Graphene : the futuristic element.....

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

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)

CERTIFICATE

This 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


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..................................................................................21
8. FUTURE ASPECTS..........................................................................22
9. CONCLUSION...................................................................................23
10. BIBLIOGRAPHY.............................................................................24



Abstract
Materials are the basis of almost all new discoveries in science. The development of
new materials can lead to the uncovering entire new fields of study, as well as new solutions
to problems that may have been thought to be unsolvable. One such material is graphene, a
deceptively simple arrangement of carbon atoms. This new material has leapt to the forefront
of material science and has numerous possible applications. It also allows for the observation
of electrons in an almost zero resistance environment. Graphene may not yet be commercially
viable 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 one
atom thick and less than fifty atoms (a few nanometres) wide, the tiny transistors made from
graphene pave the way for a new breed of computer chips smaller and faster than those based
on silicon.



2. INTRODUCTION
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 now it seems that silicon is approaching its limits. Most of the
engineers and scientists think that it will eventually become too complex and expensive to
reduce the size of silicon chips. Also, the speeds of silicon chips have stuck in the gigahertz
range. So as the electronics world is looking for new candidate materials, Graphene seems to
offers an exceptional choice. Graphene is a form of carbon. As a material it is completely new
not only the thinnest ever but also the strongest. As a conductor of electricity it performs as
well as copper. As a conductor of heat it outperforms all other known materials. It is almost
completely transparent, yet so dense that not even helium, the smallest gas atom, can pass
through it. Graphene has rapidly changed its status from being an unexpected and sometimes
unwelcome newcomer to a rising star and to a reigning champion. Research on graphene has
electronic properties is now matured but is unlikely to start fading any time soon, especially
because of the virtually unexplored opportunity to control quantum transport by strain
engineering and various structural modifications. Even after that, graphene will continue to
stand 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 may
well sustain, if not expand, the graphene boom.

2.1 Carbon vs. Silicon:
We currently live in the age of silicon nanotechnology. Silicon based transistors
drive the modern computing revolution. The size of transistors has consistently been
decreasing allowing more transistors to be packed onto a single chip thereby increasing
computer power. This rate approximately follows Moore’s law which states that the number
of transistors on a chip is doubling approximately once every 2 years. The economic reason
for such a phenomenal rate is the $1 trillion computer market is driven by a worldwide
demand for faster and more affordable computers.
The physical reason behind the growth rate is the ability of engineers and scientists
to fashion silicon into smaller and more efficient computer circuitry. The most recent Intel
processor has a transistor with a channel length of 45 nm a true nanotechnology. More
recently this ability to control silicon fabrication has extended into the mechanical realm



where interest in silicon as a mechanical material has driven MEMS technology. Silicon
MEMS are finding applications in a wide array of products. Silicon fabrication processes and
equipment are readily available due to the microelectronics boom making silicon a natural
choice for MEMS.
But is silicon the best choice? A potential alternative to silicon is carbon which forms several
distinct 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 4
valence electrons. However, unlike silicon, carbon’s 4 valence electrons have very similar
energies, so their wave functions mix easily facilitating hybridization. In carbon, these
valence electrons give rise to 2s, 2px, 2py, and 2pz orbitals while the 2 inner shell electrons
belong to a spherically symmetric1s orbital that is tightly bound and has an energy far from
the Fermi energy of carbon. For this reason, only the electrons in the 2s and 2p orbitals
contribute to the solid-state properties of graphite. This unique ability to hybridize sets carbon
apart from other elements and allows carbon to form 0D,1D, 2D, and 3D structures.
2.2.1 Diamond
The three dimensional form of carbon is diamond. It is sp3 bonded forming 4 covalent bonds
with the neighboring carbon atoms into a face-centered cubic atomic structure. Because the
carbon-carbon covalent bond is one of the strongest in nature, diamond has a remarkably high
Young’s modulus and high thermal conductivity. Un-doped diamond has no free electrons
and is a wide band gap (~5.5 eV) insulator. The exceptional physical properties and clever
advertising such as Diamonds are forever contribute to its appeal as a sought after gem. When



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 defective
crystals are used as reinforcement in tool bits which utilize its superior hardness for cutting
applications. The high thermal conductivity of diamond makes it a
potentially useful material for microelectronics where heat dissipation is currently a major
problem. However, diamond’s scarcity makes this unappealing. To this end, scientists and
engineers are trying to grow large diamond wafers. One method to do so is chemical vapor
deposition (CVD) where solid carbon is deposited from carbon containing gases such as
methane or ethylene. By controlling the growth conditions, it is possible to produce defect
free diamonds of limited size. Currently research is ongoing to scale the technology up to
wafer size diamond growth. It is only with such large scale growth that diamond will make
any 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 which
consist of the 0-dimensional C-60 molecule and its 1-dimensional derivative, carbon
nanotubes. A single walled carbon nano-tube is a single layer of graphite, referred to as
graphene, rolled into a cylindrical tube with a 1 nm diameter. Carbon nanotubes can be
metals or semiconductors and have mechanical properties similar to diamond. They attracted



Figure2: A Nanotube Schematic

Figure3: C-60 fullurenes

a lot of attention from the research community and dominated the scientific headlines during
the1990s and early 2000. This interest in nanotubes was partly responsible for the resurgent
interest in graphene as a potentially important and interesting material for electrical and
mechanical applications.

2.2.3 Graphene and Graphite:
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 vander Waals forces. The weak interaction
between the sheets allows them to slide relatively easily across one another. This gives
pencils their writing ability and graphite its lubricating properties, however the nature of this
interaction between layers is not entirely understood. A single 2-D sheet of graphene is a
hexagonal structure with each atom forming 3 bonds with each of its nearest neighbors. These
are known as the sigma bonds oriented towards these neighboring atoms and formed from 3
of the valence electrons. These covalent carbon-carbon bonds are nearly equivalent to the
bonds holding diamond together giving graphene similar mechanical and thermal properties



as diamond. The fourth valence electron does not participate in covalent bonding. It is in the
2pz 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 the
peculiar band structure of graphene, a zero band gap semiconductor with 2 linearly dispersing
bands that touch at the corners of the first Brillion zone. Bulk graphite has been studied for
decades but until recently there were no experiments on graphene. This was due to the
difficulty in separating and isolating single layers of graphene for study.

3. GRAPHENE
3.1 Introduction
Graphene is the name given to a flat monolayer of carbon atoms tightly packed into a two
dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of
all other dimensionalities. It can be wrapped up into 0D fullerenes, rolled into1D nanotubes
or stacked into 3D graphite. Theoretically, graphene (or “2D graphite”) has been studied for
sixty 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-matter
analogue of (2+1)-dimensional quantum electrodynamics, which propelled graphene into a
thriving theoretical toy model. On the other hand, although known as an integral part of 3D
materials, 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 curved
structures such as soot, fullerenes and nanotubes. Suddenly, the vintage model turned into
reality, when free-standing graphene was unexpectedly found three years ago and especially



when the follow-up experiments confirmed that its charge carriers were indeed mass-less
Dirac fermions. So, the graphene “gold rush” has begun.

Figure 4: Structure of Graphites

3.2 2-D Crystals
Before 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 a
thin film of a 3D material. But how many layers are needed before the structure is regarded as
3D? For the case of graphene, the situation has recently become reasonably clear. It was
shown that the electronic structure rapidly evolves with the number of layers, approaching the
3D limit of graphite at10 layers. Moreover, only graphene and, to a good approximation, its
bi-layer has simple electronic spectra: they are both zero-gap semiconductors (they can also
be referred to as zero-overlap semimetals) with one type of electron and one type of hole. For
three or more layers, the spectra become increasingly complicated: Several charge carriers
appear, 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 2D
crystals (“graphenes”).

3.3Materials That Should Not Exist
More than 70 years ago, Landau and Peierls argued that strictly 2D crystals were
thermodynamically unstable and could not exist. Their theory pointed out that a divergent
contribution of thermal fluctuations in low-dimensional crystal lattices should lead to such



displacements of atoms that they become comparable to inter atomic distances at any finite
temperature. For this reason, atomic mono layers have so far been known only as an integral
part of larger 3D structures, usually grown epitaxially on top of mono crystals with matching
crystal 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 other
free-standing 2D atomic crystals (for example, single-layer boron nitride and half-layer,
BSCCO)
3.4 Discovery Of Graphene
Graphene 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 viewed
them in the right way: first nanotubes and then hollow balls of carbon, fullerenes. Trapped
inside graphite, graphene was waiting to be released. No-one really thought that it was
possible. That pessimistic assumption was put to rest in 2004. A. K. GEIM, in collaboration
with then postdoctoral associate K. S. NOVOSELOV and his co-workers at the University of
Manchester in England, was studying a variety of approaches to making even thinner samples
of graphite. At that time, most laboratories began such attempts with soot, but Geim and his
colleagues serendipitously started with bits of debris left over after splitting graphite by brute
force. 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. Once the
investigators had many thin fragments, they meticulously examined the pieces- and were
astonished to find that some were only one atom thick. Even more unexpectedly, the newly
identified bits of graphene turned out to have high crystal quality and to be chemically stable
even at room temperature. The experimental discovery of graphene led to a deluge of
international research interest. Not only is it the thinnest of all possible materials, it is also
extremely strong and stiff. Moreover, in its pure form it conducts electrons faster at room
temperature than any other substance. Engineers at laboratories worldwide are currently
scrutinizing the stuff to determine whether it can be fabricated into products such as
supertough composites, smart displays, ultrafast transistors and quantum-dot computers.
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.
These characteristics are crucial as electronic devices become smaller and smaller, presenting



engineers with a fundamental problem of keeping the devices cool enough to operate
efficiently.

Figure 6: Folded sheets of graphene on a silicon plate. The image was made with a
scanning electron microscope, magnified about 5000 times.

4. GRAPHENE FABRICATION
The most common method of graphene fabrication is exfoliation which finds its roots
with a technique that has been around for centuries writing with a graphite pencil. By writing
with a pencil you create many graphene sheets spread over your paper. Unfortunately this
method 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 to
trying to find a needle in a haystack.

Following are some methods of extraction of graphene:



4.1 Mechanical Exfoliation Of Graphite:
A single plane of carbon atoms, graphene can be isolated using an exceedingly
simple method: In 2004, the University of Manchester’s Andre Geim and colleagues used
common, clear cellophane tape to peel off weakly bound layers from bulk graphite. That
process can produce millimeter-sized graphene flakes and is still common, particularly among
researchers 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 dependent
upon the size of the SiC substrate used. The face of the silicon carbide used for graphene
creation, the silicon-terminated or carbon-terminated highly influences the thickness, mobility
and 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 SKKU
University in South Korea²used chemical vapor deposition of methane to grow graphene on
thin nickel films. The graphene was then either patterned lithographically or transferred onto
silicon or plastic. The SKKU team has now adapted that approach to a scalable industrial
manufacturing process that uses copper rather than Ni. In roll-to-roll production, as outlined
in the figure, 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. To increase the
film’s conductivity, multiple layers of graphene were stacked together and chemically doped
in a bath similar to that used for etching. The technique which currently seems to have the
greatest potential for mass production is the direct growth of graphene. There are some other
methods such as Graphite oxide reduction and Pyrolysis of sodium ethoxide which are
quite economical but they lead to poor quality graphene crystals.



Figure 7: CVD process for Graphene Fabrication

5. PROPERTIES OF GRAPHENE
5.1 Atomic structure:



The atomic structure of isolated, single-layer graphene was studied by transmission
electron microscopy (TEM) on sheets of graphene suspended between bars of a metallic grid.
Electron diffraction patterns showed the expected hexagonal lattice of graphene. Suspended
graphene 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-dimensional
crystals, or may be extrinsic, originating from the ubiquitous dirt seen in all TEM images of
graphene.

Figure 8: suspended graphene showing “rippling” of the flat sheet

5.2 Electronic properties:
Most of the experimental research on graphene focuses on the electronic properties. Graphene
differs from most conventional three-dimensional materials.
5.2.1 High Electron Mobility:- Experimental results from transport measurements show that
graphene has a remarkably high electron mobility at room temperature, with reported values
in excess of 15,000 cm2/Vs. Additionally, the symmetry of the experimentally measured
conductance 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 realized
early 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 and
holes .Due to this linear (or “conical") dispersion relation atlow energies, electrons and holes
near these six points, two of which are in equivalent, behave like relativistic particles
described by the Dirac equation forspin1/2 particles. Hence, the electrons and holes are called
Dirac fermions.
5.2.3 Low resistivity and better current capacity & temperature conductivity:-



The resistivity of the graphene sheet can be as low as 0.01cm. This is less than the
resistivity of silver, the lowest resistivity substance known. Graphene nanoribbons exhibit an
impressive breakdown current density that is related to the resistivity. Graphene is being
studied as apotential replacement for copper in on-chip interconnects, the tiny wires that are
used to connect transistors and other devices on integrated circuits. In addition to the high
current carrying capacity, graphene nanoribbons also have excellent thermal conductivity.
5.2.4 Highly modifiable electrical properties:-Despite being a zero-band gap
semiconductor will extremely low resistivity, Graphene can be tweaked to takeon all the three
roles of conductor, semi-conductor and even insulator(as graphene oxide).
5.2.5 High frequency operation:- Graphene is estimated to operate at terahertzfrequencies
i.e. trillions of operations per second.The key advantage ofgraphene technology is that
electrons move at a very high velocity, thusallowing to obtain high speed and high
performance transistors

5.3 Optical properties:
5.3.1 High Opacity:- Graphene's unique electronic properties produce an unexpectedly high

opacity foran atomic monolayer, with a startlingly simple value: it absorbs πα= 2.3% of white

light, where α is the fine-structure constant.

Fig:9 photograph of graphene in transmitted light
5.3.2 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.
This has relevance for the mode locking of fiber lasers, where fullband mode locking has
been achieved by graphene-based saturable absorber. Due to this special property graphene
has wide application in ultrafast photonics.

5.4 Thermal properties:-



The near-room temperature thermal conductivity of graphene was recently measured to
be between (4.840.44) ×103 to (5.300.48) ×103W/mK. These measurements are in excess of
those measured for carbon nanotubes or diamond. The ballistic thermal conductance of
graphene 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 it
occurs naturally, will require some technological development before it is economical enough
to be used in industrial processes.

6. POTENTIAL APPLICATIONS
The possible practical applications for graphene have received much attention. Sofar, most of
them exist only in our fantasies, but many are already being tested, also by Geim and
Novoselov themselves. Graphene’s conducting ability has spurred a great deal of interest.



Graphene transistors are predicted to be substantially faster than those made out of silicon
today. 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 milestone was passed a few years ago when its key component, a graphene
transistor, was presented that was as fast as its silicon counterpart. So far, graphene
computers are nothing but a distant dream, although paper-thin transparent computer
monitors that can be rolled up and carried in a hand bag have already appeared in
commercials for tomorrow’s consumer electronics. Since graphene is practically transparent
(up to nearly98%) while simultaneously being able to conduct electricity, it would be suitable
for the production of transparent touch screens, light panels and maybe even solar cells. Also
plastics could be made into electronic conductors if only1% of graphene were mixed into
them. Likewise by mixing in just a fraction of as per mile of graphene, the heat resistance of
plastics would increase by 30 ÛC while at the same time making them more mechanically
robust. 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 out
of the new composite materials
6.1 Graphene nanoribbons:-
Graphene nanoribbons (GNRs) are essentially single layer s of graphene that are cut in a
particular pattern to give it certain electrical properties. Depending on how the un-bonded
edges are configured, they can either be in a zigzag or armchair configuration. Experimental
results 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 possible
alternative to copper for integrated circuit interconnects.

Fig 10: GNRs with their corresponding atomic force microscopic image
6.2 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). 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 to
creategraphene transistors with an on and off rate of100 gigahertz, far exceeding the rates of
previous attempts, and exceeding the speed of silicon. The 240 nm graphene transistors made
at IBM were made using extant silicon manufacturing equipment, meaning that for the first
time 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 the
channel in a FET. The issue is that single sheets of graphene arehard 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. In
May 2009 a team from Stanford University, University of Florida and Lawrence Livermore
National Laboratory announced that they have created an n-type transistor, which means that
both n and p-type transistors have now been created with graphene. At the same time, the
researchers at the Politecnico di Milano demonstrated the first functional graphene integrated
circuit 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:-
Graphene's high electrical conductivity and high optical transparency make it a
candidate for transparent conducting electrodes, required for such applications as touch
screens, liquid crystal displays, organic photovoltaic cells, and organic light-emitting diodes.



In particular, graphene's mechanical strength and flexibility are advantageous compared to
indium tin oxide, which is brittle, and graphene films may be deposited from solution over
large areas. A power conversion efficiency (PCE) up to1.71% was demonstrated, which is
5.2% 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 highly
transparent grapheme films by chemical vapor deposition three years ago. The USC team has
produced graphene/polymer sheets ranging in sizes up to150 square centimeters that in turn
can be used to create dense arrays of flexible OPV(organic photovoltaic) 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).



6.6 Ultra-capacitors:-
Due to the extremely high surface area to mass ratio of graphene, one potential application is
in the conductive plates of ultra capacitors. It is believed that graphene could be used to
produce ultra capacitors with a greater energy storage density than is currently available.

Fig 12: ultra capacitor having graphene as conductive plate
6.7 Graphene bio-devices:-
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.

6.8 Single molecule gas detection:-
Graphene makes an excellent sensor due to its 2D structure. The fact that its entire volume is
exposed to its surrounding makes it very efficient to detect adsorbed molecules. 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. While this effect occurs in other
materials, grapheme is superior due to its high electrical conductivity (even when few carriers
are present) and low noise which makes this change in resistance detectable.



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 practical
applications one would like to utilize the strong gate dependence of graphene for either
sensing or transistor applications. One of the major problem lies in the production of high
quality graphene having sufficient reproducibility. Also despite being almost similar to
silicon, even a-bit better in terms of most of the characteristics graphene lacks the ability
work 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.However
one way around this limitation, is to carve graphene into narrow ribbons. By shrinking the
ribbon the momentum of charge carriers in the transverse direction becomes quantized which
results 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 proportional
to its diameter. The opening of a band gap in graphene ribbons has recently been observed in
wide ribbon devices lithographically patterned from large graphene flakes and in narrow
chemically synthesized graphene ribbons.



8. FUTURE ASPECTS

The free-state existence of graphene has paved in ways for a large variety of
applications in the field of electronics, material sciences, photonics and many other fields.
One engineering direction deserves special mention: graphene-based electronics. It has been
emphasized that the charge carriers in graphene move at high speed and lose relatively little
energy to scattering, or colliding, with atoms in its crystal lattice. That property should make
it possible to build so-called ballistic transistors, ultrahigh-frequency devices that would
respond much more quickly than existing transistors do. Even more tantalizing is the
possibility that graphene could help the microelectronics industry prolong the life of Moore’s
law. Gordon Moore, a pioneer of the electronics industry, pointed out some 40 years ago that
the number of transistors that can be squeezed onto a given area doubles roughly every18
months. The inevitable end of that continuing miniaturization has been prematurely
announced many times. The remarkable stability and electrical conductivity of graphene even
at nanometer scales could enable the manufacture of individual transistors substantially less
than10 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 6
years of the first reported existence of graphene, a remarkable progress has been made. But
still a lot more work is to be done to put the above theories into practical being.



9. CONCLUSION

Finally we conclude that This new material has leapt to the forefront of material
science and has numerous possible applications. It also allows for the observation of
electrons in an almost zero resistance environment. Graphene may not yet be commercially
viable 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 one
atom thick and less than fifty atoms (a few nanometres) wide, the tiny transistors made from
graphene pave the way for a new breed of computer chips smaller and faster than those based
on silicon.
And if we use the graphene in the electronics and its different area then it is very helpful
for reduce the size of electronics equipment and its weight also. Main advantage it is form of
carbon then it is cheaper than the other metals.



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,
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 Flat Carbon-Faster Than Silicon for Electronics.SCIENTIFIC

AMERICAN,April-2008.
 www.google.co.in

 www.scribd.com


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