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- 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.
- ItemTerahertz magnetic response of plasmonic metasurface resonators: origin and orientation dependence(NATURE PORTFOLIO, 2024-07-03) Tesi, Lorenzo; Hrtoň, Martin; Bloos, Dominik; Hentschel, Mario; Šikola, Tomáš; van Slageren, JorisThe increasing miniaturization of everyday devices necessitates advancements in surface-sensitive techniques to access phenomena more effectively. Magnetic resonance methods, such as nuclear or electron paramagnetic resonance, play a crucial role due to their unique analytical capabilities. Recently, the development of a novel plasmonic metasurface resonator aimed at boosting the THz electron magnetic response in 2D materials resulted in a significant magnetic field enhancement, confirmed by both numerical simulations and experimental data. Yet, the mechanisms driving this resonance were not explored in detail. In this study, we elucidate these mechanisms using two semi-analytical models: one addressing the resonant behaviour and the other examining the orientation-dependent response, considering the anisotropy of the antennas and experimental framework. Our findings contribute to advancing magnetic spectroscopic techniques, broadening their applicability to 2D systems.
- ItemSpeed limits of the laser-induced phase transition in FeRh(AIP Publishing, 2024-05-01) Mattern, Maximilian; Jarecki, Jasmin; Arregi Uribeetxebarria, Jon Ander; Uhlíř, Vojtěch; Rössle, Matti; Bargheer, MatiasWe use ultrafast x-ray diffraction and the polar time-resolved magneto-optical Kerr effect to study the laser-induced metamagnetic phase transition in two FeRh films with thicknesses below and above the optical penetration depth. In the thin film, we identify an intrinsic timescale for the light-induced nucleation of ferromagnetic (FM) domains in the antiferromagnetic material of 8ps, which is substantially longer than the time it takes for strain waves to traverse the film. For the inhomogeneously excited thicker film, only the optically excited near-surface part transforms within 8ps. For strong excitations, we observe an additional slow rise of the FM phase, which we experimentally relate to a growth of the FM phase into the depth of the layer by comparing the transient magnetization in frontside and backside excitation geometry. In the lower lying parts of the film, which are only excited via near-equilibrium heat transport, the FM phase emerges significantly slower than 8ps after heating above the transition temperature.
- ItemBiodegradable WE43 Mg alloy/hydroxyapatite interpenetrating phase composites with reduced hydrogen evolution(KEAI PUBLISHING LTD, 2024-12-01) Drotárová, Lenka; Slámečka, Karel; Bálint, Tomáš; Remešová, Michaela; Hudák, Radovan; Živčák, Jozef; Schnitzer, Marek; Čelko, Ladislav; Montufar Jimenez, Edgar BenjaminBiodegradable magnesium implants offer a solution for bone repair without the need for implant removal. However, concerns persist regarding peri-implant gas accumulation, which has limited their widespread clinical acceptance. Consequently, there is a need to minimise the mass of magnesium to reduce the total volume of gas generated around the implants. Incorporating porosity is a direct approach to reducing the mass of the implants, but it also decreases the strength and degradation resistance. This study demonstrates that the infiltration of a calcium phosphate cement into an additively manufactured WE43 Mg alloy scaffold with 75 % porosity, followed by hydrothermal treatment, yields biodegradable magnesium/hydroxyapatite interpenetrating phase composites that generate an order of magnitude less hydrogen gas during degradation than WE43 scaffolds. The enhanced degradation resistance results from magnesium passivation, allowing osteoblast proliferation in indirect contact with composites. Additionally, the composites exhibit a compressive strength 1.8 times greater than that of the scaffolds, falling within the upper range of the compressive strength of cancellous bone. These results emphasise the potential of the new biodegradable interpenetrating phase composites for the fabrication of temporary osteosynthesis devices. Optimizing cement hardening and magnesium passivation during hydrothermal processing is crucial for achieving both high compressive strength and low degradation rate.
- ItemInterpreting neural networks trained to predict plasma temperature from optical emission spectra(ROYAL SOC CHEMISTRY, 2024-04-03) Képeš, Erik; Saeidfirouzeh, Homa; Laitl, Vojtěch; Vrábel, Jakub; Kubelík, Petr; Pořízka, Pavel; Ferus, Martin; Kaiser, JozefWe explore the application of artificial neural networks (ANNs) for predicting plasma temperatures in Laser-Induced Breakdown Spectroscopy (LIBS) analysis. Estimating plasma temperature from emission spectra is often challenging due to spectral interference and matrix effects. Traditional methods like the Boltzmann plot technique have limitations, both in applicability due to various matrix effects and in accuracy owing to the uncertainty of the underlying spectroscopic constants. Consequently, ANNs have already been successfully demonstrated as a viable alternative for plasma temperature prediction. We leverage synthetic data to isolate temperature effects from other factors and study the relationship between the LIBS spectra and temperature learnt by the ANN. We employ various post-hoc model interpretation techniques, including gradient-based methods, to verify that ANNs learn meaningful spectroscopic features for temperature prediction. Our findings demonstrate the potential of ANNs to learn complex relationships in LIBS spectra, offering a promising avenue for improved plasma temperature estimation and enhancing the overall accuracy of LIBS analysis. ANN can learn spectroscopic trends widely used by domain experts for plasma temperature estimation using emission spectra.