Rolling Up a Monolayer MoS₂Sheet

Monolayer MoS₂ samples were grown by chemical vapor deposition method. The as-grown MoS₂ continuous film was then treated argon plasma at a pressure of 0.3 Torr, plasma power of 25 W, and temperature of 150°C for duration of 20 min. Since defect sites in this polycrystalline film are highly reactive; after plasma treatment, the separation of grain boundaries can be clearly seen. Interestingly, the film starts to scroll along the separated edges when we further increase the plasma treatment duration to 40 min. Monolayer MoS₂ samples grown on various substrates, including sapphire, BN, and graphite substrates, were also investigated. In order to see the detailed structures of these MoS₂ nanoscrolls, high resolution transmission electron microscopy (HRTEM) studies were also carried out. XPS was further used to analyze the MoS₂ nanoscroll composition. It is concluded that the generation of S vacancies caused by argon plasma treatment is the key factor of scrolling. This convenient, solvents-free, and high-yielding approach for nanoscroll fabrication is also suitable for the fabrication of other 2D transition metal dichalcogenides.