Unexpected Reconstruction of the alpha-Boron (111) Surface

TL;DR

This paper reports a novel alpha-boron (111) surface reconstruction with lower energy and unique bonding features, discovered through ab initio structure search, revealing insights into surface stability and electronic transition mechanisms.

Contribution

It introduces a new surface reconstruction of alpha-boron (111) with a lower surface energy, identified via ab initio evolution structure search, and explains its bonding and electronic properties.

Findings

Reconstructed surface has lower energy than previous models.

Interstital boron atoms form bridges with B12 icosahedra.

Surface transition from metal to semiconductor.

Abstract

We report on a novel reconstruction of the alpha-boron (111) surface, discovered using an ab initio evolution structure search, and reveal that it has an unexpected neat structure and much lower surface energy than the recently proposed (111)-I_R,(a) surface. For this reconstruction, every single interstitial boron atom forms bridges with the unique polar-covalent bonds between neighboring B_12 icosahedra, which perfectly meet the electron counting rule and are responsible for the reconstruction-induced metal-semiconductor transition. The peculiar charge transfer between the interstitial atoms and the icosahedra plays an important role in stabilizing the surface.