Dislocations and Grain Boundaries in Two-Dimensional Boron Nitride

TL;DR

This study discovers a new low-energy dislocation structure in two-dimensional boron nitride and explores how grain boundary types affect its electronic properties, revealing potential for electronic and optical applications.

Contribution

It introduces a novel 4|8 dislocation structure in 2D BN and analyzes the impact of grain boundary polarity on electronic properties, expanding understanding of BN's defect structures.

Findings

The 4|8 dislocation pair has lower energy than 5|7 pairs.

Polar grain boundaries are B-rich or N-rich and carry net charges.

Polar GBs have smaller bandgaps than perfect BN.

Abstract

A new dislocation structure-square-octagon pair (4|8) is discovered in two-dimensional boron nitride (h-BN), via first-principles calculations. It has lower energy than corresponding pentagon-heptagon pairs (5|7), which contain unfavorable homo-elemental bonds. Based on the structures of dislocations, grain boundaries (GB) in BN are investigated. Depending on the tilt angle of grains, GB can be either polar (B-rich or N-rich), constituted by 5|7s, or un-polar, composed of 4|8s. The polar GBs carry net charges, positive at B-rich and negative at N-rich ones. In contrast to GBs in graphene which generally impede the electronic transport, polar GBs have smaller bandgap compared to perfect BN, which may suggest interesting electronic and optic applications.