Understanding metal organic chemical vapour deposition of monolayer WS2: the enhancing role of Au substrate for simple organosulfur precursors

Abstract

We find that the use of Au substrate allows fast, self-limited WS₂ monolayer growth using a simple sequential exposure pattern of low cost, low toxicity precursors, namely tungsten hexacarbonyl and dimethylsulfide (DMS). We use this model reaction system to fingerprint the technologically important metal organic chemical vapour deposition process by operando X-ray photoelectron spectroscopy (XPS) to address the current lack of understanding of the underlying fundamental growth mechanisms for WS₂ and related transition metal dichalcogenides. Au effectively promotes the sulfidation of W with simple organosulfides, enabling WS₂ growth with low DMS pressure (<1 mbar) and a suppression of carbon contamination of as-grown WS₂, which to date has been a major challenge with this precursor chemistry. Full WS₂ coverage can be achieved by one exposure cycle of 10 minutes at 700 °C. We discuss our findings in the wider context of previous literature on heterogeneous catalysis, 2D crystal growth, and overlapping process technologies such as atomic layer deposition (ALD) and direct metal conversion, linking to future integrated manufacturing processes for transition metal dichalcogenide layers.