Nanoscale patterns at molecule/MoS₂ heterostructure and their effects on the interlayer exciton dynamics.

The dynamics of interlayer excitons (IX) in transition metal dichalcogenides (TMD) heterostructures has shown to be influenced by the moiré potential formed at the interface. Similar periodic potentials can also be formed at van der Waals organic/TMD interfaces by controlling the nanoscale patterns formed by the molecule on the TMD layer. We investigated the IX dynamics in heterostructures formed by PTCDI and PTCDA with monolayer (ML) MoS₂. The two molecules have very similar electronic structures but form different lattice structures on MoS₂. Using photoemission spectroscopy, a large energy splitting in the molecular orbital was observed in PTCDI/MoS₂ but not in PTCDA/MoS₂. The energy level splitting can be attributed to the two different molecular patterns formed on the MoS₂ surface. Due to the energy level splitting, IX properties of PTCDI/MoS₂ is very different from that of PTCDA/MoS₂. Time-resolved photoemission spectroscopy measurements show that the electron within an IX is spatially trapped near the interface for PTCDI/MoS₂, whereas it is spatially delocalized across the molecular films for PTCDA/MoS₂. As a result of the trapping, photoluminescence intensity of an order of magnitude larger was observed from the IX in PTCDI/MoS₂, compared to PTCDA/MoS₂.