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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Structural Basis for the Substrate Inhibition of Proline Utilization A by Proline

Proline utilization A (PutA) is a bifunctional flavoenzyme that catalyzes the two-step oxidation of l-proline to l-glutamate using spatially separated proline dehydrogenase (PRODH) and l-glutamate-γ-semialdehyde dehydrogenase (GSALDH) active sites. Substrate inhibition of the coupled PRODH-GSALDH reaction by proline is a common kinetic feature of PutAs, yet the structural basis for this phenomenon remains unknown. To understand the mechanism of substrate inhibition, we determined the 2.15 Å resolution crystal structure of Bradyrhizobium japonicum PutA complexed with proline. Proline was discovered in five locations remote from the PRODH active site. Most notably, strong electron density indicated that proline bound tightly to the GSAL binding site of the GSALDH active site. The pose and interactions of proline bound in this site are remarkably similar to those of the natural aldehyde substrate, GSAL, implying that proline inhibits the GSALDH reaction of PutA. Kinetic measurements show that proline is a competitive inhibitor of the PutA GSALDH reaction. Together, the structural and kinetic data show that substrate inhibition of the PutA coupled reaction is due to proline binding in the GSAL site.

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

An Abundant and Diverse New Family of Electron Bifurcating Enzymes With a Non-canonical Catalytic Mechanism

Microorganisms utilize electron bifurcating enzymes in metabolic pathways to carry out thermodynamically unfavorable reactions. Bifurcating FeFe-hydrogenases (HydABC) reversibly oxidize NADH (E′∼−280 mV, under physiological conditions) and reduce protons to H 2 gas (E°′−414 mV) by coupling this endergonic reaction to the exergonic reduction of protons by reduced ferredoxin (Fd) (E′∼−500 mV). We show here that HydABC homologs are surprisingly ubiquitous in the microbial world and are represented by 57 phylogenetically distinct clades but only about half are FeFe-hydrogenases. The others have replaced the hydrogenase domain with another oxidoreductase domain or they contain additional subunits, both of which enable various third reactions to be reversibly coupled to NAD + and Fd reduction. We hypothesize that all of these enzymes carry out electron bifurcation and that their third substrates can include hydrogen peroxide, pyruvate, carbon monoxide, aldehydes, aryl-CoA thioesters, NADP + , cofactor F 420 , formate, and quinones, as well as many yet to be discovered. Some of the enzymes are proposed to be integral membrane-bound proton-translocating complexes. These different functionalities are associated with phylogenetically distinct clades and in many cases with specific microbial phyla. We propose that this new and abundant class of electron bifurcating enzyme be referred to as the Bfu family whose defining feature is a conserved bifurcating BfuBC core. This core contains FMN and six iron sulfur clusters and it interacts directly with ferredoxin (Fd) and NAD(H). Electrons to or from the third substrate are fed into the BfuBC core via BfuA. The other three known families of electron bifurcating enzyme (abbreviated as Nfn, EtfAB, and HdrA) contain a special FAD that bifurcates electrons to high and low potential pathways. The Bfu family are proposed to use a different electron bifurcation mechanism that involves a combination of FMN and three adjacent iron sulfur clusters, including a novel [2Fe-2S] cluster with pentacoordinate and partial non-Cys coordination. The absolute conservation of the redox cofactors of BfuBC in all members of the Bfu enzyme family indicate they have the same non-canonical mechanism to bifurcate electrons. A hypothetical catalytic mechanism is proposed as a basis for future spectroscopic analyses of Bfu family members.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Growth of GaAs on single-crystal layered-2D Bi 2 Se 3

This article demonstrates the successful growth of cubic GaAs (111) on single-crystal 2D layered Bi 2 Se 3 (0001) substrates achieved using a cubic ZnSe buffer layer. This growth sequence was chosen based upon observed reactions between Bi 2 Se 3 (0001) substrates and both Ga and Zn. For the conditions used in our MOCVD reactor, triethylgallium (TEGa) interacts strongly with Bi 2 Se 3 to form Ga 2 Se 3 , which can disrupt the nucleation and growth of GaAs. Therefore, a buffer layer is needed which prevents Ga-Bi 2 Se 3 interactions while simultaneously providing a suitable growth surface for GaAs. ZnSe was chosen because it is lattice-matched to GaAs, and can be created by annealing the Bi2Se3 under a diethylzinc (DEZn) flux. A sample utilizing this growth sequence has been grown, characterized and exfoliated as a possible pathway toward reducing the substrate cost for III-V devices such as solar cells.

14 SOLAR ENERGY↗
DOE OSTI2017

Liquid Metals as Plasma-facing Materials for Fusion Energy Systems: From Atoms to Tokamaks

The objective of our studies was to advance our fundamental understanding of liquid metals as plasma-facing materials for fusion energy systems, with a broad scope: from atoms to tokamaks. The flow of liquid metals offers solutions to significant problems of the plasma-facing materials for fusion energy systems. Candidate metals include lithium, tin, gallium, and their eutectic combinations. However, such liquid metal solutions can only be designed efficiently if a range of scientific and engineering issues are resolved that require advances in fundamental fluid dynamics, materials science and surface science. In our research we investigated a range of significant and timely problems relevant to current and proposed engineering designs for fusion reactors, including high-heat flux configurations that are being considered by leading fusion energy groups world-wide. Using experimental and theoretical tools spanning atomistic to continuum descriptions of liquid metals, and bridging surface chemistry, wetting/dewetting and flow, our research has advanced the science and engineering of fusion energy materials and systems. Specifically, we developed a combined experimental and theoretical program to investigate flows of liquid metals in fusion-relevant geometries, including equilibrium and stability of thin-film flows, e.g. wetting and dewetting, effects of electromagnetic and thermocapillary fields on liquid metal thin-film flows, and how chemical interactions and the properties of the surface are influenced by impurities and in turn affect the surface wetting characteristics, the surface tension, and its gradients. Because high-heat flux configurations produce evaporation and sputtering, which forces rearrangement of the liquid, and any dewetting exposes the substrate to damage from the plasma, our studies addressed such evaporatively driven liquid flows and measured and simulated properties of the different bulk phases and material interfaces. The range of our studies included (i) quantum mechanical calculations that allow inclusion of many thousands of atoms for the characterization of the interface of liquid metals exposed to continuous bombardment by deuterium and tritium as expected in fusion, (ii) molecular dynamics studies of the phase behavior of liquid metals, which (a) utilize thermodynamic properties computed using our quantum mechanical calculations and (b) establish material and wetting properties of the liquid metals, including relevant eutectics, (iii) experimental investigations of the surface science of liquid metals, interacting both with the solid substrate as well as gaseous species, and (iv) fluid dynamical studies that incorporate the material and surface science results of (ii) and (iii) in order to characterize flow in capillary porous materials and the thin-film flow along curved boundaries, both of which are potentially major components of plasma-facing materials. The outcome of these integrated studies was new understanding that enables developing design rules useful for future developments of the plasma-facing components critical to the success of fusion energy systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Methane-Linked Mechanisms of Electron Uptake from Cathodes by Methanosarcina barkeri

Methanosarcinales , a lineage of cytochrome-containing methanogens, have recently been proposed to participate in direct extracellular electron transfer interactions within syntrophic communities. To shed light on this phenomenon, we applied electrochemical techniques to measure electron uptake from cathodes by Methanosarcina barkeri , which is an important model organism that is genetically tractable and utilizes a wide range of substrates for methanogenesis. Here, we confirm the ability of M. barkeri to perform electron uptake from cathodes and show that this cathodic current is linked to quantitative increases in methane production. The underlying mechanisms we identified include, but are not limited to, a recently proposed association between cathodes and methanogen-derived extracellular enzymes (e.g., hydrogenases) that can facilitate current generation through the formation of reduced and diffusible methanogenic substrates (e.g., hydrogen). However, after minimizing the contributions of such extracellular enzymes and using a mutant lacking hydrogenases, we observe a lower-potential hydrogen-independent pathway that facilitates cathodic activity coupled to methane production in M. barkeri . Our electrochemical measurements of wild-type and mutant strains point to a novel and hydrogenase-free mode of electron uptake with a potential near -484 mV versus standard hydrogen electrode (SHE) (over 100 mV more reduced than the observed hydrogenase midpoint potential under these conditions). These results suggest that M. barkeri can perform multiple modes (hydrogenase-mediated and free extracellular enzyme-independent modes) of electrode interactions on cathodes, including a mechanism pointing to a direct interaction, which has significant applied and ecological implications. IMPORTANCE Methanogenic archaea are of fundamental applied and environmental relevance. This is largely due to their activities in a wide range of anaerobic environments, generating gaseous reduced carbon that can be utilized as a fuel source. While the bioenergetics of a wide variety of methanogens have been well studied with respect to soluble substrates, a mechanistic understanding of their interaction with solid-phase redox-active compounds is limited. This work provides insight into solid-phase redox interactions in Methanosarcina spp. using electrochemical methods. We highlight a previously undescribed mode of electron uptake from cathodes that is potentially informative of direct interspecies electron transfer interactions in the Methanosarcinales .

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Characterisation of weld zone reactions in dissimilar glass-to-aluminium pulsed picosecond laser welds

Precision welded joints, produced between fused silica glass and aluminium by a newly-developed picosecond-pulse laser technique, have been analysed for the first time using a full range of electron microscopy methods. The welds were produced as lap joints by focusing a 1.2 μm diameter laser beam through the transparent glass top sheet, slightly below the surface of the metal bottom sheet. Despite the extremely short interaction time, extensive reaction was observed in the weld zone, which involved the formation of nanocrystalline silicon and at least two transitional alumina phases, γ- and δ-Al{sub 2}O{sub 3}. The weld formation process was found to be complex and involved: the formation of a constrained plasma cavity at the joint interface, non-linear absorption in the glass, and the creation of multiple secondary keyholes in the metal substrate by beam scattering. The joint area was found to expand outside of the main interaction volume, as the energy absorbed into the low conductivity and higher melting point silica glass sheet melted the aluminium surface across a wider contact area. The reasons for the appearance of nanocrystalline Si and transitional alumina reaction products within the welds are discussed. - Highlights: •Pulsed laser welding of dissimilar materials causes extensive chemical reactivity. •Metastable Al{sub 2}O{sub 3} phases form due to laser-induced highly-transient thermal regime. •Fused silica is reduced by Al to form nanocrystalline Si. •Mechanism of joint formation is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structures and Mechanisms of a Novel Bacterial Transport System for Fatty Acids

Abstract Bacterial acquisition of metabolites is largely facilitated by transporters with unique substrate scopes. The tripartite ATP‐independent periplasmic (TRAP) transporters comprise a large family of bacterial proteins that facilitate the uptake of a variety of small molecules. It has been reported that some TRAP systems encode a fourth protein, the T component. The T‐component, or TatT, is predicted to be a periplasmic‐facing lipoprotein that enables the uptake of metabolites from the outer membrane. However, no substrates were revealed for any TatT and their functional role(s) remained enigmatic. We recently identified a homolog in Methylococcus capsulatus that binds to sterols, and herein, we report two additional homologs that demonstrate a preference for long‐chain fatty acids. Our bioinformatics, quantitative analyses of protein‐ligand interactions, and high‐resolution crystal structures suggest that TatTs might facilitate the trafficking of hydrophobic or lipophilic substrates and represent a new class of bacterial lipid and fatty acid transporters.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Coordinated induction of GST and MRP2 by cAMP in Caco-2 cells: Role of protein kinase A signaling pathway and toxicological relevance

The cAMP pathway is a universal signaling pathway regulating many cellular processes including metabolic routes, growth and differentiation. However, its effects on xenobiotic biotransformation and transport systems are poorly characterized. The effect of cAMP on expression and activity of GST and MRP2 was evaluated in Caco-2 cells, a model of intestinal epithelium. Cells incubated with the cAMP permeable analog dibutyryl cyclic AMP (db-cAMP: 1,10,100 μM) for 48 h exhibited a dose–response increase in GST class α and MRP2 protein expression. Incubation with forskolin, an activator of adenylyl cyclase, confirmed the association between intracellular cAMP and upregulation of MRP2. Consistent with increased expression of GSTα and MRP2, db-cAMP enhanced their activities, as well as cytoprotection against the common substrate 1-chloro-2,4-dinitrobenzene. Pretreatment with protein kinase A (PKA) inhibitors totally abolished upregulation of MRP2 and GSTα induced by db-cAMP. In silico analysis together with experiments consisting of treatment with db-cAMP of Caco-2 cells transfected with a reporter construct containing CRE and AP-1 sites evidenced participation of these sites in MRP2 upregulation. Further studies involving the transcription factors CREB and AP-1 (c-JUN, c-FOS and ATF2) demonstrated increased levels of total c-JUN and phosphorylation of c-JUN and ATF2 by db-cAMP, which were suppressed by a PKA inhibitor. Co-immunoprecipitation and ChIP assay studies demonstrated that db-cAMP increased c-JUN/ATF2 interaction, with further recruitment to the region of the MRP2 promoter containing CRE and AP-1 sites. We conclude that cAMP induces GSTα and MRP2 expression and activity in Caco-2 cells via the PKA pathway, thus regulating detoxification of specific xenobiotics. - Highlights: • cAMP positively modulates the expression and activity of GST and MRP2 in Caco-2 cells. • Such induction resulted in increased cytoprotection against chemical injury. • PKA signaling pathway is involved downstream of cAMP. • Transcriptional MRP2 regulation ultimately involved participation of c-JUN and ATF2.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Removal of primary nutrient degrading members severely reduces growth of soil microbial communities even when additional degraders are present

Understanding how microorganisms within a soil community interact to support collective respiration and growth remains challenging. Here we used a model substrate, chitin, and a Model Soil Consortium, MSC-2, to investigate how individual members of a microbial community contribute to decomposition and community growth. While MSC-2 can grow using chitin as the sole carbon source, we do not yet know how the growth kinetics or final biomass yields of MSC-2 vary when certain chitin degraders, or other important members, are absent. To characterize specific roles within this representative community, we carried out experiments leaving out members of MSC-2 and measuring biomass yields and CO2 production. We chose two members to iteratively leave out (referred to by genus name): Streptomyces, as it is predicted via gene expression analysis to be a major chitin degrader in the community, and Rhodococcus as it is predicted via species co-abundance analysis to interact with several other members. Our results showed that when MSC-2 lacked Streptomyces, growth and respiration of the community was severely reduced. Removal of either Streptomyces or Rhodococcus led to major changes in abundance for several other species, pointing to a comprehensive shifting of the microbial community when important members are removed as well as alterations in the metabolic profile, especially when Streptomyces was removed. These results show that when keystone, chitin degrading members are removed, other members, even those with the potential to degrade chitin, do not fill the same metabolic niche to promote community growth. In addition, highly connected members may be removed with similar or even increased levels of growth and respiration. Our findings are critical to a better understanding of soil microbiology, specifically in how communities maintain activity when biotic or abiotic factors lead to changes in biodiversity in soil systems.

McClure, Ryan S↗
DOE OSTI2023

Removal of primary nutrient degraders reduces growth of soil microbial communities with genomic redundancy

Understanding how microorganisms within a soil community interact to support collective respiration and growth remains challenging. Here, we used a model substrate, chitin, and a synthetic Model Soil Consortium (MSC-2) to investigate how individual members of a microbial community contribute to decomposition and community growth. While MSC-2 can grow using chitin as the sole carbon source, we do not yet know how the growth kinetics or final biomass yields of MSC-2 vary when certain chitin degraders, or other important members, are absent. To characterize specific roles within this synthetic community, we carried out experiments leaving out members of MSC-2 and measuring biomass yields and CO 2 production. We chose two members to iteratively leave out (referred to by genus name): Streptomyces, as it is predicted via gene expression analysis to be a major chitin degrader in the community, and Rhodococcus as it is predicted via species co-abundance analysis to interact with several other members. Our results showed that when MSC-2 lacked Streptomyces, growth and respiration of the community was severely reduced. Removal of either Streptomyces or Rhodococcus led to major changes in abundance for several other species, pointing to a comprehensive shifting of the microbial community when important members are removed, as well as alterations in the metabolic profile, especially when Streptomyces was lacking. These results show that when keystone, chitin degrading members are removed, other members, even those with the potential to degrade chitin, do not fill the same metabolic niche to promote community growth. In addition, highly connected members may be removed with similar or even increased levels of growth and respiration. Our findings are critical to a better understanding of soil microbiology, specifically in how communities maintain activity when biotic or abiotic factors lead to changes in biodiversity in soil systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Dirac Fermion Cloning, Moiré Flat Bands, and Magic Lattice Constants in Epitaxial Monolayer Graphene

Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of the 2D material, enhance electron correlations, and give rise to novel condensed-matter phases such as superconductors, Mott insulators, Wigner crystals, and quantum anomalous Hall insulators. Previous works predominantly focus on the flat band dispersion of coupled Dirac states from different twisted graphene layers. Here in this work, a new route to realizing flat band physics in monolayer graphene under a periodic modulation from substrates is proposed. Graphene/SiC heterostructure is taken as a prototypical example and it is demonstrated experimentally that the substrate modulation leads to Dirac fermion cloning and, consequently, the proximity of the two Dirac cones of monolayer graphene in momentum space. Theoretical modeling captures the cloning mechanism of the Dirac states and indicates that moiré flat bands can emerge at certain magic lattice constants of the substrate, specifically when the period of modulation becomes nearly commensurate with the ($\sqrt{3}$ x $\sqrt{3}$) R30° supercell of graphene. Our results show that epitaxial single monolayer graphene on suitable substrates is a promising platform for exploring exotic many-body quantum phases arising from interactions between Dirac electrons.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Two alternative binding mechanisms connect the protein translocation Sec71-Sec72 complex with heat shock proteins

The biosynthesis of many eukaryotic proteins requires accurate targeting to and translocation across the endoplasmic reticulum membrane. Post-translational protein translocation in yeast requires both the Sec61 translocation channel, and a complex of four additional proteins: Sec63, Sec62, Sec71, and Sec72. The structure and function of these proteins are largely unknown. This pathway also requires the cytosolic Hsp70 protein Ssa1, but whether Ssa1 associates with the translocation machinery to target protein substrates to the membrane is unclear. Here, we use a combined structural and biochemical approach to explore the role of Sec71-Sec72 subcomplex in post-translational protein translocation. To this end, we report a crystal structure of the Sec71-Sec72 complex, which revealed that Sec72 contains a tetratricopeptide repeat (TPR) domain that is anchored to the endoplasmic reticulum membrane by Sec71. We also determined the crystal structure of this TPR domain with a C-terminal peptide derived from Ssa1, which suggests how Sec72 interacts with full-length Ssa1. Surprisingly, Ssb1, a cytoplasmic Hsp70 that binds ribosome-associated nascent polypeptide chains, also binds to the TPR domain of Sec72, even though it lacks the TPR-binding C-terminal residues of Ssa1. We demonstrate that Ssb1 binds through its ATPase domain to the TPR domain, an interaction that leads to inhibition of nucleotide exchange. Taken together, our results suggest that translocation substrates can be recruited to the Sec71-Sec72 complex either post-translationally through Ssa1 or co-translationally through Ssb1.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Hydrogenation of CO 2 on ZnO/Cu(100) and ZnO/Cu(111) Catalysts: Role of Copper Structure and Metal–Oxide Interface in Methanol Synthesis

The results of kinetic tests and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) show the important role played by a ZnO–copper interface in the generation of CO and the synthesis of methanol from CO 2 hydrogenation. The deposition of nanoparticles of ZnO on Cu(100) and Cu(111), θ oxi < 0.3 monolayer, produces highly active catalysts. The catalytic activity of these systems increases in the sequence: Cu(111) < Cu(100) < ZnO/Cu(111) < ZnO/Cu(100). The structure of the copper substrate influences the catalytic performance of a ZnO–copper interface. Furthermore, size and metal–oxide interactions affect the chemical and catalytic properties of the oxide making the supported nanoparticles different from bulk ZnO. The formation of a ZnO–copper interface favors the binding and conversion of CO 2 into a formate intermediate that is stable on the catalyst surface up to temperatures above 500 K. Alloys of Zn with Cu(111) and Cu(100) were not stable at the elevated temperatures (500–600 K) used for the CO 2 hydrogenation reaction. However, reaction with CO 2 oxidized the zinc, enhancing its stability over the copper substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interaction between laser radiation and metallic powder of 316L austenitic steel during selective laser melting

Highlights: • Single and multiple tracks on a loose bulk powder substrate were generated. • Understanding of the microstructure development during SLM was achieved. • Single tracks reveal a nearly symmetrical crystallography with elongated grains. • Multiple tracks show elongated grains perpendicular to the build direction. - Abstract: During selective laser melting (SLM), a complex heat state develops that leads to a characteristic crystallography and microstructure of the processed materials. Depending on the geometry of the processed part, most scan tracks of a new layer, so-called hatches, are located above a dense substrate or already solidified structures whereas others are located above loose powder. This is, inter alia, the case for overhanging structures. Attributable to the lower thermal conductivity of loose powder, temperature gradients and cooling rates of the melt pool differentiate in these areas, resulting in a different microstructural build-up. In this work, the microstructure and the crystallographic orientation of grade 316L austenitic stainless steel processed by SLM was investigated to understand the interaction between the laser radiation and the metallic powder during SLM-processing and to investigate the remelting of a track on a previous SLM-densified track. Single and multiple tracks on a loose bulk powder substrate, as well as single tracks on a dense substrate plate, were generated. A parameter study revealed that high energy densities are necessary to build continuous tracks on a loose bulk powder substrate. In addition, the amount of adhered particles, which are sintered on the fully melted and solidified tracks, is determined in comparison to the melted powder because the sintered particles strongly influence the surface roughness. To understand the microstructure development and, particularly, the influence of adjacent hatches during SLM-processing, investigations on the resulting microstructure and crystallographic orientation of a single track and two connected multiple tracks were carried out. During SLM processing of the tracks, the substrate plate and the solidified structures influence the temperature gradient and cooling rate of the melt pool, thus directionally solidified and elongated grains occur. Furthermore, the solidification is characterized by an epitaxial growth due to a distinct thermal gradient between the melt pool and the surrounding elements.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Oriented gold nanorod arrays: self-assembly and optoelectronic applications

We present that self-assembly of anisotropic plasmonic nanomaterials into ordered superstructures has become popular in nanoscience because of their unique anisotropic optical and electronic properties. Gold nanorods (GNRs) are a well-defined functional building block for fabrication of these superstructures. They possess important anisotropic plasmonic characteristics that are resulted from strong local electric field and responsive to visible and near infrared light, which attracts extensive attention in various fields, such as biomedical technologies, plasmon-enhanced spectroscopies, and optoelectronic devices. There are recent examples of assembling the GNRs into ordered arrays or superstructures through processes such as solvent evaporation, interfacial assembly. In this review, we describe recent progresses in the development of the self-assembled GNR arrays with focus on the formation of oriented GNR arrays on substrates. We discuss key driving forces such as van der Waals (vdW), electrostatic interactions, steric force, and depletion force. We survey different strategies and self-assembly processes of forming oriented GNR arrays. Lastly, we also overview the applications of the oriented GNR arrays in optoelectronic devices especially surface enhanced Raman scattering (SERS). At the end of this review, we briefly summarize the review and discuss future challenges and perspectives.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interplay between Swelling Kinetics and Nanostructure in Perfluorosulfonic Acid Thin-Films: Role of Hygrothermal Aging

Impacts of processing, storage, and operation on thin-film perfluorosulfonic acid (PFSA) ionomer coatings used in electrodes of electrochemical devices remains unestablished. In this work, alteration of structure–function relationship in ionomers is achieved via exposure to elevated temperature and humidity (hygrothermal aging). Findings reflect a strong inverse correlation between aging-induced ionomer thin-film domain orientation and water-transport kinetics evaluated from swelling. Finally, impact of aging is shown to be more pronounced on platinum due to interactions with PFSA, as evidenced by greater increase in nanodomain orientation parallel to substrate accompanied by reduced water transport, in contrast to silicon support.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Chiral superconductivity with enhanced quantized Hall responses in moiré transition metal dichalcogenides

Experimental demonstrations of tunable correlation effects in magic-angle twisted bilayer graphene have put two-dimensional moiré quantum materials at the forefront of condensed-matter research. Other twisted few-layer graphitic structures, boron-nitride, and homo- or hetero-stacks of transition metal dichalcogenides (TMDs) have further enriched the opportunities for analysis and utilization of correlations in these systems. Recent experiments within the latter material class confirmed the relevance of many-body interactions and demonstrated the importance of their extended range. Since the interaction, its range, and the filling can be tuned experimentally by twist angle, substrate engineering and gating, we here explore Fermi surface instabilities and resulting phases of matter of hetero-bilayer TMDs. Using an unbiased renormalization group approach, we establish in particular that hetero-bilayer TMDs are platforms to realize topological superconductivity with winding number |$\mathcal{N}$| = 4. We show that this state reflects in pronounced experimental signatures, such as distinct quantum Hall features.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗