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- ItemAccelerating the Laser-Induced Phase Transition in Nanostructured FeRh via Plasmonic Absorption(WILEY-V C H VERLAG GMBH, 2024-08-01) Mattern, Maximilian; Pudell, Jan Etienne; Arregi Uribeetxebarria, Jon Ander; Zlámal, Jakub; Kalousek, Radek; Uhlíř, Vojtěch; Rössle, Matti; Bargheer, MatiasBy ultrafast x-ray diffraction (UXRD), it is shown that the laser-induced magnetostructural phase transition in FeRh nanoislands proceeds faster and more complete than in continuous films. An intrinsic 8 ps timescale is observed for the nucleation of ferromagnetic (FM) domains in the optically excited fraction of both types of samples. For the continuous film, the substrate-near regions are not directly exposed to light and are only slowly transformed to the FM state after heating above the transition temperature via near-equilibrium heat transport. Numerical modeling of the absorption in the investigated nanoislands reveals a strong plasmonic contribution near the FeRh/MgO interface. The larger absorption and the optical excitation of the electrons in nearly the entire volume of the nanoislands enables a rapid phase transition throughout the entire volume at the intrinsic nucleation timescale. Nanostructuring FeRh thin films by solid state dewetting make the laser-induced antiferromagnetic to ferromagnetic phase transition more efficient and speed the switching up to the intrinsic timescale. Ultrafast x-ray diffraction experiments directly measure the structural order parameter averaged over the entire film. Finite element modeling reveals the enhanced plasmonic light absorption near the substrate as the crucial factor. image
- ItemAssessing the ecological consequences of biodegradable plastics: Acute, chronic and multigenerational impacts of poly-3-hydroxybutyrate microplastics on freshwater invertebrate Daphnia magna(CELL PRESS, 2024-08-30) Procházková, Petra; Kalčíková, Gabriela; Maršálková, Eliška; Brtnický, Martin; Zlámalová Gargošová, Helena; Kučerík, JiříMicroplastics, pervasive contaminants in freshwater ecosystems, have raised ecological concerns. Efforts are underway to substitute conventional plastics with biodegradable alternatives that should be more easily decomposed in the environment. However, the biodegradation of these alternatives depends on specific conditions such as temperature, humidity, pH, and microorganisms, which are not always met. Consequently, these biodegradable alternatives can also fragment and generate microplastics, which can be ingested and affect biota. In this study, we investigated the acute, chronic, and multigenerational effects of two fractions (particles <63 mu m and particles <125 mu m) of biodegradable poly-3-hydroxybutyrate (P3HB) at varying concentrations on the inhibition, mortality, reproduction activity, and growth of the freshwater invertebrate Daphnia magna. No acute effects were observed for either size fraction. However, during chronic and multigenerational experiments, an increase in the concentration of P3HB microplastics corresponded with increased mortality, reduced reproductive activity, and slower growth among the mother organisms. Given the important role of D. magna in the food chain, these findings suggest that biodegradable microplastics may indeed negatively affect freshwater ecosystems.
- ItemAdvancing microplastic detection in zebrafish with micro computed tomography: A novel approach to revealing microplastic distribution in organisms(Elsevier, 2025-05-05) Parobková, Viktória; Maleček, Lukáš; Zemek, Marek; Kalčíková, Gabriela; Vykypělová, Michaela; Buchtová, Marcela; Adamovský, Ondřej; Zikmund, Tomáš; Kaiser, JozefThe analysis of microplastics with current spectroscopic and pyrolytic methods is reaching its limits, especially with regard to detailed spatial distribution in biological tissues. This limitation hampers a comprehensive understanding of the effects of microplastics on organisms. Therefore, there is a pressing need to expand the analytical approaches to study microplastics in biota. In this context, the aim of this study was to test the applicability of non-destructive 3D imaging using X-ray micro-computed tomography (microCT) for the detection of microplastics in fish. Zebrafish (Danio rerio) were gavaged with polyethylene spherical microplastics (30-110 mu m) and the distribution of microplastics in the gut was investigated using microCT. The results showed that the particle size distribution determined by microCT closely matched the data from conventional laser diffraction analysis. In addition, microCT was able to detect microplastics in spiked fish tissue and provide precise localization data by tracing particles of known type and shape. MicroCT offers a novel approach for tracking microplastics in organisms and enables accurate sizing without compromising the integrity of the tissue under investigation. It therefore represents a valuable addition to spectroscopic methods, which are widely used for the detection of microplastics based on their chemical composition but do not provide data on their spatial distribution.
- ItemDimensional crossover of microscopic magnetic metasurfaces for magnetic field amplification(AIP Publishing, 2024-07-01) Lejeune, Nicolas; Fourneau, Emile; Barrera, Aleix; Morris, Oliver; Leonard, Oscar; Arregi Uribeetxebarria, Jon Ander; Navau, Carles; Uhlíř, Vojtěch; Bending, Simon; Palau, Anna; Silhanek, Alejandro VladimiroTransformation optics applied to low frequency magnetic systems have been recently implemented to design magnetic field concentrators and cloaks with superior performance. Although this achievement has been amply demonstrated theoretically and experimentally in bulk 3D macrostructures, the performance of these devices at low dimensions remains an open question. In this work, we numerically investigate the non-monotonic evolution of the gain of a magnetic metamaterial field concentrator as the axial dimension is progressively shrunk. In particular, we show that in planar structures, the role played by the diamagnetic components becomes negligible, whereas the paramagnetic elements increase their magnetic field channeling efficiency. This is further demonstrated experimentally by tracking the gain of superconductor-ferromagnet concentrators through the superconducting transition. Interestingly, for thicknesses where the diamagnetic petals play an important role in the concentration gain, they also help to reduce the stray field of the concentrator, thus limiting the perturbation of the external field (invisibility). Our findings establish a roadmap and set clear geometrical limits for designing low dimensional magnetic field concentrators.
- ItemSingular and Nonsingular Transitions in the Infrared Plasmons of Nearly Touching Nanocube Dimers(AMER CHEMICAL SOC, 2024-05-28) Wu, Yina; Konečná, Andrea; Cho, Shin Hum; Milliron, Delia J.; Hachtel, Jordan A.; de Abajo, F. Javier GarcíaNarrow gaps between plasmon-supporting materials can confine infrared electromagnetic energy at the nanoscale, thus enabling applications in areas such as optical sensing. However, in nanoparticle dimers, the nature of the transition between touching (zero gap) and nearly nontouching (nonzero gap less than or similar to 15 nm) regimes is still a subject of debate. Here, we observe both singular and nonsingular transitions in infrared plasmons confined to dimers of fluorine-doped indium oxide nanocubes when moving from touching to nontouching configurations depending on the dimensionality of the contact region. Through spatially resolved electron energy-loss spectroscopy, we find a continuous spectral evolution of the lowest-order plasmon mode across the transition for finite touching areas, in excellent agreement with the simulations. This behavior challenges the widely accepted idea that a singular transition always emerges in the near-touching regime of plasmonic particle dimers. The apparent contradiction is resolved by theoretically examining different types of gap morphologies, revealing that the presence of a finite touching area renders the transition nonsingular, while one-dimensional and point-like contacts produce a singular behavior in which the lowest-order dipolar mode in the touching configuration, characterized by a net induced charge in each of the particles, becomes unphysical as soon as they are separated. Our results provide valuable insights into the nature of dimer plasmons in highly doped semiconductors.