Photo-induced exfoliation of monolayer transition metal dichalcogenide semiconductors

Abstract Transition metal dichalcogenide (TMDC) monolayers have attracted great attention due to their unique electronic properties, which promise their applications especially in optoelectronics and valleytronics. A simple and reliable way to fabricate the monolayers is highly desirable for wide applications. Herein, we report a photo-induced exfoliation method for the controllable fabrication of monolayer TMDCs proceeded with the oxidation reaction of TMDCs by the photo-generated holes. The commonly used microscope halogen lamp is sufficient to initiate the exfoliation in pure water. A bulk MoS ₂ flake with a surface area of 10 000 µ m ² and a thickness of 100 nm can be directly exfoliated down to monolayer within four seconds under a 94 nW µ m ⁻² 660 nm laser illumination and by applying 0.1 V potential electrochemically, achieving an astonishing exfoliation speed and efficiency. This method is demonstrated to be applicable also to other semiconducting TMDCs, such as MoSe ₂ , WSe ₂ , and WS ₂ .