  Although a considerable number of solvent based methodologies have been
developed for exfoliating black phosphorus, so far there are no reports on
controlled organization of these exfoliated nanosheets on substrates. Here, for
the first time to the best of our knowledge, a mixture of
N-Methyl-2-pyrrolidone (NMP) and deoxygenated water is employed as a subphase
in Langmuir Blodgett (LB) trough for assembling the nanosheets followed by
their deposition on substrates and studied its field effect transistor (FET)
characteristics. Electron microscopy reveals the presence of densely aligned,
crystalline, ultra-thin sheets of pristine phosphorene having lateral
dimensions larger than hundred of microns. Furthermore, these assembled
nanosheets retain their electronic properties and show a high current
modulation of 10^4 at room temperature in FET devices. The proposed technique
provides semiconducting phosphorene thin films that are amenable for large area
applications.
