We report on the shift of energies released during Auger cascades in rare-gas ions, when the ions are not isolated but embedded in a homogeneous cluster. By combining high-resolution electron spectroscopy with multielectron coincidence spectroscopy of small Ar and Xe clusters, we investigate the dependence of Auger electron emission energies on the charge state of the emitting ion in the polarizable cluster medium up to charge states of +4. Our results show deviations from the predictions of the established electrostatic Born model by a factor of ≈2 for the final step of the cascades.

Multiply charged molecules fragment under Coulomb repulsion, leaving characteristic fingerprints in ensuing electronic decay. Using K-shell ionization of HCl as a benchmark, we identify metastable intermediates that persist to internuclear separations beyond 100 a.u., where weakened Coulomb interactions enable the emergence of narrow atomic lines, while short-lived states decay at smaller separations, producing broad, red-shifted backgrounds. This work provides a previously missing dynamical description of coupled electronic and nuclear evolution in the Coulomb fragmentation regime.

Halogenated nucleosides are known candidates for enhancing X-ray damage in radiotherapy of tumors and are also excellent model systems for investigating molecular and charge dynamics following deep inner-shell ionization. We carried out electron-multi-ion coincidence measurements with two gas-phase halogenated deoxyuridine derivatives - 5-iodo-4-thio-2'-deoxyuridine (ISDU) and 5-bromo-4-thio-2'-deoxyuridine (BrSDU). We report the fragmentation patterns and kinetic energies of ions in coincidence with the I 2p, Br 2p and S 1s photoelectrons, complementing the experiment with molecular mechanics simulations and developing the parametric, stochastic model further. This work demonstrates the applicability of the multiparticle energy- and momentum-resolved coincidence technique to the relatively unexplored regime of incomplete Coulomb explosion of a biomolecular system charged up by deep inner-shell Auger cascades. Simulations of the incomplete Coulomb explosions are carried out to compare with, and complement the experimental data. Their good overall agreement shows the expected trend of more energetic Coulomb explosions and an increased degree of atomization as deeper atomic inner-shells are ionized. The presented data on ion abundances and kinetic energies extend beyond these general predictions, providing essential input for modeling the subsequent damage propagation into the surrounding environment - an aspect directly related to the radiosensitizing properties. Some observables, such as the kinetic energies of halogen ions, are particularly sensitive to the interplay of the charge and nuclear dynamics and provide valuable benchmarks for model development.

Anion interactions with cations/molecules are crucial across chemistry and biology: in battery electrolytes, synthesis, atmospheric processes, and protein denaturation. Selecting the optimum anion represents an immense challenge, as anion interactions are diverse and complex. Descriptors are needed that quantitatively capture the ability of anions to interact with cations and molecules. However, only a small number of experimental anion interaction descriptors exist, all with similar limitations. Here we show that core-level anion electron binding energies, EB(core,anion), can be used to produce a new atomic-level descriptor for each of the key donor elements for anion interactions (O, N, F, Cl, Br, I, S), the element-specific donor number (DNE-XPS). DNE-XPS descriptors are intrinsic, capturing the anion interaction abilities independent of any probe, countercation, or solvent. DNE-XPS descriptors are also interpretable, as EB(core,anion) and therefore DNE-XPS are proportional to the electrostatic potential at the specific donor atom nucleus. Experimental core-level X-ray photoelectron spectroscopy (XPS) is used to measure EB(core,anion) and therefore DNE-XPS. Furthermore, DNE-XPS descriptors are produced easily and at low cost using lone-anion-SMD (solvation model density) calculations, a significant advance on the current anion descriptors, greatly reducing and potentially removing the need for experimental anion characterization. This work will greatly facilitate anion selection, especially for complex anions capable of forming interactions through multiple different atoms. We envisage our calculation method enabling the production of a very large database of DNE-XPS for each key element, ideal for use as machine learning training data sets.

We report a detailed study of postcollision interaction (PCI) in a liquid medium. We investigate PCI for the Auger KLL electrons of solvated Cl-, K+, and Ca2+. All three isoelectronic ions exhibit a very similar PCI behavior, which is little affected by changing the solvent from water to methanol or ethanol. The two main factors modifying the PCI interaction in condensed media are the screening of Coulombic interactions and scattering of the electrons. The experimental results are compared with the predictions of a previously reported semiclassical PCI theory modified to account for screening and scattering. We show that a better agreement with experiment can be obtained by instead modeling scattering using electron transport Monte Carlo simulations. We suggest that, in turn, PCI experimental data could be used as another experimental constraint to refine the currently insufficiently well-known scattering parameters of low-energy electrons in water, which are crucial in many fields.

Two-dimensional materials, particularly transition metal dichalcogenides (TMDs), have garnered significant interest due to their tunable structural and chemical properties when exfoliated to lower dimensions. Exfoliated TMDs have been widely applied across various fields that support the United Nations Sustainable Development Goals (UN-SDGs), especially SDG 7 (Affordable and Clean Energy) and SDG 13 (Climate Action), through their use in energy storage, electrocatalysis, and water treatment membranes. Among TMDs, molybdenum diselenide (MoSe2) has received comparatively less attention; however, it exhibits outstanding properties similar to those of MoS2. This study proposes a greener synthesis route for MoSe2 via liquid-phase exfoliation using an alcoholbased solvent mixture a scalable and cost-effective alternative to conventional methods. Unlike traditional approaches that rely on toxic solvents such as N-methyl-2-pyrrolidone (NMP), our method employs a more environmentally friendly ethanol-water mixture. This eco-conscious process reduces environmental impact while preserving material quality. Comprehensive characterization techniques, including X-ray Absorption Spectroscopy (XAS) and X-ray Photoelectron Spectroscopy (XPS), were employed to investigate the crystallinity, morphology, and composition of the exfoliated MoSe2. The results highlight the importance of sustainable solvent systems in optimizing exfoliation efficiency and advancing green chemistry principles. By integrating environmentally responsible synthesis with in-depth material analysis, this work contributes to the sustainable development of 2D material production.

Understanding the interaction between metal ions and their aqueous environment is fundamental in many areas of chemistry, biology, and environmental science. In this study, we investigate the electronic structure of hydrated calcium ions, focusing on how water molecules influence the behavior of the metal ion. We employed advanced X-ray techniques, including X-ray absorption, photoelectron, and Auger spectroscopies, combined with high-level quantum chemical calculations. Our analysis reveals that, alongside normal Auger decay, distinct ultrafast charge transfer processes occur between the calcium ion and surrounding water molecules, underscoring the complex nature of metal-solvent interactions. Two primary mechanisms were identified. The first one involves electron transfer from water to the calcium ion. The second mechanism depends on the photon energy and is tentatively attributed to the decay of photoelectron satellites, the capture of free solvated electrons or electrons from a Cl^- ion in the second solvation shell. Additionally, we observed significant shifts in electron energies due to post-collision interactions and interpreted the Ca 1s-1 photoelectron satellites mainly as originating from inelastic photoelectron scattering (IPES). These findings provide deeper insights into the electronic properties of hydrated metal ions, with potential implications for fields such as catalysis and biochemistry, where metal ions play a crucial role.

Nitrogen K-edge X-ray absorption (XA) spectroscopy of aqueous ammonia reveals a splitting in the main-edge, which through theoretical modeling is shown to be related to symmetry breaking in hydrogen bonding. The XA main-edge of NH3 is formed by a pair of degenerate core-excitations into extended molecular orbitals. In aqueous solution, these form an antibonding mixture with orbitals of the surrounding water molecules. Although the spectral response to distortions is complex, we show that the degeneracy of the core-excitations is lifted by asymmetry in hydrogen bond donation (NH···O). A quantitative relation between asymmetry in the hydration shell and splitting in the main-edge of the nitrogen K-edge XA spectrum is established from systematic symmetry breaking in well-defined cluster models and through molecular dynamics sampling of simulated XA spectra of aqueous ammonia. The finding indicates that XA spectroscopy is a sensitive probe of asymmetry in solvation also around functional groups in biomolecules.

HfO2, one of the most common materials in resistive switching devices, can stabilize in a ferroelectric orthorhombic phase, enabling two nonvolatile polarization states via oxygen displacement in the unit cell. Under certain conditions, ferroelectric and resistive switching can coexist, independently addressable, within one device. This study employs operando spectroscopic analysis to elucidate the role of oxygen in both switching processes. A conductive filament is identified through a local valence change at the oxide surface via X-ray Photoelectron Emission Microscopy, allowing vacancy density and filament diameter evaluation. This provides well-founded experimental evidence of a conductive filament in orthorhombic Hf0.5Zr0.5O2-δ (HZO) in application-relevant device geometry. Depth-dependent changes in the electronic signature of HZO and La0.8Sr0.2MnO3-δ (LSMO) with ferroelectric field cycling are identified by Hard X-ray Photoelectron Spectroscopy. Polarization-dependent shifts in the Hf core level align with the oxygen vacancy migration during ferroelectric switching. Fatigue-related vacancy generation causes an inhomogeneous reduction that does not propagate into the bottom electrode and extended domain pinning at the HZO/LSMO interface. This highlights the importance of interface engineering for the ferroelectric performance and of the oxygen affinity of the bottom electrode for both switching regimes.

Supramolecular structures in solution are probed using Far-Zone Resonant Energy Transfer (FZRET) in an aqueous potassium acetate microjet. This advanced X-ray spectroscopic technique relies on the resonant energy transfer between donor atoms, i.e. core-ionised potassium ions, and acceptor atoms a few nm away. These experiments reveal an inhomogeneous distribution of ions in water, and are consistent with the presence of nm-sized ionic clusters at 4.1 M concentration.

The perpendicular magnetic anisotropy (PMA) of metal/ferromagnet (FM)/oxide trilayers is known to depend on the degree of oxidation of the FM/oxide interface. Among the different methods to tune the PMA, magnetoionics is emerging as a promising technique with potential applications in low-power spintronic devices. In this work, the PMA of Pt/Co/AlOx/HfO2 capacitorlike devices was gradually tuned by electric field gating. Hard-x-ray photoelectron spectroscopy (HAXPES) measurements at a synchrotron radiation source, guaranteeing tunable photon energies, a collimated beam, and a large photon flux, have allowed us to probe the composition of the cobalt ultrathin film buried below the dielectric layer of the capacitors, and its evolution upon the application of the gate voltage. The Co 2p HAXPES spectra of the gated devices were compared to those obtained for Pt/Co/AlOx reference samples, for which the PMA was controlled by tuning the Co oxidation with oxygen plasma. For similar magnetic anisotropy states, the two types of samples exhibit equivalent Co 2p HAXPES spectra, with the same weight of metallic Co and CoO signatures. These results constitute direct experimental proof that, in our integrated devices, the gate voltage modifies the PMA through the modification of the oxidation state of the buried cobalt layer driven by oxygen-ion migration.

Low-temperature phase manganese bismuth (LTP-MnBi) and a series of aluminum (Al) composites were synthesized using a potentially facile and scalable low-temperature liquid-phase sintering method in a vacuum at 300 degrees C. The incorporation of up to 10 at% Al led to a significant enhancement in coercivity (Hc), increasing from 2.32 +/- 0.04 to 4.15 +/- 0.07 kOe, while saturation magnetization showed a slight decrease of less than 3 %. However, beyond this concentration, a dramatic reduction in Hc was observed. The density of the freshly compacted powders, which included up to 10 at% Al, remained relatively constant at 7.47-7.58 g/cm3 but decreased with excess Al. A maximum energy product (BH)max of 1 MGOe was achieved in the fresh sample, with a 16 % enhancement in (BH)max in the MnBi composite containing 5 at% Al. Scanning electron microscopy revealed distinct MnBi and Bi-rich regions, while Al-rich areas became prominent at Al concentrations above 10 at%. Energy dispersive spectroscopy confirmed that only 3-5 at% Al could be effectively incorporated into Mn-Bi regions, with excess Al unevenly distributed on the surface. X-ray photoelectron spectroscopy indicated the formation of Al, Al2O3, and potential Mn-Bi-Al ternary alloys. Additionally, slab-DFT models, such as AlMn/ MnBi, indicate that Al inclusion enhances the magnetization in MnBi composites, providing insights into its effects on the magnetic properties of Mn-Bi systems. These findings offer promising strategies to address the challenges posed by excess Bi in the MnBi structure, potentially optimizing the magnetic performance of similar non-magnetic or soft-magnetic composite systems.

We have built and commissioned a novel standalone multi-crystal x-ray spectrometer (MOSARIX) in the von Hamos configuration based on highly annealed pyrolytic graphite crystals. The spectrometer is optimized for the energy range of 2–5 keV, but this range can be extended up to 20 keV by using higher reflection orders. With its nine crystals and a Pilatus detector, MOSARIX achieves exceptional detection efficiency with good resolving power (better than 4000), opening the door to study small cross section phenomena and perform fast in situ measurements. The spectrometer operates under a He atmosphere, which provides a flexible sample environment for measurements in gas, liquid, and solid phases.

We present first hard X-ray photoelectron spectroscopy (HAXPES) results of aqueous salt solutions and dispersions of gold nanoparticles in liquid cells equipped with specially designed microfabricated thin silicon nitride membranes, with thickness in the 15–25 nm range, mounted in a high-vacuum-compatible environment. The experiments have been performed at the HAXPES endstation of the GALAXIES beamline at the SOLEIL synchrotron radiation facility. The low-stress membranes are fabricated from 100 mm silicon wafers using standard lithography techniques. Platinum alignment marks are added to the chips hosting the membranes to facilitate the positioning of the X-ray beam on the membrane by detecting the corresponding photoemission lines. Two types of liquid cells have been used, a static one built on an Omicron-type sample holder with the liquid confined in the cell container, and a circulating liquid cell, in which the liquid can flow in order to mitigate the effects due to beam damage. We demonstrate that the membranes are mechanically robust and able to withstand 1 bar pressure difference between the liquid inside the cell and vacuum, and the intense synchrotron radiation beam during data acquisition. This opens up new opportunities for spectroscopic studies of liquids.

In this study, we integrate experimental observations and theoretical models to elucidate the complex phenomena observed in the resonant S K-edge KLL Auger scattering spectra of the SF6 molecule. A two-dimensional spectral map, constructed of incident photon energy and kinetic energy of the emitted Auger electron, is shown to be a versatile tool for understanding a character of the core-excited potential energy surface and change of the molecular geometry. Our findings reveal how the distinct dispersion behavior of multiple spectral lines enables mapping of ultrafast dynamics within the short-lived core-excited states. Our results confirm the presence of nuclear dynamics in the S1s-16a11g and S1s-16t11u core-excited states, while dynamics is absent in the S1s-17t11u state. Using a combination of ab initio analysis, simulations with Coulomb model potentials, and a simple analytical approximation, we qualitatively demonstrate how the varying characteristics of spectral dispersion-classified as Raman, non-Raman, and anti-Raman-mirror the relative gradients of the intermediate and final states in the resonant x-ray scattering process. This insight allows for the effective mapping of molecular potential energy curves, offering a prospective tool on the underlying mechanisms of resonant Auger scattering and its potential for probing molecular dynamics.

The electronic structure and geometrical organization of aqueous Cu2+ have been investigated by using X-ray photoelectron spectroscopy (XPS) at the Cu L-edge combined with state-of-the-art ab initio molecular dynamics and a quantum molecular approach designed to simulate the Cu 2p X-ray photoelectron spectrum. The calculations offer a comprehensive insight into the origin of the main peak and satellite features. It is illustrated how the energy drop of the Cu 3d levels (≈7 eV) following the creation of the Cu 2p core hole switches the nature of the highest singly occupied molecular orbitals (MOs) from the dominant metal to the dominant MO nature of water. It is particularly revealed how the repositioning of the Cu 3d levels induces the formation of new bonding (B) and antibonding (AB) orbitals, from which shakeup mechanisms toward the relaxed H-SOMO operate. As highlighted in this study, the appearance of the shoulder near the main peak corresponds to the characteristic signature of shakeup intraligand (1a1 → H-SOMO(1b1)) excitations in water, providing insights into the average dipole moment distribution (≈36°) of the first-shell water molecules surrounding the metal ion and its direct impact on the broadening of the satellite. It is also revealed that the main satellite at 8 eV from the main peak corresponds to (metal/1b2 → H-SOMO(1b1) of water) excitations due to a bonding/antibonding (B/AB) interaction of Cu 3d levels with the deepest valence O2p/H1s 1b2 orbitals of water. This finding underscores the sensitivity of XPS to the electronic structure and orientation of the nearest water molecules around the central ion.

Postcollision interaction (PCI) in near-threshold photoionization of the K shell of atomic Xe is investigated with hard-x-ray synchrotron radiation. Applying Auger electron spectroscopy, line-shape distortion is monitored in the K-L2 L 2 -> L 2 M 4 , 5 M 4 , 5 decay channel, where the initial K-L2 L 2 (K alpha 2) K alpha 2 ) x-ray-emission step mediates the emission of the two continuum electrons. The K-edge result is compared to similar data obtained on direct L 2 M 4 , 5 M 4 , 5 decay at the L 2 edge without x-ray-emission. It is found that the evolution of the PCI shift with excess photon energy is very similar at both edges, but a subtle decrease in the PCI shift is observable at the K edge due to the effect of the ultrafast x-ray emission step delaying the PCI energy exchange by a few attoseconds.

In this paper, we present the results on Auger/photoelectron coincidence spectroscopy (APECS) of molecules-propanethiol and bovine serum albumin (BSA)-deposited on a gold wire surface, using a magnetic bottle electron time-of-flight spectrometer. Although this study is preliminary and conducted under low vacuum (similar to 10-7 mbar) conditions in comparison to surface science standards, it demonstrates the APECS methods high efficiency in probing complex molecules. We also establish its versatility and potential for easy extension to other various systems.

AbstractCharge transfer between molecules lies at the heart of many chemical processes. Here, we focus on the ultrafast electron dynamics associated with the formation of charge-transfer-to-solvent (CTTS) states following X-ray absorption in aqueous solutions of Na+, Mg2+, and Al3+ ions. To explore the formation of such states in the aqueous phase, liquid-jet photoemission spectroscopy is employed. Using the core-hole-clock method, based on Auger–Meitner (AM) decay upon 1s excitation or ionization of the respective ions, upper limits are estimated for the metal-atom electron delocalization times to the neighboring water molecules. These delocalization processes represent the first steps in the formation of hydrated electrons, which are determined to take place on a timescale ranging from several hundred attoseconds (as) below the 1s ionization threshold to only 20 as far above the 1s ionization threshold. The decrease in the delocalization times as a function of the photon energy is continuous. This indicates that the excited electrons remain in the vicinity of the studied ions even above the ionization threshold, i.e., metal-ion electronic resonances associated with the CTTS state manifolds are formed. The three studied isoelectronic ions exhibit quantitative differences in their electron energetics and delocalization times, which are linked to the character of the respective excited states.

We explore ultrafast charge transfer (CT) resonantly induced by hard x-ray radiation in organic thiophene-based polymers at the sulfur K-edge. A combination of core-hole clock spectroscopy with real-time propagation time-dependent density functional theory simulations gives an insight into the electron dynamics underlying the CT process. Our method provides control over CT by a selective excitation of a specific resonance in the sulfur atom with monochromatic x-ray radiation. Our combined experimental and theoretical investigation establishes that the dominant mechanism of CT in polymer powders and films consists of electron delocalization along the polymer chain occurring on the low-femtosecond time scale.