First-principles analysis of the electronic structure and stability of Hf3N2T2 (T = Cl, S) MXene monolayers

Abstract

MXenes, a class of two-dimensional transition metal carbides and nitrides, have attracted significant interest due to their potential for energy-efficient applications, especially in thermoelectrics. Despite the material's potential, hafnium-based MXenes remain largely unexplored. Understanding how surface functionalization affects their electronic properties could reveal different functionalities and expand their practical use in advanced technologies. In this work, we use first-principles density functional theory (DFT) computations to examine the phonon dispersion and electronic structure of hafnium-based MXenes, Hf₃N₂T₂ (T = Cl, S). Our findings suggest that surface terminations are essential for altering these monolayers' structural and electrical characteristics. Hf₃N₂Cl₂ exhibits Dirac semimetallic behavior, indicating a potential for high-speed electronic applications and great carrier mobility. Conversely, Hf₃N₂S₂ demonstrates semimetallic characteristics. Phonon dispersion analysis reveals that S termination significantly enhances structural stability compared to Cl termination, reducing imaginary frequencies and improving dynamic robustness. These findings highlight the tunability of Hf₃N₂T₂ MXenes through surface modifications, paving the way for their integration into thermoelectric energy conversion and waste heat recovery technologies.