Substrate-induced variances in morphological and structural properties of MoS2 grown by chemical vapor deposition on epitaxial graphene and SiO2.

In this work, we report the impact of the substrate type on the morphological and structural properties of molybdenum disulfide (MoS2) grown by chemical vapor deposition (CVD). MoS2 synthesized on a 3D substrate, that is SiO2, in response to the change of the thermodynamic conditions yielded different grain morphologies, including triangles, truncated triangles, and circles. Simultaneously, MoS2 on graphene is highly immune to the modifications of the growth conditions, forming triangular crystals only. We explain the differences between MoS2 on SiO2 and graphene by the different surface diffusion mechanisms, namely hopping and gas-molecule-collision-like, respectively. As a result, we observe the formation of thermodynamically favorable nuclei shapes on graphene, while on SiO2 a full spectrum of domain shapes can be achieved. Additionally, graphene withstands the growth process well, with only slight changes in strain and doping. Furthermore, by the application of graphene as a growth substrate we realize van der Waals epitaxy, and achieve strain-free growth, as suggested by the photoluminescence (PL) studies. We indicate that PL, contrary to Raman spectroscopy, enables us to arbitrarily determine the strain levels in MoS2.