Role of Chalcogen atoms in In Situ Exfoliation for Large-Area 2D Semiconducting Transition Metal Dichalcogenides

Zhiying Dan Ronak Sarmasti Emami Giovanna Feraco Melina Vavali Dominic Gerlach Petra Rudolf Antonija Grubisic-Cabo ^*

• University of Groningen, Groningen, Netherlands

Two-dimensional (2D) transition metal dichalcogenides have emerged as a promising platform for next-generation optoelectronic and spintronic devices. Mechanical exfoliation using adhesive tape remains the dominant method for preparing 2D materials of highest quality, including transition metal dichalcogenides, but always results in small-sized flakes. This limitation poses a significant challenge for investigations and applications where large scale flakes are needed. To overcome these constraints, we explored the preparation of 2D WS 2 and WSe 2 using a recently developed kinetic in situ single-layer synthesis method (KISS). In particular, we focused on the influence of different substrates, Au and Ag, and chalcogen atoms, S and Se, on the yield and quality of the 2D films. The crystallinity and spatial morphology of the 2D films were characterized using optical microscopy and atomic force microscopy, providing a comprehensive assessment of exfoliation quality. Low-energy electron diffraction verified that there is no preferential orientation between the 2D film and the substrate, while optical microscopy revealed that WSe 2 consistently outperformed WS 2 in producing large monolayers, regardless of the substrate used. Finally, X-ray diffraction and X-ray photoelectron spectroscopy demonstrate that no covalent bonds are formed between the 2D material and the underlying substrate. These results identify KISS method as a non-destructive approach for a more scalable approach of high-quality 2D transition metal dichalcogenides.