Ultrafast charge transfer dynamics at the MoS 2 / Au interface observed via optical spectroscopy under ambient conditions

Integrating atomically thin transition metal dichalcogenides (TMDCs) with metallic surfaces is an effective strategy to leverage their exceptional properties in advanced devices and catalysts, as it promotes efficient charge carrier injection and extraction from TMDC monolayers. Light-matter interactions in TMDC monolayers predominantly occur at the K point, making the charge carrier dynamics at this point essential for optimizing charge transfer efficiency. However, direct probing of the dynamics at the K point of TMDCs interfaced with metal substrates remains challenging. In this Letter, we employed pump-probe azimuth- and polarization-dependent final-state sum frequency generation spectroscopy to investigate the ultrafast dynamics of charge transfer at the K point of a MoS 2 monolayer on an Au substrate. We observed ultrafast injection of photoexcited hot electrons from Au into the monolayer MoS 2 conduction band minimum, followed by a fast return ( ∼ 2 ps) and a trap-state-mediated slow return ( ∼ 60 ps) processes, driven by an internal electric field. The direct optical observation of the full electron dynamics at the K point of MoS 2 monolayer in ambient conditions provides valuable insights into optimizing the transfer of charge carrier across the TMDC/metal interface through optimized contacts, informing the design of advanced TMDC-based devices with enhanced charge transfer rates.