Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

TL;DR

This paper demonstrates a method to continuously and reversibly tune the optical band gap of suspended monolayer MoS2 by applying large biaxial strains, revealing significant shifts in optical properties and enabling strain engineering.

Contribution

The study introduces a novel approach using CVD-grown, gas-impermeable crystals to apply large biaxial strains to monolayer MoS2, achieving unprecedented strain levels and detailed optical property analysis.

Findings

Achieved up to 500 meV band gap tuning via biaxial strain.

Observed a linear band gap shift rate of 99 meV/% strain.

Applied strains as large as 5.6% across micron-sized areas.

Abstract

We demonstrate the continuous and reversible tuning of the optical band gap of suspended monolayer MoS2 membranes by as much as 500 meV by applying very large biaxial strains. By using chemical vapor deposition (CVD) to grow crystals that are highly impermeable to gas, we are able to apply a pressure difference across suspended membranes to induce biaxial strains. We observe the effect of strain on the energy and intensity of the peaks in the photoluminescence (PL) spectrum, and find a linear tuning rate of the optical band gap of 99 meV/%. This method is then used to study the PL spectra of bilayer and trilayer devices under strain, and to find the shift rates and Gr\"uneisen parameters of two Raman modes in monolayer MoS2. Finally, we use this result to show that we can apply biaxial strains as large as 5.6% across micron sized areas, and report evidence for the strain tuning of higher level optical transitions.