Substrate-Modulated Effect on the Photoluminescence and Carrier Dynamics of Large-Area Monolayer MoS₂

The monolayer thickness of MoS2 enables it to exhibit exceptional physical and chemical properties; yet, it also renders it highly susceptible to substrate modulation. Concurrently, its optical and electronic properties might be greatly affected by the intrinsic attributes, structures, and morphologies of the underlying substrates. Hereby, studies on the substrate-modulated effect stemming from interfacial interactions are essential for the applications of monolayer MoS2. Herein, large-size monolayer MoS2 films were successfully grown on sapphire, mica, and TiO2 substrates with 6 × 6 mm2 by chemical vapor transfer. The optical properties, carrier dynamics, and interface charge transfer of MoS2 for three types of substrates are investigated to evaluate the substrate-modulated effect through femtosecond laser transient absorption spectroscopy. The comparative result reveals that the semiconducting TiO2 substrate exerts significant modulatory effects on the photoluminescence, absorption properties, and exciton dynamics of MoS2, in contrast to the insulating sapphire and mica substrates. Intriguingly, the exciton dynamics display substrate-dependent variations across the investigated platforms: MoS2 on the sapphire exhibits the shortest exciton lifetime among the three substrates, while mica-supported MoS2 demonstrates exceptionally prolonged excitonic lifetimes, highlighting the critical role of substrate interactions in modulating nanoscale exciton behavior. These observed discrepancies could be attributed to three factors: heterogeneity in the dielectric environments, interfacial electron transfer, and variations in crystalline quality of the synthesized MoS2 films. The insights gained from this study on the substrate-modulating effect on the optical properties of MoS2 could be extended to other two-dimensional heterostructures, paving the way for innovative applications in optical and optoelectronic devices.