Electron-phonon and phonon-phonon anharmonic interactions in 2H-MoX2 (X=S, Te): A comprehensive Resonant Raman study

TL;DR

This comprehensive Raman study investigates how anharmonic phonon interactions in 2H-MoX2 (X=S, Te) are influenced by temperature, excitation, polarization, thickness, and substrate effects, crucial for nanoelectronic applications.

Contribution

It provides detailed insights into anharmonic phonon behavior in MoS2 and MoTe2, including effects of thickness and substrate, advancing understanding of their vibrational properties.

Findings

Anharmonicity varies with flake thickness and phonon symmetry.

Substrate influences the anharmonic properties of phonons.

Higher-order Raman processes reveal complex anharmonic interactions.

Abstract

Transition metal dichalcogenides (TMDs) are layered materials which show excellent potential for nanoelectronic and optoelectronic applications. However, as many of the exciting features of these materials are controlled by the anharmonic effects, a proper understanding of the phonon properties and anharmonicity associated with these materials is essential for the proposed applications to be realized. We present here a comprehensive study on the phonon properties of two different TMDs; viz., MoS2 and MoTe2, as a function of temperature, laser excitations, and polarization, as well as flake-thickness. Our study includes the measurement of anharmonicity in the first-order and higher order Raman scattering processes. The variations in anharmonicity with the thickness of MoS2 and MoTe2 have been explained in terms of their phonon symmetries, electron-phonon coupling, and phonon-phonon interactions. Further, the effect of the underlying substrate on the anharmonic properties of the in-plane and out-of-plane phonons has also been estimated from the Raman measurements, thus elucidating the intrinsic phonon properties of the 2D layered materials.