Substrate-induced modulation of transient optical response of large-area monolayer MoS₂

The intrinsic properties of two-dimensional (2D) transition-metal dichalcogenides (TMDs) are profoundly influenced by their interface conditions. Engineering the TMD/substrate interface is crucial for harnessing the unique optoelectronic properties of 2D TMDs in device applications. This study delves into how the transient optical properties of monolayer (ML) MoS₂ are affected by the substrate and film preparation processes, specifically focusing on the generation and recombination pathways of photoexcited carriers. Our experimental and theoretical analyses reveal that induced strain and defects during transfer process play pivotal roles in shaping these optical properties. Through femtosecond transient absorption measurements, we uncover the impact of substrate alterations on the carrier trapping process in ML MoS₂. Moreover, we investigate exciton-exciton annihilation (EEA), demonstrating that the EEA rate varies with different substrates and significantly decreases at low temperatures (77 K). This research paves the way for customizing the optoelectronic properties of TMDs through strategic interface engineering, potentially leading to the creation of highly efficient electronic devices such as optoelectronic memory, light-emitting diodes, and photodetectors.