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Identification and Elimination of Surface Emission in Lanthanide (Co)doped Zirconia Nanocrystals
No full textZirconia nanocrystals (ZrO2 NCs) are a stable host material for lanthanides, but their performance lags behind that of the leading NaYF4 nanomaterials. Here, we leverage surface chemistry and core/shell architectures to uncover the contribution of dopants at the nanocrystal surface and of dopants in the nanocrystal bulk. We first assess the doping efficiency by ICP and find that, while Eu is almost quantitatively incorporated, the other lanthanides (La, Ce, Tb, Tm, Er, Yb) have about 50% incorporation efficiency over the studied doping range of 1–10%. We then determine the nanocrystal surface chemistry using NMR spectroscopy, despite the additional spectral line broadening caused by the paramagnetic lanthanide dopants. By varying the surface ligands and measuring the photoluminescence, we resolve the spectroscopic signals that are sensitive to a change in surface chemistry. Time-resolved emission spectra further reinforce the notion of a bulk component with a long luminescent lifetime and a surface component with a fast lifetime. Upon shelling Eu- or Tb-doped zirconia NCs with pure zirconia, the surface component disappears, and the photoluminescence quantum yield increases. We further functionalized the surface of the core/shell particles with oleylphosphonic acid ligands to obtain excellent dispersibility. These results show that lanthanide-doped zirconia NCs can be engineered to eliminate deactivation pathways
Synthesis of cerium oxynitride and oxoguanidinate at high pressures
No full textThe pursuit of novel materials with tunable properties has driven significant interest in mixed-anion compounds, such as carbon nitrides and oxynitrides. In this study, we explored the Ce–O–N–C system under pressures of 35–55 GPa and temperatures of 1500–1800 K. The introduction of oxygen into the Ce–N system resulted in the formation of a novel oxynitride, Ce4O3N4, characterized by lower-order N–N bonding compared to the triple-bonded N2 molecule. In addition, we identified a new cerium oxoguanidinate, Ce2OCN3, in the Ce–O–C–N system. The crystal structures of Ce4O3N4 and Ce2OCN3 were determined using single-crystal x-ray diffraction, and their solutions were validated through Raman spectroscopy and density functional theory calculations. This experimental approach provides a robust method for investigating mixed-anion systems under high-pressure conditions. The identification of lower-bond-order nitrogen anions in oxynitride and guanidinate anions in oxoguanidinates highlights the potential for developing novel materials with unique properties based on mixed-anion species
A study combining EBSD and x-ray synchrotron diffraction using generalized pole figures
No full textThe development of advanced materials with optimum structural and mechanical properties requires a detailed control of their microstructures, textures and crystalline defects. Different techniques can be used for the characterization of those microstructures and defects, but it is their combination that could result in an exhaustive understanding of the microstructural and orientational developments on these materials.X-Ray Diffraction (XRD) can be employed to obtain a “global” characterization of microstructure and texture, since the presence of defects in the sample produces shift and broadening of diffraction peaks. Different models have been developed to quantify these defects, some of which require fitting the complete diffraction pattern while others just individual peaks. These techniques can be extended to texture measurements, often represented through pole figures (PFs), wherein diffraction patterns are obtained for different sample orientations. This allows the determination of defect density in function of orientations and their representation in Generalized Pole Figures (GPFs).On the other hand, for a more “local” characterization, Electron Backscatter Diffraction (EBSD) has proven to be extremely useful for microstructural and orientational analysis, allowing to assess defect accumulation in individual grains and orientations.In this work, a set of 32,205 duplex steel samples cold-rolled up to 79 % reduction (in steps of approximately 20 %) are studied, aiming to investigate the evolution of defect storage with deformation in different orientations and texture components. For this purpose, Laue diffraction patterns have been obtained for these samples in P07 beamline in Petra III station (DESY), from which PFs and GPFs were obtained. This information is complemented with EBSD results, where dislocation arrays and grain and subgrain structures for particular orientations are studied. This paper not only aims at describing the microstructural evolution of a cold rolled duplex steel with increasing deformation, providing both a local and a global characterization of this microstructure, but also at exploring the capabilities of the diffraction techniques used for this purpose. The combination of both techniques allowed for an exhaustive analysis of defect storage and microstructural orientations developed with increasing deformation
Two-Dimensional Reversible Supramolecular Polymorphism Governed by Weak Solvent–Solute Interactions
No full textMolecular self-assembly can be a powerful strategy for fabricating dynamic two-dimensional (2D) nanomaterials. However, formulating a rational design principle that meets the stringent thermodynamic and kinetic requirements for uniform in-plane growth, while also allowing dynamic structural rearrangement, presents a considerable challenge. We report a hydrophobic core-substituted naphthalenediimide that self-assembles in water–dioxane mixtures to form a pair of 2D polymorphs, with distinct morphological, optical, and surface characteristics. Changing the solvent composition or temperature prompts an in situ transformation between the two polymorphs in solution. A comprehensive structural investigation using solid-state NMR spectroscopy, X-ray, and electron diffraction analyses reveals not only the nature of molecular packing and noncovalent (n → π* and π-stacking) interactions stabilizing each 2D polymorph but also the role of weak solvent–solute interactions in driving polymorphic interconversion. Variations in the perfluoroalkyl side chains arrangements on the exposed 2D surface of the two polymorphs lead to distinct solvent–solute interactions at the solid–liquid interface, which affects the surface free-energy and relative stability in different solvent compositions. Further, the entropy change associated with surface ordering of perfluoroalkyl side chains and desolvation dictates thermal reorganization between the polymorphs. How changes in dioxane–water microheterogeneity with solution composition and temperature may affect these weak solvent–solute interactions and the phase equilibrium is also discussed
Visualizing the Three-Dimensional Arrangement of Hydrogen Atoms in Organic Molecules by Coulomb Explosion Imaging
No full textStructure-sensitive methods based on femtosecond light or electron pulses are now making it possible to measure how molecular structures change during light-induced processes. Despite significant progress, high-fidelity imaging of nuclear positions remains a challenge even for relatively small molecular systems and, notably, regarding the positions of hydrogen atoms. As demonstrated in recent work, X-ray-induced Coulomb explosion imaging (CEI) may overcome this obstacle, as its sensitivity does not depend on the mass of the imaged atoms. The photoinduced ring opening of the heterocyclic molecule 2(5H)-thiophenone has attracted recent interest. Here, we show that CEI offers a powerful route to imaging the peripheral H atoms in this molecule and thus, more generally, to tracking detailed nuclear motions (e.g., isomerizations) in organic molecules on ultrafast time scales. Specifically, we record momentum-space Coulomb explosion images that report on the three-dimensional positioning of all nuclei within the molecule, for instance, distinguishing H atoms in C–H bonds that lie within or are directed out of the plane defined by the heavy atoms. The prospect of imaging peripheral H atoms to probe photochemical dynamics is explored by coupling ab initio molecular dynamics with classical Coulomb explosion simulations, thereby differentiating potential photoproduct isomers, including those whose structures primarily differ in the position of the hydrogens
Recrystallization-accelerated precipitation, structural evolution, and residual stress relaxation in nanostructured Al–Cu–Li alloy: an in situ microbeam synchrotron high-energy X-ray diffraction study
No full textMultidimensional synchrotron high-energy microbeam diffraction was applied to a nanostructured Al–1.1Cu–6.8Li–0.8X alloy (at%; X contains a total of minor elements) upon a constant heating ramp from room temperature to 830 K. Crystallography of a T1 precursor intermetallic as well as the T2 phase has been identified. Radial and azimuthal reciprocal space dimensions have been analyzed to determine Laue–Bragg interferences and their orientational statistics. The residual stress and texture determine the initial nanostructure of an ultrafine-grained cubic close-packed solid solution. While stress relaxes first, precipitation of precursor T1 sets in before any recrystallization, leading to nanoscale plate-shaped precipitates in the nanograins. Inherent with the onset of recrystallization, the T2 phase appears and grows by transformation from T1 and further precipitation from the matrix. At higher temperatures, T2 slowly dissolves again, while recrystallization ends and sluggish grain growth occurs in the two-phase field. The latter is accelerated toward the disappearance of T2 and becomes unhindered once the phase is fully dissolved. All these events mark anomalies in the curves for total lattice strain, small-momentum-transfer signals, and peak widths. The morphology of reflections on the Debye–Scherrer rings allows for determining grain sizes, which have been validated by electron microscopy and diffraction
Kilohertz repetition rate capillary discharge pulse modulator with energy recuperation and energy deposition monitoring
No full textAcceleration of electrons in plasma wakefields is one of the prime candidates for complementing or partially replacing conventional accelerator technology, due to its superior acceleration gradients. The plasma acceleration medium is often supplied independently of the acceleration process by e.g. electrical discharging an external current through a gas. Such discharge plasma sources are typically operated at several 10’s of Hz but have also been operated at up to kHz repetition rate. Here, we present the design of a high voltage pulse modulator capable of supplying 10 kV, 400 A peak current pulses at 1 kHz repetition rate into a dynamic plasma load. The pulse circuit is based on a low-loss silicon carbide switch and passive pulse-recirculation, which allows reduction of the power consumption by up to 50% and also monitoring of the energy deposition in the plasma load
In situ x-ray diffraction of the α − ɛ phase transition in iron at intermediate strain rates
No full textThe (bcc)-ɛ(hcp) phase transition in polycrystalline Fe has been investigated under fast quasihydrostatic compression using piezoelectric actuator driven dynamic diamond anvil cells. X-ray diffraction data from Fe under intermediate strain rate compression were collected at megahertz repetition rates. Our results demonstrate, for the first time, the full evolution of the −ɛphase transition in powder and foil samples at strain rates of ∼102s−1. Under fast compression, the majority of the phase transforms to ɛ-Fe in a timescale of tens of microseconds, with a corresponding coexistence pressure of ∼2GPa. The observed onset phase transition pressure of 13.4–14.4 GPa is in good agreement with the results of previous quasihydrostatic compression studies, suggesting that the transition is not influenced by compression rates up to ∼80TPas−1
Virtuelle Histopathologie des Pankreas: 3D-Einblicke mittels synchrotronbasierter BildgebungVirtual histopathology of the pancreas: 3D insights using synchrotron-based imaging
No full textHintergrundDie konventionelle histopathologische Diagnostik stößt bei der Beurteilung komplexer, dreidimensionaler Gewebearchitekturen an inhärente methodische Grenzen. Insbesondere bei heterogen zusammengesetzten Geweben wie dem Pankreas oder bei komplexen Gewebspathologien erschwert die Beschränkung auf zweidimensionale Schnittbilder die ubiquitäre Erfassung morphologischer Merkmale.Ziel der Arbeit (Fragestellung)Ziel dieser Studie ist es, das Potenzial der synchrotronbasierten Phasenkontrastbildgebung (SRµCT) für die hochauflösende, dreidimensionale Visualisierung verschiedener Pankreasgewebe zu demonstrieren. Anhand dreier paradigmatischer Fallbeispiele werden morphologische Parameter volumetrisch erfasst und mit korrespondierenden immunhistochemischen Markerprofilen korreliert.Material und MethodenGewebestanzen aus formalinfixierten, paraffineingebetteten Blöcken von humanen Pankreasgewebeproben wurden mittels SRµCT volumetrisch erfasst. Das untersuchte Probenmaterial wurde als Microarrays weiterverarbeitet. Konsekutive Schnitte und immunhistochemische Färbungen wurden mit den 3D-Datensätzen korreliert.ErgebnisseDie Bildgebung ermöglichte die differenzierte räumliche Darstellung funktioneller Kompartimente und neoplastischer Infiltrationsmuster. Nichtneoplastisches Gewebe zeigte klar abgegrenzte Kompartimente. Ein gut differenzierter neuroendokriner Tumor präsentierte trabekuläre Binnenstrukturen. Das duktale Adenokarzinom zeigte ein infiltratives Wachstumsmuster mit diffuser, heterogener Architektur, irregulären Gangformationen und Stromadesmoplasie. Die virtuelle Schnittführung ermöglichte die Analyse in jeder Raumrichtung. Durch Korrelation mit immunhistochemischen Markerprofilen konnten morphofunktionelle Merkmale validiert werden.SchlussfolgerungDie SRµCT ist eine hochsensitive Methode, die nichtinvasiv und ohne Färbung dreidimensionale Einsichten in die Gewebearchitektur des Pankreas unter Nutzung archivierter Paraffinblöcke erlaubt. Die Methode bietet neue Perspektiven für Forschung, Lehre und potenziell erweiterte Spezialdiagnostik
Observation of a family of all-charm tetraquarks
No full textThree structures, X(6600), X(6900), and X(7100), have emerged from the JJ (J\to) mass spectrum. These are candidates of all-charm tetraquarks, an exotic form of hadronic matter. A clearer picture of these states is obtained using proton-proton collision data collected by the CMS detector that corresponds to 315 fb, which yields 3.6 times more JJ pairs than previous studies by CMS. All three structures, and their mutual interference, have statistical significances above five standard deviations. The presence of interference implies that the structures have common quantum numbers. Their squared masses align linearly with a resonance index and have natural widths that systematically decrease as the index increases. These features are consistent with radial excitations of tetraquarks composed of two aligned spin-1 diquarks without orbital excitation, and disfavor other interpretations. The J(2S) decay mode is also explored and the X(6900) and X(7100) states are found with significances exceeding 8 and 4 standard deviations, respectively