Similar to graphitic carbon, phosphorus monolayers, dubbed
phosphorene [1], can be exfoliated from layered black phosphorus.
Phosphorene is a p-type semiconductor with a significant
band gap. It is stable, flexible, and displays a high carrier
mobility [1], suggesting its potential use in 2D electronics. Most
interesting, based on ab initio density functional
calculations, we found that phosphorus can form four different
2D structural phases that are almost equally
stable and may be inter-connected. Connection of two planar phases
resembles a sharp origami-style fold, displayed in Fig. 1. This
fold occurs naturally in this multi-phase system, whereas in
single-phase systems like graphene it requires the presence of
defect lines or lines of adsorbed atoms. We also find the
possibility of moving this fold by structural transformation from
one allotrope to another, with an unusually low activation barrier
of <0.5 eV per bond. Since the electronic properties of
multi-phase phosphorene may also be tuned by in-layer strain,
including a semiconductor-to-metal transition, we postulate that
origami-style folded phosphorene should display an unprecedented
richness in its electronic behavior.
[1] H. Liu et al. ACS Nano 8 (2014)
[2] Z. Zhu and D. Tomanek, Phys. Rev. Lett. (2014)
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Figure 1
Structural coexistence in multi-phase phosphorene, illustrated during the
conversion of a black phosphorus monolayer (horizontal, brown)
to blue phosphorus (diagonal, blue). The 2D layers are normal to
the plane of the display.
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