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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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The Effect of Alkyl Spacers on the Mixed Ionic;#8208;Electronic Conduction Properties of N-Type Poly
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Imprinting Chirality onto the Electronic States of Colloidal Perovskite Nanoplatelets
The direct synthesis of chiroptical organic–inorganic methylammonium lead bromide perovskite nanoplatelets that are passivated by R- or S-phenylethylammonium ligands is discussed. The circular dichroism spectra can be divided into two components: (1) a region associated with a charge transfer transition between the ligand and the nanoplatelet, 300–350 nm, and (2) a region corresponding to the excitonic absorption maximum of the perovskite, 400–450 nm. The temperature- and concentration-dependent circular dichroism spectra suggest that the chiro-optical response arises from chiral imprinting by the ligand on the electronic states of the quantum-confined perovskite rather than chiral ligand-induced stereoselective aggregation.
Bis‐isoindigos: New Electron‐Deficient Building Blocks for Constructing Conjugated Polymers with Extended Electron Delocalization
Abstract Incorporation of acceptor‐acceptor (A‐A) type moieties into donor‐acceptor (D‐A) type conjugated polymers becomes a new strategy to tune their electronic properties. In this work, we first demonstrate an efficient convergent route to prepare isoindigo‐based A‐A type building blocks ‐ bis‐isoindigos ‐ via the palladium‐catalyzed oxidative coupling. Bis‐isoindigo‐based polymers show high planarity and delocalized frontier molecular orbitals with lowered LUMO and intact HOMO energy levels, in comparison with their corresponding mono‐isoindigo counterparts. Moreover, fluorine substitution on donors only lowers HOMO levels of Bis‐IID polymers. This study asserts that the D‐A‐A strategy is effective in selectively tuning FMO energy levels of conjugated polymers, complementary to the D‐D‐A approach for the HOMO energy level tuning.
Electrochemically tunable proton-coupled electron transfer in Pd-catalyzed benzaldehyde hydrogenation
Acid-functionalization of carbon support allows enhancing the electrocatalytic activity of Pd to hydrogenate benzaldehyde to benzyl alcohol in proportion to the concentration of Brønsted acid sites. The hydrogenation rate is not enhanced when H2 is used. The rate enhancement is attributed to differences in the hydrogenation mechanism between the electrochemical and the H2 induced hydrogenations, in particular to the participation of hydronium ions formed at Brønsted acid sites at the perimeter of metal particles in proton coupled electron transfer.
Coordination Tunes Selectivity: Two-Electron Oxygen Reduction on High-Loading Molybdenum Single-Atom Catalysts
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The Role of a Dipeptide Outer-Coordination Sphere on H2 -Production Catalysts: Influence on Catalytic Rates and Electron Transfer
The outer-coordination sphere of enzymes acts to fine-tune the active site reactivity and control catalytic rates, suggesting that incorporation of analogous structural elements into molecular catalysts may be necessary to achieve rates comparable to those observed in enzyme systems at low overpotentials. In this work, we evaluate the effect of an amino acid and dipeptide outer-coordination sphere on [Ni(PPh2NPh-R2)2]2+ hydrogen production catalysts. A series of 12 new complexes containing non-natural amino acids or dipeptides were prepared to test the effects of positioning, size, polarity and aromaticity on catalytic activity. The non-natural amino acid was either 3-(meta- or para-aminophenyl)propionic acid terminated as an acid, an ester or an amide. Dipeptides consisted of one of the non-natural amino acids coupled to one of four amino acid esters: alanine, serine, phenylalanine or tyrosine. All of the catalysts are active for hydrogen production, with rates averaging ~1000 s-1, 40% faster than the unmodified catalyst. Structure and polarity of the aliphatic or aromatic side chains of the C-terminal peptide do not strongly influence rates. However, the presence of an amide bond increases rates, suggesting a role for the amide in assisting catalysis. Overpotentials were lower with substituents at the N-phenyl meta position. This is consistent with slower electron transfer in the less compact, para-substituted complexes, as shown in digital simulations of catalyst cyclic voltammograms and computational modeling of the complexes. Combining the current results with insights from previous results, we propose a mechanism for the role of the amino acid and dipeptide based outer-coordination sphere in molecular hydrogen production catalysts.
A DFT Study on Structural, Electronic Mechanical and Thermodynamic Properties of 5f-Electron System BaAmO{sub 3}
The structural, electronic, mechanical and thermodynamic properties of the perovskite oxide BaAmO{sub 3} have been predicted using the full-potential linearized augmented plane wave (FP-LAPW) method. The equilibrium lattice constant, bulk modulus and pressure derivative were computed using different exchange correlations. The optimization of structure was carried out in ferromagnetic, anti-ferromagnetic and non-magnetic states, and the compound was found to be stable in the ferromagnetic state. A systematic study on the band structure and density of states was accomplished using generalized gradient approximation (GGA), Hubbard approximation (GGA + U) and modified Becke–Johnson exchange potential (mBJ),and the compound was found to have a half-metallic nature in all the approximations. The calculated total spin magnetic moment was found to be 5 μ{sub B} in all the approximations used. The second-order elastic constants, Young modulus, shear modulus, Poisson ratio and anisotropic factor have also been calculated. In order to have a complete understanding of BaAmO{sub 3}, the thermodynamic properties were studied in the pressure range of 0 to 40 GPa and the temperature range extending from 0 to 600 K.
Localized melt-scan strategy for site specific control of grain size and primary dendrite arm spacing in electron beam additive manufacturing
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Emerging hierarchical dislocation structures: Insights from scanning electron microscopy-electron backscatter diffraction in situ tensile testing and multifractal analysis
Understanding the evolution of dislocation structures during plastic deformation is critical for predicting the mechanical performance of metallic materials. In this work, we applied in situ scanning electron microscopy/electron backscatter diffraction tensile testing combined with multifractal (MF) analysis to assess deformation-induced dislocation structure evolution in solution-annealed 304 L stainless steel, both in its as-received and neutron-irradiated states (5.4 displacements per atom). The analysis of kernel average misorientation patterns revealed the formation of hierarchical dislocation arrangements that exhibit clear MF scaling behavior. Despite pronounced visual differences between nonirradiated and irradiated specimens—most notably, the appearance of dislocation channels after irradiation—the singularity spectra suggest that both conditions give rise to similar underlying hierarchical structures. MF analysis provides a quantitative measure of the spatial complexity and self-organization of dislocation patterns, highlighting the accelerated emergence and evolution of the dislocation structures in irradiated polycrystalline materials, as well as the limitation of their spatial extent. The findings indicate that irradiation not only modifies microstructure but also alters correlation-driven dislocation organization. More generally, they demonstrate that MF analysis is a powerful tool for probing mesoscale deformation mechanisms.
Probing the Structures and Electronic Properties of Dual-Phosphorus-Doped Gold Cluster Anions (AunP-2, n = 1–8): A Density functional Theory Investigation
The geometries of gold clusters doped with two phosphorus atoms, (AunP-2, n = 1–8) were investigated using density functional theory (DFT) methods. Various two-dimensional (2D) and three-dimensional (3D) structures of the doped clusters were studied. The results indicate that the structures of dual-phosphorus-doped gold clusters exhibit large differences from those of pure gold clusters with small cluster sizes. In our study, as for Au6P-2, two cis–trans isomers were found. The global minimum of Au8P-2 presents a similar configuration to that of Au-20, a pyramid-shaped unit, and the potential novel optical and catalytic properties of this structure warrant further attention. The higher stability of AunP-2 clusters relative to Au-n+2 (n = 1–8) clusters was verified based on various energy parameters, and the results indicate that the phosphorus atom can improve the stabilities of the gold clusters. We then explored the evolutionary path of (n = 1–8) clusters. We found that AunP-2 clusters exhibit the 2D–3D structural transition at n = 6, which is much clearer and faster than that of pure gold clusters and single-phosphorus-doped clusters. The electronic properties of AunP-2 (n = 1–8) were then investigated. The photoelectron spectra provide additional fundamental information on the structures and molecular orbitals shed light on the evolution of AunP-2 (n = 1–8). Natural bond orbital (NBO) described the charge distribution in stabilizing structures and revealed the strong relativistic effects of the gold atoms.
Diagenetic changes in macro- to nano-scale porosity in the St. Peter Sandstone: An (ultra) small angle neutron scattering and backscattered electron imaging analysis
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First principles study of the structural, electronic, and optical properties of Sn 2+ -doped ZnO–P 2 O 5 glasses [First principles study of the structural, electronic and optical properties of Sn-doped ZnO-P2O5 glasses]
The atomic-structural, electronic, and optical properties of Sn-doped ZnO–P 2 O 5 glasses are examined using combined semi-empirical and density functional theory calculations. From model structures for two different ZnO–P 2 O 5 glass compositions, it is found that these glasses consist of nearly ideal tetrahedral PO 4 unit and largely distorted ZnO 4 and ZnO 5 units. The concentration of ZnO 5 units is calculated to increase and exceed that of ZnO 4 as the amount of ZnO in the glass is increased. Also, the concentration of terminal oxygen atoms shared by two Zn neighbors is largely increased for 70ZnO:30P 2 O 5 (70:30) glass compared to 60:40 glass, which can be rationalized by electrostatic bond strength calculations. Regarding medium-range order, calculations show that Q 1 and Q 2 structures (where Q n refers to structures containing n bridging oxygen atoms on PO 4 tetrahedra) are dominant for the 60:40 glass, while Q 0 and Q 1 prevail for the 70:30 glass, in good agreement with experimental observations. For the Sn-doped ZnO–P 2 O 5 glass, various Sn coordination geometries are found, with trigonal pyramidal SnO 3 and largely distorted pyramidal SnO 4 configurations being dominant and a small fraction of two-fold and five-fold coordinated Sn configurations also present. From combined cluster and glass model calculations, two-fold coordinated Sn are found to exhibit slightly smaller optical transition energy than three-fold and four-fold coordinated Sn. However, local variations in coordination structures throughout the glass likely result in a broad singlet transition (S 0 →S 1 ) around 5.4 eV for all the different Sn configurations. Finally, a triplet transition (S 0 →T 1 ) driven by spin-orbit coupling can occur around 4.5 – 4.8 eV, but the magnitude of this transition is predicted to be much smaller than the spin-allowed singlet transition.