Similar to graphite, black phosphorus
is a layered structure that can be exfoliated to monolayers dubbed phosphorene.
Similar to carbon nanotubes, which are related to few-layer graphene,
we propose the existence of phosphorus nanotubes formed of phosphorene,
Different from graphite, besides the black allotrope, layered phosphorus has
three stable structural phases, called blue-P , γ-P and δ-P,
which can be connected naturally. The fact that connected structures do not lie in
a plane allows us to design nanotubes by connecting laterally nanoribbons of
different phases. Unlike single-phase nanotubes consisting of a layer rolled up to a cylinder,
multi-phase phosphorene nanotubes will have a polygonal cross-section, as shown in Fig. 1.
Both single-wall and multi-wall phosphorene nanotubes may be constructed in this way.
The availability of more than one structural phase offers much larger structural richness
than the carbon counterpart with one single phase. Consequently, we find that the
electronic properties of phosphorene nanotubes depend not only on the chiral
vector that defines the edge structure, but also the presence of the individual phosphorene
phases. In analogy to the successful synthesis of carbon nanotubes by ball milling of
graphite, we believe that phosphorene nanotubes may be formed in the same way in an
 H. Liu et al. ACS Nano 8 (2014)
 Z. Zhu and D. Tomanek, Phys. Rev. Lett. (2014)
Structure of a polygonal nanotube obtained by interconnecting phosphorene nanoribbons
with different phases.