Strain Engineering and Raman Spectroscopy of Monolayer Transition Metal Dichalcogenides

Abstract

We describe a facile technique based on polymer encapsulation to apply\nseveral percent controllable strains to monolayer and few-layer Transition\nMetal Dichalcogenides (TMDs). We use this technique to study the lattice\nresponse to strain via polarized Raman spectroscopy in monolayer WSe2 and WS2.\nThe application of strain causes mode-dependent redshifts, with larger shift\nrates observed for in-plane modes. We observe a splitting of the degeneracy of\nthe in-plane E' modes in both materials and measure the Gruneisen parameters.\nAt large strain, we observe that the reduction of crystal symmetry can lead to\na change in the polarization response of the A' mode in WS2. While both WSe2\nand WS2 exhibit similar qualitative changes in the phonon structure with\nstrain, we observe much larger changes in mode positions and intensities with\nstrain in WS2. These differences can be explained simply by the degree of\niconicity of the metal-chalcogen bond.\n