Electronic and mechanical properties of few-layer borophene

TL;DR

This study uses first-principles calculations to explore the electronic and mechanical properties of few-layer borophene, revealing enhanced interlayer interactions, increased flexibility, and unique Poisson's ratio behaviors due to van der Waals forces.

Contribution

It provides the first detailed analysis of how interlayer vdW interactions affect the properties of multilayer borophene, highlighting differences from other layered materials.

Findings

Anisotropic metallic behavior persists from monolayer to few-layer borophene.

Interlayer vdW interactions are significantly stronger than in other layered materials.

Layer number increases critical strain and flexibility.

Abstract

We report first principle calculations of electronic and mechanical properties of few-layer borophene with the inclusion of interlayer van der Waals (vdW) interaction. The anisotropic metallic behaviors are preserved from monolayer to few-layer structures. The energy splitting of bilayer borophene at $\Gamma$ point near the Fermi level is about 1.7 eV, much larger than the values (0.5--1 eV) of other layered semiconductors, indicating much stronger vdW interactions in metallic layered borophene. In particular, the critical strains are enhanced by increasing the number of layers, leading to much more flexibility than that of monolayer structure. On the one hand, because of the buckled atomic structures, the out-of-plane negative Poisson's ratios are preserved as the layer-number increases. On the other hand, we find that the in-plane negative Poisson's ratios disappear in layered borophene, which is very different from puckered black phosphorus. The negative Poisson's ratio will recover if we enlarge the interlayer distance to 6.3 $\mbox\AA$, indicating that the physical origin behind the change of Poisson's ratios is the strong interlayer vdW interactions in layered borophene.