24378 research outputs found
Sort by
Femtosecond charge and spin dynamics in a Co50Pt50 alloy
Full text linkThe use of advanced x ray sources plays a key role in the study of dynamic processes in magnetically ordered materials. The progress in x ray free electron lasers enables the direct and simultaneous observation of the femtosecond evolution of electron and spin systems through transient x ray absorption spectroscopy and x ray magnetic circular dichroism, respectively. Such experiments allow us to resolve the response seen in the population of the spin split valence states upon optical excitation. Here, we utilize circularly polarized ultrashort soft x ray pulses from the new helical afterburner undulator at the free electron laser FLASH in Hamburg to study the femtosecond dynamics of a laser excited CoPt alloy at the Co L3 edge absorption. Despite employing a weaker electronic excitation level, we find a comparable demagnetization for the Co 3d states in CoPt compared to previous measurements on CoPd. This is attributed to the distinctly different spin orbit coupling between 3d and 4d vs 3d and 5d elements in the corresponding alloys and multilayer
Impact of nitrogen functionalization and porosity on the electrosorption of ionic liquids on templated porous carbons
Full text linkThis study systematically investigates the influence of nitrogen functionalities and their content in nitrogen rich carbon materials, specifically carbon carbon nitride nanohybrids, on their performance as electrode materials in electric double layer capacitors EDLCs operated with ionic liquid electrolyte 1 Ethyl 3 methylimidazolium bis trifluoromethylsulfonyl imide . The loading amounts of cyanamide as carbon nitride precursor as well as the condensation temperature are varied over a wide range to obtain materials with significantly different porosity, nitrogen contents, and chemical properties of the nitrogen species. Thermogravimetric analysis, combustion elemental analysis, gas physisorption, and X ray photoelectron spectroscopy measurements show that the nitrogen loss from carbon nitride starts to become significant between 500 and 600 degrees C and that different nitrogen species are created shifting from more pyridinic forms to graphitic and oxidized nitrogen. For the EDLC application, it is found that the mass specific capacitance is dictated by the specific surface area whereas the capacitance normalized to the specific surface area determined by gas physisorption can be slightly enhanced by the presence of pyridinic nitrogen species. In addition, lowering of the total pore volume leads to higher areal active material loadings and lower dead volume which needs to be filled with electrolyt
Towards tender X rays by means of multi layer coated gratings as monochromator optics
Full text linkModern soft X ray beamlines use collimated plane grating monochromators cPGM [1] as monochromatization devices. Multilayer ML coated plane gratings and mirrors allow to extend the available photon energy range of cPGMs towards the so called tender X ray photon energy range up to 5keV , thereby achieving a significantly higher photon flux [2]. This X ray energy range covers the L and M absorption edges of most transition and rare earth metals as well as the K edges of lighter elements such as silicon, sulfur and phosphorus. Recently, such an ML based monochromator setup was put into operation at the beamline U41 PGM1 XM at the storage ring BESSY II in Berlin [3]. This beamline upgrade enables high resolution spectromicroscopic applications with photon energies of up to 3keV and it is expanding its capabilities to support research in areas such as life sciences, semiconductor development and battery research. We report on the construction, commissioning and performance of this beamline and discuss possible options for new developments in the area of beamlines and end stations in the tender X ray energy range up to 5keV at existing and future new accelerator based photon source
Elemental mapping of cocoa beans with laser induced breakdown spectroscopy
No full textCocoa and chocolate are important trading goods and serve as a source of minerals and essential trace elements, important in the human diet. The standard industry practice for quantifying elements in cocoa samples involves the use of inductively coupled plasma mass spectrometry and atomic absorption spectrometry. Within an experimental lab environment, X ray fluorescence with micrometer resolution XRF can reveal the spatial distribution of elements across cocoa beans. Over the past years, laser induced breakdown spectroscopy LIBS has become an emerging analytical technique for a wide range of applications. Imaging cocoa beans with LIBS is challenging because it exhibits areas with low and high density shell vs inner structure and the inner structure has a very low melting point. To minimize melting and ensure an optimal lateral resolution for LIBS imaging, a thorough assessment of the experimental parameters and data preprocessing is necessary. This study reveals the capabilities and limitations of LIBS for mapping mineral and trace element distribution in cocoa beans within only 90 amp; 8239;min. A carbon based normalization method was adopted to rectify the experimental variations resulting from sample ablation initiated by the laser beam, thus allowing for reliable sample comparisons. A side by side comparison of XRF and LIBS data from the same cocoa beans shows that both techniques yield similar elemental images, although LIBS displays somewhat lower resolution. Furthermore, detailed images of five individual cocoa beans are examined to illustrate how LIBS effectively detects variations in elemental distributions. The advantages of multi element analysis, fast response, little to no sample preparation and ease of use position LIBS alongside XRF as a promising technique for the cocoa secto
Influence of Cu purity and low temperature annealing on Cu Zn disorder and efficiency of CZTSSe monograins
No full textThin film solar cell technologies are mainly based on polycrystalline absorber layers, which is also the case for kesterite based photovoltaic devices. An alternative technology, which is promising and low cost, is based on kesterite type Cu2ZnSn S, Se 4 CZTSSe monograins as absorbers, which are fixed in a polymer matrix to form a flexible solar cell. The large band tailing observed in Cu based kesterite type semiconductors is believed to cause voltage losses, limiting the efficiency of kesterite based devices. Cu Zn disorder, which is always present in these compounds, is discussed in literature as a possible reason for band tailing. The experimental determination and quantification of Cu Zn disorder is possible by in depth analysis of neutron diffraction data. This work reveals that the purity of copper used in the synthesis of CZTSSe monograins has an influence on the degree of Cu Zn disorder in the semiconductor and thus on optical and PV parameters. Comparing CZTSSe monograins, less Cu Zn disorder was observed for the monograins synthesized using copper with higher purity; the respective monograin based solar cell shows a higher power conversion efficiency. On the other hand, the band gap energy as well as the photoluminescence maximum PLmax of both monograins are the same. Applying a low temperature annealing procedure allowed us to increase the quality of monograins synthesized using 5N copper, very close to the one grown using 6N copper. The PLmax slightly shifts into higher energy, which is most likely an indication of the decreased Cu Zn disorder, either moving the defect states toward the valence band or that it reduces the formation of the tail states near the conduction band minimu
Exploring Anionic Redox Chemistry of Battery Cathodes with Resonant Inelastic X Ray Scattering
No full textHigh capacity and reversible cathodes are important for sustainable energy development. Layered oxides present promising options, achieving a high capacity while maintaining manageable production costs. Despite the redox activity of transition metal primarily contributes to the capacity, anionic redox o amp; 64256;ers additional potential, as evidenced by the subtle voltage plateau at high voltage. However, challenges remain, particularly concerning the reversibility of anionic redox, resulting in voltage fade, hysteresis, and the formation of undesired oxygen species. Resonant inelastic X ray scattering RIXS captures not only the charge transfer processes between oxygen ligands and transition metals but also the formation of molecular oxygen, elucidating the chemical transformations of oxygen during electrochemical cycles. Mapping capability allows for the generation of spectral patterns with quantitative measures that surpass those achievable by other characterization techniques. Though early reports on its advantages, a comprehensive discussion of RIXS and its perspectives on anionic redox processes in cathode materials remains absent but necessary. This perspective aims to provide a systematic overview of RIXS, emphasizing its unique contributions to cathode material research. It also serves as a valuable reference for energy researchers and RIXS practitioners, featuring the advancements and future possibilities of this powerful techniqu
The Haber Bosch Catalyst from Solid state Chemistry to Mesotechnology
No full textAmmonia is industrially synthesized over multi promoted Fe based catalysts for more than a century. Although ammonia synthesis reflects a prototypical catalytic reaction, rational catalyst design is still impossible as the full structural complexity of this catalyst system often referred to as ammonia iron and its structural entanglement is barely understood. Here, the mesoscopic structure of a technical, multi promoted ammonia synthesis catalyst is uncovered using a scale bridging electron microscopy approach complemented by X ray diffraction and spectroscopy to explore the structural integrity of ammonia iron. Amorphous contributions and structures of the melilite type and tricalcium aluminate as additional phases are identified. Furthermore, the understanding of the ammonia iron family by unveiling the role of the platelet Fe perimeter, framework Fe, thin film Fe, and refractory Fe is extended. Their interconnectedness is highlighted, suggesting that each component has to be present to fulfill a specific task. The study demonstrates that catalysis science can only proceed if it openly explores the full complexity of catalytic system
Offset Finding of Beamline Parameters on the METRIXS Beamline at BESSY II Using Machine Learning
Full text linkBeamline alignment is challenging as the beamline components must be set up ideally so that the rays follow the desired optical path. Automated methods using a digital twin allow for faster diagnostics and improved beam properties compared to manual tuning. We introduce an automated method of finding the offsets to improve this digital twin model. These offsets represent the unknown but constant differences between the beamline parameter positions as set up at the physical beamline and the corresponding parameter positions of its digital twin. Our method assumes the capability to execute precise relative movements with a known step size for these parameters, although the absolute position information is unknown. By combining the surrogate model with a global optimizer, we successfully determine offsets for 34 beamline parameters on a simulated METRIXS beamline at the BESSY II synchrotron radiation source in Berli
Beyond natural flavonoids exploring bioisosterism in design and synthesis of influenza endonuclease inhibitors
No full textInfluenza virus, an RNA virus of the Orthomyxoviridae family, is responsible for widespread seasonal epidemics that result in 3 to 5 million severe illnesses and more than half a million deaths annually. Given the persistent circulation of pandemic influenza variants and increasing resistance to available inhibitors, there is an urgent need for new antiviral drugs effective against various viral subtypes. Viral RNA dependent RNA polymerase, essential for viral replication, has emerged as a promising drug target. The PA subunit with endonuclease function is especially interesting, as development of the highly potent baloxavir marboxil Xofluza validated its importance as a novel drug target. Flavonoids have long been studied for their anti influenza activity but have only recently been recognized as endonuclease inhibitors. We previously identified luteolin and its glucoside derivate, orientin, as potent endonuclease inhibitors, with their binding illustrated by X ray crystallography structures. Building on this, we employed a scaffold hopping approach based on the luteolin structure to design structurally distinct compounds that resemble the flavonoid scaffold. Using an AlphaScreen binding assay, we identified 33 as a submicromolar PA inhibitor with low toxicity. We solved the crystal structure of the PA endonuclease binding pseudoflavonoid 36, which has similar structure and inhibitory potency to 33. Furthermore, we identified 24, 33, 34 and 36 as inhibitors of influenza polymerase in a minireplicon luciferase reporter assay as well as inhibitors of live H1N1 virus infection in A549 human lung cell
Synthesis, structural characterization, and investigation of anti glioblastoma activity of copper complexes supported by bis pyrazol 1 yl acetate ligands functionalized with memantine
No full textThe new ligand bis 1H pyrazol 1 yl acetyl 3,5 dimethyladamantane 1 amide LMem was synthesized by conjugating the drug memantine with the bifunctional species bis pyrazol 1 yl acetic acid and used as supporting ligand of copper II and copper I complexes 1 7. In the synthesis of the CuI complexes, the lipophilic triphenylphosphine PPh3 and hydrophilic 1,3,5 triaza 7 phosphaadamantane PTA were selected as co ligands, in order to stabilize copper in 1 oxidation state and to confer different solubility properties to the corresponding metal complexes. The electronic and molecular structures of CuI and CuII coordination compounds were investigated by high resolution Synchrotron Radiation induced X ray Photoelectron Spectroscopy SR XPS , Near Edge X ray Absorption Fine Structure NEXAFS spectroscopy. The local structure around the copper ion sites was studied combining Density Functional Theory DFT modelling and X ray Absorption Fine Structure XAFS spectroscopy, in both X ray Absorption Near Edge Spectroscopy XANES and Extended X ray Absorption Fine Structures EXAFS regions. X ray diffraction XRD studies were carried out on suitable crystals to describe the molecular structure and the intermolecular contacts of the LMem ligand. Among all Cu complexes tested, compounds 4 and 5 exhibited potent antiproliferative and cytotoxic effects in U87, T98, and U251 glioma cell lines. These effects were associated with increased reactive oxygen species ROS production and mitochondrial dysfunction, as evidenced by mitochondrial depolarization and altered intracellular distribution. Furthermore, the cytotoxic activity of these compounds was shown to be Cu dependent, as it was effectively inhibited by the Cu chelator tetrathiomolybdate, confirming the essential role of copper in their mechanism of actio