Probing the Domain Architecture in 2D α-Mo₂C via Polarized Raman

MXenes are a group of two-dimensional (2D) materials with excellent stability and intriguing properties. Here, we conduct a systematic study on the Raman spectra of α-Mo₂C and use it to study the unique domain structure of 2D α-Mo₂C crystals grown by chemical vapor deposition (CVD). Six experimentally observed Raman modes are assigned with the assistance of phonon dispersion calculated from density functional theory (DFT). Angle-resolved polarized Raman spectroscopy indicates the anisotropy of α-Mo₂C in the b-c plane, which is further applied to study the domains of the CVD grown 2D α-Mo₂C crystals with different morphologies. Most of the α-Mo₂C flakes contain multiple domains and the c-axes of neighboring domains within the same flake tend to form a 60° or 120° angle, indicating the carbon chains in α-Mo₂C align along three equivalent directions. This is attributed to weak Mo-C bonds in this interstitial carbide and the low formation energy of the carbon chains along certain directions. Our study demonstrates that polarized Raman spectroscopy is a powerful and effective way to characterize the domain structures in α-Mo₂C, which will facilitate the further exploration of properties and applications of α-Mo₂C, as well as other MXenes.