Exciton–Phonon Interactions in Strained Domes of Monolayer MoS₂ Studied by Resonance Raman Spectroscopy

This work describes a resonance Raman study performed in the domes of monolayer MoS₂ using 23 different laser excitation energies covering the visible and near-infrared (NIR) ranges. The multiple excitation results allowed us to investigate the exciton–phonon interactions of different phonons (A${}^{\prime }$₁, E${}^{\prime }$, and LA) with different excitonic optical transitions in biaxially strained monolayer MoS${}_2$. The analysis of the intensities of the two first-order peaks, A${}^{\prime }$₁ and E${}^{\prime }$, and the double-resonance 2LA Raman band as a function of the laser excitation furnished the values of the energies of the indirect exciton and the direct excitonic transitions in the strained MoS${}_2$ domes. It was noticed that the out-of-plane A${}^{\prime }$₁ phonon mode is significantly enhanced only by the indirect exciton I and the C exciton, whereas the in-plane E${}^{\prime }$ mode is only enhanced by the C exciton of the MoS₂ dome, thus revealing the weak interaction of these phonons with the A and B excitons in the strained MoS${}_2$ domes. On the other hand, the 2LA Raman band is significantly enhanced at the indirect exciton I and by the A (or B) exciton but not enhanced by the C exciton, thus showing that the LA edge phonons that participate in the double-resonance process in MoS${}_2$ have a weak interaction with the C exciton.