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The Discovery of Graphene
The discovery of graphene was at once almost accidental and probably inevitable. Graphite, the most stable form of carbon composed of layers stacked atop each other, has been used by humans for hundreds of years; in 1564 it was adopted as the primary writing core of pencils, and its refractory capabilities for forging helped secure English naval superiority during the Elizabethan age. Research into the chemical and structural properties of graphite had progressed steadily since the early 1900's, but attempts to isolate the individual layers composing the graphite never managed to isolate fewer than 50 layers at once as late as 2004. Many researchers were also convinced that no material could survive in a two-dimensional, one atom thick state, and that even the heat of being at room temperature would be enough to make the material pull itself apart.
At the same time, a physics professor at the University of Manchester, Andre Geim, had been hosting what he called "Friday sessions" for his students: exploratory, experiment-driven ad hoc lab sessions fuelled by curiosity and occasionally beer. During one of these sessions, he tasked one of his students to polish a sample of graphite crystal to as thin as could be done. The initial results were far from spectacular, as the student had reduced the sample beyond the point of usefulness.
However, Geim discovered that the method the student had been using to polish the crystal, peeling off successive layers using cellophane tape, left large thin layers of graphite residue on the sticky surface of the tape; better yet, those thin layers could be divided even further by applying more tape to the other side of the graphite and splitting it apart, leaving residue on both pieces of tape. Before long, Geim was able to isolate a single two-dimensional layer of graphite, known as graphene, and he and another Ph.D. student, Konstantin "Kostya" Novoselov, were able to begin research on the material, research which would eventually earn them the 2010 Nobel Prize in Physics.
Characteristics and Properties of Graphene
Physical Structure
Graphene is a two-dimensional sheet of carbon arranged in a hexagonal grid with a thickness of only one atom. It is the lightest material on Earth: it has an area density of 0.77 mg/m^2, and aerogel constructed of graphene has a density of 160 g/m^3 (approximately 0.13 times the density of air at STP).
Strength
Graphene is approximately 200 times stronger than steel, and has a tensile stiffness of 150 million psi, surpassing even diamond. Despite this, it is remarkably flexible and pliant; it can be stretched up to an additional 20 percent of its length.
Conductivity
Graphene has both the highest thermal conductivity and electrical conductivity of any known material; it can carry over a thousand times more electricity than copper, and has up to two-hundred fifty times the electrical mobility of silicon.
Permeability
Graphene is completely impermeable to all gases, and most liquids, the notable exception being water. Despite this, it is also highly hydrophobic. Additionally, graphene has very low light absorption, at around 2.5% for white light.
Ease of Production
Due to the massive commercial and industrial interest in graphene, methods for production have advanced its affordability faster than any other known material. In the eleven years since the production of the first sub-micron size flakes of graphene, methods have been implemented for cultivating graphene by the square meter, and the global market for graphene reached approximately $9 million last year.
Commercial and Industrial Applications of Graphene
The possible uses for graphene are about as limited as human imagination; thousands of different applications and patents have been proposed, but of particular interest are its potential uses in electronics and composites.
Electronics
Probably the most well-publicized potential application for graphene is its use to create super-fast electronic circuits and flexible devices. Given its obvious advantages over silicon, it is reasonable to consider graphene as an alternative to silicon in circuitry; however, researchers have run into a major problem: it lacks a "band gap", an integral property of circuit material that confines electron energy to two or more distinct ranges and allow the material to act as a switch. A large amount of research is dedicated to addressing this problem, but currently the future for graphene circuits is less than promising.
Another field of high interest is the possibility of using graphene to make high-capacity batteries and capacitors. Energy storage has not been able to satisfactorily keep up with our advanced demands of longer lasting batteries and shorter recharge times; most solutions result in sacrificing either capacity or recharge time in favor of increasing the other. Given graphene's unique properties, it is possible that batteries could be developed to be both high-capacity and quick-recharge, and at a fraction of current battery size and weight. Additionally, graphene can be integrated into current battery designs to improve their performance now while research is being done on graphene batteries.
Composites
Of any industry, graphene has probably made the most headway in the world of composite materials. Conductive ink laced with graphene is already being sold to consumers, and boasts higher conductivity and efficiency that existing organic semiconductive ink. Graphene's inherent inertness and repelling qualities make it excellent at protecting against corrosion and oxidation. It's strength may lead to it being used in conjunction with carbon fiber and other reinforcing materials, if not replacing them entirely. Research is currently being done in attempting to replace Kevlar in protective clothing.
Another exciting area of composites research is that surrounding carbon nanotubes. A carbon nanotube, or CNT, is essentially a layer of graphene rolled into a cylinder. Carbon nanotubes combine all the physical properties of graphene with the additional structural reinforcement of its cylindrical shape, resulting in a material hundreds of times stronger than steel. One idea that has excited many in not only the composite materials community but the aerospace community is the possibility of using carbon nanotubes as a material in building a space elevator. Though the longest nanotube made is a little over half a meter in length, researchers are enthusiastic that processes could be refined to produce nanotubes of sufficient size to support such an elevator.
References
Colapinto, John. "Graphene: Fast, Strong, and Impossible to Use" - The New Yorker
de la Fuente, Jesus. "Properties of Graphene" - Graphenea