Strain-Dependent Dielectric and Optical Properties of Monolayer MoS2 with Phase-Sensitive Surface Plasmon Resonance (SPR) Method

Monolayer molybdenum disulfide (MoS2) holds great promise for strain-tunable optoelectronic devices. The strain-dependent dielectric function is a core parameter to characterize the tunability of optoelectronic properties. However, due to the extremely short light–matter interaction path length for atomically thin materials, measurements are challenging. In this work, we measured the dielectric function of strained monolayer MoS2 using the surface plasmon resonance (SPR) method with the simulated annealing particle swarm optimization (SAPSO) algorithm. When the applied strain ranged from −0.23% (compressive strain) to +0.20% (tensile strain), the dielectric function at seven characteristic wavelengths around the exciton absorption peaks was extracted. Our results demonstrate that both the real part (ε2r) and the imaginary part (ε2i) of the dielectric function evolved almost linearly with the applied strain from −0.23% to +0.20%. Based on these results, we further obtained the strain-induced variations in the refractive index (n) and the extinction coefficient (k). At exciton absorption peak B (600 nm), the strain-induced change rate for n reached a maximum of about −0.0141%−1. At the rising edge of the B exciton absorption (580 nm), the strain-induced change rate for k reached a maximum of about −0.3261%−1. This work presents a quantitative extraction of strain-dependent dielectric function of monolayer MoS2 over excitonic band-edge wavelengths using phase SPR–SAPSO fitting. The proposed method can be extended to the measurement of other atomically thin materials.