Graphene : the futuristic element.....

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Graphene : the futuristic element.....

  1. 1. A Technical seminar Report on GRAPHENE: THE FUTURISTIC ELEMENT…. TECHNICAL SEMINAR REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF BACHELOR OF TECHNOLOGY IN Electronics and Communication Engineering SUBMITTED BY NAME ROLL NO MD NAZRE IMAM 07J61A0429 MEDAK COLLEGE OF ENGINEERING & TECHNOLOGY(Affiliated toJawaharlal Nehru Technological University,Hyderabad) Kondapak V&M, Siddipet (div), Medak (dist) (Andhra Pradesh) 2011
  2. 2. GRAPHENE: THE FUTURISTIC ELEMENT……… DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGG. MEDAK COLLEGE OF ENGINEERING & TECHNOLOGY (Affiliated to JNTU, Hyderabad) KONDAPAK (VI & M), SIDDIPET (DIV), MEDAK (DIST) – 502372, (AP) CERTIFICATEThis is to certify that the Technical Seminar report submitted “Graphene: The futuristic Element….” was successfully completed by NAME ROLL NO MD NAZRE IMAM 07J61A0429 In the partial fulfillment for the award of Degree of Bachelor of Technology in Electronics and Communication Engineering by the Jawaharlal Nehru Technological University, Hyd, year 2011 SEMINAR SUPERVISOR HEAD OF DEPARTMENT (N.S.KHASIM) (Prof.S.V.S.Ramakrishnam Raju)MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  3. 3. GRAPHENE: THE FUTURISTIC ELEMENT……… CONTENTS 1. ABSTRCT..........................................................................................4 2. INTRODUCTION..........................................................................5-8 2.1Carbon vs. Silicon 2.2 Forms of Carbon 3. GRAPHENE................................................................................9-11 3.1 Introduction 3.2 2-D Crystals 3.3 Materials That Should Not Exist 3.4 Discovery of Graphene 4. GRAPHENE FABRICATION...................................................12-13 4.1 Mechanical exfoliation of graphite 4.2 Epitaxial growth on silicon carbide 4.3 Chemicals Vapor Deposition 5. PROPERTIES OF GRAPHENE................................................14-16 5.1 Atomic structure 5.2 Electronic properties 5.3 Optical Properties 5.4 Thermal Properties 5.5 Mechanical Properties 6. POTENTIAL APPLICATIONS.................................................17-20 6.1 Graphene nanoribbons 6.2 Graphene Transistors 6.3 Integrated Circuits 6.4 Transparent conducting electrodes 6.5 Solar cells 6.6 Ultra-capacitors 6.7 Graphene Bio-devices 6.8 Single molecule gas detection 7. LIMITATIONS..................................................................................218. FUTURE ASPECTS..........................................................................229. CONCLUSION...................................................................................2310. BIBLIOGRAPHY.............................................................................24MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  4. 4. GRAPHENE: THE FUTURISTIC ELEMENT……… Abstract Materials are the basis of almost all new discoveries in science. The development ofnew materials can lead to the uncovering entire new fields of study, as well as new solutionsto problems that may have been thought to be unsolvable. One such material is graphene, adeceptively simple arrangement of carbon atoms. This new material has leapt to the forefrontof material science and has numerous possible applications. It also allows for the observationof electrons in an almost zero resistance environment. Graphene may not yet be commerciallyviable but in the coming years is almost certainly going to be applied in many different fields.This paper is a brief review of graphene and some of its properties and applications. Just oneatom thick and less than fifty atoms (a few nanometres) wide, the tiny transistors made fromgraphene pave the way for a new breed of computer chips smaller and faster than those basedon silicon.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  5. 5. GRAPHENE: THE FUTURISTIC ELEMENT………2. INTRODUCTION Silicon has provided the electronics industry a solid base of favorableproperties capitalizing on which various advancements in electronics has been made (in termsof speed and size). But now it seems that silicon is approaching its limits. Most of theengineers and scientists think that it will eventually become too complex and expensive toreduce the size of silicon chips. Also, the speeds of silicon chips have stuck in the gigahertzrange. So as the electronics world is looking for new candidate materials, Graphene seems tooffers an exceptional choice. Graphene is a form of carbon. As a material it is completely newnot only the thinnest ever but also the strongest. As a conductor of electricity it performs aswell as copper. As a conductor of heat it outperforms all other known materials. It is almostcompletely transparent, yet so dense that not even helium, the smallest gas atom, can passthrough it. Graphene has rapidly changed its status from being an unexpected and sometimesunwelcome newcomer to a rising star and to a reigning champion. Research on graphene haselectronic properties is now matured but is unlikely to start fading any time soon, especiallybecause of the virtually unexplored opportunity to control quantum transport by strainengineering and various structural modifications. Even after that, graphene will continue tostand out in the arsenal of condensed matter physics. Research on graphene has non-electronic properties is just gearing up, and this should bring up new phenomena that maywell sustain, if not expand, the graphene boom.2.1 Carbon vs. Silicon: We currently live in the age of silicon nanotechnology. Silicon based transistorsdrive the modern computing revolution. The size of transistors has consistently beendecreasing allowing more transistors to be packed onto a single chip thereby increasingcomputer power. This rate approximately follows Moore’s law which states that the numberof transistors on a chip is doubling approximately once every 2 years. The economic reasonfor such a phenomenal rate is the $1 trillion computer market is driven by a worldwidedemand for faster and more affordable computers. The physical reason behind the growth rate is the ability of engineers and scientiststo fashion silicon into smaller and more efficient computer circuitry. The most recent Intelprocessor has a transistor with a channel length of 45 nm a true nanotechnology. Morerecently this ability to control silicon fabrication has extended into the mechanical realmMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  6. 6. GRAPHENE: THE FUTURISTIC ELEMENT………where interest in silicon as a mechanical material has driven MEMS technology. SiliconMEMS are finding applications in a wide array of products. Silicon fabrication processes andequipment are readily available due to the microelectronics boom making silicon a naturalchoice for MEMS.But is silicon the best choice? A potential alternative to silicon is carbon which forms severaldistinct structures that have superior electrical, mechanical, and thermal properties to silicon.2.2 Forms of Carbon: Carbon sits directly above silicon on the periodic table and therefore both have 4valence electrons. However, unlike silicon, carbon’s 4 valence electrons have very similarenergies, so their wave functions mix easily facilitating hybridization. In carbon, thesevalence electrons give rise to 2s, 2px, 2py, and 2pz orbitals while the 2 inner shell electronsbelong to a spherically symmetric1s orbital that is tightly bound and has an energy far fromthe Fermi energy of carbon. For this reason, only the electrons in the 2s and 2p orbitalscontribute to the solid-state properties of graphite. This unique ability to hybridize sets carbonapart from other elements and allows carbon to form 0D,1D, 2D, and 3D structures.2.2.1 DiamondThe three dimensional form of carbon is diamond. It is sp3 bonded forming 4 covalent bondswith the neighboring carbon atoms into a face-centered cubic atomic structure. Because thecarbon-carbon covalent bond is one of the strongest in nature, diamond has a remarkably highYoung’s modulus and high thermal conductivity. Un-doped diamond has no free electronsand is a wide band gap (~5.5 eV) insulator. The exceptional physical properties and cleveradvertising such as Diamonds are forever contribute to its appeal as a sought after gem. WhenMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  7. 7. GRAPHENE: THE FUTURISTIC ELEMENT………Figure 1: a)Diamond lattice. b)Hope Diamond. c) Lab grown diamond.Properly cut and polished, it is set to make beautiful pieces of jewelry. The smaller defectivecrystals are used as reinforcement in tool bits which utilize its superior hardness for cuttingapplications. The high thermal conductivity of diamond makes it apotentially useful material for microelectronics where heat dissipation is currently a majorproblem. However, diamond’s scarcity makes this unappealing. To this end, scientists andengineers are trying to grow large diamond wafers. One method to do so is chemical vapordeposition (CVD) where solid carbon is deposited from carbon containing gases such asmethane or ethylene. By controlling the growth conditions, it is possible to produce defectfree diamonds of limited size. Currently research is ongoing to scale the technology up towafer size diamond growth. It is only with such large scale growth that diamond will makeany technological impact beyond its current industrial uses in the machining industry.2.2.2 Fullerenes and nano-tubes:More exotic forms of carbon are the low dimensional forms known as the fullerenes whichconsist of the 0-dimensional C-60 molecule and its 1-dimensional derivative, carbonnanotubes. A single walled carbon nano-tube is a single layer of graphite, referred to asgraphene, rolled into a cylindrical tube with a 1 nm diameter. Carbon nanotubes can bemetals or semiconductors and have mechanical properties similar to diamond. They attractedMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  8. 8. GRAPHENE: THE FUTURISTIC ELEMENT………Figure2: A Nanotube SchematicFigure3: C-60 fullurenesa lot of attention from the research community and dominated the scientific headlines duringthe1990s and early 2000. This interest in nanotubes was partly responsible for the resurgentinterest in graphene as a potentially important and interesting material for electrical andmechanical applications.2.2.3 Graphene and Graphite: Graphene and Graphite are the two dimensional sp2 hybridized forms of carbon foundin pencil lead. Graphite is a layered material formed by stacks 41 of graphene sheetsseparated by 0.3 nm and held together by weak vander Waals forces. The weak interactionbetween the sheets allows them to slide relatively easily across one another. This givespencils their writing ability and graphite its lubricating properties, however the nature of thisinteraction between layers is not entirely understood. A single 2-D sheet of graphene is ahexagonal structure with each atom forming 3 bonds with each of its nearest neighbors. Theseare known as the sigma bonds oriented towards these neighboring atoms and formed from 3of the valence electrons. These covalent carbon-carbon bonds are nearly equivalent to thebonds holding diamond together giving graphene similar mechanical and thermal propertiesMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  9. 9. GRAPHENE: THE FUTURISTIC ELEMENT………as diamond. The fourth valence electron does not participate in covalent bonding. It is in the2pz state oriented perpendicular to the sheet of graphite and forms a conducting sigma band.The remarkable electronic properties of carbon nanotubes are a direct consequence of thepeculiar band structure of graphene, a zero band gap semiconductor with 2 linearly dispersingbands that touch at the corners of the first Brillion zone. Bulk graphite has been studied fordecades but until recently there were no experiments on graphene. This was due to thedifficulty in separating and isolating single layers of graphene for study.3. GRAPHENE3.1 IntroductionGraphene is the name given to a flat monolayer of carbon atoms tightly packed into a twodimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials ofall other dimensionalities. It can be wrapped up into 0D fullerenes, rolled into1D nanotubesor stacked into 3D graphite. Theoretically, graphene (or “2D graphite”) has been studied forsixty years, and is widely used for describing properties of various carbon-based materials.Forty years later, it was realized that graphene also provides an excellent condensed-matteranalogue of (2+1)-dimensional quantum electrodynamics, which propelled graphene into athriving theoretical toy model. On the other hand, although known as an integral part of 3Dmaterials, graphene was presumed not to exist in the free state, being described as an“academic” material and was believed to be unstable with respect to the formation of curvedstructures such as soot, fullerenes and nanotubes. Suddenly, the vintage model turned intoreality, when free-standing graphene was unexpectedly found three years ago and especiallyMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  10. 10. GRAPHENE: THE FUTURISTIC ELEMENT………when the follow-up experiments confirmed that its charge carriers were indeed mass-lessDirac fermions. So, the graphene “gold rush” has begun.Figure 4: Structure of Graphites3.2 2-D CrystalsBefore reviewing the earlier work on graphene, it is useful to define what 2D crystals are.Obviously, a single atomic plane is a 2D crystal, whereas100 layers should be considered as athin film of a 3D material. But how many layers are needed before the structure is regarded as3D? For the case of graphene, the situation has recently become reasonably clear. It wasshown that the electronic structure rapidly evolves with the number of layers, approaching the3D limit of graphite at10 layers. Moreover, only graphene and, to a good approximation, itsbi-layer has simple electronic spectra: they are both zero-gap semiconductors (they can alsobe referred to as zero-overlap semimetals) with one type of electron and one type of hole. Forthree or more layers, the spectra become increasingly complicated: Several charge carriersappear, and the conduction and valence bands start notably overlapping. This allows single-,double- and few- (3 to <10) layer graphene to be distinguished as three different types of 2Dcrystals (“graphenes”).3.3Materials That Should Not Exist More than 70 years ago, Landau and Peierls argued that strictly 2D crystals werethermodynamically unstable and could not exist. Their theory pointed out that a divergentcontribution of thermal fluctuations in low-dimensional crystal lattices should lead to suchMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  11. 11. GRAPHENE: THE FUTURISTIC ELEMENT………displacements of atoms that they become comparable to inter atomic distances at any finitetemperature. For this reason, atomic mono layers have so far been known only as an integralpart of larger 3D structures, usually grown epitaxially on top of mono crystals with matchingcrystal lattices. Without such a 3D base, 2D materials were presumed not to exist, until 2004,when the common wisdom was flaunted by the experimental discovery of graphene and otherfree-standing 2D atomic crystals (for example, single-layer boron nitride and half-layer,BSCCO)3.4 Discovery Of GrapheneGraphene has of course always existed; the crucial thing was to be able to spot it. Similarly,other naturally occurring forms of carbon have appeared before scientists when they viewedthem in the right way: first nanotubes and then hollow balls of carbon, fullerenes. Trappedinside graphite, graphene was waiting to be released. No-one really thought that it waspossible. That pessimistic assumption was put to rest in 2004. A. K. GEIM, in collaborationwith then postdoctoral associate K. S. NOVOSELOV and his co-workers at the University ofManchester in England, was studying a variety of approaches to making even thinner samplesof graphite. At that time, most laboratories began such attempts with soot, but Geim and hiscolleagues serendipitously started with bits of debris left over after splitting graphite by bruteforce. They simply stuck a flake of graphite debris onto plastic adhesive tape, folded thesticky 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. Once theinvestigators had many thin fragments, they meticulously examined the pieces- and wereastonished to find that some were only one atom thick. Even more unexpectedly, the newlyidentified bits of graphene turned out to have high crystal quality and to be chemically stableeven at room temperature. The experimental discovery of graphene led to a deluge ofinternational research interest. Not only is it the thinnest of all possible materials, it is alsoextremely strong and stiff. Moreover, in its pure form it conducts electrons faster at roomtemperature than any other substance. Engineers at laboratories worldwide are currentlyscrutinizing the stuff to determine whether it can be fabricated into products such assupertough composites, smart displays, ultrafast transistors and quantum-dot computers.Since its discovery in 2004, graphene has been viewed as a promising new electronic materialbecause it offers superior electron mobility, mechanical strength and thermal conductivity.These characteristics are crucial as electronic devices become smaller and smaller, presentingMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  12. 12. GRAPHENE: THE FUTURISTIC ELEMENT………engineers with a fundamental problem of keeping the devices cool enough to operateefficiently.Figure 6: Folded sheets of graphene on a silicon plate. The image was made with ascanning electron microscope, magnified about 5000 times. 4. GRAPHENE FABRICATION The most common method of graphene fabrication is exfoliation which finds its rootswith a technique that has been around for centuries writing with a graphite pencil. By writingwith a pencil you create many graphene sheets spread over your paper. Unfortunately thismethod is uncontrollable and you are typically left with many sheets of varying thicknesses.If you want to study a single graphene sheet you need to locate it. The problem amounts totrying to find a needle in a haystack.Following are some methods of extraction of graphene:MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  13. 13. GRAPHENE: THE FUTURISTIC ELEMENT………4.1 Mechanical Exfoliation Of Graphite: A single plane of carbon atoms, graphene can be isolated using an exceedinglysimple method: In 2004, the University of Manchester’s Andre Geim and colleagues usedcommon, clear cellophane tape to peel off weakly bound layers from bulk graphite. Thatprocess can produce millimeter-sized graphene flakes and is still common, particularly amongresearchers exploring graphene’s astonishing electronic properties.4 .2 Epitaxial Growth On Silicon Carbide:Yet another method of obtaining graphene is to heat silicon carbide to high temperatures(>1100°C) to reduce it to graphene. This process produces a sample size that is dependentupon the size of the SiC substrate used. The face of the silicon carbide used for graphenecreation, the silicon-terminated or carbon-terminated highly influences the thickness, mobilityand carrier density of the grapheme.4 .3 Chemical Vapour Deposition (CVD):Recently, two groups²one led by MIT’s Jing Kong, the other by Byung Hee Hong of SKKUUniversity in South Korea²used chemical vapor deposition of methane to grow graphene onthin nickel films. The graphene was then either patterned lithographically or transferred ontosilicon or plastic. The SKKU team has now adapted that approach to a scalable industrialmanufacturing process that uses copper rather than Ni. In roll-to-roll production, as outlinedin the figure, graphene-laden Cu was pressed against a polymer support, bathed in an etchantthat removed the Cu, and then dry-transferred to another flexible polymer. To increase thefilm’s conductivity, multiple layers of graphene were stacked together and chemically dopedin a bath similar to that used for etching. The technique which currently seems to have thegreatest potential for mass production is the direct growth of graphene. There are some othermethods such as Graphite oxide reduction and Pyrolysis of sodium ethoxide which arequite economical but they lead to poor quality graphene crystals.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  14. 14. GRAPHENE: THE FUTURISTIC ELEMENT………Figure 7: CVD process for Graphene Fabrication5. PROPERTIES OF GRAPHENE5.1 Atomic structure:MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  15. 15. GRAPHENE: THE FUTURISTIC ELEMENT……… The atomic structure of isolated, single-layer graphene was studied by transmissionelectron microscopy (TEM) on sheets of graphene suspended between bars of a metallic grid.Electron diffraction patterns showed the expected hexagonal lattice of graphene. Suspendedgraphene also showed "rippling" of the flat sheet, with amplitude of about one nanometer.These ripples may be intrinsic to graphene as a result of the instability of two-dimensionalcrystals, or may be extrinsic, originating from the ubiquitous dirt seen in all TEM images ofgraphene.Figure 8: suspended graphene showing “rippling” of the flat sheet5.2 Electronic properties:Most of the experimental research on graphene focuses on the electronic properties. Graphenediffers from most conventional three-dimensional materials.5.2.1 High Electron Mobility:- Experimental results from transport measurements show thatgraphene has a remarkably high electron mobility at room temperature, with reported valuesin excess of 15,000 cm2/Vs. Additionally, the symmetry of the experimentally measuredconductance indicates that the mobility for holes and electrons should be nearly the same.5.2.2 Intrinsic graphene is a semi-metal or zero-gap semiconductor:- It was realizedearly on that the E-k relation is linear for low energies near the six corners of the two-dimensional hexagonal Brillion zone, leading to zero effective mass for electrons andholes .Due to this linear (or “conical") dispersion relation atlow energies, electrons and holesnear these six points, two of which are in equivalent, behave like relativistic particlesdescribed by the Dirac equation forspin1/2 particles. Hence, the electrons and holes are calledDirac fermions.5.2.3 Low resistivity and better current capacity & temperature conductivity:-MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  16. 16. GRAPHENE: THE FUTURISTIC ELEMENT……… The resistivity of the graphene sheet can be as low as 0.01cm. This is less than theresistivity of silver, the lowest resistivity substance known. Graphene nanoribbons exhibit animpressive breakdown current density that is related to the resistivity. Graphene is beingstudied as apotential replacement for copper in on-chip interconnects, the tiny wires that areused to connect transistors and other devices on integrated circuits. In addition to the highcurrent carrying capacity, graphene nanoribbons also have excellent thermal conductivity.5.2.4 Highly modifiable electrical properties:-Despite being a zero-band gapsemiconductor will extremely low resistivity, Graphene can be tweaked to takeon all the threeroles of conductor, semi-conductor and even insulator(as graphene oxide).5.2.5 High frequency operation:- Graphene is estimated to operate at terahertzfrequenciesi.e. trillions of operations per second.The key advantage ofgraphene technology is thatelectrons move at a very high velocity, thusallowing to obtain high speed and highperformance transistors5.3 Optical properties:5.3.1 High Opacity:- Graphenes unique electronic properties produce an unexpectedly highopacity foran atomic monolayer, with a startlingly simple value: it absorbs πα= 2.3% of whitelight, where α is the fine-structure constant.Fig:9 photograph of graphene in transmitted light5.3.2 Saturable absorption:- Graphene can be saturated readily under strong excitation overthe visible to near-infrared region, due to the universal optical absorption and zero band gap.This has relevance for the mode locking of fiber lasers, where fullband mode locking hasbeen achieved by graphene-based saturable absorber. Due to this special property graphenehas wide application in ultrafast photonics.5.4 Thermal properties:-MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  17. 17. GRAPHENE: THE FUTURISTIC ELEMENT……… The near-room temperature thermal conductivity of graphene was recently measured tobe between (4.840.44) ×103 to (5.300.48) ×103W/mK. These measurements are in excess ofthose measured for carbon nanotubes or diamond. The ballistic thermal conductance ofgraphene is isotropic.5.5 Mechanical properties:- As of 2009, graphene appears to be one of the strongest materials ever tested.Measurements have shown that graphene has a breaking strength 200 times greater than steel,a bulk strength of130GPa. However, the process of separating it from graphite, where itoccurs naturally, will require some technological development before it is economical enoughto be used in industrial processes.6. POTENTIAL APPLICATIONSThe possible practical applications for graphene have received much attention. Sofar, most ofthem exist only in our fantasies, but many are already being tested, also by Geim andNovoselov themselves. Graphene’s conducting ability has spurred a great deal of interest.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  18. 18. GRAPHENE: THE FUTURISTIC ELEMENT………Graphene transistors are predicted to be substantially faster than those made out of silicontoday. In order for computer chips to become faster and more energy efficient they have to besmaller. Silicon hits a size boundary where the material ceases to function. The limit forgraphene is even lower, so graphene components could be packed on a chip more tightly thantoday. One milestone was passed a few years ago when its key component, a graphenetransistor, was presented that was as fast as its silicon counterpart. So far, graphenecomputers are nothing but a distant dream, although paper-thin transparent computermonitors that can be rolled up and carried in a hand bag have already appeared incommercials for tomorrow’s consumer electronics. Since graphene is practically transparent(up to nearly98%) while simultaneously being able to conduct electricity, it would be suitablefor the production of transparent touch screens, light panels and maybe even solar cells. Alsoplastics could be made into electronic conductors if only1% of graphene were mixed intothem. Likewise by mixing in just a fraction of as per mile of graphene, the heat resistance ofplastics would increase by 30 ÛC while at the same time making them more mechanicallyrobust. This resilience could be utilized in new super strong materials, which are also thin,elastic and lightweight. In the future, satellites, airplanes, and cars could be manufactured outof the new composite materials6.1 Graphene nanoribbons:- Graphene nanoribbons (GNRs) are essentially single layer s of graphene that are cut in aparticular pattern to give it certain electrical properties. Depending on how the un-bondededges are configured, they can either be in a zigzag or armchair configuration. Experimentalresults show that the energy gaps do increase with decreasing GNR width. Their 2D structure,high current capacity and thermal conductivity, and low noise also make GNRs a possiblealternative to copper for integrated circuit interconnects.Fig 10: GNRs with their corresponding atomic force microscopic image6.2 Graphene transistors:-Due to its high electronic quality, graphene has also attracted the interest of technologistswho see it as a way of constructing ballistic transistors. Graphene exhibits a pronouncedresponse to perpendicular external electric fields, allowing one to build FETs (field-effectMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  19. 19. GRAPHENE: THE FUTURISTIC ELEMENT………transistors). Facing the fact that current graphene transistors show a very poor on-off ratio,researchers are trying to find ways for improvement.Fig 11: Schematic representation of graphene transistor In February 2010, researchers at IBM reported that they have been able tocreategraphene transistors with an on and off rate of100 gigahertz, far exceeding the rates ofprevious attempts, and exceeding the speed of silicon. The 240 nm graphene transistors madeat IBM were made using extant silicon manufacturing equipment, meaning that for the firsttime graphene transistors are a conceivable though still fanciful²replacement for silicon.6.3 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 thechannel in a FET. The issue is that single sheets of graphene arehard to produce, and evenharder to make on top of an appropriate substrate. Researchers are looking into methods oftransferring single graphene sheets from their source of origin (mechanical exfoliation onSiO2/ Si or thermal graphitization of a SiC surface) onto a target substrate of interest. In2008, the smallest transistor so far, one atom thick,10 atoms wide was made of graphene. InMay 2009 a team from Stanford University, University of Florida and Lawrence LivermoreNational Laboratory announced that they have created an n-type transistor, which means thatboth n and p-type transistors have now been created with graphene. At the same time, theresearchers at the Politecnico di Milano demonstrated the first functional graphene integratedcircuit a complementary inverter consisting of one p- and one n-type graphene transistor.However, this inverter also suffered from a very low voltage gain.6.4 Transparent conducting electrodes:- Graphenes high electrical conductivity and high optical transparency make it acandidate for transparent conducting electrodes, required for such applications as touchscreens, liquid crystal displays, organic photovoltaic cells, and organic light-emitting diodes.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  20. 20. GRAPHENE: THE FUTURISTIC ELEMENT………In particular, graphenes mechanical strength and flexibility are advantageous compared toindium tin oxide, which is brittle, and graphene films may be deposited from solution overlarge areas. A power conversion efficiency (PCE) up to1.71% was demonstrated, which is5.2% of the PCE of a control device based on indium-tin-oxide.6.5 Solar cells:-The USC Viterbi School of Engineering lab reported the large scale production of highlytransparent grapheme films by chemical vapor deposition three years ago. The USC team hasproduced graphene/polymer sheets ranging in sizes up to150 square centimeters that in turncan be used to create dense arrays of flexible OPV(organic photovoltaic) cells. It mayeventually be possible to run printing presses laying extensive areas covered with inexpensivesolar cells, much like newspaper presses print newspapers (roll-to-roll).MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  21. 21. GRAPHENE: THE FUTURISTIC ELEMENT………6.6 Ultra-capacitors:-Due to the extremely high surface area to mass ratio of graphene, one potential application isin the conductive plates of ultra capacitors. It is believed that graphene could be used toproduce ultra capacitors with a greater energy storage density than is currently available.Fig 12: ultra capacitor having graphene as conductive plate6.7 Graphene bio-devices:- Graphenes modifiable chemistry, large surface area, atomic thickness andmolecularly-gatable structure make antibody-functionalized graphene sheets excellentcandidates for mammalian and microbial detection and diagnosis devices.6.8 Single molecule gas detection:-Graphene makes an excellent sensor due to its 2D structure. The fact that its entire volume isexposed to its surrounding makes it very efficient to detect adsorbed molecules. Moleculedetection is indirect: as a gas molecule adsorbs to the surface of graphene, the location ofabsorption experiences a local change in electrical resistance. While this effect occurs in othermaterials, grapheme is superior due to its high electrical conductivity (even when few carriersare present) and low noise which makes this change in resistance detectable.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  22. 22. GRAPHENE: THE FUTURISTIC ELEMENT………7. LIMITATIONS Despite so many fruitful promises in the field of electronics, the graphene based ICs,microprocessor, etc. are unlikely to appear for the next10-15 years. For more practicalapplications one would like to utilize the strong gate dependence of graphene for eithersensing or transistor applications. One of the major problem lies in the production of highquality graphene having sufficient reproducibility. Also despite being almost similar tosilicon, even a-bit better in terms of most of the characteristics graphene lacks the abilitywork as a switch. Without this, a chip will draw electricity continuously, unable to turn off.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.Howeverone way around this limitation, is to carve graphene into narrow ribbons. By shrinking theribbon the momentum of charge carriers in the transverse direction becomes quantized whichresults in the opening of a band gap. This band gap is proportional to the width of the ribbon.This effect is pronounced in carbon nanotubes where a nanotube has a band gap proportionalto its diameter. The opening of a band gap in graphene ribbons has recently been observed inwide ribbon devices lithographically patterned from large graphene flakes and in narrowchemically synthesized graphene ribbons.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  23. 23. GRAPHENE: THE FUTURISTIC ELEMENT………8. FUTURE ASPECTS The free-state existence of graphene has paved in ways for a large variety ofapplications in the field of electronics, material sciences, photonics and many other fields.One engineering direction deserves special mention: graphene-based electronics. It has beenemphasized that the charge carriers in graphene move at high speed and lose relatively littleenergy to scattering, or colliding, with atoms in its crystal lattice. That property should makeit possible to build so-called ballistic transistors, ultrahigh-frequency devices that wouldrespond much more quickly than existing transistors do. Even more tantalizing is thepossibility that graphene could help the microelectronics industry prolong the life of Moore’slaw. Gordon Moore, a pioneer of the electronics industry, pointed out some 40 years ago thatthe number of transistors that can be squeezed onto a given area doubles roughly every18months. The inevitable end of that continuing miniaturization has been prematurelyannounced many times. The remarkable stability and electrical conductivity of graphene evenat nanometer scales could enable the manufacture of individual transistors substantially lessthan10 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. After just 6years of the first reported existence of graphene, a remarkable progress has been made. Butstill a lot more work is to be done to put the above theories into practical being.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  24. 24. GRAPHENE: THE FUTURISTIC ELEMENT………9. CONCLUSION Finally we conclude that This new material has leapt to the forefront of materialscience and has numerous possible applications. It also allows for the observation ofelectrons in an almost zero resistance environment. Graphene may not yet be commerciallyviable but in the coming years is almost certainly going to be applied in many different fields.This paper is a brief review of graphene and some of its properties and applications. Just oneatom thick and less than fifty atoms (a few nanometres) wide, the tiny transistors made fromgraphene pave the way for a new breed of computer chips smaller and faster than those basedon silicon. And if we use the graphene in the electronics and its different area then it is very helpfulfor reduce the size of electronics equipment and its weight also. Main advantage it is form ofcarbon then it is cheaper than the other metals.MEDAK COLLEGE OF ENGG. & TECHNOLOGY 24
  25. 25. GRAPHENE: THE FUTURISTIC ELEMENT………10. BIBLIOGRAPHY  Geim, A. K. and Novoselov, K. S. (2007). "The rise of graphene". Nature Materials6  Mechanical And Electrical Properties Of Graphene Sheets by Joseph Scott Bunch(Cornell University)  Drawing Conclusions from Graphene.Antonio Castro Neto, and Nuno Miguel Peres inP hysics World,Vol.19  Wikipedia (http://en.wikipedia.org/wiki/Graphene Graphene-the perfect atomic lattice. The Nobel Prize In Physics 2010, Jannik Meyer, Science vol. 324,15 May 2009  Flat Carbon-Faster Than Silicon for Electronics.SCIENTIFIC AMERICAN,April-2008.  www.google.co.in  www.scribd.comMEDAK COLLEGE OF ENGG. & TECHNOLOGY 24

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