Controlled Plasma Thinning of Bulk MoS(2) Flakes for Photodetector Fabrication

[Image: see text] The electronic properties of layered materials are directly determined based on their thicknesses. Remarkable progress has been carried out on synthesis of wafer-scale atomically molybdenum disulfide (MoS(2)) layers as a two-dimensional material in the past few years in order to transform them into commercial products. Although chemical/mechanical exfoliation techniques are used to obtain a high-quality monolayer of MoS(2), the lack of suitable control in the thickness and the lateral size of the flakes restrict their benefits. As a result, a straightforward, effective, and reliable approach is widely demanded to achieve a large-area MoS(2) flake with control in its thickness for optoelectronic applications. In this study, thick MoS(2) flakes are obtained by a short-time bath sonication in dimethylformamide solvent, which are thinned with the aid of a sequential plasma etching process using H(2), O(2), and SF(6) plasma. A comprehensive study has been carried out on MoS(2) flakes based on scanning electron microscopy, atomic force microscopy, Raman, transmission electron microscopy, and X-ray photoelectron microscopy measurements, which ultimately leads to a two-cycle plasma thinning method. In this approach, H(2) is used in the passivation step in the first subcycle, and O(2)/SF(6) plasma acts as an etching step for removing the MoS(2) layers in the second subcycle. Finally, we show that this technique can be enthusiastically used to fabricate MoS(2)-based photodetectors with a considerable photoresponsivity of 1.39 A/W and a response time of 0.45 s under laser excitation of 532 nm.