Tuning Optical Signatures of Single- and Few-Layer MoS<sub>2</sub> by Blown-Bubble Bulge Straining up to Fracture

Emerging atomic layer semiconducting crystals such as molybdenum disulfide (MoS<sub>2</sub>) are promising candidates for flexible electronics and strain-tunable devices due to their ultrahigh strain limits (up to ∼20–30%) and strain-tunable bandgaps. However, high strain levels, controllable isotropic and anisotropic biaxial strains in single- and few-layer MoS<sub>2</sub> on device-oriented flexible substrates permitting convenient and fast strain tuning, remain unexplored. Here, we demonstrate a “blown-bubble” bulge technique for efficiently applying large strains to atomic layer MoS<sub>2</sub> devices on a flexible substrate. As the strain increases via bulging, we achieve continuous tuning of Raman and photoluminescence (PL) signatures in single- and few-layer MoS<sub>2</sub>, including splitting of Raman peaks. With proper clamping of the MoS<sub>2</sub> crystals, we apply up to ∼9.4% strain in the flexible substrate, which causes a doubly clamped single-layer MoS<sub>2</sub> to fracture at 2.2–2.6% strain measured by PL and 2.9–3.5% strain measured by Raman spectroscopy. This study opens new pathways for exploiting 2D semiconductors on stretchable substrates for flexible electronics, mechanical transducers, tunable optoelectronics, and biomedical transducers on curved and bulging surfaces.