Electrochemically Exfoliating MoS2 into Atomically Thin Planar-Stacking Through a Selective Lateral Reaction Pathway

Abstract

The production of atomically thin transition-metal dichalcogenides (TMDs) has been investigated through various top-to-down exfoliation methods, such as mechanical and chemical exfoliation, while large-scale chemical exfoliation is sluggish and needs over ten hours to achieve atomically thin TMDs. Herein, a new strategy is reported for exfoliating bulk MoS2 into two/three-layer flakes within tens of seconds through a mild electrochemical treatment. This exfoliation method is driven by a lateral inward oxidation reaction starting from the typical layer edge with a rapid depth penetration, whereby a stacked few-layer (two/three layers) structure is ultimately formed. This efficient reaction process is monitored based on an individual MoS2 on-chip device combined with in situ Raman and cross-sectional scanning transmission electron microscopy, and the uniformity of thickness is demonstrated. This preferentially initiated method can be also extended to produce few-layer MoSe2 and the selective extraction mechanism is assumed to be related to intrinsic layer-dependent energy band properties. Moreover, the special reassembled few-layer MoS2 possesses great performance as functional materials in electrocatalysis (127 mV overpotential for hydrogen evolution reaction) and surface-enhanced Raman spectroscopy (105 enhancement factor). These results illustrate the broad prospects of the reassembled few-layer MoS2 for optics, catalysis, and sensors.