Raman studies of MoS₂ under strain at different uniaxial directions

Raman spectra of bulk and few layers MoS₂ under strain at different uniaxial directions have been measured. MoS₂ samples, encapsulated in between polyethylene terephthalate (PET) of octadecagonal shape and a layer of polymethlmethacrylate (PMMA), were bended in order to apply uniaxial tensile strain along different directions of MoS₂. For bulk MoS₂, the Raman shift rates of the E¹ _2g and A_1g modes (the change of the Raman peak position versus strain level) were very small and almost the same for strains applied along different directions. On the other hand, the Raman shift rates of few layers MoS₂ were larger than those in bulk MoS₂. In addition, they also exhibited distinctive anisotropic strain responses. On the basis of our results, we believe that the armchair and zigzag directions of the exfoliated MoS₂ might be determined by monitoring the variation of Raman shifts of the E¹ _2g and A_1g modes in different strained directions of MoS₂.