Autor Mária Čaplovičová

Ni-mediated reactions in nanocrystalline diamond on Si substrates: the role of the oxide barrier

TULIČ, Semir – WAITZ, Thomas – ROMANYUK, Oleksandr – VARGA, Marián – ČAPLOVIČOVÁ, Mária – HABLER, Gerlinde – VRETENÁR, Viliam – KOTLÁR, Mário – KROMKA, Alexander – REZEK, Bohuslav – SKÁKALOVÁ, Viera

In RSC Advances. Vol. 10, iss. 14 (2020)

https://doi.org/10.1039/D0RA00809E

Abstract

Nanocrystalline diamond (NCD) films grown on Si substrates by microwave plasma enhanced chemical vapor deposition (MWPECVD) were subjected to Ni-mediated graphitization to cover them with a conductive layer. Results of transmission electron microscopy including electron energy-loss spectroscopy of cross-sectional samples demonstrate that the oxide layer on Si substrates (∼5 nm native SiO2) has been damaged by microwave plasma during the early stage of NCD growth. During the heat treatment for graphitizing the NCD layer, the permeability or absence of the oxide barrier allow Ni nanoparticles to diffuse into the Si substrate and cause additional solid-state reactions producing pyramidal crystals of NiSi2 and SiC nanocrystals. The latter are found impinged into the NiSi2 pyramids but only when the interfacial oxide layer is absent, replaced by amorphous SiC. The complex phase morphology of the samples is also reflected in the temperature dependence of electrical conductivity, where multiple pathways of the electronic transport dominate in different temperature regions. We present models explaining the observed cascade of solid-state reactions and resulting electronic transport properties of such heterostructures.

Ti3+ doped anodic single-wall TiO2 nanotubes as highly efficient photocatalyst

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.

Changes in microstructure of ledeburitic tool steel due to vacuum austenitizing and quenching, sub-zero treatments at – 140° and tempering

ĎURICA, Juraj – PTAČINOVÁ, Jana – DOMÁNKOVÁ, Mária – ČAPLOVIČ, Ľubomír – ČAPLOVIČOVÁ, Mária – HRUŠOVSKÁ, Linda – MALOVCOVÁ, Veronika – JURČI, Peter

In Vacuum. Vol. 170, (2019)

https://doi.org/10.1016/j.vacuum.2019.108977

Abstract

The microstructure of Vanadis 6 ledeburitic steel subjected to sub-zero treatments at −140 °C for different durations followed by various tempering regimes was investigated. The obtained results infer that: i) retained austenite amount is fivefold reduced by this treatment, and compressive stresses higher than 1500 MPa are generated in this phase, ii) martensite is refined due to SZT, and it contains enhanced number of crystal defects, iii) great number of “extra” cementitic carbides is formed during the sub-zero period; this number is higher than what is achieved by sub-zero treatments at −196 °C, iv) the number of “extra” carbides decreases with tempering, however, it remains higher than after in both the conventionally quenched and sub-zero treated at −196 °C steel, v) sub-zero treatments at −140 °C modify the precipitation behaviour substantially; coherent nano-sized ε-carbides and cementite were found already prior tempering the steel, and besides the cementite also M7C3 phase was detected after tempering treatment.

Tuning the orientation of few-layer MoS2 films using one-zone sulfurization

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

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.

Stoichiometry, structure and mechanical properties of co-sputtered Ti 1-x Ta x B 2±Δ coatings

GRANČIČ, B. – PLEVA, Milan – MIKULA, M. – ČAPLOVIČOVÁ, Mária – SATRAPINSKYY, L – ROCH, Tomáš – TRUCHLÝ, M. – SAHUL, Martin – GREGOR, M. – ŠVEC, Peter, Sr. – ZAHORAN, Miroslav – KÚŠ, Peter

In Surface & Coatings Technology. Vol. 367, June (2019)

https://doi.org/10.1016/j.surfcoat.2019.04.017

Abstract

Magnetron co-sputtering from TiB2 and TaB2 stoichiometric targets is used to prepare AlB2-prototype ternary Ti1-xTaxB2±Δ solid solution, with x in the range from 0 to 1. Using this technique, the boron-to-metal ratio (B/Me) varies with the actual Ti and Ta content. The boron-to‑tantalum ratio can be increased by decreasing the TaB2 target voltage, which has a considerable effect on the coating structure. Coatings with B/Me > 2 reveal highly textured nanocolumnar structure, while the coatings with B/Me < 2 tend to be nanocrystalline (without any preferred crystallite orientation) or amorphous. All the deposited coatings have a hardness higher than 32 GPa. The under-stoichiometric (B/Me < 2) coatings show material pile-up around the cube-corner indent edges, an indication for plastic flow and increased ductility.

Structure of superconducting MgB2 thin films prepared by vacuum evaporation and ex-situ annealing in Ar and O-2 atmospheres

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.

Degradation of Al4C3 Due to Atmospheric Humidity

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.

Structural, surface and magnetic properties of chalcogenide Co9S8 nanoparticles prepared by mechanochemical synthesis

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.