Centrum pre Nanodiagnostiku Materiálov

K. Smyrnova, M. Sahul, M Haršáni, Ľ. Čaplovič, V. Beresnev, Mária Čaplovičová, M. Kusy and A. Pogrebnjak

In: J. Phys.: Conf. Ser. 2712 012014, 2024

https://doi.org/10.1088/1742-6596/2712/1/012014

Abstract

In this work, WN/NbN nanolaminate coatings were synthesized by cathodic-arc physical vapor deposition (CA-PVD) technique on a stainless-steel substrate. The paper reports the microstructure, cross-sectional morphology, surface roughness, and adhesion strength changes caused by variations in the absolute values of the negative substrate bias voltage, U_s, in the 50-200 V range. Synthesized coatings were analyzed by Grazing incidence X-ray diffraction (GI-XRD), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), and Daimler-Benz test. The phase analysis revealed that multilayer coatings had complex polycrystalline microstructure. They consisted of face-cantered cubic (fcc) β-W₂N, fcc δ-NbN, and hexagonal ε-NbN phases. The total thickness and surface roughness had a descending trend with an increase in the absolute value of the negative bias voltage. Moreover, the WN/NbN coating deposited at U_s = -50 V demonstrated the best adhesion strength to the substrate, suitable for protective coatings.

Martin Škrátek, Mária Čaplovičová, Ľubomír Čaplovič, Patrícia Petrisková, Erik Šimon, Erik Rakovský, Peter Billik

In: Materials Letters. Vol. 348, (2023)

https://doi.org/10.1016/j.matlet.2023.134680

Abstract

Our work focuses on the preparation of nanocrystalline Ag₂O (n-Ag₂O) by mechanochemical decomposition (MCD) of a paramagnetic compound of an empirical formula Ag₇O₈NO₃. Electrochemically prepared millimetre-long needles of Ag₇O₈NO₃ were high-energy ball milled (HEM) for 1 min, 3 min and 5 min. A gradual decomposition of Ag₇O₈NO₃ to n-Ag₂O and AgNO₃ was observed. Ag₂O nanocrystals form in an aggregated and spherical morphology with crystallite sizes ranging from ∼10 – 30 nm. n-Ag₂O displayed weak ferromagnetism with the saturation magnetisation of 5×10^–3 emu/g. The MCD of Ag₇O₈NO₃ can be estimated as follows: 2Ag₇O₈NO₃ → 6Ag₂O + 2AgNO₃ + 5O_2.

Edgaras Markauskas,  Laimis Zubauskas, Arnas Naujokaitis, Bronislovas Čechavičius, Martynas Talaikis, Gediminas Niaura, Mária Čaplovičová, Viliam Vretenár, Tadas Paulauskas

In: Journal of Applied Physics. Vol. 133, iss. 23 (2023)

https://doi.org/10.1063/5.0152173

Abstract

Water-assisted ultrashort laser pulse processing of semiconductor materials is a promising technique to diminish heat accumulation and improve process quality. In this study, we investigate femtosecond laser ablation of deep trenches in GaAs, an important optoelectronic material, using water and ambient air environments at different laser processing regimes. We perform a comprehensive analysis of ablated trenches, including surface morphological analysis, atomic-resolution transmission electron microscopy imaging, elemental mapping, photoluminescence, and Raman spectroscopy. The findings demonstrate that GaAs ablation efficiency is enhanced in a water environment while heat-accumulation-related damage is reduced. Raman spectroscopy reveals a decrease in the broad feature associated with amorphous GaAs surface layers during water-assisted laser processing, suggesting that a higher material quality in deep trenches can be achieved using a water environment.

GERULOVÁ, Kristína – KUCMANOVÁ, Alexandra – SANNY, Zuzana – GARAIOVÁ, Zuzana – SEILER, Eugen – ČAPLOVIČOVÁ, Mária – ČAPLOVIČ, Ľubomír – PALCUT, Marián

In Nanomaterials. Vol. 12, iss. 11 (2022)

https://doi.org/10.3390/nano12111786

Abstract

Magnetic separation of microalgae using magnetite is a promising harvesting method as it is fast, reliable, low cost, energy-efficient, and environmentally friendly. In the present work, magnetic harvesting of three green algae (Chlorella vulgaris, Chlorella ellipsoidea, and Auxenochlorella protothecoides) and one cyanobacteria (Microcystis aeruginosa) has been studied. The biomass was flushed with clean air using a 0.22 μm filter and fed CO₂ for accelerated growth and faster reach of the exponential growth phase. The microalgae were harvested with magnetite nanoparticles. The nanoparticles were prepared by controlled co-precipitation of Fe²⁺ and Fe³⁺ cations in ammonia at room temperature. Subsequently, the prepared Fe₃O₄ nanoparticles were coated with polyethyleneimine (PEI). The prepared materials were characterized by high-resolution transmission electron microscopy, X-ray diffraction, magnetometry, and zeta potential measurements. The prepared nanomaterials were used for magnetic harvesting of microalgae. The highest harvesting efficiencies were found for PEI-coated Fe₃O₄. The efficiency was pH-dependent. Higher harvesting efficiencies, up to 99%, were obtained in acidic solutions. The results show that magnetic harvesting can be significantly enhanced by PEI coating, as it increases the positive electrical charge of the nanoparticles. Most importantly, the flocculants can be prepared at room temperature, thereby reducing the production costs.

BAKARDJIEVA, Snejana – MAREŠ, Jakub – KOCI, Eva – TOLASZ, Jakub – FAJGAR, Radek – RYUKHTIN, Vasyl – KLEMENTOVÁ, Mariana – MICHNA, Štefan – BIBOVÁ, Hana – HOLMESTAD, Randi – TITORENKOVA, Rositsa – ČAPLOVIČOVÁ Mária

In Nanomaterials. Vol. 12, iss. 5 (2022)

https://doi.org/10.3390/nano12050750

Abstract

Ag-decorated TiO₂ nanostructured materials are promising photocatalysts. We used non-standard cryo-lyophilization and ArF laser ablation methods to produce TiO₂ nanosheets and TiO₂ nanostructured thin films decorated with Ag nanoparticles. Both methods have a common advantage in that they provide a single multiply twinned Ag⁽⁰⁾ characterized by {111} twin boundaries. Advanced microscopy techniques and electron diffraction patterns revealed the formation of multiply twinned Ag⁽⁰⁾ structures at elevated temperatures (500 °C and 800 °C). The photocatalytic activity was demonstrated by the efficient degradation of 4-chlorophenol and Total Organic Carbon removal using Ag-TiO₂ nanosheets, because the multiply twinned Ag⁽⁰⁾ served as an immobilized photocatalytically active center. Ag-TiO₂ nanostructured thin films decorated with multiply twinned Ag⁽⁰⁾ achieved improved photoelectrochemical water splitting due to the additional induction of a plasmonic effect. The photocatalytic properties of TiO₂ nanosheets and TiO₂ nanostructured thin films were correlated with the presence of defect-twinned structures formed from Ag⁽⁰⁾ nanoparticles with a narrow size distribution, tuned to between 10 and 20 nm. This work opens up new possibilities for understanding the defects generated in Ag-TiO₂ nanostructured materials and paves the way for connecting their morphology with their photocatalytic activity.