Abstract
We investigated the optical properties of nanoscale WS2 monolayers treated with organic solvents. The photoluminescence spectra changed significantly before and after methanol treatment. The sharp spectral peak of the neutral exciton in the methanol-treated sample was shifted to the higher energy side by 18 meV compared to the peak in untreated sample. This shift made the emission peak due to charged excitons clearly visible. Detailed fitting analysis revealed that the methanol treatment relaxed the tensile strain in the nano-sized WS2 monolayer grown on SiO2/Si substrate. In addition to the measurements in air, the results in vacuum and their temperature dependence also support this interpretation. Since this methanol treatment is simple, does not cause sample loss, and does not reduce luminescence efficiency, it may be an effective means to relax strain from nanoscale transition metal dichalcogenides monolayers.
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