Hexagonal Boron Nitride Nanosheets Protect Exfoliated Black Phosphorus Layers from Ambient Oxidation

Abstract

AbstractBlack phosphorus‐based 2D materials have yet to demonstrate their full application potential because of the well‐known sensitivity of phosphorene to spontaneous oxidation under ambient conditions. It is hypothesized that this unfavorable process can be prevented by drop‐casting hexagonal boron nitride (h‐BN) nanosheets on phosphorene. Here, both materials are prepared by sonication‐assisted liquid‐phase exfoliation of bulk materials and characterized by transmission electron microscopy and Raman spectroscopy. Raman spectroscopy is also utilized for the real‐time monitoring of phosphorene oxidation by calculating the A1g/A2g intensity ratio. This value drops below 0.5 (corresponding to complete oxidation) within 100 min for pristine phosphorene layers in the air. However, it remains constant above 0.6 (indicating no oxidation) when phosphorene covered by h‐BN sheets is left in the air. Moreover, deploying h‐BN sheets at midterm during the ambient oxidation reaction is able to halt the process and maintain a steady 0.5 < A1g/A2g < 0.6 Raman intensity ratio. The experimental results are successfully interpreted within the developed theoretical framework by the charge distribution of h‐BN, which keeps O2 molecules from interacting with its surface, and the fact that the first O2 molecules in contact react with the edges of h‐BN, thus creating a barrier for subsequently arriving O2 molecules.