24378 research outputs found
Sort by
Magnetic imaging of thermally switchable antiferromagnetic ferromagnetic modulated thin films
Full text linkNanoscale magnetic patterning can lead to the formation of a variety of spin textures, depending on the intrinsic properties of the material and the microstructure. Here we report on the spin textures formed in laterally patterned antiferromagnetic AF ferromagnetic FM thin film stripes with a period of 200 nm 100 nm FM 100 nm AF . We make use of the AF to FM phase transition in FeRh thin films at amp; 8764;100 C, thereby creating a nanoscale pattern that is thermally switchable between AF FM stripes and uniformly FM. A combination of spin resolved photoemission electron microscopy, magnetic force microscopy, and magnetometry measurements allow direct nanoscale observations of the stray magnetic fields emergent from the nanopattern as well as the underlying magnetisation. Our measurements reveal pinning centres resistant to temperature cycling that govern the modulated spin texture as well as a sub texture consisting of grain driven nanoscale magnetisation structure directed out of the film plane. The nanoscale magnetic structure is thus strongly influenced by the film microstructure. Signatures of exchange bias are not observed, most likely due to the small contact area between the AF and FM regions, combined with the fact that the interfaces between the damaged and undamaged regions are likely to be highly diffuse owing to the lateral scattering of incoming ions. These results show that temperature controllable spin textures can be created in FeRh thin films which could find application in domain wall, microwave, or magnonic device
Atomic scale determination of magnetism and stoichiometry at the La0.7Sr0.3MnO3 SrTiO3 interface investigation of inverse hysteresis
Full text linkControlling the correlations and electronic reconstruction at the interface of transition metal oxide heterostructures provides a new pathway for tuning their unique physical properties. Here, we investigate the effects of interfacial nonstoichiometry and vertical phase separation on the magnetic properties and proximity induced magnetism of epitaxial La0.7Sr0.3MnO3 LSMO SrTiO3 001 oxide heterostructures. We also reinvestigate the recently observed inverse hysteresis behavior reported for this system, which we find emanates from the remanent field of the superconducting solenoid and not from antiferromagnetic intra layer exchange coupling in low coercivity LSMO thin films. Combined atomically resolved electron energy loss spectroscopy, element specific X ray magnetic circular dichroism, and interface sensitive polarized soft X ray resonant magnetic reflectivity show the formation of a Mn3 enriched interfacial LSMO layer, of a Ti3 derived magnetic interface layer coupled ferromagnetically to La0.7Sr0.3MnO3, together with a small density of O vacancies at the interface. These results not only advance the understanding of the magnetism and spin structure of correlated oxide interfaces but also hold promise for practical applications, especially in devices where the performance relies on the control and influence of spin polarization currents by the interfacial spin structur
Multimodal Operando Analysis of Lithium Sulfur Multilayer Pouch Cells An In Depth Investigation on Cell Component Design and Performance
Full text linkThis study presents an innovative operando analysis of lithium sulfur Li S multilayer pouch cells, employing a combination of lab source and synchrotron x ray imaging to investigate sulfur crystallite dissolution and lithium dendrite formation. By integrating advanced X ray imaging, impedance spectroscopy, and simultaneous monitoring of temperature and pressure, the research uncovers critical insights into the behavior of active and inactive cell components. The analysis reveals significant degradation increments, primarily driven by side product accumulation and the deterioration of lithium microstructures, which contribute to performance loss over cycling. Additionally, temperature distribution analysis shows a strong correlation between joule heating, polarization resistance, and the observed endothermic processes during crystallization. These findings provide a comprehensive understanding of the mechanistic processes within industrially relevant pouch cells, highlighting opportunities for optimizing Li S cell designs and advancing high energy density battery systems for commercial application
Mechanical Design of the VSR Cavity An elliptical 4 cell 1.5 GHz SRF cavity with strong waveguide HOM damping for high current accelerators
Full text linkThe mechanical design of an elliptical 1.5 GHz superconducting RF SRF 4 cell cavity with strong waveguide higher order mode HOM damping is presented. It was developed in the VSR Variable Storage Ring project framework to serve as part of an upgrade for the synchrotron light source BESSY II operating at beam currents of up to 300 mA. This poses a great design challenge, demanding both a system capable of extracting very high HOM powers above 2 kW per cavity , the stresses arising during operation, and an overall cavity length of less than 1 m to fit into a given magnet lattice. As a result, a compact HOM waveguide loaded cavity has been developed, fulfilling all the required criteria. The most remarkable feature of the cavity are the five waveguide extensions. The paper describes the mechanical solutions adopted in the layout of the cavity with its subgroups. Special attention is given to numerical studies aiming for high pressure resistance whilst allowing for required tuning. A standardized pressure vessel code was not followed. Instead, a dedicated quality control procedure for manufacturing including ancillary material testing and welding qualification, was developed to allow for peak pressures of 3.5 bar a of the cooling medium. This paper shows the successful mechanical design solutions developed to allow for the operation of such cavities in demanding operational regimes featuring both high gradients and strong beam currents. At time of writing, the first prototype is mechanically completed, and the first RF tests have been performed. Relevant manufacturing experiences which led to late stage design modifications are included in this pape
Insights into the stability of copper gas diffusion electrodes for carbon dioxide reduction at high reaction rates
Full text linkElectrosynthesis of value added chemicals from CO2 offers a sustainable solution to climate change, renewable energy use, and raw material shortages. This study examines the high rate production of ethylene C2H4 and ethanol CH3CH2OH through CO2 reduction reaction on copper Cu gas diffusion electrodes GDEs made by sputtering deposition. The catalyst layer thickness of the GDEs, adjusted by deposition time, significantly affects the electrode stability. During testing, a selectivity shift is observed, where C2H4 and CH3CH2OH selectivity decreases, while CH4 and H2 selectivity increases. However, an alternating operation by interrupting and restarting the polarization fully restores the C2H4 and CH3CH2OH selectivity. Operando X ray absorption spectroscopy with online product analysis reveals that at constant potentials, the dominant oxidized Cu species gradually reduces to metallic Cu, along with a decline in C2H4 selectivity. Under alternating operation, some oxidized Cu species remains, and the C2H4 selectivity is also preserved. This outcome suggests a close link between cationic Cu species and C2H4 production, offering insights into stabilizing these species for prolonged C2H4 productio
Atacamite Cu2Cl OH 3 in High Magnetic Fields Quantum Criticality and Dimensional Reduction of a Sawtooth Chain Compound
Full text linkWe report an extensive high field study of atacamite Cu2Cl OH 3, a material realization of quantum sawtooth chains with weak interchain couplings, in continuous and pulsed magnetic fields up to 58 T. In particular, we have mapped the entropy landscape for fields as high as 35 T and have identified a field induced quantum critical point at 21.9 1 T for Hkc axis. The quantum critical point separates field regions with and without magnetic order, evidenced by our thermodynamic study and H nuclear magnetic resonance spectroscopy, but lies far below full saturation of the magnetization. Corroborated by numerical results using density matrix renormalization group calculations, we find this behavior associated with a dimensional reduction of the spin system the sawtooth chain effectively decouples into an antiferromagnetic spin 1 2 chain backbone of the sawtooth chain in the presence of an exchange field produced by the remaining field polarized spin
VIS UV VUV optical functions of epitaxial ferroelectric PbTiO3 SrTiO3 thin films
No full textLead titanate PbTiO3 ferroelectric thin films were epitaxially grown by pulsed laser deposition on strontium titanate SrTiO3 substrates. Two samples of thicknesses 117 nm and 313 nm were investigated. The a c polydomain structure, which results from a partial relaxation of the epitaxial strain, was evidenced in the thicker film. The real and imaginary parts of the complex dielectric function were determined in a broad photon energy range of 2 9.8 eV using spectroscopic ellipsometry. The energy gap values and critical point energies were determined for the both films. An effect of the epitaxy on the optical functions obtained is detected and discussed. The results showed, that even in the case of a relatively small mismatch between the layer and substrate lattice constants, the effect of epitaxy on the optical properties of ferroelectric films is not negligibl
Effect of Thickness and Halide Composition on the Restive Switching and Photonic Synapse Properties of Methylammonium Lead Bromide Thin Films
Full text linkRecently, photonic synapses based on halide perovskite resistive switching devices have been intensively studied due to their low power consumption, high information processing speed, and the ability to simultaneously receive optical and electrical signals. In this study, the resistive switching behavior and photo synaptic properties of methylammonium lead bromide MAPbBr3 thin films were investigated by varying thicknesses and substituting bromine with chlorine. The thickest film 330 amp; 8239;nm exhibits a single step of resistive switching from a high resistance state to a low resistance state SET , which is attributed to the formation of conductive filaments by the migration of halide vacancies. In contrast, thinner films 100 amp; 8239;nm and 210 amp; 8239;nm show two steps of SET where both the halide vacancies and electrode ions Ag are involved in the formation of conductive filaments. Among the films, the 210 nm thick film exhibited the most effective potentiation by repeated light exposure. When incorporating Cl into the MAPbBr3 film, the resistive switching voltages and the light induced potentiation was decreased. This was attributed to the smaller ion size of Cl compared to Br, which facilitates ion migration and the formation of vacancy filaments. Short term potentiation and long term depression under light pulses were characterized using paired pulse facilitation and paired pulse depressio
Nano Infrared Imaging and Spectroscopy of Animal Cells in Liquid Environment
No full textInfrared nano spectroscopy nano IR using scattering type near amp; 64257;eld optical microscopy s SNOM is becoming an important tool for analyzing vibrational spectra in nanometer scale volumes of intact samples. Recent s SNOM experiments using ultrathin membranes have enabled nanoscopy of cells and biomolecules in liquid environments. This study reports the use of SiC membranes as a stable, biocompatible interface between cells in their medium and the atomic force microscopy AFM probe of the s SNOM, ensuring broadband nano IR experiments above 1050 cm amp; 8722;1 . Nano IR images and spectra are collected from amp; 64257;broblast cells grown adherently to con amp; 64258;uence on the membranes using a broadband synchrotron IR source, probing the membrane adjacent cellular region. Optimized tip sample interaction allows to signi amp; 64257;cantly increase the signal to noise ratio in nano IR imaging. The alteration of the tapping amplitude and set point of the AFM cantilever allows to adjust the probing depth and suggests a nano IR tomography approach that uses a single demodulation harmonic of the signal. The nano IR spectra of amp; 64257;broblast cells resemble their far amp; 64257;eld spectra, but re amp; 64258;ect a heterogeneity in the composition and structure of proteins, nucleic acids, carbohydrates, and of membrane lipid organization. The results demonstrate nano IR probing of complex samples in liquid media and suggest ways to improve e amp; 64259;ciency and standardization of existing approaches in vibrational nanoscop
Evidence for a Unifying NiI NiIII Mechanism in Light Mediated Cross Coupling Catalysis
Full text linkAdvances in nickel catalysis have significantly broadened the synthetic chemists toolbox, particularly through methodologies leveraging paramagnetic nickel species via photoredox catalysis or electrochemistry. Key to these reactions is the oxidation state modulation of nickel via single electron transfer events. Recent mechanistic studies indicate that C sp2 heteroatom bond formations proceed through NiI NiIII cycles. Related C sp2 C sp3 cross couplings operate via the photocatalytic generation of C centered radicals and a catalytic cycle that involves Ni0, NiI, and NiIII species. Here, we show that light mediated nickel catalyzed C sp2 C sp3 bond formations can be carried out without using exogenous photoredox catalysts but with a photoactive ligand. In a pursuit of expanding the scope of C sp2 heteroatom couplings using donor acceptor ligands, we identified a photoactive nickel complex capable of catalyzing cross couplings between aryl halides and benzyltrifluoroborate salts. Mechanistic investigations provide evidence that transmetalation between a photochemically generated NiI species and the organoboron compound is the key catalytic step in a NiI NiIII catalytic cycle under these condition