Year: 2019

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


In Vacuum. Vol. 170, (2019)


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 – HULMAN, Martin

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


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.

Effect of the doping of PC61BM electron transport layer with carbon nanodots on the performance of inverted planar MAPbI3 perovskite solar cells

SUBAIR, Riyas – GIROLAMOC,  Diego Di – BODIK, Michal – NÁDAŽDY, Vojtech – LI, Bo – NÁDAŽDY, Peter – MARKOVIČ, Zoran – BENKOVIČOVÁ, Monika – CHLPÍK, Juraj – KOTLÁR, Mário – HALAHOVETS, Yurily – ŠIFFALOVIČ, Peter – JERGEL, Matej – TIANE, Jianjun – BRUNETTI, Francesca – MAJKOVÁ, Eva

In Solar Energy. Vol. 189, (2019)


The doping effect of carbon nanodots (CNDs) in the PC61BM electron-transport layer on the performance of inverted planar MAPbI3 perovskite solar cells (PSCs) having two different kinds of the hole-transport layer, namely organic PEDOT:PSS and inorganic NiOx, was investigated. The CH3NH3PbI3 perovskite layer was deposited in air at 35% humidity. An average 11% and 12% enhancement of the power conversion efficiency (PCE) was achieved for 1 wt% CNDs doping in the PSCs with PEDOT:PSS and NiOx, respectively. This improvement is attributed to high electron density of CNDs resulting in a triple increase of the electrical conductivity of the PC61BM layer and passivation of the perovskite/PC61BM interface that is reflected by an increase of the open-circuit voltage. In line with this, parallel resistance and fill factor of the PSCs are also improved. Moreover, the energy-resolved electrochemical impedance spectroscopy revealed additional free-charge carriers in the PC61BM layer generated under illumination that were detected via the polaron states formation in the band gap with positive effect on the short-circuit current. All these factors contribute to the PCE improvement. Stability tests of the PSC with PEDOT:PSS under a continuous 24 hour 1.5 AM illumination showed a five times smaller final PCE decrease for the 1 wt% CNDs doping of the PC61BM layer comparing to the undoped counterpart. The passivation effect of CNDs, namely electron filling the traps formed by the photo-dimerization and photo-oxidation of PC61BM molecules, is responsible for this remarkable improvement of the short-term stability.

Covalent Diamond–Graphite Bonding: Mechanism of Catalytic Transformation

Covalent Diamond–Graphite Bonding: Mechanism of Catalytic Transformation

Semir Tulić, Thomas Waitz, Mária Čaplovičová, Gerlinde Habler, Marián Varga, Mário Kotlár, Viliam Vretenár, Oleksandr Romanyuk, Alexander Kromka, Bohuslav Rezek, Viera Skákalová

ACS Nano, 2019, 1344621-4630


Aberration-corrected transmission electron microscopy of the atomic structure of diamond–graphite interface after Ni-induced catalytic transformation reveals graphitic planes bound covalently to the diamond in the upright orientation. The covalent attachment, together with a significant volume expansion of graphite transformed from diamond, gives rise to uniaxial stress that is released through plastic deformation. We propose a comprehensive model explaining the Ni-mediated transformation of diamond to graphite and covalent bonding at the interface as well as the mechanism of relaxation of uniaxial stress. We also explain the mechanism of electrical transport through the graphitized surface of diamond. The result may thus provide a foundation for the catalytically driven formation of graphene–diamond nanodevices.

Interference-enhanced Raman scattering in SiO2/Si structures related to reflectance

Interference-enhanced Raman scattering in SiO2/Si structures related to reflectance

Ľubomír Vančo, Mário Kotlár, Magdaléna Kadlečíková, Viliam Vretenár, Marian Vojs, Jaroslav Kováč

In Journal of raman spectroscopy. Vol. 50, iss. 10 (2019)


Enhancement of Raman scattering due to optical interference may act as a source of error in the issues necessitating a determination of Raman intensity. Its dependence on thin film thickness is the conventional way how to examine the effects of optical interference in Raman signal. To provide a new platform for evaluation of signal coming from substrate in the presence of a transparent capping, we investigate its relation to reflectance (R) instead of the capping thickness. We derived a theoretical model, which was experimentally tested on simple structures consisting of SiO2 deposited on mono-Si substrates. In agreement between the model and the experiment, interference enhancement is proportional to the product of (1 − R) terms taken at excitation and scattered light wavenumbers. We experimented with two different Raman bands in Si on two different Raman systems. The model was valid regardless of excitation, Raman band, and grating. Constructed for normal incidence, it was in agreement with experiment using objectives with numerical apertures up to 0.25 (0.32). The model was valid also in ultraviolet region, where imaginary part in refractive index of Si considerably rises.

Growth of lithium hydride thin films from solutions: Towards solution atomic layer deposition of lithiated films

KUNDRATA, Ivan – FRÖHLICH, Karol – VANČO, Ľubomír – MICUŠÍK, Matej – BACHMANN, Julien

In Beilstein Journal of Nanotechnology. Vol. 10, (2019)


Lithiated thin films are necessary for the fabrication of novel solid-state batteries, including the electrodes and solid electrolytes. Physical vapour deposition and chemical vapour deposition can be used to deposit lithiated films. However, the issue of conformality on non-planar substrates with large surface area makes them impractical for nanobatteries the capacity of which scales with surface area. Atomic layer deposition (ALD) avoids these issues and is able to deposit conformal films on 3D substrates. However, ALD is limited in the range of chemical reactions, due to the required volatility of the precursors. Moreover, relatively high temperatures are necessary (above 100 °C), which can be detrimental to electrode layers and substrates, for example to silicon into which the lithium can easily diffuse. In addition, several highly reactive precursors, such as Grignard reagents or n-butyllithium (BuLi) are only usable in solution. In theory, it is possible to use BuLi and water in solution to produce thin films of LiH. This theoretical reaction is self-saturating and, therefore, follows the principles of solution atomic layer deposition (sALD). Therefore, in this work the sALD technique and principles have been employed to experimentally prove the possibility of LiH deposition. The formation of homogeneous air-sensitive thin films, characterized by using ellipsometry, grazing incidence X-ray diffraction (GIXRD), in situ quartz crystal microbalance, and scanning electron microscopy, was observed. Lithium hydride diffraction peaks have been observed in as-deposited films by GIXRD. X-ray photoelectron spectroscopy and Auger spectroscopy analysis show the chemical identity of the decomposing air-sensitive films. Despite the air sensitivity of BuLi and LiH, making many standard measurements difficult, this work establishes the use of sALD to deposit LiH, a material inaccessible to conventional ALD, from precursors and at temperatures not suitable for conventional ALD.

Tailored Langmuir-Schaefer Deposition of Few-Layer MoS2 Nanosheet Films for Electronic Applications

KALOSI, Anna – DEMYDENKO, Maksym – BODÍK, Michal – HAGARA, Jakub – KOTLÁR, Mário – KOSTIUK, Dmytro – HALAHOVETS, Yurily – VÉGSÖ, Karol – ROLDAN, Alicia Marin – MAURYA, Gulab Singh – ANGUŠ, Michal – VEIS, Pavel – JERGEL, Matej – MAJKOVÁ, Eva – ŠIFFALOVIČ, Peter

In Langmuir. Vol. 35, iss. 30 (2019)


Few-layer MoS2 films stay at the forefront of current research of two-dimensional materials. At present, continuous MoS2 films are prepared by chemical vapor deposition (CVD) techniques. Herein, we present a cost-effective fabrication of the large-area spatially uniform films of few-layer MoS2 flakes using a modified Langmuir–Schaefer technique. The compression of the liquid-phase exfoliated MoS2 flakes on the water subphase was used to form a continuous layer, which was subsequently transferred onto a submerged substrate by removing the subphase. After vacuum annealing, the electrical sheet resistance dropped to a level of 10 kΩ/sq, being highly competitive with that of CVD-deposited MoS2 nanosheet films. In addition, a consistent fabrication protocol of the large-area conductive MoS2 films was established. The morphology and electrical properties predetermine these films to advanced detecting, sensing, and catalytic applications. A large number of experimental techniques were used to characterize the exfoliated few-layer MoS2 flakes and to elucidate the formation of the few-layer MoS2 Langmuir film.

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)


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.