Growth of large sized two-dimensional MoS2 flakes in aqueous solution

A large lateral size and low dimensions are prerequisites for next generation electronics. Since the first single layer MoS2 transistor reported by Kis's group in 2011, layered transition metal dichalcogenides (TMDs) have been demonstrated to be the ideal candidate for next generation electronics. However, the development of large scale and low cost growth techniques is a crucial step towards TMDs' inclusion in modern electronics and photoelectronics. In this work we develop a cheap, wet chemical, and environment friendly deposition process for two dimensional MoS2 flakes with extended size. For our deposition process, ammonium tetrathiomolybdate (ATTM) dissolved in deionized water was used as precursor solution and was deposited on a SiO2/Si substrate through a Langmuir-Blodgett like deposition process. To our knowledge, this is the first time MoS2 flakes have been grown in an aqueous solution. Large-sized MoS2 flakes exceeding 150 mu m in lateral size were obtained after thermal decomposition. Thicknesses ranging from a monolayer to 5 monolayers were confirmed by AFM and Raman spectroscopy. Further investigations revealed that the quality of the produced flakes strongly depends on the post growth thermal treatment and its atmosphere. This simple and nontoxic deposition method is suitable for the preparation of large (hybrid) transition metal dichalcogenide nanostructures for applications in next generation electronics.