Wednesday, February 5, 2014

Graphene and Phosphorene

We've been hearing a lot about graphene the last few years.
In 2004, two scientists at the University of Manchester in England isolated a carbon-based material called graphene, with some unusual properties. Andre Geim and Konstantin Novoselov hailed it as 'the wonder material of the 21st century,' and they were awarded the 2010 Nobel Prize in physics. Scientists now say that someday, graphene may change the way we live.

... The leader of the graphene research team at Manchester University, Aravind Vijayaraghavan, said incredible strength is not its only quality.

"It's bendable, stretchable, transparent, super light. The best conductor of heat, the best conductor of electricity. It's not just one thing that makes it amazing, it's in fact all these things rolled into one," said Vijayaraghavan.

The potential of graphene is practically unlimited. It can be used in cancer therapy, in flexible touchscreens, or for batteries that will charge in seconds. ...
 However, it has a rather serious shortcoming--it does not make a good transistor. However, a similar material called phosphorene may work where graphene does not:
Graphene, a one-atom-thick layer of carbon, has charmed materials scientists with its enticing electrical properties that allow electrons to flow freely across its surface. But the material lacks a natural band gap — a range of energy states in which electrons cannot exist freely — that could be used to switch this flow on and off. This reduces graphene’s usefulness as a replacement for the semiconductor switches in computer circuits.

Last month, research groups in the United States and China reported on work towards a promising candidate that could fulfil both needs: phosphorene, an atom-thick layer of the element phosphorus that does have a natural band gap. The work is part of a trend that David Tom├ínek, a condensed-matter theorist at Michigan State University in East Lansing, dubs the “post-graphene age” — in which researchers are exploring alternatives in the hope of overcoming graphene’s deficiencies. The rationale is that phosphorene might be useful for making thin, flexible electronics that could be more easily cooled than silicon ones.

Physicists have been studying black phosphorus — a layered material held together by weak chemical bonds — since the 1960s. But it was only last year that they began trying to isolate single layers. Just as in graphene, phosphorene atoms are arranged hexagonally, but in phosphorene the surface is slightly puckered. With its band gap, phosphorene can be switched between insulating and conducting states, and it is still flat enough to confine electrons so that charge flows quickly, leading to a relatively high mobility that is prized by electrical engineers.

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