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The three-dimensional (3D) distribution of individual atoms on the surface of catalyst nanoparticles plays a vital role in their activity and stability. Optimising the performance of electrocatalysts requires atomic-scale information, but it is difficult to obtain. Here, we use atom probe tomography to elucidate the 3D structure of 10 nm sized Co 2 FeO 4 and CoFe 2 O 4 nanoparticles during oxygen evolution reaction (OER). We reveal nanoscale spinodal decomposition in pristine Co 2 FeO 4 . The interfaces of Co-rich and Fe-rich nanodomains of Co 2 FeO 4 become trapping sites for hydroxyl groups, contributing to a higher OER activity compared to that of CoFe 2 O 4 . However, the activity of Co 2 FeO 4 drops considerably due to concurrent irreversible transformation towards Co IV O 2 and pronounced Fe dissolution. In contrast, there is negligible elemental redistribution for CoFe 2 O 4 after OER, except for surface structural transformation towards (Fe III , Co III ) 2 O 3 . Overall, our study provides a unique 3D compositional distribution of mixed Co-Fe spinel oxides, which gives atomic-scale insights into active sites and the deactivation of electrocatalysts during OER. 3D imaging of catalyst nanoparticles during reactions is important but challenging. Here, the authors provide atomic-scale details of compositional and structural changes of 10 nm sized Co-Fe spinel nanoparticles during oxygen evolution reactions.

This study of manganese (Mn, Z = 25) introduces a novel combination of extended‐range high energy resolution fluorescence detection (XR‐HERFD), multiple‐crystal spectrometers and advanced binary data splicing techniques to address challenges in X‐ray emission spectroscopy. XR‐HERFD enhances spectral precision by utilizing high‐resolution crystal analysers and optimized detector configurations. The systematic application of these methods using multiple Bragg crystal analysers at Diamond Light Source has led to substantial improvements in data quality. Simultaneously, advanced binary data splicing integrates multiple datasets to correct distortions and improve resolution, resulting in sharper spectral features. Our results show a significant increase in peak counts and a notable reduction in full width at half‐maximum (FWHM), with peak amplitudes increasing by 83% and resolution improving by 46%. These developments provide greater detail for X‐ray absorption or emission spectra, offering valuable insights into complex materials, and permitting advances and breakthroughs in atomic relativistic quantum mechanics, chemical sensitivity of atomic transitions and modelling of solid‐state effects. A robust integration is introduced of the extended‐range high energy resolution fluorescence detection technique, multiple‐crystal spectrometers and binary data splicing techniques for the further refinement of spectra in X‐ray emission spectroscopy, revealing deeper insights into material properties and atomic transitions.

Understanding the effects of fast neutrons on high-temperature superconductors is of growing importance as new compact fusion reactors rely on these materials to generate the high magnetic fields needed to confine the plasma. The critical temperature of the most promising candidate material for small-scale fusion devices, rare-earth barium cuprate, is known to decrease monotonically with radiation dose, indicating the generation of lattice defects everywhere in the material. Here, we use high-energy-resolution X-ray absorption spectroscopy to probe how the local environment around the copper atoms is influenced by point defects induced by He + ion irradiation in the oxygen sublattice. Density functional theory calculations are used to interpret spectral features and we find clear evidence that ion irradiation significantly disrupts the bonding environment around the copper atoms in the copper-oxygen planes responsible for superconductivity in this compound. We propose the generation of a specific Frenkel defect that is consistent with our experimental results. Our results challenge previous assumptions in the literature that irradiation produces point defects only in the chain sites. In addition, we show that partial recovery is possible by annealing at modest temperatures, which may have implications for the operation of superconducting fusion magnets. Understanding the effects of fast neutrons on high-temperature superconductors is important for their application in fusion reactors. Here, a combined experimental and theoretical study reveals that ion irradiation disrupts superconductivity by introducing defects within the copper-oxygen planes.

There are several techniques providing quantitative elemental analysis, but very few capable of identifying both the concentration and chemical state of elements. This study presents a systematic investigation of the properties of the X-rays emitted after the atomic capture of negatively charged muons. The probability rates of the muonic transitions possess sensitivity to the electronic structure of materials, thus making the muonic X-ray Emission Spectroscopy complementary to the X-ray Absorption and Emission techniques for the study of the chemistry of elements, and able of unparalleled analysis in case of elements bearing low atomic numbers. This qualitative method is applied to the characterization of light elements-based, energy-relevant materials involved in the reaction of hydrogen desorption from the reactive hydride composite Ca(BH4)2-Mg2NiH4. The origin of the influence of the band-structure on the muonic atom is discussed and the observed effects are attributed to the contribution of the electronic structure to the screening and to the momentum distribution in the muon cascade.

We employ several X-ray based techniques, including X-ray diffraction, absorption and resonant inelastic scattering, to disentangle the contributions of individual chemical species to the structural, electronic and magnetic properties of high-entropy oxides. In the benchmark compound Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and related systems, we unambiguously resolve a sizable Jahn-Teller distortion at the Cu sites, more pronounced in the absence of Ni2+ and Mg2+, suggesting that these ions promote positional order, whereas Cu2+ ions act to destabilize it. Moreover, we detect magnetic excitations and estimate the strength of the interactions between pairs of different magnetic elements. Our results provide valuable insights into the role of the various chemical species in shaping the physical properties of high-entropy oxides.

Multi-cellular cable bacteria have evolved a unique machinery that efficiently transports electrons across centimetre-scale distances. Currents flow through a parallel network of periplasmic fibres, which display an extraordinary conductivity for a biological material. However, the conduction mechanism remains elusive as the molecular structure of the fibres has not been resolved. Here, we demonstrate that each fibre embeds a bundle of intertwined nanoribbons, which are built from Nickel Bis(Dithiolene) (NiBiD) repeat units that are formed by linking nickel centres with ethenetetrathiolate ligands. The planar and conjugated NiBiD complexes are aligned and stacked to form an elongated supramolecular coordination network, thus explaining the observed organo-metal electronic properties of the fibres. Our results hence demonstrate that biology is capable of producing extensive metal organic frameworks. These structures enable highly conductive one-dimensional conduits, ensuring efficient charge transport over macroscale distances, thus providing a novel design principle for bio-based, sustainable organo-electronic materials.

Understanding and controlling the way excitons propagate in solids is a key for tailoring materials with improved optoelectronic properties. A fundamental step in this direction is the determination of the exciton energy-momentum dispersion. Here, thanks to the solution of the parameter-free Bethe- Salpeter equation (BSE), we draw and explain the exciton energy-momentum map of hexagonal boron nitride (h-BN) in the first three Brillouin zones. We show that h-BN displays strong excitonic effects not only in the optical spectra at vanishing momentum \\(\\mathbf{q}\\), as previously reported, but also at large \\(\\mathbf{q}\\). We validate our theoretical predictions by assessing the calculated exciton map by means of an inelastic x-ray scattering (IXS) experiment. Moreover, we solve the discrepancies between previous experimental data and calculations, proving then that the BSE is highly accurate through the whole momentum range. Therefore, these results put forward the combination BSE and IXS as the tool of choice for addressing the exciton dynamics in complex materials.

The discovery in 1991 of high temperature superconductivity (SC) in A3C60 compounds, where A is an alkali ion, has been initially ascribed to a BCS mechanism, with a weak incidence of electron correlations. However various experimental evidences taken for compounds with distinct alkali content established the interplay of strong correlations and Jahn Teller distortions of the C60 ball. The importance of electronic correlations even in A3C60 has been highlighted by the recent discovery of two expanded fulleride Cs3C60 isomeric phases that are Mott insulators at ambient pressure. Both phases undergo a pressure induced first order Mott transition to SC with a (p, T) phase diagram displaying a dome shaped SC, a common situation encountered nowadays in correlated electron systems. NMR experiments allowed us to establish that the bipartite A15 phase displays Néel order at 47K, while magnetic freezing only occurs at lower temperature in the fcc phase. NMR data do permit us to conclude that well above the critical pressure, the singlet superconductivity found for light alkalis is recovered. However deviations from BCS expectations linked with electronic correlations are found near the Mott transition. So, although SC involves an electron-phonon mechanism, correlations have a significant incidence on the electronic properties, as had been anticipated from DMFT calculations.

A bstract Cascading RG flows are characteristic of N = 1 gauge theories realized by D3-branes probing singularities in the presence of fractional branes. A celebrated example is the Klebanov-Strassler model, which exhibits an infinite cascade that ends with confinement. In this work, we explore a related setup where the addition of an orientifold plane modifies the cascade structure: the RG flow now consists of a finite number of steps, originating from a UV fixed point with a finite number of degrees of freedom. We provide a supergravity solution dual to this flow, that reproduces all its salient features. The string frame curvature can be kept small up to parametrically large values of the holographic coordinate, larger than the one at which the first cascade step occurs.

Tumors develop within complex cell-to-cell interactions, with accessory cells playing a relevant role starting in the early phases of cancer progression. This event occurs in a three-dimensional (3D) environment, which to date, has been difficult to reproduce in vitro due to its complexity. While bi-dimensional cultures have generated substantial data, there is a progressive awareness that 3D culture strategies may rapidly increase the understanding of tumor development and be used in anti-cancer compound screening and for predicting response to new drugs utilizing personalized approaches. However, simple systems capable of rapidly rebuilding cancer tissues ex-vivo in 3D are needed and could be used for a variety of applications. Therefore, we developed a flat, handheld and versatile 3D cell culture bioreactor that can be loaded with tumor and/or normal cells in combination which can be monitored using a variety of read-outs. This biocompatible device sustained 3D growth of tumor cell lines representative of various cancers, such as pancreatic and breast adenocarcinoma, sarcoma, and glioblastoma. The cells repopulated the thin matrix which was completely separated from the outer space by two gas-permeable membranes and was monitored in real-time using both microscopy and luminometry, even after transportation. The device was tested in 3D cytotoxicity assays to investigate the anti-cancer potential of chemotherapy, biologic agents, and cell-based therapy in co-cultures. The addition of luciferase in target cancer cells is suitable for comparative studies that may also involve parallel in vivo investigations. Notably, the system was challenged using primary tumor cells harvested from lung cancer patients as an innovative predictive functional assay for cancer responsiveness to checkpoint inhibitors, such as nivolumab. This bioreactor has several novel features in the 3D-culture field of research, representing a valid tool useful for cancer investigations, drug screenings, and other toxicology approaches.