Lewis Acid Passivation of Mechanically Exfoliated Black Phosphorus

Abstract

Exfoliated black phosphorus (exf-BP) is a 2D material with a tunable bandgap and favorable electron transport properties for optoelectronic applications. However, its instability under ambient conditions presents challenges for successful integration into devices. Here, we present a chemical treatment method as a convenient, effective strategy for passivation. We treat the exf BP flakes with Lewis acids (gallanes, alanes, boranes), many of which interact with and stabilize the exf-BP surface against ambient degradation. Ambient stability is tracked with a combination of optical microscopy (OM) and atomic force microscopy (AFM). Both methods reveal that Lewis acid-treated exf-BP flakes have enhanced ambient stability. Moreover, the effectivity of the stabilization increases with the calculated bond dissociation energy (BDE) of adducts formed between the Lewis acid and molecular phosphine analogues. AlBr3, which was found to be the most effective of the Lewis acids tested, was used to fabricate a passivated exf BP field-effect transistor (FET). The AlBr3-treated exf-BP FET shows similar gate modulation, I–V, photocurrent, and stability as a typical AlOx-encapsulated exf-BP FET. Thus, the AlBr3 treatment method may serve as a useful alternative to AlOx passivation via atomic layer deposition (ALD).