Unusual stacking sequence of MoS2 and WS2 vertical heterostructures in one-pot chemical vapor deposition growth

Chemically well-designed one-pot growth is an efficient strategy for producing complex chemical compounds. Although the methodology has been successfully modified and adopted for growing layered transition metal dichalcogenide (LTMD) heterostructures, the simultaneous synthesis of multiple LTMDs in a single reactor may lead to unexpected stacking sequences. Since WS2 (top)/MoS2 (bottom) is known as a conventional result, here, we report that its inverted form can also rarely occur in one-pot chemical vapor deposition growth. An optimized Ar-ion bombardment process on the heterostructured area and subsequent Raman signal probing verified the initial stacking sequence of heterostructures: this sequential procedure was used for structure identification in this study. Unlike the growth of conventional heterostructures, we found that growing MoS2 can cover inactive W precursor beads. H-2 gas injection then triggers WS2 growth between the MoS2 layer and substrate, forming an inverted MoS2 (top)/WS2 (bottom) heterostructure. Although the reaction sequence is fixed, our results indicate that their stacking may lead to unintended consequences which should be closely monitored for future applications.