Centrum pre Nanodiagnostiku Materiálov

ROCH, Tomáš – GREGOR, Maroš – ŠVEC, Peter, Jr. – PLECENÍK, Tomáš – SATRAPINSKYY, Leonid – ČAPLOVIČOVÁ, Mária – BYSTRICKÝ, Roman – KÚŠ, Peter – PLECENÍK, Andrej

In Applied Surface Science. Vol. 461, (2018)

https://doi.org/10.1016/j.apsusc.2018.05.038

Abstract

Superconducting MgB₂ thin films were fabricated on c-cut sapphire substrates by vacuum co-evaporation of magnesium and boron followed by an ex situ post-annealing. We show that annealing in oxygen atmosphere can significantly improve the superconducting properties of the MgB₂ thin films compared to the typical annealing in argon atmosphere. In this work, influence of the ex-situ annealing atmosphere on the structure, texture and morphology of the superconducting MgB₂ thin films has been studied by transmission electron microscopy, X-ray diffraction and pole figure measurements. Samples annealed at 800 °C in Ar, at 800 °C in O₂ and at 500 °C in O₂ have been compared. The annealing in O₂ at 800 °C produces MgB₂ thin films with the highest superconducting transition temperature and critical current density. We show that this is thanks to the thickest MgO layer at the surface produced in this case, which acts as a protecting barrier against out-diffusion of Mg during the annealing and leads to better stoichiometry and larger MgB₂ grains compared to the samples annealed in Ar. Our method can be alternative to the customary ex-situ post annealing of Mg-B precursor in sealed vapor cell. In all samples, the MgB₂ phase showed single axis texture with the (0 0 0 1) planes slightly inclined by 0° to 15° with respect to the Al₂O₃(0 0 0 1) substrate surface incurred with the initial precursor evaporation geometry. During the annealing, the excess Mg also reacts with the Al₂O₃ substrate and minor MgAl₂O₄ and MgO phases are produced at the substrate-layer interface.

NÝBLOVÁ, Daniela – BILLIK, Peter – NOGA, Jozef – ŠIMON, Erik – BYSTRICKÝ, Roman – ČAPLOVIČOVÁ, Mária – NOSKO, Martin

In JOM. Vol. 70, iss. 10 (2018)

https://doi.org/10.1007/s11837-018-3053-3

Abstract

The degradation of Al₄C₃ was investigated by exposing powder samples to atmospheric humidity at laboratory temperature for 150 days. Samples were monitored using powder x-ray diffraction analysis, scanning and transmission electron microscopy, thermal analysis, and energy-dispersive x-ray spectroscopy. Initially, the degradation resulted in an amorphous Al–O–OH network, which gradually recrystallized as low-crystalline boehmite (γ-AlOOH), and, later, partially, as Al(OH)₃. Low-crystalline γ-AlOOH consisted of plate-like particles with diameter of 5 µm to 40 µm. The 020 diffraction position of γ-AlOOH was close to that of well-crystalline γ-AlOOH, which may be explained by accumulation of compressive stress along the b-axis of the γ-AlOOH structure.

DUTKOVÁ, Erika – ČAPLOVIČOVÁ, Mária – ŠKORVÁNEK, Ivan – BALÁŽ, Matej – ZORKOVSKÁ, Anna – BALÁŽ, Peter – ČAPLOVIČ, Ľubomír

In Journal of Alloys and Compounds. Vol. 745, (2018)

https://doi.org/10.1016/j.jallcom.2018.02.245

Abstract

In this study, the mechanochemical synthesis of Co₉S₈ nanoparticles from cobalt and sulphur by high-energy milling in a planetary mill in an argon atmosphere is reported. Structural characterization of the synthesized nanoparticles by XRD was performed. Co₉S₈ nanoparticles crystallize in the cubic structure with the crystallite size of about 16 nm. The microstructure of the Co₉S₈ nanoparticles was further studied using TEM, HRTEM and EDS-HAADF-STEM techniques. Co₉S₈ nanoparticles consist of nanocrystals exhibiting size in the range of 10–30 nm that are densely aggregated into spherical-like objects. The highest specific surface area value observed was 4 m²g^-1 and the pore properties of this sample are quite poor. The magnetic properties of mechanochemically synthesized nanoparticles were investigated using SQUID magnetometer. The room temperature magnetic data supported the paramagnetic spin structure of Co₉S₈ nanoparticles. The transition from paramagnetic to weak ferromagnetic or ferrimagnetic behaviour was indicated from temperature dependence of magnetization at cryogenic temperatures. It is demonstrated that mechanochemical synthesis can be successfully employed in the one-step solid-state preparation of Co₉S₈ nanoparticles.

BODIK, Michal – ŠIFFALOVIČ, Peter – NÁDAŽDY, Peter – BENKOVIČOVÁ, Monika – MARKOVIČ, Zoran – CHLPÍK, Juraj – CIRÁK, Július – KOTLÁR, Mário – MICUŠÍK, M. – JERGEL, Matej – MAJKOVÁ, Eva

In Diamond and Related Materials. Vol. 83, (2018)

https://doi.org/10.1016/j.diamond.2018.02.011

Abstract

In this work, we present a study of the Langmuir film formation composed of hydrophobic carbon quantum dots (hCQDs). We studied the kinetics of hCQDs pyrolysis and optimized the reaction time for maximum photoluminescence. The resulting hCQDs were analyzed by transmission electron microscopy, X-ray photoemission spectroscopy and grazing-incidence X-ray diffraction. The process of monolayer formation was studied by monitoring surface pressure, surface potential, elastic modulus and Brewster angle microscopy in real time under continuous compression conditions. The monolayer transferred onto a silicon wafer was examined on the nano- and micro-scales by means of atomic force microscopy and confocal fluorescence microscopy, respectively.

STANKOVIČ, Nenad K – BODIK, Michal – ŠIFFALOVIČ, Peter – KOTLÁR, Mário – MICUŠÍK, M. – ŠPITÁLSKY, Zdenko – DANKO, Martin – MILIVOJEVIČ, Dušan D. – KLEINOVÁ, Angela – KULBAT, Pavel – CAPÁKOVÁ, Zdenka – HUMPOLIČEK, Petr – LEHOCKY, Marian – MARKOVIČ, Biljana – MARKOVIČ, Zoran

In ACS Sustainable Chemistry and Engineering. Vol. 6, iss. 3 (2018)

https://doi.org/10.1021/acssuschemeng.7b04566

Abstract

Inimitable properties of carbon quantum dots as well as a cheap production contribute to their possible application in biomedicine especially as antibacterial and antibiofouling coatings. Fluorescent hydrophobic carbon quantum dots are synthesized by bottom-up condensation method and used for deposition of uniform and homogeneous Langmuir–Blodgett thin films on different substrates. It is found that this kind of quantum dots generates singlet oxygen under blue light irradiation. Antibacterial and antibiofouling testing on four different bacteria strains (Escherichia coli, Staphylococcus aureus, Bacillus cereus, and Pseudomonas aeruginosa) reveals enhanced antibacterial and antibiofouling activity of hydrophobic carbon dots thin films under blue light irradiation. Moreover, hydrophobic quantum dots show noncytotoxic effect on mouse fibroblast cell line. These properties enable potential usage of hydrophobic carbon quantum dots thin films as excellent antibacterial and antibiofouling coatings for different biomedical applications.