  In this letter, we show that a new class of two-dimensional phosphorus
allotropes can be constructed via assembling the previously proposed ultrathin
metastable phosphorus nanotube into planar structures in different stacking
orientations. Based on first-principles method, the structures, stabilities and
fundamental electronic properties of these new two-dimensional phosphorus
allotropes are systematically investigated. These two-dimensional phosphorus
allotropes possess remarkable stabilities due to the strong inter-tube van der
Waals interactions, which cause an energy release of about 30-70 meV/atom
depending on their stacking manners. Our results show that most of these
two-dimensional van der Waals phosphorene allotropes are energetically more
favorable than the experimentally viable black alpha-P and blue beta-P. Three
of them showing relatively higher probability to be synthesized in future are
further confirmed to be dynamically stable semiconductors with strain-tunable
band gaps and remarkable piezoelectricity, which may have potential
applications in nano-sized sensors, piezotronics, and energy harvesting in
portable electronic nano-devices.
