Temperature-Dependent Phase Transition in High-Quality Janus Transition Metal Dichalcogenide Monolayers by Controlled Plasma-assisted Selenization Process for Nanogeneration and Gas-sensing Application

Paul Albert Sino^1,2,5,6*, Tzu-Wen Kuo^1,2,5,6, Tzu-Chieh Lin^1,2,5,6, Sumayah Wani^1,2,5,6, Chieh-Ting Chen^1,2,5,6, Ming-Jin Liu^1,2,5,6, Kim Tuyen Le², Bushra Rehman^1,2,5,6, Jyh-Ming Wu^2,7, Feng-Chuan Chuang^1,3,4,8, Yu-Lun Chueh^1,2,5,6

¹Department of Physics, National Sun Yat-sen University, Kaohsiung City, Taiwan
²Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu City, Taiwan
³Department of Physics, National Tsing-Hua University, Hsinchu City, Taiwan
⁴Physics Division, National Center for Theoretical Science, Taipei City, Taiwan
⁵College of Semiconductor Research, National Tsing-Hua University, Hsinchu City, Taiwan
⁶Center for Nanotechnology, Materials Science and Microsystem, National Tsing-Hua University, Hsinchu City, Taiwan
⁷High-Entropy Materials Center, National Tsing-Hua University, Hsinchu City, Taiwan
⁸Center for Theoretical and Computational Physics, National Sun Yat-sen University, Kaohsiung City, Taiwan

* Presenter:Paul Albert Sino, email:sinopaulalbert@gmail.com

Janus transition metal dichalcogenides (TMDs) are new kinds of two-dimensional (2D) materials exhibiting unique properties due to their asymmetric structure. The breaking of out-of-plane mirror symmetry in Janus TMDs results to unconventional phenomena such as Rashba splitting and vertical piezo-electric effect. Furthermore, Janus TMDs have been theoretically predicted to be ideal candidates for gas sensing, photocatalysis and electrocatalysis applications. However, despite the increasing attention in recent years, the experimental research on Janus TMDs remains to be scant and temperature-dependent phase-transition has yet to be reported. Furthermore, the reported applications of Janus TMDs are only field-effect transistors (FETs), memory devices, and biological sensors. Here, we present, for the first time, the synthesis of Janus MoSSe and WSSe by plasma-assisted selenization process (PASP). The high-quality of the Janus TMDs was confirmed through various microscopic, spectroscopic, and electrical measurements. Phase-transition in Janus TMDs was observed for 400 °C- and 600 °C-synthesized samples. At high temperatures, the structure of MoSSe becomes unstable resulting to metastable 1T/1T’ phase from 2H phase. Our preliminary results also confirm the superior nanogeneration and gas-sensing performance of Janus MoSSe compared to MoS2. Our study provides another approach towards the synthesis of Janus TMDs for various novel applications.

Keywords: Janus TMDs, Phase-transition, Nanogeneration, Gas-sensing