Molybdenum Disulfide Film Growth by Chemical Vapor Deposition with Facial Treated Substrates

We demonstrate atmospheric pressure CVD growth of large domains of molybdenum disulfide (MoS₂) monolayers and multilayers in the presence of an alkali salt like sodium chloride (NaCl) that serves as a seeding promoter. The pre-treatment of the growth substrates with NaCl and the Mo-precursor prior to the start of the MoS₂ film growth affects the growth kinematics and influences the lateral dimensions of the film and its morphology. Using the FactSage software, the role of NaCl in determining the partial pressures of Mo- and S-based compounds in gaseous phase at the growth temperature is elucidated. Under ideal conditions, nucleation is suppressed, and domains are enlarged, resulting in large area growth of MoS₂ monolayers. These monolayers were found to be free of unintentional doping with alkali metal and halogen atoms and exhibit high crystallinity and optoelectronic quality. Field-effect measurements of these films in back-gated devices result in an ON/OFF current ratio of the order of 10⁵.