Autor Mario Kotlár

Combined in Situ Photoluminescence and X-ray Scattering Reveals Defect Formation in Lead-Halide Perovskite Films

Posted on by Mario Kotlár

Nada Mrkyvkova*, Vladimír Held, Peter Nádaždy, Riyas Subair, Eva Majkova, Matej Jergel, Aleš Vlk, Martin Ledinsky, Mário Kotlár, Jianjun Tian, Peter Siffalovic

J. Phys. Chem. Lett. 2021, 12, 41, 10156–10162

https://doi.org/10.1021/acs.jpclett.1c02869

Abstract

Lead-halide perovskites have established a firm foothold in photovoltaics and optoelectronics due to their steadily increasing power conversion efficiencies approaching conventional inorganic single-crystal semiconductors. However, further performance improvement requires reducing defect-assisted, nonradiative recombination of charge carriers in the perovskite layers. A deeper understanding of perovskite formation and associated process control is a prerequisite for effective defect reduction. In this study, we analyze the crystallization kinetics of the lead-halide perovskite MAPbI3–xClx during thermal annealing, employing in situ photoluminescence (PL) spectroscopy complemented by lab-based grazing-incidence wide-angle X-ray scattering (GIWAXS). In situ GIWAXS measurements are used to quantify the transition from a crystalline precursor to the perovskite structure. We show that the nonmonotonous character of PL intensity development reflects the perovskite phase volume, as well as the occurrence of the defects states at the perovskite layer surface and grain boundaries. The combined characterization approach enables easy determination of defect kinetics during perovskite formation in real-time.

Formation of CuCrCoFeNiO high entropy alloy thin films by rapid thermal processing of Cu/CrNiO/FeCo multilayers

Formation of CuCrCoFeNiO high entropy alloy thin films by rapid thermal processing of Cu/CrNiO/FeCo multilayers

Posted on by Mario Kotlár

AnniWanga, Manuel OlivaRamireza, MariaCaplovicovab,ViliamVretenarb, JuliusBoettchera, MarcusHopfelda, ThomasKupsa, DominikFlocka, PeterSchaafa

Surface and coatings technology, ISSN 0257-8972, 405 (2021), 126563

doi.org/10.1016/j.surfcoat.2020.126563

Abstract

This study presents the synthesis of High Entropy Alloy (HEA) films starting from elemental Cu and binary alloy CoFe and CrNiO multilayers, followed by rapid thermal processing (RTP). By that, the HEA films (HEAFs) were formed by phase formation via short-range and fast diffusion processes. Multilayers with a total thickness of 760 nm consisting of 16 repetitions of a Cu (11 nm)/CrNiO (16.5 nm)/CoFe (20 nm) sequence were annealed at temperatures from 600 °C to 1000 °C for 5 min. The reaction products were then analyzed by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS), in order to identify the phase transformations and elemental distributions. A duplex FCC structure containing CrCoFeNiO HEA and pure Cu phase was successfully synthesized at 600 °C and 800 °C by the solid-state reaction. CuCrCoFeNiO HEA formed within in a Cu nanocrystalline matrix. As the annealing temperature increased, the oxygen content in the films decreased, Both HEA and Cu possess significant 〈111〉 preferred orientation. The HEA phase demonstrated a typical microstructure of alloys with intensive nano-twins. Moreover, the grain growth kinetics of the HEA phase was evaluated, and the activation energy was found to be 185(10) kJ/mol. This is comparable to that of conventional stainless steel (~150 kJ/mol) and less than half of the value for CrCoFeNi bulk (434 kJ/mol). A surface energy-driven grain growth mechanism of the HEAFs via multilayer alloy formation is proposed in this study. The mechanical properties, hardness and Young’s modulus, were measured via nanoindentation, and the strengthening mechanism was proposed and compared with current literature.

Prestavba suterénu Nanocentra

Posted on by Mario Kotlár

V rámci projektu Accord bude zakúpený nový FIB-SEM mikroskop, ktorý bude inštalovaný v priestoroch Centra pre Nanodiagnostiku materiálov.

S nákupom je úzko spojená rozsiahla rekonštrukcia suterénu Centra pre Nanodiagnostiku materiálov, ktorá začala v Marci 2022.

Úprava priestorov sa začala odstránením priečok

Práce začali odstránením starých podláh, priečok a prácami na novej podlahe. Pre samotný mikroskop bude vytvorený samostatný betónový blok, ktorí bude oddelený od zvyšku miestnosti. Po zhotovení nových podláh, budú mať nové laboratóriá vyššiu svetlú výšku.

Miesto pre samostatný betónový blok pod FIB-SEM mikroskop.
Realizácia hydroizolácie
Miesto pre FIB-SEM mikroskop
Nové podlahy

Po ukončení rekonštrukcie vznikli z pôvodne zanedbaných priestorov nové atraktívne laboratóriá. Po inštalácii nového prístrojového vybavenia zlepšia tieto laboratóriá možnosti výskumných aktivít Slovenskej Technickej Univerzity. Týmto bola univerzita obohatená o nové reprezentatívne priestory.

Vstupná hala
Servisná miestnosť
Miesto pre inštaláciu nového FIB-SEM mikroskopu

Ag-modified LiMn2O4 cathode for lithium-ion batteries: Coating functionalization

Posted on by Mario Kotlár

ABBAS, Somia M. – HASHEM, Ahmed M. – ABDEL-GHANY, Ashraf E. – ISMAIL, Eman H. – KOTLÁR, Mário – WINTER, Martin – LI, Jie – JULIEN, Christian M.

In Energies [Open access]. Vol. 13, iss. 19 (2020)

https://doi.org/10.3390/en13195194

Abstract

In this work, the properties of silver-modified LiMn2O4 cathode materials are revisited. We study the influence of calcination atmosphere on the properties of the Ag-coated LiMn2O4 (Ag/LMO) and highlight the silver oxidation. The effect of the heat treatment in vacuum is compared with that in air by the characterization of the structure, specific surface area, Li transport properties and electrochemical performance of Ag/LMO composites. Surface analyses (XPS and Raman spectroscopy) show that the nature of the coating (~3 wt.%) differs with the calcination atmosphere: Ag/LMO(v) calcined in vacuum displays Ag nanospheres and minor AgO content on its surface (specific surface area of 4.1 m2 g−1), while Ag/LMO(a) treated in air is mainly covered by the AgO insulating phase (specific surface area of 0.6 m2 g−1). Electrochemical experiments emphasize that ~3 wt.% Ag coating is effective to minimize the drawbacks of the spinel LiMn2O4 (Mn dissolution, cycling instability, etc.). The Ag/LMO(v) electrode shows high capacity retention, good cyclability at C/2 rate and capacity fade of 0.06% per cycle (in 60 cycles).

Collapse Mechanism in Few-Layer MoS2 Langmuir Films

Posted on by Mario Kotlár

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.

A bioconjugated MoS2 based nanoplatform with increased binding efficiency to cancer cells

Posted on by Mario Kotlár

KÁLOSI, Anna – LABUDOVÁ, Martina – ANNUŠOVÁ, Adriana – BENKOVIČOVÁ, Monika – BODÍK, Michal – KOLLÁR, Jozef – KOTLÁR, Mário – KASAK, Peter – JERGEL, Matej – PASTOREKOVÁ, Sylvia – ŠIFFALOVIČ, Peter – MAJKOVÁ, Eva

In Biomaterials Science. Vol. 8, iss. 7 (2020)

https://doi.org/10.1039/C9BM01975H

Abstract

We evaluate the application of surfactant-free liquid-phase exfoliated MoS2 nanosheets as a nanoplatform for a cancer detection and treatment system equipped with an antibody–antigen based recognition element. Employing antigen–antibody binding, we increased the probability of the endocytosis of MoS2 nanosheets into CAIX expressing cells by 30%. The nanosheets are functionalized with a specific antibody M75, which forms an antigen–antibody complex with CAIX. The bioconjugation of MoS2 nanosheets involves biocompatible components with low cytotoxicity, verified in the tested cell lines by fluorescence-based cell viability assay. The cellular internalization is quantified by flow cytometry, while the internalization is confirmed by label-free confocal Raman imaging. Raman measurements show increased lysosomal activity in the proximity of the internalized nanoplatforms.

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

Posted on by Mario Kotlár

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 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.

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

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 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)

https://doi.org/10.1039/C9CP02064K

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.