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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

High Sensitivity of Non–Fullerene Organic Solar Cells Morphology and Performance to a Processing Additive

Although solvent additives are used to optimize device performance in many novel non-fullerene acceptor (NFA) organic solar cells (OSCs), the effect of processing additives on OSC structures and functionalities can be difficult to predict. Here, two polymer-NFA OSCs with highly sensitive device performance and morphology to the most prevalent solvent additive chloronaphthalene (CN) are presented. Devices with 1% CN additive are found to nearly double device efficiencies to 10%. However, additive concentrations even slightly above optimum significantly hinder device performance due to formation of undesirable morphologies. A comprehensive analysis of device nanostructure shows that CN is critical to increasing crystallinity and optimizing phase separation up to the optimal concentration for suppressing charge recombination and maximizing performance. Here, domain purity and crystallinity are highly correlated with photocurrent and fill factors. However, this effect is in competition with uncontrolled crystallization of NFAs that occur at CN concentrations slightly above optimal. This study highlights how slight variations of solvent additives can impart detrimental effects to morphology and device performance of NFA OSCs. Furthermore, successful scale-up processing of NFA-based OSCs will require extreme formulation control, a tuned NFA structure that resists runaway crystallization, or alternative methods such as additive-free fabrication.

14 SOLAR ENERGY↗
DOE OSTI2022

Hydrogen Storage in Partially Exfoliated Magnesium Diboride Multilayers

Metal boride nanostructures have shown significant promise for hydrogen storage applications. However, the synthesis of nanoscale metal boride particles is challenging because of their high surface energy, strong inter- and intraplanar bonding, and difficult-to-control surface termination. Here, it is demonstrated that mechanochemical exfoliation of magnesium diboride in zirconia produces 3-4 nm ultrathin MgB 2 nanosheets (multilayers) in high yield. High-pressure hydrogenation of these multilayers at 70 MPa and 330 °C followed by dehydrogenation at 390 °C reveals a hydrogen capacity of 5.1 wt%, which is ≈50 times larger than the capacity of bulk MgB 2 under the same conditions. This enhancement is attributed to the creation of defective sites by ball-milling and incomplete Mg surface coverage in MgB 2 multilayers, which disrupts the stable boron-boron ring structure. The density functional theory calculations indicate that the balance of Mg on the MgB 2 nanosheet surface changes as the material hydrogenates, as it is energetically favorable to trade a small number of Mg vacancies in Mg(BH 4 ) 2 for greater Mg coverage on the MgB 2 surface. To conclude, the exfoliation and creation of ultrathin layers is a promising new direction for 2D metal boride/borohydride research with the potential to achieve high-capacity reversible hydrogen storage at more moderate pressures and temperatures.

08 HYDROGEN↗
DOE OSTI2023

Reversible Iron Oxyfluoride (FeOF)–Graphene Composites as Sustainable Cathodes for High Energy Density Lithium Batteries

Two large barriers are impeding the wide implementation of electric vehicles, namely driving-range and cost, primarily due to the low specific energy and high cost of mono-valence cathodes used in lithium-ion batteries. Iron is the ideal element for cathode materials considering its abundance, low cost and toxicity. However, the poor reversibility of (de)lithiation and low electronic conductivity prevent iron-based high specific energy multi-valence conversion cathodes from practical applications. In this work, a sustainable FeOF nanocomposite is developed with extraordinary performance. The specific capacity and energy reach 621 mAh g –1 and 1124 Wh kg –1 with more than 100 cycles, which triples the specific capacity, and doubles the specific energy of current mono-valence intercalation LiCoO 2 . This is the result of an effective approach, combing the nanostructured FeOF with graphene, realized by making the (de)lithiation reversible by immobilizing FeOF nanoparticles and the discharge products over the graphene surface and providing the interparticle electric conduction. Importantly, it demonstrates that introducing small amount of graphene can create new materials with desired properties, opening a new avenue for altering the (de)lithiation process. Finally, such extraordinary performance represents a significant breakthrough in developing sustainable conversion materials, eventually overcoming the driving range and cost barriers.

25 ENERGY STORAGE↗
DOE OSTI2023

Long‐Range Electron Transport Rates Depend on Wire Dimensions in Cytochrome Nanowires

Abstract The ability to redirect electron transport to new reactions in living systems opens possibilities to store energy, generate new products, or probe physiological processes. Recent work by Huang et al. showed that 3D crystals of small tetraheme cytochromes (STC) can transport electrons over nanoscopic to mesoscopic distances by an electron hopping mechanism, making them promising materials for nanowires. However, fluctuations at room temperature may distort the nanostructure, hindering efficient electron transport. Classical molecular dynamics simulations of these fluctuations at the nano‐ and mesoscopic scales allowed us to develop a graph network representation to estimate maximum electron flow that can be driven through STC wires. In longer nanowires, transient structural fluctuations at protein‐protein interfaces tended to obstruct efficient electron transfer, but these blockages are ameliorated in thicker crystals where alternative electron transfer pathways become more efficient. The model implies that more flexible proteinprotein interfaces limit the required minimum diameter to carry currents commensurate with conventional electronics.

Chemistry↗
DOE OSTI2024

Tunable Magnetic Coupling in Graphene Nanoribbon Quantum Dots

Abstract Carbon‐based quantum dots (QDs) enable flexible manipulation of electronic behavior at the nanoscale, but controlling their magnetic properties requires atomically precise structural control. While magnetism is observed in organic molecules and graphene nanoribbons (GNRs), GNR precursors enabling bottom‐up fabrication of QDs with various spin ground states have not yet been reported. Here the development of a new GNR precursor that results in magnetic QD structures embedded in semiconducting GNRs is reported. Inserting one such molecule into the GNR backbone and graphitizing it results in a QD region hosting one unpaired electron. QDs composed of two precursor molecules exhibit nonmagnetic, antiferromagnetic, or antiferromagnetic ground states, depending on the structural details that determine the coupling behavior of the spins originating from each molecule. The synthesis of these QDs and the emergence of localized states are demonstrated through high‐resolution atomic force microscopy (HR‐AFM), scanning tunneling microscopy (STM) imaging, and spectroscopy, and the relationship between QD atomic structure and magnetic properties is uncovered. GNR QDs provide a useful platform for controlling the spin‐degree of freedom in carbon‐based nanostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Scalable Graphene Oxide Hollow Fiber Membranes for Dye Desalination Enabled by Multi‐Purpose Polyamine Functionalization

2D nanosheets such as graphene oxide (GO) can be stacked to construct membranes with fine-tuned nanochannels to achieve molecular sieving ability. These membranes are often thin to achieve high water permeance, but their fabrication with consistent nanostructures on a large scale presents an enormous challenge. Herein, GO-based hollow fiber membranes (HFMs) are developed for dye desalination by synergistically combining chemical etching to form in-plane nanopores (10–30 nm) to increase water permeance and polyamine functionalization to improve underwater stability and enable facile large-scale production using existing membrane manufacturing processes. HFM modules with areas of 88 cm 2 and GO layer thicknesses of ≈500 nm are fabricated, and they exhibited a stable dye water permeance of 75 L m −2 h −1 bar −1 , rejection of >99.5% for Direct red and Congo red, and Na 2 SO 4 /dye separation factor of 300–500, superior to state-of-the-art commercial membranes. Furthermore, the versatility of this approach is also demonstrated using different short polyamines and porous substrates. This study reveals a scalable way of designing 2D materials into high-performance robust membranes for practical applications.

amine functionalization↗
DOE OSTI2025

Pt Nanoparticle Disintegration at Oxide Interfaces Enhances CO Oxidation Catalysis

Understanding how supported metal nanoparticles dynamically evolve under reaction conditions is critical for controlling their catalytic function. Here, the mechanism behind the dynamic disintegration of Pt nanoparticles (NPs) supported on CeOx-TiO2 (CT) during CO oxidation is elucidated, leading to the formation of single atoms (SAs) and/or sub-nanometer clusters. Density functional theory (DFT) calculations reveal that strong Pt-CO interactions weaken Pt─Pt cohesion, while electronic coupling between Pt and Ce ions stabilizes Pt-CO* intermediates at the oxide interface. Surface oxygen vacancies kinetically trap Pt-CO*, but the vacancies are replenished under oxygen-rich conditions, enabling Pt-CO* surface diffusion and subsequent structural reorganization. In situ spectroscopic analyses confirm the oxygen-driven transformation of Pt NPs, correlating with a threefold increase in mass-specific activity at 150 °C. These findings demonstrate that interfacial oxygen dynamics and metal-support interactions can be leveraged to induce nanoparticle disintegration and optimize catalytic performance, highlighting the catalytic potential of interface-engineered Pt nanostructures.

CO oxidation↗
DOE OSTI2025

Mechanistic Transformation of CuI Nanoparticles Into Oxidation‐Resistant 2D Copper Nanoplates

Unconventional phase transformations reveal new crystallization mechanisms, yet direct observation of such pathways during nanoscale solution-phase synthesis remains challenging. This study uncovers an atypical growth process in which thermodynamically stable CuI nanoparticles (NPs) transform into high-energy 2D Cu plates. Using a combination of in situ transmission electron microscopy, ex situ structural analysis, and density functional theory calculations shows that the formation of structural defects induced by hexadecylamine and chloride ions facilitates the transformation by promoting surface iodine vacancies. The resulting Cu{111} nanoplates, with ultrathin thicknesses (≈4 nm) and exceptionally high aspect ratios (≈450), display enhanced oxidation resistance and long-term stability under ambient conditions. This resistance is attributed to the close-packed {111} facets, which suppress chemical oxidation even after extended exposure to air over 100 days. These findings provide new insights into non-classical crystallization pathways in metal nanomaterials and suggest a versatile approach for preparing oxidation-resistant, structurally defined Cu nanostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Electrochemical Intercalation and Exfoliation of CrSBr into Ferromagnetic Fibers and Nanoribbons

Abstract Recent studies dedicated to layered van der Waals crystals have attracted significant attention to magnetic atomically thin crystals offering unprecedented opportunities for applications in innovative magnetoelectric, magneto‐optic, and spintronic devices. The active search for original platforms for the low‐dimensional magnetism study has emphasized the entirely new magnetic properties of two dimensional (2D) semiconductor CrSBr. Herein, for the first time, the electrochemical exfoliation of bulk CrSBr in a non‐aqueous environment is demonstrated. Notably, crystal cleavage governed by the structural anisotropy occurred along two directions forming atomically thin and few‐layered nanoribbons. The exfoliated material possesses an orthorhombic crystalline structure and strong optical anisotropy, showing the polarization dependencies of Raman signals. The antiferromagnetism exhibited by multilayered CrSBr gives precedence to ferromagnetic ordering in the revealed CrSBr nanostructures. Furthermore, the potential application of CrSBr nanoribbons is pioneered for electrochemical photodetector fabrication and demonstrates its responsivity up to 30 µA cm −2 in the visible spectrum. Moreover, the CrSBr‐based anode for lithium‐ion batteries exhibited high performance and self‐improving abilities. This anticipates that the results will pave the way toward the future study of CrSBr and practical applications in magneto‐ and optoelectronics.

Chemistry↗
DOE OSTI2025

Epitaxy of Emerging Materials and Advanced Heterostructures for Microelectronics and Quantum Sciences

Abstract Epitaxy, a process to prepare crystalline materials in nanostructures and thin films, is the core technology for preparing high‐quality materials as a key enabler of next‐generation microelectronics and quantum information system. Progress in epitaxy has been expanding the choice of materials and their heterostructures beyond the combinations limited by materials compatibility. However, the improvement of material quality, physical implementation of materials with unique properties, and integration of incommensurate materials in an architecture have been the challenging issues. Emerging materials, including 2D materials and quantum materials, have opened opportunities to study epitaxy mechanisms and realize various functional devices. Acceleration of discovery and progress in epitaxy research should be accomplished by “understanding of epitaxy under various circumstances at multiple length scales” and “integration of experiments and models.” In the perspective, a basic summary of the status of epitaxially grown materials, the challenges in epitaxy research, and integration of modeling epitaxy and ultimate control of the epitaxy process with advanced characterization techniques are discussed.

Materials Science↗
DOE OSTI2025

Correlated X‐Ray and Electron Microscopies of a Single Biphasic GaAs Nanowire

Engineering the properties of semiconductors by changing their crystalline phase is a technologically and economically relevant alternative to doping using foreign elements, with strong potential for photonic and electronic applications. Although major advances have been reported recently for crystal‐phase engineering of III‐V and group IV semiconductor nanowires, interfacing two mismatched crystalline phases in a nanostructure induces several deformation mechanisms, which remain largely unexplored. Here, using state‐of‐the‐art synchrotron X‐ray nanobeam diffraction and transmission electron microscopy, subtle twisting and bending is unveiled within an individual GaAs nanowire containing cubic and hexagonal segments. Their role is discussed in accommodating the inter‐reticular spacing fluctuations, and their variations are correlated to the nanoscale phase distribution and to the effect of the NW support. This study brings direct evidence of a complex combination of deformation mechanisms in biphasic nanowires, which opens a new path to tune the nanowire properties with appealing perspectives for device engineering in nanophotonics and nanomechanics.

III-V semiconductors↗
DOE OSTI2020

High‐Efficiency Organic Solar Cells with Wide Toleration of Active Layer Thickness

Industrial printing production of organic solar cells (OSCs) requires high power conversion efficiency (PCE) with wide toleration of active layer thickness. Herein, high‐efficiency thick‐film OSCs are demonstrated using a polymer fibril network strategy (FNS), which involves a donor polymer (PT2) that can self‐assemble into fibril nanostructure, and two nonfullerene acceptors with different crystalline properties. The fibril network can form a high‐speed hole transport channel and the addition of IDIC as a third component in active layers can improve the electron transport. As a result, the OSCs show high PCEs of ≈12% with wide toleration of active layer thickness (from 100 to 500 nm). The results indicate that FNS is a promising approach for the fabrication of highly efficient thick‐film PSCs, which can facilitate the commercialization of OSCs.

Weng, Kangkang↗
DOE OSTI2020

Revealing the Atomic Structures of Exposed Lateral Surfaces for Polymorphic Manganese Dioxide Nanowires

Polymorphic 1D MnO 2 nanostructures are widely applied in fields such as catalysis, sensing, and energy storage with the functionality mainly determined by the atomic patterns of their laterally exposed facets, which largely remain unclear so far. Herein, by high‐resolution transmission electron microscopy (HRTEM) imaging directly along their axial directions, the atomic structures of the outmost lateral facets of polymorphic MnO 2 nanowires are disclosed. To generalize the findings, four most commonly seen phases with characteristic tunnel structures are targeted, i.e., β‐, γ‐, α‐, and todorokite(t)‐MnO 2 , which are synthesized conventionally using a hydrothermal method reported in the literature. Axially imaging these MnO 2 nanowires via HRTEM, the {hkl} facets covering the lateral surfaces are accurately indexed, the atomic pattern of each {hkl} facet is revealed, and it is further coupled with the outmost tunnel configuration that can significantly affect the physicochemical property of MnO 2 materials via tunnel‐driven mass adsorption/transport. This work provides a reliable reference for atomic modeling of MnO 2 to benefit the pursuit of its structure–property relationship; in addition, it can benefit surface engineering strategies to better rationalize the facet growth control with optimized functionality.

Yuan, Yifei↗
DOE OSTI2021

Thermodynamic stabilization of nanocrystalline aluminum

Nanocrystalline metals are generally unstable due to a large volume fraction of high-energy grain boundaries associated with a small grain size. Preferential dopant segregation to the high-energy grain boundaries is observed to enhance the stability of the material’s microstructure by minimizing its energy. Nanocrystalline aluminum-dopant systems were evaluated for thermodynamic stability against grain growth and phase precipitation via the mechanism of grain boundary segregation according to a modified regular nanocrystalline solution model. Fifty-one potential dopant elements have been evaluated for their efficacy in stabilizing nanostructures with three potential candidates, magnesium, lanthanum, and silicon, identified possessing the characteristics to promote grain boundary segregation and a state of thermodynamic stability in aluminum’s nanocrystalline regime. Here, the minimum dopant content required to achieve nanocrystalline microstructure stability is identified for each of the three candidate elements. Beyond this minimum content, further addition of the dopant elements decreased the final microstructure’s stability with no effects on the existence of a stable nanocrystalline state.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Barriers to carriers: faults and recombination in non-stoichiometric perovskite scintillators

Abstract Tuning the efficiency and speed of charge carrier recombination in inorganic scintillators can potentially improve their performance in diverse applications. Recent work suggests that this maybe be achieved via a two-phase scintillator AB that naturally phase separates into A -rich and B -rich domains. In addition, a favorable electronic structure and band-edge alignment such that the charge carriers are confined or are thermodynamically driven to preferentially accumulate in one of the two domains, might lead to an improved radiative recombination rate. Here, we use density functional theory computations and ab initio molecular dynamics (AIMD), including non-adiabatic molecular dynamics (NAMD) simulations, to examine an alternative phase structure and its potential impact on recombination. Using a model perovskite SrTiO $$_3$$ 3 system with one-, two- and three-dimensional Ruddlesden–Popper (RP) phases, we demonstrate that RP faults induce band structure changes in the material that can act as barriers to carrier transport. Our AIMD/NAMD simulations indicate competing effects of a lower mean free path (potentially enhancing the desired radiative recombination and overall scintillating efficiency) and faster non-radiative recombination (undesired) due to enhanced electron–phonon coupling in the faulted system. Full exploitation of such a rational design approach would require tuning of the effective scintillation efficiency by varying the perovskite chemistry using appropriate arrangements of RP faults in the bulk material. Finally, other effects, such as the tendency of point defects to segregate at the interface, that might affect the overall performance, are briefly discussed. We expect the basic results found here to apply to other nanostructured scintillators. Graphical Abstract

36 MATERIALS SCIENCE↗
DOE OSTI2022

Approaching air buoyancy in aero/cryogel vacuum vessels

Air impermeability has been observed in low-density aerogel and cryogel materials, which has led to a series of experiments to investigate the feasibility of an air buoyant vacuum vessel, as well as the fabrication and testing of sub-buoyant prototypes. Here, bulk samples of silica aerogel were shown to isolate vacuum from ambient air for several hours with optimal vacuum isolation occurring at a density of approximately 85 mg cm –3 . It was demonstrated using polyimide aerogel and cryogel materials that the ability of these foam materials to provide an air impermeable layer between vacuum and atmosphere, in spite of being comprised of mostly void space, is related to material stiffness. It is hypothesized that this behavior is due to local deformation of the random nanostructure of the material. Spherical shell vacuum vessels were produced using the polyimide cryogel, and less than 133 Pa vacuum containment was demonstrated under active pumping. In order to approach the non-buoyant to buoyant transition for these vacuum vessels, a polyimide composite was produced using helical fibers for which preliminary mechanical testing was performed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Investigation of Molecular Diffusion at Block Copolymer Thin Films Using Maximum Entropy Method-Based Fluorescence Correlation Spectroscopy and Single Molecule Tracking

Fluorescence correlation spectroscopy (FCS) has been widely used to investigate molecular diffusion behavior in various samples. The use of the maximum entropy method (MEM) for FCS data analysis provides a unique means to determine multiple distinct diffusion coefficients without a priori assumption of their number. Comparison of the MEM-based FCS method (MEM-FCS) with another method will reveal its utility and advantage as an analytical tool to investigate diffusion dynamics. Herein, we measured diffusion of fluorescent probes doped into nanostructured thin films using MEM-FCS, and validated the results with single molecule tracking (SMT) data. The efficacy of the MEM code employed was first demonstrated by analyzing simulated FCS data for systems incorporating one and two diffusion modes with broadly distributed diffusion coefficients. The MEM analysis accurately afforded the number of distinct diffusion modes and their mean diffusion coefficients. These results contrasted with those obtained by fitting the simulated data to conventional two-component and anomalous diffusion models, which yielded inaccurate estimates of the diffusion coefficients. Subsequently, the MEM analysis was applied to FCS data acquired from hydrophilic dye molecules incorporated into microphase-separated polystyrene-block-poly(ethylene oxide) (PS-b-PEO) thin films characterized under a water-saturated nitrogen atmosphere. The MEM analysis revealed distinct fast and slow diffusion components attributable to molecules diffusing on the film surface and inside the film, respectively. SMT studies of the same materials yielded trajectories for mobile molecules that appear to follow the curved PEO microdomains. Diffusion coefficients obtained from the SMT data were consistent with those obtained for the slow diffusion component detected by MEM-FCS. Furthermore, these results highlight the utility of MEM-FCS and SMT for gaining complementary information on molecular diffusion processes in heterogeneous material systems.

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

Temperature Dependent Early-Stage Oxidation Dynamics of Cu(100) Film with Faceted Holes

Fundamental understanding of surface oxidation dynamics is critical for rational corrosion protection and advanced manufacturing of nanostructured oxides. In situ environmental TEM (ETEM) provides high spatial (nano- to atomic- scale) and temporal (< 0.1 s) resolution to investigate the early-stage oxidation/corrosion dynamics of metals and alloys. Thin samples with facets are widely used to enable cross-sectional observation of the oxidation dynamics in ETEM. However, how different facet orientations oxidize under the same conditions, and how these facets change the oxidation process, has not been investigated before. Here, using in situ ETEM, we systematically compare the oxidation dynamics of Cu(001) thin films, with faceted holes exposing {100} and {110} facets at temperatures ranging from 250–600 °C under 0.03 Pa O 2 . Oxidation preference is observed to change, from Cu(110) facets at lower temperatures to Cu(100) facets at ~ 500 °C. Oxide growth mechanisms change from outward growth on Cu 2 O surfaces at low temperatures, to inward growth on Cu-Cu 2 O interfaces at high temperatures. At high temperatures (500–600 °C), a rod-like Cu 2 O morphology is observed, with side facets of ~ {024} and top facets of {100} on Cu(100). This differs from the square-shaped Cu 2 O exposing {110} facets formed on Cu(001) surfaces. Rod-like oxides exhibit directional growth along their lengths with linear growth rates, regardless of rod length and width. This suggests that O from Cu(001) surfaces, rather than Cu(100) facets, serves as an O source for oxide growth. These results show a direct comparison of oxidation at different orientations with temperature, underscoring the temperature dependence of oxidation preference. Our results also suggest future in situ ETEM experiments viewing oxidation corrosion cross-sectionally should be cautious when oxide size is comparable with sample thickness, as the oxidizing mechanism may change due to sample thickness.

36 MATERIALS SCIENCE↗