Energy Level Evolution and Oxygen Exposure of Fullerene/Black Phosphorus Interface

The heteroepitaxial growth of fullerene (C-60) on single-crystal black phosphorus (BP) has been studied using low-energy electron diffraction, X-ray and ultraviolet photoelectron spectroscopy, and density functional theory simulation. The occupied orbital features from C-60 observed in the photoelectron spectra for C-60/BP interface are slightly broadened at higher coverages of C-60 and exhibit no direct evidence of hybridization, demonstrating that the C-60/BP interaction is physisorption. Oxygen exposure of interface leads to obvious oxidation of BP in which C-60 bridges the large electron-transfer barrier from BP to oxygen and plays an important role for the production of O-2(-) and oxidation of BP. Our findings suggest that C-60 does not form an ideal protection layer as the other n-type semiconductors. With the assistance of density functional theory calculations, the oxidized phosphorus at the interface prevents further charge transfer from BP to C-60.