I’ve written before here at Associated Content about the material called graphene. I’ve attached an image to this article that shows graphenes molecular structure. It’s related to graphite, which everyone is familiar with – graphite is a greyish powder, commonly used as a lubricant for locking mechanisms. Graphite consists of huge piles of graphene sheets, all piled in a heap; the sheets slip past each other very easily, which gives graphite its slippery feel. By isolating and manipulating single sheets – known as graphene – researchers have found that the individual sheets possess incredible material strength (200 times stronger than steel) as well as excellent electronic properties. Graphene can conduct electricity just as easily as a metal, which is astronishing given that graphene is comprised of nothing more than carbon atoms.
Researchers have already used graphene to create new kinds of transistors, and have used the highly-conductive material in flat-panel displays and solar cells. They’re also being used for ultrahigh capacity electrodes, which would provide densely-packed and fast computer memory.
IBM has now announced a discovery (in the journal Nature: Nanotechnology) that utilizes this unique collection of properties shown by graphene: they are now using graphene sheets to make photodetectors. Photodetectors are an electronic component which transforms an incoming light beam into electricity, which can then be measured and used for a useful purpose. It “detects” the light by producing an electric current. Normally, light detectors are made using semiconductors from groups III, IV, and V from the Periodic Table. These elements – like gallium, and phosphorus – absorb light particles (photons) and create electrons. These electrons are then moved out of the material and used to produce an electrical current.
Graphene, which has nothing but carbon atoms (all linked together in a honeycomb) transports the electrons twenty to thirty times faster than the group III, IV, and V semiconductors. This makes the graphene photoconductors extremely efficient and detecting light. As an added bonus, graphene absorbs a wide range of wavelengths. The normal materials don’t absorb much infrared light, whereas the graphene can detect wavelengths of light ranging from the visible way down to the infrared.
Initially, researchers were not all that excited about graphenes potential in the area of optical devices. This is because the electrical charge generated in the graphene by the incoming photons is normally dissipated before a current can be generated. This is a common behavior seen in metals. The key is to apply an external electric field to the material; this separates the charges the instant they are formed by the incoming light beam, and allows the electrons to be collected fast enough to provide a measurable current.
It was already known that known that when metallic contact points are deposited onto a sheet of graphene, an electric field is generated at the interface between the two dissimilar materials. The IBM researchers took advantage of this phenomenon. Their finished device is a piece of graphene with metal contacts on the top. When a light is shone near this contact point, electrons are generated and then separated by the intrinsic electric field present as a result of the metal:graphene interface, producing a current. This current can be used to ring a bell, or spike a meter, providing an indirect indicator of the presence of light.
One single sheet of graphene can absorb two to three percent of the light hitting it. This may not sound very significant, but consider that the graphene is only one atom thick. The graphene has enormous advantages over other materials. It’s extremely fast, it absorbs a wide range of light wavelengths, and (on a per atom basis) it soaks up a large amount of light. It’s a unique combination of traits that put graphene in a great position for use in optical communications and fiber-optic data networks. It’s made of a cheap material and it performs better than any of its competitors, and we should soon see it incorporated into our electronic components.