Electronic Self-passivation of Single Vacancy in Black Phosphorus via a Controlled Ionization

TL;DR

This study introduces a novel electronic self-passivation method for single vacancies in black phosphorus through controlled ionization, reducing defect states and potentially improving charge mobility.

Contribution

It demonstrates that ionization of vacancies into negatively charged states passivates dangling bonds and suppresses in-gap states, verified by microscopy and theoretical calculations.

Findings

Passivation achieved via mild thermal annealing or STM manipulation.

Negatively charged vacancies show asymmetric Friedel oscillations.

Passivated vacancies act as weaker scattering centers.

Abstract

We report that mono-elemental black phosphorus presents a new electronic self-passivation scheme of single vacancy (SV). By means of low-temperature scanning tunneling microscopy and bond-resolved non-contact atomic force microscopy, we demonstrate that the local reconstruction and ionization of SV into negatively charged $\mathrm{SV}^-$ leads to the passivation of dangling bonds and thus the quenching of in-gap states, which can be achieved by mild thermal annealing or STM tip manipulation. SV exhibits a strong and symmetric Friedel oscillation (FO) pattern, while $\mathrm{SV}^-$ shows an asymmetric FO pattern with local perturbation amplitude reduced by one order of magnitude and a faster decay rate. The enhanced passivation by forming $\mathrm{SV}^-$ can be attributed to its weak dipole-like perturbation, consistent with density-functional theory and numerical calculations. Therefore, self-passivated $\mathrm{SV}^-$ is electronically benign and acts as a much weaker scattering center, which may hold the key to further enhance the charge mobility of BP and its analogs.