A first-principles study on the physical properties of two-dimensional Nb3Cl8, Nb3Br8 and Nb3I8

TL;DR

This study uses first-principles calculations to analyze the structural, mechanical, and stability properties of Nb3X8 (X=Cl, Br, I) monolayers, revealing their potential as stable, exfoliable 2D materials with tunable mechanical features.

Contribution

The paper provides the first detailed computational analysis of Nb3X8 monolayers, including stability, exfoliation energies, and mechanical properties, expanding understanding of this new class of 2D materials.

Findings

Phonon dispersion confirms dynamical stability of Nb3X8 monolayers.

Exfoliation energies are lower than graphene, indicating easy exfoliation.

Mechanical strength decreases with heavier halogen atoms.

Abstract

In a recent advance, Nb3Cl8 two-dimensional crystals with a kagome lattice and electronic topological flat bands has been experimentally fabricated (Nano Lett. 2022, 22, 4596). In this work motivated by the aforementioned progress, we conduct first-principles calculations to explore the structural, phonon dispersion relations, single-layer exfoliation energies and mechanical features of the Nb3X8 (X=Cl, Br, I) nanosheets. Acquired phonon dispersion relations reveal the dynamical stability of the Nb3X8 (X=Cl, Br, I) monolayers. In order to isolate single-layer crystals from bulk counterparts, we predicted exfoliation energies of 0.24, 0.27 and 0.28 J/m2, for the Nb3Cl8, Nb3Br8 and Nb3I8 monolayers, respectively, which are noticeably lower than that of the graphene. We found that the Nb3X8 monolayers are relatively strong nanosheets with isotropic elasticity and anisotropic tensile strength. It is moreover shown that by increasing the atomic weight of halogen atoms in the Nb3X8 nanosheets, mechanical characteristics decline. Presented results provide a useful vision about the key physical properties of novel 2D systems of Nb3X8 (X=Cl, Br, I).