Promoting the yield and crystallinity of synthetic WS2 via precursor pretreatment

In this work, we report on improvement of material growth tungsten disulfide (WS2) monolayer quality such as size, density as well as crystallinity with variety of pretreated tungsten trioxide (WO3) powder. The as growth WS2 mono-layer exhibit distinct different photoluminescence (PL) emission measured at room temperature such as shift of PL peak range and exhibit different full width half maximum (FWHM) variation which depends on the pretreatment preparation of WO3 precursor. This PL emission variation is indicative of different relative contribution of exciton, trion and bi-exciton emission on the WS2 surface that resulting from different surface charge state in pretreated WO3 precursor before the growth of WS2. Our comprehensive study indicates that the surface charge state in tungsten oxide precursor would be fundamental for the growth of high quality WS2 monolayer and it is essential to reveal intrinsic physical properties in device fabrication for technological applications.