Interlayer separation by laser-induced functionalized graphene for photoluminescence enhancement of graphene/MoS2 heterostructures

Tuning the optoelectronic properties of monolayer MoS2 (1L-MoS2) is highly desired for optoelectronic applications, such as molecular sensors. Stable structures that can be reproducibly fabricated are essential for this, and the mechanism leading to the optical properties can thus be well understood. Here, we demonstrate that the photoluminescence (PL) of 1L-MoS2 can be modulated by photochemically functionalized graphene (F-G), which is covalently modified by phenyl-groups. The materials and molecules, respectively, combined in a heterostructure are graphene, phenyl-groups, and 1L-MoS2. Here we show that the layer-sequence results in a significant difference in PL enhancement. MoS2 supported by F-G (F-G/MoS2) has a 5-fold PL enhancement. More importantly, MoS2 shows only a 1.8 times PL enhancement if stacked underneath F-G (MoS2/F-G). Accordingly, the results indicate that the Schottky barrier and van der Waals interaction between the graphene basal plane and MoS2 interface are dramatically weakened with the enlarged interlayer distance in F-G/MoS2. Consequently, the PL enhancement becomes reduced with the thermal de- functionalization of F-G. Due to the different PL properties induced by layer sequence, we conclude that the phenyl-groups must be considered as a separate molecular component. Thus, the F-G/MoS2 heterostructures bring us new ideas and have potential applications in optoelectronic devices.