Stability and Strength of Atomically Thin Borophene from First Principles Calculations

TL;DR

This study uses first principles calculations to evaluate the stability of different borophene structures, finding that free-standing $eta_{12}$ and $ ext{chi}_3$ are stable, while striped borophene is unstable due to directional bonding effects.

Contribution

It provides a comprehensive stability analysis of borophene structures, establishing benchmarks for their dynamical, thermodynamical, and mechanical stability.

Findings

$eta_{12}$ and $ ext{chi}_3$ borophene are stable in free-standing form.

Striped borophene is unstable due to high stiffness and directional bonding.

The work clarifies stability debates and guides future borophene research.

Abstract

A new two-dimensional (2D) material, borophene (2D boron sheet), has been grown successfully recently on single crystal Ag substrates by two parallel experiments [Mannix \textit{et al., Science}, 2015, \textbf{350}, 1513] [Feng \textit{et al., Nature Chemistry}, 2016, \textbf{advance online publication}]. Three main structures have been proposed ($\beta_{12}$, $\chi_3$ and striped borophene). However, the stability of three structures is still in debate. Using first principles calculations, we examine the dynamical, thermodynamical and mechanical stability of $\beta_{12}$, $\chi_3$ and striped borophene. Free-standing $\beta_{12}$ and $\chi_3$ borophene is dynamically, thermodynamically, and mechanically stable, while striped borophene is dynamically and thermodynamically unstable due to high stiffness along $a$ direction. The origin of high stiffness and high instability in striped borophene along $a$ direction can both be attributed to strong directional bonding. This work provides a benchmark for examining the relative stability of different structures of borophene.