Influence of Epitaxial Graphene Substrate Morphology on the Orientation of CVD-Grown MoS₂ Monolayers

In this work, we analyze the growth of monolayer MoS2 islands on two different epitaxial graphene substrates: graphene on off-axis SiC and graphene on on-axis SiC. The aim is to understand the effect of substrate steps and surface lattice directions on the growth of MoS2 islands, determining their orientation with respect to the epitaxial graphene lattice and the SiC surface morphology. We combine statistical analysis of the preferred orientation of MoS2 islands with atomic resolution imaging through STM and conductive AFM to determine the precise lattice orientation of MoS2 relative to the substrate. Our study reveals that MoS2 islands tend to align with the epitaxial graphene lattice on both substrates and that the uniform step-terrace structure of off-axis substrates reduces the number of mirror-twin domains. These results demonstrate that substrate morphology plays a crucial role in directing the evolution of monolayer MoS2, marking an important step toward wafer-scale growth of single-crystal transition metal dichalcogenides on epitaxial graphene for 2D electronics applications.