Molybdenum disulfide MoS₂ is a layered compound semiconductor material which belongs to the family of transition metal dichalcogenides (TMDC). The optoelectronic properties of these materials are strongly influenced by the thickness of the film. Particularly the band gap changes from an indirect to a direct transition by reducing the film thickness to a monolayer. In our recently started research activities, we investigate various growth procedures, including chemical vapor deposition (CVD) [1], atomic layer deposition (ALD) [2] and solution-based approaches [3]. We investigate the reaction pathway and growth mechanisms during the layer formation, and characterize the structural and opto-electronic properties. Furthermore, using deterministic stamping and film transfer techniques, we prepare free-standing TMDC sample stacks suitable for transmission electron microscopy.

Our in-house developed CVD type approach is based on a vapor-phase assisted sulphurization process (VASP) which allows for reproducible synthesis of large-scale monolayer MoS₂ on SiO₂/Si and sapphire. Current research activities focus on our recently developed ALD process which is performed inside a rapid thermal processing reactor. This process exhibits a high tolerance towards the growth parameters and allows for rapid processing of monolayer MoS₂ with different properties, such as domain size, photoluminescence yield etc.

In a novel approach, we are exploring the formation of various patterns and shapes of MoS₂ by self-assembly of molecules via a wet-chemical synthesis. We are so far able to produce highly luminescent samples which contain alternating patterns of thin (monolayer type) and thick (bulk type) domains. Further investigations on growth of defined patterns via spray pyrolysis and chemical inkjet printing are underway.

Recent publication:

[1] D. Pareek, M. A. Gonzalez, J. Zohrabian, M.H. Sayed, V. Steenhoff, C. Lattyak, M. Vehse, C. Agert, J. Parisi, S. Schäfer, L. Gütay, A vapor-phase-assisted growth route for large-scale uniform deposition of MoS₂ monolayer films, RSC advances 9, 107-113 (2019)

[2] M.A. Gonzalez, L. Büsing, D. Pareek, J. Parisi, S. Schäfer, L. Gütay, Synthesis of Large-Area MoS₂ monolayer films by a Parameter-Resilient ALD Approach (Manuscript in preparation)

[3] D. Pareek, K. G. Roach, M. A. Gonzalez, L. Büsing, J. Parisi, L. Gütay, S. Schäfer, Micro-patterned deposition of MoS₂ ultrathin-films by a controlled droplet dragging approach, Scientific Reports, 11, 13993 (2021).  doi.org/10.1038/s41598-021-93278-6