We report the synthesis and characterization of a pair of homoleptic cerium tris(amidinate) complexes, [Ce III {PhC(N t Bu) 2 } 3 ] and [Ce IV {PhC(N t Bu) 2 } 3 ][Al(OC 4 F 9 ) 4 ], containing cerium in both its trivalent (Ce III ) and tetravalent (Ce IV ) oxidation states. To the best of our knowledge, these represent the first examples of a lanthanide-amidinate system where both trivalent and tetravalent complexes have been isolated and structurally characterized in such a congruent ligand coordination. With electronic structure and bond analysis, we demonstrate that while the metal-ligand bonding in both species is dominated by interactions involving Ce 5d valence orbitals, there is a measurable participation of the 4f orbitals specifically within the Ce IV homolog. Ce L 3 -edge high-energy resolution X-ray absorption near edge structure (HR-XANES) and valence band resonant inelastic X-ray scattering (VB-RIXS) are employed to evaluate the bonding properties and are complemented with quantum chemical calculations based on density-functional theory (DFT). Crucially, the high-resolution nature of these spectroscopic techniques, coupled with theoretical modelling, enables a quantitative deconvolution of the bonding interaction directly from the experimental data. This approach allows us to partition the individual contributions of both the 4f and 5d electrons to the metal-ligand interaction. Our findings highlight the increased role of 4f electron density in stabilizing high-valent lanthanide complexes, due to improved energetic and spatial overlap between nitrogen donor lone pairs and the Ce IV acceptor manifold.

Using non-classical divalent lanthanide precursors as multi-electron reducing agents, complexes, [K(18-crown-6)(Cp” 2 LnTe 3 )], with Ln = La, Ce, and Nd, Cp” = 1,3-bis-(trimethylsilyl)cyclopentadienyl, were synthesized and investigated to elucidate the mechanism of lanthanide-tellurium bonding and the role of 4 f -element electron density in stabilizing small chalcogenide chains. Density-Functional Theory (DFT) reveals that the frontier molecular orbitals of these complexes are predominantly localized on the [Te 3 ] 2- fragment, while the trivalent lanthanide ions stabilize the tellurium chain through weak but measurable metal-ligand interactions. To experimentally resolve these interactions, we focus on complementary ligand- and metal-centered X-ray spectroscopic approaches. Ln L 3 -edge high-resolution XANES (HR-XANES) and valence-band resonant inelastic X-ray scattering (VB-RIXS) demonstrate that the Ln-Te/C interaction has substantial Ln 5 d orbitals contribution, particularly for the Ln-Te bond, and remains largely constant across the three complexes. DFT-based bond analysis provides a mechanistic interpretation of these trends. The Ln–C interaction exhibits increasing electron density at the bond critical point and a higher delocalization index (QTAIM analysis) from the lighter to the heavier lanthanides, reflecting enhanced Ln 4 f participation within an energy-driven covalency regime. The Ln–Te interaction is predominantly electrostatic, with meaningful orbital contributions arising mainly from Ln 5 d participation within an orbital-overlap driven covalency regime. These results demonstrate that the Ln-C and Ln-Te bonding in the present complexes follow fundamentally distinct covalency mechanisms, which together enable the stabilization and isolation of the small [Te 3 ] 2- fragment chain.

Defect states are crucial in many electronic devices. Oxygen vacancies, for example, are common in transparent conductive oxides and can both be beneficial (e.g., as a dopant to enhance conductivity) as well as detrimental (e.g., leading to reduced device performance by recombination at interfaces). Using soft and hard X-ray photoelectron spectroscopy (PES and HAXPES) with excitation photon energies ranging from 0.1 to 6.3 keV, we study the electronic surface structure of differently processed Ga2O3 samples in a depth-resolved fashion. Specifically, we investigate a Ga2O3 thin film, as used in Cu-(In,Ga)-Se2-based thin-film solar cells, as well as a β-Ga2O3 single crystal before and after a defect-inducing Ar+-ion treatment. Spectra calculations based on density functional theory (DFT) are used to explain the PES and HAXPES valence band signatures as a function of the excitation photon energy. The β-Ga2O3 single crystal spectra can be well described by the DFT calculations. In contrast, the Ga2O3 thin film and Ar+-ion treated β-Ga2O3 show significant spectral broadening of the valence band features and additional spectral intensity close to the valence band maximum, which we assign to defect states. This additional intensity varies as a function of probing depth, suggesting that these defects are mostly localized at the surface. We also discuss the importance of DFT-based spectra calculations to verify the proper determination of valence band maxima using a linear extrapolation.

Abstract S L2,3 X-ray emission spectroscopy (XES) and spectra calculations based on density functional theory are used to study the electronic valence structure of Mn, Fe, Co, and Cu transition metal sulfides, without (MnS, FeS, CoS, and Cu2S) and with (MnS2, FeS2, CoS2, and CuS) sulfur dimers in the crystal structure. We find the upper valence band region in the experimental spectra to be very sensitive to the transition metal, while a splitting in the transitions from the S 3s derived bands indicates the presence of sulfur dimers. This makes S L2,3 XES particularly well suited to the chemical speciation of these compounds. The spectral changes are reproduced by our spectra calculations, which allows for a detailed understanding of the electronic structure based on the band structure and the projected density of states. The splitting of the S 3s derived bands in the dimer compounds is found to increase with decreasing sulfur–sulfur distance, indicating an increase of covalency. The splitting in our experimental XES spectra is found to be smaller than in photoemission data and our spectra calculations, which we attribute to nuclear dynamics on the time scale of the X-ray emission process. In particular, the high sensitivity of S L2,3 XES to the presence of sulfur dimers, together with its suitability for operando studies, makes it a key technique for future studies on a wide range of relevant material systems.

Actinide and lanthanide binary nitrides (AnN, LnN), are isostructural cubic compounds relevant to next-generation nuclear fuels which require detailed understanding regarding their oxidative degradation for safe disposal, yet a systematic comparative description remains. Herein, the room- and high-temperature oxidation behaviour of U3+N and Ln3+N (Ln = Pr, Nd, Gd, Tb, Dy, Ho, Tm and Lu) compounds is examined via a combination of X-ray diffraction, electron microscopy, thermogravimetric, and X-ray absorption spectroscopy analysis. At room temperature, UN was found to undergo an oxygen mediated oxidising mechanism, which contrasted chemically and microstructurally to the LnN’s, which followed a consistent hydrolysis mechanism. At high temperature, more congruent behaviour is determined with direct occurrence of oxide products, where the onset temperature of oxidation was found to correlate with the ionic radii of examined Ln/U cations. The results provide insight into the behaviour of these compounds in UN-based spent fuel, particularly phase separation variability and incongruent behaviour during inadvertent oxidation.

While Zintl compounds comprising Bi-based anions of p-block elements have been used as starting materials for larger bismuth-based clusters, their potential to form nanoparticles has not yet been explored. Here, bimetallic nanoparticles are synthesized from the oxidation of bismuth-based pseudo-tetrahedral Zintl anions (InBi3)2-, (Sn2Bi2)2-, (TlBi3)2-, and (Pb2Bi2)2-. The anions rapidly oxidize at ambient conditions to form metallic seeds, with the mild oxidizing agent PVP (polyvinylpyrrolidone), which also serves as a stabilizing agent for nanoparticle growth. Each elemental combination behaves uniquely, resulting in bimetallic nanoparticles of varying forms (i.e., alloyed, core-shell, and Janus-type). The resulting nanoparticles show a relatively narrow size distribution with median diameters of ∼20-25 nm and exhibit ultraviolet (UV) absorption, with spectral features tunable by composition. The morphology and composition were analyzed by scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HRTEM), micro-X-ray fluorescence spectroscopy (µ-XFS), powder X-ray diffraction (PXRD), synchrotron-based hard and soft X-ray photoelectron spectroscopy (HAXPES and PES), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). This approach demonstrates that binary Zintl anions can serve as versatile molecular precursors for designing heterometallic nanoparticles with controlled composition, morphology, and optical properties.

Spectroscopic techniques are essential for accurately probing the electronic structures of coordination compounds and revealing the nature of their chemical bonding. This is particularly relevant for f-elements, where bonding interactions play crucial role, particularly in radiopharmaceutical developments. We present advanced spectroscopic analysis, including core-to-core resonant inelastic X-ray scattering (CC-RIXS) and high-energy resolution X-ray absorption near-edge structure (HR-XANES), to investigate metal-ligand interactions using lanthanum (La) as a non-radioactive homologue of actinium (Ac) applied in emerging and highly potent therapeutic radiopharmaceuticals. By analyzing the interplay between La 4f and 5d orbitals in various environments, we extract key information about ligand-field effects and bond covalency. Our findings demonstrate that spectroscopic features of the La L2-edge CC-RIXS map reflect the nephelauxetic effect, which arises from central-field 4f orbital-specific bond covalency. The energy separation between the pre-edge and main absorption edge of the La L2-edge HR-XANES spectra also serves as direct probe of electron density for both 4f and 5d orbitals. Quantum chemical modeling, including ligand-field density-functional theory (LFDFT) and ab initio bond analysis, complements our experiments. This allows us to establish a direct correlation between spectroscopic observables and theoretical metrics for bonding properties, offering a framework to understand the coordination chemistry of f-elements. Beyond advancing fundamental chemistry, our findings will also inform future studies on Ac3+-radiopharmaceutical agents, where precise knowledge of bonding interactions is essential for their development.

The role of the equatorial ligands and their influence on the electronic structures and bonding properties of uranyl and other actinyls are not well understood and are thus at the forefront of actinide research. In the study presented here, we found that the good energy match of uranyl(VI) with F- valence orbitals leads to substantial changes in the uranyl electronic structure, compared to uranyl-Cl- and uranyl-Br-. The good energy match between uranyl(VI) and F- likely enhances the stability of the uranyl-F- bond, contributing to the higher U-F- affinity in aqueous solution compared to uranyl-Cl-/Br-, which is also demonstrated for plutonyl(VI). These findings are based on studies of equatorial and axial ligand covalency in three uranyl halides: NaRb8(UO2)5F19·2H2O, Rb2UO2Cl4·2H2O, and Rb2UO2Br4·2H2O. We describe covalent uranium-halide interactions, following the trend Br- ≈ Cl- > F-. Ligand K-edge XANES and DFT (including TDDFT and LFDFT) reveal significant electronic structure differences, with the F-based compound having a uranyl-based HOMO, while Cl- and Br-based compounds show predominant ligand p character in the HOMO. A newly introduced theoretical index evaluates bond covalency. U M4 edge HR-XANES and RIXS exhibit unexpected σ* peak trends not directly correlated with U═O bond lengths but well explained by LFDFT RIXS calculations.

A detailed characterization of the impact of a RbF post-deposition treatment (RbF-PDT) on the chemical structure of a wide-gap Cu(In, Ga)Se2 thin-film solar cell absorber surface with a high Ga/(Ga + In) (GGI) ratio of 0.9 is presented. Using synchrotron- and lab-based x-ray photoelectron spectroscopy, as well as x-ray-excited Auger electron spectroscopy, we observe distinct differences to RbF-PDT on absorber surfaces with the common GGI of ∼0.3. In particular, RbF-PDT reduces sodium and oxide content at the surface, while the copper concentration at the surface is not affected. We find no spectral evidence for the formation of a distinct Rb–In–Se surface layer. In addition, we observe that the GGI ratio at the surface is slightly decreased due to a reduction of the Ga and an increase in the In concentration, which may explain the observed improvement in the power conversion efficiency after the PDT (from 6.8% to 7.3%).

Long-term transformations of sulfur from atmospheric deposition in ombrotrophic peatlands have rarely been studied, although the potential impact on carbon mineralization and particularly methane formation is acknowledged. To elucidate the long-term fate of sulfur in peat, we therefore applied sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy to investigate peatlands with either natural or anthropogenic atmospheric sulfur deposition. A peatland in central Europe (Germany, BBM) experienced high sulfur deposition during the Industrial Revolution, and an oceanic peatland (Chilean Patagonia, PBr) continuously exposed to aerosols from sea spray, were investigated. During early phases of site BBM, when sulfur deposition was constantly low, wet-chemical extractions indicated that 98% +/- 0.7% of sulfur was present as organic sulfur. The S K-edge XANES fitting suggested that sulfur redox transformations mainly occurred near the water table, at which reduced sulfur forms (primarily organic sulfides, and thiols) increased from similar to 40% to and stabilized at 65% +/- 4% in anoxic peat. An increased contribution of reduced sulfur forms was observed in the polluted section of BBM and entire peat profile of PBr. While increases in reduced inorganic sulfur (TRIS) likely depended on available Fe, rises in the ratio of reduced organic sulfur to total organic sulfur from both sites were pronounced. This increase in reduced organic sulfur forms likely resulted from abiotic sulphurization of organic carbon after sulfate reduction. Our study highlights the long-term fate of elevated sulfur in ombrotrophic peatlands, being mainly transformed into reduced organic sulfur.

The chemical and electronic structure of the CdS/(Ag,Cu)(In,Ga)Se 2 (CdS/ACIGSe) interface for thin‐film solar cells, involving an absorber with a bulk [Ag]/([Ag]+[Cu]) (AAC) ratio of 0.06, a state‐of‐the‐art RbF post‐deposition treatment (PDT), and a chemical‐bath deposited CdS buffer layer, is studied. To gain a detailed and depth‐resolved picture of the CdS/ACIGSe interface, synchrotron‐ and laboratory‐based hard X‐ray, soft X‐ray, and UV photoelectron spectroscopy, inverse photoemission spectroscopy, and X‐ray emission spectroscopy are combined. Compared to the bulk of the absorber, a Cu‐ and Ga‐poor ACIGSe surface is found, with a slightly increased AAC ratio. Strong evidence of a Rb–In–Se species (possibly with some Ag) at the absorber surface is compiled, with a corresponding band gap of 2.79 ± 0.12 eV. This finding is in clear contrast to comparable Ag‐free Cu(In,Ga)Se 2 absorbers with RbF‐PDT. The Rb–In–Se surface species is not removed by the (wet‐chemical) CdS deposition process, while some Se diffuses into the CdS layer and segregates at its surface. The CdS buffer layer shows a band gap of 2.48 ± 0.12 eV, and a cliff (≈ −0.4 eV) is determined in the conduction band alignment at the interface between the Rb–In–Se species and the CdS buffer.

Dimethyl sulfoxide (DMSO) is an important polar solvent that derives its unique properties from the lone pair and the strong polar bond at the sulfinyl functional group. To derive the local and symmetry-resolved electronic structure of liquid DMSO, we have used resonant inelastic soft X-ray scattering (RIXS) maps at the S L2,3, C K, and O K edges. The experimental data are compared to calculations of spectra based on density functional theory, which allows a detailed analysis of the molecular orbitals throughout the molecule. In the RIXS maps, we find the signature of molecular-field splitting of the S 2p core levels, vibronic coupling, and ultrafast nuclear dynamics on the time scale of the RIXS process.

Lanthanides are widely assumed not to form covalent bonds due to the localized nature of their 4f valence electrons. This work demonstrates that the ionic bond of Sm(II) with cyclononatetraenyl (eta(9)-C9H9-) in [Sm(eta(9)-C9H9)(2)] can be modulated and becomes more covalent by photon-induced transfer of Sm 4f electrons to Sm 5d orbitals. This photon-induced change in bonding properties facilitates a subsequent reconfiguration of [Sm(eta(9)-C9H9)(2)]. As a result, Sm-C bond length contraction is detected and the local Sm coordination environment exhibits more extensive disorder. Both Sm 4f and 5d electrons have increased participation in covalent Sm-ligand interactions. The Sm L-3-edge valence band resonant inelastic X-ray scattering (VB-RIXS), high-resolution X-ray absorption near-edge structure (HR-XANES), and quantum chemical computations showcase a spectroscopic methodology for in-depth studies of bond covalency of lanthanide atoms.

The design and first results of a high-transmission soft X-ray spectrometer operated at the X-SPEC double-undulator beamline of the KIT Light Source are presented. As a unique feature, particular emphasis was placed on optimizing the spectrometer transmission by maximizing the solid angle and the efficiencies of spectrometer gratings and detector. A CMOS detector, optimized for soft X-rays, allows for quantum efficiencies of 90% or above over the full energy range of the spectrometer, while simultaneously offering short readout times. Combining an optimized control system at the X-SPEC beamline with continuous energy scans (as opposed to step scans), the high transmission of the spectrometer, and the fast readout of the CMOS camera, enable the collection of entire rapid resonant inelastic soft X-ray scattering maps in less than 1 min. Series of spectra at a fixed energy can be taken with a frequency of up to 5 Hz. Furthermore, the use of higher-order reflections allows a very wide energy range (45 to 2000 eV) to be covered with only two blazed gratings, while keeping the efficiency high and the resolving power E/ΔE above 1500 and 3000 with low- and high-energy gratings, respectively.

The hybridization state in solids often defines the critical chemical and physical properties of a compound. However, it is difficult to spectroscopically detect and evaluate hybridization beyond just general fingerprint signatures. Here, the valence-band hybridization of metal d-derived bands (short: "metal d bands") in selected metal sulphides is studied with a combined spectroscopic and theoretical approach to derive deeper insights into the fundamental nature of such compounds. The valence bands of the studied sulphides are comprised of hybrid bands derived from the metal d, S 3s, and S 3p states. Employing S K and L2,3 X-ray emission spectroscopy and spectra calculations based on density functional theory, the degree of hybridization (i.e., the covalency) of these bands can be directly probed as a function of their relative energies. We find that the relative intensity of the "metal d band" features in the spectra scales with the inverse square of the energy separation to the respective sulfur-derived bands, which can be analytically derived from a simple two-orbital model. This study demonstrates that soft X-ray emission spectroscopy is a powerful tool to study valence state hybridization, in particular in combination with hard X-ray emission spectroscopy, promising a broad impact in many research fields. Valence-band hybridization in sulphides is studied with X-ray spectroscopy in experiment and theory. The admixture of the "atomic" states to the hybrid bands scales with their inverse energy separation, which we describe by a simple two-state model.

Advances on understanding the nature of the chemical bonding and electron correlation effects during the X-ray absorption process in ionic-covalent metal complexes has been achieved for most of the transition elements, except for scandium, due to the lack of a systematic series of spectroscopic reference spectra and the shortage of standard crystallographic data on scandium compounds. To close the gap, the chemical bonding effects in eight Sc compounds are studied using X-ray absorption spectroscopy (XAS) at Sc K and L2,3 absorption edges and X-ray photoelectron spectroscopy (XPS). Indeed, the fine structure of the XAS Sc K edge reflects the chemical sp3-like bond formed between scandium and the ligand while the L2,3 edge and the pre-edge features of the K-edge provide a direct insight into the crystal field parameters at the Sc site in the coordination compound. The XPS data provide the information on binding energies of the core electrons involved in the electron transitions caused by the absorption of high energy X-rays. XAS and XPS complement each other by accessing the information on Sc structure on bulk and the surface. Herein, comprehensive information on the electronic structure of well-known crystalline materials based on Sc is given with spectroscopic fingerprints X-ray data. This will help to predict the formation of chemical bonds in the unknown components via the systematic evaluation of the available spectroscopic fingerprints. To understand the nature of the chemical bonding and electron correlation effects eight Sc compounds are systematically studied using the X-ray absorption spectroscopy at K and L2,3 absorption edges and X-ray photoelectron spectroscopy.

This work is an investigation of the assemblages of supergene minerals occurring in hydrothermal REE-U-Au quartz-vein mineralisation at the Prakovce-Zimna Voda site, Slovakia. Heterogeneous uranyl arsenates and minor phosphates of the autunite group (nova & ccaron;ekite, kahlerite, threadgoldite, autunite, arsenuranospathite and chistyakovaite) together with scorodite and Sb-Bi-rich philipsbornite-segnitite-series minerals formed by oxidising fluids during decomposition and leaching of primary hypogene uraninite, brannerite and base-metal sulfides and sulfosalts. A progressive change of pH from acidic to near-neutral due to the gradual consumption of sulfides resulted in the formation of late phosphuranylite, pharmacosiderite and arseniosiderite. Goethite and other Fe oxides represent the latest hydrous ferric mineral phases and were formed after most of the As was already fixed in Fe arsenates. Antimony and Bi were taken up only into philipsbornite-segnitite and suggest unusual conditions during this process. X-ray absorption spectroscopy indicates that Sb in the philipsbornite-segnitite is fully oxidised (0.1-0.4 apfu Sb5+, octahedral coordination on the G site). Pentavalent Sb together with the presence of ferric oxides and arsenates and uranyl minerals suggest oxidative conditions during weathering. This study also indicates that hydrous ferric arsenates are dominant and stable secondary minerals in a supergene environment in a quartz vein rich in Fe and As accompanied by elevated concentrations of U, Pb, Sb, Bi, S, P, Ca and Ba under oxidising conditions.

The sulfur L2,3 X-ray emission spectra of the alkaline earth metal sulfides BeS, MgS, CaS, SrS, and BaS are investigated and compared with spectra calculations based on density functional theory. Very distinct spectral shapes are found for the different compounds. With decreasing electronegativity of the cation, that is, increasing ionic bonding character, the upper valence band width and its relative spectral intensity decrease. These general trends are qualitatively reproduced by the spectra calculations, which give quite an accurate description of the spectral shapes in the upper valence band region. On the low energy side of the sulfur 3s → 2p transition dominating the spectra, we find strong satellites caused by “semi-Auger” decays involving configuration interaction. These satellites, previously believed to be energetically forbidden for sulfur L2,3 emission and only observed for the L2,3 emission of Cl to Cr, increase in intensity as the bonding character becomes more ionic and dominate the spectra for SrS and BaS. The intensities, energies, and widths of the satellites vary strongly between the investigated compounds, giving a very specific spectral fingerprint that can be used for speciation analysis.