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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

The energy level alignment at metal–molecule interfaces using Wannier–Koopmans method

We apply a recently developed Wannier-Koopmans method (WKM), based on density functional theory (DFT), to calculate the electronic energy level alignment at an interface between a molecule and metal substrate. We consider two systems: benzenediamine on Au (111), and a bipyridine-Au molecular junction. The WKM calculated level alignment agrees well with the experimental measurements where available, as well as previous GW and DFT + Σ results. These results suggest that the WKM is a general approach that can be used to correct DFT eigenvalue errors, not only in bulk semiconductors and isolated molecules, but also in hybrid interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Peculiarities of the SERS Spectra of 4,4′-Bipyridine Molecule in a Single Molecule Detection Regime

The paper describes briefly main statements of the theory of the SERS spectra with regards to the single molecule regime, when the enhancement achieves the values ~10{sup 14}−10{sup 15}. Analysis of the spectra of 4,4′-bypyridine, obtained on the dimer lattice of sharp nanoparticles points out that the observed enhancement is caused exclusively by a strong quadrupole light-molecule interaction, which manifests in the presence of lines, caused by vibrations with the unit irreducible representations of the D{sub 2} and D{sub 2h} symmetry groups, which apparently describe the symmetry properties of the molecule. The study of the spectra, obtained by tip enhanced spectroscopy demonstrates that the strong quadrupole light-molecule interaction still has a governing role, however the strong dipole interaction still manifests in the existence of very weak forbidden lines. This result apparently is associated with another experimental geometry.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Diversity of Chemical Bonding and Oxidation States in MS 4 Molecules of Group 8 Elements

The geometric and electronic ground-state structures of six MS 4 molecules (M = group-8 metals Fe, Ru, Os, Hs, Sm, and Pu) have been studied by using quantum-chemical density-functional and correlated wave-function approaches. The MS 4 species are compared to analogous MO 4 species recently investi-gated (Inorg. Chem. 2016, 55: 4616). Metal oxidation state (MOS) of high value VIII appears in low- spin singlet Td geometric species (Os,Hs)S 4 and (Ru,Os,Hs)O 4 , whereas low MOS=II appears in high- spin septet D 2d species Fe(S 2 ) 2 and (slightly excited) metastable Fe(O 2 ) 2 . The ground states of all other molecules have intermediate MOS values, containing S 2- , S 2 2- , S2 1- (and resp. O 2- -, O 1- , O 2 2- , O 2 1- ) ligands, bonded by ionic, covalent and correlative contributions.

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

Quantum Confinement and Decoherence Effect on Excited Electron Transfer at the Semiconductor–Molecule Interface: A First-Principles Dynamics Study

Excited electron dynamics at the semiconductor–molecule interface play a vital role in many solar energy conversion applications and beyond. First-principles dynamics simulation is used to study how excited electron dynamics in a type-II semiconductor–molecule interface is affected when the surface of a bulk semiconductor is replaced with that of a quantum dot. In particular, the interface between the hydrogen-terminated silicon(111) surface and a simple organic molecule is investigated. Quantum confinement was found to significantly slow down the excited electron relaxation and the interfacial transfer of the excited electron. Additionally, the role of decoherence was examined. The decoherence affects the dynamics much more significantly for the interface with the quantum dot, while the bulk surface case is affected only marginally by it. Finally, compared to the excited electron relaxation within the quantum dot, the decoherence effect was found to slow down the interfacial transfer from the quantum dot to the molecule by more than an order of magnitude, exhibiting a significant quantum Zeno effect.

charge transfer↗
DOE OSTI2021

Ultrasound-Assisted Nonthermal, Nonequilibrium Separation of Organic Molecules from Their Binary Aqueous Solutions: Effect of Solute Properties on Separation

The separation of organic molecules in downstream processes, such as distillation, plays a vital role in biobased chemical production. A comprehensive study was performed here using ultrasonic energy to separate 11 organic molecules from their binary aqueous solutions under nonthermal, nonequilibrium, and phase-change free conditions. A batch sonoseparator with a three-stage mist collection unit allowed direct analysis of ultrasound-generated mist with an HPLC/GC and differentiation and quantification of the vapor and mist. The results showed that the alcohols (1-butanol, ethanol, 1-propanol, and methanol) and acetone were enriched in the ultrasound-generated mist with enrichment ratios of 3.2–5. On the other hand, ethylene glycol, glycerol, γ-valerolactone (GVL), glucose, and sucrose were diluted with dilution ratios in the range of 2.04–15.7 in the mist and vapor generated by ultrasound (or concentrated in the bulk solution). No enrichment nor dilution of acetic acid was observed. The role of various physicochemical parameters such as dynamic viscosity, surface tension, Henry’s law of solubility constant, vapor pressure, and octanol–water partition coefficient in the enrichment was examined. Furthermore, the hydrophobicity of the organic molecules represented by the octanol–water partition coefficient was found to play a crucial role in determining the separation characteristics of the molecules in ultrasound-generated mist and vapor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Intrinsically patterned two-dimensional materials for selective adsorption of molecules and nanoclusters

Two-dimensional (2D) materials have been studied extensively as monolayers, vertical or lateral heterostructures. To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe 2 can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Adsorption of two gas molecules at a single metal site in a metal–organic framework

One strategy to markedly increase the gas storage capacity of metal–organic frameworks is to introduce coordinatively-unsaturated metal centers capable of binding multiple gas molecules. Herein, we provide an initial demonstration that a single metal site within a framework can support the terminal coordination of two gas molecules—specifically hydrogen, methane, or carbon dioxide.

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

Time-resolved imaging of atoms and molecules in laser-produced uranium plasmas

Gas-phase oxidation of uranium (U), plume chemistry, and its impact on optical emission features of the uranium plasma are investigated. Plasmas were produced via nanosecond laser ablation of a natural uranium target in a chamber where uranium oxidation was controlled by varying the oxygen partial pressure within argon cover gas. Monochromatic imaging of uranium atoms and monoxide molecules was performed using narrowband optical filters, which clearly reveals the spatio-temporal evolution of these species in the plasma. Uranium oxides are found to be formed at the plasma edges, where lower temperatures favor molecular recombination. Segregation between the distribution of uranium atoms and monoxide species is observed at later times of plasma evolution, and is more apparent at lower oxygen partial pressures. At higher oxygen partial pressures, significant variation in plume morphology is noticed for UO species, which is attributed to higher rate of oxide (UxOy) formation at the plume edges. The monochromatic images of U atoms and molecules and corresponding spectral features at various oxygen partial pressures presented here provide a unique insight into gas-phase, high-temperature uranium oxidation, and its chemistry and have implications for a wide range of nuclear applications, from stand-off detection of radioisotopes to forensics and safeguards.

(140.3440) Laser-induced breakdown, (280.4788) Opt↗
DOE OSTI2020

Determining plasmonic hot-carrier energy distributions via single-molecule transport measurements

Hot carriers in plasmonic nanostructures, generated via plasmon decay, play key roles in applications such as photocatalysis and in photodetectors that circumvent bandgap limitations. However, direct experimental quantification of steady-state energy distributions of hot carriers in nanostructures has so far been lacking. We present transport measurements from single-molecule junctions, created by trapping suitably chosen single molecules between an ultrathin gold film supporting surface plasmon polaritons and a scanning probe tip, that can provide quantification of plasmonic hot-carrier distributions. Our results show that Landau damping is the dominant physical mechanism of hot-carrier generation in nanoscale systems with strong confinement. The technique developed in this work will enable quantification of plasmonic hot-carrier distributions in nanophotonic and plasmonic devices.

Science & Technology - Other Topics↗
NASA NTRS2006

Laboratory Studies of Stabilities of Heterocyclic Aromatic Molecules: Suggested Gas Phase Ion-Molecule Routes to Production in Interstellar Gas Clouds

Several ring compounds have been detected in interstellar gas clouds, ISC, including the aromatic, benzene. Polycyclic aromatic hydrocarbons, PAHs, have been implicated as carriers of diffuse interstellar bands (DIBs) and unidentified infrared (UIR) bands. Heterocyclic aromatic rings of intermediate size containing nitrogen, possibly PreLife molecules, were included in early searches but were not detected and a recent search for Pyrimidine was unsuccessful. Our laboratory investigations of routes to such molecules could establish their existence in ISC and suggest conditions under which their concentrations would be maximized thus aiding the searches. The stability of such ring compounds (C5H5N, C4H4N2, C5H11N and C4H8O2) has been tested in the laboratory using charge transfer excitation in ion-molecule reactions. The fragmentation paths, including production of C4H4(+), C3H3N(+) and HCN, suggest reverse routes to the parent molecules, which are presently under laboratory investigation as production sources.

Adams, Nigel G.↗
DOE OSTI2015

A systematic benchmark of the ab initio Bethe-Salpeter equation approach for low-lying optical excitations of small organic molecules

The predictive power of the ab initio Bethe-Salpeter equation (BSE) approach, rigorously based on many-body Green’s function theory but incorporating information from density functional theory, has already been demonstrated for the optical gaps and spectra of solid-state systems. Interest in photoactive hybrid organic/inorganic systems has recently increased and so has the use of the BSE for computing neutral excitations of organic molecules. However, no systematic benchmarks of the BSE for neutral electronic excitations of organic molecules exist. Here, we study the performance of the BSE for the 28 small molecules in Thiel’s widely used time-dependent density functional theory benchmark set [Schreiber et al., J. Chem. Phys. 128, 134110 (2008)]. We observe that the BSE produces results that depend critically on the mean-field starting point employed in the perturbative approach. We find that this starting point dependence is mainly introduced through the quasiparticle energies obtained at the intermediate GW step and that with a judicious choice of starting mean-field, singlet excitation energies obtained from BSE are in excellent quantitative agreement with higher-level wavefunction methods. The quality of the triplet excitations is slightly less satisfactory.

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

High‐Efficiency All‐Small‐Molecule Organic Solar Cells Based on an Organic Molecule Donor with Alkylsilyl‐Thienyl Conjugated Side Chains

Abstract Two medium‐bandgap p‐type organic small molecules H21 and H22 with an alkylsily‐thienyl conjugated side chain on benzo[1,2‐ b :4,5‐ b ′]dithiophene central units are synthesized and used as donors in all‐small‐molecule organic solar cells (SM‐OSCs) with a narrow‐bandgap n‐type small molecule 2,2′‐((2Z,2′Z)‐((4,4,9,9‐tetrahexyl‐4,9‐dihydro‐ s ‐indaceno[1,2‐ b :5,6‐ b ′]dithiophene‐2,7‐diyl)bis(methanylylidene))bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IDIC) as the acceptor. In comparison to H21 with 3‐ethyl rhodanine as the terminal group, H22 with cyanoacetic acid esters as the terminal group shows blueshifted absorption, higher charge‐carrier mobility and better 3D charge pathway in blend films. The power conversion efficiency (PCE) of the SM‐OSCs based on H22:IDIC reaches 10.29% with a higher open‐circuit voltage of 0.942 V and a higher fill factor of 71.15%. The PCE of 10.29% is among the top efficiencies of nonfullerene SM‐OSCs reported in the literature to date.

Bin, Haijun↗
DOE OSTI2020

Electrode-molecule energy level offsets in a gold-benzene diamine-gold single molecule tunnel junction

One means for describing electron transport across single molecule tunnel junctions (MTJs) is to use density functional theory (DFT) in conjunction with a nonequilibrium Green’s function formalism. This description relies on interpreting solutions to the Kohn–Sham (KS) equations used to solve the DFT problem as quasiparticle (QP) states. Many practical DFT implementations suffer from electron self-interaction errors and an inability to treat charge image potentials for molecules near metal surfaces. For MTJs, the overall effect of these errors is typically manifested as an overestimation of electronic currents. Correcting KS energies for self-interaction and image potential errors results in MTJ current–voltage characteristics in close agreement with measured currents. An alternative transport approach foregoes a QP picture and solves for a many-electron wavefunction on the MTJ subject to open system boundary conditions. It is demonstrated that this many-electron method provides similar results to the corrected QP picture for electronic current. The analysis of these two distinct approaches is related through corrections to a junction’s electronic structure beyond the KS energies for the case of a benzene diamine molecule bonded between two gold electrodes.

Szepieniec, Mark S.↗
DOE OSTI2025

Discovery of Signaling Small Molecules (e.g. quorum sensing molecules) from the Microbiome

Microbial communities are shaped through the interactions between their microbial members and the environment (microbe-microbe and host-microbe interactions). Signal transduction pathways in the microbiome are often modulated through the small molecule products of microbial biosynthetic gene clusters (BGCs). Advances in 16S rRNA profiling and shotgun metagenomics have revolutionized our understanding about the microbial composition of various communities and their BGCs. Environmental metagenomes contain thousands of BGCs with uncharacterized small molecule products that potentially play roles in signal transduction. The overarching aim of this proposal was to develop computational techniques for discovering these small molecules and characterizing their bioactivity.

59 BASIC BIOLOGICAL SCIENCES↗