Tracking Optical Properties During Atomic Substitution Process from MoSe2 to Janus MoSeS

Janus transition metal dichloride (TMDC) is a TMDC with two different chalcogenide elements on the upper and lower surfaces. This special structure is reported to break the out-of-plane symmetry of the monolayer TMDC and produce out-of-plane polarization. This is expected to lead to the development of new electronic properties, such as Rashba spin splitting and piezoelectricity. There have been several reports on the synthesis of Janus TMDCs, and in recent years, the use of chalcogen spices containing H2 plasma for atomic substitution on the surface of TMDC has attracted attention since Janus TMDCs can be generated at room temperature [1,2]. However, the generation process of Janus TMDCs with this method has not been well under-stood. In addition, the physical properties in the intermediate state between TMDC and Janus TMDC have also not been clarified, although the control of the intermediate state is important for tuning the physical properties of Janus TMDCs. Thus, elucidating the intermediate partially sub-stituted Janus (PSJ) state between MoSe2 and Janus MoSeS state is essential for understanding the synthesis dynamics and tuning the electrical properties of TMDCs.