Materials scientists have discovered how to make nano sheets of white phosphorus in large quantities, heralding a new era of nano electronic devices.
In recent years, two-dimensional crystals emerged some of the most interesting new materials with which to play. As a result, materials scientists are falling over themselves to discover the extraordinary properties of graphene, boron nitride, molybdenum disulfide, and so on.
A latecomer to this group is the black phosphorus, where phosphorus atoms come together to form a two-dimensional sheet wrinkled. Last year, the researchers constructed a field effect transistor of white phosphorus and have shown that performed very well. This research suggests that white phosphorus may have a bright future in nano electronic 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 friends, say they have solved this problem.
These guys have perfected a way to make large amounts of phosphorus nano-sized sheets blacks who can control. And they have used this newfound ability to test phosphorus black in a number of new applications, such as a gas sensor, an optical switch, and also to reinforce composite materials to make them stronger.
In bulk form, white phosphorus is made of many layers, such as graphite. So one way to separate the single sheets is exfoliation, simply peeling off layers using tape or other materials. This is a time consuming task, which severely limits the potential applications.
So Hanlon and co have stroked another approach. Their method is to place the phosphorus lump black in a liquid solvent and then bombard with acoustic waves that shake the material apart.
The result is that the bulk mass separates into a large number of nano sheets that filters team to size using a centrifuge. This leaves high quality nano sheets composed of a few layers. “Exfoliation liquid phase is a powerful technique to produce nanosheets in large quantities,” they say.
A potential problem with nanosheets phosphorus black is that rapidly degrade in contact with water or oxygen. So one of the team’s progress has done is to provide that certain solvents should form a solvation shell around the sheet, which prevents the oxygen or other oxidizing species reaching the phosphor.
The use team N-cyclohexyl-2-pyrrolidone as a solvent or CHP and for this, the nanosheets are surprisingly long life.
The great advantage of phosphorus black on graphene is that it has a bandgap natural that physicists can use to create electronic devices, such as transistors. But Hanlon and co say that the availability of white phosphorus found nanosheets allowed them to test a number of other ideas as well.
For example, the nano-sheets are added to a film of polyvinyl chloride, doubling its strength and higher toughness traction six times. So not only is carbon allotropes that can increase strength!
They also determined the nonlinear optical response of nano sheets to a pulsed laser measuring the amount of light that is transmitted. It appears that the amount of light black absorbs phosphorus decreases the intensity increases, a property known as the saturable absorption. What’s more, white phosphorus is better at this than even graphene.
Finally, they measured the current through the nanosheets exposing them to ammonia. They found that the strength of the material is increased when it came in contact with ammonia, probably because the ammonia donates electrons that neutralize phosphorus black holes in the sheets.
That immediately makes a black phosphorus detector ammonia decent. Hanlon and co say that the material could detect ammonia at levels of about 80 parts per billion.
All this could mark a step change in interesting research associated with white phosphorus. Many people have seen the emotion associated with the extraordinary properties of graphene. If white phosphorus is half of remarkable, there should be an interesting future for materials scientists.