Centrum pre Nanodiagnostiku Materiálov

BODÍK, Michal – DEMYDENKO, Maksym – SHABELNYK, Tetiana – HALAHOVETS, Yuriy – KOTLÁR, Mário – KOSTIUK, Dmytro – SHAJI, Ashin – BRUNOVÁ, Alica – VEIS, Pavel – JERGEL, Matej – MAJKOVÁ, Eva – ŠIFFALOVIČ, Peter

In Journal of Physical Chemistry C. Vol. 124, iss. 29 (2020)

https://doi.org/10.1021/acs.jpcc.0c02365

Abstract

Recent advances in the liquid-phase exfoliation enabled large-scale production of two-dimensional (2D) materials, including few-layer graphene and transition metal dichalcogenides. The exfoliated flakes of 2D materials allow cost-effective deposition of continuous films for various applications ranging from optoelectronics to lubrication technology. The self-assembly of 2D materials on water subphase and subsequent transfer of such a Langmuir film onto a solid substrate offers an unprecedented layer quality in terms of spatial homogeneity as it proceeds in thermodynamic equilibrium. However, while the formation of conventional organic molecular Langmuir films has been widely studied, the application of the Langmuir technique to rigid inorganic 2D materials is still rather unexplored. Here, we study the underlying mechanism behind the formation and collapse at the critical surface pressure of the Langmuir film composed of few-layer MoS₂ flakes. The in situ wide-angle X-ray scattering measured in real time and other supportive techniques applied ex situ after the film transfer onto a Si/SiO₂ substrate were employed. We identify all principal compression stages up to the Langmuir monolayer collapse and beyond, relying on the texture, surface pressure, and elastic modulus temporal evolution. The results obtained and the conclusions drawn can be extended to a large family of the inorganic Langmuir films of other 2D materials to optimize the deposition process for envisaged application.

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)

https://doi.org/10.1016/j.solener.2019.07.088

Abstract

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 NiO_x, 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 NiO_x, 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.

BODÍK, Michal – ANNUŠOVÁ, Adriana – HAGARA, Jakub – MIČUŠÍK, Matej – OMASTOVÁ, Mária – KOTLÁR, Mário – CHLPÍK, Juraj – CIRÁK, Július – ŠVAJDLENKOVÁ, Helena – ANGUŠ, Michal – ROLDAN, Alicia Marin – VEIS, Pavel – JERGEL, Matej – MAJKOVÁ, Eva – ŠIFFALOVIČ, Peter

In Physical Chemistry Chemical Physics. Vol. 21, iss. 23 (2019)

https://doi.org/10.1039/C9CP01951K

Abstract

It is generally accepted that liquid-phase exfoliation (LPE) enables large-scale production of few-layer MoS₂ flakes. In our work, we studied in detail few-layer MoS₂ oxidation in the course of standard LPE in a water/ethanol solution. We demonstrate that an increase of the initial MoS₂ concentration above a certain threshold triggers a pronounced oxidation and the exfoliation process starts to produce MoO_x nanoparticles. A subsequent decrease of the water pH along with an increased content of SO₄²⁻ suggests an oxidation scenario of few-layer MoS₂ oxidation towards MoO_x nanoparticles. Moreover, the lowered pH leads to agglomeration and sedimentation of the few-layer MoS₂ flakes, which significantly lowers their production yield. We employed a large number of physico-chemical techniques to study the MoS₂-to-MoO_x transformation and found a threshold value of 10 mg ml⁻¹ of the initial MoS₂ concentration to trigger this transformation.

ZÁPRAŽNÝ, Zdenko – KORYTÁR, Dušan – JERGEL, Matej – HALAHOVETS, Yurily – KOTLÁR, Mário – MATKO, Igor – HAGARA, Jakub – ŠIFFALOVIČ, Peter – KECKES, Jozef – MAJKOVÁ, Eva

In International Journal of Advanced Manufacturing Technology. Vol. 102, iss. 9-12 (2019)

https://doi.org/10.1007/s00170-019-03392-z

Abstract

Micro-Raman spectroscopy, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) were used to study the effect of cutting speed and cutting depth on the mode of the single-point diamond fly cutting of Ge(110) surface via crystallinity of the chips. Reducing the cutting depth from 15 to 2 μm and concurrently cutting speed from 10 to 2 mm/min at 2000 rpm, the content of amorphous phase in the chips increased at the expense of the crystalline one from 28 to 46%. Simultaneously, the chip morphology visible by SEM suggested transition from a brittle to a mixed brittle-ductile mode of nanomachining. The damage transition line indicates 1/3 portion of the ductile component at 2-μm cutting depth that produced twisted lamellae of a width of 18–20 μm without any signs of a fracture. As the feed rate here was 1 μm/rev, the tool made 18–20 revolutions while passing the same point of the nanomachined surface that was enough to gradually remove the surface region damaged by the brittle cutting component along with the entire amorphous region beneath, both being delaminated by the chips. This explains the dislocation-free single-crystal lattice beneath the Ge(110) surface machined under these conditions. A close relationship between the brittle mode of nanomachining and crystallinity of the chips observed by micro-Raman spectroscopy and SEM was confirmed by HR-TEM showing dense occurrence of nanocrystals in the chips coming from the nanomachinings with 5-μm and 15-μm cutting depths. These results demonstrate potential of the single-point diamond machining for the preparation of high-quality X-ray surfaces with undistorted single-crystal lattice beneath for next-generation X-ray crystal optics.

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.