Atomically Sharp, Closed Bilayer Phosphorene Edges by Self-Passivation

TL;DR

This study reveals that bilayer phosphorene edges can reconstruct into atomically-sharp, self-passivated configurations, enhancing stability and providing insights for synthesis and applications of phosphorene-based nanostructures.

Contribution

It uncovers the atomic-scale reconstruction behavior of bilayer phosphorene edges and demonstrates their stable, closed, self-passivated form through combined TEM observations and first-principles calculations.

Findings

Bilayer zigzag edges undergo reconstruction to form stable, closed, self-passivated structures.

Closed bilayer ZZ edges have extremely low formation energy and high stability.

Fabrication of bilayer phosphorene nanoribbons with atomically-sharp edges achieved.

Abstract

Two-dimensional (2D) crystals' edge structures not only influence their overall properties but also dictate their formation due to edge-mediated synthesis and etching processes. Edges must be carefully examined because they often display complex, unexpected features at the atomic scale, such as reconstruction, functionalization, and uncontrolled contamination. Here, we examine atomic-scale edge structures and uncover reconstruction behavior in bilayer phosphorene. We use in situ transmission electron microscopy (TEM) of phosphorene/graphene specimens at elevated temperatures to minimize surface contamination and reduce e-beam damage, allowing us to observe intrinsic edge configurations. Bilayer zigzag (ZZ) edge was found the most stable edge configuration under e-beam irradiation. Through first-principles calculations and TEM image analysis under various tilting and defocus conditions, we find that bilayer ZZ edges undergo edge reconstruction and so acquire closed, self-passivated edge configurations. The extremely low formation energy of the closed bilayer ZZ edge and its high stability against e-beam irradiation are confirmed by first-principles calculations. Moreover, we fabricate bilayer phosphorene nanoribbons with atomically-sharp closed ZZ edges. The identified bilayer ZZ edges will aid in the fundamental understanding of the synthesis, degradation, reconstruction, and applications of phosphorene and related structures.