Plazmové technologie pro materiály

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Elementary models of low-pressure plasma polymerisation into nanofibrous mats
(2025-05-01) Nečas, David
Deposition penetration depth into nanofibrous materials is a crucial but underexplored parameter for their modification using low-pressure plasma polymerisation. This work studies it using Monte Carlo simulations and two analytical approaches, a classic continuum diffusion model and a new abstract discrete model, which is fully solvable using the method of generating functions. The discrete model represents the material as a stack of cells with no further geometry and is only characterised by the sticking coefficient eta of film-forming species. The models are used to investigate other properties, such as directional coverage of fibres by the deposited film, anisotropy of the mean free path in the nanofibrous material, or the effective sticking coefficient of the material as a whole. The two very different analytical approaches are found to complement each other. When the derived expressions are compared with Monte Carlo results, we find that the discrete model can provide surprisingly relevant formulae despite the very high level of abstraction. The clearest example is the sticking coefficients of the material as a whole, for which the discrete model achieves almost perfect agreement. The other two properties require dimensional scaling factors. It shows that certain aspects of the process are fundamental and mostly independent on details of the interactions and that the dependencies on the sticking coefficient are in some sense separable. By combining the analytical and Monte Carlo results we can also obtain elementary practical formulae for the studied quantities as functions of the sticking coefficient and/or porosity. They are directly applicable to the deep penetration of low-eta species or deposition of thin coatings and can be used as local description in more complex 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.
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.
Comparing efficiencies of polypropylene treatment by atmospheric pressure plasma jets
(WILEY-V C H VERLAG GMBH, 2023-07-11) Polášková, Kateřina; Ozkan, Alp; Klíma, Miloš; Jeníková, Zdeňka; Buddhadasa, Madhuwanthi; Reniers, François; Zajíčková, Lenka
Plasma treatment of polypropylene (PP) is a well-established method of improving its surface properties. However, the efficiencies of different plasma discharges are seldom compared. Herein, we discuss the differences in PP treated by three arc-based commercial plasma jets working in dry air, Plasmatreat rotating plasma jet (PT-RPJ), AFS PlasmaJet & REG; (AFS-PJ), and SurfaceTreat gliding arc jet (ST-GA), and by the low-temperature RF plasma slit jet (RF-PSJ) working in argon. The AFS-PJ has a significantly different reactive species composition dominated by nitrogen oxides. It induced higher thermal loads leading to surface damage. The other arc-based jets (PT-RPJ and ST-GA) created the PP surface with higher oxygen and nitrogen concentration than the low-temperature RF-PSJ. It induced a higher adhesion strength measured on PP-aluminum joints.
Possible charge ordering and anomalous transport in graphene/graphene quantum dot heterostructure
(IOP Publishing Ltd, 2024-06-03) Roy, Rajarshi; Holec, David; Michal, Lukáš; Hemzal, Dušan; Sarkar, Saikat; Kumar, Gundam Sandeep; Nečas, David; Dhankhar, Meena; Kaushik, Preeti; Gomez Perez, Inmaculada Jennifer; Zajíčková, Lenka
Observations of superconductivity and charge density waves (CDW) in graphene have been elusive thus far due to weak electron-phonon coupling (EPC) interactions. Here, we report a unique observation of anomalous transport and multiple charge ordering phases at high temperatures ( T 1 similar to 213 K , T 2 similar to 325 K ) in a 0D-2D van der Waals (vdW) heterostructure comprising of single layer graphene (SLG) and functionalized (amine) graphene quantum dots (GQD). The presence of functionalized GQD contributed to charge transfer with shifting of the Dirac point similar to 0.05 eV above the Fermi level (ab initio simulations) and carrier density n similar to - 0.3 x 10 12 cm - 2 confirming p-doping in SLG and two-fold increase in EPC interaction was achieved. Moreover, we elucidate the interplay between electron-electron and electron-phonon interactions to substantiate high temperature EPC driven charge ordering in the heterostructure through analyses of magnetotransport and weak anti-localization (WAL) framework. Our results provide impetus to investigate strongly correlated phenomena such as CDW and superconducting phase transitions in novel graphene based heterostructures.

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