Investigation of the Growth Process of Continuous Monolayer MoS2 Films Prepared by Chemical Vapor Deposition

Recently, great efforts have been devoted to study of molybdenum disulfide (MoS2), particularly monolayer MoS2 semiconductor thin films, due to its excellent electrical and optical properties. Direct growth of continuous monolayer MoS2 films by ambient-pressure chemical vapor deposition is reported herein. Optical microscopy, Raman spectroscopy, photoluminescence spectra (PL), atomic force microscopy, x-ray photoelectron spectroscopy (XPS), and high-resolution transmission electronic microscopy were used to characterize the electronic and structural properties of the films, demonstrating that the MoS2 films grown on silicon dioxide/silicon (SiO2/Si) substrate with spatial size on micron scale were high quality, single crystal, continuous, and monolayer. Raman and PL mapping were performed to confirm the uniformity of the monolayer MoS2 films. The morphological variation of the MoS2 films after different reaction times was observed by optical microscopy and scanning electron microscopy, revealing the growth process and thus helping to understand that the growth mechanism during synthesis of continuous large-area films depends on the distribution of the reactive intermediate molybdenum oxide (MoO3-x) due to its lower saturation vapor density. Back-gated transistors based on MoS2 films were fabricated, exhibiting current on/off ratio of similar to 10(4) and subthreshold swing (SS) of 0.44 V dec(-1). This work contributes to synthesis of large-area continuous films, thus paving the way for future scaled-up fabrication of MoS2 electronic devices.