AMITY SCHOOL OF

ENGINEERING & TECHNOLOGY

TERM PAPER ABSTRACT ON

GRAPHENE

SUBMITTED TO- SUBMITTED BY- Mrs SHALLY GOYAL AMAN GUPTA

Asst. Professor B.TECH ECE 3 SEM

Dept. Electronics & Communication (2012-2016)

Graphene - What It Is?

In simple terms, graphene is a thin layer of pure carbon; it is a single, tightly packed layer of

carbon atoms that are bonded together in a hexagonal honeycomb lattice. In more complex

terms, it is an allotrope of carbon in the structure of a plane of sp2 bonded atoms with a

molecule bond length of 0.142 nanometres. Layers of graphene stacked on top of each other

form graphite, with an interplanar spacing of 0.335 nanometres.

Figure 1 Figure 2

It is the thinnest compound known to man at one atom thick, the lightest material known

(with 1 square meter coming in at around 0.77 milligrams), the strongest compound

discovered (between 100-300 times stronger than steel and with a tensile stiffness of

150,000,000 psi), the best conductor of heat at room temperature (at (4.84±0.44) × 103 to

(5.30±0.48) × 103 W·m−1·K−1) and also the best conductor of electricity known (studies

have shown electron mobility at values of more than 15,000 cm2·V−1·s−1). Other notable

properties of graphene are its unique levels of light absorption at πα ≈ 2.3% of white light,

and its potential suitability for use in spin transport.

The combination of familiarity, extraordinary properties and surprising ease of isolation

enabled an explosion in graphene research. Andre Geim and Konstantin Novoselov at

the University of Manchester won the Nobel Prize in Physics in 2010 "for ground breaking

experiments regarding the two-dimensional material graphene.

Figure 3

Carbon is the chemical basis for all known life on earth, so therefore graphene could well be

an ecologically friendly, sustainable solution for an almost limitless number of

applications. Since the discovery of graphene, advancements within different scientific

disciplines have exploded, with huge gains being made particularly in electronics and

biotechnology already.

Also, it was previously impossible to grow graphene layers on a large scale using crystalline

epitaxy on anything other than a metallic substrate. This severely limited its use in

electronics as it was difficult, at that time, to separate graphene layers from its metallic

substrate without damaging the graphene.

However, studies in 2012 found that by analysing graphene’s interfacial adhesive energy, it

is possible to effectually separate graphene from the metallic board on which it is grown,

whilst also being able to reuse the board for future applications theoretically an infinite

number of times, therefore reducing the toxic waste previously created by this process.

Furthermore, the quality of the graphene that was separated by using this method was

sufficiently high enough to create molecular electronic devices successfully.

While this research is very highly regarded, the quality of the graphene produced will still be

the limiting factor in technological applications. Once graphene can be produced on very thin

pieces of metal or other arbitrary surfaces (of tens of nanometres thick) then we will start to

see graphene become more widely utilized as production techniques become more simplified

and cost-effective.

Figure 4 Figure 5

Being able to create super capacitors out of graphene will possibly is the largest step in

electronic engineering in a very long time. While the development of electronic components

has been progressing at a very high rate over the last 20 years, power storage solutions such

as batteries and capacitors have been the primary limiting factor due to size, power capacity

and efficiency.

In initial tests carried out, laser-scribed graphene (LSG) supercapacitors (with graphene

being the most electronically conductive material known, at 1738 Siemens per meter

(compared to 100 SI/m for activated carbon)), were shown to offer power density

comparable to that of high-power lithium-ion batteries that are in use today. Not only that,

but also LSG supercapacitors are highly flexible, light, quick to charge, thin and as

previously mentioned, comparably very inexpensive to produce.

Graphene is also being used to boost not only the capacity and charge rate of batteries but

also the longevity. Currently, while such materials as silicone are able to store large amounts

of energy, that potential amount diminishes drastically on every charge or recharge. With

graphene tin oxide being used as an anode in lithium ion batteries for example, batteries can

be made to last much longer between charges (potential capacity has increased by a factor of

10), and with almost no reduction in storage capacity between charges, effectively making

technology such as electronically powered vehicles a much more viable transport solution in

the future.

This means that batteries can be developed to last much longer and at higher capacities than

previously realised. Also, it means that electronic devices may be able to be charged within

seconds, rather than minute or hours and have hugely improved longevity.

Figure 6

Consumers can already purchase graphene-enhanced products to use at home. One company

already produces and offers on the market conductive ink (first developed by researchers at

the University of Cambridge in 2011). This is made by effectively mixing tiny graphene

flakes with ink, enabling you to print electrodes directly onto paper. While this was

previously possible by using organic semi conductive ink, the use of graphene flakes makes

the printed material vastly more conductive and therefore more efficient.

Properties of Graphene

Graphene is, basically, a single atomic layer of graphite; an abundant mineral which is an

allotrope of carbon that is made up of very tightly bonded carbon atoms organised into a

hexagonal lattice. What makes graphene so special is its sp2 hybridisation and very thin

atomic thickness (of 0.345Nm). These properties are what enable graphene to break so many

records in terms of strength, electricity and heat conduction. Now, let’s explore just what

makes graphene so special, what are its intrinsic properties that separate it from other forms

of carbon, and other 2D crystalline compounds?

Fundamental Characteristics

Before monolayer graphene was isolated in 2004, it was theoretically believed that two

dimensional compounds could not exist due to thermal instability when separated. After

suspended graphene sheets were studied by transmission electron microscopy, scientists

believed that they found the reason to be due to slight rippling in graphene. Later research

suggests that it is actually due to the fact that the carbon to carbon bonds in graphene are so

small and strong that they prevent thermal fluctuations from destabilizing it.

Electronic Properties

One of the most useful properties of graphene is that it is a zero-overlap semimetal with very

high electrical conductivity. Carbon atoms have a total of 6 electrons; 2 in the inner shell and

4 in outer shell. The 4 outer shell electrons in an individual carbon atom are available for

chemical bonding, but in graphene, each atom is connected to 3 other carbon atoms, leaving

1 electron freely available for electronic conduction. These highly-mobile electrons are

called pi (π) elec. The electronic properties of graphene are dictated by the bonding and anti-

bonding of these pi orbitals.

Combined research over the last 50 years has proved that at the Dirac point in graphene,

electrons and holes have zero effective mass. This occurs because the energy – movement

relation is linear for low energies near the 6 individual corners of the Brillouin zone. Due to

the zero density of states at the Dirac points, electronic conductivity is actually quite low.

Tests have shown that the electronic mobility of graphene is very high, with previously

reported results above 15,000 cm2·V−1·s−1. It is said that graphene electrons act very much

like photons in their mobility due to their lack of mass. These charge carriers are able to

travel sub-micrometre distances without scattering; a phenomenon known as ballistic

transport. Silicon dioxide as the substrate, for example, mobility is potentially limited to

40,000 cm2·V−1·s−1.

Mechanical Strength

Another of graphene’s stand-out properties is its inherent strength. Due to the strength of its

0.142 Nm-long carbon bonds, graphene is the strongest material ever discovered, with an

ultimate tensile strength of 130,000,000,000 Pascal (or 130 gigapascals), compared to

400,000,000 for A36 structural steel, or 375,700,000 for Aramid (Kevlar).

Figure 7

Not only is graphene extraordinarily strong, it is also very light at 0.77milligrams per square

metre (for comparison purposes, 1 square metre of paper is roughly 1000 times heavier). It is

often said that a single sheet of graphene (being only 1 atom thick), sufficient in size enough

to cover a whole football field, would weigh under 1 single gram.

What makes this particularly special is that graphene also contains elastic properties, being

able to retain its initial size after strain. In 2007, Atomic force microscopic (AFM) tests were

carried out on graphene sheets that were suspended over silicone dioxide cavities. These tests

showed that graphene sheets (thicknesses between 2 and 8 Nm) had spring constants in the

region of 1-5 N/m and a Young’s modulus (different to that of three-dimensional graphite) of

0.5 TPa.

Again, these superlative figures are based on theoretical prospects using graphene that is

unflawed containing no imperfections whatsoever and currently very expensive and difficult

to artificially reproduce, though production techniques are steadily improving, ultimately

reducing costs and complexity.

Optical Properties

Graphene’s ability to absorb a rather large 2.3% of white light is also a unique and

interesting property, especially considering that it is only 1 atom thick. This is due to its

aforementioned electronic properties; the electrons acting like massless charge carriers with

very high mobility.

A few years ago, it was proved that the amount of white light absorbed is based on the Fine

Structure Constant, rather than being dictated by material specifics. Adding another layer of

graphene increases the amount of white light absorbed by approximately the same value

(2.3%). Graphene’s opacity of πα ≈ 2.3% equates to a universal dynamic conductivity value

of G=e2/4ℏ (±2-3%) over the visible frequency range.

Due to these impressive characteristics, it has been observed that once optical intensity

reaches a certain threshold saturable absorption takes place. This is an important

characteristic with regards to the mode-locking of fibre lasers. Due to graphene’s properties

of wavelength-insensitive ultrafast saturable absorption, full-band mode locking has been

achieved using an erbium-doped dissipative soliton fibre laser capable of obtaining

wavelength tuning as large as 30 nm.

Figure 8

In terms of how far along we are to understanding the true properties of graphene, this is just

the tip of the iceberg. Before graphene is heavily integrated into the areas in which we

believe it will excel at, we need to spend a lot more time understanding just what makes it

such an amazing material. Unfortunately, while we have a lot of imagination in coming up

with new ideas for potential applications and uses for graphene, it takes time to fully

appreciate how and what graphene really is in order to develop these ideas into reality. This

is not necessarily a bad thing, however, as it gives us opportunities to stumble over other

previously under-researched or overlooked super-materials, such as the family of 2D

crystalline structures that graphene has born.

Graphene & Graphite - How Do

They Compare??

“The attributes of graphene – transparency, density, electric and thermal conductivity,

elasticity, flexibility, hardness resistance and capacity to generate chemical reactions with

other substances – harbour the potential to unleash a new technological revolution of more

magnificent proportions than that ushered in by electricity in the 19th century and the rise of

the internet in the 1990s.” – LarrainVial

In very basic terms graphene could be described as a single, one atom thick layer of the

commonly found mineral graphite; graphite is essentially made up of hundreds of thousands

of layers of graphene. In actuality, the structural make-up of graphite and graphene, and the

method of how to create one from the other, is slightly different.

Graphite-

Way back when we were at school, it is very likely that you would have come across the

term ‘pencil lead’, referring to the central core of a pencil that is able to produce marks on

paper and other material. In fact, rather than referring to the chemical element and heavy

metal, lead, this central core is most commonly made from graphite mixed with clay.

Figure 9 Figure 10

Graphite is a mineral that occurs in metamorphic rock in different continents of the world,

including Asia, South America and North America. It is formed as a result of the reduction

of sedimentary carbon compounds during metamorphism. Contrary to common belief, the

chemical bonds in graphite are actually stronger than those that make up diamond. However,

what defines the difference in hardness of the two compounds is the lattice structure of the

carbon atoms contained within; diamonds containing three dimensional lattice bonds, and

graphite containing two dimensional lattice bonds. While within each layer of graphite the

carbon atoms contain very strong bonds, the layers are able to slide across each other,

making graphite a softer, more malleable material.

Extensive research over hundreds of years has proved that graphite is an impressive mineral

showing a number of outstanding and superlative properties including its ability to conduct

electricity and heat well, having the highest natural stiffness and strength even in

temperatures exceeding 3600 degrees Celsius, and it is also highly resistant to chemical

attack and self-lubricating. However, while it was first identified over a thousand years ago

and first named in 1789, it has taken a while for industry to realise the full potential of this

amazing material.

Graphite is one of only three naturally occurring allotropes of carbon (the others being

amorphous carbon and diamond). The difference between the three naturally occurring

allotropes is the structure and bonding of the atoms within the allotropes; diamond enjoying

a diamond lattice crystalline structure, graphite having a honeycomb lattice structure, and

amorphous carbon (such as coal or soot) does not have a crystalline structure.

While there are many different forms of carbon, graphite is of an extremely high grade and is

the most stable under standard conditions. Therefore, it is commonly used in

thermochemistry as the standard state for defining the heat formation of compounds made

from carbon. It is found naturally in three different forms: crystalline flake, amorphous and

lump or vein graphite, and depending on its form, is used for a number of different

applications.

As previously touched upon, graphite has a planar, layered structure; each layer being made

up of carbon atoms linked together in a hexagonal lattice. These links, or covalent bonds as

they are more technically known, are extremely strong, and the carbon atoms are separated

by only 0.142 nanometres. The carbon atoms are linked together by very sturdy sp2

hybridised bonds in a single layer of atoms, two dimensionally. Each individual, two

dimensional, one atom thick layer of sp2 bonded carbon atoms in graphite is separated by

0.335nm. Essentially, the crystalline flake form of graphite, as mentioned earlier, is simply

hundreds of thousands of individual layers of linked carbon atoms stacked together.

Graphene-

So, graphene is fundamentally one single layer of graphite; a layer of sp2 bonded carbon

atoms arranged in a honeycomb (hexagonal) lattice. However, graphene offers some

impressive properties that exceed those of graphite as it is isolated from its ‘mother

material’. Graphite is naturally a very brittle compound and cannot be used as a structural

material on its own due to its sheer planes (although it is often used to reinforce steel).

Graphene, on the other hand, is the strongest material ever recorded, more than three

hundred times stronger than A36 structural steel, at 130 gigapascals, and more than forty

times stronger than diamond.

Figure 11 Figure 12

Due to graphite’s planar structure, its thermal, acoustic and electronic properties are highly

anisotropic, meaning that phonons travel much more easily along the planes than they do

when attempting to travel through the planes. Graphene, on the other hand, being a single

layer of atoms and having very high electron mobility, offers fantastic levels of electronic

conduction due to the occurrence of a free pi (π) electron for each carbon atom.

Figure 13

However, for this high level of electronic conductivity to be realised, doping (with electrons

or holes) must occur to overcome the zero density of states which can be observed at the

Dirac points of graphene. The high level of electronic conductivity has been explained to be

due to the occurrence of quasiparticles; electrons that act as if they have no mass, much like

photons, and can travel relatively long distances without scattering (these electrons are hence

known as massless Dirac fermions).

Creating or Isolating Graphene

There are a number of ways in which scientists are able to produce graphene. The first

successful way of producing monolayer and few layer graphene was by mechanical

exfoliation (the adhesive tape technique). However, many research institutions around the

world are currently racing to find the best, most efficient and effective way of producing

high quality graphene on a large scale, which is also cost efficient and scalable.

The most common way for scientists to create monolayer or few layer graphene is by a

method known as chemical vapour deposition (CVD). This is a method that extracts carbon

atoms from a carbon rich source by reduction. The main problem with this method is finding

the most suitable substrate to grow graphene layers on, and also developing an effective way

of removing the graphene layers from the substrate without damaging or modifying the

atomic structure of the graphene.

Figure 14

Other methods for creating graphene are: growth from a solid carbon source (using thermo-

engineering), sonication, cutting open carbon nanotubes, carbon dioxide reduction, and also

graphite oxide reduction. This latter method of using heat (either by atomic force microscope

or laser) to reduce graphite oxide to graphene has received a lot of publicity of late due to the

minimal cost of production. However, the quality of graphene produced currently falls short

of theoretical potential and will inevitably take some time to perfect.

Graphene Applications and Uses

Graphene, the well-publicised and now famous two-dimensional carbon allotrope, is as

versatile a material as any discovered on Earth. Its amazing properties as the lightest and

strongest material, compared with its ability to conduct heat and electricity better than

anything else, mean that it can be integrated into a huge number of applications. Initially this

will mean that graphene is used to help improve the performance and efficiency of current

materials and substances, but in the future it will also be developed in conjunction with other

two-dimensional (2D) crystals to create some even more amazing compounds to suit an even

wider range of applications.

The first time graphene was artificially produced; scientists literally took a piece of graphite

and dissected it layer by layer until only 1 single layer remained. This process is known as

mechanical exfoliation. This resulting monolayer of graphite (known as graphene) is only 1

atom thick and is therefore the thinnest material possible to be created without becoming

unstable when being open to the elements (temperature, air, etc.).

Figure 15

Because graphene is only 1 atom thick, it is possible to create other materials by interjecting

the graphene layers with other compounds effectively using graphene as atomic scaffolding

from which other materials are engineered. These newly created compounds could also be

superlative materials, just like graphene, but with potentially even more applications.

After the development of graphene and the discovery of its exceptional properties, not

surprisingly interest in other two-dimensional crystals increased substantially. These other

2D crystals can be used in combination with other 2D crystals for an almost limitless number

of applications. It improves its efficiency as a superconductor. Or, another example would be

in the case of combining the mineral Molybdenite (MoS2), which can be used as a

semiconductor, with graphene layers when creating NAND flash memory, to develop flash

memory to be much smaller and more flexible than current technology.

The only problem with graphene is that high-quality graphene is a great conductor that does

not have a band gap. Therefore to use graphene in the creation of future nano-electronic

devices, a band gap will need to be engineered into it, which will, in turn, reduce its electron

mobility to that of levels currently seen in strained silicone films. This essentially means that

future research and development needs to be carried out in order for graphene to replace

silicone in electrical systems in the future

In any case, these two examples are just the tip of the iceberg in only one field of research,

whereas graphene is a material that can be utilized in numerous disciplines including, but not

limited to: bioengineering, composite materials, energy technology and nanotechnology.

Biological Engineering

Bioengineering will certainly be a field in which graphene will become a vital part of in the

future; though some obstacles need to be overcome before it can be used. Current

estimations suggest that it will not be until 2030 when we will begin to see graphene widely

used in biological applications as we still need to understand its biocompatibility. However,

the properties that it displays suggest that it could revolutionise this area in a number of

ways. With graphene offering a large surface area, high electrical conductivity, thinness and

strength, it would make a good candidate for the development of fast and efficient bioelectric

sensory devices, with the ability to monitor such things as glucose levels, haemoglobin

levels, cholesterol and even DNA sequencing. It is able to be used as an antibiotic or even

anticancer treatment.

Optical Electronics

One particular area in which we will soon begin to see graphene used on a commercial scale

is that in optoelectronics; specifically touchscreens, liquid crystal displays (LCD) and

organic light emitting diodes (OLEDs). For a material to be able to be used in optoelectronic

applications, it must be able to transmit more than 90% of light and also offer electrical

conductive properties exceeding 1 x 106 Ω1m1 and therefore low electrical

resistance. Graphene is an almost completely transparent material and is able to optically

transmit up to 97.7% of light. It is also highly conductive, as we have previously mentioned

and so it would work very well in optoelectronic applications such as LCD touchscreens.

However, recent tests have shown that graphene is potentially able to match the properties of

ITO, even in current states. While this does not sound like much of an improvement over

ITO, graphene displays additional properties which can enable very clever technology to be

developed in optoelectronics by replacing the ITO with graphene. The fact that high quality

graphene has a very high tensile strength, and is flexible makes it almost inevitable that it

will become utilized in mentioned applications.

Figure 16

In terms of potential real-world electronic applications we can eventually expect to see such

devices as graphene based e-paper with the ability to display interactive and updatable

information and flexible electronic devices including portable computers and televisions.

Ultrafiltration

Another standout property of graphene is that while it allows water to pass through it, it is

almost completely impervious to liquids and gases (even relatively small helium molecules).

This means that graphene could be used as an ultrafiltration medium to act as a barrier

between two substances. The benefit of using graphene is that it is only 1 single atom thick

and can also be developed as a barrier that electronically measures strain and pressures

between the 2 substances (amongst many other variables).

A team of researchers at Columbia University have managed to create monolayer graphene

filters with pore sizes as small as 5nm (currently, advanced nanoporous membranes have

pore sizes of 30-40nm).

Figure 17 Figure 18

While these pore sizes are extremely small, as graphene is so thin, pressure during

ultrafiltration is reduced. Co-currently, graphene is much stronger and less brittle than

aluminium oxide (currently used in sub-100nm filtration applications). What does this mean?

Well, it could mean that graphene is developed to be used in water filtration systems,

desalination systems and efficient and economically more viable biofuel creation.

Composite Materials

Graphene is strong, stiff and very light. Currently, aerospace engineers are incorporating

carbon fibre into the production of aircraft as it is also very strong and light. However,

graphene is much stronger whilst being also much lighter. Ultimately it is expected that

graphene is utilized to create a material that can replace steel in the structure of aircraft,

improving fuel efficiency, range and reducing weight. Due to its electrical conductivity, it

could even be used to coat aircraft surface material to prevent electrical damage resulting

from lightning strikes. In this example, the same graphene coating could also be used to

measure strain rate, notifying the pilot of any changes in the stress levels that the aircraft

wings are under. These characteristics can also help in the development of high strength

requirement applications such as body armour for military personnel and vehicles.

Photovoltaic Cells

Offering very low levels of light absorption (at around 2.7% of white light) whilst also

offering high electron mobility means that graphene can be used as an alternative to silicon

or ITO in the manufacture of photovoltaic cells. Silicon is currently widely used in the

production of photovoltaic cells, but while silicon cells are very expensive to produce,

graphene based cells are potentially much less so. When materials such as silicon turn light

into electricity it produces a photon for every electron produced, meaning that a lot of

potential energy is lost as heat. Recently published research has proved that when graphene

absorbs a photon, it actually generates multiple electrons.

Also, while silicon is able to generate electricity from certain wavelength bands of light,

graphene is able to work on all wavelengths, meaning that graphene has the potential to be as

efficient as, if not more efficient than silicon, ITO or (also widely used) gallium

arsenide. Being flexible and thin means that graphene based photovoltaic cells could be used

in clothing; to help recharge your mobile phone, or even used as retro-fitted photovoltaic

window screens or curtains to help power your home.

Energy Storage

One area of research that is being very highly studied is energy storage. While all areas of

electronics have been advancing over a very fast rate over the last few decades (in reference

to Moore’s law which states that the number of transistors used in electronic circuitry will

double every 2 years), the problem has always been storing the energy in batteries and

capacitors when it is not being used. These energy storage solutions have been developing at

a much slower rate. The problem is this: a battery can potentially hold a lot of energy, but it

can take a long time to charge, a capacitor, on the other hand, can be charged very quickly,

but can’t hold that much energy (comparatively speaking). The solution is to develop energy

storage components such as either a supercapacitors or a battery that is able to provide both

of these positive characteristics without compromise.

Currently, scientists are working on enhancing the capabilities of lithium ion batteries (by

incorporating graphene as an anode) to offer much higher storage capacities with much

better longevity and charge rate. Also, graphene is being studied and developed to be used in

the manufacture of supercapacitors which are able to be charged very quickly, yet also be

able to store a large amount of electricity.

Figure 19 Figure 20

Graphene based micro-supercapacitors will likely be developed for use in low energy

applications such as smart phones and portable computing devices and could potentially be

commercially available within the next 5-10 years. Graphene-enhanced lithium ion batteries

could be used in much higher energy usage applications such as electrically powered

vehicles, or they can be used as lithium ion batteries are now, in smartphones, laptops and

tablet PCs but at significantly lower levels of size and weight.

Graphene Supercapacitors -

What Are They?

Figure 21 Scientists have been struggling to develop energy storage solutions such as batteries and

capacitors that can keep up with the current rate of electronic component evolution for a

number of years. Unfortunately, the situation we are in now is that while we are able to store

a large amount of energy in certain types of batteries, those batteries are very large, very

heavy, and charge and release their energy relatively slowly.

Capacitors, on the other hand, are able to be charged and release energy very quickly, but

can hold much less energy than a battery. Graphene application developments have led to

new possibilities for energy storage, with high charge and discharge rates, which can be

made cheaply. But before we go into specific details, it would be sensible to first outline

basics of energy storage and the potential goals of developing graphene as supercapacitors.

Capacitors and supercapacitors explained

A capacitor is an energy storage medium similar to an electrochemical battery. Most

batteries, while able to store a large amount of energy are relatively inefficient in comparison

to other energy solutions such as fossil fuels. It is often said that a 1kg electrochemical

battery is able to produce much less energy than 1 litre of gasoline; but this kind of

comparison is extremely vague, and should be ignored. In fact, some electrochemical

batteries can be relatively efficient, but that doesn’t get around the primary limiting factor in

batteries replacing fossil fuels.

High capacity batteries take a long time to charge. This is why electrically powered vehicles

have not taken-off as well as we expected twenty or thirty years ago. While you are now able

to travel 250 miles or more on one single charge in a car such as the Tesla Model S, it could

take you over 43 hours to charge the vehicle using a standard 120v wall socket in order to

drive back home. This is not acceptable for many car users. Capacitors, on the other hand,

are able to be charged at a much higher rate, but store somewhat less energy.

Figure 22

Supercapacitors, also known as ultra-capacitors, are able to hold hundreds of times the

amount of electrical charge as standard capacitors, and are therefore suitable as a

replacement for electrochemical batteries in many industrial and commercial applications.

Supercapacitors also work in very low temperatures; a situation that can prevent many types

of electrochemical batteries from working. For these reasons, supercapacitors are already

being used in emergency radios and flashlights, where energy can be produced kinetically

(by winding a handle, for example) and then stored in a supercapacitors for the device to use.

A conventional capacitor is made up of two layers of conductive materials (eventually

becoming positively and negatively charged) separated by an insulator. What dictates the

amount of charge a capacitor can hold is the surface area of the conductors, the distance

between the two conductors and also the dielectric constant of the insulator. Supercapacitors

are slightly different in the fact that they do not contain a solid insulator.

While supercapacitors are able to store much more energy than standard capacitors, they are

limited in their ability to withstand high voltage. Electrolytic capacitors are able to run at

hundreds of volts, but supercapacitors are generally limited to around 5 volts. However, it is

possible to engineer a chain of supercapacitors to run at high voltages as long as the series is

properly designed and controlled.

Graphene-based supercapacitors

Figure 23

Supercapacitors, unfortunately, are currently very expensive to produce, and at present the

scalability of supercapacitors in industry is limiting the application options as energy

efficiency is offset against cost efficiency. This idea of creating graphene monolayers by

using thermo lithography is not necessarily a new one, as scientists from the US were able to

produce graphene nanowires by using thermochemical nanolithography back in 2010;

however, new method avoids the use of atomic force microscope in favour of commercially

available laser device that is already prevalent in many homes around the world.

Why are scientists looking at using graphene instead of the currently more popular activated

carbon? Well, graphene is essentially a form of carbon, and while activated carbon has an

extremely high relative surface area, graphene has substantially more. As we have already

highlighted, one of the limitations to the capacitance of ultra-capacitors is the surface area of

the conductors. If one conductive material in a supercapacitor has a higher relative surface

area than another, it will be better at storing electrostatic charge.

Figure 24

The efficiency of the supercapacitor is the important factor to bear in mind. In the past,

scientists have been able to create supercapacitors that are able to store 150 Farads per gram,

but some have suggested that the theoretical upper limit for graphene-based supercapacitors

is 550 F/g. This is particularly impressive when compared against current technology: a

commercially available capacitor able to store 1 Farad of electrostatic energy at 100 volts

would be about 220mm high and weigh about 2kgs, though current supercapacitor

technology is about the same, in terms of dimensions relative to energy storage values, as a

graphene-based supercapacitor would be.

The future for graphene-based supercapacitors

Due to the lightweight dimensions of graphene based supercapacitors and the minimal cost

of production coupled with graphene’s elastic properties and inherit mechanical strength, we

will almost certainly see technology within the next five to ten years incorporating these

supercapacitors. Also, with increased development in terms of energy storage limits for

supercapacitors in general, graphene-based or hybrid supercapacitors will eventually be

utilized in a number of different applications.

Figure 25 Figure 26

Vehicles that utilize supercapacitors are already prevalent in our society. One Chinese

company is currently manufacturing buses that incorporate supercapacitor energy recovery

systems, such as those used on Formula 1 cars, to store energy when braking and then

converting that energy to power the vehicle until the next stop.

Additionally, we will at some point in the next few years begin to see mobile telephones and

other mobile electronic devices being powered by supercapacitors as not only can they be

charged at a much higher rate than current lithium-ion batteries, but they also have the

potential to last for a vastly greater length of time.

Other current and potential uses for supercapacitors are as power backup supplies for

industry or even our own homes. Businesses can invest in power backup solutions that are

able to store high levels of energy at high voltages, effectively offering full power available

to them, to reduce the risk of having to limit production due to inadequate amounts of power.

Alternatively, if you have a fuel cell vehicle that is able to store a large amount of electrical

energy, then why not use it to help power your home in the event of a power outage?

We can expect that this scenario of using advanced energy storage and recovery solutions

will become much more widely used in the coming years as the efficiency and energy

density of supercapacitors increases, and the manufacturing costs decrease.

While graphene-based supercapacitors are currently a viable solution in the future,

technology needs to be developed to make this into a reality. But rest assured, many

companies around the world are already trialling products using this technology and creating

new ways to help subsidise the use of fossil-fuels and toxic chemicals in our ever-demanding

strive for energy.

Creating Graphene via Chemical

Vapour Deposition

There are different ways in which graphene monolayers can be created or isolated, but by far

the most popular way at this moment in time is by using a process called chemical vapour

deposition. Chemical vapour deposition, or CVD, is a method which can produce relatively

high quality graphene, potentially on a large scale. The CVD process is reasonably

straightforward, although some specialist equipment is necessary, and in order to create good

quality graphene it is important to strictly adhere to guidelines set concerning gas volumes,

pressure, temperature, and time duration.

Figure 27

The CVD Process

Simply put, CVD is a way of depositing gaseous reactants onto a substrate. The way CVD

works is by combining gas molecules in a reaction chamber which is typically set at ambient

temperature. When the combined gases come into contact with the substrate within the

reaction chamber a reaction occurs that create a material film on the substrate surface. The

waste gases are then pumped from the reaction chamber. The temperature of the substrate is

a primary condition that defines the type of reaction that will occur.

During the CVD process, the substrate is usually coated a very small amount, at a very slow

speed, often described in microns of thickness per hour. The solid compound or compounds

is/are vaporized, and then deposited onto a substrate via condensation.

The benefits of using CVD to deposit materials onto a substrate are that the quality of the

resulting materials is usually very high. Other common characteristics of CVD coatings

include imperviousness, high purity, fine grained and increased hardness over other coating

methods. It is a common solution for the deposit of films in the semiconductor industry, as

well as in optoelectronics, due to the low costs involved.

Although there are number of different formats of CVD, most modern processes come under

two headings separated by the chemical vapour deposition operating pressure: LPCVD, and

UHVCVD. LPCVD (low pressure CVD), UHVCVD (ultra-high vacuum CVD).

The disadvantages to using CVD to create material coatings are that the gaseous by-products

of the process are usually very toxic. This is because the precursor gases used must be highly

volatile in order to react with the substrate, but not so volatile that it is difficult to deliver

them to the reaction chamber. During the CVD process, the toxic by-products are removed

from the reaction chamber by gas flow to be disposed of properly.

Fundamental Processes in the Creation of CVD Graphene

CVD graphene is created in two steps, the precursor pyrolysis of a material to form carbon,

and the formation of the carbon structure of graphene using the disassociated carbon atoms.

The first stage, the pyrolysis to disassociated carbon atoms, must be carried out on the

surface of the substrate to prevent the precipitation of carbon clusters during the gas phase.

The problem with this is that the pyrolytic decomposition of precursors requires extreme

levels of heat, and therefore metal catalysts must be used to reduce the reaction temperature.

The second phase of creating the carbon structure out of the disassociated carbon atoms, also

requires a very high level of heat (over 2500 degrees Celsius).

Figure 28

The problem with using catalysts is that you are effectively introducing more compounds

into the reaction chamber, which will have an effect on the reactions inside the chamber. One

example of these effects is the way the carbon atoms dissolve into certain substrates such as

Nickel during the cooling phase.

What all this means is that it is vitally important that the CVD process is very stringently co-

ordinated, and that controls are put in place at every stage of the process to ensure that the

reactions occur effectively, and that quality of graphene produced is of the highest attainable.

Problems Associated with the Creation of CVD Graphene

In order to create monolayer or few layer graphene on a substrate, scientists must first

overcome the biggest issues with the methods that have been observed so far.

The first major problem is that while it is possible to create high quality graphene on a

substrate using CVD, the successful separation or exfoliation of graphene from the substrate

has been a bit of a stumbling block.

The reason for this is primarily because the relationship between graphene and the substrate

it is ‘grown’ on is not yet fully understood, so it is not easy to achieve separation without

damaging the structure of the graphene or affecting the properties of the material. The

techniques on how to achieve this separation differ depending on the type of substrate used.

Often scientists can choose to dissolve the substrate in harmful acids, but this process

commonly affects the quality of graphene produced.

One alternative method that has been researched involves the creation of CVD graphene on a

copper (Cu) substrate (in this example, Cu is used as a catalyst in the reaction). During CVD

a reaction occurs between the copper substrate and the graphene that create a high level of

hydrostatic compression, coupling the graphene to the substrate. It has been shown to be

possible; however, to intercalate a layer of copper oxide between the graphene and the

copper substrate to reduce this pressure and enable the graphene to be removed relatively

easily.

Scientists have also been looking into using (Poly methyl methacrylate) as a support polymer

to facilitate the transfer of graphene onto an alternate substrate. With this method, graphene

is coated with PMMA, and the previous substrate is etched. However, PMMA has been

shown to be the most effective at transferring the graphene without excessive damage.

Current and Potential Solutions

In terms of overcoming these issues, scientists have been developing more complex

techniques and guidelines to follow in order to create the highest quality of graphene

possible. One introductory technique to reducing the effects of these issues is by treating the

substrate before the reaction takes place. A copper substrate can be chemically treated to

enable reduced catalytic activity, increase the Cu grain size and rearrange the surface

morphology in order to facilitate the growth of graphene flakes that contain fewer

imperfections.

This point of treating the substrate prior to deposition is something that will continue to be

researched for a long time, as we slowly learn how to modify the structure of graphene to

suit different applications. For example, in order to enable graphene to be effectively used in

superconductors, doping must be carried out on the material in order to create a band-gap.

This process could potentially be something that is carried out on a substrate before

deposition occurs rather than treating the material after CVD.

Reduced Graphene Oxide - What

Is It? How Is It Created?

Around the world, research institutions are trying to develop ways to revolutionise the

production of graphene sheets of the highest quality. One of the most cost effective ways this

is possible is by the reduction of graphene oxide into rGO (reduced graphene oxide). The

problem with this technique is the quality of graphene sheets produced, which displays

properties currently below the theoretical potential of pristine graphene compared to other

methods such as mechanical exfoliation. However, this doesn't mean that improvements

can’t be made, or that this reduced graphene oxide is effectively unusable.

Figure 29

Graphite Oxide

Graphite oxide is a compound made up of carbon, hydrogen and oxygen molecules. It is

artificially created by treating graphite with strong oxidisers such as sulphuric acid. These

oxidisers work by reacting with the graphite and removing an electron in the chemical

reaction. This reaction is known as a redox (a portmanteau of reduction and oxidisation)

reaction, as the oxidising agent is reduced and the reactant is oxidised.

The most common method for creating graphite oxide in the past has been the Hummers and

Offeman method, in which graphite is treated with a mixture of sulphuric acid, sodium

nitrate and potassium permanganate. However, other methods have been developed recently

that are reported to be more efficient, reaching levels of 90% oxidisation, by using increased

quantities of potassium permanganate, and adding phosphoric acid combined with the

sulphuric acid, instead of adding sodium nitrate.

Graphene oxide is effectively a by-product of this oxidisation as when the oxidising agents

react with graphite, the interplanar spacing between the layers of graphite is increased. The

completely oxidised compound can then be dispersed in a base solution such as water, and

graphene oxide is then produced.

Graphite Oxide to Graphene Oxide

The process of turning graphite oxide into graphene oxide can ultimately be very damaging

to the individual graphene layers, which has further consequences when reducing the

compound further (explanation to follow). The oxidisation process from graphite to graphite

oxide already damages individual graphene platelets, reducing their mean size, so further

damage is undesirable. Graphene oxide contains flakes of monolayer and few layer

graphene, interspersed with water (depending on the base media, the platelet to platelet

interactions can be weakened by surface functionality, leading to improved hydrophilicity).

In order to turn graphite oxide into graphene oxide, a few methods are possible. The most

common techniques are by using sonication, stirring, or a combination of the two. Sonication

can be a very time-efficient way of exfoliating graphite oxide, and it is extremely successful

at exfoliating graphene (almost to levels of full exfoliation), but it can also heavily damage

the graphene flakes, reducing them in surface size from microns to nanometres, and also

produces a wide variety of graphene platelet sizes. Mechanically stirring is a much less

heavy-handed approach, but can take much longer to accomplish.

Graphene Oxide to Reduced Graphene Oxide

Reducing graphene oxide to produce reduced graphene oxide (hitherto referred to as rGO), is

an extremely vital process as it has a large impact on the quality of the rGO produced, and

therefore will determine how close rGO will come, in terms of structure, to pristine

graphene. In large scale operations where scientific engineers need to utilize large quantities

of graphene for industrial applications such as energy storage, rGO is the most obvious

solution, due to the relative ease in creating sufficient quantities of graphene to desired

quality levels.

Figure 30

In the past, scientists have created rGO from GO by:

Treating GO with hydrazine hydrate and maintaining the solution at 100 for 24 hours

Exposing GO to hydrogen plasma for a few seconds

Exposing GO to another form of strong pulse light, such as those produced by xenon

flashtubes

Heating GO in distilled water at varying degrees for different lengths of time

Combining GO with an expansion-reduction agent such as urea and then heating the

solution to cause the urea to release reducing gases, followed by cooling

Directly heating GO to very high levels in a furnace

Linear sweep voltammetry

The Price of Graphene

Everyone agrees that graphene is an amazing material. Graphene has better electron mobility

than any metal, is one atom thin, is flexible, and all that while being stronger than steel. The

2010 Nobel Prize in physics confirmed the material's potential.

The Quality of the Graphene Affects the Price

The price of graphene is linked to its quality, and not all applications require superb material

quality. For example, graphene oxide powder (oxygen and hydrogen) is inexpensive and has

been used to make a conductive graphene paper, for DNA analysis. Graphene oxide in

solution sells for 99 euros per 250 mL. The electronic properties of graphene oxide at the

moment are not sufficiently good for batteries, flexible touch screens, solar cells, LEDs,

smart windows, and other advanced opto-electronic applications.

Figure 31

Mechanically exfoliated graphene (obtained with the famous “scotch tape” technique)

comes in small, high-quality flakes. Exfoliated graphene has so far shown to hold the best

physical properties. The coverage of mechanically exfoliated graphene, however, is only on

the order of a few small flakes per square centimeter, not nearly enough for applications. In

addition, the price of such graphene can be several thousands of dollars per flake.

CVD graphene, available with high quality from Graphenea, offers sufficient quality for

almost any graphene application. The price of CVD graphene is linked to production volume

and costs of transferring from the copper substrate, on which it is grown, onto another

substrate. Graphenea's industrial scale graphene technology leads to low CVD graphene cost

for bulk orders (see graph). Bulk orders of such graphene can be cheaper than, for example,

silicon carbide, and an important semiconductor. Graphenea has filed a patent for a low cost

industrial scale CVD growth and transfer process.

Technology Reduces the Price of Graphene

In several years, bulk graphene prices may drop below that of silicon, enabling graphene to

enter all markets now dominated by silicon, such as computing, chip manufacturing, sensors,

solar cells, etc. In the meantime, graphene will continue to be used for applications that other

materials simply cannot support. For example, silicon cannot be integrated into future

flexible smartphones, because silicon is brittle and will break upon bending. Graphene offers

a competitive solution.

Figure 32

FUTURE TRENDS IN

GRAPHENE Flexible Touch Screens-

The outstanding properties of graphene make it attractive for applications in flexible

electronics. Byung Hee Hong, Jong-Hyun Ahn and co-workers have demonstrated roll-to-

roll production and wet chemical doping of mostly monolayer graphene films grown by

chemical vapour deposition onto flexible copper substrates. They also used layer-by-layer

stacking to fabricate a doped four-layer film with properties superior to those of commercial

transparent electrodes such as indium tin oxides. The photograph on the cover shows a

flexible touch-screen device containing graphene electrodes.

LCD “Smart Windows”-

Figure 33

Graphene is flexible, absorbs only 2.3% of light and conducts electricity very well. A layer

of liquid crystals is sandwiched between two flexible electrodes comprised of graphene and

transparent polymer. When there is no applied bias between the electrodes, liquid crystals

scatter light and the smart window is opaque. When a bias is applied, the voltage aligns

them, allowing light to pass through and the smart window turns transparent.

Magnetism and Graphene-

Given the great versatility of graphene’s properties and especially the ability to control many

of its characteristics by external electric field (gate voltage), graphene has a potential to

become an excellent material for spintronics. Our current efforts concentrate on ‘making

graphene magnetic’ by introducing point defects, such as vacancies or adatoms. We have

already demonstrated that vacancies in graphene act as individual magnetic moments and

lead to pronounced paramagnetism.

Graphene for Terahertz Electronics-

Conventional electronic devices are made up of silicon semiconductors, metal contacts,

doped junctions or barrier structures, etc. Each of these components must be added vertically

on top of one another. In contrast, we have recently developed novel concepts of nano-diodes

and transistors that are based on single-layered device architecture.

Figure 34

By using nano-scale electronic channels and tailoring the geometrical symmetry, the new

devices have been demonstrated to have extremely high speed up to 1.5THz (1,500GHz),

making them by far the fastest Nano devices to date The immediate applications include

high-speed electronics for next generation of computations and communications, far-infrared

THz detection and emission, ultra-high sensitive chemical sensors, etc.

Graphene Sensors-

University of Manchester scientists were the first to demonstrate single-atom sensitivity in

graphene Hall-bar devices. The most sensitive electronic detection is achieved by

constructing a Hall-bar with graphene. This transverse Hall resistivity is very sensitive to

changes in carrier concentration.

Figure 35

The binding event between the graphene sensor and analyte leads to the donation or

withdrawal of an electron from the graphene, which changes its electrical conductivity which

can be measured. When a device is fabricated with a graphene sheet suspended in free space

between two electrodes, it has a resonance frequency of vibration proportional to its mass.

3D Printing-

Even on their own, 3D printing technology and the super material graphene have the

potential to bring about the next industrial revolution. So imagine if it were possible to 3D

print objects using graphene? It's pretty mind-boggling.

It’s already possible to make everything from guns to food to human body parts. If graphene

proves workable as a 3D printable material, we could potentially add computers, solar

panels, electronics, even cars and airplanes to the list.

INTRODUCTION

Graphene is a wonder material with many superlatives to its name. It is the thinnest material

in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic

mobility, have the smallest effective mass (it is zero) and can travel micrometer-long

distances without scattering at room temperature. Graphene can sustain current densities 6

orders higher than copper, shows record thermal conductivity and stiffness, is impermeable

to gases and reconciles such conflicting qualities as brittleness and ductility. Electron

transport in graphene is described by a Dirac-like equation, which allows the investigation of

relativistic quantum phenomena in a bench-top experiment. What are other surprises that

graphene keeps in store for us? This review analyses recent trends in graphene research and

applications, and attempts to identify future directions in which the field is likely to develop.

Graphene is a novel material with very unusual properties. To be sure, silicon will reign

supreme in many of the applications in which it is now found. But carbon, silicon's little

brother, has new realms to conquer. And if graphene keeps progressing as fast as it has in the

past two years, it will surely attract the immense weight of investment in research and

development that has so far gone almost exclusively to silicon. If that happens, then little

brother will at first supplement silicon and at last supplant it, as little brothers often.

Acknowledgement

I have taken efforts in this Term Paper. However, it would not have been possible without

the kind support and help of many individuals and organizations. I would like to extend my

sincere thanks to all of them.

I am highly indebted to Dr. Bikram k. bahinipati (HOI, AUMP), Dr. Shally Goyal mam

for their guidance and constant supervision as well as for providing necessary information

regarding the Term Paper & also for their support in completing the Term Paper.

I would like to express my gratitude towards my parents & staff of Amity University,

Gwalior for their kind co-operation and encouragement which help me in completion of this

project.

I would express my special gratitude and thanks to my Mr Pawan Kumar Bansal sir for

giving me such attention and time.

My thanks and appreciations also go to my colleagues and Friends in developing the Term

Paper and people who have willingly helped me out with their abilities.

Bibliography

Books

Nikhil Koratkar; Graphene in Composite Materials: Synthesis, Characterization

and Applications

C. N. R. Rao, Ajay K. Sood; Graphene: Synthesis, Properties, and Phenomena.

On-Line Resources

www.graphene-info.com

www.google.com

www.aspbs.com

www.graphene.manchester.ac.uk

www.telegraph.co.uk

Research Papers

A. K. Geim; GRAPHENE: STATUS AND PROSPECTS

Manchester Centre for Mesoscience and Nanotechnology, University of Manchester,

Oxford Road M13 9PL, Manchester UK.

HUI Pak Ming; An Introduction to Graphene and the 2010 Nobel Physics, Chinese

University of Hong Kong.

Contents

1. Graphene - What It Is?

2. Properties of Graphene

3. Graphene & Graphite - How Do They Compare??

4. Creating or Isolating Graphene

5. Graphene Applications & Uses

6. Composite Materials

7. Graphene Supercapacitors - What Are They?

8. Creating Graphene via Chemical Vapour Deposition.

9. Reduced Graphene Oxide - What Is It? How Is It Created?

10. The Price of Graphene

11. Future Trends in Graphene.

Appendix

FIG. 1 Structure of single layered one atomic graphene material.

FIG. 2 showing top and side view of graphene structure.

FIG. 3 Inventors of magical material “Graphene”.

FIG. 4 Graphene’s conducting property.

FIG. 5 Ultracapacitors made out of graphene.

FIG. 6 Conductive ink a product of graphene.

FIG. 7 Mechanical strength of graphene in comparison to other materials.

FIG. 8 Different fermions made from graphene.

FIG. 9 Graphite materials.

FIG. 10 Structure of graphite.

FIG. 11 Graphene made thin and transparent screen.

FIG. 12 Graphene substrate.

FIG. 13 Zero band gap in graphene.

FIG. 14 Isolation or preparation of graphene.

FIG. 15 Different applications of graphene.

FIG. 16 Use of graphene in OLEDS (organic light emitting diode).

FIG. 17 Water filtration techniques from graphene, separating out Co2.

FIG. 18 Removing Cr from water by passing it through graphene.

FIG. 19 Battery made from graphene.

FIG. 20 Graphene based Super-capacitors.

FIG. 21 Classification of Super-capacitors.

FIG. 22 Capacitor v/s Super-capacitors v/s Battery.

FIG. 23 Super-capacitors better than battery.

FIG. 24 Compressible Super-capacitor made from Graphene.

FIG. 25 Use of graphene super-capacitors in car’s battery.

FIG. 26 Graphene Supercapacitor being used in mobile.

FIG. 27 CVD (chemical vapour techniques) to produce graphene.

FIG. 28 Graphene being prepared from CVD.

FIG. 29 Reduced graphene oxide.

FIG. 30 Reduced graphene oxide produced from graphene oxide.

FIG. 31 Graph showing graphene’s price change.

FIG. 32 Graph showing lowering of graphene’s price with technology.

FIG. 33 Flexible screens made from graphene.

FIG. 34 Graphene being used in Terahertz electronics.

FIG. 35 Sensors made from graphene.

CONCLUSION

Graphene has rapidly changed its status from being an unexpected and sometimes

unwelcome newcomer to a rising star and to a reigning champion. The professional

scepticism that initially dominated the attitude of many researchers (including myself) with

respect to graphene applications is gradually evaporating under the pressure of recent

Developments. Still, it is the wealth of new physics – observed, expected and hoped for –

which is driving the area form the moment.

Research on graphene’s 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 as a truly unique item in them arsenal of condensed

matter physics. Research on graphene’s non-electronic properties is just gearing up, and this

should bring up new phenomena that can hopefully prove equally fascinating and sustain, if

not expand, the graphene boom.