  One hundred years after its first successful synthesis in the bulk form in
1914, black phosphorus (black P) was recently rediscovered from the perspective
of a two-dimensional (2D) layered material, attracting tremendous interest from
condensed matter physicists, chemists, semiconductor device engineers and
material scientists. Similar to graphite and transition metal dichalcogenides
(TMDs), black P has a layered structure but with a unique puckered single layer
geometry. Because the direct electronic band gap of thin film black P can be
varied from 0.3 to around 2 eV, depending on its film thickness, and because of
its high carrier mobility and anisotropic in-plane properties, black P is
promising for novel applications in nanoelectronics and nanophotonics different
from graphene and TMDs. Black P as a nanomaterial has already attracted much
attention from researchers within the past year. Here, we offer our opinions on
this emerging material with the goal of motivating and inspiring fellow
researchers in the 2D materials community and the broad readership of PNAS to
discuss and contribute to this exciting new field. We also give our
perspectives on future 2D and thin film black P research directions, aiming to
assist researchers coming from a variety of disciplines who are desirous of
working in this exciting research field.
