Effective passivation of black phosphorus against atmosphere by quasi-monolayer of F4TCNQ molecules

2020 
Black phosphorus (BP) has drawn extensive attention due to its unique semiconducting properties, but the poor stability of BP greatly limits its practical device application. In this work, we have fabricated a passivation layer of quasi-monolayer 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) on the BP simply by vacuum evaporation and annealing. The desirable air stability and strong interface charge transfer (ICT) of quasi-monolayer F4TCNQ/BP were confirmed with photoemission spectroscopy (PES) characterization. Density functional theory (DFT) calculations were also applied to further investigate the passivation mechanism, and the results show that the lone pair electrons in BP's valence band transfer to F4TCNQ molecules and were firmly localized due to the strong withdrawing ability of F4TCNQ, which greatly enhanced the energy barrier of electrons transfer to H2O and O2 and hindered the further oxidation of phosphorus atoms. Meanwhile, a nearly Ohmic contact is formed across the F4TCNQ/BP interface which may greatly facilitate the carrier transport in BP based devices.
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