Simultaneous Successive Twinning Captured by Atomic Electron Tomography
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SEARCH · Engineering Papers
Results for “Organic electronics”
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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Substrate recognition induces sequential electron transfer across subunits in the nitrogenase-like DPOR complex
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Stabilization of NbTe 3 , VTe 3 , and TiTe 3 via Nanotube Encapsulation
The structure of MX 3 transition metal trichalcogenides (TMTs, with M a transition metal and X a chalcogen) is typified by one-dimensional (1D) chains weakly bound together via van der Waals interactions. This structural motif is common across a range of M and X atoms (e.g. NbSe 3 , HfTe 3 , TaS 3 ), but not all M and X combinations are stable. We report here that three new members of the MX 3 family which are not stable in bulk, specifically NbTe 3 , VTe 3 , and TiTe 3 , can be synthesized in the few- to single-chain limit via nano-confined growth within the stabilizing cavity of multi-walled carbon nanotubes. Transmission electron microscopy (TEM) and atomic-resolution scanning transmission electron microscopy (STEM) reveal the chain-like nature and the detailed atomic structure. The synthesized materials exhibit behavior unique to few-chain quasi-1D structures, such as multi-chain spiraling and a trigonal anti-prismatic rocking distortion in the single-chain limit. Density functional theory (DFT) calculations provide insight into the crystal structure and stability of the materials, as well as their electronic structure.
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Toward ultrafast soft x-ray spectroscopy of organic photovoltaic devices
Novel ultrafast x-ray sources based on high harmonic generation and at x-ray free electron lasers are opening up new opportunities to resolve complex ultrafast processes in condensed phase systems with exceptional temporal resolution and atomic site specificity. In this perspective, we present techniques for resolving charge localization, transfer, and separation processes in organic semiconductors and organic photovoltaic devices with time-resolved soft x-ray spectroscopy. We review recent results in ultrafast soft x-ray spectroscopy of these systems and discuss routes to overcome the technical challenges in performing time-resolved x-ray experiments on photosensitive materials with poor thermal conductivity and low pump intensity thresholds for nonlinear effects.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Sub-system self-consistency in coupled cluster theory
Here, in this article, we provide numerical evidence indicating that the single-reference coupled-cluster (CC) energies can be calculated alternatively to their copybook definition. We demonstrate that the CC energy can be reconstructed by diagonalizing the effective Hamiltonians describing correlated sub-systems of the many-body system. In the extreme case, we provide numerical evidence that the CC energy can be reproduced through the diagonalization of the effective Hamiltonian describing sub-system composed of a single electron. These properties of the CC formalism can be exploited to design protocols to define effective interactions in sub-systems used as probes to calculate the energy of the entire system and introduce a new type of self-consistency for approximate CC approaches.
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Quantitative Determination of Electronic Effects in Free Radicals through Open-Shell Hammett Substituent Constants
Hammett substituent constants (σ), which quantify the electronic effects of functional groups, are widely used for predicting the properties of organic compounds and investigating reaction mechanisms. While these values have been obtained for a wide range of closed-shell substituents, measurements of analogous values for open-shell substituents are rare due to challenges associated with their short lifetimes. Here, in this report, we developed a combined experimental and computational approach for quantifying the electronic properties of open-shell substituents based on changes in nitrile vibrational frequencies (ν(C≡N)). By coupling pulse radiolysis and time-resolved infrared spectroscopy (PR-TRIR), we measured ν(C≡N) IR bands of 30 para - and meta -substituted benzonitriles bearing C-, N-, and S-centered radicals. A linear scaling relationship was obtained between these experimental values and values obtained from DFT calculations. Using these computed values, two different Hammett constants, σ m , and σ p + , were determined for a series of C-, N-, O-, S-, Si-, and B-centered radicals. The differences between σm and σp+ values enable the separate evaluation of inductive and resonance effects in these open-shell substituents. The results suggest that there are three classes of radicals: one is electron withdrawing (σ m , σ p + > 0), one is electron donating (σm, σp+ < 0), and one is inductively withdrawing but resonance donating (σ m > 0, σ p + < 0). Our study represents a general approach to the analysis of the electronic properties of open-shell species and has potential applications in a wide range of molecular processes involving free radical intermediates.
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Dimmable Electronic Ballast for a Gas Discharge Lamp
Titanium dioxide (TiO2) is the most efficient photocatalyst for organic oxidative degradation. TiO2 is effective not only in aqueous solution, but also in nonaqueous solvents and in the gas phase. It is photostable, biologically and chemically inert, and non-toxic. Low-energy UV light (approximately 375 nm, UV-A) can be used to photoactivate TiO2. TiO2 photocatalysis has been used to mineralize most types of organic compounds. Also, TiO2 photocatalysis has been effectively used in sterilization. This effectiveness has been demonstrated by its aggressive destruction of microorganisms, and aggressive oxidation effects of toxins. It also has been used for the oxidation of carbon monoxide to carbon dioxide, and ammonia to nitrogen. Despite having many attractive features, advanced photocatalytic oxidation processes have not been effectively used for air cleaning. One of the limitations of the traditional photocatalytic systems is the ballast that powers (lights) the bulbs. Almost all commercial off-the-shelf (COTS) ballasts are not dimmable and do not contain safety features. COTS ballasts light the UV lamp as bright as the bulb can be lit, and this results in shorter bulb lifetime and maximal power consumption. COTS magnetic ballasts are bulky, heavy, and inefficient. Several iterations of dimmable electronic ballasts have been developed. Some manifestations have safety features such as broken-bulb or over-temperature warnings, replace-bulb alert, logbulb operational hours, etc. Several electronic ballast boards capable of independently lighting and controlling (dimming) four fluorescent (UV light) bulbs were designed, fabricated, and tested. Because of the variation in the market bulb parameters, the ballast boards were designed with a very broad range output. The ballast boards can measure and control the current (power) for each channel.
Raducanu, Marius↗
Recent advances in understanding the role of solvated electrons at the plasma-liquid interface of solution-based gas discharges
The solvated electron is one of the strongest known reducing species. Solution-based glow discharges, in which a gaseous discharge is ignited between a metal electrode and a liquid surface, are an emerging spectrochemical source in analytical atomic emission and mass spectrometry. In other disciplines, the similar setup is called plasma electrolysis and can be used for materials and chemical synthesis. Regardless of its name and application areas, electrons are injected into a solution and the underlying physics and chemistry in these systems is complex. Furthermore, quantitative understanding is necessary in order to maximize performance for chemical and materials applications. In this paper, we summarize the state-of-the-art in plasma-liquid interactions involving solvated electrons, with a particular emphasis on the work by our group, and highlight potential areas of future study to both fill in knowledge gaps and drive applications forward.
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Mass spectrometry.
Review of the current state of mass spectrometry, indicating its unique importance for advanced scientific research. Mass spectrometry applications in computer techniques, gas chromatography, ion cyclotron resonance, molecular fragmentation and ionization, and isotope labeling are covered. Details are given on mass spectrometry applications in bio-organic chemistry and biomedical research. As the subjects of these applications are indicated alkaloids, carbohydrates, lipids, terpenes, quinones, nucleic acid components, peptides, antibiotics, and human and animal metabolisms. Particular attention is given to the mass spectra of organo-inorganic compounds, inorganic mass spectrometry, surface phenomena such as secondary ion and electron emission, and elemental and isotope analysis. Further topics include mass spectrometry in organic geochemistry, applications in geochronology and cosmochemistry, and organic mass spectrometry.
Burlingame, A. L.↗
Kinetically Controlled Formation of Semi-crystalline Conjugated Polymer Nanostructures
Conjugated polymer (CP) materials that are considered as an attractive choice for various electronic and optoelectronic applications possess highly heterogeneous complex structures that can span several orders of magnitude in length scale. This is due to the intricate coupling effects of weak secondary interactions and entropic forces that determine molecular organization in bulk polymer materials. Understanding the influence of molecular interactions on the emergence and evolution of nano- and microscale structures is of paramount importance to the guided design and development of condensed CP materials. Such understanding is even more critical for the rational design of hierarchical systems away from equilibrium, where weak molecular interactions can guide the system along competing kinetic pathways toward local energy minima and metastable architectures. In this work, we studied a promising concept for accessing various kinetically stabilized semi-crystalline CP nanostructures that are formed in the process of controlled chain-growth Kumada catalyst-transfer polymerization initiated by a small-molecule catalytic species which can exist in equilibrium between free and aggregated states. Specifically, we chose a small-molecule perylenedicarboximide (PDCI) polymerization catalytic initiator which has a strong tendency toward reversible supramolecular assembly–disassembly that can be controlled by temperature. Addition of a thiophene monomer to a solution of the PDCI initiator starts the chain-growth polymerization process, which produces distinct nanoscale semi-crystalline polythiophene structures formed under predominant kinetic control. Furthermore, we demonstrated that, depending on the reaction temperature (which affects the fine balance between the position of PDCI assembly–disassembly equilibrium, rate of polymerization, and solvent–solute interactions for the growing polythiophene chains), a range of kinetically trapped hierarchically organized semi-crystalline CP systems with substantially varying optoelectronic properties could be obtained. In addition to spectroscopic and electron microscopic studies, in order to better reveal the structural aspects of the generated polymer nanoscale systems, we carried out a series of X-ray diffraction and neutron scattering experiments which indicated complex hierarchical organization in these kinetically stabilized CP assembled materials. We expect that this in situ polymerization-based approach can lead to a general way to expand access to various semi-crystalline CP nanostructured materials with broadly tunable electronic and optical properties.
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Absence of spin susceptibility decrease in a bulk organic superconductor with triangular lattice
The study of non-s-wave unconventional superconductivities in strongly correlated electron systems has been a central issue in condensed matter physics for more than 30 years. In such unconventional superconductivities, d-wave Cooper pairing with antiparallel spins has been often observed in various quasi-two-dimensional (quasi-2D) bulk systems. Interestingly, many theories predicted that the triangular lattice causes the d-wave pairing to be unstable and may lead to more exotic pairing such as parallel spin (spin-triplet) pairing. Here we focus on a bulk organic triangular-lattice system in which superconductivity emerges near a nonmagnetic Mott insulating phase. We demonstrate, by using low-power nuclear magnetic resonance (NMR) measurements, that the spin susceptibility of the superconducting state retains the normal state value even deep in the superconducting state. This result indicates the possibility that the material exhibits spin-triplet superconductivity. Our finding will bring insights also into understanding the 2D materials with triangular moiré superlattices that are considered also to show unconventional superconductivities near Mott-like insulating states.
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Energetic Particle Propagation in the Inner Heliosphere as Deduced from Low Frequency (less than 100 kHz) Observations of Type III Radio Bursts
Solar energetic particle (SEP) events are well-associated with solar flares. It is observed that the delay between the time of the flare and the first-arriving particles at a spacecraft increases with increasing difference between the flare longitude and the footpoint of the field line on which the spacecraft is located. This difference we call the "connection angle" and can be as large as approximately 120 deg. Recently it has been found that all SEP events are preceded by type III radio bursts. These bursts are plasma emission caused by the propagation of 2-50 keV flare electrons through the solar corona and into the solar wind. The drift of these type III radio bursts to lower and lower frequencies enables the propagation of the flare electrons to be traced from the Sun to about 1 AU. We have made an extensive analysis of the type III bursts associated with greater than 20 MeV proton events and find that, in most cases, the radio emission extends to the local plasma frequency when the energetic particles arrive within a few hours of the flare. We conclude that this emission at the lowest possible frequency is generated close to the spacecraft. We then use the time from when the burst started at the Sun to when it reached the local plasma frequency to infer the time it took the radio producing electrons to travel to the spacecraft. We find that these delay times are organized by the connection angle and correlate with the proton delay times. We also find that the differences between the radio delays at Wind and Ulysses are matched by differences in the relative arrival times of the energetic particles at the two spacecraft. The consistent timing between the relative arrival times of energetic electrons and protons and the start of the lowest frequency radio emissions suggests that the first arriving particles of both species are accelerated as part of the flare process and that they propagate to the spacecraft along trajectories similar to those of the lower energy flare electrons. To be detected by observers at locations distant from the nominal field lines originating in the flaring regions the particles must undergo lateral transport. The continuity of the radio bursts suggests that the cross-field transport may occur in the interplanetary medium.
Cane, H. V.↗
Superatomic nature of metal encapsulated dodecahedrane: The case of M@ C 20 H 20 (M = Li, Na, Mg + )
The idea of designing unprecedented materials made of superatomic building blocks, motivated the present study on endohedral M@C 20 H 20 (M = Li, Na, Mg + ) species. Here, ground and excited electronic structures of M@C 20 H 20 (M = Li, Na, Mg + ) were analyzed by means of high-level quantum calculations. In their ground states, one electron occupies a defuse superatomic s-orbital that lies around the C 20 H 20 cage. These entities populate higher angular momentum p-, d-, f-, g-superatomic orbitals in their low-lying electronic states. The proposed superatomic Aufbau shell model for Li@C 20 H 20 and Na@C 20 H 20 is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 2f slightly different from that of Mg@C 20 H 20 + which is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 3s, 2f, 2g, 3p. These introduced superatomic orbital series resemble the Aufbau principle of solvated electron precursors.
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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↗
Heterometallic multinuclear nodes directing MOF electronic behavior
Metal node engineering in combination with modularity, topological diversity, and porosity of metal–organic frameworks (MOFs) could advance energy and optoelectronic sectors.
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Advanced Electronic Structure Theories for Strongly Correlated Ground and Excited States
The aim of this project was to create widely applicable, numerically robust, and systematically improvable multireference theories based on the Driven Similarity Renormalization Group (DSRG). The DSRG is a many-body formalism recently developed in our lab that maps a complex problem involving strongly and weakly interacting electrons to a simpler one in which a few electrons interact strongly via "renormalized" interactions. During this project, we focused our efforts on developing a multireference version of the DSRG (MR-DSRG) applicable to a wide range of problems in theoretical chemistry, including the computation of global ground and excited potential energy surfaces, spin-splittings in transition metal complexes and predicting the interaction of near-degenerate electronically excited states.
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Technologies and Designs for Electronic Nanocomputers
Diverse space-related applications have been proposed for microscopic and sub-microscopic structures, mechanisms, and 'organisms'. To govern their functions, many of these tiny systems will require even smaller, nanometer-scale programmable computers, i.e. 'nanocomputers' on-board. This paper provides an overview of the results of a nearly two-year study of the technologies and designs that presently are in development for electronic nanocomputers. Strengths and weaknesses of the various technologies and designs are discussed, as well as promising directions for remedying some of the present research issues in this area. The presentation is a synopsis of a longer MITRE review article on the same subject.
Montemerlo, Michael S.↗
Ultrafast Imaging of Molecules with Electron Diffraction
Photoexcited molecules convert light into chemical and mechanical energy through changes in electronic and nuclear structure that take place on femtosecond timescales. Gas phase ultrafast electron diffraction (GUED) is an ideal tool to probe the nuclear geometry evolution of the molecules and complements spectroscopic methods that are mostly sensitive to the electronic state. GUED is a passive probing tool that does not alter the molecular properties during the probing process and is sensitive to the spatial distribution of charge in the molecule, including both electrons and nuclei. Improvements in temporal resolution have enabled GUED to capture coherent nuclear motions in molecules in the excited and ground electronic states with femtosecond and subangstrom resolution. Here we present the basic theory of GUED and explain what information is encoded in the diffraction signal, review how GUED has been used to observe coherent structural dynamics in recent experiments, and discuss the advantages and limitations of the method.
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