Friday, 21 December 2012

The secret life of Carbon, nano technology today

Carbon is the fourth most abundant chemical element in the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets.
In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 810 gigatonnes of carbon) and dissolved in all water bodies (approximately 36,000 gigatonnes of carbon). Around 1,900 gigatonnes of carbon are present in the biosphere.
Carbon is a nonmetal that can bond with itself and many other chemical elements, forming nearly ten million compounds.
There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of about 5,730 years.
Radiocarbon dating is a radiometric dating method that uses (14C) to determine the age of carbonaceous materials up to about 60,000 years old. The technique was developed by Willard Libby and his colleagues in 1949.
Atomic carbon is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with different molecular configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond.
Once considered exotic, fullerenes are nowadays commonly synthesized and used in research; they include buckyballs, carbon nanotubes, carbon nanobuds and nanofibers. Several other exotic allotropes have also been discovered, such as lonsdaleite, glassy carbon, carbon nanofoam and linear acetylenic carbon (carbyne).
Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. In particular, owing to their extraordinary thermal conductivity and mechanical and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, nanotubes form a tiny portion of the materials in some (primarily carbon fiber) baseball bats, golf clubs, or car parts.
Only recently Researchers at MIT have developed a new type of photovoltaic cell made with carbon nanotubes that captures solar energy in the near-infrared region of the spectrum, which conventional silicon solar cells don’t. The new design means solar cell efficiency could be greatly increased, boosting the chances to make solar power a more popular source of energy. The new solar cell developed at MIT is a consequence of recent advances in the large-scale production of carbon nanotubes. It also features another type of carbon, a fullerene known as C60 (aka Buckminsterfullerene). The nanotubes have to be very pure, single-walled and of the same symmetrical configuration. The material is transparent to visible light and has to be overlaid on conventional silicon cells to form a hybrid cell that could, in theory, capture most of the energy contained in the sunlight it capture.
There are several bright, optimistic spots in this research, the scientists say. Although the proof of concept devices have so far achieved an efficiency of only 0.1 percent, the researchers have already identified some of the sources of inefficiency. For instance, they have noticed that homogenous mixtures of carbon nanotubes are more efficient than heterogeneous ones. Mixing single-walled and multiwalled nanotubes is not a good idea, either. The scientists are positive they are bound to make high-efficiency near-infrared solar cells, and point out that even a low-efficiency cell that works in that region, capturing energy that current cells waste, would be worthwhile provided costs are low. They are now looking into ways to better control the shape and thickness of the layers of the material.
Graphene has been touted as the "miracle material" of the 21st Century. Said to be the strongest material ever measured, an improvement upon and a replacement for silicon and the most conductive material known to man.
Graphene as the strongest material ever measured, some 200 times stronger than structural steel.
Since its properties were uncovered, more and more scientists have been keen to work on projects. About 200 companies and start-ups are now involved in research around graphene. In 2010, it was the subject of about 3,000 research papers.
Samsung has been one of the biggest investors in research, in collaboration with South Korean Sungkyunkwan University. It has already demonstrated a 25-inch flexible touchscreen using graphene.
But companies like IBM and Nokia have also been involved in research. IBM has created a 150 gigahertz (GHz) graphene transistor the quickest comparable silicon device runs at about 40 GHz.
Despite this frenzy of progress, investment and press attention, many researchers are cautious. Some are certain that graphene will not do everything that has been thought up for the material. What has been reported as "potential" seems to be at the moment just that, with few real-world examples of it working to replace other materials. "We feel that it's rather difficult to imagine graphene as a replacement to silicon," says Dr Phaedon Avouris, of IBM.
The team, which was led by Richard Kaner of UCLA, started by smearing graphite oxide a cheap and very easily produced material films on blank DVDs. These discs are then placed in a LightScribe drive (a consumer-oriented piece of gear that costs less than $50), where a 780nm infrared laser reduces the graphite oxide to pure graphene. The laser-scribed graphene (LSG) is peeled off and placed on a flexible substrate, and then cut into slices to become the electrodes. Two electrodes are sandwiched together with a layer of electrolyte in the middle and voila, a high-density electrochemical capacitor, or supercapacitor as they’re more popularly known.
Now, beyond the novel manufacturing process the scientists are confident it can be scaled for commercial applications, incidentally the main thing about LSG capacitors is that they have very desirable energy and power characteristics. Power-wise, LSG supercapacitors are capable of discharging at 20 watts per cm3, some 20 times higher than standard activated carbon capacitors, and three orders of magnitude higher than lithium-ion batteries. It has a energy density of 1.36 milliwatt-hours per cm3, about twice the density of activated carbon, and comparable to a high-power lithium-ion battery.
The performance of capacitors is almost entirely reliant on the surface area of the electrodes, so it’s massively helpful that one gram of LSG has a surface area of 1520 square meters (a third of an acre). As previously mentioned, LSG capacitors are highly flexible, too, with no effect on its performance
In experiments, the researchers demonstrated that electrodes made of the sponge-like graphene are stable in two common electrolytes (ionic liquid and aqueous) used in supercapacitors. While many supercapacitor electrodes perform well only at temperatures of 60 °C (140 °F) or higher, the sponge-like graphene electrodes work very well at room temperature. The researchers attribute both the good room-temperature operation and the ability for fast electrolyte transfer (and resulting high power density) to the electrode's sponge-like macroporous structure. The sponge-like graphene electrodes also exhibit an excellent cycle life. After running through 10,000 charge-discharge cycles, the electrodes retained 90% of their capacity in the ionic liquid electrolyte and 98% in the aqueous electrolyte.
The energy density values of the supercapacitor are comparable to that of nickel metal hydride batteries. The new technology makes for an energy storage device that stores nearly as much energy as in a battery but which can be recharged in seconds or minutes.
The team, which includes scientists from Angstron Materials in the US and Dalian University of Technology in China, are now working hard to further improve the energy density of the device.
Graphene supercapacitors could really change the technology landscape. While computing power roughly doubles every 18 months, battery technology is almost at a standstill. Supercapacitors, which suffer virtually zero degradation over 10,000 cycles or more, have been cited as a possible replacement for low-energy devices, such as smartphones. With their huge power density, supercapacitors could also revolutionize electric vehicles, where huge lithium-ion batteries really struggle to strike a balance between mileage, acceleration, and longevity. It’s also worth noting, however, that lithium-ion batteries themselves have had their capacity increased by 10 times thanks to the addition of graphene. Carbons properties allows the possibility of life, its radioactive decay can tie us to the past. The new nano structures of carbon reveals more avenues in medicine, electronics and a possibility in the transport industry. Either way, carbon in any of its forms seems likely to play a major role in the future of of the tech industry...


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