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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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Inside polyMOFs: layered structures in polymer-based metal–organic frameworks
In this report, we explore the internal structural features of polyMOFs consisting of equal mass ratios of metal-coordinating poly(benzenedicarboxylic acid) blocks and non-coordinating poly(ethylene glycol) (PEG) blocks.
Anti-Icing Coatings using Ionomer Film Layer Structuring
This research effort examined the application of Nafion polymers in alcohol solvents as an anti-ice surface coating, as a mixture with hydrophilic polymers and freezing point depressant salt systems. Co-soluble systems of Nafion, polymer and salt were applied using dip coating methods to create smooth films for frost observation over a Peltier plate thermal system in ambient laboratory conditions. Cryo-DSC was applied to examine freezing events of the Nafion-surfactant mixtures, but the sensitivity of the measurement was insufficient to determine frost behavior. Collaborations with the Fog Chamber at Sandia-Albuquerque, and in environmental SAXS measurements with CINT-LANL were requested but were not able to be performed under the research duration. Since experimental characterization of these factors is difficult to achieve directly, computational modeling was used to guide the scientific basis for property improvement. Computational modeling was performed to improve understanding of the dynamic association between ionomer side groups and added molecules and deicing salts. The polyacrylic acid in water system was identified at the start of the project as a relevant system for exploring the effect of varying counterions on the properties of fully deprotonated polyacrylic acid (PAA) in the presence of water. Simulations were modeled with four different counterions, two monovalent counterions (K+ and Na+) and two divalent counterions (Ca2+ and Mg2+). The wt% of PAA in these systems was varied from ~10 to 80 wt% PAA for temperatures from 250K to 400K. In the second set of simulations, the interpenetration of water into a dry PAA film was studied for Na+ or Ca2+ counterions for temperatures between 300K and 400K. The result of this project is a sprayable Nafion film composite which resists ice nucleation at -20 °C for periods of greater than three hours. It is composed of Nafion polymer, hydrophilic polyethylene oxide polymer and CaCl2 anti-ice crosslinker. Durability and field performance properties remain to be determined.
Oxygen-layer structure improves lithium-doped silicon solar cells
Technique fabricates hybrid structure utilizing low oxygen silicon as bulk cell material and shallow overlay of silicon with high oxygen concentration.
Attenuation of stress waves in single and multi-layered structures
Analytical and experimental studies were made of the attenuation of the stress waves during passage through single and multilayer structures. The investigation included studies on elastic and plastic stress wave propagation in the composites and those on shock mitigating material characteristics such as dynamic stress-strain relations and energy absorbing properties. The results of the studies are applied to methods for reducing the stresses imposed on a spacecraft during planetary or ocean landings.
Shear layer structure of a low speed jet
A series of measurements of near field pressures and turbulent velocity fluctuations were made in a low speed jet with a Reynolds number near 50,000 in order to investigate more quantitatively the character and behavior of the large scale structures and their interactions with each other. The near field measurements were modelled according to the vortex pairing hypothesis to deduce the distribution of pairings along the jet axis and the variances about the mean locations. The hodograph plane description of turbulence was explored in some detail, and a complex correlation quantity was synthesized which has useful properties for turbulence in the presence of mean shear.
Interactions between volume and surface EM waves in layered structures
Using light scattering spectroscopy, the interaction of Surface Plasmon Polariton SPP in silver films on a glass substrate is with the incident radiation and with optical phonons of an external medium in contact with the film. The mean free path and the field strength of SPP are determined. The same SPP plays an important role in light emitting tunnel junctions (LETJ) in which an electrical current is converted into Volume Electromagnetic Wave VEW. The efficiency of light emission from LETJ through a prism coupler rather than through surface roughness is discussed. The coupling between phonon surface polaritons (PhSP) and optical guided waves (OGW) in thin films of GaP is also examined.
Boundary Layer Structures Over the Northwest Atlantic Derived From Airborne High Spectral Resolution Lidar and Dropsonde Measurements During the ACTIVATE Campaign
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Supercapillary Architecture‐Activated Two‐Phase Boundary Layer Structures for Highly Stable and Efficient Flow Boiling Heat Transfer
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Method for fabrication of superlattices and aperiodic layered structures using solution deposition
A method for forming inorganic structures includes (a) transferring nanocrystals to a polar protic solvent using at least one chalcogenide precursor to produce a negatively-charged chalcogen-rich nanocrystal surface, (b) removing excess anions of the chalcogenide precursor, (c) introducing a metal salt to bind a divalent metal cation to the negatively-charged chalcogen-rich nanocrystal surface to regenerate a positively-charged metal-rich nanocrystal surface, and (d) removing excess divalent metal cations of the metal acetate salt.
Pressure-driven significant phonon mode softening and robust superconductivity in layered germanium phosphide
Abstract not provided
Structural Phase Transitions between Layered Indium Selenide for Integrated Photonic Memory
The primary mechanism of optical memoristive devices relies on phase transitions between amorphous and crystalline states. The slow or energy-hungry amorphous–crystalline transitions in optical phase-change materials are detrimental to the scalability and performance of devices. Leveraging an integrated photonic platform, nonvolatile and reversible switching between two layered structures of indium selenide (In 2 Se 3 ) triggered by a single nanosecond pulse is demonstrated. The high-resolution pair distribution function reveals the detailed atomistic transition pathways between the layered structures. With interlayer “shear glide” and isosymmetric phase transition, switching between the α- and β-structural states contains low re-configurational entropy, allowing reversible switching between layered structures. Broadband refractive index contrast, optical transparency, and volumetric effect in the crystalline–crystalline phase transition are experimentally characterized in molecular-beam-epitaxy-grown thin films and compared to ab initio calculations. Finally, the nonlinear resonator transmission spectra measure of incremental linear loss rate of 3.3 GHz, introduced by a 1.5 µm-long In 2 Se 3 -covered layer, resulted from the combinations of material absorption and scattering.
Review of Polyimides Used in the Manufacturing of Micro Systems
Since their invention, polyimides have found numerous uses in MicroElectroMechanical Systems (MEMS) technology. Polyimides can act as photoresist, sacrificial layers, structural layers, and even as a replacement for silicon as the substrate during MEMS fabrication. They enable fabrication of both low and high aspect ratio devices. Polyimides have been used to fabricate expendable molds and reusable flexible molds. Development of a variety of devices that employ polyimides for sensor applications has occurred. Micro-robotic actuator applications include hinges, thermal actuators and residual stress actuators. Currently, polyimides are being used to create new sensors and devices for aerospace applications. This paper presents a review of some of the many uses of polyimides in the development of MEMS devices, including a new polyimide based MEMS fabrication process.
Structure of the magnetopause current layer
Structure of magnetopause current layer
Enhanced Spontaneous Polarization in Ultrathin SnTe Films with Layered Antipolar Structure
2D SnTe films with a thickness of as little as 2 atomic layers (ALs) have recently been shown to be ferroelectric with in–plane polarization. Remarkably, they exhibit transition temperatures (T c ) much higher than that of bulk SnTe. Here, combining molecular beam epitaxy, variable temperature scanning tunneling microscopy, and ab initio calculations, the underlying mechanism of the Tc enhancement is unveiled, which relies on the formation of γ–SnTe, a van der Waals orthorhombic phase with antipolar inter–layer coupling in few–AL thick SnTe films. In this phase, 4n – 2 AL (n = 1, 2, 3…) thick films are found to possess finite in–plane polarization (space group Pmn2 1 ), while 4n AL thick films have zero total polarization (space group Pnma). Above 8 AL, the γ–SnTe phase becomes metastable, and can convert irreversibly to the bulk rock salt phase as the temperature is increased. This finding unambiguously bridges experiments on ultrathin SnTe films with predictions of robust ferroelectricity in GeS–type monochalcogenide monolayers. Here, the observed high transition temperature, together with the strong spin–orbit coupling and van der Waals structure, underlines the potential of atomically thin γ–SnTe films for the development of novel spontaneous polarization–based devices.
Modeling of high-efficient direct methanol fuel cells with order-structured catalyst layer
Not provided.
Structural stability, elemental ordering, and transport properties of layered ScTaN 2
Ternary transition metal (TM) nitrides have gained significant attention in thin film research due to their promising properties for a broad range of applications. Particularly, some of the ternary TM nitrides have been predicted to adopt layered structures that make them interesting for thermoelectric conversion and quantum materials applications. Unfortunately, synthesis of TM ternary nitride films by physical vapor deposition often favors disordered 3D structures rather than the predicted 2D-like layered structure. In this study, we investigate the structural interplay in the Sc-Ta-N ternary system using a combinatorial approach. Combinatorial libraries Sc 𝑥 Ta 1−𝑥 N are synthesized following a two-step method: First, deposit film precursors by cosputtering and then process the resulting 3D-structured samples with rapid thermal annealing. Synchrotron grazing-incidence wide-angle x-ray scattering on films annealed at 1200 °C for 20 min leads to the nucleation of ScTaN 2 layered structure (𝑃6 3 /𝑚𝑚𝑐) near stoichiometry. We find that the layered structure can accommodate large off-stoichiometry in the Ta-rich region (𝑥 < 0.5), facilitated by the alloying with quasi-isostructural Ta 5 N 6 compound that exists on a composition tie line at 𝑥 = 0. While focusing on ScTaN 2 , we estimate the long-range order parameter in near-stoichiometric films to be 0.86, corresponding to a fraction of Sc/Ta antisites of 7%. Transport measurements on ScTaN 2 reveal a nearly temperature-independent high carrier density (10 21 cm −3 ), suggesting a heavily doped semiconductor or semimetallic character, consistent with a small positive Seebeck coefficient of +19 µV/K. The carrier mobility at 2 K is relatively small (9.5cm 2 V −1 s −1 ) and the residual-resistivity ratio is minor, suggesting that electrical conduction is dominated by defects or disorder. Measured magnetoresistance suggests possible weak antilocalization at 2 K. This paper highlights the interplay between ScTaN 2 and Ta 5 N 6 crystal structures in stabilizing layered materials, emphasizes the importance of cation order/disorder for potential tunable alloys, and suggests that ScTaN 2 is a promising platform for exploring electronic properties.