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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Investigating the Role π -Rich Solvents Play in the Growth of Cesium Lead Bromide Nanocrystals

In this report, the role that a high-boiling-point solvent type plays on the nucleation and growth, morphology, and crystal-phase transformation of cesium lead bromide nanocrystals (CsPbBr 3 ) is studied. The CsPbBr 3 products were compared between a one-pot growth mechanism at room temperature (RT) versus a hot-injection mechanism (HI) control using dibenzyl ether (DBE), diphenyl ether (DPE), dioctyl ether (DOE), or 1- octadecene (ODE). The coordination between these solvents and the PbBr 2 salt precursors resulted in different plumbate [PbSBr n ] 2−n precursors being formed. The S-to-Pb 2+ coordination within [PbSBr n ] 2−n was probed by UV−vis and solvent-phase 207 Pb NMR, both of which showed considerable coordination between [PbSBr n ] 2−n and the π-rich DBE and DPE, whose reactivity affected CsPbBr 3 growth. The effect was more pronounced for CsPbBr 3 prepared via RT, where the morphology was tunable, with π-rich solvents producing thin rod-like CsPbB r3 with a blue emission, compared to the green-emitting thicker platelets formed via HI. While XRD showed crystalline products for both RT and HI, with orthorhombic and cubic forms, respectively, the RT products had considerable surface defects, as was indicated by lower quantum yields, and to understand this the photoluminescent lifetimes were measured by time-correlated single photon counting.

207Pb NMR↗
DOE OSTI2020

Lasing from Finite Plasmonic Nanoparticle Lattices

Small lasers can generate coherent light for integrated photonics, in-vivo cellular imaging, and solid-state lighting. Unlike conventional lasers, plasmonic lasers can generate coherent light at sub-wavelength scales, although cavity architectures based on metal films and semiconducting gain exhibit large radiative losses and lack directional emission. In contrast, two-dimensional (2D) metal nanoparticle arrays surrounded by organic dyes can support lasing with high directionality at room temperature. Yet, the relationship between the number of nanoparticles in a finite lattice and their lasing emission characteristics is unknown. Here we show that the number of units in 2D gold nanoparticle lattices is critical to generate robust cavity resonances and lasing emission. Narrower lattice plasmons associated with stronger electromagnetic near fields are observed as nanoparticle number increases. Experimentally, we demonstrate lasing from a 30x30 nanoparticle lattice. Semi-quantum modeling indicates lower lasing thresholds and faster population inversion dynamics with higher nanoparticle numbers. These findings indicate that finite lattices of nanoparticles integrated with gain can function as independent, coherent light sources for optical multiplexing and lab-on-a-chip applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Broadband Circular Polarizers via Coupling in 3D Plasmonic Meta-Atom Arrays

In this work, we report broadband circular polarizers achieved by engineering the electromagnetic coupling between 3D meta-atoms in large-area arrays. The 3D meta-atoms are composed of bulk Au/Au nanocrystal (NC) bilayer helical arms, tailored in their number, length, and curvature through a one-step patterning process and postfabrication chemical and thermal treatments. By tuning the meta-atom array periodicity, hybridization originating from dipole–dipole and quadrupole–quadrupole interactions broadens the chiral response. We demonstrate circular polarizers operating at wavelengths spanning 2.5 to 5 μm, with a maximal transmission difference between left- and right-hand circularly polarized light of 43%.

3D metamaterials↗
DOE OSTI2022

Vertical Architecture Solution-Processed Quantum Dot Photodetectors with Amorphous Selenium Hole Transport Layer

Colloidal quantum dots (CQDs) provide wide spectral tunability and high absorption coefficients owing to quantum confinement and large oscillator strengths, which along with solution processability, allow a facile, low-cost, and room-temperature deposition technique for the fabrication of photonic devices. However, many solution-processed CQD photodetector devices demonstrate low specific-detectivity and slow temporal response. To achieve improved photodetector characteristics, limiting carrier recombination and enhancing photogenerated carrier separation are crucial. In this study, we develop and present an alternate vertical-stack photodetector wherein we use a solution-processed quantum dot photoconversion layer coupled to an amorphous selenium (a-Se) wide-bandgap charge transport layer that is capable of exhibiting single-carrier hole impact ionization and is compatible with active-matrix readout circuitry. This a-Se chalcogenide transport layer enables the fabrication of high-performance and reliable solution-processed quantum dot photodetectors, with enhanced charge extraction capabilities, high specific detectivity (D* ~ 0.5–5 × 10 12 Jones), fast 3 dB electrical bandwidth (3 dB BW ~ 22 MHz), low dark current density (J D ~ 5–10 pA/cm 2 ), low noise current (i n ~ 20–25 fW/Hz 1/2 ), and high linear dynamic range (LDR ~130–150 dB) across the measured visible electromagnetic spectrum (~405–656 nm).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Cascade Reaction of Ethanol to Butadiene over Multifunctional Silica-Supported Ag and ZrO 2 Catalysts

Although butadiene is currently a by-product of naphtha cracking, interest in producing butadiene from bio-based ethanol has increased because of the lower environmental impact of the ethanol to butadiene reaction. Furthermore, this work explores a multifunctional catalyst system composed of silica-supported Ag and ZrO 2 used for the cascade reaction of ethanol to butadiene at 573 K. The Ag and ZrO 2 components were synthesized on separate support particles enabling characterization of each component without interference from the other. High selectivity to butadiene (65%) at high ethanol conversion (75%) was achieved with an appropriate ratio of Ag and ZrO 2 in the reactor. Silver catalyzed the initial dehydrogenation of ethanol to acetaldehyde while ZrO 2 catalyzed the C-C coupling and subsequent dehydration reactions. The silica-supported ZrO 2 exhibited superior selectivity relative to bulk ZrO 2 in the Ag-promoted ethanol to butadiene reaction. Results from Zr K-edge X-ray absorption spectroscopy and UV-Vis spectroscopy showed that ZrO 2 was highly dispersed on the silica support over a range of loadings. Infrared spectroscopy of adsorbed pyridine, CO, and CO 2 , and kinetics of probe reactions 1-butene double bond isomerization, 2-propanol decomposition, and ethanol hydrogenation of acetone were used to compare the acid-base nature and chemical reactivity of silica-supported ZrO 2 to bulk ZrO 2 .

09 BIOMASS FUELS↗
DOE OSTI2020

Hydrogen Stabilized RhPdH 2D Bimetallene Nanosheets for Efficient Alkaline Hydrogen Evolution

The design of catalysts with high activity and robust stability for alkaline hydrogen evolution reaction (HER) remains a great challenge. Here, we report an efficient catalyst of two-dimensional bimetallene hydrides, in which H atoms stabilize the rhodium palladium bimetallene. The system exists because of the introduction of H that is in-situ chemically released from the formaldehyde solution during the synthesis. This provides a highly stable catalyst based on an unstable combination of metal elements. Density functional theory calculations show the H is confined by electronic interactions and the Miedema rule of reverse stability of the RhPd alloy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

An Exceptionally Stable Metal–Organic Framework Constructed from Chelate-Based Metal–Organic Polyhedra

In this paper, we report the rational design and synthesis of a new, water-stable metal-organic framework (MOF), Fe-HAF-1, constructed from supramolecular, Fe3+-hydroxamate-based polyhedra with mononuclear metal nodes. Owing to its chelate-based con-struction, Fe-HAF-1 displays exceptional chemical stability in organic and aqueous solvents over a wide pH range (pH 1-14), including in the presence of 5 M NaOH. Despite the charge-neutrality of the Fe 3+ -tris(hydroxamate) centers, Fe-HAF-1 crystals are negatively charged above pH 4. This unex-pected property is attributed to the formation of defects during crystallization that results in uncoordinated hydroxamate ligands or hydroxide-coordinated Fe centers. The anionic na-ture of Fe-HAF-1 crystals enables selective adsorption of pos-itively charged ions in aqueous solution, resulting in efficient separation of organic dyes and other charged species in a size-selective fashion. Fe-HAF-1 presents a new addition to a small group of chelate-based MOFs and provides a rare framework whose 3D connectivity is exclusively formed by metal-hydroxamate coordination.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Advancement of Actinide Metal–Organic Framework Chemistry via Synthesis of Pu-UiO-66

We report the synthesis and characterization of the first plutonium metal–organic framework (MOF). Pu-UiO-66 expands the established UiO-66 series, which includes transition metal, lanthanide, and early actinide elements in the hexanuclear nodes. The thermal stability and porosity of Pu-UiO-66 were experimentally determined, and multifaceted computational methods were used to corroborate experimental values, examine inherent defects in the framework, decipher spectroscopic signatures, and elucidate the electronic structure. The crystallization of a plutonium chain side product provides direct evidence of the competition that occurs between modulator and linker in MOF syntheses. Ultimately, the synthesis of Pu-UiO-66 demonstrates adept control of Pu(IV) coordination under hydrolysis-prone conditions, provides an opportunity to extend trends across isostructural UiO-66 frameworks, and serves as the foundation for future plutonium MOF chemistry.

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

Supramolecular Assembly of U(IV) Clusters and Superatoms with Unconventional Countercations

Superatoms are nanometer-sized molecules or particles that form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in lattices of quantum dots, p-block clusters, and fullerenes. In this report, we introduce a family of uranium-oxysulfate cluster anions whose hierarchical assembly in water is controlled by two parameters: acidity and the lanthanide or transition-metal countercation. In acid, larger Ln III (Ln = La–Ho) link hexamer (U 6 ) oxoclusters into body-centered cubic frameworks, while smaller Ln III (Ln = Er–Lu and Y) promote linking of 14 U 6 clusters into hollow superclusters (U 84 superatoms). U 84 assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations and U 6 clusters. Divalent transition metals (TM = Mn II and Zn II ) charge-balance and promote the fusion of 10 U 6 and 10 U monomers into a wheel-shaped cluster (U 70 ). Dissolution of U 70 in organic media shows (by small-angle X-ray scattering) that differing supramolecular assemblies are accessed, controlled by TM II -linking of U 70 clusters. Magnetic measurements of these assemblies reveal Curie–Weiss behavior at high temperatures, without pairing of the 5f 2 -electrons down to 2 K.

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

Unprecedented Radiation Resistant Thorium–Binaphthol Metal–Organic Framework

A thorium–organic framework (TOF-16) containing hexameric secondary building units connected by functionalized binaphthol linkers was synthesized, characterized, and irradiated to probe its radiation resistance. Radiation stability was examined using γ-rays and 5 MeV He 2+ ions to simulate α particles. γ-irradiation of TOF-16 to an unprecedented 4 MGy dose resulted in no apparent bulk structural damage visible by X-ray diffraction. To further probe radiation stability, we conducted the first He 2+ ion irradiation study of a metal–organic framework (MOF). Diffraction data indicate onset of crystallinity loss upon approximately 15 MGy of irradiation and total loss of crystallinity upon exposure to approximately 25 MGy of He 2+ ion irradiation. In conclusion, the high radiation resistance observed suggests MOFs can withstand radiation exposure at doses found in nuclear waste streams and highlights the need for a systematic approach to understand and eventually design frameworks with exceptional radiation resistance.

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

Tunable and Cooperative Thermomechanical Properties of Protein-Metal-Organic Frameworks

We recently introduced protein-metal-organic frameworks (protein-MOFs) as chemically designed protein crystals, composed of ferritin nodes that predictably assemble into 3D lattices upon coordination of various metal ions and ditopic, hydrox-amate-based linkers. Owing to their unique tripartite construction, protein-MOFs possess extremely sparse lattice connectivi-ty, suggesting that they might display unusual thermomechanical properties. Leveraging the synthetic modularity of ferritin-MOFs, we investigated the temperature-dependent structural dynamics of six distinct frameworks. Our results show that the thermostabilities of ferritin-MOFs can be tuned through the metal component or the presence of crowding agents. Our stud-ies also reveal a framework that undergoes a reversible and isotropic first-order phase transition near-room temperature, corre-sponding to a 4% volumetric change within ≤1 deg C and a hysteresis window of ~10 deg C. Here, this highly cooperative crystal-to-crystal transformation, which stems from the soft crystallinity of ferritin-MOFs, illustrates the advantage of modular con-struction strategies in discovering tunable–and unpredictable–material properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Reactivity, Formation, and Solubility of Polyoxometalates Probed by Calorimetry

Room temperature calorimetry methods were developed to describe the energy landscapes of six polyoxometalates (POMs), Li–U 24 , Li–U 28 , K–U 28 , Li/K–U 60 , Mo 132 , and Mo 154 , in terms of three components: enthalpy of dissolution (ΔH diss ), enthalpy of formation of aqueous POMs (ΔH f,(aq) ), and enthalpy of formation of POM crystals (ΔH f,(c) ). ΔH diss is controlled by a combination of cation solvation enthalpy and the favorability of cation interactions with binding sites on the POM. In the case of the four uranyl peroxide POMs studied, clusters with hydroxide bridges have lower ΔH f,(aq) and are more stable than those containing only peroxide bridges. Here, in general for POMs, the combination of calorimetric results and synthetic observations suggest that spherical topologies may be more stable than wheel-like clusters, and ΔH f,(aq) can be accurately estimated using only ΔH f,(c) values owing to the dominance of the clusters in determining the energetics of POM crystals.

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

Cyclopropenylidenes as Strong Carbene Anchoring Groups on Au Surfaces

The creation of stable molecular monolayers on metallic surfaces is a fundamental challenge of surface chemistry. N-Heterocyclic carbenes (NHCs) were recently shown to form self-assembled monolayers that are significantly more stable than the traditional thiols on Au system. In this study, we theoretically and experimentally demonstrate that the smallest cyclic carbene, cyclopropenylidene, binds even more strongly than NHCs to Au surfaces without altering the surface structure. We deposit bis(diisopropylamino)cyclopropenylidene (BAC) on Au(111) using the molecular adduct BAC–CO 2 as a precursor and determine the structure, geometry, and behavior of the surface-bound molecules through high-resolution X-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy. Our experiments are supported by density functional theory calculations of the molecular binding energy of BAC on Au(111) and its electronic structure. Our work is the first demonstration of surface modification with a stable carbene other than NHC; more broadly, it drives further exploration of various carbenes on metal surfaces.

77 NANOSCIENCE AND NANOTECHNOLOGY↗