Author: Ľubomír Vančo

The Recovery and Resilience Plan for Slovakia

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PROJECT

Auger electron spectroscopy for surface studies of two-dimensional MoS2 layers

ABSTRACT

In recent decades, a huge effort has been paid to the research of various 2D layers including MoS2. Their applicability to broad range of problems, including environmental and climate issues, still attracts the scientists in various fields. But due to technological challenges connected with the production of cleaner 2D surfaces, their application potential has not been fulfilled yet. The aim of the project is to determine how the contamination affects the surface composition of supported and suspended MoS2 layers and how it changes with the applied cleaning procedures. As the tool for the study, Auger electron spectroscopy (AES) will be employed, promoting itself as an exceptional analytical method for 2D layersaddressing the problems of local surface composition, contamination, homogeneity, and cleaning. Response of electrons in MoS2 surfaces to primary electrons will be studied as well, with expected interesting effects not yet described in the methodology of AES.

PROJECT DETAILS

Project number: 09I03-03-V04-00457

Framework/Call: 09I03-03-V04 – Scholarships for Excellent Researchers

Component: Component 9 – More efficient management and strengthening of funding for research, development, and innovation.

Investment: Investment 3 – Excellent Science

Funder: European Union (NextGenerationEU)

Duration: 01 September 2024−31 August 2026

PUBLICATIONS

Ľubomír Vančo, Ravi K. Biroju, Mário Kotlár, Viliam Vretenár, Dipak Maity, Tharangattu N. Narayanan

Nondestructive Imaging and Quantification of Composition in 2D MoS2 and V-Dpoed MoS2 by the Auger Scatterplot Method

In: J. Phys. Chem. C 2025, 129, 20995−21004, https://doi.org/10.1021/acs.jpcc.5c05299

Molybdenum disulfide (MoS2) monolayers have emerged as promising materials for a variety of applications. Their behavior depends critically on surface composition; therefore, careful characterization is necessary to describe their properties accurately. Although Auger electron spectroscopy (AES) is a standard method capable of addressing this issue, it suffers from beam-induced damage and variation of spectral features in complex samples. To overcome these limitations, we employed correlative analysis to examine MoS2 and V-doped MoS2 2D surfaces by using Auger scatterplots. As we demonstrate, this method enables the nondestructive imaging and assessment of the lateral and depth distributions of the elements and provides a remarkably convenient way to estimate S-rich/depleted regions. The scatterplot technique indicates that V doping in MoS2 retards desulfurization in an Ar/H2 plasma environment. By reducing the electron dose, the analysis using scatterplots can improve the accuracy of AES by up to 30%. The Auger scatterplot method provides insight into the affinity or independence of surface constituents through quantitative relationships, enabling separate analysis of the characteristic areas within a complex sample. These findings are supported by Raman spectroscopy and transmission electron microscopy, which highlight the effectiveness of the Auger scatterplots and their potential for examining the surfaces of 2D materials. Auger maps also show a strong correlation with photoluminescence features in MoS2 monolayers, thereby illustrating the overlap with practical applications.

Other publications:

Ľubomír Vančo, Ravi K. Biroju, Mário Kotlár, Viliam Vretenár, Dipak Maity, Tharangattu N. Narayanan: Analysis of two-dimensional molybdenum disulfide layers by scanning Auger microscopy. In: Extended Abstract Book of 14th Conference “Solid State Surfaces and Interfaces” November 18-20, Smolenice, Slovak republic, Comenius University, ISBN 978-80-223-5941-2.

Ľ. Vančo, M. Kotlár, P. Vogrinčič, M. Štrbák, S. Dharmapuri, Determination of thickness in suspended MoS2 layers using backgrounds in Auger electron spectra. In: Proceedings of ADEPT – the International Conference on Advances in Electronic and Photonic Technologies, Nový Smokovec, Slovakia, june 15th – 18th, 2026, EDIS-Publishing Centre of UNIZA, ISBN 978-80-554-2303-6.

Nondestructive Imaging and Quantification of Composition in 2D MoS2 and V-Doped MoS2 by the Auger Scatterplot Method

Nondestructive Imaging and Quantification of Composition in 2D MoS2 and V-Doped MoS2 by the Auger Scatterplot Method

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Ľubomír Vančo, Ravi K. Biroju, Mário Kotlár, Viliam Vretenár, Dipak Maity Tharangattu N. Narayanan

In: J. Phys. Chem. C 2025, 129, 47, 20995–21004

https://doi.org/10.1021/acs.jpcc.5c05299

Abstract

Molybdenum disulfide (MoS2) monolayers have emerged as promising materials for a variety of applications. Their behavior depends critically on surface composition; therefore, careful characterization is necessary to describe their properties accurately. Although Auger electron spectroscopy (AES) is a standard method capable of addressing this issue, it suffers from beam-induced damage and variation of spectral features in complex samples. To overcome these limitations, we employed correlative analysis to examine MoS2 and V-doped MoS2 2D surfaces by using Auger scatterplots. As we demonstrate, this method enables the nondestructive imaging and assessment of the lateral and depth distributions of the elements and provides a remarkably convenient way to estimate S-rich/depleted regions. The scatterplot technique indicates that V doping in MoS2 retards desulfurization in an Ar/H2 plasma environment. By reducing the electron dose, the analysis using scatterplots can improve the accuracy of AES by up to 30%. The Auger scatterplot method provides insight into the affinity or independence of surface constituents through quantitative relationships, enabling separate analysis of the characteristic areas within a complex sample. These findings are supported by Raman spectroscopy and transmission electron microscopy, which highlight the effectiveness of the Auger scatterplots and their potential for examining the surfaces of 2D materials. Auger maps also show a strong correlation with photoluminescence features in MoS2 monolayers, thereby illustrating the overlap with practical applications.

In-situ CVD Grown WS2-MoS2 Lateral Heterostructure with Alloyed Interface: Strong Photoluminescence Enhancement and High On-Off Ratio Field Effect Transistors

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Abdul Kaium Mia, Sourav Dey, Lubomir Vanco, Viliam Vretenar, P. K. Giri

In: Materials Today Nano 31, 100638 (2025)

https://doi.org/10.1016/j.mtnano.2025.100638

Abstract:

The semiconducting 2D transition metal dichalcogenides (TMDs) have gained substantial attention, though the progress in their lateral heterostructures (HS) and in-situ growth for electronic and optoelectronic applications has been very limited. Herein, we report a single-step in-situ chemical vapor deposition growth of bilayer WS2-MoS2 lateral HS, which ensures a clean diffused interface between WS2 and MoS2, enabling efficient charge transport. The spatial Raman, photoluminescent (PL), and Auger mapping of in-situ WS2-MoS2 lateral HS shows a clear transition from pure WS2 to pure MoS2 region through a graded WS(1-x)MoxS2 alloy interface. The composition and the width of the alloy interface could be tuned by careful choice of the proportion of precursor materials and by tuning the growth parameters. Spatially resolved PL spectra and PL mapping reveal a strongly enhanced (more than one order of magnitude) PL intensity in the HS interface attributed to the strain-induced bandstructure modification in the alloyed interface. Interestingly, the alloyed interface in the lateral HS also dramatically improves the electronic properties, resulting in an on-off ratio of 108 in the fabricated field effect transistor, which is two orders of magnitude higher than their individual counterpart. These results on lateral HS are significant, and they pave the way to synthesize other different HSs for future electronic devices and integrated circuits.

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

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A.S. Chaus, O.G. Devoino, M. Sahul, Ľ. Vančo, I. Buranský, M. Kusý

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.

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.

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

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

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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

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

In Journal of raman spectroscopy. Vol. 50, iss. 10 (2019)

https://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.

Growth of lithium hydride thin films from solutions: Towards solution atomic layer deposition of lithiated films

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KUNDRATA, Ivan – FRÖHLICH, Karol – VANČO, Ľubomír – MICUŠÍK, Matej – BACHMANN, Julien

In Beilstein Journal of Nanotechnology. Vol. 10, (2019)

https://doi.org/10.3762/bjnano.10.142

Abstract

Lithiated thin films are necessary for the fabrication of novel solid-state batteries, including the electrodes and solid electrolytes. Physical vapour deposition and chemical vapour deposition can be used to deposit lithiated films. However, the issue of conformality on non-planar substrates with large surface area makes them impractical for nanobatteries the capacity of which scales with surface area. Atomic layer deposition (ALD) avoids these issues and is able to deposit conformal films on 3D substrates. However, ALD is limited in the range of chemical reactions, due to the required volatility of the precursors. Moreover, relatively high temperatures are necessary (above 100 °C), which can be detrimental to electrode layers and substrates, for example to silicon into which the lithium can easily diffuse. In addition, several highly reactive precursors, such as Grignard reagents or n-butyllithium (BuLi) are only usable in solution. In theory, it is possible to use BuLi and water in solution to produce thin films of LiH. This theoretical reaction is self-saturating and, therefore, follows the principles of solution atomic layer deposition (sALD). Therefore, in this work the sALD technique and principles have been employed to experimentally prove the possibility of LiH deposition. The formation of homogeneous air-sensitive thin films, characterized by using ellipsometry, grazing incidence X-ray diffraction (GIXRD), in situ quartz crystal microbalance, and scanning electron microscopy, was observed. Lithium hydride diffraction peaks have been observed in as-deposited films by GIXRD. X-ray photoelectron spectroscopy and Auger spectroscopy analysis show the chemical identity of the decomposing air-sensitive films. Despite the air sensitivity of BuLi and LiH, making many standard measurements difficult, this work establishes the use of sALD to deposit LiH, a material inaccessible to conventional ALD, from precursors and at temperatures not suitable for conventional ALD.