Liquid exfoliation of solvent-stabilized few-layer black phosphorus for applications beyond electronics

Abstract

Few-layer black phosphorus (BP) is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of environmental stability severely limits its synthesis and processing. Here we demonstrate that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions in solvents such as N-cyclohexyl-2-pyrrolidone (CHP). Nanosheets are surprisingly stable in CHP, probably due to the solvation shell protecting the nanosheets from reacting with water or oxygen. Experiments, supported by simulations, show reactions to occur only at the nanosheet edge, with the rate and extent of the reaction dependent on the water/oxygen content. We demonstrate that liquid-exfoliated BP nanosheets are potentially useful in a range of applications from ultrafast saturable absorbers to gas sensors to fillers for composite reinforcement.

Highly Itinerant Atomic Vacancies in Phosphorene

“…5 Similar to graphene, phosphorene can be synthesized by mechanical cleavage and liquid-phase exfoliation. 6,7 In spite of the fast growing knowledge of phosphorene, [8][9][10][11] the origin of its notoriously low stability still remains an important puzzle. 12,13 As one of the most stable polymorphs among all phosphorus allotropes, 14 according to the thermodynamic criteria, phosphorene starts to disintegrate quickly at ambient condition, which is generally ascribed to effects from external molecules.…”

Black phosphorus: a two-dimensional reductant for in situ nanofabrication

“…18,19 BP has strong in-plane bonds in conjunction with weak van der Waals interlayer interactions thereby enabling exfoliation into few-layer BP sheets or phosphorene (single-layer BP). [20][21][22][23][24] Since 2014, BP has attracted tremendous research interest [25][26][27][28][29][30][31][32][33][34][35][36][37][38] because of its unique properties such as layerdependent direct bandgap, 28,39 anisotropy, 25,26,31,32,34,40 hingelike structure, 41 and quasi-one-dimensional excitonicnature, 42 all of which contrast markedly with those of other types of 2D materials. Nevertheless, BP degrades under ambient conditions as a result of the reaction with oxygen (P→P x O y ) and subsequent transformation to PO 4 3-in the presence of water.…”

Few‐Layer Antimonene by Liquid‐Phase Exfoliation

“…As for other 2D materials, micromechanical exfoliation provides high‐quality flakes but is unsuitable for mass production. Liquid phase exfoliation (LPE) has been successfully applied to generate single‐ or few‐layer (FL) samples of several 2D materials on large scale,7 including stable suspensions of few‐layer BP 8…”

“…Furthermore, the flakes do not show the typical terrace characteristics of layered materials but well‐defined structures with all heights being multiples of about 4 nm (Figures 1 d, e, 2 b, and S7). As it is well‐known that the apparent AFM heights of layers obtained by LPE can be overestimated because of residual solvent8, 9 as well as contributions from effects such as capillary and adhesion forces,10 it seems likely that the apparent mono/bilayer thickness is about 4 nm. The overall lateral dimensions of the isolated nanosheets are greater than 1–3 μm 2 (see Figure S4 for a statistical analysis).…”