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All papers published in this volume have been reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing Publishing.• Type of peer review: Single Anonymous• Conference submission management system: Morressier• Number of submissions received: 117• Number of submissions sent for review: 117• Number of submissions accepted: 111• Acceptance Rate (Submissions Accepted / Submissions Received × 100): 94.9• Average number of reviews per paper: 2• Total number of reviewers involved: 191• Contact person for queries:Name: Nawin JuntongEmail: nawin@slri.or.thAffiliation: Synchrotron Light Research Institute - Accelerator

Superelasticity associated with the martensitic transformation has found a broad range of engineering applications 1 , 2 . However, the intrinsic hysteresis 3 and temperature sensitivity 4 of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. Here, we report a large superelasticity up to 15.2% strain in [001]-oriented NiCoFeGa single crystals, exhibiting non-hysteretic mechanical responses, a small temperature dependence and high-energy-storage capability and cyclic stability over a wide temperature and composition range. In situ synchrotron X-ray diffraction measurements show that the superelasticity is correlated with a stress-induced continuous variation of lattice parameter accompanied by structural fluctuation. Neutron diffraction and electron microscopy observations reveal an unprecedented microstructure consisting of atomic-level entanglement of ordered and disordered crystal structures, which can be manipulated to tune the superelasticity. The discovery of the large elasticity related to the entangled structure paves the way for exploiting elastic strain engineering and development of related functional materials. NiCoFeGa single crystals exhibit large non-hysteretic superelasticity over broad temperature and composition ranges. It is attributed to the continuous phase transition with applied stress, which is related to the fluctuation of entangled ordered and disordered crystal structures.

A comprehensive understanding of the solid–electrolyte interphase (SEI) composition is crucial to developing high-energy batteries based on lithium metal anodes. A particularly contentious issue concerns the presence of LiH in the SEI. Here we report on the use of synchrotron-based X-ray diffraction and pair distribution function analysis to identify and differentiate two elusive components, LiH and LiF, in the SEI of lithium metal anodes. LiH is identified as a component of the SEI in high abundance, and the possibility of its misidentification as LiF in the literature is discussed. LiF in the SEI is found to have different structural features from LiF in the bulk phase, including a larger lattice parameter and a smaller grain size (<3 nm). These characteristics favour Li + transport and explain why an ionic insulator, like LiF, has been found to be a favoured component for the SEI. Finally, pair distribution function analysis reveals key amorphous components in the SEI. X-ray diffraction and Rietveld refinement analysis confirm the presence of LiH in the solid–electrolyte interphase of lithium metal anodes.

Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behaviour and stability at solid–solid interfaces remains limited compared to at solid–liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay among void formation, interphase growth and volumetric changes determines cell behaviour. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact that drives current constriction at the interface between lithium and the solid-state electrolyte (Li 10 SnP 2 S 12 ) is quantified and found to be the primary cause of cell failure. The interphase is found to be redox-active upon charge, and global volume changes occur owing to partial molar volume mismatches at either electrode. These results provide insight into how chemo-mechanical phenomena can affect cell performance, thus facilitating the development of solid-state batteries. Understanding electrochemical behaviour and stability at solid–solid interfaces remains challenging. Operando synchrotron X-ray computed microtomography loss reveals that reconfiguration of interfacial contact is critical to explain cell failure during solid-state battery cycling.

In the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase. Understanding the competition between thermodynamics and kinetics is a fundamental step towards the rational synthesis of target materials. Here, we use in situ synchrotron X-ray diffraction to investigate the multistage crystallization pathways of the important two-layer (P2) sodium oxides Na 0.67 MO 2 (M = Co, Mn). We observe a series of fast non-equilibrium phase transformations through metastable three-layer O3, O3′ and P3 phases before formation of the equilibrium two-layer P2 polymorph. We present a theoretical framework to rationalize the observed phase progression, demonstrating that even though P2 is the equilibrium phase, compositionally unconstrained reactions between powder precursors favour the formation of non-equilibrium three-layered intermediates. These insights can guide the choice of precursors and parameters employed in the solid-state synthesis of ceramic materials, and constitutes a step forward in unravelling the complex interplay between thermodynamics and kinetics during materials synthesis. Understanding the competition between thermodynamics and kinetics is crucial for the rational synthesis of inorganic materials. The synthesis of two-layer sodium metal oxides is investigated by in situ synchrotron XRD and a model is developed to rationalize why the observed phase progression proceeds through non-equilibrium three-layered intermediates.

Contents Summary 432 I. Introduction 433 II. Preparation of plant samples for X-ray micro-analysis 433 III. X-ray elemental mapping techniques 438 IV. X-ray data analysis 442 V. Case studies 443 VI. Conclusions 446 Acknowledgements 449 Author contributions 449 References 449 SUMMARY: Hyperaccumulators are attractive models for studying metal(loid) homeostasis, and probing the spatial distribution and coordination chemistry of metal(loid)s in their tissues is important for advancing our understanding of their ecophysiology. X-ray elemental mapping techniques are unique in providing in situ information, and with appropriate sample preparation offer results true to biological conditions of the living plant. The common platform of these techniques is a reliance on characteristic X-rays of elements present in a sample, excited either by electrons (scanning/transmission electron microscopy), protons (proton-induced X-ray emission) or X-rays (X-ray fluorescence microscopy). Elucidating the cellular and tissue-level distribution of metal(loid)s is inherently challenging and accurate X-ray analysis places strict demands on sample collection, preparation and analytical conditions, to avoid elemental redistribution, chemical modification or ultrastructural alterations. We compare the merits and limitations of the individual techniques, and focus on the optimal field of applications for inferring ecophysiological processes in hyperaccumulator plants. X-ray elemental mapping techniques can play a key role in answering questions at every level of metal(loid) homeostasis in plants, from the rhizosphere interface, to uptake pathways in the roots and shoots. Further improvements in technological capabilities offer exciting perspectives for the study of hyperaccumulator plants into the future.

The ANATOMIX beamline at Synchrotron SOLEIL, operational since 2018, is dedicated to hard X-ray full-field tomography techniques. Operating in a range of photon energies from approximately 5 to 50 keV, it offers both parallel-beam projection microtomography, in absorption and phase contrast, and nanotomography using a zone-plate transmission X-ray microscope. With these methods, the beamline covers a range of spatial resolution from 20 nm to 20 µm, expressed in terms of useful pixel size. The variable beam size of up to 40 mm allows users to image large objects. Here we describe the microtomography instrumentation of the beamline.

Photocatalytic two-electron oxygen reduction to produce high-value hydrogen peroxide (H 2 O 2 ) is gaining popularity as a promising avenue of research. However, structural evolution mechanisms of catalytically active sites in the entire photosynthetic H 2 O 2 system remains unclear and seriously hinders the development of highly-active and stable H 2 O 2 photocatalysts. Herein, we report a high-loading Ni single-atom photocatalyst for efficient H 2 O 2 synthesis in pure water, achieving an apparent quantum yield of 10.9% at 420 nm and a solar-to-chemical conversion efficiency of 0.82%. Importantly, using in situ synchrotron X-ray absorption spectroscopy and Raman spectroscopy we directly observe that initial Ni-N 3 sites dynamically transform into high-valent O 1 -Ni-N 2 sites after O 2 adsorption and further evolve to form a key *OOH intermediate before finally forming HOO-Ni-N 2 . Theoretical calculations and experiments further reveal that the evolution of the active sites structure reduces the formation energy barrier of *OOH and suppresses the O=O bond dissociation, leading to improved H 2 O 2 production activity and selectivity. Here, the authors explore how Ni single-atom sites on carbon nitride evolve under photocatalytic conditions. They show that this evolution plays a pivotal role in enhancing photocatalytic H 2 O 2 production.

Since their discovery in 2007 1 , much effort has been devoted to uncovering the sources of the extragalactic, millisecond-duration fast radio bursts (FRBs) 2 . A class of neutron stars known as magnetars is a leading candidate source of FRBs 3 , 4 . Magnetars have surface magnetic fields in excess of 10 14 gauss, the decay of which powers a range of high-energy phenomena 5 . Here we report observations of a millisecond-duration radio burst from the Galactic magnetar SGR 1935+2154, with a fluence of 1.5 ± 0.3 megajansky milliseconds. This event, FRB 200428 (ST 200428A), was detected on 28 April 2020 by the STARE2 radio array 6 in the 1,281–1,468 megahertz band. The isotropic-equivalent energy released in FRB 200428 is 4 × 10 3 times greater than that of any radio pulse from the Crab pulsar—previously the source of the brightest Galactic radio bursts observed on similar timescales 7 . FRB 200428 is just 30 times less energetic than the weakest extragalactic FRB observed so far 8 , and is drawn from the same population as the observed FRB sample. The coincidence of FRB 200428 with an X-ray burst 9 – 11 favours emission models that describe synchrotron masers or electromagnetic pulses powered by magnetar bursts and giant flares 3 , 4 , 12 , 13 . The discovery of FRB 200428 implies that active magnetars such as SGR 1935+2154 can produce FRBs at extragalactic distances. Observations of the fast radio burst FRB 200428 coinciding with X-rays from the Galactic magnetar SGR 1935+2154 indicate that active magnetars can produce fast radio bursts at extragalactic distances.

Since the discovery of X-rays by Roentgen in 1895, its use has been ubiquitous, from medical and environmental applications to materials sciences 1 – 5 . X-ray characterization requires a large number of atoms and reducing the material quantity is a long-standing goal. Here we show that X-rays can be used to characterize the elemental and chemical state of just one atom. Using a specialized tip as a detector, X-ray-excited currents generated from an iron and a terbium atom coordinated to organic ligands are detected. The fingerprints of a single atom, the L 2,3 and M 4,5 absorption edge signals for iron and terbium, respectively, are clearly observed in the X-ray absorption spectra. The chemical states of these atoms are characterized by means of near-edge X-ray absorption signals, in which X-ray-excited resonance tunnelling (X-ERT) is dominant for the iron atom. The X-ray signal can be sensed only when the tip is located directly above the atom in extreme proximity, which confirms atomically localized detection in the tunnelling regime. Our work connects synchrotron X-rays with a quantum tunnelling process and opens future X-rays experiments for simultaneous characterizations of elemental and chemical properties of materials at the ultimate single-atom limit. Using a specialized tip as a detector, the fingerprints of a single atom of iron and terbium are observed in synchrotron X-ray absorption spectra, allowing elemental and chemical characterization one atom at a time.