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DOE OSTI2024

Dynamic Transformation of High-Architectural Nanocrystal Superlattices upon Solvent Molecule Exposure

The cluster-based body-centered-cubic superlattice (cBCC SL) represents one of the most complicated structures among reported nanocrystal assemblies, comprised of 72 truncated tetrahedral quantum dots per unit cell. Our previous report revealed that truncated tetrahedral quantum dots within cBCC SLs possessed highly controlled translational and orientational order owing to an unusual energetic landscape based on the balancing of entropic and enthalpic contributions during the assembly process. However, the cBCC SL’s structural transformability and mechanical properties, uniquely originating from such complicated nanostructures, have yet to be investigated. Herein, we report that cBCC SLs can undergo dynamic transformation to face-centered-cubic SLs in response to post-assembly molecular exposure. We monitored the dynamic transformation process using in situ synchrotron-based small-angle X-ray scattering, revealing a dynamic transformation involving multiple steps underpinned by interactions between incoming molecules and TTQDs’ surface ligands. Furthermore, our mechanistic study demonstrated that the precise configuration of TTQDs’ ligand molecules in cBCC SLs was key to their high structural transformability and unique jelly-like soft mechanical properties. While ligand molecular configurations in nanocrystal SLs are often considered minor features, our findings emphasize their significance in controlling weak van der Waals interactions between nanocrystals within assembled SLs, leading to previously unremarked superstructural transformability and unique mechanical properties. Finally, our findings promote a facile route toward further creation of soft materials, nanorobotics, and out-of-equilibrium assemblies based on nanocrystal building blocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Dangling Bonds as Possible Contributors to Charge Noise in Silicon and Silicon–Germanium Quantum Dot Qubits

Spin qubits based on Si and Si 1–x Ge x quantum dot architectures exhibit among the best coherence times of competing quantum computing technologies, yet they still suffer from charge noise that limit their qubit gate fidelities. Identifying the origins of these charge fluctuations is therefore a critical step toward improving Si quantum-dot-based qubits. Here, we use hybrid functional calculations to investigate possible atomistic sources of charge noise, focusing on charge trapping at Si and Ge dangling bonds (DBs). We evaluate the role of global and local environment in the defect levels associated with DBs in Si, Ge, and Si 1–x Ge x alloys, and consider their trapping and excitation energies within the framework of configuration coordinate diagrams. We additionally consider the influence of strain and oxidation in charge-trapping energetics by analyzing Si and GeSi DBs in SiO 2 and strained Si layers in typical Si 1–x Ge x quantum dot heterostructures. Our results identify that Ge dangling bonds are more problematic charge-trapping centers both in typical Si 1–x Ge x alloys and associated oxidation layers, and they may be exacerbated by compositional inhomogeneities. In conclusion, these results suggest the importance of alloy homogeneity and possible passivation schemes for DBs in Si-based quantum dot qubits and are of general relevance to mitigating possible trap levels in other Si, Ge, and Si 1–x Ge x -based metal-oxide-semiconductor stacks and related devices.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Dangling bonds, the charge neutrality level, and band alignment in semiconductors

We present a systematic study of the electronic properties of dangling bonds (DBs) in a variety of semiconductors and examine the relationship between DBs and the charge neutrality level (CNL) in the context of band alignments of semiconductors. We use first-principles calculations based on density functional theory to assess the energetics of DBs in a set of diamond-structure group-IV and III–V or II–VI zinc-blende-structure semiconductors, considering both cation and anion-derived states. We examine the charge-state transition levels of DBs to assess whether they can serve as a CNL to align band structures, by comparing with offsets calculated from interface calculations. Our results show that this approach for evaluating the CNL yields quantitative results for band offsets and provides useful insights. We discuss the relation with alternative approaches for determination of CNLs based on branch-point energies or transition levels of interstitial hydrogen.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Dynamics and observational signatures of core-collapse supernovae with central engines: hydrodynamics simulations with Monte Carlo post-processing

A long-lived central engine embedded in expanding supernova ejecta can alter the dynamics and observational signatures of the event, producing an unusually luminous, energetic, and/or rapidly evolving transient. We use 2D hydrodynamics simulations to study the effect of a central energy source, varying the amount, rate, and isotropy of the energy deposition. We post-process the results with a time-dependent Monte Carlo radiation transport code to extract observational signatures. The engine excavates a bubble at the centre of the ejecta, which becomes Rayleigh–Taylor unstable. Sufficiently powerful engines are able to break through the edge of the bubble and accelerate, shred, and compositionally mix the entire ejecta. The breakout of the engine-driven wind occurs at distinct rupture points, and the outflowing high-velocity gas may eventually give rise to radio emission. The dynamical impact of the engine leads to faster rising optical light curves, with photon escape facilitated by the faster expansion of the ejecta and the opening of low-density channels. For models with strong engines, the spectra are initially hot and featureless, but later evolve to resemble those of broad-line Ic supernovae. Under certain conditions, line emission from ionized, low-velocity material near the centre of the ejecta may be able to escape and produce narrow emission similar to that seen in interacting supernovae. We discuss how variability in the engine energy reservoir and injection rate could give rise to a heterogeneous set of events spanning multiple observational classes, including the fast blue optical transients, broad-line Ic supernovae, and superluminous supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2013

Feasibility Study of Venus Surface Cooling Using Chemical Reactions with the Atmosphere

A literature search and theoretical analysis were conducted to investigate the feasibility of cooling a craft on Venus through chemical reformation of materials from the atmosphere. The core concept was to take carbon dioxide (CO2) from the Venus atmosphere and chemically reform it into simpler compounds such as carbon, oxygen, and carbon monoxide. This process is endothermic, taking energy from the surroundings to produce a cooling effect. A literature search was performed to document possible routes for achieving the desired reactions. Analyses indicated that on Venus, this concept could theoretically be used to produce cooling, but would not perform as well as a conventional heat pump. For environments other than Venus, the low theoretical performance limits general applicability of this concept, however this approach to cooling may be useful in niche applications. Analysis indicated that environments with particular atmospheric compositions and temperatures could allow a similar cooling system to operate with very good performance. This approach to cooling may also be useful where the products of reaction are also desirable, or for missions where design simplicity is valued. Conceptual designs for Venus cooling systems were developed using a modified concept, in which an expendable reactant supply would be used to promote more energetically favorable reactions with the ambient CO2, providing cooling for a more limited duration. This approach does not have the same performance issues, but the use of expendable supplies increases the mass requirements and limits the operating lifetime. This paper summarizes the findings of the literature search and corresponding analyses of the various cooling options.

Evans, Christopher↗

NASA NTRS2013

Feasibility Study of Venus Surfuce Cooling Using Chemical Reactions with the Atmosphere

Evans, Christopher↗

DOE OSTI2026

Cooperative Lanthanide Solvation in an Ionic Liquid for Critical Materials Separations

Effectively separating critical materials, including intra-lanthanide separations, is crucial for meeting growing application demands. Liquid–liquid extraction (LLE) is the industry standard for lanthanide separations, where the selectivity can depend on small changes in metal coordination. In this work, we investigate representative lanthanide Eu coordination with a neutral malonamide extractant in an imidazolium bistriflimide ionic liquid (IL) solvent. Through systematic titrations of the water and extractant and under extraction conditions, we observe surprising cooperative Eu solvation with the IL anion and extractant. Time-resolved fluorescence spectroscopy measurements show strong extractant coordination in water-saturated IL. Lifetime measurements show no water coordination, and extended X-ray fine structure spectroscopy data provide a coordination number of 10. Molecular dynamics simulations confirm this coordination number and reveal IL anion coordination in the final Eu complex, even though it is ordinarily a significantly weaker ligand compared to water. The lack of water in the final extracted complex and IL anion coordination potentially explain the increased extraction in LLE systems using ILs, as evidenced by higher distribution ratios for cation exchange extraction, despite the energetic cost of cation transfer to the aqueous phase. These results highlight the opportunities for tuning metal coordination to drive extraction in unique solvent systems.

Carr, Amanda J.↗

DOE OSTI2020

Reconciling Work Functions and Adsorption Enthalpies for Implicit Solvent Models: A Pt (111)/Water Interface Case Study

Implicit solvent models are a computationally efficient method of representing solid/liquid interfaces prevalent in electrocatalysis, energy storage, and materials science. However, electronic structure changes induced at the metallic surface by the dielectric continuum are not fully understood. To address this, we perform DFT calculations for the Pt(111)/water interface, in order to compare Poisson–Boltzmann continuum solvation methods with ab initio molecular dynamics (AIMD) simulations of explicit solvent. We show that the implicit solvent cavity can be parametrized in terms of the electric dipole moment change at the equilibrated explicit Pt/water interface to obtain the potential of zero charge (PZC). We also compare the accuracy of aqueous enthalpies of adsorption of phenol on Pt(111) using geometry and charge density based dielectric cavitation methods. The ability to parametrize the cavity according to individual atoms, as afforded in the geometry based approach, is key to obtaining accurate enthalpy changes of adsorption under aqueous conditions. Additionally, we show that the electronic structure changes induced by explicit solvent and our proposed implicit solvent parametrization scheme yield comparable density difference profiles and d-band projected density of states. We therefore demonstrate the capability of implicit solvent approaches to capture both the energetics of adsorption processes and the main electronic effects of aqueous solvent on the metallic surface. Therefore, this work provides a scheme for computationally efficient simulations of interfacial processes for applications in areas such as heterogeneous catalysis and electrochemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Tuning polymer-backbone coplanarity and conformational order to achieve high-performance printed all-polymer solar cells

Abstract All-polymer solar cells (all-PSCs) offer improved morphological and mechanical stability compared with those containing small-molecule-acceptors (SMAs). They can be processed with a broader range of conditions, making them desirable for printing techniques. In this study, we report a high-performance polymer acceptor design based on bithiazole linker (PY-BTz) that are on par with SMAs. We demonstrate that bithiazole induces a more coplanar and ordered conformation compared to bithiophene due to the synergistic effect of non-covalent backbone planarization and reduced steric encumbrances. As a result, PY-BTz shows a significantly higher efficiency of 16.4% in comparison to the polymer acceptors based on commonly used thiophene-based linkers (i.e., PY-2T, 9.8%). Detailed analyses reveal that this improvement is associated with enhanced conjugation along the backbone and closer interchain π-stacking, resulting in higher charge mobilities, suppressed charge recombination, and reduced energetic disorder. Remarkably, an efficiency of 14.7% is realized for all-PSCs that are solution-sheared in ambient conditions, which is among the highest for devices prepared under conditions relevant to scalable printing techniques. This work uncovers a strategy for promoting backbone conjugation and planarization in emerging polymer acceptors that can lead to superior all-PSCs.

14 SOLAR ENERGY↗

DOE OSTI2019

Varying topological properties of two-dimensional honeycomb lattices composed of endohedral fullerenes

Honeycomb lattices (HLs) have been widely explored for realization of massless Dirac quasiparticles and intriguing topological properties in both the quantum and classical regimes, with elemental and artificial atoms as the corresponding building blocks. Here we provide a demonstration showing that when the fullerene molecules of C 28 are used as prototypical building blocks, stable two-dimensional (2D) HLs can also be achieved, with the structural, electronic, and topological properties tuned via proper atom encapsulation. Specifically, whereas a closely packed structure is preferred for the C 28 lattice, honeycomb structures with different spacial symmetries are energetically favored for both the Bi@C 28 and In@C 28 endohedral fullerenes. In particular, Bi@C 28 -HL is revealed to be a quantum spin Hall insulator because of strong spin-orbit coupling effects in the f molecular orbitals, while In@C 28 -HL is a quantum valley Hall insulator resulting from mirror symmetry breaking. Here, the present study offers superatom-based platforms for realizing quantum spin Hall and quantum valley Hall effects in 2D systems, with distinctly enhanced tunability and robustness against atomic-scale imperfections.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS2018

Challenges Beyond the Standard Model: An Examination and Evaluation of Alternatives with Respect to Unsolved Problems in Energetics and Signaling

The standard model of particle physics is regarded as one of the greatest achievements of modern physics. It has successfully predicted the existence of numerous hadrons; e.g. the Higgs Boson, the W and Z Bosons, B mesons, etc. Moreover it accurately models many phenomena such as Beta and Radioactive decay, pair production, hadron mass splitting, and others. In spite of this, the standard model has many shortfalls. For example it fails to account for or explain the presence of dark matter and dark energy. Many alternative models of the substructure of matter etc. have been proposed. Some of these are examined. In addition the strongly related standard model of cosmology, that is the big bang theory, accounts for all observed celestial phenomena. What it cannot do is satisfactorily justify all astrophysical events. As noted, dark matter and dark energy are not well understood yet they are core elements of the big bang model. Many elements of this standard model of cosmology are challenged regularly, yet somehow the community always fits the problems with the model into another mysterious element. This model and others are examined for consistency and reconciliation. Evidence of particles that move faster than the speed of light has long been sought, but remains elusive. Some of the known space-like observations of physics are examined. Potential consequences of such particles are likewise investigated. Some conclusions are drawn with respect to the framework of tachyons in a rational but non-rigorous sense. Finally, some of my ideas are presented, concerning all of the above material. The framework of theories of everything is examined, considering what such a theory requires for validity. Sociological notes on the structure of research in physics are given.

Coxe, Alexander M.↗

DOE OSTI2026

Selective Bidentate Coordination Reconstructs Residual PbI 2 to Homogenize Interfacial Energetics in Perovskite Solar Cells

Spatially heterogeneous interfacial energetics, often originating from residual lead iodide (PbI 2 ), represent a fundamental bottleneck to both the efficiency and operational stability of perovskite photovoltaics. Conventional PbI 2 passivation strategies based on monodentate ligands or highly polar solvents either interact weakly with PbI 2 or undesirably perturb the underlying three-dimensional perovskite lattice. Here, we report a diammonium bidentate strategy that selectively reconstructs residual PbI 2 into corner-sharing PbI 6 octahedra while preserving the bulk perovskite. Enabled by dual-site coordination, a newly designed thiophene-based bidentate ligand (MeXT) stabilizes PbI 6 units during passivation and establishes spatially homogeneous interfacial energetics. Perovskite solar cells incorporating MeXT achieve 26.19% power conversion efficiency and retain over 80% of their initial efficiency after 1000 h of continuous 1-sun illumination at 75 °C. This dual-anchor coordination passivation strategy establishes a general design principle for selectively treating residual PbI 2 and creating electronically coherent and operationally stable interfaces in perovskite photovoltaics.

ligands↗

DOE OSTI2019

Observation and mitigation of RF-plasma-induced damage to III-nitrides grown by molecular beam epitaxy

In this work, radio-frequency (RF) plasma-induced damage to III-nitride surfaces and bulk defects is observed and mitigated. It is shown that for InN films, the surface is more sensitive to plasma-induced damage than GaN films, as observed via atomic force microscopy and reflection high energy electron diffraction. In order to isolate any possible plasma-induced damage, a growth window for InN is established, and temperature ranges are determined for other damaging effects which include roughening due to low adatom mobility, InN decomposition, and indium desorption. In situ plasma monitoring and optimization are accomplished with a combination of optical emission spectroscopy as well as a remote Langmuir probe. It is shown that by increasing the plasma nitrogen flow, the positive ion content increases; however, the ion acceleration potential reduces. Additionally, a reduced RF plasma power results in a reduction of atomic nitrogen species. These plasma species and energetic variations result in variations in the bulk unintentional background electron concentrations observed by room temperature Hall effect measurements of ~1 um thick InN films. By increasing the nitrogen flow from 2.5 to 7.5 sccm for a constant RF power of 350 W, the background electron concentration decreases by 74% from 1.36 x 1019 cm-3 to 3.54 x 1018 cm-3, while maintaining a smooth surface morphology. Additionally, photoluminescence spectra indicate optical emission energies shift from ~0.81 to 0.71 eV (closer to the fundamental bandgap of InN) by limiting the damaging plasma species. Finally, conditions are presented to further minimize plasma-induced damage in III-nitride devices.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Advanced nanoscale characterization of aluminum nanoparticles with modified surface morphology via atmospheric helium and carbon monoxide plasmas

Aluminum nanoparticles (nAl) have the potential as energetic additives in explosive/propellant formulations. Scalable methodologies must be pursued to mitigate the inactive amorphous alumina shell surrounding the active aluminum (Al) core with modified surface morphology and chemistry for increased combustion effects. This work explores the feasibility of making reactive core/shell nAl with thinned oxide shells and modified surface coatings via a two-step atmospheric plasma surface treatment process in a custom dielectric barrier discharge plasma reactor. The commercial nAl of nominal average size similar to 40-60nm was first treated with helium (He) followed by He/carbon monoxide (CO) plasmas for different durations. The resultant samples were characterized via high-resolution transmission electron microscopy (HRTEM) and Fourier transform IR (FTIR) spectra. HRTEM images revealed sporadic patchy gamma -alumina deposits on particle surfaces and in gaps among particles for all samples, suggesting the non-uniform plasma effects of the He/CO glow. Nanoscale chemical analyses via scanning transmission electron microscopy elemental mapping and x-ray energy dispersive spectroscopy were further performed. Although no carbon-associated structure appeared in electron energy loss spectroscopy (EELS) spectra, the presence of carbonaceous materials was confirmed as a thin dispersive layer evenly distributed on the nAl surface suggesting either its amorphous nature or is present at a level insufficient to generate satisfactory EELS spectra. The trend of intensity profiles for key elements acquired by drawing lines across a single particle on the elemental maps confirmed that carbonaceous materials only existed on the surface and they were most likely carboxylates that increased with increased He/CO treatment duration, as evident by FTIR results. Finally, this work demonstrated the success of atmospheric plasma-treated reactive nAl with comprehensively characterized surface features via advanced microscopy and spectroscopy.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Semiclassical model for calculating exciton and polaron pair energetics at interfaces

Exciton and polaron pair dissociation is a key functional aspect of photovoltaic devices. To improve upon the current state of interfacial transport models, we augment the existing classical models of dielectric interfaces by incorporating results from ab initio calculations, allowing us to calculate exciton and polaron binding energies more accurately. We demonstrate the predictive capabilities of this new model using two interfaces: (i) the boron subphthalocyanine chloride (SubPc) and C60 interface, which is an archetype for many organic photovoltaic devices; and (ii) pentacene and silicon (1 0 0), which represents a hybrid between organic and inorganic semiconductors. Overall, our calculations predict that the insertion of molecular dipoles at interfaces can be used for improving polaron pair dissociation and that sharp transitions in dielectric permittivity can have a stronger effect on the polaron pair dissociation than even the electron-hole Coulomb interaction.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Oxidative Deboronation of Boronic Acids by Hydrogen Peroxide in Planta Generates Borate for Cross-Linking of Rhamnogalacturonan II

Vascular plants require boron to cross-link the rhamnogalacturonan-II (RG-II) domain of pectin to form functional cell walls. Boronic acids, which form reversible esters with cis-diols like borate, have been proposed to influence RG-II cross-linking, though the mechanism remains unclear. We used suspension-cultured rose cells adapted to grow without boron to investigate the effect of boronic acids on RG-II dimerization. When grown with phenylboronic acid (PBA) as the sole boron source, nearly all RG-II was crosslinked, whereas methylboronic acid (MBA) only partially restored cross-linking. In contrast, in vitro assays showed that homogeneous RG-II monomers did not dimerize with alkyl or aryl boronic acids unless supplemented with hydrogen peroxide (H2O2), which oxidatively converts boronic acids to boric acid. Real-time NMR spectroscopy and density functional theory calculations provided insight into the reaction mechanism and energetics of oxidation respectively. Together, our data show that exogenous boronic acids are a source of boric acid for plants, and that the deboronation reaction generates aryl or alkyl alcohol byproducts that can undergo further chemical modification in planta. The fate and potential roles of these byproducts in planta remain to be determined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Influence of nanoscale interfaces on the dynamic deformation and spall failure of Cu–Fe alloy microstructures

Additively manufactured immiscible Cu–Fe alloys can exhibit a distribution of nanoscale interfaces due to the distribution of nanoscale clusters in the equilibrium and metastable phases. Molecular dynamics simulations investigate the role of such interfaces on the phase stability and transformation behavior during shock compression, as well as the mechanisms of damage nucleation during spall failure. The model multiphase Cu–Fe systems studied here comprise a distribution of Fe clusters in an FCC Cu matrix, as well as Cu clusters in a BCC Fe matrix. The length scales of the nanoscale clusters determine the energetics of the interfaces that can result in FCC/BCC (equilibrium) or FCC/FCC (metastable) interfaces in the Cu system matrix, and BCC/FCC (equilibrium) or BCC/BCC (metastable) interfaces in the Fe matrix. The MD simulations demonstrate that nanoscale metastable interface microstructures can induce plastic deformation and also stabilize phases or suppress phase transformations in metastable phase clusters. In contrast, equilibrium interfaces can influence phase transformation thresholds and serve as additional void nucleation sites during failure.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Investigation of the distribution of laser-induced damage precursors in etched grating sidewalls fabricated using inductively coupled plasma reactive-ion etching

Inductively coupled plasma reactive-ion etching for grating fabrication is explored with emphasis on the type and distribution of process-induced defects that can act as precursors to laser-induced damage initiation. To provide flexibility in the ability to perform a variety of material characterization methods, grating-like features with large pitch were fabricated in silica monolayers. The results indicate that the etch process introduces surface fluorine and subsurface carbon-containing contamination, which reduces the laser-induced damage threshold. The local relative concentrations of the laser-damage precursors introduced during the etch step of the manufacturing process were investigated using angle-resolved damage testing, taking advantage of the shift of the location of the peak electric-field intensity incident on the grating sidewall. The results suggest an increased level of etch-related defects near the base of the sidewall, with directly fluorinated silicon identified as the primary defect.

Dent, R. [Univ. of Rochester, NY (United States). ↗