title: Chemically exfoliating large sheets of phosphorene via choline chloride urea viscosity-tuning.
abstract: Exfoliation of two-dimensional phosphorene from bulk black phosphorous through chemical means is demonstrated where the solvent system of choice (choline chloride urea diluted with ethanol) has the ability to successfully exfoliate large-area multi-layer phosphorene sheets and further protect the flakes from ambient degradation. The intercalant solvent molecules, aided by low-powered sonication, diffuse between the layers of the bulk black phosphorus, allowing for the exfoliation of the multi-layer phosphorene through breaking of the interlayer van der Waals bonds. Through viscosity tuning, the optimal parameters (1:1 ratio between the intercalant and the diluting solvent) at which the exfoliation takes place is determined. Our exfoliation technique is shown to produce multi-layer phosphorene flakes with surface areas greater than 3 μm2(a factor of three larger than what has previously been reported for a similar exfoliation method) while limiting exposure to the ambient environment, thereby protecting the flakes from degradation. Characterization techniques such as optical microscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, and (scanning) transmission electron microscopy are used to investigate the quality, quantity, and thickness of the exfoliated flakes.
authors.affiliation: NRC Postdoctoral Scholar, US Naval Research Laboratory, Washington, District of Columbia, 20375, United States of America.
authors.forename: A
authors.initials: A
authors.lastname: Ng
authors.forename: T E
authors.initials: TE
authors.lastname: Sutto
authors.forename: B R
authors.initials: BR
authors.lastname: Matis
authors.forename: Y
authors.initials: Y
authors.lastname: Deng
authors.forename: P D
authors.initials: PD
authors.lastname: Ye
authors.forename: R M
authors.initials: RM
authors.lastname: Stroud
authors.forename: T H
authors.initials: TH
authors.lastname: Brintlinger
authors.forename: N D
authors.initials: ND
authors.lastname: Bassim