Black Phosphorous...

Image Source: Technology Review

Topics: Field-Effect Transistors, Materials Science, Nanotechnology

TECHNOLOGY REVIEW: In the last few years, two-dimensional crystals have emerged as some of the most exciting new materials to play with. Consequently, materials scientists have been falling over themselves to discover the extraordinary properties of graphene, boron nitride, molybdenum disulphide, and so on.

A late-comer to this group is black phosphorus, in which phosphorus atoms join together to form a two-dimensional puckered sheet. Last year, researchers built a field-effect transistor out of black phosphorus and showed that it performed remarkably well. This research suggested that black phosphorous could have a bright future in nanoelectronic devices.

But there is a problem. Black phosphorus is difficult to make in large quantities. Today, Damien Hanlon at Trinity College Dublin in Ireland, and a number of pals, say they have solved this problem.

These guys have perfected a way of making large quantities of black phosphorus nanosheets with dimensions that they can control. And they have used this newfound ability to test black phosphorus in a number of new applications, such as a gas sensor, an optical switch, and even to reinforce composite materials to make them stronger.

In bulk form, black phosphorus is made of many layers, like graphite. So one way to separate single sheets is by exfoliation, simply peeling off layers using Scotch tape or other materials. That is a time-consuming task that severely limits potential applications.

So Hanlon and co have been toying with another approach. Their method is to place the black phosphorus lump in a liquid solvent and then bombard it with acoustic waves that shake the material apart.

The result is that the bulk mass separates into a large number of nanosheets that the team filters for size using a centrifuge. That leaves high-quality nanosheets consisting of only a few layers. “Liquid phase exfoliation is a powerful technique to produce nanosheets in very large quantities,” they say.

One potential problem with black phosphorus nanosheets is that they degrade rapidly when in contact with water or oxygen. So one of the advances the team has made is to predict that certain solvents should form a solvation shell around the sheet, which prevents oxygen or other oxidative species from reaching the phosphorus.

Physics arXiv:
Liquid exfoliation of solvent-stabilised black phosphorus: applications beyond electronics
Damien Hanlon, Claudia Backes, Evie Doherty, Clotilde S. Cucinotta, Nina C. Berner, Conor Boland, Kangho Lee, Peter Lynch, Zahra Gholamvand, Andrew Harvey, Saifeng Zhang, Kangpeng Wang, Glenn Moynihan, Anuj Pokle, Quentin M. Ramasse, Niall McEvoy, Werner J. Blau, Jun Wang, Stefano Sanvito, David D. ORegan, Georg S. Duesberg, Valeria Nicolosi, Jonathan N. Coleman