Electron Holographic Mapping of Structural and Electronic Reconstruction at Mono- and Bilayer Steps of h-BN

TL;DR

This study uses electron holography and ab-initio calculations to map and understand the structural and electronic changes at edges and steps in multilayer hexagonal boron nitride, revealing covalent bond formations and charge delocalization.

Contribution

It introduces a combined experimental and computational approach to directly visualize and analyze charge and structural reconstructions in 2D materials.

Findings

Out-of-plane covalent bonds form at folded zig-zag edges and multilayer steps.

Monolayer steps lack these covalent bonds.

The technique enables studying charge localization phenomena in 2D materials.

Abstract

Here, by making use of medium and high resolution autocorrected off-axis electron holography, we directly probe the electrostatic potential as well as in-plane and out-of-plane charge delocalization at edges and steps in multilayer hexagonal boron nitride. In combination with ab-initio calculations, the data allows to directly reveal the formation of out-of-plane covalent bonds at folded zig-zag edges and steps comprising two monolayers and the absence of which at monolayer steps. The technique paves the way for studying other charge (de)localization phenomena in 2D materials, e.g., at polar edges, topological edge states and defects.