Experimental Raman investigation of thickness-dependent and oxidation-induced lattice dynamics in 2D Fe3GeTe2

Fe3GeTe2 is a representative two-dimensional (2D) magnetic material whose lattice dynamics are highly sensitive to reduced dimensionality and external perturbations. Here, we present a systematic Raman spectroscopy study of Fe3GeTe2 from the monolayer to multilayer regimes, focusing on the effects of environmental oxidation and optical excitation. Our results demonstrate a pronounced thickness-dependent evolution of phonon modes, as well as oxidation-induced shifts in Raman features, indicating reduced symmetry and lattice distortion. In addition, continuous laser irradiation leads to pronounced changes in phonon frequencies, linewidths, and relative intensities, with the response primarily governed by the combined effects of oxidation state and optical excitation rather than purely thermal effects. These results reveal a close interplay between lattice dynamics, surface chemistry, and optical excitation in Fe3GeTe2, providing insight into the environmental stability and optical responsiveness of 2D magnetic materials.