OPTICAL CHARACTERIZATION OF GRAPHENE AND GRAPHENE OXIDE

A Mini Project Report Submitted in Partial Fulfillment of the Requirement of the Degree of

BACHELOR OF TECHNOLOGY

In

ELECTRONICS AND COMMUNICATION ENGINEERING

by

PRADUMN KUMAR - 20130442

SAMA KAVYA SHREE REDDY - 20130432

Under the guidance of

Mr.Himangshu Pal

Assistant Professor

SMIT

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

SIKKIM MANIPAL INSTITUTE OF TECHNOLOGYMAJITAR, EAST SIKKIM-737136, DECEMBER 2016.

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CERTIFICATE

This is to certify that the project report entitled “Optical characterization of graphene and graphene

oxide” submitted by Pradumn Kumar(20130442) and Sama Kavyashree Reddy (20130432) to Sikkim

Manipal Institute Of Technology, Sikkim in partial fulfillment for the award of degree of Bachelor of

Technology in Electronics And Communication Engineering, is a bonafide record of the project work

carried out by him under my guidance and supervision during the academic session August–

December, 2016.

Himangshu Pal Prof. (Dr.) R. Bera

Assistant Professor H.O.D

Dept. Of Electronics & Communication Dept. Of Electronics & Communication

Sikkim Manipal Institute of Technology Sikkim Manipal Institute of Technology

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ABSTRACT

Recently, much attention has turned to the structural and optical properties of carbon based materials.

At present, especially, graphene is the hottest topics in condensed-matter physics and materials science.

The aim of this research is to develop optical properties of Graphene oxide. A simple analysis is

performed for the optical properties of graphene.

UV-VIS is used for the measurement of the optical properties of graphene powder, graphene oxide,

reduced graphene oxide and thermally exfoliated graphene. The optical properties include the

transmittance, absorption and band gap energy.

The Optical properties are studied and depending upon the characterization their possible applications

are then stated.

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ACKNOWLEDGEMENTWe would like to express our sincere gratitude and appreciation to our supervisor Prof. (Dr.)

R. Bera, Head, Department of Electronics & Communication Engineering, Sikkim Manipal

Institute of Technology, for guiding us throughout our research technically and

methodologically.

We would like to express our sincere gratitude to Brig (Dr) S.N. Mishra, Vice Chancellor,

Sikkim Manipal University, Col. (Dr.) Sadasivan Thekkey Veetil (Retd.), Director, Sikkim

Manipal Institute of Technology, Prof. (Dr.) M.K. Ghosh, Dean (Academics), Sikkim Manipal

Institute of Technology and Prof. (DR.) AJOY Kumar Ray, Dean (R&D), Sikkim Manipal

Institute of Technology for constant encouragement and motivation.

We would like to thank our project guide Mr. Himangshu Pal Sir (Asst. prof.) for his constant

support throughout the project work. We would also like to thank all the scientists, teaching

and non-teaching staffs of E&C Engg. Department, Sikkim Manipal Institute of Technology,

for providing enormous support to carry out our research works. We would also like to thank

all our colleagues of Sikkim Manipal Institute of Technology, for providing their support in

various manners during this research work.

Last but not the least, we would like to thank our family for supporting us constantly during

our research work.

Sama Kavyashree Reddy (20130432) Pradumn kumar (20130442)Department of E&C Engineering, SMIT. Department of E&C Engineering, SMIT.

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List of Figures

1. UV-Vis 1800 10

2. Cuvette 11

3. Ultrasonic Bath 13

4. Analytical Balance 15

5. Digital Hotplate 16

6. Table 1 25

7. Table 2 26

8. Table 3 29

9. Graph of Graphite powder(absorption,transmittance,energy) 30

10. Graph of Graphene Oxide(absorption,transmittance,energy) 31

11. Graph of Reduced Graphene Oxide(absorption,transmittance,energy) 32

12. Graph of Thermally Exfoliated Graphene(absorption,transmittance,

energy) 33

13. UV Spectrum 36

14. Comparative graph of Absorption 38

15. Comparative graph of Transmittance 39

16. Comparative graph of Energy 40

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Page No

List of Abbreviations

1. UV VIS - Ultraviolet visible

2. FET - Field effect transistor

3. OLED - Organic light emitting diode

4. HOMO - Highest occupied molecular orbital

5. LUMO - Lowest unoccupied molecular orbital

6. GO - Graphene Oxide

7. RGO - Reduced Graphene Oxide

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Motivation

The world today needs a revolutionary material that has the capability of handling the

demands of the future generation. But, the evolution towards such futuristic devices seems to

have come to a stand-still waiting for that ‘amazing all-round material’. Graphene, as of now,

seems to be leading in the race for hunt of such material. The graphene is breaking so many

records in terms of strength, electricity and heat conduction (as well as many others). But, we

currently know 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. So, let us explore just what makes graphene so special.

What are its optical properties that separate it from other forms of carbon, and other 2D

crystalline compounds?

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Table of Contents

Certificate 2

Abstract 3

Acknowledgement 4

List of figures 5

List of Abbreviations 6

Motivation 7

Chapter 1

Introduction and Basic aspects 10

1.1 UV-VIS Spectrometer 12

1.2 Cuvette 14

1.3 Ultrasonic bath 15

1.4 Analytical balance 16

1.5 Digital hotplate 17

1.6 De-ionized water 19

Chapter 2

Literature Review 20

2.1 Reviews on Graphene Oxide and Reduced Graphene Oxide 20

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2.2 Review on Properties of Graphene 22

Chapter 3

Optical properties 23

3.1 Absorption 24

3.2 Transmittance 28

3.3 Energy 29

Chapter 4

UV- Spectrum 36

Chapter 5

Results and Discussion 39

5.1 Future scope and applications 43

Chapter 6

Conclusion 45

References 46

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1. INTRODUCTION AND BASIC ASPECTS

Nowadays, in the development of new and efficient and optically active

materials, research is focused towards the synthesis of graphene and its composites.

But, at the same time, there is much less focus on the complex optical properties of

graphene . Graphene, a monolayer of carbon atoms packed into a dense, honeycomb

crystal structure, has shown attractive electronic and optical properties that could make

them useful in a variety of applications. These electrical and optical properties of

graphene show much promise for commercial applications in Nano electronic and

optoelectronic devices such as organic photovoltaic devices, ultrasensitive sensors and

ultra-capacitors, but perfect graphene itself does not exist. One of the most important

ways of studying graphene is through its optical properties in the UV-Vis region by

decorating its surface.

The bandgap within a graphene sheet could be opened by

reducing the dimensions of graphene to the Nano level or by introducing dopants . The

deposition of inorganic nanoparticles, such as metals or semiconductors, onto

graphene sheets would confer special features in new hybrids and be useful in optical

and electronic devices, catalysis, sensors, and so on. Optical properties exhibited by

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single materials are quite different from those of their composites and those of

graphene-based nanoparticles, which are able to absorb UV-Vis light .

Tuning the optical properties of various materials has been of

great interest due to their potential applications in optoelectronic devices . Among many

optical materials, graphene oxide (GO) has gained intense interest due to its versatility

in various devices such as flexible electronics , solar cells and chemical sensors. In recent

past, intense research has been carried out to understand the properties of GO and

transform it as reduced GO (RGO) in order to utilize in aforesaid applications.

Essentially, GO is a single layer of the graphite oxide and consists of several

oxygenated functional groups on its basal plane and at the edges. Graphite Oxide and

GO are chemically identical and the latter consists of many oxygenated functional groups such

as hydroxyl, epoxide, carbonyl and carboxyl groups. Among them, carbonyl and carboxyl

groups are arranged on the edges of GO and hydroxyl, epoxy groups exist on the basal plane .

As a result of many functional groups, GO structure is still ambiguous. The stoichiometry and

the conductance of GO change due to the fact that the oxygenated-type functional groups

change with different synthesis conditions. This would allow one to tune the electronic

structure of GO from insulator to semiconductor and hence to metal in nature. Various

methods like chemical, thermal and mechanical methods have been used to control the band

gap by controlling the electronic structure of GO.

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

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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.

1.1 UV-VIZ SPECTROMETERUltraviolet/Visible/Infrared (UV/Vis/IR) spectroscopy is a technique used to quantify

the light that is absorbed and scattered by a sample (a quantity known as the extinction, which

is defined as the sum of absorbed and scattered light). In its simplest form, a sample is placed

between a light source and a photodetector, and the intensity of a beam of light is measured

before and after passing through the sample. These measurements are compared at each

wavelength to quantify the sample’s wavelength dependent extinction spectrum. The data is

typically plotted as extinction as a function of wavelength. Each spectrum is background

corrected using a “blank” – a cuvette filled with only the dispersing medium – to guarantee

that spectral features from the solvent are not included in the sample extinction spectrum.

Nanoparticles have optical properties that are sensitive to size, shape, concentration,

agglomeration state, and refractive index near the nanoparticle surface, which makes

UV/Vis/IR spectroscopy a valuable tool for identifying, characterizing, and studying these

materials. Nanoparticles made from certain metals, such as gold and silver, strongly interact

with specific wavelengths of light and the unique optical properties of these materials is the

foundation for the field of plasmonics. A various numerical modeling algorithms that can be

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used to predict the optical properties of various nanoparticles allowing for comparison

between theoretical and measured properties.

FIG 1: UV VIS 1800-spectrophotometer

Our standard UV-Vis analysis is performed with an UV VIS 1800- spectrometer, which

collects spectra from 200-1100 nm using a slit width of 1 nm. Deuterium and tungsten lamps

are used to provide illumination across the ultraviolet, visible, and near infrared

electromagnetic spectrum. Spectra are typically collected from 1 ml of a sample dispersion,

but we can test volumes as small as 100 µL using a microcell with a path length of 1 cm.

Additionally, we have assembled a variety of light source/spectrometer custom setups for

measuring optical properties of materials from the ultraviolet to the deep-infrared (200 nm to

20 m), and can customize analytical systems to measure scattering or absorption from both

liquid and solid samples. We also have a highly instrumented chamber for aerosolizing

nanoparticles and measuring the optical properties of the suspended particles.

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1.2 CUVETTEA straight-sided clear container for holding liquid samples in a spectrophotometer or

other instrument.

A cuvette (from French cuvette = "little vessel") is a small tube of circular or square cross

section, sealed at one end, made of plastic, glass, or fused quartz(for UV light) and designed

to hold samples for spectroscopic experiments. Disposable plastic cuvettes are often used in

fast spectroscopic analysis, where speed is more important than high accuracy. Glass cuvettes

are typically for use in the wavelength range of visible light and fused quartz tends to be used

in the UV through NIR ranges.

FIG 2: Cuvette

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The other types of cuvettes are more expensive than the plastic cuvette. It is disposable and

will be eliminated once complete the spectrometric experiment to prevent risk from reusing

cuvettes and damaging expensive quartz. Colour and UV range can be analysed by this type of

cuvette. Some cuvettes will be clear only on opposite sides, so that they pass a single beam of

light through that pair of sides; often the unclear sides have ridges or are rough to allow easy

handling. Typically, cuvettes are 10 mm (0.39 in) across, to allow for easy calculations

of coefficients of absorption. To measure the sample, the transparent side must be placed

toward the light in spectrophotometer. For accurate measurement, these testing tubes should

be cleaned and without any scratches.

1.3 ULTRA SONIC BATHS

The Ultra Sonic Bath is used for the rapid and complete removal of contaminants from

objects by immersing them in a tank of liquid flooded with high frequency sounds waves.

Sonication is the act of applying sound energy to agitate particles in a sample, for various

purposes. Ultrasonic frequencies (>20 kHz) are usually used, leading to the process also being

known as ultra-sonication or ultra-sonication.

FUNCTION PRINCIPLE

A high-frequency generator in the ultrasonic bath produces about 35000 oscillations per

second, which are transferred into the cleaning solution and cause it to resonate. The energy

density of the sound field is so high that a cavitation effect sets in. Innumerable extremely

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small vacuum bubbles develop in the ultrasonic bath and collapse in microseconds due to

pressure and suction. The pulses triggered by this remove dirt particles even at the deepest,

least accessible places or they result in homogenisation, dispersion and degassing.

FIG 3: ULTRA SONIC BATH

1.4 ANALYTICAL BALANCE

An analytical balance is so sensitive that it can detect the mass of a single grain of a

chemical substance. Thus, if a method of direct weighing is used, the substance ought to be

added to the tared container which will hold it, never directly to the pan or even to weighing

paper placed on the pan. The container used should be completely dry and at room

temperature, never at an elevated or reduced temperature. Even slight temperature differences

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can produce apparent changes in mass of the container. Finally, the container ought to be

completely dry, inside and out.

TARING

First, before weighing anything on this analytical balance, it needs to be "tared," or

recalibrated to read 0.0000 g. When first turned on, or when left by the previous user, the

balance may indicate something other than 0.0000 g. The Tare button needs to be pressed and

released to effect this recalibration.

FIG 4: Analytical balance

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1.5 DIGITAL HOTPLATE

The Digital Hotplate provides powerful heating and stirring with LED digital display

of the set temperature and real-time temperature display. LED heating and analog stirring are

simply controlled turning the respective control knobs.

FIG 5: Digital Hotplate

FEATURES OF TARSON SPINOT DIGITAL

Easy-to-read LED display for heat, analog control for stirring.

Heat only, stir only or heat and stir together functions.

Low temperature stability.

 PT-1000 Sensor for medium temperature control.

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Electronic speed control for constant speed even during changes in load.

High magnetic adhesion.

Hot warning above 50°C.

1.6 DE-IONISED WATER

Deionized water is deeply demineralized, ultrapure water with the resistivity close to

18 mega ohm-cm. It is used in microelectronics, printed circuit boards, instrument

manufacture, pharmacy, washing liquids etc.

In order to obtain the high quality pure deionised water a multi-stage water purification

process can be used. After pre-cleaning, the water is supplied to the reverse osmosis

membrane, and then the water is filtered through a special deionization medium, which

removes the rest of the ions in the water. The purity of deionized water can exceed the purity

of distilled water

DIFFERENCE BETWEEN DE IONISED WATER AND DISTILLED WATER

The basis of the process is the transfer of water in the vapor phase with its subsequent

condensation. The main drawback of this method is the very high maintenance costs of the

electricity needed to convert the water into the steam. In addition, in the process of steam

formation along with water molecules other solutes can enter the steam according to their

volatility. Evaporation is achieved in various ways: the vacuum above the water, heating, etc.

The water molecules have the boiling point of 100°C or 212° F. Other substances have

different boiling points. The substance that boils at a lower temperature evaporates first. The

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boiling point of various impurities is higher, and, theoretically, they will begin to evaporate,

when the water has already boiled out. The substance that boils at a lower temperature

evaporates first. Due to this difference the water is separated. The absolute advantage of the

distilled water is the complete absence of harmful substances.

2. LITERATURE REVIEW

1.7 Reviews on Graphene Oxide, Reduced Graphene Oxide and Graphite powder

Graphene is a carbon based material that can be viewed as a one atom thick sheet of

graphite and has been investigated intensely in recent years following a report by

Konstantin Novoselov on its isolation and measurement of its unique electronic

properties. Quickly after its initial discovery, graphene was used to make electronic

devices for a variety of applications. Because high quality sheets of graphene is often

prepared by chemical vapor deposition (CVD), which requires expensive equipment,

many groups have looked at using graphene oxide as a solution process able

alternative for the preparation of graphene like materials.  Indeed, graphene oxide can

be reduced in solution and as a thin film using a variety of reducing conditions, and

reduction converts the graphene oxide into a material that has a large enhancement in

electrical conductivity. In addition to its use in making reduced graphene oxide for

electronic devices, graphene oxide has been used in catalytic oxidation

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biotechnology and as a surfactant. Graphene is also related to carbon nanomaterials

such as carbon nanotubes and fullerene.

Graphite oxide, formerly called graphitic oxide or graphitic acid, is a

compound of carbon, oxygen, and hydrogen in variable ratios, obtained by

treating graphite with strong oxidizers. The bulk material disperses in basic solutions

to yield monomolecular sheets, known as graphene oxide by analogy to graphene, the

single-layer form of graphite. Graphene oxide sheets have been used to prepare a

strong paper-like materials, membranes, thin films, composite materials. Initially

Graphene oxide attracted substantial interest as a possible intermediate for the

manufacture of graphene. The graphene obtained by reduction of graphene oxide still

has many chemical and structural defects which is a problem for some applications but

an advantage for some others.

Reduced Graphene Oxide (RGO) is obtained by reducing Graphene Oxide

(GO). It can be done chemically, thermally or via irradiation (UV or IR) to get a powder

form. Graphite powder can be used as a dry lubricant in its original form or as a

lubrication additive in greases, oils or colloidal solutions. Graphite contains high levels

of carbon and therefore offers good electrical conductivity.

.

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2.2 Review on Properties of Graphene oxide and Reduced Graphene oxide

Reduced Graphene oxide properties

· Form: Powder

· Reduction method: Chemically reduced

· Sheet dimension: Variable

· Colour: Black

· Odour: Odourless

· Solubility: Insoluble

· Dispersability: It can be dispersed at low concentrations

· Humidity : 3.7 - 4.2%

· Electrical conductivity: 666,7 S/m

· BET surface area: 422.69 – 499.85 m2/g

· Density: 1.91 g/cm3

Graphene oxide properties

· Form: layer structure with larger irregularities

· Sheet dimension:1.1 ± 0.2 nm thick

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· Colour: Black

· Odour: Odourless

· Solubility: Insoluble

·  Charge mobility: 0.1 to 10 cm2/Vs

· Electrical conductivity: 1 and 5×10−3 S/cm

3. OPTICAL PROPERTIES

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 (as well as many others). 

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. However,

once graphene was isolated, it was clear that it was actually possible, and it took scientists

some time to find out exactly how. After suspended graphene sheets were studied by

transmission electron microscopy, scientists believed that they found the reason to be due to

slight rippling in the graphene, modifying the structure of the material. However, later

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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.

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 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 2.3% equates to a universal dynamic conductivity value of over the visible frequency range.

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

reaches a certain threshold satiable absorption takes place (very high intensity light causes a

reduction in absorption). This is an important characteristic with regards to the mode-locking

of fibre lasers. Due to graphene’s properties of wavelength-insensitive ultrafast satiable

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.

3.1 ABSORPTION

When a light beam in impinged on a material surface, portion of the incident beam that

is not reflected by the material is either absorbed or transmitted through the material. Light

absorption in thin films has always been a relevant topic in optics, especially from the

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application point of view. Graphene is in many ways the ultimate thin film, only one atomic

layer thick, and has photonic properties of high interest for optoelectronic applications.

Noteworthy is that for pristine, unbiased graphene an impressive 2.3% (απ, where e c α 4/ πε

is the fine structure constant) of incident visible light is absorbed.

Crucial for the optical performance of small particles and ultra-thin structures is often that

relevant (surface) plasmon excitations are available. Recently, an optical switching

mechanism using gated graphene, coupling to external radiation through surface plasmon-

polaritons rather than directly to incoming photons, has been described. Graphene based

sensors are another area of importance, where it has been suggested that graphene ribbons can

be used to convert molecular signatures to electrical signals based on graphene plasmons

being very sensitive to the molecular analytes one is monitoring. Since for graphene we have

the possibility of controlling its “optical” properties with a proper gate voltage and/or doping,

which through the chemical potential governs the optical conductivity and thus its spectral

signature, a multitude of possible mechanisms for sensing and tuneable optics are available

over a broad frequency range .

If we were to freely tune the optical properties of a film with the thickness of a single

layer of graphene, the maximum attainable light absorption would be dictated by the contrast

of the surrounding media. This general limit for light absorption in ultrathin films may under

favourable conditions (that is for high damping materials with nearly imaginary dielectric

constant) be approached by tuning of the film thickness alone. However a more widely

applicable approach to realize these optimal conditions is to exploit Plasmon resonances in

nanostructures where metallic elements and other materials adding functionality are combined

into nanocomposites. By tuning the geometrical properties and thereby the effective dielectric

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function of the nanocomposite structure in relation to the dielectric properties of the

surrounding media, the impedance of the system can be matched to maximize the absorption .

Related contrast effects are exploited when making graphene “visible” by placing it on top of

silicon wafers or using holes in a metallic screen. Here we investigate another line of

approach, not invoking surface Plasmon or other collective excitations, to realize optimal

conditions for light absorption, namely the possibility to tune the optical properties of a single

layer of graphene by means of realistic bias voltages and doping levels, and by appropriate

choice of the dielectric environment.

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Thermal exfoliation Reduced GO.SPC Graphene oxide Graphite powderWL/nm Abs WL/nm Abs WL/nm Abs WL/nm Abs

1100 0.902 1100 0.103 1100 0.561 1100 0.331099 0.902 1099 0.103 1099 0.561 1099 0.331098 0.902 1098 0.103 1098 0.56 1098 0.331097 0.902 1097 0.104 1097 0.559 1097 0.331096 0.902 1096 0.104 1096 0.559 1096 0.3291095 0.902 1095 0.104 1095 0.56 1095 0.3291094 0.901 1094 0.105 1094 0.56 1094 0.3291093 0.901 1093 0.106 1093 0.56 1093 0.3291092 0.901 1092 0.107 1092 0.561 1092 0.3291091 0.901 1091 0.107 1091 0.562 1091 0.3291090 0.901 1090 0.107 1090 0.562 1090 0.3291089 0.901 1089 0.108 1089 0.562 1089 0.3291088 0.901 1088 0.108 1088 0.563 1088 0.3291087 0.901 1087 0.109 1087 0.563 1087 0.3291086 0.9 1086 0.109 1086 0.563 1086 0.3281085 0.9 1085 0.108 1085 0.563 1085 0.328

k1084 0.9 1084 0.108 1084 0.563 1084 0.3281083 0.9 1083 0.108 1083 0.563 1083 0.3281082 0.9 1082 0.109 1082 0.563 1082 0.3281081 0.9 1081 0.109 1081 0.564 1081 0.3281080 0.9 1080 0.11 1080 0.565 1080 0.3281079 0.899 1079 0.111 1079 0.566 1079 0.3281078 0.899 1078 0.112 1078 0.566 1078 0.3281077 0.899 1077 0.112 1077 0.566 1077 0.3281076 0.898 1076 0.113 1076 0.567 1076 0.3281075 0.898 1075 0.114 1075 0.567 1075 0.3281074 0.898 1074 0.114 1074 0.567 1074 0.3281073 0.897 1073 0.115 1073 0.567 1073 0.328

Table 1: ABSORPTION READINGS (Graphene powder, Reduced Graphene Oxide, Graphene Oxide and Thermally Exfoliated Graphene)

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3.2 TRANSMITTANCE

Graphene may outperform existing transparent conductive materials, and a graphene based

flexible touch screen. Multilayer graphene is a graphene thin film with weak van der Waals

interaction between the layers, and its electronic and optical properties are sensitive to the

number of layers as well as the stacking sequence. Multilayer graphene, the optical

transmission through a graphene films is directly dependent on the optical conductance of the

graphene stack, and the optical transmittance

In order to verify the dependence of the optical transmittance of multilayer graphene layers,

two sets of multilayer CVD graphene films were grown on a nickel coated wafer. The

multilayer graphene films are polycrystalline with an irregular number of layers, however with

uniform optical transparency on a macroscopic scale. The transmittance curves of each of

these stacks with λ ranging from 400 nm to 800 nm.

Thermal exfoliation RGO

graphene oxide Graphite powder

WL/nm %T WL/nm %T WL/nm %T WL/nm %T1100 33.1 1100 66.5 1100 71.6 1100 58.61099 33.1 1099 66.4 1099 71.6 1099 58.61098 33.1 1098 66.3 1098 71.6 1098 58.71097 33.1 1097 66.1 1097 71.6 1097 58.71096 33.1 1096 65.9 1096 71.5 1096 58.71095 33.1 1095 65.8 1095 71.5 1095 58.81094 33.1 1094 65.6 1094 71.5 1094 58.91093 33.1 1093 65.4 1093 71.5 1093 591092 33.1 1092 65.2 1092 71.4 1092 59.11091 33.1 1091 65.1 1091 71.4 1091 59.21090 33.1 1090 65 1090 71.4 1090 59.3

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1089 33.1 1089 64.8 1089 71.3 1089 59.31088 33.1 1088 64.7 1088 71.3 1088 59.41087 33.1 1087 64.6 1087 71.3 1087 59.51086 33.1 1086 64.6 1086 71.3 1086 59.61085 33.1 1085 64.5 1085 71.2 1085 59.61084 33.1 1084 64.4 1084 71.2 1084 59.71083 33.1 1083 64.2 1083 71.2 1083 59.71082 33.1 1082 64.1 1082 71.1 1082 59.81081 33.1 1081 64 1081 71.1 1081 59.81080 33.1 1080 63.9 1080 71.1 1080 59.91079 33.1 1079 63.8 1079 71.1 1079 601078 33.1 1078 63.6 1078 71 1078 601077 33.2 1077 63.5 1077 71 1077 601076 33.2 1076 63.3 1076 71 1076 601075 33.1 1075 63.3 1075 70.9 1075 601074 33.1 1074 63.2 1074 70.9 1074 601073 33.2 1073 63.1 1073 70.9 1073 60.11072 33.2 1072 63 1072 70.8 1072 60.21071 33.2 1071 63 1071 70.8 1071 60.21070 33.2 1070 62.9 1070 70.8 1070 60.21069 33.2 1069 62.8 1069 70.8 1069 60.21068 33.2 1068 62.8 1068 70.7 1068 60.21067 33.2 1067 62.7 1067 70.7 1067 60.21066 33.2 1066 62.7 1066 70.7 1066 60.21065 33.2 1065 62.7 1065 70.6 1065 60.31064 33.2 1064 62.6 1064 70.6 1064 60.31063 33.2 1063 62.4 1063 70.6 1063 60.4

Table 2: Wavelength and transmittance of GO, RGO, thermally Exfoliated Graphene and Graphite powder.

3.3 BAND GAP ENERGY

The electronic structure of an isolated C atom is (1s) 2 (2s) 2 (2p) 4; in a solid-state

environment the 1s electrons remain more or less inert, but the 2s and 2p electrons hybridize.

One possible result is four sp3 orbitals, which naturally tend to establish a tetrahedral bonding

pattern that soaks up all the valence electrons: this is precisely what happens in the best

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known solid form of C, namely diamond, which is a very good insulator (band gap ∼ 5 eV).

However, an alternative possibility is to form three sp2 orbitals, leaving over a more or less

pure p-orbital. In that case the natural tendency is for the sp2 orbitals to arrange themselves in

a plane at 120◦ angles, and the lattice thus formed is the honeycomb lattice.

The band structure of graphene can be approximated using tight-binding model considering

only the nearest neighbour hopping energy a hexagon with a unit cell of two atoms. For an

intrinsic or lightly doped graphene, the Fermi level is around the Dirac point, where charge

carriers only experience a linear dispersion. This linear dispersion is called the Dirac cone

since it is described by the relativistic Dirac equation. To calculate optical properties of

graphene in the visible range, one can consider only the Dirac cone if the photon frequency is

low compared to the resonance frequency and the Fermi energy is near the Dirac point. Since

the resonance energy is larger than the photon energy in the visible range, for intrinsic

graphene we can therefore approximate the optical properties within visible range assuming

linear energy dispersion. One can anticipate the approximation will fail if the Fermi level is

well above γ by electric gating or impurity doping. The assumption is also not valid if photon

energies are beyond the visible range.

30

Graphene oxide

Reduced GO

Thermal exfoliation

WL/nm E WL/nm E WL/nm E1100 6.6 1100 3.3 1100 1.91099 6.8 1099 3.4 1099 21098 6.9 1098 3.5 1098 21097 7.1 1097 3.6 1097 2.11096 7.3 1096 3.7 1096 2.11095 7.4 1095 3.8 1095 2.21094 7.6 1094 3.9 1094 2.21093 7.8 1093 4 1093 2.31092 8 1092 4.1 1092 2.31091 8.2 1091 4.2 1091 2.41090 8.4 1090 4.3 1090 2.51089 8.6 1089 4.3 1089 2.51088 8.8 1088 4.4 1088 2.61087 9 1087 4.5 1087 2.61086 9.1 1086 4.6 1086 2.71085 9.4 1085 4.7 1085 2.81084 9.5 1084 4.8 1084 2.81083 9.7 1083 4.9 1083 2.91082 9.9 1082 5 1082 2.91081 10.2 1081 5.1 1081 31080 10.4 1080 5.2 1080 31079 10.6 1079 5.3 1079 3.11078 10.8 1078 5.4 1078 3.21077 11 1077 5.5 1077 3.21076 11.2 1076 5.6 1076 3.31075 11.4 1075 5.7 1075 3.31074 11.6 1074 5.8 1074 3.4

Table 3: Wavelength and energy of GO, RGO. Thermally Exfoliated Graphene.

31

0 200 400 600 800 1000 12000

0.1

0.2

0.3

0.4

0.5

Graphite powder Absorption

Wavelength(nm)

Abso

rban

ce

0 200 400 600 800 1000 12000

5

10

15

20

25Graphne powder Energy

Wavelength(nm)

Ener

gy

0 200 400 600 800 1000 120054

56

58

60

62

64

66

68Graphene powder transmittance

Wavelength(nm)

Tran

smitt

ance

FIG 9: ABSORPTION, TRANSMITTANCE, ENERGY OF GRAPHITE

POWDER

32

0 200 400 600 800 1000 12000

0.2

0.4

0.6

0.8

1

1.2

GO ABSORPTION.SPC

Wavelength(nm)

Abso

rban

ce

0 200 400 600 800 1000 12000

10

20

30

40

50

60

70GO Transmittance.SPC

Wavelength(nm)

Tran

smitt

ance

0 200 400 600 800 1000 120005

1015202530354045

GO ENERGY.SPC

Wavelength(nm)

Ener

gy

FIG 10: ABSORPTION, TRANSMITTANCE, ENERGY OF GRAPHENE

OXIDE

33

0 200 400 600 800 1000 12000

0.05

0.1

0.15

0.2

0.25

RGO Absorption.SPC

Wavelength(nm)

Abso

rban

ce

0 200 400 600 800 1000 12000

10203040506070

RGO transmittance

Wavelength(nm)

Tran

smitt

ance

0 200 400 600 800 1000 12000

10

20

30

40

50

RGO Energy

Wavelength(nm)

Ener

gy

FIG 11: ABSORPTION, TRANSMITTANCE, ENERGY OF REDUCED GRAPHENE OXIDE

34

0 200 400 600 800 1000 12000.65

0.70.75

0.80.85

0.90.95

Thermal exfoliation Abs.SPC

Wavelength(nm)

Abso

rban

ce

0 200 400 600 800 1000 12000

10203040506070

RGO transmittance

Wavelength(nm)

Tran

smitt

ance

0 200 400 600 800 1000 120002468

101214

TE energy.SPC

Wavelength(nm)

Ener

gy

FIG 12: ABSORPTION, TRANSMITTANCE, ENERGY OF THERMALLY EXFOLIATED GRAPHENE

35

4. ELECTROMAGNETIC SPECTRUM

Electromagnetic radiation is the means for many of our interactions with the world:

light allows us to see; radio waves give us TV and radio; microwaves are used in radar

communications; X-rays allow glimpses of our internal organs; and gamma rays let us

eavesdrop on exploding stars thousands of light-years away. Electromagnetic radiation is the

messenger, or the signal from sender to receiver. The sender could be a TV station, a star, or

the burner on a stove. The receiver could be a TV set, an eye, or an X-ray film. In each case,

the sender gives off or reflects some kind of electromagnetic radiation. All these different

kinds of electromagnetic radiation actually differ only in a single property — their

wavelength. When electromagnetic radiation is spread out according to its wavelength, the

result is a spectrum. The visible spectrum, as seen in a rainbow, is only a small part of the

whole electromagnetic spectrum. The electromagnetic spectrum is divided into five major

types of radiation. These include radio waves (including microwaves), light (including

ultraviolet, visible, and infrared), heat radiation, X-rays, gamma rays, and cosmic rays.

Humans cannot sense any other part of the electromagnetic spectrum without the aid of

special equipment. Other animals (such as bees) can see the ultraviolet while some (snakes)

can see the infrared. In each case, the eye (or other sense organ) translates radiation (light)

into information that we (or the bee looking for pollen or the snake looking for prey) can use.

36

VISIBLE LIGHT SPECTRUM

The visible spectrum is the portion of the electromagnetic spectrum that is visible to

the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or

simply light. A typical human eye will respond to wavelengths from about 390 to 700 nm. In

terms of frequency, this corresponds to a band in the vicinity of 430–770 THz.

The spectrum does not, however, contain all the colours that the human eyes and brain can

distinguish. Unsaturated colours such as pink, or purple variations such as magenta, are

absent, for example, because they can be made only by a mix of multiple wavelengths.

Colours containing only one wavelength are also called pure colours or spectral colours.

Visible wavelengths pass through the "optical window", the region of the electromagnetic

spectrum that allows wavelengths to pass largely un-attenuated through the Earth’s

atmosphere. An example of this phenomenon is that clean air scatters blue light more than red

wavelengths, and so the midday sky appears blue. The optical window is also referred to as

the "visible window" because it overlaps the human visible response spectrum. The near

infrared (NIR) window lies just out of the human vision, as well as the Medium Wavelength

IR (MWIR) window, and the Long Wavelength or Far Infrared (LWIR or FIR) window,

although other animals may experience them.

37

FIG 13 : UV SPECTRUM(courtesy: Wikipedia)

38

5. RESULTS AND DISCUSSION

The UV VIS Spectrophotometer is used for characterization of compounds by showing

information about the electron transitions in d-orbitals. The two light sources used in the

spectrometer are the tungsten lamp and deuterium lamp. The tungsten lamp is used for

producing visible light while the deuterium lamp is used for UV light. The approximate range

visible spectrum is from 400 to 800nm while that for UV light is from 200 to 400nm. The

shorter is the wavelength, higher will be the frequency. A high frequency wave corresponds to

higher energy. Here, solution of various samples are used instead of powder form (solids)

because the solids won’t let light pass through.

As the light of various wavelengths incident on the sample solution, the

electrons in the highest occupied molecular orbital (HOMO) jump to the lowest unoccupied

molecular orbital (LUMO) by absorbing energy equal to the band gap between the two energy

levels. The HOMO comes under the bonding molecular orbital section which is at lower

energy while the LUMO falls in the section of anti-bonding molecular orbital. There are quite

a few types of electron transitions that take place when light of sufficient energy is incident on

the material under observation. These include the transition from sigma to sigma star state,

non-bonding MO state to the pie star state, pie to pie star state and the transition from n to pie

star transition.

For Absorption: The electrons move from the HOMO to the LUMO by absorbing energy

equal to the band gap between the two from the incident light. The UV VIS spectrometer used

is of high resolution (1nm). Light of various wavelengths in a step of 1nm is incident on the

39

sample solution and the corresponding graph of the absorbance is obtained using the UV VIS.

The peak of the graph at a particular wavelength indicates that a large amount of electrons

have absorbed energy from the light of that particular wavelength. From the comparative

graph of absorbance, it is evident that the graphene powder has high absorbance in UV region

(from 200 to 300nm). The absorbance of graphene oxide is again high in the UV region and is

decreasing as we go towards the visible region. The Graphite powder behaves just the

opposite while that of reduced graphene oxide is almost constantly low throughout.

110010581016 974 932 890 848 806 764 722 680 638 596 554 512 470 428 386 344 302 260 2180

0.2

0.4

0.6

0.8

1

1.2

Absorption Comparison

Thermal exfoliation Abs Reduced GO.SPC AbsGraphene oxide Abs Graphite powder Abs

Wavelength(nm)Abso

rban

ce

FIG 14: ABSORPTION COMPARISION

For Transmittance: The concept of transmittance is just the opposite of absorbance. The

amount of absorption is inversely proportional to the amount of transmittance. The

wavelengths at which absorption is low shows good transmittance. The electrons remain in the

HOMO if it does not get enough energy to jump to the LUMO. So, the light of that particular

40

wavelength is not absorbed and is hence said to be ‘transmitted’. Light of various wavelengths

in a step of 1nm is incident on the sample solution and the corresponding graph of the

transmittance is obtained using the UV VIS spectrophotometer. The peak of the graph at a

particular wavelength indicates that that particular wavelength does not supply enough energy

to the material. From the comparative graph of transmittance, it is observed that the optical

response is almost reverse of the respective absorbance characteristics.

110010541008 962 916 870 824 778 732 686 640 594 548 502 456 410 364 318 272 2260

10

20

30

40

50

60

70

80

Transmittance Comparison

Thermal exfoliation %T RGO %Tgraphene oxide %T Graphite powder %T

Wavelength(nm)

Tran

smitt

ance

FIG 15: TRANSMITTANCE COMPARISON

For Energy: The concept again remains the same. The electrons move from the HOMO to

the LUMO by absorbing energy equal to the band gap between the two from the incident light.

Light of various wavelengths in a step of 1nm is incident on the sample solution and the

corresponding graph of the absorbance is obtained using the UV VIS spectrophotometer. The

41

peak of the graph at a particular wavelength indicates the maximum energy gap. With the

reference from the base of the energy response, the relative peak indicates that energy of that

particular wavelength has given the electrons enough energy to cross even higher energy gap

states. From the comparative graph of absorbance, it is evident that the wavelength of 650 nm

supplies the maximum required energy to jump to certain higher energy state.

110010581016 974 932 890 848 806 764 722 680 638 596 554 512 470 428 386 344 302 260 2180

5

10

15

20

25

30

35

40

45

Energy Comparison

Graphene oxide E Reduced GO E Thermal exfoliation E Graphite powder E

Wavelength(nm)

Ener

gy

FIG 16: ENERGY COMPARISON

42

5.1 FUTURE SCOPE AND APPLICATIONS

Optical Electronics

Graphene’s high electrical conductivity and high optical transparency make it a

candidate for transparent conducting electrodes. Its mechanical strength and

flexibility are advantageous compared to indium tin oxide, which is brittle. It

can be used in touchscreens, liquid crystal displays, organic photovoltaic cells,

OLEDs.

The bandgap—mobility tradeoff inevitably constrains the application of

graphene for the conventional field-effect transistor (FET) devices in digital

applications.

Light-emitting devices: Organic light-emitting diodes (OLEDs) have an

electroluminescent layer between two charge-injecting electrodes, at least one

of which is transparent. In these diodes, holes are injected into the highest

occupied molecular orbital (HOMO) of the polymer from the anode, and

electrons are injected into the lowest unoccupied molecular orbital (LUMO)

from the cathode.

Photodetectors: Photodetectors measure photon flux or optical power by

converting the absorbed photon energy into electrical current. They are widely

used in a range of common devices, such as remote controls, televisions and

DVD players. Most exploit the internal photo effect, in which the absorption of

photons results in carriers excited from the valence to the conduction band,

43

outputting an electric current. The spectral bandwidth is typically limited by

the material's absorption.

Touch screens::Touch screens are visual outputs that can detect the presence

and location of a touch within the display area, permitting physical interaction

with what is shown on the display itself. Touch panels are currently used in a

wide range of applications such as cellular phones and digital cameras because

they allow quick, intuitive and accurate interaction by the user with the display

content.

Saturable absorbers and ultrafast lasers: Materials with nonlinear optical and

electro-optical properties are needed in most photonic applications. Laser

sources producing Nano- to sub picosecond pulses are a key component in the

portfolio of leading laser manufacturers.

Solar Cells

Graphene turned out to be a promising material for photo electrochemical energy

conversion in dye sensitized solar cells. The transparent, conductive, and ultrathin

graphene films are fabricated from exfoliated graphene oxide, followed by thermal

reduction.

44

6.CONCLUSION

The optical properties of graphene was studied and it was noticed that Graphene is a good

candidate for optical sensor implementation. It is also a good candidate for transparent

conducting oxide. Light of various wavelengths in a step of 1nm was incident on the sample

solution and the corresponding graph of the transmittance, absorbance and energy was

obtained using the UV VIS spectrophotometer. The peak of the graphs at a particular

wavelength indicates that at that particular wavelength, the material shows maximum of that

optical property. From the comparative graph of transmittance, it is observed that the optical

response is almost opposite of the respective absorbance characteristics. The energy was

maximum at around 650nm for all the samples.

45

REFERENCES

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[2]V Xiaorui Zheng, Baohua Jia*,Xi Chen and Min Gu ,” In Situ Third-Order Non-linear Responses During Laser Reduction of Graphene Oxide Thin Films Towards On-Chip Non-linear Photonic Devices “ 17 MAR 2014.

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[4] Chang-Hua Liu1†, You-Chia Chang2†, Theodore B. Norris1,2* and Zhaohui Zhong1,“ Graphene photodetectors with ultra-broadband and high responsivity at room temperature” Nature Nanotechnology letters ,16 MARCH 2014

[5] F. Bonaccorso, Z. Sun, T. Hasan and A.C. Ferrari, "Graphene photonics and optoelectronics", Nature Photonics 4, 611-622 (2010).

[6] S. Thongrattanasiri, F. H.L. Koppens and F.J. García de Abajo, “Total light absorption in graphene”, arXiv:1106.4460v1 (2011).

[7] S.A. Mikhailov and K. Ziegler, “New electromagnetic mode in graphene”, Phys. Rev. Lett. 99, 016803 (2007).

[8] Stauber, T., N.M.R. Peres, and A.K. Geim, “Optical conductivity of graphene in the visible region of the spectrum”, Physical Review B, 2008. 78(8): p. 085432.

[9] Gray, A., et al., “Optical detection and characterization of graphene by broadband spectrophotometry”, Journal of Applied Physics, 2008. 104(5): p. 053109-8.

[10] Taft, E.A. and H.R. Philipp, “Optical Properties of Graphite”, Physical Review, 1965. 138(1A): p. A197-A202.

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