Ultrafast Spectral\nSignatures of Laser-Induced Chalcogen\nVacancies in MoS<sub>2</sub>

Monolayer transition metal dichalcogenides\nhave a variety of unique\npropertiesmechanical flexibility, bandgaps in the visible\nregion, strain tunability, and moremaking them viable candidates\nfor a range of applications, including optoelectronic and spintronic\ndevices. Optical probes such as lasers are frequently used to characterize\nthe electronic structure and dynamics of these systems to facilitate\ndevice engineering. Critical to the interpretation of such experiments\nis the ability to distinguish intrinsic sample responses from measurement-induced\nsample modification or damage. Here, we report laser-induced trion\nformation in MoS<sub>2</sub> monolayers via the in situ formation\nof sulfur vacancies. Real-time laser exposure experiments reveal that\nspectra are significantly modified on the order of seconds of laser\nirradiation. Ultrafast time-resolved experiments on irradiated samples\nshow that the intrinsic neutral excitons can appear with an apparent\ntime delay with respect to laser-induced trions. This delayed behavior\nis particularly susceptible to being improperly assigned as, for example,\ncharge transfer in a heterostructure system, and must therefore be\nconsidered in future studies of TMDs, TMD heterostructures, and similar\nsystems.