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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 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Identifying the first folded alkylbenzene via ultraviolet, infrared, and Raman spectroscopy of pentylbenzene through decylbenzene

The conformational preferences of pentyl- through decylbenzene are studied under jet-cooled conditions in the gas phase. Laser-induced fluorescence excitation spectra, fluorescence-dip infrared spectra in the alkyl CH stretch region, and Raman spectra are combined to provide assignments for the observed conformers. Density functional theory calculations at the B3LYP-D3BJ/def2TZVP level of theory provide relative energies and normal mode vibrations that serve as inputs for an anharmonic local mode theory introduced in earlier work on alkylbenzenes with n = 2–4. This model explicitly includes anharmonic mixing of the CH stretch modes with the overtones of scissors/bend modes of the CH 2 and CH 3 groups in the alkyl chain, and is used to assign and interpret the single-conformation IR spectra. In octylbenzene, a pair of LIF transitions shifted -92 and -78 cm -1 from the all-trans electronic origin have unique alkyl CH stretch transitions that are fit by the local model to a g1g3g4 conformation in which the alkyl chain folds back over the aromatic ring π cloud. Its calculated energy is only 1.0 kJ mol -1 above the all-trans global minimum. This fold is at an alkyl chain length less than half that of the pure alkanes (n = 18), consistent with a smaller energy cost for the g1 dihedral and the increased dispersive interaction of the chain with the π cloud. Local site frequencies for the entire set of conformers from the local mode model show ‘edge effects’ that raise the site frequencies of CH 2 (1) and CH 2 (2) due to the phenyl ring and CH 2 (n - 1) due to the methyl group. The g1g3g4 conformer also shows local sites shifted up in frequency at CH 2 (3) and CH 2 (6) due to interaction with the π cloud.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Identifying the chemical and structural irreversibility in LiNi 0.8 Co 0.15 Al 0.05 O 2 – a model compound for classical layered intercalation

In this work, we extracted 95% of the electrochemically available Li from LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) by galvanostatically charging the NCA/MCMB full cell to 4.7 V. Joint powder X-ray and neutron diffraction (XRD & ND) studies were undertaken for NCA at highly charged states at the first cycle, and discharged states at different cycles. The results indicate that the bulk structure of NCA maintains the O3 structure up to the extraction of 0.90 Li per formula unit. In addition, we found that the transition metal layer becomes more disordered along the c-axis than along the a- and b-axes upon charging. This anisotropic disorder starts to develop no later than 4.3 V on charge and continues to grow until the end of charge. As Li is re-inserted during discharge, the structure that resembles the pristine NCA is recovered. The irreversible loss of Li and the migration of Ni to the Li layer have been quantified by the joint XRD and ND refinement and the results were further verified by solid state 7 Li NMR and magnetic measurements. Thus, our work clearly demonstrates that the NCA bulk retains a robust, single phase O3 structure throughout the wide delithiation range (up to 0.9 Li per formula unit of NCA) and is suitable for higher energy density usage with proper modifications.

25 ENERGY STORAGE↗
DOE OSTI2018

Identifying the acceptor state in NiO hole collection layers: direct observation of exciton dissociation and interfacial hole transfer across a Fe 2 O 3 /NiO heterojunction

NiO is widely utilized as a hole transport layer in solar energy devices where light absorption in a photoactive layer is followed by charge separation and hole injection into a NiO collection layer. Due to the complex electronic structure of the hybridized valence band in NiO, the chemical nature of the hole acceptor state has remained an open question, despite the fact that hole localization in this material significantly influences device efficiency. To comment on this, we present results of ultrafast charge carrier dynamics in a NiO based model heterojunction (Fe 2 O 3 /NiO) using extreme ultraviolet reflection–absorption (XUV-RA) spectroscopy. Element specific XUV-RA spectroscopy demonstrates the formation of transient Ni 3+ within 10 ps following selective photoexcitation of the underlying Fe 2 O 3 substrate. This indicates that hole transfer in this system occurs to NiO valence band states composed of significant Ni 3d character. Additionally, we show that this hole injection process proceeds via a two-step sequential mechanism where fast, field-driven exciton dissociation occurs in Fe 2 O 3 in 680 ± 60 fs, followed by subsequent hole injection to NiO in 9.2 ± 2.9 ps. Furthermore, these results reveal the chemical nature of the hole acceptor state in widely used NiO hole transport layers and provides a direct observation of exciton dissociation and interfacial hole transfer in this model system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Identifying hydroxylated copper dimers in SSZ-13 via UV-vis-NIR spectroscopy

Cu-Exchanged zeolites are promising materials for the selective conversion of methane to methanol. Their activity is attributed to the presence of small Cu-oxo and Cu-hydroxy clusters, but the nature of active centers in various zeolite structures is still under debate. In this contribution, we combine time dependent density functional theory with spin–orbit coupling to predict the optical spectra of various Cu monomers and dimers in SSZ-13. As a result, we furthermore compare theoretical results to experimental measurements and find that the presence of Cu-hydroxy dimers and Cu monomers could potentially explain the experimentally observed UV-vis-NIR spectra.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Identifying biochemical constituents involved in the mycosynthesis of zinc oxide nanoparticles

Filamentous fungi are known to secrete biochemicals that drive the synthesis of nanoparticles (NPs) that vary in composition, size, and shape; a process deemed mycosynthesis. Following the introduction of precursor salts directly to the fungal mycelia or their exudates, mycosynthesis proceeds at ambient temperature and pressure, and near neutral pH, presenting significant energy and cost savings over traditional chemical or physical approaches. The mycosynthesis of zinc oxide (ZnO) NPs by various fungi exhibited a species dependent morphological preference for the resulting NPs, suggesting that key differences in the biochemical makeup of their individual exudates may regulate the controlled nucleation and growth of these different morphologies. Metabolomics and proteomics of the various fungal exudates suggest that metal chelators, such as hexamethylenetetramine, present in high concentrations in exudates of Aspergillus versicolor are critical for the production dense, well-formed, spheroid nanoparticles. Further, the results also corroborate that the proteinaceous material in the production of ZnO NPs serves as a surface modifier, or protein corona, preventing excessive coagulation of the NPs. Collectively, these findings suggest that NP morphology is regulated by the small molecule metabolites, and not proteins, present in fungal exudates, establishing a deeper understanding of the factors and mechanism underlying mycosynthesis of NPs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Resurrection of ancestral effector caspases identifies novel networks for evolution of substrate specificity

Apoptotic caspases evolved with metazoans more than 950 million years ago (MYA), and a series of gene duplications resulted in two subfamilies consisting of initiator and effector caspases. The effector caspase genes (caspases-3, -6, and -7) were subsequently fixed into the Chordata phylum more than 650 MYA when the gene for a common ancestor (CA) duplicated, and the three effector caspases have persisted throughout mammalian evolution. All caspases prefer an aspartate residue at the P1 position of substrates, so each caspase evolved discrete cellular roles through changes in substrate recognition at the P4 position combined with allosteric regulation. We examined the evolution of substrate specificity in caspase-6, which prefers valine at the P4 residue, compared with caspases-3 and -7, which prefer aspartate, by reconstructing the CA of effector caspases (AncCP-Ef1) and the CA of caspase-6 (AncCP-6An). We show that AncCP-Ef1 is a promiscuous enzyme with little distinction between Asp, Val, or Leu at P4. The specificity of caspase-6 was defined early in its evolution, where AncCP-6An demonstrates a preference for Val over Asp at P4. Structures of AncCP-Ef1 and of AncCP-6An show a network of charged amino acids near the S4 pocket that, when combined with repositioning a flexible active site loop, resulted in a more hydrophobic binding pocket in AncCP-6An. The ancestral protein reconstructions show that the caspase-hemoglobinase fold has been conserved for over 650 million years and that only three substitutions in the scaffold are necessary to shift substrate selection toward Val over Asp.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Distribution system versus bulk power system: identifying the source of electric service interruptions in the US

This study reports on the results from efforts by the Institute of Electric and Electronics Engineers (IEEE) Distribution Reliability Working Group (DRWG) and the U.S. Energy Information Administration (EIA) to improve the usefulness of reliability metrics by developing and then applying consistent, yet distinct measures of the continuity of supply based on the portion of the electric power system from which power interruptions originate: the lower voltage distribution system versus the high‐voltage bulk power system. The modified metrics better support reliability planning in the US because they separately measure the effectiveness of actions to improve reliability made by the two distinct groups of firms (and their regulators or oversight bodies) that are responsible for planning and operating each portion of the US electric power system. The authors then present for the first time quantitative information on the reliability of each portion of the US electric power system. When reliability is measured using the system average interruption duration index and the system average interruption frequency index, they find that the distribution system accounts for at least 94 and 92%, respectively, of all interruptions. They also find that these relationships have been stable over the recent past.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2015

Optically confined polarized resonance Raman studies in identifying crystalline orientation of sub-diffraction limited AlGaN nanostructure

An optical characterization tool of Raman spectroscopy with extremely weak scattering cross section tool is not popular to analyze scattered signal from a single nanostructure in the sub-diffraction regime. In this regard, plasmonic assisted characterization tools are only relevant in spectroscopic studies of nanoscale object in the sub-diffraction limit. We have reported polarized resonance Raman spectroscopic (RRS) studies with strong electron-phonon coupling to understand the crystalline orientation of a single AlGaN nanowire of diameter ∼100 nm. AlGaN nanowire is grown by chemical vapor deposition technique using the catalyst assisted vapor-liquid-solid process. The results are compared with the high resolution transmission electron microscopic analysis. As a matter of fact, optical confinement effect due to the dielectric contrast of nanowire with respect to that of surrounding media assisted with electron-phonon coupling of RRS is useful for the spectroscopic analysis in the sub-diffraction limit of 325 nm (λ/2N.A.) using an excitation wavelength (λ) of 325 nm and near ultraviolet 40× far field objective with a numerical aperture (N.A.) value of 0.50.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Chemical potential shift in organic field-effect transistors identified by soft X-ray operando nano-spectroscopy

A chemical potential shift in an organic field effect transistor (OFET) during operation has been revealed by soft X-ray operando nano-spectroscopy analysis performed using a three-dimensional nanoscale electron-spectroscopy chemical analysis system. OFETs were fabricated using ultrathin (3 ML or 12 nm) single-crystalline C10-DNBDT-NW films on SiO{sub 2} (200 nm)/Si substrates with a backgate electrode and top source/drain Au electrodes, and C 1s line profiles under biasing at the backgate and drain electrodes were measured. When applying −30 V to the backgate, there is C 1s core level shift of 0.1 eV; this shift can be attributed to a chemical potential shift corresponding to band bending by the field effect, resulting in p-type doping.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Identifying site-dependent effects of an extra Co atom on electronic states of single Co-phthalocyanine molecule

We investigate the modification of electronic properties of single cobalt phthalocyanine (CoPc) molecule by an extra Co atom co-adsorbed on Au (111) surface using scanning tunneling microscopy (STM), joint with density functional theory (DFT) calculations. By manipulating CoPc molecules using the STM tip to contact individually adsorbed Co atom, two types of relatively stable complexes can be formed, denoted as CoPc-Co(I) and CoPc-Co(II). In CoPc-Co(I), the Co atom is at an intramolecular site close to aza-N atom of CoPc, which induces significant modifications of the electronic states of CoPc, such as energy shifts and splitting of nonlocal molecular orbitals. However, in CoPc-Co(II) where the Co atom is underneath a benzene lobe of CoPc, it only slightly modifies the electronic states of CoPc, and mainly local characteristics of specific molecular orbitals are affected, even though CoPc-Co(II) is more stable than CoPc-Co(I). Our DFT calculations give consistent results with the experiments, and related analyses based on the molecular orbital theory reveal mechanism behind the experimental observations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Hall and Seebeck measurements estimate the thickness of a (buried) carrier system: Identifying interface electrons in In-doped SnO{sub 2} films

We propose a simple method based on the combination of Hall and Seebeck measurements to estimate the thickness of a carrier system within a semiconductor film. As an example, this method can distinguish “bulk” carriers, with homogeneous depth distribution, from “sheet” carriers, that are accumulated within a thin layer. The thickness of the carrier system is calculated as the ratio of the integral sheet carrier concentration, extracted from Hall measurements, to the volume carrier concentration, derived from the measured Seebeck coefficient of the same sample. For rutile SnO{sub 2}, the necessary relation of Seebeck coefficient to volume electron concentration in the range of 3 × 10{sup 17} to 3 × 10{sup 20 }cm{sup −3} has been experimentally obtained from a set of single crystalline thin films doped with varying Sb-doping concentrations and unintentionally doped bulk samples, and is given as a “calibration curve.” Using this calibration curve, our method demonstrates the presence of interface electrons in homogeneously deep-acceptor (In) doped SnO{sub 2} films on sapphire substrates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗