Detecting forbidden Raman modes

2D LAYERED MATERIALS

Sci. Adv. 4, eaau6252 (2018), doi:10.1126/sciadv.aau6252

In the commonly used back-scattering Raman configuration, some theoretically active Raman modes of layered materials are undetectable in experiments. Now, a team of researchers from the Hong Kong Polytechnic University and Beijing Institute of Technology can selectively detect these forbidden Raman modes at the edge region of various layered materials (including MoS₂, WS₂, WSe₂ and black phosphorus). Yang Chai and his co-workers choose the edge type of layered materials, the polarization direction of the incident light, and the polarization direction of the scattered Raman signal. They distinctly detect the forbidden Raman modes at the edge region in the case that the polarization direction of the incident/scattered light is perpendicular to the edge of layered materials. Their comprehensively experimental and theoretical studies reveal that the anisotropic refractive index of layered materials can drastically change the polarization and propagation directions of incident and scattered light at the edge region of layered materials. The directions of the light are thoroughly different in the edge and body region of layered materials, which enables to detect forbidden Raman modes at edge region and can be validated through the calculations from Raman scattering formula. This work facilitates future exploration of unique optical properties at the edge region.

Ping-Heng Tan (Institute of Semiconductors, CAS, Beijing, China)