NanoLett.http://doi.org/xfm(2014)

The recent discovery of high charge-carrier mobility and good switching behaviour in transistors based on few layers of black phosphorus has focused attention on this two-dimensional semiconductor. However, bulk black phosphorus is known to have poor ambient stability, because it forms pits and bubbles on its surface when exposed to oxygen. Joshua Wood and colleagues have now characterized the morphological and compositional evolution of few-layer flakes of black phosphorus exposed to ambient conditions, and observed that oxidized phosphorus species are created within one day. However, if the flakes are covered with a thin layer of aluminium oxide the degradation process is retarded significantly. Transistors encapsulated with this oxide preserve high mobility and good operation as switches for more than one week. The researchers suggest that the conformal coating obtained with atomic layer deposition is the key to prevent the formation of detrimental oxygenated species both at the edges and on the top surface of the flakes.