Raman scattering studies of the lattice dynamics in layered MoS₂

We report non-resonant and resonant Raman scattering studies of layered MoS₂. Owing to its reduced dimensionality, few layered MoS2 is more sensitive to the difference between inter- and intra-layer coupling, which results in unusual frequency shifts of the Raman phonon modes. In addition, relative intensities between the two Raman active phonon modes E_2g¹ and A_1g unexpectedly depend on the laser excitation energy, which might be associated with the electronic band structure, including spin-orbit coupling and phonon dispersions. Through resonant Raman scattering measurements, the indirect-to-direct band gap behavior and electron-phonon interaction information were obtained. Raman scattering spectroscopy is seen to be very effective for studying the layer-dependent characteristics of layered MoS₂.