Fano-Type Wavelength-Dependent Asymmetric Raman Line Shapes from MoS2 Nanoflakes

Abstract

Excitation wavelength-dependent Raman spectroscopy has been carried out to study electron-phonon interaction (Fano resonance) in multi-layered bulk 2H-MoS2 nano-flakes. The electron-phonon coupling is proposed to be caused due to interaction between energy of an excitonic quasi-electronic continuum and the discrete one phonon, first-order Raman modes of MoS2. It is proposed that an asymmetrically broadened Raman line shape obtained by 633 nm laser excitation is due to electron-phonon interaction whose electronic continuum is provided by the well-known A and B excitons. Typical wavelength-dependent Raman line shape has been observed, which validates and quantifies the Fano interaction present in the samples. The experimentally obtained Raman scattering data show very good agreement with the theoretical Fano-Raman line-shape functions and help in estimating the coupling strength. Values of the electron-phonon interaction parameter obtained, through line-shape fitting, for the two excitation wavelengths have been compared and shown to have generic Fano-type dependence on the excitation wavelength.