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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Probing Hydrogen-Bonding Interactions of Water Molecules Adsorbed on Silica, Sodium Calcium Silicate, and Calcium Aluminosilicate Glasses

Vibrational sum frequency generation (SFG) spectroscopy was used to study how hydrogen bonding interactions of physisorbed water layers vary with the glass composition and surface condition. Three different glass materials were used: amorphous silica (fused quartz), sodium calcium silicate (also called soda lime silica), and calcium aluminosilicate (boron-/fluorine-free E-glass). Two different surface conditions were compared: (i) a mechanically polished, fire-polished, and then annealed surface and (ii) an acid-leached surface (pH 1, 90 °C, 24 h). Compositional and structural information obtained by X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and attenuated total reflection infrared spectroscopy were correlated with SFG spectral features. The temperature dependence of SFG spectral features revealed that regardless of the glass composition, the glass surface is free of physisorbed water at 250 °C, and during cooling in ambient air, it starts absorbing water at a temperature corresponding to a relative humidity of 1–2%. Humidity-controlled SFG measurements at room temperature showed that the hydrogen bonding interactions of water physisorbed on the glass surface cleaned with UV/O 3 are quite different depending on the glass composition and surface preparation history. This finding will be useful in understanding how surface properties of different glasses are altered by humidity in ambient air.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Electron–Rotor Interaction in Organic–Inorganic Lead Iodide Perovskites Discovered by Isotope Effects

We report on the carrier-rotor coupling effect in perovskite organic-inorganic hybrid lead iodide (CH3NH3PbI3) compounds discovered by isotope effects. Deuterated organic-inorganic perovskite compounds including CH3ND3PbI3, CD3NH3PbI3, and CD3ND3PbI3 were synthesized. Devices made from regular CH3NH3PbI3 and deuterated CH3ND3PbI3 exhibit comparable performance in band gap, current-voltage, carrier mobility, and power conversion efficiency. However, a time-resolved photoluminescence (TRPL) study reveals that CH3NH3PbI3 exhibits notably longer carrier lifetime than that of CH3ND3PbI3, in both thin-film and single crystal formats. Furthermore, the comparison in carrier lifetime between CD3NH3PbI3 and CH3ND3PbI3 single crystals suggests that vibrational modes in methylammonium (MA(+)) have little impact on carrier lifetime. In contrast, the fully deuterated compound CD3ND3PbI3 reconfirmed the trend of decreasing carrier lifetime upon the increasing moment of inertia of cationic MA(+). Polaron model elucidates the electron-rotor interaction.

Gong, Jue↗
DOE OSTI2018

Surface Organometallic Chemistry of Supported Iridium(III) as a Probe for Organotransition Metal–Support Interactions in C–H Activation

Systematic study of the interactions between organometallic catalysts and metal oxide support materials is essential for the realization of rational design in heterogeneous catalysis. Herein we describe the stoichiometric and catalytic chemistry of a [Cp*(PMe 3 )Ir(III)] complex chemisorbed on a variety of acidic metal oxides as a multifaceted probe for stereoelectronic communication between the support and organometallic center. Electrophilic bond activation was explored in the context of stoichiometric hydrogenolysis as well as catalytic H/D exchange. Further information was obtained from the observation of processes related to dynamic exchange between grafted organometallic species and those in solution. The supported organometallic species were characterized by a variety of spectroscopic techniques including dynamic nuclear polarization-enhanced solid-state NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray absorption spectroscopy. Finally, strongly acidic modified metal oxides such as sulfated zirconia engender high levels of activity toward electrophilic bond activation of both sp 2 and sp 3 C–H bonds, including the rapid deuteration of methane at room temperature; however, the global trend for the supports studied here does not suggest a direct correlation between activity and surface Brønsted acidity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Polarity governs atomic interaction through two-dimensional materials

The objective of this project is to develop two-dimensional material-based layer transfer (2DLT) for high-efficiency, low-cost III-V solar cells. More specifically, in short term, the team will develop 2DLT for cost-cost, high-throughput GaAs single-junction solar cells. The team will develop ultraclean high yield graphene transfer on GaAs and optimize the remote homoepitaxy process to obtain dislocation-free single-crystalline GaAs on graphene whose crystalline quality is identical to that of the GaAs wafer [1,2]. The team will develop the 2DLT process for a solar cell with highest achievable efficiency. The team will also strive to target GaAs solar cells with efficiency of 25~29% before and after the transfer, and reuse the substrate multiple times without CMP by damage-free transfer process enabled by 2DLT. Our team is partnered with industrial collaborators to obtain World record efficiency of flexible GaAs solar cells. Once the concept is fully realized for the GaAs solar cells, the team will expand the concept for multiple-junction solar cell targeting 35% efficiency with the 2DLT process in other projects.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural basis of amino acid surveillance by higher-order tRNA-mRNA interactions

Amino acid availability in Gram-positive bacteria is monitored by T-box riboswitches. T-boxes directly bind tRNAs, assess their aminoacylation state, and regulate the transcription or translation of downstream genes to maintain nutritional homeostasis. Here in this paper, we report cocrystal and cryo-EM structures of Geobacillus kaustophilus and Bacillus subtilis T-box–tRNA complexes, detailing their multivalent, exquisitely selective interactions. The T-box forms a U-shaped molecular vise that clamps the tRNA, captures its 3' end using an elaborate ‘discriminator’ structure, and interrogates its aminoacylation state using a steric filter fashioned from a wobble base pair. In the absence of aminoacylation, T-boxes clutch tRNAs and form a continuously stacked central spine, permitting transcriptional readthrough or translation initiation. A modeled aminoacyl disrupts tRNA-T-box stacking, severing the central spine and blocking gene expression. Our data establish a universal mechanism of amino acid sensing on tRNAs and gene regulation by T-box riboswitches and exemplify how higher-order RNA-RNA interactions achieve multivalency and specificity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Energy band structure and metal-organic interactions in tetracyanoquinodimethane (TCNQ) and N,N'-dicyanoquinonediimine (DCNQI) materials

The interplay of metal orbitals in metal TCNQ (7,7,8,8-tetracyanoquinodimethane) and DCNQI (N,N'-dicyanoquinonediimine) complexes is investigated on the basis of molecular orbital calculations. For the M(TCNQ) materials, where M = Na, K, Rb, Cs, Tl, Cu, and Ag, the conductivity decreases with the increase in dimerization. Some Cu compounds, however, exhibit uniform columns and higher conducting properties, for which hybridization of the Cu 3d orbitals with the organic radicals is expected. The energy level of Tl 6s is slightly more separated from the TCNQ LUMO, but could potentially mediate similar metal–organic interactions. A simple analytical energy band model is proposed to evaluate the hybridization of the metal orbitals, providing the criteria to form a closed Fermi surface. Accordingly, semiconducting and comparatively high-conducting states of many Cu and Tl TCNQ complexes with uniform columns are to be regarded as a Mott insulating state rather than a Peierls insulating state.

Kojima, Hirotaka↗
DOE OSTI2013

Watermelon-like iron nanoparticles: Cr doping effect on magnetism and magnetization interaction reversal

Chromium (Cr) forms a solid solution with iron (Fe) lattice when doped in core-shell iron -iron oxide nanocluster (NC) and shows a mixed phase of sigma (σ) FeCr and bcc Fe. The Cr dopant affects heavily the magnetization and magnetic reversal process, and causes the hysteresis loop to shrink near the zero field axis. Dramatic transformation happens from dipolar interaction (0 at. % Cr) to strong exchange interaction (8 at. % of Cr) is confirmed from the Henkel plot and delta M plot, and is explained by a water-melon model of core-shell NC system.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2017

Aggregation of cyclic polypeptoids bearing zwitterionic end-groups with attractive dipole–dipole and solvophobic interactions: a study by small-angle neutron scattering and molecular dynamics simulation

Aggregation behavior of cyclic polypeptoids bearing zwitterionic end-groups in methanol has been studied using a combination of experimental and simulation techniques. Here, the data from SANS and cryo-TEM indicate that the solution contains small clusters of these cyclic polypeptoids, ranging from a single polypeptoid chain to small oligomers, while the linear counterpart shows no cluster formation. Atomistic molecular dynamics simulations reveal that the driving force for this clustering behavior is due to the interplay between the effective repulsion due to the solvation of the dipoles formed by the charged end-groups in each polypeptoid chain and the attractive forces due to dipole–dipole interactions and the solvophobic effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗