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 substrate type on the morphological and structural properties of molybdenum disulfide (MoS₂) grown by chemical vapor deposition (CVD). MoS₂ synthesized on a three-dimensional (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 mechanisms, 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.