Phonon dynamics in MoSi₂N₄: insights from DFT calculations

Area of Science:

• Computational Materials Science
• Two-Dimensional Materials
• Molybdenum Silicon Nitride

Background:

• Two-dimensional (2D) materials like MoSi2N4 are gaining attention for their unique properties.
• Understanding the structural and vibrational properties of MoSi2N4 is crucial for its applications.
• Previous studies have explored MoSi2N4 synthesis and basic properties.

Purpose of the Study:

• To investigate the structural stability and vibrational properties of monolayer, bilayer, and bulk MoSi2N4.
• To explore three distinct structural modifications (α1, α2, and α3) of MoSi2N4.
• To provide a deeper understanding of the Raman spectra of MoSi2N4.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Total energies were computed for different structural phases and layer stackings.
• Vibrational analysis and Raman spectra simulations were performed.

Main Results:

• The α1 and α3 monolayer phases of MoSi2N4 exhibit very close total energies (<0.1 eV).
• All investigated MoSi2N4 structures (monolayer to bulk) are dynamically stable in favorable stackings.
• Simulated Raman spectra show variations dependent on Mo-N bond length, suggesting complex origins for experimental peaks.

Conclusions:

• MoSi2N4 exists in multiple stable structural configurations from monolayer to bulk.
• The vibrational properties, particularly Raman spectra, are sensitive to structural details and Mo-N bond lengths.
• The interpretation of experimental Raman spectra at 348 cm-1 for MoSi2N4 may require considering factors beyond simple Γ-point vibrations.