Ultrafast Spectral Signatures of Laser-Induced Chalcogen Vacancies in MoS₂

Abstract

Monolayer transition metal dichalcogenides have a variety of unique properties�mechanical flexibility, bandgaps in the visible region, strain tunability, and more�making them viable candidates for a range of applications, including optoelectronic and spintronic devices. Optical probes such as lasers are frequently used to characterize the electronic structure and dynamics of these systems to facilitate device engineering. Critical to the interpretation of such experiments is the ability to distinguish intrinsic sample responses from measurement-induced sample modification or damage. Here, we report laser-induced trion formation in MoS 2 monolayers via the in situ formation of sulfur vacancies. Real-time laser exposure experiments reveal that spectra are significantly modified on the order of seconds of laser irradiation. Ultrafast time-resolved experiments on irradiated samples show that the intrinsic neutral excitons can appear with an apparent time delay with respect to laser-induced trions. This delayed behavior is particularly susceptible to being improperly assigned as, for example, charge transfer in a heterostructure system, and must therefore be considered in future studies of TMDs, TMD heterostructures, and similar systems.