1

Table 1 – The table shows a list of functionalities that can be added to a

graphene lattice, to modify its properties.

Deposition and Analysis of Graphene Thin Films

Andy Skippins

Systems and Process Engineering Centre

College of Engineering

Swansea University

Swansea UK

711472@swan.ac.uk

I. ABSTRACT

Graphene is considered to be the wonder-material of the 21st

century. The study set out to investigate how graphene can be

produced and implemented, using current technologies and

processes. Three alternative deposition techniques to the harsh

and expensive chemical vapour deposition (CVD) technique

were investigated, including drop-cast, Langmuir Schaefer and

scattered graphene nano-platelets.The films will be analysed,

using a Scanning Electron Microscope (SEM) and a Surface

Enhanced Ellipsometric Cross-polarised microscope (SEEC).

Further studies were performed, using DigitalSurf

MountainsMap surface analysis software.

Each of the processes had their advantages and

disadvantages. However, the drop-cast technique produced the

highest quality, and thinnest film. The film quality was almost

comparable with CVD graphene, which is much more expensive,

and limited by its harsh processing temperature. The Langmuir

Schaefer method did not provide more control over film

thickness, although polymer (TPQPOH) and salt (NaCl) crystals

formed on the surface, potentially compromising its properties.

The scattered GNPs formed the poorest quality film/layer, with

heavy agglomeration on some parts of the substrate, and

nothing on others.

II. INTRODUCTION

Despite possessing a variety of superior properties, graphene has yet to be exploited on a significant scale. Since its discovery, by Novoselov and Geim [1], more than a decade ago, a considerable amount of research has been performed, providing not only theoretical research papers, but patents with practical applications to industry. Currently, the most popular technique for synthesis or deposition of graphene is chemical vapour deposition (CVD). This requires the substrate to be heated to 1000ºC, under ultra-high vacuum (usually in the order of 10µPa) [2]. This is a very harsh and expensive process, thus complicating the manufacture, and impeding the development and commercialisation of graphene’s many applications. Currently, most graphene is used for research, so quality takes priority over cost. Conversely, any commercial applications will need to compete with products already available on the market, and will be subject to very rigid cost restrictions. Most substrates, including polymers, organic materials, or any kind of complex structure would deform well before reaching the temperature required for

CVD. It has therefore been established that the material is in desperate need of a cheaper, gentler deposition technique. The purpose of the investigation is to explore alternative deposition techniques, such as basic scattering, drop-casting and the Langmuir-Schaefer. The report will also discuss the wide range of applications for graphene, and their suggested deposition techniques. Graphene has many possible applications in different industries, has the most potetntial for impact, when used in supercapacitors, biosensors (due to its high surface area) and integrated circuits (for its electronic properties).

A. Functionalities

Graphene will interact with these molecules differently,

sometimes temporarily, sometimes permanently. Specific

applications will be discussed later on in the paper. In order

to modify the properties of graphene, for instance make it

more stable, or interact/behave in a specific way, graphene

must be functionalized with atoms or molecules, including

oxygen, nitrogen and hydrogen. This often happens during

the fabrication process, with the corresponding

atoms/molecules present in the chamber/ solution.

In general, smaller structures, such as nano-ribbons or

nano-platelets will only exhibit these additional molecules

on the edge of the surface, where there are unsatisfied

(dangling) bonds. Larger surfaces would have more space,

inside from the edge, for molecules to attach.

Oxygen [3] Nitrogen

Carboxyl - COOH, Nx

Hydroxyl - COH NO2

Ketone - C=O NH3 - Amonia

Ether - C2O N=H

Sulfur [4] C ≡N

Boron NOx

Bio-molecules O=C-NH2

Antibodies Silver

Smell receptors Fluorine

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B. Statistics

According to national as well as global statistics [5],

graphene is rapidly becoming more and more prominent, as

technological knowledge and manufacturing processes

develop.

Research has been funded by corporations and academic

institutions alike. In the UK, the Universities are leading

the way, in terms of patent applications. The top 3

applicants are universities, with a total of 25 between them.

As of 2014, there are 13,355 patent families (inventions)

relating to graphene. This is evidence of the many practical

uses for graphene that just need final developments before

commercialisation. If predictions that graphene will follow

the path of other revolutionary materials, such as carbon

fibre, silicon, polyethylene, etc. are correct, then it will

reach the consumer markets very soon.

III. METHODS

There are several manufacturing/deposition techniques for

graphene, with a cost-quality tradeoff. Hence, the

manufacturing process would be chosen to correspond to a

specific application. For instance, it would be

deposited/transferred to a SiO2 substrate, as an integrated

circuit, because a monolayer can easily tear, without

additional support or functionality. Current fabrication

processes are not capable of producing large isolated films,

and some of the more advanced applications are

impractical. However, there are many, forms of graphene

and processes that are not only achievable, but competitive

with existing materials.

A. Manufacturing Graphene

There are a variety of different techniques for production of

graphene, with advantages and disadvantages for each.

These are:

1) Mechanical Exfoliation

In this case, by dissecting graphite, using scotch tape. The

tape was placed on a crystal of graphite, then pulled off (at

least twice), to remove impurities from the surface.

A new piece of tape was placed onto the clean surface, and

pulled off, with a layer of graphite attached. This layer was

then repeatedly halved by sticking it to a clean piece of

tape, and pealing it off, until the thickness was eventually

reduced to a single layer.

This is a relatively simple and cheap technique, and does

not require expensive equipment. However, it cannot be

implemented on a large scale production line.

2) Plasma

Two key manufacturers of GNPs (graphene nano-platelets),

Perpetuus Advanced Materials and Haydale Ltd both

operate in Ammanford, West Wales, using plasma.

In this method, graphite powder is turned inside a chamber

(like a cement mixer), containing electrodes, that point

towards the centre. As the chamber rotates, and graphite

particles drop from the upper electrode to the bottom, an

arc forms. The plasma between the suspended particles

causes the layers in the graphite to build up charge and

energy, so that they separate (Hall effect [6]). The high

electric current flowing between the particles causes them

to join together, laterally in order to reduce resistance.

3) Liquid-phase-exfoliation

Graphite particles may be dispersed in a solvent, such as

methanol, or acetone. The solvent would then be sonicated

(vibrated at high frequency), to break down the graphite

into single layers, known as graphene.

Vacuum filtration and transfer process

Using mixed cellulose membranes (pore size 220nm), thin

films with a diameter of around 40mm, were vacuum

filtered. The films were then punched into small circles,

and transposed onto glass slides, before dissolving the filter

Fig.3. Plasma process

Fig.1. – Distribution of patent families (inventions) made by the top 10

organisations in the UK [5].

Fig.2. Patent applications and granted patents by first publication date [34]. The inset shows a more detailed view.

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membrane in acetone. The electrical and optical properties

of the circular thin films were then measured. [6]

B. Deposition

Once the GNPs have formed, for instance by plasma or

liquid-phase exfoliation, they need to be deposited onto a

substrate.

a) Chemical Vapour Deposition (CVD)

The most popular method of production is CVD [2], which

is capable of producing very high quality films. However, it

uses very expensive equipment, at extreme temperature

(~1000ºC). This makes it unsuitable for many applications,

because the intense heat would destroy/damage the

substrate.

Silicon is already suitable, due to the high purity, pristine

surface quality and good temperature performance that can

be achieved. Depending on application, the substrate could

also be made from ceramics (e.g. SiO2, quartz, etc), due to

their insulating properties, or metals for conducting (e.g.

copper, gold, etc). However, organic materials among many

other complex structures would be severely damaged or

even burnt/melted. Therefore, if this technique was to be

implemented, it would have to occur at the beginning of the

production process. Once deposited, the film can actually

be wet transferred from a copper foil, onto a (polymer)

substrate. However, this is not a practical solution, likely to

be used on a large scale, as it is very difficult to align the

substrate accurately.

CVD is also too expensive for many of its applications to

reach consumer markets.

2) Experimental

The following alternatives to CVD have been investigated:

‘Scattering’, drop-casting and Langmuir Schaefer.

a) Scattering

Depositing the film of GNPs, using the ‘scattering’

technique, proved much more straightforward than

expected. The powder was scattered onto the substrate, so

that the entire surface was covered. Excess powder was

then blown away, using compressed air. This left a very

thin layer of GNPs, most of which was invisible to the

human eye.

b) Drop-Casting

This process has successfully deposited high electron

mobility polymer thin-film transistors [7], so the transition

to graphene as a new material should be straightforward.

The Graphene was dissolved in methanol, with

concentrations of: 0.005, 0.05, and 0.5 mg/l. The solution

was then dripped (5µl) onto SEEC slides, and left to dry.

Once the methanol had evaporated, a layer of graphene was

left behind.

The solution of the best looking film (0.05mg/ml) was then

mixed with 0.01% TPQPOH (polymeric ionomer alkaline),

and drop casted onto a SEEC slide, for comparison with the

Langmuir Schaefer film.

c) Langmuir Schaefer Approach

This technique is capable of very accurately controlled

deposition of a film [8]. Required specialist Langmuir

trough (KSV Nima by Biolin Scientific), with surface

pressure gauge.

Before any deposition, the trough had to be cleaned, by

filling up with de-ionised water, then draining it and wiping

with ethanol.

A solution of 0.1 M sodium chloride (5.844g in 1L of de-

ionised water) was mixed and poured into the trough. This

formed a continuous convex meniscus around the edge.

Once a suitable concentration of graphene had been

selected, from the drop-casting experiment explained

above, the 0.05mg/ml solution was mixed with 0.025%

(v:v) and 0.01% (v:v) TPQPOH in methanol. This solution

was dripped evenly across the surface, in volumes of 400µl

and 800µl, using a syringe.

In order to find a target pressure, an isotherm experiment

was performed, for each concentration and volume. The

barriers were closed, at a rate of 15mm per minute.

Meanwhile, a paper tab hanging from a scale measured and

recorded the surface pressure.

Fig.5. - SEEC slide (a) with Langmuir Schaefer thin film (1 layer),

from 0.5mg/ml GNPs and 0.01% TPQPOH solution, (b) with drop

cast film, from 0.5mg/ml GNPs and 0.01% TPQPOH solution (c)

with drop cast film, from 0.5mg/ml GNPs (no TPQPOH) solution (d)

with drop cast film, from 0.5mg/ml GNPs (e) with drop cast film,

from 0.5mg/ml GNPs.

(b)

(a)

(e)

(d)

(c)

Fig.4. – Langmuir trough, NSV Nima, Biolin Scientific [36]

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The Langmuir Blodgett software, provided by KSV Nima,

produced a surface pressure against area (between the

barriers) graph. A target pressure was then chosen, where

the pressure was linearly proportional to area.

To deposit the film, the trough was cleaned again, and

filled up with 0.1M NaCl, before depositing the solution,

and closing the barriers to the corresponding target

pressure. The barriers stopped, when the surface pressure

reached the target pressure (of 25mN/mm in the case of

800µl 0.01% TPQPOH).

The SEEC slide was then lowered horizontally onto the

surface, and then peeled upwards, to deposit the graphene.

An alternative technique would be Langmuir Schaefer, or

better still, Langmuir Blodgett. The difference is that the

substrate is dipped vertically, instead of horizontal,

allowing for a much larger substrate. This is therefore,

more suited to larger scale production, and is more likely to

be commercialised.

3) Analyses

a) SEEC Microscope

Apparatus used: Nanolane Sarfus High Resolution Surface

Enhanced Ellipsometric Cross-polarised (SEEC)

microscope.

A light shining on the sample (see Fig.7.), is transmitted

through the film, and reflected off the surface of a special

‘SEEC slide’. The microscope then measures the amount of

cross-polarisation of the light, as it passes through the film.

This enables the calculation of the film thickness, to a very

high degree of accuracy (±3 ångströms [9]).

For each set of samples, the microscope was calibrated,

using the calibration sample. The image was rendered from

topographical data, determined by the microscope.

For this experiment, GNPs were deposited onto the SEEC

slide in order to measure the thickness of the film. The

samples were then studied using a SEEC microscope, in

cross-polarised mode, using x10 and x50 lenses.

b) Scanning Electron Microscope

A Scanning Electron Microscope (SEM) studies a sample,

by scanning it with a beam of electrons as shown in Fig.8..

Interactions between electrons and atoms on the surface of

the sample are detected by the microscope, and indicate the

height at that specific point. SEMs can capture very high

resolution images, with depth and clarity.

For this experiment, GNPs were scattered onto a silicon

substrate, to analyse the particles at a molecular level. The

substrate was mounted onto the frame, and placed inside

the machine, before setting up the microscope. Once the

vacuum (11.2k) had been established and the lens focused

on the sample, the microscope captured a number of images

of the graphene.

IV. RESULTS AND DISCUSSION

A. Analysis of GNPs

The films have been studied using SEM and SEEC

microscopy, at the micro and macro scales, respectively.

1) Deposition

a) Scattering

The scattering deposition technique was somewhat

unsuccessful, because of the agglomeration of GNPs.

Heavy agglomeration can be observed from Fig.9.(a) The

quality of the film was poor, and would better be classified

as a layer of GNPs, rather than a film.

Fig.7. Schematic of SEEC microscope operation [9]

Fig.6. Schematic of Langmuir Schaefer and Langmuir Blodgett

Deposition [35]

Fig.8. Schematic of Scanning Electron Microscope operation [40]

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b) Drop-Cast

Once the methanol had evaporated off the SEEC slides, a

residual film was left on the surface, with a slightly

different colour to the original slide. Nevertheless, the film

was much smoother, and more homogenous than that

produced by the scattering technique. Dispersing graphene

in a solvent also provides more control over the film

thickness, by changing the concentration of graphene

(mg/ml).

c) Langmuir-Schaefer

Many of the isotherm experiments with just GNPs proved

unsuccessful. The surface pressure did not adequately, with

respect to area. This was unexpected, as in previous

experiments with TPQPOH and Nafion, a steady and

substantial pressure build up may be observed. This

suggested that despite being hydrophobic, the GNPs did not

seem to float on the surface, of the water. However, adding

a small amount of TPQPOH to the solution provided the

platelets with additional buoyancy, making them float on

the surface.

2) SEEC Microscope

Heavy agglomeration was observed in the scattered GNP

layer; this technique produced a non-homogenous layer.

Fig.9.(a) shows that the particles are not dispersed on the

surface, rather they have clumped together. This made it

very difficult for the microscope to focus on the entire

sample, particularly with the x50 lens. The most likely

cause for the agglomeration of the particles on the surface

is due to the very basic deposition method.

In the drop-cast sample from the higher concentration

solution had some agglomeration of GNPs, and less in the

lower concentration.

It can be seen from Fig.9.(d), that salt (NaCl) and polymer

(TPQPOH) crystals formed on the surface of the Langmuir

Schaefer film. These may compromise the performance of

the film.

3) Electron Microscope

A sample of scattered GNPs was studied, using an SEM. It

was observed that the platelets had agglomerated together,

so that parts of the silicon substrate were bare, and parts

were speckled.

4) MountainsMap

Further studies of the films were performed, using

DigitalSurf MountainsMap surface analysis software.

Images from the SEM were converted to surfaces, using the

colours to determine thickness. However, the SEEC images

were converted more accurately, using the topographical

data, as a pre-determined thickness.

It was observed that the average film thickness for the

drop-cast sample (from 5µl) was 12.2nm, and the Langmuir

Schaefer film was 18.3 with just 1 layer. This was an

unexpected result, because the LS technique was designed

to provide better control of film thickness.

Fig.9. – (a)Scattered GNPs. (b)Drop-cast film from 0.5mg/ml

solution of GNPs. Inset: non-homogenous region. (c)Drop-cast film from 0.05mg/ml (best) soln. (d)Langmuir Schaefer

film of GNPs with TPQPOH.

(a)

(d) (c)

(b)

Fig.12. Drop-cast GNP film with TPHPOH, rendered in

DigitalSurf MountainsMap surface analysis software.

Fig.11. – SEM image of agglomerated GNPs by scattering- Platelets are relatively large; 1-4µm in diameter, and up to

100nm thick.

-5

0

5

10

15

20

25

30

80100120140160180200

Su

rfa

ce P

ress

ure

(m

N/

m)

Surface Area (cm2)

Graphene (0.05mg/ml)

Graphene (0.005mg/ml)

Graphene (0.05mg/ml) + TPQPOH

Fig.10. Isotherm data for 800µl of various Graphene solutions dripped onto Langmuir Trough.

6

B. Defects

A defect is an irregularity in the lattice structure. These

could come from any of the fabrication processes, or even

the atmosphere or radiation [10]. This is fundamentally a

limiting factor for graphene, and its performance [11].

According to Rao [11], a variety of defects can occur in

graphene, which include adatoms, vacancies, point defects,

line defects, and edge defects. Defects can also form, due to

the absorption of ultra-violet photons, as they cause

graphene to oxidise [10].

Because graphene is a 2-D material, the occurrence of

defects has a much more significant effect on the electronic

and structural properties of the film.

1) Adatoms

A surplus or deficit of electrons in the atom’s outer shell is

the most common cause of defect. This could be due to a

contaminant molecule, donating or accepting the electron,

which would otherwise bond the carbon atoms together.

2) Impurities

Due to the extremely high surface area to volume ratio,

graphene is likely to attract impurities which would

compromise the performance of the material. Therefore, it

is crucial that it is kept in an environment free from

potential impurities. Functionalities may also be added,

which can repel additional impurities, although this is not

100% effective. Specific atoms are often added

deliberately, to enhance the properties, or simply make it

more stable.

3) Functionalities

Graphene is usually doped with other atoms/molecules,

such as oxygen, carbon or nitrogen groups, to improve the

functionality and properties of the material. These may

disrupt the lattice structure, creating a vacancy, or

donate/accept electrons, to satisfy the bond.

4) Geometry

The conductivity of a graphene sheet depends on its

orientation. For nano-platelets, the orientation would be

random, so bulk conductivity will be an average. However,

this is critical for mono-layers that rely on conduction, such

as sensors, transistors or electrodes.

Electrons flowing in the armchair direction (shown in red)

will have to travel further than the zigzag direction (yellow

arrows). Consequently, in the armchair direction, it

exhibits semiconductor properties, but metallic, in the

zigzag. Any vector between armchair and zigzag will be a

combination of each, maintaining the same aspect ratio.

C. Current Applications

1) Ink

Graphene enabled ink is derived from the drop cast method.

Perpetuus Carbon, in a joint venture with Gwent Electronic

Materials, who are operating under the name Perpetuus

Electronic Materials have developed an electrically

conductive ink, containing GNPs.

The ink has a low resistance of less than 1Ω/, which is the

best conductivity achieved by any graphene enabled ink in

the world. [12] This ink can provide a new approach to

PCB (printed circuit board) manufacture, as it is so much

easier to apply to the circuit.

The ink can be printed via ink jet or flexographic printing,

making it much cheaper and more convenient than

traditional PCB manufacture. An additional benefit is that it

can be printed on a flexible substrate, without

compromising the performance.

Circuits like RFID (Radio Frequency Identification) tags

could potentially benefit from graphene enabled inks, due

to significantly reduced cost [13]. However, the ink does

have a higher resistivity than copper, so performance and

range would be compromised.

The ink is also becoming a popular demonstration/learning

tool, allowing children to draw circuits, and even sensors

[14].

2) Transparent Electrode

GNPs may also be added to a transparent, flexible polymer

(Polyethylene terephthalate [4]), allowing it to conduct

electricity. This enhanced polymer has the potential to

replace indium tin oxide (ITO) [12], which is very rare, and

expensive to produce. A thin film can be applied to the

surface of a solar panel or various display screens, such as

OLED, LCD, electroluminescent, electro-chromatic and

plasma.

The two key characteristics are transparency and

conductivity, are difficult to find in the same material.

However, these properties are essential for the top surface

of a solar-panel, so that electrons can be transported away

from the re-generation site, and more can be promoted to

the conduction band. Transparency is also important, to

minimise reflection of photons off the surface, when used

in a bright environment.

Fig.13. Lattice geometry.

a

z

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Transparency is also important to allow the user to view the

image on screen.

The powder-coating or scattering techniques would not be

suitable for this application, because the layer is not

transparent, and would absorb many of the photons passing

through. Drop casting would produce a much more

transparent film, however, achieving an even coating across

the surface may be difficult. Modifications to the technique

would be required, such as spin-coating, where the

substrate is rotated very quickly, allowing centrifugal force

to spread the film evenly across the surface. Langmuir

Blodgett may also be feasible.

Wuxi Graphene Film Co. Ltd [15], and Gwent Electronic

Materials [12], have proven that the technology is readily

available. At the end of 2013, Wuxi Graphene finished a

“demonstration production line, with a projected annual

output of 5million pieces of graphene touchscreen

products”.

1) Electromagnetic Induction (EMI) sheilding

As an additive to various polymers [16], the electrical

conductivity of GNPs can protect sensitive circuits and

instruments from noise that would otherwise interfere with

signals passing through the circuit.

2) Strength Enhancing Additive

GNPs can be added to polymers, such as epoxy resin, to

improve its tensile strength, as well as toughness.

According to Kuilla [19], glass transition temperature, and

consequently tensile strength and toughness were

improved, with increasing concentrations of GNPs.

Improvements of 125% and 100% for tensile strength and

roughness were observed, respectively. The toughened

epoxy could then be used as a matrix for many composites,

with improved performance. The GNPs would be

manufactured by the plasma process. This application does

not require deposition; the GNPs are added directly to the

epoxy, before it is combined with the fibres.

3) Sensors

A graphene nanoribbon can be used to detect certain

molecules in the air, with a very high sensitivity. When a

molecule attaches to the graphene, the chemical reaction

releases or consumes an electron. Graphene is naturally p-

type, so a donor atom would decrease, and an acceptor

atom would or increase the conductivity, however, this can

be reversed in the presence of functional groups. Gases

such as ammonia (NH3) will donate an electron, and

nitrogen-dioxide (NO2) will accept an electron. On a

graphene nanoribbon, the graphene is sensitive enough, to

detect just one molecule.

These gases only interact temporarily via non-covalent

interactions with graphene, so when the concentration

drops, the molecules will detach, returning the graphene

nanoribbon to its normal state. This allows the

concentration to be continuously monitored.

In general, the surrounding device would be made in a

semiconductor fabrication facility, which would already

have a CVD chamber. The production line should be

engineered, so that any elements on the substrate, that are

sensitive to heat, are added after the CVD process.

In most cases, the key to fighting disease is early detection,

and graphene biosensors are capable of just that. A

graphene nanoribbon can be functionalised with biological

ligands enabling it to detect disease biomarkers [17].

Diseases, such as cancer, diabetes, HIV, etc can be

identified much earlier on, before the more severe

symptoms have taken effect, and caused damage. These

sensors will respond to just one molecule, and are therefore

much more sensitive, allowing diagnosis, before it is too

late. This also means that the tests can be non-invasive, i.e.

from a urine or saliva sample, and results are almost

immediate, so patients don’t have to wait days for

feedback.

When a biomarker interacts with a receptor, it transfers

electrons into or from the graphene, increasing or reducing

its conductivity [18].

The sensors are very small, so in the future, more different

diseases could be tested at once, from just one panel, by an

amateur with limited medical knowledge.

DNA can also be detected with this method, using a

matching DNA strand. This would be useful in forensics,

where only a very minute sample is available.

The concept of using organic ligands for detection has

already been proven successful in the GE Healthcare

BiacoreTM

Surface Plasmon Resonance (SPR) detector, [19]

which is capable of good sensitivity and selectivity. Using

graphene biosensors, however, is a much better alternative,

because it does not require expensive equipment; the

technology is on the device itself. Graphene also has the

advantage of being able to test for many different analytes

at once.

4) Photodetector

Although graphene is visually transparent, it interacts

strongly with photons anywhere between the microwave

and ultraviolet wavelengths. This means that graphene

photodetectors could span wavelengths of at least 5 orders

of magnitude. The enormous bandwidth would therefore,

provide an exceptional data-rate. According to Xia et al,

speeds of 10Gbit/s have been achieved [20].

5) Hydrogen Storage

Graphene, functionalised with hexagonal boron nitride

platelets can be stacked, to form very low density foam.

Hydrogen atoms experience weak interactions with the

graphene foam, so the extremely high surface area allows a

Fig.14.-Voltage-Current graph [18], comparing the sensor, when 80HdG

is present (green) and not present (red).

8

large quantity of hydrogen to be stored in the container, at

lower pressure. This makes the container safer, as it is less

likely to explode, and if it does the hydrogen will take

longer to expand [21].

Hydrogen has a very high energy density, and can be used

in fuel cells, which can efficiently transfer chemical energy

to electrical, before being refilled with hydrogen.

Currently, graphene foam is produced by CVD, but it is

possible that other techniques will be developed in the

future. The foam can be placed inside the container, once it

has cooled down, so heat exposure in this process would

not be a problem.

6) Contaminant Removal

Graphene is capable of removing some metals, including

radioactive nuclides from water [22], in particular,

radioactive isotopes of actinides (such as uranium,

plutonium and americium) [23] and lanthanides (‘rare

earths’ such as europium).

This would be very useful, in the clean-up after a nuclear

disaster, as the nuclides are very harmful to the

environment, for decades afterwards. Radionuclides are

also released in fracking and mining operations.

Again, graphene foam, produced by CVD would be used,

then removed from the substrate; i.e. no limitations due to

temperature exposure.

D. Future Applications

There is a lot of potential for development of graphene

applications that are in earlier stages of development

1) Integrated Circuits

A potential application for the film made by drop-casting or

Langmuir Schaefer (or similar) could be transistors.

Typically, transistors are made from silicon, which is in

many ways very suitable for integrated circuits. According

to Moore’s law, [24] “the number of transistors on an

affordable CPU will double every two years”. This

statement has been true for the past four and a half decades,

but the rate has begun to saturate. At around 14nm for

FinFETs [25] the gate length has reached its practical

minimum, due to a number of factors. Smaller devices have

been made, but their performance is inferior.

In order to continue improving the performance of

processors, new technologies and materials will require

development.

According to Murali [26], Graphene has an electron

mobility of µ=10,000cm/Vs, 10 times higher than that of

Si. This is caused by the conservation of pseudo-spin, i.e.

backscattering is forbidden. Therefore, it is effectively a

quantum well, and scattering is reduced to two dimensions.

This increases the switching rate for the device, and

consequently, the processor speed.

Using graphene nanoribbons for the channel, as well as

(carbon nanotubes) for inter-connects, between devices, the

chip performance and functionality can be significantly

improved.

Although not yet in mass production, Lin et al. [27], have

demonstrated the concept of an analogue fully integrated

circuit in the form of an RF mixer (radio-frequency

transmitter). The performance of this prototype was

degraded, due to the harsh fabrication process. Further

developments of the process allowed the production of a

more sophisticated IC, capable of sending a text message.

Thus, graphene has the potential to tackle some of the

issues faced by the semiconductor industry.

Due to its zero band-gap and high production cost (for the

quality required), transistors are not a currently viable

application for graphene.

2) Energy Storage

a) Li-ion batteries

Lithium-ion batteries already use graphite anodes, so the

transition to graphene should be relatively straightforward.

According to Zhao, et al [28], the capacity, as well as

charging rate, have both been improved by a factor of 10,

using graphene anodes instead of graphite (conventional

material). This is due to the extremely high surface area,

provided by graphene, which the ions can interact with.

Millions of holes (ϕ10-20nm) were punched into each layer

of graphene, to allow more direct access to the layers

below.

At Rice University, [21] hydrogen enriched graphene oxide

has been proven to be an effective anode in lithium-ion

batteries The addition of boron atoms helps the lithium-ions

to ‘stick’ to the graphene, allowing energy to be stored

more efficiently.

b) Supercapacitors

Graphene also has potential applications for

supercapacitors, which are made from cheaper materials

and can charge/discharge quicker and more efficiently. A

supercapacitor is essentially, two conductive plates,

separated by a dielectric. Between the plates are

electrolytes, suspended in (graphene) foam. As the charge

across the plates builds up, the electrolytes move to the

negative plate, allowing the supercapacitor to store energy.

Supercapacitors also have the benefit of high cycle

stability, which means they can last much longer than

batteries. The porous coating, which is usually activated

carbon that supports the electrolytes, may easily be

replaced by graphene.

The energy capacity of the supercapacitors is proportional

to the area of the conductor-dielectric interface [29]. This

can be optimised by using graphene, as it has much more

surface area per unit weight (1520m2/g) [30] than any other

material.

Although the current method of producing this kind of

graphene is CVD, it is possible to scribe the graphene oxide

layer into a suitable graphene film, using a standard

LightScribe DVD optical drive [32].

It has been estimated that using graphene technology, a

storage capacity of 550F/g is achievable, compared with a

standard 1 Farad capacitor weighing around 2kg.

Supercapacitors are already being used in the automotive

industry, to recapture energy, while breaking, so that it can

be re-used.

3) Filtering Membrane

A graphene membrane can act as an excellent filter,

preventing any molecules from passing through. This

includes helium, which is known for its ability to pass

through the smallest pores in a material.

In particular, this property would be useful, in the

distillation process, allowing water to evaporate off,

9

condensing the target substance (e.g. ethanol) back into the

container.

E. Health and Safety Concerns

As with any new material, there are concerns about the

health and safety implications of graphene.

For example, Carbon nanotubes (CNT) breakdown into

particles that can enter organic cells, damaging DNA.

CNTs have been classified as hazardous carcinogens,

capable of causing cancer [31].

Thankfully, graphene does not behave in the same way; it

can (usually) be broken down, and does not affect

biological processes. However, all nanomaterials should be

treated with caution [31].

V. CONCLUSIONS

It has been confirmed that graphene has a tremendous

amount of potential, with many different applications

across various industries. Some of which may take longer

to materialise, due to complications in graphene synthesis.

The transition from laboratory testing to commercial

manufacturing has proven challenging for many products

and companies working on the material. However, there are

simpler, (easier, cheaper, etc.) methods for deposition,

which are also less damaging to the substrate. Although the

films produced in the experiments were of poorer quality

than CVD (chemical vapour deposition), they are still in

very early stages of development. It is more than likely that

further developments will make these techniques capable of

surface qualities comparable with CVD films.

It was concluded that drop-casting was the overall most

effective alternative to chemical vapour deposition.

However, each of the deposition techniques, have

advantages and disadvantages, so their selection will

depend on the specific application.

1) Scattering deposition

The scattering technique is the most basic, and

consequently the cheapest, easiest, quickest, etc. However,

the film quality is poor, and would be unsuitable for most

applications.

2) Drop-Cast deposition

Drop-casting produces a much more homogenous film

(Fig.9.(b) and (c) compared with (a)), and is more

straightforward than Langmuir Schaefer. The solution can

be mixed with other chemicals, to modify the properties of

the film. The thickness of the film can also be controlled,

by changing the concentration of the solution. Both the

drop-cast, and Langmuir Schaefer processes could use

graphene dispersions, produced directly from liquid-phase

exfoliation of graphite. This would omit a large process

from manufacturing, thus reducing the cost.

3) Langmuir-Schaefer deposition

The additive used to make the GNPs float could affect the

material properties, (e.g. conductivity), thus making it

unsuitable for some applications.

The Langmuir Schaefer technique enabled more control of

the film thickness, by choosing the number of dips/layers.

Therefore, a thin film was expected on the 1 layer LS

sample. However, the average film thickness was 18.2nm;

4nm thicker than the drop-cast samples. This is most likely

due to the complexity of the experiment. There were many

variables, which have yet to be optimised, so perhaps

further developments will enable the synthesis of a thinner,

better quality film.

B. Future Recommendations

Suppose that the subphase (NaCl solution in the

experiment) can be developed, that will evaporate, leaving

no residue. This could permit the synthesis of pristine

graphene, on a much wider range of substrates, with any

number of layers.

Further developments should be made on the additive used

to float the GNPs on the surface of the Langmuir trough.

For instance, perhaps a new functionality, added during the

manufacturing of the GNPs, that forms a gap in the

graphene-water interface. Although the TPQPOH was

effective in this task, it is by no means the most effective

solution; incorporating it into the manufacturing process

could potentially help.

If the scatter technique was chosen for a manufacturing

process, it would have to be modified, for scalability, and to

ensure an even coating of the GNPs. Potentially, it could be

applied by electrostatic powder coating [32]. The particles

and substrate would be charged, with opposite polarity,

causing the particles to repel eachother (ensuring even

density), but attach to the substrate. Charging the substrate

would require it to be somewhat conductive. This technique

is widely used to produce a very robust layer, protecting the

material underneath.

Drop casting is already capable of depositing a good quality

film, without limitations of substrate material or cost, so

there is little room for improvement. Nevertheless, there are

some additives that could improve the film characteristics,

and these should be explored, in order to optimise

performance for a more specific application.

Further analysis of the films should also be performed, to

verify the results of the experiments. These would include

Raman spectroscopy, which is a better indication of film

quality.

Although the films were compared with CVD samples

found online [4], they should be studied using the same

apparatus, and the same techniques, to ensure a fair

comparison.

VI. ACKNOWLEDGEMENTS

Dr Paolo Bertoncello & Dr Thierry Maffeis, Swansea

University

Dr Afshin Tarat & Dylan Walters, Perpetuus Advanced

Materials

10

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