Solvent Exfoliation of Electronic-Grade, Two-Dimensional Black Phosphorus

TL;DR

This paper demonstrates a scalable method to produce stable, high-quality 2D black phosphorus dispersions using solvent exfoliation, enabling high-performance electronic devices with potential for large-area applications.

Contribution

It introduces a solvent exfoliation technique using anhydrous organic solvents, especially NMP, to produce high-quality, stable BP dispersions suitable for electronic applications.

Findings

Achieved stable, concentrated BP dispersions (~0.4 mg/mL) in NMP.

BP nanosheets have structure and chemistry comparable to mechanically exfoliated flakes.

BP FETs exhibit ambipolar behavior with high on/off ratios and mobilities.

Abstract

Solution dispersions of two-dimensional (2D) black phosphorus (BP), often referred to as phosphorene, are achieved by solvent exfoliation. These pristine, electronic-grade BP dispersions are produced with anhydrous, organic solvents in a sealed tip ultrasonication system, which circumvents BP degradation that would otherwise occur via solvated oxygen or water. Among conventional solvents, n-methyl-pyrrolidone (NMP) is found to provide stable, highly concentrated (~0.4 mg/mL) BP dispersions. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy show that the structure and chemistry of solvent-exfoliated BP nanosheets are comparable to mechanically exfoliated BP flakes. Additionally, residual NMP from the liquid-phase processing suppresses the rate of BP oxidation in ambient conditions. Solvent-exfoliated BP nanosheet field-effect transistors (FETs) exhibit ambipolar behavior with current on/off ratios and mobilities up to ~10000 and ~50 cm^2/(V*s), respectively. Overall, this study shows that stable, highly concentrated, electronic-grade 2D BP dispersions can be realized by scalable solvent exfoliation, thereby presenting opportunities for large-area, high-performance BP device applications.