Polarized Raman of Nanoscale Two-Dimensional Materials: Combined Optical and Structural Effects

Abstract

The intensity response of polarized Raman is studied using backscattered Raman spectroscopy. In previous works, it was confirmed that the Raman intensities of the E2g1 modes for WS2 and MoS2 as well as the G mode of graphene are independent of the polarization angle. However, a strong correlation is found between them in this work using a confocal Raman system. The E2g1 and A1g modes of nanometer-thick WS2 and MoS2 samples as well as the G mode of bulk graphene are used to investigate the polarization dependency of the Raman intensity for each mode. Additionally, the effects of temperature and sample structure on the Raman intensity are studied using the WS2 sample on both suspended and supported areas. Results of these experiments are explained and fitted by the theoretical Raman intensity profiles. This theoretical study is conducted using the classical theory of polarized Raman spectroscopy and includes all the information about polarization of excitation laser, rotation of the beam splitter, and different vibrational modes of samples, which is considered in Raman tensors. It is concluded that Raman intensity variation with incident laser polarization not only is a function of the material structure but also carries information about the optical functionality of the Raman system.