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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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Nano-layered, multilayered ?lms consisting of HfO2(dielectric)/Mo(metal)/HfO2(dielectric), (D/M/D archi-tecture) with controlled layer thickness, chemistry and microstructure were demonstrated for e?cient utiliza-tion of solar energy with well-designated spectral control. The e?ect of Mo metal interlayer on the energy performance and e?ciency of HfO2/Mo/HfO2 multilayer ?lms made by electron-beam deposition onto silicon and glass substrates has been evaluated. The Mo interlayer thickness [Mo(t)] was varied in the range of 5–25 nm while the top/bottom HfO2 layer thickness was kept constant at ~50 nm. Structural, morphological and optical characterization was performed to understand the e?ect of Mo(t) induced microstructure on mechanical dur-ability and optical behavior of the D/M/D multilayer ?lms. Structural studies revealed that D/M/D multilayer ?lms with relatively low Mo(t) were amorphous, while higher Mo(t) induces the amorphous-to-nanocrystalline microstructure transformation, which also induces surface roughening e?ects. The D/M/D multilayer ?lm with Mo(t) = 20 nm, where the nano-columnar morphology of the D-M-D layers are aligned perpendicular to the substrate surface and exhibits the optimum spectral selectivity. Such microstructure and morphological tailoring also facilitates the environmentally friendly (self-cleaning/stain repellent) nature of these multilayer ?lms by the high contact angle (~102°) achieved. Molybdenum interlayer facilitated higher contact angle leads to super-hydrophobic nature of the HfO2/Mo/HfO2 multilayered ?lm surfaces. The low surface roughness values (0.2–0.8 nm), which are primarily due to Mo at the interface, of the HfO2/Mo/HfO2 multilayered ?lms satisfy the general requirements of heat mirror applications. In addition, the microstructure of intermediate Mo layer and HfO2-Mo interfaces signi?cantly control the mechanical properties of D/M/D multilayer ?lms. Optimal me-chanical properties (hardness = 30 GPa, elastic modulus = 312 GPa, wear resistance = 0.094, adhesion strength = 2050 µN) have been obtained for Mo(t) = 20 nm D/M/D multilayer ?lm. The mechanical response strongly supports ?exible and wear resistive nature of HfO2/Mo/HfO2 multilayer ?lms.
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For LiMO 2 (M=Co, Ni, Mn) cathode materials, lattice parameters, a(b), contract during charge. Here we report such changes in opposite directions for lithium molybdenum trioxide (Li 2 MoO 3 ). A ‘unit cell breathing’ mechanism is proposed based on crystal and electronic structural changes of transition metal oxides during charge-discharge. Metal–metal bonding is used to explain such ‘abnormal’ behaviour and a generalized hypothesis is developed. The expansion of the metal-metal bond becomes the controlling factor for a(b) evolution during charge, in contrast to the shrinking metal-oxygen bond as controlling factor in ‘normal’ materials. The cation mixing caused by migration of molybdenum ions at higher oxidation state provides the benefits of reducing the c expansion range in the early stage of charging and suppressing the structure collapse at high voltage charge. These results may open a new strategy for designing layered cathode materials for high energy density lithium-ion batteries.
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Side chain engineering of the conjugated polymer backbone improves its thermal conductivity.
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Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.
Island tune spectra are introduced, beginning with curves of resonance trajectories plotted in the (Q x , Q I ) tune domain plane (where Q x is horizontal tune and Q I is island tune) for many resonance orders N. A slice in the (Q x , Q I ) plane delivers a Q I -spectrum at a fixed horizontal tune, with one spectral line for every appropriate value of N.
Here, we introduce a new quasi 1-D implosion experimental platform at the National Ignition Facility designed to validate physics models as well as to study various Inertial Confinement Fusion aspects such as implosion symmetry, convergence, hydrodynamic instabilities, and shock timing. The platform has been developed to maintain shell sphericity throughout the compression phase and produce a round hot core at stagnation. This platform utilizes a 2-shock 1 MJ pulse with 340 TW peak power in a near-vacuum AuHohlraum and a CH ablator capsule uniformly doped with 1% Si. We also performed several inflight radiography, symmetry capsule, and shock timing experiments in order to tune the symmetry of the capsule to near round throughout several epochs of the implosion. Finally, adjusting the relative powers of the inner and outer cones of beams has allowed us to control the drive at the poles and equator of the capsule, thus providing the mechanism to achieve a spherical capsule convergence. Details and results of the tuning experiments are described.
Previous work has shown that introduction of hexafluoroacetylacetone (Facac) units as nonstructural ligands for the zirconia-like nodes of the eight-connected metal-organic framework (MOF), NU-1000, greatly alters the selectivity of node-supported oxy-nickel clusters for ethylene dimerization vs oligomerization. Here we i explore a related concept: tuning of support/catalyst interactions, and therefore, catalyst activity, via parallel installation of organic modifiers on the support itself. As modifiers we focused on para-substituted benzoates (R-BA – ; R = -NH 2 , -OCH 3 , -CH 3 , -H, -F, and -NO 2 ) where the substituents were chosen to present similar steric demand, but varying electron-donating or electron-withdrawing properties. R-benzoate-engendered shifts in the node-based aqua O-H stretching frequency for NU-1000, as measured by DRIFTS (diffuse-reflectance infrared Fourier-transform spectroscopy), together with systematic shifts in Ni 2p peak energies, as measured by X-ray photoelectron spectroscopy, show that the electronic properties of the support can be modulated. The vibrational and electronic peak shifts correlate with the putative electron-withdrawing vs electron-donating strength of the para-substituted benzoate modifiers. Subsequent installation of node-supported, oxy-Ni(II) clusters for ethylene hydrogenation yield a compelling correlation between log (catalyst turnover frequency) and the electron donating or withdrawing character of the substituent of the benzoate units. Single crystal X-ray diffraction measurements reveal that each organic modifier makes use of only one of two available carboxylate oxygens to accomplish grafting. The remaining oxygen atom is, in principle, well positioned to coordinate directly to an installed Ni(II) ion. We postulate that the unanticipated direct coordination of the catalyst by the node-modifier (rather than indirect modifier-based tuning of support(node)/catalyst electronic interactions) is the primary source of the observed systematic tuning of hydrogenation activity. Here we suggest, however, that regardless of mechanism for communication with active-sites of MOF-supported catalysts, intentional elaboration of nodes via grafted, nonstructural organic species could prove to be a valuable general strategy for fine-tuning supported-catalyst activity and/or selectivity.