Physical Properties of Hf-Based MXenes Monolayers for Optoelectronic and Clean Energy

Abstract

In this work, the structural, dynamical, electronic, optical, and thermodynamic properties of Hf₂CCl₂ and Hf₂CBr₂ MXene monolayers were investigated using density functional theory, the HSE06 hybrid functional, and ab initio molecular dynamics (AIMD) simulations. Phonon dispersion calculations together with AIMD simulations at 300 K confirm the dynamical and thermal stability of both monolayers. The optimized structures exhibit lattice constants of 3.411 and 3.479 Å and cohesive energies of −6.830 and −6.513 eV/atom for Hf₂CCl₂ and Hf₂CBr₂, respectively. Electronic structure calculations indicate that both compounds are direct-bandgap semiconductors with HSE06 bandgaps of 0.82 and 0.79 eV. These values correspond to the near-infrared spectral region, making the two monolayers relevant for infrared optoelectronic applications. The calculated electron and hole effective masses are relatively small, suggesting favorable charge-transport characteristics. In addition, both materials exhibit strong optical absorption, reaching values on the order of 10⁵ cm⁻¹ in the UV–visible region. Thermodynamic analysis further shows that the two systems remain stable over a wide temperature range up to 1000 K. Overall, these results highlight the potential of Hf₂CCl₂ and Hf₂CBr₂ monolayers for applications in optoelectronic and energy-conversion technologies.