Contact strength and deformation of straining free-standing borophene

Abstract

We apply nanoindentation using molecular dynamics simulation to investigate the contact strength, deformation behaviour, anisotropic cracking propagation and self-reforming mechanism of a single-layer borophene (SLB). The effects of indenter shape, indenter size, borophene membrane size, boundary conditions, temperature, and loading rate on the indentation force, strain and stress distributions, crack directions, and the self-reform ratio of SLB are considered. Especially a cyclic indentation process on the borophene monolayer is also analysed to evaluate its long-term dynamic reliability. The single/multi loading–unloading processes show that the SLB has a perfect elastic deformation when the indentation depth is below or equal to the critical indentation depth. We found that the crack direction is not influenced when changing spherical indenter diameter from 1 to 4 nm or loading rate from 1 to 15 m/s. However, with a conical indenter, the smallest substrate size, and FTE(y) boundary condition, the cracks develop not only in the armchair direction but also in the zigzag direction. Furthermore, the borophene sheet has a high self-reform ratio of 90% (with v = 15 m/s) after being cracked along the armchair direction. Meanwhile, the cracks in the zigzag direction have no possibility of self-reform. At 100 K, after the tenth cycle indentation, the borophene sheet can still preserve its shape while it is broken at 300 K. In summary, this study further highlights the mechanical, long-term dynamic behaviour and potentially speeds up the promising applications of the SLB.