Stable Aqueous Dispersions of Optically and Electronically Active Phosphorene

Abstract: Understanding and exploiting the remarkable optical and electronic properties of phosphorene require mass production methods that avoid chemical degradation. While solution-based strategies have been developed for scalable exfoliation of black phosphorus, these techniques have thus far employed anhydrous organic solvents in an effort to minimize exposure to known oxidants, but at the cost of limited exfoliation yield and flake size distribution. Here, we present an alternative phosphorene production method based on surfactant-assisted exfoliation and post-processing of black phosphorus in deoxygenated water. From comprehensive microscopic and spectroscopic analysis, this approach is shown to yield phosphorene dispersions that are stable, highly concentrated, and comparable to micromechanically exfoliated phosphorene in structure and chemistry. Due to the high exfoliation efficiency of this process, the resulting phosphorene flakes are thinner than anhydrous organic solvent dispersions, thus allowing the observation of layer-dependent photoluminescence down to the monolayer limit. Furthermore, to demonstrate preservation of electronic properties following solution processing, the aqueous-exfoliated phosphorene flakes are employed in field-effect transistors with high drive currents and current modulation ratios. Overall, this method enables the isolation and mass production of few-layer phosphorene, which will accelerate ongoing efforts to realize a diverse range of phosphorene-based applications.

Stable Aqueous Dispersions of Optically and Electronically Active Phosphorene

This paper presents a novel method for producing phosphorene—a two-dimensional material with promising electronic and optical properties—via a stable aqueous dispersion process. The research emphasizes an alternative approach using surfactant-assisted exfoliation in deoxygenated water that addresses limitations posed by previous organic solvent-based methods.

Research Context and Methodology

Phosphorene, a few-layered form of black phosphorus (BP), is garnering attention due to its high carrier mobility and direct bandgap, which are advantageous for electronic and optoelectronic devices. However, scalable production remains challenging due to phosphorene's susceptibility to oxidation. Traditional methods utilizing anhydrous organic solvents mitigate some degradation risks but compromise exfoliation yield and uniformity of flake thickness.

This research introduces an effective liquid phase exfoliation (LPE) technique using deoxygenated water and surfactants, specifically sodium dodecyl sulfate (SDS). This approach purports to deliver a high yield of phosphorene flakes with finer thickness control and greater stability. SDS acts as a stabilizing agent, circumventing the degradation while allowing use of ultrasonication and ultracentrifugation—a dual-step enrichment process enhancing flake thinness and dispersal uniformity.

Key Findings and Technical Contributions

The resultant phosphorene displays significant chemical stability and optical coherence. Layers down to the monolayer exhibit layer-dependent photoluminescence (PL), observed at emission peaks of approximately 1.37 eV, corresponding to known properties of ultrathin phosphorene.

X-ray photoelectron spectroscopy (XPS) confirmed the preservation of phosphorene chemical quality, supported by minimal oxidized phosphorus observed—indicative of effective surfactant core-stabilization during processing. Field-effect transistors (FETs) fabricated from aqueous-exfoliated phosphorene sheets demonstrated promising electronic characteristics, with current modulation ratios and drive currents suggesting comparable performance to those derived from traditional methods.

To verify the impact of surfactants, phosphorene dispersions prepared without SDS demonstrated rapid settling, supporting the necessity of amphiphilic molecules for stable aqueous suspensions.

Implications and Future Prospects

This environmentally benign method not only facilitates scalable production of high-quality phosphorene, suitable for large-area applications, but also enhances the potential for integrating phosphorene into a broader array of electronic and photonic devices. The successful demonstration of stable phosphorene suspensions extends the toolkit for processing other chemically sensitive materials where aqueous dispersions might offer similar environmental advantages.

Future work could explore the integration of such dispersions with other two-dimensional materials to develop heterostructures with tailored electronic properties, advancing the field of next-generation materials capable of supporting a variety of applications from nanoelectronics to photovoltaics.

In essence, this work propounds a transformative approach in the preparation and utilization of phosphorene, ensuring its viability in mass-scale production while maintaining structural and functional integrity—a critical step forward in leveraging phosphorene's potential in cutting-edge technology.