Sunday, May 20, 2012

Optoelectronics: Graphene shows its colours

From The Economist:
GRAPHENE, a form of carbon that comes in sheets a single atom thick, has gained a reputation as a wonder material. It is the best conductor yet discovered of heat at room temperature and is 40 times stronger than steel. It is also a semiconductor whose electrical conductivity is 1,000 times better than silicon’s. This means it could be used to make devices far more sensitive than is possible now, leading some to predict that it will one day become the material of choice for computer chips. There was little surprise, therefore, when Andre Geim (pictured above) and Konstantin Novoselov, two physicists who were investigating graphene’s structure, won the 2010 Nobel prize for their work.

Actually converting the wonders of graphene into products has been tough. But Frank Koppens and his colleagues at the Institute of Photonic Sciences in Barcelona think they have found a way to do so. As they describe in Nature Nanotechnology, they believe graphene can be used to make ultra-sensitive, low-cost photodetectors.

Photodetectors are devices which convert light into electricity. They are used in digital cameras, night-vision gear, biomedical imagers, pollution sensors and telecommunications. A typical photodetector is made of a silicon chip a few millimetres across onto which light is focused by a small lens. Light striking the chip knocks electrons free from some of the silicon atoms, producing a signal that the chip’s electronics convert into a picture or other useful information.

Silicon photodetectors suffer, though, from a handicap: they are inflexible. Nor are they particularly cheap. And they are not that sensitive. They absorb only 10-20% of the light that falls on to them. For years, therefore, engineers have been on the lookout for a cheap, bendable, sensitive photodetector. Such a device could have many novel applications—wearable electronics, for example. With a little clever engineering, graphene seems to fit the bill.

By itself, graphene is worse than silicon at absorbing light. According to Dr Koppens only 2.7% of the photons falling on it are captured. But he and his colleague Gerasimos Konstantatos have managed to increase this to more than 50% by spraying tiny crystals of lead sulphide onto the surface of the material....MORE
The 2010 Nobel prizes: Physics--Graphene Researchers Geim and Novoselov Win
Andre Geim First in History to Win Both the Nobel and the IgNobel Prizes interviews Physics Laureate Geim about his Ig Nobel