Temperature induced modulation of resonant Raman scattering in bilayer 2H-MoS$_{2}$

TL;DR

This study investigates how temperature affects resonant Raman scattering in high-quality bilayer 2H-MoS$_{2}$ encapsulated in hexagonal BN, revealing temperature-dependent vibrational features and intensity trends of phonon modes near the A excitonic resonance.

Contribution

It provides detailed temperature-dependent Raman spectra of bilayer 2H-MoS$_{2}$ under resonant conditions, highlighting the evolution of vibrational modes and their intensities from 5 K to 320 K.

Findings

First and second order phonon modes observed across temperature range.

Raman-active A$_{1g}$ mode quenches with increasing temperature.

Infrared-active B$_{1u}$ mode becomes stronger than Raman-active mode at room temperature.

Abstract

The temperature evolution of the resonant Raman scattering from high-quality bilayer 2H-MoS$_{2}$ encapsulated in hexagonal BN flakes is presented. The observed resonant Raman scattering spectrum as initiated by the laser energy of 1.96 eV, close to the A excitonic resonance, shows rich and distinct vibrational features that are otherwise not observed in non-resonant scattering. The appearance of 1$^{st}$ and 2$^{nd}$ order phonon modes is unambiguously observed in a broad range of temperatures from 5 K to 320 K. The spectrum includes the Raman-active modes, $i.e.$ E$_\textrm{1g}^{2}$($\Gamma$) and A$_\textrm{1g}$($\Gamma$) along with their Davydov-split counterparts, $i.e.$ E$_\textrm{1u}$($\Gamma$) and B$_\textrm{1u}$($\Gamma$). The temperature evolution of the Raman scattering spectrum brings forward key observations, as the integrated intensity profiles of different phonon modes show diverse trends. The Raman-active A$_{1g}$($\Gamma$) mode, which dominates the Raman scattering spectrum at $T$=5~K quenches with increasing temperature. Surprisingly, at room temperature the B$_\textrm{1u}$($\Gamma$) mode, which is infrared-active in the bilayer, is substantially stronger than its nominally Raman-active A$_\textrm{1g}$($\Gamma$) counterpart.