Laser-induced anharmonicity vs thermally induced biaxial compressive strain in mono- and bilayer MoS2 grown via CVD

We studied the role of biaxial compressive strain in laser-induced anharmonicity effects of mono- and bilayer MoS2 grown by chemical vapor deposition. With the increased laser powers, the A1g phonon mode was strongly affected by the anharmonicity, whereas the E12g mode was negligibly affected by the anharmonic effects, which is attributed to the dominant nature of biaxial compressive strain over the effects of anharmonicity. In the case of the A1g phonon mode, anharmonicity effects dominated over the biaxial compressive strain owing to its large out-of-plane thermal expansion coefficient. The origin of biaxial compressive strain was explained by invoking the difference in linear thermal expansion coefficients of MoS2 and the substrate. Moreover, thermally induced biaxial compressive strain also influenced the exciton emission energy. The role of the substrate thermal conductivity was discussed in the light of anharmonicity of the MoS2 monolayer. In addition, the polarizability of Raman modes was found to be dependent on the second layer arrangement over the monolayer.