Tailoring exciton dynamics of monolayer transition metal dichalcogenides by interfacial electron-phonon coupling

With their strong light-matter interaction and rich photo-physics, two-dimensional (2D) transition metal dichalcogenides (TMDs) are important candidates for novel photonic and spin-valleytronic devices. It is highly desirable to control the photocarrier behaviours of monolayer TMDs to suit the needs of device functionalities. Here, through interfacial engineering, i.e., by depositing monolayer MoSe2 onto different oxide substrates (SiO2, Al2O3 and HfO2), we have revealed large tuning of the exciton relaxation times in monolayer TMDs. Significantly, the non-radiative recombination of MoSe2 is found shortened by almost one order of magnitude, from 160 ± 10 ps (on SiO2) to 20 ± 4 ps (on HfO2). Theoretical simulations based on ab initio non-adiabatic molecular dynamics (NAMD) method, together with temperature-dependent optical spectroscopy, identifies interfacial electron-phonon (e-ph) coupling as the leading mechanism for the lifetime tuning. Our results establish interface engineering as an effective knob for manipulating excited-state dynamics of monolayer TMDs. Monolayer transition metal dichalcogenides are potential candidates for photonic devices but improvement in photocarrier dynamics, such as the lifetime of excitons, are first required. Using a mixture of simulation and spectroscopy the authors demonstrate that the interface between a monolayer and substrate can be used to tune exciton relaxation times in MoSe2.