1. GRAPHENE: AN OVERVEIW OF WONDER
MATERIAL
Submitted by
MALIHA KHATUN ELA
DEPARTMENT OF PHYSICS
UNIVERSITY OF DHAKA
1

2. ABSTRACT
The recent discovery of Graphene has sparked much interest, thus far focused on
the exceptional electronic structure of this particle, in which charge carriers mimic
mass less relativistic particles. However in physical structure Graphene is one-
atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal
lattice, which is the thinnest material and also the strongest material ever measured.
As a conductor of electricity it performs as well as copper, as a conductor of it out
performs all other known materials. It is almost completely transparent, yet so
dense that not even helium, the smallest gas atom, can pass through it. Carbon, the
basis of known life on earth, has surprised the world once again. Graphene has
emerged as an exotic material of the 21st century and has grabbed appreciable
attention due to its exceptional optical, thermal and mechanical properties. The aim
of this review article is to present an overview of the production process, properties
such as electronic, optical, thermal and mechanical along with their potential
applications in various fields. The limitations of present knowledgebase and future
research directions have also been highlighted.
2

3. TABLE OF CONTENTS
1. INTRODUCTION
2. STRUCTURE OF GRAPHENE
3. SYNTHESIS OF GRAPHENE
3.1 DRAWING METHOD
3.2 THERMAL DECOMPOSITION ON SiC
3.3 GRAPHITE OXIDE REDUCTION
3.4 CHEMICAL VAPOUR DEPOSITION
4. PROPERTIES
4.1 ELECTRONIC PROPERTIES
4.2 OPTICAL PROPERTIES
4.3 THERMAL PROPERTIES
4.4 MECHANICAL PROPERTIES
4.5 QUANTUM HALL EFFECT IN GRAPHENE
5. APPLICATIONS
5.1 GRAPHENE TRANSISTOR
5.2 GRAPHENE NANORIBBONS
5.3 TRANSPARENT CONDUCTING ELECTRODES
3

4. 5.4 ULTRACAPACITORS
5.5 OPV SOLAR CELLS
5.6 INTEGRATED CIRCUITS
5.7 GRAPHENE BIODEVICE
5.8 LIMITATIONS
6. FUTURE ASPECTS
7. CONCLUSION
REFERENCES
1. INTRODUCTION:
Materials are the basis of almost all new discoveries in science. The development of new
materials can lead to the uncovering of 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 a number of unique
properties, which makes it interesting for both fundamental studies and future applications. The
Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov "for
groundbreaking experiments regarding the two-dimensional material graphene".
4

5. Fig-1: Graphene is an atomic-scale honeycomb lattice made of carbon atoms.
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. 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.
In the second chapter the basic structures of graphene has been discussed including different
forms of carbon.
5

6. The third chapter presents the synthesis of graphene and various characterization techniques
pertaining to 2D structures.
Many extraordinary properties of graphene such as electrical, mechanical, thermal and optical
are discussed in the forth chapter. These properties have generated tremendous interest among
material researchers.
The recent applications in various fields such as in large scale assembly and transistors, sensors,
transparent electrodes, solar cell, energy storage devices, integrated circuits will be reviewed
with a brief update in the fifth chapter.
In the sixth chapter some of future scopes of graphene has been discussed.
2. STRUCTURE OF GRAPHENE:
Graphene is a single layer of carbon packed in a hexagonal (honeycomb) lattice, with a carbon-
carbon distance of 0.142 nm. Although isolated graphene was reported for the first time only in
2004, the progress it made over these years is enormous, and it rightly has been dubbed "the
wonder material". Graphene sheets stack to form graphite with an interplanar spacing of
0.335 nm, which means that a stack of three million sheets would be only one millimeter thick.
Graphene is the basic structural element of some carbon allotropes including graphite, charcoal,
carbon nanotubes and fullerenes. It can also be considered as an indefinitely large aromatic
molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons.
6

7. Carbon is arguably the most fascinating element in the periodic table. It is the base for DNA and
all life on Earth. Carbon can exist in several different forms. However, 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.
A new form of molecular carbon is the so called fullerenes. The most common, called C60,
contains 60 carbon atoms and looks like a football (soccer ball) made up from 20 hexagons and
12 pentagons which allow the surface to form a sphere. The discovery of fullerenes was awarded
the Nobel Prize in Chemistry in 1996.
7

8. (a) (b) (c)
Fig- 2: Graphene can be (a)wrapped up into 0D C60 fullurences (b)rolled into 1D nanotubes or (c)stacked into
3D graphite.
A related quasi-one-dimensional form of carbon, carbon nanotubes, have been known for several
decades and the single walled nanotubes since 1993.These can be formed from graphene sheets
which are rolled up to form tubes, and their ends are half spherical in the same way as the
fullerenes. The electronic and mechanical properties of metallic single walled nanotubes have
many similarities with graphene.
It was well known that graphite consists of hexagonal carbon sheets that are stacked on top of
each other, but it was believed that a single sheet could not be produced in isolated form such
that electrical measurements could be performed. It, therefore, came as a surprise to the physics
community when in October 2004, Konstantin Novoselov, Andre Geim and their collaborators1
showed that such a single layer could be isolated and transferred to another substrate and that
electrical characterization could be done on a few such layers. In July 2005 they published
electrical measurements on a single layer.8. The single layer of carbon is what we call graphene.
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 2p z state oriented perpendicular to the sheet
of graphite and forms a conducting sigma bond. 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
8

9. graphene. This was due to the difficulty in separating and isolating single layers of graphene for
study.
3. SYNTHESIS OF GRAPHENE:
In 2004, Andre Geim and Knowstantin Novolselov came up with an ingenious method after
years of effort to isolate monolayer graphene flakes. As discovered in more detail later, they
developed the ‘scotch tap’ or ‘drawing method’ which relies on taking a large crystal of graphite
and peeling the crystal repeatedly by using an adhesive tape to generate a large number of thin
crystals. Soon after, a group headed by Philip Kim at Columbia University in the US confirmed
the existence of graphene using the same drawing tecknique, while Walt de Heer and Clair
Berger at Georgia Tech developed an epitaxial growth process that may be suitable for mass-
producing graphene for industrial applications.[22]
In 2008, graphene produced by exfoliation was one of the most expensive materials on Earth,
with a sample that can be placed at the cross-section of a human hair costing more than $1000 as
of April 2008. Since then, exfoliation procedures have been scaled up, and now companies sell
graphene in large quantities. On the other hand, the price of epitaxial graphene on SiC is
dominated by the substrate price, which is approximately $100/cm2 as of 2009. Even cheaper
9

10. graphene has been produced by transfer from nickel by Korean researchers, with wafer sizes up
to 30 inches reported.[22]
In 2011, the institute of Electronic Materials Technology and Department of Physics, Warsaw
University announced a joint development of acquisition technology of large pieces of graphene
with the best quality so far. In April, the same year, Polish scientist with support from Polish
Ministry of Economy began the procedure for granting a potent to their discovery around the
world.[22]
Some methods of production of graphene are discussed in this section, they are: Drawing
method, Thermal decomposition on SiC, Graphite oxide reduction, Chemical vapour deposition.
3.1 Drawing method:
In a time when cutting-edge scientific research is expensive and complex, it seems absurd that a
break though in physics could be achieved with simple adhesive tape. But in 2004, Andre Gein,
Kostya Novoselov and co-workers at the University of Manchester in the UK did just that. By
delicately cleaving a sample of graphite with sticky tape, they produced something that was long
considered impossible; a sheet of crystalline carbon just one atom thick, known as graphene.[3]
The basic ‘recipe’ for making graphene using “scotch tape” technique requires using 300nm of
SiO2-coated silicon wafer as a substrate and cleaning it with a mix of hydrochloric acid and
hydrogen peroxide to remove any residue that is adhering to the wafer. Following this one
patiently peels graphite by sandwiching it between scotch tape repeatedly till the tape is
translucent. Dabbing the tape on the SiO2 wafer and peeling it off leads to deposition of an
assortment of flakes of different thickness on the surface. Examining the surface with a simple
optical microscope allows seeing plenty of graphite debris and locating the very thin flakes of
graphene. Fig-3 shows an optical microscope image of such a deposition. One can clearly see
10

11. that there are several flakes with different colours. The thickest flakes at the bottom of the image
has silver colour, like a typical metal, and is very thick (~500nm), whereas ones that have a dark
blue colour are ~50nm thick and the triangular flake that is barely visible is monolayer
graphene. This method is also referred to as drawing method. The later name appeared because
the dry deposition resembles drawing with a piece of graphite.[2]
Fig-3: An optical microscope image of graphene after peeling using the ‘scotch- tape’ technique. The 300nm
thick SiO2-coated Si wafer has a purple color and the color changes where layers of graphene are
deposited. The triangular flap of mono- layer graphene is clearly seen. Other flakes of graphene show
varying colour.
3.2 Thermal Decomposition On SiC:
The drawing method, which is the simplest way to simply peel it of a piece of graphite, which is
an easy way but it is terribly uncontrolled. The other way is to start with an electronic material
called silicon carbide. In this method, silicon carbide is heated to high temperature (1100°c) to
reduce it to graphene. In this case it could be as little as one and as many as several dozen layers
of graphene.[22]
Producing graphite through ultrahigh vacuum (UHV) annealing of SiC surface has been as
attractive approach especially for semiconductor industry because the products are obtained on
SiC substrate and requires no transfer before processing devices. When SiC substrate is heated
under UHV; silicon atoms sublimate from the substrate. The removal of Si leaves surface carbon
atoms to rearrange into graphene layers. The thickness of graphene layer depends on the
annealing time and temperature. More recently, vapour phase annealing has been used to
produced graphene on SiC. At the expensive of a higher temperature, this method leads to the
11

12. formation of few layer of graphene on SiC with improved thickness homogeneity. Although
producing graphene on SiC substrate is attractive, several hurdles prevent the real application.
For example, control the thickness of graphene layers in the routine production of large area
graphene is very challenging.[8]
Many important graphene properties have been identified in graphene produced by this method.
For example, the electronic band-structure (so-called Dirac cone structure) has been first
visualized in this material. Weak anti-localization is observed in this material and not in
exfoliated graphene produced by the pencil-trace method. Extremely large, temperature-
independent mobilities have been observed in SiC-epitaxial graphene. They approach those in
exfoliated graphene placed on silicon oxide but still much lower than mobilities in suspended
graphene produced by the drawing method. It was recently shown that even without being
transferred graphene on SiC exhibits the properties of massless Dirac fermions such as the
anomalous quantum Hall effect.
The weak van der Waals force that provides the cohesion of multilayer graphene stacks does not
always affect the electronic properties of the individual graphene layers in the stack. That is,
while the electronic properties of certain multilayered epitaxial graphenes are identical to that of
a single graphene layer in other cases the properties are affected as they are for graphene layers
in bulk graphite. This effect is theoretically well understood and is related to the symmetry of the
interlayer interactions.
Epitaxial graphene on SiC can be patterned using standard microelectronics methods. The
possibility of large integrated electronics on SiC-epitaxial graphene was first proposed in 2004,
and a patent for graphene-based electronics was filed provisionally in 2003 and issued in 2006.
Since then, important advances have been made. In 2008, researchers at MIT Lincoln Lab
produced hundreds of transistors on a single chip and in 2009, very high frequency transistors
were produced at the Hughes Research Laboratories on monolayer graphene on SiC. Band gap of
the epitaxial graphene can be tuned by irradiating with laser beams; modified graphene has a lot
of advantages in device application.(Laser Patterning of Epitaxial Graphene for Schottky
Junction Photodetectors).[22]
12

13. 3.3 Graphite Oxide Reduction:
An alternative method for creating single sheets starting from graphite oxide (GO) has been
suggested. Graphite can be oxidized to produced GO and then exfoliated to create stable aqueous
dispersions of individual sheets. After deposition, GO may be reduced to graphene either
chemically or by means of thermal annealing. However, this method has drawbacks. First, many
of the resulting sheets are found to be wrinkled or folded when examined by AFM. Second,
cross-sectional step heights of more than 1nm are often observed for a single sheet, which is
much larger than the theoretical value of 0.34nm found in graphite. This increased thickness may
be attributed to unreduced surface hydroxyl and epoxide groups. Such functionality are
detrimental to the electrical properties of graphene. Third, aqueous dispersions are not ideal for
deposition as the high surface tension of water leads to aggregation during the evaporation
process. Finally, even if GO is perfectly deposited, reduction method tend to neglect the area in
direct contact with the substrate. Attempts have been made to complete the reduction stage in
solution, but sheets tend to aggregate due to the attractive forces between layers and an overall
decrease in hydrophilicity.[4]
Although this simple method has been applied on a large scale to commercially available sulfuric
acid intercalated graphite, it never results in complete exfoliation of graphite to the level of
individual graphene sheets. The extent of thermal expansion is dependent on the type of graphite
used and on the intercalation procedure. With few exception, the graphite nanoplates obtained
via this process typically consist of hundreds of stacked graphene layers and average between 30
and 100nm in thickness. In addition to the thermal expansion route, the delamination of
intercalated graphite can sometimes be achieved by inducing a gas-producing chemical reaction
within its interlayer galleries (chemical expansion). For example, a low-temperature chemical
expansion route to graphite nanoplates and nanoscrolls, based on potassium-intercalated
graphite, has been reported. However, this approach could not be reproduced in laboratory even
with a duplication of the expensive ultra-high-intensity ultrasonic equipment reported therein.
13

14. GO is produced by the oxidative treatment of graphite via one of three principle methods
developed by Brodie, Hummers, and Staudenmeier respectively. It still retains a layered
structure, but is much lighter in colour than graphite due to the loss of electronic conjugation
brought about by the oxidation. According to the most recent studies GO consist of oxidized
graphene sheets having their basal planes decorated mostly with epoxide and hydroxyl groups, in
addition to carboxyl and carboxyl groups located presumably at the edge (Lerf- Klinowski
model). These oxygen functionalities render the graphene oxide layers of GO hydropholic and
water molecules can readily intercalated into the interlayer galleries. GO can therefore be also
through of as a graphite- type intercalated compound with both covalently bound oxygen and
non-covalently bound water between the carbon layers. Indeed, rapid heating of GO results in its
expansion and determination caused by rapid evaporation of the intercalated water and evolution
of gases produced by thermal pyrolysis of the oxygen-containing functional groups. Such themal
treatment has recently been suggested to be capable of producing individual functionalized
graphene sheets.
By nature, GO is electrically insulating and thus cannot be used, without further processing, as a
conductive nanomaterial. In addition, the presence of the oxygen functional groups makes GO
thermally unstable, as it undergoes pyrolysis at elevated temperatures. Notably, it has been
demonstrated that the electrical conductivity of GO can be restored close to the level of graphite
by chemical reduction. Such reaction of GO; however have not studied in great detail. To that
end, the chemical reduction of exfoliation graphene oxide sheets with several reducing agents
and found hydrazine hydrate (H2NNH2.H2O) to be the best one in producing very thin graphene
like sheets, consistant with previous reports. High-resolution scanning electron microscopy
(SEM) also provided with evidence of thin sheets.[5]
3.4 Chemical Vapour Deposition (CVD) :
In this work, a technique is developed for growing few-layer graphene films using chemical
vapour deposition (CVD) and successfully transferring the films to arbitrary substrates without
intense mechanical and chemical treatments, to preserve the high crystalline quality of the
14

15. graphene samples. Therefore, we expect to observe enhanced electrical and mechanical
properties. The growth, etching and transferring processes of the CVD-grown large-scale
graphene films are summarized in Fig-4.
It has been known for over 40 years that CVD of hydrocarbons on reactive nickel or transition-
metal-carbide surfaces can produce thin graphitic layers. However, the large amount of carbon
sources absorbed on nickel foils usually form thick graphite crystals rather than graphene films
(Fig. 5a). To solve this problem, thin layers of nickel of thickness less than 300nm were
deposited on SiO2/Si substrates using an electron-beam evaporator and the samples were then
heated to 1,000 °C inside a quartz tube under an argon atmosphere. After flowing reaction gas
mixtures (CH4 :H2 :Ar=50:65:200 standard cubic centimeters per minute), the samples is rapidly
cooled to room temperature (~25 °C) at the rate of ~10°Cs -1 using flowing argon. It is found that
this fast cooling rate is critical in suppressing formation of multiple layers and for separating
graphene layers efficiently from the substrate in the later process.
A scanning electron microscope (SEM) image of graphene films on a thin nickel substrate
shows clear contrast between areas with different numbers of graphene layers (Fig. 5a).
Transmission electron microscope (TEM) images (Fig. 5b) show that the film mostly consists of
less than a few layers of graphene. After transfer of the film to a silicon substrate with a 300-nm-
thick SiO2 layer, optical and confocal scanning Raman microscope (CRM) images were made of
the same area (Fig. 5c, d). The brightest area in Fig. 5d corresponds to monolayers, and the
darkest area is composed of more than ten layers of graphene. Bilayer structures appear to
predominate in both TEM and Raman images for this particular sample, which was
prepared from 7 min of growth on a 300-nm-thick nickel layer. It is found that the average
number of graphene layers, the domain size and the substrate coverage can be controlled by
changing the nickel thickness and growth time during the growth process (Supplementary Figs 4
and 5), thus providing a way of controlling the growth of graphene for different applications.
15

16. Fig-4: Sunthesis, etching and transfer processes for the large scale and patterned graphene films. (a)
Synthesis of patterned graphene films on thin nickel layers. (b) Etching using FeCl3 (or acids) and transfer of
graphene film using a PDMS stamp. (c) Etching using BOE or hydrogen fluoride (HF) solution and transfer
of graphene films. RT, room temperature (~25°C).
Atomic force microscope (AFM) images often show the ripple structures caused by the
difference between the thermal expansion coefficients of nickel and graphene (Fig. 5c). These
ripples make the graphene films more stable against mechanical stretching, making the films
more expandable. Multilayer graphene samples are preferable in terms of mechanical strength
for supporting large-area film structures, whereas thinner graphene films have higher optical
transparency. It is found that a~300-nm-thick nickel layer on a silicon wafer is the optimal
substrate for the large-scale CVD growth that yields mechanically stable, transparent graphene
films to be transferred and stretched after they are formed, and that thinner nickel layers with a
shorter growth time yield predominantly mono- and bilayer graphene film for microelectronic
device applications (Supplementary Fig. 4c)
16

17. Etching nickel substrate layers and transferring isolated graphene films to other substrates is
important for device applications. Usually, nickel can be etched by strong acid such as HNO3,
which often produces hydrogen bubbles and damages the graphene. So, an aqueous iron (III)
chloride (FeCl3) solution (1 M) was used as an oxidizing etchant to remove the nickel layers. The
net ionic equation of the etching reaction can be represented as follows:
2Fe3+ (aq) + Ni (s) → 2Fe2+ (aq) + Ni2+ (aq)
Fig-5: Various spectroscopy analyses of the large-scale graphene films grown by CVD. (a) SEM images of as-
grown graphene films on thin (300nm) nickel layers and thick ( 1mm) Ni foils (inset). (b) TEM images of
17

18. graphene films of different thicknesses. (c) An optical microscope image of the graphene film transferred to a
300nm thick SiO2 layer. The inset AFM image shows typical rippled structures. (d) A confocal scanning
Raman image corresponding to (c). The number of layers is estimated from the intensities, shapes and
positions of the G-band and 2D band peaks. (e) Raman spectra (532nm laser wavelength) obtained from the
corresponding coloured spots in (c), (d)
This redox process slowly etches the nickel layers effectively within mild pH range without
forming gaseous products or precipitates. In a few minutes, the graphene film separated from the
substrate floats on the surface of the solution and the film is then ready to be transferred to any
kind of substrate. Use of buffered oxide etchant (BOE) or hydrogen fluoride solution removes
silicon dioxide layers, so the patterned graphene and the nickel layer float together on the
solution surface. After transfer to a substrate, further reaction with BOE or hydrogen fluoride
solution completely removes the remaining nickel layers.[14]
18

19. 4. PROPERTIES:
Graphene’s unique properties arise from the collective behavior of electrons. Through the
investigation of pristine graphene many charming properties were discovered in the past few
years including extremely high charge (electrons and holes) mobility with 2.3% absorption of
visible light, thermal conductivity, quantum hall effect etc. This section will focus on the
graphene properties (Electronic Properties, Optical Properties, Thermal Properties, Mechanical
Properties and Quantum Hall Effect in Graphene) which have been found in some of the recent
review articles.
4.1 Electronic Properties:
It is interesting to note that the basic structure that gives rise to graphite, carbon nanotubes and
C60 is graphene with sp2 hybridized molecular orbital; however, it was the last to be isolated.
Figure-6 shows the hexagonal lattice structure of graphene that results from
Fig-6: The lattice structure of graphene has hexagonal symmetry as indicated by the red and blue colored
‘atoms’ taken together .This class of lattice is not a Bravais lattice but can be constructed from two
interpenetrating lattices of equilateral triangles.
19

20. the sp2 hybridization of the molecular orbitals starting from the half-filled outer shell of 2s 1 2p3
(one can think of this as an intermediate state from the outer shell 2s22p2 prior to hybridization).
The p orbital that is not hybridized is the pz orbital and is oriented perpendicular to the plane of
the two-dimensional sheet. The hexagonal lattice is not a Bravais lattice and that implies that one
can describe it only in terms of two interpenetrating lattices of equilateral triangles one atom of
red lattice at the centroid of the blue lattice (see Figure 6). The sp2 bonds between the nearest
neighbour atoms have a strong wavefunction overlap and give rise to a very strong covalent
bond. However, it is the half-filled shell of unhybridized pz that gives the state its unique
electrical property due to the overlap with nearest neighbours to form π orbital.
In order to better understand the electronic properties of any material it is important to
understand the energy (E) and momentum (k) relationship for different k also known as band
structure of the material. The origin of the band structure is simply related to the fact that
unhybridized pz, perpendicular to the plane, overlap with nearest neighbours to form π orbitals
spread out in energy and give rise to a band of states extended over a range of energies. The
result of such a calculation, using the tight-binding approach, involves starting with a linear
combination of wavefunctions at blue and red sites (shown in Figure 6) and finding the energy
momentum relationship taking into account the crystal structures symmetry. Here it is
incorporated by using the fact that a blue lattice point has three next nearest neighbours (in red)
that have an angular spread of 1200.The result of such a calculation is shown in Figure 7(a).
20

21. (a)
(b) (c)
Fig-7: Understanding the bandstructure, essentially the energy and momentum relationship for the electrons
of graphene.
The key things to notice are the fact that there are two bands (lower one in Figure 7(a) is the
valence band and the upper one is the conduction band). The plane through the middle is the
position of the Fermi energy, indicating that the valence band is completely filled and the
conduction band is empty. The reason behind a completely filled valence band and completely
empty conduction band is that the starting set of pz are exactly half-filled resulting in the final
bands of the solid being filled only upto the valence band. The second key feature is that the
conduction and valence bands touch at six points. Figure 7(b) shows the contour plot of the band
gap the difference in energy between the conduction and valence band. We see that at six points
the bandgap is zero and the symmetry of the hexagonal crystal structure, in real space, is
reflected in the symmetry in the momentum (k) space, as expected. The six points are also the
points at which the Fermi energy cuts two bands and so the solid has six Fermi points.
21

22. To understand the electronic properties of any system one needs to only look at the excitations
close to the Fermi energy because far away from EF (energies much larger than kBT with kB
being the Boltzmann constant and T is the temperature), the states are either completely filled, or
are completely empty, and hence unable to participate in `transitions' between states required for
the spatial movement of electrons. Effectively the electronic properties are determined by
excitations, like waves, on the surface of the Fermi Sea; the states deep below or high above the
Fermi energy are mostly irrelevant for electrical transport. To understand graphene's electronic
properties one needs to `zoom-in' in very close to the Fermi energy and check the energy and
momentum relationship of the electrons.
Figure 7(c) shows the `view' of the band structure close to one of the Fermi points and one finds
that the bands look like two upturned cones. This implies that E ∞ k for the excitations close to
the Fermi energy. As a result, the electronic excitations inside graphene behave as if they are
mass less as their energy and momentum are linearly related, unlike electrons in most materials,
where energy and momentum are quadratically related ~ E ∞ k2. This peculiar nature of
electron's energy and momentum relationship makes them analogous to relativistic particles, say
photons, where the energy and momentum are linearly related. However, the electrons in
graphene do not flow anywhere close to the velocity of light (they travel at roughly 106 m/s, i.e.,
about 1/300 the speed of light); they are analogous only because of their linear energy
momentum (E ∞ k) relationship. As a result graphene is a ‘wonderland' for studying very
interesting quantum mechanical phenomena that typically cannot be studied in solid-state
devices, but could only be seen in particle accelerators. This unique E ∞ k relationship implies
that one cannot use Schrődinger equation to describe the quantum mechanics of electrons but
have to use Dirac equation - a more appropriate quantum mechanical description.[2]
4.2 Optical Properties:
Graphene, despite being the thinnest material ever made, is still visible to the naked eye. It can
show remarkable optical properties. For example, it can be optically visualized, despite being
only a single atom thick. Its transmittance (T) can be expressed in terms of the fine-structure
constant. The linear dispersion of the Dirac electrons makes broadband applications possible.
22

23. Saturable absorption is observed as a consequence of Pauli blocking and nonequilibrium carriers
result in hot luminescence. Chemical and physical treatments can also lead to luminescence.
These properties make it an ideal photonic and optoelectronic material.[9]
Linear optical absorption:
For identifying graphene on top of a Si/SiO2 substrate the optical image contrast can be used.
This scales with the number of layers and is the result of interference, with SiO2 acting as a
spacer. The contrast can be maximized by adjusting the spacer thickness or the light wavelength.
The transmittance of a freestanding SLG can be derived by applying the Fresnel equations in the
thin-film limit for a material with a fixed universal optical conductance G0 = e2/(4ħ) ≈ 6.08 × 10−5
Ω −1, to give:
T = (1 + 0.5 πα)-2 ≈ 1 – πα ≈ 97.7%
where α = e2/(4πε0ħc) = G0/(πε0c) ≈ 1/137 is the fine-structure constant.
Graphene only reflects <0.1% of the incident light in the visible region1, rising to ~2% for ten
layers. Thus, we can take the optical absorption of graphene layers to be proportional to the
number of layers, each absorbing A ≈ 1 – T ≈ πα ≈ 2.3% over the visible spectrum . In a few-
layer graphene (FLG) sample, each sheet can be seen as a 2D electron gas, with little
perturbation from the adjacent layers, making it optically equivalent to a superposition of almost
non-interacting SLG. The absorption spectrum of SLG is quite flat from 300 to 2,500 nm with a
peak in the ultraviolet region (~270 nm). In FLG, other absorption features can be seen at lower
energies, associated with interband transitions.[9]
Saturable absorption:
Graphene can be saturated under strong excitation over the visible to near infra-red region, due to
the universal optical absorption and zero band gap. Interband excitation by ultrafast optical
pulses produces a non-equilibrium carrier population in the valence and conduction bands. In
time-resolved experiments, two relaxation timescales are typically seen: a faster one of ~100 fs
that is usually associated with carrier–carrier intraband collisions and phonon emission, and a
23

24. slower one, on a picoseconds timescale, which corresponds to electron interband relaxation and
cooling of hot phonons.[9]
Luminescence:
Another interesting property of grapheme is photo luminescence. It could be made graphene
luminescent by including a suitable band gap, following two routes. One is by cutting it into
nanoribbons and quantum dots, the other is by chemical or physical treatments, to reduce the
connectivity of the π-electron network. Bulk graphene oxide dispersions and solids do show a
broad photo luminescence. Though graphene nanoribbons have been produced with varying band
gaps as yet no photoluminescence. Individual graphene flakes can be made brightly luminescent
by mild oxygen plasma treatment. It is possible to make hybrid structures by etching just the top
layer, while leaving underlying layers intact. This combination of photo luminescent and
conductive layers could be used in sandwich light-emitting diodes. Luminescent graphene based
materials can now be routinely produced that cover the infrared, visible and blue spectral ranges.
[9]
4.3 Thermal properties:
Graphene is a perfect thermal conductor. Carbon allotropes such as graphite, diamond, and
carbon nano tubes have shown higher thermal conductivity due to strong C-C covalent bonds and
phonon scattering. Earlier carbon nanotubes are known to have very high thermal conductivity.
The experimentally determined thermal conductivity with room temperature value for multiwall
carbon nanotube is ≈ 3000W/mK and for single-wall carbon nanotube is ≈ 3500W/mK. Recently
the highest room temperature thermal conductivity ≈ up to 5000W/mK for the single layer
graphene has been reported [3]. Methods of measuring thermal conductivity (k) can be divided
into two groups: steady state and transient. In transient methods, the thermal gradient is recorded
as a function of time, enabling fast measurements of thermal diffusivity (DT) over large T ranges.
. If K determines how well a material conducts heat, DT tells us how quickly a material conducts
heat. The first experimental study of heat conduction in graphene was made possible by
developing an optothermal Raman technique. The heating power ΔP was provided by a laser
24

25. light focused on a suspended graphene layer connected to heat sinks at its ends. Temperature rise
(ΔT) in response to ΔP was determined with a micro-Raman spectrometer. The G peak in
graphene’s Raman spectrum exhibits strong T dependence. The calibration of the spectral
position of the G peak with T was performed by changing the sample temperature while using
very low laser power to avoid local heating. The frequency of the G peak (ωG) as a function of
temperature — calibration curve ωG(T) — allows one to convert a Raman spectrometer into an
'optical thermometer'. The optothermal Raman technique for measuring the K of graphene is a
direct steady-state method. It can be extended to other suspended films, for example, graphene
films, made of materials with pronounced temperature-dependent Raman signatures.[8]
4.4 Mechanical Properties:
Generally, application of external stress on crystalline material can alter inter atomic distances,
resulting in the redistribution, in local electronic charge. This may introduce a band gap in
electronic structure and modify the electron transport property significantly. After carbon
nanotubes , graphene has been reported to have the highest elastic modulus and strength.
Researchers have already determined the intrinsic mechanical properties of the single, bilayer
and multilayer of graphene.
A single defect free graphene layer is predicted to show the highest intrinsic tensile
Strength with stiffness similar to graphite. One method to determine the intrinsic mechanical
properties is to probe the variation of the phonon frequencies upon the application of tensile and
compressive stress. The Raman spectroscopy is one of the techniques which can monitor
phonon’s frequency under uniaxial tensile and hydrostatic stress. It has been observed that the
tensile stress results in the phonon softening due to decreased vibrational frequency mode
whereas compressive stress causes the phonon hardening due to increased vibrational frequency
mode. Thus in graphene, studying the vibration of phonon frequency as a function of strain can
provide useful information on stress transfer to individual bonds (for suspended graphene) and
atomic level interaction of graphene to the underlying substrate (for suspended graphene).
Compressive and tensile strain in graphene layer was estimated using Raman spectroscopy by
monitoring change in the G and 2D peaks with applied stress. Recently, the band gap tuning was
25

26. reported under uniaxial strain. The band gap of 0.25eV was detected under the highest strain
(0.78%) for the single layer graphene. It was also suggested that the uniaxial strain affected the
electronic properties of graphene much more significantly as it breaks the bonds of C-C lattice.
[8]
4.5 Quantum Hall effect in Graphene:
The quantum mechanical version of the Hall Effect is known as Quantum Hall effect (QHE)
which is observed in two dimensional electron systems subjected to low υf temperatures and
strong magnetic fields. There are integer and fractional QHE. Both of these Hall effects have
seen in Graphene, a single layer of carbon atoms in a two dimensional hexagonal lattice, at room
temperature. The carbon atoms bond to one another via covalent bonds leaving one 2p electron
per carbon atom unbonded. The result is that the Fermi surface of graphene is characterized by
six double cones. In the absence of applied fields, the Fermi level is situated at the connection
points of these cones. Since the density of electrons is zero at the Fermi level, the electrical
conductivity of graphene is very low. However, the application of an external electric field can
change the Fermi level causing graphene to behave as a semi-conductor. In this case, near the
Fermi level the dispersion relation for electrons is linear and the electrons behave as though they
have zero effective mass (Dirac fermions). Because graphene exhibits this behavior even at room
temperature, it is observed to exhibit both the integer and fractional quantum Hall effects.
Fig-8: Energy level diagram for graphene showing the Fermi level in the absence of any applied fields.
26

27. The existence of the QHE at such high temperatures in graphene is due to the large energy gaps
characteristic of Dirac fermions. These energies are given by:
En= υf √|2neħB|
Where υf is the Fermi velocity (106m/s) and n is the Landau level quantum number. In a strong
magnetic field (B=45T), the energy level spacing is 2800K.
Graphene has a large concentration of charge carriers which keeps the lowest Landau level
completely populated at high magnetic fields. Therefore, any carriers above the lowest Landau
level will not be able to overcome the energy gap, and the quantum Hall effect is observed. The
quantum Hall effect has been observed for the integer values of the filling factor as well as the
fractional filling factors because graphene exhibits both the integer and fractional quantum Hall
effects, it is ideal for studying QHE, and may be proven useful in the development of quantum
computers.[10]
5. APPLICATIONS:
27

28. For many years it was believed that carbon nanotubes would create a revolution in nano-
electronics because of their microscopic dimension and very low electrical resistance. These
hopes however have not yet come to fruition because of various difficulties. These include
producing nanotubes with well-defined sizes, the high resistance at the connection between
nanotubes and the metal contacts that connect them to circuits and the difficulty of integrating
nanotubes into electronic devices on a mass-production scale.
Walt de Heer argues that with graphene we will be able to avoid all of these problems. Graphene
is useful in so many areas, that it is hard to pick and choose. Physicist like them because they are
a playground for understanding how electrons behave when graphene get confined in two-
dimension. Biologists are interested in using them as a way of probing biological systems.
Graphene can be either metals or semiconductors and their electrical properties can rival or even
exceed the best metals or semiconductors known. Because of this engineers are interested in
using them as building blocks for smaller transistors. Material scientists want to mix graphene
into more traditional substances to create hybrid materials that are much stronger or are
conducting, while still being malleable.[3]
Some major applications of graphene are discussed in this section.
5.1 Graphene Transistor:
Owing to its high carrier mobility and saturation velocity, graphene has attracted enormous
attention in recent years. Graphene – a sheet of carbon just one atom thick- shows great promise
for use in electronic devices because electrons can move through it at extremely high speeds.
This is because, they behave like relativistic particles with no rest mass. This , and other unusual
physical and mechanical properties, means that the wonder material could replace silicon as the
electronic material of choice and might be used to make faster transistors than any that exist
today.
28

29. Fig-9: Graphene transistor.
The field effect transistor (FET) is a key element, where the current flowing through a thin
channel layer is controlled by gate electrodes. FET can be operated faster with a channel layer of
a higher electron mobility material, which is the very point the application of graphene to FET.
In 2004, there are some reports on the characteristics of FET using graphene as a channel layer
material. For the fabrication of graphene- based FET, graphene exfoliation from HOPG is often
used. On the other hand, in 2010, IBM reported on 100 gigahartz operation of a FET based on
graphene by heat treatment of SiC, has been a major topic. The 240nm graphene transistor made
at IBM were made using extant silicon manufacturing equipment, meaning that for the first time
graphene transistors are a conceivable- though still fanciful- replacement for silicon. The
operation speed is already more than twice higher than that of silicon-based FET which uses
silicon as the channel layer with the same gate length. It strongly indicates the high potentiality
of graphene application to FET.
In 2011, the manufacturing technology for IBM’s graphene transistors has been improved and
the new 155 GHz transistor is made with 400nm technology, on par with the commercial
solution available today, which is also a record note in terms of gate length for graphene.[6]
29

30. 5.2 Graphene Nanoribbons:
While many labs are trying to efficiently synthesize large two-dimensional sheets of graphene, a
team of researcher from Sweden and the UK is investigating the synthesis of very thin strips of
graphene just a few atoms wide. In contrast to graphene, these graphene nanoribbons have a
unique electronic structures including a non zero band gap, which makes them promising
candidates for semiconductor application. But, as with graphene sheets, one of the greatest
challenges for now is finding a way to efficiently synthesize these graphene nanoribbons.[15]
Graphene nanoribbons (also called nano-graphene ribbons), often abbreviated GNRs, are thin
strips of graphene or unrolled single-walled carbon nanotubes. Graphene ribbons were originally
introduced as a theoretical model by Mitsutaka Fujita and co-authors to examine the edge and
nanoscale size effect in graphene. Theoretical calculations on the band structure of GNRs have
shown that GNRS exibit metallic properties or semiconductor properties ie, the band gap is
larger than 0, depending on the orientation of the ribbon. Two configurations of GNRs structures
are illustrated in Fig-10 (a) and (b) focusing on the edges of GNRs.
Fig-10: Illustration of Two Types of Edges, (a) Armchair Edge and (b) Zigzag Edge, and (c) Theoretically
Calculated Bandgap of Armchair-Edged Graphene Nanoribbon
30

31. The configuration illustrated in (a) is called the armchair type where the edge has a cyclic
structures of four carbon atoms, ie, two couples of carbon atoms. A GNRs of the armchair type
configuration exhibits semiconductor properties. On the other hand, the configuration in (b) is
called the zigzag type where the edge zigzags. A GNRs of the zigzag type configuration exhibits
zero band gap. However, recent DFT calculations show that armchair nanoribbons are
semiconducting with on energy gap scaling with the inverse of the GNR width. In zigzag
configurations, this gap is inversely proportional to the ribbons width.
A metallic nanoribbon inside an insulating nanotube can be a thin, insulated nanowire. Or
nanoribbons can be used directly inside of single- wall carbon nanotubes (SWNTs) to generate as
light emitting diodes. Semiconducting nanoribbons colud be used for transistor or solar cell
applications. Or a metallic combination could produce a new kind of coxial nanocable for use in
transmitting radio signals.
Their 2D structures, high electrical and thermal conductivity, and low noise also make. GNRs a
possible alternative to copper for integrated circuit interconnects.[6]
5.3 Transparent Conducting Electrodes:
As a critical component of optoelectronic devices, transparent conductive coatings pervade
modern technology. The most widely used standard coating is indium tin oxide (ITO), used in
nearly all flat panel displays and microdisplays. Causing problems for manufacturers though,
indium is expensive and scarce and demand is increasing. Recently, prices have fallen back. But
geologists say the cost of indium may not matter soon, because the earth’s supply of this element
could be gone within just a few years. This has made the search for novel transparent electrode
materials with good stability, high transparency and excellent conductivity a crucial goal for
optoelectronic researchers. Recent word by researchers in Germany exploits ultra-thin
transparent conductive graphene film as window electrodes in solar cells.[16]
These graphene films are fabricated from exfoliated graphite oxide, followed by thermal
reduction. The obtain films exhibit a high conductivity of 550 Scm and a transparency of more
than 70% over 1000-3000nm.
31

32. Graphene’s high electrical conductivity and high optical transparency make it a candidate for
transparent conducting electrodes ,required for such application as touch screen, liquid crystal
displays, organic photovoltaic cells and organic light emitting diodes. In particular, graphene’s
mechanical strength and flexibility are adventurous compared to indium tin oxide, which is
brittle and graphene films may be deposited from solution over large areas. Large-area,
continuous, transparent and highly conducting few-layered graphene films were produced by
chemical vapor deposition and used as anodes for application in photovoltaic devices. The
electronic and optical performance of devices based on graphene are shown to be similar to
devices made with indium-tin-oxide.[17]
5.4 Ultracapacitors:
2010, the ultracapacitors- the battery’s quicker cousin- just got faster and may one day help
make portable electronics a lot smaller and lighter, according to a group of researchers.
Ultracapacitors don’t store quite as much charge as batteries, but can charge and discharge in
seconds rather than the minutes batteries take. This combinations of speed and energy supply
makes them attractive for things like regenerative braking, where the ultracapacitors would have
only seconds to recharge as a car comes to a stop. But sometimes a second is still too long, using
nanometer-scale fins of graphene, the researchers built an ultracapacitor that can charge in less
than a millisecond.[21]
Recently , graphene has become a hot topic in ‘macroscopic’ applications as well, notably in the
design and manufacture of ultracapacitors , which have recently become highly valued as power
storage system in electrical light-rail vehicles, diesel-electric battery drive systems and forklift
trucks.[18]
32

33. Fig-11: ultra capacitor having graphene as conductive plate
The possibilities opened by graphene go beyond improvements in the energy density of
ultracapacitors, as the team of John Miller, president of JME, an electrochemical capacitor
company based in Shaker Heights, Ohio and Ron Outlaw of the college of William and Mary,
Williamburg, VA, have recently shown. By using electrodes made from vertically oriented
graphene nano-sheets, the team of Miller was able to improve drastically on the RC time
constant of extant ultracapacitors, opening up new possibilities for the miniaturization of AC
filtering and rectifier circuits. The graphene nano-sheets reamble ~600 nm tall “potato chips”
standing on edge in rows. The novel ultracapacitors charge and recharge in 200 microseconds,
compared to ~1 second for nano-pore –based designs. These exciting developments indicate that
graphene-based ultracapacitors are paired to take a farther step in the graphene revolution, which
has been ongoing since ground breaking work of Geim and Novoselov in 2004.[18]
5.5 OPV Solar Cell :
The most unique aspect of the OPV (organic photovoltaic cell) devise is the transparent
conductive electrode. This allows the light to react with the active materials inside and create the
electricity. Now graphene sheet are used to create thick arrays of flexible OPV cells and they are
used to convert solar radiation into electricity providing cheap solar power. Now research team
under the guidance of Chongwu Zhoa, Professor of Electrical Engineering, USC Viterbi School
33

34. 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 OPV’s gives these cells additional advantage by being operational after
repeated bending unlike the Iudium-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.[8]
5.6 Integrated Circuits :
Graphene has the ideal properties to be an excellent component of integrated circuits. Graphene
has high carrier mobility, as well as noise, allowing it to be used as the channel in a FET. 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 gaphene sheets
from their source of origin (mechanical exfoliation on SiO2/Si or thermal graphitization of a Si
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.[1]
34

35. 5.7 Graphene Biodevices :
These devices are based upon graphene’s large surface area and the fact that molecules that are
sensetive to particular diseases can attach to the carbon atoms in graphene. For example,
researchers have found that graphene, strands of DNA and fluorescent molecules can be
combined to diagnose diseases. A sensor is formed by attaching fluorescent molecules to single
strand DNA and then attaching the DNA to graphene. When an identical single strand DNA
combines with the strand on the graphene a double strand DNA it formed that floats off from the
graphene, increasing the fluorescent level. This method results in a sensor that can detect the
same DNA for a particular disease in a sample.[23]
5.8 Limitations:
Despite so many fruitful promises in the field of electronics, the graphene based IC’s;
microprocessor, etc are unlikely to appear for the next 10-15 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 problems lies in the production of high quality
graphene having sufficient reproducibility. Also despite being almost similar to silicon-even a bit
better in times of most of the characteristics graphene lacks the ability work as switch. Without
this, a chip will draw electricity continuously, unable to turn off. Unfortunately, grephene has no
bad gap and correspondingly resistivity changes are small. Therefore, a plagued by a low on/off
ratio. However one way around this limitation, is to carve graphene into narrow ribbons. By
shrinking the ribbons 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 fond 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.[1]
35

36. 6. FUTURE ASPECTS:
Despite the reigning optimism about graphene-based electronics, “graphenium” microprocessors
are unlikely to appear for the next 20 years. In the meantime, one can certainly hope
for many other graphene-based applications to come of age. In this respect, clear parallels with
nanotubes allow a highly educated guess of what to expect soon.
The most immediate application for graphene is probably its use in composite
materials. Indeed, it has been demonstrated that a graphene powder of uncoagulated
micron-size crystallites can be produced in a way scaleable to mass production. This
allows conductive plastics at less than 1 volume percent filling, which in combination with
low production costs makes graphene-based composite materials attractive for a
variety of uses. However, it seems doubtful that such composites can match the
mechanical strength of their nanotube counterparts because of much stronger entanglement
in the latter case.
Another enticing possibility is the use of graphene powder in electric batteries that are already
one of the main markets for graphite. An ultimately large surface-to-volume ratio and high
conductivity provided by graphene powder can lead to improvements in batteries’ efficiency,
taking over from carbon nanofibres used in modern batteries. Carbon nanotubes have also been
considered for this application but graphene powder has an important advantage of being cheap
to produce.
One of the most promising applications for nanotubes is field emitters and,
although there have been no reports yet about such use of graphene, thin graphite
flakes were used in plasma displays (commercial prototypes) long before graphene
was isolated, and many patents were filed on this subject. It is likely that
graphene powder can offer even more superior emitting properties.
Carbon nanotubes were reported to be an excellent material for solid-state gas sensors but
graphene offers clear advantages in this particular direction. Spin-valve and
superconducting field-effect transistors are also obvious research targets, and recent reports
describing a hysteretic magnetoresistance and substantial bipolar supercurrents prove
36

37. graphene’s major potential for these applications. An extremely weak spin-orbit coupling and the
absence of hyperfine interaction in 12C-graphene make it an excellent if not ideal material for
making spin qubits. This guarantees graphene-based quantum computation to become an active
research area. Finally, we cannot omit mentioning hydrogen storage, which has been an active
but controversial subject for nanotubes. It has already been suggested that graphene is capable of
absorbing an ultimately large amount of hydrogen and experimental efforts in this direction are
duly expected.
37

38. 7. CONCLUSION:
The field of graphene-related research has grown at a spectacular pace since single-layer flakes
were first isolated in 2004. Graphene that began its journey as an exciting material for
fundamental physics has now become the focus of efforts by scientists in a wide range of
disciplines. Organic and material chemists are busily working on new route to produce high
quality single layers, while engineers are designing novel devices to explore graphene’s
extraordinary properties. This review paper briefly discusses the significant structural attributes
of graphene in association with other closely related carbon forms. Starting from its discovery
the evolution in synthesizing process has been reviewed. Its unique characteristic properties
those made it an extraordinary material has been highlighted. A wide range of utility in different
sectors has been mentioned as well as giving idea of its future scopes and prospects. Reviewing
the characteristic properties and utilitarian values of graphene it is very much clear that graphene
is indeed a wonder material of present time and it holds great promises to become one of the
primary materials of the times to come.
38

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41. 41