Controlling sulphur precursor addition for large single crystal domains of WS2.

We show that controlling the introduction time and the amount of sulphur (S) vapour relative to the WO3 precursor during the chemical vapour deposition (CVD) growth of WS2 is critical to achieving large crystal domains on the surface of silicon wafers with a 300 nm oxide layer. We use a two furnace system that enables the S precursor to be separately heated from the WO3 precursor and growth substrate. Accurate control of the S introduction time enabled the formation of triangular WS2 domains with edges up to 370 μm which are visible to the naked eye. The WS2 domains exhibit room-temperature photoluminescence with a peak value around ∼635 nm and a full-width at half-maximum (FWHM) of ∼12 nm. Selected area electron diffraction from different regions of the triangular WS2 domains showed that they are single crystal structures