Direct bandgap engineering with local biaxial strain in few-layer MoS₂ bubbles

Strain engineering provides an important strategy to modulate the optical and electrical properties of semiconductors for improving devices performance with mechanical force or thermal expansion difference. Here, we present the investigation of the local strain distribution over few-layer MoS₂ bubbles, by using scanning photoluminescence and Raman spectroscopies. We observe the obvious direct bandgap emissions with strain in the few-layer MoS₂ bubble and the strain-induced continuous energy shifts of both resonant excitons and vibrational modes from the edge of the MoS₂ bubble to the center (10 μm scale), associated with the oscillations resulted from the optical interference-induced temperature distribution. To understand these results, we perform ab initio simulations to calculate the electronic and vibrational properties of few-layer MoS₂ with biaxial tensile strain, based on density functional theory, finding good agreement with the experimental results. Our study suggests that local strain offers a convenient way to continuously tune the physical properties of a few-layer transition metal dichalcogenides (TMDs) semiconductor, and opens up new possibilities for band engineering within the 2D plane.