Anomalous lattice vibrations of CVD-grown monolayer MoS₂ probed using linear polarized excitation light

A novel physical phenomenon and advanced application have been explored in 2D low-dimensional van der Waals layered materials due to their reduced in-plane symmetry. The light-matter interaction is observed upon rapid characterization of the 2D material's crystal orientation. Here, the effects of the sample's rotation angle and the incident light's linear polarization angle on the Raman scattering of chemical vapor deposition (CVD)-grown monolayer MoS₂ were investigated. The results show that the crystal orientation of monolayer MoS₂ can be distinguished by analyzing the intensity ratio and frequency difference of its two dominant Raman vibration modes. In addition, an increase in the incident light's power intensity causes the Raman peaks to red shift due to the photothermal effect. Strikingly, it was found that, with an increase in the incident linear polarization angle, the out-of-plane A_1g phonon mode red shifts, while the in-plane E_2g¹ phonon mode blue shifts. The frequency difference consequently decreases from 19.5 cm^-1 to 17.4 cm^-1. The anomalous lattice vibrations of monolayer MoS₂ originate from the built-in strain introduced by the SiO₂/Si substrate. This work paves the way for the investigation and characterization of 2D MoS₂, providing further understanding of the light-matter interaction in 2D materials, which is beneficial for advanced studies on anisotropic MoS₂ based electronic and photoelectric information technologies and sensing applications.