Since the isolation of 2-dimensional phosphorene (the phosphorus equivalent of graphene) in 2014, more than 100 theoretical studies have predicted that new and exciting and properties could emerge by producing narrow ‘ribbons’ of this material. These properties could be extremely valuable to a range of industries.
In a study published today in Nature, researchers from UCL, University of Bristol, Virginia Commonwealth University and Ecole Polytechnique Federale de Lausanne, describe how they formed quantities of high-quality ribbons of phosphorene from crystals of black phosphorous and lithium ions.
Study author, Dr Chris Howard from UCL’s Department of Physics and Astronomy, said: “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.”
Working closely with the University of Bristol’s Interface Analysis Centre in the School of Physics and University of Bristol spinout company, Bristol Nano Dynamics Ltd, the team were able to locate and characterise the dimensions of the nanoribbons deposited onto surfaces with unprecedented statistical scrutiny.
First author, Mitchell Watts, also from UCL’s Department of Physics and Astronomy, added: “By using advanced imaging methods, we’ve characterised the ribbons in great detail finding they are extremely flat, crystalline and unusually flexible.
“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 and each layer has distinct electronic properties.”
The team say that the predicted application areas include batteries, solar cells, thermoelectric devices (for converting waste heat to electricity), photocataysis, nanoelectronics and in quantum computing.
In addition, the emergence of ‘exotic’ effects including novel magnetism, spin density waves and topological states have also been predicted.
The new method can produce the phosphorene nanoribbons at scale in a liquid that could then be used to apply them in volume at low cost for these applications and countless more.
The nanoribbons are formed by mixing black phosphorus with lithium ions dissolved in liquid ammonia at -50 degrees C. After 24 hours, the ammonia is removed slowly and replaced with an organic solvent which makes a solution of nanoribbons of mixed sizes.
Dr Howard added: “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.”
Previous studies have confirmed the predicted extraordinarily rapid diffusion of alkali metal atoms along particular directions of black phosphorus crystals, leading to stripes of the atoms within the material, which the authors believe cause bond breaking and ribbon formation at the right lithium atom concentration.
Co-author Dr Oliver Payton from the University of Bristol’s Interface Analysis Centre, said: “Using a new type of microscope developed by University of Bristol spinout Bristol Nano Dynamics, the team at the University of Bristol’s’ Interface Analysis Centre was able to search millimetre sized areas to locate the nanoribbons measuring less than 1 billionth of a metre in height.
“The data collected represents not only a brand-new material but also a step change in the level of scrutiny by which all 2d materials can now be assessed.”
While continuing to study the exciting fundamental properties of the nanoribbons the team intends to also explore their use in applications in energy storage through existing collaborations, and form new links to study electronic transport, thermoelectric devices, and more.
The work was kindly funded by the Engineering and Physical Sciences Research Council and the Royal Academy of Engineering.