  Monolayer phosphorene provides a unique two-dimensional (2D) platform to
investigate the fundamental many-body interactions. However, owing to its high
instability, unambiguous identification of monolayer phosphorene has been
elusive. Consequently, many important fundamental properties, such as exciton
dynamics, remain underexplored. We report a rapid, noninvasive, and highly
accurate approach based on optical interferometry to determine the layer number
of phosphorene, and confirm the results with reliable photoluminescence
measurements. Based on the measured optical gap and the calculated electronic
energy gap, we determined the exciton binding energy to be ~0.4 eV for the
monolayer phosphorene on SiO2/Si substrate, which agrees well with theoretical
predictions. Our results open new avenues for exploring fundamental phenomena
and novel optoelectronic applications using monolayer phosphorene.

Materials Science