Tensile Strain-Induced Bandgap Reduction and Exciton Recombination in a Trilayer MoS2 Nanosheet Wrinkle: Implications for Nanoscale Optoelectronic and Photonic Devices

The effects of uniaxial strain on the local band structure modification in a single wrinkle in a trilayer (3L) molybdenum disulfide (MoS2) flake have been enlightened by combining complementary atomic force microscopy, Raman and photoluminescence microspectroscopies. Controlled wrinkles were introduced in 3L MoS2 flakes by using buckling instability, inducing local tensile strains of up to 0.07%. The ability to induce and fabricate stable wrinkles in 3L MoS2, which is a nanoscale system whose thickness is smaller than 2 nm, arises from the material’s reduced thickness. Submicron-scale spatial mapping of the isolated wrinkle revealed a reduction of the direct bandgap by 10 meV, accompanied by a quenching of the radiative recombination of excitons in the wrinkle compatible with an antifunneling effect, where excitons drift away from lower-bandgap areas before recombination. Finally, angle-resolved photoemission microspectroscopy further demonstrated a shift of the valence band toward higher binding energies in the isolated MoS2 wrinkle. Combining these results with the ones from optical spectroscopies results in a type-II band alignment between the flat and the strained regions, with downward shifts in both the conduction and valence bands. These new insights into the local electronic structure in locally strained 3L MoS2 nanosheets may help the design and performance of nanoscale optoelectronic and photonic devices by enabling precise control over the excitonic properties and the energetic spatial landscape.