Autor Lubomír Vančo

Effect of surface roughness on laser surface alloying of additively manufactured 17-4PH stainless steel

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Chaus Alexander, DEVOINO O.G., Sahul Martin, Vančo Ľubomír, Buranský Ivan, Kusý Martin

In: Surface & Coatings Technology. Vol. 454, (2023)

https://doi.org/10.1016/j.surfcoat.2022.129161

Abstract

In the present work, the evolution of the final microstructure in 17-4PH stainless steel additively manufactured and subjected to the laser surface alloying with boron and nitrogen is described with special emphasis on the influence of surface topography and roughness. It was shown that character of the surface topography, and hence the surface roughness of the additively manufactured samples plays a major role in the development of microstructure during laser surface alloying. Dendritic microstructure of a solid solution with a small amount of eutectic in the interdendritic space was observed in a laser-melted zone (LMZ) of so-called smooth samples. In contrast, fully eutectic microstructure was revealed in the LMZ of the rough samples. This resulted in significantly different microhardness of the LMZ of both samples, i.e. 317.0 ± 12.7 and 636.7 ± 18.5 HV0.1 for the smooth and rough samples. The microstructural features and varying microhardness were found to be attributed to the different degree of the steel alloying primarily with boron in the LMZ, significantly affected by the initial roughness of the sample surface. This mechanism can be used to enhance laser surface alloying of the additively manufactured products.

Correlated reflectance and Raman spectroscopy in substrates with coherent transparent layers

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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.

Synthesis of Sulfide Perovskites by Sulfurization with Boron Sulfides

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BYSTRICKÝ, Roman – TIWARI, Sameer K. – HUTÁR, Peter – VANČO, Ľubomír – SÝKORA, Milan

In Inorganic Chemistry. Vol. 61, iss. 47 (2022)

https://doi.org/10.1021/acs.inorgchem.2c03200

Abstract

Chalcogenide perovskites (CPs), with the general composition ABX3, where A and B are metals and X = S and Se, have recently emerged as promising materials for application in photovoltaics. However, the development of CPs and their applications has been hindered by the limitations of available preparation methods. Here we present a new approach for the synthesis of CPs, based on the sulfurization of ternary and binary oxides or carbonates with in situ formed boron sulfides. In contrast to the previously described approaches, the method presented here uses chemically stable starting materials and yields pure-phase crystalline CPs within several hours, under low hazard conditions. CP yields over 95% are obtained at temperatures as low as 600 °C. The generality of the approach is demonstrated by the preparation of CPs with compositions BaZrS3, β-SrZrS3, BaHfS3, SrHfS3, and EuHfS3. Mechanistic insights about the formation of CPs are discussed.

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.

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

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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

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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. 

Toward BaSi2/Si Heterojunction Thin-Film Solar Cells: Insights into Heterointerface Investigation, Barium Depletion, and Silicide-Mediated Silicon Crystallization

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TIAN, Yilei – MONTES, Ana Rita Bento – VANČO, Ľubomír – ČAPLOVIČOVÁ, Mária – VOGRINČIČ, Peter – SUTTA, Pavol – SATRAPINSKYY, Leonid – ZEMAN, Miro – ISABELLA, Olindo

In Advanced Materials Interfaces. Vol. 7, iss. 19 (2020)

https://doi.org/10.1002/admi.202000887

Abstract

The knowledge of the structural and compositional details of Si/BaSi2/Si heterostructure annealed at high temperature is a prerequisite for BaSi2 application in heterojunction thin-film solar cells. For this purpose, Si/BaSi2/Si heterostructures deposited by magnetron sputtering with different Si layer thickness are submitted to systematic structural and compositional characterizations. Results reveal a BaSi2/Si heterointerfacial variation caused by surface oxidation and Ba diffusion at the high temperature. Its effects on the optical and electrical properties of Si/BaSi2/Si heterostructure are presented. The outcomes of this work can be extended to BaSi2 deposited by other techniques, and generate substantial advantages in BaSi2 development ranging from improvement on material qualities and eventual deployment in thin-film solar cells.

Properties of sputtered BaSi2 thin films annealed in vacuum condition

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TIAN, Yilei – MONTES, Ana Rita – VANČO, Ľubomír – ISABELLA, Olindo – ZEMAN, Miro

In Japanese Journal of Applied Physics. Vol. 59, SF (2020)

https://doi.org/10.7567/1347-4065/ab5b59

Abstract

As a potential absorber candidate for high-efficient solar cell applications, BaSi2 films are confronted with issues of surface oxidation associated with the high-temperature annealing. Herein, BaSi2 films are deposited by the sputtering technique. A vacuum annealing process is subsequently carried out to crystallize sputtered BaSi2 films. Raman spectroscopy is used to study surface structures and crystalline quality. Elemental depth profile is measured by Auger Electron spectroscopy to understand the compositions of films. Optical and electrical properties are further investigated to reveal the effects of annealing condition. Applying vacuum annealing condition can effectively suppress diffusions of Ba and ensures a stochiometric BaSi2 layer. However, surface oxidation still occurs even in the vacuum environment owing to the high reactivity of Ba. Further attempts to prevent BaSi2 surface oxidation may focus on the combination of other methods, such as capping layer and reducing atmosphere, with vacuum (or low-pressure) annealing condition.

A systematic study of MOCVD reactor conditions and Ga memory effect on properties of thick InAl(Ga)N layers: a complete depth-resolved investigation

Posted on by Lubomír Vančo

CHAUHAN, Prerna – HASENÖHRL, Stanislav – VANČO, Ľubomír – ŠIFFALOVIČ, Peter – DOBROČKA, Edmund – MACHAJDÍK, Daniel – ROSOVÁ, Alica – GUCMANN, Filip – KOVÁČ, Jaroslav jr. – MATKO, Igor – KUBALL, Martin – KUZMÍK, Ján

In CrystEngComm. Vol. 22, iss. 1 (2020)

https://doi.org/10.1039/C9CE01549C

Abstract

Thick InAlN layers (In-molar fraction >0.37) on GaN buffer layers were prepared using a close-coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor. This work provides a discussion of the dependence of reactor parameters (pressure, ammonia flow and temperature) and unintentional Ga-incorporation on structural, optical and chemical properties of those layers down to the nanoscale. Rutherford back-scattering spectrometry, Auger electron spectroscopy, and transmission electron microscopy with the energy dispersive X-ray analysis were used for in-depth chemical analysis of layers. A diminishing Ga-auto-incorporation in thick InAlN layer creates a chemically graded InAl(Ga)N interlayer that assists in releasing of interfacial strain and paves the way toward In-rich InAlN layer. The rate of unintentional Ga-auto-incorporation in InAlN layers increases with decreasing of growth temperature, and increasing of reactor pressure and ammonia flow during growth. Raman and photoluminescence spectroscopy were used to get the crystal structural fingerprint influenced by Ga-incorporation. We suggested that Ga could incorporate at nitrogen vacancies at high reactor pressures (≥200 mbar). Screw dislocations and/or N-vacancies in InAl(Ga)N layers may be energetically favorable sites for In-incorporation and lead to compositional fluctuation and local In-rich InAl(Ga)N phase.

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

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

Posted on by Lubomír Vančo

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

Journal of Raman Spectroscopy, 2019, 0377-0486

doi.org/10.1002/jrs.5666

Abstract

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.