Strain relaxation in monolayer MoS₂ over flexible substrate

In this communication, we demonstrate uniaxial strain relaxation in monolayer (1L) MoS₂ transpires through cracks in both single and double-grain flakes. Chemical vapour deposition (CVD) grown 1L MoS₂ has been transferred onto polyethylene terephthalate (PET) and poly(dimethylsiloxane) (PDMS) substrates for low (∼1%) and high (1-6%) strain measurements. Both Raman and photoluminescence (PL) spectroscopy revealed strain relaxation via cracks in the strain regime of 4-6%. In situ optical micrographs show the formation of large micron-scale cracks along the strain axis and ex situ atomic force microscopy (AFM) images reveal the formation of smaller lateral cracks due to the strain relaxation. Finite element simulation has been employed to estimate the applied strain efficiency as well as to simulate the strain distribution for MoS₂ flakes. The present study reveals the uniaxial strain relaxation mechanism in 1L MoS₂ and paves the way for exploring strain relaxation in other transition metal dichalcogenides (TMDCs) as well as their heterostructures.