Formation of large area WS nanosheets using an oxygen-plasma assisted exfoliation suitable for optical devices.

We report a facile method to realize large area two-dimensional tungsten disulfide nanosheets. The formation of such large WS sheets is feasible through sonication in water and dimethyl-sulfoxide (DMSO) solutions, leading to well-separated mono and few layer flakes. The exfoliation has been improved by extensive immersion in near-freezing water prior to probe sonication and subsequent addition of DMSO. By applying oxygen plasma before exfoliation, the size and distribution of sheets become more uniform and larger mono and double-layered structures with sizes of the order of 1 μm are achieved. Different analyses such as SEM, TEM, AFM, DLS and Raman spectroscopy have been employed to understand the mechanism of the exfoliation and study the effects of various parameters such as water temperature, duration and plasma power. The optical properties of WS sheets have been examined with a 532 nm laser illumination and demonstrate superior responsivity and detectivity of 0.59 A W and 6.5 × 10 cm Hz W, respectively.