Oxygen-Assisted Anisotropic Chemical Etching of MoSe₂ for Enhanced Phototransistors

The etching process can serve as an effective top-down approach that facilitates direct construction of tuned patterns, reversely studying growth mechanisms and further inducing unexpected physical properties. Currently, etching behaviors of monolayer transition-metal dichalcogenides (TMDs) have been rarely explored and the intrinsic etching mechanism still needs to be fully elucidated. Here, we demonstrate a facile and controllable oxygen-assisted anisotropic chemical etching of two-dimensional (2D) materials. Taking MoSe2 as an example, a series of well-defined etched patterns can be fabricated by precisely modulating the pretreatment time of oxygen plasma and the etching time. Atomic characterization exhibits that the edges of etched patterns are mainly zigzag-terminated. Density functional theory calculations highly agree with the experimental results, indicating an energy preference for zigzag edges. The as-produced MoSe2 flakes can be used as part of heterojunctions to display intriguing optoelectronic properties. The field-effect transistor based on as-etched MoSe2 flakes and the 2D poly(3-hexylthiophene-2,5-diyl) crystal shows a distinct enhanced ambipolar photoresponse. Our strategy offers a new direction for preparing patterned 2D TMDs with desirable characteristics, opening the door for facilitating the development of optoelectronics.