Mechanism of Surfactant-Mediated Tungsten Disulfide Growth from Monolayers to Bilayers

Yu-Han Wang^1,2*, Wei-Yen Woon^1,2

¹Molecular Science and Technology Program, Taiwan International Graduate Program, Institute of Atomic and Molecular Science, Academia Sinica, Taipei, Taiwan
²Department of Physics, National Central University, Taoyuan, Taiwan

* Presenter:Yu-Han Wang, email:angelajhs2008@gmail.com

Two-dimensional transition metal dichalcogenides (TMDCs) have been a hot topic due to its outstanding optical and electrical properties. As one of the members, the direct bandgap of ~2.0 eV in tungsten disulfide (WS₂) monolayer and its high quantum yield make it a good candidate for optoelectronic devices while the nature of indirect bandgap in WS₂ bilayer is suitable for field-effect transistor (FET) fabrication. However, controllable growth of large grain WS₂ is difficult to be achieved and detailed growth dynamics from monolayer to bilayer has not been explored. In this work, we demonstrated perfectly-stacked bilayer WS₂ growth through NaCl-mediated thermal chemical vapor deposition. Basic characterizations on optical properties, structure, and chemical composition were conducted through photoluminescence (PL) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Moreover, we monitored WS₂ growth from monolayers to bilayers. Growth dynamics and the mechanism were studied by statistics of grain size, nucleation center, coverage, nucleation density, and growth rate. Moreover, the relation between the growth of monolayer and bilayer was also explored experimentally.

Keywords: Tungsten Disulfide, Chemical Vapor Deposition, Growth Dynamics