Stepwise sulfurization of MoO3 to MoS2 thin films studied by real-time X-ray scattering

Chemical vapor deposition (CVD) is commonly used for the large-scale synthesis of the films of two-dimensional (2D) transition metal dichalcogenide (TMD) materials, including MoS2 thin films, which have potential applications in optoelectronics, catalysis, and nanoelectronics. As far as thin film of MoS2 is concerned, the influence of deposition parameters on the chemical reactions in the growth process via CVD synthesis has not yet been exhaustively studied. Here we present a comprehensive, time-resolved, in-situ study of the growth of MoS2 thin film from MoO3 by sulfurization using the grazing-incidence wide-angle X-ray scattering (GIWAXS) in laboratory conditions. We tracked the basic chemical reactions during the sulfurization process in real time by monitoring the phase transformations of MoO3 to MoO2 and MoO2 to MoS2 via a MoOS2 transient phase, although it was not possible to observe it directly. Preferential crystallographic orientation of MoO3, and MoO2 phases during the growth was confirmed. In addition, their activation energies were determined from the crystallization kinetics parameters. The present work highlights the importance of understanding the basic chemical reactions inside the CVD reactor as a prerequisite for optimizing the properties of the final 2D TMD films.