Strain tuning of optical emission energy and polarization in monolayer and bilayer MoS2

TL;DR

This study investigates how uniaxial tensile strain affects the vibrational and optoelectronic properties of monolayer and bilayer MoS2, revealing significant shifts in emission energy and polarization behavior.

Contribution

It provides detailed experimental insights into strain-induced changes in MoS2's optical and vibrational properties using Raman and photoluminescence spectroscopy.

Findings

Raman E^1_{2g} mode splits under strain

Band gap shifts by approximately 48-46 meV/% strain

PL polarization decreases with strain

Abstract

We use micro-Raman and photoluminescence (PL) spectroscopy at 300K to investigate the influence of uniaxial tensile strain on the vibrational and optoelectronic properties of monolayer and bilayer MoS2 on a flexible substrate. The initially degenerate E^1_{2g} Raman mode is split into a doublet as a direct consequence of the strain applied to MoS2 through Van der Waals coupling at the sample-substrate interface. We observe a strong shift of the direct band gap of 48meV/(% of strain) for the monolayer and 46meV/% for the bilayer, whose indirect gap shifts by 86meV/%. We find a strong decrease of the PL polarization linked to optical valley initialization for both monolayer and bilayer samples, indicating that scattering to the spin-degenerate Gamma valley plays a key role.