Biaxial versus uniaxial strain tuning of single-layer MoS2

Strain engineering has arisen as a powerful technique to tune the electronic and optical properties of two-dimensional semiconductors like molybdenum disulfide(MoS). Although several theoretical works predicted that biaxial strain would be more effective than uniaxial strain to tune the band structure of MoS, 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 MoSflakes finding a redshift of the excitonic features at a rate between-40 me V/% and-110 me V/% of biaxial tension. We also directly compare the effect of biaxial and uniaxial strain on the same single-layer MoSfinding that the biaxial strain gauge factor is 2.3 times larger than the uniaxial strain one.