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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Induced Chirality in QDs Using Thermoresponsive Elastin-like Polypeptides

Circular dichroism (CD) spectroscopy has emerged as a potent tool for probing chiral small-molecule ligand exchange on natively achiral quantum dots (QDs). In this study, we report a novel approach to identifying QD–biomolecule interactions by inducing chirality in CdS QDs using thermoresponsive elastin-like polypeptides (ELPs) engineered with C-terminal cysteine residues. Our method is based on a versatile two-step ligand exchange process starting from monodisperse oleate-capped QDs in nonpolar media and proceeding through an easily accessed achiral glycine-capped QD intermediate. Successful conjugation of the ELPs onto the QDs is confirmed by the diagnostic CD response corresponding to the QD electronic transitions in the visible range. The resulting ELP:CdS conjugates demonstrate thermally reversible coacervation, as observed through dynamic light scattering, small-angle X-ray scattering, and electron microscopy. Furthermore, this research provides a foundation for using induced chirality in QD electronic transitions to probe QD conjugation to complex peptides and proteins, opening pathways for designing dynamic, stimuli-responsive hybrid nanomaterials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ultrasensitive Sub-monolayer Palladium Induced Chirality Switching and Topological Evolution of Skyrmions

Chiral spin textures are fundamentally interesting, with promise for device applications. Stabilizing chirality is conventionally achieved by introducing Dzyaloshinskii-Moriya interaction (DMI) in asymmetric multilayers, where the thickness of each layer is at least a few monolayers. Here we report an ultrasensitive chirality switching in (Ni/Co) n multilayer induced by capping with only 0.22 monolayer of Pd. Using spin-polarized low-energy electron microscopy, we monitor the gradual evolution of domain walls from left-handed to right-handed Néel walls and quantify the DMI induced by the Pd capping layer. We also observe the chiral evolution of a skyrmion during the DMI switching, where no significant topological protection is found as the skyrmion winding number varies. This corresponds to a minimum energy cost of <1 attojoule during the skyrmion chirality switching. Here, our results demonstrate the detailed chirality evolution within skyrmions during the DMI sign switching, which is relevant to practical applications of skyrmionic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Modulating Hole Transfer from CdSe Quantum Dots by Manipulating the Surface Ligand Density

The structure and density of surface capping ligands in cadmium chalcogenide quantum dots (QDs) are important considerations for controlling the efficiency of charge separation via the transfer of electrons or holes to molecular acceptors. Here we show how the manipulation of the surface ligand density of oleic acid-capped cadmium selenide (CdSe) QDs impacts the efficiency of hole transfer (HT) to polyoxovanadate alkoxides. Meerwein’s salt is used as a ligand-stripping agent, providing opportunities to quantitatively manipulate the ligand density at the surface of the nanocrystal, as evidenced by 1 H NMR spectroscopy. Time-resolved photoluminescence and transient absorption spectroscopies reveal that the extent of HT is quantitatively related to increased surface accessibility. Collectively, these results show that the reduction of surface ligand density can be used to tune the extent of interactions of molecular acceptors with QDs, providing a route to control charge-transfer processes relevant to improving the efficiency of QDs as photosensitizers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Magnetic La 0.7 Sr 0.3 MnO 3 Membranes Synthesized by Etching a Sr 3 Al 2 O 6 Sacrificial Layer Using an Intermediary Manganite Protection Layer

The integration of perovskite oxides onto flexible substrates has witnessed significant advancements owing to the development of an epitaxial lift-off technique utilizing a Sr 3 Al 2 O 6 sacrificial layer. However, Sr 3 Al 2 O 6 is susceptible to instability in both air and high-temperature oxygen atmospheres, potentially leading to degradation during the growth of the functional oxide layer. In this study, we investigate the use of an oxygen-deficient La 0.7 Sr 0.3 MnO 3 as capping layer, and demonstrate its ability to stabilize Sr 3 Al 2 O 6 films in ambient air. We successfully synthesized freestanding La 0.7 Sr 0.3 MnO 3 membranes by etching this sacrificial layer and transferring them onto flexible polymer substrates. Importantly, the magnetic properties of the La 0.7 Sr 0.3 MnO 3 films are preserved in these membranes. Furthermore, our results underline that employing a thin manganite capping layer ensures both high structural quality and the preservation of functional properties in the resulting membranes.

Deposition↗
DOE OSTI2020

Facile Fabrication of Hierarchical MOF–Metal Nanoparticle Tandem Catalysts for the Synthesis of Bioactive Molecules

Multifunctional metal–organic frameworks (MOFs) that possess permanent porosity are promising catalysts in organic transformation. Herein, we report the construction of a hierarchical MOF functionalized with basic aliphatic amine groups and polyvinylpyrrolidone-capped platinum nanoparticles (Pt NPs). The postsynthetic covalent modification of organic ligands increases basic site density in the MOF and simultaneously introduces mesopores to create a hierarchically porous structure. The multifunctional MOF is capable of catalyzing a sequential Knoevenagel condensation–hydrogenation–intramolecular cyclization reaction. The unique selective reduction of the nitro group to intermediate hydroxylamine by Pt NPs supported on MOF followed by intramolecular cyclization with a cyano group affords an excellent yield (up to 92%) to the uncommon quinoline N-oxides over quinolines. The hierarchical MOF and polyvinylpyrrolidone capping agent on Pt NPs synergistically facilitate the enrichment of substrates and thus lead to high activity in the reduction–intramolecular cyclization reaction. The bioactivity assay indicates that the synthesized quinoline N-oxides evidently inhibit the proliferation of lung cancer cells. Finally, our findings demonstrate the feasibility of MOF-catalyzed direct synthesis of bioactive molecules from readily available compounds under mild conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Vapor-Deposited n = 2 Ruddlesden–Popper Interface Layers Aid Charge Carrier Extraction in Perovskite Solar Cells

Interfacial passivation with bulky organic cations such as phenetylammonium iodide has enabled high performance for metal halide perovskite optoelectronic devices. However, the homogeneity of these interfaces and their formation dynamics are poorly understood. Here we study how Ruddlesden-Popper 2D phases form at a 3D perovskite interface when the 2D precursors are introduced via solution or via vapor. When using vapor deposition, we observe uniform coverage of the capping layer and the formation of a predominantly n = 2 Ruddlesden-Popper phase. In contrast, when using solution deposition, we observe the presence of a mixture of n = 2 and n = 1 in the film and the formation of aggregates of the organic cations. As a result of the better phase purity and uniformity, vapor deposition enables higher median solar cell performance with narrower distribution compared to solution-treated films. This study provides fundamental information that the perovskite community can use to better design capping layers to achieve higher charge extraction efficiencies.

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

Biochemical Conversion of Herbaceous Biomass to Renewable Diesel: Net Greenhouse Gas and Air Pollutant Trade-offs

This study examines greenhouse gas (GHG) and criteria air pollutant (CAP) emissions trade-offs for renewable diesel across 12 scenarios, involving different biochemical conversion designs, biorefinery scales, and feedstocks. A conventional design uses lignin for on-site heat and power, which exports excess power to the grid. An alternative design exports lignin pellets, offsetting other pellet production methods but requiring grid electricity to meet biorefinery power demands. Net emissions were quantified in Iowa and Georgia, selected considering feedstock availability, coproduct displacement, and regional power grids, assuming grid-exported power avoids coal or low-carbon electricity. Results for the conventional design remained consistent across the electricity displacement scenarios. When comparing lignin utilization strategies, pelletizing lignin reduces sulfur dioxide, carbon monoxide, nitrogen oxides, and volatile organic compounds (net emissions –0.66 mg MJ –1 , 25 mg MJ –1 , 25 mg MJ –1 , 7.8 mg MJ –1 , respectively). However, lignin pelletization increases net particulate matter (fine and coarse) and ammonia (net emissions of 4.7 mg MJ –1 , 13 mg MJ –1 , and 0.26 mg MJ –1 , respectively), alongside indirect GHG emissions due to grid electricity dependence. Additionally, processing 2000 tonnes corn stover daily minimizes emissions for both designs. Only lignin pelletization with renewable electricity and additional particulate matter and ammonia controls reduces all CAP and GHG emissions simultaneously.

09 BIOMASS FUELS↗
DOE OSTI2020

Thermal Stability of π-Conjugated n -Ethylene-Glycol-Terminated Quaterthiophene Oligomers: A Computational and Experimental Study

This work represents a joint computational and experimental study on a series of $\textit{n}$-ethylene glycol (PEO$\textit{n}$)-terminated quaterthiophene (4T) oligomers for 1 < $\textit{n}$ < 10 to elucidate their self-assembly behavior into a smectic-like lamellar phase. This study builds on an earlier study for $\textit{n}$ = 4 that showed that our model predictions were consistent with experimental data on the melting behavior and structure of the lamellar phase, with the latter consisting of crystal-like 4T domains and liquid-like PEO4 domains. The present study aims to understand how the length of the terminal PEO$\textit{n}$ chains modulates the disordering temperature of the lamellar phase and hence the relative stability of the ordered structure. In this work, a simplified bilayer model, where the 4T domains are not explicitly described, is put forward to efficiently estimate the disordering effect of the PEO domains with increasing n; this method is first validated by correctly predicting that layers of alkyl (PE)-capped 4T oligomers (for 1 < $\textit{n}$ < 10) stay ordered at room temperature. Both 4T-domain implicit and explicit model simulations reveal that the order-disorder temperature decreases with the length of the PEO capping chains, as the associated increase in conformational entropy drives a tendency toward disorder that overtakes the cohesive energy, keeping the ordered packing of the 4T domains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Reconfiguring DNA Nanotube Architectures via Selective Regulation of Terminating Structures

Molecular assemblies inside cells often undergo structural reconfiguration in response to stimuli to alter their function. Adaptive reconfiguration of cytoskeletal networks, for example, enables cellular shape change, movement, and cargo transport and plays a key role in driving complex processes such as division and differentiation. The cellular cytoskeleton is a self-assembling polymer network composed of simple filaments, so reconfiguration often occurs through the rearrangement of its component filaments’ connectivities. DNA nanotubes have emerged as promising building blocks for constructing programmable synthetic analogs of cytoskeletal networks. Nucleating seeds can control when and where nanotubes grow and capping structures can bind nanotube ends to stop growth. Such seeding and capping structure, collectively called termini, can organize nanotubes into larger architectures. However, these structures cannot be selectively activated or inactivated in response to specific stimuli to rearrange nanotube architectures, a key property of cytoskeletal networks. Here we demonstrate how selective regulation of the binding affinity of DNA nanotube termini for DNA nanotube monomers or nanotube ends can direct the reconfiguration of nanotube architectures. Using DNA hybridization and strand displacement reactions that specifically activate or inactivate four orthogonal nanotube termini, we demonstrate that nanotube architectures can be reconfigured by selective addition or removal of unique termini. Lastly, we show how terminus activation could be a sensitive detector and amplifier of a DNA sequence signal. These results could enable the development of adaptive and multifunctional materials or diagnostic tools.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Synthetic Access to a Framework-Stabilized and Fully Sulfided Analogue of an Anderson Polyoxometalate that is Catalytically Competent for Reduction Reactions

Polyoxometalates (POMs) featuring 7, 12, 18, or more redox-accessible transition metal ions are ubiquitous as selective catalysts, especially for oxidation reactions. The corresponding synthetic and catalytic chemistry of stable, discrete, capping-ligand-free polythiometalates (PTMs), which could be especially attractive for reduction reactions, is much less well developed. Among the challenges are the propensity of PTMs to agglomerate and the tendency for agglomeration to block reactant access of catalyst active sites. Nevertheless, the pervasive presence of transition metal sulfur clusters metalloenzymes or cofactors that catalyze reduction reactions and the justifiable proliferation of studies of two-dimensional (2D) metal-chalcogenides as reduction catalysts point to the promise of well-defined and controllable PTMs as reduction catalysts. Here, we report the fabrication of agglomeration-immune, reactant-accessible, capping-ligand-free Co II Mo 6 IV S 24 n– clusters as periodic arrays in a water-stable, hierarchically porous Zr-metal–organic framework (MOF; NU1K) by first installing a disk-like Anderson polyoxometalate, Co III Mo 6 VI O 24 m– , in size-matched micropores where the siting is established via difference electron density (DED) X-ray diffraction (XRD) experiments. Flowing H 2 S, while heating, reduces molybdenum(VI) ions to Mo(IV) and quantitatively replaces oxygen anions with sulfur anions (S 2– , HS – , S 2 2– ). DED maps show that MOF-templated POM-to-PTM conversion leaves clusters individually isolated in open-channel-connected micropores. Importantly, the structure of the immobilized cluster as determined, in part, by X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) analysis, and pair distribution function (PDF) analysis of total X-ray scattering agrees well with the theoretically simulated structure. PTM@MOF displays both electrocatalytic and photocatalytic competency for hydrogen evolution. Nevertheless, the initially installed PTM appears to be a precatalyst, gaining competency only after the loss of ~3 to 6 sulfurs and exposure to hydride-forming metal ions.

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

Cryo-EM Structure of the Mnx Protein Complex Reveals a Tunnel Framework for the Mechanism of Manganese Biomineralization

The global manganese cycle relies on microbes to oxidize soluble Mn(II) to insoluble Mn(IV) oxides. Some microbes require peroxide or superoxide as oxidants, but others can use O 2 directly, via multicopper oxidase (MCO) enzymes. One of these, MnxG from Bacillus sp. strain PL-12, was isolated in tight association with small accessory proteins, MnxE and MnxF. The protein complex, called Mnx, has eluded crystallization efforts, but we now report the 3D structure of a point mutant using cryo-EM single particle analysis, cross-linking mass spectrometry, and AlphaFold Multimer prediction. The ß-sheet–rich complex features MnxG enzyme, capped by a heterohexameric ring of alternating MnxE and MnxF subunits, and a tunnel that runs through MnxG and its MnxE 3 F 3 cap. The tunnel dimensions and charges can accommodate the mechanistically inferred binuclear manganese intermediates. Furthermore, comparison with the Fe(II)-oxidizing MCO, ceruloplasmin, identifies likely coordinating groups for the Mn(II) substrate, at the entrance to the tunnel. Thus, the 3D structure provides a rationale for the established manganese oxidase mechanism, and a platform for further experiments to elucidate mechanistic details of manganese biomineralization.

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

Conjugated Zwitterionic Oligomers as Ligands on Perovskite Nanocrystals: Hybrid Structures with Tunable Interparticle Spacing

Conventional ligands for CsPbBr 3 perovskite nanocrystals (NCs), composed of polar, coordinating head groups (e.g., ammonium or zwitterionic) and aliphatic tails, are instrumental in stabilizing the NCs against sintering and aggregation. Nonetheless, the aliphatic (insulating) nature of these ligands represents drawbacks with respect to objectives in optoelectronics, and yet removing these ligands typically leads to a loss of colloidal stability. Here, in this paper, we describe the preparation of CsPbBr 3 NCs in the presence of discrete conjugated oligomers that were prepared by an iterative synthetic approach and capped at their chain ends with sulfobetaine zwitterions for perovskite coordination. Notably, these zwitterionic oligofluorenes are compatible with the hot injection and ligand exchange conditions used to prepare CsPbBr 3 NCs, yielding stable NC dispersions with high photoluminescence quantum yields (PLQY, >90%) and spectral features representative of both the perovskite core and conjugated ligand shell. Controlling the chain length of these capping ligands effectively regulated inter-NC spacing and packing geometry when cast into solid films, with evidence derived from both transmission electron microscopy (TEM) and grazing incidence X-ray scattering measurements.

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

Colloidal Germanium Quantum Dots with Broadly Tunable Size and Light Emission

Germanium (Ge) colloidal quantum dots (CQDs) were synthesized by thermal decomposition of GeI 2 using capping ligand mixtures of oleylamine (OAm), octadecene (ODE), and trioctylphosphine (TOP). Average diameters could be tuned across a wide range, from 3 to 18 nm, by adjusting reactant concentrations, heating rates, and reaction temperatures. OAm promotes decomposition of GeI 2 to Ge and serves as a weakly bound capping ligand. ODE displaces OAm during the reaction to terminate particle growth and prevent surface oxidation. TOP is necessary for obtaining nanocrystals larger than 11 nm. In conclusion, the Ge CQDs have relatively narrow size distributions and exhibit size-dependent, band-edge photoluminescence (PL), with peak energies from 0.8 to 1.34 eV, across a wide spectral range in the infrared (IR).

Noh, Jungchul [Univ. of Texas, Austin, TX (United ↗
DOE OSTI2025

Vinylsilanes as Chain-Transfer Agents in Ethylene Polymerization: Direct Synthesis of Heterotelechelic Polyolefins

A single-step route to heterotelechelic polyethylene is enabled by palladium-diimine-catalyzed polymerization of ethylene using vinylsilanes as chain-transfer agents. The reaction affords α-alkenyl-ω-silyl end-capped heterotelechelic polymers whose molecular weights are controllable over a wide range by adjusting the [ethylene]/[vinylsilane] molar ratios. Notably, highly efficient end-capping with silanes carrying a variety of functionalities can be achieved under the optimized conditions. Furthermore, the alkenyl- and silyl-terminated telechelics serve as polymer precursors for further reactions and can be converted into additional telechelic functionalized polyolefins in good yields.

Chen, Zhi-Hao [University of Houston, TX (United S↗
DOE OSTI2024

The High Latitude Ionospheric Response to the Major May 2024 Geomagnetic Storm: A Synoptic View

Abstract The high latitude ionospheric evolution of the May 10‐11, 2024, geomagnetic storm is investigated in terms of Total Electron Content and contextualized with Incoherent Scatter Radar and ionosonde observations. Substantial plasma lifting is observed within the initial Storm Enhanced Density plume with ionospheric peak heights increasing by 150–300 km, reaching levels of up to 630 km. Scintillation is observed within the cusp during the initial expansion phase of the storm, spreading across the auroral oval thereafter. Patch transport into the polar cap produces broad regions of scintillation that are rapidly cleared from the region after a strong Interplanetary Magnetic Field reversal at 2230UT. Strong heating and composition changes result in the complete absence of the F2‐layer on the eleventh, suffocating high latitude convection from dense plasma necessary for Tongue of Ionization and patch formation, ultimately resulting in a suppression of polar cap scintillation on the eleventh.

Themens, David R.↗
DOE OSTI2020

Orbital-selective Dirac fermions and extremely flat bands in frustrated kagome-lattice metal CoSn

Layered kagome-lattice 3d transition metals are emerging as an exciting platform to explore the frustrated lattice geometry and quantum topology. However, the typical kagome electronic bands, characterized by sets of the Dirac-like band capped by a phase-destructive flat band, have not been clearly observed, and their orbital physics are even less well investigated. Here, we present close-to-textbook kagome bands with orbital differentiation physics in CoSn, which can be well described by a minimal tight-binding model with single-orbital hopping in Co kagome lattice. The capping flat bands with bandwidth less than 0.2 eV run through the whole Brillouin zone, especially the bandwidth of the flat band of out-of-plane orbitals is less than 0.02 eV along Γ-M. The energy gap induced by spin-orbit interaction at the Dirac cone of out-of-plane orbitals is much smaller than that of in-plane orbitals, suggesting orbital-selective character of the Dirac fermions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Atomistic insights into the nucleation and growth of platinum on palladium nanocrystals

Abstract Despite the large number of reports on colloidal nanocrystals, very little is known about the mechanistic details in terms of nucleation and growth at the atomistic level. Taking bimetallic core-shell nanocrystals as an example, here we integrate in situ liquid-cell transmission electron microscopy with first-principles calculations to shed light on the atomistic details involved in the nucleation and growth of Pt on Pd cubic seeds. We elucidate the roles played by key synthesis parameters, including capping agent and precursor concentration, in controlling the nucleation site, diffusion path, and growth pattern of the Pt atoms. When the faces of a cubic seed are capped by Br − , Pt atoms preferentially nucleate from corners and then diffuse to edges and faces for the creation of a uniform shell. The diffusion does not occur until the Pt deposited at the corner has reached a threshold thickness. At a high concentration of the precursor, self-nucleation takes place and the Pt clusters then randomly attach to the surface of a seed for the formation of a non-uniform shell. These atomistic insights offer a general guideline for the rational synthesis of nanocrystals with diverse compositions, structures, shapes, and related properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Molecular basis for polysaccharide recognition and modulated ATP hydrolysis by the O antigen ABC transporter

O antigens are ubiquitous protective extensions of lipopolysaccharides in the extracellular leaflet of the Gram-negative outer membrane. Following biosynthesis in the cytosol, the lipid-linked polysaccharide is transported to the periplasm by the WzmWzt ABC transporter. Often, O antigen secretion requires the chemical modification of its elongating terminus, which the transporter recognizes via a carbohydrate-binding domain (CBD). Here, using components from A. aeolicus, we identify the O antigen structure with methylated mannose or rhamnose as its cap. Crystal and cryo electron microscopy structures reveal how WzmWzt recognizes this cap between its carbohydrate and nucleotide-binding domains in a nucleotide-free state. ATP binding induces drastic conformational changes of its CBD, terminating interactions with the O antigen. ATPase assays and site directed mutagenesis reveal reduced hydrolytic activity upon O antigen binding, likely to facilitate polymer loading into the ABC transporter. Our results elucidate critical steps in the recognition and translocation of polysaccharides by ABC transporters.

59 BASIC BIOLOGICAL SCIENCES↗