Příprava a charakterizace nanostruktur

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Unidirectional propagation of zero-momentum magnons
(AIP Publishing, 2024-09-23) Wojewoda, Ondřej; Holobrádek, Jakub; Pavelka, Dominik; Pribytova, Ekaterina; Krčma, Jakub; Klíma, Jan; Panda, Jaganandha; Michalička, Jan; Lednický, Tomáš; Chumak, Andrii V.; Urbánek, Michal
We report on experimental observation of unidirectional propagation of zero-momentum magnons in synthetic antiferromagnet consisting of strained CoFeB/Ru/CoFeB trilayer. Inherent non-reciprocity of spin waves in synthetic antiferromagnets with uniaxial anisotropy results in smooth and monotonous dispersion relation around Gamma point, where the direction of the phase velocity is reversed, while the group velocity direction is conserved. The experimental observation of this phenomenon by intensity-, phase-, and time-resolved Brillouin light scattering microscopy is corroborated by analytical models and micromagnetic simulations.
Accelerating 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, Matias
By 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
Singular 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 García
Narrow 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.
Fundamental Limit of Plasmonic Cathodoluminescence
(American Chemical Society, 2021-01-13) Schmidt, Franz; Losquin, Arthur; Horák, Michal; Hohenester, Ulrich; Stöger-Pollach, Michael; Krenn, Joachim
We use cathodoluminescence (CL) spectroscopy in a transmission electron microscope to probe the radial breathing mode of plasmonic silver nanodisks. A two-mirror detection system sandwiching the sample collects the CL emission in both directions, that is, backward and forward with respect to the electron beam trajectory. We unambiguously identify a spectral shift of about 8 nm in the CL spectra acquired from both sides and show that this asymmetry is induced by the electron beam itself. By numerical simulations, we confirm the observations and identify the underlying physical effect due to the interference of the CL emission patterns of an electron-beam-induced dipole and the breathing mode. This effect can ultimately limit the achievable fidelity in CL measurements on any system involving multiple excitations and should therefore be considered with care in high-precision experiments.
Electron beam directed etching of hexagonal boron nitride
(Royal Society of Chemistry, 2016-09-28) Elbadawi, Christopher; Tran, Trong Toan; Kolíbal, Miroslav; Šikola, Tomáš; Scott, John; Cai, Qiran; Li, Lu Hua; Taniguchi, Takashi; Watanabe, Kenji; Toth, Milos; Aharonovich, Igor; Lobo, Charlene
Hexagonal boron nitride (hBN) is a wide bandgap van der Waals material with unique optical properties that make it attractive for two dimensional (2D) photonic and optoelectronic devices. However, broad deployment and exploitation of hBN is limited by alack of suitable material and device processing and nano prototyping techniques. Here we present a high resolution, single step electron beam technique for chemical dry etching of hBN. Etching is achieved using H2O as a precursor gas, at both room temperature and elevated hBN temperatures. The technique enables damage-free, nano scale, iterative patterning of supported and suspended 2D hBN, thus opening the door to facile fabrication of hBN-based 2D heterostructures and devices.

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