Role of hydrogen in 2D MoS2: A combined RBS and NRA study

Molybdenum disulfide (MoS₂) is a two-dimensional (2D) material that has attracted attention due to its change from an indirect to a direct bandgap in monolayer form, with possible applications in nanoelectronics, photodetectors, and catalysis [1,3]. Recent studies have shown that thermal treatments in hydrogen can induce changes in its properties, notably by introducing ferromagnetism and altering its catalytic activity for the hydrogen evolution reaction [2]. However, the mechanism behind these modifications is not yet fully understood, partly because there is little quantitative data on how much hydrogen is incorporated into the material and how this relates to the observed changes in structure and properties.

This work addresses this question by employing a multi-technique approach combining Rutherford Backscattering Spectrometry (RBS) with structural and optical characterization. Our methodology uses CVD-grown MoS₂ monolayers processed in a controlled, static atmosphere of deuterium (²H) at 200, 300, and 400 °C. RBS is used to check the film composition and to detect possible sulfur loss during the thermal treatments. Raman and photoluminescence (PL) spectroscopy track modifications to the crystal structure and optical properties, while X-ray photoelectron spectroscopy (XPS) monitors changes in the chemical state and surface composition.

As part of this ongoing work, we plan to perform Nuclear Reaction Analysis (NRA) using the deuterium as a tracer, which will allow us to quantify the amount of hydrogen incorporated under each condition. The NRA results will provide quantitative data on deuterium concentration, enabling us to correlate hydrogen incorporation with the observed changes. This quantification is expected to indicate whether hydrogen intercalates into the van der Waals gaps, substitutes sulfur atoms, or acts as a surface adsorbate. The work illustrates how RBS and other characterization techniques can be used together, with future NRA measurements, to study light element incorporation in 2D materials.