ABSTRACT Janus transition metal dichalcogenides (TMDCs), featuring intrinsic out‐of‐plane symmetry breaking and permanent electrical dipole moments, open novel avenues for atomic‐scale symmetry control. However, the absence of high‐quality, macroscopic single crystals has hindered the exploration of their predicted intriguing properties and practical applications. Herein, we demonstrate the synthesis of millimeter‐scale single‐crystal Janus TMDC monolayers, including MoSSe, WSSe, MoSeS, and WSeS. A combination of spectroscopic, microscopic, and electrical measurements confirms their exceptional crystallinity and spatial homogeneity over large areas. Notably, in contrast to conventional TMDC monolayers, the obtained Janus materials exhibit a strong out‐of‐plane piezoelectric response, with record experimental 𝑑 33 value of ∼2.06 pm/V for WSSe and ∼1.56 pm/V for MoSSe, representing an enhancement of over 15 times compared to previously reported experimental results. Moreover, field‐effect transistors (FETs) based on Janus MoSSe achieve an exceptional carrier mobility of ∼13 cm 2 ·V −1 ·s −1 , along with a device yield of 95% across an array of 100 devices. This work provides a feasible pathway for the scalable production of high‐quality, single‐crystal Janus materials and highlights their promise for integration into next‐generation electronic and optoelectronic devices.
Shen et al. (Thu,) studied this question.