Role of nuclei in controllable MoS2 growth by modified chemical vapor deposition

The large area and high-quality two-dimensional molybdenum disulfide (2D-MoS2) film has been synthesized by a modified single-zone chemical vapor deposition technique. The influence of gas environment, reaction temperature and gap distance (between MoO3 precursor and substrate) on 2D-MoS2 growth were systematically investigated. A stable gas environment was prerequisite for the formation of 2D-MoS2, and it can be achieved by adjusting the pressure and flow rate of N-2 in the furnace tube, which was numerical estimated via Antoine equation. The thickness, quality (uniformity and crystallinity), roughness, and chemical composition of the MoS2 nano-film were characterized by the optical microscopy, scanning electron microscope, Raman spectroscopy, Atomic force microscope, and X-ray photoelectron spectroscopy, respectively. The results showed that the quality of MoS2 nano-film was greatly influenced by the nucleation density on the substrate, which could be controlled by modulating the reaction temperature and gap distance. Moreover, a "frustum-like" model was established to match the practical reaction situation and clarify the internal relationship among reaction temperature, gap distance and the nucleation density of MoS2 film. Finally, a high-quality monolayer MoS2 nano-film, at 800 A degrees C with a gap distance of 3.5 mm, was obtained and verified by experimental and numerical analyses.