The WS2/graphene heterostructure in this study was fabricated via a standard all-dry transfer technique and low-temperature annealing. E-beam lithography (EBL) and thermal evaporation were then employed to define Au/Cr electrodes. Before transferring a WS2 layer on an exfoliated graphene flake, oxygen plasma treatment was first introduced to etch the graphene into a desired shape. Figure exhibits an optical microscopy image of a typical device, where both electrodes were fabricated on top of thin-layered WS2. A Raman spectrum (Figure ) collected at the heterostructure region indicates the fingerprint of WS2 (2LA(M) peak at 351.6) and graphene (G peak at 1582 cm -1 and 2D peak at 2700 cm -1 ) .