Formation of large-area MoS2 thin films by oxygen-catalyzed sulfurization of Mo thin films

Abstract

While transition metal dichalcogenide (TMD) thin films are most commonly synthesized by vapor transport using solid metal oxide precursors, directly converting metal thin films to TMDs may be more scalable and controllable, e.g., to enable large-area coating by vacuum deposition. The thermodynamics are favorable for MoS2 formation from Mo in sulfur-rich environments, but sulfurization tends to be slow and the product is highly dependent on the chemical pathway taken. Here, the authors report on the role of trace oxygen gas (O2) for the sulfurization of Mo films. They study the formation of MoS2 from Mo films in H2S vapor, between 350 and 500 °C and with varying levels of O2. They find that the presence of trace levels of O2 accelerates the crystallization of MoS2 and affects the layer orientation, without changing the kinetics of mass transport or the final film composition. O2 acts as a catalyst to promote the crystallization of MoS2 at lower temperatures than otherwise possible. These results provide new insights into the growth of MoS2 by sulfurization and suggest that introducing an appropriate catalyst during chalcogenide phase formation could enable new processes for making homogeneous, large-area MoS2 films at low processing temperature on a variety of substrates.