Atomic vacancies significantly degrade the mechanical properties of phosphorene

Abstract

Due to low formation energies, it is very easy to create atomic defects in phosphorene during its fabrication process. How these atomic defects affect its mechanical behavior, however, remain unknown. Here, we report on a systematic study of the effect of atomic vacancies on the mechanical properties and failure behavior of phosphorene using molecular dynamics simulations. It is found that atomic vacancies induce local stress concentration and cause early bond-breaking, leading to a significant degradation of the mechanical properties of the material. More specifically, a 2% concentration of randomly distributed mono-vacancies is able to reduce the fracture strength by ∼40%. An increase in temperature from 10 to 400 K can further deteriorate the fracture strength by ∼60%. The fracture strength of defective phosphorene is also found to be affected by defect distribution. When the defects are patterned in a line, the reduction in fracture strength greatly depends on the tilt angle and the loading direction. Furthermore, we find that di-vacancies cause an even larger reduction in fracture strength than mono-vacancies when the loading is in an armchair direction. These findings provide important guidelines for the structural design of phosphorene in future applications.

Failure in Two-Dimensional Materials: Defect Sensitivity and Failure Criteria

“…The fracture behavior of 2D materials may exhibit some unique features. For examples, the divacancies cause easier failure than monvacancies along the armchair direction in phosphorene [79]. The presence of S-W defect in high concentration makes the defective graphene more ductile due to trapping through atomic arrangements and blunting at a propagating crack tip [50].…”

“…The reduction in the fracture strength depends on the type of vacancies and loading direction. Atomistic simulations show that divacancies cause a larger reduction in the fracture strength of phosphorene than monovacancies along the armchair direction [79].…”

“…Similar to graphene, atomic vacancies in phosphorene lead to a significant degradation of its mechanical properties. Under tension, stress distribution in phosphorene is almost uniform, except at the small regions around vacancies where the stress is concentrated [79]. The stress concentration causes much earlier bond breaking (compared with defect-free phosphorene) at the defect region during deformation process.…”

“…As shown in Fig. 4(a), the bondbreaking results in crack nucleation around a vacancy, which spontaneously propagates perpendicular to the loading direction, leading to the ultimate failure of defective phosphorene [79]. The reduction in the fracture strength depends on the type of vacancies and loading direction.…”

“…Adapted with permission from Ref. [79]. (b) Failure mechanism of defective graphene with an S-W defect under the strain applied along the AC direction: initial structure, bond rupture, and crack propagation during the fracture.…”