Raman spectra of van der Waals layered MoSi 2 N 4 and WSi 2 N 4

Abstract Raman spectroscopy, as a rapid, nondestructive and powerful technique, has been widely used to study two-dimensional (2D) materials. The emerging 2D van der Waals layered MSi2N4 (M = Mo or W) semiconductors show remarkable electrical, optical, thermal, and mechanical properties. However, their Raman signatures and defect-related features remain poorly understood. Here, we use first-principles calculations and Raman spectroscopy to investigate the Raman spectra of MSi2N4. The first-order phonon modes are unambiguously assigned, while most of the second‑order Raman peaks are preliminarily identified. Furthermore, we observe an anomalous Davydov splitting in multilayer samples, suggesting a distinctive interlayer vibrational coupling. By controllably introducing defects into MSi2N4, defect-activated Raman features are identified, providing a practical nondestructive approach for crystal quality assessment. This work offers foundational insights into the Raman spectra of MoSi2N4 and WSi2N4, enabling rapid and nondestructive structural characterization and facilitating their controlled synthesis.