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 MoS 2 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 MoS 2 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 MoSe 2 and the selective extraction mechanism is assumed to be related to intrinsic layer‐dependent energy band properties. Moreover, the special reassembled few‐layer MoS 2 possesses great performance as functional materials in electrocatalysis (127 mV overpotential for hydrogen evolution reaction) and surface‐enhanced Raman spectroscopy (10 5 enhancement factor). These results illustrate the broad prospects of the reassembled few‐layer MoS 2 for optics, catalysis, and sensors.