The strong mechanical anisotropy of phosphorene combined with the atomic-scale thickness challenges the commonly employed elastic continuum idealizations. Using objective boundary conditions and a density functional based potential, we directly uncover the flexibility of individual α, β, and γ phosphorene allotrope layers along an arbitrary bending direction. A correlation analysis with the in-plane elasticity finds that although a monolayer thickness cannot be defined in the classical continuum sense, an unusual orthotropic plate with a directional-dependent thickness can unambiguously describe the out-of-plane deformation of α and γ allotropes. Such decoupling of the in-plane and out-of-plane nanomechanics might be generic for two-dimensional materials beyond graphene.
Bibliographical noteFunding Information:
Computations were carried out at the Minnesota Supercomputing Institute. D.V. and T.D. were supported by NSF 1552741 and NSF 1332228. R.D.J. was supported by AFOSR (Grant No. FA9550-15-1-0207), ONR (Grant No. N00014-14-1-0714), and MURI (Grant No. FA9550-12-1-0458).
© 2016 American Physical Society.