Defect-mediated strong exciton-phonon coupling between flower-like WS2 film with vicinity layers

The exciton-phonon coupling plays an important role in the optical properties of two-dimensional (2D) materials. In the preparation of 2D TMDC films, there are often different degrees of intrinsic defects, which have significant impacts on their optical and electrical properties. Here, we have investigated the effect of intrinsic defects on resonant Raman spectroscopy (RRS) in WS 2 . In a modified chemical vapor deposition (CVD) process, flower-like (with three petaloids) WS 2 bilayers (FLO-B) and trilayers (FLO-T) can be produced in S-rich condition. It was found that the LA(M), E 1 2g , A 1g Raman modes and excitons of flower-like WS 2 exhibit abnormal behaviors due to the rich defects in the flower-like WS 2 flakes. The population of X D gets increased and the shift of its binding energy is ~30 meV larger than that of A 0 for the defective flower-like WS 2 , which leads to greatly enhanced exciton-phonon interaction. Under low-frequency RRS, the appearance of petal morphology greatly enhances the scattering intensity and activate the SM 32 phonon mode, normally not seen for backscattering. The appearance of this defect-assisted phonon mode is also related to the increase of scattering cross-section and exciton Bohr radius. Our work reveals the feasibility of shape-controlled exciton-phonon interactions in defective WS 2 films and improves our understanding of the light-matter interaction principles in this material.