Electronic structures of air-exposed few-layer black phosphorus by optical spectroscopy

The electronic structure of few-layer black phosphorus(BP) sensitively depends on the sample thickness, strain and doping. Here, we show that it’s also vulnerable to air-exposure. The oxidation of BP caused by air-exposure gives several optical signatures, including the broadening of resonance peaks and increased Stokes shift between infrared absorption and photoluminescence peaks. More importantly, air exposure causes blue shifts of all resonance peaks in infrared absorption and photoluminescence spectra, with more prominent effects for thinner samples and higher order subband transitions. Our study may provides a convenient and exotic way for band-structure engineering of few-layer black phosphorus through controllable air-exposure or defect creation.