What about "phosphorine"? // EIT Digital

What about "phosphorine"?

Schematic of the “puckered honeycomb” crystal structure of black phosphorus. Credit: Vahid Tayari/McGill University

Graphene has paved the way to the study, and manufacturing, of other materials that have in common with graphene the thickness: layers one atom thick.

The last on this thin bandwagon is phosphorine, a layer made by phosphorous atoms.

It has been developed at the Australian National University (ANU) in Canberra.

As it can be seen in the drawing the phosphorous atoms are forming a wavelike grid. The structure and the outer electron shell of phosphorous atom (with 5 electrons and 3 holes, rather than 4 and 4 of silicon and carbon) give the material different, but interesting, properties that scientists are discovering now, since never before they had a single atom layer of this material.

To start with phosphorous is a semiconductor by itself (you don't need to "drug" it to make it become a semiconductor). And as all semiconductor it has a band gap (an energy difference between the top of the valence band and the bottom -related to the electrons outer shell), what is needed to control electrons flow.

Interestingly, the scientists discovered that this band gap is in the range of infrared light and that by overlaying more layers one on top of the other it is possible to change the band gap. In more simple terms the phosphorine can be manufactured in such a way to be sensitive to different wavelength in the infrared spectrum.

Being so thin it is transparent (although it adsorb infrared spectrum) and it could be layered, as an example, onto a window glass transforming it into a photovoltaic panel (by converting the infrared spectrum into electricity).

Since it can be manufactured in different "thickness" (actually "thinness") hence responding to different wavelengths it can also be used to generate different colours, like a LED. As a matter of fact the scientists are able to tell how many layers are there by looking at the colour of the surface ...

Most importantly, at ANU they have discovered a process to produce these one atom thick layers that is quite easy: you take a phosphorous crystal and by using a sticky tape you remove a single layer of atoms from it, and voilà, you have made phosphorine. 

Author - Roberto Saracco

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