Left to right: two-dimensional phosphorene nanoribbons with increasing numbers of layers. Image: Watts et al.
Left to right: two-dimensional phosphorene nanoribbons with increasing numbers of layers. Image: Watts et al.

In a world first, researchers at University College London (UCL) in the UK have made tiny, individual, flexible ribbons of crystalline phosphorus that could revolutionize electronics and fast-charging battery technology.

Since the isolation of two-dimensional phosphorene, which is the phosphorus equivalent of graphene, in 2014, more than 100 theoretical studies have predicted that new and exciting properties could emerge by producing narrow 'ribbons' of this material. These properties could be extremely valuable to a range of industries.

Now, in a paper in Nature, researchers from UCL, the University of Bristol in the UK, Virginia Commonwealth University (VCU) in the US and École Polytechnique Fédérale de Lausanne in France describe how they formed quantities of high-quality ribbons of phosphorene from crystals of black phosphorous and lithium ions.

"It's the first time that individual phosphorene nanoribbons have been made. Exciting properties have been predicted and applications where phosphorene nanoribbons could play a transformative role are very wide-reaching," said study author Chris Howard at UCL.

The ribbons typically have a thickness of just one atom, with widths of 4–50nm and lengths of up to 75μm. This aspect ratio is comparable to that of the cables spanning the Golden Gate Bridge's two towers.

"By using advanced imaging methods, we've characterized the ribbons in great detail, finding they are extremely flat, crystalline and unusually flexible," explained first author Mitch Watts, also at UCL. "Most are only a single-layer of atoms thick, but where the ribbon is formed of more than one layer of phosphorene, we have found seamless steps between 1-2-3-4 layers where the ribbon splits. This has not been seen before and each layer should have distinct electronic properties."

While nanoribbons have been made from several materials, including graphene, the phosphorene nanoribbons produced in this study have a greater range of widths, heights, lengths and aspect ratios. Moreover, they can be produced at scale in a liquid that could then be used to apply them in volume at low cost.

The team say that predicted application areas for the nanoribbons include batteries, solar cells, thermoelectric devices for converting waste heat to electricity, photocatalysis, nanoelectronics and quantum computing. What's more, the emergence of various exotic effects in the nanoribbons, including novel magnetism, spin density waves and topological states, has also been predicted.

The nanoribbons are formed by mixing black phosphorus with lithium ions dissolved in liquid ammonia at -50°C. After 24 hours, the ammonia is removed and replaced with an organic solvent to produce a solution of nanoribbons of mixed sizes.

"We were trying to make sheets of phosphorene so were very surprised to discover we'd made ribbons. For nanoribbons to have well defined properties, their widths must be uniform along their entire length, and we found this was exactly the case for our ribbons," said Howard.

"At the same time as discovering the ribbons, our own tools for characterizing their morphologies were rapidly evolving," said co-author Loren Picco at VCU. "The high-speed atomic force microscope that we built at the University of Bristol has the unique capabilities to map the nanoscale features of the ribbons over their macroscopic lengths.

"We could also assess the range of lengths, widths and thicknesses produced in great detail by imaging many hundreds of ribbons over large areas."

While continuing to study the fundamental properties of the nanoribbons, the team also intends to explore their use in energy storage, electronic transport and thermoelectric devices through new global collaborations and by working with expert teams across UCL.

This story is adapted from material from UCL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.