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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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Recent Progress on Topological Structures in Ferroic Thin Films and Heterostructures
Topological spin/polarization structures in ferroic materials continue to draw great attention as a result of their fascinating physical behaviors and promising applications in the field of high-density nonvolatile memories as well as future energy-efficient nanoelectronic and spintronic devices. Such developments have been made, in part, based on recent advances in theoretical calculations, the synthesis of high-quality thin films, and the characterization of their emergent phenomena and exotic phases. Herein, progress over the last decade in the study of topological structures in ferroic thin films and heterostructures is explored, including the observation of topological structures and control of their structures and emergent physical phenomena through epitaxial strain, layer thickness, electric, magnetic fields, etc. First, the evolution of topological spin structures (e.g., magnetic skyrmions) and associated functionalities (e.g., topological Hall effect) in magnetic thin films and heterostructures is discussed. Then, the exotic polar topologies (e.g., domain walls, closure domains, polar vortices, bubble domains, and polar skyrmions) and their emergent physical properties in ferroelectric oxide films and heterostructures are explored. Lastly, a brief overview and prospectus of how the field may evolve in the coming years is provided.
Real‐Time Optical Process Monitoring for Structure and Property Control of Aerosol Jet Printed Functional Materials
Abstract Aerosol jet printing is a popular digital additive manufacturing method for flexible and hybrid electronics, but it lacks sophisticated real‐time process control schemes that would enable more widespread adoption in manufacturing environments. Here, an optical measurement system is introduced to track the aerosol density upstream of the printhead. The measured optical extinction, combined with the aerosol flow rate, is directly related to deposition rate and accurately predicts functional materials properties such as the electrical resistance of printed graphene films. This real‐time system offers a compelling solution for process drift and batch‐to‐batch variability, rendering it a valuable tool for both real‐time control of aerosol jet printing and fundamental studies of the underlying process science.
Untangling Dynamical and Microphysical Controls for the Structure of Stratocumulus
Stratocumulus clouds that are an important component of the Earth climate system can exhibit diverse structures, from solid decks to broken cloud fields with strikingly different abilities to reflect solar radiation. Amazingly, these different cloud formations can occur within the same or nearly the same environment, as evident by a common presence of pockets of open cells surrounded by overcast areas. These intriguing features not only provide for spectacular satellite images, but also present a challenge for climate models striving to predict the correct cloud amount. While open cells have been linked to the presence of precipitation and low droplet concentrations, complete understanding of the many complex and interacting processes leading to their formation is lacking. Here we show that the structure of stratocumulus can be linked to two timescales: an updraft timescale, t_up, and a precipitation initiation timescale, t_r. When drizzle is initiated within updrafts (t_r ≤ t_up), cloud water in the outflow is depleted enough that an overcast cloud cannot be sustained. Using a simple parcel model, we relate these timescales to three observable parameters (droplet number concentration, Nc, cloud depth, H, and updraft speed, w) and derive a functional representation for this relationship. Well-documented observed and simulated cases of open and closed cell stratocumulus fit well into the classification based on our model.
Navigating Organo-Lead Halide Perovskite Phase Space via Nucleation Kinetics toward a Deeper Understanding of Perovskite Phase Transformations and Structure-Property Relationships
Organo-lead halide perovskite photovoltaics have developed faster than our understanding of the material itself. Using the vast body of work on perovskite processing created in just the past few years, it is possible to create a better picture of this material's complex phase-transformation behavior. This concept article summarizes and correlates the current understanding of structural intermediates, kinetic controls, and structure–property relationships of organo-lead iodide perovskites. To this end, a new way of graphically relating information is developed, allowing the simultaneous mapping of schematic kinetic relationships between all currently prevailing perovskite deposition and growth techniques.
Cadmium(II) terephthalates based on trinuclear units {Cd_3(bdc)_3}: control of coordination structure dimensionality and luminescence properties
Two metal-organic coordination polymers based on cadmium(II) ions and terephthalic (1,4-benzenedicarboxylic) acid were synthesized in dimethylformamide or a mixture of dimethylformamide and methanol: [Cd{sub 3}(bdc){sub 3}(dmf){sub 4}] (1, bdc is 1,4-benzenedicarboxylate, dmf is N,N´-dimethylformamide) and [Cd{sub 3}(bdc){sub 3}(dmf){sub 2}] (2), respectively. According to the single-crystal X-ray diffraction data, both compounds are built up by the trinuclear carboxylate units {Cd_3(O_2CR)_6}. Compound 1 has a layered structure, whereas compound 2 has a three-dimensional structure due to the presence of additional coordination interactions between adjacent trinuclear units and the formation of polymer chains {Cd_3(dmf)_2(μ_2-O_2CR-κ"1,κ"1)_2(μ_2-O_2CR-κ"2,κ"1)_4(O_2CR-κ"1)2}. The synthesized compounds were characterized by IR spectroscopy, thermogravimetric analysis, elemental analysis, and powder X-ray diffrac- tion. The luminescence properties of these compounds provide evidence for the existence of both intraligand and charge-transfer transitions. The luminescence quantum yields for both compounds are 10%.
Pulsed Laser Additive Manufacturing for 316L Stainless Steel: A New Approach to Control Subgrain Cellular Structure
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Structure and morphology control of amorphous Mn-doped Fe oxide composite using soft-templates for e
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Controlled preparation and structure characterization of BiFeO{sub 3} with macroscopic shapes
Graphical abstract: We firstly explored two facile and successful techniques for BiFeO{sub 3} immobilization on silica fiber, namely, a combined impregnation method with carbon nanofibers (CNFs) templates route, and a combined solvothermal method with CNFs templates route. It is expected that such materials with direct macroscopic shapes would hold promise as highly functionalized materials for potential practical applications, especially in photocatalysis. - Highlights: • BiFeO{sub 3} with macroscopic shape was successfully obtained. • The synthetic methods used here are facile, effective, and reproducible. • Phase composition was strongly affected by calcination temperatures. • The obtained materials are promising visible-light-driven photocatalysts. - Abstract: BiFeO{sub 3} was successfully immobilized on silica fiber via two synthetic techniques (a combined impregnation method with carbon nanofibers templates route; a combined solvothermal method with carbon nanofibers templates route). The phase structure, morphology and optical absorption property of the samples were characterized by X-ray diffraction, field emission scanning electron microscopy, and ultraviolet–visible diffuse reflectance spectroscopy. The results confirmed that carbon nanofibers can act as effective templates for BiFeO{sub 3} immobilization on silica fiber with the applied two methods. Compared with solvent thermal method, impregnation method tends to form a relatively uniform particle size distribution and highly-crystallized phase when the calcination temperature was kept at 773 K for 5 h. It turned out the phase composition of the samples is strongly affected by the calcination temperatures for both cases. Such materials with direct macroscopic shapes would hold promise as highly functionalized materials for potential practical applications, especially in photocatalysis.
Controlling Ion Coordination Structure and Diffusion Kinetics for Optimized Electrode-Electrolyte Interphases and High Performance Si Anodes
The cycling performance of batteries is largely determined by electrode-electrolyte interphase associated with the chemical and electrochemical properties of electrolyte salts and solvents. In this work, we used a localized high concentration electrolyte (LHCE) that enables high performance of Si anodes as a model system and investigated the scientific mechanism behind the optimization of electrolyte. The correlation between electrode (cathode/anode)-electrolyte interphase and ion coordination structure and diffusion kinetics were elucidated systematically. Among all the LHCEs tested, the one with 1.8M LiFSI concentration and 1:2 molar ratio of carbonate solvents and fluorinated diluents has the highest proportion of solvent-separated ion pairs and contact ion pairs and fastest ion diffusion. It enables the most stable electrode-electrolyte interphase and hence the best Si anode performance. These results reveal the fundamental mechanism behind the stability of LHCEs and provide guidance on the new electrolyte design for Si anodes and other battery systems.
Control of the Structural Charge Distribution and Hydration State upon Intercalation of CO 2 into Expansive Clay Interlayers
Numerous experimental investigations indicated that expansive clays such as montmorillonite can intercalate CO 2 preferentially into their interlayers and therefore potentially act as a material for CO 2 separation, capture, and storage. However, an understanding of the energy–structure relationship during the intercalation of CO 2 into clay interlayers remains elusive. Here, in this study, we use metadynamics molecular dynamics simulations to elucidate the energy landscape associated with CO 2 intercalation. Our free energy calculations indicate that CO 2 favorably partitions into nanoconfined water in clay interlayers from a gas phase, leading to an increase in the CO 2 /H 2 O ratio in clay interlayers as compared to that in bulk water. CO 2 molecules prefer to be located at the centers of charge-neutral hydrophobic siloxane rings, whereas interlayer spaces close to structural charges tend to avoid CO 2 intercalation. The structural charge distribution significantly affects the amount of CO 2 intercalated in the interlayers. These results provide a mechanistic understanding of CO 2 intercalation in clays for CO 2 separation, capture, and storage.
Structural Basis for Control of Methylation Extent in Polyketide Synthase Metal-Dependent C-Methyltr
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Oxygen Control of Atomic Structure and Physical Properties of SrRuO3 Surfaces
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Single-layered organic photovoltaics with double cascading charge transport pathways: 18% efficiencies
The chemical structure of donors and acceptors limit the power conversion efficiencies achievable with active layers of binary donor-acceptor mixtures. Here, using quaternary blends, double cascading energy level alignment in bulk heterojunction organic photovoltaic active layers are realized, enabling efficient carrier splitting and transport. Numerous avenues to optimize light absorption, carrier transport, and charge-transfer state energy levels are opened by the chemical constitution of the components. Record-breaking PCEs of 18.07% are achieved where, by electronic structure and morphology optimization, simultaneous improvements of the open-circuit voltage, short-circuit current and fill factor occur. The donor and acceptor chemical structures afford control over electronic structure and charge-transfer state energy levels, enabling manipulation of hole-transfer rates, carrier transport, and non-radiative recombination losses.
Tricyclononenes and tricyclononadienes as efficient monomers for controlled ROMP: understanding structure–propagation rate relationships and enabling facile post-polymerization modification
Grubbs 3rd-generation (G3) pre-catalyst-initiated ring-opening metathesis polymerization (ROMP) remains an indispensable tool in the polymer chemist's toolbox. Tricyclononenes (TCN) and tricyclononadienes (TCND) represent under-explored classes of monomers for ROMP that have the potential to both advance fundamental knowledge (e.g., structure-polymerization kinetics relationships) and serve as practical tools for the polymer chemist (e.g., post-polymerization functionalization). In this work, a library of TCN and TCND imides, monoesters, and diesters, along with their exo-norbornene counterparts, were synthesized to compare their behaviors in G3-initiated ROMP. Real-time 1 H NMR was used to study their polymerization kinetics; propagation rates ( k p ) were extracted for each monomer. To understand the relationships between monomer structure and ROMP propagation rates, density functional theory methods were used to calculate a variety of electronic and steric parameters for each monomer. While electronic parameters (e.g., HOMO energy levels) correlated positively with the measured k p values, steric parameters generally gave improved correlations, which indicates that monomer size and shape are better predictors for k p than electronic parameters for this data set. Furthermore, the TCND diester—which contains an electron-deficient cyclobutene that is resistant to ROMP—and its polymer p(TCND) are shown to be highly reactive toward DBU-catalyzed conjugate addition reactions with thiols, providing a protecting- and activating-group free strategy for post-polymerization modification.