Anharmonicity of optic modes in monolayer MoS2

Temperature dependent frequency shift and linewidth of Γ point optic phonon modes in monolayer MoS2 are studied using the spectral energy density method. In this study, we report the temperature evolution of experimentally forbidden Raman active E ″ and infra-red active A 2 ″ modes, in-addition to the previously reported Raman active E ′ and A 1 ′ modes. All the modes are showing a redshift with an increase in temperature. We delineated the contribution of anharmonic coupling of phonon modes and thermal expansion of the lattice to the total frequency shift and linewidth, and found that a strong anharmonic coupling of phonon modes is the predominant source of the observed redshift and broadening of peaks. The temperature dependence of all modes is quantified by computing their first-order temperature co-efficients.