Biaxial versus uniaxial strain tuning of single-layer MoS$_2$

TL;DR

This study experimentally compares biaxial and uniaxial strain effects on single-layer MoS2, demonstrating biaxial strain's greater efficiency in tuning its optical properties and providing a simple method to apply such strain.

Contribution

It introduces a straightforward experimental setup for applying biaxial strain and directly compares its effects with uniaxial strain on MoS2, confirming theoretical predictions.

Findings

Biaxial strain causes a larger redshift in excitonic features than uniaxial strain.

Biaxial strain gauge factor is 2.3 times larger than uniaxial.

Biaxial strain effectively tunes the optical properties of MoS2.

Abstract

Strain engineering has arisen as a powerful technique to tune the electronic and optical properties of two-dimensional semiconductors like molybdenum disulfide (MoS2). Although several theoretical works predicted that biaxial strain would be more effective than uniaxial strain to tune the band structure of MoS2, a direct experimental verification is still missing in the literature. Here we implemented a simple experimental setup that allows to apply biaxial strain through the bending of a cruciform polymer substrate. We used the setup to study the effect of biaxial strain on the differential reflectance spectra of 12 single-layer MoS2 flakes finding a redshift of the excitonic features at a rate between -40 meV/% and -110 meV/% of biaxial tension. We also directly compare the effect of biaxial and uniaxial strain on the same single-layer MoS2 finding that the biaxial strain gauge factor is 2.3 times larger than the uniaxial strain one.