Highly Itinerant Atomic Vacancies in Phosphorene

TL;DR

This study uses first-principles calculations to analyze vacancy mobility in phosphorene, revealing highly mobile, anisotropic vacancies at low temperatures and the effects of strain on vacancy dynamics, with implications for material applications.

Contribution

It provides detailed insights into vacancy hopping rates, anisotropic motion, and strain effects in phosphorene, a novel 2D material, based on first-principles calculations.

Findings

Vacancies in phosphorene are highly mobile at low temperatures.

Room temperature vacancy motion is 10^16 times faster than in graphene.

Strain influences vacancy motion differently along zigzag and armchair directions.

Abstract

Using detailed first-principles calculations, we investigate the hopping rate of vacancies in phosphorene, an emerging elemental 2D material besides graphene. Our work predicts that a direct observation of these mono-vacancies (MVs), showing a highly mobile and anisotropic motion, is possible only at low temperatures around 70 K or below where the thermal activity is greatly suppressed. At room temperature, the motion of a MV is sixteen orders faster than that in graphene, because of the low diffusion barrier of 0.3 eV. Built-in strain associated with the vacancies extends far along the zigzag direction while attenuating rapidly along the armchair direction. We reveal new features of the motion of di-vacancies (DVs) in phosphorene via multiple dissociation-recombination processes of vacancies owing to a small energy cost of ~ 1.05 eV for the splitting of a DV into two MVs. Furthermore, we find that uniaxial tensile strain along the zigzag direction can promote the motion of MVs, while the tensile strain along the armchair direction has the opposite effect. These itinerant features of vacancies, rooted in the unique puckering structure facilitating bond reorganization, enable phosphorene to be a bright new opportunity to broaden the knowledge of the evolution of vacancies, and a proper control of the exceedingly active and anisotropic movement of the vacancies should be critical for applications based on phosphorene.