Crystalline tungsten sulfide thin films by atomic layer deposition and mild annealing

Tungsten disulfide (WS2) is a semiconducting 2D material, which is gaining increasing attention in the wake of graphene and MoS2 owing to its exciting properties and promising performance in a multitude of applications. Herein, the authors deposited WSx thin films by atomic layer deposition using W2(NMe2)6 and H2S as precursors. The films deposited at 150 °C were amorphous and sulfur deficient. The amorphous films crystallized as WS2 by mild postdeposition annealing in H2S/N2 atmosphere at 400 °C. Detailed structural characterization using Raman spectroscopy, x-ray diffraction, and transmission electron microscopy revealed that the annealed films consisted of small (<10 nm) disordered grains. The approach proposed by the authors enables deposition of continuous and smooth WS2 films down to a thickness of a few monolayers while retaining a low thermal budget compatible with potential applications in electronics as well as energy production and storage, for example.