CPs were found to be very sensitive to both temperature and side chain length using ultraviolet–visible (UV–vis) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). We found that with slightly increasing side chain length from 2-octyldodecyl (C8C12) to 2-nonyltridecyl (C9C13), PffBT4T-based CPs show a significant decrease in aggregation-to-dissolved chain transition temperature (10 °C), degree of aggregation, enthalpy change of aggregation, and size of the aggregates in solution. At room temperature, PffBT4T polymer strongly aggregated to form fabric structure with the film thickness of a few nanometers in thickness and hundreds of nanometers in length, as probed by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and dynamic light scattering (DLS). At the elevated temperature above the aggregation-to-dissolved chain transition temperature, PffBT4T is fully dissolved and adopts a semiflexible coil conformation with the persistence length of 3.1 nm for PffBT4T-C8C12 and a slightly increased persistence length of 3.4 nm for PffBT4T-C9C13, according to temperature-dependent SANS measurements. Longer side chains of PffBT4T-C9C13 also lead to less aggregation enthalpy gain compared with PffBT4T-C8C12. This work provides a solution structure manipulating strategy of CPs and thus will inspire the molecular design and processing protocols of CPs toward higher performance electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers

The advancement in thin-film exfoliation for synthesizing oxide membranes has led to possibilities for creating artificially assembled heterostructures with structurally and chemically incompatible materials. The sacrificial layer method is a promising approach to exfoliate as-grown films from a compatible material system, allowing for their integration with dissimilar materials. Nonetheless, the conventional sacrificial layers often possess an intricate stoichiometry, thereby constraining their practicality and adaptability, particularly when considering techniques such as molecular beam epitaxy (MBE). This is where easy-to-grow binary alkaline-earth-metal oxides with a rock salt crystal structure are useful. These oxides, which include (Mg, Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range of lattice parameters compared to conventional sacrificial layers and are easily dissolvable in deionized water. In this study, we show the epitaxial growth of the single-crystalline perovskite SrTiO 3 (STO) on sacrificial layers consisting of crystalline SrO, BaO, and Ba 1–x Ca x O films, employing a hybrid MBE method. Our results highlight the rapid (≤5 min) dissolution of the sacrificial layer when immersed in deionized water, facilitating the fabrication of millimeter-sized STO membranes. Using high-resolution X-ray diffraction, atomic-force microscopy, scanning transmission electron microscopy, impedance spectroscopy, and scattering-type near-field optical microscopy (SNOM), we demonstrate single-crystalline STO membranes with bulk-like intrinsic dielectric properties. The employment of alkaline earth metal oxides as sacrificial layers is likely to simplify membrane synthesis, particularly with MBE, thus expanding the research and application possibilities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Expanding the Zinc Precursor Toolbox: A Comparative Study of Precursors for Thermal ALD of ZnO Thin Films

Atomic layer deposition (ALD) of zinc oxide (ZnO) has been widely researched using diethyl zinc (DEZ)-based methods. The significant importance of thin films of ZnO as transparent conductive oxides (TCO) in optoelectronic devices and photovoltaics warrants examining alternative Zn precursors for ZnO ALD as potential replacements for the pyrophoric DEZ. In this study, we investigated three alternative Zn precursors: Zn(EEKI)2, Zn(DMP)2, ZnEt(HMDS), in the process development for high-quality ZnO thin films and compared them to DEZ. The ALD processes were studied using in situ spectroscopic ellipsometry. The properties of the ALD ZnO films were characterized using ex situ X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry and nuclear reaction analysis (RBS/NRA), X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), and ultraviolet-visible (UV/Vis) spectrophotometry. These measurements confirmed the formation of pure, stoichiometric, and polycrystalline ZnO films using all four Zn precursors. Although the selected precursors are chemically diverse Zn compounds, they all yielded saturating ALD processes and high-quality ZnO thin films at 200 °C. This study highlights the potential benefits of alternative zinc precursors in designing ALD processes for ZnO thin films.

Obenlüneschloß, Jorit↗
DOE OSTI2022

Effect of thermal oxidation on helium implanted 316L stainless steel

The effect of thermal oxide layer on He implanted 316L stainless steel was studied to evaluate experimentally how thermal oxidation affects the diffusion and distribution of He in the material. In the case of thermal oxidation of a He implanted sample, with an increase in oxidation time, the max swelling height increases logarithmically as a function of time and finally saturates for all samples except for the lowest dose of implanted He. Concerning TEM results, two void regions are identified. Similar to the calculation, the total irradiated depth was around 250 nm and the large void region was formed around 100–150 nm depth. On the other hand, the small void region was observed immediately under oxide layer from the thermal oxidation. In contrast, there were no voids in the altered zone near the metal/oxide interface in the non-thermal oxidized/He implanted sample. This description of the phenomena was justified using the Kirkendall effect and the Point Defect Model.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Excitonic and deep-level emission from N- and Al-polar homoepitaxial AlN grown by molecular beam epitaxy

Using low-temperature cathodoluminescence spectroscopy, we study the properties of N- and Al-polar AlN layers grown by molecular beam epitaxy on bulk AlN{0001}. Compared with the bulk AlN substrate, layers of both polarities feature a suppression of deep-level luminescence, a total absence of the prevalent donor with an exciton binding energy of 28 meV, and a much increased intensity of the emission from free excitons. The dominant donor in these layers is characterized by an associated exciton binding energy of 13 meV. The observation of excited exciton states up to the exciton continuum allows us to directly extract the Γ 5 free exciton binding energy of 57 meV.

42 ENGINEERING↗
DOE OSTI2020

Structure of the (110) Ln ScO 3 ( Ln =Gd,Tb,Dy) surfaces

The surface reconstruction on the (110) surface of LnScO 3 (Ln=Gd,Tb,Dy) has been investigated using x-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron diffraction coupled with higher-level density-functional theory methods. The experimental techniques generate constraints on the surface chemistry and structure that are used to inform the theoretical comparison of a number of potential surface structures. The resulting structure is then compared to experimental aberration-corrected transmission electron microscopy results using multislice simulation. The surfaces of both single-crystalline substrates and hydrosauna synthesized nanoparticles exhibit a Sc-rich double layer with a Sc 3 O 4 termination.

36 MATERIALS SCIENCE↗
DOE OSTI2026

GeSn alloys with ∼21% Sn grown by effusion cell molecular beam epitaxy

We report the epitaxial growth of high quality GeSn alloys with Sn compositions up to 21.25 ± 1% by effusion-cell molecular beam epitaxy (MBE). Achieving such a high Sn content with effusion cells is particularly significant, since these sources typically impose stronger radiative heating on the substrate, which is a factor long considered a major obstacle to high-Sn GeSn epitaxy. Contrary to the prevailing assumption that high growth rates are good for suppressing Sn segregation, we demonstrate that carefully controlled low fluxes, combined with stable ultra-low substrate temperatures, enable significant Sn incorporation even under effusion-cell conditions. Structural analyses by high-resolution x-ray diffraction, reciprocal space mapping, atomic force microscopy, and transmission electron microscopy confirm sharp interfaces, high crystallinity, and smooth surfaces at high Sn contents. Furthermore, these findings establish the feasibility of MBE-grown high-Sn GeSn even under diffusion cells, thereby broadening opportunities for Si-compatible photonic and quantum devices.

Alloys↗
DOE OSTI2022

Manufacturing of Complex Silicon–Carbon Structures: Exploring Si x C y Materials

This paper reports on the manufacturing of complex three-dimensional Si/C structures via a chemical vapor deposition method. The structure and properties of the grown materials were characterized using various techniques including scanning electron microscopy, aberration-corrected transmission electron microscopy, confocal Raman spectroscopy, and X-ray photoelectron spectroscopy. The spectroscopy results revealed that the grown materials were composed of micro/nanostructures with various compositions and dimensions. These included two-dimensional silicon carbide (SiC), cubic silicon, and various SiC polytypes. The coexistence of these phases at the nano-level and their interfaces can benefit several Si/C-based applications ranging from ceramics and structural applications to power electronics, aerospace, and high-temperature applications. With an average density of 7 mg/cm 3 , the grown materials can be considered ultralightweight, as they are three orders of magnitude lighter than bulk Si/C materials. This study aims to impact how ceramic materials are manufactured, which may lead to the design of new carbide materials or Si/C-based lightweight structures with additional functionalities and desired properties.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Field Emission Properties of Cu-Filled Vertically Aligned Carbon Nanotubes Grown Directly on Thin Cu Foils

Copper-filled vertically aligned carbon nanotubes (Cu@VACNTs) were grown directly on Cu foil substrates of 0.1 mm thicknesses at different temperatures via plasma-enhanced chemical vapor deposition (PECVD). By circumventing the need for additional catalyst layers or intensive substrate treatments, our in-situ technique offers a simplified and potentially scalable route for fabricating Cu@VACNTs with enhanced electrical and thermal properties on thin Cu foils. Comprehensive analysis using field emission scanning microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) mappings, and X-ray diffraction (XRD) revealed uniform Cu filling within the VACNTs across a range of synthesis temperatures (650 °C, 700 °C, and 760 °C). Field emission (FE) measurements of the sample synthesized at 700 °C (S700) showed low turn-on and threshold fields of 2.33 V/μm and 3.29 V/μm, respectively. The findings demonstrate the viability of thin Cu substrates in creating dense and highly conductive Cu-filled VACNT arrays for advanced electronic and nanoelectronics applications.

36 MATERIALS SCIENCE↗
NASA NTRS1997

Microstructure Characterization and Stress Corrosion Evaluation of Autogenous and Hybrid Friction Stir Welded Al-Cu-Li 2195 Alloy

Friction stir welding process is being evaluated for application on the Al-Cu-Li 2195 Super-Light Weight External Tank of the Space Transportation System. In the present investigation Al-Cu-Li 2195 plates were joined by autogenous friction stir welding (FSW) and hybrid FSW (friction stir welding over existing variable polarity plasma arc weld). Optical microscopy and transmission electron microscopy (TEM) were utilized to characterize microstructures of the weldments processed by both welding methods. TEM observations of autogenous FSW coupons in the center section of the dynamically-recrystallized zone showed an equiaxed recrystallized microstructure with an average grain size of approx. 3.8 microns. No T(sub 1), precipitates were present in the above-mentioned zone. Instead, T(sub B) and alpha precipitates were found in this zone with a lower population. Alternate immersion, anodic polarization, constant load, and slow strain tests were carried out to evaluate the general corrosion and stress-corrosion properties of autogenous and hybrid FSW prepared coupons. The experimental results will be discussed.

Li, Zhixian↗
NASA NTRS2001

The Role of Cyanobacteria in Stromatolite Morphogenesis, Highborn Cay Bahamas: An Integrated Field and Laboratory Simulation Study

Geomicrobiological phenomena are among the most fundamental of interactions between Earth and its biosphere. Actively growing and lithifying stromatolites at Highborne Cay Bahamas, have recently been documented and allow for detailed examination of the roles microbes play in the mineralization process. These stromatolites contain a variety of complex microbial communities with distinct distribution patterns for different microbial groups. Cyanobacteria are the primary producers in this system providing energy, directly or indirectly, for the entire stromatolite microbial community. They also play key roles in the trapping and binding of sediments. Most of these species are highly motile and can adjust their position and orientation within the sediment matrix in order to optimize their access to irradiance and nutrients. As individual species have different physical and metabolic properties, this motility generally results in segregated distributions of species, which in turn contributes to the laminated textures observed in these actively forming stromatolites. Increasingly our studies suggest that the activities and locations of various cyanobacterial species also contribute greatly to the localization of new mineral precipitation through a variety of processes. We are investigating these contributions using an integrated approach combining detailed observations of field samples with manipulative experiments using both field samples and cultures of specific organisms isolated from these stromatolites. Experiments are conducted both in standard laboratory conditions and in outdoor running seawater flumes. A variety of standard techniques; SEM (scanning electron microscopy), petrographic analyses, TEM (transmission electron microscopy), are used to compare mineralization processes in field samples with those generated in laboratory-flume simulations. Using this approach we are able to more thoroughly investigate the effects of irradiance, CaCO3 saturation, and hydrodynamic regime on cyanobacterial distribution, trapping and binding and mineral precipitation. Simulation results will be presented and compared with community and mineralization distribution patterns seen in the field samples from which these communities were isolated.

Prufert-Bebout, Leslie↗
NASA NTRS2004

The Influence of Tungsten on the Chemical Composition of a Temporally Evolving Nanostructure of a Model Ni-Al-Cr Superalloy

The influence of W on the temporal evolution of gamma' precipitation toward equilibrium in a model Ni-Al-Cr alloy is investigated by three-dimensional atom-probe (3DAP) microscopy and transmission electron microscopy (TEM). We report on the alloys Ni-10 Al-8.5 Cr (at.%) and Ni-10 Al-8.5 Cr-2 W (at.%), which were aged isothermally in the gamma + gamma' two-phase field at 1073 K, for times ranging from 0.25 to 264 h. Spheroidal-shaped gamma' precipitates, 5-15 nm diameter, form during quenching from above the solvus temperature in both alloys at a high number density (approx. 10(exp 23/cu m). As gamma' precipitates grow with aging at 1073 K, a transition from spheriodal- to cuboidal-shaped precipitates is observed in both alloys. The elemental partitioning and spatially resolved concentration profiles across the gamma' precipitates are obtained as a function of aging time from three-dimensional atom-by-atom reconstructions. Proximity histogram concentration profiles of the quaternary alloy demonstrate that W concentration gradients exist in gamma' precipitates in the as-quenched and 0.25-h aging states, which disappear after 1 h of aging. The diffusion coefficient of W in gamma' is estimated to be 6.2 x 10(exp -20) sq m/s at 1073 K. The W addition decreases the coarsening rate constant, and leads to stronger partitioning of Al to gamma' and Cr to gamma.

Sudbrack, Chantal K.↗
NASA NTRS2003

Study of Dislocation-Ordered In(x)Ga(1-x)As/GaAs Quantum Dots

A report describes an experimental study of dislocation-induced spatial ordering of quantum dots (QDs) comprising nanometer-sized In(x)Ga(1-x)As islands surrounded by GaAs. Metastable heteroepitaxial structures were grown by molecular-beam epitaxy of In(x)Ga(1-x)As onto n+ GaAs and semi-insulating GaAs substrates. Then the structures were relaxed during a post-growth annealing/self-organizing process leading to the formation of surface undulations that acted as preferential sites for the nucleation of QDs. Structural effects of annealing times and temperatures on the strain-relaxed In(x)Ga(1-x)As/GaAs and the subsequent spatial ordering of the QDs were analyzed by atomic-force microscopy and transmission electron microscopy. Continuous-wave spectral and time-resolved photoluminescence (PL) measurements were performed to study the effects, upon optical properties, of increased QD positional ordering, increased QD uniformity, and proximity of QDs to arrays of dislocations. PL spectral peaks of ordered QD structures formed on strain-relaxed In(x)Ga(1-x)As/GaAs layers were found to be narrower than those of structures not so formed and ordered. Rise and decay times of time-resolved PL were found to be lower at lower temperatures -- apparently as a consequence of decreased carrier-transport times within the barriers surrounding the QDs.

Leon, Rose↗