Synthesizing Janus Transition Metal Dichalchogenides by with High Controllability and Reproducibility

In contrast to conventional transition metal dichalcogenides (TMDs) having the MX₂ structure, Janus TMDs break mirror symmetry along vertical direction, providing a novel platform for some exciting phenomena such as piezoelectricity , enhanced Rashba effect , topological superconductivity, and intrinsic skyrmions, etc. Since the first report by Lu et al.[1] of growing Janus MoSeS by hydrogen plasma, Janus TMDs have stimulated great interest and many following works by plasma induced replacement of the top chalcogen layer[2] and directly sulfurization[3,4] have appeared. However, fabricating Janus structures by a more controllable approach with high reproducibility is essential for their applications, which remains challenging. In this work, we report a two-step growth by well controlled plasma treatment and Tellurium passivation to gradually synthesize Janus MSeTe (M=Mo,W) under ultrahigh vacuum condition. We employ reflection high-energy electron diffraction (RHEED) to monitor the whole fabrication process of Janus MSeTe. Piezoelectric force microscopy (PFM) measurements reveal large vertical piezoelectricity. X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED) and scanning transmission electron microscopy (STEM) reveal its chemical composition and atomic structures.

References:

1. Lu, Ang-Yu, et al. "Janus monolayers of transition metal dichalcogenides." Nature nanotechnology 12.8 (2017): 744-749.

2. Trivedi, Dipesh B., et al. "Room-Temperature Synthesis of 2D Janus Crystals and their Heterostructures." Advanced Materials 32.50 (2020): 2006320.

3. Zhang, Jing, et al. "Janus monolayer transition-metal dichalcogenides." ACS nano 11.8 (2017): 8192-8198.

4.Gan, Ziyang, et al. "One pot chemical vapor deposition of high optical quality large area monolayer Janus transition metal dichalcogenides." arXiv preprint arXiv:2205.04751 (2022).