Structure of graphene

Graphene is an atomic-scale honeycomb lattice made of carbon atoms. Graphene is the basic structural element of

graphite, carbon nanotubes and fullerenes. In short ‘Graphene’ is the super thin, super strong, transparent, conductive and self-repairing material is poised to revolutionize the future by not only by super-charging

batteries but also by giving flexible semiconductors and much more

Graphene, fullerene, CNT and graphite structures

DESCRIPTION

• A definition of "isolated or free-standing graphene" has also recently been proposed: "graphene is a single atomic plane of graphite, which—and this is essential—is sufficiently isolated from its environment to be considered free-standing." This definition is narrower than the definitions given above and refers to cleaved, transferred and suspended graphene monolayers.

• Other forms of graphene, such as graphene grown on various metals, can also become free-standing if, for example, suspended or transferred to silicon dioxide (SiO2). A new example of isolated graphene is graphene on silicon carbide (SiC) after its passivation with hydrogen.

OCCURRENCE AND PRODUCTION

• The following processes are adopted to produce graphene:

• Exfoliated graphene• Epitaxial growth on silicon carbide• Epitaxial growth on metal substrates• Graphite oxide reduction• Pyrolysis of sodium ethoxide• From nanotubes• From graphite by sonication• Carbon dioxide reduction method

POTENTIAL APPLICATIONS• Graphene transistors• Due to its high electronic quality, graphene has also attracted the interest of technologists who see it as a way of

constructing ballistic transistors. Graphene exhibits a pronounced response to perpendicular external electric fields, allowing one to build FETs (field-effect transistors). In their 2004 paper, the Manchester group demonstrated FETs with a "rather modest" on-off ratio of ~30 at room temperature. In 2006, Georgia Tech researchers, led by Walter de Heer, announced that they had successfully built an all-graphene planar FET with side gates. Their devices showed changes of 2% at cryogenic temperatures. The first top-gated FET (on-off ratio of <2) was demonstrated by researchers of AMICA and RWTH Aachen University in 2007.Graphene nanoribbons may prove generally capable of replacing silicon as a semiconductor in modern technology.

• Facing the fact that current graphene transistors show a very poor on-off ratio, researchers are trying to find ways for improvement. In 2008, researchers of AMICA and University of Manchester demonstrated a new switching effect in graphene field-effect devices. This switching effect is based on a reversible chemical modification of the graphene layer and gives an on-off ratio of greater than six orders of magnitude. These reversible switches could potentially be applied to non-volatile memories.

Formation of a Graphene Transistor

Integrated circuits

• Graphene has the ideal properties to be an excellent component of integrated circuits. Graphene has a high carrier mobility, as well as low noise, allowing it to be used as the channel in a field-effect transistor. The issue is that single sheets of graphene are hard to produce, and even harder to make on top of an appropriate substrate. Researchers are looking into methods of transferring single graphene sheets from their source of origin (mechanical exfoliation on SiO2 / Si or thermal graphitization of a SiC surface) onto a target substrate of interest. In 2008, the smallest transistor so far, one atom thick, 10 atoms wide was made of graphene. IBM announced in December 2008 that they fabricated and characterized graphene transistors operating at GHz frequencies. In May 2009, an n-type transistor was announced meaning that both n and p-type transistors have now been created with graphene functional graphene integrated circuit was also demonstrated – a complementary inverter consisting of one p- and one n-type graphene transistor. However, this inverter also suffered from a very low voltage gain.

• The Intel LIGHTPEAK uses graphene technology.

Graphene-based nanotechnology in energy applications

• Graphene-based nonmaterials have many promising applications in energy-related areas. Just some recent examples: Graphene improves both energy capacity and charge rate in rechargeable batteries; activated graphene makes superior supercapacitors for energy storage; graphene electrodes may lead to a promising approach for making solar cells that are inexpensive, lightweight and flexible; and multifunctional graphene mats are promising substrates for catalytic systems

• Schematic models of chemical strategies towards graphene from different carbon sources

Solar cells• The most unique aspect of the OPV cell devise is the transparent conductive electrode. This allows the

light to react with the active materials inside and create the electricity. Now graphene/polymer sheets are used to create thick arrays of flexible OPV cells and they are used to convert solar radiation into electricity providing cheap power. A research team under the guidance of Chongwu Zhou, Professor of Electrical Engineering, USC Viterbi School of Engineering has put forward the theory that the graphene – in its form as atom-thick carbon atom sheets and then attached to very flexible polymer sheets with thermo-plastic layer protection will be incorporated into the OPV cells. By chemical vapour deposition, quality graphene can now be produced in sufficient quantities also. The traditional silicon solar cells are more efficient as 14 watts of power will be generated from 1000 watts of sunlight where as only 1.3 watts of power can be generated from a graphene OPV cell. But these OPV cells more than compensate by having more advantages like physical flexibility and costing less

• The flexibility of OPVs gives these cells additional advantage by being operational after repeated bending unlike the Indium-Tin-Oxide cells. Low cost, conductivity, stability, electrode/organic film compatibility, and easy availability along with flexibility give graphene OPV cell a decidedly added advantage over other solar cells

A graphene solar cell, its structure and a graphene Organic LED.

Lithium-ion batteries

• The energy densities and performances of rechargeable lithium ion batteries – which are used widely in portable electronics such as cell phones, laptop computers, digital cameras, etc. – largely depend on the physical and chemical properties of the electrode materials. Thus, many research attempts have been made to design novel nanostructures and to explore new electrode materials in order to achieve higher capacity and to increase the battery's charge rate, increasingly also employing graphene in form of nanosheets, paper, and carbon nanotube or fullerene hybrids (for a detailed review see here: "Graphene-based electrode materials for rechargeable lithium batteries").

Antibacterial Paper Made From Graphene

• Scientists at Shanghai Institute of Applied Physics have shown that graphene, a material which is a sheet of carbon exactly one atom thick, does not allow the growth of bacteria on its surface. This is in contrast to mammalian cells which seem to do just fine when in contact with the graphene. It has been found that sheets of graphene oxide are highly effective at killing bacteria such as Escherichia coli. This means graphene could be useful in applications such as hygiene products or packaging that will help keep food fresh for longer periods of time.

• We find that graphene derivatives – graphene oxide, graphene oxide and reduced graphene oxide – can effectively inhibit bacterial growth" Chunhai Fan, a professor in the Laboratory of Physical Biology at the Shanghai Institute of Applied Physics. "This is a significant finding as both previous and our own studies have proven that graphene, particularly graphene oxide, is biocompatible and cells can grow well on graphene substrates. Furthermore, while silver and silver nanoparticles have been well known to be antibacterial, they and other

nanomaterials are often cytotoxic.

A sheet of graphene paper and Schematic illustration of E.coli exposed to graphene nanosheets. (Image: Dr. Fan, Shanghai

Institute of Applied Physics)

Graphene As An Anti Corrosive Coating

• New research has established the "miracle material" called graphene as the world's thinnest known coating for protecting metals against corrosion. Corrosion results from contact of the metal's surface with air, water or other substances. One major approach involves coating metals with materials that shield the metal surface, but currently used materials have limitations. The scientists decided to evaluate graphene as a new coating. Graphene is a single layer of carbon atoms, many layers of which are in lead pencils and charcoal, and is the thinnest, strongest known material. That's why it is called the miracle material. In graphene, the carbon atoms are arranged like a chicken-wire fence in a layer so

thin that is transparent, and an ounce would cover 28 football fields.• Researchers found that graphene, whether made directly on copper or nickel or

transferred onto another metal, provide protection against corrosion. Copper coated by growing a single layer of graphene through chemical vapor deposition (CVD) corroded seven times slower than bare copper, and nickel coated by growing multiple layers of graphene corroded 20 times slower than bare nickel

• Researchers from Monash University and Rice University developed a thin graphene film anti-corrosion coating. Their new coating can maker copper more resistant to corrosion - almost 100 times better than uncoated copper. According to the researchers, that's the best graphene-based anti-corrosion material developed yet.

Graphene-based anti-corrosion composite coating.

NANOCOMPOSITE COATING• The researchers are optimistic that the new coating will be an effective replacement

for hexavalent chromium corrosion-prevention coatings, which have been linked to cancer-causing pollution. Banerjee’s work is supported by Tata Steel and the New York State Pollution Prevention Institute (a partnership among Rochester Institute of Technology, Clarkson University, Rensselaer Polytechnic Institute, University at Buffalo and the 10 NYS Regional Technology Development Centers). UB has filed an application for a provisional patent on the coatings.

• Researchers from the Shenyang National Laboratory for Materials Science and the Rensselaer Polytechnic Institute have shown that graphene can be used to create a superhydrophobic coating material that shows stable superhydrophobicity under both static as well as dynamic (droplet impact) conditions

GRAPHENE BIODEVICES• Graphene's modifiable chemistry, large surface area, atomic thickness and

molecularly-gatable structure make antibody-functionalized graphene sheets excellent candidates for mammalian and microbial detection and diagnosis devices.

• The most ambitious biological application of graphene is for rapid, inexpensive electronic DNA sequencing. Integration of graphene (thickness of 0.34 nm) layers as nanoelectrodes into a nanopore can solve one of the bottleneck issues of nanopore-based single-molecule DNA sequencing.

• The researchers grew graphene over a nickel foam template which was then leeched away. The remaining graphene foam (layered graphene sheets) was coated with a Teflon layer. They say that the pore size and structure of the graphene foam can be uniformly tuned by selecting the appropriate nickel foam template.

ANALYSIS• Now the question arises why we have chosen only “GRAPHENE” for this study and not any

other material?• The answer to this question is quite simple. First of all Graphene is the material of the present

time and it holds the key to a very eventful and bright future of our human race. With so much to offer graphene has already proven to be worthy of being called ‘The Magic Material’. Today no other material is so diverse i.e. no other material has important applications as graphene. Some of its present applications have been already discussed above. But that’s not all graphene has to offer. In addition to the above graphene is being used in top notch researches that are potent enough to entirely change our future.

• The qualities that sets apart graphene from other smart and industrial material are:• It is cost effective. And once synthesized for a particular application its cost effectiveness

increases.• Graphene, as like other smart materials has unique properties; in combination of other

materials graphene has proven to be very useful. • There are other materials but they can’t provide flexibility to work with them as graphene

does. Since it is just a layer, it can be molded and formed in whatever shape and form desired.• The current applications are very vital like alternative energy source, desalination, high speed

transistors etc. • The scope of application of this material is very wide. • And still scientists and researchers are looking for its new aspects and are at verge of making

new discoveries.

CONCLUSION

• As scientists battle to bend graphene to their will in the high-profile realm of electronic components, researchers working on more straightforward applications of this two-dimensional, atom-thin sheet of carbon are also making some interesting discoveries. Some of the important applications of graphene have been touched in this paper; but the scope of graphene is very vast and the above should not be mistaken for what this material has to offer. The applications of graphene are numerous and in future we can expect a lot from “GRAPHENE”.

GRAPHENE”- KEY TO OUR FUTURE