Centrum pre nanodiagnostiku materiálov

MOTOLA, Martin – ČAPLOVIČOVÁ, Mária – KRBAL, Miloš – SOPHA, Hannah – THIRUNAVUKKARASU,  Guru Karthikeyan – GREGOR, Maroš – PLESCH, Gustáv – MACAK, Jan M.

In Electrochimica Acta. Vol. 331, (2020)

https://doi.org/10.1016/j.electacta.2019.135374

Abstract

In this work, a two-step treatment of TiO₂ nanotube (TNT) layers towards enhanced photocatalytic performance is presented. TNT layers with a thickness of ∼7 μm and an average inner diameter of ∼190 nm were prepared via electrochemical anodization of Ti foil in a fluoride containing ethylene glycol-based electrolyte. To improve the photocatalytic activity of the produced TNT layers a two-step post-treatment was conducted. First, the inner shell of the native double-wall TNT layers was removed via a mild pre-annealing followed by a selective etching treatment of the inner shell in piranha solution yielding single-wall TNT layers. Second, reduction via annealing in H₂/Ar atmosphere was performed. The resulting Ti³⁺ doped single-wall TNT layers possess 100% enhancement of photocatalytic activity compared to their non-treated counterparts.

SOJKOVÁ, Michaela – VÉGSÖ, Karol – MRKYVKOVA, Naďa – HAGARA, Jakub – HUTÁR, Peter – ROSOVÁ, Alica – ČAPLOVIČOVÁ, Mária – LUDACKÁ, Uršula – SKÁKALOVÁ, Viera – MAJKOVÁ, Eva – ŠIFFALOVIČ, Peter – HULMAN, Martin

In RSC Advances. Vol. 9, iss. 51 (2019)

https://doi.org/10.1039/C9RA06770A

Abstract

Few-layer MoS₂ films are promising candidates for applications in numerous areas, such as photovoltaics, photocatalysis, nanotribology, lithium batteries, hydro-desulfurization catalysis and dry lubricants, especially due to their distinctive electronic, optical, and catalytic properties. In general, two alignments of MoS₂ layers are possible – the horizontal and the vertical one, having different physicochemical properties. Layers of both orientations are conventionally fabricated by a sulfurization of pre-deposited Mo films. So far, the Mo thickness was considered as a critical parameter influencing the final orientation of MoS₂ layers with horizontally and vertically aligned MoS₂ grown from thin (1 nm) and thick (3 nm) Mo films, respectively. Here, we present a fabrication protocol enabling the growth of horizontally or vertically aligned few-layer MoS₂ films utilizing the same Mo thickness of 3 nm. We show that the sulfur vapor is another parameter influencing the growth mechanism, where a sulfurization with higher sulfur vapor pressure leads to vertical MoS₂ layers and slow sulfur evaporation results in horizontally aligned layers for a thicker Mo starting layer.

Bakardjieva, S., Caplovicova, M., Mamon, F., Fajgar, R., Jandova, V., & Brovdyova, T.

In Microscopy and Microanalysis. Vol. 25, Suppl. 2 (2019)

https://doi.org/10.1017/S1431927619011413

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.

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

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

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.