In situ study of photo-induced chemical modification in transition metal dichalcogenides*

In this work, we performed an in situ Raman-PL study of the laser-induced chemical modification of transition metal dichalcogenides layers. Using a homemade sealed mini-chamber with a quartz optical viewport, a laser beam (532 nm) was focused onto the sample, consisting on MoSe₂ or WSe₂, while keeping a reactive sulfur-rich atmosphere within the chamber. The process can be tuned thereby choosing appropriate laser power, exposure time, and reactive gas environment. The time-dependent intensities of the Raman peaks were fitted to exponentially decaying functions. Depending on the reactive atmosphere, two different processes with distinct time constants can be identified for the creation of Se vacancies. The subsequent incorporation of sulfur atoms into the Se vacancy sites was also determined from time dependent Raman spectra. The optimization of this process will allow to develop techniques based on photo-induced chemical reactions for local doping, alloying and the fabrication of in-plane TMD heterostructure.