Plazmové technologie pro materiály

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    Polymerization mechanisms of hexamethyldisiloxane in low-pressure plasmas involving complex geometries
    (ELSEVIER, 2024-02-01) Navascues, Paula; Janůšová, Martina; Zajíčková, Lenka; Rupper, Patrick; Hegemann, Dirk
    Hexamethyldisiloxane (HMDSO) low-pressure plasmas are known for their versatility in the deposition of plasma polymer films (PPFs) with different properties and applications. Although they have been studied for decades, the reaction mechanisms of plasma polymer formation leave open questions, particularly when deposition on 3D materials with complex geometries such as cavities and undercuts is considered. In the present study, two configurations named "cavity" and "undercut" have been selected to study the influence of diffusion of film forming species and surface reactivity in HMDSO plasmas without and with O2 admixture. A varying spatial chemical composition of the plasma polymer deposit along the penetration depth of the studied configurations indicates different sticking probabilities of the film-forming species. Furthermore, although ion-induced effects are usually only considered for direct plasma exposure, the obtained results and additional etching experiments reveal that the contribution of high-energy particles might still be considered underneath small openings. Finally, the relevance of oxidizing chemical reactions at the surface inside the configurations is clarified when O2 is added to the plasma.
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    Permanent Plasma Surface Functionalization of Internal Surface Areas
    (Wiley, 2025-04-01) Hegemann, Dirk; Janůšová, Martina; Navascues, Paula; Zajíčková, Lenka; Guex, Anne Géraldine
    Surface functionalization technologies of fibrous or porous materials are often considered relatively unstable with a shelf life of several weeks or months at most, evoked by heterogeneous treatment of their internal surface areas. Here, it is demonstrating that the fine balance of plasma etching, deposition, and oxidation involving different reactive species, strongly enhances penetration depth within complex structures. On this basis, capillary wicking is maintained over >10 years after plasma functionalization of a scaffold material used for biomedical engineering. Electrospun membranes of poly(epsilon-caprolactone) are coated with an oxygen-functional hydrocarbon layer, deposited in a competitive ablation and plasma polymerization process with CO2 and C2H4 as reactive gases. Chemical analysis immediately after coating, 9 months later, and after storing at ambient conditions for over 10 years, indicate a stable surface coating. Using defined geometries such as a cavity and an undercut, the underlying plasma interaction mechanisms are revealed, showing different synergies of energetic particles, depositing species with different surface reactivities, and oxidizing species. A concerted action of such species during plasma functionalization is key to enabling long-term wetting properties. This has a major implication for the surface functionalization of scaffolds, textiles, membranes, or foams used in diverse fields.
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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).
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    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.
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    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.