Author: Mario Kotlár

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

Posted on by Mario Kotlár

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)

https://doi.org/10.1021/acs.langmuir.9b01000

Abstract

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.

An elevated concentration of MoS2 lowers the efficacy of liquid-phase exfoliation and triggers the production of MoOx nanoparticles

Posted on by Mario Kotlár

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 MoOx 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 MoOx 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-MoOx transformation and found a threshold value of 10 mg ml−1 of the initial MoS2 concentration to trigger this transformation.

Tailoring the interparticle distance in Langmuir nanoparticle films

Posted on by Mario Kotlár

BENKOVIČOVÁ, Monika – HOLOS, Ana – NÁDAŽDY, Peter – HALAHOVETS, Yurily – KOTLÁR, Mário – KOLLÁR, Jozef – ŠIFFALOVIČ, Peter – JERGEL, Matej – MAJKOVÁ, Eva – MOSNÁČEK, Jaroslav – IVANČO, Ján

In Physical Chemistry Chemical Physics. Vol. 21, iss. 18 (2019)

Abstract

The ability to control the interparticle distance in self-assembled arrays of nanoparticles plays an important role in a large number of applications, which require tunable electronic and photonic properties. Importantly, practical applications in real devices rely on arrays satisfying more stringent requirements of lateral homogeneity controlled over a large scale. Herein, the interparticle distance in ordered nanoparticle assemblies was controlled by varying the nanoparticle effective size via the molecular chemical nature and chain length of the ligand. Iron oxide nanoparticles (IONPs) were functionalized by three types of ligands, namely (i) a mixture of oleic acid/oleylamine (OA/OAm), (ii) poly(n-butyl acrylate) (PBA) and (iii) polystyrene (PS), while two different molar masses of PBA and PS were used. The polymeric ligands with narrow dispersity and bearing phosphonic chain-end groups were prepared by atom transfer radical polymerization. Functionalization of the IONPs with polymeric ligands was achieved using a ligand exchange method. Both the hydrodynamic diameter and size distribution of the nanoparticles in colloidal solution were determined by dynamic light scattering (DLS). The mean interparticle distances in Langmuir–Schaefer monolayers prepared on solid substrates were assessed by means of the pair correlation function calculated from the atomic force microscopy (AFM) images. Furthermore, the lateral ordering, homogeneity, and interparticle distances averaged over a mesoscopic scale of the ordered monolayers were studied by the grazing-incidence small-angle X-ray scattering (GISAXS) technique. We demonstrate that the (nanoparticle) centre-to-centre distance in the ordered assemblies constituted by the IONPs with the core diameter of about 6 nm can be varied from 7.6 to about 12 nm with the resulting interparticle gap change by a factor of about 4.

Evidence of relationship between strain and In-incorporation: Growth of N-polar In-rich InAlN buffer layer by OMCVD

Posted on by Mario Kotlár

CHAUHAN, Prerna – HASENÖHRL, Stanislav – DOBROČKA, Edmund – CHAUVAT, Marie-Pierre – MINJ, A. – GUCMANN, Filip – VANČO, Ľubomír – KOVÁČ, Jaroslav jr. – KRET, S. – RUTERANA, Pierre – KUBALL, Martin – ŠIFFALOVIČ, Peter – KUZMÍK, Ján

In Journal of Applied Physics. 125, iss. 10 (2019)

https://doi.org/10.1063/1.5079756

Abstract

Two In𝑥Al1−𝑥NInAl1−N layers were grown simultaneously on different substrates [sapphire (0001) and the Ga-polar GaN template], but under the same reactor conditions, they were employed to investigate the mechanism of strain-driven compositional evolution. The resulting layers on different substrates exhibit different polarities and the layer grown on sapphire is N-polar. Moreover, for the two substrates, the difference in the degree of relaxation of the grown layers was almost 100%, leading to a large In-molar fraction difference of 0.32. Incorporation of In in In𝑥Al1−𝑥NInAl1−N layers was found to be significantly influenced by the strain imposed by the under-layers. With the evolutionary process of In-incorporation during subsequent layer growth along [0001], the direction of growth was investigated in detail by Auger electron spectroscopy. It is discovered that the In0.60Al0.40NIn0.60Al0.40N layer grown directly on sapphire consists of two different regions with different molar fractions: the transition region and the uniform region. According to the detailed cross-sectional transmission electron microscopy, the transition region is formed near the hetero-interface due to the partial strain release caused by the generation of misfit-dislocations. The magnitude of residual strain in the uniform region decides the In-molar fraction. In𝑥Al1−𝑥NInAl1−N layers were analyzed by structural and optical characterization techniques. Our present work also shows that a multi-characterization approach to study In𝑥Al1−𝑥NInAl1−N is a prerequisite for their applications as a buffer layer.

Characterization of the chips generated by the nanomachining of germanium for X-ray crystal optics

Posted on by Mario Kotlár

 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.

On the formation of hydrophobic carbon quantum dots Langmuir films and their transfer onto solid substrates

Posted on by Mario Kotlár

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.

Antibacterial and Antibiofouling Properties of Light Triggered Fluorescent Hydrophobic Carbon Quantum Dots Langmuir-Blodgett Thin Films

Posted on by Mario Kotlár

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)

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.