Fig. 1. Experimental setup for the growth of MoS₂ based on APCVD

Fig. 2. Schematic illustration of the synthesis of Gr-MoS₂ vertical heterojunction

Fig. 3. Characterizations of monolayer MoS₂. (a) Optical image of monolayer MoS₂ triangles; (b) Raman spectrum of MoS₂, and the inset shows photoluminescence spectrum of MoS₂; (c) AFM topography of MoS₂, and the inset shows height profile for typical monolayer MoS₂; (d) (e) Raman peak intensity mappings of MoS₂ triangle; (f) PL peak intensity mapping of MoS₂ triangle

Fig. 4. Characterizations of Gr-MoS₂ vertical heterojunction. (a) Optical image of monolayer graphene film; (b) graphene strips after plasma etching; (c) optical image of Gr-MoS₂ vertical heterojunction; (d) Raman spectrum of graphene; (e) Raman spectrum of Gr-MoS₂ vertical heterojunction; (f) photoluminescence spectrum of Gr-MoS₂ vertical heterojunction

Fig. 5. Electrical properties of MoS₂ and monolayer graphene. (a) Transfer curves under different V_ds of MoS₂ device; (b) output curves of the MoS₂ device under different V_gs values, and the inset shows an optical image of the MoS₂ device; (c) transfer curves of the graphene device under different V_ds values; (d) output curves of the graphene FET device under different V_gs values, and the inset shows an optical image of this graphene FET device

Fig. 6. Photodetector based on vertical Gr-MoS₂ heterostructure and monolayer MoS₂. (a) Schematic illustration of the photodetector based on vertical Gr-MoS₂ heterostructure; (b) photocurrent switching operation of MoS₂ and Gr-MoS₂; (c) photoresponsivity of monolayer MoS₂ and Gr-MoS₂; (d) source-drain current (I_ds) versus backgate voltage (V_gs) for Gr-MoS₂ in the absence of light and in the presence of light with various illumination powers