Temperature dependence of the double-resonance Raman bands in monolayer MoS2

This work reports a detailed study of the double-resonance (DR) Raman bands of single-layer MoS2 as a function of temperature, using many different laser energies in the region of the excitonic transitions and at different temperatures between 80 and 300 K. Our measurements show that the DR bands are strongly affected by temperature and the results are explained in terms of the temperature dependence of both the phonon wavenumber and the excitonic energy. In order to distinguish these two effects, the excitonic transitions were directly measured by photoluminescence as a function of temperature. It was observed from the multiple-excitation results that the dispersion of the DR bands measured with different laser lines depends on temperature. The resonance condition was evidenced by considering the difference between energies of the laser excitation and the excitonic transition, at a given temperature. Our findings for the temperature dependence of the DR process in single-layer MoS2 can be extended to other classes of transition metal dichalcogenide materials.