Search Results (79)

X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) are analytical techniques enabling precise analysis of the electronic structure and local atomic environment in chemical compounds and materials. Their application spans materials science, chemistry, biology, and environmental sciences, supporting studies on catalytic mechanisms, redox processes, and metal speciation. A key advantage of both techniques is element selectivity, allowing the analysis of specific elements without matrix interference. Their high sensitivity to chemical state and coordination enables determination of oxidation states, electronic configuration, and local geometry. These methods are applicable to solids, liquids, and gases without special sample preparation. Modern XAS and XES studies are typically performed using synchrotron radiation, which provides an intense, monochromatic X-ray source and allows advanced in situ and operando experiments. Sub-techniques such as XANES (X-ray absorption near-edge structure), EXAFS (Extended X-ray Absorption Fine Structure), and RIXS (resonant inelastic X-ray scattering) offer enhanced insights into oxidation states, local structure, and electronic excitations. Despite their broad scientific use, applications in pharmaceutical research remain limited. Nevertheless, recent studies highlight their potential in analyzing crystalline active pharmaceutical ingredients (APIs), drug–biomolecule interactions, and differences in drug activity. This review introduces the fundamental aspects of XAS and XES, with an emphasis on practical considerations for pharmaceutical applications, including experimental design and basic spectral interpretation. Full article

Carbon nanotubes (CNTs) have remarkable mechanical, electrical, and thermal properties, making them highly attractive as foundational elements for advanced materials. However, translating their nanoscale potential into macroscale reliability and longevity requires a holistic design approach that integrates precise architectural control with robust damage mitigation strategies. This review presents a synergistic perspective on enhancing the durability of CNT-based systems by critically examining the interplay between molecular assembly, self-repair mechanisms, and the advanced characterization techniques required for their validation. We first establish how foundational architectural control—achieved through strategies like chemical functionalization, field-directed alignment, and dispersion—governs the ultimate performance of CNT materials. A significant focus is placed on advanced functionalization, such as fluorination, and its verification using high-powered spectroscopic tools, including X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Subsequently, this manuscript delves into the mechanisms of self-repair, systematically analyzing both the intrinsic capacity of the carbon lattice to heal atomic-level defects and the extrinsic strategies that incorporate engineered healing agents into composites. This discussion is uniquely supplemented by an exploration of the experimental techniques, such as electron energy loss spectroscopy (EELS) and Auger electron spectroscopy (AES), that provide crucial evidence for irradiation-induced healing dynamics. Finally, we argue that a “characterization gap” has limited the field’s progress and highlight the critical role of techniques like in situ Raman spectroscopy for quantitatively monitoring healing efficiency at the molecular level. By identifying current challenges and future research frontiers, this review underscores that the creation of truly durable materials depends on an integrated understanding of how to build, repair, and precisely measure CNT-based systems. Full article

Ce₂Pt₆Ga₁₅ is a heavy fermion compound near the quantum critical point (QCP). Its crystal structure may exhibit magnetic frustration due to a honeycomb arrangement; however, stacking faults in the crystal hinder structural analysis. As a local structure probe, extended X-ray absorption fine structure (EXAFS) is less sensitive to stacking faults and is a powerful tool for crystal structure determination. We synthesized single-crystal Ce₂Pt₆Ga₁₅, performed single-crystal and powder X-ray diffraction experiments, and conducted X-ray absorption spectroscopy (XAS) measurements. The composition of Ce₂Pt₆Ga₁₅ deviates from stoichiometry, suggesting Ce and Ga enrichment or Pt site deficiencies. A comparison of X-ray absorption near-edge structure (XANES) at the Ce L₃-edge with reference materials suggests that Ce valence is likely trivalent. To determine the exact structure, we simultaneously analyzed EXAFS spectra at the Ce L₃-, Pt L₃-, and Ga K-edges. The EXAFS spectra of Ce₂Pt₆Ga₁₅ are inconsistent with the hexagonal Sc_0.6Fe₂Si_4.9-type structure but are better explained by an orthorhombic structure with a honeycomb arrangement. Full article

This study explores the phase composition, local atomic structure, and magnetic properties of biogenic nanomaterials synthesized through microbially mediated biomineralization by the sulfate-reducing bacterium Desulfovibrio species strain A2 (Cupidesulfovibrio). Using X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray absorption near-edge structure (XANES) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and magnetic measurements, we identified a mixture of vivianite (Fe₃(PO₄)₂·8H₂O) and sulfur-containing crystalline phases (α-sulfur). XRD analysis confirmed that the vivianite phase, with a monoclinic I2/m structure, constitutes 44% of the sample, while sulfur-containing phases (α-sulfur, Fddd) account for 56%, likely as a result of bacterial sulfate-reducing activity. X-ray absorption spectroscopy (XAS) and EXAFS revealed the presence of multiple sulfur oxidation states, including elemental sulfur and sulfate (S⁶⁺), underscoring the role of sulfur in the sample’s structure. Mössbauer spectroscopy identified the presence of ferrihydrite nanoparticles with a blocking temperature of approximately 45 K. Magnetic measurements revealed significant coercivity (~2 kOe) at 4.2 K, attributed to the blocked ferrihydrite nanoparticles. The results provide new insights into the structural and magnetic properties of these microbially mediated biogenic nanomaterials, highlighting their potential applications in magnetic-based technologies. Full article

MgZnO possesses a tunable bandgap and can be prepared at relatively low temperatures, making it suitable for developing optoelectronic devices. Mg_xZn_1−xO (x~0.1) films were grown on sapphire by metal–organic vapor phase epitaxy under different substrate-growth temperatures T_s of 350–650 °C and studied by multiple characterization technologies like X-ray diffraction (XRD), spectroscopic ellipsometry (SE), Raman scattering, extended X-ray absorption fine structure (EXAFS), and first-principle calculations. The effects of T_s on the optical, structural, and surface properties of the Mg_0.1Zn_0.9O films were studied penetratively. An XRD peak of nearly 35° was produced from Mg_0.1Zn_0.9O (0002) diffraction, while a weak peak of ~36.5° indicated MgO phase separation. SE measurements and analysis determined the energy bandgaps in the 3.29–3.91 eV range, obeying a monotonically decreasing law with increasing T_s. The theoretical bandgap of 3.347 eV, consistent with the SE-reported value, demonstrated the reliability of the SE measurement. Temperature-dependent UV-excitation Raman scattering revealed 1LO phonon splitting and temperature dependency. Zn-O and Zn-Zn atomic bonding lengths were deduced from EXAFS. It was revealed that the surface Mg amount increased with the increase in T_s. These comprehensive studies provide valuable references for Mg_0.1Zn_0.9O and other advanced materials. Full article

Two new Ag(I) complexes with coumaric carboxylic acid derivatives have been synthesized. Structural studies of these noncrystalline complexes have been performed using a methodology that combines laboratory and synchrotron techniques, supported by density functional theory calculations. The arrangement of ligands around the Ag(I) cation has been refined using infrared, extended X-ray absorption fine structure, and X-ray absorption near edge structure spectroscopies. Different coordination modes of carboxylate ligands are observed for the studied compounds. Carboxylate bridges are characteristic for the Ag(I) complex with 4-oxo-4H-1-benzopyran-2-carboxylic acid (1), while a bidentate chelating motif was found for the complex with 2-oxo-2H-1-benzopyran-3-carboxylic acid (2). Additionally, the carbonyl oxygen atom of the coumarin ring coordinates to the silver cation in complex 2, while it is inactive in complex 1. Antimicrobial evaluation has been performed for both compounds. The complexes show activity against selected bacteria as well as Candida yeast. This activity is slightly lower for bacteria and the same or higher for Candida in relation to the reference substances: ciprofloxacin or fluconazole. Full article

GaN on Si plays an important role in the integration and promotion of GaN-based wide-gap materials with Si-based integrated circuits (IC) technology. A series of GaN film materials were grown on Si (111) substrate using a unique plasma assistant molecular beam epitaxy (PA-MBE) technology and investigated using multiple characterization techniques of Nomarski microscopy (NM), high-resolution X-ray diffraction (HR-XRD), variable angular spectroscopic ellipsometry (VASE), Raman scattering, photoluminescence (PL), and synchrotron radiation (SR) near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NM confirmed crack-free wurtzite (w-) GaN thin films in a large range of 180–1500 nm. XRD identified the w- single crystalline structure for these GaN films with the orientation along the c-axis in the normal growth direction. An optimized 700 °C growth temperature, plus other corresponding parameters, was obtained for the PA-MBE growth of GaN on Si, exhibiting strong PL emission, narrow/strong Raman phonon modes, XRD w-GaN peaks, and high crystalline perfection. VASE studies identified this set of MBE-grown GaN/Si as having very low Urbach energy of about 18 meV. UV (325 nm)-excited Raman spectra of GaN/Si samples exhibited the GaN E₂(low) and E₂(high) phonon modes clearly without Raman features from the Si substrate, overcoming the difficulties from visible (532 nm) Raman measurements with strong Si Raman features overwhelming the GaN signals. The combined UV excitation Raman–PL spectra revealed multiple LO phonons spread over the GaN fundamental band edge emission PL band due to the outgoing resonance effect. Calculation of the UV Raman spectra determined the carrier concentrations with excellent values. Angular-dependent NEXAFS on Ga K-edge revealed the significant anisotropy of the conduction band of w-GaN and identified the NEXAFS resonances corresponding to different final states in the hexagonal GaN films on Si. Comparative GaN material properties are investigated in depth. Full article

We have investigated the effect of the Ni substitution on the local structure and the valence electronic states of the ${\mathrm{SrFe}}_{2-x}$${\mathrm{Ni}}_x$${\mathrm{As}}_2$ (x = 0.00, 0.16, and 0.23) superconductor with a multi-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. The As K-edge and Fe K-edge EXAFS measurements in the two polarizations (E‖ab and E‖c) show a clear change in the local structure with Ni concentration. The near-neighbor bondlengths and the related mean-square relative displacements (MSRDs) decrease as the Ni content increases. The polarized XANES spectra at the As, Fe and Ni K edges reveal a systematic change in the anisotropy of the valence electronic structure. The results suggest that the quasi 2D electronic structure of this system tends to become more isotropic as the Ni content increases. The local structure and the valence electronic states are discussed in the frame of the evolving electronic transport of the ${\mathrm{SrFe}}_{2-x}$${\mathrm{Ni}}_x$${\mathrm{As}}_2$ system. Full article

Silica-supported chromium oxide catalysts, also named Phillips chromium catalysts (PCCs), provide more than half of the world’s production of high- and medium-density polyethylenes. PCCs are usually prepared in the Cr(VI)/SiO₂ form, which is subjected to reductive activation. It has been explicitly proven that CO reduces Cr(VI) to Cr(II) species that initiate ethylene polymerization; ethylene activates Cr(VI) sites as well, but the nature of the catalytic species is complicated by the presence of the ethylene oxidation products. It is widely accepted that the catalytic species are of a Cr(III)–alkyl nature, but this common assumption faces the challenge of “extra” hydrogen: the formation of similar species under the action of even-electron reducing agents requires an additional H atom. Relatively recently, it was found that saturated hydrocarbons can also activate CrO_x/SiO₂, and alkyl fragments turn out to be bonded with a polyethylene chain. In recent years, there have been numerous experimental and theoretical studies of the structure and chemistry of PCCs at the different stages of preparation and activation. The use of modern spectral methods (such as extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and others); operando IR, UV–vis, EPR, and XAS spectroscopies; and theoretical approaches (DFT modeling, machine learning) clarified many essential aspects of the mechanisms of CrO_x/SiO₂ activation and catalytic behavior. Overall, the Cosse–Arlman mechanism of polymerization on Cr(III)–alkyl centers is confirmed in many works, but its theoretical support required the development of nontrivial and contentious mechanistic concepts of Cr(VI)/SiO₂ or Cr(II)/SiO₂ activation. On the other hand, conflicting experimental data continue to be obtained, and certain mechanistic concepts are being developed with the use of outdated models. Strictly speaking, the main question of what type of catalytic species, Cr(II), Cr(III), or Cr(IV), comes into polymerization still has not received an unambiguous answer. The role of the chemical nature of the support—through the prism of the nature, geometry, and distribution of the active sites—is also not clear in depth. In the present review, we endeavored to summarize and discuss the recent studies in the field of the preparation, activation, and action of PCCs, with a focus on existing contradictions in the interpretation of the experimental and theoretical results. Full article

During the methanol-to-aromatics (MTA) process, a large amount of water is generated, while the influence and mechanism of water on the activity and selectivity of the light olefin aromatization reaction are still unclear. Therefore, a study was conducted to systematically investigate the effects of water on the reactivity and the product distribution in ethylene aromatization using infrared spectroscopy (IR), intelligent gravitation analyzer (IGA), and X-ray absorption fine structure (XAFS) characterizations. The results demonstrated that the presence of water reduced ethylene conversion and aromatic selectivity while increasing hydrogen selectivity at the same contact time. This indicated that water had an effect on the reaction pathway by promoting the dehydrogenation reaction and suppressing the hydrogen transfer reaction. A detailed analysis using linear combination fitting (LCF) of Zn K-edge X-ray absorption near-edge spectroscopy (XANES) on Zn/HZSM-5 catalysts showed significant variations in the state of existence and the distribution of Zn species on the deactivated catalysts, depending on different reaction atmospheres and water contents. The presence of water strongly hindered the conversion of ZnOH⁺ species, which served as the active centers for the dehydrogenation reaction, to ZnO on the catalyst. As a result, the dehydrogenation activity remained high in the presence of water. This study using IR and IGA techniques revealed that water on the Zn/HZSM-5 catalyst inhibited the adsorption of ethylene on the zeolite, resulting in a noticeable decrease in ethylene conversion and a decrease in aromatic selectivity. These findings contribute to a deeper understanding of the aromatization reaction process and provide data support for the design of efficient aromatization catalysts. Full article

Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)O₄⁻) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReO₄ with magnetite (Fe₃O₄), siderite (FeCO₃), vivianite (Fe₃(PO₄)₂•8H₂O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was <10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)O₆ octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReO₄⁻ in sedimentary environments requires further investigation. Full article

Currently, electrically conductive polymers based on transition metal complexes [M(Salen)], as well as their composites, are among the systems showing promise as catalysts, electrochromic and electroluminescent materials, and electrodes for energy storage (for batteries and supercapacitors). The current review focuses on elucidating the atomic and electronic structure of metal–salen complexes, their polymers, and composites with nanostructured carbon (carbon nanotubes and graphene) using modern X-ray spectroscopy methods (X-ray photoelectron (XPS) and valence-band photoemission (VB PES) spectroscopy, as well as near-edge (NEXAFS) and extended (EXAFS) X-ray absorption fine structure spectroscopy). We trust that this review will be of valuable assistance to researchers working in the field of synthesizing and characterizing metal–salen complexes and composites based on them. Full article

The interaction of fullerenes and their derivatives with environmental molecules such as oxygen or water was crucial for the rational design of low-dimensional materials and devices. In this paper, the near-edge X-ray absorption fine structure (NEXAFS), X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy (XPS) shake-up satellites were employed to distinguish the oxides and hydrates of the fullerene C₆₀ and azafullerene C₅₉N families. The study includes various isomers, such as the open [5,6] and closed [6,6] isomers of C₆₀O, C₆₀H(OH), C₆₀-O-C₆₀, C₆₀H-O-C₆₀H, C₅₉N(OH) and C₅₉N-O-C₅₉N, based on density functional theory. These soft X-ray spectra offered comprehensive insights into the molecular orbitals of these azafullerene molecular groups. The oxygen K-edge NEXAFS, carbon and oxygen K-edge XPS shake-up satellite spectra provided valuable tools for distinguishing oxides or hydrates of fullerene C₆₀ and azafullerene C₅₉N. Our findings could significantly benefit the development of fullerene functional molecular materials and expand the application scope of soft X-ray spectroscopy as a molecular fingerprinting tool for the fullerene family. Full article

Future space missions to Mars will depend on the development of bioregenerative life support systems. Mars regolith contains most of the nutrients needed for plant growth, but not organic matter (OM). Although Mars simulants have been deeply characterized and tested as growing media, no data are available about their possible modification occurring during terraforming, including the interaction of exogeneous OM with iron (Fe) oxides, particularly abundant in Mars regolith. The aim of this study was to investigate the mineral transformation and the OM evolution occurring in the early stages of the terraforming process. Potato was grown for 99 days on Mojave Mars Simulant MMS-1, alone (R100) and mixed with a compost 70:30 v:v (R70C30), and on a fluvial sand, alone (S100) and mixed with compost (S70C30), for comparison. Bulk (BK) and potato tubero/rhizo-sphere (RH) soils were fractionated to obtain particulate OM (POM) and mineral-associated OM (MAOM). Bulk samples and corresponding fractions were characterized for total nitrogen and organic carbon (C) and analyzed by Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. Organic C increased by 10 and 25 times in S70C30 and R70C30, respectively, compared to S100 and R100. Most of the organic C accumulated in the POM fraction of both growing substrates, while its content in the MAOM was 3 times higher in R70C30 than in S70C30. No significant differences between BK and RH were found. Finally, ferrihydrite mediated exogenous OM stabilization in regolith-based substrates, while Fe(III)-OM complexes were detected exclusively in sand-based growing media. Understanding mechanisms and testing potential sustainable practices for creating Mars regolith similar to terrestrial soil will be fundamental to sustain food crop production on Mars. Full article

The flux growth of InVO₄ bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V₂O₅:InVO₄ = 1:1 could not be used as a self-flux since no sign of melting was observed up to 1100 °C. Crystals of InVO₄ of typical size 0.5 × 1 × 7 mm³ were obtained using copper pyrovanadate (Cu₂V₂O₇) as a flux, using Pt crucibles. X-ray powder diffraction confirmed the orthorhombic Cmcm structure. Rests of the flux material were observed on the sample surface, with occasional traces of Pt indicating some level of reaction with the crucible. X-ray absorption spectroscopy showed that oxidation states of indium and vanadium ions are +3 and +5, respectively. The size and high quality of the obtained InVO₄ crystals makes them excellent candidates for further study of their physical properties. Full article