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DOE OSTI2020

Interplay of Open-Shell Spin-Coupling and Jahn–Teller Distortion in Benzene Radical Cation Probed by X-ray Spectroscopy

Here we report a theoretical investigation and elucidation of the X-ray absorption spectra of neutral benzene and of the benzene cation. The generation of the cation by multiphoton ultraviolet (UV) ionization and the measurement of the carbon K-edge spectra of both species using a table-top high-harmonic generation source are described in the companion experimental paper. We show that the 1sC → π transition serves as a sensitive signature of the transient cation formation, as it occurs outside of the spectral window of the parent neutral species. Moreover, the presence of the unpaired (spectator) electron in the π-subshell of the cation and the high symmetry of the system result in significant differences relative to neutral benzene in the spectral features associated with the 1sC → π* transitions. High-level calculations using equation-of-motion coupled-cluster theory provide the interpretation of the experimental spectra and insight into the electronic structure of benzene and its cation. The prominent split structure of the 1sC → π* band of the cation is attributed to the interplay between the coupling of the core → π* excitation with the unpaired electron in the π-subshell and the Jahn–Teller distortion. The calculations attribute most of the splitting (~1–1.2 eV) to the spin coupling, which is visible already at the Franck–Condon structure, and we estimate the additional splitting due to structural relaxation to be around ~0.1–0.2 eV. These results suggest that X-ray absorption with increased resolution might be able to disentangle electronic and structural aspects of the Jahn–Teller effect in the benzene cation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Nanophotonics for Chemical Imaging and Spectroscopy

The manipulation of light and light-matter interactions on the nanoscale is enabled by the unique optical properties of plasmonic metal nanostructures and nanoparticles. Indeed, engineered hybrid molecular-plasmonic nanostructures have enabled single molecule detection and identification via surface-enhanced Raman scattering (SERS). Further, the same effect is at the core of visualizing single molecules with sub-nanometer spatial resolution via tip-enhanced Raman scattering (TERS). More generally, modern applications of plasmon-enhanced spectroscopy and microscopy fueled advances in fields as diverse as quantum and semiconductor materials, heterogeneous catalysis, and the health sciences, to name a few. All these exciting developments and many more are touched in this virtual special issue (VSI) on nanophotonics. From ultra-precise chemical imaging measurements performed in a scanning tunneling microscope chamber to single molecule spectroscopic measurements performed at solid-air and solid-liquid interfaces, this VSI includes contributions from active practitioners that are all striving to better-understand increasingly complex interfaces encountered in the biological, materials, and chemical sciences.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Rapid Polyolefin Plastic Hydrogenolysis Mediated by Single-Site Heterogeneous Electrophilic/Cationic Organo-group IV Catalysts

A homologous series of cationic electrophilic group IV metal hydrides (M = Ti, Zr, Hf) created by chemisorption of the corresponding MNp 4 precursors on highly Brønsted acidic sulfated alumina (AlS) to yield loosely coordinated surface AlS/MNp 2 (Np = neopentyl) species are systematically characterized by ICP, EXAFS/XANES, DRIFTS, and solid-state high-resolution multidimensional NMR spectroscopy (SSNMR), as well as by energy span DFT computation. With effective stirring, these complexes readily undergo reaction with H 2 to yield AlS/M(alkyl)H species, which are highly active for the hydrogenolysis of diverse commercial polyethylenes, α-olefin-ethylene copolymers, isotactic polypropylene, and postconsumer polyolefins including high-density polyethylenes, yielding medium and small linear and branched hydrocarbons at turnover frequencies as high as 36,300 h –1 at 200 °C/17 atm H 2 for M = Zr. For given polyolefin and reaction conditions, turnover frequencies scale approximately as M = Zr > Hf > Ti, whereas catalyst thermal stability scales approximately as M = Hf ≈ Zr > Ti, and these trends are qualitatively understandable from the DFT analysis. These catalytic results reveal that the AlS/Hf(R)H-mediated hydrogenolysis favors wax-like and liquid products, whereas the AlS/Zr(R)H-mediated hydrogenolysis can be tuned between gases and liquids. Finally, DFT analysis identifies β-alkyl elimination as the turnover-limiting C–C scission process, which is particularly facile in these cationic d 0 complexes but not so in the neutrally charged analogues.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Combining Theory and Experiment to Map the Atomic-Level Structure–Energy Pathways of Adsorbate-Mediated Phase Changes in a Cooperatively Flexible Metal–Organic Framework

An important subclass of metal–organic frameworks (MOFs) exhibits cooperative flexibility, wherein individual crystallites undergo global structural phase changes in response to external stimuli. Where cooperative flexibility results in reversible changes between crystalline states of distinct accessible porosity, these frameworks can exhibit rare yet desirable behaviors that cannot be explained by local dynamics alone. Yet, the chemical and structural origins of cooperative flexibility and how frameworks undergo these reversible phase changes at the atomic level remain poorly understood. Deliberate design for specific applications is therefore exceedingly difficult, and there is great impetus to develop a fundamental understanding of this phenomenon. Here, an effective and widely accessible computational approach is developed, which is designed to provide microscopic resolution via direct comparison to experimental data along the desorption-guided pathway. The strategy is applied to explain the desorption-induced phase change in an experimentally well-characterized framework, CdIF-13 (sod-Cd(benzimidazolate)2), where experiment alone was unable to resolve the atomistically detailed phase change landscape. Our findings reveal that the cooperative phase change pathways are adsorbate dependent with thermodynamics of intermediate structural states dictated by a nuanced interplay of ligand orientation, skeletal symmetry, and modes of surface adsorption. The results reveal that this isotropically flexible framework is “chaperoned” through a complex energy landscape by specific adsorbates, revealed by the reported computational approach with atomic-level insight and validated by experimentally determined structures. Thus, this work facilitates both understanding and future design of flexible materials for applications in gas storage, transport, delivery, and separation technologies.

03 NATURAL GAS↗

DOE OSTI2022

Sea Ice Rheology Experiment (SIREx): 1. Scaling and Statistical Properties of Sea-Ice Deformation Fields

As the sea-ice modeling community is shifting to advanced numerical frameworks, developing new sea-ice rheologies, and increasing model spatial resolution, ubiquitous deformation features in the Arctic sea ice are now being resolved by sea-ice models. Initiated at the Forum for Arctic Modeling and Observational Synthesis, the Sea Ice Rheology Experiment (SIREx) aims at evaluating state-of-the-art sea-ice models using existing and new metrics to understand how the simulated deformation fields are affected by different representations of sea-ice physics (rheology) and by model configuration. Part 1 of the SIREx analysis is concerned with evaluation of the statistical distribution and scaling properties of sea-ice deformation fields from 35 different simulations against those from the RADARSAT Geophysical Processor System (RGPS). For the first time, the viscous-plastic (and the elastic-viscous-plastic variant), elastic-anisotropic-plastic, and Maxwell-elasto-brittle rheologies are compared in a single study. We find that both plastic and brittle sea-ice rheologies have the potential to reproduce the observed RGPS deformation statistics, including multi-fractality. Model configuration (e.g., numerical convergence, atmospheric representation, spatial resolution) and physical parameterizations (e.g., ice strength parameters and ice thickness distribution) both have effects as important as the choice of sea-ice rheology on the deformation statistics. It is therefore not straightforward to attribute model performance to a specific rheological framework using current deformation metrics. In light of these results, we further evaluate the statistical properties of simulated Linear Kinematic Features in a SIREx Part 2 companion paper.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2021

Giant phonon anomalies in the proximate Kitaev quantum spin liquid α-RuCl 3

The Kitaev quantum spin liquid epitomizes an entangled topological state, for which two flavors of fractionalized low-energy excitations are predicted: the itinerant Majorana fermion and the Z 2 gauge flux. Here, it was proposed recently that fingerprints of fractional excitations are encoded in the phonon spectra of Kitaev quantum spin liquids through a novel fractional-excitation-phonon coupling. Here, we detect anomalous phonon effects in α-RuCl 3 using inelastic X-ray scattering with meV resolution. At high temperature, we discover interlaced optical phonons intercepting a transverse acoustic phonon between 3 and 7 meV. Upon decreasing temperature, the optical phonons display a large intensity enhancement near the Kitaev energy, J K ~8 meV, that coincides with a giant acoustic phonon softening near the Z 2 gauge flux energy scale. These phonon anomalies signify the coupling of phonon and Kitaev magnetic excitations in α-RuCl 3 and demonstrates a proof-of-principle method to detect anomalous excitations in topological quantum materials.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Altering the solubility of metal–organic polyhedra via pendant functionalization of Cp 3 Zr 3 O(OH) 3 nodes

Here, the chemistry of zirconium-based metal-organic polyhedra (ZrMOPs) is often limited by their poor solubilities. Despite their attractive features—including high yielding and facile syntheses, predictable topologies, high stability, and tunability—problematic solubilities have caused ZrMOPs to be under-studied and under-applied. Although these cages have been synthesized with a wide variety of carboxylate-based bridging ligands, we explored a new method for ZrMOP functionalization via node-modification, which we hypothesized could influence solubility. Herein, we report ZrMOPs with benzyl-, vinylbenzyl-, and trifluoromethylbenzyl-pendant groups decorating cyclopentadienyl moieties. The series was characterized by 1 H/ 19 F NMR, high-resolution mass spectrometry, infrared spectroscopy, and single-crystal X-ray diffraction. The effects of node functionalities on ZrMOP solubility were quantified using inductively coupled plasma mass spectrometry. Substitution caused a decrease in water solubility, but for certain organic solvents, e.g. DMF, solubility could be enhanced by ~20×, from 16 μM for the unfunctionalized cage to 310 μM for the vinylbenzyl- and trifluoromethylbenzyl-cages.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Experimental study on the startup of the annular wick type heat pipe using fiber optical temperature measurement technique

This study used optical fiber-distributed temperature sensors to measure the internal and external temperature distributions of a water-cooled heat pipe. The sensor technology used in this study is fiber optical distributed temperature sensing, a distributed sensing technique based on the naturally occurring Rayleigh backscatter in optical fibers. This measurement technique provides maximum spatial resolution for static and semi-static applications. Using this sensor, the temperature distribution of the heat pipe's internal, external, vapor core, and the wick was measured with a spatial resolution of 0.65 mm, a sampling frequency of 40 Hz, and a temperature resolution of 0.1 °C. Through the measured temperature distribution database, the starting phenomenon, the effective length trend, and the limitation onset were observed. From the results, it is found that a high-temperature peak appears at the evaporator if a high initial power (75 W) is imposed on the heat pipe, even after the heat pipe approaches the normal operating status. The peak is not observed in a slower startup (30 W initial power then slowly increased to 75 W). It is also found that the temperature distributions and effective condenser length of the heat pipe highly depend on the cooling conditions. There are variations in the temperature according to the radial direction of the horizontal heat pipe due to gravity. In conclusion, lead and lag of the temperature evolution were observed at the onset of the operating limitations.

42 ENGINEERING↗

DOE OSTI2021

WALLABY pilot survey: H i gas disc truncation and star formation of galaxies falling into the Hydra I cluster

ABSTRACT We present results from our analysis of the Hydra I cluster observed in neutral atomic hydrogen (H i) as part of the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). These WALLABY observations cover a 60-square-degree field of view with uniform sensitivity and a spatial resolution of 30 arcsec. We use these wide-field observations to investigate the effect of galaxy environment on H i gas removal and star formation quenching by comparing the properties of cluster, infall, and field galaxies extending up to ∼5R200 from the cluster centre. We find a sharp decrease in the H i-detected fraction of infalling galaxies at a projected distance of ∼1.5R200 from the cluster centre from $\sim 85{{\ \rm per\ cent}}$ to $\sim 35{{\ \rm per\ cent}}$. We see evidence for the environment removing gas from the outskirts of H i-detected cluster and infall galaxies through the decrease in the H i to r-band optical disc diameter ratio. These galaxies lie on the star-forming main sequence, indicating that gas removal is not yet affecting the inner star-forming discs and is limited to the galaxy outskirts. Although we do not detect galaxies undergoing galaxy-wide quenching, we do observe a reduction in recent star formation in the outer disc of cluster galaxies, which is likely due to the smaller gas reservoirs present beyond the optical radius in these galaxies. Stacking of H i non-detections with H i masses below $M_{\rm {HI}}\lesssim 10^{8.4}\, \rm {M}_{\odot }$ will be required to probe the H i of galaxies undergoing quenching at distances ≳60 Mpc with WALLABY.

Reynolds, T. N. (ORCID:0000000266065953)↗

DOE OSTI2021

Unraveling the Orbital Physics in a Canonical Orbital System KCuF 3

We explore the existence of the collective orbital excitations, orbitons, in the canonical orbital system KCuF 3 using the Cu L 3 -edge resonant inelastic x-ray scattering. We show that the nondispersive high-energy peaks result from the Cu 2+ dd orbital excitations. These high-energy modes display good agreement with the ab initio quantum chemistry calculation, indicating that the d d excitations are highly localized. At the same time, the low-energy excitations present clear dispersion. They match extremely well with the two-spinon continuum following the comparison with Müller ansatz calculations. The localized d d excitations and the observation of the strongly dispersive magnetic excitations suggest that the orbiton dispersion is below the resolution detection limit. Our results can reconcile with the strong local Jahn-Teller effect in KCuF 3 , which predominantly drives orbital ordering.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2023

Ultrafast Dynamics of Intrinsic Anomalous Hall Effect in the Topological Antiferromagnet Mn 3 Sn

Here, we investigate ultrafast dynamics of the anomalous Hall effect (AHE) in the topological antiferromagnet Mn 3 ⁢Sn with sub-100 fs time resolution. Optical pulse excitations largely elevate the electron temperature up to 700 K, and terahertz probe pulses clearly resolve ultrafast suppression of the AHE before demagnetization. The result is well reproduced by microscopic calculation of the intrinsic Berry-curvature mechanism while the extrinsic contribution is clearly excluded. Our work opens a new avenue for the study of nonequilibrium AHE to identify the microscopic origin by drastic control of the electron temperature by light.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Primary track recovery in high-definition gas time projection chambers

Abstract We develop and validate a new algorithm called primary track recovery () that effectively deconvolves known physics and detector effects from nuclear recoil tracks in gas time projection chambers (TPCs) with high-resolution readout. This gives access to the primary track charge, length, and vector direction (helping to resolve the “head-tail” ambiguity). Additionally, provides a measurement of the transverse and longitudinal diffusion widths, which can be used to determine the absolute position of tracks in the drift direction for detector fiducialization. Using simulated helium recoils in an atmospheric pressure TPC with a 70:30 mixture of $$\hbox {He:CO}_2$$ He:CO 2 we compare the performance of to traditional methods for all key track variables. We find that the algorithm reduces reconstruction errors, including those caused by charge integration, for tracks with mean length-to-width ratios 1.4 and above, corresponding to recoil energies of 20 keV and above in the studied TPCs. We show that improves on existing methods for head-tail disambiguation, particularly for highly inclined tracks, and improves the determination of the absolute position of recoils on the drift axis via transverse diffusion. We find that can partially recover charge structure integrated out by the detector in the z direction, but that its determination of energy and length have worse resolution compared to existing methods. We use experimental data to qualitatively verify these findings and discuss implications for future directional detectors at the low-energy frontier.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Methods for Estimating Dose from Galactic Cosmic Rays and Jovian Radiation Belts on Reduced-Order Monte Carlo Geometries

This document outlines the methods and tools developed to estimate dose rates from galactic cosmic rays and the trapped radiation belts surrounding Jupiter using Monte Carlo particle transport software. Furthermore, the techniques described here are specific for translating high-resolution MAVRIC models to analogous but lower resolution Monte Carlo N-Particle Transport (MCNP) code models to estimate charged particle effects on models originally developed to study neutral particles only. This capability was initially developed to predict doses to various components of dynamic radioisotope power systems for spaceflight applications, but the tools and methods can be easily applied to other problem geometries and expanded to other space radiation environments.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

The (Un)reasonable Effectiveness of Neural Network in Cherenkov Calorimetry

We report a greater than factor of two improvement in the hadronic energy resolution of a simulated Cherenkov calorimeter by estimating the energy with machine learning over traditional techniques. The prompt signal formation and energy threshold properties of Cherenkov radiation provide identifiable features that machine learning techniques can exploit to produce a superior model for energy reconstruction. We simulated a quartz-fiber calorimeter via the GEANT4 framework to study the reconstruction techniques in single events. We compared the machine learning-based reconstruction performance to the traditional simple sum of signal and dual-readout techniques that use both Cherenkov and scintillation signals. We describe why this game-changing approach to Cherenkov hadron calorimetry excels and our plans for a dedicated beam test to validate these findings with a fast, radiation-hard hadron calorimeter prototype.

Akchurin, Nural↗

DOE OSTI2022

Super-localisation of a point-like emitter in a resonant environment: Correction of the mirage effect

In this paper, we show that it is possible to overcome one of the fundamental limitations of super-resolution microscopy: the necessity to be in an optically homogeneous environment. Using recent modal approximation results from [ 10 , 7 ], we show, as a proof of concept, that it is possible to recover the position of a single point-like emitter in a known resonant environment from far-field measurements, with a precision two orders of magnitude below the classical Rayleigh limit. The procedure does not involve solving any partial differential equation, is computationally light (optimisation in \begin{document}$ \mathbb{R}^d $\end{document} with \begin{document}$ d $\end{document} of the order of \begin{document}$ 10 $\end{document} ) and is therefore suited for the recovery of a very large number of single emitters.

Mathematics↗

DOE OSTI2025

The GammaTPC Gamma-Ray Telescope Concept

We present GammaTPC, a transformative 0.1-10 MeV $\gamma$-ray instrument concept featuring a tracker using a liquid argon time projection chamber (LAr TPC) technology with the novel GAMPix high spatial resolution and ultra low power charge readout. These enable an economical instrument with unprecedented effective area and sensitivity. We discuss the design and technology in some detail, including how a LAr TPC can be staged in space. Finally, we present a first study of the sensitivity of the instrument in the Compton regime using a new framework for analyzing Compton telescope data.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2020

Vertical effective stress and temperature as controls of quartz cementation in sandstones: Evidence from North Sea Fulmar and Gulf of Mexico Wilcox sandstones

Here we present quantitative petrographic data, high spatial resolution oxygen isotope analyses of quartz cement, basin modelling and a kinetic model for quartz precipitation for two Paleocene-Eocene Wilcox Group sandstones from Texas and two Jurassic Fulmar Formation sandstones from the Central North Sea. At each location, one sandstone has been buried to ca. 145 °C and one to ca. 185 °C. A key difference between the Wilcox and Fulmar burial histories is that the Wilcox sandstones are currently at higher vertical effective stresses and, from basin modelling studies, have been subjected to generally higher vertical effective stresses through their burial history. The amounts of quartz cement in the Wilcox sandstones are between 12 and 18%, and between 2 and 6% in the Fulmar sandstones. High-spatial-resolution oxygen isotope data obtained from the quartz cements suggest temperature ranges for quartz precipitation from 60 to 80 °C to values approaching maximum burial temperature. Factors such as grain coatings or the timing of petroleum emplacement cannot explain the differences in the amounts of quartz cement. Petrographic data show that most of the silica for quartz cement can be derived from intergranular pressure dissolution. Although the sample set is small, we interpret the results to suggest that the differences in quartz cementation in Fulmar and Wilcox sandstones can be explained better by differences in their vertical effective stress history than their temperature history; in this case, the supply of silica rather than the precipitation of quartz becomes an important control on the rate and extent of cementation.

58 GEOSCIENCES↗

DOE OSTI2024

High-resolution chemical patterns from negative tone resists for the integration of extreme ultraviolet patterns of metal-oxide resists with directed self-assembly of block copolymers

Extreme ultraviolet (EUV) lithography faces significant challenges in designing suitable resist materials that can provide adequate precision, while maintaining economically viable throughput. These challenges in resist materials have led to printing failures and high roughness in EUV patterns, compromising the performance of semiconductor devices. Integrating directed self-assembly (DSA) of block copolymers (BCPs) with EUV lithography offers a promising solution because, while the BCPs register to the EUV-defined chemical guiding pattern, the thermodynamically determined structures of the BCPs automatically rectify defects and roughness in the EUV pattern. Despite the superior resolution of metal-oxide EUV resists (MORs), their application to DSA is limited by the difficulty in converting them into chemical patterns that allow effective transfer of the rectified patterns of DSA films into inorganic materials. To address this challenge, this study introduces a novel strategy for fabricating chemical patterns using hydrogen silsesquioxane (HSQ), a high-resolution negative tone inorganic resist, as a model system for MORs. Initially, a sacrificial Cr pattern is generated from HSQ patterns via reactive ion etching. The sacrificial Cr pattern is converted into a chemical pattern by first grafting a water-soluble polyethylene oxide brush onto the substrate, then wet etching the Cr, and finally grafting nonpolar polystyrene brushes. Assembling polystyrene-block-poly(methyl methacrylate) on these patterns results in structures oriented and registered with the underlying pattern, achieving 24 nm full-pitch resolutions. In conclusion, this approach has the potential to integrate MOR patterns into the DSA process, thereby enabling the generation of high-quality sub-10 nm patterns with high-χ BCPs.

Atomic force microscopy↗