Multilayered heterostructures of two-dimensional materials have recently attracted increased interest because of their unique electronic and optical properties. Here, we present chemical vapor deposition (CVD) growth of triangular crystals of monolayer MoS2 on single-crystalline hexagonal graphene domains which are also grown by CVD. We found that MoS2 grows selectively on the graphene domains rather than on the bare supporting SiO2 surface. Reflecting the heteroepitaxy of the growth process, the MoS2 domains grown on graphene present two preferred equivalent orientations. The interaction between the MoS2 and the graphene induced an upshift of the Raman G and 2D bands of the graphene, while significant photoluminescence quenching was observed for the monolayer MoS2. Furthermore, photoinduced current modulation along with an optical memory effect was demonstrated for the MoS2-graphene heterostructure. Our work highlights that heterostructures synthesized by CVD offer an effective interlayer van der Waals interaction which can be developed for large-area multilayer electronic and photonic devices.

The growth of single-layer graphene on Cu metal by chemical vapor deposition (CVD) is a versatile method to synthesize high-quality, large-area graphene. It is known that high CVD temperatures, close to the Cu melting temperature (1083 ºC), are effective for the growth of large graphene domains, but the growth dynamics of graphene over the high-temperature Cu surface is not clearly understood. Here, we investigated the surface dynamics of the single-layer graphene growth by using heteroepitaxial Cu(111) and Cu(100) films. At relatively lower temperatures, 900~1030 ºC, the as-grown graphene showed the identical orientation with the underlying Cu(111) lattice. However, when the graphene was grown above 1040 ºC a new stable configuration of graphene with 3.4º-rotation became dominant. This slight rotation is interpreted by the enhanced graphene-Cu interaction due to the formation of long-range ordered structure. Further increase of the CVD temperature gave the graphene which is rotated with a wide angle distributions, suggesting the enhanced thermal fluctuation of the Cu lattice. The band structures of CVD graphene grown at different temperatures are well correlated with the observed structural change of the graphene. The strong impact of high CVD temperature on a Cu catalyst was further confirmed by the structural conversion of a Cu(100) film to Cu(111) which occurred during the high temperature CVD process. Our work presents important insight on the growth dynamics of CVD graphene, which can be developed to high quality graphene for future high-performance electronic and photonic devices.