Revisiting the Epitaxial Growth Mechanism of 2D TMDC Single Crystals

Abstract Epitaxial growth of 2D transition metal dichalcogenides (TMDCs) on sapphire substrates has been recognized as a pivotal method for producing wafer‐scale single‐crystal films. Both step‐edges and symmetry of substrate surfaces have been proposed as controlling factors. However, the underlying fundamental still remains elusive. In this work, through the molybdenum disulfide (MoS 2 ) growth on C/M sapphire, it is demonstrated that controlling the sulfur evaporation rate is crucial for dictating the switch between atomic‐edge guided epitaxy and van der Waals epitaxy. Low‐concentration sulfur condition preserves O/Al‐terminated step edges, fostering atomic‐edge epitaxy, while high‐concentration sulfur leads to S‐terminated edges, preferring van der Waals epitaxy. These experiments reveal that on a 2 in. wafer, the van der Waals epitaxy mechanism achieves better control in MoS 2 alignment (≈99%) compared to the step edge mechanism (<85%). These findings shed light on the nuanced role of atomic‐level thermodynamics in controlling nucleation modes of TMDCs, thereby providing a pathway for the precise fabrication of single‐crystal 2D materials on a wafer scale.