Growth of Two-Dimensional Molybdenum Disulfide via Chemical Vapor Deposition

Graphene has successfully been a 2D material applied in various fields, but it is not the most appropriate candidate for many electronic devices unless its bandgap structure is tuned through functionalization. Among all other 2D material families, transition metal dichalcogenides (TMDs), represented by molybdenum disulfide (MoS2), are promising and emerging in power electronics due to their large direct bandgap and other electronic properties. 2D MoS2 has been fabricated through different approaches such as mechanical exfoliation, chemical etching, and chemical vapor deposition (CVD). The current major challenge in fabricating 2D MoS2 films is to produce a high-quality large-area monolayer film at a controlled condition. This thesis study is to grow 2D MoS2 films by CVD method at various experimental settings and to characterize the size, thickness, and morphology of the films, towards finding an optimal processing condition. Experimental settings for the growth parameters include the precursor amounts and placements, growth time, growth temperature, carrier gas flow rate, substrates, and seeding promoters. The growth films are characterized with the help of optical microscopy, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM). It is found that 1) MoS2 growth is sensitive to the carrier flow rate and temperature; and 2) 2D MoS2 grain size and areal coverage are correlated with grow time as well as the distance from the promoter PTAS (perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt) resource. Existence of monolayer MoS2, in the presence of PTAS promotor, is confirmed with Raman Spectroscopy and AFM. Multilayer MoS2 films with grains up to several hundreds of micrometers, confirmed with optical microscopy, SEM and Raman, are successfully grown on clean Si/SiO2 substrate in the presence of PTAS promotor vapor in the vicinity. Growth of monolayer/multilayer MoS2 on sapphire and graphene was also demonstrated.