Impact of Sapphire Substrate Reconstruction on the Structural, Electronic, and Photonic Properties of MoS₂

Transition metal dichalcogenides (TMDs) are commonly grown on single-crystal sapphire via chemical vapor deposition. Understanding how TMD-sapphire interactions affect the structural and photonic properties of TMDs is critical for accurately interpreting optical characterization and distinguishing intrinsic material properties from substrate-induced effects. Here, we report the impact of sapphire surface reconstruction on the structural and photonic properties of MoS₂ monolayers grown by metal-organic chemical vapor deposition. Kelvin probe force microscopy measurements indicate that sapphire step-edge formation during growth enhances surface potential variations, consistent with substrate-induced charge doping at the MoS₂/sapphire interface. Raman and photoluminescence measurements reveal that film/substrate interactions introduce considerable strain and substrate-induced charge doping inhomogeneities across the film, broaden and shift MoS₂ Raman modes, and induce heterogeneous emission. In contrast, photoluminescence, Raman, and transport measurements of MoS₂ films transferred away from their sapphire growth substrates reveal uniform optical responses and device characteristics, indicating that the observed heterogeneity originates from interfacial coupling rather than intrinsic film quality. Together, these results demonstrate that growth-induced TMD-substrate interactions not only influence optical metrology on as-grown films but also impact the transfer processes that underpin device fabrication, emphasizing the importance of controlling interfacial effects for reliable characterization and integration of wafer-scale 2D semiconductors.