Synthesis and Transfer of Large-Area Monolayer WS₂ Crystals: Moving Toward the Recyclable Use of Sapphire Substrates

Abstract

Two-dimensional layered transition metal dichalcogenides (TMDs) show intriguing potential for optoelectronic devices due to their exotic electronic and optical properties. Only a few efforts have been dedicated to large-area growth of TMDs. Practical applications will require improving the efficiency and reducing the cost of production, through (1) new growth methods to produce large size TMD monolayer with less-stringent conditions, and (2) nondestructive transfer techniques that enable multiple reuse of growth substrate. In this work, we report to employ atmospheric pressure chemical vapor deposition (APCVD) for the synthesis of large size (>100 μm) single crystals of atomically thin tungsten disulfide (WS₂), a member of TMD family, on sapphire substrate. More importantly, we demonstrate a polystyrene (PS) mediated delamination process <i>via</i> capillary force in water which reduces the etching time in base solution and imposes only minor damage to the sapphire substrate. The transferred WS₂ flakes are of excellent continuity and exhibit comparable electron mobility after several growth cycles on the reused sapphire substrate. Interestingly, the photoluminescence emission from WS₂ grown on the recycled sapphire is much higher than that on fresh sapphire, possibly due to <i>p</i>-type doping of monolayer WS₂ flakes by a thin layer of water intercalated at the atomic steps of the recycled sapphire substrate. The growth and transfer techniques described here are expected to be applicable to other atomically thin TMD materials