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Graphene is an allotrope of carbon. The carbon have different crystal structure such as diamond, graphite etc. Graphene is the latest invented allotrope of carbon. It is the world’s first 2D crystal lattice. It is the strongest and thinnest material. Graphene is the combination of two words graphite and ene. The suffix ene was given by Hanns-Peter-Boehm. In 1962, he described about single layer carbon foils. The Graphene is like a honeycomb which is made up of carbon atoms and their bonds. The Graphene is stacked together to form 3D Graphite. Graphene is wrapped to form 1D nanotubes and 0D fullerenes. Scientists literally took a piece of Graphite and divided it into layer by layer until only one single layer remained. This process is called mechanical exfoliation.
By stacking about 3 million graphene sheets, it will produce only 1mm thick graphite. The structure of Graphene is given below.
The conduction band and valence band of Graphene meet at Dirac points. So the Graphene is a zero energy gap semiconductor with high electrical conductivity. The conductivity can be increased further by applying an electric field. The electrons can move through graphene more easily than copper due to the tight bond of Graphene sheet. The electrons travel through the Graphene sheet as fast as one hundredth than that of speed of light.
Atomic Force Microscopy is a technique used to calculate the strength of Graphene. It is harder than diamond and 300 times harder than steel. It has an intrinsic tensile strength of 130GPa and stiffness of 1TPa.It is stretchable upto 20% of its initial strength.
It is the most reactive form of carbon. Due to its 2D structure, each single atom takes part in chemical reaction from its two sides. It is a unique feature of Graphene among all solid materials. The Graphene requires very low temperature to burn.
It is a perfect thermal conductor. Its thermal conductivity is much higher than other carbon structures like graphite, diamond etc at room temperature. Graphite is the 3D form of Graphene has thermal conductivity is 5 times smaller than Graphene. Due to its high thermal conductivity and electron mobility, it will produce chips which are faster and better in heat dissipation.
Graphene is a one atom thick crystal which can visible with naked eye. It can absorb 2.3% of light which is passing through it.
The vacuum tube is replaced by transistors. Silicon is mostly used material in all electronic components. Graphene has no band gap. So it cannot use in digital electronics applications. By introducing bandgap in between layers of Graphene sheets, it can be utilized for electronics applications. Graphene require bandgap for making ON/OFF logical state. Research is going on to develop bandgap in Graphene. The existing methods are carbon nanotubes, nanoribbons, use of Graphite substrates etc. Researchers say that the Graphene will replace the silicon in many electronic applications. Graphene is the most useful material that replaces silicon and nanoscale transistors. Due to its high mobility and low noise, the Graphene could be used as a channel in Field Effect Transistor. It is difficult to produce single sheet Graphene and also harder to make an appropriate substrate. In 2008, a small transistor is made with one atom thick and ten atom wide. In 2008, IBM announced that they developed Graphene transistors operating in GHZ frequencies. In 2009, n-type and p-type transistors have been created. Inverter is fabricated using n-type and p-type transistors. But it has very low voltage gain. IBM built processors operating with 100GHz transistors on 2-inch Graphene sheets. In 2011, IBM announced that they created first Graphene based integrated circuit to produce a broadband mixer. It can handle frequencies up to 10GHZ.In June 2013, an 8 transistor operating at 1.28 GHz ring oscillator have been created.
Some of the applications are
Due to its several properties, the Graphene could used to produce several electronic components. Some of them are given below.
The technologies for developing new and efficient battery are standstill. Batteries can store more charges. But it is heavy and it takes long time to recharge. Capacitors are lightweight and recharge quickly. But it does not have much capacity to store charge. A Graphene foam based battery which is developed by Chinese researchers, may bridge the gap between battery and capacitor. It uses lithium technologies. It can charge and discharge quickly like capacitor. It is also flexible and perfectly working when it is bent. CalBattery (California Lithium Battery) has worked with Argonne National Laboratory (ANL) for commercialization of innovative lithium battery anode used with GEN3 Silicon Graphene composite anode material. It will achieve high performance level. The capacity is increased 10 times with the addition of Graphene into lithium ion batteries. Testing results shows that the new lithium ion battery has excellent performance characteristics and energy density. It reduces the lifetime cost of battery in consumer electronics, etc. Due to its high power density, the battery can also used in electrical vehicles. This battery will play a major role in future electronics.
The Graphene has extremely high surface area. So it could be used as conductive plates of supercapacitors. It is expected that Graphene could be produce supercapacitor with greater energy storage density than conventional energy storage devices.
Indium tin oxide is a commercial product used as transparent conductor in touch screens on table computers or smart phones etc. It is also used ass electrode in OLED and solar cells. Rice University researchers developed Graphene based thin film. It integrates high conductivity Graphene single layer with fine metal nanowire grid. The material produces a low resistance and excellent conductivity. The transparent electrode developed by Rice University researchers has high conductivity and flexible than other competing electrodes. The film is eco-friendly and cannot deteriorate easily.
Transparent flexible memory chips are developed by Rice University researchers. The active component is Silicon Oxide. A strong charge is pushed through standard silicon dioxide to produce a transparent memory.
Graphene has no band gap between valence and conduction band. So it can’t used as a transistor. An energy gap is introduced by applying some electric field, then it can use as semiconductor. Graphene has high carrier mobility and low noise. So it can be used as a channel in Field Effect Transistor (FET). Graphene based integrated circuits can handle frequencies up to 10GHz. The transistors printed on flexible plastic can operate at 25GHz. In 2010, IBM produced a working transistor with Graphene. The Graphene transistor overcomes the technical limitations of Graphene. It operated at twice speed than conventional Silicon transistor. It can be effectively used in complex systems. IBM faces number of challenges to produce Graphene transistor. It includes protecting the ultra-thin Graphene layer during the etching process with electron beam lithography. Electron beam lithography is a standard process for creating nanoscale features in silicon-based electronics. The IBM could commercially produce the Graphene transistors in future. Graphene transistors are classified into two according to their working principles. In the first, single Graphene layer, carbon nanotubes, nanoribbon can act as transistor channels. The current is transmitted through horizontal axis. In the second, tunneling (band to band on a single Graphene layer) or vertically between adjacent Graphene layers.
Electronic sensors based on Field Effect Transistors (FET) are favored due to their high sensitivity, low cost, miniaturization of device and real time detection. It is based on the change of conductance of FET channels upon adsorption of target molecules.
The researchers at the Institute of Photonic Science (ICFO), in collaboration with Massachusetts Institute of Technology, Max Plank Institute for Polymer Research, and Graphenea S.L Donostia-San Sebastian discovered that Graphene is able to convert a single photon that it absorbs into multiple electrons could drive electric current. Graphene can be used as a promising material for photoelectrochemical energy conversion in dye sensitized solar cells. Graphene films, which are transparent, conductive and ultra-thin, can be fabricated from exfoliated graphite oxide by thermal reduction. These films are highly conductive and transparent.
In 2009, researchers created experimental Graphene frequency multipliers. It takes certain frequency as input and gives output as multiple of the input signal.
Graphene strongly interact with photons, with the potential for creating direct band gap. It can be used for optoelectronics and nanophotonic devices. It is expected that Graphene will be used in touch screens, Liquid Crystal Display (LCD), Organic Liquid Crystal Display (OLED). Graphene can transmit light up to 97.7% of incident light due to its transparent property. It has high conductivity, So it can be used in smartphone, tablet, desktop computers, televisions etc. recent research shows that optical absorption of Graphene can be changed by adjusting Fermi level. Due to its high tensile strength and flexibility, it could be used in flexible displays.
It can be used as a Ultrafiltration medium to behave as barrier between two substances. Researchers at Columbia University create monolayer Graphene filter with pore size approximately 5nm. It has high strength and less brittle than conventional filtration systems. So it can be used in water filtration systems, desalination systems etc.
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