GRAPHENE -Successor to silicon

 Silicon has provided the electronics industry a solid base of favorable properties capitalizing on which various advancements in electronics has been made (in terms of speed and size) but seems to approach its limits. The above limitations offered an exceptional choice to GRAPHENE, a form of carbon.

a)Diamond lattice. b)Hope Diamond. c) Lab grown diamond. A Nanotube Schematic C-60 Fullerence Fullerences and nanotubes Diamond

 Graphene and Graphite are the two dimensional sp2 hybridized forms of carbon found in pencil lead.  Graphite is a layered material formed by stacks 41 of graphene sheets separated by 0.3 nm and held together by weak van der Waals forces which allows them to slide relatively easily across one another. Mother of all graphitic forms. Graphene is a 2D building material for carbon materials of all other dimensionalities

 Graphene is not an Invention but it’s just a Discovery.  Graphene has of course always existed; the crucial thing was to be able to spot it. Mr.A.K.GEIM and his postdoctoral associate Mr.K.S.NOVOSELOV who won the NOBEL PRIZE for the discovery of Graphene.  They simply stuck a flake of graphite debris onto plastic adhesive tape, folded the sticky side of the tape over the flake and then pulled the tape apart, cleaving the flake in two. As the experimenters repeated the process, the resulting fragments grew thinner.

Folded sheets of graphene on a silicon plate. The image was made with a scanning electron microscope, magnified about 5000 times.  Since its discovery in 2004, graphene has been viewed as a promising new electronic material because it offers superior electron mobility, mechanical strength and thermal conductivity.

 The most common method of graphene fabrication is exfoliation– writing with a graphite pencil.  Unfortunately this method is uncontrollable and you are typically left with many sheets of varying thicknesses.

CVD process for Graphene Fabrication  It can also be fabricated using chemical vapor deposition of methane to grow graphene on thin Nickel and Copper(Cu) films.  In roll-to-roll production, as outlined above, graphene-laden Cu was pressed against a polymer support, bathed in an etchant that removed the Cu, and then dry-transferred to another flexible polymer.

Atomic structure Suspended graphene showing "rippling" of the flat sheet  Suspended graphene also showed "rippling" of the flat sheet, with amplitude of about one nanometer.  Because of this Graphene has got several properties.

High Electron Mobility  Experimental results from transport measurements show that graphene has a remarkably high electron mobility at room temperature, approximately 15,000 cm 2 V −1 s −1.electron mobility Low resistivity and better current capacity & temperature conductivity  The resistivity of the graphene sheet can be as low as 10 −6 Ω·cm, less than the resistivity of silver, the lowest resistivity substance known.resistivitysilver  In addition to the high current carrying capacity, graphene Nano ribbons also have excellent thermal conductivity.

High frequency operation  Graphene is estimated to operate at terahertz frequencies i.e. trillions of operations per second.  The key advantage of graphene technology is that electrons move at a very high velocity, thus allowing to obtain high speed and high performance transistors.

Photograph of graphene in transmitted light. High Opacity Graphene's unique electronic properties produce an unexpectedly high opacity for an atomic monolayer, with a startlingly simple value: it absorbs2.3% of white lightlight Saturable absorption  Graphene can be saturated readily under strong excitation over the visible to near-infrared region, due to the universal optical absorption and zero band gap.  Due to this special property, graphene has wide application in ultrafast photonics.photonics

Integrated circuits  Graphene has the ideal properties to be an excellent component of integrated circuits.integrated circuits  Graphene has a high carrier mobility, as well as low noise, allowing it to be used as the channel in a FET.carrier mobility Solar cells  It may eventually be possible to run printing presses laying extensive areas covered with inexpensive solar cells, much like newspaper presses print newspapers (roll-to-roll).roll-to-roll

Single molecule gas detection  Graphene makes an excellent sensor due to its 2D structure.  Molecule detection is indirect: as a gas molecule adsorbs to the surface of graphene, the location of absorption experiences a local change in electrical resistance.electrical resistance  While this effect occurs in other materials, graphene is superior due to its high electrical conductivity (even when few carriers are present) and low noise which makes this change in resistance detectable.

Graphene transistors  Graphene’s conducting ability has spurred a great deal of interest.

 Due to its high electronic quality, graphene has also attracted the interest of technologists who see it as a way of constructing ballistic transistors.ballistic transistors  In order for computer chips to become faster and more energy efficient,they have to be smaller. Silicon hits a size boundary where the material ceases to function, the limit for graphene is even lower, so graphene components could be packed on a chip more tightly than today.

 One of the major problem lies in the production of high quality graphene having sufficient reproducibility.  Graphene lacks the ability to work as a switch.  Unfortunately, graphene has no band gap and correspondingly resistivity changes are small. Therefore, a graphene transistor by its very nature is plagued by a low on/off ratio. However one way around this limitation, is to carve graphene into narrow ribbons.

 The remarkable stability and electrical conductivity of graphene even at nanometer scales could enable the manufacture of individual transistors substantially less than 10 nanometers across and perhaps even as small as a single benzene ring.  In the long run, one can envision entire integrated circuits carved out of a single graphene sheet.

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