Probing the Domain Architecture in 2D α-Mo₂ C via Polarized Raman Spectroscopy

MXenes are emerging 2D materials with intriguing properties such as excellent stability and high conductivity. Here, a systematic study on the Raman spectra of 2D α-Mo₂ C (molybdenum carbide), a promising member in MXene family, is conducted. Six experimentally observed Raman modes from ultrathin α-Mo₂ C crystal are first assigned with the assistance of phonon dispersion calculated from density functional theory. Angle-resolved polarized Raman spectroscopy indicates the anisotropy of α-Mo₂ C in the b-c plane. Raman spectroscopy is further used to study the unique domain structures of 2D α-Mo₂ C crystals grown by chemical vapor deposition. A Raman mapping investigation suggests that most of the α-Mo₂ C flakes contain multiple domains and the c-axes of neighboring domains tend to form a 60° or 120° angle, due to the weak MoC bonds in this interstitial carbide and the low formation energy of the carbon chains along three equivalent directions. This study demonstrates that polarized Raman spectroscopy is a powerful and effective way to characterize the domain structures in α-Mo₂ C, which will facilitate the further exploration of the domain-structure-related properties and potential applications of α-Mo₂ C.