Highly Itinerant Atomic Vacancies in Phosphorene

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.

Engineering the Kondo state in two-dimensional semiconducting phosphorene

“…While there are many other possible DV configurations, their formation energies are found to be higher, which has been discussed in literature in great details. [21,33,52,53] A different divacancy configuration (5|7|5|7) was reported, [54] however, we find this structure to be 113 meV higher in energy.…”

The role of H 2 O and O 2 molecules and phosphorus vacancies in the structure instability of phosphorene

“…Similar For the DV-contained phosphorene, it is found that the 5757 DV defect shifts the VBM and conduction band minimum (CBM) downward and upward, respectively, which leads to an increase in the band gap up to 1.04 eV (figure 1(c)). This increase may arise from the large lattice distortion and local strain induced by the DV [36]. Unlike MV defect, there is no defect state in the band gap for the DV-contained phosphorene due to the absence of dangling bond and the full passivation of atoms.…”

“…It is known that for atomically thin 2D materials, lattice imperfections can be easily introduced during fabrication or intentionally produced via electron beam or other high-energy particle excitations [33][34][35]. For phosphorene, this issue seems to be even more critical since the atomic vacancies in phosphorene are calculated to be easily formed and abundant at ambient condition with their much lower formation energy (1.65 eV) than other 2D materials [36]. In addition, vacancies in phosphorene are highly mobile with an ultralow diffusion barrier of 0.30 eV compared of 1.39 eV for vacancy in graphene [36].…”

“…For phosphorene, this issue seems to be even more critical since the atomic vacancies in phosphorene are calculated to be easily formed and abundant at ambient condition with their much lower formation energy (1.65 eV) than other 2D materials [36]. In addition, vacancies in phosphorene are highly mobile with an ultralow diffusion barrier of 0.30 eV compared of 1.39 eV for vacancy in graphene [36]. Such itinerant vacancies may greatly affect the stability of phosphorene in air with respect to the interaction with environmental molecules.…”

“…Since vacancies in phosphorene are abundant and itinerant [36], as a consequence, oxygen molecules may be easily trapped at those defect sites. We find that the vacancies have significant effects on the oxidation of phosphorene with a 5000 faster oxidizing rate at the defect site than at the perfect site.…”