Ústav fyzikálního inženýrství

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Engineering of Active and Passive Loss in High-Quality-Factor Vanadium Dioxide-Based BIC Metasurfaces
(AMER CHEMICAL SOC, 2024-08-27) Aigner, Andreas; Ligmajer, Filip; Rovenská, Katarína; Holobrádek, Jakub; Idesová, Beáta; Maier, Stefan A.; Tittl, Andreas; Menezes, Leonardo de S.
Active functionalities of metasurfaces are of growing interest in nanophotonics. The main strategy employed to date is spectral resonance tuning affecting predominantly the far-field response. However, this barely influences other essential resonance properties like near-field enhancement, signal modulation, quality factor, and absorbance, which are all vital for numerous applications. Here we introduce an active metasurface approach that combines temperature-tunable losses in vanadium dioxide with far-field coupling tunable symmetry-protected bound states in the continuum. This method enables exceptional precision in independently controlling both radiative and nonradiative losses. Consequently, it allows for the adjustment of both the far-field response and, notably, the near-field characteristics like local field enhancement and absorbance. We experimentally demonstrate continuous tuning from under- through critical- to overcoupling, achieving quality factors of 200 and a relative switching contrast of 78%. Our research marks a significant step toward highly tunable metasurfaces, controlling both near- and far-field properties.
Influence of Deposition Parameters on the Plasmonic Properties of Gold Nanoantennas Fabricated by Focused Ion Beam Lithography
(AMER CHEMICAL SOC, 2024-08-20) Foltýn, Michael; Patočka, Marek; Řepa, Rostislav; Šikola, Tomáš; Horák, Michal
The behavior of plasmonic antennas is influenced by a variety of factors, including their size, shape, and material. Even minor changes in the deposition parameters during the thin film preparation process may have a significant impact on the dielectric function of the film, and thus on the plasmonic properties of the resulting antenna. In this work, we deposited gold thin films with thicknesses of 20, 30, and 40 nm at various deposition rates using an ion-beam-assisted deposition. We evaluate their morphology and crystallography by atomic force microscopy, X-ray diffraction, and transmission electron microscopy. Next, we examined the ease of fabricating plasmonic antennas using focused-ion-beam lithography. Finally, we evaluate their plasmonic properties by electron energy loss spectroscopy measurements of individual antennas. Our results show that the optimal gold thin film for plasmonic antenna fabrication of a thickness of 20 and 30 nm should be deposited at the deposition rate of around 0.1 nm/s. The thicker 40 nm film should be deposited at a higher deposition rate like 0.3 nm/s.
Late Ordovician scolecodonts and chitinozoans from the Pin Valley in Spiti, Himachal Pradesh, northern India
(Instytut Paleobiologii PAN, 2024-05-08) Tonarová, Petra; Suttner, Thomas J.; Hints, Olle; Liang, Yan; Zemek, Marek; Kubajko, Michal; Zikmund, Tomáš; Kaiser, Jozef; Kido, Erika
The end of the Ordovician witnessed major perturbations in the ecosystem, seriously affecting global marine biodiversity. Nevertheless, some marine organism groups and their crisis-bound palaeogeographic distribution are still understudied. Among the outliers are eunicid polychaetes, even though they flourished and diversified extensively during the Ordovician. A collection of seven genera of jaw-bearing polychaetes, including the new ramphoprionid genus Spitiprion Tonarová, Suttner, & Hints, with type new species of Spitiprion khannai Tonarová, Suttner, & Hints, is described here from Katian (Upper Ordovician) deposits of Spiti, northern India. The new species is preserved as isolated maxillae and a jaw cluster, and 3D models of the maxillary apparatus are reconstructed based on submicron-CT. Along with the scolecodonts, a low-diversity assemblage of chitinozoans was recovered, comprising five genera. The most common chitinozoan species are Acanthochitina cf. cancellata and Spinachitina suecica.
Mechanism of WS₂ Nanotube Formation Revealed by in Situ/ex Situ Imaging
(AMER CHEMICAL SOC, 2024-05-03) Kundrát, Vojtěch; Novák, Libor; Bukvišová, Kristýna; Zálešák, Jakub; Kolíbalová, Eva; Rosentveig, Rita; Sreedhara, M.B.; Shalom, Hila; Yadgarov, Lena; Zak, Alla; Kolíbal, Miroslav; Tenne, Reshef
Multiwall WS2 nanotubes have been synthesized from W18O49 nanowhiskers in substantial amounts for more than a decade. The established growth model is based on the "surface-inward" mechanism, whereby the high-temperature reaction with H2S starts on the nanowhisker surface, and the oxide-to-sulfide conversion progresses inward until hollow-core multiwall WS2 nanotubes are obtained. In the present work, an upgraded in situ SEM mu Reactor with H-2 and H2S sources has been conceived to study the growth mechanism in detail. A hitherto undescribed growth mechanism, named "receding oxide core", which complements the "surface-inward" model, is observed and kinetically evaluated. Initially, the nanowhisker is passivated by several WS2 layers via the surface-inward reaction. At this point, the diffusion of H2S through the already existing outer layers becomes exceedingly sluggish, and the surface-inward reaction is slowed down appreciably. Subsequently, the tungsten suboxide core is anisotropically volatilized within the core close to its tips. The oxide vapors within the core lead to its partial out-diffusion, partially forming a cavity that expands with reaction time. Additionally, the oxide vapors react with the internalized H2S gas, forming fresh WS2 layers in the cavity of the nascent nanotube. The rate of the receding oxide core mode increases with temperatures above 900 degrees C. The growth of nanotubes in the atmospheric pressure flow reactor is carried out as well, showing that the proposed growth model (receding oxide core) is also relevant under regular reaction parameters. The current study comprehensively explains the WS2 nanotube growth mechanism, combining the known model with contemporary insight.
Study of plasma activated water effect on heavy metal bioaccumulation by Cannabis sativa Using Laser-Induced Breakdown Spectroscopy
(Elsevier, 2024-09-15) Čechová, Ludmila; Holub, Daniel; Šimoníková, Lucie; Modlitbová, Pavlína; Novotný, Karel; Pořízka, Pavel; Kozáková, Zdenka; Krčma, František; Kaiser, Jozef
Contamination of the environment with toxic metals such as cadmium or lead is a worldwide issue. The accumulator of metals Cannabis sativa L. has potential to be utilized in phytoremediation, which is an environmentally friendly way of soil decontamination. Novel non-thermal plasma-based technologies may be a helpful tool in this process. Plasma activated water (PAW), prepared by contact of gaseous plasma with water, contains reactive oxygen and nitrogen species, which enhance the growth of plants. In this study, C. sativa was grown in a short-term toxicity test in a medium which consisted of plasma activated water prepared by dielectric barrier discharge with liquid electrode and different concentrations of cadmium or lead. Application of PAW on heavy metal contaminated C. sativa resulted in increased growth under Pb contamination as was determined by ecotoxicology tests. Furthermore, the PAW influence on the bioaccumulation of these metals as well as the influence on the nutrient composition of plants was studied primarily by applying Laser-induced breakdown spectroscopy (LIBS). The LIBS elemental maps show that C. sativa accumulates heavy metals mainly in the roots. The results present a new proof-of-concept in which PAW could be used to improve the growth of plants in heavy metal contaminated environment, while LIBS can be implemented to study the phytoremediation efficiency.

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