Phonon and exciton temperature-dependent properties of twisted MoS2
Abstract
In the present work, Raman and photoluminescence spectroscopies were used to study the dynamics of phonons and different excitons of MoS2 bilayer under a rotation of 29 dependent of the temperature. The twisted bilayer (T-2L) of MoS2 was obtained through mechanical exfoliation, and subsequently rotated using a dimethyl polysiloxane (PDMS) substrate and deterministic transferred to a SiO2 substrate. The Raman spectrum of the twisted bilayer presents three peaks E' (386 cm-1), A'1 (405 cm-1) and an FA' peak at approximately 409 cm-1 linked to the A'1 mode, which is attributed to a Moir\'e pattern phonon. Both modes (A'1 and FA') are dependent of light polarization in a way that demonstrates an effective coupling between the layers. It was also verified through the Gr\"uneisen parameter, an increase in the anharmonicity of the mode in the E' plane and a decrease the same for A'1. In the PL measurements, the appearance of an exciton in T-2L was verified, which generated a second shoulder measured at ≈1.58 eV attributed to an indirect transition of an I trion. The interaction between the rotated monolayers of MoS2 proved to be an important parameter for possible fine-tuning of the properties of bilayer samples.
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