Highly Itinerant Atomic Vacancies in Phosphorene

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 monovacancies (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 16 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 divacancies (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.