  Phosphorene is a new two-dimensional material composed of a single or few
atomic layers of black phosphorus. Phosphorene has both an intrinsic tunable
direct band gap and high carrier mobility values, which make it suitable for a
large variety of optical and electronic devices. However, the synthesis of
single-layer phosphorene is a major challenge. The standard procedure to obtain
phosphorene is by exfoliation. More recently, the epitaxial growth of
single-layer phosphorene on Au(111) has been investigated by molecular beam
epitaxy and the obtained structure has been described as a blue-phosphorene
sheet. In the present study, large areas of high-quality monolayer phosphorene,
with a band gap value at least equal to 0.8 eV, have been synthesized on
Au(111). Our experimental investigations, coupled with DFT calculations, give
evidence of two distinct phases of blue phosphorene on Au(111), instead of one
as previously reported, and their atomic structures have been determined.
