Abnormal intensity and polarization of Raman scattered light at edges of layered MoS₂

The edges of two-dimensional (2D) materials can exhibit special structure and thus distinctive properties differing from the interior, such as the modified photoluminescence emission, the improved electrocatalytic activity, and the enhanced nonlinear optical response. In this work, we report the observation of abrupt enhancement of Raman scattered light at edges of layered MoS₂, which is closely related to the polarization of the incident light. More importantly, the intensity of out-of-plane A_1g mode is enhanced much more obviously than the in-plane ${\mathrm{E}}_{2\mathrm{g}}^1$ mode. The unique optical effect at edges is also reflected on the alteration of Raman selection rule. The forbidden Raman modes are observed at edge region, and the polarization of Raman scattered light can be modulated by the edge structure, which differs obviously from that of the interior. We attribute these particular performances to the modulation of the intensity and distribution of the electric field for the incident and Raman scattered light at the edge. This work provides a systematic research on the intensity and polarization modulation of the Raman scattering at edges, which would be helpful for understanding the distinctive optical properties of the edge structure.