Jean Pascal Rueff

Determining the intrinsic electronic structure of the surfaces of soft materials, typically polymers, that are easily degraded when exposed to X-ray radiation is a crucial matter that must be addressed meticulously. Before any consistent characterization is undertaken, it is mandatory to determine the damage caused by the radiation and set the optimal running parameters of the specific XPS instrument used for the experiments. Here, we propose a systematic method to carry out such a task and apply it to the case of Nafion, a well-known and widely used material containing highly radiation-sensitive sulfonate groups and focus on its ability as thin films to efficiently capture divalent metal cations such as Cd2+ and Pb2+, two common toxic contaminants found in drinking water. Nafion films have the potential for efficient and fast water purification strategies for environmental remediation and require a detailed analysis to ascertain the ionic-exchange mechanisms involved at the Nafion/water interfaces.

We investigate the Yb valence instabilities in the strongly correlated YbPd compound using resonant x-ray emission spectroscopy as a function of pressure across the charge-order (CO) transition. At a low temperature ( T = 30 K ) in the CO phase, the Yb 4 f valence remains nearly constant up to a pressure P L = 1.5 ± 0.2 GPa , and then increases gradually at higher pressures. In contrast, at room temperature in the normal phase, an anomalous decrease of the Yb 4 f valence is observed, without any accompanying structural phase transition. This behavior is corroborated by a systematic pressure-dependent decrease of the unit-cell volume. Based on a Birch-Murnaghan analysis, the compressibility indicates hardening of the lattice with applied pressure up to a distinct kink seen at P K = 1.6 ± 0.2 GPa . In contrast, for P > P K , the Yb 4 f valence saturates, and the compressibility reveals a counterintuitive pressure-induced softening. The results show a minimum in the compressibility of YbPd (with f 0 – f 1 hole-type mixed valence), reminiscent of the maximum in compressibility seen in the γ – α first-order isostructural phase transition in cerium (with f 0 – f 1 electron-type mixed valence).

X-ray cavity quantum optics with inner-shell transitions has been limited by the spectral overlap between resonant and continuum states. Here, we report the first experimental demonstration of cavity-controlled core-to-core resonant inelastic x-ray scattering (RIXS). We suppress the absorption-edge effects by monitoring the RIXS profile, thereby resolving the resonant state from the overlapping continuum. We observe distinct cavity-induced energy shifts and cavity-enhanced decay rates in the 2 p 3 d RIXS spectra of WSi 2 . These effects, manifesting as stretched or shifted profiles in the RIXS planes, enable novel spectroscopic applications via cavity-controlled core-hole states. Our results establish core-to-core RIXS as a powerful tool to manipulate inner-shell dynamics in x-ray cavities, offering new avenues for integrating quantum optical effects with x-ray spectroscopy.

In this combined experimental and theoretical work, we present state-of-the-art liquid jet experiments based on x-ray emission spectroscopy of the [Fe(CN)6]4− and [Fe(CN)6]3− molecular ions in the hard-x-ray energy range. The ab initio simulations of the valence-to-core and Kβ spectra reveal insights into the valence and metal’s d-shells, respectively. These results open new perspectives for applying spectroscopy to organometallic complexes in order to disentangle and probe various environmental effects, including solvent interactions, pH variations, and ligand field influences and dynamical processes, such as charge transfer or photoinduced ligand exchange reactions such as photoaquation in solution.

The solid-phase speciation of Pb in legacy plastics controls its leaching behaviour upon ingestion. Risk assessments of plastic pollution should move beyond bulk geochemical approaches and account for metal speciation.

We present the design and performance of a new multi-crystal x-ray emission spectrometer installed at the GALAXIES beamline at Synchrotron SOLEIL. The new instrument, which we name “MULTIXS,” can host up to five analyzer crystals and supersedes our previous XES spectrometer design, providing a compact, simple design with all the analyzer crystals contained in the horizontal sample plane. This feature provides a direct view of the sample area and avoids the potential masking of the sample for constrained sample environments. This new design allows for the use of both 0.5 m and 1 m radius spherical analyzer crystals. In addition, the ability to continuously scan the spectrometer energy provides relatively fast scanning with high quality emission data and minimum dead-time overhead.