In Situ Raman Study on Thermal Decomposition of Exfoliated Two-Dimensional α-MoO ₃

Two-dimensional (2D) orthorhombic molybdenum trioxide (α-MoO3) single crystals have major applications in fields such as optoelectronics. Thermal stability, a critical metric for device implementation, has thus attracted significant attention. Herein, in situ Raman spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D α-MoO3 single crystals. Significant shifts in multiple Raman characteristic peaks were observed during the temperature range from 80 to 710 K, which are categorized into three types: quasi-linear mode, nonlinear mode, and temperature-insensitive transition mode. Furthermore, decomposition of 2D α-MoO3 is observed to initiate at ∼723 K in vacuum, with notable decomposition occurring at 803 K. The decomposition behavior is revealed to be modulated by phonon dynamics and oxygen defects. These findings provide critical insights into the lattice vibrational mechanisms and thermal stability of α-MoO3 single crystals.