Probing Single Vacancies in Black Phosphorus at the Atomic Level

TL;DR

This study combines advanced microscopy and calculations to analyze atomic vacancies in black phosphorus, revealing their structure, electronic effects, and impact on the material's band properties at the atomic level.

Contribution

It provides the first detailed atomic-level characterization of vacancies in black phosphorus using combined experimental and theoretical methods.

Findings

Vacancies are highly delocalized and anisotropic.

In-gap resonance states are observed near vacancies.

Vacancies enable visualization of black phosphorus's anisotropic band structure.

Abstract

Utilizing a combination of low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) and electronic structure calculations, we characterize the structural and electronic properties of single atomic vacancies within several monolayers of the surface of black phosphorus. We illustrate, with experimental analysis and tight-binding calculations, that we can depth profile these vacancies and assign them to specific sublattices within the unit cell. Measurements reveal that the single vacancies exhibit strongly anisotropic and highly delocalized charge density, laterally extended up to 20 atomic unit cells. The vacancies are then studied with STS, which reveals in-gap resonance states near the valence band edge and a strong p-doping of the bulk black phosphorus crystal. Finally, quasiparticle interference generated near these vacancies enables the direct visualization of the anisotropic band structure of black phosphorus.