Scalable synthesis and defect modulation of large monolayer WS2 via annealing in H2S atmosphere/thiol treatment to enhance photoluminescence

Monolayer WS2 (1L-WS2) possesses direct band gap, which is beneficial for light emitting applications. However, high quality sample obtained via mechanical exfoliation suffers from ultralow yield of large flakes while large 2D material monolayers synthesized by chemical vapour deposition (CVD) unintentionally induce many defects, resulting in low photoluminescence (PL) intensity. Herein, we firstly control the 1L-WS2 scalable growth through H-2 introduction at the beginning of the CVD synthesis. Its domain size can be increased from 1 mu m up to 20 mu m with higher coverage, compared to that synthesized without H-2 introduction. Then, we propose scalable ways to anneal the obtained large 1L-WS2 in Ar diluted hydrogen sulfide (H2S) atmosphere at 750 degrees C or to treat it with (3-mercaptopropyl) trimethoxysilane (MPS). Its PL intensity can be increased to 12 times by H2S or more interestingly to 30 times by MPS, respectively. Our systematic analyses show that the drastic PL improvements are mainly attributed to the reduction of structural defects by H2S and MPS, which is facilitated via the H- bond in them. The results help to explore routes to obtaining large-size single crystalline transition metal dichalcogenides monolayer (1L-TMDCs) and intense PL emission.