Interface Kinetics Assisted Barrier Removal in Large Area 2D-WS Growth to Facilitate Mass Scale Device Production.

Growth of monolayer WS of domain size beyond few microns is a challenge even today; and it is still restricted to traditional exfoliation techniques, with no control over the dimension. Here, we present the synthesis of mono- to few layer WS film of centimeter size on graphene-oxide (GO) coated Si/SiO substrate using the chemical vapor deposition CVD technique. Although the individual size of WS crystallites is found smaller, the joining of grain boundaries due to -bonded carbon nanostructures (~3-6 nm) in GO to reduced graphene-oxide (RGO) transformed film, facilitates the expansion of domain size in continuous fashion resulting in full coverage of the substrate. Another factor, equally important for expanding the domain boundary, is surface roughness of RGO film. This is confirmed by conducting WS growth on Si wafer marked with few scratches on polished surface. Interestingly, WS growth was observed in and around the rough surface irrespective of whether polished or unpolished. More the roughness is, better the yield in crystalline WS flakes. Raman mapping ascertains the uniform mono-to-few layer growth over the entire substrate, and it is reaffirmed by photoluminescence, AFM and HRTEM. This study may open up a new approach for growth of large area WS film for device application. We have also demonstrated the potential of the developed film for photodetector application, where the cycling response of the detector is highly repetitive with negligible drift.