Plasma Thinning of Large Black Phosphorus Flakes

The growing interest over the 2D materials has led to the discovery of exfoliated black phosphorus (bP), a semiconductor with a thickness-dependent bandgap. The direct bandgap energy varies from 0.3 eV for bulk materials to 1.9 eV for the monolayer of black phosphorus. The fabrication of thin layers is, however, difficult because the layers photo-oxidize in air into phosphoric acid with kinetic that gets faster for thinner layers1. Inspired by a new method to produce thin layers of black phosphorus using oxygen plasma, we work to optimise the process for making large few-layers bP flakes2. Using ICP-RIE oxygen plasma, exfoliated flakes of black phosphorus were etched in a controlled way and Raman spectroscopy was used to evaluate the quality of the flakes after plasma treatments. The results show no sign of high-degradation of the bP crystal structure after the plasma treatment. Here we show that the method can be adapted to produce high quality thin flakes of black phosphorus towards incorporation into electronic and optoelectronic applications. 1 Favron, A., Gaufrès, E., Fossard, F. et al. Photooxidation and quantum confinement effects in exfoliated black phosphorus. Nature Mater 14, 826–832 (2015) 2 Pei, J., Gai, X., Yang, J. et al. Producing air-stable monolayers of phosphorene and their defect engineering. Nat Commun 7, 10450 (2016)