Strain-shear coupling in bilayer MoS2

Condensed Matter - Materials Science Science Q Materials Science (cond-mat.mtrl-sci) FOS: Physical sciences 02 engineering and technology 0210 nano-technology 01 natural sciences Article 0104 chemical sciences
DOI: 10.1038/s41467-017-01487-3 Publication Date: 2017-11-03T11:17:17Z
ABSTRACT
AbstractLayered materials such as graphite and transition metal dichalcogenides have extremely anisotropic mechanical properties owing to orders of magnitude difference between in-plane and out-of-plane interatomic interaction strengths. Although effects of mechanical perturbations on either intralayer or interlayer interactions have been extensively investigated, mutual correlations between them have rarely been addressed. Here, we show that layered materials have an inevitable coupling between in-plane uniaxial strain and interlayer shear. Because of this, the uniaxial in-plane strain induces an anomalous splitting of the degenerate interlayer shear phonon modes such that the split shear mode along the tensile strain is not softened but hardened contrary to the case of intralayer phonon modes. We confirm the effect by measuring Raman shifts of shear modes of bilayer MoS2 under strain. Moreover, by analyzing the splitting, we obtain an unexplored off-diagonal elastic constant, demonstrating that Raman spectroscopy can determine almost all mechanical constants of layered materials.
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