  Single crystals of orthorhombic black phosphorus can be grown by a short way
transport reaction from red phosphorus and Sn/SnI4 as mineralization additive.
Sizes of several millimeters can be realized with high crystal quality and
purity, making a large area preparation of single or multilayer phosphorene
possible. An in situ neutron diffraction study has been performed addressing
the formation of black phosphorus. Black phosphorus is formed directly via gas
phase without the occurrence of any other intermediate phase. Crystal growth
was initiated after cooling the starting materials down from elevated
temperatures at 500 {\deg}C.
