Centrum pre nanodiagnostiku materiálov

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 14^th 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 15^th – 18^th, 2026, EDIS-Publishing Centre of UNIZA, ISBN 978-80-554-2303-6.

Recently, the Supplementary Cover Art for manuscript: “Graphene-ZnO Thin-Film Heterostructure-Based Efficient  UV Photosensors” has been published in the ACS Applied Electronic Materials. Dr Ravi K. Biroju, who is the main author of this article explains, that this work basically demonstrates fabrication of CVD grown graphene/ZnO thin-film van der Waals heterostructures. When we combine a wide direct band gap semiconductor such as ZnO and a highly conductive layer of graphene, we get a unique platform for applications such as photosensors and gas sensors. Under light illumination, the effective separation of photo-generated electron−hole pairs by the local electric field suppresses carrier recombination rates and increases carrier lifetime. This leads to an increased free carrier density. It can reduce the Schottky barrier between graphene and the ZnO thin film, facilitating the transport and collection of photocarriers. As a result, a high I_light/I_dark ratio can be achieved, much higher than for bare ZnO thin films or ZnO nanostructures.