Plazmové technologie pro materiály

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Sample Thickness and Edge Proximity Influence Spatial Behavior of Filaments and Treatment Uniformity of RF Cold Atmospheric Pressure Plasma Jet
(SPRINGER, 2025-01-01) Polášková, Kateřina; Nečas, David; Dostál, Lukáš; Klíma, Miloš; Zajíčková, Lenka
The ability of atmospheric pressure plasma jets to treat complex non-planar surfaces is often cited as their advantage over other atmospheric plasmas. However, the effect of complex surfaces on plasma parameters and treatment efficiency has seldom been studied. Herein, we investigate the interaction of the atmospheric pressure plasma slit jet (PSJ) with block polypropylene samples of different thicknesses (5 and 30 mm) moving at two different speeds. Even though the distance between the slit outlet and the sample surface was kept constant, the treatment efficiency of PSJ ignited in the Ar and Ar/O2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {Ar/O}_2$$\end{document} gas feeds varied with the sample thickness due to the plasma parameters such as filament count and speed being affected by the different distances of the ground (the closer the ground is, the higher the discharge electric field). On the other hand, the Ar/N2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {Ar/N}_2$$\end{document} PSJ diffuse plasma plumes were less affected by the changes in the electric field, and the treatment efficiency was the same for both sample thicknesses. Additionally, we observed a difference in the efficiency and uniformity of the PSJ treatment of the edges and the central areas in some working conditions. The treatment efficiency near the edges depended on the duration of the filament contact, i. e., how long the local electric field trapped the filaments. Conversely, the treatment uniformity near the edges and in the central areas was different if the number of filaments changed rapidly as the discharge moved on and off the sample (the 5 mm samples treated by easily sustained Ar PSJ).
Stitching accuracy in large area scanning probe microscopy
(IOP Publishing Ltd, 2024-10-04) Klapetek, Petr; Nečas, David; Heaps, Edward; Sauvet, Bruno; Klapetek, Vojtěch; Valtr, Miroslav; Korpelainen, Virpi; Yacoot, Andrew
Image stitching is a technique that can significantly enlarge the scan area of scanning probe microscope (SPM) images. It is also the most commonly used method to cover large areas in high-speed SPM. In this paper, we provide details on stitching algorithms developed specifically to mitigate the effects of SPM error sources, namely the presence of scanner non-flatness. Using both synthetic data and flat samples we analyse the potential uncertainty contributions related to stitching, showing that the drift and line mismatch are the dominant sources of uncertainty. We also present the 'flatten base' algorithm that can significantly improve the stitched data results, at the cost of losing the large area form information about the sample.
Self-consistent autocorrelation for finite-area bias correction in roughness measurement
(IOP Publishing Ltd, 2024-06-01) Nečas, David
Scan line levelling, a ubiquitous and often necessary step in AFM data processing, can cause a severe bias on measured roughness parameters such as mean square roughness or correlation length. Although bias estimates have been formulated, they aimed mainly at assessing the severity of the problem for individual measurements. Practical bias correction methods are still missing. This work exploits the observation that the bias of autocorrelation function (ACF) can be expressed in terms of the function itself, permitting a self-consistent formulation. From this two correction approaches are developed, both with the aim to obtain convenient formulae which can be easily applied in practice. The first modifies standard analytical models of ACF to incorporate, in expectation, the bias and thus actually match the data the models are used to fit. The second inverts the relation between true and estimated ACF to realise a model-free correction. Both are tested using simulated and experimental data and found effective, reducing the total error of roughness parameters several times in the typical cases.
Multifunctional graphene quantum dots: A therapeutic strategy for neurodegenerative diseases by regulating calcium influx, crossing the blood-brain barrier and inhibiting A-protein aggregation
(Elsevier, 2024-02-01) Gomez Perez, Inmaculada Jennifer; Křížková, Petra; Dolečková, Anna; Cardo, Lucia; Wetzl, Cecília; Pizúrová, Naděžda; Prato, Maurizio; Medalová, Jiřina; Zajíčková, Lenka
Multifunctional nanoparticles could be the hallmark for the treatment of neurodegenerative diseases. Dissociation of protein aggregates causing neuronal damage and transfer of specific drugs which can downregulate neuronal excitotoxicity by inhibiting glutamatergic N-Methyl-D-Aspartate-receptors (NMDA) and then reducing calcium influx are among the main factors to consider for proper therapy. Here, we present a multiplatform based on nitrogen-doped graphene quantum dots (NGQDs) with such functionalities. The NGQDs were functionalized with Memantine, the clinically used drug, via covalent and non-covalent coupling, and we confirmed that the pharmaceutical activity was not altered. Apart from that, using xCELLigence technology and flow cytometric analysis of ABC transporter function, we uncovered that the ABC transporters of the blood-brain barrier (BBB) do not affect the ability of NGQD to cross BBB. Surprisingly, this study found that NGQDs have an inhibitory effect on NMDA receptors, thus supporting the action of Memantine. Moreover, NGQDs and their derivatives demonstrated the potential to dissociate beta-amyloid aggregates while possessing features suitable for bioimaging in various cell lines.
Electric field and higher harmonics of RF plasma slit jet measured by antennas and VI probes
(IOP Publishing, 2024-05-29) Polášková, Kateřina; Drexler, Petr; Klíma, Miloš; Macháč, Jan; Nečas, David; Švanda, Milan; Zajíčková, Lenka
The cold atmospheric plasma jets change their character when interacting with the different surfaces. Since such interaction is the primary area of plasma jet applications, it is essential to monitor the process. The non-linearity of the RF plasma slit jet (PSJ) was analyzed using the VI probes and a novel method, the non-intrusive antenna measurements. Regardless of the experimental setup and gas mixture (Ar, Ar/O2, Ar/N2), the PSJ frequency spectrum consisted of the following main features: dominant fundamental frequency peak, relatively strong odd harmonics, and significantly weaker even harmonics. The lowest degree of non-linearity was recorded for the Ar PSJ ignited against a grounded target. Admixing a molecular gas increased the discharge non-linearity. It was attributed to the enhancement of secondary electron emission from the dielectric surfaces. In addition to the non-linearity analysis, the antenna spectra were for the first time used to determine the semi-quantitative values of the PSJ-radiated electric field. The electric fields decreased by a factor of 2 after the admixing of nitrogen and oxygen molecular gases. Out of the studied targets, the highest electric fields were observed when plasma impinged on the grounded targets, followed by the floating target (2x lower) and the PSJ ignited in the open space configuration (4x lower than in the grounded target configuration).

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