Plazmové technologie pro materiály

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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.
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.
Enhanced Adhesion of Electrospun Polycaprolactone Nanofibers to Plasma-Modified Polypropylene Fabric
(MDPI, 2023-03-28) Janů, Lucie; Dvořáková, Eva; Polášková, Kateřina; Buchtelová, Martina; Ryšánek, Petr; Chlup, Zdeněk; Kruml, Tomáš; Galmiz, Oleksandr; Nečas, David; Zajíčková, Lenka
Excellent adhesion of electrospun nanofiber (NF) to textile support is crucial for a broad range of their bioapplications, e.g., wound dressing development. We compared the effect of several low- and atmospheric pressure plasma modifications on the adhesion between two parts of composite-polycaprolactone (PCL) nanofibrous mat (functional part) and polypropylene (PP) spunbond fabric (support). The support fabrics were modified before electrospinning by low-pressure plasma oxygen treatment or amine plasma polymer thin film or treated by atmospheric pressure plasma slit jet (PSJ) in argon or argon/nitrogen. The adhesion was evaluated by tensile test and loop test adapted for thin NF mat measurement and the trends obtained by both tests largely agreed. Although all modifications improved the adhesion significantly (at least twice for PSJ treatments), low-pressure oxygen treatment showed to be the most effective as it strengthened adhesion by a factor of six. The adhesion improvement was ascribed to the synergic effect of high treatment homogeneity with the right ratio of surface functional groups and sufficient wettability. The low-pressure modified fabric also stayed long-term hydrophilic (ten months), even though surfaces usually return to a non-wettable state (hydrophobic recovery). In contrast to XPS, highly surface-sensitive water contact angle measurement proved suitable for monitoring subtle surface changes.
Depth profiling of thin plasma-polymerized amine films using GDOES in an Ar-O-2 plasma
(ELSEVIER, 2022-04-15) Kovač, Janez; Ekar, Jernej; Čekada, Miha; Zajíčková, Lenka; Nečas, David; Janů, Lucie; Wang, Jiang Yong; Mozetič, Miran
Thin polymer films were deposited on polished stainless-steel samples by PECVD from a cyclopropylamine precursor and characterized by X-ray photoelectron spectroscopy, secondary-ion mass spectrometry and glow discharge optical emission spectroscopy (GDOES) depth profiling. These depth profiles exhibited reasonable agreement. The GDOES involved the erosion of the polymer films in plasma sustained by an asymmetric RF capacitively coupled discharge using both Ar and Ar-O-2 gases. The application of pure Ar caused unwanted effects, such as the broadening of the polymer-film/substrate interface, which were suppressed when using the mixture with oxygen. Another benefit of oxygen was a significant increase in the etching rate by a factor of about 15 as compared to pure argon. The mechanisms involved in the depth profiling using the mixture of gases were elaborated in some detail, taking into account plasma parameters typical for an asymmetric, capacitively coupled RF discharge in a small volume. The main benefit of using the Ar/O-2 GDOES profiling with respect to XPS and SIMS depth profiling is the increased sputtering rate for polymer films. Comparing the GDOES depth profiling with the Ar/O-2 mixture with profiling in pure Ar, the benefits are a higher sputtering rate and better depth resolution at the polymer/substrate interface.
Biodegradable Nanohybrid Materials as Candidates for Self-Sanitizing Filters Aimed at Protection from SARS-CoV-2 in Public Areas
(MDPI, 2022-02-01) Manakhov, Anton; Permyakova, Elizaveta; Sitnikova, Natalya A.; Tsygankova, Alphiya R.; Alekseev, Alexander Yu.; Solomatina, Mariia; Baidyshev, Victor S.; Popov, Zakhar; Janů, Lucie; Eliáš, Marek; Zajíčková, Lenka; Kovalskii, Andrey; Sheveyko, A.N.; Kiryukhantsev-Korneev, Philip; Shtansky, Dmitry V.; Nečas, David; Solovieva, Anastasiya
The COVID-19 pandemic has raised the problem of efficient, low-cost materials enabling the effective protection of people from viruses transmitted through the air or via surfaces. Nanofibers can be a great candidate for efficient air filtration due to their structure, although they cannot protect from viruses. In this work, we prepared a wide range of nanofibrous biodegradable samples containing Ag (up to 0.6 at.%) and Cu (up to 20.4 at.%) exhibiting various wettability. By adjusting the magnetron current (0.3 A) and implanter voltage (5 kV), the deposition of TiO2 and Ag+ implantation into PCL/PEO nanofibers was optimized in order to achieve implantation of Ag+ without damaging the nanofibrous structure of the PCL/PEO. The optimal conditions to implant silver were achieved for the PCL-Ti0.3-Ag-5kV sample. The coating of PCL nanofibers by a Cu layer was successfully realized by magnetron sputtering. The antiviral activity evaluated by widely used methodology involving the cultivation of VeroE6 cells was the highest for PCL-Cu and PCL-COOH, where the VeroE6 viability was 73.1 and 68.1%, respectively, which is significantly higher compared to SARS-CoV-2 samples without self-sanitizing (42.8%). Interestingly, the samples with implanted silver and TiO2 exhibited no antiviral effect. This difference between Cu and Ag containing nanofibers might be related to the different concentrations of ions released from the samples: 80 mu g/L/day for Cu2+ versus 15 mu g/L/day for Ag+. The high antiviral activity of PCL-Cu opens up an exciting opportunity to prepare low-cost self-sanitizing surfaces for anti-SARS-CoV-2 protection and can be essential for air filtration application and facemasks. The rough cost estimation for the production of a biodegradable nanohybrid PCL-Cu facemask revealed $0.28/piece, and the business case for the production of these facemasks would be highly positive, with an Internal Rate of Return of 34%.

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