Encapsulation-Free, Air-Stable Monolayer WS2 Using Graphene Substrate

Abstract

In this study, we report the special role of graphene substrates in substantially enhancing the air-stability of two-dimensional transition metal dichalcogenides (TMDs) flakes. Compared to the well-known, short-term air degradation of TMDs flakes grown on the conventional SiO2/Si substrate (representatively, WS2/SiO2), epitaxially grown WS2 flakes on graphene substrate (WS2/Gr) maintain their clean and uniform surface without any encapsulation even after a year in ambient air conditions. Our investigations indicate that high crystal quality is one of the key factor that determines the air-stability of TMDs, and we present experimental evidences of the relation between defects and aging progress. Furthermore, we propose the significant contribution of the charge transfer-induced doping effect to the prevention of aging for the first time. This work emphasizes the importance of the substrate for enhancing the stability of TMDs materials and can pave the way for the long-term performance and practical TMDs applications.