Atomic-Scale Control and In Situ Raman Probing of Hot Carrier Transport in Two-Dimensional Heterojunctions.

Chemical reactions triggered by plasmonic hot carriers attract growing attention due to their high activity and widely adjustable selectivity. However, precise control of hot carrier behaviors and catalytic reactions driven by them on the subnanometer scale remains challenging. Herein, the transportation of plasmonic hot carriers in two-dimensional (2D) van der Waals (vdW) heterojunctions consisting of graphene and MoS₂, as well as its influence on photocatalytic reactions, has been in situ monitored by surface-enhanced Raman spectroscopy (SERS) with atomic layer accuracy. Direct spectral results prove that when the MoS₂ layer gradually moves closer to the top Au nanoparticles (NPs), the reduction reaction efficiency induced by hot electrons improves, while the oxidation process induced by hot holes is inhibited and vice versa. This originates from the redistribution of electromagnetic fields in the plasmonic nanogap as well as the change in the hot carrier generation and transfer efficiency with different MoS₂/graphene vdW heterojunction stacking modes, as revealed by time-resolved transient absorption spectra (TAS), electromagnetic field simulations, and density functional theory (DFT). This work provides valuable insights to deepen the understanding of vdW heterojunction-modulated hot carrier behaviors and reveals the importance of precise photocatalyst design.