Anomalous excitonic resonance Raman effects in few-layer MoS2

TL;DR

This study investigates anomalous resonance effects in the Raman spectra of few-layer MoS2, revealing unique enhancement behaviors linked to excitonic interactions at specific excitation energies.

Contribution

It uncovers novel anomalous resonance effects in MoS2 Raman spectra, highlighting the role of excitons and exciton-polaritons in these phenomena.

Findings

Maximum Raman intensity at ~2.8 eV for single layer

Anomalous enhancement at 1.96 eV excitation energy

Observation of a broad peak at ~38 cm-1 linked to excitonic resonance

Abstract

The resonance effects on the Raman spectra from 5 to 900 cm-1 of few-layer MoS2 thin films up to 14-layers were investigated by using six excitation energies. For the main first-order Raman peaks, the intensity maximum occurs at ~2.8 eV for single layer and at ~2.5 eV for few-layer MoS2, which correspond to the band-gap energy. At the excitation energy of 1.96 eV, several anomalous behaviors are observed. Many second-order peaks are anomalously enhanced even though the main first-order peaks are not enhanced. In the low-frequency region (<100 cm-1), a broad peak centered at ~38 cm-1 and its second order peak at 76 cm-1 appear for the excitation energy of 1.96 eV. These anomalous resonance effects are interpreted as being due to strong resonance with excitons or exciton-polaritons.