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DOE OSTI2023

Author Correction: High-fidelity qutrit entangling gates for superconducting circuits

The original version of this Article contained an error in the second sentence of the Acknowledgements, which incorrectly read: ‘This work was supported by the Quantum Testbed Program of the Advanced Scientific Computing Research for Basic Energy Sciences program, Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231’. The correct version states ‘the Quantum Testbed Program of the Advanced Scientific Computing Research Division’ in place of ‘the Quantum Testbed Program of the Advanced Scientific Computing Research for Basic Energy Sciences program’. This has been corrected in both the PDF and HTML versions of the Article.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Physics and chemistry from parsimonious representations: image analysis via invariant variational autoencoders

Electron, optical, and scanning probe microscopy methods are generating ever increasing volume of image data containing information on atomic and mesoscale structures and functionalities. This necessitates the development of the machine learning methods for discovery of physical and chemical phenomena from the data, such as manifestations of symmetry breaking phenomena in electron and scanning tunneling microscopy images, or variability of the nanoparticles. Variational autoencoders (VAEs) are emerging as a powerful paradigm for the unsupervised data analysis, allowing to disentangle the factors of variability and discover optimal parsimonious representation. Here, we summarize recent developments in VAEs, covering the basic principles and intuition behind the VAEs. The invariant VAEs are introduced as an approach to accommodate scale and translation invariances present in imaging data and separate known factors of variations from the ones to be discovered. We further describe the opportunities enabled by the control over VAE architecture, including conditional, semi-supervised, and joint VAEs. Several case studies of VAE applications for toy models and experimental datasets in Scanning Transmission Electron Microscopy are discussed, emphasizing the deep connection between VAE and basic physical principles. Python codes and datasets discussed in this article are available at https://github.com/saimani5/VAE-tutorials and can be used by researchers as an application guide when applying these to their own datasets.

36 MATERIALS SCIENCE↗

DOE OSTI2020

A caloritronics-based Mott neuristor

Abstract Machine learning imitates the basic features of biological neural networks at a software level. A strong effort is currently being made to mimic neurons and synapses with hardware components, an approach known as neuromorphic computing. While recent advances in resistive switching have provided a path to emulate synapses at the 10 nm scale, a scalable neuron analogue is yet to be found. Here, we show how heat transfer can be utilized to mimic neuron functionalities in Mott nanodevices. We use the Joule heating created by current spikes to trigger the insulator-to-metal transition in a biased VO 2 nanogap. We show that thermal dynamics allow the implementation of the basic neuron functionalities: activity, leaky integrate-and-fire, volatility and rate coding. This approach could enable neuromorphic hardware to take full advantage of the rapid advances in memristive synapses, allowing for much denser and complex neural networks.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Acidity of surface-infiltrated binary oxides as a sensitive descriptor of oxygen exchange kinetics in mixed conducting oxides

Improving the kinetics of O 2 reduction on oxide surfaces is critical in many energy and fuel conversion technologies. Here we show that the acidity scale for binary oxides is a powerful descriptor for tuning and predicting oxygen surface exchange kinetics on mixed conducting oxides. By infiltrating a selection of binary oxides from strongly basic (Li 2 O) to strongly acidic (SiO 2 ) onto the surface of Pr 0.1 Ce 0.9 O 2-δ samples, it was possible to vary the chemical surface exchange coefficient k chem by 6 orders of magnitude, with basic oxides such as Li 2 O increasing k chem by nearly 1,000 times, with surface concentrations as low as 50 ppm impacting k chem . Strikingly, although the pre-exponential of k chem scales linearly with the acidity of the infiltrated binary oxide, there is nearly no change in the activation energy. Here, the origin of these dramatic changes is proposed to arise from the systematic increase in electron concentration at the Pr 0.1 Ce 0.9 O 2-δ surface with the decreasing acidity of the infiltrated binary oxide.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2021

Introduction to (Photo)electrocatalysis For Renewable Energy

Humanity is facing a significant and growing energy demand, necessitating a new energy paradigm built on clean and abundant renewable energy.1 Within this context, electrocatalysis and (photo)electrocatalysis hold great promise for enabling renewable energies such as solar and wind power to overcome the transient nature of their energy output.2-6 Developing catalysts that operate efficiently and selectively, and that are also robust, has been the focus of much research. This special issue brings together the latest advances in the fundamental and applied science addressing the synthesis, characterization, mechanisms, and performance of (photo)electrocatalysts for energy storage and conversion of small molecules into useful specialty and commodity chemicals and fuels. The electrocatalysts and (photo)electrocatalysts highlighted in this issue include metalloenzymes, homogeneous and supported molecular catalysts, and diverse heterogeneous nanoparticulate and thin film systems. The reports span across basic and applied studies and encompass both experimental and theoretical investigations.

Dey, Abhishek↗

DOE OSTI2020

X-ray photoelectron spectroscopy of piperidinium ionic liquids: a comparison to the charge delocalised pyridinium analogues

In this study, nine piperidinium-based ionic liquids are analysed by X-ray photoelectron spectroscopy. The effect of alkyl substituent length and the nature of the anion on the electronic environment of the cation are investigated. The electronic environment of the hetero carbon and the cationic nitrogen is compared between two structurally similar cations, 1-octyl-1-methylpiperidinium ([C 8 C 1 Pip] + ) versus 1-octylpyridinium ([C 8 Py] + ). Due to the charge delocalisation, the hetero carbon component within [C 8 Py] + is more positively charged, which exhibits much higher binding energy; whilst the cationic nitrogen component is in the similar electronic environment. The impact of the charge delocalisation on the electronic environment of the anion is also compared between [C 8 C 1 Pip] + and [C 8 Py] + . Here, it is found that for the more basic anion, the cation can significantly affect the electronic environment of the anion; for the less basic anion, such an effect concentrates on the component bearing more negative point charges.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Emerging investigator series: local pH effects on carbon oxidation in capacitive deionization architectures

In this work, the effect of pH and potential is examined for the oxidation of carbon cloth electrodes used in capacitive deionization (CDI) processes. The degree of oxidation of the electrode surface, examined using the electrode's potential of zero charge (E pzc ) and measured using chronoamperometry and cyclic voltammetry, is found to be strongly correlated to the pH of the solution at the interface. Local pH measurements are examined at anodes and cathodes in full CDI and membrane-assisted capacitive deionization (MCDI) cells at cell voltages ranging from 0.3–1.2 V. The cathode is shown to be basic under charging potentials while the anode is found to be acidic. This local pH is found to be highly transient during charging and discharging in CDI cells while the pH is found to be relatively static in the MCDI cells, maintaining a basic pH at the cathode and an acidic pH at the anode even when the cell is discharged. Ion exchange membranes (IEM) are found to have two functions: (1) limiting co-ion expulsion that results from specific ion adsorption and (2) limiting the effects of parasitic Faradaic reactions on the separation process by stabilizing the local pH thereby mitigating dissolved oxygen reduction at the cathode and lessening carbon oxidation at the anode. Performance comparisons including the salt adsorption capacity and charge efficiency are also compared for these systems.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

X-ray photoelectron spectroscopy of morpholinium ionic liquids: impact of a long alkyl side substituent on the cation–anion interactions

In this study, X-ray photoelectron spectroscopy is used to analyse nine morpholinium ionic liquids, which are of great interest in green chemistry because of their low toxicity and high recyclability. Here, the effect of the alkyl chain length on the aliphatic C 1s binding energy and the impact of the anion basicity on the cationic N 1s and O 1s binding energies are investigated. It is concluded that by changing the basicity of the anion, there is a more notable change in the electronic environment of the oxygen centre. The impact of a long alkyl side substituent on the cation–anion interactions is also discussed. It is observed that there is an intense charge shielding effect of the alkyl side chain in the cases of octyl and dodecyl substituents, which is reflected in the reduced Br 3d 5/2 binding energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Non-thermal atmospheric pressure plasma–liquid synthesis of organic acids in aqueous solution from carbon monoxide

This work aims at understanding the conversion of CO to organic acids, namely oxalic acid and formic acid, using non-thermal atmospheric pressure plasma over aqueous solutions. CO exhibited significantly higher conversion to organic acids (more than 15×) compared to CO 2 under the same reaction conditions. The result bolsters a proposed two-step process for CO 2 fixation, whereby CO 2 is first converted to CO, and then CO is converted to organic acids. The organic acids produced from CO are intermediates in the water–gas shift (WGS) reaction of CO in the presence of an aqueous solution to dissolved CO 2 and hydrogen gas. Based on a simple thermodynamic analysis, the organic acid yield was increased by lowering the plasma–liquid reaction temperature using an ice bath to cool the reaction flask. The composition of the organic acids could be varied by changing the pH of the solution. Oxalate was formed in higher concentrations with increasing solution pH above the pK a of the radical species (CO 2 )˙ − . Below the pK a value, formate was the exclusive organic acid formed. The production of formate has a rather weak pH dependence but is enhanced slightly at a basic pH above 10. Furthermore, at basic pH, the effect of electrolyte concentration comes into play. Higher electrolyte concentrations, leading to shorter electrolyte Debye lengths, resulted in lowered organic acid yields. The highest yields of organic acids obtained in our system were 122 mg L −1 for oxalate and 77 mg L −1 for formate at an optimum 1 mM NaOH concentration in the starting solution. This work is a successful pioneering example of CO to organic acids conversion using non-thermal plasmas, which opens the pathway for a promising two-step conversion process of CO 2 to organic acids.

Sudagar, Alcina Johnson [Washington University in ↗

DOE OSTI2022

The MeerKAT Galaxy Cluster Legacy Survey I. Survey Overview and Highlights

MeerKAT’s large number (64) of 13.5 m diameter antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900–1670 MHz) observations of 115 galaxy clusters, observed for ~6–10 h each in full polarisation. The first legacy product data release (DR1), made available with this paper, includes the MeerKAT visibilities, basic image cubes at ~8" resolution, and enhanced spectral and polarisation image cubes at ~8" and 15" resolutions. Typical sensitivities for the full-resolution MGCLS image products range from ~3–5 μJy beam –1 . The basic cubes are full-field and span 2° × 2°. The enhanced products consist of the inner 1.2° × 1.2° field of view, corrected for the primary beam. The survey is fully sensitive to structures up to ~10' scales, and the wide bandwidth allows spectral and Faraday rotation mapping. Relatively narrow frequency channels (209 kHz) are also used to provide H I mapping in windows of 0 < z < 0.09 and 0.19 < z < 0.48. Here, in this paper, we provide an overview of the survey and the DR1 products, including caveats for usage. We present some initial results from the survey, both for their intrinsic scientific value and to highlight the capabilities for further exploration with these data. These include a primary-beam-corrected compact source catalogue of ~626 000 sources for the full survey and an optical and infrared cross-matched catalogue for compact sources in the primary-beam-corrected areas of Abell 209 and Abell S295. We examine dust unbiased star-formation rates as a function of cluster-centric radius in Abell 209, extending out to 3.5 R 200 . We find no dependence of the star-formation rate on distance from the cluster centre, and we observe a small excess of the radio-to-100 μm flux ratio towards the centre of Abell 209 that may reflect a ram pressure enhancement in the denser environment. We detect diffuse cluster radio emission in 62 of the surveyed systems and present a catalogue of the 99 diffuse cluster emission structures, of which 56 are new. These include mini-halos, halos, relics, and other diffuse structures for which no suitable characterisation currently exists. We highlight some of the radio galaxies that challenge current paradigms, such as trident-shaped structures, jets that remain well collimated far beyond their bending radius, and filamentary features linked to radio galaxies that likely illuminate magnetic flux tubes in the intracluster medium. We also present early results from the H I analysis of four clusters, which show a wide variety of H I mass distributions that reflect both sensitivity and intrinsic cluster effects, and the serendipitous discovery of a group in the foreground of Abell 3365.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Role of sheared E × B flow in self-organized, improved confinement states in magnetized plasmas

A great scientific success story of magnetic fusion research in the past several decades is the theoretical development and experimental testing of the process of turbulence decorrelation and stabilization by sheared E×B flow which shows that E×B shear effects are ubiquitous in magnetized plasmas. This concept of turbulence decorrelation and stabilization has the universality needed to explain the H-mode edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines; the broader edge transport barrier seen in VHmode plasmas; and the core transport barriers formed in tokamaks. Similar effects are seen in linear devices. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to reduce transport when an additional source of free energy is applied to it. The transport decrease associated with E×B velocity shear is also of great practical benefit to fusion research, since it contributed to substantially increased fusion yield in all DT magnetic fusion experiments conducted to date. The fundamental physics involved in transport reduction is the effect of E×B shear on the growth, radial extent, and phase correlation of turbulent eddies in the plasma. The same basic transport reduction process can be operational in various portions of the plasma because there are a number of ways to change the radial electric field Er. An important secondary theme in this area is the synergistic effect of E×B velocity shear and magnetic shear. Although the E×B velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of E×B velocity shear and facilitate turbulence stabilization. Our present understanding in this area is the result of a multi-decade, intertwined effort in theory, modeling and diagnostic development combined with continuing experimental investigations. These experiments have clearly demonstrated that increased E×B shear causes reductions in turbulence and transport. Finally, the experimental findings are generally consistent with the basic theoretical models although considerable work remains to be done before we have a fully predictive theory of transport in magnetized plasmas including E×B shear effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Pulsed-laser epitaxy of metallic delafossite PdCrO 2 films

Alternate stacking of a highly conducting metallic layer with a magnetic triangular layer found in delafossite PdCrO 2 provides an excellent platform for discovering intriguing correlated quantum phenomena. Thin film growth of delafossites may enable not only the tuning of the basic physical properties beyond what bulk materials can exhibit, but also the development of novel hybrid materials by interfacing with dissimilar materials, yet this has proven to be extremely challenging. Here, we report the epitaxial growth of metallic delafossite PdCrO 2 films by pulsed laser epitaxy (PLE). The fundamental role of the PLE growth conditions, epitaxial strain, and chemical and structural characteristics of the substrate is investigated by growing under various growth conditions and on various types of substrates. While strain plays a large role in improving the crystallinity, the direct growth of epitaxial PdCrO 2 films without impurity phases was not successful. We attribute this difficulty to both the chemical and structural dissimilarities with the substrate and volatile nature of the PdO sublayer, which make nucleation of the right phase difficult. This difficulty was overcome by growing CuCrO 2 buffer layers before PdCrO 2 films were grown. Unlike PdCrO 2 , CuCrO 2 films were readily grown with a relatively wide growth window. Only a monolayer thick buffer layer was sufficient to grow the correct PdCrO 2 phase. This result indicates that the epitaxy of Pd-based delafossites is extremely sensitive to the chemistry and structure of the interface, necessitating near perfect substrate materials. The resulting films are commensurately strained and show an antiferromagnetic transition at 40 K that persists down to as thin as 3.6 nm in thickness. This work provides key insights into advancing the epitaxial growth of the broader class of metallic delafossites for both studying the basic physical properties and developing new spintronic and computing devices.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Quadrupole-mediated dielectric response and the charge-asymmetric solvation of ions in water

Treating water as a linearly responding dielectric continuum on molecular length scales allows very simple estimates of the solvation structure and thermodynamics for charged and polar solutes. While this approach can successfully account for basic length and energy scales of ion solvation, computer simulations indicate not only its quantitative inaccuracies but also its inability to capture some basic and important aspects of microscopic polarization response. Here, we consider one such shortcoming, a failure to distinguish the solvation thermodynamics of cations from that of otherwise-identical anions, and we pursue a simple, physically inspired modification of the dielectric continuum model to address it. The adaptation is motivated by analyzing the orientational response of an isolated water molecule whose dipole is rigidly constrained. Its free energy suggests a Hamiltonian for dipole fluctuations that accounts implicitly for the influence of higher-order multipole moments while respecting constraints of molecular geometry. Finally, we propose a field theory with the suggested form, whose nonlinear response breaks the charge symmetry of ion solvation. An approximate variational solution of this theory, with a single adjustable parameter, yields solvation free energies that agree closely with simulation results over a considerable range of solute size and charge.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Molecular qubits based on photogenerated spin-correlated radical pairs for quantum sensing

Photogenerated spin-correlated radical pairs (SCRPs) in electron donor–bridge–acceptor (D–B–A) molecules can act as molecular qubits and inherently spin qubit pairs. SCRPs can take singlet and triplet spin states, comprising the quantum superposition state. Their synthetic accessibility and well-defined structures, together with their ability to be prepared in an initially pure, entangled spin state and optical addressability, make them one of the promising avenues for advancing quantum information science. Coherence between two spin states and spin selective electron transfer reactions form the foundation of using SCRPs as qubits for sensing. We can exploit the unique sensitivity of the spin dynamics of SCRPs to external magnetic fields for sensing applications including resolution-enhanced imaging, magnetometers, and magnetic switch. Molecular quantum sensors, if realized, can provide new technological developments beyond what is possible with classical counterparts. While the community of spin chemistry has actively investigated magnetic field effects on chemical reactions via SCRPs for several decades, we have not yet fully exploited the synthetic tunability of molecular systems to our advantage. This review offers an introduction to the photogenerated SCRPs-based molecular qubits for quantum sensing, aiming to lay the foundation for researchers new to the field and provide a basic reference for researchers active in the field. We focus on the basic principles necessary to construct molecular qubits based on SCRPs and the examples in quantum sensing explored to date from the perspective of the experimentalist.

Mani, Tomoyasu (ORCID:0000000241255195)↗

DOE OSTI2022

Structure and dynamics of SARS-CoV-2 proofreading exoribonuclease ExoN

High-fidelity replication of the large RNA genome of coronaviruses (CoVs) is mediated by a 3'-to-5' exoribonuclease (ExoN) in nonstructural protein 14 (nsp14), which excises nucleotides including antiviral drugs misincorporated by the low-fidelity viral RNA-dependent RNA polymerase (RdRp) and has also been implicated in viral RNA recombination and resistance to innate immunity. Here, we determined a 1.6-Å resolution crystal structure of severe acute respiratory syndrome CoV 2 (SARS-CoV-2) ExoN in complex with its essential cofactor, nsp10. The structure shows a highly basic and concave surface flanking the active site, comprising several Lys residues of nsp14 and the N-terminal amino group of nsp10. Modeling suggests that this basic patch binds to the template strand of double-stranded RNA substrates to position the 3' end of the nascent strand in the ExoN active site, which is corroborated by mutational and computational analyses. We also show that the ExoN activity can rescue a stalled RNA primer poisoned with sofosbuvir and allow RdRp to continue its extension in the presence of the chain-terminating drug, biochemically recapitulating proofreading in SARS-CoV-2 replication. Molecular dynamics simulations further show remarkable flexibility of multidomain nsp14 and suggest that nsp10 stabilizes ExoN for substrate RNA binding to support its exonuclease activity. Our high-resolution structure of the SARS-CoV-2 ExoN–nsp10 complex serves as a platform for future development of anticoronaviral drugs or strategies to attenuate the viral virulence.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2025

Automated Resonance Fitting for Nuclear Data Evaluation

Global and national efforts to deliver high-quality nuclear data to users have a wide-ranging impact, affecting applications in national security, reactor operations, basic science, medicine, and more. Cross section evaluation is a major part of this effort, combining theory and experimentation to produce recommended values and uncertainties for reaction probabilities. Resonance region evaluation is a specialized type of nuclear data evaluation that can require significant manual effort and months of time from expert scientists. In this article, non-convex non-linear optimization methods are combined with concepts of inferential statistics to infer a resonance model from experimental data in an automated manner that is not dependent on prior evaluation(s). This methodology aims to enhance the workflow of a resonance evaluator by minimizing time, effort, and the potential for bias from prior assumptions, while enhancing reproducibility and documentation, thereby addressing well-known challenges in the field.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Electric field determination in transient plasmas: in situ & non-invasive methods

Abstract One of the primary basic plasma parameters within transient nonequilibrium plasmas is the reduced electric field strength, roughly understood as the ratio of the electrical energy given to the charged species between two collisions. While physical probes have historically been used for electric field measurements, recent advances in high intensity lasers and sensitive detection methods have allowed for non-invasive optical electric field determination in nearly any discharge configuration with time-resolution up to the sub-nanosecond range and sub-millimeter spatial resolution. This topical review serves to highlight several non-invasive methods for in situ electric field strength determination in transient plasmas ranging from high vacuum environments to atmospheric pressure and above. We will discuss the advantages and proper implementation of (i) laser induced fluorescence dip spectroscopy for measurements in low pressure RF discharges, (ii) optical emission spectroscopy based methods for nitrogen, helium or hydrogen containing discharges, (iii) electric field induced coherent Raman scattering, and (iv) electric field induced second harmonic generation. The physical mechanism for each method will be described as well as basic implementation and highlighting recent results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Volume IV. The DUNE far detector single-phase technology

The preponderance of matter over antimatter in the early universe, the dynamics of the supernovae that produced the heavy elements necessary for life, and whether protons eventually decay -- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our universe, its current state, and its eventual fate. DUNE is an international world-class experiment dedicated to addressing these questions as it searches for leptonic charge-parity symmetry violation, stands ready to capture supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model. Central to achieving DUNE's physics program is a far detector that combines the many tens-of-kiloton fiducial mass necessary for rare event searches with sub-centimeter spatial resolution in its ability to image those events, allowing identification of the physics signatures among the numerous backgrounds. In the single-phase liquid argon time-projection chamber (LArTPC) technology, ionization charges drift horizontally in the liquid argon under the influence of an electric field towards a vertical anode, where they are read out with fine granularity. A photon detection system supplements the TPC, directly enhancing physics capabilities for all three DUNE physics drivers and opening up prospects for further physics explorations. The DUNE far detector technical design report (TDR) describes the DUNE physics program and the technical designs of the single- and dual-phase DUNE liquid argon TPC far detector modules. Volume IV presents an overview of the basic operating principles of a single-phase LArTPC, followed by a description of the DUNE implementation. Each of the subsystems is described in detail, connecting the high-level design requirements and decisions to the overriding physics goals of DUNE.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗