Second order resonant Raman scattering in single layer tungsten disulfide (WS$_{2}$)

TL;DR

This study investigates the resonant Raman spectra of single-layer WS$_{2}$, revealing a second order Raman peak that affects layer number estimation and depends on polarization angle, emphasizing the need for careful spectral analysis.

Contribution

It demonstrates the presence of a second order Raman peak in single-layer WS$_{2}$ and highlights the importance of considering polarization effects in spectral analysis.

Findings

Second order Raman peak (2LA) appears near the E$^{1}_{2g}$ mode.

Intensity of 2LA strongly depends on polarization angle.

Neglecting 2LA can lead to incorrect layer number assignment.

Abstract

Resonant Raman spectra of single layer WS$_{2}$ flakes are presented. A second order Raman peak (2LA) appears under resonant excitation with a separation from the E$^{1}_{2g}$ mode of only $4$cm$^{-1}$. Depending on the intensity ratio and the respective line widths of these two peaks, any analysis which neglects the presence of the 2LA mode can lead to an inaccurate estimation of the position of the E$^{1}_{2g}$ mode, leading to a potentially incorrect assignment for the number of layers. Our results show that the intensity of the 2LA mode strongly depends on the angle between the linear polarization of the excitation and detection, a parameter which is neglected in many Raman studies.