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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Trade-off between processability and device performance in donor–acceptor semiconductors revealed using discrete siloxane side chains

Donor–acceptor polymeric semiconductors are crucial for state-of-the-art applications, such as electronic skin mimics. The processability, and thus solubility, of these polymers in benign solvents is critical and can be improved through side chain engineering. Nevertheless, the impact of novel side chains on backbone orientation and emerging device properties often remains to be elucidated. Here, we investigate the influence of elongated linear and branched discrete oligodimethylsiloxane (oDMS) side chains on solubility and device performance. Thereto, diketopyrrolopyrrole–thienothiophene polymers are equipped with various oDMS pendants (PDPPTT-Si n ) and subsequently phase separated into lamellar domains. The introduction of a branching point in the siloxane significantly enhanced the solubility of the polymer, as a result of increased backbone distortion. Simultaneously, the charge carrier mobility of the polymers decreased by an order of magnitude upon functionalization with long and/or branched siloxanes. This work unveils the intricate balance between processability and device performance in organic semiconductors, which is key for the development of next-generation electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Rationalizing energy level alignment by characterizing Lewis acid/base and ionic interactions at printable semiconductor/ionic liquid interfaces

Charge transfer and energy conversion processes at semiconductor/electrolyte interfaces are controlled by local electric field distributions, which can be especially challenging to measure. Furthermore, we leverage the low vapor pressure and vacuum compatibility of ionic liquid electrolytes to undertake a layer-by-layer, ultra-high vacuum deposition of a prototypical ionic liquid EMIM + (1-ethyl-3-methylimidazolium) and TFSI – (bis(trifluoromethylsulfonyl)-imide) on the surfaces of different electronic materials. We consider a case-by-case study between a standard metal (Au) and four printed electronic materials, where interfaces are characterized by a combination of X-ray and ultraviolet photoemission spectroscopies (XPS/UPS). For template-stripped gold surfaces, we observe through XPS a preferential orientation of the TFSI anion at the gold surface, enabling large electric fields (~10 8 eV m –1 ) within the first two monolayers detected by a large surface vacuum level shift (0.7 eV) in UPS.

14 SOLAR ENERGY↗
DOE OSTI2023

Metal–Organic Frameworks: Challenges Addressed via Magnetic Resonance Spectroscopy

Magnetic resonance spectroscopies occupy a premier position within the chemical sciences by revealing structure and dynamics in molecules and solids associated with photosynthesis, enzymology, Alzheimer proteins, pharmaceuticals, catalysts, polymers, and electronic materials. Here, we review the recent literature contributions of NMR and EPR spectroscopy towards the study of metal–organic frameworks from 2017 to mid-2022. We organize the review around what we perceive to be the intellectual challenges in MOF research: structure, dynamics, synthesis, properties, and function.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Electron and Electron-Nuclear Dynamics of Open Quantum Subsystems

Leveraging an open-subsystem formulation of Density Functional Theory (DFT) we aim at describing periodic and molecular systems alike, including their electronic and nuclear dynamics. Subsystem DFT enables first principles simulations to approach realistic time- and length-scales, and most importantly sheds light on the dynamical behavior of complex systems. Taking subsystem DFT to the time domain allows us to inspect the electron dynamics of condensed-phase systems in real time. In liquids and interfaces, we observe all the relevant regimes proper of non-Markovian open quantum system dynamics, such as electronic energy transfer, and screening. In addition, the ab-initio modeling of system-bath interactions brought us to observe and justify the holographic time-dependent electron density theorem. Contrary to interactions between molecular (finite) systems, when molecules interact with metal or semiconductor surfaces the electron dynamics is strongly non-Markovian with dramatic repercussions to the molecule’s response to external perturbations. Metals and semiconductors typically have large polarizabilities, and even in a regime of low coupling their effect on impinging molecular species is significant–line broadening, peak shift, and intensity borrowing are observed, characterized, and explained in terms of inter-subsystem dynamical interactions and a many-body decomposition of the system’s density-density response function in a way that transcends the canons of Fermi Golden Rule.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2020

Free Electron Laser Measurement of Liquid Carbon Reflectivity in the Extreme Ultraviolet

Ultrafast time-resolved extreme ultraviolet (EUV) reflectivity measurements of optically pumped amorphous carbon (a-C) have been performed with the FERMI free electron laser (FEL). This work extends the energy range used in previous reflectivity studies and adds polarization dependence. The EUV probe is known to be sensitive to lattice dynamics, since in this range the reflectivity is essentially unaffected by the photo-excited surface plasma. The exploitation of both s- and p-polarized EUV radiation permits variation of the penetration depth of the probe; a significant increase in the characteristic time is observed upon increasing the probing depth (1 vs. 5 ps) due to hydrodynamic expansion and consequent destruction of the excited region, implying that there is only a short window during which the probed region is in the isochoric regime. A weak wavelength dependence of the reflectivity is found, consistent with previous measurements and implying a maximum electronic temperature of 0.8 eV ± 0.4.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A measure of active interfaces in supported catalysts for high-temperature reactions

Formulating knowledge of structure-function relationships in heterogeneous catalysis is central to the design of efficient catalysts; yet, the elucidation of dominant reaction sites has remained as a challenge. Here, in this paper, we present a methodology that can be used to visualize metal-gas and metal-oxide-gas interfaces in three dimensions and to quantify their catalytic activity levels. As a case study, CH 4 oxidation occurring in a Pt/CeO 2 system is chosen. By employing thermally robust Pt@CeO 2 model catalysts with size-tunable and monodisperse cores, and gas-permeable shells, we reconstruct a series of structures in 3D via electron tomography and match the information to activity data and theoretical calculations. This strategy reveals that two different interfaces catalyze the CH 4 oxidation and that their contribution to the overall rate changes with the Pt size, temperature, and gas atmosphere. Our results provide an analytic platform on which to explore reaction pathways and mechanisms applicable to multiple reactions and materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Modeling Molecules under Pressure with Gaussian Potentials

The computational modeling of molecules under high pressure is a growing research area that augments experimental high-pressure chemistry. Here, a new electronic structure method for modeling atoms and molecules under pressure, Gaussians On Surface Tesserae Simulate HYdrostatic Pressure (GOSTSHYP) approach, is introduced. In this method, a set of Gaussian potentials is distributed evenly on the van der Waals surface of the investigated chemical system, leading to a compression of the electron density and the atomic scaffold. Since no parameters other than pressure need to be specified, GOSTSHYP allows straightforward geometry optimizations and ab initio molecular dynamics simulations of chemical systems under pressure for nonexpert users. In this work, calculated energies, bond lengths, and dipole moments under pressure fall within the range of established computational methods for high-pressure chemistry. A Diels-Alder reaction and the cyclotrimerization of acetylene showcase the ability of GOSTSHYP to model pressure-induced chemical reactions. The connection to mechanochemistry is pointed out.

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

Extracting Inelastic Scattering Cross Sections for Finite and Aperiodic Materials from Electronic Dynamics Simulations

Explicit time-dependent electronic structure theory methods are increasingly prevalent in the areas of condensed matter physics and quantum chemistry, with the broad-band optical absorptivity of molecular and small condensed-phase systems nowadays routinely studied with such approaches. Here, in this paper, it is demonstrated that electronic dynamics simulations can similarly be employed to study cross sections for the scattering-induced electronic excitations probed in nonresonant inelastic X-ray scattering and momentum-resolved electron energy loss spectroscopies. A method is put forth for evaluating the electronic dynamic structure factor, which involves the application of a momentum boost-type perturbation and transformation of the resulting reciprocal space density fluctuations into the frequency domain. Good agreement is first demonstrated between the dynamic structure factor extracted from these electronic dynamics simulations and the corresponding transition matrix elements from linear response theory. The method is then applied to some extended (quasi)one-dimensional systems, for which the wave vector becomes a good quantum number in the thermodynamic limit. Finally, the dispersion of many-body excitations in a series of hydrogen-terminated graphene flakes (and twisted bilayers thereof) is investigated to highlight the utility of the presented approach for capturing morphology-dependent effects in the inelastic scattering cross sections of nanostructured and/or noncrystalline materials.

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

Combinatorial Membrane Synthesis: Fundamentals of Hybrid Metal-Organic Brush (MOB) Membranes for Organic Solvent Nanofiltration (Renewal)

(a) Goals: The goals of our current 3-year research project are (i) expansion of the novel modification technique Single Electron Transfer- Living Radical Polymerization (SET-LRP) to graft polymer brushes on a polyimide stable support followed by characterization and testing of the ensuing membrane (ii) stiffen brush network utilizing (a) metal organic frameworks and (b) covalent bonds formed as a result of crosslinking the grafted brush network. (b) Approach: The approach taken for this research was: (i) to graft branches terminated with a carboxyl group on each bristle (or bristle branch) allowing (a) metal immobilization to form MOF-like structures between branches or (b) crosslink bristles using aliphatic or aromatic diamines; (ii) to test the performance of the membranes using organic dyes, pure solvents (alcohols) and industrially relevant organic solvent separations; and (iii) to characterize these modified brush membranes. (c) Findings: The significant findings from the past one year are summarized below (papers resulting from this work are listed below and in D. PUBLICATIONS and relevant references are found in E. REFERENCES.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Electric field gradients at rubidium sites in rubidium uranyl nitrate and quadrupole moments of 85 Rb and 87 Rb

The electronic structure along the axial direction of the uranyl ion in rubidium uranyl nitrate (RbUO 2 (NO 3 ) 3 ) has been studied by nuclear quadrupole resonance and nuclear magnetic resonance measurements of 85 Rb and 87 Rb quadrupole couplings. Here, the parameter of interest in these experiments is the electric field gradient at the Rb sites, which may be compared with values com- puted by various theoretical approaches. From this analysis an accurate ratio of the quadrupole moments of 85 Rb and 87 Rb has also been obtained.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Determining the Ensemble N -Representability of Reduced Density Matrices

The N-representability problem for reduced density matrices remains a fundamental challenge in electronic structure theory. Following our previous work that employs a unitary-evolution algorithm based on an adaptive derivative-assembled pseudo-Trotter variational quantum algorithm to probe pure-state N-representability of reduced density matrices [J. Chem. Theory Comput. 2024, 20, 9968], in this work we propose a practical framework for determining the ensemble N-representability of a p-body matrix. This is accomplished using a purification strategy that embeds an ensemble state into a pure state defined on an extended Hilbert space, such that the reduced density matrices of the purified state reproduce those of the original ensemble. By iteratively applying variational unitaries to an initial purified state, the proposed algorithm minimizes the Hilbert-Schmidt distance between its p-body reduced density matrix and a specified target p-body matrix, which serves as a measure of the N-representability of the target. This methodology facilitates both error correction of defective ensemble reduced density matrices and quantum-state reconstruction on a quantum computer, offering a route for density-matrix refinement. We validate the algorithm with numerical simulations on systems of two, three, and four electrons in both simple models as well as molecular systems at finite temperature, demonstrating its robustness.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Evidence of Alpha Radiolysis in the Formation of a Californium Nitrate Complex

Well-characterized complexes of transplutonium elements are scarce because of the experimental challenges of working with these elements and the rarity of the isotopes. This leads to a lack of structural and spectroscopic data needed to understand the nature of chemical bonds in these compounds. In this work, the synthesis of Cf(DOPO q ) 2 (NO 3 )(py) (DOPO q =2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate; py=pyridine) is reported, in which the nitrate anion is hypothesized to form through the α-radiolysis-induced reaction of pyridine and/or the ligand. Here, computational analysis of the electronic structure of the complex reveals that the Cf III –ligand interactions are largely ionic.

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

“Self-trapping” in solar cell hybrid inorganic-organic perovskite absorbers

In the simplest picture, a “self-trapped” polaron forms when an excess electron or hole deforms a crystal lattice, creating a potential well with bound states. Properties of self-trapped polarons in methylammonium lead iodide perovskite (MAPbI 3 ), which is widely used as solar cell absorber, are of great interest, and are a subject of ongoing investigations and debates concerning the existence of large polarons with the co-presence of metastable self-trapping. Herein, we employ a self-interaction-free density functional theory method to investigate the stability of small polarons in tetragonal MAPbI 3 phase. The electron small polaron is found to be unstable, while the hole small polaron is found to be metastable at realistic operation temperatures of solar cells. Further, the hole polaron is found to have a hole band close to the conduction band, which in conjunction with its metastability suggests that small polarons will have an appreciable effect on charge-carrier recombinations in MAPbI 3 . Further, in this study, we posit that the existence of the metastable polarons in addition to the large polarons may explain the experimentally observed non-monotonic temperature dependence of bimolecular charge-carrier recombination rate in tetragonal MAPbI 3 phase.

14 SOLAR ENERGY↗
DOE OSTI2024

Unexpected Photodriven Linker-to-Node Hole Transfer in a Zirconium-Based Metal–Organic Framework

Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 node cores are indispensable building blocks for almost all zirconium-based metal–organic frameworks. Consistent with the insulating nature of zirconia, they are generally considered electronically inert. Contrasting this viewpoint, we present spectral measurements and calculations indicating that emission from photoexcited NU-601, a six-connected Zr-based MOF, comes from both linker-centric locally excited and linker-to-node charge-transfer (CT) states. The CT state originates from a hole transfer process enabled by favorable energy alignment of the HOMOs of the node and linker. This alignment can be manipulated by changing the pH of the medium, which alters the protonation state of multiple oxy groups on the Zr-node. Thus, the acid–base chemistry of the node has a direct effect on the photophysics of the MOF following linker-localized electronic excitation. In conclusion, these new findings open opportunities to understand and exploit, for energy conversion, unconventional mechanisms of exciton formation and transport in MOFs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Soluble Iron Enhances Extracellular Electron Uptake by Shewanella oneidensis MR‐1

Abstract Extracellular electron transfer (EET) is a process that microorganisms use to reduce or oxidize external insoluble electron acceptors or donors. Much of our mechanistic understanding of this process is derived from studies of transmembrane cytochrome complexes and extracellular redox shuttles that mediate outward EET to anodes and external electron acceptors. In contrast, there are knowledge gaps concerning the reverse process of inward EET from external electron donors to cells. Here, we describe a role for soluble iron (exogenous FeCl 2 ) in enhancing EET from cathodes to the model EET bacterium Shewanella oneidensis MR‐1, with fumarate serving as the intracellular electron acceptor. This iron concentration‐dependent electron uptake was eradicated upon addition of an iron chelator and occurred only in the presence of fumarate reductase, confirming an electron pathway from cathodes to this periplasmic enzyme. Moreover, S. oneidensis mutants lacking specific outer membrane and periplasmic cytochromes exhibited significantly decreased current levels relative to wild‐type. These results indicate that soluble iron can function as an electron carrier to the EET machinery of S. oneidensis .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Electronic Structure and Stacking Arrangement of Tungsten Disulfide at the Gold Contact

There is an intensive effort to control the nature of attractive interactions between ultrathin semiconductors and metals and to understand its impact on the electronic properties at the junction. In this work, we present a photoelectron spectroscopy study on the interface between WS 2 films and gold, with a focus on the occupied electronic states near the Brillouin zone center (i.e., the Γ point). To delineate the spectra of WS 2 supported on crystalline Au from the suspended WS 2 , we employ a microscopy approach and a tailored sample structure, in which the WS 2 /Au junction forms a semi-epitaxial relationship and is adjacent to suspended WS 2 regions. The photoelectron spectra, as a function of WS 2 thickness, display the expected splitting of the highest occupied states at the Γ point. In multilayer WS 2 , we discovered variations in the electronic states that spatially align with the crystalline grains of underlying Au. Corroborated by density functional theory calculations, we attribute the electronic structure variations to stacking variations within the WS 2 films. We propose that strong interactions exerted by Au grains cause slippage of the interfacing WS 2 layer with respect to the rest of the WS 2 film. Our findings illustrate that the electronic properties of transition metal dichalcogenides, and more generally 2D layered materials, are physically altered by the interactions with the interfacing materials, in addition to the electron screening and defects that have been widely considered.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Topological Frustration as a New Parameter to Tune Morphology Revealed through Exploring the Continuum between A-B-C 3-Arm Star and Linear Triblock Polymers

Block polymers assemble into a variety of phase-separated morphologies based on volume fraction (φ) and interactions (χ) of the respective blocks. The arrangement of three different polymer blocks could either be a 3-arm star, with each block having one terminus attached to a common junction point or a linear A-B-C architecture. A versatile strategy is reported to synthesize a series of well-defined graft polymers that lie along the unexplored continuum between a 3-arm star and an A-B-C linear triblock polymer architecture. Using the technique of single-molecule insertion, precise control over the position of graft arm C along the B chain was achieved. A series of discrete graft polymers (PMMA-b-PS-g-PEO) with fixed φ and prescribed ω values that lie on the continuum between a 3-arm star (ω = 0) and linear triblock polymer (ω = 1) were synthesized. Morphological studies using small-angle X-ray scattering and conventional and energy-filtered transmission electron microscopy reveal the transition between lamellae, perforated lamellae, and cylindrical morphologies with systematic variation in the ω values, a trend attributed to the topological frustration and the associated χ values between the three blocks. Molecular dynamic simulations of coarse-grained models were found to predict phase diagrams that are consistent with the experimentally observed morphologies. Furthermore, our results suggest that changes in ω lead to topological frustration which is an important additional new design parameter that can be used to tune the morphology of multiblock polymers in addition to φ and χ.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗