Strain Relaxation of Monolayer WS2 on Plastic Substrate

Strain‐dependent electrical and optical properties of atomically thin transition metal dichalcogenides may be useful in sensing applications. However, the question of how strain relaxes in atomically thin materials remains not well understood. Herein, the strain relaxation of triangular WS2 deposited on polydimethylsiloxane substrate is investigated. The photoluminescence of trions (X–) and excitons (X0) undergoes linear redshifts of ≈20 meV when the substrate tensile strain increases from 0 to 0.16. However, when the substrate strain further increases from 0.16 to 0.32, the redshifts cease due to strain relaxation in WS2. The strain relaxation occurs through formation of wrinkles in the WS2 crystal. The pattern of wrinkles is found to be dependent on the relative angle between an edge of the triangular WS2 crystal and tensile strain direction. Finite element simulations of the strain distribution inside the WS2 crystals explain the experimental observations. Strain relaxation with wrinkle formation is observed on monolayer WS2 triangular crystals at high tensile strain. Raman and photoluminescence mapping, atomic force microscopy, and finite element simulation are applied to investigate the characteristics of wrinkles. The results reveal the distribution of wrinkles is highly dependent on the orientation of the triangle crystals relative to the tensile strain direction.