Enhanced Exciton Thermal Stability and Phonon Anharmonicity in Twisted Bilayer MoS₂: Implications for Nano-Optoelectronic Devices

In this study, we present a comparative analysis of the temperature-dependent optical properties of monolayer (1L) and twisted bilayer MoS₂ (TBM) nanosystems using Raman and photoluminescence (PL) spectroscopies. We investigate the behavior of phonon modes, as well as exciton and trion energies, over a temperature range from 93 to 573 K. Our findings reveal a pronounced increase in the anharmonicity of the A₁′ and moiré-induced FA₁′ phonon modes in the TBM sample. This enhanced anharmonicity is attributed to an increase in normal and Umklapp phonon scattering processes, enabled by the emergence of phonon branches due to the nanoscale moiré effects induced by interlayer rotation. Furthermore, PL measurements demonstrate improved thermal stability of the negatively charged A^- and neutral A⁰ excitons in TBM, reinforcing its potential for nanoscale optoelectronic applications. These results provide valuable insights into the temperature-dependent optical behavior of MoS₂ moiré superlattices, advancing the understanding of phonon and exciton interactions in twisted 2D nanosystems and guiding the design of functional nanomaterials.