Davydov Splitting, Resonance Effect and Phonon Dynamics in CVD grown Layered MoS2

TL;DR

This study investigates the phonon dynamics and Davydov splitting in CVD-grown layered MoS2 using temperature-dependent Raman spectroscopy, revealing strong interlayer interactions and resonance effects across a broad temperature range.

Contribution

It provides new insights into Davydov splitting and phonon anharmonicity in MoS2, highlighting the temperature-dependent resonance effects and layer-dependent phonon mode behavior.

Findings

Davydov splitting observed in A1g and E12g modes, more pronounced at low temperature.

Number of Davydov components increases with the number of layers.

Resonance effects cause a sixty-fold increase in phonon mode intensity at low temperature.

Abstract

We present a comprehensive temperature dependent Raman measurements for horizontally aligned CVD grown layered MoS2 in a temperature range of 4 to 330 K under resonance condition. Our analysis of temperature dependent phonon frequency shift and linewidth suggest a finite role of three and four phonon anharmonic effect. We observed Davydov splitting of the out-of-plane (A1g ) and in-plane (E12g ) modes, attributed to the weak interlayer interaction, and reflected in the appearance of additional modes with decreasing temperature for both 3 layers and few layers system. We also observed that the number of Davydov splitting components are more in few layers as compared to 3L MoS2, suggesting it increases with increasing number of layers. Temperature evaluation of the Raman spectra shows that the Davydov splitting, especially for A1g mode, is very strong and well resolved at low temperature. We note that A1g mode shows splitting at low temperature, while E12g mode is splitted even at room temperature, and that suggests to prominent role of A1g mode to the interlayer interaction. Further, the temperature dependence tuning of resonance effect is observed, via almost sixty fold increase in the intensity of the phonon modes at low temperature.