Paul Scherrer Institut

Shorter period undulators typically require a higher on-axis magnetic field in order to achieve a practical deflection parameter, K . Recent simulations and experiments have demonstrated that high-temperature superconducting (HTS) undulators, constructed from staggered-array bulk superconductors, can generate high undulator fields with period length as short as 10 mm. This advanced HTS technology has the potential to significantly enhance the photon energy range of synchrotron radiation light sources and free electron laser facilities. This paper reports on the progress made in developing of a 50-period bulk HTS undulator with period length of 12 mm for Shanghai soft x-ray free electron laser facility. It details the engineering design of the undulator prototype, thermal and mechanical analysis of the HTS variable temperature insert, and the current status of the system.

The phenomena occurring in a weld seam during advancement of a laser beam over a metallic component are still under dispute. The occurrence and evolution of porosity and the occasional blowout of melt need to be understood. Here, a recently developed X‐ray tomoscopy setup is applied, providing one hundred 3D images per second to capture the temporal evolution of the melt pool in an AlSi9Cu3(Fe) die‐casting while a laser beam advances. The number of pores, their size, shape and distribution are quantified with 10 ms time resolution and reflect a complex dynamic pattern. Apart from conventional welding, a variant involving a dynamic beam modulation superimposed onto the linear motion is studied. Reductions of porosity and surface roughness are observed and explained by increased pore mobility and stepwise degassing as the beam repeatedly cuts through pores. The keyhole formed in the melt pool integrated over 10 ms is represented in 3D.

We report a study on the photoionization of the C6H6 isomer 3,4‐dimethylenecyclobutene, DMCB. The molecule is an intermediate in the formation of benzene from the propargyl radical self‐reaction, a suggested first step in the formation of polycyclic aromatic hydrocarbons and soot. From a threshold photoelectron spectrum we determine an adiabatic ionization energy of 8.75 eV. The geometry change upon ionization is associated with considerable vibrational activity, which is assigned to a symmetric in‐plane bending mode of the =CH2 groups. A breakdown diagram shows that the dissociative photoionization resembles the one observed for benzene. Computations reveal that DMCB cation isomerizes to the benzene cation and dissociates from there.

Wave-front propagation simulations have been a tool to design and optimize X-ray interferometry devices. The often used plane wave approaches, however, lack the angular resolution to describe effects like system imperfections or inhomogeneous samples in conjunction with the X-ray source size. We developed a framework that allows to simulate optical components as well as samples with any source size in arbitrary configurations by inducing the mentioned effects within the wave propagation instead of adding intermediate models. The simulation results were able to predict and explain the impact of local grating defects for different focal spot sizes and provided a spectral sampling optimization for image acquisition. The simulation framework can run on GPU, do out-of-memory calculations, and is publicly available on Github.

Non‐fullerene acceptors have revolutionised organic photovoltaics. However, greater fundamental understanding is needed of the crucial relationships between molecular structure and photophysical mechanisms. Herein, a combination of spectroscopic, morphology, and device characterization techniques are used to explore these relationships for a high‐performing non‐fullerene acceptor, anti‐PDFC. It focuses on transient absorption spectroscopy across multiple timescales and ultrafast time‐resolved vibrational spectroscopy to acquire the “holy grail” of simultaneous structural and dynamic information for anti‐PDFC and its blend with the well‐known conjugated polymer PM6. Most significantly, it is observed that the singlet exciton of anti‐PDFC is localised on the perylene diimide central core of the molecule, but the radical anion is primarily localised on the fluorinated indene malonitrile terminal units (which are common to many state‐of‐the‐art non‐fullerene acceptors, including the Y6 family). This electron transfer from the central core to the termini of an adjacent molecule is facilitated by a close interaction between the termini and the central core, as evidenced by single crystal diffraction data and excited state calculations. Finally, the very efficient charge extraction measured for PM6:anti‐PDFC photovoltaic devices may be correlated with this anion localization, enabling effective charge transport channels and thus enhancing device performance.

Single-shot ptychography is a quantitative phase imaging method wherein overlapping beams of light arranged in a grid pattern simultaneously illuminate a sample, allowing a full ptychographic dataset to be collected in a single shot. It is primarily used at optical wavelengths, but there is interest in using it for x-ray imaging. However, constraints imposed by x-ray optics have limited the resolution achievable to date. In this work, we reinterpret single-shot ptychography as a structured illumination method by viewing the grid of beams as a single, highly structured illumination function. Pre-calibrating this illumination and reconstructing single-shot data using the randomized probe imaging algorithm allows us to account for the overlap and coherent interference between the diffraction arising from each beam. We achieve a resolution 3.5 times finer than the numerical aperture-based limit imposed by traditional algorithms for single-shot ptychography. We argue that this reconstruction method will work better for most single-shot ptychography experiments and discuss the implications for the design of future single-shot x-ray microscopes.

Bulk properties of two-phase systems comprising methane and liquid p-xylene were derived experimentally using neutron imaging and theoretically predicted using molecular dynamics (MD). The measured and predicted methane diffusivity in the liquid, Henry’s law constant, apparent molar volume, and surface tension compared well within the experimentally studied conditions (273.15 to 303.15 K, ≤ 100 bar). Since MD is a physical model, extrapolations of the two-phase systems properties were performed for a broader temperature range (260 to 400 K, ≤ 100 bar). Moreover, the species diffusivities in single phases formed by infinitely diluted p-xylene in methane were predicted under conditions relevant to the methane liquefaction (90 to 290 K, 50 bar). The predicted p-xylene diffusivity in the supercritical methane was one order of magnitude higher than that calculated using Wilke–Chang and He–Yu correlations. This study provides novel experimental and MD-simulated characteristics for this industrially relevant system, for which intensive freeze-out formation from the supercritical methane is predicted.

We present an experimental study of the magnetoelectric coupling in the Fe-Ga/Pb[(Mg 1 / 3Nb 2 / 3)O 3] 0.68-[PbTiO 3] 0.31 thin-film multiferroic composite using x-ray magnetic circular dichroism and ferromagnetic resonance (FMR). Our measurements show evidence for a charge-mediated coupling mechanism, suggested by the asymmetric magnetic remanence (M r e m) behavior under opposite electric fields ( ±E) and the asymmetric resonance field (H r) in the FMR measurements. Also, the FMR measurements reveal a perpendicular magnetic anisotropy that can be related to an interface charge effect and it is tunable by the E field. Ab initio calculations support the existence of a charge-mediated coupling at the Fe–Ga/PMN-PT interface.

While photochemical aging is known to alter secondary organic aerosol (SOA) properties, this process remains poorly constrained for anthropogenic SOA. This study investigates the photodegradation of SOA produced from the hydroxyl radical-initiated oxidation of naphthalene under low- and high-NOx conditions. We used state-of-the-art mass spectrometry (MS) techniques, including extractive electrospray ionization and chemical ionization MS, for the in-depth molecular characterization of gas and particulate phases. SOA were exposed to simulated irradiation at different stages, i.e., during formation and growth. We found a rapid (i.e. >30 min) photodegradation of high-molecular-weight compounds in the particle-phase. Notably, species with 20 carbon atoms (C20) decreased by 2/3 in the low-NOx experiment which was associated with particle mass loss (∼12%). Concurrently, the formation of oligomers with shorter carbon skeletons in the particle-phase was identified along with the release of volatile products such as formic acid and formaldehyde in the gas-phase. These reactions are linked to photolabile functional groups within the naphthalene-derived SOA products, which increases their likelihood of being degraded under UV light. Overall, photodegradation caused a notable change in the molecular composition altering the physical properties (e.g., volatility) of naphthalene-derived SOA.

The detailed anisotropic dispersion of the low-temperature, low-energy magnetic excitations of the candidate spin-triplet superconductor UTe 2 is revealed using inelastic neutron scattering. The magnetic excitations emerge from the Brillouin zone boundary at the high symmetry Y and T points and disperse along the crystallographic $\hat{b}$ b ̂ -axis. In applied magnetic fields to at least μ 0 H = 11 T along the $\hat{c}-{\rm{axis}}$ c ̂ − axis , the magnetism is found to be field-independent in the ( h k 0) plane. The scattering intensity is consistent with that expected from U ³⁺ /U ⁴⁺ f -electron spins with preferential orientation along the crystallographic $\hat{a}$ a ̂ -axis, and a fluctuating magnetic moment of μ e f f =1.7(5) μ B . We propose interband spin excitons arising from f -electron hybridization as a possible origin of the magnetic excitations in UTe 2 .

Solving the surface (electro−)chemical instability and the fading behavior of high voltage cathode materials cycled above 4.3 V vs Li⁺/Li remains a major challenge for the next generation of high energy density Li‐ion batteries. Here, we present a facile, environmentally friendly, cost effective and scalable method to address this problem by uniformly fluorinating the surface of cathode materials with a mild fluorinating agent (CHF3) using a gas flow‐type reactor. CHF3, well known as a potent greenhouse gas, is successfully transformed into a stable ~2 nm LiF homogenous layer by converting the adventitious Li2CO3 layer covering the surface of the vast majority of layered‐oxide cathode materials. The fluorination mechanism and the interface stability of the LiF coating layer is systematically studied on LiNi0.8Co0.15Al0.05O2 using synchrotron surface spectroscopy techniques, operando XRD and TEM. In addition, we demonstrate improved electrochemical cycling performance of the LiF coated LiNi0.8Co0.15Al0.05O2 when cycled up to 4.5 V where the impedance and overpotential decrease by 30 % and 100 mV respectively after 100 cycles, with a capacity retention better than 94 % and improved rate performance at high current density. Furthermore, the universality of the fluorination approach is validated further on Ni‐rich LiNi0.85Co0.1Mn0.05O2 cathode material cycled up to 4.3 and 4.8 V vs Li⁺/Li.

The plastic waste crisis is among humanity’s most urgent challenges. However, widespread adoption of sustainable plastics is hindered by their often inadequate processing characteristics and performance. Here, we introduce a bio-inspired strategy for the modification of a representative high molar mass, biodegradable aliphatic polyester that helps overcome these limitations and remains effective at molar masses far greater than the entanglement molar mass. We use co-assembly of oligopeptide-based polymer end groups and a low molar mass additive to create a hierarchical structure characterized by regularly spaced nanofibrils interconnected by entangled polymer segments. The modified materials show a rubbery plateau at temperatures above their melting point, associated with strongly increased melt strength, extraordinary melt extensibility, improved dimensional stability, and accelerated crystallization. These thermomechanical property changes open up otherwise inaccessible processing routes and offer considerable scope for improving solid-state properties, thereby addressing typical shortcomings of sustainable alternatives to conventional plastics.

For many synchrotron radiation experiments, it is critical to perform continuous, real-time monitoring of the X-ray flux for normalization and stabilization purposes. Traditional transmission-mode monitors included metal mesh foils and ionization chambers, which suffered from low signal stability and size constraints. Solid-state detectors are now considered superior alternatives for many applications, offering appealing features like compactness and signal stability. However, silicon-based detectors suffer from poor radiation resistance, and diamond detectors are limited in scalability and are expensive to produce. Silicon carbide (SiC) has recently emerged as an alternative to both materials, offering a high-quality mature semiconductor with high thermal conductivity and radiation hardness. This study focuses on a systematic exploration of the SiC ‘free-standing membrane’ devices developed by SenSiC GmbH. In particular, we performed in-depth sensor-response analysis with photon energies ranging from tender (1.75 keV) to hard (10 keV) X-rays at the Four-Crystal Monochromator beamline in the PTB laboratory at the synchrotron radiation facility BESSY II, studying uniformity of transmission and responsivity compared with the state-of-the-art beam monitors. Furthermore, we theoretically evaluated the expected signal in different regions of the sensors, also taking into account the effect of charge diffusion from the SiC substrate in the case of the not-carved region.

One of the main limitations of conventional absorption-based X-ray micro-computed tomography imaging of biological samples is the low inherent X-ray contrast of soft tissue. To overcome this limitation, the use of ethanol as contrast agent has been proposed to enhance image contrast of soft tissues through dehydration. Some authors have shown that ethanol shrinks and hardens the tissue too much, also causing small tissue ruptures due to fast dehydration. However, the local tissue deformation occurring as a consequence of tissue dehydration and whether tissue shrinkage can modify myocardial architecture has not been quantified yet. The aim of this paper is to quantify the local myocardial tissue deformation due to ethanol dehydration based on 3D non-rigid registration and perform a detailed characterization of its myocardial tissue organization, before and after ethanol dehydration. A rat adult heart was imaged with synchrotron-radiation-based X-ray phase contrast imaging (X-PCI) three times: before, 9 h after and 342 h after ethanol immersion. The total volume shrinkage as well as changes in the left ventricular myocardial thickness were computed. Then, to determine local deformation of the heart caused by ethanol dehydration, the related 3D tomographic datasets were registered by means of a non-rigid registration algorithm. Finally, changes on the orientation and organization of myocytes were assessed. Our results show that the use of ethanol in synchrotron X-PCI can improve image contrast, but the tissue shrinkage is not homogeneous thus changing the local myocardial organization.

Gap junction intercellular communication (GJIC) between two adjacent cells involves direct exchange of cytosolic ions and small molecules via connexin gap junction channels (GJCs). Connexin GJCs have emerged as drug targets, with small molecule connexin inhibitors considered a viable therapeutic strategy in several diseases. The molecular mechanisms of GJC inhibition by known small molecule connexin inhibitors remain unknown, preventing the development of more potent and connexin-specific therapeutics. Here we show that two GJC inhibitors, mefloquine (MFQ) and 2-aminoethoxydiphenyl borate (2APB) bind to Cx32 and block dye permeation across Cx32 hemichannels (HCs) and GJCs. Cryo-EM analysis shows that 2APB binds to “site A”, close to the N-terminal gating helix of Cx32 GJC, restricting the entrance to the channel pore. In contrast, MFQ binds to a distinct “site M”, deeply buried within the pore. MFQ binding to this site modifies the electrostatic properties of Cx32 pore. Mutagenesis of V37, a key residue located in the site M, renders Cx32 HCs and GJCs insensitive to MFQ-mediated inhibition. Moreover, our cryo-EM analysis, mutagenesis and activity assays show that MFQ targets the M site in Cx43 GJC similarly to Cx32. Taken together, our results point to a conserved inhibitor binding site in connexin channels, opening a new route for development of specific drugs targeting connexins.

Discontinuous solid-solid phase transformations play a pivotal role in determining the properties of rechargeable battery electrodes. By leveraging operando Bragg Coherent Diffractive Imaging (BCDI), we investigate the discontinuous phase transformation in LixNi0.5Mn1.5O4 within an operational Li metal coin cell. Throughout Li-intercalation, we directly observe the nucleation and growth of the Li-rich phase within the initially charged Li-poor phase in a 500 nm particle. Supported by the microelasticity model, the operando imaging unveils an evolution from a curved coherent to a planar semi-coherent interface driven by dislocation dynamics. Our data indicates negligible kinetic limitations from interface propagation impacting the transformation kinetics, even at a discharge rate of C/2 (80 mA/g). This study highlights BCDI’s capability to decode complex operando diffraction data, offering exciting opportunities to study nanoscale phase transformations with various stimuli.

Transparent polymers are low‐cost, light, and flexible, making them prospective for a plethora of applications. Still, their usage in photonics is impeded by a low refractive index, usually less than 1.7. In this work, an alternative strategy is proposed for improving optical characteristics by developing poly(ionic liquids) (PILs) with a gradient refractive index (GRIN) in thin films. The obtained PILs are transparent, environmentally friendly, and possess the GRIN effect in thin films. Inspired by the architecture of the animal's eye, PILs are employed for inkjet fabrication of microlenses with a giant GRIN value of 0.8, which is up to several times higher than that in previous studies on nanolayered polymeric and 3D printed GRIN lenses. Furthermore, in terms of focusing power, lens transparency, and depth of field, these microlenses outperform the result of high refractive index polymers. Hence, the findings open a novel platform for compact optical components based on new types of ionic polymers.