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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Autocorrelation and Multifractal Detrended Fluctuation Analyses Reveal Superdiffusive Mass Transport in Solvent-Filled Nanoporous Media

Fluorescence fluctuation spectroscopy experiments were conducted to better understand the complex mass transport dynamics of organic molecules in liquid-filled nanoporous media. Anodic aluminum oxide (AAO) membranes incorporating 10 and 20 nm diameter cylindrical pores were employed as model materials. Nile red (NR) dye was used as a fluorescent tracer. The dye was dissolved separately in ethanol and toluene at a concentration of 20 nM and used to fill the membrane nanopores. Confocal fluorescence microscopy was employed to capture photon intensity time series data reflecting apparent diffusion of the dye within the pores. Autocorrelation of these data revealed that NR diffusion within the membranes occurred over a broad range of time scales. The autocorrelation decays were fit to a model for one-dimensional diffusion incorporating both fast and slow components having apparent diffusion coefficients, D f and D s , differing by a factor of ∼100. The fast mechanism was attributed to hindered bulk-like diffusion in the central pore cavity, while slow diffusion likely involved absorption of the dye to the pore surfaces. Unfortunately, important evidence of diffusion anomalies is lost in the broad autocorrelation decays obtained. The method of multifractal detrended fluctuation analysis (MF-DFA) was applied to the same data as a means to overcome this limitation. MF-DFA revealed that time series acquired from within the nanopores were multifractal and exhibited evidence of anomalous superdiffusion, likely resulting from the participation of a desorption-mediated diffusion mechanism. Monte Carlo simulations of time series modeling desorption-mediated diffusion in cylindrical nanopores provided support for this assignment. Here, the new knowledge gained affords an improved understanding of hydrocarbon dynamics within nanoporous oil and gas shales.

Diffusion↗
DOE OSTI2025

Distinguishing Desirable and Undesirable Reactions in Multicomponent Systems for Redox Activation of the Uranyl Ion

Although it has been established that covalent functionalization of the U–O bonds in the uranyl dication (UO 2 2+ ) generally requires use of strong reductants and electrophiles, little work has examined how interactions between the individual reaction components could affect final outcomes in solution. Here, the patterns of such reactivity have been studied in a UO 2 2+ -containing model system supported by a workhorse pentadentate ligand, 2,2′-[(methylimino)bis(2,1-ethanediylnitrilomethylidyne)]bis-phenol. Oxo activation and functionalization have been tested with (i) electrochemical and chemical reduction, and (ii) coordinating and noncoordinating solvents. In acetonitrile, uranyl reduction was achieved cleanly, but treatment of the reduced species with tris(pentafluorophenyl)borane (BCF) resulted in a mixture of products arising from direct electron transfer to BCF. In dichloromethane (CH 2 Cl 2 ), electrochemical reduction of uranyl was achieved cleanly, but clean chemical reactivity was inaccessible. Despite these challenges, one trinuclear and oxo-deficient uranium-containing product was crystallized from CH 2 Cl 2 solution and characterized; thus, desirable electrophilic reactivity can proceed to some degree in CH 2 Cl 2 with BCF. Computational studies were used to investigate the properties of the trinuclear uranium product and the changes that could be inducible by further reduction. Here, taken together, the reactivity patterns identified here could inform design of improved systems for actinyl oxo functionalization.

cations↗
DOE OSTI2025

Accurate Force Field for Carbon Dioxide–Silica Interactions Based on Density Functional Theory

Fluid–silica interfaces are ubiquitous in chemistry, occurring in both natural geochemical environments and practical applications ranging from separations to catalysis. Simulations of these interfaces have been, and continue to be, a significant avenue for understanding their behavior. A constraining factor, however, is the availability of accurate force fields. Most simulations use traditional “mixing rules” to determine nonbonded dispersion interactions, an approach that has not been critically examined. Here, in this study, we present Lennard-Jones parameters for the interaction of carbon dioxide with silica interfaces that are optimized to reproduce density functional theory (DFT)-based binding energies. The modeling is based on the recently developed silica-DDEC force field, whose atomic charges are consistent with DFT calculations. Standard mixing rules are found to predict weaker CO 2 binding to silica than that obtained from DFT, an effect corrected by the optimized parameters given here. This behavior extends to other silica force fields (Clayff and Gulmen-Thompson), and the present Lennard-Jones parameters improve their performance as well. The effects of improved Lennard-Jones parameters on the structural and dynamical properties of condensed CO 2 in silica slit pores are also examined.

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

Ab Initio Molecular Dynamics Study of the Reduction of Acetone by the Hydrated Electron

We have investigated the reaction dynamics of the reduction of acetone by the solvated electron in water using ab initio molecular dynamics simulations at 298 and 373 K. The rate constants derived from the simulations are consistent with experimental observations that the reaction has a low activation energy. Detailed analyses carried out to shed light on the mechanism of the reaction show that solvent reorganization plays a key role as a reaction coordinate, as expected from the Marcus electron transfer theory. Furthermore, constrained density functional theory calculations indicate that the electronic coupling is large, placing the reaction in the adiabatic limit. Indeed, the activation energies and rate constants of the simulations are in accordance with the predictions of adiabatic Marcus theory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Imaging Three-Dimensional Molecular Structure and Dynamics with Multiparticle Covariance and Cumulant Coulomb Explosion Analysis

Coulomb explosion imaging (CEI) provides a direct means of imaging molecular geometry by correlating fragment ion momenta following the fragmentation of a molecular polycation. Here, we demonstrate the use of three-body covariance and four-body cumulant analysis to extract three-dimensional (3D) structural information from the X-ray-induced Coulomb explosion of tert-butyl iodide (C4H9I). Site-selective ionization at the iodine 4d edge with intense femtosecond soft X-ray pulses from an X-ray free-electron laser (XFEL) enables rapid charge buildup and molecular breakup. By correlating ionic fragments in the molecular frame, we isolate complete dissociation channels and reveal subtle structural changes, such as umbrella-type motion of the branched alkyl chain, during the ionization process. Comparison with point-charge simulations of the Coulomb explosion shows close agreement, validating the approach. Furthermore, these results establish covariance/cumulant mapping as a powerful strategy for imaging complex three-dimensional molecular structures and point the way toward time-resolved CEI using both XFEL and tabletop sources for capturing ultrafast structural dynamics.

Imaging↗
DOE OSTI2026

Resolving Competing Ultraviolet Photoinduced Ring-Opening and Dissociation Pathways in Iodothiophenes by Ultrafast Electron Diffraction

The ultraviolet photochemistry of halothiophenes is thought to proceed via competing pathways, prompt C–X (X = halogen) bond fission, and parent ring opening followed by fragmentation, yet direct structural evidence distinguishing these mechanisms is limited. Here, time-resolved gas-phase ultrafast electron diffraction (UED) has been used to directly follow the structural dynamics of 2- and 3-iodothiophene following photoexcitation at 247 nm. For both isomers, the time-resolved pair distribution functions reveal the appearance of new interatomic distances that cannot be explained by simple C–I bond cleavage and formation of C 4 SH 3 radical cofragments. The signatures, particularly those for 2-iodothiophene, are consistent with a rival ring-opening channel of the intact parent, which evolve on time scales distinct from those associated with the direct C–I bond cleavage. In addition, the extracted kinetics indicate that the ring-opening channel occurs faster in 2-iodothiophene than in the 3-isomer at this excitation wavelength. Furthermore, these measurements provide direct geometric evidence for competing pathways leading to different structures following photodissociation in a model heteroaromatic and further establish UED as a sensitive probe of complex excited-state chemistry.

Bond cleavage↗
DOE OSTI2025

Suppressing Polaronic Defect–Photocarrier Interaction in Halide Perovskites by Pre-distorting Its Lattice

In halide perovskites, photocarriers can have strong polaronic interactions with point defects. For iodide-deficient MAPbI 3 , we found that the Fermi level can shift significantly by 0.6–0.7 eV upon light illumination. This energy level shift is accompanied by the formation of deep electron traps. These experimental observations are consistent with the formation of a Pb–Pb dimer when photoexcited electrons are trapped at an iodide vacancy. Interestingly, we found that this polaronic interaction is suppressed when a portion of MA + cations is replaced by smaller Cs + ions. Density functional theory calculations reveal that Cs-doping can reduce the distance between two Pb atoms across an iodide vacancy, even without electron trapping. The predistortion of the lattice induced by cation replacement resembles the Pb–Pb dimer formed by electron trapping at the defect site, which explains the suppression of light-induced effects observed in the experiment. Furthermore, our finding unveils a counterintuitive strategy to enhance the photostability of halide perovskites by preintroducing distortions into its lattice.

14 SOLAR ENERGY↗
DOE OSTI2025

Attosecond control and measurement of chiral photoionization dynamics

Many chirality-sensitive light–matter interactions are governed by chiral electron dynamics. Therefore, the development of advanced technologies making use of chiral phenomena would critically benefit from measuring and controlling chiral electron dynamics on their natural attosecond timescales. Such endeavours have so far been hampered by the lack of characterized circularly polarized attosecond pulses, an obstacle that has recently been overcome. Here we introduce chiroptical spectroscopy with attosecond pulses and demonstrate attosecond coherent control over photoelectron circular dichroism (PECD), as well as the measurement of chiral asymmetries in the forward–backward and angle-resolved photoionization delays of chiral molecules. We show that co-rotating attosecond and near-infrared (IR) pulses can nearly double the PECD and even change its sign compared with single-photon ionization. We demonstrate that chiral photoionization delays depend on both polar and azimuthal angles of photoemission in the light-propagation frame, requiring 3D momentum resolution. We measure forward–backward chiral-sensitive delays of up to 60 as and polar-angle-resolved photoionization delays of up to 240 as, which include an asymmetry of about 60 as originating from chirality in the continuum–continuum transitions. Attosecond chiroptical spectroscopy opens the door to quantitatively understanding and controlling the dynamics of chiral molecules on the electronic timescale.

Atomic and molecular interactions with photons↗
DOE OSTI2025

Tracking oxygen vacancy migration in memristor devices using operando hard X-ray photoelectron spectroscopy

Fabrication of ultrathin (sub-2 nm) oxide semiconductor memristors poses the fundamental challenge of achieving oxide growth with atomic precision in terms of electronic structure and defect formation. Recently, ultrathin memristors consisting of bilayers of mixed Al 2 O 3 and MgO atomic layers were fabricated using an in vacuo atomic layer deposition process. This approach offers a unique platform for precise atomic control of oxygen vacancies in the device in which the vacancies are introduced by placing MgO atomic layers between pristine Al 2 O 3 layers. In this work, we present a systematic operando Hard X-ray PhotoElectron Spectroscopy (HAXPES) study of the switching of such memristors, combined with complementary current-voltage and capacitance-voltage (C-V) measurements. We used a memristor stack of Al 2 O 3 /MgO atomic layers, with the MgO-containing oxide deposited on the bottom Al metal electrode and a pure Al 2 O 3 layer below the top Pd electrode. HAXPES analysis shows a substantial change in the chemical shift of the Aluminum oxide when switching between the ”OFF” and ”ON” states indicative of a redistribution of oxygen vacancies in the device active layer. Interestingly, subsequent switching to the OFF state shows hysteretic behavior indicating the retention of some oxygen vacancies in the top Al 2 O 3 layer. This vacancy retention can be correlated with the stochastic behavior of the switching voltage observed in these devices. C–V measurements show a clear frequency-dependent response in the OFF state, consistent with enhanced polarization and vacancy trapping at low frequencies.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Effects of confinement and pressure on the structure and dynamics of carbon dioxide in silica slit pores

An understanding of carbon dioxide fluid properties within geological mesopores is important in applications ranging from carbon sequestration to shale oil recovery. Here, a molecular dynamics study is presented that aims to shed light on these systems by simulation of CO 2 fluid confined in β-cristobalite silica slit pores with different pore widths and pressure conditions. The weakly associating nature of carbon dioxide leads to little difference in structural and interfacial dynamical properties for different pore sizes and pressures. Rather, the behavior is found to be dominated by the entropic effects, namely, how the CO 2 organizes next to the silica surface. The CO 2 self-diffusion coefficient shows the strongest pore size dependence. It is strongly diminished in small pores and does not reach the bulk fluid value even in 6 nm pores. It also decreases with pressure, yielding an activation volume that increases with pore size. These results provide new insight into the behavior of a compressible fluid in nanoscale confinement.

Godahewa, Sahan M. [Univ. of Kansas, Lawrence, KS ↗
DOE OSTI2026

Structural characterization of neutron irradiated hexagonal boron-10 nitride-15 single crystals

The negatively charged boron vacancy ($V$$^{–}_{⁠B}$⁠) in hexagonal boron nitride (hBN) is a promising quantum defect that can be used to sense pressure, temperature, and magnetic field with high spatial resolution. hBN enriched with the boron-10 and nitrogen-15 isotopes, denoted h 10 B 15 N, has good contrast and coherence for quantum sensing because nitrogen-15 has nuclear spin (1/2), reducing hyperfine interactions. Boron vacancies can be generated by neutron irradiation, which causes the transmutation of the boron-10 isotope to lithium-7. In this study, the ancillary structural, compositional, and mechanical properties of h 10 B 15 N crystals that have been subjected to neutron irradiation fluences from 1.4 × 10 16 to 8.4 × 10 17 n/cm 2 were thoroughly characterized. Besides creating $V$$^{–}_{⁠B}$⁠, the process also induces other defects that generate strain in the crystal lattice. In turn, the mechanical properties of these crystals change drastically. Investigated here are the visual changes, lattice integrity, composition, crystal strain, and elastic constants (C 33 and C 66 ) to assess how these characteristics change as a function of neutron fluence.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Photocarrier dynamics at the interface between WS 2 and ozone-irradiated graphene

We investigate the photocarrier properties of heterostructures (HSs) formed by WS 2 and ozone-irradiated graphene (OI-graphene), with a focus on the impact of ozone irradiation. Photoluminescence and Raman spectroscopy reveal a pronounced doping effect induced by ozone irradiation on the graphene layer. Transient absorption measurements demonstrate a substantial suppression of charge transfer efficiency across the interface in the presence of ozone molecules. Spatially resolved pump-probe measurements further show a significant reduction in the diffusion coefficient of photocarriers in WS 2 on OI-graphene compared to that of individual WS 2 monolayers. The slower diffusion suggests enhanced spatial separation of electrons and holes in the WS 2 layer, induced by a built-in electric field at the interface. This effect arises from the combined influences of doping and dielectric property changes caused by ozone molecules. These findings highlight the critical influence of ozone irradiation on graphene and HS interfaces, offering valuable insights for the design of future graphene-based two-dimensional HSs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Search for the production of Higgs-portal scalar bosons in the NuMI beam using the MicroBooNE detector

We present the strongest experimental limits to date on the mixing angle, 𝜃, with which a new scalar particle, 𝑆, mixes with the Higgs field in the mass range 110 MeV < 𝑚 𝑆 <155 MeV. This result uses the MicroBooNE liquid argon time projection chamber to search for decays of these Higgs-portal scalar particles through the 𝑆 → 𝑒 + ⁢𝑒 − channel with the decays of kaons in the NuMI neutrino beam acting as the source of the scalar particles. The analysis uses an exposure of 2.01 × 10 21 protons on target of NuMI beam data including periods when the beam focusing system was configured to focus positively charged hadrons and separate periods when negatively charged hadrons were focused. The analysis searches for scalar particles produced from kaons decaying in flight in the beam’s decay volume and at rest in the target and absorber. At 𝑚 𝑆 =125 MeV (𝑚 𝑆 =150 MeV) we set a limit of 𝜃 < 3.19 ×10 −4 (𝜃 < 2.79 ×10 −4 ) at the 95% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Continuum-electron interferometry for enhancement of photoelectron circular dichroism and measurement of bound, free, and mixed contributions to chiral response

We develop photoelectron interferometry based on laser-assisted extreme ultraviolet ionization for flexible and robust control of photoelectron circular dichroism in randomly oriented chiral molecules. A comb of XUV photons ionizes a sample of chiral molecules in the presence of a time-delayed infrared or visible laser pulse promoting interferences between components of the XUV-ionized photoelectron wave packet. In striking contrast to multicolor phase control schemes relying on pulse shaping techniques, the magnitude of the resulting chiral signal is here controlled by the time delay between the XUV and laser pulses. Furthermore, we show that the relative polarization configurations of the XUV and IR fields allow for disentangling the contributions of bound and continuum states to the chiral response. Our proposal provides a simple, robust, and versatile tool for the control of photoelectron circular dichroism and experimentally feasible protocol for probing the individual contributions of bound and continuum states to the photoelectron circular dichroism in a time-resolved manner.

atomic and molecular processes in external fields↗
DOE OSTI2025

Measurement of single- and double-differential cross sections for mesonless charged-current muon neutrino interactions on argon with final-state protons using the MicroBooNE detector

Charged-current neutrino interactions with final states containing zero mesons and at least one proton are of high interest for current and future accelerator-based neutrino oscillation experiments. Using the Booster Neutrino Beam and the MicroBooNE detector at Fermi National Accelerator Laboratory, we have obtained the first double-differential cross-section measurements of this channel for muon neutrino scattering on an argon target with a leading proton momentum threshold of 0.25 GeV/𝑐. We also report a flux-averaged total cross section of 𝜎 = (11.8±1.2) × 10 −38 cm 2 /Ar and several single-differential measurements which extend and improve upon previous results. Statistical and systematic uncertainties are quantified with a full treatment of correlations across 359 kinematic bins, including correlations between distributions describing different observables. The resulting dataset provides the most detailed information obtained to date for testing models of mesonless neutrino-argon scattering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Real singlet scalar benchmarks in the multi-TeV resonance regime

Scalar extensions of the Standard Model (SM) are of much interest at the Large Hadron Collider (LHC) and future colliders. In particular, these models can give rise to resonant di-Higgs production and alter the Higgs trilinear coupling. In this paper, we study di-Higgs production in the Standard Model extended by a real scalar singlet with no additional symmetries. We determine how large the resonant di-Higgs rate and variation in the Higgs trilinear coupling can be in four scenarios: current LHC results and projected results at the high luminosity LHC (HL-LHC), the HL-LHC combined with a circular 𝑒 − ⁢𝑒 + collider such as the Circular Electron Positron Collider or Future Circular Collider with electron-positron collisions, and the HL-LHC combined with a linear 𝑒 − ⁢𝑒 + collider such as the International Linear Collider. While these are updated results from a previous study by [I. M. Lewis and M. Sullivan, Benchmarks for double Higgs production in the singlet extended standard model at the LHC, Phys. Rev. D 96, 035037 (2017).] using current LHC data, we go further and find benchmark points in the multi-TeV resonance regime for future colliders beyond the HL-LHC. Considering current LHC results, the resonant di-Higgs rate can still be an order of magnitude larger than the SM predicted di-Higgs rate. In the HL-LHC scenario, the Higgs trilinear coupling can still be a factor of three larger than the SM prediction for resonance masses in the 1.5–3.5 TeV range, where resonant searches may have less reach. This enhancement is just at the projected 2⁢𝜎 sensitivity of the HL-LHC. We find there are resonance masses for which the change in the Higgs trilinear is maximized while the resonant rate is negligible. We provide an analytical understanding of these effects with a discussion on the interplay of various constraints on the parameter space and the Higgs trilinear coupling.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Demonstration of new MeV-scale capabilities in large neutrino LArTPCs using ambient radiogenic and cosmogenic activity in MicroBooNE

Large neutrino liquid argon time projection chamber (LArTPC) experiments can broaden their physics reach by reconstructing and interpreting MeV-scale energy depositions, or blips, present in their data. We demonstrate new calorimetric and particle discrimination capabilities at the MeV energy scale using reconstructed blips in data from the MicroBooNE LArTPC at Fermilab. We observe a concentration of low-energy (<3 MeV) blips around fiberglass mechanical support struts along the time projection chamber edges with energy spectrum features consistent with the Compton edge of 2.614 MeV 208 Tl decay 𝛾 rays. These features are used to verify proper calibration of electron energy scales in MicroBooNE’s data to few percent precision and to measure the specific activity of 208 Tl in the fiberglass composing these struts, (11.7 ± 0.2⁢(stat) ± 3.1⁢(syst)) Bq/kg. Cosmogenically produced blips above 3 MeV in reconstructed energy are used to showcase the ability of large LArTPCs to distinguish between low-energy proton and electron energy depositions. An enriched sample of low-energy protons selected using this new particle discrimination technique is found to be smaller in data than in dedicated corsika cosmic-ray simulations, suggesting either incorrect corsika modeling of incident cosmic fluxes or particle transport modeling issues in geant4.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Data-driven model validation for neutrino-nucleus cross section measurements

Neutrino-nucleus cross section measurements are needed to improve interaction modeling to meet the precision needs of neutrino experiments in efforts to measure oscillation parameters and search for physics beyond the Standard Model. We review the difficulties associated with modeling neutrino-nucleus interactions that lead to a dependence on event generators in oscillation analyses and cross section measurements alike. We then describe data-driven model validation techniques intended to address this model dependence. The method relies on utilizing various goodness-of-fit tests and the correlations between different observables and channels to probe the model for defects in the phase space relevant for the desired analysis. These techniques shed light on relevant mismodeling, allowing it to be detected before it begins to bias the cross section results. We compare more commonly used model validation methods which directly validate the model against alternative ones to these data-driven techniques and show their efficacy with fake data studies. These studies demonstrate that employing data-driven model validation in cross section measurements represents a reliable strategy to produce robust results that will stimulate the desired improvements to interaction modeling.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗