Author: Mario Kotlár

Electrochemical modified Pt nanoflower @ rGO for non- enzymatic electrochemical sensing of glucose

Posted on by Mario Kotlár

Saravanan Gengan, R.M. Gnanamuthu, Sanjay Sankaranarayanan, Venumbaka Maneesh Reddy, Bhanu Chandra Marepally, Ravi Kumar Biroju

Sensors and Actuators A: Physical, Volume 353, (2023)

https://doi.org/10.1016/j.sna.2023.114232

Abstract

Since lower danger of biorecognition element degradation, enzymes-less glucose have the potential for more reliable in vivo activity, but it suffers due to lack of linear response and poor selectivity. We made attempt to improve selectivity, linear response and stability, environmentally benign electrochemical method adopted to fabricate Pt nanoflowers (PtNF) anchored on rGO modified GCE (PtNF-rGO/GCE). The PtNF-rGO/GCE electrode demonstrated good glucose electrooxidation in alkaline solution, with a linear range, sensitivity and detection limit are up to 3.5 mM, 335.5 μA mM−1 cm−1 and 53 μM (S/N = 3) respectively. The PtNF-rGO/GCE electrode is not only selective also inhibit interfering molecules like uric, dopamine, ascorbic acid. This allows for broadly sensitive, work at low-potential, stable, and quick glucose current detection, which is capable for the expansion of non-enzymatic glucose detectors.

Defective Graphene/Plasmonic Nanoparticle Hybrids for Surface-Enhanced Raman Scattering Sensors

Posted on by Mario Kotlár

Biroju Ravi K., Marepally Bhanu Chandra, Malik Pariksha, Dhara Soumen, Gengan Saravanan, Maity Dipak, Narayanan Tharangattu N., Giri Pravat K.

In: ACS Omega 2023, 8, 4, 4344–4356, (2023)

https://doi.org/10.1021/acsomega.2c07706

Abstract

Two-dimensional–zero-dimensional plasmonic hybrids involving defective graphene and transition metals (DGR-TM) have drawn significant interest due to their near-field plasmonic effects in the wide range of the UV–vis–NIR spectrum. In the present work, we carried out extensive investigations on resonance Raman spectroscopy (RRS) and localized surface plasmon resonance (LSPR) from the various DGR-TM hybrids (Au, Ag, and Cu) using micro-Raman, spatial Raman mapping analysis, high-resolution transmission electron microscopy (HRTEM), and LSPR absorption measurements on defective CVD graphene layers. Further, electric field (E) mappings of samples were calculated using the finite domain time difference (FDTD) method to support the experimental findings. The spatial distribution of various in-plane and edge defects and defect-mediated interaction of plasmonic nanoparticles (NPs) with graphene were investigated on the basis of the RRS and LSPR and correlated with the quantitative analysis from HRTEM, excitation wavelength-dependent micro-Raman, and E-field enhancement features of defective graphene and defective graphene-Au hybrids before and after rapid thermal annealing (RTA). Excitation wavelength-dependent surface-enhanced Raman scattering (SERS) and LSPR-induced broadband absorption from DGR-Au plasmonic hybrids reveal the electron and phonon interaction on the graphene surface, which leads to the charge transfer from TM NPs to graphene. This is believed to be responsible for the reduction in the SERS signal, which was observed from the wavelength-dependent Raman spectroscopy/mappings. We implemented defective graphene and DGR-Au plasmonic hybrids as efficient SERS sensors to detect the Fluorescein and Rhodamine 6G molecules with a detection limit down to 10–9 M. Defective graphene and Au plasmonic hybrids showed an impressive Raman enhancement in the order of 108, which is significant for its practical application.

Correlated reflectance and Raman spectroscopy in substrates with coherent transparent layers

Posted on by Mario Kotlár

VANČO, Ľubomír – KOTLÁR, Mário – VRETENÁR, Viliam – KADLEČÍKOVÁ, Magdaléna – VOJS, Marian – VOGRINČIČ, Peter

In Surfaces and Interfaces. Vol. 34, (2022)

https://doi.org/10.1016/j.surfin.2022.102309

Abstract

Intensity of Raman bands in substrates covered with transparent overlayers can be enhanced due to optical interference, leading to incorrect quantitative interpretation of Raman signals. If thickness and optical properties of the overlayer are known, correction can be done using appropriate models. We theoretically discuss and experimentally evaluate a model where thickness and refractive index of the overlayer remain unknown and determination of enhancement factor is possible via linear relationship to reflectance-related response of the whole structure. Correct interpretation of the spectra is then possible since refractive index and thickness of the transparent layer are implicitly introduced in the measured reflectance. For experimental evidence we exploit SiNx/Si and SiO2/Si structures to find a significant correspondence with the model, aiming toward correlative reflectance and Raman spectroscopy.

Raman spectroscopy of silicon with nanostructured surface

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KADLEČÍKOVÁ, Magdaléna – VANČO, Ľubomír – BREZA, Juraj – MIKOLÁŠEK, Miroslav – HUŠEKOVÁ, Kristína – FRÖHLICH, Karol – PROCEL, Paul – ZEMAN, Miro – ISABELLA, Olindo

In Optik. Vol. 257, (2022)

https://doi.org/10.1016/j.ijleo.2022.168869

Abstract

We compared the morphology and Raman response of nanoscale shaped surfaces of Si substrates versus monocrystalline Si. Samples were structured by reactive ion etching, and four of them were covered by a RuO2-IrO2 layer. Raman bands, centred at approx. 520 cm–1, belonging to samples processed by etching the Si surface have intensities higher by approximately one order of magnitude than those of reference non-etched samples. For nanostructured samples, the rise in the Raman signal was 12–14 × , which is in agreement with the model of the electric field at the tips of Si due to their geometry. This phenomenon is related to the high absorption of excitation radiation. Nanostructured surfaces of samples containing a layer of RuO2-IrO2 give rise to the phenomenon of surface enhancement of the Raman response most likely due to the charge transfer at the interface between silicon and conductive oxides. The nanostructured surface of Si without a metal layer behaves as a SERS substrate and detects the analytes at a low concentration.

Mesoporous SnO2 Nanoparticle-Based Electron Transport Layer for Perovskite Solar Cells

Posted on by Mario Kotlár

ULLAH, Sami – FARAZ, Muhammad Ud Din – KHAN, Kasi Jafar – KHAN, Kasi Ajab – VÉGSÖ, Karol – KOTLÁR, Mário – MIČUŠÍK, Matej – JERGEL, Matej – NÁDAŽDY, Vojtech – ŠIFFALOVIČ, Peter – MAJKOVÁ, Eva – FAKHARUDDIN, Azhar

In ACS Applied Nano Materials. Vol. 5, iss. 6 (2022)

https://doi.org/10.1021/acsanm.2c00840

Abstract

A perovskite solar cell (PSC) featuring a mesoporous architecture can facilitate perovskite layer formation over a large area via increasing the number of heterogeneous nucleation sites. The morphology of the electron transport layer (ETL) and its interface with the perovskite layer is one of the key factors to boost the performance of a PSC. Tin dioxide (SnO2) is considered as a promising ETL in PSCs owing to its high carrier mobility, good transmittance, deep conduction band level, and efficient photoelectron extraction. Generally, the mesoporous SnO2 (m-SnO2) ETL has a higher surface-to-volume ratio compared to a compact SnO2 layer. Herein, we report on an m-SnO2 ETL prepared by anodizing a metallic tin film on a fluorine-doped tin oxide (FTO) substrate in NaOH solution under an ambient atmosphere. In particular, we developed a bilayer architecture of the m-SnO2 ETL based on the fabrication of two consecutive m-SnO2 layers. The morphology of each layer was controlled by varying the anodization voltage and time at a constant solution concentration during the growth process. This unique approach enabled the deposition of an m-SnO2 ETL with sufficient coverage of the FTO substrate, which is difficult to achieve with a single layer of m-SnO2. In particular, the scanning electron and atomic force microscopy analyses confirmed that the m-SnO2 layer covers completely the FTO substrate. The device fabricated with this bilayer m-SnO2 ETL achieved a 27% improvement in power conversion efficiency compared to that with a single layer of m-SnO2.

Contribution of photocatalytic and Fenton-based processes in nanotwin structured anodic TiO2 nanotube layers modified by Ce and V

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THIRUNAVUKKARASU,  Guru Karthikeyan – GOWRISANKARAN, Sridhar – ČAPLOVIČOVÁ, Mária – SATRAPINSKYY, Leonid – GREGOR, Maroš – LAVRIKOVA, Aleksandra Y. – GREGUŠ, Ján – HALKO, Radoslav – PLESCH, Gustav – MOTOLA, Martin – MONFORT, Olivier

In Dalton Transactions. Vol. 51, iss. 28 (2022)

https://doi.org/10.1039/D2DT00829G

Abstract

In the present work, nanotwin structured TiO2 nanotube (TNT) layers are prepared by the electrochemical anodization technique to form the anatase phase and by surface modification via spin-coating of Ce and V precursors to form Ce-TNT and V-TNT, respectively. The surface and cross-sectional images by SEM revealed that the nanotubes have an average diameter of ∼130 nm and a length of ∼14 μm. In addition, the TEM images revealed the nanotwin structures of the nanotubes, especially the anatase (001) and (112) twin surfaces, that increase the transport of photogenerated charges. The photoinduced degradation of caffeine (CAF) by TNT, Ce-TNT, and V-TNT led to a degradation extent of 16%, 26% and 33%, respectively, whereas it increased to 26%, 38%, and 46% in the presence of H2O2, owing to the involvement of Fenton-based processes (in addition to photocatalysis). The effect of the Fenton-based processes accounts for about 10% of the total degradation extent of CAF. Finally, the mechanism of the photoinduced degradation of CAF was investigated. The main oxidative species were the hydroxyl radicals, and the better efficiency of V-TNT over Ce-TNT and TNT was ascribed to its negative surface, thus improving the interactions with CAF.

Ni-Fe Cathode Catalyst in Zero-Gap Alkaline Water Electrolysis

Posted on by Mario Kotlár

ZÁCHENSKÁ, Jana – JORÍK, Vladimír – VANČO, Ľubomír – MIČUŠÍK, Matej – ZEMANOVÁ, Matilda

In Electrocatalysis. Vol. 13, iss. 4 (2022)

https://doi.org/10.1007/s12678-022-00734-6

Abstract

Ni–Fe cathode catalyst for zero-gap alkaline water electrolysis was studied. Ni–Fe coatings on nickel foam were prepared by direct current (DC) and pulse current (PC) electrodeposition. The influence of different plating conditions and composition of the electrolyte on the morphology of the samples was studied. It was found that under DC electrodeposition, iron is dominant in the coating. Under PC plating conditions, Ni is the dominant element in Ni–Fe coatings. Ni–Fe coatings prepared under DC electrodeposition provide an effective catalyst in zero-gap electrolysis. Increasing Fe content in the coatings improves the catalytic activity of Ni–Fe catalyst. The study of convenient parameters of PC electrodeposition seems to be complex to reach a highly active surface area.

Microstructure, Mechanical and Tribological Properties of Advanced Layered WN/MeN (Me = Zr, Cr, Mo, Nb) Nanocomposite Coatings

Posted on by Mario Kotlár

Smyrnova K., Sahul M., Haršáni M., Pogrebnjak A., Ivashchenko V., Beresnev V., Stolbovoy V., Čaplovič L., Čaplovičová M., Vančo L., Kusý M., Kassymbaev A., Satrapinskyy L., Flock D.

Nanomaterials, 12 (3), art. no. 395

https://doi.org/10.3390/nano12030395

Abstract

Due to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W2N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W2N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10−6 mm3/Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb2O5 and WO3 tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions. 

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

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

Wang, Anni; Oliva Ramírez, Manuel; Caplovicova, Maria; Vretenar, Viliam; Böttcher, Julius; Hopfeld, Marcus; Kups, Thomas; Flock, Dominik; Schaaf, Peter

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.