An Inexpensive and Rapid Route to Printable Phosphorene Quantum Dots from Red Phosphorus

Black phosphorene is a very promising two-dimensional material composed of a single sheet of black phosphorus. Black phosphorene exhibits fascinating characteristics, such as in-plane anisotropy, tunable band gap and high carrier mobility. As a consequence of these properties, black phosphorene has shown a great potential to be utilized in a diverse array of applications – ranging from electronic and optoelectronic devices to the energy storage and energy conversion. Black phosphorene quantum dots (bPQDs) are a zero-dimensional variety of black phosphorene with lateral widths under 100 nm. The additional quantum confinement and higher proportion of edges versus their one- and two-dimensional counterparts makes them an intriguing tunable candidate material for many applications. Unfortunately, to date bPQDs have been exclusively formed from expensive individual sub-gram black phosphorus crystals.<br/>In this work, an inexpensive, rapid and scalable synthesis of black phosphorene quantum dots from widely-available low-cost red phosphorus is demonstrated. Initially, the red phosphorus powder material is ball-milled to obtain black phosphorus nanodomains, and subsequently an etching pathway utilizing lithium electride-containing ammonia solution allows for the conversion to black phosphorene quantum dots through removal of defective regions. The result is a salt of bPQDs which spontaneously dissolve at room temperature in several solvents as individual monolayer quantum dots. These solutions can be cast to give isolated individual bPQDs on a range of substrates. Ball-milled samples were analyzed using various analytical techniques, such as Raman spectroscopy and x-ray diffraction, which revealed that red phosphorus was converted into black phosphorus. Additionally, optimal conditions for the ball milling of red phosphorus powder were determined. Conclusively, the formation of the black phosphorene quantum dots after etching was evidenced using microscopy, such as atomic force microscopy.